title: Toxicity of abamectin and difenoconazole mixtures to a Neotropical cladoceran after simulated run-off and spray drift exposure.
abstract: Aquatic risk assessments of pesticides in tropical countries have often been disputed for being largely based on risk evaluations conducted in temperate regions. Although pesticide sensitivity comparisons between temperate and tropical freshwater organisms have indeed not revealed consistent differences, risk assessments are currently still based on a relatively small tropical toxicity dataset. In addition, greater levels of runoff and spray drift may be expected in tropical than in temperate agroecosystems, indicating that aquatic life in edge-of-field water bodies is likely to be subjected to higher concentrations of pesticides and their mixtures. The aim of the present study was to evaluate the toxicity of Kraft®36 EC (a.i. abamectin), Score®250 EC (a.i. difenoconazole) and their mixture to the Neotropical cladoceran Macrothrix flabelligera. Laboratory toxicity tests with the individual formulated products indicated EC50-48h values of 3.1 and 659μg a.i./L given as nominal test concentrations, respectively. Mixtures of the two pesticides revealed a concentration-dependent deviation of the independent action model, with antagonism at low and synergism at high pesticide mixture concentrations. Laboratory toxicity tests were also conducted with microcosm water that was treated with the individual or mixtures through runoff or direct overspray. Microcosm tanks receiving runoff water from experimental soil plots applied with recommended doses of the individual pesticides did not show toxicity to the test organism. Microcosms that received runoff water containing the pesticide mixture, however, did cause a short-term effect on immobility. The microcosms that were treated by direct overspray of both pesticide formulations showed the most pronounced toxic effects. Study findings suggest a potential risk of these pesticides at environmentally relevant concentrations, especially when they are both present.
authors.affiliation: Post-Graduate Program of Ecology and Natural Resources, Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Rodovia Washington Luis, km 235, 13565-905, São Carlos, SP, Brazil. Electronic address: raquel.moreira87@yahoo.com.br.
authors.forename: Raquel Aparecida
authors.initials: RA
authors.lastname: Moreira
authors.affiliation: NEEA/CRHEA/SHS, São Carlos Engineering School, University of São Paulo, Av. Trabalhador São Carlense, 400, 13.560-970 São Carlos, Brazil; Department of Environmental Sciences and Engineering, Faculty of Sciences and Technology, New University of Lisbon, Quinta da Torre, 2829-516 Caparica, Portugal.
authors.forename: Michiel Adriaan
authors.initials: MA
authors.lastname: Daam
authors.affiliation: NEEA/CRHEA/SHS, São Carlos Engineering School, University of São Paulo, Av. Trabalhador São Carlense, 400, 13.560-970 São Carlos, Brazil.
authors.forename: Bruna Horvath
authors.initials: BH
authors.lastname: Vieira
authors.affiliation: NEEA/CRHEA/SHS, São Carlos Engineering School, University of São Paulo, Av. Trabalhador São Carlense, 400, 13.560-970 São Carlos, Brazil.
authors.forename: Ana Letícia Madeira
authors.initials: AL
authors.lastname: Sanches
authors.affiliation: NEEA/CRHEA/SHS, São Carlos Engineering School, University of São Paulo, Av. Trabalhador São Carlense, 400, 13.560-970 São Carlos, Brazil.
authors.forename: Marina Vanderlei
authors.initials: MV
authors.lastname: Reghini
authors.affiliation: Post-Graduate Program of Ecology and Natural Resources, Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Rodovia Washington Luis, km 235, 13565-905, São Carlos, SP, Brazil.
authors.forename: Adrislaine
authors.initials: A
authors.lastname: da Silva Mansano
authors.affiliation: Post-Graduate Program of Ecology and Natural Resources, Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Rodovia Washington Luis, km 235, 13565-905, São Carlos, SP, Brazil.
authors.forename: Emanuela Cristina
authors.initials: EC
authors.lastname: de Freitas
authors.affiliation: NEEA/CRHEA/SHS, São Carlos Engineering School, University of São Paulo, Av. Trabalhador São Carlense, 400, 13.560-970 São Carlos, Brazil.
authors.forename: Evaldo Luiz Gaeta
authors.initials: EL
authors.lastname: Espindola
authors.affiliation: Post-Graduate Program of Ecology and Natural Resources, Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Rodovia Washington Luis, km 235, 13565-905, São Carlos, SP, Brazil.
authors.forename: Odete
authors.initials: O
authors.lastname: Rocha
mesh_terms: D000818:Animals; D033361:Cladocera / Q000187:drug effects*; D004148:Dioxolanes / Q000633:toxicity*; D007559:Ivermectin / Q000031:analogs & derivatives* / Q000633:toxicity; D010575:Pesticides / Q000633:toxicity; D018570:Risk Assessment; D013045:Species Specificity; D018675:Toxicity Tests; D023382:Toxicity Tests, Acute; D014230:Triazoles / Q000633:toxicity*; D014329:Tropical Climate; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D004148:Dioxolanes; D010575:Pesticides; D014230:Triazoles; D014874:Water Pollutants, Chemical; C048324:abamectin; D007559:Ivermectin; C115058:difenoconazole
keywords: Environmental risk assessment; Macrothrix flabelligera; Microcosms; Pesticide mixtures; Tropics