Mercury speciation and remediation strategies at a historically elemental mercury spilled site.

This study quantified the mercury speciation in a contaminated area three decades after an elemental mercury spill from a sodium nuclear reactor experiment, and evaluated ex situ and in situ remediation strategies. Soil samples were taken across multiple sites with different soil depths. A majority of total mercury was distributed in surface soils with depths between 0-0.5 m, and decreased exponentially with depths. In top soils with depths between 0-0.5 m, a considerable fraction of mercury exists in chemical forms that are highly mobile (i.e., bound to inorganic ions) or potential mobile (i.e., bound to soil humic substances). This suggests that bioremediation and phytoremediation may be effective to remove mercury in the top soils at contaminated sites. In deep soils below 1 m, mercury predominantly exists as elemental form that is tightly bound to soil particles. While this fraction of mercury poses no immediate health risk, in situ thermal treatment may be evaluated to remove this mercury fraction. Furthermore, size fractionation data suggest that as an ex situ excavation cleanup option, reducing the volume of contaminated soils is possible by only selecting the sand and gravel size fractions of soil for offsite treatment.