USING VETIVER GRASS TO REMOVE LEAD FROM RESIDENTIAL SOILS OF SAN ANTONIO, TEXAS: A SIMULATED FIELD STUDY

Public health initiatives such as the use of unleaded gasoline and lead hazard mitigation in residential properties have resulted in substantial decrease in blood lead levels in children and adults since 1976. In 2012, CDC further lowered the reference elevated blood lead level for children from 10μg/dL to 5µg/dL, as research has revealed no demonstrable threshold for deleterious neurodevelopmental effects of lead in children. Soils and house dust are the principal sources of lead absorption among children. Traditional methods of soil remediation are expensive and unrealistic for residential soils. Chemical remediation techniques also have limitations, due to the risk of inhalation of soil-bound lead, which remains bioavailable and toxic. Phytoremediation is an attractive option for soil-lead cleanup in pre-1978 homes. We developed an ethylenediaminedisuccinic acid (EDDS) catalyzed vetiver grass phytoremediation model that performed well under greenhouse conditions during our Phase I study. In Phase II, the model was tested under simulated field conditions in lead-contaminated residential soils collected from San Antonio. Soils from 3 house sites with lead content between 1000 – 2400 mg/kg were collected. The experiment was setup in wooden platforms loaded with the contaminated soil that were left exposed to the elements. Vetiver and fescue grass were grown in the platforms for 3 months before the first application of chelating agents (CA) EDDS or EDTA, which was repeated every 3-4 months. Plant tissue was harvested 15 days after CA application. Both CAs significantly increased lead uptake and root to shoot translocation in vetiver. EDTA was more effective than EDDS at increasing lead uptake. However, EDDS degraded in soil within 15 days whereas EDTA remained in the soil for a longer period. Lead uptake in vetiver was 35-50 times higher than fescue grass. Moreover, fescue grass platforms leached higher levels of lead compared to vetiver platforms. To test for disposability of the grass clippings, lead leachates from grass clipping composts was evaluated using TCLP. The concentration of lead in the decomposed clipping leachates was significantly lower than the USEPA TCLP limit for lead, indicating that the harvested tissue can be disposed as non-hazardous waste.