Abstract
Systemic neonicotinoids are commonly used in forest pest management programs. Senescent leaves containing neonicotinoids may, however, fall from treated trees into nearby streams. There, leaf-shredding invertebrates are particularly exposed due to their diet (feeding on neonicotinoid-contaminated leaves) or collaterally via the water phase (leaching of a neonicotinoid from leaves) – a fact not considered during aquatic environmental risk assessment. To unravel the relevance of these pathways we used leaves from trees treated with the neonicotinoid thiacloprid to subject the amphipod shredder Gammarus fossarum for 21 days (n = 40) either to dietary, waterborne or a combined (dietary + waterborne) exposure. Dietary exposure caused – relative to the control – similar reductions in gammarids’ leaf consumption (~35%) and lipid content (~20%) as observed for the waterborne exposure pathway (30 and 22%). The effect sizes observed under combined exposure suggested additivity of effects being largely predictable using the reference model “independent action”. Since gammarids accumulated – independent of the exposure pathway – up to 280 ng thiacloprid/g, dietary exposure may also be relevant for predators which prey on Gammarus. Consequently, neglecting dietary exposure might underestimate the environmental risk systemic insecticides pose for ecosystem integrity calling for its consideration during the evaluation and registration of chemical stressors.
Highlights
Neonicotinoids are one of the most widely used insecticides class worldwide[1]
The impact of the first neonicotinoid insecticide, i.e., imidacloprid, on aquatic systems has recently been evaluated in the European Union[9], the United States[10] and Canada[11], since neonicotinoids’ frequent use, environmental persistence and physico-chemical properties favour their off-site transport via spray drift, 1Institute for Environmental Sciences, University of Koblenz-Landau, Landau Campus, Fortstrasse 7, 76829, Landau, Germany. 2Department Effect-Directed Analysis, Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318, Leipzig, Germany. 3Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Box 7050, 75007, Uppsala, Sweden
The present study aimed to unravel the relevance of these pathways by subjecting the shredder Gammarus fossarum (Koch) – an amphipod frequently used in non-standard aquatic toxicity studies26– for 21 days to leaves from neonicotinoid-treated black alder trees, using thiacloprid (THI) as a model substance
Summary
Neonicotinoids are one of the most widely used insecticides class worldwide[1]. Their tremendous success is due to multiple factors: Firstly, their systemic action facilitates a rapid uptake and distribution in plants and allows for a broad range of application methods thereby reducing the total amount of insecticide needed to be applied[1,2]. The present study aimed to unravel the relevance of these pathways by subjecting the shredder Gammarus fossarum (Koch) – an amphipod frequently used in non-standard aquatic toxicity studies26– for 21 days to leaves from neonicotinoid-treated black alder trees, using thiacloprid (THI) as a model substance These leaves served as the only neonicotinoid source: gammarids either faced dietary exposure – i.e., feeding on THI-contaminated leaves while a flow-through system prevented THI from accumulating in the water phase – waterborne exposure (through leaching of THI from leaves) or combined exposure (i.e., dietary + waterborne). Thereby, the present work assessed the relevance of a pathway – i.e., dietary exposure – that is not well reflected in current aquatic risk assessment of neonicotinoids or systemic pesticides in general
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