The effects of cobalt on male reproduction were evaluated in mice after acute and chronic cobalt treatment. The impact of acutely administered cobaltous chloride (200 $\mu$moles/kg, i.p., for 3 days) was assessed using the dominant lethal assay over seven weeks. There were significant increases in early embryonic losses at each week after cobalt treatment. There were no significant changes in late embryonic losses at any time measured. Evaluation of testicular weight and sperm parameters, including concentration, motility and head morphology, were unchanged except for a decrease in motility at week 1. Fertility was significantly decreased during weeks 2 and 3 only The time course of the reproductive effects of chronic, oral administration of 400 ppm of cobalt was evaluated from 7 to 13 weeks of treatment. Sperm concentration significantly decreased between weeks 9 and 11 (from 87% to 26% of control), and remained depressed at week 13. Fertility sharply decreased between weeks 11 and 13 of treatment. After 13 weeks of cobalt treatment, a group was placed on distilled water for 20 weeks and evaluated for recovery of fertility. No significant functional recovery was observed at the end of 33 weeks Histological studies demonstrated a progressive degeneration of the germinal epithelium, beginning with vacuole formation at 9 weeks, continuing with degeneration at 11 weeks, and almost complete destruction by 13 weeks The dose response effects of chronically administered cobalt on male reproduction were studied at 0, 100, 200 and 400 ppm of cobalt in drinking water at 10 and 12 weeks of treatment. Testicular weight was decreased significantly in all of the cobalt-treated groups. Sperm motility declined only after 12 weeks of treatment. A dose-related decline in sperm concentration after 12 weeks of cobalt treatment was observed. Fertility was significantly decreased only in the group given 400 ppm of cobalt for 12 weeks. Serum testosterone levels significantly increased in the groups treated with 200 ppm of cobalt for 10 weeks and in all groups at 12 weeks. The evidence suggests that cobalt represents a reproductive hazard to males who are chronically exposed. (Abstract shortened with permission of author.)
