Polycyclic aromatic hydrocarbons in soil of the backfilled region in the Wuda coal fire area, Inner Mongolia, China

摘要

The Wuda coal fire area in Inner Mongolia, China, has existed for 50 years and been controlled by digging and backfilling for many years. However, few studies have focused on its impact on the local environmental and ecological systems due to emission of organic contaminants from the backfilled region. In the study, topsoil samples were collected at a 0-5 cm depth from the backfilled region of the Wuda coal fire area, which has existed for five years. The samples were analyzed for 16 priority control contaminants, namely polycyclic aromatic hydrocarbons (PAHs), with a standard operation procedure and high-performance liquid chromatograph (HPLC). The results showed that the total mass contentration of 16 PAHs (Sigma(16)PAHs) ranged from 279 to 8258 mu g kg(-1), with an average value of 2853 +/- 2948 g kg(-1), which exceeded the stipulated limit for heavily contaminated soil (1000 mu g kg(-1)). Among the 16 PAHs, 2- and 3-ring compounds accounted for more than half of Sigma(16)PAHs. Furthermore, the results show that the main contaminants were the naphthalene (Nap), phenanthrene (Phe), pyrene (Pyr), chrysene (Chr), and benzo[b]fluoranthene (BbF) in this area (24.8%, 51.1%, 3.9%, 4.5%, and 5.7% of Sigma(16)PAHs, respectively). The diagnostic ratio of FLA/(FLA + PYR) exceeded 0.4 and IcdP/(IcdP + BghiP) was less than 0.5, indicating gentle smoldering or spontaneous combustion of coal fire, which differs from traditional coal burning. The environmental health risk or specifically the cancer risk (CR), calculated using the surface soil of the backfilled region, was 2.84 x 10(-6) for adults and 1.01 x 10(-6) for children, thus indicating potential cancer risks. Therefore, PAHs pollution in the surface soil of the backfilled region in the studied coal fire area is an issue that deserves urgent attention.