Citric acid-assisted phytoextraction of lead: a field experiment

Soil contamination with heavy metals has become a serious environmental problem that requires affordable strategies of remediation. This study was carried out to assess the performance of maize and vetiver in the phytoextraction of Pb from a soil contaminated by battery recycling activities. The species were planted with different spacings between rows (0.80, 0.65 and 0.50m). Citric acid (40mmolkg(-1)) was applied on each experimental plot on the 61st d of cultivation in order to solubilize the Pb and assist the phytoextraction. The results showed that the chelating agent promoted a 14-fold increase in the Pb concentration in maize shoots as compared to the control, which accumulated only 111mgkg(-1) of the metal. The citric acid induced a Pb concentration in vetiver shoots that was 7.2-6.7-fold higher than the control at both the 0.65 and 0.50m plant spacing, respectively. The use of citric acid increased substantially the uptake and translocation of Pb to the shoots, regardless of plant spacing. Citric acid was efficient in solubilizing Pb from the soil and inducing its uptake by both species. Environmentally-friendly and cost effective, commercial citric acid is recommended for assisting Pb-phytoextraction in the studied area. Due to the low natural solubility of Pb and a time frame needed of longer than 150yr to accomplish the clean-up, phytoextraction with no chelate assistance is not recommended for the area.