Remediation of mercury contaminated sediments

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Mercury is a highly toxic element often present at elevated concentrations in sediment, soils and water as a result of industrial and other activities. Under reducing conditions, inorganic mercury can be converted to more toxic methylmercury which bioaccumulates in the food chain. Ingestion of elevated concentrations of methylmercury can lead to severe neurological disorders and should be avoided. In this study, treatment experiments will be conducted to evaluate the effectiveness of natural materials for stabilizing mercury in a contaminated river floodplain to minimize its release to local ecosystems. Laboratory batch and column studies will be conducted to characterize physical and biogeochemical processes influencing mercury cycling in the floodplain sediment, soils and aquifer solids. Uncontaminated river water will be reacted with the contaminated floodplain materials to evaluate the extent of mercury release to the river water. The contaminated water will be passed through solid-phase natural materials, such as biochar and modified biochar, to evaluate the extent of mercury removal under representative flow conditions. Experiments will be conducted to develop design parameters for full-scale installations of engineered reactive treatment mats along river discharge zones to prevent release of mercury to local ecosystems. Natural reagents will be co-blended with floodplain soils to promote mercury binding and thus potentially inhibit uptake by organisms. The experiments will be monitored temporally and spatially to determine changes in aqueous concentrations of mercury, methylmercury and associated geochemical parameters in response to the treatment system. During and at the termination of the experiments, solid-phase samples will be collected and analysed using synchrotron x-ray techniques to evaluate mercury binding mechanisms. The study is expected to benefit Canada by providing alternative approaches for managing mercury-contaminated sites to decrease exposure of humans and other organisms to highly toxic mercury and methylmercury compounds.