Laboratory study on the survival of water hyacinth under several conditions of heavy metal concentrations

Abstract

To study the survival and behaviour of water hyacinth [ Eichhornia crassipes (Mart.) Solms] under varying conditions of heavy metal concentrations, groups of the plants were grown in different media (distilled water, Nile water, wastewater and different concentrations of heavy metals). Simultaneously, blank experiments were carried out for comparison. Visual changes in the plants observed during each experiment were noted. The heavy metal (Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) concentrations, pH and conductivity of the media were measured before, during and at the termination of experiments. In addition, analyses for heavy metals were carried out on the plant samples after termination of the experiments to determine the effect of different media on metal accumulation by the plants. The results showed that water hyacinth can survive in a mixture of heavy metal concentrations up to 3 mg l −1 and in 100 mg Pb l −1 solution, whereas higher concentrations of metals as mixtures and 100 mg Cd l −1 led to rapid fading of the plants. Water hyacinth exhibited a deprotonation reaction during the uptake of metal ions, which was detected as a result of a decrease in pH of the growth media. The results indicated that water hyacinth plays an outstanding role as a heavy metal decontaminator; in addition, its role as a pollutant by releasing metal ions into the aquatic environment was also noted. Elevated pH and ammonia concentrations, along with the low dissolved oxygen content in the microenvironment around the root hairs, are suggested as the main factors for the rapid wilting of plants growing in Kima drain wastewater.