The toxicology of particulate matter emitted from coal combustion and the geological origin of lung cancer epidemic in Xuanwei City, Yunan Province, China

Xuanwei City in Yunnan Province is the area struck by the most severe lung cancer in China, with the incidence and mortality of lung cancer ranking first in the world. The study of genomics of lung cancer patients has shown that lung cancer in Xuanwei City has distinctive genetic characteristics and a unique incidence mode related to the environment. This study reviewed the epidemiological characteristics of the lung cancer epidemic in Xuanwei, as well as the level of pollution and toxicological characteristics of emissions from coal combustion. Moreover, this study discussed the geological origins of the lung cancer epidemic in the city by combining the geochemical characteristics of coal seam C₁ formed at the end of the Permian. The epidemiological characteristics of the lung cancer epidemic in Xuanwei are as follows: (1) The mortality ratio of male to female patients approximates to 1.22, indicating a significantly higher mortality rate of female patients; (2) From 1973 to 2016, the lung cancer mortality exhibited a trend of first increase and then decrease, and the areas with a high incidence of lung cancer constantly expanded. Previous studies proposed that a major predisposing factor of lung cancer in Xuanwei City is long-term exposure to high-concentration particulate matter emitted from indoor coal combustion. As shown by the review of toxicology studies, compared to other areas, the particulate matter emitted from indoor coal combustion in Xuanwei City contains higher concentrations of heavy metals, polycyclic aromatic hydrocarbons, and microcrystalline quartz minerals, which have been confirmed to be able to induce more severe DNA damage and cell destruction. As indicated by a comparison of the spatial distribution of the lung cancer mortality and the distribution of coal seams in different coal mines in Xuanwei City, the Laibin and Longchang coal mines, where the recoverable coal seams contain coal seam C₁, are areas with a high incidence of lung cancer. Therefore, it can be inferred that the high incidence of lung cancer in Xuanwei may be related to the combustion of coals from coal seam C₁. As the last coal seam of the Late Permian, coal seam C₁ was subjected to the Permian-Triassic mass extinction event during its coal formation, forming unique geochemical characteristics. In addition to occurring in coals from coal seam C₁, potential carcinogens including high concentrations of heavy metals, polycyclic aromatic hydrocarbons, and microcrystalline quartz minerals are also released into the air along with indoor coal burning and enter the human body through the respiratory system. As a result, they damage cells and DNA structure and cause a series of respiratory diseases, such as lung obstruction, pneumonia, and even lung cancer.