Avaliação da toxicidade de metais sobre os macroinvertebrados bentônicos tropicais >i<Tramea cophysa>/i< (Libelullidae, Odonata), >i<Chlamydotheca>/i< sp.(Cyprididae, Ostracoda) e >i<Strandesia trispinosa>/i< (Cyprididae, Ostracoda)

Abstract

Metals are very important for live beings in general and particularly for men. Some metals are essential to metabolismo in small amounts, but in higher concentrations they become toxic. With the exponencial increase of human population and technological development, metal pollution has become a severe worldwide problem. In this study we investigated the acute toxicity of isolately and in mixture combinations of four common metals on Earth, which are widely used, but well recognized as toxicants to both, terrestrial and aquatic organisms. The acute toxicity of copper, cadmium, mercury and manganese on the survival of tropical invertebrates, Tramea cophysa (Odonata), Chlamydotheca sp. and Strandesia trispinosa (Ostracoda) was evaluated for each metal isolately and as binary mixtures. The survival of this species exposed to a series of concentrations of each metal was evaluated and their sensitivity compared among the species studied and with different species of tropical and temperate regions by constructing Species Sensitivity Distribution curves (SSDs). Manganese was the least toxic compared to other tested metals, possibly due to its immobilization in the cuticle of the test species. T. cophysa was among the species more tolerant to these metals and S. trispinosa among the most sensitive species when compared to other invertebrates used in ecotoxicological tests. From the responses observed in the tests with the isolated compounds it was concluded that the selected species are adequate to toxicity evaluations. For the combinations of the copper sulfate/cadmium chloride compounds the Concentration Addition model was the one which best explained the toxicity on S. trispinosa survival indicating antagonistic adjustment. For copper sulphate and mercury chloride mixture and copper sulphate and manganese sulphate, the Concentration Addition model also best explained the toxicity of S. trispinosa survival, but indicating synergism when copper sulphate predominated in the mixture and antagonism when mercury chloride and manganese sulphate predominated in the mixtures. For the mixture of cadmium chloride andmercury chloride, the model that best explained the effects of the mixture on the survival of S. trispinosa was that of Independent Action, being the best fit to the data given by the synergistic deviation. Other aspects of the toxicity of the evaluated metals were the effects of the exposure of Tramea cophysa and Chlamydotheca sp. to sub-lethal concentrations of the four metals. It was verified that the predation rate of T. cophisa decreased when exposed to increasing concentrations of copper sulphate, cadmium chloride and mercury chloride, whereas for Chamydotheca sp. there was an increase in the rate of predation for most concentrations of the metals tested. Therefore, to understand how metals affect communities, it is necessary to assess the toxicity for each species both acute and chronic. Addressing this challenge in Ecotoxicology is essential for understanding how contaminants can affect from the behavior of in...