Cobalt and nickel content in Hydrocharis morsus-ranae and their bioremoval from single- and binary solutions

Abstract

Aquatic macrophytes are known to remove trace metals from surrounding water. In the present study, an attempt was made to evaluate the phytofiltration capacity of Hydrocharis morsus-ranae and to show competition between cobalt (Co) and nickel (Ni) for the better understanding of metal bioaccumulation in the species. In a laboratory experiment, H. morsus-ranae was exposed to separate (single) and binary solutions of these metals: Ni 10.7, 18.7, 32.7, 57.1, and 100 (μg L^-1); Co 5.33, 9.32, 16.3, 28.6, and 50.0 (μg L^-1); and 10.7 Ni + 5.33 Co, 18.7 Ni + 9.32 Co, 32.7 Ni + 16.3 Co, 57.1 Ni + 28.6 Co, 100 Ni + 50.0 Co (μg L^-1). The content of Co and Ni in the plant increased with the increasing concentration in the growth medium. Competition between the metals was seen during uptake in binary solutions. Ni interfered with the accumulation of Co, resulting in a lower Co content than in plants cultivated in Co solutions. A particularly high Co content (up to 155 mg kg^-1 dry weight [d.w.]) and high efficiency of Ni uptake (Bioaccumulation Factor (BF) 2572-7239) makes the species a very good accumulator of these metals. The high content of both trace metals in plant tissues (up to 511 mg kg^-1 d.w. Ni and 155 mg kg^-1 d.w. Co) did not affect its growth, indicating tolerance of these toxicants. The plant showed excellent ability in removing Co (up to 98.6% in solution with 5.33 μg L^-1 Co) and Ni (up to 91.4% in solution with 57.1 μg L^-1 Ni and 28.6 μg L^-1 Co) from nutrient solution. The results suggest that H. morsus-ranae may be useful for the phytoremediation of water bodies contaminated with Co and Ni.

Keywords: Aquatic macrophyte; Bioremoval; European frog-bit; Metal interactive effects; Phytoremediation; Trace metal.