There are certain professions that require contact with substances or toxic physical agents that increase the risk of infertility. The list of agents that decrease the quality of sperm includes: pesticides (farmers), radiation, heat (workers that use ovens, cast iron workers, drivers), metals (metalworkers), glycol ethers (shipyard and cast iron workers).
Physical agents such as heat and radiation have been documented on specific cases rather than epidemiological studies at a larger scale, whilst others, such as the effect of microwaves and electromagnetic fields on human beings, lack further study. Metals – especially lead and mercury – have been demonstrated to be toxic for spermatozoids in intoxicated workers or others submitted to a regular exposition.
Before jumping to definitive conclusions it is necessary to carry on further and thorougher investigations.