Bioavailability of pesticides to benthic invertebrates : the role of aquatic biofilms and humic substances

Abstract: In agricultural landscapes, pesticides are frequently contaminating nearby aquatic ecosystems. Unlike most other contaminants, pesticides are targeted against specific organism groups, but will also have negative effects on non-target organisms. When pesticides enter aquatic environments they tend to sorb to fine organic matter. Thus, benthic organisms inhabiting sediment and biofilms are constantly exposed to elevated concentrations. Depending on the bioavailability of these contaminants, benthic organisms play a key-role in the uptake and transfer to higher trophic levels. The bioavailability is partly deter-mined by the presence of organic matter, where their quantity and quality reflects the aquatic ecosystem’s trophic status and catchment area features. The broader aim of this thesis was to study the effects of different organic matter in artificial bottom substrate, and aquatic biofilms on pesticide bio-availability to benthic invertebrates with different feeding behaviour. We used organic matter of different sources, and short-term exposures to mimic peak exposures of pesticides in agricultural aquatic ecosystems. The results show that sediments with microbial biofilms strongly increase chlorpyrifos bioavailability to selective feeding larvae. However, chlorpyrifos bioavailability showed a negative correlation to extracellular polymeric substances (EPS) and humic substances (HS) quantities in an artificial bottom substrate. Furthermore, uptake of carbofuran, lindane and chlorpyrifos in non-selective feeding snails were affected by dissolved organic matter (DOM) quantity and quality, and related to pesticide hydrophobicity. Also, pesticide fate in microcosm compartments was affected by DOM-quantity and quality depending on pesticide physicochemical characteristics. These results lead on to a study where we wanted to quantify pesticide sorption to molecular size-fractions of different DOM, however, unfortunately without success. This thesis highlights the importance of quantity and quality of organic matter, based on our high resolution of different organic matter, and their impact on pesticide fate and bioavailability to lower trophic levels in aquatic ecosystems. Consequently, pesticide fate and bioavailability, and thus their effects on biota, changes between aquatic environments, and this should be taken into consideration in tests protocols for pesticide regulations.