‘Intersex’ fish still rife in UK rivers despite improved sewage treatment

A new study published by Environment Science and Technology has shown that laws on the levels of hormone-disrupting chemicals allowed to enter English rivers are still not preventing endocrine disruption.

While the amount of the content of treated sewage winding up in freshwater streams and sources has improved in the last two decades, scientists say the situation is still concerning. 

A team from Brunel University London and the University of Exeter took samples from 10 river sites. In 60% of locations male roaches – a small, hardy, silvery fish – had suffered endocrine disruption, whereby males produce female proteins and begin to develop eggs in their reproductive systems, essentially becoming intersex. In 90% of samples the male fish were showing high concentrations of female proteins, a biomarker for estrogen exposure. 

Treated sewages carries a mixture of potent chemicals due to the way it is processed, with other naturally occurring and industrial pollutants can also contribute to this phenomena, which has been understood since the 1980s. During the following decade well into the early-2000s, the Environment Agency conducted a huge study at 50 sites across the UK, trying to determine the prevalence and impact of endocrine disruption.

Those closest to textile making facilities were found to be the worst effected. However, oestrogens excreted naturally by men and women, which are then passed into wastewater, can also contribute to the problem. This latest investigation revisited some of those original locations in a bid to determine how improvements to water treatment plants had made any difference, for example introducing sand filters and reed beds. Those which have switched from a trickling filter to activated sludge process, such as Great Billing works on the River Nene, were among the least impacted, with the River Arun revealed to have the most sex-reversed fish, at 10.7%, rising to 40% for upstream locations. 

‘What was interesting is that in the past, you’d be able to predict which sites would have higher levels, mainly on how big the sewage works was. If it was a normal sewage works, you’d expect lots of endocrine disruption downstream. Now it seems some of those bigger sewage works that have had more investment and have done more and are now actually cleaner than some of the works in smaller towns and villages,’ said Brunel University Lonon’s Dr Alice Baynes. ‘So some of these smaller sewage works still need a lot of improvement to provide healthy rivers.’

More on rivers and water pollution: 

Giving rivers and communities a voice: Environmental Law Foundation

Great Ouse Rivers Trust launches ‘safeguarding biodiversity’

Just one water supplier contributes to Rivers Trust real-time sewage map

Image: rigel