Evaluation of Cu potential bioavailability changes upon coastal sediment resuspension: an example on how to improve the assessment of sediment dredging environmental risks.

Purpose: Metal bioavailability-based sediment quality analysis, inferred from geochemical partitioning data, may contribute to improve sediment management policies. This is important because decision-making processes should not give similar priorities to sediments offering contrasting environmental risks associated to metal bioavailability. However, current uses of Sediment Quality Guidelines (SQGs) as interpretive tools to support decisions about dredging-related activities have not considered the changes in metal bioavailability upon sediment resuspension.

Methods: Sediments from a Cu-contaminated site in Guanabara Bay (Brazil) were submitted to 16-h resuspension experiments in estuarine water to assess the susceptibility of Cu mobilization to the dissolved phase and alteration in the solid phase partitioning between a potentially bioavailable (1 mol/l HCl-extractable) phase and concentrated HNO(3)-extractable phase.

Results: After sediment resuspensions, dissolved Cu levels became slightly lower (in a surface water-resuspension treatment) or slightly higher (in a bottom water-resuspension treatment). In both treatments, the 1 mol/l HCl-extractable solid phase concentrations changed from seven times lower to two times higher values than an SQG adopted in Brazilian legislation. This change was explained by a transition from concentrated HNO(3)-extractable phases to reactive HCl-extractable phases upon resuspension.

Conclusions: An evaluation of metal susceptibility to present geochemical partitioning changes, as can be inferred from HCl-extractable fraction analyses before and after resuspension experiments, is recommended as an additional criterion to assess environmental risks of sediment dredging in relation to resuspension-sensitive metals, such as Cu.