Exposure to diesel exhaust affects the male reproductive system of mice.

Several recent reports have suggested that sperm count and quality in normal men are declining. Various environmental chemical compounds may affect the male reproductive system. We propose here that diesel exhaust is an environmental pollutant with the potential to influence male reproductive function. Ultrastructural changes were observed in Leydig cells of mice exposed to diesel exhaust (0.3 mg diesel exhaust particles (DEP)/ m 3 through the airway, 12 h daily, up to 6 months) and reduction in LH receptor mRNA expression in Leydig cells was observed at a concentration of 1 mg DEP/m 3 . Daily sperm production per gram of testis dose-dependently decreased with exposure to DE for 6 months; 29%, 36%, and 53% reductions were observed at 0.3, 1.0, and 3.0 mg DEP/m 3 , respectively. A no-observed-adverse-effect level (NOAEL) was observed with approximately 30 μg DEP/m 3 , which is lower than the WHO-recommended limit.