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In situ stabilization of soil lead using phosphorus
G M Hettiarachchi1, G M Pierzynski, M D Ransom
1Remediation and Containment Branch, National Risk Management Research Lab, USEPA, Cincinnati, OH 45224-1702, USA. hettiarachchi.ganga@epa.gov
Journal of Environmental Quality
|July 31, 2001
Summary
Adding phosphorus (P) effectively stabilizes lead (Pb)-contaminated soils. This study shows P amendments significantly reduce bioavailable Pb in various soils and mine wastes, offering a cost-effective in situ remediation alternative.
Area of Science:
- Environmental Science
- Soil Science
- Geochemistry
Background:
- Lead (Pb) contamination in soils poses significant environmental and health risks.
- Current soil remediation methods like excavation and replacement are expensive and disruptive.
- In situ stabilization offers a more sustainable and cost-effective approach.
Purpose of the Study:
- To evaluate the efficacy of phosphorus (P) amendments in reducing bioavailable lead (Pb) in contaminated soils and mine wastes.
- To compare the effectiveness of different phosphorus sources (triple superphosphate, phosphate rock, phosphoric acid) and application rates.
- To assess the long-term stability of Pb stabilization.
Main Methods:
- Five metal-contaminated soils and mine wastes were treated with seven different amendments, including varying rates and sources of phosphorus.
- Bioavailable Pb was quantified using the physiologically based extraction test (PBET).
- X-ray diffraction (XRD) was used to analyze mineralogical changes post-treatment.
Main Results:
- All tested phosphorus amendments significantly reduced bioavailable Pb compared to the unamended control.
- Higher P application rates (5,000 mg/kg) resulted in greater Pb bioavailability reduction.
- Phosphate rock was as effective or more effective than other P sources in most tested materials.
- Pb bioavailability reductions were observed within 3 days and remained stable for up to 365 days.
- XRD analysis indicated the formation of pyromorphite-like minerals, suggesting a mechanism for Pb stabilization.
Conclusions:
- Phosphorus addition is a viable in situ remediation strategy for Pb-contaminated soils.
- Phosphate rock presents a cost-effective and efficient option for Pb stabilization.
- The formation of pyromorphite-like minerals is a key mechanism in reducing Pb bioavailability.