Effects of heavy metals on water hyacinths ( Eichhornia crassipes (Mart.) Solms)

Abstract

Water hyacinths ( Eichhornia crassipes (Mart.) Solms) were exposed for 6 wk to solutions containing 0–5 mg/1 Ph, Cd or Cu. The metal concentrations and metal accumulations within plant tissues increased linearly with solution concentration in the order leaves < stems < roots. The order of increasing mobility at solution concentrations ≥ 1.0 mg/l was Pb < Cu < Cd. There was no apparent effect of Pb on plant growth, but both Cd and Cu were toxic and caused substantial reductions in growth. The threshold toxicity of Cd was approximately 0.5 mg/l, whereas that for Cu was between 1.0 and 2.0 mg/l. Concentrations of Cd and Cu beyond the threshold toxicity produced chlorosis, suppressed development of new roots, and reduced relative growth rates to about ten percent of those of either the controls or plants exposed to Pb. These studies indicate that caution should be exercised when using results of short-term laboratory studies in combination with data on biomass production under optimum field conditions to predict the ability of plants to absorb toxic substances from waste water.