Agricultural Drainflow: Landscape risk mapping to facilitate field level risk assessments of plant protection products in Great Britain

To date, there are very few studies focusing on risk mapping of agricultural drainflow losses of pesticides in Great Britain (GB). A spatially distributed landscape implementation of the UK higher tier drainflow environmental risk assessment modelling framework at 1 km resolution was developed for three example pesticide active substances and used to derive substance-specific drainflow risk index (DFRI) maps covering GB. The DFRI mapping approach comprised of: (A) definition of high-resolution landscape scenarios in the drainflow simulation modelling that would underpin the DFRI; and (B) construction of 2 and 3 class bivariate DFRI aligned with the existing GB regulatory approach for use in field scale risk assessment and communication. Visual comparison of the DFRI maps for the three active substances indicates the influence of substance properties, with the mobile non-persistent substance demonstrating large areas of safe use, while the slightly-mobile moderately persistent substance demonstrated less low-risk areas. Across all three substance DFRI maps, there are locations where no/few drained soils are present, indicating inherently safe usage locations exist alongside the low-risk areas. A limiting factor of the DFRI approach is the reliance on generalised soil association data as being an accurate representation of the soils actually present at a location. The DFRI approach offers an opportunity to move away from a binary regulatory decision of a product being registered or not, to one that allows use in locations where it is safe to do so, while prohibiting use in those locations where it is not. This more targeted approach would allow users access to a wider range of crop protection options to leverage greater benefits whilst simultaneously reducing risks to aquatic habitats. In order to adopt such an approach, regulators would require reassurance that users could undertake and comply with the results of a field level risk assessment.