Chromium trioxide

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

NTP guideline study

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

NTP guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Principles of method if other than guideline:

The induction of peripheral blood erythrocyte micronuclei was investigated in mice following the oral administration of sodium dichromate for 3 months. In study 1, male and female B6C3F1 mice were administered sodium dichromate dihydrate over an exposure concentration range of 62.5 to 1,000 mg/L for 3 months. In study 2, micronucleus frequencies were evaluated in male B6C3F1, BALB/c, and am3-C57BL/6 mice administered sodium dichromate dihydrate over an exposure concentration range of 62.5 to 250 mg/L in drinking water for 3 months.

GLP compliance:

yes

Type of assay:

mammalian erythrocyte micronucleus test

Species:

mouse

Strain:

other: B6C3F1, BALB/c, and am3-C57BL/6

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:
B6C3F1: Taconic Laboratory Animals and Services (Germantown, NY)
BALB/c: Charles River Laboratory (Portage, MI)
am3-C57BL/6: Charles River Laboratory (Wilmington, MA)
- Age at study initiation: 6 (B6C3F1 and BALB/c mice) or 7 (am3-C57BL/6 mice) weeks
- Assigned to test groups randomly: [no/yes, under following basis: ]
- Housing: 1 animal per cage, Cages: Polycarbonate (Lab Products, Inc., Maywood, NJ), changed at least once weekly; Bedding: Irradiated hardwood bedding chips (P.J. Murphy Forest Products, Inc., Montville, NJ), changed at least once weekly; Cage Filters: Spun-bonded polyester (Snow Filtration Co., Cincinnati, OH); Racks: Stainless Steel (Lab Products, Inc., Seaford, DE), changed every 2 weeks
- Diet (e.g. ad libitum): Irradiated NTP-2000 wafer rodent feed (Zeigler Brothers, Inc., Gardners, PA), available ad libitum
- Water (e.g. ad libitum): Tap water (Columbus, OH, municipal supply) via glass bottles with Teflon®-lined septa and stainless steel sipper tubes (Wheaton, Millville, NJ), available ad libitum
- Acclimation period:
B6C3F1: 12 days
BALB/c: 16 days
am3-C57BL/6: 17 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72° +/- 3° F (20.6 - 23.9 °C)
- Humidity (%): 50% +/- 15%
- Air changes (per hr): 18/hour
- Photoperiod (hrs dark / hrs light): 12 hours/day light, 12 hours dark

IN-LIFE DATES: From: (first exposure)
B6C3F1: August 20, 2002
BALB/c: August 22, 2002
am3-C57BL/6: August 23, 2002
To: (necropsy)
B6C3F1: November 19, 2002
BALB/c: November 21, 2002
am3-C57BL/6: November 22, 2002

Route of administration:

oral: drinking water

Vehicle:

- Vehicle(s)/solvent(s) used: water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The dose formulations were prepared fore times during the 3-month studies in B6C3F1 mice (study 1) and five times during the 3-month studies in male B6C3F1, BALB/c, and am3-C57BL/6 mice (study 2). Formulations used in study 1 were stored in NALGENE® containers at room temperature and protected from light. Formulations used in study 2 were stored in NALGENE® containers and refrigerated at approximately 5° C.

Duration of treatment / exposure:

90 days (3 months)

Frequency of treatment:

Continuous

Post exposure period:

None

Dose / conc.:

62.5 mg/L drinking water

Dose / conc.:

125 mg/L drinking water

Dose / conc.:

250 mg/L drinking water

Dose / conc.:

500 mg/L drinking water

Remarks:

in study 1 only

Dose / conc.:

1 000 mg/L drinking water

Remarks:

in study 1 only

No. of animals per sex per dose:

study 1: 5 animals/sex/dose
study 2: 5 B6C3F1 mice/dose, 5 BALB/c mice/dose, and 10 am3-C57BL/6 mice /dose (males only)

Control animals:

yes, concurrent no treatment

Tissues and cell types examined:

Peripheral blood erythrocytes

Details of tissue and slide preparation:

CRITERIA FOR DOSE SELECTION:
Doses were seleted based on effects reported in previous studies and the present study was performed primarily to aid the design and dose selection for the 2-year carcinogenicity studies.

DETAILS OF SLIDE PREPARATION:
At the ends of the 3-month exposure periods, peripheral blood samples were obtained from mice, and smears were immediately prepared and fixed in absolute methanol. The methanol-fixed slides were stained with acridine orange and coded. Slides were scanned to determine the frequency of micronucleated cells in 2,000 normochromatic erythrocytes (NCEs) in each of five mice per treatment group for all except the am3-C57BL/6 strain; for the am3-C57BL/6 mice, five core study and four or five mutagenicity study mice per treatment group were evaluated. In addition to assessment of micronucleus frequencies, the percentage of polychromatic erythrocytes (PCEs) in a population of 1,000 erythrocytes was determined as a measure of bone marrow toxicity.

METHOD OF ANALYSIS:
The results were tabulated as the mean of the pooled results from all animals within an exposure group plus or minus the standard error of the mean.
A final call of positive for micronucleus induction is preferably based on reproducibly positive trials (as noted above). Because additional test data could not be obtained, results of the 3-month studies were accepted without repeat tests. Ultimately, the final
call is determined by the scientific staff after considering the results of statistical analyses, the reproducibility of any effects observed, and the magnitudes of those effects.

Statistics:

The frequency of micronucleated cells among NCEs and PCEs was analyzed by a statistical software package that tested for increasing trend over exposure groups with a one-tailed Cochran-Armitage trend test, followed by pairwise comparisons between each exposed group and the control group (ILS, 1990).
In the presence of excess binomial variation, as detected by a binomial dispersion test, the binomial variance of the Cochran-Armitage test was adjusted upward in proportion to the excess variation. In the micronucleus test, an individual trial is considered positive if the trend test P value is less than or equal to 0.025 or if the P value for any single exposed group is less than or equal to 0.025 divided by the number of exposed groups.

Sex:

male/female

Genotoxicity:

ambiguous

Remarks:

Positive in one strain

Toxicity:

yes

Remarks:

Reduced PCE count in one assay

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

see any other information on results

The results of the micronucleus tests conducted in three strains of mice were variable:

Study 1

Micronucleus frequencies were determined in peripheral blood erythrocytes of male and female B6C3F1 mice administered sodium dichromate dihydrate over an exposure concentration range of 62.5 to 1000 mg/L for 3 months. No significant increases were seen in micronucleated normochromatic erythrocytes in male or female mice over the exposure concentration range tested; there was a decrease in the percentage of polychromatic erythrocytes among total erythrocytes (an indication of bone marrow toxicity), but the changes were small and did not clearly correlate with exposure concentration.

Study 2

Micronucleus frequencies were evaluated in male B6C3F1, BALB/c, and am3 -C57BL/6 mice administered sodium dichromate dihydrate over an exposure concentration range of 62.5 to 250 mg/L in drinking water for 3 months. An increase in micronucleated erythrocytes that was judged to be equivocal was noted in male B6C3F1 mice, based on the trend test (P=0.031), which showed an increase in micronucleated normochromatic erythrocytes that did not reach statistical significance (required P value of 0.025); no exposed groups were significantly increased over the control group in this study. No increase in micronucleated normochromatic erythrocytes was observed in male BALB/c mice (Table B4). A significant exposure concentration-related increase (P<0.001) in micronucleated erythrocytes was noted in male am3-C57BL/6 mice. In this study, two of three dose groups were significantly (P<0.008) elevated over the control group. No significant effect of chemical exposure on the percentage of polychromatic erythrocytes was observed in any of the three micronucleus tests conducted in study 2.

Study 1	B6C3F1
	Male	Female	Male	Female
	Micronucleated NCEs (/1000)		PCEs (%)
0	2.70	1.70	4.1	3.6
62.5	2.60	1.20	3.5	2.5
125	2.20	1.60	3.1	3.4
250	3.70	1.80	3.3	3.9
500	2.50	2.10	2.7	3.2
1000	2.00	1.90	3.3	2.7
Study 2	B6C3F1
0	2.20	-	3.3	-
62.5	3.20	-	3.6	-
125	3.00	-	3.2	-
250	3.80*	-	2.8	-
BALB/c
0	4.70	-	3.7	-
62.5	3.90	-	4.0	-
125	3.30	-	3.3	-
250	4.20	-	3.5	-
am3-C57BL/6
0	1.65	-	2.9	-
62.5	2.50	-	2.8	-
125	3.05	-	2.9	-
250	3.72*	-	2.6	-

*significant by the trend test

Conclusions:

A significant increase in the frequency of peripheral blood erythrocyte micronuclei was seen in one (transgenic) mouse strain under the conditions of this study; similar findings were not apparent in the other strains. The results of this study are therefore equivocal.

Executive summary:

The potential of sodium dichromate to induce micronuclei was investigated in the peripheral blood erythrocytes of three strains of mice following administration via drinking water for 3 months. A significant increase in the frequency of micronuclei was seen in the transgenic am3 -C57/BL6 strain, however similar findings were not apparent in B6C3F1 of BALB/c mice. The results of this study are therefore equivocal.

Cross-reference 2

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

NTP GLP guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

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

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

Limit test:

no

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: obtained from Taconic Farms (Germantown, NY)
- Age at study initiation: 5 to 7 weeks old on the first day of the study
- Weight at study initiation: mean initial body weights for males and females were between 17.9 +/-0.4 g to 21.6 +/- 0.3 g.
- Housing: 1 male or 5 females per cage, Cages: Solid bottom polycarbonate (Lab Products, Inc., Maywood, NJ), changed at least twice weekly; Bedding: Irradiated 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; Racks: Stainless Steel (Lab Products, Inc., Maywood, NJ), changed every 2 weeks
- Diet (e.g. ad libitum): Irradiated NTP-2000 wafer rodent feed (Zeigler Brothers, Inc., Gardners, PA), available ad libitum
- Water (e.g. ad libitum): Tap water (Birmingham, AL municipal supply) via amber glass water bottles with Teflon®-lined caps and stainless steel sipper tubes (Wheaton, Millville, NJ), available ad libitum
- Acclimation period: 13 to 14 days

DETAILS OF FOOD AND WATER QUALITY:

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72° +/- 3° F (20.6 - 23.9 °C)
- Humidity (%): 50% +/- 15%
- Air changes (per hr): 18/hour
- Photoperiod (hrs dark / hrs light): 12 hours/day light, 12 hours dark

IN-LIFE DATES: From: Nov 13 and 14, 2001 (first exposure) To: Feb 13 and 14, 2002 (necropsy)

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

The dose formulations were prepared four times during the 3-month studies in B6C3F1 mice. Formulations used in study 1 were stored in NALGENE® containers at room temperature and protected from light.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

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 during study 1 by the study laboratory using ultraviolet spectroscopy. During study 1, the dose formulations were analyzed three times. All of the dose formulations for rats were within 10% of the target concentrations.

Duration of treatment / exposure:

90 days (3 months)

Frequency of treatment:

Continuous

Dose / conc.:

62.5 mg/L drinking water

Remarks:

equivalent to 9 mg/kg bw/d (3.1 mg Cr(VI)/kg bw/d)

Dose / conc.:

125 mg/L drinking water

Remarks:

equivalent to 15 mg/kg bw/d (5.2 mg Cr(VI)/kg bw/d)

Dose / conc.:

250 mg/L drinking water

Remarks:

equivalent to 26 mg/kg bw/d (9.1 mg Cr(VI)/kg bw/d)

Dose / conc.:

500 mg/L drinking water

Remarks:

equivalent to 45 mg/kg bw/d (15.7 mg Cr(VI)/kg bw/d)

Dose / conc.:

1 000 mg/L drinking water

Remarks:

equivalent to 80 mg/kg bw/d (27.9 mg Cr(VI)/kg bw/d)

No. of animals per sex per dose:

10

Control animals:

yes, concurrent no treatment

Details on study design:

Doses were seleted based on effects reported in previous studies and the present study was performed primarily to aid the design and dose selection for the 2-year carcinogenicity studies.

Observations and examinations performed and frequency:

see any other information on materials and methods below

Clinical signs:

no effects observed

Description (incidence and severity):

No clinical findings were attributed to sodium dichromate dihydrate exposure.

Mortality:

no mortality observed

Description (incidence):

All mice survived to the end of the study.

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.

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.

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

Mice demonstrated an erythrocyte microcytosis (decrease in mean cell volume) similar to that seen in the NTP rat study (NTP, 2007). However, the mice were much less affected, and no contradictory data from hematocrit values or mean cell hemoglobin concentrations, as described for rats, occurred for mice. The decreases in mean cell hemoglobin reflected the mean cell volume decrease. Similar to the occurrence at week 14 in the rat studies, erythrocyte counts increased, and hemoglobin concentrations decreased, but only in females.

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.

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 is not considered to be a direct effect of treatment.

Dose descriptor:

LOAEL

Effect level:

62.5 mg/L drinking water

Based on:

test mat.

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Remarks on result:

other: no NOAEL identified, histopathological findings starting at the lowest dose

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 ay 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, but the severity was less than in the comparable NTP rat study. 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.

Cross-reference 3

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

NTP GLP guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

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

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

Limit test:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: obtained from Taconic Farms (Germantown, NY)
- Age at study initiation: 5 to 7 weeks old on the first day of the study
- Weight at study initiation: mean initial body weights for males and females were between 89 +/-1 g to 101+/- 1 g.
- Housing: 5 animals per cage, Cages: Solid bottom polycarbonate (Lab Products, Inc., Maywood, NJ), changed at least twice weekly; Bedding: Irradiated 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; Racks: Stainless Steel (Lab Products, Inc., Maywood, NJ), changed every 2 weeks
- Diet (e.g. ad libitum): Irradiated NTP-2000 wafer rodent feed (Zeigler Brothers, Inc., Gardners, PA), available ad libitum
- Water (e.g. ad libitum): Tap water (Birmingham, AL municipal supply) via amber glass water bottles with Teflon®-lined caps and stainless steel sipper tubes (Wheaton, Millville, NJ), available ad libitum
- Acclimation period: 11 to 12 days

DETAILS OF FOOD AND WATER QUALITY:

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72° +/- 3° F (20.6 - 23.9 °C)
- Humidity (%): 50% +/- 15%
- Air changes (per hr): 18/hour
- Photoperiod (hrs dark / hrs light): 12 hours/day light, 12 hours dark

IN-LIFE DATES: From: Nov 12 and 11, 2001 (first exposure) To: Feb 12 and 11, 2002 (necropsy)

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

The dose formulations were prepared four times during the 3-month studies in F344/N rats. Formulations used in study 1 were stored in NALGENE® containers at room temperature and protected from light.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

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 during study 1 by the study laboratory using ultraviolet spectroscopy. During study 1, the dose formulations were analyzed three times. All of the dose formulations for rats were within 10% of the target concentrations.

Duration of treatment / exposure:

90 days (3 months)

Frequency of treatment:

Continuous

Dose / conc.:

62.5 mg/L drinking water

Remarks:

equivalent to 5 mg/kg bw/d in males and females (1.7 mg Cr(VI)/kg bw/d)

Dose / conc.:

125 mg/L drinking water

Remarks:

equivalent to 9 mg/kg bw/d in males (3.1 mg Cr(VI)/kg bw/d) and 10 mg/kg bw/d in females (3.5 mg Cr(VI)/kg bw/d)

Dose / conc.:

250 mg/L drinking water

Remarks:

equivalent to 17 mg/kg bw/d in males (5.9 mg Cr(VI)/kg bw/d) and 18 mg/kg bw/d in females (6.3 mg Cr(VI)/kg bw/d)

Dose / conc.:

500 mg/L drinking water

Remarks:

equivalent to 32 mg/kg bw/d in males (11.2 mg Cr(VI)/kg bw/d) and 33 mg/kg bw/d in females (11.5 mg Cr(VI)/kg bw/d)

Dose / conc.:

1 000 mg/L drinking water

Remarks:

equivalent to 60 mg/kg bw/d in males (20.9 mg Cr(VI)/kg bw/d) and 61 mg/kg bw/d in females (21.3 mg Cr(VI)/kg bw/d)

No. of animals per sex per dose:

10 animals/sex/dose

Control animals:

yes, concurrent no treatment

Details on study design:

Doses were seleted based on effects reported in previous studies and the present study was performed primarily to aid the design and dose selection for the 2-year carcinogenicity studies.

Observations and examinations performed and frequency:

see any other information on materials and methods below

Clinical signs:

no effects observed

Description (incidence and severity):

No clinical findings were attributed to sodium dichromate dihydrate exposure.

Mortality:

no mortality observed

Description (incidence):

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

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.

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 (equivalent to 1.7, 3.5, 5.9, 11.2 and 20.9 mg Cr(VI)/kg bw/d) and 5, 10, 18, 33, and 61 mg/kg to females (equivalent to 1.7, 3.1, 6.3, 11.5 and 21.3 mg Cr(VI)/kg bw/d).

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

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 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 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 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 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.

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 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.

Dose descriptor:

LOAEL

Effect level:

62.5 mg/L drinking water

Based on:

test mat.

Remarks:

equivalent to 1.7 mg Cr(VI)/kg bw/d

Sex:

male/female

Basis for effect level:

haematology

Remarks on result:

other: no NOEAL identified, haematolofical findings starting at the lowest dose

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 of exposure were seen 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 non-neoplastic lesions (focal ulceration, regenerative epithelial hyperplasia, and squamous epithelial metaplasia) occurred in the glandular stomach of males and females exposed to 1000 mg/L.

Cross-reference 4

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

NTP GLP guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

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

Principles of method if other than guideline:

NTP 90-day toxicity study protocol; used as a sighting study for the subsequent carcinogenicity study. This additional 3-month comparative toxicity study of Cr VI was conducted with three strains (B6C3F1, BALB/c, and am3-C57BL/6) of male mice to determine possible differences between strains in sensitivity to hepatotoxic effects of chromates.

GLP compliance:

yes

Limit test:

no

Species:

mouse

Strain:

other: B6C3F1, BALB/c, and am3-C57BL/6

Details on species / strain selection:

This additional 3-month comparative toxicity study of Cr VI was conducted with three strains (B6C3F1, BALB/c, and am3-C57BL/6) of male mice to determine possible differences between strains in sensitivity to hepatotoxic effects of chromates.

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:
B6C3F1: Taconic Laboratory Animals and Services (Germantown, NY)
BALB/c: Charles River Laboratory (Portage, MI)
am3-C57BL/6: Charles River Laboratory (Wilmington, MA)
- Age at study initiation: 6 (B6C3F1 and BALB/c mice) or 7 (am3-C57BL/6 mice) weeks
- Weight at study initiation: mean initial body weights were between 24.1 +/-0.3 g to 24.3 +/- 0.3 g.
- Housing: 1 animal per cage, Cages: Polycarbonate (Lab Products, Inc., Maywood, NJ), changed at least once weekly; Bedding: Irradiated hardwood bedding chips (P.J. Murphy Forest Products, Inc., Montville, NJ), changed at least once weekly; Cage Filters: Spun-bonded polyester (Snow Filtration Co., Cincinnati, OH); Racks: Stainless Steel (Lab Products, Inc., Seaford, DE), changed every 2 weeks
- Diet (e.g. ad libitum): Irradiated NTP-2000 wafer rodent feed (Zeigler Brothers, Inc., Gardners, PA), available ad libitum
- Water (e.g. ad libitum): Tap water (Columbus, OH, municipal supply) via glass bottles with Teflon®-lined septa and stainless steel sipper tubes (Wheaton, Millville, NJ), available ad libitum
- Acclimation period:
B6C3F1: 12 days
BALB/c: 16 days
am3-C57BL/6: 17 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72° +/- 3° F (20.6 - 23.9 °C)
- Humidity (%): 50% +/- 15%
- Air changes (per hr): 10/hour
- Photoperiod (hrs dark / hrs light): 12 hours/day light, 12 hours dark

IN-LIFE DATES: From: (first exposure)
B6C3F1: August 20, 2002
BALB/c: August 22, 2002
am3-C57BL/6: August 23, 2002
To: (necropsy)
B6C3F1: November 19, 2002
BALB/c: November 21, 2002
am3-C57BL/6: November 22, 2002

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

The dose formulations were prepared five times during the 3-month studies in male B6C3F1, BALB/c, and am3-C57BL/6 mice (study 2). Formulations used in study 2 were stored in NALGENE® containers and refrigerated at approximately 5° C.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

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 during study 2 by the analytical chemistry laboratory using IC.
During study 2, the dose formulations were analyzed three times. All nine of the dose formulations for mice were within 10% of the target concentrations.

Duration of treatment / exposure:

90 days (3 months)

Frequency of treatment:

Continuous

Dose / conc.:

62.5 mg/L drinking water

Remarks:

equivalent to 8 mg/kg bw/d (2.8 mg Cr(VI)/kg bw/d)

Dose / conc.:

125 mg/L drinking water

Remarks:

equivalent to 15 mg/kg bw/d (5.2 mg Cr(VI)/kg bw/d)

Dose / conc.:

250 mg/L drinking water

Remarks:

equivalent to 25 mg/kg bw/d (8.7 mg Cr(VI)/kg bw/d)

No. of animals per sex per dose:

10 males (B6C3F1 and BALB/c mice)
5 males (am3-C57BL/6 mice, core study)

Control animals:

yes, concurrent no treatment

Details on study design:

A top sodium dichromate dihydrate concentration of 250 mg/L in drinking water was chosen based on the poor palatability of higher concentrations in the first study with B6C3F1 mice (see cross reference 'Study 1' in mice)

Observations and examinations performed and frequency:

see any other information on materials and methods below

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

No clinical findings of toxicity were observed in B6C3F1 and am3-C57BL/6 mice. In BALB/c mice ruffled fur was observed in the 250 mg/L group and was attributed to reduced water consumption and decreased body weight gain.

Mortality:

no mortality observed

Description (incidence):

All mice survived to the end of the study

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

B6C3F1 mice: Statistically significant decreases in final mean body weights and body weight gains occurred in the 125 and 250 mg/L groups
BALB/C mice: Final mean body weights and body weight gains in the 125 and 250 mg/L groups were significantly less than those of the controls
am3-C57BL/6 mice: Final mean body weights and body weight gains of all exposed groups were significantly less than those of the control group

Description (incidence and severity):

B6C3F1 mice: Water consumption by the 250 mg/L group was less than that by the control group. Exposure concentrations of 62.5, 125, and 250 mg/L resulted in average daily doses of approximately 8, 15, and 26 mg/kg, respectively.
BALB/C mice: Water consumption by the 250 mg/L group was less than that by the control group. Exposure concentrations of 62.5, 125, and 250 mg/L resulted in average daily doses of approximately 9, 14, and 24 mg/kg.
am3-C57BL/6 mice: Water consumption by 250 mg/L mice was less than that by the controls. Exposure concentrations of 62.5, 125, and 250 mg/L resulted in average daily doses of approximately 8, 15, and 25 mg/kg, respectively.

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

B6C3F1 mice: An erythrocyte microcytosis (decrease in mean cell volume) and a decrease in mean cell hemoglobin similar to those in the B6C3F1 mice in study 1 and in the BALB/c and am3-C57BL/6 mice in study 2 occurred. The erythrocyte count in the 250 mg/L group was significantly increased.
BALB/C mice: An erythrocyte microcytosis (decrease in mean cell volume) and a decrease in mean cell hemoglobin similar to those in the B6C3F1 mice in study 1 and in the B6C3F1 and am3-C57BL/6 mice in study 2 occurred. Increased erythrocyte counts occurred in the 125 and 250 mg/L groups. A small (30%) increase in alanine aminotransferase activity occurred in the 250 mg/L group, and total protein and albumin concentrations decreased (less than 12%) in the 125 and 250 mg/L groups.
am3-C57BL/6 mice: An erythrocyte microcytosis (decrease in mean cell volume) and a decrease in mean cell hemoglobin similar to those in the B6C3F1 mice in study 1 and in the B6C3F1 and BALB/c mice in study 2 occurred. Decreases occurred in automated hematocrit values in the 125 and 250 mg/L groups and in the manual hematocrit value and hemoglobin concentration in the 250 mg/L group. An increase (92%) in alanine aminotransferase activity occurred in the 250 mg/L group.

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

B6C3F1 mice: Statistically significant decreases in absolute weight were seen in the kidney of the 125 mg/L group and in the kidney, lung, spleen, and thymus of the 250 mg/L group. Changes in organ weights were attributed to changes in body weights with the exception of thymus weight changes, which were considered related to treatment or stress.
BALB/C mice: Statistically significant decreases in absolute weights of the heart and kidney in 125 mg/L mice and of the heart, kidney, and liver in 250 mg/L mice were consistent with the mild reductions in body weights in the 125 and 250 mg/L groups
am3-C57BL/6 mice: Statistically significant decreases in absolute heart, liver, and thymus weights and absolute and relative spleen weights in the 250 mg/L core study group were related to decreased body weights

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

B6C3F1 mice: Incidences of minimal to mild histiocytic cellular infiltrates and mucosal epithelial hyperplasia in the duodenum of all exposed groups were significantly greater than those in the control groups, and, in general, the severities increased with increasing exposure concentration. The histiocytic infiltrates and epithelial hyperplasia were similar to those observed in the B6C3F1 mice in study 1 (Plate 14). Incidences of minimal to mild glycogen depletion in the liver and minimal secretory depletion in the pancreas were significantly increased in the 125 and 250 mg/L groups. The severity of liver glycogen depletion in all exposed groups was greater than that of the controls.
BALB/C mice: Except for epithelial hyperplasia in the 62.5 mg/L group, the incidences of histiocytic cellular infiltration and epithelial hyperplasia of the small intestine (duodenum) and secretory depletion of the pancreas were significantly increased in all exposed groups. Although, generally minimal to mild, there were slight increases in the average severities of these lesions with increasing exposure concentration. The histiocytic infiltrates and epithelial hyperplasia were similar to those observed in B6C3F1 mice.
am3-C57BL/6 mice: In the duodenum of core study mice, incidences of histiocytic cellular infiltration at 125 and 250 mg/L and epithelial hyperplasia at 62.5 mg/L and greater were significantly greater than those in the controls, and severities of these lesions increased with exposure concentration. Incidences of glycogen depletion in the liver of all exposed groups, secretory depletion in the pancreas of the 125 and 250 mg/L groups, and histiocytic cellular infiltration of the mesenteric lymph node in the 250 mg/L group were also significantly increased compared to those in the control group. The histiocytic infiltrates and epithelial hyperplasia were similar to those observed in B6C3F1 mice.

Other effects:

effects observed, non-treatment-related

Description (incidence and severity):

B6C3F1 mice: Reproductive tissue evaluations in B6C3F1 mice found no significant differences from controls in left cauda epididymis, left epididymis, or left testis weights or in spermatid measurements or epididymal sperm motility for any of the exposed groups.
BALB/C mice: No differences in left cauda epididymis, left epididymis, or left testis weights or in spermatid or spermatozoal measurements were attributed to exposure to sodium dichromate dihydrate.
am3-C57BL/6 mice: A statistically significant decrease in the left testis weight observed in the 250 mg/L group was related to the decreased body weight in this group. No other significant differences in reproductive parameters were observed.

Dose descriptor:

LOAEL

Effect level:

62.5 mg/L drinking water

Based on:

test mat.

Sex:

male

Basis for effect level:

histopathology: non-neoplastic

Remarks on result:

other: no NOAEL identified, histopathological findings starting at the lowest dose

Critical effects observed:

not specified

There was little difference in the response of the three strains to sodium dichromate dihydrate. All showed an exposure concentration-related decrease in water consumption and body weight gain, an increase in erythrocytic microcytosis, histiocytic infiltration of the small intestines, and pancreatic secretory depletion. However, there were differences in some clinical pathology parameters including serum alanine aminotransferase, which showed higher increases in exposed BALB/c mice compared to the B6C3F1 and am3-C57BL/6 mice. In addition to the pancreatic secretory depletion, exposed B6C3F1 and am3-C57BL/6 mice showed liver glycogen depletion that was likely also due to depressed food consumption, which is frequently observed when water consumption is decreased. Thus, with the exception of the minor alanine aminotransferase response, this study did not confirm the earlier findings with the BALB/c strain, and instead suggests that the liver effects in all three strains more likely reflected nutritional inequalities than a toxic response to sodium dichromate dihydrate.

Conclusions:

Administration of sodium dichromate in the drinking water to mice for 90 days caused effects on body weight and water consumption. There was little difference in the response of the three strains to sodium dichromate dihydrate. All showed an exposure concentration-related decrease in water consumption and body weight gain, an increase in erythrocytic microcytosis, histiocytic infiltration of the small intestines, and pancreatic secretory depletion. No biologically significant differences in reproductive parameters were observed in any strain. Similar to study 1 in rats and mice (NTP, 2007), but less severe, anemia was evident in mice receiving drinking water containing sodium dichromate dihydrate; histiocytic infiltration was noted in the duodenum of all three strains studied (B6C3F1, BALB/c, and am3-C57BL/6) at all concentrations employed, in the mesenteric lymph nodes at 125 mg/L or greater in the B6C3F1 strain, and at 250 mg/L in the am3-C57BL/6 strain. There was no consistent evidence of hepatocyte injury in mice in any of the strains tested.

Executive summary:

Sodium dichromate dihydrate was administered in drinking water to groups of 10 male B6C3F1, 10 male BALB/c, and five male am3-C57BL/6 mice for 3 months at exposure concentrations of 0, 62.5, 125, or 250 mg/L (equivalent to average daily doses of approximately 8, 15, or 25 mg/kg sodium dichromate dihydrate or 2.8, 5.2, or 8.7 mg/kg chromium to B6C3F1, BALB/c, and am3-C57BL/6 mice). All mice in study 2 survived until study termination. Mean body weights of 125 and 250 mg/L B6C3F1 and BALB/c mice and all exposed groups of am3-C57BL/6 mice were less than those of the control groups. Mice exposed to 250 mg/L consumed less water than the control groups. Exposure concentration-related decreases in mean red cell volumes and mean red cell hemoglobin values were observed in all three mouse strains. Erythrocyte counts were increased in exposed B6C3F1 and BALB/c mice but not in am3-C57BL/6 mice. Changes in organ weights were generally consistent with reduced body weights in exposed groups in all mouse strains. No biologically significant differences in reproductive parameters were observed in any strain.

Histiocytic cellular infiltration and epithelial hyperplasia of the duodenum occurred in most mice exposed to 125 or 250 mg/L, and the incidences of these lesions were increased in the 62.5 mg/L group compared to controls. Secretory depletion was present in the pancreas of most mice exposed to 125 or 250 mg/L. The incidences of glycogen depletion of the liver were significantly increased in male B6C3F1 mice exposed to 125 or 250 mg/L and in all exposed groups of male am3-C57BL/6 mice. The incidence of histiocytic cellular infiltration in the mesenteric lymph node was significantly increased in the 250 mg/L group of male am3-C57BL/6 mice.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2007

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

yes

Remarks:

deviates with respect to the number of tested strains

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Sodium dichromate

EC Number:

234-190-3

EC Name:

Sodium dichromate

Cas Number:

10588-01-9

Molecular formula:

Cr2Na2O7

IUPAC Name:

sodium dichromate

Details on test material:

See details given in other NTP studies: a coded aliquot of the test material was sent to the testing laboratory.

Method

Target gene:

Reversion to histidine independence

Species / strain

Species / strain 1

Species / strain / cell type:

S. typhimurium TA 98

Species / strain 2

Species / strain / cell type:

S. typhimurium TA 100

Species / strain 3

Species / strain / cell type:

E. coli WP2 uvr A pKM 101

Metabolic activation:

with and without

Metabolic activation system:

Aroclor 1254-induced rat liver S9

Test concentrations with justification for top dose:

5-300 µg/plate

Controls

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

sodium azide

methylmethanesulfonate

other: 4-nitro-o-phenylenediamine; 2-aminoanthracene

Results and discussion

Test results

Test results 1

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

positive

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not specified

Positive controls validity:

not specified

Test results 2

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

positive

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not specified

Positive controls validity:

not specified

Test results 3

Species / strain:

E. coli WP2 uvr A pKM 101

Metabolic activation:

with and without

Genotoxicity:

positive

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not specified

Positive controls validity:

not specified

Any other information on results incl. tables

Sodium dichromate dihydrate (5 to 300 µg/plate) was clearly mutagenic in Salmonella typhimurium strains TA100 and TA98 and in Escherichia coli strain WP2 uvrA pKM101 with and without 10% induced rat liver S9 enzymes. Responses were stronger in the strains that mutate via base substitution (TA100, E. coli WP2); in all three tester strains, mutagenicity was more pronounced in the absence of S9, based on the lowest concentration that elicited a significant mutagenic response.

Applicant's summary and conclusion

Conclusions:

The results of this study show that sodium dichromate is mutagenic in the Ames test

Executive summary:

Sodium dichromate dihydrate (5 to 300 µg/plate) was mutagenic in Salmonella typhimurium strains TA100 and TA98 and in Escherichia coli strain WP2 uvrA pKM101 with and without 10% induced rat liver S9 enzymes. Responses were stronger in the strains that mutate via base substitution (TA100, E. coli WP2); in all three tester strains, mutagenicity was more pronounced in the absence of S9, based on the lowest concentration that elicited a significant mutagenic response.