THE ASSESSMENT OF TOLERANCE TO HEAVY METALS (Cd,Pb and Zn) AND THEIR ACCUMULATION IN THREE WEED SPECIES

Phytoextraction is gaining great attention as an alternative technique for remediation of heavy metal contaminated soils. A greenhouse study was conducted to assess heavy metal (Cd, Pb, and Zn) accumulation in three weed species viz., Avena sterils, Isatis tinctoria and Xanthium strumarium. A range of phytoavailable Cd, Pb and Zn concentrations in soils was created by applications of five different levels of Cd (0, 25, 75, 150 and 300 mg kg), Pb (0, 100, 200, 400 and 800 mg kg) and Zn (0, 150, 300, 600 and 1200 mg kg). Data indicated that in terms of relative yield, the most sensitive weed among the species used in this study was A. sterils. On the other hand, the most tolerant one was I. tinctoria. Increasing metal concentrations in soils increased shoot metal concentrations. Shoot Cd concentrations ranged from 2 to 93 mg kg -1 for I. tinctoria, <0.1 to 77 mg kg -1 for A. sterils and <0.1 to 6 mg kg -1 for X. strumarium. The highest shoot Pb concentration was in I. tinctoria having no significant relative yield decrease, whereas A. sterils and X. strumarium had a closer Pb accumulation in shoots. A. sterils had significantly higher shoot Zn concentrations compared to I. tinctoria and X. strumarium. Shoot Zn concentrations varied from 24 to 264 mg kg -1 for A. sterils, 10 to 101 mg kg -1 for I. tinctoria and 28 to 48 mg kg -1 for X. strumarium. I. tinctoria extracted the highest metals among the three weed species used in this study.