Concerns have been raised over what lasting damage will be caused to marine life inhabiting the waters across two of the UK’s south-coast harbours, after an investigation into local water quality revealed the presence of a “worryingly wide range of chemicals and pollutants” derived from over 100 unique pharmaceuticals, pesticides, and illegal, recreational drugs.

Varying concentrations of each have been found in all of the almost 340 samples of seawater, seaweed, and shellfish collected from 21 test sites between Chichester and Langstone, with recorded readings hitting an ‘all-time high’ when wet weather led to spikes in sewage overflow discharges.

These findings – published today in the journal Environmental International – land just one week after the release of Environment Agency data showing that last year, raw sewage was released into England’s rivers and seas for a record-breaking 3.61 million hours.

Led by environmental scientists from the University of Portsmouth alongside those from Brunel University of London and Imperial College London, this study is one of the most comprehensive investigations into the health of Britain’s coastal waters to date.

Until now much of the focus has been on water quality across Britain’s rivers. 

While the subject of combined sewage overflow discharges has garnered much media attention in recent months, the scale of the impact on coastal regions, such as the 21 sites tested within this study has been vastly under-reported. From the 339 surface water samples taken in this study, 67 unique pharmaceuticals, 29 different pesticides, and nine types of recreational drug were recorded.

“CSO discharges were an obvious source of chemical pollution in these waters,” said Dr Thomas Miller from Brunel University of London. “Our study found that some chemicals increased by over 100-fold in water after these discharges, making them a high risk to aquatic wildlife.”

Startlingly, nine out of the 29 different pesticides measured are no longer approved for agricultural use, with some of them having been banned more than a decade ago. While the scientists behind the study concede that these may originate from sources beyond farming or are linked to legacy pollution, the findings still raise important questions about the long-term impact their historic use will have on the environment.

When it comes to the many types of chemicals detected across the samples, one area of particular concern is the “worryingly high presence” of imidacloprid – an insecticide used for the treatment of ticks and fleas among cats and dogs. Its discovery has led scientists to call for “urgent reassessment of the preventative treatments for dogs and cats” to help lower the risk to the environment.

“The research underscores the complexity of chemical mixtures present in transitional and coastal water systems, highlighting the need for more comprehensive monitoring to investigate their sources, including the impacts of CSO discharges,” said the study’s lead author, Jarmin Uhlhorn, a PhD student from Brunel University.

“While studies on chemical pollution in these environments are limited, these findings suggest that the true risks of chemical mixtures may be underestimated, particularly for marine species.”

The study was a key output of Project Spotlight, crowdfunded through the University of Portsmouth and Brunel University of London by the Clean Harbours Partnership and its community partners. The overall aim of the project is to reveal what chemical contaminants are impacting important coastal environments and, as a result, inlfuence change.

“As CSO discharges continue to be an important source of chemical pollution, further research is needed to asses the composition, volume, and frequency of these discharges to fully understand the pressure they place on freshwater and marine ecosystems,” said Dr Miller.

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