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- Effects of dietary exposure to herbicide and of the nutritive quality of contaminated food on the reproductive output of Daphnia magnaPublication . Silva, M. Bessa da; Abrantes, N.; Rocha-Santos, T.A.P.; Duarte, A.C.; Freitas, A.C.; Gomes, Ana M. P.; Carvalho, A.P.; Marques, J.C.; Gonçalves, F.; Pereira, R.tRisk assessment of pesticides has been based on direct toxic effects on aquatic organisms. Indirect effectsdata are taken into account but with limitations, as it is frequently difficult to predict their real impactsin the ecosystems. In this context the main aim of this work was to assess how the exposure to theherbicide pendimethalin (Prowl®), under environmentally relevant concentrations, may compromise thenutritional composition of food for a relevant group of primary consumers of freshwater food webs—thedaphnids, thus affecting their reproduction performance and subsequently the long-term sustainabilityof active populations of this grazer. Therefore, Daphnia magna individuals were chronically exposed in aclean medium to a control diet (NCF – i.e., non-contaminated green algae Raphidocelis subcapitata) and to acontaminated diet (CF – i.e., the same monoalgal culture grown in a medium enriched with pendimethalinin a concentration equivalent to the EC20for growth inhibition of algae), during which reproductiveendpoints were assessed. The algae were analysed for protein, carbohydrate and fatty acid content. Thechemical composition of R. subcapitata in the CF revealed a slight decrease on total fatty acid levels, witha particular decrease of essential 9 monounsaturated fatty acids. In contrast, the protein content washigh in the CF. D. magna exposed to CF experienced a 16% reduction in reproduction, measured as thetotal number of offspring produced per female. Additionally, an internal pendimethalin body burden of4.226 g g−1was accumulated by daphnids fed with CF. Hence, although it is difficult to discriminate thecontribution of the pesticide (as a toxic agent transferred through the food web) from that of the food witha poor quality—compromised by the same pesticide, there are no doubts that, under environmentallyrelevant concentrations of pesticides, both pathways may compromise the populations of freshwatergrazers in the long term, with consequences in the control of the primary productivity of these systems.