Soil Properties Governing Potentially Plant Available Lead in Contaminated Residential Sites

Syam Sundar P. Andra, Rupali Datta, Dibyendu Sarkar, and Sumathi K. M. Saminathan
Environmental Geochemistry Laboratory, University of Texas at San Antonio, San Antonio, TX

Lead (Pb) based paints pose a serious health problem to people living in residential settings that were constructed prior to 1978. Children are at a greater risk to Pb exposure resulting from hand-to-mouth activity in Pb-contaminated residential soils. For soil Pb, the most environmentally friendly, potentially cheap, and visually unobtrusive, in situ technology is phytoremediation. However, the limiting factor in a successful phytoremediation strategy is the availability of Pb for plant uptake. The purpose of this study was to establish a relationship between soil properties and plant available/ exchangeable Pb fraction in the selected Pb-based paint contaminated residential sites. We selected 20 such sites from two different locations (San Antonio, TX and Baltimore, MD) with varying soil properties and total soil Pb concentrations ranging between 256 mg/kg and 4,182 mg/kg. Although the total Pb concentrations in many of these contaminated residential soils exceed the EPA permissible limit of 400 mg/ kg soil, the plant available Pb fraction is usually very low due to the strong association of Pb with organic matter, Fe-Mn oxides, clays, and precipitation as carbonates, hydroxides, and phosphates. Principal component analysis and hierarchical clustering showed that potentially plant available Pb fraction is controlled by soil pH in case of acidic, Baltimore soils; while soil organic matter plays a major role in alkaline, San Antonio soils. Statistical models developed suggest that Pb is likely to be more available for plant uptake in Baltimore soils, and a chelate-assisted phytoextraction strategy will be potentially necessary for San Antonio soils in mobilizing Pb from ‘complexed’ to plant available pool. Hence a thorough knowledge of site-specific factors is essential in developing a suitable and successful phytoremediation model.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas