What do fish swimming in 51 rivers running throughout the U.K. and infertility in human males have to do with each other? A lot, according to a January 2009 study called “Statistical Modelling Suggests That Anti-Androgens in Wastewater Treatment Works Effluents are Contributing Causes of Widespread Sexual Disruption in Fish Living in English Rivers” (PDF), published in the journal Environmental Health Perspectives.

The catalyst for the research project was the continued appearance of “feminized” male fish downstream of some wastewater treatment plants. These males that had one of three conditions:

• Elevated plasma vitellogenin levels (VTG) — Vitellogenin is a protein produced in the liver in female vertebrates and transported to the ovaries. It is the precursor of the yolk that will later form when the oocyte (egg cell) becomes fertilized and matures.
• A feminized reproductive duct
• Developing oocytes (egg cells) in the testes

British ecologists and public health officials believed that the “sexual disruption” phenomenon being displayed in these male fish was also manifesting itself in human males, and that both instances were being caused by exposure to contaminants in the water that act as “anti-androgens”, that is, agents that block testosterone function, which interferes with male fertility. However, there was little evidence to prove this causality, or the connection between fish and human.

The accepted explanation for Testicular Dygenesis Syndrome in human males, a condition in which the embryo’s gonad doesn’t fully develop into a testis, was, in fact, exposure to mixtures of anti-androgenic chemicals. This had been proven in laboratory testing in which rodent models had been exposed to these agents. But the accepted explanation for the feminization of male fish was exposure to steroid estrogens coming from human excretion.

The researchers involved in the study believed that that steroid estrogens were only one cause for the male fish taking on more feminine qualities; and that these fish were exhibiting these traits as a result of exposure to anti-androgen chemicals in the water in addition to their exposure to the estrogens.

To prove their hypothesis, the scientists took 1000 fish samples from 30 rivers throughout the country. All of the sites had both estrogenic and anti-androgenic agents. Using statistical modeling, they were able to examine the correlations between what chemical agents the fish had been exposed to and what non-male traits they were exhibiting. It took over three years to evaluate all of the data, but when all was said and done, they did make two significant discoveries. The first is that there is a much broader range of chemicals than was previously suspected that is leading to sexual disruption in fish. This means that the chemicals are probably coming from more sources than originally thought. The second is that the “cocktail of chemicals”, as the researchers refer to it, in the water is a contributing factor to the rise in male reproductive problems.

Because the researchers identified a new group of chemicals whose sources are unknown that are impacting fish, they have decided that their next step is to identify the origins of these pollutants. Another of their goals is to work with environmental regulators to test the effects of a mixture of these chemicals and already known estrogens. They believe that only through continued study into the nature of these pollutants will scientists be able to identify the exact causes for male infertility, and what can be done to protect humans from their effects.