A study of the uptake by duckweed of aluminum, copper, and lead from aqueous soltuion

The uptake of Al3+, Cu2+ and Pb2+ from aqueous solution by duckweed has been observed at pH 4.0, 4.5, and 5.0. The results showed that the uptake of Pb2+ was much faster than Al3+ and Cu2+. The uptake of Cu2+ was suppressed by the presence of Pb2+ and Al3+. The proportion of metal uptake (PMUT) by duckweed was dependent on the metal concentration in the solution when only one kind of metal ion was present. It was decreased by increasing concentrations of other metals in mixtures of solutions. The metal uptake by the duckweed was always less than the loss of metal content 1n the relevant solution. This fact implied that the process of the uptake of metal ions by the duckweed may involve two stages. In the first, the metal is absorbed but then later 1t 1s adsorbed by the duckweed. The aluminum ion was found to be more toxic than the copper ion at lower pH and higher concentration, but the situation is reversed at higher pH. A possible explanation of toxicit of Cu2+ and Al3+ is that the Mg2+ in chlorophyll was replaced by the Cu2+ or Al3+. This may lead the chlorophyll to lose its normal activity and kill the duckweed.