Bioaccumulation and toxicity of mercury in rooted-submerged macrophyte Vallisneria spiralis

Laboratory experiments were carried out to determine mercury (Hg) accumulating potential and toxicity in the submerged aquatic macrophyte Vallisneria spiralis. Young plants were subjected to different concentrations (0.5, 1.0, 5.0, 10, 20 μM) of Hg for 24, 48, 96 and 168 h. Plants showed a Hg accumulation of 0.25 μmol/g dry weight in leaf and 1.12 μmol/g dry weight in roots, respectively, at 20 μM Hg after 168 h. The chlorophyll, protein and nitrogen, phophorus, potassium contents decreased significantly with increasing Hg concentrations and treatment durations. In vivo nitrate reductase activity also decreased from the lowest concentration of Hg to the highest. Cysteine content of leaf and root material increased at low Hg concentration and then significantly declined at higher doses of Hg. The results suggested a strong uptake potential for Hg by the roots which can act to monitor metal contamination in the environment, although the negative physiological implications cannot be ruled out, which are relevant for transfer of metal via food chain at different trophic levels.