Effect of Phosphates on the Bioavailability and Phytotoxicity of Pb and Cd in Contaminated Soil and Phytoextraction by Vetiver Grass

Column and vessel experiments were conducted to investigate changes in mobility, leaching, and availability of lead (Pb) and cadmium (Cd) in contaminated soil (Santo Amaro Municipality, Bahia State, Brazil) after treatment with different sources of phosphate followed by assessment of phytoextraction by vetiver grass [Vetiveria zizanioides (L.)]. Columns were filled with contaminated soil and KH2 PO4 (T1 treatment), reactive natural phosphate fertilizer (NRP) (T2 treatment), KH2PO4 mixed with NRP (T3 treatment), and untreated contaminated soil used as reference soil (T0 treatment). After 60 days, soil samples were collected from each column every 10 cm in depth and vessel experiments were initiated by planting vetiver grass. After 90 days, Pb and Cd were extracted from the soil and from the plant tissues using diethylenetriaminepentaacetic acid (DTPA) and nitro-peroxide extraction, respectively. Metal mobility was assessed using two methods: the toxicity characteristic leaching procedure (TCLP) and the sequential extraction proposed by the Community Bureau of Reference (BCR). The most effective treatment in reducing mobility, availability, and toxicity was T1 (KH2PO4). With regard to reduction of bioavailability to plants, T1 treatment was more effective for Pb than for Cd. According to the BCR method, Cd was more soluble and had higher mobility than Pb. (C) 2016 American Society of Civil Engineers.