Praseodymium effect on growth and antioxidant systems in Lemna minor

The increasing use of rare earth elements (REEs) elicits concerns about their release into freshwater environments and potential effects on primary producers. This study investigated the toxicity of praseodymium (Pr) to the aquatic macrophyte Lemna minor during a 7-day exposure, centring on growth inhibition, Pr accumulation, oxidative stress and responses of related enzymes. A tenfold increase in Pr concentration in the medium from 0.01 to 0.1 mM resulted in a 56-fold increase in Pr content in plant tissue, with a bioconcentration factor of 608 L/kg. Further increases (0.2–0.4 mM) worsened the plant’s physiological state, yielding less than a 50% additional increase in Pr content. No significant effects were observed at 0.01 mM Pr, whereas inhibition of root growth occurred at 0.1 mM and frond growth at 0.2 mM. At the highest tested concentration (0.4 mM), frond and root growth rates were reduced by 37% and 94%, respectively, and visible chlorosis developed from 0.1 mM onward. Pr induced oxidative stress in L. minor , as evidenced by significantly elevated hydrogen peroxide and malondialdehyde levels at 0.3–0.4 mM. These changes were accompanied by marked alterations in antioxidant and detoxification-related enzyme activities, including a 76% increase in glutathione S-transferase activity at 0.4 mM Pr. Overall, the combined physiological and biochemical data demonstrate that L. minor readily accumulates praseodymium, which induces pronounced growth inhibition and oxidative stress at elevated concentrations. These findings provide element-specific quantitative evidence of Pr toxicity in L. minor . The strong accumulation capacity of this duckweed indicates potential relevance for Pr removal from contaminated waters, while also showing a possible route for Pr, and presumably other REEs, to enter aquatic food webs.