Metais pesados em solos, plantas e qualidade da água em área de mineração fósforo-uranífera

Abstract

The Itataia-CE deposit contains the largest known Brazilian uranium (U) reserve associated with phosphate (PO4), however, the exploitation of the ore may lead to anthropogenic contamination of the natural resources by toxic elements, due to the large tailings disposal. Thus, knowledge of the mobility, interrelationships and distribution of these elements in soil, water and plant is a starting point for the identification of the actual concentration of these metals in this environment. The work was carried out in three stages; each one studied a different phase with influence of the toxic elements. First, heavy metals were studied in soils of the deposit, and aimed to verify the quantification, spatial distribution and their relations using multivariate (AM) and geostatistical (GA) analyzes, investigating the potential of environmental risk in the area. The second study was related to the bioavailability of U in soils of the deposit and its absorption capacity in a greenhouse study, in which the induced phytoextraction of U by sunflower, corn and beans was evaluated. The third stage studied the chemical and physical attributes of waters and soils coming from reservoirs near the Itataia deposit. Quantification and verification of the established relationships among the variables were carried out to evaluate the influence of the soils of the reserve on the water quality alterations. In the first study, it was verified that the multivariate analysis allowed identifying the interactions between the attributes of the soil with heavy metals, to identify the geochemical groups of the heavy metals, and to verify the sources and relationships of the metals in the area. With the use of GA was possible to create the maps of spatial distributions and to ratify the contribution of the sources of heavy metals and elements in the area. The study was able to provide information regarding the contents of elements and their dynamics in the area. In the second study, it was observed that the application of citric acid to soils did not potentialize the phytoextraction U efficiency by plants. The corn, sunflower and bean species were not efficient in translocating U to shoot in the studied soils, which increased proportionally with U content in soils and varied according to the characteristics of these soils. The sunflower was the species that accumulated higher levels of U in both, roots and the aerial part, but still can not be recommended in remediation programs of U contamination by phytoextraction, due to the low percentage of removal and translocation factor and high recovery time. The application of citric acid decreased the mobilization of U to the more soluble forms and little influenced the more stable fractions. In the third study it was observed that there is a decreasing trend of the following ions in the analyzed waters: Ca> Na> Mg> K> HCO3> P, in which the highest levels were found in reservoir waters near the deposit and under agricultural influence. The low levels of chemical and physical attributes found in soils had little influence on the quality of the chemical and physical attributes of water. This was verified by the low correlation intensities found between soil and water attributes. The multivariate analysis and spatial distribution techniques are considered as important tools for the analysis of hydrological attributes and, have generated significant information about the quality of the areas influenced by the ItataItataia-CE deposit, as well as for the proper management program of its water resources.