Effects of humic acids on phytoextraction of Cu and Cd from sediment by Elodea nuttallii

Growth and metal-accumulation of Elodea nuttallii exposed to Cu and Cd-contaminated sediment were examined and the effects of humic acids on phytoextraction of Cu and Cd were also investigated. The growth of plants were promoted with the increasing concentration of Cu in sediment, while inhibited by Cd during the 21d exposure. The concentrations of Cu in roots and shoots of E. nuttallii ranged 25-99mgkg(-1) dry weight (DW) and 23-83mgkg(-1)DW under different concentration of Cu treatments in sediment at the end of exposure, and they were 0-6.5mgkg(-1)DW and 0-7.9mgkg(-1)DW for Cd, respectively. With addition of humic acids from 3.0 to 7.8gkg(-1)DW, the bioavailability of heavy metals in the sediment were reduced significantly, therefore, the accumulation of Cd was inhibited and the Cd concentrations in roots and shoots of plants decreased. However, as the result of release Cu from sediment into water column with addition of humic acids, and E. nuttallii could uptake Cu from water directly, the Cu concentrations in roots and shoots in plant increased 26-69% and 40-78%, respectively. In conclusion, E. nuttallii could be suitable for remedying Cu and Cd-contaminated sediment in situ as a pioneer species, but for phytoextraction of Cd, the application of humic acids should be careful.