Sex reversal in fish linked to chemical cocktail.

Mar 02, 2009

Jobling, S, RW Burn, K Thorpe, R Williams and C Tyler. Statistical modeling suggests that anti-androgens in wastewater treatment works effluents are contributing causes of widespread sexual disruption in fish living in English rivers. Environmental Health Perspectives doi:10.1289/ehp.0800197.


Research using a powerful statistical model suggests that chemical mixes in wastewater feminize male fish.

Scientists in the United Kingdom report that more than one type of hormonally active chemical -- not just those that act like estrogen -- play a role in sex reversal of male fish. Like estrogenic compounds, these other pollutants are also found downstream of wastewater treatment plants in rivers across the country.

Male fish living in water contaminated with female hormones (or estrogen mimics) can become feminized, developing female sex characteristics and behaviors. Only compounds acting like the natural estrogen hormone estradiol were thought to cause this type of sex reversal in male fish.

This study shows that is not the case and affirms that male fish are also feminized by compounds that disrupt -- or possibly block -- the male sex hormones. These compounds are described as antiandrogens.

This is one of the first studies to link antiandrogens alone, and in concert with estrogenic compounds, with fish feminization. Much prior research has focused on the ability of estrogenic compounds to increase estrogen hormone actions that can bypass male development and lead to female characteristics.

Normally, testosterone and other androgens jump start and then guide the reproductive tract development that gives rise to the male sex organs. Antiandrogens can derail this process, preventing male attributes from developing and allowing the female versions to develop instead.

Antiandrogens are widespread in the environment and their effects on wildlife, and perhaps people, are possibly underestimated. Drugs used to treat prostate cancer such as flutamide and bicalutamide and several chemicals present in the environment including the antifungal herbicide vinclozolin and phthalates used in the manufacture of plastics, paints, and perfumes are known to act as antiandrogens.

Male fish turning into females is of concern for the fish and for fish populations. But, it also has implications for humans. Reproductive problems -- collectively called testicular dysgenesis syndrome -- are on the rise in men living in industrialized countries.  Low sperm quality/quantity, cancers and infertility are some of the symptoms.

 In rats, similar types of abnormal male reproductive development is readily caused by exposure to antiandrogenic chemicals.

Given the similarity in reproductive hormones and their functions across vertebrates, removing or reducing environmental contaminants linked to male abnormalities should be a high priority.

In the study, the researchers used data on water chemistry and fish abnormalities collected by the UK's Environment Agency, as well as sampling additional fish, at 30 different sites. The wastewater was analyzed for certain chemical levels and its estrogenic, antiestrogenic, androgenic and antiandrogenic activity. Fish were considered abnormal if they had higher than normal blood hormone levels, eggs in testis and/or abnormal reproducitve ducts.

The authors plugged the data into sophisticated statistical tools to examine the association between estrogenic and antiandrogenic chemicals and several biological markers of feminization in fish.

Anti-androgenic activity, in addition to the estrogenic, was found in nearly all of the sewage treatment effluent tested. The model demonstrated that "feminizing effects in wild fish could be best modelled as a function of their predicted exposure to both anti-androgens and estrogens or to antiandrogens alone."