Changes in Cd and Zn bioavailability upon an experimental resuspension of highly contaminated coastal sediments from a tropical estuary

Abstract

Bioavailability evaluations can be an important tool to determine the quality of dredging sediments. Sequential extractions are commonly used to assess the different chemical forms of trace metals in coastal sediments; however, sometimes they are expensive and time-consuming. Additionally, these analyses do not represent possible changes due to resuspension during and after dredging activity. Newer, easier options to evaluate bioavailability are necessary to understand and preview bioavailability changes resulting from trace metals in dredging and disposal areas. This study aims to evaluate changes in Cd and Zn bioavailability due to sediment resuspension in a highly contaminated area in Sepetiba Bay, Brazil. Twelve surface sediment samples from this location were submitted to a resuspension experiment during two different time intervals (1 and 24 h). The extraction of potentially bioavailable (1 mol L−1 HCl-extractable) fractions and strongly bound (concentrated HNO3-extractable) fractions were sequentially carried out. More than 50 % of the concentrations were in potentially bioavailable fractions. Bioavailability change indexes were proposed; these were estimated as relative changes in bioavailability percentage after resuspension. However, two of these stations presented increases in the Cd and Zn HCl-extractable fractions after sediment resuspension above effects range low and effects range medium National Oceanic and Atmospheric Administration which are the same limits adopted for Brazilian environmental jurisdiction. Positive correlation of Zn and Cd with TOC in strongly bound fractions evidenced the importance of organic matter binding to preserve metals in this fraction. Fe and Mn partitioning was a major geochemical control on bioavailability of Cd and Zn upon short-time resuspension periods.