Tuesday, May 22, 2007

Estrogen: Good for Birth Control, Bad for Fish

A recent paper in the Proceedings of the National Academy of Sciences (PNAS) by members of Fisheries and Oceans Canada and the U.S. EPA reports on the detrimental effects of synthetic estrogen on wild fish populations. Estrogen is a naturally occurring sex hormone found in vertebrates. This hormone is responsible for stimulating the development of female secondary sex characteristics and, in mammals anyways, for readying the uterus for the fetus embryo during pregnancy. The production of estrogen by the placenta and corpus luteum during pregnancy in turn helps maintain the pregnancy and prevents further ovulation.

For this last reason, synthetic estrogen, specifically 17α-ethynylestradiol, is a main component of the birth control pill (essentially the pill tricks the body into thinking that it's pregnant, thereby preventing ovulation, thus preventing pregnancy - ironic, no?). It turns out however, that the efficacy of the pill (which I will go on record as saying I think is a good thing for a multitude of reasons) has resulted in a large amount of estrogen being released into our waterways (normally via waste water treatment plants). Excess estrogen in the water has serious effects on the resident wildlife - including male sterility, delayed sexual development, and the feminization of males (males having female sex organs/characteristics). These effects have been reported before (e.g. here and here)

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The new study in PNAS takes this issue a step further by following a population of fish over seven years to assess the effects of estrogen-related sexual disruptions on the population as a whole. In this study, the sizes, numbers, gonad development, and male feminization of individuals were compared between two populations of flat-head minnows. One population was kept under natural conditions (the control) while the other was kept in a lake augmented with low doses of synthetic estrogen. As expected, those fish exposed to estrogen showed high levels of male feminization, irregular gonad develppment, and delayed sexual maturity.

However, the estrogen not only messed with individuals' reproductive system, but also had serious consequences for the long-term survival of the minnow population. Low doses of synthetic estrogen not only lead to feminization of males and delayed maturity in females, but also to the near extinction of the population. Compared with the control population, the experimental population showed little reproductive ability (and possibly higher mortality if I am interpreting the data/graphs correctly). As adult fish got older and died, there were no young fish to take their place.

This is an example of how the presence of anthropogenic chemicals in our waterways is not just causing a few biological freaks, but is messing with survival of populations and, perhaps, species. It's also an example of how complex most environmental issues are. Synthetic estrogen and the pill have given us cultural, social, and medical benefits. It's also given us environmental benefits by limiting human population growth. Of course, few things give benefits without a cost (and some would argue that the benefits I allude to are nothing of the sort), so we need to make choices - do we sacrifice fish and other wildlife and, potentially, human health? do we spend money on updating/improving our waste water treatment plants? do we limit the use of synthetic estrogen? do we make women on the pill pee into hazardous waste bottles?

(go ahead, I dare you to try that last one, but I take no responsibility for any physical harm rained down on you.)