Thursday, April 19, 2007 By Steven Milloy
Seven months after the World Health Organization reversed its deadly 30-year ban on the use of DDT to fight malaria, the anti-DDT movement is up to its old tricks.
“South African medical researchers have reported alarming evidence of low sperm counts and other damage to the male reproductive system linked to the use of the pesticide DDT in anti-malaria spray campaigns,” reported the Mercury/Independent Online (South Africa) on April 12.
The lead researcher told Mercury that there is sufficient evidence to be concerned about the health impacts of DDT and to consider moving toward safer alternative methods for malaria control.
To be published in an upcoming issue of the Journal of Andrology, the study compared levels of DDT and its metabolites in the blood of 311 South African men aged 18 to 40 with the quantity and quality of their semen. The men were selected from three communities where malaria is endemic and DDT is sprayed to control mosquitoes.
“Laboratory analysis showed abnormally low sperm counts, lower semen volumes, slower-moving sperm and fewer viable sperm,” reported the Mercury. “The results imply that non-occupational exposure to DDT is associated with impaired seminal parameters in men.”
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The only thing that actually appears “impaired,” as far as I can tell, is the researchers’ willingness to communicate what they actually found — precisely nothing.
Before going into their specific results, it’s necessary to have a basic understanding of the sort of statistical analysis they undertook.
The researchers conducted a so-called “regression analysis” to evaluate the nature of any statistical relationships between blood levels of DDT and various characteristics of the men’s semen/sperm. The key result in this type of analysis is called the “beta.”
In the context of these analyses, a non-zero beta (either positive or negative) means that a statistical relationship between DDT levels and sperm characteristics was observed, while a beta of zero means no relationship was observed.
The greater the beta is (either positive or negative), the stronger the statistical association; the closer to zero, the weaker the statistical relationship.
The sign (positive or negative) of the beta indicates the direction of the relationship: A negative beta indicates decreasing semen/sperm quality with increasing blood DDT while a positive sign indicates the opposite. Keep in mind that statistical relationships do not necessarily represent actual biological or cause-and-effect relationships.
For semen volume and blood DDT, the researchers reported a beta of -0.0005, meaning that they measured a very slight decline in semen volume with increasing blood DDT levels. But this beta result is so close to zero — and statistically insignificant, to boot — that it cannot constitute evidence of a relationship between semen volume and DDT exposure.
Though the researchers reported a beta of -27.63 for DDT and sperm motility, this result was also not statistically significant, meaning it could have occurred simply by chance. The likelihood that this beta is a spurious result is strengthened by the fact that the average sperm motility of the study subjects was within the standards of normalcy as determined by the World Health Organization.
In terms of sperm count, the results were, if anything, self-contradictory. While the beta for the DDT metabolite known as DDE was a statistically insignificant -0.0003, the beta for DDT was 0.0022 — meaning that sperm counts slightly increased with greater levels of blood DDT. Both betas, however, are so close to zero that, once again, they are probably meaningless.
For the final sperm endpoint mentioned in The Mercury article, sperm viability, the researchers reported betas of -0.6571 and -1.7258 for DDE and DDT, respectively. But neither result was statistically significant.
Not only have these researchers failed to statistically link DDT with harm to semen/sperm — let alone have they linked the two biologically — their study flies in the face of a couple of key touch points with reality.
First, there weren’t
any reproductive health issues among the men studied, with the researchers acknowledging that the semen/sperm characteristics were either within or close to World Health Organization standards.
Next, despite the past widespread use of DDT, no prior studies credibly link DDT with semen/sperm problems. Keep in mind that the period of heaviest use of DDT in the U.S. and other Western countries — the years 1946 to 1960, when DDT was indiscriminately applied all over the place — coincides precisely with the “baby boom” generation. If DDT use harms sperm, one can hardly prove it by the worldwide proliferation of boomers.
This study represents the vanguard of the coming backlash against the WHO’s lifting of the DDT ban by anti-DDT environmental activists who are advocating an international treaty that would essentially ban DDT once and for all.
Last year, the WHO bravely moved to rectify one of the greatest tragedies in public health by lifting its DDT ban. The mosquito-killer has proven to be the most effective tool against malaria, a disease that annually kills 1 million children, sickens hundreds of millions and reduces economic development in poverty-stricken regions of the world.
It would be a shame if junk science is once against used to thwart the desperately needed use of DDT.
Steven Milloy publishesJunkScience.comandCSRWatch.com. He is a junk science expert, and advocate of free enterprise and an adjunct scholar at the Competitive Enterprise Institute.
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