Spring 2026
Despite the importance of critical minerals to the United States, occupational exposure limits for almost all rare earth elements have yet to be established, and their potential health risks are not fully understood.
In 2025, the United States Geological Survey (USGS) published its most recent list of critical minerals, consisting of 60 minerals “vital to the US economy and national security that face potential risks from disrupted supply chains” (USGS, 2025). Included in the USGS list of critical minerals are a subset of 15 rare earth elements (see Table), for which occupational exposures and health risks are not as well characterized as many of the other critical minerals. Despite the name, rare earth elements are not particularly rare. They are abundant in the Earth’s crust but exist dispersed and intermingled with other minerals, making them challenging to obtain and process into more concentrated forms (Balaram, 2019).
Workers employed in the mining of rare earth elements are subject to human health risks posed by a number of potential hazards. Some hazards are associated with mining operations in general and are not unique to rare earth element mining. These include, for example, exposure to noise, thermal stress, diesel engine exhaust, and chemicals that co-exist with rare earth elements in the Earth’s crust, such as silica, lead, and arsenic (Gendron, 2024). Other hazards are more prominent in rare earth element mining and processing than in most other mining contexts, including exposure to radiation and to rare earth elements themselves. Naturally occurring uranium and thorium are often present in rare earth element deposits, posing radiation risks that can impact the health of workers in rare earth element mining areas (Gendron, 2024; Yin et al., 2021). While many of the potential hazards in rare earth mineral mining are well characterized (e.g., silica, lead, and arsenic have various established recommended or regulatory exposure limits), the rare earth elements – despite increasing attention – are relatively lacking in this regard, such that their potential health risks are not fully understood (Yin et al., 2021).
Of the 17 rare earth elements, yttrium is the only one for which an occupational exposure limit (OEL) has been established.”
Rare earth elements can enter the human body through inhalation, oral, and dermal routes of exposure, with potential accumulation in different tissues or organs. Evidence informing the toxicity of the rare earth elements on various biological systems is mostly limited to cellular and animal studies and human case studies. Findings in the current literature have considerable variability, and knowledge about the relationship between exposure and health effects remains inadequate (Wang et al., 2025). As a result, established safe exposure thresholds for rare earth elements exposure are limited. Of the 17 rare earth elements, yttrium is the only one for which an occupational exposure limit (OEL) has been established. “OEL” is a general term used to reflect an airborne concentration of a chemical that serves as a recommended or regulatory exposure limit to protect worker health. Information about exposure concentrations in air that are experienced by workers in a specific work scenario can be compared to an OEL to inform decisions about management of worker health risks and whether additional controls are needed to adequately protect worker safety (e.g., additional ventilation, use of respirators, changes in work practices). For yttrium, the American Conference of Governmental Industrial Hygienists (ACGIH), Occupational Safety and Health Administration (OSHA), and National Institute for Occupational Safety and Health (NIOSH) have established an OEL of 1 mg/m3 based on limited toxicity data and industrial experience.
Understanding the toxicity of rare earth elements and the potential health risks they pose to workers in mining activities is necessary for the establishment of safe exposure guidelines, such as OELs, and for ensuring that potential health risks are mitigated through efficient management of hazards. As discussed above, critical minerals – including rare earth elements – are vital to the US economy and national security, but information on health risks and scientifically supportable exposure limits are not keeping pace. It will be important for mining industries in rare earth elements to consider the scientific uncertainty in this area, monitor emerging science, and engage in proactive worker protection and exposure management.
The authors can be reached at David.Dodge@gradientcorp.com and Steven.Boomhower@gradientcorp.com.
Balaram, V. 2019. “Rare earth elements: A review of applications, occurrence, exploration, analysis, recycling, and environmental impact.” Geosci. Front. 10(4):1285-1303. doi: 10.1016/j.gsf.2018.12.005.
Gendron, C. 2024. “The hazards of critical minerals: Assessing occupational health risks in the rare earth element mining industry.” Synergist (Akron) 35(5). Accessed on March 18, 2026, at https://publications.aiha.org/202405-rare-earth-element-mining.
US Geological Survey (USGS). 2025. “Interior Department releases final 2025 List of Critical Minerals.” November 14. Accessed on March 18, 2026, at https://www.usgs.gov/news/science-snippet/interior-department-releases-final-2025-list-critical-minerals.
Wang, X; Wang, F; Yan, L; Gao, Z; Yang, S; Su, Z; Chen, W; Li, Y; Wang, F. 2025. “Adverse effects and underlying mechanism of rare earth elements.” Environ. Health 24(1):31. doi: 10.1186/s12940-025-01178-3.
Yin, X; Martineau, C; Demers, I; Basiliko, N; Fenton, NJ. 2021. “The potential environmental risks associated with the development of rare earth element production in Canada.” Environ. Rev. 29(3):354-377. doi: 10.1139/er-2020-0115.