Heavy metals removal from contaminated soil by Siam!Weed (Chromolaena odorata) and vetiver grass (Vetiveria zizanioides)

The ability for heavy metals removal by C. odorata and V zizanioides grown on contaminated soil and synthetic contaminated soil in experimental pots was investigated. Both contaminated and uncontaminated soils, for preparing the synthetic contaminated soil in this study, were obtained from Mae Sot district, Tak province. The contaminated synthetic soil was prepared by adding a solution of cadmium nitrate, zinc sulfate, lead nitrate and copper sulfate to uncontaminated soil to make the concentration of each metal: Cd, Zn, Pb, and Cu 100 mg/kg soil above its initial concentration. In both plants grown on-site contaminated soil and on the synthetic soil, although some abnormal symptoms such as chlorosis, scorching in leaves and necrosis appeared, the plants still grew well. Each part Of the plant was examined for heavy metal uptake at 30, 60, 90 and 120 days after planting. Root uptake was greater than that of stem and leaves in all samples. For the on-site contaminated soil, the highest concentrations found in the root part for Cd, Zn, Pb and Cu of C. odorata were 50.22, 123.45, 29.07 and 31.89 mg/kg on a dry weight basis respectively and of,V zizanioide were 11.24, 163.18, 40.63 and 15.62 mg/kg on a dry weight basis respectively. The synthetic contaminated soil plants also showed higher concentration in root part than the other two parts for all metals both in C. odorata and in V zizanioide. This is due to the metals being present in a readily available form. Accumulation of Cd in mass for both plants grown in contaminated soil at the time of harvesting showed that C. odorata performed better than V zizanioide, especially for the aboveground parts and the time for harvesting that yielded the highest uptake of Cd was at 120 days.