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A comparative study of the acute toxicity of the herbicide atrazine to cladocerans Daphnia magna, Ceriodaphnia silvestrii and Macrothrix flabelligera Um estudo comparativo da toxicidade aguda do herbicida atrazina aos cladóceros Daphnia magna, Ceriodaphnia silvestrii e Macrothrix flabelligera Abstract: Aim: In this study we compared the sensitivity of three species of Cladocera, Daphnia magna, Ceriodaphnia silvestrii and Macrothrix flabelligera, to the commercial product of the herbicide Atrazine, the Atrazine Atanor 50 SC® (500 g/L), widely used on crops in Brazil. Methods: Acute toxicity tests were performed at the nominal atrazine concentrations 2. 25, 4.5, 9.0, 18.0, 36 and 72 mg L -1 , on C. silvestrii and M. flabelligera and at 2. 25, 4.5, 9.0, 18.0, 36, 72 and 144 mg L -1 on D. magna. The range of concentrations tested was established in a series of preliminary tests. Results: The toxicity tests showed that the two species naturally occurring in water bodies in Brazil were more susceptible than Daphnia magna. The effective concentrations of Atrazine Atanor 50 SC® (EC 50 -48 h) to the species M. flabelligera, C. silvestrii and D. magna were 12.37 ± 2.67 mg L -1 , 14.30 ± 1.55 mg L -1 and 50.41 ± 2.64 mg L -1 , respectively. Furthermore, when EC 50 observed here for M. flabelligera and C. silvestrii were compared with published values of EC 50 or LC 50 (mg L -1 ) for various aquatic organisms exposed to atrazine, it was seen that these two cladocerans were the most sensitive to the herbicide. Conclusions: Considering these results and the broad distribution of C. silvestrii and M. flabelligera in tropical and subtropical regions, it is concluded that these native species would be valuable test organisms in ecotoxicological tests, for the monitoring of toxic substances in tropical freshwaters. Resumo: Objetivo:Neste estudo comparamos a sensibilidade de três espécies de cladóceros, Daphnia magna, Ceriodaphnia silvestrii e Macrothrix flabelligera quando expostas ao herbicida Atrazina Atanor 50 SC® (500 g/L), amplamente utilizado em plantações no Brasil. Métodos: Foram realizados testes de toxicidade aguda das concentrações nominais de atrazina nos valores de 2,25; 4,5; 9,0; 18,0; 36 e 72 mg L -1 para C. silvestrii e M. flabelligera e de 2,25; 4,5; 9,0; 18,0; 36; 72 e 144 mg L -1 para D. magna. Estas faixas de concentrações foram estabelecidas em testes preliminares. Resultados: Os testes de toxicidade mostraram que as duas espécies que ocorrem naturalmente nos corpos d'água do Brasil foram mais sensíveis do que Daphnia magna. As concentrações efetivas de Atrazina Atanor 50 SC® (CE 50 -48 h) para M. flabelligera, C. silvestrii e D.magna, foram 12.37 ± 2.67 mg L -1 , 14.30 ±1.55 mg L -1 e 50.41 ± 2.64 mg L -1 , respectivamente. Comparando-se os valores de CE 50 da atrazina obtidos para M. flabelligera e C. silvestrii com valores de CE 50 ou CL 50 (mg L -1 ) disponíveis na literatura para diferentes organismos aquáticos observa-se que os cladóceros testados foram mais sensíveis ao herbicida do que os demais. Con...

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In order to contribute to the increase of the body of knowledge on the sensitivity of tropical indigenous species to pesticides, acute and chronic toxicity tests were conducted with the neotropical cladoceran Ceriodaphnia silvestrii. Tests were carried out with the active ingredients diuron and carbofuran and one of their commercial formulations, the Diuron Nortox® 500 SC and the Furadan® 350 SC, respectively. For carbofuran, the active ingredient was more toxic than the commercial product, whereas for diuron, the commercial product appeared more toxic. In addition, hormetic effects on fertility were recorded for intermediate diuron concentrations. Acute and chronic toxicity data indicated that C. silvestrii was among the most sensitive invertebrate species for both test compounds. Based on concentrations measured in Brazilian water bodies, these compounds represent ecological risks for causing direct and indirect toxic effects on C. silvestrii and other aquatic organisms. Our results support previous claims on the advantages of using native species to better tune ecological risk assessment of chemicals in tropical ecosystems.

As compared to their temperate counterparts, few toxicity tests have been conducted so far into the evaluation of the sensitivity of indigenous tropical species to pesticides. Especially mixture toxicity assessments appear to be scarce. To contribute to increase our knowledge in this arena, we evaluated the acute toxicity of diuron and carbofuran and their mixtures to the neotropical oligochaetes Allonais inaequalis and Dero furcatus, and the ostracod Strandesia trispinosa. Tests were performed with both the pure active ingredients, as well as their formulated products. The toxicity of the latter to the three test organisms was generally greater than that of the pure active ingredients, although absolute differences were rather small. The sensitivity of the indigenous species was slightly greater than temperate test species from the same taxonomic groups. The concentration addition conceptual model best described the results of the mixture toxicity data. Derived deviations of this model appeared to be dependent on the test organism and as to whether the pesticides were applied as active ingredients or their commercial products. Reported field concentrations of the two pesticides indicate risks to freshwater biota, especially if they are both present. The test species used in the present study are concluded to be suitable candidates as surrogate test organisms in local pesticide risk evaluations.

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