Bioaccumulation and translocation of rare earth elements in Medicago sativa L. grown in coal fly ash-amended substrates

A greenhouse pot experiment investigated the bioaccumulation and translocation of Cerium (Ce), Erbium (Er), Europium (Eu), Neodymium (Nd), and Praesodymium (Pr) in Medicago sativa L. grown in a substrate amended with 0, 20, 30, and 40% coal fly ash (CFA, w/w). Bioaccumulation factors (BAF) were highest in the unamended control, indicating that CFA loading reduced uptake efficiency consistent with pH-driven REE immobilization. Shoot REE concentrations exceeded root concentrations for most elements at later growth stages, with Eu dominating accumulation, peaking at 304.44 µg g−1 (shoot + root) under 20% CFA at 120 days. Translocation factors (TF) exceeded 1 for most elements in specific treatments by 180 days, except Eu and Pr, which exceeded 1 across all treatments, with plant maturity emerging as a critical determinant of REE distribution between roots and shoots. CFA amendment stimulated shoot biomass production and increased shoot REE accumulation for all five elements at later growth stages, with the optimal amendment rate shifting between growth stages. These findings suggest that Medicago sativa has meaningful potential for REE accumulation from CFA-amended substrates, particularly for Eu, Nd, and Pr, and that plant maturity and amendment rate should be considered jointly when evaluating phytoextraction strategies in CFA-amended systems.