Antioxidant Enzymes Response in Vetiver Grass: A Greenhouse Study for Chelant-Assisted Phytoremediation of Lead-Contaminated Residential Soils

In a previous study we have demonstrated the suitability of using vetiver grass (Vetiveria zizanioides L.) for the phytostabilization of lead-based paint contaminated residential soils. Vetiver did not show any growth retardation or toxicity symptoms despite high soil Pb levels. Antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) reportedly allow plants to combat metal stress. Thus, we hypothesized that in vetiver, these antioxidant enzymes can play an important role in combating Pb induced stress, and that chelant-bound Pb is less toxic to vetiver compared to free Pb in soil. The response of antioxidant enzymes was studied in vetiver grass grown in Pb paint-contaminated residential soils collected from San Antonio, Texas and Baltimore, Maryland. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) were used to mobilize Pb from bound fractions to the labile pool, facilitating Pb uptake by vetiver. Although the Pb concentration in vetiver from these treatments was significantly higher than those grown in the absence of a chelant, the antioxidant enzymes activities were lower compared to the latter. Antioxidant enzymes activity of vetiver plants grown in the presence of chelants is lower compared to those in without chelant treatment, while they tended to increase with dose in treatments with varying chelant concentrations. Data obtained support the proposed hypothesis.