PHYTOACCUMULATION OF TRACE-ELEMENTS BY WETLAND PLANTS - I - DUCKWEED

There has been much interest recently in the use of constructed wetlan ds for the removal of toxic trace elements from wastewaters. Wetland p lants play an important role in the trace elements removal process. It is not known, however, which wetland plant species absorb specific tr ace elements at the fastest rates. Such knowledge is essential to maxi mize the efficiency of trace element removal by wetlands. In this stud y, me investigated the potential of duckweed (Lemna minor L.) to accum ulate Cd, Cr, Cu, Ni, Pb, and Se when supplied individually in a nutri ent solution at a series of concentrations ranged from 0.1 to 10 mg L- 1. The results show that under experimental conditions, duckweed prove d to be a good accumulator of Cd, Se, and Cu, a moderate accumulator o f Cr, and a poor accumulator of Ni and Pb. The highest concentrations of each trace element accumulated in duckweed tissues were 13.3 g Cd k g(-1), 3.27 g Se kg(-1), 3.36 g Cu kg(-1), 2.87 g Cr kg(-1), 1.79 g Ni kg(-1), and 0.63 g Pb kg(-1). Duckweed exhibited some symptoms of tox icity (e.g., reduced growth, chlorosis) at higher levels of element su pply (except for Cr). The toxicity effect of each trace element on pla nt growth was, in descending order of damage, Cu > Se > Pb > Cd > Ni > Cr. We conclude that duckweed shows promise for the removal of Cd, Se , and Cu from contaminated wastewater since it accumulates high concen trations of these elements. Further, the growth rates and harvest pote ntial make duckweed a good species for phytoremediation activities.