I recently found a photo showing how ethinylestradiol (the estrogen used in birth control pills) can effectively completely sex reverse male fish and turn them into something that's virtually indistinguishable from a female.
The amount of ethinylestradiol that caused this to happen was astonishingly small, the equivalent of one contraceptive pill dissolved in hundreds of gallons of water.
I've since discovered that the problem of intersexed fish was first spotted right here in the UK, and there was quite a bit of research into the cause of it carried out by our Environment Agency during the 1990s and early 2000's. It's due to estrogens in the wastewater discharged from sewage treatment plants. Despite all the stuff you hear about BPA, pesticides etc, the problem is almost entirely due to just 3 chemicals: estradiol, estrone and ethinylestradiol. The first two are naturally occurring hormones and excreted in an inactive form in women's urine, but become activated during the sewage treatment process. The third (which is about 20x more potent as a sex change agent) is the manmade estrogen used in contraceptive pills, and because contraceptive pills are used by so many women and it survives the sewage treatment process fairly well, enough of it is getting into wastewater that it's become one of the main contributors to intersex in fish.
If minute traces of it can cause fish to change sex, what is the undiluted form that millions of women use each day for contraception doing to us! That's one reason why I think it's important that the full facts of what happened with DES come out. If one pharmaceutical hormone can cause transsexuality, then there could be others that are as well.
