Metal bioavailability in contaminated estuarine sediments from a highly-impacted tropical bay

Resumo

The aim of this study is to assess possible spatial variability of trace metal (Cd, Cu, Pb and Zn) bioavailability along the main channel of a highly eutrophic tropical estuary (Iguaçu River estuary, Guanabara Bay, Brazil). Metal potentially-bioavailable concentrations (soluble in 1 mol L-1 HCl) and strongly-bound concentrations (soluble in concentrated HNO3) were sequentially extracted and determined by a Coupled Plasma Optical Emission Spectrometry (ICP OES). These sediments generally have high trace metal contents associated to weakly-bound fractions, while Zn was the most bioavailable metal (approximately 83% of Zn concentrations were weakly-bound to sediments) while Cu showed the greatest heterogeneity of proportion between weakly- and strongly-bound fractions. The employed sampling strategy combined results from sediments taken along and across the estuarine channel, evidencing that care is required when using only a single sampling transect along estuarine channels, particularly for metals sensitive to changes in geochemical partitioning during sediment transport and redistribution, as evidenced by the Cu concentrations in this work.