A Chemically Catalyzed Phytoremediation Model for Lead-Paint Contaminated Residential Soils: Greenhouse Study

In spite of considerable national public health efforts to reduce lead (Pb) exposure, Pb poisoning remains the most common environmental health problem affecting the children in U.S. Phytoremediation is emerging as an attractive option for cleanup of Pb-paint contaminated soils in the pre-1978 housing facilities. The objective of this study was to investigate the usage of a high biomass, metal tolerant grass, Vetiveria zizanioides (vetiver grass) to remediate Pb-paint contaminated residential soils of variable physico-chemical properties. Developing a successful phytoremediation model requires a good understanding on the role of soil properties governing Pb availability for plant uptake, biochemical mechanisms involved in Pb tolerance and changes in Pb bioaccessibility. Hence, a comprehensive greenhouse-based study was conducted to evaluate the effectiveness of vetiver in Pb uptake and reducing soil Pb concentrations. Chelation of Pb is an important factor in enhancing its solubility and hence, availability to vetiver to promote phytoremediation. We compared the effects of two chelating agents, namely, ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) at 4 different concentrations such as 0, 5, 10 and 15 mmol kg^-1 soils. Our studies indicate that (1) soil properties determine the extent of soluble Pb (2) EDTA is more effective in mobilizing bound soil Pb compared to EDDS (3) EDDS reduced the leachable Pb fraction in soils compared to EDTA (4) antioxidant enzymes like superoxide dismutase, catalase, and glutathione peroxidase activities were elevated in vetiver under Pb stress and (5) Pb bioaccessibility in soils decreased with an increase in Pb uptake by vetiver. This study demonstrated that EDDS could be regarded as a good candidate chelant for the environmentally safe phytoextraction of Pb using vetiver grass in contaminated residential soils.