Pesticides may end up in surface waters at the edges of agricultural fields through spray drift, run-off and drainage. The potential risk to aquatic biota from this contamination may occur in various environmental scenarios and is addressed in several tiers in the risk assessment (RA) process. Mechanistic effects models have been proposed as excellent tools for the refinement of the RA process, and their appropriate use was the topic of the Modelink workshop. Here we report the results of a case study with the freshwater amphipod, Gammarus pulex, that has a key role in leaf litter decomposition in freshwater ecosystems, exposed to a hypothetical insecticide. The insecticide - a typical pyrethroid with high toxicity to aquatic invertebrates - was applied five times in one year. Exposure was based on the pesticide fate modelling framework, with estimated concentrations in edge of field surface waters including ditches (slow flowing) and streams (fast flowing). The spatially explicit individual based model (IBM) of the freshwater amphipod was developed by accounting for species life history and movement patterns. Exposure concentrations and effects on individuals were coupled with the reduced stochastic death version of the General Unified Threshold model for Survival, that simulated both toxicokinetic and toxicodynamic effects at the level of individuals. In a number of simulations, we show that the adverse effects on populations were largest in several ditch scenarios with long population recovery times. A combination of extended insecticide presence in the water column and slow population growth resulted in very long recovery times in ditch scenarios typical of Scandinavian regions. Due to faster flows, populations in streams were less affected and recovered within one year after the first application event. Finally, populations in scenarios typical of regions with a warmer climate showed faster recovery relative to those with a colder climate.

Modelling population-level effects and recovery of aquatic invertebrates after multiple applications of an insecticide: The case study of a freshwater amphipod

248th National Meeting (2014)

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