MALE REPRODUCTIVE TOXICITY OF LEAD IN ANIMALS AND HUMANS

Objective-To critically review the literature on male reproductive tox icity of lead in animals and humans. Methods-A systematic literature s earch identified a total of 32 experimental studies in animals and 22 epidemiological studies, one case report on humans and five review art icles or documents. The studies were evaluated by paying attention mai nly to sample size, study design, exposure, and dose characterisation, analytical method standardisation, and quality assurance. Results-Sev eral studies on rats and other rodents indicated that blood lead conce ntrations >30-40 mu g/dl were associated with impairment of spermatoge nesis and reduced concentrations of androgens. However, other animal s tudies, mainly about histopathological, spermatozoal, and hormonal end points, indicated that certain species and strains were quite resista nt to the reproductive toxicity of lead and that different testicular lead concentrations could account for these differences. The human stu dies focused mainly on semen quality, endocrine function, and birth ra tes in occupationally exposed subjects, and showed that exposure to co ncentrations of inorganic lead >40 mu g/dl in blood impaired male repr oductive function by reducing sperm count, volume, and density, or cha nging sperm motility and morphology. No relevant effects were detected on endocrine profile. Conclusion-Several factors make it difficult to extrapolate the animal data to the human situation. The difficulties are mainly due to differences between species in reproductive end poin ts and to the level of exposure. Concentrations of blood lead >40 mu g /dl seemed to be associated with a decrease in sperm count, volume, mo tility, and morphological alterations and a possible modest effect on endocrine profile. Dose-response relation, in particular at a threshol d level, is poorly understood, and site, mode, or mechanism of action are unknown. Also, the effects were not always the same or associated in the same way, although the prevalent effects were on sperm count an d concentration. Some methodological issues and indications for future studies are discussed.