Sample drying effects on lead bioaccessibility in reduced soil

Risk-assessment tests of contaminated wetland soils often use experimental protocols that artificially oxidize the soils. Oxidation may impact bioavailability of contaminants from the soils, creating erroneous results and leading to improper management and remediation. The goal of this study was to determine if oxygenation of reduced sediments and soils influences Pb bioaccessibility measurements. The study site is located on the Coeur d'Alene River floodplain, downstream from the Silver Valley Mining District in Idaho. A physiologically based extraction test designed to simulate the gastrointestinal tract of waterfowl (W-PBET) was used to measure relative Pb bioavailability (bioaccessibility) from the soils. The soils were collected from a submerged wetland. One set of samples was allowed to air-dry, another set was freeze-dried, and a third set was analyzed wet. The wet soil showed decreased Pb bioaccessibility compared with the air- and freeze-dried soils. The changes in extractability of Fe and Mn on air-drying were opposite from each other: Fe extractability decreased while Mn increased. The results from this study show that redox changes may have significant impacts on Pb bioavailability, and should be considered when assessing Pb contamination risks in reduced soils.