- 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
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 Clean Harbours Partnership , a campaign group keen to turn the tide on worsening water quality.
Their investigation, published today in the journal Environment International, 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 Sites of Special Scientific Interest 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 Dr Thomas Miller from Brunel University of London , 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 Dr Leon Barron , one of the co-authors undertaking analysis at Imperial College London .
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 Jasmin Uhlhorn , 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 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 influence change.
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.
Professor Alex Ford, University of Portsmouth's Institute of Marine Sciences, and research lead on Project Spotlight
Professor Alex Ford , from the University of Portsmouth's Institute of Marine Sciences , 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."
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."
