Long-term effectiveness of sediment dredging on controlling the contamination of arsenic, selenium, and antimony

This study assessed the effectiveness of dredging in controlling arsenic (As), selenium (Se), and antimony (Sb) contamination in sediments, by examining contaminant concentrations in sediments six years after dredging was completed. High-resolution diffusive gradients in thin films (DGT) and dialysis (HR-Peeper) techniques were used to monitor the concentrations of DGT-labile metalloids and soluble metalloids in sediments, respectively. Results revealed that dredging effectively remediated metalloid contamination in sediments only in April, July and/or January. Compared to non-dredged sediments, the concentrations of soluble and DGT-labile As, Se, and Sb in dredged sediments decreased on average by 42%, 52%, and 43% (soluble), and 54%, 50%, and 53% (DGT), respectively. The effectiveness of the dredging was primarily due to the transformation of metalloids from labile to inert fractions, which increased the ability of the sediments to retain the metalloids, and the slowed rate of resupplied metalloids from available solid pools. In contrast, negligible/negative effects of dredging were seen in October, and the concentrations of soluble and DGT-labile metalloids even increased in some profiles of dredged sediments. This was mainly caused by a release of the metalloids from algal degradation, which may offset the dredging effectiveness.