Abstract
Lead (Pb) contamination in environment has been identified as a threat to human health and ecosystems. In an effort to reduce the health and ecological risks associated with Pb mining wastes, a field study was conducted to stabilize Pb using phosphate (P)-enriched biosolid amendments in the contaminated mining wastes (average of 1004 mg Pb kg−1) located within the Jasper County Superfund Site, southwest Missouri. Experiments consisted of six biosolid amendment treatments, including Mizzou Doo compost (MD); Spent mushroom compost (SMC); Turkey litter compost (TLC); Composted chicken litter (CCL); Composted sewage sludge (CSS); and Triple superphosphate (TSP). Kentucky tall fescue seeds were planted following the treatments, and soil and plant samples were collected and analyzed 8–10 years post treatment. Results indicated that, in all cases, the biosolid treatments resulted in significant reductions in bioaccessible Pb (96.5 to 97.5%), leachable Pb (95.0 to 97.1%) and plant tissue Pb (45.5 to 90.1%) in the treated wastes, as compared with the control. The treatments had no significantly toxicological effect to soil microbial community. Analysis of the Pb fractionation revealed that the Pb risk reduction was accomplished by transforming labile Pb fractions to relatively stable species through the chemical stabilization reactions as induced by the treatments. The solid-phase microprobe analysis confirmed the formation of pyromorphite or pyromorphite-like minerals after the treatment. Among the six biosolid amendments examined, SMC and MD treatments were shown most effective in the context of Pb stabilization and risk reduction. This field study demonstrated that the treatment effectiveness of Pb stabilization and risk reduction in mining wastes by P-enriched biosolid amendments was long-term and environmental-sound, which could be potentially applied as a cost-effective remedial technology to restore contaminated mining site and safeguard human health and ecosystems from Pb contamination.
Highlights
Lead (Pb) contamination in environment has been identified as a threat to human health and ecosystems
Lead toxicological risk to human health was proportional to Pb bioavailability, which is the ability of Pb to be dissolved in the gastrointestinal (GI) tract and absorbed into the blood system through oral ingestion, while the Pb ecological risk was related to the Pb dissolution in water and mobility in ecosystems[5,6]
Bioaccessible Pb represented the potential toxicity or exposure risk of soil Pb to human health based on the modified physiology-based extraction test (PBET)
Summary
Lead (Pb) contamination in environment has been identified as a threat to human health and ecosystems. In situ soil treatment using phosphate or organic materials has been evaluated as a cost-effective and environmental-sound remedial technology for immobilizing or stabilizing heavy metals in contaminated soils and reducing the human health and ecological risks. Specific objectives were to: (1) assess the health risk reduction by the biosolid treatments through in vitro bioavailability test; (2) evaluate the mobility or stability of the stabilized Pb by leachability assessment; (3) determine the treatment impacts on plant Pb uptake with plant tissue analysis; (4) investigate the toxicological effect of the amendments to soil microbes using bacteria-based assay; and (5) examine the Pb species responsible for the risk reduction by sequential chemical fractionation and solid-phase speciation analyses
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