Biodisponibilidade de metais pesados em plantas cultivadas em rejeito da Barragem do Fundão, Mariana - MG

Abstract

Impact on nature caused by anthropogenic activities has become increasingly extensive, as a result of human evolution and needs. One of such activities is mining. In Brazil, the main mineral extracted is iron, mainly taken from the Quadrilátero Ferrífero. In 2015, the rupture of the dam, released an approximate volume of 34 million m3 iron ore tailings, causing the destruction of the sub-district of Bento Rodrigues and Paracatu de Baixo, located below the dam. Some impacts caused by tailings deposition still need to be studied, especially those related to the presence of heavy metals. The tailings deposited on the banks of the affected watercourses have a high pH and a concentration of heavy metals that can cause contamination to the environment. Considering that the ecosystem processes start in this tailings and with the entry of organic material an acidification occurs, the hypothesis of this study is that with the reduction of the tailings pH, the release of heavy metals contained in the tailings deposited in the Rio Doce watershed occurs. Thus, the work aimed to evaluate the effect of changing pH and availability and concentration of heavy metals as well as the absorption and accumulation of heavy metalsin different plants grown without and with tailings acidification and in a reference soil . Two studies were carried out: the first consisted of assessing the bioavailability of the heavy metals present tailings by different extraction methods at different pHs, the tailings being acidified with an HNO3 solution; in the second study,consisted of assessing evaluating the initial growth of plants, availability and absorption capacity heavy metal in four plant species (Lactuca sativa, Raphanus sativus L, Sorghum bicolor e Solanum lycopersicum), with different edible parts (leafy, tuberous and fruitful) that are used for human and animal consumption was analyzed . In all studies, a reference soil was collected, collected close to the tailings, in an area not affected by the spill. They were analyzed for physical, chemical and mineralogical composition. The chemical analyzes performed consisted of the extraction of metals by the USEPA 3051, Mehlich-3, Mehlich-1, DTPA (acido dietileno-triaminopentacéticoand) and water methods. The acidification of the tailings promotes greater availability of Ni, Pb and Mn, however at levels not considered harmful to human health by COPAM (State Council for Environmental Policy) . The levels of heavy metals in tailings are lower than those found in the soil. When checking the levels of metals in the edible part of the cultivated plants, both in tailings with and without acid, with the exception of Cr, they were within standards those allowed by ANVISA (National Health Surveillance Agency). Therefore, the tailings in general did not present risks in terms of metal content, with the exception of Cr, which may have been favored by cultivation in a greenhouse, but harmful in terms of plant growth, mainly caused by the high presence of silt and sand.