Phytoextraction of Ni, Pb and, Cd by duckweeds.

Heavy metals phytoextraction potential of swollen duckweed ( Linn.) and lesser duckweed ( Welw.) was determined under greenhouse conditions by exposing to untreated industrial/municipal effluent for a period of 21days. The nickel (Ni), lead (Pb), and cadmium (Cd) concentrations in water samples were measured weekly and in plant biomass at the termination of experiments. Significant differences (<0.05) between initial and final physicochemical parameters and in heavy metal concentrations of plant and water samples were observed. Periodically measured metal concentrations in mediums revealed that removal percentage was dependent on initial Ni (2.15mg L), Pb (1.51mg L), and Cd (0.74mg L) concentrations. The final metal removal percentages were in the sequence of Ni (97%) > Pb (94%) > Cd (90%) when treated with L. as compared to control (9-12% reduction). High biomass production of L. resulted in a large metal reduction in the growth medium and the total plant metal contents were in the sequence of Ni (427µg) > Pb (293µg) > Cd (105µg). The lesser duckweed did not survive under experimental conditions. Based on these results, we concluded that L. is a good candidate for phytoremediation of wastewater.