EPA-600/8-83-025F
June 198b
Fi nal
UPDATED MUTAGENICITY AND CARCINOGENICITY ASSESSMENT OF
CADMIUM
Addendum to the Health Assessment Document for Cadmium
(May 1981) EPA-600/8-81-023
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
Protection Agency policy and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or recommendation for
use.
The Health Assessment Document for Cadmium (May 1981;
EPA 600/8-81-023) is available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
Order No.: P3-82-115163
Cost: $28.00 (subject to chanye)
11
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CONTENTS
Abstract vi
Preface vii
Authors, Contributors, and Reviewers viii
SUMMARY AND CONCLUSIONS 1
Summary 1
Qualitative Assessment 1
Quantitative Assessment 8
Conclusions 10
MUTAGENICITY 12
Gene Mutations in Prokaryotes 12
Salmonella Assay 12
Escherichia coli MP2 Assay 17
Bacillus subtilis Rec-Assay . . . . . 17
Gene Mutations in Yeast 18
Gene Mutations in Mammalian Cell Cultures . . . 20
Mouse Lymphoma Assay . . . . . . . . 20
Chinese Hamster Cell Assay 20
Studies in Drosophila and Other Insects 22
Chromosomal Aberrations in Human and Other Mammalian Systems. ... 27
Studies on Human Chromosomes in vitro 27
Studies on Rodent Chromosomes in vi tro 35
Studies on Human Chromosomes in vi vo 38
Studies on Rodent Chromosomes in vivo 41
Micronucleus Assay 42
Dominant Lethal Assay 42
Heritable Translocation Assay . 45
Chromosomal Nondisjunction (Aneuploidy) in Whole Mammals ... 45
Sperm Abnormality Assay in Mammals 48
Chromosomal Aberrations in Plants 48
Biochemical Studies Indicative of Mutagenic Damage . . 49
Summary 50
i i i
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CARCINOGENICITY 52
Animal Studies 52
Inhalation Study in Rats .52
Intratracheal Studies in Rats 58
Injection Studies in Mice and Rats 61
Oral Studies in Mice and Rats 67
Surma ry 70
Epidemiologic Studies 73
Potts ( 1965) 73
Kipling and Waterhouse (1967) 75
Hunperdinck (1968) 76
Hoi den ( 1969 ) 78
Kolonel (1976) 78
Lemen et al . { 1976) 81
McMichael et al. ( 1976a, b) 84
Monson and Fine (1978) 86
Kjell strom et al. (1979) 88
Goldsmith et al. ( 1980) 91
Hoi den (1980) 92
Sorahan (1981) 96
Inskip and Beral ( 1982) 99
Andersson et al. (1982) 102
Kjellstrom (1982) 103
Armstrong and Kazantzis (1983, 1982) 108
Sorahan and Waterhouse (1983) . 115
Varner (1983, unpublished) 118
Tnun et al . (1985) 123
Summary. . 132
QUANTITATIVE ESTIMATION 138
Introduction 138
°rocedures for Determining Carcinogenic Potency . 142
Description of the Low-Dose Animal Extrapolation Model .... 142
Selection of Data 145
Calculation of Human Equivalent Dosages from Animal Data. . 146
Calculation of the Unit Risk from Animal Data 149
Unit 3is'< Estimates for Cadmium 150
Unit Risk Estimate Based on an Animal Study 150
i v
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Unit Risk Estimate Based on a Hunan Study 153
Data Base 153
Model Jsed 156
Use of Parameter Estimates of a to Estimate Unit Risk. . . 161
Recommended Unit Risk Estimate 161
Relative Potency 163
Appendix A. Comparison of Results by Various Extrapolation Models . . .170
Appendix B. International Agency for Research on Cancer (1ARC)
Classification System for Evaluation of the Carcinogen
Risk of Chemicals to Humans . . . . . . . ..... . 174
References 179
v
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ABSTRACT
This document evaluates the mutagenicity and carcinogenicity of cadmium,
supplementing an earlier document (Health Assessment Document for Cadmium, May
1981) which dealt with all health effects. Since the earlier document was
prepared, a rat inhalation carcinogenicity study has been reported and several
epidemiology and mutagenicity papers have been published.
This document concludes that: (1) there is mixed evidence on the mutage-
nicity of various cadmium salts; (2) cadmium chloride aerosol induces lung
cancer in rats; (3) injected cadmium salts induce injection site sarcomas and
testicular tumors in both mice and rats; (4) there is limited epidemiologic
evidence that inhaled cadmiun is dose-related to lung cancer in exposed wor-
kers; (5) there is no evidence that cadmium is carcinogenic via ingestion,
which is a major route of human exposure, and the upper limit of potency via
ingestion is at least 100 times less than via inhalation.
vi
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PREFACE
This document, a review and assessment of the current information rela-
ting to the mutagenicity and carcinogenicity of cadmium, contains a detailed
discussion of information on those subjects that became available since the
earlier Health Assessment Document for Cadmium was prepared by the Office of
Health and Environmental Assessment (OHEA) in May 1981, The literature search
supporting the carcinogenicity assessment is current through November 1984,
although an updated Thun et al . (1985) study is included; the literature
search-supporting the mutagenicity section is current through December 1983.
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
The Carcinogen Assessment Group, Office of Health and Environmental
Assessment, was responsible for preparing this document. Participating members
are as follows (principal authors are designated by asterisks):
Roy E. Albert, M.D. (Chairman)
*Larry D. Anderson, Ph.D.
*Steven Bayard, Ph.D.
*David L. Bayliss, M.S.
*Robert P. Bellies, Ph.D.
Chao W. Chen, Ph.D.
Arthur Chili, M.D., Ph.D.
Margaret M. L. Chu, Ph.D.
James C, Cogliano, Ph.D.
*Herman J. Gibb, B.S., M.P.H.
Bernard H. Haberman, D.V.M., M.S.
Charalingayya B. Hiremath, Ph.D.
James W. Holder, Ph.D.
Robert E. McGaughy, Ph.D.
Jean C. Parker, Ph.D.
*Wi11iam E. Pepelko, Ph.D.
Charles H. Ris, M.S., P.E.
Dharm V. Singh, D.V.M., Ph.D.
Hugh L. Spitzer, B.S.
*Nancy A. Tanchel, B.A.
*Todd W. Thorslund, Sc.D.
The Reproductive Effects Assessment Group, Office of Health and
Environmental Assessment, was responsible for preparing the section on
mutagenicity. Participating members are as follows (principal authors are
designated by asterisks):
John R. Fowle III, Ph.D.
Ernest R. Jackson, M.S.
David Jacobson-Kram, Ph.D.
*K.S. Lavappa, Ph.D.
Sheila L. Rosenthal, Ph.D.
Carol N. Sakai, Ph.D.
Lawrence R. Valcovic, Ph.D.
Vicki Vaughan-Dellarco, Ph.D.
Peter E. Voytek, Ph.D.
vi i i
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The following individuals provided peer review of this draft and/or earlier
drafts of this document:
U. S. Environmental Protection Agency
Michael Dourson
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Ci nci nnati , OH
John B. Fink
Strategies and Air Standards Division
Office of Air Quality Planning and Standards
Research Triangle Park, NC
Charles H. Nauman
Exposure Assessment Group
Office of Health and Environmental Assessment
Washington, DC
Joseph Padgett
Strategies and Air Standards Division
Office of Air Quality Planning and Standards
Research Triangle Park, NC
Fred Smith
Health Effects Researcn Laboratory
Research Triangle Park, North Carolina
Other Government Agencies
Peter W. Preuss
Consumer Products Safety Commission
Washington, DC
Jay Klemme
Center for Disease Control
National Institute for Occupational Safety and Health
Cincinnati, Ohio
Other
Gunter Oberdoerster
University of Rochester
Rochester, New York
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Science Advisory Board
Previous external review drafts of this document were peer reviewed by the
Environmental Health Committee of EPA's Science Advisory Board.
The authors wish to acknowledge the editorial assistance of Judy Theisen
without whose assistance this document could not have been completed.
x
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SUMMARY AND CONCLUSIONS
SUMMARY
Qualitative Assessment
Cadmium has been investigated for mutagenic activity in both prokaryotic
and eukaryotic systems. Gene nutation studies in Salmonella typhinurium and
E_. col i have produced inconclusive results. In yeast, gene mutation studies
have also been inconclusive. In three gene mutation studies (in mammalian
cell cultures, mouse lymphoma cells, and Chinese hamster lung and ovary cells)
marginally positive responses to cadmium were observed.
Rec-assay in Baci11 us subti1is resulted in a weak mutagenic response.
In the Drosophila sex-linked recessive lethal test, cadmium was found to be
nonmutagenic. The dominant lethal test in Drosophila resulted in a positive
response with a dose-response relationship.
The results of chromosomal aberration studies in human lymphocytes from
exposed workers and human cell lines treated with cadmium have been conflict-
ing. In Chinese hamster cells, chromosomal aberrations were noted following
treatment with cadmium; however, in mouse carcinoma cells, no aberrations
were recorded in response to cadmium treatment. In rodents, treatment with
cadmium did not induce chromosomal aberrations or micronuclei in bone marrow
cells. Similarly, no dominant lethal mutations or heritable translocations
were noted in mice treated with cadmium.
The evidence that cadmium interferes with spindle formation cones from
both j_n_ vi tro and i_n_ vi vo studi es i n mammal s . In i_n_ vi t ro studi es using the
Chinese hamster cell line "Hy," cadmium induced an effect similar to that of
colchicine, which is a known spindle poison. Cadmium also was found to in-
crease numerical chromosome aberrations (aneuploidy) in these cells. Similar
1
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results were obtained in studies on aneuploidy in whole mammals. In female
mice and Syrian hamsters, cadmium induced chromosomal nondisjunction leading
to aneuploidy in germ cells. A recent study demonstrated that the numerical
aberrations induced by cadmium chloride in female germ cells of mice are in-
herited in the embryos.
Chronic exposure of rats to aerosols of cadmium chloride at airborne
concentrations of 12.5, 25, and 50 ug/m^ cadmium as cadmium chloride for 18
months followed by a nonexposed 13-month period produced significant increases
in lung tumors (Takenaka et al., 1983). A single 30-minute exposure of rats
to cadmium oxide at a concentration of 60 mg/m^ did not significantly increase
the occurrence of lung tumors in the year that followed, although increases in
testicular degeneration were observed. The estimated total dose in mg/kg was,
however, lower than that producing testicular neoplasia following parenteral
administration (Poirier et al., 1983). Intratracheal instillation of cadmium
oxide produced an increase in mammary tumors and an increase in tumors at
multiple sites among male rats (Sanders and Mahaffey, 1984). Intrathoracic
injections of cadmium powder were found to be highly toxic, but when their
toxicity was reduced by co-administration of zinc, mesotheliomas developed
(Furst et al., 1973). Intramuscular or subcutaneous injection of cadmium as
metal powder, or as the chloride, sulfate, oxide, or sulfide, produced injec-
tion-site sarcomas and/or testicular interstitial cell (Leydig cell) tumors
in rats after necrosis and regeneration of testicular tissue (Table 10). One
study suggested that the incidence of pancreatic islet cell tumors in labora-
tory animals may be increased by administering cadmium chloride by injection
(Poirier et al., 1983). In another study, injection of cadmium chloride into
the prostate gland induced tumors of that tissue in male rats (Scott and
Aughey, 1979).
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Cadmium appears to be much less potent a carcinogen by ingestion than
by injection or inhalation. For example, the total dose of inhaled cadmium
in the Ta
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from one site to another in the body is not based on chemical solubility, the
carcinogenic n'sks of exposure to cadmium and its compounds are now seen to
be greater than orginally anticipated.
Epidemiologic studies reviewed since the publication of OHEA's Health
Assessment Document for Cadmium (May 1981) have not appreciably changed the
earlier findings of insufficient evidence of a risk of prostate cancer from
exposure to cadmium oxide and fumes. On the other hand, recent evidence of a
significant lung cancer risk from exposure to cadmium is available from the
Thun et al. (1985) study, in which a greater than twofold excess risk of lung
cancer seen in cadmium smelter workers was found to result from cadmium expo-
sure rather than from the presence of arsenic in the plant or increased
smoking by the workers. Thun et al. (1985) analyzed both of the above factors
(arsenic and smoking) as potential confounders, and presented evidence that
these factors, alone or in combination, could not have caused the excess lung
cancer risk observed, and that a significant portion of the estimated risk was
likely to be due to cadmium. Tne earlier version of this study, by Lemen et
al. (1976), also demonstrated a significantly elevated risk of lung cancer.
Lemen et a"!. ( 1975) also reported a dose-response relationship with respect to
lung cancer and cunulative exposure to cadmium.
Varner (1983), in an updated and enlarged version of the Lemen et al.
(1976) study, also found a statistically significant excess of lung cancer.
In addition, Varner noted a dose-response relationship for both lung cancer
and total malignant neoplasms with increasing cumulative exposure. Varner
thought that the significant excess ris< of lung cancer was probably due to
smoking or to the presence of arsenic in the plant. However, Varner did not
analyze the impact of these factors. The Varner (1983) study also suffers
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from several other limitations, which are described in greater detail in the
Epidemiology section of this document.
Sorahan and Waterhouse (1983) noted an unqualified statistically signifi-
cant risk of lung cancer in their study population via the Standard Mortality
Ratio (SMR) method. In addition, a significantly high test statistic was noted
for excess lung cancer utilizing the Kneale and Cox "regression models in life
tables (RMLT)" method in the "high to moderately exposed" group but not in the
"highest exposure" category, although the test-statistic was elevated. Sorahan
suggested that the excess might be due to exposure to welding fumes of oxyace-
tylene. No significantly high test-statistic was found in his "highest expo-
sure" group, however, possibly because of a lack of sensitivity due to small
numbers.
In his earlier paper, Sorahan (1981) found the risk of lung cancer to be
nonsignificantly elevated through SMRs calculated in a retrospective prospec-
tive cohort study of workers who began employment before and after.the amal-
gamation of two factories into a nickel-cadmium battery plant.
Armstrong and Kazantzis (1983) also demonstrated a significant risk of
lung cancer in workers designated by them as having worked in "low exposure"'
jobs for a minimum of 10 years. Little sensitivity remained in the "highly
exposed" group with which to detect a risk after a minimum of 10 years' employ-
ment, and such a significant risk was not shown. However, a suggestion of an
excessive risk was evident in the "ever mediumly" exposed group of workers with
a minimum of 10 years of employment. This study, however, does not deal in
sufficient detail with latent factors 15 or 20 years after initial exposure in
combination with length of employment. The major problem with this study is
the distinct possibility that most members of the author's seemingly large
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cohort of 6,995 were only minimally exposed to cadmium. Only 199 (3%) of his
cohort could qualify for inclusion in his "highly exposed" category, which was
defined by the author as working in a job which entailed exposure to cadmium
that was judged by the author to be "likely in the long term to lead to cadmium
urine concentrations of over 20 ug/L." The remaining 6,796 would never have
qualified for inclusion in the "highly exposed" category, as a consequence.
On the other hand, measured cadmium urine levels exceeded 20 Ug/L for 81% of
Thun's cohort of 602, out Thun indicated that 100% of his cohort could even-
tually be expected to exceed "in the long term" a cadmium urine concentration
of 20 ug/i..
Holden (1980) reported a significant excess risk of lung cancer in
"vicinity" workers, which he maintained could have been due to the presence
of other metals such as arsenic. No excess risk was seen in the group with
the highest exposure, however, latent factors were not considered, nor was the
possible movement of wor
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for less than one year. Kjellstrom cautioned against placing too nuch credence
in this finding, since most of the workers "have had a relatively short expo-
sure duration and latency period."
Inskip and Beral (1982) noted a slightly increased but nonsignificant risk
of lung cancer among female residents of two small English villages who pre-
sumably were exposed to cadmium-contaminated soil via the oral route. However,
again only a small number of lung cancers were observed. Furthermore, evidence
of similar cadmium contamination appeared in the soil of the "control" village
as well as in the soil of the "exposed" village.
Problems concerning lack of power, no consideration of latent effects, or
insufficient evidence of exposure to cadmium characterize the non-positive
studies.
Overall, the weight of the epidemiologic evidence is suggestive of a
significant risk of lung cancer from exposure to cadmium. The contribution
of the confounding factors of smoking and/or the presence of arsenic has been
shown by Thun et al. (1985) not to have produced the significant dose-response
risk of lung cancer that was found.
Altogether, the epidemiologic data appear to provide limited evidence of
lung cancer risk from exposure to cadmium, based on the I ARC classification
system (Appendix B) and the U.S. Environmental Protection Agency's Proposed
Guidelines for Carcinogen Risk Assessment (U.S. EPA, 1984).
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Quantitative Assessment
Since humans are exposed to cadmium dust or fumes, and the rats used for
study were exposed to cadmium chloride aerosol, a limitation inherent in the
use of such studies for estimating human risk is the possible difference be-
tween humans and rats with regard to lung retention of particulates, or between
the biological effectiveness of cadmium chloride aerosol administered to rats
and the dust and fumes inhaled by workers. Since the data are not clear on
this point, assumptions of equal lung uptake and equal effectiveness have been
made herein for the purpose of arriving at an assessment of the human risks.
Given these assumptions, combined with other assumptions and conventions
used in quantitative risk assessment procedures, the Takenaka et al . (1983)
data on lung carcinomas in rats during lifetime inhalation exposures to cad-
mium chloride aerosol were analyzed. As a result of this analysis, the upper-
bound incremental cancer risk to humans who continuously breathe 1 pg/m^ of
elemental cadmium for a lifetime is estimated to be 9.2 x 10~2.
3ased or respiratory cancer rates from the Thun et al. (1985) study of
cadnrum smelter workers, and using a linear model that is consistent with the
data, the upper-bound incremental cancer risk from lifetime exposure to 1 tig/m^
of cadmium in the air is estimated to be 1.8 x 10"^.
The 95% confidence bound on this estimate, which takes into account only
the statistical variability of the cancer rates, gives a range of 3.5 x 10"^
to 1.7 x lO"'1. However, this range does not account for possiole deviations of
the true ^unknown) model from the linear model or of actual exposure from esti-
mated exposure. For example, an empirical threshold model that is also consis-
tent with the observed data gives a unit risk estimate of zero. Even with the
uncertainties surrounding the estimate nased on human data, it is felt that this
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estimate is more reliable for environmentally exposed humans than the estimate
based on animal data. Further detailed analysis and laboratory studies are
needed before the large difference between the estimates based on animal and
human data are resolved.
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CONCLUSIONS
Cadmium has been tested in a variety of mutagenicity tests with both
negative and positive results reported. Because a variety of end points and
protocols have been used, a resolution of the apparently conflicting data is
not currently possible. Several of the positive results have been observed
at concentrations in which some cytotoxicity was apparent, suggesting the
possibility that the mutagenic effect of cadmium may be an indirect one.
However, the appropriate studies required to resolve this question have not
been performed.
A significant dose-response relationship of lung cancer from exposure to
cadmium chloride aerosol via inhalation has been found in experimental rats.
In addition, significant injection site sarcomas and distant testicular cell
tumors have been found in experimental mice and rats exposed to cadmium metal
or cadmium salts.
A sigrificant dose-response relationship of lung cancer from exposure to
airborne cadmium oxide and fumes has been found in humans that cannot be
explained by the potential confounders, arsenic and/or smoking. However, no
evidence of a carcinogenic response has been detected in either animals or man
from the ingestion of cadmium.
According to the Agency's Proposed Guidelines for Carcinogen Risk
Assessment, (U.S. EPA, 1984) cadmium is classified as a Group R1 substance and
is thus considered to be a "probable" human carcinogen. Sufficient evidence in
animal studies is provided by the findings of lung carcinomas in rats exposed
to cadmium chloride aerosol by inhalation, and by injection site and testicular
tumors in mice and rats given cadmium metal or cadmium salts. Limited evidence
for carcinogenicity of cadmium in humans is provided by the finding of a dose-
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related increase in lung cancer in humans exposed to airborne cadmium and
cadmium compounds that cannot be explained by the potential confounders, arsenic
and smoking. Using the IARC classification system (Appendix B), cadmium would
be considered a Group 2A substance, indicating again that cadmium is considered
to be a "probable" human carcinogen.
An estimate of the carcinogenic potency of cadmium, presuming that it is
a human carcinogen, can be developed from both the human and animal inhalation
data. The upper-bound incremental unit risk estimate for continuous inhalation
exposure at a cadmium concentration of 1 gg/m^ ranges from 1.7 x 10"^ to
3.5 x 10"3, with a most plausible estimate of 1.8 x 10~3, based on lung cancer
from one study of cadmium production workers, although there is uncertainty in
these estimates because of the lack of differential exposure in the workplace.
Since these estimates are based on human studies, they are regarded as more
realistic than the estimate based on the rat inhalation study, which is
approximately 51 times higher.
Although there have been no studies showing cadmium to be carcinogenic by
the ingestion route, it is estimated that if cadmium is carcinogenic via inges-
tion, its maximum ingestion potency would be about 1/100 that of inhalation.
Expressed in terms of relative potency, cadmium would rank in the second
quartile among the 54 chemicals that the Carcinogen Assessment Group has eval-
uated as suspect or known human carcinogens.
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MUTAGENICITY
Cadmium has been investigated for its mutagenic potential in both pro-
karyotic and eukaryotic systems. In the former category are assays for gene
mutation and reparaole genetic damage in bacteria. In the latter category are
gene nutation studies in yeast, Drosophila, and mammalian cells; and chromoso-
mal aberration studies in human and other mammalian cells exposed to cadmium
both in vitro and in vivo. The following is an analysis of the literature
pertaining to the mutagenic effects of cadmium.
GENE MUTATIONS IN PROKARYOTES
Gene mutation studies that have-been conducted in prokaryotic systems
are summarized in Table 1. A discussion of each study follows.
Salmonella Assay
Heddle and Bruce (1977) tested tne mutagenic effects of cadmium chloride
in the histidine reverse mutation assay using Salmonella typhinurium tester
strains TA100, TA98, anu TA1537. The test compound (purchased from ICN Phar-
maceuticals, 3lainview, New Yor:<) was dissolved in water and used at concen-
trations of 0.05, 0.5, 5, 50, and 500 ug/plate with and without the appli-
cation of a metabolic activation system (S9 mix) derived from phenobarbita1 -
induced rat liver homogerate. According to these authors, cadmium chloride
did not induce a significant mutagenic response over the control value. The
criterion set for a positive response was 50%, or a 1.5-fold increase in the
revertant frequency over the negative control or spontaneous frequency.
Revertant counts we^e given only for strain TA100; the spontaneous frequency
of revertants in this strain was 140 colonies per plate. The purity of the
cadmium chloride test compound was not given in this report.
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TABLF. 1. MUTAGENICITY EVALUATION OF CADMIUM: GENE MUTATIONS IN PROKARYOTES
Test system
Salmonel1 a
typhimuri um
Strai n
TA98
TA100
TA1535
TA1537
TA153B
Cadmi um
compound
Cadmi uin
chl oride
aqueous
soluti on
Dose
S9 Activation
system
Results
Comments
0.05
0.5
5.0
50.0
500 py/plate
Phenobarbital-
induced rat
1 i ver
Reported as
negative
1. Data are not presented
clearly as revertants/
plate for each strain.
2. Purity of compound not
di scussed.
Reference
Heddle and Bruce
(1977)
Salmonel1 a
typhimuri um
TA9B
TA1535
TA1537
Cadmi um
red i n DMSO
1 ug/mL
Aroclor 1254-
induced mouse
1 i ver
Reported as
negative
Data provided only for
the preincubation or
suspension assay. No
data on the spot test
given.
Only a single dose was
employed; no dose-
response data.
Mi Ivy and Kay
(1978)
Salmonel1 a TA1S35 Cadmium 10, 20, 20, uninduced mouse Reported as 1. Spontaneous reversion
typhimurTum TA1537 chloride 45, 90 mM liver negative data and experimental
(solvent reversion data have not
not specified) been given in terms of
numbers.
2. Used uninduced mouse
liver S9 activation
system.
3. No positive controls.
Polukhi na et al,
(197/)
(continued on the following page)
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TABLE 1.
(continued)
Test system
Salmonc 11 a
typhimun urn
Strain
Cadmium
compound
TA98
IA100
TA1S35
TA1S37
T A1S 38
Cadini um
diethyl-
thiocar-
bamate in
DMSO
Uose
S9 Activation
system
1
b
10
100 uy/plate
ArocI or-
induced rat
I i ver
Results
Reported
positive for
TA1538 and TA98
in the absence
ot S9 activation.
Reported weakly
positive both in
the presence and
absence of S9
acti vation.
Comments
3.
Lowest effecti ve
dose was 10 u 9/
pi ate.
Reported positive
only for one dose.
No dose-response
relationship.
Reference
Hedenstedt et al,
( 1979)
1—'
Baci1lus
HI 7
Cadrni um
0.05 M/plate
None
Reported as
subt i1i s
Rec +
chloride
weakly (+)
rec-assay
M45
aqueous
positive
Rec-
solution
Cadmium
Reported as
nitrate
negati ve
aqueous
solution
Nishioka
(19/5)
Baci11 us
subtilis
rec-assay
H17
Rec+
M4S
Rec-
Aqueous
solutions
of cadmium
chloride,
nitrite, and
sulfite
0.00b
M/plate
None
Reported as
weakly (+)
posi ti ve
1. Compounds were pure.
Kanematsu et al.
(1980)
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In an abstract published by Kalinina and Polukhina (1977), cadmium chlo-
ride was reported to be nonmutagenic in the Salmonella assay. However, impor-
tant variables such as the number of strains used, the dosage employed, and
the number of revertants per plate were not reported. Polukhina et al.
( 1977) also reported negative results with cadmium chloride on Salmonel1 a
typhimurium strains TA1535 and TA1537 both in the presence and absence of an
S9 activation system derived from uninduced mouse liver homogenate. In this
report a suspension assay with cadmium chloride concentrations of 10, 20, 30,
45, and 90 mM was employed. Positive and negative control data were not
presented in this paper, so it is not possible to know whether or not the
assay system was functioning properly. The toxicity of the test compound was
not reported by these investigators.
Milvy and Kay (1978) studied the mutagenic effects of cadmium red (cad-
mium sulfide and selenium), a dye used in the printing industry, using the
Salmonella spot test (Ames et al., 1973) and the preincubation assay (Ames et
al., 1975). Salmonella typhimurium strains TA1538, TA98, and TA1535 were
employed in these studies. The test compound (10 wg) was dissolved in 0.01
mL dimethyl sulfoxide (DMS0) and added to 0.9 mL of incubation mixture for 30
minutes at 37°C with shaking before plating 0.1 mL onto minimal plates.
Experiments were carried out both in the presence and absence of an S9 acti-
vation system derived from Aroclor 1254-induced mouse liver homogenate.
Cadmium red was reported to be nonmutagenic in both tests. However, data
were presented only for the suspension assay. These investigators used only
one concentration, and hence, no dose-response relationship was demonstrated.
The toxicity of the compound for each strain was not reported. Consequently,
this study may be regarded as inconclusive.
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Hedenstedt et al. (1979) studied the mutagenic effects of cadmium
diethyldithiocarbamate (used in rubber and plastic industries) in Salmonella
typhimuriurn strains TA1535, TA1537 , TA1538, TA98, and TA100. The concentra-
tions used were 1, 5, 10, 50, and 100 yg/p-late. The compound was dissolved
in DMSO. Concentrations of 50 and 100 ^9/pi ate were toxic in many of these
strains.- The concentration of 10 ug/plate exhibited mutayenic activity in
strains TA1538 and TA98 in the absence of a metabolic activation (S9) system
obtained from Aroclor 1254-induced rat liver homoyenate (Ames et al., 1975).
In TA 1538 trie revertent frequency increased more than twofold at 10 yg/
plate, i.e., 26.3 ± 3.7 revertants/plate compared to a control value of 11.8 ±
2.6 revertants/plate in the absence of metabolic activation. In the presence
of metabolic activation, the revertant frequencies in treated organisms and
controls were the same. In TA98, the revertant frequency was 58.8 ± 2.3 at
10 ug/plate (almost a twofold increase) compared to the control frequency
of 31.5 _ 4.2 revertants/pl ate in the absence of metabolic activation. No data
were yiven for studies in the presence of metabolic activation. Positive con-
trol data were not presented, although the authors indicated that positive
controls were employed in the experiment. Since both cadmium diethyldithio-
carbanate and zinc diethyldithiocaroamate were found to be mutagenic in this
study, it may not be appropriate to infer that cadmium was the mutagenic
moiety.
Mandel and Ryser (1981) reported the induction of frameshift mutations in
Salmonella typhimurium TA1537 and missense mutations in Salmonella typhimurium
TA1535 by cadmium chloride in concert with N-nethyl-N'-nitro-N-nitrosoyuanidine
(MNNG). A concentration of 0.5 mM cadmium chloride facilitated a dose-related
increase in the induction of mutation frequency by MNNG that was up to tenfold
16
-------
higher than the control value. This synergism was also noted for the induction
of forward mutations to 8-azoguanine (8AG) resistance in the HPRTase locus
of these strains.
These studies indicate that cadmium induces mutations in Salmonella
typhimurium in a synergistic manner with other mutagenic chemicals. Similar
studies have also been reported in rat embryo cultures (Zasukhina et al.,
1977).
Escherichia coli WP2 Assay
Venitt and Levy (1974), in a report on the mutagenicity of chromates in
the Escherichia coli WP2 mutation system, mentioned that they also tested cad-
mium compounds for mutagenicity and found them to be negative. These authors
did not mention what types of cadmium compounds they employed, nor did they
present data to support their negative conclusions.
Bacillus subtil is Rec-Assay
Nishioka (1975) investigated the mutagenicity of cadmium chloride and
cadmium nitrate using the rec-assay of Kada et al. (1972). In the rec-assay,
which measures reparable DNA damage, differences in growth sensitivities of
Bacillus subtil is strains H17 (recombination-competent wild type rec+) and M45
(recombination-deficient rec-) to mutagenic chemicals are measured. When a
chemical is more inhibitory to rec- than to rec+ cells, it is suspected of
being mutagenic. Concentrations of 2.5 x 10"? cells/0.1 mL were streaked
outward from the center of agar plates. Aqueous solutions of cadmium chloride
and cadmium nitrate (0.05 M) were applied in 0.05 ml aliquots to disks of
filter paper (diameter 10 mm) and placed in the centers of the plates, at the
starting point of the streaks of rec+ and rec- cells. All of the plates were
incubated at 37°C for 24 hours. The degree to which bacterial growth was
17
-------
innibited was indicated by the relative distance (mm) between the edges of the
paper d i s '< s and the ends of the bacteria streaks. This inhibition of growth
is known as "rec- effect" and is expressed as: no difference between rec+ and
rec- plates (-), less than 5 mm difference ( + ), 5-10 mm difference (++), or
more than ID mm difference (+++). Cadmium nitrate showed no difference in
growth inhibition (-), whereas cadmium chloride exhibited a weak positive
response (+). Each experiment was repeated three times. These experiments
did not use a metabolic activation system. The cadmium compounds used were of
reagent yrade.
Similar results were obtained by Kanematsu et al. (1980) using the rec-
assay. Cadmium chloride, cadmium nitrite, and cadmium sulfate were employed
at a concentration of 0.005 M in 0.05 mL aqueous solution. All of these com-
pounds exhibited a weak mutagenic response ( + ) (growth inhibition zones of 4-5
mm). According to these authors, the test compounds used were of the highest
purity commercially available.
GENE MUTATI0NS IN YEAST
Cadmium chloride nas been investigated for the induction of gene mutations
in the yeast Saccnaromyces cerevisiae (Tasle 2) (Takahas'ni , 1972; Putrament et
al ., 1977 ). Takahashi ( 1972) studied the induction of petite mutations (p-
mutations) and auxotrophs in the Saccharomyces cerevisiae heterozyyous diploid
strain C3116. He treated 10^ cells with 10 (5.5 x 10"^M), 12 (6.6 x 10~^M),
anc 20 ppm (1.1 x 1Q~^M) for 2 days (48 hours) at 25°C. After 2 days of
growth, the cell number was determined and the cell suspension was diluted to
give a concentration of 2.8 x 10"^ cells per mL. One-tenth of the diluted
suspension was spread on the vEPD-agar plate and incubated at 28°C. When small
colonies appeared on the plate, they were replica-plated onto YEP-glycerol-agar
-------
Test system
Saccharomyces
cerevisiae
(Yeast)
P-mutants and
auxotrophs
C3116
Cadmi um
chloride
10
12
20 ppm
None
Reported
posi ti ve
as
1.
2.
P-mutants may not represent
true yene mutations because
they arise by damage in
mitochondrial UNA.
Vayue protocol.
Takahashi
(1972)
Saccharomyces
cerevisiae
P-mutants
19 7/ 2d
Cadmi um
chl ori de
8 ppm
None
Reported
neyative
as
1.
2.
3.
Only one concentration of
test compound was used.
This concentration was too
toxic for the eel 1s.
No mutants observed in the
few survivors.
Putrament et al.
(1977)
Mouse lymphoma
I.5178Y
TK+/"
Cadmi um
chl ori de
0.0b
0.06
0.08
0.11
0.15 ug/mL
None
Reported
weakly
positive
as
1.
Application of t-test to de-
termine the siynificance
has been challenged by Clive
et al. (1981).
Amacher and
Pai11et (1980)
Chi nese
hamster
eel 1 s
Luny (Don)
eel 1s;
resi stance
to 8-
azoyuani ne
Cadmi um
acetate
Cadmi um
chloride
2.5
5
10 uy/mL
None
Reported
positive
as
1.
2.
Very low survival due to
high toxicity.
Observations not repeated
or confirmed.
Casto (1976)
Chi nese
hamster
eel 1 s
Ovary cells
(CHO)
Cadmi um
. chloride
2.5
5
5
10 uy/mL
None
Reported
weakly
positive
as
1.
Data not presented.
Hsi e et al.
(1978)
Chinese
hamster
eel 1 s
V79
Cadmi urn
chloride
1x10"6M
2x10~6M
3x10"6M
None
Reported
positive
as
Ochi and Ohsawa
(1983)
Mouse
1ymphoma
L5178Y
TK+/"
Cadmi um
sulfate
0.10
0.15
0.20
0.30 uy/mL
None
Reported
positive
as
Oberly et al.
(1982)
-------
nedium and minimal medium. After overnight incubation at 28°C, induced p-
nutants and auxotrophs were scored. At the dose of 12 ppm (1.1 x lCT^M), no
p-mutants or auxotrophs were found in the 786 colonies counted; at the dose
of 10 ppm, 10 p-nutants and 3 auxotrophs were detected in the 871 colonies
counted; and at the dose of 20 ppm, there were 12 p-mutants and 9 auxotrophs in
1,182 colonies, indicating that cadmium .chloride may be mutagenic. In the con-
trols there were five p-mutants and two auxotrophs in 2,875 colonies counted.
According to this paper, however, mutants were induced at dosages of 10 ppm and
20 ppm but not at the dosage of 12 ppm. Such erratic fluctuations in nutation
frequency, and the low number of mutants, suggest that the positive results may
similarly be questionable. Since p-mutants occur by damage involving mitochon-
drial DNA -ather than nuclear DNA, caution should be exercised in assessing the
mutagenic potential of chemicals with tnis system.
DJtrament et al. (197/) also reported a negative result in a test for
irduction of p-nutation by cadmium chloride in Saccharomyces cerevisiae. The
concentration of cadmium chloride tested (3 mM) was very toxic, however, and
less than 1;'- of the cells survived a 6-hour incubation in YEP-glucose, medium.
No increase of p-mutants was observed, and no data were presented. This study
is regarded as inconclusive.
jENE mutations :n mammalian cell cultures
Gere mutation studies in cultured mammalian cells have also been summa-
rized in Table 2. A discussion of each study follows.
Mouse Lymphoma Assay
Amacher and Paillet (1980) reported that cadmium choloride (ICN Pharma-
ceuticals) was mutagenic in -he mouse lymphoma L5178Y TK+/~ assay. When cad-
mium chloride, dissolved in normal saline, was tested at concentrations of
20
-------
2.35 x 10~7m (cell survival 100 _+ 11%), 3.57 x 10~?M (cell survival 78 _+ 24%),
4.5 x 10"^M (cell survival 62 _+ 4%), 6.00 x 10~?M (cell survival 38 _+ 11%),
and 8.00 x 10"^M (cell survival 12 _+ 1%), there was a dose-related increase in
mutation frequency. The mutation frequencies per 10^ survivors for the above
doses were 0.48 +_ 0.01, 0.58 +_ 0.06, 0.56 +_ 0.05, 0.63 _+ 0.16, and 0.68 +_ 0.04,
respectively. The mutation frequency at the highest nontoxic dosage of 6.00 x
10"^M was approximately 1.5-fold higher than the control frequency of'0.40 _+
0.03 (survival 100% _+ 5). The dose-response curve obtained by Amacher and
Paillet (1980) has been criticized by Clive et al. (1981), who claim that the
application of a t-test for low numbers of samples to determine significance is
mi sieadi ng.
Oberly et al. (1982) clearly demonstrated the mutagenicity of cadmium
sulfate in mouse lymphoma L5178Y gene mutation assay. The test compound at
concentrations of 0.10, 0.15, 0.20, and 0.35 gg/mL resulted in mutation
frequency increases of 1.7-fold (survival 81%), 4.0-fold (survival 55%), 10.5-
fold (survival 12%), and 9.9-fold (survival 4%), respectively, over the solvent
control value.
Chinese Hamster Cell Assay
Casto (1976), in a report submitted to Dr. Richard Troast of the Office of
Pesticide Programs, U.S. Environmental Protection Agency, stated that cadmium
acetate and cadmium chloride are mutagenic in Chinese hamster-lung cells (Don)
as determined by induction of mutations that confer resistance to 8-azoguanine.
Cells were treated with 2.5 (1.36 x 10~®M), 5 (2.72 x 10"®M), and 10 ug/mL
(5.45 x 10"®M) of cadmium acetate and cadmium chloride, respectively, for 18
hours, followed by 48 hours of expression time. Cadmium acetate induced muta-
tion frequencies of 2.8, 50, and 10 per 10"6 survivors, respectively, for the
21
-------
above dosages. The survival rate was 0.70%, 0.92%, and 0.43%, respectively.
Cadmium cnloride induced mutation frequencies of 6, 7, 14, and 37 per 10~6
survivors. The neyative control rate was 2 per 10^ survivors. According to
this investigation, both cadmium acetate and cadmium chloride are weakly muta-
genic. These results are questionable, however, because of the low survival
rates at the high concentrations used. Hsie et al. (1978) also reported cad-
mium chloride to be weakly mutagenic at the HGPRT locus in the Chinese hamster
ovary cells, but no data were presented.
Ochi and Ohsawa (1983) investigated the inducibility of 6-thioguanine-
resistant (6TG) mutants in the Chinese hamster cell line, V79, by cadmium:
chloride. They also investigated single-strand scission of DNA by cadmium
chloride in these cells. The frequency of 6TG-resistant mutants was found to
increase with increased concentration of cadmium chloride. Single-strand
scission of DNA oy cadmium was detected in combination with proteinase K
digestion of the cell lysates, indicating formation of DNA-protein cross-
link! ng. by the metal .
Based on the weight of evidence from the data available from both bio-
logical and biochemical procedures, and also on the basis of personal discus-
sions with the authors of the above publications, cadmium is regarded as muta-
genic in mammalian cell culture gene mutation assays.
STUDIES IN DR0S0PHILA AND OTHER INSECTS
Studies on the genetic effects of cadmium in Drosophila are summarized in
Table 3. A discussion of each study follows:
Sorsa and Pfeifer (1973) reported that cadmium chloride at concentrations
of 1.25 (6.81 x 10"6M), 2.5 (1.36 x 10"5M), 5.0 (2.72 x 10"5M), 10.0 (5.45 x
10~5m), 20.0 (1.09 x 10"4m), and 50 my/L (2.27 x 10"^M) of media caused signi-
22
-------
TABLE 3. MUTAGENICITY EVALUATION OF CADMIUM: GENE MUTATIONS AND
CHROMOSOMAL ABERRATIONS IN DROSOPHILA AND OTHER INSECTS
Cadmium
Treatment
Test system
compound
Dosage
period
Results
Comments
Reference
Drosophila melanoqaster
Cadmium
50.0 mg/L
Larvae
Reported as
1.
Data not presented.
Sorsa and Pfei fer
sex-linked recessive
chloride
(Z.72x10"4M)
feeding
negati ve
2.
Only one dose was used.
(1973)
lethal test
Orosophila melanoqaster
Cadmium
6b my/L
Larvae
Reported as
1.
Treatment was done 1n
Ramel and Friberq
larval development
chlori de
feeding
negative
larvae only.
(1974)
sex chromosome loss
sex-linked recessi ve
62 mg/L
lethal test
+ 3,000 R
X-rays
Drosophila melanoqaster
Cadmium
5
Larvae
Reported as
1.
Dose-response reported.
Vasudev and
dominant lethal mutations
chloride
10
feeding
positive
2.
Confirmation of these
Krishnamurthy (1979)
20 ppm
results in an independent
laboratory would be of
interest for comparative
purposes.
Drosophila melanoqaster
Cadmium
10-20 mg/L
5-10 days
Reported as
1.
Rationale for selecting
Sahalina
sex-linked recessive
stearate
(feeding
negative
the dosage not given.
(1968)
lethal test
larvae)
50-100 mg/L
10-12 days
(feeding
adults)
100 mg/L
(feeding
larvae)
3 mg/m^
(inhalation
adult)
(continued on the followiny page)
-------
Test system
Cdri'iii uin
compound
Dosage
Tredtment
per i or)
Orosophi1d melanogaster
sex chromosome loss
Cadini uni
chloride
6? ppin
ro
Drosophila inel anogaster
sex -1inked recessi ve
lethal test
Cadini uni
chlor ide
aqueous
solution
SO- ppin
Larvae
feed!nq
Poeki 1 occrus pictus
(grasshopper)
testis (mciotic
chrunosoma1)
Cadmium 0.001%
chl oride 0.01%
aqueous 0.0 b%
per animal
TABLE 3. (continued)
Kesults
C oinnio n t s
Deference
Reported as
nega t i ve
1. No data nave been
been presented.
Reported as 1. Toxicity was determined,
negative 2. Development and survival
was affected by cadmium.
Ramel and Maynusson
(19/9)
Inoue and Watanabe
(19 78)
Reported as 1. The effect may be cyto- Kuinaraswamy and
positive toxic rather than Rajasekarasetty
genet ic . ( 1977 )
2. No controls.
-------
ficant delay in the development of larvae as compared with controls. In the
sex-linked recessive lethal nutation test (Muller-5 test), only one concen-
tration of 50 rny/L (2.72 x 10~4M) was used, with no indication of mutagenic
response. The number of chromosomes tested and the criteria set for scoring
the lethals were not reported, however, and no data were presented to indicate
the sensitivity of different stages of spermatogenesis.
Ramel and Friberg (1974), using a dose of 62 mg (3.32 x 10~4M) of cadmium
chloride/L of media, which was the maximum non-lethal dose in the toxicity
test, found a delay in larval development. They also studied the induction of
sex chromosome loss. In the sex chromosome loss test, a total of 23,360 chro-
mosomes from the treated group and 28,143 chromosomes from the control group
were tested. The frequencies of sex chromosome losses were 0.3% and 0.2% for
the treated and the control groups, respectively.
The mutagenic activity of cadmium stearate was studied by Yu. A. Reva-
zova (quoted in Sabalina 1968) in Drosophila melanogaster using the sex-linked
recessive lethal test. Flies were fed a medium containing 10-20 mg (5.45 x
10~5M to 1.09 x 10"4M) and 50-100 mg (2.72 x 10"4 to 5.45 x 10"4M) of cadmium
stearate/L substrate for 5-10 and 10-12 days, respectively. The number of sex-
linked recessive lethal mutations in 805 chromosomes analyzed was 1 (0.12%) for
the 5-10 day treatment, and the number of sex-linked recessive lethal mutations
in 2,192 chromosomes examined was 8 (0.36%) for the 10-12 day treatment. When
larvae were treated with cadmium stearate concentration of 100 mg/L substrate
for 12 days and scored for sex-linked recessive lethal mutants in 380 chromo-
somes, no mutants were discovered. Cadmium stearate was also administered by
inhalation to adult flies for 32 hours (4 hours daily for 8 days). The mean
cadmium concentration was 3 mg/m^. The percentage of sex-linked recessive
lethal mutations among the 498 chromosomes was reported to be 0.2%. The con-
25
-------
tro1 frequency of sex-linked recessive lethal mutations was not provided in
the paper, "he number of chromosomes tested was not adequate in this study.
Tnis study provides no evidence of mutagenicity of cadmium in Drosophila, but
the scale of the study was too small to be considered an adequate test even if
appropriate controls were presented.
Induction of dominant lethal nutations in Drosophila melanogaster with
cadmium chloride has been reported Dy Vasudev and Krishnamurthy (1979). The
doses used were 5 (2.72 x 10"5M), 10 (5.5 x 10-&M), and 20 ppn (1.1 x 10"4M).
The frequencies of dominant lethals were 11.8%, 14.3%, and' 14.3%, respec-
tively, in 1,244, 1,375, and 1,390 eggs counted. The control frequency was
4.83% in 1,076 eggs counted. These investigators performed' the experiment
according to the procedure described by Shankaranarayanan (1967) and deter-
mined the statistical significance to be at the 5% level, although they did
not mention the type of statistical test employed. Based on these observa-
tions, this study is evaluated as an indicator of a positive response. A
comparable study in an independent laboratory would be of interest for com-
parative purposes.
Inoue and Watanabe (1978) studied the effects of cadmium chloride in the
sex-linked recessive lethal test (attac'ned-X method) in Drosophila melanogas-
ter, Oregon-R flies. In this test, the induction of mutations was measured by
the reduction in the proportion of males. The sex ratio (0.528) in the experi-
mental group treated with 50 ppm (2.72 x 10"^M) was not statistically different
from the sex ratio of controls (0.54), indicating that cadmium chloride is
nonmutagenic. The dosage selected was a maximally tolerated dose. Both posi-
tive (AF-2) and negative controls were used in the experiment.
Ramel and Magnusson (1979) failed to detect nondisjunction and sex chromo-
some loss in Drosophila following treatment of larvae with 62 ppm (3.32 x 10"^M)
26
-------
of cadmium chloride. No data were presented; therefore, this study cannot be
eval uated.
Chromosomal aberrations were observed in the testes of the grasshopper,
Poekilocerus pictus, injected abdominally with 0.001% (5.45 x 10"^M), 0.01%
(5.45 x 10"^M), and 0.05% (2.27 x 10"?M) cadmium chloride in 0.05 mL volumes
(Kumaraswamy and Rajasekarasetty, 1977 ). Stickiness of chromosomes, bridge
formation at anaphase-1, and tetraploidy at metaphase were noted. The test
cannot be considered adequate, however, because no controls were used and no
tabulated data were presented. The possibility of technical artifacts must
also be considered, particularly because chromosomal preparations were made by
a squash technique, and no controls were used.
CHROMOSOMAL ABERRATIONS IN HUMAN AND OTHER MAMMALIAN SYSTEMS
Chromosomal damage studies of cadmium, both in vitro and in vivo, are
summarized in Tables 4 and 5. A discussion of each study follows.
Studies on Human Chromosomes in vitro
Shiraishi et al. ( 1972) tested cadmium sulfide for the induction of
chromosomal aberrations in cultured human blood lymphocytes. Lymphocytes
from a normal human female were cultured for 72 hours at 37°C. At 8 and 4
hours prior to harvesting, the cultures were treated with cadmium sulfide
at a concentration of 6.2 x lO'^M. Control cultures were incubated similar-
ly, without the addition of cadmium sulfide. Three hours prior to harvesting,
cells were treated with 0.02 wg/mL of colcemid to obtain cells in the meta-
phase stage of mitosis. Chromosome preparations were made with the standard
procedure (air-drying technique) and stained with Giemsa stain. Fifty metaphase
cells were scored from each treatment group for chromosomal aberrations. The
types of aberrations described include chromatid and isochronatid breaks, and
27
-------
TABLE 4. MUTAGFN1CITY EVALUATION Of CADMIUM; IN VITRO CHROMOSOMAL AllFHHATIONS
lest system
Human
blood
lymphocytes
Human
bl ood
psj lymphocytes
.CO
Human
blood
Iymphocytes
Gq stage
Duration of
cultures
n hr
48 hr
12 hr
Human 48 hr
blood
lymphocytes
Cell Ii ne 24 hr
una and MCA5
48 hr
Cadmium
compound
Dosage
Durat i on of
treatment
Activat ion
system
ResuIts
Comments
Cadmium
sulfide
(solvent not-
specified)
6.2xl0"2
ug/mL
4 hr
8 hr
None
Reported as
pos i 11ve
Cadmium
chloride
aqueous
solution
Cadmium
chloride
aqueous
solut i on
Cadini urn
acetate
aqueous
solut i on
5xl()"6M
24 hr
48 hr
7? hr
None
Reported as
negat i ve
None
4b hr
24 hr
Reported as
negat i ve
Reported as
negative
1. Ulood lymphocytes were
derived from only one
individual.
2. Only bO metaphases for
each end point were scored.
3. Only one concentration of
the test compound was used.
1. Data were not provided.
2. Concentrations of the
pest compound not
specified.
10"8
10"7
10"[?
l(Tb
io-"m
3 hr
None
Reported as
weakly positive
1, No dose-response.
2, Experiments were not
repeated to confirm
the positive finding.
Reference
Shiraishi
et al. (1972)
1. Toxicity was determined. Dekundt and
2. Appropriate dosages used. Deminatti
3. 100 metaphases scored for (1978)
each poi nt,
Paton and
Allison
(1972)
Gasiorek and
Uauchi nger
(1981)
(continued on the following page)
-------
IAHLE 4. (continued)
Test system
Duration of
cultures
Chinese hamster
"Hy" cell line
Ch inose hams te
CHO cell I i ne
PO
kO
Mouse mammary
carcinoma
FM3A
Ca«i"n I U'ii
C o/npourid
Cadmium
sul fate
aqueous
solution
Dosd'je
10-4M
Duration of
treatment
Act ivation
system
Cddmiu.n
chl undc
in 0.1 HHC1
2xlO"0M
1 hr and
ha rvested
at 2,4,6,8,
10,12,1b, 18,
21,24,27,30,
days
12, 24, 26,
and 48 hrs
None
None
Kesults
Cadmi urn
chloride
aqueous
solution
6.4xl0"5n
3.2x1()-5m
I.0x10-5M
24 and 48 hrs
24 and 4B hrs
24 and 48 hrs
None
Reported as
positive
Reported as
positive only
in the presence
of newborn cal f
(bovine) or
human serum.
Negative in the
presence of
fetal calf serum.
Reported as
negative
Comments
1.
2.
3.
Colchicine-iike effect
The type of sera has
not been speci f i ed.
Protocol for chromosome
preparation has not been
speci f led.
Threshold dosaye was
establi shed as lxl0_1M
for chrcmosomal
aberration with
newborn calf and
human sera.
Classification of
aberration types not
given.
Active only in the presence
of fetal calf serum.
1. 6.4x10"^ too toxic .
2. Experiments were
repeated to confirm
the results.
Reference
Rohr and
BducM1nger
(1970)
Deaven and
CampbeI I
(\W0)
Umeda and
Ni shimura
(1979)
-------
TABLE 5. MUTAGENIC!IY EVALUATION 01 CADMIUM: IN VIVO CHROMOSOMAl ABI.RRATIONS IN HUMANS
Species
Number of
exposed
Number of
cont rols
Human
blood
lymphocytes
Human
bl ood
Iymphocytes
Human
bl ood
OJ lymphocytes
O
14
40
13
7. \?
Human
blood
lymphocytes from
cadmi um-exposed
workers
6, 9
Duration of
exposure
3 months-
26 years
6 weeks-
34 years
Not yiven
Duration of
culture
(hrs)
48
48
7?
Number of
metaphases
analyzed
5-?4 years 48-72
2800
(exp)
900
(control)
3/40
(exp)
1243
(control)
156/
person
100/
person
Resu1ts
Reported as
neyat i ve
Reported as
positive
Reported as
negative
Comments
1. Sample size too small.
Reported as 1. Study was conducted
negative following yood cytogenetic
procedure.
The hi story of the
patients, including
exposure to other
druys » was not
-------
TABLE b. (continued)
Species
Mouse bone marrow
Mouse ini cronuc 1 eus
Source of
eel Is
Cadmi urn
compound
Bone marrow Cadmium
eel 1 s chl on dc
Hone marrow Cadmium
cells chloride
Dosage
Duration of
treatment Results
Comments
0.06%
in diet
30 days
Reported as
negati ve
1. Good technical
procedure.
2. Data were anlyzed
statistical ly.
4 mcj/k
-------
I AIM I S . (cont i nui'd )
SpPi'. i ps
Miii'
dominant Irthals
Sourtt* ul
COlls
,kIhi i uin
i.ompound
Von: dead (adnii uin
proport mnjl ( hloridr
imp)anl s in
• thp utems
PON.IijO
Dut dli on nt
I n\it ttienl
1. /'.) my/kt| 1 <1,iy
Hl'MlllS
( umnonl 'j
Reported its
MP'Jrlt 1 Ve
). A) 1 c.p 11 st ayes
not sampled.
Ret L*r crir e
bi1 Ii avod and
I eonard (1 y7'_>)
Mice ( f ohm Ip)
dominant lethal'.
Score dead
.i rul I i vr
implants in
thp uterus
I'ailnii inn
i h loridi-
2 my/kg
U.1) i (j 4.
day.
Reported as
nryat i ve
1. Lxpenments repeated
three times.
Suter (197c_>)
Mi i o her i t , 7/ hr Rpported as Watanabp and
chloride 3.0 mg/ky posit.ivp tor Fndo (1982)
anpup1oidy
-------
symmetrical and asymmetrical translocations. Increased incidences of chrono-
sonal aberrations, 52% in the 4-hour treatment group and 60% in the 8-hour
treatment group, were noted over tne control value of 0%. This study utilized
a blood sample from only one donor; the history of the donor was not discussed.
Since only one concentration of the compound was used, no dose-response rela-
tionship is available for this study. In addition, no information was given on
the solvent used to dissolve the test compound, and the number of cells scored
was small. For these reasons, and because no indication as to the reproduci-
bility of the results was given, this study cannot be regarded as strong evi-
dence for the cytogeneticity of cadmium.
Dekundt and Deminatti (1978) investigated the mutagenic effects of cadmium
chloride in cultured human lymphocytes. They treated two batches of cell cul-
tures and analyzed chromosomes as follows: One batch of cultures was treated
at 0 hours and at 24 hours after the initiation of cell cultures with 5 x 10"^M
and 5 x 10"^M cadmiun chloride. Chromosome preparations were made 48 hours
after the initiation of the culture, using the standard air-drying technique.
In cultures treated 0 hours after the initiation, one hundred metaphases were
scored for each dose. There were 3% aberrations (1% aneuploidy, 2% gaps) at
5 x 10~^M, and 7% aberrations (5% aneuploidy, 2% gaps) at 5 x 10"^M. In cul-
tures treated 24 hours after the initiation of cultures, there were 5% aber-
rations (1% aneuploidy, 4% gaps) at 5 x and 2% aberrations (1% gaps and
\% fragments) at 5 x 10"^M. The control aberration frequency was 5% (3% anue-
ploidy, 2% gaps). The other batch of cultures was treated at 0 hours and 24
hours, and chromosome preparations were made 72 hours after the initiation of
cell cultures. One hundred netaphases were analyzed for aberration frequencies
from each group. In cultures treated at 0 hours, there were 4% aberrations
(3% aneuploidy, 1% gaps) at 5 x 10"^M, and 3% aberrations (3% aneuploidy) at 5
33
-------
x 10~6m. Cultures treated acter 24 hours of initiation exhibited 6% aberra-
tions (2% aneuploidy, 1% fragment, 3% gaps) at 5 x 10~^M, and 4% aberrations
(1% aneuploidy, 2% gaps) at 5 x 10"^M. The control frequencies were 1% aneu-
ploidy and 1% gaps. The first batch of cultures exhibited aberration frequen-
cies similar to the control levels. The second batch of cultures, treated only
24 hours after the initiation, exhibited aberration frequencies two to three
tines above the control levels. These aberrations occurred mostly in the form
of aneuploidy and gaps. The significance of chromosomal gaps is not yet under-
stood, and they nay not represent true chromosomal aberrations because of their
tendency toward restitution. Furthermore, the slight increase in the incidence
of aneuploidy may be due to technical difficulties, such as the scattering of
chronosones during the preparation of slides, which tends to result in uneven
distributions of cells.
Paton and Allison (1972) exposed human lymphocyte cultures and cultures of
the establisned human cell lines W138 and MRC5 to at least two concentrations
(not specified) of cadmium chloride. The duration of treatment was 48 hours
for lymphocytes anc 24 hours for W138 and MRC5. Chromosomal preparations from
100-200 cells were analyzed for aberrations. No aberrations were recorded in
treated cells, but because the actual data from the experiment were not given,
the study cannot be critically evaluated.
Gasiorek anc 3aucninger (1981) exposed unstimulated human blood lympho-
cytes (G0) in 1 nl quantities to 10"4, 10"^, 10"^, 10"^, and 10"^M of cadmium
acetate for 3 ho^rs. The cells were washed free of cadmium acetate and grown
in medium containing fetal calf serum and PHA for 48 hours at 37°C; chromosome
preparations we^e made with the standard air-crying technique. Chromosome
analysis of 200 cells per treatment indicated a dose-related increase in the
incidence of chromosome gaps. The frequencies of gaps were 0.16U, 0.115,
34
-------
0.135, 0.085, and 0.055 per cell, respectively, for the above doses, as com-
pared to the control frequency of 0.058 per cell. Data were analyzed by the
Mann-Whitney rank U-test to compare the incidence of chromosome changes in
different samples (significance taken as p < 0.05). The frequencies of struc-
tural aberrations (chromatid deletions and acentric fragments) were 0.025,
0.010, 0.005, 0.020, and 0.010 per cell, respectively, for the same doses,
whereas in controls the frequency of structural aberrations was 0.005 +_ 0.005
per cell. Analysis by Mann-Whitney rank U-test indicated that structural
chromosome aberrations were significantly higher than in controls, although no
dose-response relationship was evident. No metabolic activation system was
used. Sufficient numbers of metaphases (200 per dose) were scored, and a
standard protocol was employed. Although these data suggest a mutagenic
response, the lack of a dose-dependent response makes it important that the
results of this experiment be confirmed in another study.
Studies on Rodent Chromosomes in vitro
Rohr and Bauchinger (1976) studied the effects of cadmium sulfate in the
Chinese hamster cell line "Hy" using three types of experiments. In a long-
term experiment without recovery, cells were exposed to cadmium sulfate at
concentrations of 10"® to 10"^M. Chromosome preparations were made following
treatment of cells for 16 hours with 0.2 ug/mL of colecemid and hypotonic
solution. The 16-hour time period was chosen in order to analyze the cells
after exposure during a whole cell cycle. Because concentrations of lO'^M
were toxic to cells after 16 hours of exposure, chromosome analysis could not
be made. In a short-term experiment without recovery, cells were treated only
for 3 hours at a concentration range of 10"® to 10"^M, and chromosome prepara-
V,
tions were made without the addition of colcemid and hypotonic solution. This
35
-------
experiment indicated a typical stathmokinetic effect (spindle inhibition)
similar to that caused by colcenid. The mitotic index increased with higher
concentrations of cadmium sulfate. In a short-term experiment with recovery,
a concentration of 10-^M was chosen, and cells grown on coverslips were ex-
posed for 1 hour. Cells with coverslips were washed free of cadmium sulfate,
transferred to fresh medium, and grown for 2 to 33 hours. Chromosome prepa-
rations were made at 2, 4 , 6, 8, 10, 12, 15, 18, 21, 24, 27, 30, and 33 hours
after the cells were transferred to the test medium. In all, 500 cells were
scored for each recovery period. The incidences of aberrations (0.2 to 0.6%
structural and 2.4 to 3.7% numerical) after 2 to 12 hours of recovery were
similar to control levels (0.1% structural and 2.4% numerical). Between 15
and 21 hours, the structural anerrations ranged from 10.2% to 22.8%, and the
numerical aberrations ranged from 3.0% to 4.9%. The aberration frequencies for
the interval of 24 to 33 hou^s were lower than for the interval of 15 to 21
hours. During this period {24-33 hours), tne structural aberrations ranged
from 1.2 to 4.4%, and the numerical aberrations ranged from 7.8% to 10.3%
(2.4% in controls).
The significance o* this study is tnat cadmium was found to induce numer-
ical chromosomal aberrations by interfering with spindle function. Numerical
chromosomal aberrations have been well documented in many forms of cancers.
Many chromosomally fragile syndromes, such as Fanconi's anemia, are predis-
posed for cancer induction.
Deaven and Campbell (1980) studied the effects of cadmium chloride on
chromosomes in CH0 cells grown in the presence of bovine serum and fetal calf
serum. A concentration of 2 x 10_5f1 cadmium produced 17, 26, 62, and 74%
damaged cells, respectively, at 12-, 24-, 36-, and 48-hour analyses of meta-
phase chromosomes. However, the presence of fetal calf serum and 2 x 10_6m
36
-------
cadmium chloride did not induce growth inhibition or chromosome aberrations.
According to these investigators, fetal calf serum appeared to protect the
cells from the damaging effects of cadmium, whereas newborn calf serum and
human serum actively transported cadmium ions into the cell nuclei, thus
damaging the chromosomes. These authors also examined the frequencies of
sister chromatid exchanges (SCEs) in cells grown in F-10 containing 15% new-
born calf serum at a concentration of 4 x 10~?M cadmium chloride (low to
marginal toxicity). The SCE rate was not elevated above control levels (10
SCEs/cell). The range of SCEs was 2 to 18 for cadmium-treated cells, and the
range for controls was 4 to 19 per cell. This study is assessed as inconclu-
sive for the reason that the exact role of serum in causing chromosome aber-
rations is still not known. The importance of these data resides in the fact
that virtually all other studies have failed to consider the potential impor-
tance of the choice of serum in such experiments.
Umeda and Nishimura (1979) investigated the clastogenic effects of cadmium
chloride in FM3A cells derived from C3H mouse carcinoma. Cells were grown in
Eagles minimal essential medium supplemented with 10% oovine serum. Cells were
exposed to 6.4 x 10'^, 3.2 x 10"^, and 1.0 x lO'^M of aqueous cadmium chloride.
After 24 and 45 hours of exposure, chromosome preparations were made and ana-
lyzed. One hundred metaphases were scored for each dose. No significant
increase in the aberration frequency was noted in treated cultures as compared
to control cultures. There were no metaphases in cells treated with 6.4 x
10"5M either at 24 hours or at 48 hours--an indication of toxicity. At 3.2
x 10~5m tne aberration frequencies were 2% and 3%, at 24 and 48 hours respec-
tively. At the lowest concentration of 1.0 x 10~5, the aberration frequen-
cies were 1% each for the 24- and 48-hour treatments. The control cultures
exhibited 2% aberrations at 24 hours and 1% aberrations at 48 hours. Experi-
37
-------
ments were performed using accepted procedures. Three concentrations of the
test compound were used, and 100 metaphases were scored for evaluation.
Zasukhina et al . ( 1977) reported increased aberration yields in rat
embryos exposed to virus and cadmium chloride. Rat embyro cultures were in-
fected with Kilhman virus, and cadmium chloride (3.5 x 10"®M) was then intro-
duced into the cell cultures. Chromosome preparations were performed 24 hours
after the infections. Examination of inetaphase cells revealed a 10% aberration
rate as compared to a rate of 2% in controls. In control cultures infected
with virus only, the aberration frequency was 6%, and in cultures treated with
cadmium chloride only, the aberrations frequency was 3%. These results indi-
cate that cadmium chloride enhances virus-induced chromosomal aberrations. The
researchers also studied the effect of cadmium chloride on DNA; they reported
cadmium chloride-induced degradation with evidence for induction of nonrepara-
ole DNA synthesis.
Studies on Human Chromosomes in vivo
Shi rai shi and Yoshida ( 1972) and Shiraishi ( 1975) obtained markedly
positive results from Japanese Itai-ltai patients. The Itai-Itai disease is
believed to be induced by cadmium contamination. Analysis of blood lymphocytes
from 72-hour cultures derived from these patients exhibited a high rate of
chromosomal aberrations (26.7%) compared to the aberration rate in controls
(2.6%). Blood cadmium levels were not given. The exposure parameters used in
this study are presented in Table 5.
The results obtained by Shiraishi and Yoshida (1972) and Shiraishi (1975)
contradicted the results obtained by Bui et al. (1975), who performed chromo-
somal analysis in four Itai-Itai patients (Dlood cadmium level 15.5-28.8 ng/g),
five Swedish workers exposed to cadmium (blood cadmium level 24.7-61 ng/g),
-------
four Japanese controls (blood cadmium level 4.4-6.1 ng/g), and three Swedish
controls (blood cadmium level 1.4-3.2 ng/g). The incidences of aberrations
after 72 hours of culture were 2.3% numerical and 6.6% structural aberrations
in the Itai-Itai patients, as compared with the Japanese controls, in which
frequencies of 4.5" numerical and 6.0% structural aberrations occurred--a
finding which indicates that no differences existed between the controls and
the Itai-Itai patients. In the five Swedish workers exposed to cadmium, chro-
mosomal aberration incidences were 1.0% numerical and 2.0% structural aberra-
tions, while in the three Swedish controls the frequencies were 0.7% numerical
and 4.7% structural aberrations, indicating nonmutagenic responses.
The discrepancy between the results of Shirashi and Yoshida (1972) and
Bui et al. (1975) in Itai-Itai patients could possibly be due to factors other
than exposure to cadmium chloride, such as the time of initiation of cultures
after the blood was drawn. In the experiment of Bui et al., the subjects were
not exposed to drugs and X-rays, nor did they suffer from viral infections at
the time of venipuncture. These factors were not controlled for in the study
by Shirashi and Yoshida.
Dekundt et al. (1973) investigated the incidence of chromosomal aberra-
tions in 14 workers who had been exposed to zinc, lead, and cadmium in a zinc
sine 1 tiny plant. The workers were classified into three groups based on degree
of exposure. Group 1 consisted of five workers who had been exposed to high
levels of zinc (concentrations not specified), low levels of lead (1% w/w of
the mineral), and cadmium (concentration negligible). Group 2 consisted of
five workers who had been exposed to dust containing high levels of all three
metals: zinc (concentration not specified), lead (4% w/w), and cadmium (1%
w/w). Group 3 consisted of four workers who had been exposed to mud and dust
containing high levels of lead (60% w/w) and cadmium (1% w/w). The control
39
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group consisted of three normal individuals. Chromosomal analysis from blood
lymphocytes cultured for 72 hours indicated 3.87%, 1.6%, and 2.76% aberrant
cells, respectively, in groups 1, 2, and 3, while the control frequency was
1.55%. Since the incidence of aberrations in group 3 was less than that in
group 1, it does not appear that cadmium contributed to the frequency of aber-
rations in this study. The authors' analysis of their data using the t-test
also indicated that cadmium exposure did not induce a significant increase in
the frequency of aberrations. Blood cadmium levels were not determined in this
experi ment.
Bauchinger et al. (1976) studied 24 workers (25-53 years of age) exposed
to lead (mean blood lead level 1 ± 7 _g/100 riL) and cadmium (mean blood cad-
mium level 0.40 ± 0.27 yg/mL). The workers were exposed to these metals for
approximately 3 to 6.5 years at a smelting plant. Of the 4,800 metaphases
scored from lymphocytes cultured for 48 hours, an increase in both chromosomal
and chronatid-type aberrations (1.354 ± 0.994%) was noted, in comparison with
an aberration 'requency of 0.467 _+ 0.916% in 1,650 metaphases derived from 15
controls (Tiean blood cadmium level 0.15 -g/mL). The authors point out that
"the observed chromosome aberrations cannot be causally related to cadmium
because the workers were also exposed to lead and zinc." Dekundt and Leonard
(1975) reported a significant (p < 0,02) increase in the incidence of "complex
chromosomal aberrations" in a group of 23 men exposed to high levels of
cadmium and lead (23.5 to 75.9 ug/100 mL), as compared with controls.
0'Riordan et al. (1978) studied chromosomal aberrations in blood lympho-
cytes from 40 workers exposed to cadmium salts (chemical names not specified,
mean blood cadmiun level 1.95 ug/100 ml range < 0.2 to 14.0 pg/100 mL) for
a period of 6 weeks to 34 years. In 3,740 cells examined from these workers,
four chromatid interchanges were observed. In the control population of 1,243
40
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cells derived fron 13 normal subjects (mean blood cadmium level less than 0.2
uy/'100 ml. in 8 donors and 0.6 to 2.9 uy/mL in 5 donors), no aberrations were
observed. Since data were pooled from all of the 40 workers studied, it is
not clear whether the four chromatid interchanges came from one exposed
worker or from more than one worker. The occurrence of chromatid exchanges,
thouyh small in number (4/3,740 cells), does not necessarily indicate a nega-
tive response, but does indicate that the study should be considered inconclu-
sive.
Most of these studies of smelting plant workers reflect mixed exposures
to cadmium and to other metals such as zinc, lead, chromium, and nickel.
Since smelters commonly process relatively crude materials, exposure to these
other metals cannot be eliminated as possible contributors to the observed
effects.
Studies on Roaent Chromosomes in vivo
Dekundt and Gerber (1979) investigated the in vivo cytogenetic effects of
cadmium chloride (3.27 x 10~?M, 0.06%) in mice. Mice were maintained on a
standard diet (1.1% calcium) or on a low-calcium diet (0.03%) for one month.
In both cases the diet was supplemented with cadmium chloride. Cadmium
chloride did not induce chromosomal aberrations in bone marrow cells signifi-
cantly above the control level either in the normal or in the low-calcium diet
groups. The frequency of aberrations in animals treated with cadmium chloride
that were given the standard diet (1.1% calcium) was 2.20%, and the frequency
in animals treated with cadmium chloride that were given the low calcium diet
(0.03%) was 1.60%. The control frequencies were 1.8% and 2.0%, respectively.
The results indicate that cadmium chloride does not induce chromosomal aberra-
tions in mice by this route of exposure.
41
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Micronucleus Assay
The micronjcleus assay is based on the fact that chromosome fragments
induced by mutagenic chemicals are unable to segregate normally due to lack
of centromeres during cell division, and form small nuclei or micronuclei in
daughter cells. Heddle and Bruce (1977) studied the ability of cadmium
chloride to induce micronuclei in the mouse. Three groups of mice (F^ of
C575L/6X C3H/He), each group containing three animals, were given daily
intraperitoneal injections of cadmium chloride for 5 days with total doses of
1, 6, and 16 mg/kg, respectively. Mice were sacrificed, bone marrow smears
were prepared, and 333 polychromatic erythrocytes from each mouse were scored
for the presence of micronuclei. No increase in the incidence of micronuclei
was observed. In this study, 1,000 cells were analyzed for each dose group
(333 cells from each of 3 mice). The spontaneous frequency of micronuclei was
0.5%. An observation of 1% over the control value was considered a positive
response. According to these authors, the frequency of micronuclei in the
experimental groups did not differ from tne control level. These results are
presently considered to be inconclusive. The data snoulti be confirmed with
larger numbers of animals (10 per dose group) and analyses of at least 2,000
polychromatic erythrocytes per dose group.
Dominant Lethal Assay
"""ne ability of cadrr jm chloride to induce dominant lethal mutations, which
result in the death of fetuses during various stages of development, has been
investigated (Epstein et al., 1972; Gilliavod and Leonard, 1975; Ramaiya and
Pomera^tseva, 1977; Suter, 1975; Sutou et al ., 1980 a, b).
Epstein et al. (1972) evaluated tne dominant lethal effects of cadmium
chloride in ICR/Ha mice. Groups of seven or nine male mice, 8 to 10 weeks of
42
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age, were injected int^-aperitoneal ly with 1.35, 2.7, 5.4, and 7.0 mg/ky of
cadmium chloride in distilled water. Treated males were bred with virgin
females 8 to 10 weeks of age. Each male was allowed to mate with three virgin
females per week for 8 weeks. Mated females were sacrificed on the 13th day
and analyzed for dead (dominant lethals) and live implants. According to
these authors, cadmium chloride did not induce a statistically signficant
increase in dominant lethal mutations over the control value. This study
sampled all germ cell stages, spermatozoa, spermatids, spermatocytes, and
sperinatogoni a.
Gilliavod and Leonard (1975) investigated the dominant lethal effects of
cadmium chloride in another strain of mice, BALB/c. One dose of 1.75 mg/kg
cadmium chloride was injected into male mice (11-13 weeks of age) through the
intraperitoneal route. The treated males were bred with three virgin females
every week for 3 weeks. The mated females were sacrificed on the 10th day,
and the number of corpora lutea and dead and live implants were counted and
compared with controls. No dominant lethal effects were observed in treated
or control groups.
These investigators treated the parent male mice with only one acute dose
of the test compound. Furthermore, they bred the treated males with normal
females for only 3 weeks, which is too short a period of time in which to
sample stages of spermatogenesis. The standard method of performing a dominant
lethal test is to breed the treated males for 8 weeks. For the above reasons,
this report is judged to be inconclusive.
Suter (1975) studied the mutagenic effects of cadmium chloride using the
dominant lethal assay in female mice (F^ progeny of C3H and C57BLA). According
to this investigator, cadmium chloride had no dominant letnal effects in female
mice. Female mice of tne Fi (10 x C3H) stock were injected intraperitoneally
£3
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with 2 mg/kg cadmium cnloride, exposing the germ cells (oocytes) at the dic-
tyate stage of development, and were bred with untreated males for 0.5 to 4.5
days postinjection. Mated females, as evidenced Dy the vaginal plug, were
sacrified 12-15 days later, and the numbers of corpora lutea, total implants,
living implants, and percent of dead implants per female were determined. No
differences were noted between the treated and control groups. In the treated
group, the frequencies of corpora lutea, total implants, living implants, and
dead implants per female were 8.2, 7.8, 6.9, and 6.9% respectively, as compared
to control frequencies of 7.6, 6.8, 6.4, and 6.1% per female.
Ramaiya and Pomerantseva (1977) investigated the mutagenic effect of
cadmium chloride using the dominant letnal test. F} hybrid mice (CBA x C57BL)
aged 2.5 to 3 months were selected *or these studies. Males were given a
single intraperitoneal injection o* aqueous cadmium chloride solution. Three
doses, 1.0, 2.C, and 4 mg/kg, were employed. LD5Q was determined to be 6.9
ny/kg. Treated males were mated with untreated females for a period of 6
weeks, covering the entire spermatogenic cycle. Dominant lethals, as noted by
preimplantation and postimplantation losses and the ratio between the dead and
live implants, were recorded. No siynificant (p > 0.01) increases in the
Gomirant letnal frequencies were recorded. These results are reyarded as
negative since the authors followed appropriate protocols, the dosage selection
was based on LDcg, and the data were analyzed statistically.
From the above studies it appears that cadmium chloride has no mutagenic
potential as measured by the mammalian dominant lethal test. However, the
exact nature of the damage that results in dominant lethal effects is not known.
The mammalian dominant lethal test is not considered to be a sensitive test for
detecting all types of mutagens (Russell and Matter, 1980) because of the high
spontaneous levels of dominant lethal events that occur during development.
44
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Heritable Translocation Assay
Gilliavod ana Leonard (1975) evaluated the mutagenic effects of cadmium
chloride in BALB/c nice using the heritable translocation assay. Male nice
(number not specified) were treated with 1.75 my/kg of cadmium chloride in-
traperitoneal ly , and each treated male was bred with three untreated virgin
females once weekly for 3 weeks. The spermatocytes of the resulting 120
nale progeny were analyzed for the presence of heritable chromosomal trans-
location by standard cytogenetic methods. No evidences of heritable trans-
location were noted in the spermatocytes of F]_ males. This portion of the
study is regarded as inconclusive for the following reasons: Only a single
concentration of cadmium chloride was used; treated males were mated for only
3 weeks instead of for 8 weeks; and no experimental controls were used.
Gilliavod and Leonard (1975) also investigated the mutayenic effects of
cadmium chloride in BALB/c mice using the spermatocyte assay. Males in groups
of 10 were treated with 0.5, 1.75, and 3.0 my/kg of cadmium chloride intra-
peritoneal ly . After 3 months, treated males were sacrificed and spermatocytes
(100 cells per animal) in the testes were analyzed for translocations that may
have been passed on from treated spermatogonia. No translocations were found
in either treated or control animals. The spermatocyte assay is not a very
sensitive test and is not commonly employed in mutagenicity tests; therefore
this portion of the Gilliavod and Leonard (1975) study is also regarded as
i nconclusi ve.
Chromosomal Nondisjunction (Aneuploidy) in Whole Mammals
The effects of cadmium chloride on oocytes of mice (Shimada et alf, 1976),
on oocytes of Syrian hamsters (Watanabe et al., 1979), and on spermatocytes of
mice (Gilliavod and Leonard, 1975) have been investigated.
45
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Shimada et al. (1976) induced superovulation by injecting female mice,
ddy strain, witn 5 international units (iu) of pregnant mare's serum (PMS)
followed 48 hours later by 5 iu of human chorionic gonadotrophin (HCG). '"lice
were given 3 ng/
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cadmiun in inducing numerical chromosomal abnormalities in mammalian oocytes.
Watanabe and Endo (1982) analyzed the chromosomes of the blastocysts from
nice treated with cadmiun at the metaphase 1 stage of oogenesis to determine
the effects of cadmium from the oogenesis stage to the preimplantation stage.
Female virgin mice of 8-12 weeks of age were induced to superovulate by admin-
istering 5 iu of pregnant mare's serum (PMS) followed in 48 hours by 5 iu of
of human chorionic gonadotrophin (HCG). Three hours after HCG administration,
the animals were injected subcutaneously with 1.5 my or 3.0 mg/kg body weight
of cadmium chloride. Shortly after the treatment with cadmium chloride, they
were mated with males of the same age group. About 80 hours after mating,
the females were injected intraperitoneally with 4.0 mg/kg of colchicine, and
2 hours later the animals were sacrificed, blastocysts from the uterus were
placed into Hanks' balanced salt solution, and chromosome preparations were
made. Aneuploid cells were found in 8 out of 65 blastocysts from the group
treated with 1.5 mg/kg of cadmium, and 10 out of 63 blastocysts from the
group treated with 3.0 mg/kg of cadmium, indicating that chromosomal nondis-
junctions induced in oocytes are transmitted to embryos. In the control
group, aneuploidy was found in 2 blastocysts out of 59.
All of the above studies strongly indicate that cadmium acts mutageni-
cally to alter the number of chromosomes through spindle inhibition. The
concentrations of cadmium used in these studies were similar to those that
have been used in cancer bioassays. Supporting evidence that another metal
induces chromosomal nondisjunction can be obtained from studies of methyl
mercury in Drosophila melanogaster (Ramel and Magnusson, 1979) and in Syrian
hamsters (Mailhes, 1983). The occurrence of aneuploidy is well documented in
cancer cells. Many chromosomally fragile syndromes, such as Fanconi's anemia,
ataxia telangiectasia, and Bloom's syndrome, have been known to be predisposed
-------
for cancer induction. Colchicine, the well-known spindle inhioitor, has been
used clinically 'for the treatment of gout. There have been reports that these
patients carry numerical chromosomal abnormalities in their blood lymphocytes
(Ferreira and Buoniconti, 1968). Epidemiologic studies at the National
Cancer Institute (Dr. Robert Hoover, personal communication) are presently
beiny conducted to determine the susceptibility of these types of patients to
career.
Sperm Abnormality Assay in 'Mammals
Meddle and Bruce (1977) evaluated the effects of cadmium by means of the
sperm abnormality assay. The sperm abnormality assay is based on the observa-
tion of increased incidence of sperm heads with abnormal shapes as a result of
exposure to cnemica] mutagens (Wyrobek and Bruce, 1975). Three groups of mice
of the genotype (C57BL/6 x C3H/He)F^, each consisting of three mice, were given
daily intraperitoneal injections o£ cadmium chloride for 5 days with doses of
1, 4, and 16 mg/kg, respectively. After sacrifice of the animals by means of
cervical dislocation, sperm suspensions were made from sperm collected from the
cauda epididymis. Tne sperm suspensions were stained with 1% eosin-Y in water,
anc smears were dried and mounted under coverslips. One thousand sperm heads
were evaluated for morphological abnormalities. The background frequency of
sperm head abnormalities in the control populations was 1%. Under the condi-
tions of the test, no increases in sperm head abnormalities were observed in
the treated group as compared to controls.
CHROMOSOMAL ABERRATIONS IN PLANTS
Levan ( 1945) reported that treatment of A11ium cepa root-tips with cad-
mium chloride induced C-mitosis. This observation was later confirmed by
Avanzi (1950), using cadmium chloride concentrations ranging from 2 x 10~^H to
48
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5 x 10-2m. Oehlkers (1953) reported that cadmium nitrate induced chromosomal
aberrations in Vicia faba. Van Rosen (1953, 1954) reported the genotoxicity of
cadmium as evidenced by chromosomal aberrations in the root-tips of plants such
as A11i um cepa, Beta vulgari s, Pi sum abysi nni cum, and Vi ci a sati va. Simi1ar
observations were made by Degraeve (1971) in Horedeum sativum and by Ruposhev
and Garina (1977) in Crepis capillaris. Aberrations reported in these studies
were of both chromatic and chromosomal types, with dose-related responses.
Since many of these studies were published in foreign languages, the present
report utilizes a summary derived from the review article published by Degraeve
(1981).
BIOCHEMICAL STUDIES INDICATIVE OF MUTAGENIC DAMAGE
Some information is available on the effects of cadmium on animals, and
although this information cannot, strictly speaking, be considered mutagenicity
test data, it may be useful in evaluating the ability of cadmium to reach and
damage the gonads. Dixon et al. (1976) reported that cadmium chloride at 2.24
mg/kg, administered intraperitoneal^, caused damage to rat testes. A single
10 mg/kg intraperitoneal injection caused selective destruction of rat testes.
Cadmium chloride, when administered intraperitoneally at 1 mg/kg, reduced the
fertility of male mice at all sperm cell stages except that of spermatozoa (Lee
and Dixon, 1973). However, single oral doses up to 25 mg/kg had no effect on
the fertility of male rats (Dixon et al., 1976), and cadmium chloride at 0.1
mg/L in drinking water for up to 90 days had no effect on the fertility of male
rats. Intraperitoneal injection of cadmium chloride at 1 mg/kg decreased the
incorporation of thymidine into spermatogonia in mice (Lee and Dixon, 1973).
These authors also observed the binding of cadmium to late spermatids in
vivo and in vitro. Friedman and Staub (1976) studied the effects of cadmium
49
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chloride on DNA synthesis in Swiss nice. Cadmium chloride at 10 my/kg inhi-
bited DNA synthesis s1' yni f i cantl y. An aqueous solution of cadnium chloride was
injected intraperitoneally at tne above dose into five male mice, and the mice
were sacrificed 3.5 hours later. Thirty minutes prior to sacrifice, mice were
injected with 10 uCi [^H] thymidine. Controls received only 10 uCi [^H] thymi-
dine. Testes were removed following cervical dislocation, DNA was isolated,
and the specific activity was determined. Cadmium chloride was found to induce
a statistically significant (p < 0.01) inhibition of [^H] tnymidine uptake
(1.90 +_ 0.58) in the testes as compared to controls (7.45 _+ 1.44).
Mitra and Bernstein ( 1977, 1973) reported that when E_. col i cultures were
exposed to 3 x 1U"^M cadmium (Cd^+), 82£ to 95% of the cells lost their ability
to form colonies on ayar plate. Analysis of DNA strands from cells treated
with variojs doses of Cd2+ indicated that there was a dose-related increase in
the breakage of sinyle-stranc DNA. These investigators believe that the loss
of viability in cadmium-treated cells is due to the single-strand DNA breakage.
Cadmium-treated cells recovered viability when grown in Cd^-free liquid medium
containing 10 rrtf-1 Hydroxyurea.
Sirover and Loeb (1976) investigated tne infidelity of DNA synthesis
Drought about by cacmiun cnlorice and cadniun acetate. Their assay measured
the perturbation ir the fiGelity of DNA synthesis in vitro caused by soluble
metal salts. Cadmium chloride ane cadmium acetate were found to decrease the
fidelity of DNA synthesis. Cadmium chloride has also been found to induce
concentration-dependent inhibition of RNA synthesis (Hoffman and Niyogi, 19/7).
SUMMARY
Cadnium has been investigated for mutagenic activity in both prokaryotic
and eukaryotic systems. Gene nutation studies in Salmonella typhimuriurn and
50
-------
E_. coli have produced inconclusive results. In yeast, gene mutation studies
have also been inconclusive. In three gene mutation studies (in mammalian
cell cultures, mouse lymphoma cells, and Chinese hamster lung and ovary
cells) marginally positive responses to cadmium were observed.
Rec-assay in Bacillus subtilis resulted in a weak mutagenic response.
In the Drosophila sex-linked recessive lethal test, cadmium was found to be
nonmutagenic. The dominant lethal test in Drosophila resulted in a positive
response with a dose-response relationship.
The results of chromosomal aberration studies in human lymphocytes from
exposed workers and human cell lines treated with cadmium have been conflict-
ing. In Chinese hamster cells, chromosomal aberrations were noted following
treatment with cadmium; however, in mouse carcinoma cells, no aberrations
were recorded in response to cadmium treatment. In rodents, treatment with
cadmium did not induce chromosomal aberrations or micronuclei in bone marrow
cells. Similarly, no dominant lethal mutations or heritable translocations
were noted in mice treated with cadmium.
The evidence that cadmium interferes with spindle formation comes from
both i_n vitro and J_n vivo studies in mammals. In j_n vitro studies using the
Chinese hamster cell line "Hy," cadmium induced an effect similar to that of
colchicine, which is a known spindle poison. Cadmium also was found to in-
crease numerical chromosome aberrations (aneuploidy) in these cells. Similar
results were obtained in studies on aneuploidy in whole mammals. In female
mice and Syrian hamsters, cadmium induced chromosomal nondisjunction leading
to aneuploidy in germ cells. A recent study demonstrated that the numerical
aberrations induced by cadmium chloride in female germ cells of mice are
inherited in the embryos.
51
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CARCINOGENICITY
Much of the evidence fo° the carcinogenicity of cadmium has been reviewed
critically in earlier documents {I ARC, 1973 , 1976 ; U.S. EPA, 1977 , 1981 ; Sun-
derman, 1977 , 1973; Hernbery, 1977 ). Th i s section updates findings mentioned
previously and discusses recent findinys not mentioned in earlier reviews.
ANIMAL STUDIES
Inhalation Study in Rats
A carcinogenicity study of cadmium administered to male Wistar rats by
inhalation was reported by Takenaka et al. (1983). The animals were placed
in a 225-liter inhalation chamber for exposure to cadmium chloride aerosol.
Aerosol was generated oy atomizing a solution of cadmium cnloride, and air-
flow through the atomizer was 0.7 L/fin. Analytical measurements of cadmium
levels we^e made by collecting aerosol samples in membrane filters in the
inta
-------
The aninals were initially 6 wee
0.05).
A dose-related increase in the incidence of primary lung carcinomas in
treated animals was evident, as shown in Table 8. The first epidermoid car-
cinoma and the first adenocarcinoma were found at 20 and 22 months, respec-
tively, after treatment commenced. Several treated rats also developed adeno-
nas and nodular hyperplasia in the lung. Metastases to the regional lymph
nodes and the kidneys and invasion into the regional lymph nodes and the heart
occurred in some rats with lung carcinomas. No lung tumors were found in
control animals,
Nonneoplastic lesions and various tumors in other organs were found in
both control and treated animals. None of these additional tumor types and
nonneoplastic lesions was significantly (p > 0.05) different among the four
groups.
The data in Table 9 show that cadmium was retained in the lungs, livers,
and kidneys of survivors for as long as 13 months after cessation of exposure.
53
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TABLE 7. AVERAGE BODY WEIGHTS OK RATS EXPOSED
TO CADMIUM CHLORIDE
Average
body weiyhts
(months after the beyinniny of
the inhalation)
0
3
7
10
12
15
Exposure groups
Control
135.2a
333.3
385.2
411.6
422.9
425.1
(4.8)
(27.4)
(30.5)
(31.2)
(31.7)
(31.8)
12.5 uy/in3
135.1
320.9
375.3
405.2
417.2
420.0
(6.6)
(29.4)
(37.1)
(39.4)
(41.4)
(38.8)
25 iiy/in^
133.4
326.6
382.1
410.0
425.7
428.3
(6.7)
(28.6)
(32.1)
(32.8)
(35.9)
(36.1)
50 u y / in 3
133.3
323.5
375.1
403.2
417.0
422.0
(6.7)
(29.0)
(32.2)
(34.8)
(36.6)
(38.5)
18b
21
24
27
30
Control
434.9
428.2
406.2
405.7
367.3
(32.4)
(31.4)
(41.3)
(31.3)
(39.8)
12.5 uy/in3
424.6
421.8
409.5
408.5
372.5
(41.0)
(41.2)
(45.9)
(40.9)
(41.8)
25 u y / in 3
437.6
441.2
429.2
423.9
375.4
(38.1)
(37.7)
(45.9)
(37.6)
(47.8)
50 ;jy/in3
424.3
424.9
415.2
398.4
357 .8
(40.6)
(43.8)
(42.6)
(35.8)
(41.5)
aMean value (_+ S.D.).
bEnd of the inhalation.
SOURCE: Takenaka et al., 1983.
-------
TAE.I.E 8. SURVIVAL TIMES AND LUNG CHANGES OF WISTAR RATS AFTER EXPOSURE TO CADMIUM CHLORIDE AEROSOLS
Number of rats with lung adenomas and carcinomas
Concen-
t rati on
(ug Cd/m3)
Initial
no. of
rats
Survi val
time in
weeks
mean value
+ S.D.
No. of
rats
exami ned
hi sto-
logically
Adeno-
matous
proli -
ferati on
Adenomas
adeno-
epi der-
moi d
Carci nomas
combi ned
adeno- and
epi dermoi d
muco-
epi der- Total
moid (%)
Control
41
122+19
38a
1
0
0
0
0
0 0
12.5
40
119+17
39b
6
1
4
2
0
0 6(15.4%)e
25
40
125+15
38c
5
0
15f
4
1
0 20(52.6%)f
50
40
116+23
35d
3
1
14f
7
1
3 25( 71 .4'Z,)f
aTwo rats died during the first 18 months; another rat was not examined because of autolysis.
^One rat was not examined because of autolysis.
cTwo rats were not examined because of autolysis.
dThree rats died during the first 18 months; two other rats were not examined because of autolysis.
eSiynificantly different from controls (p < 0.01) X2 testing.
^Significantly different from controls (p < 1.0 x 10"^) X testing.
SOURCE: Takenaka et al., 1983
-------
TABLE 9. CONCENTRATIONS OF CADMIUM IN LIJNGS, LIVER, AND KIDNEYS OE RATS EXPOSED TO
CADMIUM CHLORIDE FOR 18 MONTHS (13 MONTHS AFTER THE END OF THE INHALATION)
C 1
CT>
Exposure yroups
Control
12.5 uy/in3
2b uy/m3
50 u y/in 3
No. of
rats
Cadmium concentrations (ug/y wet wei ght)
Lunys Livers Kidneys
dMean value _+ S.D.
SOURCE: Takenaka et al., 1983
0.03
5.6 +_ 1.0
4.7 1.5
10.4 + 4.2
0.1 + 0.1a
2.2 +_ 0.6
5.9 +_ 1.5
13.5 + 3.0
0.3 +_ 0.1
13.5 + 3.2
16.4 + 3.6
33.6 + 10.7
-------
Analy5 i 5 of these tissues indicated that cadmium was absorbed and circulated
throughout the body and that, although the lung was the target organ for car-
cinogenicity, the kidney retained the largest amounts of cadmium. Increases
in cadmium levels were dose-related in liver in all treatment groups and in
lung and kidney in the mid-dose and high-dose groups. Pathologic changes
apparently were not observed in kidney and liver, thus suggesting that the
cadmium levels found did riot have a toxic effect in these tissues.
The authors attributed their success in demonstrating the carcinogenicity
of cadmium to: 1) performance of a long-term study using cadmium chloride
aerosols that were retained at a rather high level in the lungs after cessa-
tion of exposure, and 2) continuous observation of the animals over an extended
duration (31 months). Host of the lung carcinomas were detected after the 27th
month of the study.
In a pilot study in the same laboratory, four adenomas and one adenocar-
cinoma were found in 10 rats after 18 months of continuous exposure to a cad-
mium chloride aerosol (20 ^g/m^). There was no observation period after the
18-month exposure (Heering et al., 1979). These results fit well with the
data obtained in the more detailed study conducted by Takenaka et al-. (1983).
In a recent investigation, Greenspan and Morrow (1984) showed that expo-
sure of rats to an aerosol of cadmium chloride at 5 mg cadmium/m^ for 30
minutes reduced the number of particles phagocytized by the lung macrophages
for up to 8 days. At an airborne concentration of 1.5 mg cadmium/m^ the
phagocytization of particles was stimulated. The adhering properties of the
phagocytes were reduced at both exposure concentrations for as long as 12
days. The potential of cadmium chloride for altering the normal phagocytic
activity could explain why Takenaka et al. (1983) were able to produce such
a marked carcinogenic response.
57
-------
In an earlier study, Hadley et al, (1979) reported one lung tumor amony
34 nale Wistar rats one year after a single inhalation exposure to 60 yg/L
of cadmium oxide for 30 minutes. While this regimen was not adequate for a
determination of carcinogenicity, it is noteworthy that the authors of the
study observed testicu1ar alterations after this treatment. They pointed.out
that these changes occurred at doses lower than the mininum effective dose
required to induce degeneration with soluble cadmium salts given parenterally
if no more tnan a 20% pulmonary retertion is assumed (1.5 yg cadmium/ky for
inhalation versus 5-10 ymoles cadmium/ky).
Oberdoerster et al. (1979) compared the lung clearance of cadmium oxide
and cadmium chloride after a 45-minute exposure to airborne concentrations
of 930 yy/^n^ and 750 yg/m^, respectively. The aerodynamic mass medium
dianeters were 0.38 and 0.46 ux. for cadmium chloride and cadmium oxide,
respectively. Despite the differences in chemical solubility, the long-term
clearances were equal. The only difference was that cadmium oxide was cleared
more rapidly in the first 8 days after exposure. The authors suggested that
this might oe due to bronchial clearance mechanisms for the less soluble
cadmium oxide particles.
Intratracheal Studies in Rats
Sanders and Mahaffey (1984) evaluated the carcinogenicity of cadmium
oxide in male Fiscner 344 rats. Four groups of 46 to 50 rats each were
treated as follows: Group 1 (untreated controls) received one intratracheal
instillation of 0.9% sodium chloride solution (the dosing vehicle); Group 2
was given an intratracheal instillation of 25 u g cadmium oxide when 70 days
old; Group 3 received intratracheal instillations of 25 ug cadmium oxide when
70 and 100 days old for a total dose of 50 py; Group 4 was given intratra-
58
-------
cheal instillations of 25 hg cadmium oxide when 70, 100, and 130 days old
for a total dose of 75 ug. The authors stated that the 25-yg dose was
75% of the LD5q by the route of administration used. Instilled cadmium oxide
Had a count median diameter of 0.5 un. Tne animals were allowed to survive
until spontaneous death. All animals were necropsied, organs were weighed,
and tumors, lesions, and major tissues and organs fron all of the rats (except
12 lost due to autolysis or cannioalism) were examined histopathologically.
Median survival tines were 793, 824, 785, and 788 days for Groups 1, 2,
3, and 4, respectively. Survival times and organ weights (body weights were
not obtained) were similar (p > 0.05) between control and treated groups.
Statistical analysis of tumor data by life-table and contingency table
methods revealed no significant (p > 0.05) differences among the four yroups.
Lung tumor findings consisted of adenocarcinomas in two rats of 48 in Group 3
that were killed at 880 days. However, when all cadmiun oxide-treated groups
were pooled and tested by life-table methods for differences in tumor inci-
dences from the controls (Group 1), a statistically significant (p = 0.043)
increase in mammary tumors was observed. In addition, the frequency of rats
with three or more tumors was increased in the high-dose group (p = 0.044).
Since cadmium has been shown by Chandler et al. (1976) to inhibit testosterone
release and increase circulating levels of luteinizing hormone, a possible
tumor promoter, the finding of increased mammary tumors in the males is more
than plausible when one considers the rather high background rate normally
found in female rats of this strain.
While cadmium, as cadmium oxide, did not produce lung tumors under the
conditions of this study, the protocol used may not have been as sensitive an
indicator of the respiratory carcinogenic potential of cadniurn as would a de-
sign that included lifetime exposures by inhalation, particularly in reference
59
-------
to the carcinogenicity study by Takenaka et al. (1983) discussed herein.
Lung tissue was not analyzed for cadmium content in the Sanders and Mahaffey
(1984) study. However, clearance of 80% of an i intratracheal ly instilled dose
of 15 -jg -^cadmi jin oxide from the lung in nale Fischer 344 rats, with an
elimination half-life of 4 hours, has been observed (Had!ey et al., 1980).
In addition, the distributor of the cadmium within the lung was probably not
equivalent to that which would have resulted from an inhalation exposure.
Oberdoerster at al. (1980) showed, using cadmium chloride, that after a
1-hour nose-only inhalation exposure, 16-7, more cadmium was deposited in the
alveolar area as compared with intratracheal instillation. Hence, a lifetime
inhalation exposure to cadmium oxide also might have presented a stronger
challenge ''or carcinogenicity by providing a greater cumulative dose of
cadmium within target (lung) tissue.
The increase of mammary tutors observed in the Sanders and Manaffey (1984)
investigation is in keeping with the finding of relatively rapid clearance of
cadmium oxide from the lungs and translocation into other tissues following
inhalation (Hadley et al., 1979) or intratracheal instillation of cadmium
oxice (Had^y et al ., 1980). In view of the positive pulmonary findings with
cadirrum chloride (Takenaka et al . , 1983) and less severe but more marked
extrapulmonary effects (Sanders and Mahaffey, 1984; Hadley et al., 1979) and
increased extrapulmonary tissue concentrations (Hadley et al., 1980) with the
cnerically less soluble cadriun oxice, the observation of Haaley et al. (1979)
tnat airborne cadmium may constitute a potential hazard to both lung and extra-
pul'norary tissues is noteworthy. It is necessary, however, to apply caution
when the chemical (rather tnan the biological or the pulmonary) solubility of
cadniu.- salts is used n predicting the behavior of chemicals in complex
biological systems. This view is also supported by the work of Oberdoerster
60
-------
et al. ( 1979), which showed no difference i n the long-term lung clearance
rate of inhaled cadmium oxide or cadmium cnloride.
Furst et al. (1973), as part of a larger investigation of the induction
of mesotheliomas by netal in asbestos, performed a preliminary assessment of
the effects of intrathoracic injections of powdered cadmium. The test mater-
ials, suspended in saline solution, were injected into the right portion of
the thoracic cavity through the intercostal muscles. The authors indicated
that injection of 3 mg of cadmium once a month for 5 months did not produce
any tumors, but was too toxic. The rats treated with cadmium became emaciated
and lethargic. In an effort to reduce the toxicity of the cadmium, a second
group of five male and five female Fischer 344 rats were injected intrathor-
acically with 3 ng of cadmium powder and 6 mg of zinc powder in physiological
saline once a month for 5 months. The zinc reduced the overt toxicity of the
cadmium. At the end of the 10-month experimental period, 3 of the 10 exposed
rats had developed tumors, as compared to 0/20 in the controls. The first of
these tumors was evident at 120 days after the first injection. The tumors
were diagnosed as mesothelionas, probably malignant. No tumors were observed
in the rats treated with zinc only.
Injection Studies in Mice and Rats
Injection of cadmium metal or certain salts of cadmium has been shown to
produce sarcomas at the site of the injection, as well as testicular tumors
(Leydig cell, interstitial cell) in experimental animals. These studies are
summarized in Table 10. The usefulness of subcutaneous injections in determi-
ning carcinogenic potential has been discussed by a number of authors, whose
conclusions are summarized below.
Grasso and Goldberg (1966) doubted the usefulness of the technique of
61
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TABLE 10. AN I MAI TUMOR IGENfS i S INDUCTI) BY CADMIUM INJKTION
Author
Sper.i es
Compound
Route
Tumor and incidence
cn
ro
Haddow
ct al . (1961)
Heath (1962)
Heath and
Daniel (1961)
Kazantzis ( 1963)
Kazant/is and
Hanbury ( 1966)
Rats
Mice
Hooded rat.s
Hooded rats
Chester-Beatty
rats
Wistar rats
("erri 11 n-cont.n ni ny cadmium s.c.a
Cd powder
0.28 y in 0.4 inL fowl serum
0.011 y in 0.4 mL fowl scrum
Cd powder
0.014 y in 0.4 ml fowl serum
0.028 y in 0.4 ml fowl serum
25 my CdS in 0.2'j mL
physiological saline
25 my CdS in 0.25 mL
physioloyical saline
bO rmj CdS in 0.50 mL
phys i ol oyi c.a I sa I i ne
25 my CdO in 0.2b mL
physi oloyi ca1 saline
0.25 mL physiological
sali nc a I one
i .m.
s.c.
s.c.
Sarcomas 8/20
Interstitial cell tumors 10/20
Sarcomas 0/20
Sarcomas 2/10
(later in the study 10 more
rats developed tumors; the
test yroup they were i ri was
not specified)
Sarcomas 3/10
Sarcomas 9/10
Sarcomas 6/8 (2 were killed
early)
Sarcomas 6/10
Sarcomas 6/10, 6/26
Sarcomas 5/14
Sarcomas 8/10
Sarcomas 0/10
Haddow et al.
( 1964)
aSut>cut.aneous.
b Intramuscular.
Rats
Mi ce
0.5 my C1ISO4.H2O
in 1.0 ml sten 1 e
distilled water once weekly
for 10 weeks
0.0b iny CdS04.H20 in 0.2 mL
H2O once weekly for 11 weeks
s.c.
Sarcomas 14/20;
controls 0/15
0/20 injection site tumors;
controls 0/15
(continued on the following page)
-------
I AHl 1 10. (:.ont i nucd )
Author
Spec, i es
Compou rul
Route
Tumor (ind incidence
cr>
oo
Roe et al . (1964)
Gunn et al. (1963)
Gunn et al . (1964)
Gunn et al. (1967)
Knorre (1970)
Knorre (1971)
Lucis et a 1 . ( 1972)
Redely et al . (19/3)
hurst and
Cassette (1972)
Favino et al. ( 1968)
Rats
Al bi no mice
Wistar rats
Wistar rats
Wistar rats
Wistar rats
Wistar rats
Wistar rats
Fischer 344
rats
Fischer 344
Sprayue-Dawley
rats
0.5 my CdSO^.I^O in 1.0 mL s.c.
HpO once weekly for 10 weeks
0.0b my CdS0/).4H^0 in 0.2 mL
0.03 inM/ky CdC 1 2 s.c.
0.03 mM/ky CdCl 2 s.c.
0.03 mM/ky CdCI 2
1.8 my CdCl2
0.003 inM CdC I 3/100 y b.w.
0.003 mM CdCl^/lOO y b.w.
0.02-0.03 mM/ky CdC12 in
isotonic NaCI solution
0.03 mM/ky CdC 1 2
5 my Cd powder
(suspended in 0.2 mL
synthetic trioctanoin)
1 my/100 y CdCl2
s.c.
simultaneous s.c.
and i.m.
sinyle s.c.
s 1 nyl e s.c.
sinyle s.c.
si nyle s.c.
2 monthly i.m.
i nject i ons
single s.c.
Interstitial cell tumors 11/lb;
controls 0/lb
Int.erst. 11.1 al cell tumors 0/16
Interstitial cell tumors 20/26;
controls 0/2b
I nt.ers t i L1 a 1 cell tumors 17/25;
cont rols 0/25
Sarcomas 9/22; controls 0/18
Interstitial cell tumors 21/24;
controls 0/18
Sarcomas 10/23
Sarcomas 3/26
Sarcomas 6/45
Interstitial cell tumors 10/25
Interstitial cell tumors 13/15
Sarcomas 2/15 (two animals died
early)
Interstitial cell tumors 16/20;
cont rols 0/10
Sarcomas 26/50
Interstitial cell tumors 6/6
("continued on the followiny paye)
-------
Author
Species
Malcolm (1972)
Levy et al. (1973)
Scott and Auyhey (1979) Rats
Rats
Hats
C.B. hooded
rat s
Poirier et al. ( 1983) Wistar rats
TABLE 10. (continued)
Compound
Route
Tumor and incidence
CdCI;
0.? my 3CdS04.H20 in
0.2 liiL H20
0.1 my 3CdS0/).8H20 in
0.? ml H20
0.05 my 3CdS04-BH20 in
0.2 mL H20
controls - 0.2 my H^O only
0.05 inL i nject i on i nto
1 mo I CdCI2 prostate
0.0b mL
1 mol CdCI2
7. 3 my/ky CdCI 2
in 0.9% NaCl
3.6 my/ky CdCI?
in 0.9% NdCl
controls - 0.9% NaCl
weekly s.c.
injection into
alternate Hanks
for 2 yrs
s.c. five times
sinyle s.c.
Sarcomas (?)
Interstitial cell tumors (?)
(Experiment not completed at
t ime of pubIi cat i on)
Sarcomas
-------
assessing the carcinoyenic potential of chemicals on the basis of injection
site sarcomas. They did indicate, however, that the development of tumors at
sites distant from the injection site was very suggestive of carcinogenic
potential in the material under investigation. The testicular tumors produced
by the injection of cadmium salts certainly fulfill the criteria set forth by
these authors for the assessment of positive carcinogenic potential.
Tonatis (1977) reviewed the appropriateness of the subcutaneous injection
route for bioassays of carcinogenicity by comparing it with other routes of
administration. He surveyed a number of chemicals tested by the subcutaneous
injection route in rodents to see if there was a correlation between the capa-
cities of these chemicals to induce local and/or distant tumors in one species
and their capacities to induce tumors by another route in another species. A
total of 102 chemicals, which have been reviewed by the International Agency
for Research on Cancer (IARC) and have been tested by the subcutaneous injec-
tion route as well as by other routes of administration, were surveyed. Of
those, 69 were positive for carcinogenic activity when administered by subcu-
taneous injection and by another route, and 18 were negative or inconclusive
whether given by subcutaneous injection or by another route. Nine were posi-
tive only when administered by subcutaneous injection, and six were negative
by subcutaneous injection and positive by another route. The author concludes
that "administration of a chemical by the subcutaneous injection route pro-
duced what one could call false negative results for six (5.6%) of the 102
chemicals tested and, if we accept all the criticisms of this route of admin-
istration, false positive results for nine (8.7%) of the 102 chemicals
tested." Even so, according to the author, it appears that the subcutaneous
injection route of administration is not too much worse than any other route
of administration.
65
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More recently Tneiss (1932) reviewed the IARC data base. He concluded
that if a compound produces distant tumors by subcutaneous injection it is
almost always tunorigenic by at least one other route of exposure. Theiss
recommended that the results of investigations of materials producing tumors
at sites other than the injection site should be considered to be as signifi-
cant as results obtained Dy routes of administration more relevant to man.
Thus, by all accounts the induction of tumors distant from the injection
site is regarded as highly useful in the classification and identification
of carcinogens. Tne work of Chellman and Diamond (1984) provides a possible
reason for the consistent induction of cancer following injection of cadmium
or its salts at other sites. These investigations showed that in the testes,
significant amounts of cadmium were not bound to metal 1othianein, a protein
to which cadmium is normally bound, rendering the metal in the tissues less
toxic.
Poirier et al. (1983), in addition to observing increased testicular
tumors, showed an increase (p < 0.02) in pancreatic islet cell tumors follow-
ing subcutaneous injection over a 2-year period of cadmium chloride (22/259,
8.5%) as compared to rats not receiving cadmium chloride (3/137, 2.2%) and
surviving more than one year, the time to the first such tumor. In the same
report, it was shown that simultaneous injections of magnesium acetate preven-
ted the development of injection-site tumors, but had no effect on testicular
tumorigenesis. No inhibitory effect was elicited by calcium acetate in the
diet, by simultaneous injection, or by magnesium acetate in the diet.
The induction of pancreatic tumors by cadmium chloride is not altogether
unexpected, since high concentrations of cadmium in the pancreas of humans and
animals have been reported (Friberg and Odeblad, 1957), and the effects of
cadmium on carbohydrate metabolism and insulin secretion are well documented
66
-------
(Ghafghazi and Mennear, 1973).
Oral Studies in Mice and Rats
Schroeder et al. (1964, 1965) conducted two lifetime exposure studies in
which Swiss mice were given drinking water containing cadmium acetate at 5
ppn. The purpose of this low exposure level was to simulate the human exper-
ience, according to the authors. In the first study, only males experienced
decreased longevity in comparison with controls. The mean concentration of
cadmium in the kidneys of mice at the end of the study was only 3 yg/g wet
weight. Tnis appears to be very low in comparison with the concentrations of
18 ug/g that have been reported in man, and the 13.5 pg/g in rats exposed
to 12.5 ug/m^ reported by Takenaka et al. (1983). The exposed males had
fewer "visible" tunors (1/50) than the controls (11/50), a result (p < 0.005)
which was possibly related to the shortened lifespans of the exposed males.
Only abnormal tissues were histopathological1y evaluated. The reduced survival
times of the animals, and the limited amount of histopathological evaluation
that was conducted, limit the usefulness of this study in the evaluation of
the carcinogenic potential of cadmium.
In the second lifetime exposure study by Scnroeder et al. (1965), male
and female Long-Evans rats ingested cadmium acetate at 5 ppm in water as the
sole source of fluid; the treated group developed 28/84 tumors versus 24/70
in controls. The authors stated that "no significant differences appeared
among the various groups as to type of tumor." This study, like the authors'
1964 study, was complicated by being performed in a low-metal environment
and with a diet low in many trace metals. When the essential trace element
chromium (111) was added to the diet of one group of fats that were not given
cadmium, they thrived better tnan the control group and had 34/71 tumors
67
-------
(Schroeder et al., 1965).
Maico1 in ( 1972), in one experiment, gave male Chester-Beatty hooded rats
up to 0.2 my of cadmium sulfate subcutaneously and up to 0.8 my weekly by
stomach tube for 2 years. In another experiment, he gave Swiss mice doses of
cadmium sulfate in distilled water of up to 0.02 mg/ky of body weight subcutan-
eously at weekly intervals for 2 years. Except for a few sarcomas and Leydig
cell tumors seen in the rats given subcutaneous injections (both also seen in
the controls), these studies were negative at the time reported.
Experiments w'th male specified pathogen-free Chester-Beatty hooded rats,
using doses of 3.087, 0.18, and 0.35 mg/kg of cadmium as cadmium sulfate in
distilled water given by gastric instillation once weekly for 2 years, were
carried out by Levy and Clack (1975). Ninety males received 1 mL distilled
water on the same regimen, and served as controls. No difference in tumor
incidence between exposed and control groups was observed. It is noted, how-
ever, that th^s particular strain of rats has a very high lifetime incidence
of spontaneous interstitial cell tumor formation (75% in the untreated control
group), such that "if exposure to cadmium had any effect on the incidence of
the lesions it was entirely overshadowed by their spontaneous occurrence,"
according to the authors. Effects on the prostate were especially scrutin-
ized, with no neoplastic lesions observed. Only a limited number of tissues
(kidney, spleen, liver, lung, testes, and prostate) were histopathological ly
evaluated from 10 rats of the high-dose group and 10 rats of tne control
group.
Levy et al. ( 1975) similarly gave groups of 50 male Swiss mice 0.44,
0.88, or 1.75 my/kg/week cadmium sulfate by gavage for 18 months. A group of
150 male mice served as controls. The stated oojective of the study was the
detection of an increased incidence of prostate tumors attributable to cadmium,
68
-------
but neither that nor any other treatment-related effect was reported at any
of the three dose levels. As in the study with rats, the histopathological
examination was not sufficiently thorough to make this constitute a compelling
negative study. The set of tissues fixed was limited to prostate, urethra,
bladder, stomach, kidney, testes, lung, liver, spleen, seminal vesicles, and
coagulatory gland, and these tissues were examined microscopically for only
20 of the high-dose and 20 of the control males, along with any abnormal
tissues noted macroscopically. Although measurements of cadmium concentration
in various tissues were not made, Levy et al. (1975) speculated that the
reason no pathological changes attributable to cadmium were observed during
the study may have been that absorption of cadmium through the intestinal
tract is low.
An unpublished chronic toxicity study of cadmium chloride was conducted
at the U.S. Food and Drug Administration (U.S. FDA, 1977). The compilation
of animals examined pathologically shows that six groups of Charles River
COBS (SD) rats, each consisting of 26 to 32 males and 26 to 29 females, were
studied. These groups were given 0 (untreated controls), 0.6, 6, 30, 60, or
90 ppm cadmium chloride in the diet for 103 weeks. Five males and five
females per group were sacrificed at 24 and 52 weeks. The renainder were
sacrificed at 103 weeks. All animals were necropsied, and tissues, organs,
and tissue nasses were examined histopathologically. Kidney tissue from five
or fewer males in each sacrificed group was evaluated by electron microscopy;
sections of liver and kidney from these animals were stained to assess fibro-
sis, lipid content, liver glycogen, and the basement membrane of tubuli and
Bowman's capsules in kidney.
No significant (p > 0.05) differences in survival between control and
treated groups were reported, and, excluding interim sacrificed animals, no
59
-------
nore than two animals per group died before 77 weeks. Results of necropsy and
histopathologic and histochemical evaluations did not show treatment-related
effects. Electron microscopy, however, revealed dose-related changes in the
form of small cytoplasmic lipid droplets in renal tubular epithelium, in-
creased number of residual bodies in renal nephron cells, and swelling and
sloughing of cells in distal tubular epithelium and the collecting ducts of
the kidney.
A 2-year oral carcinogenicity study of Wistar rats given cadmium chloride
was carried out by Loser (1980). Doses of 1, 3, 10, and 50 ppm of cadmium
were yiven in food to BO male and BO female rats, with 100 controls of each
sex. Food consumption was similar in all the test groups. The mean body
weignts of treated males were significantly reduced (p < 0.01) at the highest
dose level. Other than reduced weignt in the hiyh-dose males, the male and
female treatment and control groups were comparable for weight and mortality.
On the basis of a complete histopathological evaluation, the author concluded
tnat tnere was no significant increase in the incidence of any particular
tunor type or in the frequency of tumor-bearing animals.
The reason for the discrepancy between the U.S. FDA (1977) study with
•regard to the lack of effects of cadmium on body weight at 60 and 90 ppm as
compared to the highly significant effect (p < 0.01) at 50 ppn is not readily
apparent. Strain differences or differences in dietary factors (such as
selenium, zinc, copper, or estrogen concentrations) may account for the lack
of comparabi1ity.
Summary
Chronic exposure of rats to aerosols of cadmium chloride at airborne con-
centrations of 12.5, 25, and 50 ug/m- for 18 months followed by an additional
7n
-------
nonexposed 13-month period produced significant increases in lung tumors. An
18-month exposure to 20 uy/m^ also increased lung tumors among exposed rats.
A single 30-ninute exposure of rats to cadmium oxide did not significantly
increase the occurrence of lung tumors in the year that followed. However,
increases in mammary tumors and testicular degeneration were observed. The
estimated total dose in mg/kg was, however, lower than that producing testi-
cular neoplasia following parenteral administration. It is likely that the
potency of cadmium chloride is related to a high degree of bioavailability,
due in part to its solubility. On the other hand, the potency of other
cadmium compounds cannot necessarily be predicted, since tumor induction may
occur with some chemicals despite their relative insolubility.
Intratracheal instillation of cadmium oxide produced an increase in
mammary tumors and an increase in tumors at multiple sites among male rats.
Intrathoracic injections of cadmium powder are highly toxic, but when their
toxicity is reduced by co-administration of zinc, mesotheliomas develop.
Intramuscular or subcutaneous injection of cadmium as metal powder, or as
chloride, sulfate, oxide, or sulfide, produces injection-site sarcomas and/or
testicular interstitial cell (Leydig cell) tumors after necrosis and regene-
ration of testicular tissue. The results obtained by Poirier et al. (1983)
suggest that the incidence of pancreatic islet cell tumors may be increased
by administration of cadmium chloride via the injection route. In addition,
injection of cadmium chloride into the prostate gland in rats has induced
tumors of that tissue. The translocation and long-term pulmonary clearance
of cadmium salts do not appear to be related to the chemical's solubility.
Cadmium appears to be much less potent as a carcinogen by ingestion than
by injection or inhalation, regardless of the site of cancer induction. For
example, the total dose of inhaled cadmium in the Takenaka et al. (1983) study,
71
-------
in which the rats developed a 71% incidence of lung cancer, was about 7 mg
(0.25 m^/day x 0.05 mg/m^ x 355 days/year x 1.5 years). By contrast, in the
Schroeder et al. (1965) drinking water study in rats, which had one of the
smallest total doses of all of the ingestion studies, a total dose of about
60 mg (5 ppn x 0.5 x 0.35 kg x 730 days) induced no cancer responses. If a
10% upper linit of detection of tumors in the Schroeder et al. (1965) study
is assuned, the highest reasonable potency for cadniun via ingestion is about
0.0017 (0.1/60), compared with a potency of about 0.1 (0.7/7) for inhalation.
While it is possible that cadmium is not at all carcinogenic by ingestion
because of very limited absorption, the negative animal evidence can only set
an upper limit on the carcinogenic potency of ingested cadmium, which in the
rat appears to be about two orders of maynitude less than for inhalation.
In 1982 the IARC concluded that sufficient evidence existed for the deter-
mination that cadmium is carcinogenic in animals. The IARC was aware at that
time of the negative findings of Loser (1980) following dietary administration
of cadmium chloride to laboratory animals. However, studies reporting a marked
carcinogenic response in rats to inhalation of cadmium chloride aerosols were
not available to the IARC, nor were the highly suggestive reports of pancreatic
islet tumors following parenteral administration of cadmium chloride (Poirier
et al., 1983), or the study of male mammary tumors following intratracheal
instillation of cadmium oxide (Sanders ar.d Mahaffey, 1984). Apparently the
IARC did not consider the intratracheal induction of mesotheliomas reported by
Furst et al. (1973) or the induction of prostate tumors by injection of cad-
mium chloride into that tissue (Scott and Aughey, 1979). As a result of these
newer investigations, together with additional information suggesting a distri-
bution not based on chemical solubility, the carcinogenic risks of cadmium and
its compounds are now seen to be greater than originally anticipated.
VI
-------
EPIDEMIOLOGIC STUDIES
The epidemiologic studies reviewed here deal specifically with cancer
risks resulting from cadmium exposure. Although five of these studies were
reviewed in the 0HEA Health Assessment Document for Cadmium (U.S. EPA, 1981),
they are covered here also for the convenience of the reader.
Potts (1965)
Potts (1965) reported the results of a clinical study of an unstated num-
ber of current and former employees of a British alkaline battery factory who
were exposed to cadmium oxide dust beginning in 1920 and ending in 1963. In
1946 the manufacture of these batteries was moved to a new location not far
from the site of the earlier factory. The first measurements of cadmium dust
in the air were made in 1949. At that time, the cadmium content of the air
varied from 0.6 to 2.8 mg/m3 in the platenaking and assembly shops to 236
mg/m^ in the negative active material department. After the installation of
local exhaust ventilation in 1950, cadmium in the air was reduced to less than
0.5 mg/m3. Improvements to the exhaust system in 1956 further reduced the
cadmium dust to less than 0.1 ng/m^. The policy at the time of the study's
publication was to take steps to reduce exposures whenever the measurement of
cadmium dust exceeded 0.5 ny/m^.
Of 70 battery workers for which Potts's clinic had medical records and
who were exposed for at least 10 years, proteinuria was observed in 44%.
Although no comparison group was provided, this number is probably excessive,
since proteinuria is the result of renal tubular dysfunction. A 200-248 ug/
day cadmium dietary intake over a 50-year exposure period is required to pro-
duce the critical renal cortex concentration associated with renal dysfunction.
Only 1% of Americans ingest more than 50 ug/day (U.S. EPA, 1981). However,
73
-------
the author did note that earlier studies of the urine protein of cadnium-
exposed workers in this same plant had revealed "similar characteristics" to
tnose of the present study. Four individuals with persistent proteinuria were
examined further. Two of then died during the study period. Kidney function
tests prior to death revealed no abnormalities, nor were any gross abnormali-
ties observed following microscopic examination of the
-------
prostate cancer deaths is statistically significant. Therefore, this study
provides only the suggestion of an association of prostate cancer and exposure
to cadmium.
TABLE 11. MORTALITY DATA FOR CADMIUM WORKERS EXPOSED FOR MORE THAN 10 YEARS
Year of death
Age
Length
cadmi
exposure
of
um
(years)
Cause of death
1960
65
31
Auricular fibrillation
1960
75
14
Carcinoma of prostate
1961
65
37
Carcinoma of prostate
1962
63
34
Bronchitis and atheroma
1962
78
18
Bronchiti s
1963
53
35
Carcinoma of bronchus
1964
65
38
Carcinoma of prostate
1964
59
24
Carci nomatosi s
SOURCE: Potts,
1965
•
Kipling and Waterhouse (1967)
Ki pii ng and
Waterhouse (1967)
, in a letter to The
Lancet, reported on 246
workers who had
been
exposed for a
minimum of
one year
to cadmium oxide dust.
The authors compared
the number of
cancers observed from several sites with
the number expected
from those sites based on
i nci dence
rates from the Bi r-
mingham Regional Cancer Registry. The number of observed cancer cases of the
prostate was significantly greater than expected (4 observed vs. 0.58 expected,
p < 0.003). Three of the four prostate cancer cases are the same as those
75
-------
reported in Potts's paper (personal communicati on f roin. Ki pi i ny .to the IARC
in 1976), indicating that sone overlapping is acknowledged, and therefore,the
two studies cannot be said to be independent of each other. No significant
differences between observed and expected deaths were found for cancer of,:the
bronchus, bladder, testis, or for cancers of all sites.
Latency period, altnough obliquely referred to in the letter, is poorly
addressed. Furthermore, the letter states that expected cases were calculated
by "computing the number-of cases of cancer which would be expected to occur
in such a group of men of known age" and by excluding the tine spent in other
jobs or retirement. It is not clear how the latter was to be done; the dis-
cussion is s
-------
prostate, 6.4 years; and cardiac, 3.0 years.
There was no comparison group for the 1949-67 time period. However, the
author did compare the average of the cancer death rates for the years 1963-66
in the city where the plant is located with the average 1963-66 rate for the
whole plant and the average 1963-66 rate for the departments of the plant
where there was exposure to cadmium hydroxide. The author did not state whe-
ther these rates were age-adjusted, race-adjusted, or sex-adjusted. No dif-
ferences were found among the three rates or in the proportion of lung cancer
deaths between the city population and the plant population. The proportion
of lung cancer deaths for the department in which cadmium exposure occurred
was not reported.
Previously, Baader (1951) had reported on "20 to 30 males and females"
suffering from chronic cadmium poisoning at the same dry cell plant. Of this
group, Hunperdinck reported that four of eight had died, one of lung cancer;
these four are included in the seventeen deaths described previously. No
mention is made of any of the other "20 or 30" workers.
Because Hunperdinck found no excess cancer mortality among workers exposed
to cadmium when compared to the city population or to the plant population as a
whole, he concluded that there was insufficient information to establish an
association between cadmium and cancer.
A major weakness of this study is that it did not include an appropriate
comparison group for the years of the study, 1949-67. Comparison of average
death rates for the years 1963-66 among the city, plant, and cadmium depart-
ments is not appropriate since it is not known whether all workers in the
cadmium departments for the years 1963-66 had experienced a latency period of
sufficient duration to have developed cancer. Secondly, there is no indication
that the city population or the population of the rest of the battery plant
77
-------
were similar enough to the caoni 'jrn -e xpos group in tenns of race, sex, smoking
habits', age, etc. tu nake these groups objectively comparable. Third, had a
prope" comparison grou,j been used and an increase in cancer anong workers
exposed to cadmium been demonstrated, a possible confounding variable would
have been the concomitant nickel exposure to which these workers were subjec-
ted, since nickel has previously been associated with cancer of the 'uny, nasal
sinus, large intestine, no.; to, and pharynx (Fraunen,; , 1975). •
In conclusion, the study clesi -jn and metnods :•) Hjnperd i nek render his data
inadequate for the assessment of an association b.'tweon cadnion exposure and
cancer.
*
Hoi den ( 1969_)
holoen (196^), in d 'etter to The Larcet, reported on 42 nen exposed to
cajiniu;i funes fron 2 to 40 year;. Hi-> st.Jte-i that six of the men had been
exposed to corcentrdtics of cddni j i in excess of 4 ny/-n3, and the remainder
had been exposed to an concent ra t i on of 0.1 my/m^. The author repor-
ted that of the 42 men, ore developed a carcinoma of the prostate and one
developed a carcinoid of the bronchus.
No evaljation of the cancer risk fron cadmium can be 'nade on the basis of
this letter, vnee the author did not report important variables such as age,
time since f'rst exposure, and smoking history.
Kol onej_ f 1_9_7_6_L
k o I o n oI f 1^76) compared the cadmium exposure of 64 cases of renal cancer
ti 197 non-a1ijnant digestive disease controls and 72 colon cancer controls.
According to the author, "a career control group was included to address the
problem of potential noncomparabi1ity" between cases and controls when a non-
cancer control group was used. Cases and controls were taken frum patients
78
-------
admitted from 1957 to 1964 to Roswel1 Park Memorial Institute, Buffalo, New
Yor<. Cadmium exposure was assessed using data on occupational exposure, ciga-
rette smoking, and dietary intake. A person was considered to have experienced
occupational exposure to cadmium only if he had worked for one or more years at
a high-risk job in a high-risk industry. High-risk industries included elec-
troplating, alloy-making, welding, and the manufacture of storage batteries.
A person was considered to be exposed to cadmium through smoking if he had at
least 10 "pack.-years" of cigarette use during a lifetime. Dietary exposure to
cadmium was determined by applying reports of cadmium content in foods to
individual dietary histories based on a frequency recall for a one-week period.
An individual was considered exposed through diet if his mean daily intake
exceeded the third quartile, determined from the distribution of intakes for
the noncancer control group.
The author found that the relative risk of developing renal cancer in
occupationally exposed patients who smoked was 4.4 when compared to controls
who also smoked and had nonmalignant diseases of the digestive system. This is
significant at p < 0.05. The risk of developing renal cancer in patients who
were occupationally exposed was 2.5 (p < 0.05) when compared to colon cancer
controls. The latter is not significant (0.05 < p < 0.10). Because of the
finding of a greatly increased risk* when the effects from smoking and occupa-
tional exposure were added together, the author concluded that the effects of
smoking and occupational exposure must be synergistic.
The risk of developing renal cancer when consideration is given to cad-
mium exposure through cigarette smoking only, and separately through diet only
(utilizing colon cancer controls), was 1.2 and 1.6, respectively, neither of
~Risk in this context is an estimated relative risk derived by use of tne odds
rati o.
/y
-------
which was significant (0.05 < p < 0.10, two-tailed).
A major criticism of this study is the confounding exposures to other
industrial materials in the electroplating, alloy-makiny, welding, and storage
battery manufacturing industries, The author stated that renal cancer result-
ing from cadmium exposure is biologically plausible because the kidney concen-
trates cadmium to a greater degree than any other organ. Furthermore, Kolonel
pointed out, on the basis of an earlier study by Ellman (1959), that the :
-------
animal, are necessary to adequately address the issue.
Lemen et al. (1976)
Lemen et al. (1976) conducted a historic prospective study on 292 white
male employees of a cadmium production facility who had worked a minimum of 2
years in the facility at some time during the period from January 1, 1940 to
December 31, 1969. Vital status was determined for this group through January
1, 1974. Death certificates listing the causes of death were acquired for 89
of a reported 92 deceased. Some 20 (6.8%) remained lost to follow-up. For
comparison, expected deaths by cause were generated through a modified life-
table technique based on person-years multiplied by the corresponding age,
calendar time, and cause-specific mortality rates for the total U.S. white
male population.
The authors stated that the plant was engaged in the production of cadmium
metal and cadmium compounds. However, they reported that some lead was also
produced. The plant ceased full-scale lead production in 1918 and began to
produce arsenic instead. In the early twenties, arsenic production ceased.
The plant remained closed until 1926, when cadmium production began. The
authors cited an industrial hygiene survey in 1947 that had reported average
air concentrations of cadmium fumes ranging from 0.04 to 6.59 mg/m^ and cadmium
dust at 17.23 mg/in^. It was also reported in that survey that for most opera-
tions in the plant, total cadmium air concentrations were less than 1.5 mg/m^.
The present study included a 1973 industrial hygiene evaluation of cadmium dust
levels which stated that 8-hour time-weighted average (TWA) gross concentra-
tions of cadmium ranged infrequently up to 24 mg/m^, but generally remained be-
low 1 ng/m3. The authors reported, following a 1973 industrial hygiene survey,
that an effective respirator program had been instituted at the plant, and had
81
-------
allegedly reduced exposure by a factor of 10. However, it is known that in
other occupational settings workers tend to remove respirators because of their
inconvenience. Two air measurements taken in the prenelt department showed that
in addition to air concentrations of 74.8 and 90.3 ug/m^ of cadmium, arsenic
was measured at 0.3 and 1.1 ug/in3. This is about 1% of the cadmium measure-
ment. In the retort department, however, where the cadmium concentration was
measured at 1,105 pg/n^, arsenic measured 1.4 pg/n3, which was about 1/1,000
that of cadmium. On the other hand, analyses of bulk samples revealed 42.2% to
70% cadmium, 3.53% to 6% zinc, 0% to 4.3% lead, and 0.02% to 0.3% arsenic. The
remaining ingredients were not identified. The authors concluded that the
exposures from the remaining ingredients were insignificant.
A statistically significant excess of total malignant neoplasms (27 ob-
served vs. 17.5 expected, p < 0.05) was found, as well as a statistically sig-
nificant excess of malignant respiratory disease (12 observed vs. 5.1 expected,
p < 0.05). Without regard to latent effects, an excess of prostate cancer was
reported by the authors to be not significant (4 observed vs. 1.15 expected).
However, utilizing a one-tailed Poisson variable, the Carcinogen Assessment
Group (CAG) found the latter observation to be statistically significant
(p < 0.05). After a lapse of 20 years from initial exposure, the finding of
a statistically significant excess in prostate cancer (4 observed vs. 0.88
expected, p < 0.01) was even stronger.
Information concerning exposure and latency of the four prostate cancer
cases is given in Table 12. Of the 12 malignant respiratory cancer cases, the
cell types of eight were known. Three were squamous cell carcinomas, one was
an undifferentiated small cell carcinoma, three were anaplastic carcinomas,
and one was an oat cell carcinoma. Unfortunately, smoking histories were not
available for members of the cohort in this study. However, it was determined
82
-------
in the later Thun et al . (1985) study that although smoking was more prevalent
among the members of this cohort, it could not have caused the significant
elevated risk of lung cancer. Furthermore, Lemen et al. reported the presence
in the cadmium production plant of other substances, including arsenic, lead,
and zinc, that are either known or suspected carcinogens. Any conclusions made
from this study regarding the carcinogenic potential of cadmium should be
tempered with the knowledge that these other substances were also known to be
present in the atmosphere of the smelter. In addition, it is apparent that the
authors
did not
identi fy
all
of the constituents of the
processed ores, since
the percentages
given do
not
add up to
100%.
TABLE 12
. PROSTATE
WITH
CANCER DEATHS AMONG
MORE THAN 2 YEARS
CADMIUM
EXPOSURE
SMELTER WORKERS
Case
Age
Exposure
Latency
Date of death
1
71
4
32
2/26/72
2
77
13
25
3/19/68
3
79
18
31
12/10/60
4
64
17
26
4/03/51
SOURCE: Lenen et al., 1976.
However, when consideration is given to the fact that the vital status of
6.8X of the study cohort remains unknown, it is apparent that additional causes
of death in this group of 20 people potentially might add a few more cancer
deaths to the observed group. In contrast, the expected deaths were over-
estimated because person-years were counted to the cut-off date for these
83
-------
sane individuals.
This study provides support to the supposition that exposure to cadmium
is associated with a significant excess risk of prostate cancer and broncho-
genic cancer. The other metals known to be present have not been shown to be
associated with an elevated risk of prostate cancer. On the other hand, the
presence of arsenic in the atmosphere of the smelter, and the possibility of
increased smoking among these workers, were potential confounding factors that
contributed toward the significant association of oronchogenic cancer and cad-
mium exposure in the workers. However, in the updated Thun et al. study, the
combined effect of smoking and exposure to arsenic was shown not to cause the
significant elevated risk of bronchogenic cancer.
McMichael et al. (1976a, b)
Mcllichael et a'. ( 1976a), as part of a nistoric prospective study of
cancer -nortality among rubber workers, followed 18,903 active and retired male
workers, aged 43 to 84, for a period of 10 years. They were divided into four
separate cohorts, each consisting of workers fron the four tire manufacturing
plants of the companies under study.
The mortality experience during the 10-year observation period was
determined fron death claims filed with the conpanies under the group life
"insurance policy in effect. In tnree of the four plants, workers were included
if they were employed on January 1, 1964, whereas in the fourth plant they were
includec if they were employed on January 1, 1963. About \% were lost to
follow-up, and death certificates listing causes of death were obtained for 98%
of the deceased. Expected deaths were calculated based on the 1968 U.S. male
race- and age-specific death rates. The calculation of standard mortality
ratios (SMRs) utilizing such rates produces an underestimate of the risk.
84
-------
This bias, known as the "healthy worker effect," is a consequence of the se-
lection of the healthiest individuals into a given workforce from the general
population from which the expected deaths were derived. Apparently, little
turnover occurred in these four plants because the former employees who
switched to another place of employment formed the group of IX lost to follow-
up during the 10-year follow-up period.
The total number of deaths equaled 5,160, for an overall SMR of 94. The
total number of cancer deaths equaled 1,014 for an SMR of 100, while the SMR
for prostate cancer was 119 (103 observed, nonsignificant at 0.05 < p < 0.1).
The authors hypothesized an association of prostate cancer with the compound-
ing and mixing areas of the four plants, work areas that they claimed entailed
contact with metallic oxides (including cadmium oxides). The authors also
hypothesized an association of prostate cancer with three additional work
areas (cement mixing, janitoring, and trucking) of one particular plant after
"exploratory work-history" analyses were completed for stomach, bladder, and
prostate cancer, lymphosarcoma, and Hodgkin's disease at this plant.
In a similar mortality study of just one of the above four plants,
McMichael et al. (1976b) confirmed a significant excess risk of prostate cancer
(SMR = 140, observed = 53, p < 0.05) in 6,678 male rubber workers, and found
that the risk was associated with the calendering, janitoring-trucking, com-
pounding, and mixing occupational groups. He stated that cadmium compounds
were used as vulcanization (curing) accelerators in these broad occupational
groups. The method of classifying workers utilized by McMichael et al. is
discussed further in a later critique by Goldsmith et al. (1980).
The object of the earlier McMichael et al. ( 1976a) study was not to single
out the association of prostate cancer with cadmium exposure as the main topic
of study, but rather to examine site-specific cancer mortality, in general, in
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rubber workers. Hence, the authors found excesses in cancer mortality at a
number of different sites, but did not test the significance of any of these
excesses. Data from the McMichael et al. (1976a) study are summarized in Table
13. The tests of significance were calculated by the CAG using the method of
Chiang (1961).
One major problem with this study is that rubber workers are potentially
exposed to numerous organic and inorganic chemicals, some of them known or
suspected carcinogens, including benzene, which is a known human carcinogen,
"ne SMRs may thus be confounded by additional exposures to chemicals other
tnan cadmium. Exposure levels for the many different compounds found in these
plants are not given.
A second problem with this study is the relatively short observation time
!10 years) from the beginning of the study to its cut-off date. This is an
insufficient period in which to assess latent effects, and in fact, no data
are presented in which latency is considered. This cohort should be followed
for several additional years before a final conclusion is made regarding car-
cinogenic effects resulting from exposure to cadmium. While the paper is of
interest as a basis for further studies, it does not provide adequate evidence
for the association of cadmium with prostate cancer.
Honson and Fine (1978)
In another mortality and morbidity study of cancer in 13,570 white male
rubber workers (Monson and Fine, 1978), an elevated risk of prostate cancer was
noted (4 observed, 0.04 expected, p < 0.05) in two unrelated departments,
material conservation and final finish. In no other department of this plant
was an elevated risk of prostate cancer evident. However, the authors do not
attribute this excess risk to any common exposure in these departments, except
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TABLE 13. STANDARD MORTALITY RATIOS (SMRs) BY SITE
Site
Observed
deaths
SMRs
Probability of
occurrence3
Lymphatic leukemia
20
158
0.039
Stomach
80
148
<0.001
All leukemias
46
130
0.073
Hodgkin's disease
32
129
0.150
Prostate
103
119
0.077
Col on
103
116
0.131
Pancreas
57
103
0.826
B1 adder
32
92
0.638
Respi ratory
252
85
0.002
Rectum
27
82
0.303
Brain, central
nervous system
14
78
0.352
All cancer
1014
100
1.000
All causes
5106
94
<0.001
aTaken from Chiang (1961).
SOURCE: McMichael et al., 1976a.
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possibly to oils used in machine maintenance. The authors claim that cadmium
exposure was not "appreciable" in this plant. Data on the U.S. white male
population provided the comparison population for the expected prostate cancer
deaths. This study, which uses the same plant that was studied earlier by
McMichael et al. ( 1975a, b) and later by Goldsmith et al. (1980), does not sup-
port the hypothesis suggested by McMichael et al. that cadmium in the plant was
responsible for tne excess i sk of prostate cancer.
Kjellstrom et al. (1979)
Kjellstrom et al. (1979) reported on a historic prospective cohort study
of 269 male Swedish cadmium-nickel battery factory workers and 94 Swedish male
cadniurn-copper alloy factory workers having more than 5 years exposure since
the factories oeyar production. As an internal reference yroup, the study also
included 328 alloy factory workers who had been employed in the alloy factory
for at least 5 years but had not been exposed to cadmium. It was estimated
that the average cadmium levels for one of the two factories were as follows:
in excess of 1 my/m^ prior to 1947, 200 yg/m^ between 1962 and 1974, 50 pg/m^
in 1574, and below 5 ug/m^ at the time of the study. At the other factory,
concentrations were in the range of 100 to 400 ug/m^ in the mid-1960s and
50 uy/m^ in 1971 and after. The battery study population was also exposed to
nickel hydroxide dust.
National average age- and cause-specific death rates and cancer incidence
rates were used to generate expected deatns and expected new cancer cases in
the two study groups. New cases of cancer were found in the battery factory by
matching the names of the 269 workers with those of the Swedish National Cancer
Registry. This was not done w'tn the alloy factory workers. With respect to
mortality in the battery factory, 43 deaths occurred between 1949 and 1975, of
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which 8 were due to cancer. This contrasts with 67 expected total deaths
during the same period. No further breakdown is given of the cancer deaths, and
no expected cancer mortality is given. However, the authors state that there
was no increase in "general" cancer nortality. Furthermore, the total number
of new cases of cancer equaled 15 during the period from 1959 to 1975, while the
expected number of new cases equaled 16.4, based on incidence data provided by
the Swedish National Cancer Registry. A breakdown by site is given in Table
14. Only cancer of the nasopharynx was found to be significantly in excess (2
observed vs. 0.2 expected, p < 0.05) possibly due to exposure to nickel dust.
In the alloy factory, only "preliminary" calculations of prostate cancer
mortality were done; cause-specific mortality and incidence were not examined
in these workers. Among 94 exposed workers, four prostate cancer deaths were
noted versus 2.69 expected (p = 0.29). In the reference group of 328 unexposed
workers, four prostate cancer deaths were noted versus 6.42 expected (p = 0.23)
(Table 15). A corrected "healthy worker effect" risk ratio was derived by
dividing the risk of developing prostate cancer in the exposed group by that of
the reference group. The resulting ratio was 2.4 (p = 0,087), which is still
nonsignificant. Although the results of these two studies are not significant
with respect to prostate cancer, and are basically inconclusive because of the
small study groups, they do suggest a positive association of prostate cancer
and exposure to cadmium.
Two problems with this work are apparent. The first is that terminated
employees were apparently not included in any of the study cohorts unless they
had died. The resulting cohorts are healthier than the general population
because former employees, who would be expected to carry the greatest burden of
potential disease, are not represented. These employees are represented in the
general population's death rates, however. The net result is to overestimate
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TABLE 14. EXPECTED AND OBSERVED NEW CASES OF CANCER BETWEEN 1959 AND 1975
IN THE WHOLE GROUP OF BATTERY FACTORY WORKERS (N = 228)
Cancer cases
Site
Expected3
Observed
Risk ratios
Prostate
1.2
2
1.67
Lung
1.35
2
1.48
Kidney
0.87
0
0
B1adder
1.07
1
0.93
Colon-rectum
2.25
5
2.22
Pancreas
0.60
0
0
Nasopharynx
0.20
2
10.Ob
Other
9.81
3
0.31
All sites
16.4
15
0.91
aExpectec deaths based on Swedish National Cancer Registry.
^Statistically significantly greater than 1 (p < 0.05).
SOURCE: Kjellstrom et al., 1979.
TABLE 15. CUMULATIVE EXPECTED AN
DEATHS FROM 1940 TO 1975
D OBSERVED NUMBER OF PROSTATIC CANCER
AMONG ALLOY FACTORY WORKERS
Prostatic cancer
deaths
Expected
Observed
Risk ratios
P value
Exposed group
2.69
4
1.49
0.29
Reference group
(N = 328)
6.42
4
0.62
0.23
SOURCE: Kjellstron et al ., 1979.
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tne expected deaths, thus masking the potential risks to battery workers.
The second problem is that, because the Swedish National Cancer Register
was not established until 1959, the study's incidence data would not have
included cancer cases occurring in the 1950s, thus leading to an underestimation
of new cancer cases.
Another potential source of selection bias would be the exclusion of all
members with incomplete information in the factory files. However, since
there is no reason to assume differential selection of subjects for study
through this procedure, it may not be a problem.
Goldsmith et al. (1980)
In a later case-control study by Goldsmith et al. (1980) of prostate
cancer in one of the four tire and rubber manufacturing plants studied earlier
by McMichael et al. (1976a, b), an excess risk of prostate cancer could not be
directly attributable to cadmium because no evidence could be found that cadmium
was used regularly in the study plant. The authors identified some 88 cases of
prostate cancer from death certificates in the years 1964 to 1975. These were
matched with 258 controls on the factors of age, race, and date of entry into
the plant. Only the batch-preparation work area produced a statistically
significant risk ratio (p < 0.025) over the exposure periods of (1) more than a
month, (2) more than 24 months, and (3) more than 60 months. No identifiable
use of cadmium was noted by the authors in this work area. The methods employed
in this study, i.e., the technique of grouping employees according to general
production areas called occupational title groups (OTGs) for analysis of work
history data, tend to result in distorted risk estimates of the carcinogenic
potential of substances to which individuals might be exposed in the workplace.
In any given 0TG, employees who may never have been exposed to any potential
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carcinogen are lumped together with employees who were exposed to one or more
substances, some of which might be classified as potential carcinogens. It
becomes difficult to attribute a significant risk ratio to any particular
substance ^n question under these circumstances. Furthermore, since this was
a study of only one of the four original plants, the possibility remains that
cadmium might have been used in the remaining three plants. Further investi-
gatory work must be done to identify any and all uses of cadmium in the three
remaining study plants. It might have been more appropriate to conduct case-
control studies of prostate cancer in all four study plants. Instead of using
"assignment to particular OTGs" as an indicator of excess risk, it would have
been more appropriate to use direct evidence of exposure to cadmium as the
dependent variable of interest. Similarly, a case-control study of lung cancer
and risk of exposure to cadniun might also be initiated in the rjbber industry.
This study does not support the earlier McMichael hypothesis that the
excess risk of prostate cancer night have been due to exposure to cadmium
compounds used as vulcanization accelerators. Some questions remain, however,
about the choice of the study population and the use of OTGs in assessing
exposure.
Hoi den (1980)
Holden (1980) reported the results of a preliminary cohort mortality study
of workers in a British cadmium factory who were employed at some time between
August 1940 and August 1962, and were followed until December 31, 1979. Iron
and brass foundry workers in a second factory served as controls. The cadmium
factory data were subdivided by the author into two parts for purposes of
analysis. One end of the building contained the cadmium-copper alloy depart-
ment, where 347 men worked for a minimum of 12 months. Another 624 men worked
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for a minimum of 12 months in the remainder of the factory. The latter group
was dubbed "vicinity" workers by the author because they worked in the same
buildiny with, but not directly in, the cadmiun-copper alloy department.
Another 537 brass and iron workers were employed in the second British factory
for a minimum of 12 months, and their social and physical environments were
reported by the author to be similar to those of workers in the first factory.
Industrial hygiene surveys carried out at the cadmium factory in 1953 and
1957 showed the mean level of airborne cadmium in the cadmium-copper alloy de-
partment to be 70 g/m^ (S.D. = 62 g/m^), based on 12-hour sampling,
while the mean level in the other parts of the building (the "vicinity") was
6 g/m^ (S.D. = 8 g/m^). The author reports that vicinity workers were
exposed to considerably less cadmium than were the cadmium-copper alloy workers.
Actually, neither figure represents a substantial exposure. Follow-up was
over 95% complete on all three subcohorts. Expected deaths were generated on
the basis of death rates for England and Wales in 5-year age intervals.
A statistically significant elevated risk of dying from all causes (ob-
served = 158, SMR = 112) was evident in the cadmium-copper alloy workers.
This excess was not due to malignant neoplasms. The excess risk remained when
malignant neoplasms were excluded (observed = 122, SMR = 113). Mortality from
neoplasms was not significant in the cadmium-copper alloy workers, except for
leukemia (observed = 3, SMR = 441, p < 0.05). The author contends that the
excess risk observed overall in the study was due to deaths from pulmonary
disease. On the other hand, a statistically significant elevated risk of can-
cer in general (observed = 72, SMR = 120) was apparent in vicinity workers,
due chiefly to significant excesses of cancer in two sites: the lung (ob-
served = 36, SMR = 138, p < 0.05) and the prostate (observed = 8, SMR = 267,
p < 0.01). The author attributed the elevated risk of lung cancer in these
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workers to the presence of metals other than cadmium, including arsenic. The
vicinity workers were reported by the author to have been involved in the
manufacture of arsenical copper, and during its refining, to have been exposed
to silver and nickel. However, no environmental measurements are reported to
have been taken of any of these other metals anywhere in the building in which
both groups worked. It was reported by the author that a "considerable evolu-
tion of cadmium oxide funes" resulted when cadmium was dumped into the much
hotter molten copper to form cadmium-copper alloy. This effect resulted be-
cause cadmium boils at a much lower temperature than that of copper.
With respect to prostate cancer, the author indicated that there was an
absence of a dose-response relationship since five of the eight prostate can-
cers occurred to individuals who were exposed for less than 15 years. Of
these five, three were exposed for only one year, if it is assumed that "years
of exposure" neans years of employment throughout the entire plant. The author
attributes only three of the prostate cancer deaths to cadmium exposure because
the remaining five were exposed for a "relatively short time." This last
observation is somewhat strong in view of the fact that every prostate cancer
death occurred 15 or more years following initial exposure.
Furthermore, since the author has "an integrated exposure and work sched-
ule history on each man" (comments of the Cadmium Council, Inc., 1984) a better
way to establish whether or not a dose-response relationship exists is to de-
velop a cumulative exposure index for each member of the cohort so that change
in risk could be related to increasing cumulative dosage, as in Thun et al.
(1985) or Varner (1983).
Latency as a factor was not considered in calculating expected deaths, so
that the actual risk of prostate cancer may have been greater in vicinity
workers. With respect to the risk of prostate cancer in the cadmium-copper
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alloy cohort (observed = 1, SMR = 63), trie numbers involved are too snail to
warrant the author's finding of no excess risk. In addition, if both the
cadmiun-copper subcohort and the vicinity workers are re-evaluated after
15 years of latency, the chance of detecting a significant prostate cancer risk
in the cadmium-copper workers is probably nonexistent, while at the same time,
a better estimate of the risk of lung cancer attributable to cadmium exposure
in both subcohorts might be had.
It should be noted that the work force of any factory may be rotated many
times during the factory's operating life. The fact that cadmiurn-copper alloy
workers, under the author's definition, apparently experienced a lower risk of
prostate cancer than did "vicinity" workers may not be unexpected, since it is
possible that many of the eight cases may have worked in the cadmium-copper
alloy department as well as in the remaining part of the plant at some time
during their working careers.
The observed risk of cancer may actually be greater than calculated be-
cause of the presence of the "healthy worker" effect, in which less than expec-
ted mortality is seen in the control group not only in the overall risk of
death from all causes (observed = 95, SMR = 88), but also with respect to the
risk of cancer (observed = 21, SMR = 83). If latency had been considered in
this study, this confounding effect could have been eliminated.
Because of the preliminary nature of the findings of excess lung and
prostate cancer in "vicinity" workers, and further questions that need to be
answered regarding the extent of exposures to cadmium, the findings of an
excess risk of prostate cancer in these workers should be regarded only as
suygestive. The finding of an excess risk of lung cancer due to cadmium expo-
sure must also be considered only suggestive at this time because of the pos-
sible confounding effects of smoking and of exposure to other metals such as
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arsenic. A greater effort should be made to assess the impact of these con-
founders and to evaluate the possibility of a dose-response relationship.
Sorahan (1981)
Sorahan (1981), in a preliminary report to the Third International Cadmium
Conference, related the findings of a historic prospective mortality study of
3,026 nickel-cadmium battery workers first employed during the period 1923
througn 1975 and still alive in 1946 but followed to June 30, 1980, and who had
worked at least one month. A subset of these same workers had been studied
earlier by Kipling and Waterhouse (1967). The Sorahan (1981) cohort was derived
from workers who had been employed in two separate factories, which were amalga-
mated in 1947. The earliest mention of cadmium in the air breathed by these
workers was reported in 1949, In the platemakiny assembly shops, the cadmium
content in the air ranged from 0.6 to 2.8 mg/m^, but in the "negative active
material" department, where cadmium oxide powder was prepared, the levels were
reported to be "considerably higher," although no numbers were provided.
Extensive local exhaust ventilation was installed in 1950, and as a consequence,
cadmium levels in the air were reduced to below 0.5 mg/m3 in most parts of the
factory. By 1967, when a new platemaking department was built, the level of
cadmium oxide dust in the air had been reduced to less than the threshold limit
value (TLV) of 0.2 mg/m^. From 1975 to the end of the study, the factory's
levels of cadmium oxide dust were within the current TLV of 0.05 mg/m^.
For the purposes of analysis, the author divided his cohort into 218 fe-
male employees, 1,066 male employees who were first employed before the amalga-
mation in 1947, and 1,494 males and 248 females who were first employed after
the amalgamation.
Standard mortality ratios (SMRs) were computed.. Expected deaths were
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generated on the assumption that the general population rates for England and
Wales were operating in the study cohorts. Overall, the observed number of
male deaths from all causes was slightly less than expected (observed = 591,
SMR = 97). With respect to all forns of cancer, there was virtually no diff-
erence between observed and expected deaths (observed = 152, SMR = 100). On
the other hand, a deficit of cancer deaths occurred to the subcohort of male
enployees who had been employed prior to the amalgamation (observed = 30, SMR =
84). But in males who were employed for the first time after the amalgamation,
a significantly increased risk of total cancer deaths was apparent (observed =
72, SMR = 129, p < 0.05). This increased risk was partially attributable to an
excess of lung cancer (observed = 32, SMR = 134, 0.05 < p < 0.10) in the latter
subcohort. In females, a slight nonsignificant risk of cancer was evident
(observed = 22, SMR = 111). No detailed breakdown of female cancer mortality
was provided by the author.
In both male subcohorts, those hired before 1947 and those hired after
1947, an excess but nonsignificant risk of cancer of the bronchus was evident
(observed = 45, SMR = 114; observed = 32, SMR = 134, respectively). No signi-
ficant excess risk of prostate cancer occurred in either group (observed = 4,
expected = 4.1; observed = 3, expected = 1.9, respectively). Even after cons-
ideration was given to the time since first employed, no significant excess
risk was seen in workers who were alive 15 years after first employment but who
had left the company in any of the following cause-of-death categories: all
causes, combined cancer, cancer of the bronchus, and cancer of the prostate.
Upon further subdividing the cohort according to "exposed" versus "nonex-
posed" status, the author reported no significant excess risk due to prostate
cancer (observed = 1, expected = 0.7) or cancer of the bronchus (observed = 10,
expected = 8.3) in the "exposed" subcohort. The numbers became rather small,
-------
however, and as a consequence, the power of this study to detect a significant
risk is diminished.
When consideration is given to length of employment and latency together,
i.e., males formerly employed at the factory for less than 1 year and from 1 to
14 years but followed for over 15 years since the onset of employment, again no
significant excess risk of bronchial cancer or prostate cancer is apparent. No
information was provided concerning mortality in those workers with more than
14 years of employment in a factory manufacturing nickel-cadmium batteries.
The author concluded, on the basis of his analysis, that no evidence exists to
suggest an increased risk of cancer mortality due to exposure to cadmium oxide
dust.
Sorahan's analysis of latent effects included only terminated employees
who were alive 15 years or longer after initial employment but who terminated
before achieving 15 years enployment. Person-years of individuals who were
employed for more than 15 years with the company by the cut-off date were not
enumerated. Only if the individual left employment with the company by the
15th year were his person-years counted. This arrangement has the effect of
altering the expected deaths by the non-inclusion of person-years of indivi-
duals who were at risk of death but who were still alive and working after 15
years, as well as those who worked longer than 15 years but had terminated.
Although the study controlled for the healthy worker effect and problems
with overlapping exposure and follow-up period, no comparison of persons who
worked longer than 15 years and who were either working or terminated was pro-
vided. Additionally, 82 persons remain untraced with respect to their vital
status, while 10 additional deaths were noted for which causes of death could
not be found. The non-inclusion of the causes of death of the deceased members
of this subgroup would tend to create a slight downward bias in the SMRs.
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Furthermore, the tabular data presented classifies the cohort into two
categories of exposure: "exposed" and "non-exposed," although in the "Popul-
ation" section of the study, the author describes the jobs in the factories in
terms of "high," "slight," and "minimal" exposure to cadmium. A clearer de-
tailed description is needed of how the three latter categories were reconsti-
tuted as "exposed" and "non-exposed" for the purposes of presenting the find-
ings in tabular form. The author's treatment of the subject suggests that some
portion of the study population received little exposure to cadmium. Further,
no urinary cadmium concentrations are given to substantiate exposure. If this
is so, perhaps these individuals should have been excluded from the study
group. A better definition of intensity of exposure should have been utilized
to present the tabul ar findings. It might have been more i nfomati ve to pre-
sent the tabular findings in terms of "high, "slight," and minimally" exposed
subgroups, as described by the author in the text.
Overall, this paper presents no evidence of an increased risk of prostate
cancer in cadmium-exposed workers. However, since several problems exist con-
cerning the structure of the study, the diminishing sensitivity of the study in
relation to certain highly exposed subgroups, the questionable evidence of
exposure in a larye portion of the cohort, and the lack of comparisons among
certain subgroups, the study cannot be said to provide conclusive evidence that
cadmium is not carcinogenic. Although 14 of the 15 analyses presented show
small, statistically insignificant excesses of lung cancer, it might be more
appropriate to call the results inconclusively positive for lung cancer.
Inskip and Beral (1982)
Inskip and Beral (1982) conducted a cohort mortality study on residents of
two small English villages, Shipham and Hutton, situated within seven miles of
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each otner. Shiphan is located in an area of substantial soil contami nat i on
by cadmium from the renains of a zinc mine that had operated on the site for
nearly 400 years, until the middle of the nineteenth century. The villaye of
Hutton was selected as a control. Investigations accomplished by the British
Department of the Knvironnent1s Shipham Survey Committee revealed average gar-
den soil cadmium levels ranging fron 2 to 360 g/g in the area, while national
leve's rarely exceeded 2 g/g. Cadmium was believed to be absorbed in the diet
mainly through the consumption of home-grown vegetables. According to a survey
conducted by "nomas (1980), the dietary intake of cadmium in Shiphan averaged
0.20 mg per week (range 0.04 to 1.08), while the national consumption averaged
0.1- ~ij per wee* (range 0.09 :o 0.18).
Seme 501 residents of Shipham and 410 residents of Hutton were entered
into the cohort on September 29, 1939, and were followed until December 31,
1979, •-,'he', Sr"^s were generated by cause of death. Data for both cohorts were
coTpar^d wsth population statistics fo- England and Wales. Excess risks of
mortality c^e to Hypertensive and cerebrovascular disease and geni touri nary
disease wene fourc in tne Slvuham residents. Cerebrovascular disease (observed
= 65, S'-'P. = 140, p < 0.05) was significantly high in residents of Shipham,
especially females (observed = 44, SMR = 144, p < 0.05), and although the
authors stated that a significant risk of genitourinary disease occurs only at
0.05 < p < 0.1, recalculating the ri sk using the Poisson method gives a value
oc p _< 0.03, for an SMR of 222 based on eight deaths, a statistically signifi-
cant result that aopea^s not to be due to chance alone.
Orly two prostate cancer cases were observed in each village. Thus, SMRs
were produced that do not differ significantly from those expected, although
they were based on small numbers. With respect to lung cancer, no significant
risks are evident, although the risk of lung cancer in females appears slightly
100
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elevated in both Shipham (observed = 4, SMR = 199} and Hutton (observed = 3,
SMR = 181), based on small nmnbers.
The autnors noted that overall mortality for these two rural communities
is low compared to that of England and Wales, partially because of urban-rural
confounding. They maintain that some evidence exists that cadmium influenced
the "pattern of disease" in Shipham, specifically as regards kidney disease.
On the other hand, the authors claim that the results do not support an assoc-
iation of cadmium and cancer or respiratory disease in cadmium-exposed
persons. However, with respect to cause-specific cancer mortality, their data
lack sensitivity because of diminishing power due to small numbers.
Another problem with this study, in addition to its low sensitivity
is the lack of information concerning each person's actual exposure to cadmium.
Although length of residence prior to 1939 could not be ascertained for
individuals in the Shipham cohort, the authors were able to establish that all
of the people studied in Shipham had lived there for at least 5 years. Fur-
thermore, only 70% could be assigned to exposure categories based on the loca-
tions of their residences in areas of high or low cadmium content in the soils.
Also, as the authors pointed out, the soil cadmium content, measured in 1974,
may not accurately reflect exposures in 1939.
The greatest difficulty with this study, however, is in the knowledge that
the average dietary consumption of cadmium in Shipham at 0.20 mg per week
(range 0.04 to 1.08) was really not very different from the national average of
0.14 mg per week (range 0.09 to 0.18). The failure to find a detectable signi-
ficant excess of cancer in Shipham residents may be due to a lack of sufficient
dietary exposure to cadmium in Shipham residents. Furthermore, the presumption
is that the cadmium was introduced through the gastrointestinal tract and not
via the inhalation route, that the luruj was not the target organ for cancer,
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and that therefore a significant excess of lung cancer would not be expected in
this study. Hence, this paper should he judged inadequate with respect to the
detection of a risk of lung or prostate cancer.
Andersson et al. (1982)
Andersson et al. (1982) updated the earlier Kjellstrofn et al. (1979) study
by enlarging his cohort to 548 men and 101 women and requiring that cohort
members have had a ninimum of one year of cadniun exposure between 1940 and
1980 at only one alkaline battery factory in Oskarshamn, Sweden. Exposure
levels were as described in the earlier Kjellstroin study, except that more re-
cent data indicated that cadmium levels in the air generally fell below
20 g/m^, and that nickel levels were below 50 g/m^. Indeed, exposure to nic-
kel seems to have been more prevalent in this factory than exposure to cadmium.
Periods of exposure for members of the cohort ranged from 1 year to 52 years,
with a median of 10 years. Twenty-five percent of the cohort were exposed for
better than 22 years. Expected deaths were derived from cause-, calendar
year-, and age-specific national rates of the Central Bureau of Statistics from
1951 to 1980. A total of 118 of the males died before 1981; the analysis was
limited to deaths prior to age 80 because of the unreliability of death certi-
ficate data after age 79. The authors noted 103 deaths versus 122.6 expected,
a deficit that was more than likely due to the "healthy wor
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The lithors concluded that a causal relationship probably exists between
earlier heavy cociiir un exposure and the risk of renal disease, as well as a pos-
s^ile causal relationship with obstructive luny disease. The authors felt that
one case of nasopharyngeal cancer was possibily due to exposure to nickel
hy-jroxide, which is believed to cause, nasal sinus cancer in nan.
With regard to prostate cancer, the authors felt that their data suggested
an increased risK--a finding that agrees with the earlier study by Kjellstrom
et al. ( 1979). Because of this study's lack of sensitivity, however, nothing
can be concluded from it with respect to lung cancer risks. Furthermore,
latency was not evaluated in these workers. Useful data might have resulted if
the lung cancer risk could have been evaluated without the requirement of a
lengthy exposure. Former employees who worked less than 15 years, and who died
from lung cancer many years later, could not be counted in tabulations in which
15 years of exposure were required for inclusion. The presence of nickel also
precludes any definitive statement about the risk of cancer in these workers.
For the above reasons, this paper nust be judged inadequate for use in evalua-
ting the risks of prostate cancer or lung cancer due to cadmium.
Kjellstrom (1982)
Kjellstrom (1982), in an updated historic prospective study of a cadmium
nickel-battery factory, reported on mortality patterns in a cohort of 619 male
employees (including 269 from an earlier study). During the study period from
1951 to 1980, 103 workers died, as compared to 126.4 expected on the basis of
Swedish mortality statistics. The highest SMR was for urogenital disease,
with 4 observed deaths versus 2.5 expected. This SMR is considered to be non-
significant. Only 4 prostate cancer deaths occurred, versus 3.1 expected. The
workers in this study cohort had a mininun of one year's exposure to cadmium.
103
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The author noted that, based on preliminary data, prostate cancer mortality was
"more increased than the mortality due to other causes." This increase was not
statistically significant, however.
The average historic exposure levels within this plant are depicted in
. Figure 1. From 1946 to 1976, there appears to have been a 1,000-fold drop in
average exposure levels. A detailed analysis of past and present cadmium
exposures in this factory has been published (Adamsson, 1979). The author
reports that nickel exposure levels have been at least the same as that of
cadmium, and often as much as 10 times higher.
This study presents a number of problems. The records of employees
terminated prior to 1945, a group in which the greatest risk is likely to be
found, are nonexistent. Almost 31% of this group had exposures to cadmium of
less than 2 years' duration. Almost 50% of the cohort (301 workers) received
their first exposures to cadmium after 1959, which neans that a large propor-
tion of the cohort had not been followed even for 20 years, and thus, not
enough time had elapsed for reliable evaluation of cancer risks. Furthermore,
smoking information was not available for the older workers, a subgroup in
which the greatest cancer risk is likely to be found. This may have been the
reason why no results evaluating the effects of smoking were presented in the
study, although a detailed data base was reported by the author to be in the
development stages as an extension of the study for future follow-ups. Addi-
tionally, the author reported that for cancer of the prostate, the rate ratio
increased with increasing latency and increasing dose. He reported rate ratios
of 1.27, 1.33, and 1.55, corresponding to the exposure categories of > 0 years,
> 1 year, and > 5 years. In the > 1 year exposure duration category, prostate
mortality rate ratios of 1.33, 1.44, and 1.81, corresponding to latency periods
of 1, 10, and 20 years, respectively, were given. However, since no tabular
104
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Cd/m3 air
10,000
1000
100
10
1946
1956
1966
1976 Year
Figure 1. Concentration of cadmium in the air (uy Cd/m3) from 1949 to 1976.
Arithmetic mean of stationary and personal samples.
SOURCE: '<; all Strom, 1982.
105
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data were presented, it is not possible to determine how the four observed
prostate cancer deaths were distributed into the subcategories referred to by
the author. The author did note that the numbers were too small for the detec-
tion of statistically significant differences.
Kjellstrom repeated tne analysis for urogenital diseases. For those with
more than 20 years' exposure and 20 years' latency, 4 observed urogenital
deaths occurred versus 0.93 expected (p < 0.05). This type of disease was
found exclusively in the form of nephritis of the kidney. Again, it is diffi-
cult to conclude without evaluation that cadmium exposure was implicated,
although the author himself stated that it is "clear that cadmium exposure
increases mortality from kidney diseases" after high exposure intensity and
long duration of exposure. The author noted a tendency in his data for a
slightly increased nonsignificant risk of prostate cancer from exposure to
cadmium.
In addition to the main study discussed above, Kjellstrom (1982) included
discussions of three Japanese studies (Japan Public Health Association [JPHA],
1979 , also reported by Shigematsu et al., 1981; Nogawa et al., 1978; and
Nogawa et al., 1981) and a description of another ecological study planned by
himself and the Department of Epidemiology at the University of Tokyo, for
which only preliminary findings are available. In this latter study, age-
standardized death rates in cadmium-polluted areas for persons 35-84 years of
age were compared with the respective rates in non-cadmium-polluted areas.
Preliminary data, according to Kjellstrom, suggested a nonsignificant tendency
toward higher mortality rates in cadmium-exposed areas as compared with control
areas (an age-adjusted mortality rate of 176 per 1,000 in cadmium-exposed areas
versus 139 in the control areas). Prostate cancer and kidney disease mortality
rates were also' higher in the cadmium-exposed areas, but most of the prostate
106
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cancer mortality excess occurred in individuals 85 and over. No tests of
significance were done. This analysis was reported by KjellStrom as tending to
support the hypothesis of a cadmium effect, but "definite conclusions have to
be left until all the analyses are completed."
Of the Japanese studies referred to by Kjellstrom (1982), the first (JPHA,
1979 , also reported by Shigetnatsu et al., 1981) was an analysis of cadmium
exposure and mortality in the general environment. According to the author,
people in many areas of Japan endure high cadmium exposures of up to several
micrograms per day from consumption of contaminated rice. For each of four
prefectures of Japan, age-standardized mortality rates were calculated in a
cadmiun-exposed area and compared to those calculated in a nonexposed reference
area of the same prefecture. It was found that cancer mortality rates were
generally about the same in the nonpolluted areas as in the polluted areas, but
no significance tests were done. The only diseases for which death rates were
found to be lower in the non-cadmium-polluted areas were kidney diseases and
diabetes. With respect to prostate cancer mortality, two of the polluted areas
had higher death rates than did the controls, while in two others the reverse
was true. The author noted that the two prefectures with higher death rates of
prostate cancer were the areas with the "highest likely cadmium exposure to the
population." The former two prefectures tended to have higher rates of mortal-
ity from kidney disease and hyperplasia of the prostate as well. Because this
was an ecological study, it can only be considered as suggestive of areas for
future research.
The second Japanese study (Nogawa et al., 1978) found that in 2,689 men
and women over age 50, the village-specific prevalence of low molecular weight
proteinuria (LMWP) increased with an increase in the village-specific average
cadmium concentration in rice. LMWP was measured by urinary retinol binding
107
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protein. It is very likely that this ecoloyical study included persons who
nad never been exposed to cadmium in rice, as well as persons with prior-exis-
ting conditions, possiDly introduced long before they were exposed to rela-
tively high concentrations of cadmium in rice. The positive association noted
Dy the author should not be construed to signify a causal association.
In the third study, Nogawa et al . (1981) conducted a mortality study of
the 81 men and 124 women identified in the earlier study as having LMWP. They,
along with the remaining men and women not found to have LMWP, were followed
from 1974 to 1979. The authors found a significant (p < 0.05) twofold
excess risk of death for men with LMWP and a nonsignificant 1.2-fold excess
risk of death for women with LMWP. Mortality rates were based on 27 deaths of
males witn LMWD and 30 deatos of females with LMWP. A positive association of
LMWP with heart disease, cerebrovascular disease, nephritis, and nephrosis was
noted. This association raises the specter of a possiole confounding effect
of hypertension with LMWP. If hypertension is a cause of LMWP, the higher
mortality of the individuals that had LMWP may nave been due to hypertension
and not, as the author suyyested, to cadmium exposure. Tne correlation with
L'-1W3 may tnus be spurious, and hence, conclusions drawn from this study regar-
ding an association of higher mortality with cadmium exposure must be charac-
terized as certainly ro more than suggestive.
Armstrong and Kazantzis (1983, 1982)
Armstrong ana Kazantzis (1983) recently completed a cohort mortality study
of 5,995 male cadm1' jm workers born before 1940, who had had at least one year
of employment during 1942-1970 in one of five British industries (primary pro-
duction 64%; copper-cadmium alloy 8%; silver-cadmium alloy 14%; pigments and
oxides 8%; anc stabilizers 5%). The authors classified their cohort (derived
108
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fron 17 major plants) into tne following three categories of exposure: 1)
"always low" (80%; 5,623 workers); 2) "ever medium" (17%; 1,173 workers); and
3) "ever high" (3%; 199 workers). Expected deaths were derived from SMRs based
on mortality rates for the population of England and Wales. In addition, the
authors referred to "approxinately accounting" for regional variations in
mortality by the use of cause-specific SMRs for standard regions published by
the British Office of Population Censuses and Surveys during the period 1969-
1973. This procedure is not completely described. The authors stated that in
one instance they used the urban aggregate of a primarily rural region to
derive SMRs for a plant that was situated in an urban portion of the region.
The authors developed two-sided confidence intervals for significance testing
through the use of the "exact" Poisson distribution method for some comparisons
and the "normal" distribution for others.
These authors developed job categories that reflect the categories of
intensity of exposure ("ever high," "ever medium," and "always low") based in
part on expected cadmium urine concentrations. The authors' classification
scheme is described as follows in their detailed report of April, 1982 to the
International Lead Zinc Research Organization:
The classification of a job was based on an assessment of the
absorption of cadmium by those working in that job, as indica-
ted by concentrations of cadmium in urine, where these were
available. "High" jobs entailed exposures which were judged
likely in the long term to lead to cadmium urine concentrations
of over 20 ;.g/l. This category was assigned only to certain
jobs in the past, when conditions were often very much worse
than any pertaining today. Workers exposed for long periods
in these jobs have shown levels of cadmium in urine as high as
100 iig/1 or more. "Medium" jobs entailed mean exposure less
than "High" jobs, but would lead to cadmium in urine concen-
trations sufficiently elevated for these to be clearly distin-
guishable from an occupationally unexposed group, even by the
methods of evaluation of urinary cadmium which were available
in the 1960s. An appreciable number of cadmium in urine concen-
trations over 5 yg/1 would be expected in a group of workers
with long term service in a "Medium" job. The remaining jobs
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are classified as "Low." Such jobs would involve some
occupational exposure to cadmium, but at concentrations
too low to meet the criterion for inclusion in the
"Medium" category.
In the author's "ever high" exposed group, only 3%, or 199 members of their
cohort, qualified (a minimum of at least one year spent in a high-exposure
job) (see Table 16).
Approximately 96% of this conort was classified with a known vital status,
whereas 4% either emigrated or were not traced. The authors excluded 38 deaths
occurring to individuals 85 years of age or over. Presumably the authors
ceased counting person-years for those live individuals who reached age 85 and
over as well in order to retain comparability. The SMR for all causes of death
was 97 (based on 1,902 deaths). The SMR for the first 10 years of follow-up
was 79 (oased on 205 observed deaths) and for later years was 99 (based on
1,697 deaths), a phenomenon cue most likely to the healthy worker effect. The
authors found a significant excess of mortality due to bronchitis in the "ever
high" exposure group, which appears to be dose-related (12 observed vs. 2.8
expected, o < 0.01) without regard for latency. This risk diminishes to a
nonsignificant SMR of 138 in the "ever medium" group and finally to an SMR of
121 in the "always low" group, without regard for latent factors. Prostate
cancer remained nonsignificant in all three exposure categories, without regard
for latent factors. Because of the small numbers involved, however, the study
could not detect a prostate cancer risk in the "ever high" exposure category.
Although the authors stated that this cohort had seen analyzed according to
years since time of initial exposure, in the published version only the overall
SMR was presented for those with 10 years or more of follow-up. Also, no
detailed tab^ar data were provided with respect to lung cancer or prostate
cancer by time since onset of initial employment in the published results.
110
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TABLE 16. PERCENT DISTRIBUTION OF STUDY POPULATION
BY LEVEL OF INTENSITY OF EXPOSURE
Intensity of
exposure3
Urine cadmium
concentrati on3
Armstrong et al.
(1983)
Always low
< 5 ug/L
80%
Ever medium
5-20 pg/L
17%
Ever high
> 20 pg/L
3%
Cohort size
—
6,995
definition from Armstrong and Kazantzis, 1982.
The authors agreed that the number of persons in the "ever high" exposure
group (N = 199) was too small to preclude the possibility of the existence of a
risk of prostate cancer from exposure to cadmium in this group. They further
noted that no cases of prostate cancer turned up in tne "ever medium" group,
whereas 2.5 were expected. Prostate cancer was near to expected levels in the
"always low" exposure group (23 observed, 20.4 expected) into which the large
majority of the cohort fell. However, the authors provide no breakdown of
site-specific cancer by time {10, 15, or 20 years) since onset of initial
employment according to their three categories of exposure. Of interest is
whether sufficient power remains in the study to detect a significant excess
risk of prostate cancer in the latter two categories of exposure, particularly
the "ever medium" group, 10, 15, or 20 years after the onset of exposure.
Furthermore, the possibility exists that when workers of 17 different
plants are thrown together to form a massive cohort for study, some of these
workers may have had little or no exposure to cadmium. If this occurred in the
study under discussion, the likelihood of detecting a risk is reduced by the
111
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inclusion of person-yea^ for ircividuals who essentially w.^e not exposed
to cadmium. Tnis is especially :rue if tnere is a dose-response relationship
operating in the cohort. Unless reliable criteria ore established to quantify
indi vidua" exposures to cad-n:ui;i dust and compounds of cadmium, in addition to
other conf-jund' ncj substances that nay be oresiint, it cannot be presumed that
every -ne.nber of this cohort was exposed to cacbrum in high enough quantities to
jrociuce a detectable health r- sk. Furthermore, although some recent monitoring
cata nay ex: st with wilier to quant i fy exposures, it is questionable that suffi-
c i ert industrial exposure measurement data exist fron the 1940s or 1950s and
earli er no pro/ide more than a guess at the levels of exposure to cadmium and
otne" :ieta 1 s that existed when these persons were first employed. It may be
that the ni styri ca ^ prospective study design i s not. a sensitive enough ana-
lytical tool to be used "in assessing cancer risks in a cohort of workers who,
"n general, were exposed to only "low' love's of cadmium. On the basis of the
above factors, this study is seer to provide no evidence that cadmium is a
powerful prostate ca^ci nogen.
On the other hare, a:trough the ri sk of lung cancer overall was not sig-
nificant (observed - 19-J, SMR - 107) without regard to intensity of exposure,
the subgroup of workers who were employed for 10 or more years in low-exposure
jobs exhibited a statistically significant excess risk of lung cancer (SMR =
126, observed = 100, p < G.Q5) (Tab'e 17). 7-ne authors, in an earlier draft
cf this paper (Armstrong and Kazantzis, 19S2), presented data concerning the
1 v.ny cancer risk in workers having a mininu" of 1C years' employment in the
categor-es of "ever high" and "ever medium" exposure to cadmium. With respect
to the "ever high" exposure category, no evidence exists of an elevated risk
of lung cancer 'SMR = 87*, observed = 2) a^ter 10 years' employment; however,
*Due to an error in the authors' calculations, this SMR was given as 37 when
it should have been 83.
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little power remains with which to detect an elevated risk in that group.
The power to detect a twofold excess of lung cancer in this category is only
0.11, and for a threefold risk it is 0.30. On the other hand, a suggestion of
an elevated risk is apparent in the "ever medium" exposure group (SMR = 142,
observed = 16) with 10 or mo re years of employment in the industry. It would
have been valuable, however, to include a discussion of the lung cancer risk by
longer tine intervals since onset of exposure (i.e., 15 or 20 years). Power
considerations probably would render such calculations of lung cancer risk in
the "high" exposure subcohort and the "medium" exposure subcohort questionable.
TABLE 17. LUNG CANCER SMRs BY EXPOSURE GROUP
FOR MEN WITH TEN OR MORE YEARS OF EXPOSURE
Exposure level
Observed
Expected
SMR
(95% CI).
Always low
100
79.1
12 6a
(102-151)
Ever medium
16
11.3
142
( 81-230)
Ever high
2
2.4
83
( 10-301)
Total
118
93.2
127 a
(104-150)
dSigni ficant.
SOURCE: Kazantzis, letter of February 10, 1984.
The increased risk of lung cancer in the "always low" exposure category
cannot be ascribed necessarily to cadmiun exposure. It is generally accepted
that manual workers smoke more than the general population; thus, it Is not
inconceivable that some of this increased risk is due to smoking. The authors
state further that the absence of a gradient of risk with intensity of exposure
113
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makes it unlikely that the excess is due to cadmium, A full tabulation of SMRs
in the three exposure intensity categories by tine since onset of exposure
(10, 15, and 20 years) and similar duration of employment intervals Tiight pro-
vide better dose-response information.
The exceptionally high risk of bronchitis in the "ever high" exposure
group cannot be attributed to a cigarette smoking link because of the lack of
a social-class gradient in the three exposure intensity categories. Although
it is possible that other industrial pollutants may have contributed to this
excess in the "ever high" exposure group, tne autnors point out that the size
of the excess is much too great to be solely attributable to sjch confounding
effects. Hence, they conclude that cadmium may have contributed to the excess
of bronchitis.
Overall, this study did not sufficiently address the impact of latency and
duration of exposure on tne risk of prostate cancer, lung cancer, and hyper-
tensive disease, i.e., because it considered only a single cut-off point (10
years). Perhaps additional tabulations that the authors state are in their
possession- can provide answers to the questions raised. While this study pro-
vides no evidence of a risk of prostate cancer, the possibility remains that at
the exposure intensities indicated following a lapse of 10, 15, or 20 years
fron initial exposure, the historic prospective metnod may no longer be sensi-
tive enough to detect a prostate cancer risk, if in fact one exists.
Based on the authors' definition of exposure, only 3% (or 199 employees)
could have been expected to t-ave achieved a urine concentration of 20 g/L
cadmium, as contrasted with 100% (or 602 employees) of the Thun et al. (1985)
cohort. It appears that there is an absence of evidence of exposure to con-
centrations of cadnium that would produce a detectable cancer effect in this
cohort. Eighty-one percent of this cohort fell into the exposure category
114
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"Always low," i.e., < 5 g/L cadmium urine concentration, considerably less
than the exposures sustained by the Thun et al. (1985) cohort. The vast
majority of the Armstrong and Kazantzis cohort consisted of members who had had
very little exposure to cadmium.
A significant excess risk of lung cancer appears evident in workers with
10 years of "low" exposure to cadmium; however, this excess risk is not neces-
sarily due to exposure to cadmium. Comparable data in the "ever medium" expo-
sure yroup indicates a nonsignificant risk of lung cancer, but latency is not
evaluated in sufficient detail. Perhaps further follow-up night sharpen the
excess found in this category. The data from the "ever high" group lack suf-
ficient sensitivity to be judged adequate for the detection of a risk of lung
cancer. It would be of interest to see if the addition of the 38 causes of
death of persons over age 85 would alter the calculated risks. It might also
he of some value to repeat the analysis on a plant-by-plant basis to determine
which plants exhipit the highest risks by cause, and then develop exposure
indices for those plants.
Nothing can be said on the basis of this study concerning the risk of
hypertensive disease, except that it bears watching. However, the risk of
bronchitis, which the authors conclude is probably due to exposure to cadmium
dust, appears to be very significant. The dose-response relationship noted
by the authors for bronchitis cannot entirely be attributed to confounding
effects.
Sorahan and Waterhouse (1983)
Sorahan and Waterhouse (1983), in an update of the earlier study by
Sorahan (1981), employed a technique referred to as the "method of regression
models in life tables (RMLT.)" by Cox ( 1972) and Kneale et al . (1981) to test
115
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the null hypothesis that occupational exposure to cadmium is not associated
with excess mortality. Only one set of mortality data was derived by means of
calculating SMRs. Without qualification, only the risk of respiratory cancer
was found to be statistically significant (observed = 89, expected = 70.2,
p < 0.05). The risk of prostate cancer was elevated slightly but not signifi-
cantly (observed = 8, expected = 6.6) in this phase of the study. These data,
however, nay not include one to four of the earlier prostate cancer cases found
by Kipling and Waterhouse (1967), for the reasons stated below.
In the second part of their study, utilizing the RMLT, the authors pre-
pared analyses with and without tne four original cases included. The authors
believed that only new cases of prostate cancer should be used to determine an
RMLT-deMved asymptotically normally distributed test-statistic measuring the
significance of cancer of the prostate in their cohort. Tne potential con-
'ounde.rs of sex, nixing date, age at hire, length of enpl oynent, and employment
states were controlled for by stratifying the data into sub-groups defined by
all possible combinations of various levels of these controlling variables.
Exposure was defined to be cumulative duration of employment in a "high"
exposure job,- and secondly as cumulative duration of employment in a "high or
moderate" exposure job. Job categories were classified by exposure to cadmium
as "hign exposure," "moderate (or slight) exposure," and "minimal exposure."
Only 8 jobs were considered to involve "high" exposure, while 14 were consi-
dered to involve "moderate 'or slight)" exposure, and 53 were considered to
involve "rr,in"imal exposure." With the four original cases included, the test-
statistic (3.10, p < 0.05) was significant cor the variable "highly exposed,"
but was nonsignificant (-0.32) when the original four cases were excluded.
Even when reduction in exposure levels over calendar year periods was pro-
grammed into tne analysis (assumed exposure levels from 1968 to 1972 were 40%
116
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of levels existing prior to 1967, and 10% post-1972) the test-statistic
increased to 3.52 (p < 0.01) with the original four prostate cancers included.
The authors, however, chose to note instead that "the effect of excluding the
four previously reported cases of prostatic cancer is to reduce the statis-
tically significant positive statistic to a small nonsignificant negative sta-
tistic." They concluded that "no new evidence has been produced which suggests
an association between occupational exposure to cadmium and cancer of the
prostate." If these persons are to be excluded, such exclusion should be
accomplished by redefining the study cohort so that selection biases do not
creep into the results. This could perhaps be accomplished by defining a later
time of initial employment.
The test-statistic generated for respiratory cancer in the "high-exposure"
category in men is nonsignificant at 1.28, but for "high to moderately exposed"
individuals, it is significant at 2.51 (p < 0.05). The authors suggested that
exposures to the welding fumes of oxyacetylene found in jobs of "moderately
exposed" workers might have accounted for this excess, which was chiefly con-
fined to workers who began employment prior to 1940 (3.09, p < 0.05), to those
who worked a minimum of 5 years (2.49, p < 0.05) and to those observed for 30
years or longer (3.18, p < 0.05). A significant test-statistic (2.36, p <
0.05) was also obtained for a third exposure estimate (duration of "high" or
"moderate" exposure employment, excluding welding) for the period 30+ years
after first employment. In no instance did age, sex, year of starting employ-
ment, or years of follow-up produce a significant test-statistic for lung
cancer in the group with the highest potential exposure to cadniuri.
The authors pointed out the possibility that since job applicants with
histories of lung and kidney disease were traditionally excluded from "high-
exposure" jobs, this would tend to work against the demonstration of a poten-
11.7
-------
tial hazard for related diseases in this category. They also indicated that
since only 12* of their 599 deaths were in workers with more than 5 years'
high-exposure employment, but 24% were in workers with moderate- or high-
exposure employment of more than 5 years, this might explain why a significant
statistic was not found for lung cancer in the "high" exposure group if, in
fact, occupational exposure to cadmium oxide is a risk factor. Presumably,
this differential mortality may indicate a lack of sensitivity in the "highly"
exposed group due to small numbers. If such a risk dose not exist in truth,
the explanation for tne seemingly inverse dose-response effect may be due to
exposure to oxyacetylene welding fumes, exposure to nickel hydroxide dust, or
to chance alone.
The authors felt also that although information on their cohort's smoking
habits was not available, if smoking were the reason for an excess of respir-
atory cancer, then similar associations should be expected for diseases of the
circulatory system, and such associations were not found. The authors stated
that the analysis could not differentiate between exposure to cadmium oxide
dust and exposure to nickel hydroxide because almost every job with high cad-
"nun exposure also had high nickel exposure.
In conclusion, Sorahan and Waterhouse (1983) found an increased risk
of prostate cancer that was entirely dependent on the original four cases of
Kipling and Waterhouse (1967), but found no association with prostate cancer
for cases subsequent to these. They also found an increased risk of respir-
atory cancer among workers moderately or highly exposed to cadmium oxide dust
and initially employed before 1940--a finding which was confounded by expo-
sures to oxyacetylene welding fumes and to nickel hydroxide dust.
Varner (1983, unpublished)
ASARCO Inc., the owners of the cadmium processing plant that had been
118
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studied by Lemen et al. (1976), updated toat study with one of their own
(Varner, 1983, unpublished) in which all employees were included who had had at
least six months of emp1 cynient at the cadniun processing plant between January
1, 1940 and December 31, 1969. The size of the cohort was enlarged to 644.
T' is preliminary report was accompanied by a letter to David Bayliss of the CAG
fro'i Lowell White of ASARCO, dated January 11, 1984, in which White indicated
that the follow-up for this study extended to the end of 1981.
Varner (1983) used a methodological technique called the Standardized
Cause Ratio (SCR), which is analogous to the calculation of proportionate
nortality ratios. Expected deaths for particular causes of death are derived
by dividing age- and cause-specific attributable deaths by total deaths in the
age and year category corresponding to each particular decedent's age and
year of death. The resulting proportions are summed to arrive at the number
of expected deaths. Their analysis was reported at the time to be under peer
review, according to White (letter to David Bayliss, CAG, January 11, 1984).
The preliminary findings of Varner ( 1983) differed from the Lemen et al .
(1976) study in that the risk of prostate cancer was found to be no longer
statistically significant, although it was still elevated (observed = 5,
SCR = 169)*, while the risk of lung cancer remained statistically significant
(observed = 23, SCR = 163). The author attributed the excess risk of lung
cancer in his study to several factors: increased cumulative exposure to cad-
mium, years of exposure, age at death, latent period, and/or cigarette smoking.
The author maintains that a "substantially higher than nornal prevalence
of heavy ciyarette smokiny" in a subcohort of the main study cohort may have
contributed to "part or all" of the increased lung cancer incidence. Other
findings include a significant risk of urinary tract cancer (observed = 6, SCR
= 252, p < 0.U5); specific bladder cancers (observed = 5, SCR = 374, p < O.lU);
119
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total cancer (observed = 53, SCR = 126, p < 0.05); nonrnal i ynant respi ratory
disease (observed = 7, SCR = 153, p < 0.05); ulcer of the stomach and duodenum
(observed = 7, SCR = 452, p < 0.01); and accidents (observed = 19, SCR = 150;
p < 0.05). However, the findings also reflect a significant deficit of deaths
due to heart disease (observed = 68, SCR = 77, p < 0.01) and stroke (observed =
6, SCR = 40, p < 0.05).
Calculated cumulative exposure to cadmium (mg-years/m^) was determined for
every member of the cohort on the basis of personal monitoring measurements made
during the period 1973-1976. The author pointed out that this variable assumes
that exposures over several decades were about the same. The author felt that
such a procedure tends to underestimate exposures of many years ago when cadmium
levels were probably higher, while at the same tine tending to overestimate
exposures of recent years.
Varner (1983) found that a dose-response relationship existed with respect
to lung cancer, and to a lesser degree, total malignant neoplasms, as follows:
Exposure Lung cancer Malignant neoplasms
(mg-years/m3) Observed SCR Observed SCR
0-4 7 95 23 108
5-15 6 159 14 123
16+ 10 332 (p < 0.01) 16 168
Lung cancer was also found to be related to smoking in the following manner:
Pack-years Observed SCR
Unknown 10 115
Nonsmokers 0 —
1-19 2 183
19 11 313 Ip < 0.01)
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No such effects were seen for bladder cancer.
With respect to Tuny cancer, the author reports that 77.5% of the cad-
niun workers had been snOKers, and tnat 53.2% had achieved 20 or more pack
years. Varner, citing statistics from a 1970 Household Interview Survey by
ttie National Center for Health Statistics, reported that 69.2% of Dlue collar
workers had ever smoked, and that 28% had snoked a pack or inore of cigarettes a
day at some time in their lives. Thus, Varner concluded that evidence exists
for a potential confounding effect due to cigarette smoking, since the propor-
tion of smokers in the Varner (1983) cohort appears to be somewhat greater than
that shown by survey data.
In the letter attached to this preliminary paper, Dr. White cautioned
that several problems had to be: solved concerning the validity of the study's
findings, not the least of which involved the credibility of the derivation of
SCRs. The National Institute for Occupational Safety and Health (NIOSH) update
of the Lemen et al. (1976) study, which is reviewed later in this section, also
contained 63 fewer individuals, who were allegedly excluded by NIOSH for "vari-
ous reasons" upon which Varner does not elaborate. Varner claimed that he in-
cluded all individuals "regardless of exposure." However, Or. Michael Thun of
NIOSH, in an internal memorandum, a copy of which was given to the Carcinogen
Assessment Group (CAG), states that the eligibility requirement for inclusion
of workers into the study cohort was decided on, in advance, by NIOSH and
ASARCO, and that both Varner and Lowell White were aware of it (memorandum,
October 17, 1984). Therefore, Dr. Thun maintains, NIOSH was not inconsistent
in adhering to the eligibility criteria, contrary to the letter from White.
NIOSH removed 10 persons from the cohort because they were either non-white or
female; hence, only 602 males were included in the NIOSH study by Dr. Thun.
Another problem with the study is that the death certificates were
121
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received oily 2 weeks prior to the presentation of the paper at the Fourth
International Cadmiun Conference, thus necessitating the use of cause-of-death
codes that appeared on the death certificates as they were received. Both the
NIOSH cause-of-death codes and those of the state are described as differing.
White referred to the presence of what he termed "nosology bias" in the ascer-
tainment of underlying causes of death. He stated that some 93 death certifi-
cates were coded by a different nosologist than the one who performed the
coding for the preliminary report, leading to 21 distinctly different cause of
death codes. The authors are seeking a neutral "unbiased" method for coding
death certificates prior to the issuance of a final report on the study.
Furthermore, White believes that the possible presence of confounding variables
as an explanation for elevated risks, especially of lung cancer, has not been
properly or completely addressed in this preliminary report. White reported
that Michael Thun and his cowor
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exp::>sure. Additionally, although the risk of prostate cancer is elevated, it
is no longer statistically siynificant. Whether the final version of the study
will sustain such a finding is not presently clear, in view of the -:any problems
that nust be solved. It does not appear at this tine that the final version of
the study will be forthcoming in the very near future.
Hence, tne Varner study cannot, at present, be used either to substantiate
an excess risk of lung cancer due to cadnium exposure or to refute the earlier
findings of siynificant prostate cancer in the Lemen et al. study.
Thun et al. (1985)
In an enlargement and update of the Lemen et al. (1976) study, Thun et
al. (1985) broadened the cohort to include 602 white nales who had worked a
minimum of 6 months in production work during the period 1940-1969. The resul-
ting cohort was followed an additional 5 years to the end of 1978. The differ-
ence between the size of the Varner (1983) cohort of 644-602 = 42 and the Thun
et al. (1985) cohort was described by Thun as being due to the inclusion of 32
persons who had worked less than one year and 10 non-whites and females in. the
Varner cohort (memorandum, August 17, 1984). Cause-specific mortality rates ¦'
for seven causes of death, suspected a priori of being related to cadmium
exp.os'ure, were compared between the cohort and U.S. white males. Death certi-
ficates were coded by a qualified nosologist according to the protocol of the
version of the International Classification of Diseases (ICD) in effect at the
time of death. Expected deaths were calculated using the life-table system
developed by NIOSH. The risk of ^ung cancer (observed = 20, SMR = 265, p <
0.05) was significantly in excess among workers hired both before and after the
cessation of arsenic smelting in 1925 and having been employed for 2 or more
years (Table 18). Prostate cancer was no longer excessive in these workers.
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TABLE 18. MORTALITY FROM LUNG CANCER (ICO 152-163)
BY DATE OF HIRE, WITH MALE CADMIUM PRODUCTION WORKERS
Hired prior
to 1/1/26
Hi red on or
after 1/1/26
Overall cohort
_> 2 years
e:np 1 oyment
Total _> 2 years
empl oyment
Observed
16
16
20
Expected
0.56
10.87
7.00
7.56
95%
confidence
SMR interval
714
147
195-1,829
84-239
229 131-371
265
SOLRCE: Tnun et al., 1985.
From the data given in Table 19, it was estimated that inhaled exposure
concentrations decreased with the introduction o£ a mandatory respirator pro-
gram in the early 1940s and ventilation controls in about 1970. The estimates
are based or personal work history area monitoring data, adjusted to reflect
actual inhaled exposures during the wearing of respirators. The source of the
data--the plant's personnel records — provided enough detail so that broad job
categories could be assigned to each period of a worker's employment.
The plant studied has produced cadmium metals and cadmium compounds from
1925 to the present. It was an arsenic smelter from 1918 to the early 1920s,
when it was shut down for several years, and was a lead smelter from 1886 to
1918. brine cadmium data, which were available for 261 members of the cohort
employed beyond 1960, suggested a highly exposed population. Since arsenic
124
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TABLE 19. ESTIMATES OF INHALATION EXPOSURES (mg/m3) BY PLANT DEPARTMENT AND TIME PERIOD3
Time
Peri od
Sampli ng
Roaster
Mi xi ng
Calci ne
Sol uti on
Tankhouseb
Foundry
Retort
Pi gment
Oft ice an<
Labc
Pre-1950
1.0
1.0
1.5
1.5
0.8
0.04
0.8
1.5
0.2
0.02
1950-1954
0.6
0.6
0.4
1.5
0.8
0.04
0.1
0.2
0.2
0.01
1955-1959
0.6
0.6
0.4
1.5
0.4
0.04
0.1
0.2
0.04
0.01
1960-1964
0.6
0.6
0.4
0.4
0.4
0.02
0.1
0.2
0.04
0.007
1965-1976
0.6
0.6
0.4
0.15
0.04
0.02
0.04
0.2
0.04
0.007
Estimated inhalation exposures occurred in various departments and were based on area monitoring data adjusted
to reflect the actual exposures of workers wearing respirators.
bTankhouse estimates were also used for non-production plant departments (e.g., repair shops) that were not
measured di rectly.
c0ffice estimates were also used for non-plant areas (e.g., the plant guard) that were not measured directly.
SOURCE: Smith et al., 1980.
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is a known lung carcinogen, the authors separated arsenic-exposed workers
from the rest of the cohort by dividing their cohort into two subgroups,
those employed on or before January 1, 1926, and those employed after that
date.
In the first group, 4 lung cancer deaths were observed versus 0.56
expected, while in those employed 2 years or longer after January 1, 1926,
16 observed lung cancer deaths were observed versus 6.99 expected, p < 0.05
(Table 18).
A dose-response relationship was also observed between lung cancer
mortality and cumulative exposure to cadmium (Table 20). At a cumulative
exposure of less than 584 mg-days/m^, both the SMR and the SRR are less than
expected at 53 and 0.48, respectively. As cumulative exposure increases to
between 584 and 2,920 mg-days/m3, the SMR and SRR increase to 152 and 1.55,
respectively. Finally, at cumulative exposures above 2,921 mg-days/m^, the
SMR and SRR increase significantly to 280 and 3.45, respectively. Cumulative
exposure to cadnium was calculated based upon length of employment and jobs
within the plant. Average exposure to airborne cadmium was calculated based
on the industrial hygiene data in Table 19. Each worker's cumulative exposure
over time was the sum of the products of number of days worked in each given
job category by the average inhalation exposure of each job category during
each respective time period throughout the entire period of employment of
that indi vidual.
With respect to arsenic exposure after 1925, a small and unspecified
number of workers processed arsenic intermittently in one building of the
complex. This lasted into the 1930s. A second, continuing source of arsenic
exposure came in the sampling, mixing, roasting, and calcine furnace areas.
Six industrial hygiene measurements in 1950 showed arsenic concentrations
126
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TABLE 20. LUNG CANCER (1CD 162-163) MORTALITY
BY CUMULATIVE EXPOSURE TO CADMIUM:
WHITE MALES HIRED ON OR AFTER JANUARY 1, 1926
Cumulative Forty-year
exposure TWA
(mg-days/m^) equivalenta Deaths SMR15 SRRC
£ 584
< 40 ug/m3
2
53
0.48
585-2,920
41-200 ug/m^
7
152
1.55
_> 2,921
> 200 yg/m^
7
280d
3.45
U.S. white mal es
100
1.00
Represents the time-weig'nted average (TWA) that, over a 40-year working life-
time, would result in this cumulative exposure.
&SMR = Indirectly standardized mortality ratio.
CSRR = Directly standardized rate ratio, relative to the U.S. white male
general population.
dp < 0.05.
SOURCE: Thun et al., 1985.
127
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ranging from 300 to 700 ug/m3 in the vicinity of the roasting and calcine
furnaces, the highest measurement anywhere in the plant. The authors report
that later measurements by the company and the U.S. Occupational Safety and
Healtn Administration (OSHA), in 1979, indicated a decrease in arsenic con-
centration to around 100 pg/m^ in this area. However, the author points out
tnat although air levels of arsenic in this specified area were 10 times the
OSHA tnreshold of 10 ug/m3, the personal exposures of individuals in this
area were lower because of respirator usage--a practice that had been in
effect since the 1930s (Smith et al., 1980). In fact, on the basis of the
assumption that workers received more exposure to.arsenic then they really
did, the authors estimate that the average arsenic exposure of persons in
this study would have been no more than 25 pg/m^ under the following con-
ditions:
(1) assuming the average airborne arsenic exposure was 500
in the high-arsenic work areas (i.e., calcine furnace, mixing,
roasting, and sampling);
(2) assuming a respiratory protection factor of 75%; and
(3) estimating that 20% of the person-years of exposure were spent
in high-arsenic work areas (based on personnel and biological
moni tori ng data).
Hence, according to the authors, if the 586 workers hired after 1926 were
employed for an average of 3 years, they would have acquired 1,758 person-
years of exposure to 25 i: g/m3 of arsenic. Based on an OSHA risk assessment
model for arsenic (OSHA, 1983), such an exposure should have resulted in no
more than 0.78 lung cancers. The authors feel that the 25 ; g/m^ figure
overestimates actual exposures because only a fraction of jobs in the "high-
arsenic" areas involved exposures as high as those in the furnace areas.
128
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Hiyh-exposure jobs in the roaster area were frequently staffed by entry-level
workers with less than 6 months' employnent, who would for that reason never
qualify for inclusion in the study, although the authors included them in
their estimate tnat 20% of the person-years of exposure were in "high-
arsenic" jobs. Furthermore, the authors point out that urinary arsenic
levels from I960 to 1980 averaged 46 yg/L, which is consistent with an in-
haled arsenic concentration of 14 yg/m^. Therefore, if one assumes an
average inhaled concentration of 125 yg/m^ (25% of 500 yg/m^) over 3
years, as did Thun et al ., a ninefold overestimate of exposure results, which
more than offsets the unquantified high exposures during the early years.
Based on the above analysis, the authors concluded that arsenic alone could
not explain the observed excess of lung cancer deaths in this cohort.
With respect to cigarette smoking, information concerning the smoking
habits of 70% of the cohort was obtained from survivors and next-of-kin. Some
77.5% for whom information was available were current or former smokers. This
prevalence of "ever" smokers is close to the 72.9% prevalence noted among white
males over 20 in the 1965 Health Interview Survey referred to previously. The
authors pointed out that even if the percentage of heavy smokers (25+ ciga-
rettes/day) in the cadmium cohort were double that of the 20% white male 1965
population, the rate ratio would increase by only 1.25, according to the method
of Axel son ( 1978). Hence, the authors conclude tnat c-garette smokiny is
unlikely to account for the twofold increase in lung cancer ceaths observed
among workers in this cohort with 2 or more years of employment.
Besides an increase in the risk of lung cancer brought about by expo-
sure to cigarette smoke per se, there is also potentially an added component
to this risk due to the presence of cadmium in cigarette smoke. However, it
is not likely that the added burden of cadmium found in cigarette smoke would
129
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have contributed in any substantial way to the risk of lung cancer already
sustained by members of this cohort from the rather high concentrations of
airborne cadmium found in the cadmium production plant. The earlier 1981 EPA
Health Assessment Document on Cadmium estimates that a 1 pack/day smoker
would retain an estimated 1.41 ;jg./day of cadmium in his lungs from an
estimated exposure level of 2.2 :Jg/day, which is the equivalent of exposure
to 0.28 pg/m3 of cadmium in ambient air. Estimates derived by Smith et
al. (1980) indicate that inhalation exposures in the production plant ranged
from an average low of 20 ug/m^ in the tankhouse in the period after 1960
to an average high of 1,S00 ug/m^ in the mixing department prior to 1950.
Overall, it appears that the levels of airborne cadmium to which the workers
of this cohort were subjected were considerably higher than those which
smokers would have sustained from expos jre to cadmi jci in cigarette smoke.
Indeed, the increase in the lifetime burden of cadmijm from a pack/day smoker
for 40 years at 2.2 jg/n^ of cadmium would equal onTy
0.28 ug/ri^ x 40 years x 365 days/year = 4,1 mg-days/m^. """his total additive
1,000 .jg/mg
cumulative exposure from cadmiut in cigarette smoke is less than \% of
the lower limit of the cumulative exposure in which the first excess nonsigni-
ficant lung cancer risk is seen.
Of concern in this study is the possibility that the combined effect
of increased cigarette smoking and exposure to arsenic might have served to
produce the significant positive risk of King cancer observed in this cohort.
Such an effect is not likely to be present in this cohort.
In a study by Pinto et al. (1978) of arsenic-exposed workers at the ASARC0
copper smelter, the authors actually *ound an inverse relationship between
cigarette smoking and arsenic exposure (Table 21). In this table from the
Pinto et al. (1978) study, the relationship of smoking status and the risk of
130
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dying from respiratory cancer in retired arsenic workers is presented. The
SMR was actually higher at 506 in nonsmokers, but lower in smokers at 287.
TABLE 21. NUMBER OF RETIREES, OBSERVED RESPIRATORY CANCER DEATHS,
AND STANDARDIZED MORTALITY RATIOS BY SMOKING STATUS
OF 377 MEN ALIVE ON JANUARY 1, 1961
Number of Number of
Smoking status retirees deaths SMR
Smokers 189 15 287.3a
Ex-smokers 69 3 245.1
Nonsmokers 119 3 506.5a
ap < 0.05
SOURCE: Pinto et al., 1978.
On the other hand, a study by Pershagen et al. (1981) found that the
synergistic effects of concurrent exposure to both cigarette smoking and
arsenic exceeded the sum of the separate individual contributions. However,
the Carcinogen Assessment Group (CAG) has had an opportunity to review and
evaluate the Pershagen et al. (1981) case control study of 190 arsenic ex-
posed individuals and their controls. It was found that the synergistic
effect of arsenic and smoking was not statistically significant by either the
Schlesselnan (1982) test for synergy or by a test for interaction with a
log-linear model. We judged his results to be inconclusive.
By contract, in another study by Welch et al . (1982), the effects of
arsenic exposure and smoking habits of 1,800 Anaconda copper smelter workers
were examined. Although the authors found an additive effect, no synergistic
131
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effect (Table 22) was found. Welch and his colleagues reported that there
was a "relative lack of importance of smoking as compared to arsenic exposure."
In commenting on the Pershagen (1981) case-control study, these same authors
said, "Our findings contrast with those of these researchers (Pershagen et
al.) in that we found no evidence of interaction, and found arsenic to be
relatively more important than cigarette smoking."
Summary
Of the many epidemiologic studies of cancer in cadmium-exposed persons
reviewed by the CAG, only four (Kipling and Waterhouse, 1967; Lemen et.al.,
1975; Hoi den, 1930; and Sorahan and Waterhouse, 1983) provide evidence of. a
statistically significant positive association (p < 0.05) of cadmium with
prostate cancer.
Several other studies (Potts, 1965; Kj ell Strom et al. , 1979 ; McMichael
et al . , 1975a, b; Anderssen et al . , 1982; Kjellstrom, 1982; Varner, 1933,
unpublished; and Tnun et al., 1985) provide the suggestion of an increased
r i s k. of orostate cancer (although statistically nonsignificant) with exposure
to cadmium.
With respect to these studies, however, several comments are in order.
The studies by Potts (1965), Kipling and Waterhouse (1957), Sorahan (1981),
and Sorahan and Waterhouse (1983) cannot be considered independently of one
anotner._ The workers in the McMichael et al. (1976a, b) studies were sub-
sequently shown not to have hac any exposures to cadmium, and the observed
excess of prostate cancer in this study was felt by Monson and Fine (1978)
and Goldsmith et al. (1980) to be due to other,'unexplained factors at the
companies studied.
Furthermore, tne significant excess risk of prostate cancer in the
13?
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TABLE 22. MORTALITY FOR RESPIRATORY CANCER FROM 1938 TO 1978
BY SMOKING HABITS AND ARSENIC EXPOSURE
Time weighted
Arsenic average Cei 1 i ng
category
(uy/m3)
Smoking habits
N
Obs
Exp
SMR
N
Obs
Exp
SMR
Low
Smokers
362
7
5.8
120
297
4
4.5
88
(< 100)
Nonsmokers
72
1
1.1
95
54
0
0.8
--
Medi urn
Smokers
364
16
5.1
312 a
185
2
2.6
76a
(100-499)
Nonsmokers
71
1
1.1
89 a
33
1
0.4
256
High
Smokers
386
20
5.6
359 a
558
31
8.3
37 3a
(500-4,999)
Nonsmokers
77
4
1.4
286a
120
4
2.1
186
Very high
Smokers
104
16
2.0
803a
176
22
3.0
728a
(> 5,000)
Nonsmokers
20
2
0.3
620a
33
3
0.6
506a
Significant at 0.01 level.
SOURCE: Welch et al1982.
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Lemen et al. (1976) study dropped to a nonsignificant excess risk in both of
the updated versions of that study (Varner, 1983 and Thun et al ., 1986).
Kjel 1 strum's "correctea nealthy worker effect" risk ratio of 2.4 is non-
significant because of the small numbers involved, although it approaches
borderline significance at p < 3.09, offering the suggestion of a possible
association of prostate cancer with cadmium exposure. However, the sta-
tistical power of most of the studies to detect an underlying twofold risk of
death from prostate cancer was low. In the Thun et al. study, the power was
only 34*o, and when the subgroup of workers with 2 or more years of employment
a^e looked at 20 years after initial exposure, it drops to only 15%.
Two other studies (^unperdinek, 1958 and Holden, 1969) did not report
evidence of an association of prostate cancer with cadmium exposure, chiefly
oecause the comparison population was eitner inadequate for the assessment
o£ r"^sk (hunperdi-ck) or absent entirely (Holden).
An update by :
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cancer in persons occupationally exposed to cadmium, and an even greater risk
in occupationally exposed people who smoke, thus raising the possibility of a
synergism. The chance of selection bias and concurrent occupational exposures
to nickel, lead, zinc, and a variety of metals also minimizes the importance
of the fi ndi ngs.
With respect to a risk of prostate cancer from exposure to cadmium and
its compounds, the evidence is weak at best, and is considered by the CAG to
be insufficient to conclude that cadmium is a prostate carcinogen.
On the other hand, recent evidence of a significant dose-response lung
cancer risk from exposure to cadmium is available from the Thun et al. (1985)
study, in which the more than twofold excess risk of lung cancer seen in
cadmium smelter workers was found to result from cadmium exposure rather than
from the presence of arsenic in the plant or increased smoking by the workers.
Thun et al. analyzed both of the above factors as potential confounders and
convincingly demonstrated that the significant excess risk of lung cancer could
not be due to smoking, to exposure to arsenic, or to any combination of these
factors acting synergistically. The earlier version of this study, by Lemen.
et al. (1976), also demonstrated a significantly elevated risk of lung cancer.
Varner (1983) also found a statistically significant excess of lung
cancer in his updated version of the earlier Lemen et al. study. Varner also
noted a dose-response relationship for both lung cancer and total malignant
neoplasms with increasing cumulative exposure. Varner indicated, however,
that the significant excess is probably due to smoking or to the presence of
arsenic in the plant. However, he had not had a chance to analyze their
impact because his paper was preliminary.
Sorahan and Waterhouse (1983), using the SMR method, also noted a clear-
ly statistically significant risk of lung cancer in their study population.
135
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In addition, a significantly high test-statistic was noted for excess lung
cancer utilizing the "regression models in life tables (RMLT)" method in the
"high to moderately exposed" group but not in the "highest exposure" category,
although the test-statistic was elevated. Sorahan suggested that the excess
might be due to exposure to fumes from oxyacetylene welding. No significantly
high test-statistic was found in his "highest exposure" group, however,
possibly because of a lack of sensitivity due to small numbers.
In his earlier paper, Sorahan (1981) found the risk of lung cancer to be
nonsignificantly elevated through SMRs calculated in a retrospective/pros-
pective cohort study of workers who began employment before and after the
amalgamation of two factories into a nickel-cadmiurn battery plant.
Armstrong and Kazantzis (1983) also demonstrated a significant risk of
lung cancer in workers designated by them as having worked in "low exposure"
jobs for a minimum of 10 years. Little sensitivity remained in the "highly
exposed" group with which to detect a risk after a minimum of 10 years' employ-
ment, and such a significant risk was not shown. Furthermore, a nonsignficant
excess risk was evident in the "ever mediumly" exposed group in workers with
a minimum of 10 years' employment. This study, however, did not deal with
latent factors 15 or 20 years after initial exposure in combination with
length of employment in sufficient detail. Also, 17 different plant popula-
tions were combined to form one cohort, thus raising the possibility that
very little exposure occurred to most members of the cohort. Furthermore,
definitions of "ever high," "ever medium," and "always low" categories of
exposure, based partially on expected cadmium urine concentrations, suggest
a cohort with little exposure to cadmium.
Holden (1980) reported a significantly excess risk of lung cancer in
"vicinity" workers, which he maintained could have been due to the presence
136
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of other metals, such as arsenic. No excess risk was seen in the group with
the highest exposure, however. Latent factors were not considered, nor was
the movement of workers from jobs with high exposure to jobs with low expo-
sure, possibly because of seniority.
Andersson et al. (1982), in their update of the Kjellstrom et dl. (1979)
study, noted a slight but nonsignificant lung cancer risk in alkaline battery
factory workers; however, this observation was based on only three-lung
cancer deaths occurring to this cohort, and the study also suffers from a
"small numbers" problem. In the earlier study, Kjellstrom et al. (1979)
observed a slight but nonsignificant excess of lung cancer based on two cases
in the same small group of cadmium-nickel battery factory workers.
Inskip and Beral (1982) noted a slightly increased but nonsignificant
risk of lung cancer among female residents of two small English villages who'
presumably were exposed to cadmium-contaminated soil via the oral route.
However, again only a small number of lung cancers were observed.
Overall, the weight of epidemiologic evidence is limited with respect
to the risk of lung cancer from exposure to cadmium and/or cadmium oxide,
although not compelling with respect to finding cadmium to be a prostate
carcinogen. At best, the epidemiologic evidence for the carcinogenicity of
cadmium must be described as limited, according to the criteria of the IARC.
137
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iJUANTITATIVE ESTIMATION
INTRODUCTION
Tnis quantitative section deals with the unit risk for cadmijm in air
and the uotency of cadmium relative to other carcinogens that the Carcinogen
Assessment Group (CAG) nas evaluated. Tne unit risk estimate for an air pol-
lutant is defined as the incremental lifetime cancer risk occurring in a
hypothetical population' in which all individuals are exposed continuously
from trrth throughout their lifetimes to a concentration of 1 .y/m^ of the
acent ir the air that they breathe. These calculations a^e done to estimate,
if quantitative terms, the impact of the agent as a carcinogen. Unit risk;
estimates are used for two purposes: 1) to compare the carcinogenic potencies
of.severa" ayerts with each other, and 2) to give a crude indication of the
population risk that would be associated with air or water exposure to these
agents, if the actual exposures were known.
The data usee for quantitative estimation are taken from one or both of
tne following: l) lifetime animal studies, and 2} hunan studies where excess
cancer risk has been associated with exposure to the agent. In animal studies
it is assumed, unless evidence exists to the contrary, that if a carcinogenic
response occurs at the dose levels used in the study, then response will also
occur at all lower doses with ar incidence determined by the extrapolation
~ocel .
There is no so1,id scientific basis *or any mathematical extrapolation
model that relates carcinoyen exposure to cancer risks at the extremely low
concentrations that must ne dea-t with in evaluating environmental hazards.
For practical reasons, si.cn low levels of risk cannot be measured directly
either by animal experiments or by epidemiologic studies. We must, therefore,
138
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depenc on cur current understanding of the mechanisms of carcinogcnesis for
guidance as to which risk model to use. At the present time the dominant view
of the carcinogenic process involves the concept that most cancer-causiny
agents also cause irreversible damage to DNA. This position is reflected by
the fact that a very large proportion of agents that cause cancer are also
mutagenic. There is reason to expect that the quantal type of biological
response, which is cnaracteristic of mutagenesis, is associated with a linear
nonthreshold dose-response relationship. Indeed, there is substantial evi-
dence (from mutagenicity studies with both ionizing radiation and a wide
variety of chemicals) tnat this type of dose-response model is the appropriate
one to use. This is particularly true at the lower end of the dose-response
curve; at higher doses, there can be an upward curvature, probably reflecting
the effects of multistage processes on the mutagenic response. The linear
nonthreshold dose-response relationship is also consistent with the relatively
few epidemiologic studies of cancer responses to specific agents that contain
enouyh information to make the evaluation possible (e.g., radiation-induced
leukemia, breast and thyroid cancer, skin cancer induced by arsenic in drink-
iny water, and liver cancer induced by aflatoxins in the diet). Some suppor-
ting evidence also exists from animal experiments (e.g., the initiation stage
of the two-stage carcinogenesis model in rat liver and mouse skin). Linearity
is also supported when the mode of action of the carcinogen in question is
similar to that of the background cancer occurrence in the exposed population.
Because its scientific basis, although limited, is the best of any of the
current mathematical extrapolation models, a linear nonthreshold model has
been adopted as the primary basis for estimating risk at low levels of expo-
sure. The risk estimates made with this model should be regarded as conser-
vative, representing the most plausible upper limit for the risk, i.e., the
139
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true risk is not likely to be higher tnan the estimate, but it could be lower.
For several reasons, the unit risk estimate based on aninal bioassays is
only a* approximate indication of the absolute risk in populations exposed'
to know, carcinogen concertrations. First, there are important species dif-
ferences in uptake, metabolism, and organ distribution of carcinoyens, as well
as species differences in taryet site susceptibility, immunoloyical responses,
hormone function, dietary factors, and disease. Second, the concept of equi-
valent doses for humans compared to animals on a my/surface area basis is
virtually without experimental verification reyardiny carcinogenic response.
Finally, human populations are variable with respect to yenetic constitution
and diet, living environment, activity patterns, and other cultural factors.
"he urit risk estimate can yive a rouyn indication of the relative pot-
ency of a given agent as compared with other carcinoyens. Comparative potency
estimates for different agents are more reliable wnen the comparisons are
based or studies ir the same test species, strain, and sex, and by the same
route cf exposjre, preferably inhalation.
Tne quantitative aspect of carcinogen risk assessment is included here
because it x,ay oe of use in the regulatory decision-making process, e.g., in
setting regulatory priorities, evaluating the adequacy of technology-based
controls, etc. However, it should be recoyrized that the estimation of cancer
risks to humans at low leve^ of exposure is uncertain. At best, the linear
extrapol ation model usea here provides a rough but plausible estimate of the
upper lirit of risK. The risk estimates presented "in subsequent sections
snoulc not be regardec as accurate representations of the true cancer risks
even when the exposures are accurately defined. However, the estimates pre-
sented may be factored ~rito regulatory decisions to tne extent that the
concept of upjen r'sk limits is founc to be useful.
143
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The mathematical formulation chosen to describe the linear -lonthreshol a
dose-response relationship at low doses is the linearized multistage model.
This .node 1 employs enough arbitrary constants to be able to fit almost any
monotonically increasing dose-response data, and it incorporates a procedure
for estimating the largest possible linear slope (in t'ne 95% confidence limit
sense) at low extrapolated doses that is consistent with the data at all dose
levels of the experiment.
In addition to the multistage model currently used by the CAG for low-
dose extrapolation (a detailed description of the procedure is given in
Appendix A), three more models, the probit, the Weibull, and the one-hit, ore
employed for purposes of comparison. These models cover almost the entire
spectrum of risk estimates that could be generated from the existing mathema-
tical extrapolation models. The models are generally statistical in character
and are not derived from biological arguments, except for the multistage
model, which has been used to support the somatic mutation hypothesis of
carcinogenesis (Armitage and Doll, 1954; Whittemore, 1978; Whittemore and
Keller, 1978).
The main difference among the above models is the rate at which the
response function P(d) approaches zero or P(0) as dose d decreases. For
instance, the probit model would usually predict a smaller risk at low doses
than the multistage model because of the difference of the decreasing rate in
the low-dose region. However, it should be noted that the multistage model
could always be artificially made to have the same (or even greater) rate of
decrease as tne probit model, by making some dose transformation and/or by
assuming that some of the parameters in the multistage model are zero. This,
of course, is not reasonable without knowing, a priori, what tne carcinogenic
process for the agent is.
141
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Although the mjlti stage model appears to be tie most reasonable or at
least the most general model to use, the point estimates generated from this
model are of 1imi tec value because of jncertai nty as to the shape of the dosa-
"esponse curve beyond the experimental exposure levels. Furthermore, the
point estimates a* low doses extrapolated beyond the experimental dose could
he extremely unstable and could differ drastically, depending on the size of
tne lowest experimental dose. Since the upper-bound estimates at low doses
fro-i the multistage -nodal are relatively more stable than the point estimates,
tne CAG suggests that tne upper-pound estimate of the risk (or the lower-bound
estimates of the dose) be used in evaluating the carcinogenic potency of a
suspect carcinogen. The upper-bound estimate can be taken as a plausible
estimate if the true dose-response curve is actually 1'"ear at low doses. The
upper-Dound estimate means that the n sks are not likely to be higher but
cojld be lower if tne comound 'ras a concave upward dose-response curve or a
threshold at low doses. Another reason why, at best, only an upper-bound
estimate of the risk can be obtained when animal data are used is that the
estimated risk is no more than conditional probability under the assumption
that an animal carcinogen is also a hun-an carcinogen. Therefore, in reality,
the actual risk could range from a value near zero to an upper-bound estimate.
PROCEDURES FOR DETERMINING CARCINOGENIC POTENCY
Jescriptior of the Lew-Dose Animal Extrapolation Mooel
_et P(d) represent the lifetime ris< (probability) of cancer at dose d.
The multistage model has the form
P ' c} = 1 - exp [ - (q,-i + q, c ^ + ... - q i(.dk ) ]
where
— 0,l,?|...,k
142
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Equi valently,
Pt(d) = 1 - exp [-(q1d + q^d2 + ... + q kdk) ]
where
P (d) = P(<0 - P(0)
* 1 - P(
w
is the extra risk over background rate at dose d or the effect of treatment.
The point estimate of the coefficients q-j, i = 0, 1, 2, k, and
consequently the extra risk function Pt(d) at any given dose d, is calculated
by maximizing the likelihood function of the data.
The point estimate and the 95% upper confidence limit of the extra risk
Pt(d) are calculated by using the computer program GL0BAL83 (Howe, 1983),
which is an update to the computer program GL0BAL79, originally developed
by Crump and Watson (1979). At low doses, upper 95% confidence limits on the
extra risk and lower 95% confidence limits on the dose producing a given risk
are determined from a 95% upper confidence limit, q^, on parameter q^.
Whenever q^ > 0, at low doses the extra risk Pt(d) has approximately the form
Pt(d) = q* x d. Therefore, q^ x d is a 95% upper confidence limit on the
extra risk, and R/q^ is a 95% lower confidence limit on the dose producing
an extra risk of R. Let Lq be the maximum value of the log-likelihood func-
tion. The upper limit, q^, is calculated by increasing to a value of
q^ such that when the log-likelihood is remaxinized subject to this fixed
value q^ for the linear coefficient, the resulting maximum value of the
log-likelihood satisfies the equation
2 (L0 - li) = 2.70554
143
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where 2.70554 is the cumulstive 90% point of the cni-square distribution with
one decree of freedom, which corresponds to a 95% upper-limit (one-sided).
This approach of computing the upper confidence limit for the extra risk Pt(d)
is an improvement on the Crump et al. (1977) model. The upper confidence
limit for tne extra risk calculated at low doses is always linear. This is
conceptually consistent with the linear nonthreshold concept discussed earl-
*
'er. The slope, qj, is taken as an upper bound of the potency of the
chemical in inducing cancer at low doses. (In the section calculating the
risk estimates, pt(d) will be abbreviated as 3.) In fitting the dose-response
model, the number of terns in tne polynomial is chosen equal to (h-1), where h
is the number of dose groups in the experiment, including the control group.
Whenever the rnt-1 ti stage mode: does not fit the data sufficiently well,
data at the highest dose is deleted, and the model is refitted to the rest of
the data. This is continued until an acceptable fit to the data is obtained.
To deteririre whether or not a fit is acceptable, the chi-square statistic
h , , Z
, . . . . v2 - -- <*i Nfpi)
LVi (i-Pi).
— • .i = 1
i s -cal cul ated 'where. is the number of animal s in the i1*1 dose group, X| is
the number., of'animal s in the i1""1 dose group with a tumor response, is the
probab.il ity of a response ;n the ith dose group estimated by fitting the multi-
stage model to the data, anc h s the number of remaining yroups. The fit is •
determined to be unacceptable wnenever X^ is larger that the cumulative 99%
point o£ the chi-square distribution witn f decrees of freedom, where f equals
the number of dose groups mi ^us the number of non-zero multistage coefficients.
144
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Selection of Data--
For some chemicals, a number of studies in different animal species,
strains, and sexes, each run at varyiny doses and routes of exposure, are
available. A choice must be made as to which of the data sets is appropriate
for use with the model. It may also be necessary to correct for metabolism
differences between species and absorption factors via different routes of
administration. The following procedures have been used by the CAG in evalu-
ating these particular data; they are consistent with the approach of making
a maximum-likely risk estimate.
1. Tne data on tumor incidence are separated according to organ sites or
tumor types. The dose and tumor incidence data set used in the model is the
set in which the incidence is statistically significantly higher than: in con-
trols for at least one test dose level, and/or where the tumor incidence rate
shows a statistically significant trend with respect to dose level. The data
set that gives the highest estimate of the lifetime carcinogenic risk, ,
is selected in most cases. However, efforts are nade to exclude data sets
that produce spuriously high risk estimates because of small numbers of
animals. That is, if two sets of data show a similar dose-response relation-
ship, and one has a very small sample size, the data set having the larger
sample size is selected for calculating the carcinogenic potency.
2. If there are two or more data sets of comparable size that are iden-
tical with respect to species, strain, sex, and tumor sites, the geonetric
mean of q^, estimated from each of these data sets, is used for risk assess-
ment. The geometric mean of numbers Aj, Aj, ..., A^ is defined as
(A^ x A^ * ... x Aj^) l/111
3. If two or more significant tumor sites are observed in the same study,
14b
-------
and if the data are available, the nunoer of animals with at least one of trie
specific tumor sites under consideration is jsed as incidence data in the
model .
Calculation of Hunan Equivalent Dosayes from Animal Qata--
Followiny the suggestion of Mantel and Schneiderman (1975), it is assumed
that my/surface area/day is an equivalent dose between species. Since, to a
close approximation, the surface area is proportional to the two-thirds power
of the weiyht, as would be the case for a perfect sphere, the exposure in iny
day/two-thirds power of the weiyfit is also considered to be equivalent expo-
sure. In an animal experiment this equivalent dose is computed in the follow-
ing manner: Let
Le = duration of experiment
le = duration of exposure
t, = averaye dose per day in ny dupiny administration of the ayent
(i.e., duri ny 1e), and
W = averaye weight of the experimental animal
Then, the lifetime averaye exposure is
le x m
I. x w2/3
e
Innalation--Wnen exposure is via inhalation, the dose for inhaled parti-
culate matter, in rig/day, car De expressed as
m = I x v x f
where I = the volume uf air inspired/day in , v = my/m^ of the ayent in air,
and f =* the fraction deposited in the lunys.
146
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The inhalation rates, I, for various species can -je calculated f.°on the
observations of the Federation of American Societies for Experimental Biology
(1974) that 2S-g nice breathe 3^.h liters/day and 113-y rats breathe 105
liters/day. For -nice and rats of other weights, W (in kilograms), the surface
area proportionality can be used to find breathing rates in rn^/day as follows:
For mice, I = 0.0345 (W/0.025)2/3 rn3/day
For rats, I = 0.105 (W/'J.113)2/3 m3/day
For humans, the value of 20 n^/day is adopted as a standard breathing
rate. The equivalent exposure in mg/w2/3 f0r these agents can be derived
from the air intake data in a way analogous to the food intake data. The
empirical factors for the air per kg per day, i = I/W, based upon the prev-
iously stated relationship, are tabulated as follows:
Sped es W i = 1/W
Man 70 0.29
Rats 0.35 0.64
Mice 0.03 1.3
Therefore, for particulate matter, the equivalent exposure in ng/w2/3 is
d _ m - Ivf iWvf = iwl/3Vf
W2/3 w2/3 w2/3
The fraction of inhaled particles deposited in the lung will vary with
species, particle size, rate and depth of respiration, etc. In the only
animal inhalation study available for conducting a risk assessment on cadmium
(Takenaka et al., 1983), the mean particle size of the aerosol was 0.55 pm
in diameter. Raabe et al. ( 1977) reported, for rats inhaling particles in
this size range, that 10% was deposited in the gas exchange reyions of the
147
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lungs, with an additional 3% deposited in the conductiny airways. In differ-
ent hunan studies in which 0.5 pn diameter particles were inhaled, the
fraction deposited in the deep luny varied from = 9% to 21% (Lippman, 1977).
In the human studies, considerable variability was noted, not only among
studies, but among individuals within a study and within individuals due to
changes in breathing patterns. Since a considerable deyree of variability in
deposition fractions along with minimal differences between the means of the
rat study and the humar. studies occurred, an adjustment for dose between rats
and humans based upon deposition efficiency was not considered appropriate.
The fraction of particles deposited in the deep lung will also vary with
partHcle size. An adjustment in dose would be indicated if cadmium particles
in amiert air differ markedly in size from those used in the appropriate
aninal exposure study. Unfortunately, precise data is unavailable. In
studies of point source emissions, however, cadmium was shown to be concen-
trated in the smallest particles. For example, 66« of cadmium-containing par-
ticles emitted from municipal incinerators were less than 2 jjm in diameter,
with a median diameter of less than 1 uin (Jacko and Neuendorf, 1977). Trace
netals, including cadmium, were also concentrated in the smallest fly ash
particles emitted from electric power generating plants (Natusch et al.,
1973). The oata from point sources indicate that cadnium-containing particles
in ambient air, while very small, are probably somewhat larger and more
variable in size than those used in the Takenaka et al. (1983) study. Since
cadmium or cadmium compounds, however, are seldom present in ambient partic-
ulates in a pure state, and since cadmium concentration is greater in the
smallest particles, it was again considered inappropriate to adjust for
deposited dose saseG upon particle size.
A third factor possibly influencing dose is residence times of particu-
148
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late 'patter in the lungs. A longer resicence time may allow less soluble
Torus of :d'Jmiu:n to be leached from the particles, thereby increasing bio-
availability. Clearance half-times for cadmium particles deposited in the
alveolar region have been reported to vary from about 60 cays in rats (Ober-
doerster et al., 19791 to 225 days for dogs (Oberdoerster and Morrow, 1983)
and even longer for primates (Oberdoerster, 1984). Based on this informa-
tion, it would appear that humans may be at greater risk than rats following
inhalation of relatively insoluble cadmium compounds.
Although the data available do not provide definitive information for
making an adjustment in dose based on any of the individual factors discussed,
collectively the data suggest that humans could be at somewhat greater risk
than rats exposed to similar cadmium aerosols. Ambient air particulates, how-
ever, are considerably different from those used experimentally. In the
Takenaka et al. (1983) study, the cadmium chloride aerosol used was quite
soluble. As an indication of this, tumors were found in the bronchial region
where clearance half-times were less than one day. While there is little
direct information relating to the bioavailability of cadmium in ambient air
particulate matter, on the basis of information regarding solubility of fly
ash and other point source particle emissions, it appears that cadmium is
likely to be much less bioavailable than in the chloride form. As a result,
it was felt that a unit risk estimate based upon the Takenaka et al . (1983)
study with no adjustment for deposition fraction or bioavailability was
sufficiently conservative to protect human populations.
Calculation of the Unit Risk from Animal Data--
The 95% upper-limit risK associated with d mg/kg2/3/(jay -js obtained from
GL0BAL83 and, for most cases of interest to risk assessment, can be adequately
149
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approxinated by P(d) = 1 - exp (-q|d). A "unit risk" in units X is simply the
risk corresponding to an exposure of X = 1. Tnis value is estimated by finding
the nunber of iny/ky2/3/jay that corresponds to one unit of X and substitutiny
this value into the above relationsnip. Thus, for example, if X is in units
of uy/m^ in the air, we have a = 0.29 x 701/3 x jq-3 my/kg2/3/day. Note that an
equivalent method of calculating unit risk would be to use my/kg for the animal
exposures and then increase the jth polynomial coefficient by an amount
. (tywa)J/3 j - i» 2, k
and use "y/
-------
13.4 jg/n3, 25.7 ug/m3, and 50.8 pg/m3 elemental cadmiun for the three dose
groups, the lifetime continuous exposure can be estimated as 10.05 ng/m3,
19.3 ug/m3, and 38.1 ug/
-------
assumed to be 70 kg, and Ua is the mean weight of the animals; thus,
q* = qj (Wh/Wa)1/3 = 6.3 x 10"2 (70/0.429)1/3 » 3.4 x 10"1 (yg/kg/day)-1
Using the linearized multistage model, the 95% upper-limit unit risk esti-
mate for induced cancers based on elemental cadmium exposure is = 3.4 x 10"*.
If it is assumed that cadmium chloride is the carcinogenic agent and not the
cadnium ion, an adjustment must be made for the weight of the two cadmium
chloride ions. In that case, the molecular weight contribution of cadmium to
the total molecular weight is 112.4/183.3 = 0.613. The interpretation in
terms of risk is that a for inhalation of cadmium chloride is
q* = 3.4 x 10"! (yg/kg/day)"1 x 0.613 = 2.1 x 10~1 (ng/ky/day)"l
h
Tnis can be converted back to human exposure in terms of yg/m3 by assuming
that a human weighing 70 kg breathes 20 m3 of air per day. Thus,
q* = 2.1 x 10"! (yg/kg/day)-! x 1 x 20 m3 = 6.0 x 10"2 (ug/m3)-l
^ 70 kg day
for cadmium ion exposure, and
q* = 3.4 x 10"1 (:jg/kg/day)-l x 1 x 20 m3 = 9.7 x 10~2 (ng/rn3)-1
1 70 kg day
Dased on innalation exposure to the cadmium ion. Therefore, the incremental
unit risk from the inhalation of 1 yg of elemental cadmium per m3 of air is
approximately
R = 1 - exp -(0.097 x 1) = 0.092
This is an upper-bound estimate of risk based on the direct experimental
152
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evidence presently available. Using other dose-response models to estimate
risk (as shown in Appendix A) can give considerably lower estimates than those
obtained using the upper-bound multistage model. However, there is no direct
evidence suggesting that these alternative models provide a more rational
basis for estimating risk than the upper-bound multistage model. It must be
kept in mind that the alternative models have the potential for seriously
underestimating the true risk at low levels of environmental exposure to
cadmi urn.
Unit Risk Estimate Based on a Human Study
Data Base--
At the present tine the strongest evidence in humans suggesting a cadmium-
induced carcinogenic response is found in the Thun et al. (1985) study. This
response was observed in a cohort of cadmium smelter workers who were hired
on or after January 1, 1926, and were employed for at least 2 years in a
production capacity in the same plant from January 1, 1940, to December 31,
1969. This cohort of white males had a total of 16 respiratory cancer deaths
through December 31, 1978, while only 6.99 would be expected based on calendar
time age-specific respiratory cancer death rates for U.S. white males.
Assuming that the U.S. white male population is a valid control population
for the cohort of cadmium smelter workers, the'probabi1ity of obtaining 16 or
more respiratory cancer deaths, if there was no effect due to cadmium, is only
0.0024, based on the exact Poisson test.
Thun et al. (Table 9, page 29 of their paper) divided the cohort of
white males hired on or after January 1, 1926, into three groups based on
cumulative exposure. This cohort included individuals with less than 2 years
of exposure. In an April 10, 1984, letter from Thun to the U.S. EPA, the
153
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approximate midpoints of the exposure intervals were given. The data shown
in Table 23 were generated using these two sources of information. The expo-
sure (in terms of 24 nours ug/m^-years) needed to estimate environmental
risk is obtained under the assumption of 3 hours worked per day, 240 days per
year, and is shown in column 3 of Table 23. It should be noted that the
240/365 adjustment is required because Thun et al. computed exposure days on
the basis of elapsed calendar time in an exposure category, not on the basis
of working days.
A number of problems arise in using these data to obtain a quantitative
estimate of human respiratory cancer risk due to cadmium exposure. Among them
are the following:
1. Tnere is some evidence that the smoking rate for the cadmium workers
was higher than that of the general white male population.
2. The exposure to cadmium is confounded with exposure to arsenic, a
known respiratory carcinogen.
3. Very limited evidence exists concerning the exposure rate and the
duration of exposure for the members of the cohort.
4. No exposure estimates exist for individuals.
5. The extent of the deviations of the exposure estimates from the ..
actual exposure is unknown.
In March 1985, Thun began a new study with ARSARCO to obtain estimates of
individual exposures to cadmium, arsenic, and, where possible, cigarette smoke
for the cohort he had originally studied. This new study could considerably
reduce the severity of the proDlems cited previously, and could be critical
in evaluating the potency of cadmium. At a minimum, it should be a valuable
source of data for use in testing the hypothesis that the observed increases in
respiratory cancer rate are due to confounding effects of arsenic and cigarette
154
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TABLE 23. BASIC DATA USED FOR ESTIMATING UNIT RISK
Cumulative
exposure
(my/days/m3)
Medi ana
observati on
in interval
ib
24-hour/uy/mJ
equivalent Xj
Expected ICD 162-163°
assuminy no cadmium
effect EOj
Observed number
of deaths
ICD 162-163 Oj
< 584
280
168
3.77
2
585-2920
1210
727
4.61
7
> 2921
4200
2522
2.50
7
aProvided by Thun (letter dated April 10, 1984).
bMedian observation multiplied 10-3 x 8/24 x 1/365 x 240/365.
cEOj = Oj x 102 v SMRj.
SOURCE: Thun et al., 1985.
-------
smoke rather than cadmium. Unfortunately, this information is not expected
in the near term.
Without such data, the approach taken to estimate unit risk assumes that
the entire observed effect is due to cadmium. Several factors suggest that
this approach is not unreasonable. First, if the effect were due to a
differential smoking rate oetween the study cohort and the general population,
one would expect to see an elevated risk in all exposure groups for smoking-
caused diseases. Tnis was not the case. The lowest exposure group had a
relative risk (for respiratory cancer) of only 2/3.77 = 53.1%, as indicated
in Taaie 23. Also, as shown in Table 3, page 23 of the Thun et al. (1985)
paper, the relative risk for diseases of the circulatory system (ICD 400-468)
is only 65, suggesting no elevated cigarette use.
Second, Brown and Chu (1982) offer highly suggestive evidence that
arsenic is a late-stage carcinogen. As a result, the risks 10 to 15 years
after the cessation of exposure to arsenic are not expected to be highly
elevated. Arsenic exposure, for the most part, was terminated 20 or more
years prior to the observed 1 jng cancer cases in the Thun et al. cohort.
Tnis fact argues against arsenic being a major contributor to the elevated
respiratory cancer rates observed in the Thun et al. cohort.
However, it must be recognized that while these arguments are reasonable,
they are no substitute for real data, and the upper-bound estimates for
cadmium cancer risk presented in the following section could be considerably
altered when the results of Thun's new study become available.
Model Used--
To estimate lifetime risk from the data shown in Table 23, the simplest
possible model that can be used with this level of information is assumed.
156
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It is postulated that the age-specific rate at any point in time is increased
by an amount proportional to the cunulative exposure up to that point in
time. This implies that
h(t) = A X
where X is cumulative exposure and A is the proportional increase. If expo-
sure is constant from time o to t at level x, it follows that
h(t) = A xt
The preceding model is one of the models used in the BE IR III report
(National Research Council, 1980) to estimate risk due to ionizing radiation.
This model is also equivalent to assuming a two-stage model with only the
first stage affected by exposure. As a first approximation, it is assumed that
the total median cumulative exposure for each group can be related to each year
of the observation period for that group. This assumption would tend to over-
estimate exposure and thus underestimate risk. However, the bias is less than
a factor of two since using the lower bounds would not increase the estimate
more than that. Under the assumed model the total expected number of cases
in the observation period for the jth exposure group may be expressed as
Ej = Eoj + AXjWj
where Eoj is the expected number of cases due to background causes, Xj is
cunulative exposure, and Wj is the number of person-years of observation for
the jth exposure group. The observed number of cases in the jth exposure
gr^up is a Poisson random variable with mean Ej under the assumed model.
Thus, the likelihood of the observed results may be expressed as
157
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L H e
j = l
3 -CEo- + AXjWj] Oj
[E°j + AXjWj] /Oj !
where Oj is the observed number of cases in the jth exposure group. The
maximum likelihood estimate of the unknown parameter a is obtained by solving
the equation
dlnL = ; -
dA j=l J
Wj
0
Eoj + AXjWj
for A.
the asymptotic variance for the parameter A, is
a^l nL
d2A
I . "J "J r
J=1 (Eoj + AXjWj)
-1
This variance can then be used to obtainan approximate 95% upper bound for
the parameter A. In Table 24 the data used to obtain the estimate of A ana
its variance are shown.
TABLE 24. DATA USED TO ESTIMATE A AND ITS VARIANCE
Cumulati ve
exposure
Person-years
observati on
Wn
Background
expected
Observed
Oi
xjw:
xjwj °j
168
7005
3.77
2
1.18x10s
2.35xl06
727
5825
4.61
7
4.23x10s
29.63x10s
2522
2214
2.50
7
5.58x10s
39.09x10s
V = 10.99xl06
158
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An estimate of A* = A x 10® is obtained from the equation
in qq = 2.35 + 29.63 + 39.09
3.77 + 1.18 A* 4.61 + 4.23 A* 2.50 + 5.58 A*
which has the solution a* = 0.642 so that A = 6.42 x 10"?. The V (a) is esti-
mated to be V (A) = 1.27 x 10"^ so that\|v (a) = 3.56 x ID-?, and the 95%
upper and 5% lower confidence bounds are approximately A^ = 12.26 x 10"^ and
Afc = 0.58 x 10"^, respectively. It should be noted that this measure of varia-
bility only takes into account random sampling error. It does not account for
potential error due to an assumed incorrect model or biased exposure estimates.
To show how a different assumed model could influence risk estimates, the
following ad-hoc "threshold" model can be considered. This model is not based
on any biological information. It simply uses the highest dose group with no
observable statistically elevated risk as the threshold and assumes linearity
in accumulated dose beyond that point. It is assumed that
0 X < 1754
h(t) =
A (X - 1754) 1754 < X
where 1754, the guessed-at threshold, is the boundary point of the maximum
exposed group in ug/m^-years. For this model an estimate of A is
A = (7 - 2.5) x (2522 - 1754) x 2214 = 2.65 x 10"5
In Table 25 the fit of each model is shown and evaluated using the X?
goodness-of-fit test.
We note that both the "threshold" and linear models give an adequate fit
to the data. As a result, arguments other than purely statistical must be
used to select the appropriate model.
159
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TABLE 25. GOODNESS-OF-FIT MODELS FITTED TO THE THUN DATA
Exposure
i nterval
ug/m^-years
mi dpoi nt
< 350
(168)
351-1754
( 727 )
> 1754
(2522)
Number of cases expected under
linear model usiny as the
estimate of parameter a the
Lower bound
3.84
4.85
2.82
MLE
4.53
7.33
6.08
Upper bound
5.21
9.80
9.34
X2 yoodness-of-fit statistic
7.971 1.567 3.364
Expected number of cases
under threshold model
A = 2.65 x ID"6 if x > 1754
A = 0 if X < 1754
3.77
4.61
7.00
Observed
2.070
SOURCE: Thun, letter of April 10, 1984; Thun et al ., 1985.
-------
Use of Parameter Estimates of i to Estimate Unit '^isk--
Mathematically, tne risk clue to a constant lifetime exposure of x ppm in
the air may be expressed as
.t
j [^2(x»v) + hi(v)]dv
j
P(x) =/ {h2tx»t)e 0 ~ * }dt
0
where h2(x,t) is the age-specific death rate at aye t due to a constant life-
time exposure at level x, and hj(t) is the aye-specific death rate for all
other causes. See Gail (1975) for a derivation of this result.
In the present situation
I^U.t) = 6.42 x 10"7 * xt
for the linear nodel and
0 xt < 1754
h2(x,t) =
2.65 x 10-6 . [xt-17543 1754 < xt
for the "threshold" model.
Using these models and the assumption that hj(t) is the same as the over-
all rates in the United States in 1978 (the most recent year for which complete
vital statistics data are available), the lifetime cancer risks for various
constant exposure levels of cadmium have been calculated and are shown in
Table 26.
Recommended Unit Risk Estimate—
A number of approaches have been used to obtain unit risk estimates. It
is suggested that if a single estimate of unit risk is desired, it be based on
the MLE of the linear parameter obtained from human data. This results in a
161
-------
TABLE 26. ESTIMATED RISKS FOR VARIOUS MODELS BASED ON THUN DATA
Risk clue to a constant lifetime exposure of
Model used 1 ug/m3 10 pg/m3 100 yg/m3
Linear nonthreshold
Upper bojnd
3.5
X
10"3
3.4
X
10-2
2.9
X
10"1
MLE
1.8
X
10-3
1.8
X
10-2
1.7
X
10'1
Lower bound
1.7
X
10"4
1.7
X
10"3
1.6
X
10-2
Threshold nodel
0.0
0.0
3.7
X
10"1
Apri1 1984 node!a
1.9
X
10-3
1.9
X
10-2
1.7
X
10"1
aUsed in the External Review Draft of tne Updated Mutagenicity and Carcinogeni-
city Assessnent of Cadmium, prepared by the Office of Health and Environmental
Assessment, U.S. Environnental Protection Agency, April 1984.
SOURCES: Thun, letter of April 10;, 1984;- Thun et al ., 1985.
162
-------
unit risk estimate of 1.8 x 10_3. A higher estimate of 3.5 x 10~3 would be
obtained if the 95% upper bound of the parameter were used. However, it is
felt that this is an unnecessary added level of conservatism, since the model
used already inflates the risk estimate if nonlinear components exist or
confoundiny factors are present.
The unit risk estimate based on the animal bioassay, 9.2 x 10-2, also
gives a higher estimate. However, species differences and cadmium form dif-
ferences make an estimate from this source intrinsically less reliable than
the one derived from the assumed human exposures. In addition, it must be
kept in nind that these are upper-bound estimates. The true unit risk could
range from this upper bound to a very small value approaching zero.
RELATIVE POTENCY
One of the uses of the concept of unit risk is to compare the relative
potencies of carcinogens. For the purposes of the present analysis, potency
is defined as the linear portion of the dose-response curve, and is used to
calculate the required unit risk factors. In this section, the potency of
cadrnium is compared with that of other chemicals that the CAG has evaluated
as suspect carcinogens. To estimate the relative potency on a per mole
basis, the unit risk slope factor is multiplied by the molecular weight and
the resulting number, expressed in terms of (mnol/kg/day)~1, is called the
relative potency index.
Figure 2 is a histogram representing the frequency distribution of rela-
tive potency indices for 54 chemicals that have been evaluated by the CAG as
suspect carcinogens. The actual data summarized by the histogram are presen-
ted in Table 27. Where human data have been available for a compound, such
data have been used to calculate these indices. Where no human data have been
163
-------
3rd
QUARTILE
2nd
QUARTILE
4th
QUARTILE
QUARTILE
•Jfc
Figure 2. Histogram representing frequency distribution of tne
potency indices of '54 suspect carcinogens evaluated by the
Carcinogen Assessment Group.
164
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TABLE 27. RELATIVE CARCINOGENIC POTENCIES AMONG 54 CHEMICALS EVALUATED BY THE CARCINOGEN ASSESSMENT GROUP
AS SUSPECT HUMAN CARCINOGENS
Compounds
CAS Number
Level
of evidence3
Humans Animals
Groupi ng
based on
IARC
cri teri a
SI ope
(mg/kg/day)"1
Molecular
weight
Potency
i ndex
Order of
magni tude
(log10
lndex)
Acrylonitrile
107-13-1
L
S
2A
0.24(H)
53.1
lxlO+1
+ 1
Aflatoxin Bj
1162-65-8
L
S
2A
2900
312.3
9xl0+5
+ 6
Aldrin
309-00-2
I
L
2B
11.4
369.4
4xl0+3
+4
Allyl chloride
107-05-1
1.19xl0-2
76.5
9x10"!
0
Arsenic
7440-38-2
S
I
1
15(H)
149.8
2xl0+3
+ 3
B[a]P
50-32-8
I
S
2B
11.5
252.3
3xl0+3
+ 3
Benzene
71-43-2
S
S
1
2.9xlO"2(W)
78
2x10°
0
Benzidene
92-87-5
S
S
1
234(W)
184.2
4xl0+4
+ 5
Beryl 1i urn
7440-41-7
L
S
2A
2.6
9
2xl0+1
+ 1
1,3-Butadi ene
106-99-0
I
S
2B
1.0xl0_1(I)
54.1
5x10°
+ 1
Cadmi um
7440-43-9
L
S
2A
6.1(W)
112.4
7xl0+2
+ 3
Carbon tetrachloride
56-23-5
I
S
2B
1.30X10"1
153.8
2xl0+1
+ 1
Chiordane
57-74-9
I
L
3
1.61
409.8
7xl0+2
+ 3
(continued on the following page)
aS = Sufficient evidence; L = Limited evidence; I = Inadequate evidence.
-------
IABI.F 21. (continued)
Level
of evidence3
Group i ng
based on
I ARC
SI ope
Molecular
Potency
Order of
magni tude
(log10
i ndex)
Compounds
CAS Number
Humans Animals
criteria
(my/kg/day)-l
wei ght
i ndex
Chlorinated ethanes
1,2-Dichloroethane 107-06-2
hexachloroethane 67-72-1
1,1,2 ,2-Tetrachloroethane 79-34-5
1,1,2-Trichloroethane 79-00-5
1 S
1 L
1 L
1 L
2B
3
3
3
9.1xl0-2
1.42xl0-2
0.20
5.73x10-2
93.9
236.7
167.9
133.4
9x10°
3x10°
3xl0+1
8x10°
+ 1
0
+ 1
+ 1
Chloroform
67-66-3
1 S
2B
7x10-2
119.4
8x10°
+ 1
Chromium VI
7440—4 7-3
S S
1
41 (W)
100
4xl0+3
+ 4
DDT
50-29-3
1 S
2B
0.34
354.5
lxl0+2
+ 2
Di chlorobenzi di ne
91-94-1
I S
2B
1.69
253.1
4x10+2
+ 3
1,1-Di chloroethylene
(Vinylidene chloride)
75-35-4
I L
3
1.16 ( 1)
97
1x10+2
+ 2
Di chloromethane
(Methylene chloride)
75-09-2
1 L
3
6.3xl0"4(1)
84.9
5x10-2
-1
Di eldri n
60-57-1
1 S
2B
30.4
380.9
1x10+4
+4
2,4-Di ni trotoluene
121-14-2
I S
2B
0.31
182
6xl0+1
+ 2
Di phenylhydrazi ne
122-66-/
1 S
2B
0.7,7
180
lx10+2
+2
Epi chlorohydri n
106-89-8
I s
2B
9.9xl0-3
92.5
9X10"1
0
Ris(2-cnloroethyl)ether
111-44-4
I s
2B
1.14
143
2xl0+2
+ 2
flS = Sufficient, evidence
1 - limited
evidence; I - Inadoij.ia'.c evidence.
(contlnued
on the following page)
-------
TABLE 27. (continued)
Level
of evidence3
Groupi ng
based on
IARC
SI ope
Molecular
Potency
Order of
magni tude
O^IO
index)
Compounds
CAS Number
Humans Animals
criteri a
(mg/kg/day)"1
wei ght
i ndex
Bis(chloromethyl)ether
542-88-1
S S
1
9300(1)
115
lxl0+6
+6
Ethylene dibromide (EDB)
106-93-4
I S
2B
41
187.9
8xl0+3
+ 4
Ethylene oxide
75-21-8
L S
2A
3.5xl0"1(I)
44.1
2xl0+1
+ 1
Heptachlor
76-44-8
I S
2B
3.37
373.3
lxl0+3
+ 3
Hexachlorobenzene
118-74-1
I S
2B
1.67
284.4
5xl0+2
+ 3
Hexachlorobutadiene
87-68-3
I L
3
7.75x10-2
261
2xl0+1
+ 1
Hexachlorocycl ohexane
technical grade
alpha isomer
beta isomer
gamma isomer
319-84-6
319-85-7
58-89-9
I S
I L
I L
2B
3
2B
4.75
11.12
1.84
1.33
290.9
290.9
290.9
290.9
lxl0+3
3xl0+3
5xl0+2
4xl0+2
+ 3
+ 3
+ 3
+ 3
Hexachlorodibenzodioxin
34465-46-8
I S
2B
6.2xl0+3
391
2xl0+6
+6
Nickel
7440-02-0
L S
2A
1.15(W)
58.7
7xl0+1
+2
Ni trosami nes
Dimethyl nitrosami ne
Diethylnitrosamine
Dibutylnitrosamine
62-75-9
55-18-5
924-16-3
I S
I S
I S
2B
2B
2B
25.9(not by
43.5(not by
5.43
qt) 74.1
qf) 102.1
158.2
2xl0+^
4x10
9xl0+2
+ 3
+4
+ 3
aS = Sufficient evidence;
L = Limited
evidence; I = Inadequate evidence.
(continued
on the foil
owing page)
-------
TABLE 27. (continued)
Compounds
CAS Number
Level
of evidence3
Humans Animals
Groupi ng
based on
I ARC
cri teri a
SI ope
(mg/kg/day)"1
Molecular
weight
Potency
i ndex
Order ot
magni tucle
(1 °y io
i ndtx)
N-ni trosopyrrolidi ne
930-55-2
I
S
2B
2.13
100.2
2x10+2
+ 2
N-ni troso-N-ethylurea
759-73-9
I
S
2B
32.9
117.1
4xl0+3
~ 4
N-ni troso-N-methylurea
684-93-5
I
S
2B
302.6
103.1
3xl0+4
f4
N-ni troso-di phenyl ami ne
86-30-6
I
S
?B
4.92xl0-3
198
1x10°
0
PCBs
1336-36-3
I
S
2B
4.34
324
lxl0+3
+ 3
Phenols
2,4 ,6-Trichlorophenol
88-06-2
I
S
2B
1.99xl0-2
197.4
4x10°
+ 1
Tetrachlorodibenzo-
p-dioxin (TCDD)
1746-01-6
I
S
2B
1.56xl0+5
322
5xl0+7
+8
Tetrachloroethylene
127-18-4
I
L
3
5.1x10-2
165.8
8x10°
+ 1
Toxaphene
8001-35-2
I
S
2B
1.13
414
5xl0+2
+ 3
Trichloroethylene
79-01-6
I
L/S
3/2B
1.1x10-2
131.4
1x10°
0
Vinyl chloride
75-01-4
S
S
1
1.75x10"2(I)
62.5
1x10°
0
aS = Sufficient evidence; L = Limited evidence; T~= Inadequate evidence.
Remarks:
1. Animal slopes are 95% upper-limit slopes based on the linearized multistage model. They are calculated based on
animal oral studies, except for those indicated by I (animal inhalation), W (human occupational exposure), and H
(human drinking water exposure). Human slopes are point estimates based on the linear nonthreshold model.
2. The potency index is a rounded-off slope in (mmol/kg/day)"1 and is calculated by multiplying the slopes in
(mg/kg/day)"l by the molecular weight of the compound.
3. Not all of the carcinogenic potencies presented in this table represent the same degree of certainty. All are
subject to change as new evidence becomes available.
-------
available, data from animal oral studies and animal inhalation studies have
been used in that order, since animal oral studies have been conducted for
most of these compounds, and the use of such studies provides a more consis-
tent basis for potency comparisons.
Tne potency index for cadmium based on the Thun et al. (1985) study of
cadmium smelter workers is 6.9 x 10+2 (mmol/kg/day)"*. This is derived as
follows: Assuming that an individual breathes 20 m^ of air per day and weighs
70 kg, tne slope estimate from the human study, 1.8 x 10~3 (ug/m3)-1, is first
converted to units of (my/kg/day)"1 or
1.8 x 10~3 (pg/n,3) — 1 x 1 day x 1 x 70 kg = 6.1 (my/kg/day)"1
20 io~3 mg
Multiplying by the molecular weight of 112.4 give a potency index of
6.9 x 10+2. Rounding off to the nearest order of magnitude gives a value of
10+3, which is the scale presented on the horizontal axis of Figure 2. The
index of 6.1 x 10+2 lies in the second quartile of the 54 suspect carcinogens.
Ranking of the relative potency indices is subject to the uncertainty of
comparing estimates of potency of different species using studies of different
quality. Furthermore, all of the indices are based on estimates of low-dose
risk using the linearized multistage extrapolation model fitted to the data at
relatively high doses. Thus, relative potencies could be different at high
exposures, where nonlinearities in the dose-response curve could exist.
169
-------
APPENDIX A
COMPARISON OF RESULTS BY VARIOUS EXTRAPOLATION MODELS
Tne estimate of unit ris< from animals presented in the body of this
docunent was calculated by use of the linearized multistage model. This non-
threshold model is part of a methodology for estinatiny a conservative linear
slope at low extrapolation doses that is usually consistent with the data at
all dose levels in an experiment. The model holds that the most plausible
upper limits of risk are those predicted by linear extrapolations to low levels
of the dose-response relationship.
Other nonthreshold models that have oeen used for risk extrapolation are
the one-hit, the log-probit, and the Weibull models. The one-hit model is
characterized by a continuous downward curvature, but is linear at low doses.
.= Because of its functional form, the one-hit model can be considered the linear
*orm or first stage of the multistage moael . This fact, toyether with the
downward curvature of the one-hit model, means that the model wi.l 1 always
yield low-level risk etimates tnat are at least as large as those obtained with
the multistage model. In addition, whenever the data can be fitted adequately
to the one-hit model , estimates based on the one-hit model and the multistage
model"will be comparable.
The log-probit and the Weibull models, because of their general "S" cur-
vature, are often used for the interpretation of toxicological data in the
observable range. The low-dose upward curvatures of these two models usually
yield lower low-dose risk estimates than those of the one-hit or multistage
models.
The log-probit model was originally used in biological assay problems
such as potency assessments of toxicants and drugs, and is most often used to
170
-------
estimate such values as percentile lethal dose or percentile effective dose.
The log-probit model was developed along stictly empirical lines, in studies
where it was observed that several log dose-response relationships followed
the cunulative normal probability distribution function, o. In fitting the
log-probit model to cancer bioassay data, assuming an independent background,
this relationship becomes
P(D;a,b,c) = c + (1-c) $ (a+blog^o D) a,b > 0 <_ c < 1
where P is the proportion responding at dose D, c is an estimate of the back-
ground rate, a is an estimate of the standardized mean of individual tolerances,
and b is an estimate of the log-probit dose-response slope.
The one-hit model arises from the theory that a single molecule of a
carcinogen has a quantifiable probability of transforming a single normal cell
into a cancer cell. This model has the probability distribution function
P(D;a,b) = l-exp-(a+bd) a,b > 0
where a and b are the parameter estimates (a = the background or zero dose rate,
and b = the linear component or slope of the dose-response model). In consider-
ing the added risk over background, incorporation of Abbott's correction leads
to
P(D;b) = l-exp-(bd) b > 0
Finally, a model from the theory of carcinogenesis arises from the multihit model
applied to multiple target cells. This model, known as the Weibull model, is
of the forn
P(D;b,k) = l-exp-(bdk) b.k > 0
171
-------
For tne power of cose only, the restriction k > 0 nas been placed on this
model. Wher k > 1, the model yields low-dose estimates of risks that are
usually significantly lower than either the multistage or the one-hit models,
Doth of which are linear at low doses. All tnree of these rnodels--the multi-
stage, the one-hit, and tne Ijeibul 1 — usual ly project risk estimates tnat are
significantly higher at low exposure levels than those projected by the log-
probit model.
Tne estimates of added risk for low duses for these models are given in
Table A-l for tne cacmiuin cnloMde rat inhalation studies by Takenaka et al.
(1983). 3oth naximum likelihood estimates and 95% upper confidence limits are
presented. The results show that the maximum likelihood estimates of risk for
the loy-probit model are all less than those for tne other models, and this
difference increases sharply at low doses. The one-'nit model yields maximum
likelihood estimates slightly higher than those obtained with the multistage
model, while those obtained with the Ueibjll model are somewhat lower.
172
-------
TABLE A-1. ESTIMATES OF LOW-DOSE RISK TO HUMANS EXPOSED TO CADMIUM CHLORIDE BASED ON MALE W1STAR
RATS FROM THE TAKENAKA ET AL. (1983) INHALATION STUDY DERIVED FROM FOUR DIFFERENT MODELS
additional risks additional risks
Dose Multistage One-hit Weibull Log-probit Multistage One-hit Weibull Loy-probit
(uy/in3) model model model model model3 model model model
10"4 5.5xl0-6 8.1xl0-6 1.9xl0"7 0 9.7xl0"6 1.0x10-5 1.3xl0"6 1.2xl0"38
10-3 5.5x10-5 B.lxlO"5 4.1xl0"6 0 9.7xl0"5 l.OxlO"4 2.6xl0"5 8.9xl()-2b
10-2 5.5xl0"4 8.lxlO-4 8.8x10-5 2.0x10-15 9.7xl0"4 1.0x10-3 3.8xl0"4 4.4x10"!
10"1 5.5x10-3 8.1X10-3 1.9x10-3 1.3xlO"7 9.7xl0"3 1.0x10-2 5.9xl0"3 l.bxlO"6
1 5.5x10-2 7.8x10-2 3.9X10"2 7.0xl0"3 9.2xl0"2 9.5xl0"2 8.1x10-2 2.3xl0"2
aq* = 9.7 x 10_2 (ug/m3)-l for the multistage model; P(d) = 1 - e -q*d
h h
-------
APPENDIX B
INTERNATIONAL AGENCY FOR RESEARCH ON CANCER CLASSIFICATION SYSTEM
FOR THE EVALUATION OF THE CARCINOGENIC RISK
OF CHEMICALS TO HUMANS*
ASSESSMENT OF EVIDENCE FOR CARCINOGENICITY FROM STUDIES IN HUMANS
Evidence of carcinogenicity from human studies comes from three main
sources:
1. Case reports of individual cancer patients who were exposed to the
chemical or process.
2. Descriptive epidemiological studies in which the incidence of cancer
in human populations was found to vary in space or time with exposure
to the agents.
3. Analytical epidemiological (case-control and cohort) studies in which
individual exposure to the chemical or group of chemicals was found
to be associated with an increased risk of cancer.
Three criteria must be net before a causal association can be inferred
between exposure and cancer in humans:
1. There is no identified bias which could explain the association.
2. The possibility of confounding has been considered and ruled out as
explaining the association.
3. The association is unlikely to be due to chance.
In general, although a single study nay be indicative of a cause-effect
relationship, confidence in inferriny a causal association is increased when
several independent studies are concordant in showing the association, when
*Adapted from IARC, 1982.
174
-------
the association is strong, when there is a dose-response relationship, or
when a reduction in exposure is followed by a reduction in the incidence of
cancer.
The degrees of evidence for carcinogenicity from studies in humans are
categorized as:
1. Sufficient evidence of carcinogenicity, which indicates that there
is a causal relationship between the agent and human cancer.
. Limited evidence of carcinogenicity, which indicates that a causal
interpret n is credible, but that alternative explanations, such as chance,
bias, or confounding, could not adequately be excluded.
3. Inadequate evidence, which indicates that one of three conditions
prevailed: (a) there were few pertinent data; (b) the available studies,
while showing evidence of association, did not exclude chance, bias, or
confounding; (c) studies were available which do not show evidence of carcin-
ogeni ci ty.
ASSESSMENT OF EVIDENCE FOR CARCINOGENICITY FROM STUDIES IN EXPERIMENTAL ANIMALS
These assessments are classified into four groups:
!• Sufficient evidence of carcinogenicity, which indicates that there
is an increased incidence of malignant tumors: (a) in multiple species or
strains; or (b) in multiple experiments (preferably with different routes of
administration or using different dose levels); or (c) to an unusual degree
with regard to incidence, site or type of tunor, or age at onset. Additional
evidence nay be provided by data on dose-response effects, as well as infor-
mation from short-term tests or on chemical structure.
175
-------
2* Limited evidence of carcinogenicity, which means that the data sug-
gest a carcinogenic effect but are limited because: (a) the studies involve
a single species, strain, or experiment; (b) the experiments are restricted
by inadequate dosage levels, inadequate duration of exposure to the agent,
inadequate period of follow-up, poor survival, too few animals, or inadequate
reporting; or (c) the neoplasms produced often occur spontaneously and, in the
past, have been difficult to classify as malignant by histological criteria
alone (e.g., lung and liver tumors in mice).
3. Inadequate evidence, which indicates that because of major qualita-
tive or quantitative limitations, the studies cannot be interpreted as showing
either the presence or absence of a carcinogenic effect; or that within the
limits of the tests used, the chemical is not carcinogenic. The number of
negative studies is small, since, in general, studies that show no effect are
less likely to be published than those suggesting carcinogenicity.
4. No data indicates that data were not available to the Working Group.
The categories suffici ent evidence and 1imited evidence refer only to the
strengtn of the experimental evidence that these chemicals are carcinogenic
and not to the extent of their carcinogenic activity nor to the mechanism
involved. Tne classification of any chemical may change as new information
becomes available.
EVALUATION OF CARCINOGENIC RISK TO HUMANS
At present, no objective criteria exist to interpret data from studies
in experimental animals or from short-term tests directly in terms of human
risk. Thus, in the absence of sufficient evidence from human studies, evalua-
tion of the carcinogenic risk to humans was based on consideration of both
the epidemiological and experimental evidence. The breadth of the categories
176
-------
of evidence defined above allows substantial variation witnin each. The de-
cisions reached by the Working Group regarding overall riskJncorporated these
differences, even though they could not always be reflected adequately in the
placement of an exposure into a particular category.
The chemicals, groups of chemicals, industrial processes, or occupational
exposures were thus put into one of three groups:
Group 1
The chemical, group of chemicals, industrial process, or occupational
exposure is carcinogenic to humans. This category was used only when there
was sufficient evidence from epidemiological studies to support a causal
association between the exposure and cancer.
Group 2
The chemical, group of chemicals, industrial process, or occupational
exposure is probably carcinogenic to hunans. This category includes exposures
for which, at one extreme, the evidence of human carcinogenicity is almost
"sufficient," as well as exposures for which, at the other extreme, it is
inadequate. To reflect this range, the category was divided into higher
(Group A) and lower (Group B) decrees of evidence. Usually, category 2A was
reserved for exposures for which there was at least limited evidence of
carcinogenicity to humans. The data from studies in experimental animals
played an important role in assigning studies to category 2, and particularly
those in Group B; thus, the combination of sufficient evidence in animals and
inadequate data in humans usually resulted in a classification of 2B.
In some cases, the Working Group considered that the known chemical prop-
erties of a compound and the results from short-term tests allowed its trans-
fer from Group 3 to 2B or from Group 2B to 2A.
177
-------
Group 3
The chenical, group of chemicals, industrial process, or occupational
exposure cannot be classified as to its carcinogenicity to humans.
178
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REFERENCES
Adamsson, •!. 1979. i.ong-term sampling of airborne cadmium duct in an
al
-------
Cadmium Council. 1984 (Aug.). Comments of the Cadmium Council in the
matter of: Draft updated mutagenicity and carcinogenicity assessment
for cadium, before the U.S. Environmental Protection Agency.
Federal Register 48:31297.
Casto, B. 1976. Letter to Richard Troast, EPA, enclosing mutagenicity data
on cadmium chloride and cadmium acetate.
Chandler J.A., B.G. Timms, M.S. Morton, and G.V. Groom. 1976. Proceedings:
Effect of cadmium administration in vivo in pi asrna testosterone and the
ultrastructure of accessory sex organs of the rat. J. Endocrinol.
59(3):21.
Chellman, G.J., and C.L. Diamond. 1984. Use of a modified 109-cadmium-heno-
globin assay for quantitation of metal 1othionein in biological tissues.
Toxicoloyist 4:130.
Chiang, C.L. 1961. Vital statistics. Special Report No. 47. U.S. Depart-
ment of Commerce, Division of Vital Statistics, Washington, DC, p. 275.
Clive, D., G. Hajian, and M.M. Moore. 1981. Letter to the Editor. Mutat.
Res. 89:241-244.
Cox, C.R. 1972. Regression models and 1ife tables. J. Roy. Stat. Soc. ,B
34:187-220.
Crunp, K.S., and W.W. Watson. 1979. GL0DAL79: A Fortran program to
extrapolate dichotomous animal carcinogenicity data to low doses.
Natl. Inst. Environ. Health Sciences, Contract No. 1-ES-21
Crump, K.S., H.A. Guess, and L.L. Deal. 1977. Confidence intervals and test
of hypotheses concerning dose-response relations inferred from animal
carcinogenicity data. Biometrics 33:437-451.
Deaven, L.L., and E.W. Campbell. 1980. Factors affecting the induction of
chronosomal aberrations by cadmium in Chinese hamsters cells. Cytogenet.
Cell Genet. 26:251-260.
Degraeve, N. 1971. Modification des effets du methane sulfonate d'ethyl au
niveau chromosotni que. 1. Lesions metal 1 i ques . Rev. Cytol. Biol. Veget.
34:233-244.
Degraeve, N. 1981. Carcinoyenic, teratogenic, and mutagenic effects of
cadmium. Mutat. Res. 86:115-135.
Dekundt, G., and G.B. Gerber. 1979. Chromosomal aberrations in bone marrow
cells of mice given a normal or a-calcium-deficient diet supplemented
with various .h.eavy metals. Mutat.- Res. 68:163-168.
Dekundt, G., and M. Deminatti. 1978. Chromosome studies in human lymphocytes
after in vitro exposure to metal salts. Toxicology 10:67-75.
180
-------
Dexundt, G., and A. Leonard. 1975 . Cytogenic investiyations on leukocytes
of workers from a cadmium plant. Environ. Physiol. Biochem. 5:319-327.
Dekundt, G., A. Leonard, and R. Ivanov. 1973. Chromosome aberrations in
male workers occupationally exposed to lead. Environ. Physiol. Biochem.
3:132-138.
¦Dixon, R.L., I.P. Lee, and R.J. Sherins. 1976. Methods to assess reproduc
tive effects of environnental chemicals: Studies of cadmium and boron
administered orally. Environ. Health Perspect. 13:59-67.
Dripps, R.D., J.E. Eckenhoff, and L.D. Vandam. 1977. Introduction to
anethesia: The principles of safe practice. 5th ed. Philadelphia, PA:
W.B. Saunders Company, pp. 121-123.
Ellman, G.L. 1959. Tissue sulfhydryl groups. Arch. Biochen. Biophys.
82:70.
Epstein, S.S., E. Arnold, 0. Andrea, W. Bass, and'Y. Bishop. 1972.
Detection of chemical mutagens by the doninant lethal assay in the
mouse. Toxicol. Appl. Pharmacol. 23:288-325.
Favino, A., A. Cavalleri, G. Nazari, and M. Tilli. 1968. Testosterone
excretion in cadmium chloride-induced tumours in rats. Med. Lav.
59:36-40.
Federation of American Societies for Experimental Biology (FASEB). 1974.
Biological data books. 2nd ed., Vol. 3. (Philip L. Altman and
Dorothy S. Dittmen, eds.). Bethesda, MD. Library of Congress No.
72-87738.
Ferreira, N.R., and A. Buoniconti. 1968. Trisomy after colchicine therapy.
Lancet 2:1304.
Fraumeni, J.F. 1975. Persons at high risk of cancer. New York, NY: Aca-
demic Press.
Friberg, L., and E. Odeblad. 1957. Localization of CdH5 in different or-
gans. An autoradiographic study. Acta Pathol. Microbiol. Scand.
41:96.
Friedman, M.A., and J. Staub. 1976. Inhibition of mouse testicular DNA
synthesis by mutagens and carcinogens as a potential simple mammalian
assay for mutagenesis. Mutat. Res. 37:67-76.
Furst, A., and D. Cassetta. 1972. Failure of zinc to negate cadmium
carcinogenesis. Proc. Am. Assoc. Cancer Res. 13:62.
Furst, A., D.M. Cassetta, and D.P. Sasmore. 1973. Proc. West. Pharmacol.
16:150-153.
Gail, M. 1975. Measuring the benefit of reduced exposure to environmental
carcinogens. 0. Chronic Dis. 28:135-147.
181
-------
Gasiorek, K., and Mv Bauchinger. 1981. Chronosome changes in human
lymphocytes after separate and combined treatment with divalent salts of
lead, cadmium, and zinc. Environ. Mutagen. 3:513-518.
Ghafghazi , T., and J.H. Meinear. 1973. Effects of acute and subacute cadmium
administration on carbohydrate metabolism in mice. Toxicol. Appl. Phar-
macol . 26:231-240.
Gilliavod, N., and A. Leonard. 1975. Mutagenicity tests with cadmium in the
mouse. Toxicology 5:43-47.
Goldsmith, D.F., A.H. Smith, and A.J. McMichael. 1980. A case-control study
of prostate cancer within a cohort of rubber and tire workers. J.
Occup. Med. 22(8):533-541.
Grasso, P., and L. Goldberg. 1966, Subcutaneous sarcomas as an index of
carcinogenic potency. Food Cosmet. Toxicol. 4:297-312.
Greenspan, B.J., and P.E. Morrow. 1984. The effects of in vitro and aerosol
exposure to cadmium as phagocytosis by rat pulmonary macrophages.
Fund. Appl. Toxicol. 4:48-57.
Gunn, S.A., T.C. Gould, and W.A.D. Anderson. 1963. Cadmium-induced inter-
stitial cell tumors in rats and mice.and their prevention by zinc. J.
Natl. Cancer Inst. 31:745-759.
Gunn, S.A., T.C. GouVd, and W.A.D. Anderson. 1964. Effect of zinc on carci-
nogenesis by cadmium. Proc. Soc. Exp. 3io1. Med. 115:653-657.
Gunn, S.A., T.C. Gould, and W.A.D. Anderson. 1967. Specific response of
mesenchymal tissue to carcinogenesis by cadmium. Arch. Path.
83:493-499.
Haddow, A., et al. 1961. Carcinogenicity of iron preparations and metal-
carbonate complexes. Rep. Br. Emp. Cancer Campaign 39:74.
Haddow, A., F.J.C. Roe, C.E. Dukes, and B.C.V. Mitchley. 1964. Cadmium
neoplasia: Sarcomata at the site of injection of cadmium sulfate in
rats and mice. Br. J. Cancer 18:667-673.
hadley, J.G., A.W. Conklin, and C.L. Sanders. 1979. Toxicol. Letters
4:107-111.
Hadley, J.G., A.W. Conklin. ana C.L. Sanders. 1980. Rapid solubilization
anc translocation of 109(^0 following pulmonary deposition. Toxicol.
Appl. Pharmacol. 54:156-160.
Heath, J.C. 1962. Cadmium as a carcinogen. Nature 193:592.
Heath, J.C., and M.R. Daniel. 1964. The production of malignant tumors by
cadmium in the rat. Br. J. Cancer 18:124.
-------
Heddle, J.A., and W.R. Bruce. 1977. Comparison of tests for mutagenicity or
carcinogenicity using assays for sperm abnormalities, formation of
micronuclei, and mutations in Salmonella. In: Origins of human cancer
(H.H. Hiatt, J.D. Watson, and J.A. Winsten, eds.). Cold Spring Harbor
Conferences on Cell Proliferation, cold Spring Harbor Laboratory, Cold
Spring Harbor, NY.
Hedenstedt, A., U. Rannug, C. Ramel, and V. Wachtmeister. 1979. Mutagenicity
and metabolism studies on 12 thiuram and dithiocarbamate compounds used
as accelerators in the Swedish rubber industry. Mutat. Res. 68:313-325.
Heering, H., G. Oberdoerster, D. Hochrainer, and H.P. Baumert. 1979. Learn-
ing behavior and memory of chronically cadmium exposed rats and organ
distribution of cadmium. Commission of the European Communities,
Brussels, Doc XII/ENV/64/79, pp. 61-62.
Hernberg, S. 1977. Cadmium. In: Origins of human cancer, Book A:
Incidence of cancer in humans (H.H. Hiatt, J.D. Watson, and J.A. Winsten,
eds.). Cold Spring Harbor Conferences on Cell Proliferation. Cold
Spriny Harbor Laboratory, Cold Spring Harbor, NY.
Hirayama, T. 1977. Changing patterns of cancer in Japan, with special
reference to the decrease in stonach cancer mortality. In: Origins of
human cancer, Book A: Incidence of cancer in humans (H.H. Hiatt, J.D.
Watson, and J.A. Winsten, eds.). Cold Spring Harbor Conferences on Cell
Proliferation. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY.
Hoffman, D.J., and S.K. Niyogi. 1977. Metal mutagens and carcinogens affect
RNA synthesis rates in a distinct manner. Science 198:513-514.
Holden, H. 1969. Cadmium toxicology. Lancet 2:57.
Holden, H. 1980. Further mortality studies on workers exposed to cadmium
fumes. Presented at Seminar on Occupational Exposure to Cadmium,
March 20, 1980, London, England.
Howe, R.B. 1983. GL0BAL83: an experimental program developed for the U.S.
Environmental Protection Agency as an update to GL0BAL82: a computer
program to extrapolate quantal animal toxicity data to low doses (May,-
1982). K.S. Crump and Co., Ruston, LA, Unpublished.
Hsie, A.W., J.P. 0'Nei1 , J.R.S. Sabastian, D.B. Couch, et al. 1978. Quanti-
tative mammalian cell genetic toxicology. In: Application of short-term
bioassays in the fractionation and analysis of complex environmental
mixtures (Michael D. Waters, Stephen Nesnow, Joellen L. Huisingh, Shahbey
Sandhu, and Larry Claxton, eds.). EPA-6U0/9-78-027. U.S. Environmental
Protection Agency, Health Effects Research Laboratory, Environmental
Toxicology Division, Research Triangle Park, NC, pp. 293-315.
Humperdinck, K. 1968. Kadmium und lungenkrebs. Med. Klin. 63:948.
Inoue, Y., and T.K. Watanabe. 1978. Toxicity and mutagenicity of cadmium
and furylfuramide in Drosophila melanogaster. Jpn. J. Genet. 53:183-189.
183
-------
Inskip, H., and V. Beral. 1982. Mortality of Shiphan residents: 40-year
follow-up. Lancet, April 17, 1982:896-899,
International Agency for Research on Cancer (I ARC). 1973. Cadmium and
inorganic cadmium compounds. Monographs on the evaluation of carci-
nogenic risk of chemicals to man 2:74. Lyon, France.
International Agency for Research on Cancer (IARC). 1976. Cadmium and
the cadmium compounds. Monographs on the evaluation of carcinogenic
risk of chemicals to man 11:3974. Lyon, France.
International Agency for Research on Cancer (IARC). 1982 (Oct.) Supplement
4 to IARC Monographs on the evaluation of carcinogenic risk of chemicals
to nan, Lyon , France.
Jacko, R.B., and D.W. Neuendorf. 1977. Trace metal particulate emission
test results from a number of industrial and municipal point sources.
J. Air Poll. Control Assoc. 17:989-994.
Japan Public Health Association (JPHA). 1979. Epidemiological research on
the causes of death in cadmium polluted areas. Japan Public Health
Association, Tokyo, Japan. (In Japanese).
Kada, T., K. Tutikawa, and Y. Sodaie. 1972. In vitro and host-mediated assay
"rec-assay" procedures for screening chemical mutagens and phloxine, a
mutagenic red dye detected. Mutat. Res. 16:165-174.
Kahn, H.A. 1966. The Dorn study of smoking and mortality among U.S.
veterans: Report on 8 1/2 years of observation. In: Epidemiological
approaches to the study of cancer and other chronic diseases.
Monoyraph No. 19. National Cancer Institute, Bethesda, MD, pp. 1-125.
Kalinina, L.M., and G.N. Polukhina. 1977. Mutagenic effects of heavy metal
salts on Salmonella in activation systems in vivo and in vitro. Mutat.
Res. 46:223-224. ("Abstract).
Kanematsu, N., M. Hara, and T. Kada. 1980. Rec-assay and mutagenicity
studies on metal compounds. Mutat. Res. 77:109-116.
Kazantzis, G. 1963. Induction of sarcoma in the rat by cadmium sulfide
pigment. Nature 198:1213.
Kazantzis, G., and W.J. Hanbury. 1966. The induction of sarcoma in the rat
by cadmium sulfide and cadmium oxide. Br. J. Cancer 20:190.
Ki pi ing,. M.D., and J.A.H. Waterhouse. 1967. Cadmium and prostatic carcinoma.
Lancet 1:730.
Kjellstron, T. 1982. Mortality and cancer morbidity in people exposed to
cadmium. Report prepared for Health Effects Research Laboratory, U.S.
Environmental Protection Agency, Research Triangle Park, N.C. Grant No.
R806036101.
184
-------
Kjellstrom, T., L. Fribery, and B. Rahnster. 1979. Mortality and cancer
morbidity among cadmium-exposed workers. Environ. Health Perspect.
28:199-204.
Kneale, G.W., T.F. Mancuso, and A.M. Steward. 1981. A cohort study of the
cancer risks from radiation to workers at Hanford. Br. J. Ind. Med.
38:156-166.
Knorre, K. 1970. Ortliche Hautschadigungen an der AlDinoratte in der
Latenzperiode der Sarkomentwicklung nach Kadmlumchloridinjection.
Zentralbl. Allg. Pathol. 113:192-197.
Knorre, D. 1971. Zur Induktion von Hodenzwischenzel1tumoren an der
Albinoratte durche Kadmiumchlorid. Arch. Geschwulstforsch.
38:257-263.
Kolonel, L.N. 1976. Association of cadmium with renal cancer. Cancer
37:1782-1787.
Kumaraswamy, K.R., and M.R. Rajasekarasetty. 1977. Preliminary studies on
the effects of cadmium chloride on the meiotic chromosomes. Curr.
Science 46:475-478.
Lee, I., and R. Dixon. 1973. Effects of cadmium on spermatogerTtsi s studied
by velocity sedimentation cell separation serial nating. J. Pharmacol.
Exp. Ther. 187:641-652.
Lemen, R.A., J.S. Lee., J.K. Wagoner, and H.P. Blejer. 1976. Cancer mortal-
ity among cadmium production workers. Ann. N.Y. Acad. Sci. 271:273.
Levan, A. 1945. Cytological reactions induced by inorganic salt solutions.
Nature 156:751-752.
Levy, L.S., and J. Clack. 1975. Further studies on the effect of cadmium on
the prostate gland. I. Absence of prostatic changes in rats given oral
cadmium sulfate for two years. Ann. Occup. Hyg. 17:205-211.
Levy, L.S., J. Clack, and F.J.C. Roe. 1975. Further studies on the effect of
cadmium on the prostate gland. II. Absence of prostatic changes in mice
given oral cadmium sulfate for eighteen months. Ann. Occup. Hyg. 17:213.
Levy, L.S., F.J.C. Roe, D. Malcolm, G. Kazantzis, J. Clack, and H.S. Piatt.
1973. Absence of prostatic changes in rats exposed to cadmium. Ann.
Occup. Hyg. 16:111-118.
Lippman, M. 1977. Regional deposition of particles in the human respiratory
tract. In: D.H.K. Lee, ed. Handbook of physiology, Section 9:
Reactions to environmental agents. Baltimore: Williams & Wilkins,
pp. 213-232.
Loser, E. 1980. A two year oral carcinogenicity study with cadmium on rats.
Cancer Letters 9:191.
185
-------
Lucis, O.J., R. Lucis, and K. Atennan. 1972. Tunorigenesis by cadmium.
Oncology 26:53-67.
Mailhes, J.B. 1983. Methyl mercury effects on Syrian hamster metaphase II
oocyte chromosomes. Environ. Mutagen. 5:679-686.
Malcolm, D. 1972. Potential carcinogenic effect of cadmium in animals and
man. Ann. Occup. Hyg. 15:33.
Handel, R., and H.J.P. Ryser. 1981. The mutagenic effect of cadmium in
bacteria and its synergism with alkylating agents. Abstracts of the
Environmental Mutagen Society's Twelfth Annual Meetiny, p. 89.
Mantel, N., and M.A. Schneiderman. 1975. Estimating "safe" levels, a
hazardous undertaking. Cancer Res. 35:1379-1386.
McMichael, A.J., D.A. Andjelkovic, and H.A. Tyroler. 1976a. Cancer mortality
among rubber workers: an epidemiologic study. Ann. N.Y. Acad. Sci.
271:124-
McMichael, A.J., R. Spirtas, J.E. Gamble, and P.M. Tousey. 1976b. Mortality
among rubber workers: relationship to specific jobs. J. Occup. Med.
13(3):178-185.
Mi Ivy, P., and K. Kay. 1978. Mutagenicity of 19 major graphic arts and
printing dyes. J. Toxicol. Environ. Health 4:31-36.
Mitra, R., and I. Bernstein. 1977. Nature of the repair process associated
with the recovery of _E. col i after exposure to Cd2+. Biochem. 3iophys.
Res. Commun. 74:1450-1455.
Mitra, R., and I. Bernstein. 1978. Single-strand breakage in DNA of _E. col i
exposed to Cd2+. j. Bacteriol. 133:75-80.
Monson, R.R., and L.J. Fine. 1978. Cancer mortality and morbidity among
rubber workers. J. Natl. Cancer Inst. 61(4):1047-1053.
National Institute for Occupational Safety and Health (NIOSH). 1984
(Aug. 17). Internal memorandum to Director, OSDTT, from Chief, EPI 2
section, IWSB. Subject: Review of EPA assessment of the mutagen-
icity and carcinogenicity of cadmium.
National Researcn Council, Advisory Committee on the Biological Effects of
Ionizing Radiations. 1980. The effects on populations of exposure
to low levels of ionizing radiation: 1980 (BEIR III). Washington, DC:
National Academy of Sciences.
Natusch, D.F.S., J.R. Wallace, and C.N. Evans, Jr. 1973. Toxic trace
elements: preferential concentration in respirable particles. Science
183:202-204.
Nishioka, H. 1975. Mutagenic activities of metal compounds in bacteria.
Mutat. Res. 311:185-189.
186
-------
Nogawa, K., et al. 1978. Statistical observations of the dose-response
relationships of cadmium based on epidemiological studies in the
Kakehashi River basin. Environ. Res. 15:185.
Nogawa, K., S. Kawano, and M. Nishi. 1981. Mortality study of inhabitants
in a cadmium-polluted area, with special reference to low molecular
weight proteinuria. In: Proceedings of the Third Cadmiun Conference,
Mi ami , FL.
Oberdoerster, G. 1984. Bioavailability of cadmiun compounds deposited in
the lung. Presented at International Symposium on the Bioavailability
of Environmental Chemicals, p. 19.
Oberdoerster, G., and P.E. Morrow. 1983. Lymphatic uptake and translocation
of heavy metals. Eighth annual report. National Institute of Environ-
mental Health Sciences Grant No. ES 01247, Division of Toxicology.
Rochester, NY: University of Rochester.
Oberdoerster, G., H. Oldiges, and B. Zimmermann. 1980. Lung deposition and
clearance of cadmium in rats exposed by inhalation or by intratracheal
instillation. Zbl. Bakt. I Abt. Orig. B 170:35-43.
Oberdoerster, G., H.P. Baumert, D. Hochrainer, and U. Stoeber. 1979.
The clearance of cadmium aerosols after inhalation exposure. Am. Ind.
Hygiene Assoc. J. 40:443-450.
Oberly, T.J., C.E. Piper, and D.S. McDonald. 1982. Mutagenicity of metal
salts in the L5178 Y mouse lymphoma assay. J. Toxicol. Environ. Health
9:367-376.
Ochi, T., and M. Ohsawa. 1983. Induction of 6-thioguanine-resistant mutants
and single-strand scission DMA by cadmium chloride in cultured Chinese
hamster cells. Mutat. Res. 111:69-78.
Oehlkers, F. 1953. Chromosome breaks influenced by chemicals. Heredity
Suppl. 6:95-105.
0'Riordan, M.L., E.G. Hughes, and H.J. Evans. 1978. Chromosomal studies on
blood lymphocytes of men occupationally exposed to cadmium. Mutat. Res.
58:305-311.
Paton, G.R., and A.C. Allison. 1972. Chromosome damage in human cell culture
induced by metal salts. Mutat. Res. 16:332.
Pershagen, G., S. Wall, A. Taube, and L. Linnman. 1981. On the inter-
action between occupational arsenic exposure and smoking and its
relation to lung cancer. Scand. J. Work Environ, health 7:302-309.
Pinto, S.S., V. Henderson, and P. Enterline. 1978. Mortality experience of
arsenic-exposed workers. Arch. Env. Health (Nov./Dec.):325-331.
187
-------
Poirier, L.A., K.S. Kasprzak, K.L. Hoover, and M.L. Wenk. 1983. Effects of
calcium and magnesium acetates on the carcinogenicity of cadmium chloride
in Wistar rats. Cancer Res. 43:4575-4581.
Polukhina, G.N., L.M. Kalinina, and L.I. Lukasheva. 1977. A test system for
the detection of the mutagenic activity of environmental pollutants. II.
Detection of mutagenic effect of heavy metal salts using in vitro assay
with metabolic activation. Genetika 13:1492-1494.
Potts, C.L. 1965. Cadmium proteinuria: The health of battery workers
exposed to cadmium oxide dust. Ann. Occup. Hyg. 8:55-61.
Putrament, A.H., H. Baranowska, A. Ejchart, and W. Jachymczyk. 1977.
Manganese mutagenesis in yeast. VI. Mn?+ uptake, mitochondrial DNA
replication and ER induction, comparison with other divalent cations.
Mol. Gen. Genet. 151:69-76.
Raabe, O.G., H.C. Yeh, G.J. Newton, R.F. Phalen, and D.J. Velasquez. 1977.
Deposition of inhaled monodisperse aerosols in snail rodents. In:
Inhaled particles and vapors IV (W.H. Walton, ed.) New York: Peryamon
Press, pp. 3-25.
Ramaiya, L.K., and M.D. Ponerantseva. 1977. Investigation of cadmium
mutagenic effect on germ cells of male mice. Genetika 13:59-63.
Ranel, C., and M. Fribery. 1974. Carcinogenic and genetic effects. In:
Cadmium in the environment (M. Fribery et al., eds.). Cleveland, OH:
CRC Press, p. 133.
Ramel , C., and J. Magnusson. 1979 . Chemical induction of nondisjunction in
Drosophi1 a. Environ. Health Perspect. 31:59-66.
Reddy, J., D. Svoboda, D. Azarnoff, and R. Dawas. 1973. Cadmium-induced
Leydiy cell tumors of rat testis: Morphological and cytochenical study.
J. Natl. Cancer Inst. 51:891-903.
Roe, F.J.C., C.E. Dukes, K.M. Cameron, R.C.B. Pugh, and B.C.V. Mitchley.
1964. Cadmium neoplasia: Testicular atrophy and Leydig cell hyperplasia
and neoplasia in rats and mice following the subcutaneous injection of
cadmium salts. Br. J. Cancer 18:674-681.
Rohr, G., and M. Bauchinger. 1976. Chromosome analysis in cell cultures of
the Chinese hamster after application of cadmium sulfate. Mutat. Res.
40:125.
Ruposhev, A., and K. Garina. 1977. Modification of mutagenic effects of
ethyleneimine by cadmium in Cre.pis capi 11 aris. Genetika 13:32-36.
Russell, L.B., and B.E. Matter. 1980. Whole mammal mutagenicity tests.
Evaluation of five methods. Mutat. Res. 75:279-302.
Sabalina, L.P. 1968. Industrial hygiene in the production and use of cadmium
stearate. Hyg. Sanit. (U.S.S.R.) 33( 7/9):187-191 -
188
-------
Sanders, C.L., and J.A. Ma.naffey. 1984. Carcinogenicity of single and nul-
tiple intratracheal instillations of cadmium oxide in the rat. Environ.
Res. 33:227-233.
Schlesselman, J.J. 1982. Case-control studies design, conduct, analysis.
Oxford, England: Oxford University Press, pp. 197-198.
Schmauz, R., and P. Cole. 1974. Epidemiology of cancer of the renal pelvis
and ureter, J. Natl. Cancer Inst. 52( 5): 1431-1434'.
Schroeder, H.A., J.J. Balassa, and W.H. Vinton, Jr. 1964. Chromiun, lead,
cadmium, nickel, and titanium in mice: effect on mortality, tumors and
tissue levels. J. Nutr. 83:239-250.
Schroeder, H.A., J.J. Balassa, and W.H. Vinton, Jr. 1965. Chromium, cadmi-
um, and lead in rats: Effects on life span, tumors, and tissue levels.
J. Nutr. 86:51-66.
Scott, R., and E. Auyhey. 1979. Methylcholanthrene and cadmium-induced
changes in rat prostate. Br. J. Urol. 50:25.
Shankaranarayanan, K. 1967. The effects of nitrogen and oxygen treatments on
the frequency of X-ray induced dominant lethals and on the physiology of
the sperm in Drosophila melanogaster. Mutat. Res. 4:641-661.
Shigenatsu, I., S. Kitamura, and J. Takeuchi. 1981. A retrospective
mortality study on cadmium-polluted population in Japan. In: Proceed-
ings of Third Cadmium Conference, Miami, FL.
Shimada, T., T. Watanabe, and A. Endo. 1976. Potential mutagenicity of
cadmium in mammalian oocytes. Mutat. Res. 40:389-396.
Shiraishi, Y. 1975. Cytogenetic studies in 12 patients with Itai-Itai
disease. Humanogenetik 27:31-44.
Shiraishi, Y., and T.H. Yoshida. 1972. Chromosomal abnormalities in cultured
leucocyte cells from Itai-Itai disease patients. Proc. Jap. Acad.
48:248-251.
Shiraishi, Y., H. Kurahashi, and T.H. Yoshida. 1972. Chromosomal aberrations
in cultured human leucocytes induced by cadmium sulfide. Proc. Jap.
Acad. 48:133-137,
Sirover, M.A., and L.A. Loeb. 1976, Infidelity of DNA synthesis in vitro:
Screening for potential metal mutagens or carcinogens. Science
194:1434-1436.
Smith, T.J,, R.J. Anderson, and J.C. Reading. 1980a. Chronic cadmium expo-
sures associated with kidney function effects. Am. J. Ind. Med. 1:
319-337.
189
-------
Smith, T.J., W.C. Ferrell, M.O. Varner, and R.D. Putnam. 1980b. Inhalation
exposure of cadmium workers: effects of respirator usage. Am. Ind.
Hyg. Assoc. j. (Sept.):624-629.
Sorahan, T. 1931. A mortality study of ni ckel-cadmi utn battery workers.
Cancer Epidemiology Research Unit, University of Birmingham, Birmingham,
Engl and.
Sorahan, T., and J.A.H. Waterhouse. 1983. Mortality study of nickel-cadmium
battery workers by the method of regression models in life tables.
Br. J. Ind. Med. 40:293-300.
Sorsa, M., and S. Pfeifer. 1973. Effects of cadmium on development time and
prepupal puffing patterns in Drosophila melanogaster. Hereditas 71:273-
277.
Sundermar,, F.W., .Jr. 1977. Cadmium. In: R.A. Goyer and M.A. Mehlman, eds.
Advances in modern toxicology, Vol. 2. New York, NY: John Wiley and
Sons.
Sunderman, F.W., Jr. 1978. Carcinogenic effects of metals. Fed. Proc.
37:40-46.
Sjter, K.E. 1975. Studies on the dominant-lethal and fertility effects of
the heavy metal compounds methylmercuric hydroxide, mercuric chloride,
and cadmium chloride in male and female mice. Mutat. Res. 30:36S-374.
Sutou, $., K. Yanarnoto, H. Sendota, K. Tomomatsu, Y. Shimizu, and M. Sugiyama.
1980a. Toxicity, fertility, teratogenicity, and dominant lethal tests in
rats administered cadniun subchronically. I. Toxicity studies.
Ecotoxicol. Environ. Safety 4:39-50.
Sutou, S., K. Yamamoto, H. Sendota, and M. Sugiyana. 1980b. Toxicity,
fertility, teratogenicity, and dominant lethal tests in rats administered
cadmium subchronically. II. Fertility, teratogenicity, and dominant
letnal tests. Ecotoxicol. Environ. Safety 4:51-56.
Takahashi , T. 1972. Abnormal mitosis by some mutagens in J>. cerevi si ae.
Bull. Brewery Sci. 18:37-48.
Takenaka, S., H. Oldiges, H. Konig, D. Hochrainer, and G. Oberdoerster. 1983.
Carcinogenicity of cadmiun aerosols in Wistar rats. J. Natl. Cancer
Inst. 70:367-373.
Tarkowski , A.K. 1966. An air-drying rnetnod for chromosome preparations
from mouse eggs. Cytogenetics 5:394-400.
Theiss, J.C. 1982. Utility of injection site tumorigenicity in assessing the
carcinogenic risk of chemicals to man. Reg. Toxicol. Pharmacol. 2:213-222.
Thomas, J.F.A. 1980 (Dec.). Soil contamination at Shipham: Report on
studies completed in the village and advice to residents (Shipham Survey
Committee). Department of the Environment, London, England.
190
-------
Thun, M. J., T.M. Schnorr, A.B. Smith, and W.E. Halperin. 1985. Mortality
among a cohort of U.S. cadmium production workers: an update. J. Natl.
Cancer Inst. 74(2):325-333.
Tomatis, L. 1977. The value of long-term testing for the implementation of
primary prevention in organs of human cancer. In: Origins of human
cancer (H.H. Hiatt, J.D. Watson, and J.A. Winsten, eds.). Cold Spring
Harbor Conferences on Cell Proliferation. Cold Spring Harbor Laboratory.
Cold Spring Harbor, NY, pp. 1339-1357.
Uneda, M., and M. Nishimura. 1979. Inducibility of chromosomal aberrations
by metal compounds in cultured mammalian cells. Mutat. Res. 67:221-229.
U.S. Environmental Protection Agency. 1977. The Carcinogen Assessment
Group's assessment of cadmium. Washington, DC. (Unpublished).
U.S. Environmental Protection Agency. 1981 (May). Health assessment document
for Cadmium. EPA 600/8-81-023 (NTIS PB82-115163). Office of Health and
Environmental Assessment, Washington, DC.
U.S. Environmental Protection Agency. 1984 (November). Proposed guidelines
for carcinogen risk assessment. Federal Register 49(227):46294-46301.
U.S. Food and Drug Administration. 1977. Total diet studies (7320.08).
Compliance Program Evaluation, Bureau of Foods, Washington, DC.
U.S. Occupational Safety and Health Administration (0SHA). 1983 (Aug. 24).
Occupational exposure to inorganic arsenic: Comments of ASARC0, Inc.
Federal Register 48:1864-1903.
Van Rosen, G. 1953. Radionimetic activity and the periodical system of the
element. Bot. Notis. 140-141.
Van Rosen, G. 1954. Breaking of chromosomes by the action of elements of
the periodical system and some other participants. Hereditas 40:258-263.
Varner, M.0. 1983 (April). Updated epidemiologic study of cadmium smelter
workers. Presented at the Fourth International Cadmium Conference.
(Unpubli shed).
Vasudev, V., and N.B. Krishnamurthy. 1979. Dominant lethals induced by
cadmium in Drosophila melanogaster. Curr. Science 48:1007-1008.
Venitt, S., and L. Levy. 1974. Mutagenicity of chromates in bacteria and its
relevance to chromate carcinogenesis. Nature 250:493-495.
Watanabe, T., and A. Endo. 1982. Chromosome analysis of preimplantation
embryos after cadmium treatment of oocytes at meiosis. I. Environ.
Mutagen. 4:563-567.
Watanabe, T., T. Shimada, and A. Endo. 1979. Mutagenic effects of cadmium
on mammalian oocyte chromosomes. Mutat. Res. 67:349-356.
191
-------
Welch, K., I. Higgins, M. Oh, and C. Burchfield. 1982. Arsenic exposure,
smoking, and respiratory cancer in copper smelter workers. Arch. Env.
Health 37(6):325-335.
White, L.D. 1984. Letter from L.O. White, ASARCO, Inc., to the Carcinogen
Assessnent Group, U.S. Environmental Protection Agency.
Whittemore, A. 1978. Quantitative theories of carcinogenesis. In: Advances
in cancer research, Vol. 27. New York, NY: Academic Press, pp. 55-58.
Whittemore, A., and B. Keller. 1978. Quantitative theory of carcinogenesis.
Society;for Industrial and Applied Mathematics Review 20:1-30,
Wynder, E.L., K. Mabuc'ni , and W.F. Whitmore, Jr. 1974. Epidemiology
of adenocarcinoma of the kidney. J. Natl. Cancer Inst. 53( 6) -.1619-1634.
Wyrobek, A.J., and U.R. Bruce. 1975. Chemical induction of sperm abnor-
malities. Proc. Natl. Acad. Sci. (U.S.A.) 72:4425-4429.
Zasukhina, G.D., T.A. Sinelschikova, G.N. Lvova, and Z.A. Kirkova. 1977.
Molecular mutagenic effects of cadmium chloride. Mutat. Res. 45:169-174.
192
------- |