Toxic potential of sewage sludge: Histopathological effects on soil and aquatic bioindicators

Abstract

Abstract Sewage sludge has been used as a soil amendment because it is rich in plant essential nutrients and can serve as a substitute for chemical fertilizers. However, sewage sludge can contain a complex mixture of pollutants that are harmful to organisms. Considering that the management of the waste should not result in risks to environmental health, the toxic potential of sewage sludge to organisms at different trophic levels should be measured before it final disposal. Diplopod (Rhinocricus padbergi) and fish (Xiphophorus maculatus) were exposed to sewage sludge or sewage sludge treated with lime (biosolid) at different dilutions under laboratory conditions. Semiquantitative histopathological analyses were performed on target organs (midgut and fat body for the diplopod and gills for the fish). Toxins from sludge or biosolid caused tissue damage and activated detoxification processes in both the diplopod and fish. In comparison to other sludge concentrations, the highest sludge concentrations tested were more toxic, and millipedes likely reduced their food intake to avoid toxins, resulting in weight loss. Our data suggest that sewage sludge pathogens promoted specific histological alterations. Chemical analysis revealed that the concentrations of priority pollutants did not exceed the limits established by Brazilian law. Therefore, this outcome indicates that R. padbergi and X. maculatus are sensitive to low levels of toxins from sewage sludge.