COBALT-COPPER AND COBALT-ZINC EFFECTS ON DUCKWEED GROWTH AND METAL ACCUMULATION

Zn+2. Cu+2 and Co+2 were added to Jacob nutrient medium with constant pH value at concentrations ranging from 0.10-10.0 ppm, 0.20-2.00 ppm and 0.20-20.0 ppm, respectively. The IC50's for these metals as well as their effects on the growth and the accumulation efficiency by Lemna minor L. were determined. The IC50's for Co+2, Zn+2 and Cu+2 were 16.90. 10.00 and 1.54 ppm, respectively. At 0.20-2.00 ppm concentrations, the potential of Lemna minor L. to accumulate these metals with respect to their inital concentrations In the medium was in the following order : Co+2 > Zn+2 > Cu+2 The effects of the metal pairs of Co+2-Cu+2 and Co+2-Zn+2 at concentration levels ranging from 0.10 to 2.00 ppm were also tested. The accumulation of Zn+2 was stimulated by Co+2 and the accumulation of Co+2 was inhibited by Zn+2. Also a decrease in the growth of Lemna minor L. was observed. especially at 2.00 ppm. The accumulation of Co+2 was suppressed by Cu+2 whereas the accumulation of Cu+2 was slightly promoted by Co+2. The growthinhibition effect of Cu+2 was not changed by Co+2 at 0.10 through 1.00 ppm, but at 2.00 ppm, Co+2 reduced the growth inhibitory effect of Cu+2.