Assessment of Mercury In Soils, Crops, Earthworms, and Water When Soil Is Treated with Gypsum.

Flue gas desulfurization (FGD) gypsum from modern fossil fuel combustion systems has many potential uses in agriculture. One concern is its elevated mercury (Hg) concentration, which varies based on the operating configuration. The wet limestone scrubbing process that removes sulfur from flue gas (and produces gypsum) is also effective in removing Hg from flue gas. Mercury concentrations in gypsums, soils, crops, earthworms, and vadose water were measured in studies of FGD gypsum and mined gypsum as soil amendments in Alabama (2 studies), Indiana, Ohio, New Mexico, North Dakota, and Wisconsin. Each study was designed using a standard protocol with three rates, plus an untreated control treatment. The agronomic rates varied in the different studies depending on the crop and intended effects on soil properties. Mercury concentrations in FGD gypsum varied from 198 to 1332 ng/g (mean = 560 ng/g) and were one or more orders of magnitude greater than in the corresponding mined gypsum and 7 to 39 times higher than in corresponding soil before treatment. Mercury in mined gypsum was lower than in corresponding soil before treatment except in New Mexico. Soil Hg was sometimes increased by FGD gypsum compared to the control treatment, but only the 66% increase for Wisconsin was statistically significant. Compared to mined gypsum and the untreated control, FGD gypsum increased Hg concentrations in plant tissue from a mixed (grass-legume) pasture in Ohio, but not in alfalfa in New Mexico and Wisconsin, wheat grain in North Dakota, corn grain or soybean foliage in Indiana, and bermudagrass or cottonseed in Alabama. Compared to the control, FGD gypsum did not significantly increase Hg concentrations in earthworms or vadose water. If care is taken to remove as much mercury as possible during production of FGD gypsum, it seems mercury should not preclude the use of FGD gypsum as an agricultural amendment.