National Cancer Institute 

CARCINOGENESIS 

Technical Report Series 

No. 24 

1978 

BIOASSAY OF 

MALATHION 

FOR POSSIBLE CARCINOGENICITY 

CAS No. 121-75-5 

NCI-CG-TR-24 

U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE 

Public Health Service 

National Institutes of Health 

BIOASSAY OF
 

MALATHION
 

FOR POSSIBLE CARCINOGENICITY
 

Carcinogenesis Testing Program
 

Division of Cancer Cause and Prevention
 

National Cancer Institute
 

National Institutes of Health
 

Bethesda, Maryland 20014
 

IKS· DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
 

Public Health Service
 

National Institutes of Health
 

DHEW Publication No. (NIH) 78-824 

BIOASSAY OF
 

MALATHION
 

FOR POSSIBLE CARCINOGENICITY
 

Carcinogenesis Testing Program
 

Division of Cancer Cause and Prevention
 

National Cancer Institute
 

National Institutes of Health
 

FORWARD; This report presents the results of the bioassay of
 

malathion conducted for the Carcinogenesis Testing Program,
 

Division of Cancer Cause and Prevention, National Cancer
 

Institute (NCI), National Institutes of Health, Bethesda,
 

Maryland· This is one of a series of experiments designed to
 

determine whether selected environmental chemicals have the
 

capacity of produce cancer in animals. Negative results, in
 

which the test animals do not have a greater incidence of cancer
 

than control animals, do not necessarily mean that the test
 

chemical is not a carcinogen, inasmuch as the experiments are
 

conducted under a limited set of circumstances. Positive results
 

demonstrate that the test chemical is carcinogenic for animals
 

under the conditions of the test and indicate that exposure to
 

the chemical is a potential risk to man. The actual determination of the risk to man from animal carcinogens requires a wider
 

analysis.
 

CONTRIBUTORS: The bioassay of malathion was conducted by Gulf
 

South Research Institute, New Iberia, Louisiana, initially under
 

direct contract to the NCI and currently under a subcontract to
 

Tracor Jitco, Inc., prime contractor for the NCI Carcinogenesis
 

Bioassay Program.
 

The experimental design was determined by Drs. J. Η.
 

Weisburger*>2 an<j R # R # Bates*»-*. t h e doses were selected by
 

Drs. T. E. Shellenberger4»5, J. Η. Weisburger, and R. R. Bates.
 

Administration of the test chemical and observation of the
 

laboratory animals were supervised by Drs. T. E. Shellenberger
 

and H. P. Burchfield^, with the technical assistance of Ms. D.
 

H. Monceaux^ and Mr. D. Broussard^. Histopathology was performed
 

by Drs. E. Bernal4 and B. Buratto4 at Gulf South Research
 

iii
 
Institute, and the diagnoses included in this report represent
 

the interpretation of these pathologists.
 

Animal pathology tables and survival tables were compiled at EG&G
 

Mason Research Instituted Statistical analyses were performed
 

by Dr. J. R. Joiner?, using methods selected for the bioassay
 

program by Dr. J. J. Gart8. Chemicals used in this bioassay were
 

analyzed under the direction of Dr. H. P. Burchfield, and the
 

results of the analyses were reviewed by Dr. S. S. Olin?.
 

This report was prepared at Tracor Jitco? under the direction of
 

NCI. Those responsible for the report at Tracor Jitco were
 

Dr. Marshall Steinberg, Director of the Bioassay Program; Dr. L.
 

A. Campbell, Deputy Director for Science; Dr. J. F. Robens,
 

toxicologist; Dr. R. L. Schueler, pathologist; Dr. G. L. Miller,
 

Ms. Y. E. Presley, and Mr. W. D. Reichardt, technical writers;
 

and Dr. E. W. Gunberg, technical editor, assisted by Ms. P. J.
 

Graboske.
 

The statistical analysis was reviewed by members of the
 

Mathematical Statistics and Applied Mathematics Section of NCI8:
 

Dr. John J. Gart, Mr. Jun-mo Nam, Dr. Hugh M. Pettigrew, and Dr.
 

Robert E. Tarone.
 

The following other scientists at NCI were responsible for
 

evaluating the bioassay experiment, interpreting the results, and
 

reporting the findings:
 

Dr. Kenneth C. Chu
 

Dr. Cipriano Cueto, Jr.
 

Dr. J. Fielding Douglas
 

Dr. Dawn G. Goodman
 

Dr. Richard A. Griesemer
 

Dr. Harry A. Milman
 

Dr. Thomas W. Orme
 

Dr. Robert A. Squire9
 

Dr. Jerrold M. Ward
 

iv
 
^•Carcinogenesis Testing Program, Divison of Cancer Cause and
 

Prevention, National Cancer Institute, National Institutes of
 

Health, Bethesda, Maryland.
 

with the Naylor Dana Institute for Disease Prevention,
 

American Health Foundation, Hammond House Road, Valhalla,
 

New York.
 

% o w with the Office of the Commissioner, Food and Drug
 

Administration, Rockville, Maryland.
 

^Gulf South Research Institute, Atchafalaya Basin Laboratories,
 

P. 0. Box 1177, New Iberia, Louisiana.
 

% o w with the National Center for Toxicological Research,
 

Jefferson, Arkansas.
 

6

EG&G Mason Research Institute, 1530 East Jefferson Street,
 

Rockville, Maryland.
 

7

Tracor Jitco, Inc., 1776 East Jefferson Street, Rockville,
 

Maryland.
 

"Mathematical Statistics and Applied Mathematics Section,
 

Biometry Branch, Field Studies and Statistics, Division of
 

Cancer Cause and Prevention, National Cancer Institute, National
 

Institutes of Health, Bethesda, Maryland.
 

with the Division of Comparative Medicine, Johns Hopkins
 

University, School of Medicine, Traylor Building, Baltimore,
 

Maryland.
 

SUMMARY
 

A bioassay of technical-grade malathion for possible carcinogenicity was conducted by administering the test chemical in feed
 

to Osborne-Mendel rats and B6C3F1 mice·
 

Groups of 50 rats of each sex were administered malathion at one
 

of two doses for 80 weeks, then observed for 33 weeks. Time-


weighted average doses were 4,700 or 8,150 ppm· Matched controls
 

consisted of groups of 15 untreated rats of each sex; pooled
 

controls consisted of the matched controls combined with 40
 

untreated male and 40 untreated female rats from similar
 

bioassays of four other test chemicals· All surviving rats were
 

killed at 108-113 weeks·
 

Groups of 50 mice of each sex were administered malathion at one
 

of two doses, either 8,000 or 16,000 ppm, for 80 weeks, then
 

observed for 14 or 15 weeks· Matched controls consisted of
 

groups of 10 untreated mice of each sex; pooled controls
 

consisted of the matched controls combined with 40 untreated male
 

and 40 untreated female mice from similar bioassays of four other
 

test chemicals· All surviving mice were killed at 94 or 95
 

weeks·
 

Mortality in either rats or mice was not significantly related to
 

the administration of malathion· Sufficient numbers of animals
 

were at risk in the dosed and control groups of rats and mice of
 

each sex for development of late-appearing tumors·
 

In female rats, three follicular-cell carcinomas and one follicular-cell adenoma of the thyroid occurred in the high-dose group,
 

and three follicular-cell hyperplasias occurred in the low-dose
 

group· The incidence of these tumors showed a statistically
 

significant (P = 0·026) dose-related trend; however, the results
 

of the Fisher exact test for direct comparison between the dosed
 

and control groups were not significant· More dosed males than
 

dosed females had either tumors or hyperplasia of the follicular
 

vii
 
cells of the thyroid; however, because of the higher incidence of
 

tumors among the male controls, none of the results of the 

statistical tests were significant. These thyroid tumors were 

not considered to be associated with the administration of 

malathion. 

In male mice, hepatocellular carcinoma occurred at the following
 

incidences: matched controls 2/10, pooled controls 5/49, low-


dose 7/48, high-dose 11/49. In addition, neoplastic nodules
 

occurred in 3/49 pooled-control and 6/49 high-dose animals. When
 

the combined incidence of these neoplasms in the dosed animals
 

was compared with that of the pooled controls, the dose-related
 

trend was Ρ = 0.019 and the direct comparison of the high-dose
 

group with the control group was Ρ » 0.031. Thus, none of the
 

direct comparisons of dosed groups with controls were significant
 

using the Bonferroni criteria. In addition, the historical
 

controls from this laboratory had several qontrol groups with
 

incidences of 35-40% hepatocellular carcinoma, rates which are
 

comparable with the incidence of this tumor in the dosed male
 

mice of the present study. Thus, these liver tumors are not
 

considered to be associated with the administration of malathion.
 

The incidences of liver tumors in dosed females were not 

statistically significant when compared with that in control 

animals. 

It is concluded that under the conditions of this bioassay, there
 

was no clear evidence of the association of the tumor incidence
 

with the administration of malathion to Osborne-Mendel rats or
 

B6C3F1 mice.
 

viii
 
TABLE OF CONTENTS
 

Page
 

I· Introduction· ···· ··· ········ · 1
 

II· Materials and Methods 3
 

A· Chemical 3
 

. Dietary Preparation 3
 

C · Animals ··· · · · ····· 4
 

D· Animal Maintenance· ········· · 5
 

E· Subchronic Studies 6
 

F. Designs of Chronic Studies · 7
 

G. Clinical and Pathologic Examinations 11
 

H· Data Recording and Statistical Analyses 12
 

III· Results - Rats 19
 

A. Body Weights and Clinical Signs (Rats) 19
 

B. Survival (Rats) 22
 

C· Pathology (Rats) 22
 

D. Statistical Analyses of Results (Rats) 27
 

IV. Results - Mice 29
 

A. Body Weights and Clinical Signs (Mice) 29
 

B. Survival (Mice) 31
 

C. Pathology (Mice) 31
 

D. Statistical Analyses of Results (Mice) 35
 

V. Discussion ··· · 37
 

VI. Bibliography 41
 

APPENDIXES
 

Appendix A Summary of the Incidence of Neoplasms in
 

Rats Fed Malathion in the Diet 43
 

Table Al Summary of the Incidence of Neoplasms in
 

Male Rats Fed Malathion in the Diet 45
 

Table A2 Summary of the Incidence of Neoplasms in
 

Female Rats Fed Malathion in the Diet 49
 

ix
 
Page 

Appendix Β Summary of the Incidence of Neoplasms in 

Mice Fed Malathion in the Diet · 53 

Table Bl Summary of the Incidence of Neoplasms in 

Male Mice Fed Malathion in the Diet 55 

Table B2 Summary of the Incidence of Neoplasms in 

Female Mice Fed Malathion in the Diet 58 

Appendix C Summary of the Incidence of Nonneoplastic 

Lesions in Rats Fed Malathion in the Diet 61 

Table CI Summary of the Incidence of Nonneoplastic 

Lesions in Male Rats Fed Malathion in the Diet 63 

Table C2 Summary of the Incidence of Nonneoplastic 

Lesions in Female Rats Fed Malathion in the Diet··· 67 

Appendix D Summary of the Incidence of Nonneoplastic 

Lesions in Mice Fed Malathion in the Diet 71 

Table Dl Summary of the Incidence of Nonneoplastic 

Lesions in Male Mice Fed Malathion in the Diet····· 73 

Table D2 Summary of the Incidence of Nonneoplastic 

Lesions in Female Mice Fed Malathion in the Diet·.. 76 

Appendix Ε Analyses of the Incidence of Primary Tumors 

in Rats Fed Malathion in the Diet 79 

Table El Analyses of the Incidence of Primary Tumors 

in Male Rats Fed Malathion in the Diet ···· 81 

Table E2 Analyses of the Incidence of Primary Tumors 

in Female Rats Fed Malathion in the Diet 86 

Appendix F Analyses of the Incidence of Primary Tumors 

in Mice Fed Malathion in the Diet 91 

Table Fl Analyses of the Incidence of Primary Tumors 

in Male Mice Fed Malathion in the Diet 93 

Table F2 Analyses of the Incidence of Primary Tumors 

in Female Mice Fed Malathion in the Diet 95 
Page 

Appendix G Analysis of Formulated Diets for 

Concentrations of Malathion 97 

TABLES 

Table 1

Table 2

 Design of Malathion Chronic Feeding Studies 

in Rats

 Design of Malathion Chronic Feeding Studies 

8 

in Mice 10 

FIGURES 

Figure 1

Figure 2

 Growth Curves for Male Rats Fed Malathion 

in the Diet

 Growth Curves for Female Rats Fed Malathion 

in the Diet

 20 

 21 

Figure 3 Survival Curves for Rats Fed Malathion 

in the Diet 23 

Figure 4 Growth Curves for Mice Fed Malathion in the 

Diet , 30 

Figure 5 Survival Curves for Mice Fed Malathion in 

the Diet 32 

xi
 

I. INTRODUCTION
 

Malathion (CAS 121-75-5; NCI C00215) is the generic name for
 

S-(l,2-dicarbethoxyethyl)-0,0-dimethyldithiophosphate, which is
 

an organophosphorus insecticide and acaricide first synthesized
 

in the United States in 1952. Malathion primarily affects the
 

nervous system by inhibition of cholinesterase activity and
 

subsequent accumulation of acetylcholine (Koelle, 1975). However, it has a low mammalian toxicity (Eto, 1974). Malathion is
 

approved for a wide variety of uses as an insecticide and acaricide on field crops, fruits, nut trees, vegetables, livestock,
 

agricultural premises, and land. Tolerances for residues of
 

malathion have been established on many of these products (EPA,
 

1972).
 

Malathion was selected for the Carcinogenesis Testing Program
 

because of its wide use in agriculture and the absence of
 

adequate chronic studies of the chemical.
 

1 

II . MATERIALS AND METHODS 

A. Chemical
 

The technical-grade malathion used for the chronic study was
 

obtained in a single batch (Lot No. SPS-10127) from American
 

Cyanamid Company, Agricultural Division, Princeton, New Jersey.
 

The identity of the chemical was confirmed at Gulf South Research
 

Institute by infrared, nuclear magnetic resonance, and mass
 

spectral analyses. Gas-liquid chromatographic analysis (electron
 

capture detector, DC-200 column) showed a single peak, consistent
 

with the manufacturer's specification of 95% minimum purity. No
 

attempt was made to identify or quantitate impurities.
 

The chemical was stored in the original container at approximately 0°C until used.
 

B. Dietary Preparation
 

All test diets were formulated using Wayne® Lab Blox animal meal
 

(Allied Mills, Inc., Chicago, 111.) to which was added the
 

required amount of malathion for each dietary concentration. The
 

test chemical was first dissolved in a small amount of acetone
 

(Mallinckrodt, Inc., St. Louis, Mo.), which was then added to the
 

feed. Corn oil (Louana®, Opelousas Refinery, Opelousas, La.) was
 

also added to the feed, primarily as a dust suppressant, and the
 

3 
diets were mixed mechanically to assure homogeneity of the
 

mixtures and evaporation of the acetone. Final diets, including
 

those for the control groups of animals, contained corn oil equal
 

to 2% of the final weight of feed· The diets were stored at
 

approximately 17°C until used, but no longer than 1 week.
 

The stability of malathion in feed was tested by determining the
 

concentration of the chemical in formulated diets at intervals
 

over a 7-day period. Diets containing 1,000, 8,000, or 10,000
 

ppm malathion showed no change on standing at ambient temperature
 

for this period.
 

As a quality control test on the accuracy of preparation of the
 

diets, the concentration of malathion was determined in different
 

batches of formulated diets during the chronic study. The
 

results are summarized in Appendix G. At each dietary concentration, the mean of the analytical concentrations for the
 

checked samples was within 2.5% of the theoretical concentration,
 

and the coefficient of variation was never more than 5.0%. Thus,
 

the evidence indicates that the formulated diets were prepared
 

accurately.
 

C. Animals
 

Rats and mice of each sex, obtained through contracts of the
 

Division of Cancer Treatment, National Cancer Institute, were
 
used in these bioassays. The rats were of the Osborne-Mendel
 

strain obtained from Battelle Memorial Institute, Columbus, Ohio,
 

and the mice were B6C3F1 hybrids obtained from Charles River
 

Breeding Laboratories, Inc., Wilmington, Massachusetts. On
 

arrival at the laboratory, all animals were quarantined (rats for
 

4 days, mice for 15 days) and were then assigned to control or
 

dosed groups.
 

D. Animal Maintenance
 

All animals were housed in temperature- and humidity-controlled
 

rooms. The temperature range was 22-24°C, and the relative
 

humidity was maintained at 40-70%. The air in each room was
 

changed 10-12 times per hour. Fluorescent light provided
 

illumination 10 hours per day. Food and water were available ad
 

libitum.
 

The rats were housed individually in hanging galvanized steel
 

mesh cages, and the mice were housed in plastic cages covered
 

with filter bonnets, five animals per cage for females, and two
 

or three animals per cage for males. Initially, rats were
 

transferred once per week to clean cages; later in the study,
 

cages were changed every 2 weeks. Mice were transferred once per
 

week to clean cages covered with filter bonnets; bedding used for
 

the mice was Absorb-Dri® (Lab Products, Inc., Garfield N. J.).
 

5 
For rats, absorbent sheets under the cages were changed three
 

times per week. Feeder jars and water bottles were changed and
 

sterilized three times per week·
 

Cages for control and dosed mice were placed on separate racks in
 

the same room· Animal racks for both species were rotated
 

laterally once per week; at the same time, each cage was changed
 

to a different position in the row within the same column· Rats
 

receiving malathion, along with their matched controls, were
 

housed in a room by themselves. Mice receiving malathion were
 

maintained in a room housing mice fed tetrachlorvinphos (CAS
 

961-11-5) and dieldrin (CAS 60-57-1), together with their
 

respective matched controls.
 

E. Subchronic Studies
 

Subchronic feeding studies were conducted to estimate the maximum
 

tolerated doses of malathion, on the basis of which low and high
 

concentrations (hereinafter referred to as "low doses" and "high
 

doses") were determined for administration in the chronic
 

studies. In these subchronic studies, malathion was added to the
 

animal feed in twofold increasing concentrations, ranging from
 

1,000 to 8,000 ppm for rats and 250 to 8,000 ppm for mice.
 

Treated and control groups each consisted of five male and five
 

female animals. The chemical was provided in feed to dosed
 

6 
groups for 6 weeks, followed by observation for 2 weeks· Because
 

there were no deaths in any dosed group of rats or mice during
 

the study, a second study was performed with doses of 8,000 to
 

32,000 ppm for rats and 4,000 to 32,000 ppm for mice.
 

In the second study, all rats and four male mice receiving 32,000
 

ppm died by week 3· No animal receiving 16,000 ppm died, but
 

mean weight gains decreased early in the study· The low and high
 

doses for the chronic studies using both rats and mice were set
 

at 8,000 and 16,000 ppm.
 

F· Designs of Chronic Studies
 

The designs of the chronic studies are shown in tables 1 and 2.
 

The matched-control groups for restarted high-dose rats included
 

five animals of each sex; initially, 16,000 ppm was fed to rats
 

of each sex as the high dose, and 10 matched controls of each sex
 

were used· Because this dose of malathion was too toxic, the
 

high-dose study was terminated and new high-dose groups were
 

started, as shown in table 1.
 

Since the numbers of animals in the matched-control groups were
 

small, pooled-control groups also were used for statistical comparisons· The pooled-control groups consisted of the matched
 

controls from the bioassay of malathion combined with matched
 

controls from the bioassays of tetrachlorvinphos, toxaphene (CAS
 
Table 1. Design of Malathion Chronic Feeding Studies in Rats
 

Sex and Initial Malathion Time on Study Time-Weighted
 

Test No. of in Dietb Dosed Observed0 Average Dose0

*
 

Group Animalsa (ppm) (weeks ) (weeks) (ppm)
 

Male
 

Low-Dose 

Matched-Control 10 0 113 

High-Dose 

Matched-Control 5 0 108 

Low-Dose 50 8,000 

4,000 

0 

14 

66 

33 

4,700 

High-Dosee 50 12,000 

8,000 

0 

3 

77 

29 

8,150 

Female 

Low-Dose 

Matched-Control 10 0 113 

High-Dose 

Matched-Control 5 0 109 

Low-Dose 50 8,000 

4,000 

0 

14 

66 

33 

4,700 

High-Dose 50e 12,000 

8,000 

0 

3 

77 

29 

8,150 

aAll animals were 35 days of age when placed on study·
 

^Doses were lowered after 3 and 14 weeks on study, based on the pattern
 

of mortality, changes in body weight, and the general condition of the
 

animals in this and other carcinogen bioassays; it was believed that
 

excessive mortality might otherwise occur before termination of the
 

study·
 
Table 1. Design of Malathion Chronic Feeding Studies in Rats
 

(continued)
 

c

When diets containing malathion were discontinued, low-dose rats and
 

their matched controls were fed a control ciiet without corn oil for 2
 

weeks, then the control diet (2% corn oil added) for an additional 31
 

weeks. High-dose rats received the control diet until termination
 

of the study.
 

d

Time-weighted average dose = Σ(dose in ppm χ no. of weeks at that dose)
 

Σ(no. of weeks receiving each dose)
 

e

Original high-dose groups were terminated due to the toxic effects of
 

malathion, and new high-dose groups were started at the doses indicated.
 
Table 2. Design of Malathion Chronic Feeding Studies in Mice
 

Sex and 

Test 

Group 

Initial 

No. of 

Animalsa 

Malathion 

in Diet 

(ppm) 

Time on 

Dosed 

(weeks) 

Study 

Observed13 

(weeks) 

Male 

Matched-Control 10 0 95 

Low-Dose 50 8,000 

0 

80 

14-15 

High-Dose 50 16,000 

0 

80 

15 

Female 

Matched-Control 10 0 95 

Low-Dose 50 8,000 

0 

80 

14 

High-Dose 50 16,000 

0 

80 

15 

aAll animals were 35 days of age when placed on study·
 

bwhen diets containing malathion were discontinued, all mice received
 

the control diet (2% corn oil added) until termination of the study·
 

10
 
8001-35-2), endrin (CAS 72-20-8), and lindane (CAS 58-89-9), to
 

give groups of 55 male and 55 female rats, and 50 male and 50
 

female mice· The bioassays of chemicals other than malathion
 

were also conducted at Gulf South Research Institute and
 

overlapped the bioassay of malathion by at least 1 year. The
 

matched-controls were of the same strain and from the same
 

supplier and were examined by the same pathologists· Because
 

additional matched controls were started simultaneously with
 

restarted dosed groups for some of these bioassays, the number of
 

animals in the pooled-control groups varied·
 

G. Clinical βχιά Pathologic Examinations
 

All animals were observed twice per day for signs of toxicity,
 

weighed at regular intervals, and palpated for masses at each
 

weighing· Animals that were moribund at the time of daily
 

examination were killed and necropsied·
 

The pathologic evaluation consisted of gross and microscopic
 

examination of major tissues, major organs, and all gross lesions
 

from killed animals and from animals found dead· The following
 

tissues were examined microscopically: skin, lungs and bronchi,
 

trachea, bone and bone marrow, spleen, lymph nodes, heart,
 

salivary gland, liver, gallbladder (mice), pancreas, stomach,
 

small intestine, large intestine, kidney, urinary bladder,
 

11
 
pituitary, adrenal, thyroid, parathyroid, mammary gland, prostate
 

or uterus, testis or ovary, and brain. Occasionally, additional
 

tissues were also examined microscopically. The different
 

tissues were preserved in 10% buffered formalin, embedded in
 

paraffin, sectioned, and stained with hematoxylin and eosin.
 

Special staining techniques were utilized when indicated for more
 

definitive diagnosis.
 

A few tissues from some animals were not examined, particularly
 

from those animals that died early. Also, some animals were
 

missing, cannibalized, or judged to be in such an advanced state
 

of autolysis as to preclude histopathologic evaluation. Thus,
 

the number of animals from which particular organs or tissues
 

were examined microscopically varies, and does not necessarily
 

represent the number of animals that were placed on study in each
 

group.
 

H. Data Recording and Statistical Analyses
 

Pertinent data on this experiment have been recorded in an automatic data processing system, the Carcinogenesis Bioassay Data
 

System (Linhart et al., 1974). The data elements include descriptive information on the chemicals, animals, experimental design,
 

clinical observations, survival, body weight, and individual
 

pathologic results, as recommended by the International Union
 

12
 
Against Cancer (Berenblum, 1969). Data tables were generated for
 

verification of data transcription and for statistical review.
 

These data were analyzed using the statistical techniques
 

described in this section. Those analyses of the experimental
 

results that bear on the possibility of carcinogenicity are
 

discussed in the statistical narrative sections.
 

Probabilities of survival were estimated by the product-limit
 

procedure of Kaplan and Meier (1958) and are presented in this
 

report in the form of graphs. Animals were statistically
 

censored as of the time that they died of other than natural
 

causes or were found to be missing; animals dying from natural
 

causes were not statistically censored. Statistical analyses for
 

a possible dose-related effect on survival used the method of Cox
 

(1972) for testing two groups for equality and Tarone's (1975)
 

extensions of Cox's methods for testing for a dose-related trend.
 

One-tailed Ρ values have been reported for all tests except the
 

departure from linearity test, which is only reported when its
 

two-tailed Ρ value is less than 0.05.
 

The incidence of neoplastic or nonneoplastic lesions has been
 

given as the ratio of the number of animals bearing such lesions
 

at a specific anatomic site (numerator) to the number of animals
 

in which that site is examined (denominator). In most instances,
 

13
 
the denominators included only those animals for which that site
 

was examined histologically. However, when macroscopic examination was required to detect lesions prior to histologic sampling
 

(e.g·, skin or mammary tumors), or when lesions could have
 

appeared at multiple sites (e.g., lymphomas), the denominators
 

consist of the numbers of animals necropsied.
 

The purpose of the statistical analyses of tumor incidence is to
 

determine whether animals receiving the test chemical developed a
 

significantly higher proportion of tumors than did the control
 

animals. As a part of these analyses, the one-tailed Fisher
 

exact test (Cox, 1970) was used to compare the tumor incidence of
 

a control group with that of a group of dosed animals at each
 

dose level. When results for a number of dosed groups (k) are
 

compared simultaneously with those for a control group, a
 

correction to ensure an overall significance level of 0.05 may be
 

made. The Bonferroni inequality (Miller, 1966) requires that the
 

 value for any comparison be less than or equal to 0.05/k. In
 

cases where this correction was used, it is discussed in the
 

narrative section. It is not, however, presented in the tables,
 

where the Fisher exact Ρ values are shown.
 

The Cochran-Armitage test for linear trend in proportions, with
 

continuity correction (Armitage, 1971), was also used. Under the
 

assumption of a linear trend, this test determines if the slope
 

14
 
of the dose-response curve is different from zero at the one-


tailed 0.05 level of significance· Unless otherwise noted, the
 

direction of the significant trend is a positive dose relationship. This method also provides a two-tailed test of departure
 

from linear trend.
 

A time-adjusted analysis was applied when numerous early deaths
 

resulted from causes that were not associated with the formation
 

of tumors. In this analysis, deaths that occurred before the
 

first tumor was observed were excluded by basing the statistical
 

tests on animals that survived at least 52 weeks, unless a tumor
 

was found at the anatomic site of interest before week 52. When
 

such an early tumor was found, comparisons were based exclusively
 

on animals that survived at least as long as the animal in which
 

the first tumor was found. Once this reduced set of data was
 

obtained, the standard procedures for analyses of the incidence
 

of tumors (Fisher exact tests, Cochran-Armitage tests, etc.) were
 

followed.
 

When appropriate, life-table methods were used to analyze the
 

incidence of tumors. Curves of the proportions surviving without
 

an observed tumor were computed as in Saffiotti et al. (1972).
 

The week during which an animal died naturally or was sacrificed
 

was entered as the time point of tumor observation. Cox's
 

methods of comparing these curves were used for two groups;
 

15
 
Tarone's extension to testing for linear trend was used for three
 

groups. The statistical tests for the incidence of tumors which
 

used life-table methods were one-tailed and, unless otherwise
 

noted, in the direction of a positive dose relationship.
 

Significant departures from linearity (P < 0.05, two-tailed test)
 

were also noted.
 

The approximate 95 percent confidence interval for the relative
 

risk of each dosed group compared to its control was calculated
 

from the exact interval on the odds ratio (Gart, 1971). The
 

e tn e tru e
 relative risk is defined as p^/Pc wner Pt ^s binomial
 

probability of the incidence of a specific type of tumor in a
 

dosed group of animals and pc is the true probability of the
 

spontaneous incidence of the same type of tumor in a control
 

group. The hypothesis of equality between the true proportion of
 

a specific tumor in a dosed group and the proportion in a control
 

group corresponds to a relative risk of unity. Values in excess
 

of unity represent the condition of a larger proportion in the
 

dosed group than in the control.
 

The lower and upper limits of the confidence interval of the
 

relative risk have been included in the tables of statistical
 

analyses. The interpretation of the limits is that in
 

approximately 95% of a large number of identical experiments, the
 

true ratio of the risk in a dosed group of animals to that in a
 

16
 
control group would be within the interval calculated from the
 

experiment· When the lower limit of the confidence interval is
 

greater than one, it can be inferred that a statistically
 

significant result (P < 0.025 one-tailed test when the control
 

incidence is not zero, Ρ < 0·050 when the control incidence is
 

zero) has occurred· When the lower limit is less than unity, but
 

the upper limit is greater than unity, the lower limit indicates
 

the absence of a significant result while the upper limit
 

indicates that there is a theoretical possibility of the
 

induction of tumors by the test chemical, which could not be
 

detected under the conditions of this test.
 

17
 

III. RESULTS - RATS
 

A. Body Weights and Clinical Signs (Rats)
 

During the period of rapid growth, the mean body weights of the
 

low- and high-dose male rats were slightly lower than those of
 

the controls (figure 1); thereafter, no differences between
 

weights of dosed and control groups were discernible. In
 

females, the mean body weights were generally lower in the dosed
 

groups than in the controls throughout the study (figure 2).
 

Fluctuations in the growth curve may be due to mortality; as the
 

size of a group diminishes, the mean body weight may be subject
 

to wide variation.
 

After 2 weeks on study, generalized body tremors were observed in
 

one low-dose male and one high-dose male. During the remainder
 

of the first year, the dosed animals were generally comparable to
 

the controls in appearance and behavior. A few animals showed
 

evidence of an eye infection that was diagnosed by the pathologists at the laboratory as viral conjunctivitis.
 

During the second year of study, clinical signs including rough
 

hair coats, pale mucous membranes, dermatitis, ataxia, alopecia,
 

hematuria, and vaginal bleeding were observed with increasing
 

frequency in dosed animals.
 

19
 
TIME ON STUDY (WEEKS)
 

Figure 1. Growth Curves for Male Rats Fed Malathion in the Die
 

20
 
TIME ON STUDY (WEEKS)
 

Figure 2. Growth Curves for Female Rats Fed Malathion in the Diet
 

21
 
. Survival (Rats)
 

The Kaplan and Meier curves estimating the probabilities of
 

survival for male and female rats fed malathion at the doses used
 

in this bioassay, together with those of the matched controls,
 

are shown in figure 3· Two groups of matched controls, one
 

consisting of 5 animals and the other of 10 animals, were used in
 

this study· In the statistical analyses, these two groups were
 

combined to give matched-control groups of 15 animals for each
 

sex·
 

Neither male nor female rats showed a statistically significant
 

dose-related trend in mortality· Fifty-eight percent of the
 

high-dose males and 67% of the high-dose females survived to the
 

end of the study, and survival was higher in the low-dose and
 

control groups.
 

Sufficient numbers of rats of each sex were at risk for
 

development of late-appearing tumors·
 

C. Pathology (Rats)
 

Histopathologic findings on neoplasms in rats are summarized in
 

Appendix A, tables Al and A2; findings on nonneoplastic lesions
 

are summarized in Appendix C, tables Cl and C2·
 

In general, the majority of the tumors occurred in the dosed
 

22
 
45 60 75 

TIME ON STUDY (WEEKS) 

Figure 3. Survival Curves for Rats Fed Malathion in the Diet
 

23
 
animals; however, these tumors were found with a low frequency,
 

except for chromophobe adenomas of the pituitary gland, fibroadenomas of the mammary gland, and follicular-cell carcinomas of
 

the thyroid gland.
 

There were higher incidences of proliferative lesions of the
 

thyroid gland in the dosed groups than in the matched controls·
 

The incidences of these lesions were as follows:
 

MALES FEMALES
 

Matched Low High Matched Low High
 

Control Dose Dose Control Dose Dose
 

Number of
 

Tissues Examined (14) (41) (47) (15) (48) (49)
 

Thyroid
 

C-cell
 

Hyperplasia 0 1 3 0 5 3
 

C-cell
 

Adenoma 0 1 3 0 1 2
 

Follicular-cell
 

Hyperplasia 1 7 8 0 3 0
 

Follicular-cell
 

Adenoma 1 1 1 0 0 1
 

Follicular-cell
 

Carcinoma 0 2 6 0 0 3
 

Follicular-cell carcinomas of the thyroid occurred unilaterally
 

and were nodular in appearance· They varied in size, the largest
 

being 0.9 cm in diameter, while the smallest, 0.2 cm in diameter,
 

was not detected by gross examination. Microscopically, they
 

24
 
were well-differentiated neoplasms made up of densely cellular
 

zones interrupted by less cellular areas containing follicular
 

structures of variable sizes and shapes and containing colloid·
 

Papillary and acinar features occurred essentially with equal
 

frequency. Some lesions appeared to have an incomplete connective tissue capsule through and beyond which neoplastic follicular cells had extended· Invasive growth into preexisting thyroid
 

parenchyma was common, and an occasional example of extension
 

into surrounding musculature was also seen· The cells were
 

somewhat small and cuboidal in outline with pale eosinophilic
 

cytoplasm· Nuclei were relatively large and essentially oval in
 

outline, having well-delineated nuclear membranes and ample,
 

finely stippled nucleoplasm. Mitoses were infrequent· Degenerative changes were evident, but not abundant· Distant metastases
 

were not observed·
 

Follicular-cell hyperplasia occurred unilaterally, and foci were
 

small in size, thus undetected by gross examination· Microscopically, a single focus, or occasionally two foci, occurred within
 

the thyroid lobe· These foci were unencapsulated and did not
 

seem to be compressing the surrounding thyroid tissue to any
 

great degree· They consisted of several thyroid follicles of
 

variable sizes; many contained normal-appearing colloid· The
 

epithelial wall of these follicles was most commonly cuboidal in
 

25
 
appearance, but epithelial height showed somewhat of an inverse
 

relationship to the diameter of the follicle· Within the larger
 

follicles, thin papillary infoldings in the epithelial wall,
 

suggestive of a colloid involutionary change, were observed.
 

This lesion was thought to be most compatible with a reactive-


metabolic change. Microscopically, there was a more or less
 

diffuse increase in the number of interfollicular cells in the
 

thyroid. The cells were pale-staining and polygonal in shape
 

with ill-defined borders. There was a subtle tendency toward
 

nesting. The cytoplasm was somewhat amphophilic and fairly
 

stippled. The nuclei were also pale and uniformly stippled.
 

These cells were positioned around and between thyroid follicles
 

and seemed to encroach upon the follicles, probably causing a
 

reduction in their size. These, changes could be seen in one or
 

both lobes, and occasionally in the same lobe with follicularcell hyperplasia or follicular-cell adenoma.
 

Numerous nonproliferative lesions, including testicular atrophy
 

and chronic inflammation of the kidney, occurred with low
 

frequency in the control and dosed rats. In addition, cysts of
 

the pituitary gland were seen in 12/43 (28%) low-dose and 10/46
 

(22%) high-dose males receiving malathion, but the dosed female
 

rats, except for one high-dose female, did not have these lesions
 

of the pituitary gland.
 

26
 
The neoplastic and nonneoplastic lesions that occurred in the
 

rats used in this study appeared in a variety of tissues of most
 

organ systems, and for the most part, the incidences in dosed and
 

control animals were comparable· In a few instances, lesions
 

appeared in dosed animals only, but not in significant numbers·
 

This was particularly true for some of the neoplastic lesions in
 

the endocrine and reproductive systems of the rats· These
 

pathologic changes have commonly been observed in control animals
 

of the same strain in other studies of carcinogenicity and are,
 

therefore, considered to be coincidental· In the judgment of the
 

pathologists, this study shows no evidence of carcinogenicity
 

induced by administration of malathion in the Osborne-Mendel rats
 

at the doses used·
 

D. Statistical Analyses of Results (Rats)
 

Tables El and E2 in Appendix Ε contain the statistical analyses
 

of the incidences of those specific primary tumors that occurred
 

in at least two animals in one group and with an incidence of at
 

least 5% in one or more than one group·
 

The incidences of tumors in the matched and pooled controls in
 

this study do not differ statistically from the incidences seen
 

in data compiled to date from similar studies in the same
 

laboratory.
 

27
 
In male rats, the Cochran-Armitage test results for dose-related
 

trend had levels of significance greater than Ρ = 0·05 for incidences of all tumors listed. Also, the results of the Fisher
 

exact test for the comparison of dosed groups with either group
 

of controls were not statistically significant. There was no
 

statistical evidence, therefore, for carcinogenicity of malathion
 

in the male rats.
 

In female rats, follicular-cell carcinoma or follicular-cell
 

adenoma of the thyroid appeared in 4/49 (8%) of the high-dose
 

group, but in no animals in either set of controls. The Cochran-


Armitage test indicates a significant (P = 0.026) positive linear
 

trend in incidence using pooled controls; however, the results of
 

the Fisher exact test are not significant. The spontaneous rate
 

of this tumor in female Osborne-Mendel rats as observed to date
 

at this laboratory is 6/271 (2.2%). No other tumor in the rats
 

appeared at any site in statistically significant incidences. In
 

each of the 95% confidence intervals, shown in the tables, one is
 

included; this indicates the absence of significant positive
 

results. It should also be noted that each of the intervals has
 

an upper limit greater than one, indicating the theoretical
 

possibility of the induction of tumors in rats from malathion,
 

which could not be detected under the conditions of this test.
 

28
 
IV. RESULTS - MICE
 

A. Body Weights and Clinical Signs (Mice)
 

Throughout the study, the mean body weights of the dosed male and
 

female mice were lower than those of their controls (figure 4)·
 

The data also indicate dose-related effects of malathion on mean
 

body weight. Fluctuations in the growth curve may be due to
 

mortality; as a size of the group diminishes, the mean body
 

weight may be subject to wide variation.
 

During the first 6 months of the study, the dosed animals were
 

generally comparable to the controls in appearance and behavior.
 

At week 31, all of the female controls appeared to be hyperexcitable, but this condition did not persist.
 

During the second year of the study, clinical signs including
 

alopecia, rough and discolored hair coats, poor food consumption,
 

hyperexcitability, and abdominal distention were noted with
 

increasing frequency in dosed animals. A few animals appeared to
 

be hyporeactive, and some had a hunched appearance. At week 71,
 

five high-dose females exhibited generalized body tremors, a
 

condition which persisted until week 79. At week 72, a majority
 

of the high-dose males and females began coughing and sneezing;
 

this condition persisted until termination of the study.
 

29
 
TIME ON STUDY (WEEKS)
 

Figure 4. Growth Curves for Mice Fed Malathion in the Diet
 

30 
. Survival (Mice)
 

The Kaplan and Meier curves estimating the probabilities of
 

survival for male and female mice fed malathion at the doses used
 

in this bioassay, together with those of the matched controls,
 

are shown in figure 5. Neither male nor female mice exhibited a
 

statistically significant dose-related trend in mortality·
 

Ninety-four percent of the high-dose males and 88% of the
 

high-dose females survived to termination of the study. Survival
 

in each sex was higher in the dosed than in the control group·
 

Sufficient numbers of animals of each sex were at risk for
 

development of late-appearing tumors.
 

C. Pathology (Mice)
 

Histopathologic findings on neoplasms in mice are summarized in
 

Appendix B, tables Bl and B2; findings on nonneoplastic lesions
 

are summarized in Appendix D, tables Dl and D2·
 

In mice, the only frequently occurring tumor was hepatocellular
 

carcinoma in the males (controls 2/10 [20%], low-dose 7/48 [15%],
 

high-dose 11/49 [22%]); none were found in female mice· The
 

hepatocellular carcinomas varied in microscopic tinctorial
 

qualities, architectural patterns, and cytologic morphology·
 

Some of these lesions, particularly the smaller ones, were
 

observed, not at necropsy, but only after the liver had been
 

31
 
TIME ON STUDY (WEEKS) 

Figure 5. Survival Curves for Mice Fed Malathion in the Diet
 

32
 
fixed. Grossly, the neoplasms varied in size from microscopic to
 

2-3 cm in diameter, and were usually round and well limited.
 

Some had a multinodular appearance, and their boundaries were not
 

conspicuous. The tumors were located either immediately under
 

the capsule and bulged on the visceral surface or were deep
 

within the parenchyma. In the majority of cases, a single tumor
 

was found, but multifocal lesions were also observed.
 

Microscopically, the tumors were clearly discernible, because of
 

changes in the architectural and/or tinctorial characteristics
 

that distinguish the neoplastic from the normal tissues. In
 

addition, the surrounding normal liver plates were compressed and
 

narrowed, due to expansion of the tumor. No capsule formation
 

was evident. The neoplastic hepatocytes were variable in size
 

and shape, but often resembled normal liver cells. Anaplastic
 

features were common and served to differentiate malignant and
 

benign neoplastic lesions of the liver. As mentioned previously,
 

the liver cells in the tumors were arranged in different patterns, some of which closely resembled the normal architecture,
 

while others exhibited disorganized or disoriented liver plates.
 

Degenerative changes were often associated with the hepatocellular carcinomas. No metastases to other organs were observed.
 

Neoplastic nodules of the liver occurred in six high-dose male
 

and two high-dose female mice. These nodules consisted of one or
 

33
 
several small, well-circumscribed nodules located within the
 

hepatic substance. Some of these lesions had gross and cytologic
 

features similar to those of the hepatocellular carcinomas, but
 

size, degree of anaplasia, and lack of invasiveness were the
 

criteria used to distinguish them from hepatocellular carcinomas.
 

Nevertheless, a diagnosis of borderline malignancy was given to a
 

number of the neoplastic nodules. These lesions are considered
 

by the original pathologists to be comparable to neoplastic
 

nodules in rats as described by Squire and Levitt (1975).
 

A low incidence of miscellaneous degenerative, proliferative, and
 

'inflammatory lesions was distributed among the males and females
 

of the control and dosed groups. An exception to this was cystic
 

endometrial hyperplasia, found in 1/9 (11%) control, 12/47 (26%)
 

low-dose, and 10/42 (24%) high-dose female mice.
 

The neoplastic and nonneoplastic lesions that occurred in the
 

mice used in this study appeared in a variety of tissues of most
 

organ systems, and for the most part, with similar incidences for
 

dosed and control animals. In a few instances, lesions occurred
 

only in animals of the dosed groups, but not in significant
 

numbers. These pathologic changes have been observed in control
 

animals in other studies of carcinogenicity and are, therefore,
 

not considered dose related. In the judgment of the
 

pathologists, this study shows no evidence of carcinogenicity
 

34
 
induced by the administration of malathion in B6C3F1 mice at the
 

doses used·
 

D. Statistical Analyses of Results (Mice)
 

Tables Fl and F2 of Appendix F contain the statistical analyses
 

of the incidences of those specific primary tumors that occurred
 

in at least two animals in one group and with an incidence of at
 

least 5% in one or more than one group·
 

In male mice, the incidence of hepatocellular carcinoma combined
 

with that of neoplastic nodules showed a significant linear trend
 

when either the matched controls (P = 0·041) or the pooled
 

controls (P = 0.019) were used· The Fisher exact test for the
 

comparison between the results of the high-dose (17/49, 35%) and
 

pooled-control groups had a probability level of Ρ = 0·031, but
 

this probability of 0.031 is above the 0.025 level required by
 

the application of the Bonferroni criterion. When time-adjusted
 

analysis is performed, eliminating those male mice that died
 

before 52 weeks on study, the following incidences resulted:
 

matched controls, 2/9 (22%); pooled control, 8/48 (17%); low-


dose, 7/47 (15%); high-dose, 17/49 (35%). Neither the Fisher
 

exact tests nor the Cochran-Armitage test of these time-adjusted
 

incidences are significant (P > 0.05) when the matched controls
 

are used. It should be observed that when the incidences of
 

35
 
hepatocellular carcinoma and neoplastic nodules were analyzed
 

separately, none of the Fisher exact test results were
 

significant· The results of all the similar bioassays from this
 

laboratory for which data are available for the B6C3F1 mouse show
 

an incidence of spontaneous liver tumors of 19% of 285 male mice;
 

this is close to the incidence (16%) seen in the male pooled-


control group in the present bioassay· In female mice, there
 

were no statistically significant incidences of any tumor in the
 

dosed groups when compared with those of either set of controls·
 

In each of the 95% confidence intervals, shown in the tables, one
 

is included; this indicates the absence of significant positive
 

results· It should also be noted that each of the intervals has
 

an upper limit greater than one, indicating the theoretical
 

possibility of the induction of tumors by this chemical, which
 

could not be detected under the conditions of this test·
 

36
 
V. DISCUSSION
 

Malathion is a member of the organophosphorus class of pesticides
 

whose predominant mode of inducing toxicity is by inhibition of
 

cholinesterase. Cholinesterase activity in the cerebral cortex,
 

erythrocytes, and plasma of rats is reduced when the animals are
 

fed diets containing malathion (Desi et al., 1976) or when the
 

chemical is administered by oral intubation (Mendoza, 1976).
 

Mean body weights for females of either species were lower for
 

the dosed groups than for the matched controls· Other clinical
 

signs also appeared with greater frequency in the dosed animals
 

than in the controls. In rats, these included rough hair coats,
 

pale mucous membranes, dermatitis, ataxia, alopecia, hematuria,
 

and vaginal bleeding; in mice, the signs included rough and
 

discolored hair coats and abdominal distention. Mortality in
 

either rats or mice was not significantly related to the
 

administration of malathion. Sufficient numbers of animals were
 

at risk in all groups of rats and mice to termination of the
 

study for the development of late-appearing tumors.
 

In female rats, three follicular-cell carcinomas and one follicular-cell adenoma of the thyroid occurred in the high-dose group,
 

and three follicular-cell hyperplasias occurred in the low-dose
 

group. The incidence of these tumors showed a statistically
 

37
 
significant (P = 0·026) dose-related trend; however, the results
 

of the Fisher exact test for direct comparison between the dosed
 

and control groups were not significant· More dosed males than
 

dosed females had either tumors or hyperplasia of the follicular
 

cells of the thyroid; however, because of the higher incidence of
 

tumors among the male controls, the results of none of the
 

statistical tests were significant· These thyroid tumors were
 

not considered to be associated with the administration of
 

malathion·
 

In male mice, hepatocellular carcinoma occurred at the following
 

incidences: matched controls 2/10, pooled controls 5/49, low-


dose 7/48, high-dose 11/49· In addition, neoplastic nodules
 

occurred in 3/49 pooled-control and 6/49 high-dose animals·
 

When the combined incidence in the dosed animals was compared
 

with that of the pooled controls, the dose-related trend was Ρ ­

0·019 and the direct comparison of the high-dose group with the
 

control-group was Ρ = 0·031· Thus, none of the direct comparisons of dosed groups with controls were significant using the
 

Bonferroni criteria. In addition, the historical controls for
 

this laboratory had several control groups with incidences of
 

35-40% hepatocellular carcinomas, rates which are comparable with
 

the incidence of this tumor in dosed male mice in the present
 

study· Thus, these liver tumors are not considered to be
 

38
 
associated with the administration of malathion. The incidences
 

of liver tumors in dosed females were not statistically
 

significant when compared with that in control animals.
 

In previous studies of the long-term toxicity of malathion,
 

Hazleton and Holland (1953) fed groups of rats 100, 1,000, or
 

5,000 ppm of either 65, 90, or 99% preparations of malathion for
 

2-year periods. No lesions associated with the administration of
 

malathion were found by microscopic examination of representative
 

tissues. The highest dose, 5,000 ppm, approximates the time-


weighted average low dose used in the present bioassay. The only
 

evidence of the possible induction of tumors from the administration of malathion in the literature is that of the inconclusive
 

studies of Okey (1972), in which Sprague-Dawley rats fed a diet
 

containing 250 ppm malathion showed a higher incidence and
 

shorter induction time of tumors after the administration of
 

dimethylbenzanthracene (1.31 + 0.18 tumors/rat) than controls
 

administered dimethylbenzanthracene alone (1.07 + 0.15
 

tumors/rat).
 

It is concluded that under the conditions of this bioassay, there
 

was no clear evidence of the association of the tumor incidence
 

with the administration of malathion to Osborne-Mendel rats or
 

B6C3F1 mice.
 

39
 

VI. BIBLIOGRAPHY
 

Armitage, P., Statistical Methods in Medical Research, John Wiley
 

& Sons, Inc·, New York, 1971, pp. 362-365.
 

Berenblum, I·, ed., Carcinogenicity Testing: A Report of the
 

Panel on Carcinogenicity of the Cancer Research Commission
 

of the UICC, Vol. l^ International Union Against Cancer,
 

Geneva, 1969.
 

Cox, D. R., Regression models and life tables. ^J._ IU_ Statist.
 

Soc. Β 34(2):187-220, 1972.
 

Cox, D. R., Analysis of Binary Data, Methuen & Co., Ltd., London,
 

1970, pp. 48-52.
 

Desi, I·, Dura, G., Gonczi, L., Kneffel, Z., Strohmayer, A· , and
 

Szabo, Z·, Toxicity of malathion to mammals, aquatic
 

organisms and tissue culture cells. Arch. Environ. Contam.
 

Toxicol. 3(4):410-425, 1976.
 

Environmental Protection Agency, EPA Compendium of Registered
 

Pesticides, U. S. Government Printing Office, Washington,
 

D.C., 1972, III-M-2.1-2.20.
 

Eto, M., Organophosphorus Pesticides: Organic and Biological 

Chemistry» CRC Press, Inc., Cleveland, Ohio, 1974, pp. 

254-255. 

Gart, J. J·, The comparison of proportions: a review of
 

significance tests, confidence limits and adjustments for
 

stratification. Rev. Int. Stat. Inst. 39(2):148-169, 1971.
 

Hazleton, L. W. and Holland, E. G., Toxicity of malathion. Ind.
 

Hgy. Occup. Med. 8: 399-405, 1953.
 

Kaplan, E. L. and Meier, P., Nonparametric estimation from
 

incomplete observations. J^ Amer. Statist. Assoc.
 

53^:457-481, 1958.
 

Koelle, G. B·, Anticholinesterase agents, In: Goodman, L. S. and
 

Gilman, A·, eds·, The Pharmacological Basis of Therapeutics,
 

Macmillan Publishing Co., Inc., New York, 1975, pp. 445-466.
 

41
 
Linhart, Μ. S., Cooper, J. Α., Martin, R. L. , Page, N. P· , and
 

Peters, J. Α., Carcinogenesis bioassay data system. Comp.
 

and Biomed. Res. 7:230-248, 1974.
 

Mendoza, C. E., Toxicity and effects of malathion on esterases of
 

suckling albino rats.. Toxicol. Appl. Pharmacol.
 

jtf (2)-.229-238, 1976.
 

Miller, R. G. , Jr., Simultaneous Statistical Inference,
 

McGraw-Hill Book Co., New York, 1966, pp. 6-10.
 

Okey, A. B., Dimethylbenzanthracene-induced mammary tumors in
 

rats: Inhibition by DDT. Life Sciences 11(1):833-843,
 

1972.
 

Saffiotti, U. , Montesano, R., Sellakumar, A. R. , Cefis, F., and
 

Kaufman, D. G., Respiratory tract carcinogenesis in hamsters
 

induced by different numbers of administrations of
 

benzo(a)pyrene and ferric oxide. Cancer Res. 32:1073-1081,
 

1972.
 

Squire, R. A. and Levitt, M. H., Report of a workshop on
 

classification of specific hepatocellular lesions in rats,
 

Cancer Res. 35:3214-3223, 1975.
 

Tarone, R. E., Tests for trend in life table analysis.
 

Biometrika 62(3):679-682, 1975.
 

42
 
APPENDIX A
 

SUMMARY OF THE INCIDENCE OF NEOPLASMS IN
 

RATS FED MALATHION IN THE DIET
 

43
 

TABLE ΑΙ.
 

SUMMARY OF THE INCIDENCE OF NEOPLASMS IN MALE RATS
 

FED MALATHION IN THE DIET
 

iNIMALS INITIALLY IN STUDY
 

PNIMALS NECROPSIED
 

iNIHALS EXAMINED HISTOPATHOLOGICALLY
 

INTEGUMENTARY SYSTEM
 

• SKTN
 

BASAL-CELL TUMOR
 

FIBROUS HISTIOCYTOMA
 

PIBFCUS HISTIOCYTOMA, MALIGNANT
 

FESPIRATCRY SYSTEM
 

fLUNG
 

SQUAMOUS CELL CARCINOMA, METASTA
 

OSTEOSARCOMA, METASTATIC
 

HEMATOPOIETIC SYSTEM
 

«SPLEEN
 

HFHANG Ι SARCOMA
 

#THYHOS
 

SARCOMA, NOS
 

CIRCULATORY SYSTEM
 

NONE
 

DIGESTI7E SYSTEM
 

«SALIVARY GLAND
 

FIBROMA
 

«LIVER
 

HEOPLASTIC NODDLE
 

HIGH DOSE
 

CONTROL
 

5
 

5
 

5
 

(5)
 

(5)
 

(5)
 

(5)
 

1 (20%)
 

(5)
 

LOW DOSE
 

CONTROL
 

10
 

10
 

10
 

(10)
 

(10)
 

:io)
 

(10)
 

(9)
 

LOW DOSE
 

50
 

48
 

48
 

(48)
 

1 (2%)
 

1 (2%)
 

(48)
 

1 (2%)
 

(47)
 

1 (2%)
 

(»8)
 

(47)
 

1 rtA\
 

HIGH DOSE
 

50
 

50
 

50
 

(50)
 

1 (2%)
 

1 [2%)
 

(48)
 

1 (2%)
 

(46)
 

(1)
 

1 (100*)
 

(«17)
 

(50)
 

1 r?«i
 

« NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 * NUMBER OF ANIMALS NBCBOPSI1D
 

45
 
TABLE A1. MALE RATS: NEOPLASMS (CONTINUED)

 

HIGH DOSE LOW DOSE 

CONTROL CONTROL 

HEPATOCELLULAR CARCINCHA SARCOMA, NOS 

OPINAPY SYSTEM
 

«KIDNEY (1O)
 

MIXED TUMOR, MALIGNANT
 HAMARTOMA
 

ENDOCRINE SYSTEM
 

•PITUITARY	 (4) (6)
 

CARCINOMA,NOS
 

ADENOMA, NOS
 

CHROMOPHOBE ADENOMA
 

#ADRENAL	 (5) (10)
 

CARCINOMA,NOS
 

COPTICA1 ADENOMA
 

PHEOCHROMOCYTOMA
 

«THYROID (5) (9)
 

POLLTCULAR-CELL ADENOMA 1 (20%)
 

POLLICULAR-CELL CARCINOMA
 C-CELL ADENOMA
 

«PANCREATIC ISLETS (5) (10)
 

ISLET-CELL ADENOMA
 

REPRODUCTIVE SYSTEM
 

*MAMMARY GLAND (5) (10)
 

FIBROMA 1 (10%)
 

SFRVOUS SYSTEM
 

«BRAIN (5) (10)
 

MENINGIOMA
 

«CEREBELLUM (5) (10)
 

GRANULAR-CELL TUMOR, BENIGN
 

•TRIGEMINAL NERVE	 (5) (10)
 

SQUAMOUS CELL CARCINOMA
 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

• NUMBER OF ANIMALS NECROPSIID
 

46
 

LOW DOSE
 

1 (2%)
 

[48)
 

2 (4%)
 

(43)
 

2 (5%)
 

1 (2%)
 

6 (14%)
 

(46)
 

1 (2%)
 

2 (4%)
 

(41)
 

1 (2%)
 

2 (5%)
 

1 (2%)
 

(45)
 

1 (2%)
 

(48)
 

(48)
 

(48)
 

(48)
 

HIGH DOSE
 

1 t2%)
 

(50)
 

1 (2%)
 

1 t2%)
 

(46)
 

1 (2%)
 

3 (7%)
 

(50)
 

3 (6%)
 

(47)
 

1 (2%)
 

6 t13%)
 

3 (6%)
 

(4 9)
 

3 (6%)
 

(50)
 

C48)
 

1 (2%)
 

(48)
 

1 (2%)
 

(50)
 

1 (2%)
 
TABLE A1. MALE RATS: NEOPLASMS (CONTINUED)

 

HIGH DOSE CONTROL LOW DOSE CONTROL LOW DOSE HIGH DOSE 

SPECIAL SENSE ORGANS 

NONE 

MUSCULOSKELETAL SYSTEM 

•.HUMERUS 

OSTEOSARCOMA (5) (10) (48) 1 [2%) 

(50) 

15ODY CAVITIES 

•ABDOMINAL

LIPOMA 

 CAVITY (10) 

1 (10%) 

(48) (50) 

ALL OTHER SYSTEMS 

^MULTIPLE ORGANS 

FIBROUS HISTIOCYTOMA, MALIGNANT (5) (10) (48) (2%) 

(50) 

ANIMAL DISPOSITION SUMMARY 

ANIMALS INITIALLY IN STUDY 

NATUPAI DEATH* 

MORIBUND SACRIFICE SCHEDULED SACRIFICE ACCIDENTALLY KILLED TERMINAL SACRIFICE ANIMAL MISSING 

5 

5 

10 

10 

50 

7 

10 

33 

50 

9 

12 

29 

3 INCLUDES AUTOLYZED ANIMALS 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED

• NUMBER OF ANIMALS NECROFSIiC 

 MICROSCOPICALLY 

47
 
TABLE A1. MALE RATS: NEOPLASMS (CONTINUED) 

HIGH DOSE LOW DOSE
 

CONTROL CONTROL LOW DOSE HIGH DOSE
 

TUMOK SUMMARY
 

TOTAL ANIMALS WITH PRINAPY TUMCPS* 2 2 22 23
 TOTAL PRIMAPY TUMORS 2 2 26 30
 

TOTAL ANIMALS WITH BENIGN TUMORS 2 2 1U 13
 TOTAL BENIGN TUMORS 2 2 14 16
 

TOTAL ANIMALS WITH MALIGNANT TUMORS 10 12
 

TOTAL MALIGNANT TUHCRS 11 13
 

TOTAL ANIMALS WITH SECONDARY TUMORS» 1 1
 

TOTAL SECONDARY TUMORS 1 1
 

TOTAL ANIMALS WITH TUMORS UNCERTAINBENIGN OR MALIGNANT 1 1
 TOTAL UNCERTAIN TUMORS 1 1
 

TOTAL ANIMALS WITH TUMORS UNCERTAINPRIMARY OR METASTATIC
 

TOTAL UNCERTAIN TUMORS
 

• PRIMARY TUMORS: ALL TUMORS EXCEPT SECONDARY TUMORS
 

I SECONDARY TUMORS: METASTATIC TUMORS OR TUMORS INVASIVE INTO AN ADJACENT ORGAN
 

48
 
TABLE A2.
 

SUMMARY OF THE INCIDENCE OF NEOPLASMS IN FEMALE RATS
 

FED MALATHION IN THE DIET 

HIGH DOSE 

CONTROL 

LOW DOSE 

CONTROL LOW DOSE HIGH DOSE 

iNIMALS INITIALLY IN STODT 

INIMALS MBCBOPSIED 

iNIMALS EXAMINED HISTOFATHOIOGICALLY 

5 

5 

5 

10 

10 

10 

50 

50 

50 

50 

50 

50 

INTEGUMENTARY SYSTEH 

•SUBCOT TISSUE 

FIBROSARCOMA 

(5) (10) (50) 

1 (2%) 

(50) 

1 {2%) 

BESPIRATOBY SYSTEH 

•NASAL CAVITY 

CABCINOMA,NOS 

«LONG 

ALVEOLAR/BRONCHIOLAR ADINOHA 

FIBROSARCOMA, METASTATIC 

:5> 

(5) 

(10) 

(10) 

(50) 

(50) 

1 (2%) 

1 [2%) 

J50) 

1 i2%) 

(50) 

 :2*) 

HEMATOPOIETIC SYSTEM 

«SPLEEN 

HEMANGIOMA 

:io) 149) 

1 (2%) 

r^9) 

1 12%) 

CIRCULATOBY SYSTEM 

NONE 

DIGESTIVE SYSTEM 

«LIVER 

NEOPLASTIC NODDLE 

HEPATOCELLULAR CARCINOMA 

HEMANGIOMA 

(5) (10) (50) 

1 [2%) 

(49) 

2 («%) 

1 (2%) 

DBINAFY SYSTEM 

«KIDNEY 

WIXEE TUMOR. MALIGNANT 

:5) no) 

1 f10%) 

« NUMBER OF ANIMALS HITH TISSUE EXAMINED MICROSCOPICALLY • NUMB*P OF ANIMALS NECRCPSIED 

:50) 

1 12%) 

(50) 

49
 
TABLE A2. FEMALE RATS: NEOPLASMS (CONTINUED)
 

HIGH DOSE LOW DOSE
 

CONTROL CONTROL
 

ENDOCRINE SYSTEM
 

•PITUITARY	 (42)
 

CARCINCMA,NOS
 

ADENOMA, NOS
 

CHROMOPHOBE ADENOMA 3 (30%)
 

CHROMOPHOBE CARCINOMA
 

«ADRENAL (5) (10)
 

CORTICAL ADENOMA
 

PHEOCHROMOCYTOMA 1 (10%)
 

tTHYROID (5) (10)
 

FOLLICULAR-CELL ADENOMA
 

FOLLICULAR-CELL CARCINOMA
 

C-CELL ADENOMA
 

#PANCREATIC ISLETS (5) (10)
 

ISLET-CELL ADENOMA
 

ISLET-CELL CARCINOMA
 

REPRODUCTIVE SYSTEM
 

«MAMMARY GLAND	 Π0)
 

ADENOMA, NOS
 

ADENOCARCINOMA, NOS
 

FIBROMA
 

FIBROADENOMA
 

iUTERUS (5) (10)
 

LEIOMYOSARCOMA
 

ENDOMETRIAL STROMAL POLYP 2 £20%)
 

NERVOUS SYSTEM
 

tBRAIN C10)
 

CARCINOMA, NOS, METASTATIC
 

HAMARTOMA
 

GRANULAR-CELL TUMOR, BENIGN
 

GLIOMA, NOS
 

SPECIAL SENSE ORGANS
 

NONE
 

i NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 • NUMBER OF ANIMALS NECBOPSIED
 

50
 

LOW DOSE
 

(42)
 

2 (5%)
 

8 (19%)
 

(49)
 

3 (6%)
 

(48)
 

1 t2%)
 

(50)
 

2 (4%)
 

(50)
 

1 (2%)
 

2 :«%>
 6 (12*)
 

(»8)
 

1 t2%)
 

:50)
 

1 12%)
 

1 (2%)
 

HIGH DOSE
 

:u5)
 

 :2%)
 

7 (16%)
 

1 J2%)
 

C*8)
 

(U9)
 

1 (2%)
 

3 t6%)
 

2 :<»%)
 

(50)
 

1 t2%)
 

:50)
 

1 (2%)
 

1 12%)
 

1 <2%)
 

7 114%)
 

(ft6)
 

1 (2%)
 

1 (2%)
 

(49)
 

1 (2%)
 

1 :2%)
 

1 J2%)
 
TABLE A2. FEMALE RATS: NEOPLASMS (CONTINUED)
 

HIGH DOSE 

CONTROL 

LOW DOSE 

CONTROL LOW DOSE HIGH DOSE 

MUSCULOSKELETAL SYSTEM 

NONE 

EODY CAVITIES 

NONE 

ALL OTHEP SYSTEMS 

•MULTIPLE ORGANS 

FIBROUS HISTIOCYTOMA, MALIGNANT 

MO) :50) J50) 

1 (2*) 

PNTMAL DISPOSITION SUMMARY 

ANIMALS INITIALLY IN STUDY 

NATURAL DEATHS 

MORIBUND SACRIFICE 

SCHEDULED SACRIFICE 

ACCIDENTALLY KILLED 

TERMINAL SACRIFICE 

ANIMAL MISSING 

5 

1 

α 

10 

1 

9 

50 

2 

10 

38 

50 

1 

18 

31 

3 INCLUDES AUTOLYZED ANIMALS 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED

• NUMBER OF ANIMALS NECRCPSIED 

 MICROSCOPICALLY 

51
 
TABLE A2. FEMALE RATS: NEOPLASMS (CONTINUED)
 

HIGH DOSE LOW DOSE
 

CONTROL CONTROL LOW DOSE
 

TUMOF SUMMARY
 

TOTiL ANIMALS WITH PRIMARY TUMORS* 6 23
 

ΤΟΤAL PBIMARY TUMORS 7 33
 

TOTAL ANIMALS WITH BENIGN TUMORS 6 20
 

TOTHL EENIGN TUMORS 6 29
 

TOTAL ANIMALS WITH MALIGNANT TUMORS 1 U
 

ΤΌ^Α MALIGNANT TUMORS 1 U
 

TOTAL ANIMALS WITH SECONDARY TUMORS# 1
 

TOTAL SECONDARY TUMORS 1
 

TOTAL ANIMALS WITH TUMORS UNCERTAINBENIGN OF MALIGNANT
 

TOTAL UNCERTAIN TUMORS
 

TOTAL ANIMALS WITH TUMORS UNCERTAINPRIMARY OR METASTATIC
 

TOTAL UNCERTAIN TUMORS
 

* PRIMARY TUMORS: ALL TUMORS EXCEPT SECONDARY TUMORS
 

# SECONDARY TUMORS: METASTATIC TUMORS OR TUMORS INVASIVE INTO AN ADJACENT ORGAN
 

HIGH DOSE
 

28
 

37
 

21
 

23
 

12
 

12
 

2
 

2
 

2
 

2
 
APPENDIX B
 

SUMMARY OF THE INCIDENCE OF NEOPLASMS IN
 

MICE FED MALATHION IN THE DIET
 

53
 

TABLE B1.
 

SUMMARY OF THE INCIDENCE OF NEOPLASMS IN MALE MICE
 

FEOMALATHIONINTHEDIET
 

CONTROL LOW DOSE 

?NIMALS ΙΝΙΤΪΑΙΙ IN STUDY 10 50 

ANIMALS NECBOPSIED 10 48 

ANIMALS EXAMINED HISTOFATHOLOGICALLY 10 48 

INTEGUMENTARY SYSTEM
 

NONE
 

RESPIRATORY SYSTEM
 

#LUNG (9) (48)
 

ALVEOLAR/BRONCHIOLAP ADENOMA 1 (2%)
 

HEMATOPOIETIC SYSTEM
 

•MULTIPLE ORGANS	 J10) ;<*8)
 

LYMPHOCYTIC IEUKEMTA 1 (10%)
 

#BONE MARROW (10) (48)
 

LEUKEMIA,NOS
 

#LIVER (10) (48)
 

LEUKEMIA,NOS
 

CIRCULATORY SYSTEM
 

NONE
 

DIGESTIVE SYSTEM
 

«SALIVARY GLAND (9) (48)
 

ADENOCARCINOMA, NOS
 

#LIVER (10) (48)
 

NEOPLASTIC NODULE
 

HEPATOCELLULAR CARCINOMA 2 (20%) 7 (15%)
 

f NUMBER OP ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 * NUMBER OF ANIMALS NECROPSIED
 

55
 

HIGH DOSE
 

50
 

49
 

49
 

(49)
 

1 (2%)
 

:49)
 

(46)
 

1 (2%)
 

(49)
 

1 (2%)
 

(47)
 

1 (2%)
 

(49)
 

6 (12%)
 

11 (22%)
 
TABLE B1. MALE MICE: NEOPLASMS (CONTINUED)

 

CONTROL LOW DOSE HIGH DOSE
 

HEHANGIOHA 1 (2%)
 

URINARY SYSTEM
 

NONE
 

ENDOCRINE SYSTEM
 

NONE
 

REPRODUCTIVE SYSTEH
 

NONE
 

NERVOUS SYSTEH
 

NONE
 

SPECIAL SENSE ORGANS
 

NONE
 

MUSCULOSKELETAL SYSTEH
 

NONE
 

EODY CAVITIES
 

NONE
 

ALL OTHER SYSTEHS
 

NONE
 

# NDHBER OF ANIHALS WITH TISSUE EXAHINED MICROSCOPICALLY
 

• NUHBER OP ANIHALS NBCROPSIBD
 

56
 
TABLE B1. MALE MICE: NEOPLASMS (CONTINUED) 

CONTROL LOW DOSE HIGH DOSE
 

ANIHAL DISPOSITION SUMMARY 

ANIMALS INITIALLY IN STUDY 

NATURAL DEATH» 

MORIBOND SACRIFICE 

SCHEDULED SACRIFICE 

ACCIDENTALLY KILLED 

TERMINAL SACRIFICE 

ANIMAL MISSING 

10 

1 

1 

8 

 INCLUDES ADTOLYZED ANIMALS 

TUMOR SUMMARY
 

TOTAL ANIMALS WITH PRIMARY TUMORS* 3
 TOTAL PRIMARY TUMORS 3
 

TOTAL ANIMALS WITH BENIGN TUHOFS
 

TOTAL BENIGN TUMORS
 

TOTAL ANIMALS WITH MALIGNANT *"UMOFS 3
 TOTAL MALIGNANT TUMCRS 3
 

TOTAL ANIMALS WI^H SECONDARY TUMORS»
 

TOTAL SECONDARY TUPCRS
 

TOTAL ANIMALS WITH TUPCRS UNCERTAINBENIGN OR MALIGNANT
 

TOTAL UNCERTAIN TUMCRS
 

TOTAL ANIHALS WITH TUMORS UNCERTAINPRIMARY OP METASTATIC
 

TOTAL UNCERTAIN TUMCRS
 

50 

3 

50 

1 

2 

47 47 

9 

9 

2 

2 

7 

7 

19 

21 

1 

1 

12 

14 

6 

6 

* PRIMARY TUMORS: ALL TUMORS EXCEPT SECONDARY TUMORS
 

f SECONDARY TUMORS: METASTATIC TUMORS OR TUMORS INVASIVE INTO AN ADJACENT OEGAN
 

57
 
TABLE B2.

 

SUMMARY OF THE INCIDENCE OF NEOPLASMS IN FEMALE MICE 

FED MALATHION IN THE DIET 

CONTROL LOW DOSE 

ANIMALS INITIAIIY IN STUDY 10 50 

ANIMALS NECROPSIFD 10 49 

ANIMALS EXAMINED HISTOPATHOLOGICALLY 10 49 

INTEGUMENTARY SYSTEM
 

NONE
 

RESPIRATORY SYSTEM
 

NONE
 

HEMATOPOIETIC SYSTEM
 

•MULTIPLE ORGANS (10) (49)
 

MALIGNANT LYMPHOMA, NOS 1 i2%)
 

LEUKEMIA,NOS
 

GRANULOCYTIC LEUKEMIA 1 (10%)
 

tSPLEEN (10) (48)
 

HEMANGIOMA
 

#LIVER (10) (<*9)
 

MALIG.LYMPHOMA, HISTIOCYTIC TYPE
 

CIRCULATORY SYSTEM
 

NONE
 

DIGESTIVE SYSTEM
 

iLIVER (10) (49)
 

NEOPLASTIC NODULE
 

URINARY SYSTEM
 

NONE
 

• NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

* NUMBER OF ANIMALS NECROPSIED
 

58
 

HIGH DOSE
 

50
 

48
 

47
 

(48)
 

1 12%)
 

(46)
 

1 (2%)
 

(47)
 

1 (2%)
 

(47)
 

2 (4%)
 
TABLE B2. FEMALE MICE: NEOPLASMS (CONTINUED)

 

ENDOCRINE SYSTEH
 

•PITUITARY
 

CHROMOPHOBE ADENOMA
 

•THYROID
 

FOLLICULAR-CELL ADENOMA
 

REPRODUCTIVE SYSTEM
 

«UTERUS
 

LFIOHYCMA
 

#OVARY
 TERATOMA, BENIGN
 

NERVOUS SYSTEM
 

NONE
 

SFECIAL SENSE ORGANS
 

NONE
 

MCSCULOSKEIETA1 SYSTEM
 

NONE
 

BODY CAVITIES
 

NONE
 

ALL OTHER SYSTEMS
 

CONTROL
 

(7)
 

(9)
 

(9)
 

(10)
 

LOW DOSE
 

(39)
 

1 (3%)
 

(38)
 

1 (3%)
 

(47)
 

1 (2%)
 

(48)
 

1 (2%)
 

f NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 * NUMBER OF ANIMALS NECROPSIED
 

59
 

HIGH DOSE
 

(39)
 

(40)
 

(42)
 

(45)
 
TABLE B2. FEMALE MICE: NEOPLASMS (CONTINUED) 

CONTROL LOW DOSE HIGH DOSE 

JNIMAL DISPOSITION SUMMARY 

ANIMALS INITIALLY IN STUDY

NATURAL DEATH»

MORIBUND SACFIFICE

SCHEtOIID SACRIFICE 

ACCIDENTALLY KILLED 

TERMINAL SACFIPICE

ANIMAL HISSING 

 10

 1

 1 

8

5

 50

 2

 43

 50 

4 

2 

 44 

3 INCLUDES ADTOLYZED ANIMALS 

TUMOR SUMMARY
 

TOTAL ANIMALS WITH PRIMARY TUMORS* 1 5 5
 

TOTAL PRIMARY TOHOBS 1 5 5
 

TOTAL ANIMALS WITH BENIGN TOMORS 4 1
 

TOTAL BENIGN TUMORS 4 1
 

TOTAL ANIMALS WITH MALIGNANT TUMORS 1 1 2
 

TOTAL MALIGNANT TUMORS 1 1 2
 

TOTAL ANIMALS WITH SECONDARY TUHORS#
 

TOTAL SECONDARY TUHOBS
 

TOTAL ANIMALS WITH TUMORS UNCERTAINBENIGN OR MALIGNANT 2
 

TOTAL UNCERTAIN TUHOBS 2
 

TOTAL ANIMALS WITH TUMORS UNCERTAINPRIMARY OR METASTATIC
 

TOTAL UNCERTAIN TUMORS
 

• PRIMARY TUMORS: ALL TUMORS EXCEPT SECONDARY TUMORS
 

t SECONDARY TUMORS: METASTATIC TUMORS OR TUMORS IHYASIfE INTO AN ADJACENT ORGAN
 

60
 
APPENDIX C
 

SUMMARY OF THE INCIDENCE OF NONNEOPLASTIC LESIONS
 

IN RATS FED MALATHION IN THE DIET
 

61
 

TABLE CI.

 

SUMMARY OF THE INCIDENCE OF NONNEOPLASTIC 

LESIONS IN MALE RATS FED MALATHION IN THE DIET 

HIGH DOSE 

CONTROL 

LOW DOSE 

CONTROL LOW DOSE HIGH DOSE 

INIHALS INITIALLY IN STUDY 

ANIMALS NECFOPSIED ANIMALS EXAMINED HISTOEATHOLOGICALLY 

5 

5 

5 

10 

10 

10 

50 

48 

48 

50 

50 

SO 

INTEGUMENTARY SYSTEM 

•SKIN 

INFLAMMATION, GRANULOMATOUS 

GRANULATION, TISSUE 

(5) (10) (50) 

RESPIRATORY SYSTEM 

#LONG 

ATELECTASIS 

CONGESTION, NOS EDEMA, NOS 

INFLAMMATION, CHRONIC FOCAL 

MO) 

1 

1 

1 

2 

(2%)

J2%) 

J2%) 

(48) 

1 (2%) 

«LONG/ALVEOLI 

CALCIFICATION, METASTATIC 

(5) (10) 8) (48) 

1 (2%) 

HEMATOPOIETIC SYSTEM 

«SPLEEN 

FIBROSIS 

FIBROSIS, FOCAL 

«LYMPH NODE 

INFLAMMATION, CHRONIC 

C5) 

(5) 

MO) 

(10) 

1 (10%) 

(44) 

2 (4%) 

2 (4%) 

CIRCULATORY SYSTEM 

«HEART THROMBOSIS, NOS 

THROMBUS, ORGANIZED ARTERIOSCLEROSIS, NOS 

«MYOCARDIUM 

INFLAMMATION INTERSTITIAL 

(5) 

1 (20%) 

(5) 

(10) 

(10) 

t*7)

1 (2%) 

 (50) 

(50) 

C2%) 

« NUMBER OF AVIHALS WITH TISSUE BXAHINBD • NUMBER OF ANIMALS NBCROPSIED MICROSCOPICALLY 

63
 
TABLE C1. MALE RATS: NONNEOPLASTIC LESIONS (CONTINUED)

 

HIGH DOSE
 

HIGH DOSE LOW DOSE 

CONTROL CONTROL 

FIBROSIS 

FIBROSIS, FOCAL 

fENDOCARDIOH FIBROSIS 

FIBROSIS, FOCAL 

(5) (10)

1 (10%) 

•AORTA ARTERIOSCLEROSIS, NOS 

(5) (10) 

MEDIAL CALCIFICATION 

DIGESTIVE SYSTEM
 

•LIVER	 ;5)
 

INFLAHHATION, FOCAL GRANOLOHATOD 1 (20%)
 

GRANULOMA, FOREIGN BODY
 DEGENERATION, BALLOONING
 

DE'GENERATION PARENCHYMATOUS
 

METAMORPHOSIS FATTY 1 (20%)
 

FOCAL CELLULAR CHANGE
 ANGIECTASIS
 

•HEPATIC CAPSULE	 (5) (9)
 

ANGIECTASIS
 

•BILI DOCT	 (5) (10)
 

INFLAHHATION, CHRONIC
 

HYPERPLASIA, NOS
 

HYPERPLASIA, FOCAL
 HYPERPLASIA, DIFFUSE
 

•PANCREAS	 (5) (10)
 

INFLAMMATION, CHRONIC
 

PERIARTERITIS
 

•PANCREATIC ACINUS	 (5) (10)
 

ATROPHY, NOS
 

•STOMACH	 (5) (10)
 

CALCIFICATION, METASTATIC 1 (20%)
 

UPINARY SYSTEM
 

tKIDNEY 

INFLAMMATION. CHRONIC 4 (80%l 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

• NUMBER OF ANIMALS NECROPSIED
 

LOW DOSE
 

t2%)
 

(47)
 

(48)
 

1 J2%)
 

1 (2%)
 

2 t4%)
 

1 :2%)
 

2 !4%)
 

(47)
 

(48)
 

1
 

1
 

1
 

(45)
 

3
 

1 (2%)
 

(48)
 

2
 

33
 

(50)


3
 

1
 

(50)
 

1
 

4
 

2
 

2
 

(50)
 

1
 

(50)
 

1
 

1
 

1
 

(49)
 

1
 

(4 9)
 

1
 

(47)
 

3
 

(6%)
 

[2%)
 

t2%)
 

<8%)


t4%)
 

(2%)
 

t2%)
 

(2%)
 

12%)
 

(2%)
 

(2%)
 

(6%)
 

33 (66%1
 
LOW DOSE HIGH DOSE 

iURINARY BLADDER
 

INFLAMMATION, ACUTE DIFFUSE
 

INFLAMMATION, CHRONIC
 

INFLAMMATION, CHRONIC FOCAL
 

ENDOCRINE SYSTEM
 

• PITUITARY
 

CYST, NOS
 

HYPERPLASIA, NOS
 

HYPERPLASIA, FOCAL
 

#ADRENAL
 

DEGENERATION, CYSTIC
 

#ADREN*L CORTEX
 

METAMORPHOSIS FATTY
 

HYPERPLASIA, FOCAL
 

fTHYROIE
 

CYSTIC FOLLICLES
 

FOLLICULAR CYST, NOS
 

MULTIPLE CYSTS
 

ATROPHY, NOS
 

HYPERPLASIA, C-CELL
 

HYPERPLASIA, FOLLICULAR-CELL
 

METAPLASIA, SQUAMOUS
 

fTHYROIE FOLLICLE
 

ATROPHY, NOS
 

•PARATHYROID
 

HYPERPLASIA, NOS
 

HYPERPLASIA, DIFFUSE
 

REPRODUCTIVE SYSTEM
 

•MAMMARY GLAND
 

CYST, NOS
 

HYPERPLASIA, NOS
 

DYSPLASIA, NOS
 

fPPOSTATE
 

INFLAMMATION, SUPPUBA^VJ.
 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

* NUMBER OF ANIMALS NECROPSIED
 

TABLE CI. MALE RATS: NONNEOPLASTIC LESIONS (CONTINUED)
 

HIGH DOSE 

CONTROL 

J5) 

[l\)
 

(5)
 

(5)
 

(5)
 

(5) 

(3) 

2 (67%) 

(5)
 

LOW DOSE
 

CONTROL
 

no) 

(10)
 

(10)
 

(9)
 

1 (11*)
 

(9) 

(3) 

)
 

1 (10%)
 

(10)
 

1

1

12 

1 

1 

(46) 

1 

(46) 

1 

3 

(41) 

1 

1 

7 

(41) 

(24) 

2 

ι


(45)
 

[2%) 

[2%) 

(28%) 

\2%) 

[2%) 

(2%) 

(2%) 

:7%) 

\2%) 

\2%) 

(17%) 

(8%) 

 :2%)
 

t42) 

1

10 

2 

2 

(50) 

(50) 

2 

(47) 

3 

1 

1 

3 

8 

1 

(47) 

1 

(26) 

1 

1 

(50)
 

(48)
 

 (2%) 

(22%) 

:4%) 

(4%) 

(6%) 

(2%) 

[2%) 

J6%) 

{17%) 

t2%) 

(2%) 

(4%) 

f4%) 

65
 
TABLE C1. MALE RATS: NONNEOPLASTIC LESIONS (CONTINUED) 

HIGH DOSE

CONTROL

 LOW DOSE 

 CONTROL LOW DOSE HIGH DOSE 

INFLAMMATION, ACUTE SUPPURATIVE INFLAMMATION, ACUTE NECROTIZING

INFLAMMATION ACUTE AND CHRONIC

tTESTTS

PERIARTERITIS

ATROPHY, NOS

HYPERPLASIA, INTERSTITIAL CELL

 (5)

 1 (20%)

 1 (10%)

 1 (10%)

 (9)

 1 J11%)

 2 J4%) 

 (45)

 2 (4%) 

 11 [24%)

 1 (2%) 

 1 {2%) 

 (49) 

 4 {8%) 

 1 J2%) 

NERVOUS SYSTEM 

#BRAIN/HENINGES

MULTIPLE CYSTS

 (5) (10) (48) (48) 

 1 (2%) 

SFECIAL SENSE ORGANS 

NONE 

MUSCULOSKELETAL SYSTEM 

NONE 

BODY CAVITIES 

• MESENTERY

PERIARTERITIS

 (5) (10) (48)

 4 (8%) 

 (50) 

ALL OTHER SYSTEMS 

NONE 

SPECIAL MORPHOLOGY SUMMARY 

NO LESION REPORTED 4

AUTOLYSIS/NO «ECBOPSY

f «UMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY • «UMBER OF ANIMALS NECROPSIED 

3

 2 

7 

66
 
TABLE C2.
 

SUMMARY OF THE INCIDENCE OF NONNEOPLASTIC LESIONS
 

IN FEMALE RATS FED MALATHION IN THE DIET
 

HIGH DOSE 

CONTROL 

LOW DOSE 

CONTROL 

iNIMALS INITIAtlY IS STUDY 

INIMALS NECFOPSIED 

ANIMALS EXAMINED HISTOPATHCLOGIOALLΥ 

5 

5 

5 

10 

10 

10 

INTFGOHFNTARY SYSTEM
 

*SKIN (5) (10)
 

ULCER, NOS
 

RISPIFATORY SYSTEM
 

«LUNG (5) (10)
 

INFLAMMATION, FOCAL
 

INFLAMMATION, ACUTE HEMORRHAGIC
 

HEMATOPOIETIC SYSTEM
 

«SPLEEN (5) (10)
 

INFLAMMATION, CHFONIC
 

HYPERPLASIA, RETICULUM CELL
 

MYELOID METAPLASIA 1 (10%)
 

tPANCRFATIC L.NODE (5) (9)
 

INFLAMMATION, NOS 1 (11%)
 

:iRCDLATORY SYSTEM
 

tMYOCARDIOM (5) (10)
 

INFLAMMATION, CHRONIC FCCAL
 

FIBROSIS, FOCAL
 

«ENDOCARDIUM (5) (10)
 

FIBROSIS
 

DIGESTIVE SYSTEM
 

(10) •LIVER
 

CONGESTION. NOS 1 (20%)
 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

* NUMBER OF ANIMALS NECROPSIED
 

67
 

LOW DOSE
 

50
 

50
 

50
 

(50)
 

1 (2%)
 

(50)
 

1 :2%)
 

(49)
 

(43)
 

(5o)
 

1 (2%)
 

(50)
 

1 (2%)
 

(50)
 

HIGH DOSE
 

50
 

50
 

50
 

(50)
 

J50)
 

1 (2%)
 

(49)
 

1 (2%)
 

1 (2%)
 

(U3)
 

:50)
 

1 (2*)
 

(50)
 

(49)
 
TABLE C2. FEMALE RATS: NONNEOPLASTIC LESIONS (CONTINUED)
 

DEGENERATION PARENCHYMATOUS
 

NFCROSIS, NOS
 

NECROSIS, FOCAL
 

METAMORPHOSIS FATTY
 

FOCAL CELLULAR CHANGE
 

ANGIECTASIS
 

•BILE DDCT
 

INFLAMMATION, NOS
 

INFLAMMATION, ACUTE
 

INFLAMMATION, CHRONIC
 

HYPERPLASIA, NOS
 

HYPERPLASIA, FOCAL
 

«PANCREATIC ACINOS
 

ATROPHY, FOCAL
 

«STOMACH
 

EROSION
 

URINARY SYSTEM
 

«KIDNEY
 

GLOMERULONEPHRITIS, NOS
 

INFLAMMATION, CHRONIC
 

INFARCT, NOS
 

•KIDNEY/CORTEX
 

CYST, NOS
 

«KIDNEY/TUBULE
 

DEGENERATION, NOS
 

ENDOCRINE SYSTEM
 

fPITUITARY
 

CYST, NOS
 

CONGESTION,· NOS
 

HEMORRHAGE
 

DEGENERATION, CYSTIC
 

HYPERPLASIA, NOS
 

HYPERPLASIA, FOCAL
 

ANGIECTASIS
 

«ADRENAL
 

HIGH DOSE
 

CONTROL
 

1 (20%)
 

1 (20%)
 

(5)
 

(5)
 

(5)
 

t5)
 

2 (40%)
 

(5)
 

(5)
 

!5)
 

(5)
 

LOW DOSE
 

CONTROL
 

2 f20%)
 

(10)
 

(10)
 

(10)
 

(10)
 

(10)
 

(10)
 

CIO)
 

(10)
 

LOW DOSE
 

 :2%)
 2 :u%)
 

 :2%)
 2 ;u%)
 

(50)
 

 :2%)
 

 :2%)
 

2 {*%)
 

(50)
 

1 (2%)
 

(*8)
 

1 (2%)
 

:50)
 

3 :e%)
 

(50)
 

1 (2%)
 

(50)
 

[H2)
 

 :2%)
 

1 (2%)
 

3 {!%)
 

(*9)
 

2 IW
 

HIGH DOSE
 

2 (U%)
 

1 :2%)
 

8 :16%)
 

2 :«»%)
 

8 (16%)
 

(50)
 

2 Ji»%)
 

1 t2%)
 

 :2%)
 

U t8%)
 

(50)
 

1 (2%)
 

(<»9)
 

(50)
 

1 (2%)
 

11 (22%)
 

1 J2%)
 

(50)
 

(50)
 

1 (2%)
 

(U5)
 

1 (2%)
 

1 !2%)
 

1 (2%)
 

3 (7%)
 

(i*8)
 

* NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

• NUMBER OF ANIMALS NECROPSIED
 

68
 
TABLE C2. FEMALE RATS: NONNEOPLASTIC LESIONS (CONTINUED) 

HIGH DOSE LOW DOSE
 

CONTROL CONTROL LOW DOSE HIGH DOSE
 

NECROSIS, NOS 1 (2%)
 

HETAHORPHOSIS FATTY 1 (2%)
 

ANGTECTASIS 1 (10%) 2 (2%) 1 (2%)
 

#ADRENAI CORTEX (5) (10) (49) (48)
 

DEGENERATION, CYSTIC 7 (14%) 1 (2%)
 

HETAHORPHOSIS FATTY 2 J4%)
 

HYPERPLASIA, FOCAL 1 (10%) 1 C2%)
 

ANGIECTASIS 4 !8%)
 

#THYROIE (5) (10) (48) (4 9)
 

CYSTIC FOLLICLES 3 (6%)
 

HYPERPLASIA, C-CELL 5 (1O%) 3 C6%)
 

HYPERPLASIA, FOLLICOLAR-CELL 3 (6%)
 

fTHYROir FOLLICLE (5) (10) (48) (49)
 

ATROPHY, MOS 1 (2%)
 

REPRODUCTIVE SYSTEH
 

•HAHHARY GLAND	 (5) (10) (50) (50)
 

HYPERPLASIA, NOS 1 (10%) 4 (8%)
 

DYSPLASIA, NOS 1 Σ2%)
 

FIBROSING ADENOSIS 1 (10%)
 

•HAHHARY LOEULE	 (5) (10) (50) (50)
 

HYPERPLASIA, NOS 1 t10%)
 

# UTERUS (5) (10) (48) (46)
 

HYDROHETRA 1 (2%)
 

INFLAHHATION, CHRONIC 1 t2%)
 

•OVARY	 (5) (10) (49) (48)
 

FOLLICULAR CYST, NOS 1 (2%)
 

NERVOUS SYSTEH
 

NONE
 

SPECIAL SENSE ORGANS
 

NONE
 

HUSCULOSKELETAL SYSTEH
 

NONE
 

t RUBBER OF ANIHALS WITH TISSUE KAHINB D MICROSCOPICALLY
 * NUHBBR OF ANIHALS NECBOPSI1D
 

69
 
TABLE C2. FEMALE RATS: NONNEOPLASTIC LESIONS (CONTINUED)
 

HIGH DOSE 

CONTROL 

LOW DOSE 

CONTROL LOW DOSE HIGH DOSE 

ECDY CAVITIES 

•MESENTERY 

PERIARTERITIS (10) (10) :50) (50) 

1 12%) 

ALL OTHER

NONE 

 SYSTEMS 

SPECIAL MORPHOLOGY SUMMARY 

NO LESION REPORTED 2 

# NUMBER Cf ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY 

* NUMBER OF ANIMALS NECPOPSIED 

2 Θ 6 

70
 
APPENDIX D
 

SUMMARY OF THE INCIDENCE OF NONNEOPLASTIC LESIONS
 

IN MICE FED MALATHION IN THE DIET
 

71
 

TABLE 01.

 

SUMMARY OF THE INCIDENCE OF NONNEOPLASTIC LESIONS 

IN MALE MICE FEO MALATHION IN THE DIET 

HIGH DOSE
 

50
 

49
 

49
 

(49)
 

C35)
 

(35)
 

2 C6»)
 

(49)
 

1 [2%)
 

2 :4*)
 

(46)
 

1 ?2%1
 

JNIMALS INITIALLY IN STODI
 

iNIMALS NECFOPSXED
 1NIHALS IXAHINED HISTOEATHOLOGICALLY
 

INTEGUMENTARY SYSTEM
 

NONE
 

RFSPIRATCRY SYSTEM
 

#LONG
 

INFLAMMATION, NOS
 

HEMATOPOIETIC SYSTEM
 

iLYHPH NODE
 

INFLAMMATION, FOCAL
 

iMESENTERIC L· NODE
 

INFLAMMATION, CHRONIC
 

HYPERPLASIA, LYMPHOID
 

CIRCULATORY SYSTEM
 

NONE
 

DIGESTIVE SYSTEM
 

#LIVEP
 

INFLAMMATION, CHRONIC
 

DEGENERATION PARENCHYMATOUS
 

NECROSIS, NOS
 

#PEYERS PATCH
 

INFLAMMATION, NOS
 

HYPERPLASIA. LYMPHOID
 

CONTROL LOW DOSE
 

10 50
 

10 48
 

10 48
 

(S)
 

C8)
 

(8)
 

(10)
 

(10)
 

(48)
 

1 (2%)
 

(43)
 

1 (2%)
 

(4 3)
 

1 (2%)
 

1 12%)
 

(48)
 

1 (2%)
 

(44)
 

1 (2%)
 

1 f2%l
 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

• NUMBER OF ANIMALS NECROPSIED
 

73
 
TABLE D1. MALE MICE: NONNEOPLASTIC LESIONS (CONTINUED)
 

URINARY SYSTEM
 

•KIDNEY
 

INFLAMMATION, CHRONIC FCCAL
 

«KIDNIY/CORTEX
 

INPARCT, NOS
 

ENDOCRINE SYSTEM
 

«PITUITARY
 

CYST, NOS
 

REPRODUCTIVE SYSTEM
 

«TESTIS
 

ATROPHY, NOS
 

NERVOUS SYSTEM
 

NONE
 

SPECIAL SENSE ORGANS
 

NONE
 

MUSCULOSKELETAL SYSTEM
 

NONE
 

BODY CAVITIES
 

NONE
 

ALL OTHER	 SYSTEMS
 

NONE
 

CONTROL
 

no)
 

(10)
 

(6)
 

Π0)
 

1	 (10%)
 

LOW DOSE
 

:*»7)
 

(<»7)
 

1 (2%)
 

:u2)
 

1 (2%)
 

rue)
 

HIGH DOSE
 

:4 9)
 

1 (2%)
 

(49)
 

C40)
 

J46)
 

* NUMBER Of ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

• NUMBER OF ANIMALS NECROPSIID
 

74
 
TABLE D1. MALE MICE: NONNEOPLASTIC LESIONS (CONTINUED)

 

CONTROL LOW DOSE HIGH DOSE 

SPECIAL MORPHOLOGY SUMMARY 

NO LESION REPORTED 

AUTOLYSIS/NO NECROPSY 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED

• NUMBER OF ANIMALS NECROPSIED 

6 33 

2 

 MICROSCOPICALLY 

25 

1 

75
 
TABLE D2.
 

SUMMARY OF THE INCIDENCE OF NONNEOPLASTIC LESIONS
 

IN FEMALE MICE FED MALATHION IN THE DIET
 

iNIMALS INITUIIY I* STUDY
 

INIMALS NECROPSIED
 

ANIMALS EXAMINED HISTOFATHCLOGICAtLY
 

INTIGUHENIAPY SYSTEM
 

NONE
 

RESPIRATORY SYSTEH
 

«LONG
 

INFLAMMATION, NOS
 

HYPERPLASIA, ALVEOLAR EPITHELIUM
 

HEMATOPOIETIC SYSTEH
 

«SPLEEN
 

INPLAHBATION, NOS
 

HYPERPLASIA, LYMPHOID
 

«HEPATIC IYHPH NODE
 

INFLAMMATION, GRANULOMATOUS
 

•THYMUS
 

HYPERPLASIA, LYHPHOIE
 

CIRCULATORY SYSTEH
 

NONE
 

DIGESTIVE SYSTEM
 

«LIVER
 

DEGENERATION PARENCHYMATOUS
 

*BILE DUCT
 

INFLAMMATION. CHRONIC
 

CONTROL
 

10
 

10
 

10
 

(9)
 

Π0)
 

1 00%)
 

(10)
 

1 (10%)
 

(10)
 

(10)
 

LOW DOSE HIGH DOSE
 

50 50
 

48
 

49 47
 

(49) (47)
 

1 (2%)
 

1 :2%)
 

:<*8) :46)
 

1 (2%)
 

1 t2%)
 

(4 3) (38)
 

(5)	 (1)
 

1 (100%)
 

(<*9) (47)
 

1 (2%)
 

(49)	 (48)
 

1 (2%)
 

« NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 • HOHBER OP AMTHA1S NECRCPSIBD
 

76
 
TABLE D2. FEMALE MICE: NONNEOPLASTIC LESIONS (CONTINUED)

 

HIGH DOSE
 

:<»5)
 

1 (2%)
 

(«2)
 

3 (7%)
 

1 {2%)
 

(42)
 

1 12%)
 

10 J2ft%)
 

(45)
 

2 (4%)
 

«PETERS PATCH
 HYPERPLASIA, ITHPHOID
 

OFINARY SYSTEM
 

NONE
 

ENDOCRINE SYSTEM
 

NONE
 

REPRODUCTIVE SYSTEH
 

# UTERUS
 

HYDROHETRA
 PYOMETRA
 INFLAMMATION, CHRONIC
 

«UTERUS/ENEOMETRIUH
 

TNPLAMHATION, SUPPURATIVE
 DEGENERATION, CYSTIC
 

HYPERPLASIA, CYSTIC
 

#OVARY
 

FOLLICULAR CYST, NOS
 

INFLAMMATION, NOS
 

INFLAMMATION, SUPPURATIVE
 NECROSIS, NOS
 

NERVOUS SYSTEM
 

NONE
 

SFECIAL SENSF ORGANS
 

NONE
 

MDSCULOSKEIETAII SYSTE SYSTEMM
 

.NON NON
E
 E

CONTROL
 

no)
 

(9)
 

(9)
 

1 (11%)
 

(10)
 

4 :«*o%)
 

1 (10%)
 

LOW DOSE
 

:47)
 

(47)
 

1 12%)
 

(47)
 

1 (2%)
 

12 £26%)
 

(48)
 

3 (6%)
 

2 J4%)
 

# NUMBER OF ANIMALS WITH TISSUE EXAMINED MICROSCOPICALLY
 

• NUMBER OF ANIMALS NECROFSIED
 

77
 
TABLE D2. FEMALE MICE: NONNEOPLASTIC LESIONS (CONTINUED)
 

CONTROL LOW DOSE HIGH DOSE 

ECDY CAVITIES 

NONE 

ALL OTHER

NONE 

 SYSTEMS 

SPECIAL MORPHOLOGY SUMMARY 

NO LESION REPORTED 

ΑϋΤΟ/NECROPSY/NO HISTO 

ADTOLYSIS/NO NECROPSY 

α 29 

1 

t NOHBER OF ANIHALS WITH TISSUE EXAMINED MICROSCOPICALLY 

* N0M6ER OF ANIMALS NECROPSIED 

25 

1 

2 

78
 
APPENDIX E
 

ANALYSES OF THE INCIDENCE OF PRIMARY TUMORS
 

IN RATS FED MALATHION IN THE DIET
 

79
 

00 

Table El· Analyses of the Incidence of Primary Tumors in Male Rats
 

Fed Malathion in the Dieta
 

Matched Pooled
 

Topography: Morphology Control Control
 

Pituitary: Adenoma, NOS
 

(not otherwise specified)
 

or Carcinoma*5 0/10(0.00) 0/46(0.00)
 

 Valuesc , d N.S. N.S.
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Pituitary: Chromophobe Adenoma^ 0/10(0.00) 6/46(0.13)
 

 Valuesc>d N.S. N.S.
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor —
 —
 

Low
 

Dose
 

3/43(0.07)
 

N.S.
 

Infinite
 

0.155
 

Infinite
 

Infinite
 

0.646
 

Infinite
 

113
 

6/43(0.14)
 

N.S.
 

Infinite
 

0.415
 

Infinite
 

1.070
 

0.308
 

3.693
 

99
 

High
 

Dose
 

1/46(0.02)
 

N.S.
 

Infinite
 

0.013
 

Infinite
 

Infinite
 

0.054
 

Infinite
 

109
 

3/46(0.07)
 

N.S.
 

Infinite
 

0.145
 

Infinite
 

0.500
 

0.086
 

2.186
 

102
 
Table El. Analyses of the Incidence of Primary Tumors in Male Rats
 

Fed Malathion in the Dieta
 

(continued)
 

Topography: Morphology
 

Thyroid: Follicular-cell
 

Adenoma or Carcinoma*5
 

 Values0>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)^
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Thyroid: C-cell Adenoma**
 

 Values0»d
 

Relative Risk (Matched Control)^
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Matched
 

Control
 

1/14(0.07)
 

N.S.
 

108
 

0/14(0.00)
 

N.S.
 

—
 

Pooled Low 

Control Dose 

4/46(0.09) 3/41(0.07) 

N.S. N.S. 

1.024 

0.094 

52.448 

0.841 

0.131 

4.671 

__ 113 

2/46(0.04) 1/41(0.02) 

N.S. N.S. 

Infinite 

0.019 

Infinite 

0.561 

0.010 

10.353 

— 113 

High
 

Dose
 

7/47(0.15)
 

N.S.
 

2.085
 

0.314
 

91.743
 

1.713
 

0.469
 

7.483
 

100
 

3/47(0.06)
 

N.S.
 

Infinite
 

0.192
 

Infinite
 

1.468
 

0.176
 

16.917
 

109
 
Table El. Analyses of the Incidence of Primary Tumors in Male Rats
 

(continued)
 

Topography: Morphology
 

Pancreatic Islets:
 

Islet-cell Adenomab
 

 Valuesc>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Adrenal Gland: Cortical Adenoma*5
 

 Values0»d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Fed Malathion in the Dieta
 

Matched Pooled
 

Control Control
 

0/15(0.00) 2/53(0.04)
 

N.S. N.S.
 

mmmm
 

0/15(0.00) 2/52(0.04)
 

N.S. N.S.
 

— __
 

Low
 

Dose
 

1/45(0.02)
 

N.S.
 

Infinite
 

0.019
 

Infinite
 

0.589
 

0.010
 

10.912
 

113
 

2/46(0.04)
 

N.S.
 

Infinite
 

0.102
 

Infinite
 

1.130
 

0.086
 

15.029
 

113
 

High
 

Dose
 

3/49(0.06)
 

N.S.
 

Infinite
 

0.195
 

Infinite
 

1.622
 

0.194
 

18.739
 

100
 

0/50(0.00)
 

N.S.
 

——
 

0.000
 

0.000
 

3.516
 

„
 
Table El. Analyses of the Incidence of Primary Tumors in Male Rats
 

(continued)
 

Topography: Morphology
 

Adrenal: Pheochromocytoma"
 

 Values0>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Kidney: Mixed Tumor, Malignant^
 

 Valuesc>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Fed Malathion in the Dieta
 

Matched Pooled
 

Control Control
 

0/15(0.00) 2/52(0.04)
 

N.S. N.S.
 

__ ...
 

0/15(0.00) 0/53(0.00)
 

N.S. N.S.
 

—
 —
 

Low High 

Dose Dose 

0/46(0.00) 3/50(0.06) 

N.S. N.S. 

Infinite 

— 0.192 

— Infinite 

0.000 1.560 

0.000 0.186 

3.814 18.027 

113 100 

2/48(0.04) 1/50(0.02) 

N.S. N.S. 

Infinite Infinite 

0.098 0.016 

Infinite Infinite 

Infinite Infinite 

0.327 0.056 

Infinite Infinite 

100 100 
Table El· Analyses of the Incidence of Primary Tumors in Male Rats
 

Fed Malathion in the Dieta
 

(continued)
 

Topography: Morphology 

Matched 

Control 

Pooled 

Control 

Low 

Dose 

High 

Dose 

Liver: Neoplastic Nodule or 

Hepatocellular Carcinoma^ 0/14(0.00) 1/53(0.02) 2/47(0.04) 1/50(0.02) 

 Valuesc , d N.S. N.S. N.S. N.S. 

Relative Risk (Matched Control)f 

Lower Limit 

Upper Limit 

Infinite 

0.093 

Infinite 

Infinite 

0.016 

Infinite 

Relative Risk (Pooled Control)f 

Lower Limit 

Upper Limit 

2.255 

0.121 

130.193 

1.060 

0.014 

81.565 

Weeks to First Observed Tumor 113 109 

a

Dosed groups received time-weighted average doses of 4,700 or 8,150 ppm in feed.
 

^Number of tumor-bearing animals/number of animals examined at site (proportions).
 

c

Beneath the incidence of tumors in a control group is the probability level for the Cochran-


Armitage test when Ρ < 0.05; otherwise, not significant (N.S.) is indicated. Beneath the incidence of tumors in a dosed group is the probability level for the Fisher exact test for the
 

comparison of that dosed group with the matched-control group (*) or with the pooled-control
 

group (**) when Ρ < 0.05 for either control group; otherwise, not significant (N.S.) is indicated·
 

d

A negative trend (N) indicates a lower incidence in a dosed group than in a control group.
 

e

The probability level for departure from linear trend is given when Ρ < 0.05 for any comparison.
 

f

The 95% confidence interval of the relative risk between each dosed group and the
 

specified control group.
 
Table E2. Analyses of the Incidence of Primary Tumors in Female Rats
 

Fed Malathion in the Dieta
 

Matched Pooled Low High
 

Topography: Morphology Control Control Dose Dose
 

Pituitary: Adenoma, NOS
 

(not otherwise specified)
 

or Carcinoma*5 0/15(0.00) 1/46(0.02) 2/42(0.05) 1/45(0.02)
 

 Values0>d N.S. N.S. N.S. N.S.
 

Relative Risk (Matched Control)f Infinite Infinite
 

Lower Limit 0.112 0.019
 

Upper Limit Infinite Infinite
 

Relative Risk (Pooled Control)f 2.190 1.022
 

oo
 Lower Limit 0.120 0.013
 ON Upper Limit 126.082 78.492
 

Weeks to First Observed Tumor _—
 105 109
 

Pituitary: Chromophobe Adenoma*5 3/15(0.20) 9/46(0.20) 8/42(0.19) 7/45(0.16)
 

 Values0»d N.S. N.S. N.S. N.S.
 

Relative Risk (Matched Control)f 0.952 0.778
 

Lower Limit 0.277 0.214
 

Upper Limit 5.086 4.276
 

Relative Risk (Pooled Control)f 0.974 0.795
 

Lower Limit 0.358 0.275
 

Upper Limit 2.571
 2.187
 

Weeks to First Observed Tumor 98 — 108 102
 
Table E2. Analyses of the Incidence of Primary Tumors in Female Rats
 

(continued)
 

Topography: Morphology
 

Thyroid: Follicular-cell
 

Adenoma or Carcinoma*5
 

 Valuesc>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Thyroid: C-cell Adenomab
 

 Values0>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Fed Malathion in the Dieta 

Matched 

Control 

Pooled 

Control 

Low 

Dose 

High 

Dose 

0/15(0.00) 0/46(0.00) 0/48(0.00) 4/49(0.08) 

N.S. - 0.026 N.S. N.S. 

— 

— 

Infinite 

0.301 

Infinite 

— 

— 

Infinite 

0.872 

Infinite 

__ 105 

0/15(0.00) 1/46(0.02) 1/48(0.02) 2/49(0.04) 

N.S. N.S. N.S. N.S. 

Infinite 

0.018 

Infinite 

Infinite 

0.096 

Infinite 

0.958 

0.012 

73.689 

1.878 

0.101 

108.485 

113 109 
__ 

__ 

Table E2. Analyses of the Incidence of Primary Tumors in Female Rats
 

Fed Malathion in the Dieta
 

(continued)
 

Topography: Morphology
 

Pancreatic Islet:
 

Islet-cell Adenoma*5
 

 Values0>d
 

Departure from Linear Trende
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Adrenal Gland: Cortical Adenomab
 

 Values0

>d
 

Departure from Linear Trende
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 —
 

Low
 

Dose
 

2/50(0.04)
 

N.S.
 

Infinite
 

0.094
 

Infinite
 

Infinite
 

0.315
 

Infinite
 

113
 

3/49(0.06)
 

N.S.
 

Infinite
 

0.195
 

Infinite
 

Infinite
 

0.615
 

Infinite
 

113
 

High
 

Dose
 

0/50(0.00)
 

N.S.
 

—
 

——
 

—
 

0/48(0.00)
 

N.S.
 

Matched
 

Control
 

0/15(0.00)
 

N.S.
 

0/15(0.00)
 

N.S.
 

Pooled
 

Control
 

0/53(0.00)
 

N.S.
 

 = 0.042
 

_._
 

0/50(0.00)
 

N.S.
 

 - 0.014
 

—
 
Table E2. Analyses of the Incidence of Primary Tumors in Female Rats
 

(continued)
 

Topography: Morphology


Liver: Neoplastic Nodule or
 

Hepatocellular Carcinoma1

*


 Valuesc

»d


Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Mammary Gland: Fibroadenoma15


 Valuesc>d


Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Fed Malathion in the Dieta 

Matched 

 Control 

Pooled 

Control 

Low 

Dose 

High 

Dose 

 0/15(0.00) 1/53(0.02) 0/50(0.00) 3/49(0.06) 

 N.S. N.S. N.S. N.S. 

— 

— 

Infinite 

0.196 

Infinite 

0.000 

0.000 

19.777 

3.245 

0.271 

166.782 

109 

 0/15(0.00) 8/54(0.15) 6/50(0.12) 7/50(0.14) 

 N.S. N.S. N.S. N.S. 

Infinite 

0.513 

Infinite 

Infinite 

0.621 

Infinite 

0.810 

0.249 

2.468 

0.945 

0.313 

2.758 

61 80 
Table Ε2· Analyses of the Incidence of Primary Tumors in Female Rats
 

Fed Malathion in the Dieta
 

(continued)
 

a

Dosed groups received time-weighted average doses of 4,700 or 8,150 ppm in feed.
 

^Number of tumor-bearing animals/number of animals examined at site (proportions)·
 

c

Beneath the incidence of tumors in a control group is the probability level for the Cochran-


Armitage test when Ρ < 0.05; otherwise, not significant (N.S·) is indicated· Beneath the incidence of tumors in a dosed group is the probability level for the Fisher exact test for the
 

comparison of that dosed group with the matched-control group (*) or with the pooled-control
 

group (**) when Ρ < 0·05 for either control group; otherwise, not significant (N.S·) is indicated.
 

^A negative trend (N) indicates a lower incidence in a dosed group than in a control group·
 

e

The probability level for departure from linear trend is given when Ρ < 0·05 for any
 

comparison·
 

f

The 95% confidence interval of the relative risk between each dosed group and the
 

specified control group·
 
APPENDIX F
 

ANALYSES OF THE INCIDENCE OF PRIMARY TUMORS
 

IN MICE FED MALATHION IN THE DIET
 

91
 

Table Fl. Analyses of the Incidence of Primary Tumors in Male Mice
 

Fed Malathion in the Dieta
 

Topography: Morphology
 

Liver: Neoplastic Noduleb
 

 Valuesc , d
 

Departure from Linear Trende
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Liver: Hepatocellular
 

Carcinoma*5
 

 Values0>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Matched
 

Control
 

0/10(0.00)
 

 = 0.016
 

2/10(0.20)
 

N.S.
 

94
 

Pooled
 

Control
 

3/49(0.06)
 

N.S.
 

 = 0.030
 

5/49(0.10)
 

N.S.
 

—
 

Low
 

Dose
 

0/48(0.00)
 

N.S.
 

—
 

—
 

0.000
 

0.000
 

1.695
 

7/48(0.15)
 

N.S.
 

0.729
 

0.180
 

6.704
 

1.429
 

0.419
 

5.331
 

94
 

High
 

Dose
 

6/49(0.12)
 

N.S.
 

Infinite
 

0.364
 

Infinite
 

2.000
 

0.455
 

11.748
 

95
 

11/49(0.22)
 

N.S.
 

1.122
 

0.320
 

9.678
 

2.200
 

0.767
 

7.496
 

58
 
Table Fl· Analyses of the Incidence of Primary Tumors in Male Mice
 

Fed Malathion in the Dieta
 

(continued)
 

Topography: Morphology 

Matched 

Control 

Pooled 

Control 

Low 

Dose 

High 

Dose 

Liver: Neoplastic Nodule or 

Hepatocellular Carcinoma'5 2/10(0.20) 8/49(0.16) 7/48(0.15) 17/49(0.35) 

 Values0 » d = 0.041 = 0.019 N.S. = 0.031** 

Relative Risk (Matched Control)f 

Lower Limit 

Upper Limit 

0.729 

0.180 

6.704 

1.735 

0.540 

14.271 

Relative Risk (Pooled Control)f 

Lower Limit 

Upper Limit 

0.893 

0.300 

2.594 

2.125 

0.967 

5.122 

Weeks to First Observed Tumor 94 — 94 58 

a

Dosed groups received doses of 8,000 or 16,000 ppm in feed·
 

^Number of tumor-bearing animals/number of animals examined at site (proportions)·
 

c

Beneath the incidence of tumors in a control group is the probability level for the Cochran-


Armitage test when Ρ < 0.05; otherwise, not significant (N.S·) is indicated. Beneath the incidence of tumors in a dosed group is the probability level for the Fisher exact test for the
 

comparison of that dosed group with the matched-control group (*) or with the pooled-control
 

group (**) when Ρ < 0·05 for either control group; otherwise, not significant (N.S·) is indicated·
 

^A negative trend (N) indicates a lower incidence in a dosed group than in a control group·
 

e

The probability level for departure from linear trend is given when Ρ < 0·05 for any comparison·
 

f

The 95% confidence interval of the relative risk between each dosed group and the
 

specified control group·
 
APPENDIX G
 

ANALYSIS OF FORMULATED DIETS FOR
 

CONCENTRATIONS OF MALATHION
 

97
 

__ 

__ __ 

Table F2. Analyses of the Incidence of Primary Tumors in Female Mice
 

Fed Malathion in the Dieta
 

Topography: Morphology
 

Liver: Neoplastic Nodule*5
 

 Values0>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

VO
 

Weeks to First Observed Tumor
 

Liver: Hepatocellular
 

Carcinomab
 

 Valuesc>d
 

Relative Risk (Matched Control)f
 

Lower Limit
 

Upper Limit
 

Relative Risk (Pooled Control)f
 

Lower Limit
 

Upper Limit
 

Weeks to First Observed Tumor
 

Matched
 

Control
 

0/10(0.00)
 

N.S.
 

0/10(0.00)
 

N.S.
 

Pooled
 

Control
 

1/48(0.02)
 

N.S.
 

2/48(0.04)
 

N.S.
 

Low
 

Dose
 

0/49(0.00)
 

N.S.
 

—
 

—
 

0.000
 

0.000
 

18.270
 

0/49(0.00)
 

N.S.
 

—
 

—
 

0.000
 

0.000
 

3.309
 

High
 

Dose
 

2/47(0.04)
 

N.S.
 

Infinite
 

0.069
 

Infinite
 

2.043
 

0.111
 

117.919
 

0/47(0.00)
 

N.S.
 

——
 

—
 

—
 

0.000
 

0.000
 

95 

3.447 
Table F2· Analyses of the Incidence of Primary Tumors in Female Mice
 

Fed Malathion in the Dieta
 

(continued)
 

Matched Pooled Low High 

Topography: Morphology Control Control Dose Dose 

Liver: Neoplastic Nodule or 

Hepatocellular Carcinoma13 0/10(0·00) 3/48(0.06) 0/49(0.00) 2/47(0.04) 

 Values0>d N.S. N.S. N.S. N.S. 

Relative Risk (Matched Control)f Infinite 

Lower Limit — 0.069 

Upper Limit — Infinite 

Relative Risk (Pooled Control)f 0.000 0.681 

Lower Limit 0.000 0.059 

vo Upper Limit 1.628 5.673 

Weeks to First Observed Tumor 95 

a

Dosed groups received doses of 8,000 or 16,000 ppm in feed.
 

^Number of tumor-bearing animals/number of animals examined at site (proportions).
 

c

Beneath the incidence of tumors in a control group is the probability level for the Cochran-


Armitage test when Ρ < 0.05; otherwise, not significant (N.S.) is indicated. Beneath the incidence of tumors in a dosed group is the probability level for the Fisher exact test for the
 

comparison of that dosed group with the matched-control group (*) or with the pooled-control
 

group (**) when Ρ < 0.05 for either control group; otherwise, not significant (N.S.) is indicated·
 

^A negative trend (N) indicates a lower incidence in a dosed group than in a control group.
 

e

The probability level for departure from linear trend is given when Ρ < 0.05 for any comparison.
 

^The 95% confidence interval of the relative risk between each dosed group and the
 

specified control group.
 
APPENDIX G
 

Analysis of Formulated Diets for
 

Concentrations of Malathion
 

A 10-g sample of the diet mixture was shaken with 125 ml hexane
 

at room temperature for 16 hours, then filtered through Celite
 

with hexane washes, and reduced in volume to 10 ml. After
 

appropriate dilutions, the solution was quantitatively analyzed
 

for malathion by gas-liquid chromatography (electron-capture
 

detector, 10% DC-200 on Gas-Chrom Q column). Recoveries were
 

checked with spiked samples, and external standards were used for
 

calibration.
 

Theoretical 

Concentrations 

in Diet (ppm) 

No. of 

Samples 

Sample 

Analytical 

Mean (ppm) 

Coefficient of 

Variation (%) 

Range (ppm) 

4,000 20 4,098 4.9% 3,690-4,570 

8,000 35 8,188 4.2% 7,390-8,880 

16,000 25 16,290 5.0% 14,950-17,790 

99
 

Review of the Bloassay of Malathion* for Carcinogenicity
 

by the Data Evaluation/Risk Assessment Subgroup of the
 

Clearinghouse on Environmental Carcinogens
 

January 18, 1978
 

The Clearinghouse on Environmental Carcinogens was
 

established in May, 1976 under the authority of the
 

National Cancer Act of 1971 (P.L. 92-218). The purpose
 

of the Clearinghouse is to advise on the National Cancer
 

Institute's bioassay program to identify and evaluate
 

chemical carcinogens in the environment to which humans
 

may be exposed. The members of the Clearinghouse have
 

been drawn from academia, industry, organized labor, public
 

interest groups, State health officials, and quasi-public
 

health and research organizations. Members have been
 

selected on the basis of their experience in carcinogenesis
 

or related fields and, collectively, provide expertise in
 

organic chemistry, biochemistry, biostatistics, toxicology,
 

pathology, and epidemiology. Representatives of various
 

environmental agencies participate as ad hoc members.
 

The Data Evaluation/Risk Assessment Subgroup of the
 

Clearinghouse is charged with the responsibility of
 

providing a peer review of NCI bioassay reports on chemicals
 

studied for carcinogenicity. In this context, below is the
 

edited excerpt from the minutes of the Subgroupf

s meeting
 

at which Malathion was reviewed.
 

The primary reviewer agreed with the conclusion of
 

the report that there was no clear evidence of an association
 

between the tumor incidence in the treated animals and the
 

administration of Malathion. He stressed the fact that the
 

dose levels administered were sufficiently high to produce
 

an effect. The primary reviewer was particularly critical
 

of the small size of the matched control groups. He pointed
 

out the incidence of hepatocellular carcinomas in the treated
 

male mice, although it was not statistically significant.
 

The secondary reviewer questioned the validity of the
 

bioassay in terms of its significance as a valid "negative"
 

study. He pointed out the increased incidence of adenomas
 

of the thyroid in the treated rats, as well as their earlier
 

appearance in the animals at the high dose level. He argued
 

this may indicate an important biological effect despite
 

101
 
the statistical insignificance of the finding. Considering
 

this finding and the high human exposure, he suggested that
 

the study be repeated using a different route of exposure.
 

A Program staff pathologist commented that the time
 

to the detection of the thyroid tumors in the treated
 

animals may be misleading. Since it was not possible to
 

detect the cause of the animals' deaths, he noted that
 

the difference in survival time between the treated and
 

control animals may not be truly significant. It was the
 

feeling of the Program staff that there was no evidence
 

to indicate the carcinogenicity of Malathion, although
 

there is always a probability of obtaining a false negative,
 

The Subgroup agreed unanimously to accept the report
 

on the bioassay of Malathion.
 

Members present were:
 

Arnold Brown (Acting Chairman), Mayo Clinic
 

Lawrence Garfinkel, American Cancer Society
 

Joseph Highland, Environmental Defense Fund
 

Charles Kensler, Arthur D. Little Company
 

Verald K. Rowe, Dow Chemical, U.S.A.
 

Sheldon Samuels, Industrial Union Department, APL-CIO
 

Louise Strong, University of Texas Health Sciences Center
 

Sidney Wolfe, Health Research Group
 

Subsequent to this review, changes may have been made
 

in the bioassay report either as a result of the review
 

or other reasons. Thus, certain comments and criticisms
 

reflected in the review may no longer be appropriate.
 

•Ct U. S. GOVERNMENT PRINTING OFFICE 1978—260-899/3011 

102 

DHEW Publication No. (NIH) 78-824