Pesticides and male reproduction: How to quantify the real impact?

Many chemicals discharged into the environment induce alterations in growth, development and reproduction in humans and wildlife animals. Nowadays, the increase of environmental chemical pollution is estimated to reach amounts to 4 millions of organic environmental contaminants, and this number increases annually. Globally, there are 100.000 products -manufactured in the order of 200 million tons per year- that contaminate 30% of the water and 70% of the general environment. Moreover, many research groups in the world are starting to analyze the so-called emerging pollutants. This broad spectrum of chemical compounds derived from social habits, life conditions, working hazards or drugs and medicines may act as testicular toxicants and therefore reduce reproductive efficiency. The human male has relatively low fertility compared with other animals; thus, could be at greater risk when facing reproductive toxicants compared to common laboratory animal model species. Analyses of human male reproductive alterations involve monitoring seminal sperm motility and morphology and measuring the sperm count or concentration. Computer-assisted, morphometric approaches promise the decrease of the subjective nature of these evaluations and increase their value in risk assessment procedures. Improvements in predicting human reproductive risks can be expected to come from increased knowledge about reproductive mechanisms in man and animals, along with the utilization of objective measures of cellular indicators of male reproductive function. On the other hand, sperm count has long been the most feasible approach for human semen evaluation, but may be an insensitive indicator of reproductive function because of high sample-to-sample variability. Finally, animal -especially murine- models have been used to further understand the mechanisms of environmental pollutants' effect on male reproductive parameters. However, interspecies extrapolation should be taken cautiously since several differences between species have been described at the cellular and molecular levels.In this review, we will focus on current knowledge about chemical hazards that affect male fertility, as well as new technologies developed to monitor human male reproductive parameters.