UK Approves Amendment to Prosulfuron Approval, Lifts Application Restrictions

Background: Approval and Previous Restrictions on Prosulfuron

Originally approved in the UK under the retained EU Regulation No 1107/2009, prosulfuron faced strict usage limitations to protect groundwater from contamination. Concerns stemmed from prosulfuron’s metabolites, which could potentially reach groundwater, necessitating usage restrictions to one application every three years as per the 2017 European Commission Implementing Regulation (EU) 2017/375​​.

In 2021, Syngenta Crop Protection AG submitted a request to remove this restriction, presenting a dossier that included updated scientific findings on the herbicide’s environmental and toxicological effects. The dossier supported that under revised assessment conditions, annual applications of prosulfuron would not exceed the UK’s legal groundwater contamination threshold of 0.1 µg/L for plant protection products​.

HSE’s Evaluation and Public Consultation

HSE’s assessment included comprehensive analysis of prosulfuron’s toxicological, environmental, and residue behaviour data. The HSE also considered new field and lab studies demonstrating that revised prosulfuron application intervals could safely support annual use. A public consultation on the draft assessment report (DAR) was conducted from October to December 2023. With no public objections, the HSE proceeded to finalise its conclusion.

The HSE’s final decision was reached in September 2024 and determined that annual applications of prosulfuron at up to 20 g/ha meet the required environmental and human health safety standards. The HSE concluded that prosulfuron could remain approved as a candidate for substitution in the UK without the former restriction​​.

Environmental and Health Safety Measures

While the restriction is removed, HSE has outlined that product-specific authorisation conditions will still require manufacturers to mitigate any groundwater risks, particularly in sensitive or high-risk soil areas. Additionally, this amendment maintains that manufacturers must continuously evaluate the environmental impact of metabolites generated by prosulfuron degradation.

This decision aligns with the updated FOCUS (Forum for the Co-ordination of Pesticide Fate Models and their Use) guidance, as HSE re-assessed the metabolites’ levels against environmental benchmarks using refined groundwater modelling. This update indicated that, even with increased application frequency, prosulfuron and its metabolites should remain within acceptable groundwater thresholds for non-target exposure risks​.

Implications for UK Agriculture

The UK’s regulatory adjustment provides farmers more latitude in prosulfuron application, supporting effective weed management in maize and sweetcorn. The HSE’s decision underscores the UK’s ongoing commitment to science-backed regulatory adaptations that balance agricultural productivity with rigorous environmental protection standards.