In this study, the mercury (Hg) removal capacities of two aquatic macrophytes, Pistia stratiotes and Azolla pinnata, were investigated against the coal mining effluent. These plants reduced mercury from the effluent via rhizofiltration and subsequent accumulation in plant. The removal rate of P stratiotes and A. pinnata was 80% and 68%, respectively, after 21 days of exposure to the effluent containing 10 mu g L-1 of Hg. As mercury from the effluent was accumulated in the root and shoot tissues of both aquatic macrophytes, they were proven to be a root accumulator with a translocation factor of less than one during the entire study. The decreasing Hg content in effluent (from 10 to 2.0 mu g L-1) was reflected by its accumulation in roots (0.57 +/-0.02 mg g(-1) in P. stratiotes) and leaves of the experimental plants (0.42 +/- 0.01 mg g(-1), P. stratiotes). As a result, Hg concentrations in the coal mining effluent were tightly associated with those observed from macrophytes. Considering the high removal efficiencies of Hg by these aquatic macrophytes, these plants can be recommended for the actual treatment of Hg-containing waste waters. (C) 2009 Elsevier B.V. All rights reserved.