Análise qualitativa de metais nos sedimentos de reservatórios na região tropical semiárida do Rio Grande do Norte

Abstract

Reservoirs are artificial aquatic compartments created to meet the population demands in their area. The use of water / soil in its surroundings directly influences the supply of elements and nutrients offered to the artificial ecosystems in question. Economic activities such as mining, especially if conducted improperly, increase the availability of metals in areas near reservoirs. The bottom sediment act as a nutrient storage for the other compartments due to its capacity of accumulating chemical elements. In addition to the ability to carry trace elements, there is the possibility of transport and contamination because the sediment is able to release contaminating species. Such species are generally released from the sediment bed due to changes in environmental and physicochemical conditions, which may contaminate water and other environmental systems, leading to bioaccumulation and transfer processes in the food chain. This study aims to verify the quality of sediments from four reservoirs in the tropical semiarid region of Rio Grande do Norte, which suffered a decrease in water availability due to a prolonged drought. Possible relationships between the mining activity, the level of eutrophication of the reservoirs and the quality of the sediments will be discussed. In the study, the 4 metals with the highest concentration detected were Iron (Fe), Silicon (Si), Aluminum (Al) and Potassium (K), respectively. Chromium (Cr), Zinc (Zn) and Barium (Ba) were the most concerning out of the detected heavy metals due to their bioaccumulation potential. With the exception of the reservoir of Boqueirão de Parelhas, all systems presented the heavy metal Chromium in their composition. Zinc was detected in the composition of all analyzed reservoirs and Barium only in Boqueirão and Gargalheiras. Besides the previously mentioned elements, other metals such as Calcium (Ca), Manganese (Mn), Titanium (Ti), Magnesium (Mg), Rubidium (Rb), Strontium (Sr) and Yttrium (Y) were detected in all samples. With the method used, no significant quantities of other heavy metals like Arsenic (As), Cadmium (Cd), Copper (Cu), Nickel (Ni), Lead (Pb) and Mercury

(Hg) were detected. The Gargalheiras reservoir presented the largest mass of cross- sectional area from amongst all samples analyzed, and was the only one where the

iron composition exceeded 50% as well as the presence of non-metals Phosphorus (P), Sulfur (S) and Bromine (Br) was detected. It was also the reservoir that presented the greatest absolute variability in the number of elements detected. It was concluded that, among all the analyzed dams, Gargalheiras is the one that presents the worst quality of the sediments, probably as a consequence of the mining activity in its surroundings and the low volume of water.