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Sewage sludge toxicity in edaphic organism: Analysis of midgut responses in the diplopod Rhinocricus padbergi

Diplopods are agile saprophagous invertebrates with the ability to colonize several soil layers. They feed on waste and decaying organic matter, making the soil in which they are present better aerated and mineral‐enriched. Because of their habits, diplopods have been suggested to be used in studies to analyze possible toxic effects of impacted soils in edafic fauna. In that respect, this study aimed at checking the feasibility of using morphological analysis from millipede's midgut as a biomarker for soils exposed to sewage sludge from sewage treatment plants. Histological and histochemical techniques, applied to the species Rhinocricus padbergi's midgut, were used. Two sewage sludge samples were used; they were collected in two small towns in the countryside of São Paulo State. Both cities are part of the Piracicaba–Capivari–Jundiaí basin (PCJ‐1 and PCJ‐3). For 7 and 15‐day periods, the animals were exposed to 10% concentrations and crude sludge for the PCJ‐1sample and to 1, 10, and 50% concentrations and sludge for the PCJ‐3 sample. The material exposed to the PCJ‐1 sample showed an increase in the presence of cytoplasmic granules in both concentrations in all periods and a slight increase in the rate of epithelial renewal. The material of PCJ‐3 sample presented the same alterations observed in PCJ‐1 sample in higher frequence and over that high quantity of neutral polysaccharides in the hepatic cells layer. We can conclude that with the increase of sewage sludge concentrations tested, there is an increase in morphophysiologicals alterations frequencies found in the diplopods' midgut. Microsc. Res. Tech. 2012. © 2012 Wiley Periodicals, Inc.