Prediction of Metal Bioavailability to Plants Using Soil Physico-Chemical Properties: An Approach to Improving Risk Estimates. S. Sigethy, L. Baron, C. Harman, and S. Venkatraman, McLaren/Hart, 25 Independence Blvd., Warren, NJ, 07059
Risk assessments conservatively assume that measured concentrations of inorganic analytes in the soil represent the total amount bioavailable for plant uptake. However, the physico-chemical properties of the soil can significantly affect the amount of metals absorbed by plants and higher trophic levels. A case study was performed at an industrial site in New Jersey to determine the extent to which soil physico-chemical parameters limit the availability of metals in surface soils (0-6") to plants. Results of surface soil analysis indicated concentrations of cadmium (5.2-80,700 mg/kg), lead (163.8-2770 mg/kg), nickel (22.7-69,000 mg/kg), and zinc (577-2,122 mg/kg). Soil samples were collected and analyzed to determine soil physico-chemical properties such as oxidation-reduction potential, pH, cation exchange capacity, organic matter, and nutrient content (phosphorus, nitrogen, and sulfur). The bioavailable fraction of metals in the soil was estimated based on a literature review of studies on soils with similar soil physico-chemical properties. This evaluation estimated that less than 50% of the total metals in the soil may be bioavailable to the plants due to the soil physico-chemical conditions. Concentrations in plants were estimated based on the predicted bioavailable percentage of metals (soil metal concentration x bioaccumulation factor x % bioavailable). Vegetation samples were collected from the site and analyzed for the target metals. Predicted metal concentrations were then compared to actual plant metal concentrations to validate the approach. This approach may be applied to estimate exposures to animal herbivores and humans consuming plants obtained from sites where inorganics may pose potential risks. The results from this study stress the importance of incorporating soil physico-chemical properties in the estimation of the bioavailability of metals to plants. This may lead to more realistic predictions of risk to both ecological and human receptors.