New study linking wastewater discharges to feminized male fish

Sometimes human impacts on our environment and natural resources manifest themselves in strange ways. For years, we have been warned of the dangers associated with consuming certain species of fish and shellfish, especially those fish sourced from contaminated waters. Health officials warn of the potential of mercury poisoning from tuna and continue to debate how many times per month we can eat certain fish without being exposed to toxic, life-threatening quantities of mercury. Today, scientists have exposed a new threat to aquatic species

A recent article published by EPA scientists (and mentioned in the June 2017 Fish and Shellfish Newsletter) addresses the phenomenon of the feminization of fish. While reports of fish feminization started nearly 20 years ago, scientists are still trying to understand the phenomenon. So, what is this “fishy feminization?” Scientifically, it is referred to as “intersex” or the occurrence of male fish exhibiting female appearance, reproductive traits, and abilities. In a 2012 study jointly conducted by the United States Fish & Wildlife Service and the United States Geological Survey across 19 wildlife refuges, at least 60% of all smallmouth bass, Micropterus dolomieu, had female egg cells within their testes.

Intersex is a serious condition, especially when occurring in non-hermaphrodite species, and can result in sterilization of the organism. It is a result of endocrine or hormone disruption, and while for several years the occurrence has been linked to polluted waters, there was relatively little research regarding the matter. Yet, years after question and speculation of what has been causing this feminization, it seems we finally have some answers. In Re-evaluating the Significance of Estrone as an Environmental Estrogen, authors discuss the relationship between exposure to estrone and the feminization of fish. While for years estrone has been relatively overlooked as a potential cause of intersex fish, this study examines that when male fish are exposed to estrone they can convert estrone to estradiol, which in turn results in their feminization.

Problematically, estrone is often found in high quantities in wastewater discharge. This study is critical to explaining the relationship between wastewater discharge and feminization of fish. While legislation such as the Clean Water Act has been influential in preserving and protecting our waters, hormones such as estrone and many others are essentially a “new class of chemicals” not currently regulated by the CWA and therefore called "unregulated contaminants." Equally as troubling is the fact that even if wastewater treatment facilities wanted to rid wastewater of these hormones, it would be difficult. Unfortunately, most modern treatment facilities do not have the technology or infrastructure to treat wastewater for hormones. It’s a concerning situation that “downstream from wastewater treatment plants, are some of the most common locations where we can find intersex (fish)” yet no action has been taken to classify hormones as regulated contaminants under the CWA or identify cost-effective ways for reducing the presences of estrone in wastewater.

The presence of estrone in rivers and the resulting feminization of fish, is not just a problem for the United States. Intersex fish have been found across Europe. As we know, the improper handling and discharge of wastewater can lead to a host of issues, and the feminization of fish is presents one more threat It’s a threat to the existence of aquatic species, human health, and fishing economies, that if left unaddressed could have tragic consequences on water resources and ecosystems.