Assessing pesticide effects on macroinvertebrates under field relevant conditions

Exposure to pesticides may affect non-target aquatic macroinvertebrates even below the regulatory acceptable concentrations. Similar low pesticide concentrations can force the organisms for adaptation. Aquatic organisms are often exposed to multiple stressors acting simultaneously or sequentially, including agrochemicals and suboptimal environmental conditions. However, a little is known about the pesticide effects on aquatic macroinvertebrates under field relevant conditions. In order to improve the existing risk assessment, this dissertation aims to assess important factors for pesticide effects in the field that are still not well understood. It contributes to the understanding of adaptation to pesticides, assessment of toxic pressure, interaction of mixtures, and the role of environmental stressors for the eco-toxicological effects of pesticides. To identify environmental parameters that govern the development of increased pesticide tolerance, a field investigation was conducted (Chapter 2). Gammarus pulex were collected from 15 sites within the central Germany that cover a wide range from un-contaminated to highly contaminated streams. Populations from contaminated streams showed almost 3-fold higher tolerance to the neonicotinoid insecticide clothianidin as compared to non-exposed populations. This tolerance of exposed populations increased from 2- to 4-fold with increasing distance to the next refuge area. Thus, distance from the refuge area and local toxic pressure were important factors that drive the development of pesticide resistance.In the second investigation (Chapter 3), pesticide body burden was applied to assess the pesticide exposure and potential effects in freshwater organisms. Body burdens of a crustacean G. pulex were converted into equivalent pesticide concentrations in the water, and linked with the observed ecological effects on freshwater macroinvertebrates. The toxic pressure derived from body burden was reliable to explain the effect on the macroinvertebrate community composition and the development of insecticide tolerance in G. pulex. For better understanding of multiple stressors in the environment (Chapter 4), interaction between food stress and a mixture of a pyrethroid esfenvalerate and prochloraz was investigated. To predict the joint effects of multiple stress, commonly applied models i.e. effect addition (EA), concentration addition (CA), and stress addition model (SAM) were compared. Results showed that the strength of interaction between esfenvalerate and prochloraz was increased with an increasing concentration of prochloraz. The combination of both pesticides and food stress caused highly synergistic effects even at 1 µg/L of prochloraz. Moreover, synergistic effects of pesticides and food stress were predicted best with the SAM model. The fourth investigation contributed to understand the mechanisms behind delayed effects at very low pesticide exposure in the field (Chapter 5). The metabolic response of Daphnia magna exposed to a pyrethroid esfenvalerate under suboptimal food supply was investigated. Metabolomic effects were observed at ultra-low concentrations, and were more pronounced under low food conditions. Interaction between food- and chemical stress was mainly responsible for extreme stress, and thereby strong down-regulation of different metabolites