Toxicidade de cromo e mercúrio sobre allium cepa L. em concentrações observadas após o rompimento da barragem de Brumadinho

Abstract

The B1 dam of the Córrego do Feijão mine complex, in Brumadinho-MG, broke in January 2019, causing the death of hundreds of people and animals, and causing incalculable damage to the environment. The tailings plume spread several dissolved metals, such as chromium and mercury, along the Paraopeba River, reaching as far as the São Francisco River. Due to the potential for bioaccumulation in organisms and biomagnification in the food chain, metals are elements that are dangerous to the environment and the riverside population and, therefore, need monitoring and investigation of their impacts. Thus, the Allium cepa test system as a bioindicator can be used to assess the toxic potential of these contaminants in the ecosystem. The present study evaluated the toxicity in A. cepa seeds exposed to synthetic samples of chromium (0.025 and 2.47 mg.L-1), mercury (0.1 and 4.23 µg.L-1) and a compound solution with the two metals (2.47 mgCr.L-1 and 4.23 µgHg.L-1). Concentrations were selected based on data from Brazilian legislation for class 2 rivers and water quality reports from the Paraopeba River, shortly after the disaster. The tests were performed in quadruplicates and in an environment with controlled photoperiod and temperature. The germination parameters and root length were evaluated during 288h and the cell cycle, chromosomal aberrations and fresh and dry masses in 120h. The results indicated that the metals decrease the germination rate of the seeds, interfere in the cell cycle and induce chromosomal aberrations, mainly the compound solution with both metals. Even the smallest concentrations, permitted in legislation, caused cytogenotoxic effect, evidencing the high response potential of the test with A. cepa and the fragility of the Brazilian legislation in relation to the permitted concentrations and the synergistic effect of mixtures. Through these results, it can be inferred that the use of the area affected by the mud should be avoided as much as possible and the use of this type of ecotoxicological test intensified.