Unraveling the mystery of feminized fish

Date of publication : 5/21/2009
Source : Environmental Health Sciences news

In the Potomac River, male smallmouth bass are growing eggs. This phenomenon now poses one of the most important water quality problems of our time. Five years of research has failed to uncover the chemical contaminants responsible for the abnormal sexual development of these fish. Nevertheless, we should not view this lack of a smoking gun as disempowering. Rather, it is a testimonial to the difficulty of the environmental problems we face today. These problems are solvable, but it will take substantial scientific innovation and a reinvigorated dose of political will.

Since 2004, scientists from the U.S. Fish and Wildlife Service and the U.S. Geological Survey have been trying to solve the mystery of why the Potomac's fish exhibit biological characteristics of both males and females. Since it has been well documented in laboratory studies that exposure to water pollutants can create intersex animals, the attempt to link a chemical contaminant to it is certainly prudent. However, an update published in the Washington Post on April 22 highlights the fact that relationships between organic pollutants and intersex creatures can be very difficult to establish.

One of the first places that the scientists looked for the cause was downstream from wastewater treatment plants. Pharmaceuticals, steroids and cleaning compounds can pass through some wastewater treatment plants intact, so sampling downstream from them was a good start. Fish collected from these sites experienced alarmingly high rates of intersex, but the rates were not different from that of fish collected in cleaner waters upstream. These results have led to the speculation that the abnormal fish could be due to exposure to a pharmaceutical or an agricultural compound or something else entirely. Furthermore, the scientists have speculated that the problem may be caused by a mixture of pollutants arising from human sewage, farm manure and pesticide runoff. Not a very convincing conclusion from a multi-year, multi-agency environmental study!

What a far cry from the studies of the 1960s and 1970s. In those days, the issues were focused on point source contamination, that is, industrial contaminants being discharged through pipelines into water bodies such as the Great Lakes. The most flagrant polluters were quite obvious. The Cuyahoga River really did catch on fire. This highly visible pollution led to enactment of legislation including the Clean Water Act and Safe Drinking Water Act. Once enacted, these laws prohibited discharge from the most egregious polluters.

So why is it that a clear cause-and-effect relationship is not forthcoming in the studies on the Potomac? Simply put, the reason is that the water quality issues that we are struggling with today are much more difficult to solve. For one thing, the chemical compounds responsible for the feminized fish may be having effects at levels that were analytically unquantifiable just a few years ago. The issue is no longer one solely related to toxicity, but may also include endocrine disruption, organizational effects, and the hijacking of cell signaling pathways. This signal mimicry and inappropriate pattern development can occur at astonishingly low exposure concentrations, and can lead to bizarre changes in development, such as ovarian follicles within the testes of male fish.

In addition, the sources of the contaminants may be much less visible than those being released from an industrial discharge pipe. They could be coming from the waste products of animals that we consume or from chemicals we apply to our croplands and to our lawns. If so, there is no discharge structure, but rather an insidious trickle of effluent from a very large number of sources. Furthermore, these compounds may not remain in one form in the environment, but rather may morph into an array of different metabolites, each one with its own environmental potency.

How do we deal with such an insidious yet pressing issue? Technical innovation will help, as contaminant assessment will become less expensive and more widely available. But scientific innovation is not enough without education and public awareness. The articles in the Washington Post have already popularized the issue. It is up to us to turn this popular attention into political will.

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