AZOLLA-PINNATA R BR AND LEMNA-MINOR-L FOR REMOVAL OF LEAD AND ZINC FROM POLLUTED WATER

The uptake of lead and zinc by Azolla pinnata R.Br. (water velvet) and Lemma minor L. (duckweed) was investigated in solutions, enriched with 1.0.2.0.4.0 and 8.0 mg/l of these two metal ions, which were renewed on alternate days over a 14 day test period. The uptake rate of both metal ions was highest when the initial concentration in the test solution was 1.0 mg/l. The concentration of lead or zinc remaining in the residual solutions after treatment with duckweed or water velvet at 1.0 and 2.0 mg/l levels, increased with the passage of time. At 4.0 and 8.0 mg/l levels, the concentration of lead or zinc remaining in the residual solutions either continuously increased with the passage of time or, first sharply increased (8-10 days) and then remained almost constant. The presence of one metal ion in solution decreased the uptake rate of the other; e.g. when water velvet was kept in a solution containing lead alone at 8.0 mg/l level, the value of the concentration factor was 54.5. However, in the presence of equal concentrations of zinc (mixed metal group), the value of the concentration factor for lead decreased to 35.44, indicating the influence caused by the presence of the zinc ion. The effect of these metal ions on biomass growth rate was also studied. © 1990.