Environmental impacts of 222Rn, Hg and CO2 emissions from the fault zones in the western margin of the Ordos block, China

Investigating the emissions of soil gas including radon, mercury and carbon dioxide (Rn-222, Hg and CO2) from the solid earth to the atmosphere through active fault zones is of great significance for accession of atmospheric environment. In this study, the concentrations and fluxes of Rn-222, Hg and CO2 were measured at the main active fault zones at the western margin of the Ordos block, China. The concentrations of Rn-222, Hg and CO2 were in the range of 0-60.1 kBq m(-3), 3-81 ng m(-3) and 0.04-9.23%, respectively, while the fluxes of Rn-222, Hg and CO2 are in the range of 1.99-306.99 mBq m(-2) s(-1), 0-15.12 ng m(-2) h(-1) and 0-37.91 g m(-2)d(-1), respectively. Most of the major fault zones at the study area are CO2 risk-free regions (CO2 concentration in soil gas < 5%). However, the extend of Rn-222 pollution at the fault zones of F-1, F-4, F-5 and F-9 (the fault number) and that of Hg pollution at the fault zones of F-2, F-4, F-5 and F-7 were higher than the pollution level of 1. The annual emission of Hg and CO2 from the western margin of the Ordos block was estimated to be 2.03 kg and 0.70 Mt, respectively. Comprehensive analyses indicated that the higher emission rates of soil gases from the active fault zones were related to the seismic activities. The results suggest that the earthquake activity is a dominant factor enhancing the emission of Rn-222, Hg and CO2 from the solid earth through active fault zones and, furthermore, resulting great impact on the atmospheric environment.