What are exposure biomarkers of rare earth elements for the ionic rare earth occupational population?

Rare earth elements (REEs) are widely utilized in industries. However, The specific exposure features of REEs and potential biomarkers of exposure in occupational populations remain unclear. In this study, we evaluated the external and internal REEs exposure levels among the participants working in the ionic rare earth smelting plant. For the external exposure, the concentrations of 14 REEs and total rare earth elements (ΣREEs) in airborne particles were significantly elevated in the REEs-exposed versus non-exposed group (P < 0.05). Meanwhile, the levels of Yttrium (Y), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Thulium (Tm), Ytterbium (Yb), and ΣREEs in urine were higher in the REEs-exposed group compared to the non-exposed group (P < 0.05). Notably, a significant positive correlation was observed between Y in both the airborne particles and urine samples as well as Gd, and the Spearman correlation coefficient was 0.53 and 0.39 respectively, both P < 0.05. Conversely, no statistically significant differences were found in the levels of 15 REEs or ΣREEs in the blood samples between the REEs-exposed group and non-exposed group. Moreover, the concentrations of ΣREEs and 9 REEs in nail samples of the exposed group were significantly higher than those of the non-exposed group (P < 0.05), and the composition ratios of REEs in the nail samples closely resembled those found in individual airborne particles. Therefore, nail and urine samples were proposed to reflect long-term and short-term exposure to ionic rare earth respectively. Exposure biomarkers confirmed by external and internal exposure characteristics accurately provide the situation of human exposure to REEs environment, and have profound significance for monitoring and evaluating the level of REEs pollution in human body. It also provides a vital basis to find out the effect biomarkers, susceptible biomarkers and the health effects of rare earth environment for the future research.