Phytoremediation Potential of Lemna minor for Removal of Cr(VI) in Aqueous Solution at the Optimum Nutrient Strength

Toxic heavy metal pollution of water and soil is a major environmental concern for which conventional remediation approaches do not provide an appropriate solution. Phytoremediation, which involves removal of pollutants from water and soil through plants, is of low cost and environmentally friendly. In this study, the phytoremediation potential of Lemna minor for the uptake of Cr(VI) at the optimum nutrient strength for Cr(VI) uptake was investigated. Capacity assessment for chromium absorption by Lemna minor was carried out for 7 days at different levels of chromium concentrations. The time required for significant absorption of chromium was estimated in a time course experiment by growing Lemna minor in 3 mg/L chromium solution in which the plant showed no toxicity. Plant samples were harvested at 24 hour intervals for 5 days and wet weight was obtained to determine relative growth; the dried samples were analyzed for chromium using Atomic absorption spectrophotometer. Plant growth decreased significantly with increasing concentration of chromium in the nutrient solution and chlorophyll content (greenness) was also affected. Maximum uptake of chromium (5.8 x 103 μg/g dw) was at 8 mg/L in ambient solution. However, the bio-concentration factor (BCF) decreased with increasing chromium in the ambient solution. The BCF was 1000 for chromium up to 3 mg/L. In the time course experiment, growth of Lemna minor and chromium accumulation increased significantly with time up to the 3rd day (3119 μg/g dw). These results suggest that Lemna minor is an extreme accumulator of chromium and could be considered for chromium (VI) removal from waterways.