title: Deciphering mechanisms of malathion toxicity under pulse exposure of the freshwater cladoceran Daphnia magna.
abstract: The organophosphate pesticide (OP) malathion is highly toxic to freshwater invertebrates, including the cladoceran Daphnia magna, a widely used test organism in ecotoxicology. To assess whether toxic effects of malathion are driven primarily by exposure concentration or exposure duration, D. magna was pulse exposed to equivalent integrated doses (duration × concentration): 3 h × 16 μg/L, 24 h × 2 μg/L, and 48 h × 1 μg/L. After recovery periods of 3 h, 24 h, and 48 h, the toxicity of malathion on different biological levels in D. magna was examined by analyzing the following endpoints: survival and immobilization; enzyme activities of acetylcholinesterase (AChE), carboxylesterase (CbE), and glutathione S-transferase (GST); and AChE gene expression. The results showed no difference in survival among equivalent integrated doses. Adverse sublethal effects were driven by exposure concentration rather than pulse duration. Specifically, short pulse exposure to a high concentration of malathion resulted in more immobilized daphnids, lower AChE and CbE activities, and a higher transcript level of AChE gene compared with long pulse exposure to low concentration. The expression of the AChE gene was up-regulated, indicating a compensatory mechanism to cope with enzyme inhibition. The study shows the need for obtaining a better understanding of the processes underlying toxicity under realistic exposure scenarios, so this can be taken into account in environmental risk assessment of pesticides.
authors.affiliation: Department of Environmental, Social and Spatial Change, Roskilde University, Roskilde, Denmark.
authors.forename: Lam Ngoc
authors.initials: LN
authors.lastname: Trac
authors.affiliation: Department of Nature, Systems and Models, Roskilde University, Roskilde, Denmark.
authors.forename: Ole
authors.initials: O
authors.lastname: Andersen
authors.affiliation: Department of Environmental, Social and Spatial Change, Roskilde University, Roskilde, Denmark.
authors.forename: Annemette
authors.initials: A
authors.lastname: Palmqvist
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D003621:Daphnia; D005618:Fresh Water; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005982:Glutathione Transferase / Q000378:metabolism; D007306:Insecticides / Q000633:toxicity*; D008294:Malathion / Q000633:toxicity*; D009043:Motor Activity / Q000187:drug effects; D018570:Risk Assessment; D016019:Survival Analysis; D015854:Up-Regulation / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D007306:Insecticides; D014874:Water Pollutants, Chemical; D005982:Glutathione Transferase; D000110:Acetylcholinesterase; D008294:Malathion
keywords: Acetylcholinesterase; Delayed response; Enzyme activities; Gene expression; Organophosphate insecticide