Smog is not only bad for the lungs, it is bad for sperm too. A survey of men in Los Angeles has shown that their sperm counts fell as ozone levels in the air increased. Rebecca Sokol and colleagues at the University of Southern California Keck School of Medicine in Los Angeles looked at sperm counts of 48 men who donated to an LA sperm bank at least 10 times in a two-year period. Using air pollution measurements from the zip code where each man lived, the team estimated the amount of various air pollutants that the men were exposed to in the days leading up to each donation. Ozone, formed when sunlight triggers reactions between nitrogen oxides and hydrocarbons in smoggy air, was the only pollutant that appeared to be linked to decreased sperm production. It had a damaging effect throughout the 90 day spermatogenesis process. Carbon monoxide, nitrogen oxides and particulate matter seemed to have no effect (Environmental Health Perspectives, vol 114, p 360). Ozone cannot reach the testicles directly. Sokol suggests it may cause an inflammatory response or produce toxic substances in the blood that damage sperm. She stresses that the changes she saw […]