Is human fecundity declining--and does occupational exposures play a role in such a decline if it exists?

Demographers have analyzed fertility over time and between many populations for many decades. Much less is known about fecundity. Recent publications seem to indicate a decline in semen quality over time, but still no good data corroborate or refute this hypothesis. The very sparse data do not indicate any substantial changes in fecundity over the last 10-30 years in the United States, but none of the studies have a comparability which permit any firm conclusion. Several chemical and physical exposures interfere with human fecundity. Some are found at the worksite, sometimes in an intensity which does harm. The marked effect of dibromochloropropane on semen quality and fecundity was a clear warning to occupational health workers. Several other occupational exposures have shown an effect on gonads in men or women, and it is time to give more research priority to the topic. The rapidly rising cost of infertility treatment could be the stimulus to trigger the development of this research field.