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Toxicological information

Repeated dose toxicity: oral

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Administrative data

Endpoint:
sub-chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: NTP study
Cross-reference
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2007

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other:
Principles of method if other than guideline:
NTP 90-day toxicity study protocol; used as a sighting study for the subsequent carcinogenicity
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
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 3-month studies in F344/N rats and B6C3F1 mice (study 1). An additional shipment of lot 13822LI was obtained from Aldrich Chemical Company and used in the 3-month studies in male B6C3F1, BALB/c, and am3-C57BL/6 mice (study 2). Identity, purity, and stability analyses were conducted by the analytical chemistry laboratory (lots 062001 and 13822LI) and by the study laboratories at Southern Research Institute (Birmingham, AL; lot 062001) and Battelle Columbus Operations (Columbus, OH; lot 13822LI). Karl Fischer titration (lots 062001 and 13822LI) and elemental analysis using inductively coupled plasma-atomic emission spectroscopy (ICP-AES; lot 062001) were performed by Galbraith Laboratories, Inc. (Knoxville, TN); elemental analysis using ICP-AES (lot 13822LI) was performed by Battelle Northwest Operations (Richland, WA); and elemental analysis using proton-induced X-ray emission spectroscopy (PIXE; lots 062001 and 13822LI) was performed by Elemental Analysis Corporation (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 Galbraith Laboratories, Inc., using elemental analysis by ICP-AES, and by Elemental Analysis Corporation using elemental analysis by PIXE. Lot 13822LI, an orange crystalline solid, was identified as sodium dichromate dihydrate by the analytical chemistry laboratory using XRD, by the analytical chemistry laboratory and Battelle Northwest Operations using elemental analysis by ICP-AES, and by Elemental Analysis Corporation using elemental analysis by PIXE. The XRD powder patterns were consistent with a reference pattern. Elemental analyses for chromium and sodium were in agreement with the theoretical values for sodium dichromate dihydrate, and PIXE indicated the absence of significant metallic impurities.The moisture content of lots 062001 and 13822LI was determined by Karl Fischer titration and, for lot 13822LI, weight loss on drying was performed by the analytical chemistry laboratory. 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 liquidchromatography-inductively coupled plasma-mass spectrometry (LC-ICP-MS) and by the study laboratory using potentiometric titrimetric analysis. The purity of lot 13822LI was determined by the analytical chemistry laboratory using DSC, titration of the dichromate ion with sodium thiosulfate and potassium ferrocyanide, and LC-ICP-MS and by the study laboratory using titration with sodium thiosulfate. For lot 062001, Karl Fischer titration indicated a moisture 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%. For lot 13822LI, Karl Fischer titration indicated a moisture content of 9.16%, less than the theoretical value of 12.09%; however, the percentage weight loss on drying agreed well with the theoretical value. DSC indicated a purity of 99.10% ± 0.27%. Titration with sodium thiosulfate and potassium ferrocyanide at the analytical chemistry laboratory indicated purities of 99.1% ± 1.2% and 99.6% ± 1.6%, respectively. Titration with sodium thiosulfate at the study laboratory indicated a purity of 101.8%. LC-ICP-MS indicated that the concentration of Cr III, if present,
was less than 0.1%. The overall purity of lot 13822LI was determined to be greater than 99%. To ensure stability, the bulk chemical was stored at room temperature, protected from light in amber glass bottles (lot 062001) or in a white plastic bottle (lot 13822LI). During the studies, stability of the bulk chemical was monitored by the study laboratories using potentiometric titration (lot 062001) or titration of the dichromate ion with sodium thiosulfate (lot 13822LI). No degradation of the bulk chemical was detected.

Test animals

Species:
rat
Strain:
Fischer 344
Sex:
male/female

Administration / exposure

Route of administration:
oral: drinking water
Vehicle:
water
Analytical verification of doses or concentrations:
yes
Duration of treatment / exposure:
90 days (3 months)
Frequency of treatment:
Continuous (access to drinking water)
Doses / concentrationsopen allclose all
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 no treatment

Results and discussion

Effect levels

Dose descriptor:
NOAEL
Effect level:
62.5 mg/L drinking water
Sex:
male/female
Basis for effect level:
other: Hamatological effects were seen in all treated groups
Remarks on result:
not determinable
Remarks:
no NOAEL identified

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables

Administration of sodium dichromate dihydrate in the drinking water had no effect on survival of male or female rats but produced mild deficits in body weight gain for male and female rats exposed to 1000 mg/L. The final mean body weights of male and female rats in the 1000 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. 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 1000 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. No clinical findings were attributed to sodium dichromate dihydrate exposure.

Haematology

An exposure-related microcytic, hypochromic, responsive anaemia 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 1000 mg/L rats, the severity of the microcytosis was unchanged in females and increased with time in males; and, at week 14, erythrocytes in 1000 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 haematocrit 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 haematocrit values and haemoglobin 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 haemoglobin 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. The small erythrocytes and erythrocyte fragments may have been erroneously classified as platelets resulting in 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 haematopoiesis or possibly an iron deficiency-like process. Increased platelet counts have been demonstrated in instances of iron deficiency or iron deficiency-like processes. 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 chemistry

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 1000 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 1000 mg/L males and 250, 500, and 1000 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 1000 mg/L males and by 17% and 58%, respectively, in 1000 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 1000 mg/L females. By week 14, creatine kinase activities were increased in 250, 500, and 1,000 mg/L rats; the increases in 1000 mg/L males and females were 75% and 120%, respectively. An exposure concentration-relationship was evident and suggests muscle injury. 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 1000 mg/L groups. The mechanism of these transient calcium and phosphorus changes was unknown. Changes in other clinical pathology variables were minor or sporadic.

Organ weights

Absolute and relative liver weights of males in the 500 and 1000 mg/L groups were significantly less than those of the controls. Absolute spleen weights of 500 and 1000 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 1000 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.

Pathology

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 1000 mg/L exposure concentration. 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 1000 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. 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 1000 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 1000 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 1000 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 1000 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 1000 mg/L females.

Applicant's summary and conclusion

Conclusions:
Administration of sodium dichromate in drinking water to rats for 90 days at dose levels of up to 1000 mg/L caused effects of exposure were seen on the red blood cell (microcytic anaemia) and liver. Local irritant effects on teh 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.