Metal bioaccumulation in spontaneously grown aquatic macrophytes in Fe-rich substrates of a passive treatment plant for acid mine drainage

Abstract

Some plants may thrive in polluted environments, accumulating high concentrations of metal/loids in their organs. This study investigates for the first time the bioaccumulation and translocation of metal/loids in Typha domingensis spontaneously grown in extremely Fe-rich substrates (38–44% of Fe2O3) from different components of an acid mine drainage disperse alkaline substrate passive treatment. Most metal/loids were predominantly accumulated in the roots over the aerial parts of the plant, with concentrations of 0.66–9.5% of Fe, 0.02%–0.18% of Al, 55–2589 mg kg-1 of Mg, 51–116 mg kg-1 of Zn, 17–173 mg kg-1 of Cu, and 5.2–50 mg kg-1 of Pb. Bioconcentration factors were mostly below 1 for metal/loids in the studied aneas (e.g. 0.03–0.47 for Cu, 0.10–0.73 for Zn, 0.04–0.28 for As, 0.07–0.55 for Pb, 0.27–055 for Cd, 0.24–0.80 for Ni), which evidences that T. domingensis behaves as an excluder species in these substrates. Translocation factors were below 1 for most elements (e.g. 0.01–0.42 for As, 0.06–0.50 for Pb, 0.24–0.65 for Cd, and 0.10–0.56 for Sb), except for Mn, Ni and in some cases for Tl, Cu and Zn, which indicates limited transfer of metals between plant tissues. Mineralogical and geochemical substrate properties are pointed out as the main factors responsible for the lower bioconcentration and translocation of potentially toxic elements. In addition, the oxidizing conditions existent in the pore water-root system may also limit the mobility of metals from Fe oxides and hydroxysulfates, the main component of the substrate. The formation of a Fe plaque inside the roots may also limit the transfer of metals to the aerial parts. The spontaneous occurrence of T. domingensis in the substrates of the acid mine drainage passive treatments is an environmental indicator of the efficiency of the system and could be used as a complementary polishing step, given the strong tolerance of this plants to high concentrations of metal/loids.