In this post, Mirco Bundschuh talks about their recently published paper “Multiple exposure routes of a pesticide exacerbate effects on a grazing mayfly”.

Mayflies grazing on biofilms growing on tiles in a laboratory setting (photo by U. Noerum)

In the agricultural landscape freshwater systems are often exposed towards a suite of agrochemicals including pesticides and nutrients. Depending on their physico-chemical properties pesticides have a distinct fate with hydrophobic substances rapidly adsorbing to organic surfaces in the freshwater systems. In collaboration with researchers from the Department of Biosciences at Aarhus University, the role of multiple exposure routes (via water and adsorbed to biofilm) for the effects on mayflies was investigated using the strongly hydrophobic pyrethroid insecticide lambda-cyhalothrin as model substance in a full- factorial test design. Biofilm acts as single food resource for the mayfly. We observed a significant increase in mortality and decrease in moulting frequency with increasing concentrations of the pyrethroid in the water phase whereas exposure via biofilm caused no significant effects on these endpoints. Effect predictions systematically underestimated and overestimated the joint effects of both exposure pathways for mortality and moulting frequency, respectively. Similarly, mayfly feeding rate was significantly reduced by water phase exposure whereas pre-exposed biofilm did not significantly affect this variable. However, we found a significant interaction between water phase and biofilm exposure on mayfly feeding rate.

Our results clearly show that exposure to the same pesticide via multiple exposure routes cannot be predicted from single phase exposures, while interactions between pesticide exposure is depending on the assessed variable. These insights clearly call for an evaluation of the aquatic risk assessment procedure of hydrophobic pesticides.

The paper was authored by Mathias Joachim Skov Pristed, Mirco Bundschuh and Jes Jessen Rasmussen and is published in Aquatic Toxicology.

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