Screening of selenium-tolerant duckweeds and evaluation of their selenium removal capability

Soluble forms of selenium (Se), selenite [Se(IV)], and selenate [Se(VI)] are recognized as important pollutants in the aquatic environment. This study attempted to identify Se-tolerant duckweed species as potential agents for sustainable Se(IV)/Se(VI) phytoremediation and examined their Se removal capacity. Among six tested duckweed species, Landoltia punctata (LAp) and Lemna aequinoctialis (La) demonstrated relatively high tolerance against Se(IV) and Se(VI) in the presence of both high- and low-sulfate concentrations. Both LAp and La could grow in healthy states and increasingly remove substantial amounts of Se(IV) and Se(VI) at typical low and high Se concentrations commonly found in contaminated sites, though they failed in removing Se(VI) under high-sulfate conditions. Major portions of removed Se accumulated in the duckweed biomass and could be recovered as a usable micronutrient. These results indicate that LAp and La are promising candidates as agents for the phytoremediation of Se-contaminated aquatic environments, while La is particularly preferable due to its ability to remove up to 40 % of both Se(IV) and Se(VI). Additionally, Se accumulation in the biomass of La reached 0.35 and 0.99 mg-Se/g dry weight for Se(IV) and Se(VI), respectively, which was higher than LAp. • Landoltia punctata and Lemna aequinoctialis were identified as Se-tolerant duckweeds. • Selected Se-tolerant duckweeds could sustain Se(IV)/Se(VI) removal. • Presence of sulfate inhibits Se(VI) removal by the duckweeds. • Major portions of removed Se were accumulated in the duckweed biomass. • Se-accumulating duckweed biomass can be used as micronutrient source.