Distribuição e fracionamento geoquímico de metais em sedimentos superficiais do Delta do Rio Parnaíba

Abstract

Estuaries are a connection between the mainland and the coastal zone, ensuring the maintenance of ecological activities along the water body, in addition to transporting geochemical carriers that may be associated with contaminants. In these environments, the sediments come from the processes of erosion, leaching and deposits of rocks and soils present in the floodplain coming from the drainage basin. The main objective of the present work is to understand the distribution and geochemical mobility of metals (Cu, Zn, Cr and Fe) in superficial sediments of the Parnaíba River Delta, an open sea delta, characterized by its fluvial-marine dynamics and for harboring important plant communities. and animals. The collection was carried out in December 2019 and distributed in 6 sampling points along the Parnaíba River Delta. Total concentrations and sequential extraction of metals were determined with quantification by Flame Atomic Absorption Spectrometry (AAS). The Geoaccumulation Index (Igeo) was applied to verify anomalous concentrations and the Risk Assessment Code (RAC) was used to classify the level of mobility of these contaminants. The average total concentration results for Cu were 13,39 ± 6,08 μg.g–1 (0,28 – 19,44 μg.g–1), Zn of 46,38 ± 22,96 μg.g–1 (1,11 – 68,81 μg.g–1), Cr equal to 20,13 ± 4,78 μg.g–1 (10,57 – 25,46 μg.g–1) and Fe of 3,24 ± 0,80 % (1,27 – 4,82 %). For the geochemical fractionation, it was observed that all metals are mostly associated with the residual fraction, the fraction linked to organic matter has the main role to operate as a geochemical carrier for Cu, Cr and Fe, while the fraction linked to Fe and Mn oxides presented a function of secondary geochemical carrier for Zn, Cr and Fe. In relation to Igeo, Zn showed higher values indicating a moderately polluted level. RAC showed no mobility risk for Cr and Fe, and medium risk for P01 in Cu and P02, P04 and P05 in Zn, it may be available in chemical forms that may pose a risk to human health and for the aquatic biota present in the Parnaíba River Delta.