Pollution Characteristics and Risk Assessments of Mercury in the Soil of the Main Regions in a China’s Typical Agricultural County: Dehui

Abstract Dehui county is a typical agricultural area, with cultivated land accounting for more than 70% of the total land area. It has become a national agricultural demonstration area of "high yield, high quality and high efficiency". As a typical agricultural county in northeastern China and with the only title “China’s famous food city” in all the county-level cities, the environmental conditions of the soil in Dehui County with over 100 years city history face high ecological risks. In the present study, in order to more fully understand the characteristics of the soil mercury content and its related health risks in the main areas of Dehui County, the pollution degrees were evaluated using the data of land accumulation indexes (Igeo), potential ecological risk indexes (Er), and health risk assessment methods. The mercury content (TSM) levels in the soil, along with the atmospheric mercury content (TGM) levels, were analyzed. The results showed that the mean value of the mercury content in the soil in Dehui County was 0.0481 ± 0.0866 mg/kg, and the concentration range was between 0.0055 and 0.8155mg/kg. It was found that the mercury content levels in 34% of the soil samples exceeded the background value of soil (0.040 mg/kg). There was no significant correlation between atmospheric mercury concentration at 0 cm and soil mercury content. This may be due to the obvious migration of surface soil and fugitive dust due to the scouring of urban streets by runoff, which affects the distribution of mercury in surface soil. In addition, the low population density of small towns, the small number of large centralized coal-fired boilers, the low height of exhaust funnel and the absence of mercury removal measures for tail gas lead to the multi-source dry and wet deposition of atmospheric mercury on the surface. The mercury content levels in the soil were found to vary from different directions, with the mercury content found to be the highest in the central and eastern section of the county. However, there were no significant differences in mercury content of any direction. Igeo showed that 24.0% of the sample points were polluted. The insanitary areas were mainly concentrated in the central and western sections of the county. The mercury content levels in the soil of Dehui County ranged from pollution-free to mild pollution levels overall. The Er indicated that the potential ecological risk level was high in the central and eastern sections of Dehui County. However, the soil mercury levels in Dehui County presented a low level of ecological risk overall. The average values of the non-carcinogenic risks (HQ) and the total non-carcinogenic risk assessment indexes (HI) in all directions within Dehui County were determined to be far less than 1. Therefore, it was concluded that the soil mercury levels were not potentially harmful to human health.