EFFECT OF ETHYLENEDIAMINEDISUCCINIC ACID (EDDS) APPLICATION ON LEAD GEOCHEMICAL FORMS IN PAINT-CONTAMINATED RESIDENTIAL SOILS

Lead (Pb) based paint contaminated residential soils were collected from ten sites each in two cities, namely Baltimore, MD and San Antonio, TX. The soils were analyzed for their physical and chemical properties. Sequential extraction was performed to determine the geochemical partitioning of lead in various soil fractions at time-zero. While the San Antonio soils were basic, and Baltimore soils were acidic in nature. Sequential extraction revealed that the soluble and exchangeable fractions in both San Antonio and Baltimore soils were less than 1% of the total lead. While the Fe–Mn oxide (60–63%) and carbonate (25–33%) fractions dominated in Baltimore soils, majority of the Pb was bound to the organic (64–70%) and Fe–Mn oxide (15–20%) fractions in San Antonio soils. Three Pb contaminated residential soils from each city were selected for the field experiment to study the phytoextraction of lead by vetiver grass. The experiments for the phytoextraction study were setup in San Antonio, TX and Stockton, NJ in the custom-made wooden platforms. Lead contaminated soils were loaded in the platforms and vetiver grass was planted, and allowed to grow for three months, after which time the first application of 10 mmol EDDS/kg soil was performed. The results show that the EDDS application brought about nearly 15% reduction in the Fe–Mn oxide fraction in Baltimore soils and 10-12% reduction in the organic fraction in San Antonio soils. The second EDDS application after eight months resulted in further reduction in the Fe–Mn oxide and carbonate fractions in Baltimore soils and organic bound fraction in San Antonio soils. Overall, significant amounts of bound form Pb were mobilized into the soluble and exchangeable form in both San Antonio and Baltimore soils after first and second EDDS applications.