Arsenic and selenium speciation in aged flue gas desulfurization amended soil

The application of flue gas desulfurization (FGD) residue to soil was thought to have potential as a viable re-use option for coal combustion waste products, as well as being a solution for nutrient deficient soil. Previous studies found that application of certain FGD materials increased crop biomass and calcium (Ca) concentration of the soil, but also added boron (B), selenium (Se) and arsenic (As). These findings are a cause for concern and could hinder research into how various by-products can be recycled. Studies of long term metalloid bioavailability arising from FGD application are lacking but are needed to assess the safety of coal by-products. We investigated the concentration and speciation of As and Se in Southeastern coastal plain soils that has been amended with a weathered, stabilized FGD material (0, 2.5, 5, 7.5 and 10%) five years previously, using ion chromatography coupled to an inductively coupled plasma mass spectrometer (IC-ICP-MS). We also studied the speciation of As and Se in naturally invading plant tissue (Vicia cracca L., Leguminosae), as a simulation of a site of previous FGD application that had been allowed to vegetate naturally. Total As and Se concentrations in mesocosm soils were elevated in proportion to the FGD application rate, but water soluble As and Se concentrations were low five years after application (0.04 and 0.08 mg kg(-1) respectively at 10%). In all treatments arsenate [As (V)] and selenite [Se (IV)] were the predominant As and Se species. Ligand-exchangeable metalloids were significantly elevated to a depth of 0-0.15 m only; again As (V) and Se (IV) predominated, generally considered potentially available for plant uptake. While a large proportion of the Se had leached from the soil profile or been taken up by plants, the majority of the As from applied FGD remained in the soil profile.