NTP TECHNICAL REPORT

ON THE

TOXICOLOGY AND CARCINOGENESIS

STUDIES OF SODIUM DICHROMATE DIHYDRATE

(CAS NO. 7789-12-0)

IN F344/N RATS AND B6C3F1 MICE

(DRINKING WATER STUDIES)

NATIONAL TOXICOLOGY PROGRAM

P.O. Box 12233

Research Triangle Park, NC 27709

July 2008

NTP TR 546

NIH Publication No. 08-5887

National Institutes of Health

Public Health Service

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
FOREWORD

The National Toxicology Program (NTP) is an interagency program within the Public Health Service (PHS) of the 

Department of Health and Human Services (HHS) and is headquartered at the National Institute of Environmental 

Health Sciences of the National Institutes of Health (NIEHS/NIH). Three agencies contribute resources to the 

program: NIEHS/NIH, the National Institute for Occupational Safety and Health of the Centers for Disease 

Control and Prevention (NIOSH/CDC), and the National Center for Toxicological Research of the Food and Drug 

Administration (NCTR/FDA). Established in 1978, the NTP is charged with coordinating toxicological testing 

activities, strengthening the science base in toxicology, developing and validating improved testing methods, and 

providing information about potentially toxic substances to health regulatory and research agencies, scientific and 

medical communities, and the public. 

The Technical Report series began in 1976 with carcinogenesis studies conducted by the National Cancer Institute. 

In 1981, this bioassay program was transferred to the NTP. The studies described in the Technical Report series 

are designed and conducted to characterize and evaluate the toxicologic potential, including carcinogenic activity, 

of selected substances in laboratory animals (usually two species, rats and mice). Substances selected for NTP 

toxicity and carcinogenicity studies are chosen primarily on the basis of human exposure, level of production, and 

chemical structure. The interpretive conclusions presented in NTP Technical Reports are based only on the results 

of these NTP studies. Extrapolation of these results to other species, including characterization of hazards and 

risks to humans, requires analyses beyond the intent of these reports. Selection per se is not an indicator of a 

substance’s carcinogenic potential.

The NTP conducts its studies in compliance with its laboratory health and safety guidelines and FDA Good 

Laboratory Practice Regulations and must meet or exceed all applicable federal, state, and local health and safety 

regulations. Animal care and use are in accordance with the Public Health Service Policy on Humane Care and 

Use of Animals. Studies are subjected to retrospective quality assurance audits before being presented for public 

review.

NTP Technical Reports are indexed in the NIH/NLM PubMed database and are available free of charge 

electronically on the NTP website (http://ntp.niehs.nih.gov) or in hardcopy upon request from the NTP Central 

Data Management group at cdm@niehs.nih.gov or (919) 541-3419.
NTP TECHNICAL REPORT

ON THE

TOXICOLOGY AND CARCINOGENESIS

STUDIES OF SODIUM DICHROMATE DIHYDRATE

(CAS NO. 7789-12-0)

IN F344/N RATS AND B6C3F1 MICE

(DRINKING WATER STUDIES)

NATIONAL TOXICOLOGY PROGRAM

P.O. Box 12233

Research Triangle Park, NC 27709

July 2008

NTP TR 546

NIH Publication No. 08-5887

National Institutes of Health

Public Health Service

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
2

CONTRIBUTORS

National Toxicology Program

Evaluated and interpreted results and reported findings

M.J. Hooth, Ph.D., Study Scientist

R.A. Herbert, D.V.M., Ph.D., Study Pathologist

D.W. Bristol, Ph.D.

J.R. Bucher, Ph.D.

L.T. Burka, Ph.D.

R.S. Chhabra, Ph.D.

B.J. Collins, M.S.

A.P. King-Herbert, D.V.M.

G.E. Kissling, Ph.D.

D.E. Malarkey, D.V.M., Ph.D.

S.D. Peddada, Ph.D.

J.H. Roycroft, Ph.D.

C.S. Smith, Ph.D.

G.S. Travlos, D.V.M.

K.L. Witt, M.S.

Southern Research Institute

Conducted studies and evaluated pathology findings

C.D. Hébert, Ph.D., Principal Investigator

J.E. Heath, D.V.M.

R.B. Thompson, D.V.M., Ph.D.

Experimental Pathology Laboratories, Inc.

Provided pathology review

M.H. Hamlin, II, D.V.M., Principal Investigator

R.A. Miller, D.V.M., Ph.D.

J.C. Peckham, D.V.M., M.S., Ph.D.

C.C. Shackelford, D.V.M., M.S., Ph.D.

Dynamac Corporation

Prepared quality assessment audits

S. Brecher, Ph.D., Principal Investigator

S. Iyer, B.S.

V. Tharakan, D.V.M.

NTP Pathology Working Group

Evaluated slides and prepared pathology report on rats

(September 26, 2006)

M.P. Jokinen, D.V.M., Chairperson

Pathology Associates, A Charles River Company

J.M. Cullen, V.M.D., Ph.D.

North Carolina State University

S.A. Elmore, D.V.M., M.S.

National Toxicology Program

G.P. Flake, M.D.

National Toxicology Program

R.A. Herbert, D.V.M., Ph.D.

National Toxicology Program

W.G. Lieuallen, D.V.M., Ph.D.

Pathology Associates, A Charles River Company

D.E. Malarkey, D.V.M., Ph.D.

National Toxicology Program

E.E. McConnell, D.V.M., M.S.

ToxPath, Inc.

R.A. Miller, D.V.M., Ph.D.

Experimental Pathology Laboratories, Inc.

J.C. Peckham, D.V.M., M.S., Ph.D.

Experimental Pathology Laboratories, Inc.

Evaluated slides and prepared pathology report on mice

(November 9, 2006)

M.P. Jokinen, D.V.M., Chairperson

Pathology Associates, A Charles River Company

S.A. Elmore, D.V.M., M.S.

National Toxicology Program

R.A. Herbert, D.V.M., Ph.D.

National Toxicology Program

D.E. Malarkey, D.V.M., Ph.D.

National Toxicology Program

R.R. Maronpot, D.V.M.

National Toxicology Program

J.C. Peckham, D.V.M., M.S., Ph.D.

Experimental Pathology Laboratories, Inc.

C.C. Shackelford, D.V.M., M.S., Ph.D.

Experimental Pathology Laboratories, Inc.
Sodium Dichromate Dihydrate, NTP TR 546 3

Constella Group, Inc.

Provided statistical analyses

P.W. Crockett, Ph.D., Principal Investigator

L.J. Betz, M.S.

M.R. Easterling, Ph.D.

K.P. McGowan, M.B.A.

Biotechnical Services, Inc.

Prepared Technical Report

S.R. Gunnels, M.A., Principal Investigator

P.A. Gideon, B.A.

B.F. Hall, M.S.

L.M. Harper, B.S.

D.C. Serbus, Ph.D.

G.E. Simmons, M.A.
4

CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

EXPLANATION OF LEVELS OF EVIDENCE OF CARCINOGENIC ACTIVITY . . . . . . . . . . . . . . . . 12

TECHNICAL REPORTS REVIEW SUBCOMMITTEE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

SUMMARY OF TECHNICAL REPORTS REVIEW SUBCOMMITTEE COMMENTS . . . . . . . . . . . . 14

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

DISCUSSION AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Appendix A Summary of Lesions in Male Rats in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Appendix B Summary of Lesions in Female Rats in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Appendix C Summary of Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Appendix D Summary of Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Appendix E Clinical Pathology Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

Appendix F Chemical Characterization and Dose Formulation Studies . . . . . . . . . . . . . . . . . . . . . . . 157

Appendix G Water and Compound Consumption in the 2-Year Drinking Water Studies

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Appendix H Ingredients, Nutrient Composition, and Contaminant Levels 

in NTP-2000 Rat and Mouse Ration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Appendix I Sentinel Animal Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Appendix J Chromium Tissue Distribution Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Sodium Dichromate Dihydrate, NTP TR 546 5

SUMMARY

Background

Chromium is a metal that exists in a variety of valence states, depending on surrounding conditions and what 

other atoms it is bound to. The most stable forms are metallic chromium, trivalent chromium (chromium III), and 

hexavalent chromium (chromium VI). Chromium VI has already been shown to cause cancer when inhaled in the 

air. Because some compounds containing chromium VI occur as contaminants in drinking water, we studied the 

effects of sodium dichromate dihydrate in drinking water on male and female rats and mice to identify potential 

toxic or cancer-related hazards.

Methods

We gave drinking water containing 14.3, 57.3, 172, or 516 mg of sodium dichromate dihydrate per liter of water 

to groups of 50 male and female rats and female mice for 2 years. Similar groups of male mice were given 14.3, 

28.6, 85.7, or 257.4 mg of sodium dichromate dihydrate per liter of water. Control animals received the same tap 

water with no chemical added. At the end of the study, tissues from more than 40 sites were examined for every 

animal. 

Results

Male and female rats exposed to sodium dichromate dihydrate had carcinomas of the mouth, but none occurred 

in the control rats. Male and female mice receiving sodium dichromate dihydrate had greatly increased rates of 

cancer of the small intestine. 

Conclusions

We conclude that sodium dichromate dihydrate in the drinking water caused oral cancers in rats and cancer of the 

small intestine in mice.
6 Sodium Dichromate Dihydrate, NTP TR 546 
ABSTRACT

SODIUM DICHROMATE DIHYDRATE

CAS No. 7789-12-0

Chemical Formula: Na2Cr2O7 • 2H2O Molecular Weight: 298.0

Synonyms: Chromic acid; dichromic acid, dihydrate; disodium dichromate dihydrate; chromium VI

Sodium dichromate dihydrate is one of a number 

of inorganic compounds containing hexavalent chromium (Cr VI) found in drinking water source supplies 

as a contaminant resulting from various industrial 

processes including electroplating operations, leather 

tanning, and textile manufacturing. Because of the 

lack of adequate experimental data on the toxicity 

and carcinogenicity of hexavalent chromium ingested 

orally and because hexavalent chromium has been 

found in drinking water source supplies, the California 

Congressional Delegation, the California Environmental 

Protection Agency, and the California Department of 

Health Services nominated hexavalent chromium to 

the National Toxicology Program for study. Results of 

3-month toxicity studies in F344/N rats and B6C3F1, 

BALB/c, and am3-C57BL/6 mice were reported earlier 

in NTP Toxicity Report 72. In the current study, male 

and female F344/N rats and B6C3F1 mice were exposed 

to sodium dichromate dihydrate (greater than 99.7% 

pure) in drinking water for 2 years.

2-Year Study in Rats

Groups of 50 male and 50 female rats were exposed to 

drinking water containing 0, 14.3, 57.3, 172, or 516 mg/L 

sodium dichromate dihydrate (equivalent to 0, 5, 20, 60, 

or 180 mg/L chromium) for 2 years (equivalent to average daily doses of approximately 0.6, 2.2, 6, or 17 mg 

sodium dichromate dihydrate/kg body weight for males 

and 0.7, 2.7, 7, or 20 mg/kg for females). Survival of 

exposed groups was similar to that of the control groups. 

Mean body weights of 516 mg/L males and females 

were less than those of the controls throughout the study. 

The lower body weights were partly attributed to poor 

palatability of the dosed water and consequent reductions in water consumption. Water consumption by 172 

and 516 mg/L rats was less than that by the controls 

throughout the study. Exposure to sodium dichromate 

dihydrate caused a microcytic hypochromic anemia in 

rats that ameliorated with time.

Exposure to sodium dichromate dihydrate resulted in the 

development of neoplasms of the squamous epithelium 

that lines the oral mucosa and tongue. The incidences 

of squamous cell carcinoma in the oral mucosa of 

516 mg/L male and female rats were significantly greater 

than those in the controls. The incidence in 172 mg/L 

females exceeded the historical control ranges for drinking water studies and for all routes of administration. 

The incidences of squamous cell papilloma or squamous 

7
8 Sodium Dichromate Dihydrate, NTP TR 546 

cell carcinoma (combined) of the oral mucosa or tongue 

of 516 mg/L male and female rats were significantly 

greater than those in the controls.

Exposure concentration-related nonneoplastic liver 

lesions were observed in males and females exposed 

to 57.3 mg/L or greater. These included histiocytic 

cellular infiltration, chronic inflammation, fatty change 

(females), basophilic focus (males), and clear cell focus 

(females). Increased incidences of histiocytic cellular 

infiltration also occurred in the small intestine (duodenum), mesenteric lymph node, and pancreatic lymph 

node of males and/or females exposed to 57.3 mg/L or 

greater.

2-Year Study in Mice

Groups of 50 male mice were exposed to drinking water 

containing 0, 14.3, 28.6, 85.7, or 257.4 mg/L sodium 

dichromate dihydrate (equivalent to 0, 5, 10, 30, or 

90 mg/L chromium) for 2 years (equivalent to average daily doses of approximately 1.1, 2.6, 7, or 17 mg 

sodium dichromate dihydrate/kg body weight). Groups 

of 50 female mice were exposed to drinking water containing 0, 14.3, 57.3, 172, or 516 mg/L sodium dichromate dihydrate (equivalent to 0, 5, 20, 60, or 180 mg/L 

chromium) for 2 years (equivalent to average daily doses 

of approximately 1.1, 3.9, 9, or 25 mg/kg). Survival 

of exposed groups was similar to that of the control 

groups. Mean body weights of 257.4 mg/L males were 

less than those of controls from months 2 through 6 of 

the study, but by the end of the study, the mean body 

weight of 257.4 mg/L males was only slightly less 

than that of the control group. Mean body weights of 

172 mg/L females were less than those of the controls 

from months 3 through 12 of the study, and mean body 

weights of 516 mg/L females were less than those of the 

controls from month 2 until the end of the study. By 

the end of the study, the mean body weight of 172 mg/L 

females was 8% less than that of the controls, and the 

mean body weight of 516 mg/L females was 15% less 

than that of the controls. The lower body weights were 

partly attri-buted to poor palatability of the dosed water 

and consequent reductions in water consumption. Water 

consumption by 85.7 and 257.4 mg/L males and 172 

and 516 mg/L females was less than that by the controls 

throughout the study. A treatment-related microcytosis 

occurred in exposed mice; the mice were less affected 

than the rats.

The incidences of neoplasms of the small intestine (duodenum, jejunum, or ileum) were increased in exposed 

groups of male and female mice. The incidences of 

adenoma of the duodenum in 257.4 mg/L males and 172 

and 516 mg/L females were significantly greater than 

those in the controls. The incidence of carcinoma of 

the duodenum was significantly increased in 516 mg/L 

females. The incidence of adenoma of the jejunum in 

516 mg/L females was significantly increased compared 

to that in the controls. When the incidences of adenoma 

and carcinoma were combined for all sites of the small 

intestine, the incidences were significantly increased 

in 85.7 and 257.4 mg/L males and 172 and 516 mg/L 

females compared to those in the controls. The incidences in 57.3 mg/L females exceeded the historical 

control ranges for drinking water studies and for all 

routes of administration. 

The incidences of diffuse epithelial hyperplasia were 

significantly increased in the duodenum of all exposed 

groups of male and female mice. The incidences of histiocytic cellular infiltration were significantly increased 

in the duodenum of 85.7 and 257.4 mg/L males and 

in 172 and 516 mg/L females. In the jejunum, the 

incidences of diffuse epithelial hyperplasia and histiocytic cellular infiltration were significantly increased in 

516 mg/L females. 

The incidences of histiocytic cellular infiltration of the 

liver in all exposed groups of females, of the mesenteric lymph node in all exposed groups of males and 

females, and of the pancreatic lymph node of 85.7 and 

257.4 mg/L males and 172 and 516 mg/L females were 

significantly increased.

Tissue distribution studies showed that total chromium concentrations tended to increase with increasing 

exposure concentration and duration of exposure.

Conclusions

Under the conditions of these 2-year drinking water 

studies, there was clear evidence of carcinogenic activity* of sodium dichromate dihydrate in male and female 

F344/N rats based on increased incidences of squamous 
Sodium Dichromate Dihydrate, NTP TR 546 9

cell neoplasms of the oral cavity. There was clear evidence of carcinogenic activity of sodium dichromate 

dihydrate in male and female B6C3F1 mice based on 

increased incidences of neoplasms of the small intestine 

(duodenum, jejunum, or ileum).

Exposure to sodium dichromate dihydrate resulted in 

histiocytic cellular infiltration in the liver, small intestine, and pancreatic and mesenteric lymph nodes of rats 

and mice and diffuse epithelial hyperplasia in the small 

intestine of male and female mice.

__________

* Explanation of Levels of Evidence of Carcinogenic Activity is on page 12. A summary of the Technical Reports Review Subcommittee 

comments and the public discussion on this Technical Report appears on page 14.
10 Sodium Dichromate Dihydrate, NTP TR 546 

Summary of the 2-Year Carcinogenesis Studies of Sodium Dichromate Dihydrate

Male Female Male Female

F344/N Rats F344/N Rats B6C3F1 Mice B6C3F1 Mice

Concentrations in 0, 14.3, 57.3, 172, or 0, 14.3, 57.3, 172, or 0, 14.3, 28.6, 85.7, or 0, 14.3, 57.3, 172, or 

drinking water 516 mg/L 516 mg/L 257.4 mg/L 516 mg/L

Body weights 516 mg/L group less than 516 mg/L group less than Exposed groups similar 172 and 516 mg/L groups 

the control group the control group to control group less than control group

Survival rates 28/50, 30/50, 30/49, 33/50, 32/50, 32/50, 33/50, 35/50, 35/50, 37/50, 39/50, 45/50, 

36/50, 29/49 36/50, 31/50 38/50, 32/50 42/50, 42/50

Nonneoplastic effects Liver: infiltration Liver: infiltration Small intestine, Liver: infiltration 

cellular, histiocyte (1/50, cellular, histiocyte (1/50, duodenum: epithelium, cellular, histiocyte (2/49, 

0/50, 2/49, 5/50, 34/49) 5/50, 21/50, 42/50, 47/50) hyperplasia, diffuse 15/50, 23/50, 32/50, 

(0/50, 11/50, 18/50, 45/50)

Small intestine, Small intestine, 42/50, 32/50); infiltration 

duodenum: infiltration duodenum: infiltration cellular, histiocyte (0/50, Small intestine, 

cellular, histiocyte (0/48, cellular, histiocyte (0/46, 2/50, 4/50, 37/50, 35/50) duodenum: epithelium, 

0/48, 6/47, 36/46, 47/48) 0/49, 1/48, 30/46, 47/50) hyperplasia, diffuse 

Lymph node, mesenteric: (0/50, 16/50, 35/50, 

Lymph node, mesenteric: Lymph node, mesenteric: infiltration cellular, 31/50, 42/50); infiltration 

infiltration cellular, infiltration cellular, histiocyte (14/47, 38/47, cellular, histiocyte (0/50, 

histiocyte (13/49, 11/50, histiocyte (21/50, 18/50, 31/49, 32/49, 42/46) 0/50, 4/50, 33/50, 40/50)

30/49, 39/50, 41/49) 27/50, 36/50, 42/50)

Lymph node, pancreatic: Small intestine, jejunum: 

Lymph node, pancreatic: infiltration cellular, epithelium, hyperplasia, 

infiltration cellular, histiocyte (0/5, 2/13, diffuse (0/50, 2/50, 1/50, 

histiocyte (17/29, 20/36, 2/10, 5/8, 12/16) 0/50, 8/50); infiltration 

23/30, 32/34, 27/33) cellular, histiocyte (0/50, 

0/50, 0/50, 2/50, 8/50)

Lymph node, mesenteric: 

infiltration cellular, 

histiocyte (3/46, 29/48, 

26/46, 40/50, 42/50)

Lymph node, pancreatic: 

infiltration cellular, 

histiocyte (0/14, 1/12, 

2/15, 7/14, 8/13)
Sodium Dichromate Dichromate Dihydrate, Dihydrate, NTP TR 546 11

Summary of the 2-Year Carcinogenesis Studies of Sodium Dichromate Dihydrate

Male Female Male Female

F344/N Rats F344/N Rats B6C3F1 Mice B6C3F1 Mice

Neoplastic effects Oral mucosa: squamous Oral mucosa: squamous Small intestine, Small intestine, 

cell carcinoma (0/50, cell carcinoma (0/50, duodenum: adenoma duodenum: adenoma 

0/50, 0/49, 0/50, 6/49) 0/50, 0/50, 2/50, 11/50) (1/50, 0/50, 1/50, 5/50, (0/50, 0/50, 2/50, 13/50, 

15/50) 12/50); carcinoma (0/50, 

Oral mucosa or tongue: Oral mucosa or tongue: 0/50, 0/50, 1/50, 6/50)

squamous cell papilloma squamous cell papilloma Small intestine, 

or squamous cell or squamous cell duodenum, jejunum, Small intestine, jejunum: 

carcinoma (0/50, 1/50, carcinoma (1/50, 1/50, or ileum: adenoma adenoma (0/50, 1/50, 

0/49, 0/50, 7/49) 0/50, 2/50, 11/50) (1/50, 1/50, 1/50, 5/50, 0/50, 2/50, 5/50)

17/50); carcinoma (0/50, 

2/50, 1/50, 3/50, 5/50); Small intestine, 

adenoma or carcinoma duodenum, jejunum, 

(1/50, 3/50, 2/50, 7/50, or ileum: adenoma 

20/50) (0/50, 1/50, 2/50, 15/50, 

16/50); carcinoma (1/50, 

0/50, 2/50, 3/50, 7/50); 

adenoma or carcinoma 

(1/50, 1/50, 4/50, 17/50, 

22/50)

Level of evidence of Clear evidence Clear evidence Clear evidence Clear evidence

carcinogenic activity
12 Sodium Dichromate Dihydrate, NTP TR 546 

EXPLANATION OF LEVELS OF EVIDENCE OF CARCINOGENIC ACTIVITY

The National Toxicology Program describes the results of individual experiments on a chemical agent and notes the strength of the evidence 

for conclusions regarding each study. Negative results, in which the study animals do not have a greater incidence of neoplasia than control 

animals, do not necessarily mean that a chemical is not a carcinogen, inasmuch as the experiments are conducted under a limited set of 

conditions. Positive results demonstrate that a chemical is carcinogenic for laboratory animals under the conditions of the study and indicate 

that exposure to the chemical has the potential for hazard to humans. Other organizations, such as the International Agency for Research on 

Cancer, assign a strength of evidence for conclusions based on an examination of all available evidence, including animal studies such as those 

conducted by the NTP, epidemiologic studies, and estimates of exposure. Thus, the actual determination of risk to humans from chemicals 

found to be carcinogenic in laboratory animals requires a wider analysis that extends beyond the purview of these studies.

Five categories of evidence of carcinogenic activity are used in the Technical Report series to summarize the strength of the evidence observed 

in each experiment: two categories for positive results (clear evidence and some evidence); one category for uncertain findings (equivocal 

evidence); one category for no observable effects (no evidence); and one category for experiments that cannot be evaluated because of major 

flaws (inadequate study). These categories of interpretative conclusions were first adopted in June 1983 and then revised in March 1986 for 

use in the Technical Report series to incorporate more specifically the concept of actual weight of evidence of carcinogenic activity. For each 

separate experiment (male rats, female rats, male mice, female mice), one of the following five categories is selected to describe the findings. 

These categories refer to the strength of the experimental evidence and not to potency or mechanism.

• Clear evidence of carcinogenic activity is demonstrated by studies that are interpreted as showing a dose-related 

 (i) increase of malignant neoplasms, (ii) increase of a combination of malignant and benign neoplasms, or (iii) marked increase of 

 benign neoplasms if there is an indication from this or other studies of the ability of such tumors to progress to malignancy.

• Some evidence of carcinogenic activity is demonstrated by studies that are interpreted as showing a chemical-related increased 

 incidence of neoplasms (malignant, benign, or combined) in which the strength of the response is less than that required for clear 

 evidence.

• Equivocal evidence of carcinogenic activity is demonstrated by studies that are interpreted as showing a marginal increase of 

 neoplasms that may be chemical related.

• No evidence of carcinogenic activity is demonstrated by studies that are interpreted as showing no chemical-related increases in 

 malignant or benign neoplasms.

• Inadequate study of carcinogenic activity is demonstrated by studies that, because of major qualitative or quantitative limitations, 

 cannot be interpreted as valid for showing either the presence or absence of carcinogenic activity.

For studies showing multiple chemical-related neoplastic effects that if considered individually would be assigned to different levels of evidence 

categories, the following convention has been adopted to convey completely the study results. In a study with clear evidence of carcinogenic 

activity at some tissue sites, other responses that alone might be deemed some evidence are indicated as “were also related” to chemical 

exposure. In studies with clear or some evidence of carcinogenic activity, other responses that alone might be termed equivocal evidence are 

indicated as “may have been” related to chemical exposure.

When a conclusion statement for a particular experiment is selected, consideration must be given to key factors that would extend the actual 

boundary of an individual category of evidence. Such consideration should allow for incorporation of scientific experience and current 

understanding of long-term carcinogenesis studies in laboratory animals, especially for those evaluations that may be on the borderline between 

two adjacent levels. These considerations should include:

• adequacy of the experimental design and conduct;

• occurrence of common versus uncommon neoplasia;

• progression (or lack thereof) from benign to malignant neoplasia as well as from preneoplastic to neoplastic lesions;

• some benign neoplasms have the capacity to regress but others (of the same morphologic type) progress. At present, it is impossible to 

 identify the difference. Therefore, where progression is known to be a possibility, the most prudent course is to assume that benign 

 neoplasms of those types have the potential to become malignant;

• combining benign and malignant tumor incidence known or thought to represent stages of progression in the same organ or tissue;

• latency in tumor induction;

• multiplicity in site-specific neoplasia;

• metastases;

• supporting information from proliferative lesions (hyperplasia) in the same site of neoplasia or in other experiments (same lesion in 

 another sex or species);

• presence or absence of dose relationships;

• statistical significance of the observed tumor increase;

• concurrent control tumor incidence as well as the historical control rate and variability for a specific neoplasm;

• survival-adjusted analyses and false positive or false negative concerns;

• structure-activity correlations; and

• in some cases, genetic toxicology. 
Sodium Dichromate Dihydrate, NTP TR 546 13

NATIONAL TOXICOLOGY PROGRAM BOARD OF SCIENTIFIC COUNSELORS

TECHNICAL REPORTS REVIEW SUBCOMMITTEE

The members of the Technical Reports Review Subcommittee who evaluated the draft NTP Technical Report on sodium dichromate dihydrate 

on May 16, 2007, are listed below. Subcommittee members serve as independent scientists, not as representatives of any institution, company, 

or governmental agency. In this capacity, subcommittee members have five major responsibilities in reviewing the NTP studies:

• to ascertain that all relevant literature data have been adequately cited and interpreted,

• to determine if the design and conditions of the NTP studies were appropriate,

• to ensure that the Technical Report presents the experimental results and conclusions fully and clearly,

• to judge the significance of the experimental results by scientific criteria, and

• to assess the evaluation of the evidence of carcinogenic activity and other observed toxic responses.

Nancy Kerkvliet, Ph.D., Chairperson

Department of Environmental and Molecular Toxicology

Oregon State University

Corvallis, OR

Christopher Bradfield, Ph.D.

McArdle Laboratory for Cancer Research

University of Wisconsin

Madison, WI

Kenny S. Crump, Ph.D.

Environ International

Ruston, LA

Prescott Deininger, Ph.D.

Tulane University Medical Center

New Orleans, LA

Jon Mirsalis, Ph.D.

SRI International

Menlo Park, CA

Harish Sikka, Ph.D., Principal Reviewer

Environmental Toxicology and Chemistry Laboratory

State University of New York College at Buffalo

Buffalo, NY

Keith Soper, Ph.D. 

Merck Research Laboratories

West Point, PA

Vernon Walker, D.V.M., Ph.D., Principal Reviewer

Lovelace Respiratory Institute

Albuquerque, NM

Special Ad Hoc Reviewers

Russell C. Cattley, V.M.D., Ph.D.

Amgen

Thousand Oaks, CA

Raymond F. Novak, Ph.D., Principal Reviewer

Institute of Environmental Health Sciences

Wayne State University

Detroit, MI

Michael V. Pino, D.V.M., Ph.D.

Drug Safety Evaluation

Sanofi-aventis

Bridgewater, NJ
14 Sodium Dichromate Dihydrate, NTP TR 546 

On May 16, 2007, the draft Technical Report on 

the toxicology and carcinogenesis studies of sodium 

dichromate dihydrate received public review by the 

National Toxicology Program’s Board of Scientific 

Counselors’ Technical Reports Review Subcommittee. 

The review meeting was held at the National Institute 

of Environmental Health Sciences, Research Triangle 

Park, NC.

Dr. M.J. Hooth, NIEHS, introduced the toxicology and 

carcinogenesis studies of sodium dichromate dihydrate 

by discussing the uses of chromium, the rationale for 

study, and the short-term studies; describing the design 

of the long-term studies; and reporting on survival and 

body weight effects and compound-related neoplastic 

and nonneoplastic lesions. Dr. R.A. Herbert, NIEHS, 

described the histopathologic details of several of the 

observed lesions. The proposed conclusions for the 

2-year studies were clear evidence of carcinogenic 

activity of sodium dichromate dihydrate in male and 

female F344/N rats and clear evidence of carcinogenic 

activity of sodium dichromate dihydrate in male and 

female B6C3F1 mice.

Dr. Walker, the first principal reviewer, agreed with 

the proposed conclusions. He differed with one of 

the public responses to the report that suggested there 

should be more discussion of sites with decreased tumor 

incidence, noting that the primary purpose of the study 

was to detect carcinogenic responses. He felt the discussion of other studies, some with conflicting results, 

was balanced. He felt it was noteworthy that, although 

chromium was detected at other tissue sites, the main 

carcinogenic response in mice was in the small intestine, 

primarily in the duodenum and decreasing farther down 

the intestinal tract.

Dr. Novak, the second principal reviewer, also agreed 

with the proposed conclusions. He inquired whether 

any clinical chemistry panel had been performed to 

detect changes in hormone levels. He asked if any of the 

observed histiocytic cellular infiltration could be associated with inflammation. 

Dr. Sikka, the third principal reviewer, agreed with the 

proposed conclusions and inquired if there was any 

explanation for the difference in the organ-specific susceptibility of the two rodent species to the carcinogenic 

effects of sodium dichromate dihydrate. 

Dr. Hooth noted that a couple of tumors were seen in 

the ileum of male mice, and Dr. Walker replied that 

it was still interesting that the numbers of tumors did 

decrease progressively down the intestinal tract. In 

response to Dr. Novak, Dr. Hooth replied that because 

this was a study of hexavalent chromium, examinations 

of the effects of trivalent chromium on lipid or carbohydrate metabolism were not performed. Regarding 

the histiocytic cellular infiltration, Dr. Herbert replied 

that these were not granulomas, with some causative 

agent like bacteria or fungus or necrosis, and no additional inflammatory cells were seen in association with 

the infiltration. In response to Dr. Sikka, Dr. Hooth 

replied that in a survey of 21 NTP studies that caused 

neoplasms of the oral cavity in rats, none caused similar 

neoplasms in male mice and only one in female mice. 

Dr. Hooth added that further studies were underway to 

characterize the absorption of chromium in the stomach 

and intestine. 

Dr. Mirsalis inquired if the palatability of the chemical 

may have affected water consumption or body weights of 

the animals. Dr. Cattley asked about the sampling procedures for oral cavity lesions and if all the carcinomas 

were detected by gross examination. Dr. Herbert replied 

that a reexamination of all the tissue samples provided 

confidence that all potential lesions were detected. 

Dr. Kirkvliet said that written comments had been 

submitted by six organizations: the Sapphire Group; 

the Department of Health Sciences of the University of 

Genoa, Italy; the Interfaith Community Organization; 

Exponent, Inc.; Consulting Scientists; and the 

Environmental Working Group. 

Mr. T. McKee, representing the Interfaith Community 

Organization of New Jersey, said the NTP had produced 

a well-designed and meticulously executed study and 

an insightful and illuminating report. He urged that the 

report be completed expeditiously in light of the need for 

the study results by regulatory agencies.

Dr. D.M. Proctor, representing Tierra Solutions, Inc., 

noted that the chromium concentrations in the NTP 

SUMMARY OF TECHNICAL REPORTS REVIEW SUBCOMMITTEE COMMENTS
Sodium Dichromate Dihydrate, NTP TR 546 15

study were 50 to 100 times higher than the existing 

drinking water standards. She indicated that no epidemiology studies in the literature indicated increases in 

oral cavity or intestinal tumors as a result of exposure 

to chromium. She also claimed that the body weights 

and water consumption of the study animals were significantly lower than for the control groups and suggested that lower palatability and dehydration may have 

affected the physiology of the exposed animals. She 

speculated that dehydration could lead to lower production of saliva, which might affect the ability of animals 

to reduce chromium VI. 

Dr. Walker inquired if the water consumption was 

indeed altered significantly in this study. Dr. Hooth 

discussed the criteria for the diagnosis of dehydration, which included clinical observations of circulatory hypo-volemia, including loss of skin turgor, dry 

mucous membranes, retraction of eyes, and even shock 

and increases in clinical pathology parameters such as 

albumin, hematocrit, urea nitrogen, or urine specific 

gravity. None of these indicators was observed in the 

present study. Dr. Hooth also presented plots showing 

that only one dosed group of male rats varied by more 

than 10% from controls late in the study, and that water 

consumption on a body weight basis was nearly identical 

for exposed and control rats. 

Dr. Walker moved, and Dr. Soper seconded, that the 

conclusions be accepted as written. The motion was 

approved unanimously with seven votes.
16 Sodium Dichromate Dihydrate, NTP TR 546 
17

INTRODUCTION

SODIUM DICHROMATE DIHYDRATE

CAS No. 7789-12-0

Chemical Formula: Na2Cr2O7 • 2H2O Molecular Weight: 298.0

Synonyms: Chromic acid; dichromic acid, dihydrate; disodium dichromate dihydrate; chromium VI

Chemical and Physical Properties

Sodium dichromate dihydrate exists in solid form as reddish to bright orange crystals, which become anhydrous 

when heated to approximately 100° C. The anhydrous 

form has a melting point of 356.7° C (Merck, 1996). 

The water solubility of sodium dichromate dihydrate is 

230 g/L at 0° C. Chromium is a group 6 transition metal 

and occurs in the earth’s crustal rock at a concentration 

averaging 122 ppm. It has six oxidation states. The most 

stable states are metallic chromium (Cr), trivalent chromium (Cr III), and hexavalent chromium (Cr VI). Cr VI 

is typically present in complexes with halide (chromyl 

chloride) and oxygen ligands (chromium trioxide, chromate, dichromate). Sodium dichromate dihydrate is one 

of a number of inorganic compounds that contain Cr VI. 

Other representatives of this class of compounds include 

calcium chromate, chromium trioxide, sodium chromate 

and dichromate, potassium chromate and dichromate, 

lead chromate, strontium chromate, and zinc chromate. 

The physical properties and water solubility of these 

compounds vary considerably. In aqueous solution, 

dichromate and chromate are in equilibrium. The form 

of Cr VI present depends on pH and concentration. At 

physiological pH and millimolar concentrations, Cr 

VI exists primarily as the chromate ion (Hamilton and 

Wetterhahn, 1988). The proportion existing as dichromate increases as the concentration increases and/or the 

pH is decreased. 

Cr VI is easily reduced to Cr III in acidic solutions 

containing organic molecules such as proteins, DNA, 

or glutathione. Glutathione is also capable of reducing 

Cr VI at neutral pH at a slower rate than under acidic 

conditions (Zhitkovich, 2005).

Production, Use, 

and Human Exposure

Metallic chromium is produced by reduction of chromite 

ore. Sodium dichromate is produced by roasting chromite ore with soda ash and is used for the production of 

other chromium compounds (Hartford, 1979; Westbrook, 

1979). Metallic chromium is used in the metallurgical 

industry for the production of stainless steel and ferrous 

and nonferrous alloys. The major uses of chromium in 

the chemical and manufacturing industries include the 

production of chromium pigments and in metal finishing, leather tanning, and wood preservation (Barnhart, 

1997). Chromium enters the environment from combus-
18 Sodium Dichromate Dihydrate, NTP TR 546 

tion processes and ore processing mainly as chromium 

(III) oxide. Cr VI has been detected in fly ash from 

power plants (Stern, 1982). Both Cr III and Cr VI enter 

water resources by leaching from soil or from industrial 

contamination (Pellerin and Booker, 2000) as well as 

from atmospheric fallout. A Cr VI concentration as high 

as 580 μg/L was found in a groundwater monitoring 

well in Hinkley, California (Pellerin and Booker, 2000). 

Detectable levels of hexavalent chromium have been 

reported in approximately 30% of the drinking water 

sources monitored in California, which has a 1 μg/L 

detection limit for purposes of reporting (CDHS, 2004); 

87% of those sources had concentrations ranging from 1 

to 10 μg/L. The United States Environmental Protection 

Agency has set a maximum contaminant level of 100 

μg/L for total chromium in drinking water (ATSDR, 

2000). The California state limit is 50 μg/L of total 

chromium in drinking water (CDHS, 2004). Human 

exposure to chromium occurs through food, water, and 

air. The highest exposure to Cr VI occurs occupationally to workers involved in chrome plating, chromate 

production, and stainless steel welding. Exposure in 

these situations is typically by inhalation or dermal contact. Dermal exposure to chromium compounds results 

in irritation and ulceration of the skin and causes allergic 

contact dermatitis in sensitized individuals. Additional 

information on human exposure to chromium and chromium compounds can be found in the Toxicological 

Profile for Chromium (ATSDR, 2000).

Absorption, Distribution, 

Metabolism, and Excretion

Chromium and chromium compounds are found to 

be absorbed after oral, dermal, or inhalation exposure 

(Wahlberg and Skog, 1965; Wahlberg, 1970; Kerger 

et al., 1997; Mancuso, 1997). Current analytical procedures cannot differentiate between the oxidation states 

of chromium in biological tissues so total chromium 

content is measured in excreta and tissues. Most studies 

of absorption of Cr III or Cr VI after oral administration 

to rodents found that only 1% or 2% of the administered 

dose is bioavailable, whereas similar studies with humans 

report somewhat higher numbers (ATSDR, 2000), particularly for Cr VI. It is thought that Cr VI is poorly 

absorbed when ingested due to its rapid reduction to 

less soluble Cr III in the presence of food and the acidic 

environment encountered in the stomach (Sutherland 

et al., 2000). Cr III is less efficiently absorbed than Cr 

VI compounds, and this is attributed to a difference in 

their respective methods of transport into cells. Cr VI 

enters cells by facilitated diffusion via nonspecific anion 

channels, while Cr III enters cells by passive diffusion 

or phagocytosis of precipitates resulting in much lower 

uptake (ATSDR, 2000). 

Human and animal studies show that chromium is 

widely distributed in the body after exposure to Cr VI, 

with liver, kidney, spleen, and bone having higher concentrations than other tissues (MacKenzie et al., 1959; 

Coogan et al., 1991; Kargacin et al., 1993; Costa, 1997; 

Mancuso, 1997). Rats consuming up to 10 mg/L Cr VI 

as potassium chromate in drinking water for 44 weeks 

had elevated chromium levels in bone, kidney, liver 

(females only), and testis (males only) (Sutherland et 

al., 2000). Other studies showed that chromium can 

cross the placenta (Casey and Hambidge, 1984; Saxena 

et al., 1990; Kirpnick-Sobol et al., 2006). Higher tissue chromium levels were found in rats receiving Cr VI 

orally than in those receiving an equivalent dose of Cr 

III (Costa, 1997). Following uptake by erythrocytes 

and tissues, Cr VI is thought to undergo reduction to Cr 

III intracellularly, primarily by ascorbate (Sugiyama, 

1992).

Ingested chromium is excreted primarily in the feces 

because of its poor absorption. Absorbed chromium 

appears to be primarily excreted in the urine (Donaldson 

and Barreras, 1966; Sayato et al., 1980). O’Flaherty 

(1993, 1996) has constructed a physiologically based 

pharmacokinetic model for Cr VI compounds in the rat, 

and the ATSDR (2000) has outlined distribution and 

clearance models for Cr III in humans.

Prior to selection of rats and mice as the test species for 

the studies in the current Technical Report, the National 

Toxicology Program (NTP) conducted a comparative 

absorption study of sodium dichromate dihydrate (Cr VI) 

administered in the drinking water to F344/N rats, 

B6C3F1 mice, and Hartley guinea pigs (NTP, 2007a). 

Concentrations of total chromium were determined in 

blood and kidney. Guinea pigs were chosen for study, 

in addition to rats and mice, because they more closely 

resemble humans in that they do not have a forestomach 

and they require vitamin C (a reducing agent) in their 

diet. In all three species, chromium in blood and kidney 

increased with exposure concentration (NTP, 2007a). 

Although differences were seen in the absolute amounts 

of chromium in kidney and blood, uptake as a function of exposure concentration did not appear to differ 

qualitatively in guinea pigs when compared to rats and 
Sodium Dichromate Dihydrate, NTP TR 546 19

mice. This suggests that the presence of a forestomach 

did not fundamentally alter the handling of Cr VI in the 

gastrointestinal tract. Kidney chromium concentration 

was highest in rats, followed by mice and guinea pigs. 

For blood, guinea pigs had the highest concentrations, 

followed by mice and rats. The concentrations of chromium in blood and kidney were in general agreement 

with values observed by Sutherland et al. (2000).

Toxicity

Cr III is an essential trace element. The recommended 

daily intake of Cr III for adults ranges between 25 and 

45 μg (IOM, 2001). Cr III deficiency contributes to 

glucose intolerance and diabetes mellitus (Type 2). 

Chromium appears to increase sensitivity to insulin. The 

mechanism involves increased insulin binding through 

increasing the number of insulin receptors and increasing insulin receptor phosphorylation in the presence of 

insulin and a low molecular weight chromium complex 

(Anderson, 1998). Cr III displays little to no toxicity in 

humans and animals (ATSDR, 2000).

The toxicity of Cr VI in humans and animals has 

been reviewed extensively (Costa 1997; USEPA, 1998; 

ATSDR, 2000; Costa and Klein, 2006). More recently, 

the NTP performed 3-month studies of sodium dichromate dihydrate in male and female F344/N rats and 

B6C3F1 mice to aid in the design and dose selection for 

these 2-year carcinogenicity studies of sodium dichromate dihydrate (NTP, 2007a). Rats and mice were given 

drinking water containing 0, 62.5, 125, 250, 500, or 

1,000 mg sodium dichromate dihydrate/L for 3 months. 

All rats and mice survived to the end of the studies. 

Final mean body weights and body weight gains were 

less than those of controls in male rats exposed to 500 or 

1,000 mg/L, female rats exposed to 1,000 mg/L, and in 

male and female mice exposed to 125 mg/L or greater. 

Exposure to sodium dichromate dihydrate caused a 

microcytic hypochromic anemia in rats and mice, but the 

severity was less in mice. The primary nonneoplastic 

lesions were observed in the glandular stomach of rats 

exposed to 1,000 mg/L and included focal ulceration, 

regenerative epithelial hyperplasia, and squamous epithelial metaplasia. Histiocytic cellular infiltration was 

observed in the duodenum of rats and mice, the liver 

of female rats, and the mesenteric lymph nodes of mice 

exposed to 125 mg/L or greater. Histiocytic cellular 

infiltration was also observed in the pancreatic lymph 

nodes of rats exposed to 1,000 mg/L. All exposed 

groups of mice had significantly increased incidences of 

epithelial hyperplasia of the duodenum.

The NTP examined the potential of sodium dichromate 

dihydrate exposure via drinking water to modulate 

immune function in female B6C3F1 mice, F344/N rats, 

and Sprague-Dawley rats by conducting 28-day range 

finding studies (NTP, 2007b,c,d). Sodium dichromate 

dihydrate exposure concentrations in the mice were 

0, 15.6, 31.25, 62.5, 125, or 250 mg/L and in the rats 

were 0, 14.3, 57.3, 172, or 516 mg/L. No significant 

signs of overt toxicity were observed in these studies. 

Reductions in final mean body weight and body weight 

gain were observed in 250 mg/L B6C3F1 mice and 

516 mg/L Sprague-Dawley rats. F344/N and SpragueDawley rats in the 172 and 516 mg/L groups consumed 

significantly less water than the control animals, which 

was attributed to poor palatability of the drinking water 

solutions. Sodium dichromate dihydrate exposure did 

not produce significant changes in organ weights. In 

250 mg/L mice, some of the erythroid parameters were 

significantly decreased (5% to 7%) including hemoglobin, hematocrit, mean cell volume, and mean cell 

hemoglobin. In rats, hematology parameters were not 

affected. Sodium dichromate dihydrate exposure produced minimal effects in the various immunological 

parameters evaluated in mice and rats. There were no 

biologically meaningful changes in spleen cell numbers 

or in the percentage and absolute number of B cells, 

T cells, CD4+ T cells, CD8+ T cells, natural killer cells, 

and macrophages. Sodium dichromate dihydrate exposure did not produce a reproducible significant effect 

on the IgM antibody-forming cell response to sheep red 

blood cells or to the T-dependent antigen keyhole limpet 

hemocyanin. There was no effect of sodium dichromate 

dihydrate on cell-mediated immunity and natural killer 

cells evaluated using anti-CD3 antibody mediated T cell 

proliferation and the cytotoxic assay of YAC-1 cells, 

respectively. 

Renal effects observed in rats administered Cr VI (as 

potassium chromate, 13.5 mg/kg per day for 20 days) by 

gavage included increased accumulation of lipid, triglycerides, and phospholipids in different regions of the 

kidney than in controls and inhibited kidney membrane 

enzymes (alkaline phosphatase, acid phosphatase, glucose-6-phosphatase, and lipase) (Kumar and Rana, 1982, 

1984). Oliguria and proteinuria were also observed in 

rats exposed to Cr VI (as sodium chromate, 100 mg/kg 

per day for 28 days) in drinking water (Diaz-Mayans 

et al., 1986). 

A number of studies have reported reproductive effects 

in rats and mice orally exposed to Cr VI. These studies utilized similar exposure concentrations (250 to 
20 Sodium Dichromate Dihydrate, NTP TR 546 

1,000 mg/L) of potassium dichromate provided in the 

drinking water of female rats and mice prior to mating or 

during gestation. Cr VI exposure consistently resulted in 

increased preimplantation and postimplantation losses, 

resorptions, and stillbirths and decreased numbers of 

corpora lutea and numbers of fetuses (live and dead) 

(Trivedi et al., 1989; Junaid et al., 1996a,b; Kanojia 

et al., 1996, 1998). In addition, these studies provided 

evidence that Cr VI is a developmental toxicant in rats 

and mice. Fetuses were consistently reported to have 

retarded development, decreased fetal body weight and 

crown-rump length, and higher incidences of subdermal 

hemorrhagic patches and kinky short tails. There was 

also a significant reduction in ossification in caudal, 

parietal, and interparietal bones of the fetuses. 

In contrast, results of NTP studies in BALB/c mice and 

Sprague-Dawley rats showed that potassium dichromate 

was not a reproductive toxicant when administered in the 

diet for 9 weeks followed by an 8-week recovery period 

(NTP, 1996a,b). However, rats and mice administered 

potassium dichromate by diet (8.4 and 9.8 mg Cr VI/kg 

body weight per day for male and female rats, respectively; 32.2 and 48 mg Cr VI/kg body weight per day 

for male and female mice, respectively) showed reduced 

mean red cell volume and mean red cell hemoglobin. 

This effect was not seen at lower exposure concentrations. Similar decreases were seen in a multigeneration 

study of mice given potassium dichromate in the diet. 

The decreases were seen in BALB/c males receiving 

Cr VI at 16 mg/kg per day and 36.7 mg/kg per day and 

BALB/c females receiving Cr VI at 7.8 mg/kg per day 

(NTP, 1997). 

Toxicity of Cr VI has not been confirmed in all animal 

studies. In a drinking water study, rats given Cr VI 

(as potassium chromate, 3.6 mg/kg per day) for 1 year 

showed no evidence of hepato- or nephrotoxicity and no 

alteration in hematology or clinical chemistry parameters (MacKenzie et al., 1958).

Carcinogenicity

Exposure to Cr VI compounds by inhalation has long 

been recognized as carcinogenic to humans. The United 

States Department of Health and Human Services, the 

United States Environmental Protection Agency, and 

the International Agency for Research on Cancer classified Cr VI compounds as human carcinogens based on 

increased incidences of lung cancers in workers in the 

chromium industry and in experimental animals exposed 

to these compounds by inhalation (IARC, 1990; Cohen 

et al., 1993; NTP, 1998). The specific compounds 

listed as carcinogens include calcium chromate, chromium trioxide, lead chromate, strontium chromate, and 

zinc chromate.

Although Cr VI compounds are demonstrated carcinogens by the inhalation route, it has been suggested that 

the reductive capacity of the gut would be adequate to 

prevent Cr VI from being a carcinogen when ingested 

(De Flora et al., 1997; Proctor et al., 2002). Little data 

exist regarding health effects resulting from ingestion of 

Cr VI compounds. A review of the few epidemiological 

studies that evaluated populations that were exposed to 

Cr VI in drinking water or in soil or slag fill concluded 

that these studies did not provide definitive evidence 

of an increase in cancer incidence or mortality rates 

(Proctor et al., 2002). However, a retrospective mortality study of a population living near a chromium smelting 

plant in the People’s Republic of China found increased 

incidences of lung and stomach tumors as compared to 

those of the general population. The authors did not estimate exposure levels nor was the size of the population 

specified (Zhang and Li, 1987; ATSDR, 2000). More 

recently, Sedman et al. (2006) reevaluated the findings 

of this study as well as additional reports by the investigators and confirmed the significant increases in lung 

and stomach neoplasms. 

Only one lifetime animal carcinogenicity study was 

identified in the literature in which hexavalent chromium was administered in the drinking water. Three 

generations of NMRI mice were exposed to 9 mg Cr 

VI/kg body weight administered in the drinking water 

as potassium chromate. In treated mice, two of 66 

females developed forestomach carcinomas and nine of 

66 females and one of 35 males developed forestomach 

papillomas. Forestomach papillomas were observed in 

the vehicle controls (2 of 79 females and 3 of 47 males), 

but no carcinomas were observed in the vehicle controls. 

Most of the tumors were observed in the F0 generation. 

The increased incidence of forestomach tumors in the 

treated mice was not statistically significant (Borneff 

et al., 1968; ATSDR, 2000). However, when benign 

and malignant forestomach neoplasms were combined in 

the three generations of female mice, there was a statistically significant increase compared to the control group 

(Sedman et al., 2006). This study has several limitations 

including high early mortality in the F0 generation as a 
Sodium Dichromate Dihydrate, NTP TR 546 21

result of ectromelia (mousepox) virus. 

Davidson et al. (2004) showed that exposure to potassium chromate in drinking water enhanced the incidence 

of ultraviolet radiation-induced skin tumors in a hairless 

mouse model. Female SK1-hrBR mice were exposed 

for 6 months to ultraviolet light at a constant energy 

of 1.18 kJ/m2 and to potassium chromate in drinking 

water at 0.5, 2.5, or 5.0 mg/L. There was an exposure 

concentration-dependent increase in the number of skin 

neoplasms in mice exposed to ultraviolet light and potassium chromate, which was statistically significant at the 

two highest chromate doses. The authors concluded that 

Cr VI can increase susceptibility to carcinogenesis following drinking water exposure. 

Trivalent chromium exposure is not considered to pose a 

significant cancer risk in humans or in animals (ATSDR, 

2000). There was no evidence of carcinogenicity in 

male or female Becton Dickinson rats fed diets containing up to 5% chromium oxide (2,040 mg Cr III/kg per 

day), 5 days per week for 2 years, or in the offspring 

of rats treated for 60 days prior to gestation and during 

gestation, after 600 days of observation (Ivankovic and 

Preussmann, 1975).

Genetic Toxicity

Most studies measuring genetic damage endpoints in 

humans occupationally exposed to atmospheric hexavalent chromium reported results consistent with chromium-induced chromosomal damage (IARC, 1990). In 

several studies, elevated frequencies of sister chromatid 

exchanges and chromosomal aberrations were reported 

in lymphocytes of Cr VI-exposed workers. Correlations 

were documented in some of these studies between the 

concentrations of chromium in the workplace or the 

duration of exposure and the amount of genetic damage detected. In recent studies, evaluation of biological 

samples including exfoliated buccal cells and peripheral 

lymphocytes from workers (electroplaters or welders) 

exposed to chromium by inhalation revealed significant 

increases in micronuclei, which are indicators of structural and numerical chromosome changes (Vaglenov et 

al., 1999; Benova et al., 2002; Danadevi et al., 2004). 

Chromosomal aberrations have also been observed in 

cultured human bronchial epithelial cells exposed to 

soluble sodium chromate (VI) and particulate lead chromate (VI) (Wise et al., 2006). No studies were located 

regarding genotoxic effects in humans after oral exposure to hexavalent chromium compounds. 

Hexavalent chromium is genotoxic in a number of 

in vitro and in vivo test systems, although responses are 

somewhat variable depending on protocol details and the 

type of chromium salt that is assayed. Overall, the data 

clearly indicate that in appropriate test systems, Cr VI 

exposure results in increased frequencies of gene mutations and chromosomal alterations. The extensive literature on the mutagenicity of chromium compounds has 

been reviewed by a number of authors, most recently by 

IARC (1990) and by De Flora et al. (1990). To summarize the findings briefly, positive results were obtained 

in vitro with Cr VI compounds in gene mutation tests 

using Salmonella typhimurium or Escherichia coli (most 

recently, positive results reported in NTP, 2007a); 

forward mutation and mitotic gene conversion assays 

in yeast; mammalian cell (including human cell lines) 

chromosomal damage assays that measured increases in 

sister chromatid exchanges, chromosomal aberrations, 

or micronuclei; mutation induction at the tk locus in 

L5178Y mouse lymphoma cells; and tests for induction 

of DNA strand breaks or DNA synthesis inhibition in 

a variety of mammalian cells. In vivo, positive results 

were seen in short-term assays in laboratory rodents for 

induction of chromosomal damage and micronuclei following administration of Cr VI by intraperitoneal injection. Comparative micronucleus assays in various strains 

of male and female mice (ms, BDF1, CD-11, ddY, ICR) 

revealed no sex- or strain-related differences in overall 

results (CSGMT, 1986, 1988). Route of administration 

was shown to be a factor, however, with intraperitoneal 

injection administration (up to 80 mg/kg) of potassium 

dichromate giving positive results and oral gavage (up to 

320 mg/kg) giving negative results in two strains (MS/

Ae and CD-1) of male mice (Shindo et al., 1989). 

Recent results from in vivo chromosomal damage assays 

in animals using drinking water as the route of administration have given mixed results. De Flora et al. (2006) 

measured the frequency of micronucleated erythrocytes 

in peripheral blood of BDF1 or Swiss mice exposed to 

sodium dichromate dihydrate or potassium dichromate 

in drinking water (up to 500 mg chromium VI/L for 

210 days); no alterations in the frequencies of micronucleated erythrocytes were seen and the authors suggested 

that the absence of genotoxicity by this route of exposure 

provided evidence for gastrointestinal detoxification of 

Cr VI. In contrast, exposure of adult BDF1 or Swiss 

mice to Cr VI by intraperitoneal injection (50 mg/

kg potassium dichromate or sodium dichromate dihydrate) produced significant increases in micronucleated 

erythrocytes (De Flora et al., 2006). NTP peripheral 
22 Sodium Dichromate Dihydrate, NTP TR 546 

blood micronucleus studies conducted in B6C3F1, 

BALB/c, and am3-C57BL/6 mice with sodium 

dichromate dihydrate administered in drinking water 

for 3 months gave mixed results (NTP, 2007a); significant increases in micronucleated erythrocytes were 

seen only in am3-C57BL/6 mice. Kirpnick-Sobol et 

al. (2006) reported that exposure of pregnant mice 

(C57BL/6J pun/pun) to either potassium dichromate 

(Cr VI; 62.5 or 125.0 mg/L) or chromium (III) chloride 

(1,875 or 3,750 mg/L) in drinking water during gestational days 10 to 20 resulted in significant increases in 

the frequencies of large-scale DNA deletions in their 

pups examined at 20 days of age. Kirpnick-Sobol et al.

(2006) reported that in embryos exposed to Cr III, significant increases in DNA deletions were seen at threefold 

lower chromium tissue concentrations than in embryos 

exposed to Cr VI. They concluded that, although only 

small amounts of Cr III were absorbed, Cr III was highly 

effective at inducing DNA damage.

Study Rationale

The California Congressional Delegation, California 

Environmental Protection Agency, and the California 

Department of Health Services nominated Cr VI for 

toxicity and carcinogenicity testing because of concerns 

over its presence in drinking water source supplies, its 

potential health effects, including carcinogenicity, and 

the lack of adequate carcinogenicity studies of ingested 

Cr VI. The results of 3-month toxicity studies of Cr 

VI administered in drinking water to F344/N rats and 

B6C3F1, BALB/c, and am3-C57BL/6 mice as sodium 

dichromate dihydrate have been published (NTP, 2007a). 

Hexavalent chromium is a human carcinogen by inhalation exposure, but available data are inadequate to evaluate its carcinogenic potential when ingested in drinking 

water. This Technical Report summarizes the results 

of 2-year toxicology and carcinogenesis drinking water 

studies conducted in male and female F344/N rats and 

B6C3F1 mice.
23

Procurement

and Characterization

of Sodium Dichromate Dihydrate

Sodium dichromate dihydrate was obtained from Aldrich 

Chemical Company (Milwaukee, WI) in two lots. The 

two lots were combined at the analytical chemistry 

laboratory, Battelle Memorial Institute (Columbus, OH), 

and assigned a new lot number (062001) for use in the 

2-year studies. Identity and purity analyses were conducted by the analytical chemistry laboratory, the study 

laboratory (Southern Research Institute, Birmingham, 

AL), Galbraith Laboratories, Inc. (Knoxville, TN), and 

Elemental Analysis Corp. (Lexington, KY) (Appendix 

F). Reports on analyses performed in support of the 

sodium dichromate dihydrate studies are on file at the 

National Institute of Environmental Health Sciences.

Lot 062001, an orange crystalline solid, was identified 

as sodium dichromate dihydrate by the analytical chemistry laboratory using X-ray diffraction, by the analytical chemistry laboratory and by Galbraith Laboratories, 

Inc., using elemental analysis by inductively coupled 

plasma-atomic emission spectroscopy (ICP-AES), and 

by Elemental Analysis Corp. using proton-induced X-ray 

emission spectroscopy (PIXE). Elemental analyses for 

chromium and sodium by ICP-AES were in agreement 

with the theoretical values for sodium dichromate dihydrate, and PIXE indicated the absence of significant 

metallic impurities. 

The moisture content of lot 062001 was determined by 

Galbraith Laboratories, Inc., using Karl Fischer titration. The purity of lot 062001 was determined by the 

analytical chemistry laboratory using differential scanning calorimetry (DSC), titration of the dichromate ion 

with sodium thiosulfate and potassium ferrocyanide, and 

speciation of the chromium ions using liquid chromatography-inductively coupled plasma-mass spectrometry 

(LC-ICP-MS) and by the study laboratory using potentiometric titration with sodium thiosulfate. Karl Fischer 

titration indicated a water content of 11.62%, which is 

in agreement with the theoretical value of 12.09%. DSC 

indicated a purity of 99.73% ± 0.15%. Titration with 

sodium thiosulfate by the analytical chemistry laboratory indicated a purity of 99.7% ± 0.1%. Titration with 

sodium thiosulfate by the study laboratory indicated 

purities of 101% and 102% relative to a frozen reference standard of the same lot. Titration with potassium 

ferrocyanide indicated a purity of 103.1% ± 0.2%. 

LC-ICP-MS indicated that the concentration of Cr III, 

if present, was less than 0.1%. The overall purity of 

lot 062001 was determined to be greater than 99.7%.

To ensure stability, the bulk chemical was stored at 

room temperature, protected from light in amber glass 

bottles. 

Periodic reanalyses of the bulk chemical were performed 

by the study laboratory using potentiometric titration as 

described for the purity assays; no degradation of the 

bulk chemical was detected. 

Preparation and Analysis

of Dose Formulations

The dose formulations were prepared approximately 

every 2 weeks by mixing sodium dichromate dihydrate 

with tap water (Table F1). Formulations were stored in 

NALGENE® containers at room temperature for up to 

42 days.

Stability studies of a 41.8 μg/mL dose formulation 

were performed by the analytical chemistry laboratory 

using ion chromatography. Stability was confirmed for 

at least 42 days for dose formulations stored in sealed 

NALGENE® containers, protected from light, at temperatures up to room temperature and for at least 7 days 

when stored in drinking water bottles under simulated 

animal room conditions.

Periodic analyses of the dose formulations of sodium 

dichromate dihydrate were conducted by the study 

laboratory using ultraviolet/visible/near infrared spectroscopy (350 to 390 nm). The dose formulations were 

analyzed approximately every 10 weeks (Table F2). Of 

the dose formulations analyzed, all 44 for rats and all 

84 for mice were within 10% of the target concentraMATERIALS AND METHODS

23
24 Sodium Dichromate Dihydrate, NTP TR 546 

tions. Animal room samples and unused carboy storage 

samples of these dose formulations were also analyzed; 

all 16 animal room samples for rats and 34 of 35 animal 

room samples for mice were within 10% of the target 

concentrations. Fourteen of 16 carboy samples for rats 

and 33 of 35 carboy samples for mice were within 10% 

of the target concentrations. 

The sodium dichromate dihydrate dosed water used in 

these studies was slightly acidic. Based on an equilibrium 

constant of 50, dichromate predominates at the highest 

exposure concentration and the chromate:dichromate 

ratio approaches 1 at the lowest exposure concentration. 

These ratios would be obtained when the starting material was a chromate or dichromate salt.

Exposure Concentration

Rationale for Rats and Mice

The 2-year studies were designed after an NTP public meeting on hexavalent chromium held on July 24, 

2002, at the National Institute of Environmental Health 

Sciences in Research Triangle Park, NC, to consider the 

results of the prechronic studies and recommendations 

from the panel of scientific experts convened at this 

meeting (NTP, 2006). Exposure concentrations were 

selected based on these public discussions and careful 

review of the data from the 3-month toxicity studies. 

Based on source water concentrations, an additional low 

exposure concentration group was added to the 2-year 

studies to provide a concentration that was closer to concentrations to which humans might be exposed through 

the drinking water. A wider spacing of the exposure 

concentrations was also recommended to extend the 

dose-response curve. The highest exposure concentration in rats and mice was limited by toxicity observed in 

the 3-month studies. In the 3-month studies, reductions 

in body weight and water consumption and increased 

incidences of ulcers in the glandular stomach were 

observed in male and female rats exposed to 1,000 mg 

sodium dichromate dihydrate/L. Based on these considerations, the exposure concentrations of total chromium 

recommended were 0, 5, 20, 60, or 180 mg/L for male 

and female rats. These exposure concentrations are 

equivalent to 0, 14.3, 57.3, 172, or 516 mg/L sodium 

dichromate dihydrate. In mice, significant reductions 

in body weight and water consumption were observed 

in males exposed to 500 or 1,000 mg/L and females 

exposed to 1,000 mg/L. Based on these considerations, 

the exposure concentrations of total chromium recommended were 0, 5, 10, 30, or 90 mg/L for male mice 

and 0, 5, 20, 60, or 180 mg/L for female mice. These 

exposure concentrations are equivalent to 0, 14.3, 28.6, 

85.7, or 257.4 mg/L and 0, 14.3, 57.3, 172, or 516 mg/L 

sodium dichromate dihydrate for males and females, 

respectively.

2-Year Studies

Study Design

Groups of 50 male and 50 female core study rats and 

mice were exposed to sodium dichromate dihydrate in 

drinking water at concentrations of 0, 14.3, 57.3, 172, 

or 516 mg/L (rats and female mice) or 0, 14.3, 28.6, 

85.7, or 257.4 mg/L (male mice) for 105 to 106 weeks. 

Groups of 40 male special study rats and 40 female special study mice were exposed to the same concentrations 

for up to 53 weeks, and these animals were used for 

clinical pathology (Appendix E) and for tissue distribution (Appendix J) studies. Groups of 12 male clinical 

pathology rats and 16 female clinical pathology mice 

were exposed to the same concentrations for 22 days.

Source and Specification of Animals

Male and female F344/N rats and B6C3F1 mice were 

obtained from Taconic Farms, Inc. (Germantown, NY), 

for use in the 2-year studies. Core study rats and mice 

were quarantined for 14 days before the beginning of 

the studies. Five male and five female rats and mice 

were randomly selected for parasite evaluation and gross 

observation of disease. Rats and mice were approximately 6 to 7 weeks old at the beginning of the studies. 

The health of the animals was monitored during the 

studies according to the protocols of the NTP Sentinel 

Animal Program (Appendix I).

Animal Maintenance

Core study rats were housed three (males) or five 

(females) per cage, and core study mice were housed one 

(males) or five (females) per cage. Feed and water were 

available ad libitum. Water consumption was measured 

weekly for the first 13 weeks and then every 4 weeks 

for a 7-day period each time. Cages were changed once 

(male mice) or twice weekly, and cages and racks were 

rotated every 2 weeks. Further details of animal maintenance are given in Table 1. Information on feed composition and contaminants is provided in Appendix H.
Sodium Dichromate Dihydrate, NTP TR 546 25

Clinical Examinations and Pathology

All animals were observed twice daily and were weighed 

initially, weekly for the first 13 weeks, at 4-week intervals thereafter, and at the end of the studies. Clinical 

findings were recorded at 4-week intervals beginning 

at week 5. 

Hematology and clinical chemistry (rats only) evaluations were performed on up to 10 clinical pathology rats 

on day 4, clinical pathology rats and mice on day 22, and 

special study rats and mice at 3, 6, and 12 months. At 

these time points, rats and mice were anesthetized with 

CO2/O2, and blood was taken from the retroorbital sinus. 

Clinical pathology animals were removed from the study 

after blood collection on day 22. Blood samples for 

hematology analyses were placed in tubes containing 

potassium EDTA as the anticoagulant; blood samples 

for the clinical chemistry analyses were placed in tubes 

not containing an anticoagulant, allowed to clot at room 

temperature, and centrifuged, and the serum was separated. Slides for hematology were stained with a modified Wright’s stain using an Ames HEMATEK®

 slide 

stainer (Miles Laboratory, Elkhart, IN), and hematology 

determinations including erythrocyte and leukocyte 

counts, hemoglobin concentration, hematocrit, mean cell 

volume, mean cell hemoglobin, and mean cell concentration were performed on an ADVIAtm 120 automated 

hematology analyzer (Bayer, Inc., Tarrytown, NY) 

with reagents provided by Bayer, Fisher Scientific 

(Norcross, GA), or Sigma Diagnostics (St. Louis, MO). 

Nucleated erythrocyte counts were determined by blood 

smears stained with neutral Wright-Giemsa stain and 

microscopically examined. Reticulocyte counts were 

obtained through sphering of blood smears with a 

zwitterionic agent and stained with an Oxazine dye; 

blood smears stained with New Methylene Blue Stain 

(Accustain Reticulocyte Stain; Sigma Diagnostics) 

were examined microscopically for the determination 

of manual reticulocyte counts. Clinical chemistry 

measurements were performed on a Hitachi 911 random access automated chemistry analyzer (Boehringer 

Mannheim, Indianapolis, IN) using reagents from Roche 

Sigma Diagnostics, Trinity Biotech (Overland, MO), or 

Diagnostic Chemicals, Ltd. (Oxford, CT). 

Complete necropsies and microscopic examinations were 

performed on all core study rats and mice. At necropsy, 

all organs and tissues were examined for grossly visible 

lesions, and all major tissues were fixed and preserved in 

10% neutral buffered formalin, trimmed and processed, 

embedded in paraffin, sectioned to a thickness of 4 to 

6 μm, and stained with hematoxylin and eosin for microscopic examination. For all paired organs (e.g., adrenal 

gland, kidney, ovary), samples from each organ were 

examined. Tissues examined microscopically are listed 

in Table 1. During the audit of the pathology specimens 

for the rat and mouse studies, the residual wet tissues of 

the gastrointestinal tract from male and female rats and 

mice from all groups were examined to ensure that the 

entire gastrointestinal tract was adequately opened. Any 

untrimmed potential lesions were collected for microscopic evaluation.

Microscopic evaluations were completed by the study 

laboratory pathologist, and the pathology data were 

entered into the Toxicology Data Management System 

(TDMS). The slides, paraffin blocks, and residual wet 

tissues were sent to the NTP Archives for inventory, 

slide/block match, and wet tissue audit. The slides, 

individual animal data records, and pathology tables 

were evaluated by an independent quality assessment 

laboratory. The individual animal records and tables 

were compared for accuracy; the slide and tissue counts 

were verified; and the histotechnique was evaluated. 

For the 2-year studies, a quality assessment pathologist 

evaluated slides of all neoplasms and all potential target 

organs for all animals which included the glandular 

stomach, small intestine (duodenum, ileum, jejunum), 

large intestine (cecum, colon), liver, oral mucosa, and 

tongue of rats and the forestomach, glandular stomach, 

small intestine (duodenum, ileum, jejunum), and large 

intestine (cecum, colon) of mice. In addition, slides 

for all animals were reviewed for specific lesions in the 

bone marrow, kidney, pancreatic and mesenteric lymph 

nodes, and salivary glands of rats and the bone marrow, 

kidney, pancreatic and mesenteric lymph nodes, pancreas, spleen, thymus, and urinary bladder of mice.

The oral mucosa and tongue are not protocol-required 

tissues, and as such, only lesions that are observed 

grossly in these sites are routinely evaluated histologically. Because the gross lesions observed in the oral 

mucosa were diagnosed as neoplasms, the oral mucosa 

(present on slides of the three standard sections of the 

nasal cavity required to be evaluated for each study) 

from all male and female rats and mice in all exposure concentration groups was evaluated for neoplastic 

and nonneoplastic lesions by the quality assessment 

and Pathology Working Group (PWG) pathologists. 

Histologic sections of the tongue were prepared for all 

male and female rats and mice in all exposure concentration groups and were evaluated for neoplastic and nonneoplastic lesions. 
26 Sodium Dichromate Dihydrate, NTP TR 546 

The quality assessment report and the reviewed slides 

were submitted to the NTP PWG chairperson, who 

reviewed the selected tissues and addressed any inconsistencies in the diagnoses made by the laboratory and 

quality assessment pathologists. Representative histopathology slides containing examples of lesions related to 

chemical administration, examples of disagreements in 

diagnoses between the laboratory and quality assessment 

pathologists, or lesions of general interest were presented by the chairperson to the PWG for review. The 

PWG consisted of the quality assessment pathologist 

and other pathologists experienced in rodent toxicologic 

pathology. When the PWG consensus differed from the 

opinion of the laboratory pathologist, the diagnosis was 

changed. Final diagnoses for reviewed lesions represent 

a consensus between the laboratory pathologist, reviewing pathologist(s), and the PWG. Details of these review 

procedures have been described, in part, by Maronpot 

and Boorman (1982) and Boorman et al. (1985). For 

subsequent analyses of the pathology data, the decision 

of whether to evaluate the diagnosed lesions for each 

tissue type separately or combined was generally based 

on the guidelines of McConnell et al. (1986).

Table 1

Experimental Design and Materials and Methods in the 2-Year Drinking Water Studies 

of Sodium Dichromate Dihydrate

Study Laboratory

Southern Research Institute (Birmingham, AL)

Strain and Species

F344/N rats

B6C3F1 mice

Animal Source

Taconic Farms, Inc. (Germantown, NY)

Time Held Before Studies

14 days

Average Age When Studies Began

6 to 7 weeks

Date of First Exposure

Rats: October 2, 2002

Mice: September 4, 2002

Duration of Exposure

105 to 106 weeks

Date of Last Exposure

Rats: October 7, 2004

Mice: September 9, 2004

Necropsy Dates

Rats: September 29 to October 7, 2004

Mice: September 1 to 9, 2004

Average Age at Necropsy

110 to 112 weeks

Size of Study Groups

Core study: 50 males and 50 females

Clinical pathology study: 12 male rats and 16 female mice

Special study: 40 male rats and 40 female mice
Sodium Dichromate Dihydrate, NTP TR 546 27

Table 1

Experimental Design and Materials and Methods in the 2-Year Drinking Water Studies 

of Sodium Dichromate Dihydrate

Method of Distribution

Animals were distributed randomly into groups of approximately equal initial mean body weights.

Animals per Cage

Rats: 3 (males) or 5 (females)

Mice: 1 (males) or 5 (females)

Method of Animal Identification

Tail tattoo

Diet

Irradiated NTP-2000 wafers (Zeigler Brothers, Inc., Gardners, PA), available ad libitum, changed weekly

Water

Tap water (Birmingham municipal supply) via amber glass bottles (Wheaton Science Products, Millville, NJ) with Teflon®-lined plastic screw 

caps fitted with stainless steel, double-ball sipper tubes, available ad libitum, changed twice weekly

Cages

Solid-bottom polycarbonate (Lab Products, Maywood, NJ), changed once (male mice) or twice weekly

Bedding

Heat-treated, irradiated hardwood chips (P.J. Murphy Forest Products, Inc., Montville, NJ), changed once (male mice) or twice weekly

Rack Filters

Reemay® spun-bonded polyester (Andico, Birmingham, AL), changed every 2 weeks

Racks

Stainless steel (Lab Products, Maywood, NJ), changed and rotated every 2 weeks

Animal Room Environment

Temperature: 72° ± 3° F

Relative humidity: 50% ± 15%

Room fluorescent light: 12 hours/day

Room air changes: 10/hour

Exposure Concentrations

Rats: 0, 14.3, 57.3, 172, and 516 mg/L in drinking water, available ad libitum

Mice: 0, 14.3, 28.6, 85.7, and 257.4 mg/L (males) or 0, 14.3, 57.3, 172, and 516 mg/L (females) in drinking water, available ad libitum

Type and Frequency of Observation

Observed twice daily; core study animals were weighed initially, weekly for the first 13 weeks, at 4-week intervals thereafter, and at the end of 

the studies; clinical findings for core study animals were recorded at 4-week intervals beginning at week 5. Water consumption by core study 

animals was recorded weekly for the first 13 weeks and every 4 weeks thereafter with each water consumption measurement covering a 7-day 

period.

Method of Sacrifice

Carbon dioxide asphyxiation

Necropsy

Necropsies were performed on all core study animals. 
28 Sodium Dichromate Dihydrate, NTP TR 546 

Table 1

Experimental Design and Materials and Methods in the 2-Year Drinking Water Studies 

of Sodium Dichromate Dihydrate

Clinical Pathology

Blood was collected from the retroorbital sinus of clinical pathology male rats and female mice on days 4 (rats only) and 22 and from special 

study male rats and female mice at 3, 6, and 12 months for hematology and clinical chemistry (rats only).

Hematology: hematocrit; hemoglobin concentration; erythrocyte, reticulocyte, and platelet counts; erythrocyte and platelet morphology; mean 

cell volume; mean cell hemoglobin; mean cell hemoglobin concentration; and leukocyte count and differentials

Clinical chemistry: urea nitrogen, creatinine, total protein, albumin, alanine aminotransferase, alkaline phosphatase, creatine kinase, sorbitol 

dehydrodrogenase, bile acids

Histopathology

Complete histopathology was performed on all core study rats and mice. In addition to gross lesions and tissue masses, the following tissues 

were examined: adrenal gland, bone (with marrow), brain, clitoral gland, esophagus, eye, gallbladder (mice only), Harderian gland, heart, large 

intestine (cecum, colon, rectum), small intestine (duodenum, jejunum, ileum), kidney, liver, lung, lymph nodes (mandibular and mesenteric), 

mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, skin, spleen, stomach 

(forestomach and glandular), testis (with epididymis and seminal vesicle), thymus, thyroid gland, tongue, trachea, urinary bladder, and uterus.

Chromium Tissue Distribution

On days 4 and 11 and at 6 and 12 months, 10 special study rats and 8 or 10 special study mice were removed from treatment; five rats and 

all mice were placed in metabolism cages for 48 hours for urine and feces collection. Urine volume, feces weight, and urine creatinine 

concentration were determined. All special study rats and mice were anesthetized with CO2/O2, and following blood collection for clinical 

pathology, the liver, kidneys, and stomach (glandular and nonglandular) were collected. Urine, feces, and tissues were frozen until further 

analysis.

Statistical Methods

Survival Analyses

The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958) and is 

presented in the form of graphs. Animals found dead 

of other than natural causes or missing were censored 

from the survival analyses; animals dying from natural 

causes were not censored. Statistical analyses for possible dose-related effects on survival used Cox’s (1972) 

method for testing two groups for equality and Tarone’s 

(1975) life table test to identify dose-related trends. 

All reported P values for the survival analyses are two 

sided.

Calculation of Incidence

The incidences of neoplasms or nonneoplastic lesions 

are presented in Tables A1, A4, B1, B4, C1, C4, D1, 

and D4 as the numbers of animals bearing such lesions 

at a specific anatomic site and the numbers of animals 

with that site examined microscopically. For calculation 

of statistical significance, the incidences of most neoplasms (Tables A2, B2, C2, and D2) and all nonneoplastic lesions are given as the numbers of animals affected 

at each site examined microscopically. However, 

when macroscopic examination was required to detect 

neoplasms in certain tissues (e.g., Harderian gland, 

intestine, mammary gland, and skin) before microscopic 

evaluation, or when neoplasms had multiple potential 

sites of occurrence (e.g., leukemia or lymphoma), the 

denominators consist of the number of animals on which 

a necropsy was performed. Tables A2, B2, C2, and D2 

also give the survival-adjusted neoplasm rate for each 

group and each site-specific neoplasm. This survivaladjusted rate (based on the Poly-3 method described 

below) accounts for differential mortality by assigning 

a reduced risk of neoplasm, proportional to the third 

power of the fraction of time on study, only to sitespecific, lesion-free animals that do not reach terminal 

sacrifice.

Analysis of Neoplasm 

and Nonneoplastic Lesion Incidences

The Poly-k test (Bailer and Portier, 1988; Portier and 

Bailer, 1989; Piegorsch and Bailer, 1997) was used to 

assess neoplasm and nonneoplastic lesion prevalence. 

This test is a survival-adjusted quantal-response procedure that modifies the Cochran-Armitage linear trend 

test to take survival differences into account. More 

specifically, this method modifies the denominator in 

the quantal estimate of lesion incidence to approximate 

more closely the total number of animal years at risk. 
Sodium Dichromate Dihydrate, NTP TR 546 29

For analysis of a given site, each animal is assigned a 

risk weight. This value is one if the animal had a lesion 

at that site or if it survived until terminal sacrifice; if 

the animal died prior to terminal sacrifice and did not 

have a lesion at that site, its risk weight is the fraction 

of the entire study time that it survived, raised to the kth 

power.

This method yields a lesion prevalence rate that depends 

only upon the choice of a shape parameter for a Weibull 

hazard function describing cumulative lesion incidence 

over time (Bailer and Portier, 1988). Unless otherwise 

specified, a value of k=3 was used in the analysis of sitespecific lesions. This value was recommended by Bailer 

and Portier (1988) following an evaluation of neoplasm 

onset time distributions for a variety of site-specific neoplasms in control F344 rats and B6C3F1 mice (Portier 

et al., 1986). Bailer and Portier (1988) showed that the 

Poly-3 test gave valid results if the true value of k was 

anywhere in the range from 1 to 5. A further advantage 

of the Poly-3 method is that it does not require lesion 

lethality assumptions. Variation introduced by the use 

of risk weights, which reflect differential mortality, 

was accommodated by adjusting the variance of the 

Poly-3 statistic as recommended by Bieler and Williams 

(1993).

Tests of significance included pairwise comparisons of 

each exposed group with controls and a test for an overall exposure-related trend. Continuity-corrected Poly-3 

tests were used in the analysis of lesion incidence, and 

reported P values are one sided. The significance of 

lower incidences or decreasing trends in lesions is represented as 1–P with the letter N added (e.g., P=0.99 is 

presented as P=0.01N). 

Analysis of Continuous Variables

Two approaches were employed to assess the significance of pairwise comparisons between exposed and 

control groups in the analysis of continuous variables. 

Body weight data, which historically have approximately 

normal distributions, were analyzed with the parametric 

multiple comparison procedures of Dunnett (1955) 

and Williams (1971, 1972). Hematology and clinical 

chemistry data, which have typically skewed distributions, were analyzed using the nonparametric multiple 

comparison methods of Shirley (1977) (as modified by 

Williams, 1986) and Dunn (1964). Jonckheere’s test 

(Jonckheere, 1954) was used to assess the significance 

of the dose-related trends and to determine whether a 

trend-sensitive test (Williams’ or Shirley’s test) was 

more appropriate for pairwise comparisons than a test 

that does not assume a monotonic dose-related trend 

(Dunnett’s or Dunn’s test). Prior to statistical analysis, 

extreme values identified by the outlier test of Dixon and 

Massey (1957) were examined by NTP personnel, and 

implausible values were eliminated from the analysis. 

Average severity values were analyzed for significance 

with the Mann-Whitney U test (Hollander and Wolfe, 

1973). 

Historical Control Data

The concurrent control group represents the most valid 

comparison to the treated groups and is the only control 

group analyzed statistically in NTP bioassays. However, 

historical control data are often helpful in interpreting potential treatment-related effects, particularly for 

uncommon or rare neoplasm types. For meaningful 

comparisons, the conditions for studies in the historical 

database must be generally similar. One significant factor affecting the background incidence of neoplasms at a 

variety of sites is diet. In 1995, the NTP incorporated a 

new diet (NTP-2000) that contains less protein and more 

fiber and fat than the NIH-07 diet previously used in 

toxicity and carcinogenicity studies (Rao, 1996, 1997). 

The NTP historical database contains all studies that use 

the NTP-2000 diet with histopathology findings completed within the most recent 5-year period. A second 

potential source of variability is route of administration. 

In general, the historical database for a given study will 

include studies using the same route of administration, 

and the overall incidences of neoplasms for all routes of 

administration are included for comparison, including 

the present study.

Quality Assurance Methods

The 2-year studies were conducted in compliance with 

Food and Drug Administration Good Laboratory Practice 

Regulations (21 CFR, Part 58). In addition, as records 

from the 2-year studies were submitted to the NTP 

Archives, these studies were audited retrospectively by 

an independent quality assurance contractor. Separate 

audits covered completeness and accuracy of the pathology data, pathology specimens, final pathology tables, 

and a draft of this NTP Technical Report. Audit procedures and findings are presented in the reports and are 

on file at NIEHS. The audit findings were reviewed and 

assessed by NTP staff, and all comments were resolved 

or otherwise addressed during the preparation of this 

Technical Report.
30 Sodium Dichromate Dihydrate, NTP TR 546 
31

RESULTS

Rats

2-Year Study

Survival

Estimates of 2-year survival probabilities for male and

female rats are shown in Table 2 and in the KaplanMeier survival curves (Figure 1). Survival of exposed 

groups was similar to that of the control groups.

Body Weights, Water and Compound 

Consumption, and Clinical Findings

Mean body weights of the 14.3, 57.3, and 172 mg/L 

groups of male and female rats were generally similar 

to those of the control groups throughout the study 

(Tables 3 and 4; Figure 2). Mean body weights of 

516 mg/L males and females were less than those of 

controls throughout the study and by the end of the study 

were 88% and 89% that of the respective controls. The

lower body weights were partly attributed to poor palatability of the dosed water and consequent reductions 

in water consumption rather than direct toxic effects 

of sodium dichromate dihydrate exposure. Water consumption by 172 and 516 mg/L rats was less than that 

by the controls throughout the study (Tables G1 and 

G2). Decreases were evident from the first week of the 

study and continued until terminal sacrifice. During the 

second year of the study, the average water consumption was reduced by 15% and 22% and by 15% and 27% 

that of the controls in the 172 and 516 mg/L male and 

female rats, respectively. Drinking water concentrations 

of 14.3, 57.3, 172, or 516 mg/L resulted in average daily 

doses of approximately 0.6, 2.2, 6, or 17 mg sodium 

dichromate dihydrate/kg body weight for male rats and 

0.7, 2.7, 7, or 20 mg/kg for female rats. No clinical 

findings were attributed to sodium dichromate dihydrate 

exposure.
32 Sodium Dichromate Dihydrate, NTP TR 546 

Table 2

Survival of Rats in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Male

Animals initially in study 50 50 50 50 50

Missinga 0 0 1 0 1

Moribund 16 15 16 9 16

Natural deaths 6 5 3 5 4

Animals surviving to study termination 28 30 30 36 29

Percent probability of survival at end of studyb 56 60 61 72 59

Mean survival (days)c 695 670 672 692 694

Survival analysisd P=0.904N P=1.000N P=1.000N P=0.221N P=1.000N

Female

Animals initially in study 50 50 50 50 50

Moribund 12 15 9 10 18

Natural deaths 5 3 9 4 1

Animals surviving to study termination 33e 32 32 36 31

Percent probability of survival at end of study 66 64 64 72 62

Mean survival (days) 696 691 694 686 685

Survival analysis P=0.748 P=0.959 P=0.965 P=0.806N P=0.745

a Censored from survival analyses b Kaplan-Meier determinations c Mean of all deaths (uncensored, censored, and terminal sacrifice) d The result of the life table trend test (Tarone, 1975) is in the control column, and the results of the life table pairwise comparisons 

(Cox, 1972) with the controls are in the exposed group columns. A negative trend or lower mortality in an exposed group is indicated by N. e Includes one animal that died during the last week of the study
Sodium Dichromate Dihydrate, NTP TR 546 33

Figure 1

Kaplan-Meier Survival Curves for Male and Female Rats Exposed to Sodium Dichromate Dihydrate 

in Drinking Water for 2 Years

Sodium Dichromate Dihydrate, NTP TR 546 33
34 Sodium Dichromate Dihydrate, NTP TR 546 

Table 3

Mean Body Weights and Survival of Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 0 mg/L 14.3 mg/L 57.3 mg/L

on Av. Wt. No. of Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) Survivors (g) controls) Survivors (g) controls) Survivors

1 118 50 117 99 50 117 99 50

8 151 50 149 99 50 146 97 50

15 185 50 183 99 50 181 98 50

22 218 50 215 99 50 213 98 50

29 243 50 240 99 50 239 99 50

36 261 50 257 99 50 257 99 50

43 275 50 271 99 50 272 99 50

50 289 50 286 99 50 285 99 50

57 305 50 301 99 50 302 99 50

64 317 50 312 99 50 313 99 50

71 334 50 329 98 50 331 99 50

78 345 50 340 99 50 339 98 50

85 351 50 345 98 50 348 99 50

113 387 50 381 98 50 383 99 50

141 410 50 404 99 50 407 99 50

169 434 50 427 98 50 431 99 50

197 451 50 443 98 50 448 99 50

225 468 50 458 98 50 464 99 50

253 480 50 471 98 50 477 99 50

281 488 50 478 98 50 483 99 49

309 490 50 485 99 50 488 100 49

337 501 50 495 99 48 497 99 48

365 511 50 502 98 47 505 99 48

393 515 50 507 98 47 512 99 48

421 523 50 515 98 47 519 99 48

449 524 50 515 98 47 519 99 48

477 525 50 516 98 45 518 99 48

505 525 48 517 98 45 520 99 46

533 530 47 519 98 45 525 99 45

561 532 47 518 97 44 525 99 44

589 531 46 515 97 42 522 98 43

617 529 45 519 98 40 519 98 40

645 526 44 517 98 38 520 99 36

673 513 41 515 100 36 517 101 32

701 515 32 503 98 33 514 100 31

Mean for weeks

1-13 261 257 99 257 99

14-52 457 449 98 453 99

53-101 523 514 98 518 99
Sodium Dichromate Dihydrate, NTP TR 546 35

Table 3

Mean Body Weights and Survival of Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 172 mg/L 516 mg/L

on Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) controls) Survivors (g) controls) Survivors

1 117 99 50 118 100 50

8 147 97 50 143 95 50

15 180 97 50 173 93 50

22 210 97 50 201 93 50

29 235 97 50 225 93 50

36 254 97 50 243 93 50

43 267 97 50 257 93 50

50 279 96 50 270 93 50

57 295 96 50 285 93 50

64 304 96 50 295 93 50

71 321 96 50 311 93 50

78 330 96 50 320 93 50

85 338 96 50 324 92 50

113 373 96 50 363 94 50

141 395 96 50 386 94 50

169 418 96 50 407 94 50

197 437 97 50 424 94 50

225 449 96 50 437 94 50

253 462 96 50 447 93 50

281 469 96 50 454 93 50

309 477 97 50 461 94 50

337 486 97 50 468 94 50

365 490 96 50 475 93 50

393 496 96 50 479 93 50

421 503 96 49 485 93 50

449 504 96 49 484 92 50

477 503 96 49 484 92 50

505 501 96 49 483 92 50

533 508 96 47 487 92 50

561 507 95 46 483 91 48

589 506 95 44 473 89 47

617 502 95 42 480 91 41

645 501 95 39 474 90 39

673 500 97 39 462 90 36

701 500 97 38 455 88 32

Mean for weeks

1-13 252 97 243 94

14-52 441 96 427 94

53-101 502 96 477 91
36 Sodium Dichromate Dihydrate, NTP TR 546 

Table 4

Mean Body Weights and Survival of Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 0 mg/L 14.3 mg/L 57.3 mg/L

on Av. Wt. No. of Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) Survivors (g) controls) Survivors (g) controls) Survivors

1 100 50 99 99 50 100 99 50

9 122 50 120 99 50 121 99 50

16 135 50 132 98 50 134 99 50

23 150 50 146 97 50 147 98 50

30 157 50 154 98 50 154 98 50

37 164 50 161 98 50 162 98 50

44 170 50 168 99 50 167 98 50

51 175 50 172 98 50 172 98 50

58 180 50 178 99 50 177 98 50

65 183 50 180 99 50 180 98 50

72 188 50 184 98 50 185 98 50

79 193 50 189 98 50 188 97 50

86 198 50 193 97 50 192 97 50

114 208 50 203 97 50 202 97 50

142 217 50 211 97 50 209 96 50

170 229 50 223 98 50 221 97 50

198 237 50 229 97 50 229 97 50

226 246 50 239 97 50 237 96 50

254 255 50 248 97 50 246 97 50

282 263 50 255 97 50 253 96 50

310 272 50 261 96 50 262 96 50

338 281 50 271 96 50 271 96 50

366 289 50 279 97 50 278 96 50

394 297 50 288 97 49 287 97 50

422 309 50 297 96 49 297 96 50

450 314 50 302 96 49 304 97 50

478 317 50 307 97 48 310 98 49

506 323 49 312 97 48 315 98 49

534 332 48 323 97 48 322 97 48

562 337 48 328 98 46 325 97 47

590 341 46 332 97 46 333 98 44

618 336 42 332 99 43 333 99 43

646 348 40 336 96 41 340 98 43

674 350 39 339 97 37 346 99 38

702 351 35 338 96 34 346 98 34

Mean for weeks

1-13 163 160 98 160 98

14-52 245 238 97 237 96

53-101 326 316 97 318 98
Sodium Dichromate Dihydrate, NTP TR 546 37

Table 4

Mean Body Weights and Survival of Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 172 mg/L 516 mg/L

on Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) controls) Survivors (g) controls) Survivors

1 99 99 50 99 98 50

9 119 98 50 115 94 50

16 131 97 50 129 95 50

23 145 97 50 144 96 50

30 153 97 50 152 97 50

37 161 98 50 159 97 50

44 166 98 50 165 97 50

51 171 97 50 170 97 50

58 175 97 50 175 97 50

65 178 97 50 178 97 50

72 183 98 50 182 97 50

79 186 97 50 186 96 50

86 192 97 50 190 96 50

114 201 97 50 199 96 50

142 206 95 50 207 95 50

170 218 95 50 215 94 50

198 226 95 50 222 94 50

226 235 96 50 230 94 50

254 242 95 50 237 93 50

282 248 94 50 242 92 50

310 256 94 50 248 91 50

338 265 94 50 254 90 50

366 272 94 50 263 91 50

394 279 94 49 268 90 50

422 290 94 49 275 89 50

450 296 94 48 281 89 50

478 302 95 48 284 90 48

506 308 95 47 290 90 47

534 318 96 46 298 90 47

562 319 95 45 300 89 46

590 325 95 42 307 90 42

618 326 97 40 314 93 40

646 333 96 39 315 90 40

674 337 96 37 318 91 36

702 340 97 36 312 89 35

Mean for weeks

1-13 158 97 157 96

14-52 233 95 228 93

53-101 311 95 294 90
38 Sodium Dichromate Dihydrate, NTP TR 546 

Figure 2

Growth Curves for Male and Female Rats Exposed 

to Sodium Dichromate Dihydrate in Drinking Water for 2 Years
Sodium Dichromate Dihydrate, NTP TR 546 39

Hematology and Clinical Chemistry

The hematology and clinical chemistry data for male 

rats are listed in Tables 5 and E1. An exposure concentration-related erythrocyte microcytosis, evidenced 

by decreased mean cell volumes, occurred on day 4 and 

persisted throughout the study in the 172 and 516 mg/L 

groups; the 57.3 mg/L group demonstrated minor changes 

on day 22 and at months 3 and 6. In the 516 mg/L animals, the severity of the microcytosis peaked with an 

approximately 20% to 25% decrease in red cell size on 

day 22 and at month 3. The severity of the microcytosis 

ameliorated with time. For example, by 12 months, the 

red cells of the 516 mg/L animals were only 5% smaller 

than those of the controls. Changes in the mean cell 

hemoglobin value mimicked the alterations in mean cell 

volume and were a reflection of the smaller red cells. 

Mean cell hemoglobin concentration demonstrated 

small, exposure concentration-related decreases (less 

than or equal to 10%) in the 172 and 516 mg/L animals. 

The mean cell hemoglobin concentration decreases were 

most severe on day 22 or at month 3; they ameliorated 

with time.

An exposure-related anemia, evidenced by decreases 

in hematocrit (instrument-derived), packed cell volume 

(spun microhematocrit), hemoglobin, and erythrocyte 

count values, developed by day 22 and affected the 

57.3, 172, and 516 mg/L groups. The anemia was most 

severe on day 22 (an approximate 30% decrease in the 

516 mg/L group) but resolved with time. In fact, at 

3 months, erythrocyte counts were increased, in contrast 

to the lower hematocrit and hemoglobin values in the 516 

mg/L group; the erythrocyte counts remained slightly 

elevated (less than 10%) in the higher-exposed animals 

out to the 12-month time point. The increased numbers 

of nucleated erythrocytes and/or reticulocytes in the 516 

mg/L animals on day 22 and at month 3 were indicative 

of an erythropoietic response. Microscopic evaluation 

of the blood smears demonstrated increased poikilocytes, erythrocyte fragments/schizocytes, keratocytes, 

erythrocyte hypochromia, and microcytes that suggested 

increased erythrocyte injury or turnover. These changes 

were most prominent in the higher-exposed animals on 

day 22 and at month 3. Taken together, it appears that 

the erythropoietic tissues were able to respond to the 

anemia (also evidenced by slightly increased incidences 

of bone marrow hyperplasia in the core study male rats 

(0 mg/L, 4/50; 14.3 mg/L, 12/50; 57.3 mg/L, 7/49; 172 

mg/L, 7/50; 516 mg/L, 6/49; Table A4), but there was 

some ineffective erythropoiesis resulting in production 

of increased numbers of smaller erythrocytes. This 

effect was not observed at 6 or 12 months demonstrating 

that, with time, the animals adapted to exposure. 

Increases in serum alanine aminotransferase activity 

occurred in the 57.3 mg/L or greater groups; however, serum sorbitol dehydrogenase activities and bile 

acid concentrations were unaffected (Table E1). The 

severity of the serum alanine aminotransferase activity increases peaked at 3 months (e.g., greater than a 

twofold increase in the 516 mg/L group), stabilized, 

and remained elevated at this level to the 12-month 

time point. While there was an indication of a chronic 

inflammatory process of minimal severity in the liver, 

the lack of corroborating evidence in other markers of 

liver injury suggests that the alanine aminotransferase 

increases may have been related to enzyme induction in 

the liver instead of increased hepatocellular membrane 

leakage. 
40 Sodium Dichromate Dihydrate, NTP TR 546 

Table 5

Selected Hematology Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n

Day 4 9 10 9 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 8 10

Hematocrit (auto) (%)

Day 4 37.5 ± 0.5 37.7 ± 0.5 36.4 ± 0.8 35.8 ± 0.7 37.0 ± 0.6

Day 22 46.5 ± 0.9 45.3 ± 0.5 44.2 ± 0.7 38.4 ± 0.8** 28.0 ± 0.6**

Month 3 45.1 ± 0.3 44.6 ± 0.4 44.7 ± 0.5 44.6 ± 0.5 43.0 ± 0.5**

Month 6 46.5 ± 0.3 46.7 ± 0.5 46.3 ± 0.5 46.5 ± 0.4 46.0 ± 0.3

Month 12 48.8 ± 0.6 48.0 ± 0.4 48.8 ± 0.7 49.3 ± 0.5 48.6 ± 0.4

Hematocrit (spun) (%) 

Day 4 38.2 ± 0.5b 38.4 ± 0.6 36.7 ± 0.9 36.4 ± 0.6 37.3 ± 0.6

Day 22 46.0 ± 1.1 44.4 ± 0.4 43.2 ± 0.6* 38.7 ± 0.6** 33.5 ± 0.8**

Month 3 45.3 ± 0.4 44.5 ± 0.3 44.5 ± 0.4 44.1 ± 0.5 41.0 ± 0.5**

Month 6 45.9 ± 0.4 45.7 ± 0.5 45.5 ± 0.4 45.5 ± 0.5 45.0 ± 0.3

Month 12 47.6 ± 0.5 46.6 ± 0.4 47.4 ± 0.5 47.7 ± 0.4 47.3 ± 0.4

Hemoglobin (g/dL)

Day 4 12.9 ± 0.2 13.0 ± 0.2 12.5 ± 0.3 12.3 ± 0.2 12.8 ± 0.2

Day 22 15.5 ± 0.3 15.1 ± 0.2 14.2 ± 0.2** 12.0 ± 0.3** 10.1 ± 0.2**

Month 3 15.1 ± 0.1 14.9 ± 0.1 14.9 ± 0.2 14.6 ± 0.2* 12.9 ± 0.2**

Month 6 15.2 ± 0.1 15.2 ± 0.2 15.0 ± 0.2 14.9 ± 0.1 14.5 ± 0.1**

Month 12 15.8 ± 0.2 15.4 ± 0.2 15.6 ± 0.2 15.6 ± 0.2 15.3 ± 0.1*

Erythrocytes (106/μL)

Day 4 6.75 ± 0.11 6.80 ± 0.10 6.67 ± 0.17 6.73 ± 0.11 6.98 ± 0.12

Day 22 7.80 ± 0.13 7.74 ± 0.15 8.06 ± 0.16 8.10 ± 0.14 6.21 ± 0.13**

Month 3 9.28 ± 0.05 9.24 ± 0.06 9.46 ± 0.11 9.75 ± 0.11** 10.93 ± 0.16**

Month 6 9.34 ± 0.06 9.43 ± 0.08 9.54 ± 0.11 9.71 ± 0.08** 10.15 ± 0.13**

Month 12 9.27 ± 0.10 9.17 ± 0.07 9.40 ± 0.12 9.61 ± 0.11 9.74 ± 0.08**

Reticulocytes (auto) (106/μL)

Day 4 0.62 ± 0.04 0.56 ± 0.04 0.50 ± 0.04 0.24 ± 0.02** 0.19 ± 0.02**

Day 22 0.38 ± 0.03 0.34 ± 0.02 0.38 ± 0.03 0.43 ± 0.04 0.63 ± 0.07**

Month 3 0.23 ± 0.01 0.24 ± 0.01 0.22 ± 0.01 0.21 ± 0.01 0.30 ± 0.01**

Month 6 0.24 ± 0.00 0.22 ± 0.01 0.22 ± 0.01 0.24 ± 0.01 0.24 ± 0.01

Month 12 0.23 ± 0.01 0.23 ± 0.01 0.24 ± 0.01 0.26 ± 0.02 0.23 ± 0.01

Reticulocytes (manual) (106/μL)

Day 4 0.30 ± 0.06 0.29 ± 0.03 0.29 ± 0.06 0.30 ± 0.03 0.27 ± 0.02

Day 22 0.32 ± 0.04 0.27 ± 0.03 0.30 ± 0.03 0.41 ± 0.05 0.52 ± 0.04**

Month 3 0.12 ± 0.02 0.14 ± 0.02 0.10 ± 0.02 0.11 ± 0.03 0.13 ± 0.02

Month 12 0.19 ± 0.02 0.18 ± 0.01 0.21 ± 0.02 022 ± 0.03 0.17 ± 0.01

Nucleated erythrocytes (103/μL) 

Day 4 0.50 ± 0.17b 0.60 ± 0.22 0.20 ± 0.13b 0.50 ± 0.17 0.10 ± 0.10

Day 22 0.20 ± 0.13 0.20 ± 0.13 0.30 ± 0.15 0.30 ± 0.21 1.40 ± 0.22**

Month 3 0.20 ± 0.13 0.40 ± 0.22 0.30 ± 0.21 0.20 ± 0.13 0.00 ± 0.00

Month 6 0.30 ± 0.15 0.10 ± 0.10 0.20 ± 0.13 0.10 ± 0.10 0.40 ± 0.22

Month 12 0.30 ± 0.21 0.30 ± 0.21 0.10 ± 0.10 0.38 ± 0.26 0.10 ± 0.10

Mean cell volume (fL)

Day 4 55.6 ± 0.3 55.5 ± 0.3 54.6 ± 0.3 53.3 ± 0.1** 53.0 ± 0.2**

Day 22 59.5 ± 0.4 58.6 ± 0.5 54.9 ± 0.5** 47.4 ± 0.4** 45.0 ± 0.7**

Month 3 48.6 ± 0.2 48.3 ± 0.2 47.3 ± 0.2** 45.7 ± 0.2** 39.2 ± 0.6**

Month 6 49.8 ± 0.1 49.5 ± 0.1 48.6 ± 0.1** 47.8 ± 0.2** 45.4 ± 0.5**

Month 12 52.6 ± 0.2 52.4 ± 0.2 51.9 ± 0.3 51.4 ± 0.3** 49.9 ± 0.2**
Sodium Dichromate Dihydrate, NTP TR 546 41

Table 5

Selected Hematology Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n

Day 4 9 10 9 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 8 10

Mean cell hemoglobin (pg) 

Day 4 19.1 ± 0.1 19.1 ± 0.1 18.7 ± 0.1* 18.3 ± 0.1** 18.4 ± 0.1**

Day 22 19.8 ± 0.1 19.5 ± 0.2 17.7 ± 0.2** 14.8 ± 0.2** 16.3 ± 0.5**

Month 3 16.2 ± 0.1 16.2 ± 0.1 15.7 ± 0.0** 15.0 ± 0.1** 11.9 ± 0.3**

Month 6 16.3 ± 0.1 16.1 ± 0.1 15.7 ± 0.1** 15.3 ± 0.1** 14.3 ± 0.2**

Month 12 17.0 ± 0.1 16.8 ± 0.1 16.6 ± 0.1* 16.2 ± 0.1** 15.7 ± 0.1**

Mean cell hemoglobin concentration (g/dL)

Day 4 34.4 ± 0.2 34.4 ± 0.2 34.3 ± 0.2 34.4 ± 0.2 34.7 ± 0.2

Day 22 33.3 ± 0.1 33.3 ± 0.1 32.2 ± 0.2 31.2 ± 0.2** 36.2 ± 0.8

Month 3 33.4 ± 0.1 33.5 ± 0.2 33.2 ± 0.1 32.7 ± 0.1** 30.2 ± 0.3**

Month 6 32.7 ± 0.1 32.5 ± 0.1 32.3 ± 0.1* 32.1 ± 0.1** 31.6 ± 0.2**

Month 12 32.3 ± 0.2 32.1 ± 0.3 32.0 ± 0.2 31.6 ± 0.2* 31.5 ± 0.2*

* Significantly different (P#0.05) from the control group by Dunn’s or Shirley’s test

** P#0.01 a Mean ± standard error. Statistical tests were performed on unrounded data. b n=10
42 Sodium Dichromate Dihydrate, NTP TR 546 

Pathology and Statistical Analyses

This section describes the statistically significant or 

biologically noteworthy changes in the incidences of 

mononuclear cell leukemia and neoplasms or nonneoplastic lesions of the oral cavity (oral mucosa and 

tongue), liver, small intestine (duodenum), mesenteric 

lymph node, pancreatic lymph node, salivary gland, 

pancreas, and adrenal medulla. Summaries of the 

incidences of neoplasms and nonneoplastic lesions, 

statistical analyses of primary neoplasms that occurred 

with an incidence of at least 5% in at least one animal group, and historical incidences for the neoplasms 

mentioned in this section are presented in Appendix A 

for male rats and Appendix B for female rats.

Oral Cavity (Oral Mucosa and Tongue): Exposure to 

sodium dichromate dihydrate resulted in the development of neoplasms of the squamous epithelium that lines 

the oral mucosa and tongue. The incidences of squamous 

cell carcinoma in the oral mucosa of 516 mg/L male and 

female rats were significantly greater than those in the 

controls (Tables 6, A2, and B2). None were seen in concurrent or historical controls for drinking water studies. 

Squamous cell carcinomas were also observed in the 

oral mucosa of two 172 mg/L female rats and exceeded 

the historical control ranges for drinking water studies 

and for all routes of administration. One squamous cell 

carcinoma of the tongue occurred in a 14.3 mg/L male 

and one in a 172 mg/L female. A squamous cell papilloma of the oral mucosa occurred in one 516 mg/L male, 

and a squamous cell papilloma of the tongue occurred 

in one 516 mg/L male. One control and one 14.3 mg/L 

female had squamous cell papillomas of the tongue. 

The incidences of squamous cell papilloma or squamous 

cell carcinoma (combined) of the oral mucosa or tongue 

of 516 mg/L male and female rats were significantly 

greater than those in the controls (Table 6).

Microscopically, the squamous cell carcinomas of the 

oral mucosa were highly invasive, irregular masses. 

Typically, they appeared to originate in the oral mucosa 

of the palate adjacent to the upper molar teeth; invaded the 

tongue, Harderian gland, and the soft tissues surrounding 

the nose in some animals; and penetrated the maxilla 

and invaded the brain in one case. Carcinomas consisted of a mixture of variably sized islands and short, 

irregular cords of relatively welldifferentiated stratified 

squamous epithelium, surrounded by moderate amounts 

of dense fibrous connective tissue stroma (Plates 1 and 

2). Frequently, the epithelium formed cyst-like structures filled with keratin (keratin pearls). The squamous 

cell papillomas of the oral mucosa and tongue were 

exophytic masses that projected from the mucosa and 

consisted of irregular papillary proliferations of mature 

squamous epithelium supported by a core of fibrovascular stroma. In the tongue, squamous cell carcinoma was 

diagnosed when the stroma of these papillary masses 

had evidence of invasion in the form of irregular foci of 

dysplastic epithelium (Plates 3 and 4).
Sodium Dichromate Dihydrate, NTP TR 546 43

Table 6

Incidences of Neoplasms of the Oral Cavity in Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Male

Number Necropsied 50 50 49 50 49

Oral Mucosa

Squamous Cell Papillomaa 0 0 0 0 1

Squamous Cell Carcinomab

Overall Ratec 0/50 (0%) 0/50 (0%) 0/49 (0%) 0/50 (0%) 6/49 (12%)

Adjusted Rated 0.0% 0.0% 0.0% 0.0% 13.6%

Terminal Ratee 0/28 (0%) 0/30 (0%) 0/30 (0%) 0/36 (0%) 1/29 (3%)

First Incidence (days) —g — — — 543

Poly-3 Testf P<0.001 —h — — P=0.015

Tongue

Squamous Cell Papilloma 0 0 0 0 1

Squamous Cell Carcinoma 0 1 0 0 0

Oral Mucosa or Tongue

Squamous Cell Papilloma or Squamous Cell Carcinomai

Overall Rate 0/50 (0%) 1/50 (2%) 0/49 (0%) 0/50 (0%) 7/49 (14%)

Adjusted Rate 0.0% 2.4% 0.0% 0.0% 15.7%

Terminal Rate 0/28 (0%) 1/30 (3%) 0/30 (0%) 0/36 (0%) 1/29 (3%)

First Incidence (days) — 729 (T) — — 543

Poly-3 Test P<0.001 P=0.487 — — P=0.007

Female

Number Necropsied 50 50 50 50 50

Oral Mucosa

Squamous Cell Carcinomaj

Overall Rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 2/50 (4%) 11/50 (22%)

Adjusted Rate 0.0% 0.0% 0.0% 4.6% 23.9%

Terminal Rate 0/33 (0%) 0/32 (0%) 0/32 (0%) 1/36 (3%) 2/31 (7%)

First Incidence (days) — — — 646 506

Poly-3 Test P<0.001 — — P=0.233 P<0.001

Tongue

Squamous Cell Papilloma 1 1 0 0 0

Squamous Cell Carcinoma 0 0 0 1 0
44 Sodium Dichromate Dihydrate, NTP TR 546 

Table 6

Incidences of Neoplasms of the Oral Cavity in Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Female (continued)

Oral Mucosa or Tongue

Squamous Cell Papilloma or Squamous Cell Carcinomak

Overall Rate 1/50 (2%) 1/50 (2%) 0/50 (0%) 2/50 (4%) 11/50 (22%)

Adjusted Rate 2.2% 2.3% 0.0% 4.6% 23.9%

Terminal Rate 0/33 (0%) 1/32 (3%) 0/32 (0%) 1/36 (3%) 2/31 (7%)

First Incidence (days) 618 729 (T) — 646 506

Poly-3 Test P<0.001 P=0.756 P=0.503N P=0.491 P=0.002

(T)Terminal sacrifice a Number of animals with neoplasm b Historical incidence for 2-year drinking water studies with controls given NTP-2000 diet (mean ± standard deviation): 

0/350; all routes: 5/1,499 (0.3% ± 0.7%), range 0%-2% c Number of animals with neoplasm per number of animals necropsied d Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality e Observed incidence at terminal kill f Beneath the control incidence is the P value associated with the trend test. Beneath the exposed group incidence are the P values 

corresponding to pairwise comparisons between the controls and that exposed group. The Poly-3 test accounts for differential mortality in 

animals that do not reach terminal sacrifice. A lower incidence in an exposed group is indicated by N. g Not applicable; no neoplasms in animal group h Value of statistic cannot be computed. i Historical incidence for drinking water studies: 1/300 (0.3% ± 0.8%), range 0%-2%; all routes: 10/1,449 (0.6% ± 0.8%), range 0%-2% j Historical incidence for drinking water studies: 0/300; all routes: 5/1,400 (0.4% ± 0.8%), range 0%-2% k Historical incidence for drinking water studies: 3/250 (1.2% ± 1.1%), range 0%-2%; all routes: 14/1,350 (1.1% ± 1.6%), range 0%-6%

Liver: The incidences of minimal to moderate histiocytic 

cellular infiltration in 516 mg/L males and in females 

exposed to 57.3 mg/L or greater were significantly 

greater than those in the controls (Tables 7, A4, and B4). 

The incidences of chronic inflammation in 172 mg/L 

males and all exposed groups of females were significantly increased. Chronic inflammation was generally 

of minimal to mild severity in most groups, including 

the controls, except 516 mg/L females in which there 

appeared to be a slight increase in the severity (mild to 

moderate). There were statistically significant, exposure 

concentration-related increases in the incidences of fatty 

change in female rats exposed to 57.3 mg/L or greater. 

The incidences of basophilic focus in males exposed 

to 57.3 or 172 mg/L were significantly increased. The 

incidence of clear cell focus in females exposed to 172 

mg/L was significantly increased.

Histiocytic infiltrates were characterized by the presence 

of individual, small clusters and sometimes syncytia 

of histiocytes (macrophages) that were typically randomly scattered throughout the hepatic parenchyma but 

often occurred in increased numbers within the portal 

areas. The histiocytes were large (approximately 20 to 

80 microns in diameter) and had abundant pale, lightly 

eosinophilic, faintly stippled cytoplasm and single, 

small, peripheral, dark basophilic nuclei (Plates 5 and 

6). In minimally affected livers, the histiocytes often 

occurred singly, whereas in more severely affected livers, the histiocytes occurred as small clusters of a few 

cells. The biological significance of the histiocytic 

cellular infiltrates is unknown but may suggest phagocytosis of some insoluble chemical precipitate. Chronic 

inflammation consisted of small, randomly scattered 

aggregates of macrophages, lymphocytes, and neutrophils in variable numbers and in some cases were 

associated with the larger histiocytic infiltrates (Plate 7). 

Chronic inflammation is consistent with changes that 

are considered to be background or spontaneous lesions 

commonly observed in aged rats and appears to be exac-
Sodium Dichromate Dihydrate, NTP TR 546 45

Table 7

Incidences of Nonneoplastic Lesions of the Liver in Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Male

Number Examined Microscopically 50 50 49 50 49

Infiltration Cellular, Histiocytea 1 (1.0)b 0 2 (1.0) 5 (1.4) 34** (1.4)

Inflammation, Chronic 19 (1.1) 25 (1.2) 21 (1.3) 28* (1.1) 26 (1.3)

Basophilic Focus 22 28 29* 32* 30

Female

Number Examined Microscopically 50 50 50 50 50

Infiltration Cellular, Histiocyte 1 (1.0) 5 (1.0) 21** (1.3) 42** (2.0) 47** (2.6)

Inflammation, Chronic 12 (1.3) 21* (1.2) 28** (1.3) 35** (1.6) 39** (2.1)

Fatty Change 3 (3.3) 7 (3.6) 10* (2.5) 13** (2.5) 16** (2.8)

Clear Cell Focus 7 5 7 20** 7

* Significantly different (P#0.05) from the control group by the Poly-3 test 

** P#0.01 a Number of animals with lesion b Average severity grade of lesions in affected animals: 1=minimal, 2=mild, 3=moderate, 4=marked

erbated by exposure. Fatty change consisted of scattered 

hepatocytes that contained one to several variably sized, 

discrete, clear, cytoplasmic vacuoles (fat droplets).

Small Intestine (Duodenum): The incidences of minimal 

to mild histiocytic cellular infiltration were significantly 

increased in males exposed to 57.3 mg/L or greater and 

in 172 and 516 mg/L females (Tables 8, A4, and B4). 

The infiltrating histiocytes were morphologically similar 

to those observed in the liver and occurred singly or as 

clusters of cells within the lamina propria at the tips of 

the duodenal villi (Plate 8).

Mesenteric Lymph Node: The incidences of histiocytic 

cellular infiltration in males exposed to 57.3 mg/L or 

greater and in 172 and 516 mg/L females were significantly increased compared to the controls (Tables 8, 

A4, and B4); there was a slight increase in the severity 

of infiltrates in 172 and 516 mg/L females with more 

animals in these groups having mild severity grades 

relative to the controls and the lower exposure concentration groups. The incidences of minimal lymph node 

hemorrhage in males exposed to 57.3 mg/L or greater 

and in 516 mg/L females were significantly increased 

and may have been caused by the histiocytic infiltrates 

in the lymph node. The histiocytic infiltrates were 

morphologically similar to those that occurred in the 

liver and duodenum. They formed numerous variably 

sized clusters randomly scattered within the cortex and/

or medullary sinuses (Plates 9 and 10). Frequently, the 

clusters coalesced to form sheets that in some cases 

replaced much of the lymph node parenchyma.

Pancreatic Lymph Node: The incidences of histiocytic 

cellular infiltration were increased in the 516 mg/L males 

and in 57.3 mg/L or greater females with the incidence 

in 172 mg/L females being significantly greater than 

that in the controls (Tables 8, A4, and B4); the average 

severity of infiltration in 57.3 mg/L or greater females 

increased with increasing dose. Histiocytic infiltrates 

were morphologically similar to those that occurred in 

the liver, duodenum, and mesenteric lymph nodes.

Salivary Gland: The incidence of salivary gland atrophy was significantly increased in 172 mg/L females 

compared to that in the controls; in general, the average 
46 Sodium Dichromate Dihydrate, NTP TR 546 

Table 8

Incidences of Selected Nonneoplastic Lesions in Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Male

Small Intestine, Duodenuma 48 48 47 46 48

Infiltration Cellular, Histiocyteb 0 0 6* (1.2)c 36** (1.1) 47** (1.5)

Lymph Node, Mesenteric 49 50 49 50 49

Infiltration Cellular, Histiocyte 13 (2.0) 11 (1.5) 30** (1.9) 39** (2.1) 41** (2.1)

Hemorrhage 2 (1.5) 7 (1.1) 9* (1.3) 8* (1.1) 17** (1.3)

Lymph Node, Pancreatic 32 34 34 36 33

Infiltration Cellular, Histiocyte 17 (2.0) 22 (1.6) 17 (2.0) 17 (2.1) 25 (2.1)

Female

Small Intestine, Duodenum 46 49 48 46 50

Infiltration Cellular, Histiocyte 0 0 1 (1.0) 30** (1.0) 47** (1.2)

Lymph Node, Mesenteric 50 50 50 50 50

Infiltration Cellular, Histiocyte 21 (1.7) 18 (1.4) 27 (1.5) 36** (2.0) 42** (2.4)

Hemorrhage 11 (1.1) 13 (1.3) 16 (1.3) 14 (1.1) 21* (1.3)

Lymph Node, Pancreatic 29 36 30 34 33

Infiltration Cellular, Histiocyte 17 (2.0) 20 (1.9) 23 (2.6) 32** (2.8) 27 (3.0)

Salivary Gland 50 50 50 50 50

Atrophy 9 (1.3) 7 (1.4) 10 (1.2) 17* (1.4) 17 (2.1)

* Significantly different (P#0.05) from the control group by the Poly-3 test 

** P#0.01 a Number of animals with tissue examined microscopically b Number of animals with lesion c Average severity grade of lesions in affected animals: 1=minimal, 2=mild, 3=moderate, 4=marked

severity was minimal in the controls and in the 14.3, 

57.3, and 172 mg/L groups, but mild in the 516 mg/L 

group. Microscopically, atrophy occurred as single, 

focal lesions in the salivary glands. Minimal lesions 

consisted of small, poorly defined foci of atrophic acini, 

whereas mild lesions were larger, well-defined foci. 

The atrophic foci consisted of shrunken glandular acini 

lined by low cuboidal epithelial cells devoid of secretory material, accompanied by an increased prominence 

of the interstitial stroma and ducts, some of which were 

variably dilated (Plates 11 and 12). Atrophy is an agerelated spontaneous change commonly observed in rats. 

The biological significance of the increases in female 

rats in this study is uncertain.

Other Findings: Exposure to sodium dichromate 

dihydrate resulted in statistically significant increased 

incidences of neoplasms in one or more exposed groups. 

In general, the increased incidences occurred in one 

sex, one or more exposed groups, and were not exposure concentration related. These lesions included 

pancreatic acinar adenoma in males (0 mg/L, 1/50; 

14.3 mg/L, 2/50; 57.3 mg/L, 6/49; 172 mg/L, 2/50; 

516 mg/L, 2/49; Table A2); benign pheochromocytoma of the adrenal medulla in males (6/49, 13/50, 

14/49, 5/50, 4/49; Table A2); and mononuclear cell 

leukemia in females (8/50, 18/50, 13/50, 7/50, 11/50; 

Table B2). The relationship of these changes to exposure is uncertain.
Sodium Dichromate Dihydrate, NTP TR 546 47

Mice

2-Year Study

Survival

Estimates of 2-year survival probabilities for male 

and female mice are shown in Table 9 and in the 

Kaplan-Meier survival curves (Figure 3). Survival of 

all exposed groups was similar to that of the control 

groups.

Body Weights, Water and Compound 

Consumption, and Clinical Findings

The mean body weights of 257.4 mg/L male mice were 

less than those of the controls from months 2 through 6 

of the study but were only slightly less than the control 

group by the end of the study; mean body weights of 

172 mg/L females were less than those of the controls 

from months 3 through 12 of the study; and mean body 

weights of 516 mg/L females were less than those of 

the controls from month 2 until the end of the study 

(Tables 10 and 11; Figure 4). By the end of the study, the

mean body weight of 172 mg/L females was 8% less 

than that of the controls, and the mean body weight of 

516 mg/L females was 15% less than that of the control 

group. The lower body weights were partly attributed 

to poor palatability of the dosed water and consequent 

reductions in water consumption rather than direct toxic 

effects of sodium dichromate dihydrate exposure. Water 

consumption by 85.7 and 257.4 mg/L males and 172 

and 516 mg/L females was less than that by the controls 

throughout the study (Tables G3 and G4). During the 

second year of the study, the average water consumption 

was reduced by 15% and 35% than that of the controls 

in 85.7 and 257.4 mg/L males, respectively, and by 

25% and 32% than that of the controls in the 172 and 

516 mg/L females, respectively. Drinking water concentrations of 14.3, 28.6, 85.7, or 257.4 mg/L for males 

and 14.3, 57.3, 172, or 516 mg/L for females resulted 

in average daily doses of approximately 1.1, 2.6, 7, or 

17 mg sodium dichromate dihydrate/kg body weight for 

male mice and 1.1, 3.9, 9, or 25 mg/kg for female mice. 

No clinical findings were attributed to sodium dichromate dihydrate exposure.
48 Sodium Dichromate Dihydrate, NTP TR 546 

Table 9

Survival of Mice in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Male

Animals initially in study 50 50 50 50 50

Moribund 7 5 5 4 3

Natural deaths 10 10 10 8 15

Animals surviving to study termination 33a 35 35 38 32a

Percent probability of survival at end of studyb 66 70 70 76 64

Mean survival (days)c 700 694 682 708 689

Survival analysisd P=0.724 P=0.949N P=0.982N P=0.387N P=0.918

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Female

Animals initially in study 50 50 50 50 50

Moribund 5 0 2 2 3

Natural deaths 8 11 3 6 5

Animals surviving to study termination 37e 39a 45a 42e 42

Percent probability of survival at end of study 74 78 90 84 84

Mean survival (days) 696 705 714 709 709

Survival analysis P=0.504N P=0.780N P=0.068N P=0.333N P=0.285N

a Includes one animal that died during the last week of the study b Kaplan-Meier determinations c Mean of all deaths (uncensored, censored, and terminal sacrifice). d The result of the life table trend test (Tarone, 1975) is in the control column, and the results of the life table pairwise comparisons 

(Cox, 1972) with the controls are in the exposed group columns. A negative trend or lower mortality in an exposed group is indicated by N. e Includes two animals that died during the last week of the study
Sodium Dichromate Dihydrate, NTP TR 546 49

Figure 3

Kaplan-Meier Survival Curves for Male and Female Mice Exposed to Sodium Dichromate Dihydrate 

in Drinking Water for 2 Years
50 Sodium Dichromate Dihydrate, NTP TR 546 

Table 10

Mean Body Weights and Survival of Male Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 0 mg/L 14.3 mg/L 28.6 mg/L

on Av. Wt. No. of Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) Survivors (g) controls) Survivors (g) controls) Survivors

1 23.2 50 23.2 100 50 23.5 101 50

8 25.3 50 25.3 100 50 25.7 102 50

15 26.8 50 26.9 101 50 27.1 101 50

22 28.0 50 28.2 101 50 28.5 102 50

29 29.9 50 30.0 100 50 30.3 101 50

36 31.5 50 31.5 100 50 31.9 101 50

43 32.9 50 33.0 100 50 33.4 102 50

50 34.2 50 34.5 101 50 34.8 102 50

57 35.9 50 36.3 101 50 36.6 102 50

64 37.5 50 37.8 101 50 38.2 102 49

71 38.9 50 39.4 101 50 39.9 103 49

78 40.3 50 40.6 101 50 41.2 102 49

85 41.7 50 41.8 100 50 42.4 102 49

113 46.7 50 46.5 100 50 47.2 101 49

141 48.9 50 48.7 100 50 49.2 101 49

169 50.1 50 49.9 100 50 50.2 100 49

197 51.4 50 51.8 101 50 51.8 101 49

225 52.2 50 52.6 101 50 52.5 101 49

253 52.7 50 52.7 100 50 52.7 100 49

281 53.8 50 53.8 100 50 53.7 100 49

309 53.8 50 53.6 100 50 53.9 100 49

337 54.5 50 54.6 100 50 54.7 100 49

365 55.2 50 55.0 100 49 55.0 100 49

393 55.5 50 55.2 100 49 55.2 100 49

421 55.1 50 54.9 100 49 54.1 98 49

449 55.3 49 55.0 100 49 54.4 98 49

477 55.6 49 55.2 99 49 54.2 98 49

505 55.1 48 53.7 97 49 53.6 97 47

533 54.0 48 52.6 97 48 52.9 98 47

561 54.3 48 52.5 97 48 53.1 98 45

589 53.0 48 52.1 98 45 52.3 99 43

617 52.0 48 51.6 99 44 50.7 98 42

645 51.7 44 50.7 98 41 49.3 96 39

673 51.7 38 50.5 98 37 48.8 94 38

701 50.3 36 49.9 99 35 46.9 93 37

Mean for weeks

1-13 32.8 33.0 101 33.3 102

14-52 51.6 51.6 100 51.8 100

53-101 53.8 53.0 99 52.3 97
Sodium Dichromate Dihydrate, NTP TR 546 51

Table 10

Mean Body Weights and Survival of Male Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 85.7 mg/L 257.4 mg/L

on Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) controls) Survivors (g) controls) Survivors

1 23.2 100 50 23.2 100 50

8 25.2 100 50 24.4 97 50

15 26.6 99 50 25.4 95 50

22 27.8 99 50 26.3 94 50

29 29.5 99 50 27.5 92 50

36 31.0 98 50 28.6 91 50

43 32.1 98 50 29.5 90 50

50 33.6 98 50 30.4 89 50

57 35.0 98 50 31.4 88 50

64 36.5 97 50 32.2 86 50

71 37.9 98 50 33.3 86 50

78 39.1 97 50 34.4 85 50

85 40.4 97 50 35.2 84 50

113 45.1 97 50 38.9 83 50

141 47.9 98 50 42.2 86 50

169 49.5 99 50 44.5 89 50

197 51.6 100 50 47.4 92 50

225 51.8 99 50 48.3 93 50

253 52.4 99 50 48.9 93 50

281 53.3 99 50 49.7 92 50

309 53.5 99 50 49.9 93 50

337 54.4 100 50 50.4 93 50

365 54.4 99 50 50.8 92 50

393 55.0 99 50 50.9 92 49

421 54.6 99 50 50.8 92 48

449 55.1 100 50 50.8 92 48

477 55.1 99 50 50.9 92 46

505 54.4 99 50 50.3 91 46

533 53.8 100 50 49.9 92 46

561 52.8 97 49 49.8 92 46

589 52.1 98 47 48.8 92 46

617 51.3 99 46 49.3 95 44

645 49.6 96 44 49.3 95 41

673 48.6 94 42 48.1 93 40

701 48.4 96 39 47.2 94 37

Mean for weeks

1-13 32.1 98 29.4 90

14-52 51.1 99 46.7 91

53-101 52.7 98 49.8 93
52 Sodium Dichromate Dihydrate, NTP TR 546 

Table 11

Mean Body Weights and Survival of Female Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 0 mg/L 14.3 mg/L 57.3 mg/L

on Av. Wt. No. of Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) Survivors (g) controls) Survivors (g) controls) Survivors

1 17.8 50 17.5 99 50 17.4 98 50

9 19.2 50 19.2 100 50 19.0 99 50

16 20.6 50 20.6 100 50 20.3 98 50

23 21.3 50 21.4 100 50 21.0 99 50

30 22.5 50 22.3 99 50 21.8 97 50

37 23.2 50 23.2 100 50 22.7 98 50

44 24.4 50 24.4 100 50 23.8 98 50

51 26.0 50 25.4 98 50 24.8 96 50

58 26.9 50 26.4 98 50 25.4 95 50

65 27.9 50 27.4 98 50 26.2 94 50

72 28.9 50 28.3 98 50 27.1 94 50

79 30.3 50 29.7 98 50 28.6 94 50

86 31.2 50 31.0 99 50 29.7 95 50

114 37.0 50 36.9 100 50 34.4 93 50

142 41.5 50 41.3 100 50 38.5 93 50

170 44.8 50 44.9 100 50 41.9 93 50

198 48.7 50 48.2 99 50 46.5 96 50

226 51.6 49 51.7 100 50 48.8 95 50

254 53.3 49 53.6 101 50 50.6 95 50

282 55.2 49 55.6 101 50 52.5 95 50

310 59.0 49 57.9 98 50 55.1 93 50

338 59.8 49 59.0 99 50 56.7 95 49

366 62.1 49 62.1 100 50 60.0 97 49

394 61.5 49 60.9 99 50 59.0 96 49

422 62.2 49 62.5 100 50 60.1 97 49

450 63.1 49 62.8 100 50 61.6 98 49

478 64.3 49 64.8 101 49 62.7 97 49

506 63.9 49 65.0 102 48 62.4 98 49

534 62.7 49 64.0 102 48 61.6 98 49

562 61.8 48 62.9 102 48 60.8 99 49

590 61.3 47 62.7 102 46 59.8 98 49

618 60.3 45 62.1 103 46 59.7 99 47

646 60.6 42 61.1 101 44 58.6 97 46

674 59.8 39 60.2 101 43 58.1 97 46

702 60.6 37 60.7 100 40 58.1 96 46

Mean for weeks

1-13 24.6 24.4 99 23.7 96

14-52 50.1 49.9 100 47.2 94

53-101 61.9 62.4 101 60.2 97
Sodium Dichromate Dihydrate, NTP TR 546 53

Table 11

Mean Body Weights and Survival of Female Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Days 172 mg/L 516 mg/L

on Av. Wt. Wt. (% of No. of Av. Wt. Wt. (% of No. of

Study (g) controls) Survivors (g) controls) Survivors

1 17.7 100 50 17.5 99 50

9 19.1 100 50 18.4 96 50

16 20.2 98 50 19.3 93 50

23 20.8 98 50 19.9 94 50

30 21.5 96 50 20.8 93 50

37 22.4 97 50 21.3 92 50

44 23.1 95 50 22.3 92 50

51 23.9 92 50 23.3 99 50

58 24.6 92 50 23.8 89 50

65 25.2 90 50 24.6 88 50

72 25.9 89 50 24.7 86 50

79 26.8 88 50 25.5 84 50

86 27.5 88 50 26.2 84 50

114 31.4 85 50 28.6 77 50

142 35.1 85 50 30.8 74 50

170 37.6 84 50 32.8 73 49

198 41.5 85 50 36.0 74 49

226 43.7 85 50 37.5 73 49

254 45.5 85 50 38.9 73 49

282 47.8 87 50 41.0 74 49

310 50.4 85 50 43.9 74 49

338 52.7 88 50 45.4 76 49

366 55.4 89 50 48.1 78 49

394 55.8 91 50 48.4 79 49

422 57.1 92 50 49.2 79 49

450 57.7 91 49 50.0 79 49

478 59.1 92 49 51.9 81 49

506 58.4 91 49 51.9 81 49

534 57.7 92 49 51.9 83 49

562 57.6 93 47 51.8 84 49

590 57.1 93 47 51.2 84 49

618 57.5 95 45 51.6 86 49

646 56.5 93 44 50.7 84 47

674 56.1 94 44 50.8 85 45

702 55.8 92 44 51.4 85 42

Mean for weeks

1-13 23.0 93 22.1 90

14-52 42.9 86 37.2 74

53-101 57.1 92 50.7 82
54 Sodium Dichromate Dihydrate, NTP TR 546 

Figure 4

Growth Curves for Male and Female Mice Exposed 

to Sodium Dichromate Dihydrate in Drinking Water for 2 Years
Sodium Dichromate Dihydrate, NTP TR 546 55

Hematology

The hematology data for female mice in the 2-year study 

of sodium dichromate dihydrate are listed in Tables 12 

and E2. Similar to the rat study, an exposure-related 

microcytosis, evidenced by decreased mean cell volume 

values, occurred in mice. The female mice were less 

affected than the male rats. A minimal (less than or 

equal to 8%) decrease in mean cell volume occurred at

all time points; the 172 and 516 mg/L groups were consistently affected. Changes in mean cell hemoglobin 

values mimicked the alterations in mean cell volume and 

reflected the smaller erythrocytes. Erythrocyte counts 

demonstrated small (less than or equal to 14%) increases 

at all time points with the 516 mg/L group most consistently affected. However, no other estimators of the 

erythron demonstrated any effects. 
56 Sodium Dichromate Dihydrate, NTP TR 546 

Table 12

Selected Hematology Data for Female Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 9 10 10

Hematocrit (auto) (%)

Day 22 50.0 ± 0.7 49.2 ± 0.4 50.0 ± 0.9 50.6 ± 0.7 49.6 ± 0.5

Month 3 47.7 ± 0.7 49.9 ± 0.5* 49.2 ± 0.8 49.4 ± 0.6 50.4 ± 0.5*

Month 6 48.4 ± 0.7 49.2 ± 0.5 47.8 ± 0.6 48.0 ± 0.8 49.2 ± 0.8

Month 12 45.0 ± 0.5 45.6 ± 0.3 45.2 ± 0.6 45.0 ± 0.7 45.1 ± 0.8

Hematocrit (spun) (%) 

Day 22 50.0 ± 0.7 49.0 ± 0.3 49.4 ± 0.8 49.6 ± 0.7 48.5 ± 0.5

Month 3 48.3 ± 0.6 50.4 ± 0.5* 49.3 ± 0.6 49.4 ± 0.5 50.4 ± 0.4*

Month 6 49.0 ± 0.6 50.2 ± 0.5 48.7 ± 0.5 48.9 ± 0.8 49.9 ± 0.7

Month 12 46.5 ± 0.4 47.4 ± 0.2 46.9 ± 0.5 46.4 ± 0.6 46.7 ± 0.6

Hemoglobin (g/dL)

Day 22 16.8 ± 0.2 16.5 ± 0.1 16.7 ± 0.3 16.9 ± 0.2 16.4 ± 0.2

Month 3 16.0 ± 0.2 16.7 ± 0.2* 16.4 ± 0.3 16.3 ± 0.2 16.5 ± 0.2

Month 6 16.1 ± 0.2 16.4 ± 0.2 16.0 ± 0.2 16.0 ± 0.3 16.2 ± 0.3

Month 12 14.9 ± 0.1 15.3 ± 0.2 15.1 ± 0.2 15.0 ± 0.2 14.9 ± 0.3

Erythrocytes (106/μL)

Day 22 10.25 ± 0.15 10.20 ± 0.08 10.47 ± 0.19 10.77 ± 0.13* 10.61 ± 0.13*

Month 3 10.10 ± 0.16 10.66 ± 0.13* 10.55 ± 0.17* 10.95 ± 0.10** 11.55 ± 0.16**

Month 6 10.56 ± 0.15 10.81 ± 0.10 10.60 ± 0.13 10.77 ± 0.20 11.50 ± 0.20**

Month 12 9.58 ± 0.10 9.72 ± 0.09 9.77 ± 0.10 9.95 ± 0.13* 10.30 ± 0.21**

Reticulocytes (106/μL)

Day 22 0.32 ± 0.01 0.30 ± 0.01 0.33 ± 0.02 0.31 ± 0.01 0.32 ± 0.02

Month 3 0.33 ± 0.01 0.31 ± 0.01 0.34 ± 0.02 0.34 ± 0.03 0.34 ± 0.02

Month 6 0.36 ± 0.02 0.37 ± 0.01 0.39 ± 0.04 0.36 ± 0.03 0.35 ± 0.02

Month 12 0.32 ± 0.02 0.33 ± 0.01 0.32 ± 0.01 0.36 ± 0.02 0.37 ± 0.02

Nucleated erythrocytes (103/μL)

Day 22 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Month 3 0.00 ± 0.00 0.10 ± 0.10 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Month 6 0.10 ± 0.10 0.10 ± 0.10 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Month 12 0.00 ± 0.00b 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Mean cell volume (fL)

Day 22 48.8 ± 0.2 48.3 ± 0.1* 47.8 ± 0.2** 47.0 ± 0.2** 46.8 ± 0.2**

Month 3 47.2 ± 0.1 46.9 ± 0.3 46.7 ± 0.1 45.1 ± 0.2** 43.7 ± 0.3**

Month 6 45.8 ± 0.2 45.5 ± 0.3 45.1 ± 0.2* 44.6 ± 0.2** 42.8 ± 0.3**

Month 12 46.9 ± 0.3 46.9 ± 0.3 46.3 ± 0.3 45.2 ± 0.2** 43.9 ± 0.5**

Mean cell hemoglobin (pg) 

Day 22 16.4 ± 0.1 16.2 ± 0.0* 15.9 ± 0.1** 15.7 ± 0.1** 15.5 ± 0.1**

Month 3 15.8 ± 0.0 15.7 ± 0.1 15.6 ± 0.0** 14.9 ± 0.1** 14.3 ± 0.1**

Month 6 15.3 ± 0.1 15.2 ± 0.1 15.1 ± 0.1 14.9 ± 0.1** 14.1 ± 0.1**

Month 12 15.5 ± 0.1 15.7 ± 0.2 15.5 ± 0.1 15.1 ± 0.1* 14.4 ± 0.2**

Mean cell hemoglobin concentration (g/dL)

Day 22 33.6 ± 0.1 33.5 ± 0.1 33.3 ± 0.2 33.4 ± 0.1 33.1 ± 0.1**

Month 3 33.5 ± 0.1 33.5 ± 0.1 33.3 ± 0.1 33.1 ± 0.1** 32.8 ± 0.1**

Month 6 33.4 ± 0.2 33.4 ± 0.1 33.5 ± 0.2 33.4 ± 0.1 32.9 ± 0.1

Month 12 33.1 ± 0.2 33.5 ± 0.2 33.4 ± 0.1 33.3 ± 0.1 32.9 ± 0.1

* Significantly different (P#0.05) from the control group by Dunn’s or Shirley’s test

** P#0.01 a Mean ± standard error. Statistical tests were performed on unrounded data. b n=9
Sodium Dichromate Dihydrate, NTP TR 546 57

Pathology and Statistical Analyses

This section describes the statistically significant or 

biologically noteworthy changes in the incidences of 

neoplasms and/or nonneoplastic lesions of the small 

intestine (duodenum, jejunum, ileum), liver, mesenteric 

lymph node, pancreatic lymph node, and pancreas. 

Summaries of the incidences of neoplasms and nonneoplastic lesions, statistical analyses of primary neoplasms that occurred with an incidence of at least 5% in 

at least one animal group, and historical incidences for 

the neoplasms mentioned in this section are presented in 

Appendix C for male mice and Appendix D for female 

mice.

Small Intestine (Duodenum, Jejunum, and Ileum): In the 

duodenum, the incidences of adenoma occurred with a 

positive trend in males and females. The incidences of 

adenoma in 257.4 mg/L males and 172 and 516 mg/L 

females were significantly greater that those in the 

controls (Tables 13, C2, and D2). The incidences of 

multiple adenoma were also significantly increased in 

257.4 mg/L males and in 516 mg/L females. Adenomas 

were observed in one control, one 28.6 mg/L, and five 

85.7 mg/L males and in two 57.3 mg/L females; none of 

these increased incidences were statistically significant. 

However, the incidences of adenoma in 85.7 mg/L males 

and 57.3 mg/L females exceeded the historical control 

ranges for drinking water studies and for all routes of 

administration (Tables 13, C3, and D3). The incidences 

of carcinoma of the duodenum were increased in 85.7 

and 257.4 mg/L males and in 172 and 516 mg/L females; 

the incidence in 516 mg/L females was significantly 

greater than that in the controls. The incidences of 

carcinoma in 257.4 mg/L males and 516 mg/L females 

exceeded the historical control ranges for drinking water 

studies and for all routes of administration.

In the jejunum, the incidence of adenoma in 516 mg/L 

females was significantly increased compared to that 

in the controls (Tables 13 and D2). In females, one 

adenoma occurred in the 14.3 mg/L group and two 

adenomas occurred in the 172 mg/L group; the incidence in 172 mg/L females exceeded the historical 

control ranges for drinking water studies and for all 

routes of administration (Tables 13, C3, and D3). The 

incidence of adenoma was greater in 257.4 mg/L males 

but was not significantly increased compared to the 

controls. However, the incidence exceeded the historical control ranges for drinking water studies and for all 

routes of administration (Tables 13 and C3). In the historical controls for the jejunum, adenoma has not been 

observed in mice in drinking water studies, and only 

one adenoma has been observed in males for all routes 

of administration. Low incidences of carcinoma of the 

jejunum occurred in exposed male and female mice; in 

males, the incidences of carcinoma in the 14.3, 85.7, and 

257.4 mg/L groups did not exceed the historical control 

ranges for drinking water studies or for all routes of 

administration (Tables 13, C2, and C3). In females, the 

incidences of carcinoma of the jejunum in the 57.3 and 

172 mg/L groups exceeded the historical control ranges 

for drinking water studies and for all routes of administration (Tables 13, D2, and D3).

For the entire small intestine (duodenum, jejunum, and 

ileum), the incidences of adenoma and carcinoma in 

257.4 mg/L males and the incidences of adenoma or 

carcinoma (combined) in 85.7 and 257.4 mg/L males 

were significantly greater than those in the controls. The 

incidences of adenoma in 85.7 mg/L males exceeded the 

historical control ranges for drinking water studies and 

for all routes of administration (Tables 13, C2, and C3). 

For the entire small intestine, the incidence of adenoma 

in 172 mg/L females, the incidences of adenoma and 

carcinoma in 516 mg/L females, and the incidences of 

adenoma or carcinoma (combined) in 172 and 516 mg/L 

females were significantly increased. The incidences of 

adenoma, carcinoma, and adenoma or carcinoma (combined) in 57.3 mg/L females exceeded the historical control ranges for drinking water studies and for all routes of 

administration (Tables 13, D2, and D3). The incidences 

of carcinoma in 172 mg/L females exceeded the historical control ranges for drinking water studies and for all 

routes of administration (Tables 13 and D3).

Adenomas were discrete, broad based, focally extensive, plaque-like lesions that thickened the mucosa 

and protruded into the lumen (Plates 13 and 14). They 

were composed of irregular, elongated, often branching 

crypts and irregular, glandular structures lined by one to 

several layers of densely packed, atypical, cuboidal to 

tall columnar, hyperchromatic epithelial cells with large 

oval to elongated nuclei. Increased mitotic activity was 

commonly evident.

Carcinomas were extensive, sessile, plaque-like neoplasms distinguished from adenomas by dysplastic epithelial growth, complete effacement of the mucosa with 

invasion of the submucosa and/or muscularis mucosa, 

degree of cellular atypia, and the presence of variable 

fibroplasia/desmoplasia (Plates 15 and 16). They were 

composed of hyperchromatic, atypical, pleomorphic 
58 Sodium Dichromate Dihydrate, NTP TR 546 

Table 13

Incidences of Neoplasms and Nonneoplastic Lesions in the Small Intestine of Mice 

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Male

Number Necropsied 50 50 50 50 50

Duodenum

Epithelium, Hyperplasia, Focala 0 0 0 1 (3.0)b 2 (3.5)

Epithelium, Hyperplasia, Diffuse 0 11** (2.0) 18** (1.6) 42** (2.1) 32** (2.1)

Infiltration Cellular, Histiocyte 0 2 (1.0) 4 (1.0) 37** (1.2) 35** (1.7)

Adenoma, Multiple 0 0 0 0 6*

Adenoma (includes multiple)c

 Overall Rated 1/50 (2%) 0/50 (0%) 1/50 (2%) 5/50 (10%) 15/50 (30%)

 Adjusted Ratee 2.2% 0.0% 2.3% 10.8% 32.9%

 Terminal Ratef 0/33 (0%) 0/35 (0%) 1/35 (3%) 5/38 (13%) 10/32 (31%)

 First Incidence (days) 665 —h 729 (T) 729 (T) 451

 Poly-3 Testg P<0.001 P=0.505N P=0.751 P=0.106 P<0.001

Carcinomai

 Overall Rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 2/50 (4%) 3/50 (6%)

 Adjusted Rate 0.0% 0.0% 0.0% 4.3% 6.8%

 Terminal Rate 0/33 (0%) 0/35 (0%) 0/35 (0%) 2/38 (5%) 3/32 (9%)

 First Incidence (days) — — — 729 (T) 729 (T)

 Poly-3 Test P=0.011 —j — P=0.243 P=0.113

Jejunum

Adenomak

 Overall Rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 0/50 (0%) 3/50 (6%)

 Adjusted Rate 0.0% 0.0% 0.0% 0.0% 6.8%

 Terminal Rate 0/33 (0%) 0/35 (0%) 0/35 (0%) 0/38 (0%) 2/32 (6%)

 First Incidence (days) — — — — 714

 Poly-3 Test P=0.002 — — — P=0.114

Carcinoma, Multiple 0 1 0 0 0

Carcinoma (includes multiple)l 0 2 0 1 2

Duodenum, Jejunum, or Ileum

Adenomam

 Overall Rate 1/50 (2%) 1/50 (2%) 1/50 (2%) 5/50 (10%) 17/50 (34%)

 Adjusted Rate 2.2% 2.3% 2.3% 10.8% 37.2%

 Terminal Rate 0/33 (0%) 1/35 (3%) 1/35 (3%) 5/38 (13%) 11/32 (34%)

 First Incidence (days) 665 729 (T) 729 (T) 729 (T) 451

 Poly-3 Test P<0.001 P=0.755 P=0.751 P=0.106 P<0.001

Carcinoman

 Overall Rate 0/50 (0%) 2/50 (4%) 1/50 (2%) 3/50 (6%) 5/50 (10%)

 Adjusted Rate 0.0% 4.5% 2.3% 6.5% 11.4%

 Terminal Rate 0/33 (0%) 2/35 (6%) 1/35 (3%) 3/38 (8%) 5/32 (16%)

 First Incidence (days) — 729 (T) 729 (T) 729 (T) 729 (T)

 Poly-3 Test P=0.014 P=0.233 P=0.492 P=0.123 P=0.028

Adenoma or Carcinomao

 Overall Rate 1/50 (2%) 3/50 (6%) 2/50 (4%) 7/50 (14%) 20/50 (40%)

 Adjusted Rate 2.2% 6.8% 4.6% 15.1% 43.8%

 Terminal Rate 0/33 (0%) 3/35 (9%) 2/35 (6%) 7/38 (18%) 14/32 (44%)

 First Incidence (days) 665 729 (T) 729 (T) 729 (T) 451

 Poly-3 Test P<0.001 P=0.296 P=0.485 P=0.032 P<0.001
Sodium Dichromate Dihydrate, NTP TR 546 59

Table 13

Incidences of Neoplastic and Nonneoplastic Lesions in the Small Intestine of Mice 

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Female

Number Necropsied 50 50 50 50 50

Duodenum

Epithelium, Hyperplasia, Focal 0 0 1 (2.0) 2 (3.0) 0

Epithelium, Hyperplasia, Diffuse 0 16** (1.6) 35** (1.7) 31** (1.6) 42** (2.2)

Infiltration Cellular, Histiocyte 0 0 4 (1.3) 33** (1.2) 40** (2.0)

Adenoma, Multiple 0 0 0 1 6*

Adenoma (includes multiple)p

 Overall Rate 0/50 (0%) 0/50 (0%) 2/50 (4%) 13/50 (26%) 12/50 (24%)

 Adjusted Rate 0.0% 0.0% 4.2% 27.8% 25.2%

 Terminal Rate 0/37 (0%) 0/39 (0%) 2/45 (4%) 13/42 (31%) 11/42 (26%)

 First Incidence (days) — — 729 (T) 729 (T) 693

 Poly-3 Test P<0.001 — P=0.251 P<0.001 P<0.001

Carcinomaq

 Overall Rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 1/50 (2%) 6/50 (12%)

 Adjusted Rate 0.0% 0.0% 0.0% 2.1% 12.6%

 Terminal Rate 0/37 (0%) 0/39 (0%) 0/45 (0%) 1/42 (2%) 5/42 (12%)

 First Incidence (days) — — — 729 (T) 625

 Poly-3 Test P<0.001 — — P=0.507 P=0.019

Jejunum

Epithelium, Hyperplasia, Diffuse 0 2 (2.0) 1 (2.0) 0 8** (1.9)

Infiltration Cellular, Histiocyte 0 0 0 2 (1.0) 8** (1.6)

Adenoma, Multiple 0 0 0 0 1

Adenoma (includes multiple)r

 Overall Rate 0/50 (0%) 1/50 (2%) 0/50 (0%) 2/50 (4%) 5/50 (10%)

 Adjusted Rate 0.0% 2.2% 0.0% 4.3% 10.6%

 Terminal Rate 0/37 (0%) 1/39 (3%) 0/45 (0%) 2/42 (5%) 5/42 (12%)

 First Incidence (days) — 729 (T) — 729 (T) 729 (T)

 Poly-3 Test P=0.002 P=0.504 — P=0.246 P=0.035

Carcinomas 1 0 2 2 1

Duodenum, Jejunum, or Ileum

Adenomat

 Overall Rate 0/50 (0%) 1/50 (2%) 2/50 (4%) 15/50 (30%) 16/50 (32%)

 Adjusted Rate 0.0% 2.2% 4.2% 32.0% 33.7%

 Terminal Rate 0/37 (0%) 1/39 (3%) 2/45 (4%) 15/42 (36%) 15/42 (36%)

 First Incidence (days) — 729 (T) 729 (T) 729 (T) 693

 Poly-3 Test P<0.001 P=0.504 P=0.251 P<0.001 P<0.001

Carcinomau

 Overall Rate 1/50 (2%) 0/50 (0%) 2/50 (4%) 3/50 (6%) 7/50 (14%)

 Adjusted Rate 2.2% 0.0% 4.2% 6.4% 14.7%

 Terminal Rate 1/37 (3%) 0/39 (0%) 2/45 (4%) 3/42 (7%) 6/42 (14%)

 First Incidence (days) 729 (T) — 729 (T) 729 (T) 625

 Poly-3 Test P<0.001 P=0.496N P=0.521 P=0.319 P=0.037
60 Sodium Dichromate Dihydrate, NTP TR 546 

Table 13

Incidences of Neoplastic and Nonneoplastic Lesions in the Small Intestine of Mice 

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Female (continued)

Adenoma or Carcinomav

 Overall Rate 1/50 (2%) 1/50 (2%) 4/50 (8%) 17/50 (34%) 22/50 (44%)

 Adjusted Rate 2.2% 2.2% 8.3% 36.3% 45.9%

 Terminal Rate 1/37 (3%) 1/39 (3%) 4/45 (9%) 17/42 (41%) 20/42 (48%)

 First Incidence (days) 729 (T) 729 (T) 729 (T) 729 (T) 625

 Poly-3 Test P<0.001 P=0.756N P=0.198 P<0.001 P<0.001

(T)Terminal sacrifice

* Significantly different (P#0.05) from the control group by the Poly-3 test 

** P#0.01 a Number of animals with lesion b Average severity grade of lesions in affected animals: 1=minimal, 2=mild, 3=moderate, 4=marked c Historical incidence for 2-year drinking water studies with controls given NTP-2000 diet (mean ± standard deviation): 

6/299 (2.0% ± 2.2%), range 0%-6%; all routes: 9/1,549 (0.6% ± 1.3%), range 0%-6% d Number of animals with neoplasm per number of animals necropsied e Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality f Observed incidence at terminal kill

g Beneath the control incidence is the P value associated with the trend test. Beneath the exposed group incidence are the P values 

corresponding to pairwise comparisons between the controls and that exposed group. The Poly-3 test accounts for differential mortality in 

animals that do not reach terminal sacrifice. A lower incidence in an exposed group is indicated by N h Not applicable; no neoplasms in animal group i Historical incidence for drinking water studies: 1/299 (0.3% ± 0.8%), range 0%-2%; all routes: 3/1,549 (0.2% ± 0.8%), range 0%-4% j Value of statistic cannot be computed. k Historical incidence for drinking water studies: 0/299; all routes: 1/1,549 (0.1% ± 0.4%), range 0%-2% l Historical incidence for drinking water studies: 5/299 (1.7% ± 1.5%), range 0%-4%; all routes: 25/1,549 (1.6% ± 2.2%), range 0%-8% m Historical incidence for drinking water studies: 6/299 (2.0% ± 2.2%), range 0%-6%; all routes: 10/1,549 (0.7% ± 1.3%), range 0%-6% n Historical incidence for drinking water studies: 6/299 (2.0% ± 1.8%), range 0%-4%; all routes: 30/1,549 (2.0% ± 2.2%), range 0%-8% o Historical incidence for drinking water studies: 11/299 (3.7% ± 3.7%), range 0%-10%; all routes: 39/1,549 (2.6% ± 2.7%),

range 0%-10% p Historical incidence for drinking water studies: 1/350 (0.3% ± 0.8%), range 0%-2%; all routes: 3/1,648 (0.2% ± 0.6%), range 0%-2% q Historical incidence for drinking water studies: 0/350; all routes: 1/1,648 (0.1% ± 0.4%), range 0%-2% r Historical incidence for drinking water studies: 0/350; all routes: 0/1,648 s Historical incidence for drinking water studies: 2/350 (0.6% ± 1.0%), range 0%-2%; all routes: 5/1,648 (0.3% ± 0.7%), range 0%-2% t Historical incidence for drinking water studies: 1/350 (0.3% ± 0.8%), range 0%-2%; all routes: 3/1,648 (0.2% ± 0.6%), range 0%-2% u Historical incidence for drinking water studies: 3/350 (0.9% ± 1.1%), range 0%-2%; all routes: 8/1,648 (0.5% ± 0.8%), range 0%-2% v Historical incidence for drinking water studies: 4/350 (1.1% ± 1.6%), range 0%-4%; all routes: 11/1,648 (0.7% ± 1.1%), range 0%-4%
Sodium Dichromate Dihydrate, NTP TR 546 61

(cuboidal, round, polygonal, columnar) epithelial cells 

that had round, oval, or elongated hyperchromatic nuclei. 

Increased mitotic activity was evident to a greater extent 

than in adenomas, and many mitoses were atypical.

Low incidences of focal epithelial hyperplasia occurred 

in the duodenum of exposed male and female mice 

(Tables 13, C4, and D4). Although the increased 

incidences were not exposure concentration-related or 

statistically significant, this lesion was considered a 

preneoplastic lesion related to exposure to sodium 

dichromate dihydrate because of its morphologic similarities to adenoma. Focal epithelial hyperplasias were 

distinguished from adenomas in that they were smaller, 

commonly located in the superficial mucosa, and were 

less discrete with margins that tended to blend with the 

normal surrounding mucosal epithelium. These hyperplastic lesions occurred as focal disorganized areas of 

increased cellularity that stained more basophilic than 

the surrounding histologically normal mucosa (Plates 

17 and 18). They were composed of crypts and villi 

that were lined by increased numbers of cuboidal to 

tall columnar epithelial cells that were morphologically 

similar to those of the adenomas.

The incidences of diffuse epithelial hyperplasia were 

significantly increased in the duodenum of all exposed 

groups of male and female mice (Tables 13, C4, and D4). 

In the jejunum, the incidence of diffuse epithelial hyperplasia was significantly increased in 516 mg/L females. 

Diffuse epithelial hyperplasia generally involved the 

entire mucosa. Compared to the controls, the duodenal 

villi of exposed mice were short, broad, blunt, and lined 

by densely packed, tall columnar epithelial cells that 

were more basophilic than the shorter epithelial cells 

lining the duodenum villi of the controls (Plates 19 to 

22). The epithelial cells and cell nuclei were often piled 

up in multiple layers along the long axis of the villi. 

Intestinal crypts were often elongated and generally 

appeared to contain increased numbers of epithelial cells 

with increased numbers of mitotic figures. Collectively, 

these lesions are considered consistent with regenerative 

hyperplasia secondary to previous epithelial cell injury.

The incidences of histiocytic cellular infiltration were 

significantly increased in the duodenum of 85.7 and 

257.4 mg/L males and of 172 and 516 mg/L females 

(Tables 13, C4, and D4). In the jejunum, the incidence of histiocytic cellular infiltration was significantly 

increased in 516 mg/L females compared to the controls. 

Histiocyte infiltrates in the duodenum and jejunum were 

consistent with those observed in the duodenum of rats. 

Infiltrates ranged from small clusters of three to five 

cells in the lower exposure groups to larger clusters 

that expanded the tips of the affected villi in the higher 

exposure groups.

Liver: The incidences of hepatoblastoma in 14.3, 85.7, 

and 257.4 mg/L males were significantly less than that 

in the controls (0 mg/L, 17/50; 14.3 mg/L, 8/50; 28.6 

mg/L, 11/50; 85.7 mg/L, 2/50; 257.4 mg/L, 0/50; Table 

C2). The incidences of hepatocellular adenoma or carcinoma (combined) in 28.6 mg/L males (42/50, 42/50, 

33/50, 37/50, 41/50) and hepatocellular adenoma, hepatocellular carcinoma, or hepatoblastoma (combined) in 

28.6 and 85.7 mg/L males (46/50, 42/50, 37/50, 37/50, 

41/50) were significantly decreased. The incidences of 

hepatocellular adenoma in 172 and 516 mg/L females 

were significantly less than that in the controls (0 mg/L, 

14/49; 14.3 mg/L, 21/50; 57.3 mg/L, 13/50; 172 mg/L, 

6/50; 516 mg/L, 3/50; Table D2). The biological significance of these decreases is unknown.

The incidences of histiocytic cellular infiltration were 

significantly increased in all exposed groups of females 

(Tables 14 and D4). The incidence of chronic inflammation was significantly increased in 172 mg/L females. 

The incidences of histiocytic cellular infiltration and 

chronic inflammation in female mice were consistent 

with those observed in rats. The incidence of clear cell 

focus in 257.4 mg/L males was significantly less than 

that in the controls (Tables 14 and C4). The incidences 

of eosinophilic focus in 257.4 mg/L males and 172 and 

516 mg/L females were significantly less than those in 

the controls. 

Mesenteric Lymph Node: The incidences of minimal to 

moderate histiocytic cellular infiltration in all exposed 

groups of male and female mice were significantly 

greater than those in the controls (Tables 14, C4, and 

D4). In general, there was a slight increase in the severity with increasing exposure concentration. Histiocytic 

cellular infiltration in mice was consistent with that 

observed in rats.

Pancreatic Lymph Node: The incidences of minimal 

to moderate histiocytic cellular infiltration in 85.7 and 

257.4 mg/L males and in 172 and 516 mg/L females 

were significantly greater than those in the controls 

(Tables 14, C4, and D4). Histiocytic cellular infiltration 

in mice was consistent with that observed in rats.
62 Sodium Dichromate Dihydrate, NTP TR 546 

Table 14

Incidences of Selected Nonneoplastic Lesions in Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Male

Livera 50 50 50 50 50

Clear Cell Focusb 20 17 19 16 7**

Eosinophilic Focus 27 26 19 21 12**

Lymph Node, Mesenteric 47 47 49 49 46

Infiltration Cellular, Histiocyte 14 (1.2)c 38** (1.1) 31** (1.2) 32** (1.5) 42** (2.5)

Lymph Node, Pancreatic 5 13 10 8 16

Infiltration Cellular, Histiocyte 0 2 (1.0) 2 (1.0) 5* (1.4) 12** (2.3)

Pancreas 49 49 50 49 48

Acinus, Cytoplasmic Alteration 0 1 (3.0) 1 (3.0) 9** (2.1) 8** (2.6)

 

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Female

Liver 49 50 50 50 50

Infiltration Cellular, Histiocyte 2 (1.0) 15** (1.1) 23** (1.0) 32** (1.0) 45** (1.9)

Inflammation, Chronic 16 (1.1) 21 (1.1) 22 (1.1) 27* (1.1) 24 (1.0)

Eosinophilic Focus 14 18 8 5* 4**

Lymph Node, Mesenteric 46 48 46 50 50

Infiltration Cellular, Histiocyte 3 (1.0) 29** (1.3) 26** (1.1) 40** (1.9) 42** (2.7)

Lymph Node, Pancreatic 14 12 15 14 13

Infiltration Cellular, Histiocyte 0 1 (1.0) 2 (1.5) 7** (1.9) 8** (2.5)

Pancreas 48 50 49 50 50

Acinus, Cytoplasmic Alteration 0 6* (2.5) 6* (2.0) 14** (2.4) 32** (2.6)

* Significantly different (P#0.05) from the control group by the Poly-3 test 

** P#0.01 a Number of animals with tissue examined microscopically b Number of animals with lesion c Average severity grade of lesions in affected animals: 1=minimal, 2=mild, 3=moderate, 4=marked

Pancreas: The incidences of cytoplasmic alteration 

in the pancreatic acini of males exposed to 85.7 or 

257.4 mg/L and in all exposed groups of females 

were significantly increased (Tables 14, C4, and D4). 

Cytoplasmic alteration was characterized by depletion 

of cytoplasmic zymogen granules from the pancreatic 

acinar epithelial cells. The biological significance of 

this change was uncertain. 
Sodium Dichromate Dihydrate, NTP TR 546 63

Chromium Tissue Distribution

Study

As part of the 2-year study, total chromium concentration in selected tissues and excreta were determined in 

additional groups of animals (tissue distribution groups) 

composed of male rats and female mice (Appendix J). 

These animals were treated the same as the animals in 

the core study groups with respect to exposure, housing, 

and handling. Two days prior to scheduled tissue collection, up to 10 animals in each exposure group of both 

species were placed in individual metabolism cages for 

the separate collection of urine and feces. Animals were 

provided undosed drinking water during this time to 

allow unabsorbed chromium to be excreted. The 48-hour 

washout period was based on an elimination half-life of 

8 to 21 hours (Bragt and van Dura, 1983; Vanoirbeek 

et al., 2003). Increased chromium concentrations in 

plasma after the washout period should represent the 

chromium entering plasma from the tissues. Insufficient 

mouse urine was collected for analysis at most time 

points; incomplete separation of urine and feces and low 

urine volumes for mice are typical in metabolism cages. 

After 48 hours, the animals were euthanized, and erythrocytes, plasma, liver, kidney, glandular stomach, and 

forestomach were removed for chromium analysis. The 

analytical procedure could not differentiate between the 

oxidation states of chromium, so the values reported are 

for total chromium irrespective of oxidation state. The 

complete data sets for rats and mice are presented in 

Tables J1 and J2, respectively. 

Chromium concentration in tissues from the 172 and 

516 mg/L rats and mice were significantly higher than 

their respective controls on days 6, 13, 182, and 371, 

with the exception of the forestomach on day 6. In the 

57.3 mg/L rats, chromium concentrations in the glandular stomach were also significantly elevated at all 

four time points, while concentrations in the liver and 

kidney were elevated at three of the four time points. 

In the 57.3 mg/L mice, chromium concentrations in the 

liver, kidney, and glandular stomach were significantly 

elevated at all four time points. In the 14.3 mg/L rats, 

chromium concentrations were significantly elevated 

above the controls in the glandular stomach on days 

6, 13, and 182, in the kidney on days 13, 182, and 

371, and in the liver on days 182 and 371. In the 14.3 

mg/L mice, chromium concentrations were significantly 

elevated in the liver and kidney at all four time points. 

In the lowest exposed group, chromium concentrations 

in erythrocytes and the forestomach were generally 

similar to those in control rats and mice. In all tissues, 

the chromium concentration at each time point tended 

to increase as the exposure concentration increased; 

however, the increases were not proportional to exposure concentration as shown for the liver in Figure 5. 

A nonproportional increase in tissue concentration with 

increasing exposure concentration is consistent with 

saturation of an active uptake mechanism for Cr VI. In 

accumulating tissues, such as the kidney, liver, forestomach, and glandular stomach, chromium concentration increased through day 371, but the increases were 

not proportional to the duration of exposure (Figure 6). 

In nonaccumulating tissues such as erythrocytes, chromium concentration did not increase after day 6. This 

observation can be interpreted as the tissues approaching 

equilibrium between Cr VI uptake and Cr III diffusion 

from the tissues and from cell turnover. In addition, 

there was a slight decrease in chromium exposure per 

day as the animals aged, based on decreased water consumption and increased body weight (Tables 3, 11, G1, 

and G4), which was also reflected in lower chromium 

concentration in feces at the later time points. In rats 

and mice, the tissues with the highest chromium concentrations were the glandular stomach, kidney, and liver. 

Mean concentrations of chromium in the kidney were 

greater than those in the liver at most time points for rats, 

whereas, the reverse was generally true for mice. Most 

of the ingested chromium was excreted in the feces of 

both species. The 48-hour feces collection contained up 

to 2 mg of chromium for rats and 160 μg for mice. The 

48-hour urine collection from rats contained up to 20 

μg total chromium, but urine collection from mice was 

unsuccessful as noted above.
64 Sodium Dichromate Dihydrate, NTP TR 546 

Figure 5

Chromium Concentrations on Days 6, 13, 182, and 371 in the Liver of Male Rats Exposed 

to Sodium Dichromate Dihydrate in Drinking Water

Figure 6

Chromium Concentrations in the Kidney, Liver, Erythrocytes, and Glandular Stomach 

of Male Rats Exposed to 516 mg/L Sodium Dichromate Dihydrate in Drinking Water
PLATE 1

Low magnification of a section of the nasal cavity demonstrating the

location of a squamous cell carcinoma (arrows) arising from the oral

mucosa of the soft palate that has invaded the adjacent submucosal

tissue and surrounded a molar tooth. Male rat exposed to 516 mg/L

sodium dichromate dihydrate in drinking water for 2 years. H&E

PLATE 2

Higher magnification of Plate 1 demonstrating the malignant features

of the squamous cell carcinoma. The neoplasm is composed of

pleomorphic islands, cords, and clusters of dysplastic squamous

epithelium (arrows) surrounded by dense proliferative connective

tissue stroma. Oral mucosa (M). H&E

PLATE 3

Squamous cell carcinoma projecting from the dorsal mucosal surface

of the tongue (arrows). The carcinoma is composed of thick papillae

of well-differentiated, mature, keratinized squamous epithelium

(arrows) supported by connective tissue stroma. Female rat exposed

to 14.3 mg/L sodium dichromate dihydrate in drinking water for

2 years. H&E

PLATE 4

Higher magnification of Plate 3. Note foci of dysplastic epithelium

(short arrows) within the stroma and extending from the base of the

surface epithelium (arrows). H&E
PLATE 5

Liver demonstrating histiocytic cellular infiltrates within the

parenchyma (thin arrows) and in portal areas (thick arrows). Female

rat exposed to 516 mg/L sodium dichromate dihydrate in drinking

water for 2 years. H&E

PLATE 6

Higher magnification of the histiocytic cellular infiltrates (arrows)

within a portal area. Histiocytes have abundant pale, lightly

eosinophilic, faintly stippled cytoplasm and single, small, dark

peripheral nuclei. Female rat exposed to 516 mg/L sodium

dichromate dihydrate in drinking water for 2 years. H&E

PLATE 7

Liver demonstrating focal chronic inflammation (thin arrows)

composed of a mixture of lymphocytes and small macrophages. Note

also adjacent histiocytic infiltrates within a portal area (thick arrows)

and hepatocytes with fatty change (curved arrow). Female rat

exposed to 516 mg/L sodium dichromate dihydrate in drinking water

for 2 years. H&E

PLATE 8

Duodenum demonstrating histiocytic cellular infiltrates (arrows)

within the lamina propria at the tips of the villi. Male rat exposed to

516 mg/L sodium dichromate dihydrate in drinking water for 2 years.

H&E
PLATE 9

Low magnification of a mesenteric lymph node demonstrating

variably sized clusters and syncytia of histiocytic cellular infiltrates

(arrows) within the parenchyma and sinusoids. Female rat exposed

to 172 mg/L sodium dichromate dihydrate in drinking water for

2 years. H&E

PLATE 10

agnification of Plate 9. Note that the histiocytes have

coalesced to form irregularly sized syncytia (arrows). H&E

PLATE 11

Low magnification demonstrating a well-defined focus of mild

atrophy (arrows) in the sublingual salivary gland. Female rat

exposed to 516 mg/L sodium dichromate dihydrate in drinking water

for 2 years. H&E

PLATE 12

Higher magnification of Plate 11. Histologically normal salivary

gland acini (A) are located at the right of the panel and within the

atrophic focus. The atrophic acini (arrows) have lost the pale

secretory material that is clearly evident in the normal acini and are

lined by low cuboidal epithelial cells. Salivary gland ducts (D). H&E
PLATE 13

Adenoma of the duodenum (arrows) that has distorted and replaced a

focally extensive segment of the mucosa and protruded into the

lumen. Normal mucosa is seen at either side of and opposite the

adenoma. Female mouse exposed to 172 mg/L sodium dichromate

dihydrate in drinking water for 2 years. H&E

PLATE 14

Higher magnification of Plate 13 showing a portion of the adenoma

composed of irregular glandular structures (arrows) lined by tall

columnar, hyperchromatic epithelial cells with piling up of the cells

in some areas. H&E

PLATE 15

Large carcinoma of the duodenum (arrows) that has effaced the

mucosa invading the submucosa, muscle layers, and the pancreas.

Male mouse exposed to 257.4 mg/L sodium dichromate dihydrate in

drinking water for 2 years. H&E

PLATE 16

Higher magnification of Plate 15 demonstrating dysplastic growth of

atypical cells (arrows) and extensive fibroplasia. H&E
PLATE 17

Focal epithelial hyperplasia (arrows) occurring in the superficial

mucosa of the duodenum. Female mouse exposed to 172 mg/L

sodium dichromate dihydrate in drinking water for 2 years. H&E

PLATE 18

Higher magnification of Plate 17. Villi are lined by increased

numbers of tall columnar, hyperchromatic epithelial cells (arrows)

that are similar to those in the adenomas. H&E

PLATE 19

Normal microscopic anatomy of the duodenum in a control female

mouse in the 2-year drinking water study of sodium dichromate

dihydrate. Note tall, slender villi (arrows) protruding into the lumen.

H&E

PLATE 20

Higher magnification of Plate 19. Duodenal villi (arrows) are tall

and slender and lined by a single layer of tall columnar epithelial

cells. H&E
PLATE 21

Diffuse epithelial hyperplasia in the duodenum. Duodenal villi

(arrows) are short, wide, and blunt. Female mouse exposed to

516 mg/L sodium dichromate dihydrate in drinking water for 2 years.

H&E

PLATE 22

Higher magnification of Plate 21. Note the hyperplastic epithelial

cells extending along the villi with piling up in some areas. Note the

histiocytes expanding the lamina propria at the tips of the villi

(arrows). H&E
65

Hexavalent chromium (Cr VI) was nominated for study 

because of its occurrence as a contaminant in drinking 

water source supplies and the potential for exposure 

of large populations of humans. Although Cr VI compounds are classified as human carcinogens following inhalation exposure (IARC, 1990; NTP, 1998), 

evidence regarding the carcinogenic potential of Cr 

VI compounds following exposure by other routes has 

been lacking. The results of 3-month toxicity studies 

of Cr VI administered in the drinking water to F344/N 

rats and B6C3F1, BALB/c, and am3-C57BL/6 mice 

as sodium dichromate dihydrate have been published 

(NTP, 2007a). Briefly, exposure to sodium dichromate 

dihydrate caused a microcytic hypochromic anemia in 

rats and mice, which was more severe in rats. The primary nonneoplastic lesions were observed in the glandular stomach of rats exposed to 1,000 mg/L and included 

focal ulceration, regenerative epithelial hyperplasia, and 

squamous epithelial metaplasia. Additional nonneoplastic lesions included histiocytic cellular infiltration in 

the duodenum of rats and mice, the liver of female rats, 

the mesenteric lymph nodes of mice, and the pancreatic 

lymph nodes of rats. 

The 2-year studies presented in this Technical Report 

were designed after an NTP public meeting on hexavalent chromium held on July 24, 2002, at the National 

Institute of Environmental Health Sciences in Research 

Triangle Park, NC, to consider the results of the prechronic studies and recommendations from the panel of 

scientific experts convened at this meeting (NTP, 2006). 

Exposure concentrations for the 2-year studies were 

selected based on these public discussions and careful 

review of the data from the 3-month toxicity studies. 

Based on concentrations found in source waters, an 

additional low exposure group was added to the 2-year 

studies to provide a concentration that was closer to concentrations to which humans might be exposed through 

the drinking water. The lowest concentration of sodium 

dichromate dihydrate (14.3 mg/L) used in the current 

2-year studies is equivalent to 5 mg/L chromium and 

is less than 10 times the reported hexavalent chromium 

concentration of 0.58 mg/L that was found in a groundwater monitoring well in Hinkley, CA (Pellerin and 

Booker, 2000). A wider spacing of exposures was also 

recommended to extend the exposure-response curve.

In the current 2-year studies, administration of sodium 

dichromate dihydrate in drinking water did not affect 

survival or produce clinical signs of toxicity in rats or 

mice of either sex. Significant exposure-related reductions in body weight gain and water consumption were 

observed for male and female rats and mice in the highest exposure groups. These effects were partly attributed to poor palatability of the dose formulations rather 

than direct toxicity from sodium dichromate dihydrate 

exposure. Lesions were not observed in the glandular 

stomach with increased duration of exposure in contrast 

to the 3-month studies, which used higher exposure 

concentrations.

Similar to the results from the 3-month toxicity studies 

in rats and mice, exposure-related erythrocyte microcytosis, hypochromia, and responsive anemia occurred 

in exposed rats. However, there was an amelioration 

of the effects by the 12-month time point, suggesting 

that the erythron effect was transient and resolved with 

time. The transient nature suggests an adaptive response 

by the exposed animals. The decreased red blood cell 

size and hypochromia is consistent with an ineffective 

erythropoiesis and could suggest some perturbation in 

iron metabolism and/or hemoglobin production. The 

mice were less affected compared to rats and had 

only a mild erythrocyte microcytosis. Similar hematological effects have been reported for rats and mice 

following oral exposure to Cr VI (Kumar and Barthwal,

1991; NTP, 1996a,b, 1997, 2007a; ATSDR, 2000). 

Hematological findings of reduced red blood cell, hematocrit, and hemoglobin values have also been reported in 

a 90-day inhalation toxicity study of soluble hexavalent 

chromium trioxide [CrO3 (VI)] in male Sprague-Dawley 

rats (Kim et al., 2004). 

In the 3-month toxicity studies (NTP, 2007a) and in the 

current 2-year studies of sodium dichromate dihydrate, 

histiocytic cellular infiltration was consistently observed 

in several tissues including the liver, duodenum, and 

mesenteric and pancreatic lymph nodes of rats and mice. 

DISCUSSION AND CONCLUSIONS
66 Sodium Dichromate Dihydrate, NTP TR 546 

The severities of these lesions were generally minimal 

to moderate and were characterized by the presence of 

individual, small clusters, and sometimes syncytia of 

macrophages. The significance of these lesions is not 

known. 

In the 2-year rat study, increased incidences of neoplasms of the squamous epithelium that lines the oral 

mucosa and tongue were observed in male and female 

rats, indicating a neoplastic effect of sodium dichromate 

dihydrate exposure on epithelial tissues of the upper 

alimentary system (oral cavity). There were positive 

trends in the incidences of squamous cell carcinoma 

of the oral cavity in male and female rats. The incidences of squamous cell carcinoma of the oral mucosa 

in 516 mg/L males and females were significantly 

increased. Two females exposed to 172 mg/L also had 

squamous cell carcinoma of the oral mucosa. The incidences of squamous cell carcinoma of the oral mucosa in 

males and females exceeded the historical control ranges 

for drinking water studies and for all routes of administration. The oral mucosa carcinomas were highly 

aggressive neoplasms that originated in the oral mucosa 

of the palate and invaded the underlying submucosa, the 

soft tissue surrounding the nose, and in a few cases, the 

tongue, Harderian gland, and brain. A positive trend also 

occurred in males and females when incidences of papilloma and carcinoma of the oral mucosa or tongue were 

combined, and the incidences in the 516 mg/L groups 

were significantly increased. Nonneoplastic lesions 

were not observed in the oral mucosa. Because of the 

increased incidences of squamous cell neoplasms of the 

oral cavity in both male and female rats and the rarity of 

these neoplasms in historical controls, these neoplasms 

were considered to be clear evidence of carcinogenicity 

of sodium dichromate dihydrate exposure. 

In contrast to rats, neoplasms in epithelial tissues of the 

lower alimentary system (small intestine) were observed 

in mice. The incidences of adenoma of the duodenum were significantly increased in males exposed to 

257.4 mg/L and females exposed to 172 or 516 mg/L. 

The incidence of adenoma of the jejunum was significantly increased in females exposed to 516 mg/L. The 

incidence of carcinoma was significantly increased in the 

duodenum of 516 mg/L female mice. When adenomas 

and carcinomas were combined for all sites of the small 

intestine, including the duodenum, jejunum, and ileum, 

there was a clear exposure response relationship, and 

the incidences were statistically significant in the two 

highest exposure groups of male and female mice. In 

addition, low incidences of focal epithelial hyperplasia 

were observed in the duodenum and jejunum of male 

and female mice. Although not statistically significant, 

this lesion was considered a preneoplastic lesion related 

to chemical exposure because of the cytologic similarities to adenomas. The incidence of diffuse epithelial 

cell hyperplasia was also elevated in exposed male and 

female mice compared to the control groups. The background incidence of adenoma or carcinoma (combined) 

in the small intestine (all sites) of B6C3F1 mice is very 

low in NTP studies (Tables C3 and D3). For example, 

only one adenoma has been observed in the duodenum 

of 350 historical control female mice, and no adenomas 

have been observed in the jejunum of 299 historical control male or 350 female mice in drinking water studies. 

The combined incidences of adenoma and carcinoma in 

57.3 mg/L female mice exceeded the historical control 

ranges. Based on these observations, the increased incidences of intestinal neoplasms were considered to be 

clear evidence of carcinogenicity of sodium dichromate 

dihydrate exposure. Only two other chemicals tested by 

the NTP, captan and o-nitrotoluene (NCI, 1977; NTP, 

2002), have caused increased incidences of neoplasms 

in the intestines of male or female mice; neither of these 

chemicals were administered in the drinking water. The 

2-year study of captan (NCI, 1977) is the only other 

study performed by the NTP in B6C3F1 mice in which 

both benign and malignant intestinal neoplasms of epithelial origin have been definitely attributed to chemical 

exposure (Shackelford and Elwell, 1999).

The lower body weights observed in male and female 

rats and mice exposed to the two highest exposure concentrations were partly attributed to poor palatability of 

the dosed water and consequent reductions in water consumption. However, several lines of evidence suggest 

that the animals were not dehydrated. When water consumption is adjusted for body weight (data not shown), 

dosed male and female rats and female mice drank 

approximately the same quantities of water per gram 

of body weight as the controls after the first 20 weeks 

on study. Male mice exposed to 257.4 mg/L drank less 

water per gram of body weight than did the controls 

throughout the study. Although mean body weights 

and water consumption were reduced in the higher 

exposure concentration groups, the average daily doses 

(mg sodium dichromate dihydrate per kilogram body 

weight) were in the same proportions as the drinking 

water concentrations (mg/L) for male and female rats 

and mice. Clinical observations related to dehydration 

including loss of skin turgor, dry mucous membranes, 
Sodium Dichromate Dihydrate, NTP TR 546 67

retraction of eyes, hypoactivity, and poor hair coats 

were not observed in rats or mice in the 2-year studies of 

sodium dichromate dihydrate. Abnormalities in hematology and clinical chemistry parameters that typically 

indicate dehydration include increases in hematocrit, 

urine specific gravity, and serum concentrations of 

albumin, total protein, and urea nitrogen. In the current 

2-year studies, hematology and clinical chemistry parameters were measured in male rats on days 4 and 22 and at 

months 3, 6, and 12. Significant decreases in hematocrit 

and serum concentrations of albumin and total protein 

were observed in males exposed to 516 mg/L. Taken 

together, these data suggest that the neoplastic and nonneoplastic effects of sodium dichromate dihydrate were 

not associated with dehydration.

There are few human or animal studies in the literature 

reporting the potential effects of Cr VI following oral 

exposure. However, inhalation exposure to Cr VI compounds has been shown to affect the gastrointestinal 

system in humans resulting in stomach pain, gastritis, 

and stomach and intestinal ulceration (ATSDR, 2000). 

Oral exposure also occurs after inhalation of chromium 

compounds due to mucociliary clearance and subsequent swallowing of particulates. Although lung cancer 

related to chromium exposure is well documented, there 

are conflicting reports in the literature (reviewed by 

Cohen et al., 1993; Costa 1997; ATSDR, 2000; Proctor 

et al., 2002; Costa and Klein 2006; Sedman et al., 

2006) regarding the occurrence of other types of cancer 

attri-buted to chromium exposure. Cohen et al. (1993) 

reported that increased incidences of stomach cancer 

were seen in numerous epidemiological studies; excesses 

of kidney, prostate gland, and bladder cancers were also 

seen in workers exposed to Cr VI. Costa (1997) compiled standardized mortality ratios from several studies 

that showed increased incidences of lymphoma and 

leukemia and cancers of the prostate gland, stomach, 

bladder, brain, and genital system in workers occupationally exposed to chromium. Only one epidemiology 

study has specifically addressed human exposure to Cr 

VI in drinking water (Zhang and Li, 1987); these authors 

reported increased incidences of lung and stomach 

tumors in a population consuming water contaminated 

by a nearby chromium ore smelting facility, although 

chromium exposure was likely by multiple routes (inhalation, drinking water, food, and soil). Similar to the 

results observed in the current 2-year rat study, occupational exposure to Cr VI in the electroplating industry 

may also be associated with oral cavity cancer, based 

on the diagnosis of oral cavity papillomas in employees 

of chromium electroplating factories in Czechoslovakia 

(ATSDR, 2000). While some reports described above 

suggest that Cr VI is a potential human carcinogen via 

the oral route of exposure, the USEPA (1998) and IARC 

(1990) concluded that there was insufficient data to 

make this determination. A review of human and animal 

data by Proctor et al. (2002) concluded that Cr VI is not 

carcinogenic in humans at permissible drinking water 

concentrations.

Nevertheless, based on the studies reviewed above, neoplasms in the oral cavity and stomach might be expected 

in animal carcinogenesis studies. In the current studies, 

oral cavity neoplasms were only observed in F344/N 

rats. Of 21 chemicals that have caused neoplasms of 

the oral cavity in NTP studies, none produced these 

neoplasms in male mice and only one, 1,2,3-trichloropropane, (NTP, 1993) produced oral cavity neoplasms 

in female mice. These results demonstrate the greater 

sensitivity of the oral cavity of rats to chemical-induced 

neoplasms compared to mice. Only one other lifetime 

animal carcinogenicity study was identified, in which 

Cr VI was administered in the drinking water as potassium chromate to three generations of NMRI mice 

(Borneff et al., 1968). In treated mice, two of 66 females 

exposed to 9 mg Cr VI/kg developed forestomach carcinoma compared with none of the control mice. This difference was not statistically significant. However, when 

benign (9/66 papillomas) and malignant (2/66 carcinomas) forestomach neoplasms were combined in three 

generations of female mice, there was a statistically 

significant increase compared to the control group (2/79) 

(Sedman et al., 2006). This study had several limitations 

including the use of only one exposure concentration of 

Cr VI and high early mortality in the F0 generation as a 

result of ectromelia (mousepox) virus. 

It has been hypothesized that oral exposure to Cr VI 

would not produce an increase in cancer, except perhaps 

in the stomach, due to the efficient reducing capacity 

of the stomach (De Flora et al., 1997; De Flora, 2000; 

Proctor et al., 2002). Notably, no neoplasms or nonneoplastic lesions were observed in the forestomach 

or glandular stomach of rats or mice. However, the 

exposure-related increases in the incidences of neoplasms in the duodenum and jejunum of mice in the 

current 2-year study suggests that under the conditions 

of this study, a portion of the administered Cr VI exited 

the stomach unreduced and exerted a carcinogenic 

effect on the proximal segments of the small intestine 

in mice. Differences in the oral toxicities of hexavalent 
68 Sodium Dichromate Dihydrate, NTP TR 546 

and trivalent chromium (Cr III) in animal studies provide additional evidence that hexavalent chromium is 

not completely converted to trivalent chromium in the 

stomach (ATSDR, 2000).

As part of the 2-year studies, total chromium content 

in excreta and selected tissues was determined in additional groups of male rats and female mice (Appendix 

J). Since hexavalent chromium as chromate structurally 

resembles sulfate and phosphate, it can be taken up by 

all cells and organs throughout the body (Costa, 1997). 

Chromate and dichromate are in equilibrium in aqueous 

solutions, so both forms will be present regardless of the 

form initially provided. Animals were removed from 

sodium dichromate dihydrate exposure, and urine and 

feces were collected for 2 days before the time of tissue 

collection. Animals were euthanized, and erythrocytes, 

plasma, forestomach, glandular stomach, liver, and kidney were removed for total chromium analysis. Current 

analytical procedures can not differentiate between 

the oxidation states of chromium in biological tissues. 

However, the speciation of absorbed chromium can be 

inferred from studies comparing Cr VI and Cr III based 

on the relative pattern of partitioning and retention of 

total chromium in the erythrocytes and tissues compared 

to plasma. Cr VI is transported into the erythrocytes and 

tissues, while Cr III remains in blood plasma because it 

is not a substrate for transport (Proctor et al., 2002). 

Significantly increased tissue concentrations of total 

chromium were observed in the erythrocytes, liver, 

kidney, forestomach, and glandular stomach of exposed 

rats and mice compared to controls indicating that additional Cr VI absorption occurs in these tissues, where it 

appears to accumulate with exposure concentration and 

time (Tables J1 and J2). The tissue concentrations of 

chromium were higher than would be expected based 

only on the presence of erythrocytes in the blood of these 

tissues. Additional studies have been conducted by the 

NTP to analyze the concentrations of chromium in similar tissues following Cr III administration in the diet as 

chromium picolinate monohydrate, a dietary supplement 

designed to increase Cr III absorption (Figure 7). Taken 

together, these studies demonstrate that at equivalent 

chromium exposures there were significantly increased 

concentrations of chromium in each tissue when the 

chromium was administered as Cr VI, compared to when 

the chromium was administered as Cr III. For example, 

at 25 weeks, chromium concentrations in these tissues 

were 5 to 16 times higher in animals administered chromium as Cr VI than in animals administered chromium 

as Cr III. In the current studies, the small intestine was 

not collected for total chromium analysis. However, 

other reports suggest that hexavalent chromium is also 

likely to be absorbed in the small intestine to a greater 

extent than trivalent chromium. Infusion of trivalent 

chromium into the duodenum or jejunum resulted in 1% 

to 2% of the dose being absorbed in humans or 1% to 

4% in rats, whereas infusion of hexavalent chromium 

resulted in marked increases in absorption in humans 

and rats (Donaldson and Barreras, 1966; Febel et al., 

2001). 

The tissue distribution data are consistent with those 

reported in the literature where tissue concentrations 

of chromium were reported following 11 months of 

exposure in male and female rats given chromium in 

the drinking water at 25 mg/L in both hexavalent and 

trivalent forms (Costa, 1997; Costa and Klein, 2006). 

In these studies, concentrations of chromium in the 

liver, kidney, and bone were 5.7, 12.0, and 6.4 μg/g, 

respectively, in rats administered hexavalent chromium 

as potassium chromate and 0.38, 1.6, and 0.36 μg/g, 

respectively, in rats administered trivalent chromium 

as chromium trichloride. The authors concluded that a 

significant amount of Cr VI escapes reduction in the red 

blood cells and stomach. The study by Davidson et al.

(2004) demonstrating increased susceptibility to skin 

cancer induction in hairless mice following coexposure 

to ultraviolet light and Cr VI in the drinking water provides additional evidence that Cr VI can have systemic 

effects that are distant from the site of exposure.

The postulated mechanism(s) underlying chromiuminduced genotoxicity and carcinogenicity is the subject 

of much research and some debate. Cr VI readily enters 

cells via nonspecific anion channels, in contrast to Cr III 

which cannot easily pass through the cell membrane 

(IARC, 1990). Cr VI has been postulated by a number 

of authors to exert its genotoxic effects, in part, through 

the generation of oxygen radicals (Sugden et al., 1990; 

Sugiyama, 1992; Kasprzak, 1995; Shi et al., 1999; 

Vaglenov et al., 1999; Benova et al., 2002; O’Brien 

et al., 2003) during intracellular reduction from the 

hexavalent form through the more reactive Cr V and 

Cr IV valences to Cr III. It has been suggested that both 

enzymatic and nonenzymatic pathways may be involved 

in chromium reduction, although at normal physiological 
Sodium Dichromate Dihydrate, NTP TR 546 69

Figure 7

Comparison of Chromium (Cr) Concentrations on Day 182 in Male Rat Tissues 

Following Oral Administration as Cr III or Cr VI

* P<0.05 compared to corresponding control group

** P<0.01

§ P<0.001 compared to corresponding chromium picolinate (CP) dose group

a

 The NTP conducted two studies of Cr, a 2-year bioassay of CP monohydrate in feed (NTP, 2008) and the current 2-year 

bioassay of sodium dichromate dihydrate (SDD) in drinking water. To provide a basis of comparison between the two 

studies, exposure concentrations were converted to mg Cr/kg body weight using the food and water consumption data for 

weeks 1 to 25 of each study. The lowest exposure concentration used in the CP study was 2,000 ppm and 15.2 mg Cr/kg 

body weight. The comparable exposure concentration used in the SDD study was 516 mg/L and 8.95 mg Cr/kg body weight.
70 Sodium Dichromate Dihydrate, NTP TR 546 

conditions, nonenzymatic reduction is believed to dominate (De Flora et al., 1990; Standeven and Wetterhahn, 

1991a). The primary reductants of Cr VI are ascorbic 

acid, glutathione, and cysteine, with ascorbic acid being 

the main reductant. During reduction of Cr VI to Cr III, 

it has been suggested that formation of reactive carbonbased radical species may result in DNA strand breakage 

and other types of damage (reviewed by O’Brien et al., 

2003). Although there are numerous studies providing 

experimental evidence in support of the role of reactive oxygen species in the genotoxicity of chromium 

(Chorvatovicova et al., 1991, 1993; Sarkar et al., 1993; 

Pattison et al., 2001; Cemeli et al., 2003), other studies 

raise questions about the relative contribution of this 

mechanism (O’Brien et al., 2003; Zhitkovich, 2005; 

Quievryn et al., 2006).

Cr III, the final product of intracellular reduction of 

Cr VI, has been shown to interact directly with DNA and 

other macromolecules to induce chromosomal alterations and mutational changes (Zhitkovich et al., 2001, 

2002; O’Brien et al., 2003; Quievryn et al., 2003, 2006; 

Zhitkovich, 2005; Reynolds et al., 2007). The availability of intracellular ascorbate for Cr VI reduction may 

be directly related to the amount of Cr-induced DNA 

damage observed (Standeven and Wetterhahn, 1991b; 

Quievryn et al., 2006; Reynolds et al., 2007). DNA 

adducts, DNA-protein crosslinks, and DNA-interstrand 

crosslinks have all been identified as products of Cr 

III-DNA interactions. Detailed discussions of the 

types of Cr-DNA adducts that are formed in vivo and 

in vitro, along with the biological consequences of 

these adducts, including mutagenicity, DNA replication inhibition, and cytotoxicity, and the DNA repair 

pathways that may be invoked in response to these kinds 

of damage, have recently been provided (O’Brien et al., 

2003; Zhitkovich, 2005). The relative contributions of 

the multiple, complex pathways of chromium-induced 

genotoxicity are not yet fully understood and continue 

to be investigated.

In summary, administration of sodium dichromate dihydrate in the drinking water to F344/N rats and B6C3F1 

mice for 2 years resulted in increased incidences of epithelial neoplasms in the alimentary system of male and 

female rats and mice. There were increased incidences 

of neoplasms of the oral cavity (oral mucosa and tongue) 

in rats and exposure concentration-related increased incidences of adenoma and carcinoma of the small intestine 

in mice. Histiocytic cellular infiltration was observed in 

the small intestine, liver, and pancreatic and mesenteric 

lymph nodes of rats and mice. There was evidence of 

systemic exposure to Cr VI following oral administration in the drinking water based on the tissue distribution 

data, toxicity to the hematopoietic system, and the presence of microscopic changes in multiple tissues.

Conclusions

Under the conditions of these 2-year drinking water 

studies, there was clear evidence of carcinogenic activity* of sodium dichromate dihydrate in male and female 

F344/N rats based on increased incidences of squamous 

cell neoplasms of the oral cavity. There was clear evidence of carcinogenic activity of sodium dichromate 

dihydrate in male and female B6C3F1 mice based on 

increased incidences of neoplasms of the small intestine 

(duodenum, jejunum, or ileum).

Exposure to sodium dichromate dihydrate resulted in 

histiocytic cellular infiltration in the liver, small intestine, and pancreatic and mesenteric lymph nodes of rats 

and mice and diffuse epithelial hyperplasia in the small 

intestine of male and female mice.

__________

* Explanation of Levels of Evidence of Carcinogenic Activity is on page 12. A summary of the Technical Reports Review Subcommittee 

comments and the public discussion on this Technical Report appears on page 14.
71

REFERENCES

Agency for Toxic Substances and Disease Registry 

(ATSDR) (2000). Toxicological Profile for Chromium. 

U.S. Department of Health and Human Services, Public 

Health Service, Agency for Toxic Substances and 

Disease Registry.

Anderson, R.A. (1998). Chromium, glucose intolerance 

and diabetes. J. Am. Coll. Nutr. 17, 548-555.

Bailer, A.J., and Portier, C.J. (1988). Effects of treatment-induced mortality and tumor-induced mortality on 

tests for carcinogenicity in small samples. Biometrics

44, 417-431.

Barnhart, J. (1997). Chromium, chemistry and implications for environmental fate and toxicity. J. Soil 

Contam. 6, 561-568.

Benova, D., Hadjidekova, V., Hristova, R., Nikolova, T., 

Boulanova, M., Georgieva, I., Grigorova, M., Popov, T., 

Panev, T., Georgieva, R., Natarajan, A.T., Darroudi, F., 

and Nilsson, R. (2002). Cytogenetic effects of hexavalent chromium in Bulgarian chromium platers. Mutat. 

Res. 514, 29-38.

Bieler, G.S., and Williams, R.L. (1993). Ratio estimates, the delta method, and quantal response tests for 

increased carcinogenicity. Biometrics 49, 793-801.

Boorman, G.A., Montgomery, C.A., Jr., Eustis, S.L., 

Wolfe, M.J., McConnell, E.E., and Hardisty, J.F. (1985). 

Quality assurance in pathology for rodent carcinogenicity studies. In Handbook of Carcinogen Testing

(H.A. Milman and E.K. Weisburger, Eds.), pp. 345-357. 

Noyes Publications, Park Ridge, NJ.

Borneff, J., Engelhardt, K., Griem, W., Kunte, H., and 

Reichert, J. (1968). Carcinogens in water in soil. XXII. 

Experiment with 3,4-benzopyrene and potassium chromate in mouse drinking water [in German]. Arch. Hyg. 

Bakteriol. 152, 45-53.

Bragt, P.C., and van Dura, E.A. (1983). Toxicokinetics 

of hexavalent chromium in the rat after intratracheal 

administration of chromates of different solubilities. 

Ann. Occup. Hyg. 27, 315-322.

California Department of Health Services (CDHS) 

(2004). Chromium-6 in Drinking Water Standard: 

Sampling Results. <http://www.dhs.ca.gov/ps/ddwem/

chemicals/chromium6/samplingresults.htm>

Casey, C.E., and Hambidge, K.M. (1984). Chromium 

in human milk from American mothers. Br. J. Nutr. 52, 

73-77.

Cemeli, E., Carder, J., Anderson, D., Guillamet, E., 

Morillas, M.J., Creus, A., and Marcos, R. (2003). 

Antigenotoxic properties of selenium compounds on 

potassium dichromate and hydrogen peroxide. Teratog. 

Carcinog. Mutagen. 23 (Suppl. 2), 53-67.

Chorvatovicova, D., Ginter, E., Kosinova, A., and 

Zloch, Z. (1991). Effect of vitamins C and E on toxicity and mutagenicity of hexavalent chromium in rat and 

guinea pig. Mutat. Res. 262, 41-46.

Chorvatovicova, D., Kovacikova, Z., Sandula, J., and 

Navarova, J. (1993). Protective effect of sulfoethylglucan against hexavalent chromium. Mutat. Res. 302, 

207-211.

Code of Federal Regulations (CFR) 21, Part 58.

Cohen, M.D., Kargacin, B., Klein, C.B., and Costa, M. 

(1993). Mechanisms of chromium carcinogenicity and 

toxicity. Crit. Rev. Toxicol. 23, 255-281.

Collaborative Study Group for the Micronucleus Test 

(CSGMT) (1986). Sex differences in the micronucleus 

test. Mutat. Res. 172, 151-163.
72 Sodium Dichromate Dihydrate, NTP TR 546 

Collaborative Study Group for the Micronucleus Test 

(CSGMT) (1988). Strain differences in the micronucleus test. Mutat. Res. 204, 307-316.

Coogan, T.P., Squibb, K.S., Motz, J., Kinney, P.L., and 

Costa, M. (1991). Distribution of chromium within cells 

of the blood. Toxicol. Appl. Pharmacol. 108, 157-166.

Costa, M. (1997). Toxicity and carcinogenicity of 

Cr(VI) in animal models and humans. Crit. Rev. 

Toxicol. 27, 431-442.

Costa, M., and Klein, C.B. (2006). Toxicity and carcinogenicity of chromium compounds in humans. Crit. 

Rev. Toxicol. 36, 155-163.

Cox, D.R. (1972). Regression models and life-tables. 

J. R. Stat. Soc. B34, 187-220. 

Danadevi, K., Rozati, R., Banu, B.S., and Grover, P. 

(2004). Genotoxic evaluation of welders occupationally 

exposed to chromium and nickel using the Comet and 

micronucleus assays. Mutagenesis 19, 35-41.

Davidson, T., Kluz, T., Burns, F., Rossman, T., Zhang, Q., 

Uddin, A., Nadas, A., and Costa, M. (2004). Exposure 

to chromium (VI) in the drinking water increases susceptibility to UV-induced skin tumors in hairless mice. 

Toxicol. Appl. Pharmacol. 196, 431-437.

De Flora, S. (2000). Threshold mechanisms and site specificity in chromium(VI) carcinogenesis. Carcinogenesis

21, 533-541.

De Flora, S., Bagnasco, M., Serra, D., and Zanacchi, 

P. (1990). Genotoxicity of chromium compounds. A 

review. Mutat. Res. 238, 99-172.

De Flora, S., Camoirano, A., Bagnasco, M., Bennicilli, C., 

Corbett, G.E., and Kerger, B.D. (1997). Estimates of 

the chromium (VI) reducing capacity in human body 

compartments as a mechanism for attenuating its potential toxicity and carcinogenicity. Carcinogenesis 18, 

531-537.

De Flora, S., Iltcheva, M., and Balansky, R.M. (2006). 

Oral chromium(VI) does not affect the frequency of 

micronuclei in hematopoietic cells of adult mice and 

of transplacentally exposed fetuses. Mutat. Res. 610, 

38-47.

Diaz-Mayans, J., Laborda, R., and Nunez, A. (1986). 

Hexavalent chromium effects on motor activity and 

some metabolic aspects of Wistar albino rats. Comp. 

Biochem. Physiol. C. 83, 191-195.

Dixon, W.J., and Massey, F.J., Jr. (1957). Introduction 

to Statistical Analysis, 2nd ed., pp. 276-278, 412. 

McGraw-Hill Book Company, Inc., New York.

Donaldson, R.M., Jr., and Barreras, R.F. (1966). 

Intestinal absorption of trace quantities of chromium. 

J. Lab. Clin. Med. 68, 484-493.

Dunn, O.J. (1964). Multiple comparisons using rank 

sums. Technometrics 6, 241-252.

Dunnett, C.W. (1955). A multiple comparison procedure for comparing several treatments with a control. 

J. Am. Stat. Assoc. 50, 1096-1121.

Febel, H., Szegedi, B., and Huszar, S. (2001). Absorption 

of inorganic, trivalent and hexavalent chromium following oral and intrajejunal doses in rats. Acta Vet. Hung.

49, 203-209.

Hamilton, J.W., and Wetterhahn, K.E. (1988). Chromium. 

In Handbook on Toxicity of Inorganic Compounds (H.G. 

Seiler and H. Sigel, Eds.), pp. 239-250. Marcel Dekker, 

Inc., New York.

Hartford, W.H. (1979). Chromium compounds. In 

Kirk-Othmer Encyclopedia of Chemical Technology, 3rd 

ed., (M. Grayson, Ed.), Vol. 6, pp. 82-120. John Wiley 

and Sons, New York.

Hollander, M., and Wolfe, D.A. (1973). Nonparametric 

Statistical Methods, pp. 120-123. John Wiley and Sons, 

New York.

Institute of Medicine (IOM) (2001). Dietary Reference 

Intakes for Vitamin A, Vitamin K, Arsenic, Boron, 

Chromium, Copper, Iodine, Iron, Manganese, 

Molybdenum, Nickel, Silicon, Vanadium, and Zinc. 

Food and Nutrition Board. National Academies Press, 

Washington, DC.

International Agency for Research on Cancer (IARC) 

(1990). IARC Monographs on the Evaluation of 

Carcinogenic Risks to Humans: Chromium. Vol. 49, 

pp. 49-256. IARC, Lyon, France.
Sodium Dichromate Dihydrate, NTP TR 546 73

International Centre for Diffraction Data (2000 Release). 

Newtown Square, PA.

Ivankovic, S., and Preussmann, R. (1975). Absence of 

toxic and carcinogenic effects after administration of 

high doses of chromic oxide pigment in subacute and 

long-term experiments in rats. Food Cosmet. Toxicol.

13, 347-351.

Jonckheere, A.R. (1954). A distribution-free k-sample test against ordered alternatives. Biometrika 41, 

133-145.

Junaid, M., Murthy, R.C., and Saxena, D.K. (1996a). 

Embryo- and fetotoxicity of chromium in pregestationally exposed mice. Bull. Environ. Contam. Toxicol. 57, 

327-334.

Junaid, M., Murthy, R.C., and Saxena, D.K. (1996b). 

Embryotoxicity of orally administered chromium in 

mice: Exposure during the period of organogenesis. 

Toxicol. Lett. 84, 143-148.

Kanojia, R.K., Junaid, M., and Murthy, R.C. (1996). 

Chromium induced teratogenicity in female rat. Toxicol. 

Lett. 89, 207-213.

Kanojia, R.K., Junaid, M., and Murthy, R.C. (1998). 

Embryo and fetotoxicity of hexavalent chromium: A 

long-term study. Toxicol. Lett. 95, 165-172.

Kaplan, E.L., and Meier, P. (1958). Nonparametric 

estimation from incomplete observations. J. Am. Stat. 

Assoc. 53, 457-481.

Kargacin, B., Squibb, K.S., Cosentino, S., Zhitkovich, A., 

and Costa, M. (1993). Comparison of the uptake and 

distribution of chromate in rats and mice. Biol. Trace 

Elem. Res. 36, 307-318.

Kasprzak, K.S. (1995). Possible role of oxidative damage in metal-induced carcinogenesis. Cancer Invest. 13, 

411-430.

Kerger, B.D., Finley, B.L., Corbett, G.E., Dodge, D.G., 

and Paustenbach, D.J. (1997). Ingestion of chromium 

(VI) in drinking water by human volunteers: Absorption, 

distribution, and excretion of single and repeated doses. 

J. Toxicol. Environ. Health 50, 67-95.

Kim, H-Y., Lee, S-B., and Jang, B-S. (2004). Subchronic 

inhalation toxicity of soluble hexavalent chromium trioxide in rats. Arch. Toxicol. 78, 363-368.

Kirpnick-Sobol, Z., Reliene, R., and Schiestl, R.H. 

(2006). Carcinogenic Cr(VI) and the nutritional supplement Cr(III) induce DNA deletions in yeast and mice. 

Cancer Res. 66, 3480-3484.

Kumar, A., and Barthwal, R. (1991). Hexavalent chromium effects on hematological indices in rats. Bull. 

Environ. Contamin. Toxicol. 46, 761-768.

Kumar, A., and Rana, S.V.S. (1982). Lipid accumulation in chromium-poisoned rats. Int. J. Tissue React. 4, 

291-295.

Kumar, A., and Rana, S.V.S. (1984). Enzymological 

effects of hexavalent chromium in the rat kidney. Int. J. 

Tissue React. 6, 135-139.

McConnell, E.E., Solleveld, H.A., Swenberg, J.A., and 

Boorman, G.A. (1986). Guidelines for combining neoplasms for evaluation of rodent carcinogenesis studies. 

JNCI 76, 283-289.

MacKenzie, R.D., Byerrum, R.U., Decker, C.F., Hoppert, 

C.A., and Langham, R.F. (1958). Chronic toxicity studies. II. Hexavalent and trivalent chromium administered 

in drinking water to rats. A.M.A. Arch. Ind. Health 18, 

232-234.

MacKenzie, R.D., Anwar, R.A., Byerrum, R.U., and 

Hoppert, C.A. (1959). Absorption and distribution of 

Cr51 in the albino rat. Arch. Biochem. Biophys. 79, 

200-205.

Mancuso, T.F. (1997). Chromium as an industrial carcinogen: Part II. Chromium in human tissues. Am. J. 

Ind. Med. 31, 140-147.

Maronpot, R.R., and Boorman, G.A. (1982). Interpretation 

of rodent hepatocellular proliferative alterations and 

hepatocellular tumors in chemical safety assessment. 

Toxicol. Pathol. 10, 71-80.

The Merck Index (1996). 12th ed. (S. Budavari, Ed.), 

p. 1475. Merck and Company, Whitehouse Station, 

NJ.
74 Sodium Dichromate Dihydrate, NTP TR 546 

National Cancer Institute (NCI) (1977). Bioassay of 

Captan for Possible Carcinogenicity (CAS No. 133-06-2). 

Technical Report Series No. 15. NIH Publication No. 

77-815. U.S. Department of Health, Education, and 

Welfare, Public Health Service, National Institutes of 

Health, Bethesda, MD.

National Toxicology Program (NTP) (1993). NTP 

Technical Report on the Toxicology and Carcinogenesis 

Studies of 1,2,3-Trichloropropane (CAS No. 96-18-4) 

in F344/N Rats and B6C3F1 Mice (Gavage Studies). 

Technical Report Series No. 384. NIH Publication 

No. 94-2839. U.S. Department of Health and Human 

Services, Public Health Service, National Institutes of 

Health, Research Triangle Park, NC.

National Toxicology Program (NTP) (1996a). Final 

Report. Potassium Dichromate (Hexavalent): The 

Effects of Potassium Dichromate in BALB/c Mice 

Administered in the Diet. November 26, 1996.

National Toxicology Program (NTP) (1996b). Final 

Report. Potassium Dichromate (Hexavalent): The 

Effects of Potassium Dichromate on Sprague-Dawley 

Rats when Administered in the Diet. December 13, 

1996.

National Toxicology Program (NTP) (1997). Final 

Report on the Reproductive Toxicity of Potassium 

Dichromate (CAS No. 7778-50-9) Administered in Diet 

to BALB/c Mice. NTIS No. PB97-144919. National 

Institute of Environmental Health Sciences, National 

Toxicology Program, Research Triangle Park, NC.

National Toxicology Program (NTP) (1998). 8th Report 

on Carcinogens. 1998 Summary, pp. 29-31. U.S. 

Department of Health and Human Services, Public 

Health Service, National Institute of Environmental 

Health Sciences, Research Triangle Park, NC.

National Toxicology Program (NTP) (2002). NTP 

Technical Report on the Toxicology and Carcinogenesis 

Studies of o-Nitrotoluene (CAS No. 88-72-2) in F344/N 

Rats and B6C3F1

 Mice (Feed Studies). Technical 

Report Series No. 504. NIH Publication No. 02-4438. 

U.S. Department of Health and Human Services, Public 

Health Service, National Institutes of Health, Research 

Triangle Park, NC.

National Toxicology Program (NTP) (2006). NTP 

Study of the Hexavalent Chromium Compound Sodium 

Dichromate Dihydrate. <http://ntp.niehs.nih.gov/go/

13859>

National Toxicology Program (NTP) (2007a). NTP 

Toxicity Report on the Toxicity Studies of Sodium 

Dichromate Dihydrate (CAS No. 7789-12-0) 

Administered in Drinking Water to Male and Female 

F344/N Rats and B6C3F1 Mice and Male BALB/c 

and am3-C57BL/6 Mice. Toxicity Report Series No. 

72. NIH Publication No. 07-5964. National Institutes 

of Health, Public Health Service, U.S. Department of 

Health and Human Services, Research Triangle Park, 

NC.

National Toxicology Program (NTP) (2007b). Final 

Range-Finding Report: Immunotoxicity of Hexavalent 

Chromium in Female B6C3F1 mice. National Institutes 

of Health, Public Health Service, U.S. Department of 

Health and Human Services, Research Triangle Park, 

NC.

National Toxicology Program (NTP) (2007c). Final 

Range-Finding Report: Immunotoxicity of Hexavalent 

Chromium in Female Fischer 344 Rats. National 

Institutes of Health, Public Health Service, U.S. 

Department of Health and Human Services, Research 

Triangle Park, NC.

National Toxicology Program (NTP) (2007d). Final 

Range-Finding Report: Immunotoxicity of Hexavalent 

Chromium in Female Sprague-Dawley Rats. National 

Institutes of Health, Public Health Service, U.S. 

Department of Health and Human Services, Research 

Triangle Park, NC.

National Toxicology Program (NTP) (2008). NTP 

Technical Report on the Toxicology and Carcinogenesis 

Studies of Chromium Picolinate Monohydrate 

(CAS No. 27882-76-4) in F344/N Rats and B6C3F1 

Mice (Feed Studies). Technical Report Series No. 556. 

NIH Publication No. 08-5897. National Institutes of 

Health, Public Health Service, U.S. Department of 

Health and Human Services, Research Triangle Park, 

NC (in press).
Sodium Dichromate Dihydrate, NTP TR 546 75

O’Brien, T.J., Ceryak, S., and Patierno, S.R. (2003). 

Complexities of chromium carcinogenesis: Role of cellular response, repair, and recovery mechanisms. Mutat. 

Res. 533, 3-36.

O’Flaherty, E.J. (1993). A pharmacokinetic model for 

chromium. Toxicol. Lett. 68, 145-158.

O’Flaherty, E.J. (1996). A physiologically based 

model of chromium kinetics in the rat. Toxicol. Appl. 

Pharmacol. 138, 54-64.

Pattison, D.I., Davies, M.J., Levina, A., Dixon, N.E., 

and Lay, P.A. (2001). Chromium(VI) reduction by 

catechol(amine)s results in DNA cleavage in vitro: 

Relevance to chromium genotoxicity. Chem. Res. 

Toxicol. 14, 500-510.

Pellerin, C., and Booker, S.M. (2000). Reflections on 

hexavalent chromium: Health hazards of an industrial heavyweight. Environ. Health Perspect. 108, 

A402-A407.

Piegorsch, W.W., and Bailer, A.J. (1997). Statistics for 

Environmental Biology and Toxicology, Section 6.3.2. 

Chapman and Hall, London.

Portier, C.J., and Bailer, A.J. (1989). Testing for 

increased carcinogenicity using a survival-adjusted 

quantal response test. Fundam. Appl. Toxicol. 12, 

731-737.

Portier, C.J., Hedges, J.C., and Hoel, D.G. (1986). 

Age-specific models of mortality and tumor onset for 

historical control animals in the National Toxicology 

Program’s carcinogenicity experiments. Cancer Res.

46, 4372-4378.

Proctor, D.M., Otani, J.M., Finley, B.L., Paustenbach,D.J., 

Bland, J.A., Speizer, N., and Sargent, E.V. (2002). Is 

hexavalent chromium carcinogenic via ingestion? A 

weight-of-evidence review. J. Toxicol. Environ. Health 

A 65, 701-746.

Quievryn, G., Peterson, E., Messer, J., and Zhitkovich, A. 

(2003). Genotoxicity and mutagenicity of chromium(VI)/

ascorbate-generated DNA adducts in human and bacterial cells. Biochemistry 42, 1062-1070.

Quievryn, G., Messer, J., and Zhitkovich, A. (2006). 

Lower mutagenicity but higher stability of Cr-DNA 

adducts formed during gradual chromate activation with 

ascorbate. Carcinogenesis 27, 2316-2321.

Rao, G.N. (1996). New diet (NTP-2000) for rats in the 

National Toxicology Program toxicity and carcinogenicity studies. Fundam. Appl. Toxicol. 32, 102-108.

Rao, G.N. (1997). New nonpurified diet (NTP-2000) 

for rodents in the National Toxicology Program’s 

 toxicology and carcinogenesis studies. J. Nutr. 127, 

842s-846s.

Reynolds, M., Stoddard, L., Bespalov, I., and Zhitkovich, 

A. (2007). Ascorbate acts as a highly potent inducer of 

chromate mutagenesis and clastogenesis: Linkage to 

DNA breaks in G phase by mismatch repair. Nucleic 

2

Acids Res. 35, 465-476.

Sarkar, D., Sharma, A., and Talukder, G. (1993). 

Differential protection of chlorophyllin against clastogenic effects of chromium and chlordane in mouse bone 

marrow in vivo. Mutat. Res. 301, 33-38.

Saxena, D.K., Murthy, R.C., Jain, V.K., and 

Chandra, S.V. (1990). Fetoplacental-maternal uptake 

of hexavalent chromium administered orally in 

rats and mice. Bull. Environ. Contam. Toxicol. 45, 

430-435.

Sayato, Y., Nakamuro, K., Matsui, S., and Ando, 

M. (1980). Metabolic fate of chromium compounds. 

I. Comparative behavior of chromium in rat administered with Na 51CrO and 51CrCl . J. Pharmacobiodyn. 2 4 3

3, 17-23.

Sedman, R.M., Beaumont, J., McDonald, T.A., Reynolds, 

S., Krowech, G., and Howd, R. (2006). Review of the 

evidence regarding the carcinogenicity of hexavalent 

chromium in drinking water. J. Environ. Sci. Health C

24, 155-182.

Shackelford, C.C., and Elwell, M.R. (1999). Small 

and large intestine, and mesentery. In Pathology of the 

Mouse (R.R. Maronpot, Ed.), pp. 81-118. Cache River 

Press, Vienna, IL. 
76 Sodium Dichromate Dihydrate, NTP TR 546 

Shi, X., Chiu, A., Chen, C.T., Halliwell, B., 

Castranova, V., and Vallyathan, V. (1999). Reduction 

of chromium(VI) and its relationship to carcinogenesis. 

J. Toxicol. Environ. Health B Crit. Rev. 2, 87-104.

Shindo, Y., Toyoda, Y., Kawamura, K., Kurebe, 

M., Shimada, H., Hattori, C., and Satake, S. (1989). 

Micronucleus test with potassium chromate(VI) administered intraperitoneally and orally to mice. Mutat. Res.

223, 403-406.

Shirley, E. (1977). A non-parametric equivalent of 

Williams’ test for contrasting increasing dose levels of a 

treatment. Biometrics 33, 386-389.

Standeven, A.M., and Wetterhahn, K.E. (1991a). Is 

there a role for reactive oxygen species in the mechanism of chromium(VI) carcinogenesis? Chem. Res. 

Toxicol. 4, 616-625.

Standeven, A.M., and Wetterhahn, K.E. (1991b). 

Ascorbate is the principal reductant of chromium (VI) 

in rat liver and kidney ultrafiltrates. Carcinogenesis 12, 

1733-1737.

Stern, R.M. (1982). Chromium compounds: Production 

and occupational exposure. In Biological and 

Environmental Aspects of Chromium (S. Langård, Ed.), 

pp. 5-47. Elsevier Biomedical Press, New York.

Sugden, K.D., Burris, R.B., and Rogers, S.J. (1990). An 

oxygen dependence in chromium mutagenesis. Mutat. 

Res. 244, 239-244.

Sugiyama, M. (1992). Role of physiological antioxidants in chromium(VI)-induced cellular injury. Free 

Radic. Biol. Med. 12, 397-407.

Sutherland, J.E., Zhitkovich, A., Kluz, T., and Costa, 

M. (2000). Rats retain chromium in tissues following chronic ingestion in drinking water containing 

hexavalent chromium. Biol. Trace Elem. Res. 74, 

41-53.

Tarone, R.E. (1975). Tests for trend in life table analysis. Biometrika 62, 679-682.

Trivedi, B., Saxena, D.K., Murthy, R.C., and 

Chandra, S.V. (1989). Embryotoxicity and fetotoxicity 

of orally administered hexavalent chromium in mice. 

Reprod. Toxicol. 3, 275-278.

U.S. Environmental Protection Agency (USEPA) (1998). 

Toxicological Review of Hexavalent Chromium (CAS 

No. 18540-29-9). In Support of Summary Information 

on the Integrated Risk Information System (IRIS). U.S. 

Environmental Protection Agency, Washington, DC.

Vaglenov, A., Nosko, M., Georgieva, R., Carbonell, E., 

Creus, A., and Marcos, R. (1999). Genotoxicity and 

radioresistence in electroplating workers exposed to 

chromium. Mutat. Res. 446, 23-34.

Vanoirbeek, J.A.J., Hoet, P.H.M., Nemery, B., 

Verbeken, E.K., Haufroid, V., Lison, D., and Dinsdale, D. 

(2003). Kinetics of an intratracheally administered chromium catalyst in rats. J. Toxicol. Environ. Health A 66, 

393-409.

Wahlberg, J.E. (1970). Percutaneous absorption of 

trivalent and hexavalent chromium (51Cr) through 

excised human and guinea pig skin. Dermatologica

141, 288-296.

Wahlberg, J.E., and Skog, E. (1965). Percutaneous 

absorption of trivalent and hexavalent chromium. Arch. 

Dermatol. 92, 315-318.

Westbrook, J.H. (1979). Chromium and chromium 

alloys. In Kirk-Othmer Encyclopedia of Chemical 

Technology, 3rd ed. (M. Grayson, Ed.), Vol. 6, pp. 54-62. 

John Wiley and Sons, New York.

Williams, D.A. (1971). A test for differences between 

treatment means when several dose levels are compared 

with a zero dose control. Biometrics 27, 103-117.

Williams, D.A. (1972). The comparison of several 

dose levels with a zero dose control. Biometrics 28, 

519-531.

Williams, D.A. (1986). A note on Shirley’s nonparametric test for comparing several dose levels with a 

zero-dose control. Biometrics 42, 183-186.
Sodium Dichromate Dihydrate, NTP TR 546 77

Wise, S.S., Holmes, A.L., and Wise, J.P., Sr. (2006). 

Particulate and soluble hexavalent chromium are cytotoxic and genotoxic to human lung epithelial cells. 

Mutat. Res. 610, 2-7.

Zhang, J.D., and Li, X.L. (1987). Chromium pollution 

of soil and water in Jinzhou [in Chinese]. Zhonghua Yu 

Fang Yi Xue Za Zhi 21, 262-264.

Zhitkovich, A. (2005). Importance of chromium—DNA 

adducts in mutagenicity and toxicity of chromium (VI). 

Chem. Res. Toxicol. 18, 3-9.

Zhitkovich, A., Song, Y., Quievryn, G., and Voitkun, 

V. (2001). Non-oxidative mechanisms are responsible 

for the induction of mutagenesis by reduction of Cr(VI) 

with cysteine: Role of ternary DNA adducts in CR(III)-

dependent mutagenesis. Biochemistry 40, 549-560.

Zhitkovich, A., Quieveryn, G., Messer, J., and Motylevich, 

Z. (2002). Reductive activation with cysteine represents 

a chromium(III)-dependent pathway in the induction of 

genotoxicity by carcinogenic chromium(VI). Environ. 

Health Perspect. 110 (Suppl. 5), 729-731.
78 Sodium Dichromate Dihydrate, NTP TR 546 
79

APPENDIX A

SUMMARY OF LESIONS IN MALE RATS

IN THE 2-YEAR DRINKING WATER STUDY

OF SODIUM DICHROMATE DIHYDRATE

Table A1 Summary of the Incidence of Neoplasms in Male Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 80

Table A2 Statistical Analysis of Primary Neoplasms in Male Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 84

Table A3 Historical Incidence of Oral Cavity Neoplasms in Control Male F344/N Rats . . . . . . . . . . 90

Table A4 Summary of the Incidence of Nonneoplastic Lesions in Male Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 91
80 Sodium Dichromate Dihydrate, NTP TR 546 

Table A1

Summary of the Incidence of Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 16 15 16 9 16

Natural deaths 6 5 3 5 4

Survivors

Terminal sacrifice 28 30 30 36 29

Missing 1 1

Animals examined microscopically 50 50 49 50 49

Alimentary System

Intestine large, cecum (45) (48) (46) (47) (48)

Lipoma 1 (2%)

Intestine large, colon (47) (49) (49) (48) (48)

Leiomyosarcoma 1 (2%)

Intestine small, duodenum (48) (48) (47) (46) (48)

Intestine small, ileum (45) (46) (46) (45) (47)

Intestine small, jejunum (44) (47) (45) (46) (46)

Leiomyoma 1 (2%)

Leiomyosarcoma 1 (2%)

Leiomyosarcoma, metastatic, 

 intestine, large, colon 1 (2%)

Liver (50) (50) (49) (50) (49)

Hepatocellular adenoma 1 (2%) 2 (4%) 1 (2%)

Leiomyosarcoma, metastatic, spleen 1 (2%)

Mesentery (12) (4) (15) (14) (15)

Hemangioma 1 (7%)

Oral mucosa (50) (50) (49) (50) (49)

Squamous cell carcinoma 6 (12%)

Squamous cell papilloma 1 (2%)

Pancreas (50) (50) (49) (50) (49)

Mixed tumor benign 1 (2%)

Acinus, adenoma 1 (2%) 2 (4%) 4 (8%) 2 (4%) 1 (2%)

Acinus, adenoma, multiple 2 (4%) 1 (2%)

Salivary glands (50) (50) (49) (49) (49)

Schwannoma malignant, metastatic,

 peripheral nerve 1 (2%)

Stomach, forestomach (50) (50) (49) (50) (49)

Stomach, glandular (50) (50) (49) (50) (49)

Lipoma 1 (2%) 1 (2%)

Tongue (49) (50) (47) (49) (48)

Squamous cell carcinoma 1 (2%)

Squamous cell papilloma 1 (2%)

Tooth (1) (4)

Squamous cell carcinoma, metastatic,

 oral mucosa 1 (25%)

Cardiovascular System

Blood vessel (4) (3)

Heart (50) (50) (49) (50) (49)

Schwannoma benign 1 (2%)

Schwannoma malignant 1 (2%) 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 81

Table A1

Summary of the Incidence of Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Endocrine System

Adrenal cortex (50) (50) (49) (50) (49)

Adenoma 1 (2%)

Adrenal medulla (49) (50) (49) (50) (49)

Pheochromocytoma benign 5 (10%) 13 (26%) 10 (20%) 4 (8%) 3 (6%)

Pheochromocytoma malignant 1 (2%) 2 (4%) 3 (6%) 1 (2%)

Bilateral, pheochromocytoma benign 1 (2%) 4 (8%) 1 (2%) 1 (2%)

Islets, pancreatic (50) (50) (49) (50) (49)

Adenoma 4 (8%) 6 (12%) 3 (6%) 7 (14%) 5 (10%)

Adenoma, multiple 1 (2%)

Carcinoma 1 (2%)

Parathyroid gland (46) (46) (46) (49) (48)

Adenoma 1 (2%)

Pituitary gland (50) (50) (49) (50) (49)

Pars distalis, adenoma 15 (30%) 19 (38%) 19 (39%) 10 (20%) 16 (33%)

Pars distalis, adenoma, multiple 1 (2%) 1 (2%)

Pars intermedia, adenoma 1 (2%)

Thyroid gland (50) (50) (49) (50) (49)

C-cell, adenoma 5 (10%) 6 (12%) 3 (6%) 7 (14%) 7 (14%)

C-cell, carcinoma 1 (2%) 2 (4%) 1 (2%) 3 (6%) 2 (4%)

Follicular cell, carcinoma 1 (2%) 3 (6%)

General Body System

None

Genital System

Epididymis (50) (50) (49) (50) (49)

Preputial gland (50) (50) (49) (50) (49)

Adenoma 4 (8%) 3 (6%) 3 (6%) 2 (4%) 3 (6%)

Carcinoma 1 (2%) 4 (8%) 7 (14%) 3 (6%) 2 (4%)

Prostate (50) (50) (49) (50) (49)

Adenoma 2 (4%) 2 (4%) 1 (2%)

Seminal vesicle (50) (50) (49) (50) (49)

Testes (50) (50) (49) (50) (49)

Bilateral, interstitial cell, adenoma 41 (82%) 34 (68%) 32 (65%) 39 (78%) 35 (71%)

Interstitial cell, adenoma 7 (14%) 10 (20%) 11 (22%) 10 (20%) 7 (14%)

Hematopoietic System

Bone marrow (50) (50) (49) (50) (49)

Lymph node (14) (7) (6) (11) (9)

Deep cervical, carcinoma, metastatic,

 thyroid gland 1 (11%)

Lymph node, mandibular (5) (2) (2)

Lymph node, mesenteric (49) (50) (49) (50) (49)

Lymph node, pancreatic (32) (34) (34) (36) (33)

Spleen (50) (50) (49) (50) (49)

Hemangiosarcoma 1 (2%)

Leiomyosarcoma 1 (2%)

Thymus (48) (50) (46) (49) (47)

Thymoma malignant 1 (2%)
82 Sodium Dichromate Dihydrate, NTP TR 546 

Table A1

Summary of the Incidence of Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Integumentary System

Mammary gland (50) (49) (48) (50) (49)

Carcinoma 1 (2%) 1 (2%)

Fibroadenoma 2 (4%) 2 (4%) 6 (13%) 3 (6%) 1 (2%)

Fibroadenoma, multiple 1 (2%)

Skin (50) (50) (49) (50) (49)

Basal cell adenoma 2 (4%) 3 (6%) 1 (2%) 1 (2%)

Basal cell carcinoma 2 (4%) 2 (4%)

Keratoacanthoma 2 (4%) 3 (6%) 1 (2%) 4 (8%) 1 (2%)

Squamous cell carcinoma 1 (2%)

Squamous cell papilloma 1 (2%) 1 (2%) 1 (2%)

Trichoepithelioma 1 (2%)

Sebaceous gland, adenoma 1 (2%)

Subcutaneous tissue, fibroma 7 (14%) 11 (22%) 13 (27%) 7 (14%) 7 (14%)

Subcutaneous tissue, fibroma, multiple 1 (2%) 1 (2%) 2 (4%) 1 (2%)

Subcutaneous tissue, fibrosarcoma 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Subcutaneous tissue, fibrous histiocytoma 1 (2%)

Subcutaneous tissue, hemangioma 1 (2%)

Subcutaneous tissue, lipoma 1 (2%) 1 (2%)

Subcutaneous tissue, sarcoma 2 (4%)

Subcutaneous tissue, schwannoma malignant, multiple 1 (2%)

Musculoskeletal System

Bone (50) (50) (49) (50) (49)

Chordoma 1 (2%)

Osteosarcoma 1 (2%)

Skeletal muscle (3) (2) (2) (1)

Nervous System

Brain (50) (50) (49) (50) (49)

Astrocytoma malignant 1 (2%)

Peripheral nerve (4) (6) (5) (2) (5)

Schwannoma malignant 1 (20%)

Spinal cord (4) (6) (5) (2) (5)

Respiratory System

Lung (50) (50) (49) (50) (49)

Alveolar/bronchiolar adenoma 3 (6%) 3 (6%) 2 (4%) 1 (2%) 1 (2%)

Alveolar/bronchiolar adenoma, multiple 1 (2%)

Alveolar/bronchiolar carcinoma 1 (2%) 1 (2%)

Basal cell carcinoma, metastatic, skin 1 (2%)

Carcinoma, metastatic, thyroid gland 1 (2%)

Chordoma, metastatic,

 uncertain primary site 1 (2%)

Fibrosarcoma, metastatic, skin 1 (2%)

Osteosarcoma, metastatic, 

 uncertain primary site 2 (4%)

Sarcoma, metastatic, skin 1 (2%)

Sarcoma, metastatic, uncertain primary site 1 (2%)

Nose (50) (50) (49) (50) (49)
Sodium Dichromate Dihydrate, NTP TR 546 83

Table A1

Summary of the Incidence of Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Special Senses System

Eye (50) (50) (49) (50) (49)

Squamous cell carcinoma, metastatic, 

 oral mucosa 1 (2%)

Harderian gland (50) (50) (49) (50) (49)

Squamous cell carcinoma, metastatic, 

 oral mucosa 2 (4%)

Urinary System

Kidney (50) (50) (49) (50) (49)

Urinary bladder (50) (50) (49) (50) (49)

Systemic Lesions

Multiple organsb (50) (50) (49) (50) (49)

Histiocytic sarcoma 1 (2%)

Leukemia mononuclear 26 (52%) 18 (36%) 22 (45%) 17 (34%) 19 (39%)

Mesothelioma malignant 2 (4%) 2 (4%) 1 (2%)

Neoplasm Summary

Total animals with primary neoplasmsc 50 48 49 50 49

Total primary neoplasms 143 151 162 137 142

Total animals with benign neoplasms 49 47 47 49 49

Total benign neoplasms 107 120 122 105 100

Total animals with malignant neoplasms 29 25 31 29 31

Total malignant neoplasms 36 31 40 32 42

Total animals with metastatic neoplasms 1 3 6

Total metastatic neoplasms 1 3 12

Total animals with malignant neoplasms

of uncertain primary site 1 3

a Number of animals examined microscopically at the site and the number of animals with neoplasm b Number of animals with any tissue examined microscopically c Primary neoplasms: all neoplasms except metastatic neoplasms
84 Sodium Dichromate Dihydrate, NTP TR 546 

Table A2

Statistical Analysis of Primary Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Adrenal Medulla: Benign Pheochromocytoma

Overall ratea 6/49 (12%) 13/50 (26%) 14/49 (29%) 5/50 (10%) 4/49 (8%)

Adjusted rateb 13.6% 31.1% 33.5% 11.2% 9.3%

Terminal ratec 3/28 (11%) 10/30 (33%) 9/30 (30%) 4/36 (11%) 4/29 (14%)

First incidence (days) 639 687 636 595 729 (T)

Poly-3 testd P=0.018N P=0.042 P=0.024 P=0.493N P=0.386N

Adrenal Medulla: Malignant Pheochromocytoma

Overall rate 1/49 (2%) 0/50 (0%) 2/49 (4%) 3/50 (6%) 1/49 (2%)

Adjusted rate 2.3% 0.0% 4.9% 6.8% 2.3%

Terminal rate 1/28 (4%) 0/30 (0%) 2/30 (7%) 2/36 (6%) 1/29 (3%)

First incidence (days) 729 (T) —e 729 (T) 721 729 (T)

Poly-3 test P=0.585 P=0.510N P=0.476 P=0.309 P=0.758

Adrenal Medulla: Benign or Malignant Pheochromocytoma

Overall rate 7/49 (14%) 13/50 (26%) 15/49 (31%) 7/50 (14%) 5/49 (10%)

Adjusted rate 15.9% 31.1% 35.9% 15.7% 11.6%

Terminal rate 4/28 (14%) 10/30 (33%) 10/30 (33%) 5/36 (14%) 5/29 (17%)

First incidence (days) 639 687 636 595 729 (T)

Poly-3 test P=0.030N P=0.076 P=0.027 P=0.606N P=0.397N

Lung: Alveolar/bronchiolar Adenoma

Overall rate 4/50 (8%) 3/50 (6%) 2/49 (4%) 1/50 (2%) 1/49 (2%)

Adjusted rate 9.0% 7.2% 4.9% 2.3% 2.3%

Terminal rate 3/28 (11%) 3/30 (10%) 2/30 (7%) 1/36 (3%) 1/29 (3%)

First incidence (days) 677 729 (T) 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.140N P=0.538N P=0.379N P=0.181N P=0.189N

Lung: Alveolar/bronchiolar Adenoma or Carcinoma

Overall rate 4/50 (8%) 3/50 (6%) 3/49 (6%) 1/50 (2%) 2/49 (4%)

Adjusted rate 9.0% 7.2% 7.4% 2.3% 4.7%

Terminal rate 3/28 (11%) 3/30 (10%) 3/30 (10%) 1/36 (3%) 2/29 (7%)

First incidence (days) 677 729 (T) 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.277N P=0.538N P=0.549N P=0.181N P=0.353N

Mammary Gland: Fibroadenoma

Overall rate 2/50 (4%) 2/50 (4%) 7/49 (14%) 3/50 (6%) 1/49 (2%)

Adjusted rate 4.5% 4.8% 17.1% 6.8% 2.3%

Terminal rate 1/28 (4%) 1/30 (3%) 6/30 (20%) 3/36 (8%) 1/29 (3%)

First incidence (days) 689 559 652 729 (T) 729 (T)

Poly-3 test P=0.182N P=0.674 P=0.059 P=0.496 P=0.512N

Mammary Gland: Fibroadenoma or Carcinoma

Overall rate 3/50 (6%) 2/50 (4%) 7/49 (14%) 3/50 (6%) 2/49 (4%)

Adjusted rate 6.8% 4.8% 17.1% 6.8% 4.6%

Terminal rate 2/28 (7%) 1/30 (3%) 6/30 (20%) 3/36 (8%) 1/29 (3%)

First incidence (days) 689 559 652 729 (T) 667

Poly-3 test P=0.279N P=0.525N P=0.124 P=0.659 P=0.513N
Sodium Dichromate Dihydrate, NTP TR 546 85

Table A2

Statistical Analysis of Primary Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Oral Cavity (Oral Mucosa): Squamous Cell Carcinoma 

Overall rate 0/50 (0%) 0/50 (0%) 0/49 (0%) 0/50 (0%) 6/49 (12%)

Adjusted rate 0.0% 0.0% 0.0% 0.0% 13.6%

Terminal rate 0/28 (0%) 0/30 (0%) 0/30 (0%) 0/36 (0%) 1/29 (3%)

First incidence (days) — — — — 543

Poly-3 test P<0.001 —f — — P=0.015

Oral Cavity (Oral Mucosa or Tongue): Squamous Cell Carcinoma

Overall rate 0/50 (0%) 1/50 (2%) 0/49 (0%) 0/50 (0%) 6/49 (12%)

Adjusted rate 0.0% 2.4% 0.0% 0.0% 13.6%

Terminal rate 0/28 (0%) 1/30 (3%) 0/30 (0%) 0/36 (0%) 1/29 (3%)

First incidence (days) — 729 (T) — — 543

Poly-3 test P<0.001 P=0.487 — — P=0.015

Oral Cavity (Oral Mucosa or Tongue): Squamous Cell Papilloma or Squamous Cell Carcinoma

Overall rate 0/50 (0%) 1/50 (2%) 0/49 (0%) 0/50 (0%) 7/49 (14%)

Adjusted rate 0.0% 2.4% 0.0% 0.0% 15.7%

Terminal rate 0/28 (0%) 1/30 (3%) 0/30 (0%) 0/36 (0%) 1/29 (3%)

First incidence (days) — 729 (T) — — 543

Poly-3 test P<0.001 P=0.487 — — P=0.007

Pancreas: Adenoma

Overall rate 1/50 (2%) 2/50 (4%) 6/49 (12%) 2/50 (4%) 2/49 (4%)

Adjusted rate 2.3% 4.8% 14.6% 4.5% 4.7%

Terminal rate 1/28 (4%) 1/30 (3%) 5/30 (17%) 2/36 (6%) 2/29 (7%)

First incidence (days) 729 (T) 706 560 729 (T) 729 (T)

Poly-3 test P=0.468N P=0.478 P=0.044 P=0.498 P=0.489

Pancreatic Islets: Adenoma 

Overall rate 4/50 (8%) 7/50 (14%) 3/49 (6%) 7/50 (14%) 5/49 (10%)

Adjusted rate 8.9% 16.7% 7.4% 15.8% 11.4%

Terminal rate 2/28 (7%) 5/30 (17%) 3/30 (10%) 6/36 (17%) 3/29 (10%)

First incidence (days) 666 687 729 (T) 692 595

Poly-3 test P=0.550 P=0.222 P=0.552N P=0.254 P=0.486

Pancreatic Islets: Adenoma or Carcinoma

Overall rate 4/50 (8%) 7/50 (14%) 4/49 (8%) 7/50 (14%) 5/49 (10%)

Adjusted rate 8.9% 16.7% 9.8% 15.8% 11.4%

Terminal rate 2/28 (7%) 5/30 (17%) 3/30 (10%) 6/36 (17%) 3/29 (10%)

First incidence (days) 666 687 636 692 595

Poly-3 test P=0.562N P=0.222 P=0.595 P=0.254 P=0.486

Pituitary Gland (Pars Distalis): Adenoma

Overall rate 16/50 (32%) 19/50 (38%) 20/49 (41%) 10/50 (20%) 16/49 (33%)

Adjusted rate 35.4% 44.4% 46.1% 22.7% 35.2%

Terminal rate 9/28 (32%) 16/30 (53%) 13/30 (43%) 10/36 (28%) 9/29 (31%)

First incidence (days) 639 477 503 729 (T) 557

Poly-3 test P=0.251N P=0.256 P=0.207 P=0.135N P=0.580N
86 Sodium Dichromate Dihydrate, NTP TR 546 

Table A2

Statistical Analysis of Primary Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Preputial Gland: Adenoma 

Overall rate 4/50 (8%) 3/50 (6%) 3/49 (6%) 2/50 (4%) 3/49 (6%)

Adjusted rate 9.0% 7.2% 7.3% 4.5% 7.0%

Terminal rate 3/28 (11%) 1/30 (3%) 1/30 (3%) 2/36 (6%) 3/29 (10%)

First incidence (days) 677 652 652 729 (T) 729 (T)

Poly-3 test P=0.495N P=0.532N P=0.543N P=0.341N P=0.519N

Preputial Gland: Carcinoma 

Overall rate 1/50 (2%) 4/50 (8%) 7/49 (14%) 3/50 (6%) 2/49 (4%)

Adjusted rate 2.3% 9.5% 17.0% 6.8% 4.7%

Terminal rate 1/28 (4%) 2/30 (7%) 5/30 (17%) 3/36 (8%) 2/29 (7%)

First incidence (days) 729 (T) 595 652 729 (T) 729 (T)

Poly-3 test P=0.300N P=0.163 P=0.022 P=0.303 P=0.489

Preputial Gland: Adenoma or Carcinoma

Overall rate 4/50 (8%) 6/50 (12%) 8/49 (16%) 5/50 (10%) 5/49 (10%)

Adjusted rate 9.0% 14.2% 19.3% 11.3% 11.6%

Terminal rate 3/28 (11%) 3/30 (10%) 5/30 (17%) 5/36 (14%) 5/29 (17%)

First incidence (days) 677 595 652 729 (T) 729 (T)

Poly-3 test P=0.464N P=0.339 P=0.141 P=0.494 P=0.478

Skin: Keratoacanthoma

Overall rate 2/50 (4%) 3/50 (6%) 1/49 (2%) 4/50 (8%) 1/49 (2%)

Adjusted rate 4.5% 7.2% 2.4% 9.0% 2.3%

Terminal rate 1/28 (4%) 1/30 (3%) 0/30 (0%) 3/36 (8%) 1/29 (3%)

First incidence (days) 587 636 503 549 729 (T)

Poly-3 test P=0.375N P=0.470 P=0.528N P=0.336 P=0.514N

Skin: Squamous Cell Papilloma or Keratoacanthoma

Overall rate 3/50 (6%) 3/50 (6%) 1/49 (2%) 5/50 (10%) 2/49 (4%)

Adjusted rate 6.7% 7.2% 2.4% 11.2% 4.7%

Terminal rate 1/28 (4%) 1/30 (3%) 0/30 (0%) 4/36 (11%) 2/29 (7%)

First incidence (days) 587 636 503 549 729 (T)

Poly-3 test P=0.517N P=0.632 P=0.334N P=0.355 P=0.519N

Skin: Basal Cell Adenoma

Overall rate 2/50 (4%) 3/50 (6%) 0/49 (0%) 1/50 (2%) 1/49 (2%)

Adjusted rate 4.5% 7.2% 0.0% 2.3% 2.3%

Terminal rate 2/28 (7%) 2/30 (7%) 0/30 (0%) 1/36 (3%) 1/29 (3%)

First incidence (days) 729 (T) 713 — 729 (T) 729 (T)

Poly-3 test P=0.370N P=0.471 P=0.257N P=0.502N P=0.511N

Skin: Trichoepithelioma or Basal Cell Adenoma

Overall rate 2/50 (4%) 3/50 (6%) 1/49 (2%) 1/50 (2%) 1/49 (2%)

Adjusted rate 4.5% 7.2% 2.5% 2.3% 2.3%

Terminal rate 2/28 (7%) 2/30 (7%) 1/30 (3%) 1/36 (3%) 1/29 (3%)

First incidence (days) 729 (T) 713 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.314N P=0.471 P=0.530N P=0.502N P=0.511N
Sodium Dichromate Dihydrate, NTP TR 546 87

Table A2

Statistical Analysis of Primary Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Skin: Trichoepithelioma, Basal Cell Adenoma, or Basal Cell Carcinoma

Overall rate 2/50 (4%) 5/50 (10%) 3/49 (6%) 1/50 (2%) 1/49 (2%)

Adjusted rate 4.5% 11.8% 7.4% 2.3% 2.3%

Terminal rate 2/28 (7%) 3/30 (10%) 3/30 (10%) 1/36 (3%) 1/29 (3%)

First incidence (days) 729 (T) 345 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.133N P=0.198 P=0.461 P=0.502N P=0.511N

Skin: Squamous Cell Papilloma, Keratoacanthoma, or Squamous Cell Carcinoma

Overall rate 4/50 (8%) 3/50 (6%) 1/49 (2%) 5/50 (10%) 2/49 (4%)

Adjusted rate 8.9% 7.2% 2.4% 11.2% 4.7%

Terminal rate 1/28 (4%) 1/30 (3%) 0/30 (0%) 4/36 (11%) 2/29 (7%)

First incidence (days) 587 636 503 549 729 (T)

Poly-3 test P=0.429N P=0.539N P=0.205N P=0.496 P=0.358N

Skin: Squamous Cell Papilloma, Keratoacanthoma, Trichoepithelioma, Basal Cell Adenoma, Basal Cell Carcinoma,

or Squamous Cell Carcinoma

Overall rate 5/50 (10%) 8/50 (16%) 4/49 (8%) 6/50 (12%) 3/49 (6%)

Adjusted rate 11.1% 18.7% 9.7% 13.4% 7.0%

Terminal rate 2/28 (7%) 4/30 (13%) 3/30 (10%) 5/36 (14%) 3/29 (10%)

First incidence (days) 587 345 503 549 729 (T)

Poly-3 test P=0.180N P=0.243 P=0.553N P=0.495 P=0.381N

Skin (Subcutaneous Tissue): Fibroma 

Overall rate 8/50 (16%) 12/50 (24%) 13/49 (27%) 9/50 (18%) 8/49 (16%)

Adjusted rate 17.8% 28.0% 31.3% 20.2% 18.1%

Terminal rate 5/28 (18%) 8/30 (27%) 10/30 (33%) 8/36 (22%) 3/29 (10%)

First incidence (days) 652 584 617 595 609

Poly-3 test P=0.225N P=0.186 P=0.110 P=0.493 P=0.596

Skin (Subcutaneous Tissue): Fibrous Histiocytoma, Fibrosarcoma, or Sarcoma

Overall rate 3/50 (6%) 1/50 (2%) 1/49 (2%) 1/50 (2%) 1/49 (2%)

Adjusted rate 6.7% 2.4% 2.4% 2.3% 2.3%

Terminal rate 1/28 (4%) 0/30 (0%) 0/30 (0%) 1/36 (3%) 1/29 (3%)

First incidence (days) 696 617 560 729 (T) 729 (T)

Poly-3 test P=0.387N P=0.327N P=0.333N P=0.308N P=0.317N

Skin (Subcutaneous Tissue): Fibroma, Fibrous Histiocytoma, Fibrosarcoma, or Sarcoma

Overall rate 11/50 (22%) 13/50 (26%) 14/49 (29%) 9/50 (18%) 9/49 (18%)

Adjusted rate 24.4% 30.1% 33.3% 20.2% 20.3%

Terminal rate 6/28 (21%) 8/30 (27%) 10/30 (33%) 8/36 (22%) 4/29 (14%)

First incidence (days) 652 584 560 595 609

Poly-3 test P=0.165N P=0.358 P=0.247 P=0.412N P=0.418N

Testes: Adenoma

Overall rate 48/50 (96%) 44/50 (88%) 43/49 (88%) 49/50 (98%) 42/49 (86%)

Adjusted rate 97.5% 93.8% 94.5% 99.7% 90.3%

Terminal rate 28/28 (100%) 29/30 (97%) 30/30 (100%) 36/36 (100%) 28/29 (97%)

First incidence (days) 484 454 501 520 543

Poly-3 test P=0.101N P=0.343N P=0.404N P=0.464 P=0.110N
88 Sodium Dichromate Dihydrate, NTP TR 546 

Table A2

Statistical Analysis of Primary Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Thyroid Gland (C-cell): Adenoma

Overall rate 5/50 (10%) 6/50 (12%) 3/49 (6%) 7/50 (14%) 7/49 (14%)

Adjusted rate 11.2% 14.4% 7.3% 15.6% 16.2%

Terminal rate 4/28 (14%) 4/30 (13%) 0/30 (0%) 5/36 (14%) 6/29 (21%)

First incidence (days) 617 687 631 549 652

Poly-3 test P=0.255 P=0.452 P=0.399N P=0.383 P=0.356

Thyroid Gland (C-cell): Carcinoma

Overall rate 1/50 (2%) 2/50 (4%) 1/49 (2%) 3/50 (6%) 2/49 (4%)

Adjusted rate 2.3% 4.8% 2.4% 6.8% 4.7%

Terminal rate 1/28 (4%) 2/30 (7%) 0/30 (0%) 3/36 (8%) 2/29 (7%)

First incidence (days) 729 (T) 729 (T) 640 729 (T) 729 (T)

Poly-3 test P=0.439 P=0.477 P=0.743 P=0.303 P=0.489

Thyroid Gland (C-cell): Adenoma or Carcinoma

Overall rate 6/50 (12%) 7/50 (14%) 4/49 (8%) 10/50 (20%) 9/49 (18%)

Adjusted rate 13.4% 16.8% 9.6% 22.2% 20.8%

Terminal rate 5/28 (18%) 5/30 (17%) 0/30 (0%) 8/36 (22%) 8/29 (28%)

First incidence (days) 617 687 631 549 652

Poly-3 test P=0.163 P=0.447 P=0.414N P=0.207 P=0.262

Thyroid Gland (Follicular Cell): Carcinoma

Overall rate 0/50 (0%) 0/50 (0%) 0/49 (0%) 1/50 (2%) 3/49 (6%)

Adjusted rate 0.0% 0.0% 0.0% 2.3% 6.9%

Terminal rate 0/28 (0%) 0/30 (0%) 0/30 (0%) 1/36 (3%) 0/29 (0%)

First incidence (days) — — — 729 (T) 605

Poly-3 test P=0.007 — — P=0.499 P=0.116

All Organs: Mononuclear Cell Leukemia

Overall rate 26/50 (52%) 18/50 (36%) 22/49 (45%) 17/50 (34%) 19/49 (39%)

Adjusted rate 52.6% 41.9% 47.5% 35.2% 42.1%

Terminal rate 9/28 (32%) 12/30 (40%) 11/30 (37%) 8/36 (22%) 10/29 (35%)

First incidence (days) 482 617 272 399 557

Poly-3 test P=0.250N P=0.204N P=0.384N P=0.060N P=0.205N

All Organs: Benign Neoplasms

Overall rate 49/50 (98%) 47/50 (94%) 47/49 (96%) 49/50 (98%) 49/49 (100%)

Adjusted rate 99.4% 99.4% 99.7% 99.7% 100.0%

Terminal rate 28/28 (100%) 30/30 (100%) 30/30 (100%) 36/36 (100%) 29/29 (100%)

First incidence (days) 484 454 501 520 543

Poly-3 test P=0.859 P=0.998N P=0.997 P=0.995 P=0.993

All Organs: Malignant Neoplasms

Overall rate 29/50 (58%) 26/50 (52%) 31/49 (63%) 29/50 (58%) 33/49 (67%)

Adjusted rate 58.7% 56.3% 65.3% 60.0% 69.8%

Terminal rate 11/28 (39%) 15/30 (50%) 17/30 (57%) 20/36 (56%) 18/29 (62%)

First incidence (days) 482 337 272 399 543

Poly-3 test P=0.129 P=0.491N P=0.319 P=0.527 P=0.174
Sodium Dichromate Dihydrate, NTP TR 546 89

Table A2

Statistical Analysis of Primary Neoplasms in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

All Organs: Benign or Malignant Neoplasms

Overall rate 50/50 (100%) 49/50 (98%) 49/49 (100%) 50/50 (100%) 49/49 (100%)

Adjusted rate 100.0% 99.8% 100.0% 100.0% 100.0%

Terminal rate 28/28 (100%) 30/30 (100%) 30/30 (100%) 36/36 (100%) 29/29 (100%)

First incidence (days) 482 337 272 399 543

Poly-3 test P=1.000 P=1.000N — — —

(T) Terminal sacrifice

a Number of neoplasm-bearing animals/number of animals examined. Denominator is number of animals examined microscopically for adrenal medulla, 

lung, pancreas, pancreatic islets, pituitary gland, preputial gland, testes, and thyroid gland; for other tissues, denominator is number of animals necropsied. b Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality c Observed incidence at terminal kill d Beneath the control incidence is the P value associated with the trend test. Beneath the exposed group incidence are the P values corresponding to 

pairwise comparisons between the controls and that exposed group. The Poly-3 test accounts for the differential mortality in animals that do not reach 

terminal sacrifice. A negative trend or a lower incidence in an exposed group is indicated by N. e Not applicable; no neoplasms in animal group f Value of statistic cannot be computed.
90 Sodium Dichromate Dihydrate, NTP TR 546 

Table A3

Historical Incidence of Oral Cavity Neoplasms in Control Male F344/N Ratsa

 Incidence in Controls

 Oral Mucosa All Sitesb

Study Squamous Cell Carcinoma Papilloma, Squamous Cell Papilloma,

 or Squamous Cell Carcinoma

Historical Incidence: Drinking Water Studies

Bromochloroacetic acid 0/50 0/50

Bromodichloromethane 0/50 1/50

Dibromoacetic acid 0/50 0/50

Dibromoacetonitrile 0/50 0/50

Dipropylene glycol 0/50 0/50

Sodium chlorate 0/50 0/50

Sodium dichromate dihydrate 0/50 —

Overall Historical Incidence: Drinking Water Studies

Total 0/350 1/300 (0.3%)

Mean ± standard deviation 0.3% ± 0.8%

Range (0%-2%)

Overall Historical Incidence: All Routes

Total (%) 5/1,499 (0.3%) 10/1,449 (0.7%)

Mean ± standard deviation 0.3% ± 0.7% 0.6% ± 0.8%

Range (0%-2%) (0%-2%)

a Data as of March 5, 2007, with sodium dichromate dihydrate data added from Table A1 b All sites includes the oral mucosa, tongue, pharynx, tooth, and gingiva; sodium dichromate dihydrate data not included
Sodium Dichromate Dihydrate, NTP TR 546 91

Table A4

Summary of the Incidence of Nonneoplastic Lesions in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 16 15 16 9 16

Natural deaths 6 5 3 5 4

Survivors

Terminal sacrifice 28 30 30 36 29

Missing 1 1

Animals examined microscopically 50 50 49 50 49

Alimentary System

Intestine large, cecum (45) (48) (46) (47) (48)

Edema 1 (2%) 1 (2%) 2 (4%) 2 (4%)

Erosion 1 (2%)

Ulcer 1 (2%) 1 (2%)

Intestine large, colon (47) (49) (49) (48) (48)

Edema 1 (2%)

Infiltration cellular, lymphocyte 1 (2%)

Intestine small, duodenum (48) (48) (47) (46) (48)

Erosion 1 (2%) 1 (2%)

Infiltration cellular, histiocyte 6 (13%) 36 (78%) 47 (98%)

Ulcer 1 (2%)

Intestine small, ileum (45) (46) (46) (45) (47)

Hyperplasia 1 (2%)

Lymphoid tissue, hyperplasia 10 (22%) 11 (24%) 9 (20%) 7 (16%) 10 (21%)

Intestine small, jejunum (44) (47) (45) (46) (46)

Hyperplasia 1 (2%)

Epithelium, hyperplasia 1 (2%)

Liver (50) (50) (49) (50) (49)

Angiectasis 1 (2%) 1 (2%)

Basophilic focus 22 (44%) 28 (56%) 29 (59%) 32 (64%) 30 (61%)

Clear cell focus 23 (46%) 19 (38%) 16 (33%) 29 (58%) 25 (51%)

Degeneration, cystic 7 (14%) 3 (6%) 2 (4%) 2 (4%)

Eosinophilic focus 10 (20%) 5 (10%) 4 (8%) 8 (16%) 9 (18%)

Fatty change 12 (24%) 10 (20%) 10 (20%) 8 (16%) 12 (24%)

Hematopoietic cell proliferation 1 (2%) 3 (6%)

Hemorrhage 2 (4%) 1 (2%) 4 (8%) 3 (6%)

Hepatodiaphragmatic nodule 5 (10%) 6 (12%) 6 (12%) 7 (14%) 10 (20%)

Infiltration cellular, histiocyte 1 (2%) 2 (4%) 5 (10%) 34 (69%)

Inflammation, chronic 19 (38%) 25 (50%) 21 (43%) 28 (56%) 26 (53%)

Mixed cell focus 11 (22%) 7 (14%) 5 (10%) 13 (26%) 10 (20%)

Necrosis 3 (6%) 3 (6%) 2 (4%) 1 (2%)

Regeneration 2 (4%) 2 (4%)

Syncytial alteration 1 (2%)

Thrombosis 1 (2%)

Bile duct, hyperplasia 47 (94%) 38 (76%) 33 (67%) 22 (44%) 15 (31%)

Centrilobular, necrosis 8 (16%) 1 (2%) 3 (6%) 2 (4%) 5 (10%)

Hepatocyte, hyperplasia, focal 1 (2%)

Intima, vein, hyperplasia 1 (2%)

Kupffer cell, pigmentation 2 (4%) 1 (2%)

a Number of animals examined microscopically at the site and the number of animals with lesion
92 Sodium Dichromate Dihydrate, NTP TR 546 

Table A4

Summary of the Incidence of Nonneoplastic Lesions in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Alimentary System (continued)

Mesentery (12) (4) (15) (14) (15)

Accessory spleen 1 (8%) 1 (7%) 1 (7%) 1 (7%)

Hemorrhage 1 (7%)

Fat, necrosis 11 (92%) 3 (75%) 10 (67%) 12 (86%) 13 (87%)

Oral mucosa (50) (50) (49) (50) (49)

Pancreas (50) (50) (49) (50) (49)

Atrophy 25 (50%) 16 (32%) 24 (49%) 24 (48%) 31 (63%)

Cyst 9 (18%) 7 (14%) 9 (18%) 9 (18%) 12 (24%)

Acinus, cytoplasmic alteration 1 (2%) 3 (6%)

Acinus, hyperplasia, focal 6 (12%) 10 (20%) 9 (18%) 7 (14%) 9 (18%)

Salivary glands (50) (50) (49) (49) (49)

Atrophy 3 (6%) 1 (2%) 2 (4%) 4 (8%) 3 (6%)

Necrosis 1 (2%) 2 (4%)

Duct, cyst 1 (2%)

Stomach, forestomach (50) (50) (49) (50) (49)

Edema 3 (6%) 3 (6%) 3 (6%)

Erosion 1 (2%) 1 (2%)

Inflammation, chronic active 1 (2%) 1 (2%) 1 (2%)

Ulcer 1 (2%) 3 (6%) 3 (6%) 2 (4%) 1 (2%)

Epithelium, hyperplasia 1 (2%) 2 (4%) 2 (4%) 5 (10%) 1 (2%)

Stomach, glandular (50) (50) (49) (50) (49)

Cyst 1 (2%)

Edema 1 (2%) 1 (2%)

Erosion 8 (16%) 4 (8%) 6 (12%) 5 (10%) 2 (4%)

Hyperplasia 8 (16%) 4 (8%) 9 (18%) 12 (24%) 12 (24%)

Infiltration cellular, lymphocyte 1 (2%)

Ulcer 1 (2%) 3 (6%) 1 (2%) 1 (2%)

Epithelium, glands, dilatation 1 (2%)

Glands, dilatation 1 (2%) 1 (2%) 1 (2%)

Tongue (49) (50) (47) (49) (48)

Fibrosis 1 (2%)

Hemorrhage 1 (2%) 1 (2%)

Hemorrhage, chronic 1 (2%)

Inflammation, chronic 2 (4%) 5 (50%) 6 (13%) 6 (12%) 3 (6%)

Epithelium, hyperplasia 2 (4%) 2 (4%) 1 (2%)

Vein, thrombosis 1 (2%)

Tooth (1) (4)

Malformation 1 (25%)

Cardiovascular System

Blood vessel (4) (3)

Dilatation 1 (33%)

Heart (50) (50) (49) (50) (49)

Cardiomyopathy 46 (92%) 44 (88%) 44 (90%) 45 (90%) 45 (92%)

Inflammation, chronic 1 (2%)

Thrombosis 5 (10%) 3 (6%) 1 (2%) 2 (4%)
Sodium Dichromate Dihydrate, NTP TR 546 93

Table A4

Summary of the Incidence of Nonneoplastic Lesions in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Endocrine System

Adrenal cortex (50) (50) (49) (50) (49)

Accessory adrenal cortical nodule 17 (34%) 18 (36%) 13 (27%) 17 (34%) 8 (16%)

Angiectasis 1 (2%) 1 (2%) 1 (2%)

Degeneration, fatty 7 (14%) 10 (20%) 9 (18%) 7 (14%) 11 (22%)

Hyperplasia, focal 2 (4%) 1 (2%) 6 (12%) 3 (6%)

Hyperplasia, diffuse 1 (2%) 1 (2%)

Hypertrophy 1 (2%)

Hypertrophy, focal 2 (4%) 4 (8%) 4 (8%)

Necrosis 2 (4%) 1 (2%) 1 (2%) 1 (2%)

Adrenal medulla (49) (50) (49) (50) (49)

Hyperplasia 12 (24%) 11 (22%) 17 (35%) 9 (18%) 14 (29%)

Islets, pancreatic (50) (50) (49) (50) (49)

Hyperplasia 2 (4%) 1 (2%) 1 (2%)

Parathyroid gland (46) (46) (46) (49) (48)

Hyperplasia 1 (2%)

Pituitary gland (50) (50) (49) (50) (49)

Pars distalis, angiectasis 2 (4%) 3 (6%) 2 (4%) 5 (10%) 3 (6%)

Pars distalis, cyst 3 (6%) 4 (8%) 7 (14%) 5 (10%) 5 (10%)

Pars distalis, cytoplasmic alteration, focal 2 (4%) 2 (4%) 3 (6%) 2 (4%) 2 (4%)

Pars distalis, hyperplasia 1 (2%) 1 (2%) 1 (2%)

Pars distalis, hyperplasia, focal 12 (24%) 6 (12%) 12 (24%) 14 (28%) 11 (22%)

Pars intermedia, angiectasis 1 (2%) 1 (2%) 2 (4%)

Pars intermedia, cyst 1 (2%) 1 (2%) 2 (4%) 1 (2%) 1 (2%)

Pars intermedia, metaplasia, atypical 1 (2%)

Pars intermedia, pars nervosa, metaplasia, atypical 1 (2%)

Thyroid gland (50) (50) (49) (50) (49)

Ultimobranchial cyst 1 (2%) 2 (4%)

C-cell, hyperplasia 11 (22%) 13 (26%) 18 (37%) 14 (28%) 5 (10%)

Follicle, cyst 1 (2%) 1 (2%) 2 (4%)

General Body System

None

Genital System

Epididymis (50) (50) (49) (50) (49)

Granuloma sperm 2 (4%) 1 (2%)

Inflammation, chronic 1 (2%) 2 (4%) 2 (4%) 2 (4%)

Preputial gland (50) (50) (49) (50) (49)

Cyst 1 (2%) 1 (2%) 1 (2%)

Hyperplasia 1 (2%) 1 (2%) 2 (4%) 1 (2%)

Inflammation, chronic 16 (32%) 11 (22%) 13 (27%) 17 (34%) 16 (33%)

Prostate (50) (50) (49) (50) (49)

Cyst 1 (2%)

Inflammation, chronic 19 (38%) 17 (34%) 14 (29%) 8 (16%) 14 (29%)

Epithelium, hyperplasia 7 (14%) 11 (22%) 7 (14%) 7 (14%) 8 (16%)

Seminal vesicle (50) (50) (49) (50) (49)

Inflammation, chronic 1 (2%)

Testes (50) (50) (49) (50) (49)

Germinal epithelium, atrophy 5 (10%) 4 (8%) 6 (12%) 4 (8%) 8 (16%)

Interstitial cell, hyperplasia 4 (8%) 5 (10%) 3 (6%) 4 (8%) 4 (8%)
94 Sodium Dichromate Dihydrate, NTP TR 546 

Table A4

Summary of the Incidence of Nonneoplastic Lesions in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematopoietic System

Bone marrow (50) (50) (49) (50) (49)

Hemorrhage 1 (2%)

Hyperplasia 4 (8%) 12 (24%) 7 (14%) 7 (14%) 6 (12%)

Myelofibrosis 2 (4%) 1 (2%) 2 (4%)

Lymph node (14) (7) (6) (11) (9)

Deep cervical, ectasia 2 (22%)

Deep cervical, hyperplasia, lymphoid 2 (22%)

Mediastinal, ectasia 2 (14%) 1 (14%) 1 (9%) 1 (11%)

Mediastinal, hemorrhage 1 (7%) 2 (29%) 1 (17%) 1 (9%) 1 (11%)

Mediastinal, hyperplasia, lymphoid 1 (7%) 1 (14%) 1 (17%) 3 (27%) 2 (22%)

Mediastinal, pigmentation 1 (17%)

Lymph node, mandibular (5) (2) (2)

Ectasia 1 (20%) 1 (50%) 2 (100%)

Lymph node, mesenteric (49) (50) (49) (50) (49)

Hemorrhage 2 (4%) 7 (14%) 9 (18%) 8 (16%) 17 (35%)

Hyperplasia, lymphoid 1 (2%) 6 (12%) 2 (4%) 1 (2%)

Infiltration cellular, histiocyte 13 (27%) 11 (22%) 30 (61%) 39 (78%) 41 (84%)

Lymph node, pancreatic (32) (34) (34) (36) (33)

Congestion 1 (3%)

Ectasia 1 (3%) 1 (3%) 1 (3%)

Hemorrhage 3 (9%) 4 (12%) 2 (6%) 1 (3%)

Hyperplasia, lymphoid 1 (3%)

Infiltration cellular, histiocyte 17 (53%) 22 (65%) 17 (50%) 17 (47%) 25 (76%)

Pigmentation 1 (3%) 1 (3%)

Spleen (50) (50) (49) (50) (49)

Accessory spleen 1 (2%) 2 (4%) 1 (2%)

Fibrosis 2 (4%) 3 (6%) 2 (4%) 1 (2%)

Hematopoietic cell proliferation 18 (36%) 25 (50%) 20 (41%) 20 (40%) 16 (33%)

Hemorrhage 1 (2%) 1 (2%) 1 (2%)

Metaplasia, lipocyte 1 (2%)

Necrosis 4 (8%) 4 (8%) 2 (4%)

Pigmentation 3 (6%) 2 (4%) 1 (2%) 3 (6%)

Lymphoid follicle, atrophy 1 (2%)

Lymphoid follicle, hyperplasia 1 (2%)

Thymus (48) (50) (46) (49) (47)

Atrophy 1 (2%) 1 (2%) 1 (2%)

Integumentary System

Mammary gland (50) (49) (48) (50) (49)

Hyperplasia 25 (50%) 17 (35%) 19 (40%) 11 (22%) 14 (29%)

Inflammation, granulomatous 1 (2%)

Skin (50) (50) (49) (50) (49)

Angiectasis 1 (2%) 1 (2%)

Cyst 1 (2%) 1 (2%)

Cyst epithelial inclusion 5 (10%) 3 (6%) 2 (4%) 3 (6%) 6 (12%)

Edema 1 (2%)

Hyperkeratosis 5 (10%) 2 (4%) 1 (2%) 4 (8%) 1 (2%)

Epidermis, hyperplasia 1 (2%) 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 95

Table A4

Summary of the Incidence of Nonneoplastic Lesions in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Musculoskeletal System

Bone (50) (50) (49) (50) (49)

Cranium, osteopetrosis 1 (2%) 2 (4%) 1 (2%)

Femur, osteopetrosis 1 (2%)

Skeletal muscle (3) (2) (2) (1)

Atrophy 1 (100%)

Nervous System

Brain (50) (50) (49) (50) (49)

Compression 7 (14%) 6 (12%) 9 (18%) 3 (6%) 3 (6%)

Hemorrhage 1 (2%)

Hydrocephalus 1 (2%) 1 (2%)

Peripheral nerve (4) (6) (5) (2) (5)

Atrophy 1 (17%)

Spinal cord (4) (6) (5) (2) (5)

Vacuolization cytoplasmic 1 (25%)

Respiratory System

Lung (50) (50) (49) (50) (49)

Edema 1 (2%)

Foreign body 1 (2%)

Hemorrhage 10 (20%) 7 (14%) 7 (14%) 6 (12%) 8 (16%)

Infiltration cellular, histiocyte 28 (56%) 27 (54%) 32 (65%) 29 (58%) 33 (67%)

Inflammation, suppurative 1 (2%) 1 (2%)

Inflammation, granulomatous 1 (2%)

Inflammation, chronic 1 (2%) 1 (2%) 1 (2%)

Metaplasia, osseous 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Thrombosis 1 (2%) 1 (2%) 1 (2%)

Alveolar epithelium, hyperplasia 11 (22%) 6 (12%) 4 (8%) 8 (16%) 5 (10%)

Alveolar epithelium, metaplasia, squamous 1 (2%)

Nose (50) (50) (49) (50) (49)

Foreign body 9 (18%) 11 (22%) 9 (18%) 15 (30%) 1 (2%)

Hemorrhage 1 (2%)

Inflammation, chronic 8 (16%) 11 (22%) 8 (16%) 16 (32%) 7 (14%)

Thrombosis 1 (2%)

Nasolacrimal duct, cyst 2 (4%) 1 (2%)

Respiratory epithelium, hyperplasia 5 (10%) 5 (10%) 4 (8%) 11 (22%) 4 (8%)

Respiratory epithelium, metaplasia,

 squamous 1 (2%) 3 (6%) 1 (2%)

Special Senses System

Eye (50) (50) (49) (50) (49)

Cataract 1 (2%) 3 (6%) 2 (4%) 1 (2%) 3 (6%)

Hemorrhage 1 (2%)

Inflammation, chronic 1 (2%) 3 (6%)

Cornea, hyperplasia 1 (2%)

Retina, degeneration 2 (4%) 3 (6%) 4 (8%) 2 (4%) 4 (8%)

Harderian gland (50) (50) (49) (50) (49)

Inflammation, chronic 2 (4%) 1 (2%)

Pigmentation 1 (2%)
96 Sodium Dichromate Dihydrate, NTP TR 546 

Table A4

Summary of the Incidence of Nonneoplastic Lesions in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Urinary System

Kidney (50) (50) (49) (50) (49)

Cyst 2 (4%) 1 (2%) 4 (8%) 1 (2%)

Hydronephrosis 1 (2%)

Infarct 1 (2%)

Infiltration cellular, lipocyte 1 (2%)

Inflammation, chronic 5 (10%) 9 (18%) 8 (16%) 2 (4%) 2 (4%)

Nephropathy 45 (90%) 43 (86%) 45 (92%) 43 (86%) 41 (84%)

Renal tubule, accumulation, hyaline droplet 2 (4%)

Renal tubule, dilatation 3 (6%) 1 (2%)

Renal tubule, hyperplasia 2 (4%)

Renal tubule, necrosis 2 (4%) 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Renal tubule, pigmentation 5 (10%) 1 (2%) 1 (2%) 3 (6%)

Transitional epithelium, hyperplasia 1 (2%)

Urinary bladder (50) (50) (49) (50) (49)

Calculus microscopic observation only 1 (2%)

Edema 1 (2%)

Hemorrhage 1 (2%) 1 (2%)

Inflammation, chronic 1 (2%)

Necrosis 1 (2%)

Transitional epithelium, hyperplasia 1 (2%) 1 (2%)
97

APPENDIX B

SUMMARY OF LESIONS IN FEMALE RATS

IN THE 2-YEAR DRINKING WATER STUDY

OF SODIUM DICHROMATE DIHYDRATE

Table B1 Summary of the Incidence of Neoplasms in Female Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 98

Table B2 Statistical Analysis of Primary Neoplasms in Female Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 102

Table B3 Historical Incidence of Oral Cavity Neoplasms in Control Female F344/N Rats . . . . . . . . 106

Table B4 Summary of the Incidence of Nonneoplastic Lesions in Female Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 107
98 Sodium Dichromate Dihydrate, NTP TR 546 

Table B1

Summary of the Incidence of Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 12 15 9 10 18

Natural deaths 5 3 9 4 1

Survivors

Died last week of study 1

Terminal sacrifice 32 32 32 36 31

Animals examined microscopically 50 50 50 50 50

Alimentary System

Intestine large, cecum (46) (47) (48) (47) (50)

Intestine large, colon (49) (49) (49) (48) (50)

Adenoma 1 (2%)

Intestine small, duodenum (46) (49) (48) (46) (50)

Leiomyoma 1 (2%)

Intestine small, ileum (45) (47) (44) (47) (50)

Intestine small, jejunum (46) (46) (44) (45) (49)

Liver (50) (50) (50) (50) (50)

Hepatocellular adenoma 1 (2%) 1 (2%)

Pheochromocytoma malignant, metastatic,

 adrenal medulla 1 (2%)

Sarcoma, metastatic, tissue NOS 1 (2%)

Mesentery (11) (13) (12) (15) (10)

Sarcoma 1 (7%)

Oral mucosa (50) (50) (50) (50) (50)

Squamous cell carcinoma 2 (4%) 11 (22%)

Pancreas (50) (50) (50) (50) (50)

Mixed tumor benign 1 (2%)

Salivary glands (50) (50) (50) (50) (50)

Stomach, forestomach (50) (50) (50) (50) (50)

Stomach, glandular (50) (50) (50) (50) (50)

Tongue (45) (49) (48) (48) (48)

Squamous cell carcinoma 1 (2%)

Squamous cell carcinoma, metastatic,

 oral mucosa 2 (4%)

Squamous cell papilloma 1 (2%) 1 (2%)

Cardiovascular System

Heart (50) (50) (50) (50) (50)

Schwannoma malignant 1 (2%) 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 99

Table B1

Summary of the Incidence of Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Endocrine System

Adrenal cortex (50) (50) (50) (50) (50)

Adenoma 1 (2%) 1 (2%)

Adrenal medulla (49) (50) (49) (50) (50)

Pheochromocytoma benign 2 (4%) 1 (2%) 2 (4%) 4 (8%)

Pheochromocytoma benign, multiple 1 (2%)

Pheochromocytoma malignant 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Pheochromocytoma malignant, multiple 1 (2%)

Islets, pancreatic (50) (50) (50) (50) (50)

Adenoma 2 (4%) 1 (2%) 2 (4%) 2 (4%) 2 (4%)

Adenoma, multiple 1 (2%)

Parathyroid gland (46) (47) (47) (45) (47)

Pituitary gland (50) (50) (50) (50) (49)

Pars distalis, adenoma 26 (52%) 29 (58%) 25 (50%) 21 (42%) 12 (24%)

Pars distalis, adenoma, multiple 2 (4%) 1 (2%)

Pars distalis, carcinoma 2 (4%) 1 (2%) 1 (2%) 1 (2%)

Pars intermedia, adenoma 1 (2%)

Thyroid gland (50) (50) (50) (50) (50)

C-cell, adenoma 8 (16%) 5 (10%) 7 (14%) 4 (8%) 9 (18%)

C-cell, carcinoma 2 (4%) 2 (4%) 2 (4%)

Follicular cell, adenoma 1 (2%)

Follicular cell, carcinoma 1 (2%) 1 (2%) 1 (2%)

General Body System

Tissue NOS (2)

Abdominal, sarcoma 1 (50%)

Genital System

Clitoral gland (50) (50) (50) (50) (50)

Adenoma 2 (4%) 9 (18%) 8 (16%) 5 (10%) 4 (8%)

Carcinoma 8 (16%) 8 (16%) 5 (10%) 3 (6%) 5 (10%)

Carcinoma, multiple 3 (6%)

Fibrosarcoma 1 (2%)

Bilateral, adenoma 1 (2%)

Ovary (49) (50) (50) (50) (50)

Granulosa cell tumor benign 1 (2%) 1 (2%)

Uterus (49) (50) (50) (50) (50)

Adenoma 1 (2%)

Leiomyosarcoma 1 (2%)

Polyp stromal 10 (20%) 14 (28%) 13 (26%) 15 (30%) 8 (16%)

Polyp stromal, multiple 1 (2%) 1 (2%) 2 (4%)

Schwannoma malignant 1 (2%) 1 (2%) 1 (2%)

Schwannoma malignant, metastatic, uterus 1 (2%)

Vagina (8) (12) (4) (4) (10)

Polyp 1 (8%)

Schwannoma malignant 1 (10%)

Schwannoma malignant, metastatic, vagina 1 (13%)
100 Sodium Dichromate Dihydrate, NTP TR 546 

Table B1

Summary of the Incidence of Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematopoietic System

Bone marrow (50) (50) (49) (50) (50)

Pheochromocytoma malignant, metastatic,

 adrenal medulla 1 (2%)

Lymph node (8) (11) (9) (4) (11)

Lymph node, mandibular (4) (3) (2) (3)

Lymph node, mesenteric (50) (50) (50) (50) (50)

Lymph node, pancreatic (29) (36) (30) (34) (33)

Spleen (50) (50) (50) (50) (50)

Pheochromocytoma malignant, metastatic,

 adrenal medulla 1 (2%)

Thymus (50) (49) (49) (48) (47)

Integumentary System

Mammary gland (50) (50) (50) (50) (50)

Adenoma 2 (4%) 1 (2%) 3 (6%)

Carcinoma 3 (6%) 1 (2%) 1 (2%)

Fibroadenoma 13 (26%) 16 (32%) 20 (40%) 19 (38%) 14 (28%)

Fibroadenoma, multiple 24 (48%) 15 (30%) 17 (34%) 11 (22%) 9 (18%)

Skin (50) (50) (50) (50) (50)

Basal cell carcinoma 1 (2%)

Keratoacanthoma 1 (2%)

Sebaceous gland, adenoma 1 (2%) 1 (2%)

Subcutaneous tissue, fibroma 1 (2%) 4 (8%) 1 (2%) 3 (6%)

Subcutaneous tissue, fibroma, multiple 1 (2%)

Subcutaneous tissue, fibrosarcoma 1 (2%)

Subcutaneous tissue, lipoma 1 (2%) 1 (2%)

Subcutaneous tissue, liposarcoma 1 (2%)

Subcutaneous tissue, sarcoma 1 (2%)

Subcutaneous tissue, schwannoma malignant 1 (2%)

Musculoskeletal System

Bone (50) (50) (50) (50) (50)

Nervous System

Brain (50) (50) (50) (50) (50)

Carcinoma, metastatic, pituitary gland 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Squamous cell carcinoma, metastatic,

 oral mucosa 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 101

Table B1

Summary of the Incidence of Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Respiratory System

Larynx (1) (1)

Squamous cell carcinoma 1 (100%)

Lung (50) (50) (50) (50) (50)

Alveolar/bronchiolar adenoma 4 (8%) 3 (6%) 2 (4%) 3 (6%) 3 (6%)

Carcinoma, metastatic, clitoral gland 1 (2%)

Carcinoma, metastatic, 

 uncertain primary site 1 (2%)

Squamous cell carcinoma, metastatic,

 oral mucosa 2 (4%)

Nose (50) (50) (50) (50) (50)

Squamous cell carcinoma, metastatic, 

 oral mucosa 1 (2%)

Special Senses System

Eye (50) (50) (50) (50) (50)

Harderian gland (50) (50) (50) (50) (50)

Adenoma 1 (2%)

Squamous cell carcinoma, metastatic,

 oral mucosa 1 (2%) 1 (2%)

Zymbal’s gland (1) (1)

Carcinoma 1 (100%) 1 (100%)

Urinary System

Kidney (50) (50) (50) (50) (50)

Urinary bladder (49) (50) (50) (50) (49)

Papilloma 1 (2%)

Systemic Lesions

Multiple organsb (50) (50) (50) (50) (50)

Leukemia mononuclear 8 (16%) 18 (36%) 13 (26%) 7 (14%) 11 (22%)

Neoplasm Summary

Moribund 12 15 9 10 18

Total animals with primary neoplasmsc 49 48 50 49 47

Total primary neoplasms 126 144 130 114 104

Total animals with benign neoplasms 47 46 47 46 37

Total benign neoplasms 103 103 106 93 68

Total animals with malignant neoplasms 19 30 19 18 30

Total malignant neoplasms 23 41 24 21 36

Total animals with metastatic neoplasms 2 3 2 8

Total metastatic neoplasms 3 5 2 10

Total animals with malignant neoplasms

of uncertain primary site 1

a Number of animals examined microscopically at the site and the number of animals with neoplasm b Number of animals with any tissue examined microscopically c Primary neoplasms: all neoplasms except metastatic neoplasms
102 Sodium Dichromate Dihydrate, NTP TR 546 

Table B2

Statistical Analysis of Primary Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Adrenal Medulla: Benign Pheochromocytoma

Overall ratea 2/49 (4%) 2/50 (4%) 2/49 (4%) 4/50 (8%) 0/50 (0%)

Adjusted rateb 4.6% 4.6% 4.6% 9.3% 0.0%

Terminal ratec 2/33 (6%) 2/32 (6%) 1/31 (3%) 4/36 (11%) 0/31 (0%)

First incidence (days) 729 (T) 729 (T) 662 729 (T) —d

Poly-3 teste P=0.200N P=0.692N P=0.693 P=0.334 P=0.240N

Adrenal Medulla: Benign or Malignant Pheochromocytoma

Overall rate 3/49 (6%) 4/50 (8%) 3/49 (6%) 5/50 (10%) 0/50 (0%)

Adjusted rate 6.9% 9.0% 6.8% 11.6% 0.0%

Terminal rate 3/33 (9%) 3/32 (9%) 1/31 (3%) 5/36 (14%) 0/31 (0%)

First incidence (days) 729 (T) 618 571 729 (T) —

Poly-3 test P=0.084N P=0.509 P=0.658N P=0.352 P=0.121N

Clitoral Gland: Adenoma

Overall rate 2/50 (4%) 9/50 (18%) 8/50 (16%) 5/50 (10%) 5/50 (10%)

Adjusted rate 4.5% 20.5% 18.0% 11.6% 11.5%

Terminal rate 1/33 (3%) 8/32 (25%) 7/32 (22%) 5/36 (14%) 4/31 (13%)

First incidence (days) 689 689 689 729 (T) 605

Poly-3 test P=0.437N P=0.023 P=0.044 P=0.204 P=0.204

Clitoral Gland: Carcinoma

Overall rate 8/50 (16%) 11/50 (22%) 5/50 (10%) 3/50 (6%) 5/50 (10%)

Adjusted rate 17.9% 24.6% 11.3% 6.8% 11.7%

Terminal rate 6/33 (18%) 8/32 (25%) 5/32 (16%) 1/36 (3%) 5/31 (16%)

First incidence (days) 654 605 729 (T) 447 729 (T)

Poly-3 test P=0.138N P=0.302 P=0.283N P=0.100N P=0.302N

Clitoral Gland: Adenoma or Carcinoma

Overall rate 10/50 (20%) 19/50 (38%) 13/50 (26%) 8/50 (16%) 10/50 (20%)

Adjusted rate 22.3% 42.3% 29.3% 18.0% 23.1%

Terminal rate 7/33 (21%) 15/32 (47%) 12/32 (38%) 6/36 (17%) 9/31 (29%)

First incidence (days) 654 605 689 447 605

Poly-3 test P=0.156N P=0.032 P=0.301 P=0.406N P=0.564

Lung: Alveolar/bronchiolar Adenoma

Overall rate 4/50 (8%) 3/50 (6%) 2/50 (4%) 3/50 (6%) 3/50 (6%)

Adjusted rate 9.0% 6.8% 4.5% 6.9% 7.0%

Terminal rate 4/33 (12%) 3/32 (9%) 2/32 (6%) 3/36 (8%) 2/31 (7%)

First incidence (days) 729 (T) 729 (T) 729 (T) 729 (T) 721

Poly-3 test P=0.579N P=0.507N P=0.339N P=0.514N P=0.518N

Mammary Gland: Fibroadenoma

Overall rate 37/50 (74%) 31/50 (62%) 37/50 (74%) 30/50 (60%) 23/50 (46%)

Adjusted rate 77.3% 67.4% 79.3% 66.4% 52.1%

Terminal rate 26/33 (79%) 23/32 (72%) 26/32 (81%) 25/36 (69%) 18/31 (58%)

First incidence (days) 489 560 571 559 560

Poly-3 test P=0.003N P=0.191N P=0.505 P=0.165N P=0.007N
Sodium Dichromate Dihydrate, NTP TR 546 103

Table B2

Statistical Analysis of Primary Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Mammary Gland: Adenoma

Overall rate 2/50 (4%) 1/50 (2%) 3/50 (6%) 0/50 (0%) 0/50 (0%)

Adjusted rate 4.5% 2.3% 6.7% 0.0% 0.0%

Terminal rate 2/33 (6%) 1/32 (3%) 2/32 (6%) 0/36 (0%) 0/31 (0%)

First incidence (days) 729 (T) 729 (T) 586 — —

Poly-3 test P=0.119N P=0.504N P=0.503 P=0.243N P=0.245N

Mammary Gland: Fibroadenoma or Adenoma

Overall rate 37/50 (74%) 31/50 (62%) 38/50 (76%) 30/50 (60%) 23/50 (46%)

Adjusted rate 77.3% 67.4% 80.6% 66.4% 52.1%

Terminal rate 26/33 (79%) 23/32 (72%) 26/32 (81%) 25/36 (69%) 18/31 (58%)

First incidence (days) 489 560 571 559 560

Poly-3 test P=0.002N P=0.191N P=0.439 P=0.165N P=0.007N

Mammary Gland: Carcinoma

Overall rate 0/50 (0%) 3/50 (6%) 1/50 (2%) 1/50 (2%) 0/50 (0%)

Adjusted rate 0.0% 6.8% 2.3% 2.3% 0.0%

Terminal rate 0/33 (0%) 2/32 (6%) 1/32 (3%) 1/36 (3%) 0/31 (0%)

First incidence (days) — 686 729 (T) 729 (T) —

Poly-3 test P=0.236N P=0.117 P=0.499 P=0.495 —f

Mammary Gland: Adenoma or Carcinoma

Overall rate 2/50 (4%) 4/50 (8%) 4/50 (8%) 1/50 (2%) 0/50 (0%)

Adjusted rate 4.5% 9.1% 9.0% 2.3% 0.0%

Terminal rate 2/33 (6%) 3/32 (9%) 3/32 (9%) 1/36 (3%) 0/31 (0%)

First incidence (days) 729 (T) 686 586 729 (T) —

Poly-3 test P=0.050N P=0.333 P=0.340 P=0.509N P=0.245N

Mammary Gland: Fibroadenoma, Adenoma, or Carcinoma

Overall rate 37/50 (74%) 31/50 (62%) 39/50 (78%) 30/50 (60%) 23/50 (46%)

Adjusted rate 77.3% 67.4% 82.7% 66.4% 52.1%

Terminal rate 26/33 (79%) 23/32 (72%) 27/32 (84%) 25/36 (69%) 18/31 (58%)

First incidence (days) 489 560 571 559 560

Poly-3 test P=0.002N P=0.191N P=0.335 P=0.165N P=0.007N

Oral Cavity (Oral Mucosa): Squamous Cell Carcinoma

Overall rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 2/50 (4%)g 11/50 (22%)

Adjusted rate 0.0% 0.0% 0.0% 4.6% 23.9%

Terminal rate 0/33 (0%) 0/32 (0%) 0/32 (0%) 1/36 (3%) 2/31 (7%)

First incidence (days) — — — 646 506

Poly-3 test P<0.001 — — P=0.233 P<0.001

Oral Cavity (Oral Mucosa or Tongue): Squamous Cell Papilloma or Squamous Cell Carcinoma

Overall rate 1/50 (2%) 1/50 (2%) 0/50 (0%) 2/50 (4%) 11/50 (22%)

Adjusted rate 2.2% 2.3% 0.0% 4.6% 23.9%

Terminal rate 0/33 (0%) 1/32 (3%) 0/32 (0%) 1/36 (3%) 2/31 (7%)

First incidence (days) 618 729 (T) — 646 506

Poly-3 test P<0.001 P=0.756 P=0.503N P=0.491 P=0.002
104 Sodium Dichromate Dihydrate, NTP TR 546 

Table B2

Statistical Analysis of Primary Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Pancreatic Islets: Adenoma

Overall rate 2/50 (4%) 1/50 (2%) 2/50 (4%) 3/50 (6%) 2/50 (4%)

Adjusted rate 4.5% 2.3% 4.5% 6.9% 4.7%

Terminal rate 1/33 (3%) 1/32 (3%) 1/32 (3%) 3/36 (8%) 2/31 (7%)

First incidence (days) 721 729 (T) 586 729 (T) 729 (T)

Poly-3 test P=0.491 P=0.504N P=0.692N P=0.488 P=0.682

Pituitary Gland (Pars Distalis): Adenoma

Overall rate 28/50 (56%) 29/50 (58%) 25/50 (50%) 22/50 (44%) 12/49 (24%)

Adjusted rate 60.5% 61.3% 54.0% 48.3% 27.8%

Terminal rate 20/33 (61%) 18/32 (56%) 16/32 (50%) 16/36 (44%) 9/31 (29%)

First incidence (days) 489 461 534 580 647

Poly-3 test P<0.001N P=0.553 P=0.334N P=0.164N P<0.001N

Pituitary Gland (Pars Distalis): Adenoma or Carcinoma

Overall rate 30/50 (60%) 30/50 (60%) 25/50 (50%) 23/50 (46%) 13/49 (27%)

Adjusted rate 63.8% 63.4% 54.0% 50.5% 30.1%

Terminal rate 20/33 (61%) 19/32 (59%) 16/32 (50%) 17/36 (47%) 10/31 (32%)

First incidence (days) 489 461 534 580 647

Poly-3 test P<0.001N P=0.571N P=0.221N P=0.135N P<0.001N

Skin (Subcutaneous Tissue): Fibroma

Overall rate 1/50 (2%) 0/50 (0%) 4/50 (8%) 2/50 (4%) 3/50 (6%)

Adjusted rate 2.3% 0.0% 9.1% 4.6% 6.9%

Terminal rate 1/33 (3%) 0/32 (0%) 4/32 (13%) 2/36 (6%) 2/31 (7%)

First incidence (days) 729 (T) — 729 (T) 729 (T) 605

Poly-3 test P=0.226 P=0.502N P=0.177 P=0.491 P=0.296

Skin (Subcutaneous Tissue): Fibroma, Fibrosarcoma, or Sarcoma

Overall rate 1/50 (2%) 1/50 (2%) 4/50 (8%) 3/50 (6%) 3/50 (6%)

Adjusted rate 2.3% 2.2% 9.1% 6.9% 6.9%

Terminal rate 1/33 (3%) 0/32 (0%) 4/32 (13%) 2/36 (6%) 2/31 (7%)

First incidence (days) 729 (T) 461 729 (T) 559 605

Poly-3 test P=0.299 P=0.760N P=0.177 P=0.300 P=0.296

Thyroid Gland (C-cell): Adenoma

Overall rate 8/50 (16%) 5/50 (10%) 7/50 (14%) 4/50 (8%) 9/50 (18%)

Adjusted rate 17.8% 11.2% 15.8% 9.1% 20.8%

Terminal rate 6/33 (18%) 3/32 (9%) 7/32 (22%) 3/36 (8%) 8/31 (26%)

First incidence (days) 580 560 729 (T) 379 595

Poly-3 test P=0.250 P=0.280N P=0.515N P=0.185N P=0.466

Thyroid Gland (C-cell): Adenoma or Carcinoma

Overall rate 10/50 (20%) 5/50 (10%) 7/50 (14%) 5/50 (10%) 10/50 (20%)

Adjusted rate 22.0% 11.2% 15.8% 11.3% 23.1%

Terminal rate 7/33 (21%) 3/32 (9%) 7/32 (22%) 4/36 (11%) 9/31 (29%)

First incidence (days) 580 560 729 (T) 379 595

Poly-3 test P=0.232 P=0.135N P=0.316N P=0.140N P=0.555
Sodium Dichromate Dihydrate, NTP TR 546 105

Table B2

Statistical Analysis of Primary Neoplasms in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Uterus: Stromal Polyp

Overall rate 10/50 (20%) 15/50 (30%) 14/50 (28%) 17/50 (34%) 8/50 (16%)

Adjusted rate 22.5% 32.7% 31.0% 37.8% 18.1%

Terminal rate 10/33 (30%) 9/32 (28%) 10/32 (31%) 13/36 (36%) 5/31 (16%)

First incidence (days) 729 (T) 554 586 493 461

Poly-3 test P=0.139N P=0.198 P=0.251 P=0.087 P=0.399N

All Organs: Mononuclear Cell Leukemia

Overall rate 8/50 (16%) 18/50 (36%) 13/50 (26%) 7/50 (14%) 11/50 (22%)

Adjusted rate 17.4% 38.4% 27.9% 15.3% 24.5%

Terminal rate 2/33 (6%) 8/32 (25%) 7/32 (22%) 2/36 (6%) 6/31 (19%)

First incidence (days) 575 387 554 379 472

Poly-3 test P=0.348N P=0.019 P=0.170 P=0.503N P=0.282

All Organs: Benign Neoplasms

Overall rate 47/50 (94%) 46/50 (92%) 47/50 (94%) 46/50 (92%) 37/50 (74%)

Adjusted rate 95.7% 94.6% 96.8% 94.9% 79.6%

Terminal rate 32/33 (97%) 31/32 (97%) 32/32 (100%) 35/36 (97%) 26/31 (84%)

First incidence (days) 489 461 534 379 461

Poly-3 test P<0.001N P=0.596N P=0.620 P=0.628N P=0.009N

All Organs: Malignant Neoplasms

Overall rate 20/50 (40%) 30/50 (60%) 19/50 (38%) 18/50 (36%) 31/50 (62%)

Adjusted rate 42.1% 62.4% 39.4% 37.2% 63.1%

Terminal rate 10/33 (30%) 18/32 (56%) 10/32 (31%) 8/36 (22%) 15/31 (48%)

First incidence (days) 575 387 454 379 461

Poly-3 test P=0.057 P=0.034 P=0.475N P=0.389N P=0.029

All Organs: Benign or Malignant Neoplasms

Overall rate 49/50 (98%) 48/50 (96%) 50/50 (100%) 49/50 (98%) 47/50 (94%)

Adjusted rate 98.0% 96.6% 100.0% 98.0% 94.0%

Terminal rate 32/33 (97%) 31/32 (97%) 32/32 (100%) 35/36 (97%) 28/31 (90%)

First incidence (days) 489 387 454 379 461

Poly-3 test P=0.126N P=0.575N P=0.500 P=0.760 P=0.306N

(T) Terminal sacrifice

a Number of neoplasm-bearing animals/number of animals examined. Denominator is number of animals examined microscopically for adrenal medulla, 

clitoral gland, lung, pancreatic islets, pituitary gland, and thyroid gland; for other tissues, denominator is number of animals necropsied. b Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality c Observed incidence at terminal kill d Not applicable; no neoplasms in animal group e Beneath the control incidence is the P value associated with the trend test. Beneath the exposed group incidence are the P values corresponding to 

pairwise comparisons between the controls and that exposed group. The Poly-3 test accounts for the differential mortality in animals that do not reach 

terminal sacrifice. A negative trend or a lower incidence in an exposed group is indicated by N. f Value of statistic cannot be computed. g One animal that had a squamous cell carcinoma of the oral mucosa also had a squamous cell carcinoma of the tongue.
106 Sodium Dichromate Dihydrate, NTP TR 546 

Table B3

Historical Incidence of Oral Cavity Neoplasms in Control Female F344/N Ratsa

 Incidence in Controls

 Oral Mucosa All Sitesb

Study Squamous Cell Carcinoma Papilloma, Squamous Cell Papilloma, or 

 Squamous Cell Carcinoma

Historical Incidence: Drinking Water Studies

Bromochloroacetic acid 0/50 1/50

Dibromoacetic acid 0/50 0/50

Dibromoacetonitrile 0/50 1/50

Dipropylene glycol 0/50 1/50

Sodium chlorate 0/50 0/50

Sodium dichromate dihydrate 0/50 —

Overall Historical Incidences: Drinking Water Studies

Total (%) 0/300 3/250 (1.2%)

Mean ± standard deviation 1.2% ± 1.1%

Range (0%-2%)

Overall Historical Incidence: All Routes

Total (%) 5/1,400 (0.4%) 14/1,350 (1.0%)

Mean ± standard deviation 0.4% ± 0.8% 1.1% ± 1.6%

Range (0%-2%) (0%-6%)

a Data as of March 5, 2007, with sodium dichromate dihydrate data added from Table B1 b All sites includes the oral mucosa, tongue, pharynx, tooth, and gingiva; sodium dichromate dihydrate data not included
Sodium Dichromate Dihydrate, NTP TR 546 107

Table B4

Summary of the Incidence of Nonneoplastic Lesions in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 12 15 9 10 18

Natural deaths 5 3 9 4 1

Survivors

Died last week of study 1

Terminal sacrifice 32 32 32 36 31

Animals examined microscopically 50 50 50 50 50

Alimentary System

Intestine large, cecum (46) (47) (48) (47) (50)

Edema 2 (4%) 1 (2%) 1 (2%) 1 (2%)

Hemorrhage 1 (2%)

Intestine large, colon (49) (49) (49) (48) (50)

Intestine small, duodenum (46) (49) (48) (46) (50)

Infiltration cellular, histiocyte 1 (2%) 30 (65%) 47 (94%)

Intestine small, ileum (45) (47) (44) (47) (50)

Lymphatic, hyperplasia 1 (2%)

Lymphoid tissue, hyperplasia 16 (36%) 10 (21%) 8 (18%) 6 (13%) 12 (24%)

Intestine small, jejunum (46) (46) (44) (45) (49)

Liver (50) (50) (50) (50) (50)

Angiectasis 1 (2%) 4 (8%) 2 (4%)

Basophilic focus 45 (90%) 41 (82%) 44 (88%) 47 (94%) 43 (86%)

Clear cell focus 7 (14%) 5 (10%) 7 (14%) 20 (40%) 7 (14%)

Eosinophilic focus 5 (10%) 5 (10%) 5 (10%) 3 (6%) 3 (6%)

Fatty change 3 (6%) 7 (14%) 10 (20%) 13 (26%) 16 (32%)

Hematopoietic cell proliferation 1 (2%) 2 (4%) 3 (6%)

Hemorrhage 1 (2%) 1 (2%) 1 (2%)

Hepatodiaphragmatic nodule 5 (10%) 3 (6%) 9 (18%) 10 (20%) 9 (18%)

Infiltration cellular, histiocyte 1 (2%) 5 (10%) 21 (42%) 42 (84%) 47 (94%)

Inflammation, chronic 12 (24%) 21 (42%) 28 (56%) 35 (70%) 39 (78%)

Mixed cell focus 9 (18%) 6 (12%) 10 (20%) 20 (40%) 18 (36%)

Necrosis 5 (10%) 7 (14%) 4 (8%) 1 (2%)

Regeneration 1 (2%) 1 (2%)

Bile duct, hyperplasia 2 (4%) 5 (10%) 3 (6%) 4 (8%)

Centrilobular, necrosis 4 (8%) 2 (4%) 1 (2%) 2 (4%)

Hepatocyte, syncytial alteration 1 (2%) 1 (2%)

Kupffer cell, pigmentation 1 (2%) 1 (2%)

Lymphatic, infiltration cellular 1 (2%)

Mesentery (11) (13) (12) (15) (10)

Accessory spleen 1 (8%) 1 (7%) 1 (10%)

Fat, necrosis 11 (100%) 10 (77%) 11 (92%) 12 (80%) 9 (90%)

Oral mucosa (50) (50) (50) (50) (50)

Pancreas (50) (50) (50) (50) (50)

Atrophy 6 (12%) 12 (24%) 11 (22%) 9 (18%) 5 (10%)

Cyst 2 (4%) 4 (8%) 3 (6%) 6 (12%) 4 (8%)

Acinus, cytoplasmic alteration 3 (6%)

Acinus, hyperplasia, focal 1 (2%) 1 (2%) 1 (2%)

a Number of animals examined microscopically at the site and the number of animals with lesion
108 Sodium Dichromate Dihydrate, NTP TR 546 

Table B4

Summary of the Incidence of Nonneoplastic Lesions in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Alimentary System (continued)

Salivary glands (50) (50) (50) (50) (50)

Atrophy 9 (18%) 7 (14%) 10 (20%) 17 (34%) 17 (34%)

Fibrosis 1 (2%)

Vacuolization cytoplasmic 1 (2%)

Stomach, forestomach (50) (50) (50) (50) (50)

Edema 1 (2%) 3 (6%) 1 (2%) 2 (4%) 2 (4%)

Erosion 1 (2%) 1 (2%) 1 (2%)

Inflammation, chronic active 1 (2%)

Ulcer 2 (4%) 3 (6%) 2 (4%) 2 (4%) 3 (6%)

Epithelium, hyperplasia 2 (4%) 3 (6%) 4 (8%) 4 (8%) 4 (8%)

Stomach, glandular (50) (50) (50) (50) (50)

Edema 1 (2%) 1 (2%) 1 (2%)

Erosion 2 (4%) 3 (6%) 2 (4%) 1 (2%) 5 (10%)

Hyperplasia 4 (8%) 6 (12%) 4 (8%) 7 (14%) 4 (8%)

Inflammation 1 (2%)

Ulcer 1 (2%) 2 (4%) 1 (2%) 1 (2%) 2 (4%)

Glands, dilatation 1 (2%)

Tongue (45) (49) (48) (48) (48)

Granuloma 2 (4%)

Hemorrhage 1 (2%) 1 (2%)

Inflammation, chronic 8 (18%) 3 (6%) 4 (8%) 14 (29%) 12 (25%)

Ulcer 3 (6%)

Epithelium, hyperplasia 1 (2%) 1 (2%) 1 (2%)

Cardiovascular System

Heart (50) (50) (50) (50) (50)

Cardiomyopathy 27 (54%) 32 (64%) 35 (70%) 33 (66%) 28 (56%)

Inflammation, chronic 1 (2%)

Necrosis 1 (2%)

Thrombosis 1 (2%) 1 (2%) 2 (4%) 1 (2%)

Endocrine System

Adrenal cortex (50) (50) (50) (50) (50)

Accessory adrenal cortical nodule 6 (12%) 9 (18%) 10 (20%) 6 (12%) 8 (16%)

Angiectasis 1 (2%) 1 (2%)

Degeneration, fatty 12 (24%) 12 (24%) 17 (34%) 14 (28%) 20 (40%)

Hyperplasia, focal 2 (4%) 6 (12%) 8 (16%) 12 (24%) 6 (12%)

Hypertrophy 1 (2%)

Hypertrophy, focal 4 (8%) 4 (8%) 6 (12%) 1 (2%) 7 (14%)

Necrosis 3 (6%) 2 (4%)

Adrenal medulla (49) (50) (49) (50) (50)

Hyperplasia 2 (4%) 3 (6%) 1 (2%) 2 (4%) 2 (4%)

Islets, pancreatic (50) (50) (50) (50) (50)

Hyperplasia 1 (2%)

Parathyroid gland (46) (47) (47) (45) (47)

Hyperplasia 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 109

Table B4

Summary of the Incidence of Nonneoplastic Lesions in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Endocrine System (continued)

Pituitary gland (50) (50) (50) (50) (49)

Pars distalis, angiectasis 11 (22%) 6 (12%) 7 (14%) 4 (8%) 3 (6%)

Pars distalis, cyst 18 (36%) 18 (36%) 18 (36%) 18 (36%) 27 (55%)

Pars distalis, cytoplasmic alteration, focal 1 (2%)

Pars distalis, hyperplasia 1 (2%)

Pars distalis, hyperplasia, focal 9 (18%) 8 (16%) 9 (18%) 8 (16%) 10 (20%)

Pars intermedia, angiectasis 1 (2%) 2 (4%)

Pars intermedia, cyst 1 (2%) 3 (6%) 1 (2%) 1 (2%) 3 (6%)

Thyroid gland (50) (50) (50) (50) (50)

Ultimobranchial cyst 2 (4%) 2 (4%)

C-cell, hyperplasia 28 (56%) 28 (56%) 25 (50%) 23 (46%) 16 (32%)

Follicle, cyst 1 (2%)

General Body System

Tissue NOS (2)

Genital System

Clitoral gland (50) (50) (50) (50) (50)

Cyst 2 (4%) 2 (4%) 4 (8%) 1 (2%)

Hyperplasia 4 (8%) 1 (2%) 2 (4%) 3 (6%) 1 (2%)

Inflammation 1 (2%)

Inflammation, chronic 3 (6%) 4 (8%) 6 (12%) 8 (16%) 4 (8%)

Ovary (49) (50) (50) (50) (50)

Angiectasis 1 (2%) 1 (2%)

Cyst 9 (18%) 6 (12%) 7 (14%) 10 (20%) 5 (10%)

Uterus (49) (50) (50) (50) (50)

Angiectasis 2 (4%)

Dilatation 1 (2%)

Hemorrhage 1 (2%)

Hyperplasia, cystic 5 (10%) 5 (10%) 4 (8%) 9 (18%) 5 (10%)

Inflammation, chronic 1 (2%)

Vagina (8) (12) (4) (4) (10)

Angiectasis 1 (13%)

Hematopoietic System

Bone marrow (50) (50) (49) (50) (50)

Hyperplasia 6 (12%) 8 (16%) 7 (14%) 6 (12%) 9 (18%)

Infiltration cellular, histiocyte 1 (2%) 2 (4%)

Myelofibrosis 1 (2%) 1 (2%) 1 (2%)
110 Sodium Dichromate Dihydrate, NTP TR 546 

Table B4

Summary of the Incidence of Nonneoplastic Lesions in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematopoietic System (continued)

Lymph node (8) (11) (9) (4) (11)

Hemorrhage 1 (13%) 1 (25%)

Hyperplasia, lymphoid 1 (25%)

Deep cervical, hemorrhage 1 (13%) 1 (11%)

Mediastinal, ectasia 1 (9%) 2 (6%)

Mediastinal, hemorrhage 3 (38%) 4 (36%) 2 (22%) 3 (75%) 4 (36%)

Mediastinal, hyperplasia, lymphoid 2 (25%) 5 (45%) 2 (22%) 1 (25%) 6 (55%)

Mediastinal, pigmentation 1 (13%) 4 (36%) 2 (50%) 1 (9%)

Lymph node, mandibular (4) (3) (2) (3)

Ectasia 1 (33%)

Lymph node, mesenteric (50) (50) (50) (50) (50)

Fibrosis 1 (2%)

Hemorrhage 11 (22%) 13 (26%) 16 (32%) 14 (28%) 21 (42%)

Hyperplasia, lymphoid 2 (4%)

Hyperplasia, reticulum cell 1 (2%) 1 (2%)

Infiltration cellular, histiocyte 21 (42%) 18 (36%) 27 (54%) 36 (72%) 42 (84%)

Lymph node, pancreatic (29) (36) (30) (34) (33)

Hemorrhage 3 (10%) 2 (7%) 4 (12%)

Hyperplasia, lymphoid 2 (6%)

Infiltration cellular, histiocyte 17 (59%) 20 (56%) 23 (77%) 32 (94%) 27 (82%)

Pigmentation 2 (7%) 1 (3%)

Spleen (50) (50) (50) (50) (50)

Accessory spleen 1 (2%) 1 (2%)

Fibrosis 2 (4%)

Hematopoietic cell proliferation 36 (72%) 28 (56%) 38 (76%) 36 (72%) 33 (66%)

Hemorrhage 1 (2%) 1 (2%)

Infiltration cellular, mixed cell 3 (6%)

Necrosis 3 (6%) 1 (2%) 1 (2%) 2 (4%)

Pigmentation 26 (52%) 23 (46%) 13 (26%) 6 (12%) 3 (6%)

Lymphoid follicle, atrophy 1 (2%) 4 (8%)

Lymphoid follicle, hyperplasia 1 (2%) 3 (6%)

Thymus (50) (49) (49) (48) (47)

Atrophy 3 (6%)

Integumentary System

Mammary gland (50) (50) (50) (50) (50)

Hyperplasia 47 (94%) 50 (100%) 45 (90%) 49 (98%) 44 (88%)

Skin (50) (50) (50) (50) (50)

Cyst epithelial inclusion 1 (2%) 1 (2%)

Edema 1 (2%)

Hyperkeratosis 1 (2%)

Ulcer 1 (2%)

Musculoskeletal System

Bone (50) (50) (50) (50) (50)

Cranium, osteopetrosis 1 (2%) 1 (2%) 2 (4%)
Sodium Dichromate Dihydrate, NTP TR 546 111

Table B4

Summary of the Incidence of Nonneoplastic Lesions in Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Nervous System

Brain (50) (50) (50) (50) (50)

Compression 8 (16%) 13 (26%) 15 (30%) 11 (22%) 7 (14%)

Gliosis 1 (2%)

Hemorrhage 1 (2%) 3 (6%) 1 (2%)

Hydrocephalus 2 (4%) 2 (4%)

Necrosis 1 (2%)

Vacuolization cytoplasmic 1 (2%)

Respiratory System

Larynx (1) (1)

Lung (50) (50) (50) (50) (50)

Edema 1 (2%)

Foreign body 1 (2%) 1 (2%)

Hemorrhage 2 (4%) 4 (8%) 4 (8%) 1 (2%) 2 (4%)

Infiltration cellular, histiocyte 45 (90%) 48 (96%) 42 (84%) 46 (92%) 47 (94%)

Inflammation, chronic 2 (4%) 1 (2%) 3 (6%) 1 (2%)

Alveolar epithelium, hyperplasia 11 (22%) 7 (14%) 12 (24%) 9 (18%) 10 (20%)

Alveolar epithelium, metaplasia, squamous 1 (2%)

Nose (50) (50) (50) (50) (50)

Foreign body 3 (6%) 1 (2%) 1 (2%) 1 (2%) 3 (6%)

Inflammation, chronic 3 (6%) 2 (4%) 3 (6%) 3 (6%)

Nasolacrimal duct, cyst 1 (2%)

Respiratory epithelium, hyperplasia 1 (2%) 1 (2%) 1 (2%) 1 (2%) 2 (4%)

Special Senses System

Eye (50) (50) (50) (50) (50)

Cataract 2 (4%) 2 (4%) 4 (8%) 1 (2%) 1 (2%)

Inflammation, chronic 3 (6%)

Retina, degeneration 4 (8%) 2 (4%) 3 (6%) 2 (4%) 2 (4%)

Harderian gland (50) (50) (50) (50) (50)

Hemorrhage 1 (2%)

Inflammation, chronic 1 (2%)

Zymbal’s gland (1) (1)

Urinary System

Kidney (50) (50) (50) (50) (50)

Cyst 1 (2%) 2 (4%)

Glomerulosclerosis 1 (2%)

Hydronephrosis 1 (2%)

Infarct 3 (6%) 1 (2%) 1 (2%) 1 (2%) 4 (8%)

Inflammation, chronic 2 (4%) 1 (2%) 1 (2%) 1 (2%)

Nephropathy 33 (66%) 23 (46%) 32 (64%) 37 (74%) 41 (82%)

Renal tubule, accumulation, hyaline droplet 7 (14%) 4 (8%) 2 (4%) 2 (4%)

Renal tubule, dilatation 1 (2%)

Renal tubule, necrosis 3 (6%) 2 (4%)

Renal tubule, pigmentation 2 (4%) 1 (2%) 1 (2%) 2 (4%)

Transitional epithelium, hyperplasia 3 (6%) 2 (4%) 2 (4%) 1 (2%)

Urinary bladder (49) (50) (50) (50) (49)

Hemorrhage 1 (2%)
112 Sodium Dichromate Dihydrate, NTP TR 546 
113

APPENDIX C

SUMMARY OF LESIONS IN MALE MICE

IN THE 2-YEAR DRINKING WATER STUDY

OF SODIUM DICHROMATE DIHYDRATE

Table C1 Summary of the Incidence of Neoplasms in Male Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 114

Table C2 Statistical Analysis of Primary Neoplasms in Male Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 119

Table C3 Historical Incidence of Small Intestine Neoplasms in Control Male B6C3F1 Mice . . . . . . 123

Table C4 Summary of the Incidence of Nonneoplastic Lesions in Male Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 124
114 Sodium Dichromate Dihydrate, NTP TR 546 

Table C1

Summary of the Incidence of Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 7 5 5 4 3

Natural deaths 10 10 10 8 15

Survivors

Died last week of study 1 1

Terminal sacrifice 32 35 35 38 31

Animals examined microscopically 50 50 50 50 50

Alimentary System

Esophagus (50) (50) (50) (50) (50)

Squamous cell papilloma 1 (2%)

Gallbladder (47) (45) (44) (44) (39)

Sarcoma, metastatic, uncertain primary site 1 (2%)

Intestine large, cecum (42) (44) (47) (46) (39)

Carcinoma 1 (2%) 1 (2%)

Intestine large, colon (44) (45) (47) (46) (40)

Carcinoma 1 (3%)

Intestine large, rectum (42) (47) (47) (46) (42)

Intestine small, duodenum (39) (43) (45) (48) (40)

Adenoma 1 (3%) 1 (2%) 5 (10%) 9 (23%)

Adenoma, multiple 6 (15%)

Carcinoma 2 (4%) 3 (8%)

Hemangiosarcoma, metastatic, liver 1 (3%)

Hepatoblastoma, metastatic, liver 1 (3%)

Sarcoma, metastatic, mesentery 1 (2%)

Intestine small, ileum (40) (42) (44) (45) (38)

Adenoma 1 (2%)

Carcinoma 1 (2%)

Intestine small, jejunum (41) (42) (42) (46) (38)

Adenoma 3 (8%)

Carcinoma 1 (2%) 1 (2%) 2 (5%)

Carcinoma, multiple 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Liver (50) (50) (50) (50) (50)

Hemangioma 1 (2%)

Hemangiosarcoma 1 (2%) 1 (2%) 5 (10%) 2 (4%) 3 (6%)

Hemangiosarcoma, multiple 1 (2%)

Hepatoblastoma 14 (28%) 7 (14%) 10 (20%) 2 (4%)

Hepatoblastoma, multiple 3 (6%) 1 (2%) 1 (2%)

Hepatocellular adenoma 11 (22%) 12 (24%) 10 (20%) 12 (24%) 18 (36%)

Hepatocellular adenoma, multiple 25 (50%) 21 (42%) 18 (36%) 19 (38%) 10 (20%)

Hepatocellular carcinoma 10 (20%) 14 (28%) 8 (16%) 12 (24%) 14 (28%)

Hepatocellular carcinoma, multiple 4 (8%) 10 (20%) 9 (18%) 4 (8%)

Hepatocholangiocarcinoma 1 (2%)

Ito cell tumor malignant 2 (4%) 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Sarcoma, metastatic, uncertain primary site 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 115

Table C1

Summary of the Incidence of Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Alimentary System (continued)

Mesentery (16) (10) (9) (16) (5)

Carcinoma, metastatic, intestine large, cecum 1 (6%)

Fibrosarcoma 1 (6%)

Fibrosarcoma, metastatic, lung 1 (6%)

Hemangiosarcoma 2 (13%)

Hepatoblastoma, metastatic, liver 2 (13%) 2 (20%)

Sarcoma 1 (6%)

Sarcoma, metastatic, uncertain primary site 1 (6%)

Oral mucosa (50) (50) (50) (50) (50)

Pancreas (49) (49) (50) (49) (48)

Fibrosarcoma, metastatic, lung 1 (2%)

Hepatoblastoma, metastatic, liver 2 (4%) 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Salivary glands (49) (50) (49) (50) (50)

Basal cell carcinoma, metastatic, skin 1 (2%)

Stomach, forestomach (50) (50) (48) (50) (48)

Carcinoma, metastatic, intestine large, cecum 1 (2%)

Sarcoma, metastatic, uncertain primary site 1 (2%)

Squamous cell carcinoma 1 (2%)

Squamous cell papilloma 2 (4%)

Stomach, glandular (50) (48) (48) (50) (47)

Hepatoblastoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Sarcoma, metastatic, uncertain primary site 1 (2%)

Tongue (50) (50) (50) (50) (50)

Tooth (1) (3) (2) 

Cardiovascular System

Blood vessel (2) (1) (1) (1) (1)

Aorta, fibrosarcoma, metastatic, lung 1 (50%)

Heart (50) (50) (50) (50) (50)

Fibrosarcoma, metastatic, lung 1 (2%)

Hemangiosarcoma 1 (2%) 1 (2%)

Osteosarcoma, metastatic, bone 1 (2%)

Sarcoma, metastatic, uncertain primary site 1 (2%)

Endocrine System

Adrenal cortex (49) (49) (50) (50) (50)

Adenoma 1 (2%) 1 (2%)

Hepatoblastoma, metastatic, liver 2 (4%)

Hepatocellular carcinoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Capsule, adenoma 7 (14%) 5 (10%) 4 (8%) 6 (12%) 1 (2%)

Adrenal medulla (49) (48) (50) (50) (50)

Pheochromocytoma benign 1 (2%) 1 (2%)

Islets, pancreatic (49) (49) (50) (50) (49)

Adenoma 3 (6%) 1 (2%) 1 (2%)

Parathyroid gland (46) (47) (45) (49) (47)

Pituitary gland (49) (49) (48) (50) (47)
116 Sodium Dichromate Dihydrate, NTP TR 546 

Table C1

Summary of the Incidence of Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Endocrine System (continued)

Thyroid gland (50) (50) (50) (50) (50)

Basal cell carcinoma, metastatic, skin 1 (2%)

Follicular cell, adenoma 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Follicular cell, carcinoma 1 (2%) 1 (2%)

General Body System

None

Genital System

Epididymis (50) (50) (50) (50) (50)

Hepatoblastoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Preputial gland (50) (50) (50) (50) (50)

Prostate (50) (49) (50) (50) (50)

Seminal vesicle (50) (50) (50) (50) (50)

Hepatoblastoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Testes (50) (50) (50) (50) (50)

Hematopoietic System

Bone marrow (49) (50) (50) (50) (50)

Hemangiosarcoma 1 (2%) 1 (2%) 1 (2%)

Lymph node (8) (4) (6) (6) (5)

Bronchial, hepatoblastoma, metastatic, liver 1 (17%)

Bronchial, hepatocellular carcinoma, metastatic,

liver 1 (17%)

Bronchial, hepatocholangiocarcinoma, metastatic,

liver 1 (20%)

Iliac, hemangiosarcoma, metastatic, skin 1 (17%)

Mediastinal, alveolar/bronchiolar carcinoma,

metastatic, lung 1 (17%)

Mediastinal, hepatocholangiocarcinoma,

metastatic, liver 1 (20%)

Mediastinal, sarcoma, metastatic,

uncertain primary site 1 (17%)

Renal, hepatoblastoma, metastatic, liver 1 (17%)

Lymph node, mandibular (47) (49) (49) (48) (46)

Hemangiosarcoma 1 (2%)

Hemangiosarcoma, metastatic, spleen 1 (2%)

Lymph node, mesenteric (47) (47) (49) (49) (46)

Carcinoma, metastatic, intestine large, colon 1 (2%)

Hemangioma 1 (2%)

Hemangiosarcoma 1 (2%)

Hepatoblastoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Lymph node, pancreatic (5) (13) (10) (8) (16)

Hepatoblastoma, metastatic, liver 1 (10%)
Sodium Dichromate Dihydrate, NTP TR 546 117

Table C1

Summary of the Incidence of Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Hematopoietic System (continued)

Spleen (49) (48) (49) (49) (46)

Hemangiosarcoma 2 (4%) 1 (2%) 2 (4%) 2 (4%) 2 (4%)

Thymus (49) (50) (46) (49) (40)

Hepatoblastoma, metastatic, liver 1 (2%)

Osteosarcoma, metastatic, bone 1 (2%)

Integumentary System

Skin (50) (50) (50) (50) (50)

Basal cell carcinoma 1 (2%)

Hemangioma 1 (2%)

Subcutaneous tissue, fibrosarcoma 1 (2%)

Subcutaneous tissue, hemangiosarcoma 1 (2%) 1 (2%) 1 (2%)

Musculoskeletal System

Bone (50) (50) (50) (50) (50)

Osteosarcoma 1 (2%)

Skeletal muscle (4) (2) (4) (1)

Hepatoblastoma, metastatic, liver 1 (50%)

Hepatocellular carcinoma, metastatic, liver 1 (25%)

Osteosarcoma, metastatic, bone 1 (25%)

Sarcoma, metastatic, mesentery 1 (100%)

Nervous System

Brain (50) (50) (50) (50) (50)

Alveolar/bronchiolar carcinoma, metastatic,

lung 1 (2%)

Respiratory System

Lung (50) (50) (50) (50) (50)

Alveolar/bronchiolar adenoma 13 (26%) 8 (16%) 8 (16%) 6 (12%) 9 (18%)

Alveolar/bronchiolar adenoma, multiple 2 (4%) 1 (2%) 1 (2%) 2 (4%) 2 (4%)

Alveolar/bronchiolar carcinoma 2 (4%) 5 (10%) 10 (20%) 6 (12%) 5 (10%)

Alveolar/bronchiolar carcinoma, multiple 1 (2%) 1 (2%)

Basal cell carcinoma, metastatic, skin 1 (2%)

Carcinoma, metastatic, Harderian gland 1 (2%)

Carcinoma, metastatic, thyroid gland 1 (2%)

Fibrosarcoma 1 (2%)

Hemangiosarcoma 1 (2%)

Hepatoblastoma, metastatic, liver 7 (14%) 3 (6%) 2 (4%)

Hepatocellular carcinoma, metastatic, liver 4 (8%) 7 (14%) 2 (4%) 4 (8%) 7 (14%)

Hepatocholangiocarcinoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Sarcoma, metastatic, uncertain primary site 1 (2%)

Mediastinum, alveolar/bronchiolar carcinoma, 

metastatic, lung 1 (2%)

Mediastinum, osteosarcoma, metastatic, bone 1 (2%)

Nose (50) (50) (50) (50) (50)
118 Sodium Dichromate Dihydrate, NTP TR 546 

Table C1

Summary of the Incidence of Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Special Senses System

Eye (48) (49) (49) (50) (47)

Harderian gland (50) (50) (49) (50) (50)

Adenoma 6 (12%) 3 (6%) 4 (8%) 3 (6%) 2 (4%)

Basal cell carcinoma, metastatic, skin 1 (2%)

Carcinoma 1 (2%)

Urinary System

Kidney (50) (50) (50) (50) (49)

Sarcoma, metastatic, mesentery 1 (2%)

Renal tubule, adenoma 1 (2%)

Renal tubule, carcinoma 1 (2%) 1 (2%)

Urethra (1) (1) (1) 

Urinary bladder (49) (50) (50) (49) (46)

Systemic Lesions

Multiple organsb (50) (50) (50) (50) (50)

Histiocytic sarcoma 1 (2%) 1 (2%)

Lymphoma malignant 2 (4%) 2 (4%)

Mesothelioma malignant 2 (4%)

Neoplasm Summary

Total animals with primary neoplasmsc 49 45 47 44 48

Total primary neoplasms 115 99 104 96 107

Total animals with benign neoplasms 42 37 33 42 37

Total benign neoplasms 69 54 49 60 63

Total animals with malignant neoplasms 31 29 36 27 29

Total malignant neoplasms 46 45 55 36 44

Total animals with metastatic neoplasms 15 11 9 8 10

Total metastatic neoplasms 38 17 11 26 13

Total animals with malignant neoplasms

of uncertain primary site 1

a Number of animals examined microscopically at the site and the number of animals with neoplasm b Number of animals with any tissue examined microscopically c Primary neoplasms: all neoplasms except metastatic neoplasms
Sodium Dichromate Dihydrate, NTP TR 546 119

Table C2

Statistical Analysis of Primary Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Adrenal Cortex: Adenoma

Overall ratea 7/49 (14%) 5/49 (10%) 5/50 (10%) 6/50 (12%) 2/50 (4%)

Adjusted rateb 15.6% 11.4% 11.4% 13.0% 4.6%

Terminal ratec 7/33 (21%) 5/35 (14%) 3/35 (9%) 6/38 (16%) 2/32 (6%)

First incidence (days) 729 (T) 729 (T) 664 729 (T) 729 (T)

Poly-3 testd P=0.091N P=0.398N P=0.395N P=0.476N P=0.083N

Harderian Gland: Adenoma

Overall rate 6/50 (12%) 3/50 (6%) 4/50 (8%) 3/50 (6%) 2/50 (4%)

Adjusted rate 13.3% 6.8% 9.1% 6.4% 4.6%

Terminal rate 6/33 (18%) 3/35 (9%) 3/35 (9%) 2/38 (5%) 1/32 (3%)

First incidence (days) 729 (T) 729 (T) 623 567 719

Poly-3 test P=0.168N P=0.251N P=0.388N P=0.224N P=0.141N

Harderian Gland: Adenoma or Carcinoma

Overall rate 6/50 (12%) 4/50 (8%) 4/50 (8%) 3/50 (6%) 2/50 (4%)

Adjusted rate 13.3% 9.0% 9.1% 6.4% 4.6%

Terminal rate 6/33 (18%) 4/35 (11%) 3/35 (9%) 2/38 (5%) 1/32 (3%)

First incidence (days) 729 (T) 729 (T) 623 567 719

Poly-3 test P=0.137N P=0.382N P=0.388N P=0.224N P=0.141N

Small Intestine (Duodenum): Adenoma

Overall rate 1/50 (2%) 0/50 (0%) 1/50 (2%) 5/50 (10%) 15/50 (30%)

Adjusted rate 2.2% 0.0% 2.3% 10.8% 32.9%

Terminal rate 0/33 (0%) 0/35 (0%) 1/35 (3%) 5/38 (13%) 10/32 (31%)

First incidence (days) 665 —e 729 (T) 729 (T) 451

Poly-3 test P<0.001 P=0.505N P=0.751 P=0.106 P<0.001

Small Intestine (Duodenum): Carcinoma

Overall rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 2/50 (4%) 3/50 (6%)

Adjusted rate 0.0% 0.0% 0.0% 4.3% 6.8%

Terminal rate 0/33 (0%) 0/35 (0%) 0/35 (0%) 2/38 (5%) 3/32 (9%)

First incidence (days) — — — 729 (T) 729 (T)

Poly-3 test P=0.011 —f — P=0.243 P=0.113

Small Intestine (Jejunum): Adenoma

Overall rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 0/50 (0%) 3/50 (6%)

Adjusted rate 0.0% 0.0% 0.0% 0.0% 6.8%

Terminal rate 0/33 (0%) 0/35 (0%) 0/35 (0%) 0/38 (0%) 2/32 (6%)

First incidence (days) — — — — 714

Poly-3 test P=0.002 — — — P=0.114

Small Intestine (Duodenum, Jejunum, or Ileum): Adenoma

Overall rate 1/50 (2%) 1/50 (2%) 1/50 (2%) 5/50 (10%) 17/50 (34%)

Adjusted rate 2.2% 2.3% 2.3% 10.8% 37.2%

Terminal rate 0/33 (0%) 1/35 (3%) 1/35 (3%) 5/38 (13%) 11/32 (34%)

First incidence (days) 665 729 (T) 729 (T) 729 (T) 451

Poly-3 test P<0.001 P=0.755 P=0.751 P=0.106 P<0.001
120 Sodium Dichromate Dihydrate, NTP TR 546 

Table C2

Statistical Analysis of Primary Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Small Intestine (Duodenum, Jejunum, or Ileum): Carcinoma

Overall rate 0/50 (0%) 2/50 (4%) 1/50 (2%) 3/50 (6%) 5/50 (10%)

Adjusted rate 0.0% 4.5% 2.3% 6.5% 11.4%

Terminal rate 0/33 (0%) 2/35 (6%) 1/35 (3%) 3/38 (8%) 5/32 (16%)

First incidence (days) — 729 (T) 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.014 P=0.233 P=0.492 P=0.123 P=0.028

Small Intestine (Duodenum, Jejunum, or Ileum): Adenoma or Carcinoma

Overall rate 1/50 (2%) 3/50 (6%) 2/50 (4%) 7/50 (14%) 20/50 (40%)

Adjusted rate 2.2% 6.8% 4.6% 15.1% 43.8%

Terminal rate 0/33 (0%) 3/35 (9%) 2/35 (6%) 7/38 (18%) 14/32 (44%)

First incidence (days) 665 729 (T) 729 (T) 729 (T) 451

Poly-3 test P<0.001 P=0.296 P=0.485 P=0.032 P<0.001

Liver: Hemangiosarcoma

Overall rate 1/50 (2%) 1/50 (2%) 5/50 (10%) 2/50 (4%) 4/50 (8%)

Adjusted rate 2.2% 2.3% 11.4% 4.3% 9.1%

Terminal rate 1/33 (3%) 1/35 (3%) 4/35 (11%) 2/38 (5%) 2/32 (6%)

First incidence (days) 729 (T) 729 (T) 621 729 (T) 701

Poly-3 test P=0.202 P=0.756 P=0.094 P=0.509 P=0.171

Liver: Hepatocellular Adenoma

Overall rate 36/50 (72%) 33/50 (66%) 28/50 (56%) 31/50 (62%) 28/50 (56%)

Adjusted rate 77.2% 71.3% 62.5% 65.7% 60.8%

Terminal rate 29/33 (88%) 28/35 (80%) 24/35 (69%) 28/38 (74%) 22/32 (69%)

First incidence (days) 483 533 482 616 391

Poly-3 test P=0.098N P=0.333N P=0.085N P=0.147N P=0.059N

Liver: Hepatocellular Carcinoma

Overall rate 14/50 (28%) 24/50 (48%) 17/50 (34%) 12/50 (24%) 18/50 (36%)

Adjusted rate 29.3% 50.2% 36.8% 25.0% 38.0%

Terminal rate 5/33 (15%) 15/35 (43%) 11/35 (31%) 7/38 (18%) 8/32 (25%)

First incidence (days) 435 349 482 567 451

Poly-3 test P=0.504N P=0.028 P=0.291 P=0.405N P=0.251

Liver: Hepatocellular Adenoma or Carcinoma

Overall rate 42/50 (84%) 42/50 (84%) 33/50 (66%) 37/50 (74%) 41/50 (82%)

Adjusted rate 86.3% 85.5% 71.2% 76.7% 82.9%

Terminal rate 30/33 (91%) 30/35 (86%) 26/35 (74%) 31/38 (82%) 26/32 (81%)

First incidence (days) 435 349 482 567 391

Poly-3 test P=0.544 P=0.570N P=0.050N P=0.159N P=0.422N

Liver: Hepatoblastoma

Overall rate 17/50 (34%) 8/50 (16%) 11/50 (22%) 2/50 (4%) 0/50 (0%)

Adjusted rate 35.8% 17.7% 24.0% 4.3% 0.0%

Terminal rate 9/33 (27%) 6/35 (17%) 6/35 (17%) 2/38 (5%) 0/32 (0%)

First incidence (days) 435 587 544 729 (T) —

Poly-3 test P<0.001N P=0.039N P=0.153N P<0.001N P<0.001N
Sodium Dichromate Dihydrate, NTP TR 546 121

Table C2

Statistical Analysis of Primary Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Liver: Hepatocellular Carcinoma or Hepatoblastoma

Overall rate 25/50 (50%) 26/50 (52%) 26/50 (52%) 14/50 (28%) 18/50 (36%)

Adjusted rate 51.3% 53.9% 54.0% 29.2% 38.0%

Terminal rate 12/33 (36%) 16/35 (46%) 16/35 (46%) 9/38 (24%) 8/32 (25%)

First incidence (days) 435 349 482 567 451

Poly-3 test P=0.035N P=0.482 P=0.477 P=0.020N P=0.132N

Liver: Hepatocellular Adenoma, Hepatocellular Carcinoma, or Hepatoblastoma

Overall rate 46/50 (92%) 42/50 (84%) 37/50 (74%) 37/50 (74%) 41/50 (82%)

Adjusted rate 92.7% 85.5% 76.5% 76.7% 82.9%

Terminal rate 30/33 (91%) 30/35 (86%) 26/35 (74%) 31/38 (82%) 26/32 (81%)

First incidence (days) 435 349 482 567 391

Poly-3 test P=0.323N P=0.198N P=0.023N P=0.022N P=0.114N

Lung: Alveolar/bronchiolar Adenoma

Overall rate 15/50 (30%) 9/50 (18%) 9/50 (18%) 8/50 (16%) 11/50 (22%)

Adjusted rate 32.6% 20.1% 20.5% 17.2% 24.9%

Terminal rate 11/33 (33%) 8/35 (23%) 7/35 (20%) 7/38 (18%) 9/32 (28%)

First incidence (days) 631 533 604 693 632

Poly-3 test P=0.495N P=0.130N P=0.144N P=0.069N P=0.282N

Lung: Alveolar/bronchiolar Carcinoma

Overall rate 3/50 (6%) 5/50 (10%) 11/50 (22%) 6/50 (12%) 5/50 (10%)

Adjusted rate 6.6% 11.2% 25.0% 13.0% 11.3%

Terminal rate 2/33 (6%) 3/35 (9%) 8/35 (23%) 6/38 (16%) 4/32 (13%)

First incidence (days) 631 646 587 729 (T) 600

Poly-3 test P=0.481N P=0.348 P=0.015 P=0.250 P=0.342

Lung: Alveolar/bronchiolar Adenoma or Carcinoma

Overall rate 16/50 (32%) 12/50 (24%) 16/50 (32%) 13/50 (26%) 16/50 (32%)

Adjusted rate 34.7% 26.4% 36.0% 28.0% 35.8%

Terminal rate 12/33 (36%) 9/35 (26%) 12/35 (34%) 12/38 (32%) 13/32 (41%)

First incidence (days) 631 533 587 693 600

Poly-3 test P=0.394 P=0.262N P=0.536 P=0.317N P=0.546

Pancreatic Islets: Adenoma

Overall rate 3/49 (6%) 1/49 (2%) 1/50 (2%) 0/50 (0%) 0/49 (0%)

Adjusted rate 6.6% 2.3% 2.3% 0.0% 0.0%

Terminal rate 2/33 (6%) 0/35 (0%) 0/35 (0%) 0/38 (0%) 0/32 (0%)

First incidence (days) 435 588 482 — —

Poly-3 test P=0.107N P=0.319N P=0.317N P=0.116N P=0.128N

All Organs: Hemangiosarcoma

Overall rate 4/50 (8%) 1/50 (2%) 6/50 (12%) 6/50 (12%) 6/50 (12%)

Adjusted rate 8.9% 2.3% 13.7% 12.8% 13.6%

Terminal rate 4/33 (12%) 1/35 (3%) 5/35 (14%) 4/38 (11%) 4/32 (13%)

First incidence (days) 729 (T) 729 (T) 621 645 701

Poly-3 test P=0.181 P=0.185N P=0.350 P=0.392 P=0.354
122 Sodium Dichromate Dihydrate, NTP TR 546 

Table C2

Statistical Analysis of Primary Neoplasms in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

All Organs: Hemangioma or Hemangiosarcoma

Overall rate 4/50 (8%) 2/50 (4%) 6/50 (12%) 8/50 (16%) 6/50 (12%)

Adjusted rate 8.9% 4.5% 13.7% 17.0% 13.6%

Terminal rate 4/33 (12%) 2/35 (6%) 5/35 (14%) 5/38 (13%) 4/32 (13%)

First incidence (days) 729 (T) 729 (T) 621 645 701

Poly-3 test P=0.222 P=0.346N P=0.350 P=0.197 P=0.354

All Organs: Benign Neoplasms

Overall rate 42/50 (84%) 37/50 (74%) 33/50 (66%) 42/50 (84%) 37/50 (74%)

Adjusted rate 86.9% 79.1% 72.7% 86.3% 77.0%

Terminal rate 31/33 (94%) 31/35 (89%) 27/35 (77%) 35/38 (92%) 25/32 (78%)

First incidence (days) 435 533 482 545 391

Poly-3 test P=0.334N P=0.214N P=0.058N P=0.587N P=0.146N

All Organs: Malignant Neoplasms

Overall rate 31/50 (62%) 29/50 (58%) 36/50 (72%) 28/50 (56%) 29/50 (58%)

Adjusted rate 63.2% 60.1% 74.1% 57.2% 61.0%

Terminal rate 17/33 (52%) 19/35 (54%) 24/35 (69%) 20/38 (53%) 17/32 (53%)

First incidence (days) 435 349 482 545 451

Poly-3 test P=0.337N P=0.457N P=0.172 P=0.344N P=0.493N

All Organs: Benign or Malignant Neoplasms

Overall rate 49/50 (98%) 45/50 (90%) 47/50 (94%) 45/50 (90%) 48/50 (96%)

Adjusted rate 98.0% 91.6% 95.9% 91.5% 96.0%

Terminal rate 32/33 (97%) 33/35 (94%) 33/35 (94%) 36/38 (95%) 30/32 (94%)

First incidence (days) 435 349 482 545 391

Poly-3 test P=0.552 P=0.146N P=0.493N P=0.145N P=0.500N

(T)Terminal sacrifice a Number of neoplasm-bearing animals/number of animals examined. Denominator is number of animals examined microscopically for adrenal cortex, liver, 

lung, and pancreatic islets; for other tissues, denominator is number of animals necropsied. b Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality c Observed incidence at terminal kill d

 Beneath the control incidence is the P value associated with the trend test. Beneath the exposed group incidence are the P values corresponding to pairwise 

comparisons between the controls and that exposed group. The Poly-3 test accounts for the differential mortality in animals that do not reach terminal 

sacrifice. A negative trend or a lower incidence in an exposed group is indicated by N. e Not applicable; no neoplasms in animal group f Value of statistic cannot be computed.
Sodium Dichromate Dihydrate, NTP TR 546 123

Table C3

Historical Incidence of Small Intestine Neoplasms in Control Male B6C3F1 Micea

 Incidence in Controls

 Duodenum Jejunum Duodenum, Jejunum, or Ileum

Study Adenoma Carcinoma Adenoma Carcinoma Adenoma Carcinoma Adenoma

 or Carcinoma

Historical Incidence: Drinking Water Studies

Bromochloroacetic acid 3/50 1/50 0/50 1/50 3/50 2/50 5/50

Dibromoacetic acid 0/49 0/49 0/49 0/49 0/49 0/49 0/49

Dibromoacetonitrile 1/50 0/50 0/50 1/50 1/50 1/50 1/50

Dipropylene glycol 0/50 0/50 0/50 1/50 0/50 1/50 1/50

Sodium chlorate 1/50 0/50 0/50 2/50 1/50 2/50 3/50

Sodium dichromate dihydrate 1/50 0/50 0/50 0/50 1/50 0/50 1/50

Overall Historical Incidence: Drinking Water Studies

Total (%) 6/299 (2.0%) 1/299 (0.3%) 0/299 5/299 (1.7%) 6/299 (2.0%) 6/299 (2.0%) 11/299 (3.7%)

Mean ± standard deviation 2.0% ± 2.2% 0.3% ± 0.8% 1.7% ± 1.5% 2.0% ± 2.2% 2.0% ± 1.8% 3.7% ± 3.7%

Range (0%-6%) (0%-2%) (0%-4%) (0%-6%) (0%-4%) (0%-10%)

Overall Historical Incidence: All Routes

Total (%) 9/1,549 (0.6%) 3/1,549 (0.2%) 1/1,549 (0.1%) 25/1,549 (1.6%) 10/1,549 (0.6%) 30/1,549 (1.9%) 39/1,549 (2.5%)

Mean ± standard deviation 0.6% ± 1.3% 0.2% ± 0.8% 0.1% ± 0.4% 1.6% ± 2.2% 0.7% ± 1.3% 2.0% ± 2.2% 2.6% ± 2.7%

Range (0%-6%) (0%-4%) (0%-2%) (0%-8%) (0%-6%) (0%-8%) (0%-10%)

a Data as of March 2, 2007, with sodium dichromate dihydrate data added from Table C1
124 Sodium Dichromate Dihydrate, NTP TR 546 

Table C4

Summary of the Incidence of Nonneoplastic Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 7 5 5 4 3

Natural deaths 10 10 10 8 15

Survivors

Died last week of study 1 1

Terminal sacrifice 32 35 35 38 31

Animals examined microscopically 50 50 50 50 50

Alimentary System

Esophagus (50) (50) (50) (50) (50)

Gallbladder (47) (45) (44) (44) (39)

Intestine large, cecum (42) (44) (47) (46) (39)

Angiectasis 1 (2%)

Fibrosis 1 (2%)

Lymphoid tissue, hyperplasia 2 (4%)

Intestine large, colon (44) (45) (47) (46) (40)

Fibrosis 1 (2%)

Lymphangiectasis 1 (2%)

Lymphoid tissue, hyperplasia 1 (2%) 2 (4%) 2 (5%)

Intestine large, rectum (42) (47) (47) (46) (42)

Inflammation, suppurative 1 (2%)

Intestine small, duodenum (39) (43) (45) (48) (40)

Erosion 1 (2%)

Infiltration cellular, histiocyte 2 (5%) 4 (9%) 37 (77%) 35 (88%)

Infiltration cellular, mixed cell 1 (2%)

Epithelium, hyperplasia, focal 1 (2%) 2 (5%)

Epithelium, hyperplasia, diffuse 11 (26%) 18 (40%) 42 (88%) 32 (80%)

Intestine small, ileum (40) (42) (44) (45) (38)

Cyst 1 (2%)

Infiltration cellular, polymorphonuclear 1 (2%)

Inflammation, chronic active 1 (2%)

Epithelium, hyperplasia, diffuse 1 (2%)

Epithelium, inflammation, acute 1 (2%)

Goblet cell, hyperplasia 1 (2%)

Lymphoid tissue, hyperplasia 1 (2%) 2 (4%) 1 (3%)

Intestine small, jejunum (41) (42) (42) (46) (38)

Fibrosis 1 (2%)

Infiltration cellular, histiocyte 1 (2%)

Inflammation, suppurative 1 (2%)

Inflammation, chronic active 1 (2%)

Epithelium, hyperplasia, focal 1 (2%)

Epithelium, hyperplasia, diffuse 2 (4%) 1 (3%)

Lymphoid tissue, hyperplasia 2 (5%) 7 (17%) 5 (12%) 8 (17%) 3 (8%)

Liver (50) (50) (50) (50) (50)

Angiectasis 2 (4%)

Basophilic focus 3 (6%) 4 (8%) 1 (2%)

Basophilic focus, multiple 1 (2%) 1 (2%)

Clear cell focus 8 (16%) 9 (18%) 13 (26%) 11 (22%) 6 (12%)

Clear cell focus, multiple 12 (24%) 8 (16%) 6 (12%) 5 (10%) 1 (2%)

a Number of animals examined microscopically at the site and the number of animals with lesion
Sodium Dichromate Dihydrate, NTP TR 546 125

Table C4

Summary of the Incidence of Nonneoplastic Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Alimentary System (continued)

Liver (continued) (50) (50) (50) (50) (50)

Congestion 1 (2%)

Cyst 1 (2%) 1 (2%) 2 (4%)

Eosinophilic focus 17 (34%) 16 (32%) 13 (26%) 16 (32%) 10 (20%)

Eosinophilic focus, multiple 10 (20%) 10 (20%) 6 (12%) 5 (10%) 2 (4%)

Fibrosis 2 (4%)

Hematopoietic cell proliferation 1 (2%)

Hemorrhage 1 (2%) 1 (2%) 1 (2%)

Hepatodiaphragmatic nodule 1 (2%) 2 (4%) 1 (2%)

Infarct 1 (2%)

Infiltration cellular, histiocyte 1 (2%) 3 (6%) 4 (8%) 4 (8%) 3 (6%)

Infiltration cellular, lymphocyte 1 (2%)

Inflammation, chronic 1 (2%) 1 (2%) 4 (8%) 2 (4%) 1 (2%)

Mixed cell focus 3 (6%) 1 (2%) 1 (2%) 3 (6%)

Mixed cell focus, multiple 1 (2%) 1 (2%)

Necrosis, focal 1 (2%) 3 (6%) 4 (8%) 5 (10%)

Bile duct, hyperplasia 1 (2%)

Centrilobular, necrosis 2 (4%) 1 (2%)

Hepatocyte, vacuolization cytoplasmic 5 (10%) 5 (10%) 1 (2%) 1 (2%) 3 (6%)

Mesentery (16) (10) (9) (16) (5)

Fibrosis 2 (22%) 1 (6%)

Inflammation, suppurative 1 (20%)

Inflammation, granulomatous 1 (6%)

Fat, necrosis 11 (69%) 7 (70%) 7 (78%) 12 (75%) 5 (100%)

Oral mucosa (50) (50) (50) (50) (50)

Pharyngeal, hyperplasia, squamous, focal 1 (2%)

Pancreas (49) (49) (50) (49) (48)

Atrophy 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Cyst 1 (2%)

Fibrosis 1 (2%)

Acinus, cytoplasmic alteration 1 (2%) 1 (2%) 9 (18%) 8 (17%)

Salivary glands (49) (50) (49) (50) (50)

Atrophy 2 (4%)

Parotid gland, atrophy 1 (2%)

Submandibular gland, atrophy 1 (2%)

Stomach, forestomach (50) (50) (48) (50) (48)

Angiectasis 1 (2%)

Cyst 1 (2%)

Fibrosis 1 (2%)

Ulcer 3 (6%)

Epithelium, hyperplasia 4 (8%) 3 (6%) 3 (6%)

Stomach, glandular (50) (48) (48) (50) (47)

Atrophy, focal 2 (4%)

Cyst 1 (2%)

Erosion 1 (2%) 1 (2%) 1 (2%)

Erosion, focal 1 (2%)

Hyperplasia, focal 1 (2%) 1 (2%)

Infiltration cellular, polymorphonuclear 1 (2%)

Ulcer 1 (2%) 1 (2%)

Tongue (50) (50) (50) (50) (50)

Cyst 1 (2%) 1 (2%) 1 (2%)

Hyperplasia, squamous 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Inflammation, chronic 5 (10%) 4 (8%) 4 (8%) 2 (4%)

Mineralization 1 (2%) 2 (4%) 1 (2%) 2 (4%)
126 Sodium Dichromate Dihydrate, NTP TR 546 

Table C4

Summary of the Incidence of Nonneoplastic Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Alimentary System (continued)

Tongue (continued) (50) (50) (50) (50) (50)

Ulcer 1 (2%) 2 (4%)

Artery, inflammation, chronic 1 (2%) 1 (2%)

Tooth (1) (3) (2) 

Malformation 1 (100%) 2 (67%) 2 (100%)

Cardiovascular System

Blood vessel (2) (1) (1) (1) (1)

Heart (50) (50) (50) (50) (50)

Cardiomyopathy 45 (90%) 46 (92%) 43 (86%) 46 (92%) 36 (72%)

Inflammation, suppurative 1 (2%) 1 (2%)

Mineralization 1 (2%) 1 (2%)

Thrombosis 1 (2%) 1 (2%) 3 (6%)

Endocrine System

Adrenal cortex (49) (49) (50) (50) (50)

Accessory adrenal cortical nodule 1 (2%)

Angiectasis 1 (2%) 1 (2%)

Degeneration, fatty 1 (2%)

Hyperplasia, focal 1 (2%) 2 (4%) 2 (4%)

Hypertrophy, focal 7 (14%) 12 (24%) 11 (22%) 13 (26%) 9 (18%)

Capsule, hemorrhage 1 (2%)

Capsule, hyperplasia 5 (10%) 13 (27%) 11 (22%) 12 (24%) 7 (14%)

Adrenal medulla (49) (48) (50) (50) (50)

Hyperplasia 1 (2%)

Islets, pancreatic (49) (49) (50) (50) (49)

Hyperplasia 39 (80%) 40 (82%) 34 (68%) 43 (86%) 20 (41%)

Parathyroid gland (46) (47) (45) (49) (47)

Cyst 1 (2%) 1 (2%)

Pituitary gland (49) (49) (48) (50) (47)

Pars distalis, cyst 2 (4%) 1 (2%) 2 (4%) 4 (8%) 1 (2%)

Pars distalis, hyperplasia, focal 1 (2%) 1 (2%) 2 (4%)

Thyroid gland (50) (50) (50) (50) (50)

Follicle, cyst 1 (2%) 2 (4%) 1 (2%) 3 (6%)

Follicle, degeneration, focal 3 (6%) 5 (10%) 4 (8%) 5 (10%) 1 (2%)

Follicular cell, hyperplasia, focal 1 (2%) 1 (2%) 1 (2%) 2 (4%)

General Body System

None

Genital System

Epididymis (50) (50) (50) (50) (50)

Degeneration 1 (2%)

Granuloma sperm 1 (2%) 2 (4%) 1 (2%)

Infiltration cellular, lymphocyte 1 (2%) 1 (2%) 1 (2%)

Inflammation, chronic 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 127

Table C4

Summary of the Incidence of Nonneoplastic Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Genital System (continued)

Preputial gland (50) (50) (50) (50) (50)

Atrophy 1 (2%)

Cyst 2 (4%) 1 (2%) 3 (6%) 4 (8%) 4 (8%)

Infiltration cellular, lymphocyte 1 (2%)

Inflammation, chronic 1 (2%)

Prostate (50) (49) (50) (50) (50)

Infiltration cellular, lymphocyte 2 (4%) 1 (2%)

Inflammation, suppurative 1 (2%) 1 (2%)

Inflammation, chronic 2 (4%) 1 (2%)

Seminal vesicle (50) (50) (50) (50) (50)

Fibrosis 1 (2%)

Inflammation, chronic 2 (4%) 1 (2%) 1 (2%)

Epithelium, hyperplasia 1 (2%)

Testes (50) (50) (50) (50) (50)

Germinal epithelium, atrophy 2 (4%) 3 (6%) 3 (6%) 2 (4%) 1 (2%)

Interstitial cell, hyperplasia 1 (2%)

Hematopoietic System

Bone marrow (49) (50) (50) (50) (50)

Angiectasis 1 (2%)

Hyperplasia 5 (10%) 5 (10%) 1 (2%) 3 (6%)

Pigmentation 47 (96%) 50 (100%) 50 (100%) 50 (100%) 50 (100%)

Lymph node (8) (4) (6) (6) (5)

Bronchial, hyperplasia, lymphoid 1 (25%) 1 (17%)

Iliac, hemorrhage 1 (13%)

Iliac, hyperplasia, lymphoid 1 (13%) 1 (17%) 2 (33%)

Iliac, hyperplasia, plasma cell 1 (20%)

Iliac, pigmentation 4 (67%) 1 (20%)

Inguinal, hyperplasia, lymphoid 2 (25%) 1 (17%)

Inguinal, pigmentation 2 (50%) 1 (17%) 3 (60%)

Mediastinal, hemorrhage 1 (20%)

Mediastinal, hyperplasia, histiocytic 1 (17%)

Mediastinal, hyperplasia, lymphoid 1 (25%)

Popliteal, hyperplasia, lymphoid 1 (13%)

Renal, angiectasis 1 (13%)

Renal, hyperplasia, lymphoid 2 (25%) 1 (17%)

Renal, hyperplasia, plasma cell 1 (20%)

Lymph node, mandibular (47) (49) (49) (48) (46)

Hyperplasia, lymphoid 6 (13%) 6 (12%) 2 (4%) 4 (8%) 2 (4%)

Pigmentation 2 (4%)

Lymph node, mesenteric (47) (47) (49) (49) (46)

Ectasia 3 (6%)

Fibrosis 1 (2%)

Hemorrhage 1 (2%) 2 (4%)

Hyperplasia, lymphoid 4 (9%) 2 (4%) 3 (6%)

Infiltration cellular, histiocyte 14 (30%) 38 (81%) 31 (63%) 32 (65%) 42 (91%)

Inflammation, granulomatous 2 (4%) 1 (2%)

Necrosis, lymphoid 1 (2%)

Lymph node, pancreatic (5) (13) (10) (8) (16)

Hyperplasia, lymphoid 1 (13%) 1 (6%)

Infiltration cellular, histiocyte 2 (15%) 2 (20%) 5 (63%) 12 (75%)
128 Sodium Dichromate Dihydrate, NTP TR 546 

Table C4

Summary of the Incidence of Nonneoplastic Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Hematopoietic System (continued)

Spleen (49) (48) (49) (49) (46)

Hematopoietic cell proliferation 17 (35%) 14 (29%) 13 (27%) 19 (39%) 25 (54%)

Hyperplasia, histiocytic 1 (2%)

Necrosis, lymphoid 1 (2%)

Lymphoid follicle, atrophy 1 (2%) 2 (4%) 1 (2%) 3 (7%)

Lymphoid follicle, hyperplasia 1 (2%) 6 (13%) 3 (6%) 5 (10%) 4 (9%)

Thymus (49) (50) (46) (49) (40)

Atrophy 2 (4%) 7 (14%) 2 (4%) 2 (4%) 1 (3%)

Hyperplasia, lymphoid 3 (6%) 3 (6%) 1 (2%) 2 (4%)

Necrosis, lymphoid 1 (2%)

Integumentary System

Skin (50) (50) (50) (50) (50)

Congestion 1 (2%)

Cyst 1 (2%)

Cyst epithelial inclusion 2 (4%) 1 (2%) 1 (2%)

Edema 1 (2%) 1 (2%)

Hyperkeratosis 1 (2%)

Inflammation, granulomatous 1 (2%) 1 (2%)

Inflammation, chronic 2 (4%) 2 (4%) 1 (2%)

Ulcer 1 (2%) 3 (6%) 1 (2%)

Dermis, cyst 1 (2%)

Epidermis, hyperplasia 1 (2%) 1 (2%) 1 (2%)

Musculoskeletal System

Bone (50) (50) (50) (50) (50)

Hyperostosis 1 (2%)

Cranium, osteopetrosis 1 (2%) 2 (4%) 1 (2%) 1 (2%)

Skeletal muscle (4) (2) (4) (1) 

Fibrosis 2 (50%)

Hemorrhage 1 (25%)

Nervous System

Brain (50) (50) (50) (50) (50)

Cyst epithelial inclusion 1 (2%)

Respiratory System

Lung (50) (50) (50) (50) (50)

Congestion 1 (2%)

Infiltration cellular, histiocyte 1 (2%) 6 (12%) 3 (6%) 1 (2%)

Infiltration cellular, lymphocyte 1 (2%) 1 (2%)

Inflammation, granulomatous 1 (2%)

Inflammation, chronic 1 (2%)

Metaplasia, osseous 2 (4%)

Alveolar epithelium, hyperplasia 4 (8%) 3 (6%) 2 (4%) 5 (10%) 3 (6%)

Nose (50) (50) (50) (50) (50)

Glands, inflammation 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 129

Table C4

Summary of the Incidence of Nonneoplastic Lesions in Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 28.6 mg/L 85.7 mg/L 257.4 mg/L

Special Senses System

Eye (48) (49) (49) (50) (47)

Atrophy 1 (2%) 1 (2%)

Harderian gland (50) (50) (49) (50) (50)

Hyperplasia, focal 1 (2%)

Urinary System

Kidney (50) (50) (50) (50) (49)

Atrophy 1 (2%)

Cyst 3 (6%) 6 (12%) 4 (8%) 3 (6%) 2 (4%)

Fibrosis 1 (2%)

Hydronephrosis 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Infarct 5 (10%) 1 (2%) 2 (4%) 6 (12%) 4 (8%)

Infiltration cellular, lymphocyte 1 (2%) 1 (2%) 1 (2%) 4 (8%)

Inflammation, suppurative 1 (2%) 1 (2%)

Metaplasia, osseous 1 (2%) 1 (2%) 1 (2%)

Mineralization 1 (2%)

Nephropathy 39 (78%) 43 (86%) 45 (90%) 45 (90%) 41 (84%)

Thrombosis 1 (2%)

Papilla, necrosis 1 (2%)

Renal tubule, atrophy 1 (2%)

Renal tubule, mineralization 1 (2%) 1 (2%)

Renal tubule, necrosis 1 (2%)

Renal tubule, pigmentation 7 (14%) 3 (6%) 3 (6%)

Urethra (1) (1) (1) 

Angiectasis 1 (100%) 1 (100%)

Urinary bladder (49) (50) (50) (49) (46)

Fibrosis 1 (2%)

Infiltration cellular, lymphocyte 1 (2%) 1 (2%) 1 (2%)
130 Sodium Dichromate Dihydrate, NTP TR 546 
131

APPENDIX D

SUMMARY OF LESIONS IN FEMALE MICE

IN THE 2-YEAR DRINKING WATER STUDY

OF SODIUM DICHROMATE DIHYDRATE

Table D1 Summary of the Incidence of Neoplasms in Female Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 132

Table D2 Statistical Analysis of Primary Neoplasms in Female Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 136

Table D3 Historical Incidence of Small Intestine Neoplasms 

in Control Female B6C3F1 Mice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Table D4 Summary of the Incidence of Nonneoplastic Lesions in Female Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 141
132 Sodium Dichromate Dihydrate, NTP TR 546 

Table D1

Summary of the Incidence of Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 5 2 2 3

Natural deaths 8 11 3 6 5

Survivors

Died last week of study 2 1 1 2

Terminal sacrifice 35 38 44 40 42

Animals examined microscopically 50 50 50 50 50

Alimentary System

Gallbladder (44) (47) (48) (45) (50)

Sarcoma, metastatic, mesentery 1 (2%)

Intestine large, colon (43) (43) (48) (45) (48)

Intestine small, duodenum (42) (42) (48) (42) (48)

Adenoma 2 (4%) 12 (29%) 6 (13%)

Adenoma, multiple 1 (2%) 6 (13%)

Carcinoma 1 (2%) 6 (13%)

Intestine small, ileum (42) (43) (47) (44) (47)

Intestine small, jejunum (41) (42) (48) (44) (48)

Adenoma 1 (2%) 2 (5%) 4 (8%)

Adenoma, multiple 1 (2%)

Carcinoma 1 (2%) 2 (4%) 2 (5%) 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Liver (49) (50) (50) (50) (50)

Hemangioma 1 (2%)

Hemangiosarcoma 1 (2%) 3 (6%)

Hepatocellular adenoma 6 (12%) 11 (22%) 10 (20%) 5 (10%) 3 (6%)

Hepatocellular adenoma, multiple 8 (16%) 10 (20%) 3 (6%) 1 (2%)

Hepatocellular carcinoma 7 (14%) 9 (18%) 7 (14%) 6 (12%) 6 (12%)

Hepatocellular carcinoma, multiple 1 (2%) 1 (2%) 1 (2%)

Mesentery (20) (23) (23) (23) (9)

Carcinoma, metastatic, Harderian gland 1 (4%)

Fibrosarcoma 3 (15%)

Fibrosarcoma, metastatic, skin 1 (4%) 1 (11%)

Granulosa-theca tumor malignant, metastatic,

ovary 1 (4%)

Hemangiosarcoma, metastatic, spleen 1 (5%)

Liposarcoma, metastatic, skin 1 (4%)

Sarcoma 2 (9%) 2 (9%)

Sarcoma, metastatic, skin 1 (4%)

Pancreas (48) (50) (49) (50) (50)

Fibrosarcoma, metastatic, skin 1 (2%)

Hepatocellular carcinoma, metastatic, liver 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Salivary glands (50) (50) (50) (48) (49)

Fibrosarcoma, metastatic, skin 1 (2%)

Stomach, forestomach (49) (49) (50) (48) (50)

Squamous cell papilloma 1 (2%) 2 (4%) 3 (6%)

Stomach, glandular (49) (48) (50) (48) (50)

Sarcoma, metastatic, mesentery 1 (2%)

Tongue (50) (50) (49) (48) (50)
Sodium Dichromate Dihydrate, NTP TR 546 133

Table D1

Summary of the Incidence of Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Cardiovascular System

Heart (50) (50) (50) (50) (50)

Granulosa-theca tumor malignant, metastatic,

ovary 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Endocrine System

Adrenal cortex (49) (50) (50) (50) (50)

Sarcoma, metastatic, mesentery 1 (2%)

Capsule, adenoma 1 (2%)

Capsule, carcinoma 1 (2%)

Adrenal medulla (49) (50) (50) (50) (50)

Pheochromocytoma benign 1 (2%) 2 (4%) 1 (2%)

Islets, pancreatic (49) (50) (50) (50) (50)

Adenoma 1 (2%)

Carcinoma 1 (2%)

Parathyroid gland (48) (49) (50) (44) (49)

Pituitary gland (48) (48) (48) (48) (49)

Pars distalis, adenoma 3 (6%) 3 (6%) 2 (4%) 3 (6%) 3 (6%)

Thyroid gland (50) (50) (50) (49) (50)

Adenoma 1 (2%)

Fibrosarcoma, metastatic, skin 1 (2%)

C-cell, carcinoma 1 (2%)

Follicular cell, adenoma 1 (2%) 1 (2%) 2 (4%)

Follicular cell, carcinoma 1 (2%)

General Body System

Tissue NOS (1) 

Genital System

Clitoral gland (50) (50) (50) (50) (48)

Sarcoma, metastatic, skin 1 (2%) 1 (2%)

Ovary (50) (49) (47) (48) (49)

Cystadenoma 1 (2%) 3 (6%) 3 (6%) 2 (4%) 2 (4%)

Granulosa cell tumor benign 1 (2%)

Granulosa-theca tumor malignant 1 (2%)

Hemangioma 1 (2%)

Hemangiosarcoma 1 (2%) 1 (2%)

Teratoma benign 1 (2%)

Uterus (50) (50) (50) (50) (50)

Hemangiosarcoma 2 (4%)

Polyp stromal 1 (2%)

Sarcoma stromal 1 (2%)

Vagina (1) 

Squamous cell papilloma 1 (100%)
134 Sodium Dichromate Dihydrate, NTP TR 546 

Table D1

Summary of the Incidence of Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematopoietic System

Bone marrow (50) (50) (50) (50) (50)

Lymph node (10) (7) (6) (5) (6)

Axillary, sarcoma, metastatic, skin 1 (17%)

Bronchial, liposarcoma, metastatic, skin 1 (14%)

Inguinal, sarcoma, metastatic, skin 1 (17%)

Mediastinal, fibrosarcoma, metastatic, skin 1 (14%)

Mediastinal, granulosa-theca tumor malignant,

metastatic, ovary 1 (14%)

Mediastinal, liposarcoma, metastatic, skin 1 (14%)

Mediastinal, sarcoma, metastatic, skin 1 (17%)

Lymph node, mandibular (50) (48) (49) (48) (48)

Carcinoma, metastatic, Harderian gland 1 (2%)

Fibrosarcoma, metastatic, skin 1 (2%)

Lymph node, mesenteric (46) (48) (46) (50) (50)

Fibrosarcoma, metastatic, mesentery 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Lymph node, pancreatic (14) (12) (15) (14) (13)

Granulosa cell tumor malignant, metastatic, 

 ovary 1 (8%)

Spleen (48) (48) (50) (50) (50)

Hemangiosarcoma 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Sarcoma, metastatic, mesentery 1 (2%)

Sarcoma, metastatic, skin 1 (2%)

Thymus (46) (38) (43) (40) (47)

Integumentary System

Mammary gland (50) (48) (50) (50) (50)

Carcinoma 1 (2%)

Fibroadenoma 1 (2%)

Skin (50) (50) (50) (49) (50)

Fibrosarcoma 1 (2%)

Hemangioma 1 (2%)

Squamous cell papilloma 1 (2%)

Pinna, fibrosarcoma 1 (2%)

Subcutaneous tissue, fibrosarcoma 1 (2%) 1 (2%) 1 (2%) 2 (4%)

Subcutaneous tissue, liposarcoma 1 (2%)

Subcutaneous tissue, sarcoma 1 (2%) 1 (2%) 1 (2%) 1 (2%) 1 (2%)

Musculoskeletal System

Bone (50) (50) (50) (50) (50)

Osteoma 1 (2%)

Osteosarcoma 1 (2%)

Cranium, osteoma 1 (2%)

Skeletal muscle (2) (6) (1) (1) (1)

Carcinoma, metastatic, Harderian gland 1 (100%)

Fibrosarcoma, metastatic, skin 1 (50%) 1 (17%)

Granulosa-theca tumor malignant, metastatic,

ovary 1 (17%)

Liposarcoma, metastatic, skin 1 (17%)

Sarcoma 1 (17%)

Sarcoma, metastatic, mesentery 1 (17%)
Sodium Dichromate Dihydrate, NTP TR 546 135

Table D1

Summary of the Incidence of Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Nervous System

Brain (50) (50) (50) (50) (50)

Respiratory System

Lung (50) (50) (50) (50) (50)

Alveolar/bronchiolar adenoma 1 (2%) 5 (10%) 7 (14%) 2 (4%) 2 (4%)

Alveolar/bronchiolar carcinoma 2 (4%) 2 (4%) 2 (4%) 1 (2%)

Carcinoma, metastatic, Harderian gland 1 (2%)

Fibrosarcoma, metastatic, skin 2 (4%)

Granulosa-theca tumor malignant, metastatic,

ovary 1 (2%)

Hepatocellular carcinoma, metastatic, liver 2 (4%) 1 (2%) 1 (2%)

Liposarcoma, metastatic, skin 1 (2%)

Sarcoma, metastatic, skin 1 (2%)

Nose (50) (50) (50) (50) (50)

Carcinoma, metastatic, Harderian gland 1 (2%)

Special Senses System

Eye (49) (48) (48) (46) (50)

Harderian gland (49) (49) (50) (50) (50)

Adenoma 4 (8%) 5 (10%) 5 (10%) 7 (14%) 5 (10%)

Carcinoma 1 (2%) 1 (2%) 1 (2%)

Urinary System

Kidney (50) (49) (50) (49) (50)

Ureter (1) 

Urinary bladder (50) (48) (50) (48) (49)

Systemic Lesions

Multiple organsb (50) (50) (50) (50) (50)

Histiocytic sarcoma 2 (4%) 1 (2%) 1 (2%) 1 (2%)

Lymphoma malignant 7 (14%) 3 (6%) 2 (4%) 5 (10%) 5 (10%)

Neoplasm Summary

Total animals with primary neoplasmsc 36 37 37 39 38

Total primary neoplasms 58 71 62 61 65

Total animals with benign neoplasms 27 28 27 25 29

Total benign neoplasms 30 43 40 37 38

Total animals with malignant neoplasms 22 23 19 21 18

Total malignant neoplasms 28 28 22 24 27

Total animals with metastatic neoplasms 5 6 3 1 3

Total metastatic neoplasms 5 29 13 1 3

a Number of animals examined microscopically at the site and the number of animals with neoplasm b Number of animals with any tissue examined microscopically c Primary neoplasms: all neoplasms except metastatic neoplasms
136 Sodium Dichromate Dihydrate, NTP TR 546 

Table D2

Statistical Analysis of Primary Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Harderian Gland: Adenoma

Overall ratea 4/50 (8%) 5/50 (10%) 5/50 (10%) 7/50 (14%) 5/50 (10%)

Adjusted rateb 8.9% 10.8% 10.4% 15.0% 10.6%

Terminal ratec 4/37 (11%) 4/39 (10%) 5/45 (11%) 7/42 (17%) 5/42 (12%)

First incidence (days) 729 (T) 671 729 (T) 729 (T) 729 (T)

Poly-3 testd P=0.516 P=0.517 P=0.538 P=0.283 P=0.531

Harderian Gland: Adenoma or Carcinoma

Overall rate 5/50 (10%) 5/50 (10%) 6/50 (12%) 7/50 (14%) 6/50 (12%)

Adjusted rate 11.0% 10.8% 12.4% 15.0% 12.7%

Terminal rate 4/37 (11%) 4/39 (10%) 5/45 (11%) 7/42 (17%) 6/42 (14%)

First incidence (days) 583 671 611 729 (T) 729 (T)

Poly-3 test P=0.462 P=0.620N P=0.541 P=0.398 P=0.527

Small Intestine (Duodenum): Adenoma

Overall rate 0/50 (0%) 0/50 (0%) 2/50 (4%) 13/50 (26%) 12/50 (24%)

Adjusted rate 0.0% 0.0% 4.2% 27.8% 25.2%

Terminal rate 0/37 (0%) 0/39 (0%) 2/45 (4%) 13/42 (31%) 11/42 (26%)

First incidence (days) —e — 729 (T) 729 (T) 693

Poly-3 test P<0.001 —f P=0.251 P<0.001 P<0.001

Small Intestine (Duodenum): Carcinoma

Overall rate 0/50 (0%) 0/50 (0%) 0/50 (0%) 1/50 (2%) 6/50 (12%)

Adjusted rate 0.0% 0.0% 0.0% 2.1% 12.6%

Terminal rate 0/37 (0%) 0/39 (0%) 0/45 (0%) 1/42 (2%) 5/42 (12%)

First incidence (days) — — — 729 (T) 625

Poly-3 test P<0.001 — — P=0.507 P=0.019

Small Intestine (Jejunum): Adenoma

Overall rate 0/50 (0%) 1/50 (2%) 0/50 (0%) 2/50 (4%) 5/50 (10%)

Adjusted rate 0.0% 2.2% 0.0% 4.3% 10.6%

Terminal rate 0/37 (0%) 1/39 (3%) 0/45 (0%) 2/42 (5%) 5/42 (12%)

First incidence (days) — 729 (T) — 729 (T) 729 (T)

Poly-3 test P=0.002 P=0.504 — P=0.246 P=0.035

Small Intestine (Duodenum, Jejunum, or Ileum): Adenoma

Overall rate 0/50 (0%) 1/50 (2%) 2/50 (4%) 15/50 (30%) 16/50 (32%)

Adjusted rate 0.0% 2.2% 4.2% 32.0% 33.7%

Terminal rate 0/37 (0%) 1/39 (3%) 2/45 (4%) 15/42 (36%) 15/42 (36%)

First incidence (days) — 729 (T) 729 (T) 729 (T) 693

Poly-3 test P<0.001 P=0.504 P=0.251 P<0.001 P<0.001

Small Intestine (Duodenum, Jejunum, or Ileum): Carcinoma

Overall rate 1/50 (2%) 0/50 (0%) 2/50 (4%) 3/50 (6%) 7/50 (14%)

Adjusted rate 2.2% 0.0% 4.2% 6.4% 14.7%

Terminal rate 1/37 (3%) 0/39 (0%) 2/45 (4%) 3/42 (7%) 6/42 (14%)

First incidence (days) 729 (T) — 729 (T) 729 (T) 625

Poly-3 test P<0.001 P=0.496N P=0.521 P=0.319 P=0.037
Sodium Dichromate Dihydrate, NTP TR 546 137

Table D2

Statistical Analysis of Primary Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Small Intestine (Duodenum, Jejunum, or Ileum): Adenoma or Carcinoma

Overall rate 1/50 (2%) 1/50 (2%) 4/50 (8%) 17/50 (34%) 22/50 (44%)

Adjusted rate 2.2% 2.2% 8.3% 36.3% 45.9%

Terminal rate 1/37 (3%) 1/39 (3%) 4/45 (9%) 17/42 (41%) 20/42 (48%)

First incidence (days) 729 (T) 729 (T) 729 (T) 729 (T) 625

Poly-3 test P<0.001 P=0.756N P=0.198 P<0.001 P<0.001

Liver: Hemangiosarcoma

Overall rate 1/49 (2%) 3/50 (6%) 0/50 (0%) 0/50 (0%) 0/50 (0%)

Adjusted rate 2.2% 6.5% 0.0% 0.0% 0.0%

Terminal rate 0/37 (0%) 2/39 (5%) 0/45 (0%) 0/42 (0%) 0/42 (0%)

First incidence (days) 668 688 — — —

Poly-3 test P=0.149N P=0.313 P=0.489N P=0.494N P=0.491N

Liver: Hepatocellular Adenoma

Overall rate 14/49 (29%) 21/50 (42%) 13/50 (26%) 6/50 (12%) 3/50 (6%)

Adjusted rate 31.0% 45.5% 27.1% 12.8% 6.3%

Terminal rate 13/37 (35%) 21/39 (54%) 13/45 (29%) 6/42 (14%) 3/42 (7%)

First incidence (days) 696 729 (T) 729 (T) 729 (T) 729 (T)

Poly-3 test P<0.001N P=0.109 P=0.429N P=0.029N P=0.002N

Liver: Hepatocellular Carcinoma

Overall rate 8/49 (16%) 10/50 (20%) 7/50 (14%) 6/50 (12%) 7/50 (14%)

Adjusted rate 17.7% 21.3% 14.6% 12.7% 14.6%

Terminal rate 7/37 (19%) 7/39 (18%) 7/45 (16%) 5/42 (12%) 4/42 (10%)

First incidence (days) 696 629 729 (T) 555 664

Poly-3 test P=0.327N P=0.432 P=0.451N P=0.351N P=0.452N

Liver: Hepatocellular Adenoma or Carcinoma

Overall rate 17/49 (35%) 25/50 (50%) 17/50 (34%) 10/50 (20%) 10/50 (20%)

Adjusted rate 37.6% 53.2% 35.5% 21.1% 20.9%

Terminal rate 16/37 (43%) 22/39 (56%) 17/45 (38%) 9/42 (21%) 7/42 (17%)

First incidence (days) 696 629 729 (T) 555 664

Poly-3 test P=0.003N P=0.094 P=0.501N P=0.062N P=0.058N

Lung: Alveolar/bronchiolar Adenoma

Overall rate 1/50 (2%) 5/50 (10%) 7/50 (14%) 2/50 (4%) 2/50 (4%)

Adjusted rate 2.2% 10.8% 14.6% 4.3% 4.2%

Terminal rate 1/37 (3%) 5/39 (13%) 6/45 (13%) 2/42 (5%) 1/42 (2%)

First incidence (days) 729 (T) 729 (T) 722 729 (T) 625

Poly-3 test P=0.205N P=0.106 P=0.037 P=0.513 P=0.520

Lung: Alveolar/bronchiolar Adenoma or Carcinoma

Overall rate 2/50 (4%) 7/50 (14%) 9/50 (18%) 3/50 (6%) 2/50 (4%)

Adjusted rate 4.4% 15.2% 18.8% 6.4% 4.2%

Terminal rate 2/37 (5%) 7/39 (18%) 8/45 (18%) 2/42 (5%) 1/42 (2%)

First incidence (days) 729 (T) 729 (T) 722 599 625

Poly-3 test P=0.075N P=0.084 P=0.032 P=0.521 P=0.673N
138 Sodium Dichromate Dihydrate, NTP TR 546 

Table D2

Statistical Analysis of Primary Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Mesentery: Fibrosarcoma

Overall rate 3/50 (6%) 0/50 (0%) 0/50 (0%) 0/50 (0%) 0/50 (0%)

Adjusted rate 6.6% 0.0% 0.0% 0.0% 0.0%

Terminal rate 2/37 (5%) 0/39 (0%) 0/45 (0%) 0/42 (0%) 0/42 (0%)

First incidence (days) 655 — — — —

Poly-3 test P=0.197N P=0.116N P=0.109N P=0.113N P=0.111N

Ovary: Cystadenoma

Overall rate 1/50 (2%) 3/49 (6%) 3/47 (6%) 2/48 (4%) 2/49 (4%)

Adjusted rate 2.2% 6.7% 6.7% 4.4% 4.3%

Terminal rate 0/37 (0%) 3/38 (8%) 3/42 (7%) 2/41 (5%) 2/41 (5%)

First incidence (days) 695 729 (T) 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.541N P=0.304 P=0.303 P=0.500 P=0.509

Pituitary Gland (Pars Distalis): Adenoma

Overall rate 3/48 (6%) 3/48 (6%) 2/48 (4%) 3/48 (6%) 3/49 (6%)

Adjusted rate 6.7% 6.8% 4.3% 6.7% 6.5%

Terminal rate 1/37 (3%) 3/37 (8%) 2/44 (5%) 3/41 (7%) 3/41 (7%)

First incidence (days) 552 729 (T) 729 (T) 729 (T) 729 (T)

Poly-3 test P=0.559 P=0.652 P=0.488N P=0.659 P=0.649N

Skin: Fibrosarcoma or Sarcoma

Overall rate 2/50 (4%) 3/50 (6%) 2/50 (4%) 2/50 (4%) 3/50 (6%)

Adjusted rate 4.4% 6.4% 4.2% 4.2% 6.3%

Terminal rate 1/37 (3%) 2/39 (5%) 2/45 (4%) 1/42 (2%) 1/42 (2%)

First incidence (days) 695 461 729 (T) 646 646

Poly-3 test P=0.484 P=0.516 P=0.673N P=0.679N P=0.526

Stomach (Forestomach): Squamous Cell Papilloma

Overall rate 1/50 (2%) 2/50 (4%) 0/50 (0%) 0/50 (0%) 3/50 (6%)

Adjusted rate 2.2% 4.3% 0.0% 0.0% 6.3%

Terminal rate 0/37 (0%) 2/39 (5%) 0/45 (0%) 0/42 (0%) 3/42 (7%)

First incidence (days) 616 729 (T) — — 729 (T)

Poly-3 test P=0.145 P=0.505 P=0.490N P=0.494N P=0.320

All Organs: Hemangiosarcoma

Overall rate 2/50 (4%) 3/50 (6%) 2/50 (4%) 4/50 (8%) 0/50 (0%)

Adjusted rate 4.4% 6.5% 4.2% 8.5% 0.0%

Terminal rate 0/37 (0%) 2/39 (5%) 2/45 (4%) 3/42 (7%) 0/42 (0%)

First incidence (days) 583 688 729 (T) 646 —

Poly-3 test P=0.140N P=0.505 P=0.677N P=0.350 P=0.230N

All Organs: Hemangioma or Hemangiosarcoma

Overall rate 3/50 (6%) 3/50 (6%) 4/50 (8%) 4/50 (8%) 0/50 (0%)

Adjusted rate 6.6% 6.5% 8.3% 8.5% 0.0%

Terminal rate 1/37 (3%) 2/39 (5%) 4/45 (9%) 3/42 (7%) 0/42 (0%)

First incidence (days) 583 688 729 (T) 646 —

Poly-3 test P=0.072N P=0.658N P=0.524 P=0.515 P=0.113N
Sodium Dichromate Dihydrate, NTP TR 546 139

Table D2

Statistical Analysis of Primary Neoplasms in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

All Organs: Malignant Lymphoma

Overall rate 7/50 (14%) 3/50 (6%) 2/50 (4%) 5/50 (10%) 5/50 (10%)

Adjusted rate 15.3% 6.4% 4.2% 10.4% 10.5%

Terminal rate 4/37 (11%) 1/39 (3%) 2/45 (4%) 2/42 (5%) 4/42 (10%)

First incidence (days) 616 632 729 (T) 428 652

Poly-3 test P=0.472 P=0.149N P=0.068N P=0.346N P=0.351N

All Organs: Benign Neoplasms

Overall rate 27/50 (54%) 28/50 (56%) 27/50 (54%) 25/50 (50%) 29/50 (58%)

Adjusted rate 56.6% 60.4% 55.9% 53.4% 59.3%

Terminal rate 21/37 (57%) 26/39 (67%) 25/45 (56%) 25/42 (60%) 26/42 (62%)

First incidence (days) 212 671 646 729 (T) 170

Poly-3 test P=0.479 P=0.434 P=0.555N P=0.457N P=0.475

All Organs: Malignant Neoplasms

Overall rate 22/50 (44%) 23/50 (46%) 19/50 (38%) 21/50 (42%) 18/50 (36%)

Adjusted rate 46.7% 47.1% 38.2% 42.5% 36.8%

Terminal rate 15/37 (41%) 14/39 (36%) 15/45 (33%) 14/42 (33%) 12/42 (29%)

First incidence (days) 583 461 311 428 625

Poly-3 test P=0.202N P=0.564 P=0.262N P=0.417N P=0.220N

All Organs: Benign or Malignant Neoplasms

Overall rate 36/50 (72%) 37/50 (74%) 37/50 (74%) 39/50 (78%) 38/50 (76%)

Adjusted rate 73.4% 75.8% 74.0% 79.0% 76.2%

Terminal rate 26/37 (70%) 28/39 (72%) 32/45 (71%) 32/42 (76%) 31/42 (74%)

First incidence (days) 212 461 311 428 170

Poly-3 test P=0.441 P=0.484 P=0.566 P=0.342 P=0.465

(T)Terminal sacrifice a Number of neoplasm-bearing animals/number of animals examined. Denominator is number of animals examined microscopically for liver, lung, ovary, 

and pituitary gland; for other tissues, denominator is number of animals necropsied. b Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality c Observed incidence at terminal kill d

 Beneath the control incidence is the P value associated with the trend test. Beneath the exposed group incidence are the P values corresponding to pairwise 

comparisons between the controls and that exposed group. The Poly-3 test accounts for the differential mortality in animals that do not reach terminal 

sacrifice. A negative trend or a lower incidence in an exposed group is indicated by N. e Not applicable; no neoplasms in animal group f Value of statistic cannot be computed.
140 Sodium Dichromate Dihydrate, NTP TR 546 

Table D3

Historical Incidence of Small Intestine Neoplasms in Control Female B6C3F1 Micea

 Incidence in Controls

 Duodenum Jejunum Duodenum, Jejunum, or Ileum

Study Adenoma Carcinoma Adenoma Carcinoma Adenoma Carcinoma Adenoma

 or Carcinoma

Historical Incidence: Drinking Water Studies

Bromochloroacetic acid 1/50 0/50 0/50 1/50 1/50 1/50 2/50

Bromodichloromethane 0/50 0/50 0/50 0/50 0/50 1/50 1/50

Dibromoacetic acid 0/50 0/50 0/50 0/50 0/50 0/50 0/50

Dibromoacetonitrile 0/50 0/50 0/50 0/50 0/50 0/50 0/50

Dipropylene glycol 0/50 0/50 0/50 0/50 0/50 0/50 0/50

Sodium chlorate 0/50 0/50 0/50 0/50 0/50 0/50 0/50

Sodium dichromate dihydrate 0/50 0/50 0/50 1/50 0/50 1/50 1/50

Overall Historical Incidence: Drinking Water Studies

Total (%) 1/350 (0.3%) 0/350 0/350 2/350 (0.6%) 1/350 (0.3%) 3/350 (0.9%) 4/350 (1.1%)

Mean ± standard deviation 0.3% ± 0.8% 0.6% ± 1.0% 0.3% ± 0.8% 0.9% ± 1.1% 1.1% ± 1.6%

Range (0%-2%) (0%-2%) (0%-2%) (0%-2%) (0%-4%)

Overall Historical Incidence: All Routes

Total (%) 3/1,648 (0.2%) 1/1,648 (0.1%) 0/1,648 5/1,648 (0.3%) 3/1,648 (0.2%) 8/1,648 (0.5%) 11/1,648 (0.7%)

Mean ± standard deviation 0.2% ± 0.6% 0.1% ± 0.4% 0.3% ± 0.7% 0.2% ± 0.6% 0.5% ± 0.8% 0.7% ± 1.1%

Range (0%-2%) (0%-2%) (0%-2%) (0%-2%) (0%-2%) (0%-4%)

a Data as of March 2, 2007, with sodium dichromate dihydrate data added from Table D1
Table D4

Summary of the Incidence of Nonneoplastic Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydratea

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Disposition Summary

Animals initially in study 50 50 50 50 50

Early deaths

Moribund 5 2 2 3

Natural deaths 8 11 3 6 5

Survivors

Died last week of study 2 1 1 2

Terminal sacrifice 35 38 44 40 42

Animals examined microscopically 50 50 50 50 50

Alimentary System

Gallbladder (44) (47) (48) (45) (50)

Intestine large, colon (43) (43) (48) (45) (48)

Edema 1 (2%)

Lymphoid tissue, hyperplasia 2 (5%) 3 (7%) 1 (2%) 1 (2%) 2 (4%)

Intestine small, duodenum (42) (42) (48) (42) (48)

Cyst 1 (2%)

Dilatation 1 (2%)

Hyperplasia, lymphoid 1 (2%)

Infiltration cellular, histiocyte 4 (8%) 33 (79%) 40 (83%)

Epithelium, hyperplasia, focal 1 (2%) 2 (5%)

Epithelium, hyperplasia, diffuse 16 (38%) 35 (73%) 31 (74%) 42 (88%)

Lymphoid tissue, hyperplasia 1 (2%) 1 (2%) 2 (4%)

Intestine small, ileum (42) (43) (47) (44) (47)

Inflammation, suppurative 1 (2%)

Intestine small, jejunum (41) (42) (48) (44) (48)

Fibrosis 1 (2%)

Infiltration cellular, histiocyte 2 (5%) 8 (17%)

Inflammation, suppurative 4 (10%) 1 (2%) 1 (2%)

Epithelium, hyperplasia, focal 1 (2%) 1 (2%)

Epithelium, hyperplasia, diffuse 2 (5%) 1 (2%) 8 (17%)

Lymphoid tissue, hyperplasia 6 (15%) 6 (14%) 6 (13%) 4 (9%) 3 (6%)

Liver (49) (50) (50) (50) (50)

Basophilic focus 3 (6%) 4 (8%) 2 (4%) 1 (2%)

Basophilic focus, multiple 2 (4%)

Clear cell focus 3 (6%) 5 (10%) 2 (4%) 1 (2%)

Cyst 1 (2%) 1 (2%)

Cyst, multiple 1 (2%)

Eosinophilic focus 11 (22%) 13 (26%) 5 (10%) 4 (8%) 4 (8%)

Eosinophilic focus, multiple 3 (6%) 5 (10%) 3 (6%) 1 (2%)

Hematopoietic cell proliferation 3 (6%) 1 (2%) 1 (2%)

Hemorrhage 1 (2%) 2 (4%)

Infiltration cellular, histiocyte 2 (4%) 15 (30%) 23 (46%) 32 (64%) 45 (90%)

Infiltration cellular, lymphocyte 2 (4%) 1 (2%) 2 (4%)

Inflammation, chronic 16 (33%) 21 (42%) 22 (44%) 27 (54%) 24 (48%)

Mixed cell focus 2 (4%) 4 (8%) 1 (2%) 1 (2%)

Necrosis, focal 1 (2%) 1 (2%) 2 (4%) 1 (2%)

Tension lipidosis 1 (2%) 1 (2%)

Thrombosis 1 (2%)

Hepatocyte, vacuolization cytoplasmic 4 (8%) 5 (10%) 5 (10%) 2 (4%)

a Number of animals examined microscopically at the site and the number of animals with lesion

Sodium Dichromate Dihydrate, NTP TR 546 141
142 Sodium Dichromate Dihydrate, NTP TR 546 

Table D4

Summary of the Incidence of Nonneoplastic Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Alimentary System (continued)

Mesentery (20) (23) (23) (23) (9)

Fibrosis 1 (4%)

Hemorrhage 1 (11%)

Inflammation, granulomatous 1 (4%)

Inflammation, chronic 1 (4%) 1 (11%)

Fat, hemorrhage 1 (4%)

Fat, necrosis 16 (80%) 20 (87%) 20 (87%) 21 (91%) 6 (67%)

Pancreas (48) (50) (49) (50) (50)

Atrophy 1 (2%) 1 (2%) 2 (4%)

Cyst 1 (2%) 1 (2%)

Necrosis 1 (2%)

Acinus, atrophy 2 (4%)

Acinus, cytoplasmic alteration 6 (12%) 6 (12%) 14 (28%) 32 (64%)

Acinus, hyperplasia, focal 1 (2%)

Salivary glands (50) (50) (50) (48) (49)

Atrophy 1 (2%)

Fibrosis 1 (2%)

Infiltration cellular, lymphocyte 1 (2%) 1 (2%)

Inflammation, chronic 2 (4%)

Submandibular gland, atrophy 1 (2%)

Stomach, forestomach (49) (49) (50) (48) (50)

Cyst 2 (4%)

Diverticulum 1 (2%)

Edema 1 (2%) 1 (2%)

Erosion 1 (2%)

Infiltration cellular, lymphocyte 1 (2%)

Inflammation, chronic 1 (2%)

Mineralization 2 (4%)

Ulcer 3 (6%) 1 (2%) 1 (2%) 2 (4%)

Epithelium, hyperplasia 2 (4%) 2 (4%) 2 (4%) 3 (6%)

Stomach, glandular (49) (48) (50) (48) (50)

Cyst 1 (2%) 1 (2%)

Degeneration, cystic 1 (2%)

Erosion 2 (4%) 1 (2%)

Fibrosis 1 (2%)

Infiltration cellular, mixed cell 1 (2%)

Inflammation, suppurative 1 (2%)

Ulcer 1 (2%)

Glands, hyperplasia 1 (2%)

Tongue (50) (50) (49) (48) (50)

Inflammation, chronic 7 (14%) 6 (12%) 3 (6%) 5 (10%) 5 (10%)

Mineralization 1 (2%) 1 (2%) 2 (4%)

Artery, inflammation, chronic 1 (2%) 3 (6%)

Cardiovascular System

Heart (50) (50) (50) (50) (50)

Cardiomyopathy 40 (80%) 34 (68%) 43 (86%) 42 (84%) 43 (86%)

Mineralization 1 (2%)

Artery, inflammation, chronic 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 143

Table D4

Summary of the Incidence of Nonneoplastic Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Endocrine System

Adrenal cortex (49) (50) (50) (50) (50)

Accessory adrenal cortical nodule 3 (6%) 1 (2%) 1 (2%) 3 (6%)

Hematopoietic cell proliferation 1 (2%) 1 (2%)

Hyperplasia, focal 1 (2%) 1 (2%) 1 (2%)

Hyperplasia, diffuse 1 (2%) 1 (2%)

Hypertrophy, focal 2 (4%) 1 (2%) 1 (2%)

Vacuolization cytoplasmic 1 (2%) 1 (2%)

Capsule, hyperplasia 10 (20%) 4 (8%) 6 (12%) 9 (18%) 14 (28%)

Adrenal medulla (49) (50) (50) (50) (50)

Hyperplasia 1 (2%) 1 (2%) 1 (2%)

Islets, pancreatic (49) (50) (50) (50) (50)

Hyperplasia 10 (20%) 5 (10%) 3 (6%) 5 (10%) 7 (14%)

Parathyroid gland (48) (49) (50) (44) (49)

Cyst 1 (2%) 1 (2%)

Pituitary gland (48) (48) (48) (48) (49)

Pars distalis, angiectasis 1 (2%)

Pars distalis, cyst 1 (2%)

Pars distalis, hyperplasia, focal 5 (10%) 3 (6%) 3 (6%) 2 (4%) 1 (2%)

Pars intermedia, fibrosis 1 (2%)

Rathke’s cleft, cyst 1 (2%) 1 (2%)

Thyroid gland (50) (50) (50) (49) (50)

Infiltration cellular, lymphocyte 1 (2%) 1 (2%)

Infiltration cellular, mixed cell 1 (2%) 2 (4%)

Inflammation, suppurative, focal 1 (2%)

Inflammation, chronic 1 (2%)

Follicle, cyst 2 (4%) 1 (2%) 3 (6%) 2 (4%) 2 (4%)

Follicle, degeneration, focal 12 (24%) 11 (22%) 14 (28%) 10 (20%) 11 (22%)

Follicular cell, hyperplasia 1 (2%)

Follicular cell, hyperplasia, focal 1 (2%) 1 (2%) 2 (4%)

Follicular cell, hypertrophy 1 (2%)

General Body System

Tissue NOS (1)

Genital System

Clitoral gland (50) (50) (50) (50) (48)

Cyst 1 (2%) 1 (2%) 1 (2%)

Inflammation, chronic 1 (2%)

Ovary (50) (49) (47) (48) (49)

Angiectasis 1 (2%) 1 (2%) 1 (2%) 2 (4%)

Atrophy 1 (2%) 2 (4%)

Cyst 10 (20%) 13 (27%) 12 (26%) 11 (23%) 10 (20%)

Hematocyst 1 (2%)

Hemorrhage 1 (2%) 9 (18%) 2 (4%) 4 (8%) 3 (6%)

Hyperplasia 1 (2%)

Infiltration cellular, lymphocyte 1 (2%)

Mineralization 1 (2%)

Thrombosis 1 (2%)
144 Sodium Dichromate Dihydrate, NTP TR 546 

Table D4

Summary of the Incidence of Nonneoplastic Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Genital System (continued)

Uterus (50) (50) (50) (50) (50)

Angiectasis 1 (2%) 1 (2%)

Hyperplasia, cystic 43 (86%) 45 (90%) 42 (84%) 43 (86%) 45 (90%)

Inflammation, suppurative 1 (2%)

Serosa, cyst 1 (2%)

Vagina (1) 

Hematopoietic System

Bone marrow (50) (50) (50) (50) (50)

Fibrosis 1 (2%)

Hemorrhage 1 (2%)

Hyperplasia 5 (10%) 3 (6%) 5 (10%) 1 (2%) 1 (2%)

Hyperplasia, reticulum cell 1 (2%)

Pigmentation 47 (94%) 47 (94%) 49 (98%) 49 (98%) 50 (100%)

Lymph node (10) (7) (6) (5) (6)

Bronchial, hyperplasia, lymphoid 1 (10%) 1 (14%) 1 (17%)

Iliac, hematopoietic cell proliferation 1 (10%)

Iliac, hyperplasia, lymphoid 1 (10%) 2 (33%) 1 (20%) 1 (17%)

Iliac, pigmentation 1 (10%)

Mediastinal, hyperplasia, lymphoid 4 (40%) 1 (14%) 2 (33%) 1 (17%)

Renal, hyperplasia, lymphoid 2 (33%)

Lymph node, mandibular (50) (48) (49) (48) (48)

Ectasia 1 (2%)

Hyperplasia, lymphoid 4 (8%) 2 (4%) 4 (8%) 6 (13%) 3 (6%)

Lymph node, mesenteric (46) (48) (46) (50) (50)

Ectasia 6 (13%) 1 (2%) 2 (4%) 2 (4%) 2 (4%)

Hematopoietic cell proliferation 1 (2%) 1 (2%)

Hemorrhage 1 (2%) 1 (2%)

Hyperplasia, lymphoid 3 (7%) 4 (8%) 6 (13%) 4 (8%) 2 (4%)

Infiltration cellular, histiocyte 3 (7%) 29 (60%) 26 (57%) 40 (80%) 42 (84%)

Mineralization 1 (2%)

Lymph, node, pancreatic (14) (12) (15) (14) (13)

Hyperplasia, lymphoid 1 (7%) 1 (8%) 2 (13%) 1 (8%)

Infiltration cellular, histiocyte 1 (8%) 2 (13%) 7 (50%) 8 (62%)

Spleen (48) (48) (50) (50) (50)

Hematopoietic cell proliferation 15 (31%) 24 (50%) 19 (38%) 15 (30%) 15 (30%)

Necrosis 1 (2%)

Lymphoid follicle, atrophy 1 (2%)

Lymphoid follicle, hyperplasia 17 (35%) 19 (40%) 28 (56%) 22 (44%) 18 (36%)

Thymus (46) (38) (43) (40) (47)

Angiectasis 1 (3%)

Atrophy 2 (4%) 1 (3%) 1 (2%)

Hyperplasia, lymphoid 30 (65%) 20 (53%) 17 (40%) 25 (63%) 32 (68%)

Integumentary System

Mammary gland (50) (48) (50) (50) (50)

Cyst 3 (6%) 1 (2%)

Hyperplasia 1 (2%) 1 (2%)

Duct, cyst 1 (2%)

Skin (50) (50) (50) (49) (50)

Edema 1 (2%)

Inflammation, granulomatous 1 (2%)

Inflammation, chronic 1 (2%)

Ulcer 1 (2%) 1 (2%) 1 (2%)

Dermis, cyst 1 (2%)
Sodium Dichromate Dihydrate, NTP TR 546 145

Table D4

Summary of the Incidence of Nonneoplastic Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Musculoskeletal System

Bone (50) (50) (50) (50) (50)

Fibrosis 1 (2%)

Cranium, fibrosis 1 (2%)

Cranium, osteopetrosis 1 (2%) 1 (2%)

Skeletal muscle (2) (6) (1) (1) (1)

Fibrosis 1 (100%)

Nervous System

Brain (50) (50) (50) (50) (50)

Compression 1 (2%) 2 (4%) 2 (4%)

Cerebellum, vacuolization cytoplasmic 1 (2%)

Cerebrum, edema 1 (2%)

Respiratory System

Lung (50) (50) (50) (50) (50)

Fibrosis 1 (2%)

Hemorrhage 1 (2%) 1 (2%)

Infiltration cellular, histiocyte 2 (4%) 2 (4%) 2 (4%)

Infiltration cellular, lymphocyte 1 (2%) 4 (8%) 6 (12%) 4 (8%) 5 (10%)

Infiltration cellular, mixed cell 1 (2%)

Metaplasia, osseous 1 (2%)

Alveolar epithelium, hyperplasia 1 (2%) 2 (4%) 1 (2%)

Capillary, infiltration cellular, mixed cell 1 (2%)

Nose (50) (50) (50) (50) (50)

Special Senses System

Eye (49) (48) (48) (46) (50)

Atrophy 1 (2%) 1 (2%)

Harderian gland (49) (49) (50) (50) (50)

Hyperplasia, focal 1 (2%) 1 (2%) 1 (2%)

Inflammation, chronic 1 (2%)

Urinary System

Kidney (50) (49) (50) (49) (50)

Accumulation, hyaline droplet 1 (2%)

Calculus microscopic observation only 4 (8%) 3 (6%) 5 (10%)

Casts protein 1 (2%)

Cyst 2 (4%) 1 (2%)

Hemorrhage 1 (2%) 1 (2%)

Hydronephrosis 1 (2%) 2 (4%) 1 (2%)

Infarct 4 (8%) 3 (6%) 2 (4%) 2 (4%)

Infiltration cellular 1 (2%) 1 (2%) 2 (4%)

Infiltration cellular, lymphocyte 10 (20%) 5 (10%) 10 (20%) 10 (20%) 7 (14%)

Inflammation, chronic 1 (2%) 2 (4%)

Metaplasia, osseous 1 (2%) 1 (2%) 3 (6%) 1 (2%)

Mineralization 2 (4%) 1 (2%)

Nephropathy 21 (42%) 30 (61%) 30 (60%) 26 (53%) 28 (56%)

Papilla, necrosis 1 (2%) 1 (2%)

Renal tubule, accumulation, hyaline droplet 1 (2%)

Renal tubule, mineralization 1 (2%)

Renal tubule, pigmentation 1 (2%)
146 Sodium Dichromate Dihydrate, NTP TR 546 

Table D4

Summary of the Incidence of Nonneoplastic Lesions in Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Urinary System (continued)

Ureter (1) 

Urinary bladder (50) (48) (50) (48) (49)

Infiltration cellular, lymphocyte 42 (84%) 33 (69%) 37 (74%) 27 (56%) 38 (78%)
147

APPENDIX E

CLINICAL PATHOLOGY RESULTS

Table E1 Hematology and Clinical Chemistry Data for Male Rats 

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 148

Table E2 Hematology Data for Female Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
148 Sodium Dichromate Dihydrate, NTP TR 546 

Table E1

Hematology and Clinical Chemistry Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematology

n

Day 4 9 10 9 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 8 10

Hematocrit (auto) (%)

Day 4 37.5 ± 0.5 37.7 ± 0.5 36.4 ± 0.8 35.8 ± 0.7 37.0 ± 0.6

Day 22 46.5 ± 0.9 45.3 ± 0.5 44.2 ± 0.7 38.4 ± 0.8** 28.0 ± 0.6**

Month 3 45.1 ± 0.3 44.6 ± 0.4 44.7 ± 0.5 44.6 ± 0.5 43.0 ± 0.5**

Month 6 46.5 ± 0.3 46.7 ± 0.5 46.3 ± 0.5 46.5 ± 0.4 46.0 ± 0.3

Month 12 48.8 ± 0.6 48.0 ± 0.4 48.8 ± 0.7 49.3 ± 0.5 48.6 ± 0.4

Hematocrit (spun) (%) 

Day 4 38.2 ± 0.5b 38.4 ± 0.6 36.7 ± 0.9 36.4 ± 0.6 37.3 ± 0.6

Day 22 46.0 ± 1.1 44.4 ± 0.4 43.2 ± 0.6* 38.7 ± 0.6** 33.5 ± 0.8**

Month 3 45.3 ± 0.4 44.5 ± 0.3 44.5 ± 0.4 44.1 ± 0.5 41.0 ± 0.5**

Month 6 45.9 ± 0.4 45.7 ± 0.5 45.5 ± 0.4 45.5 ± 0.5 45.0 ± 0.3

Month 12 47.6 ± 0.5 46.6 ± 0.4 47.4 ± 0.5 47.7 ± 0.4 47.3 ± 0.4

Hemoglobin (g/dL)

Day 4 12.9 ± 0.2 13.0 ± 0.2 12.5 ± 0.3 12.3 ± 0.2 12.8 ± 0.2

Day 22 15.5 ± 0.3 15.1 ± 0.2 14.2 ± 0.2** 12.0 ± 0.3** 10.1 ± 0.2**

Month 3 15.1 ± 0.1 14.9 ± 0.1 14.9 ± 0.2 14.6 ± 0.2* 12.9 ± 0.2**

Month 6 15.2 ± 0.1 15.2 ± 0.2 15.0 ± 0.2 14.9 ± 0.1 14.5 ± 0.1**

Month 12 15.8 ± 0.2 15.4 ± 0.2 15.6 ± 0.2 15.6 ± 0.2 15.3 ± 0.1*

Erythrocytes (106/μL)

Day 4 6.75 ± 0.11 6.80 ± 0.10 6.67 ± 0.17 6.73 ± 0.11 6.98 ± 0.12

Day 22 7.80 ± 0.13 7.74 ± 0.15 8.06 ± 0.16 8.10 ± 0.14 6.21 ± 0.13**

Month 3 9.28 ± 0.05 9.24 ± 0.06 9.46 ± 0.11 9.75 ± 0.11** 10.93 ± 0.16**

Month 6 9.34 ± 0.06 9.43 ± 0.08 9.54 ± 0.11 9.71 ± 0.08** 10.15 ± 0.13**

Month 12 9.27 ± 0.10 9.17 ± 0.07 9.40 ± 0.12 9.61 ± 0.11 9.74 ± 0.08**

Reticulocytes (auto) (106/μL)

Day 4 0.62 ± 0.04 0.56 ± 0.04 0.50 ± 0.04 0.24 ± 0.02** 0.19 ± 0.02**

Day 22 0.38 ± 0.03 0.34 ± 0.02 0.38 ± 0.03 0.43 ± 0.04 0.63 ± 0.07**

Month 3 0.23 ± 0.01 0.24 ± 0.01 0.22 ± 0.01 0.21 ± 0.01 0.30 ± 0.01**

Month 6 0.24 ± 0.00 0.22 ± 0.01 0.22 ± 0.01 0.24 ± 0.01 0.24 ± 0.01

Month 12 0.23 ± 0.01 0.23 ± 0.01 0.24 ± 0.01 0.26 ± 0.02 0.23 ± 0.01

Reticulocytes (manual) (106/μL)

Day 4 0.30 ± 0.06 0.29 ± 0.03 0.29 ± 0.06 0.30 ± 0.03 0.27 ± 0.02

Day 22 0.32 ± 0.04 0.27 ± 0.03 0.30 ± 0.03 0.41 ± 0.05 0.52 ± 0.04**

Month 3 0.12 ± 0.02 0.14 ± 0.02 0.10 ± 0.02 0.11 ± 0.03 0.13 ± 0.02

Month 12 0.19 ± 0.02 0.18 ± 0.01 0.21 ± 0.02 0.22 ± 0.03 0.17 ± 0.01

Nucleated erythrocytes (103/μL) 

Day 4 0.50 ± 0.17b 0.60 ± 0.22 0.20 ± 0.13b 0.50 ± 0.17 0.10 ± 0.10

Day 22 0.20 ± 0.13 0.20 ± 0.13 0.30 ± 0.15 0.30 ± 0.21 1.40 ± 0.22**

Month 3 0.20 ± 0.13 0.40 ± 0.22 0.30 ± 0.21 0.20 ± 0.13 0.00 ± 0.00

Month 6 0.30 ± 0.15 0.10 ± 0.10 0.20 ± 0.13 0.10 ± 0.10 0.40 ± 0.22

Month 12 0.30 ± 0.21 0.30 ± 0.21 0.10 ± 0.10 0.38 ± 0.26 0.10 ± 0.10
Sodium Dichromate Dihydrate, NTP TR 546 149

Table E1

Hematology and Clinical Chemistry Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematology (continued)

n

Day 4 9 10 9 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 8 10

Mean cell volume (fL)

Day 4 55.6 ± 0.3 55.5 ± 0.3 54.6 ± 0.3 53.3 ± 0.1** 53.0 ± 0.2**

Day 22 59.5 ± 0.4 58.6 ± 0.5 54.9 ± 0.5** 47.4 ± 0.4** 45.0 ± 0.7**

Month 3 48.6 ± 0.2 48.3 ± 0.2 47.3 ± 0.2** 45.7 ± 0.2** 39.2 ± 0.6**

Month 6 49.8 ± 0.1 49.5 ± 0.1 48.6 ± 0.1** 47.8 ± 0.2** 45.4 ± 0.5**

Month 12 52.6 ± 0.2 52.4 ± 0.2 51.9 ± 0.3 51.4 ± 0.3** 49.9 ± 0.2**

Mean cell hemoglobin (pg) 

Day 4 19.1 ± 0.1 19.1 ± 0.1 18.7 ± 0.1* 18.3 ± 0.1** 18.4 ± 0.1**

Day 22 19.8 ± 0.1 19.5 ± 0.2 17.7 ± 0.2** 14.8 ± 0.2** 16.3 ± 0.5**

Month 3 16.2 ± 0.1 16.2 ± 0.1 15.7 ± 0.0** 15.0 ± 0.1** 11.9 ± 0.3**

Month 6 16.3 ± 0.1 16.1 ± 0.1 15.7 ± 0.1** 15.3 ± 0.1** 14.3 ± 0.2**

Month 12 17.0 ± 0.1 16.8 ± 0.1 16.6 ± 0.1* 16.2 ± 0.1** 15.7 ± 0.1**

Mean cell hemoglobin concentration (g/dL)

Day 4 34.4 ± 0.2 34.4 ± 0.2 34.3 ± 0.2 34.4 ± 0.2 34.7 ± 0.2

Day 22 33.3 ± 0.1 33.3 ± 0.1 32.2 ± 0.2 31.2 ± 0.2** 36.2 ± 0.8

Month 3 33.4 ± 0.1 33.5 ± 0.2 33.2 ± 0.1 32.7 ± 0.1** 30.2 ± 0.3**

Month 6 32.7 ± 0.1 32.5 ± 0.1 32.3 ± 0.1* 32.1 ± 0.1** 31.6 ± 0.2**

Month 12 32.3 ± 0.2 32.1 ± 0.3 32.0 ± 0.2 31.6 ± 0.2* 31.5 ± 0.2*

Platelets (103/μL)

Day 4 1,011.0 ± 16.0 1,063.0 ± 27.0 1,068.0 ± 22.0 1,203.0 ± 37.0** 1,172.0 ± 27.0**

Day 22 987.9 ± 32.9 993.3 ± 23.6 1,128.1 ± 58.9 1,847.4 ± 127.4** 3,537.1 ± 199.7**

Month 3 689.7 ± 18.8 714.4 ± 17.0 704.1 ± 15.9 706.8 ± 14.7 898.4 ± 64.9**

Month 6 644.7 ± 9.2 651.5 ± 13.2 649.3 ± 15.7 648.1 ± 22.2 663.8 ± 8.7

Month 12 575.1 ± 10.3 577.5 ± 8.2 579.1 ± 10.1 562.3 ± 21.4 587.1 ± 17.0

Platelet estimates

Day 4 1,397.0 ± 84.0b 1,439.0 ± 56.0 1,512.0 ± 84.0 1,628.0 ± 80.0 1,401.0 ± 55.0

Day 22 1,199.0 ± 30.0 1,254.0 ± 47.0 1,268.0 ± 55.0 1,237.0 ± 48.0 1,359 ± 44.0

Month 3 949.2 ± 29.7 976.5 ± 31.0 1,010.1 ± 47.3 926.1 ± 22.2 984.9 ± 31.8

Month 6 707.7 ± 38.5 638.4 ± 24.9 688.8 ± 27.3 648.9 ± 25.5 636.3 ± 18.8

Month 12 1,138.2 ± 30.5 1,163.4 ± 29.1 1,089.9 ± 38.3 1,002.8 ± 73.6 999.6 ± 63.1

Leukocytes (103/μL)

Day 4 9.23 ± 0.40 9.81 ± 0.42 7.94 ± 0.59 8.40 ± 0.46 9.88 ± 0.42

Day 22 10.85 ± 0.31 11.52 ± 0.33 10.29 ± 0.34 11.00 ± 0.48 11.45 ± 0.63

Month 3 11.52 ± 0.21 11.80 ± 0.21 10.88 ± 0.22 11.43 ± 0.23 12.96 ± 0.43*

Month 6 9.99 ± 0.27 9.81 ± 0.23 9.92 ± 0.27 9.19 ± 0.17 10.22 ± 0.27

Month 12 8.74 ± 0.17 8.76 ± 0.15 8.43 ± 0.19 8.45 ± 0.33 7.81 ± 0.12**

Segmented neutrophils (103/μL)

Day 4 1.08 ± 0.05 1.09 ± 0.07 0.87 ± 0.04* 0.93 ± 0.03 0.98 ± 0.05

Day 22 0.98 ± 0.05 1.06 ± 0.06 0.92 ± 0.03 0.93 ± 0.05 1.05 ± 0.14

Month 3 1.36 ± 0.04 1.47 ± 0.06 1.44 ± 0.04 1.52 ± 0.04* 1.75 ± 0.10**

Month 6 1.54 ± 0.05 1.53 ± 0.05 1.57 ± 0.05 1.54 ± 0.05 1.68 ± 0.03

Month 12 2.22 ± 0.11 2.12 ± 0.07 1.80 ± 0.08** 1.82 ± 0.12* 1.77 ± 0.07**
150 Sodium Dichromate Dihydrate, NTP TR 546 

Table E1

Hematology and Clinical Chemistry Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Hematology (continued)

n

Day 4 9 10 9 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 8 10

Lymphocytes (103/μL)

Day 4 7.89 ± 0.37 8.43 ± 0.35 6.83 ± 0.56 7.26 ± 0.45 8.65 ± 0.38

Day 22 9.59 ± 0.27 10.10 ± 0.29 9.05 ± 0.31 9.76 ± 0.45 10.08 ± 0.49

Month 3 9.76 ± 0.19 9.90 ± 0.21 9.04 ± 0.18 9.52 ± 0.23 10.79 ± 0.36

Month 6 7.98 ± 0.24 7.82 ± 0.19 7.92 ± 0.25 7.24 ± 0.17 8.06 ± 0.24

Month 12 6.08 ± 0.14 6.21 ± 0.12 6.23 ± 0.13 6.21 ± 0.26 5.71 ± 0.11

Activated lymphocytes (103/μL)

Day 4 0.06 ± 0.00 0.06 ± 0.01 0.06 ± 0.01 0.04 ± 0.01 0.07 ± 0.01

Day 22 0.06 ± 0.01 0.07 ± 0.01 0.06 ± 0.01 0.08 ± 0.01 0.07 ± 0.01

Month 3 0.05 ± 0.00 0.06 ± 0.01 0.07 ± 0.00 0.05 ± 0.00 0.06 ± 0.00

Month 6 0.09 ± 0.00 0.09 ± 0.01 0.09 ± 0.01 0.09 ± 0.01 0.10 ± 0.01

Month 12 0.05 ± 0.01 0.05 ± 0.00 0.04 ± 0.00 0.04 ± 0.01 0.04 ± 0.00

Monocytes (103/μL)

Day 4 0.16 ± 0.01 0.17 ± 0.02 0.14 ± 0.02 0.13 ± 0.01 0.14 ± 0.01

Day 22 0.15 ± 0.01 0.22 ± 0.02* 0.19 ± 0.02 0.19 ± 0.01 0.20 ± 0.03

Month 3 0.22 ± 0.01 0.23 ± 0.01 0.19 ± 0.01 0.21 ± 0.01 0.23 ± 0.01

Month 6 0.24 ± 0.01 0.24 ± 0.01 0.22 ± 0.01 0.21 ± 0.01 0.25 ± 0.01

Month 12 0.27 ± 0.03 0.24 ± 0.02 0.24 ± 0.01 0.25 ± 0.02 0.20 ± 0.01

Basophils (103/μL)

Day 4 0.029 ± 0.002 0.031 ± 0.003 0.031 ± 0.004 0.029 ± 0.003 0.034 ± 0.003

Day 22 0.032 ± 0.003 0.040 ± 0.004 0.034 ± 0.003 0.027 ± 0.003 0.028 ± 0.003

Month 3 0.056 ± 0.004 0.060 ± 0.006 0.052 ± 0.004 0.054 ± 0.002 0.048 ± 0.003

Month 6 0.044 ± 0.004 0.043 ± 0.003 0.037 ± 0.003 0.035 ± 0.003 0.048 ± 0.010

Month 12 0.031 ± 0.004 0.038 ± 0.004 0.029 ± 0.004 0.021 ± 0.004 0.021 ± 0.002

Eosinophils (103/μL)

Day 4 0.02 ± 0.00 0.03 ± 0.00 0.02 ± 0.00 0.02 ± 0.00 0.02 ± 0.00

Day 22 0.04 ± 0.00 0.04 ± 0.00 0.03 ± 0.00* 0.02 ± 0.00** 0.02 ± 0.01**

Month 3 0.08 ± 0.01 0.08 ± 0.01 0.09 ± 0.01 0.08 ± 0.00 0.08 ± 0.01

Month 6 0.09 ± 0.01 0.08 ± 0.00 0.08 ± 0.01 0.07 ± 0.01 0.08 ± 0.01

Month 12 0.09 ± 0.01 0.10 ± 0.01 0.09 ± 0.01 0.10 ± 0.01 0.07 ± 0.01

Clinical Chemistry

n

Day 4 10 9 10 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 10 10

Urea nitrogen (mg/dL) 

Day 4 9.1 ± 0.3 9.4 ± 0.3 10.2 ± 0.4* 10.9 ± 0.4** 11.5 ± 0.3**

Day 22 15.6 ± 0.4 15.0 ± 0.5 15.6 ± 0.5 16.0 ± 0.3 16.6 ± 0.3

Month 3 17.8 ± 0.4 16.4 ± 0.6 18.2 ± 0.4 17.5 ± 0.3 17.5 ± 0.4

Month 6 15.7 ± 0.3 15.2 ± 0.4 15.4 ± 0.4 17.1 ± 0.4 15.8 ± 0.2

Month 12 16.1 ± 0.3 16.8 ± 0.3 16.8 ± 0.3 18.2 ± 0.6** 17.7 ± 0.3**
Sodium Dichromate Dihydrate, NTP TR 546 151

Table E1

Hematology and Clinical Chemistry Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Clinical Chemistry (continued)

n

Day 4 10 9 10 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 10 10

Creatinine (mg/dL) 

Day 4 0.41 ± 0.01 0.41 ± 0.02 0.44 ± 0.02 0.40 ± 0.00 0.41 ± 0.01

Day 22 0.52 ± 0.02 0.50 ± 0.02 0.52 ± 0.01 0.48 ± 0.02 0.47 ± 0.02

Month 3 0.70 ± 0.02 0.70 ± 0.02 0.69 ± 0.02 0.67 ± 0.02 0.66 ± 0.02

Month 6 0.70 ± 0.02 0.67 ± 0.02 0.62 ± 0.03** 0.65 ± 0.03* 0.62 ± 0.01**

Month 12 0.70 ± 0.03 0.74 ± 0.02 0.78 ± 0.02 0.66 ± 0.02 0.73 ± 0.03

Total protein (g/dL) 

Day 4 5.2 ± 0.1 5.3 ± 0.1 5.2 ± 0.2 5.0 ± 0.1 5.0 ± 0.1

Day 22 6.1 ± 0.1 6.1 ± 0.1 6.0 ± 0.1 5.8 ± 0.1 5.7 ± 0.1*

Month 3 6.9 ± 0.1 6.9 ± 0.1 6.8 ± 0.1 6.7 ± 0.1 6.6 ± 0.1**

Month 6 6.5 ± 0.2 6.6 ± 0.0 6.6 ± 0.1 6.5 ± 0.1 6.3 ± 0.1*

Month 12 7.2 ± 0.1 7.2 ± 0.1 7.3 ± 0.1 7.0 ± 0.1 6.9 ± 0.1*

Albumin (g/dL)

Day 4 3.7 ± 0.0 3.7 ± 0.1 3.7 ± 0.1 3.6 ± 0.0 3.6 ± 0.0

Day 22 4.2 ± 0.1 4.2 ± 0.0 4.1 ± 0.0 4.1 ± 0.0 4.1 ± 0.0

Month 3 4.5 ± 0.0 4.5 ± 0.0 4.5 ± 0.0 4.5 ± 0.0 4.5 ± 0.0

Month 6 4.5 ± 0.0 4.5 ± 0.0 4.5 ± 0.0 4.5 ± 0.0 4.3 ± 0.0**

Month 12 4.4 ± 0.0 4.5 ± 0.0 4.5 ± 0.0 4.4 ± 0.1 4.4 ± 0.0

Alanine aminotransferase (IU/L)

Day 4 54 ± 2 53 ± 2 60 ± 3 68 ± 1** 70 ± 2**

Day 22 45 ± 1 46 ± 1 58 ± 2** 75 ± 3** 73 ± 4**

Month 3 82 ± 4 82 ± 12 135 ± 18* 176 ± 13** 216 ± 21**

Month 6 122 ± 15 114 ± 9 150 ± 12 238 ± 20** 210 ± 12**

Month 12 102 ± 6 107 ± 8 135 ± 10* 261 ± 23** 223 ± 15**

Alkaline phosphatase (IU/L) 

Day 4 639 ± 16 634 ± 22 592 ± 23 550 ± 11** 504 ± 9**

Day 22 542 ± 19 508 ± 15 498 ± 20 495 ± 19 471 ± 6**

Month 3 219 ± 3 204 ± 5* 195 ± 6** 168 ± 3** 182 ± 7**

Month 6 167 ± 3 160 ± 3 142 ± 5** 129 ± 3** 115 ± 2**

Month 12 146 ± 4 141 ± 3c 131 ± 8** 112 ± 6** 101 ± 2**

Creatine kinase (IU/L) 

Day 4 395 ± 39 405 ± 45 412 ± 15 431 ± 37 486 ± 43

Day 22 392 ± 65 319 ± 15 361 ± 31 334 ± 18 357 ± 42

Month 3 423 ± 41 388 ± 49 495 ± 65 531 ± 50 517 ± 54

Month 6 289 ± 35 293 ± 32 242 ± 14 367 ± 22 399 ± 14*

Month 12 176 ± 17 187 ± 18 184 ± 21 288 ± 28** 305 ± 20**

Sorbitol dehydrogenase (IU/L) 

Day 4 17 ± 1 15 ± 1 14 ± 1 15 ± 1 13 ± 1

Day 22 11 ± 1 10 ± 1 10 ± 1 9 ± 1 10 ± 1

Month 3 18 ± 3 20 ± 5 21 ± 4 28 ± 4 30 ± 4

Month 6 29 ± 2 27 ± 3 31 ± 2 49 ± 5** 36 ± 2*

Month 12 27 ± 1 27 ± 1 27 ± 1 31 ± 3 27 ± 0
152 Sodium Dichromate Dihydrate, NTP TR 546 

Table E1

Hematology and Clinical Chemistry Data for Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

Clinical Chemistry (continued)

n

Day 4 10 9 10 10 10

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 10 10 10

Bile acids (μmol/L)

Day 4 27.6 ± 2.9 26.9 ± 2.0 29.8 ± 2.1 31.6 ± 2.9 26.6 ± 1.3

Day 22 22.1 ± 1.9 24.5 ± 1.7 22.8 ± 1.5 24.7 ± 1.9 26.8 ± 1.4

Month 3 23.9 ± 3.2 24.0 ± 2.5 22.4 ± 2.2 27.7 ± 3.5 24.2 ± 2.2

Month 6 17.8 ± 1.7 25.5 ± 2.4* 18.7 ± 1.5 22.0 ± 1.7 20.0 ± 1.1

Month 12 29.2 ± 3.2 29.8 ± 4.7 26.8 ± 3.6 39.6 ± 4.2 27.4 ± 2.2

* Significantly different (P#0.05) from the control group by Dunn’s or Shirley’s test

** P#0.01 a Mean ± standard error. Statistical tests were performed on unrounded data. b n=10 c n=9
Sodium Dichromate Dihydrate, NTP TR 546 153

Table E2

Hematology Data for Female Mice in the 2-Year Drinking Water Study of Sodium Dichromate Dihydratea

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 9 10 10

Hematocrit (auto) (%)

Day 22 50.0 ± 0.7 49.2 ± 0.4 50.0 ± 0.9 50.6 ± 0.7 49.6 ± 0.5

Month 3 47.7 ± 0.7 49.9 ± 0.5* 49.2 ± 0.8 49.4 ± 0.6 50.4 ± 0.5*

Month 6 48.4 ± 0.7 49.2 ± 0.5 47.8 ± 0.6 48.0 ± 0.8 49.2 ± 0.8

Month 12 45.0 ± 0.5 45.6 ± 0.3 45.2 ± 0.6 45.0 ± 0.7 45.1 ± 0.8

Hematocrit (spun) (%) 

Day 22 50.0 ± 0.7 49.0 ± 0.3 49.4 ± 0.8 49.6 ± 0.7 48.5 ± 0.5

Month 3 48.3 ± 0.6 50.4 ± 0.5* 49.3 ± 0.6 49.4 ± 0.5 50.4 ± 0.4*

Month 6 49.0 ± 0.6 50.2 ± 0.5 48.7 ± 0.5 48.9 ± 0.8 49.9 ± 0.7

Month 12 46.5 ± 0.4 47.4 ± 0.2 46.9 ± 0.5 46.4 ± 0.6 46.7 ± 0.6

Hemoglobin (g/dL)

Day 22 16.8 ± 0.2 16.5 ± 0.1 16.7 ± 0.3 16.9 ± 0.2 16.4 ± 0.2

Month 3 16.0 ± 0.2 16.7 ± 0.2* 16.4 ± 0.3 16.3 ± 0.2 16.5 ± 0.2

Month 6 16.1 ± 0.2 16.4 ± 0.2 16.0 ± 0.2 16.0 ± 0.3 16.2 ± 0.3

Month 12 14.9 ± 0.1 15.3 ± 0.2 15.1 ± 0.2 15.0 ± 0.2 14.9 ± 0.3

Erythrocytes (106/μL)

Day 22 10.25 ± 0.15 10.20 ± 0.08 10.47 ± 0.19 10.77 ± 0.13* 10.61 ± 0.13*

Month 3 10.10 ± 0.16 10.66 ± 0.13* 10.55 ± 0.17* 10.95 ± 0.10** 11.55 ± 0.16**

Month 6 10.56 ± 0.15 10.81 ± 0.10 10.60 ± 0.13 10.77 ± 0.20 11.50 ± 0.20**

Month 12 9.58 ± 0.10 9.72 ± 0.09 9.77 ± 0.10 9.95 ± 0.13* 10.30 ± 0.21**

Reticulocytes (auto) (106/μL)

Day 22 0.32 ± 0.01 0.30 ± 0.01 0.33 ± 0.02 0.31 ± 0.01 0.32 ± 0.02

Month 3 0.33 ± 0.01 0.31 ± 0.01 0.34 ± 0.02 0.34 ± 0.03 0.34 ± 0.02

Month 6 0.36 ± 0.02 0.37 ± 0.01 0.39 ± 0.04 0.36 ± 0.03 0.35 ± 0.02

Month 12 0.32 ± 0.02 0.33 ± 0.01 0.32 ± 0.01 0.36 ± 0.02 0.37 ± 0.02

Reticulocytes (manual) (106/μL) 

Day 22 0.21 ± 0.04 0.12 ± 0.02 0.16 ± 0.02 0.11 ± 0.01* 0.14 ± 0.02

Month 3 0.25 ± 0.02b 0.19 ± 0.03 0.21 ± 0.03c 0.24 ± 0.02 0.23 ± 0.02

Nucleated erythrocytes (103/μL)

Day 22 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Month 3 0.00 ± 0.00 0.10 ± 0.10 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Month 6 0.10 ± 0.10 0.10 ± 0.10 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Month 12 0.00 ± 0.00c 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00c

Mean cell volume (fL)

Day 22 48.8 ± 0.2 48.3 ± 0.1* 47.8 ± 0.2** 47.0 ± 0.2** 46.8 ± 0.2**

Month 3 47.2 ± 0.1 46.9 ± 0.3 46.7 ± 0.1 45.1 ± 0.2** 43.7 ± 0.3**

Month 6 45.8 ± 0.2 45.5 ± 0.3 45.1 ± 0.2* 44.6 ± 0.2** 42.8 ± 0.3**

Month 12 46.9 ± 0.3 46.9 ± 0.3 46.3 ± 0.3 45.2 ± 0.2** 43.9 ± 0.5**

Mean cell hemoglobin (pg) 

Day 22 16.4 ± 0.1 16.2 ± 0.0* 15.9 ± 0.1** 15.7 ± 0.1** 15.5 ± 0.1**

Month 3 15.8 ± 0.0 15.7 ± 0.1 15.6 ± 0.0** 14.9 ± 0.1** 14.3 ± 0.1**

Month 6 15.3 ± 0.1 15.2 ± 0.1 15.1 ± 0.1 14.9 ± 0.1** 14.1 ± 0.1**

Month 12 15.5 ± 0.1 15.7 ± 0.2 15.5 ± 0.1 15.1 ± 0.1* 14.4 ± 0.2**
154 Sodium Dichromate Dihydrate, NTP TR 546 

Table E2

Hematology Data for Female Mice in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 9 10 10

Mean cell hemoglobin concentration (g/dL)

Day 22 33.6 ± 0.1 33.5 ± 0.1 33.3 ± 0.2 33.4 ± 0.1 33.1 ± 0.1**

Month 3 33.5 ± 0.1 33.5 ± 0.1 33.3 ± 0.1 33.1 ± 0.1** 32.8 ± 0.1**

Month 6 33.4 ± 0.2 33.4 ± 0.1 33.5 ± 0.2 33.4 ± 0.1 32.9 ± 0.1

Month 12 33.1 ± 0.2 33.5 ± 0.2 33.4 ± 0.1 33.3 ± 0.1 32.9 ± 0.1

Platelets (103/μL)

Day 22 905.7 ± 48.4 939.2 ± 36.5 933.3 ± 47.4 851.4 ± 54.9 963.9 ± 48.0

Month 3 890.7 ± 37.4 839.5 ± 63.4 837.2 ± 57.0 888.2 ± 73.9 720.0 ± 47.1

Month 6 972.9 ± 62.5 819.3 ± 55.4 928.9 ± 91.0 923.1 ± 55.7 921.4 ± 62.9

Month 12 1,078.1 ± 67.6 925.0 ± 37.9 932.6 ± 78.1 879.9 ± 46.7* 761.5 ± 34.4**

Platelet estimates (103/μL)

Day 22 1,630.0 ± 105.0 1,903.0 ± 83.0 1,462.0 ± 91.0 1,319.0 ± 61.0 1,825.0 ± 105.0

Month 3 1,296.0 ± 92.0 1,208.0 ± 104.0 1,166.0 ± 81.0 1,342.0 ± 98.0 1,126.0 ± 90.0

Month 6 1,073.1 ± 52.7 998.0 ± 71.8 890.4 ± 74.0 978.6 ± 55.8 940.8 ± 39.5

Month 12 968.3 ± 61.6c 932.4 ± 57.4 987.0 ± 90.4 915.6 ± 44.8 828.3 ± 44.2c

Leukocytes (103/μL)

Day 22 5.10 ± 0.51 6.58 ± 0.35* 7.19 ± 0.49** 7.26 ± 0.57* 7.89 ± 0.39**

Month 3 4.46 ± 0.24 4.48 ± 0.33 5.05 ± 0.30 5.32 ± 0.36 4.74 ± 0.48

Month 6 6.49 ± 0.42 5.69 ± 0.22 6.25 ± 0.51 6.62 ± 0.54 5.30 ± 0.33

Month 12 5.86 ± 0.51 4.84 ± 0.28 5.64 ± 0.35 5.67 ± 0.53 5.12 ± 0.40

Segmented neutrophils (103/μL) 

Day 22 0.48 ± 0.06 0.60 ± 0.03 0.63 ± 0.06 0.75 ± 0.11* 0.83 ± 0.07**

Month 3 0.53 ± 0.04 0.47 ± 0.07 0.60 ± 0.05 0.66 ± 0.05 0.53 ± 0.05

Month 6 0.85 ± 0.08 0.72 ± 0.04 0.80 ± 0.08 0.89 ± 0.07 0.75 ± 0.10

Month 12 1.06 ± 0.11 0.88 ± 0.08 1.03 ± 0.06 0.93 ± 0.07 0.73 ± 0.05**

Lymphocytes (103/μL)

Day 22 4.36 ± 0.44 5.66 ± 0.32* 6.22 ± 0.41** 6.17 ± 0.46** 6.61 ± 0.33**

Month 3 3.67 ± 0.21 3.68 ± 0.24 4.09 ± 0.28 4.32 ± 0.32 3.85 ± 0.43

Month 6 5.17 ± 0.34 4.61 ± 0.17 4.96 ± 0.42 5.22 ± 0.44 4.14 ± 0.23

Month 12 4.42 ± 0.40 3.62 ± 0.22 4.14 ± 0.33 4.30 ± 0.45 4.05 ± 0.32

Activated lymphocytes (103/μL)

Day 22 0.02 ± 0.00 0.03 ± 0.00 0.03 ± 0.00 0.03 ± 0.00 0.04 ± 0.00**

Month 3 0.02 ± 0.00 0.02 ± 0.00 0.02 ± 0.00 0.02 ± 0.00 0.02 ± 0.00

Month 6 0.03 ± 0.01 0.03 ± 0.00 0.04 ± 0.01 0.04 ± 0.01 0.02 ± 0.00

Month 12 0.03 ± 0.01 0.02 ± 0.00 0.03 ± 0.01 0.02 ± 0.01 0.02 ± 0.00*

Monocytes (103/μL) 

Day 22 0.08 ± 0.01 0.10 ± 0.01 0.10 ± 0.01 0.12 ± 0.01* 0.16 ± 0.01**

Month 3 0.10 ± 0.01 0.08 ± 0.01 0.09 ± 0.01 0.08 ± 0.00 0.09 ± 0.01

Month 6 0.22 ± 0.02 0.16 ± 0.02 0.18 ± 0.02 0.22 ± 0.02 0.16 ± 0.02

Month 12 0.22 ± 0.02 0.19 ± 0.02 0.25 ± 0.02 0.23 ± 0.03 0.17 ± 0.02 

Basophils (103/μL)

Day 22 0.014 ± 0.003 0.017 ± 0.002 0.023 ± 0.003 0.019 ± 0.002 0.031 ± 0.005**

Month 3 0.024 ± 0.004 0.022 ± 0.003 0.023 ± 0.004 0.022 ± 0.004 0.024 ± 0.003

Month 6 0.015 ± 0.002 0.015 ± 0.003 0.035 ± 0.009 0.021 ± 0.006 0.016 ± 0.003

Month 12 0.016 ± 0.003 0.016 ± 0.003 0.028 ± 0.007 0.031 ± 0.007 0.020 ± 0.003
Sodium Dichromate Dihydrate, NTP TR 546 155

Table E2

Hematology Data for Female Mice in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n

Day 22 10 10 10 10 10

Month 3 10 10 10 10 10

Month 6 10 10 10 10 10

Month 12 10 10 9 10 10

Eosinophils (103/μL)

Day 22 0.15 ± 0.02 0.18 ± 0.02 0.18 ± 0.02 0.18 ± 0.02 0.22 ± 0.03

Month 3 0.12 ± 0.02 0.21 ± 0.04 0.23 ± 0.04* 0.21 ± 0.02* 0.23 ± 0.03**

Month 6 0.20 ± 0.05 0.16 ± 0.03 0.23 ± 0.04 0.23 ± 0.05 0.21 ± 0.04

Month 12 0.12 ± 0.02 0.11 ± 0.02 0.16 ± 0.03 0.16 ± 0.02 0.13 ± 0.02

* Significantly different (P#0.05) from the control group by Dunn’s or Shirley’s test

** P#0.01 a Mean ± standard error. Statistical tests were performed on unrounded data. b n=8 c n=9
156 Sodium Dichromate Dihydrate, NTP TR 546 
157

APPENDIX F

CHEMICAL CHARACTERIZATION

AND DOSE FORMULATION STUDIES

Procurement and Characterization of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . 158

Preparation and Analysis of Dose Formulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Figure F1 X-Ray Diffraction Diffractograms of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . 160

Figure F2 Proton-Induced X-Ray Emission Spectrum of Sodium Dichromate Dihydrate . . . . . . . . . . 160

Figure F3 Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry

Selected Ion-Current Profiles of Cr III and CR VI in Sodium Dichromate Dihydrate . . . 161

Table F1 Preparation and Storage of Dose Formulations in the 2-Year Drinking Water Studies 

of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Table F2 Results of Analyses of Dose Formulations Administered to Rats and Mice

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . 163
158

CHEMICAL CHARACTERIZATION

AND DOSE FORMULATION STUDIES

Procurement and Characterization of Sodium Dichromate Dihydrate

Sodium dichromate dihydrate was obtained from Aldrich Chemical Company (Milwaukee, WI) in two lots 

(15301BI and 13822LI). The two lots were combined at the analytical chemistry laboratory, Battelle Memorial 

Institute (Columbus, OH), and assigned a new lot number (062001). Lot 062001 was used in the 2-year studies. 

Identity and purity analyses were conducted by the analytical chemistry laboratory, the study laboratory (Southern 

Research Institute, Birmingham, AL), Galbraith Laboratories, Inc. (Knoxville, TN), and Elemental Analysis Corp. 

(Lexington, KY). Reports on analyses performed in support of the sodium dichromate dihydrate studies are on file 

at the National Institute of Environmental Health Sciences.

Lot 062001, an orange crystalline solid, was identified as sodium dichromate dihydrate by the analytical chemistry 

laboratory using X-ray diffraction (XRD), by the analytical chemistry laboratory and by Galbraith Laboratories, 

Inc., using elemental analysis by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and by 

Elemental Analysis Corp. using proton-induced X-ray emission spectroscopy (PIXE). The XRD powder patterns 

were consistent with a reference pattern (International Centre for Diffraction Data, 2000); XRD diffractograms 

are presented in Figure F1. Elemental analyses for chromium and sodium by ICP-AES were in agreement with 

the theoretical values for sodium dichromate dihydrate, and PIXE indicated the absence of significant metallic 

impurities. A PIXE spectrum is presented in Figure F2. 

The moisture content of lot 062001 was determined by Galbraith Laboratories, Inc., using Karl Fischer titration. 

The purity of lot 062001 was determined by the analytical chemistry laboratory using differential scanning 

calorimetry (DSC), titration of the dichromate ion with sodium thiosulfate and potassium ferrocyanide, and 

speciation of the chromium ions using liquid chromatography-inductively coupled plasma-mass spectrometry 

(LC-ICP-MS) and by the study laboratory using potentiometric titration with sodium thiosulfate. DSC was 

performed using a Perkin-Elmer DSC-7 scanning calorimeter from 342° to 365° C with a temperature increase 

of 1° C per minute under a nitrogen atmosphere. Titration with sodium thiosulfate was performed by titrating 

a solution of sodium dichromate dihydrate and potassium iodide in dilute hydrochloric acid with 0.1 N sodium 

thiosulfate using a double sheet platinum electrode and a Brinkman Metrohm titrator or its equivalent. Titration 

with potassium ferrocyanide was performed by titrating a solution of sodium dichromate dihydrate with 

0.1 N potassium ferrocyanide trihydrate as previously described. LC-ICP-MS was conducted using system A. 

A) Hewlett-Packard (Palo Alto, CA) 1100 series high performance liquid chromatography system, a 

 Dionex Corp. (Sunnyvale, CA) IonPac® AS7 ion exchange column (250 mm × 4 mm), with an 

 isocratic mobile phase of 35 mM ammonium sulfate adjusted to pH 9.2 with ammonium hydroxide at 

 a flow rate of 1 mL/minute and ICP-MS detection

Karl Fischer titration indicated a water content of 11.62%, which is in agreement with the theoretical value of 

12.09%. DSC indicated a purity of 99.73% ± 0.15%. Titration with sodium thiosulfate by the analytical chemistry 

laboratory indicated a purity of 99.7% ± 0.1%. Titration with sodium thiosulfate by the study laboratory indicated 

purities of 101% and 102% relative to a frozen reference standard of the same lot. Titration with potassium 

ferrocyanide indicated a purity of 103.1% ± 0.2%. LC-ICP-MS indicated that the concentration of Cr III, if 

present, was less than 0.1%. Representative LC-ICP-MS spectra are presented in Figure F3. The overall purity of 

lot 062001 was determined to be greater than 99.7%.

To ensure stability, the bulk chemical was stored at room temperature, protected from light in amber glass bottles. 

Periodic reanalyses of the bulk chemical were performed by the study laboratory using potentiometric titration as 

described for the purity assays; no degradation of the bulk chemical was detected. 

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 159

Preparation and Analysis of Dose Formulations

The dose formulations were prepared approximately every 2 weeks by mixing sodium dichromate dihydrate with 

tap water (Table F1). Formulations were stored in NALGENE® containers at room temperature for up to 42 days.

Because all dose formulations in these studies were determined to be solutions, no homogeneity studies were 

required. Stability studies of a 41.8 μg/mL dose formulation were performed by the analytical chemistry 

laboratory using ion chromatography by system B. Stability was confirmed for at least 42 days for dose 

formulations stored in sealed NALGENE® containers, protected from light, at temperatures up to room temperature 

and for at least 7 days when stored in drinking water bottles under simulated animal room conditions.

B) Dionex Corp. IonPac® AS7 ion exchange column (250 mm × 4 mm), using an 

 isocratic mobile phase of 250 mM ammonium sulfate and 100 mM ammonium hydroxide at a flow rate of

 1 mL/minute, with postcolumn derivitization using 2 mM 1,5-diphenylcarbazide in

 methanol:water:concentrated sulfuric acid (100:872:28) at a flow rate of 0.5 mL/minute and visible light

 (520 nm) detection

Periodic analyses of the dose formulations of sodium dichromate dihydrate were conducted by the study laboratory 

using ultraviolet/visible/near infrared spectroscopy (350 to 390 nm). The dose formulations were analyzed 

approximately every 10 weeks (Table F2). Of the dose formulations analyzed, all 44 for rats and all 84 for mice 

were within 10% of the target concentrations. Animal room samples and unused carboy storage samples of these 

dose formulations were also analyzed; all 16 animal room samples for rats and 34 of 35 animal room samples for 

mice were within 10% of the target concentrations. Fourteen of 16 carboy samples for rats and 33 of 35 carboy 

samples for mice were within 10% of the target concentrations. 

The sodium dichromate dihydrate dosed water used in these studies was slightly acidic. Based on an equilibrium 

constant of 50, dichromate predominates at the highest exposure concentration and the chromate:dichromate ratio 

approaches 1 at the lowest exposure concentration.
160 Sodium Dichromate Dihydrate, NTP TR 546 

Figure F1

X-Ray Diffraction Diffractograms of Sodium Dichromate Dihydrate 

Upper plot: lot 062001. Lower plot: reference sample

Figure F2

Proton-Induced X-Ray Emission Spectrum of Sodium Dichromate Dihydrate
Sodium Dichromate Dihydrate, NTP TR 546 161

Figure F3

Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry

Selected Ion-Current Profiles of Cr III and Cr VI in Sodium Dichromate Dihydrate
162 Sodium Dichromate Dihydrate, NTP TR 546 

Table F1

Preparation and Storage of Dose Formulations in the 2-Year Drinking Water Studies

of Sodium Dichromate Dihydrate

Preparation

A premix was prepared in a beaker with tap water and then thoroughly mixed with additional tap water in a mixing tank. The dose 

formulations were prepared approximately every 2 weeks.

Chemical Lot Number

062001

Maximum Storage Time

42 days

Storage Conditions

Stored in NALGENE® containers at room temperature and protected from light

Study Laboratory

Southern Research Institute (Birmingham, AL)
Sodium Dichromate Dihydrate, NTP TR 546 163

Table F2 

Results of Analyses of Dose Formulations Administered to Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate

Target Determined Difference

Date Prepared Date Analyzed Concentration Concentrationa from Target

(mg/L) (mg/L) (%)

Rats

September 18, 2002 September 19, 2002 14.3 14.0 –2

57.3 59.8 +4

172 172 0

516 517 0

October 16, 2002b 14.3 14.0 –2

57.3 60.8 +6

172 177 +3

516 529 +3

October 16, 2002c 14.3 14.7 +3

57.3 61.7 +8

172 179 +4

516 531 +3

November 27, 2002 December 2, 2002 14.3 14.4 +1

57.3 59.5 +4

172 175 +2

516 521 +1

February 5, 2003 February 6 and 10, 2003 14.3 15.3 +7

57.3 60.3 +5

172 189 +10

516 523 +1

April 18, 2003 April 21, 2003 14.3 14.6 +2

57.3 59.7 +4

172 174 +1

516 526 +2

May 14, 2003b 14.3 13.3 –7

57.3 59.7 +4

172 177 +3

516 522 +1

May 14, 2003c 14.3 15.0 +5

57.3 62.0 +8

172 191 +11

516 520 +1

June 27, 2003 June 30, 2003 14.3 15.0 +5

57.3 59.4 +4

172 175 +2

516 519 +1

September 5, 2003 September 8, 2003 14.3 14.8 +3

57.3 59.8 +4

172 175 +2

516 520 +1
164 Sodium Dichromate Dihydrate, NTP TR 546 

Table F2 

Results of Analyses of Dose Formulations Administered to Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate

Target Determined Difference

Date Prepared Date Analyzed Concentration Concentration from Target

(mg/L) (mg/L) (%)

Rats (continued)

November 14, 2003 November 17, 2003 14.3 14.0 –2

57.3 58.0 +1

172 171 –1

516 515 0

December 10, 2003b 14.3 14.4 +1

57.3 57.5 0

172 175 +2

516 513 –1

December 10, 2003c 14.3 14.8 +3

57.3 57.6 +1

172 173 +1

516 523 +1

January 23, 2004 January 26, 2004 14.3 15.6 +9

57.3 59.2 +3

172 173 +1

516 515 0

April 2, 2004 April 5, 2004 14.3 15.3 +7

57.3 59.6 +4

172 175 +2

516 521 +1

June 11, 2004 June 14, 2004 14.3 14.2 –1

57.3 59.7 +4

172 177 +3

516 529 +3

July 8, 2004b 14.3 14.6 +2

57.3 63.1 +10

172 185 +8

516 546 +6

July 8, 2004c 14.3 14.9 +4

57.3 65.6 +14

172 186 +8

516 550 +7

August 20, 2004 August 23, 2004 14.3 14.4 +1

57.3 58.9 +3

172 176 +2

516 526 +2
Sodium Dichromate Dihydrate, NTP TR 546 165

Table F2 

Results of Analyses of Dose Formulations Administered to Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate

Target Determined Difference

Date Prepared Date Analyzed Concentration Concentration from Target

(mg/L) (mg/L) (%)

Mice

August 20, 2002 August 22, 2002 14.3 14.4 +1

28.6 29.3 +2

57.3 57.3 0

85.7 87.9 +3

 172 169 –2

257.4 261 +1

516 517 0

September 19, 2002b 14.3 14.4 +1

28.6 29.0 +1

57.3 57.5 0

85.7 87.1 +2

 172 132 –23

257.4 265 +3

516 515 0

September 19, 2002c 14.3 14.3 0

28.6 29.1 +2

57.3 57.6 +1

85.7 87.3 +2

 172 169 –2

257.4 265 +3

516 517 0

September 18, 2002 September 19, 2002 14.3 14.0 –2

28.6 28.1 –2

57.3 59.8 +4

85.7 85.0 –1

 172 172 0

257.4 254 –1

516 517 0

October 16, 2002b 14.3 14.7 +3

28.6 29.2 +2

57.3 61.4 +7

85.7 88.6 +3

 172 177 +3

257.4 264 +3

516 524 +2

October 16, 2002c 14.3 14.7 +3

28.6 29.7 +4

57.3 61.7 +8

85.7 89.1 +4

 172 179 +4

257.4 264 +3

516 531 +3
166 Sodium Dichromate Dihydrate, NTP TR 546 

Table F2 

Results of Analyses of Dose Formulations Administered to Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate

Target Determined Difference

Date Prepared Date Analyzed Concentration Concentration from Target

(mg/L) (mg/L) (%)

Mice (continued)

November 27, 2002 December 2, 2002 14.3 14.4 +1

28.6 29.8 +4

57.3 59.5 +4

85.7 88.7 +4

 172 175 +2

257.4 266 +3

516 521 +1

February 5, 2003 February 6 and 10, 2003 14.3 15.3 +7

28.6 29.2 +2

57.3 60.3 +5

85.7 91.1 +6

 172 189 +10

257.4 268 +4

516 523 +1

April 18, 2003 April 21, 2003 14.3 14.6 +2

28.6 29.3 +2

57.3 59.7 +4

85.7 85.9 0

 172 174 +1

257.4 258 0

516 526 +2

May 14, 2003b 14.3 13.7 –4

28.6 29.4 +3

57.3 58.8 +3

85.7 88.6 +3

 172 177 +3

257.4 259 +1

516 518 0

May 14, 2003c 14.3 15.0 +5

28.6 30.1 +5

57.3 62.0 +8

85.7 89.2 +4

 172 191 +11

257.4 262 +2

516 520 +1

June 27, 2003 June 30, 2003 14.3 15.0 +5

28.6 28.8 +1

57.3 59.4 +4

85.7 88.2 +3

 172 175 +2

257.4 250 –3

516 519 +1
Table F2 

Results of Analyses of Dose Formulations Administered to Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate

Target Determined Difference

Date Prepared Date Analyzed Concentration Concentration from Target

(mg/L) (mg/L) (%)

Mice (continued)

September 5, 2003 September 8, 2003 14.3 14.8 +3

28.6 28.5 0

57.3 59.8 +4

85.7 86.0 0

 172 175 +2

257.4 258 0

516 520 +1

November 14, 2003 November 17, 2003 14.3 14.0 –2

28.6 28.8 +1

57.3 58.0 +1

85.7 82.9 –3

 172 171 –1

257.4 255 –1

516 515 0

December 10, 2003b 14.3 14.7 +3

28.6 29.5 +3

57.3 57.7 +1

85.7 85.8 0

 172 177 +3

257.4 256 –1

516 511 –1

December 10, 2003c 14.3 14.8 +3

28.6 29.5 +3

57.3 57.6 +1

85.7 85.4 0

 172 173 +1

257.4 253 –2

516 523 +1

January 23, 2004 January 26, 2004 14.3 15.6 +9

28.6 30.0 +5

57.3 59.2 +3

85.7 90.9 +6

 172 173 +1

257.4 257 0

516 515 0

April 2, 2004 April 5, 2004 14.3 15.3 +7

28.6 28.9 +1

57.3 59.6 +4

85.7 87.9 +3

 172 175 +2

257.4 256 –1

516 521 +1

Sodium Dichromate Dihydrate, NTP TR 546 167
168 Sodium Dichromate Dihydrate, NTP TR 546 

Table F2 

Results of Analyses of Dose Formulations Administered to Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate

Target Determined Difference

Date Prepared Date Analyzed Concentration Concentration from Target

(mg/L) (mg/L) (%)

Mice (continued)

June 11, 2004 June 14, 2004 14.3 14.2 –1

28.6 28.9 +1

57.3 59.7 +4

85.7 85.8 0

 172 177 +3

257.4 261 +1

516 529 +3

July 8, 2004b 14.3 14.6 +2

28.6 30.8 +8

57.3 62.8 +10

85.7 92.2 +8

 172 185 +8

257.4 277 +8

516 546 +6

July 8, 2004c 14.3 14.9 +4

28.6 31.0 +8

57.3 65.6 +14

85.7 91.9 +7

 172 186 +8

257.4 275 +7

516 550 +7

August 20, 2004 August 23, 2004 14.3 14.4 +1

28.6 28.9 +1

57.3 58.9 +3

85.7 85.8 0

172 176 +2

257.4 254 –1

516 526 +2

a Results of duplicate analyses b Animal room samples from drinking water bottles c Unused samples from carboy storage containers
169

APPENDIX G

WATER AND COMPOUND CONSUMPTION

IN THE 2-YEAR DRINKING WATER STUDIES

OF SODIUM DICHROMATE DIHYDRATE

Table G1 Water and Compound Consumption by Male Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 170

Table G2 Water and Compound Consumption by Female Rats

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 172

Table G3 Water and Compound Consumption by Male Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 174

Table G4 Water and Compound Consumption by Female Mice

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 176
170

Table G1

Water and Compound Consumption by Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Weeks 0 mg/L 14.3 mg/L 57.3 mg/L

on Water Body Water Body Dose Water Body Dose

Study (g/day)a Weight (g/day) Weight (mg/kg)b (g/day) Weight (mg/kg)

 (g) (g) (g)

1 16.7 118 16.6 117 2.0 16.0 117 7.9

2 17.1 151 17.2 149 1.7 16.9 146 6.6

3 19.5 185 19.3 183 1.5 19.0 181 6.0

4 19.4 218 19.0 215 1.3 19.3 213 5.2

5 18.7 243 18.7 240 1.1 18.5 239 4.4

6 18.4 261 17.8 257 1.0 17.8 257 4.0

7 18.0 275 17.7 271 0.9 17.3 272 3.6

8 18.1 289 18.1 286 0.9 17.2 285 3.5

9 18.0 305 18.2 301 0.9 17.3 302 3.3

10 18.0 317 18.0 312 0.8 17.3 313 3.2

11 17.6 334 17.4 329 0.8 16.7 331 2.9

12 17.7 345 17.1 340 0.7 17.0 339 2.9

13 17.3 351 17.7 345 0.7 17.2 348 2.8

17 16.2 387 16.2 381 0.6 15.9 383 2.4

21 16.7 410 16.5 404 0.6 16.3 407 2.3

25 16.6 434 16.1 427 0.5 15.9 431 2.1

29 17.2 451 17.0 443 0.5 16.7 448 2.1

33 17.4 468 17.3 458 0.5 17.1 464 2.1

37 16.8 480 16.2 471 0.5 16.1 477 1.9

41 14.8 488 14.6 478 0.4 14.8 483 1.8

45 15.6 490 15.4 485 0.5 16.4 488 1.9

49 16.0 501 16.1 493 0.5 16.5 497 1.9

53 16.4 511 17.1 502 0.5 16.9 505 1.9

57 17.3 515 17.2 507 0.5 17.4 512 1.9

61 16.7 523 16.9 515 0.5 17.1 519 1.9

65 16.5 524 16.1 515 0.4 16.7 519 1.8

69 15.7 525 16.1 516 0.4 16.0 518 1.8

73 15.7 525 15.7 517 0.4 16.1 520 1.8

77 17.0 530 16.2 519 0.4 16.6 525 1.8

81 16.3 532 16.4 518 0.5 16.1 525 1.8

85 15.9 531 16.1 515 0.4 16.0 522 1.8

89 16.2 527 16.4 518 0.5 15.6 518 1.7

93 17.4 526 18.2 517 0.5 18.7 520 2.1

97 15.7 513 16.5 515 0.5 15.9 517 1.8

101 18.1 515 16.2 503 0.5 16.7 514 1.9

Mean for weeks

1-13 18.0 261 17.9 257 1.1 17.5 257 4.3

14-52 16.4 457 16.2 449 0.5 16.2 453 2.1

53-101 16.5 523 16.5 514 0.5 16.6 518 1.8

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 171

Table G1

Water and Compound Consumption by Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Weeks 172 mg/L 516 mg/L

on Water Body Dose Water Body Dose

Study (g/day) Weight (mg/kg) (g/day) Weight (mg/kg)

 (g) (g)

1 14.4 117 21.2 12.6 118 55.2

2 15.0 147 17.5 13.2 143 47.8

3 16.8 180 16.1 14.9 173 44.4

4 16.6 210 13.6 14.8 201 37.9

5 16.3 235 11.9 14.7 225 33.7

6 15.5 254 10.5 14.2 243 30.2

7 14.8 267 9.5 13.8 257 27.7

8 14.5 279 8.9 13.8 270 26.4

9 14.5 295 8.5 14.7 285 26.6

10 14.5 304 8.2 13.4 295 23.4

11 14.4 321 7.7 13.1 311 21.8

12 13.9 330 7.2 12.7 320 20.5

13 14.1 338 7.2 14.5 324 23.1

17 13.4 373 6.2 13.0 363 18.5

21 14.1 395 6.1 13.3 386 17.8

25 14.4 418 5.9 13.5 407 17.1

29 14.7 437 5.8 14.0 424 17.0

33 14.9 449 5.7 13.9 437 16.4

37 14.0 462 5.2 13.6 447 15.7

41 13.2 469 4.8 12.2 454 13.9

45 14.0 477 5.0 13.2 461 14.8

49 13.8 486 4.9 12.8 468 14.1

53 14.9 490 5.2 14.0 475 15.2

57 14.7 496 5.1 13.8 479 14.9

61 14.5 503 5.0 13.4 485 14.3

65 14.1 504 4.8 13.4 484 14.3

69 14.0 503 4.8 12.9 484 13.8

73 13.8 501 4.7 12.7 483 13.6

77 13.7 508 4.6 12.5 487 13.3

81 13.4 507 4.5 12.3 483 13.2

85 13.5 506 4.6 12.3 473 13.4

89 13.1 502 4.5 12.3 478 13.3

93 14.1 500 4.9 13.4 474 14.6

97 14.1 500 4.9 11.7 459 13.2

101 14.1 500 4.9 12.0 455 13.6

Mean for weeks

1-13 15.0 252 11.4 13.9 243 32.2

14-52 14.1 441 5.5 13.3 427 16.1

53-101 14.0 502 4.8 12.8 477 13.9

a Grams of drinking water consumed per animal per day b Milligrams of sodium dichromate dihydrate consumed per kilogram body weight per day
172

Table G2

Water and Compound Consumption by Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Weeks 0 mg/L 14.3 mg/L 57.3 mg/L

on Water Body Water Body Dose Water Body Dose

Study (g/day)a Weight (g/day) Weight (mg/kg)b (g/day) Weight (mg/kg)

 (g) (g) (g)

1 13.5 100 13.3 99 1.9 13.5 100 7.8

2 13.3 122 13.0 120 1.6 12.8 121 6.1

3 14.2 135 13.7 132 1.5 13.6 134 5.8

4 13.7 150 13.2 146 1.3 13.1 147 5.1

5 13.5 157 13.3 154 1.2 12.6 154 4.7

6 12.9 164 13.1 161 1.2 12.5 162 4.4

7 12.8 170 12.9 168 1.1 12.1 167 4.1

8 13.0 175 13.0 172 1.1 12.0 172 4.0

9 12.8 180 12.6 178 1.0 12.4 177 4.0

10 12.8 183 12.4 180 1.0 11.7 180 3.7

11 12.7 188 12.3 184 1.0 12.1 185 3.8

12 13.0 193 12.5 189 0.9 11.4 188 3.5

13 12.3 198 11.5 193 0.9 10.9 192 3.2

17 12.1 208 11.4 203 0.8 10.7 202 3.0

21 12.2 217 11.9 211 0.8 11.2 209 3.1

25 11.6 229 11.6 223 0.7 11.2 221 2.9

29 12.1 237 11.6 229 0.7 11.8 229 2.9

33 12.8 246 12.9 239 0.8 12.3 237 3.0

37 12.3 255 12.0 248 0.7 11.7 246 2.7

41 10.8 263 10.7 255 0.6 10.6 253 2.4

45 12.1 272 11.8 261 0.6 11.6 262 2.5

49 12.3 281 11.8 271 0.6 11.1 271 2.3

53 12.1 289 12.1 279 0.6 11.5 278 2.4

57 12.6 297 12.6 288 0.6 12.2 287 2.4

61 12.6 309 12.2 297 0.6 11.8 297 2.3

65 12.4 314 12.2 302 0.6 12.2 304 2.3

69 12.5 317 11.9 307 0.6 11.9 310 2.2

73 12.4 323 12.5 312 0.6 11.6 315 2.1

77 13.4 332 12.3 323 0.5 11.4 320 2.0

81 12.8 337 12.0 328 0.5 12.0 325 2.1

85 12.5 341 12.5 332 0.5 11.8 333 2.0

89 13.4 334 11.9 333 0.5 12.6 333 2.2

93 15.1 348 13.3 333 0.6 12.6 340 2.1

97 13.9 350 13.7 339 0.6 12.9 346 2.1

101 15.0 351 14.4 338 0.6 12.7 346 2.1

Mean for weeks

1-13 13.1 163 12.8 160 1.2 12.4 160 4.6

14-52 12.0 245 11.7 238 0.7 11.4 237 2.8

53-101 13.1 326 12.6 316 0.6 12.1 318 2.2

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 173

Table G2

Water and Compound Consumption by Female Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydrate

Weeks 172 mg/L 516 mg/L

on Water Body Dose Water Body Dose

Study (g/day) Weight (mg/kg) (g/day) Weight (mg/kg)

 (g) (g)

1 10.7 99 18.5 9.6 99 50.2

2 10.9 119 15.8 9.4 115 42.3

3 11.2 131 14.7 10.5 129 42.1

4 11.0 145 13.1 10.0 144 35.9

5 10.8 153 12.2 10.0 152 33.9

6 11.3 161 12.1 9.4 159 30.5

7 10.4 166 10.8 9.5 165 29.7

8 10.0 171 10.1 9.3 170 28.3

9 10.0 175 9.8 9.5 175 28.1

10 10.0 178 9.7 9.2 178 26.7

11 10.0 183 9.4 8.8 182 25.0

12 9.8 186 9.0 8.9 186 24.8

13 9.6 192 8.6 8.4 190 22.8

17 9.6 201 8.2 9.0 199 23.3

21 9.9 206 8.3 9.0 207 22.4

25 9.8 218 7.7 8.9 215 21.3

29 9.7 226 7.4 9.1 222 21.1

33 11.0 235 8.1 9.3 230 20.9

37 10.2 242 7.2 9.2 237 20.1

41 9.5 248 6.6 8.6 242 18.3

45 10.3 256 6.9 9.1 248 19.0

49 10.3 265 6.7 9.3 254 18.9

53 10.7 272 6.8 9.4 263 18.4

57 11.1 279 6.9 9.8 268 18.8

61 11.1 290 6.6 9.4 275 17.7

65 10.6 296 6.2 9.4 281 17.3

69 10.6 302 6.0 9.4 284 17.1

73 11.0 308 6.1 9.5 287 17.1

77 12.1 318 6.5 9.6 298 16.6

81 10.4 319 5.6 8.8 300 15.2

85 10.6 323 5.7 9.9 307 16.6

89 11.0 324 5.8 9.8 314 16.1

93 11.5 328 6.0 10.0 315 16.4

97 11.6 337 5.9 9.7 318 15.7

101 11.5 340 5.8 9.8 312 16.2

Mean for weeks

1-13 10.4 158 11.8 9.4 157 32.3

14-52 10.0 233 7.5 9.1 228 20.6

53-101 11.1 310 6.1 9.6 294 16.9

a Grams of drinking water consumed per animal per day b Milligrams of sodium dichromate dihydrate consumed per kilogram body weight per day
174

Table G3

Water and Compound Consumption by Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

Weeks 0 mg/L 14.3 mg/L 28.6 mg/L

on Water Body Water Body Dose Water Body Dose

Study (g/day)a Weight (g/day) Weight (mg/kg)b (g/day) Weight (mg/kg)

 (g) (g) (g)

1 3.9 23.2 4.0 23.2 3 4.3 23.5 5

2 4.0 25.3 3.9 25.3 2 4.0 25.7 5

3 3.8 26.8 3.9 26.9 2 3.8 27.1 4

4 3.8 28.0 3.7 28.2 2 3.9 28.5 4

5 3.9 29.9 4.0 30.0 2 3.8 30.3 4

6 3.7 31.5 3.7 31.5 2 3.8 31.9 3

7 3.7 32.9 3.8 33.0 2 3.7 33.4 3

8 3.6 34.2 3.6 34.5 2 3.6 34.8 3

9 3.5 35.9 3.5 36.3 1 3.6 36.6 3

10 3.3 37.5 3.4 37.8 1 3.4 38.2 3

11 3.4 38.9 3.4 39.4 1 3.4 39.9 2

12 3.3 40.2 3.5 40.6 1 3.4 41.2 2

13 3.3 41.7 3.4 41.8 1 3.5 42.4 2

17 3.1 46.7 3.3 46.5 1 3.3 47.2 2

21 3.4 48.9 3.6 48.7 1 3.6 49.2 2

25 3.7 50.1 3.8 49.9 1 3.9 50.2 2

29 3.9 51.4 4.3 51.8 1 4.1 51.8 2

33 3.9 52.2 4.1 52.6 1 4.2 52.5 2

37 4.0 52.7 4.2 52.7 1 4.6 52.7 3

41 4.2 53.8 4.4 53.8 1 4.6 53.7 3

45 4.2 53.8 4.4 53.6 1 4.7 53.9 3

49 4.2 54.5 4.6 54.6 1 4.6 54.7 2

53 4.4 55.2 4.4 55.0 1 4.6 55.0 2

57 4.3 55.5 4.7 55.2 1 4.7 55.2 2

61 4.9 55.1 4.9 54.9 1 5.0 54.1 3

65 4.8 55.3 4.8 55.0 1 4.8 54.4 3

69 5.4 55.6 5.2 55.2 1 5.0 54.2 3

73 5.1 55.1 5.1 53.7 1 5.1 53.6 3

77 5.0 54.0 4.9 52.6 1 5.0 52.9 3

81 4.9 54.3 5.0 52.5 1 4.9 53.1 3

85 4.7 53.0 4.7 52.1 1 4.6 52.3 3

89 4.6 52.0 4.5 51.6 1 4.6 50.7 3

93 4.7 51.7 4.6 50.0 1 4.8 49.3 3

97 4.7 51.7 4.9 50.5 1 5.1 48.8 3

101 4.5 50.3 5.0 49.9 1 4.9 46.9 3

Mean for weeks

1-13 3.6 32.8 3.7 33.0 2 3.7 33.3 3

14-52 3.8 51.6 4.1 51.6 1 4.2 51.8 2

53-101 4.8 53.8 4.8 52.9 1 4.9 52.3 3

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 175

Table G3

Water and Compound Consumption by Male Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

Weeks 85.7 mg/L 257.4 mg/L

on Water Body Dose Water Body Dose

Study (g/day) Weight (mg/kg) (g/day) Weight (mg/kg)

 (g) (g)

1 3.7 23.2 14 2.7 23.2 30

2 3.5 25.2 12 2.7 24.4 29

3 3.5 26.6 11 2.5 25.4 25

4 3.5 27.8 11 2.5 26.3 25

5 3.5 29.5 10 2.6 27.5 24

6 3.5 31.0 10 2.6 28.6 23

7 3.6 32.1 10 2.5 29.5 22

8 3.5 33.6 9 2.5 30.4 21

9 3.5 35.0 9 2.4 31.4 20

10 3.3 36.5 8 2.5 32.2 20

11 3.3 37.9 8 2.4 33.3 19

12 3.2 39.1 7 2.5 34.4 19

13 3.1 40.4 7 2.4 35.2 18

17 3.1 45.1 6 2.4 38.9 16

21 3.4 47.9 6 2.7 42.2 17

25 3.3 49.5 6 2.5 44.5 15

29 3.7 51.6 6 2.7 47.4 15

33 3.7 51.8 6 2.5 48.3 13

37 3.8 52.4 6 2.7 48.9 14

41 3.9 53.3 6 2.7 49.7 14

45 3.9 53.5 6 2.6 49.9 13

49 4.0 54.4 6 2.7 50.4 14

53 3.9 54.4 6 2.7 50.8 14

57 4.0 55.0 6 2.8 50.9 14

61 4.1 54.6 6 2.8 50.8 14

65 4.2 55.1 7 2.9 50.8 15

69 4.3 55.1 7 3.1 50.9 16

73 4.4 54.4 7 3.1 50.3 16

77 4.2 53.8 7 3.3 49.9 17

81 4.2 52.8 7 3.2 49.8 17

85 3.9 52.1 6 3.3 48.8 17

89 3.8 51.3 6 3.1 49.3 16

93 4.1 49.0 7 3.1 49.3 16

97 4.3 48.6 8 3.3 48.1 18

101 4.3 48.4 8 3.5 47.2 19

Mean for weeks

1-13 3.4 32.1 10 2.5 29.4 23

14-52 3.6 51.1 6 2.6 46.7 15

53-101 4.1 52.7 7 3.1 49.8 16

a Grams of drinking water consumed per animal per day b Milligrams of sodium dichromate dihydrate consumed per kilogram body weight per day
176

Table G4

Water and Compound Consumption by Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

Weeks 0 mg/L 14.3 mg/L 57.3 mg/L

on Water Body Water Body Dose Water Body Dose

Study (g/day)a Weight (g/day) Weight (mg/kg)b (g/day) Weight (mg/kg)

 (g) (g) (g)

1 2.9 17.8 2.9 17.5 2 2.8 17.4 9

2 3.0 19.2 3.0 19.2 2 2.8 19.0 8

3 3.2 20.6 3.1 20.6 2 2.8 20.3 8

4 3.1 21.3 3.2 21.4 2 2.9 21.0 8

5 3.3 22.5 3.2 22.3 2 3.0 21.8 8

6 3.1 23.2 3.2 23.2 2 2.9 22.7 7

7 3.5 24.4 3.3 24.4 2 3.0 23.8 7

8 3.1 26.0 3.2 25.4 2 3.1 24.8 7

9 3.2 26.9 3.3 26.4 2 3.2 25.4 7

10 3.1 27.9 3.3 27.4 2 2.9 26.2 6

11 3.1 28.9 3.3 28.3 2 3.3 27.1 7

12 3.2 30.3 3.3 29.7 2 3.4 28.6 7

13 3.1 31.2 3.1 31.0 1 3.0 29.7 6

17 2.8 37.0 3.0 36.9 1 3.0 34.4 5

21 2.6 41.5 2.6 41.3 1 2.6 38.5 4

25 2.3 44.8 2.5 44.9 1 2.8 41.9 4

29 2.6 48.7 2.5 48.2 1 2.6 46.5 3

33 2.6 51.6 2.5 51.7 1 2.5 48.8 3

37 2.5 53.3 2.8 53.6 1 2.5 50.6 3

41 2.8 55.2 2.8 55.6 1 2.3 52.5 3

45 2.4 59.0 2.5 57.9 1 2.3 55.1 2

49 2.7 59.8 2.7 59.0 1 2.8 56.7 3

53 2.6 62.1 2.5 62.1 1 2.3 60.0 2

57 2.6 61.5 2.6 60.9 1 2.4 59.0 2

61 2.5 62.2 2.5 62.5 1 2.4 60.1 2

65 2.6 63.1 2.6 62.8 1 2.4 61.6 2

69 2.6 64.3 2.6 64.8 1 2.4 62.7 2

73 2.9 63.9 2.7 65.0 1 2.4 62.4 2

77 2.5 62.7 2.4 64.0 1 2.2 61.6 2

81 2.9 61.8 2.6 62.9 1 2.3 60.8 2

85 2.4 61.3 2.5 62.7 1 2.7 59.8 3

89 2.7 60.3 2.7 62.1 1 2.3 59.7 2

93 2.9 60.6 3.0 61.1 1 2.4 58.5 2

97 3.5 59.1 3.5 60.2 1 2.7 58.1 3

101 3.1 60.6 3.6 60.7 1 2.6 58.1 3

Mean for weeks

1-13 3.1 24.6 3.2 24.4 2 3.0 23.7 7

14-52 2.6 50.1 2.7 49.9 1 2.6 47.2 3

53-101 2.8 61.8 2.8 62.4 1 2.4 60.2 2

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 177

Table G4

Water and Compound Consumption by Female Mice in the 2-Year Drinking Water Study

of Sodium Dichromate Dihydrate

Weeks 172 mg/L 516 mg/L

on Water Body Dose Water Body Dose

Study (g/day) Weight (mg/kg) (g/day) Weight (mg/kg)

 (g) (g)

1 2.5 17.7 24 1.6 17.5 47

2 2.2 19.1 20 1.7 18.4 48

3 2.2 20.2 19 1.6 19.3 43

4 2.2 20.8 18 1.8 19.9 47

5 2.6 21.5 21 1.7 20.8 42

6 2.3 22.4 18 1.7 21.3 41

7 2.8 23.1 21 2.0 22.3 46

8 2.6 23.9 19 1.9 23.3 42

9 2.4 24.6 17 1.9 23.8 41

10 2.5 25.2 17 1.9 24.6 40

11 2.4 25.8 16 1.9 24.7 40

12 2.5 26.8 16 1.9 25.5 39

13 2.5 27.5 16 1.9 26.2 37

17 2.3 31.4 13 1.9 28.6 34

21 3.0 35.1 15 1.9 30.8 32

25 2.2 37.6 10 1.8 32.8 28

29 2.4 41.5 10 1.9 36.0 27

33 2.2 43.7 9 2.0 37.5 28

37 2.2 45.5 8 1.9 38.9 25

41 2.3 47.8 8 2.0 41.0 25

45 2.1 50.4 7 1.8 43.9 21

49 2.3 52.7 8 1.9 45.4 22

53 2.0 55.4 6 1.9 48.1 20

57 2.1 55.8 7 1.9 48.4 20

61 2.1 57.1 6 1.9 49.2 20

65 2.1 57.7 6 1.9 50.0 20

69 2.0 59.1 6 2.0 51.9 20

73 2.0 58.4 6 1.8 51.9 18

77 1.9 57.7 6 2.0 51.9 20

81 2.1 57.6 6 1.8 51.8 18

85 2.0 57.1 6 1.7 51.2 17

89 2.0 57.5 6 1.8 51.6 18

93 2.0 56.0 6 1.9 50.3 20

97 2.4 56.1 7 2.2 50.8 22

101 2.2 55.8 7 2.0 51.4 20

Mean for weeks

1-13 2.4 23.0 19 1.8 22.1 43

14-52 2.3 42.9 10 1.9 37.2 27

53-101 2.1 57.0 6 1.9 50.7 19

a Grams of drinking water consumed per animal per day b Milligrams of sodium dichromate dihydrate consumed per kilogram body weight per day
178 Sodium Dichromate Dihydrate, NTP TR 546 
179

APPENDIX H

INGREDIENTS, NUTRIENT COMPOSITION,

AND CONTAMINANT LEVELS

IN NTP-2000 RAT AND MOUSE RATION

Table H1 Ingredients of NTP-2000 Rat and Mouse Ration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Table H2 Vitamins and Minerals in NTP-2000 Rat and Mouse Ration . . . . . . . . . . . . . . . . . . . . . . . . . 180

Table H3 Nutrient Composition of NTP-2000 Rat and Mouse Ration . . . . . . . . . . . . . . . . . . . . . . . . . . 181

Table H4 Contaminant Levels in NTP-2000 Rat and Mouse Ration . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
180

Table H1

Ingredients of NTP-2000 Rat and Mouse Ration

Ingredients Percent by Weight

Ground hard winter wheat 22.26

Ground #2 yellow shelled corn 22.18

Wheat middlings 15.0

Oat hulls 8.5

Alfalfa meal (dehydrated, 17% protein) 7.5

Purified cellulose 5.5

Soybean meal (49% protein) 5.0

Fish meal (60% protein) 4.0

Corn oil (without preservatives) 3.0

Soy oil (without preservatives) 3.0

Dried brewer’s yeast 1.0

Calcium carbonate (USP) 0.9

Vitamin premixa 0.5

Mineral premixb 0.5

Calcium phosphate, dibasic (USP) 0.4

Sodium chloride 0.3

Choline chloride (70% choline) 0.26

Methionine 0.2

a Wheat middlings as carrier b Calcium carbonate as carrier

Table H2

Vitamins and Minerals in NTP-2000 Rat and Mouse Rationa

Amount Source

Vitamins

A 4,000 IU Stabilized vitamin A palmitate or acetate

D 1,000 IU D-activated animal sterol

K 1.0 mg Menadione sodium bisulfite complex

“-Tocopheryl acetate 100 IU

Niacin 23 mg

Folic acid 1.1 mg

d-Pantothenic acid 10 mg d-Calcium pantothenate

Riboflavin 3.3 mg

Thiamine 4 mg Thiamine mononitrate

B12 52 μg

Pyridoxine 6.3 mg Pyridoxine hydrochloride

Biotin 0.2 mg d-Biotin

Minerals

Magnesium 514 mg Magnesium oxide

Iron 35 mg Iron sulfate

Zinc 12 mg Zinc oxide

Manganese 10 mg Manganese oxide

Copper 2.0 mg Copper sulfate

Iodine 0.2 mg Calcium iodate

Chromium 0.2 mg Chromium acetate

a Per kg of finished product

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 181

Table H3

Nutrient Composition of NTP-2000 Rat and Mouse Ration

Mean ± Standard

Nutrient Deviation Range Number of Samples

Protein (% by weight) 14.8 ± 0.45 13.8 – 15.8 26

Crude fat (% by weight) 8.1 ± 0.35 7.4 – 9.0 26

Crude fiber (% by weight) 9.1 ± 0.45 8.2 – 9.9 26

Ash (% by weight) 5.0 ± 0.24 4.4 – 5.6 26

Amino Acids (% of total diet)

Arginine 0.750 ± 0.048 0.670 – 0.850 15

Cystine 0.225 ± 0.025 0.150 – 0.250 15

Glycine 0.701 ± 0.039 0.620 – 0.750 15

Histidine 0.365 ± 0.090 0.310 – 0.680 15

Isoleucine 0.533 ± 0.038 0.430 – 0.590 15

Leucine 1.077 ± 0.059 0.960 – 1.150 15

Lysine 0.703 ± 0.125 0.310 – 0.830 15

Methionine 0.402 ± 0.049 0.260 – 0.460 15

Phenylalanine 0.615 ± 0.035 0.540 – 0.660 15

Threonine 0.492 ± 0.040 0.430 – 0.590 15

Tryptophan 0.135 ± 0.018 0.110 – 0.160 15

Tyrosine 0.378 ± 0.048 0.280 – 0.460 15

Valine 0.658 ± 0.043 0.550 – 0.710 15

Essential Fatty Acids (% of total diet)

Linoleic 3.90 ± 0.256 3.49 – 4.54 15

Linolenic 0.30 ± 0.035 0.21 – 0.35 15

Vitamins

Vitamin A (IU/kg) 5,031 ± 115 3,400 – 8,900 26

Vitamin D (IU/kg) 1,000a

“-Tocopherol (ppm) 84.2 ± 16.60 52.0 – 110.0 15

Thiamine (ppm)b 8.7 ± 3.58 5.9 – 25.2 26

Riboflavin (ppm) 6.8 ± 2.11 4.20 – 11.20 15

Niacin (ppm) 79.0 ± 10.50 66.4 – 98.2 15

Pantothenic acid (ppm) 23.9 ± 3.73 17.4 – 29.8 15

Pyridoxine (ppm)b 9.21 ± 2.20 6.4 – 13.7 15

Folic acid (ppm) 1.75 ± 0.54 1.20 – 3.27 15

Biotin (ppm) 0.332 ± 0.12 0.225 – 0.704 15

Vitamin B12 (ppb) 60.5 ± 46.5 18.3 – 174.0 15

Choline (ppm)b 3,064 ± 270 2,700 – 3,790 15

Minerals

Calcium (%) 0.964 ± 0.047 0.873 – 1.050 26

Phosphorus (%) 0.585 ± 0.027 0.538 – 0.641 26

Potassium (%) 0.665 ± 0.023 0.626 – 0.694 15

Chloride (%) 0.376 ± 0.041 0.300 – 0.474 15

Sodium (%) 0.191 ± 0.017 0.160 – 0.222 15

Magnesium (%) 0.201 ± 0.009 0.185 – 0.217 15

Sulfur (%) 0.170 ± 0.029 0.116 – 0.209 15

Iron (ppm) 182 ± 46.7 135 – 311 15

Manganese (ppm) 54.1 ± 7.89 42.1 – 73.1 15

Zinc (ppm) 55.0 ± 9.55 43.3 – 78.5 15

Copper (ppm) 6.65 ± 1.790 3.21 – 10.50 15

Iodine (ppm) 0.512 ± 0.221 0.233 – 0.972 15

Chromium (ppm) 0.604 ± 0.253 0.330 – 1.380 14

Cobalt (ppm) 0.25 ± 0.074 0.20 – 0.47 14

a From formulation b As hydrochloride (thiamine and pyridoxine) or chloride (choline)
182

Table H4

Contaminant Levels in NTP-2000 Rat and Mouse Rationa

 Mean ± Standard

 Deviationb Range Number of Samples

Contaminants

Arsenic (ppm) 0.38 ± 0.158 0.14 – 0.50 26

Cadmium (ppm) 0.07 ± 0.022 0.04 – 0.10 26

Lead (ppm) 0.08 ± 0.031 0.05 – 0.17 26

Mercury (ppm) <0.02 26

Selenium (ppm) 0.19 ± 0.027 0.14 – 0.23 26

Aflatoxins (ppb) <5.00 26

Nitrate nitrogen (ppm)c 15.2 ± 4.09 10.0 – 24.4 26

Nitrite nitrogen (ppm)c <0.61 26

BHA (ppm)d <1.0 26

BHT (ppm)d <1.0 26

Aerobic plate count (CFU/g) 25 ± 68 10 – 360 26

Coliform (MPN/g) 0.3 ± 0.0 3.0 – 3.0 26

Escherichia coli (MPN/g) <10 26

Salmonella (MPN/g) Negative 26

Total nitrosoamines (ppb)e 4.3 ± 1.93 2.3 – 8.5 26

N-Nitrosodimethylamine (ppb)e 2.6 ± 1.68 1.1 – 6.9 26

N-Nitrosopyrrolidine (ppb)e 1.7 ± 0.74 0.9 – 4.1 26

Pesticides (ppm)

“-BHC <0.01 26

$-BHC <0.02 26

(-BHC <0.01 26

*-BHC <0.01 26

Heptachlor <0.01 26

Aldrin <0.01 26

Heptachlor epoxide <0.01 26

DDE <0.01 26

DDD <0.01 26

DDT <0.01 26

HCB <0.01 26

Mirex <0.01 26

Methoxychlor <0.05 26

Dieldrin <0.01 26

Endrin <0.01 26

Telodrin <0.01 26

Chlordane <0.05 26

Toxaphene <0.10 26

Estimated PCBs <0.20 26

Ronnel <0.01 26

Ethion <0.02 26

Trithion <0.05 26

Diazinon <0.10 26

Methyl chlorpyrifos 0.082 ± 0.069 0.020 – 0.259 26

Methyl parathion <0.02 26

Ethyl parathion <0.02 26

Malathion 0.284 ± 0.477 0.020 – 1.850 26

Endosulfan I <0.01 26

Endosulfan II <0.01 26

Endosulfan sulfate <0.03 26

a All samples were irradiated. CFU=colony-forming units; MPN=most probable number; BHC=hexachlorocyclohexane or 

benzene hexachloride b For values less than the limit of detection, the detection limit is given as the mean. c Sources of contamination: alfalfa, grains, and fish meal d Sources of contamination: soy oil and fish meal e All values were corrected for percent recovery.

Sodium Dichromate Dihydrate, NTP TR 546 
183

APPENDIX I

SENTINEL ANIMAL PROGRAM

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Table I1 Murine Virus Antibody Determinations for Rats and Mice 

in the 2-Year Drinking Water Studies of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . 185
184

SENTINEL ANIMAL PROGRAM

Methods

Rodents used in the Carcinogenesis Program of the National Toxicology Program are produced in optimally clean 

facilities to eliminate potential pathogens that may affect study results. The Sentinel Animal Program is part of 

the periodic monitoring of animal health that occurs during the toxicologic evaluation of chemical compounds. 

Under this program, the disease state of the rodents is monitored via serology on sera from extra (sentinel) animals 

in the study rooms. These animals and the study animals are subject to identical environmental conditions. The 

sentinel animals come from the same production source and weanling groups as the animals used for the studies of 

chemical compounds.

During the 2-year study, serum samples were collected from five or six male and five female sentinel rats and mice 

at 6, 12, and 18 months; from five male and five female rats and five female mice in the 516 mg/L group at study 

termination; and from five male mice in the 257.4 mg/L group at study termination. In addition, serum samples 

were collected from six male and five female treated rats at 19 months, and fecal samples were collected from 

five male and five female mice at 18 months. Blood from each animal was collected and allowed to clot, and the 

serum was separated. The samples were processed appropriately and sent to BioReliance Corporation (Rockville, 

MD) for determination of antibody titers. The laboratory serology methods and viral agents for which testing was 

performed are tabulated below; the times at which blood was collected during the studies are also listed.

Method and Test Time of Analysis

Rats

ELISA

Mycoplasma arthritidis Study termination

Mycoplasma pulmonis Study termination

PVM (pneumonia virus of mice) 6, 12, and 18 months, study termination

RCV/SDA

 (rat coronavirus/sialodacryoadenitis virus) 6, 12, and 18 months, study termination

Sendai 6, 12, 18, and 19 months, study termination

Immunofluorescence Assay

Parvovirus 6, 12, and 18 months, study termination

Sendai 18 and 19 months

Western Blot

Sendai 18 months

Sodium Dichromate Dihydrate, NTP TR 546 
Sodium Dichromate Dihydrate, NTP TR 546 185

Method and Test Time of Analysis

Mice

ELISA

Ectromelia virus 6, 12, and 18 months, study termination

EDIM (epizootic diarrhea of infant mice) 6, 12, and 18 months, study termination

GDVII (mouse encephalomyelitis virus) 6, 12, and 18 months, study termination

LCM (lymphocytic choriomeningitis virus) 6, 12, and 18 months, study termination

MMV (mouse minute virus) Study termination

Mouse adenoma virus-FL 6, 12, and 18 months, study termination

MHV (mouse hepatitis virus) 6, 12, and 18 months, study termination

M. arthritidis Study termination

M. pulmonis Study termination

Parvovirus Study termination

PVM 6, 12, and 18 months, study termination

Reovirus 3 6, 12, and 18 months, study termination

Sendai 6, 12, and 18 months, study termination

Immunofluorescence Assay

EDIM 12 months

Helicobacter bilis 18 months

Helicobacter hepaticus 18 months

MCMV (mouse cytomegalovirus) Study termination

Parvovirus 6, 12, and 18 months

PVM 18 months and study termination

Results of serology tests are presented in Table I1.

Table I1

Murine Virus Antibody Determinations for Rats and Mice in the 2-Year Drinking Water Studies 

of Sodium Dichromate Dihydrate

 Incidence of Antibody Positive Serologic

Interval in Sentinel Animals Reaction for

Rats

6 Months 0/10 None positive

12 Months 0/10 None positive

18 Months 1/11a Sendai

19 Months 0/11 None positive

Study termination 0/10 None positive

Mice

6 Months 0/10 None positive

12 Months 0/10 None positive

18 Months 0/10 None positive

Study termination 0/10 None positive

a Based on retesting of serum samples at 19 months, this most likely represents a false positive result in one rat. There was no evidence of 

 infection by a viral organism in these animals.
186 Sodium Dichromate Dihydrate, NTP TR 546 
187

APPENDIX J

CHROMIUM TISSUE DISTRIBUTION STUDY

Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

Table J1 Tissue Concentrations and Excreta Content of Chromium in Male Rats 

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 190

Table J2 Tissue Concentrations and Excreta Content of Chromium in Female Mice 

in the 2-Year Drinking Water Study of Sodium Dichromate Dihydrate . . . . . . . . . . . . . . . 191
188 Sodium Dichromate Dihydrate, NTP TR 546 

CHROMIUM TISSUE DISTRIBUTION STUDY

Materials and Methods

Groups of 40 special study male rats and female mice were randomly assigned to the tissue distribution study at 

the beginning of the 2-year study and treated identically to the core study groups. On days 4, 11, 180, and 369, 

up to 10 animals per exposure group were removed from treatment and placed in individual metabolism cages 

to allow separate collection of urine and feces. The animals had access to undosed water and feed ad libitum. 

Two collections of urine and feces were made to include the intervals from 0 to 24 and 24 to 48 hours; measured 

values were combined to yield the reported 48-hour values. Urine and feces collections were frozen at –20° C and 

shipped to the analytical laboratory (RTI International, Research Triangle Park, NC).

At the end of 48 hours, the animals were anesthetized with CO2/O2, and blood was taken from the retroorbital 

sinus into heparinized centrifuge tubes. The blood was separated into cells and plasma. While the animals were 

still under CO2/O2 anesthesia, the abdominal wall was opened and the aorta was severed. The entire liver, both 

kidneys, and the stomach (separated into glandular and forestomach parts) were removed, weighed, and frozen at 

–20° C and shipped frozen to the analytical laboratory. Stainless steel was avoided during the tissue collection; 

only plastic, TeflonTM, ceramic, or tungsten carbide instruments were used.

The tissue samples were stored in a freezer. Prior to homogenization, the samples were allowed to thaw at room 

temperature in a Class 100 environment. Tissue samples were added to tared glass scintillation vials, and the 

whole wet tissue mass was recorded. A minimal amount of deionized water was added to each sample, and the 

total mass (tissue plus deionized water) was recorded. Each tissue sample was homogenized using a Polytron 

tissue homogenizer (Brinkmann Instruments, Westbury, NY) and returned to frozen storage.

Prior to aliquot transfer, the tissue homogenate was removed from frozen storage and allowed to thaw at 

room temperature in a Class 100 environment. Each tissue homogenate was mixed well to ensure complete 

homogeneity. An aliquot of homogenate containing approximately 0.500 g of tissue was transferred to a tared 

50 mL centrifuge tube, and the mass was recorded. Approximately 5% of the rat kidney samples were prepared 

with duplicate aliquots, and masses were recorded. The actual mass for each sample was calculated by applying 

the percent tissue in the homogenate to the measured mass. Homogenization was not necessary if the tissue mass 

was less than 0.500 g, but duplicate aliquots for these samples could not be prepared.

Five mL of concentrated nitric acid was added to each centrifuge tube containing tissue. The tubes were capped 

with microwavable caps and allowed to stand overnight at room temperature. The following morning, 2 mL of 

deionized water was added to each centrifuge tube. The tubes were arranged in a microwave tray; the thermowell 

and temperature sensors were inserted into one of the sample tubes to monitor the digestion; and the samples were 

subjected to a four-stage microwave digestion program that ramped the power from 60% to 100% with hold times 

of 5 to 20 minutes. Samples achieved a maximum temperature of 110° C, which was held for 10 minutes.

After the digestion was complete, the samples were allowed to cool to room temperature. To each tube, 0.500 mL 

of hydrogen peroxide and 0.125 mL of hydrofluoric acid were added as was more deionized water, if necessary, 

to avoid charring. The samples were subjected to the same microwave program a second time and then allowed 

to cool. The content of each tube was transferred to a 25 mL volumetric flask, and 0.250 mL of a previously 

prepared 1.00 μg/mL internal standard solution was added. The internal standard solution was prepared by 

transferring 100 μL aliquots of NIST-traceable yttrium, bismuth, indium, and scandium stock solutions (1,000 μg/

mL) to a 100 mL volumetric flask, adding 1 mL of concentrated nitric acid, and diluting to volume with deionized 

water. The tubes were rinsed with deionized water, and the rinses were added to the flasks. Each flask was 

brought to volume with deionized water and mixed well. Samples were transferred to clean plastic storage bottles 

and stored in a refrigerator until the day of analysis.

The solvent standards, digested matrix standards, and experimental samples were analyzed by inductively coupled 
Sodium Dichromate Dihydrate, NTP TR 546 189

plasma-mass spectrometry using a Thermo X7 instrument (ThermoElectron Corp., Winsford, Cheshire, U.K.) or 

a Plasma Quad XR Instrument (VG Elemental Ltd., Winsford, Cheshire, U.K.) with a concentric nebulizer and a 

Peltier impact-bead spray chamber cooled to 5° C. A calibration curve was constructed at the beginning of each 

analysis, and the performance of the calibration was evaluated prior to sample analysis. A successful calibration 

was indicated by an acceptable correlation coefficient (r > 0.99) and residual percent read-backs within 20% of 

the lowest standard and within 10% of all other solvent standards. A valid calibration included a minimum of six 

calibration standards and a calibration blank.

Analysis data were considered valid if they were bracketed by valid quality control (QC) sets. A maximum of 

10 samples (including method blanks and controls) were bracketed by a QC set, which consisted of the calibration 

blank and two midlevel calibration standards. A QC set passed when the measured concentration for one midlevel 

calibration standard was within 10% of its nominal value. This selected midlevel calibration standard was then 

required to pass consistently throughout the analysis. If the selected midlevel calibration standard failed, it was 

necessary to reanalyze the bracketed samples. Samples with responses greater than the calibration range were 

diluted with diluent solution to get a response within the range. The diluent solution was prepared by adding 1 mL 

of the internal standard solution and 20 mL of concentrated nitric acid to a 100 mL plastic volumetric flask and 

diluting to volume with deionized water.
190 Sodium Dichromate Dihydrate, NTP TR 546 

Table J1

Tissue Concentrations and Excreta Content of Chromium in Male Rats in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n 3 3 3 3 3

Erythrocytes (μg/g)

Day 6 0.044 ± 0.002 0.051 ± 0.002 0.126 ± 0.012* 0.252 ± 0.022* 0.391 ± 0.012**

Day 13 0.051 ± 0.002 0.036 ± 0.005 0.203 ± 0.019 0.504 ± 0.066* 0.899 ± 0.134**

Day 182 0.050 ± 0.014 0.054 ± 0.003 0.208 ± 0.002 0.591 ± 0.014* 0.997 ± 0.051**

Day 371 0.055 ± 0.003 0.064 ± 0.006* 0.160 ± 0.059** 0.526 ± 0.031** 0.693 ± 0.029**

Plasma (μg/g)b

Day 6 0.052 ± 0.003 0.068 ± 0.007* 0.079 ± 0.003** 0.087 ± 0.008** 0.109 ± 0.007**

Day 13 0.054 ± 0.004 0.048 ± 0.006 0.079 ± 0.005* 0.103 ± 0.008** 0.146 ± 0.008**

Day 182 0.063 ± 0.005 0.064 ± 0.003 0.081 ± 0.004* 0.099 ± 0.007** 0.146 ± 0.009**

Day 371 0.054 ± 0.014 0.062 ± 0.005 0.071 ± 0.011 0.110 ± 0.010** 0.146 ± 0.003**

Liver (μg/g)

Day 6 0.072 ± 0.007 0.097 ± 0.015 0.326 ± 0.027* 1.116 ± 0.200** 1.589 ± 0.125**

Day 13 0.080 ± 0.013 0.080 ± 0.005 0.700 ± 0.065 1.899 ± 0.347* 3.239 ± 0.385**

Day 182 0.081 ± 0.004 0.249 ± 0.007* 1.568 ± 0.040** 4.101 ± 0.110** 6.650 ± 0.249**

Day 371 0.092 ± 0.003 0.289 ± 0.029* 1.145 ± 0.334** 4.383 ± 0.419** 7.735 ± 0.155**

Kidney (μg/g)

Day 6 0.376 ± 0.070 0.252 ± 0.049 0.591 ± 0.043 1.122 ± 0.087* 1.570 ± 0.024**

Day 13 0.089 ± 0.006 0.225 ± 0.009* 1.125 ± 0.041** 2.556 ± 0.390** 4.409 ± 0.596**

Day 182 0.083 ± 0.003 1.153 ± 0.036* 5.464 ± 0.054** 10.847 ± 0.195** 15.263 ± 0.280**

Day 371 0.170 ± 0.011 1.564 ± 0.055* 4.879 ± 1.259** 13.423 ± 0.307** 18.530 ± 0.430**

Glandular stomach (μg/g)

Day 6 0.076 ± 0.003 0.143 ± 0.008* 0.333 ± 0.040** 0.773 ± 0.105** 1.967 ± 0.109**

Day 13 0.095 ± 0.008 0.254 ± 0.073* 0.310 ± 0.049* 1.331 ± 0.060** 1.762 ± 0.042**

Day 182 0.197 ± 0.031 0.414 ± 0.012* 1.043 ± 0.081** 4.300 ± 0.367** 9.886 ± 0.354**

Day 371 0.253 ± 0.066 0.334 ± 0.029 1.038 ± 0.115* 4.801 ± 0.345** 14.643 ± 0.121**

Forestomach (μg/g)

Day 6 0.098 ± 0.024 0.076 ± 0.004 0.122 ± 0.008 0.294 ± 0.029 0.285 ± 0.123

Day 13 0.091 ± 0.015 0.102 ± 0.034 0.171 ± 0.050 0.221 ± 0.055* 0.593 ± 0.159**

Day 182 0.089 ± 0.018 0.099 ± 0.003 0.338 ± 0.022* 0.574 ± 0.171* 1.654 ± 0.244**

Day 371 0.090 ± 0.015 0.118 ± 0.008 0.328 ± 0.081* 1.338 ± 0.444** 2.849 ± 0.975**

Feces (μg)c,d

Day 6 11.56 ± 3.06 26.87 ± 5.56* 122.29 ± 5.49** 246.86 ± 84.73** 1,030.2 ± 117.71**

Day 13 9.056 ± 1.977 52.335 ± 6.275* 171.734 ± 9.232** 362.994 ± 74.118** 972.867 ± 54.316**

Day 182 10.04 ± 2.06 63.64 ± 6.07* 229.71 ± 17.38** 467.84 ± 33.30** 1,947.6 ± 287.25**

Day 371 6.869 ± 1.126 36.299 ± 4.185* 139.488 ± 11.446*e 311.849 ± 10.293** 1,146.27 ± 114.235**

Urine (μg)c,d

Day 6 0.275 ± 0.073 0.480 ± 0.053* 2.520 ± 0.732** 4.594 ± 1.118** 6.967 ± 0.717**

Day 13 0.139 ± 0.028 0.396 ± 0.114* 1.100 ± 0.253** 1.943 ± 0.390** 4.561 ± 0.486**

Day 182 0.630 ± 0.131 1.145 ± 0.101* 7.076 ± 0.075** 12.580 ± 0.898** 20.137 ± 0.579**

Day 371 0.588 ± 0.087 2.023 ± 0.267* 7.406 ± 1.020** 13.702 ± 2.107** 23.969 ± 3.875**

* Significantly different (P#0.05) from the control group by Shirley’s test

** P#0.01 a Mean ± standard error. Statistical tests were performed on unrounded data. b n=6 for all plasma values c Cumulative chromium content for 48 hours ending on the day indicated d Measured values less than the experimental limit of quantitation (ELOQ) (2.00 μg Cr/g feces; 0.100 μg Cr/g urine) were included in the analysis 

as 1⁄2 ELOQ × sample mass. e n=2
Sodium Dichromate Dihydrate, NTP TR 546 191

Table J2

Tissue Concentrations and Excreta Content of Chromium in Female Mice in the 2-Year Drinking Water Study 

of Sodium Dichromate Dihydratea

 0 mg/L 14.3 mg/L 57.3 mg/L 172 mg/L 516 mg/L

n 3 3 3 3 3

Erythrocytes (μg/g)

Day 6 0.040 ± 0.003 0.056 ± 0.010 0.108 ± 0.009* 0.260 ± 0.047** 0.374 ± 0.078**

Day 13 0.043 ± 0.005 0.042 ± 0.002 0.341 ± 0.100 0.747 ± 0.087* 1.190 ± 0.137**

Day 182 0.058 ± 0.004 0.079 ± 0.008 0.194 ± 0.016* 0.719 ± 0.052** 1.561 ± 0.165**

Day 371 0.036 ± 0.004 0.042 ± 0.011 0.094 ± 0.002 0.340 ± 0.020* 0.795 ± 0.089**

Plasma (μg/g)b

Day 6 0.064 ± 0.006 0.075 ± 0.016 0.111 ± 0.026 0.150 ± 0.039** 0.213 ± 0.059**

Day 13 0.034 ± 0.016 0.038 ± 0.018 0.133 ± 0.024** 0.204 ± 0.045** 0.311 ± 0.077**

Day 182 0.051 ± 0.006 0.070 ± 0.010 0.116 ± 0.005** 0.167 ± 0.009** 0.253 ± 0.016**

Day 371 0.065 ± 0.004 0.086 ± 0.010 0.118 ± 0.014** 0.150 ± 0.012** 0.209 ± 0.009**

Liver (μg/g)

Day 6 0.098 ± 0.039 0.340 ± 0.010* 1.421 ± 0.146** 4.638 ± 0.950** 5.622 ± 0.795**

Day 13 0.126 ± 0.003 0.591 ± 0.027* 2.659 ± 0.094** 9.374 ± 0.892** 14.830 ± 2.347**

Day 182 0.147 ± 0.015 0.746 ± 0.068* 4.575 ± 0.559** 17.270 ± 2.746** 52.047 ± 2.890**

Day 371 0.069 ± 0.007 0.792 ± 0.019* 3.782 ± 0.143** 13.777 ± 0.951** 39.450 ± 1.655**

Kidney (μg/g)

Day 6 0.095 ± 0.011 0.166 ± 0.011* 0.415 ± 0.020** 0.892 ± 0.106** 1.338 ± 0.157**

Day 13 0.127 ± 0.032 0.245 ± 0.003* 1.259 ± 0.051** 4.061 ± 0.718** 4.027 ± 0.286**

Day 182 0.067 ± 0.006 0.361 ± 0.061* 2.062 ± 0.191** 10.187 ± 1.078** 17.487 ± 0.500**

Day 371 0.070 ± 0.002 0.340 ± 0.014* 1.291 ± 0.064** 7.868 ± 0.510** 21.827 ± 2.446**

Glandular stomach (μg/g)

Day 6 0.306 ± 0.056 0.645 ± 0.253 1.258 ± 0.290* 2.450 ± 0.266** 5.785 ± 0.131**

Day 13 0.207 ± 0.053 0.324 ± 0.030 2.614 ± 0.190* 7.048 ± 1.751** 13.130 ± 2.604**

Day 182 0.305 ± 0.078 0.644 ± 0.035* 3.659 ± 0.547** 11.520 ± 3.017** 52.673 ± 12.310**

Day 371 0.731 ± 0.306 0.676 ± 0.104 2.807 ± 0.330* 9.994 ± 1.079* 49.867 ± 12.251**

Forestomach (μg/g)

Day 6 0.328 ± 0.132 0.683 ± 0.262 1.308 ± 0.553 1.102 ± 0.373 1.286 ± 0.116

Day 13 0.201 ± 0.094 0.288 ± 0.056 0.400 ± 0.044 2.030 ± 0.532* 3.849 ± 1.811*

Day 182 0.173 ± 0.064 0.444 ± 0.099 1.033 ± 0.102* 2.141 ± 0.643** 9.624 ± 3.638**

Day 371 0.320 ± 0.049 0.381 ± 0.077 1.271 ± 0.300* 1.812 ± 0.208* 7.442 ± 0.764**

Feces (μg)c,d

Day 6 2.598 ± 0.899 9.364 ± 1.422* 12.869 ± 2.918* 43.632 ± 10.221** 162.588 ± 31.040**

Day 13 2.348 ± 1.173 12.103 ± 3.355* 85.798 ± 21.386** 46.865 ± 4.905* 107.822 ± 30.842**

Day 182 1.275 ± 0.568 5.266 ± 0.425* 17.633 ± 3.070** 24.583 ± 5.796** 122.734 ± 21.606**

Day 371 7.484 ± 2.862 9.502 ± 1.566 18.682 ± 2.165* 40.853 ± 3.288** 72.071 ± 19.116**

Urine (μg)c,d

Day 6 0.034 ± 0.007 0.122 ± 0.033* 0.347 ± 0.152*e —f —

Day 13 0.020 ± 0.008 0.233 ± 0.009e 0.501g — 2.190 ± 0.126*e

Day 182 0.089 ± 0.051 0.145 ± 0.035e 0.648 ± 0.213* 1.339 ± 0.199*e —

Day 371 0.074 ± 0.008 0.470 ± 0.103* 1.343 ± 0.234** 3.953 ± 1.460**e 3.251 ± 1.263**

* Significantly different (P#0.05) from the control group by Shirley’s test

** P#0.01 a Mean ± standard error. Statistical tests were performed on unrounded data. b n=6 for all plasma values c Cumulative chromium content for 48 hours ending on the day indicated d Measured values less than the experimental limit of quantitation (ELOQ) (2.00 μg Cr/g feces; 0.100 μg Cr/g urine) were included in the analysis 

as 1⁄2 ELOQ × sample mass. e n=2 f Data not available

g n=1
192 Sodium Dichromate Dihydrate, NTP TR 546