Field Testing of Arsenic and Mercury Bioavailability Model from Land- Applied Coal Combustion Byproducts Final Report

The objective of the study was to provide a model to predict the uptake of arsenic and mercury by plants in response to coal combustion byproducts (CCB) application rates to soil, based on CCB/soil characteristics as determined by sequential extraction of the amended soil. Two greenhouse studies were conducted. The first study consisted of sorghum sudan grass, sunflower, and brake fern, an arsenic accumulator, grown in potted soil (Sango series) amended with flyash (0, 10, 25, 50, and 100 g/kg, corresponding to tons/acre), and the second study consisted of corn, soybean, and brake fern grown in soil amended with FGD gypsum (0, 1, 2.5, 5, and 10 g/kg). Immediately before planting, soil samples were analyzed for arsenic and mercury using sequential extraction procedures that employ successively stronger extractants to first remove arsenic and mercury weakly bound to the soil, followed by arsenic and mercury held increasingly more tightly. The largest proportion of arsenic and mercury were found in the more strongly extracted soil fractions for both flyashand FGD gypsum-amended soils, indicating that arsenic and mercury were not readily available for plant uptake. Plant biomass was detrimentally affected by flyash amendments, decreasing with increasing flyash levels, whereas FGD gypsum amendments increased plant biomass for corn and brake fern. Arsenic concentrations in sorghum sudan grass and brake fern increased up to the 50 and 25 g flyash/kg soil, respectively, and decreased at the higher flyash levels. For corn, soybeans, and brake fern grown in FGD gypsum-amended soil, in general arsenic concentrations did not differ greatly, and little or no arsenic was found in corn cobs and kernels or in soybean pods. Mercury concentrations for plants grown on flyashand FGD gypsumamended soil were the same or less than for plants grown on non-amended (control) soil. For model development, multiple linear regression analysis was used to regress plant arsenic and mercury concentrations against concentrations in the soil fractions. Arsenic in sorghum sudan grass grown on flyash-amended soil was found to be significant (P=0.013, R=0.689) for the statistical analysis. The application of this predictive model would be used for sites being considered for amending the soil with flyash or FGD gypsum, to assess the potential for arsenic and mercury plant uptake and resultant bioavailability of these contaminants.