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Insecticides, antibiotics and illicit drugs that threaten aquatic life are present throughout UK waterways, research by 911���պ��� and Earthwatch finds.

911���պ��� scientists and have collected and are analysing chemical residues in more than a thousand samples collected by the public, some of which pose high risks to aquatic life.

The insecticide imidacloprid, banned for agricultural use but still applied in spot-on flea and tick treatments for pets, posed the highest risk to aquatic invertebrates, according to the scientists. The researchers also found human and veterinary antibiotics at concentrations high enough to suggest that antimicrobial resistance should be studied further in UK freshwaters. 

The scientists found chemical pollutants from every single sample tested in the UK-wide water testing project. Illicit drugs including ketamine and benzoylecgonine (a cocaine metabolite) were also prevalent, although at concentrations posing limited risk to aquatic life. 

The team, led by at the School of Public Health, required only a thimble full of water to rapidly identify and measure more than 100 everyday-use chemicals, such as pharmaceuticals, illicit drugs and pesticides. 

, Earthwatch enrolled 5000 citizen scientists to test the UK’s waterways as part of the Great UK WaterBlitz, which ran between 19-22 September 2025. Over a thousand of these people were also given sampling kits to collect water to be analysed by the 911���պ��� team.  

Pet treatments for ticks and fleas pose the highest risk 

Every single water sample tested contained additional chemical pollutants including those from wastewater discharges, as well as agricultural and surface runoff.  The level of pollutants in several samples posed risks to aquatic life despite being present at ultra-low concentrations in water, at the equivalent of a sugar cube in roughly 500 Olympic sized swimming pools. 

Of the chemicals tested, the insecticide imidacloprid, used in flea and tick treatments for pets, posed the highest risk to aquatic invertebrates.  Despite its ban for outdoor agricultural use since 2018, a market shift towards its use in flea and tick treatments for household pets means the chemical enters waterways via wastewater after washing off from contaminated fabrics, surfaces and owners’ hands for up to 28 days after application. 

Professor Barron said: "It’s not always something obvious that poses the highest risk. We’ve been tracking a rise in pet parasiticide treatments such as imidacloprid in waterways for some time, particularly in urban areas. Combining the local knowledge of so many people allows us to create a massive snapshot of how big the issue is. Thankfully, there are solutions outlined in the report that can benefit both pet and environmental health.”  

Antibiotics fuel antimicrobial resistance concerns 

The analysis also found human and veterinary antibiotics at concentrations suggesting that antimicrobial resistance should be studied further in UK freshwaters. Four antibiotics – sulfamethoxazole, trimethoprim, clarithromycin and sulphapyridine – were among those most frequently detected. 

Illicit drugs including ketamine and benzoylecgonine (a cocaine metabolite) were also prevalent, although at concentrations posing limited risk to aquatic life. 

Analysis of the results 

The results from the first 100 locations sampled already show how the priority risks posed by chemicals could be quickly mapped across Great Britain and Northern Ireland. The team previously demonstrated the scalability of its technology including for national-scale monitoring, but this represents the largest application to date. When complete, it will be the largest dataset of its kind, comprising over 200,000 measurements.  

The study forms part of a larger initiative coordinated by 911���պ���’s Grantham Institute for Climate Change and the Environment to tackle the impacts of pesticides on human and planetary health. This includes engagement with government, industry, the general public and the veterinary profession to improve awareness of the responsible use of pet parasiticides. This interdisciplinary team of chemists, biologists, ecologists, policymakers, social scientists, veterinarians, and community ambassadors were recently recognised as part of the 911���պ��� President’s Awards for Excellence in Culture and Community in 2024, and again in 2025 for Excellence in Societal Engagement. For a full list of their recent activities, see here. 

The laboratory analysis itself involved development of rapid and more sustainable robotic and mass spectrometric methodologies to cope with the scale and tight turnaround time required for the Great UK WaterBlitz. The approach is ready for application to large-scale monitoring programmes and the team will conduct future blitzes and are already working towards monitoring even more substances, including “forever chemicals” such as per- and polyfluoroalkyl substances (PFAS).  

In particular, the risks to human and wildlife health will be studied as part of additional projects involving citizen science, such as chemical exposure via drinking water and wild swimming, as well as studying the impacts on fish and invertebrates in contaminated UK rivers. 

, Research Fellow within the team said: “We embody sustainability in everything we do, from reducing the logistics of large-scale monitoring programmes through working with communities to identify problem areas and refining our laboratory practice to ensure we are not part of the problem we are trying to solve. It is very rewarding to see it all come together in this latest WaterBlitz.” 

Call for stricter regulations by government  

911���պ��� and Earthwatch Europe are calling on the UK government to implement stricter regulations for environmental risk assessment of pet medications like imidacloprid and restrict blanket preventative use of flea and tick treatments in the UK.  

from Earthwatch UK said: “Our partnership demonstrates that we can put cutting-edge science in the hands of huge numbers of people so that, together, we can shape the policies that protect the environment we live in.” 

The charity also urges authorities to integrate citizen science data into national freshwater monitoring frameworks and improve wastewater treatment processes.