Chelant-assisted Phytostabilization of Paint-contaminated Residential Sites

Following the basic incubation study, a greenhouse experiment was conducted to elucidate the efficiency of vetiver grass (Vetiveria zizanioides L.), with or without chelating agents, in remediating lead (Pb)-contaminated soils from actual residential sites where Pb-based paints were used. Because the primary factor affecting Pb phytoavailability in soils is soil pH, we used two soil types widely varying in pH that have total Pb concentrations above 1500 mg kg(-1) soil. Lead-contaminated, low pH, acidic soils were collected from residential sites in Baltimore, MD and high pH, alkaline soils were collected from residential sites in San Antonio, TX. Based on the soil characterization results, two most appropriate soils (one from each city, having similar Pb levels but variable soil physico-chemical properties) were selected for this study. Ethylenediaminetetraacetic acid (EDTA) and [S,S']ethylenediaminedisuccinate (EDDS) were applied at 5, 10, and 15 mmol kg(-1) soil. Lead uptake and translocation in vetiver was determined on day 10 after chelants addition. Plant and soil analysis show that EDTA treated soils have maximum Pb uptake and lower total soil Pb levels. Prediction models developed for exchangeable Pb show a strong correlation for total Pb accumulated in vetiver grass. Results of the sequential chemical extraction of the soils at both initial and final time-points, indicates a significant mobilization of Pb by the two chelants from carbonate-bound fraction to exchangeable pool. Information on physico-chemical properties of contaminated residential soils help in predicting Pb phytoextraction and thus further help in calibrating a successful chelant-assisted phytoremediation model.