Richard Denison, Ph.D., is a Senior Scientist.
As reported by Rob Stein in the Washington Post this morning, a NIOSH-funded study of male Chinese workers conducted by researchers at Kaiser-Permanente in Oakland, California has found that exposure to the endocrine-disrupting chemical bisphenol A (BPA) significantly increases the incidence of low sperm counts and concentrations, as well as lowered sperm motility and higher mortality.
The 5-year study, published in the peer-reviewed journal Fertility and Sterility (that's a title only slightly more cheery than the CDC's publication Morbidity and Mortality!), shows that the same kinds of adverse effects of BPA on sperm already observed in animal studies also occur in humans with detectable levels of BPA in their urine.
And while the most pronounced effects were observed in highly exposed workers, the authors of the study note:
Similar dose-response associations were observed among participants with only environmental BPA exposure at levels comparable to men in the general United States population.
Despite a markedly reduced sample size in this group of men exposed only to low environmental BPA sources, the inverse correlation between increased urine BPA level and decreased sperm concentration and total sperm count remain statistically significant.
The new study is the authors' third in a series examining effects of BPA in exposed humans (and recall that CDC biomonitoring data show that more than 90% of the U.S. population has detectable levels of BPA in their urine). The first one appeared in November 2009 in Human Reproduction, and found that exposure to high levels of BPA in the workplace increased the risk of erectile dysfunction in men. The second study appeared in May 2010 in the Journal of Andrology; it correlated increasing BPA levels in urine with declining male sexual function.
This latest study elicited the stock, predictable response from the chemical industry, though with a slightly updated twist on its usual state of denial. The American Chemistry Council (ACC) posted a statement from Steven G. Hentges, manager of its Polycarbonate/BPA Global Group, that states:
This study of Chinese workers with high exposure to BPA is of limited relevance to consumers who, by contrast, are exposed to only very low levels of BPA.
That statement of course completely glosses over the fact that the study found the same dose-dependent effects in workers exposed to low levels, as noted above. But it also tacitly seems to acknowledge, however grudgingly – and if I'm not mistaken for the first time – that BPA can affect people.
After years of challenging the validity of effects documented in animal studies, the mounting animal evidence forced the industry to abandon that tack and argue instead that the animal studies were not relevant to humans. Now, in the face of a growing number of human studies, it's been forced to retreat again to the questionable position that we still needn't worry despite the fact that reproductive effects very similar to those found in the animal studies are readily detectable even among a small population of a few hundred male workers.
ACC's last-resort argument about dose strikes me as particularly desperate. Everything we know about how BPA acts indicates an exceedingly low likelihood that there is a level of exposure below which there will be no adverse effects. Add to this the fact that the current study found the same effects seen at high doses, albeit with less intensity, at doses comparable to those to which men in the general U.S. population are now being exposed – and one has to wonder just how much longer the industry is willing to fight the inevitable.