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.