Toxicity of Binary Metal Mixtures to the Tropical Ostracod Strandesia Trispinosa.

The ecotoxicity of metals is generally assessed individually, in part because current knowledge does not allow for the accurate prediction of the toxicity of metal mixtures to aquatic organisms. The objective of this study was to investigate the toxic effects of binary combinations of metal salts (copper sulphate-CuSO4, cadmium chloride-CdCl2, mercury chloride-HgCl2 and manganese sulphate-MnSO4) on the tropical ostracod Strandesia trispinosa through acute toxicity tests. To this end, ostracods were exposed to each individual metal salt as well as to their combinations by applying a full factorial design. The model that best explained the effects of the mixtures CuSO4 x CdCl2, CuSO4 x HgCl2 and CuSO4 x MnSO4 on the survival of S. trispinosa was Concentration Addition, whereas this was Independent Action for the CdCl2 x HgCl2 mixture. The observed synergistic interactions are likely to result in unacceptable risks to aquatic ecosystems under real field conditions. This is especially the case if CuSO4 predominates the metal mixture, as observed for its combination with mercury and manganese.

Sensitivities of three tropical indigenous freshwater invertebrates to single and mixture exposures of diuron and carbofuran and their commercial formulations.

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.