Sex-Reversed Frogs

A story published this morning on Reuters reports that a new study in the Proceedings of the National Academy of Sciences (PNAS) shows that Atrazine, the most commonly used weedkiller in the United States can turn male frogs into females.

The study describes experiments performed in the U.C. Berkeley laboratory of Tyrone Hayes, who has published a number of earlier studies related to Atrazine and amphibians here, here, and here, showing that exposure to Atrazine could create males with both male and female features, but the recent study is the first to document complete sex-reversal under laboratory conditions.

And most importantly, the study shows that this sex-reversal is hormonally-caused, and demonstrates that regardless of the “blueprint” of the genes, hormones can override genes.

As with practically every article regarding sexual changes in animals due to exposure to hormonal chemicals, the Reuters author makes the usual caveat, saying: “Whether the effects translate to humans is far from clear. Frogs have thin skin that can absorb chemicals easily and they literally bathe in the polluted water.”

While it is true that amphibians do have more porous skin, this merely affects the pathway of exposure that determines the dose. There is no evidence suggesting that the pathway of exposure per se plays any role in developmental outcomes, what matters is the ultimate chemical dose, and the developmental time frame when exposure occurs. So this comment is actually a non-sequitur.

Furthermore, as stated in the last blog entry, nobody is even looking for these types of effects in humans. The closest that any researcher has come is Shanna Swan, who studied male children born to mothers that had varying degrees of exposure to Phthalates, chemicals often added to plastics to make them more flexible. The methodology of the study was widely attacked by industry, with several industry representatives actually disputing the validity of the study in a subsequent issue of the same journal where it was printed, Environmental Health Perspectives. This is a peer-reviewed journal published by the National Institutes of Environmental Health Sciences, a division of the National Institutes of Health, yet industry representatives brazenly attacked it immediately here.

As was mentioned in my last post, the EPA has not yet performed any studies regarding the outcomes of endocrine disruption, and the protocol suggested by the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC) does not plan to examine outcomes such as sex-reversal or any other changes to sexuality. So the EPA will not be reporting these kinds of outcomes in humans because – they are not looking.

And so it goes. There is a circular argument that has been going on in this area for a long time. First it is admitted – often by psychologists - that, yes, it is theoretically possible to alter sexuality and gender identity due to chemical exposure, but there is no evidence of such outcomes. And at the same time, the researchers who could potentially study these sorts of outcomes claim that the outcomes are so rare that they would not have the statistical power to detect them, so why bother even looking? This is followed by more claims that no evidence exists, ad infinitum.

The fact is that practically nobody wants to really study this linkage properly. There was a wonderful opportunity to do so in the case of diethylstilbestrol (DES), the “anti-miscarriage” drug given from anywhere between 4 and 8 million pregnant women from 1940 to 1971. Over the next few weeks, I’ll be discussing the research on children born to mothers who were given this drug, which was marketed as a wonder-drug and in many cases as a “vitamin.” As an incredibly potent estrogen mimic, this research holds the key to exposing the human effects of exposure to endocrine disruptors.