Rare earth elements (REE) in soils and plants of a uranium-REE mine site and exploration target in Central Queensland, Australia

Investigations on the biogeochemical behaviour of rare earth elements (REEs) in natural systems broaden our understanding on their occurrence and fate in ecosystems. The aim of this study was to assess the prevailing REE concentration patterns in soils and plants in a uranium REE-rich area in Central Queensland, Australia. We collected and analysed matching soil and plant material samples from both undisturbed and mine-affected areas enriched in REEs near the now abandoned Mary Kathleen Mine. We found that in the soil, Ce had the highest concentrations (1550 μg g−1), followed by La (645 μg g−1), whereas that of Gd (25 μg g−1) and Lu (1.5 μg g−1) were comparatively low. Soil REE patterns had a slight HREE enrichment relative to LREE, with a positive Ce anomaly, suggesting oxidizing conditions. The REE patterns of the DTPA-extracts had LREE enrichment relative to HREE. Soil pH was negatively correlated with DTPA-REE (−0.68 ≤ R ≤ -0.40; p < 0.001). In the plants, we found interspecies variation in REE accumulation, with REE concentrations higher in the dicots than in the monocots. The plant REE patterns displayed HREE enrichment relative to LREEs, and foliar REE concentrations were correlated with Mn, Fe, Mg, Al and Ca in some species (0.57 ≤ R ≤ 0.96; p < 0.05). Our findings suggest that Mn-Fe-oxyhydroxides and soil pH influenced REE accumulation patterns, while within the plant, foliar REE accumulation could be attributed to a mechanism which is common for macronutrients and certain trace metals.