Repurposed Waste Products Ineffective for Reducing Pb Bioaccessibility in a Mine Contaminated Soil.

Lead (Pb) is one of the most common soil contaminants in urban areas, and is a major contributor to elevated childhood blood Pb. Blood Pb can result in permanent neurological damage manifested through reduced academic performance and behavioral issues. In situ chemical remediation of soil Pb is common because it is inexpensive and minimally disruptive. Repurposed waste materials including compost and fishbone meal are appealing soil amendments to reduce Pb bioavailability because they are perceived to be more “natural” than widely studied amendments such as triple super phosphate and phosphoric acid. This study evaluates the efficacy of composted yard waste and fishbone meal to immobilize Pb as compared to immobilization by triple super phosphate and phosphoric acid in mine-contaminated soil. Quadruplicate treatments of fishbone meal, triple super phosphate, and phosphoric acid were add at rates of 1000 mg P/kg soil and compost was added to a depth of 8 cm. Elemental sulfur was also added to the fishbone meal treatment at a rate of 790 mg S/kg soil. The amendments were rototilled to a depth of approximately 10 cm, then seeded with tall fescue grass. After 90 days, the soils were retested for Pb bioaccessibility as determined by the Relative Bioaccessibility Leaching Procedure. Preliminary results show insignificant reductions in Pb bioaccessibility in all but the TSP and phosphoric acid treatment. The poor performance of compost and fishbone meal amendments is concerning because these materials are commonly employed for soil Pb remediation. While there is no evidence that these additions increased Pb bioaccessibility, use of these amendments for Pb remediation may threaten human health by creating a false sense of security about the safety of amended soils. These results suggest that compost and fishbone meal amendments are inappropriate to reduce Pb bioaccessibility in mining contaminated soils.