Toxicological effects and risk assessment of lanthanum ions on leaves of Vicia faba L. seedlings

Vicia faba L. seedlings were hydroponically cultivated in 0–12 mg/L of extraneous lanthanum (La) for 15 d to investigate ecotoxicological effects and risk assessment of rare earth elements (REEs). The results showed that reactive oxygen species (ROS) production such as superoxide radical (O2·–) and hydrogen peroxide (H2O2) were overproduced at higher concentrations of La, resulting in oxidatively modified proteins and shoot growth retardation. While, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) isoenzymes were elevated to some extent to eliminate excess of ROS. HSP70 production and endopeptidase isoenzymes were also enhanced, which were involved in repairing or degradation of the oxidatively modified proteins due to La. Thus, the antioxidant isoenzymes, endoprotease isoenzymes and HSP70 worked cooperatively to alleviate the La-induced oxidative damage. The significant enhancement of CAT and APX isoenzymes and HSP70 could also be used as early bioindicators of La-polluted solution. The threshold dose range was firstly delimited as 1–2 mg/L of extraneous La, corresponding to 7.34–9.37 μg/g dry weight in the leaves. These results would be helpful to further understand the toxicological effects and possible mechanisms of REE(s) on crop seedlings.