Growth response of the duckweed <Emphasis Type="Italic">Lemna gibba</Emphasis> L. to copper and nickel phytoaccumulation

To assess the tolerance and phytoaccumulation ability of the duckweed Lemna gibba L. to copper (Cu) and nickel (Ni), the plants were exposed to different concentrations of Cu and Ni (0.1–2.0 mg/l) under laboratory conditions. The results showed that Cu and Ni were tolerated by L. gibba at concentrations ≤0.3 and ≤0.5 mg/l, respectively. However, plant growth decreased by 50% (I₅₀) when the medium contained 0.45 mg Cu/l or 0.75 mg Ni/l. The observed LCI (lowest concentration causing complete inhibition) were 0.5 and 1.0 mg/l respectively in the presence of Cu and Ni. Results from metal analysis in plant biomass revealed a high accumulation of Cu (1.5 mg g⁻¹ DW), a low accumulation of Ni (0.5 mg g⁻¹ DW) within the plants and a corresponding decrease of metals in the water. The removal percentage of Cu was about 60–80%. We conclude that the duckweed L. gibba L. showed a higher accumulation potential for Cu from polluted water than Ni after 4 days of exposure.