Trace metal partitioning in the parnaíba delta in dry season, equatorial coast of Brazil.

Trace metal concentrations in the particulate fractions (MP), dissolved fractions (MD) and sediments (MS), such as Ba, Cu, Co, Cr, Pb, Ni and Zn, were determined during the dry season of the largest open sea delta of Americas, the Parnaíba River Delta (Brazil). This study aimed to comprehend the distribution, dynamic changes of metal speciation and environmental quality index of trace metals in the particulate fractions and subsurface sediments in scenario of major marine influence over the delta. The trace metals bound to suspended particulate material (SPM) from weathering the drainage basin exhibited a removal trend under increases in salinity and pH. Desorption influenced the partitioning of Ba, Zn, Ni, Co, Cu, and the adsorption and precipitation of Pb and Cr to the surface sediments. The organic matter contents in the sediments acts as an important geochemical carrier of these contaminants, and the dissolved organic carbon influences the binding of Pb in the subsurface waters. The geoaccumulation index (Igeo) plays a crucial role in revealing potential contamination with Zn contents and weak association to this fraction. These results make possible the assessment of ecological risk by metal contamination and global pollution mitigation in coastal tidal estuaries under intensive physical mixing along the equatorial coast.