Reagent-Assisted Phytoextraction Potential for Heavy and Critical Metals on a Contaminated Post-Mining Substrate as NBS

Restoring contaminated and degraded land, including post-mining sites, industrial areas, and urban brownfields, is central to sustainable land management, and nature-based solutions (NBSs) such as phytoextraction can combine soil remediation with wider landscape-restoration goals. This screening-stage pot study evaluated how three mobilising agents, potassium iodide (KI), calcium chloride (CaCl2), and ammonium chloride (NH4Cl), applied at 20, 50, and 80 mg kg−1 against a common citric-acid background, affect the uptake and translocation of 27 potentially toxic elements and critical raw materials in Brassica juncea and Cichorium intybus grown on a met-al-contaminated post-mining substrate from Srednogorie, Bulgaria, which is used as a model of severely degraded technogenic material relevant to industrial and urban brownfield conditions. Bioconcentration and translocation factors were calculated from XRF measurements of the substrate, root, and leaf tissue and examined descriptively with exploratory principal component analysis and clustering, since each combination was one composite sample. Plant species identity, rather than reagent, was the strongest determinant of accumulation: Brassica juncea more often retained Y, Sr, Th, and Zn in roots, whereas C. intybus translocated Rb, Sr, Pb, and Cu more readily to leaves. KI produced the most distinct profile, increasing root and, at the highest dose, shoot enrichment of V, whereas CaCl2 and NH4Cl mainly enhanced root retention with limited, non-monotonic effects on shoot transfer. These species- and element-specific strategies indicate screening-stage potential for phytoextraction, pending validation with replicated biomass and yield data.