Analysis and management of herbicidal mixtures in a high‐intensity agricultural landscape in Belgium

• Published in: Integrated environmental assessment and management Vol. 19; no. 5; pp. 1297 - 1306
• Main Authors: Schuster, Hanna S., Taylor, Nadine S., Sur, Robin, Weyers, Arnd
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.09.2023
• Subjects: Agricultural land; Agricultural practices; Agricultural watersheds; Agrochemicals; Algae; Anthropogenic factors; Aquatic plants; Catchment area; Daily; Datasets; Environmental assessment; Environmental Impact Assessment; Environmental management; Environmental risk; Environmental risk assessment; Exposure; Herbicides; Integrated environmental assessment; Landscape; Macrophytes; Metabolites; mixture toxicity; Mixtures; Rainfall; Risk assessment; risk management; Stewardship; Temporal resolution; Toxicity; Toxicology; Environmental risk assessment; mixture toxicity; risk management; herbicides
• ISSN: 1551-3777; 1551-3793
• DOI: 10.1002/ieam.4727

Water bodies located in anthropogenically influenced environments, such as agricultural landscapes, may be exposed to different chemicals simultaneously or sequentially. Yet, current environmental risk assessments focus on single active substances for unintended mixtures. For 3.5 years, the present study monitored the mixture of herbicides, within an intensively managed agricultural catchment, accompanied by a stewardship program. Twelve herbicides and one metabolite were monitored on a daily to sub‐daily basis, generating a unique, high temporal resolution data set, enabling an assessment of cumulative exposure in a worst‐case scenario. Analyses focused on the number of events at which the herbicide mixture concentration exceeded the regulatory accepted concentration for algae and macrophytes, based on concentration addition, and the potential factors influencing the frequency of these events are considered. A low number of individual herbicides drove the toxicity and only two of these overlapped for the two organism groups, algae and macrophytes. The observed exceedance events coincided with seasonal influences, and low rainfall during the 2011 season correlated with a highly reduced number of these events. The major influence was found to be the implementation of the stewardship program, which directed farmers to use more advanced farming techniques, avoid spillages, and other point sources. The number of exceedance events was reduced by more than half for algae (9% of the daily mean samples in 2010 and 4% in 2013) and by approximately 10 times for macrophytes (36% in 2010 to 3% in 2013). This high‐resolution monitoring data set illustrates how knowledge of the influencing factors can help reduce unintended exposure to chemicals and achieve real‐world improvements. Overall, a single‐substance assessment is protective of mixture effects. Where mixture effects do play a role, local measures to manage point sources are more effective than changes to the desk‐based environmental risk assessments that focus on diffuse sources. Integr Environ Assess Manag 2023;19:1297–1306. © 2022 Cambridge Environmental Assessments RSK ADAS Ltd and Bayer AG. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points Mixture exceedance events are rare. Point source mitigation measures are an effective risk assessment approach with real‐world improvements.