Avaliação geoquímica de elementos-traços em testemunhos no estuário do Rio Potengi - RN

Abstract

Estuaries are areas of complex investigations representing environments in constant evolutionary process, constituting the means of interaction between sea, rivers and anthropic activities. In these regions, the abundance, distribution and speciation of chemical elements (metals and non-metals) in the sediments can be affected by hydrodynamic processes related to variations in lithology, topography, vegetation, rainfall, river flows, input of tidal currents during flood and ebb and/or tidal cycles, among others. The main objective of this research was to understand the processes that control the variability of the chemical elements in cores along the Potengi river estuary, including the possible contribution of anthropogenic sources. Statistical tools, such as the coefficient of variation, were used for duplicate samples and for analytical results obtained in different grading classes (total fraction and fraction less than 0.063 mm). The results were also compared to toxicological limits established by the National Oceanic and Atmospheric Administration (NOAA) in order to diagnose the quality of the sediments and their influence on the existing biota in the estuary. Applying specific methodologies it was possible to estimate the background of the studied estuarine region. The results were also compared with other tropical estuaries that used similar methodologies in Brazil and in the World. A total of 13 elements (Al, As, Ba, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn) were evaluated along three cores distributed longitudinally in the Potengi River estuary, being one more upstream (CPOT A), one in the middle part (CPOT B) and another at the mouth of the estuary (CPOT C), where the results indicated anthropogenic action and geogenic enrichment for the area investigated. The core collected in the intermediate region of the estuary (CPOT B) was more worrisome, mainly the chromium element. The influence of the proximity of the urbanized area of the city of Natal, which discharges sanitary waste without previous treatment, associated to manufactured goods industries contributed to alarming levels of contamination in this sampling region.