EPA-600/f 86-001
February %
Final.
THE ASSESSMENT OF THE GARCINOGENICITY
OF DICOFOL (KELTHANE™),
DDT, DDE, and ODD (TDE)
by
J. W. Holder
Office of Health and Environmental Assessment
U.S. Environmental. Protection Agency
Washington, DC 20460
EPA Contract 68-02-4038
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C.
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DISCLAIMER
This document has been reviewed in accordance with U.S. Environmental Pro-
tection Agency policy and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
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CONTENTS
Preface v
Authors, Contributors, and Reviewers vii
1. SUMMARY AND CONCLUSIONS . 1
2. INTRODUCTION 6
2.1. SCOPE OF REPORT CONCERNING DICQFOL AND RELATED COMPOUNDS
DDT, DDE, AND ODD 6
2.2. BACKGROUND INFORMATION ON DICOFOL 10
3. ANIMAL STUDIES - QUALITATIVE DISCUSSION 13
3.1. ANIMAL STUDIES ON THE CARCIN06ENICITY OF DICOFOL. 13
3.2. ANIMAL STUDIES ON THE CARCINOGENICITY OF DDT. . 14
3.2.1. Mice 14
3.2.2. Hamsters ...... . 17
3.2.3. Rats 17
3.2.4. Fish . . . 19
3.2.5. Dogs 19
3.2.6. Monkeys 20
3.3. ANIMAL STUDIES ON THE CARCINOGENICITY OF DDT METABOLITES,
DDE AND ODD 20
3.3.1. DDE. 20
3.3.2. ODD 22
4. EPIDEMIOLOGIC CONSIDERATIONS ......... . . 24
5. ADDITIONAL EVIDENCE OF CARCINOGENICITY ...... 25
5.1. DDT PROMOTION OF HEPATOCARCINOGENESIS ...... 25
5.1.1. Definitions of Tumor Initiation and Tumor Promotion
Processes in Chemical Carcinogenesis 25
5.1.2. Possible Mechanism of Tumor Promotion in the
Target Tissue - Liver . 26
5.1.3. Tumor Promotion as Additional Evidence that DDT,
DDE, and ODD Are Carcinogenic in Rats 27
5.2. GENOTOXICITY OF DDT, DDE, AND ODD 29
6. WEIGHT OF EVIDENCE THAT DDT IS A CHEMICAL CARGINOGEN . . 32
6.1. POSSIBLE CHEMICAL CARCINOGENICITY TO BIOTEST ANIMALS AS A
RESULT OF DDT EXPOSURE 32
Til
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6.2. POSSIBLE CHEMICAL CARCING6ENICITY TO HUMANS AS A RESULT
OF DDT EXPOSURE 34
6.3. OVERALL EVALUATION OF THE EVIDENCE FOR THE CARCINOGENICITY
OF DDT. 34
7. SELECTED ANIHAL STUDIES TO ESTIMATE THE PUTATIVE CANCER POTENCIES
OF DICOFOL, DDT, DDE, AND ODD - QUANTITATIVE DISCUSSION. ........ 36
7.1. JUSTIFICATION AND RISK METHODOLOGY. .............. 36
7.2. DICOFOL - MICE AND RATS 38
7,3. DDT - MULTIGENERATION STUDIES - MICE. . 38
7,3.1. Hungarian Study. 38
7.3.2. French Study .......... 42
7.3.3. Italian Study 42
7.4. DDT - SINGLE-GENERATION STUDIES - MICE. 45
7.4.1. English Study 45
7.4.2. U.S.A. Study ... ..... 45
7.4.3. Italian Limited-Exposure Study ..... 45
7.5. DDT - SINGLE-GENERATION STUDIES - RATS 49
7.5.1. U.S.A. Study . ....... 49
7.5.2. Italian Study. , . 49
7.6. DDT - SINGLE-GENERATION STUDIES - HAMSTERS 51
7.6.1. U.S.A. Study ... ....... 51
7.6.2. Italian Study. . . ........ 54
7.7. DDE AND ODD SINGLE-GENERATION STUDIES 54
7.7.1. Italian Study (Rossi et al., 1983) 54
7.7.2. U.S.A. Study ... 54
7.7.3. Italian Study (Tomatis et al., 1974) .... 55
7.8. SUMMARY OF QUANTITATIVE CANCER POTENCY ESTIMATION . 58
7.9. EXAMPLE RISK ESTIMATION 61
8. DISCUSSION 63
REFERENCES 70
IV
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PREFACE
The Carcinogen Assessment Group (CAG) within the Office of Health and
Environmental Assessment has prepared this dicofol (Kelthane™) cancer assessment
at the request of and for the use of the Hazard Evaluation Division (HED),
Office of Pesticide Programs, Office of Pesticides and Toxic Substances.
The scientific literature was reviewed on the carcinogenicity of dicofol
as well as on the dicofol contaminants (and possible metabolites) DDT, DDE,
and ODD. Those studies that exhibited adequate design, conduct, and reporting
were employed to assess the carcinogenicity of dicofol and the related compounds
DDT, DDE, and DDD. Furthermore, the upper bound cancer potency of these com-
pounds was also determined in order to place an upper limit on the unit risk
expected from dietary exposure to these compounds.
According to EPA's system for categorizing the evidence of carcinogenicity,
.dicofol has been assessed to be in the category range C to B2, based on one
positive cancer study in mice and chemical inference from other structurally
related compounds, such as DDT, DDE, DDD, and chlorobenzylate, which also
show positive carcinogenic activity. The CAG has concluded that the weight
of evidence for the carcinogenicity of dicofol is based on: no human evidence,
one positive mouse study, one negative rat study, and on structural comparisons
to other animal (and possibly human) carcinogens.
A comprehensive search of the scientific literature supporting this docu-
ment is complete through January 1985.
The cancer category C to B2 range described and supported in this document
was communicated to the Office of Pesticide Programs in a memorandum from
Robert E. McGaughy (with attachments prepared by James W. Holder and Bernard
H. Haberman), U.S. EPA, CAG, to John Melone, U.S. EPA, HED, June 20, 1985.
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In the opinion of the CAG, the carcinogenicity of dicofol is best reflected by
a range of C up to B2, which connotes that dicofol is at least possibly carcino-
genic to humans and is likely to be intermediate between a possible human
carcinogen (category C) and a probable human carcinogen (category B2). Further
studies are indicated to delineate the extent to which dicofol is, or is not,
a human carcinogen.
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
AUTHORS
The Carcinogen Assessment Group (CAG) within EPA's Office of Health and
Environmental Assessment (OHEA) is responsible for the preparation of this
document. The principal author of the qualitative toxicology sections, and
the organizer of the quantitative cancer potency estimation sections, is
James W. Holder, Ph.D.
The quantitative cancer potency estimation sections were reviewed in detail
^
Chao W. Chen, Ph.D.
Participating members of the CAG are as follows:
Roy E. Albert, M.D., Chairman
Steven Bayard, Ph.D.
David L. Bayliss, M.S.
Margaret M.L. Chu, Ph.D.
Herman J. Gibb, B.S., M.P.H.
Bernard H. Haberman, D.V.M., M.S.
Charalingayya B. Hiremath, Ph.D.
Robert E. McGaughy, Ph.D.
Jean C. Parker, Ph.D.
William E. Pepelko, Ph.D.
Dharm V. Singh, D.V.M., Ph.D.
Todd W. Thorslund, Sc.D.
CONTRIBUTORS
The CAG also acknowledges the contributions of the following individuals
in the preparation of this document:
vii
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J. Fielding Douglas, Ph.D.
President, Scientific Services, Inc.
Front Royal, VA
James Joiner, Ph.D.
Statistician, Scientific Services, Inc.
Front Royal, VA
William Jordan, J.D.
Office of General Counsel
U.S. Environmental Protection Agency
Lawrence R. Valcovic, Ph.D.
Reproductive Effects Assessment Group
Office of Health and Environmental Assessment
U.S. Environmental Protection Agency
REVIEWERS
This document, and its earlier drafts, were reviewed within the Office of
Health and Environmental Assessment. A preliminary draft was reviewed by Kyle
Barbehenn of the Hazard Evaluation Division, Office of Pesticide Programs. A
preliminary draft and the final document were reviewed by Donald Barnes, Office
of Pesticides and Toxic Substances.
ACKNOWLEDGEMENT
The authors wish to express appreciation to the CAG staff for their efforts
in reviewing this document. Our special thanks to Judy Theisen (OHEA) and Rhoda
Granat (WAPORA) for editing and proofreading assistance.
viii
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1. SUMMARY AND CONCLUSIONS
A comprehensive literature search has been conducted by the Carcinogen
Assessment Group (CAS) in order to determine the carcinogenic potential of
dicofol and the associated compounds DDT, ODE, and ODD (also known as IDE).
Dicofol was tested for carcinogenicity as the technical-grade material (re-
ported by the Office of Pesticide Programs to be 85% to 901 active ingredient)
which contains DDT, DDE, and ODD as impurities. In other studies technical-
grade DDT, DDE, and DDD were each tested for carcinogenicity in 2-year bio-
assays.
In the case of DDT (the largest data base), 25 animal carcinogenicity
studies are reviewed, including the following biotest species: mice, hamsters,
rats, fish, dogs, and monkeys. Most of the positive tests that are reviewed
(13 tests in all, including mice, rats, and fish) showed the liver to be the
primary target site for DDT, although two studies showed only lung tumors and
leukemias. The overall qualitative determination of the carcinogenic potential
of DDT reveals adequate positive evidence in mice and limited positive evidence
in rats and fish, while in contrast, adequate negative evidence is determined
in hamsters and limited negative evidence in monkeys. The canine data are
judged inadequate for determining the carcinogenic potential of DDT. The over-
all weight of evidence indicates that DDT has a more positive than negative
carcinogenic character. The combined weight of evidence for the carcinogeni-
city of DDT from all of these studies is judged to be greater than one positive
test species but not as great as two test species.
Additional qualitative evidence for the carcinogenicity of DDT in animals
has been obtained from jn vivo two-stage initiation/promotion studies and from
genotoxicity studies. In the initiation/promotion studies, DDT exhibited tumor
1
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promotion activity in conjunction with a number of known carcinogens, including
2-acetylaminofluorene (2-AAF), 2-acetamidophenanthrene (AAP), and :t rans-4-acetyl-
aminostilbene (trans-AAS). In genotoxicity studies, DOT showed negative effects
in a number of studies and positive effects in others. The positive effects
included point mutations, chromosome aberrations, increased sister chromatid
exchanges, and direct interactions with DNA (all in eukaryotic cells). However,
few of these genotoxicity studies have been replicated, and generally the pos-
itive effects were not measured in the same assays as the'negative effects.
These additional observations, in the opinion of the CAG, elevate the
weight of evidence for DDT to be equivalent with two positive test species.
Epidemiologic evidence does not factor into the weight-of-evidence considera-
tion for the carcinogenicity of DDT, since adequate epideniologic data appa-
rently do not exist at this time. Thus, according to the classification scheme
of the International Agency for Research on Cancer (IARC), DDT is judged to be-
long in Group 2B. This classification is equivalent to EPA's Group B2 accord-
ing to the Proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1984).
This classification designates that there is a sufficient amount of animal
carcinogenicity data to indicate the likelihood of cancer in man.
Dicofol was tested in both sexes of Qsborne-Mendel rats and B6C3F1 mice
in a National Cancer Institute (NCI) study reported in 1978. In this study,
only male B6C3F1 mice responded with excess tumors,(carcinomas of the liver).
Normally, this singular set of observations would place the chemical in IARC-
Group 3 (or EPA's Group C), but since dicofol bears a close structural similar-
ity to DDT, the EPA category is elevated. The likelihood that dicofol is a
human carcinogen is considered to be in the range from possibly carcinogenic to
humans to probably carcinogenic to humans. Therefore the weight of evidence
for its carcinogenicity suggests a C to 82 range, using the 1984 Proposed
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Guidelines for Carcinogen Risk Assessment. Further study is necessary to
determine the extent to which dicofol may, or may not, be carcinogenic to humans
The DDT metabolites DDE and DDD both demonstrated carcinogenic activity
in animal biotests. Both the DDE and DDD metabolites retain a substantial
structural similarity to DDT, Due to the carcinogenic activity of these meta-
bolites, both DDE and DDD are judged to belong in IARC Group 2B (equivalent to
ERA'S Group B2).
The above qualitative considerations concerning the carcinogenicity stu-
dies of dicofol, DDT, DDE, and DDD indicate a sufficient level of carcinogen-
icity that it is deemed prudent, for purposes of risk estimation, to quantita-
tively estimate the expected cancer potency of these substances in humans.
The actual extent to which these compounds are, in fact, carcinogenic to man
remains to be established, since the appropriate epidemiologic studies are
lacking. The lack of human epidemiologic data is unfortunate since DDT, DDE,
and to a lesser extent DDD, are known to be persistent in the environment and
in human tissues where DDT has been used. The persistence of dicofol has not
been adequately reported.
In estimating the cancer potencies of dicofol, DDT, DDE, and DDD, the CAG
has employed only adequately conducted and reported bioassays for carcinogeni-
city. The quantitative estimation of the upper-bound cancer potency showed
that the oncogenic potential for DDT does not increase in multigeneration feed-
ing experiments, but rather, remains approximately the same from generation to
generation. However, the cancer potency estimates do vary from experiment to
experiment, with only one DDT study being rejected as an outlier value. The
remaining studies had values which were grouped closely enough so that an aver-
age estimate of cancer potency could be made. The average q^ values for all of
the compounds reviewed are as follows:
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Cancer potency Dlcofol DDT DDE ODD
qj (frig/kg/day)'1 0.44 0.34 0.34 : ... 0.25
The qj values for the upper-bound limit of cancer potency are judged by the
CAG to be essentially the same for each of the above compounds. The closeness
of q-i values among these compounds suggests either that all the compounds
have a similar carcinogenic activity, or that they share a common metabolite
or impurity which is the effector of the carcinogenic process.
Other studies that support the careinogenicity of DDT to man (and presum-
ably the other compounds by comparison) are two-stage initiation/promotion
experiments and genotoxicity studies. DDT was found to operationally complete
the subcarcinogenic doses of known rat carcinogens, thereby producing tumors
in rats. Such activity is known to be characteristic of tumor-promoting com-
pounds. The fact that DDT has been shown to interface with a number of rat
carcinogens adequately demonstrates its tumor-promotion characteristics.
Since tumor-promotion activity is also thought to be operative in man, this
promotion activity in rats is seen as pointing to a similar activity in man.
Still other studies that supported the careinogenicity of DDT and DDE to
man (and presumably dicofol and ODD as well) are positive genotoxicity studies.
In a number of genotoxicity studies in eukaryotic cells, DDT and DDE were found
to be genotoxic. DDT did not cause genotoxicity in prokaryotic bacterial and
fungal cells. In those studies that were positive for genotoxicity, DDT exhi-
bited point mutations in V79 hamster cells, chromosome aberrations in cultured
human lymphocytes, sister chromatid exchanges in V79 and CHO cells, and direct
interactions with DNA in the presence of a cytosol activation system. These
positive genotoxicity studies suggest that DDT may act as a tumor initiator.
If DDT has both tumor-initiating and tumor-promoting characteristics, it can
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be predicted that DDT should be able to act as a complete carcinogen. This
is true for mice, in which DDT apparently does act as a complete carcinogen.
The CAG has determined, as a result of the above considerations, that
dieofol, DDT, DDE, and ODD all have carcinogenic potential to man. On the
basis of this determination, an upper-bound value for cancer potency of
q^ = 0.34 (mg/kg/day)'1 has been estimated which can be employed in the
risk management of these compounds. - This cancer potency value is in the
third quartile of the ranked potency values of compounds previously evaluated
by the CAG.
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2. INTRODUCTION
2.1. SCOPE OF REPORT CONCERNING DICOFOL AND RELATED COMPOUNDS DDT, DDE,
AND ODD
The intent of this report is to assess the carcinogenicity of dicofol
(Kel thane1"), DDT, DDE, and ODD (also known as TDE). Evidence from human, ani-
mal, tumor-promotion, and genotoxicity studies is evaluated. These evaluations
are combined into a weight-of-evidence determination of the carcinogenic poten-
tial of dicofol, DDT, DDE, and ODD. The weight of evidence indicates the like-
lihood that these substances are carcinogenic in humans, and therefore a quan-
titative cancer potency estimate is determined for each of these compounds.
The structure of dicofol, as well as the structures of the other compounds
referred to in this report, are presented in Table 1. For purposes of compari-
son, Table 1 also includes some pesticides that are structurally related to
dicofol.
The uptake, storage, metabolism, and metabolic interrelationships of DDT,
DDE, and ODD have been discussed in detail elsewhere [World Health Organization
(WHO), 1979; International Agency for Research on Cancer (IARC), 1974; U.S.
Environmental Protection Agency (U.S. EPA), 1980a], However, little is known
at this time about .the irv'vitro and in vivo metabolism of dicofol. The possi-
bility exists that technical-grade dicofol {containing 85% to 90% active ingre-
dient, plus the related compounds DDT, DDE, and DDD as contaminants) can
metabolize to DDT-related compounds in the environment and in vivo. The meta-
bolic interrelationships that could exist among dicofol and these DDT-related
compounds are summarized in Figures 1 and 2.
Because of the close structural and possible metabolic relationships of
DDT, DDE, and DDD to dicofol, the present report assesses the putative carcino-
6
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TABLE 1. STRUCTURE OF DiCOFOL AND OF p,p'-ODT AND ITS ANALOGUES OF THE FORM*
R'
R"
Mime
DOT and its major
metabolite
dicofol6
{Kelthane")
DDTb
Chemical name R
4-chloro~a-{ 4-chlorophenyl )-
(trichloromethyl Jbenzenemethanol — Cl
l,l'-(2,2,2-trichloroethylidene)-
bis[4-chl arobenzene] — Cl
l,l'-{2»2-dichloroethenylidene)- -Cl
R' R"
-OH -CC13
-H -CCIj
None sCClg
TOE(OOD)b.c,d
DDHUC
BDNtT
DDOHC
Some related insecticides
Bulan*
bi s[4-chlorobenzene]
l,l'-(2,2-dichloroetnylidene)-
bis[4-chlorobenzene]
l,l'-(2-chloroethenylidene)-
bis[4-chlorobenzene]
l,l'-(2-ch1oroethylidene)-
bis[4-ch]orobenzene]
1,1'-b1s(4-chlorophenylJetrylene
2,2'-bis(4-chlorophenyljethanol
2,2'-bis(4-chlorophenyl)-
acetic add
2-nitro-l,l-bis
(4-chlorophenyl)butane
-Cl
-Cl
-Cl
-Cl
-Cl
-H
None
""*" H
None
-H
-H
-CHC1
-C{0)OH
11
HCjHs
Prolan*
2-nitro-l,l-bis
(4-chlorophenyl Jpropane
4-chloro-a-(4-chlorophenyl}-
-Cl
-H
DHC
chiorobenzi late6
chloropropopylate6
inethoxychlor
Perthane*
DFPT
afrntthyl Jbenzenemethanol
ethyl 4-chloro-a-(4-chloropnenyl )-
a-hydroxybenzeneacetate
1-methylethyl 4-chl oro-o
(4-eMoropttenyl )-a-hydroxy-
• berizeneacetate
1, !'-( 2,2, E-t rich! oroethy 11 dene! -
bis[4-methoxy benzene]
l,l'-(2,2,-dichloroethyl1dene)-
bist4-ethylbsnzene]
l,r-(2,2,2-trich1oroetfiyl1dens5-
bis£*-f luorobenzeni}
•-C1 -OH
-Cl -OH
-OCHj--. -H •
-C2H5 -H
_p -H
-CH3
-C(0)OC H
2 5
~C(0)OCH (CH,)2
-CCIj
-CHC1?
-CCIj
»Many of the compounds also exist as o.p'-isomers and other isomers in the technical grade and in the environment.
karcinogenicity discussed, evalyated, and quantitatively estimated in this report.
^Recognized metabolite of DOT in the rat, and i possible dlcofol metabolite.
dAs an insecticide, this compound has the International Or§aniz»tion for Standardization (ISO) approved name ofTOE,
-it has been sold under the name of Rothane"; in metabolic studies the same compound his been referred to as DUU; as
a drug, it 1s called mltotane.
eCommon name approved by the ISO.
SOURCE: Adapted from World Health Organization, 1979.
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CO
c>—c—ei
DICOFOL ci
(Kclthsnt)
*_ Exefetion \
V in th* Urine '
._*•» s
Figure 1. Theoretical metabolism of dicofql» and known metabolism of DDT, DDE, and ODD,
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Fal Storage in Adipose or Organ Tissues
Exposure to:
DMA * Carcinogenic
^ Target '**" Process Q
^ X / /\
a ci
If E*posur« Ceases:
Clearance Rales,
DDT |V4» 10 20 yews
DDF I'/; ^ SO-60 yeiif5
: x' ^s
/ %
CBrcinogenic / ONA *
I Target ,'
RVcJ^CIHO/Vc/Ac, / \VS// V0
"Phenol" Type Metabolites Excretion in (he Urine
Figure 2. The ring oxidation of DDE.
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genicity of these compounds in addition to that of dicofol. The present report
considers the cancer potency of dicofol, DDT, DDE, and ODD. • The "Carcinogen
Assessment Group (CAG) has reviewed the existing animal carcinogenicity data
(mouse, rat, hamster, fish, dog, and monkey) and any available human cancer
data on dicofol, DDT, DDE, and ODD. The Reproductive Effects Assessment Group
(REAG) has reviewed the positive genotoxicity tests on DDT. As far as is
known, no adequate studies have been done on the mutagenicity of dicofol. The
present review by the CAG encompasses all available carcinogenicity studies of
dicofol, DDT, DDE, and DDT available in the published literature as of January
1985, including a reconsideration of the mouse study previously used for risk
estimation and from which a cancer potency estimate of 8.42 (mg/kg/day)"l was
made (Tarjan and Kemeny, 1969). A current weight-of-evidence evaluation is
made in this report of all adequate studies in order to determine the likeli-
hood that these chemicals are carcinogenic. The CAG has determined that these
chemicals are potentially carcinogenic to man, and therefore has selected the
most appropriate carcinogenicity studies for determining the upper-bound
estimate of the cancer potency.
Consideration is also given to the possible role of DDT in the mechanism
of carcinogenesis, as either a complete carcinogen, a tumor promoter, a tumor
initiator, or a genotoxic. compound. Such mechanistic considerations could
supply additional information as to the carcinogen:! city of dicofol, DDT, DDE,
and ODD.
2.2. BACKGROUND INFORMATION ON DICOFOL
Dicofol, also called Kelthane™, is a miticide used in the United States on
berries, pome and stone fruits, citrus fruits, nut crops, cotton, field corn,
seed crops, ornamental plants, greenhouse crops, and around domestic, commercial,
and farm dwellings. Cotton and citrus fruits constitute the largest uses of
10
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dicofol and account for about two-thirds of the two to three million pounds of
dicofol (on an active Ingredient basis) used each year in the United States.
Dicofol, a compound that is structurally related to DDT (see Table 1), is
made in Israel by the Makhteshim-Agan Chemical Company and is distributed in
the United States by Rohm and Haas. DDT and DDT-related compounds like dicofol
are in current use in many countries, where the perceived benefits-of these
uses outweigh the anticipated risks. DDT was banned from use in the United
States in 1972 by EPA Administrator William Ruckelshaus. The ban was based on
the bioaecumulation of DDT, DDE, and DDD, which had been found to produce
deleterious effects in birds, fish, and other organisms. While the ban was not
based on demonstrated effects to public health, there was concern that such
effects might exist, on the basis of known human exposures to DDT and the fact
that some studies at that time indicated that DDT produced liver and lung
tumors in mice. In addition, there was concern that DDT might have reproductive
effects in humans, since reproductive effects had been noted in lower animals,
especially birds.
DDT and DDE are both readily absorbed into the human body in direct pro-
portion to dietary exposure (WHO, 1979). An estimate of the extent of such
absorption in milligrams incorporated per kilogram of body weight (ppm) is:
log Ci = 0.7 log I + 1.3, where 1 is the average dietary intake in mg/kg/day.
The residues of these compounds are retained throughout the body, usually in
proportion to the percentage of fat in an organ and in depot lipids. The body
burden is long-lived, with clearance rates for man (in half-lives) of as long
as 10 to 20 years for DDT and 60 to 70 years for DDE. It is clear that once
humans are exposed, such residues are retained for long periods in the body,
with subsequent exposures adding to the preexisting body burden. These resi-
dues are thus of concern in the United States in spite of the 1972 ban on DDT,
11
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since the populace is still being exposed to the residues, which continue to
add to the preexistent DDT/DDE body burden. ; ,
The pervasiveness of DDT, DDE, and ODD residues in geographic areas in
which DDT formulations have been used is well known. Due to the striking
similarities in chemical structure between dlcofol and DDT, this pervasiveness
presumably holds for dicofol as well, but this is not known at this time. It
is suggested in Figure.1 that metabolic interrelationships may exist among
dicofol, DDT, and DDT metabolites. In Figure 2 a scheme is proposed in which
possible carcinogenic intermediates could occur in DDE degradation. A long
half-life in soil allows incorporation of DDT and/or DDE residues into crops,
which in turn are ingested by the human population. DDT and DDE residues are
also passed from the simpler organisms up the food chain to higher organisms,
such as wild game, which are eaten by the human population, further adding to
the body burden. Thus, residues of dicofol, DDT, DDE, and ODD in food present
an environmental problem.
A five-generation mouse carcinogenicity study conducted in Hungary (Tar-
jan and Kemeny, 1969) was previously selected for hazard evaluation by the CAG
from five different positive studies on DDT. This study was used by the CAG to
estimate the upper limit of cancer potency for DDT, if DDT is a human carcino-
gen (U.S. EPA, 1980a). At an average lifetime dietary dose of 0.45 mg/kg body
weight/day, a cancer potency (q-jj for DDT was estimated to be'8.422 (mg/kg/
day)'1, based on malignant (but not metastasizing) lung tumors in BALB/c mice.
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3. ANIMAL STUDIES - QUALITATIVE DISCUSSION
3.1. ANIMAL STUDIES ON THE CARCINOGENICITY OF DICOFOL
A 2-year bioassay was performed by the National Cancer Institute (NCI) on
technical-grade dicofol in B6C3F1 mice (NCI, 1978a). Dicofol was mixed into the
feed at 264 and 528 ppm for male mice and 122 and 243 ppm for female mice. The
animals were dosed with dicofol for 78 weeks, followed by 15 weeks of observa-
tion until terminal sacrifice. There were 50 mice of each sex per dose group.
B6C3F1 mice of both sexes exhibited no specific nonneoplastic lesions, and
no increased mortality was observed in either males or females fed dicofol.
Female mice showed a mild decrease in body weight at the high dose (243 ppm)
from 37 weeks to termination, and showed an even milder decrease at the low
dose (122 ppm) from 41 weeks to termination.
Female B6C3F1 mice, as compared with controls, did not respond to dicofol
with excess tumors of any kind. The neoplastic responses for male B6C3F1 mice
were positive and were as follows:
Control Low dose Highdose
1. Male mice at start 20 50 50
2. Male mice examined 18 48 47
histologically ,
3. Male mice with primary 5 34 38
tumors of any tissue
kind, including benign
and malignant
4. Hepatocellular
adenomas (male) 0 1 1
5. Hepatocellular
carcinomas (males) 3 22 35
6. Combined hepatocellular
tumor response (males) 3 23 36
13
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The dose-response trend of the combined liver tumors in the males is significant
at the p < 0.001 level, with the low-dose liver tumor incidence increased over
controls at p = 0.0035 and the high-dose incidence increased over controls at p
< 0.001, These statistical tests suggest a significant quantitative response
based upon a highly significant qualitative response which was characterized by
a high proportion of malignant hepatocellular tumors in male B6C3F1 mice.
Osborne-Mendel rats were tested also with technical-grade dicofol (85% to
90% active ingredient) at a rate of as high as 942 ppm ( = 122 mg/kg body
weight/day). No excess tumors were observed in treated rats as compared with
control rats.
3.2. ANIMAL STUDIES ON THE CARCINOGENICITY OF DDT
3.2.1. Mice
Nine dietary feeding studies have been conducted on DDT in mice. These
carcinogenicity bioassays were done in the USSR, Italy, England, the United
States, India, and Hungary on a total of 4,333 mice of various strains (Table
2). Only one of these studies (NCI, 1978b) indicated no excess tumors due
to DDT exposure, while six other studies indicated excess liver (and, in two
studies, lung) tumors in the mouse. In the one negative study, mice were dosed
for a relatively short period of 78 weeks.
The general pattern of the carcinogenic response to DDT in mice is described
below and qualitatively summarized in Table 2. Quantitative cancer potency
estimates from adequately conducted studies are presented in Chapter 7.
Both benign tumors (hepatocellular adenomas) and malignant tumors (hepato-
cellular carcinomas) were observed in the six positive liver tumor studies.
Benign and malignant lung tumors were observed in the two multigeneration
studies. Generally, the mouse tumors were not life-threatening in that dosed
mice lived as long as control mice and as long as expected for the various
14
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TABLE 2, SUMMARY OF DOT DIETARY CARCtNOGENIClTY STUDIES IN MICE
1.
?.
3.
4.
5.
6.
7.
8.
9.
Study
(in order of
Increasing
maximum dose)
Shahad et al., 1973
Tarjan and Keraeny, 1969
Walker et al., 1972
Thorpe and Walker, 1973
Kastvyap et al ., 1977
Innes et al., 1969
NCI, 1978b
Terracinl et al., 1973
Turusoif.et al., 1973
Mouse
strain
A-strain
8ABL/C
CF-1
CF-1
S*!ss/
Bombay
C57BL
C3HxAKR
fl
86C3F1
8ftLC/c
CF-l
Total no.
of dosed
mice
234-
683
60*
33
60
72
200
227
2,764
Maximum
length of
treatment
(weeks)
Hfeti(tiec
11fetfmec
112
110
80
85
?8d
135^
Hfettmec
Hasimufli
dosage
(nig/kg/day)
0.15
0.45
15
15
15
21
Z6.3
37.5
37.5
Evidence of Tumor
carcinogenldty3 location
* Lung
* Lung/
Leukemia
+ Liver
* Liver
* LyinphoiBiS/
Lung/Liver
* Liver
-
* Liver
+ L1*er
State of
malignancy'3
(benign/malignant)
Benign
Benign 8 malignant
Benign S malignant
Benign & malignant
Malignant
Beni gn
—
Benign (* malignant?)
Benign
(with only a
few malignant)
Comments
--
Used In 198U Water Criteria
Document to determine cancer
risk from DDT
--
—
-
--
--
Two-generation study;
malignancy not well
characterized or described
Six-generation study;
tumor yield about the
same for eacn generation
afi "+" • a statistically significant (p £0.05) Increase in the number of mice with tumors, as compared
with controls; a "-" - no excess number of mice with tumors as compared with controls (p > 0.05).
bNo tumors observed In any of the studies were metastatlc.
*-A multigeneration study in which animals treated with DOT were exposed in utero until death.
^Included 78 weeks of dietary exposure plus 15 weeks of observation, w1t"n~sacr1fice at 93 weeks.
®A two-generation study in which each generation was observed from week 5 until week 140.
-------
strains tested.
The most common response to DDT in mice occurred in the liver. Hetero-
geneous cellular responses in mouse liver were observed, indicating various
stages of stimulated growth and tumorigenicity, as well as certain necrotic
conditions, seen especially at higher DDT dose levels. The livers first showed
reversible focal hyperplasia. With continued DDT exposure, some of these foci
are known to be able to convert to nodules. The nodules resulting from DDT
varied in size and cellular organization, but were most often composed of solid
cords of closely packed cells one to two cells thick. These cells differed
little from normal hepatocytes. The larger nodules compressed the surrounding
parenchyma. More malignant states were also observed in the mouse livers and
were classified as hepatocellular carcinomas. These DDT-induced lesions were
morphologically organized in wide trabeculae that formed papillary, glandular,
and sometimes whorl patterns. Occasionally, anaplastic regions were observed,
arranged in rosettes. Necrotic or hemorrhagic areas were observed along with
cystic areas. Invasiveness was limited locally in the liver and lung, and
dissemination followed by metastasis was not observed in any of the studies.
These studies indicate either that DDT is acting in the mouse liver and
lung as a complete carcinogen (that is, as both an initiator and a promoter) or
that laboratory mice are already inherently initiated and are thus uniquely sen-
sitive to a compound such as DDT, which has well-documented promotion poten-
tial (Periano et al., 1975; Scribner et al. 1983; Hi!pert et a!., 1983, Ito
et al., 1982, 1983; and discussions and references in Pitot and Sirica, 1980).
In either case, however, DDT by itself causes liver and lung tumors In mice,
a finding which indicates that there is a potential for the same reaction in
humans.
16
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3.2.2. Hamsters
Syrian Golden hamsters were fed 0, 125, and 500 ppm technical-grade DDT
for their lifetimes (Cabral et al.» 1982a). Calculated doses were 0, 10, 20,
and 40 mg DDT/kg body weight/day. No statistical increase in any specific
tumor type was observed. It is especially relevant to note that, contrary to
the mouse response, no increase in liver or lung tumors was observed. Thus,
although the doses given to the hamsters were comparable to the doses in the
mouse studies, no tumors were produced in the hamsters, thereby indicating
that the hamster is refractory to DDT in the diet.
In another study, DDT or DDE was incorporated into the diet of hamsters
(Rossi et al.t 1983). DDE was active in producing liver tumors (neoplastic
nodules, not carcinomas); DDT did not produce tumors. This observation is
interpreted to mean that the metabolite of DDT (that is, DDE) could be the
active agent (Rossi et al», 1983). It should be noted that in mice, both DDE
(liver tumors) and DDD (lung tumors) are oncogenic (Tomatis, 1974).
It is likely that DDT is not carcinogenic in hamsters, since it only
accumulates in the hamster's body tissues,and does not readily undergo the con-
version from DDT to DDE (Gold and Brunk, 1983). In contrast, mice and humans
readily convert DDT to DDE and DDT to DDD (WHO, 1979). The hamster bioassay
data indicate that the DDT metabolites, DDE and DDD, are carcinogenic, but that
DDT is not carcinogenic in the hamster.
3.2.3. Rats
Eight studies have been reported in which DDT was fed to rats in the diet.
The carcinogenicity results of these studies are presented in Table 3. A total
of 1,095 rats of various strains at various laboratories were exposed to DDT
in these studies. Three of the studies were positive for DDT-induced tumors at
doses of _>_ 25 mg/kg body weight/day, while one study (NCI, 1978b) had negative
17
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TABLE 3. SUMMARY OF DOT DIETARY CRRCINOGEN1CITY STUDIES IN RATS
Study
(in order of
Increasing
maximum dose)
1. Treon and Cleveland, 1955
2. Klmbrough et al., 1964
3. Delthmann et al., 196?
4. RadorasM et a I., 1965
5. Rossi et al., 197?
Maximum
Total no. length of Maximum State of
Rat or dosed treatment dosage Evidence of Tumor malignancy1'
strain rats (weeks) (mg/kg/day) carcinogenicity9 location (benign/malignant) Comments
Carworth 240 104 1.2
Sherman '75 40 2
Osborne- 60 104 10 - —
Mendel
Osborne- 60 ' 104 12
Mendel
Histar 72 152 25 + Uver Benign At 0 end 25 mg/kg/day,
6. Cabral et al., 1982b MRC Portion 196 120
(Mistar-derlved)
Liver
7. NCI, 1978b
Osborne- 200
Mendel
26.5
Benl gn
hepatomasc 0/67 and 24/50;
ODT compared to phenobarbital
in same study, both produced
only nodules; TBA invariant.
No. of TBA constant with dose;
only females affected; at 0, 6.3,
125, and ?5 wg/!cy/day, tiepatenias
were 0/38, 2/30, 4/30, and 7/38,
1 .6., oiild response
8. Fitzhugh and Nelson, 1947
Osborne-
Mende!
104
40
Liver
Benign
Centr!looular necrosis observed
aA "+" = a statistically significant (p <_ 0.05) Increase in the number of rats with tumors, as compared
with controls; a "-" - no excess number of rats with tumors as compared with controls (p > 0.05).
hNone of the tumors observed were metastatic.
cHepatomas are generally defined in this document as benign liver tumors, sometimes referred tn as "hepatocellular
adenomas." "Hepatomas" is used where the authors use this tern to refer to liver tumors.
^78 weeks dosing with DDT, plus an additional 35 weeks for observation.
~ total tunsor bearing animals; denotes tumors of any type.
-------
results. The time period of dietary exposure was comparatively short for the
one negative study (78 weeks). In all three of the positive studies, only
benign liver tumors were produced, with the total of tumor-bearing animals
invariant among treated and control groups. Mortality was not increased in the
dosed groups. As seen in the qualitative presentation in Table 3, doses of
less than 25 mg/kg/day in the rat produced no excess tumor response of any kind
—a finding that suggests the existence of an experimental threshold dose
level.
3.2.4. Fish
Trout, which normally live as long as 5 to 6 years, were exposed to DDT
at 75 ppm in the diet for 20 months. Trout fed DDT exhibited hepatomas
(author's terminology) at 20 months, with an incidence rate of 11/30 (37%),
whereas the incidence in controls at 20 months was 0/400 (0%) (Halver, 1967).
A second experiment was performed with the same protocol and showed similar
results.
On the basis of the above evidence, it is concluded that dietary exposure
to DDT causes carcinogenesis in trout.
3.2.5. Dogs
Dogs were exposed to DDT in the diet at concentrations of 0 (2 dogs), 400
(2 dogs), 2,000 (4 dogs), and 3,200 ppm (14 dogs) (Lehman, 1952 and 1965). This
was equivalent to dosing rates of 0, 10, 50, and 80 mg DDT/kg body weight/day.
All of the 14 dogs at 3,200 ppm died of toxicity. At 2,000 ppm, 2 of 4 dogs
died of toxicity. The remaining 6 dogs survived to the time of sacrifice (39
to 49 months), which is approximately 30 to 40 percent of the life expectancy
of the dog.
None of the dogs dying of toxicity, and none of the dogs surviving to
planned sacrifice, had excess tumors upon autopsy (0/18). Liver damage was
19
-------
observed, but no liver tumors were evident. Thus, in the dog, DDT may not be
carcinogenic at maximum tolerated doses during 30 to 40 percent of the animals'
lifetimes. Such a conclusion, or any other conclusion for that matter, would
be questionable since so few dogs survived the toxicity of DDT.
3.2,6. Monkeys
In two studies (Adamson and Sieber, 1979 and 1983), monkeys from an NCI
colony were treated with a control diet or a control diet containing technical-
grade DDT five times/week at 20 mg/kg/body weight/day. Positive controls
were given aflatoxin B in the diet. The negative control monkeys exhibited a
baseline tumor rate of 3.2 percent. The animals treated with aflatoxin B
showed an overall tumor rate of 40 percent, with one-half of the tumor-bearing
animals developing liver tumors. This result indicated that the monkeys from
the NCI colony could, if treated with a known hepatocarcinogen, produce liver
tumors as early as 5 years after the start of dosing.
In these studies, DDT did not produce excess tumors of any kind in monkeys.
The monkey species, which included rhesus, cynomolgus, African green, and bush
babies, did not produce a carcinogenic response in 134 months, which is approx-
imately one-third of a rhesus monkey's lifetime. This negative finding in the
monkey is seemingly corroborated by another study of monkeys by Durham et al.
(1963), in which no DDT-iiiduced tumors were found in 7.5 years in rhesus mon-
keys at a DDT dose rate as high as 100 mg/kg/day. These results suggest that
DDT is not carcinogenic in monkeys; however, the studies were not conducted for
long enough periods for a firm determination of noncarcinogenicity to be made.
3.3. ANIMAL STUDIES ON THE CARCINOGENICITY OF DDT METABOLITES, DDE AND ODD
3.3.1. DDE
In a study conducted by the NCI (1978b), B6C3F1 mice were fed 148 ppm
(19.2 mg/kg/day) and 261 ppm (34 mg/kg/day) DDE for 78 weeks, with 15 additional
t
20
-------
weeks of observation before termination. DDE 1n the females caused a DDE-depen-
dent loss in weight as early as 10 weeks; the male weights were unaffected.
The mortality curve (increased deaths before termination of the experiment)
in the female mice was also affected by DDE (p < 0.001), whereas male mortality
was not affected. Hepatocellular carcinomas were observed in nice of both
sexes, with the strongest response occurring in the females. The incidences
of carcinoma in the control, low-, and high-dose animals, respectively, were
as follows: females, 0 (0%), 19/47 (40%), and 34/48 (71%); males 0/19 (01),
7/41 (17%), and 17/47 (36%).
In a parallel NCI study (1978b), Osborne-Mendel rats did not respond with
tumors when fed DDE in a 2-year bioassay. The rats did exhibit liver involve-
ment in the form of centrilobular necrosis and fatty metamorphosis.
In a study by Tomatis et al. (1974b), CF-1 mice were fed 250 ppm (32,5 mg/
kg/day) DDE for 130 weeks. The female mice treated with DDE showed increased
hepatomas (authors' terminology) (54/55 vs. 1/90 in controls) as well as early
appearance of hepatomas, thereby indicating that DDE-induced hepatomas may have
been life-threatening. Male CF-1 mice responded similarly (39/53 vs. 33/98 in
controls) and died earlier with hepatomas. The hepatomas were largest in size
and occurred with the greatest multiplicity (hepatomas/mouse) in DDE-treated
mice as compared with .control mice. Residue data from autopsies performed on
the CF-1 mice showed that DDE was retained in the liver to a degree second only
to its rate of retention in body fat and in liver tumors (at about the same
levels). DDE residues also occurred in normal livers at about the same levels
as in tumorous livers, thereby indicating that the residual presence of DDE is
not, in and of itself, a sufficient cause for carcinogenesis in mice,
DDE was also tested for carcinogenldty in the hamster (Rossi et al.,
1983). At doses of 500 ppm (40 mg/kg/day) and 1,000 ppm (80 mg/kg/day), DDE
21
-------
in the diet of hamsters caused neoplastic nodules (hepatomas) in males (4/39
and 6/39) and in females (7/30 and 8/39). These hamster liver tumors had a
relatively long latency period of more than 76 weeks, DDT did not produce
tumors In hamsters at 500 and 1,000 ppm (Cabral et al., 1982a; Rossi et al,,
1983).
These DDE studies indicate that the Osborne-Mendel rat is refractory to
DDE-induced carcinogenesis, but that the mouse (B6C3F1 and CF-1 strains) and
hamster (Syrian Golden) are susceptible. Since humans absorb and produce DDE
in the metabolism of DDT, and since DDE has a higher affinity for body fat than
DDT, and appears to be carcinogenic in the hamster, whereas DDT is not, it is
relevant to consider the human risks of DDE. An upper-limit estimate of the
cancer potency of DDE in humans is presented in Section 7.7.
3.3.2. ODD
An NCI report on a 2-year study in which Osborne-Mendel rats were fed ODD
indicated no significant excess liver tumors in either sex at doses of 850 to
3,294 ppm (NCI, 1978b). These rats did, however, respond with some thyroid
adenomas and carcinomas in the follieular cells and C-cells at these high
doses. The C-cell response was only marginal, and neither of the thyroid
responses showed a trend with ODD dose. The past wide variation in rat his-
torical controls for these tumor types (especially in older animals) confounds
the interpretation of these results.
In the same NCI study, B6C3F1 mice were dosed with ODD at 411 and 822 ppm.
No significant excess tumors were observed, except for hepatocellular carcino-
mas [controls 2/11 (18X), low-dose 12/44 (27$), and high-dose 14/50 (281)].
This liver response was also judged by the NCI to be insignificant, since con-
trols had responded with excess tumors of up to 2Q% in the past.
In another feeding study of CF-1 mice given DDD at 0 and 250 ppm, it was
22
-------
found that lung tumors, as well as liver tumors, were induced by ODD (Tomatis
et al., 1974b). Lung tumors in male mice increased from 53/98 -(54%) in controls
to 51/59 (86%) at 250 ppm; and in female CF-1 mice, lung adenomas increased
from 37/90 (41%) to 43/59 (73%). Liver tumors in males were increased from
33/98 (34*) to 31/59 (52%), whereas female CF-1 livers were unaffected. ODD
caused only a slightly accelerated increase in the mortality of mice with
hepatomas (authors' terminology), whereas DDE caused markedly early deaths of
CF-1 mice with hepitomas, and ODD + DDE (same total level, 250 ppm) caused an
intermediate acceleration in the mortality of mice with hepatomas. ODD did not
cause an increase in the total number of tumor-bearing animals, nor did it
cause an increase in the multiplicity of tumors. These data from Tomatis et
al. (1974) suggest that DDD is only a mild carcinogen in CF-1 mice.
No cancer bioassays of DDD in hamsters have been reported. Such studies
would be helpful in determining the possible carcinogenicity of DDT as compared
with DDT metabolites such as DDD.
23
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4. EPIDEMIOLOGIC CONSIDERATIONS
There are no known epidemiologic studies on dicofol.
The effects of DDT on humans have been reviewed previously (IARC, 1974;
WHO, 1979; U.S. EPA, 1980a), It was the consensus of these reviews, which
included several prospective and case-control studies, that the data were based
on studies that were too limited and/or too short for any conclusions to be
made as to carcinogenesis. No further review of the literature on DDT epidemi-
ology has been conducted since 1980.
It is, therefore, concluded, due to a lack of evidence, that epidemiology
does not factor into the present weight-of-evidence consideration for the
carcinogenicity of DDT, and, by comparison, dicofol.
24
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5. ADDITIONAL EVIDENCE OF CARCINOGENICITY
5.1. DDT PROMOTION OF HEPATOCARCIN06ENESIS
5.1.1. Definitions of Tumor Initialrion and Tumor Promotion Processes iji
Chemical Carcinogenesls
Since the possibility exists that dicofol, DDT, and/or DDT metabolites are
carcinogenic to humans, ft is germane to further examine the carcinogenic pro-
perties of these substances. The mechanistic investigations to date have been
conducted primarily on DDT, mainly because of the ubiquitous usage of DDT
worldwide and the known body burdens of DDT residues due to direct contact and
to movement up the food chain. It is assumed that dicofol, because of its
structural similarity to DDT, might behave similarly to DDT in the stages of
the carcinogenic process.
Cancer is essentially a lack of coordination and temporal control of cell-
ular maintenance and growth in a normal field of cells. When the loss of con-
trol is persistent, the result is an evolving neoplastic process, followed by
tumorigenesis. The whole process, if caused by a chemical agent, is called
chemical carcinogenesis. Chemical carcinogenesis has been divided conceptually
into two distinct sequential events; initiation and promotion.
Tumor initiation is thought to be an oncogenic process in which some of
the cells in a normal field of cells are altered by changing {often by mutation)
the cellular DNA function. The process of tumor initiation is thought to be
essentially an irreversible, additive, and nonthreshold set of events (Pitot
and Sirica, 1980).
Tumor promotion is thought to be a process in which the usage of the cell-
ular genetic information is altered by the imposition of perturbation events
that disrupt the normal negative cellular control mechanisms. Such perturba-
25
-------
tions cause uncoordinated and untimely growth events, which are usually con-
trolled in a normal field of cells by cellular contact inhibition. If such
growth events are persistent, local hypertrophy and hyperplasia result, with
the previously initiated cells demonstrating a relative growth advantage.
5.1.2. Possible Mechanism of Tumor Promotion in the TargetTissue -Liver
Promotion has been adequately demonstrated in the skin and liver, and has
been implicated in the mammary gland, bronchus, esophagus, and bladder (Pitot
and Sirica, 1980; Pitot, 1982). Some, but not all, of the early-forming neo-
plasms progress to fully grown tumors. While promotion in the liver is thought
to be reversible in the early stages, such promotion tends to change, with time
of exposure, to an essentially irreversible phase characterized by uncontrolled
propagation of the affected cells, leading to various stages of malignancy. The
degree of "promoted" malignancy can vary from benign, noninvasive, circumscribed
tumors to malignant tumors, which can be locally invasive, regionally dissemi-
nating, or metastatic throughout the body.
Unlike initiation, the process of promotion is thought by some to be a
threshold set of events; that is, there would be a level of exposure below
which tumor promotion would not occur (Pitot, 1982; Boutwell, 1964). In the
liver, the initial phase of promotion is thought to be reversible because ces-
sation of repeated exposure to the chemical agent, such as, DDT, causes reversal
of the foci both in size and in number (Schulte-Hermann et al., 1982; Ito et
al., 1982, 1983). Mechanistically, this initial tumor promotion phase for DOT
is thought to be brought about by dissolution of DDT into the cell membrane and
disruption of cell membrane-mediated events, including cell-to-cell communication
(Madhukar et al.» 1983; Williams, 1981). Continued exposure to a chemical such
as DDT can then release a sufficient number of cells from contact inhibition so
that a majority of the affected cells would be isolated from normal cells.
26
-------
The neoplasm would progress in stages to more malignant states by becoming
progressively more independent of promoter exposure (Williams, 1981). When
these later events take place, propagation of the tumor is essentially irrever-
sible, since it has escaped integrated organismic control (Tomatis and Turusov,
1975). It has been proposed that the main events of DDT promotion are solely
epigenetic in the liver, since DDT has not been found to be genotoxic, i.e., to
cause unscheduled DNA synthesis, in mouse, rat, and hamster hepatocytes (Mas-
lansky and Williams, 1981). The explanation of these negative findings in
hepatocytes, with respect to the positive genotoxic tests reported in Section
5.2, is not yet clear.
5.1.3. TumorPromotion as Additional Evidencethat DDT, DDE, and POP Are Car-
cinogenicinRats
It is apparent that DDT, DDE, ODD, and dicofol are carcinogenic in various
mice strains (see Chapter 3). This could mean that the mice, are already initi-
ated by DDT (or DDE or ODD), or it could mean that in mice DDT is a complete
carcinogen, i.e., an initiator and a promoter. In either case, DDT exhibits
promoter activity, and presumably, dicofol, DDE, and ODD can too.
Liver tumors have been induced by DDT in the rat by the classical promotion
protocol: a short dietary exposure of a known rat liver initiator, 2-acetylami-
nofluorene (2-AAF},-followed by a lifetime dietary exposure to DDT. Rats
receiving only a. short dietary exposure of 18 days of 0.02% 2-AAF in the diet
had a tumor incidence pattern similar to sham-treated control rats, whereas
rats treated for 18 days with 0.02% 2-AAF, followed by 0.05% {= 40 mg/kg/day)
of technical-grade DDT in the diet, showed a significant liver tumor response
(Peraino et al,» 1975). At this average dose of 40 mg DDT/mg body weight/day,
45 percent of the rats had tumors (adenomas or carcinomas) at 100 days, while
the average liver tumor load was 0.6 tumors per liver; at 300 days, approximate-
27
-------
ly 80 percent of the rats had tumors {controls = 30 percent), while the average
liver tumor load was 2.5 tumors per liver. • -•"•""•. .
In another DDT promoter study in rats, DDT caused the acceleration of 2-
acetamidophenanthrene (2-AAP)-initiated mammary tumors and ear duct tumors in
males, but was negative for liver tumors (Scribner and Mottet, 1981). In yet
another rat study from the same laboratory with 2-acetylaminofluorene (2-AAF)
or 2-acetamidophenanthrene (2-AAP) as initiators, DDT as a promoter caused
.foci formation in the liver with elevated gamma-glutamyltranspeptidase stain-
ing, a marker for the preneoplastic state in liver (Scribner et al., 1983).
DDT has been compared to phenobarbital, a known liver promoter, and was found
to be similar to phenobarbita.l in its promotion characteristics (Pitot, 1982;
Scribner et al., 1983; Peraino et al., 1975).
Finally, rats initiated with trans-4-acetylaminostilbene were found to
have precancerous'conditions in many tissues, including the liver, but only
mammary tissue responded with tumors when promoted with exposures to DDT in the
diet (Hilpert et al., 1983). Such tissue specificity indicates that the con-
junction of initiator and promoter is important to the organ localization of
tumors, and emphasizes the importance of identifying tumor promotion potential
in a chemical such as DDT. ,
It is concluded that. DDT acts as a complete carcinogen in the mouse, caus-
ing adenomas' and carcinomas primarily in the liver and also in the lung in some
multigeneration studies. The possibility cannot be ruled out that DDT is a
strong promoter only, and that the mouse liver tumors had already been initia-
ted by intrinsic, vertically transmitted factors. The problems in interpret-
ing the mouse liver tumor response have been reviewed by Doull et al. (1983).
It should be pointed out that (1) the tumors produced in the mice were
never metastatic; (2) the total numbers of tumor-bearing mice were usually not
28
-------
very different among control ,and DDT-treated groups—a factor which indicates
that any increase of mice with liver tumors was at the expense of tumors of
other types (i.e., DDT is causing only a shift in tumor pattern); and (3) the
liver tumors were usually discovered late in the lifetimes of the test mice,
and appeared not to be life-threatening. These observations suggest that
chemical carcinogenesis (tumor initiation, promotion, and propagation) due to
DDT in mice is limited and does not progress to more advanced malignant states,
In the eight studies (Table 3) done on rats, five were, negative for carci-
nogenicity and three were positive with hepatomas (benign liver tumors). The
same three tumor characteristics described for mice in the previous paragraph
also apply to rats. It appears that at higher doses, DDT can be a promoter of
benign hepatomas in rats. In most of the studies, however, DDT did not produce
liver tumors. On the basis of the above results, the CAG has concluded that
DDT has carcinogenic potential in the rat based on the limited positive oncogenic
results observed at or higher than 25 mg/kg/day in the rat diet.
5.2. GENOTQXICITY OF DDT, DDE, AND DDD
DDT has been tested extensively for genotoxicity, and both positive and
negative results were obtained, thereby precluding an unequivocal determination
of genotoxicity for DDT. In the mouse dominant lethal tests conducted by Ep-
stein and Schafner (1968). and Wallace and Knights (1976), no increase in mor-
tality was observed, nor was there an increase in visible or-lethal mutations
after five generations. Mutagenesis in the wasp was also found to be negative
(Grosch and Valcovic, 1969). Negative evidence for an effect of DDT on unsched-
uled DNA synthesis in human fibroblasts in culture has been shown (Ahmed et
al., 1977), as well as negative evidence in mouse, rat, and hamster hepatocytes
for unscheduled DNA synthesis (Maslansky and Williams, 1981; Probst et al.,
1981). Further, DDT was found not to be mutagenic |n vitro in rat liver epithe-
• 29
-------
lial cells (Williams, 1979). Human fibroblast cells (also in G.M. Williams'
laboratory) were not genotoxically,effected in a rat hepatocyte-mediated assay
(long et al., 1981), and did not produce chromosome aberrations in cultured
human lymphocytes (Lessa et al., 1976). In the classic Ames Salmonel1 a
typhimuriurn systems, DDT was'not mutagenic with or'without the S.-9 metabolizing
eel 1-fraction preincubation (Van Dijck and Van de Voorde, 1976; Marshall et
al., 1976; Planche et al., 1979). Lastly, no genetic effects were found in
yeast (Fahrig, 1974).
In contrast to the above negative studies, DDT induced positive mutageni-
city in V79 Chinese hamster cells in vitro (Bradley et al., 1981). Chromosome
aberrations in cultured human lymphocytes were observed in two studies (Rabello
et al., 1976; Preston et al., 1981). DDT was shown to increase the frequency
of sister chromatid exchanges in V79 and in CHO cells (Ray-Chaudhuri et al.,
1982). In one study (Kubinski et al., 1981), DDT was reported to interact
directly with DNA. In another study, however, in which the metabolizing system
was lacking (Griffin and Hill, 1978), DDT. did not interact with DNA.
DDE, a contaminant and putative metabolite of dicofol, was found to have
positive mutagenic effects in mouse lymphoma cells (L5178Y cells) and Chinese
hamster cells (V79 cells) [International Commission for Protection Against
Environmental Mutagens and Carcinogens (ICPEMC)]. ICPEMC (1984) reported
that positive genotoxic effects were also found in mammalian cytogenetic assays
of DDE and ODD.
In a recent review of the above genotoxicity studies, ICPEMC arrived'at
the conclusion that the genotoxicity studies of DDT do not present either
clearly positive or clearly negative findings (ICPEMC, 1984). Further, Dr.
Lawrence R. Valcovic of the Reproductive Effects Assessment Group (REAG) has
been requested by the CA6 to review the studies on the genotoxicity of DDT
30
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(memorandum from James W. Holder, CAG, to Peter E. Voytek, REAG, 8/8/84).
Dr.1 Valcovic Is in agreement with the conclusions of the ICPEMC report and has
stated that the positive genotoxicity data (if proven to be valid) suggest a
-------
S. WEIGHT OF EVIDENCE THAT DDT IS A CHEMICAL CARCINOGEN
6.1. POSSIBLE CHEMICAL CARCINOGENICITY TO BIOTEST ANIMALS AS A RESULT OF DDT
EXPOSURE
Results from biotests in various strains of mice (Table 2) indicate that
eight of nine studies were positive, with the types of oncogenic response being
mostly liver tumors, and sometimes lung tumors and Teukemias. Both carcinomas
and adenomas were observed in the eight positive studies in a wide dose-rate
range of 0.45 to 37.5 mg DDT/kg body weight/day of dietary exposure. On the
basis of these results, the CAG feels that adequate evidence exists for the
carcinogenicity of DDT in the mouse.
Results from biotests in various strains of rats (Table 3) indicate that
three of eight studies were positive, with positive oncogenesis occurring only
at rather high dose-rates of dietary exposure (_>. 25 mg DDT/kg body weight/day).
Osborne-Mendel rats did not respond at 26.5 mg/kg/day but did respond at 40
nig/kg/day. The oncogenic responses in all three of the positive rat studies
were in the liver, in the form of benign tumors only (often referred to as
hepatomas). The total number of tumor-bearing animals (TBA) in rats did not
change under DDT exposure, as compared with controls, and no DDT-induced early
mortalities were observed; only a change in tumor pattern was evidenced (con-
stant number of TBA) and not life-threatening effects from DDT. These results
indicate only limited evidence for carcinogenicity in the rat.
The hamster was refractory to biotest DDT doses of up to 40 mg/kg/day.
This result could be due to the slow metabolic conversion of DDT to DDE. Only
DDE (not DDT) produced benign liver tumors, but did so only at higher doses
(40 and 80 mg DDE/kg/day). The DDE response in liver is a marginally signifi-
cant response (treated animals versus controls, p = 0.05) but showed no trend
32
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with dose. These results In the hamster are judged as evidence for no carcino-
genicity for DDT and only limited evidence for DDE,
Trout were exposed to DDT concentrations of 75 ppm in the diet for one-
third of their lifetimes. A significant response of 37 percent (11/30) in the
form of benign hepatocellular adenomas was observed in treated fish, as compared
to no responses (Q%) in the 400 trout controls. The benign oncogenic response
after a limited exposure period to DDT is judged to constitute limited evidence
for carcinogenicity in the fish. Further, fish do not represent a close biolog-
ical surrogate for humans, and thus, the qualitative weight of this piscine
evidence is unclear at the present.
Dogs were treated with 10, 50, and 80 mg DDT/kg body weight/day in the
diet. All of the dogs at 80 mg/kg/day (14 dogs) died of toxicity, and one-half
of the dogs (2 of 4) at 50 mg/kg/day died of toxicity. The rest (4 dogs) were
treated for about one-third of the average dog lifetime. No tumors were observed.
The data are based on a small number of dogs that were treated for only part of
their lifetimes, and therefore are judged to constitute inadequate evidence
that DDT is not a carcinogen.
Twenty-four monkeys treated at 20 mg/kg/day for approximately one-third of
their lifetimes showed no excess tumors, while rhesus monkeys in another study
treated at dose rates of up to 100 mg/kg/day for 7.5 years did not produce
excess tumors. The results of both of these primate biotests taken together,
form limited evidence for no effect from DDT.
The metabolites of DDT, namely DDE and ODD (and possibly the metabolites
of dicofol, as shown in Figure 1), can produce oncogenesis. A ring epoxide in
the oxidation of DDE (Figure 2) could be a candidate for a carcinogen because
of its structural similarity to carcinogenic intermediates of polyaromatic
hydrocarbons. DDE is judged to be carcinogenic, having caused both benign and
33
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malignant liver tumors in two strains of mice, and benign liver tumors in
Syrian Golden hamsters. ODD has been found to produce carcinogenic responses
in mice and rats, and has not been tested in hamsters. The positive results of
these DDT metabolites are seen by the CAG as constituting limited additional
evidence of the carcinogenicity of DDT (and possibly also of dicofol).
The observed lack of advanced states of malignancy, i.e., no extensive
invasiveness and no metastasis, in any of the long-term positive bioassay
studies is viewed as indicative of the limited carcinogenic potential of dicofol,
DDT, DDE, or DDD. The absence of advanced malignant states in any of the
positive rodent studies constitutes a diminution of the likelihood that these
substances are carcinogenic in biotest animals.
In summary, the animal evidence for carcinogenicity of DDT is as follows:
Animal Evidence for (+) or against (-) the
biotest species carcinogenicity of DDT
mice adequate (+)
rats limited (+)
hamster adequate negative evidence (-}
fish limited (+)
dogs inadequate
monkeys limited negative evidence (-)
6.2. POSSIBLE CHEMICAL CARCINOGENICITY TO HUMANS AS A RESULT OF DDT EXPOSURE
The existing epidemiologic data base, because of its inadequacy, is not
seen to contribute to the weight of evidence for the carcinogenicity of either
DDT or dicofol.
6.3. OVERALL EVALUATION OF THE EVIDENCE FOR THE CARCINOGENICITY OF DDT
It has been customary within the EPA to assume that an overall carcinogenic
response constitutes sufficient evidence for the carcinogenicity of a substance
if two different biotest species respond in a sufficiently positive fashion,
34
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This has not occurred in the case of DDT. While the above results show a wide
species variability in oncogenic responses to dietary DDT residues, the results,
taken as a whole, indicate a more positive than negative character in the test
responses. The response in mice has clearly been positive, while rats have
shown limited positive responses. Trout, although showing positive responses,
provide an uncertain biotest for determining carcinogenicity to man. These
results fall short of the two positive tests in animal species necessary for
considering that sufficient evidence exists for the.-carcinogenicity of DDT.
The negative result in hamsters is not an important factor in the present
weight-of-evidence decision, since hamsters, unlike mice and humans, do not
readily convert DDT to DDE. The results 'in dogs do not represent adequate evi-
dence, and the negative results.in monkeys, although important and interesting,
were from studies whose duration was insufficient for a complete evaluation to
be made. Taking into account the auxiliary information on positive genotoxi-
city and on the promotion character of DDT with a number of known carcinogens,
the evidence for the carcinogenicity of DDT is judged to be equivalent to that
representing positive biotest results in two animal species. This would place
DDT in Group 2B of the lARC's classification system, which is equivalent to
EPA's Group B2 (U.S. EPA, 1984), indicating that there is sufficient evidence
in animals and inadequate data in humans as to the carcinogenicity of DDT.
Agents in lARC's Group 28 (EPA's Group B2) are considered probably (p > 0) car-
cinogenic in humans. The lack of human data and the difficulties in relating
test animal tumors to tumors in man preclude the exact quantitation of'the
likelihood that DDT is a human carcinogen.
35
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' 7. SELECTED ANIMAL STUDIES TO ESTIMATE THE PUTATIVE CANCER POTENCIES
OF DICOFOL, DDT, DDE, AND ODD - QUANTITATIVE DISCUSSION .
7.1. JUSTIFICATION AND RISK METHODOLOGY
The weight of evidence for the carcinogenicity of DDT is assumed to mirror
that of dicofol, DDE, and ODD, for which the data bases are less extensive.
The evidential conclusions on the basis of animal studies are that DDT is
definitely carcinogenic in one species (the mouse).,, is .of limited carcinogeni-
city in two other species (rat and fish), and is not carcinogenic in hamsters
(although DDE is carcinogenic to some extent in hamsters). Experimentally
limited studies in dogs and monkeys suggest that DDT may have no carcinogenic
effect in these species, but this has not been established. Epidemiologic
studies have been inadequate to determine whether or not DDT has any carcino-
genic effect in humans.
Additional positive mutagenicity data, especially positive trans! ocation
data and tumor initiation/promotion studies, in which DDT has been shown to
promote the initiation effects of some carcinogens, have contributed to the
positive evidence in one species and to the limited evidence in two other
species. The result has been to increase the weight of evidence for the
carcinogenicity of DDT so that it is equivalent to positive evidence in two
animal species. DDT is consequently judged to belong in lARC's Group 2B (which
is equivalent to EPA's Group B2).
The weight of evidence concerning DDT and dicofol indicates that they are
probable (p > 0) human carcinogens. Under these circumstances, it is the CAG's
policy to estimate the 95% upper confidence limit (UCL) of cancer potency from
the appropriate animal studies. This is done with recognition of the uncertain-
ties that unavoidably enter into such weight-of-evidence considerations, and
36
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with the recognition that DDT and dicofol could, in fact, be human carcino-
gens. In such an instance, where a compound is assumed to be a human car-
cinogen, risk management employs the use of the 95% UCL of cancer potency to
estimate a level of risk not likely to be exceeded under anticipated exposure
conditions.
Only those studies that were well-conducted, showed significant increases
in tumors in treated test animals, and showed a significant positive trend
were chosen for the purposes of risk estimation. Generally, such factors as
inadequate animal care, inadequate reporting, insufficient number of animals,
etc., were criteria for rejection of a study. In retrospect, however, no
rejected study would have significantly changed the CAG's overall estimation of
cancer potency.
The CAG calculates cancer potency estimations by means of the linearized
multistage model originally described by Crump et al. (1976, 1977). The
finalized methodology for risk estimation using the multistage model was
published 1n the Federal Register in 1980 (U.S. EPA, 1980b) and is recommended
for use in the Proposed Guidelines for Carcinogen Risk Assessment (U.S. EPA,
1984). These methods also have been described in some detail by Dr. E. Ander-
son and the CAG (Anderson et al., 1983). The computer program used to estimate
cancer potency in this document was written by Crump and his collaborators.
The program, GLOBAL79, generated maximum likelihood estimates of the 95% UCL
of cancer potency. The upper-bound limit of 95% was selected as a reasonable
upper limit, but is not linked to a known biological truth of the actual cancer
potency estimate. The cancer potency is estimated by the qj term of the
multistage model and has the unit (mg/kg body weight/day) . This q^ indi-
cates the 95% UCL of the slope at low exposure levels, and when multiplied by
the best average lifetime exposure estimate ("d" in units of mg/kg/day), gives
37
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an upper-bound estimate of the lifetime risk (unitless): upper bound risk
2 q* d. .
1,2. DICOFOL - MICE AND RATS
The main thrust of this document is to determine the carcinogenicity of
dicofol and its contaminants, DDT, DDE, and ODD. Technical-grade dicofol
(85%-90% active ingredient, according to the Office of Pesticide Programs)
containing these contaminants, was tested by NCI in a 2-year bioassay in mice
and rats (NCI, 1978a). Only B6C3F1 male mice responded with tumors; Osborne-
Mendel rats in a parallel experiment did not (Table 4).
Considering the possibility that dicofol is, in fact, a human carcinogen,
its quantitative cancer potency was estimated as shown in Table 4. It Is nota-
ble that this response occurred as mostly malignant {> 97%), but non-metasta-
sizing, tumors in B6C3F1 male mouse livers. The estimated cancer potency of
technical-grade dicofol is as follows:
q* = 0,44 (mg/kg/day)"1
7.3. DDT - MULTIGENERATION STUDIES - MICE
7.3.1. Hungarian Study - Institute for Nutrition, Budapest, Hungary
One of the first -studies of DDT was a multigeneration study in which
BALB/c mice were fed DDT continuously for their lifetimes (Tarjan and Kemeny,
1969). Five generations were each fed 3 ppm DDT, and each mouse was examined
for tumors after a lifetime of ingesting DDT.
Unlike studies of dicofol (Section 7.2.) and other studies of DDT in
mice (Sections 7.3. and 7.4.), this study did not produce a significant liver
response: 3 benign hepatomas/683 mice, as compared to 0/406 in control BALB/c
mice. Only lung tumors (41.3% of the observed tumors) and leukemias (30.2% of
38
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TABLE 4. INCIDENCE OF HEPATOCELLULAR CARCINOMAS
AND BENIGN LIVER TUMORS IN B6C3F1 MALE MICE FED DICOFOL3 ,.
Site/Dose group
Hepatocellular
Hepatomas carcinomas
Combined
Liver
0
264 ppmc
528
0/18 (0)
1/50 (2)
1/47 (2)
ND
3/18 (17)
22/50 (44)
35/47 (74)
ND
3/18 (17)
p<0.001d
23/50 (46)
p=0.035e
36/47 (76)
p<0.00ie
0.44
aNumber of animals with tumors/number of animals examined (percent). Only male
mice responded; female B6C3F1 mice did not respond. Male B6C3F1 responses were
mostly malignant liver tumors, but no metastases.^
^Technical-grade dlcofol (85%-90% active ingredient) was obtained from Rohm and
Haas; OPP states that this is representative of present-day technical-grade
dicofol.
cHuman equivalent dose (mg/kg/day) = 0.006067 (ppm in mouse diet); 0.006067 =
[0.13 mg/kg/ day x (Q.Q3/70)1/3 x 5 days/7 days/wk x 78 wk/90 wk average life-
time]. The factor 0.13 mg/kg/day comes from the correlation of ppm concentra-
tion in the mouse diet to an average daily rate of intake in units of mg/kg/day.
The average test mouse is assumed to weigh 0.03 kg and man, 70 kg.
^Probability that there is a trend to this data set at a statistical level of "p".
Probability that this incidence is significant compared to controls at a
statistical level of "p".
ND = not done. ,
SOURCE: NCI, 1978a.
39
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the observed tumors) are considered significant; the remaining tumors appeared
not to be dose-related or in excess of those same tumors occurring in control
mice.
Table 5 shows the tumor incidence of Tung carcinomas and leukemias gener-
ation by generation. Generation F]_ does not have enough .animals for the carci-
nogenic results to be interpreted, but lung tumors were significantly increased
by F2» and then through F5; in addition, leukemias were increased by FI, and
then through f§. The authors state that the historical rate of lung carcinomas
in BALB/c mice is < 0.1 percent, and that spontaneous leukemias are unknown in
BALB/c mice. Therefore, these increases in lung carcinomas and leukemias are
significant when compared to external as well as internal negative controls.
The q^ is likely not to be statistically stable by Fg in the case of the
lungs, due to the small number of mice generated by the F2 generation. The FS,
F4, and FS generations are not dissimilar in cancer potency for both lung car-
cinomas and leukemias. The overall tumor results for all five generations are
summarized at the bottom of Table 5.
These potency results are not dissimilar to those in Table 5 (top) f$ -
Fg, and further, lung carcinoma and leukemia potencies are also not dissimilar.
Thus, an overall geometric collective average of FS - F§ for lung and leukemia
cancer potencies =,7.27 (mg/kg/day)"l (potency variation: 4.83 to 9.98). These
results compare to the CAG's estimate of 8.42 (mg/kg/day)~l for lung tumors for
DDT presented in the previous Water Quality Document on DDT (prepared by Drs,
McGaughy and Singh,of the CAG (U.S. EPA, 1980a).
The results of this 1969 study by Tarjan and Kemeny are clearly different
in organ site (lung/leukemia versus liver) and cancer potency (about an order
of magnitude greater) from most of the other studies reviewed in Table 1.
40
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TABLE 5, INCIDENCE OF THE HOST COMMONLY OCCURRING MALIGNANT TUMORS IN EACH OF FIVE GENERATIONS
OF BAL8/C MCE F£0 DOT
Incidence by generation4
(combined wale and female) (X)
Site/Dost group
Lung (carcinomas)
Control
3 ppm DDT6
Significancec
qi
qi
Leukemia
Control
3 pprn ODTb
Significances
q*d
1
Q-
FI Fz
0/3(00.0) 0/39(00.0)
2/10(20.0) 10/35(28.5)
p=0.001
' 18.78
17.20
2/3(66.6) 1/39(2.6)
4/10(40.0} 2/35(5.7)
p.Q. 924
4.67
5.01
F3
3/51(5.9)
13/69(18.8)
p=0.007
9.09 '
9.95
0/51(00.0)
11/69(15.9)
p-0,008
9.48
8.98
F4
• 0/144(00.0)
41/264(15.5)
p<0.002
7.45
7.16
3/144(2.1)
35/264(13.2)
p<0.001
5.79
6.22
F5
2/169(1.2)
50/305(16.4)
p<0.001
7.37
7.68
4/169(2,4)
33/305(10.8)
p.Q. 002
4,50
4.83
aNumber of animals with tumors/number of animals examined (percent). The,Fj generation contained too few
effective animals for reliable statistical analysis.
^The human equivalent doses are calculated by multiplying the ppm values by 0.13 and then by the cube root of
0.030/70. 3 ppm DDT to 8AIB/C mice « 0.029 rag/kg body weight/day for hynans. The DOT was given to the mice for
lifetime via the diet every day, so no time correction is necessary.
cBtneath each dose group Incidence is the p value for the comparison of the dose group incidence with that'of
the cgntrol group. The F^ generation was not analyzed.
"The li's were calculated using the human equivalent dose. The index values assume that DOT contamination
in th| control diets was zero. ,
eThe tli's were calculated using a level of 0.20 ppm DOTr (combined DDT-related residues) in the control feed,
as reported by the authors.
SUMMARY OF THE ABOVE TUHOR INCIDENCE
(combined males plus females for all five generations)
Site/DOT dose group
(ppm)
Liver
(beni gn)
Leukemia
Lung
(carcinomas)
0
3
0
3
0
3
Resulting
Combined cancer potency q*
incidence 1
(mg/kg/day)'1
0/406
3/683
10/406
85/683
5/406
116/683
(0) , '
(0.444) . not calculated
(2.51)
(12.4%) 4.68
(1.2%) . .
(17.0%) 7.06
.SOURCE: Tadan and Kemeny, 1969.
41
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7.3.2. French Study - lARC,Lyon, France
A six-generation study in CF-1 mice has been reported in which DDT was
incorporated in the diet at 0, 2, 10, 50, and 250 ppm (Turusov et al., 1973).
Table 6 shows the benign liver tumor results (referred to as hepatomas) by
generation for each of six generations. Historical control incidences for hepa-
tomas in CF-1 mouse livers have been found to be 20 percent in males and 13 per-
cent in females. The liver response appears to be an increase In an already-
present event in untreated CF-1 mice controls. There is no statistical trend
in the qj values with the successive generations, which indicates that there
is no buildup of cancerous effects passed vertically from generation to genera-
tion. The CAG therefore views each generation as an independent trial, and has
calculated geometric averages to express the central tendency of the data.
Thus, the geometric averages of the q^ values are 0.80 (mg/kg/day} (males) and
0.42 (mg/kg/day1) (females), with variation from 0.37 to 1.10 (mg/kg/day)'1.
7.3.3. Italian Study - National Institute for the Study and Cure of Cancer,
Milan, Italy
A two-generation study in BALB/C mice was performed in which 0, 2, 20, and
250 ppm DDT was incorporated into the diet (Terracini et al., 1973). Mice were*
fed DDT continuously for a lifetime. The results (Table 7) indicated only
benign liver tumors. While these tumors were benign in appearance, they had a
malignant characteristic in that they were transplantable in syngenetic mice.
No metastases were observed. Essentially, doses at 20 ppm and below were
inactive in producing liver tumors, whereas at the next highest dose, 250 ppm,
liver tumors became abundant. At the highest dose tested, 250 ppm, there were
body weight losses and decreased survivals due to toxicity.
The total number of tumor-bearing BALB/c mice did not vary among treat-
ment groups and controls, thereby indicating only a change in tumor pattern at
42
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TABLE 6. INCIDENCE OF BENIGN LIVER TUMORS IN EACH OF SIX GENERATIONS
OF CF-1 MICE FED DDT
Sex/Dose group
Benign liver tumor Incidence by generation(%)a
Parental
F4
Males
Control
*5 t)
10 ppm
50 ppm
250 ppm
qi
Females
Control
o h
10 ppm
50 ppm
250 ppm
ql
14/60(24)
26/60(44)
32/60(53)
27/60(45)
46/60(76)
0.572
3/60( 5)
3/60( 5)
2/60( 3)
8/60(13}
37/60(61)
0.372
13/60(21)
29/60(48)
28/60(47)
35/60(58)
51/60(85)
0.873
2/60( 3)
1/60( 2)
8/60(13)
7/60(12)
43/60(71)
0.471
20/60(34)
38/60(63)
33/60(55)
41/60(69)
53/60(89)
0.935
1/60( 2)
3/60 ( 5)
8/60(13)
8/60(13)
31/60(52)
0.369
21/60(35)
30/60(50)
36/60(60)
36/60(60)
53/60(89)
0.878
2/60 ( 3)
5/60( 9)
3/60 ( 5)
9/60(15)
40/60(67}
0.434
16/60(26)
34/60(57)
24/60(40)
32/60(53}
57/60(95)
1.096
4/60 ( 7)
0/60( 0)
5/60( 8)
10/60(16)
48/60(80)
0.526
23/60(39)
25/60(42)
26/60(44)
28/60(47)
48/60(80)
0.598
5/60( 8)
0/60( 0)
6/60(10)
7/60(11)
.38/60(64)
0.370
aNumber of animals with tumors/number of animals examined (percent). The effective number of animals was given
by Turusov et al. as 50-60; 60 has been used for every group because the exact number was not given.
^The human equivalent doses are calculated by multiplying the ppm values by 0.13 and then by the cube root of
0.030/70 (=0.0753949). No adjustment for time was made because these were lifetime tests and CF-1 mice were
fed DDT continuously during that time. For example, human equivalent doses are: 2 ppm=0.0196, 10 ppm=0.0980,
50 ppig-0.4900, and 250 ppm=2.45 mg/kg body weight/day.
cThe q^'s of the upper-bound limits in units of (mg/kg body weight/day of dietary exposure) were calcula-
ted using the multistage model as described in section 7.1).
SOURCE: Turusov et al., 1973.
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TABLE 7. INCIDENCE OF BENIGN LIVER TUMORS IN BALB/C
MICE FED DDT DURING A TWO-GENERATION EXPERIMENTS
Dose
group
0 ppm
Trendc
2 ppm
20 ppm
250 ppm
q*d
High dose q^
Incidence of benign
Males
Parental + Fj
2/107(1,9)
p<0.001
3/112(2.7)
1/106(0.9)
15/106(14.2)
0.074
Q.-Q86
liver tumors
by generation^3
Females
Parental
0/62(0)
p<0.001
0/63(0)
1/61(1.6)
28/63(44.4)
0.080
0.324
f:
0/69(0)
p<0.001
0/73(0)
0/67(0)
43/58(74.1)
0.094
0.718
aNumber of animals with tumors/number of animals examined (percent). Malignant
tumors were not observed in liver.
^The numbers in the groups of males were reduced by fighting, so the two gene-
rations of males were pooled. Each high-dose group shown is statistically
different from its control group (p<0.001). Other pairwise tests were not
significant.
cBeneath the control incidence is the p value for positive trend in incidence
over the dose levels.
^The q*'s were calculated using the human equivalent dose. The "high-dose q*
is the result of using only the controls and the high-dose groups in the
calculations. The human .equivalent doses are calculated by multiplying the
ppm values by 0.13- and then by the cube root of 0.030/70 (* 0.0753949). For
example, 250 ppm =2.45 mg/kg/day for humans.
SOURCE: Terracini et al.f 1973.
44
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the highest dose tested, 250 ppm. Assuming that this- study is predictive to
humans, and for the sake of .comparison to the other multigeneration studies in
mice (Sections 7.3,1. and 7.3.2.), the qj was calculated (Table 7). The
values are similar between parental and Fj generations and between males and
females. Thus, a collective qj was calculated. The geometric average'was q^ =
0.082 (mg/kg/day)-1, with a range of variation of 0.074 - 0.094 (mg/kg/day)-1.
7.4. DDT - SINGLE-GENERATION STUDIES - MICE
7.4.1. English Study - Shell Research Ltd., Kent, England
CF-1 mice were fed 0 and 100 ppm DDT continuously (in the feed) for a
lifetime (110 weeks) (Thorpe and Walker, 1973). Survivals were good in this
experiment and no overt toxicity from DDT was observed at 100 ppm; however,
liver enlargement was observed as early as 50 weeks. The tumor results are
given in Table 8. Both benign and malignant liver tumors were increased signifi-
cantly in the liver of CF-1 mice, but the total tumor-bearing CF-1 mice did not
differ among controls and treated groups. The q* values were calculated for
males [0.52 (mg/kg/day)-1] and for females [0.81 (mg/kg/day)-1] (Table 8).
7.4.2. U.S.A. Study - NCI. Bethesda, Maryland
B6C3F1 mice were fed DDT at 0, 22, and 44 ppm (males) and 87 and 175 ppm
(females) for 78 weeks of continuous dosing followed by 15 weeks of observation
before terminal sacrifice. (NCI, 1978b). No evidence for carcinogenicity was
observed in this study.
7.4.3. Italian Limited-Exposure Study - National Institute for the Study and
the Cure of Cancer, Milan, Italy
In another studyj CF-1 mice were fed 0 or 250 ppm DDT for 15 or 30 weeks
and then observed for 65, 95, or 120 weeks before sacrifice (Tomatis and Turusov,
1975). Table 9 gives the incidence of benign liver tumors. No other tumor
types were significantly increased. Increased time of exposure to 250 ppm DDT
4V .
-------
TABLE 8. INCIDENCE OF LIVER TUMORS (BENIGN AND MALIGNANT) IN CF-1 MICE FED
DDT FOR A SINGLE GENERATION
Incidence of Incidence of
Dose benign liver malignant liver
group tumors3 tumors9
Hales • • ' .
Controls 11/45 (24%) 2/45 (4.4%)
100 ppm 23/30 (80%) 9/30 (30%)
q* ND 0,52
Females
Controls 10/44 (23%) 0/44 (0%)
100 ppm 26/30 (87%) 12/30 (40%)
q* ND 0.81
aBenign liver tumors in this study were referred to as "type a" and malignant
liver tumors as "type b."
ND - Not determined.
SOURCE: Thorpe and Walker, 1973.
46
-------
TABLE 9. INCIDENCE OF BENIGN LIVER TUMORS IN CF-1 MICE FED DDT FOR 15 OR 30 WEEKS
AND THEN SACRIFICED AT 65, 95, AND 120 WEEKSab
Males at week —
Dose
group
0 ppm
250 ppm for
15 weeks**
250 ppm for
30 weeksd
q*e values
all q*
JL
30 week
65
12/70(17)
13/60(22)
p=0.142
38/60(63)
p<0.001
0.36
1.38
95
24/83(29)
25/60(42)
p=0.040
41/60(68)
p<0.001
1.04
1.43
120
33/98(34)
25/60(42) .
p=0.080
37/60(62)
p<0.001
0.84
1.06
65
0/69(0)
3/60(5)
p=0.097
4/54(7)
p =0.034
Q.19
0.19
Females at
95
0/72(0)
11/60(14)
p<0.001
11/55(20)
p<0.001
0.49
0.79
week —
120
1/90(1)
5/50(10)
p=0.034
11/54(20)
p<0.001
0.35
0.43
aNumber of animals with tumors/number of animals examined (percent).
^Some groups were exposed for 15 weeks; other groups were exposed for 30 weeks. All groups were sacrificed
serially at 30, 65, 95, and 120 weeks.
cThe human equivalent dose for 1 ppm for 15 weeks is 0.4084 mg/kg/day and for 30 weeks is 0.8168 mg/kg/day.
The human equivalent doses are calculated by multiplying the ppm values by 0.13 and then by the cube root of
0.030/70 (= 0.0753949). Adjustments for time consist of multiplying the 15-week dose by 15/90 and the 30-week
exposure by 30/90.
"Beneath each dosed group incidence is the p value for comparison of the incidence in the dose group with that
in th| control group. ^
eThe qj's were calculated based on the human equivalent dose shown in footnote c. The term "all qi"
indicates that the dosed groups and the control group were used in the calculation. The "30 week row con-
tains the results of using only the 30-week exposure cancer data with the control cancer data.
SOURCES: Tomatis and Turusov, 1975; Tomatis et al.» 1974a.
-------
was proportional to increased total dose of DDT, which in turn appears to be
functionally linked to increased benign liver tumors in both males", and females.
The appearance of benign liver tumors was observed earlier than in other studies
using this strain. These liver tumors increased in size with longer exposure
to DDT. Thus, the latency period for benign liver tumors in CF-1 mice* was
decreased in the 250-ppm dose group. Removal of CF-1 mice from DDT exposure
did not cause tumor regression in the liver; instead, the DDT-induced benign
liver tumors continued to grow. Such a continuance of growth, even in the
absence of DDT, suggests autonomous growth, a malignant characteristic. The
response in males was manifest by 65 weeks in the 250-ppm group, which was
dosed for 30 weeks {p < 0.001,, Table 9) and in females was manifest by 65 to
95 weeks. The response was greatest in the males, but male controls also had
benign liver tumors as early as 65 weeks (12/70, 17%), whereas female controls
at 65, 95, or 120 weeks were devoid of benign liver tumors. The male liver
response is apparently a stimulation of a process occurring in controls, in
contradistinction to the female liver response, which is the de novo formation
of tumors with exposure to DDT.
The comparable cancer potency, q^, to other studies reviewed in this
document is at 95 weeks, approximately equivalent to the lifetime of a mouse,
and the usual time of termination in other studies reviewed in this document.
A dosage rate of 250 ppm for 15 weeks is one-half of"the total dose of 250 ppm
for 30 weeks, and thus, the two dose times of 15 and 30 weeks will be treated
as different graded dose groups, with the resulting upper-bound limit of cancer
potencies being as follows:
Hales: q£ = 1.04 (mg/kg/day)'1
Females: q^ = 0.49 (mg/kg/day)"^
48
-------
7.5. DDT - SINGLE-GENERATION STUDIES - RATS
7.5.1. U.S.A. Study- Eppley Institute for Research In Cancer, Omaha, Nebraska
MRC Portion rats (W1star-derived) were fed 0, 125, 250, or 500 ppm DDT for
essentially the natural lifetime of this strain of rat (Cabral et al,, 1982b),
The total number of tumor-bearing rats did not vary with dosage. The female
rats responded with a slight increase in benign liver tumors, which were nei-
ther invasive locally nor disseminated to other organs (Table 10). The male
rats did not respond. The tumor response in female rats was weak compared to
the response in mice (Section 7.4.). The upper-bound limit of cancer potency
for the female MRC Portion rat is estimated to be:
qf = 0.084 (mg/kg/day)"1
7.5.2. Italian Study - Institute of Oncology, Genoa, _I_t_ajly_.
Wistar strain rats were fed 0 or 500 ppm DOT in the diet for their life-
times (Rossi et al., 1977). The total number of tumor-bearing animals (TBA)
increased to some degree; male TBA controls, 19/35 (54.3%), increased to 19/27
(70.4%) in the 500-ppm DDT group, whereas female TBA controls, 19/32 (59.4%),
increased to 23/28 (82.1%). Such increases in tumor-bearing animals are con-
sidered moderate. '.-.'" • - .
The incidence of benign liver tumors was increased (p < 0.001) at the
rather high dose of 500 ppm DDT (Rossi et al., 1977) (Table 10). Liver tumors
that were similar in appearance and incidence were observed in rats treated
with phenobarbital, thereby suggesting that DDT, like phenobarbital, is a liver
tumor promoter. The upper-bound limits of the cancer potency for DDT are esti-
mated to be as follows:
49
-------
TABLE 10. INCIDENCE OF BENIGN LIVER TUMORS IN RATS FED DDTa
Dose
group"
0 ppni
Trend6
125 ppm
250 ppm
500 ppm
n*f
Cabral
Males
1/38(0}
NS
0.30(0)
NS
1/30(3.3)
NS
2/38(5.3)
NS
wng
et al .b
Femal es
0/38(0)
p=0.003
2/30(6.7)
NS
4/30(13.3)
p=0.033
7/38(18.4)
p=0.005
n . om
Rossi et al.c
Males . Females
0/35(0) 0/32(0)
--
9/27(33.3) 15/28(53.6)
p<0.001 p<0.001
n.ifi n_?7
1
aNumber of animals with tumor/number of animals examined (percent).
^These were Portion (Wistar derived) rats.
cThese were Wistar rats.
^The human equivalent doses are calculated by multiplying the ppm values by
0.0085499, which is 0,05 tng/kg/day (for rats) multiplied by the cube root of
0.350/70 (=0.0753949). No adjustment for time was made because rats were fed
continously for a lifetime.
eBeneath the control group incidence is the p value for a positive trend of
incidences as the~dose increases, when the p value is less than p=0.05, other-
wise NS (not significant). Beneath each dosed group incidence is the p value
for the comparison of the incidence in the dosed group with its control group
when jt is less than p=0.05, otherwise NS.
"The qj's were calculated using the human equivalent dose. For example,
500 ppm = 4.275 m§/kg/day for humans.
9Not calculated due to lack of statistical increase in hepatomas.
NS = Not significant.
ND = Not determined. .
SOURCES: Cabral et al., 1982b; Rossi et al.s 1977.
50
-------
Males: qj = 0.16 (mg/kg/day)'1
Females: q = 0,27 (mg/kg/day)'1
7.6. DDT - SINGLE-GENERATION STUDIES - HAMSTERS
7.6.1. U.S.A. Study - National Institutes of Health. Bethesda, Maryland
Syrian Golden hamsters were fed DDT at levels of 0, 125, and. 500 ppm
(Cabral et al., 1982a). The number of tumor-bearing animals in male Portion-
Wistar rats did not vary with dosage of DDT. Male hamsters did not exhibit
liver tumors, but mice and rats did exhibit liver tumors at comparable levels of
DDT (Cabral et al., 1982a) (Table 11).
Female hamsters showed a mild trend in the total tumor-bearing animals
(p < 0.05):
Total tumor-bearing
Dose . female
Control 3/40 (7.5%)
125 ppm 5/30 (16.6%)
250 ppm 8/31 (25.8%)
500 ppm 11/39 (28.2%)
Female hamsters, however, did not show a liver tumor response (Cabral et al.,
1982a) (Table 10). \ , '
Responses were marginal or nonexistent in male and female hamster adrenal
glands (Table 12). The male hamster adrenal response is not considered statis-
tically significant, nor is that of the female, which did not differ from con-
trols, even though there 1s a trend of p = 0.022. All other tumors appeared
random in occurrence in both male and female hamsters.
The Cabral et al. (1982a) study indicated a lack of DDT activity 1n
hamsters.
51
-------
TABLE 11. INCIDENCE OF BENIGN LIVER CELL TUMORS IN HAMSTERS
FED DDT OR DDE3
01
Dose
Group!3
Controls
Trendc
125 ppm
250 ppm
500 ppm
1000 ppm
q*d
1
Cabral et al
Males
0/40(0) '
NS
0/30(0)
NS
3/31(10)
NS
0/39(0)
NS
— -
NDe
. (1982a) DOT
Femal es
0/39(0)
NS
0/28(0)
NS
0/28(0)
NS
0/40(0)
NS
—
NO
Rossi et al. (1977) DDT
Males
0/10(0)
NS
—
—
—
0/17(0)
NS
ND
Females
0/31(0)
NS
—
—
—
0/26(0)
NS
ND
Rossi et al. (1983) DDE
Males
0/10(0)
NS
- —
—
7/15(46)
p=0.013
8/24(33)
p=0.040
0.093
Females
0/31(0)
p=0.011
— •
. —
4/26(15)
p=0.037
5/24(21)
p=0.012
0.046
aNumber of animals with tumors/number of animals examined (percent).
&The human equivalent doses are calculated by multiplying ppm by 0.08 and by the cube root of 0.120/70 =
0.119682. For example, 1000 ppm = 9.57 mg/kg/day for humans.
cBeneath the control group incidence is the p value for positive trend over increased dose and beneath the
dosed group incidences is the p value for increased incidence in that group when compared with the controls.
If the value is larger than p=0.05 then NS is entered. '
^The q*'s were calculated based on the human equivalent doses.
eDue to lack of statistical increase in tumors, q^ was not determined.
NS = Not significant.
ND = Not determined.
SOURCE: Cabral et al.» 1982a; Rossi et al.» 1977, 1983.
-------
TABLE 12. INCIDENCE OF ADENOMAS IN THE ADRENAL IN
SYRIAN GOLDEN HAMSTERS RECEIVING DOT3
Dose
group'
1000 ppm
Cabral et al.
Males
Females
Rossi et al.
Males
14/35(40)
NS
Females
0 ppm
Trend0
125 ppm
250 ppm
500 ppm
3/40(8)
NS
4/30(13)
NS
6/31(19)
• NS
8/39(20)
NS
0/39(0)
p=0.022
0/28(0)
NS
1/28(3)
NS
3/40(8)
NS
8/31(26) 2/42(5)
_-d ..d
__e, • . __e
— e e
_>e . __e
10/36(28)
P=0.005
0.051
aNumber of animals with tumors/number of animals examined (percent),
^The human equivalent doses are calculated as ppm x 0.0095746, which is 0.08
multiplied by the cube root of Q.12Q/70(=0.119862), For example, 1000 ppm = 9.57
mg/kg/day human equivalent dose.
C8eneath the control group incidence is the p value for positive trend as doses
increase. Beneath each dosed group incidence is the p value for a significant
increase in incidence in that dosed group compared with the control group inci-
dence. When the p value is greater than p=0,05, NS (not significant) is used.
^It is not possible to determine a valid trend with only one control and one dose
group.
eHamsters were not dosed at this level in this experiment.
^Since the dosed groups |re not significantly Increased over controls, neither
the calculated female q^ = 0,038 nor the male q^ = 0.039 is considered
relevant.
NS = Not significant,
SOURCE: Cabral et al., 1982a; Rossi et al., 1983.
53
-------
7.6.2. Italian Study - Scientific Institute for the Study and Cure of Cancer,
Genoa, Italy
In this study, Syrian Golden hamsters were dosed with 0 or 1000 ppm DDT
(Rossi et al., 1983). The tumor-bearing animals (TBA) did not vary with DDT
dosage, and there were no dose-related increases in any specific tumor type,
including liver tumors. Rossi did observe an adrenal response (Table 12),
where the response gave rise to a q^ of 0.051 (mg/kg/day)"1.
7,7, DDE AND DDD: SINGLE-GENERATION STUDIES
7.7,1, -rtalj^anStudy - Institute for the Study and Cure of Cancer, Genoa,
Italy (Rossi et al., 1983)
In the same Italian study as cited in Section 7.6.2. above, DDE was fed in
doses of 0, 500, and 1000 ppm to hamsters (Table 11). As with DDT, the TBA did
not vary with DDE dosage. However, a carcinogenic response in the liver was
observed in the form of neoplastlc nodules. The number of nodules/hamster
(multiplicity = 2 to 5) increased with dose, as did the size of the liver
nodules (diameter variation = 4 to 10 mm). These incidences (Rossi et al.,
1983) (Table 11) indicate marginal, but real, hamster liver carcinogenicity of
DDE, a DDT metabolite.
Thus, the upper-bound limits of cancer potency for DDE in hamsters are
estimated to be as follows:
Males: qj = 0.093 (mg/kg/day)~l
Females: q* = 0.046 (mg/kg/day)"1
7,7,2. U.S.A. Studjf, National Institutes of Health, Bethesda, Maryland
In an NCI study of Osborne-Mendel rats (1978b), DDE doses of up to 839 ppm
in the diet did not induce carcinomas. In the same study, DDE doses of 0, 148,
54
-------
and 261 ppm in the diet of 86C3F1 mice were given for 78 weeks, and the sur-
viving mice were observed for 15 weeks more before termination. The tumor
response in B6C3F1 mice is shown in Table 13.
There were clear increases both in total tumor-bearing animals {both
sexes) and in a specific tumor type, namely, liver hepatocarcinomas {both
sexes). Table 13 shows both a significant trend and increases in the hepato-
cellular carcinomas at 148 and 261 ppm DDE as compared to controls.
The DDE cancer potencies in mice are estimated to be as follows:
Males: qj = 0.34 {mg/kg/day)"1
Females: q^ = 0.82 {mg/kg/day)"1
7.7.3. jtalian Stydj'__-_ Nationaj Institute for the Study and the Cure of Cancer,
Hi Ian. Italy (Tomatis et a!., 1984)
This study was designed to test the carcinogenic responses of DDE or ODD
or a combination of the two fed to CF-1 mice for a lifetime {Tomatis et al.,
•f
1974b). Dosages in the feed were Q, 250 ppm DDE, 250 ppm ODD, or 125 ppm DDE +
125 ppm ODD. Exposure to DDE caused higher incidences of mice dying early with
hepatomas than did exposure to ODD, with the DDE + DDD group falling in the in-
termediate range. The numbers of tumor-bearing animals {TBA) of both sexes did
not vary significantly from controls at terminal sacrifice. However, benign
liver tumors were increased in a dose-related manner in all three groups, DDE,
DDD, and DDE + DDD (Table 14). DDE seems to be somewhat more potent than DDD
in causing benign tumors. The resulting upper-bound limits of cancer potency
are estimated in Table 14.
55
-------
TABLE 13. INCIDENCE OF HEPATOCELLULAR CARCINOMAS IN
B6C3F1 MICE FED DDES
Dose
group'
Tumor-bearing animals
with malignant tumors
Cancer potency
Number of animals with
hepatocellular carcinomas
Males
0 ppm
148 pprn
261 ppm
0
13/41
22/47
(0)
(31.7)
(46.8)
0/19 (0)
p<0.00ic
7/41 (17)
NS
17/47 (36)
p<0.001
« 0.34
Females
0 ppm
148 ppm
261 ppm
Cancer potency"
.2/19 (10.5)
24/47 (51.1)
35/48 (72.9)
0/19 (0)
p<0.001
19/47 (40)
p<0.001
34/48 (71)
p<0.001
q* = 0.82
aNumber of animals with tumors/number of animals examined (percent),
^The human equivalent doses are calculated by multiplying the ppm by 0.006067,
which is 0.13 x (cube root of 0.030/70) x 5/7 x 78/90. The 5/7 value repre-
sents 5 days a week of dosing, and 78/90 is intended to adjust for 78 weeks
of exposure rather than a lifetime. For example, 148 ppm = 0.8979 mg/kg/day
and 261 ppm = 1.584 mg/kg/day for humans.
C8eneath the control incidence is the p value for trend, and beneath each dosed
group incidence is the p value for the comparison of that incidence with the
control incidence.
^The q* values were calculated using both of the dosed groups and the control
group from each compound.
SOURCE: NCI, 1978b.
56
-------
TABLE 14. INCIDENCE OF BENIGN LIVER TUMORS IN MICE RECEIVING DDE
(WITH OR WITHOUT DDD)a .. -.--.
• Benign liwr tumors
Dose
groupb . Males Females
0 ppm 33/98(34) 1/90(1)
Trendc
250 ppm DDE 39/53(74) 54/55(98)
p<0.001 p<0.001
250 ppm ODD 31/59(52) 1/59(2)
p=0.009 NS
125 ppm DDE+ 42/56(75) 42/55(76)
125 ppm ODD p<0.001 p<0.001
g*d
1
DDE~alone 0.553 2.544
ODD alone 0.248 —e
DDE + ODD 0.576 0.765
aNumber of animals with tumors/number of animals examined (percent).
^The human equivalent doses are calculated by multiplying the ppm values by
0.13 and then by the cube root of 0.030/70 (= 0.0753949). No time correction
was necessary.
cBeneath each dose group Incidence 1s the p value for a positive increase in
incidence in the dosed group when compared with its control group incidence.
^If th| p value is greater than p=0.05, NS is entered.
"The Q|'S were calculated based on the human equivalent doses, e.g., 250 ppm
= 245 mg/kg/day. , .
eNot calculated.
NS = Not significant.
SOURCE: Tomatis et a!., 1974b.
57
-------
7.8. SUMMARY OF QUANTITATIVE CANCER POTENCY ESTIMATION
Table 15 summarizes the studies modeled for low-dose risk extrapolation.
Variability in qj estimation can be seen in the following factors:
(1) differences from study to study in the same species and strains,
(2) differences among species,
(3) degree of malignancy, and .
(4) differences in sex, with no discernible trend toward either sex
Notwithstanding the variability in q| estimation, the DDT data fall into
a range of qj values of 0.082 to 7.27 (mg/kg/day) , an 88-fold difference.
It is judged to be likely that the Tarjan and Kemeny (1969) study provides an
outlier value of the q^. The Dixon statistical criterion for rejecting
outlier values was applied, and the Tarjan and Kemeny study value was rejected
from the remaining body of DDT carcinogenic potency data in Table 15 at the
0.01 level of probability (Natrella, 1966). This judgment is also based on the
fact that the Tarjan and Kemeny bioassay is an old study, from an unaudited
laboratory, using feed that was contaminated with DDT. It accounts for tumors
in the lung and leukemias with no excess liver tumors, which is different from
the organ site (liver) of the other six DDT studies selected for q^ estima-
tion in Table 15. V .
Rejecting the Tarjan and Kemeny DDT study readjusts the range for q*
values to 0.082 to 1.04, a 13-fold difference, which is close to the order-of-
magnitude difference that might be expected for inter-study variability. With-
in the 0.082 to 1.04 (mg/kg/day)"1 range, no further refinement or rejection
can be logically made, and thus a geometric average of these values (Table 15)
is viewed as the best rational estimate of the upper-bound limit of the unit
58
-------
TABLE 15. SUMMARY OF QUANTITATIVE CRNCER POTENCY ESTIMATION FOR SELECTED
- POSHIVE BIPASSAYS FUR CARCINDUENICITY OF OICQFOL, UIM . ODE, AND ODD
Chemical
Oicofol
DOT
DOT
DOT
DDT
DDT
ODT
DDT
ODE
ODE
DDE
0»e
Study
name
(section of
this document)
NCI (7.2)
Tarjan (7.3.1)
Turusov (7.3.2)
Terracini (7.3.3)
Thorpe (7.4.1)
Tomatis (7.4.3)
Gabral (7.5.1)
Rossi (7.5.?)
Rossi (7.7.1)
NCI (7.7.2)
Totiiatls (7.7.3)
Tomatis (7.7.3)
Positive
surrogate
test
animal
B6C3F1 mice
BALB/C mice
CF-1 mice
BALB/C mice
CF-1 mice
CF-1 mice
HRC portion rati
Hi star rats
Syrian Golden
hamsters
B6C3F1 mice
CF-1 mice
CF-l mice
Sex
M
H+F
H/F
H+F
M/F
H/F
F
M/F
H/F
H/F
M/F
M
Tumor site
Liver
Lung/leukemia
Liver
Liver
Liver
Liver
Liver
Liver
Liver
L1wer
Liver
Liver
Carcinogenic response
State of malignancy Metastasis
Benign X malignant
Malignant
Ben1gnc
Benign (S malignant?)'1
Benign & malignant
Benign (* mal1gnant?)d
Benign only
Benign only
Benign
Malignant
Benign
Benign
None
None
None
None
None
None
None
None
None
None
None
None
Multistage cancer potency
q* (mij/kg/day)"l q* range
Males Females (mg/kg/day )-l
0.44
7.27b
0.8Ub
O.OBZb
0.52
1.04
0.16
0..093
0.34
B.S5 "
' 0.25 ''
— a 0 - 0.44
(sexes combinert) 4.83 - 9.98
Q.Wb 0.37 - l.O'jfi
(sexes combined) 0.074 - 0.09*
0.81
0.49
0.084
0.27
0.046 . — .
O.B2
2.54 "
— *
a3id not respond with tumors, so no cancer potency was calculated.
A geometric mean was taken of the Individual generation q, values in the multigeneration cancer bioassay.
CA few malignant tumors were observed, but most of the responses were In the form of benign tumors.
^It »as not certain, due to reporting and/or pathological uncertainty in the degree of malignancy, whether there
*ere malignant cells present, but possible malignant, neoplasms were Indicated.
Is'also known as TOE.
-------
risk. Hence,
q^ geometric average) =
(0.80 x 0.42 x 0.082 x 0.52 x 0.81 x 1.04 x 0.49 x 0.084 x 0.16 x 0.27)1/10
qj ~ 0.34 (mg DDT/kg of human body weight/day of dietary exposure)^
This qj is different from the previous q^ estimation of 8.42 (mg/kg/day)"1
using the Tarjan and Kemeny (1969) study. The above geometric average q-i for
the mouse and rat carcinogenic response of 0.34 is 24-fold less than the previous
estimate.
Interestingly, the geometric average of the DDE q^ data is the same as
for DDT.
q^ (geometric average) =
(0.093 x 0.046 x 0.34 x 0.82 x 0.55 x 2.54)1/6
qj = 0.34 (mg DDE/kg of human body weight/day of dietary exposure)"1
The singular value for ODD in Table 15 is q-i = 0.25 (mg/kg/day)
-1
The
CAG does not view this difference (0.25 versus 0.34) as significant given the
errors inherent in cancer potency estimation.
Lastly, the cancer potency of dicofol is compared to the potencies of DDT,
DDE, and ODD as follows: •-
Estimated q*:
Range of values:
Number of studies
used to estimate
the average q* value;
Dicofol
0.44
no range
DDT
DDE
0.34 0.34
0.084-1.04 0.046-2.54
ODD
0.25
no range
60
-------
The differences between 0.44 (dicofol) and any of the other values are con-
sidered not significant. Furthermore, more statistical weight can be placed
on DDT since more studies were done on DDT as compared to dicofol. The overall
weighted average of the cancer potencies, of. the four compounds is calculated to
be 0,34. The rather close potency values of the four compounds suggest that
all of these compounds, if carcinogenic to man, either have essentially the
same cancer potency, or that they have a metabolite or an impurity common to'
all, which induces the liver carcinogenesis. It is judged, then, that the
upper confidence limit of the cancer potencies for dicofol, DDT, DDE, and ODD
can all be represented by the single value of 0.34 (mg/kg/day)~l.
7.9. EXAMPLE RISK ESTIMATION
The recommended upper confidence limit of the cancer potency, 0.34 (mg/kg/
day)"l, can be used to estimate the upper confidence limit of risk expected for
an anticipated average dietary exposure to humans. This assumes that DDT or
dicofol causes human cancer, although such is not known, in fact, to be true at
the present time. For example, if it is assumed that the average exposure, via
the diet, is a combination of DDT, DDT metabolites, or dicofol adding up to
0,2 pg/day, then the equivalent exposure in mg/kg/day, for a 70-kg person,
converts to 2.86 x 10~6 mg/kg/day. This exposure correlates to an upper confi-
dence limit of risk of 0..971 x 10~6 [= 0.34 (mg/kg/day)-1 x 2.86 x 10~6 mg/kg/
day], or approximately one in a million chances of getting cancer.
Realistic estimates of exposure to DDT or dicofol in the human diet can be
used to estimate upper confidence limits of expected cancer risks. Exposures
have been taken from a recent DDT residue review {Spinder, 1983) in which aver-
age exposures at the maximum DDT usage in 1965 have been estimated in the past
to be as high as 5.7 x 10"* mg/kg/day for a 70-kg individual, whereas a more
recent estimate in 1978 is 0.11 x 1Q-4 mg/kg/day. The later exposure follows
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after the 1972 cancellation of DDT in the United States. These average exposure
estimates correspond to upper-limit lifetime risks of 1.9 x 10"^ for 1965 and
3.9 x 10~6 for 1978. Presumably, risks from DDT in the diet would be even less
today than the 1978 estimate of risk, since DDT residues have undoubtedly dis-
sipated since 1978,
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8. DISCUSSION
The major concern of this report is the estimation of the carcinogeni-
city of dicofol. In 1978 a 2-year bioassay by the NCI on dicofol-was found to
be negative for carcinogerricity in both sexes of Osborne-Mendel rats, and also
negative in female B6C3F1 mice. The response in male B6C3F1 mice, however, was
positive, consisting of hepatocellular carcinomas. Dicofol is therefore judged
to be a possible (p > 0) human carcinogen. Normally, .on this limited basis,
dicofol would be judged as belonging in EPA's Group C, but because of the large
data base on DDT (EPA Group B2), the classification of dicofol is raised from
Group C to the range of C to B2 due to the close similarities of the chemical
structure of difocol to that of DDT and similarity in cancer potency estimates.
To encompass the eventuality that difofol is, in fact, a human carcinogen, the
CAG estimates the cancer potency of dicofol, on the basis of the hepatocellular
carcinoma response in ma1e,B6C3Fl mice, to be qi = 0.44 (nig/kg/day)" .
Much more information has been obtained as to the carcinogenicity of DDT
and DDE. In eight of nine studies using dietary DDT, mice,showed benign and
malignant liver tumors. In two multigeneration biotests, lung carcinomas and
leukemias were observed (but not liver tumors). In two other muHi generation
studies in mice, liver tumors observed (mostly benign liver tumors, sometimes
referred to as hepatomas in the literature) did not'increase with the successive
generations. This rather flat response with passing generations tends to allay
concerns about the cancerous effects of DDT being vertically transmitted.
Clearly, however, tests in mice have been positive for DDT carcinogenicity.
Rats, in some contrast to mice, showed a limited carcinogenic response to
DDT, with positive results only above a rather highfdose of 25 mg/kg/day, only
with benign liver tumors, and with the total number of rats with tumors invari-
63
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ant among dosed groups and controls. Hamsters fed DDT did not respond with
excess tumors but did show a weak response to DDE. Fish developed benign liver
tumors with limited exposure. Dogs and monkeys did not respond with tumors,
although these studies were not conducted for long enough periods, or with
enough animals, to firmly establish negative carcinogenicity. All of these
biotest results, taken together, were not considered to be sufficient evidence
of carcinogenicity according to the lARC's or EPA's proposed classification
scheme. The results for carcinogenicity represented more than one positive
test species (mice), but not as much as two positive test species.
It seems clear that the rat is more refractory to DDT in the diet than
the mouse. This conclusion is based on the following factors: (1) rats formed
only benign tumors, (2) excess tumors were observed only in the liver and not
in the lung, (3) excess tumors were observed only above a certain dose (>_ 25
nig/kg/day), and (4) only the tumor pattern was changed in those experiments in
which increased liver tumors were observed, since the number of tumor-bearing
animals was the same for control and treated groups. On the other hand, (1)
mice formed benign and malignant tumors, (2) tumors were observed in more than
one organ (liver and lung tumors, and sometimes leukemia), (3) tumors were
observed at all doses from 0.15 to 37,5 mg/kg/day (although the lower doses in
the Shabad et al. (197.3) and the Tarjan and Kemeny (1969) studies were multi-
generation exposures), and (4) increased numbers of tumor-bearing animals and
tumor loads (multiplicity), were observed, as well as increased organ-specific
tumors (i.e., liver and lung). These differences indicate species variability
in response to DDT administered in the diet.
It should be noted that the propensity of B6C3F1 mice to respond to chlo-
rohydrocarbon compounds (such as DDT) with liver tumors, which are usually
benign adenomas, has been reviewed and cited as a potential problem in inter-
64
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preting the oncogenic risk of these compounds to humans (Doull et al.» 1983,
p. 29). Since the metabolism in the mouse is similar to the metabolism in hu-
mans (WHO, 1979), dicofol should be considered a potential cancer problem. To
date, however, there have been no epidemiologic studies on dicofol in humans.
Furthermore, carcinomas and not adenomas were identified in male mouse livers,
thereby making consideration of the cancer potential of dicofol more compelling
and necessary.
The negative DOT data in the hamster indicate that, although present in
hamster tissues, DDT is not carcinogenic even at high doses. On the other
hand, DDE was active in the hamster, but only mildly so; no change was observed
in total tumor-bearing animals among controls and dosed groups, and only neo-
plastic nodules (not malignant tumors) were produced. The failure of such high
doses of DDT to cause tumors, while DDE does cause some tumors at these doses,
suggests that perhaps DDT is a procarcinogen and that DDE is a proximate carci-
nogen in the hamster. An explanation of the inactivity of DDT in the hamster
has been given by Gold and Brunk (1983). They found that DDT-is stored in
animals' bodies, but is poorly converted to DDE. It is not likely that this is
the case in humans, since both DDT and DDE are found to occur in human body fat
throughout the world wherever DDT has been used; moreover, it has been found
that man, unlike the hamster, can convert DDT to DDE (WHO, 1979). However, the
CAG concludes that these results could be unique to the hamster, since similar
responses have not been demonstrated in other species.
The degree of malignancy produced by DDT was somewhat variable 1n blotests
that were positive for carcinogenicity. Rats produced only neoplastic liver
nodules and benign liver tumors best designated as hepatocellular adenomas.
Mice produced nodules and carcinomas, but in no case was there DDT-induced
dissemination of cells leading to metastasis. In a study by Tomatis et al.
65
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(1974a), limited dosing followed by sequential sacrifices showed that {1} the
mouse nepatomas grew in size and number with continued time of DDT..dosing, (2)
the hepatomas maintained growth even after dietary DDT was removed, and (3)
mice with hepatomas died somewhat earlier. The latter observation, however,
was generally not substantiated by most of the other studies reviewed in this
document. In one study, the benign liver tumors continued to grow after being
transplanted into syngenetic mice. All of the above observations suggest a
malignant character of the DDT-induced liver tumors, but not enough to defi-
nitely cause the death of tumor-bearing animals, or to cause the spreading of
the cancer to other organ sites.
Additional support for the carcinogenicity of DDT was gained from positive
genotoxicity results. The types of tests that were positive, i.e., increased
point mutations, chromosome aberrations, increased frequency of sister chroma-
tid exchange, and direct interaction with DNA, suggest that these positive
results could portend genotoxic effects in man. It has been theoretically
suggested that rearrangement of oncogene segments in DNA from transcriptionally
inactive to active regions can lead to tumor formation and progression (Klein
and Klein, 1984).
Furthermore, recent studies on the classic tumor promoters TPA {12-0-tetra
decanoyl-phorbol-13-acetate) and teleocidin in CH3 10Ti/2 fibroblast cells
indicate that oncogene-induced transformation is enhanced irreversibly at the
time of transfection by these tumor promoters (Hsiao, 1984). The CA6 views
these mechanisms as possible for DDT, although DDT has been historically
thought by some to act (when positive for carcinogenicity) as a tumor promoter
only by acting via epigenetic mechanisms. The positive genotoxicity suggests
the potential for oncogene activation by DDT, and thus would indicate a tumor-
initiation capacity for DDT, The initiation capacity, plus the well-recognized
66
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promotion capacity (discussed in Section 5.1.}» constitute complete carcinoge-
nic activity for DDT. Complete carcinogenic activity is, in fact, observed in
the mouse even at low dietary doses of DDT, which could indicate that the mouse
studies reflect the true carcinogenic potential of DDT, Such a conclusion
would be in contradistinction to the hypothesis that chlorohydrocarbons may
be unusually sensitive in the mouse (Doull et al.» 1983).
Additional support for the carcinogenicity of DDT is given by the ability
of DDT to promote the tumor-initiation activity of diethylnitrosamine (liver),
trans-4-acetylaminostilbene (mammary gland), 2-acetylaminofluorene (liver), and
2-acetamidophenanthrene (liver). Such a capacity to interface with different
known initiators enhances the idea that DDT has intrinsic promotion capacity.
DDT has also been compared to phenobarbital and was found to be similar to this
well-recognized liver tumor promoter; such a similarity again adds to the idea
that DDT has tumor promotion characteristics. Both DDT and phenobarbital are
thought to incorporate into liver cell plasma membranes, thereby interrupting
cellular communication, disassociating cell-field integrity, and evolving a
progressively unregulatable neoplasm. Tetradecanoylphorbol acetate, a well-
known tumor promoter in mouse skin, is thought to generate free radicals at
the plasma membrane, thereafter leading to tumor-promotion sequelae similar to
those of DDT and phenobarbital.
The genotoxicity and tumor-promotion results offer enough additional evi-
dence for the carcinogenicity of DDT to raise the estimation for carcinogenicity
to the equivalent of two positive animal species. Since inadequate human data
exist for DDT, the IARC classification for DDT is Group 2B (EPA's Group B2).
The CAG has reviewed the carcinogenicity of two other compounds that bear
structural similarity to dicofol, DDT, DDE, and ODD. The compounds are chloro-
benzilate (CAG, 1978) and Perthane" (CAG, 1977). Both compounds (structures
67
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given in Table 1) induced liver tumors similar to those induced by dicofol,
DDT, DDE, and ODD, and dicofol, but at higher feed concentrations,;
Some light is shed on the potential human cancer potency of dicofol, DDT,
DDE, and ODD when the q-i values for each of these chemicals are summarized
by taking the geometric mean of each of the studies within each chemical group.
Surprisingly, the qj values are quite close in magnitude:
Dicofol DDT DDE ODD
qj (mg/kg/day)"1 = 0.44 0.34 , 0.34 0.24
The comparability of these results in terms of cancer potency is remarkable,
given the diverse bioassay conditions under which the positive data were ob-
tained and the assumptions of the mathematical unit risk estimation process.
The CAG views these similarities in q^ values as having the following possi-
ble meanings:
1. The compounds are similar in intrinsic carcinogenic activity (at least
in Rodentia); or
2, The compounds share a common metabolite or a common impurity which is
the cause of the carcinogenic process.*
At the present time it is not possible to distinguish between these alternatives,
The CAG recommends that technical grades of dicofol, DDT, DDE, and ODD all
be considered potential human carcinogens, and that an aggregate estimate of
the upper confidence limit on the cancer potency of 0.34 (mg/kg/day)~1 be used
in the risk management of these compounds. The potency index (qj x molecular
weight) for DDT is 1.20 x 10+2 (mmol/kg/day)-l, which places DDT, the other DDT
*Figures 1 and 2 present a theoretical scheme for carcinogenic activity that
shows the interrelation of these compounds (Figure 1), and a putative reac-
tive intermediate in DDE ring oxidation (Figure 2), which could be the com-
pound for carcinogenesis.
68
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analogues discussed in this document, and technical-grade dicofol in the third
quartile of potency for compounds reviewed by the CA6.
It should be understood that any incremental risks incurred from dicofol
use should be compared, during the risk-management phase, to risks extant in
the United States from the presence of DDT, DDE, and ODD in the soil and the
biotic communities related to those use areas. DDT, DDE, and ODD have been
found throughout the world in the food chain up to and including humans (WHO,
1979). The persistence of DDT residues in soil is likelyto be quite long,
with a half-life estimated to be approximately 12 years. Humans in the United
States are exposed to these substances, even 12 years after the ban on DDT,
from conceptus until death. DDT and structurally related compounds have been
found in fetuses, neonates (mother's milk contains DDT), and adults. This
persistence is mainly due to the slow breakdown of these compounds in the en-
vironment, their very high lipid solubility in body fat, and the very slow in
vivo breakdown of DDT and DDE. The half-life of DDE in human body fat may be
seven decades, while that of DDT may be two decades (WHO, 1979). The perva-
siveness of DDT that was placed in the environment years ago, therefore, could
affect any considerations of the present use of dicofol.
69
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TECHNICAL REPORT DATA
(Please tead Instructions on the revene before completing)
1. REPORT NO.
EPA/600/6-86/Q01
2.
3, RECIPIENT'S ACCESSIONS
11 0
4. TITLE AND SUBTITLE
The Assessment of the Carcinoaenicitv of Dicofol
(KELTHANE™), DDT, DDE, and ODD (IDE)
E, REPORT DATE
February 1986
6. PERFORMING ORGANIZATION CODE
7, AUTHOmS)
James W. Holder, Ph. D.
8. PERFORMING ORGANIZATION REPORT NO
B, PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Protection Agency
Carcinogen Assessment Group (RD-689)
401 M Street S.W.
Washington, DC 20460
10. PROGRAM ELEMENT NO,
tl. CONTRACT /GRANT NO.
68-02-4038
12. SPONSORING AGENCY NAME AND ADDRESS
OFFICE OF HEALTH AND ENVIRONMENTAL ASSESSMENT
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460 _
13, TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/21
16. SUPPLEMENTARY NOTES
Document prepared with assistance and review of the Carcinogen Assessment
Group .
. ABSTRACT
carc-j n0gen-jc activity of the pesticides dicofol and associated pesticide
compounds DDT, DDE, and ODD are reviewed. All of these compounds exhibit carcinogenic
activity in surrogate test animals. The largest literature base exists on DDT which
indicates a positive carcinogenic activity in 13 separate biotests for cancer activity,
The primary target organ was the liver, but in some tests lung tumors and leukemias
were significantly increased. DDT is judged on the bases of these biotests, positive
mutagenicity in vivo , two-stage chemical carcinogenesis tests, and the lack of rele-
vant epidemioTogTcal tests to be probably carcinogenic to man. The EPA cancer
classification is determined to be B2 based on a sufficient cancer response. Dicofol
has only one test which is positive in the liver for carcinogenicity in B6C3F1 mice.
DDE and ODD were also tested positive for carcinogenicity. Dicofol has a striking
structural analogy to DDT, DDE, and ODD (all of which are categorized as B2). Dicofol
is categorized in the B2 to C range and is considered to be at least possibly carcino-
genic to man. Dicofol, DDT, DDE, ODD animal test data, when analyzed by the
linearized multistage model for low-dose extrapolation, show similar cancer potencies:
Qj = 0.44, 0.34, 0.34, 0.25, respectively, (mg/kg/day)"*. Such similiarity in cancer
potency values suggests that either a common carcinogenic metabolite is generated
from these compounds, or each compound has intrinsic carcinogenic activity and need
not be metabolized to any other compound in order to cause cancer.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
C. CDSATI Field/Gtoup
Dicofol, DDT, DDE, ODD, TOE
Chemical Carcinogenesis
Tumor Promotion
Persistant Pesticides
Liver Tumors
a. DISTRIBUTION STATIMENT
RELEASE TO PUBLIC
EPA Form 2270-1 (i-7J)
IB. SECURITY CLASS (This Report}
UNCLASSIFIED
21. NO, OF PAGES
34
20. SECURITY CLASS (This pagt)
UNCLASSIFIED
22. PRICE
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