Effects of chromium uptake on the growth characteristics of Eichhornia crassipes (Mart.) Solms

Abstract

The uptake of chromium from fresh water by Eichhornia crassipes was studied under greenhouse conditions where the species was raised in culture solutions containing varying concentrations of chromium (VI) ions. There were positive correlations between the concentration of chromium in the culture media and the amounts of the metal accumulated in the tissues of E. crassipes at any given time. Furthermore, the total accumulated chromium in the tissues of E crassipes increased with increase in the duration for which the plant was exposed to the nutrient solutions containing chromium ions. Most of the absorbed chromium was accumulated in the roots of the treated plants and only a small fraction (1.71 – 4.37%) was translocated to the shoot system. The highest concentration factors of chromium in E. crassipes shoots and roots were 12.2 and 466.1 respectively. Plant growth analysis techniques were applied to assess the effects of chromium on the growth characteristics of the treated E. crassipes plants. It was observed that the accumulation of chromium did not result in significant differences (p>0.01) in the relative growth rates and net assimilation rates of E. crassipes between the various treatments at each harvest. On the other hand, the accumulation of chromium was positively correlated (r = 0.8112) with increases in the leaf are ratio and negatively correlated (r = -0.6605) with biomass increments of E. crassipes plants. The differences in leaf area ratio and biomass increments among the treatments were significant (p<0.01) from the third week of the experiment onwards for the plants exposed to culture media with chromium concentrations of 3.00 mg/ml. and above. The implications of these results in terms of the control of chromium pollution in fresh water lakes and rivers are discussed.