Biological effects of sewage sludge – does its incorporation into agricultural soils in the state of Paraná, Brazil, represent an environmental risk?

In the state of Paraná, Brazil, calcined sewage sludge (biosolid) without remediation is used as a fertilizer in different crops, such as soybeans and corn. Evaluated the chemical composition, pathogenic potential, and toxic potential to plants and E. fetida of biosolid produced in the state. The analysis of metals and pathogens, based on the Brazilian Resolution 498/2020 of the National Council for the Environment (CONAMA), classified the residue as suitable for incorporation into crop soils in Brazil. However, all concentrations of the biosolid (6.25, 25, 50, and 100%) caused phytotoxicity to Lactuca sativa, Allium cepa, Cucumis sativus, and Triticum aestivum. A. cepa meristematic cells exposed to the residue revealed division disruption, including clastogenic damage to chromosomes, and death. All concentrations promoted swelling in onion roots, drastic inhibition of ascorbate peroxidase and superoxide dismutase, activation of guaiacol peroxidase, and lipid peroxidation in their meristems. Studies with Eisenia fetida showed biosolid has strong repellent effects and higher concentrations caused 100% mortality. In surviving animals, catalase and guaiacol peroxidase showed higher tissue levels of activity, suggesting a response to increased environmental free radicals, including reactive oxygen species. Therefore, in Paraná, the current and recurring incorporation of biosolids, without adequate remediation, into cropping soils has the potential to trigger extensive oxidative stress in plants and animals, representing an environmental risk. Furthermore, this study brings important elements that advance the understanding of how biosolids trigger phytotoxicity and cellular toxicity in different organisms.