Men at work--sperm on break. (Reproductive Toxicology).

Men who are regularly exposed to moderate to high levels of organic solvents on the job may increase their chances of having a low active sperm count, or reduced sperm motility, report Canadian and British researchers in the October 2001 issue of Occupational and Environmental Medicine. The researchers found that among infertile couples, men with the highest solvent exposure--including professional printers, painters, dry cleaners, and marine craft builders--were twice as likely as men without such exposure to have a low number of active sperm. Reduced sperm motility can contribute to male infertility.

Organic solvents are chemicals found in paints, adhesives, lacquers, and cleaning agents. Some commonly used organic solvents include styrene, perchloroethylene, trichloroethylene, and ethylene glycol ethers. Solvents, whether inhaled or absorbed through the skin, are known to invade the part of the male reproductive system where sperm are developed, says lead author Nicola Cherry, a professor of occupational health at the University of Alberta in Edmonton.

The researchers reviewed data from two Canadian cohorts comprising 1,200 manual workers attending fertility clinics. Over half of the subjects went to one clinic in Montreal between 1972 and 1991 (the Montreal series). The other subjects went to 10 other Canadian clinics between 1984 and 1987 (the Canadian Infertility Therapy Evaluation Study series).

The researchers used a job exposure matrix to classify how likely each man was to have been exposed to organic solvents at work. Cases were defined as men with less than 12 x 106/mL active sperm.

The researchers found that cases were more likely to have been exposed to solvents at work than were controls. Among the Montreal series subjects, moderate occupational exposure to organic solvents was associated with a doubled risk of having low numbers of active sperm. In both series, exposure to high solvent levels was associated with triple the likelihood of a low active sperm count.

The team also factored in alcohol and tobacco use data (where available) as possible confounders, but found no evidence that use of either was related to lowered numbers of active sperm.

"Even though only a small number of subjects were exposed at high doses, this study suggests that effects on sperm increased with amount of exposure," says Peter Rabinowitz, an assistant professor of medicine in the occupational and environmental medicine program at Yale University in New Haven, Connecticut. The study provides further evidence that exposure to high levels of solvents may interfere with normal sperm formation. However, Rabinowitz adds that, as with any retrospective case-control study, some caution should be taken in interpreting the results.

Regardless of whether organic solvent exposure actually does affect active sperm count, Cherry says, men exposed to high levels should try to minimize their exposure because of the solvents' known adverse effects on the nervous system. Such effects include nervous system depression and possibly death at very high levels of exposure, as well as chronic effects on mood and behavior following repeated exposure over years at work.