STUDY1 OF POLY'NUCLEAR AROMATIC
HYDROCARBONS
(PNA'S)
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF SOLID WASTE
1985
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I. INTRODUCTION
The EPA Office of Solid Waste (OSW) has conducted a
review of available information on polynuclear aromatic*
hydrocarbons (PNA), evaluating the potential for contamination
of groundwater and the risks to human health and the environment,
This is an interim analysis to be used only for
consideration of delisting petitions filed by MSD and Amoco.
A more complete analysis, and application of the vertical and
horizontal spread model explained in the February 26, 1985
Federal Register will be used in the future.
Specifically, studies have focused on: (1) the toxicity of
PNAs; (2) background levels in the environment; (3) the
mobility of PNA from waste. Several interim reports have
been prepared (JRB Associates 1984, 1985a, 1985b; ERCO 1984a,
and Liber and Whaley 1984). This report summarizes the major
conclusions of the work conducted, in terms of OSW's perspective
on regulating the disposal of certain PNA-contaminated waste.
The PNAs in the waste covered by the MSD petition (fly
ash) and the Amoco petition (waste stabilized in a silicate
matrix) will behave similarly to PNAs on soil. Accordingly,
we have used the reported behavior of the PNAs on soil to
predict the behavior of the PNAs in the petitioned wastes.
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II. Background Levels
General Considerations
Before describing the levels of PNA's typically found in
various matrices, a number of general observations, which may
affect the reported levels, should be described in order £o
put the data in proper prospective.
When PNAs are present in samples at low concentrations
losses of the PNAs are significant. These losses are generally
believed to result from physical and chemical processes which
either oxidize, reduce, or otherwise remove the PNA from the
samples. Oxidative mechanisms such as ultraviolet light
adsorption followed by reaction with oxygen are known to occur
when PNAs are not protected from UV (sun light and floure-
cent light) radiation.(1) When low levels of PNAs are present
(i.e. on the order of tens of ppt) adsorption on sampling
equipment and sample storage containers and volitilization
are also known to significantly reduce obsevered levels of
PNAs even when storage times are mininized.(2,3) Choice of analytical
method will also effect reported levels. For example,
one study of PNAs in water used activated carbon as a
concentrating media for the PNAs, however, the efficiency of
extraction of the PNAs from the charcoal caused reported levels
to be biased toward lower values than actually present.(4)
Finally, one must keep in mind that there are a number
of mechanisms which would cause higher than actual values to
be observed, especially if care is not taken to exclude contamination
during sampling. Cigarette smoke, exhaust fumes from automobiles,
and condensation from atmospheric sources have been implicated
in.this regard.(5,6,7,8) Therefore, unless care.was taken to exclude
these .possible interferences, the reported levels may be
higher than actual levels. Information necessary to assess
whether reported levels are biased (either high or low) is
often not reported in literature articles dealing with PNAs.
The Agency has used the best available information in this
study, however, some of the material cited may not provide
this information.
As pointed out above, there are factors which operate
both to decrease and increase reported values and that there
effects become more pronounced at lower (i.e. ppt) levels.
We believe that this information should be used in conjuction
with the data presented in this report especially when low
levels of PNAs are considered.
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TABLE 1. CONCENTRATION OF POLYNUCLEAR AROMATIC
HYDROCARBONS IN LIQUID FUELS
QtllfMtlO*
Jit A rml.
Ld» Sulfur
j«i A r
MO (
.«.)
»«..
140
140
IM
170
It
IM
too
710
•raio(i.li.l)
MO («1)
MO ,0)
140
110
MO l<10)
41
MD <<10)
i:
M
it
MD (<»
MD (<1)
MD <<20)
MB (<20)
M" (<20)
KD (<20)
Ml (<20)
ND (<10)
MD (<20)
MO ("20)
NU (<])
Mb CJ)
ND ('10}
MD (<2U)
MD (<:0)
KD (<.'C)
MD (<20)
KD (<10)
Mb (<20)
H> (p'»«>t* Ik* 4>t
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CMyoiita to. 2 Itoal
froa 10 MM.
API Gravity 96.9
Danalty .1425
Cataa* Index 90
PIA
Aroaatlca 26.0
Olafina 0.5
Sulfur: t 0.17
Dictlllatloo: *F.
10X 417
501 498
90X 589
PNA Content vg/^g
BaP 41
BaA 108
B«? ; 75
BghlP " 26
Cbryaene 72
Triphenylene 35
Pyrene 1**
Fluoranthene 869
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Sources of PNAs
Combustion and high temperature pyrolysis of organic
matter are major sources of PNAs in the environment. In
addition to this, however, PNAs are biosynthesized on a-w©rld
wide scale by plants and microorganisms on land and in water
(9).
Groundwater
PNAs have been found in uncontaminated ground water.
The levels found are typically less than 50 ppt.(10,ll)
Concentrations for various PNAs range from less than 1 ppt
(the detection limit) up to 2000 ppt.(12) The 2000 ppt .
value was reported for naphthalene in a lignite (brown coal) ^^
formation. Benzopyrenes and benzofluoranthenes have been
reported at 10-30 ppt and 80-600 .ppt, respectively.(13)
Groundwater contaminated with PNAs has been observed resulting
from energy-related activities (i.e. in situ coal gasification)
with levels of PNAs ranging from low ppt to ppm levels. (12)
_s
Soils
PNAs have been found in upper soil layers between 100
to 1000 ug/kg (ppb) with the highest levels found near highways
and industrial areas. (9) This observation is consistent with
the general view that PNAs were formed during combustion processes.
Since combustion processes are more concentrated in urban and
industrial areas it is reasonable to observe higher levels of
PNAs in soils in these locations.
Fly Ash
PNAs in fly ash have been observed from sub ppb to
100s of ppb varying with sample source.(14) Comparable levels
have been observed in municipal incinerator ash samples.
Fuels
Tables 1 and 2 summarize levels of various PNAs found in
fuels used in diesel and jet engines. Levels of PNAs range
from less than .7 ppb up to .1% (15,16)
Diesel Engine Particulates
Particulate matter from diesel engines is known to
contain a variety of PNAs. Levels of PNAs emitted are a function
of load and engine speed. The highest levels are observed under
full load conditions with an average yield of 16 ug/kg fuel
for both Benzo(a)pyrene and Benzo(a)anthracene. (16)
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III. Migration
Direct information about the mobility of PNAs in the
environment is available in the open literature.
PNAs are characterized by low aqueous solubility (e.g.
31.7 mg/1 for naphthalene to 5.0 x 10~4 mg/1 for dibenzo(ah)anthracene)
and high octanol-water and organic carbon-water partition coefficients
(e.g. 1.95 x 1Q3 and 940 respectively, for naphthalene, to
1.5 x 10^ and 5.5 x 10^ respectively, for benzo(a)pyrene)(19)
The matrices studied include soil, fly ash, and water.
It is generally believed that the mobility of PNAs in the environment
are related to their water solubility and their ability to be
adsorbed onto particulates. Two and three ring PNA's are
much more mobile then four, five, or six ring PNAs. These
higher member ring PNAs are not very mobile.
Soils
Migration of various PNAs on soils has been studied
extensively. Partition coefficients for PNAs between soils and
water (i.e. the mobile phase which transports the PNA) range
as follows:
Naphthalene 1300
2 Methyl naphthalene 8500
Phenanthrene 23000
Anthracene 26000
9 Methyl Anthracene 65000
Pyrene 84000
These values were taken directly from studies conducted by
the Agencyd?) and compared with results obtained from similar
studies conducted by other investigators(18). In both
investigations actual partition coefficents were determined
for several soils and sediments and the results were modeled
using linear regression methods. The relationships derived
compare very well considering that both groups used different
compounds and soils for their investigations. (The two
derived relationships differ by only a factor of 1.3).
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These values indicate that PNA's are strongly adsorbed
to soils and that the greater the number of rings the greater
the adsorbtion.
Based on the data above one can estimate the leachate
concentration from soil containing 1% organic carbon and _
lOppm of pyrene (a four ring PNA), using the following relationship:
Where Cw is the aqueous or leachable concentration of the PNA; Cs
is the concentration of the PNA in the waste; Koc is the organic
carbon partition coefficient; and foc is the fractional mass of
organic carbon in the waste (expressed as a percentage). The
estimated concentration of pyrene in the leachate would be about
.1 ppb pyrene.
Under similar conditions the concentration in the leachate
of Benzo(a)pyrene (a five ring PNA with Koc=5.5xlO^)
would be about 2 ppt.(19)
As part of this evaluation the Agency has also estimated
the migration potential of benzo(a)pyrene (BaP) using a model
developed by Arthur D. Little, Inc. This model, Seasonal
Cycles of Water, Sediment, and Pollutants in Soil Environments
(SESOIL), was used to estimate the migration of BaP in a
sandy soil. The agency used this model with worst case
assumptions (e.g. permeable soil with low organic content,
no degradation etc.). The results of this analysis indicate
that wastes containing 20 ppm of BaP in a soil type matrix
do not migrate in the soil. In fact, the only losses predicted
were to air at a level eight orders of magnitude (100,000,000)
lower than the level in the waste.
Finally, comparison of Rf values for selected PNAs on
silica and alumina indicates that no measurable migration of
PNAs occur on these matrices without the use of organic solvents
capable of altering the interaction of the PNAs with the support.
These solvents are among the most non-polar solvents known
(cyclohexane, benzene, etc.) (26). Migration of PNAs using
water as the mobile phase would therefore yield Rf values
many orders of magnitude lower. Furthermore, silica and
alumina have been used by chemists to quantitatively separate
PNAs from other material because of their ability to strongly
bind PNAs. Since the Rf value is a measure of a compounds
mobility in a solid/liquid system, these data support the
observation that PNAs are not mobile. Also the addition of
alumina or silica to an extraction column increases the PNA
binding capacity (i.e., increases the number of binding sites
available) of that column.
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Fly Ash
PNAs are nonpolar, nonionizing organic compounds that
adsorb very strongly to soils high in organic matter as well
as to the aluminosilicate matrix of which fly ash is composed.
Because PNAs are bound so tighly (particularly the 4, 5,'
and 6 ring compounds) researchers often report poor recovery
of these contaminants in studies to quantify levels on solid
waste matrices, e.g. soil and fly ash. A compreshensive
overview of existing methods for analysis/extraction of PNA
has been done(1).
Because PNAs adhere strongly to ash, the kinds and
quantities recovered are influenced by the extraction procedures
used. Poor recoveries of PNAs are reported by conventional
solvent extraction techniques (20) Recent studies indicate
that a combination of solvent extraction, rotary shaking and
ultrasonication greatly improves extraction and recovery of
PNAs from fly ash (21,22,23) From the available information,
measured levels of PNAs on fly ash appear to be very low.
Levels of PNAs on municipal incinerator and power plant fly
ash typically range from sub-ppb to several hundred ppb for each
individual PNA. The study by Zelenski (24), however, documented
total concentrations in the low ppm range from coal and oil
power plant fly ash. These were the highest concentrations
reported in the literature. In a study of PNAs in coal fired
power plant fly ash the following levels were determined:
26 ng/g (ppb) for 3,6-dimethyl phenanthrene to 200 ng/g for
2-methyl chrysene.(21) Griest and Guerin (20) report levels
in the sub-ppb range for individual compounds, and total
quantities of PNAs of aproximately 4 ng/g.
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Two of the available studies specifically considered the
environmental hazard posed by release of PNAs from fly ash.
Griest and Gurerin (20) calculated maximum concentrations
of PNA in a "worst case" extract (i.e. the entire content of
the constituent is extracted) of electrostatic precipitator
ash using the EP Toxicity methodology (refered to by the
authors as the "Toxicant Extraction Procedure"). The resalts
for fluoranthene and pyrene were 1.0 and 1.2 ug/1 respectively.
In the work by Harrison et. al. (23), the authors noted that
the PNAs found in largest concentrations in the extracts were
naphthalene and its derivatives (total concentrations of two
ring aromatics in wet scrubber (WS) and electrostatic precipitator
(ESP) ash were 10 and 520 ppb respectively). The authors
measured the partitioning of [l^C] napthalene between fly
ash and scrubber water. The ratios for ESP fly ash and
scrubber water was 1100:1 and for WS fly ash and scrubber
water, 2400:1. Harrison and coworkers concluded that expected
aqueous concentrations of naphthalene in equilibrium with ESP
and WS fly ash would be approximately 0.08 ug/1 and 0.004
ug/1 respectively, and that this would constitute maximum
concentration of any PNA in water (because all PNAs larger
than naphthalene were lower in concentration in their extracts
and are of lower aqueous solubility). The study by Roy
et al. (22), focused specifically on the solubility of fly
ash contaminants. As part of this study, 5 of 12 fly ash
samples were extracted with benzene, and organic analyses of
the extracts were conducted. These results were compared
with the carbon content of the ashes. Roy and coworkers
found that in two western fly ashes, less than 1% of the
organic carbon present in the fly ash was extractable into
benzene. In two other fly ashes, less than 0.1% of the
organic carbon was extracted into benzene-. The results of
Roy et al. (22), demonstrate that organic contaminants of
fly ash are strongly bound to the alumino-silicate matrix.
Given the greater affinity of PNA compounds for an organic
phase (e.g., benzene or octanol) than water, the concentration
of PNA in leachate from fly ash (to water) will be extremely low.
Available water extraction data further supports the high
affinity of PNAs to fly ash and their inability to be extracted
with water. ERCO (1981) found PNAs to be non-detectable in water
extracts from coal fly ash residues at a detection limit of 1 ppb.
Data submitted by the Amoco Oil Company in support of its petition
to delist refinery waste that was treated using an alumino-silicate
stabilization technology, also showed non-detectable levels
of PNAs in the acetic acid/water and nitric/sulfuric acid/water extracts
of the EP Toxicity and Multiple Extraction procedures. (Detection
limits were 10 ppb).
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Extraction Efficiences
Numerous studies have been conducted where the efficiency of
extraction and concentration of PNAs are investigated. (Reference
1 contains a detailed listing of these studies). These
studies, on the whole indicate that:
1. PNAs are often found in matrices from which they are
not readily extracted. Recoveries of PNAs can range
from less than 20% (C14Bap on fly ash) to 100% with the
highest recoveries for 2 and 3 ring PNAs and the lowest
recoveries for 4 or more ring PNAs.
2. Adsorption effects are significant and should be minimized.
3. Suspended solids decrease extraction efficiency.
4. Highest recoveries are observed when PNAs are adsorbed onto
a resin designed to provide reversible binding.
Extraction efficency is essentially a measure of how
difficult (or easy) it is to move a particular compound or
compound class from one particular matrix into a solvent system.
Therefore, extraction efficency can be considered a reflection
of the binding capacity of PNAs to the matrix.
The information described above is supporting evidence
that PNAs are not mobile under conditions normally experienced
in the environment (e.g., aqueous mobile phases). Futhermore
the data indicates, that even in the presence of strong
organic solvents PNAs with 4 or more rings are poorly
recovered which means that PNAs are so tightly bound to
various matrices that even strong solvent is not entirely
effective in mobilizing the PNA from the matrix.
Damage Cases - Migration of PNAs into Ground Water
Data obtained from the Damage Incident Data Base* (JRB
Associates/SAIC) indicated that PNA contamination of ground
water occurs infrequently. Ground-water supplies that are
reported to be contaminated with PNAs have been found to
contain only 2 and 3 ring PNAs in the majority of cases.
Napthalene is the primary contaminant identified. Only in
one instance was a PNA with more than 3 rings detected in
ground water. Pyrene, a 4 ring PNA, was measured at levels
* This data base was developed from information
contained in EPA files from Regions II and V. While this
information represents the best available information
documenting cases where migration of PNAs has occurred,
information contained in the files may not be adequate to
access migration potential of all PNAs in all disposal
situations.
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of 54 ug/1 in ground water below an oil and chemical service
open pit disposal site. High concentrations of solvents were
also present however (e.g. , toluene, substitued toluenes,
benzene, substituted benzenes) as well as nitro phenols and
chlorophenols. Movement of pyrene to ground water at this
site may have occurred by partitioning to, and transport in
a liquid organic matrix, rather than dissolution and movement
in water.
IV. TOXICITY OF PNAs
Limited information is available on acute or chronic
toxicity of PNAs in mammalian species. From the existing data
PNAs appear to be low in acute toxicity: oral LD5Q in rats 50
mg/kg for benzo (a) pyrene to 4360 mg/kg for 1,2 methylnaphtalene
(27,28). The main toxicological concern of exposure of PNA
is carcinogencity. The majority of identified 4, 5, and 6
ring PNA are confirmed human or animal carcinogens. Anthracene,
a 3 ring PNA, is a suspect human and animal carcinogen (limited
evidence). There is no evidence that 2 ring PNAs are
carcinogens or mutagens.
Toxicity data for PNA compounds categorized by the number of
aromatic rings in general, indicates that:
1. The majority of 4, 5, and 6-ring PNAs are confirmed
human or animal carcinogens, and many are experimental
mutagens. 70% of all PNAs are in these structural groups;
2. Half of the 3-ring PNAs are suspected human or
animal carcinogens or suspected experimental mutagens.
Data on the remaining 3-ringed PNAs is insuffecient
to characterize;
3. Data on the 2-ring PNAs is insufficient to characterize;
4. Available acute toxicity data suggests that acute
toxicity is not a common characteristic of PNAs and
occurs only with very large doses (>200 mg/kg).
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V. Conclusions
General
Based on the information presented in this report the
Agency has made a number of tentative conclusions regarding PNAs.
1. PNAs are found in a variety of matrices including
soil, fly ash, and groundwater. They occur primarily
as products of combustion and have been found at
levels up to 1 ppm in soils and at somewhat lower
levels in fly ash and groundwater.
2. PNAs are not very mobile in the environment, especially
if small particles (such as in soils, fly ash, and
aguifers) are present. The two and three ring PNAs are
much more mobile than the four or higher ring PNAs.
3. The chronic toxicity of PNAs is related to the number
of rings they contain. Two and three ring PNAs are
relatively non-toxic while the four and higher ring
PNAs are extremely toxic.
Fly Ash
The guantities of solvent-extractable PNAs on fly ash
(e.g. , use of benzene, toluene, methylene chloride, etc.) have
been typically shown to be very low. Of the PNAs present,
the two and three ring compounds are most easily extracted
and are found in the highest concentrations. Naphthalene and
its derivatives commonly make up the greatest percentage
of PNAs found in extracts. It is clear that if PNAs on fly
ash cannot be readily removed by vigorous extraction with
organic solvent, .it is unlikely they would be removed in any
environmentally significant guantity by a nonorganic solvent
(e.g., water). Non-detectable PNA levels in water extracts
collected to date support this. PNAs that are removed from
fly ash in agueous leachate will preferentially adsorb to
soil containing organic matter. Soil-water (Kp) and organic
carbon-water (Koc) partition coefficients are extremely high
for the 4, 5, and 6 ring PNAs. Only the two and three ring
compounds are mobile in soil. The PNAs that are most mobile
in the environment however, are those of the least toxicological
concern. It is the 4, 5, and 6 ring compounds that adsorb
most strongly to soils and fly ash that are the proven or
suspect carcinogens or mutagens in animals or humans.
Fly ash has a composition very similar to soil in that
it is composed chiefly of silica, alumina, carbon, etc.
Most soils are chiefly composed of silica or sand (8102)
and Alumina (A^OS). These materials usually comprise 80 to
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90% of soil which is about the same percentage as in fly ash.
Since fly ash is very similar to soil the Agency has used the
data presented for soil (i.e., the soil water petition coefficients
and the data available on BaP using the SESOIL Model)
to estimate the levels of PNAs that could migrate from the
ash. Furthermore, because data presented by Harrison for fly
ash is in close agreement with partition coefficients derived
for soil and sediment we believe this is a reasonable approach.
Based on this information we estimate that 4, 5, and 6 ring
PNAs on fly ash at levels in the 10 to 20 ppm range (and possibly
higher) would not present a hazard to human health or the
environment from a groundwater exposure route.
Soils and Alumino-Silicates
As pointed out above, PNAs are strongly bound to soils,
especially when small guantities of organic carbon are present.
Because of this binding the conclusions drawn about the
mobility of PNAs from soils (and matrices like soils) will
be the same as those from fly ash. The toxicity information
is also the same.
Silicate, silica, and alumina are generally added, as
reagents, during waste stabilization processes. The processes
which use these reagents provide a solid support for the
adsorption and subsequent immobilization of PNAs in the same
manner as fly ash with similar results. The addition of these
reagents to a treatment residue would be expected to increase
the available number of PNA binding sites in that residue.
Based on this observation and in conjunction with experimental
evidence on the mobility of PNAs from particular silica
stabilized wastes the Agency believes that levels in the 10 to
20 ppm range (and possibly higher) of the higher ring PNAs
are not of concern when present in these matrices.
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References
1. ERCO, September 30, 1984, PNA Literature Search, Draft
Report, Prepared by ERCO/ENSECO for EPA, OSW Washington, DC.
2. Acheson et al. 1976
3. Ogan, K., Katz, E., Slavin, W., J. Chromatogr. Sci.f
16 (1978) 517-522.
4. Griest, W. H. , Caton, J. E., Handbook of Polycyclic Aromatic
Hydrocarbons. (Bjorseth, A. Ed) Marcel Dekker, NY.
5. Carugno, N., Rossi, S., J. of Gas Chromatogr., 5 (1967) 103-106,
6. Hoffman, D., Wynder, E. L., Anal. Chem., 32 (1960) 295-296.
7. Daisey, J. M., Leyko, M. A., Kneip, T. J., Source
Identification and Allocation of Polynucear Aromatic
Hydrocarbon Compounds in the New York City Aerosol:
Methods and Applications in Polynucear Aromatic Hydrocarbons,
(Jones, P. W., Leter, P., Eds.) Ann Arbor Science, Ann
Arbor, MI. 201-215.
8. Blumer, M., Contamination Control, 4 (1965) 13-14.
9. Suess, M. J., The Science of the Total Environment,
6 (1976) 239-250.
10. Borneff, V. J., Kunte, H., Arch. Hyg. Bacteriol., 147
(1964) 401-409.
12. Mattox, C. F., Humenick, M. J., In Situ 4 (1980) 129-151.
14. Tomkins, B. AS., Reagan, M. P., Maskarineck, Harmon, S. H.,
Griest, W. H. , Polynuclear Aromatic Hydrocarbons: Formation
Metabolisum and Measurement. (Cooke and Dennis Eds.)
Batelle Press, Columbus, OH. 1173.
15. Gulf Research and Development Co., Second Year Report
to CRC APRAC, PB-267 774, January 1977.
16. Environmental Protection Agency, Environmental Sciences
Research Laboratory, RTP., EPA-600/2-80-069, PB80-187 388,
April 1980.
17. Karickhoff, S. W. , Brown, D. S., Scott, T. A., Research,
13 (1979) 241-248.
18. Means, J. C., Wood, S. G., Hassett, J. J., Banwart, W. L.,
Environmental Science and Technology, 14 (1980) 1524-1528.
19. JRB Associates, January 1985, Draft Report to EPA OSW.
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20. Griest W. H. and Guerin, M. R., Interim Report prepared
by Oak Ridge National Lab for DOE and EPRI. RTS 77-58,
Research Project W57-1.
21. Tomkins, B. A., Reagan, R. R., Maskarinec, M. P., Harmon,
S. H., Griest, W. H., Caton, J. E. Oak Ridge National Lab,
Oak Ridge, TN. Conference 8210100-6. (1982). r
22. Roy, W. R., Griffin, R. A., Dickerson, D. R., Schuller,
R. M., Environmental Science and Technology, 18 (1984)
734-739.
23. Harrison, F. L., Bishop, D. J., Mallon, B. J., Environmental
Science and Technology, 19 (1985) 186-193.
24. Zielinski, W. L. , Janini, G. M., J. of Chromatogr. 186
(1979) 237-247.
26. Zweig, G., Sherma, J., Ed., Handbook of Chromatography,
Chemical Rubber Company, (1972).
27. Liber, H. L., Whaley, B. A., Report to ERCO, September, 1984,
28. JRB Associates, December, 1984, Report on Toxicity of
PNAs, to Barbara Bush, EPA OSW.
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