Imidacloprid in UK surface waters: trends, sources, and pathways

Abstract Imidacloprid is an insecticide used in the UK for plant protection, biocides, and veterinary medicine. Concerns over its potential impact on non-target pollinators such as bees led to a ban in agricultural use in the EU in 2018 and earlier in the UK. It was added to the EU Water Framework Directive (WFD) watch list in 2015, with UK surface water monitoring starting in 2016. An assessment of monitoring data from 2016 to 2023 was conducted following WFD guidelines, using EU environmental quality standards (EQS) proposed for 2027, as no UK EQS has been established. The assessment checked site representativity and imputed missing data in England’s monitoring dataset to improve statistical analysis. Results showed a consistent decline in imidacloprid concentrations in surface water since 2016, aligning with the agricultural ban and tighter restrictions on other uses. Environmental imidacloprid sources include legacy residues in soils, sediments, groundwater, and wastewater treatment emissions. The role of veterinary products and biocides in imidacloprid detections was also explored, though biocide impact assessment was complicated by less stringent usage reporting. Current trends suggest further declines in surface water concentrations due to ongoing restrictions and responsible use programmes. Draft EU legislation aims for compliance with EQS by 2039, which seems achievable in the UK given current trends, though this timeline may not be adopted into UK law. The assessment of surface water monitoring data requires careful consideration and would benefit from more frequent, representative measurements. Highlights. A systematic evaluation of imidacloprid in surface waters across the UK was conducted. Monitoring indicates a consistent decline of imidacloprid concentrations in surface water since 2016. Sources may include veterinary products, biocides, and legacy residues in soils. More extensive monitoring of imidacloprid would improve understanding of source contributions.