The ability of Azolla caroliniana to remove heavy metals (Hg(Ⅱ), Cr(Ⅲ), Cr(Ⅵ)) from municipal waste water

摘要

The aim of this paper was to investigate the capacity of a small water fern, Azolla caroliniana Willd. (Azollaceae), to purify waters polluted by Hg and Cr. Many plants are capable of accumulating heavy metals (called hyperaccumu-lators) and one of them is the water fern A. caroliniana. During 12 days of the experiment the fern was grown on the nutrient solution containing Hg~(2+), Cr~(3+) and CrO_4~(2-) ions, each in a concentration 0.1, 0.5 and 1.0 mg dm~(-3). The presence of these ions caused a 20-31% inhibition of A. caroliniana growth, the highest in the presence of Hg(Ⅱ) ions, in comparison to the control. After day 12 of the experiment, metal contents the solution decreased to 0-0.25 mg dm~(-3), and this decrease comprised between 74 (Cr~(3+) 1.0 mg dm~(-3) treatment) and 100% (CrO_4~(2-) 0.1 mg dm~(-3) treatment). The fern took a lesser quantity of the metals from 0.1 mg dm~(-3) treatments compared to 0.5 and 1.0 mg dm~(-3) treatments. In the A. caroliniana tissues the concentration of heavy metals under investigation ranged from 71 to 964 mg kg~(-1) dm; the highest level being found for Cr(Ⅲ) containing nutrient solution.