Sodium dichromate

Endpoint summary

Description of key information

Repeated dose toxicity: oral

Five weight of evidence studies for this endpoint are available. Two of these studies were conducted with sodium dichromate and three with potassium dichromate. Based on the information available from these five weight of evidence studies, it was concluded using a category read-across concept that the formal data requirments are fulfilled. The approach for read-across is described in detail in the document attached in IUCLID section 13.

Repeated dose toxicity: inhalation

No key study for this endpoint is available. Epidemiological data are availabe (see section 7.10.2) indicating that occupational exposure to hexavalent chromium compounds is linked to increased incidences of lung tumors. Supporting animal data are reported in this section.

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2001-11-13 to 2002-02-14

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Remarks:

This reference had reporting and experimental deficiencies as follows: details of test chemical diet preparation not given; the palatability of the drinking water was not determined beforehand; no details on female status (nulliparous and non pregnant) given; this study had an inappropiate dosing scheme (lowest dose should have no effect); clinical observation was perfromed but no details on evaluated parameters were given; ophthalmological examination was not performed; sensory reactivity to stimuli of differrent types, assessment of grip strength and motor activity assessment was not performed; food consumption was not reported; blood clotting time was not analysed; no clinical biochemistry was conducted; the following organs weight were missing: epididymides, only one kidney, adrenals, only one testis, uterus, ovaries and brain; histopathology was not performed on bone marrow, peripheral nerve, spinal cord and gall bladder; individual data were not presented

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Version / remarks:

21 September 1998

Deviations:

yes

Remarks:

Please refer to the filed rationale for reliability incl. deficiencies

Principles of method if other than guideline:

NTP protocol: 90-day sighting study for a subsequent carcinogenicity study

GLP compliance:

not specified

Remarks:

in compliance with Food and Drug Administration Good Laboratory Practice Regulations (21 CFR, Part 58)

Limit test:

no

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic Farms (Germantown, NY)
- Body weight at study start: males: 20.4-21.6, females: 17.9-18.8
- Age on receipt: 4-5 weeks, Age at study start: 5-7 weeks
- Housing: Solid bottom polycarbonate (Lab Products, Inc., Maywood, NJ), changed at least twice weekly, bedding: irradated hardwood bedding chips (P.J. Murphy Forest Products, Inc., Montville, NJ), changed at least twice weekly, Cage filters: Reemay spun-bonded polyester (Andico, Birmingham, AL), changed every 2 weeks, Rack: Stainless Steel (Lab Products, Inc., Maywood, NJ), changed every 2 weeks
- Animals per cage: males: 1; females: 5
- Diet: Irradiated NTP-2000 wafer rodent feed (Zeigler Brothers, Inc., Gardners, PA), ad libitum
- Water: Tap water (Brimingham, AL municipal supply) via amber glass water bottles with Teflon-lined caps and stainless steel sipper tubes (Wheaton, Millville, NJ), ad libitum
- Acclimation period: 13 days males, 14 days females

ENVIRONMENTAL CONDITIONS
- Temperature: 72± 3°F
- Humidity: 50%± 15%
- Air changes: 18/hour
- Photoperiod: 12/12

IN-LIFE DATES: From 2001.11.13 to 2002.02.14

Other:
Before the study began, five male and five female mice were randomly selected for parasite evaluation and gross observation for evidence of disease. Blood was collected from five male and five female study control rats at study termination. The sera were analyzed for antibody titers to rodent viruses. All results were negative.

Route of administration:

oral: drinking water

Vehicle:

water

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The dose formulations were prepared four times during the 3-month study in mice. Formulations were stored in NALGENE® containers at room temperature and protected from light. Stability studies of a 41.8 μg/mL sodium dichromate dihydrate dose formulation were performed by the analytical chemistry laboratory using ion chromatography (IC). 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 spectroscopy. The dose formulations were analyzed three times. All 15 of the dose formulations were within 10% of the target concentrations. Animal room samples and unused carboy storage samples of these dose formulations were also analyzed; 14 of 15 animal room samples were within 10% of target concentrations. All 15 of the unused carboy samples were within 10% of the target concentrations.

Duration of treatment / exposure:

14 weeks

Frequency of treatment:

Continuous (access to drinking water)

Remarks:

Doses / Concentrations:
0, 62.5, 125, 250, 500, 1000 mg/l
Basis:
nominal in water

Remarks:

Doses / Concentrations:
0, 9, 15, 26, 45, 80 mg/kg bw/d
Basis:
actual ingested

Remarks:

Doses / Concentrations:
0, 3.1, 5.2, 9.1, 15.7, 27.9 mg/kg bw/d
Basis:
other: Cr (VI) equivalents

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:
- Rationale for animal assignment: Animals were distributed randomly into groups of approximately equal initial mean body weights.

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule:
twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule:
weekly

BODY WEIGHT: Yes
- Time schedule for examinations:
animals were weighed initially, weekly and at the end of the study

WATER CONSUMPTION AND COMPOUND INTAKE: Yes
Water consumption was recorded weekly by cage.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: at the end of the study
- Parameters examined: automated and manual hematocrit; hemoglobin concentration; erythrocyte, reticulocyte, nucleated erythrocyte, platelet counts, and platelet estimates; erythrocyte and platelet morphology; mean cell volume; mean cell hemoglobin; mean cell hemoglobin concentration; leukocyte count and differentials.
Hematology analyses and reticulocyte counts were conducted on the day of sample collection using an ADVIA 120 Hematology System Analyzer (Boehringer Mannheim Corp., Indianapolis, IN). Blood smears were prepared within approximately 2 hours of sample collection for evaluation of platelet and erythrocyte morphology by light microscopy.

CLINICAL CHEMISTRY: No

URINALYSIS: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Necrospy was performed on all animals. The heart, right kidney, liver, lung, spleen, right testis, and thymus of all animals were weighed.

HISTOPATHOLOGY: Yes
In addition to gross lesions and tissue masses, the following tissues were examined: adrenal gland, bone, brain, clitoral gland, esophagus, eye, harderian gland, heart and aorta, large intestine (cecum, colon, rectum), small intestine (duodenum, jejunum, ileum), kidney, liver, lung and mainstem bronchi, lymph nodes (mandibular, mesenteric, and pancreatic), mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, seminal vesicle, skin, spleen, stomach (forestomach and glandular), testis with epididymis and vaginal tunics, thymus, thyroid gland, trachea, urinary bladder, and uterus.
Tissues for microscopic examination were fixed and preserved in 10% neutral buffered formalin with the exception of eyes, which were initially fixed in Davidson’s solution, then transferred to 10% neutral buffered formalin approximately 24 hours after collection. Tissues were processed and trimmed, embedded in paraffin, sectioned to a thickness of approximately 5 μm and stained with hematoxylin and eosin. Complete histopathological examinations were performed on all animals in the 0 and 1,000 mg/L groups and on 6 of 10 randomly selected mice in each of the other exposed groups. Tissues identified as target organs in the 1,000 mg/L group were examined in lower exposure concentration groups until a no-effect level had been determined or all animals had been examined.

Statistics:

STATISTICAL METHODS
Calculation and Analysis of Lesion Incidences
The Fisher exact test (Gart et al., 1979), a procedure based on the overall proportion of affected animals, was used to determine significance.

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. Organ and 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, clinical chemistry, urinalysis, spermatid, and epididymal spermatozoal 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 exposure concentration-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 exposure concentration-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). Treatment effects were investigated by applying a multivariate analysis of variance (Morrison, 1976) to the transformed data to test for simultaneous equality of measurements across exposure concentrations.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Final mean body weights and body weight gains of mice exposed to 125 mg/L or greater and the body weight gains of 62.5 mg/L male mice were significantly less than those of the control groups.

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

Male and female mice exposed to 125 (except males at week 13), 250, 500, or 1,000 mg/L consumed less water than did the respective control groups. Exposure concentrations of 62.5, 125, 250, 500, and 1,000 mg/L resulted in average daily doses of approximately 9, 15, 26, 45, and 80 mg/kg to mice.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

The mice demonstrated an erythrocyte microcytosis (decrease in mean cell volume). The decreases in mean cell hemoglobin reflected the mean cell volume decrease. Erythrocyte counts increased, and hemoglobin concentrations decreased, but only in females.

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Absolute liver weights of males exposed to 250 mg/L or greater and females exposed to 500 or 1,000 mg/L were significantly less than those of the respective controls, but liver weights relative to body weights were unchanged. Relative kidney weights of males exposed to 1,000 mg/L were significantly greater than those of the control group. Other differences in organ weights were attributed to the reduced body weights of the mice.

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In the duodenum, the incidences of minimal to mild epithelial hyperplasia were significantly increased in all exposed groups, and severities increased slightly with increasing exposure concentration. Compared to the controls, the duodenal villi were short, thick, and blunted, the crypts elongated, and diffuse hyperplasia of the crypt epithelium extended towards the tips of the villi. The hyperplasic epithelial cells were tall, columnar, densely packed, and stained more basophilically than the shorter columnar epithelial cells lining the duodenal villi of the control mice. There were also increased numbers of mitotic figures in the hyperplastic epithelium. In addition, the epithelial cells lining the tips of the villi of many of the exposed mice were swollen and had vacuolated cytoplasm. Collectively, these duodenal lesions suggest regenerative hyperplasia secondary to previous epithelial cell damage or degeneration. In mice receiving 125 mg/L or greater, the incidences of minimal to mild histiocytic cell infiltration in the duodenum and mesenteric lymph nodes (except 500 mg/L males) were significantly increased. Histiocytic cell infiltration in the duodenum and the mesenteric lymph nodes was morphologically similar to that observed in the duodenum and pancreatic lymph nodes of rats. Slight glycogen depletion in hepatocytes was noted in exposed groups, but because it was associated with poor weight gain or diminished food intake, it was not recorded as a lesion.

Histopathological findings: neoplastic:

no effects observed

Other effects:

not examined

Details on results:

Clinical signs:
No clinical findings were attributed to sodium dichromate dihydrate exposure.

Mortality:
All mice survived to the end of the study.

Dose descriptor:

LOAEL

Effect level:

62.5 mg/L drinking water

Sex:

male/female

Basis for effect level:

other: Incidences of epithelial hyperplasia of the duodenum were significantly increased in all exposed groups of mice.

Critical effects observed:

not specified

Conclusions:

Administration of sodium dichromate in the drinking water to mice for 90 days caused effects on body weight and water consumption. Haematological investigations revealed a microcytic hypochromic anaemia consistent with an effect on iron homeostasis or haemoglobin synthesis. Histopathology revealed duodenal hyperplasia in all treated groups, consistent with a local irritant effect. A NOAEL could not be determined for this study due to histopathology findings at the lowest dose level, however findings indicate a local rather than systemic effect.

Executive summary:

Groups of 10 male and 10 female B6C3F1 mice were given drinking water containing 0, 62.5, 125, 250, 500, or 1000 mg sodium dichromate dihydrate/L for 3 months. Dose levels were equivalent to average daily doses of approximately 9, 15, 26, 45, or 80 mg/kg; on a molecular weight basis, doses are equivalent to approximately 3.1, 5.2, 9.1, 15.7, and 27.9 mg/kg Cr (VI) per day. All mice survived to the end of the study. Reduced body weights occurred in male and female mice exposed to 125 mg/L or greater. Water consumption by male and female mice exposed to 125 mg/L or greater was generally less than that by the control groups. A microcytic hypochromic anemia was seen in mice. The incidences of histiocytic cellular infiltration were generally significantly increased in the duodenum and the mesenteric lymph node of mice exposed to 125 mg/L or greater. Incidences of epithelial hyperplasia of the duodenum were significantly increased in all exposed groups of mice.

Based on these results, the lowest observed effect level (LOAEL) is 62.5 mg sodium dichromate dihydrate/L. The no observed effects level (NOAEL) cannot be determined since effects were observed in all dose groups.

This reference had reporting and experimental deficiencies as follows: details of test chemical diet preparation not given; the palatability of the drinking water was not determined beforehand; no details on female status (nulliparous and non pregnant) given; this study had an inappropiate dosing scheme (lowest dose should have no effect); clinical observation was perfromed but no details on evaluated parameters were given; ophthalmological examination was not performed; sensory reactivity to stimuli of differrent types, assessment of grip strength and motor activity assessment was not performed; food consumption was not reported; blood clotting time was not analysed; no clinical biochemistry was conducted; the following organs weight were missing: epididymides, only one kidney, adrenals, only one testis, uterus, ovaries and brain; histopathology was not performed on bone marrow, peripheral nerve, spinal cord and gall bladder; individual data were not presented

Reference 2

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2001-11-11 to 2002-02-12

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

This reference had reporting and experimental deficiencies as follows: details of test chemical diet preparation not given; the palatability of the drinking water was not determined beforehand; no details on female status (nulliparous and non pregnant) given; this study had an inappropiate dosing scheme (lowest dose should have no effect); clinical observation was perfromed but no details on evaluated parameters were given; ophthalmological examination was not performed; sensory reactivity to stimuli of differrent types, assessment of grip strength and motor activity assessment was not performed; food consumption was not reported; blood clotting time was not analysed; no overnight fasting before blood sampling for clinical biochemistry; urea was not measured in clinical biochemistry; the following organs weight were missing: epididymides, only one kidney, adrenals, only one testis, uterus, ovaries and brain; histopathology was not performed on bone marrow, peripheral nerve and spinal cord; individual data were not presented

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Version / remarks:

21 September 1998

Deviations:

yes

Remarks:

Please refer to the field rationale for reliability incl. deficiencies

Principles of method if other than guideline:

NTP 90-day toxicity study protocol; used as a sighting study for the subsequent carcinogenicity study

GLP compliance:

yes

Remarks:

in compliance with Food and Drug Administration Good Laboratory Practice Regulations (21 CFR, Part 58)

Limit test:

no

Species:

rat

Strain:

other:

Remarks:

Fischer 344/N

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic Farms (Germantown, NY)
- Body weight at study start: males: 100-101, females: 88-91
- Age on receipt: 4-5 weeks, Age at study start: 5-7 weeks
- Housing: Solid bottom polycarbonate (Lab Products, Inc., Maywood, NJ), changed at least twice weekly, bedding: irradated hardwood bedding chips (P.J. Murphy Forest Products, Inc., Montville, NJ), changed at least twice weekly, Cage filters: Reemay spun-bonded polyester (Andico, Birmingham, AL), changed every 2 weeks, Rack: Stainless Steel (Lab Products, Inc., Maywood, NJ), changed every 2 weeks
- Animals per cage: 5
- Diet: Irradiated NTP-2000 wafer rodent feed (Zeigler Brothers, Inc., Gardners, PA), ad libitum
- Water: Tap water (Brimingham, AL municipal supply) via amber glass water bottles with Teflon-lined caps and stainless steel sipper tubes (Wheaton, Millville, NJ), ad libitum
- Acclimation period: 12 days males, 11 days females

ENVIRONMENTAL CONDITIONS
- Temperature: 72± 3°F
- Humidity: 50%± 15%
- Air changes: 18/hour
- Photoperiod: 12/12

IN-LIFE DATES: From 2001.11.11 to 2002.02.12

Other:
Before the study began, five male and five female rats were randomly selected for parasite evaluation and gross observation for evidence of disease. Blood was collected from five male and five female study control rats at study termination. The sera were analyzed for antibody titers to rodent viruses. All results were negative.

Route of administration:

oral: drinking water

Vehicle:

water

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The dose formulations were prepared four times during the 3-month study in F344/N rats. Formulations were stored in NALGENE® containers at room temperature and protected from light. Stability studies of a 41.8 μg/mL sodium dichromate dihydrate dose formulation were performed by the analytical chemistry laboratory using ion chromatography (IC). 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 spectroscopy. The dose formulations were analyzed three times. All 15 of the dose formulations for rats were within 10% of the target concentrations. Animal room samples and unused carboy storage samples of these dose formulations were also analyzed; 14 of 15 animal room samples for rats were within 10% of target concentrations. All 15 of the unused carboy samples were within 10% of the target concentrations.

Duration of treatment / exposure:

14 weeks

Frequency of treatment:

Continuous (access to drinking water)

Remarks:

Doses / Concentrations:
0, 62.5, 125, 250, 500, 1000 mg/l
Basis:
nominal in water

Remarks:

Doses / Concentrations:
0, 5, 10, 17, 32, 60 mg/kg bw/d
Basis:
actual ingested

Remarks:

Doses / Concentrations:
0, 1.7, 3.5, 5.9, 11.2 mg/kg bw/d
Basis:
other: Cr (VI) equivalents

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:
- Rationale for animal assignment: Animals were distributed randomly into groups of approximately equal initial mean body weights.

Positive control:

none

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly

BODY WEIGHT: Yes
- Time schedule for examinations: animals were weighed initially, weekly and at the end of the study

WATER CONSUMPTION AND COMPOUND INTAKE: Yes
Water consumption was recorded weekly by cage.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: on days 5 and 23 and at the end of the study
- Parameters examined: automated and manual hematocrit; hemoglobin concentration; erythrocyte, reticulocyte, nucleated erythrocyte, platelet counts, and platelet estimates; erythrocyte and platelet morphology; mean cell volume; mean cell hemoglobin; mean cell hemoglobin concentration; leukocyte count and differentials.
Hematology analyses and reticulocyte counts were conducted on the day of sample collection using an ADVIA 120 Hematology System Analyzer (Boehringer Mannheim Corp., Indianapolis, IN). Blood smears were prepared within approximately 2 hours of sample collection for evaluation of platelet and erythrocyte morphology by light microscopy.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: on days 5 and 23 and at the end of the study
- Parameters examined: urea nitrogen, creatinine, glucose, sodium, potassium, chloride, calcium, phosphorus, total protein, albumin, cholesterol, triglycerides, alanine aminotransferase, alkaline phosphatase, creatine kinase, sorbitol dehydrogenase, 5N-nucleotidase, total bile acids.
Clinical chemistry analyses were conducted on a Hitachi 911 Clinical Chemistry Analyzer (Boehringer Mannheim Corp., Indianapolis, IN). Clinical chemistry reagents were supplied by Sigma Diagnostics (St. Louis, MO), Roche Diagnostics (Indianapolis, IN), or Boehringer Mannheim Corp.

URINALYSIS: Yes
- Time schedule for collection: on day 16 for 24-hour urine collection in metabolic cages
- Parameters examined: creatinine, glucose, protein, alkaline phosphatase, aspartate aminotransferase, N-acetyl-glucosaminidase, volume, specific gravity, pH

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Necrospy was performed on all animals. The heart, right kidney, liver, lung, spleen, right testis, and thymus of all animals were weighed.

HISTOPATHOLOGY: Yes
In addition to gross lesions and tissue masses, the following tissues were examined: adrenal gland, bone, brain, clitoral gland, esophagus, eye, harderian gland, heart and aorta, large intestine (cecum, colon, rectum), small intestine (duodenum, jejunum, ileum), kidney, liver, lung and mainstem bronchi, lymph nodes (mandibular, mesenteric, and pancreatic), mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, seminal vesicle, skin, spleen, stomach (forestomach and glandular), testis with epididymis and vaginal tunics, thymus, thyroid gland, trachea, urinary bladder, and uterus.
Tissues for microscopic examination were fixed and preserved in 10% neutral buffered formalin with the exception of eyes, which were initially fixed in Davidson’s solution, then transferred to 10% neutral buffered formalin approximately 24 hours after collection. Tissues were processed and trimmed, embedded in paraffin, sectioned to a thickness of approximately 5 μm and stained with hematoxylin and eosin. Complete histopathological examinations were performed on all animals in the 0 and 1,000 mg/L groups and on 6 of 10 randomly selected rats in each of the other exposed groups. Tissues identified as target organs in the 1,000 mg/L group were examined in lower exposure concentration groups until a no-effect level had been determined or all animals had been examined.

Statistics:

STATISTICAL METHODS
Calculation and Analysis of Lesion Incidences
The Fisher exact test (Gart et al., 1979), a procedure based on the overall proportion of affected animals, was used to determine significance.

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. Organ and 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, clinical chemistry, urinalysis, spermatid, and epididymal spermatozoal 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 exposure concentration-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 exposure concentration-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). Treatment effects were investigated by applying a multivariate analysis of variance (Morrison, 1976) to the transformed data to test for simultaneous equality of measurements across exposure concentrations.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Administration of sodium dichromate dihydrate in the drinking water produced mild deficits in body weight gain for male and female rats exposed to 1,000 mg/L. The final mean body weights of male and female rats in the 1,000 mg/L group were 89% and 94%, respectively, of the final mean body weights of male and female control rats; the final mean body weights and body weight gain of 500 mg/L males were also less than those of the controls.

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

Water consumption by male and female rats in the 250, 500, and 1,000 mg/L groups was less than that by the controls. Exposure concentrations of 62.5, 125, 250, 500, and 1,000 mg/L resulted in average daily doses of approximately 5, 9, 17, 32, and 60 mg/kg body weight to males and 5, 10, 18, 33, and 61 mg/kg to females.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

The most dramatic effect of sodium dichromate dihydrate administration involved the erythron. An exposure-related microcytic, hypochromic, responsive anemia occurred in exposed rats. The microcytosis, evidenced by decreased mean cell volumes, occurred at day 5 and persisted throughout the study in all exposed groups. In 1,000 mg/L rats, the severity of the microcytosis was unchanged in females and increased with time in males; and, at week 14, erythrocytes in 1,000 mg/L rats were approximately 30% and 25% smaller in males and females, respectively. At lower exposure concentrations, microcytosis was most pronounced on day 23 (approximately 25% smaller in 500 mg/L males and females) and, in general, ameliorated with time.
The anemia, evidenced by decreases in automated and manual hematocrit values, hemoglobin concentrations, and erythrocyte counts, developed in all exposed groups by day 23 and persisted to week 14; it was most severe at day 23 and ameliorated with time. At week 14, erythrocyte counts were increased and contradictory to the lower hematocrit values and hemoglobin concentrations. The increased numbers of reticulocytes and nucleated erythrocytes were indicative of an erythropoietic response. Thus, while there was an apparent erythropoietic response resulting in increased numbers of circulating erythrocytes, the erythrocytes produced were smaller, which resulted in a decreased erythron in the 250 mg/L or greater groups at week 14. Microscopic evaluation of the blood smears demonstrated increased erythrocyte fragments, keratocytes, and blebbing that suggested increased erythrocyte injury or turnover. Additionally, increased numbers of hypochromic microcytes were observed suggesting that blood loss or altered iron metabolism or hemoglobin production was involved. Gastric ulcers may have resulted in blood loss, but this lesion was only seen in the 1,000 mg/L groups, and the hypochromic microcytosis occurred in most exposed animals. Thus, some alteration in iron metabolism or hemoglobin production was suspected.
Normally, instrument-derived hematocrit values should closely approximate the manual hematocrit value, which is considered the “gold standard” method. However, in this study, the instrument-derived values were noticeably lower than the manual hematocrit values in the 125 mg/L or greater groups at day 23 and in the 1,000 mg/L males at week 14. Microscopic evaluations of the blood smears demonstrated increased numbers of microcytic erythrocyte fragments, keratocytes, and hypochromic microcytes. The decreased instrument-derived hematocrit values could possibly be explained by the instrument’s inability to recognize and count the small erythrocytes or erythrocyte fragments or adequately determine the erythrocyte size (mean cell volume). Because mean cell hemoglobin concentration (MCHC) is calculated using the instrument-derived hematocrit values, a decrease in these hematocrit values would result in increased MCHCs. However, recalculated mean MCHCs using the mean manual hematocrit values were decreased compared to control MCHC values and suggested a hypochromia (iron deficiencylike process). The small erythrocytes and erythrocyte fragments may have been erroneously classified as platelets resulting in the very high platelet counts observed throughout the study. However, a platelet estimate performed on blood smears on day 23 and at week 14 suggested an increased platelet count existed in exposed male rats on day 23, but no increased platelet counts occurred in exposed animals at week 14. The increased platelet counts on day 23 may indicate or be consistent with a general increase in hematopoiesis or possibly an iron deficiency-like process. Increased platelet counts have been demonstrated in instances of iron deficiency or iron deficiency-like processes (e.g., cupric sulfate administration; NTP, 1993).
Increased neutrophil and monocyte counts (primarily an effect at higher exposures) were considered to represent an inflammatory response related to the inflammatory lesions observed histologically (e.g., gastric lesions). Leukocyte and lymphocyte counts were increased. While the increases in neutrophil and monocyte counts probably contributed to the increased leukocyte counts, the apparent increases in lymphocyte counts appeared to be the controlling factor. The increases in lymphocyte counts were not consistent between sexes until week 14, when the increased lymphocyte counts were primarily an effect of high exposure and could suggest altered lymphocyte distribution peripherally.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Progressive increases in alanine aminotransferase and sorbitol dehydrogenase activities occurred in all exposed rats; on day 5, only alanine aminotransferase demonstrated the effect. By week 14, alanine aminotransferase activities were increased in all exposed groups by approximately 2- to 8-fold in males and 3- to 7-fold in females; sorbitol dehydrogenase activities were increased in all exposed groups by approximately 2- to 6-fold in males and 3- to 5-fold in females. These increases, however, did not occur in an exposure concentration-related fashion. Increased serum activities of alanine aminotransferase and sorbitol dehydrogenase suggest increased hepatocellular membrane leakage or injury.
Increased bile acid concentrations occurred on day 23 and progressed; by week 14, bile acid concentrations were increased in the 500 and 1,000 mg/L males and in most female groups. As with alanine aminotransferase and sorbitol dehydrogenase, these increases did not occur in an exposure concentration-related fashion. Increased bile acid concentration is typically used as a marker of cholestasis, but it may also occur in situations of hepatocellular injury or altered hepatic function. In this study, alkaline phosphatase and 5N-nucleotidase activity (serum enzyme markers of cholestasis) were decreased or unchanged. Thus, it would appear that bile acid concentration increases were related to a hepatocellular effect rather than a cholestatic event.
There was an apparent alteration in lipid metabolism, evidenced by decreases in cholesterol and triglyceride concentrations that appeared to affect males more than females. Small (approximately 8%) decreases in cholesterol concentration occurred on day 5 in all exposed males and progressed; by week 14, cholesterol concentrations were decreased in 250, 500, and 1,000 mg/L males and 500 and 1,000 mg/L females. No exposure concentrationrelationship was evident. Decreased triglyceride concentrations occurred on day 23 in males; by week 14, triglyceride concentrations were decreased in 1,000 mg/L males and 250, 500, and 1,000 mg/L females. An exposure concentration-related decrease was apparent in females. The mechanism of the the decreased serum lipids was unknown, but the cholesterol and triglyceride concentrations decreased by 20% and 42%, respectively, in 1,000 mg/L males and by 17% and 58%, respectively, in 1,000 mg/L females, at week 14.
Increased creatine kinase activities occurred on day 5 in 500 and 1,000 mg/L males and in 250, 500, and 1,000 mg/L females. By week 14, creatine kinase activities were increased in 250, 500, and 1,000 mg/L rats; the increases in 1,000 mg/L males and females were 75% and 120%, respectively. An exposure concentration-relationship was evident and suggests muscle injury.

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

In urine, decreased volume and increased specific gravity were consistent with the observed decreases in water intake and suggested poor water palatability. The minor increases in urea nitrogen concentration were also consistent with decreased water intake and minimal dehydration. Transient, small (≤6%) decreases in calcium concentration occurred on day 5 in exposed males and females. On day 23, transient, small (≤12%) increases in phosphorus concentration that were unrelated to exposure concentration occurred in the 500 and 1,000 mg/L groups. The mechanism of these transient calcium and phosphorus changes was unknown. Changes in other clinical pathology variables were minor or sporadic.

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Absolute and relative liver weights of males in the 500 and 1,000 mg/L groups were significantly less than those of the controls. Absolute spleen weights of 500 and 1,000 mg/L males and relative spleen weights of 250 and 500 mg/L males were also significantly less than those of the controls. Relative spleen and kidney weights of 500 and 1,000 mg/L females were significantly increased. Other differences in organ weights were considered to be related to the lower body weights of animals in these groups, rather than to a specific toxic effect of sodium dichromate dihydrate.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

In the glandular stomach, gross lesions described as deformity, pale foci, pale nodules, or thick, pale mucosa were observed in males and females exposed to 1,000 mg/L and correlated well with the microscopic lesions observed in this group. The lesions occurred immediately adjacent to the limiting ridge, the anatomic demarcation between the rodent forestomach and glandular stomach.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

The administration of sodium dichromate dihydrate in the the drinking water of rats was associated with increased incidences of nonneoplastic lesions in the glandular stomach, duodenum, and pancreatic lymph nodes of males and females and in the liver and bone marrow of females. The severities of the lesions in the duodenum, glandular stomach, and pancreatic lymph node were generally greater at the 1,000 mg/L exposure concentration. Microscopically, the incidences of glandular stomach lesions, which included ulcers, regenerative epithelial hyperplasia, and squamous epithelial metaplasia were significantly increased in male and female rats exposed to 1,000 mg/L. These microscopic lesions were similar in all affected rats and were strikingly site specific within the glandular stomach, consistently occurring immediately adjacent to the limiting ridge. Ulcers were focal to focally extensive lesions characterized by complete loss of the lining of the mucosal epithelium with necrosis of the underlying tissue. Necrosis often extended through the submucosa and muscle layers. Invariably, mild to marked chronic inflammation consisting of infiltrates of neutrophils, macrophages, lymphocytes, and eosinophils in varying numbers and proliferation of fibrous connective tissue extended from the base of the ulcer through the submucosa to the serosal surface. Regenerative glandular hyperplasia occurred at the lateral borders of the ulcers as focal areas of irregular disorganized hyperplastic gastric glands lined by well-differentiated tall columnar epithelium. Squamous epithelial metaplasia was diagnosed when well-differentiated, keratinized, squamous epithelium extended from the limiting ridge to partially or completely cover the ulcerated areas replacing the normal tall columnar epithelium of the gastric glands.
In the pancreatic lymph nodes, the incidences of minimal to mild histiocytic cell infiltration were increased in all exposed males and females; the increases were statistically significant in 1,000 mg/L females and in all exposed males, except the 125 mg/L group. The incidences of lymphoid hyperplasia and sinusoidal ectasia were significantly increased in 1,000 mg/L males and females. Histiocytic cell infiltrates were multifocal, randomly scattered, small clusters of enlarged macrophages with pale foamy cytoplasm. Lymphoid hyperplasia consisted of minimal to mild proliferation of lymphocytes, primarily in the paracortical areas, and sinusoid ectasia was characterized by minimal to mild dilatation of the subcapsular or medullary sinuses.
In the duodenum, the incidences of minimal to mild histiocytic infiltration were significantly increased in the groups exposed to 125 mg/L or greater. Histiocytic infiltrates occurred in the lamina propria at the tips of duodenal villi and were morphologically similar to those observed in the pancreatic lymph nodes.
In the liver, the incidences of minimal histiocytic cellular inflammation were significantly increased in 125 mg/L or greater females; focal chronic inflammation was significantly increased at 1,000 mg/L. Histiocytic infiltrates were randomly scattered and morphologically similar to those observed in the duodenum and pancreatic lymph nodes. Chronic inflammation consisted of scattered, small clusters of lymphocytes and macrophages occasionally mixed with a few neutrophils.
In the bone marrow, the incidence of minimal hyperplasia was significantly increased in 1,000 mg/L females.

Histopathological findings: neoplastic:

no effects observed

Other effects:

not examined

Details on results:

Clinical signs:
No clinical findings were attributed to sodium dichromate dihydrate exposure

Mortality:
Administration of sodium dichromate dihydrate in the drinking water had no effect on survival of male or female rats.

Dose descriptor:

LOAEL

Effect level:

62.5 mg/L drinking water

Sex:

male/female

Basis for effect level:

other: Hamatological effects were seen in all treated groups

Critical effects observed:

not specified

Conclusions:

Administration of sodium dichromate in drinking water to rats for 90 days at dose levels of up to 1000 mg/L caused effects on the red blood cell (microcytic anaemia) and liver. Local irritant effects on the non-glandular gastric mucosa were apparent at the highest dose level.

Executive summary:

Groups of 10 male and 10 female F344/N rats were given drinking water containing 0, 62.5, 125, 250, 500, or 1,000 mg sodium dichromate dihydrate/L for 3 months. Dose levels are equivalent to average daily doses of approximately 5, 10, 17, 32, or 60 mg sodium dichromate dihydrate/kg body weight and approximately 1.7, 3.5, 5.9, 11.2, and 20.9 mg hexavalent chromium/kg body weight per day. All rats survived to the end of the study. Reduced body weights occurred in 500 and 1000 mg/L males and in 1000 mg/L female rats. Water consumption by male and female rats exposed to 250 mg/L or greater was generally less than that by the control groups, and decreases in urine volume and increases in urine specific gravity seen in rats were related to reduced water consumption. Exposure to sodium dichromate dihydrate caused a microcytic hypochromic anemia. Serum cholesterol and triglyceride concentrations were decreased. Increased bile acid concentrations in exposed groups may have been due to altered hepatic function. The incidences of histiocytic cellular infiltration were generally significantly increased in the duodenum of both sexes and in the liver of females. Significantly increased nonneoplastic lesions (focal ulceration, regenerative epithelial hyperplasia, and squamous epithelial metaplasia) occurred in the glandular stomach of males and females exposed to 1000 mg/L.

Based on these results the lowest observed effect level (LOAEL) is 62.5 mg sodium dichromate dihydrate/L. The no observed effects level (NOAEL) cannot be determined based on the results presented in this study.

This reference had reporting and experimental deficiencies as follows: details of test chemical diet preparation not given; the palatability of the drinking water was not determined beforehand; no details on female status (nulliparous and non pregnant) given; this study had an inappropiate dosing scheme (lowest dose should have no effect); clinical observation was perfromed but no details on evaluated parameters were given; ophthalmological examination was not performed; sensory reactivity to stimuli of differrent types, assessment of grip strength and motor activity assessment was not performed; food consumption was not reported; blood clotting time was not analysed; no overnight fasting before blood sampling for clinical biochemistry; urea was not measured in clinical biochemistry; the following organs weight were missing: epididymides, only one kidney, adrenals, only one testis, uterus, ovaries and brain; histopathology was not performed on bone marrow, peripheral nerve and spinal cord; individual data were not presented

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

5 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Weight of evidence

System:

haematopoietic

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The discussion of all endpoints is included in the endpoint summary of the hexavalent chromium substances category and the read-across approach is described in detail in the attached document in section 13 of the IUCLID.