Potencial de uso do rejeito de minério de ferro oriundo do rompimento da barragem de Fundão (Mariana, MG) para o cultivo de espécies agrícolas

Abstract

With the collapse of the Fundão dam (Mariana, 2015), a large amount of iron ore tailings was released into the Doce River basin. Some publications have warned of possible impacts that this material could have on local agricultural activity, suggesting possible losses in productivity, as well as the accumulation of metals to levels that could be toxic to humans and animals. In order to clarify these aspects, this study evaluated the cultivation of six species of special interest to agriculture, two grain crops (beans and maize), two forage species (braquiária and crotalária) and two vegetables, a leafy vegetable (arugula), and with tuberous roots (radish), in both tailing and soil. Morphoagronomic characteristics, photosynthetic performance, and metal accumulation were analyzed. The substrates were previously mixed with sand, considering a ratio of 3: 1, and fertilized with NPK. The chemical composition of substrates and plant tissues (aerial part of beans, maize, crotalária, braquiária, and arugula; grains of the beans and maize; radish tuberous roots) was analyzed. In addition, we calculated the bioconcentration factor (FB) of beans, maize, braquiária, and crotalária plants, to verify the phytoextractor potential of these species. Daily metal intake was estimated through the consumption of vegetables grown in the tailings, based on the average daily consumption of these food items by an adult Brazilian. The tailings presented higher levels of Fe, Mn, and Na in comparison to the control soil, pH of 7.2, and absence of toxic metals in its composition. Beans, maize, crotalária, arugula and radish grown in the tailings did not differ in terms of productivity and, in general, photosynthetic performance was not influenced by the soil, proving that the main obstacle to cultivation in the tailings is low fertility. Braquiária plants showed less dry mass when cultivated in the tailings, which may be related to the high level of compaction found in this substrate, and consequently to the compromise of root expansion. Except for braquiária, Fe and Mn were found in higher concentrations in plants grown in tailings, which reflects the high levels of these elements in this substrate. Associated to the higher concentration of metals, another factor that may have favored its greater absorption was the source of N used (NH4 +). When absorbed, NH4 + releases H + ions, reducing the pH of the tailingsand increasing the availability of Fe and Mn. The levels of the elements detected in plants grown in the tailings are within acceptable limits for human consumption. Crotalária and maize showed high concentrations of Fe and Mn, as well as FB> 1 for Mn, Zn, and Cu, being indicated as promising for phytoextraction. The results presented here, support the resumption of agricultural activity in the region affected by the tailings of Fundao dam.