it. .
United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
EPA-600/8-83-025B
April 1984
External Review Draft
Research and Development
Updated
Mutagenicity and
Carcinogenicity
Assessment of
Cadmium
Review
Draft
(Do Not
Cite or Quote)
Addendum to the Health Assessment
Document for Cadmium (May 1981)
EPA-600/8-81-023
Available only from: National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
Order No. PB 82-115 163
Cost: $28.00 (subject to change)
Notice
This document is a preliminary draft. It has not been formally
released by EPA and should not at this stage be construed to
represent Agency policy. It is being circulated for comment on its
technical accuracy and policy implications.
-------
V f <»>
.i.
\
-------
DRAFT EPA-600/8-83-025B
DO NOT QUOTE OR CITE April 1984
External Review Draft
<;
-1
UPDATED MUTAGENICITY AND CARCINOGENICITY ASSESSMENT OF
CADMIUM
Addendum to the Health Assessment Document for Cadmium
(May 1981) EPA-600/8-81-023
NOTICE
This document is a preliminary draft. It has not been formally released by the
U.S. Environmental Protection Agency and should not at this stage be construed
tp represent Agency policy. It is being circulated for comment on its technical
accuracy and policy implications. .
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
DISCLAIMER
This report is intended for review purposes only and does not constitute
Agency policy. 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 Technica) Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-4^7-4650
Order No.: PB-82-115163
Cost: $28.00 (subject to change)
-------
CONTENTS (CADMIUM)
Abstract. Y1
AUfihors, Contributors, and Reviewers . .. . vn
JSUMMARY AND CONCLUSIONS. 1
Summary .........«.«
Qualitative Assessment .."-.' 1
Quantitative Assessment .......«« °
Conclusions - '
INTRODUCTION 8
MUfAGENICITY' 9
Gene Mutations in Prokaryotes . 9
Salmonella Assay
Escherichia coli WP2 Assay
Bacillus subtil is Rec-Assay
Gene Mutations in Yeast . ...... . . ...... .15
Gene Mutations in Mammalian Cell Cultures .......... 17
Mouse Lymphoma Assay ..
Chinese Hamster Cell Assay
Studies in Drosophila and Other Insects. . ... 19
Chromosomal Aberrations in Human and Other Mammalian Systems. ... 24
Studies on Human Chromosomes in vitro. ......... 24
Studies on Rodent Chromosomes in vitro . . ..... « 32
Studies on Human Chromosomes in vivo .......... ^
Studies on Rodent Chromosomes in vivo. ......... 38
Micronucleus Assay ....... ......... ;f°
Dominant Lethal Assay ....... ........ ^
Heritable Translocation Assay . . ...... ' " * ' /To
Chromosomal Nondis junction (Aneuploidy) in Whole Mammals . . . 42
Sperm Abnormality Assay in Mammals. ... ...... .44
Chromosomal Aberrations in Plants. . . . ..... 45
Biochemical Studies Indicative of Mutagenic Damage . . . . i . . 46
47
Summary .... ....... ..........
-------
CARCINOGENICITY 49
Animal Studies 49
Inhalation Study in Rats ,( 49
Intratracheal Studies in Rats 55
Injection Studies in Mice and Rats 58
Oral Studies in Mice and Rats 63
Summa ry 67 ^ |;
Epidemiologic Studies. ......... 68
Potts (1965) 69
Kipling and Waterhouse (1967) ... 71
Humperdinck (1968) ... 72
Holden (1969) 74
Kolonel (1976) 74
Lemen et al. (1976). ..!............. 76
McMichael et al. (1976a, b) 79
Monson and Fine (1978). 83
Kjellstrom et al. (1979) 83
Goldsmith et al. (1980) 86
Holden (1980) 87
Sorahan (1981) 90
Inskip and Beral (1982) ..; 94
Andersson et al. (1982) 96
Kjellstrom (1982) 98
Armstrong and Kazantzis (1983, 1982) .......... 103
Sorahan and Waterhouse (1983) .... 108
Varner (1983, unpublished)! .... Ill
Thun et al. (1984, unpublished). 115
Summary . . . . . . . . . . . . 121
QUANTITATIVE ESTIMATION. .... .... 126
Introduction 126
Procedures for Determining Carcinogenic Potency ........ 130
i
Description of the Low-Dose Animal Extrapolation Model .... 130
Selection of Data. 132
Calculation of Human Equivalent Dosages from Animal Data. . 133
Calculation of the Unit Risk from Animal Studies .... 136
Model for Estimation of Unit Risk Based on Human Data .... 1*37
Unit Risk Estimates for Cadmium 139
Unit Risk Estimate Based on an Animal Study. ....... 139
iv
-------
Unit Risk Estimate Based on a Human Study . . . . . . . . 141
Data Base 141
Estimation of the Factors Used in the Calculation of B^ . . 143
Calculation of Average Lifetime Exposure (X) . 148
Calculation of Human Slope (B^) 148
Relative Potency 150
Appendix A. Comparison of Results by Various Extrapolation Models . . . 156
Appendix B. International Agency for Research on Cancer (IARC) Criteria
for Evaluation of the Carcinogenicity of Chemicals .... 160
References 163
-------
ABSTRACT
This draft document evaluates the mutagenicity and cardnogenicity of
cadmium, supplementing an earlier document (Health Assessment Document for
Caamium, 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 draft document tentatively .concludes that: (1) there is evidence
suggesting that cadmium and certain cadmium compounds are weakly mutagenic;
(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 cadmium induces
prostate and/or lung cancer in highly exposed workers; (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 200 times
less than via inhalation.
VI
-------
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)
Elizabeth L. Anderson, Ph.D.
*Larry D. Anderson, Ph.D. ;
*Steven Bayard, Ph.D.
*David L. Bayliss, M.S. I
*Robert P. Beliles, Ph.D. !
Chao W. Chen, Ph.D. ;
Margaret M. L. Chu, Ph.D. !
Herman J. Gibb, B.S., M.P.H.
Bernard H. Haberman, D.V.M., M.S.
Charalingayya B. Hiremath, Ph.D.
Robert E. McGaughy, Ph.D. I
Dharm V. Singh, D.V.M., Ph.D. j
*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
mucagenicity. Participating members are as follows (principal authors are |
designated by asterisks):
John R. Fowle III, Ph.D.
Ernest R. Jackson, M.S.
*K.S. Lavappa, Ph.D.
Sheila L. Rosenthal, Ph.D.
Carol N. Sakai, Ph.D.
Vicki Vaughan-Dellarco, Ph.D.
Peter E. Voytek, Ph.D.
The following individuals provided peer review of this draft and/or earlier
drafts of this document:
vii
-------
U. S. Environmental Protection Agency
t
Michael Dourson :
Environmental Criteria and [Assessment Office
Office of Health and Environmental Assessment
Cincinnati, OH
.»
John B. Fink
Strategies and Air Standards Division
Office of Air Quality Planning and Standards , *
Research Triangle Park, NC;
Charles H. Naunan
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 Research Laboratory
Research Triangle Park, North Carolina
Other Government Agencies
Peter W. Preuss
Consumer Products Safety Commission
Washington, DC
Michael Thun .
Center for Disease Control
National Institute for Occupational Safety and Health
Cincinnati, Ohio
Other ;
Gunter Oberdoerster
University of Rochester »
Rochester, New York ' ^
Science Advisory Board '
The first external review draft:, of this document was peer reviewed by the
Environmental Health Committee of EPA's Science Advisory Board.
vm
-------
SUMMARY AND CONCLUSIONS
SUMMARY
Qualitative Assessment
Chronic exposure of rats to aerosols of cadmium chloride at airborne
cdiiceh'trations of 12.5, 25, and 50 ug/m3 for 18 months followed by an additional
nonexposed 13-month period produced significant increases in lung tumors. An
18-month exposure to 20 ug/m3 also increased lung tumors among exposed rats. A
single 30-minute exposure of rats to cadmium oxide did not significantly increase
the occurrence of lung tumors in the year that followed. However, increases in
testicular degeneration were observed. The estimated total dose in mg/kg was,
however, lower than that producing testicular neoplasia following parenteral
administration. Intratracheal instillation of cadmium oxide has produced an
increase in mammary tumors and an increase in tumors at multiple sites among
mal-2 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
regeneration of testicular tissue. A recent study suggests that the incidence
of f-ancreatic islet cell tumors may be increased by administration of cadmium
chloride by this route. In addition, injection of cadmium chloride into the
-
prostate has induced tumors of that tissue.
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,
in which rats developed a 71% incidence of lung cancer, was about 7 mg
-------
(0.25 m3/day x 0.005 mg/m3 x 365 days/year x 1.5 years). By contrast, in
the Schroeder et al. (1965) drinking water study in rats, which had one of
th4 smallest total doses of all the ingestion studies, a total dose of about
60 mg (5 ppm x 0.5 x 0.35 kg x 730 days) induced no cancer responses. If a
10$ Upper limit of detection of tumors in the Schroeder et al. (1965) study is
assumed, the highest reasonable potency for cadmium 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 magnitude less than for inhalation.
The IARC (1982) concluded that sufficient evidence exists to determine
that cadmuim is carcinogenic in animals. The IARC was aware of the negative
findings following the dietary administration of cadmium chloride by Loser
(I960). The marked carcinogenic response of rats to inhalation exposure to
aerosols of cadmium chloride was not available to IARC for consideration, nor
were the highly suggestive reports pf pancreatic islet tumors following parenteral
administration of cadmium chloride (Poirier et al. 1983), and of male mammary
tumors following intratracheal instillation of cadmium oxide (Sandisrs and
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 injections of cadmium chloride into that tissue (Scott and Aughey 1979).
As a result of these newer investigations, together with additional information
suggesting that long-term pulmonary clearance and translocation from one site to
another in the body is not based on chemical solubility, the carcinogenic risks
of cadmium and its compounds are now seen to be possibly greater than orginally
anticipated.
-------
Gene mutation studies in mammalian cell cultures, rec-assays in bacteria,
chromosomal nondisjunction studies in intact mammals, and other indicators of
mlitag'enlc damage do indicate that cadmium is mutagenic.
Epidemiologic studies reviewed after the May 1981 OHEA Health Assessment
Document for Cadmium have not appreciably changed the earlier findings of
insufficient evidence of a risk of prostate cancer from exposure to cadmium.
On the other hand, recent evidence from the same studies seems to provide
better evidence of a lung cancer risk from exposure to cadmium. Strong evidence
is available from the Thun et al. (1984) study that the significant twofold
excess risk of lung cancer seen in cadmium smelter workers is probably not due
to the presence of arsenic in the plant or to increased smoking by such workers.
Thun et al. analyzed both factors as potential confounders and convincingly
dismissed both in their updated and enlarged version of the earlier Lemen et al.
(1976) study, which also demonstrated a significantly elevated risk of lung cancer.
Varner (1983) in a very preliminary updated and enlarged version of the earlier
Lemen et al. study also found a statistically significant excess of lung cancer.
Varner noted a dose-response relationship for both lung cancer and total
malignant neoplasms with increasing cumulative exposure. Varner indicated that
the significant excess risk of lung cancer was probably due to smoking or to
the,presence of arsenic in the plant. However, he had not had a chance to
analyze their impact since his paper was preliminary. It suffers from several
problems which must be resolved.
Sorahan and Waterhouse (1983) also noted an unqualified statistically
significant 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
oxyacetylene. 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 non-
significantly elevated through Standard Mortality Ratios calculated in a retrospec-
tive prospective cohort study of workers who began employment before and after
the amalgamation 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"
i
group with which to detect a risk after a minimum of 10 years' employment, and
such a significant risk was not shown. Furthermore, only a suggestion of an
excessive risk was evident in the "ever mediumly" exposed group of workers with
a minimum of 10 years 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. Also, 17 different plant populations are combined
to form one cohort for study, thus raising the possibility that very little
exposure occurred to most members of the cohort.
Holden (1980) reported a significantly excessive 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
movement of workers from jobs with high exposure to jobs with low exposure,
possibly because of seniority.
-------
Anders son et al. (1982), in their update of the Kjellstrom et al. (1979)
study, noted a slight hut 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.
Negative findings of a lung cancer risk cannot be considered useful because
of problems" concerning lack of power, no consideration of latent effects, or
insufficient evidence of exposure to cadmium in the studies in which a lung
cancer risk was evaluated.
Overall, the weight of the human epidemiologic evidence is suggestive of a
significant risk of lung cancer from exposure to cadmium. The contribution of
the confounders, smoking and/or the presence of arsenic, has been shown by
Thun et al. (1984) not to have produced the significant risk of lung cancer
that they found in their study. Further evidence provided by the Carcinogen
Assessment Group, under the assumption that arsenic is additive to the background
rate of lung cancer and smoking is multiplicative, indicates that the upper bound
for the expected number of lung cancer cases is still significantly below that
of the observed number of cases at the P < 0.05 level in the Thun et al. study.
Altogether, the human epidemiologic evidence appears to provide limited
evidence of lung cancer risk from exposure to cadmium, based on the International
Agency for Research on Cancer (IARC) classification system.
-------
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
rat studies for estimating human risk is the possible difference between humans
ahd rats in terms of 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 a preliminary assessment of the human risks,,
Given these assumptions, combined with other assumptions and conventions
used in quantitative risk assessment procedures, the Takenaka et a'l. (1983)
data on lung carcinomas in rats during lifetime inhalation exposures to cadmium
chloride aerosol were analyzed. The result of the analysis is that the upper-
bound cancer risk to humans who continuously breathe 1 ug/m3 of elemental
cadmium for a lifetime is 0.15.
Based on respiratory cancer rates from the Thun et al. (1984) study of
cadmium smelter workers, the upper-bound cancer risk from lifetime exposure to
1 ug/m3 of cadmium in the air has a range of 4.3 x 10-6 to 3.8 x 10-2, with a
most plausible estimate of 2.3 x 10-3. The most plausible estimate is based on
"best guesses" for each of a series of terms, that are multiplied to form the
final estimate. Because only fragmentary information is available concerning
cadmium exposures of workers, and many potential biases exist at a range of
almost four orders of magnitude, the human risk is considered to be reasonable.
Further detailed analysis and laboratory studies are needed before the large
difference between the estimates based on animal and human data are resolved.
-------
CONCLUSIONS
Applying the IARC approach (Appendix B) for classifying the weight-of-
ev1den.ce for carcinogenicity in experimental animals, lung carcinomas in rats
exposed to cadmium chloride aerosol by inhalation provide sufficient evidence
faf* the carcinogenicity of cadmium and certain cadmium compounds in experimental
animals along with injection site and testicular tumors in mice and rats given
cadmium metal or cadmium salts. No carcinogenic response has been observed
with ingested cadmium, and the potency via the oral route is at least 200 times
&
less than via inhalation in experimental animals.
The available human epidemiologic data provide limited evidence, according
to the IARC criteria, that airborne concentrations of cadmium and cadmium
compounds are carcinogenic in humans, producing a significant risk of lung cancer
by the inhalation route.
The overall evidence for carcinogenicity, applying the IARC criteria, places
cadmium and cadmium compounds in the 2A category, meaning that they are probably
carcinogenic in humans.
The upper-bound unit risk estimate for continuous inhalation exposure at a
cadmium concentration of 1 ug/m^ ranges from 4.3 x 10~6 to 3.8 x 10~2 with a most
plausible estimate of 2.3 x 10~3 based on lung cancer from one smelter worker
study, although there is considerable uncertainty in these estimates because of
the lack of differential exposure in the workplace. Nevertheless, these estimates
are regarded as more realistic than the estimate based on the rat inhalation
study, which is about 65 times higher.
-------
. INTRODUCTION
This document is a review and assessment of the current information
relating to the mutagenicity and carcinogenicity of cadmium. It contains a
detailed discussion of information on those subjects which became available
since the earlier Health Assessment Document for Cadmium was prepared by the
Office of Health and Environmental Assessment (OHEA) in May 1981. It includes
all pertinent material from the 1981 document but does not attempt to repeat
details of the animal carcinogenicity studies discussed there.
-------
MUTAGENICITY
Cadmium has been investigated for its mutagenic potential in both
prokaryotic and eukaryotic systems.. In the former category are assays for gene
mutation and reparable genetic damage in bacteria. In the latter category are
gene mutation studies in yeast, Drosophila, and mammalian cells; and chromosomal
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 PROKARVOTES
Gene mutation studies that have been conducted in prokaryotic systems are
summarized in Table 1. A discussion of each study follows.
Salmonella Assay
.Meddle and Bruce (1977) tested the mutagenic effects of cadmium chloride
in the histidine reverse mutation assay using Salmonella typhimurium tester
strains TA100, TA98, and TA1537. The test compound (purchased from ICN Pharma-
.ceuticals, Plainview, New York) was dissolved in water and used at concentrations
of 0.05, 0.5, 5, 50, and 500 ug/plate with and without the application of a
metabolic activation system (S9 mix) derived from phenobarbital-induced rat
liver homogenate. 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 were
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.
-------
N PROKARYOTES
CO
o
1 1
1
UJ
Ul
0
§
§
o
u.
o
o
1
^3
Ul >
^-
1
0
UJ
CD
1
t-4
J
CO
^c
" "
0)
u
c
u
m
o >i
01
CO
in
Q
O
Cadmium
compound
c
r-
(O
t_
to
^
+J
in
in
in
H?
QJ
U
3
C_
cc
-c
c
«o
OJ
i r*.
a t~-
c cr>
^C * *
;a are not presented
sarly as revertants/
ite for each strain.
'ity of compound not
jcussed.
(O 1 t 3 -r-
O U CLO- "O
i-4 Cvl
in
(O
o
O IO
Q. en
r- IO
10 -a
xi a>
o o t-
C 3
0. -t- r
2
U- C- 3E CO 3E
O OJ
>, 4J OJ »
r c co a;
C O >i -P O CO
0 -i- ?0 0 T3 0
+J CO CX T3
"O to co co tt) fO
O 3 eu en c (O
! -r- O C J= C -O
> C O 4-> T- «
o .(-»- to -o eu
t- oj co c a> co
CXC-CO (0 >) C=
O. O) C O O
1 (O O. fO QJ >> r~* CX
o .p co -a cno a) t,
.
^4 OJ
to
(0
a
t5
. O (O
a. cn
OJ <1J
o; c:
t OJ
"=! CO
ID 3
S §
O OJ
t O 3 OJ
o -a >
t- c **-
)
to +*'
* ,,_^
*« >!U
s. , I
03 C"
,,_
£ > g
3 r~- i
, en i
o i fO
u.
OJ
O
o
Q.
C i C O '-
o -i +J O3 C
OJ C- n3 -O > O
t- OJ -P C OJ -r- O
CX rtJ -r- O 4->
CO X T3 3 U Q)
3 OJ C T3 (O >
O C OJ C !-
CUT3O> T- O^ 4-*
C C -r- -^ CO C CO -
40 "^ L! cu c_ a; o :
1-^25 g5^S?S
rH OJ CO
CO
to
"S >
"tf *4J
O ffl
cx cn
cu a
oc c:
cu
LO
3
i
a
O
E -a c a)
^ >r_ dj CX
r- £_ > V)
-O i O -P
« j= to o
O U* ' C
irt i
CO CO
IT) LO
i H T-H
h- H-
E
(C 3
r*~ "^
3
C. fc
E* !c
^- o.
m >,
tO 4J
10
-------
» *
XJ
QJ.
rs
c
c
o
o
i-H
UJ
_J
03
I
QJ
o
c:
O)
C_
QJ
4-
QJ
t/l
C
E
O
o
, ' 01
zi
a:
c:
o
.,_
ai
r- 4-3
4J (/)
0 >>
cn
CO
OJ
Ul
O
a
"D
E c
5 i
E Q-
0 E
to o
o u
cr
fO
t_
£
E
ai
Ul
>^
£
a '""" '"
OJ
^3
QJ
4J
W> --^
cr CT>
cu i*-
"C CT^
OJ ,-H
QJ OJ
QJ > t/l 0)
> -^ -r- O U>
r- Cn 4-3 T3 C
+J 3 - O
U (/I (1) Q. CL
OJ O O C W -i-
M- r-* CL o ^ "O CO
O O r QJ C O >T~ C
Ch QJ -i- r (O
QJ O O
4-3-1 CO 0) , 4J-r-L_OrtJ
O *r- LO 40 CO O -r- QJ -r-
CL Ul I O-UlQJt/)4->,
QJ O
«£ .^- r-
a>
4-3
ra
o.
en
ra
T-H LO O O
T-H O
i 1
C
1 1 T-
E r- t-
i3 >) ra QJ
i- JZ O 4->
E 4-3 O (O O
T3 QJ 'T- E CO
O X3 4-3 -Q D
LO I*- CO
O CO CO CO
CO O LO LO LO
CTl r-H r-H T-H <-H
£££££
s
ra 3
i ll
fl) 3
c E
0 T-
E x:
1 CL
ra >,
CO 4->l
ra
o
Ul O^
Ul U)
+
a - 0) T3 a>
0) > 0) >
t>,.r- 4-> !-
i 4-3 C- 4->
O J^ -r- O «
cu ra ui ("v en
OJ 0) O OJ QJ
ce: 3 a. a: c
OJ
c:
O
z.
ai
ra
Q-
LO
o
o
aj c: c
ET3U1O EOJUJC3
3 T- 3 - 3 4-J 3 -
r- £_ O 4-J -I- ra O +J
O 1 3 1 T34-)3r-
ooraui ocraui
-1- i
1 o LT> U
En (S s: iS
ui ui ra
3 -r- Ul
I I VI
r -t- ra
r- 4-> 1
0 J3 U
re 3 OJ
OQ Ul £_
i
"S
3
<1J OO
C01
ra I-H
£
CL
OJ
OJ
3
Ul
-a
c1
3
O
O-
E
o
o
t-H
Ul
-t-
"O - OJ
01 >
O J«I -t
o- ra ui
O) OJ O
Q; 3 Q.^
ai
cr
0
QJ
LO ra
0 r-
O CL
OS
-o
S a
Ul 3 «
c: -r- OJ . >
ui o E "a OJ OJ
3 i- -0 -r- 4-3 4J
o 4J ra c- !-!
O) 3 O O C- U-
cr o M- S i- 3
^a: ui o o c: ui
+ i
. r-. u LO u
t-H QJ -^- OJ
re a: z or
ui ui ra
3 T- Ul
i i Ul
r !- ra
o ja o
ra 3 o)
CO Ul C-
11
-------
In an abstract published by Kalinina and PoluKhina (1977), cadmium chloride
waj reported to be nonmutagenic in the Salmonella assay. However, important
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 Salmonella typhinuirium
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 pro-
perly. The toxicity of the test compound was not reported by these investigators.
Milvy and Kay (1978) studied the mutagenic effects of cadmium red (cadmium
' :
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 ug) was dissolved in 0.01 ml dimethyl sulfoxide
(DMSO) 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 activation 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 incon-
clusive.
Hedenstedt et al. (1979) studied the mutagenic effects of cadmium diethyl-
dithiocarbamate (used in rubber and plastic industries) in Salmonella typhimurium
12
-------
strains TA1535, TA1537, TA1538, TA98, and TA100. The concentrations used were
la 5, 10, 50, and 100 ug/plate. The compound was dissolved in DMSO. Concen-
trations of 50 and 100 ug/plate were toxic in many of these strains. The
concentration of 10 ug/plate exhibited mutagenic activity in strains TA1538
arid TA98 in the absence of a metabolic activation (S9) system obtained from
Aroclor!l254-induced rat liver homogenate (Ames et al. 1975). In TA 1538 the
revertent frequency increased more than twofold at 10 ug/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 jf 2.3 at 10-ug/plate (almost a twofold
increase) compared to the control frequency of 31.5-+_4.2 revertants/plate in
the absence of metabolic activation. No data were given for studies in the
presence of metabolic activation. Positive control data were not presented,
although the authors indicated that positive controls were employed in the
experiment. Since both cadmium diethyldithiocarbamate and zinc diethyldithio-
.carbamate 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 TA153.7 and missense mutations in Salmonella typhimurium
TA1335 by cadmium chloride in concert with N-methyl-N'-nitro-N-nitrosoguanidine
(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
higher than the control value. This synergism was also noted for the induc-
tion of forward mutations to 8-azoguanine (SAG) resistance in the HPRTase locus
of these strains. In a recent telephone communication (9/25/83), Dr. Ryser
13
-------
indicated that he had further confirmation of the above work, and forwarded a
I
preprint of his forthcoming publication to the Reproductive Effects Assessment
Group of the U.S. Environmental Protection Agency.
These studies indicate that cadmium induces mutations in Salmonella
typhljnUMurn 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 HP2 mutation system, mentioned that they also tested
cadmium 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 subtilis 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 subtilis 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 10~7 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 inhibited was indicated
by the relative distance (mm) between the edges of the paper disks and the ends of
14
-------
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 10 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 grade.
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 compounds
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 MUTATIONS IN YEAST
Cadmium chloride has been investigated for the induction of gene mutations
in the yeast Saccharomyces cerevisiae (Table 2) (Takahashi 1972; Putrament et
al. 1977). Takahashi (1972) studied the induction of petite mutations (p-
mutatiqns) and auxotrophs in the Saccharomyces cerevisiae heterozygous diploid
strain C3116. He treated 10^ cells with 10 (5.5 x 10-5M), 12 (6.6 x 1Q-5M),
and 20 ppm (1.1 x IQ-^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 10-3 ce-|is per ml. One-tenth of the diluted suspension
was spread on the YEPD-agar plate and incubated at 28°C. When small colonies
appeared on the plate, they were replica-plated onto YEP-glycerol-agar medium
and minimal medium. After overnight incubation at 28°C, induced p-mutants and
auxotrophs were scored. At the dose of 12 ppm (1.1 x 1Q-4M), no p-mutants or
auxotrophs were found in the 786 colonies counted; at the dose of 10 ppm, 10
15
-------
to
s^
»,-,
^"
O
.-*
UJ
(J
§
HH
_J
§
o
z
g
UJ
s-
tn
g
1
g
|
UJ
o
§
» «
1
o
0
z:
o
t
i
5
uj
£
3
jc
UJ
I
CM
UJ
t
5
cu
u
c
£
CU
(*.
cu
fl£
U)
c
g
o
in
4-»
1
c
o
ra E
> cu
4J tn
en
tn
cu
in
Ǥ
Cadmium
compound
**"
r _,
CO
^
en
to
4->
tn
.E
in
.C^T
JM: en
nj **
1
4*> CU
c in
CU 3
tn re
cu u c
t-
c re
4J O E ^
C 4-> "O Q
Si-0 .5 g
01 «- 4->
to cu in "O o
4J C .r- C L.
C CO C- O Q.
fO Ol (O -C
JJ O CU
3 CU >» 0 3
E 3 CU 4-> C7>
O. 4_» 4-> E >
* *
r-4 CM
tn
to
D CU
cu >
o
&in
o
Q: o.
cu
1
E
o.
D.
O CM O
^-*rH CM
i!
e o
o u
to
CO
0
tn -o
cu c
U (O
fc
E ra in j=
O f- 4-> CL
t_ tn * * c o
ra >r- 4-> ra t.
j^ ^ in 4J 4J
o cu ra 3 o
0 C_ CU E X
ra cu >- 3
ra
cu
c
ro r^
4J Ol
3 rH
Q. *
O CU
t*- O -C
O +-> 4->
c ~o in c:
o cu ra T-
r- tn 3
+J 3 U) T3
ra c i cu
t- tn o i >
C X 4-> O CU
cu ra in
o -o <- cu J3 tn
cr c +J j= o i-
O 3 C +J O
u o o tn >
0. O t_ +J !-
cu e c o c: >
c o o i- ra t-
O U O +J 3
u 3 in
>,+j in .r- E
i H 4-> SS '[
rH CM CO
tn
o cu
cu >
if **~
o ra
o. en
cu cu
cu c
cu
c .
o
z:
CL
CL
CO
O r
ra j=
o o
a
CM
Ol
rH
in
cu
u
>! CU
E re in
O !- 4J
c- in c.
re T- re
O 01 3
ro cu T
tn u|o-
^i^
o
co
a o>
C rH
ra *
C.1 4->
CU CU
J= I
O i
E re
C CL
1 CU
o cu o
4-> 0
4J re-a"
So
r--O
+J H_ CU
1. -i-.cn
4-> C C
1 en cu
14-. .r- i
o in i *-~
re rH
1= CU J= CO
o J= o en
r- +J rH
+J C-
o c cu
r^ 'E lo
CL C- tn
CL cu ra 4^
^C *M J^ CU
rH
ra
a cu
cu >
"tf ^TJ
O S -r-
CL ra m
cu cu' o
^v* 3c o.
CU
c:
^
_j
en
If) UD CO rH m
O O O rH rH
O O O O O
'E o
Oi-
lO -C
CJ 0
CO 1
to M;
-li-
re
E
o
g-
^
cu
3
O
a:
to
r-
en
rH
O
1/1
re
~a
o cu
4*^ 4J
re
cu cu
3 CL
-o cu
C.
> o
i- cr
C- 4-> in T3
3 »i C CO
in o o £
r- >r~ t-
3 X +J !-
o o re 1*-
r- 4-> > C
I- O
>>j= cu o
c. en m
> J=0 0
rH CM
in
re . .
-o .cu . . .
cu > .
t'^ .
O !-
Q. in
CU O
r\* i->
0)
1
E
LO I"
CM in r-i
cu
E 0) E -0
3 4J 3 -f-
r- it) -I- t_
E 4J E 0
O ftJ O U
. -v CU CU
c o c
O C 'i-
CS ns c:
in v> I 3 .
CTli - >r- OO. Ol
c: r- in o
3 CD CU O N
__i o t- +J re
OJ C-
tn cu
cu 4-> tn
c tn r
i- E r-
jC (O CU
O il O
a
»
re
*" 0?
cu r*-
r- CT>
tft i 1
3C '
.
a
0)
M
C
CU
tn
cu
c_
0.
o
cr
re
s
rH
re
T3, 0)
cu >
> .-{j >>-r* ,
O S i-'
CL re in
Q) CO O,,
cu
1
-?.
cn
3
in
CM in in r-n
§|
'i o
a i
ra jr:
o o
42
cu
o
^'*~N
t_ o
ra a:
> o
0«-^
CO t-
l/) CU
co +J in
c in i
!£ re "ai
CJ J= 0
re
3
re
tn
JZ
O
o
c
iro
r- ISO
j= a>
O V ^
O '
in
re
T3 CU
cu >
"t! Tj
d in
a: a.'
,
cu
i
E s: s:
UD >>D 1«O
O O O
i 1 r-H «-l
, r-i CM CO
CU
E -0
il
us J=
o o
CTi
r^t
^
a) t_
l/l CO
a> 4J in
c: in i
!£: ra "cu
O J= O
re '
cu
"tl'co
CU Ol
J2 rH
O ~
'
in
XI 0)
t- +J
O *r
a. in
cu o
K CL
CU
i
J
. en
3
o in o o
rH rH CM CO
O O O O
E CO
1- «
a i
ra 3
o in
CO 1
in ^
~"~"
E
cuJ?
in o.
3 E
o >»
. [
16
-------
p-mutants and three 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 controls 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 mutation frequency,
and the low number of mutants, suggest that the positive results may similarly be
questionable. Since p-mutants occur by damage involving mitochondria! DNA
rather than nuclear DNA, caution should be exercised in assessing the mutagenic
potential of chemicals with this system.
Putrament et al. (1977) also reported a negative result in a test for
induction of p-mutation by cadmium chloride in Saccharomyces cerevisiae. The
concentration of cadmium chloride tested (8 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.
GENE MUTATIONS IN MAMMALIAN CELL CULTURES
Gene mutation studies in cultured mammalian cells have also been summarized
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 the mouse lymphoma L5178Y TK+/- assay. When cadmium
chloride, dissolved in normal saline, was tested at concentrations of 2.35 x
10-?M (cell survival 100^11%), 3.57 x 1Q-7M (cell survival 78 _+ 24%), 4.5 x
10-7M (cell survival 62^4%), 6.00 x 10-?M (cell survival 38 _+!!%), and 8.00
x 10~7M (cell survival 12 +_"!%), there was a dose-related increase in mutation
17
-------
frequency. The mutation frequencies per 104 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"7M was
approximately 1.5-fold higher than the control frequency of 0.40 +_ 0.03 (survival
IQQ% + 5). The dose-response curve obtained by Amacher and Pail let (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 misleading.
In a recent study, Oberly et al. (1982) have 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 ug/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 lO-^M), 5 (2.72 x 10-^1), and 10 ug/mL
(5.45 x 10-8M) of cadmium acetate and cadmium chloride, respectively, for 18
hours, followed by 48 hours of expression time. Cadmium acetate induced mutation
frequencies of 2.8, 50, and 10 per 10~6 survivors, respectively, for the above
dosages. The survival rate was 0.70%, 0.92%, and 0.43%, respectively. Cadmium
chloride induced mutation frequencies of 6, 7, 14, and 37 per 10"6 survivors.
Tha negative control rate was 2 per 106 survivors. According to this investiga-
tion, both cadmium acetate and cadmium chloride are weakly mutagenic. These
18
-------
results are questionable, however, because of the low survival rates at
the high concentrations used. Hsie et al. (1978) also reported cadmium 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 by cadmium was detected in combination with proteinase K diges-
tion of the cell lysates, indicating formation of DNA-protein cross-linking 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 discussion
with the authors of the above publications, cadmium is regarded as mutagenic in
mammalian cell culture gene mutation assays.
STUDIES IN DROSOPHILA AND OTHER INSECTS
Studies on the genetic effects of cadmium in Drosophila are summarized in
T?ble 3. A discussion of each study follows. I
Sorsa and Pfeifer (1973) reported that cadmium chloride at concentrations
of 1.25 (6.81 x 10-6M), 2.5 (1.36 x 1Q-5M), 5.0 (2.72 x 1Q-5M), 10.0 (5.45 x
IO-SM), 20.0 (1.09 x 10-4M), and 50 mg/L (2.27 x 1Q-4M) of media caused
significant delay in the development of larvae as compared with controls. In the
sex-linked recessive lethal mutation test (Muller-5 test), only one concentration
of 50 mg/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
19
-------
o
z:
tn
£§£
t-> O
t UJ
a: g
lg
11
0
OF CADMIUM:
OSOPHILA AN
%°
r >"*
3S5
LU \
t §
i-H LU
O ca
z
LU _J
CD «C
^ O
.1
co in
o
LU
_j
CD
*~"
Ol
O t-H
B
Ol
1/1
__J
at tn
Ol
VI Ol
ai tn
c_ o
O- -O
4-) Ol
o c
c o
re >,
re c:
Q 0
t-l OJ
t/i
re
Reported
negative
en
Ol C
re -r-
> T3
t- Ol
re at
_i 1-
_j TE
en i
£<=>
, . |
O X
oR
tr>
OJ
*fcx
o
E-a
'E'O
T3 r
O O
t.
4-*
tn d)
re >
CT !
o tn
c tn
n3 03
i O
fl) QJ
re *o tn
r d) dl
pi >r~ i""
O «~~ O3
£X 4->
QJ re
re >
(L) t-
^
rH
CO
re
o d)
d) >
o ta
aucn
d) d)
en
dj c
re *r-
> -a
e- co
re di
i t-
0£
_J 1 1 0
*-*. "^.O tn
E E *» AO + X
d)
E-o
'i o
-a i
cS "o
L_
OJ
tn d)
re tn >
CT 4-> tn-i
O c o1 tn
C m P tn
(O fc U
^- Q_ CJi O
g r O t-
d) tn 4->
re > O *o tn
r d) E fl) I .c
o c- x, x +j
Q r tn in i
r-
cn
tr<
£
It
re 3
> re
d) c
in -r-
re <-
>- ^
cr OJ
at >
a -a M- !-
01 01 c: o +J
4-1 tn Ol re
C- OJ QL Ol C_
o J= ot JD re
O.4J T3 CL
OJ C T3 E
t- 1- -r- r- 0
O = O
at co
tn c re S <-
CO O
0 - c >> 1-
0. 4-1 !- <- '
t/i re o 4^ t/i
aj E tn 4-> t/i 01
c_ c_ 4-1 ca at in
1 -r- t t- t_ O
Ol l>- 3 O Ol CL
i/i c tn .a 4J «-
o o 01 re c 3
O O C- t -i- O_
^ B
t-l OJ
tn
re
O !-
o. tn
at o
QZ CL
en
OJ C
re -r-
t- ^
re 01
_J ti-
e
O-
0-
LO O O
vH OJ
01
e -a
'i o
(O _C
C_3 O
tn
t- O
Q) !-
tn (tJ
re 4->
W3
O £
C
rt) r
i re
d) _g
d)
03 r
' j_»
£ C
a. re
o c
tn !-
o E
t_ o
0 TO
*
3.
re
CL
en
3~ i
S F
re I-H r-
L
c
0
o
Ol
3
en c
C !-
1- 4J
4-> C C
O Ol O
Ol >
.
T-< ' '"
tn
re
o d)
dJ >
^j .r-
o re
ex en
d) d>
a; c
c
tn o
tn >> 'r-
>^ CT> re en o1! ' 4-*
0 .r^'oT^3 .^'Jn.S'or^'
t 1 QJ t_ 1 QJ 3
CT'r-
o tn
c tn
re cu
r O
OJ QJ
E <-
re "tu tn
^" ^ P^
1-^r-
1/1 1 JT
O X 4->
c- ai at
O l/l i
20
-------
-a
01
3
C
C
O
o
CO
UJ
CO
1
O)
o
c
Ol
l_
n
oj
CsL
VI
c
E
O
o
to
4->
3
to
01
4-9
C T3
OJ O
re oj
01 0.
t_
1
OJ
Ol
re
to
o
E"?
3 rs
i o
E 0-
rC O
C_> 0
E
OJ
4J
I/I
in
$
c
o
10
3
§1 .
s:
a
c
re
E 01
re r-t
c .
OJ
OJ
-O "O
OJ
OJ -4->
> c
re oj
OJ
re c_
-u a.
re
-o c
QJ
z _o
i (
to
re
-o OJ
01 >
o m '
a. 01
OJ OJ
o: c
.
E
O.
0-
CVJ
OJ
'i o
T3 i
re .c:
o o
OJ
t/i
re to
0 0
C i
re
E 0
in
re o
_!= I_
O O
10
O X
C- OJ
a to
OJ
re
c ;
re
re
3
T3
C
re
O) CO
O Ol
C r-H
T3 re E
O) > 3
i- '> 'i
E t-T3
t- 3 re
OJ to O
OJ T3 >,
re
to -a
re jj oj
f <= 4->
>} E OJ
r- O "4-
o i re
v- OJ
X > to
o aj re
1- 0 s
<-l CM
re
o oj
OJ >
o re
CL 01
OJ QJ
a: c:
en
OJ C
re !-
> -o
C_ flj
re aj
I 4-
i.
a.
o
in
OJ C
E "a to o
3 -r- 3 -r-
r- t_ O 4J
E O OJ 3
T3 i 3 r
re .c cr o
o o re to
OJ
10 OJ
re >
01 -r-
O to
C t/>
re aj
^J O
E ti
re *o 10
r OJ OJ
0. -i- i
o i re
ui I j:
o x j->
C- Ol OJ
O 01 1
'
a >,
C 4->
re »->
t^
re i-
3 re
to j^
re oi-
re re r-^
E T-jCTI
3 re «-<
o
u
OJ C
^3 re
E <-
OJ to
+J JC .
O 4-> O
OJ re c_
"4- t- O +J
14- -I- C
flj o i % o
^ 01 O
OJ x c:
J= O OJ O
1 +J 012:
i4 CM
to
re
.-a 01
OJ >
O -r-
o. t/>
OJ O
tt a.
re
E
** c
o i t in
o o o t-
OJ
CD O O CL
OJ C
E XJ to o
r- C- 0 4->
E O 0) 3
T3 i 3 i
<_> u re t/i
Wl
3
+J
O
,- 0
04 -r-
IO t_ O ^^
t_ Q. oj re
OJ O. E E
o o o
o .c: t/>
^ to t/l o
f to .,- E
j»: re +j o
CO t- 10 t-
o o> o> j:
21
-------
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 IQ-^M) of cadmium
chlon'de/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 chromosomes
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. Revazova
(quoted in Sabalina 1968) in Drosophila melanogaster using the sexi-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 1Q-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/m3. The percentage of sex-linked recessive
lethal mutations among the 498 chromosomes was reported to be 0.2%. The con-
trol frequency of sex-linked recessive lethal mutations was not provided in the
paper. The number of chromosomes tested was not adequate in this study. This
study provides no evidence of mutagenicity of cadmium in Drosophila, but the
22
-------
scale of the study was too small to be considered an adequate test even if
appropriate controls were presented.
Induction of dominant lethal mutations in Drosophila melanogaster with
'- ;'- ' -" .'-'-'-*?,".. .',' ^
cadmium chloride has been reported by Vasudev and Krishnamurthy (1979). The
doses Used were 5 (2.72 x 10-5^), 10 (5.5 x 10-5M), and 20 ppm (1.1 x IQ-^M).
The frequencies of dominant lethals were 11.8%, 14.3%, and 14.3%, respectively,
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 determined the
statistical significance to be at the 5% level, although they did not mention
the type of statistical test employed. Based on these observations, this
study is evaluated as an indicator of a positive response. A comparable study
in an independent laboratory would be of interest for comparative purposes.
Ihoue and Watanabe (19780 studied the effects of cadmium chloride in the
sex-linked recessive lethal test (attached-X method) in Drosophila melanogaster,
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 experimental
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 positive (AF-2) and
negative controls were used in the experiment.
Ramel and Magnusson (1979) failed to detect nondisjunction and sex chromosome
loss in Drosophila following treatment of larvae with 62 ppm (3.32 x 10-%) of
cadmium chloride. No data were presented; therefore, this study cannot be
evHuated. \
Chromosomal aberrations were observed in the testes of the grasshopper,
Poekilocerus pictus, injected abdominally with 0.001 (5.45 x lO-^M), 0.01
23
-------
(5.45 x 10-7M), and 0.05% (2.27 x 1Q-7M) cadmium chloride in 0.05 ml volumes
(Kumaraswamy and Rajasekarasetty 1977). Stickiness of chromosomes, bridge
formation at anaphase-I, 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 jn_ vrvp_, 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 10-2M. Control cultures were incubated similarly,
without the addition of cadmium sulfide. Three hours prior to harvesting, cells
were treated with 0.02 ug/mL of colcemid to obtain cells in the metaphase 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 isochromatid breaks, and symmetrical
and asymmetrical translocations. Increased incidences of chromosomal aberrations,
52% 1n the 4-hour treatment group and 60% in the 8-hour treatment group, were
noted over the 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
24
-------
OJ
o
c
OJ
a:
c:
o
-P
3
VJ
OJ
ce
| g
> in
"~ V?
tj *"
4-
O 4->
c:
o e
-p cd
O
QJ
O>
O
E li
(d O
O O
4-
o
I/)
C= QJ
O t_
-r~ 3
rt) i
L. 3
3 O
Q
E
OJ
V)
tn
OJ
h-
OJ
r-.
r- «
V>
(d »
c_ (d
OO QJ
TD TD
QJ 4^ QJ
t_ O V)
0 =J
OJ t- U C
c_ OJ o 1/1 o tn
OJ C 4- T- fd
SO QJ -P 5
in t_ fd
tn >> QJ QJ £- TD
QJ i i/i ^ 4_) d
4-) C (0 C 3
>» O .C 4-> O> O
o CL c: O CL
O E O O O
O. I- r QJ Q. O O
E 4- rd E
>j 3 TD QJ 4-1
r- TD TD O C C W
QJ ( ID QJ O QJ
TD > > 4->
O .- -r- >> .C >>
0 t- -0 r U f-? QJ
i QJ C C (d C JC
CD TD -r- CD OJ O 4J
~ «
M
rd
TD QJ
t!!p
o <-
CL V)
a; o
cc CL
Q)
c
in vi
c. t_
_£. _c;
* co
CJ
o
*X E
en
O
^₯
E QJ C-ri-
3 TD QJ *4-
T3 r O CJ
rd 3 in CX
O in * * in
*-
c
CVJ
QJ
O
C TD JZ
Z J3 >
tD
c:
4->
C C CO
3 - r*.
Q) OJ «
a a -
TD O
TD OJ 4-
QJ in
C 3 TD
- OJ ,
E v> C-
t- OJ O
QJ C71 O
OJ V)
TD O tf>
a QJ
I/) V)
Toxicity'wa
Appropriate
100 metapha
each point.
i-< OJ CO
v>
4.J -i
Q. Ol -
QJ OJ
QJ
S
v> v» in
(_ £_ L.
** CO 04
f1?
O CD
X X
QJ C
E TD in o
*i o S "3
TD r 3 r
t. O O
CL c
4-> C -Q
O O C
c£g .
OJ fd CXTD
C- L. E 0)
l£8c
OJ .r
(d O +J O
P c: v> O)
«j O OJ Q.
CD O 4-i V)
-'~
vi in
TD OJ TD QJ
OJ > OJ >
t! !p tf '43
CL CT CX cn
OJ QJ OJ O>
CXL c a: c
OJ
5
VI V)
JZ . -C
co «*
^J- OJ
CL) C
E TD in o
^ C O 4->
E O QJ 3
T3 r 3 i
fO JC CT O
c_3 o re tn
V) I/)
£_ t_
-£I .C
CO «*
** OJ
a;
v> o
OJ z:
4-> O)
>, C TD
O ! C
O i rd
cr TD j=
rd O CX i CO
EOS r CO
31 J=lr^ 03
TD
rd t-
QJ
OJ C
r- OCC
in 3 co
ra rd »-H
CD CO -
+j cn
O E c:
C t_ «r-
oj a> 4- c
CO t- C -i
C Q) O 4-
O 3= O
CL QJ
tn v> o >
OJ 4-3 4-i <-
t_ C 4-»
1 0» -0 *i-
QJ e QJ tn
(/)« 4_) O
o t- ra CL
TD QJ QJ
CL CX QJ
O x oj _c:
^ LU £_ +J
f-H CVJ
V) -r-
IT3 VI
O
TD CX
OJ
O ^£
OJ OJ
ce s
OJ
c:
£
V)
c-
co .
co r-- 10 in 5?
i i i i t
O O O O CD
E QJ V> O'
3 4-> 3 «i
t rd O 4-»
E -P QJ 3
TD QJ 3 i
re o a~ o
£_
^
CO
QJ
o fd
H 0 E" *"
:n .Q i CD
25
-------
2*1- C_
_ t- J= (/»
^£ QJ C3. O
r O) 4-J O QJ fl)
O XT O C_ C_ Q.
tj i c O- o. tn
3 « i E
1= 0-S5
re e CT»
-
*!S
C Q.
(/> re E !- O >> -r- M-
O o J <*- -I- 4-> i
T3 in i
O -r- t- 4-> c tn U- .
XT i x: re t- -
.,_ Q ,
o c: t/i c_ c > oj
~ re tn t_ Q) »*«-
e re QJ > 4J
t- C-
3-1- o "4-
_____ __Q)(O
QJ > jao>(/)>ou
4-> - QJ S C -r- C
t_ +-» ^T O)*r- C 4J (U i
O E Dl QJ ^_
QJ
O.T-
Q.4-
e^3
f t-
E O O
at ^-
VI i« L
~°
OJ C
E "O tn o
E O QJ 3
-O « 3 r-
re x: cr O
o o re w
O «c
C. CO
« 3E
t ou.
26
-------
CO
z:
1 =
to
a=
L ABERRATIO
o
to
o
I
o
0
z=
§
i
a:
0
Lu
O
21
O
s
^
LU
1
O
UJ
CD
Z
LO
LU
CO
£
QJ
o
C
0)
O)
or
V)
c:
O
Results
CO
t| QJ "O
O to OJ
ro N
t- .C >j
O) CLr
ro ro
4-> t=
t-
o
O 3 01
i 4-> t_
4-> r JT
(O 3
t_ O
*«-
O
Q)
£= l~
O 3
4-> O
ro CL
1- X
S""
4-
0 V)
(U C-
-§£
3 O
SE O
<*-
o -o to
OJ t-
t- to a)
QJ O rv;
E X O
2=
tn
0)
*O
O)
CL
CO
ro
O)
^* *
C CO
ass
o *
B
^
E
O
O
-p
to
OJ
1
to
1 t
to
ro
-O QJ
QJ >
o ro
CL Cn
QJ Q)
«: c
^_^
'o
t-
O X C3 O
CO Q) O O
CM
O--'
O
P
0)
I
ss
p >1
o o
3
O T3
C 0
o o
o cn
to cn cu
ro c: c_
*?§
&2S
3^-0
4-> O C-
to <*- cx
-H
V)
ro. .
T3 QJ
QJ >
o ro
CL cn
QJ QJ
es* c
,^_^
'o
c.
O Q.CO C
S SS 5
CO
I to
V> C-
ass
s ^
ro
0
i
o
i!"§L
zS J*
LO
13 r*.
c CM cn
ro t** «-*
CT>
r ( 1 !-*
.C J=
to to w
ro T- ro
t. -<^ t_
»- wi T-
J= O .E
to >- to
cz
cn QJ
QJ c: >
4J "O Q) cn
3 J=
4-1 4J 4-}
O O O O £_
C CO)
>>.r- 0 CL
o * ro CL
P (/) QJ 7
tO 4-> L. >tO
r- C 3 *-i-
^.2 gas .
QJ 4J CL 3
JT ro x t_ c
P CL QJ T3 !-
r-t
to
T3 QJ
QJ >
11
C£ CL
C
LO" L!
2 g.
CM
4J
cn
|
ID
CM
» ;
fe
Q
ro o CL
zS 5
0 0)
^H CL
I T3
o
O 3
J= -r-
cn 4^
t- i «
-
-
-I-OCL
ro o E
ty
cti
The possibi of
synergistic on
of various tals
cannot be ignored.
£
o
o
27
-------
OJ
U
c
QJ
t_
oj
<*-
0)
Ol
4-1
C
O
o
l/l
£
trt
05
0 4->
ll
4J (0
ro QJ
t_ c.
0
QJ
O
ra
o
a
il
t'" °
0 0
«*-
O
Q} r
(J ,
C_ QJ
=3 O
V)
QJ
'o
a
co
ra
"O £- »*
c QJ cr>
3 -Q I
OJ QJ i-l
Q C3 '
-o
QJ
IM
'ra r >,
0 e r-
- ro i
c ro
J= QJ QJ O
0 t_ C_'r-
QJ 3
tf'-p
o ra
o. 01
QJ QJ
tt e
c/>
ra
o
CO
4-1
OJ
o
c
O -p-
ll
'? o
T3 »
ro j=
O U
1
c_
E
C I
O QJ
CD 0
o
t_
i
QJ
0
JD
Q)
in
1
a
C
QJ ^^
i QJ r-.
1 -O 3 CTt
OJ I- «-«
31 CO
QJ
t- 1 (A
0) O 3
CL t Ul O
I .c ra E
OJ >>4J S
r- O t- "O CL QJ E in U-
.a 3 ^ o fl)
E 0 E t- 4-10
3= 013= O O CO
, rH CNJ
' ro
O QJ
QJ >
tf£ ,
o ro
CL Ol
QJ QJ
a; c
>»
-o
in
[ 01 '
'' 01
* T3
QJ
E -0
1 'i o
Ji
1
t_
(U
QJ i
o "aj
CD U
QJ
o
' 3
1 c
1 2
o
'i
Q)
, 3
o
QJ
ro
3 r-
wcn
QJ
jr
4-1
T3 W «
S2S
C -r- QJ
ro > c:
J= O Q)
QJ O 'to T-
E 01 E o
3 4-1 3 QJ
-r- 0 -r- U-
E
ra
"O QJ
QJ >
Q- C/l
QJ 0
C£ CL
QJ
ra 3 -i
E i- t-
j= E 0
i "O r
'r- (O -C
^ o o
U
c:
o
UJ U
t/)
o
1
QJ
4-1
ra
ro
QJ
QJ CM
t/1 CTt
CL> <
UJ
1
o
_p
ra ro t_ 01
c s QJ ro
'i >» 01"^
o ro QJ
a v> QJ i
(/) "O t_ O
a ro QJ T- >, -
t- E 4-> O -0
ra > t- c QJ
-a ra o QI o t_
c: jr M- T- QJ
ra 4_> i_ QJ c >
4-> Q> OJ -C QJ O
to i Q.I 01 o
il CM
Ol
ra
"SJ
ara
Ol
QJ QJ
Ct- C
ro
i i
r-T
CM
ro^J- *t
Cf>
^H in E
ll
r- £_
f^
ro JT
tJ O
o
c:
a c; -if ui
ro o 3
QJ *i Ol t-
a 4-1 4-> QJ
L. C 4J
QJ o ro 3
t- CLr-
O O Q- QJ
O t- E J=
CO CLT- 4-1
ro
c
'E
-o^w
QJ ro
=5 4-1
O QJ
28
-------
Q)
o
C
OJ
t-
OJ
OJ
a;
t/>
c
o
£
3
in
S
<*-
O 40
C OJ
O E
4-> td
t- t_
O
ai
01
rd
o
o
-o
3 3
'i CL
TD E
id O
0 0
<*-
0 .
tn
QJ
O i
f- OJ
3 O
OJ
*o
OJ
CL
to
TD to"
id cn
TD -^
O
> t3
id t-
r- Id
i C
i O
VI
OJ
CTI
4->-0
tn QJ
.:=§
QJ rd
O W
r- 0
«£ C
« 1
in
«j
"O OJ
tf 4^
O id
CL 01
OJ OJ
o; c
fd
TD
i-H
o>
^;
Cn
E
LO
OJ
E-o
3 -
"i o
TD i
4-J OJ
t. C 4->
QJ O id 3
t- CLI
S 2 §£
to 0-.,- 4->
Id
4-*
1
I
o 'i
r- O
Z TD
tr>
01
f i
* '
OJ
4->
3
4-*
QJ
Q.
QJ
c_
in in
4J Q}
c: E
e 4J
*- OJ
x x:
UJ 4->
i-H
rd
TD 0)
£ '£
O id
CL Ol
OJ QJ
CH C
m.
*3-
O
in
O TD
O)
E
OJ
QJ
E T3
3 -i
'i o
TD r
Id JC
tJ 0
c:
TD M~ tn ,
OJ OJ tn C
QJ r^ 10 3
O TD CL QJ
tn fd E
ro
^4->
i QJ
e*"~
OJ +J
tl
p- O
s: -a
-a'ir>
ro cn
i t
ro ^
r- id
r- C
o
r- QJ
CD _J
t/l
id
TD QJ
QJ. >
tf '43
O rd
CL Ol
OJ QJ
C£ C
o
01
Ol
in
QJ
3 t-
11
o "6
*- E
i L. in
O i
r I/) IO
QJ1^ ^H
1 U LU
OJ
^1 O ~
40 4_)
^ Id
I_ o
OJ O
l/l
QJ C
O (O
'£ 4->
TD lO
ro cn
£"2
r- rd
« c
i O
r QJ
CS _J
fd
TD QJ
QJ >
O) QJ
c£ cr
tin
fO
T3
O
cn
^
LO cn
*** ^1
LO CD
O CO
§1
E O
u 'u
in
QJ
o
L.
S.
to
OJ
1
OJ
o
£
fC
QJ
TD
id ^D
.^ (5
C
t/i in
E OJ
QJ 4-*
JD O
0 0 "D
t_ O OJ
CL tn
01 m
, C 3
Id -r- 0
o vi cn
i t/1 -r-
C QJ TD
.C O
O O 4-J
QJ t- O
H- a. c
t i
fO
a OJ
- OJ >
o *r-
QJ O
Qi CL
t/1
j=
OJ
. t
Ol Ol
Ol Ol
E E
CO ^0
Q)
3 -r-
II
5-5
4J
&
O
O
"0?
E
OJ
QJ
O
£
4-J
QJ
QJ
fd -
c en
4_> cn
3~
c- ,
VI
1 >J
O TD
L. OJ
O- (/)
cn t/>
i 3
id O
o in
[Z "TD
O 4->
OJ O
1 D. C
in
id
TD OJ
OJ >
O T-
CL V)
QJ O
a; CL
in
OJ
,_j-
* O)
OJ ji^
^E
il
*i o
TD i
(d .c-
CJ O
t/1
QJ
&
o
O
c
4J
tn
E
ro
QJ
C r
fO fd
ri
t^1^
ra OJ
CO
QJ cn
c
id O
4J "O
«3 C
S LU
t/1 O
fO f- >,
TD QJ -r-
QJ > O
£- 4-) CL
O *r- 3
CL in O)
QJ O C
(i; CL rd
in
cn
^1
Ol
LO CD
^-t CO
ll
*E 0
TD i
O O
in
u1
O
4->
tn
rd
CO
. QJ
*i
t^
QJ
O
E
-------
concentration of the compound was used, no dose-response relationship 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 reproducibility
of the results was given, this study cannot be regarded as strong evidence 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 10-5
and 5 x 10~6M cadmium chloride. Chromosome preparations were made 48 hours after
the initiation of the culture, using the standard air-drying technique. In cul-
tures treated 0 hour after the initiation, one hundred metaphases were scored
for each dose. There were 3% aberrations (1% aneuploidy, 2% gaps) at 5 x lO-SM,
and 7% aberrations (5% aneuploidy, 2% gaps) at 5 x 10~6M. In cultures treated
24 hours after the initiation of cultures, there were 5% aberrations (1%
aneuploidy, 4% gaps) at 5 x 10-5M, and 2% aberrations (1% gaps and 1% fragments)
at 5 x 10"6M. The control aberration frequency was 5% (3% aneuploidy, 2% gaps).
The other batch of cultures was treated at 0 hour and 24 hours, and chromosome
preparations were made 72 hours after the initiation of cell cultures. One
hundred metaphases were analyzed for aberration frequencies from each group.
In cultures treated at 0 hour, there were 4% aberrations (3% aneuploidy, 1%
gaps) at 5 x 10-5M, and 3% aberrations (3% aneuploidy) at 5 x 10-6M. Cultures
treated after 24 hours of initiation exhibited 6% aberrations (2% aneuploidy,
1%,fragment, 3% gaps) at 5 x 10~5M, and 4% aberrations (1% aneuploidy, 2% gaps)
at 5 x 10~6M. The control frequencies were 1% aneuploidy and 1% gaps. The
first batch of cultures exhibited aberration frequencies similar to the control
30
-------
levels. The second batch of cultures, treated only 24 hours after the initiation,
exhibited aberration frequencies two to three times above the control levels.
These aberrations occurred mostly in the form of aneuploidy and gaps. The signifi-
cance of chromosomal gaps is not yet understood, and they may 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 chromosomes 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- established human cell lines WI38 and MRC5 to at least two concentrations
(not specified) of cadmium chloride. The duration of treatment was 48 hours
for lymphocytes and 24 hours for WI38 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 and Bauchinger (1981) exposed unstimulated human blood lymphocytes
(GQ) in 1 ml quantities to 10'4, 10~5, 10'6, 10~7, and 10~8M of cadmium acetate
for 3 hours. 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
were made with the standard air-drying technique. Chromosome analysis of 200
cells per treatment indicated a dose-related increase in the incidence of
chromosome gaps. The frequencies of gaps were 0.160, 0.115, 0.135, 0.085, and
0.055 per cell, respectively, for the above doses, as compared 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 (signifi-
cance taken as P < 0.05). The frequencies of structural aberrations (chromatid
deletions and acentric fragments) were 0.025, 0.010, 0.005, 0.020, and 0.010 per
31
-------
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
r*nk U-test indicated that structural chromosome aberrations were significantly
higher than in controls, although no dose-response relationship was evident.
No metabolic activiation 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 10-8 to 10~5M. 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 10~5M 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 10-8 to 10-4M, and chromosome preparations
were made without the addition of colcemid and hypotonic solution. This e'xperi-
i
i
ment indicated a typical stathmokinetic effect (spindle inhibition) similajr to
that caused by colcemid. The mitotic index increased with higher concentrations
of cadmium sulfate. In a short-term experiment with recovery, a concentration
i
of 10"4M was chosen, and cells grown on coverslips were exposed for 1 hour.
Cells with coverslips were washed free of cadmium sulfate, transferred to fresh
i
medium, and grown for 2 to 33 hours. Chromosome preparations were made atj
32
-------
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 aberrations 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 hours were lower than for the interval of 15 to 21 hours. During this
period :(24-33 hours), the structural aberrations ranged from 1.2 to 4.4%, and
the numerical aberrations ranged from 7.8% to 10.8% (2.4% in controls).
The significance of this study is that cadmium was found to induce numerical
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 predisposed for cancer induction.
Deaven and Campbell (1980) studied the effects of cadmium chloride on
chromospmes in CHO cells grown in the presence of bovine serum and fetal calf
serum. A concentration of 2 x 10~^M cadmium produced 17, 26, 62, and 74%
damaged cells, respectively, at 12-, 24-, 36-, and 48-hour analyses of metaphase
chromosomes. However, the presence of fetal calf serum and 2 x IQ-^M 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% newborn 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
33
-------
for cadmium-treated cells, and the range for controls was 4 to 19 per cell.
This study is assessed as inconclusive for the reason that the exact role of
serum in causing chromosome aberrations is still not known. The importance of
these data resides in the fact that virtually all other studies have failed to
consider the potential importance 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% bovine serum.
Cells were exposed to 6.4 x 10"5, 3.2 x 10~5, and 1.0 x 10~5M of aqueous cadmium
chloride. After 24 and 45 hours of exposure, chromosome preparations were made
and analyzed. 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 hoursan, indication of toxicity. At 3.2 x 10-5M the
aberration frequencies were 2% and 3%, at 24 and 48 hours respectively. At the
lowest concentration of 1.0 x 10-5, the aberration frequencies 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. Experiments 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 infected with
Kilhman virus, and cadmium chloride (3.5 x 10-6M) was then introduced into the
cell cultures. Chromosome preparations were performed 24 hours after the
infections. Examination of metaphase 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
34
-------
chloride only, the aberrations frequency was 3%. These results indicate 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 nonreparable DNA
synthesis.
Studies on Human Chromosomes In Vivo
Shiraishi and Yoshida (1972) and Shiraishi (1975) obtained markedly
positive results from Japanese Itai-Itai 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 chromosomal
analysis in four Itai-Itai patients (blood 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 occurreda finding which
indicates that no differences existed between the controls and the Itai-Itai
patients. In the five Swedish workers exposed to cadmium, chromosomal aberration
incidences were 1.0% numerical and 2.0% structural aberrations, while in the
three Swedish controls the frequencies were 0.7% numerical and 4.7% structural
aberrations, indicating nonmutagenic responses.
35
-------
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 aberrations
in 14 workers who had been exposed to zinc, lead, and cadmium in a zinc smelting
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 (concen-
tration 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 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 aberrations 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 experiment.
Bauchinger et al. (1976) studied 24 workers (25-53 years of age) exposed
to lead (mean blood lead level 1 +_ 7 ug/100 ml) and cadmium (mean blood cadmium
36
-------
level 0.40 j^ 0.27 ug/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 chromatid-type aberrations (1.354 +_ 0.994%) was noted, in comparison with
an aberration frequency of 0.467 _+ 0.916% in 1,650 metaphases derived from 15
controls (mean blood cadmium level 0.15 ug/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.
O'Riordan et al. (1978) studied chromosomal aberrations in blood lympho-
cytes from 40 workers exposed to cadmium salts (chemical names not specified, mean
blood cadmium level 1.95 ug/100 ml range < 0.2 to 14.0 ug/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
cells derived from 13 normal subjects (mean blood cadmium level less than 0.2
ug/100 ml in 8 donors and 0.6 to 2.9 ug/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,
though small in number (4/3,740 cells), does not necessarily indicate a negative
response, but does indicate that the study should be considered inconclusive.
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
37
-------
other metals cannot be eliminated as possible contributors to the observed
effects.
Studies on Rodent Chromosomes In Vivo ,
Dekundt and Gerber (1979) investigated the in vivo cytogenetic effects of
ChdnVium chloride (3.27 x 10-7M, 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
aberrations in mice by this route of exposure.
Micronucleus Assay
The micronucleus 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. Meddle and Bruce (1977) studied the ability of cadmium
chloride to induce micronuclei in the mouse. Three groups of mice (F"i of
C57BL/6X C3H/He), each group containing three animals, were given dally
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
38
-------
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 the control level. These results are
presently considered to be inconclusive. The data should 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
The ability of cadmium 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
Ppmerantseva 1977; Suter 1975; Sutou et al. 1980 a, b).
Epstein et al. (1972) evaluated the dominant lethal effects of cadmium
chloride in ICR/Ha mice. Groups of seven or nine male mice, 8 to 10 weeks of
aga, were injected intraperitoneally with 1.35, 2.7, 5.4, and 7.0 mg/kg 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
spermatogonia.
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
39
-------
intraperitoneal route. The treated males were bred with three virgin females
evary week for 3 weeks. The mated females were sacrificed on the 10th day,
; i
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 (FI progeny of C3H and C57BLA). According
to this investigator, cadmium chloride had no dominant lethal effects in female
mice. Female mice of the Fj_ (10 x C3H) stock were injected intraperitoneal ly with
2 mg/kg cadmium chloride, exposing the germ cells (oocytes) at the dictyate stage
of development, and were bred with untreated males for 0.5 to 4.5 days post-
injection. Mated females, as evidenced by 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 lethal test. FI hybrid mice (CBA x C57BL)
aged 2.5 to 3 months were selected for these studies. Males were given a
40
-------
single intraperitoneal injection of aqueous cadmium chloride solution. Three
doses, 1.0, 2.0, and 4 mg/kg, were employed. LDso was determined to be 6.9
trig/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 significant (P > 0.01) increases in the
dominant lethal frequencies were recorded. These results are regarded as
negative since the authors followed appropriate protocols, the dosage selection
was based on 1059, 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 (Russel and Matter 1980) because of the high
spontaneous levels of dominant lethal events that occur during development.
Heritable Trans!ocation Assay
Gilliavod and Leonard (1975) evaluated the mutagenic effects of cadmium
chloride in BALB/c mice using the FI heritable translocation assay. Male mice
(number not specified) were treated with 1.75 mg/kg of cadmium chloride
intraperitoneally, and each treated male was bred with three untreated virgin
females once weekly for 3 weeks. The spermatocytes of the resulting 120 Female
progeny were analyzed for the presence of heritable chromosomal translocation
by standard cytogenetic methods. No evidences of heritable translocation were
noted in the spermatocytes of FI males. This portion of the study is regarded
as inconclusive for the following reasons: Only a single concentration of
41
-------
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 mutagenic 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 mg/kg of cadmium chloride intra-
peritoneally. 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
inconclusive.
Chromosomal Nondisjunction (Aneuploidy) in Whole Mammals
The effects of cadmium chloride on oocytes of mice (Shimada et al. 1976),
on oocytes of Syrian hamsters (Watanabe et al. 1979), and on spermatocytes of
mice (Gilliavod and Leonard 1975) have been investigated.
Shimada et al. (1976) induced superovulation by injecting female mice, ddy
strain, with 5 international units (iu) of pregnant mare's serum (PMS) followed
48 hours later by 5 iu of human chorionic gonadotrophin (HCG). Mice* were
given 3 mg/kg or 6 mg/kg of cadmium chloride 3 hours after the administration
of HCG, and were dissected 12 hours after the cadmium chloride administration.
Chromosome preparations were made from unfertilized oocytes at the second
meiotic metaphase, using the method described by Tarkowski (1966). No structural
chromosome abnormalities were found. However, numerical aberrations (aneuploidy)
were found to be statistically significant (P = 0.015) in the dose group of 3
mg/kg group as compared to controls. The authors postulated that this non-
disjunction may be due to the spindlerinhibiting effects of cadmium*
42
-------
Watanabe et al. (1979), using Syrian hamster oocytes and cadmium chloride,
reported even more pronounced incidences of aneuploidy. Cadmium chloride at
concentrations of 1.0, 2.0, and 4 mg/kg was injected subcutaneously to groups
of 20 female Syrian hamsters 5 hours before ovulation. Matched controls were
given equal volumes of normal saline. Females were sacrificed 12 hours after
the treatment, and the oocytes were recovered from the ampulla. Analysis
revealed that 6 females out of 20 from the 1.0 mg/kg group, 11 females out of
20 from the 2.0 mg/kg group, and 12 females out of 20 from the 4.0 mg/kg group
had numerical chromosomal abnormalities, such as hyperhaploidy and diploidy in
oocytes, as compared to 3 out of 20 in control females. The results were
statistically significant (P < 0.05 and P < 0.01) in the treated groups as com-
pared to the control group. Cadmium-treated animals were also analyzed for
cadmium accumulation in the ovary, using atomic absorption spectrophotometry.
The results indicated statistically significant (P < 0.05) increases in the
accumulation of cadmium in the ovaries of treated females as compared to
control females. Both of these results appear to indicate a positive response
of cadmium in inducing numerical chromosomal abnormalities in mammalian oocytes.
Watanabe and Endo (1982) analyzed the chromosomes of the blastocysts from
mice treated with cadmium 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 mg 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
43
-------
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 nondisjunctions
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 mutagenically
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).
Th2 occurrence of aneuploidy is well documented in cancer cells. Many chromoso-
maily 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 inhibitor, 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). Epidemiological studies at the National Cancer Institute (Dr. Robert
Hoover, personal communication) are presently being conducted to determine the
susceptibility of these types of patients to cancer.
Sperm Abnormality Assay in Mammals
Heddle 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
44
-------
exposure to chemical mutagens (Wyrobek and Bruce 1975). Three groups of mice
of the genotype (C57BL/6 x C3H/He)Fi, each consisting of three mice, were given
daily ihtraperitoneal injections of cadmium chloride for 5'days with doses of
1, 43 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. The sperm suspensions were stained with 1% eosin-Y in water,
and 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 IMPLANTS
Levan (1945) reported that treatment of Alii urn cepa root-tips with cadmium
chloride induced C-mitosis. This observation was later confirmed by Avanzi
(1950), using cadmium chloride concentrations ranging from 2 x lO'^M to 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 Alii urn
cepa, Beta vulgaris, Pi sum abyslnnicum, and Vi ci a sativa. Similar 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).:
45
-------
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
m&/kg, administered intraperitoneally, 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 viyo
and in vitro. Friedman and Staub (1976) studied the effects of cadmium chloride
on ONA synthesis in Swiss mice. Cadmium chloride at 10 mg/kg inhibited DNA
synthesis significantly. An aqueous solution of cadmium chloride was injected
intraperitoneally at the above dose into five male mice, and the mice were
i
sacrificed 3.5 hours later. Thirty minutes prior to sacrifice, mice were
injected with 10 uCi [3H] thymidine. Controls received only 10 uCi [3H] thymidine.
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 [3H] thymidine uptake (1.90
+. 0*58) in the testes as compared to controls (7.45 +_ 1.44).
Mitra and Bernstein (1977, 1978) reported that when E_. coli cultures were
exposed to 3 x 1Q-6M cadmium (Cd2+), 82 to 95% of the cells lost their ability
46
-------
tn form colonies on agar plate. Analysis of DNA strands from cells treated with
various doses of Cd2+ indicated that there was a dose-related increase in the
breakage of single-strand DNA. These investigators believe that the loss of
viability in cadmium-treated cells is due to the single-strand DNA breakage.
GadmiUm'-treated cells recovered viability when grown in Cd2+-free liquid medium
containing 10 mM hydroxyurea.
Si rover and Loeb (1976) investigated the infidelity of DNA synthesis brought
about by cadmium chloride and cadmium acetate. Their assay measured the pertur-
bation in the fidelity of DNA synthesis in vitro caused by soluble metal salts.
Cadmium chloride and 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 1977).
SUMMARY
Cadmium has been investigated for mutagenic activity in both prokaryotic
and eukaryotic systems. Gene mutation studies in Salmonella typhimurium and
E. coli have produced inconclusive results. However, cadmium in concert with
MNNG induced dose-related increases in both reverse and forward mutations in
Sal monel1 a typhimuriurn. 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) weak mutagenic
responses to cadmium were observed. In another gene mutation study, which
used mammalian cell cultures, dose-related increases in mutation frequency
were obtained, indicating that cadmium is mutagenic.
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. However, the negative response in this study may have been due
47
-------
tu inadequate test controls. 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 and
human cell lines treated with cadmium have been conflicting and contradictory.
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 induced
no chromosomal aberrations or micronUclei in bone marrow cells. Similarly, no
dominant lethal mutations were noted in mice treated with cadmium. Chromosomal
aberrations and gene mutations in plants exposed to cadmium have also been
recorded.
The evidence that cadmium is a mutagen that interferes with spindle
formation comes from both in vitro and in vivo studies in mammals. In in vitro
studies using the Chinese hamster cell line "Hy," cadmium induced a stathmokinetic
(spindle-inhibitory) effect similar to that of colchicine, which is a known spindle
poison. Cadmium also was found to increase numerical chromosome aberrations
(aneuploidy) in these cells. Similar and more significant results were obtained
in otudies 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.
The results of gene mutation studies in mammalian cell cultures, rec-assays
in bacteria, chromosomal nondisjunction studies in cultured mammalian cells and
intact mammals, chromosomal aberration studies in plants, and biochemical studies
indicative of mutagenic damage, together with the synergistic effect in Salmonella
and rat embryo cultures, support the conclusion that cadmium is mutagenic.
48
-------
CARCINOGENICITY
Much of the evidence for the carcinogenicity of cadmium has been reviewed
Critically in earlier documents (IARC 1973, 1976; U.S. EPA 1977, 1981; Sunderman
19^7, 1978; Hernberg 1977). This section updates findings mentioned previously
and discusses recent findings 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 (CdCl^) aerosol.
Aerosol was generated by atomizing a solution of CdCl?, and airflow through .the
atomizer was 0.7 L/min. Analytical measurements of cadmium levels were made by
collecting aerosol samples in membrane filters in the intake and exhaust of the
'inhalation chamber. The data in Table 6 show that measured and nominal cadmium
levels were quite close. An aerosol centrifuge was used to estimate particle
size distribution. Aerodynamic mass median diameters were 0.55 urn with an
arithmetic standard deviation of 0.48 urn.
TABLE 6. NOMINAL AND MEASURED CADMIUM CONCENTRATIONS OF
CADMIUM CHLORIDE AEROSOLS USED FOR INHALATION
(Takenaka et al. 1983)
Nominal concentrations
Measured concentrations
Standard deviation
Number of measurements
ug/m3
ug/m3
ug/m3
--
50.0
50.8
5.9
212
25.0
25.7
3.6
220
12.5
13.4
2.1
210
49
-------
The animals were initially 6 weeks old and weighed 133 to 135 g. For 18
»
months, 40 rats per group were continuously exposed to cadmium concentrations
of 12.5 ug/m3, 25 ug/m3, and 50 ug/m3. A control group of 41 rats received
filtered air during the same period. Following the treatment period, the
animals were allowed to survive for an additional 13 months until sacrifice.
Body weights were recorded every 3 months during the entire study period.
Decedents and survivors were necropsied, and tissues and organs were removed
for histopathologic examination. Skulls were decalcified for pathologic
evaluation. Samples of liver, lung, and kidney were digested in acid for
estimation of cadmium content by atomic absorption spectroscopy.
Differences in body weights (Table 7) and mean survival times (Table 8)
among control and treated animals were not statistically significant (P > 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 epidertnoid carcinoma
and the first adenocarcinoma were found at 20 and 22 months, respectively, after
treatment commenced. Several treated rats also develped adenomas 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 non-
neoplastic 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.
Analysis of these tissues indicated that cadmium was absorbed and circulated
throughout the body and that, although the lung was the target organ for carcino-
genicity, the kidney retained the largest amounts of cadmium. Increases in cadmium
50
-------
UJ
a
a:
o
-T-
1
o
^5
14
^
O
o
o
1
t .1
GO .*
O CO
CL. OO
X CT>
* * * t~H
co
1 '
«=C 03
a:
u. co
o
03
CO -^
H- 03
3= C
15 CO
UJ 03
3C 1
*>-
a
o
CD
UJ
cs
1^
fy*
UJ
^J
a:
..
r*.
UJ
1
CQ
«=C
- C
O
1
03
C
r
CO
f
P
i,
0
CD
C
c
c
CD
CO
01
jj
t_
G^
<*-
03
(/)
-E
C
£
^.x-
01
CD
1
<1>
>^
-a
o
o
CD
CD
03
t_
CO
«=c
V)
Q.
3
O
CD
eu
^3
(/)
0
Q.
X
UJ
« 1
CVI
o
i i
!^
CO
O
t-ICO OOO COi-l OLO
LOt-H OOO CO-*o
cvico i-t«d- cvico t-ico
«3- «d- - «3- * ' *
<£>CVI CVI«d- C5CO CVIOO
t t r-i LOCT) OCVI CO'd'
i-ICO OCO .-ICO OCO
^J-^_- ^J-*-^ «** «d-*
CVILO COt-< 1-H.-H r-4CVI
LOO LOI**. CVICV1 LOCVI
coco r*-co coco r*-co
co - co co ' co -
CO «d" CTi «d" ^O ID LO O
COI OO1 VOCO COCTS
COCVI CVICVI CVICVI CVICVI
CO * CO « CO «~" CO
(rj *^"^- ^^-- ** ^ *""^»
cvi co f~* ^o *»}" i**- co r*-
LO-d- LOIO COVO COIO
OO ' CO CO CO
t-4 « 1 I 1 « 1
CO CO CO
E E E
t CD CD CD
O 3 3 3
t_
4J LO
c
O CVI LO O
t3 t-H , CVI LO
'
o
CO
cvi
:*
CVI
< 1
CVI
CO
t 1
"
^- ^-, ^- ^
COCO LOCO «*CO COLO
r*»cn CVI<-H LOI**. r*-«-(
vo co r** *d~ r** ^" LO *^jr
CO * ' CO * ' CO * ^ CO * ^
I~-OO LOCT> CTi^O -*CO
LOr-i coo COP*-OOLO
OCO O«d- CVICO CT>CO
^J-* ^f> . «d-* CO*
cvico LOCTI cvicncvi<£>
ID i 1 OLO CT>LO LOCVI
O^J" O^- CVI'd' t i^-
«3- > «d- * «3- -^
CVI«^- 00 CVI CVlf*~ CTiOO
OO t-H r^-t t-l i-t !** * CO
cvico cvi «3- «d- co cvi-ci-
cj" **-^ ^* *-^ ^ * ^ ^" * ^
^*~*. X**H ^""-* ^"*^
01-* *OCZ> VO^H CO<£>
COCO CVI«* COCO CVI«=J-
1-
o
c
03 TD
O) C
21 UJ
(ti ^f^
51
-------
CO
0
CO
o
os
UJ
a
* i
g
* *
3:
CJ
5
hHI
2C
C3
i <
CO
I
«£
OS ro
OS 4-3
a
CO
CO
CO
E
o
c
CD
c
O
1 CO 1 T-
O 3 T- 4-3
C O r- CO
QJ 4-3 O C.
T3 CO t_ CD
cC E 0-4-
-0 i
CD r-.
4- C 1 CO
O -i- O O
CO E 4-3 !-
4-3 co c/> cn
O CO X -i- O
s: f_ CD .c: i-*-
Ol
3
r~ i
CO C CO
> *r ^ «
r- I/) Q
> CD J«f C »
«- E O) CO CO
3 !- CD CD
CO 4J 3 E +|
^
CO 4-
i O
4-3 (/)
r- 4-3
C O tO
** C C
CD
c_
3 0)
in CL
O 3
O. O
X C_
LU cn
4- 4-
CD ^ ' *
S* CO "*
CM «-l
in in i
r 1 *--^ * ^
C3 IT)
O IO Cvl CN1
O CD O CO
O O !-< .-I
C3 ^^1 ^i" P^*-
4- 4-
o «d- un «*
r-H t-H
O i-H O i-H
r-H CO LT) CO
CO J3 O T3
oo cr> oo m
CO CO CO CO
cn r~ cn co
1-1 1 *-*i " CSJ.
A' S1 i1 i'
OJ i-H CM i 1
r 1 i 1 t-H i-H
1-1 O O O
^"
r- 3 i.
CO CO
i 4-
O 0
4-3
3 CD
CO CO
3
4- CO
o .0
0)
CD -Q
CO
3 T3
CO CD
O C
CD T-
JO E
CO
o x
CD O)
C
1 4-3
E 0
CO C
X
Ol O)
4-3 CD
0 3
10
co CO
5 t-
co o>
C_ JC
t- O
CD
JZ VI O
4-3 « -i- 5
O IO CO 4-3
C *- >i
CO CO r >
>, O CO
CO O 3 4-3
jr 40 co c
4-33 O
C CO 4- E
§o
4- CO
O O) i-l
CO VI
-I CD 3 4-3
CO CO VI
4-3 3 0 t-
l/l CO CD T-
t_ P XI 4-
r- CD
^-^-g^
CD -D C 4-3
4-3 C 'E CD
r- CO C
o> E x !-
C CO O) t-
i- X 3
t- CD 4-3 t3
3 O
T3 4-3 C T3
O CD I-O
a c a) T- i
Ol S- -O O
r- CO CD i 1
"O CO S f < '
3 4-3 O X
CO CO CO a
4-34-34-3 r o o
CO CO CO .
t_ £_ t_ CD V i-H
CD '
0 01 O t- II V
3 c: S -C
1 O f H- O. O-
CO JO P -O tt) 'l|-
52
-------
o
h-
Q
UJ
1/5 **~^
o -z.
CL. O
UJ H-
1 CTi
t < U_ r-<
1 err"
J ^1.
«t OO ^~*
oo nr (0
cs (
=> o "S
-12:
(O
:z co ^^
i i i 1 tO
**** CT
s: a>
Z3 OO ^
i i 2C nj
O Z= '
<0
o 2:
u. oo
O r-T
oo o;
z o
0 U-
1 UJ
«=C 0
H" o*^
z o
UJ 1
O 3=
z o
o
0 -S
O>'Q
uj o
1
_]
CO
let'--
H-
w
^ V
4J
cn
i_
O)
] >
O)
cn
^»^.
cn
3
(O
t_
1 *
C
0)
o
c
o
0
3
i
E
TD
O
to
>.
a>
c
^u
i
XX
LO
O
-------
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
i
found did not 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 CdCl2 aerosols that
were retained at a rather high level in the lungs after cessation of exposure,
and 2) continuous observation of the animals over an extended duration (31
months). Most 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 adenocarcinoma
i *3
were found in 10 rats after 18 months of exposure to a CdCl2 aerosol (20 ug/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
, o
exposure of rats to an aerosol of CdCl2 at 5 mg Cd/m for 30 minutes reduced
the number of particles phagocytized by the lung macrophages for up tb 8 days.
At an airborne concentration of 1.5 mg Cd/m3 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 CdCl2 for
altering the normal phagocytic activity could explain why Takenaka et al.
(1983)-were able to produce such a marked carcinogenic response.
In an earlier study, Hadley et al. (1979) reported one lung tumor among 34
male Wistar rats one year after they had been exposed to 60 ug/L of cadmium
oxide (CdO) for 30 minutes. While this regimen was not adequate for a determina-
tion of carcinogenicity, it is noteworthy that the authors of the study observed
54 :
-------
testicular alterations after this treatment. They pointed out that these changes
occurred at doses lower than the minimum effective dose required to induce degen-
eration with soluble cadmium salts given parenterally if no more than a 20%
pulmonary retention is assumed (1.5 u moles Cd/kg for inhalation versus 5-10 u
itHJleS Cti/kg).
Oberdoerster et al. (1979) compared the lung clearance of CdO and CdCl2 after
a 45-minute exposure to airborne concentrations of 930 ug/m^ and 760 ug/m^, respec-
tively. The aerodynamic mass medium diameters were 0.38 and 0.46 urn for CdCl2
and CdO, respectively. Despite the differences in chemical solubility, the long-
term clearances were equal. The only difference was that cadmium was cleared more
rapidly in the first eight days after exposure. The authors suggested that this
might be due to bronchial clearance mechanisms for the less soluble CdO particles.
Intratracheal Studies in Rats " ;.-..
Sanders and Mahaffey (1984) evaluated the carcinogenicity of CdO in male
Fischer 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 ug CdO when 70 days old; Group 3 received intratracheal
instillation of 25 ug CdO when 70 and 100 days old for a total dose of 50 ug;
Group 4 was given intratracheal instillations of 25 ug CdO when 70, 100, and
130 days old for a total dose of 75 ug. The authors stated that the 25-ug dose
was 75% of the 1050 by the route of administration used. Instilled CdO had a
count median diameter of 0.5 urn. The animals were allowed to survive until
spontaneous death. All animals were necropsied, organs were weighed, and
tumors, lesions, and major tissues and organs from all of the rats (except 12
lost due to autolysis or cannibalism) were examined histopathologically.
55
-------
Median survival times 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 groups. Lung tumor findings
consisted of adenocarcinomas in two rats of 48 in Group 3 that were killed at
880 days. However, when all CdO-treated groups were pooled and tested by life-
table methods for differences in tumor incidences 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
leuteinizing 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 CdO, 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 cadmium as would a design that included
lifetime exposures by inhalation, particularly in reference 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 intratracheally instilled dose of 15 ug 109CdO from the lung in
male Fischer 344 rats, with an elimination half-life of 4 hours, has been observed
(Hadley et al. 1980). In addition, the distribution within the lung of the
cadmium was probably not equivalent to that which would have resulted from an
inhalation exposure. Oberdoerster et al. (1980) showed, using CdCl2» that after
a 1-hour nose-only inhalation exposure, 16% more cadmium was deposited in the
56
-------
alveolar area as compared with intratracheal instillation. Hence, a lifetime
inhalation exposure to CclO also might have presented a stronger challenge for
carcirtdgenicity by providing a greater cumulative dose Of cadmium within target
(lung) tissue.
The increase of mammary tumors observed in the Sanders and Mahaffey (1984)
investigation is in keeping with the finding of relatively rapid clearance of
CdO from the lungs and translocation into other tissues following inhalation
(Hadley et al. 1979) or intratracheal instillation of CdO (Hadley et al. 1980).
In view of the positive pulmonary findings with CdCl2 (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 chemically less soluble CdO, the observation of
Hadley et al. (1979) that airborne cadmium may constitute a potential hazard to
both lung and extrapulmonary tissues is noteworthy. It is necessary, however,
to apply caution when the chemical (rather than the biological or the pulmonary)
solubility of cadmium salts is used in predicting the behavior of chemicals in
complex biological systems. This view is also supported by the work of
Oberdoerster et al. (1979), which showed no difference in the long-term lung
clearance rate of inhaled CdO or CdCl2.
Furst et al. (1973), as part of a larger investigation of the induction of
mesotheliomas by metal in asbestos, performed a preliminary assessment of the
effects of intrathoracic injections of powdered cadmium. The test materials,
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
57
-------
of five male and five female Fischer 344 rats were injected intrathoracically
with 3 mg 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 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 mesotheliomas,
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 determining
carcinogenic potential has been discussed by a number of authors, whose con-
clusions are summarized below.
Grasso and Goldberg (1966) doubted the usefulness of the technique of
assessing the carcinogenic 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.
Tomatis (1977) reviewed the appropriateness of the subcutaneous injection
route for bioassays of carcinogenicity by comparing it with other routes of admin-
istration. He surveyed a number of chemicals tested by the subcutaneous injection
route in rodents to see if there was a correlation between the capacities 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,
58
-------
0
t
O
UJ
-3
t i
§
g
CD.
<:
o
03
Q
UJ
ID
O
z.
ANIMAL TUMORI6ENESIS :
CD
t"H
UJ
_J
CQ
1
CU
O
c
cu
-a-
o
c
-a
c
re
O '
1
cu
4-5
3
O
Oi ,.
.- Compound
01
cu
u
cu
a.
CO
c_
o
4-5
«£
CD
CM
^K^_
O
I-H
O1
O
E
3
4-5
r
CU
0 ° 0
CM r- CM
re -
CO !- 0
4-5
01 T- O1
re 4-5 re
E 01 E
0 t- 0
o cu o
t- 4-5 <-
re c re
CO i i CO
.
re
.
o
01
E
3
-a
re
o
cn
c
re
4-5
C
O
O
c
'tL
cu
U-
01 a>
4-5 O
re !-
C*. jr
^~~-
« i
ID
cn
, i
o re
T3
-0 4-5
re cu
in
CU 01
c- cu re
o JT 3
E 4-5
0 .. =
i-H 00
£_ CU
>i 2 t-
o E cu
333
01 >,
"id CU .* .
CU CU -C T3
CD x: Q-4-5 CU
,-1 4J O t-
->. em-
CM c: cu 3 !-
r- > O O
O1 CU £- CU
ft "O cn f*
CU 01
4-5 ol 4-5
o re 4-5 01 4-5
t- r- re 01 o
re t_ 4-5 c
CO
j-.
«
E
i-
S
2
cu
01
1
t-
_J
E
CD
c
c_ .,
cu
T3 cn
O CO
Q.CM
T3 CD
O
Ol
4-5
re
o
cu
a
o
o
;n
CM
CTv
4-5
re
cu
o
01
f
r
y^
cu
L-
cu
*
CM
0 0^"
.-I i 1 00
oo cn 10
,
o o o .
O O O t-
«- t- i_ re
E _>,
LO Q. LO CX
CM CM
01
re
c_
t_
re
4-5
01
r
^O
o vo
c cn
re i t
oo
'N£>
4-5 3
C J3
re c
N re
re :r
^
«\
o in
O CM f-H
^ ^"o"
O i-l
> o o cu
J= i CO r XJ CU
Q- re T3 E CU 3
.J CU ° 0 ! 0
EC cn .r- t-i
LO |H E "^ to t.
CM re LO c -r- o
CD *" CD "*~ "° "*"
01
4-5
re
re
4-5
CU
§s
T3 Cn
O rH
re~
«s
IS
o
!3
4-5
CU
4-5
C/)
C LO
O r-t
0/20 inject-
controls 0,
t/1
_1u
CM
O rH
C t-
r- 0
O CU
o cu
o
cn c:
E 0
LO CD
O CM
O
CU
O
^_^^
flj
m
Q.
O)
c
o
r
Q
ni
4-5
C
O
o
cu
c
»
c
o
o
*-^
t*
01 re
3 r
O 3
CU U
c: c/>
aSubcutai
blntramui
59
-------
X)
1
r-
C
Q
*ii
*
o
f«-4
UJ
CO
0)
o
c
-o
I
U
tj
XI
c
1C
t_
3
O)
3
o
Q
c
3
O
CL
O
O
to
r
o
01
CO
c_
o
1
X
to
rH
rH
rH
CO
C-
g:
3
P
^»
O)
O LO
1C O
4J CO
P O
tn c-
t- .p
0
c o
I-H
o
tn
to
cu
_J 0)
E 3
00
rH
rH
t_
r* *f
0 >>
ss
CO o
e -^
LO CM
O
tn
o:
^-^
^-
to
rH
r~
1 %
Q)
O)
o
to
rH
0
t!
g:
3
P
r*
O)
O
r r
OJ 0)
U LO O LO
CM CM
1C O (C O
+j to -P tn
4-> O -P O
in C- in £-
t- +J t_ 4J
HI C 03 C
4-J O 4J O
C O C U
HH 1 1
o o
tn tn
CM CM
G O
O O
co cn
i i
CO CO
CD O
CD 0
ai in
0 -P
r~* *tj
e c-
o *-
c to
r- 4-*
.a w
S 3
^_^
CO
to
cn
rH
^
^_
1C
, %
0}
c:
c
3
CD
.
CM
CO *-.
rH rH
O
tn
tn «-
i O
0 E
t- 3
_^> _|_*
C
O r
O i
a>
.. (j CO
CM rH
CM r *»^
-^. 1C O
CTl .1-
P VI
to -r- i
§*> o
in t_
o ;d) c
£_ 40 o
id ic o
to -<
0
in
CM
O
ml
CO
0
CD
CO
1C
t_
t_
1C
CO
5
^.^^
^.
\Q
CTi
d-
c ,
,J
1C
1 ^
U)
c
c
3
ta
co
CM to
o --^
rH CO
tn to
,00
0 O
C- <-
1C fC
co to
o
tn
3 E
o
0) *r-
C
1C XJ
i (C
3
E
in
CM
O
CO
co
£
CO
rH
tn
+J
1C
f
t-
1C
to
5
^^^
p^
to
rH
4
_.
a
i %
0)
a
c
3
CD
LO
CM
*i^
O
rH
f2
g:
3
4^
r
a>
to °
~~- 1C
IO *r-
4\J
tO !-
1C 4->
O 0)
ft »^
1C C
CO t-H
o o
a
tn in
0) a>
r r
CO CO
c c
r- 'r-
tn tn
. .
cn cn
§0
CD
rH rH
CM CM
0 0
S S
I 1
co co
0 0
o o
o o
to in
1C 1C
c_ c_
C- [_
rO ia
| \ [ ^
to i/i
5 3
^_ ,
O rH
o^ cn
rH rH
CO GJ
t- <-
C. C.
O O
*£ ^.
-o
LO a>
rH .r-
XJ
CO
rH VI
r
in g
O -r-
E c
3 1C
4-9
O
r-; S
SL^
1 rH
1C -^-
r- CM
4^
r- CO
4-> ld*-~
V) E >)
£- O r
ai o c_
P (- 1C
C 1C O)
»-< to
o
to
01
CO
c
r-
in
c
r- C
O
CM-r-
CJ 3
XJ r**
0 0
VI
CO
E: 10
CO O
O !-
cz
CD 0
CM O
CD in
o >r"
to
1C
f
j_
1C
[ '
in
3
CM
r-
CTi
rH
r
1C
0)
to
p
U
_I
o
CM
^^
to
rH
CO
t_
O
E
3
4->
i
So
rH
to CD
r-
4J C/1
r r
4^ O
in <-
C- 4->
0) c
4J 0
c o
14
O
a
to
a>
cn
c
r-
in
CM
r
CJ
XJ
CO
CO
O
*
CD
^
CO
cc
0
LO
to
CM
in
(C
o
o
t.
«
co
E
to
r- C
O
1 .P
^= O
4-> a>
C "f-J
§c
"1
CM
. .
c:
_1 !-
E 0
c
CM 1C
b'tj
O
C_ C -i-
OJ T- t-
"§ 'T3 **
O OJ O
D.X1 -r-
C 4->
x> a> ai
o cxx:
in -p
CO 3 C
E in >,
^- in
LO
CO
1C +->
(U
P to
tn to
t-
i- 03
4-> 3
VI C
t- -i-
O) 4->
4-> C
C O
t-H O
O
o
in
CU
CO
c.
r-
tn
CM
0
XI
o
cn
o
o
rH
CO
E
rH
*3
1C
o
I
03
3
co tn
1C 4-J
C- 1C
rv t_
to
co"
to
cn
rH
.
^>
1C
4->
a>
o
c
r«
1C
U-
60
-------
. .
"O
03
c
c.
o
o
o
T-H
UJ
CO
O)
o
C_
r- ro >,
i O t_ CM
.!£ CU CU
CU v-j +J f_
CU C r 0
5 *" (O *l
C
O
CM
O
CO O
TD CM
o 3:
CO
_1
o. E
E
CM
CM
0°
a
CU
o
o
o
J-3
CD ro
t_
o
co~
Cn
d.
*
03
rt)
>>
.3
CM
1
CO
t_
3 ro
o
i -C
r Q.
CU E
CM i *"
* ro +J
+3 re
CO -r- C
ro 4J cn
e co -r-
0 t- r-
o cu re
t- +J E
ro c
CO > 1 r-l
c
C5
CM
3T
CO
3-
O
OO O
s^
co
cn E
CM
i-H
o
o
in
CM
"^ CO
(£> ro
c_
CO O
i c
E o.
3
o
Sarcomas 1/25
Interstitial cell
1 adenocarcinoma
i
CM
00
o
co
"O O
O CM
co 3:
cn_i
E E
LO CM
O «
O
O
ir> tu
oo" c?
«* o
003
3 S
O T
i C CU
1 !- O
CU O
O t_ f_
Lf> ro CU
1^- r 0 >
^. ro .r
O T- CO I
+J 3
Ol *r- O C
ro 4-> E cn
E co ro !-
O t- 3 c
O O) O" CU
t- +J CO ^2
ro C
CO 1 1 r-l ,1
c
0
o
CM
Id
cn
E
CM
O
CO
"o
c_
c
o
o
^
CM
p^"
Prostate tumors 1
o
4-> CU
C +3
4-5
c co
0 0
CU CM
"-31
c <_>
i- XI
o
1
E i
ID §
O
t-H
O
ro
o:
CT>
1
CTl
T-l
^^^
0?
cn
<*>
CO
£_
3
*-*
Sarcomas 14/50
Interstitial cell
o
CO
OJ
l~
cn
c
CO
CM
0 i
o o
<-3 re
cn
n >a
*^1**, CT>
cn .
EO
CO C
CO
ro
C-
(_
ro
4->
CO
-
CO
oo
rji '
^^
1o
03
C-
cu
r
o
Q_
O
ID
oo"
CO
CO
C-
3
-t-*
Sarcomas 12/50
Interstitial cell
CM
O ro
cn
cn .
E 0
to c
CO '"~
o
tr>
CO
CO
'3
4->
Sarcomas 0/50
Interstitial cell
CJ
ro
z:
a«
cn
o
CO
o
o
o
61
-------
which have been reviewed by the International Agency for Research on Cancer (IARC)
and have been tested by the subcutaneous injection route as well as by other routes
of administration, were surveyed. Of those, 69 were positive for carcinogenic
activity when administered by subcutaneous injection and by another route, and 18
Were negative or inconclusive whether given by subcutaneous injection or by another
route. Nine were positive 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 produced what one could call false negative results for six (6.6%) of the 102
chemicals tested and, if we accept all the criticisms of this route of administra-
tion, 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.
More recently Theiss (1982) reviewed the IARC data base. He concluded that
if a compound produces distant tumors by subcutaneous injection it is almost
always tumorigenie 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 significant as results
obtained by 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. The recent 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 metallothianein, 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,
62
-------
showed an increase (P < 0.02) in pancreatic islet cell tumors following sub-
cutaneous injection over a 2-year period of CdCl2 (22/259, 8.5%) as compared
to rats not receiving CdCl2 (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 prevented 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 of CdCl2 is not altogether unexpected
since high concentrations of cadmium. in:the pancreas of humans and animals has
been reported (Friberg and Odeblad 1957), and the effects of cadmium on carbo-
hydrate metabolism and insulin secretion are well documented (Ghafghazi and
Mennear 1973).
Oral Studies in Mice and Rats
Schroeder et al. (1964 and 1965) conducted two lifetime exposure studies in
which Swiss mice were given drinking water containing cadmium acetate at 5 ppm.
The purpose of this low exposure level was to simulate the human experience,
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 ug/g wet weight. This
appears to be very low in comparison with the concentrations of 18 ug/g that have
been reported in man, and the 13.5 ug/g in rats exposed to 12.5 ug/m3 reported
by Takenaka et al. (1983). The exposed males had fewer "visible" tumors (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
histopathologically evaluated. The reduced survival times of the animals, and
the limited amount of histopathological evaluation that was conducted, limit the
63
-------
usefulness of this study in the evaluation of the carcinogenic potential of
cadmium.
In the second lifetime exposure study by Schroeder 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 Cr(III) was
added to the diet of one group of rats that were not given cadmium* they thrived
better than the control group and had 34/71 tumors (Schroeder et al,,. 1965).
Malcolm (1972), in one experiment, gave male Chester-Beatty hooded rats up
to 0.2 mg of cadmium sulfate subcutaneously and up to 0.8 mg weekly by stomach
tube for 2 years. In another experiment, he gave Swiss mice doses of cadmium
sulfate in distilled water up to 0.02 mg/5g of body weight subcutaneously 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 with male specified pathogen-free Chester-Beatty hooded rats,
using doses of 0.087, 0.18, and 0.35 mg/kg of 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, however, that this 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 over-
64
-------
shadowed by their spontaneous occurrence," according to the authors. Effects
on the prostate were especially scrutinized, with no neoplastic lesions observed.
Only a limited number of tissues (kidney, spleen, liver, lung, testes, and
prostate) were histopathologically evaluated from 10 rats of the high-dose
group and 10 rats of the control group.
Levy et al. (1975) similarly gave groups of 50 male Swiss mice 0.44, 0.88,
or 1.75 mg/kg/week cadmium sulfate by gavage for 18 months. A group of 150 male
mice served as controls. The stated objective of the study was the detection
of an increased incidence of prostate tumors attributable to cadmium, 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 CdCl2 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 CdCl2 in
the diet for 103 weeks. Five males and five females per group were sacrificed
at 24 and 52 weeks. All animals were necropsied, and tissues, organs, and
65
-------
tissue masses 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 fibrosis,
Hpid content, liver glycogens 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
more 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, increased
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 CdCl2 was carried
out by Loser (1980). Doses of 1, 3, 10, and 50 ppm of cadmium were given in
food to 50 male and 50 female rats, with 100 controls of each sex. Food consump-
tion was similar in all the test groups- The mean body weights of treated
males were significantly reduced (P < 0.01) at the highest dose level. Other
than reduced weight in the high-dose males, the male and female treatment and
control groups were comparable for weight and mortality. On the basis of a com-
plete histopathological evaluation, the author concluded that there was no
significant increase in the incidence of any particular tumor type or in the
frequency of tumor-bearing animals.
The reason for the discrepancy between the FDA (1977) study with regard to
the lack of effects of cadmium at 60 and 90 ppm as compared to the highly
significant effect (P < 0.01) at 50 ppm is not readily apparent. Strain differ-
ences or differences in dietary factors (such as selenium, zinc, copper, or
estrogen concentrations) may account for the lack of comparability.
66
-------
Summary .
Chronic exposure of rats to aerosols of CdCl2 at airborne concentrations
of 12.5, 25, and 50 ug/m3 for 18 months followed by an additional non-exposed
13-month period produced significant increases in lung tumors. An'18-month-
exposure to 20 ug/m3 also increased lung tumors among exposed rats. A single 30-
mi.nu.te exposure of rats to CdO 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 testicular neoplasia following parenteral
administration.
Intratracheal instillation of CdO 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 regeneration of testicular tissue.
A recent study suggests that the incidence of pancreatic islet cell tumors may
be increased by administration of CdCl2 by this route. In addition, injection
of CdCl2 into the prostate 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,
where the rats developed a 71% incidence of lung cancer, was about 7 mg (0.25
m3/day x 0.05 mg/m3 x 365 days/year x 1.5 years). By contrast, in the Schroeder
67
-------
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 ppm x 0.5
X 0.35 kg x 730 days) induced no cancer responses. If a 10% upper limit of
detection of tumors in the Schroeder et al. (1965) study is assumed, the highest
reasonable potency for cadmium 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
magnitude less than for inhalation.
In 1982 the IARC concluded that sufficient evidence existed for the determina-
tion that cadmium is carcinogenic in animals. The IARC was aware at that time of
the negative findings of Loser (1980) following dietary administration of CdCl2
to laboratory animals. However, studies reporting a marked carcinogenic response
in rats to inhalation of CdCl2 aerosols were not available to the IARC for con-
sideration, nor were the highly suggestive reports of pancreatic islet tumors
following parenteral administration of CdCl2 (Poirier et al. 1983), and of male
mammary tumors following intratracheal instillation of CdO (Sanders and 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 CdClg into that tissue (Scott and Aughey 1979). As a result of
these newer investigations, together with additional information suggesting a
distribution not based on chemical solubility, the carcinogenic risks of cadmium
and its compounds are now seen to be greater than originally anticipated.
*
if
EPIDEMIOLOGIC STUDIES
The epidemiologic studies reviewed here deal specifically with cancer
risks resulting from cadmium exposure. Although five of these studies were
68
-------
reviewed in the OHEA Health Assessment Document for Cadmium (U.S. EPA 1981)
4- ''- --...-
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 number
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 platemaking and assembly shops to 236 mg/m3 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
O
mg/m-3. 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 mg/m3.
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 produce the
critical renal cortex concentration associated with renal dysfunction. Only
1% of Americans ingest more than 50 ug/day (U.S. EPA 1981). However, the
author did note that earlier studies of the urine protein of cadmium-exposed
workers in this same plant had revealed "similar characteristics" to those of the;
present study. Four individuals with persistent proteinuria were examined
further. Two of them ultimately died. Kidney function tests prior to death
69
-------
revealed no abnormalities, nor were any gross abnormalities observed following
microscopic examination of the kidneys of the deceased.
In a second phase of this study, Potts claimed that a "careful search"
produced records for a total of 74 men who had been exposed to cadmium dust for
more than 10 years. Eight of these men had died. The author did not reveal
whether the source of this information \was his clinic's medical records or the
employment records of the factory, nor:did he specify the relationship between
these 74 men and the 70 battery workers mentioned earlier. Furthermore, the source
of his information on the eight deceased individuals was not given, although
presumably it came from his clinical files. Five of the eight deaths were
reportedly due to cancer; three of these were cancer of the prostate. The
death data from Potts's paper is summarized in Table 11. Whether or not the
author made any attempt to determine the vital status of the remaining 66
individuals is unclear. Since all of the deaths occurred in the early 1960s, and
nearly all of these individuals had had lengthy exposures, it can be inferred
that they had all been exposed to the highest cadmium dust levels that existed
at the plant during their years of employment prior to 1950. No information
was given on workers exposed for fewer than 10 years.
In the absence of selection bias (a distinct possibility if clinical records
were used), the distribution of the eight deaths is striking, as was noted by
the author. But because of the possibility of selection bias, the lack of a
comparison group, and the unknown ages of the 74 members of this population, it
is impossible to determine whether the observation of three prostate cancer
deaths is statistically significant. Therefore, this study provides only the
suggestion of an association of prostate cancer and exposure to cadmium.
70
-------
TABLE 11. MORTALITY DATA FOR CADMIUM WORKERS EXPOSED FOR MORE THAN 10 YEARS
(Potts 1965)
Year of death
1960
1960
1961
1962
1962
1963
1964
1964
Kipling and Waterhouse
Age
65
75
65
63
78
53
65
59
(1967)
Length of
cadmium
exposure (yrs)
31
14
37
34
18
35
38
24
Cause of death
Auricular fibrillation
Carcinoma of prostate
Carcinoma of prostate
Bronchitis and atheroma
Bronchitis
Carcinoma of bronchus
Carcinoma of prostate
Carcinomatosis
Kipling 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 incidence rates from the Birmingham
Regional Cancer Registry. The number of observed cancer deaths 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 reported in Potts's
paper (personal communication from Kipling to the IARC in 1976), indicating that
some 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
71
-------
for cancers of all sites.
i
Latency period, although 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 time spent in other
jobs or retirement. It is not clear!how the latter was to be done; the dis-
cussion is sketchy at best. The authors mention that "judging from work in
similar fields, fairly short exposure may be sufficient to initiate a tumor."
Whether this generalized conclusion can be extended to the specific case of
cadmium exposure and cancer remains uncertain. The authors' failure to allow
for a sufficient latency period weakens the significance of their findings.
Because of these problems and the lack of an adequate discussion of the derivation
of expected deaths, the results, although statistically significant, cannot be
considered definitive with respect to the carcinogenicity of cadmium.
1
Humperdinck (1968)
Humperdinck (1968) reported on mortality among 536 people who worked or
had worked at an alkaline dry cell battery plant during the period 1949-67 and
who had been exposed to cadmium hydroxide and "to a large extent nickel
hydroxide." Seventeen of the 536 had died, five from cancer. Of the five who
died from cancer, two died from lung cancer, one from liver cancer, one from
prostate cancer, and one from cardiac cancer. The length of exposure to cadmium
for these cases was: lung, 2.3 years and 9.3 years; liver, 3.5 years; 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
72
-------
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 whether
these rates were age-adjusted, race-adjusted, or sex-adjusted. No differences
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 where 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, Humperdinek 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 Humperdinck 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 departments
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 were similar
enough to the cadmium-exposed group in terms of race, sex, smoking habits, age,
etc. to make these groups objectively comparable. Third, had a proper comparison
group been used and an increase in cancer among workers exposed to cadmium been
demonstrated, a possible confounding variable would have been the concomitant
nickel exposure to which these workers were subjected, since nickel has previously
73
-------
been associated with cancer of the lung, nasal sinus, large intestine, mouth,
and pharynx (Fraumeni 1975).
In conclusion, the study design and methods of Humperdinck render his data
inadequate for the assessment of an association between cadmium exposure and cancer.
Hoi den (1969)
Hoi den (1969), in a letter to The Lancet, reported on 42 men exposed to
cadmium fumes from 2 to 40 years. He stated that six of the men had been
exposed to concentrations of cadmium in excess of 4 mg/m3, and the remainder
had been exposed to an average concentration of 0.1 mg/m3. The author reported
that of the 42 men, one developed a carcinoma of the prostate and one developed a
carcinoma of the bronchus. i .
No evaluation of the cancer risk from cadmium can be made on the basis of
this letter, since the author did not report important variables such as age,
time since first exposure, and smoking history.
Kolonel (1976)
Kolonel (1976) compared the cadmium exposure of 64 cases of renal cancer
to 197 nonmalignant digestive disease controls and 72 colon cancer controls.
According to the author, "a cancer control group was included to address the
problem of potential noncomparability" between cases and controls when a non-
cancer control group was used. Cases and controls were taken from patients
admitted from 1957 to 1964 to Roswell Park Memorial Institute, Buffalo, New York.
Cadmium exposure was assessed using data on occupational exposure,: cigarette
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 electro-
plating, alloy-making, welding, and the manufacture of storage batteries. A
74
-------
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 odds* of developing renal cancer in occupationally-
exposed patients who smoked were 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 odds of developing renal cancer in patients who were occupationally
exposed were 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 occupational exposure were added
together, the author concluded that the effects of smoking and occupational
exposure must be synergistic.
The odds of developing renal cancer when consideration is given to cadmium
exposure through cigarette smoking only, and separately through diet only
(utilizing colon cancer controls), were 1.2 and 1.6, respectively, neither of
which was significant (0.05 < P < 0.10, two-tailed).
A major criticism of this study is the confounding exposures to other indus-
trial materials in the electroplating, alloy-making, welding, and storage battery
manufacturing industries. The author stated that renal cancer resulting from
cadmium exposure is biologically plausible because the kidney concentrates cadmium
to a greater degree than any other organ. Furthermore, Kolonel pointed out, on
Although the author referred to "relative risk" in his article, it is more
correct to use the term "odds ratio" or "estimated relative risk."
tRisk in this context is an estimated relative risk derived by use of the
odds ratio.
75
-------
the basis of an earlier study by Ellman (1959), that the kidney contains the body's
highest concentration of sulfhydryl groups, which are often found in zinc-
containing enzymes. Cadmium inhibition of a variety of sulfhydryl-containing
enzymes has been reported, the author notes, and this may be the mechanism of
action* The kidney concentrates many trace metals, however, and a variety of
metals are found in the industries mentioned above, including nickel, lead, and
zinc. Also, it is interesting to note that the odds ratio for occupational
exposure to cadmium is significant (P < 0.05) only when compared to noncancer
controls, but not significant (0.5 < P < 0.10) when compared to colon cancer
controls. This indicates that the renal cancer cases may not be comparable to
the noncancer cases, and selection bias may have occurred.
Smoking has previously been associated with kidney cancer (Wynder et al.
1974, Schmauz and Cole 1974, Kahn 1966, Hirayama 1977) as well as with cancers
of other sites. Although cadmium may be the carcinogen in tobacco smoke that
causes kidney cancer, the issue is confounded by the presence in tobacco smoke
of many other carcinogens as well. Although the smoke may serve only as a
possible synergist or a carrier mechanism for cadmium exposure from other
sources, it remains to be demonstrated that cadmium is the agent of concern in
smoking.
In conclusion, Kolonel's study provides suggestive, but not sufficient
evidence that cadmium is a renal carcinogen. More studies, epidemiologic and
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 smeller who had worked a minimum of 2 years in the
smelter at some time during the period from January 1, 1940 to December 31, 1969.
76
-------
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 United States white male population.
The authors stated that the smelter 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 1925, arsenic production ceased and 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/m3 and cadmium dust at 17.23 mg/m3, but it was reported in that survey
that most operations in the plant had cadmium air concentrations of lower than
1.5 mg/m3. The present study included a 1973 industrial hygiene evaluation of
cadmium dust levels which stated that 8-hour time-weighted average (TWA) gross
concentrations of cadmium ranged infrequently up to 24 mg/m3, but generally
remained below 1 mg/m3. The authors reported, following a 1973 industrial
hygiene,survey, that a respirator program had been instituted at the plant, which
had allegedly reduced exposure by a factor of 10, although the workers tended to
remove the respirators because of their inconvenience. Two air measurements taken
in the preweld department showed that in addition to air concentrations of 74.8
and 90.3 ug/m3 of cadmium, arsenic was measured at 0.3 and 1.1 ug/m3. This is
about 1% of the cadmium measurement. In ;the retort department, however, where
the cadmium concentration was measured at 1,105 ug/m3, arsenic measured 1.4 ug/m3,
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
. i,
77
-------
0.02% to 0.3% arsenic. The remaining ingredients were not identified. Tfie authors
concluded that the exposures from the remaining ingredients were insignificant.
A statistically significant excess of total malignant neoplasms (27 observed
vs. 17.6 expected, P < 0.05) was found, as well as a statistically significant
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 < O.OK). 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.
TABLE 12. PROSTATE CANCER DEATHS AMONG CADMIUM SMELTER WORKERS
WITH MORE THAN 2 YEARS EXPOSURE
(Lemen et al. 1976)
Case Age
1 71
2 77
3 79
4 64
Exposure
4
13
18
17
Latency
32
25
31
26
Date of death
2/26/72
3/19/68
12/10/60
4/03/51
Of the 12 malignant respiratory cancer cases, the cell types of eight were
known. Three were squamous cell carcinomas, one was an undifferentiated small
78
-------
cell carcinoma, three were anaplastic carcinomas, and one was an oat cell
carcinoma. Unfortunately, smoking histories were not available for members
of the cohort. Therefore, confounding of the results due to smoking could not
be assessed. Furthermore, Lemen et al. reported the presence in the smelter
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 identify all of
the constituents of the processed ores, since the percentages given do not add
up to 100%.
However, when consideration is given to the fact that the vital status of
6.8% of the study cohort remains unknown, it is apparent that additional causes
of death in this group of 20 people potentially might have added additional
prostate cancers to the observed deaths. In contrast, the expected deaths were
overestimated because person-years were counted to the cut-off date for these
same individuals. This could slightly bias downward the finding of an excess
risk of prostate cancer and bronchogenic cancer.
This study provides support to the supposition that exposure to cadmium
is associated with a significant excess risk of prostate 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, might be confounding factors that reduce the significance of the
association between bronchogenic cancer and cadmium exposure in the workers.
McMichael et al. (1976a. b)
McMichael et al. (1976a), as part of a historic prospective study of cancer
79
-------
mortality among rubber workers, followed 18,903 active and retired male workers,
aged 40 to 84, for a period of 10 yearsi They were divided into four separate
cohorts, each consisting of workers from the four tire manufacturing plants of
the companies under study.
The mortality experience during th<2 10-year observation period was deter-
mined from death claims filed with the companies under the group life insurance
policy in effect. In three of the four plants, workers were included if they
were employed on January 1, 1964, whereas in the fourth plant they were included
if they were employed on January 1, 1963. About 1% 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. This bias, known
as the "healthy worker effect," is a consequence of the selection 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 1% 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 that for
prostate cancer was 119 (103 observed, nonsignificant at 0.05 < P < 0.1). The
authors hypothesized an association of prostate cancer with the compounding and
mixing areas of the four plants, work areas that entail contact with metallic
oxides (including cadmium oxides). The authors also hypothesized an association
of prostate cancer with three additional wprk areas (cement mixing, janitoring,
and trucking) of one particular plant after "exploratory work-history" analyses
80
-------
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 a'l. (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 calenderings janitoring-trucking, compounding, 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
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.
The SMRs may thus be confounded by additional exposures to chemicals other
than 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
81
-------
presented in which latency is considered. This cohort should be followed for
several additional years before a final conclusion is made regarding carcinogenic
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.
TABLE 13. STANDARD MORTALITY RATIOS (SMRs) BY SITE
(McMichael et al. 1976a)
Site
Lymphatic leukemia
Stomach
All leukemias
Hodgkin's disease
Prostate
Colon
Pancreas
Bladder
Respiratory
Rectum
Brain, central
nervous system
All cancer
All causes
Observed
deaths
20
80
46
32
103
103
57
32
252
27
14
1014
5106
SMRs
158
148
130
129
119
116
103
92
85
82
78
100
94
Probability of
occurrence3
0.039
<0.001
0.073
0.150
0.077
0.131
0.826
0.638
0.002
0.303
0.352
1.000
<0.001
aTaken from Chiang (1961),
82
-------
.Monson 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
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. (1976a, b) and later by Goldsmith et al. (1980), does not support
the hypothesis suggested by McMichael et al. that cadmium in the plant was
responsible for the excess risk 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
cadmium-copper alloy factory workers having more than 5 years exposure since'the
factories began production* As an internal reference group, 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 mg/m3 prior to 1947, 200 ug/m3 between 1962 and 1974, 50 ug/m3
in 1974, and below 5 ug/m3 at the time of the study. At the other factory,
concentrations were in the range of 100 to 400 ug/m3 in the mid-1960s and 50
ug/m3 in 1971 and after. The battery study population was also exposed to
nickel hydroxide dust.
83
-------
National average age- and cause-specific death rates and cancer incidence
rates were used to generate expected deaths 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
Register. This was not done with the alloy factory workers. With respect to
mortality in the battery factory, 43 deaths occurred between 1949 and 1975, of
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 mortality. 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 Register. 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 thesq two studies are not significant with respect
f
to prostate cancer, and basically inconclusive because of the small study groups,
they do suggest a positive association of prostate cancer and exposure to cadmium.
84
-------
TABLE 14. EXPECTED AND OBSERVED NEW CASES OF CANCER BETWEEN 1959 AND 1975
IN THE WHOLE GROUP OF BATTERY FACTORY WORKERS (N = 228)
(Kjellstrom et al. 1979)
Site
Prostate
Lung
Ki dney
Bladder
Colon-rectum
Pancreas
Nasopharynx
Other
All sites
Cancer
Expected3
1.2
1.35
0.87
1.07
2.25
0.60
0.20
9,81
16.4
cases
Observed
2
2
0
1
5
0
2
3
15
Risk ratios
1.67
1.48
0
0.93
2.22
0
10. Ob , .
0.31
0.91
aExpected deaths based on Swedish National Cancer Registry,
bStatistically significantly greater than 1 (P < 0.05).
TABLE 15. CUMULATIVE EXPECTED AND OBSERVED NUMBER OF PROSTATIC CANCER
DEATHS FROM 1940 TO 1975 AMONG ALLOY FACTORY WORKERS
(Kjellstrom et al. 1979)
Prostatic cancer deaths
Exposed group
Reference group
Expected
2.69
6.42
Observed
4
4
Risk ratios
1.49
0.62
P value
0.29
0.23
(N = 328)
85
-------
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
the 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
86
-------
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 OT6, employees who may never have been exposed to any potential
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 in 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 investigatory
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 "assign-
ment 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 cadmium might also be initiated in the rubber industry.
This study does hot support the earlier McMichael hypothesis that the excess
risk of prostate cancer might 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.
Holden (1980)
Hoi den (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
87
-------
factory data were subdivided by the author into two parts for purposes of analysis.
One section of the building contained the cadmium-copper alloy department, where
347 men worked for a minimum of 12 months. Another 624 men worked for a minimum
of 12 months in the remaining part of the factory. The latter group was dubbed
"vicinity" workers by the author because they worked in the building but not in
the cadmium-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
department to be 70 ug/m3 (S.D. = 62 ug/m3), based on 12-hour sampling, while the
mean level in the other parts of the building (the "vicinity") was 6 ug/m3
(S.D. - 8 ug/m3). The author reports that vicinity workers were exposed to
considerably less cadmium than were the cadmium-copper alloy workers. 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 (observed
= 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 cancer in general
(observed = 72, SMR = 120) was apparent in vicinity workers, due chiefly to
significant excesses of cancer in two sites: the lung (observed = 3(5, SMR = 138,
88
-------
P < 0.05) and the prostate (observed = 8, SMR = 267, P < 0.01). The author
attributed the elevated risk of lung cancer in these 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 evolution of cadmium oxide fumes"
resulted when cadmium was dumped into the much hotter molten copper to form
cadmium-copper alloy. This effect resulted because cadmium boils at a much
lower temperature than that of copper.
.With respect to prostate cancer, the author noted the absence of a dose-
effect relationship since fi.ve of the eight prostate cancers occurred to indi-
viduals 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" means 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. 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 alloy cohort (observed = 1, SMR = 63), the numbers
involved are too small to warrant the author's finding of no excess risk. In
addition, if both the cadmium-copper subcohort and the vicinity workers are
re-evaluated only after more than 15 years of follow-up, the chances of detecting
a significant prostate cancer risk in the cadmium-copper workers is probably
89
-------
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 cadmium-copper alloy
workers, under the author's .definition, apparently experienced a lower risk of
prostate cancer than did "vicinity" workers may not be unexpecteds 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 because
of the presence of the "healthy worker" effect, in which less than expected
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
suggestive. The finding of an excess risk of lung cancer due to cadmium exposure
must also be considered only suggestive at this time because of the possible
confounding effects of smoking and of exposure to other metals such as arsenic,
and because of the lack 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 employed prior to and during the period
90
-------
from 1946 to June 30, 1980, 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 amalgamated in 1947. The earliest mention of
cadmium in the air breathed by these workers was reported in 1949. In the
platemaking assembly shops, the cadmium content in the air ranged from 0.6 to
2.8 mg/m3, 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/m3. 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/m3.
For the purposes of analysis, the author divided his cohort into 566 female
employees, 1,066 male employees who were first employed before the amalgamation
in 1947, and 1,494 males who were first employed after the amalgamation.
Standard mortality ratios (SMRs) were computed. Expected deaths were
generated on the assumption that the general population rates for England and
Wales were operant 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 forms of cancer, there was virtually no difference
between observed and expected deaths (observed = 152, SMR = 100). On the other
hand, a deficit of cancer deaths occurred to the subcohort of male employees
who had been employed prior to the amalgamation (observed = 80, SMR = 84).
But in males who were employed for the first time after the amalgamation, a
91
-------
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 significant
excess risk of prostate cancer occurred in either group (observed = 4, expected
= 4.1; observed = 3, expected = 1.9, respectively). Even after consideration
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 "nonexposed"
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 i-n those workers with more than
14 years of employment in cadmium smelter work. The author concluded, on the
92
-------
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.
Person-years of individuals still employed with the company were not enumerated,
and only if the individual left the employment of the company (through death or
other cause) were his person-years counted. This arrangement has the effect of
altering the expected deaths by the non-inclusion of person-years of individuals
who were at risk of death but who were still alive and workingan effect that
could conceivably bias the SMRs. If differential mortality is considerable in
the group still employed, as compared with the cohort, the extent of the bias
might be even greater.
The study also suffers from the "healthy worker" effect brought about by the
comparison of observed deaths with expected deaths based on the mortality rates
of England and Wales. The SMRs are biased toward the null for all causes where
the SMRs are greater than 100, while the deficit of deaths is increased in those
cases where the SMRs are less than 100. Additionally, some 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.
Furthermore, the tabular data presented classifies the cohort into two
categories of exposure: "exposed" and "non-exposed," although in the "Population"
section of the study, the author describes the jobs in the factories in terms of
"high," "slight," and "minimal" exposure to cadmium. A clearer description is
needed of how the thre^e latter categories were reconstituted as "exposed" and
"non-exposed" for the purposes of presenting the findings in tabular form. The
author's treatment of the subject suggests that some portion of the study popula-
93
-------
tion received little exposure to cadmium. 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 tabular findings. It might
have been more informative to present 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, and questionable evidence of
exposure in a large portion of the cohort, the study cannot be said to provide
conclusive evidence that cadmium is not carcinogenic.
Inskip and Beral (1982)
Inskip and Beral (1982) conducted a cohort motality study on residents of
two small English villages, Shipham and Hutton, situated within seven miles of
each other. Shipham is located in an area of substantial soil contamination by
cadmium from the remains of a zinc mine that had operated on the site for
nearly 400 years, until the middle of the nineteenth century. The village of
Hutton was selected as a control. Investigations accomplished by the British
Department of the Environment's Shipham Survey Committee revealed average
garden soil cadmium levels ranging from 2 to 360 ug/g in the area, while national
levels rarely exceeded 2 ug/g. Cadmium was believed to be absorbed in the diet
mainly through the consumption of home-grown vegetables. According to a survey
conducted by Thomas (1980), the dietary intake of cadmium in Shipham averaged
0.20 mg per week (range 0.04 to 1.08), while the national consumption averaged
0.14 mg per week (range 0.09 to 0.18).
94
-------
Some 501 residents of Shipham and 410 residents of Mutton were entered
into the cohort on September 29, 1939, and were followed until December 31,
1979, when SMRs were generated by cause of death. Data for both cohorts were
compared with population statistics for England and Wales. Excess risks of
mortality due to hypertensive and cerebrovascular disease and genitourinary
disease were found in the Shipham residents. Cerebrovascular disease (observed
= 65, SMR = 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 risk using the Poisson method gives a value of P <
0.03S for an SMR of 222 based on eight deaths, a statistically significant result
that appears not to be due to chance alone.
Only 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
elevated in both Shipham (observed = 4, SMR = 199) and Hutton (observed =3,
SMR = 181), based on small numbers.
The authors 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
association 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.
95
-------
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. Further-
more, only 70% could be assigned to exposure categories based on the locations 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 signifi-
cant 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 lung was not the target organ for cancer,
and that therefore a significant excess of lung cancer would not be expected in
this study. Hence, this paper should be judged inadequate with respect to the
detection of a risk of lung or prostate cancer.
Andersson et al. (1982)
Anderssen et al. (1982) updated the earlier Kjellstrom et al. (1979) study
by enlarging his cohort to 548 men and 101 women and requiring that cohort
members have had a minimum of one year of cadmium exposure between 1940 and
1980 at only one alkaline battery factory in Oskarshamn, Sweden. Exposure
levels were as described in the earlier Kjellstrom study, except that more
recent data indicated that cadmium levels in the air generally fell below
96
-------
20 ug/m3,. and that nickel levels were below 50 ug/n)3. Indeed, exposure to nickel
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 certifi-
cate data after age 79. The authors noted 103 deaths versus 122.6 expected, a
deficit that was more than likely due to the "healthy worker" effect, and was
confined mainly to cardiovascular disease (46 observed, 57.3 expected). If the
analysis is limited to workers with a minimum exposure of 15 years, again a
deficit occurs (50 observed, 58.4 expected). However, a significant increase
in mortality due to nephritis and nephrosis was noted (3 observed, 0.41 expected,
P < 0.05). A nonsignificant increase in the risk of prostate cancer was evident
(3 observed, 2.5 expected).
The authors concluded that a causal relationship probably exists between
earlier heavy cadmium exposure and the risk of renal disease, as well as a possible
causal relationship with obstructive lung disease. The authors felt that one
case of nasopharyngeal cancer was possibily due to exposure to nickel hydroxide,
which is believed to cause nasal .sinus cancer in man.
With regard to prostate cancer, the authors felt that their data suggested
an increased riska 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
97
-------
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 must be judged inadequate for use in evaluating
the risks of prostate cancer or lung cancer due to cadmium. ;
K.iellstrom (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
deaths versus 2.5 expected. This SMR is considered to be nonsignificant. Only
4 prostate cancer deaths occurred, versus 3.1 expected. The workers in this
study cohort had a minimum of one year's exposure to cadmium. 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 l,000r-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
98
-------
fjg Cd/m3 air
10,000
1000
100
10
1946 1956 1966 1976 Year
Figure .1. Concentration of cadmium in the air (ug Cd/m3) from 1949 to 1976
Antnmetic mean of stationary and personal samples
(Kjellstrom 1982)
99
-------
less than 2 years' duration. Almost 50% of the cohort (301 workers) received
their first exposures to cadmium .after 1959, which means that a large proportion
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 develop-
ment stages as an extension of the study for future follow-ups. Additionally,
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
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 detection
of statistically significant differences.
Kjellstrom repeated the 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
100
-------
slightly increased nonsignificant risk of prostate' canter'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 cancer
mortality excess occurred in individuals 85 and over. No significant tests
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 Shigematsu 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
cadmium-exposed area and compared to those calculated in a nonexposed reference
area of the same prefecture. It was found that can'cer mortality rates were
101
-------
generally about the same in the nonpol"luted 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 thfe "highest likely cadmium exposure to the
population." The former two prefectures tended to have higher rates of mortality
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 pro-
teinuria (LMWP) increased with an increase in the village-specific average
cadmium concentration in rice. LMWP was measured by urinary retino! binding
protein. It is very likely that this ecological study included persons who
had never been exposed to cadmium in rice, as well as persons with prior-existing
conditions, possibly introduced long before they were exposed to relatively
high concentrations of cadmium in rice. The positive association noted by 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 nonsignificant (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 with LMWP and 30 deaths of females with LMWP. A positive association of
102
-------
LMWP with heart disease, cerebrovascular disease, nephritis, and nephrosis was
noted. This association raises the specter of a possible confounding effect
of hypertension with LMWP. If hypertension is a cause of LMWP, the higher
mortality of the individuals that had LMWP may have been due to hypertension
and not, as the author suggested, to cadmium exposure. The correlation with
LMWP may thus be spurious, and hence, conclusions drawn from this study regarding
an association of higher mortality with cadmium exposure must be characterized
as certainly no more than suggestive.
Armstrong and Kazantzis (1983, 1982)
Armstrong and Kazantzis (1983) recently completed a cohort mortality study
of 6,995 male cadmium workers born before 1940, who had had at least one year of
employment during 1942-1970 in one of five British industries (primary production
64%; copper-cadmium alloy 8%; silver-cadmium alloy 14%; pigments and oxides 8%;
and stabilizers 6%). The authors classified their cohort (derived from 17
major plants) into the 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 "approximately 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.
. . 103
-------
Jobs were classified in the categories of high, medium, or low exposure
to cadmium on the basis of discussions with hygienists and others with
knowledge of past working procedures, taking into account biological or
environmental monitoring results available. '
Approximately 96% of this cohort 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 followup was
79 (based on 205 observed deaths) and for later years 99 (based on 1,697 deaths),
a phenomenon due 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, P <
t i
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 non-
significant in all three exposure categories, without regard for latent factors.
Because of the small numbers involved, however, the study could not detect a
f * '"
prostate cancer risk in the "ever high" exposure category. Although the authors
stated that this cohort had been analyzed according to years since time of
initial exposure, only the overall SMR was presented for those with 10 years or
more of follow-up in the published version. No detailed tabular data were
provided with respect to lung cancer or prostate cancer by time since onset of
initial employment in the published results.
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
104 :
-------
risk of prostate cancer from exposure to cadmium in this group. They further
noted that no cases of prostate cancer turned up in the "ever medium" group,
whereas 2.5 were expected. Prostate cancer was near to expected levels in the
"always low" exposure group (23 observed, 2CL4 expected) into which the large
majority of the cohort,fell. Hpwever, 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 inclusion of
person-years for individuals who essentially were not exposed to cadmium. This
is especially true if there is a dose-response relationship operating in the
cohort. Unless reliable criteria are established to quantify individual exposures
to cadmium dust and compounds of cadmium, in addition to other confounding
substances that may be present, it cannot be presumed that every member of this
cohort was exposed to cadmium in high enough quantities to produce a detectable
health risk. Furthermore, although some recent monitoring data may exist with
which to quantify exposures, it is questionable that sufficient industrial
exposure measurement data exist from the 1940s or 1950s and earlier to provide
more than a guess at the levels of exposure to cadmium and other metals that
existed when these persons were fir^t employed. It may be that the historical
prospective study design is not a sensitive enough analytical tool to be used
in assessing cancer risks in a cohort of workers who, in general, were exposed
105 ,
-------
to only "low" levels of cadmium. On the basis of the above factors, this study
is seen to provide no evidence that cadmium is a powerful prostate cancer
carcinogen.
On the other hand, although the risk of lung cancer overall was not
significant (observed = 199, 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 < 0.05). The authors, in an earlier draft of this paper
(Armstrong and Kazantzis 198.2), presented data concerning the lung cancer risk
in workers having a minimum of 10 years' employment in the categories 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) after 10 years' employment; however, little power remains with
which to detect an elevated risk in that group. 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 more years of employment in the industry. It would
have been valuable, however, to include a discussion of the lung cancer risk by
longer time 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.
The increased risk of lung cancer in the "always low" exposure category
cannot be ascribed necessarily to cadmium 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
makes it unlikely that the excess is due to cadmium. A full tabulation of SMRs
in the three exposure intensity categories by time since onset of exposure
106
-------
(10, 15, and 20 years) and similar duration of employment intervals might
provide 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, the authors point out that the size
of the excess is much too great to be solely attributable to such 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 the risk of prostate cancer, lung cancer, and
hypertensive 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
provides 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
from initial exposure, the historic prospective method may no longer be sensitive
enough to detect a prostate cancer risk, if in fact one exists. 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 necessarily due to exposure
to cadmium. Comparable data 1n the "ever medium" exposure group indicates a
nonsignificant risk of lung cancer, but latency is not evaluated in sufficient
detail. The data from the "ever high" group lack sufficient 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
«5 would alter the calculated risks. It might also be of some value to repeat
107
-------
the analysis on a pi ant-by-pi ant basis to determine which plants exhibit 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 irisk 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 a recently published 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 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 significantly
(observed = 8, expected = 6.6) in this phase of the study. These data, however,
may 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 prepared
analyses with and without the four original cases included. The authors believed
that only new cases of prostate cancer should be used to determine an RMLT-
derived asymptotically normally distributed test-statistic measuring the signifi-
cance of cancer of the prostate in their cohort. The potential confounders of
sex, hiring date, age at hire, length of employment, and employment status were
regressed against the test-statistic in order to eliminate the influence of
108
-------
these factors. Employment status was defined to be cumulative duration of
employment in a "high" exposure job versus cumulative duration of employment in
a "high or moderate" exposure job. Job categories were classified by exposure
to cadmium as "high exposure," "moderate (or slight) exposure," and "minimal
exposure." Only 8 jobs were considered to involve "high" exposure, while 14
were considered to involve "moderate (or Slight)" exposure, and 53 were considered
to involve "minimal exposure." With the four original cases"included, the test-
statistic (3.10, P < 0.05) remained statistically significant in the "highly"
exposed group but remained nonsignificant (-0.32) when the original four cases
were excluded. Even when reduction in exposure levels over calendar year periods
was programmed into the analysis (assumed exposure levels from 1968 to 1972
were 40% 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 statistically
significant positive statistic to a small nonsignificant negative statistic."
They concluded that "no new evidence has been produced which suggests an
association between occupational exposure to cadmium and cancer of the prostate."
Actually this conclusion may be unwarranted. One must wonder about the propriety
of excluding persons who carry the disease in question from the study cohort
if they fit the definition for inclusion. 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 accom-
plished 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 1s significant at 2.51 (P < 0.05). The authors suggested that
109
-------
exposures to the welding fumes .of oxyacetylene found in jobs of "moderately
exposed" workers might have accounted for this excess, which was chiefly confined
to workers who began employment prior to 1940 (3.09, P < 0.05), to those who
worked a minimum of 6 months (2.49, ;P < 0.05) and to those observed for 30
years or longer (3.18, P < 0.05). Minimally exposed workers who wore also
followed for 30 years or longer exhibited a significant test-statistic (2.36, P
< 0.05). In no instance, did age, sex, year of starting employment, or years
of follow-up produce a significant test-statistic for lung cancer In the group
with the highest potential exposure to cadmium.
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 potential
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 the 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 respiratory
cancer, then similar associations should be expected for diseases of the circula-
tory system, and such associations were not found. The authors stated that the
110
-------
analysis could not differentiate between exposure to cadmium oxide dust and
exposure to nickel hydroxide because almost every job with high cadmium exposure
alSb had high nickel exposure.
In conclusion, Sorahan and Water-house (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 respiratory
cancer among workers moderately or highly exposed to cadmium oxide dust and
initially employed before 1940--a finding which was confounded by exposures to
oxyacetylene welding fumes and to nickel hydroxide dust.
Varner (1983. unpublished)
ASARCO Inc., the owners of the cadmium smelter that had been studied by
Lemen et al. (1976), updated that study with one of their own (Varner 1983,
unpublished) in which all employees were included who had had at least six
months' employment at the smelter between January 1, 1940 and December 31, 1969.
The size of the cohort was enlarged to 644. This very preliminary report was
accompanied by a letter to David Bayliss of the CA6 from Lowell White of ASARCO,
January 11, 1984, in which White indicated that the follow-up for this study
would extend to the end of 1981. According to the letter, the National Institute
for Occupational Safety and Health (NIOSH) staff scientists, in a cooperative
arranqeinont, agreed to provide follow-up services on all members of this cohort,
and.to .provide copies of death certificates to ASARCO in exchange for available
work history and biological monitoring data.
As 1n the Lemen et al. (1976) study, Varner (1983) used a methodological
technique called the Standardized Case Ratio (SCR), which is analogous to the
calculation of SMRs, with the exception that expected deaths for particular
causes of death are derived by dividing age- and cause-specific attributable
111
-------
deaths by total deaths in the age and year category corresponding to each
particular decendent's age and year of death. The resulting proportions are
summed to arrive at the number of expected deaths. These methods are still
under peer review, according to White (letter to David Bayliss, CAG, January 11,
1984) and cannot yet be considered reliable.
The preliminary findings of Varner (1983) differed from the Lenten 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 to
several factors: increased cumulative exposure to cadmium, years of exposure,
age at death, latent period, and/or cigarette smoking.
The author maintains that a "substantially higher than normal prevalence
of heavy cigarette smoking" 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 = < 0.05); specific bladder cancers (observed = 5, SCR = 374, P < 0.01);
total cancer (observed = 53, SCR = 126, P < 0.05); nonmalignant respiratory
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 < 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).
*SCR (Standardized Case Ratio) is analogous to the Standard Mortality Ratio,
differing in that expected deaths for a specific cause were derived by dividing
age- and cause-specific attributable deaths by total deaths in the age and year
of death category of each decedent. The resulting proportions are summed to
obtain expected deaths. These methods are under peer review, according to
White (January 11, 1984).
112
-------
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 time 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
5-15
16+
7
6
10.
95
159
, 332 (P
< 0.01). -
23
14
16
108
123
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 (P < 0.01)
No such effects were seen for bladder cancer.
With respect to lung cancer, the author reports that 77.5% of the cadmium
workers had been smokers, and that 53.2% had smoked, the .equivalent' of one pack a
day for 20 years. In a 1970 Household Interview, Survey by the National Center
for Health Statistics,. i t. was reported that 69.2% of blue collar workers had
smoked a pack or more of cigarettes a day at some time in their lives. .Thus,
so mo evidence exists for a confounding effect due to cigarette smoking, since
113
-------
the proportion of smokers in the Varner (1983) cohort was 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 derivation of SCRs.
The MIOSH update of the Lemen et al. (1976) study, which is reviewed later in
this section, also contains 60 fewer individuals, who were allegedly excluded
by NIOSH for "various reasons" upon which Varner does not elaborate. Varner
included all individuals "regardless of exposure."
Another problem with the study is that the death certificates were received
only 2 weeks prior to the presentation of the paper at the 4th International
Cadmium 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 the state's cause-of-death codes are described as
differing. White referred to the presence of what he termed "nosology bias" in
the ascertainment of underlying causes of death. He states that some 93 death
certificates 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 coworkers at NIOSH (Thun et al. 1984) have attempted
to account for the contribution of arsenic exposure and cigarette smoking in
their study, which is reviewed below. Additionally, White reported that the
follow-up through 1981 was Incomplete, although the percentage remaining with
114
-------
an unknown vital status was not given. He reported that ASARCO, Inc. recently
contracted with the Social Security Administration to provide vital status
irtformation, and that it is hoped that the "final procurement" of death
certificates for the study can begin soon (presumably after the date of his
letter of January 11, 1984). The cohort has been expanded, and a number of newly
found personnel records have been included for evaluation in the final report.
Because of the very preliminary nature of the Varner (1983) study in its
present form, the results will not be prejudged here. Although the author
found a dose-related significant excess risk of lung cancer, as he explains,
this may be due in part to the confounding effects of smoking and/or arsenic
exposure. Additionally, although the risk of prostate cancer is elevated, it
is no longer statistically significant. Whether the final version of the study
will sustain such a finding is not presently clear, in view of the many problems
that must be solved. It does not appear at this time that the final version of
the study will be forthcoming in the very near future.
Hence, the Varner study cannot, at present, be used either to substantiate
an excess risk of lung cancer due to cadmium exposure or to refute the earlier
findings of significant prostate cancer in the Lemen et al. study.
Thun et al. (1984, unpublished)
In a separate enlargement and update of the Lemen et al. (1976) study,
Thun et al. (19R4, unpublished) broadened the cohort to Include white males Who
worked a minimum of 6 months 1n production work during the period 1940-1969.,
The resulting 612 members were followed an additional 5 years to the end of 1978.
The difference between the size of the Varner (1983) cohort of 644-612 = 32 and
the Thun et al. (1984) cohort is not completely explained, but may consist of
non-production employees such as guards, office workers, and office area janitors.
Cause-specific mortality rates for seven causes of death were compared between
115
-------
the cohort and U.S. white males. Death certificates were coded by a qualified
nosologist according to the protocol of the version of the International Classifi-
cation 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 lung
cancel* (observed = 20, SMR = 265, P < 0.05) was significantly in excess in
workers employed for 2 or more years before and after the cessation of arsenic
smelting in 1925. Prostate cancer was no longer excessive in these workers.
From Table 16, it can be seen that air exposure measurements chronologically
decreased with the introduction of a mandatory respiratory program introduced
in the 1940s. The estimates in Table 16 are based on area monitoring data,
adjusted to reflect actual exposures during the wearing of respirators. The source
of the datathe plant's personnel recordsprovided 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 had been an arsenic smelter from 1918 to 1925, and a
lead smelter from 1886 to 1918. Urine cadmium data, which were available for
261 members of the cohort employed beyond 1960, suggested a highly exposed
population. Since arsenic 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 0.5(5 oxpected, while 1n those employed 2 years or longer after January
1, 19?6, 16 observed lung cancer deaths were observed versus 6.99 expected, P
< 0.05. Directly standardized rate ratios (SRRs) for these data exhibit a
constant twofold Increase in lung cancer mortality with longer duration of
employment (Table 17). The authors state that a similar pattern results when
the indirectly standardized mortality ratios are stratified for latency.
116
-------
Q
O
14
(*V*
UJ
CL.
UJ
!§ i
t : i
0 !
- 03
CO !
o .
-CO
TV" CM 1
E t"H " i
**^-
IV ' !
> ' CO
C/") 4 >
uj cu |
Q£ I
CO 4~> !
O T- ,
Q- E
X CO
UJ
o |
h i
t
«£
.-J
^«
_n
"ZZ.
t t
U-
o
CO
UJ
I
*^.
SI
1 1
l__
CO
UJ
D
to
r-H
UJ
1
'££>
1
"O
C
o3 O
CU 03
0 1
I
4
4-
O
4-3
c:
QJ
l^i
cC
c_
o
cu
oi
>.
t
-a
o
u_
f^
cu
3
O
j^jj
c:
03
I
C
O
1
4-3
=5
O
cu
c
i
o
"re
o
en
c:
x ,
jg^
f
cu
4-3
(/I
03
O
C£
CO
r-
O-
O3
-a
cu o
E *r~
i C-
1 CU
Q-
CM
0
O
CM
O
LO
I 1
00
o
<=f
0
o
CO
a
LO
r-H
LO
^
O
,_(
o
r-<
0
LO
en
f i
i
cu
£_
CL.
t-H
O
O
CM
O
CM
O
r-i
O
«_,.
o
o
00
o
LO
t-H
*3-
o
to
o
to
0
LO
01
i-H
1
o
LO
en
i i
< i
o
0
0
0
CM
0
<l
o
^J.
0
0
^
CO
LO
r- 1
«5f
0
to
o
to
o
en
LO
en
r 1
, i
LO
LO
en
.i
^
o
o
o
o
o
CM
O
r-1
0
CM
O
O
._,.
a
0
**
o
**
0
to
CD
to
0
to
en
t i
i
o
to
en
.-t
^
o
o
o
o
o
CM
O
*^-
O
0
CM
O
O
0
C3
LO
r- 1
0
*
o
to
o
to
0
VO
1
en
t H
|
LO
to
en
r 1
1 -o
cu
LTi
3
'<>
-a
03
03
' 03
CT)
C
r-
£_
O
1
o
^
. 03
^
03
C
0
"O
cu
t/)
03
CU
4_
CU
3
T3
03
«
CO 01
4-) C
C 0
£ fl3
4-3 £-
£- !
03 Q.
Q. CO
CU CU
T3 S-
in CD
- 3 C
' O !-
1- t-
£- 03
03 CU
> £
C CO
i C-
cu
"O *^
CU £-
£_ 0
£- 3
3
O '[
0 0
o
to cu
QJ C_
t- 3
3 CO
CO O
0 CL
X QJ
CU
C 03
O 3
r 4-3
4-3 O
03 03
03 CU
C 4-3
i
| N
T3 O
CU CU
4-3 r
03 4-
E 0)
r- t_
4-3
CO O
UJ 4-3
03
4-3
O
C
CU
c.
3
1 1
03
4->
't?
Q.
Q
CO
t_
03
Q-
0)
£_
^
CD
CU
CO
4J
S
4->
03
D-
CU
a
4-3
c
03
a.
c
o
f
ti
3
O
£_
a.
i
0
c:
c_
o
4-
CU
3
o
to
1
(O
cu
c_
cu
s
CO
t/1
CU
cu
o
"4-
4-
O
O
117
-------
TABLE 17. LUNG CANCER (ICD 162-163) MORTALITY BY DURATION OF EMPLOYMENT,
WHITE MALES HIRED ON OR AFTER 1/1/26
(Thun e;t al. 1984)
Duration of employment
6-23 months
2-9 years
10-19 years
20+ years
U.S. white males
No. of
deaths
0
9
3
4
-
Mortality
rate3
0
15.73
14.28
16.28
7.27
SRRb
-
2.2
2.0
2.2
1
aRate x 10,000 person-years was directly standardized for age and calendar time
to the person-years distribution of the overall cadmium cohort.
bStandardized rate ratio (SRR) is the directly standardized mortality rate of
subgroup/summary rate for U.S. white males.
With respect to arsenic exposure, even after 1925, the author states that
a small and unspecified number of workers processed arsenic intermittently in,
one area of the plant. 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
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
Health Administration (OSHA), in 1979, indicate a decrease in arsenic concentra-
tion to 100 ug/m3 in this area. However, the author points out that although
air levels of arsenic in this specified area were 10 times the OSHA threshold
of 10 ug/m3, the personal exposures of individuals in this area were lower
because of respirator usagea practice that had been in effect since 1940. In
118
-------
fact, on the basis of a "most-likely-case" scenario, the authors estimate that
the average arsenic exposure of persons in this study would have been 25 ug/m3
Under the following conditions:
(1) the average airborne arsenic exposure was 500 ug/m3 in the
high-arsenic work areas;
(2) there was a respiratory protection factor of 75%; and
(3) 20% of the person-years of exposure were spent in such areas
(based on personnel and biological monitoring data).
Hence, according to the authors, if the 586 workers hired after 1926 were
employed an average of 3 years, they would have acquired 1,758 person-years of
exposure to 25 ug/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 ug/m3 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. High-exposure jobs
in the roaster area were frequently staffed by entry-level workers with less
than 6 months' employment, who would for that reason never qualify for inclusion
in the study, although the authors included them in their estimate that 20% of
the person-years of exposure were in "high-arsenic" jobs. Furthermore, the
authors point out that urinary arsenic levels from 1960 to 1980 averaged 46
ug/L, which is consistent with an inhaled arsenic concentration of 14 ug/m3.
If one assumes an average inhaled concentration of 125 ug/m3 (25% of 500
ug/m3) over 3 years, 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.
119
-------
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+
cigarettes/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 that cigarette
smoking is unlikely to account for the twofold increase in lung cancer
deaths observed among workers in this cohort with 2 or more years or employment.
The authors also note the lack of a clear dose-response relationship-'-a
situation which they suggest could be an artifact of using length of employment
as a surrogate for dose. They point out that, in plants such as the one studied,
one of the privileges of seniority is that long-term workers can bid into more
desirable, less exposed jobs, and that for this reason, the use of data on
duration of employment can lead to overestimation of exposure in long-term
workers.
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 lung cancer observed in this cohort.
This possibility is all the more distinct because the risk of lung cancer in the
study was not seen to be overwhelming. A subtle combination of factors such as
the ones mentioned above could conceivably have served to produce the excess
risks found, even though such an eventuality is unlikely. Thus, although this
study cannot be said to be conclusive with respect to risks of lung cancer from
exposure to cadmium, it constitutes the most clear-cut evidence yet leading to
this conclusion.
120
-------
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. 1976,
Holden 1980, 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; Kjellstrom et al. 1979; McMichael et al.
1976a, b; Anderssen et al. 1982; Kjellstrom 1982; Varner 1983, unpublished; and
Thun et al. 1984, unpublished) provide the suggestion of an increased risk of
prostate 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 (1967), Sorahan (1981), and
Sorahan and Waterhouse (1983) cannot be considered independently of one another.
The workers in the McMichael et al. (1976a, b) studies were subsequently shown not
to have had 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, the significant excess risk of prostate cancer in the Lemen et
al.-(197.fi) study dropped to a nonsignificant excess risk in both of the updated
versions of that study (Varner 1983 and Thun et al. 1984). Kjellstrom's "corrected
healthy worker effect" risk ratio of 2.4 is nonsignificant because of the small
numbers involved, although it approaches borderline significance at P < 0.09,
offering the suggestion of a possible association of prostate cancer with
cadmium exposure.
Two other studies (Humperdinck 1968 and Holden 1969) did not report evidence
of an association of prostate cancer with cadmium exposure, chiefly because the
comparison population was either inadequate for the assessment of risk (Humperdinck)
or absent entirely (Holden).
121
-------
An update by Kjellstrom (1982) of his earlier 1979 study again failed to
demonstrate a significant risk of cancer of the prostate due to cadmium. One
of the failings of this study was that members of the cohort were not observed
long enough to permit the evaluation of latent effects. More than half of the
cohort had received no exposure to cadmium prior to 1959, and thus could not
have been followed even for 20 years.
The study by Armstrong and Kazantzis (1983) of 6,994 workers also failed
to demonstrate an increased risk of prostate cancer due to cadmium. This study
combined cohorts from 15 different plants, each with its own unique exposure
history, and none of which were necessarily comparable. Exposures to cadmium in
most of these plants may have been below the level at which the study design
could detect a risk.
Kolonel (1976) found a statistically significant elevated risk of renal
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 findings.
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 CAS to
be insufficient to conclude that cadmium is a prostate carcinogen.
On the other hand, recent evidence from the same studies seems to provide
better evidence of a lung cancer risk from exposure to cadmium. Strong evidence
is available from the Thun et al. (1984) study that the significant twofold excess
risk of lung cancer seen in cadmium smelter workers is probably not due to the
presence of arsenic in the plant or to increased smoking by such workers. Thun
et al. analyzed both factors as potential confounders and convincingly dismissed
122
-------
both in this updated and enlarged version of the earlier Lemen et al. (1976)
study, which also demonstrated a significantly elevated risk of lung cancer.
Varner (1983) also found a statistically significant excess of lung cancer
in his updated enlarged version of the earlier Lemen et al. study. But unlike
fhun et al., Varner noted a dose-response relationship for both lung cancer and
total malignant neoplasms with increasing cumulative exposure. Varner indicated
that the significant excess is probably due to the smoking factor 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 clearly
statistically significant risk of lung cancer in their study population.
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/prospective
cohort study of workers who began employment before and after the amalgamation
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'
employment, and such a significant risk was not shown. Furthermore, only a
123
-------
suggestion of an excessive risk was evident in the "ever mediumly" iaxposed
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 populations were combined to form one cohort study, thus raising the
possibility that very little exposure occurred to most members of the cohort.
Hoi den (1980) reported a significantly excessive 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
movement of workers from jobs with high exposure to jobs with low exposure,
possibly because of seniority.
Anderssen et al. (1982), in their update of the Kjellstrom et al. (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 human epidemiologic evidence is suggestive of a
significant risk of lung cancer from exposure to cadmium and/or cadmium oxide,
although the human evidence is not compelling with respect to finding cadmium
124
-------
to be a strong lung carcinogen. At best, the epidem.iologic evidence of the
carcinogenicity, of cadmium must be described as limited, according to the
criteria of the IARC.
125
-------
QUANTITATIVE ESTIMATION
INTRODUCTION ...... _-..-.
This quantitative section deals with the unit risk for cadmium in airand
the potency of cadmium relative to other carcinogens that the Carcinogen Assess-
ment Group (CAG) has evaluated. The unit risk estimate for an air pollutant is
defined as the lifetime cancer risk occurring in a hypothetical population in
which all individuals are exposed continuously from birth throughout their life-
times to a concentration of 1 ug/m3 of the agent in the air that they breathe.
These calculations are done to estimate in 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 several agents 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 used for quantitative estimation are taken from one or both of
the following: 1) lifetime animal studies, and 2) human 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 an incidence determined by the extrapolation model.
There is no solid scientific basis for any mathematical extrapolation
model that relates carcinogen exposure to cancer risks at the extremely low
concentrations that must be dealt with in evaluating environmental hazards.
For practical reasons, such low levels of risk cannot be measured directly either
by animal experiments or by epidemiologic studies. We must, therefore, depend
on our current understanding of the mechanisms of carcinogenesis for guidance
as to which risk model to use. At the present time the dominant view of the
126
-------
carcinogenic process involves the concept that most cancer-causing 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
charaeteristic of mutagenesis, is associated with a linear nonthreshold dose-
response relationship. Indeed, there is substantial evidence from mutagenicity
studies with both ionizing radiation and a wide variety of chemicals that 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 enough information to make the evaluation
possible (e.g., radiation-induced leukemia, breast and thyroid cancer, skin
cancer induced by arsenic in.drinking water, liver cancer induced by aflatoxins
in the diet). Some supporting 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 exposure.
The risk estimates made with this model should be regarded as conservative,
representing the most plausible upper limit for the risk, i.e., the true risk
is not likely to be higher than the estimate, but it could be lower.
127
-------
For several reasons, the unit risk estimate based on animal bioassays is
only an approximate indication of the absolute risk in populations exposed to
known carcinogen concentrations. First, there are important species differenced
in uptake, metabolism, and organ distribution of carcinogens, as well as species
differences in target site susceptibility, immunological responses, hormone
function, dietary factors, and disease. Second, the concept of equivalent
doses for humans compared to animals on a mg/surface area basis is virtually
without experimental verification regarding carcinogenic response. Finally,
human populations are variable with respect to genetic constitution and diet,
living environment, activity patterns, and other cultural factors.
The unit risk estimate can give a rough indication of the relative potency
of a given agent as compared with other carcinogens. Comparative potency estimates
for different agents are more reliable when the comparisons are based on studies
in the same test species, strain, and sex, and by the same route of exposure,
preferably inhalation.
The quantitative aspect of carcinogen risk assessment is included here
because it may be 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 recognized that the estimation of cancer
risks to humans at low levels of exposure is uncertain. At best, the linear
extrapolation model used here provides a rough but plausible estimate of the
upper limit of risk. The risk estimates presented in subsequent sections
should not be regarded as accurate representations of the true cancer risks
even when the exposures are accurately defined. However, the estimates presented
may be factored into regulatory decisions to the extent that the concept of
upper risk limits is found to be useful.
128
-------
The mathematical formulation chosen to describe the linear nonthreshold
dose-response relationship at low doses is the linearized multistage model.
This model 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 the 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 B),
three more models, the probit, the Weibull, and the one-hit, are employed for
purposes of comparison. These models cover almost the entire spectrum of risk
estimates that could be generated from the existing mathematical 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 the 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 the carcinogenic
process for the agent is.
129
-------
Although the multistage model appears to be the most reasonable or at
least the most general model to use, the point estimates generated from this
model are of limited value because of uncertainty as to the shape of the
dose-response curve beyond the experimental exposure levels. Furthermore, the
point estimates at low doses extrapolated beyond the experimental dose could be
extremely unstable and could differ drastically, depending on the size of the
lowest experimental dose. Since the upper-bound estimates at low doses from
i
the multistage model are relatively more stable than the point estimates, the
CAG suggests that the upper-bound 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 linear at low doses. The
upper-bound estimate means that the risks are not likely to be higher but could
be lower if the compound has 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 human carcinogen. Therefore, in reality, the actual risk could range
from a value near zero to an upper-bound estimate.
PROCEDURES FOR DETERMINING CARCINOGENIC POTENCY I
Description of the Low-Dose Animal Extrapolation Model
Let P(d) represent the lifetime risk (probability) of cancer at dose d.
The multistage model has the form
P(d) = 1 - exp C-(q0
qRdk)]
where
q-j >_ 0, i =0, 1, 2, ..., k
130
-------
Equivalently,
Pt(d) = 1 - exp [-(qxd + q2d2 + ... + qkdk)]
where
P (d) = P(d) - P(0)
t 1 - P(0)
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
P-t(d) are calculated by using the computer program GLOBAL79, develped 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 qi > 0, at low
doses the extra risk P^(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 Lg be the
maximum value of the log-likelihood function. The upper limit, q*, is calcula-
ted by increasing q to a value of q* such that when the log-likelihood is
remaximized subject to this fixed value q* for the linear coefficient, the
resulting maximum value of the log-likelihood LI satisfies the equation
2 (L0 - LI) = 2.70554
where 2.70554 is the cumulative 90% point of the chi -square distribution with
one degree of freedom, which corresponds to a 95% uppers-limit (one-sided).
This approach of computing the upper confidence limit for the extra risk P
131
-------
is an improvement on the Crump et al . (1977) model. The upper confidence limit
for the extra risk calculated at low doses is always linear. This is conceptually
consistent with the linear nonthreshold concept discussed earlier. The slope, q*s
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 P.) In fitting the dose-response model, the number of terms in
the polynomial is chosen equal to (h-1), where h is the number of dose groups
in the experiment, including the control group.
Whenever the multistage model does not fit the data sufficiently well,
data at the highest dose is deleted, and the model is refit to the rest of the
data. This is continued until an acceptable fit to the data is obtained. To
determine whether or not a fit is acceptable, the chi-square statistic
.
NT Pi (1-P-j)
i=l
is calculated where Ni is the number of animals in the ith dose group, Xi is
the number of animals in the ith dose group with a tumor response., P1 is the
probability of a response in the ith dose group estimated by fitting the multi-
stage model to the data, and h is the number of remaining groups. The fit is
determined to be unacceptable whenever X2 is larger that the cumulative 99%
point of the chi-square distribution with f degrees of freedom, where f equals
the number of dose groups minus the number of non-zero multistage coefficients.
Selection of Data--
For some chemicals, a number of studies in different animal species, strains,
and sexes, each run at varying 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
132
-------
model. It may also be necessary to correct for metabolism differences between
species and absorption factors via different routes of administration. The
following procedures are used by the CAG in evaluating these data; they are
consistent with the approach of making a maximum-likely risk estimate.
1. The 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 controls
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, q*, is selected in
most cases. However, efforts are made 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 relationship, and one has a
very small sample size, the data set having the larger sample size is selected I
for calculating the carcinogenic potency.
2. If there are two or more data sets of comparable size that are identical
with respect to species, strain, sex, and tumor sites, the geometric mean of q*,
estimated from each of these data sets, is used for risk assessment. The
geometric mean of numbers AI, A£, ..., Am is defined as
x A2 x ... x
3. If two or more significant tumor sites are observed in the same study,
and if the data are available, the number of animals with at least one of the
specific tumor sites under consideration is used as incidence data in the model*
Calculation of Human Equivalent Dosages from Animal Data
Following the suggestion of Mantel and Schneiderman (1975), it is assumed
133
-------
that mg/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 weight, as would be the case for a perfect sphere, the exposure in mg/day
per two-thirds power of the weight is also considered to be equivalent exposure.
In an animal experiment this equivalent dose is computed in the following manner:
Let
Le = duration of experiment
le » duration of exposure
m = average dose per day in mg during administration of the agent
(i .e., during le), and
W = average weight of the experimental animal
Then, the lifetime average exposure is
d =
x m
L x W2/3
e
InhalationWhen exposure is via inhalation, the calculation of dose can
be considered for two cases where 1) the carcinogenic agent is either a completely
water-soluble gas or an aerosol and is absorbed proportionally to the amount of
air breathed in, and 2) where the carcinogen is a poorly water-soluble gas
which reaches an equilibrium between the air breathed and the body compartments.
After equilibrium is reached, the rate of absorption of these agents is expected
to be proportional to the metabolic rate, which in turn is proportional to the
rate of oxygen consumption, which in turn is a function of surface area.
Case 1Agents that are in the form of particulate matter or virtually
completely absorbed gases, such as sulfur dioxide, can reasonably be expected
to be absorbed proportionally to the breathing rate. In this case the exposure
in mg/day maybe expressed as
m = I x v x r
134
-------
where I = inhalation rate per day in m3, v = mg/m3 of the agent in air, and r
= the absorption fraction.
The inhalation rates, I, for various species can be calculated from the
observations of the Federation of American Societies for Experimental Biology
(1974) that 25-g mice breathe 34.5 liters/day and 113-g rats breathe 105 liters/
day. For mice and rats of other weights, W (in kilograms), the surface area
proportionality can be used to find breathing rates in m3/day as follows:
For mice, I = 0.0345 (W/0.025)2/3 m3/day
For rats, I = 0.105 (W/0.113)2/3 m3/day
For humans, the value of 20 m3/day is adopted as a standard breathing rate.
The equivalent exposure in mg/W2/3 for 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 intake per kg per day, i = I/W, based upon the previously stated
relationships, are tabulated as follows:
Species W i = I/W
Man
Rats
Mice
70
0.35
0.03
0.29
0.64
1.3
Therefore, for particulates or completely absorbed gases, the equivalent exposure
in mg/W2/3 -js
d - * = Ivr = jWyr = iwl/3vr
W2/3 W2/3 W2/3
In the absence of experimental information or a sound theoretical argument to
the contrary, the fraction absorbed, r, is assumed to be the same for all species.
Case 2--The dose in mg/day of partially soluble vapors is proportional to
the 02 consumption, which in turn is proportional to W2/3 and is also proportional
135
-------
to the solubility of the gas in body fluids, which can be expressed as an
absorption coefficient, r, for the gas. Therefore, expressing the Og consumption
as 02 = k W2/3, where k is a constant independent of species, it follows that
m = k W 2/3
or
d = -JL- = kvr
W2/3
As with Case 1, in the absence of experimental information or a sound theoretical
argument to the contrary, the absorption fraction, r, is assumed to be the same
for all species. Therefore, for these substances a certain concentration in
ppm or ug/m3 in experimental animals is equivalent to the same concentration in
humans. This is supported by the observation that the minimum alveolar concen-
tration necessary to produce a given "stage" of anesthesia is sinriliar in man
and animals (Dripps et al. 1977). When the animals are exposed via the oral
route and human exposure is via inhalation, or vice versa, the assumption is
made, unless there is pharmacokinetic evidence to the contrary, that absorption
is equal by either exposure route.
i
Calculation of the Unit Risk from Animal Studies
The 95% upper-limit risk associated with d mg/kg2/3/day is obtained from
6LOBAL79 and, for most cases of interest to risk assessment, can be adequately
approximated by P(d) = 1 - exp(-q*d). A "unit risk" in units X is simply the
risk corresponding to an exposure of X = 1. This value is estimated by finding
the number of mg/kg2/3/day that corresponds to one unit of X and substituting
this value into the above relationship. Thus, for example, if X is in units
of ug/m3 in the air, we have that for case 1, d = 0.29 x 7fll/3 x 10~3 mg/kg2/3/
day, and for case 2, d = 1, when ug/m3 is the unit used to compute parameters
in animal experiments.
136
-------
If exposures are given in terms of ppm in air, the following calculation
may be used:
1 ppm = 1.2 x molecular weight (gas)
molecular weight (air)
Note that an equivalent method of calculating unit risk would be to use mg/kg
for the animal exposures and then increase the jtn polynomial coefficient by an
amount
(Wh/Wa)J/3 j = 1, 2, ..., k
and use mg/kg equivalents for the unit risk values.
Model for Estimation of Unit Risk Based on Human Data
If human epidemiologic studies and sufficiently valid exposure information
are available for the compound, they are always used in some way. If they
show a; carcinogenic effect, the data are analyzed to give an estimate of the
linear dependence of cancer rates on lifetime average dose. If they show no
carcinogenic effect when positive animal evidence is available, then it is
assumed that a risk does exist, but it is smaller than could have been observed
in the epidemiologic study, and an upper limit to the cancer incidence is
calculated assuming hypothetically that the true incidence is just below the
level of detection in the cohort studied, which is determined largely by the
cohort size. Whenever possible, human data are used in preference to animal
bioassay data.
Very little information exists that can be used to extrapolate from high
exposure occupational studies to low environmental levels. However, if a number
of simplifying assumptions are made, it is possible to construct a crude dose-
response model whose parameters can be estimated using vital statistics,
epidemiologic studies, and estimates of worker exposures.
137
-------
In human studies, the response is measured in terms of the relative risk
of the exposed cohort of individuals compared to the control group. The
mathematical model employed assumes that for low exposures the lifetime
probability of death from lung cancer (or any cancer), PQ» may be represented
by the linear equation
P0 = A + BHx
where A is the lifetime probability in the absence of the agent, and x is the
average lifetime exposure to environmental levels in units such as ppm. The
factor BH is the increased probability of cancer associated with each unit
increase of x, the agent in air.
If it is assumed that R, the relative risk of cancer for exposed workers
as compared to the -general population, is independent of the length of exposure
or age at exposure and depends only on the average lifetime exposure,, it follows
that
R = p = A + BH (xi + X2)
" A + BH xi .
or
RP0 = A + BH (xi + X2)
where xi = lifetime average daily exposure to the agent for the general population,
X2 = lifetime average daily exposure to the agent in the occupational setting, and
PQ - lifetime probability of dying of cancer with no or negligible exposure.
Substituting PO = A + BH xl and rearranging gives
BH = PO (R - 1)/X2
To use this model, estimates of R and X2 must be obtained from the epidemiologic
studies. The value Pg is derived by means of the life table methodology from
138
-------
the age- and cause-specific death rates for the genera, population found In the
1978 U.S. Vital Statistics tables.
UNIT RISK ESTIMATES FOR CADMIUM
Unit Risk Estimate Based on an Animal Study
The bloassay by Takenaka et al. (1983) using male wistar rats and cadmium
chloride aerosol was chosen for estimating the quantitative unit risk
This was the only positive anlma, Inhalation study with cadmium and/or cadmium
^pounds that showed a dose-response trend of primary lung carcinomas to animals
continuously exposed to cadmium chloride aerosols for 18 months. The primary
lung carcinomas were historically differentiated as adenocardnomas, epldenrcid
carcinomas, combined epldermotd and adenocardnomas, and mucoepldermold carcinomas
but were combined for this unit risk analysis. The Incidences of total primary
lung carcinomas was 15% (6/39), 53» (20/38), and 71* (25/35) for the low (12.5
ug/m3), medium (25 ug/m3), and high (50 ug/m3). exposure groups_ respective]y.
No tumors were found among 38 controls.
In arriving at an upper-limit unit risk estimate for humans, dose is
calculated on a lifetime continuous basis with 2 years considered a full lifetime
exposure for rats. Thus, by multiplying by 0.75 the measured concentrations
of 13.4 ug/m3, 25.7 ug/m3, and 50.8 ug/m3 for the three dose group$j ^ ^.^
continuous exposure can be estimated as 10.05 ug/m3, 19.3 ug/m3, and 38.1 ug/m3s
respectively. The corrections for animal to human weight differences are given
below.
In transforming from animal exposure to human equivalence, the method for
treating inhalation of an aerosol (presented earlier in the section for-calcula-
tion of human equivalent dosages from animal data [Case 1]), assumes aerosols
to be absorbed proportionally to the breathing rate. The breathing rate for
139
-------
113-g rats is 0.105 m3/day. For the Wistar rats used in the Takenaka et al.
bioassay, the average weights at 18 months were 424.6 g (for the 13.4 ug/m3
group), 437.6 g (for the 25.7 ug/m3 group), and 424.3 g (for the 50.8 ug/m3
group). To adjust for these weights the foloowing formula is used:
I = 0.105 (W/0.113)2/3 m3/day
where I = the daily inhalation rate of a rat weighing W kilograms. For the
three groups the I values are 0.254 m3/day, 0.259 m3/day, and 0.254 m3/day,
respectively. Combining these with the lifetime continuous exposure estimates
above, daily exposure is estimated to be 2.55 ug/day, 5.00 ug/day, and! 9.68
ug/day, respectively. Equivalently, dose can be estimated on a ug/kg/day basis
as 6.0 ug/kg/day, 11.4 ug/kg/day, and 22.8 ug/kg/day.
Based on the above data for animals, the 95% upper-limit unit risk of cancer
resulting from cadmium chloride exposure is q* = 6.3 x 10-2(ug/kg/day)-1 using
the linearized multistage model. When transformed to equivalent human dose, the
CA6 method requires multiplying q* by the weight ratio factor (Wh/Wa)1/3, where
Wfo = weight of a human, which is assumed to be 70 kg. Thus,
f : '
q* = q* (Wh/WJ1/3 = 6.3 x 10~2(70/0.429)1/3 = 3.4 x 10-1(ug/kg/day)'1
h 1
Thus, using the linearized multistage model, the 95% upper-limit unit risk
estimate for induced cancers based on cadmium chloride exposure is q* = 3.4 x 10"1.
ri
If it is assumed that the Cd++ ion is the carcinogenic agent and not the cadmium
chloride molecule, then an adjustment must be made for the weight of the two
chloride ions. In this 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 q* for the cadmium ion based on inhalation of cadmium chloride is
h
140
-------
q* = 3.4 x 10-l(ug/kg/day)-l/0.613 = 5.5 x l
This can be converted back to human exposure in terms of ug/m3 by assuming that
a 70-kg human breathes 20m3 air/day. Thus,
q* = 3.4 x lO-ltug/kg/day)-1 x 1 x 20 m3 = 9.7 x
h 70 kg day
for cadmium chloride exposure, and
q* = 9.7 x 10-2(Ug/m3)-l/0.613 = 1.5 x IQ
based on inhalation exposure to the cadmium ion. Therefore, the unit risk from
the inhalation of one microgram of elemental cadmium per cubic meter of air is
approximately
R = 1 - exp -(0.16 x 1) = 0.15
This is an upper-bound estimate of risk based on the direct experimental
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 cadmium.
Unit Risk Estimate Based on a Human Study
Data Base--
At the present time the strongest evidence in humans suggesting a cadmium-
induced carcinogenic response is found in the Thun et al. (1984) study. This
141
-------
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 probability 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.
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. There 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. To obtain an estimate of risk, a mathematical model must be assumed
that cannot be evaluated for goodness of fit in any reasonable manner
using the available data.
In spite of these considerable shortcomings, the CAG nevertheless feels
that a risk estimate based on this limited and potentially biased data base
could be of use for the following reasons:
1. The observed human respiratory cancer response corresponded to the animal
response in regard to site, which increases the likelihood that the
response was real.
142
-------
2. Most of the factors that are potentially biasing would work to increase
the apparent cadmium-induced cancer risk. Thus, such a risk estimate
should be considered an upper-bound estimate. If this upper-bound
estimate is lower than the one obtained in the animal experiment, it
should be used in preference to the animal estimate.
Estimation of the Factors Used in 'the Calculation of BH--
As noted, three factors need to be addressed in order to estimate the human
slope B^: PQ, the lifetime background risk due to respiratory cancer for the
environmentally exposed population; R, the relative risk in the epidemiologic
study; and X, the average lifetime exposure for the cadmium-exposed cohort in
the epidemiologic study.
Because of the rather limited information available at the present time,
considerable uncertainty surrounds the estimation of these factors. Therefore
the most prudent approach seems to be to use this limited information to make
an educated guess as to the best estimates of each quantity under consideration.
Where appropriate, upper and lower bounds are given for each quantity, giving a
range of values that in each case is likely to include the true value. A
discussion of each of the terms follows.
Lifetime background respiratory cancer risk in the environmentally exposed
population (Pp)The underlying mathematical model for human slope assumes that
the background rate for an environmentally exposed population is increased per
unit of lifetime exposure by the same "percentage" as the epidemiologically
studied population. At present, there is no indication that the environmentally
exposed population differs in sex-race distribution from the general U.S.
population. As a result, the value calculated from the 1978 vital statistics
for the total U.S. population can be used for the lifetime respiratory cancer
background death rate. Using the techniques discussed by Gail (1975) the
value, :Pg = 0.046, is calculated and used as the best estimate.
143
-------
Vital statistics for 1978 were used for the above calculation because
they are the most current available. However, the most appropriate rate to
use would be the future unknown value. Since smoking is the most.important
factor in determining the risk of respiratory cancer, and the smoking rate for
females is beginning to approach that of males, the value calculated for the
U.S. male population in 1978 is used as an upper bound for the calculation of
PQ. This gives a value of PQU = 0.068. The rate based on vital statistics
of never-smokers during the 1960s is used as a lower limit. This gives a value
for POL of 0.0082.
True relative risk of respiratory cancer due to cadmium in exposed cohort (R)
The observed number is taken as a best estimate of the expected number of cases
in the cadmium exposure group, so that Ex = 16. The expected number of cases
under the assumption of no cadmium effect is taken as the expected number of cases
«t
calculated by Thun et al. (1984) to be 6.99. Thus the CAG's best estimate of
relative risk is R = EX/E = 16/6.99 = 2.29.
With regard to the' calculation of a lower bound for the relative risk, the
following should be noted. Based on a worst-case scenario and an arsenic risk
model from the National Institute for Occupational Safety and Health, Thun et al.
(1984) calculated that at most the number of expected cases of respiratory cancer
due to exposure to arsenic for the cadmium worker cohort was 0.78» Also, based
on a retrospective smoking survey of cadmium workers and their surviving rela-
tives, and using the smoking adjustment methods developed by Axelson (1978),
Thun et al. (1984) estimated that the increase in the expected number of respira-
tory cancers in the cadmium-exposed worker population due to excess over standard
U.S. smoking rates was less than 25%.
Under the assumption that arsenic is additive to background, and smoking is
multiplicative, the upper bound for the expected number of cases, assuming no
144
-------
cadmium effect, is Eu = (6.99 + 0.78) x 1.25 = 9.71.
The 95% lower bound on the expected number of cases in the exposed
population where 16 were observed is calculated from the relationship
15 _E ,
0.95 = E e xLEXL/j
j=0 XL
which has the solution EXL = 10.11.
Thus the CAG's lower bound estimate for the relative risk is
i
Eyl
RL = *k = io.ii/9.7i = i.o4i
u
To calculate an upper bound for the relative risk, the following approach is
taken. The white male respiratory cancer rate is 10-25% lower for Colorado-
i
Denver males than the U.S.. rates used in the expected-value calculations. Since
Denver is the area where the plant is located, a lower bound on the expected
number of cases under the assumption of no cadmium effect is E|_ = 6.99 x 0.75 =
5.24. The 95% upper bound for the expected number of cases in the cadmium-exposed
population, given that 16 were observed, is calculated from the relationship
i
16 -_E 1
0.05 = E e XUEXU/J!
j=0
which has the solution
Exu = 23.23
Thus the upper bound for the relative risk is
. , 145
-------
= 23.23 * 5.24 - 4.43
Lifetime average exposure for members of cadmium cohort (X)--To estimate
the average lifetime exposure on a continuous basis, a number of factors need to
be estimated. They are:
The average age, t, of the cohort at the end of the observation period.
The average duration, d, of exposure for the cohort in years.
The average exposure rate, e, on the job.
The fraction, f, of time per year exposed on the job.
Given these factors, an estimate of the average exposure rate over the
cohort's lifetime is
X = def /t
A discussion of each of these factors follows.
Average age at end of observation period (t)--No direct information is
available concerning the ages of the entire cohort at the end of the observation
period. However, the average of the 51 individuals who died of causes thought
to be possibly cadmium-related can be used as an upper bound. This results in
tu = 63.3 years. In calculating a lower bound, it is noted that 50% of the
population had 33 years or more of follow-up. Assuming that an average starting
age is 20 years and that the mean and median ages are equal, the result is a
lower bound of ti_ = 20 + 33 = 53 years. For a best estimate, the midpoint of
the upper and lower bounds is used to yield an estimate of t = (63,B3 + 53) * 2
= 58.2 years.
Average duration of exposure (d) As noted by Thun et al . (1934), the
standard rate ratios (SRRs) were closely related to the standard mortality
146
-------
ratios (SMRs) and virtually uniform over duration of employment. Thus, the
expected number of cases is proportional to the observed number of cases. As a
first-order approximation it is assumed that person-years of observation are
also proportional to the observed number of cases. Table 18 shows the weighted
average low, best, and high estimated durations as calculated using this approach,
TABLE 18. ESTIMATED DURATIONS OF EXPOSURE
Duration of
employment
2-10
10-20
20+;
Weighted
average(d)
Assumed
Low
2
10
20
8.00
average in
Best
6
15
30
13.69
interval
High
10
20
40
19.38
Number of
deaths
9
3
4
Average exposure rate on the job (e)Smith et al. (1980) estimated inhala-
tion exposures that occurred in various work areas, as shown in Table 16.
These estimated exposures were time-weighted with approporiate adjustments for
the use of respirators.
Since information concerning the distribution of person-years of observation
associated with exposures over time and location is not presently available,
the best estimate would be the average, giving equal weight to each time period
and production department. The resulting estimate is e = 0.53 mg/m3. For an
upper bound, the average for the eight plant production departments during the
pre-1950 period is calculated as ey = 1.04 mg/m3. The lower bound is the
average for the eight production departments during the 1965 to 1976 time
period, or ej_ = 0.26 mg/m3.
147
-------
Fraction of the time per year exposed on the job (f)--It is assumed that
individuals worked 40 hours per week and were absent 20 days per year due to
vacation, holidays, and illness. This results in an estimate of
Calculation of Average Lifetime Exposure (X)--
The previous information concerning exposure is summarized in Table 19
TABLE 19. SUMMARY OF EXPOSURE
Value
maximizing
Factor average exposure
t
d
e
f
X » def/t x
103 ug/m3
53.0
19.4
1.04
0.22
83.4
Value giving
best estimate
average exposure
58.2
13.7
0.53
0.22
27.4
Value
minimizing
average exposure
63.3
8.0
' 0.26
0.22
7.2
Calculation of Human Slope
The values needed to calculate the estimated human slope for a constant
exposure of 1 ug/m3 are given in Table 20. The effects of compounding, especially
multiplying together, a series of assumptions that consistently overestimates
or underestimates the true values of parameters used to estimate risk leads to
very different estimates. This is true even when the mathematical model itself,
a major source of uncertainty, remains the same. However, it is highly unlikely
148
-------
TABLE 20. VALUES USED TO ESTIMATE HUMAN SLOPE AND ITS BOUNDS
Factor
PO
E
EX
R - EX/E
X
BH = P0(R-1)/X =
Value
maximizing
slope
0.068
5.24
23.23
4.43
7.2
3.3 x lO'2
Value giving
best estimate
of slope
0.046
6.99
16
2.29
27.4
2.0 x 10'3
, Value
minimizing
slope
0.008
9.71
10.11
1.04
83.4
3.8 x lO'6
that either extreme is close to the true value. The CAG takes as its estimate
the value obtained by compounding the series of best guesses. Although a
single term may not be conservative, the overall result is probably more
reasonable than either of the extremes.
One final correction is needed. The assumption is that human exposure
was to cadmium oxide (CdO); thus, the risk from elemental cadmium is increased
by the ratio
(C'dO/Cd) = (128.4/112.4) = 1.14
with a corresponding unit risk estimate of
BH = 2.0 x lO"3 x 1.14 = 2.3 x 10'3 (ug/m3)'1
This estimate is two orders of magnitude lower than the estimate based on
the rat inhalation study of Takenaka et al. (1983), which was 0.156. The range
149
-------
is 4.3 x 10~6 to 3.8 x 10-2, so that the upper bound is also smaller than in the
rat study cited. Some of this difference might be due to variation in biological
activity between cadmium compounds (i.e., cadmium chloride in rats versus cadmium
fumes and dust in humans). For example, in the Takenaka et al. (1983) study, it
may be that these concentrations tended to inhibit lung clearance by suppression
of macrophage activity. In any event, the final unit risk estimate is based on
data from the human study (Thun et al. 1984), which is also used for calculating
the relative potency of cadmium.
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 cadmium is
compared with that of other chemicals that the CA6 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 (mMol/kg/day)-1, is called the relative potency
index.
Figure 2 is a histogram representing the frequency distribution of relative
potency indices for 54 chemicals that have been evaluated by the CA6 as suspect
carcinogens. The actual data summarized by the histogram are presented in
Table 21. Where human data have been available for a compound, such data have
been used to calculate these indices. Where no human data have been 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 consistent basis for
potency comparisons.
150
-------
(J
z:
ULJ
o
LU
cc
u_
20
8
16
14
1?
10
8
fi
4
2
0
,« * ',%
S: 2 :::
Xv«%*X*I
SIS&S
4th 3rd 2nd 1st
QUARTILE
QUARTILE QUARTILE QUARTILE ~~
1xio+1 4x'm+2 9-*m+3 ~
iji: 6 ijiii
B
*I*X*X*X*i
X*X"*'X*l
""*«***«»'
pi
Jlxll
H
|^|:|:j
*«*«v«vX
JsSii^
IIS
;:::$!*:::
i%'&$i»5
%"*%%%**
ip
il
:|:j:j:j:j:j:j:
!%'i°i'X'
^i§x:^
HI
X'I'X'X*!
ijft$l*l$
?:§!<§!
x*x*x*x
~"
mi
ijl;i$i$iS
l^xl
x'A-X'X*
x-x'x-x"
"X >*X' ^~
"X* 2 X*
^m M priHT^xi "
-2
0
2 4
LOG OF POTENCY INDEX
8
Figure 2. Histogram representing the frequency distribution of the potency
indices of 54 suspect carcinogens evaluated by the Carcinogen
Assessment Group.
151
-------
TABLE 21. RELATIVE CARCINOGENIC POTENCIES AMONG 54 CHEMICALS EVALUATED BY
THE CARCINOGEN ASSESSMENT GROUP AS SUSPECT HUMAN CARCINOGENS*»2,3
SI ope .
Compounds (mg/kg/day)~l
Acrylonitrile
Aflatoxin B^
Al dri n
Ally! chloride
Arsenic
B[a]P
Benzene
Benzidene
Beryllium
Cadmi urn
Carbon tetrachloride
Chlordane
Chlorinated ethanes
1,2-dichloroethane
hexachloroethane
1,1,2,2-tetrachloroethane
1,1,1-trichloroethane
1,1,2-trichloroethane
Chloroform
Chromium
DDT
Di chl orobenzi di ne
1,1-dichloroethylene
Die! dri n
0.24(W)
2924
11.4
1.19x10-2
15(H)
11.5
5.2xlO-2(W)
234 (W)
1.40(W)
7.8(W)
1.30x10-1
1.61
6.9x10-2
1.42x10-2
0.20
1.6x10-3
5.73x10-2
7x10-2
41 (W)
8.42
1.69
1.47x10-1(1)
30.4
Molecular
weight
53.1
312.3
369.4
76.5
149.8
252.3
78
184.2
9
112.4
153.8
409.8
98.9
236.7
167.9 .
133.4
133.4
119.4
100
354.5
253.1
97
380.9
" '''-'--7 - -;
Potency
i ndex
1x10+1
9xlO+5
4x10+3
9x10-1
2x10+3
3x10+3
4x10°
4x1 0+4
1x10+1
9x10+2
2x10+1
i
7x10+2
7x100
3x10°
3x10+1
2x10-1
8x100
8x100
4x10+3
3x10+3
4x10+2
1x10+1
1x10+4
Order of
magnitude
index)
+1
+6
+4
0
+3
+3
+1
+5
+1
+3
+1
+3
+1
0
+1
-1
+1
+1
+4
+3
+3
+1
+4
152
-------
TABLE 21. (continued)
Compounds
Dinitfdtoluene
Diphenylhydrazine
Epichlorohydrin
Bis(2-chloroethyl )ether
Bis(chloromethyl )ether
Ethylen.e dibromide (EDB)
Ethylene oxide
Heptachlor
Hexachloro benzene
Hexachlorobutadiene
Hexachlorocycl ohexane
technical grade
alpha isomer
beta isomer
gamma isomer
Hexachl orodi benzodi oxi n
Methyl ene chloride
Nickel
Nitrosamines
Dimethylnitrosamine
Di et hy 1 n i tr osami n e
Di butyl nitrosamine
N-ni trosopyrrol i di ne
N-ni troso-N-ethylurea
N-ni troso-N-methyl urea
N-nitroso-diphenylamine
PCBs
Slope Molecular
(mg/kg/day)_i weight
0.31
0.77
9.9xlO-3
1.14
9300(1)
8.51
1.26(1)
3.37
1.67
7.75x10-2
4.75
11.12
1.84
1.33
1.1x10+4
6.3x10-4
1.15(W)
25.9(not by q*)
43.5(not by q*)
5.43
2.13
32.9
302.6
4.92x10-3
4.34
182
180
92.5
143
115
187.9
44.1
373.3
284.4
261
290.9
290.9
290.9
290.9
391
84.9
58.7
74.1
102.1
158.2
100.2
117.1
103.1
198
324
Potency
index
6x10+1
1x10+2
9x10-1
2x10+2
1x10+6
2x10+3
6x10+1
1x10+3
5x10+2
2x10+1
1x10+3
3x10+3
5x10+2
4x10+2
4x10+6
5x10-2
7x10+1
2x10+3
4x10+3
9x10+2
2x10+2
4x10+3
3x10+4
1x100
1x10+3
Order of
magnitude
(logic
index)
- +2
+2
0
+2
. +6 .
+3
+2
+3
+3 .
+1 \
:+3
+3
+3
+3
+7
-1
+2
+3
+4
+3
+2
+4
+4
0
+3
(continued on the following page)
153
-------
TABLE 21. (continued)
Compounds
Phenols
2,4,6-trichlorophenol
Tetrachl orodi benzo-p-di oxi
Tetrach 1 oroethy 1 ene
Toxaphene
Trichloroethylene
Vinyl chloride
Remarks:
1. Animal slopes are 95%
Slope
(mg/kg/day)_i v
1.99x10-2
n 1.56xlO+5
3.5x10-2
1.13
1.9x10-2
1.75x10-2(1)
upper-limit slopes
Molecular Potency
weight index
197.4
322
165.8
414
131.4
62.5
based on
< -1
4x10°
5xlO+7
6x10°
5x10+2
2.5x10°
1x10°
the linearized
Order of
magnitude
. index)
; +1
+8
+1
+3
0
: 0
multistage
.C A « -U (A n >-. A
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 non-threshold 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)-1 by 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.
154
-------
The potency index for cadmium based on the Thun et al . (1984) study of
cadmium smelter workers is 8.8 x 10+2 (mMol /kg/day)"1. This is derived as
follows: Assuming that an individual breathes 20 m3 of air per day and weighs
70 kg, the slope estimate from the human study, 2.3 x 10~3 (ug/m3)'1, is first
converted to units of (mg/kg/day)~l or
2.3 x lO-^ug/m3)-1 x. 1 day x l U9 x 70 kg = 7.8 (mg/kg/day)'1
- 20 m3 10-3 mg
Multiplying by the molecular weight of 112.4 give a potency index of
8.8 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 8.8 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 non-linearities in the dose-response curve could exist.
155
-------
APPENDIX A
COMPARISON OF RESULTS BY VARIOUS EXTRAPOLATION MODELS
The estimate of unit risk from animals, presented in the body of this ,
document was calculated by use of the linearized multistage model. This non-
threshold model is part of a methodology for estimating 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 been 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
form or first stage of the multistage model. This fact, together with the
downward curvature of the one-hit model, means that the model will always
yield low-level risk etimates that 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" curva-
ture, 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 estimate
such values as percentile lethal dose or percent!le effective dose. The log-
156
-------
Probit model was developed along stictly empirical lines, in studies where it
was observed that several log dose-response relationships followed the cumulative
normal probability distribution function, $. 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+blogio 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 form
P(D;b,k) = l-exp-(bdk) b,k > 0
For the power of dose only, the restriction k > 0 has been placed on this model.
When k > 1, the model yields low-dose estimates of risks that are usually
157
-------
significantly lower than either the multistage or the one-hit models, both of
which are linear at low doses. All three of these modelsthe multistage, the
one-hit, and the Weibull--usually project risk estimates that are significantly
higher at low exposure levels than those projected by the log-Probit model.
The estimates of added risk for low doses for these models are given in
Table A-l for the cadmium chloride rat inhalation studies by Takenaka et al.
(1983). Both maximum likelihood estimates and 95% upper confidence limits are
presented. The results show that the maximum likelihood estimates of risk for
the log-Probit model are all less than those for the other models, and this
difference increases sharply at low doses. The one-hit model yields maximum
likelihood estimates slightly higher than those obtained with the multistage
model, while those obtained with the Weibull model are somewhat lower.
158
-------
i*V
*v
UJ UJ
00 U.
=t u_ ;
CO > 1
i ^
UJ
Q fv
i i i
rv O
O U.
1
~T ^r"
0 0
Q£
ST LI,
ii^
i i O
"5T" jj|^)
o >
T^
r O
cu E
3
i \
., f«
-c cu
i -a
cu o
c E
0
cu
CD
to to
to CU
i- ~O
r~~ E
2:
4-5
O
0 r
£- 0)
Q- T3
1 O
oi E
0
^J
^JJ--
p J
rs a;
f^ "CD
t- O
cu E
3
^_>
r- r
-E a>
i -o
cu o
c E
0
cu
0)
to
4-5 1
to cu
t- T3
s§
2:
^-^
oo
0) E
O 05
Q 3
CO
oo
1
CD
r-H
X
CM
i-H
to
1
0
t-H
X
oo
t-H
LO
1
O
I 1
X
CD
> t
to
1
o
i i
X
r*^.
cy>
CD
r^
i
CD
t I
X
en
t 1 .
to
1
o
r-H
X
t-H
OO
to
i
o
t (
X
LO
LO
«^J-
1
CD
t-H
LO
CM
1
O
t-H
X
CTl
CO
LO
|
0
t-H
X
to
CM
i^-
1
0
t l
X
CD
t-H
LO
1
O
t 1
X
CTl
O ,
to
1
o
t 1
X
t-H
«3~
LO
1
o
r-H
X
r-H
co
LO
1
0
t-H
X
LO
LO
00
1
O
t-H
r1
1
O
t-H
X
«=*
*
C^J-
I
o
t-H
X
oo
oo
oo
i
o
t-H
X
CD
t-H
«^f-
|
0
r-H
X
CTi
LO
t 1
1
O
r 1
X
0
CM
LO
|
CD
t-H
X
OO
oo'
^
i
o
t-H
. X
t-H
CO
^i"
1
CD
r-H
X
LO
LO
CM
1
0
1 1
to
1 ,
o
r1
X
LO
r-H
OO
1
O
t-H
X
CTi
LO
CM
1
O
t-H
X
0
1-H
oo
i
0
t-H
X
CTi
1
1
O
r-H
X
00
r-H
00
1
0
t-H
X
CTi
r 1
00
0
r-l
X
't-H
CO
00
1
CD
t-H
X
LO
LO
i 1
1
0
1 1
CM
1
O
r-H
X
oo
CM
CM
1
0
t 1
X
i-H
00
CM
1
O
t 1
X
LO
CTl
CM
1
O
r-H
X
CM
CTi
CO
1
O
1 1
X
o
f"^
CM
1
0
t 1
X
CTi
. «
00
CM
1
O
t-H
X
oo
r^
CM
i
0
t-H
X
LO
LO
r1
-T-J
K -£
CT
CU
|
, |
I*
^ ^
-a
Q-
«x
l
cu
-a
o
E
CU
OV
to
to
;,_
4-5
3
E
cu
.c
+*
£_
o
tf-
r-H
1
OO
E
. «^
3
CM
O
i 1
X
1^
CTi
II
fc r
cr
159
-------
APPENDIX B
INTERNATIONAL AGENCY FOR RESEARCH ON CANCER (IARC) CRITERIA FOR
EVALUATION OF THE CARCINOGENICITY OF CHEMICALS*
ASSESSMENT OF EVIDENCE FOR CARCINOGENICITY FROM STUDIES IN HUMANS
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.
2. Limited evidence of carci nogenicity, which indicates that a causal
interpretation 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 carcinogenicity.
ASSESSMENT OF EVIDENCE OF CARCINOGENICITY FROM STUDIES IN EXPERIMENTAL ANIMALS
These assessments are classified into four gruops:
1. Sufficient evidence of carcinogenicity, which indicates that there is
an increased incidence of malignant tumors; (a) in multiple species or strains;
(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, type of tumor, or age at onset. Additional evidence may be
provided by data on dose-response effects, as well as information from short-
term tests or on chemical structure.
international Agency for Research on Cancer. 1982. IARC Monographs: Evaluation
of the Carcinogenic Risk of Chemicals to Humans, Supplement 4. Lyon, France.
160
-------
2. Limited evidence of carcinogenicity, which means that the data suggest
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 qualitative
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, indicating that data were not available to the working group.
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, evaluation of
the carcinogenic risk to humans was based on consideration of both the epidemio-
logic and the experimental evidence. The breadth of the categories of evidence
defined above allows substantial variation within each category. The decision's
reached.by the IARC Working Group regarding overall risk incorporate these
differences, even though the differences cannot always be reflected adequately
when placing exposures into particular categories.
161
-------
The chemical, group 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 epidemiologic studies to support a causal association
t
between the exposure and cancer.
Group 2
The chemical, group of chemicals, industrial process, or occupational
exposure is probably carcinogenic to humans. 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) degrees of evidence. Usually, category 2A is reserved for
exposures for which there is at least limited evidence of carcinogenlcity to
humans. The data from studies in experimental animals play 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 results in a classification of 2B.
In some cases, the IARC Working Group considered that the known chemical
properties of a compound and the results from short-term tests allowed its
transfer from Group 3 to 2B or from 2B to 2A.
Group 3
The chemical, group of chemicals, industrial process, or occupational
exposure cannot be classified as to its carcinogenicity to humans.
162
-------
REFERENCES
Adamsson, E. 1979. Long-term sampling of airborne cadmium duct in an
alkaline battery factory. Scand. J. Work Environ. Health 5:178. .
Amacher, D.E., and S.C. Paillet. 1980. Induction of trifluorothymidine-
resistant mutants by metal ions in L5178Y/TK+/~ cells. Mutat. Res.
78:279-288.
Ames, B.N., W.E. Durston, E. Yamasaki, and F.D. Lee. 1973. Carcinogens are
mutagens: A simple test system combining liver homogenates for activa-
tion and bacteria for detection. Proc. Natl. Acad. Sci. (USA) 70:
2281-2285.
Ames, B.N., J. McCann, and E. Yamasaki. 1975. Methods for detecting carcinogens
and mutagens with the Salmonel1 a/mammalian microsome mutagenicity test.
Mutat. Res. 31:347-364.
Andersson, K., C.G. Elinder, C. Hqgstedt, and T. Kjellstrom. 1982. Mortality
among cadmium workers in a Swedish battery factory. Translated from the
article in Swedish entitled "Mortality in battery workers exposed to
cadmium and nickel." Report to the Swedish Work Environment Fund.
Armitage, P., and R. Doll. 1954. The age distribution of cancer and a multi-
stage theory of carcinogenesis. Br. J. Cancer 8:1-12. .
Armstrong, B.G., and 6. Kazantzis. 1983. The mortality of cadmium workers.
Lancet, June 25, 1983:1425-1427.
Armstrong, B.G., and G. Kazantzis. 1982;(April). A mortality study of cadmium
workers in England: Report to the International Lead Zinc Research
Organization. TVC Centenary Institute of Occupational Health, London School
of Hygiene and Tropical Medicine, London, England.
Avanzi, M. 1950. Osservazioni sull'attivita citologica di alcuni composti
chimici. Caryologia 3:234-248.
Axelson, 0. 1978. Aspects on confounding in occupational health epidemiology.
Scand. J. Work Environ. Health 4:85-89.
Baader, E.W. 1951. Dtsch. Med. Wochenschr. 484.,
Bauchitiger, M., E. Schmid, H.J. Einbrodt, and J. Dresp. 1976. Chromosome
aberrations in lymphocytes after occupational exposure to lead and
cadmium. Mutat. Res. 49:57-62.
Bui, T.H., J. Lindsten, and G.J. Nordberg. 1975. Chromosome analysis of
lymphocytes from cadmium workers and Itai-Itai patients. Environ. Res.
9:187-195.
Casto, B. 1976. Letter to Richard Troast, EPA, enclosing mutagenicity data on
cadmium chloride and cadmium acetate.
163
-------
Chandler J.A., B.6. Timms, M.S. Morton, and G.V. Groom. 1976. Proceedings:
Effect of cadmium administration in vivo in plasma testosterone and the
ultrastructure of accessory sex organs of the rat. J. Endocrinol.
69(3):21. ,
Chellman, G.J., and C.L. Diamond. 1984. Use of a modified 109-cadmiurn-hemo-
globin assay for quantitation of metallothionein in biological tissues.
Toxicologist 4:130.
Chiang, C.L. 196.1. Vital statistics* Special Report No. 47. U.S. Department
of Commerce, Division of Vital Statistics, Washington, DC, p. 275.
dive, D., 6. Hajian, and M.M. Moore. 1981. Letter to the Editor. Mutat.
Res. 89:241-244.
Cox, C.R. 1972. Regression models and life tables. J. Roy. Stat. Soc. B
34:187-220.
Crump, K.S., and W.W. Hatson. 1979. GLOBAL79: A Fortran program to
extrapolate dichotomous animal carcinogenicity data to low doses.
Natl. Inst. Environ. Health Sciences, Contract No. l-ES-2123.
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
chromosomal 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 chromosomique. I. Lesions metalliques. Rev. Cytol. Biol. Veget.
34:233-244.
Degraeve, N. 1981. Carcinogenic, 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 heavy 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.
Dekundt, G., and A. Leonard. 1975. Cytogenic investigations on leukocytes
of workers from a cadmium plant. Environ. Physiol. Biochem. 5:319-327.
Dekundt, G., A. Leonard, and B. 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 reproductive
effects of environmental chemicals: Studies of cadmium and boron adminis-
tered orally. Environ. Health Perspect. 13:59-67.
164
-------
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. Biochem. Biophys.
82:70.
Epstein, S.S., E. Arnold, J. Andrea, W. Bass, and Y. Bishop. 1972. Detection
of chemical mutagens by the dominant lethal assay in the mouse. Toxicol.
Appl. Pharmacol. 23:288-325.
Favino, A., A. Cavalleri, 6. 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 Cd115 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 synthe-
sis 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. J. Chronic Dis. 28:135-147.
Gasiorek, K., and M. Bauchinger. 1981. Chromosome 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. Mennear. 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.
165
-------
Goldsmith, D.F., A.M. 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. Gould, and W.A.D. Anderson. 1964. Effect of zinc on carci-
nogenesis by cadmium. Proc. Soc. Exp. Biol. 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.O.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. 1980. Rapid solubilization and
translocation of 109CdO following pulmonary deposition. Toxicol Appl.
Pharmacol. 54:156-160. '
Hadley, J.G., A.W. Conklin, and C.L. Sanders. 1979. Toxicol. Letters
4:107-111.
Heath, O.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.
166
-------
Hearing, 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 Spring
Harbor Laboratory, Cold Spring Harbor, NY.
Hirayama, T. 1977. Changing patterns of cancer in Japan, with special
reference to the decrease in stomach 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.
Hsie,' A.W., J.P. O'Neil, J.R.S. Sabastian, D.B. Couch, et al. 1978. Quantita-
tive mammalian cell genetic toxicology. In: Application of short-term
bioassays in the fractionation and analysis of complex environmental
mixtures (Michael D. Waters, Stephen Nesnow, JoellervL. Huisingh, Shahbey
Sandhu, and Larry Claxton, eds.). EPA-600/9-78-027. 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 Drosophi 1 a melanogaster. Jpn. J. Genet. 53:183-189.
Inskip, H., and V. Beral. 1982. Mortality of Shipham residents: 40-year
follow-up. Lancet, April 17, 1982:896-899.
International Agency for Research on Cancer (IARC). 1973. Cadmium and
inorganic cadmium compounds.. Monographs on the evaluation of carcinogenic
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. IARC criteria
for evaluation of the carcinogenicity of chemicals. Monographs on
the evaluation of carcinogenic risk of chemicals to man: Supplement 4.
Lyon, France.
167
-------
Japan Public Health Association. 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 ph'loxine, 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.
Monograph 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.TAbstract).
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.
Kipling, M.D., and J.A.H. Waterhouse
Lancet 1:730.
1967. Cadmium and prostatic carcinoma.
Kjellstrom, 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.
Kjellstrom, T., L. 'Friberg, 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 Albinoratte in der
Latenzperiode der Sarkomentwicklung nach Kadmiumchloridinjection.
Zentralbl. Allg. Pathol. 113:192-197.
Knorre, D. 1971. Zur Induktion von Hodenzwischenzelltumoren an der
Albinoratte durche Kadmiumchlorid. Arch. Geschwulstforsch.
38:257-263.
Kolonel, L.N. 1976. Association of cadmium with renal cancer. Cancer
37:1782-1787.
\)
168
-------
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 spermatogenesis studied
by velocity sedimentation cell separation serial mating. J. Pharmacol.
.Exp. Then. 187:641-652.
Lemen, R.A., J.S. Lee., J.K. Wagoner, and H.P. Blejer. 1976. Cancer mortality
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. Platt.
,1973. Absence of prostatic changes in rats exposed to cadmium. Ann.
Occup. Hyg. 16:111-118.
Loser, E. 1980. A two year oral carcinogenicity study with cadmium on rats.
Cancer Letters 9:191.
Lucis, O.J., R. Lucis, and K. Aterman. 1972. Tumorigenesis 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.
Mandel, 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 Meeting, 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.F. Gamble, and P.M. Tousey. 1976b. Mortality
among rubber workers: Relationship to specific jobs. J.'Occup. Med.
18(3):178-185.
169
-------
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_. coli after exposure to Cd2+. Biochem. Biophys.
Res. Commun. 74:1450-1455.
Mitra, R., and I. Bernstein. 1978. Single-strand breakage in DNA of IE_, coli
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.
Nishioka, H. 1975. Mutagenic activities of metal compounds in bacteria.
Mutat. Res. 311:185-189.
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 Cadmium Conference, Miami, FL.
Oberdoerster, 6., H.P. Baumert, 0. Hochrainer, and W. Stoeber. 1979.
The clearance of cadmium aerosols after inhalation exposure. Am. Ind.
Hygiene Assoc. J. 40:443-450.
Oberdoerster, 6., 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.
Oberly, T.O., 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 DNA 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.
O'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, 6.R., and A.C. Allison. 1972. Chromosome damage in human cell culture
induced by metal salts. Mutat. Res. 16:332.
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.
170
-------
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. Mn2+ uptake, mitochondrial DNA
replication and EK induction, comparison with other divalent cations.
,Mol. Gen. Genet. 151:69-76.
Ramaiya, L.K., and M.D. Pomerantseva. 1977. Investigation of cadmium
mutagenic effect on germ cells of male mice. Genetika 13:59-63.
Ramel, C., and M. Friberg. 1974. Carcinogenic and genetic effects. In:
Cadmium in the environment (M. Friberg et al., eds.). Cleveland, OH:
CRC Press, p. 133.
Ramel,, C., and J. Magnusson. 1979. Chemical induction of nondisjunction in
Drosophila. Environ. Health Perspect. 31:59-66.
Reddy, J., D. Svoboda, D. Azarnoff, and R. Dawas. 1973. Cadmium-induced
Leydig cell tumors of rat, testis: Morphological and cytochemical 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 Crepis capillaris. 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.'
Sanders, C.L., and J.A. Mahaffey. 1984. Carcinogenicity of single and multiple
intratracheal instillations of cadmium oxide in the rat. Environ. Res.
33:227-233.
Schmauz, R., and P. Cole. 1974. Epidemiology of cancer of the renal pelvis
and ureter. J. Natl. Cancer Inst. 52(5):1431-1434.
171
-------
Schroeder, H.A., J.O. Balassa, and W.H. Vinton, Jr. 1964. Chromium, 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.9 and E. Aughey. 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.
Shigematsu, I., S. Kitamura, and J. Takeuchi. 1981. A retrospective
mortality study on cadmium-polluted population in Japan. In: Proceedings
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.
Si rover, 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. 1980. Chronic cadmium exposures
associated with kidney function effects. Am. J. Ind. Med. l;;319-337.
Sorahan, T. 1981. A mortality study of nickel-cadmium battery workers.
Cancer Epidemiology Research Unit, University of Birmingham, Birmingham,
England.
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.
Sunderman, 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.
172
-------
Suter, K.E. 1975. Studies on the dominant-lethal and fertility effects of the
heavy metal compounds methyl mercuric hydroxide, mercuric chloride, and
cadmium chloride in male and female mice. Mutat. Res. 30:365-374.
Sutou, S., K. Yamamoto, H. Sendota, K. Tomomatsu, Y. Shimizu, and M. Sugiyama.
1980a. Toxicity, fertility, teratogenicity, and dominant lethal tests in
fats administered cadmium subchronically. I. Toxicity studies.
Ecotoxicol. Environ. Safety 4:39-50.
Sutou, S., K. Yamamoto, H. Sendota, and M. Sugiyama. 1980b. Toxicity,
fertility, teratogenicity, and dominant lethal tests in rats administered
cadmium subchronically. II. Fertility, teratogenicity, and dominant
lethal tests. Ecotoxicol. Environ. Safety 4:51-56.
Takahashi, T. 1972. Abnormal mitosis by some mutagens in S^ cerevisiae.
Bull. Brewery Sci. 18:37-48.
Takenaka, S., H. Oldiges, H. Konig, D. Hochrainer, and 6. Oberdoerster. 1983.
Carcinogenicity of cadmium aerosols in Wistar rats. J. Natl. Cancer
Inst. 70:367-373.
Tarkowski, A.K. 1966. An air-drying method 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 Com-
mittee). Department of the Environment, London, England.
Thun, M. J., T.M. Schnorr, A.B. Smith, and W.E. Halperin. 1984. Mortality
among a cohort of U.S. cadmium production workers: An update. National
Institute for Occupational Safety & Health, Washington, DC. (Unpublished).
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.
Umeda, 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. Food and Drug Administration. 1977. Total diet studies (7320.08).
Compliance Program Evaluation, Bureau of Foods, Washington, DC.
173
-------
U.S. Occupational Safety and Health Administration (OSHA). 1983 (Aug. 24).
Occupational exposure to inorganic arsenic: Comments of ASARCO, Inc.
Federal Register 48:1864-1903.
Van Rosen, 6. 1953. Radiomimetic activity and the periodical system of the
element. Bot. Notis. 140-141.
Van Rosen, 6. 1954. Breaking of chromosomes by the action of elements of
the periodical system and some other participants. Hereditas 40:258-263.
Varner, M.O. 1983 (April). Updated epidemiologic study of cadmium smelter
workers. Presented at the Fourth International Cadmium Conference.
(Unpublished).
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.
White, L.D. 1984. Letter from L.D. White, ASARCO, Inc., to the Carcinogen
Assessment 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. Mabuchi, and W.F. Whitmore, Jr. 1974. Epidemiology
of adenocarcinoma of the kidney. J. Natl. Cancer Inst. 53(6):1619-1634.
Wyrobek, A.J., and W.R. Bruce. 1975. Chemical induction of sperm
abnormalities. 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.
174
-------
' jf.
*-
-------
I *
'i
------- |