NTP Toxicity Studies of Sodium Selenate and Sodium Selenite (CAS Nos. 13410-01-0 and 10102-18-8) Administered in Drinking Water to F344/N Rats and B6C3F1 Mice.

Sodium selenate and sodium selenite are used as supplements to poultry and livestock feed to promote growth and prevent selenium deficiency diseases. Both compounds have been found in chemical waste sites. Thirteen-week toxicity studies were conducted by administering the chemicals to groups of male and female F344/N rats and B6C3F1 mice in drinking water. Animals were evaluated for hematology, clinical chemistry, urinalysis (rats only), histopathology, and reproductive system effects. In the studies of sodium selenate, groups of 10 male and 10 female rats and mice received 0, 3.75, 7.5, 15, 30, or 60 ppm sodium selenate for 13 weeks. These concentrations were estimated to deliver 0, 0.1, 0.2, 0.4, 0.6, 1.1 (males), or 0.8 (females) mg selenium/kg body weight for rats and 0, 0.3, 0.5, 0.8, 1.5, or 2.6 mg/kg selenium for mice. All male and female rats exposed to 60 ppm died. The final mean body weights of rats exposed to 30 ppm sodium selenate and of mice exposed to 30 or 60 ppm were 13% to 29% lower than those of the controls. Water consumption by rats and mice exposed to 15 ppm or greater was decreased. Decreases in urine volume and increases in erythrocyte counts, hematocrit, hemoglobin concentrations, alanine aminotransferase activities, urea nitrogen, and urine specific gravity were considered related to dehydration, as indicated by the decreased water consumption and mean body weights in groups showing these differences. Administration of 7.5 ppm sodium selenate or greater was associated with increased incidences of renal papillary degeneration in rats. Dehydration may have been a contributing factor. No lesions related to sodium selenate administration occurred in mice. In the studies of sodium selenite, groups of 10 male and 10 female rats and mice received 0, 2, 4, 8, 16, or 32 ppm sodium selenite for 13 weeks. These concentrations were estimated to deliver 0, 0.08, 0.13, 0.2, 0.4, 0.8 (males), or 0.9 (females) mg/kg selenium for rats and 0, 0.14, 0.3, 0.5, 0.9, or 1.6 mg/kg selenium for mice. Two female rats exposed to 32 ppm died during the study. The final mean body weights of rats and mice exposed to 32 ppm were 17% to 54% lower than those of the controls. Water consumption by exposed rats and mice decreased with increasing exposure concentration. Changes in hematology, clinical chemistry, and urinalysis parameters similar to those observed in rats exposed to sodium selenate were observed in rats exposed to sodium selenite. These effects were also considered related to dehydration, as indicated by the decreased water consumption and mean body weights in exposed groups. Sodium selenite administration was associated with increased incidences of renal papillary regeneration in rats. Dehydration may have been a contributing factor. No lesions related to sodium selenite administration occurred in mice. Based on mortality in rats, body weight depression, and renal lesions, sodium selenate and sodium selenite were more toxic to rats than to mice. These chemicals caused increases in estrous cycle length in rats; sodium selenite also caused an increase in estrous cycle length in mice. Based on mortality, body weight depression, decreased water consumption, and renal papillary lesions, the estimated no-observed-adverse-effect level (NOAEL) in rats was 0.4 mg selenium/kg body weight for sodium selenate and for sodium selenite. Based on body weight depression and decreased water consumption, the estimated NOAEL in mice was 0.8 mg selenium/kg body weight for sodium selenate and 0.9 mg selenium/kg body weight for sodium selenite. NOTE: These studies were supported in part by funds from the Comprehensive Environmental Response, Compensation, and Liability Act trust fund (Superfund) by an interagency agreement with the Agency for Toxic Substances and Disease Registry, U.S. Public Health Service.