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Hg release from soils amended with Flue Gas Desulfurization solids
AuthorBriggs, Christian W.
AdvisorGustin, Mae S.
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Flue Gas Desulfurization derived gypsum (FGD) can be applied for beneficial use as an agricultural soil amendment however concern has been raised regarding the release of mercury (Hg) from these materials to the environment. Recent work showed that a component of Hg present in the pure FGD material could be lost to the atmosphere. This study investigated Hg release to the air and water from planted and bare soils from Indiana, Alabama, and Ohio amended with FGD in a laboratory setting. FGD was homogenized into each soil at rates of 4.5, 45, and 170 t ha<super>−1</super> and added at 4.9 t ha<super>−1</super> as a thin layer to represent a tilled and no-till agricultural setting, respectively. Data was also collected from unamended soils and those with applications of commercial mined gypsum. Twenty four hour Hg flux was measured from each material on a seasonal time step over one year. Water that had leached through select materials was collected seasonally and analyzed for total dissolved and methyl mercury. Hg accumulation in perennial rye grass (<italic>Lolium perenne</italic>) grown in a subset of soil treatments was quantified. Hg bioaccumulation in earthworm tissue was measured between 41 and 44 days after introduction in a subset of Indiana soil treatments. Additionally, the data collected was used to refine a conceptual model for factors controlling Hg release to the air from low Hg containing soils.Total Hg concentrations in amended soils were within the range of those considered to have background values and did not change significantly over the course of a year (46 ± 9 to 47 ± 2 ng g<super>−1</super>, 24 ± 4 to 27 ± 6 ng g<super>−1</super>, and 56 ± 9 to 56 ± 12 ng g<super>−1</super> for Indiana, Alabama, and Ohio soil, respectively; paired two–sample t–test, p–value (two-tailed) = 0.212, n = 17). Hg concentrations in leach solutions from the FGD amended soils were not different from those reported for US surface waters. Emissions from amended soils were higher initially relative to unamended soils however became similar over time. Rye grass Hg concentrations were not related to amendment rate and were similar to values reported for foliage grown in uncontaminated settings. Also, the earthworm bioaccumulation factors reported in this study (1.5−2) were at the low end of the range reported for other studies that investigated uptake in background soils (1 up to ∼10).We found four stages of Hg flux associated with soil water content. The first is saturation where flux is suppressed. In the second stage, where actual evaporation (E<sub>a</sub>) is equal to potential evaporation (E<sub>p</sub>), solar radiation and correlated temperature are the most important parameters influencing Hg flux. For soils where E<sub>a</sub> < E<sub>p</sub>, soil moisture evaporated was the variable best correlated with Hg flux with solar radiation being next. The last stage is when soils have little water loss and light, temperature and the presence of atmospheric oxidants are important in promoting Hg release from the surface. This indicates that for modeling Hg release from soils, moisture could be used as a framework for predicting Hg flux with other parameters added depending on water content.