Researchers report in Environmental Health Perspectives (February 1999) no threshold for adverse effects for endocrine disrupters.
The study is based on exposing turtle embryos to varying doses of the natural estrogen 17-beta estradiol.
The researchers reported the sex of turtles was reversed in 14.4 percent at the lowest dose tested. But even assuming the experimental protocol is as robust as claimed, the result is probably less than meaningful.
The natural estrogen used (17-beta estradiol) is 10,000 times more estrogenic than the pesticide DDT and the chemical bisphenol A. It's 30 to 1,000 times more estrogenic than PCBs.
So similar application of these supposed "endocrine disrupters" would probably have no detectable effect on sex determination in the turtles -- otherwise the experiment would have been done with some manmade chemical as opposed to a relatively potent natural estrogen.
I also question the experimental protocol.
Turtle eggs incubated below 28.6 degrees Centigrade become males. Starting at 28.6, females develop in increasing proportions with increasing temperatures.
In this experiment, the researchers incubated the turtle eggs precisely at 28.6 degrees -- a gender development coin toss.
To avoid this uncertainty in another experiment by the same authors reported in the same issue of EHP, turtle eggs exposed to estrogens were incubated at 26 degrees.
Why were turtle embryos given a better chance to develop into females in the present experiment? Who knows? But it certainly does not lend credence to the claims of low dose activity.
Finally, my junk science-ometer always goes off when researchers reach HUGE conclusions based on one study. Here, the researchers conclude "We demonstrate dose-dependent risk at any dose of exogenous [estrogen], no matter how low, thereby providing a biologically justified explanation for low-dose effects of endocrine disruptors... we expect our conclusions are not idiosyncratic, but are widely applicable. Our findings and their implications reinforce our concern for the health of humans and wildlife exposed to low doses."
All this from one study of questionable relevance and protocol? Gimme a break....
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