As increasing demand for green energy and high-tech devices grows, so does the rising prospecting of rare earth metals required for their production. Protecting the environment and public health from rare earth element (REE) mining as well as emerging pollutants is urgently required to achieve sustainable development. This study mapped Earth's hidden REE deposits to identify potential contamination hotspots with the aim of preventing its deleterious effects on the environment. We worry that there would be widespread tailing facilities concomitant with serious pollutions, such as the Bayan Obo tailings site, and argue that a tradeoff between the underground REE exploration and environment conservation should be reached as soon as possible.On a global scale, demand for rare earth elements (REE) is ever increasing, leading to rapid growth of REE production and consumption (Figure 1) because REE compounds are extensively used in modern high-tech, agriculture, and medicine products [Migaszewski and Gałuszka, 2015]. For example, REE are peppered throughout smartphones, permanent magnets, hybrid engines, wind turbines, fluorescent bulbs, solar panels etc., making them more sophisticated and small in size [Hurst, 2010;Migaszewski and Gałuszka, 2015]. The intensive geological prospecting for REE ore deposits, however, causes extreme damage to the environment [e.g., Huang, 2011;Liu, 2013]. REE ores and their mining/processing are chemically and mineralogically complex and commonly radioactive. Nearly all rare earth ores contain the radioactive elements thorium (Th) and uranium (U). For example, monazite contains relatively high amounts of ThO 2 and U 3 O 8 in the range of 0-200,000 and 0-160,000 ppm, respectively; xenotime contains a similar range (0-50,000 ppm) of ThO 2 and U 3 O 8 [Jordens et al., 2013]. REE processing often produces appreciable amounts of waste and pollution-intensive materials, including tailings, which are mixtures of crushed rocks and processing fluids from mills and/or concentrators. These REE tailings usually contain potentially hazardous contaminants, which are accumulated from rocks and additional extraction regents, because extracting a high grade of REE often involves many steps of processing/smelting/refining and requires the substantial addition of acids, alkaline, and organic solvents [e.g., Huang, 2011; Kumari et al., 2015 and Supporting Information]. In particular, the frequent occurrence of some radionuclide residues (e.g., Th, U, Rn) and their radioactive rays (e.g., alpha, beta, gamma rays) in REE tailings may also pose a radioactive threat to animal and human health. The adverse outcomes of exposure to elevated REE concentrations include growth inhibition, cytogenetic effects, and organ-specific toxicity to abiotic and biotic systems [e.g., Zhang et al., 2000;Pagano et al., 2015]. Therefore, one of the priorities for a feasible and effective facility must be to proactively isolate the REE mining waste so as to prevent it from entering groundwater, rivers, lakes, soil and air...
