Os metais são de grande importância para os seres vivos em geral e particularmente para o homem. Alguns metais são essenciais ao metabolismo em pequenas quantidades, mas em maiores concentrações tornam-se tóxicos. Com o aumento da população humana e o desenvolvimento tecnológico, a poluição pelos metais tem se tornado um problema mundialmente grave. Nesta pesquisa foi investigada a toxicidade aguda, de forma isolada e em misturas, de quatro metais comuns na face da Terra, o cobre, o cádmio, o mercúrio e o manganês, os quais são muito utilizados e reconhecidamente tóxicos a diversos organismos, sobre a sobrevivência dos invertebrados tropicais, Tramea cophysa (Odonata), Chlamydotheca sp. e Strandesia trispinosa (Ostracoda). A sobrevivência das espécies expostas a uma série de concentrações de cada metal foi avaliada e a sensibilidade comparada entre as espécies estudadas e entre diferentes espécies de regiões tropicais e temperadas por meio de curvas de distribuição das sensibilidades (SSDs). O manganês foi o metal menos tóxico dentre aqueles testados, possivelmente devido à imobilização deste na cutícula das espécies-teste. T. cophysa esteve entre as espécies mais tolerantes aos metais e S. trispinosa entre as espécies mais sensíveis, quando comparadas a outros invertebrados utilizados em testes ecotoxicológicos. Pelas respostas observadas nos testes com os compostos isolados concluiu-se que as espécies selecionadas são organismos adequados para avaliações de toxicidade. Para as combinações dos compostos sulfato de cobre/cloreto de cádmio o modelo da Adição da Concentração foi o que melhor explicou a toxicidade sobre a sobrevivência de S. trispinosa indicando ajuste antagonístico. Para sulfato de cobre/cloreto de mercúrio e sulfato de cobre/sulfato de manganês, o modelo da Adição da Concentração também foi o que melhor explicou a toxicidade sobre a sobrevivência de S. trispinosa, mas indicando sinergismo quando o sulfato de cobre predominou na mistura e antagonismo quando o cloreto de mercúrio e o sulfato de manganês predominaram nas misturas. Já para a mistura cloreto de cádmio/cloreto de mercúrio, o modelo que melhor explicou os efeitos da mistura sobre a sobrevivência de S. trispinosa foi o de Ação Independente, sendo o melhor ajuste aos dados dado pelo desvio sinergístico. Um outro aspecto da toxicidade dos metais avaliados foram os efeitos da exposição de Tramea cophysa e de Chlamydotheca sp. a concentrações sub-letais dos quatro metais. Foi verificado que a taxa de predação de T. cophysa diminuiu quando exposta a concentrações crescentes de sulfato de cobre, cloreto de cádmio e cloreto de mercúrio, enquanto para Chamydotheca sp. houve um aumento na taxa de predação para a maioria das concentrações dos metais testados. Portanto, para entender como os metais afetam as comunidades, é preciso avaliar a toxicidade para cada espécie tanto aguda quanto crônica. Enfrentar esse desafio na Ecotoxicologia é essencial para a compreensão do modo como os contaminantes podem afetar desde o comportamento de indivíduos a comunidades ecológicas. / 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 world-wide 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 individuals to ecological communities.

Pesticide use in rice farming is a common practice in the Mekong Delta and poses ecological risks to aquatic organisms, the environment, and human health. This study focused on the ecological risk assessment of pesticide use in rice farming using the PRIMET model as a decision support tool to evaluate the risks of pesticide exposure, ecotoxicity, and risk characterization, as well as employing the species sensitivity distribution (SSD) assessment model to calculate the potentially affected fraction (PAF) of species based on the computed predicted environmental concentrations (PECs) from PRIMET. The study involved collating and analyzing data on pesticide inventories and the application of 138 farmers, which formed the basis for pesticide use, farming practices,environmental variables, and ecological indicators from two provinces in the Mekong Delta: Dong Thap and Hau Giang. This study showed that pesticide use was high with a wide range of pesticide types. The ecotoxicity assessment indicated that some pesticides pose a potential acute and chronic risk to non-target organisms. The active ingredient identified as posing acute toxicity risk with an ETR >100 is the insecticide indoxacarb, which belongs to the chemical class of oxadiazine of which Arthropods were seen to be highly sensitive to when exposed making them more at risk even at very low concentrations. In contrast, fish generally exhibit moderate tolerance and are sensitive to certain chemicals. The risk characterization revealed that the ecological risks of pesticide use were higher in Dong Thap than in Hau Giang due to differences in ecological conditions, pesticide practices, and farming systems. Overall, this study highlights the need for improved pesticide management practices in rice farming in the Mekong Delta region to reduce ecological risks and protect the environment and human health. The practical and theoretical implications of this study are discussed.