Mercury pollution control and Marphysa sanguinea bio-response in active-capped sediment with calcium alginate/activated carbon composite.

Anthropogenic and industrial activities have released large amounts of mercury (Hg) into the hydrosphere. Hg ultimately deposits in sediments and could be re-released into the water environment, threatening the ecological system. Active capping is considered a suitable remediation method due to its relatively low cost and in-situ decontamination feasibility. Powder activated carbon (PAC) is commonly applied as an active capping material; gelation could increase PAC's particle size to facilitate separation of GAC from sediment. Nevertheless, gelation may impact the benthic ecosystem. This work prepared calcium alginate-PAC beads (CaA/P) as an active capping material to comprehend the adverse effects of calcium-alginate-gelation on a benthic bioindicator (i.e., Marphysa sanguinea). Sequential extraction procedure results indicate over 90 % of Hg in the contaminated sediments remained in the residual phase. PAC capping shows positive results with over 60 % survival and the same weight of biotas at 3 % and 10 % capping dosage. However, capping with a 10 % dosage of CaA/P lowers the pH to that below a tolerable value (7.5) for Marphysa sanguinea, impacting its survival. Overall, though CaA/P has a separable particle size (≈ 2 mm) in sediment, capping with an excess dosage (10 %) of it impacts the organism's survival.