Amplified growth and heavy metal toxicity of Chlorococcum sp. from exposure to low-dose Lanthanum(III)

Rare earth elements (REEs) are extensively utilized in industry, agriculture, advanced materials and other fields, leading to their dispersion in water bodies as emerging contaminants. Meanwhile, the coexistence of REEs and heavy metals (HMs) has become a novel form of water contamination (REE-HM co-contamination), though scientists have limited understanding of its hazards. Here, Chlorococcum sp. cultured in Taihu Lake water was selected to examine the effects of low-dose lanthanum(III) [La(III)] on its growth and HM accumulation. Low-dose La(III) (0.5-30 μg/L) promoted algal growth and increased the contents of Cd (136.7%), Pb (92.0%), and Cr (84.3%), along with the bioconcentration factor of Cd (135.5%), Pb(91.7%), and Cr(84.0%) in Chlorococcum sp. These changes were attributed to La(III)-induced adaptive physiological regulations, including essential element uptake, photosynthesis, and antioxidant enzyme activities, achieved through La(III)-enhanced clathrin-mediated endocytosis. In summary, low-dose La(III) increased the growth and HM accumulation of Chlorococcum sp. in REE-HM co-contaminated water. This phenomenon amplified the toxicity of Chlorococcum sp., causing the HM accumulation in predators in the grazing food chain and posing a new threat to aquatic ecosystems.