Within the earth’s crust, radioactive elements such as uranium (U) and thorium (Th) exist; creating a field of radiation that can vary depending upon the specific location’s geology. Typically, most coal mines around the world will have U and Th elements present in acceptable concentrations of 1-3 parts per million (ppm).
A recent study conducted by a joint effort between Duke University and China University of Mining and Technology found coal deposits containing U concentrations as high as 476 ppm.
Radioactive Decay and Its Hazards
Radioactive decay is a process in which unstable elements such as U and Th lose energy, thereby emitting radiation in various forms such as alpha and beta particles. When 238U and 232Th decay, several types of elements can arise including radium (226Ra and 228Ra), radon (222Rn and 220Rn), lead (210Pb) and Polonium (210Po) and collectively termed Naturally Occurring Radioactive Materials (NORM). While the presence of U in coal deposits has been studied previously, the concentrations of these decay elements and their possible effect upon human exposure has not been characterized prior to the study published by Duke and China.
The Importance of CCRs
As both the largest producer and consumer of approximately 50% of the coal present in the world, China is also the world’s largest producer of coal combustion residues (CCRs). CCRs, which are otherwise referred to as coal ash, arise following the burning of coal that is often used to provide power for electricity plants and other purposes. In China, CCRs can be used in a wide variety of ways such as building materials including cement and bricks, road and dam construction, structural fill and fertilizer for agriculture purposes, while the remaining 30% of CCRs will typically be deposited into coal ash ponds and landfills.
Routes of Exposure
By selectively isolating the carbon for power storage, CCRs that include a variety of elements such as U and Th, remain in a higher concentration than before when these elements were incorporated into the pure carbon form. Uranium enriched coal deposits in China can be found throughout the northwestern, southwestern and southern provinces, all of which exhibit concentrations that greatly exceed several hundred ppm.
The extraction of such U-rich coals in these mines therefore poses a serious risk to workers who can become easily exposed to such high levels of radiation. Long-term exposure to radiation can induce a variety of health effects including cancer, nausea, skin burns, hair loss, reduced organ function and even death.
The enriched presence of harmful radionuclides in the CCRs can significantly limit the safe application of these materials for industrial purposes. For example, if CCRs are incorporated into construction materials that are used to build walls of a building, there is a high risk of human exposure that can result from the presence of the radioactive decay particles and NORM. Concentrations of U in building materials that measure 10 ppm or higher therefore pose a serious radiation risk for materials used in residential and business buildings.
The potential of CCRs to migrate within the ambient environment as well as enter water supplies also poses a serious health hazard for humans. Bioaccumulation in the air could result in the inhalation of very radioactive particulate matter, whereas bioaccumulation of these materials in our water supplies could also eventually lead to human consumption of these extremely harmful elements.
By determining the potential hazards that can be associated with the use of such radioactive coal and CCR products should push the Chinese government to look to other coal deposits that may be safer for human use. While the push for more environmentally friendly power sources continues to grow, the traditional utilization of coal remains a primary source of power for most of the world. Therefore, if this source will continue to be mined and used for such a variety of applications, its safety must be of the utmost concern for all involved in the manufacturing process.
- “Naturally Occurring Radioactive Materials in Uranium-Rich Coals and Associated Coal Combustion Residues from China” N. Lauer, A. Vengosh, et al. Environmental Science & Technology. (2017). DOI: 10.1021/acs.est.7b03473.