title: Low-Dose Effects: Nonmonotonic Responses for the Toxicity of a Bacillus thuringiensis Biocide to Daphnia magna.
abstract: Currently, there is a trend toward an increasing use of biopesticides assumed to be environmentally friendly, such as Bacillus thuringiensis (Bt). Studies of the Bt toxicity to nontarget organisms have reported low effects at high exposure levels, which is interpreted as indicating negligible risk to nontarget organisms. We investigated the response of the nontarget organism Daphnia magna to waterborne DiPel ES, a globally used Bt formulation. Neonates and adults were exposed for 48 h to a wide range of concentrations, and immobilization and mortality were monitored. Whole body biomarkers (body weight, protein, chitobiase, catalase, xenobiotic metabolism, and acetylcholinesterase) were measured in the adults. The immobilization and mortality of the neonates were affected in a nonmonotonic and inverted U-shaped pattern with EC50s that were ∼105-fold lower than those reported by the manufacturer. The immobilization of adults demonstrated a similar pattern, but significant mortality was not observed. The biomarker results revealed multiphasic dose-response curves, which suggested toxicity mechanisms that affected various physiological pathways. The main particle size in exposure media was in the size range of bacterial spores and crystal toxins. However, the chemical heterogeneity was nonmonotonic, with a change in the phase at the maximum of toxicity (∼5 μL L-1), which might explain the observed nonmonotonic effects. These results demonstrate the vulnerability of a nontarget organism to a biopesticide that is considered to be safe, while challenging the universal applicability of the central ecotoxicological assumption of monotonicity.
authors.affiliation: Department of Biology, Chemistry and Pharmacy, Freie Universität Berlin , 14195 Berlin, Germany.|School of Geography, Queen Mary, University of London , London E1 4NS, United Kingdom.|Leibniz-Institute of Freshwater Ecology and Inland Fisheries , 12587 Berlin, Germany.
authors.forename: Anderson Abel
authors.identifier: 0000-0001-6969-7430
authors.initials: AA
authors.lastname: de Souza Machado
authors.affiliation: Center for Applied Geosciences, Eberhard Karls Universität Tübingen , 72074 Tübingen, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Zarfl
authors.affiliation: Department of Biology, Chemistry and Pharmacy, Freie Universität Berlin , 14195 Berlin, Germany.|Leibniz-Institute of Freshwater Ecology and Inland Fisheries , 12587 Berlin, Germany.
authors.forename: Saskia
authors.initials: S
authors.lastname: Rehse
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries , 12587 Berlin, Germany.|Faculty of Life Sciences, Humboldt-Universität zu Berlin , 10099 Berlin, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Kloas
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D001413:Bacillus thuringiensis; D002374:Catalase / Q000378:metabolism; D003621:Daphnia / Q000187:drug effects*; D004202:Disinfectants / Q000494:pharmacology; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D004202:Disinfectants; D014874:Water Pollutants, Chemical; D002374:Catalase; D000110:Acetylcholinesterase