Fixing the Urban Soil Lead Predicament: The Application of In Situ Fixation Technology as an Ecologically Sustainable Method of Lead Abatement in Urban Soils

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Journal Article

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Lead (Pb) has been used to produce a large number of materials and manufactured products. In areas with a history of lead paint use, high vehicular traffic, or areas close to urban and industrial centers, atmospheric lead deposition may be very high. The aerosol form of Pb can be re-suspended and easily inhaled on fine dust particles or inadvertently consumed in crops grown in lead contaminated soils. At low levels, Pb will impair psychological and neurobehavioral functions particularly in young children. Remediation of lead contaminated soils by conventional methods is expensive. The use of low cost environmentally safe amendments for the in situ fixation of lead in contaminated soil is a promising remediation approach. In situ lead fixation does not reduce the total concentration of soil lead but changes its speciation, thus rendering the lead less toxic and potentially non bio-extractable in the eco-system. The objectives of this study were: (1) to determine if various agricultural, municipal and industrial by-product treatments can reduce levels of Mehlich III lead in lead contaminated urban soils, (2) to determine if by-product treatments can reduce or prevent Mehlich III lead absorption into the tissues of crops grown in lead contaminated soils, (3) to determine if by-product treatments will affect crop yields, and (4) to determine if by-product treatments can reduce soil and crop tissue lead levels to within Environmental Protection Agency (EPA) or joint World Health Organization and Food and Agriculture Organization (WHO/FAO) standards. Four different agricultural, municipal and industrial by-products that are known to contain chemical compounds that will absorb and fix lead were tested. The by-products selected for study were: poultry litter ash (PLA) as a phosphate source; drinking water treatment residual (DWTR) as an aluminum, sulfate and iron oxide source; steel slag (SS) as an alumina, iron, and magnesium oxide source; and leaf compost (LC) as a source of organic matter. Soils were collected from three urban locations: Ft. DuPont National Park, Washington, DC; a residence in Washington, DC; and a residence in Baltimore City, MD, with average total lead concentrations of 37, 919 and 1528 mg kg-1 respectively. By-products were mixed with each soil at three rates and incubated moist for 58 days. By-product treatments (except DWTR) resulted in decreasing Mehlich III extractable Pb in the residential DC and Baltimore soils, compared to the un-amended soils. PLA, LC, and SS treatments reduced Mehlich III Pb in the residential DC and Baltimore soils to within EPA permissible limits for garden soil. In comparison, high rate treatments of WTR significantly increased Mehlich III extractable lead levels in both residential DC and Baltimore soils. No treatments met the WHO/FAO standard. Low and high rate treatments of WTR resulted in non-statistically significant Pb increases in crop tissues. LC and PLA treatments were found to stress crops and reduce crop yields when compared to controls. DWTR increased yields with most crops. The most consistent by-product to reduce or prevent Mehlich III Pb uptake into crop tissues of leafy and root vegetables to within EPA and/or WHO/FAO permissible limits was LC. However, due to the high levels of trace elements and salts in some of these by-products, caution is suggested when using these materials to grow crops.




Public Health