CEA Scientists and Associates Provide New Insights into Levels of Imidacloprid in UK Surface Waters
Cambridge Environmental Assessments (CEA) scientists and collaborators have contributed to a new study that offers the clearest picture yet of how imidacloprid, a widely used insecticide, is behaving in the UK’s rivers and streams. The research, published in Environmental Sciences Europe, is titled “Imidacloprid in UK surface waters: trends, sources, and pathways.”
Understanding imidacloprid and why it matters
Imidacloprid has been used for decades to protect crops and control insect pests. However, concerns about its potential impact on pollinators such as bees led to a ban on agricultural use in 2016. Despite this, imidacloprid is still used in veterinary medicines—mainly in flea and tick treatments for cats and dogs—and as a biocide in pest control products such as ant and cockroach baits. It can also be found on imported foods from countries where its use on crops remains permitted.
These remaining uses, along with legacy residues in soils and sediments, may still contribute to trace levels detected in UK surface waters. The study set out to understand how imidacloprid levels have changed since the agricultural ban and what national monitoring data can tell us about its current presence and potential sources.
What the study found
Researchers analysed national monitoring records from 2016 to 2023 and found a steady decline in imidacloprid concentrations in surface waters across the UK. This decline aligns with the agricultural ban and tighter restrictions on other uses.
On average, the annual mean concentration fell by more than 50% since 2016, and over 60% of river samples are now below the limit of quantification—meaning that in most cases, imidacloprid levels are too low to measure accurately.
Associate Director David Brown said:
“This study has really shone a light on imidacloprid in the UK. We can see that concentrations in surface waters are decreasing, but it also highlights where our understanding is still limited—especially when it comes to biocide use and data availability.”
Challenges with the data
The study also revealed several data limitations that make it difficult to form a complete national picture. A large proportion of samples were below the limit of detection (LOD), and many of those results were not included in the public datasets. CEA scientists had to impute these missing values to gain a more accurate understanding of where imidacloprid was actually being detected. Once that was done, it became clear that imidacloprid is not widespread, but rather detected infrequently and at low concentrations.
Another challenge was representativity. Most monitoring data came from England, with limited sampling in Scotland, Wales, and Northern Ireland. Many sites were also sampled only once, meaning that long-term, UK-wide trends are difficult to confirm.
Why more data are needed
While the contribution of veterinary medicines to surface water levels is relatively well understood, there is very little information about biocide use or emissions. The study recommends establishing a formal reporting mechanism for biocidal product sales and usage data to fill this crucial knowledge gap.
Moving forward
Overall, the findings show that imidacloprid concentrations in UK surface waters are declining, reflecting the positive impact of regulatory action. However, the research also underscores the need for more comprehensive and representative monitoring, and for the inclusion of all low-level detection data in public datasets.
Improving data transparency—particularly around biocide use—will be essential for understanding the remaining sources of imidacloprid and ensuring the continued protection of UK aquatic ecosystems.
Link to the paper https://rdcu.be/ePpaH
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