Remediation and Stabilization of Soils Contaminated by Lead Resulting from the Removal of Paint from Bridges

Abstract

Lead (Pb)-based paints are commonly used for painting steel bridge structures. Soils in the immediate vicinity of older bridges have been contaminated with Pb as a result of normal weathering and peeling of the paint coupled with removal prior to repainting. The objectives of this project were to assess the extent of Pb contamination near highway bridges and to evaluate phytoremediation and immobilization as means of remediation. The authors examined soils in the vicinity of approximately 20 bridges in Indiana that had been repainted recently and were known to have been painted originally with Pb-based paint. They found only three bridges in which the extensive areas of soil were contaminated by Pb in concentrations greater than 400 mg/kg. Two of these sites were used for this project. In the field study, soluble phosphate was added to the soil and transformations of Pb were monitored using chemical extractants. Simultaneously, sunflowers were grown in the field to test the feasibility of phytoextraction for these conditions. Phosphate additions were effective in significantly reducing bioaccessible Pb, but the sunflowers were unable to remove Pb from the soils. A laboratory study using columns of contaminated soils demonstrated the very low mobility of Pb in soils. The recommendation from this study is that the immediate vicinity of recently painted bridges be tested for Pb in the soils. Elevated concentrations can be treated with soluble phosphate to reduce bioavailability of Pb.