Although invertebrates are recognized by the great facility to accumulate pollutants present in their environment and many of them are used as sentinel species in biomonitoring studies, little is known about the impact of toxicants on the immune system of these animals. In this regard, hemocytes play a fundamental role: these cells circulate freely through the hemolymph of invertebrates and act on the recognition of foreign material to the organism, mediating and effecting the cellular defense, such as phagocytosis, nodulation, and encapsulation. Different morphological types can be recognized but still there is controversy among the researchers about the exact classification of the hemocytes due to the diversity of techniques for the preservation and observation of these cells. In the present study, a review on the main hemocyte responses to environmental stress in different invertebrate organisms is presented, emphasizing the contamination by heavy metals. It is discussed parameters such as: alteration in the number of cells involved in the defense reaction, phagocytic activity, lysosomal responses, and production of reactive oxygen species.

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The destination of sewage sludge is a problem faced by sewage treatment plants (STPs). Many alternatives have been sought, such as the application of sewage sludge in degraded soils and in agriculture as fertilizer. However, due to the risk of contamination with pathogens and/or metals, the use of sludge should be done cautiously. By the habits that diplopods present, they have been considered good environmental indicators for soil analysis. In this study, animals from the Rhinocricus padbergi species were exposed to two sewage sludge samples from two STPs in the São Paulo State, for different periods. The midgut of the animals were removed and histologically processed and subjected to histochemical tests. It was detected the following tissular responses: clusters of haemocytes through the cells of the fat body layer, increase in the quantity of intracellular granules in the cells of the fat body layer, increase in the release of secretion vesicles of the intestinal epithelium, and intense vacuolization of the cytoplasm of epithelial cells. The results suggest the presence of toxic substances to the studied species in both sludge samples used.

Due to the constant release of potentially harmful substances in the environment, it is necessary the use of biomonitoring as a form to assess the impact of these substances on animals that inhabit this environment. Therefore, there is a better understanding of the possible effects that these exogenous substances may cause in the organisms present there. In the present study it was verified the feasibility of the use of the diplopod Rhinocricus padbergi as bioindicator of impacted soils by their exposition to substrates containing different concentrations of sewage sludge from different Sewage Treatment Stations (STSs). It was observed animals' behavior and the survival rate was analyzed by log-rank test (p=0,05). The analysis showed that the animals exposed to pure sewage sludge presented higher mortality index than the specimens exposed to different concentrations of the sludge mixed with soil. In general, the survival rate and the analysis of the behavior of the diplopod R. padbergi showed efficiency of this species in biomonitoring impacted soils.Key words: millipede, sewage sludge, STS, toxicity. Biomonitoramento de substratos contendo lodo de esgoto: avaliação da viabilidade do uso do diplópodo Rhinocricus padbergi ResumoDiante da constante liberação de substâncias potencialmente danosas no ambiente, faz-se necessário o uso do biomonitoramento como forma de avaliar o impacto destas substâncias sobre os animais que os habitam. Com isso, tem-se uma maior compreensão dos possíveis efeitos que estes agentes exógenos podem causar nos organismos ali presentes. No presente estudo, verificou-se a viabilidade do uso do diplópodo Rhinocricus padbergi como bioindicador de solos impactados, por meio de sua exposição a substratos contendo diferentes concentrações de lodo de esgoto oriundo de diferentes Estações de Tratamento de Esgoto (ETEs). Foi observado o comportamento dos animais e a taxa de sobrevivência foi analisada pelo teste log-rank (p=0,05). As análises evidenciaram que os animais expostos ao lodo de esgoto puro apresentaram maior índice de mortalidade do que os espécimens expostos a diferentes concentrações de lodo misturado com terra. De um modo geral, a taxa de sobrevivência e a análise do comportamento do diplópodo R. padbergi demonstraram eficiência desta espécie no biomonitoramento de solos impactados.Palavras chave: milipede, lodo de esgoto, ETE, toxicidade. 50 J. Braz. Soc. Ecotoxicol. v.7, n. 1, 2012 Fontanetti et al.