Exposure to lead and male fertility.

Lead is a reproductive toxicant. Exposure to inorganic lead is detrimental to human semen quality. The studies of the risk of spontaneous abortion and congenital malformation have shown contradictory findings. The aim of the following review is to summarise the epidemiological evidence of the effects of inorganic lead on male fertility. The focus is on epidemiological studies of time-to-pregnancy and related fertility measures. Blood lead measurements were applied to exposure assessment in all the studies. The results of the studies on fertility rates are consistent in showing an association between lead and reduced fertility. Also, there seems to be a tendency towards stronger association at older age with increasing duration of exposure. The independent roles of exposure duration and effect modification by age may have been difficult to distinguish. There is a paucity of studies on time taken to conceive. The studies conducted only weakly suggest that male exposure to lead is associated with delayed conception. The findings of time-to-pregnancy and fertility rate studies contradict. The possible reasons for this discrepancy is discussed briefly. There are a number of mechanisms by which exposure to lead may reduce male fertility. On the basis of animal studies, alterations in sperm chromatin stabilitv or epigenetic effects may be the most probable mechanisms involved at low exposure level.