Chemical speciation and bioavailability of copper: Uptake and accumulation by eichornia

The uptake of copper by water hyacinth (Eichornia crassipes) was studied using solution culture techniques in the greenhouse. The bioassays indicated that the uptake of copper was a direct function of its speciation. For example, only free Cu2+ was absorbed by the plant in the presence of strong ligands such as EDTA and humic acid. Other ligands tested (fulvic acid, amino acids and simple organic acids), however, failed to suppress the uptake of copper even when the free Cu2+ in solution initially was negligibly small. Copper could have been taken up directly by the plant as various complexes or in the free Cu2+ form after dissociation from the ligands prior to uptake. Complete inhibition of copper uptake in the presence of humic acid, in contrast to fulvic acid, suggests that the chemical stability constants of these complexes with copper were not correlated to the metal's bioavailability. The potential of Eichornia for removing heavy metals from wastewaters is demonstrated by its tremendous capacity to bioaccumulate copper. Depending on the presence or absence of ligands, from 200 to more than 2,400 μg Cu g−1 dry matter could be taken up by the plant.