In May of 1993 the British medical journal The Lancet published a paper by a Danish researcher that linked a global decline in sperm counts in healthy men over the past 50 years to accumulation of estrogenlike compounds, mainly organochlorines, in the environment. While enviros grabbed the study as another proof of the health threat from chemical pollutants, many toxicologists say no such link has been established.
The authors of the Lancet article, reproductive biologists Neils Skakkebaek of National University Hospital in Copenhagen, Denmark, and Richard Sharpe of the British Medical Research Council, analysed 61 sperm count studies published between 1938 and 1990. The found that the sperm counts had declined drom 113 million per millilitre in 1940 to 66 million per millilitre in 1990. The Lancet paper suggestted that environmental estrogens may be one of the culprits.
Sceptics advise caution while interpreting such studies. They argue, for instance, that the sperm counts have not, as the study seems to suggest, dropped steadily throughout the half-century. On a closer look, they found that in the 48 studies published since 1970 -- accounting for 88 per cent of men -- sperm counts actually increased slightly. The implication is that the decline occured before 1970.
Other scientists ask whether the drop in pserm count might be due to increases in venereal diseases such as chlamydia. Untangling such potential confounding factors is a nearly impossible task, says Neil MacLusky, a researcher at the University of Toronto Medical School.