Accurate and efficient risk assessment from contaminated soils requires detailed information on how contaminant speciation impacts bioavailability. Currently many clean-up regulations are based on total contaminant concentration. However, for many contaminants, such as heavy metals and metalloids, their speciation in soils changes bioavailability. The focus of this project is to discover the underlying processes responsible for changes in bioavailability of Pb, Cd, and Zn in a reduced soil upon oxidation. We characterized the contaminant speciation in the soils using microprobe associations and geochemical modeling, and accessed bioavailability using a modified physiologically based extraction test, which was optimized for waterfowl (W-PBET). The results indicate that in the reduced soil Pb, Cd and Zn bioavailability was lower compared to the oxidized soils. Using speciation results we will interpret these findings to determine how speciation impacts bioavailability. In summary we conclude that W-PBET is a quick and accurate method that can be used to investigate how speciation impacts bioavailability.