High levels of intersex fish are found in wild populations that live downstream to a pharmaceutical production plant, showing for the first time that the two are linked.

A French study finds that more than three-quarters of wild gudgeon fish examined had a mix of male and female traits in their sex organs if they lived directly downstream to a plant that manufactures pharmaceutical drugs.

Exposure to the chemical mix discharged from the nearby drug plant may contribute to the abnormalities, the researchers report in the journal Environment International. The study is important because it is the first to link discharge from a drug manufacturing plant – rather than a sewage treatment plant – with physical and chemical changes in fish living downstream.

The researchers found that up to 80 percent of the fish they tested were intersex – that is, the fish had both male and female characteristics in their ovaries or testis. Intersex indicates endocrine disruption in fish that can foreshadow larger effects on fish populations because of reductions in breeding abilities.

Pharmaceuticals can enter the environment through sewage treatment plants after people excrete them or flush unwanted drugs down the toilet. They can also directly enter waterways via discharge into rivers and streams by drug manufacturing plants. Which source contributes more is not known.

This study provides an important step toward understanding their relative contributions.

Anglers – sometimes the first to see when things go awry in the fish they catch – noticed the swollen bellies and abnormal innards of these wild fish called gudgeons. Intrigued, a cadre of researchers from several French laboratories followed up. They collected fish by electroshock once in 2008 and once in 2009 from three points along the Dore River in France. Site A – used as the reference site – was upstream of a pharmaceutical manufacturing plant but below a city wastewater treatment facility. Site B was downstream to the plant and a different waste treatment facility for the city of Vertolaye.

Fish ovaries or testis were examined to identify gender and abnormalities. Species diversity and abundance were also calculated at each site to see if there were any site-specific effects on fish populations.

Researchers found that 80 percent of wild gudgeons caught downstream to a pharmaceutical processing plant in 2008 were intersex. This was in stark contrast to the 5 percent of intersex fish detected at site A, the location upstream to a drug manufacturing plant. The findings were consistent the following year – 55 percent of the fish at sites B were intersex when compared to 8 percent at site A.

The scientists also collected fish even further downstream from the factory and site B. They wanted to see if the intersex effect persisted far from the point of origin. At this distant site – site C – they found 56 and 44 percent of intersex fish in 2008 and 2009 respectively.

Interestingly, the increase in intersex fish coincided with a decrease in the number of females. This suggests that “something in the water” at sites B and C masculinized female fish. What exactly that is could not be determined from this study.

Finally, there were far fewer fish at sites B and C (177 and 74) relative to the 301 fish at site A. Species diversity was also lower at sites B and C:  eight species were identified at site A upstream of the drug manufacturing plant compared to six species at site B and only three at site C.

The main finding – that pharmaceutical plant discharge is associated with intersex in fish – is new. However, the study would have benefited if the authors had identified the types and levels of pharmaceutical drugs in the water at each site. More targeted research is needed to understand the degree of the association.