Chromium trioxide

Endpoint summary

Description of key information

High quality (NTP) studies using oral dosing are available for sodium dichromate and potassium dichromate in the rat and mouse. Repeated dose inhalation exposure studies are available for chromium trioxide. Longer term toxicity and carcinogenicity studies are also available for compounds in this group.

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

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.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

1.7 mg/kg bw/day

Study duration:

subchronic

Species:

rat

System:

other: cardiovascular / hematological: hematopoiesis

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

Well reported literature study, but with a non-standard design. Findings are consistent with those in other similar studies.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study investigated toxicity to the respiratory tract following repeated inhalation exposure to chromic acid mist for two 60 minute periods a week for 8-12 months.

GLP compliance:

no

Remarks:

Literature study

Limit test:

no

Species:

mouse

Strain:

C57BL

Sex:

female

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: Data are not reported, but other studies by the same authors report particles of inhalable size (predominantly <5 µm)

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

Mice were exposed for 8-12 months.

Frequency of treatment:

Mice were exposed for two periods of 60 minutes per week

Dose / conc.:

1.81 mg/m³ air (analytical)

No. of animals per sex per dose:

Exposed animals were terminated at 8-12 months (23 animals, including 3 decedents) or 12-18 months (20 animals including 3 decedents). Twenty unexposed controls were terminated at 18 months.

Control animals:

yes, concurrent no treatment

Observations and examinations performed and frequency:

Examinations focused on local effects on the respiratory tract

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Irritant and corrosive effects in the respiratory tract (perforated nasal septum, tracheal and bronchial epithelial hyperplasia, emphysema) occurred in treated animals

Dose descriptor:

LOAEC

Effect level:

1.81 mg/m³ air (analytical)

Based on:

test mat. (total fraction)

Sex:

female

Basis for effect level:

other: Single exposure level: irritant and corrosive effects

Critical effects observed:

not specified

Conclusions:

Exposure to chromic acid mist at the exposure level equivalent to 1.81 mg Cr/m3 for 8-12 months was found to induce changes consistent with irritation and corrosion in the respiratory tract of female mice.

Executive summary:

Female ICR mice were exposed to chromic acid mist at a concentration equivalent to 1.81 mg Cr/m3 for two 60 -minute periods a week for 8 -12 months. Exposure was found to induce changes consistent with irritation and corrosion in the respiratory tract.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEC

1.81 mg/m³

Study duration:

subchronic

Species:

mouse

System:

other: respiratory

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEC

1.81 mg/m³

Study duration:

subchronic

Species:

mouse

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

Repeated dose oral toxicity

No studies of repeated dose oral toxicity are available for chromium (VI) trioxide, however studies are not required as the primary route of occupational exposure is likely to be inhalation. Reliable repeated dose studies are available, however, for potassium dichromate and sodium dichromate and the results of these studies can be extrapolated to the other members of the group.

Two NTP combined repeat dose / reproductive toxicity screening studies have been performed with potassium dichromate in the rat and mouse; the studies used dietary administration for up to 9 weeks. Although there was some evidence for a treatment-related effect on erythrocyte parameters in both studies, findings were of small magnitude and were not considered to be of toxicological significance. Findings of toxicological significance were limited to reduced bodyweight gain in male mice at the high dose level of 400 ppm (32 mg/kg bw/d Cr (VI)).

Two NTP 90-day carcinogenicity sighting studies were performed with sodium dichromate in the rat and mouse using administration in drinking water. The results of these studies show effects on bodyweight and food consumption and (most markedly), a microcytic hypochromic anaemia consistent with an effect of Cr (VI) on iron homeostasis and/or haemoglobin synthesis. Histopathology revealed local irritant effects on the gastric mucosa. Findings were apparent at the lowest dose levels in these studies, equivalent to 1.7 and 3.1 mg/kg bw/d Cr (VI) in the rat and mouse respectively.

Repeated dose dermal toxicity

No studies of repeated dose dermal toxicity are available for this group of compounds, however the relevance of such studies to human occupational risk assessment will be severely limited by the corrosive nature of the compound. In practice, human dermal exposure will also be self-limiting. Given the corrosivity and the low dermal penetration of these compounds, findings in repeat-dose dermal toxicity studies will be limited to local (site of contact) effects; systemic effects are not predicted with the exception of non-specific effects secondary to local corrosivity. Additionally, performing repeated dose dermal toxicity studies cannot be justified on animal welfare grounds.

Repeated dose inhalation toxicity

The results of two published repeated exposure inhalation studies in the mouse (Adachi et al, 1986; Adachi, 1987) performed over periods of up to 12 months show that the primary effects of exposure are local corrosion and irritation of the respiratory tract. Findings were observed in mice following exposure to a concentration of 3.63 mg/m3 for 30 minutes, twice a week for up to one year; or in mice exposed to concentrations of 1.81 mg/m3 for 60 minutes, twice a week for one year. The results of this study can be extrapolated to the other compounds in this group.

Justification for classification or non-classification

Chromium (VI) trioxide, sodium chromate, sodium dichromate and potassium dichromate are classified under Annex I to directive 67/548/EEC. Chromium (VI) trioxide is listed in Annex VI to Regulation (EC) No 1272/2008 under Index No 024-001-00-0 with the following harmonised classification:

STOT RE 1, H372 ‘Causes damage to the respiratory tract and to the kidney’

No change to this classification is proposed.