Farmer engagement projects to reduce metaldehyde runoff to watercourses used as drinking water sources.

Metaldehyde, the active ingredient in common slug pellets, is very difficult to remove from drinking water, but often exceeds the Drinking Water Standard (DWS) in raw water used as drinking water sources. Thames Water has therefore been working with farmers across the Thames basin to reduce
the amount of metaldehyde reaching rivers, using two main approaches: product substitution and payment for ecosystem services.

In some areas, farmers were offered a subsidy of £1/kg for ferric phosphate slug pellets used in the high-risk autumn season as an alternative to metaldehyde. Results have shown significant reductions in metaldehyde concentrations, often below the DWS. In addition, the project has supported farmers in using ferric phosphate as an alternative to metaldehyde.

In other areas, a Payment for Ecosystem Services scheme recognised farmers as producers of clean water and rewarded them for it. It enabled farmers to select the most appropriate land management practices for their farm to reduce metaldehyde pollution including cultural control methods (creating a less favourable environment for slugs) and integrated pest management. Payments were made based on metaldehyde concentrations in the local river.

Both project approaches have been rolled out gradually across the Thames basin since 2011, and in 2018, 350 farmers were involved across 91 WFD waterbodies.

NB – The future of metaldehyde in the UK is currently under review and it may be withdrawn from use. Thames Water will continue working with farmers to reduce the impact of metaldehyde on drinking water sources for as long as metaldehyde remains available for outdoor use and an issue in the Thames basin.