Distribuição geoquímica de metais traços e nutrientes em perfis sedimentares do Delta do Rio Parnaíba – PI

Abstract

Estuaries are environments characterized by being regions of exchange of continental and marine materials presenting a relevant importance for the transport of these materials and an ecological importance, because many species reproduce, protect, and feed in this ecosystem. They are important regions for the establishment and development of human populations and all the associated infrastructure, and are subject to the impacts generated by the use and occupation by urban centers, agricultural plantations, and aquaculture tanks. As a result, there is an increase in pollutant discharges to the region of anthropic origin, including trace metals, which may also be naturally present in the estuarine environment. When the trace metals enter the aquatic environment they are partitioned between the water and the particulate material, and may be precipitated in the bottom sediments. Deposition in sediments occurs through interactions that include adsorption, complexation, precipitation, and biological assimilation processes. The present work aimed to determine the concentrations of trace metals (chromium, Cr; copper, Cu; nickel, Ni; zinc, Zn and iron, Fe) and to identify geochemical correlations that determine the variability of the sedimentary depositions and the metal enrichment factor in sedimentary profiles in different regions of the Parnaíba River Delta. This study presents results from 3 sedimentary samples (P1, P2, P3), collected with 6 cm diameter PVC tubes. The height of the profiles was 45cm and they were sectioned every 3 cm. During the sectioning, stainless steel tubes of 2 cm in length and 1 cm in diameter were introduced in each division for the determination of the DE. The sediments were dried in an oven at 60°C and disaggregated using mortar and pestle for subsequent elemental analysis. The density ranged from 0.61 to 0.85 g.cm-3. The MO contents ranged from 9.05-27.98 %. The analytical recovery was 87.81%, 76.30%, 96.62%, 73.56%, 86.48%, respectively for Cu, Cr, Ni, Zn and Fe. The contents of metals ranged from 7.08-28.08 mg.kg-1 for Cu, 18.14-70.74 mg.kg-1 for Cr, 5.68-28.70 mg.kg-1 for Ni, 22.29-93.66 mg.kg-1 for Zn and 1.51- 5.90% for Iron. TOC contents ranged from 2.18-6.97 %. The NT contents ranged from 81.5-1608 μg.g-1. The C/N ratio ranged from 4.35-151. The geochemical correlation in profile 1 and 3 occurred with TOC and Fe and in profile 2 was not significant with these carriers, and it is likely that this profile is dominated by correlation with another geochemical carrier. Considering that this is an environment of little anthropic influence, the values found are close to those of a tropical river with little impact. The results showed that the organic matter predominantly originates from detrital mangrove materials and the trace metals enrichment factor classified the environment as an environment without enrichment to lower enrichment. These data are important to characterize the Parnaíba River delta in its initial state of anthropic influence, and can support databases of environmental regional monitoring.