Utilização de Allium cepa na avaliação ecotóxicologica de esgoto sanitário em diferentes etapas do tratamento

Abstract

A worrying problem regarding the wastewater treatment is the quality with which it returns to the environment. The water’s toxicity can directly affect the process of cell division in living beings, causing chromosomal abnormalities and alterations to occur, as well as other problems mentioned in this study. Thus, this research aimed to evaluate the effectiveness in reducing the toxicity of two sewage treatment plants (ETE) located in the State of Paraná: an ETE that operates with anaerobic biological treatment, here called ETE ANA, and another where the biological treatment process through activated sludge, the ETE LA. The plant test organism used to verify toxicity indices, divided into genotoxicity, mutagenicity and cytotoxicity of these ETEs was Allium cepa. It was found that the affluent of both ETEs had cytotoxic, genotoxic and mutagenic indicators equal to the positive control, made with the herbicide Trifuralina. In both ETEs, the treated effluents met the release standards for COD, NTK and NNH4 required by current legislation. It was identified that the ETE LA effluent isn't considered cytotoxic, genotoxic or mutagenic, presenting a mitotic index (MI) of 11.5%, chromosomal aberrations around 0.3% and absence of cells with micronuclei, statistically equal results to the control treatment, made with water. ETE ANA also showed efficiency in reducing toxicity throughout the processes, with samples with some treatment showing the best results in terms of toxicity indices. An ecotoxicity test was also carried out with a sample of the scum collected in the anaerobic biodigester of the ETE ANA and it was observed total inhibition of root growth, which means high toxicity. The 100-fold diluted scum did not present cytotoxic potential, with an IM of 10.4%, but presented a genotoxic capacity of 1.0% and a mutagenic capacity of 0.4%, with no statistical difference from the positive control. The same assays were performed with NH4Cl and NaNO3 where root growth wasn't affected, but potentiated, and both substances were found to be genotoxic to Allium cepa cells.