The Fungicide Methyl 2-Benzimidazole Carbamate Causes Infertility in Male Sprague-Dawley Rats12

Abstract

A serial breeding technique was used to evaluate the fertility of male Sprague-Dawley rats after exposure to the fungicide carbendazim (methyl 2-benzyimidazole carbamate). Proven-fertile male rats (90 days old) received 10 daily doses of corn oil or carbendazim (400 mg/kg/day) peroral. Each male was bred with a new female each week; breeding began on the third day of treatment and continued for 32 wk after the last day of chemical exposure. Twelve days after each breeding period, the females were killed, their uteri were examined for resorptions, and the number of dead and viable fetuses was determined. All males were killed 35 wk post exposure, and testicular tissue was prepared for histopathological examination by vascular perfusion. Fertility (percent fertile as indicated by pregnant females) of males in the carbendazim-treated group was depressed the first post-exposure week; 10 of the 24 treated males failed to produce a pregnant female as compared with no failure in the control group. By the fifth post-exposure week, 16 of the 24 carbendazim-treated males were infertile. Of these 16 males, 4 recovered fertility after a failure to produce a pregnant female for 5-11 consecutive breeding periods. However, 12 of the males did not recover fertility during the remainder of the 32-wk post-exposure period. Histological examinations of testicular sections 245 days post exposure revealed that exposure to carbendazim caused severe seminiferous tubular atrophy (> 85% of tubules were atrophic) in those carbendazim treated males that failed to recover fertility. The seminiferous tubules of these males often showed "Sertoli cell-only" epithelium surrounded by a thickened basement membrane; < 2% of the tubules showed spermatozoa in the lumen. Seminiferous tubules of the carbendazim-treated males that recovered fertility had various numbers of atrophic tubules (13-85%) 245 days post exposure. Data from this study indicates that exposure to carbendazim produced an early, reversible infertility in some males (i.e. recovery of fertility after failure to breed for 5-11 consecutive breeding periods) and irreversible infertility in others.