Abstract
The industrial-scale production and use of mercury (Hg) has resulted in numerous Hg-contaminated watersheds globally. The Oak Ridge Reservation (Tennessee, USA) is an example of a site where industrial use of Hg until the 1960’s led to significant contamination of the East Fork Poplar Creek (EFPC) watershed and the buildup of large Hg inventories in creek banks and floodplain soils. Precipitation and flooding can cause erosion of creek bank soils and mobilization of Hg into the downstream environment. This study evaluated the release of Hg from contaminated EFPC soil samples to identify geochemical factors that drive Hg release. Total Hg concentrations in soil samples ranged from 27.2 to 1,425 mg·kg−1. The amount of Hg released in batch experiments with artificial creek water ranged from 0.011 to 0.17% of soil Hg at a solid:solution ratio of 1:30 and correlated with total Hg concentration in soils. Differences in Hg release between size fractions suggests heterogeneity with respect to labile Hg species among size fractions. Examining the Hg release from soil samples of over a range of solid:solution ratios indicated the existence of two distinct solubility regimes. Experiments evaluating the effect of water chemistry on Hg mobilization suggested that dissolved organic matter enhanced Hg release from soils. Time-resolved experiments indicated initial leaching of Hg from soils is followed by a decrease of dissolved Hg over time. Identifying geochemical factors controlling the mobilization of Hg from soils improves our ability to estimate Hg fluxes from contaminated bank and floodplain soils into downstream environments.
