External Review
Draft No. 1
May 1978
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HEALTH ASSESSMENT DOCUMENT
FOR
POLYCYCLIC ORGANIC MATTER
Ui
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DRAFT
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External Review
Draft No. 1
May 1978
HEALTH ASSESSMENT DOCUMENT
FOR
POLYCYCLIC ORGANIC MATTER
NOTICE
This document is a preliminary draft.
It has not been formally released by
EPA and should not be construed to
represent Agency policy. It is being
circulated for comment on its technical
accuracy and policy implication.
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U.S. Environmental Protection Agency
Office of Research and Development
Washington, D.C. 20460
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QUOTE OR CUE
CONTRIBUTORS AND REVIEWERS
The Syracuse Research Corporation (SRC) and its consultants were the major
authors of this document. Dr. Robert Bruce served as the EPA Project Director.
SRC Staff:
Mr. Joseph Santodonato
Dr. Philip Howard
Dr. Dipak Basu
Dr. Sheldon Lande
SRC Consultants:
Dr. James K. Selkirk
Biology Division
Oak Ridge National Laboratory
Oak Ridge, TN 37830
Dr. Paul Sheehe
Department of Preventive Medicine
State University of New York
College of Medicine
Syracuse, NY 13210
The following people from the Environmental Research Center, U.S. Environ-
mental Protection Agency, Research Triangle Park, North Carolina, served on the
EPA Task Force on POM:
Mr. Micheal Berry
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Robert M. Bruce
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
ii
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Mr. Joseph Bumgarner
Environmental Monitoring Surveillance Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Neil Chernoff
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Robert Faoro
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Douglas Fennel!
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Robert Morton
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Robert Jungers
Environmental Monitoring Surveillance Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Justice Manning
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. David McKee
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Thomas McMullen
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
ill
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Mr. James Mulik
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Steve Nesnow
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Shabeg Sandhu
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Eugene Sawicki
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. James R. Smith
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Ms. Beverly Til ton
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
The following people served as consulting contributors and reviewers in
the preparation of this document:
Dr. Ian T. Higgins
Professor of Epidemiology
School of Public Health
University of Michigan
Ann Arbor, MI 48109
Dr. Dietrich Hoffmann
Chief, Division of Environmental Carcinogenesis
Nay!or Dana Institute for Disease Prevention
American Health Foundation
Dana Road
Valhalla, NY 10592
iv
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Dr. Peter W. Jones
Program Manager
Analytical and Environmental Chemistry Division
Battelle Columbus Laboratories
505 King Avenue
Columbus, OH 43201
Dr. Edmond J. LaVoie
Head, Section of Metabolic Biochemistry
Naylor Dana Institute for Disease Prevention
American Health Foundation
Dana Road
Valhalla, NY 10592
Dr. David F.S. Natusch
Professor of Chemistry
Colorado State University
Fort Collins, CO 80523
Dr. Herbert S. Rosenkranz
Professor and Chairman
Department of Microbiology
New York Medical College
Valhalla, NY 10595
Dr. Warren Winkelstein
Professor of Epidemiology
Department of Biomedical and Environmental Health Sciences
School of Public Health
University of California
Berkeley, CA 94750
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TABLE OF CONTENTS
Page
1. EXECUTIVE SUMMARY 1-1
2. INTRODUCTION 2-1
3. PHYSICAL AND CHEMICAL DATA 3-1
4. SAMPLING AND ANALYTICAL METHODS FOR POM's 4-1
5. AMBIENT LEVELS 5-1
6. HEALTH AND ECOLOGICAL EFFECTS 6-1
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1. EXECUTIVE SUMMARY
This document was prepared in response to the Clean Air Act Amendments
of 1977 which add Section 122 to the 1970 Act requiring the Administrator
to decide whether atmospheric emissions of polycyclic organic matter (POM)
may reasonably be anticipated to endanger public health. This document
reviews POM data on chemical and physical properties, atmospheric forms,
atmospheric fate and transport, measurement techniques, ambient levels,
toxicology, and occupational health and epidemiology.
1.1 DEFINITION AND FORMATION
The two POM chemical groups most commonly found in ambient air are
polycyclic aromatic hydrocarbons (PAH's), such as the well known carcinogen
benzo[a]pyrene (BaP), and the PAH nitrogen analogs. In addition, a small
number of oxygen-containing POM's have been detected in ambient air. The
major environmental sources of POM's appear to be the combustion or pyroly-
sis of materials containing carbon and hydrogen. Although hundreds of
individual compounds could be formed under various combustion or pyrolysis
conditions or from various carbon-emitting sources, only about 25 parent
PAH's and 32 nitrogen and oxygen analogs have been quantitatively analyzed
so far in ambient air. The failure to detect POM's may be attributable to
the low concentrations of some compounds and a lack of an appropriate
1-1
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quantitative analytical method for these agents (the presence of over
100 individual PAH in ambient air has been documented but quantitative data
are not available).
It is generally agreed that POM compounds are associated with suspended
particulate matter from both mobile and stationary sources, principally
respirable particles. Many of the compounds are susceptible to oxidation
or photochemical reactions in laboratory experiments, but this suscepti-
bility varies considerably among individual compounds, the physical form of
POM tested, and the reaction conditions used. However, available monitor-
ing data suggest that many POM compounds associated with particulate matter
are probably stable in ambient air for several days. A recent study in
Norway has demonstrated that at least 20 PAH's associated with particulate
matter are stable enough in the atmosphere to travel from England or France
to Norway.
1.2 ANALYTICAL METHODS
A number of methods are available for sampling POM's from various
sources and for the analysis of collected samples for quantification of
individual compounds. POM's in ambient air are usually collected as par-
ticulate matter on filters. Some of the more volatile POM's may not be
efficiently collected, but the collection efficiency for POM's (including
BaP) has not been determined. Because of the large number of individual
compounds in the POM family, careful fractionation and separation proce-
dures are necessary to assure accurate quantisation. Distinquishing
between individual compounds is important because slight alterations in
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chemical structure modify carcinogenic activity, and thus alter the potential
health hazard.
There are several relatively simple, inexpensive analytical procedures
that are capable of reliably measuring several individual POM compounds.
However, as the number of compounds to be measured increases, the cost and
time of analysis increase dramatically. It is apparent that not all of the
individual POM compounds can be monitored on a routine basis because of the
cost and labor that would be required. However, the current practice of
only monitoring BaP seems equally unacceptable. Since BaP levels are not
necessarily representative of the carcinogenic activity of particulate
fractions collected from ambient air, in the future a multi-component
analysis of POM compounds would be more desirable. The actual components
selected should be easy to determine analytically and should be repre-
sentative of those POM air pollution fractions which demonstrate carcino-
genic activity.
1.3 AMBIENT CONCENTRATIONS
While POM compounds have been detected in ambient air, the most
extensive data available are on BaP. The following trends have been noted
3 3
for BaP: the median urban value declined from 3.2 ng/m in 1966 to 0.5 ng/m
in 1975, an 80 percent decrease; levels in the winter were higher than in
the summer, probably due to greater coal consumption; the levels in urban
cities with coke ovens were 40 to 70 percent higher than in cities without
coke ovens, but this is thought to be due in part to higher heating and
industrial emissions in those cities. Some correlation between the amount
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of BaP and the amount of other PAH's has been noted, but there are several
exceptions. These exceptions suggest that the relative amount of each
individual POM compound depends upon local combustion or pyrolysis sources.
The accuracy of the absolute values of BaP is unknown because of the
lack of information on the collection efficiencies, oxidation during col-
lection, or degradation in the time between collection and analysis.
However, the observed trend of overall decreasing BaP levels is believed to
be essentially valid, even if absolute levels are difficult to determine.
Nevertheless this trend cannot be used to imply that the concentration of
other POM's is declining or that the carcinogenic activity of POM fractions
of air particulates is reduced. For the most part, monitoring data for the
other POM compounds has been collected only once at a limited number of
sites.
1.4 HEALTH AND ECOLOGICAL EFFECTS
The major human health concern over exposure to POM's is the possible
development of cancer. It is well-established that POM-containing extracts
of particulate air pollutants are carcinogenic when painted on the skin of
rodents or injected into newborn mice. Although it cannot be unequivocally
stated that any of the POM's are human carcinogens, several of these com-
pounds are among the more potent animal carcinogens known to exist.
POM's gain ready access to the body's circulation either by inhalation,
ingestion, or contact with the skin. In their parent form, however, POM's
produce no major adverse effects. Instead, these compounds must first be
metabolized by enzyme systems of the body to produce chemically-reactive
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intermediates which are then capable of inducing cancer. As would be
expected, the alteration of enzymic activity involved in the formation of
reactive POM metabolites can have a marked effect on the carcinogenic
process. This enzyme activity can be either enhanced or depressed by
exposure to non-carcinogenic chemicals (such as food additives and pollu-
tants), drugs, and naturally-occurring agents in the diet. Moreover, a
wide variation exists in the drug-metabolizing enzyme activity of humans;
and it may be that the degree of this activity is a determinant for the
susceptibility of humans to carcinogenic ROM's. The body also possesses
mechanisms to repair carcinogen-induced damage, and the individual capacity
for such processes is another likely determinant of susceptibility.
Numerous agents have also been identified which either promote or
inhibit the carcinogenicity of ROM's when simultaneous exposure occurs, and
their mechanism of action is as yet undetermined. Because of the diversity
of human lifestyles and the multitude of chemicals to which humans are
exposed that may either enhance or diminish their susceptibility, human
response to carcinogenic ROM's is expected to vary considerably. Moreover,
the risk of carcinogenic POM exposure to individuals who are in danger of
developing cancer from other causes (e.g., radiation, chemicals, viruses)
has never been fully evaluated. It is for these reasons that animal studies
may not accurately reflect the cancer risk to humans of POM exposure.
In studies with animals, an apparent "threshold" level for POM exposures
is often seen, below which no carcinogenic response is produced. This may
be due to the fact that body defense mechanisms are capable of deactivating
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certain minimum amounts of a carcinogenic substance. On the other hand, in
experimental situations it is not surprising to observe deviations from the
predicted number of responses at very low doses, simply because limited
numbers of animals are generally employed. Furthermore, it has been shown
in animal studies that, even at levels which do not produce tumors, BaP can
still interact with critical cellular constituents (e.g., DNA) in a dose-
related fashion. Such interaction is regarded to represent an initial
event in malignant transformation. Therefore, no one can presently say
whether there exists a safe level for human exposure to ROM's. However, in
real-life situations most scientists agree that the effects of carcinogenic
ROM's will most likely be a continuous function of dose, no matter how
small.
Whereas exposure to POM's in occupational situations can clearly be
associated with increased lung cancer development, epidemiological evidence
in community settings does not permit a definitive conclusion. This is
primarily because of the overriding impact that cigarette smoking has on
POM exposure compared to inhalation of POM-containing particulate air
pollutants. Nevertheless, when smoking habits are taken into considera-
tion, urban residents have a two-fold risk for the development of lung
cancer in relation to residents in rural environments. Since no other
variables (e.g., lifestyle, medical care, etc.) can adequately account for
this difference, most investigators feel it is reasonable to attribute at
least some of this lung cancer excess among urban dwellers to the higher
relative concentration of POM's in city air. Moreover, it has been shown
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that cities having the highest levels of POM-containing pollutants in the
air also report a higher rate of lung cancer mortality than other cities.
Even among migrant groups who leave these polluted environments, an excess
of lung cancer still appears while they are residing in an adopted country.
Thus, it is evident that lifetime exposures to POM may not be necessary to
result in an increased cancer risk.
Since all carcinogens are mutagens as well, it is not surprising that
numerous POM's produce mutations in certain animal and bacterial cells in
culture. However, POM's have not been conclusively shown to produce muta-
tions in either animals or man which can be passed from one generation to
the next. Furthermore, there is no evidence to indicate that POM's in the
air may be producing mutations to lower organisms in the environment, or
that POM's are presently disturbing the ecological balance in any way.
POM's are apparently not bioaccumulated in any species, nor are they trans-
ferred through the food chain. On the other hand, the high sensitivity of
certain fish and amphibians to carcinogenic chemicals suggests that specific
adverse ecological effects may result from low levels of contamination.
In conclusion, it is evident that the risk of lung cancer development
by exposure to POM's is real. The magnitude of that risk to the general
population, however, cannot be accurately determined based on our present
knowledge. It is almost certainly much less than the lung cancer risk
associated with cigarette smoking, since POM exposure from smoking is far
greater than that from inhaling polluted air. Nevertheless, in conjunction
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with smoking and the other foreign chemicals (carcinogenic and non-carcino-
genic) to which man is exposed, it is likely that the absolute risk of POM
exposure at any concentration is magnified in real-life situations. Thus,
in adopting the most conservative approach for evaluating the human health
hazard of ROM's, most scientists conclude that although the risk of cancer
by exposure to low doses of ROM's is probably very small, it will not be
possible to completely eliminate the risk unless all exposures are pre-
vented.
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2. INTRODUCTION
123
A number of documents ' ' have reviewed polycyclic organic matter (POM)
in considerable detail, but a considerable amount of information has been
developed since then which needs to be evaluated in determining whether the
release of POM into the atmosphere will endanger public health. The Clean Air
Act Amendments of 1977 amended Part A of Title I of the 1970 Act by adding
Section 122 as a new section entitled, "Listing of Certain Unregulated Pollu-
tants." The new section reads as follows:
Not later than one year after date of enactment of this section
(two years for radioactive pollutants) and after notice and oppor-
tunity for public hearing, the Administrator shall review all avail-
able relevant information and determine whether or not emissions of
radioactive pollutants (including source material, special nuclear
material, and by-product material), cadmium, arsenic and polycyclic
organic matter into the ambient air will cause, or contribute to,
air pollution which may reasonably be anticipated to endanger public
health. If the Administrator makes an affirmative determination
with respect to any such substance, he shall simultaneously with
such determination include such substance in the list published
under section 108(a) (1) or 112(b) (1) (A) (in the case of a sub-
stance which, in the judgment of the Administrator, causes, or
contributes to, air pollution which may reasonably be anticipated to
result in an increase in mortality or an increase in serious irre-
versible, or incapacitating reversible, illness), or shall include
each category of stationary sources emitting each substance in
significant amounts in the list published under section lll(b) (1)
(A), or take any combination of such actions.
In an effort to comply with the legislated mandate, this publication has
been prepared as part of the basis to allow the Administrator to decide
whether or not POM emissions cause or contribute to air pollution which may
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reasonably be anticipated to endanger public health. Given that the above
determination is positive, this document will assist the Administrator in
determining which regulatory mechanism is the most appropriate for POM.
In order to accomplish this objective this document has reviewed the
following information on ROM's: chemical and physical properties, form in
ambient air, formation, fate and transport, measurement techniques, ambient
levels, toxicology, and occupational and epidemiological information. The
status of control technology for ROM's has not been considered in this report.
The scientific literature has been reviewed through 1977 and the early
part of 1978. Because POM includes literally hundreds of individual com-
pounds, all the papers ever published relating to POM in the environment and
their effects could not be cited. Emphasis was placed upon those chemicals
and chemical groups which had the highest potential for affecting public
health. For this reason two chemical groups, - the polycyclic aromatic hydro-
carbons (PAH's), including benzo[a]pyrene (BaP), and the aza arenes - were
focused upon because of their association with carcinogenesis.
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References
1. Participate Polycyclic Organic Matter. National Academy of Sciences.
Washington, D.C. 1972, 361 pp.
2. Scientific and Technical Assessment Report on Particulate Polycyclic
Organic Matter (PPOM). U.S. Environmental Protection Agency.
Washington, D.C. Publication No. EPA-600/6-75-001. 1975.
3. Preferred Standards Path Report for Polycyclic Organic Matter. U.S.
Environmental Protection Agency. Office of Air Quality Planning and
Standards. North Carolina. 1974.
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3. PHYSICAL AND CHEMICAL DATA
3.1 DEFINITION AND FORMATION
Polycyclic organic matter (POM) can include many chemical groups as indi-
cated by the following list developed by an EPA Task Force in 1975:
Polycyclic aromatic hydrocarbons (PAH) (see Table 3-1)
Aza arenes (arenes containing a ring nitrogen) (see Table 3-2)
Imino arenes (ring nitrogen with a hydrogen) (see Table 3-2)
Carbonyl arenes (see Table 3-3)
Dicarbonyl arenes (quinones) (see Table 3-3)
Hydroxy carbonyl arenes
Oxa arenes and thia arenes
Polychloro compounds
Pesticides (e.g., aldrin, chlordane, DDT)
Chemically, any organic compound that contains two or more rings could be
considered a POM. However, of major concern are the carcinogenic polycyclic
aromatic hydrocarbons (PAH's), such as benzo[a]pyrene, and their nitrogen
analogs, aza and inn'no arenes, which are formed during organic combustion
p c f
processes. ' ' Because of their common sources, their existence in urban
air, and the considerable experimental data on their carcinogenic effects,
the PAH's and the nitrogen analogs have received the most attention, and
therefore this report has focused on these POM's. However, some of the
other arenes (for example, 7H-Benz(de)anthracen-7-one) have been detected in
urban atmospheres. The latter compounds will be considered in this report
even though a limited amount of data are available.
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ROM's may be formed in most combustion or elevated temperature processes
which involve compounds containing carbon and hydrogen. The amounts and types
of individual chemicals that are formed are dependent upon the starting hydro-
carbons and the conditions of combustion or pyrolysis. Although the exact
intermediates that are postulated vary considerably, free-radical paths are
commonly suggested at the high temperatures attained in the flame front (500-
800°C) or under pyrolysis conditions. Badger first postulated the synthetic
route to POM formation outlined in Figure 3-1. His pyrolysis studies were
conducted by passing the hydrocarbon vapor in nitrogen through a silica tube at
700°C. Although the use of nitrogen atmospheres has been criticized as
c
lacking relevance to actual combustion, the reducing conditions are similar
to those of the oxygen-deficient environments of a flame and the data are in
2
good qualitative agreement with the POM combustion products formed. For
example, Boubel and Ripperton found that benzo[a]pyrene (BaP) is produced
during combustion even at high percentages of excess air, but that the
amount of BaP is greater at lower percentages of excess air. Lending support
p
to the postulated route to ROM's, Badger and Spotswood pyrolyzed toluene,
ethylbenzene, propylbenzene, and butylbenzene and obtained the highest
Q
yields of benzo[a]pyrene with butylbenzene. Badger and Spotswood also
found that when 1,3-butadiene is pyrolyzed with pyrene at 700°C, no increase
in the yields of benzpyrenes is observed, which suggests that Diels-Alder
type reactions are probably not important.
More recent studies tend to confirm most of the mechanism proposed by
4 10
Badger. Crittenden and Long determined the chemical species at various
flame heights of oxy-acetylene and oxy-ethylene flames. Compounds identified
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I
Co
BaP
Figure 3-1. Mechanism of benzo[a]pyrene formation.4
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suggest that the C2 species react to form C., Cg, and C» species, and that
reactions involving styrene and phenylacetylene are probably important in
the formation of polycyclic aromatic hydrocarbons. Also, a C-IQH-IQ species
was detected in the gases of both flames and, although its identity is
uncertain, it may correspond to the Cg-C, species (butylbenzene, phenylbuta-
diene, or related radicals) postulated by Badger.
With the Badger step-wise sequence mechanism, various free radical
intermediates, and aliphatic and aromatic fuels, one could form hundreds of
ROM's.
By far the most significant source of atmospheric ROM's is pyrolitic or
combustion processes. However, some investigators have suggested that some
polycyclic aromatic hydrocarbons in the environment may be synthesized by
plants and microorganisms and that part of the PAH's could be from natural
12 13
combustion sources. However, recent studies of aqueous sediment cores
suggest that the concentrations detected correspond relatively well with
energy production from various fuels, which indicates that anthropogenic
combustion may be the major source of PAH's even in aqueous media.
3.2 STRUCTURE AND PROPERTIES
3.2.1 Chemical Structure
The nomenclature of POM compounds has suffered from considerable ambi-
guities in the past due to different peripheral numbering systems. For
example, carcinogenic benzo[a]pyrene was named "3,4-benzpyrene" by American
scientists and "1,2-benzpyrene" by European workers, while the noncarcino-
genic isomer, benzo[e]pyrene, was named "1,2-benzpyrene" by American scientists
and "4,5-benzpyrene" by European scientists. Thus, 1,2-benzpyrene could be
3-4
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the carcinogenic or noncarcinogenic isomer, depending upon where a scientist
14
worked.
The currently accepted nomenclature is that adopted by the International
2
Union of Pure and Applied Chemistry (IUPAC) and by Chemical Abstracts Service.
Of major importance are the following rules that determine the orientation from
which the numbering is assigned:2'14'15'16'17'18
1. The maximum number of rings lie in a horizontal row;
2. As many rings as possible are above and to the right of the horizontal
row; and
3. If more than one orientation meets these requirements, the one with
the minimum number of rings at the lower left is chosen.
The carbons are then numbered in a clockwise fashion, starting with the first
most counterclockwise carbon which is not part of another ring and is not en-
gaged in a ring fusion. Letters are assigned in alphabetical order to faces
of rings, beginning with "a" for the side between carbon atoms 1 and 2 and
continuing clockwise around the molecule; ring faces common to two rings are
not lettered. Thus, benzo[a]pyrene would have a benzene ring fused to the
"a" bond of the parent pyrene structure (Figure 3-2).
The following tables provide lists of the ROM's that in most instances
have been detected in air. However, some compounds (e.g., 7,12-dimethyl-
benz[a]anthracene and 3-methylcholanthrene) have been included in the table
even though they are synthesized compounds which are not formed during com-
bustion nor are they present in ambient air. These synthetic compounds were
included because they are used as model compounds in experimental carcinogen-
esis studies and have provided fundamental information concerning mechanisms
of tumor formation. The chemical names, synonyms, structures, numbering
3-5
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benzo[a]pyrene
pyrene
Figure 3-2. Accepted nomenclature for benzo[a]pyrene.
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system, and acronyms used throughout the report, along with their relative
carcinogenicity, are presented. The tables are divided into polycyclic
aromatic hydrocarbons (PAH), aza and imino arenes, and miscellaneous other
ROM's that have been detected in air. The structures are presented in the
p
same way as those in the NAS report, Particulate Polycyclic Organic Matter,
in that aromatic rings are shown as plain hexagons and a methylene group as
C^. The indications of carcinogenicity, taken from the NAS report, were
obtained from several Public Health Service (PHS) surveys of compounds tested
19 20 21 22 23
for carcinogenicity. ' ' * 'In some instances, indications of carcin-
ogenicity were obtained from individual references; in these cases the refer-
ences are provided. The indications of carcinogenicity which are a summary of
all routes correspond to the following simple code:
not carcinogenic
± uncertain or weakly carcinogenic
+ carcinogenic
++, +++, ++++ strongly carcinogenic
Additional compounds besides those listed in the NAS report were added in this
report when they have been detected in air. Older nomenclature are included
in parentheses and names with an asterisk indicate disagreement with standard
numbering.
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Table 3-1. POLYCYCLIC AROMATIC HYDROCARBONS
CO
00
Compound
Structure
Formula
Carclnogenlclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xraax , nm
Log e
Solvent
Anthracene Benz[a]anthracene 7, 12-Dime thy Ibenz [a] anthracene
(9,10-dlmethyl-l,2-benzanthracena)
5 »o 1 «"j
(not an air pollutant)
C14H10 C18H12 C20H16
A BaA DMBA
216 159.5-160.5 122-123
340 400
1.95 x 10~* 1.10 x 10"'
308 323 338 355 375 314 327 341 359 376 386 296 345 364 384
3.15 3.47 3.75 3.86 3.87 3.67 3.81 3.87 3.72 2.73 3.86 4.90 3.83 3.94 3.83
EtOH-MeOH EtOH EtOH
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Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Dibcnz[a,j]anthracene
(1,2-6,7-dibenzanthracene)
Dibenz[a,h]anthracene
(1,2-5,6-dibenzanthracene)
Dibenz[a,c]anthracene
(1,2-3,4-dibenzanthracene)
Structure
co
vo
Formula
Carclnogenlclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log e
Solvent
C22H14
C22H14
DBahA
266-266. S
C12H14
299 322 335 350 374 384
5.20 4.28 4.23 4.16 3.00 2.61
dioxane
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Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Structure
' 1
Phenanthrene Ben2o[c]phenanthrene Fluorene
(3,4-benzphenarthrene)
/a i
t * »
CO
_J
o
Formula
CarcinogenIclty
Acronym
Physical properties
Melting point, "C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
C14H10
6.8 x 10 *
309 314 323 330 337 345
2.40 2.48 2.54 2.52 3.40 3.46
EtOH-MeOH
C18H12
BcP
68
296 3f.3 313 323 353 372
4.13 4.07 4.06 3.67 2.63 2.38
EtOH
C13H10
116
293
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Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Benzo[a]'luorene
(1,2-benzfluorene)
Benzo[b]fluorene Dibenzo[a,hifluorene
(2,3-benzfluorene) (1,2-6,7-dlbenzfluorene)
Dibenzo[a,g]fluorene
(1,2-5,6-dIbenzofluorene)
Structure
ofco
Formula
Carcinogenicity
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log e
Solvent
C17H12
189-190
C17H12
208-209
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Structure
Benzo[c]fluorene Dibenzo[a,c]fluorene
(3,4-benzfluorene) (1,2-3,4-dlbenzfluorene)
**•
Benzo[b]fluorant hene
(2,3-benzfluoranthene)
c&o
CO
ro
Formula
Carclnogeniclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log c.
Solvent
C17H12
C21H14
C16H10
Flour
110
393
C20H12
BbF
167
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Benzo[J)fluoranthene Benzo[k)fluoranthene
(7,8-benzfluoranthene) (8,9-benzfluoranthene)
Benzo[ghl)fluoranthene
Aceanthrylene
Structure
C*>
Formula
Carcinogenicity
Acronym
Physical properties
Melting point. *C
Boiling point. *C
Vapor pressure, Torr
Xmax, nm
Log c
Solvent
C20H12
BJF
165-167
C20H12
BkF
215-216
9.59 x 10
"11
C20H10
C16H12
113
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Structure
Benzo[j]aceanthrylene
(cholanthrene)
3-Methylcholanthrene
(not an air pollutant)
Naphthacene
(benzo[b]anthracene;
CA>
Formula
Carcinogenicity
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nra
Log e
Solvent
C20H14
+ +
C21H16
MCA
179
no absorption above
300 run
C18H12
341
sublimes
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Napht ho [ 2 , 1 , 8-qra ) naphthacene Pyrene
(naphtho(2,3-a)pyrenc)
(2 , 3-naphtho-l, 2-pyrene)
1-Hethylpyrene
5"3
Denzo[a]pyrene !
(1,2-benzpyrene) 1
(3,4-benzpyrene*) I
Structure
T t *
Formula
Carclnogenlclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
\rnax, no
Log c
Solvent
C24H14
C16H10
152.
>360
6.8S x 10
C17H12
,-7
C20H12
BaP
178.8-179.3
5.49 x l
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Structure
Benzo|e]pyrene
(4,5-benzpyrene)
(1,2-benzpyrene*)
Dibenzo[a,1]pyrene
(2,3-4,5-dibenzpyrene)
(Dlbenzo [def, p ] clirysene)
(1,2-3,4-dlbenzpyrene*)
Dlbenzo[a,h]pyrene
(1,2-6,7-dibenzpyrene)
(Dlbenzo[b,def ]chrysene)
(3,4-8,9-dibenzpyrene*)
oS9°
Dlbenzo[a,1]pyrene
(2,3-6,7-dibenzpyrene)
(4,5-8,9-dibenzpyrene*)
Formula
Carcinogeniclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Amax, no
Log e
Solvent
C20H12
BeP
178.9
5.54 x 10
C24H14
.-9
C22H14
•f + +
DBahP
320-320.5
290 301 313 379
4.54 4.94 5.23 3.60
benzene
C22H14
DBalP
281-282.5
401
4.03
424
4.40
451
4.59
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
I
~J
Compound Dibenzo[a,e]pyrene
Structure IT J. J
Formula C22Hli
Carcinogeniclty + +
Acronym
Physical properties
Melting point, "C
Boiling point, °C
Vapor pressure, Torr
A max, nm
Log c
Solvent
Dibenzo[cd,jk]pyrene Indeno[l,2,3-cd]pyrene Chrysene
(anthanthrene) (o-phenylenepyrene)
(dibenzo[def ,mno] chrysene)
U '
r'V'V^i r^r^ "r^T^**!*
rVrV rrVrS .^fWv^0^3
kAAx1 kA-kAx1 KJL/ly *
7 t
C22H12 C22H12 C18H12
+ +52
Ch
257 254
A48
344 351 360
2.88 2.62 3.00
EtOH
-------
Table 3-1 (Cont'd). POLYCYCLIC AROMATIC HYDROCARBONS
Compound
Ferylene
Benzo[ghi]perylene
Coronene
Structure
Formula
oj Carcinogenicity
00 Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log e
Solvent
C20H12
Per
273
ca 500
C22H12
BghiP
273
1.01 x 10
,-10
C24H12
Cor
438
525
1.47 x 10
-12
-------
Table 3-2. AZA AND IMINO ARENES
Compound
Acridine
Benz[a]acrJdine
(1,2-benzacridine)
Benz[c]acridine
(3,4-benzacridine)
Structure
OCX?
Formula
Carcinogenicity
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
111
>360
C17H11N
C17H11N
Xmax , nm
Log c
Solvent
-------
Table 3-2 (Cont'd). AZA AND IMINO ARENES
Compound
Dibenz[a,J ]acridine
(1,2-7,8-dibenzacridine)
Dibenz[a,h]acridine
(1,2-5,6-dibenzacridine)
Dibenz[c,h]acridlne
(3,4-5,6-dibenzacridine)
Structure
F°rmula
Carclnogenicity
Acronym
Physical properties
Melting point, °C
Boiling point, "C
Vapor pressure, Torr
Xmax, nm
Log E
Solvent
C21H13N
+ +
220
C21H13N
228
C21H13N
-------
Table 3-2 (Cont'd). AZA AND IMINO ARENES
Compound
Structure
Carbazole
Benzo[a]ca rba zole
(1,2-benzcarbazole)
oi?
Dibenzo[a,g]carbazole
(1,2-5,6-dlbenzcarbazole)
ro
Formula
Carcinogeniclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log c
Solvent
246
355
C16H11N
C20H13N
-------
Table 3-2 (Cont'd). AZA AND IMINO ARENES
Compound
Dibenzo[c,g]carbazole
(3,4-5,6-dibenzcarbazole)
Dibenzo[a,i]carbazole
(1,2-7,8-dibenzcarbdzole)
Quinoline
Structure
co
ro
ro
Formula
Carcinogenicicy
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log e
Solvent
C20H13N
DBcgC
C20H13N
53
-------
Table 3-2 (Cont'd). AZA AND IMINO ARENES
Compound
Benzo[f Iquinoline
Benzo[h]quinoline
H-Indeno(l,2-b)quinoline
Structure
to
ro
Formula
Carcinogenicity
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Amax , nm
Log E
Solvent
54
-------
Table 3-2 (Cont'd). AZA AND IMINO ARENES
Compound
Isoquinoline
Benzo[f]isoquinoline
Phenanthridine
Structure
ro
Formula
Carcinogenicity
Acronym
Physical properties
Melting point, °C
Roiling point, °C
Vapor pressure, Torr
Xmax, nm
Log e
Solvent
-------
Table 3-2 (Cont'd). AZA AND IMINO ARENES
Compound
4-Azafluorene
(5-H-indeno[l,2b]-pyridine)
4-Azapyrene
(Benzo(lam)phenanthridine)
1-Azafluoranthene
(Indeno-[1,2,3-ij]isoquinoline)
Structure
cxo
oS.
ro
tn
Formula
Carcinogenicity
Acronym
Physical properties
Melting point, "C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log c
Solvent
-------
Table 3-3. MISCELLANEOUS POLYCYCLIC ORGANIC MATTER
Compound
Phenalene-1-one
Anthanthrone
Xanthene-9-one
7-H-Benz(de)anthracene-7-one
(benzanthrone)
Structure
oio
I
l\>
CTl
Formula
Carcinogeniclty
Acronym
Physical properties
Melting point, °C
Boiling point, °C
Vapor pressure, Torr
Xmax, nm
Log c
Solvent
-------
3.2.2 Physical Properties
Most of the POM compounds are high melting/high boiling point solids that
appear to be extremely insoluble in water. With the exception of the basic
nitrogen heterocyclics (e.g., quinolines, acridines), the major POM compounds
do not dissociate and, therefore, are found in the neutral fractions of
extracts of particulate material. '
Only limited physical data are available on the numerous POM compounds.
The information that is available is tabulated in Tables 3-1, 3-2, and 3-3.
Melting points are available for most compounds and most values are consider-
ably over 100°C (phenanthrene [101°C] and benzo[c]phenanthrene [68°C] are
unusual exceptions).
Vapor pressures of the pure chemical are available for nine PAH's.
Depending upon the ring size and molecular weight of the compounds, the vapor
pressure of the pure compound varies from 6.8 x 10 Torr for phenanthrene
-12
(3 rings and 14 carbons) to 1.5 x 10" Torr for coronene (7 rings and 24
24 ?*5 ?fi
carbons). ^»"«to This property has considerable impact on the amount of
PAH's that remain adsorbed on particulate matter in the atmosphere and retain-
ed on particulate matter during collection of air samples on glass fiber
filters. In one study the following compounds experience the indicated
losses at the various times when filtered air is drawn over particulate
1 27
matter at 1.2 cubic meters per minute: * (1) tetracyclic or larger PAH, 2
hours - no loss; (2) tetracyclic PAH, 24 hours - some loss; and (3) penta-
cyclic or larger PAH, 3 weeks - no loss. The actual retention of POM on
particulate during collection is likely to depend upon temperature, face
3-27
-------
£
200
300 400
WAVELENGTH, nm
Figure 3-3. Absorption spectrum of benzo[a]pyrene in ethanol :28
a, 4030 (3.60); p, 3845 (4.44), 3635 (4.36), 3470 (4.10), 3300
(3.76); B, 2965 (4.76), 2843 (4.66), 2740 (4.50); Bf, 2655 (4.66),
2540 (4.60); g", 2250 (4.44).
3-28
-------
velocity of the air with respect to the filter, and the adsorption character-
istics of the individual ROM's.
The ultraviolet absorption spectra are also available for many compounds
(Table 3-1). Most of the PAH's absorbed light strongly at wavelengths longer
28
than 300 nm. The absorption spectra for benzo[a]pyrene (Figure 3-3) is
typical. Because these compounds absorb light at wavelengths found in sun-
light (>300 nm), it is possible that they may photochemically react by direct
excitation (see Section 3.3.1). However, the available spectra were taken for
PAH's in organic solvents, while PAH's in the environment are usually found
associated with particulate matter and adsorbed PAH's may have considerably
different absorption properties.
3.2.3 Atmospheric Forms of POM
Relatively little information is available on the exact form of the
various POM's in the atmosphere. Because of the high melting points and low
vapor pressures of most POM's, the compounds are generally considered to be
associated with particulate matter, either as pure material or adsorbed to
2
other particulate matter.
Some information is available on the relationship of POM's to particle
size, and this has particular significance with respect to respiratory tract
entry, retention and deposition. The aerodynamic size of particles will
determine how much and where the particles are deposited. Relatively large
particles (> diameter of 10-15 ym) are deposited in the nasal and oral cavi-
ties. Smaller particles will pass into the tracheo-bronchial regions. The
actual deposition efficiencies within the respiratory tract will vary consider-
ably. They are dependent upon the dimensions and configurations of the
3-29
-------
Individual air path, the pattern and depth of respiration, and the character-
pa
istics of the particles.
The particle size also affects the residence time of participate matter.
Urban aerosols appear to have a residence time without precipitation of 4 to
40 days for particles less than 1 urn in diameter and 0.4 to 4 days for par-
ticles 1 to 10 ym in diameter.
Tebbens et al. have separated particulates into different size frac-
tions before extraction. They found a constant weight of BaP per unit weight
of carbonaceous particles for all particle sizes.
32
DeMaio and Corn collected particles with a two-stage elutriator. The
first stage collected 50 percent of particles with a diameter of 4.6 ym and
100 percent of 6.5 ym particles. The second stage, which consisted of a
glass fiber filter paper collected 100 percent of all particles greater than
0.3 ym. The amount collected in the two stages varied considerably for the
six compounds analyzed and depended upon the sampling period. Only 5 percent
of the BaP was detected in stage one while more than half the pyrene was found
33
in stage one. Kerte"sz-Saringer and coworkers used a four stage Casella
cascade impactor backed up with a glass fiber filter and determined the BaP on
various size fractions at various times (September 11 to September 24; October
15 to November 14; and November 21 to December 16) of the year in Budapest.
32
Their results (Figure 3-4) agree with those of DeMaio and Corn in indicating
that the great majority of BaP is in the respirable size range. In winter,
when the concentration of BaP is the highest, the pollutant is associated more
with smaller particles. Also, about half the weight of atmospheric BaP is
associated with particles of radii less than 0.15 ym.
3-30
-------
99
98
97
96
95
-J 90
i-
z
LU
oc 80
UJ
a.
? 70
60
50
40
30
0.1
1.0
R ADI US (r). tun
• 9/11 to 9/24 _
O 10/15 to 11/14
A 11/21 to 12/16
D AVERAGE
10
Figure 3-4. Size distribution of particles containing benzo[a]pyrene.
33
3-31
-------
34 35
Katz and Pierce ' have conducted a detailed study of the relationship
of PAH's to relative size of particulate matter in Toronto, Ontario. Partic-
ulates were collected at five locations by a five-stage Anderson Hi-Vol
cascade impactor. The size ranges (urn) for the five stages were: 1 >_ 7.0;
2 = 3.3 to 7.0; 3 = 2.0 to 3.3; 4 = 1.1 to 2.0; and 5 _< 1.1. Twenty PAH
compounds were monitored, but since the data for the other compounds were
similar to data for BaP (Figure 3-5), only a few data on other isomers were
presented. A seasonal relationship to submicron BaP particulates was found,
with the highest mass fractions of submicron BaP particles (^ 60 percent total
aerosol mass) found during winter. At two locations, 40 to 60 percent of the
PAH was associated with submicron particles; at another location only 6 to
14 percent PAH was thus associated. Differences were also found between the
fractional mass of submicron BaP particulates samples taken at 50 feet and at
300 feet above the ground at different locations. Similar size distribution
curves were also found for two oxygen heterocyclic PAH's. These results
demonstrate that BaP and PAH's are associated primarily with small, respirable
particles.
In elevated temperature combustion systems, substantial amounts of ROM's
probably exist in the vapor state. However, they appear to condense or adsorb
on other particles rapidly once they are away from the high temperature areas.
OC
Thomas et al. determined the BaP in deposited soot in the upper portion of
the glass chimney of a combustion system and compared it to the BaP in soot
collected on a filter. No difference was detected, suggesting that BaP
rapidly adsorbs onto particulate matter as soon as it leaves the combustion
area. Thomas et al. also determined the amount of BaP from the combustion
3-32
-------
100
50
i- 30
E
s
o
C 10
I 5
I-
Ul
u
a:
§ 50
|, 30
%
CO
£ 10
UJ
U
5 5
a.
I I I I
YORK-S
BATHURST-S
MacDONALD
CARTIER
.COLLEGE-S
COLLEGE-W
STAGE NO.
Figure 3-5. Percent mass of benzo[a]pyrene in relation to
stage number for five sampling sites in Toronto, Canada.35
3-33
-------
system collected on a filter (maintained at 80° to 90°C) or collected in a
water and cold trap. Even at the elevated temperature of the filter, 96.3
percent of the total BaP was found on the filter. Sublimation of BaP off the
particulate trap was ruled out.
37
Krstulovic et al. have placed polyurethane plugs behind a standard
glass fiber filter (1.0 pro retention with 98 percent efficiency) to collect
particles that pass through. The authors refer to these particles as the gas
phase because they act as gas or vapor in that they follow fluid streamlines
and are subject to Brownian movement. Concentrations of several individual
compounds in air samples taken in Rhode Island were greater on the foam plug
than on the filter. For example, the concentration of dibenz[a,c]anthracene
3 3
in Providence was 3709 ng/1000 m on the foam plug but 806 ng/1000 m on the
34 35
filter. These results are consistent with those of Pierce and Katz ' which
indicated that sizable amounts of PAH's will be associated with particles less
than 1 ym in diameter.
38
Natusch and Tomkins have developed a mathematical description of the
process of adsorption of PAH's vapors on fly ash particles. Their calcula-
tions indicated that PAH's would almost certainly exist as vapors at tempera-
f
tures (>150°C) encountered in the stack systems of fossil-fueled power plants.
However at ambient temperatures (-10 to 30°C), "essentially quantitative
38
adsorption [to particulates] would be expected." Their theoretical study
also suggests that since "the extent of adsorption of PAH's is proportional to
the frequency of collision with the available surface area, then adsorption
will result in small respirable particles being preferentially enriched (per
38
unit mass) in potentially carcinogenic PAH's."
3-34
-------
3.3 ATMOSPHERIC CHEMISTRY
The POM compounds emitted to the atmosphere have been shown to have con-
siderably different stability. Unknown, however, is whether the degradation
39
products are more or less toxic. Preliminary evidence by Pitts and coworkers
suggests that in some instances (e.g., nitrous oxide reaction with benz[a]-
pyrene to form 6-nitrobenzo[a]pyrene and a mixture of 1-nitro and 3-nitro-
benzo[a]pyrene) the products are more mutagenic.
The atmospheric stability of different POM compounds is dependent upon
such factors as molecular structure, amount of available light, and presence
of oxidizing pollutants. Also, because ROM's in the atmosphere are mostly
found in the atmosphere adsorbed to particulate matter, such factors as
particle size (affects rate of deposition and surface area exposed), porosity
of the particle, and adsorption factors are also likely to be important to
environmental stability. The rates that have been measured vary considerably
depending upon the experimental conditions. 3.3.1 Photooxidation
Most investigators have used light sources that simulate sunlight (>300 nm),
However, the form of the ROM's being photolyzed has been much more varied.
Solutions of compounds are one of the most convenient forms for photolysis
studies but the relevance of solution photochemistry to photolysis of POM
40
adsorbed on particul ate matter is probably remote. Kuratsune and Hirohata
photolyzed 13 PAH's in cyclohexane and dichloromethane with sunlight and with
fluorescent lamps filtered through glass to provide wavelengths longer than
300 nm. They found that naphthacene was the most unstable of the PAH's
tested and that benzo[a]pyrene and alkyl derivatives of benz[a]anthracene were
labile to light. The following compounds were stable under the experimental
3-35
-------
conditions: phenanthrene, fluorene, pyrene, fluoranthene, chrysene, benz[a]-
anthracene, and benzo[k]fluoranthene. In another study by Kuratsune, photol-
ysis of BaP in benzene (light >280 nm and oxygen was present) allowed the
isolation of 6,12-, 1,6-, and 3,6-benzo[a]pyrenequinones.
Because POM's in the environment are usually found adsorbed to partic-
ulate matter, many investigators have studied the photolysis of POM's natur-
ally occurring on particulates from combustion, POM's coated on some solid
particles, and POM's coated in thin films on a smooth surface. Typical of
42
photolysis studies of pure POM's adsorbed on solids is the work of Inscoe
wh'o examined photodecomposition of PAH's during thin layer chromatography.
She exposed 15 PAH's adsorbed on four different adsorbents (silica gel G,
aluminum oxide G, cellulose powder, and acetylated cellulose) to ultraviolet
light and ordinary room light. No changes were noted for phenanthrene,
chrysene, triphenylene, and picene, but pronounced changes were detected for
the other 11 compounds when silica gel and aluminum oxide were used; less
dramatic changes were found with the other two adsorbents. Exposure to
ordinary room light gave slower but similar results. The eleven compounds
that were photosensitive were anthracene, naphthacene, benz[a]anthracene,
dibenz[a,c]anthracene, dibenz[a,h]anthracene pyrene, benzo[a]pyrene, benzo[e]-
pyrene, perylene, benzo[ghi]perylene, and coronene. Inscoe also identified
1,6-pyrenedione and 1,8-pyrenedione as photoproducts of pyrene. As will be
discussed later, some of these compounds appear to be fairly stable when
adsorbed on natural particulate matter and, therefore, the above results may
be only indicative of what occurs during thin layer chromatography.
3-36
-------
43
Andelman and Suess attempted to simulate photodecomposition of PAH's in
water by adsorbing BaP on calcium carbonate and irradiating aqueous suspensions
with white fluorescent light. BaP was found to be unstable under laboratory
illumination with 80 to 90 percent lost in 17 hours in 15 to 50 percent
dioxane-water; but it is apparently somewhat dependent upon the liquid system
since BaP is stable for 17 hours in 100 percent dioxane or 50 percent methanol/
water.
A couple of investigators have examined the effect of some common air
44
constituents on the photochemistry of adsorbed POM. Jager and Rakovic
adsorbed pyrene and BaP to fly ash and alumina from an acetone solution and
irradiated the adsorbed compounds in a quartz tube filled with 10 percent S02
in air at room temperature and at 60° to 70°C. From irradiation of pyrene at
room temperature, the authors were able to isolate many compounds containing
sulfur, including 1-pyrenesulfonic acid (15 percent); from BaP, benzo[a]-
pyrene-4-sulfonic acid was detected. Whether this type of reaction occurs in
ambient air samples is unknown since the experimental concentration of S02 is
39
much higher than is normally present in ambient air. Pitts and coworkers
have also indicated that POM's may react with nitrous oxide to form nitro
derivatives.
45
Geacintov studied the photolysis of 20 PAH's adsorbed on solid poly-
styrene fluffs in the presence of oxygen and nitric oxide. He found neglig-
ible photochemical degradation compared to quenching by the paramagnetic
gases, Op and NO. However, the PAH's were efficient photocatalysts for the
formation of singlet oxygen, a reactive oxidizing agent which may react with
the PAH's.
3-37
-------
Perhaps the earliest study of POM photochemistry was conducted by Falk
46
and coworkers. They noted that the amount of BaP in ambient air compared
with other PAH's was greater than one would expect on the basis of amounts
emitted and thought this could be explained by a difference in atmospheric
stability. They studied the stability of two forms of PAH: "pure" (dissolved
in solvent and applied to a filter) and "adsorbed" (combustion particles
collected on filter - sample divided into control and exposed sample). The
samples were exposed to air and to a synthetic smog (1 hour of exposure
equivalent to approximately 100 hours of exposure to natural smog) with and
without irradiation. Their results are presented in Table 3-4. For most
compounds, destruction of the "pure" samples is essentially similar in dark or
light. However, BaP stability is significantly different with and without
light. Also, the lower rate of reaction of the adsorbed form of BaP suggests
that adsorption may provide some protection from photooxidative processes.
The results for pure unadsorbed chrysene with light are difficult to explain.
47
Falk et al. concluded that the three-ring compounds disappear rapidly and
that differences in atmospheric stability can explain why the ratio of pyrene
to BaP is reversed following atmospheric residence. Also adsorption on
particulate matter seems to have a stabilizing effect compared to coating on a
filter.
Tebbens et al. also used the filter paper procedure of Falk et al.
to study photolysis of BaP by sunlight or simulated sunlight. With BaP
deposited on various filters from an ether solution, different filter material
31
resulted in different losses (60 to 92 percent loss). Tebbens et al. also
studied the chemical modification of BaP and perylene in smoke passed through
3-38
-------
GO
1O
Table 3-4. PERCENT DESTRUCTION OF POLYCYCLIC AROMATIC HYDROCARBONS
UNDER ATMOSPHERIC CONDITIONS^
Pure Unadsorbed Compounds
Anthanthrene
Phenanthrene
Pyrene
Fluoranthene
Benzo[a]pyrene
Benzo[e]pyrene
Benzo[ ghi]perylene
Coronene
Chrysene
Air
24 hr
44
39
24
17
0
—
0
0
0
in dark
48 hr
49
61
43
20
0
--
0
0
0
Air in
24 hr
42
34
20
16
21
--
0
0
11
light
48 hr
44
60
42
24
22
—
0
0
0
Smog in light
1 hr
—
--
83
59
50
—
27
5
15
Adsorbed on
Air in light
48 hr
5
-
1
4
10
7
0
—
_-
soot
Smog
1 hr
55
—
58
59
18
51
67
—
__
-------
a 22-foot dynamic flow chamber (Pyrex pipe surrounded with fluorescent lamps)
by comparing the difference between irradiated and non-irradiated samples.
They found that irradiation caused disappearance or modification of 35 to
65 percent of the original content and that oxygen although its presence
increases the rate of photodegradation, is not necessary for photoalterations.
oc
Thomas et al. used a dynamic flow-through chamber that was coupled to
a furnace and controlled lighting having one-quarter the intensity of an
average July noonday sun. They measured the BaP/soot at the entrance and
exit of the chamber. A 58 percent decrease in the ratio was noted with the
light turned on compared to when the light was off (retention time of 40
•tc
minutes). Thomas et al. also examined the effect of particle size by
coating glass beads (1 g of either 220 urn or 28 pm diameters) by evaporating
the solvent. The beads were then exposed to sunlight in flasks and agitated
hourly to expose new surfaces. BaP on small beads decreased 1 percent in 12
hours; on large beads, 1 percent in 7 days. The authors concluded that the
60 percent decrease in the 40 minutes retention time of the BaP/soot in the
dynamic chamber may be related to the much greater surface area of the soot
exposed to light.
48
Lane and Katz have recently concluded that the previous experiments
were not representative of actual atmospheric conditions, since the oxidant
levels used were often too high and fluorescent lamps are poor simulators of
sunlight. They used a dynamic flow reaction chamber (20-liter glass jar) with
0, levels of zero to 2.28 ppm and irradiation from a Quartzline lamp. They
studied the disappearance of 500 ng of BaP, benzo[b]fluoranthene (BbF), and
benzo[k]fluoranthene (BkF), distributed in a thin dispersion in a petri dish.
3-40
-------
Table 3-5. THE HALF LIVES OF BaP, BbF, and BkF UNDER VARIOUS
REACTION CONDITIONS48
Reaction
Irradiation
None
Quartzline
Q500T/CL
lamp
conditions
Ozone
concentration (ppm)
0.19
0.70
2.28
0.0
0.19
0.70
2.28
BaP
0.62
0.4
0.3
5.3
0.58
0.2
0.08
Half lives,
BbF
52.7
10.8
2.9
8.7
4.2
3.6
1.9
hra
BkF
34.9
13.8
3.3
14.1
3.9
3.1
0.9
aThe half life was determined from the linear regression analysis of the
initial linear portion of each decomposition curve.
3-41
-------
The results presented in Table 3-5 show that BaP reacts rapidly with ozone
compared to BbF and BkF, even in the absence of light. This is particularly
significant because this type of non-photochemical oxidation could occur
during the normal 24-hour high-volume procedure used for sampling ambient air.
The authors also found that the rate of decomposition slowed in time, suggest-
ing that the surface-exposed layer reacted quickly but hindered the decomposi-
tion of subsurface material. However, it should be kept in mind that these
results are based upon PAH's coated in a thin film on glass. Whether these
are the same results that would be obtained with PAH's adsorbed on soot is
45
unknown. Falk et al. have shown that soot adsorption can have a stabilizing
effect on BaP.
Relatively few studies have attempted to identify the photooxidative
41 42
products. As indicated earlier, Masuda and Kuratsune and Inscoe have
identified quinones of BaP and pyrene. This is consistent with the monitoring
49
results of Pierce and Katz, who tentatively identified five polycyclic
quinones in air samples in Toronto. The seasonal increase of polycyclic
quinones during the summer is compatible with a photochemical mechanism.
3.3.2 Oxidation
As indicated in some studies in the previous section, light is not
necessarily required for the atmospheric decomposition of POM's. Falk et
al. found that for many PAH's (excluding BaP) the amount of loss of an
individual compound coated on a filter was the same in air in dark as in
light. Also, the amount of loss of PAH's adsorbed on soot was very high in a
synthetic smog that had a high oxidant concentration. In addition, Lane and
48
Katz found that BaP reacted rapidly in reasonably low ozone concentrations
3-42
-------
(0.19-0.70 ppm) without irradiation and that the addition of irradiation had
little effect on the rate. However, the other two PAH's (BbF and BkF) were
not nearly as susceptible to ozone oxidation. Thus, it appears that ROM's
will be susceptible to air oxidation without light irradiation and that the
reactivity is likely to vary for different structures.
27
Commins also provided suggestive evidence of nonphotochemical decompo-
sition of PAH by collecting PAH particulate matter from air and comparing the
results of immediate analysis to results from analysis after 1 year of
storage in a sealed envelope (Table 3-6). Significant loss of lower molecular
weight PAH's was noted but little loss with the higher molecular weight com-
pounds was found. This loss could be explained by evaporation of the lower
molecular weight compounds rather than by oxidation.
3.3.3 Atmospheric Stability
The above results would suggest that many ROM's oxidize or photodegrade
at a significant rate under atmospheric conditions. However, no satisfactory
quantitative rate data are available. In contrast to the results reported
above, Lunde and Bj0rseth published suggestive evidence that many ROM's are
stable enough in the atmosphere to travel long distances. They monitored air
samples in Norway which had different trajectories. They identified 20
different PAH's and determined that samples with trajectories from western
Europe contained about 20 times more PAH than samples with trajectories from
northern Norway or stationary air from southern Norway. The PAH found in high
concentrations under appropriate wind trajectories were phenanthrene, anthra-
cene, methylphenanthrene/-anthracene, fluoranthene, dihydrobenzo[a&b]fluorenes,
3-43
-------
co
Table 3-6. COMPARISON OF PAH CONTENT OF AIR SOLIDS BEFORE
AND AFTER STORAGE27
PAH
Fluoranthrene
Pyrene
Benzo[a]pyrene
Benzo[e]pyrene
Anthanthrene
Benzo[ghi]perylene
Coronene
Vapor pressure of pure
compound25,26
6.83xlO"7
5.49xlO"9
5. 54x1 O"9
l.OlxlO'10
1.47xlO"12
Analyzed immediately
after collection
225
328
111
71
70
252
142
Concentration of PAH, yg/5
Analyzed 1 yr after
collection
18
38
76
55
55
226
140
smoke
Loss
%
92
88
32
23
21
10
1
-------
pyrene, benzo[a]fluorene, benzo[b]fluorene, 1-methylpyrene, benzo[c]phenan-
threne, benz[a]anthracene, chrysene/triphenylene, benzo[b&k]fluorathene,
benzo[e]pyrene, benzo[a]pyrene, perylene, indeno[l,2,3-cd]pyrene, benzo[ghi]-
perylene, anthanthrene, coronene. These results suggest that the above com-
pounds are relatively stable in the atmosphere in the form in which they are
naturally present.
3.4 SUMMARY AND CONCLUSIONS
The POM chemical groups most commonly found in ambient air are polycyclic
aromatic hydrocarbons (PAH's), such as benzo[a]pyrene, and their nitrogen
analogs, aza and imino arenes. Other related compounds such as carbonyl
arenes and dicarbonyl arenes (quinones) are less commonly detected.
The major environmental sources of POM's appears to be from combustion or
pyrolysis processes which use materials containing carbon and hydrogen.
Current theory suggests a free-radical, step-wise, sequence mechanism which
with various fuels could results in the formation of hundreds of POM's.
Most of the POM's are high melting/high boiling point solids that are
very insoluble in water. The available vapor pressures of the pure compounds
A TO
vary for the individual compounds from 10 Torr (3 rings) to 10 Torr (7
rings). The PAH's are strong adsorbers of ultraviolet light of wavelengths
from 200 nm to 400 nm.
It is generally agreed that most POM compounds are associated with sus-
pended particle matter, with a large portion found with particles smaller than
1 pm. However, two or three ring compounds may be partially found in the
vapor phase. Whether POM are condensed into discrete particles after cooling
or are adsorbed on surfaces of existing particles is still unknown. Urban
3-45
-------
aerosols appear to have a residence time without precipitation of 4 to 40 days
for particles less than 1 \m in diameter and 0.4 to 4 days for particles 1 to
10 ym in diameter. Thus the atmospheric lifetime of a POM particle will be
closely related to its particle size.
Experimental chemical and photochemical reactivities of ROM's on particu-
late matter vary considerably from half-lives of less than a day to several
days. Particularly interesting are the different reactivities noted for the
various compounds studied and the indication that reaction rates of compounds
on smaller particle sizes are likely to be faster than those of larger particles,
Light irradiation considerably accelerates the decomposition of some compounds
but not others. Also, various experimental conditions have given contradic-
tory results. One report has indicated that oxidation by ozone is the most
important decomposition process for BaP in air, but many other reports have
documented the photochemical susceptibility of BaP. However, monitoring data
suggest that at least 20 PAH's are stable enough in the form found in the
atmosphere that they can travel long distances with particulate matter. Thus,
although an exact residue time of POM is difficult to estimate from the avail-
able data, many of the POM compounds are stable enough to remain at signifi-
cant concentrations during transport from the source to where they are inhaled.
Although the smaller particles will have a longer atmospheric residence time,
they will probably also react faster because of the greater surface area
exposed to oxidants and light. All the available information does support
previous conclusions that at least the outer layer of some POM's adsorbed on
particles are relatively reactive. However, this may mean that there is an
inner layer of POM's that would be relatively stable and perhaps available for
3-46
-------
elution by biological fluids following inhalation. The relatively long
stability of several PAH's based upon monitoring data is consistent with this
possibility. Only limited information is available on the products of decom-
position or their toxicologic properties. Quinones appear to be common
atmospheric degradation products of PAH's.
3-47
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3. Sawicki, E. Airborne carcinogens and allied compounds. Arch. Environ.
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6. Hoffman, D. and E. L. Wynder. Organic particulate pollutants-chemical
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7. Boubel, R. W. and L. A. Ripperton. Benzo[a]pyrene production during
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10. Crittenden, B. D., and R. Long. The mechanisms of formation of polynuclear
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11. Suess, M. J. The environmental load and cycle of polycyclic aromatic
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12. Blumer, M., and W. W. Youngblood. Polycyclic aromatic hydrocarbons in
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13. Hites, R. A., R. E. LaFlamme, and J. W. Farrington. Sedimentary polycyclic
aromatic hydrocarbons: The historical record. Science, 198:829-831,
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14. Dipple, A. Polynuclear aromatic carcinogens. In; Chemical Carcinogens,
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15. Patterson, A. M., L. T. Capell, and D. F. Walker. The ring index. A
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16. Capell, L. T. and D. F. Walker. Supplement I (1957-1959) to the ring
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17. Capell, L. T. and D. F. Walker. Supplement II (1960-1961) to the ring
index. American Chemical Society, Washington, D.C. 1964.
18. Capell, L. T. and D. F. Walker. Supplement III (1962-1963) to the ring
index. American Chemical Society, Washington, D.C. 1965.
19. Hartwell, J. L. and P. Shubik. Survey of compounds which have been treated
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Bomberger, and C. V. Fojo. The environmental fate of selected polynuclear
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25. Murray, J. J., R. F. Pottie, and C. Pupp. The vapor pressures and enthalpies
of sublimation of five polycyclic aromatic hydrocarbons. Can. J. Chem.,
5£(4):557-563, 1974.
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26. Pupp, C., R. C. Lao, J. J. Murray, and R. F. Pottie. Equilibrium vapor
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27. Commins, B. T. Interim report on the study of techniques for determination
of polycyclic aromatic hydrocarbons in air. Natl. Cancer Inst. Monograph
No. 9, 225-233, 1962.
28. Clar, E. Polycyclic Hydrocarbons. New York and London, Academic Press.
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borne Particles. Washington, D.C. 1977.
30. Eswea, N.A. and M. Corn. Residence time of particles in urban air.
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31. Tebbens, B. D., J. F. Thomas, and M. Mukai. Fate of arenes incorporated
with airborne soot. J. Amer. Ind. Hyg. Assoc., 27_:415-422, 1966.
32. DeMaio, L., and M. Corn. Polynuclear aromatic hydrocarbons associated
with particles in Pittsburgh air. J. Air. Pollut. Contr. Assoc., 16:67-
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33. Kertesz-Saringer, M., E. Meszaros, and T. Varkonyi. Technical Note on the
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Atmos. Environ., J>:429-431, 1971.
34. Katz, M., and R. C. Pierce. Quantitative distribution of polynuclear
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40. Kuratsune, M. , and T. Hirohata. Decomposition of polycyclic aromatic
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3-52
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DRAFf
JPO NOT QUOTE OR CITE
4. SAMPLING AND ANALYTICAL METHODS FOR POM'S
4.1 INTRODUCTION
In vivo biassays have demonstrated that the greatest carcinogenic activ-
ity of organic pollutants in air is associated (1) with the neutral fraction
containing both polynuclear aromatic compounds (PAH's) and their neutral
nitrogen analogs, the aza-arenes, and (2) with the basic fraction containing
the basic aza and imino arenes. Therefore, it is necessary to monitor these
three classes of compounds in environmental samples both for assessment of
carcinogenic potential and enforcement of any pollution discharge standard
that may be set to control their emission. Excluding the natural sources,
some of the contributing sources of ROM's in the air are from mobile sources
entering the atmosphere as vehicular and aircraft emissions and from station-
ary sources that include home heating, power plants utilizing fossil fuels,
refuse burning, road abrasions and industrial processes. The monitoring of
these POM compounds can be divided into four distinct steps: (1) sample
collection; (2) desorption of the collected compounds from the collection
media; (3) clean up and separation of the desorbed compounds; and (4) detec-
tion and analysis for quantisation.
The objective(s) of sampling must be defined clearly before the initia-
tion of sample collection. Three primary objectives in the consideration of
POM sampling include determination of (1) airborne concentrations of total
4-1
-------
suspended particulate matter, (2) distribution of particle size associated
with the ROM's, and (3) chemical composition of the particles and their
levels in the environment. In addition to these objectives, the selection of
sampling site(s) and implementation of appropriate sampling strategy play
important roles in the acquisition of relevant data desired from ambient air
sampling.
ROM's can be present in the air samples in three forms: (1) adsorbed on
foreign particulate matter, (2) condensed ROM's in suspension with air, i.e.,
aerosol form, and (3) vapor phase. Evidently, POM from different sources will
be present in all the three forms, although their proportion will depend on
the nature of the source. Any collection method for monitoring POM's should
take these factors into consideration. The errors in most sample collection
methods arise from the inability to collect either wholly or partly all three
forms of POM's, particularly the volatile components.
The desorption of the collected compounds is no less problematic. The
particulate adsorbed part of the POM's is bound firmly to the medium. This
often leads to incomplete and unreproducible desorption. The selection of
both the method of desorption and the nature of solvent (whenever used) play
an important role in the recovery of POM's obtained from this step.
The lack of clean up and separation of POM's in environmental samples
poses a serious hindrance to a better understanding of the composition. Yet
separation of hard-to-separate isomers and the trace constituents is quite
important. Small differences in the structure of these compounds may cause
great differences in the biological activities. Also, due to the specificity
of biological reactions, sometimes a trace component may produce more adverse
4-2
-------
biological effects than the predominant components. Therefore, the selection
of the clean up and separation procedure will not only depend on the nature of
the sample but also on the objective of the analysis.
With regard to the method of detection, any technique chosen must be
sensitive and selective to provide interference-free quantitation of the trace
components as well as the predominant ones.
Despite the greatest of precautions, there are some unavoidable losses,
both during collection and analysis of ROM's. The losses during analysis
alone may vary considerably depending on the nature of sample, method used,
and the experience of the analyst. To secure quantitative data internal
standards must be used from the beginning of the analysis. This is usually
done by spiking the sample with radioactive compounds, such as, C -benzo[a]-
pyrene, C -benzo[a]anthracene or some other nonisotopic compounds not present
in the original sample. A number of compounds including £-terphenyl, bi-
benzyl, and benzo[b]chrysene have been used for the latter purpose.
The instability of the ROM's resulting from volatility, photosensitivity,
and chemical transformation/degradation dictate that special precautions be
used in handling these samples. Losses and chemical transformation during
sampling and separation caused by these factors should be avoided whenever
possible. The state-of-the-art of the four individual steps required for POM
monitoring is discussed in the following sections with the above mentioned
difficulties in mind.
4.2 SAMPLING
The POM sampling methods can be divided into four groups: (1) mobile
sources, (2) tobacco smoke,(3) stationary sources, and (4) ambient air.
4-3
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4.2.1 Mobile Sources
The most important mobile source of ROM's in the air is from vehicular
exhaust. The sampling methods for ROM's from this source is treated in this
section.
Certain vehicular parameters play important roles in the characteristics
of POM emissions from this source. It is important to ascertain and define
these parameters even before initiating any sampling procedures. Performance
characteristics of the engine, its condition at the time of experimentation,
and the fuel characteristics influence the nature and amount of POM emissions.
The effects of performance characteristics, such as engine load, speed, cycle
of operation, fuel-to-air ratio, and operating temperature, have been demon-
1 2
strated by Spindt. Gross has shown the effect of accumulation of deposits
in the combustion chamber of the engine on the POM emission. A number of
3-7
investigators have demonstrated the relationship between POM emission
characteristics and fuel composition, namely, its aromaticity and PAH content.
A variety of procedures are available for sampling POM's from automobile
exhausts. It is not possible, however, to discuss all these procedures in
detail. The general principle of sampling auto exhausts and references to a
few procedures are presented here.
o
In one procedure, the participate matter and condensable vapors from
auto exhausts are collected by a total condensation trap. In another proce-
g
dure, the exhaust aerosols from the automobile are passed through a glass
cooler to bring the aerosol to an optimum temperature. The cooled aerosol is
then passed through a fiberglass filter and finally through a double filter
4-4
-------
of silica gel. The ROM's collected at different stages of the system are
individually eluted with organic solvents for their analysis.
Recently, Spindt used an air dilution method for the collection of
ROM's from auto exhausts. In this procedure, the hot exhaust aerosol is
precooled to 75-170°C by a precooler and is mixed with clean and dry air.
The air is chilled by passing it through a coil immersed in a bath of dry ice
and methanol to a temperature that gives a diluted sample temperature of 20°
to 30°C. The mixture is passed through a pretreated filtering system consist-
ing of a fiberglass pad placed ahead of a glass fiber filter. The purpose of
the fiberglass pad is to collect the bulk of the large soot particles before
the aerosol comes in contact with the glass fiber filter. The residual from
the aerosol is finally passed through a Chromosorb-102 trap. The sample flow
rate is measured by a dry gas test meter.
Irrespective of the collection method used, the efficiency of collection
must be known and must be reproducible. This is hardly the case for samples
q
collected from automobile exhausts. While some investigators have described
the efficiency of removal of particles of certain sizes, they did not report
the overall efficiency. By the use of radioactive tracer, one investigator
reported the recovery efficiency of BaP from automobile exhausts as low as
6 percent, under no-load condition, but failed to determine whether the loss
was principally during sample collection or in the analytical procedure. It
appears that there is a need for a standardized procedure for the collection
of POM from automobile exhausts which can determine the collection efficiency
and reproduce the technique with reasonable accuracy.
4-5
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4.2.2 Tobacco smoke—POM content In tobacco smoke depends primarily on the
processing methods used for the manufacture of tobacco products, namely, the
nature of the curing and drying process and steps involving incorporation
of additives, such as, flavoring materials. In addition, substantial amounts
of ROM's originate from the paper used to roll the tobacco of the cigarette.
In determining the POM content in tobacco smoke, it is important to realize
that mainstream smoke and sidestream smoke do not necessarily have the same
composition. The sampling method, therefore, should specify the part of
smoke that has actually been sampled.
For collection of mainstream smoke, the standard method consists of
using a fully automatic smoking machine where the cigarettes are smoked to a
butt length of 23 mm under standard conditions. These include a puff volume
of 35 ml, puff duration of 2 seconds and puff frequency of one per minute.
The collection of particulate matter is accomplished by an electrostatic
precipitator. In some methods, a cold-trap system replaces the eleclro-
12
static precipitator for the collection of smoke condensates.
For collection of sidestream smoke, a wide glass tube fitted on the
cigarette holder at the end opposite to the smoking side has been used.
The sidestream smoke from this tube is drawn through a side-arm and collected
by means of two traps in series, packed with glass-wood and cooled to -70°C.
4.2.3 Stationary Sources
Emission from stationary sources can be divided into two groups: (1)
Stack emissions and (2) fugitive emissions from road-way dust.
4.2.3.1 Emissions from stacks—Several methods are available for collecting
POM samples from these sources which include fossil fuel-fired steam generators,
4-6
-------
home heating stacks, municipal incinerators, Portland cement plants and coke-
oven plants. Only a few collection methods are described here.
The EPA Method-5 is designed to determine the particle emissions from
stationary sources under isokinetic conditions. The sample is isokinetically
withdrawn from the stack by means of a heated probe (minimum temperature of
250°F at the exit end) to prevent condensation of vapors and passed through a
heated (minimum temperature of 225°F) filter holder containing a precondi-
tioned glass fiber filter. The particulate-filtered gases are subsequently
passed through four impingers, the first two containing 100 ml water, the
third one empty and the fourth one containing 200 g silica gel. All the
impingers are cooled in an ice bath. The exit gases from the last impinger
pass through a dry test meter for recording the flow rate. The flow rate is
adjusted by the valves attached to the air pump(s).
Doubts have frequently been expressed regarding the collection of volatile
organic compounds by the EPA Method-5 sampling procedure described above. The
adsorbent sampler method developed by Jones et al. utilizes a Tenax bed to
adsorb these volatile organic compounds and reduce the sampling errors. The
stack gases, according to this method, are sampled isokinetically by a sampling
probe and passed through a heated filter as in EPA Method-5. After leaving the
hot filter, the emissions are cooled in a glass coil (120 by 0.8 cm) of the
adsorbent sampler and, then, pass through a Pyrex frit and into a cylindrical
column of Tenax bed (7 by 3 cm) containing 12 g of the resin. The flow rate
through the adsorbent sampler is typically 14 liters/min. The cooling coil and
Tenax adsorbent are maintained at a constant temperature by means of a thermo-
stated circulating water bath. The gases leaving the sampler are drawn through
4-7
-------
an aqueous Implnger, a silica gel trap and a dry gas meter by means of a vacuum
pump as in EPA Method-5.
Laboratory validation studies for the recovery of a few ROM's from spiked
samples by the above adsorbent sampler method is presented in Table 4-1.
Table 4-1. RECOVERY OF POM'S FROM ADSORBENT SAMPLER METHOD14
POM
Pyrene
Chrysene
Perylene
Benzo[ghi]perylene
Coronene
Recovery from
test #1
91+3
90+5
91+4
101+10
80+7
Recovery from
test #2
98+4
92+5
105+5
106+10
92+8
Recovery from
test #3
104+4
106+5
102+6
103+7
100+14
Although the absolute collection efficiency is difficult to determine
under actual field sampling conditions, a comparison of the total POM loading
14
between adsorbent sampler method and EPA method 5 was made by Jones et al.
Field studies with a 50-hp oil/gas fired boiler and effluents from carbon
3
black manufacturing facilities showed total POM loading of 55.2 and 124 yg/m ,
respectively, with adsorbent sampler and 4.2 and 56.5 yg/m with EPA method 5.
The higher collection efficiency for the adsorbent sampler is apparent from
this study. In addition, the adsorbent sampler method reduces the sampling
time by as much as 50 percent and demonstrates superiority in its performance
for collecting POM's from combustion systems burning higher sulfur fuel at a
relatively high particle loading.
As a phased approach to environmental sampling, a Source Assessment
Sampling System (SASS) has been developed by EPA's Industrial Environmental
Research Laboratory. Elements in the SASS train are designed to separate
source samples into size fractionated particulate, organic vapors and inorganic
4-8
-------
components. The sample from the stack is introduced into this sampling
system by a stainless steel inlet nozzle and a heat controlled stainless steel
probe at a flow rate of approximately 4 scfm. The sample from the probe
enters three cyclones with a backup filter to give four sizing intervals of
MO ym, 10-3 ym, 3-1 ym, and less than 1 ym. The temperature of the cyclones
and filter is maintained at 205°C. After particulate removal, the hot sample
gas is cooled to 20°C and passed through the XAD-2 sorbent. The condensate
passing through the XAD-2 is collected separately.
To trap the residual volatile inorganic materials, the sample next
enters three oxidative impingers cooled in an ice bath. A fourth ice-cooled
impinger containing indicating desiccant is used to prevent moisture from
entering the pump. A continuous sampling time of approximately five hours is
required for collection of acceptable sample size.
It should be mentioned that the SASS train has been used for a limited
field validation study. In one study conducted with doped fuel fired
boiler, the recovery of four volatile metals was found to vary between 33% to
75%. Another field evaluation study conducted with the SASS train proved that
the particulate concentrations determined by this method compared very well
with EPA method-5 in terms of both precision and accuracy. Although the
reproducibility of the SASS train for POM collection was not individually
evaluated in this study, organic materials collected by two SASS trains agreed
well in quantity and composition.
Recent studies have demonstrated that the stainless steel gas cooler
and XAD-2 cartridge of the SASS train may cause sample contamination with the
incoming gas stream. Replacing stainless steel with pyrex glass appears to
have obviated this problem.
4-9
-------
A simple non-isokinetic sampling procedure has been described by Parson
18
and Mitzner in which Pyrex glass tubing containing Tenax resin is directly
inserted into the stack. A portable pump is used to draw the sample through
the Tenax column at a rate determined by a rotameter. However, the serious
drawback with this system is its obvious inability to quantitatively adsorb
all the POM's at elevated stack temperatures.
19
A recent study conducted by Adams et al. to characterize the behavior
of different resins used as the sorbent trap showed that XAD-2 has a greater
volumetric and weight capacity than Tenax GC resins. Therefore, XAD-2 is
preferred as a sorbent trap for collection of POM's. A modified EPA Method-5
train with a sorbent trap operating for four hours is capable of collecting
all materials boiling above 190°C when using XAD-2 and above 240°C when using
Tenax GC traps. Both materials efficiently collect POM's, but the XAD-2 will
have a much greater capacity for the lower boiling compounds. A source
sampling train using XAD-2 as the adsorbent has been described earlier.
4.2.3.2 Fugitive Emissions from road-way dust—Owing to abrasions of tar and
bituminous road surfaces, particles are liberated which contain carcinogenic
POM's. It is, however, important to distinguish the contribution of vehicular
traffic towards the overall POM emissions near a highway. Emission from
exhausts, burning or spillage of lubricating oils and tire wear—all these
factors arising from vehicular traffic cause POM emission in the air. One
way to evaluate the POM emissions arising from abrasion of road materials
alone is to make comparative measurements alongside a highway section of tar-
on
asphalt and one of concrete, both subjected to an identical traffic load.
20
The POM emissions due to road abrasion are also dependent on seasonal variation.
4-10
-------
For collecting road abrasion samples according to particle size, an
21
Andersen sampler has been used by Ciaccio et al. When properly calibrated,
the sampler can be used to collect particles on stages 2 through 7, repre-
senting aerodynamic diameters from 0.43 to 7.0 ym which are purported to be
deposited in the three compartments of the lung.
The Model 21-000 Andersen sampler containing stages 0-7 having 1 mil
thick polypropylene circle on each stage, is conditioned at a controlled
temperature and humidity and the polypropylene circles on each stages are
weighed and placed again on the stages. The sampler is assembled and the
collection started at an appropriate rate. At the end of the sampling period,
the polypropylene circles containing the collected particles are conditioned
and analyzed for determining the particle size distribution.
For collecting total particulate matter, a Hi-Vol sampler with the
21
filter holder containing a flash-fired glass fiber filter has been used.
The flow rate during sampling can be adjusted to a suitable value for effi-
ciently collecting the particulate matter.
4.2.4 Ambient Air
The sampling of POM in ambient air is usually performed with the objec-
tive of determining the particle size distribution and nature and concentra-
tions of individual components at various points in the environment. The
selection of sampling sites play important roles in sample collection.
Sampling sites are determined to evaluate the following: (1) characterize
the rural or urban background levels, (2) assess the health hazards to people
in the vicinity, (3) determine source effects, and (4) establish transport
4-11
-------
22 23
mechanisms. Reference should be made to the available sources ' for
detailed treatment of these aspects in the selection of sites.
In addition to the selection of a preferable method and site, certain
other factors must be adequately taken into consideration during ambient
sampling. The height of the sampler intake above ground level, the local
topography and climate - each has influence on the data obtained. For example,
the influence of summer-like temperature on losses of benzo[a]pyrene from
airborne particles has been studied during real high-volume atmospheric samp-
24
lings. Occurence of seasonal variation in specific surface areas and
25
densities of suspended particulate matters has been observed. The effects
of wind on the collection efficiencies of particulate matter has been demon-
26
strated by Ogden and Wood. Other factors, such as sampling rate and time,
are also important in the overall sampling strategy. The total amount of
samples to be collected usually depends on the sensitivity of the analytical
method intended to be used for the determination of individual components.
The method for collection of ROM's from ambient air will be divided into
two sections depending on the objective of the sampling.
4.2.4.1 Collection of total air particulate matter—Air particulate matter
is usually collected on flash-fired glass fiber filters using a high volume
air sampler. The sampler consists of three units: (1) the face plate and
gasket, (2) the filter adapter assembly, and (3) the motor unit. The sampler
2
must be capable of passing environmental air through an approximate 400 cm
area of a clean 20.3 x 25.4 cm glass fiber filter at a rate of at least 1.13
3
m /min. The glass fiber filters should have collection efficiencies of at
least 99 percent for particles of 0.3 micron or larger in diameter. The
4-12
-------
motor must be capable of continuous operation for at least 24 hour periods.
It is important that the sampler be properly installed in a suitable shelter
to protect it from extreme weather conditions and debris. For measuring the
air flow rates through the sampling unit, it must be provided with either a
calibrated flow meter (rotameter) or a gauge. The details of this method are
27
given by Sholtes et al.
On the average, when a high volume sampler is located in an urban area,
it will collect approximately 250-350 mg of particulate matter while sampling
2000-2400 m3 of air during a 24 hour period. Of the total amount of the
particulate matter, approximately 10 percent, that is, 25 mg, will be the
28
organic fraction. The quantity of organic fraction generally needed for
the analysis of POM fraction depends on the sensitivity of the analytical
method used. However, to obtain the needed amount of organic fraction it may
become necessary to pool together organic fractions of several individual
high-volume air samples from a single monitoring site.
ROM's are present in polluted air sorbed onto airborne particulate
matter, usually characterized as primary and secondary. Primary particulate
29
matter is found in sizes between 1 urn and 20 \im. Secondary particulate
matter ranges in size from molecular clusters of the order of 5 nm to particles
29
with diameter as large as several micrometers. Very fine particles that
cannot be retained on fiberglass filters act like a gas or vapor in that they
follow fluid streamlines and are subject to Brownian motion. For collection
of this gaseous phase various adsorbents have been used.
In one of the methods, polyurethane foam has been used as adsorbent.
An aluminum sampling probe used to collect suspended particulate matter
4-13
-------
consists of a piece of tubing with a grid for holding a glass-fiber filter
and two cylindrical polyurethane plugs (8.5 x 6.0 cm). The plugs located
behind the glass-fiber filter prevents loss of volatile fraction of POM. A
31
similar method has been used by Fox and Staley for collecting both particu-
late and gas phase components from atmospheric samples.
32
Schuetzle et al. designed an apparatus for simultaneous sampling of
gaseous and particulate air pollutants. An adjustable one-stage impactor has
been used for sampling aerosols greater than 1-2 urn in diameter and is follow-
ed by a glass-fiber filter for collection of particles less than 1-2 pm in
diameter. A properly conditioned Chromosorb-102 support is used to trap
gaseous air pollutants.
33
A sampling system using only an adsorbent has also been used. It is a
simple system consisting of a vacuum pump, a flow measuring and regulating
device, and a sample tube containing the adsorbent. The sample tubes are 110
by 10 mm and contained 4 ml of conditioned Tenax GC held in position by plugs
of silanized glass wool.
The usefulness of the adsorbent in collecting ROM's not otherwise retained
on the glass-fiber filter is shown by Krstulovic et al. Table 4-2 shows that
the amount of ROM's collected on the adsorbent depends both on the nature of
ROM's and the location of collected sample.
4.2.4.2 Distribution of particle size—An assessment of the POM content of
the polluted atmosphere with respect to size of particles in an aerosol often
becomes necessary. Knowledge of the fraction of the air particulate matter
which can cause deposition in the various compartments of the respiratory
system is of prime importance since some of the ROM's are proven carcinogens.
4-14
-------
Table 4-2. AMOUNTS OF POM'S COLLECTED ON GLASS-FIBER FILTER AND POLYURETHANE FOAM
30
I
O1
Compound
Naphthalene
Biphenyl
Phenanthrene
Fluoranthene
Benzo[a]pyrene
1 ,2,3,4-dibenzanthracene
Location
Amt. on
filter 3
ng/1000 m
248.0
95.7
337.7
1249.8
29.7
806.4
A
Amt. on
adsorbent-,
ng/1000 m
100.7
8.5
5.6
281.3
N.D.
3709.2
Location
Amt. on
filter 3
ng/1000 m
31.1
11.3
46.6
N.D.
N.D.
102.5
B
Amt. on
adsorbent.,
ng/1000 m
27.9
N.D.a
4.9
165.4
3.5
N.D.
Location
Amt. on
filter 3
ng/1000 m
31.8
N.D.
4.9
159.4
4.2
N.D.
C
Amt. on
adsorbent.,
ng/1000 mj
49.1
N.D.
6.4
N.D.
N.D.
29.7
'N.D.: Not detected.
-------
There is considerable disagreement regarding the aero dynamics sizes which can
cause deposition of participate matter in the three compartments of the lung
(see Section 6).
34
Whitby et al. have presented evidence that the mass distribution of
atmospheric aerosols is usually bimodal, with one mode occurring below 1.0 ym
and the other mode occurring in the 5 to 15 pm range. A dichotomous sampler
for particulates has been designed to collect and fractionate samples into two
35
size ranges. Membrane filters in the two air paths collect the respective
samples. However, such a sampling technique has rarely been applied to
collect POM from air particulate matter.
The experimental determination of particulate distribution is frequently
done by five-stage Andersen Hi-Vol cascade impactors. The first four
stages of the sampler comprise the fractionating head, while the fifth stage
is a backup filter positioned between the fractionating head and a standard
Hi-Vol air sampler. When operated at a flow rate of 20 cfm, the sampler
fractionates suspended particulate matter into five aerodynamic size ranges
according to certain cut-off diameters.
4.3 DESORPTION OF POM FROM COLLECTION MEDIA
A number of methods are available for the desorption of the collected
POM's from the filter and adsorption traps used for sample collection. Three
methods most commonly used are: (1) extraction, (2) thermal desorption, and
(3) vacuum sublimation. Each of these methods has been individually discussed,
4.3.1 Extraction
In the extraction method, collected POM's are desorbed from the filtering
medium by means of a solvent. Depending on the technique used, the extraction
4-16
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method can be subdivided into three distinctly different groups: (1) solvent
extraction, (2) mechanical disruption, and (3) HF acid dissolution.
4.3.1.1 Solvent extraction—The principle behind solvent extraction is to
dissolve the collected ROM's from the filtering medium by digesting in a
suitable solvent. The usual method involves refluxing of the filter in a
Soxhlet extractor for a certain length of time. A wide variety of solvents
44.47 fi 28 47-
have been used for this purpose. These include acetone, benzene, ' '
49 cyclohexane,47'49'51"53 methanol,47'49 tetrahydrofuran,19'30'47 methylene
chloride,28'47'55'56 chloroform,57 pentane,22 carbon disulfide,49 and a
methanol-benzene mixture. ' Potthast and Eigner used propylene carbonate
as a solvent for extraction of ROM's from meat products. They claim that the
ROM's are more soluble in this solvent than any other. The selection of a
particular solvent or a mixture of solvents is based on the efficiency of
extraction, selectivity in dissolution, time required for extraction, and the
47
reproducibility of extraction. Liberti et al. carried out the extraction
process with various solvents, such as cyclohexane, benzene, dichloromethane,
tetrahydrofuran, acetone, and methanol. Not only was the extraction yield
for PAH maximum with benzene but benzene also showed selectivity towards POM
extraction. The extraction time was found to be reasonable and a 10 hour
period was found adequate for complete extraction. Experiments carried out
with cyclohexane showed a poorer efficiency and a much longer extraction
time. Based on these data, these authors recommended benzene as the solvent
for POM extraction.
49
Cautreels and Cauwenberghe also made a comparative study of the various
solvents for extraction of organic compounds from an artificial aerosol model
4-17
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which may not be representative for real atmospheric suspended matter. Their
study of various solvents, e.g., benzene, carbon disulfide, cyclohexane,
hexane, and methanol is presented in Table 4-3.
Table 4-3. COMPARISON OF THE EXTRACTION YIELD OF POM'S
WITH DIFFERENT SOLVENTS^
% extraction yield
Compound
Phenanthrene
Fluoranthene
Pyrene
Benzo[b]fluorene
Benz[a]anthracene
Benzo[a]pyrene
Di benzLa ,h]anthracene
Benzo[ghi]perylene
Benzene
96
99
96
101
102
75
43
39
Carbon
disulfide
98
100
97
99
106
65
39
40
Cyclohexane
46
52
52
31
68
6
Hexane
69
58
62
28
__a
a Below the detection limit.
Although the yields of extraction of POM's were found to be 10 to 20
percent higher with methanol than with benzene, the latter solvent showed
more selectivity towards POM's than methanol. The quantitative extraction
time was determined to be 8 hours. Both cyclohexane and hexane proved un-
49
suitable for the extraction of POM's. These authors also showed that
larger errors could occur during the extraction of particulate matter than
during the analytical method itself.
It should be mentioned that due to the nature of the artificial sample
the extraction yields of PAH as reported by the above authors may have signi-
ficance only for comparison of various solvents. The absolute extraction
yields from natural samples may vary considerably from these results. Various
laboratories have reported a much higher cyclohexane extraction efficiency
4-18
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for BaP from glass-fiber filter samples.50
4.3.1.2 Mechanical disruption—The widely used Soxhlet extraction is time
consuming, decomposes some of the pollutants, and lacks good precision. In
order to avoid these errors, a mechanical disruptive technique which makes
fi?
use of a specially designed blender has been used by Bove and Kukreja. The
method has been claimed to be rapid and precise for the extraction of organic
contents from glass-fiber filters. A superior procedure has been described
52
by Golden and Sawicki. In this procedure, the sample is suspended in
cyclohexane and subjected to ultrasonic waves at room temperature. Silica
powder (5 micron size) is added to adsorb polar co-extractives. At the end
of sonification, the extract is filtered on a sintered glass filter. The
C"i
entire method has been evaluated by Sawicki et al.
The recovery of ROM's by the sonification method was found to be 95 to
98.2 percent. A comparison of the recovery of aromatic compounds between
ultrasonic and Soxhlet method showed that the ultrasonic method extracted 49
percent of the total particulate matter collected on glass-fiber filters with
a relative standard deviation of +1.33 percent compared to 30 percent for the
Soxhlet extraction with a relative standard deviation of ±26.1 percent of the
total extractables. Not only the extraction efficiency but the reproducibil-
ity of the ultrasonic method was superior to the Soxhlet method.
Disadvantages with the sonification method lies in the fact that the
ultrasonic extraction must be done in a way that avoids an unacceptably high
noise level.
4.3.1.3 Hydrofluoric acid dissolution—This technique utilizes the ability
of HF acid to chemically dissolve the glass-fiber filters, leaving the organic
4-19
-------
residue of the filter paper free to extract quickly with an appropriate sol-
vent. For samples collected on more than one 8 by 10 inch filter, the extrac-
tion time was about 30 minutes.
Comparison of the HF method with the 6-hour Soxhlet extraction technique
is given in Table 4-4.
Table 4-4. COMPARISON OF HF EXTRACTION WITH SOXHLET EXTRACTION64
weight of extractives, mg
Sample number
1
2
3
4
5
6
7
8
9
10
11
12
13
Blank
HF Method
2.7
2.4
2.6
3.0
2.3
2.3
3.4
2.7
3.5
3.0
2.6
2.4
2.5
1.0
Soxhlet Method
3.4
2.0
1.9
3.3
2.6
2.4
2.6
2.2
3.2
3.1
2.1
2.8
2.7
1.0
Determination of absolute efficiency of extraction for three ROM's by
the HF method showed high percent recovery values (97.7 to 100 percent). It
was also proven that a Lewis acid such as HF did not cause ring and/or side
chain rearrangements for alkyl-substituted aromatics. The authors suggested
that the new method should prove highly useful for enriching POM content
collected on glass-fiber filters. However, this procedure lacks general
applicability since some of the collected organics would react with HF and
4-20
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the hazards associated with trie handling of highly reactive HF acid are
considerable.
4.3.2 Thermal Stripping
The extractive methods discussed above require that the extract be con-
centrated and usually only a small aliquot of the concentrate be used for
analysis, such as, gas chromatography. This results in overall reduced re-
covery and sensitivity. Gas-phase extraction, however, is more efficient.
According to this method the ROM's trapped on the collecting media are therm-
ally stripped directly into the separating and detecting device. Since the
method involves no evaporative concentration, it eliminates the corresponding
loss factor. Another advantage of this method is that the whole sample col-
lected (instead of a fraction of it) can be used for a single analysis,
thereby increasing the sensitivity of the method and eliminating the need for
collecting large amounts of sample.
Burchfield et al. used this method for the analysis of ROM's from air-
borne particulate matters. The Hi-Vol filter was ground to about 20 mesh in
a Wiley mill. The samples were, then, loosely packed into a special stripper
tube and the organic components desorbed by a stream of nitrogen at 300°C.
The desorbed compounds were trapped in a cold column containing the same
packing that would subsequently be used for GLC. Although a minimum of 10
hours was required, stripping was carried out overnight. Due to the long
stripping time, variations in gas flow rates between the tubes were unimportant.
The compounds trapped in the cold column were finally heated and the compounds
were separated on the main column.
4-21
-------
00
A very similar method employed by Bertsch et al. consisted of heat
desorption of organic compounds from a porous polymer (Tenax GC) phase instead
of a glass-fiber filter-trapped phase. The desorbed compounds were trapped on
Emulphor ON-870 cooled at dry ice or liquid N« temperature. The advantage of
this method was the substantial reduction of stripping time from 10 hours to
15 minutes only.
A slight modification of the above methods which eliminates the cold
trap, utilizes direct injection of the heat-desorbed components onto a packed
18
column by way of a gas sampling valve. This method is simpler than the
other two stripping methods since it eliminated the special accessory equip-
ment needed for the cold trap.
There are several disadvantages with the thermal stripping methods.
Even though the recovery of the adsorbed compounds by thermal stripping
methods may be high, data showing this effect are still lacking. This is
primarily due to the difficulty in introducing internal standards in the
system. That the high temperature used during the thermal desorption process
does not cause any rearrangement and/or decomposition remains to be established.
Since the injection technique to the final gas chromatographic phase cannot
be instantaneous, it is bound to broaden some peaks resulting in resolution
problems. Finally, replicate injections of the same sample is not possible
with this technique.
4.3.3 Vacuum Sublimation
This technique for the extraction of atmospheric pollutants has been
developed b,/ Japanese researchers. A more recent apparatus for extracting
seven participate samples by one operation is given by Matsushita et al.
4-22
-------
The extraction apparatus used is constructed with a rotary pump, a MacLeod
manometer, a connector, vacuum sublimation tubes, sublimation flasks and an
electric furnace. Seven participate samples are put in seven sublimation
flasks connected with their respective sublimation tubes. These tubes are
attached via a common connector to a manometer and a rotary pump. After
cooling the sublimation tubes with ice water, these are evacuated to 0.005-
0.001 mm Hg. The sublimation flasks are next heated to 310-315°C. ROM's
sublimed from the particulates are deposited on the cold part of the sublima-
tion tube. At the end of 40 minutes of sublimation, the deposited sublimates
from the individual tubes are dissolved in a small amount of benzene.
The recovery and reproducibility of the above method was evaluated
with spiked samples and for three ROM's tested the recovery varied between
97.4 and 98.1 percent and the maximum coefficient of variation was 2.13 per-
cent (relative standard deviation). A comparative study between this method
and ultrasonic extraction method proved that they both have almost identical
recoveries for BaP from air borne particulate samples. However, studies
cq
conducted by Monkman et al. contradicted these findings.
The vacuum sublimation technique is faster than Soxhlet extraction and
is routinely used by Japanese researchers ' for extraction of ROM's from
CO
Hi-Vol glass-fiber filters. It has also been recommended by Schultz et al.
as a routine method for a limited POM analysis.
4.4 CLEAN-UP AND SEPARATION
The next step following the desorption of ROM's from the collection
media consists of clean-up and separation of these compounds from undesirable
impurities and from one another. Of course, the extent of clean-up and
4-23
-------
separation will depend on the nature of the collected sample. This section
deals with the various methods used for this purpose. Depending on the
method employed, the clean-up and separation process can be divided into:
(1) Solvent Partitioning, (2) Column Chromatography, (3) Paper Chromatography,
(4) Thin Layer Chromatography, (5) Gas Chromatography, and (6) High Pressure
Liquid Chromatography. The individual processes are dealt with separately.
4.4.1 Solvent Partitioning
This is one of the oldest methods used for the isolation of POM's as a
group from the bulk of impurities. According to this method, the POM's in a
certain solvent are allowed to distribute in another immiscible solvent which
has either higher or lower distribution coefficient for the POM's than the
original solvent. In the former instance, the POM's are extracted in the
second solvent, and in the latter instance, the impurities accumulate in the
second solvent leaving the first solvent relatively free of impurities. A
variety of solvents which have been used for solvent partitioning are: (1)
methanol-water, (2) tetramethyl uric acid in methanol, (3) acetonitrile, (4)
dimethyl formamide, (5) nitromethane, and (6) dimethyl sulfoxide.
4.4.1.1 Methanol-water—In this solvent partitioning step originally proposed
by Hoffmann and Wynder, the POM's in cyclohexane solution are allowed to
partition in methanol-water solution. The polar impurities in cyclohexane
solution preferentially distribute themselves in more polar methanol-water
phase, leaving the cyclohexane phase containing the POM's relatively free of
impurities. It should be mentioned that a single partitioning step like this
is only a part of several partitioning or other separatory steps in the overall
clean-up scheme. However, methanol-water phase has been used by a number of
4-24
-------
other authors ' as a preliminary step for getting rid of the polar com-
ponents from the POM fraction.
4.4.1.2 Tetramethyl uric acid in methano!--A solvent system incorporating
tetramethyl-uric acid in methanol as a selective complexing agent has been
used to separate several ROM's. Distribution coefficients for a number of
74
ROM's in this solvent system have been given by Mold et al. However, this
solvent system lacks wide applicability.
75
4.4.1.3 Acetonitri1e--Haenni et al. determined the distribution of POM's
between n-heptane and acetonitrile and found low distribution ratios. These
authors concluded that this solvent is not very effective in concentrating
POM compounds.
4.4.1.4 Dimethyl formamide--This solvent was found to be much more efficient
for the removal of POM's from heptane phase. Consequently, this solvent has
9 73
been used by other authors ' for extracting POM's from cyclohexane phase as
well.
4.4.1.5 Nitromethane--The partition coefficients of POM's between nitro-
12
methane and cyclohexane was determined by Hoffmann and Wynder and varied
between 4.4 and 1.65 for a number of POM's tested. The same partition coeffi-
cients determined between nitromethane and other aliphatic solvents '
showed values quite similar to that determined by the above authors. This
solvent has been used by a number of authors, particularly for the clean-up
53 55 71 77
of automobile exhaust samples. • ' '
4.4.1.6 Dimethyl sulfoxide--The first evaluation of this solvent as a parti-
tioning medium for POM's was made by Haenni et al. A comparison of four
solvents, e.g., acetonitrile, nitromethane, dimethyl formamide, and dimethyl
4-25
-------
sulfoxide, showed that the last solvent was much more suitable on the basis
of distribution coefficients and selectivity for POM compounds. Comparative
study of the percent recovery between two widely used solvents made by Acheson
78
et al. is given in Table 4-5.
Table 4-5. EFFICIENCIES OF SOLVENT-PARTITION PURIFICATION PROCEDURE78
Compound % Recovery Compound % Recovery
Nitromethane DMSO Nitromethane DMSO
Fl uoranthene 48-83
Pyrene 38-42
Benz[a]anthracene 50-64
& chrysene
Benzo[k]fl uoranthene 54-59
Benzo[ghi]perylene 15.8-45
92-96
94-96
90-92
91-94
90-91
Benzo[a]pyrene
& Benzo[e]pyrene
Perylene
Indeno[l,2,3-cd]-
pyrene
Coronene
33-36
< 10-24
41-49
10.0-44
95-99
84-90
97-100
82-93
78
From their investigations Acheson et al. conclude that DMSO is the
79 80
best extractive medium for POM compounds. Other investigators ' have
effectively used this solvent for isolating POM compounds from impurities.
It should be mentioned that in a complex mixture, it often becomes nec-
essary to first fractionate the POM extract into acid, basic and neutral
55 77
fractions prior to further clean-up procedures. ' In this method, the POM
mixture in a suitable solvent is extracted with an aqueous alkaline solution
to separate the acidic components. Subsequent extraction with an aqueous
acid solution separate the basic components from the neutral fraction. By
carefully controlling the acidic and basic strength of the aqueous solution,
the individual fractions can be further subdivided into groups of compounds
with varying acidic and basic strength. By carrying out the extraction with
4-26
-------
49
IN sodium hydroxide or HC1, Cautreels and Cauwenberghe, found that on the
average 99 percent of n-paraffins stayed in the neutral fraction. About
90 percent of neutral polyaromatics was found in the neutral fraction and
10 percent in the acidic fraction. The yield of other neutrals, e.g., phthal-
ate ester, was about 96 percent in the neutral fraction. The basic fraction
gave an average of 75 percent yield for the acidic compounds. The results
obtained from the isolation of some selected basic compounds, however, showed
very poor recovery.
4.4.2 Column Chromatography
This is the most widely used separation method for the ROM's. A large
variety of adsorbents, such as, (1) alumina, (2) silica gel, (3) Florisil, (4)
cellulose acetate, and (5) gel materials, have been used for separation.
Adsorbents with uniform particle size, 60-80, 80-100, and 100-120 mesh and
column diameter:length ratios of at least 1.25 are suggested. The laboratory
temperature should be kept reasonably constant and the solvent used for
elution should be of highest purity. Maximal separation can be achieved by
slowly and evenly increasing the polarity of the eluting solvents. The
hydrocarbons are eluted from the column in the following order: aliphatics,
olefins, benzene derivatives, naphthalene derivatives, dibenzofuran fraction,
anthracene fraction, chrysene fraction, benzpyrene fraction, and coronene
28
fraction. The factors that affect the chromatography of the organic frac-
tions are: (!) the retardation volume, i.e., the volume of eluent passing
through the column per gram of adsorbent before the substance in question
leaves the column; (2) the volume spread of the eluted substances, i.e., the
volume of eluent in which the substance is found; and (3) the volume separation,
4-27
-------
i.e., the volume of eluent separating one eluent substance from another.
These factors can be affected by three variables: (1) percentage of water in
the sorbent, (2) percentage of polar solvent in the solvent mixture, and (3)
possible miscellaneous factors, such as, the composition and weight of the
organic fraction.
4.4.2.1 Alumina—Alumina is available in various grades, sizes, pH and
activity. For the separation of neutral POM fractions, Woelm Neutral Alumina
is generally used. The sample:adsorbent ratio varies between 1:100 and
1:1000. The alumina is deactivated with 13.7 percent water prior to use.
Elution of the adsorbed compounds is done by gradually increasing the polarity
of the solvent system. Ether-pentane, cyclohexane-ether, cyclohexane-
flfi ft?
benzene, and benzene-methanol are some of the solvent systems used by
46
various researchers. Some investigators have successfully separated PAH's
on very long alumina column. However, such separation procedures need auto-
matic fraction collectors to collect a number of eluting fractions.
The main disadvantage with alumina column separation is that it is very
time consuming, sometimes causes decomposition of compounds on the column
(particularly polynuclear aromatic amines) and good reproducibility is often
difficult to achieve.
4.4.2.2 Silica gel--It is difficult to get silica gel with a standardized
preparation. Material of 100-200 mesh or Davison grade 12 or equivalent is
28 71
found suitable for chromatographic purposes. ' The sample:adsorbent ratio
varies between 1:50 and 1:500. Some investigators used silica gel with 3 to
47 57 51 71
5 percent moisture content, ' while others used the dried silica gel *
4-28
-------
without deactivation with water. The elution of adsorbed compounds is usually
done by benzene ' * or hexane-benzene.
It should be recognized that silica gel is normally used in combination
with other adsorbents or other separation methods and is rarely used as the
sole separation process. A separation method using both alumina and silica
47
gel chromatography was used by Liberti et al. The average percent recovery
for 9 PAH compounds was found to be 77.2 percent. The individual recoveries
as reported by these authors are listed in Table 4-6.
Table 4-6. RECOVERY OF PAH BY LINEAR ELUTION ADSORPTION CHROMATOGRAPHY47
PAH % Recovery from alumina
& silica gel chromatography
Fluoranthene 68.8
Pyrene 82.0
1-2 Benzanthracene 77.6
Chrysene 82.1
3-4 Benzofluoranthene 82.4
Benzo[a]pyrene 80.5
Benzo[e]pyrene 80.5
Indeno[l,2,3-cd]pyrene 90.6
Benzo[g,h,i]perylene 90.3
Average 77.2
Column chromatography with silica gel suffers from all the disadvantages
normally encountered with alumina. The relatively slow flow rates of solvents
through silica gel causes additional problems.
4.4.2.3 Flori si I—Column chromatography using Florisil is not as widespread
for the separation of POM's as the other two methods already described.
Activated Florisil, 60-100 mesh, have been used for fractionation of PAH com-
77 87
pounds ' and also for isolation of PAH compounds as a group from other
4-29
-------
79 80
impurities. ' The eluting solvent for this sorbent is usually hexane-
87 80
benzene or benzene alone. The advantage with Florisil column is that
PAH's separate rather well, despite a short elution time. To prevent photo-
oxidation during chromatography, the Florisil column should be protected from
light.
4.4.2.4 Cellulose acetate--A1though cellulose acetate is a promising sorbent
for separation of ROM's, its use as a column chromatographic material is very
79
limited. Griest et al. have reported using this technique for the purifica-
tion of PAH's.
88
4.4.2.5 Gel filtration—Milk et al. were the first to use this technique for
the separation of ROM's. Others have since found the system to be valuable for
14 89 55 90
separation of PAH from automobile exhausts, ' air particulate matter, '
73 90 91
cigarette smoke and biological samples. ' Separation of neutral aza-
92
arenes has also been achieved by this technique. The separation is best
achieved isothermally on Sephadex LH-20 (ratio, about 1:1000) columns with 2-
89
propanol as solvent at a flow rate of 6-7 ml/min. Gladen determined the
recovery efficiencies of 8 PAH's by this technique which is shown in Table 4-7.
on
Table 4-7. RECOVERY OF PAH'S BY SEPHADEX LH-20 CHROMATOGRAPHYoy
Compound % Recovery
Anthracene 101
Phenanthrene 98
Pyrene 94
Fluoranthene 102
Benz[a]anthracene 100
Benzo[a]pyrene 97
Perylene 98
Benzo[g,h,i]perylene 98
4-30
-------
Although gel filtration is free from most of the drawbacks of other
column chromatographic methods, its main disadvantage is that it takes a long
time (1 to 3 days) for separation.
4.4.3 Paper Chromatography
Paper chromatographic methods are used for the separation of individual
fractions and are usually preceeded by a preliminary separation by column
Chromatography. For optimum separation, the commonly used paper is acetyl-
ated cellulose * and the Chromatography is carried out by ascending tech-
nique. A slight modification of the paper by impregnating with 10 percent
82
liquid paraffin has also been used for chromatographic separation. Develop-
ing is done with a variety of solvent mixtures. These include toluene-
methanol-water (1:10:1), methanol-ether-water (4:4:1), methanol-chloroform
(3:1), ethanol-toluene-water (17:4:1) and ethanol-benzene-water (12:6:1).
In modern separation techniques paper Chromatography is rarely used.
There are several reasons for this. The time required for separation, diffi-
culty in getting reproducible papers, inadequate resolution of compounds and
the non-quantitative nature of analysis are disadvantages for this technique.
4.4.4 Paper and Thin-layer Electrophoresis
Separation of basic aza arene by this technique was accomplished by
83
Sawicki. However, this method has restrictive use for reasons similar to
paper chromatographic technique.
4.4.5 Thin-Layer Chromatography
This technique is quick, inexpensive, reasonably reproducible, and one
of the better methods for the separation of isomeric compounds. With the
availability of in situ scanning technique (thin-layer scanner), this method
4-31
-------
has been used for quantification of ROM's with reasonably good accuracy. A
number of materials have been used as sorbent materials for the plates.
These are: (1) silica,47'76'96'97 (2) alumina,95'99'100 (3) cellulose,83 (4)
cellulose acetate,68'90'93"95 and (5) polyamide.101 A number of modifications
102
including silinazation of silica gel and channel thin-layer chromatography
have been proposed. In the latter procedure, the components which need to be
fractionated on a thin-layer plate are made to flow into narrow development
channels in order to prevent the spreading of the chromatographic spots.
Both PAH and polynuclear aza-heterocyclic compounds have been separated
by TLC method. A large number of variations of TLC procedure, such as,
variation of developing solvents, use of a mixture of sorbents, developing in
one or two dimensions have been used to affect better resolution of the
components. The effect of solvent variations on cellulose acetate TLC has
95
been discussed in detail by Woidich et al. Although alumina-cellulose
98
(2:1) has been used as a composite adsorbent, the best resolution is
obtained when two-dimensional TLC on a composite plate of aluminum oxide-
40 percent acetylated cellulose (2:1) is used. ' The percent recovery
of a few isomeric arenes separated by this method is given in Table 4-8.
Table 4-8. RECOVERY OF VARIOUS PAH'S DURING THIN-LAYER CHROMATOGRAPHY105
Compound
BeP
BaP
BbF
BkF
Perylene
Dibenzo[def,
mno] chrysene
% Recovery
86.
85.
92.
91.
90.
90.
0+5.
2+5.
1+3.
2+3.
4+4.
9+3.
3
1
5
7
6
9
Compound
B[ghi]p
Naphtha[l,2,3,4-def]
Chrysene
Benzo[rst]pentaphene
Di benzo[b ,def ]chrysene
Naptho[2,18-gra]naphtha-
cene
Dibenzo[def,b]chrysene
% Recovery
88.
87.
91.
89.
90.
84.
7+4.
9+5.
8+4.
8+3.
7+5.
1+6.
0
5
2
9
1
2
4-32
-------
A large number of aza-heterocyclic compounds found in urban airborne
particulates and in air pollution source effluents have been separated by TLC
procedure. The basic fraction from a coal-tar-pitch sample when subjected to
a two-dimensional TLC separation on silica gel-cellulose (2:1) with pentane-
ether (9:1, v/v) and dimethyl formamide-water (35:15, v/v) solvent systems
yielded the results shown in Table 4-9.
98
Two-dimensional TLC separation has also been successfully used during
the quantification of acridine, benz[c]acridine, 7H-benz[de]anthracen-7-one
and phenalen-1-one in airborne particulate samples.
Table 4-9. AMOUNTS OF AZA-HETEROCYCLIC COMPOUNDS IN A
COAL-TAR-PITCH POLLUTED AIR SAMPLE SEPARATED BY TLC85
Concentration Concentration
in ma/ in ma/
Compound 1000 m3 air Compound 1000 m3 air
Acridine 0.870 Indeno[l,2,3-ij]- 0.030
Benzo[f]quinoline 0.420 isoquinoline
Benzo[h]quinoline 0.260 11 H-Indeno[l,2-b]- 0.190
Phenanthridine 0.020 quinoline
Benz[a]acridine 0.200 Dibenz[a,h]acridine 0.010
Benz[c]acridine 0.120 Dibenz[a,j]acridine 0.001
There are several disadvantages with the TLC procedure. Mass spectrometry
and liquid chromatography, when applied as additional analytical tools for
identification of POM's, have demonstrated that the individual spots or bands
are sometimes, in fact, mixtures of two or more compounds. Also, the TLC pro-
cedure cannot be used when separation of a large number of compounds is re-
quired since TLC resolution is limited. Furthermore, during TLC procedure,
4-33
-------
trace amounts of compounds may photodecompose, requiring addition of an
internal standard to correct for the losses.
4.4.6 Gas Chromatography
The closeness of the chemical structures among some of the ROM's and
their relatively high boiling points demand the stringent requirements of high
resolution and thermal stability at high temperature for the chromatographic
column packings. Unfortunately, until recently the available liquid phases
that were thermally the most stable were barely adequate for the temperature
required to separate some of the high boiling POM. However, a large variety
of column packing materials have since been used for POM separation. Depend-
ing on their mode of operation, gas chromatographic methods used so far can be
divided into: (1) packed column, and (2) capillary columns, such as, surface-
coated open tubular column, and wall -coated open tubular column.
4.4.6.1 Packed column—A number of packing materials have been used in packed
column chromatography. A gas-solid chromatographic phase using Chromosorb
101115 and GLC (gas liquid) phases using OV-1,65'106 OV-7,98 OV-25,79 poly-
metaphenoxylene,93 apiezon L,98'108 apiezon W,79 SE-30,86*108'109 SE-52,57'110
Dexsil 300 Gc....l. 113,114 Dexsil 40Q Gc>106
nematic liquid crystals ' ' have found their applications as the pack-
ing materials.
One of the superior column packing materials available for POM separation
is Dexsil -300 or Dexsil -400. The column bleeding characteristic and resolution
capability for these packing materials make them highly suitable for POM anal-
ysis. The resolution of Dexsil-400 is even better than Dexsil-300. The
separation of both PAH and aza arenes in samples containing coal tar has been
4-34
-------
accomplished with these packing materials. Dong et al. have used
Dexsi 1-300 column for the separation and quantification of a number of aza
arenes in the basic fraction of airborne particulate matter.
Nematic liquid crystals with the general formula N,N'-bis(p-substituted
benzyl i dene) -a ,a'-bi-p-tolui dine have been shown to resolve hard to separate
PAH isomers. Three p-substituted compounds, methoxy (BMBT), hexyloxy (BHxBT),
and phenyl (BPhBT) have been investigated. * ' However, column bleed-
ing at higher temperatures remains a problem with this packing material. For
routine separation of benzpyrene isomers, a BMBT packed column operated iso-
1 14
thermally at 130°C has been found useful.
4.4.6.2 Capillary column — These columns are more advantageous than packed
columns due to their ability to affect higher resolution. The number of
119
theoretical plates obtained from such columns may vary between 20,000-70,000.
Versamid 900,102 SE-30,119 XE-60,119 SE-52,11 .53,58,72,119,120.123 ,.^125
191 1 A OO
m-bis-m-(phenoxylphenoxy)-benzene, Dexsil 300, Emulphor ON 870,
carbowax-20 polymer,122 OV-1,124 OV-17,9 OV-101 ,9'73'91 apiezon L,47'76 and
SP-2100 all have been used as packing materials for capillary columns. The
119
most widely used column for separation of ROM's is SE-52. Cantuti et al.
compared several liquid phases and found that a SE-52 column of 50 m length
was most effective for POM separation and had a theoretical plate of 40,000.
125
Recent investigations by Bjtfrseth have demonstrated that capillary columns
using SE-54 as the stationary phase have excellent separation efficiency, low
column bleed and long-term stability. Both PAH and aza arenes have been
125
separated with this packing material. A 40 m capillary column with Versamid-
900 as the stationary phase is very effective for the separation of aza arenes
(theoretical plate of 60, 000). 102
4-35
-------
127
Investigations by Lao et al. with Dexsil-300 coating liquid has shown
that the separation of ROM's on surface coated open tubular column is better
than packed columns for the range from fluoranthene to methylchrysene. How-
ever, the resolution of the later peaks with longer retention times remains
incomplete.
Analysis of ROM's carried out by wall-coated capillary columns coated
with SE-52 of liquid phase thickness of 0.27 y showed excellent reproducibil-
ity, high sensitivity and high resolution between individual isomers in
1 to
128
128
comparison to regular packed columns. WCOT columns have been claimed to
offer numerous advantages over packed or porous-layer open tubular columns.
Some of these are superior resolution, minimum adsorption effect, and high
stability.
4.4.7 High Pressure Liquid Chromatography
The ability of HPLC to separate POM compounds not normally accomplished
by GLC indicates the great potential of this method for POM analysis. In
addition HPLC offers many advantages over GLC: it operates at much lower
temperatures, fraction collection is simple and convenient, the capacity to
accept sample is high, and fluorescence spectroscopic detection demonstrate
high sensitivity and selectivity for POM compounds.
In HPLC, the mobile phase modifier is the most powerful variable for
changing retention times. The choice of mobile phase is dictated by the mode
of separation accomplished by the sorbent. In the normal mode, generally
hydrocarbon solvents are used as the mobile phase. Any solvent that dissolves
POM in fair amounts, is miscible with water and is transparent at U.V. absorp-
tion wavelength (for U.V. or fluorescence detector) can be used as a modifier
in the reverse phase-L.C.
4-36
-------
Table 4-10. HPLC CONDITIONS AND SEPARATION MECHANISMS USED FOR PNA ANALYSIS
OJ
Nature of Sample
Standard PAH
solution
Carbon Black
Sediment &
Sea water
Automobile
exhaust
Standard PAH
solution
Standard PAH
metabolite &
solution
Standard PAH
solution
Standard PAH
solution
Automobile exhause
condensates
Standard PAH
solution
Standard PAH
solution
Stationary Phase
120/170 mesh Alumina
ODS-Sil-X-I
Coupled Bondapak C-\g-v Bondapak
C18
Porasil T
ODS-Permaphase
ODS-Permaphase
2,4,7-trinltrofluorenone
impregnated Coras 11 I
3(2,4,5.7)tetranitrofluore-
iminopropyldiethyl siloxane
ODS-Permaphase
Spheres il XOA-400
Coras il-C18
Mobile Phase
Mode of Elutlon
n-pentane
isocratic at 211°C
30% HZ0:70% HeOH
Isocratic at SO°C
Gradient elution
30% HeOH: 70% H-0 to
100% HeOH i
n-heptane
isocratic at 51.5°C
65% MeOH: 35% H.O
isocratic at room temp.
30% HeOH: 70% H?0 to
70% HeOH: 30% H20
gradient elution
n-heptane
isocratic at 25°C
Acetonitrile-Isooctane
Isocratic
Linear gradient
20% MeOH: 80% H.O to
100% HeOH i
Isooctane
isocratic
80% HeOH: 20% H-0
Isocratic
Separation
Mechanism
Adsorption
Reversed
phase
Reversed
phase
Adsorption
Reversed
phase
Reversed
phase
Charge-
transfer
Charge-
transfer
Reversed
phase
Adsorption
Reversed
phase
Detection
Mode
Disc conveyor
FID
U.V.
U.V.. Fluor.
U.V.
U.V.
U.V.
U.V.
U.V.
U.V.
Fluor.
Fluor.
Reference
129
130
131
132
133
134
l
135
136
137
1
138
139
-------
Table 4-10. HPLC CONDITIONS AND SEPARATION MECHANISMS USED FOR PNA ANALYSIS (CONT'D)
Nature of Sample
Standard PAH
solution
Atmospheric parti-
cipate matters
Atmospheric parti-
culate matters
Standard PAH
solution
Standard PAH
•^ solution
10
00 Standard PAH
solution
Atmospheric
participate matters
Marine sediment
ft oil samples
Coal liquefaction
products
Stationary Phase
Octadecyl trichlorosilanized
silica gel
Zorbax-ODS
Zorbax-OOS
Equal portions of 8. IX dimethyl -
formamide and carbowax-350 on
gas chromatograph
30X Cellulose Monacetate
100/115 mesh Woe 1m Basic Alumina
u-Bondapak/Cjo S p-porasil
u-Bondapak/C18 i u-Bondapak NH?
Cross-linked polyvinyl-
pyrrolidone
Mobile Phase
Mode of Elution
90S MeOH.lOX H20
isocratic
70% MeOH:30X H.O
Isocratic
65% MeOH:35X H,0
to IX MeOH/minT gradient
Isooctane
isocratic
Ethanol/MeCl- (2:1)
Isocratic
Pressure programmed
95* n-pentane:5X MeOH
20-80% MeCN in water at
2X/min and IX propanol-2
in hexane
50-70X Acetomtrile in
water and hexane
Propanol-2
Separation
Mechanism
Reversed
phase
Reversed
phase
Reversed
phase
partition
Reversed
phase
Adsorption
Reversed
adsorption
Reversed
phase
Adsorption
Detection
Mode
Fluor.
Fluor.
Fluor.
U.V.
U.V.
U.V.
Fluor.
Fluor.
Fluor.
Reference
140
31
97
141
142
143
144
145
146
-------
It should be mentioned that solvent programming has proven to be a power-
ful tool In separating the compounds from each other. Several researchers
have taken advantage of Increased temperature (70 to 80°C) of the column to
obtain a similar objective. At higher temperature reduced viscosity of the
mobile phase increases column efficiency and decreases relative retention
times. The sample capacity is also increased at higher temperatures allowing
larger amounts of sample injection. Table 4-10 summarizes the different
columns and mobile phases used by various authors for the analysis of POM by
HPLC. The most versatile columns for POM analysis operate on the principle of
reversed-phase mechanism. One such column containing y-Bondapak C1P has been
97 144
applied for the separation of both PAH and aza arenes.
18
4.5 DETECTION
The different methods of detection with their relative advantages and
disadvantages have been individually discussed in the following sections.
4.5.1 Flame lonization and Electron Capture
When gas chromatography is used for separation and analysis of POM's the
usual method of detection is either flame ionization detection (FID) ' ' '
Q1 TOR 77 Q3 1 flQ
' or electron capture detection (ECD).//»*J'IUO One advantage with the
EC detector is its greater selectivity towards BaP compared with BeP.
However, the high temperature used in the column oven for the separation of
higher boiling compounds requires even higher temperature capability for the
detector. Most EC detectors do not fulfill this requirement. As a result,
most of the recent GC analysis have been performed with FI detectors. The
advantage with flame ionization detector is its wide dynamic range of linear
response for most POM's.
4-39
-------
4.5.2 U.V. Absorption
Q TO 9fi
This technique is the most widely used method for POM detection. '*'
' * " ' The advantages of this technique include the commercial avail-
ability of high quality spectrophotometers, the relative insensitivity of the
degree of absorption to trace impurities, and the fact that the absorption
spectrum of a mixture is usually the sum of the spectra of the components.
The latter characteristic offers a crosscheck of the total concentration in a
complex mixture determined by other methods. The disadvantages include the
requirement of two or more separation steps for reliable identification and
the relatively lower detection sensitivity compared to other detection devices.
Although the total spectrum for each POM compound is unique, the indivi-
dual features are not. Therefore, identification and quantification of a POM
compound on the basis of only one peak is unreliable. A computer program
utilizing the U.V. spectra has been developed for rapid screening and simul-
147
taneous identification of a large number of peaks.
Incomplete separation of individual compounds is a major problem in
interpreting U.V. spectra and since the compounds rarely completely separate,
questionable results are obtained with U.V. detection of complex mixtures even
with a programmed spectral analysis.
4.5.3 Luminiscence Analysis
4.5.3.1 U.V. excited luminescence emission—This technique has become well
established as a sensitive and selective technique for POM detection. '
fift 71 79 fl/L Ql QQ
oo,/i,/d,oH,»i,»s Several groups have found it to be at least an order of
138 149
magnitude more sensitive than absorption spectroscopy. ' It is also more
sensitive (lower detection limit) and less expensive than mass spectral
4-40
-------
detectors. Mass spectrometers normally have a nanogram detection limit,150
although integrated ion-current techniques reduce this limit to the subpico-
gram range.
Since luminescence spectroscopy is nondestructive, individual fractions
can easily be collected and subjected to further analysis. Furthermore, this
method provides additional selectivity. While many interferring compounds may
absorb light, only a few emit in the region of particular POM compounds.
Various modifications of this method have been used to increase the
sensitivity and selectivity of the method. Application of low temperature
fluorescence and phosphorescence for the characterization of aromatic com-
152
pounds with enhanced sensitivity has been utilized by Sawicki and Johnson.
However, this technique is rarely used at the present time. Room temperature
phosphorescence measurements have been made without the problems of typical
low temperature sample matrix preparation, yet maintain good sensitivity and
selectivity. Phosphorescence is increased by adsorption of the sample on to
rigid matrix-like backing such as filter paper, thereby quenching non-radia-
153
tive vibrational de-excitation, and by the addition of a heavy atom per-
turber which increases the spin-orbit coupling between the singlet and the
154
triplet excited states.
The selectivity of fluorescence detection for POM compounds has been
increased by characterization at two wavelength combinations, e.g., at 313/360
and 365/445 nm as a double fingerprint. By means of a selective excitation
and/or oxygen quenching method, POM compounds have been quantitatively analyzed
without chromatographic separation. Identification of compounds showing
minor features in zeroth derivative fluorescence spectra has been accomplished
4-41
-------
by first and/or second derivative fluorescence and fluorescence modulation
techniques. Since derivative spectroscopy deals with the shape characteris-
tics of the spectral absorption rather than the intensity changes, increased
sensitivity and selectivity are obtained over conventional absorption spectro-
meters. The curvature characteristics are often quite large and specific to
individual compounds, thus allowing selective analysis of a component in a
rather complex mixture. In addition to the scanning mode of operation where
a complete spectrum is obtained, the second derivative spectrometer can be
operated in a "dwell" mode at a specific wavelength allowing for real-time
monitoring of a selected component.
In situ fluorescence detection on a thin-layer plate with a scanner has
80 90 94 95
also been used to increase the detection limit of POM compounds. "»'"»"»*
Fluorescence spectroscopy using variable wavelength detectors has been used
to increase the selectivity of detection in the HPLC method. ' Finally,
multicomponent analysis by the use of rapid scanning fluorescence spectro-
scopy interfaced with a computer for data reduction by algorithm programming
has been studied.
However, there are quite a few complications with this detection technique.
All emission techniques are influenced by repeatability of wavelength settings,
scatter of light in monochromators, and random fluctuations in source inten-
sity. Quenching by oxygen is a serious problem and may be very selective.
Impurities which introduce intersystem crossing will enhance phosphorescence
at the expense of fluorescence intensity.
4.5.3.2 ShpoTskii effect--Detection of PAH compounds by this technique was
158
first demonstrated by ShpoTskii in 1952. The characteristic sharp-line
4-42
-------
(quasi-linear) luminescence emission spectra obtained by U.V. irradiation of
the crystalline matrix of PAH in n-paraffin solvents at 77°K or below have
been used for the identification of these compounds. The original n-paraffin
solvents used for this study were n-hexane and n-heptane. However, most PAH
compounds may not be soluble in n-paraffins. Therefore, Kirkbright and
DeLima used 10% (v/v) cyclohexane in n-paraffin as the solvent mixture
which was demonstrated not to disturb appreciably the spectrum obtained. From
the study of ShpoTskii effect with 23 PAH compounds in several n-paraffin
solvents, such as, n-hexane, n-octane, and n-decane, these authors also con-
cluded that some PAH produced more well-defined spectra in a particular n-
paraffin solvent compared to another.
Although it appears that direct measurement of the intensity of quasi -
linear luminescence emission is capable of permitting the quantitative deter-
mination of PAH compounds directly, real samples pose several problems. The
effects of energy transfer the inner-filter effect, and experimental variables
- all of these cause error in the analysis. The use of combined internal
standard - standard additions technique has been demonstrated to yield accept-
159
able results in such samples. This luminescence emission method is also
suitable as a "fingerprinting" technique for qualitatively identifying PAH in
a mixture.
4.5.3.3 X-ray excited optical luminescence (XEOL)—This method is a slight
o
variation of ShpoTskii effect in that it uses X-ray (1 to 10A) to obtain
quasi-linear fluorescence and phosphorescence-emission from samples frozen in
n-heptane matrix at 90°K. D'Silva et al. reported this technique as a
method for the detection of nanogram levels of PAH. The suitability of this
4-43
-------
method in the analysis of real samples remains to be established. However,
some of the potential advantages for X-ray over U.V. excitation are: (i)
freedom from optical cross-talk between the exciting and luminescence radia-
tion, (ii) larger population of higher energy electron levels, thereby reveal-
ing additional lines, and (iii) substantial phosphorescence emission, aiding
further characterization from these lines.
4.5.3.4 Sensitized fluorescence—The inherent fluorescence of PAH compounds
is greatly enhanced in the presence of certain sensitizers, thereby decreasing
the fluorescence detection limit of the former compounds by several orders of
magnitude. This technique has been employed as a spot test method for screen-
ing environmental samples for the presence of PAH. According to this
method, naphthalene as sens.itizer is co-spotted with the sample spot on a
Whatman #42 filter paper. The dried spot is exposed to light of appropriate
wavelength and intensity and any sensitized fluorescence emission is recorded.
On filter paper, 10 pg of PAH in a spot can generally be visualized when
treated with naphthalene. Experiments with a few real-life samples have shown
that the method is specific for PAH's with minimum interference from other
compounds. However, large concentrations of nitroaromatic compounds have been
shown to act as fluorescence quencher in this method.
4.5.3.5 Synchronous luminescence spectroscopy--A recently developed method
162
termed synchronous luminescence spectroscopy where the excitation and
emission wavelengths are simultaneously varied with a fixed wavelength differ-
1 go
ence of 3 nm between the two has been proposed for the routine monitoring
of PAH in complex samples. The spectra obtained from this technique is simpli-
fied with improved resolution between component peaks.
4-44
-------
4.5.4 Mass Spectrometry
Mass spectrometry affords a sensitive means of determining the probable
identity and relative purity of POM chromatographic fractions. This method
has gained wide acceptance for analysis of POM compounds.31'33'59'73'112'
51 Generally, this has been accomplished by low voltage ionization
methods which produce spectra containing mainly singly-changed, intact molecu-
lar ions.
In POM analysis, the most widely used methods for sample introduction to
3? 11? 1 *>1 1 fi^
the mass spectrometer are direct insertion probe ' ' ' and direct
interfacing GC-MS method.106'115'121*127 The sample ionization is commonly
done by electron impaction and the separation of ion beams is accomplished by
either low resolution quadrupole instrument or high resolution magnetic scan-
113
ning equipment. The claimed advantage of quadrupole instrument is: (i) its
initial relatively low cost, (ii) ability for straightforward maintenance and
repair, and (iii) extremely high-speed linear mass scan, simplifying system
control, data logging and spectra interpretation. The disadvantage of the
quadrupole method is its low mass resolution and low mass sensitivity at higher
masses. Both high resolution32'151'163'164 and low resolution106'113'114 mass
spectrometers have been used for PAH and aza arene analysis.
The analysis of complex samples usually produces numerous spectra and the
spectrometer generates an enormous amount of data from a single chromatogram.
Therefore, the data reduction and quantification requires a computerized data
processor with an appropriate programming system. At the end of the GC run,
the computer is used to plot a reconstructed gas chromatogram of total ion
amplitude versus the spectrum number (ion abundance chromatogram).
4-45
-------
Identification of these chromatographic peak is accomplished by plotting the
mass spectrum of a specified peak or by specific ion monitoring (mass frag-
mentography).
One problem with electron impact ionization is that isomeric ROM's may
give identical mass spectra making unambiguous identification sometimes
165
impossible. Hites and Dubay found that charge-exchange-chemical ionization
mass spectrometry can be used to distinguish many isomeric ROM's. They have
established that spectra of ROM's have characteristic ratios of the protonated
molecular ion to the molecular ion when 5% to 10% methane in argon is employed
as the reagent gas. This technique is not expected to replace electron impact
GC-MS, but it should be a useful supplemental tool for differentiating both
isomeric PAH and aza arene.
4.5.5 Other Techniques
CC TO
Fourier-transform NMR spectroscopy ' has been used for the elucidation
of the position of substitution in the benzene ring positions of the ROM's.
Other techniques of detection utilizing matrix isolation Fourier-transform
IR, and Piezoelectric crystal need considerable improvement to become
viable methods for POM analysis.
4.6 ANALYTICAL METHOD USED BY EPA FOR NASN MONITORED SAMPLES:
The following method was used for the quantification of BaP from NASN
monitored samples collected during the period 1966-1972.
The particulate sample collected on glass fiber filter was extracted with
benzene in a Soxhlet extractor for at least 6 hours. The filtered extract was
dried in a 60°C oven. The residue was dissolved in methylene chloride (1.0 ml
for 25 mg residue) and a portion of this solution was spotted on a scribed and
4-46
-------
activated TLC plate coated with 250 y alumina. After developing the spots in
benzene-pentane (2:8), the BaP spot was scraped from the plate. The quantita-
tive elution of BaP from the adsorbent was accomplished by shaking with
pentane:acetone (95:5). The eluant was dried in a vacuum oven at 30 to 35°C
and about 50 torr. The residue was dissolved in concentrated sulfuric acid
and the fluorescence of this solution was recorded at excitation and emission
wavelength of 470 nm and 540 nn, respectively. The concentration of BaP in
the unknown was determined by comparison with standard BaP solutions.
For samples collected during the period 1973 to the present, the follow-
174
ing modified procedure was used for the quantification of BaP.
The quarterly composites of glass fiber filter were Soxhlet extracted
with cyclohexane for six hours. The extract was concentrated in a Kuderna-
Danish evaporator at 50°C with a stream of dry nitrogen. 50 yl of the con-
centrate was spotted on a channelled 20% acetylated cellulose plate with a
multispotter. Plates were developed with 2:1 ethanol:methylene chloride
solvent mixture and air dried. The BaP spot on the plate was scanned with a
thin layer plate scanning attachment at excitation and emission wavelength of
388 nm and 430 nm, respectively. The concentration was evaluated from the
integrated strip chart area reading obtained by a digital integrator.
Since the BaP in this procedure did not separate from anthanthrene, the
plate was then scanned at an excitation and emission wavelength of 434 nm and
470 nm, respectively, for the determination of anthanthrene concentration.
The anthanthrene contribution in BaP could be corrected by subtracting 16% of
anthanthrene concentration from the BaP reading (at BaP wavelengths, anthan-
threne was found to be 84% less efficient).
4-47
-------
4.7 DIFFICULTIES IN POM MONITORING AND ANALYSIS
The data reported on the levels of POM in different sources are suscept-
ible to various 'kinds of errors and uncertainties at different stages of the
monitoring and analytical phase. The first source of uncertainty in monitor-
ing POM levels arise from the lack of knowledge regarding the degradation of
these compounds under environmental conditions (See Section 3.3). The eval-
uation of adverse health effects requires a judicious selection of parameters
that need to be monitored. The selection process becomes difficult in the
absence of specific information regarding the form of POM that may exist in a
certain atmosphere as a result of environmental reactions. Even in cases
where a specific form of POM's, for example, a selected group of PAH has been
decided to be monitored, the reported values are subject to substantial errors.
Such errors and uncertainties may arise during defining the monitoring stra-
tegy, sampling procedure, transportation and storage of samples, and analytical
procedures. Possible sources of error in each of the individual categories
will be discussed in the following sections.
4.7.1 Sampling Errors
4.7.1.1 Nonisokinetic sampling—Most ambient sample collections are done non-
isokinetically: That is, as the air containing the particulate matter is
drawn into the sampler inlet, the speed and direction of the air are changed.
The inertial characteristics of suspended particulates bring about losses of
larger particles both by drift from the sampled air stream and by impact!on on
the surface of the sampler inlet. Although it is difficult to estimate the
error arising from nonisokinetic sampling, such errors may be minimized by
avoiding eddy current, turbulence, divergence or convergence, and changes in
the direction of the sampled air stream.
4-48
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4.7.1.2 Non-incorporation of sampling efficiency—The evaluation of sampling
efficiency is particularly difficult under ambient atmospheric sampling condi-
tions. The percent recovery of a collected sample is, however, rarely deter-
mined either during ambient or source sampling. The lack of incorporation of
sampling efficiency lends considerable uncertainty in the reported POM levels.
4.7.1.3 Evaporative losses and reactive conversion—Collection of ROM's on
widely-used glass-fiber filter alone without the back-up adsorbent is subject
to two kinds of errors. First, lower-molecular-weight compounds on adsorbed
participate phase may have some equilibrium vapor concentrations under atmos-
pheric conditions. This vapor part will escape collection on the filter.
Second, air passing through a filter containing the collected substances will
carry away amounts equal to or less than the equilibrium vapor concentration
because of desorption from the adsorbed substrate. Quantitative data on
losses of POM from soot particles collected on filter have been reported by
37 24 38 39
Thomas et al., DeWeist and Rondia, Murray et al., and Rondia. Pupp et
40
al. determined the equilibrium vapor concentration for a number of POM's and
concluded that considerable losses occur during ambient sampling of compounds
3 3
having equilibrium vapor concentration of 0.5 mg/10 m or higher at ambient
temperature. Considerable losses are expected with pyrene, anthracene,
phenanthrene and BaA. However, the equilibrium vapor concentration of com-
pounds adsorbed to particulate matter may be quite different and lead to much
different conclusions.
Besides sublimation, the chemical changes of POM's which may occur on the
sampling probe and on the filter paper require further investigations. The
first of the chemical changes may occur as the result of catalytic effects of
4-49
-------
the probe material used during sampling. Hermann studied this effect and
concluded that neither Vycor nor stainless steel used as probe material causes
any catalytic effect in promoting chemical reactions. However, there are many
oxidants in the air which are drawn through the filter during sampling. Lane
and Katz using simulated atmospheric conditions have demonstrated that ROM's
coated on a glass surface will be rapidly oxidized by the prevailing oxidants
in the atmosphere. Their work also indicates that BaP is more prone to oxida-
tion than BbF.
Since atmospheric ROM's exist on the surface and in the interstices of
soot particles in a multi-layered form, the surface exposed ROM's on the
filter may be oxidized rapidly by the prevailing oxidants in the atmosphere
followed by a slower penetration reaction of the subsurface ROM's and ROMs
adsorbed in the pores of particles. However, reactions in the latter two
cases can be expected to be slower not only because the oxidants have to
penetrate to their surfaces but also a layer of oxidized material may protect
them from further oxidation. Quantitative data regarding this oxidative con-
version of ROM's during collection are not available. There is also conflict-
ing evidence regarding the importance of this process. For example, passing
clean air at a rate of 100 liters/min through filters containing airborne
41
particulates Matsushita et al. found negligible losses of PAH's when air
treatment was less than 7 days. But by passing air for 3 weeks through
168
particulate collected filters at a rate of 3 liters/min, Commins reported
76 percent and 87 percent losses of fluoranthene and pyrene, respectively. No
significant losses were observed for high molecular weight compounds including
BaP. It should be mentioned that Sawicki pointed out that he failed to observe
4-50
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168
significant changes in pyrene concentrations under similar conditions.
Whether the lower temperature of the filter and the passed air was responsible
for the lack of loss was not made clear in his comments made in the above
reference. It is also not clear from these experiments whether the losses of
PAH are due to oxidative conversion, purely evaporative process or both.
4.7.2 Losses During Transportation and Storage
Another source of error that needs to be properly addressed is the loss
of ROM's during transportation and possible storage of the collected samples
prior to analysis. Losses during this period can occur from three sources:
(1) photooxidation, (2) volatilization, and (3) chemical oxidation. The first
of these losses can be easily prevented by transporting and storing the sample
in the dark. Losses of ROM's due to the other two factors have been noted by
various investigators. A decrease in the concentrations of fluoranthene,
phenanthrene and pyrene by 40 to 60 percent and rearrangement of dibenzo[a,l]-
pyrene to dibenzo[a,e]fluoranthene and BaA to chrysene have been noted by
storing the sample for 3 weeks. Hermann has noted considerable error due
to degradation or reaction on storing the sample at room temperature and
exposing to air. Similar results have been observed by other investigators
168
and the results of Commins are shown in Table 4-11.
Since the samples in Table 4-11 were stored in the dark at room tempera-
ture and in access to air, the losses may be due to oxidation, sublimation, or
42
both. By storing the sample in glass bottles not exposed to air, Hermann
reported no significant loss of POM's. The storage of samples at cooler
temperature (in a refrigerator or in contact with ice) will further prevent
the possibility of losses due to both volatilization and chemical reaction.
4-51
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Table 4-11. PERCENTAGE LOSSES OF POM FROM FILTER PAPER DUE TO
VARIATION OF STORAGE TIME158
% losses under different storage times3
Compound
Fl uoranthene
Pyrene
Benzo[a]pyrene
Benzo[e]pyrene
Anthranthrene
Benzo[ghi ]peryl ene
Coronene
3 wks. at
room temp.
37
34
5k
+22b
+gb
9
""
1 yr. at
room temp.
92
88
32
23
21
10
1
? The samples were stored in sealed envelopes.
These are the % gain (instead of loss) observed.
4-52
-------
4.7.3 Errors In Analytical Procedures
4.7.3.1 Losses during desorptlon process—Several sources of losses are
possible during analytical treatment of samples. The first of these takes
place during desorption of ROM's from the sampling filter. The loss during
this step depends on the nature of POM and the method used for desorption.
The widely used method of Soxhlet extraction can give poor recovery for some
POM's and the recovery is dependent on the solvent used (See Section 4.3.1.1).
4.7.3.2 Column and thin-layer chromatographic and storage losses—Analytical
procedures involving column chromatography can cause losses of POM's either
85
due to irreversible adsorption or photoreaction. ,The photoreactivity of a
number of POM's on some adsorbed phase is considerably greater than in solu-
tion. Similar losses due to photoreaction on TLC plates have been observed by
Inscoe. Therefore, it is absolutely necessary that all analytical proce-
dures be performed with long wavelength (red) light of low intensity. The
storage of samples during analysis should, likewise, be done at -4°C and in
the dark to avoid losses.
4.7.3.3 Losses in evaporative concentration step—The loss of POM's in evapor-
ative concentration steps is another most frequently encountered source of
error. Fox and Staley reported a recovery of only 81 to 83 percent of BaP
when the flash evaporation of solvent from extract was allowed to proceed to
dryness. The loss from this step can be expected to be even greater for other
POM's with higher volatility, such as pyrene, BaA, anthracene and phenanthrene.
4.7.3.4 Errors due to incomplete resolution—The greatest discrepancies in
the reported literature values for monitored POM (as in 1-Aza-fluoranthene in
Table 5-5) probably arise due to incomplete resolution of isomeric compounds.
4-53
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In some instances separations of isomers are very important from a toxicological
point of view because two isomers may exhibit different carcinogenic character-
istics, e.g., BaP and BeP. Some of the hard to separate isomeric compounds
are BaA, chrysene, and triphenylene; BbF and BkF; BaP and BeP; benzo[b]chrysene
and indeno[l,2,3-cd]pyrene; benzo[ghi]perylene and anthranthrene; and the
alky] substituted products of the respective group of compounds. Most packed
columns including the widely used Dexsil 300 GC will not separate these com-
pounds. Although the separation is better with Dexsil 400 GC columns, it
is by no means complete. Columns packed with liquid nemaiic crystals have
been claimed to accomplish much better resolution. ' But column bleed at
higher temperature has restricted the use of this packing material. Improved
resolution using WCOT columns has been obtained. However, using a 50 m
capillary column coated with OV-1, Lunde and Bj/6rseth failed to separate BbF
from BkF. Lee et al. used a 11 m capillary column coated with SE-52
and showed that alkyl substituted derivatives of many isomers could not be
separated.
TLC can provide better resolution when the mixture is spotted on the
plates coated with composite adsorbents and developed in two dimensions with
appropriate solvent systems. The limitation of the TLC method lies in its in-
ability to separate a mixture when a multitude of components are present.
Even in cases where separations can be achieved, losses are encountered during
the quantification procedure no matter whether solvent elution of the TLC spot
or in situ scanning is used.
The commonly used modern technique of HPLC separation has the advantage
of better resolution of the hard-to-separate components already mentioned.
4-54
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The reverse-phase packing material, y-Bondapak C,g, provides a good separation
of alkyl substituted components. In complex samples containing alkyl substi-
tuted as well as unsubstituted parent PAH's, the use of reversed-phase HPLC
could yield misleading results. For example, 1,3,5-trimethyl naphthalene, 1-
methyl phenanthrene, and fluoranthene elute simultaneously with CH-CN-H^O
mobile phase even though these compounds consist of two, three, and four
145
rings, respectively.
It should be mentioned that in some instances correction for the losses
during the analytical procedures have been attempted by the use of internal
standard(s). However, when the quantification of a number of parameters are
attempted, correction by the addition of one or two internal standards may not
be adequate since the losses are not uniform and vary from compound to com-
pound.
4.7.4 Uncertainty in the Number of Parameters to be Monitored
Lee et al. compiled a list of more than 100 PAH compounds which have
been detected in airborne particulate matter. The list could be considerably
higher if other neutral and basic aza-arenes are included. The vastness of
the POM's and the uncertainty in the number of parameters which need monitor-
ing, constitutes one of the biggest problems. Certainly, it is necessary to
determine the levels of hitherto undetected compounds which may be present in
the air in order to evaluate their potential health effects. But a cost-
effective routine analysis requiring good precision and accuracy often demand
that the number of parameters be restricted to a few selected ones. There-
fore, there is a great need to define a few representative POM's which will
measure the carcinogenic potential of atmospheric POM's to man.
4-55
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4.8 ECONOMIC CONSIDERATION IN THE SELECTION OF THE ANALYTICAL TECHNIQUE
The cost of POM analysis will depend on the selected method of analysis.
The method selection is, in turn, dependent on the objective of the analysis.
When a method is intended to be used for dosimetric purposes in occupational
settings, it must be capable of real-time monitoring of ROM's in the event of
a process leak or other increase in the POM content in the working atmosphere.
In addition to this requirement, integrating dosimeters are needed for deter-
mining the integrated exposure received by workers and the extent of contamin-
ation of the tools, and the working areas. Irrespective of the economic con-
siderations the commonly used analytical methods are time consuming and do not
meet these dosimetric requirements. Monitoring instruments, such as, time-
resolved fluorescence, correlation spectroscopy, second derivative spectro-
meters and other methods which fulfill dosimetric requirements, are in the
developing stages and it is difficult to project cost estimates for these
methods. The reader is referred to a report by Hawthorne et al. for a
review on this subject.
On the other hand, several analytical methods are presently available for
the determination of the nature and the level of POM collected from environ-
mental samples. The selection of a particular analytical method depends on,
(1) number of parameters to be determined, (2) desired accuracy for each
determination, and (3) sensitivity of the analytical method which determines
the lowest detection limit of the measured parameters. A comparative cost
estimate, through-put and other relevant data for four commonly used tech-
niques is shown in Table 4-12. All the data in this table are estimates with
31 172
some values taken from available literature. *
4-56
-------
Table 4-12. COMPARATIVE COST, THROUGHPUT, AND OTHER RELEVANT DATA
FOR FOUR COMMONLY USED ANALYTICAL METHODS.
Applicability
Operational cost/sample
Sample turnaround
Samples/day
js. Sensitivity, analytical
en
"^ Capital and peripheral
TLC/fluor.
2 compounds
$11.25
1 day
8
1-2 ng
-412,800
Methods
Column chrom/U.V.
^12 compounds
-,$600
3 days
1/3
"x/1 yg
-v-20,000
GC-MS-Computer HPLC-fluor.
80-125 compounds
$800
80 min.
6
>10 pg
$150,350
10-15 compoi
<$13
65 min.
7
25-50 pg
-416,000
investments, initial
-------
It can be concluded from Table 4-12 that GC-MS-computer technique is
preferred over other methods for non-routine analysis involving a vast number
of parameters. The initial capital investment for this method is extremely
high, although the recurring expenditure is comparatively low. For routine
analysis of a dozen or so parameters, HPLC-fluorimetric technique appears most
promising in view of its cost effectiveness. The TLC fluorimetric method
should be the method of choice when one or two parameters are intended to
be monitored. This method needs the least amount of capital investment and
operator skill for performing the analysis.
It should be pointed out that Table 4-12 is not intended to include all
the available methods, but rather serves as a guideline for the evaluation of
cost effectiveness between methods. It is also evident that the selection of
a particular analytical method is rarely based on pure economic considerations
alone, but primarily depends on the intended objective of the analysis. The
vast number of ROM's in the environment and the uncertainty in the number of
parameters which need monitoring, constitutes one of the biggest problems in
the consideration of cost evaluation. Certainly, monitoring of BaP as an
indicator for environmental POM pollution is cost effective. But, the selec-
tion of this parameter alone for the aforementioned purpose remains question-
able. One of the great needs in this regard is to define a few representative
parameters (instead of BaP alone) which will be indicative of carcinogenic
potential of environmental ROM's to man and restrict the monitoring to these
parameters. This will be one of the most important steps towards cost reduc-
tion in POM analysis.
4-58
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4.9 SUMMARY AND CONCLUSIONS
Polycyclic organic matter (POM) in environmental samples consist of a
vast array of compounds. Some of these compounds show carcinogenic activity
necessitating the need for their monitoring. The monitoring is usually per-
formed with the objective of determining the particle size distribution and
evaluating the nature and concentrations of a few individual components in the
sample. This section briefly describes the various methods available for
sampling ROM's from various sources and the analytical methods presently
available for quantification of data from the collected samples. Particular
emphasis has been placed on the difficulties commonly encountered in the
various monitoring phases.
Collection of various source samples is usually performed by filtration
through a suitable medium. With high temperature effluent samples, the air is
passed through a cooling train prior to passage through the filtering medium.
High-volume samplers are used commonly to collect total ambient particulate
matter with glass fiber filter (99 percent efficient for 0.3 ym particles).
Some investigators have used additional back-up filters consisting of adsorp-
tive medium to collect ROM's present in the vapor phase and to prevent evapor-
ative losses of POM's. The high-volume air samplers do not provide informa-
tion relative to aerosol particle size-weight distribution which is essential
for the prediction of areas of deposition in man as a result of inhalation of
aerosol. Cascade or cyclone impactors are often used for this purpose.
Limited information is available on sample recovery from sample collection
procedures. More research is needed to establish the extent of evaporative
and oxidative losses which may occur during sample collection.
4-59
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The recovery of ROM's from the widely used Soxhlet extraction for desorp-
tion of ROM's from the filtering/adsorbing medium is poor for some compounds
and is dependent on the solvent(s) used. A method utilizing dissolution by
sonification yields better results. Techniques which use sublimation and a
thermal method for desorption of ROM's from collection medium are promising,
although the latter method is only applicable when coupled with gas chroma-
tographic analysis.
The problem of any analytical method for the quantification of ROM's,
which usually occur as a small quantity in a large matrix of impurities, is
three-fold. First, the compounds of interest must be adequately separated
from impurities to the extent necessary for their interference-free detection.
Second, the ROM's (many of which are isomeric compounds) must be adequately
resolved from each other. Third, a high sensitivity of detection is required
to quantitate small amounts of ROM's usually collected from environmental
samples.
Separation procedures involving solvent partitioning is generally used
for the isolation of ROM's from paraffinic hydrocarbons. Column chromatog-
raphy with alumina, silica gel, Florisil, or, occasionally, cellulose, and
cellulose acetate, has been used not only for the enrichment of ROM's but also
for the resolution of the individual ROM's. However, separation is rarely
complete and quantitative. Gel filtration produces better resolution but the
procedure is very time consuming.
TLC is widely used for resolution of ROM's, particularly the isomeric
compounds. The method is quick and inexpensive but is hardly suitable for
separations involving a large number of compounds. Moreover, this method
4-60
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results in some losses of ROM's. Gas chromatography offers a good method for
the separation of ROM's. The separation is more quantitative than either
column or thin-layer chromatography. With the exception of liquid nematic
crystal phases, most liquid phases used in GLC, however, do not separate
isomeric compounds. Even with nematic crystals, column bleed at higher temp-
eratures has limited this packing material to lower temperature use. Better
resolution is achieved with wall-coated open tubular capillary columns.
HPLC offers several advantages including higher speed, higher resolution,
and lower operating temperature than gas chromatography. The method is non
destructive and the injected sample can be recovered easily. This technique
is gaining wide acceptance as a modern method for the separation of ROM's,
although the separation of isomeric ROM's from real-life samples may not be
complete.
With regard to detection, flame ionization and electron capture detectors
are used when the mode of analysis is gas chromatographic. Fluorescence
spectroscopy has, however, become well established as a sensitive and selec-
tive analytical technique for ROM's when other chromatographic procedures are
used. Several groups have found it to be at least ten times more sensitive
than the U.V. method. It is also more sensitive and less expensive than mass
spectral detectors. Mass spectrometers normally have a nanogram detection
limit, although integrated ion-current techniques reduce this limit to sub-
pi cogram range.
No single analytical separation procedure to date is capable of providing
complete separation and resolution of the POM fractions. Therefore, POM is
actually analyzed with a combination of separation and detection methods. The
4-61
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selection of analytical methods Is dependent on the number of parameters to be
monitored and the required accuracy and cost of analysis. In the past, the
most widely used combined method consisted of column chromatography followed
by TLC and U.V./fluorescence detection. More recent methods utilize column
chromatography in combination with HPLC and U.V./fluorescence detection. When
the number of parameters to be monitored is very large, column chromatography
coupled with gas chromatography-mass spectrometry is used as the method of
analysis.
The widely accepted practice of monitoring benzo[a]pyrene alone, as an
indicator for other ROM's, is questionable. More research effort should be
directed towards defining a few representative parameters which would be
indicative of carcinogenic potential of ROM's present in the environment.
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4-77
-------
DRAFT
NOT QUOTE OR CITE
5. AMBIENT LEVELS
5.1 AMBIENT ATMOSPHERIC LEVELS
A variety of polycyclic aromatic hydrocarbons (PAH's), aza arenes, and
carbonyl arenes have been detected in ambient air. Because of its carcino-
genic properties, benzo[a]pyrene (BaP) has been the most extensively monitored
and has frequently been used as an indicator of PAH's. However, the relative
amount of individual POM compounds released from different sources can vary
considerably but most are present in ambient air samples. For example, auto-
mobile emissions contain a relatively low amount of BaP as compared to other
PAH's. Also, there are several other social or occupational sources of POM's
which may result in larger exposures to humans than those from ambient air.
For example, Bridbord et al. has tabulated human exposure to PAH in terms of
BaP from a number of occupational and other sources (Table 5-1). This treat-
ment suggests that smoking one pack of cigarettes a day results in an appro-
priate exposure of BaP twenty times greater than that of a person exposed to
ambient air BaP levels (assumed 2 ng/m BaP). The exact amount of BaP intake
is difficult to determine because of the different modes of inhalation during
2 1
smoking, working, or exposure to ambient air. Bridbord et al. recognize
"that to the extent that polynuclear aromatic compounds besides BaP are also
present, BaP represents a poor surrogate..."
5-1
-------
Table 5-1. INFLUENCE OF OCCUPATIONAL AND.OTHER
FACTORS UPON BENZO[a]PYRENE EXPOSURE1
Factor
Smoking one pack of cigarettes
each day
Coke oven workers
Top side workers
Side and bench exposure
Coal tar pitch worker
Airplane pilots
Transatlantic flights
Domestic cross country
Employee in restaurant
BaP Exposure
(yg/day)
0.4
180
70
750
0.93
1.38
0.8
Cigarette
equivalents
(packs/day)
1
450
175
1875
2.3
3.5
2
Source of
data
NAS report 1972
NIOSH data!*
NIOSH data3
1962 report
NIOSH data*
NIOSH data3
1975 data
Person living near expressway
24-hr/day (adverse
meteorology)
Commuter on an expressway
2-hr/day (adverse
meteorology)
Exposure to ambient BaP levels
8-hr/day
0.02
0.04
0.02
0.05 1976 projection
from 1974 data
0.10 1976 projection
from 1974 data
0.05 assumed exposure
to 2 ng/m3
Unreferenced NIOSH data - presumably the latest data in 1976.
5-2
-------
Concentrations of BaP are different in various cities and at different
times of the year. In general, the concentrations are usually highest during
O A
the winter months (Figure 5-1), probably due to heating sources. However,
there are some exceptions. Cleveland, for instance, does not follow the high
winter-low summer concentration pattern. It has been suggested that this may
be due to significant industrial emissions of BaP that would be uniform
throughout the year. The higher BaP concentrations in the winter in most
cities are not due to an increase in particulate matter, but rather, can be
attributed to an increase in the amount of BaP in the particulates.
During 1966 through 1970, the benzene-soluble organics (BSO) of quarterly
composite samples of suspended particulate matter collected on glass fiber
filters (99 percent efficient for particles of 0.3 ym) by the 250 National Air
Surveillance Network (NASN) stations were analyzed for BaP. These data, in
the form of annual arithmetic averages for the numerous NASN urban and non-
urban stations, are presented in Tables 5-2 and 5-3 for the years 1966 to
1970. The quarterly composite average for all the stations during the same
years is presented in Figure 5-1. The levels from year to year remain rela-
tively constant and do not necessarily correlate to city size. Particularly
interesting is Los Angeles, where high auto emissions do not result in high
BaP levels. During the period from 1971 to 1976 a more limited number of NASN
stations (40) were sampled for BaP. The data from these stations for the
total period from 1966 to 1976 are presented in Table 5-4.
Other polycyclic organic compounds are frequently found in higher concen-
trations than BaP. Sawicki found that benzo[ghi]perlene (BghiP) concentra-
tions during the summers of 1958 to 1960 were higher than BaP levels in the
5-3
-------
I I I I I I I I
CO
00
I I II I I I I
COMPOSITE AVERAGE
URBAN STATIONS
LU
O
O
°- 1
« I
CO
COMPOSITE AVERAGE
NONURBAN STATIONS
12341234123412341234
1966 1967 1968 1969 '1970
TIME, year and quarter
Figure 5-1. Composite quarterly averages for BaP at
32 urban and 19 nonurban NASN stations.
5-4
-------
Table 5-2. ANNUAL AVERAGE AMBIENT BENZO[a]2YRENE CONCENTRATIONS
AT NASN URBAN STATIONS5*
(ng/m3)
Station
Alabama
Birmingham
Gad sen
Huntsville
Mobile
Montgomery
Alaska
Anchorage
Arizona
Phoenix
Tucson
Arkansas
Little Rock
West Memphis
California
Burbank
Glendale
Long Beach
Los Angeles
Oakland
Ontario
Pasadena
Riverside
Sacramento
San Bernardino
San Diego
San Francisco
Colorado
Denver
Connecticut
Hartford
New Haven
1966
18.5
3.5
6.5
2.3
1.7
0.6
1.2
1.1
2.5
2.1
2.7
1.8
1.7
1.1
2.3
2.3
3.5
1967
3.1
2.3
1.9
2.5
0.7
0.9
2.2
1.0
2.1
1.3
1.7
1.6
1.5
2.4
2.1
1.9
1968
2.4
2.7
4.2
2.9
1.7
2.1
0.7
0.9
2.2
1.6
2.1
1.8
1.6
0.9
2.3
1.3
1.4
1.0
1.2
1.8
2.3
1.4
1.4
1969
1.8
1.8
2.6
2.0
1.3
2.2
0.5
1.1
2.4
2.9
1.6
2.3
1.9
1.6
0.6
0.8
1.8
0.9
1.4
1.2
2.5
2.0
2.1
1970
2.5
1.6
1.3
0.8
0.4
0.7
0.6
1.9
1.0
1.0
1.2
1.0
0.6
0.7
0.7
0.7
0.8
0.7
0.6
2.2
1.4
1.2
5-5
-------
Table 5-2 (Cont'd). ANNUAL AVERAGE AMBIENT BEN70[a]PYRENE CONCENTRATIONS
AT NASN URBAN.STATIONS5
(ng/m3)
Station
Delaware
Newark
Wilmington
District of Columbia
Florida
Jacksonville
Tampa
Georgia
Atlanta
Hawaii
Honolulu
Idaho
Boise City
Illinois
Chicago
Springfield
Indiana
East Chicago
Hammond
Indianapolis
Muncie
New Albany
South Bend
Terre Haute
Iowa
Davenport
Des Moines
Cedar Rapids
Kansas
Kansas City
Topeka
Wichita
1966
1.0
2.2
2.4
1.4
0.2
3.5
3.3
6.8
3.9
10.4
2.4
5.4
2.2
3.2
2.5
1.2
0.8
1967
1.4
2.7
1.9
3.0
0.5
2.4
3.0
•
5.7
2.5
5.7
1.6
2.6
3.7
2.7
0.8
0.5
0.5
1968
0.9
1.9
1.9
2.9
1.5
1.8
0.6
2.0
3.1
1.1
1.9
2.1
4.1
3.7
1.1
0.7
1.2
0.7
1.0
1969
1.7
4.3
2.3
1.0
1.9
0.6
6.0
3.9
1.3
6.8
3.3
5.2
4.3
3.7
4.0
1.7
0.9
1.1
0.4
0.7
1970
0.4
1.1
1.4
0.5
0.9
0.2
1.1
2.0
0.9
5.3
1.7
2.3
3.7
2.4
2.8
0.9
0.7
0.3
2.4
0.3
0.5
5-6
-------
Table 5-2 (Cont'd). ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS
AT NASN URBAN STATIONS5
(ng/m3)
Station
Kentucky
Ashland
Coving ton
Lexington
Louisville
Louisiana
New Orleans
Maine
Portland
Maryland
Baltimore
Massachusetts
Worchester
Michigan
Detroit
Flint
Grand Rapids
Trenton
Minnesota
Duluth
Minneapolis
Moorhead
St. Paul
Missouri
Kansas City
St. Louis
Montana
Helena
Nebraska
Omaha
1966
10.5
3.1
2.5
2.3
2.8
4.7
2.2
1.6
0.7
1.8
2.7
1967
1.9
1.8
2.1
1.8
3.8
5.4
1.4
2.8
1.3
2.3
2.3
0.8
1.3
1968
9.3
3.6
3.0
2.7
1.6
2.3
2.3
1.7
5.1
0.8
3.4
1.4
2.7
1.1
0.9
1.8
1.8
0.9
1.9
1969
10.9
4.1
1.9
1.5
2.8
1.5
3.9
1.7
1.7
1.6
2.1
1.4
1.0
1.8
1.6
3.3
0.5
1.6
1970
6.7
4.4
1.6
1.1
1.1
2.1
1.6
2.6
1.5
0.9
0.8
1.1
0.6
1.6
1.0
1.1
1.0
5-7
-------
Table 5-2 (Cont'd). ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS
AT NASN URBAN STATIONS5
(ng/m3)
Station 1966 1967 1968 1969 1970
Nevada
Las Vegas 1.3 1.1 1.4
Reno 4.6 3.1
New Hampshire
Concord 0.6 1.5 1.0 0.7 0.6
New Jersey
Camden 3.0 1.6 2.4 1.9
Glassboro 0.7 0.8 1.2 1.1 1.2
Jersey City 4.2 3.5 2.3 2.7 4.7
Marlton 1.2 1.6 1.3 1.4
Newark 2.1 3.3 2.1 1.8 1.5
Patterson 1.9 2.0 1.2 1.2
Perth Amboy 2.1 2.1 1.2 1.2 1.0
Trenton 2.2 1.0 1.5 1.1
New Mexico
Albuquerque 2.0 1.9 1.8 1.1 1.1
New York
New York City 4.1 3.9 3.6 3.0
North Carolina
Charlotte 5.7 6.3 5.6 4.9 1.9
Durham 8.0 3.4 3.9
North Dakota
Bismarck 0.9 1.0 0.4
Ohio
Akron 4.1 3.7 3.0
Cincinnati 3.6 1.9 1.8 2.9 2.6
Cleveland 3.1 2.9 3.0 3.8 2.8
Columbus 2.9 1.7 2.2 2.7 1.6
Dayton 2.7 3.7 2.4 1.9 1.5
Toledo 1.8 1.9 1.8 1.5 1.4
Youngstown 7.3 8.2 5.6 9.9 7.1
5-8
-------
Table 5-2 (Cont'd). ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS
AT NASN URBAN STATIONS5
(ng/m3)
Station
Oklahoma
Oklahoma City
Tulsa
Oregon
Eugene
Medford
Portland
Pennsylvania
All en town
Al toona
Bethlehem
Harrisburg
Lancaster
Philadelphia
Pittsburgh
Reading
Scranton
Warminster
West Chester
Mi Ikes Barre
York
Rhode Island
East Providence
Providence
South Carolina
Columbia
Greenville
Tennessee
Chattanooga
Knoxville
Memphis
Nashville
1966
1.5
0.7
3.3
2.3
3.8
4.9
2.3
0.9
3.6
5.0
8.4
1.7
5.5
1967
0.7
0.6
2.4
4.8
3.5
1.8
29.5
2.9
5.9
7.0
2.9
5.2
2.2
1.1
1.8
1.6
2.8
4.2
22.9
7.0
1.6
7.0
1968
0.7
0.8
8.2
4.1
1.2
18.0
2.1
1.3
2.9
6.3
2.4
6.1
0.9
1.0
1.6
1.9
1.2
2.0
6.2
18.6
7.4
9.8
1.3
6.0
1969
0.7
0.5
4.1
2.6
1.9
22.3
2.0
1.5
4.0
13.8
1.8
7.7
1.0
1.3
1.5
2.0
1.2
2.2
1.3
7.0
4.2
4.7
0.7
2.8
1970
0.9
0.8
2.3
2.4
19.3
2.7
1.5
2.4
5.9
1.6
2.9
1.3
1.2
1.2
2.1
3.4
5.5
1.4
3.6
5-9
-------
Table 5-2 (Cont'd). ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS
AT NASN URBAN STATIONS5
(ng/m3)
Station 1966 1967 1968 1969 1970
Texas
Dallas
Houston
San Antonio
Utah
Ogden
Salt Lake City
Vermont
Burlington
Virginia
Danville
Hampton
Lynchburg
Norfolk
Portsmouth
Richmond
Roanoke
Washington
Seattle
West Virginia
Charleston
Wisconsin
Kenosha
Madison
Milwaukee
Superior
Wyomi ng
Casper
Cheyenne
1.4
0.9
0.6
0.5
1.2
0.8
3.2
2.8
2.7
3.4
4.1
0.5
1.4
0.7
2.2
9.2
3.5
7.7
5.2
7.5
1.8
0.9
0.8
1.0
0.7
2.5
1.5
8.7
4.9
10.2
7.7
2.0
4.6
1.4
1.3
4.7
3.3
0.9
0.6
2.0
0.6
0.7
0.7
0.5
1.8
0.9
6.3
3.9
3.4
2.2
5.3
1.6
2.6
1.7
4.0
1.6
0.6
0.5
1.9
1.2
1.0
2.5
1.4
0.7
2.7
1.1
4.5
1.8
4.9
2.1
6.2
1.5
2.1
1.3
1.1
2.5
1.5
0.4
0.4
5-10
-------
Table 5-3. ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS
AT NASN NONURBAN STATIONS5
(ng/m3)
Station
Arizona
Grand Canyon
Maricopa County
Arkansas
Montgomery County
California
Humboldt Coutny
Idaho
Butte County
Indiana
Monroe County
Parke County
Maine
Acadia National Park
Missouri
Shannon County
Montana
Glacier National Park
Nebraska
Thomas County
Nevada
White Pine County
New Hampshire
Coos County
New York
Jefferson County
1966 1967 1968
0.3 0.2 0.2
0.2 0.5
0.3 0.1 0.2
0.4 0.4 0.3
0.2
0.5 0.5
0.9 0.4
0.2 0.3
0.2 0.2
0.3 0.4
0.2 0.2
0.1 0.1
0.2 0.2 0.2
0.2 0.2
1969
0.2
0.3
0.2
0.5
0.1
0.3
0.3
0.1
0.2
0.4
0.1
0.1
0.1
0.3
1970
0.1
0.3
0.1
0.1
0.1
0.2
0.4
0.2
0.2
0.1
0.1
0.1
0.2
5-11
-------
Table 5-3 (cont'd). ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS
AT NASN NONURBAN STATIONS5
(ng/tn3)
Station
North Carolina
Cape Hatteras
Oklahoma
Cherokee County
Oregon
Curry County
Pennsylvania
Clarion County
Texas
Matagorda County
Vermont
Orange County
Virginia
Shenandoah National Park
1966 1967
0.2
0.2 0.2
0.1 1.1
1.5 2.1
0.3 0.1
0.9
0.9 0.3
1968
0.2
0.2
0.1
1.0
0.2
0.3
0.3
1969
0.1
0.2
0.1
1.2
0.1
0.3
0.3
1970
0.2
0.2
0.1
1.2
0.3
0.2
0.2
5-12
-------
Table 5-4. ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS AT NASN
URBAN STATIONS IN ng/m3.6
Birmingham, Ala.
Gadsden, Ala.a»b
Montgomery, Ala.a
Grand Canyon Nat. Park, Ariz.
Jacksonville, Fla.a
Honolulu, Hawaiia
Chicago, Ill.a»b
Gary, Ind.a»b
Hammond, Ind.a»b
Indianapolis, Ind.a»b
Terre Haute, Ind.a»b
Ashland, Ky.a>b
New Orleans, La.a
Baton Rouge, La.a
Arcadia Nat. Park, Maine
Baltimore, Md.a»b
Detroit, Mich.a»b
Dearborn, Mich.a»b
Trenton, Mich.a»b
Duluth, Minn.
St. Paul, Minn.a»b
St. Louis, Missouria>b
New York City, N.Y.a
Buffalo, N.Y.a»b
Cleveland, Ohipa»b
Toledo, Ohioa»b
Youngstown, Ohioa»b
Bethlehem, Pa.a>b
Erie, Pa.a>b
Philadelphia, Pa.a»b
Pittsburgh, Pa.a»b
1966
18.5
3.5
—
0.3
--
0.2
3.3
—
3.9
10.4
__
10.5
2.3
--
0.2
2.8
4.7
__
--
2.2
1.8
4.1
__
3.1
1.8
7.3
--
__
3.8
4.9
1967
..
—
2.3
0.2
--
0.5
3.0
—
2.5
5.7
3.7
—
1.8
—
__
3.8
5.4
--
__
2.3
2.3
3.9
__
2.9
1.9
8.2
2.9
__
5.9
7.0
1968
..
2.4
2.9
0.2
2.9
0.6
3.1
--
2.1
4.1
__
9.3
1.6
--
0.3
2.3
5.1
1.4
2.7
1.8
_ _
--
__
3.0
1.8
5.6
2.1
__
2.9
6.3
1969
_.
1.8
2.0
0.2
2.3
0.6
3.9
—
3.3
5.2
4.0
10.9
1.5
--
0.1
2.8
3.9
1.6
2.1
1.8
3.3
3.6
__
3.8
1.5
9.9
2.0
__
4.0
13.8
1970
„
2.5
1.3
0.1
1.4
0.2
2.0
--
1.7
2.3
2.8
6.7
1.1
--
0.2
2.1
2.6
0.8
1.1
1.0
__
3.0
__
2.8
1.4
7.1
2.7
__
2.4
5.9
1971
4.0
1.2
0.5
--
2.2
0.2
2.5
1.6
3.8
0.9
__
9.0
0.9
0.4
__
2.8
1.4
0.7
4.8
0.5
0.8
2.3
__
__
0.8
3.7
0.9
1.5
2.3
6.1
1972
2.3
1.2
0.5
--
0.4
0.1
1.3
1.2
1.4
4.9
1.1
8.5
0.4
0.2
0.3
1.3
1.9
0.6
0.5
19.1
0.5
0.6
1.8
1.5
1.3
0.4
3.2
0.8
2.4
0.9
10.6
1973
1.5
0.8
0.3
< 0.1
0.2
< 0. 1
0^4
0.3
0.2
0.4
__
2.9
0.3
0.1
—
0.4
1.0
1.0
0.1
0.3
0.1
0.2
0.7
0.6
__
0.4
1.1
0.5
0.7
0.6
—
1974
2.5
0.5
0.4
< 0.1
--
< 0 .1
--
0.5
0.4
0.3
0.3
0.1
0.1
0.5
1.7
0.2
0.5
0.3
0.9
0.8
0.2
1.9
0.1
0.6
0.8
1.3
1975
0.9
0.6
0.3
—
0.4
— —
1.0
--
0.7
0.6
4.7
0.2
0.1
0.1
0.6
1.0
--
_ —
— —
0.3
0.9
0.5
0.4
2.1
—
0.4
0.6
2.1
1976
1.6
0.6
0.3
< 0.1
0.4
< 0. 1
—
0.7
0.5
0.6
0.6
2.9
0.2
0.3
0.1
0.5
1.1
0.3
0.2
0.5
0.3
0.5
0.3
0.6
0.5
1.5
0.3
0.2
1.0
2.0
-------
Table 5-4 (Cont'd). ANNUAL AVERAGE AMBIENT BENZO[a]PYRENE CONCENTRATIONS AT
NASN IIRRAN STATIONS TN nn/m3 6
NASN URBAN STATIONS IN ng/m
Chattanooga, Tenn. '
Houston, Texasa»b
Newport News, Va.
Norfolk, Va.a
Shennandoah Nat. Park, Va.
Seattle, Wash.a
Spokane, Wash.a»b
Charleston, W.V.a
Milwaukee, Wisc.a»b
1966
8.4
0.9
—
2.8
0.9
2.7
--
3.4
4.1
1967
22.9
—
—
3.5
0.3
1.8
__
--
1968
7.4
—
--
4.9
0.3
2.0
4.6
4.7
1969
4.2
—
--
3.9
0.3
1.6
2.6
4.0
1970
5.5
1.2
--
1.8
0.2
1.5
2.1
2.5
1971
• «
0.5
0.4
1.2
__
0.5
1.7
0.9
1.8
1972
9.9
0.4
0.3
0.6
0.1
0.5
1.5
0.7
3.6
1973
— —
0.4
0.2
0.4
0.1
0.3
0.4
0.2
0.6
1974
— —
0.2
—
0.2
--
__
-_
0.5
--
1975
0.8
0.2
—
0.2
--
_ _
—
0.5
1.1
1976
0.7
0.1
—
0.5
--
__
—
0.4
0.4
? Urban site used for Figure 5-2.
Y1 Urban site where a coke oven is located.
-------
10 cities examined, but the reverse was true during winters in those communi-
ties that burn coal.
An early study of the various PAH compounds in urban air was reported by
Sawicki and coworkers. They analyzed eight compounds in seven cities during
the summer of 1958 and winter of 1959. They collected their samples on glass
fiber filters, Soxhlet extracted with benzene, separated isomers with column
chromatography, and quantitated the compounds from ultraviolet absorption
spectra. Their results are presented in Table 5-5. Good relative correlation
between BaP and the other PAH's except coronene was found, and the authors
concluded that concentrations of the other compounds could be predicted from
BaP data. The advantage of this is that costly and laborious work could be
avoided if one can calculate other PAH values from BaP values. Hauser and
coworkers, in an unpublished study of PAH's in Birmingham, Ala., found a
similar correlation between many of the compounds they examined (Table 5-6).
Their results indicated the effect of localized sources on the immediate sur-
roundings.
This correlation between the concentration of BaP and other compounds
o
does not always occur. For example, a study by Kertesz-Saringer and Mori in
found little or no relationship between BaP and other PAH's. They analyzed
11 PAH's in Budapest air by collection on glass fiber filters, Soxhlet extrac-
tion with benzene, and thin layer chromatography separation. Bands of the
chromatographic plate were selected so that no more than three compounds were
found in each band to be analyzed spectrophotometrically. The lowest correla-
tion coefficient was found between BaP and chrysene or phenanthrene. Some
relationship was found between pyrene and BaP, but the authors concluded that
5-15
-------
Table 5-5. POLYCYCLIC AROMATIC COMPOUNDS IN THE AIR OF SELECTED CITIES5
(ng/m3)
City
Winter 1959
Atlanta
Birmingham
Detroit
Los Angeles
Nashville
New Orleans
San Francisco
Summer 1958
Atlanta
Birmingham
Detroit
Los Angeles
Nashville
New Orleans
San Francisco
BghiP
8.
18.
9
0
33.0
18.
17.
7.
7.
5.
8.
9.
2.
3.
4.
2.
0
0
3
5
1
3
5
3
4
6
6
BaP
7.
25.
31.
5.
25.
4.
2.
1.
6.
6.
0.
1.
2.
0.
4
0
0
3
0
1
3
6
4
0
5
4
0
3
BeP
4.7
10.0
23.0
8.1
14.0
6.4
2.9
1.5
5.9
5.3
0.6
1.2
3.1
0.5
BkF
6.0
13.0
20.0
5.7
15.0
3.9
1.7
1.3
4.6
4.9
0.5
1.0
1.8
0.2
P
6.0
17.0
36.0
6.0
30.0
2.3
1.9
0.7
2.1
2.8
0.3
0.6
0.3
0.1
Cor
4.3
3.5
6.4
12.0
4.6
27.0
4.9
2.5
2.4
1.8
2.2
1.3
2.5
1.6
Per
1.1
5.5
6.0
1.6
4.4
0.8
0.3
0.4
2.1
1.7
0.03
0.2
0.4
<0.1
A
0.5
2.2
2.0
0.2
1.8
0.1
0.1
0.2
0.3
0.4
0.0
0.1
0.1
0.02
Total
38.9
94.2
146.4
56.9
111.8
27.6
21.6
13.3
32.1
32.4
6.4
9.2
14.8
5.4
5-16
-------
Table 5-6. ANNUAL AVERAGE CONCENTRATION OF PAH COMPOUNDSCIN THE
AIR OVER GREATER BIRMINGHAM, ALABAMA, 1964 and 19655
(ng/m3)
City
Bessemer
Birmingham
Fairfield
Irondale
Mt. Brook
Tarrant
Vestavia
Site
1
3
4
5
7
1
1
1
1
1
Fluor
7.0
4.9
11.2
10.8
2.6
10.0
3.4
1.0
3.4
1.0
P
7.6
4.6
10.8
9.1
2.5
8.1
2.8
1.0
3.6
1.0
BaA
7.8
5.3
21.2
14.5
3.4
13.3
4.2
1.0
3.9
1.0
Ch
13.1
8.1
27.9
14.2
4.4
11.3
5.7
2.2
7.6
2.0
BeP
10.5
7.6
26.1
15.0
5.6
13.3
6.3
3.0
7.6
2.9
BaP
13.5
9.0
35.8
20.5
6.0
18.2
7.6
2.6
7.4
2.4
Per
1.3
0.9
4.1
2.0
0.4
1.4
0.6
0.2
0.8
0.2
BghiP
14.1
9.5
22.4
15.3
7.9
11.8
7.0
3.7
8.2
3.5
A
1.2
0.7
2.2
1.2
0.3
1.1
0.4
0.1
0.2
0.1
Cor
2.6
2.7
3.8
3.5
2.7
2.1
1.9
1.4
2.2
1.2
Average 5.5 5.1 7.6 9.6 9.8 12.3 1.2 10.3 0.8 2.4
-------
"the concentration of 3,4-benzpyrene[BaP] is a poor indicator for other com-
pounds."
g
Gordon and Bryan found similar results while monitoring PAH's at four
sites in Los Angeles. They found that the amount of coronene paralleled the
estimated traffic density at the four sites. At three of the four sites, the
PAH's patterns normalized to coronene were similar and resembled patterns of
auto exhaust. However, at the remaining site (near petroleum refineries and
chemical plants), the PAH pattern, including BaP, was distinctly different.
An interesting monitoring trend has been developed from the NASN BaP
values for the past ten years. ' ' The declining trend for BaP during 1966
to 1970 is depicted in Figure 5-1 and is based upon BaP data at 32 urban and
19 non-urban stations. As can be seen, the average BaP concentration decreased
3 3
from 3.2 nanograms/m in 1966 to 2.1 nanograms/m in 1970, approximately a
30 percent decrease. A recent analysis of BaP trends during the ten year
period of 1966 to 1975 has been based upon 34 urban (24 with coke ovens) and
3 rural sites. These trends for the urban sites (Figure 5-2) are consistent
with previous results indicating a steady decline of BaP. Even concentrations
in the three remote rural areas (Grand Canyon National Park, Arizona; Acadia
National Park, Maine; and Shennandoah National Park, Virginia) (Table 5-4) in-
dicated a downward trend. The following limitations to the study were noted:
(1) small number of areas were covered and data was only available from one
single monitoring site (located in center city business area); and (2) a
relatively high number of urban sampling sites were located in areas where
coke ovens were present.
5-18
-------
10.0
8.0
!i
T
T
DASHED LINE • PERCENTILES OF QUARTERLY
MEASUREMENTS
- 4 QUARTER MOVING AVERAGE
OF PERCENTILE VALUES
6.0
ee
4.0
2.0
QUARTERLY MEASUREMENTS
~~ 50™ PERCEWTILb
OF QUARTERLY MEASUREMENTS
(LOWER CURVES)
66
67
68
69
70
71
72
73
74
75
YEAR
Figure 5-2 Benzo[a]pyrene - seasonality and trends
(1966 to 1975) in the 50th and 90th
percent!les for 34 NASN urban sites9
5-19
-------
Although a large number of the NASN sites were in areas that had coke
oven emissions, the monitoring stations were not sited for those emissions.
Comparison of the coke oven sites to the non-coke oven sites showed that the
coke oven sites had generally higher (40 to 70 percent) BaP concentrations and
the downward trend for both types of sites was parellel. The authors con-
cluded that the higher values could not necessarily be attributed to coke oven
emissions alone since coke oven sites were usually located in more industrial-
ized northern cities where industrial and heating sources may contribute
significant amounts of BaP. Also noted was a decline of BaP summer levels for
coke sites that was greater than the non-coke sites.
Examination of Figure 5-2 also illustrates the high winter-low summer
seasonal concentration of BaP. "This seasonality is most dominant in the
first five years (1966 to 1970) and is much less pronounced for the most
recent years."
During the ten year period of 1966 to 1975 the BaP concentrations at
urban sites decreased about 84 percent, dropping from a median of the individ-
3
ual annual average concentration of 3.2 nanograms/m in 1966 to 0.5 nano-
•3
grams/m in 1975 (Fig. 5-2). The urban sites used for this trend analysis are
indicated in Table 5-4 along with an indication of areas where coke ovens are
located. Nashville, Tennessee was used by Faoro and Manning for the trend
analysis but is not presented in Table 5-4. The decline in BaP is believed to
be due primarily to decreases in coal consumed in family dwellings or build-
ings in and around the central business districts of urban areas. Also
contributing to the decline is the improved disposal of solid wastes and the
restrictions on open burning.
5-20
-------
Because of the importance of the NASN BaP monitoring data to the assess-
ment of exposure, evaluation of the analytical procedure used is necessary.
During the total period of 1966 to 1976 all the samples were collected on
glass fiber filter (99 percent efficient at 0.3 pm) with high-volume samplers.
Twenty-four-hour samples were taken biweekly and sent to a central laboratory
where individual samples were combined by quarter to save time and expense.
Up until 1972, the sample was extracted with benzene in a Soxhlet extractor
for six hours followed by thin layer chromatography (TLC). BaP was removed
from the TLC plate, dissolved in sulfuric acid, and measured by fluorescence
spectroscopy. Starting in approximately 1973, a faster method of analysis was
used which may have had some affect on the data generated. This consisted of
cyclohexane extraction of the filter (cyclohexane was found to be as efficient
in extraction as benzene), TLC separation, and fluorescence spectroscopy of
BaP on the plate. Anthanthrene interferes with the latter procedure but its
contribution to the fluorescence spectra can be subtracted using a character-
istic emission band for anthanthrene.
The efficiency of collection and stability of BaP during the analytical
procedure has not been completely examined. Many studies have indicated that
12 13 14
BaP is primarily associated with particulate matter, ' ' with a sizeable
percentage (up to 60 percent) in the less than one pm range. ' How much
BaP might pass through the 0.3 ym glass fiber filter is unknown although the
efficient of collection should increase as the filter is loaded with particles,
Also, DeWiest and Rondia have provided experimental evidence that sizeable
differences between the BaP collected by high volume samplers in summer as
compared to winter temperatures will occur.
5-21
-------
1 Q
Stability during collection has been addressed by Commins. He collect-
o
ed two identical samples of smoke on glass fiber filters at 1.2 m per minute
for two hours. He then drew filtered air through one of the filters for two
hours at the same flow rate. None of the eight hydrocarbons (including BaP)
18
had changed significantly. A similar study by Sawicki indicated no loss
of BaP between identical samples whose only difference was that one set had
twice as much air drawn through the filter. Thus BaP adsorbed on particulate
matter that is collected on a glass fiber filter appears to be stable to an
identical volume of air. However, if oxidation of the outer layer of BaP
occurs during the first sampling period but not during the second period
19
because of protection of the inner BaP by the oxidized outer layer, then the
values for the above experiments should be the same. This possibility would
result in lower reported BaP values than the quantities being inhaled.
1 p
Commins also examined the stability of BaP on storage of filter paper
or in cyclohexane. BaP from a smoke sample stored on a glass fiber filter in
a sealed envelope for a year lost 32 percent compared to a sample immediately
analyzed. However, with BaP kept in cyclohexane in the dark for six months,
18
no loss was detected. Commins concluded that the filters should be extract-
ed as soon as possible. Since BaP samples are combined into three month
samples and at times during the early 1970's backlogs of over a year were
encountered, substantial losses of BaP could occur if the samples were not
extracted soon after collection.
Declining trends for PAH's have also been noted in Great Britian.
20
Leahey found that the concentration of BaP and BeP in downtown London was
decreasing while coronene was remaining about the same. The author attributed
5-22
-------
the reduction of BaP and BeP to reduction in coal use and suggested that
coronene had remained constant because of its greater proportion in auto
exhaust which is increasing. The samples were collected on glass fiber
filters, sealed in glass tubes at the end of each month, and analyzed at the
end of a year. The filters were extracted with cyclohexane, separated by
column chromatography (alumina), and analyzed by ultraviolet spectrophoto-
metry.
Aza arene compounds have recently received considerable monitoring
21 22
effort. Brocco et al. and Dong and coworkers have detected a number of
new compounds including quinolines, azafluoranthene, azapyrene, and isoquino-
lines. Their results are included in the tabulation in Table 5-8. The con-
centrations of aza arenes are usually considerably lower than PAH and the New
22
York City monitoring of Dong et al. are compatible with previous data.
21
However, the results of the Brocco et al. analysis of Rome air samples are
considerably higher than any previously reported values. Many of these com-
pounds (e.g., the quinolines) are very volatile and, therefore, the different
values may be due to the different collection and analytical procedures which
22 21
were used. Both Dong et al. and Brocco et al. collected their samples on
21 22
glass fiber filters and then extracted with benzene or benzene/methanol
21
(4:1). Brocco et al. cleaned up their sample by TLC and analyzed by gas
22
chromatography. Dong et al. partitioned the aza arenes into sulfuric acid,
neutralized and extracted them back into chloroform, and analyzed by HPLC.
Qualitative confirmation was accomplished by GC/MS.
Very few studies have examined the possibility of long term transport of
POM's which might result in POM contamination of areas that are down wind from
5-23
-------
25
large emission sources. Lunde and Bj0rseth monitored air samples in Norway
which had different trajectories. They identified 20 different PAH's (see
Table 5-7) and determined that samples with trajectories from western Europe
contained about 20 times more PAH than samples with trajectories from northern
Norway or stationary air from southern Norway. When the wind was blowing from
the right direction, the POM concentrations in Norway were of the same order
of magnitude as in downtown London. This study is particularly important
because it provides a list of at least 20 PAH compounds that are stable enough
to be transported from the source to humans where they will be inhaled. At
least four compounds (benzo[c]phenanthrene, benz[a]anthracene, benzo[a]pyrene,
and indeno[l ,2,3-cd]pyrene) which have well-resolved peaks are suspected
carcinogens.
Table 5-8 tabulates the various compounds for which monitoring concentra-
tions have been reported. As many as one hundred compounds have been found
3 23
in urban atmospheres, ' but they are not listed in Table 5-8 because quanti-
tative information could not be found.
Table 5-8 illustrates the vast number of POM that have been detected in
the atmosphere and there are probably many others that have not been quanti-
tated for lack of an appropriate analytical method. The accuracy of the
concentrations reported in Table 5-8 probably varies considerably, especially
for the lower molecular weight compounds which are likely to sustain substan-
tial losses by volatilization during collection on glass fiber filter in high
volume samplers.
5-24
-------
Table 5-7. CONCENTRATION OF POLYCYCLIC AROMATIC HYDROCARBONS
IN NORWAY AEROSOLS, ng/m3.26
Sample Number
Sampling period
PAH
Phenanthrene \
Anthracene /
Methyl -phenanthrene/-
anthracene
Fluoranthene
Di hydrobenzo[a&b]f 1 uor-
enes
Pyrene
Benzo[a]fluorene
Benzo[b]fluorene
1 -Methyl pyrene
Benzo[c]phenanthrene
Benz[a]anthracene
Chrysene/Triphenylene
Benzo[b&k]f 1 uoranthene
Benzo[e]pyrene
Benzo[a]pyrene
Perylene
Indeno[l ,2,3-cd]pyrene
Benzo[ghi]perylene
Anthanthrene
Coronene
1
Feb. 20-21
1976
England,
France
4.725
0.661
6.637
0.874
4.864
0.815
0.571
0.147
1.021
0.585
1.756
4.312
1.191
0.965
0.090
1.306
1.142
0.225
0.212
Total Identified PAH 32.099
2
Nov. 25-26
1975
Origin of
Northern Eng.
Scotland
1.216
0.278
0.216
3.965
0.363
3.293
0.318
0.149
0.099
0.957
0.740
3.269
4.013
2.635
2.053
0.191
1.920
1.971
0.423
0.183
28.252
3
Jan. 25-27
1976
air
Northern
Norway
0.036
0.038
--
0.171
0.032
0.135
0.021
0.117
0.009
0.038
0.041
0.099
0.083
0.066
0.059
trace
0.062
0.064
0.007
--
1.108
4
Feb. 1
1976
Stationary
air
Southern
Norway
0.146
0.052
0.324
0.032
0.286
0.026
0.148
0.009
0.108
0.073
0.194
0.464
0.135
0.098
0.011
0.144
0.140
0.022
0.020
2.435
5-25
-------
Table 5-8. POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
ro
CT>
Name Concentration,
ug/1000 m3
(unless other-
wise Indicated)
Naphthalene 0.052-.350
Anthracene >1.9
0.1-2.2
0.0-0.4
0.068-0.278
6.15
Benz[a]anthracene 0.4-21.6
0.1-16.0
^4
0.74-0.041
11-14
2
1.2-8.0
4.6
102
8.2
0.5-2.8
0.18
0.011 ug/g parti -
culate
0.022 yg/g parti -
1.1-3.1
0.1-13.1
Location Publication
Date
Providence area
Near industry handling
coal tar pitch
Winter - seven cities
monthly composite
Summer - seven cities
monthly composite
Norway - air from
N. England
Budapest
3 sites in Detroit
(20 samples)
4 sites in New York
(47 samples)
Average U.S. urban
atmosphere
Norway - air from
N. England
Average urban air-Detroit
Average suburban air -
Detroit
Rome
College Park, Md.
Baltimore Harbor Tunnel
Budapest
Los Angeles
Los Angeles
Summer - Toronto
Winter - Toronto
5 samples - Rome, Italy
14 samples - Rome, Italy
1977
1962
1962
1962
1977
1975
1965
1966
1965
1977
1965
1965
1975
1976
1976
1975
1971
1976
1975
1975
1966
1972
Reference
32
4
5
4
26
8
24
24
24
26
27
27
28
29
29
8
30
31
16
16
25
25
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
ro
Name
Di benz[a ,c]anthracene
Methyl phenanthrene/-anthracene
Phenanthrene
Benzo[c]phenanthrene
Benzo[a]fluorene
Benzo[b]fluorene
Di hydrobenzo[a&b]f 1 uorenes
Fluoranthene
Concentration,
yg/1000 m3
(unless other-
wise indicated)
4.5-0.029
0.216-0.661
>7.5
0.036-1.2
2.9-25
1.0
0.011-0.340
1.021-0.038
0.9
0.815-0.021
0.571-0.117
1.1
0.874-0.032
0.19-15.0
*4
6.6-0.17
Location
Providence area
Norway - air from
N. England
Near industry handling
coal tar pitch
Norway - air from
N. England
Rome
Budapest
Providence area
Norway - air from
N. England
Rome
Norway - air from
N. England
Norway - air from
N. England
Rome
Norway - air from
N. England
3 sites in Detroit
(6 samples)
Average U.S. urban
atmosphere
Norway - air from
N. England
Publication
Date
1977
1977
1962
1977
1975
1975
1977
1977
1975
1977
1977
1975
1977
1965
1963
1977
Reference
33
26
4
26
28
8
33
26
28
26
26
28
26
24
24
26
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
Name Concentration, Location Publication
yg/1000 m3 Date
(unless other-
wise indicated)
Fluoranthene (Cont'd) 3.1-11.0
4.1
93
1.04
0.31
1.5-0.16
0.3-10.6
0.6-41
0.06-2.6
V1 1.0-18.0
fv» ? 1_4 R
00 *" ' H- J
0.1-3.4
Benzo[b]fl uoranthene 2.3-7.4
0.54
0.1-1.6
Benzo[j]fl uoranthene 0.8-4.4
0.17
0.01-0.8
Benzo[k]fl uoranthene 1.1-15.7
1.7-20
0.2-4.9
0.2
0.12-0.96
Rome
College Park, Md.
Baltimore Harbor Tunnel
Budapest
Los Angeles
Providence area
20 sites - Ontario
(5 samples each location)
20 sites - Ontario
(1962 inversion period)
1 site - Sidney, Australia
(12 samples)
14 samples - Rome
5 samples - Rome
4 sites - Los Angeles
3 sites in Detroit
(6 samples)
Los Angeles
4 sites - Los Angeles
3 sites in Detroit
(6 samples)
Los Angeles
4 sites - Los Angeles
2 sites in Detroit
(6 samples)
7 cities, winter, monthly
composites
7 cities, summer, monthly
composites
Los Angeles
Toronto
1975
1976
1976
1975
1976
1977
1966
1966
1965
1972
1966
1973
1965
1976
1973
1965
1976
1973
1965
1962
1962
1976
1975
Reference
28
29
29
8
31
33
25
25
25
25
25
25
24
31
9
24
31
9
24
5
5
31
16
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
Name Concentration, Location
pg/1000 m3
(unless other-
wise Indicated)
Benzo[k]fluoranthene 1.3-14.0
(Cont'd) 0.03-1.3
20 sites in Ontario
4 sites in Los Angeles
(4 samples)
Publication
Date
1966
1973
Refarer.ce
25
9
Benzo[b&k]f1uoranthene
Benzo[ghi]fluoranthene
Pyrene
en
i
ro
1-Methylpyrene
4.312-0.083
0.9-9.1
1.3-19.3
Trace-35
10
4.86-0.135
2.2-6.8
5.2
120
2.06
0.45
0.18-3.8
0.08-4.0
0.4-12.0
0.4-17.0
2.4-5.1
0.147-.009
Norway - air from 1977
N. England
Rome 1975
3 sites in Detroit 1965
(6 samples)
12 U.S. cities 1962
Near industry handling 1962
coal tar pitch
Norway - air from 1977
N. England
Rome 1975
College Park, Md. 1976
Baltimore Harbor Tunnel 1976
Budapest 1975
Los Angeles 1976
4 sites in Los Angeles 1973
1 site in Sidney, Australia 1965
20 sites (5 samples at each 1966
site) in Ontario
14 samples - Rome 1972
5 samples - Rome 1966
Norway - air from
N. England
1977
22
28
24
24
4
26
28
29
29
8
31
9
25
25
25
25
26
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
en
CO
O
Name Concentration,
yg/1000 m3
(unless other-
wise indicated)
Benzo[a]pyrene 0.01-75
0.73
2.3-31
0.3-6.4
6
2.053-0.059
6-7
1
2-37
1.0-11.0
3.2
66
2.68
0.31-2.1
0.5-1.0
0.46
0.11-0.85
0.6-8.2
20-39
Benzo[e]pyrene 1-25
5.0
12-26
2.635-0.066
2-25
Location Pub
Urban and non-urban areas
Near industry handling
coal tar pitch
Winter, 7 cities, monthly
composite
Summer, 7 cities, monthly
compos i te
"Average" urban air
Norway - air from
N. England
Average urban air-Detroit
Average suburban air -
Detroit
4 cities in Europe
Rome
College Park, Md.
Baltimore Harbor Tunnel
Budapest
Los Angeles
London
Los Angeles
Toronto
1 site - Sidney, Australia
London street
12 U.S. cities (est. from
data)
Average U.S. urban
atmosphere
London street
Norway - air from
N. England
4 cities in Europe
lication
Date
1962
1962
1962
1962
1967
1977
1965
1965
1967
1975
1976
1976
1975
1971
1976
1976
1975
1965
1965
1962
1963
1965
1977
1967
Reference
4
4
5
5
23
26
27
27
32
28
29
29
8
30
20
31
16
25
25
24
24
24
26
32
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
in
Name Concentration,
pg/1000 nH
(unless other-
wise indicated)
Berizo[e]pyrene (Cont'd) 2.6-15.0
4.6
69
1.52
0.52-1.2
0.90
0.3-11
4.3-42
8
Dibenzo[cd,jk]pyrene 1.1
(anthanthrene) Trace - 3
0.26
2-6
0.11
0.423-0.007
0.1-1.3
0.23
1.8 ug/g parti-
Location Publication
Date
Rome
College Park, Md.
Baltimore Harbor Tunnel
Budapest
London
Los Angeles
20 sites - Ontario
(5 samples each location)
20 sites - Ontario
(during inversion)
Copenhagen (mean annual
value)
Detroit
12 U.S. cities (est. from
data)
Average U.S. urban
atmosphere
London street
Near industry handling
coal tar pitch
Norway - air from
N. England
Rome
Los Angeles
Summer - Toronto
1975
1976
1976
1975
1976
1976
1966
1966
1966
1965
1962
1965
1965
1962
1977
1975
1976
1975
Reference
28
29
29
8
20
31
25
25
25
24
24
24
24
4
26
28
31
16
Dibenzo[a,e]pyrene
culate
2.6 ug/g parti -
culate
100-730 yg/g
benzene soluble
fraction
Winter - Toronto
1975
Birmingham, Ala. composite 1968
16
34
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
OJ
PO
Name Concentration,
M9/1000 m3
(unless other-
wise Indicated)
Indeno[l ,2,3-cd]pyrene 1.5-8.2
1.9-0.062
3.8-12.8
1.34
0.03-1.2
Chrysene 1.3-11.6
Present
3.4-15.0
4.8
106
7.15
0.60
11.6 pg/g parti -
culate
17.5 ug/g parti -
culate
0.2-6.65
0.4-39.0
1.3-4.1
Perylene Trace - 5.0
0.7
0.15
0.191 - trace
Location Publication
Date
3 sites in Detroit
(6 samples)
Norway - air from
N. England
Rome
Los Angeles
4 sites - Los Angeles
3 sites in Detroit
(6 samples)
6 U.S. cities
Rome
College Park, Md.
Baltimore Harbor Tunnel
Budapest
Los Angeles
Summer - Toronto
Winter - Toronto
1 site - Sidney, Australia
(12 samples)
14 samples - Rome, Italy
5 samples - Rome, Italy
12 U.S. cities (est. from
data)
Average U.S. urban
atmosphere
Near industry handling
coal tar pitch
Norway - air from
1965
1977
1975
1976
1973
1965
1965
1975
1976
1976
1975
1976
1975
1975
1965
1972
1966
1962
1965
1962
1977
Reference
24
26
28
31
9
24
24
28
29
29
8
31
16
16
25
25
25
24
24
4
26
N. England
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
Name
Perylene (Cont'd)
Benzo[ghi]perylene
Concentration,
yg/1000 m3
(unless other-
wise Indicated)
0.2-1.9
1.1
0.10
0.034-0.306
0.3-0.6
0.01-1.2
2.3-11.5
2-35
Location
Rome
Budapest
Los Angeles
Toronto
4 samples - Rome
4 sites - Los Angeles
3 sites in Detroit
(6 samples)
12 U.S. cities (est.
Publication
Date
1975
1975
1976
1975
1966
1973
1965
from 1962
Reference
28
8
31
16
25
9
24
24
00
CO
8
12-46
0.55
20 yg/g parti-
culate
30 yg/g parti-
culate
1.971-0.064
3-26
3.5-21
3.9
85
0.86
0.7-3.2
3.27
1.0-31
1000
1
data)
Average U.S. urban 1965
atmosphere
London street 1965
Near industry handling 1962
coal tar pitch
Summer - Toronto 1975
Winter - Toronto 1975
Norway - air from 1977
N. England
4 cities in Europe 1967
Rome 1975
College Park, Md. 1976
Baltimore Harbor Tunnel 1976
Budapest 1975
London 1976
Los Angeles 1976
2 sites - London 1967
(1954-1964)
1 site - London 1967
(inversion - 1957)
24
24
4
16
16
26
32
28
29
29
8
20
31
25
25
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
CO
Name
Benzo[ghi]pery1ene (Cont'd)
Coronene
Acrid ine
Methyl acri dines
Concentration,
yg/1000 m3
(unless other-
wise indicated)
6.3-46
45
0.9-9.7
1.4-3.6
0.2-9.2
2.3-12.2
Trace - 8
2
4-20
0.05
0.212-0
1-6
4.4-18.3
1.05
0.3-1.9
2.13
12.3
8.2
3-48
0.2-6.4
0.7-1.0
0.040-0.041
ND - 0.007
Location Publication
Date
20 sites - Ontario
(inversion - 1962)
Liverpool, England mean
value
1 site - Sidney, Australia
4 samples - Rome
4 sites - Los Angeles
2 sites in Detroit
12 U.S. cities (est. from
data)
Average U.S. urban
atmosphere
London street
Near industry handling
coal tar pitch
Norway - air from
N. England
4 cities in Europe
Rome
Budapest
London
Los Angeles
Winter - Toronto
Summer - Toronto
20 sites - Ontario
4 sites - Los Angeles
4 samples - Rome
New York City air
New York City air
1966
1966
1965
1966
1973
1965
1962
1965
1965
1962
1977
1967
1975
1975
1976
1976
1975
1975
1966
1973
1966
1977
1977
Reference
25
25
25
25
9
24
24
24
24
4
26
32
28
8
20
31
16
16
25
9
25
22
22
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
in
i
10
en
Name
Benz[a]acridine
Benz[a]acridine
Benz[c]acridine
Dibenz[a,j]acridine
Dibenz[a,h]acridine
Carbazole
Quinoline
Methylquinoline
2,6-Dimethylquinoline
Di methyl qui no! ines
Ethyl quinolines
3C-quinolines
Concentration,
pg/1000 m3
(unless other-
wise indicated)
0.2
3-80 (ug/g benzene
soluble fraction)
1
0.6
1-30 ug/g BSF
0.1-1.5
0.04
0-8 yg/g BSF
0.1
0.08
1.9
1.1
0.022-0.069
0.6
0.033-0.035
0.3
0.044-0.088
0.014-0.022
ND-0.010
Location Publication
Date
Urban air
6 cities urban air
"Average" urban air
Urban air
Urban air 6 cities
50 samples from different
U.S. cities
Urban air
Urban air
"Average" urban air
Urban air
Near industry handling
coal tar pitch
Rome
New York City air
Rome
New York City air
Rome
New York City air
New York City air
New York City air
1977
1967
1965
1968
1965
1967
1965
1962
1973
1977
1973
1977
1973
1977
1977
1977
Reference
24
5
23
24
5
36
24
5
23
24
4
21
22
21
22
21
22
22
22
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
at
Name
Benzo[f]quinoline
Benzo[h]qu1no11ne
n-Indeno[l ,2b]quinoline
Phenanthridine
Isoquinoline
5 or 8 Methyl isoqu incline
Other Methyl isoqu inclines
Di methyl i soqu i nol i nes
Ethyl isoquinolines
3C-isoquinolines
Benzo[f ] i soqui nol i ne
4-Azafluorene
4-Azapyrene (other isomers)
Concentration,
pg/1000 m3
(unless other-
wise indicated)
0.2
0-200 (ug/g benzene
soluble fraction)
0.010-0.011
0.3
1-30 (Mg/g BSF)
0.010-0.013
0.1
4-30 (pg/g BSF)
Trace
0.018-0.022
0.140-0.180
0.170-0.310
0.070-0.076
ND-0.062
0.068-0.160
ND-0.028
0.034-0.110
0.005
0.021
13.1
Location
Urban air
Urban air (6 cities)
New York City air
Urban air
Urban air (6 cities)
New York City air
Urban air
Urban air (6 cities)
New York City air
New York City air
New York City air
New York City air
New York City air
New York City air
New York City air
New York City air
New York City air
New York City air
New York City air
Rome
Publication
Date
1965
1977
1965
1977
1965
1977
1977
1977
1977
1977
1977
1977
1977
1977
1977
1977
1973
Reference
24
5
22
24
5
22
24
5
22
22
22
22
22
22
22
22
22
22
22
21
-------
Table 5-8 (Cont'd). POLYCYCLIC ORGANIC MATTER IN AMBIENT AIR
GO
Name
1-Azafluoranthane
Benzo[c]cinnoline
2-Methylindole
Phenalen-1-one
7-H-benz[d ,e]anthracen-7-one
(benzanthrone)
Perinaphthanone
Concentration,
yg/1000 m3
(unless other-
wise indicated)
0.005 (other isomers
3.0
1.0
2.0
2
0.3-17
0-1.01
0.57-15.52
30.5 yg/g parti -
culate
39.1 gg/g parti -
culate
2-48
0.9-13
26.5 ug/g parti -
culate
15.9 yg/g parti -
Location Publication
Date
) New York City air
Rome
Rome
Rome
"Average" urban air
Urban site
Non-urban air
Urban air
Summer - Toronto
Winter - Toronto
Urban air
50 samples from different
U.S. cities
Summer - Toronto
Winter - Toronto
1977
1973
1973
1973
1967
1969
1969
1969
1975
1975
1969
1968
1975
1975
Reference
22
21
21
21
23
35
13
13
16
16
35
36
16
16
culate
-------
5.2 SUMMARY AND CONCLUSIONS
Numerous POM compounds have been detected in ambient air (Table 5-8) with
the most extensive data available on benzo[a]pyrene (BaP). The concentrations
of BaP are different in various cities and at different times of the year. In
general, the concentrations are usually highest during the winter months and
lowest during the summer (Figure 5-2) which has been attributed to heating
sources of BaP during the winter. The most comprehensive monitoring data on
BaP are available from the National Air Surveillance Network (NASN). BaP data
are available on the following stations during the indicated years: 1966 to
1970, 250 stations; 1971 to 1976, 40 stations. Trend analysis of the NASN
data indicates that BaP concentrations have declined considerably from an
3 3
annual median value for urban sites of 3.2 ng/m in 1966 to 0.5 ng/m in 1975,
an 84 percent decrease. The decline is believed to be due primarily to
decreases in coal consumption in residential dwellings and buildings as well
as to improved disposal of solid wastes and restrictions on open burning.
Concentrations of BaP in urban cities where coke ovens were located were
considerably higher (40 to 70 percent) than the non-coke sites. However, this
may be due to the fact that most of the coke ovens are located in the north
(BaP from heating) and in highly industrialized areas. Recent trends on other
POM compounds are not available.
The accuracy of the absolute values of BaP from the NASN data is unknown.
The collection efficiencies of glass fiber filters with high volume air
samples has not been determined and the importance of BaP associated with
particles less than 0.3 pm (could pass through the glass fiber filter) is
unknown. Oxidative loss of BaP during collection is another unknown and BaP
5-38
-------
degradation may occur between the time when the sample is collected and
extracted. In addition there is experimental evidence indicating that recov-
ery efficiencies are considerably different at summer versus winter tempera-
tures.
Trends for other POM have not necessarily followed the decrease for BaP;
for example, in London, the concentration of coronene has remained the same
while BaP was decreasing. This was attributed to the greater proportion of
coronene in auto emissions which are increasing in London.
Whether BaP can be used as an indicator of other POM compounds is not
fully established. Some investigators have found good correlations between
BaP and other PAH's while others have reported little or no relationship.
Correlations between BaP and other POM's probably vary in different areas and
are dependent upon the local POM emission sources which will provide different
ratios of individual POM's. Because the ratio of many of the individual POM's
changes in various locations, the use of BaP as an indicator of carcinogenic
potential should be reevaluated. A reasonable alternative would appear to be
some form of multi-component analysis that would include some of the other
carcinogenic or tumor promoting POM's.
A little information on the nitrogen heterocycles, aza and imino arenes,
is available. In general, these compounds are found at concentrations 10 to
100 times lower than the PAH, although a recent study in Rome found 1 to
10 ng/m of individual aza arene compounds. The monitoring trends of aza
arene concentrations are unknown. Whether they are increasing or decreasing
in concentration and whether there is a seasonal fluctuation is also
5-39
-------
undetermined. They have been detected near coal conversion plants, but their
major emission source is unknown.
A recent study in Norway has demonstrated that at least 20 PAH's associ-
ated with particulate matter are stable enough in the atmosphere to travel
long distances. Four of these compounds including BaP have been shown to have
carcinogenic activity.
In summary, the concentrations of at least 25 PAH and 32 aza arenes or
oxygen-substituted ROM's have been determined in ambient air, which suggests
that they are stable enough to come in contact with humans, animals, and
plants. The concentration of BaP has decreased significantly over the last 10
years (84 percent decrease), but data in the United States on whether other
POM compounds have followed this trend are unavailable. Data in other coun-
tries have indicated that POM compounds (e.g., coronene) which are found in
relatively large proportions in automotive emissions are remaining constant
while BaP levels are decreasing.
5-40
-------
REFERENCES
1. Bridbord, K., J. F. Finklea, J. K. Wagoner, 0. B. Moran, and P. Cap!an.
Human exposure to polynuclear aromatic hydrocarbons. In: Carcinogenesis,
Vol. 1. Polynuclear Aromatic Hydrocarbons: Chemistry, Metabolism, and
Carcinogenesis, edited by R. I. Freudenthal and P. W. Jones. New York,
Raven Press. 1976. p. 319-324.
2. Hoffman, D. Benzo[a]pyrene in polluted air. Prev. Med., 1:450-451, 1972.
3. Special Report: Trends in Concentrations of Benzene-soluble Suspended
Particulate Fraction and Benzo[a]pyrene. 1960-1972. U.S. Environmental
Protection Agency, Research Triangle Park, N. Carolina. Publication No.
EPA-450/2-74-022. 1974.
4. Sawicki, E. Analysis for airborne particulate hydrocarbons: Their
relative proportions as affected by different types of pollution. Nat.
Cancer Inst. Monograph No. 9. 1962. p. 201-220.
5. Scientific and Technical Assessment Report on Particulate Polycyclic
Organic Matter (PPOM). U.S. Environmental Protection Agency.
Washington, D.C. Publication No. EPA-600/6-75-001. 1975.
6. Manning, J. Environmental Protection Agency, Research Triangle Park, N.C.
Personal Communication.
7. Sawicki, E., T. R. Hauser, W. C. Elbert, F. T. Fox, and J. E. Meeker.
Polynuclear aromatic hydrocarbon composition of the atmosphere in some
large American cities. Am. Ind. Hyg. Asscc J. 23_(2):137-143. 1962.
8. Kertesz-Saringer, M., and Z. Mori in. On the occurrence of polycyclic
aromatic hydrocarbons in the urban area of Budapest. Atmos. Environ.
9_:831-834, 1975.
9. Gordon, R. J., and R. J. Bryan. Patterns in airborne polynuclear hydro-
carbon concentrations at four Los Angeles sites. Environ. Sci. Technol.,
7,: 1050-1053.
10. Faoro, R. B. Trends in concentrations of benzene soluble suspended parti-
culate fraction and benzo[a]pyrene. J. Air Pollut. Contr. Assoc., 25:638-
640, 1975. ~~
11. Faoro, R. B., and J. A. Manning. Trends in benzo[a]pyrene (1966-1975),
preprint.
12. Thomas, J. F., M. Mukai, and B. D. Tebbens. Fate of airborne benzo[a]-
pyrene. Environ. Sci. Technol., 1(1):33-39, 1968.
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13. National Academy of Sciences, Committee on Biological Effects of Atmos-
pheric Pollutants. Participate Polycyclic Organic Matter. Washington,
D.C., 1972, pp. 361.
14. Natusch, D. F. S., and B. A. Totnkins. Theoretical consideration of the
adsorption of polynuclear aromatic hydrocarbon vapor onto fly ash in a
coal-fired power plant. In: Carcinogenesis, Vol. 3: Polynuclear Aromatic
Hydrocarbons. P. W. Jones and R. I. Freudenthal (eds.), Raven Press,
New York, 1978, pp. 145-153.
15. Katz, M., and R. C. Pierce. Quantitative distribution of polynuclear
aromatic hydrocarbons in relation to particle size of urban particulates.
In: Carcinogenesis, Vol. 1, Polynuclear Aromatic Hydrocarbons: Chemistry,
Metabolism, and Carcinogenesis, R. I. Freudenthal and P. W. Jones (eds.).
New York, Raven Press. 1976.
16. Pierce, R. C., and M. Katz. Dependency of polynuclear aromatic hydrocarbon
content on size distribution of atmospheric aerosols. Environ. Sci. Technol.,
9_(4):347-353, 1975.
17. DeWiest, F., and D. Rondia. On the validity of determinations of benzo[a]
pyrene in airborne particles in the summer months. Atmos. Environ., 6:
487-489, 1976.
18. Commins, B. T. Interim report on the study of techniques for determination
of polycyclic aromatic hydrocarbons in air. Natl. Cancer Inst. Monograph
No. 9, 225-233, 1962.
19. Lane, D. A., and M. Katz. The photomodification of benzo[a]pyrene, benzo[b]-
fluoranthene, and benzo[k]fluoranthene under simulated atmospheric conditions.
In: Fate of Pollutants in the Air and Water Environments Part 2.
I. A. Suffet (ed.), New York, Wiley-Interscience. 1977.
20. Leahey, D. M. Changing pattern in concentrations of polycyclic aromatic
hydrocarbons in the air of central London. Atmos. Environ., 10:561-562,
1976. ~~
21. Brocco, D., A. Cimmino, and M. Possanzini. Determination of aza-hetero-
cyclic compounds in atmospheric dust by a combination of thin-layer and
gas chromatography. J. Chromat., 84:371-377, 1973.
22. Dong, M. W., D. C. Locke, and D. Hoffmann. Characterization of aza-arenes
in basic organic portion of suspended particulate matter. Environ. Sci.
Technol., jj_:612-618, 1977.
23. Sawicki, E. Airborne carcinogens and allied compounds. Arch Environ.
Health, 14:46-53, 1967.
5-42
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24. Hoffman, D., and E. L. Wynder. Chemical analysis and carcinogenic bio-
assays of organic participate pollutants. l]n: Air Pollution, Vol. II,
2nd Ed. A. C. Stern (ed.), Academic Press, New York, 1968, pp. 187-247.
25. Hoffman, D., and E. L. Wynder. Organic particulate pollutants - chemical
analysis and bioassays for carcinogenicity. In: Air Pollution, Vol. II,
3rd Ed., A. C. Stern (ed.), Academic Press, New York, 1977, op. 361-455.
26. Lunde, G., and A. Bjprseth. Polycyclic aromatic hydrocarbons in long-range
transported aerosols. Nature, 268_:518-519, 1977.
27. Colucci, J. M., and C. R. Begeman. The automotive contribution to airborne
polynuclear aromatic hydrocarbons in Detroit. J. Air Pollut. Control Assoc.
15:113-122, 1965.
28. Liberti, A., G. Morozzi, and L. Zoccolillo. Comparative determination of
polynuclear hydrocarbons in atmospheric dust by gas liquid chromatography
and spectrophotometry. Annali di Chimica, 615:573-580, 1975.
29. Fox, M. A., and S. W. Staley. Determination of polycyclic aromatic hydro-
carbons in atmospheric particulate matter by high pressure liquid chroma-
tography coupled with fluorescence techniques. Analytical Chem., 48:
992-998, 1976. ~~
30. Colucci, J. M., and C. R. Begeman. Polynuclear aromatic hydrocarbons and
other pollutants in Los Angeles air. In: Proceedings of the International
Clean Air Congress, Vol. 2. Academic Press: New York, U.S.A.; London,
England. 1971. pp. 28-35.
31. Gordon, R. J. Distribution of airborne polycyclic aromatic hydrocarbons
throughout Los Angeles. Environ. Sci. Technol., Kh370-373, 1976.
32. Waller, R. E., and B. T. Commins. Studies of the smoke and polycyclic
aromatic hydrocarbon content of the air in large urban areas. Environ.
Res., 1:295-306, 1967.
33. Krstulovic, A. M., D. M. Rosie, and P. R. Brown. Distribution of some
atmospheric polynuclear aromatic hydrocarbons. Amer. Lab. (July 1977),
11-18, 1977.
34. Bender, D. F. Thin-layer chromatographic separation and spectrophoto-
fluorometric identification and estimation of dibenzo[a,e]pyrene. Environ.
Sci. Technol., 2:204-206, 1968.
35. Stanley, T. W., M. T. Morgan, and J. E. Meeker. Rapid estimation of
7-H-benz[de]anthracen-7-one and phenalen-1-one in organic extracts of
airborne particulates from 3-hour sequential air samples. Environ. Sci.
Technol., 3:1198-1200, 1969.
5-43
-------
36. Stanley, T. W., M. J. Morgan, and E. M. Grisby. Application of a rapid
thin-layer chromatographic procedure to the determination of benzo[a]-
pyrene, benz[c]acridines, and 7H-benz[de]anthracen-7-one in airborne
participates from many American cities. Environ. Sci. Technol., 2:
699-702, 1968.
5-44
-------
DRAFT
DO NOT QUOTE OR CITE
6. HEALTH AND ECOLOGICAL EFFECTS
6.1 ABSORPTION, DISTRIBUTION, AND EXCRETION
Early studies conducted on the intestinal absorption of BaP confirmed
that transfer across the gut readily occurs and, moreover, that tissue
accumulation is exponential as BaP concentrations increase. These results
are consistent with a mechanism involving physical adsorption of BaP to the
intestinal mucosa as a first step. A unilayer is presumably formed at
saturation concentrations and a multilayer at higher BaP levels. Increases
in the medium concentration of BaP above the saturation level would thereby
permit an exponential transport into the cells by passive diffusion. The
authors indicated further that the intestinal transport of MCA, DMBA,
chrysene, and benz[a]anthracene was similar to BaP. Assuming that the
ability of various organs to absorb BaP (and other POM) also follows an
exponential relationship, relatively small differences in the magnitude of
environmental exposures could be expected to exert a dramatic influence on
the body burden of POM. Such a relationship has been demonstrated for the
accumulation of BaP in adipose tissue.
The absorption of POM through the lungs has particular relevance to
environmental exposure situations. However, the major health-related
effects of inhalation exposure involve local lesions in the respiratory
6-1
-------
tract and, unfortunately few investigators bother to measure systemic
levels of POM. Nevertheless, it is known that BaP when administered intra-
tracheally to rats appears in the tissues with the same pattern of distribu-
2 3
tion as when given parenterally. Vainio and coworkers recently showed
that unchanged BaP quickly appears in the perfusion fluid of isolated
perfused rat lungs following intratracheal administration of a 200 nmole
dose. Pretreatment of rats with an intraperitoneal injection of MCA to
induce microsomal enzyme activity caused an increase in the amount of
water-soluble metabolites of BaP appearing in the perfusate. An increased
covalent binding of BaP metabolites to the lung tissue also accompanied the
MCA-mediated induction of microsomal monooxygenases. The significance of
tissue-binding of POM metabolites is discussed in Section 6.2.2 of this
report.
Because POM generally reaches the lung under environmental conditions
by adsorption on carrier particles, the extent of particle deposition in the
lungs and the elution of the chemical from the particle have an important
4
bearing on its biological effect. In this regard, Creasia and coworkers
showed that when BaP is adsorbed to large carbon particles (15-30 ym) and
instilled into the lungs, 50 percent of both the BaP and the carrier parti-
cles were cleared from the lungs in four to five days. Little carcinogen
was released from the carbon particles in this case, and therefore contact
with the respiratory epithelium (and careinogenicity) was low. With smaller
carbon particles (0.5-1.0 ym), however, 50 percent particle clearance was
not achieved until seven days after administration. In this case, 15 percent
6-2
-------
of the adsorbed BaP was eluted from the particles and left free to react
with the respiratory tissues. In the complete absence of carrier parti-
cles, BaP was cleared from the lung at 20 times the rate of adsorbed BaP.
This observation may explain the difficulty in producing experimental
pulmonary tumors with BaP without the use of carrier particles. Other
investigators confirmed that carbon particle size affects BaP retention in
the lung, but also demonstrated that BaP retention was not affected by
particle size when adsorbed on ferric oxide or aluminum oxide.
Regardless of its route of administration, POM, once absorbed, becomes
localized in a wide variety of body tissues. The distribution of radio-
14
activity derived from C-BaP in the rat and mouse was determined following
2
subcutaneous, intravenous, and intratracheal administration. The pattern
of distribution was found to be similar in all cases, except for high local
pulmonary concentrations following intratracheal administration (Tables 6-1
and 6-2). Concentrations of BaP-derived radioactivity in the liver reached
a maximum within only 10 minutes after injection and represented 12 percent
of the total dose. Radioactivity in the liver was reduced to one to three
percent of the administered dose within 24 hours. Similarly, maximum blood
levels of BaP following intravenous injection were reached very quickly,
and radioactivity became barely detectable after 10 minutes. Minimal
tissue localization of BaP and/or its metabolites occurred in the spleen,
kidney, lung, and stomach; maximum radioactivity derived from labeled BaP
was recovered in the bile and feces. Levels of radioactivity in fat, skin,
and muscle were not determined, nor was the amount of unchanged BaP measured
6-3
-------
Table 6-1. DISTRIBUTION AND RATE OF ELIMINATION OF RADIOACTIVITY AFTER INTRAVENOUS INJECTION OF
14C-BENZO[a]PYRENE INTO RATS3 2
Time after injection of aqueous
suspension, hr.
Time after injection of human
plasma solution, hr.
Site
Feces
Stomach
Intestine
Liver
Urine
Kidney
Lung
Spleen
Other organs (testes and myocardium)
Percent recovered
4
0.35
0.69
23.5
3.9
4.3
1.05
0.5
1.0
0.8
36.09
24
% of injected
8.2
3.7
43.8
1.3
12.9
0.9
0.27
0.06
0.07
71.20
4
dose
2.8
0.5
47.0
4.2
4.5
1.9
0.3
0.68
0.74
62.62
10
37.4
0.31
25.5
2.5
8.3
0.99
0.69
0.15
0.16
76.00
a Dose: 30 wg C-benzo[a]pyrene in 0.9 ml vehicle
-------
Table 6-2. DISTRIBUTION AND RATE OF ELIMINATION OF RADIOACTIVITY AFTER INTRATRACHEAL INSTILLATION
OF 14C-BENZO[a]PYRENE INTO RATS3 2
I
01
Time after instillation of Time after instillation of
aqueous suspension, hr. triethylene glycol solution, hr.
1 24
Site % of administered dose
Feces
Stomach
Intestine
Liver
Urine
Kidney
Lung
Spl een
Other organs (testes and myocardium)
Percent recovered
0
0
37.0
1.3
0
0
43.2
0
0.08
81.58
28.0
0
11.1
4.3
1.2
2.4
38.6
0
0.43
86.03
17.2
0
44.2
5.8
8.8
2.6
17.7
0
0.29
96.59
Dose: 25 pg C-benzo[a]pyrene in 0.3 ml vehicle.
-------
in any tissue. Bock and Dao later showed that relative to other tissues,
unmetabolized BaP was extensively localized in the mammary gland and general
body fat after a single feeding of the carcinogen (10-30 mg). This accumula-
tion of BaP was greater than that resulting from 3-methylcholanthrene
(MCA), 7,12-dimethylbenz[a]anthracene (DMBA), or phenanthrene administra-
tion (Table 6-3). In all cases, the level of carcinogen achieved in the
tissue was directly related to the dose administered, and was dependent
upon the use of a lipid vehicle. The authors suggested that the mammary
fat pad may act as a carcinogen trap, which slowly releases the unchanged
hydrocarbon to the glandular cells. In the rat, the glandular tissue is
the main site for POM-induced breast cancer.
A more complete study on the tissue distribution of MCA was reported
in 1959 by Dao and coworkers after it was shown that oral administration
of MCA produces mammary cancers. A quantitative analysis of MCA in rat
tissues 24 hours after its oral administration demonstrated that the hydro-
carbon was mainly localized in the fatty and breast tissues (Table 6-4).
In virgin animals, levels of MCA were higher in fat than in breast tissues,
whereas in lactating rats this relationship was reversed. Moreover, sig-
nificant amounts of MCA appeared in the milk at 24 hours after administra-
Q
tion (Table 6-5). On the other hand, West and Horton reported that the
transfer of ingested BaP and MCA to the milk of rabbits and sheep was far
less than that in rats; a phenomenon which is probably common to all ruminants.
Detailed studies concerning the tissue distribution of tritiated DMBA
g
produced similar results as for MCA. Twenty-four hours after receiving a
6-6
-------
Table 6-3. EFFECT OF MOLECULAR STRUCTURE ON HYDROCARBON LOCALIZATION IN MAMMARY
GLAND AND FAT* 6
Hydrocarbon concentration,
ug/gm +_ S.E.b
Hydrocarbon
3-Methyl chol anthrene
Benzo[a]pyrene
7 , 1 2-Dimethyl benz[a]anthracene
Phenanthrene
I1UIIIL/CI
of rats
30
10
10
5
Mammary fat
18.0 + 1.6
29.1 + 4.0
23.4 + 1.7
1.8 + 0.1
Fat
39.2 + 3.9
55.9 + 5.3
39.3 + 4.4
2.8 + 0.3
Levels of hydrocarbon were determined 24 hours after a single intragastric
feeding of 30 mg test compound in 1 ml of sesame oil. Quantitative assays
were conducted by fluorescence measurements of the crude benzene extract
of tissue containing hydrocarbon.
+ Standard deviations.
6-7
-------
Table 6-4. LEVELS OF ORALLY ADMINISTERED 3-METHYLCHOLANTHRENE IN TISSUES OF
50-DAY-OLD VIRGIN FEMALE RATS?
Level of 3-methylcholanthrene,
Tissue ug/g tissue^
Breast, rat 1 15
Fat, rat 1 70
Breast, rat 2 12
Fat, rat 2 17
Breast, rat 3 24
Fat, rat 3 38
Brain, pooled 3.5
Lung, pooled 2.1
Kidney, pooled 1.1
Thymus, pooled 1.4
Liver, pooled 0.3
Muscle, pooled 0.04
Heart, pooled NFC
Spleen, pooled NF
Uterus, pooled NF
Ovaries, pooled • NF
Adrenals, pooled NF
Pituitaries, pooled NF
a MCA was given as a single 30 mg dose in 1 ml of sesame oil. Animals were
sacrificed 24 hours later and levels of MCA in crude benzene extracts of
tissue determined by fluorescence.
Total content of 3-methylcholanthrene was less than 0.1 yg in pooled
tissues of 3 rats.
c Not found.
6-8
-------
vo
Table 6-5. LEVELS OF ORALLY ADMINISTERED 3-METHYLCHOLANTHRENE IN BREAST AND FAT OF VIRGIN RATS
AND IN MILK, BREAST, AND FAT OF LACTATING RATS* 7
Rat No.
Virgin rats 50 days old 1
2
Lactating rat
(7 days postpartum) 1
Tissues
Breast
Fat
Breast
Fat
Breast
Fat
Milk (fetus 1)
(fetus 2)
Weight,
9
2.6
0.9
2.1
0.9
11.5
1.7
3-Methylcholanthrene,
pg/g tissueb
6.5
7.1
6.4
10.9
17
11
23
13
One single feeding of 3-methylcholanthrene of 10 mg in 1 ml of sesame oil was given and animals
were sacrificed 24 hours later.
Crude benzene extracts of tissue were analyzed in a spectrophotofluorometer using either 295 my
or 355 my excitation light.
-------
single oral dose of 30 mg H-DMBA at two levels of radioactivity (26 pCi
and 2600 yCi), the greatest amount of activity recovered from rat tissues
was in the peri renal fat. Moderate levels of radioactivity were also
detected in kidney, liver, and mammary tissue. Radioactivity in the fat
and mammary gland persisted for at least 3 days and represented predominant-
ly unmetabolized DMBA. In contrast, most of the radioactivity localized in
the liver was due to the presence of polar DMBA metabolites, some of which
were bound to nucleic acids and cellular proteins.
3
The tissue distribtuion of H-dibenzo[g,c]carbazole (DBcgC) following
intratracheal instillation was qualitatively and quantitatively similar to
BaP. Except for high local concentrations of DBcgC in the lungs, the
greatest amount of radioactivity was localized in the intestines of treated
hamsters (Table 6-6).
Transplacental passage of POM is a critical factor in determining the
risk for transplacental toxicity and carcinogenesis resulting from maternal
exposures. The ability of BaP, DMBA, and MCA to cross the placenta in rats
was investigated following a single intragastric dose of 200 mg/kg of the
hydrocarbon as a suspension in sunflower oil. With DMBA, the concentra-
tion of the carcinogen in fetal tissues reached a maximum (1.53 to 1.6 ug/g)
2 to 3 hours after maternal administration. At 2 hours, the ratio of DMBA
concentrations in maternal liver, placenta, and fetuses was 10:1.5:1.
Passage of BaP into the fetus was even greater than for DMBA. MCA, on the
other hand, crossed the placenta in only trace amounts. These data are
summarized and compared in Table 6-7. Intravenous injection of a 25 mg/kg
6-10
-------
Table 6-6. DISTRIBUTION AND ELIMINATION OF RADIOACTIVITY AFTER INSTALLATION
OF 3H-DIBENZO[c,g]CARBAZOLE IN SYRIAN HAMSTERSa 10
Percent instilled dose recoverd at:
Site
Trachea
Lungs
Liver
Kidneys
Brain
Intestines (large and small)
Fat
Urine
Feces
Total % recovered
11
63
1.4
0.0
0.0
11
0.0
0.0
0.0
86.4
1 hr.
+ 1.2
+ 2.2
+ 0
+ 1.4
+ 5.44
3 hr.
4.0 + 0.35
32 + 4.1
4.6 + 0.40
2.0 + 0.36
0.7 + 0.06
31 + 2.6
0.6 + 0.15
0.6 + 0.07
8.2 +0.12
83.7 +4.65
6 hr.
3.0 + 0.34
18 + 2.6
4.3 + 0.15
1.8 + 0.11
0.7 + 0.01
35 + 5.8
0.6 + 0.04
3.2 + 0.13
15.6 + 1.45
82.2 +4.23
a Animals were treated once with 3 mg H-dibenzo[c,g]carbazole suspended with
FeO- particles in 0.2 ml saline.
6-11
-------
Table 6-7. CONCENTRATION (yg/g) OF DMBA, BaP, AND MCA IN TISSUES OF 21-DAY FETUSES, THEIR PLACENTAS,
AND THE LIVER OF PREGNANT RATS 3 HOURS AFTER ADMINISTRATION OF THE COMPOUNDS IN A DOSE
OF 200 mg/kg BY GASTRIC
Carcinogen
administered
Fetuses
Placentas
Liver
Mean and limits
of variations
Number of
analyses
Mean and limits
of variations
Number of
analyses
Mean and limits
of variations
Number of
analyses
I
tv>
DMBA 1.53 (0.63-3.50) 4
BaP 2.77 (1.67-5.00) 5
MCA 0.0013 (traces-0.002) 6
1.28 (0.86-1.60) 4
3.94 (2.24-6.15) 5
0.009 (traces-0.03) 6
8.80 (5.50-11.80) 4
23.50 (11.10-50.20) 4
0.10 (0.03-0.22) 6
-------
dose of DMBA produced similar fetal tissue levels as the intragastric
administration of 200 mg/kg DMBA.
As long ago as 1936, it was recognized that various polycyclic aromatic
hydrocarbons were primarily excreted through the hepatobiliary system and
12 13
the feces. ' With the advent of radiotracer methodologies, it became
14 2
possible to study more quantitatively the elimination of POM. ' Patterns
14
of C-BaP excretion were determined in both intact rats and in rats with
2
biliary fistulas. When BaP was given intratracheally, or by subcutaneous
and intravenous injection, maximum excretion of radioactivity always occurred
through the feces (Tables 6-1 and 6-2). In addition, the bile contained
significant amounts of radioactivity, which was enhanced by increasing the
administered dose of BaP until a saturation level was reached at 150 wg BaP
(intravenous dose). Radioactivity was detectable in the bile for 24 hours
following treatment, and a total of 1 percent of the administered BaP was
recovered unchanged. The total recovery of radioactivity in BaP-treated
rats having biliary fistulas is shown in Table 6-8. The importance of
enterohepatic circulation in the excretion of BaP was indicated by the fact
that urinary excretion of radioactivity was reduced from 7 to 14 percent of
the total dose in intact rats to 3 to 4 percent of the total dose in rats
with biliary fistulas.
The influence of route of administration on the rate of POM elimination
is likely to be an important determinant in quantitative studies. Following
the intragastric administration of MCA to rats, 82% of the dose is excreted
in the feces within 24 hours. However, when injected intraperitoneally,
6-13
-------
Table 6-8. DISTRIBUTION OF RADIOACTIVITY IN RATS WITH BILIARY FISTULAS AFTER INTRAVENOUS INJECTION
of 14C-BNEZO[a]PYRENE IN PLASMA SOLUTION2
CT>
1
-£»
Dose,
ug
19
26
45
134
400
Bile flow rate,
ul /minute
7.2
18.9
18.0
12.6
15.3
Duration of
experiment,
hours
4
12
12
14
24
Recovery in bile,
% of injected dose
1 hr.
17
21
27
26
4
2 hr.
9
19
18
30
3
3 hr.
9
9
7
13
3
Total
39
78
75
96
32
-------
only 30 percent of the dose appeared in the feces after 3 days. Assuming
that MCA is readily absorbed through the gastrointestinal tract (a valid
assumption based on the data of Rees and coworkers ), it was apparent that
rapid absorption and metabolism accounted for the lack of appreciable MCA
retention. It may thus be postulated that liver "first-pass" metabolism as
well as biotransformation by enzymes of the intestinal mucosa represent an
effective means of handling ingested ROM's. On the other hand, ROM's
reaching the circulation by absorption through the lungs or skin will not
make an initial passage through the liver and thus are more likely to reach
internal target organs in the parent form. Since environmental exposures
are most likely to occur by inhalation, it cannot be assumed that excretion
of ROM's will be sufficiently rapid to prevent their accumulation in various
tissues.
When administered by subcutaneous injection or by application to the
skin of female mice, BaP, MCA, and DBahA are eliminated almost entirely by
14
the feces. However, the rate of disappearance from the site of applica-
tion or injection varies considerably in the decreasing order BaP>MCA>DBahA.
In particular, the elimination of DBahA when applied to the skin is extremely
slow, and none of the compound or its metabolites are found in the feces.
Poor dermal absorption of DBahA probably accounts for this observation
since binding of metabolites to skin proteins was not extensive, nor is
DBahA known as a potent skin carcinogen.
The rate of disappearance of BaP from the various tissues can be
altered by prior treatment with any one of several POM. Schlede and
6-15
-------
20
coworkers reported that inducers of microsomal enzymes (BaP, pheno-
barbital) can enhance the rate of biliary excretion of metabolites of BaP.
In addition, pretreatment of rats with BaP, DMBA, or MCA stimulated the
rate of disappearance of an intravenous dose of BaP, and decreased the
21
concentration of BaP in various tissues (lung, fat, adrenals). Taken
together, these results indicated that BaP can stimulate its own metabolism.
Furthermore, in the pregnant rat, pretreatment with BaP, MCA, chrysene,
benz[a]anthracene, or DBahA had a marked stimulatory effect on the in vitro
metabolism of a subsequent dose of BaP in maternal liver, placenta, and
fetal liver.22
Elimination of BaP from the lung is generally regarded to be influenced
by the presence of carrier particles to which the hydrocarbon is adsorbed.
Most investigators have found that BaP retention by the lung is increased
when administered with particulate material. ' However, recent studies
have also indicated that intratracheal instillation of BaP to hamsters in
combination with ferric oxide did not increase carcinogen retention over
that obtained with BaP alone. Moreover, it is now known that carrier
particles are not an absolute requirement for the induction of respiratory
18
tract tumors by BaP. Rather than affecting retention, it was suggested
that carrier particles determine tissue localization and thereby tumor
development. A crucial factor in determining adequate lung retention of
carcinogens for tumor development is the concommitant exposure to agents
23
which inhibit ciliary activity. The tracheobronchial epithelium is
normally protected by a mucous blanket and ciliated cells. These cells
6-16
-------
propel foreign materials captured in the mucous flow upward and out of the
respiratory tract to be swallowed and excreted. It has been known for many
years that Irritants (e.g., S02» polluted air, cigarette smoke) can Inhibit
ciliary activity, thus increasing the time available for elution of ROM's
from soot particles in the lungs. This process can be expected to markedly
influence the response to carcinogenic POM.
On the other hand, it should not be assumed that particles cleared
from the lungs by ciliary activity are necessarily removed from the body.
These particles are usually swallowed and thus present the opportunity for
POM absorption via the gastrointestinal tract; a process which is known to
result in tumor formation (see Section 6.5).
A thorough examination has been conducted on the clearance of intratra-
2
cheally instilled H-BaP (5 mg total dose) from various tissues of the ham-
19
ster. The effect of the presence of adsorbents (asbestos, carbon black)
was also studied. Elimination of radioactivity from the lung was found to
be biphasic; an initial rapid phase lasted about 2 weeks and was not signifi-
cantly influenced by the presence of adsorbents (Figure 6-1). During this
phase, 99 percent of the administered dose was eliminated from the respira-
tory tract. In the second (slow) phase of elimination, a significant
retention of radioactivity became evident only among animals given H-BaP
together with an adsorbent. This accumulation of H-BaP-derived radio-
activity in the lung, although small, was considered toxicologically signifi-
cant. The levels of radioactivity in other organs and in blood, urine, and
feces were not apparently influenced by co-administered adsorbents, but did
6-17
-------
3
I
100
•O
£
a
I
g 10
•a
1
a
S?
V)
n
"S
a
x
OJ
C>
c
_3
.£ 0.1
o
(B
O
1
cc
0.01
[3 H] 3.4- Benzopyrene alone
[3H] 3,4— Benzopyrene + abestos
9 ^ [3H] 3,4— Benzopyrene + carbon black
I
_L
14 21
Time in days from single mtratracheal injection
28
35
Figure 6-1. Clearance of radioactivity derived from
o 17
[ H]3,4-benzopyrene in the lung.
6-18
-------
appear to follow a biphasic pattern of elimination (Figures 6-2 - 6-6).
However, blood and fecal levels of radioactivity dropped off more rapidly
o
in those animals given H-BaP with carbon black. These results (and those
of numerous similar studies) are presented with the assumption that the
pattern of distribution and elimination of the tritium label is an accurate
reflection of the BaP molecule and/or its metabolites. In most cases, no
attempt is made to identify metabolites or determine the extent of tritium
loss into body water or of bioexchange of the label.
Excretion of intratracheal doses of DBcgC in hamsters proceeds in much
the same way as for BaP. The principal route of excretion is via the
feces. Retention of DBcgC by the respiratory tissues was dependent on the
administration vehicle (saline or water suspension), but in all cases was
less than for BaP. Only 6 percent of an intratracheal dose of DBcgC in
saline remained in the lung after 18 hours, whereas with BaP, 25 percent of
the administered compound was still present after 18 hours.
6-19
-------
100
[3 H ] 3,4- Benzopyrene alone
[3H] 3,4- Benzopy rene + asbestos
[3H] 3,4— Benzopy rene + carbon black
6 14 21
Time in days form single intratracheal injection
Figure 6-2. Clearance of radioactivity derived from
3 17
[ H]3,4-benzopyrene in liver.
6-20
-------
100 r-
10
0.01
• • [3H] 3,4-Benzopyrene alone
o—o [3H] 3,4- Benzopyrene + abestos
•---• [3H] 3,4- Benzopyrene + carbon black
I
I
3 7 14
Time in days from single intratracheal injection
36
Figure 6-3. Excretion of radioactivity derived from
[ H]3,4-benzopyrene in feces.
6-21
-------
10
Q.
2
•o
CO
CC
0.1
0.01
[3H] 3,4- Benzopyrene alone
[3H] 3,4-Benzopyrene + asbestos
•—•• [3H] 3,4- Benzopyrene + carbon black
I
7 13
Time in days from single intratracheal injection
36
Figure 6-4. Excretion of radioactivity derived from
3 17
[ H]3,4-benzopyrene in urine.
6-22
-------
10
0.1
0.01 J
•——• [3 H] 3.4 - Benzopyrene alone
o—o [3H] 3,4- Benzopyrene + abestos
•— -• [3 H] 3,4- Benzopyrene + carbon black
I
I
7 14 21 28
Time in days from single intratracheal injection
35
Figure 6-5. Clearance of radioactivity derived from
[ H]3,4-benzopyrene in kidneys.
6-23
-------
10 r
• • 13 H ] 3,4- Benzopyrene alone
o—o [3 H ] 3,4- Benzopyrene + abestos
*—• [3 H] 3,4- Benzopyrene + carbon black
0.1
0.01
7 14 21
Time in days from single intratracheal injection
28
Figure 6-6. Blood level of radioactivity derived from
[ H]3,4-benzopyrene.
6-24
-------
6.2 METABOLISM AND ACTIVATION TO REACTIVE ELECTROPHILES
6.2.1 Carcinogenic Polycyclic Hydrocarbons
That carcinogenic chemicals are human hazards became apparent with the
advent of the industrial revolution. During the last century, the logarithmic
growth of chemical technology has resulted in the development of vast amounts
of synthetic compounds for industry, agriculture, and medical and consumer
products, such as cosmetics, food preservatives, and colorants. Most of these
compounds are not natural to the environment and some are toxic by virtue of
their chemical structure. However, others have low reactivity when released
into the air, water, or soil, but when taken into the organism are activated
by the biochemical pathways of the body to form detoxified and carcinogenic
species of the parent molecule.
Several major types of carcinogenic molecules have evolved as prototype
structures for the study of chemical carcinogenesis, such as aromatic amines,
nitrosamines, aflatoxins, and polycyclic hydrocarbons. Large numbers of
derivatives of these basic structures have been synthesized and tested for
carcinogenic activity in many animals in addition to mammals, including
birds, amphibians, reptiles, and fish. Research into the biochemical mecha-
nisms of action of chemical carcinogens is fairly recent and is primarily the
result of innovative methods of organic synthesis, several new sensitive
bioa'ssays, and new analytical techniques for accurate analysis of highly
reactive transient intermediates formed during the metabolic processing of the
carcinogen (see Section 6.5). At present, no complete mechanism of action is
known for any carcinogenic molecule nor is the target site definitely under-
stood, although the current literature suggests nuclear macromolecules as the
6-25
-------
most probable targets (see Section 6.2.2). However, the divergent molecular
structure of chemical carcinogens and the wide variation in tissue and species
susceptibility have only recently enabled investigators to begin comparing
structurally different chemical carcinogens with regard to their relative
carcinogenic potency, target tissues, and species specificity. The ultimate
aim will be to draw this large body of data into formulation of a mechanism
describing the cause of cancer by chemicals.
Early attempts to explain the careinogenicity of'polycyclic hydrocarbons
24
utilized physico-chemical calculations. These early hypotheses were based on
the assumption that those regions of the molecule most likely to react in
chemical substitution or addition reactions would be most likely to react with
cellular target sites, causing an irreversible disruption of cell homeostasis.
This concept has not been successful for polycyclic hydrocarbons.
It is generally accepted that the ultimate forms of carcinogens are
electron deficient (see Section 6.5). Alkylation of critical sites by these
electrophiles represents the basis of tumor initiation. The significance of
potentiation of the transformation by tumor promoters such as phorbol esters
or environmental modifiers such as catechol is particularly relevant to man.
Since POM contains a mixture of chemical components and human exposures are
almost always in conjunction with several components in air pollution, sub-
threshold doses could be potentiated by other environmental factors.
In animal models the initiation-promotion concept has been widely studied
(see Section 6.5). In general, a low dose of a carcinogenic POM is applied
once as a tumor initiator to an epithelial tissue. This dose alone does not
6-26
-------
induce tumors; however, when the tissue is subsequently treated with a non-
carcinogenic tumor promoter, such as the phorbol ester, tumors will appear in
20 to 40 weeks. The concurrent application of very low doses of carcinogenic
POM with a cocarcinogen such as catechol or pyrene will also induce tumors in
epithelial tissues.
Since human exposure to carcinogenic chemicals is, in most cases, a
continuous assault of very low doses (e.g., cigarette smoke, auto exhaust,
etc.), other noncarcinogenic vectors in our environment probably enhance the
effect of the relatively low doses of initiating carcinogen.
6.2.1.1 Historical perspectives—The human population is being exposed to
polycyclic aromatic hydrocarbon (PAH) carcinogens at an increasing rate as a
consequence of industrial growth. Pott's observation in 1775 that scrotal
cancer found in chimney sweeps was the result of some agent in soot was the
first suggestion that cancer could be caused by environmental contaminants.
However, it was not until more than a century later that skin tumors were pro-
25
duced experimentally in rabbits by painting them with coal tar extracts.
This marked the beginning of the search for the active carcinogenic substance
in soot, culminating in the isolation and identification of BaP by British
?fi 77
investigators two decades later. " Synthetic dibenz[a,h]anthracene (DBahA)
28
had been shown to be a carcinogen and the structural similarities between the
two molecules implicated polycyclic aromatic hydrocarbons as potential car-
cinogens in man. Many other PAH's were subsequently synthesized, with most
29
proving to be non-carcinogenic. Nevertheless, several PAH's were discovered
that are routinely used as tumorigens in laboratory animals, such as MCA and
6-27
-------
several of the methylated benz[a]anthracenes. Elucidation of the metabolic
mechanisms by which these compounds transform normal cells into malignant
cells necessarily rests in a complete description of their physical and chemi-
cal similarities and the molecular conformation formed between the carcinogen
and target site(s) inside the cell. Although a general mechanism by which PAH
carcinogens interact with the target site or sites where transformation to
malignancy occurs is now unknown, it is hoped that complete assembly of the
metabolic pathways will reveal whether there is an overall mechanism of acti-
vation for transformation.
Polycyclic hydrocarbons are metabolized by the microsomal mixed function
oxidase system (MFO), often termed aryl hydrocarbon hydroxylase (AHH), which
is most abundant in liver. This enzyme system has been studied extensively
and is the subject of several reviews. ' While it is known that this
enzyme complex is involved with detoxification of xenobiotics in conjunction
with various P-450 type cytochromes, it is apparent that this system is also
directly involved with the metabolism of polycyclic hydrocarbons to their
active species. A second microsomal enzyme, epoxide hydrase (EH), converts
epoxides into vicinal glycols. Since some epoxides are more active carcino-
gens than the parent hydrocarbon, this enzyme would likely affect both car-
cinogenesis and detoxification. Information on epoxide hydrase has been
32 33
recently summarized ' and its importance in the formation of the three
34 35
known dihydrodiols of BaP has recently been demonstrated. ' Figure 6.7
presents a schematic representation of the various enzymes involved in acti-
vation and detoxification pathways for BaP, that is also representative of
the known mechanisms of POM metabolism in general.
6-28
-------
i
m
(ENDOPLASMIC
RETICULUM)
GLUTATHIONE
CYTOCHROME P-450
MIXED-FUNCTION OXIDASE (MFO)
MFO
BaP-O-SG
(DETOXIFICATION TRANSFERASE
PRODUCTS) (CYTOSOL)
BaP OXIDES
EPOXIDE
HYDRASE
(ENDOPLASMIC
RETICULUM)
•»• BaP PHENOLS
MFO
BaP QUINONES
MFO
BaP DIOL EPOXIDES
(PROPOSED ULTIMATE
CARCINOGENS)
BaP DIHYDRODIOLS (PROPOSED PROXIMATE CARCINOGENS)
UDP-GLUCURONOSYL TRANSFERASE
(ENDOPLASMIC RETICULUM)
H2O -SOLUBLE CONJUGATES
(DETOXIFICATION PRODUCTS)
Figure 6-7. Enzymatic pathways involved in the activation
and detoxification of BaP.
6-29
-------
Other intermediates currently under investigation in several laboratories,
primarily using BaP as the starting compound, are transient free radicals.
This type of intermediate is known to be generated easily both chemically and
enzymically. ' Because it is too unstable to isolate and study, it is not
yet possible to determine if, or how, this labile species is involved in the
carcinogenic activity of BaP.
Several reports on the metabolic production of a 6-oxy-BaP radical suggest
that this activated BaP derivative is involved in DNA binding, and thus may
38-41 38
induce tumors. " Kodama and Nagata incubated 6-oxy-BaP radical with the
synthetic nucleotide poly G and obtained a strong ESR signal in the resulting
bound complex. This signal was comparable to that for free 6-oxy-BaP radical
and indicated covalent binding to guanosine residues. However, when 6-oxy-BaP
was incubated with calf thymus DNA, only a small ESR signal could be observed.
Moreover, the 6-oxy-BaP radical does not possess significant carcinogenic
activity.
The one-electron oxidation of POM to produce radical cations which bind
to cellular constituents has been proposed as a general pathway of metabolic
42 42
activation leading to tumorigenesis. Cavalieri and coworkers have con-
ducted studies to show that correlations exist between the ease of radical
cation formation and carcinogenic activity for certain polycyclic hydrocar-
bons. In particular, binding to nucleophiles by the trapping of radical
cations occurs as a result of preferential positive charge localization at
position 6 of BaP and at position Cl of MCA. Evidence which supports this
mechanism is the observed binding of BaP to mouse skin DNA and RNA at the
6-position and the apparent lack of carcinogenic activity for MCA derivatives
6-30
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substituted at the 1-position. Nevertheless, numerous exceptions to the
radical cation hypothesis, and the well-demonstrated potent careinogenicity of
diol epoxides derived from POM, argue against the critical involvement of
radical cations as either proximate or ultimate carcinogens for all POM.
It is suggested that hydroxymethyl derivatives of alkyl-substituted POM's
may be critical carcinogenic intermediates, even though these metabolites
generally show little tumorigenic activity. ' In this regard, data exist
to support the view that for certain methyl-substituted POM (e.g., 7-methyl-
benz[a]anthracene), the hydroxymethyl derivative is a proximate carcinogen
42
giving rise to an ester which serves as the ultimate carcinogen. A com-
parison of two less active intermediates showed that the carcinogenicity of
6-hydroxymethyl BaP is far less than for its sulfate ester.
It seems clear that specific mechanisms and transient intermediates are
important steps in carcinogen activation, detoxification, and the physico-
chemical binding to transformation receptor(s) in the cell. It is essential
that critical methodology be employed to determine the ultimate carcinogenic
form(s) of metabolically activated POM. Advances in systematic identification
of proximate forms or efficient and relevant trapping of the reactive ultimate
carcinogen are required to further the understanding of the mode of metabolic
activation of POM.
6.2.1.2 Chemical reactivity and care inogeni city—For many years, investiga-
tors have sought a common molecular feature among POM carcinogens which would
serve to explain their biological activity. The "electronic theory of car-
cinogenesis" has relied upon an analysis of the influence of electron density
6-31
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at specific molecular regions to explain unique reactivity with cellular
constituents. A basic assumption arising from the work of the Pullmans and
9/1
others was that a meso-phenanthrenic region ("K-region") of high ir-electron
density and with a propensity for addition reactions was a critical structural
feature for polycyclic carcinogens. In expanding this hypothesis, further
biologic significance was attributed to the concommitant presence of a rather
unreactive meso-anthracenic region ("L-region") for high carcinogenicity. In
addition, a region of comparatively low reactivity which characteristically
undergoes metabolic perhydroxylation (corresponding to the 3,4-positions of
benz[a]anthracene) has been designated the M-region. According to the theory,
only binding of the K-region to critical cellular sites would cause tumor
formation; protein binding at the L-region causes no tumorigenic effect, while
inactivation is produced by metabolic perhydroxylation in the M-region. The
three regions of reactivity are readily distinguished in the benz[a]anthracene
skeleton: _ _ .
M-region of metabolic
perhydroxylation
L-region «^^ ^^ K-region
The electronic K-L theory of carcinogenic reactivity has encountered numerous
inconsistencies, primarily because these relationships were derived from
properties of the parent hydrocarbon and gave no consideration to activated
metabolites.
Advances in recent years have focused attention on the potential reac-
tivity of diol epoxide metabolites of POM, and their ease of conversion to
6-32
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trioi carbom'um ions. Under the assumption that diol epoxides which are more
readily converted to carbonium ions will be better alkylating agents to pro-
duce carcinogenesis and mutagenesis, the "bay region" theory has been pro-
43 44
posed. ' Examples of a "bay region" in a polycyclic hydrocarbon are the
regions between the 10 and 11 positions of BaP and the 1 and 12 positions of
benz[a]anthracene:
Bay region Bay region
Benzo[a]pyrene Benz[a]anthracene
The theory predicts that diol epoxides in which the oxirane oxygen forms part
of a "bay region" (e.g., BaP 7,8-diol-9,10-epoxide) will be more reactive and
hence more carcinogenic than diol epoxides with the oxirane oxygen not situa-
ted in a "bay region." Experimentally, the "bay region" diol epoxides of
benz[a]anthracene, BaP, and chrysene were more mutagenic in vitro and/or
tumorigenic than other diol epoxide metabolites, their precursor dihydrodiols,
the parent hydrocarbons, or other oxidative metabolites (see Sections 6.4
and 6.5). Moreover, quantum mechanical calculations were in accord with the
concept that reactivity at the "bay region" is highest for all the diol
epoxides derived from polycyclic hydrocarbons.
6.2.1.3. Metabolism of PAH--Polycyclic aromatic hydrocarbon metabolites have
been arbitrarily divided into two groups on the basis of solubility. In the
first group are those metabolites that can be extracted from an aqueous incu-
bation mixture by an organic solvent, e.g., ethyl acetate. This group consists
6-33
-------
of ring-hydroxylated products such as phenols and dihydrodiols, ' and
hydroxymethyl derivatives of those polyaromatics having aliphatic side chains,
such as DMBA and MCA. In addition to the hydroxylated metabolites are
quinones that are produced enzymically by microsomes and non-enzymically from
air oxidation of phenols. Labile metabolic intermediates such as epoxides can
AQ AQ Cn
also be found in this fraction. "'^'^
In the second group are the water soluble products that remain after
extraction with an organic solvent. While it is believed that many of these
derivatives are formed by conjugation of the hydroxylated products to gluta-
51 52 53
thione or glucuronic acid and sulfate, rendering the compound more
hydrophilic and presumably less toxic, this group of derivatives has not been
rigorously studied.
The metabolite profile of BaP which has been largely worked out using
high pressure liquid chromatography is seen in Figure 6-8. It consists of
three groups of positional isomers. There are three dihydrodiols, three
quinones, and two phenols. The major BaP metabolite found in microsomal
incubations is 3-hydroxybenzo[a]pyrene, with 9-hydroxybenzo[a]pyrene present
in lesser amounts. The BaP-4,5-epoxide has been isolated and identified as a
precursor of the BaP-4,5-diol. Other studies indicate that epoxides are the
precursors of the 7,8-diol and 9,10-diol as well. There have been no inter-
mediates isolated as phenol precursors, although recent evidence using deu-
terium labeling suggests that at least a portion of 3-OH-BaP is derived from
54
an intermediate 2,3-epoxide. Evidence also exists for epoxide involvement
qc
in the formation of 9-hydroxybenzo[a]pyrene. The metabolite profile has
6-34
-------
[9,IO-diol-7,8-ep«]
[7,8,9,10-tetroi]
6-OH
CONJUGATES
7 8-epox
7.8-diol
"- » c , Jt-W
4,5-diok
9,10-epox
— [7,8-diol-9,IO-ep(«]
[7,8,9,10-tetroi]
7-OH
BOUND MACROMOLECULES
ONA
RNA
PROTEIN
Figure 6-8. Metabolites of benzo[a]pyrene.
6-35
-------
been extended to include two additional phenols (7-OH and 1-OH) by the use of
recycle chromatography, which allows multiple passages through the column and
55
will resolve all BaP phenols. In addition, solvent regimen changes have
resolved some of the tetrols that were too polar for separation in the stand-
ard water-methanol gradients. There is little further knowledge of the
chronological order and kinetics of metabolite formation. The effect of
various metabolites on microsomal enzyme activity has not been thoroughly
studied. However, it has been demonstrated that there are different types of
hepatic microsomal oxygenase induction ' »b8»59 that appear to be dependent
upon the chemical nature of the inducer. This may significantly influence
the amount of active intermediate species of carcinogen formed and its proba-
bility of reaching a target site. Removal of reactive intermediates and
toxic metabolites is certain to affect the probability of cell survival, both
normal and transformed.
Considerable progress has been made in the isolation and characterization
fiO 61 62 ?R ?6
of the AHH enzyme complex ' ' and similar work is in progress for EH. '
Polycyclic aromatic hydrocarbons are relatively inert chemically and
quite hydrophobic, and cell lipids are probably needed for these compounds to
be dispersed in the cytoplasm. Autoradiographic studies in vitro indicate
that PAH's possess access to all parts of the cell, although at present there
C O C A
is no evidence for active transport. ' It was already apparent in 1950
that for metabolism to occur, some form of biochemical action was necessary to
raise the molecule to a higher reactive state because of the stability of the
polyaromatic molecule. Since several dihydrodiols and phenols had been isola-
ted from tissue incubations, it was suggested that reactive epoxides were
6-36
-------
likely precursors that could then be hydrated to dihydrodiols or opened non-
enzymically to form phenols. Epoxide intermediates for a number of poly-
cyclic hydrocarbons, both carcinogenic and noncarcinogenic, have now been
isolated and suggest that the arene oxide intermediate is a general biochemi-
cal scheme for biotransformation of these xenobiotics. °»49>50»^5
Since the resonance level of the polyaromatic system makes ring openings
difficult, the enzymatic attack is designed to open double bonds and add an
oxygen moiety, such as a hydroxyl group, to give it more polarity and,
therefore, more solubility in aqueous media such as body fluid; and to
facilitate removal by the kidney. The effect on removal is plainly seen
when extremely high concentrations of labeled polyaromatics given to test
animals are almost completely excreted within 48 hours. Only residual
radioactivity remains, and it is below the resolution of most standard
assays to confirm that the remaining radioactivity is on the polyaromatic
molecule and has not been exchanged onto another substance.
In the formation of a reactive metabolic intermediate, stable compounds
are converted to unstable metabolites. In the case of polyaromatics, this
step is the formation of an arene oxide ring that is highly strained and
favors ring opening. Thus, nucleophilic attack of this reactive intermedi-
ate either directly or through the formation of a transient carbonium ion
would be greatly enchanced. Alkylations of this type are common to many
classes of carcinogenic chemicals. So, paradoxically, an active carcinogen
is created in the process of detoxification. Early calculations relied upon
the participation of the most chemically reactive region of the molecule,
6-37
-------
the so-called "K-region" (corresponding to the meso-phenanthrenic double
bond), for carcinogenicity predictions. This theory was formulated at a
time before the identification of metabolic products and advanced in vitro
and in vivo assays for determining their biological activity.
Taking epoxides to be the intermediates and the transient ring-opened
carbonium ion to be the alkylating species, the "bay region" concept has been
developed, using new knowledge concerning the role of electrophilic inter-
mediates. The concept was derived from the prediction that the portion of
the molecule most likely to form an epoxide intermediate (that once opened,
would be long-lived enough to have a relatively high probability of hitting
the critical target site) would be the carcinogenic determinant of this
molecule.
While a general mechanism that will undoubtedly be complicated by
species variation and structural and chemical differences (e.g., solubility)
between different polycyclic molecules, this concept has worked quite well
for BaP.68'69
Since BaP has three known metabolic epoxide intermediates, the use of
this concept to predict relative carcinogenicity and mutagenicity has been
tested. While the K-region epoxide (4,5 epoxide) is an effective mutagen in
bacterial and mammalian V79 cells, it is a very weak carcinogen in mice (see
Sections 6.4 and 6.5). It is far less effective as a carcinogen than the non
K-region 7,8-epoxide.70'71'72'73
Moreover, evidence for remetabolism of dihydrodiols has simply established
a higher level of certainty for this "bay region" concept. The finding that
BAP 7,8-dihydrodiol was metabolized to BaP 7,8-diol-9,10-epoxides showed that
6-38
-------
the microsomal oxygenases were capable of recycling the BaP molecule through
an additional epoxldatlon. This dlol-epoxlde was also hydrated to form a
7d
tetrol.
The stereochemical nature of the diol-epoxlde intermediates allows the
possibility of two optically active enantiomers from (-)-BaP 7,8-dihydrodiol
and two optically active enantiomers from (+)-BaP 7,8-dihydrodiol. In two of
the diol-epoxides, the 7-hydroxyl would be in the same plane (syn) as the
oxide ring, and in the other two, the 7-hydroxyl would be on the opposite
plane (anti-) to the epoxide ring.
In vivo experiments with tumor formation in mouse skin and in vitro
assays using mammalian cells and bacteria have implicated the anti-config-
uration as the biologically active BaP 7,8-diol-9,10-epoxide isomer. ' In
addition, studies with the (-) trans-7,8-diol isomer as substrate in the
microsomal system indicate the (+)-anti-configuration of the epoxide [r_-7,;t-
8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene] is that which is
also biologically active. The isolation and characterization of the DNA-
bound product in which guanosine predominates support these observations.
To date, the diol-epoxide is too unstable for direct isolation from bio-
logical systems. While researchers conducting molecular and chemical studies
have made strides in discovering the putative reactive species of BaP and its
probable mode of macromolecular interaction, the basic problem still exists
of how the transformation event occurs and why there are different suscepti-
bilities between species.
The advances in the "bay region" theory of PAH carcinogenesis and in
determining the identity of proximate and possibly ultimate carcinogenic
6-39
-------
forms of PAH have been achieved using homogenates of liver. In combination
with bacterial mutagenicity assays, similar advances can be expected for
carcinogens of particular environmental concern. The need for further test-
ing of the data obtained from these in vitro experiments in suitable in vivo
animals models, however, is essential. If such in vitro experiments can
permit the identification of proximate or ultimate carcinogenic intermediates,
the influence of other environmental agents on modifying enzyme induction or
metabolic activation to specific compounds could be studied in greater detail.
The metabolic fate of most PAH's has not been studied as extensively as
that of BaP. Nevertheless, several generalizations are evident which apply
to most unsubstituted and alkyl-substituted polycyclics. To a limited extent,
direct attack on saturated carbon atoms may occur to form, sequentially,
78
alcohols, ketones, aldehydes, and carboxylic acids. More commonly, meta-
bolic attack on one or more of the aromatic double bonds (K-region and non-K-
region) leads to the formation of isomeric dihydrodiols by the intermediate
79 78
formation of reactive epoxides. ' Dihydrodiols'are further metabolized by
the microsomal monoxygenases to yield diol-epoxides, compounds which are
implicated as ultimate biologically reactive intermediates. Removal of
activated intermediates by conjugation with glutathione or glucuronic acid,
or by further metabolism to tetrahydrotetrols, is a key step in protecting
80 81
the organism from toxic interaction with cell macromolecules. '
With unsubstituted POM, such as benz[a]anthracene and DBahA, oxidation
80 82 83 84
occurs with rat liver homogenates to produce phenols and dihydrodiols. '''
Both K-region and non K-region oxidative metabolites are formed, which may
6-40
-------
subsequently be conjugated with glutathione and excreted in the urine as
mercapturic acids. In addition, hydration of the epoxide intermediates
formed from these compounds may yield dihydrodiols. Figure 6-9 presents
some of the significant routes of metabolism for DBahA. Evidence indicates
that K-region epoxides are better substrates for the formation of glutathione
conjugates than non K-region epoxides.
Among the simpler unsubstituted ROM's, such as phenanthrene, no evidence
for the formation of a K-region phenol or a conjugate thereof can be detec-
78
ted. The major phenanthrene metabolite is a K-region dihydrodiol which may
also be excreted as a conjugate with glucuronic or sulfuric acid.
In contrast to the unsubstituted compounds, ROM's bearing alkyl substitutes
(e.g., MCA, DMBA) are primarily hydroxylated at the alkyl side chain. The
CO QC QC
metabolism of DMBA has been carefully studied using rat liver homogenates. °>oa'00
These studies clearly showed that the main products of DMBA metabolism are
the isomeric 7-hydroxymethyl-12-methylbenz[a]anthracene and 12-hydroxymethyl-
7-methylbenzanthracene. In addition, DMBA and its hydroxymethyl derivatives
are metabolized into 8,9-dihydrodiols (non K-region). In contrast, a
K-region 5,6-epoxide is also formed, but instead of being hydrated to the
QC
dihydrodiol, it is conjugated with glutathione. Although all of the polar
DMBA metabolites have not yet been identified, no derivative has thus far
been detected which involves enzymic oxidation at both the 5,6- and 8,9-bonds
in the same molecule. Recent studies have implied that metabolic activation
of DMBA for binding with DMA occurs through the generation of a diol epoxide
87
in the 1,2,3,4-ring. Ring hydroxylation at the 3- and 4-positions of DMBA
6-41
-------
12
R« CH2 —CH —CO — NH— CH2—C02H
NH — CO — CH2 — CH2 — CH (IMH2) — CO2H
SR
Figure 6-9. Metabolism of dibenz[a,h]anthracene by
rat-liver homogenate.82
6-42
-------
u w
(M-region) had previously been shown to occur. Thus, evidence for the
"bay region" theory being of general applicability is increasing.
Metabolism of the carcinogens 7- and 12-methylbenz[a]anthracene is
88
qualitatively similar to DMBA. The products formed by rat liver homogen-
ates include: dihydrodiols at the 5,6-(K-region) and 8,9-(non K-region)
positions; hydroxymethyl derivatives; various phenols; and glutathione con-
jugates at the K-region. Figure 6-10 presents a probable scheme for the
metabolism of 7-methylbenz[a]anthracene which would also apply to 12-methyl-
benz[a]anthracene.
The metabolites of MCA formed by rat liver homogenates, liver microsomes,
or a highly purified cytochrome P-448-dependent monooxygenase system with
89 90
epoxide hydrase are all similar. ' Formation of 1-hydroxy MCA and 2-
hydroxy MCA predominates. Smaller amounts of the K-region trans 11,12-
dihydrodiol and a glutathione conjugate derived therefrom are formed from
MCA, as well as trans 1,2-dihydroxy MCA and several phenols. The two major
dihydrodiols which are produced by the action of epoxide hydrase on (+) 1-
hydroxy MCA are the diastereometrically related trans 9,10-dihydrodiol.
90
These results led Thakker and coworkers to postulate that the ultimate
carcinogenic metabolite of MCA may be the "bay region" diol epoxides (9,10-
diol-7,8-epoxides) derived from 1-hydroxy MCA.
An important consideration in evaluating the health hazards of POM is
whether metabolism in rat liver preparations is indicative of the pattern of
POM metabolism in more likely target organs (e.g., lung). Moreover, it is
vital to determine whether metabolism in rodents mimics metabolism in man.
6-43
-------
"OH | HO'
CH, —CH —CO —Gly
I
NH—Glu
CH2 — OH
Figure 6-10. Probable metabolic pathways of 7-methylbenz[a]anthracene.
6-44
-------
In this regard, it has been shown that the metabolism of benz[a]anthracene,
7-methy1benz[a]anthracene, and BaP was qualitatively similar in rat liver and
91 92
lung. ' Both K-region and non K-region dihydrodiols were detected,
which almost certainly arose from epoxide precursors. Earlier work estab-
lished that both rat and human lung preparations converted benz[a]anthracene
80
to the corresponding K-region expoxide. Furthermore, tracheal slices of
Wistar rat and Syrian hamster, and human bronchial tissue in culture all
produced qualitatively similar products from benz[a]anthracene, 7-methyl-
80
benz[a]anthracene, and BaP. Metabolite profiles with these same hydro-
Rfl
carbons in mouse, rat, and human skin were also qualitatively similar.
Patterns of BaP metabolism in hepatic microsomes from primates, rats, and
93
miniature swine were qualitatively similar, as were the metabolite pro-
files (by thin-layer analysis) of BaP in microsomes from mouse liver, spleen,
94
kidney, and lung. However, among different strains of mice with varying
responsiveness to the microsomal enzyme-inducing effects of BaP pretreatment,
94
metabolite profiles could be quantitatively altered. Among several tis-
sues of the human adult and fetus (liver, adrenal, placenta), the same types
of BaP metabolites are obtained, although microsomal enzyme activity was
95
lower in the fetus. Moreover, no significant differences were found in
the pattern of BaP metabolism between laboratory animals and man. However,
recent studies indicate that rat liver and lung preparations differ with
96
respect to the nature of free radical metabolites produced from BaP. In
93
addition, Leber and coworkers reported that unidentified oxidative metabo-
lites of BaP are obtained with rhesus monkey lung microsomes (analysis by
6-45
-------
high-pressure liquid chromatography) which are not obtained with liver micro-
somes from the same species. Differences are also seen in the BaP metabolites
formed by human lymphocytes and liver microsomes when analyzed by high-
97
pressure liquid chromatography. Thus, it seems that interspecies compari-
sons of POM metabolism in a single tissue may be a valid practice, whereas
differences in tissue-specific metabolism may prevent the extrapolation of
data from hepatic to extrahepatic (i.e., target organ) tissues.
An additional factor having crucial importance to the metabolic activation
of POM in various tissues and species is the level of drug metabolizing
98
enzymes present. As indicated in Section 6.3.4, tissue susceptibility to
POM-mediated carcinogenesis may be obligatorily coupled to the presence and
amount of microsomal mixed-function oxidase enzymes and epoxide hydrase.
Protection from POM-induced tumorigenesis, on the other hand, may be largely
determined by the.capacity for target tissues to enzymatically detoxify
(e.g., by glutathione or glucuronic acid conjugation) and remove activated
metabolites.
6.2.2 Intracellular Binding of POM
Investigators have known for a number of years that, when applied to the
skin of animals or added to cells in culture, carcinogenic POM's become cova-
99
lently bound to tissue constituents. The molecular basis for carcinogenic
and cytotoxic consequences of exposure to POM was attributed to the binding
of the compounds to nuclear DNA, ' although binding occurs to RNA and
protein as well. ' In the regenerating rat liver, DMBA produced an inhibi-
tion of DNA synthesis accompanied by a long-lasting (more than 4 weeks) DMBA-
DNA binding. In contrast, benz[a]anthracene, a weak carcinogen, inhibited
6-46
-------
DMA synthesis only slightly, and benz[a]anthracene binding to DNA was greatly
diminished between 11 and 24 hours after administration. It was suggested
that cells in the S phase of the cell cycle were primarily affected by the
carcinogen. Similar effects on DNA synthesis were obtained using single
applications of initiating doses of DMBA or DBahA to the skin of mice.
The weak tumor initiator, DBacA, had little effect on DNA synthesis. In
mouse skin, it was also shown that DMBA preferentially binds to non-replicating
105
DNA. Moreover, DNA-bound DMBA moieties could still function as templates
for further DNA synthesis. This finding suggested that newly synthesized
abnormal daughter DNA may be genetically altered by an error-prone post-
replicative repair process which leads to mutations and/or carcinogenesis.
Such a hypothesis supports the somatic mutation theory of carcinogenesis.
Binding of a carcinogen to DNA is believed to be a critical step in
tumor initiation. The application of BaP to mouse epidermis resulting in the
formation of BaP-DNA adducts has been used in examining dose-response rela-
259
tionships for BaP tumorigenesis. Albert and coworkers found that the
formation of BaP adducts was a linear function of dose between 4 and
100 nmoles/mouse. Since BaP carcinogenesis in mouse skin was a linear
fuction between 16 and 500 nmoles/mouse, binding to DNA may allow for ex-
trapolation of the dose-response curve down to levels which are unsuitable
for carcinogenesis studies with limited numbers of animals. Furthermore, it
allows one to evaluate the biological effects of environmentally realistic
108
exposures to a particular POM. Lutz and coworkers noted that over a do:
range of 40 yg/kg to 4 mg/kg (approximately 50-5000 nmoles/animals, given
6-47
-------
i.p.) the binding of BaP to rat liver DNA was linear with doses up to about
1 mg/kg. A non-linear dose-response relationship between 1 mg/kg and 2 mg/kg
was evident, which could have been caused by an induction of microsomal
enzyme activity. Above 2 mg/kg, microsomal enzyme activity was further
enhanced, while DNA binding increased only slightly.
Because polycyclic aromatic hydrocarbons are not highly reactive
chemically, it was believed that a reactive metabolite was responsible for
the DNA-binding phenomenon. Gelboin and Grover and Sims independently
confirmed this hypothesis by demonstrating that polycyclic hydrocarbons bind
covalently to DNA in the presence of rat liver microsomes. The low level of
binding for BaP to DNA (one molecule per 50,000 to 500,000 nucleotides)
suggested the possibility of a unique binding site for BaP derivatives on the
31
DNA. Subsequent studies conducted in vitro with hamster tracheal epi-
thelial cells incubated in the presence of 7,8-benzoflavone (an inhibitor of
microsomal drug-metabolizing enzymes) confirmed that BaP binding to DNA was
dependent on an intact drug-metabolizing system. '0'''' in a related study,
the binding of BaP and MCA to rat liver DNA in vitro was enhanced in the
112
presence of an epoxide hydrase inhibitor. It is now known, however, that
both aryl hydrocarbon hydroxylase and epoxide hydrase are required for the
metabolic activation and subsequent binding of BaP to DNA. These data
implied that active epoxide intermediates are involved in the binding of
polycyclic carcinogens to DNA. Others have argued, however, that a 6-oxy-
benzo[a]pyrene free radical may be involved in the binding of BaP to DNA and
38 39 40 114
synthetic polynucleotides. ' ' ' It was suggested that metabolic
6-48
-------
hydroxylation of BaP at position -6 leading to the formation of the 6-oxy BP
41
radical may be only a minor route for binding to DNA.
The role of K-region arene oxides as reactive intermediates in the
metabolism of polycyclic hydrocarbons has been extensively reviewed, ' '
although the structure of the bound material was not known at the time.
Further confusion resulted from the demonstration that high levels of non-
enzymatic binding of polycyclic hydrocarbons to DNA occurred with in vitro
microsomal systems. Nevertheless, extensive microsome-dependent binding
of BaP to synthetic polynucleotide acceptors has been shown, which could be
both inhibited or enhanced by conditions which affect microsomal enzyme
activity. ' Similar studies using DMBA-epoxides revealed that covalent
complexes formed primarily with poly G, indicating that guanosine residues in
119
nucleic acids may be preferred targets for reactive arene oxides.
Systematic studies were undertaken to elucidate the relative role of
K-region epoxides in binding reactions with nucleic acids. Blobstein and co-
ion
workers examined the in vitro binding of both K- and non K-region arene
oxides to poly G by measuring changes in the absorption and fluorescence
spectra of the modified nucleic acid. Reactivity with nucleic acids was
found to vary considerably, depending upon the structure of the parent hydro-
carbon and position of the epoxide moiety. Significant binding to poly G
occurred with K-region arene oxides of DMBA, BaP, and MCA (all strong carcino-
gens) and benz[a]anthracene (a weak carcinogen). K-region arene oxides of
the non-carcinogens pyrene and phenanthrene produced no changes in the absorp-
tion spectra for poly G. However, the non K-region BaP 9,10-, BaP 7,8-, and
6-49
-------
phenanthrene 3,4-oxides also produced alterations in poly G as measured by
changes in fluorescence spectra. Further investigations revealed that RNA
adducts formed when cultured bronchial mucosa is exposed to BaP or when BaP
121
is painted on mouse skin are produced when BaP 7,8-diol-9,10-epoxides
react at the 2-amino group of guanosine. Whereas Weinstein and coworkers
observed the formation of an adduct only between RNA and (jO-7B,8a-dihydroxy-
'9a,10a-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (diol epoxide 2), Moore and
122
coworkers found that both diol epoxide 2 and (+)-7B,8a-dihydroxy-9B,10B-
epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (diol epoxide 1) reacted with RNA in
vivo by cis and trans addition. Diol epoxide 1 arises mainly from the (+)-
enantiomer of BaP 7,8-dihydrodiol while the (-)-enantiomer produces primarily
diol epoxide 2 (see Section 6.2.1). This observation explains why both AHH
and epoxide hydrase are required for BaP binding to DNA, since BaP 7,8-oxide
must be reduced by epoxide hydrase to form BaP 7,8-dihydrodiol, which is
further metabolized to the BaP 7,8-diol-9,10-epoxide by the microsomal
monoxygenases. Thus the K-region BaP 4,5-oxide does not appear to be re-
sponsible for most of the observed covalent binding of BaP to RNA. In addi-
tion, examination of DNA adducts formed in vitro with primary cultures of
123 124 113
Syrian hamster embryo cells, ' cultured human bronchi, or BHK 21/C13
125
cells in culture exposed to BaP corroborated the results obtained for RNA,
and disputed the involvement of a BaP K-region oxide in the binding reaction.
Further support for the importance of BaP 7,8-diol-9,10-epoxides in the
binding of BaP to nucleic acids was provided by studies which demonstrated
that BaP 7,8-dihydrodiol is highly carcinogenic, and both diastereomeric BaP
6-50
-------
7,8-diol-9,10-epoxides are potent mutagens (see Sections 6.4 and
6.5).66'75'72'76'126'127'128 A diol-epoxide of DMBA was also shown to be
87
involved in the binding reaction with DMA of mouse embryo cells.
Not all investigators agree that polycyclic hydrocarbon binding to DNA
represents the essential interaction leading to mutagenesis/carcinogenesis.
129
Sarrif and coworkers were able to purify an "h-protein" from C3H mouse
liver and skin which could covalently bind to metabolites of MCA. The pro-
tein was postulated as a primary target in hydrocarbon-induced carcinogenesis,
playing a similar role to hormone receptors in transporting carcinogens to a
target site(s) in the nucleus. Alternatively it was suggested that the
protein-carcinogen conjugate may in itself act as an abnormal derepressor to
give rise to tumor formation. In related studies, MCA and DBahA were found
to bind with high affinity to a nuclear subfraction from cultured mouse
embryo cells. This subfraction contained 15 percent of the nuclear DNA
and represented that fraction of the nuclear chromatin which is transcrip-
tionally active. The specific macromolecule responsible for the binding
could have been, in addition to DNA, either RNA or one of the chromatin
proteins involved in gene regulation. In support of the possible involvement
of polycyclic carcinogens with essential chromatin components, it was noted
that the weak carcinogen DBacA exhibited minimal binding to this same nuclear
subfraction. Other investigators incubated BaP with isolated calf thymus
nuclei in the presence of NADPH and rat liver microsomes and demonstrated
that an uneven distribution of carcinogen in chromatin occurs. The data
suggested a localization of carcinogen in the outermost "spacer" regions of
DNA in the nucleosome.
6-51
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6.3 TOXICOLOGY
The potential for POM to induce malignant transformation dominates the
consideration given to health hazards resulting from exposure. Although the
emphasis on careinogenicity is certainly justified when dealing with public
health issues concerning POM, one must recognize that non-neoplastic lesions
may also result from environmental and occupational contact. Such effects
can be seen with subthreshold doses of carcinogenic POM and with those
compounds which possess no tumorigenie activity.
As long ago as 1937, it was known that carcinogenic POM produced
systemic toxicity as manifested by an inhibition of body growth in rats and
132
mice. Tissue damage resulting from the administration of various POM to
experimental animals is often widespread and severe, although selective
organ destruction may occur (e.g., adrenal necrosis, lymphoid tissue damage).
Few investigators, however, have attempted to ascertain the molecular mecha-
nsim of POM-induced cytotoxicity. Nevertheless, current opinion favors the
concept that normally proliferating tissues (intestinal epithelium, bone
marrow, lymphoid organs, testis) are preferred targets for POM, and this
susceptibility may be due to a specific attack on DNA of cells in the S
133
phase of the mitotic cycle. Additional factors which may have an important
bearing on the adverse effects resulting from POM exposure are primary and
secondary alterations in enzyme activity and immunologic competence. More-
over, these toxicant-induced changes may play an important role in the
eventual induction of neoplasia.
6-52
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6.3.1 Acute Exposures
Target organs for the toxic action of POM are diverse, due partly to
extensive distribution in the body and also to the selective attack by these
chemicals on proliferating cells. Damage to the hematopoietic and lymphoid
systems in experimental animals is a particularly common observation.
134
Yashuhira described severe degeneration of the thymus and marked reduction
in weight of the spleen and mesenteric lymph nodes of CF1 Swiss and C57BL mice
given a single intraperitoneal injection of MCA (0.3-1.0 mg) between 12 hours
and 9 days after birth. Degeneration of young cells in the bone marrow and
retardation of thyroid gland development were also noted. Newborn mice were
highly susceptible to the toxic effects of MCA, with many animals dying from
acute or chronic wasting disease following treatment. Among surviving CF1
mice, numerous thymomas eventually developed; none were evident, however, in
C57BL mice despite serious thymic damage.
DMBA is well-known for its effects on the bone marrow and lymphoid
tissues. With single feedings (112 or 133 mg/kg B.W.) to female Sprague-
Dawley rats, age 50 days, DMBA induced pancytopenia by causing a severe
depression of hematopoietic and lymphoid precursors. Maturation arrest
occurred at the proerythroblast levels; no injury to the stem cells or the
formed elements in the peripheral blood was evident. The fact that only the
more rapidly proliferating hematopoietic elements were vulnerable to attack
by DMBA led the authors to suggest that inhibition of DNA replication may be
involved in the toxicologic response.
Philips and coworkers provided strong support for the argument that
DMBA-induced cytotoxicity is mediated via an interaction with DNA. Female
6-53
-------
Sprague-Dawley rats receiving 300 mg/kg B.W. DMBA orally and male rats
receiving an intravenous injection of 50 mg/kg B.W. DMBA displayed injury to
the intestinal epithelium, extreme atrophy of the hematopoietic elements,
shrinkage of lymphoid organs, agranulocytosis, lymphopenia, and progressing
anemia. Mortality among rats receiving DMBA by gastric intubation (females)
was about 65 percent; the group treated by intravenous injection showed
about 25 percent mortality. In rats given 50 mg/kg B.W. DMBA intravenously,
14
incorporation of C-labeled thymidine into DMA of small and large intestine,
spleen, bone marrow, cervical lymph nodes, thymus, and testis was signifi-
cantly inhibited. This inhibition was as high as 90 percent in several
organs at 6 hours, and indicated a strong inhibition of DNA synthesis.
Consequently, the authors postulated that DNA in S phase cells is particu-
larly susceptible to DMBA attack. This contention probably holds true for
other carcinogenic POM as well.
Similarities between the effects of DMBA and ionizing radiation on the
bone marrow suggest a common cytotoxic action. The depressive effect of
DMBA injection (5 to 60 yg) or ionizing radiation (200 to 600 rads) on the
bone marrow of newborn DFW/D mice could be shown within a few hours of
I og
treatment. Either of these treatments would be sufficient to induce
thymic lymphomas in nearly all exposed mice, evidence which strongly sug-
gests a relationship between mechanisms of cytotoxicity and tumor induction
which probably involve an attack on DNA.
Another lesion which is characteristic of that produced by X-rays is
the severe testicular damage induced by DMBA in rats. Single intravenous
6-54
-------
injections of DMBA (0.5 to 2.0 mg) given to adolescent (25 days of age) rats
caused transient degenerative changes in the testis which were most evident
38 to 40 days after treatment. Essentially the same effects were produced
in adult rats, age 60 days, given DMBA orally (20 mg) and intravenously
(5 mg). Lesions of the testes were highly specific and involved destruction
of spermatogonia and resting spermatocytes, both of which are the only
testicular cells actively synthesizing DNA. Neither the remaining germinal
cells nor the interstitial cells were damaged by DMBA. Surprisingly, no
testicular damage was produced by single feedings of BaP (100 mg), MCA
(105 mg), or 2-acetoaminophenanthrene (40 mg).
For many years it has been known that the application of carcinogenic
polycyclic hydrocarbons to mouse skin leads to the destruction of sebaceous
130
glands, hyperplasia, hyperkeratosis, and even ulceration. Sebaceous
glands are the skin structures most sensitive to polycyclic hydrocarbons, and
assay methods for detection of carcinogens have been based on this effect.
Although a good correlation can be obtained between carcinogenic activity and
sebaceous gland suppression for many ROM's (e.g., MCA, DMBA, BaP, DBahA,
benz[a]anthracene), such an effect is neither necessary nor sufficient for
carcinogenesis. However, workers exposed to POM-containing materials such as
coal tar, mineral oil, and petroleum waxes are known to show chronic derma-
139 452
titis, hyperkeratoses, etc., ' and the possible significance of these
skin disorders to human cancer is not known.
In female animals, ovotoxicity has been reported to result from
administration of POM. DMBA was shown to cause the destruction of small
6-55
-------
oocytes and reduced the numbers of growing and large oocytes after oral
140
administration to mice. More recently it was reported that destruction of
primordial oocytes in mice by injection of MCA was correlated with the
genetic capability for POM-induced increases in ovarian aryl hydrocarbon
141
hydroxylase activity. Thus, it is apparent that ovarian metabolism of POM
and ovotoxicity are linked and are under genetic control.
A toxic reaction which is apparently unique to DMBA is the selective
destruction of the adrenal cortex and induction of adrenal apoplexy in
142
rats. Adrenal apoplexy, increased adrenal gland weight, and increased
adrenal hemoglobin content were induced in female Sprague-Dawley rats by a
single intragastric dose of 30 mg DMBA. The same amount of adrenal damage
could be produced by a 5 mg dose of the principal DMBA oxidative metabolite,
7-hydroxymethyl-12-methylbenz[a]anthracene. Other DMBA metabolites produced
no adrenal damage, thus indicating that a specific reactive intermediate may
be responsible for this phenomenon.
6.3.2 Subchronic and Chronic Exposures
Repeated injections of benz[a]anthracene derivatives to mice and rats
have produced prominent changes in the lymphoid tissue. Early investigators
administered DBahA, benz[a]anthracene, and anthracene to mice in weekly sub-
143
cutaneous injections for 40 weeks. Each animal received a total dose of
10 mg, and 19 to 38 mice were treated with each of the three hydrocarbons.
Analysis of lymph glands removed at weekly intervals showed an increase of
reticulum (stem) cells and an accumulation of iron in all treatment groups.
Lymphoid cells were reduced and lymph sinuses dilated in all groups, although
6-56
-------
these effects were more common in mice receiving DBahA. The weights of the
spleens in mice treated with DBahA were significantly reduced in comparison
to controls and those animals receiving benz[a]anthracene or anthracene.
A more detailed study of the subchronic effects of DBahA on lymph nodes
144
of male rats was reported in 1944. Subcutaneous injections given five
times weekly for several weeks caused normal lymph nodes to undergo hemo-
lymphatic changes. These changes are characterized by the presence of
extravascular red blood cells in the lymph spaces and the presence of large
pigmented cells. These changes were not observed by Hoch-Ligeti in mice,
but could be produced in rats by BaP and MCA in addition to DBahA. The non-
carcinogen, anthracene, on the other hand, did not produce as dramatic a
change in the lymph nodes of rats.
Since the most likely route of environmental exposure to POM is by
inhalation, there is considerable interest in its effect on the respiratory
epithelium. In light of the concern over POM-induced neoplasms of the
respiratory tract (see Section 6.5), an understanding of early pathological
alterations and pre-neoplastic lesions in this tissue has particular signifi-
cance.
Repeated intratracheal applications of DMBA or BaP (100 pg in gelatin
or mineral oil) to male and female hamsters over periods from 4 to 16 months
resulted in significant mortality (60 percent) before the appearance of lung
145
tumors. All groups of treated hamsters commonly displayed acute pneumonia
and chronic pneumonitis. The latter condition was associated with a prolif-
eration of large squamoid alveolar cells, which occasionally formed tissue
6-57
-------
masses filling one or more air spaces. As this proliferating alveolar
epithelium began to destroy the adjacent reticulin framework, the lesions
were considered to be malignant. Damage to the trachea occurred in prac-
tically all animals and consisted of mucosal and submucosal chronic exuda-
tive inflammation, ulceration, hyperplasia of reserve cells, squamous meta-
/
plasia, and squamous cell carcinoma (in the DMBA group only).
In a subsequent study conducted by Reznik-Schiiller and Mohr, BaP-
induced damage to the bronchial epithelium of Syrian golden hamsters was
examined in detail using semi thin (1 ym) tissue sections. Animals were
treated intratracheally with 0.63 mg BaP (total dose) dispersed in a solu-
tion of saline, dodecylsulfate, Tris-HCl, and EDTA once weekly for life.
Animals were serially sacrificed at weekly intervals following the first
month of treatment, and semi thin sections of the bronchi were examined
microscopically. In the first animals sacrificed, minimal focal cell pro-
liferation in the area of the basement membrane was evident in the bronchial
epithelium. By 7 weeks, cytoplasmic vacuolization of both goblet and cilia-
ted cells had occurred. Epithelial and basal cell proliferation continued
for several weeks and led to the formation of three- to four-layered hyper-
plastic regions by the llth week. Epithelial cells began to penetrate
through the basement membrane by the 12th week, and within 2 more weeks the
bronchial epithelium began to continuously grow into the surrounding lung
tissues. Microscopic bronchogenic adenomata had developed by the 20th week.
These tumors consisted primarily of ciliated cells and goblet cells, with
only a few basal cells present. The apparently small amount of basal cell
6-58
-------
proliferation may have been the reason why squamous metaplasia was not
observed by the time the experiment had ended after 21 weeks. Squamous
metaplasia and keratinization were found in the trachea, but not in the
bronchi, after 21 weeks of treatment. Although these investigators found no
increase in the number of alveolar macrophages, others have reported numer-
ous alveolar macrophage responses in BaP-treated hamsters as well as focal
areas of accumulated macrophages containing a yellow pigment. ' '
Epithelial proliferation and cell hyperplasia in the absence of necrosis
and/or marked inflammation is a common observation in the tracheobronchial
mucosa of animals directly exposed to carcinogenic POM. This phenomenon was
shown with repeated exposures of DB[c,g]C, DMBA, BaP, and dibenzo[a,i]pyrene
in hamsters.10'149'146'150'148
6.3.3 Effects on the Immune Systems
Numerous investigators have demonstrated that carcinogenic POM can
produce an immunosuppressive effect. This action was first observed by
Malmgren and coworkers in 1952 using high doses of MCA and DB[a,h]A in
mice. Subsequent studies established that single carcinogenic doses of MCA,
DMBA, and BaP caused a prolonged depression of the immune response to sheep
1 S7 1S^
red blood cells. ' Noncarcinogenic hydrocarbons such as benzo[e]pyrene
and anthracene reportedly had no immunosuppressive activity. In a recent
review on immunosuppression and chemical carcinogenesis, substantial evidence
was presented to indicate that the degree of immunosuppression was correlated
with carcinogenic potency for I
reactions are affected by POM.
154
with carcinogenic potency for POM. Both cell-mediated and humoral immune
6-59
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The cellular mechanism of immunosuppression by POM has been investigated
155
by several groups of researchers in recent years. Rowland and Hurd re-
ported that spleens from DMBA-treated (1 mg in 0.2 ml corn oil by single
intramuscular injection) mice are deficient in bone marrow-derived lympho-
cytes but not in thymus-derived lymphocytes. Since the marrow-derived cells
are short-lived and quickly replaced by the rapidly dividing marrow-derived
lymphocyte population, it was suggested that DMBA preferentially attacked
this population. Because immune capacity was determined only 7 days after
DMBA treatment, an effect on the long-lived thymus-derived cells could
probably not have been seen. This explanation was supported by data from
Yamashita and coworkers who analyzed the effects of DMBA on marrow- and
thymus-derived lymphocytes of mice up to six weeks after exposure. In these
studies, a bimodal immunosuppressive effect was obtained; a short-acting
depression of marrow-derived cells and a long-lasting depression of thymus-
derived cells could be seen.
In contrast to the results presented above, long-term (6 to 9 months)
exposure of guinea pigs to MCA (4 mg every 4 weeks) resulted in no sustained
suppression of cell-mediated or humoral immunity. These investigators
T
suggested"that immunosuppression resulting from exposure to POM is a function
of its general toxic effect, but does not persist long enough to be involved
in neoplastic induction.
The importance of an intact immune system in resisting the effects of
chemical carcinogens is debatable. Immunosuppression induced by thymectomy
or treatment with antilymphocyte serum has a more dramatic effect on carcino-
154
genesis induced by viruses than that induced by chemicals. Moreover, a
6-60
-------
dissociation between the carcinogenic and inmiunosuppresive effects of MCA
l *ift
was shown at low doses in C3H mice/ That is, single doses of MCA less
than 0.1 mg induced subcutaneous sarcomas in many treated animals in the
absence of serum antibody responses to sheep red blood cells. In addition,
one-time administration of MCA intragastrically (0.2 to 2.0 mg) to C3H mice
was carcinogenic but had no effect on immune responses.
6.3.4 Effects on Enzyme Activity
The metabolism of most lipophilic xenobiotics is catalyzed by the
microsomal mixed-function oxidase system. ' One of the oxidases in this
system, designated aryl hydrocarbon hydroxylase (AHH), is responsible for
both the detoxification and metabolic activation of POM. AHH is the term
used for the multiple monooxygenase systems that metabolize BaP to fluores-
cent phenols. The activity of AHH can be induced (i.e., enhanced) by sub-
strate and non-substrate xenobiotics, either in vivo or in cultured mam-
59
malian cells. This enzyme can be found in 90 percent of the tissues
159
examined in rats, mice, hamsters, and monkeys. These include liver, lung,
testis, muscle, bone marrow, skin, brain, intestine, placenta, and cultured
mammary gland, lymphocytes, leukocytes, and monocytes. " The ultimate
cytotoxicity and/or careinogenicity of POM may in large part be determined by
the level of AHH activity in the organ of exposure. The important role of
AHH in the susceptibility to POM-induced damage results from the fact that
POM must usually be metabolized to reactive intermediates before toxicity can
be expressed. In this regard, it has been shown that cell lines which were
highly resistant to the toxic effects of BaP were also lacking in AHH activi-
ty.159
6-61
-------
For more than 20 years it has been known that ROM's such as BaP, DBahA,
59
MCA, and chrysene are potent inducers of AHH in liver microsomes. Thus it
is not surprising that cigarette smoke has a marked stimulatory effect on
AHH in lung, liver, intestine, and human placenta. Intragastric administra-
tion of MCA increases AHH activity of rat liver, kidney, and intestinal
15
mucosa, and intraperitoneal injection increases AHH activity in rabbit
bone marrow. In cultured hamster fetus cells, Nebert and Gelboin
established that AHH activity was readily induced by carcinogenic and non-
carcinogenic POM. Maximum enzyme induction was generally produced with a POM
concentration of 10 yM in the culture medium (Table 6-9). AHH inducibility
in animals is under genetic control, and it can be shown that noninducible
strains of mice are also resistant to the carcinogenic effect of subcuta-
l fift
neously injected MCA.
KeHerman and coworkers have used human lymphocytes to demonstrate
that AHH inducibility by MCA may also be under genetic control in humans,
and further that the extent of AHH induction may correlate with suscepti-
bility to chemical carcinogenesis. These investigators observed a virtual
absence of lung cancer among patients having little capacity for AHH induc-
tion. Therefore, it may be postulated that genetic heterogeneity with
regard to microsomal enzyme induction might account for the apparently
inherited susceptibility (i.e., familial clustering) for bronchogenic car-
cinoma. However, difficulty in reproducibility of the assay for AHH induci-
bility in lymphocytes and monocytes, as well as large temporal and inter-
individual variability have prevented an evaluation of its genetic control
6-62
-------
Table 6-9. ARYL HYDROCARBON HYDROXYLASE INDUCTION IN CELL CULTURE
167
Compound0
Amount of compound
medium
in AHH activity,
units^/mg protein
Control
Benz[a]anthracene
8-Methyl benz[a]anthracene
1 0-Methyl benz[a]anthracene
7 , 1 2-Dimethyl benz[a]anthracene
3-Methyl chol anthrene
Di benz[a ,c]anthracene
Di benz[a , h]anthracene
Chrysene
Pyrene
none
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
100 yM
10 yM
1 yM
10
118
188
56
34
8
8
65
80
33
78
84
25
3
38
29
2
67
10
4
21
57
2
59
26
27
57
22
3 Compounds tested as inducers for hamster fetus cell aryl hydrocarbon
hydroxylase system. The cells were exposed to various concentrations of
. each compound for 16 hours.
One unit of enzyme activity is defined as that catalyzing the production,
during the 30 minute incubation period, of an amount of fluorescence
equivalent to that of 1 nmole of 3-hydroxybenzo[a]pyrene.
6-63
-------
in humans. ' ' ' At the present time, attempts to confirm several
aspects of Kellerman's studies have been unsuccessful.
Recent studies with other human tissues (liver and placenta) have
provided important new data concerning the carcinogen-metabolizing capacity
173
of man and its implications for cancer susceptibility. Conney and coworkers
examined individual differences in the metabolism of drugs and carcinogens
in human tissues, and have identified drugs which may serve as model sub-
strates to provide an indirect index of carcinogen metabolism for man. The
rates of antipyrene, hexobarbital, and zoxazolamine hydroxylation in human
autopsy livers were highly, but not perfectly, correlated with the rates of
BaP metabolism. In human placenta, an almost perfect correlation was found
between zoxazolamine hydroxylase activity and BaP hydroxylase activity.
Thus, metabolism of BaP and zoxazolamine by human placenta occurs by the
same enzyme system(s) or by different enzyme systems under the same regula-
tory control. BaP and zoxazolamine hydroxylase activities were also
shown to be significantly enhanced in placentas obtained from women who
smoked cigarettes. The lack of perfect correlations for the hepatic metabo-
lism of BaP and certain drugs in many subjects indicated the presence of
several monooxygenases in human liver which catalyze the oxidative metabo-
lism of these compounds. Furthermore, large inter-individual differences
exist in the capacity of humans to metabolize foreign chemicals both ij^
vitro and in vivo. Further studies showed that 7,8-benzoflavone markedly
stimulated the hydroxylation of BaP, antipyrene, and zoxazolamine in human
liver samples, but with a wide variation in magnitude among different samples.
6-64
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These results suggested the presence of multiple monooxygenases or cytochrome
P-450's in the different liver samples. Moreover, 7,8-benzoflavone did
not affect the hydroxylation of coumarin or hexobarbital, thereby indicating
the existence of different monooxygenases for the metabolism of these sub-
strates. Multiple forms of cytochrome P-450 have been shown in the livers
of rats, rabbits, and mice, but not thus far in humans. More importantly,
however, MCA is a potent inducer of BaP hydroxylase activity in rats but
does not stimulate antipyrine hydroxylase; clearly suggesting that metabolism
of POM in rodents may be regulated by different enzyme systems than in
humans.
In contrast to the apparent multiplicity of cytochrome P-450-dependent
enzyme systems for the oxidative metabolism of POM in man, a single epoxide
hydrase with broad substrate specificity may be present in human liver. '
Because the hydration of arene oxides may lead to the formation of dihydro-
diol carcinogen precursors, the capacity of different humans to metabolize
epoxides may affect cancer susceptibility. It is not known, however, if
enhanced dihydrodiol formation would increase cancer risk or decrease cancer
risk.
178
Thomson and Slaga did not obtain a correlation of AHH induction with
skin-tumor-inducing ability in mice for a series of unsubstituted hydrocar-
bons. Nevertheless, the highest AHH enzyme activity was found in the epi-
dermal layer of the skin, which is the major point of contact with many
environmental chemicals. These results may be interpreted to indicate that
a chemical carcinogen may not necessarily induce its own bioactivation, but
6-65
-------
instead can be transformed into a reactive intermediate by virtue of increased
AHH activity stimulated by other non-carcinogenic compounds.
Due consideration must also be given to the fact that, in addition to
the initiation of resting cells by a chemical carcinogen, a promotion phase
1 yg
involving cell proliferation is also involved in skin carcinogenesis.
Therefore, although certain aromatic hydrocarbons are effective enzyme
inducers, their bioactivated metabolites may function only as an initiator
having no promoting ability. A potent complete carcinogen, however, will be
transformed not only into a powerful tumor initiator but will also be able
to interact with cellular membranes, alter genetic expression, and ultimately
cause irreversible cell proliferation. These observations raise certain
doubts concerning the validity and/or reliability of equating enzyme induci-
bility with carcinogenic potential for chemical agents. Further reinforce-
180
ment of this opinion has been provided by Shulte-Hermann who showed that
cell proliferation is not a direct result of enzyme induction, even though
both processes are normally coupled.
The further possibility that the genetics of AHH inducibility is organ-
dependent rather than strain-dependent in animals has important implications
181
for evaluating susceptibility to POM-induced cancers. Most significant is
the demonstration that pulmonary AHH may be inducible in all strains of mice,
regardless of the inducibility of hepatic AHH. Since the respiratory
epithelium represents a primary portal of entry for POM, AHH activity which
is induced in this tissue may bear importantly on susceptibility to malignancy.
6-66
-------
182
Enzyme induction by POM is not limited to AHH. Owens recently
demonstrated that MCA can induce hepatic UDP-glucuronosyltransferase activity
in certain inbred strains of mice. This enzyme catalyzes the conjugation
and excretion of POM substrates after they have first been oxygenated by
AHH. The induction of this transferase activity and that of AHH was apparently
regulated by a single genetic locus. However, transferase inducibility does
not depend on AHH levels, but rather is stoichiometrically related to the
concentration of a specific and common cytosolic receptor regulating both
enzyme induction processes. Owens further demonstrated that AHH activity
can be fully induced in certain mouse strains (e.g., by 2,3,7,8-tetrachloro-
dibenzo-£-dioxin) without greatly enhancing the transferase activity.
Earlier studies had established that chrysene and chlorpromazine were potent
inducers of AHH activity while having little effect on transferase activi-
183
ty. Subsequent exposure to carcinogenic POM (i.e., MCA) could lead to
maximal oxidative metabolism but little transferase-catalyzed removal of
metabolites by glucuronic acid conjugation. This situation would be exacer-
bated by the fact that metabolites of MCA are incapable of further inducing
the transferase activity. This effect may have considerable toxicologic
significance in that highly reactive epoxides of POM formed by the action of
AHH under these circumstances may not be adequately removed by glucuronida-
tion. Thus, one must consider the total exposure to all environmental
agents and their possible effect on critical enzymatic processes before
attempting to assess the toxicologic impact of exposure to a specific POM.
In summary, there is a need to further explore the relative effects of
6-67
-------
enzyme induction on the metabolic activation of chemicals to toxic products
versus metabolism of chemicals via detoxification pathways.
6-68
-------
6.4 MUTAGENESIS
It is presently believed that fundamental similarities exist between
the molecular mechanisms of mutagenesis and carcinogenesis induced by
184
POM. These assumptions are based on the theory that highly electrophilic
metabolites (e.g., epoxides) are generated from POM by the action of micro-
49
somal mixed-function oxidase enzymes. These reactive intermediates are
capable of binding to DMA and/or other critical cellular macromolecules
185
presumably to initiate a mutagenic or carcinogenic transformation. The
concept that carcinogenesis is an expression of an alteration in the genetic
material of a treated cell (i.e., somatic mutation) implies that a relation-
ship exists between mutagenesis and carcinogenesis. Therefore, it is
believed that an investigation of the mutagenicity of POM: (1) may be
predictive of carcinogenic potential, (2) may help elucidate the mechanism
for malignant transformation in certain systems and (3) may indicate the
presence of a potential threat to human health posed by a particular POM.
6.4.1 In Vitro Studies
6.4.1.1 Microbial systems—Early attempts to demonstrate mutagenicity by
POM failed because of the inability of microorganisms to metabolize these
99
compounds to reactive derivatives. The addition of subcellular prepara-
tions and the development of sensitive tester strains of Salmonella typhi-
murium have resulted in a mutagenesis test system (Ames assay) now receiving
wide application as a powerful screening tool for evaluating environmental
186
agents. The most commonly employed tester strains of S. typhimurium
used when working with POM are those designated TA98, TA1537, and TA1538.
6-69
-------
All of these strains are histidine-dependent and which can be reverted to
histidine independence by mutation. When a large series of polycyclic
aromatics was tested in this system, a high correlation was found between
carcinogenicity in mammals and mutagenicity to S. typhimurium in the presence
of microsomes. When a limited number of noncarcinogens were tested, the
number of revertant colonies produced was typically less than 0.01 revertants
per nmol of test substance. Mutagenicity in the Salmonella/microsome
system displayed a high correlation with carcinogenicity. Teranishi and
187
coworkers also found that a quantitative correlation existed between
carcinogenicity and mutagenicity of seven polycyclic hydrocarbons when
strain TA1538 was tested using rat liver enzymes.
In discussing the significance of the Salmonella/microsome assay,
188
McCann and coworkers believed that their results supported the somatic
mutation theory of cancer, and that a common link between mutagenesis and
carcinogenesis by chemicals is the ability to produce DNA damage.
In Japan, a data base has been developed on 60 chemicals (POM and non-
POM) which correlates mutagenic activity in various strains of S. typhimurium
189
in vitro with carcinogenicity in vivo. With the use of an activating
system from liver microsomes and the introduction of the R-factor plasmid
into S. typhimurium for increased sensitivity, a strong correlation between
mutagenicity and carcinogenicity was obtained. Studies conducted in the
United States on 102 compounds tested in vitro using S. typhimurium generally
190
confirm the high capability of this system to detect carcinogens. In
addition, a further improvement in the detection of carcinogens could be
6-70
-------
obtained by combining the results from Salmonella with those from polymerase
A-deficient E. coli. On the other hand, the use of S. typhimurium in vivo
(host-mediated assay) was considerably less reliable for the detection of
190
carcinogenic hydrocarbons and aromatic amines.
In recent studies, the Ames Salmonella test system has been employed
to assess the mutagenicity of organic extracts of airborne particulate
204
pollutants. Although the total extract displayed marked mutagenicity,
assays of various subfractions of the extract indicated that much of the
activity is due to compounds other than polycyclic hydrocarbons and which
do not require metabolic activation. These results, which are supported by
data from in vivo studies (see Section 6.5.1), indicate that caution must
be exercised in attributing the mutagenic/carcinogenic effects of air
pollutants solely to the presence of polycyclic hydrocarbons. The recent
demonstration of the mutagenicity of quinoline and its 5-hydroxy- and 8-
hydroxy-derivatives in the Ames assay emphasizes the potential role of
205
nitrogen-containing ROM's as hazardous air pollutants.
Several years ago a joint program was undertaken by scientists at the
National Institute of Arthritis, Metabolism, and Digestive Diseases, and at
the Department of Biochemistry and Drug Metabolism of Hoffmann-LaRoche,
Inc., to determine the structures of BaP metabolites that are responsible
for its mutagenicity and carcinogenicity. It had been previously demonstra-
191
ted that epoxides of carcinogenic POM are frameshift mutagens. In 1975,
127
it was established that the K-region BaP 4,5-oxide and non K-region BaP
192
7,8-diol (with metabolic activation) were more mutagenic than the parent
6-71
-------
compound in S. typhimurium strains TA TOO and TA1538. Subsequently, nearly
all of the possible primary oxidative metabolites of BaP were synthesized
and tested for mutagenicity.70'72'193'126'71 The results of these tests
have been recently reviewed ' ' and are summarized in Table 6-10. It
was emphasized that diol epoxide-1 ( (±)-78,8a-dihydroxy-9B,10e-epoxy-7,8,
9,10-tetrahydro BaP) is a very potent mutagen in S. typhimurium, and that
the BaP 7,8-diol-9,10-epoxides are likely candidates as the ultimate bio-
logically reactive metabolites of BaP. It was subsequently demonstrated
by these researchers that the mutagenicity of the optical enantiomers of
the diastereomeric BaP 7,8-diol-9,10-epoxides is highly stereospecific.
These results are of considerable significance in light of evidence indica-
ting that the in vitro metabolism of BaP is stereoselective, depending upon
i pc 9(")1
the source of the microsomes and conditions of the incubation. '
Further evidence implicating the obligatory role of epoxide inter-
195
mediates in the mutagenicity of BaP was reported by Oesch and coworkers.
They stated in support of this contention that: (1) epoxide hydrase inhibi-
tors potentiated BaP mutagenicity, even though epoxide hydrase activity is
necessary for the conversion of BaP-oxides to BaP-dihydrodiols prior to
formation of the diol-epoxide; and (2) homogeneous epoxide hydrase prevented
mutagenicity even though it is required for the formation of diol epoxides
from BaP-oxides.
In this same regard, Levin and coworkers reported on extensive
studies into the role of epoxide hydrase in the metabolic activation of BaP
to mutagenic products. The addition of purified epoxide hydrase decreased
6-72
-------
Table 6-10. COMPARISON OF INHERENT MUTAGENIC ACTIVITY OF THIRTY BaP DERIVATIVES IN Salmonella
C*J
typhimurium TA98 AND
Compound
Diol epoxide-1
Diol epoxide-2
H4 9,10-epoxide
H« 7,8-epoxide
BaP 4,5-oxide
BaP 7,8-oxide
BaP 9,10-oxide
BaP 11,12-oxide
6-HOBaP
12-HOBaP
1-HOBaP
3-HOBaP
2-, 4-, 5-, 7-, 8-, 9-, 10-, 11-HOBaP
BaP 1,6-, 3,6-, 6,12-, 4,5-, 11 ,12-quinone
BaP 4,5-, 7,8-, 9,10-, 11 ,12-dihydrodiol
BaP
IN CHINESE HAMSTER V79 CELLSa 69
Relative °i
Strain TA98
100
35
95
10
20
1
1
0.5
5
1.5
0.5
0.5
<0.1
<0.1
<0.1
<0.1
i activity
V79
40
100
40
0.2
1
<0.1
<0.1
1
0.3
<0.1
0.1
<0.
<0.
<0.
<0.
<0.
The relative percent mutagenic activities are approximations since the data were compiled from
several separate studies conducted at different times. In some experiments, BaP 7,8-dihydrodiol
was 0.1-0.4% as active as diol epoxide-2 in V79 cells.
Abbreviations used: BaP, benzo[a]pyrene; 1-HOBaP, l-hydroxybenzo[a]pyrene; 2- to 12-HOBaP,
other BaP phenols; BaP 1,6-quinone, benzo[a]pyrene 1,6-quinone; BaP 3,6-quinone, BaP 4,5-
quinone, BaP 6,12-quinone, and BaP 11, 12-quinone, other BaP quinones; BaP 4,5-dihydrodiol,
trans-4,5-dihydroxy-4,5-dihydrobenzo[a]pyrene; BaP 7,8-, 9,10- and 11, 12-dihydrodiol, other
dihydrodiols of BaP; BaP 4,5-oxide, benzo[a]pyrene 4,5-oxide; BaP 7,8-, 9,10- and 11,12-
oxide, other BaP oxides; diol epoxide-1 (+)-7B,8a-dihydroxy-98,106-epoxy-7,8,9,10-tetrahydro BaP;
diol epoxide-2, (jO-7B,8a-dihydroxy-9a,10a-epoxy-7,8,9,10-tetrahydro BaP; H4 9,10-epoxide, 9,10-
epoxy-7,8,9,10-tetrahydro BaP; H. 7,8-epoxide, 7,9-epoxy-7,8,9,10-tetrahydro BaP.
-------
mutation frequency in S. typhimurium by 30 to 50 percent. However, muta-
genicity could not be completely abolished by high levels of epoxide hydrase.
Evidence showing that mutations induced by BaP 4,5-oxide could be reduced
90 percent by the addition of very small quantities (units) of epoxide
hydrase argued against a central role for the K-region epoxide. Further-
more, these researchers established that epoxide hydrase converts BaP 7,8-
oxide to BaP 7,8-dihydrodiol, which is further metabolized by the monoxy-
genase system to the highly mutagenic BaP diol epoxides. Moreover, these
proposed ultimate mutagens were not substrates for epoxide hydrase, and
therefore were not affected by addition of the purified enyzme.
6.4.1.2 Somatic cells in culture—Current methods of identifying chemically
induced mutants from cultured mammalian cells rely upon the mass selection
of variants resistant to the cytotoxicity of certain drugs (e.g., 8-aza-
guanine, 6-thioguanine, ouabain). Among the most suitable cells for this
type of study are Chinese hamster cell lines, particularly V79 cells derived
from male lung tissue. However, V79 cells do not have the capacity for
metabolic activation of POM.197
I go
In 1974, Huberman and Sachs reported a successful system for cell-
mediated mutagenesis which combines V79 cells for the identification of
mutants and lethally irradiated rodent embryo "feeder" cells for the meta-
bolic activation of test chemicals. Mutagenicity was obtained with DMBA,
MCA, and BaP at rates which correlated with their respective carcinogenic
potentcies. Large numbers of 8-azaguanine-resistant mutants were produced
by treatment with as little as 0.1 yg/ml (Table 6-11). The non-carcinogen
benz[a]anthracene produced no mutations in this system.
6-74
-------
Table 6-11. MUTAGENICITY OF CARCINOGENIC HYDROCARBONS TO CHINESE HAMSTER V79 CELLS CO-CULTIVATED
WITH SYRIAN GOLDEN HAMSTER EMBRYO CELLSa 198
Con
Treatment
Solvent
7 , 1 2-Dimethyl benz[a ]anthracene
-lj 3-Methylcholanthrene
in
Benzo[a]pyrene
Benzo[a]pyrene
a The cul tures were treated for 2 days
and seeded to determine the cloning
resistant mutants: co-cultivation wa
centration
0
0.1
0.1
0.1
1.0
with carcinogenic
efficiency of the
s with 2 x 10-6 ir
Number of V79
x 10'6
3.0
1.3
2.3
2.7
1.9
hydrocarbons.
V79 cells and
radiated qolde
Cloning efficiency
• of the V79 cells,
99
7
78
89
15
Number of
8-azaguanine-
resistant
mutants/105
survivors
7
270
110
70
320
The cells were then trypsinized
the frequency of 8-azaguanine-
n hamster cells oer Petri dish.
-------
199
Huberman and Sachs subsequently conducted expanded studies on the
mutagem'city of ten polycyclic hydrocarbons at three different genetic loci
in hamster cells. V79 cells (together with metabolizing cells) were used
for identification of ouabain- and 8-azaguanine-resistant mutants induced
by these polycyclics. The induction of temperature-resistant mutants was
also examined by using Chinese hamster ovary cells derived from a clone of
temperature-sensitive cells. Tables 6-12 and 6-13 summarize their results
and indicate that DMBA was consistently the most potent mutagen tested,
having significant activity at concentrations as low as 0.01 yg/ml.
The V79 cell system without the addition of metabolizing cells has
been used to identify structures which may be the ultimate mutagenic/carcino-
genic metabolites of BaP.70>66'72>71>69>67>75 Numerous oxidative metabolites
of BaP were surveyed, and the stereoisomeric BaP 7,8-diol-9,10-epoxides
(diol expoxides 1 and 2) were found to be highly mutagenic (Table 6-10).
The very short half-life (30 seconds) for diol epoxide 1 in tissue culture
medium made comparisons of activity between the two diol epoxides very
difficult, however. Nevertheless, the high mutagenicity of diol epoxides 1
and 2, coupled with the high carcinogenicity of their precursors, BaP 7,8-
dihydrodiol and BaP 7,8-oxide, suggests a strong formal relationship between
mutagenicity and carcinogenicity insofar as a common pathway of metabolic
activation is concerned.
Modifications of the V79 cell-mediated mutagenesis system have recently
been developed which involve new means of metabolizing test compounds.
Newbold and coworkers combined baby Syrian hamster kidney cells (BHK21)
6-76
-------
Table 6-12. INDUCTION OF OUABAIN- AND 8-AZAQUANINE-RESISTANT MUTANTS BY DIFFERENT CHEMICAL
crt
i
Treatment
Solvent
Pyrene
Phenanthrene
Chrysene
Benz[a]anthracene
Dibenz[a,c]anthracene
Dibenz[a,h]anthracene
7-Methyl benz[a]anthracene
3-Methyl chol anthrene
Benzo[a]pyrene
7 , 1 2-Dimethyl benz[a]anthracene
Cloning
efficiency,
%
92*
94*
79*
85*
92*
95*
79*
61*
49**
41 1
38*
47**
27t
21*
50 §
2**
Ouabain-resistant
mutants
per 10^ survivors
1
1
1
2
2
3
4
24
14
38
108
18
45
121
22
66
8-Azaguanine-
resistant
mutants per
10$ survivors
6
5
8
9
9
22
17
75
72
152
366
54
128
425
41
281
3 The cells were treated for 2 days with the polycyclic hydrocarbons with *1 ug/ml, tO.3
**0.1 pg/ml, or §0.01 ug/ml. After treatment there were with 0.01-0.1 pg/ml of DMBA, 0.3-1 ug/ml
of BaP, and 0.3-1 pg/ml of MCA, 1.0 to 2.5 x 106 V79 cells per petri dish. In all other cases,
there were 2.7 to 3.6 x 106 V79 cells per petri dish.
-------
Table 6-13. INDUCTION OF TEMPERATURE-RESISTANT MUTANTS IN CHINESE HAMSTER
OVARY TMPERATURE-SENSITIVE CELLS BY DIFFERENT CHEMICAL
CARCINOGENS 199
Concen-
tration,
Treatment yg/ml
Solvent
Pyrene
Phenanthrene
Benz[a]anthracene
Benz[a]pyrene
3-Methyl chol anthrene
7 , 1 2-Dimethyl benz[a]anthracene
0
1.0
1.0
1.0
0.1
0.3
1.0
0.1
0.3
1.0
0.01
0.1
Cloning
efficiency,
93
88
88
78
67
45
9
78
32
10
65
3
Temperature-
resistant
mutants per
10^ survivors
0.6
0.9
0.7
0.7
21
56
170
20
46
125
51
494
Three days after treatment with the polycyclic hydrocarbons at 34°, the cells
were seeded to determine the cloning efficiency of the ts cells and the fre-
quency of temperature-resistant mutants. For selection of temperature-resis-
tant mutants, the ts cells were shifted from 34° to 39°, 3 days after cell
seeding. At the time when the cells were seeded for cloning efficiency and
the frequency of mutations, there were after treatment with 0.01-0.1 yg/ml of
DMBA, 0.3-1 yg/ml of BaP or MCA, 0.5 to 1.9 x 106 ts cells per petri dish.
In all other cases, there were 2.1 to 2.3 x 10& ts cells per petri dish.
6-78
-------
for metabolism of POM with V79 cells for detection of ouabain- and 8-
azaguanine-resistant mutants. This system produced binding reactions
between DNA and BaP or 7-methylbenz[a]anthracene which accompanied mutagene-
sis in the same cells and were typical of those which occur in vivo or in
primary cell cultures. Chromatographic analyses of the BaP-DNA reaction
indicated that BaP 7,8-diol-9,10-epoxide was involved in the binding inter-
action. These results strengthened the argument which supports the role of
diol epoxides in BaP-mediated mutagenesis and carcinogenesis. Furthermore,
the cell-mediated mutagenesis system as modified and validated by Newbold
et al_. is proposed as a convenient and representative mammalian cell
screening system which may prove to be superior to mutagenicity assays with
S. typhimurium in providing a rank-order correlation with carcinogenic
potency in mammals (e.g., Iball index). However, additional screening of
polycyclic hydrocarbons and aza-arenes is required before a definitive
conclusion may be drawn for these classes of carcinogens.
The current belief that neoplastic transformation may arise from a
chemically induced somatic mutation was made more convincing by the recent
202
studies of Huberman and coworkers. They demonstrated for the first time
that BaP and BaP 7,8-dihydrodiol can induce both neoplastic transformation
and mutagenesis (ouabain resistance) in the same normal diploid hamster
embryo cells. A ratio between transformation and mutagenesis for ouabain
resistance was only about 20:1.
A further adaptation of the V79 cell-mediated mutagenesis system has
been employed which provides metabolic activation by rat liver homogenates
6-79
-------
203
containing microsomes and cofactors. Mutants of V79 cells were detected
by their resistance to the cytotoxic effects of 6-thioguanine. The muta-
genic activity of BaP, MCA, DMBA, and benz[a]anthracene in this system
showed a limited correlation with their respective carcinogenic potencies.
With DBahA and DBacA, an inverse relationship between mutagenicity and
carcinogenicity was obtained. Such a relationship has also been shown for
186
the dibenzanthracenes when tested in the Salmonella/microsome assay.
Although mammalian cell-mediated mutagenesis is hindered because it is
technically more difficult, time-consuming, and thus permits fewer compounds
to be screened, there are advantages over the microbial system: (1) bacteria
indicate reverse mutations and V79 cells indicate forward mutations, the
latter type of mutation being more relevant to the process of neoplastic
transformation; and (2) cells can be employed which are the same kind as
found in the actual targets for mutagenesis and carcinogenesis induced by
chemicals.
The analysis of chromosomal aberrations and sister chromatid exchanges
(SCE's) is often recommended as a screening technique for potential mutagens
and carcinogens. Several investigators have examined the effects of POM on
the chromosomes of mammalian cells. Early studies indicated that variations
in chromosome number and structure may accompany tumors induced by BaP,
206
MCA, and DMBA in the rat, mouse, and hamster. However, in cultured
human leukocytes exposed to DMBA, chromosome damage was not the same as
that produced in hamster cells. Although it is argued that chromosome
207 208 209 107
changes in POM-induced tumors are non-random, ' others ' claim
6-80
-------
that detectable chromosome changes are not specific for the carcinogenic
agent nor are they a prerequisite for neoplastic growth. Moreover, it was
shown that an increased rate of SCE's could be produced by BaP in cultured
210 211
human lymphocytes ' but this was not correlated with different rates
210
of BaP metabolism; a surprising result in light of the known importance
of metabolic activation for BaP mutagenicity. BaP-induced SCE's rates did
not differ between lymphocytes taken from normal humans and those from
211
patients with lung cancer. In recent studies with cultured Chinese
hamster cells exposed to DMBA, BaP, and MCA, none of the chemicals produced
212
chromosome breaks and only DMBA could successfully induce SCE's.
Although it cannot be denied that POM causes chromosome damage, it is not
clear whether this effect may represent an epigenetic phenomenon which is
merely secondary to mutagenesis and neoplastic transformation. Furthermore,
in cases where a chemically-induced mutation is "silent" (i.e., neutral
amino acid substitutions), there is no reason to believe that detectable
chromosome damage should occur.
In recent comparisons of three cytogenetic tests: (1) induction of
chromosome aberrations, (2) induction of micronuclei, and (3) in vivo
induction of sister chromatid exchanges, the latter test proved to be the
213
most sensitive with carcinogenic polycyclic hydrocarbons. However,
positive results were also obtained with phenanthrene, and thus limits the
usefulness of sister chromatid exchange as a screening technique for carcino-
gen detection. BaP was positive in the sister chromatid exchange test, but
6-81
-------
weakly active in the chromosome aberration test, and negative in the micro-
nucleus test. On the other hand, DMBA was clearly positive in all three
tests. It was concluded that cytological tests do not provide reliable
correlations with all carcinogens tested and thus cannot be used alone in
mutagenicity/carcinogenicity evaluations.
Damage to the genome resulting from chemical insult can theoretically
214
also be detected by examining DMA repair. The suggestion that DNA
repair is applicable as a screening procedure for evaluating potential
chemical mutagens is based on the assumption that the level of DNA repair
synthesis in a cell reflects the extent of DNA damage produced by a chemical
3
Indeed, unscheduled incorporation of H-thymidine into nuclear DNA of
normal human cells exposed to epoxides of benz[a]anthracene and MCA has
214
been observed. However, since a metabolic activation system was not
present in this system, the parent hydrocarbons showed no activity. More
recent studies confirmed that K-region epoxides of BaP, DMBA, and DBahA
caused DNA damage in human skin fibroblasts which was repaired with the
215
same system used for repairing lesions induced by ultraviolet radiation.
As would be expected, the parent hydrocarbons exerted no effect. More
importantly, results were obtained which indicated that the DNA repair
process itself does not induce mutations, but rather that mutagenesis
occurs before the DNA lesion can be excised. In fact, there is no a priori
reason why POM should exert a mutagenic effect by inducing DNA lesions
which require any kind of repair synthesis at all.
6-82
-------
21 fi ?1 7 ?1 ft
Nevertheless, DNA repair synthesis in human fibroblasts, ' '
219 220
rat liver cells, and Chinese hamster V79 cells has been successfully
used for the detection of chemical carcinogens, including numerous ROM's.
However, the percentage of carcinogens giving positive results for DNA
repair is considerably less than in the cell transformation or microbial
mutagenesis assays. For example, benz[a]anthracene is negative in the DNA
repair assay utilizing human or rat liver cells, and BaP is only positive
in the DNA damage assay utilizing hamster V79 cells.
6.4.2 In Vivo Studies
6.4.2.1 Effects in somatic tissues—Tumors induced in vivo by POM are
commonly associated with chromosome abnormalities in the neoplastic cells.
In particular, sarcomas induced by DMBA, MCA, and BaP in the rat display
karyotype variations which were reportedly nonrandom and distinctly differ-
207- 221
ent from sarcomas induced by Rous sarcoma virus. ' The chromosome
patterns of DMBA- induced sarcomas were found to be identical with those
observed in primary rat leukemias and primary carcinomas of the auricular
223
o no
skin induced by DMBA. Consistent chromosome abnormalities in DMBA-
induced rat leukemias were first reported in 1967 by Kurita and coworkers.
These changes were characterized by trisomy in the C-l and/or A-6 chromosomes.
Earlier researchers reported that DMBA-induced leukemias in mice consistently
224
showed 41 chromosomes in the modal cell lines instead of the normal 40.
ppc
Sugiyama obtained an apparent relationship between sarcomatogenic potency
and the incidence of chromosome breakage in rat bone marrow cells produced
6-83
-------
by a single intravenous injection (50 mg/kg B.W.) of various benz[a]-
anthracene derivatives. It was apparent that benz[a]anthracene and several
non- or weakly-carcinogenic derivatives (7,12-diethyl-; 7-ethyl-; 12-ethyl-)
produced no elevation of chromosome aberrations, whereas the more active
carcinogens (7,12-dimethyl-; 6,8,12-trimethyl; 7,8,12-trimethyl) produced
aberrant metaphase cells.
Considerable evidence is also available to indicate that chromosome
alterations in POM-induced tumors in vivo are not consistent either in
frequency or in pattern. DMBA-induced tumors (fibrosarcoma, squamous
carcinoma, lymphosarcoma) of the uterine cervix in ICR mice revealed various
ope 997
karyotypic compositions. ' These tumors displayed diploid, aneuploid,
tetraploid, and octaploid chromosome constitutions. Tumors induced in mice
with MCA and dibenzo[a,i]pyrene also showed a wide variation in chromosome
pop ppq
constitution. ' Mice treated with 30 yg DMBA, a dose sufficient to
produce a 100% incidence of thymic lymphomas, did not reveal an excess of
230
chromosome abnormalities in bone marrow or thymus. Even at higher doses
(60 ug DMBA), the incidence of abnormal chromosomes did not significantly
differ from controls. Subcutaneous tumors in Syrian hamsters induced by
single injections of BaP (0.1 ng) or DMBA (0.1 mg), and cultured cell
populations derived from these tumors, failed to reveal common karyotypic
231
changes. Tumor cells had subdiploid, diploid, and hypotetraploid chromo-
some constitutions; further karyotype rearrangements occurred with subse-
quent growth jjrc v i tro.
6-84
-------
In humans, the presence of the "Philadelphia" chromosome in myeloid
leukemia appears to be the only example of a human chromosome abnormality
232
which is tumor-specific. In ROM-induced experimental tumors, lymphatic
leukemia in mice produced by DMBA also displays consistent chromosome
226
abnormalities. Beyond this common feature, convincing data have not
been presented to indicate that somatic cells exposed to POM may suffer
characteristic or reproducible damage to the genome. Instead, it is proposed
that random karyotypic mutants of transformed cells are selected in response
to growth pressures in the host environment (e.g., tissue necrosis, infec-
226
tion, anoxia, lack of nutrition).
Evidence has not been encountered in the published literature concern-
ing the likelihood of POM-induced somatic mutation in the absence of neo-
plastic transformation.
6.4.2.2 Effects in germinal tissues—The fruit fly, Drosophila melanogaster,
is commonly used as a whole animal submammalian genetic test system.
Assays can be conducted for gene mutations at specific loci and for small
deletions resulting in recessive lethal and visible mutations. Moreover,
Drosophila is apparently capable of activating compounds that are not
233
mutagenic or carcinogenic in their administered form. The use of Drosophila
has been suggested as a valuable bridge between microbial and mammalian
assays.238
A series of studies was undertaken by Fahmy and Fahmy which demonstra-
ted conclusively that carcinogenic polycyclic hydrocarbons were selectively
6-85
-------
mutagenic to the male germ cell line of Drosophila.234'235'236'237 Muta-
genicity was restricted to the t- and rRNA loci, yielding Minute (M) and
bobbed (bb) mutants, respectively. The activity of benz[a]anthracene, 7-
methylbenz[a]anthracene, MCA, DMBA, their epoxides, and some other deriva-
tives was determined in tests of both general mutagenicity on the whole
237
genome and specific locus mutability on the t- and rRNA genes. The
overall yield of sex-linked recessive lethals and visibles (general muta-
genicity test) was not significantly enhanced over control levels by the
parent hydrocarbons. However, several of the K-region epoxides of these
compounds were appreciably mutagenic (Table 6-14). In the specific locus
test, DMBA, MCA, and 7-methylbenz[a]anthracene produced significant increases
in the yields of phenotypic bb plus M and transmitted bb's, whereas benz[a]-
anthracene did not induce significant numbers of mutations on the RNA genes
(Table 6-15). Thus, mutagenicity was correlated with carcinogenicity,
although mutation frequencies did not vary with the dose employed. On the
other hand, the mutagenicity of the hydrocarbon epoxides on the RNA genes
was apparently dose-related.
It was significant to note that the K-region epoxides of all derivatives
tested displayed appreciable nonspecific mutagenicity as evidenced by the
high number of X chromosome mutations (lethals and visibles) in comparison
to controls and the parent hydrocarbons. An explanation was offered based
upon the high reactivity of electrophilic carbonium ions derived from the
epoxides which may react nonspecifically with nucleophilic centers in DNA,
especially the N-7 of guanine. The fact that the parent hydrocarbons
6-86
-------
Table 6-14. MUTAGENIC RESPONSE OF THE X CHROMOSOMES IN Drosophila
a 237
cr>
oo
Compound
Controls
Benz[a]anthracene
7-Methylbenz[a]anthracene
7,12-Dimethylbenz[a]anthracene
3-Hethylcholanthrene
5,6-Epoxy-5,6-dihydrobenz[a]anthracene
8,9-Epoxy-8,9-dihydrobenz[a]anthracene
5.6-Epoxy-5,6-dihydro-7-methylbenz[a]-
anthracene
5,6-Epoxy-5,6-dihydro-7,12-dimethyl-
benz[a]anthracene
ll,12-Epoxy-ll,12-dihydro-3-methylchol-
anthrene
Benz[a]anthracene-cis-5,6-dihydro-5,6-diol
7-Bromomethylbenz[a]anthracene
Dose,
mM
1.0
5.0
10.0
5.0
10.0
1.0
5.0
10.0
1.0
5.0
1.0
5.0
10.0
1.0
5.0
5.0
10.0
5.0
1.0
5.0
Gametes
tested
3707
A
3790
3473
1773
1703
1709
1833
1753
2399
B
1639
1606
1588
2623
1709
1725
1710
1779
1695
1891
1890
3260
Lethals
Number
6(1 )C
Parent hydrocarbons
9(2)
12
7(2)
5
4(2)
7(3)
5(1)
5(3)
Reactive derivatives
10)
12(2)
3
12
14(2)
3
11(1)
12(1)
12(1)
4
5
15(1)
Visibles
Per 103
1 6
2.4
3.5
3.9
2.9
2.3
3.8
2.9
2.1
0.6
7.5
1.9
4.6
8 2
1.7
6.4
6 7
7.1
2.1
2.6
4.6
Number
2
2
4(2)
3
0
0
0
0
2(1)
5(2)
4(1)
0
6(1)
7
KD
0
3
3
0
1
5
Per 103
0 5
0.5
1.2
1.7
0 0
0.0
0.0
0.0
0.8
3.1
2.5
0.0
2.3
4.1
0.6
0.0
1.7
1.8
0.0
0.5
1.5
Total X ,
mutations/10
2.2 + 0.8
2.9 + 0 9
4.6 +" 1 1
5.6 + 1.8
2.9 +" 1.3
2.3 + 1.2
3.8 7 1.4
2.9 + 1.3
2.9+1 1
3.7 + 1.5
10.0 + 2.5
1.9 + 1.1
6.9 + 1.6
12.3 +27
2.3 + 1.2
6.4 +_ 1.9
8.4 + 2.2
88 + 23
2.1 + 1 1
3.2 + 1 3
6.1 + 1 4
a General mutagenicity of various benz[a]anthracenes and their reactive derivatives as indicated by the yield of sex-linked
recessive lethals and visible;
b Response with administration vehicle only; 21 dimethylformamide in arachis oil
e Mosaic mutants are entered in parentheses.
-------
Table 6-15. MUTAGENIC RESPONSE OF THE BB LOCI IN Drosophila
a 237
en
i
00
00
Compound
Controls
Dose,
mM
Gametes
Phenotypic bb + M
Transmitted bb
tested Number Per 103 Number Per 103
124.724 156(7)c 1.3 + 0.1 45(1) 0.4 +.0.1
A. Parent hydrocarbons
Benz[a]anthracene
7 -Methyl benz[a]anthracene
7 , 1 2-Dimethyl benz[a ]anthracene
3-Methylcholanthrene
1.0
5.0
10.0
5.0
10.0
1.0
5.0
10.0
44,314 49(13) 1.1+0.2 61
36,854 73(10) 2.0 + 0.2 24 4
9,986 14(1) 1.4+0.4 9 !
7,798 34
10,804 52 5
29,204 259 7
16,887 134 8
18.263 86 5
4.4 +0.7 93
4.8 + 0.7 14(1
8.8 + 0.5 182(4
7.9 + 0.7 97(£
) 0.1 + 0.1
) 0.7 +0.1
) 0.9+0.3
1.2 + 0.4
1.3 + 0.3
6.2 + 0.5
5.7 + 0.6
4.7 + 0.5 62(5) 3.4 + 0.4
B. Reactive derivatives
5,6-Epoxy-5,6-d1hydrobenz[a]anthracene
8,9-Epoxy-8,9-dihydrobenz[a]anthracene
5,6-Epoxy-5,6-dihydro-7-nethylbenz[a]-
anthracene
5.6-Epoxy-5,6-dihydro-7,12-dimethyl-
benz[a]anthracene
ll,12-Epoxy-ll,12-dihydro-3-methylchol-
anthrene
Benz[a]anthracene-cis-5,6-dihydro-5,6-diol
7-Bromomethylbenz[a]anthracene
1.0
5.0
1.0
5.0
10.0
1.0
5.0
5.0
10.0
5.0
5.0
14,426 27(4) 1.9+0.4 1(1) 0.1+0.1
4,626 7(2
16,078 23(4
1.5 + 0.6 1
0.2 + 0.2
1.4 TO. 3 3(2) 0.2+0.1
32,468 56(7) 1.7 + 0.2 18(3) 0.6 + 0.1
7,828 28
3.6 + 0.7 12(2) 1.5 + 0.4
23,660 44(2) 1.9+0.3 18(1
6,356 38(2) 6.0+1.0 29(4
19,326 25(1
30.995 63(4
19,870 26(5
1.3 + 0.3 18
2.0 + 0.3 28 1
1.3 +0.3 52
0.8 + 0.2
4.6 TO. 8
0.9 + 0.2
0.9 + 0.2
0.3 + 0 1
21,233 26(3) 1.2 + 0.2 4(2) 0.2 + 0.1
The yield of transmissible bb's among the phenotypically scored bristle mutations with various benz[a]anthracenes and their reactive derivatives
Response with administration vehicle only, 2S dimethylformamide in arachis oil.
c Mosaic mutants are entered in parentheses.
-------
displayed greater mutagenic specificity than their K-region epoxides argued
in favor of the involvement of a different reactive metabolite (i.e., non
K-region epoxides, dihydrodiols, or diol-epoxides). Moreover, the correla-
tion of mutagenic activity to RNA genes with carcinogenicity in rodent skin
(DMBA>MCA>benz[a]anthracene) implied a common intracellular target and/or
ultimate reactive metabolite.
For the detection of mutagenicity in the whole mammal, the male dominant
lethal assay in mice is most commonly employed. However, it is felt that
239 240
this test is not particularly sensitive. Kennedy and coworkers
administered BaP (50 and 100 mg/kg B.W.) and benz[a]anthracene (15 and
30 mg/kg B.W.) by intraperitoneal injection to male albino mice which were
subsequently mated to virgin females. The females were sacrificed after
one week and the mutation rate determined by counting the numbers of fetal
resorptions versus the total number of implantations. These investigators
found no evidence of genetic damage which might have been manifested as a
dominant lethal mutation.
241
In contrast to these results, Epstein and coworkers observed an
excess incidence of dominant lethal mutations in ICR/Ha Swiss mice using
high doses of BaP and MCA (Table 6-16). The authors noted a lack of con-
sistency in the results obtained, both in terms of dose (for MCA) and in
magnitude of response and parameters affected (for BaP). Nevertheless, in
control animals, the mean weekly pregnancy rate was 66 percent, the mean
number of total implants per pregnancy was 11.5 to 11.9, and mean early
6-89
-------
Table 6-16. AGENTS PRODUCING EARLY FETAL DEATHS AND/OR PREIMPLANTATION LOSSES SIGNIFICANTLY BEYOND
CONTROL LIMITS BUT REQUIRING FURTHER VERIFICATION BECAUSE OF LACK OF INTERNAL
CONSISTENCY241
(ft
o
Benzo[a]pyrene
20-Me thyl chol anthrene
Route Total
and frequency weeks
of of
administration mating
ip 3
ip 3
ip 8
1p 8
Doses,
mg/kg
500
1000
750
1000
750
1000
100
200
No. Of
males
(No. of
deaths)
5(1)
5
14
14
7(4)
9(2)
7(2)
9(1)
Parameters selected in screen (mating weeks)
%
Pregnancy
25(2)
13(3)
—
29(3)
<30(4-8)
<30(4-8)
19(1)
—
Implants/ % Pregnancy
pregnancy ED /pregnancy with ED
__. -_ _ ___
7.5(3) 1.00(1), 1.00(2) 60(1);67(2)
... — —
53(3)
7.6(3);6.3(4)
4.0(6)
— —
8.2(7)
Comments
Lack of
consistency
between
experiments
Dose reversal
in other weeks
a ED, early deaths.
-------
fetal deaths per pregnancy were almost always less than 0.95. Thus, con-
siderable differences are evident between ROM-treated groups and untreated
controls.
Additional evidence which may indicate a potential for POM-induced
242
mutagenesis in germinal tissues was provided by Wyrobek and Bruce. They
found that five daily intraperitoneal injections of BaP or MCA at doses up
to 100 mg per day caused abnormally shaped sperm in (C57BL x C3H)F, mice.
These effects were most pronounced at four and ten weeks after treatment,
thereby indicating damage to the primary spermatocytes and spermatogonia.
Since abnormalities in sperm morphology were found, these results may be
indicative of mutagenesis in the male germ cell line.
6-91
-------
6.5 CARCINOGENESIS
6.5.1 l*i Vivo
Numerous polycyclic aromatic compounds are distinctive in their
ability to produce tumors in skin and most epithelial tissues of practically
all species tested. Malignancies are often induced by acute exposures to
microgram quantities of POM. Latency periods can be short (4-8 weeks) and
the tumors produced may resemble human carcinomas. Carcinogenesis studies
involving POM have historically been directed at studies primarily involving
effects on the skin or lungs. In addition, subcutaneous or intramuscular
injections are frequently employed to produce sarcomas at the injection
site.
Concern over potential human cancer risk posed by POM's present in the
atmosphere stems from studies demonstrating that crude extracts of airborne
243-246
particulate matter were carcinogenic to animals. Fractions soluble
in benzene or benzene-methanol produced tumors in mice by skin painting or
subcutaneous injection. Both the aromatic and oxygenated neutral sub-
fractions were active as complete carcinogens, and indicated the presence
of numerous carcinogenic materials, including non-POM's. The further
demonstration that the basic fraction of organic pollutants was carcino-
genic to newborn mice (see Section 6.5.1.4) indicated the presence of aza-
heterocyclic hydrocarbons. Since the carcinogenicity of the total organic
particulates and aromatic neutral subfractions could only partly be ex-
plained by the presence of BaP, its usefulness as a measure of carcinogenic
risk may, therefore, be limited.
6-92
-------
From investigations in which polycyclic carcinogens were painted on
the skin of mice has emerged the two-stage theory of skin carcinogene-
247 248
sis. ' The first stage, initiation, results from the ability of a
carcinogen to effect a permanent change within a cell or cell population
following a single application. The measure of carcinogenic potency is
often regarded as the capacity for tumor initiation. However, some weak or
non-carcinogens can be active as tumor initiators (e.g., dibenz[a,c]anthra-
cene, 1-methylchrysene, benz[a]anthracene). The second stage, promotion,
is a prolonged process which does not necessarily require the presence of a
carcinogen, but nevertheless a chemical stimulus must be supplied (e.g., by
croton oil). A complete carcinogen is one which, if applied in sufficient
quantity, can supply both initiating and promoting stimuli (e.g., DMBA,
BaP). The formation of skin tumors by polycyclic hydrocarbons may also be
influenced by inhibitors and accelerators, thus complicating the inter-
pretation of experimental data.
The carcinogenic effects of POM when applied to the skin of animals
249
have been known for decades. In 1939, Iball collected the results of a
series of experiments to arrive at a method for comparing the carcinogenic
potencies of various polycyclic aromatic chemicals. His results, presented
in Table 6-17, express tumorigenie potency in mouse skin as the ratio of
percent tumor incidence to the average latency period. This expression,
commonly referred to as the Iball index, is still used as a means of com-
paring the relative activity of carcinogens. An important data compilation
on agents tested for carcinogenicity has more more recently been published
6-93
-------
Table 6-17. CARCINOGENIC COMPOUNDS IN DESCENDING ORDER OF POTENCY
249
er>
i
10
-p.
1.
2.
3
4
5.
6
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18
19.
20.
21.
22
23.
24.
Compound
7 ,1 2-Dimethyl benz[a ]anthracene
3-Metnylcholanthrene (a)
3-Methylcholanthrene (b)
3-lethylcholanthrene
(a ana b added together)
BenzoLajpyrene (from pitch)
Benzo[a]pyrene (synthetic)
BenzoLajpyrene
(5 and 6 added together)
Cholanthrene
5,6-cycloPenteno-benz[a]anthracene
2 -Methyl -benzo[c]phenanthrene
10-Methyl-benz[a]anthracene
5 ,6-Dimethyl -benz[a]anthracene
6-isoPropyl-benz|.a]anthracene
Dibenzo[c,g]carbazole
Dibenzo[a ,h]pyrene
5 -Methyl -benz[a]anthracene
5-Ethyl-benzj.a]anthracene
DibenzLa,h]anthracene
Benzole ]phenanthrene
Dibenzo[a,g]carbazole
5-n-Propyl-benz[a]anthracene
Dibenz[c,h]acridine
3 -Methyl -dibenz[a ,h]anthracene
Dibenz[a,h]acridine
Number of
nice alive
when first
tumor appears
20
18
8
26
10
9
19
49
14
16
18
19
IS
19
17
8
9
65
18
9
20
28
25
25
Number of
tumors
13
18
5
23
10
7
17
28
13
12
12
16
11
9
10
7
7
41
12
4
6
11
7
6
Percentage of
tumors (A)
65
100
62.5
88.5
100
78
89.5
57
93
75
66.5
84
73.5
47.5
59
87.5
77.5
63
67
44.5
30
39.3
28
24
Papilloma
6
1
0
1
2
2
4
5
1
5
2
0
1
4
0
2
2
8
5
1
3
2
1
2
Epithelioma
7
17
5
22
8
5
13
23
12
7
10
16
10
5
10
5
5
33
7
3
3
9
6
4
Average latent
period (B)
43
99
151
109
127
109
119
112
194
155
147
220
204
143
205
317
285
239
387
263
192
357
325
350
Index
(A/B x 100)
151
101
41
80
79
72
75
51
48
48
45
38
36
33
29
28
27
26
17
17
16
11
9
7
Totals
305
60
245
-------
29
by the U.S. Public Health Service which lists the results of tests on
hundreds of polycyclic chemicals in numerous species including rodent,
avian, and amphibian.
Experimental models for respiratory carcinogenesis have major limitations
in that the delivery of carcinogens to the tracheobronchial tree in measured
amounts and their adequate retention at the target tissue are poorly con-
trolled. Therefore, the conduct of dose-response studies for lung tumor
induction has been seriously hampered. Moreover, the possible relevance of
the two-stage theory of carcinogenesis to lung cancer has not been clearly
established. Much of the bioassay data on POM-induced lung cancer has been
derived from animal model systems employing various modes of administration
(inhalation, intratracheal instillation, intravenous injection), and the
use of carrier particles (e.g., ferric oxide) for the delivery of the
carcinogen to the bronchial epithelium. Thus, the results obtained from
these studies cannot always be directly compared.
6.5.1.1 Structure-activity relationships—Following the identification of
the first carcinogenic hydrocarbon from soot, BaP, an intensive effort was
250
mounted to isolate the various active components of carcinogenic tars.
From the earliest studies conducted, the realization emerged that carcino-
genic POM are structurally derived from the simple angular phenanthrene
251
nucleus. However, unsubstituted POM with less than four condensed rings
that have been tested have not shown tumorigenic activity. Furthermore, of
the six possible arrangements with four benzene rings, only two of these
compounds are active: benzo[c]phenanthrene and benz[a]anthracene. The
6-95
-------
unsubstituted penta-and hexacyclic aromatic hydrocarbons are clearly the
most potent of the series. These include BaP, DBahA, dibenzo[a,h]pyrene,
dibenzo[a,i]pyrene, dibenzo[a,l]pyrene, dibenzo[a,e]pyrene, benzo[b]fluoran-
thene, and benzo[j]fluoranthene. Somewhat less potent as carcinogens are
the dibenzanthracenes and dibenzophenanthrenes. Only a few heptacyclic
hydrocarbons show carcinogenic activity. These include phenanthro-
[2',3':3,4']pyrene peropyrene and dibenzo[h,rst]pentaphene. Beyond seven
unsubstituted aromatic rings, there are very few known carcinogenic hydro-
carbons. However, many physical-chemical and enzymatic parameters must be
dealt with when speaking of carcinogenic POM. Factors such as solubility
and intracellular localization to achieve metabolic activation are likely
to be important determinants of the true carcinogenicity of a particular
POM.
Among the unsubstituted polycyclic hydrocarbons containing a nonaromatic
ring, a number of active carcinogens are known. The most prominent examples
of this type of compound are cholanthrene, 11,12-ace-benz[a]anthracene,
8,9-cyclopentanobenz[a]anthracene, 6,7-ace-benz[a]anthracene, acenaphthan-
thracene, 1,2,5,6-tetrahydrobenzo[j]cyclopent[f,g]aceanthrylene, and
"angular" steranthrene. It should be noted that all of these compounds
retain an intact conjugated phananthrene segment.
The addition of alkyl substituents in certain positions in the ring
system of a fully aromatic hydrocarbon will often confer carcinogenic
activity or dramatically enhance existing carcinogenic potency. In this
6-96
-------
251
regard, Arcos and Argus noted that monomethyl substitution of benz[a]-
anthracene can lead to strong carcinogenicity in mice, with potency depending
on the position of substitution in the decreasing order, 7>6>8=12>9. A
further enhancement of carcinogenic activity is produced by appropriate
dimethyl substitution of benz[a]anthracene. Active compounds are produced
by 6,8-dimethyl-, 8,9-dimethyl-, 8,12-dimethyl-, 7,8-dimethyl-, and 7,12-
dimethyl-substitution. The latter compound is among the most potent POM
carcinogens known, although it has not been shown as a product of fossil
fuel pyrolysis. Methyl substitution in the angular ring of benz[a]anthracene,
however, tends to deactivate the molecule, although 4,5-dimethylbenz[a]-
anthracene may be an exception. Carcinogenic trimethyl- and tetramethyl-
benz[a]anthracenes are known, and their relative potencies are comparable
to the parent 7,12-DMBA. In general, free radical synthesis of polycyclic
hydrocarbons by pyrolysis does not favor alkyl side chain formation.
Alkyl substitution of partially aromatic condensed ring systems may
also add considerable carcinogenic activity. The best examples of this
icti
252
251
type of activation are MCA, a highly potent carcinogen, and 5-methyl-
chrysene.
With alkyl substituents longer than methyl, carcinogenicity tends to
decrease, possibly due to a decrease in transport through cell membranes.
However, different positions in the benz[a]anthracene molecule will vary
with respect to the effect of n.-alkyl substitution on carcinogenicity.
Benz[a]anthracene is especially sensitive to decreased carcinogenicity
caused by the addition of bulky substituents at the 7-position, and is
6-97
-------
indicative of a once widely-held view for most polycyclics that high
reactivity of the meso-phenanthrenic region (now called the "K-region") was
251
a critical determinant for carcinogenicity. Current studies show that
the K-region is not involved in critical binding to DNA (see Section 6.2.2).
Alkyl groups notwithstanding, the substitution of highly polar groups
(e.g., -OH, -COOH) in the 7-position of benz[a]anthracene abolishes tumori-
genic activity whereas a wide variety of less-polar substituents can enhance
activity in position 7 (e.g., -CH2OH, -CH2CH2OH, -CH2COONa, -CH2COOCH3,
-CH2OOCCH3, -CN, -CH2CN, -CHO, -NHg, -SH, -COCC13> -OCHg).
Recent studies have indicated that methylation of the angular "bay
region" (see Section 6.2.1.2) benzene ring not only in benz[a]anthracene
but also in other four, five, and six-ring aromatic hydrocarbons leads to a
significant decrease, or even to elimination, of the carcinogenic activity
of the molecule. Methylation in other positions does not diminish, but
frequently increases, carcinogenicity. For example, 7- and 8-methyl-BaP
are inactive, whereas 2-,3-,4-,5-,6-,11-, and 12-methyl-BaP are strong
carcinogens.
Partial hydrogenation of the polycyclic aromatic skeleton can generally
be expected to decrease carcinogenic potency. This was shown with various
hydrogenated derivatives of BaP, benz[a]anthracene, and MCA. On the other
hand, the carcinogenicity of DBahA, dibenzo[a,i]pyrene, and dibenzo[a,h]pyrene
is not significantly altered by meso-hydrogenation. This may be due to the
fact that extensive resonance capability is preserved. Moreover, 5,6-
dihydro-DBahA actually displayed a fourfold increase in carcinogenicity in
6-98
-------
251
comparison to the parent hydrocarbon, possibly due to the hydrophilicity
and ease of intracellular transport of its dihydrodiol derivative.
Structure-activity relationships for nitrogen-containing heterocycles
have not been as thoroughly investigated as for the polycyclic hydrocar-
251
bons. Nevertheless, several generalizations can be derived from availa-
251
ble data. Arcos and Argus observed that the benz[c]acridine nucleus is
more likely to yield carcinogenic derivatives than benz[a]acridine. In
addition, they noted that the general rule of increased activity resulting
from methyl substitution on one of the meso-anthracenic carbons of benz[a]-
anthracene also applies to this series (i.e., position 10 in benz[c]acri-
dine or position 9 for benz[a]acridine). Lengthening of the alkyl sub-
stituent or addition of a second methyl group to benz[c]acridine will not
increase activity, and may, in fact, abolish it. Dimethyl substitution of
benz[a]acridine, on the other hand, appears to enhance careinogenicity.
In the dibenzacridine series, carcinogenicity appears to decrease in
the order dibenz[c,h]acridine>dibenz[a,h]acridine>dibenz[a,j]acridine, with
all compounds being less active than the monomethyl- and dimethylbenz[a]-
acridines. Addition of meso alkyl substituents will generally enhance
carcinogenicity, but hydrogenation of the aromatic skeleton or addition of
further benzene rings will substantially reduce or abolish activity.
Other POM carcinogens containing one or more nitrogen heteroatoms
belong to the benzocarbazole series. Most prominent among these is di-
benzo[c,g]carbazole. However, dibenzo[a,g]carbazole also shows some car-
cinogenic activity. The activity of dibenzo[a,g]carbazole, however, is
6-99
-------
considerably less than for the isosteric benzopyridocarbazoles. Further-
more, although dibenzo[a,i]carbazole shows only very weak activity, intro-
duction of a second nitrogen atom to form 7,8-benzo-pyrido[2',3':1,3]-
carbazole produces a dramatic potentiation of sarcomatogenic activity.
While the acridines, carbazoles, and other nitrogen heterocycles have not
been studied in as great detail as polycyclic hydrocarbons, their impor-
tance as potentially hazardous environmental pollutants is likely to
increase in the future. Greater emphasis on alternatives to solid fuel
combustion (e.g., coal liquefaction) is expected to result in greater
emissions of these nitrogen-containing compounds.
6.5.1.2 Skin carcinogenesis and induction of local sarcomas
6.5.1.2.1 Benzo[a]pyrene. The ability of BaP and its various metabolic
products to initiate skin tumors in the two-stage mouse carcinogenesis
system has been extensively evaluated in recent years. Emphasis has been
placed on the identification of a BaP derivative which acts as the princi-
ple ultimate carcinogen resulting from metabolic activation. Various BaP-
oxides, -phenols, -dihydrodiols, and diol-epoxides were assayed for tumori-
genicity and compared to the parent compound as a measure of bioactiva-
t.on 73,79,253-258
The tumor response obtained when BaP alone is applied weekly to the
259
skin of mice is shown in Figure 6-11. It is apparent from the data pre-
sented that increasing weekly doses of BaP caused a shortening of the
latency period for carcinoma formation. Furthermore, it was determined
that the development of papillomas as a precursor lesion to carcinoma
6-100
-------
1.4
1.0
3
o
2
3
0.1
0.01
I Slope = 8.0
Slope = 7.8
Slope = 10.0
• 128 jug
• 64/ug
A 32 jug
o 16jug
I I i i i I
100
Time (days)
1000
Figure 6-11. Log-log plot of the cumulative incidence of skin carcinomas per
mouse versus time. BaP was applied topically every week at the indicated
doses. Time was measured from the first BaP treatment.259
6-101
-------
formation occurred only at higher BaP doses (e.g., 32 pg and 64 pg per
week). At the lower dose levels (8 yg and 16 pg per week), carcinomas
appeared de novo without precursor papilloma formation.
Among the arene oxides of BaP tested as complete carcinogens by
repeated topical applications to mouse skin (0.4 pmole once every two weeks
73
for 60 weeks), BaP 7,8-oxide was shown to be highly carcinogenic. At
lower doses (0.1 pmole), BaP 7,8-oxide was not as potent a carcinogen as
BaP. The K-region BaP 4,5-oxide was only weakly carcinogenic at high
doses, whereas BaP 9,10-oxide was inactive. Subsequent studies to deter-
mine if the phenolic non-enzymatic rearrangement products of BaP oxides
were carcinogenic established that none of the seven phenols of BaP tested
256
(4-,5-,6-,7-,8-,9-, and 10-hydroxybenzo[a]pyrene) were active. Among
the remaining five possible isomeric phenols of BaP, only 2-hydroxybenzo[a]-
257
pyrene was shown to be highly carcinogenic at the 0.4 pmole dose. How-
ever, this compound has not been found as a metabolite of BaP in biological
systems.
Following the demonstration of the careinogenicity of BaP 7,8-oxide to
255
mouse skin, Levin et al. demonstrated that BaP 7,8-dihydrodiol, which
can form in vivo by the action of epoxide hydrase on BaP 7,8-oxide, was
254
even more potent than the parent epoxide. In fact, it was shown that
BaP 7,8-dihydrodiol was a slightly stronger skin carcinogen than BaP. In
the same study it was established that the diastereomeric BaP 7,8-diol-
9,10-epoxides were either inactive or weakly active as complete carcinogens
on mouse skin.
6-102
-------
A summary of the available information concerning carcinogenicity of
BaP and its derivatives to mouse skin is presented in Table 6-18. It
cannot be determined with certainty from these data, however, which prod-
ucts of BaP biotransformation may act as ultimate carcinogens. The apparent
lack of carcinogenicity of the BaP 7,8-diol-9,10-epoxides to mouse skin,
despite abundant evidence concerning their mutagenicity (see Section 6.4),
binding to nucleic acids (see Section 6.2), and high carcinogenicity to new
yen OC"\
born mice, ' may be explained by poor penetration of the skin. Since
it is a highly reactive electrophile, a BaP diol epoxide may readily alkyl-
ate nucleophilic sites of any kind and thus have a reduced probability of
passing intact through the cytoplasm to reach critical cellular receptors,
which most likely are in the nucleus.
The possibility that susceptibility to BaP-induced skin cancer may be
?fi?
related to age was examined by Peto and coworkers. The incidence of
skin cancer in mice resulting from regular BaP application (20 pg) starting
at 10, 25, 40, or 55 weeks of age was related to duration of exposure and
not to age at the start of treatment. This suggests that the induction of
the carcinogen-activating enzyme system does not change with increasing
age.
The activity of BaP and its derivatives as tumor initiators in the
two-stage mouse skin carcinogenesis system has received considerable atten-
tion. The rationale for investigating the tumor-initiating capabilities of
BaP derivatives stems from the knowledge that hydroxylated intermediates
6-103
-------
Table 6-18. SKIN TUMORS IN MICE TREATED WITH BENZO[A]PYRENE AND DERIVATIVES
Treatment3
BaP
BaP
BaP
BaP
BaP
BaP
BaP
BaP
BaP
BaP
BaP
BaP
1-HOBaP
2-HOBaP
3-HOBaP.
4-HOBaP^
5-HOBaP^
6-HOBaP^
7-HOBaP^
8-HOBaP^
9-HOBaPcr
10-HOBaPc
11-HOBaP
12-HOBaP
Total number
of animals
25
30
26
30
27
30
30
30
30
30
30
30
25
29
29
26
26
28
30
27
26
28
28
23
Dose,
umoles
0.4
0.4
0.4
0.15
0.1
0.1
0.1
0.1
0.05
0.025
0.02
0.02
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
% of mice
with tumors
100
100
92
100
96
38
50
91
59
7
4
0
0
100
0
0
0
0
0
0
0
0
14
0
Total number .
of skin tumors
32
34
34
40
28
13
15
24
20
2
1
0
0
37
0
0
0
0
0
0
0
0
4
0
Reference
257
257
256
255
257
254
254
254
254
254
254
254
257
257
257
256
256
256
256
256
256
256
257
257
a Female C57BL/6J mice were treated with BaP or BaP derivaties (0.02-0.4 ymole) once every two weeks for
60 weeks by topical application to the shaved skin of the back.
Skin tumors consisted mostly of squamous cell carcinomas; other skin tumors were fibrosarcomas, papillomas,
and keratocanthomas.
c Mice were treated once every two weeks for 56 weeks.
-------
Table 6-18 (continued). SKIN TUMORS IN MICE TREATED WITH BENZO[A]PYRENE AND DERIVATIVES
O
01
Treatment3
BaP 4,5-oxide
BaP 4,5-oxide
BaP 7,8-oxide
BaP 7,8-oxide
BaP 7,8-oxide
BaP 7,8-oxide
BaP 9,10-oxide
BaP 11,12-oxide
BaP 11,12-oxide
BaP 7,8-dihydrodiol
BaP 7,8-dihydrodiol
BaP 7,8-dihydrodiol
BaP 7,8-dihydrodiol
BaP 7,8-dihydrodiol
(+)-7B,8a-Dihydroxy-
9B,10B-epoxy-7,8,9,
Total number
of animals
30-39
30-39
30-39
30
30
30-39
30-39
28
27
30
30
30
30
30
10-
Dose,
umoles
0.4
0.1
0.4
0.3
0.15
0.1
0.4
0.4
0.1
0.3
0.15
0.1
0.05
0.025
% of mice
with tumors
4
6
94
53
18
9
0
0
0
100
100
92
76
7
Total number .
of skin tumors
1
2
37
16
5
3
0
0
0
42
40
28
24
2
Reference
73
73
73
255
255
73
73
257
257
255
255
73
73
73
tetrahydrobenzo[a]pyrene
(diol epoxide 1)
diol epoxide 1
diol epoxide 1
(+)-7B,8a-Dihydroxy-
9a,10a-epoxy-7,8,9,
30
30
30
10-
0.4
0.1
0.02
0
0
0
0
0
0
73
73
73
tetrahydrobenzo[a]pyrene
(diol epoxide 2)
diol epoxide 2
diol epoxide 2
30
30
30
0.4
0.1
0.02
13
7
0
3
2
0
73
73
73
a Female C57BL/6J mice were treated with BaP or BaP derivatives (0.02-0.4 umoles) once every two weeks for
60 weeks by topical application to the shaved skin of the back.
Skin tumors consisted mostly of squamous cell carcinomas; other skin tumors were fibrosarcomas, papillomas,
and keratocanthomas.
-------
may be better substrates for activation to a proximate or ultimate carcino-
gen. Moreover, it would not be expected that all carcinogenic POM metab-
olites should be equally effective as tumor initiators, since different
tissues or species may have greater or lesser capacity to activate a
specific molecule.
Among the various metabolites of BaP investigated for tumor-initiating
activity, only BaP 7,8-dihydrodiol is as potent a tumor initiator as
253
BaP. In addition, the tumorigenicity of BaP 7,8-dihydrodiol is highly
stereospecific. At equimolar doses, (-)-BaP 7,8-dihydrodiol was more
active than BaP as a tumor initiator, whereas the (+)-enantiomer was con-
siderably less active than BaP. This selectivity indicates a preferential
orientation at the active site of the enzyme complex. Other effective
tumor-initiating metabolites of BaP are BaP 7,8-oxide and BaP 7B,8a-diol-
9B,10e-epoxide (diol epoxide 1) and BaP 4,5-, 9,10-, and 11,12-oxides (all
79
of the above compounds are racemic except where indicated). However,
both diol epoxide 1 and diol epoxide 2 (BaP 73,8a-diol-9a,10a-epoxide) were
severalfold more active than BaP in the induction of epidermal, hyper-
pco
plasia. A summary of the skin tumor initiating activities of BaP and
its metabolites is presented in Table 6-19.
Following the subcutaneous administration of BaP to rats and mice,
sarcomas commonly develop at the site of injection, since the carcinogen is
introduced below the basal cell layer. A total dose of 6 to 7 ymoles (1.5
to 1.7 mg) of BaP is sufficient to produce sarcomas in nearly all treated
animals (Table 6-20). Although a single dose of 0.31 mg or less of BaP
6-106
-------
Table 6-19. SUMMARY OF THE SKIN TUMOR INITIATING ACTIVITIES OF BENZO[A]PYRENE AND ITS METABOLITES
o
•vl
Initiator
Bap
BaP
BaP
BaP 4,5-epoxide
BaP 7,8-epoxide
BaP 9,10-epoxide
BaP 11 ,12-epoxide
BaP 7e,8a-diol-9a,10a-epoxide
BaP 7B,8a-diol-9B,108-epoxide
BaP 7,8-dihydrodiol
(-)-BaP 7,8-dihydrodiolb
(+)-BaP 7,8-dihydrodiolD
Number
of mice
30
30
30
30
29
29
30
29
28
29
30
30
Dose,
nmoles
200
200
100
200
200
200
200
200
200
200
100
100
Weeks of
promotion
23
30
21
23
23
30
30
30
30
30
21
21
% of mice
with tumors
94
92
77
20
81
15
38
69
7
86
77
23
Papillomas/
mouse
4.8
5.3
2.6
0.2
1.9
0.15
0.45
1.5
0.07
5.0
3.8
0.43
Reference
253
79
76
253
253
79
79
79
79
79
76
76
Female CD-I mice were treated with a single dose of initiator dissolved in acetone, acetoneiNfyOH (1000;!),
or dimethyl sulfoxide:acetone (1:3) and-followed one week later by twice-weekly applications of 10 vg of TPA.
Promotion was by twice-weekly applications of 16 nmoles of TPA beginning 11 days after treatment with
initiator.
-------
Table 6-20. INDUCTION OF SARCOMA BY BENZO[A]PYRENE
o
oo
Species Number and (sex)
Rat
(Sprague-Dawley)
Mouse
Mouse
Mouse
Mouse
Mouse
Mouse
13 (female)
14 (male
16 (female)
9 (?)
10 (?)
12 (?)
15 (?)
Total dose,
ymoles
6.0a
7.1b
7.1b
15. 9C
5.0C
0.5C
.002C
Animals with
sarcoma, %
100
93
50
66.6
70
66.6
0
Average latency,
days
101 + 2.7
129
160
112
122
155
N.A.d
Reference
274
285
285
379
379
379
379
Administered as 0.2 umole dissolved in 0.1 ml sesame oil by subcutaneous injection on alternate days for
. 30 doses beginning at 30 days of age.
Administered as three injections of 2.4 pmoles each, given at one month intervals.
. Administered as a single injection under the skin of the abdomen, dissolved in 0.5 ml of neutral olive oil.
Not applicable.
-------
produced no tumors in C3H mice, others reported that 0.0004, 0.004, and
0.04 mg produced sarcomas in one, five, and 23 mice (strain unknown),
250
respectively, out of groups of 50.
6.5.1.2.2 7,12-Dimethylbenz[a]anthracene. DMBA is a potent carcinogen
used extensively in the laboratory. It is not found, however, in ambient
air. When applied topically, DMBA is both an effective tumor initiator and
7fiA ?fift ?7fi
a complete carcinogen, depending upon the dose administered. '
Numerous studies have indicated that a single dose of DMBA greater than
400 nmoles is sufficient to produce tumors in mouse skin in the absence of
269
a promoting stimulus. Attempts to produce skin tumors in CD-I female
mice with a single application of 200 nmoles of DMBA were unsuccessful
after 35 weeks. DMBA is metabolized much faster than BaP and has a more
complicated metabolite profile, suggesting that more biochemical parameters
may be modulating DMBA tumorigenesis.
259
Albert and coworkers found that DMBA readily induces tumors on the
skin of rats as well as mice. In general, the temporal and dose-response
features of the action of DMBA on rat skin were very similar to that shown
in mouse skin treated with BaP (Figure 6-12). The data suggested that a
similar mechanism of action may be operating for these compounds in both
species.
Not only are skin tumors induced by single topical applications of
DMBA, but they may also be formed after intravenous injection of the car-
270
cinogen. Bennington and coworkers reported that six of 70 female
Sprague-Dawley rats developed seven pilosebaceous tumors within one year
after receiving 3 mg of DMBA by intravenous injection.
6-109
-------
10.0
o
E
3
1.0
0.1
500/jg
10
DMBA
Rat Skin
100 jug
20 ng
100
Time (weeks)
Figure 6-12. Incidence of cancer per rat after weekly topical application of
either 20, 100, or 50 pg DMBA in 1.0 ml acetone.259
6-110
-------
When applied to the skin of guinea pigs, high doses of DMBA can induce
271 272
malignant melanomas which resemble the melanomas of man. ''»'•"- Four of
20 female guinea pigs developed malignant melanomas and subsequent metastases
279
after receiving 50 to 100 applications of 0.5 mg DMBA in benzene.
Twenty-six male guinea pigs developed only alopecia and hyperpigmentation
at the site of DMBA application; one male developed a non-metastasizing
subcutaneous liposarcoma.
As a tumor initiator, DMBA is equal to and possibly greater than BaP
269
in potency. Slaga and coworkers provided dose-response data in female
CD-I mice for tumor production by single dose DMBA application followed by
twice weekly treatment with 0.25 percent croton oil. A single dose of
either 0.5, 5, 10, 20, 100, or 200 nmoles DMBA produced 0.4, 2.3, 6.0, 5.5,
6.2, and 16 papillomas per mouse, respectively, at 24 weeks. At the lowest
DMBA dosage (0.5 nmoles), 31 percent of treated mice bore tumors after 34
weeks. With higher doses of DMBA, the tumor incidence ranged from greater
than 60 percent (5 nmoles) to 100 percent (200 nmoles). When TPA, the
active phorbol ester ingredient in croton oil, (17 nmoles) was used as the
promoter instead of croton oil, both tumor incidence and tumor yield were
increased. In this study, the effect of higher DMBA doses (i.e., 10, 20,
or 100 nmoles) was primarily a shortening of the tumor latency period,
since tumor incidences and the average number of tumors per mouse were
similar after 24 weeks. However, at the 200 nmole dose level, DMBA pro-
duced more than twice the number of tumors as the 100 nmole treatment. The
authors suggested that by increasing the dose of DMBA to 200 nmoles, a
6-111
-------
promoting stimulus is superimposed upon initiation while at the same time
increasing the number of effectively initiated sites. Therefore, it was
implied that the magnitude of an initiating stimulus can be evaluated in
terms of the number of tumors eventually produced and their latency period,
rather than by the final tumor incidence. It must be kept in mind, how-
ever, that the effectiveness of DMBA in the two-stage skin carcinogenesis
system is influenced by species susceptibility and factors which modify the
273
promotion process (diet, hormonal status). These principles probably
apply as well to most polycyclic carcinogens.
Sarcomas developing at the site of injection are frequently observed
with DMBA, much the same as with BaP injection. A single injection of
2.5 mg DMBA produced sarcomas in all of a group of eight female Sprague-
Dawley rats. In a similar study, 6 pmoles of DMBA (administered as 30
injections of 0.2 pmoles each on alternate days) produced a 100 percent
274
incidence of sarcoma in 10 female Sprague-Dawley rats. The same treat-
ment employing BaP instead of DMBA led to essentially identical results.
Injections of principal DMBA hydroxylated metabolites or its K-region
epoxide, on the other hand, were much less effective in producing sarcomas.
In C57 black mice, 10 weekly injections of one mg DMBA produced local
tumors (sarcomas and carcinomas) in four of six males and three of five
46
females. Monohydroxymethyl derivatives of DMBA were active as carcino-
gens, but less potent than the parent compound.
6.5.1.2.3 3-Methylcholanthrene. As with DMBA, MCA is a potent carcinogen
which is produced synthetically for use in the laboratory. The action of
6-112
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MCA as a complete carcinogen in mouse skin was recently investigated by
275
Burki and coworkers. A single application of 3 ymoles MCA produced
16 tumors in 18 BALB/c male mice after 57 weeks. In a subsequent series of
experiments, repeated applications of 1.5 to 3 ymoles MCA twice weekly for
three or 17 weeks induced larger numbers of skin tumors in nearly all
animals. Nevertheless, MCA is not as potent a skin carcinogen as either
BaP or DMBA. However, the incidence and number of tumors produced by MCA
could be increased by the administration of trichloropropene oxide, an
epoxide hydrase inhibitor. Despite this effect, which implicates the
involvement of a carcinogenic epoxide intermediate by increasing its half-
life, the K-region epoxide of MCA (MCA-ll,12-oxide) was much less effective
than the parent compound. It is possible, however, that such epoxides are
too unstable to pass through the cornified layer in the skin to reach the
dividing cells in the epidermis.
The skin tumor initiating activity of MCA is comparable to that of BaP
when TPA is used as a promoting agent. In CD-I female mice, a 50 nmole
application of MCA followed by twice weekly applications of 10 yg TPA
277
produced an average of 1.9 papillomas per mouse after 30 weeks. The
tumor incidence was greater than 50 percent. Pretreatment of mice with the
enzyme inhibitor TCPO slightly increased the yield of MCA-induced papil-
lomas per mouse, again suggesting the involvement of an epoxide intermediate.
278
Cavalieri and coworkers have demonstrated an isotope effect for
skin tumor induction by MCA. Deuteration at positions C-l and C-5 diminished
the tumorigenic activity of MCA (0.2 umoles twice weekly for 20 weeks) on
6-113
-------
the skin of female Swiss mice. It was suggested that metabolic activation
and binding of MCA may involve C-l hydroxylation followed by binding to
critical intracellular sites. In support of this hypothesis, it was noted
that 1-hydroxy-MCA and MCA-1-one are sarcomagenic for mice by subcutaneous
injection.
Subcutaneous injection of relatively high doses of MCA produced tumors
27Q
in high yields at the injection site in C57 black mice. Three weekly
injections of 1 mg MCA produced sarcomas in all of a group of 10 male mice.
Ten of 11 female mice developed local tumors after receiving 10 injections
of 1 mg MCA each.
6.5.1.2.4 Pibenz[a,h]anthracene. A skin tumor incidence of 11.7 percent
resulted within 28 weeks after female CD-I mice received ten daily applica-
277
tions of DBahA at 1.0 mg (3.6 ymoles) each. Other investigators have
clearly established the ability of DBahA to act as a complete carcinogen in
mouse skin; tumor production by DBahA is dose-related and similar in potency
to BaP.281'282'283 The K-region epoxide of DBahA (DBahA-5,6-epoxide)
produced about the same tumor response as the parent compound in female
CD-I mice.277
DBahA was shown to be as effective a tumor initiator in mouse skin as
277
BaP. A single application of 200 nmoles DBahA followed by twice weekly
applications of 10 yg TPA for 30 weeks yielded an average of four papillomas
per animal in about 90 percent of a group of 30 CD-I female mice. As
little as 0.02 yg (0.07 nmoles) DBahA can initiate skin carcinogenesis in
n,1ce.280
6-114
-------
By subcutaneous Injection, DBahA has produced sarcomas and carcinomas
46
at the injection site in C57 black mice. Ten weekly injections of
1 mg DBahA produced tumors in all of a group of 20 male mice and in 17 of
19 female mice. The K-region epoxide of DBahA produced tumors in mice of
both sexes, but was not as potent as the parent compound.
6.5.1.2.5 Dibenzo[a,h]pyrene. Skin application of DBahP was first associated
250
with the development of epitheliomas in 1939. More recently, Hoffmann
284
and Wynder reported strong carcinogenic activity on mouse skin when
applied for one year, thrice weekly in 0.05% and 0.1% concentrations.
DBahP was also a strong tumor initiator. Both the carcinogenic and tumor
initiating activity of DBahP, however, were less than that of BaP.
Several investigators have demonstrated that DBahP will consistently
250
induce sarcomas when injected in rats or mice. A total administration
of 1.8 mg DBahP produced 34 sarcomas among 35 male mice; only one of ten
por
female mice developed a sarcoma, however.
The reduced carcinogenic activity relative to BaP for DBahP (and other
related POM's) may be due to the very large decrease in solubility re-
sulting from the addition of another benzene ring. A decreased solubility
would imply a reduced ability to metabolize (and presumably activate) these
compounds, although confirming biochemical studies are not available.
Moreover, it is difficult to compare compounds such as the dibenzopyrenes
to the more potent carcinogens (e.g., BaP, DMBA), since high doses over
long periods are used to assess tumorigenicity. In such cases, purity of
the test compound and saturation of metabolic pathways may confuse the
interpretation of results.
6-115
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OOA
6.5.1.2.6 Pibenzo[a,i]pyrene. Hoffmann and Wynder have established the
carcinogenicity of DBaiP in mouse skin. Among 20 female Swiss Albino mice
painted three times a week for one year with a 0.1 percent DBaiP solution,
16 animals developed 15 epitheliomas and 29 papillomas. With a 0.05 per-
cent DBaiP solution, the results were essentially the same (13 epithelio-
mas, 28 papillomas). The tumor latency period for DBaiP-induced skin
tumors was longer than the latency period with BaP. DBaiP was also an
active tumor initiator, but less effective than either DBahP or BaP.
Large numbers of sarcomas in mice and hamsters are produced by
250
subcutaneous and/or intramuscular injections of DBaiP. Single sub-
cutaneous injections of only 0.5 mg DBaiP into the groin of C57 mice pro-
duced local sarcomas in 98 percent of the animals in 24 weeks.
6.5.1.2.7 Pibenzo[c,g]carbazo!e. Skin tumors have been produced in mice
by painting with DBcgC, although a high mortality associated with the
treatment hampers the interpretation of results. Studies summarized by the
250
International Agency for Research on Cancer reported that repeated
applications of DBcgC in solutions of 0.1 to 0.5 percent induced papillomas
and carcinomas in high percentages.
Local sarcomas have been induced by DBcgC in as many as 100 percent of
mice receiving injections. In single doses as low as 0.2 mg, DBcgC pro-
250
duced 17 sarcomas among 20 mice within 40 weeks. Depending on vehicle
of administration (lard, olive oil, sesame oil) and strain of mouse em-
ployed (C3H, A, C), the incidence of DBcgC-induced sarcomas by a single
0.2 mg injection was as follows: 17/93 (C3H mice; lard); 72/133 (A mice,
6-116
-------
sesame oil); 20/27 (Amice, olive oil); 5/19 (C3H mice, lard); 22/41 (C3H
mice, sesame oil); 46/67 (C3H mice, sesame oil).
6.5.1.2.8 Benzo[c]phenanthrene. Benzo[c]phenanthrene and several of its
monomethyl derivatives were tested for carcinogenicity by skin painting at
286
high doses and subcutaneous injection in C3H mice. Twice weekly appli-
cation of a 0.5 percent solution in acetone to the shaved backs of 20 mice
produced three carcinomas and two sarcomas over the 638 day experimental
period. Single subcutaneous injections of 5 mg benzo[c]phenanthrene to
20 mice resulted in three sarcomas. Markedly enhanced tumorigenic potency
was evident for the 4-methyl and 5-methyl derivatives of benzo[c]phenanthrene
when applied to the skin surface, and for the 5-methyl derivative when
injected subcutaneously.
6.5.1.2.9 Benzo[b]f1uoranthene. BbF is a common pyrolysis product found
250
in automobile exhaust, polluted air, and cigarette smoke. In 1959,
287
Wynder and Hoffmann reported that BbF had relatively high carcinogenic
activity when applied repeatedly to the skin of female Swiss mice. Among
20 mice receiving thrice weekly applications of BbF (0.5% in acetone), all
of the animals developed papillomas within five months, and 19 of the
20 mice developed carcinomas after eight months. None of the mice survived
beyond eight months. At a dose of 0.1%, BbF produced papillomas in 13 ani-
mals and carcinomas in 17 animals with 12 months. At 0.01%, the lowest
dose tested, five of the ten surviving mice after 14 months developed
papillomas. By comparison, BaP at the same 0.01% dose level caused car-
cinomas in 17 of 20 mice after 12 months of treatment.
6-117
-------
288
In later studies by Van Duuren and coworkers, BbF was shown to be a
potent tumor initiator. A single application of 1 mg BbF in acetone to
20 female KCR/Ha Swiss mice followed by thrice weekly applications of 25 yg
croton resin produced 18 mice with papillomas and five mice with carcinomas
within 63 weeks. The same dose of BbF followed with no promoting agent
yielded no tumors. By comparison, a 150 ug dose of BaP followed by the
same croton resin treatment produced 20 mice with papillomas and six mice
with carcinomas over the same time period. The tumor initiating potency of
BbF in this test system was slightly greater than for chrysene.
Three subcutaneous injections of 0.6 mg BbF given over two months
produced local sarcomas in 8 of 16 males (average latency 130 days) and 10
250 285
of 14 females (average latency 133 days). ' The sarcomagenic potency
of BbF was considered to be not much less than for BaP, especially in
females.
6.5.1.2.10 Benzo[j]f1uoranthene. Little biological information is available
concerning BjF, despite the fact that it is a pyrolysis product found in
automobile exhaust, polluted air, and cigarette smoke. Nevertheless,
287
Wynder and Hoffmann reported in 1959 that BjF produced carcinomas on the
skin of mice. Among 20 female Swiss mice receiving thrice weekly applica-
tions of BjF (0.5% in acetone), 19 animals developed papillomas and car-
cinomas within seven months. None of the mice survived beyond seven months.
At a dose level of 0.19% in acetone, BjF produced papillomas in 14 mice and
carcinomas in all 20 mice within nine months.
6-118
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6.5.1.3 Respiratory tract carcinogenesis--Unti1 recently, the investigation
of POM-induced carcinogenesis in tissues of the respiratory tract has been
hindered by the lack of a reliable animal model system. Nevertheless, many
compounds of the POM class, depending upon the assay system, display marked
carcinogenic activity in the respiratory tissues. However, the carcino-
genic potency of a polycyclic compound for the pulmonary tissues may not
necessarily parallel its activity either as a complete carcinogen on mouse
and hamster epidermis, as a tumor initiator on mouse skin, or as a sarcoma-
genie agent. Nevertheless, bioassay data can serve as guidelines for the
prevention of neoplastic diseases in man in at least two ways: (1) the
carcinogenic potential of a single chemical can be assessed by examining
its effects in multiple animal systems with comparison of target tissues,
and by various routes of administration, or (2) a series of related chemi-
cals can be compared within the same bioassay system and ranked according
to their tumorigenic potency based on dose-response relationships.
An examination of comparative carcinogenicities within the same tumor
system can provide valuable insight concerning relative risks of various
POM. By single intravenous injection of about 0.25 mg of aqueous disper-
sions of polycyclic hydrocarbons to mice, a direct comparison of carcino-
genic potency was possible (Table 6-21). In this test system, MCA dis-
played the greatest lung tumor-forming capability; DBahA followed closely
in activity, with DBcgC and BaP being considerably less potent. These
results demonstrate the variability in tissue-specific response to POM's,
since BaP is a more active carcinogen in skin and as a transforming agent
jji vitro.
6-119
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Table 6-21. COMPARATIVE CARCINOGENICITY OF POLYCYCLIC HYDROCARBONS AND RELATED COMPOUNDS, MEASURED
BY INDUCTION OF LUNG TUMORS (LT)a 471
Dose,
Compound pinoles/ kg
3-Methylcholanthrene, 0.1 mg
3-Methylcholanthrene, 0.5 mg
Dibenz[a,h]anthracene
7H-Di benzo[c , g]carbazol e
Benzo[a]pyrene
Di benz[a , j ]aceanthryl ene
Dibenz[a,h]acridine
8-Methyl benzo[c]phenanthrene
7-Methylbenzo[a]pyrene
5-Methoxy-7-propylbenz[a]anthracene
Benz[a]anthracene
Untreated controls
15
74
36
38
40
33
36
42
38
33
44
--
Mice with LT/
no. of mice
15/15
6/6
10/10
12/12
10/10
9/10
11/12
6/11
5/10
1/10
2/11
4/19
Mean no.
LT/mouse
11 }
47 ;
31
5.7
3.7
2.7
2.0
0.7
0.6
0.1
0.2
0.2
gMoles/kg for
1 LT response
0.9
1.0
6.0
9.5
14
18
--
--
--
--
--
a Strain A mice, 8-12 weeks old, received single intravenous injection of 0.24 mg of methylcholanthrene
in aqueous dispersion and were killed 20 weeks later.
-------
Intratracheal instillation of POM to Syrian golden hamsters289'290'148
has become widely utilized for the conduct of dose-response studies for
pulmonary carcinogenesis. Several studies are summarized in Table 6-22 and
indicate that: (1) dose-response relationships are clearly evident, and
(2) the co-administration of carrier particles such as Fe203 (i.e., with
BaP) can markedly increase tumor incidence, depending upon the physical
characteristics of the particle. Since environmental exposures to BaP
occur in conjunction with particulate material in air, this effect may be
particularly relevant to human situations. In addition, increasing doses
of carcinogen generally decreased the tumor latency period.
Preliminary results have recently become available on a study to
establish temporal and dose-response relationships for BaP carcinogenesis
259
in the hamster respiratory tract. Weekly intratracheal instillations of
BaP (2.0, 1.0, 0.5, or 0.25 mg) with or without an equivalent amount of
Fe203 were conducted for 15 or 30 weeks. Initial results, based on gross
observation only, indicated that the incidence of respiratory nodule forma-
tion was dose-dependent; 0.25 mg BaP with 0.25 Fe203 given for 15 or
30 weeks produced no nodules, whereas 2.0 mg BaP with 2.0 mg Fe203 given
for 15 or 30 weeks resulted in a tumor incidence of 44% and 86%, respec-
tively. Dose-response information is depicted in Figure 6-13. Surpris-
ingly, the use of Fe90, as a carrier for BaP had no apparent effect on the
c. *5
incidence of lung nodule formation (Figure 6-14). While tumor latency
periods decreased with increasing BaP weekly dose, no clear trend was ob-
tained in temporal aspects of tumor development between 15 and 30 week
treatments at the same dose.
6-121
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Table 6-22. INDUCTION OF RESPIRATORY TRACT TUMORS IN SYRIAN GOLDEN HAMSTERS BY INTRATRACHEAL
INSTILLATION OF POM
rv>
ro
Number Total dose,
Compound
BaP
BaP
BaP
BaP
BaP
BaP
BaP and Fe-0,
BaP and Fe^O,, coated
BaP and Fe^O,, ground
BaP and Fe-O.,, mixed
BaP and gelatin
BaP and Fe,0,
BaP and Fe,0,
BaP and Fe,0,
BaP and Fe,0,
BaP i J
BaP
DB[a,i]P
DB[a,i]P
DMBA and Fe-O,
DMBA and Fe^Cu
DBC and Fe-O,
DBC and Fe^O,
Respiratory tumor
incidence,
of animals mg %
30
30
30
29
28
48
48
49
49
43
46
3.25a
6.5a
13a
26*
"»?
3°h
30b r
26. 1
-------
ro
oo
1.0 —
0.9 —
0.8 —
g 0.7H
o
2 0.6 —
O
tr 0.4 —
2
o
£ 0.3-
0.2 —
0.1 —
0.0
2mg.\
30 WEEKS
1 mg.
30 WEEKS
2mg.
15WEEKS
I
200
I
400
TIME (DAYS)
I
600
I
800
259
Figure 6-13. Respiratory nodule incidence in hamsters given BaP by intratracheal instillation.
(Hamsters were given weekly intratracheal instillations of either 1.0 or 2.0 mg BaP with equivalent
amounts of Fe?0^ for either 15 or 30 weeks as indicated. Proportion with tumor was calculated from
the life table procedure on the basis of tumors found at death. Time was measured from the first
BaP dose.)
-------
t\>
Figure 6-14. Respiratory nodule incidence in hamsters given BaP by intratracheal instillation with
and without Fe203."y (Hamsters were given weekly intratracheal instillations of 2.0 mg BaP for
either 15 or 3u weeks with and without 2.0 mg ferric oxide (Fe?0,). There were 36 hamsters per
group and tumors found at death were analyzed by the life table procedure to give the proportion
with tumor. Time was measured from the first BaP dose.)
-------
In addition to the hamster model system, respiratory lesions and
carcinomas have been readily induced by POM in rats and mice by various
routes of administration. The results of several representative studies
are summarized in Table 6-23.
An additional approach used to evaluate the effects of POM on the
291
pulmonary tissue was reported by Flaks and Sims. Pulmonary tissue taken
from tumor susceptible female BALB/c mice was incubated for 30 minutes in
the presence of 4 ug/ml of DMBA, DBahA, BaP, or one of their related K-
region epoxides, and subsequently implanted into isologous mice. Under
these conditions, only DMBA showed marked carcinogenic activity.
Squamous cell carcinomas have been induced in rat tracheal grafts by
292
instillation of MCA, BaP, or BaP mixed with Fe«0~ particles. Neoplasms
were induced by 5 mg of carcinogen after 35 weeks of contact in 3 of 5, 2
of 5, and 2 of 3 tracheal grafts exposed to MCA, BaP, and BaP-Fe203,
respectively. Subsequent studies in the same test system using DMBA in a
sustained release formulation established that carcinomas could be induced
293
in tracheal epithelium at doses as low as 40 yg. With this procedure,
294
the lowest dose of BaP tested which produced a carcinoma was 300 yg.
6.5.1.4 Carcinogenesis in newborn mice—The newborn mouse is known to be
295
highly susceptible to carcinogenic POM, presumably because of its large
296
numbers of rapidly dividing cells, and is thus a useful model for car-
297
cinogenesis studies. In studies reported by Asahina and coworkers,
various fractions of an organic extract of atmospheric particulate pol-
lutants displayed high carcinogenic activity when injected subcutaneously
6-125
-------
Table 6-23. INDUCTION OF RESPIRATORY TRACT TUMORS IN RATS AND MICE
CT>
CT»
Compound
DHBA and Indian ink
DHBA and Indian ink
DMBA and Indian ink
DB[a,h]A
MCA
MCA
MCA
MCA
MCA
MCA
MCA
Organism
Rat (Hi star and random-bred)
Rat (Mistar and random-bred)
Rat (Wistar and random-bred)
Mouse (DBA/ 2)
Rat (Osborne-Mendel)
Rat (Osborne-Mendel)
Rat (Osborne-Mendel)
Rat (Osborne-Mendel)
Rat (Osborne-Mendel)
Rat (Osborne-Mendel)
Rat (Osborne-Mendel)
Number of
animals
34
56
61
14 (male)
13 (female)
100
100
100
100
100
100
100
Total dose,
mg
2.5a
6b
10C
236 (male)d ,
179 (female)0
0.005f
o.osf
0.1 Of
0 20
0 30f
0.40f
0.50f
Route of
administration
Intratracheal
instillation
Intratracheal
instillation
Intratracheal
instillation
Oral
Pulmonary injection
Pulmonary injection
Pulmonary injection
Pulmonary injection
Pulmonary injection
Pulmonary injection
Pulmonary injection
Tumor
incidence, t
17.6
35.7
26.2
100 (male)6 „
77 (female)
19
139
2?9
479
409
519
459
Reference
383
383
383
384
385
385
385
385
385
385
385
? Administered as a single dose with 0.2 mg of Indian ink in 0 2 ml of a colloid protein solution.
° Administered as three 2 mg doses at monthly intervals with 0.2 mg of Indian ink in 0.2 ml of a colloid protein solution.
. Administered as five 2 mg doses at monthly intervals with 0 2 mg of Indian ink in 0 2 ml of a colloid protein solution
° Administered as an aqueous-olive oil emulsion of DB[a,h]A given in place of drinking water for 237 to 279 days
, Tumors were alveologenic carcinomas, a 100% incidence of pulmonary adenomatosis was also observed.
Administered as a single MCA-containing beeswax pellet placed directly into the lower peripheral segment of the left lung.
s Overt squamous cell carcinoma.
-------
to infant Swiss mice of both sexes. Various combinations of remote tumors
(hepatomas, lymphomas, pulmonary adenomas) were produced by the basic,
neutral, and aromatic fractions of the benzene soluble organic extract.
Three oxyneutral subfractions also produced multiple tumors. These results
indicated that a variety of different chemical carcinogens are present in
organic extracts of air pollutants in addition to BaP, which is found
298
mainly in aromatic fractions. Walters administered DMBA by single
injection to male and female newborn (<24 hours old) BALB/c mice at doses
ranging from 0.625 to 40 yg. At the lowest dosage, the incidence of lung
tumors was greater than 50 percent in females and greater than 75 percent
in males. Subcutaneous injections of 0.005 yg MCA or 0.003 yg DBahA were
sufficient to produce fibrosarcomas at the injection site of newborn
299
mice. However, on a mg/kg of body weight basis, these doses are com-
parable to carcinogenic doses in adult animals. Attempts to determine
whether the appearance of DMBA-induced lung tumors is more likely at a
definite point in the life span of a mouse have not produced definitive
results.300
The K-region epoxides of DBahA and MCA were found to be negative for
carcinogenic activity in newborn mice, despite reports that the parent
301
hydrocarbons were active at the same dose levels (60 yg). These results
suggested that K-region epoxides may not be the ultimate metabolites in-
volved in POM carcinogenesis as once was thought. In support of the con-
tention that a dihydrodiol precusor of the "bay region" diol epoxide may be
?fifl
a proximate carcinogenic metabolite of BaP, Kapitulnik and coworkers ou>
6-127
-------
recently showed that BaP 7,8-dihydrodiol is more carcinogenic than BaP in
newborn mice. Moreover, one of the stereoisomeric BaP 7,8-diol-9,10-
epoxides, (+)-trans-7B,8a-dihydroxy-9a,10a-epoxy-7,8,9,10-tetrahydro-BaP,
demonstrated extremely high carcinogenic activity in newborn mice, as would
be predicted by the "bay region" theory (see Section 6.2.1.2). Since the
metabolism of BaP results in three known diols, all via epoxide intermedi-
ates, it thus appears that the major pathway for carcinogenic activation
may be:
BaP >• BaP 7,8-oxide >- BaP 7,8-dihydrodiol >- BaP 7,8-diol-9,10-epoxide
which results in formation of the diol epoxide as an ultimate carcinogen.
302
Wislocki and coworkers recently presented evidence supporting the
"bay region" theory with regard to the carcinogenicity of benz[a]anthra-
cene. They demonstrated that benz[a]anthracene-3,4-dihydrodiol possessed
about 35 times the activity of the parent hydrocarbon and more than 300 times
the activity of the other four isomeric dihydrodiols in producing lung
adenomas in the newborn mouse. The "bay region" theory predicts that
benz[a]anthracene-3,4-diol-l,2-epoxide would be the reactive ultimate
carcinogenic metabolite of benz[a]anthracene. Since the 3,4-dihydrodiol is
the metabolic precursor of the 3,4-diol-l,2-epoxide, it acts as a proximate
carcinogen according to "bay region" theory predictions.
0-128
-------
6.5.1.5 Tumors in other tissues--Mammary cancer induced in rodents by DMBA
has become an important model system for the study of human breast can-
cer. ' ' The demonstration of the production of hormone-responsive
mammary tumors in normal female Sprague-Dawley rats by a single intragas-
305
trie dose of DMBA by Huggins and coworkers in 1961 introduced a simple
and yet sensitive model for the experimental investigation of the biology
of mammary tumor growth. A year later, Huggins and coworkers demon-
strated that a single intragastric feeding of 20 mg DMBA resulted in the
production of mammary cancer or fibroadenoma in 100 percent of the treated
animals.
In 1965, Huggins reported that intragastric feeding of DMBA could
be substituted with a single intravenous injection of 5 mg DMBA in lipid
emulsion for the purpose of producing mammary cancer in rats. By this
technique, Huggins successfully induced mammary carcinoma in 1500 consecu-
tive female Sprague-Dawley rats, age 50 days. Tumors were detected by
palpation as early as 20 days after DMBA injection. In a study with
90 rats, mammary cancer was detected in 28 to 92 days, with a mean time of
appearance of 42.8 + 11 days. In 1966, Griswold303 adapted the DMBA-
induced mammary cancer technique in rats as a routine for the evaluation of
potential anti-cancer agents. Using the Huggins system, Griswold found
that tumor regression was produced in DMBA-treated tumor-bearing rats by
hypophysectomy or ovariectomy at 90 days after feeding of DMBA and by
injection of testosterone propionate beginning 120 days after DMBA feeding.
6-129
-------
It is now known that mammary cancer can be induced by DMBA in rats not
only by systemic administration but also by local application of the carcino-
308
gen to the mammary gland. These tumors were primarily adenocarcinomas
of ductal origin and were microscopically evident as early as 30 days after
local application of 1 mg DMBA. The minimal dose of DMBA to produce a
mammary tumor was 300 yg. It is important to note that in this study
hyperplastic alveolar nodules did not form in the mammary glands after
local DMBA application, thereby disputing earlier contentions that these
"preneoplastic" lesions were a prerequisite to mammary carcinogenesis.
Thus, it was demonstrated that transformation to a neoplastic state may
occur directly and require no intermediate steps.
In addition to DMBA, ingestion of BaP may also result in mammary tumor
259
formation. Albert and coworkers reported the development of multiple
mammary nodules in Lewis rats following a single intragastric feeding of
50 mg BaP. Numerous nodules were present within 50 days of the treatment.
POM-induced cancers of the endocrine target organs are not limited to
the mammary gland. Ovarian granulosa cell tumors in mice result from
141
exposure to BaP and MCA. In Mi star rats, a silk thread impregnated with
DMBA and inserted in the region of the ovary produced 47 ovarian solid
206
tumors among 121 animals.
In addition to ovarian cancers, DMBA can also produce carcinoma by
309
local application to the pancreas of Sprague-Dawley rats. Less than
1 mg of DMBA placed directly into the pancreas induced adenocarcinoma in
eight of ten treated animals within 180 days.
6-130
-------
Oral administration of POM frequently results in papillomas and
carcinomas in the forestomach of rodents. Numerous studies conducted with
BaP, DBahA, and DBcgC given orally to rats, mice, and hamsters have
250
recently been reviewed, and some of these data are summarized in
Table 6-24. Tumors of the stomach have also been induced by MCA and
DMBA. A single feeding of 3 mg DMBA induced nine stomach papillomas in
18 surviving Swiss mice after 1 year. Ovarian, lymphoid, mammary, and
hepatic tumors were also observed. In addition, the tumorigem'city of DMBA
312
in the rat submandibular gland has been repeatedly demonstrated.
6.5.2 In Vitro Carcinogenesis Studies
The published literature regarding chemical carcinogenesis in cultures
is vast, despite the fact that systematic studies were not begun until the
early 1960's due to the lack of a reproducible transformation assay. It
313
was first demonstrated by Berwald and Sachs in 1963 that polycyclic
hydrocarbons (MCA, BaP) could cause the direct malignant transformation of
hamster embryo cells in culture. Transformed colonies have growth charac-
teristics visually distinct from normal colonies and are readily seen above
a background of normal cells. This assay can therefore be easily used as a
screen to compare carcinogenic activity of suspect compounds. A common
feature of these, and nearly all, transformed cells is that they give rise
to fibrosarcomas upon inoculation into immunosuppressed animals. In addi-
tion to hamster embryo cells, malignant transformation has been demonstrated
in organ cultures, liver cell cultures, fibroblastic cells derived from
mouse ventral prostate, 3T cell lines derived from mouse embryo cells, and
various types of epithelial cells from humans and other animals. >3'
6-131
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Table 6-24. CARCINOGENICITY OF POM BY ORAL ADMINISTRATION TO VARIOUS MAMMALS250
Compound
BaP
Species Dose
Mouse 0.2 mg in PEG3
Mouse 50-250 ppm
(age 17-116 days)
Route of
administration
Intragastric
Dietary
(110-197 days)
Effects
14 tumors of the forestomach in
5 animals out of 11
>7Q% incidence of stomach tumors
at 50-250 ppm for 197 days; no
tumors with diets containing up
to 30 ppm for 110 days
PO
Mouse
Mouse
(age 18-30 days)
Rat
(Sprague-Dawley;
age 105 days)
Hamster
Hamster
250 ppm
250 ppm
2.5 mg per day
500 ppm
Dietary
Dietary
(140 days)
Oral
2-5 mg bi-weekly Intragastric
Dietary
(4 days per week
for up to
14 months)
100% stomach tumor incidence when
diet was fed for 30 days; 5-7 days
of feeding, 30-40*; 2-4 days of
feeding, 10%; one day of feeding, 0%
Leukemias, lung adenomas, and stomach
tumors produced
Papillomas developed in the esophagus
and forestomach in 3 out of
40 animals
5 stomach papillomas in 67 animals
treated for 1-5 months; 7 papillomas
and 2 carcinomas in 18 animals
treated for 6-9 months; 5 papillomas
in 8 animals treated for 10-11 months
12 tumors (2 esophagus, 8 forestomach,
2 intestinal) in 8 animals
Polyethylene glycol
-------
Table 6-24 (continued). CARCINOGENICITY OF POM BY ORAL ADMINISTRATION TO VARIOUS MAMMALS250
Compound
DB[a,h]A
Species
Mouse
Mouse
(A backcross)
Mouse
(DBA/ 2)
Dose
9-19 mg
(total dose)
0.4 mg per day
0.76-0.85 mg
per day
Route of
administration
Dietary
(5-7 months)
Oil emulsion
(drinking water
replacement)
Oil emulsion
(drinking water
Effects
Forestomach tumors in 7 of
22 survivors after one year;
one tumor was a carcinoma
11 papillomas of the forestomach
in 20 animals within 406 days
Pulmonary adenoma tos is in all
27 survivors at 200 days; 24 animal:
co
CO
DB[c,g]C
Mouse
(Swiss, male)
Mouse
(BALB/c, female)
Mouse
(CBA or Strong A
strain)
1.5 mg in PEGa
15 mg
total dose in
almond oil
7-23 mg
total dose in
arachis oil
replacement)
Oral (single dose)
Intragastric
(twice weekly for
15 weeks)
Oral
(twice weekly)
had alveologenic carcinomas; 16
had hemangio-endotheliomas; 12 of 13
females had mammary carcinomas;
2 pulmonary adenomatoses seen among
35 controls
Papillomas of the forestomach in
2 out of 42 animals within 30 weeks
Mammary carcinomas in one out of
20 intact animals and 13 out of 24
pseudo-pregnant animals
Among 55 mice surviving 17 to 59
weeks, 64% had papillomas and 13%
had squamous carcinomas of the
forestomach; 19 animals had benign
hepatomas and another 19 animals
had malignant hepatomas; pulmonary
adenomas observed in all Strong A
mice and none of the CBA mice
a Polyethylene glycol
-------
317 318
Early reports by Berwald and Sachs and Dipaolo and Donovan
described alterations in hamster embryo cells induced by BaP, DMBA, and MCA
which could be used as indicators of a change from a normal to neoplastic
state. The compounds were applied to cells in culture either dissolved in
paraffin and impregnated on filter disks or as a colloidal suspension in
growth medium. Following marked cytotoxicity, foci of transformed cells
developed which displayed continuous proliferation in vitro, chromosomal
abnormalities, and the ability to grow indefinitely in culture. In addi-
tion, these transformed mass cultures, when transplanted to 4- to 6-week
old hamsters, continued to grow and form tumors. A good correlation was
obtained between in vitro carcinogenicity of a polycyclic hydrocarbon and
the number of transformed clones they produced. The maximum rate of cell
transformation in these studies was 25.6 percent in surviving cells,
obtained by treatment with 10 pg/ml of BaP for 6 days. BaP treatment at
1 pg/ml for 6 days produced 19.9 percent transformation in surviving cells.
Further data indicating the activity of several polycyclic carcinogens and
their derivatives are summarized in Table 6-25. It is significant to note
that the K-region epoxides of DBahA and MCA are more active in the pro-
duction of malignant transformation in hamster embryo cells than the parent
320 321
hydrocarbons or the corresponding K-region phenols. ' Although these
results confirm the view that metabolism is necessary for carcinogenic
activity, they conflict with data generated in vivo (see Section 6.5.1)
which indicate that K-region epoxides of polycyclic carcinogens are less
active than the parent compound in various species. A possible reason for
6-134
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Table 6-25.
HAMSTER EMBRYO CELL TRANSFORMATION PRODUCED BY SEVERAL POLYCYCLIC HYDROCARBONS AND
THEIR DERIVATIVES
Compound
DB[a,h]Aa
DB[a,h]Ab
DB[a,h]A5,6-epoxide*
Ct DB[a,h]A5,6-epoxide
i
— *
CJ
tn
MCAC
MCAd
MCA epoxide0
BaPd
Concentration,
ug/ml
2.5
5
10
2.5
5.0
10
2.5
5
7.5
10
2.5
5.0
7.5
10
2.5
5
7.5
2 5
3.5
5
7
1
5
Total number
of colonies
760
690
790
1341
1363
1365
598
601
395
350
895
866
817
707
404
370
349
664
364
245
103
1016
394
Cloning
efficiency, %
4.2
3.8
4.4
13.4
14.0
14.5
3.3
3.3
2.5
1.9
10.1
9.3
9.3
7.7
10.1
9.2
8.7
9.6
2.4
1.5
0.7
8.46
7.17
Number of
transformed
colonies
4
4
7
3
11
7
3
12
31
14
7
20
22
30
9
10
15
20
13
8
17
25
21
%
transformation
0.5
0.7
0.9
0 2
0.8
0.5
0.5
2 0
7 8
4 0
0.8
2.3
2.7
4.2
2.2
2.7
4.3
3.46
3.6
3.3
16.5
2.46
5.33
Reference
321
321
321
320
320
320
321
321
321
321
320
320
320
320
321
321
321
323
321
321
321
323
323
4 7-day treatment of cells seeded on a feeder layer.
b 7-8 day treatment of cells.
c 4-hour treatment of cells seeded in conditioned medium.
d 8-day treatment of cells.
-------
the lack of correlation is the relative instability of K-region epoxides as
compared to the parent hydrocarbon when applied to the skin. It is likely
that in vivo far less of the reactive K-region epoxide can survive passage
through the skin to reach the basal cell layer. Several investigators have
also made it evident that the toxicity and transforming activity of POM are
322 323
dissociable and occur by different processes, ' with the toxicity
being due to random alkylation of nucleophilic regions within the cell.
However, when hamster embryo cells are pretreated with weak chemical car-
cinogens which can induce microsomal enzyme activity (e.g., benz[a]anthra-
cene, methyl methanesulfonate, ethyl methanesulfonate) before the addition
of a potent carcinogen (e.g., MCA, BaP, DMBA), transformation may be con-
siderably enhanced.323'324
As a prescreen for chemical carcinogens, cell transformation in vitro
may be one of the most sensitive techniques available. Pienta and co-
OOK
workers reported that 90% (54/60) of the carcinogens they tested trans-
formed hamster embryo cells in vitro, whereas none of the non-carcinogens
tested showed any activity. Moreover, many of the carcinogens which have
not been shown to be mutagenic toward S. typhimurium in vitro (e.g., chry-
sene) were capable of transforming the hamster cells. Calculations have
been made which show that a battery of tests using S. typhimurium (Ames
assay), polymerase A-deficient E. coli, and hamster embryo cell trans-
formation is capable of detecting nearly all carcinogens tested, both POM
and non-POM types.
6-136
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It is known that alteration of microsomal enzyme activity either jni
vitro or jr^ vivo can have a marked effect on the carcinogenic response to
326
POM. Nesnow and Heidelberger reported that in 10T1/2CL8 cells, a line
of contact-sensitive C3H mouse embryo fibroblasts, transformation in culture
was altered by chemical modifiers of microsomal enzymes. Pretreatment of
10T1/2C18 cells with benz[a]anthracene, a microsomal enzyme inducer, caused
a doubling in MCA-mediated transformation. Similarly, treatment with
inhibitors of epoxide hydrase (e.g., cyclohexene oxide; styrene oxide;
l,2,3,4-tetrahydronaphthalene-l,2-oxide) caused an increase in transforma-
tion over that obtained with MCA treatment alone. Thus, it seemed that
treatments which can induce epoxide-forming enzymes and/or lower the
activity of epoxide-degrading enzymes will enhance the degree of trans-
formation in cultured cells by altering steady-state levels of oncogenic
epoxides.
327 328
Chen and Heidelberger ' developed a system using C3H mouse
ventral prostate cells to examine transformation by carcinogenic hydrocar-
bons under conditions in which no spontaneous malignant transformation
occurred. Cells treated with MCA (1 yg/ml) for 6 days in culture produced
malignant fibrosarcomas in 100 percent of mice into which they were sub-
cutaneously injected. When treated for only one day with MCA at the single
cell stage, 100 percent of the clones were transformed to malignancy. A
good quantitative correlation was obtained between the in vivo oncogenic
activity of eight hydrocarbons (including BaP, MCA, DMBA, and DBahA) and
the number of transformed colonies produced in this system. In contrast to
6-137
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the enhanced transforming ability of K-region epoxides relative to the
parent hydrocarbon in hamster embryo cells, the K-region epoxide derived
from DMBA was less active and the K-region epoxides from MCA, DBahA, and
benz[a]anthracene were more active than the parent compound in mouse
329 330
prostate cells. ' Moreover, the epoxide derived from DMBA was more
toxic than DMBA itself. The anomalous behavior of DMBA may have been due,
however, to a decreased intracellular half-life of the epoxide because of
its greater chemical reactivity.
Transformation of mouse, rat, and hamster embryo cells by organic
331 332 333
extracts of airborne particulate matter has been reported. '*
Cells preinfected with RNA tumor viruses led to accelerated transformation,
as well as transformation in cells not inducible by crude extracts alone.
332
Rhim and coworkers reported that the benzene extract had 100 to 1000 times
the cell transformation activity attributable to the pure BaP contained in
it. In addition, the methanol extract, although containing only 1/30 as
much BaP, showed activity comparable to the benzene fraction. Thus, a
diversity of carcinogenic material (POM or otherwise) is apparently con-
tained in extracts of particulate pollutions; a conclusion which is sup-
ported by in vivo studies (see Section 6.5.1 and 6.5.1.4).
Attempts to transform human cells in culture with POM (e.g., BaP, MCA,
O O/l O O C
DMBA) have generally met with failure. However, Rhim and coworkers
reported that a human osteosarcoma clonal cell line could be further trans-
formed in vitro with DMBA. Morphologic alterations and abnormal growth
patterns became evident in cells treated with DMBA at 2.5 and 1.0 yg/ml in
6-138
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the fifth subculture 52 to 57 days after exposure. One of the altered cell
lines obtained from the 1 ug/ml treatment was tumorigenic in nude mice by
subcutaneous and intracerebral injection. Interpretation of the signifi-
cance of these results is made difficult by the fact that an aneuploid
sarcomatous cell line had to be employed in order to demonstrate successful
transformation.
The use of organ cultures for the assessment of chemical carcinogenicity
suffers from the lack of reliable biochemical and morphological parameters
for measuring early neoplastic changes. Nevertheless, pioneering work in
the application of organ culture to chemical carcinogenesis was performed
•JOC
by Lasnitzki. Microgram quantities of MCA added to organ cultures of rat
and mouse prostate fragments caused extensive hype'rplasia and squamous
metaplasia. However, these preneoplastic morphological effects are
generally not associated with subsequent tumor development when carcinogen-
314
treated pieces of tissue are implanted into host animals. Limited
success has been achieved with organ cultures of rat tracheas, which showed
characteristic morphologic alterations when treated with DMBA, BaP, and
MCA. In addition, Crocker has exposed respiratory epithelia from the
hamster, rat, dog, and monkey to BaP at 7 to 15 yg/ml and observed occa-
sional squamous metaplasia. More commonly, pleomorphic cells in a dys-
plastic epithelium were evident as a result of the treatment. Using this
system, it was also possible to demonstrate a protective effect of vita-
min A against BaP-induced abnormal differentiation. It has been suggested
that rat tracheas maintained in organ culture may be a useful system for
338
the predictive screening of potential carcinogens.
6-139
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A unique organ culture technique has recently been reported in which
BaP (4 or 12 mg) was administered to pregnant mice (strain A and C57 Bl),
and lung tissue of their 19 to 20 day old embryos was subsequently explanted
339
in culture. A transplacental influence of BaP was manifested as a
proliferative stimulus in embryonic lung tissue. Hyperplasia arising in
the bronchial epithelium led to the development of adenomas in a large
percentage of the explants.
6.5.3 Dose-Response Models in Carcinogenesis
Published in the early 1940's, Bryan and Shimkin's paper is a good
summary of the "state of the art" in the design and analysis of experiments
with carcinogenic agents. The development of tumors at local sites of
injection with varying doses of carcinogenic hydrocarbons (MCA, BaP, DBahA)
into mice or rats was characterized in terms of: (1) latent periods be-
tween injection and appearance of tumor and (2) incidence (percent) of
tumor bearing animals.
Assuming that the logarithms of minimal effective doses for individual
animals are normally distributed, an S-shaped cumulative normal incidence
curve is expected as a function of log dose. Consequently, the inverse
transformation to probits is expected to fit a straight line. The authors
presented data which fit this well, at least when doses were not extremely
high. Average latent periods, on the other hand, appeared as a linearly
decreasing function of log dose until a flat minimum was reached at high
doses of carcinogen.
6-140
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Since departures from parallelism in bioassays defy interpretation in
terms of simple relative potencies, the authors recommended comparison of
doses and mean latent periods at the 50 percent level of incidence. Other
specific problems in the design and analysis of experiments in carcinogene-
sis were discussed: species and animal variability, planning of sample
sizes, duration of observation, and competing risks of death.
The principal focus of this paper was on demonstrating the usefulness
of formal statistical methods. No concern was expressed about the low-dose
validity of the incidence and latency models, and no attempt was made to
extrapolate to human populations. In the context of the times when this
article was written, however, it is quite understandable that the authors
had to set their sights on more modest objectives.
341
In 1953, Heston and Schneiderman referred briefly to the initiation-
promotion theory but subsequently focused on the question of whether one or
more somatic gene mutations are involved in carcinogenesis. Specific
reference was made to earlier experiments by Charles and Luce-Clausen who
produced lung papillomas in mice painted repeatedly with BaP; the square
roots of numbers of tumors per mouse were found to fit a linear relation-
ship with dose. If this had been the result of single short-term exposures
to carcinogens, it would suggest a two-step recessive mutation mechanism.
However, the confounding of a long-term dose schedule with latency made
interpretation unclear. Heston and Schneiderman therefore designed a new
experiment using 2-month old strain A mice given a single injection of 0,
0.1, 0.2, 0.3, 0.4, or 0.5 mg DBahA and sacrificed 6 months later.
6-141
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The average numbers of tumors per mouse in the latter experiment
exhibited a good fit to a straight line dose response and a poor quadratic
fit, thus providing greater support for a one-step dominant than for a two-
step recessive gene mutation mechanism.
The mean number of tumors at zero dose exceeded the linearly extrapolated
value. This discrepancy from linearity was attributed by the authors to a
combination of natural carcinogenic processes active at zero dose, and
deactivation or other pharmacological factors operating to discount nominal
doses to lower effective levels. The authors mentioned a "threshold" dose
of 0.03 mg under the experimental circumstances. However, they quickly
rejected this idea in favor of speculation that the dose-response curve may
have convex curvature in the 0 to 0.1 mg range of DBahA, presumably because
of variability among the thresholds of individual mice.
342
Mantel and coworkers considered the consequences of assuming a
linear rise in expected numbers of tumors elicited by injecting a carcinogen
into a mouse at doses above some threshold level. The authors interpreted
the slope of the line as indicative of the animal's sensitivity to the
carcinogen, once the dose exceeds the threshold level. It was shown that,
in a population of mice having variable dose thresholds and variable sensi-
tivities, the average number of tumors per mouse remains a linear function
of dose at levels above the maximum value of the mouse thresholds. It was
shown that at doses lower than this the relationship is convex.
A weighted least squares fit to a replicate experiment with DBahA
gives additional support to the linearity result reported previously by
6-142
-------
341
Heston and Schneider-man. While the authors also demonstrated a linear
range of dose response with intraperitoneal urethane, deceleration at very
high doses occurs, presumably as the result of competition between, or
coalescence of, multiple tumors.
More important from the standpoint of safety regulations, it was shown
that extrapolation of the straight portion of the dose response for groups
of mice could give a biased estimate of the average threshold - an arti-
ficially high one if mice sensitivities are positively associated with
their thresholds, but artificially low in the more likely case of decreas-
ing sensitivity with an increasing threshold. In the latter case, a linear
extrapolation would provide a conservatively low estimate of the average
threshold. However, one may criticize the use of an "average threshold" as
a parameter for safety. It is not ideal for such a purpose, since it does
not directly indicate the proportion of individuals at risk of tumorigene-
sis at extrapolated low dose levels.
343
More recently, in 1976, Yanysheva and Antomonov emphasized the
importance of, but really provided no principles for, choosing animal
species and schedules of exposure which might be appropriate for extrapo-
lating to permissible levels in man. They, like others, were forced to use
highly informal judgments in choosing their experimental conditions.
From 16 to 40 random-bred white rats at each of several doses received
intratracheal BaP at monthly intervals for up to 10 months. Total adminis-
tered doses ranged from 0 to 25 mg. Presumably (though this is not entirely
clear) each rat was observed throughout its entire life in order to determine
6-143
-------
the age at onset, the location, and the histological type of the first
malignant or benign tumor. The authors do not say how they determined the
age at onset, and it is difficult to imagine that they could be very accurate
in that endeavor unless special attention were given to the problem.
The reported lifetime incidences of tumor-bearing rats vary from
9.5 percent (non-lung sites) in controls and 0 percent in those at low dose
levels of benzpyrene, to over 80 percent reported after 25 mg. Responses
appeared as a concave increasing function of untransformed doses or as a
convex function of log doses.
The reported "time to occurrence" of first tumor appeared to be the
average of onset times of first tumors for affected rats at a given dose
level, but the authors were not explicit about this. Generally, these
times decreased with increasing doses in the authors' experience.
By a crude empirical fit, the expected occurrence time of the first
observed tumor in an animal was given as:
16.79
where T = average first appearance time, and d = total dose (mg). Extrapo-
lating from this, the authors estimated that a dose of 0.02 mg would cor-
respond to first tumors at an expected time of 67.9 months. Since this
exceeds the lifespan limit of such rats, it became the authors' recommended
dose. One fault with this approach is that, even when correctly indicated,
the expected time of first tumor onset is merely an average; many tumors
6-144
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could first appear within the lifetimes of members of the species, even if
the extrapolated average exceeded the lifespan limit. Another major diffi-
culty is lack of clarity as to whether or how the experimental experience
should be extrapolated to man.
344
Cornfield provided a valuable review of approaches to the regulation
of involuntary exposure to harmful substances. Particular attention was
given to carcinogens in food. In addition, he examined a formal kinetic
model which suggests the existence of a threshold, or near-threshold, in
the dose-response curve. Cornfield recognized the governmental regulatory
principle of balancing risk against benefits, but the subsequent discussion
focused on problems relating to risks, as expressed by lifetime cancer
incidences at low doses.
344
A regulatory rule-of-thumb is cited by which the no-observed-effect
level (NOEL) is divided by 100 to set an acceptable daily intake (ADI)
tolerance specification for humans. Another technique is to extrapolate
downward from doses that elicit observable lifetime incidences so as to
reach doses expected to produce arbitrarily low incidences of the order of
-6 -8
10" to 10" . The difficulty cited here is in the diversity of results,
depending on the choice of models which perform comparably well in ranges
of observable responses.
The theoretical case for low dose linearity of response (down to 0
response at 0 dose) is favored by: (1) its conservativeness compared with
probit model extrapolation; (2) .an approximate low dose linearity in the
one-hit Poisson-like model of carcinogenesis; and (3) by results of all too
6-145
-------
few epidemiological studies of large groups of people exposed to low doses
(references by the author are to H.A. Kahn, "National Cancer Institute
Monograph No. 19," 1966, and J. Cornfield et al., "Proceedings of the First
International Toxicology Congress," in press).
At least when using formal models, Cornfield argues against the practice
of mingling informal conservatism with extrapolated incidence expectations,
since this may overly weight the risks of harm against offsetting benefits.
A similar argument also would apply to using pessimism or optimism factors
when estimating benefits.
Cornfield presented a kinetic model which yields steady state equations
with interesting implications for dose response curves. The steady state
solutions indicate:
1. No toxic reaction in a host as long as the quantity (moles) of
toxic substance is less than the quantity (moles) of host deactivator,
provided that the host deactivation process is irreversible.
2. No threshold, but an approximately linear dose-response at low
dose levels, provided that the host deactivation process is reversible.
3. That any irreversible component in a vertical chain of deactivation
steps results in a threshold.
4. That any incremental step in a chain of reversible deactivation
components lowers the linear low dose slope.
One assumption in the underlying kinetic model which may not prove to
be correct is that the lifetime probability of a toxic effect is said to be
proportional to the steady state quantity of activated carcinogen. Another
6-146
-------
342
complication, established clearly by Mantel et al. and explicitly recog-
nized by Cornfield, is that individual thresholds (or near-thresholds) do
not preclude convexity in the dose-response for groups of animals because
of variability in individual thresholds.
Finally, and perhaps most important, the formal results apply only to
steady-state conditions. Even in irreversible deactivation processes,
there may be extended periods during which activated carcinogens can con-
stitute a risk of harmful effects prior to the host achieving a steady
state. A zero risk achieved in the steady state would apply only after the
host had survived an initial period at risk. It further seems realistic to
suppose that repeated pulses of carcinogenic exposures throughout life
would complicate the dynamics of the process. Thus, the steady-state
solutions of this formulation may not be particularly useful in establish-
ing new rules for acceptably low doses of harmful substances in the human
population. Perhaps a far greater potential for this kind of model may be
in stimulating new investigations of variability in low dose thresholds in
very large groups of different species and strains of experimental animals,
possibly leading to the identification of endogenous deactivation mechanisms
for carcinogenic substances and, consequently, the raising of thresholds in
those species having increased capacity for carcinogen deactivation.
Unfortunately, the application of animal-derived dose-response relation-
ships to human situations is not likely to provide reliable estimates of
cancer risk. Assuming that the incidence of carcinoma is proportional to
steady state levels of activated carcinogen, the dynamics of this process
6-147
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would be dependent on the species employed and the target tissue examined.
Wide variation in both species susceptibility and metabolite kinetics are
known to exist, and would require the compilation of numerous data sets to
provide meaningful results. For human risk assessment, reliance on epi-
demiologic data, coupled with the apparently conservative assumption of low
dose linearity of response, presently appears to be the most practical
approach.
6.5.4 Synergistic and Antagonistic Interactive Effects
It is well-known that the development of polycyclic hydrocarbon-
induced tumors can be altered by: (1) components in the diet, (2) agents
which affect the activity of certain enzymes, (3) other co-administered
non-carcinogenic or weakly carcinogenic chemicals, or (4) the vehicle used
to deliver a carcinogen to experimental animals. These factors further
complicate the extrapolation of experimental animal data to human situations.
Early work on the inhibition of carcinogenesis was reviewed by Falk
345
and coworkers. In addition, they conducted a series of studies to
evaluate the carcinogenic action of MCA, DBahA, and BaP in the presence of
closely related POM. Simultaneous administration of DBahA or MCA (30 yg)
with 15 times the molar equivalent of their respective dihydro- or hexa-
hydro-reduction products by subcutaneous injection to male C57 black mice
caused either a complete inhibition or dramatic reduction of the normal
carcinogenic response. Administration of the dihydro- and hexahydro-
derivatives at intervals extending from 14 days prior to and seven days
subsequent to DBahA (60 or 135 yg) injection also caused significant
6-148
-------
inhibition of tumor development. The injection vehicle (tricaprylin or
ethyl laurate) also affected the inhibiting response. Injections of the
non-carcinogen phenanthrene together with DBahA in molar ratios of 1:24 and
1:48 significantly reduced tumor yield. In simulated environmental studies
BaP was administered to mice together with various non-carcinogenic POM
commonly found in polluted atmospheres. The results (Figure 6-15) demon-
strated that in all cases a marked inhibition of carcinogenisis resulted.
Neutral fractions isolated from polluted urban atmospheres produced similar
inhibitory effects with BaP.
345
The experiments of Falk and coworkers were modified and repeated by
346 347
Pfeiffer, ' who obtained different results. Ten non-carcinogenic
polycyclic aromatic hydrocarbons found in automobile exhaust were tested in
combination with BaP (3-100 yg) and DBahA (2-75 yg) by subcutaneous injec-
tion in 3000 female NMRI mice. The ten non-carcinogens tested were:
benzo[e]pyrene (2-70 yg); benz[a]anthracene (3-100 yg); phenanthrene (125-
4000 yg); anthracene (31-1000 yg); pyrene (65-2100 yg); fluoranthene (28-
900 yg); chrysene (3-100 yg); perylene (0.2-7.0 yg); benzo(ghi)perylene
(12.8-410 yg); and coronene (3-100 yg). The tumor incidence resulting from
all 12 compounds being administered together could be attributed to the
presence of DBahA, with little influence from BaP or the other ten chemi-
cals. No inhibitory effect of the ten non-carcinogens was evident; more-
over, an increased tumor yield resulted from injection of mixtures contain-
ing increasing amounts of the components. This effect, however, was less
6-149
-------
CARCINOGEN 400^9 BENZO(a)PYRENE
VEHICLE: TRICAPRYLIN
DURATION 15 MONTHS
ANTICARCINOGENS ENCOUNTERED IN AIR POLLUTION
BENZO(a)FLUORENE 0.1:1
PERYLENE0.1:!
PERI NAPTHOXANTHENE 0.1:1
BENZ (a) CARBAZOLE0.15:1
CHRYSENE 0.15:1
BENZO(k)FLUORANTHENE 1:1
BENZ(m, n,o)FLUORANTHENE 1:1
2-NAPHTHOL5:!
ANTHRACENE : PHENANTHRENE : PYRENE 10:10:10:1
i i i
i i i i
0 10 20 30 40 50 60 70 80 90
PERCENT T. B. A.
Figure 6-15. The inhibiting effect of hydrocarbons found in polluted urban
air and cigarette smoke in concentrations approximating those occurring
naturally when injected in combination with BaP.345
6-150
-------
dramatic than if BaP were administered alone, and paralleled the dose-
response curve of DBahA acting singly. It is not known how the relative
tumor susceptibility of NMRI mice as compared to C57 mice used by Falk may
have affected the results.
Many studies on cocarcinogenesis have been concerned with the identifi-
cation of tumor accelerating substances present in cigarette smoke. These
compounds are generally tested for cocarcinogenic activity by repeated
application to mouse skin together with low doses of BaP. A positive
response would be obtained in cases where the tumor yield of the combina-
tion exceeds that produced by either agent alone at the same doses. Van
348 349 248
Duuren and coworkers ' ' established that a pronounced cocarcino-
genic effect could be obtained with catechol and the non-carcinogens pyrene,
BeP, and benzo[g,h,i]perylene. Doses of 2000, 12, 15, and 21 pg, respec-
tively, were applied 3 times a week for 52 weeks to female ICR/Ha Swiss
mice. Each animal also received 5 yg of BaP in 0.1 ml acetone with each
dose of test substance. Although phenol has been regarded as a tumor-
promoter in the two-stage carcinogenesis system, this compound had a slight
inhibitory effect on BaP carcinogenesis when administered in combination.
These results therefore indicated that tumor-promoters and cocarcinogens
may not have the same mode of action, and that the two terms should not be
used interchangeably. Other POM's (e.g., fluoranthene, pyrene, pyrogallol)
248
also possess cocarcinogenic activity but have no tumor-promoting activity.
350
Additional studies by Schmeltz and coworkers established that most of
the naphthalenes found in cigarette smoke have an inhibitory effect on skin
6-151
-------
tumorigenesis (250 yg, 3 times a week) as induced by BaP (3 pg, 3 times a
week). On the other hand, several of the alky]naphthalenes tested (di-
methyl-, trimethyl-, tetramethyl-) enhanced the carcinogenic activity of
BaP on mouse skin.
Numerous investigators have shown that antioxidants are effective
inhibitors of POM-induced tumor development. This action has been demon-
strated with selenium,351'352'353 dl-a-tocopherol (Vitamin E),351'352 and
354
ascorbic acid in mice treated with DMBA and croton oil. The carcino-
genic action of MCA has been reduced by tocopherol-rich diets in rats and
ore OCC
mice. ' The antioxidant food additives butylated hydroxytoluene
(BHT), ethoxyquin, and butylated hydroxyanisole (BHA) have inhibited lung,
breast, and gastric tumor formation induced in rats and mice by various
carcinogens in the diet. ' ' The sulfur-containing antioxidants
disulfuram, dimethyldithiocarbamate, and benzyl thiocyanate inhibited DMBA-
induced mammary cancer in rats when they were added to the diet; in the
mouse, disulfuram prevented the formation of forestomach tumors induced by
BaP in the diet, but had no effect on BaP-induced pulmonary adenoma.
The agricultural herbicide, maleic hydrazide, and its precursor, maleic
anhydride, can inhibit the initiating activity of DMBA in the mouse skin
361
two-stage carcinogenesis system.
Investigators have attempted to explain the mechanism for the anti-
carcinogenic action of antioxidant chemicals. Chromosomal breakage in
human leukocyte cultures induced by DMBA was reduced by simultaneous addi-
tion of ascorbic acid (31.7 percent reduction), butylated hydroxytoluene
6-152
-------
(63.8 percent), Na2Se03 (42.0 percent), or dl-a-tocopherol (63.2 per-
cent). ' It was not apparent from this study whether anticarcinogene-
sis by antioxidants may be due to a direct protective effect against chromo-
some damage or to an interference with metabolic activation of carcinogens,
although the latter seems most likely. This aspect was further pursued by
364
Rahimtula and coworkers who examined the abilities of several antioxi-
dants to affect BaP hydroxylation by rat liver microsomal mixed-function
oxidases. Their results indicated that antioxidants can markedly inhibit
BaP hydroxylation by an apparently direct action on microsomal oxidation
mechanisms. Furthermore, all of the antioxidants tested reduced the bac-
terial mutagenicity of BaP in the presence of rat liver microsomes and
cofactors (Table 6-26). The authors suggested that antioxidants may exert
their protective effect in vivo by inhibiting the formation of carcinogenic
intermediates from POM. This conclusion, however, seems to conflict with
data indicating that inducers of increased BaP hydroxylase activity can
365
also inhibit tumor formation. However, flavones are also inhibitors of
BaP metabolism in vitro, thereby indicating that their specific effects
depend upon how and where they are used. These investigators found that
several synthetic and naturally occurring flavones when incorporated in the
diet (3 to 5 mg/g) or applied to the skin caused a profound increase in BaP
hydroxylase activity in the small intestine and skin, respectively. In
addition, pulmonary adenoma formation resulting from oral administration of
BaP was totally prevented, and skin tumors initiated by BaP application to
mice were significantly reduced (>50 percent) by treatment with the synthetic
6-153
-------
Table 6-26. EFFECT OF ANTIOXIDANTS ON BENZO[A]PYRENE METABOLISM AS ASSAYED
BY Salmonella typhimurium (STRAIN TA98) MUTAGENICITY IN THE
PRESENCE OF RAT LIVER MICROSOMAL FRACTION AND NADPH364
Revertants of strain
Antioxidant Concentration TA 98 per plate
None 384
Butylated hydroxyanisole 100 uM 193
Ethoxyquin 25 yM 148
Pryogallol 100 yM 156
Glutathione 1 mM 92
6-154
-------
flavone, B-naphthoflavone. Pulmonary tumor formation was also reduced
50 percent by incorporation of the naturally occurring flavone, quercetin
pentamethyl ether, into the diet. The possibility that only specific
components of the drug metabolizing enzyme system may be induced by anti-
366
oxidants has not been fully explored. Sullivan and coworkers recently
demonstrated that BHA, BHT, phenothiazine, phenothiazine methosulfate, and
ethoxyquin can all reduce the quantitative yield of BaP metabolites in
incubations with rat liver microsomes. On the other hand, these antioxi-
dants did not react with 6-oxy-BaP free radical, although some reduction in
the enzymatic in vitro formation of 6-oxy-BaP free radical could be obtained.
The authors concluded that the antioxidant effect on BaP tumorigenesis is
probably not due to a direct reaction with BaP free radicals.
In addition to flavones, other naturally-occurring compounds have
exhibited protective effects against POM-induced tumor formation. Vita-
min A has clearly been shown to play a role in reducing carcinogen-induced
tumors.367'368'369'370 Nettesheim and Williams371 recently undertook to
determine whether inadequate vitamin A consumption may predispose indi-
viduals to carcinogenesis, or whether increased vitamin A intake exerts a
protective effect against neoplasia. They found that a diet deficient in
vitamin A increased the formation of MCA-induced metaplastic lung nodules
in female Fisher 344 rats, even though adequate amounts of the vitamin were
stored in the liver. On the other hand, moderate amounts of vitamin A
added to the diet markedly reduced the development of MCA-induced lesions
of the lung. High doses of the vitamin given intragastrically provided no
additional protection, however.
6-155
-------
Further studies on naturally occurring antineoplastic compounds were
372
recently reported by Wattenberg. Benzyl isothiocyanate and phenethyl
isothiocyanate, both found in cruciferous plants such as cabbage, brussel
sprouts, cauliflower, etc., inhibited DMBA-induced mammary cancer in
Sprague-Dawley rats. When added to the diet together with DMBA, these
compounds inhibited the development of forestomach tumors and pulmonary
adenomas in female ICR/Ha mice. Similar anticarcinogenic actions were
obtained when BaP was incorporated into the diet. These results lead to
interesting speculation regarding the role and importance of diet in human
susceptibility to environmental carcinogens. In cases where dietary con-
stituents can alter the metabolism of xenobiotics such as ROM's, then the
anticarcinogenic effect may result from an alteration of steady state
levels of activated versus detoxified metabolites.
Studies have shown that not only can specific substances in the diet
affect the response to carcinogens, but protein deprivation in general may
also decrease the activation of carcinogens. The feeding of protein-
deficient diets to male mice caused decreased liver weights, and reduced
cytochrome P-450 content in the total liver. Diets deficient in both
protein and choline produced even further reductions in liver weight and
cytochrome P-450 content. Liver microsomes isolated from these animals
displayed a decreased ability to activate dimethylnitrosamine to a mutagen
(in the Ames Salmonella test system), which paralleled the reduction in
cytochrome P-450 content produced by the diet. Conversely, the inactiva-
tion of the direct-acting (ultimate) carcinogen N-methyl-N'-nitro-N-nitro-
soguanidine was reduced in liver microsomes from mice receiving a protein-
deficient diet.
6-156
-------
In humans fed charcoal-broiled beef, the metabolism of the drug
phenacetin was enhanced; in pregnant rats a similar diet stimulated the
59
activity of AHH in the placenta and liver. Further studies showed that
high-protein diets enhanced the metabolism of antipyrene and theophylline
in man, while a high-carbohydrate diet depressed the rate of metabolism of
these drugs. Additional agents in man's environment which inhibit AHH
activity include certain organophosphate pesticides, piperonyl butoxide,
carbon tetrachloride, ozone, carbon monoxide, nickel carbonyl, nickel, tin,
59
cobalt, and other metals.
In a review on cocarcinogenesis Salaman and Roe discussed the
numerous factors which can modify the host response to a carcinogenic
substance. Dietary restriction, stress, hormone balance, and administra-
tion vehicles may all change the outcome of carcinogen administration.
Cocarcinogenesis in skin involves the action of potential tumor initiators
(e.g., ethyl carbamate, isopropyl N-phenylcarbamate, N-(3-chlorophenyl)-
carbamate) and tumor promoters (e.g., citrus oils, croton oil, anthralin,
surface-active agents). The incidence of BaP-induced gastrointestinal
tumors in mice was also increased by ingestion of citrus oils. In addition
to chemical agents, oncogenic viruses (Shope papilloma, Shope fibroma, Rous
sarcoma, polyoma, and Graffi leukemogenic virus) and non-oncogenic viruses
(vaccinia, poliovirus 2, myxoviruses) can increase the tumor yield result-
ing from exposure to POM.
The effect of cyclic AMP on skin tumor formation is paradoxical in the
sense that both inhibition and enhancement can be manifested, depending on
6-157
-------
the conditions of the experiment. In the two-stage skin carcinogenesis
system, cyclic AMP inhibits tumor formation by apparently interfering with
375
the promotion phase. In follow-up studies, cyclic AMP enhanced DMBA-
induced skin tumor development in strain A mice under conditions when
T7fi
repeated doses of the carcinogen and no promoting agent were used. In
this instance, cyclic AMP exhibited cocarcinogenic activity, although its
mechanism is not understood. It is possible, however, that the stimulatory
effects of cyclic AMP on tumor development may be mediated via the drug
metabolizing enzyme system (MFO). Numerous investigators have observed
that the specific events which accompany a trophic response (increased
cyclic AMP levels, induction of ornithine decarboxylase, increased RNA
synthesis) are produced by nearly all mitogenic stimuli, including carcino-
gens. ' Although many tumors are associated with sustained increases
in cyclic nucleotide levels, the events which lead from cell proliferation
to neoplasia are not clear.
6-158
-------
6.6 REPRODUCTION AND TERATOLOGY
The interference with reproductive success by exposure to POM has only
been documented for a few compounds. When large doses (0.5 to 5.0 mg) of MCA
in olive oil were injected in mice on the first or seventh day of pregnancy,
ooc
fetal resorption usually occurred in most of the treated animals. However,
sham-treated controls were not included in the study, thereby making inter-
pretation of the results quite difficult. Treatment with MCA at mid-term
(day 11) was ineffective in interrupting pregnancy (Table 6-27). Among those
animals going to full term and giving birth, the offspring displayed reduced
body weights in comparison to controls but no congenital abnormalities were
evident at birth or during a 3-month observation period. Although similar
treatment of non-pregnant mice with MCA had no apparent effect, it is diffi-
cult to determine whether pregnancy was interrupted by a direct action on the
embryo. This is especially difficult in light of evidence which indicates
that MCA does not readily cross the placenta (see Section 6.1).
Subsequent studies did establish, however, that if MCA directly contacts
387
mid-term mouse embryos, fetal resorptions and malformations will occur. In
these experiments, 0.01 ml of a 0.025 percent solution of MCA in benzene was
injected directly into the embryonic fluids of 10-day-old CSH(Jax) mouse
embryos. Their results, presented in Table 6-28, indicate that fetal resorp-
tions and malformations were very common. From the data presented, it is not
possible to determine the contribution of the benzene injection vehicle in
producing the embryopathic effects observed. Moreover, a 9.3 percent inci-
dence of fetal resorptions in sham-operated (incisions made but no MCA or
vehicle injected) control mice was observed, which could not be attributed to
a specific cause.
6-159
-------
CTi
o
Table 6-27. EFFECT OF 3-METHYLCHOLANTHRENE ON PREGNANCY IN MICE386
Route of
administration
Intraperitoneal
Subcutaneous
Subcutaneous
Duration of pregnancy,
days
1
1
6-7
11
1
1
6-7
6-7
6-7
11
11
7
7
Total dose of 3-methylcholanthrene,
mg
0.5
1.0
1.0
1.0
2.0
5.0
1.0
2.0
5.0
2.0
5.0
2.0
5.0
Number of animals in which
pregnancy was interrupted
Total number studied
4/5a
7/7a
2/3
0/3
3/5a
ll/ll3
3/5
3/4
6/6
0/2
0/4
2/5b
7/7°
a A total of 50 mice, in which vaginal plugs were found, received no treatment; 39 of these animals became pregnant.
Mice ovariectomised and received 1.5 mg of progresterone per day.
-------
Table 6-28. DATA ON MOUSE EMBRYOS TREATED WITH 0.01 ml OF 3-METHYLCHOLANTHRENE
387
Group
0.025* Methyl chol anthrene
in benzene9
0.025% Methyl chol anthrene
In benzene"
Sham-operated control
Number
pregnant
animals
19
10
6
Number
breeders
that
delivered
10
4
6
Number
embryos
treated
122
67
43
Number
young
born
34
19
39
Prenatal
mortality.
%
72.1
71.7
9.3
Tall
Hemorrhages defects
7 5
4 2
Other
defects
2
4
Abnormalities.
Total %
14 41.2
10 52.6
0 0
* Offspring delivered normally.
b Offspring delivered by Caesarean section.
-------
Little success has been achieved in demonstrating a marked effect of BaP
on reproduction, despite its ease of absorption and extensive tissue distri-
bution (including transplacental). Early studies involved the feeding of BaP
to dogs, rats, mice, chickens, ducks, and cockroaches and indicated that a
period of infertility may occur in the chicken, and fetal resorptions may
388
occur in the rat. Rats fed 1.0 mg BaP per gram of food displayed no abnor-
malities in the ovarian cycle, ovulation, fertilization, and implantation; a
few resorptions were observed, however. A more detailed investigation was
subsequently pursued to establish if lower doses of BaP might affect fertility
389
and development in Swiss mice. At levels of 0.25 mg or 0.50 mg BaP per
gram of food given either before, during, or after mating, no adverse effects
could be shown on fertility or the developing embryo. Even when BaP concen-
trations were increased to 1.0 mg per gram of food, mice continued to repro-
duce normally. Neither males nor females were affected by this ration. Mice
fed BaP in their diet at 1.0 mg per gram of food since the time of weaning
appeared normal and gained weight readily.
Although the effects of BaP on reproductive function are apparently not
severe, a transplacental carcinogenic action has been shown with very large
390
doses of BaP. Mice of the Ha/ICR strain were administered BaP (4 mg) in
carbowax-400 subcutaneously on days 11, 13, and 15 of pregnancy. Offspring
were delivered by Caesarean section and nursed on untreated foster mothers to
ensure that no BaP exposure could occur through the milk. After weaning at
4 weeks of age, mice received twice weekly applications of 1 percent croton
oil in acetone dropped on the back to determine if BaP-initiated tumors could
be promoted. Mice were sacrificed at age 28 weeks and examinations made 'for
6-162
-------
the formation of pulmonary adenomas. As the data in Tables 6-29 and 6-30
indicate, prenatal treatment with BaP considerably enhanced tumor development
in both lung and skin during the postnatal period.
In contrast to the questionable teratogenic effects produced by MCA or
BaP, DMBA and its hydroxymethyl derivatives possess considerable teratogenic
391 392
potency. ' Treatment of Sprague-Dawley rats with a single intravenous
dose of 7-hydroxymethyl-12-methylbenz[a]anthracene (about 5.5 to 7.0 mg) in
olive oil on day 8 of pregnancy produced 100 percent fetal resorptions. A
similar dose of DMBA on day 8 of pregnancy produced a smaller incidence of
fetal resorptions. Resorptions in control rats given olive oil with or with-
out saline averaged 7 percent (maximum 9 percent). Treatment with 7-hydroxy-
methyl-12-methylbenz[a]anthracene on day 12 to day 14 of pregnancy resulted in
malformations in every surviving fetus. Characteristic pathology was found in
all littermates: stunting, lordosis of cervical and upper thoracic parts of
the vertebral column, and an encephalocele and a spina bifida. No skeletal
deformities were seen among 2000 controls. Teratogenic effects in the absence
of an increased resorption rate were also obtained with DMBA given on day 13
of pregnancy. However, these effects were not as pronounced as those produced
by the hydroxymethyl derivative. Since 7-hydroxymethyl-12-methylbenz[a]-
anthracene is a principal metabolite of DMBA and also exceeds the parent
compound in teratogenic potency, it was postulated that metabolic activation
precedes fetal damage. Furthermore, it was proposed that the ultimate embryo-
pa thic substance derived from DMBA may be a metabolite of 7-hydroxymethyl-12-
methylbenz[a]anthracene, since teratogenesis could be inhibited by pretreat-
ment of mice with microsomal enzyme inhibitors before administration of the
6-163
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Table 6-29. EFFECT OF BENZO[A]PYRENE ADMINISTRATION TO PREGNANT MICE ON PULMONARY ADENOMA FORMATION
IN THE PROGENY390
en
-P.
group
Absolute controls
Vehicle controls
Benzo[a]pyrene
Material
administered
Nothing
Carbowax-400
Benzo[a]pyrene
in carbowax-400
No of
mice
82
89
55
No. of
adenomas9
6
10
34
% of
adenomas
7.3
11.2
61.8
No. of
per group
7
13
130
No. of
per mouse
0.09
0.15
2.36
No. of
mice with
multiple
adenomas
3-6
0
1
13'
7-9
0
0
6
a Number of mice with pulmonary adenomas at 28 weeks of age.
-------
Table 6-30. EFFECT OF BENZO[A]PYRENE ADMINISTRATION TO PREGNANT MICE ON SKIN PAPILLOMA
FORMATION IN THE PROGENY390
Experimental
group
Absolute controls
Vehicle controls
Benzo(a)pyrene
No. of
mice
82
89
55
No. of
mice with
papillomas
6
8
13
% of
mice with
papillomas
7.3
9.0
23.6
No. of
papillomas
per group
8
9
18
No. of
papillomas
per mouse
0.10
0.10
0.33
a Number of mice with skin papillomas after 24 weeks of topical treatment twice weekly with 1% croton
oil. Mice were 28 weeks of age.
-------
392
hydroxymethyl compound. Unfortunately, the use of large doses of DMBA and
its derivatives precludes the possibility of risk assessment under realistic
environmental exposure situations.
6-166
-------
6.7 HUMAN STUDIES
6.7.1 Review of Epidemiologic Evidence
Epidemiological evidence on the health effects of polycyclic organic
matter (POM) comes from both occupational studies and community air pollution
studies. Occupational studies, especially among gas production workers and
coke plant workers, have shown that long-term exposure to the products of the
destructive distillation of coal can cause an elevated rate of lung cancer as
well as cancer of other sites and chronic non-malignant lung disease. Com-
munity studies, which involve much lower levels of exposure and are more
problematic because of the heterogenous populations involved, attempt to
detect an association between community morbidity and mortality rates and some
direct or indirect index of air pollution.
In both types of studies, exposure is not limited to POM alone but
includes exposure to irritant gases, such as S0?, NO , particulate matter, and
w A
trace metals (e.g., arsenic, nickel, chromium) which may exert their own
effects or may enhance the effects of the POM. Additionally, in both occupa-
tional and non-occupational air pollution studies, smoking is a powerful
393 394
causative factor of similar diseases; ' and in community air pollution
studies, occupational exposure represents another potential causative factor,
especially in areas where a sizeable proportion of the work force is employed
395
in occupations with high levels of exposure to toxic substances.
6.7.1.1 Occupational studies—The most extensive epidemiological studies of
occupational groups with exposure to POM are those of coke plant workers and
6-167
-------
of gas production workers. Other relevant studies include those of wax
pressmen and roofers. In most of these studies, exposure is not limited to
POM, and other substances are also usually present such as gases S02 and NO ,
particulate matter, and trace elements such as arsenic, nickel, and chromium.
POM is present in the fumes from coal carbonization and coal gasification in
concentrations that are orders of magnitude higher than community levels. It
has been hypothesized that the proportion of carcinogenic compounds released
396
into the air increases with the temperature of carbonization.
6.7.1.1.1 Historical perspective. Epidemiological studies in different
countries have demonstrated that workers exposed to the products of the
combustion and distillation of bituminous coal experience an increased inci-
dence of cancer of several sites (lung, pancreas, kidney, bladder, skin).
These studies are discussed below, and the overall results are summarized in
Tables 6-31 through 6-33.
The earliest association of skin cancer with occupations involving
exposure to coal-combustion products was that of Percival Pott, who in 1775
observed a high incidence of scrotal cancer among chimney sweeps exposed to
soot. His observation has now become a classic reference of occupational
medicine for cancer and for discussions of coal tar products. In the early
20th century, several studies established the association between the handling
397 398
of coal tar products and pitch products and skin cancer. ' Kennaway and
Kennaway, in a later series of reports, found an increased rate of bladder
and lung cancer in occupations involving exposure to coal gas, tar, pitch,
and soot.399'400-401
6-168
-------
Table 6-31. SUMMARY OF-EPIDEMIOLOGICAL EVIDENCE OF CARCINOGENICITY
Investigator
Kuroda and Kawahata
Kawai , Amamoto
and Harada
Henry. Kennaway
and Kennaway
Kennaway and
Kennaway
i
Z? Kennaway and
10 Kennaway
Doll
Doll
Date of
study
1936
1967
1931
1936
1947
1952
1965
Type of
study
Historical
prospective
Historical
prospective
Historical
prospective
Historical
prospective
Historical
prospective
Historical
prospective
8-year pro-
spective
Site
Lung
Lung
Bladder
Lung
Lung
Lung
Lung
Results
(12 lung cancer deaths out of a total of 15
deaths for all cancers) Relative risks cannot
be calculated but there is suggestion of
26-fold excess over general population
(Lloyd. 1971)
33 times the rate for other steelworkers
1-1/2 to 4-fold Increased risk relative to
general population
3-fold excess for "gas stokers and coke-oven
chargers"
81% excess of lung cancer deaths
Those with heavy exposure showed 694 excess
relative to those with minimal exposure (by-
Characterization of exposure
Producer gas workers
Workers in producer gas works
Workers in 5 out of 10 occupations
involving exposure to coal products
British producer gas workers;
chimney sweeps and several cate-
gories of gas-works employees
Former gas retort workers
(pensioners)
Gas-worker mortality was greatest
for those with greatest exposure
Bladder
Doll
1972
4-year follow- Lung
up of 8-year
prospective
products workers)
Those with heavy exposure showed 4-fold excess
relative to those with minimal exposure
Heavily exposed workers showed highly signifi-
cant excess; by-products workers showed no excess
(retort house workers)
-------
Table 6-31 (continued). SUMMARY OF EPIDEMIOLOGICAL EVIDENCE OF CARCINOGENICITY
Investigator
Reid and Buck
Brunsgaard
Lloyd, Lundin,
Redmond, and
Geiser
Lloyd
Date of Type of Site
study study
1956 Retrospective Lung
study of
deaths among
coke plant
workers during
1949-1954
1959 Retrospective Lung
study of
deaths among
employed and
retired gas- Bladder
workers over
a 15-year
period
1970 Prospective Lung
study of
mortality
among steel -
workers over
work- area
1971 Prospective Lung
study
Results Characterization of exposure
No excess in number of cancer deaths among Coke plant workers
coke plant workers as a whole nor of lung
cancer for oven workers
6.4-fold increase over general population All deaths occurred among gas-workers
with at least 5 years experience; most
had more than 10 years
5 deaths that appeared to be a significant
excess
Coke plant workers had 2-fold excess Coke plant workers
relative to rate among steelworkers
Coke-oven workers showed 2-1/2-fold excess Coke plant workers
over steelworker population,
Pancreas Top-side workers had 5-fold risk; top-side
workers with 5 years full-time
Intestine Top-side had 10-fold risk, nonoven workers
may have excess risk of digestive cancer
-------
Table 6-31 (continued). SUMMARY OF EPIDEMIOLOGICAL EVIDENCE OF CARCINOGENICITY
Investigator Date of Type of
study study
Redmond, Ciocco, 1972 Follow-up to
Lloyd, and Rush prospective
study
Redmond 1976 Follow-up to
previous study
en
m—l
^ Redmond et al. 1976 Historical
prospective
of by-products
workers
Site
Lung
Kidney
Prostate
Lung
Intestine
Pancreas
Kidney
Lung
Pancreas
Intestine
Buccal
Pharygeal
Results Characterization of exposure
Coke oven workers had 1.34 excess risk Coke plant workers
relative to nonoven workers
Coke oven workers had a 7.49 excess risk
over nonoven workers
Coke oven workers had 1.64 excess risk
over nonoven workers
15.72 excess for full-time top-side oven
workers
2.37 excess for nonoven workers
4.29 excess for nonoven workers
5 excess for all coke plant workers;
3.31 excess for oven workers
4.95 excess for nonoven workers
2.93 excess for nonoven workers
-------
ro
Table 6-32. SUMMARY OF MORTALITY DATA IN GAS WORKERS OBSERVED BY DOLL
A. Causes of death of pensioners from 1939 to 1948 compared with the experience of Londoners
Cause of death Expected deaths
at England and
Wales rates
Cancer and other tumors 123.5
Cancer of stomach and 25.0
duodenum
Cancer of lungs and pleura 10.4
All causes 831.5
London
weights
1.10
0.93
1.33
1.03
No. of deaths Test of significance of difference
Exnected at Observed between observed ft* expected value
London rates
135.9 156
23.3 32
13.8 25 <0.01
856.4 840
,406
Table 6-32 A adapted from Doirub (1952), Table 6-32 B adapted from Doll (1956)408.
The values for P are probabilities with which as great or greater differences between the observed and expected deaths might
occur by chance. Values greater than 0.05 are not recorded.
B. Standardized annual death rate per 1000 men: all four original boards grouped together, and England and Wales
Cause of death
Cancer of lung
Cancer of bladder
Cancer of skin
and scrotum
Other cancer
Bronchitis
All causes
1 Sept. 1953 to
31 Aug. 1961
Class Aa
3.39 (55)
0.28 (4)
0.07 (1)
2.11 (36)
3.53 (51)
19.68 (304)
Class C^
1.16 (5)
0.00 (0)
0.00 (0)
2.41 (9)
2 10 (9)
15.00 (61]
E&W
2.05
0.17
0.02
2.57
1.61
18.66
1 Sept. 1961 to
31 Aug. 1965
Class A
4.08 (44)
0.42 (6)
0.19 (2)
3.02 (34)
2.42 (26)
21.69 (243)
Class Cj
1.78 (6)
0.29 (1)
0.00 (0)
2.37 (8)
3.12 (9)
14.50 (46)
E&W
2.24
0.17
0.02
2.51
1.64
18.69
1 Sept. 1953 to
31 Aug. 1965
Class A
3.82 (99
0.40 (10
0.12 (3)
2.70 (70)
2.98 (77]
21.21(547]
Class C1
1.59 (11)
0.13 (2)
0.00 (0)
2.39 (17]
2.57 (18]
14.91(107]
E&W
2.13
0.17
0.02
2.55
1.63
18.67
Significance of diff-
erence between observed
[Class A) and expected
(E&W), value of P
< 0.001
0.03; 0.02
< 0.001
Standard population -- total number of man-years at risk for both occupational classes and all four boards, 1953-65. The one
untraced man in Class A is counted as alive at the end of the study.
a Class A = heavy exposure, i.e., coal carbonizing process workers.
Class C. = exposure only to by-products, i.e., process and maintenance workers in chemical and by-products plant.
-------
Table 6-33. SUMMARY OF OBSERVATIONS ON OBSERVED DEATHS AND RELATIVE RISKS OF DEATH FROM ALL CANCERS,
RESPIRATORY CANCER, AND CANCER OF THE DIGESTIVE TRACT*
cr>
co
Distribution
of workers
Length
of employment, yr
Total coke oven
Coke
Oven
Oven
Oven
oven
topside full-time
topside part-time
side
only
Nonoven
No one
coke
plant area
5+
1860
993
ISO
290
553
836
31
10+
1194
574
72
245
257
578
42
15+
790
325
29
159
137
392
73
Deaths and RR1
malignant
5+
Obs.
166
101
35
26
40
65
0
RR
1.47b
1.66b
3.70b
1.59b
1.17
1.28
d
s of death
neoplasms
10+
Obs.
136
85
22
31
32
48
3
RR
1.50
1.95
5.12
1 85
1.46
1.10
d
from
15+
Obs.
b 108
" 63
b 12
b 32
19
39
6
Deaths and RR's of death from
respiratory cancer
5+ 10+ L5+
RR Obs. RR Obs. RR Obs. RR
1.62b
2 40b 54 3 02b 44 3.42b 33 4.14b
7.63b 25 9.19b 16 11.79b 8 15.72b
2.73b 12 2.29b 16 3.07b 18 4 72b
1.51 17 1.79C 12 1.99b 7 2.00
1.13
1.34
Deaths and
digestive
All malignant neoplasms of
Large
digestive
system
Intestine
Pancreas
Other
Obs.
28
11
8
9
5+
RR
1.58
2 31
3.67
0.83
RR's of death from
system among nonoven
Obs.
c 23
c 10
b 7
6
10+
RR
1.53
2.52
3.75
0.65
cancer of
workers
15+
Obs . RR
b
b
19 1.
8 2.
6 4.
5 0.
53
37C
29b
65
! Redmond411 (1976).
° P<0.01.
5 P<0.05.
less than 5 deaths.
-------
In these studies, the number of workers in any one occupational group
was small, and it was not possible to calculate relative risks for exposed
groups with certainty or to obtain evidence for a dose-response relationship.
402
Kuroda demonstrated a high incidence of lung cancer among Japanese gas
generator workers. Although lung cancer was a relatively rare form of cancer
in Japan during the 1930's (accounting for only 3.1 percent of all cancer),
this study showed that lung cancer accounted for 80 percent of all cancer
among the gas generator work force who were exposed to extremely high quanti-
ties of coal tar pitch volatiles.
6.7.1.1.2 Recent studies. In a study of 504 deaths among former gas workers
403
at a Japanese steel plant, Kawai et al. found six deaths from lung cancer
in contrast with the expected number, 0.180, using other workers at the same
plant with no gas generator work experience as a control. Age-standardized
mortality from lung cancer in the control group was close to that of the
general male population. The large excess of lung cancer deaths among the
gas workers could not be attributed to smoking. The authors noted that the
excess of lung cancer mortality occurred only in the age group of 45 to
54 years. Data for those in this group with 10 to 19 years of gas generator
work experience showed a marked increase in lung cancer risk, whereas data
for those under 45 years of age having the same work experience (10 to
19 years) showed no significant excess mortality.
Bruusgaard studied 125 deaths among former gas works employees in
Norway, all of whom had at least five years' work experience and most of whom
had more than ten years. The number of respiratory cancers was higher than
6-174
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expected (12, or 1.6 percent of the total number of deaths, against 1.5 per-
cent in males for the country as a whole). The proportion of lung cancers to
•
cancer of all sites among the gas workers (29.8 percent) was also significantly
higher than that in the general population, 9.2 percent. In addition, there
were five deaths from cancer of the bladder--!2 percent of all cancers.
Although Bruusgaard gives no exposure data and occupational histories for
most cases are incomplete, he notes that workers with a history of employment
in the retort houses had an especially high incidence of respiratory cancer.
405
Reid and Buck conducted a mortality study in 1956 among 800 coke plant
workers randomly selected from a total of 8000 employed over the years 1949-
1954, inclusive. The study did not show an elevated cancer risk when death
rates for all causes and for cancer were compared with age-specific rates
prevailing in the period 1950-1954 among workers in a large unspecified
industrial organization. The cause of death was ascertained either by refer-
ence to the union's funeral fund records, which were required to be supported
by a copy of the death certificate, or by a special search at the General
Register Office. The coke plant workers were categorized by occupation:
coke oven workers, those handling by-products, and maintenance workers (further
grouped as laborers, workers, and foremen). No total excess in the number of
cancer deaths was found among the coke plant workers as a whole, and there was
a "complete lack" of any excess of respiratory cancer for men working on the
ovens. When occupational history was taken into account, no excessive cancer
risk was found for by-product workers and only a small excess was found for
men who had at some time worked at the oven.
6-175
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This study was criticized by Lloyd, who pointed out that Reid and Buck
may have underestimated the number of lung cancer deaths, since the records
included only men dying while still "on the books" during the period 1949-
1954. Lloyd also states that "the population at risk and the distribution by
age and area of prior employment were based on an estimate of figures which
excluded retirees and those who had left employment."
In an effort to further quantify the Kennaway and Kennaway data suggest-
ing a correlation between occupational exposure and cancer mortality, Doll
studied the mortality among male pensioners (over age 60) of a large London
gas works company for a 10-year period (1939-1948) and compared the data with
mortality data for the population of Greater London. Men who retired early
were included in the study on reaching 60, so as not to bias the investigation
by the exclusion of a particularly unhealthy group who retired early because
of health reasons. Age-standardized mortality ratios were calculated by use
of mortality rates for England and Wales, which were weighted to approximate
higher rates in Greater London. The causes of death recorded by the company
had been copied from death certificates. The pensioners' mortality from all
causes was close to the expected (840 deaths against 856 expected), but the
mortality from cancer was in excess of the expected (156 against 123.5;
p<0.01). Cancer of the lung accounted for the greatest excess (25 against
10.4; p< 0.001) which constitutes a significant increase in mortality.
To assess differences in risk among different jobs within the gas works,
Doll categorized the pensioners as those employed outside the works and those
involved directly in the production of gas or in handling of the waste products,
6-176
-------
representing a low- and a high-exposure group, respectively. Excess lung
cancer among the high-exposure group was significant (17 observed versus 8.6
expected, 0.01 < p< 0.02).
407
In a separate study, Doll carried out an 8-year prospective analysis
of mortality from different causes among several occupational groups of gas
workers and retirees covering the years 1953-1961. The study included
11,499 men between 40 and 65 years of age at the start of the study with five
or more years in the gas works plant. Observed gas worker mortality rates
were compared with those expected in populations of England and Wales and
regional metropolitan areas.
The workers were grouped into three classes according to their exposure:
heavy exposure; intermediate exposure; light exposure, or exposure only to
by-products. Again, elevated mortality was attributed to respiratory system
disease, specifically, cancer of the lung and bronchitis. The lung cancer
mortality rate was 69 percent higher for the heavy exposure group than for
the low exposure group. A fourfold higher rate of bladder cancer observed in
the heavy exposure group as compared with the light exposure group verged on
significance (p = 0.06) according to Doll. He concluded that the mortality
of gas workers varied significantly with the type of work and that mortality
was highest among workers with greatest exposure to the products of coal
carbonization.
A report on an additional four years of observation of the cohort
provided follow-up information on 2,449 coal-carbonizing process workers and
579 maintenance workers for mortality rates gathered at annual intervals from
6-177
-------
1961 to 1965. Additional employees of four other gas boards were also fol-
lowed over periods of 7 to 8 years. Cause of death in the original studies
was obtained from death certificates. The new data showed a pattern similar
to that of data for the first eight years.
Heavily exposed workers experienced a highly significant elevated mortality
from lung cancer (p<0.001) and bronchitis (p<0.001). Data on by-product
workers showed no excessive mortality and over the 12-year period provided no
substantial evidence of increased occupational risk for this group.
The additional four years of data in this study support the earlier
association between exposure to the products of coal carbonization and in-
creased lung cancer and also a risk of bladder cancer (p = 0.06).
The long-term study of mortality among steel workers conducted by Lloyd,
Redmond, and coworkers has confirmed and extended the well-established findings
that workers exposed to the coal-carbonization process experience a markedly
increased cancer risk. The successive phases of this study also showed in-
reasing cancer response rates with increasing exposure and dose.
The coke plant workers studied by Lloyd were employed in by-product coke
plants. Exposure to effluents from by-product coke ovens is due to the
escape of volatiles during charging, quenching, discharging, and to their
escape through improperly sealed openings.
In these studies, the workers were classified by work area within the
plant in terms of function and exposure to effluents. The by-product coke
plant was analyzed in terms of three distinct areas: (1) the coal-handling
area, (2) the coke oven area, and (3) the by-products plants for recovery of
6-178
-------
gas and chemical products. Since earlier work (e.g., Doll, Kennaway and
Kennaway ' ) had shown no apparent increased cancer risk for men involved
in work similar to that performed in areas (1) and (3), some of the initial
study groups included only those workers employed in area (2).
In the first phase of this long-term study, Lloyd undertook a 9-year
prospective analysis of 2,552 coke plant workers employed in 1953. He examined
the mortality records of the workers in relation to length of employment and
work area within the coke plant and compared the cause-specific mortality of
coke plant workers as a whole with the mortality of the total steelworker
population of 58,828 workers. Coke plant workers were categorized as oven
workers and non-oven workers. The excess lung cancer mortality among coke
plant workers indicated that risk was elevated nearly threefold among coke
oven workers (20 observed deaths versus 7.5 expected). Men working on the
tops of the coke ovens had nearly a fivefold increased risk, and men employed
five or more years at full-time topside jobs had a tenfold risk (15 observed
deaths versus 1.5 expected). Furthermore, a significant excess of cancers of
the digestive system was observed in both long- and short-term non-oven
workers (17 versus 9.7 expected; significant at the 5 percent level). Cancer
of the pancreas and large intestine accounted for the greatest excess.
409
Redmond et al., in a follow-up of earlier reports in the series,
examined the mortality records of cohorts of coke oven workers in an expanded
study at 12 steel plants. In addition, the data from the earlier study of
two Allegheny County steel plants with coke plants were updated from 1969 to
1966 and were compared with data from 10 other plants for the same period.
6-179
-------
The cohorts at the 10 additional plants included all men who had worked at or
on the oven at any time in the 5-year period, 1951 through 1955. (The cri-
terion for inclusion in the prior Allegheny County study was employment in
one of seven steel plants during 1953).
The findings of Redmond et al.409 further indicate that both the level
and duration of exposure to coke oven emissions are correlated with mortality
from various types of cancer, further demonstrating the additivity of time and
dose.
Overall mortality of white coke oven workers is somewhat less than
expected. When mortality is categorized by cause, the rates for coke oven
workers are significantly elevated for malignant neoplasms (relative risk,
RR 1.34; p<0.01), for malignant neoplasms associated primarily with respira-
tory cancer (RR 2.85; p<0.01), for kidney cancer (RR 7.49; p<0.01), and for
prostate cancer (RR 1.64; not significant).
The study showed that men employed at full-time topside jobs for five
years or more have a relative risk of lung cancer of 6.87 (p< 0.01), compared
to risks of 3.22 (p< 0.01) for men with five years of mixed topside and side-
oven experience and 2.10 (p< 0.05) for men with more than five years of side-
oven experience. These data indicate a definite gradient in response based on
both type and duration of exposure.
396
Overall, the study confirmed the Lloyd findings of a more than twofold
excess of mortality due to respiratory cancers in all coke oven workers. A
new finding of Redmond's was a significant excess of kidney cancer among coke
oven workers (RR 7.49; p<0.01).
6-180
-------
Redmond concludes that the 6.87 (p<0.01) relative risk for malignant
neoplasms of the respiratory system for men employed full-time topside and the
1.70 relative risk (not significant) for men employed less than five years
constituted further evidence of a dose-response relationship, which Mazumdar
further substantiated by calculating cumulative exposures of the cohort to
coal tar pitch volatiles.
411
In a later paper, Redmond summarized and analyzed additional data
(from 1967 to 1970) for the cohort that demonstrated a consistent increase in
the level of risk of malignant neoplasms of various sites with increased
exposure for each of the coke oven exposure groups studied. Further, the
risk for side-oven workers, which had not been statistically significant in
the earlier studies, reached significance (RR 1.79; p<0.05). Although no
dose-response relationship was apparent, the relative risk for cancer of the
pancreas and the relative risks for respiratory diseases other than cancer
increased markedly with length of exposure (see Table 6-33).
412
A recent study by Redmond et al. again confirmed elevated risks for
coke oven workers for lung cancer (44 deaths versus 24.5 expected; RR 2.01;
p<0.01), and genitourinary cancer (RR 1.82; p<0.05), due primarily to a
fivefold increase in kidney cancer. Data on non-oven coke plant workers
continue to demonstrate excess kidney cancer, and the most recent studies in
this series show that incidences of buccal and pharyngeal malignancies are
highly significant. The overall conclusion of the paper is that "these
observations indicate the need to consider non-oven as well as oven workers
when evaluating cancer hazards in the coke plant." This finding is of great
6-181
-------
importance since non-oven coke plant workers are exposed to considerably lower
concentrations of coke oven emissions and, hence, of POM than oven workers.
413
Hendricks et al. examined the incidence of cancer of the scrotum among
82 wax pressmen over a 20-year period. The refinery population as a whole
had a cancer incidence close to that expected on the basis of the age-adjusted
rate for the general white male population. The 82 wax pressmen, with 10 or
more years of employment, represented 3 percent of the refinery population
but accounted for about 11 percent of the cancer cases. The cancer rate
among wax pressmen was 4 times that of refinery workers as a whole, which was
similar to that of the general male population. Of the 19 cancer cases among
pressmen with 10 years or more experience, 11 were scrota! cancers. The
greatly increased risk for scrotal cancer of the pressmen can be accounted
for by their skin contact with the crude wax, which contained large amounts
of aromatic compounds. Workers handling the finished wax did not show a
significantly elevated risk.
Hammond et al. studied the lung mortality among 5,939 roofers and
waterproofers over a 10-year period. The study population included active,
probational, and retired union members with at least 9 years membership at
the start of the study (January 1, 1960). The total U.S. male population was
used as a standard for calculating the expected numbers of deaths.
Workers with 9 to 19 years' experience had slightly elevated standardized
mortality ratios (SMR's) for all causes of death (102) and for all cancers
(107); and had a marked excess for respiratory disease, not including pneu-
monia, influenza, and tuberculosis (196). Workers with more than 20 years'
6-182
-------
experience showed excess mortality from all causes (109), all cancers (145),
and respiratory disease, not including pneumonia, influenza, and tuberculosis
(167).
The rates for cancer of specific sites included: lung, 159 (based on
99 deaths); upper respiratory tract (buccal, pharyngeal, larynx, esophagus),
195 (based on 31 deaths); stomach, 167 (based on 24 deaths); colon, rectum,
132 (based on 37 deaths); prostate, 138 (based on 29 deaths); bladder, 168
(based on 13 deaths); skin cancer except melanoma, 400 (based on 3 deaths);
leukemia, 168 (based on 13 deaths). No levels of statistical significance
were given.
The SMR for lung cancer was found to increase with increased length of
employment: 0.98 (9 to 19 years); 1.52 (20 to 29 years); 1.61 (30 to 39 years),
Assays of some environmental conditions were obtained from breathing
samples of dust collected on masks worn by workers engaged in various roofing
occupations. The assays showed that the inhaled BaP could potentially range
from 53.0 yg BaP/7-hour working day to 1.4 ug BaP, with an average over all
jobs of 16.7 pg BaP. The authors noted the BaP was not the only agent con-
tained in hot pitch fumes and that the increased mortality of roofers could
be due to other factors or to the combined effect of BaP and one or more
other factors. The effects of smoking were not controlled for in this study.
A 40 percent excess lung cancer rate in males in the south-central area
415 416
of Los Angeles County led Menck and Henderson to examine the lung cancer
rates associated with different occupations and industries in Los Angeles
County. They reviewed all lung cancer data for white males in Los Angeles
6-183
-------
County for a 5-year period. These included 2,161 death certificates in white
males aged 20 to 64 for the period 1968-1970 and 1,777 incident cases of lung
cancer in white males of the same age group of 1972-1973. The authors justi-
fied pooling mortality and morbidity data by the "high mortality rate of lung
cancer and the relatively high accuracy of death certification regarding lung
cancer." The occupation and industry of each subject (obtained from death
certificates) was coded into one of 417 occupational codes, and one of 215
industry codes, per the 1970 U.S. Census occupational classification system.
Detailed occupational and industrial population at risk figures for white
males were calculated from sample material from the 1970 U.S. Census for Los
Angeles County containing information on the current occupation and industry
for 31,216 white males, aged 20 to 64.
Expected deaths and expected incidence cases were computed for each
occupation, assuming the age-specific rates of cancer in each occupation were
the same as those for all occupations. The standardized mortality ratio
(SMR)--the ratio of observed death plus incident cases to the expected deaths
plus incident cases—was used to measure the risk for each occupation. Most
occupational groups showing an excess lung cancer rate had exposure to asbestos
or polycyclic aromatic hydrocarbons (PAH) or both. Those occupations charac-
terized by exposure to PAH and found to be at excess lung cancer risk in Los
Angeles County included: heat treaters (SMR = 433; p<0.05), metal machine
shop workers (SMR = 137; p<0.05); plumbers (SMR = 138, p<0.05); and steel
industry workers (SMR = 279, p<0.01) (see Table 6-34).
6-184
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Table 6-34. STANDARD MORTALITY RATIOS (SMR = 100 FOR ALL OCCUPATIONS) FOR OCCUPATIONS AT
SIGNIFICANTLY INCREASED RISK TO LUNG CANCER. WHITE MALES 20-64 YEARS,
LOS ANGELES COUNTY4I6
cr>
i
_j
00
en
Occupation
Asbestos* insulation workers
Roofers
Heat treaters
Dental lab technicians
Decorators
Taxi drivers
Mechanics, exluding auto
Photoengravers
Pressmen
Clothing ironers
Mariners, longshoremen
Shoe repairers
Mine operatives
Electricians
Bartenders
Plasterers, dry wall workers
Cooks
Machine shop workers
Truck drivers
Restaurant, bar managers
Painters
PI umbers
Welders
Janitors
Subtotal
All occupations
Estimated
population
at risk (23)
400
2,000
550
900
1,200
3,100
8,050
1,350
5,300
1,100
3,150
1,350
1,250
12,400
7,100
3,800
11,450
52,500
34,800
8,150
19,500
9,700
15,300
27,050
231,500
1,560,800
Number of
deaths
1968-1970
3
6
1
2
6
16
19
4
10
6
11
3
5
40
16
3
23
117
58
16
45
25
21
48
504
1,738
Incident
cases
1972-1973
2
5
3
3
1
7
27
4
10
3
12
4
3
18
19
14
18
82
51
11
42
11
27
61
438
1,511
SMR
878
496
433
405
358
344
332
320
276
267
266
233
217
205
204
200
180
167
165
159
158
138
137
127
175
100
-------
The authors noted that since smoking data were not available for the
study population, it was not possible to attribute the elevated rates among
certain occupational groups to occupational exposure alone.
6.7.1.2 Community studies--Non-occupationa1 epidemiological studies have, in
general, attempted to correlate excess malignant and non-malignant disease
with differences in urbanization or with increases in air pollution, measured
directly or indirectly. Comparison of urban and rural lung cancer mortality
rates when adjusted for age and smoking habits shows that people who live in
cities have roughly twice the rate of lung cancer of those who live in rural
populations (Table 6-35). »418»419 It is apparentj however, that not only
duration of residence in a polluted area but also the degree of mobility are
factors which may determine lung cancer mortality. While there is general
agreement on the existence of an "urban factor," there is no consensus that
the "urban factor" is air pollution. Alternative explanations that have been
proposed to account for the urban/rural difference in lung cancer mortality
are: (1) migration to cities for medical treatment; (2) increased bacterial
and viral infection in cities; (3) increased bronchitis in cities; and (4) in-
creased occupational exposure.
A great problem in the analysis of community air pollution studies is the
confounding effect of cigarette smoking which is the major etiologic agent in
394
lung cancer. A second confounding factor is occupational exposure. This
is of much smaller magnitude for the general population than smoking, but it
393
is thought to be large in comparison to any effect caused by air pollution.
6-186
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00
Table 6-35. STANDARDIZED MORTALITY RATIOS FOR URBAN AND RURAL AREAS BY CURRENT
RESIDENCE AND DURATION OF RESIDENCE IN A SPECIFIC COMMUNITY3
Men
Women
Current
residence
Urban
Rural
Ratio
Urban
Rural
Ratio
All
durations
113
79
1.43
108
85
1.27
Less than
1 yr
166
154
1.08
163
205
0.80
1-9 yrs
107
88
1 .22
82
117
0.70
10-39
yrs
117
83
1.41
118
79
1.49
40 & more
yrs
117
75
1.56
124
86
1.44
Lifetime
100
50
2.00
86
49
1.76
From Higgins (443),
-------
Thus, an Increase in lung cancer caused by air pollution will be difficult to
attribute to a particular etiologic agent. Few of the community studies of
air pollution have controlled for these two factors.
420
Hammond has pointed out other problems that arise in air pollution
studies. First, the kinds of information on which estimates of increased risk
in smokers and certain occupational groups are based are not obtainable for
the subjects in general air pollution studies. These include: the interval
since first exposure and a rough estimate of the degree of exposure. Second,
the amount and type of air pollution varies within the same metropolitan area
from day to day and from year to year. Also, the levels of air pollution in
most cities have changed substantially over the past 30 years so that recent
measurements do not give an accurate picture of exposure at an earlier time.
Even current sampling procedures may not adequately reflect differences in
exposure in different neighborhoods of the same metropolitan area. The high
degree of mobility among Americans further complicates the problem of deter-
mining the type and degree of exposure.
Even if excess risk for certain diseases is attributable to air pollution,
there is the problem of identifying the specific etiologic agent(s) in air
pollution that may be responsible for an increase in certain diseases. As in
the case of occupational exposure, community air pollution contains other
agents besides POM; and these may exert their own separate effects on health
or may interact with POM. In some studies of community air pollution, BaP (a
known animal carcinogen) is used as an indicator for the presence of other
POM. However, BaP is an imperfect indicator because the proportion of BaP to
other POM varies with the type of pollution (automobile exhaust, coal burning,
6-188
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etc.). It has also been shown experimentally that BaP alone does not ade-
quately account for the careinogenicity of complex mixtures such as air
422 423
pollution and cigarette tar. '
Early studies noted the increase in lung cancer mortality with increasing
urbanization. Males in urban areas had roughly twice the lung cancer rate of
males in highly rural areas.
417
Curwen et al. reported that SMR's for lung cancer in both sexes and
cancer of the larynx in males increased with increasing urbanization. The
SMR's for lung cancer in males in county boroughs (towns with 100,000 popula-
tion or over), urban districts (other towns), and rural districts (the rest
of the country) for the period 1946 to 1949 were 117, 86, and 62, respectively
(see Table 6-36).
418
Hoffman and Gilliam examined the distribution of lung cancer deaths in
the U.S. from 1948 and 1949. They adjusted state lung cancer rates for
residence (urban-rural) in addition to age, race, and sex. Using a broad
definition of urban population (persons living in places of 2,500 or more
people), they found mortality of urban residents to be substantially higher
than that of rural residents in all race and sex groups. Among white males
the urban rate was 22.3 per 100,000 compared to 1.3 per 100,000 for rural
white males. Among urban non-white males the rate was 16.9 compared to 7.3
for rural non-white males. Urban women had higher rates than rural women:
4.7 compared to 3.7 for whites and 4.2 compared to 2.1 for non-whites. It
was not possible, however, to determine whether these differences were due to
occupational, environmental, economic, diagnostic, or other factors. Data
from Hoffman and Gilliam are given in Tables 6-37 and 6-38.
6-189
-------
Table 6-36. MORTALITY IN ENGLAND AND WALES (1946-1949) DUE TO CANCER
OF THE LUNG AND LARYNX417
Cancer of lung Cancer of larynx
Male
Female Male Female
Total registered deaths, England
and Wales
Average death-rate (per million)
32,547
409
7,097
80
3,296
41
1,115
13
Standard mortality ratio (SMR)
England and Wales
Greater London
North
Midland
Wales
Rest
County boroughsx
Urban districts I Outside greater London
Rural districts,)
100
137
100
93
79
83
(117
\ 86
162
100
132
98
93a
69a
89
108
88
74
100
113
100
103a
83a
94
118
93
76
100a
72a
120a
84a
202?
88a
106a
96a
128a
Based on 100-400 deaths and therefore subject to a coefficient of variation
of 5-10 percent. No SMR in this table is based on fewer than 100 deaths.
6-190
-------
Table 6-37. AVERAGE ANNUAL AGE, RACE, AND SEX SPECIFIC MORTALITY RATES PER
100,000,000 POPULATION FOR CANCER OF THE LUNG AMONG THE URBAN
AND RURAL POPULATION OF THE UNITED STATES, 1948-19493 418
Urban5
White
Age (years)
Total crude rate
Total adjusted rate
0-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75 and over
0-44
45-64
65 and over
Male
235.2
223.4
2.6
16.8
46.0
111.7
274.8
502.8
819.5
1,053.1
1,109.5
1,104.6
867.9
20.1
622.9
1,037.5
Female
53.2
47.4
1.6
7.9
17.6
28.0
54.8
81.2
126.0
172.7
228.2
279.4
319.0
6.9
102.7
272.3
Nonwhite
Male
140.7
169.1
3.9
29.0
55.3
146.4
265.3
495.6
709.3
761.8
586.6
476.0
501.6
26.2
497.8
535.8
Female
33.7
41.6
1.2
8.2
25.6
47.0
68.4
119.4
123.7
153.8
142.7
135.9
181.6
9.1
106.6
151.5
Rural
White
Male
118.0
123.23
2.1
10.5
34.6
66.4
158.1
302.3
453.4
560.6
556.7
570.2
488.9
11.6
348.7
539.0
Female
35.2
36.8
1.3
4.7
9.1
20.1
42.4
59.6
92.0
141.4
185.1
225.3
260.1
4.0
78.7
221.2
Nonwhite
Male
53.9
73.2
2.2
19.2
26.2
53.3
108.4
212.6
317.3
311.6
270.8
158.7
255.0
8.5
220.6
236.4
Female
15.3
21.4
0.5
5.3
5.1
30.2
54.0
27.9
79.4
60.1
89.2
133.7
52.6
3.1
53.1
89.6
Deaths according to International List Nos. 47b, c, d, and e (1948) and Nos. 162 and 163 (1949);
population according to 1950 census.
Urban population is generally that living in places of 2,500 and over.
Adjusted to the age distribution of the total United States population at the 1950 census.
6-191
-------
Table 6-38. AVERAGE ANNUAL AGE, RACE, AND SEX SPECIFIC MORTALITY RATES PER 100,000,000 POPULATION
FOR CANCER OF THE LUNG IN THE UNITED STATES, 1948-493 418
I
•_J
PO
White
Age (years)
Total crude rate
Total adjusted rate
0-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75 and over
0-44
45-64
65 and over
Male
185.6
183.1
2.3
14.3
41.4
93.7
229.5
427.0
679.7
861.3
881.9
874.6
698.0
16.4
517.6
824.1
Female
46.0
43.6
1.5
6.7
14.4
25.1
50.4
73.7
114.0
161.7
212.9
260.2
297.8
5.7
94.2
254.0
Total
Nonwhite
Male
103.7
130.6
3.1
25.7
45.4
114.8
211.8
397.3
558.8
578.1
439.1
320.3
372.2
18.4
392.3
389.3
Female
26.3
34.1
0.9
7.3
19.2
41.6
63.8
87.9
107.6
118.4
120.5
135.0
124.5
6.6
88.0
125.2
All persons
110.1
110.1
1.9
11.0
28.1
61.0
139.6
249.3
392.9
501.3
515.3
530.5
462.9
11.2
300.6
503.1
a Deaths according to International List Nos. 47b, c, d, and e (1948) and Nos. 162 and 163 (1949);
population according to 1950 census.
Urban population is generally that living in places of 2,500 and over.
c Adjusted to the age distribution of the total United States population at the 1950 census.
-------
424
Manos and Fisher studied the correlations between the age-adjusted
mortality data (1949-1951) and different indices based on sources of air pol-
lution, urbanization, and socioeconomic factors for 163 metropolitan areas.
The mortality ratios in this study represented the mortality experience for a
specific population group divided by an expected number of deaths based on
the age-specific death rates among all the population groups in the combined
163 metropolitan areas. A total of 10,176 linear correlation coefficients
was obtained. Of 50 causes of death examined, cancer of the esophagus and
stomach, cancer of the lung, arteriosclerotic heart disease, and chronic non-
rheumatic endocarditis gave the highest correlations with various pollution
indices (based on home heating, non-specific industry, specific industry, and
motor vehicle usage). The authors emphasize the preliminary nature of their
findings. They point out that simple linear correlation does not establish a
causal connection but, rather, indicates an area for further investigation
which would take other variables into account.
425
A similar study was carried out by Schiffman and Landau in which
indirect measures of air pollution were tested for correlations with mortality
from different disease categories. The working assumption was that the 20
standard metropolitan areas (SMA's) with the highest air pollution indexes
(based on: (1) all fuel; (2) all coal; (3) all gas; (4) coke; (5) S02
exhaust emissions; and (6) organic exhaust emissions) would have higher
mortality rates from selected diseases than the 20 SMA's with the lowest air
pollution indices. Comparisons showed that the 20 highest SMA's had higher
SMR's than the 20 lowest SMA's by a margin of at least 10 percent for chronic
6-193
-------
rheumatic heart disease, arteriosclerotic heart disease including coronary
disease, and non-rheumatic endocarditis. The differences were significant at
the 5 percent level. Other categories of heart disease did not show a cor-
relation with the air pollution indices. SMA's with the highest indirect
measures of industrial air polltuion showed consistently higher mortality
ratios (1.1 and above) for cancer of the esophagus and stomach (higher in
each case by a margin of at least 15 percent) and for lung cancer (higher in
each case by at least 20 percent) than the 20 lowest SMA's. Like Manos and
Fisher, Schiffman and Landau point out the preliminary nature of their
correlations which serve to identify areas for further study rather than to
establish definite causal associations.
Levin et al. compared age-adjusted incidence rates for several types
of cancer in New York State, Connecticut, and Iowa and found generally simi-
lar urban-rural differences for cancer of the respiratory system, esophagus
(males), and intestine and rectum (males). The ratios of urban and rural
age-adjusted incidence rates per 100,000 population for lung cancer were 1.41
(New York State excluding New York City), 1.57 (Connecticut), and 2.84 (Iowa).
Within New York State, the urban-rural differences persisted when data for
metropolitan and non-metropolitan counties were examined separately (see
Table 6-39).
419 427
Haenszel and coworkers ' conducted one of the few studies of lung
cancer mortality as related to residence which controlled for smoking. They
obtained lifetime residence histories (by means of interviews with family
members) for a 10 percent sample of all white male lung cancer deaths (2,553
6-194
-------
VO
cn
Table 6-39. AGE-ADJUSTED3 CANCER-INCIDENCE RATES PER 100,000 POPULATION, BY PRIMARY SITE AND SEX
FOR URBANb.C AND RURAL AREAS: NEW YORK STATE (EXCLUSIVE OF NEW YORK CITY), 1949-51; CONNECTICUT,
1947-51; AND IOWA, 1970*26
Urban
a
b
c
d
e
Primary site
All sites
Buccal cavity and pharynx
Lip
Digestive system
Esophagus
Stomach
Intestines
Rectum
Other digestive organs
Respiratory system
Lung and bronchus, total
Primary
Unspecified
Larynx
Hale genital organs
Prostate
Urinary organs
Kidney
Bladder and other
Skin
Lympjiatic tissues
Leukemia
Rates adjusted for age to the
For New York State and Iowa,
classified by the U.S. Bureau
76 towns with high population
New York Connecticut
264.5
15.8
6.8
87.1
6.6
23.7
23.9
18.3
14.6
37.9
27.2
16.3
10.9
5.4
32 5
28.7
18.2
4.6
13.6
34.7
9.9
8.9
total population
'urban" includes
271.8
17.9
5.4
98.3
8.7
28.5
25.6
20.1
15.4
35.2
28.0
5.8
33.2
27.8
19.4
5.6
13.8
31.0
7.9
9.9
Iowa
350.6
32.1
17.3
87.6
3.9
24.7
26.9
16.3
15.8
32.8
29.0
2.9
43.5
37.8
25.1
4.8
20.3
72.1
12.2
d
of the United States.
all Incorporated places
of the Census under special
density.
Rates for urban and rural areas have not been
adjusted to
New York
HALES
212.8
12.9
3.8
68.6
3.7
20.8
17.9
13.8
12.4
26.%
19.3
9.3
10.0
3.7
27.7
24.1
13.8
3.5
10.3
32.6
8.0
6.8
1950.
of 2.500
Rural
Ratio
'Urban/Rural
Connecticut Iowa New York Connecticut
200.3
13.5
5.6
69.1
3.7
21.3
17.5
15.5
11.1
20.5
17.8
1.4
27.0
23.3
15.0
4.1
11.0
30.2
5.1
7.5
population and
250
24
15
68
2
24
18
12
10
12
10
1
39
34
16
3
13
52
6
d
.2 1.24
.1 1.22
.7 1.79
.7
.1
.7
.6
.4
•9
.1
.2
•4
.0
•2
.5
.5
.0
.27
.78
.14
.34
.33
.18
.43
.41
.46
.17
.19
.32
.31
.32
.1 1.06
.1 1.24
1.31
over, and certain other political
rules relating to population size and density;
correct for
bias in
reporting place
for Connecticut, "urban
1.36
1.33
0.96
1.42
2.35
1 34
1.46
1.30
1.39
1.72
1.57
4.14
1.23
1.19
1.29
1.37
1.25
1.03
1.55
1.32
subdivisions
" comprises
Iowa
1.40
1.33
1.10
1.28
1.86
1.00
1.45
1.31
1.45
2.71
2.84
2.07
.12
.11
.52
.37
.56
1.38
2.00
—
so
of residence on medical records.
Comparable Iowa data not available.
In Iowa, unspecified uterus was distributed between the cervix and corpus, based on additional
histologic-type information.
data collected for a sample of cases and on
-------
AGE-ADJUSTED'
10
en
iuuic u-oj v <-«-"' <• mucuy . nuc-nuuuo I tu ^Mliv*tl\- ilNUiUCINOt KM I to rtK IUU,UUU HUrULAIl
SITE AND SEX FOR URBANb.c AND RURAL AREAS: NEW YORK STATE (EXCLUSIVE OF NEW YORK
CONNECTICUT, 1947-51; AND IOWA, 1 970*26
Urban
Primary site New York Connecticut
All sites
Buccal cavity and pharynx
Lip
Digestive system
Esophagus
Stomach
Intestines
Rectum
Other digestive organs
Respiratory system
Lung and bronchus, total
Primary
Unspecified
Larynx
Breast
Female genital organs
Cervix
Corpus
Uterus, unspecified
Ovary
Urinary organs
Kidney
Bladder and other
Skin
Lymphatic tissues
Leukemia
3 Rates adjusted for age to the
b For New York State and Iowa,
classified by the U.S. Bureau
76 towns with high population
248.2
3.8
0.4
62.9
1.1
11.7
25.7
11.9
12.5
5.1
3.2
1.3
1.9
0.3
57.4
58.1
26.5
15.8
1.9
9.5
7.3
2.8
4.5
23.9
6.9
5.8
total
261.
3.
0.
73.
1.
15.
28.
14.
14.
5.
4.
0.
59.
58.
22.
12.
8.
13.
7.
3.
4.
22
5.
7.
population of
"urban" includes all
of the Census under
density.
c Rates for urban and rural areas have
1
1
2
6
5
5
4
0
2
8
7
4
8
4
1
0
9
1
7
6
0
0
6
8
Iowa New York
351.6
7.2
1.2
68.5
0.6
13.1
29.3
10.0
15.5
9.0
7.8
0.9
78.0
88.7
46.8*
21. 2e
—
15.1
10.6
3.3
7.3
45.4
7.2
d
the United States,
FEMALES
218.3
2.9
0.3
55.6
1.2
10.1
22.3
9.9
12.1
4.2
3.0
1.2
1.8
0.3
49.9
53.2
23.4
14.9
2.1
9.2
5.6
1.9
3.7
20.9
6.1
5.3
1950.
Rural
Connecticut
204.4
2.6
0.8
59.0
0.7
12.0
22.2
13.6
10.5
4.2
3.8
0.3
49.4
43.4
15.0
8.3
7.2
11.4
6.3
2.9
3.3
18.5
4.2
5.2
Iowa
261.5
4.1
0.8
65.2
1.2
14.1
23.8
11.0
15.1
6.3
5.3
0.0
62.4
59.8.
26 4*
17. 3e
—
12.3
6 1
2.8
3.3
24 9
5.5
d
Ratio:
UN, BY PRIMARY
CITY), 1949-51;
Urban/ Rural
New York Connecticut
1.
1.
1.
1.
0.
1.
1.
1
1.
1.
1.
1.
1
1.
1.
1
1.
1.
1.
1.
1
1.
1.
14
31
33
13
92
16
15
20
03
21
07
00
15
09
13
06
03
30
47
22
14
13
09
1.28
1.19
0 25
1 25
2 14
1 29
1.28
1.03
1 35
1.38
1.24
1 33
1.21
1.35
1.47
1.45
1.15
1.22
1 24
1 21
1 19
1.33
1.50
incorporated places of 2,500 population and over, and certain other political subdivisions
special rules relating to population size and density, for Connecticut, "urban" comprises
not been adjusted to
correct for
bias in
reporting place
of residence on
Iowa
1.34
1.76
1.50
1.05
0.50
0.93
1.23
0.91
1.03
1.43
1.47
—
1.25
1.48
1.77
1.23
1 23
1.74
1.18
2 21
1 82
1.31
—
so
medical records.
Comparable Iowa data not available.
e . .
__ J J _ i
histologic-type information.
-------
deaths) in the U.S. during 1958, and for a 10 percent sample of all white
female lung cancer deaths (852 deaths) in the U.S. during 1958-1959. The
major findings of the study were: (1) smoking showed the strongest correla-
tion with lung cancer mortality in all population subgroups; (2) insignificant
differences in lung cancer mortality by residence history among non-smokers;
(3) higher SMR's for urban than for non-urban population in every residence
duration class; ranging from 123 in cities of over half a million to 65 in
farm areas for males, and from 132 in the large cities to 69 in farm areas
for females; (4) combined effects of residence and smoking histories on lung
cancer rates far greater than would be expected on the basis of additivity of
separate effects (this finding was not confirmed by the data on female lung
428
cancer and does not agree with some other studies—Stocks and Campbell,
Waller ); (5) lower risks among lifetime residents, both urban and rural,
than those of populations with more varied residence histories; and (6) high
lung cancer risk among two migrant populations: U.S. farm-born and foreign-
born residents of large metropolitan centers (see Tables 6-40 and 6-41).
It is difficult, however, to quantify the effects observed with respect to
air pollution because no index of pollution was used in these studies by
Haenszel and coworkers.
An epidemiological survey of lung cancer in Japan considered both
smoking habits and the degree of air pollution by dust, sulfer dioxide,
430
suspended particulates, trace elements, and aromatic hydrocarbons. The
lung cancer death rate displayed a dose-related relationship to the total
number of cigarettes smoked, regardless of the extent of air pollution.
6-197
-------
Table 6-40. STANDARDIZED LUNG-CANCER MORTALITY RATIOS* - ADJUSTED FOR AGE AND SMOKING HISTORY
BY POPULATION SIZE OF CURRENT RESIDENCE AND DURATION OF RESIDENCE IN A SPECIFIC
COMMUNITY (U.S. WHITE MALES, AGE 35 AND OVER, 1965)419
vo
00
Duration (years)
Current residence
White males, total d
Metropolitan counties
500,000 and over
50,000-500,000
10,000-50,000
2,500-10,000
Rural nonfarm
Nonmetropol i tan counties
10,000-50,000
2,500-10,000
Rural nonfarm
Farm
White males, total j
Metropolitan counties
500,000 and over
50,000-500,000
10,000-50,000
2,500-10,000
Rural nonfarm
Nonmetropol i tan counties
10,000-50,000
2,500-10,000
Rural nonfarm
Farm
a SMR (adjusted for age and
b Size as of 1950.
All
nil
durations
100
123
111
164
107
91
89
84
80
65
2381
534
529
203
87
243
204
115
304
162
smoking history
Under 1
160
500
175
257
91
394
111
140
87
76
101
10
14
9
4
26
12
7
14
5
by the indirect
1-9
98
126
106
201
64
85
92
68
94
77
447
51
71
58
21
74
45
20
82
25
method)
10-39C
SMR
105
122
121
159
107
96
90
108
79
77
Observed deaths
1046
179
259
96
36
102
99
67
140
68
40 and over0
106
128
111
165
324
101
98
54
83
53
406
136
108
31
12
25
24
14
34
22
= 100 for U.S. white males, age 35
Lifetime
81
116
86
78
259
41
71
56
57
50
381
158
77
9
14
16
24
7
34
42
and over, 1958.
c Excluding lifetime residents.
Ps\iin+ i AC in c fra nHa *•<•! mA + w
irts\1 i tan a tr*a» e
-------
Table 6-41.
STANDARDIZED LUNG-CANCER MORTALITY RATIOS3 - ADJUSTED FOR AGE AND SMOKING HISTORY
BY NATIVITY AND FOR THE NATIVE-BORN BY POPULATION SIZE OF BIRTHPLACE AND CURRENT
RESIDENCE (U.S. WHITE MALES, AGE 35 AND OVER, 1958)419
cr>
vo
10
Native-born - birthplace1*
Current residence
White males, total A
Metropolitan counties
500,000 and over
50,000-500,000
10,000-50,000
2,500-10.000
Rural nonfarm
Nonmetropol i tan counties
10,000-50,000
2.500-10,000
Rural nonfarm
Farm
White males, total d
Metropolitan counties
500,000 and over
50.000-500,000
10.000-50,000
2.500-10,000
Rural nonfarm
Nonmetropol i tan counties
10,000-50,000
2.500-10,000
Rural nonfarm
Farm
Foreign-
born
138
144
154
266
116
126
87
98
89
75
521
204
118
63
15
51
21
9
26
14
All
places
93
123
109
136
102
89
87
79
76
56
1860
330
411
140
72
192
183
106
278
148
500.000
and over
106
117
75
133
32
111
74
129
82
53
320
200
25
32
5
33
7
4
13
1
50.000-
500.000
88
116
89
63
93
88
82
184
68
28
Observed
225
25
126
10
8
28
10
7
10
1
10.000-
50,000
SMR
88
139
82
124
77
59
76
79
67
145
deaths
180
24
29
31
7
11
49
6
15
8
2.500-
10,000
78
97
109
173
158
75
33
37
60
57
130
15
30
14
22
12
7
13
12
5
Rural
nonfarm
77
125
119
103
88
64
69
56
62
84
347
35
69
16
12
50
33
18
93
21
Farm
100
159
156
247
158
129
133
109
93
50
626
25
123
36
16
55
73
57
132
109
a SMR (adjusted for age and smoking history by the indirect method) = 100 for U.S. white males, age 35 and over, 1958.
b Size as of 1950
c Includes 32 descendants for whom size of birthplace was not ascertained.
d Counties in standard metropolitan areas.
-------
Furthermore, it was shown that the age- and smoking-adjusted lung cancer
death rate for males increased slightly with the extent of air pollution.
Among females and non-smokers the lung cancer death rate was not apparently
affected by the parameters of air pollution measured. The authors speculated
on a possible synergistic effect of air pollution and cigarettes on the
incidence of lung cancer.
In a study of respiratory cancer in ten Polish cities, an apparent
correlation was found between cancer death rates and degree of pollution by
431
representative POM. Data on ambient levels of dust, tars, BaP, BeP,
BghiPer, and pyrene for the period 1966 to 1967 were compared with the age-
and sex-adjusted respiratory cancer death rates for the period 1962 to 1963
in the same cities (Table 6-42). For the most part, it was shown that
cities with the highest death rates had the highest levels of POM pollution
(correlation coefficient, R = 0.66). No apparent relationship was seen
between respiratory cancer death rate and air pollution as measured by other
indices (e.g., dust, tar substances). Caution must be exercised, however,
in the interpretation of cancer incidence data in the absence of historical
information on ambient levels of POM. The long latency period for tumor
appearance (10 to 30 years) often makes it impossible to establish levels of
exposure at the time of the initial carcinogenic event. Moreover, it cannot
be stated with certainty whether carcinogenesis in humans is determined by
intensity or duration of exposure, or a combination of both. In addition, a
presumed log normal distribution of incubation periods for neoplastic
disease may complicate the attempt to correlate time of exposure with car-
432
cinogenic effect.
6-200
-------
I
ro
Table 6-42. RANKING OF THE CITIES INVESTIGATED BY THE VALUES OF THE ATMOSPHERIC AIR POLLUTION
INDICES AND DEATH RATE IN THE POPULATION FROM CANCER OF THE LUNGS AND BRONCHI (THE NUMBERS IN
PARENTHESES INDICATE THE RANK OR SEQUENTIAL POSITION OF THE CITY BY THE GIVEN CHARACTERISTIC)^
Average concentration
City
Gdansk
Katowice
Kratow
Lodz
Poznan
Szczecin
Warszawa
Wroclaw
Zabrze
Dust in
yg/m3
121 (1)
293 (8)
248 (7)
155 (3)
155 (4)
175 (5)
133 (2)
191 (6)
336 (9)
Tar sub-
stances-,
in ng/m
21 (1)
33 (7)
34 (8)
28 (5)
23 (3)
26 (4)
21 (2)
30 (6)
38 (9)
in the atmosphere in
BaP
74 (7)
75 (8)
63 (6)
45 (2)
49 (3)
53 (4)
29 (1)
61 (5)
117 (9)
BcP
the period
BghiPer
3
In pg/1000 m
37 (7)
39 (8)
32 (6)
22 (2)
26 (3)
27 (4)
15 (1)
29 (5)
65 (9)
79 (7)
81 (8)
69 (6)
46 (2)
53 (3)
57 (4)
32 (1)
68 (5)
117 (9)
1966-1967
P Sta
y
107 (8)
95 (7)
90 (6)
54 (2)
55 (3)
61 (4)
35 (1)
79 (5)
146 (9)
ndardized combined
eath rate for the
ears 1962 and 1963
31.9 (7)
31.3 (6)
28.4 (5)
27.1 (3)
27.7 (4)
33.1 (8)
16.8 (2)
13.8 (1)
47.3 (9)
-------
, Studies on lung cancer rates in migrant populations tend to indicate that
exposures occurring early in life can lead to the development of cancers, even
though the victims have migrated to a different environment. In this regard,
it can be seen that the age-standardized lung cancer death rates among British
and Norwegian migrants to the United States are intermediate between those in
433
their original homeland and adopted country. Other studies of cancer
mortality among migrants support the concept that these persons are affected
434
by their former environments and length of exposure in that environment. '
435,436,437,438 Jt ig suggested that differences in smoking habits are
unlikely to account for discrepancies in lung cancer rates among migrant and
resident populations.
439
Hagstrom et al. analyzed mortality from various types of cancer by
air pollution level in a population with a relatively homogeneous socio-
economic profile (Nashville Air Polltuion Study). All cancer deaths for
the years 1949 through 1960 were classified by pollution indices (SO,,
soiling, dustfall, 24-hour S0») and socioeconomic category (upper class,
middle class, lower class) as determined by residence at time of death. No
association was found between lung cancer and air pollution. However, for
stomach cancer, there were significant correlations with the level of
dustfall (the age-adjusted rate in "high" pollution areas was twice that in
"moderate" pollution areas); and for cancer of the esophagus, prostate, and
bladder, there were positive correlations with soiling. Bladder cancer
deaths were highest for areas of high pollution as measured by all four
indices (see Tables 6-43 - 6-45).
6-202
-------
Table 6-43. ADJUSTED DEATH RATES PER 100,000 FOR CANCER AMONG THE POPULATION EXPOSED TO MODERATE
POLLUTION BY FOUR AIR POLLUTANTS BY JQCJOECONOMIC CLASS, NASHVILLE SMSA, 1949 THROUGH
196C
9
ro
o
CJ
Pollutant
S03
Soiling
Dustfall
24-hr S02
so3
Soiling
Dustfall
24-hr S02
so3
Soiling
Dustfall
24-hr S02
Estimated
population
Ian 1
1955
13,633
17,972
25,009
7,237
157,862
136,171
158,117
152.660
31,367
39,142
29,669
35,516
All cancer
No
304
387
459
173
2,472
2,016
2,495
2,365
513
663
551
605
Rate
146
141.15
131.66
139.59
128.92
129.99
129.83
129.06
148.47
150.41
156.49
155.47
Stomach cancer
No.
16
20
23
11
156
122
157
151
41
49
39
43
Rate
7.51
7.14
6.56
8.27
8.09
7.9
8.14
8.23
12.01
11.19
11.06
11.19
Large
Esophagus intestine
cancer cancer
Deaths
No. Rate
Upper Class
4 1.83
5 1.86
5 1.43
2 1.61
Middle Class
47 2.47
42 2.72
50 2.62
40 2.19
Lower Class
18 5.19
23 5.16
16 4.51
19 4.86
No.
27
36
39
14
234
178
236
216
47
57
46
47
Rate
12.97
13.07
11.21
10.59
12.08
11.52
12.19
11.71
13.83
13.17
13.2
12.26
Cancer of
prostate
No.
11
13
14
4
158
126
154
145
31
40
35
38
Rate3
12.45
11.17
9.6
6.96
17.35
17.55
17.16
17.01
17.81
18.57
19.71
19.61
Cancer of
bladder
No.
11
13
13
5
63
56
61
61
9
12
11
15
Rate
5.1
4.54
3.65
3.72
3.25
3.64
3.14
3.3
2.66
2.77
3.15
3.89
a For age-adjusted prostate cancer rates, the standard population was the total male population.
-------
Table 6-44. ADJUSTED DEATH RATES PER 100,000 FOR CANCER AMONG THE MIDDLE CLASS EXPOSED TO AIR
POLLUTANTS, BY DEGREE OF EXPOSURE, NASHVILLE SMSA, 1949 THROUGH 1960*39
en
i
PO
o
Pollutant
S03
Soiling
Oustfall
24-hr S02
Estimated
population
Ian 1
1955
8,178
14,934
12,924
20,801
All cancer
No.
187
314
217
391
Rate
149.95
152.59
145.35
140.7
Stomach cancer
No.
17
31
29
35
Rate
13.88
14.95
19.63
12.75
Large
Esophagus Intestine
cancer cancer
Deaths
No.
High
5
8
4
12
Rate
Pollution
3.82
3.87
2.59
4 29
No.
14
26
13
35
Rate
11.03
12.46
8.89
12.42
Cancer of
prostate
No.
15
24
19
29
Rate3
22 17
20.92
23.5
19.9
Cancer of
bladder
No.
7
9
8
11
Rate
5.41
4.31
5.35
3.87
Moderate Pollution
so3
Soiling
Dustfall
24-hr S02
S03
Soiling
Dustfall
24 -hr S02
157,862
136,171
158,117
152,660
20,131
35,066
15,130
12,710
2,472
2,016
2,495
2,365
253
582
200
156
128.92
129.99
129.83
129.06
144.66
123.75
130.91
138.4
156
122
157
151
18
38
5
5
8.09
7.9
8.14
8 23
10.27
8.02
3 38
4.3
47
42
50
40
Low
4
6
2
4
2.47
2.72
2.62
2.19
Pollution
2.2
1.26
1.21
3.79
234
178
236
216
17
61
16
14
12.08
11.52
12.19
11.71
10.83
12.54
11.19
13.17
158
126
154
145
11
34
11
10
17.35
17.55
17.16
17.01
17.98
15.41
15.96
20.66
63
56
61
61
4
9
5
2
3.25
3.64
3.14
3.3
2.8
1.81
3.39
1.85
a For age-adjusted prostate cancer rates, the standard population was the total male population.
-------
Table 6-45. ADJUSTED DEATH RATES PER 100,000 FOR CANCER AMONG THE MIDDLE CLASS POPULATION EXPOSED
TO SUSPENDED PARTICULATES (SOILING), BY DEGREE OF POLLUTION, BY SEX, AND BY RACE,
NASHVILLE SMSA, 1949 THROUGH 1960439
PO
o
in
Sex-Race
Hale
Female
White
Nonwhite
Estimated
population
Ian 1
1955
7,123
7,811
9.716
5,218
All cancer
No.
167
147
207
107
Rate
170.51
136.79
151.97
152.05
Stomach cancer
No.
22
9
20
11
Rate
22.29
8.54
14.33
15.29
Large
Esophagus intestine
cancer cancer
Deaths
No.
High
7
1
7
1
Rate
Pollution
7.08
0.85
5.07
1.27
No.
13
13
22
4
Rate
13.13
11.6
15.69
5.29
Cancer of
prostate
No.
24
0
16
8
Rate9
20.92
19.97
24.66
Cancer of
bladder
No.
4
5
5
4
Rate
3.97
4.65
3.64
5.42
Moderate Pollution
Hale
Female
Hhlte
Nonwhite
Hale
Female
White
Nonwhite
64.761
71,410
109,873
26,298
15.830
19,236
32,651
2.415
986
1,030
1,652
364
262
320
549
33
148.51
117.29
128.98
133.42
141.24
113.49
123.46
118.94
77
45
78
44
16
22
36
2
11.70
5.09
6.09
16.51
8.65
7.68
7.96
6.87
32
10
29
13
Low
2
4
6
0
4.77
1.14
2.28
4.69
Pollution
1.13
1.24
1.33
._.
79
99
152
26
24
37
55
66
11.95
11.03
11.87
9.66
12.91
12.52
11.96
22.14
126
0
90
36
34
0
32
2
17.55
—
15.37
26.67
15.41
—
15.31
13.68
36
20
50
6
5
4
8
1
5.6
2.23
3.91
2.26
2.72
1.18
1.66
3.53
For age-adjusted prostate cancer rates, the standard population was the total male population.
-------
440
Winkelstein et al.t using mortality data from Buffalo and Erie
County, New York, for the years 1951-1961, found a positive association
between air pollution as indexed by suspended particulates, and total
mortality and chronic respiratory disease, but none with lung cancer.
Economic status was taken into account by classifying the population into
five levels, based on a median family income assigned to each census tract.
Although low and high pollution levels were strongly correlated with high
and low economic status respectively, there was still a consistent trend of
increasing mortality with increasing air pollution within each of five
economic levels.
Information concerning occupation, smoking, and residence history was
not available in this study. Winkelstein and coworkers later reported
441
associations between stomach cancer and particulate air pollution and
442
between prostate cancer and air pollution. These two additional findings
439
confirmed similar findings of Hagstrom et al. based on the Nashville Air
Pollution Study.
Hammond found no correlation between lung cancer death rates (adjusted
for age and smoking) and suspended particulate matter (in 33 cities) or
benzene soluble organic matter (in 31 cities) among men without occupa-
tional exposure. The data are given in Table 6-46.
443
Higgins found no association between BaP concentrations or particulate
matter and lung cancer death rates in some 50 Standard Metropolitan Statisti-
cal Areas (MSAS). But there was an expected correlation between sulfate
levels and lung cancer death rates.
6-206
-------
Table 6-46. OBSERVED AND EXPECTED NUMBER OF LUNG CANCER DEATHS BY PLACE OF RESIDENCE AND BY
OCCUPATIONAL EXPOSURE TO DUST, FUMES, GASES, OR X-RAYS (ADJUSTED FOR AGE AND
SMOKING HABITS: CONFINED TO MEN WHO HAD LIVED IN SAME NEIGHBORHOOD FOR LAST
10+ YEARS)420
ro
O
Occupational ly exposed
to dust, fumes, etc.
Place of residence
Total, all male subjects
Metropolitan area, pop. 1,000,000 +
City
Town or rural
Metropolitan area, pop. <1 , 000, 000
City
Town or rural
Non-metropolitan area
Town
Rural
Los Angeles, Riverside, and Orange
Counties, California
Farmers
8 Cities: High particulates (130-180 ^g/m3) ,
11 Cities: Moderate particulates (100-129 ug/mj)
14 Cities: Low particulates (35-99 ,jg/m3)
9 Cities: High benz. sol. (8.5-15.0 ug/m3) ,
10 Cities: Moderate benz. sol. (6.5-7.9 ug/m )
12 Cities: Low benz. sol. (3.4-6.3 i.g/m3)
Observed
number
576
165
92
73
166
92
74
245
102
143
30
63
45
21
48
28
44
33
Exposed
number
530.5
134.1
69.1
65.0
145.4
83.3
62.1
251.0
104.9
146.1
21.9
77.6
32.9
18.8
37.4
21.0
32.7
29.2
Ratio
1.09
.23
.33
.12
.14
.10
.19
0.98
0.97
0.98
1.37
0.81
1.37
1.12
1.28
1.33
1.35
1.13
Not occupational ly exposed
to dust, fumes, etc.
Observed
number
934
281
168
113
271
170
101
382
200
182
38
71
66
39
110
52
65
76
Exposed
number
979.7
285.7
158.3
127.4
280.5
184.0
96.5
413.5
199.1
214.4
39.6
92.9
73.9
49.5
100.1
51.5
75.1
81.8
Ratio
0.96
0.98
1.06
0.89
0.97
0.92
1.05
0.92
1.00
0.85
0.96
0.76
0.89
0.79
1.10
1.01
0.87
0.93
-------
On the assumption that populations exposed to PAH from the petroleum
industry could be expected to have higher rates for certain cancers than
395
unexposed populations, Blot et al. conducted a survey of cancer mortality
from 1950 to 1969 in 39 counties where the petroleum industry is most
heavily concentrated. They found that white male residents of these
counties had significantly higher rates for cancer of the lung, the nasal
cavity and sinuses, and the skin (including malignant melanoma) compared
with the residents of counties with similar demographic features but with-
out petroleum processing plants. Ratios of age-adjusted mortality rates
among white males in the petroleum-industry counties to the rates in
control counties were: 1.15 for lung cancer (significant at 1 percent
level); 1.48 for cancer of nasal cavity and sinuses (significant at 1 per-
cent level); 1.10 for melanoma and other skin cancers (significant at
5 percent level). The ratio for all sites combined was 1.06 (significant
at the 1 percent level). White females in petroleum-industry counties also
had significantly elevated rates for lung cancer (though not for cancer of
the nasal cavity and skin, nor for all cancers combined), suggesting the
possibility that community exposure might be involved as well as occupa-
443
tional exposure. Data from Blot et al. are given in Table 6-47.
Using death certificate data from 1968-1969, Menck et al.415 found
elevated lung cancer mortality rates in white males living in certain
heavily industrialized areas of Los Angeles County. Populations at risk
were determined from the 1970 Census data. Age-adjusted lung cancer
mortality rates for Caucasian males and females were calculated for 13
6-208
-------
Table 6-47. RATIOS OF AGE-ADJUSTED MORTALITY RATES, 1950 TO 1969, AMONG WHITE
1DUSTRY COUNT I E<
BY CANCER SITE^
MALES IN PETROLEUM INDUSTRY COUNTIES TO THOSE IN CONTROL COUNTIES
r443
Cancer site Rate
Buccal cavity and pharynx 1.04
Esophagus 1.06
Stomach 1.09a
Colon 1.02.
Rectum 1.07°
Liver 1.06
Pancreas 1-05a
Nasal cavity and sinuses 1.48
Larynx 1.09
Lung 1.15a
Prostate °-98h
Testis 1.10°
Kidney 1.05
Bladder 1.02.
Melanoma and other skin ^-^b
Brain 0.94
Thyroid and endocrine 1.04
Bone and connective tissue 0.98
Hodgkins's disease 0.96
Other lymphomas 1.01
Multiple myeloma 1.05
Leukemia 1.03
All sites combined 1.06a
a P<.01.
b .01
-------
areas from Los Angeles County death certificates. A direct method of age-
adjustment using the U.S. 1970 Census population as a standard was carried
out, and socioeconomic class index based on average income and education
level was assigned to each census tract.
The age-adjusted lung cancer rates in 1968 and 1969 for male Caucasians
in the 13 study areas ranged from 43 to 75 per 100,000. In three contiguous
areas of south-central Los Angeles County, however, the mortality rate was
70 per 100,000 or greater. The excess of male lung cancers for these areas
was 40 percent above the rate for the rest of Los Angeles County.
The inhabitants of the three areas of south-central Los Angeles County
are mainly lower and middle class, and the lung cancer rates for Los Angeles
County were 1.73 times higher in the lower than in the upper socioeconomic
classes. However, the excess for the three south-central areas remained
when deaths for the 13 study areas were examined for the lower socioeconomic
groupings.
Measurements of BaP and other PAH in the air and soil (made at four
sampling stations with and adjoining the three south-central areas) showed
the highest pollution levels at the center of the three study areas with
increased lung cancer mortality.
Neither smoking nor occupational history data were available in this
study, but the authors argue that neither smoking nor occupational exposure
could account for the excess. They suggest that synergistic action between
smoking and neighborhood air pollution, primarily of industrial origin,
provides the best explanation of the elevated lung cancer rates in south-
central Los Angeles County.
6-210
-------
444
A follow-up study including additional mortality data from 1970 and
morbidity data from 1972 confirmed the findings of an elevated lung cancer
rate for south-central Los Angeles County. Age-adjusted lung cancer rates
per 100,000 were 70.9, 70.2, and 69.2 for the three south-central areas
compared to an average rate of 55.8 for all 14 study areas in Los Angeles
444
County. Henderson et al. reported that the increased risk was present in
different social classes as well as in six of eight non-factory occupational
categories. Females did not have an elevated risk. Although current
occupation was an important factor in the lung cancer risk of Los Angeles
County men, current occupation did not explain the excess male risk in the
south-central area. The authors note that detailed work histories might
reveal an occupational risk. It was suggested that the excess lung cancer
rate was not due to differences in smoking, since cancers of other sites
normally associated with smoking showed no excess in the three south-
central areas.
The authors are currently undertaking a case-control study of smoking
and occupational and residential hi sotry in south-central Los Angeles
County to determine whether air pollution contributes to the excess lung
cancer rate.
Stocks has carried out many studies relating lung cancer mortality to
445
air pollution. In 1952, he reported that, in towns, lung cancer mortality
increased in proportion to the number of inhabited dwellings (from a compara-
tive mortality ratio of 89 in towns with less than 20,000 occupied dwellings
to 162 in towns with over 200,000 occupied dwellings). Differences in
6-211
-------
smoking habits could not account for the lung cancer excess in towns compared
with rural areas. Stocks put forward the hypothesis that the effects of
tobacco and atmospheric pollution are additive.
428
Stocks and Campbell compared the lung cancer rates among men with
different smoking habits in a rural area, a mixed urban-rural area, and a
highly urbanized area (Liverpool County borough) using data from a study of
environmental histories of persons with and without cancer carried out by
the British Cancer Campaign. The death rates were related to levels of BaP
and other PAH and sulfur dioxide in the air in each area.
The rural death rate increased with increased number of cigarettes
smoked per week. Liverpool rates were higher than the rural rates in every
smoking category, but the urban-rural ratio decreased progressively from
about 9 to 1 for non-smokers to near unity for heavy cigarette smokers.
There was an "absolute urban excess" in each smoking group, suggesting
that an urban factor was added to the effects of smoking. Stocks and
Campbell estimated that about half the male lung cancer deaths in Liverpool
were due to smoking and about three-eighths were due to "a factor which is
only slightly present in the rural areas."
The level of air pollution increased with increasing urbanization.
The concentration of BaP in Liverpool was from 8 to 11 times that in rural
areas, and this ratio corresponded to the estimated mortality ratio among
non-smokers in urban and rural areas. The data are given in Table 6-48.
446 447
Stocks ' reported significant correlations between SMR's for lung
cancer and bronchitis and air pollution (undissolved deposit and smoke)
6-212
-------
Table 5-48. LUNG CANCER DEATH RATES (MEAN ANNUAL PER 100,000 FROM MID-1952 TO MID-1954) OF MEN IN
RURAL, MIXED, AND URBAN AREAS CLASSIFIED ACCORDING TO PAST SMOKING HABITS428
INS
oo
Ages 45-54
Smoking category
Non-smokers
Pipe smokers
Cigarette-
Light
Moderate
Heavy
Number of deaths
Rural
0
0
69
90
117
16
Mixed
0
0
57
83
214
26
Urban
31
104
112
138
205
124
Ages 55-64
Rural
0
34
70
205
626
25
Mixed
0
59
224
285
362
56
Urban
147
143
378
386
543
232
Ages 65-74
Rural
70
145
154
362
506
27
Mixed
0
26
259
435
412
36
Urban
336
232
592
473
588
183
S
Rural
14
41
87
183
363
68
.D.R. 54-74*
Mixed
0
25
153
132
303
118
Urban
131
143
297
287
394
539
Standardized rate based on Liverpool population.
-------
levels in 58 county boroughs (towns) In England and Wales when population
density was held constant. Stomach cancer was also positively correlated
with air pollution. Lung cancer gave a correlation of 0.500 with the
amount of deposit when the population density was held constant (p< .002).
Lung cancer gave a significant partial coefficient with smoke of 0.510
(p< .01). Bronchitis gave a partial coefficient with amount of deposit of
0.579 in males and 0.511 in females.
448
In an expanded study, a high correlation was reported between smoke
density and lung cancer mortality (r = 0.873). Differences in mortality
were only partially explainable by social differences (housing indices
based on numbers of persons per room and the proportion of employed and
retired males in unskilled jobs). Bronchitis and pneumonia in males
(r = 0.869 and r = 0.666, respectively) and bronchitis in females (r = 0.751,
significant at the 5 percent level) were also strongly related to smoke.
Analysis for the relative correlation of four different PAH indicated that
BaP was the "substance of prime importance" for lung cancer. The trace
elements beryllium and molybdenum also showed associations with lung cancer.
449
Stocks reported the results of three separate analyses:
(1) Lung cancer mortality showed "substantial and independent correla-
tions" with smoking and air pollution (measured by smoke, BaP, and three other
PAH) in six European cities and two areas of Wales.
(2) Lung cancer mortality showed positive correlations with the per
capita consumption of cigarettes and solid fuel (but not with liquid fuel)
in 19 countries. Smoking appeared to account for about two-thirds of the
deaths in the average country and coal consumption for about one-third.
6-214
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(3) There was a large urban excess of lung cancer in English metropoli-
tan areas relative to surrounding regions after the effects of differences in
social and other factors were eliminated. This excess was attributed to air
pollution.
The analysis of lung cancer and mortality in relation to smoking and
450
per capita fuel consumption in 19 countries was repeated with more recent
mortality data. When lung cancer rates were adjusted for smoking differences,
the adjusted rates were generally higher in countries with high coal consump-
tion than in countries with low coal consumption. Smoking showed a greater
effect than air pollution from solid fuel burning on the lung cancer rate
in men aged 35 to 44 (the correlation coefficients with lung cancer were 0.634
for smoking and 0.470 for solid fuel), but in men aged 55-64, air pollution
showed a greater effect even when smoking was held constant (the correlation
coefficients were 0.599 for solid fuel and 0.380 for smoking).
451
Carnow and Meier carried out a regression analysis similar to that
449
reported by Stocks. They related lung cancer mortality rates for both
sexes and for white and non-white populations during the years 1959 to 1961
to BaP concentrations in the 48 contiguous United States. BaP was measured
quarterly at various urban and rural locations in 1967-1969, and an urban-
rural weighting, based on the urban fraction of each state, was used.
Final estimates of BaP for each state were obtained by a series of averaging
procedures. Cigarette smoking was reflected in the regression analysis by
using cigarette sales per person aged 15 and over. The regression coeffi-
cients for BaP for each age-specific group of white males indicated "that an
6-215
-------
Increase in urban pollution associated with an average BaP concentration of
3 3
1 pg/lQOO m (1 ng/m ) corresponds to an increase of 5 percent in the death
rate." Carnow and Meier observed that on the basis of this correlation, a
60 percent reduction in urban air pollution could be expected to reduce the
deaths of smokers and non-smokers from lung cancer by 20 percent. This
analysis figured prominently in the National Academy of Science's report on
Biologic Effects of Atmospheric Pollutants: Particulate Polycyclic Organic
452
Matter. Data from Carnow and Meier are given in Table 6-49.
The Carnow and Meier study has been criticized for using inadequate
cigarette consumption data and crude BaP measurements which could be
expected to have little validity for an area as large as a state. *443
Taking a different approach based on the risk of highly exposed workers,
394
Pike et al. calculated a small but non-negligible risk associated with air
pollution. Pike et al. used the level of exposure to BaP among British gas
workers showing an excess lung cancer rate in order to extrapolate to the
lung cancer rate attributable to BaP in general urban air pollution. They
explain the algorithm used in the extrapolation as follows:
"...The carbonization workers were exposed to an estimated 2,000 ng/m3 BaP
for about 22 percent of the year (assuming a 40-hour working week,
2 weeks paid leave, 1 week sick leave); very roughly, the men were
exposed to the equivalent of 440 (2000 x 0.22) ng/mJ BaP general air
pollution. This exposure caused an extra 160/105 lung cancer cases,
so that we may estimate, assuming a proportional effect, that each
ng/m3 BaP causes 0.4/10$ (160/105 * 440) extra lung cancer cases per
year..."
This calculation yielded an excess rate of 18/100,000 lung cancer
cases per year for a city with 50 ng/m BaP air pollution. The authors
took this calculation and Stocks's comparable findings as support for the
6-216
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Table 6-49. REGRESSION ON LUNG CANCER DEATH RATES IN THE UNITED STATES PER 1 MILLION POPULATION
a 451
i
ro
Age group
Male - white
Age-adjusted
35-44
45-44
55-64
65-74
Male - nonwhite
Age-adjusted
35-44
45-54
55-64
65-74
Female - white
Age-adjusted
35-44
45-54
55-64
65-74
Female - nonwhite
Age-adjusted
35-44
45-54
55-64
65-74
Average
death rate
867.4
101.6
497.8
1,405.8
2,064.7
844.6
132.3
606.0
1,367.6
1,722.4
129.5
32.9
86.5
163.1
255.2
156.3
34.31
85.8
184.9
381.7
Constant
(CQ)
460.7
86.5
125.2
894.4
835.4
184.2
22.8
245.9
141.6
162.6
92.1
12.7
36.4
113.5
184.7
151.5
66.0
32.4
-375.0
1,286.4
Tobacco sales
(Cj)
11.8
0.3
3.0
14.4
35.3
16.5
1.6
7.8
34.0
38.8
1.0
0.8
1.1
2.0
1.7
0.1
-1.0
-0.4
17.3
-19.2
BaP
concentration,
(C2)
ug/1 ,000 cu m
47.5
4.6
18.7
70.5
152.6
133.1
46.4
97.7
179.0
318.8
7.1
-1.1
14.2
-6.2
16.3
1.2
-1.1
46.6
44.5
-246.1
3 Tobacco sales (average 28.8) expressed as dollars spent per capita by individuals
15 years of age or older. Average BaP concentration was 1.38 pg/1,000 cu m.
-------
"notion of a simple proportional relationship between Increasing BaP concen-
tration in the air and excess rate of lung cancer." Pike et al. further
calculated that the excess lung cancer rate associated with smoking one
cigarette per day (in the U.S.) was equivalent to the rate due to exposure to
10 ng/m BaP in the air.
While occupational studies have provided strong evidence that exposure to
high levels of POM causes an increased risk for cancer of several sites and
for non-malignant respiratory disease, the results of general air pollution
studies remain inconclusive. At present, there seems to be no absolute
consensus that the differences between lung cancer rates in urban and rural
areas are due to general air pollution. In his review of the epidemiology of
443
lung cancer in the U.S., Higgins has written that "while an urban effect is
undoubted, it is still not certain that it is due to carcinogenic pollutants
453
in the air." Goldsmith and Friberg, in their review of the literature on
air pollution and lung cancer, conclude that the evidence does not support the
hypothesis that "pollution per se is the urban factor," but they add that it
is also not possible to reject the possibility.
6-218
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6.8 ECOLOGICAL EFFECTS
POM is ubiquitous in the natural environment, arising partly from human
activity (e.g., petroleum spillage, transport of combustion products), but also
originating from natural sources, such as biosynthesis by plants, algae, and
454 455
bacteria, ' although some investigators have argued that aerobic and
456
anaerobic bacteria do not synthesize POM. Therefore, an assessment of the
ecological impact of POM in our terrestrial and aquatic environments is com-
plicated by uncertainty over the natural role which these compounds may have
in contributing to environmental stability.
457
Payer and coworkers have indicated that the green alga, Scenedesmus
acutus, may contain significant quantities of POM which vary depending on
the geographical location where it is grown (Table 6-50). From the log-
normal distribution of carcinogenic POM which was detected, these investi-
gators concluded that most of the POM present was due to bioaccumulation
from environmental (i.e., anthropogenic) sources as opposed to endogenous
formation. Effects of these POM on algal growth were not indicated.
Although it was reported that phenanthroquinone, a degradation product of
phenanthrene, reduced the survival of various algal species at concentrations
458
of 40 to 800 yg/liter, others demonstrated that POM at low levels can
459
enhance algal growth. The growth of Chlorella vulgaris, Scenedesmus
obliquus, and Ankistiodesmus oranum'i was enhanced by exposure to 10 to
20 vig/liter fluoranthene; 1,12-benzoperylene; 3,4-benzofluoranthene; indeno-
(1,2,3,cd)pyrene; 1,2-benzanthracene; BaP; and DBahA. Moreover, the degree of
growth enhancement appeared to correlate with carcinogenic potency. Following
6-219
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Table 6-50. POLYCYCLICS CONTENT (ppb) OF DRIED MICROALGAE AS A FUNCTION OF GEOGRAPHICAL LOCATION3 457
CD
1
ro
r\i
0
3,4-Benzopyrene
3,4-Benzofluoranthene
Indenopyrene
Fluoranthene
1 ,12-Benzoperylene
11 ,12-Benzofluoranthene
Dortmund,
Germany
39.5 (2.149^)
85.4 d.795^1)
50.9 (1.923^)
444 (1.505^)
52.1 (1.932-1)
36.3 d.863^1)
No. of
samples
19
19
19
18
19
19
Bangkok,
Thailand
1.39 (1.605^)
5.94 d.639^1)
2.36 (l.Sie^1)
91.2 + 38.2
3.89 + 2.36
2.40 +_ 1.02
No. of
samples
15
14
8
8
8
8
The scattering of values is indicated by median values and scattering factors in the case of
lognormal distributions, or by arithmetic means and standard deviations in the case of normal
distributions.
-------
the demonstration that Chlorella yulgaris could utilize acetate in the growth
medium to biosynthesize BaP, an hypothesis was presented that POM may act as
455
an endogenous growth promoter in plants. This contention is also supported
by the observation that growth of higher plants (rye, radish, tobacco) is
459
promoted by POM in the same fashion as the growth of algae. However, in
comparison to the POM accumulated in plants from anthropogenic sources, the
contribution by endogenous synthesis is likely to be quite insignificant. '
In various microorganisms, POM may either promote or inhibit growth.
Toxicity may be expressed more as a function of increasing concentration
rather than specific chemical structure. On the other hand, Mass and Applegate
reported that a structure-activity correlation may exist for the effects of
polycyclic aromatic hydrocarbons on the growth of Escherichia coli. At con-
centrations in the medium of 10 to 10" molar, anthracene, phenanthrene,
chrysene, DBacA, and pentacene inhibited bacterial growth. The more angular
configurations, 1,2-benzanthracene, DBahA, and BaP, promoted the growth of £._
coli. It was concluded from these limited data that growth promotion may
require the presence of POM with an angular acene conformation, whereas inhi-
bition might occur with both linear and angular acene molecules.
Recent studies conducted with marine bacteria do not support the hypo-
thesis that the effect of POM on microorganisms might be structure-specific.
462
Instead, Calder and Lader reported that aromatic hydrocarbons inhibited the
growth of Serratia marinoruba and Vibrio parahaemolyticus in a manner which
was dose-related and a function of water solubility. Thus, a saturated solu-
tion of BaP would have the same impact on bacterial growth as a saturated
6-221
-------
solution of naphthalene, even though their respective solubilities differ by
several orders of magnitude. Consequently, when evaluating the effects of POM
on aquatic organisms it may be necessary to balance inherent toxicity on a
molar basis against water solubility. The significance of considering both
variables in the ranking of POM for toxicity to marine bacteria is depicted in
Table 6-51. Furthermore, one must recognize that under normal conditions
the low-to-medium molecular weight POM may contribute less to overall en-
vironmental toxicity than the higher weight molecules because the former are
more readily lost by volatilization and degradation.
It has also been suggested that once polycyclic aromatic hydrocarbons are
absorbed by microorganisms they can be transferred throughout the cell popula-
tion by cell surface contact. Studies with various yeasts grown in the
presence of BaP demonstrated that greater than half of the hydrocarbon accumu-
lated by yeast cells could be transferred to recipient yeast cells which were
, .. 463
grown in a normal medium.
Sludge microorganisms were adversely affected by a variety of carcino-
464
genie POM. An inhibition of oxygen uptake of varying degrees was obtained
with different sludge microorganisms exposed to: DBahA; 7-methyl-1,2-benz-
anthracene; 1,2,4,5-dibenzopyrene; MCA; 2-nitrofluorene; 2-fluoreneamine; N-2-
fluorenylacetamide; 7,9-dimethylbenz[c]acridine; 7,10-dimethylbenz[c]acridine;
dibenz[a,h]acridine; dibenz[a,j]acridine.
The toxicity of POM has not been extensively studied in fish, amphibians,
or aquatic invertebrates. Nevertheless, it is known that marine fish and
invertebrates can accumulate BaP from polluted waters. ' Furthermore,
6-222
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Table 6-51. EFFECT OF AROMATIC HYDROCARBONS IN MARINE BACTERIA'
462
ro
ro
co
Hydrocarbon
Naphthalene
2-Methyl naphthal ene
2 , 6-Dimethyl naphthal ene
Phenanthrene
Pyrene
Benzopyrene
2 , 3-Di hydroxynaphthal ene
a In distilled water at 25°C,
U mm — ——Jj-.-J-^ • £ 4- L« A 4> A u 4 M 4 4- n
Mol wt
128.16
142.19
156.22
178.22
202.24
252.3
160.16
1 a tin.
(A> a
Solubility3 M
2.43 x 10"J
1.73 x 10";
0.83 x 10"?
0.66 x 10"?
0.73 x 10":
~0.30 x 10 ~i
>16.5 x 10"
(B) b
0.4
2.1
12.8
4.0
170
881
.68
(C)
Toxicity index,-
(C = A x B x 10°)
97
363
106
26
124
>26
>1,120
, ^ i . • IJ.B
to growth of controls.
-------
fresh-water and marine fish are capable of metabolizing a wide variety of
465 14 3
hydrocarbons. Lee and coworkers showed that C-naphthalene and H-BaP
were readily taken up through the gills of three marine fish - mudsucker,
sculpin, and sand dab. BaP was metabolized in the liver and, within a few
hours, metabolites were transferred to the gall bladder and excreted pre-
dominantly in the urine. The main product of BaP metabolism was 7,8-dihydro-
7,8-dihydroxybenzopyrene, which indicated that the pattern of biotransforma-
tion was similar to that in the rat. With naphthalene, however, a greater
tissue uptake was demonstrated than for BaP, and excretion of metabolites was
principally via the feces. The rate of elimination of radioactivity derived
14 3
from C-naphthalene was more rapid than for H-BaP. Overall, it was con-
cluded that marine fish are able to dispose efficiently of certain non-halo-
genated polycyclic aromatic chemicals.
The fact that sub-mammalian species can metabolize POM would lead one to
speculate that they may also be able to form activated intermediates from
these compounds. Indeed it has been shown that tumors can be readily induced
in fish and amphibians by exposure to chemicals which are known to be carcino-
genic in mammals. In addition, Ahokas and coworkers recently demonstrated
that the oxidative metabolism of BaP by trout liver led to the formation of
reactive intermediates which became covalently bound to protein. Furthermore,
trout liver microsomal enzymes activated BaP, 2-aminofluorene, and 2-acetyl-
aminofluorene to compounds which were potent frameshift mutagens in the Ames
Salmonella assay system. In comparison to the Sprague-Dawley rat microsomes,
trout liver microsomes metabolized BaP 15 to 30 times faster when the quantity
6-224
-------
of BaP metabolites produced In 15 minutes was expressed per nmole of cyto-
chrome P-450 or per unit of cytochrome c reductase. Hepatic levels of
cytochrome P-450 are higher than in the rat, whereas cyctochrome c reductase
levels are lower. However, the Vmax is higher than for the rat and the Km is
lower when BaP is used as a substrate.
Carcinogen!city testing of POM in lower organisms has been pursued for
many years. For the most part, compounds which are carcinogenic in mammals
also produce hyperplastic reactions or tumors in lower animals. Arffman and
ACO
Christensen summarized much of the early work performed with the newt, a
member of the salamander family. These studies showed that an early prolifer-
ation of the epidermis accompanies the subcutaneous injection of tar, BaP, and
MCA in the tail region of the newt. They confirmed these results by showing
that an epithelial proliferation commonly occurred with the injection of BaP,
MCA, or DBahA. The highest incidence of epithelial reaction was obtained with
DBahA.
Following the demonstration in the clawed toad, Xenopus laevis. that
implantation of MCA crystals-induced lymphoid tumors, a similar study was
469
undertaken to confirm this result using BaP. The implantation of BaP
crystals (1.5 mg) in the abdominal cavity of adult Xenopus laevis laevis
produced lymphosarcomas in 11 of 13 animals within 86 to 288 days. Advanced
tumors were found which affected the liver and kidneys and which were trans-
pi antable to immature recipient Xenopus.
POM's are widely distributed in the environment as evidenced by their
detection in sediments, soils, air, surface waters, and plant and animal tis-
470
sues. The ecological impact of these chemicals, however, is uncertain.
6-225
-------
Numerous studies show that despite their high lipid solubility, ROM's show
little tendency for bioaccumulation in the fatty tissues of animals or man
(see Section 6.1). This observation is not unexpected, in light of convincing
evidence to show that ROM's are rapidly and extensively metabolized (see
Sections 6.1 and 6.2). Since only low levels of ROM's are detected in plants
470
and lower organisms, transfer of ROM's through the food chain does not seem
likely. The direct impact of ROM's on plants, animals, or the ecological
balance of nature is difficult to evaluate, since few data are available which
suggest that adverse effects may occur.
6-226
-------
SUMMARY AND CONCLUSIONS
6.1 ABSORPTION, DISTRIBUTION, AND EXCRETION
In the environment, exposure to ROM's occurs by direct inhalation of
polluted air and tobacco smoke, and possibly in ingestion of contaminated
food and water, or by dermal contact with soot, tars, and oils. Regardless
of the route of exposure, it can be demonstrated in laboratory animals that
ROM's are readily absorbed across all epithelia which are in contact with
the external environment. The fact that POM's are generally highly lipid-
soluble neutral molecules greatly facilitates their passage through the
predominantly lipid-like cell membranes of animals, including man.
Under environmental conditions, POM's reach the lungs by adsorption on
carrier particles. Moreover, the regional deposition and retention of
inhaled POM's in the respiratory tract will be primarily determined by the
physical size of carrier particles and, to a lesser extent, by their composi-
tion. Once deposited in the lungs, two processes begin to act on the
particulate material. First, depending on their size, particles are cleared
from the respiratory tract by upward flow in the mucociliary tree or by
phagocytic action of pulmonary macrophages. Second, adsorbed POM is eluted
from the carrier particles and left free to react with the respiratory
tissues or traverse the epithelium to reach the systemic circulation. A
balance apparently exists between the rate of particle clearance and the
degree of POM elution which ultimately establishes the degree of toxicant
exposure via the lungs. However, clearance of particles by mucus and
6-227
-------
ciliary action does not necessarity remove them from the body, since most
materials cleared from the lungs are subsequently swallowed, thus allowing
for absorption via the gastrointestinal tract.
Upon reaching the bloodstream, ROM's are rapidly distributed to most
internal body organs. Under experimental conditions with laboratory animals,
the route of exposure has little apparent influence on the tissue localiza-
tion of ROM's. Extensive localization in the fat and fatty tissues (e.g.,
breast) is observed, and suggests that these tissues may act as a chemical
trap, creating a situation for sustained release of the unchanged substance.
In pregnant rats, it is apparent that BaP and DMBA, but probably not MCA,
are capable of transplacental passage and localization in the fetus.
Excretion of POM is rapid and occurs mainly via the feces; elimination
in the bile may account for a significant percentage of administered doses.
The influence of route of administration on patterns of POM excretion is
not entirely clear. However, elimination of H-BaP from various tissues
(lung, liver, kidney, urine, feces) of the hamster following intratracheal
instillation appeared to be biphasic. The slow phase of elimination from
the lung (involving less than 1 percent of the treatment dose) seemed
dependent on the administration of H-BaP together with an adsorbent. It
is not known to what extent bioexchange of the tritium label may have
accounted for retention of radioactivity. Although some investigators find
that retention of BaP in the lungs of experimental animals is dependent
upon the co-administration of particulates, others maintain that carrier
particles are more important in determining localization in the respiratory
tract.
6-228
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6.2 METABOLISM AND METABOLIC ACTIVATION
The relative lack of chemical reactivity for tumorigenic POM's has in
the past been puzzling in light of their biological effects. More recently,
however, it has become recognized that these molecules are enzymatically
activated by oxidative mechanisms to form reactive electrophiles. These
activated metabolites are capable of covalent interaction with cellular
constituents (RNA, DNA, proteins), and it is suggested that one of these
metabolites is the true ultimate carcinogenic form.
Metabolic reactions on the POM skeleton may take place at nearly any
position, although chemical theory predicts that certain locations will be
more reactive. The earliest theories designated a K-region having particu-
lar relevance to the biological activity of the molecule subsequent to
oxidative attack. More recently, a "bay region" hypothesis was formulated
which takes into account the ease of benzylic carbonium ion formation such
as would be formed from the epoxides of diol-epoxides on tetrahydrobenzo
rings in the "angular" region of a POM. These diol epoxides are postulated
as ultimate carcinogenic metabolites of POM; a contention which is supported
by circumstantial experimental data showing high mutagenicity/carcino-
genicity for such structures and specific alkylation products of genetic
material identical to that obtained with the parent compound under metabolic
activation conditions. Examples of a K-region and a bay region on the BaP
molecule can be depicted as follows:
Bay
region
-------
POM is metabolized by the microsomal mixed-function oxidase system,
often designated aryl hydrocarbon hydroxylase. This enzyme system is
readily inducible and is found in most mammalian tissues, although predomi-
nantly in the liver. In conjuction with various P-450 type cytochromes,
this enzyme complex is involved in detoxification of many xenobiotics, but
may also catalyze the formation of reactive epoxide metabolites leading to
carcinogenesis. A second microsomal enzyme, epoxide hydrase, converts
epoxide metabolites of ROM's to vicinal glycols, a process which may also
have critical importance to carcinogenesis.
Because of the importance of metabolic activation for the expression
of carcinogenic effects by POM, the chemical fate of many representative
compounds in mammalian cells has been extensively explored. By far the
most widely studied of the POM's has been BaP, one of the principal carcino-
genic products from the combustion of organic material. The metabolites of
BaP (and all POM) can be divided into a water-soluble and an organic solvent-
soluble fraction. Components of the latter fraction are primarily ring-
hydroxylated products, quinones, and labile epoxide intermediates. For BaP
there are at least three dihydrodiols, three quinones, and two phenols
which can be detected as positional isomers. The K-region (4,5-) and non
K-region (7,8-; 9,10-) epoxides are precursors of the corresponding diols,
which are formed by the action of the epoxide hydrase enzyme. A subsequent
oxidative attack by the aryl hydrocarbon hydroxylase may convert the diols
to diol epoxides, one of which (7,8-diol-9,10-epoxide) is the proposed
ultimate carcinogenic form of BaP.
6-230
-------
In the water-soluble fraction containing BaP metabolites are mainly
conjugates of hydroxylated products with glutathione, glucuronic acid, and
sulfate. This group of metabolites is tenatively regarded to be composed
of non-toxic excretion products.
The general scheme of metabolism for unsubstituted ROM's closely
parallels that for BaP, although several other major environmental PAH and
aza arenes have not been studied. It is also evident that K-region deriva-
tives of POM's may be preferred targets for conjugation and excretion,
whereas non K-region epoxides undergo further reductions and oxidative
attack to form toxicologically important molecules. For POM's bearing
alkyl substituents (e.g., DMBA, MCA), the primary metabolites formed are
hydroxymethyl derivatives. Nevertheless, epoxidation reactions at K-region
and non K-region aromatic double bonds occur which are catalyzed by aryl
hydrocarbon hydroxylase. Removal of activated intermediates occurs by
conjugation with glutathione or glucuronic acid, or by further metabolism
to tetrahydrotetrols.
Alternative explanations for the generation of reactive POM metabolites
exist, although supporting evidence for their toxicologic significance is
not as strong as for the diol epoxide (bay region) theory. One argument
supports the role of reactive radical cation intermediates of POM as the
critical metabolites capable of interaction with cellular constituents.
Others have indicated that a 6-oxy-BaP free radical or a hydroxymethyl
derivative of POM's may be biologically important reactive metabolites.
6-231
-------
The exact intracellular event by which a reactive POM metabolite
initiates a toxic or carcinogenic response is not known. However, it is a
widely held view that covalent binding of metabolites to DNA forms the
molecular basis of the carcinogenic and/or mutagenic consequence of exposure
to certain POM. In this regard it has been shown that carcinogenic POM's
in the presence of rat liver microsomes become bound to DNA and synthetic
polynucleotides, and moreover that the extent of binding is correlated with
the known carcinogenic potency of the compound and levels of microsomal
enzyme activity. Covalent binding of reactive POM metabolites also takes
place with RNA and other cellular proteins, and these processes cannot be
excluded as potentially important mediators of toxic response. Various
epoxide derivatives of POM's have been tested for their ability to bind to
nucleic acids, and it appears that guanosine residues may be the preferred
targets for reactive arene oxides. Reactivity with nucleic acids and syn-
thetic polynucleotides (poly G) varied with the position of the epoxide
moiety; K-region and non K-region epoxides were capable of extensive co-
valent binding. It was further shown that, for BaP, the binding to RNA
occurring after in vivo exposures may be due to the reaction of BaP 7,8-
diol-9,10-epoxides with the 2-amino group of guanosine. A DMBA diol epoxide
was also shown to be involved in DNA binding in cultured mouse embryo
cells. These studies have helped to strengthen the concept that:
(1) reaction with nucleic acids may be the molecular basis by which a POM
exerts its oncologic effects, and (2) non K-region diol epoxide metabolites
may be the ultimate reactive chemical forms of POM.
6-232
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6.3 TOXICOLOGY
Not a great deal of attention has been paid to the non-carcinogenic
effects of exposure to ROM's. Nevertheless, it is known that tissues of
the rapidly proliferating type (e.g., intestinal epithelium, bone marrow,
lymphoid organs, testis) seem to be preferred targets for ROM-induced
cytotoxicity. This action is probably due to a specific attack on DNA of
cells in the S phase of the mitotic cycle.
Acute and chronic exposure to various carcinogenic ROM's has resulted
in selective destruction of hematopoietic and lymphoid elements, ovotoxicity
and anti-spermatogenic effects, adrenal necrosis, and changes in the intesti-
nal and respiratory epithelia. For the most part, however, tissue damage
occurs at dose levels that would also be expected to induce carcinomas, and
thus the threat of malignancy predominates in evaluating POM toxicity. For
ROM's which are not carcinogenic, very little seems to be known concerning
their involvement in toxic responses.
Immunosuppression by exposure to ROM's has been reported, although it
is not clear whether this effect may be involved in carcinogenesis. However,
it appears that the degree of immunosuppression (cell-mediated and humoral)
by ROM's is correlated with carcinogenic potency. On the other hand, a
dissociation between carcinogenic and immunosuppresive effects can be
shown, whereby doses which are insufficient to affect immunity can still
induce tumors.
One of the most lexicologically significant processes involved in the
response to POM absorption is the interaction with drug metabolizing enzyme
6-233
-------
systems. The induction of this enzyme activity in various body tissues by
substrate and non-substrate xenobiotics may be a critical determinant in
the generation of reactive POM metabolites at the target site for tumor
induction. Recent emphasis has been placed on determining the drug metabo-
lizing capacity of humans as a measure of their potential to form activated
POM metabolites. Although it has not thus far been possible to definitely
correlate enzyme activity in humans with susceptibility to carcinogenesis,
it is known that wide variations occur in human carcinogen-metabolizing
capacity. Moreover, tissue-specific enzyme inducibility may affect the
response of different organs to carcinogen action. Nevertheless, the
obligatory coupling of metabolic activation with POM-induced neoplasia in
animals indicates that the modulation of drug metabolizing enzymes in
humans plays a central role in carcinogenesis.
6.4 MUTAGENESIS
The demonstration of mutagenic effect in bacterial and mammalian cells
by exposure to ROM's is generally equated with the capability to induce
tumor formation. This assumption is based on the participation of a common
electrophilic metabolite in producing the carcinogenic/mutagem'c event, and
the common target site in the cell (i.e., DNA or other components of the
genome) for the effect to be produced.
In recent years, considerable research effort has been directed at
determining the mutagenicity of various POM derivatives as a means of
identifying structural features associated with the biological effect
produced. Working with bacterial mutants which can be reverted to histidine
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independence by a chemically-induced mutation, it was discoverd that epoxides
of carcinogenic ROM's displayed significant mutagenicity. In particular,
it was found that a non K-region 7,8-diol-9,10-epoxide of BaP possesses the
highest mutagenic activity of all its possible oxidative metabolites.
Further work with cultured mammalian cells established that carcino-
genic ROM's can produce forward mutations when a drug metabolizing enzyme
system is available. Once again, a 7,8-diol-9,10-epoxide of BaP displayed
the highest mutagenicity among its various metabolites. This effect was
seen in the absence of drug metabolizing enzymes; strongly suggesting that
the diol epoxide derivative is an ultimate mutagenic agent. Additional
investigations on the interaction of BaP derivatives with constituents of
the same mammalian cells in which mutations are induced revealed that a BaP
7,8-diol-9,10-epoxide was involved in binding to DNA. The link between
carcinogenicity and mutagenicity was strengthened by the demonstration that
both neoplastic transformation and mutagenesis could be induced by BaP or
BaP 7,8-dihydrodiol (precursor of the 7,8-diol-9,10-epoxide) in the same
normal diploid hamster embryo cells.
Numerous attempts have been made to correlate exposure to ROM's with
the induction of chromosomal aberrations. Although variations in chromosome
number and structure accompany POM-induced tumors in rodents, it is not
clear whether these changes are consistently observable. No evidence in
the published literature has been found to indicate that POM may produce
somatic mutations in the absence of neoplastic transformation.
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Mutations in germinal tissues induced by ROM's have been more easily
demonstrated in Drosophila than in mammals. The male dominant lethal assay
in mice has produced conflicting results, although it is known that BaP and
MCA can induce sperm abnormalities.
6.5 CARCINOGENESIS
Polycyclic aromatic hydrocarbons were the first compounds ever shown
to be associated with carcinogenesis. To this day, carcinogenic ROM's are
still distinguished by several unique features: (1) several of the ROM's
are among the potent carcinogens known to exist, producing tumors by single
exposures to microgram quantities; (2) they act both at the site of applica-
tion and at organs distant to the site of absorption; and (3) their effects
have been demonstrated in nearly every tissue and species tested, regard-
less of the route of administration. Among the more common ROM's at least
one, BaP, is ubiquitous in the environment and produces tumors in animals
which resemble human carcinomas. The demonstration that organic extracts
of particulate air pollutants are carcinogenic to animals has raised concern
over the involvement of ROM's in human cancer formation.
Oral administration of ROM's to rodents can result in tumors of the
forestomach, mammary gland, ovary, lung, liver, and lymphoid and hemato-
poietic tissues. Exposure to ROM's by inhalation or intratracheal instilla-
tion can also be an effective means of producing tumors of the respiratory
tract using very small doses of chemical. However, for both oral and
intratracheal routes of administration, BaP is less effective than other
ROM's (e.g., DMBA, MCA, DBcgC) in producing carcinomas. On the other hand,
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BaP has a remarkable potency for the induction of skin tumors in mice that
cannot be matched by any other environmental POM. Thus, caution must be
exercised in considering the carcinogenicity of POM's as a class, or in
using BaP as a representative example in evaluating carcinogenic risk of
POM's.
The induction of skin cancer by POM's is regarded to be a two-stage
process, involving an irreversible initiation step and requiring the
subsequent presence of a promoting agent for tumors to develop. Certain
POM's may act only as initiating agents (e.g., DBacA, chrysene, benz[a]-
anthracene), or may supply both initiating and promoting stimuli (e.g.,
BaP, DMBA, MCA, DBahA, DBcgC, DBahP, DBaiP). The administration of a
single subcarcinogenic dose of a POM (e.g., 100 nmoles of BaP) followed by
repeated application of a non-carcinogenic promoting agent (e.g., croton
oil) can cause the appearance of numerous skin tumors in mice. The two-
stage mechanism of carcinogenesis may also apply to nonepidermal tissues.
For the induction of respiratory tumors by POM's, several species and
modes of carcinogen administration are employed. In studies conducted with
the Syrian golden hamster, intratracheal instillation of POM's established
that dose-related increases in tumor yield are clearly evident, and the co-
administration of carrier particles such as Fe203 can markedly affect tumor
incidence.
Several in vitro procedures hold promise as useful screening tools for
the detection of environmental carcinogens, including POM. Morphological
transformation of cultured mammalian cells has proven to be a reliable
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indicator of carcinogenicity by a chemical in vivo. Examination of DNA
repair synthesis in cultured human and animal cells exposed to a carcinogen
is also predictive of in vivo carcinogenicity for certain compounds. When
combined with the results of microbial mutagenicity tests, cell transforma-
tion assays are capable of accurately distinguishing nearly all known
carcinogens from non-carcinogens.
An analysis of dose-response relationships for ROM-induced tumors in
animals raises several important points having relevance to environmental
risk assessment. A fundamental relationship which must be considered is
the deviation from linearity in dose-response curves, especially at low
doses, and whether or not this indicates the existence of a threshold
level. It can be argued that individual variability in thresholds for
tumor induction resulting from saturation of detoxification mechanisms may
account for a convex curvature in the dose-response curve in the low dose
range. Once the dose exceeds threshold levels, tumor yield should remain a
linear function of dose, with the slope of the dose-response curve being
indicative of the animal's sensitivity to the carcinogen. Thus, the
extrapolation of the straight portion of the dose-response curve for groups
of animals is often regarded to provide a conservatively low estimate of
the average threshold for tumor induction, assuming the most likely case of
decreasing sensitivity with an increasing threshold. However, the use of
an average threshold as a parameter of safety would not indicate the propor-
tion of individuals still at risk of tumorigenesis at extrapolated low dose
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levels. Furthermore, the existence of a threshold for POM-induced careino-
genesis has not been documented in either animals or man, and, in fact, it
is more likely that in diverse populations the effect of ROM's will be a
continuous function of dose. In support of this contention are data which
indicate that, in the two-stage model, tumor initiation with BaP is consis-
tent with a linear non-threshold pattern. Overt tumor induction, on the
other hand, follows a dose response relationship consistent with a multi-
hit promotion process. It is conceivable that in human populations, the
multi-hit component of carcinogenesis may be supplied by environmental
stimuli not necessarily linked or related to POM exposure.
The we!1-documented existence of cocarcinogenic and anticarcinogenic
agents dictates that only a multifactorial analysis can provide a true
assessment of carcinogenic risk to humans for a particular POM. Although
non-carcinogenic POM's were reported to antagonize the effects of carcino-
genic POM's in animals, others have shown that they have little influence
on tumor incidence or yield. On the other hand, several non-carcinogenic
POM's found in cigarette smoke (pyrene, fluoranthene, BeP) have potent
cocarcinogenic activity. A significant decrease in carcinogenicity can be
achieved with antioxidant food additives, certain vitamins, and other
naturally occuring components in the diet in the experimental setting. The
molecular basis of anticarcinogenesis cannot be fully explained, but may be
due, at least in part, to an effect on the production of activated POM
metabolites.
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6.6 REPRODUCTION AND TERATOLOGY
Little information is presently available to indicate whether ROM's
present a significant hazard to reproductive success. Furthermore, effects
on the fetus which may be due to maternal toxicity or experimental conditions
(e.g., injection vehicle, stress) have not been adequately dissociated from
true embryotoxicity or teratogenesis. In cases where teratogenic effects
are clearly evident (e.g., with DMBA), the required doses are far in excess
of realistic environmental exposures.
6.7 HUMAN STUDIES
The presence of ROM's in the air, or as components of soot, tars, and
oils, have long been associated with an excess incidence of cancer in human
populations. However, it has never been possible to study a population
having exposure to ROM's in the absence of other potential carcinogens,
cocarcinogens, tumor initiators, or tumor promoters.
Convincing evidence indicates an excess in lung cancer mortality among
workers exposed to large amounts of coal gas, tars, and coke oven emissions.
In such cases, cancer mortality can be correlated with both the type and
duration of exposure. Although occupational exposure to ROM-containing
substances is far greater than would occur in most communities, our under-
standing of chemical carcinogenesis would lead to the conclusion that the
number of cancers produced is directly proportional to the dose received.
One must assume, therefore, that the smaller amounts of POM in ambient air
contribute in some degree to the observed incidence of lung cancer in most
populations. It should be recognized, however, that the influence of
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cigarette smoking may have an overriding impact on the evaluation of the
carcinogenic threat of ROM's in occupational or environmental settings.
Nevertheless, an approximately two-fold excess of lung cancer occurs
in urban settings as compared to rural environments, which generally cannot
be accounted for by differences in cigarette smoking, age, or sex. Several
investigators have shown that the incidence of lung cancer is highest in
cities where POM pollutants are the most concentrated. Moreover, it is
clear that among groups which have migrated from one country to another,
the influence of pollution exposure in their former residence is still
expressed as a higher rate of lung cancer mortality while in their adopted
country. This observation cannot be explained on the basis of differences
in cigarette smoking habits.
Sampling studies from different communities have attempted to separate
the various factors which may be contributing to lung cancer excesses in
urban settings. These studies have not provided the kind of definitive
results which have been achieved with homogeneous worker populations exposed
to pollutants which are well-defined both quantitatively and qualitatively.
On the one hand, it was shown that lung cancer can be correlated with the
extent of solid fuel combustion, and particularly BaP concentration in air.
On the other hand, it has been concluded that POM in community air does
little to contribute to lung cancer incidence except insofar as it may
interact, synergistically or additively, with the effects of cigarette
smoking.
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A fundamental problem in relating exposure to ROM's with the incidence
of cancer may involve the use of BaP levels as an indicator of total exposure.
Demonstrated variation in the sources and degree of BaP emission to the
atmosphere with respect to the levels of other POM's precludes the accurate
estimation of body burdens. In addition, animals exposed to basic and
aromatic neutral subfractions of organic air pollutants commonly develop
tumors; indicating that several highly active POM-type carcinogens are
present in polluted air. Moreover, the carcinogenic and mutagenic activity
of organic extracts of air pollutants cannot be accounted for solely on the
basis of the amount of BaP contained in them. Further studies which indi-
cate that BaP is a less effective carcinogen for the respiratory tissues
than other POM's (e.g., DBcgC) raise doubts concerning the validity of
risk-assessments derived from data concerning BaP.
6.8 ECOLOGICAL EFFECTS
Although POM's are found nearly everywhere in man's environment, it is
not clear whether these agents may affect the ecological balance. Adverse
effects on plants, microorganisms, fish, or other wildlife cannot be clearly
shown. Moreover, there are no data to indicate that POM's may bioaccumulate
in any species, or that transfer of POM's through the food chain may occur.
Indeed, animal studies showing that POM's are rapidly metabolized and
excreted support the contention that biomagnification is an unlikely possi-
bility.
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