In what ACSH’s Dr. Gilbert Ross calls one of the “worst studies ever,” a team of researchers from the University of Texas School of Public Health reported in the Journal of Pediatrics that exposure to a widely used herbicide during pregnancy may raise the risk of a birth defect.
According to the findings, atrazine — the most commonly used herbicide in the U.S. — appeared to increase the risk of choanal atresia (an extremely rare congenital defect) by almost two-fold in pregnant women. Even a quick perusal of the paper reveals that this claim cannot possibly be valid.
The so-called study used U.S. Geological Survey data on a county’s annual crop acreage likely to have been sprayed by the chemical to estimate the atrazine exposure — basically making a guess based solely upon the county-wide distribution of crops.
The researchers then looked at the population-based Texas Birth Defects Registry for links between at-home maternal exposure to atrazine and birth defects. (Again, the “at-home” exposures were estimated based upon county-wide crops). What they found was that women “exposed” to the highest levels of the herbicide were 65 percent more likely to give birth to a child with choanal atresia than women in the “lowest” exposure group.
However, the study is replete with technical flaws: its county-level estimates of atrazine used, rather than the actual amount of atrazine used; speculation about which crops were likely to have been treated with atrazine; and the retrospective analysis finding some “statistical” relationship to the very-rare choanal atresia, clearly the result of data-dredging of the worst sort. Even the study authors noted that the results have to be interpreted with caution, since they never actually measured the pregnant mothers’ exposure to atrazine.
“This is such an incredible approximation,” says Dr. Ross. “There are no data on how much chemical was actually sprayed, thus the claim of dose-dependence is ludicrous. Not to mention that every study by the EPA and every other scientific body worldwide has shown atrazine to pose no threat to humans at the levels to which we are exposed. This is pure junk science.”