Environmental exposure to rare earth elements and respiratory health: an emerging public health concern

Rare earth elements (REEs) are increasingly released into the environment due to intensive mining, industrial processing, and expanding technological applications, resulting in widespread human exposure. Within the respiratory exposome framework, REEs have increasingly been recognized as a potentially important class of airborne contaminants. Fine and ultrafine REE-containing particles can penetrate deeply into the distal lung, where they exhibit high biopersistence and limited clearance. Epidemiological evidence from mining and industrial regions suggests that elevated internal REE burdens may be associated with increased prevalence of respiratory symptoms and chronic lung diseases, including bronchitis and interstitial lung disease. Toxicokinetic and experimental studies provide mechanistic support, demonstrating that inhaled REEs preferentially deposit in the alveolar region, interact with epithelial and immune cells, and may translocate into systemic circulation. At the molecular level, REEs have been shown to induce oxidative stress, immune and inflammatory dysregulation, and calcium homeostasis imbalance in experimental models, thereby promoting tissue injury and remodeling. These processes may contribute to a progressive pathological continuum from persistent inflammation to fibrosis and, potentially, tumorigenesis. Notably, exposure characteristics-including particle physicochemical properties, dose, co-exposure scenarios, and host susceptibility-critically shape health outcomes in real-world settings. Despite accumulating evidence, key uncertainties remain regarding human-relevant exposure thresholds, long-term dose-response relationships, and validated biomarkers of effect. Current knowledge is still largely derived from experimental models, with limited integration into population-based risk assessment. Overall, this review uses a structured literature search and narrative synthesis approach to integrate environmental exposure pathways, toxicokinetic characteristics, and mechanistic evidence within an exposome-oriented framework. It highlights that REEs represent emerging inhalation hazards with the potential to contribute to the burden of chronic respiratory diseases, underscoring the need for improved exposure assessment, biomonitoring strategies, and evidence-based public health interventions.