Estimation of the increased risk of human infertility from alterations in semen characteristics.

Although many toxicants lower sperm counts in exposed men, there is no means of estimating the resulting increase in infertility. A mathematical model was developed to provide such estimates, using sperm counts (i.e., concentration) as an indicator of fertility potential. Continuous functions were fit to published distributions of sperm counts of men from fertile and infertile couples. A distribution of sperm counts for the overall population was constructed from these two functions. Equations were derived for calculating the infertility risk for a man with a given sperm count and the incidence of infertility in an exposed population. The increase in infertility was calculated for a proportional reduction of all sperm counts within a population and for a group of workers exposed to dibromochloropropane.