Evaluation of sediment capping effectiveness in Hyeongsan River for in-situ management of total mercury and methylmercury contamination

Abstract

Purpose In this study, the effectiveness of in situ sediment capping was investigated as a remediation option for total mercury (THg) and methylmercury (MeHg) in the Hyeongsan River estuary, South Korea. Materials and methods A small plot study was conducted by capping four different sites with different capping materials (HS1 with zeolite, HS2 with activated carbon (AC)/zeolite, HS3 with AC/sand, and HS4 with zeolite/sand), and one uncapped site (HS5) was used as a control. The capping effectiveness was evaluated ex situ by collecting sediment cores after 2 months, 1 year, and 2 years of cap residence. Results and discussions Capping in HS1, HS2, and HS3 reduced > 90% of the THg sediment after 2 months and > 83% of the MeHg after 1 year. HS4 reported a relatively low reduction (56% for THg and 83% for MeHg). In pore water, after 2 months, HS1, HS3, and HS4 led to higher reductions (93-95% for THg and 34-41% for MeHg) than HS2 (77% for THg and 20% for MeHg). The capping effectiveness declined after 1 year and 2 years, presumably because of the redistribution of contaminated sediments onto the small capped demonstration area. Despite reduced effectiveness over time, the capped sites reported lower concentrations of THg and MeHg compared to the uncapped site, which may be attributed to the combined effects of the treatment and natural attenuation. Conclusions Overall, the results imply that AC and zeolite as active sorbents and sand as passive caps can be potential mercury remediation options for contaminated sediments.