Phytoremediation, recovery and toxic effects of ionic gadolinium using the free-floating plant Lemna gibba

The biosorption and recovery of ionic gadolinium (Gd) from contaminated water by the free-floating duckweed Lemna gibba was studied. The highest non-toxic concentration range was determined as (6.7 mg L^-1). The concentration of Gd in the medium and in the plant biomass was monitored and a mass balance was established. Tissue Gd concentration of Lemna increased with increasing Gd concentration of the medium. The bioconcentration factor was up to 1134 and in nontoxic concentrations up to 2.5 g kg^-1 Gd tissue concentration was reached. Lemna ash contained 23.2 g Gd kg^-1. Gd removal efficiency from the medium was 95%, however, only 17-37% of the initial Gd content of the medium accumulated in Lemna biomass, an average of 5% remained in the water, and 60-79% was calculated as a precipitate. Gadolinium-exposed Lemna plants released ionic Gd into the nutrient solution when they were transferred to a Gd-free medium. The experimental results revealed that in constructed wetlands, L. gibba is able to remove ionic Gd from the water and can be suitable for bioremediation and recovery purposes.