Relating Selenium Bioavailability to Calcareous Soil Physiochemical Properties and Mineralogical Sinks.

Concern over selenium (Se) toxicity in wildlife and foraging livestock has become increasingly apparent in the Western Phosphate Field of the US. Phosphate mining practices and associated waste rock have left high concentrations of soluble Se in calcareous soils that accumulate in vegetation. Se-hyperaccumulating and accumulating plant species can be palatable to livestock, causing acute toxicity and mortality following ingestion. The objectives of this work were to first determine plant and soil total Se concentrations in calcareous soils and then to examine and correlate soil chemical and physical properties that control bioavailability. Soil and plant samples were collected from transects established at three study sites in Soda Springs, Idaho that were adjacent to phosphate mines. Se soil concentrations were found to be exceptionally high, reaching upwards of 435 mg Se kg-1 soil. Western mountain aster (Symphyotrichum spathulatum) exhibited accumulations exceeding 6800 mg Se kg-1. Secondary accumulators, such as bulbous bluegrass (Poa bulbosa) and alfalfa (Medicago sativa), showed extensive accumulations exceeding 400 mg Se kg-1 soil. Soil properties examined included pH, surface charge (zeta-potential), particle size, total elemental composition, total organic carbon, and total inorganic carbon. These properties were correlated to Se plant tissue concentrations using multiple linear regression analysis. Additionally, a sequential extraction procedure was employed to identify mineralogical and organic sinks for sorbed Se. High concentrations were observed in the organic and residual fractions. Associations with carbonate and amorphous iron oxides were also determined.