- Chemical pollutants surged over 100-fold in south-coast waters following sewage discharges, posing significant risks to marine life
105 unique pharmaceuticals, pesticides, and illegal drugs detected in seawater, seaweed, and shellfish samples from Chichester and Langstone harbours
The presence of banned pesticides, pet flea treatments, and tyre-wear chemicals highlights the need for stricter monitoring and action to protect coastal ecosystems
Langstone Harbour, credit: University of Portsmouth
News — A worryingly wide range of chemical pollutants has been found by researchers studying two of the UK’s south-coast harbours, raising concerns about the impact on wildlife and the human activities responsible for this contamination.
Seawater, seaweed and shellfish from Chichester and Langstone harbours were analysed by environmental scientists from three universities – Brunel University of London, the University of Portsmouth and Imperial College London – working alongside citizen scientists from the , a campaign group keen to turn the tide on worsening water quality.
Their investigation, published today in the journal , reveals that 105 unique pharmaceuticals, pesticides and illegal drugs were found across their samples, and that the readings hit a high when wet weather led combined sewer overflows (CSOs) to discharge into the delicate ecosystems.
Site map showing sampling locations, sewer overflow spots and wastewater treatment plants (WWTP). Credit: Uhlhorn et al
The findings come a week after the release of Environment Agency data showing that raw sewage was released into England’s rivers and seas for a recording-breaking 3.61 million hours last year. But with coastal waters having been studied far less than rivers, the newly published study brings a fresh view of the foul problem.
The research team and volunteers took 339 samples from 21 spots in the two straddling Hampshire and West Sussex – including sites near Budds Farm, Bosham, Thornham and Chichester sewage treatment works – during the spring and autumn of 2022.
A range of compounds was detected in surface water samples, including 67 pharmaceuticals, 29 pesticides and nine recreational drugs, collectively termed contaminants of emerging concern.
The contaminants can slip through some wastewater treatment plants any time of year, but the autumn sampling coincided with rainy days which caused CSOs to emit sewage directly into surface waters.
“CSO discharges were an obvious source of chemical pollution in these waters,” said from, who led the study. “Our study found that some chemicals increased by over 100-fold in water after these discharges, making them a high risk to aquatic wildlife.”
Of the pesticides measured, nine were no longer approved for agricultural use, with some having been banned more than a decade ago – and may originate from sources beyond farming or linked to legacy pollution. These findings raise important questions about the long-term environmental impact of these chemicals.
The study also investigated the exposure of marine life in Langstone Harbour to these chemicals. Generally, seaweed soaked up more chemicals than shellfish.
Imidacloprid was the highest risk based on levels found in surface water, which is an insecticide regularly used on domestic pets in the form of flea and tick medication.
“Out of so many chemicals detected, the presence of pet tick and flea treatments in the harbours was especially concerning. We urgently need to reassess the practice of blanket preventative treatment of our dogs and cats to help bring the risk down,” said, one of the co-authors undertaking analysis at .
Other compounds of interest included 1,3-diphenylguanidine, which is used in rubber production and could indicate the input from tyre-wear particles and road run-off after rainfall events.
Lead author , a PhD student from Brunel University, said: “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. While studies on chemical pollution in these environments are limited, the findings suggest that the true risks of chemical mixtures may be underestimated, particularly for marine species.”
The study was a key output of, 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 influence change.
, from the University of Portsmouth’s , and research lead on Project Spotlight said: “The impact of these contaminants we are yet to fully understand, but it’s clear from our data that they increase substantially under storm events which discharge untreated sewage. Having the team at the Clean Harbours Partnership gave us a unique opportunity to use citizen scientists to be proactive and reactive in helping us monitor a large number of locations simultaneously.”
Bianca Carr from the Final Straw Foundation collecting samples at Budds Farm. Credit: Bianca Carr
CHP co-founder, Rob Bailey, said: ““Our vision for CHP was to shed a spotlight on the human pressures impacting our precious harbours. Through the financial support and sampling efforts of our volunteers we are delighted to have contributed to this project and help the team find some of these answers. However, it is concerning to see such a large cocktail of chemicals being detected and hear their effects are largely unknown. As a community based organisation we will continue to push for better monitoring of these protected marine habitats used by our members.”
Dr Miller added: “As CSO discharges continue to be an important source of chemical pollution, further research is needed to assess the composition, volume and frequency of these discharges to fully understand the pressure they place on freshwater and marine ecosystems.”
Ends
Notes to editor
‘Chemical profiling of surface water and biota in protected marine harbours impacted by combined sewer overflows’, by Jasmin Uhlhorn, Keng Tiong Ng, Leon Barron, Alex Ford and Thomas Miller, is available here:
DOI: 10.1016/j.envint.2025.109417
Supporting images are available to .
For more information contact:
Robyn Montague, PR and Media Manager, University of Portsmouth, Tel: 0798 0419979, Email: [email protected]
About the University of Portsmouth
The is a progressive and dynamic university with an outstanding reputation for innovative teaching, outstanding learning outcomes and globally significant research and innovation.
We were awarded the in the most recent Teaching Excellence Framework, one of only 27 Gold rated universities in England and one of five Gold rated universities in the South East. We’re proud to be one of the UK’s top 50 universities (with a 5-star rating) in the QS World University Rankings and one of the top 10 Young Universities in the UK based on Times Higher Education Young University rankings.
Our world-class research is validated by our where Portsmouth was ranked third of all modern UK universities for research power in the Times Higher Education REF rankings.
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About Brunel University of London
Brunel University of London, based in Uxbridge, is an international university committed to bringing benefit to society through excellence in education, research and knowledge transfer.
Brunel has a reputation for high-impact academic research and entrepreneurial flair. The university works extensively with industry partners, contributing to global innovation and policy change.
A civic university, Brunel uses innovation and entrepreneurialism to drive the local economy, and to build important strategic partnerships with local organisations to bring benefit to – and increase its impact in – the local community.
About Imperial College London
We are Imperial – a world-leading university for science, technology, engineering, medicine and business (STEMB), where scientific imagination leads to world-changing impact.
As a global top ten university in London, we use science to try to understand more of the universe and improve the lives of more people in it. Across our nine campuses and throughout our Imperial Global network, our 22,000 students, 8,000 staff, and partners work together on scientific discovery, innovation and entrepreneurship. Their work navigates some of the world’s toughest challenges in global health, climate change, AI, business leadership and more.
Founded in 1907, Imperial’s future builds on a distinguished past, having pioneered penicillin, holography and fibre optics. Today, Imperial combines exceptional teaching, world-class facilities and a habit of interdisciplinary practice to unlock scientific imagination.
About the Clean Harbours Partnership
The Clean Harbours Partnership was formed in response to local outcry and concern about pollution in Chichester and Langstone Harbours. For the first time, it has brought together like-minded interest groups providing funding, manpower and expertise.
The Partnership adopts a professional, evidence-based approach to influence change. It brings the community together with a single focus on harbour pollution. This allows local groups to leverage the benefits of scale and clearly communicate the facts.
CHP aims to “Investigate – Inform – Improve” and represents groups with c.40,000 individual members.
About Chichester & Langstone Harbours
Large-scale natural and inter-connecting harbours extending to some 15,000 acres. Part in West Sussex and part in Hampshire.
Chichester Harbour is a designated . Both harbours are designated: Sites of Special Scientific Interest, Ramsar, Special Protection Areas and contain Local Nature Reserves.
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