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SETAC Spotlight: What are the main drivers that contribute to herbicidal mixture toxicity in a highly agriculturally influenced landscape?

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SETAC Spotlight: What are the main drivers that contribute to herbicidal mixture toxicity in a highly agriculturally influenced landscape?

CEA presented 17 posters and platforms at SETAC Copenhagen in May 2022. Since then we have been showcasing each of these presentations in a series of 'SETAC Spotlight' articles. This week it is:

What are the main drivers that contribute to herbicidal mixture toxicity in a highly agriculturally influenced landscape

Author: Hanna Schuster

In the natural environment chemicals rarely occur as single entities but in undetermined mixtures. Despite this, the environmental risk assessment for plant protection products (PPPs) within the EU focusses on single substance registrations, except for products containing more than one active ingredient. Freshwater bodies in urban and agricultural areas may harbour an infinite number of combinations of anthropogenic chemicals. The assessment and regulation of these mixtures has raised concerns and prompted discussions by researchers, the public and regulators for at least the last three decades. These have included the implementation of a mixture assessment factor (MAF), but also more differentiated approaches e.g., addressing potential risks by managing critical compounds in spatio-temporal hotspots and their common mode of action (MOA). 

It has been demonstrated that only a limited number of chemicals drive the mixture toxicity, i.e., mixtures are not equitoxic. For photosynthetic organisms, mixture toxicity is primarily related to herbicides. A monitoring program carried out for 3.5 years in a highly agriculturally influenced catchment included sub-daily sampling of 12 herbicides and 1 metabolite. Here, we assess the relevance of this herbicide mixture in surface waters and propose how the data could be used for future regulatory decision-making processes. We identified how often the mixture exceeded the regulatory accepted concentration (RAC), assuming additive toxicity, which herbicide(s) contributed most to the exceedance events and determined if any factors could be identified contributing to these events (e.g., flow, rainfall, seasonality). Additionally, a stewardship program added to the influencing factors by implementing differing farming techniques and avoidance of missuses, spillages, and other point sources during study. 

The data were analysed separately for algae and macrophytes and although there are a low number of common herbicides driving the potential toxicity in both groups, there were also distinct differences where one group was more sensitive to a compound than the other (i.e. lower RAC). We found a clear seasonal influence driven by the growing season and rainfall and a stark reduction of exceedance events for both algae and macrophytes during the stewardship program. 

Overall, the analysis illustrates how monitoring projects can enhance the knowledge of the influencing factors that will enable improved decision making in the future. 

This poster is avaliable for free download

You can find all of the other posters and platforms that CEA presented at SETAC Copenhagen here. You can also find all of our publications from previous conferences and links to journal articles we have authored on our library page.

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