ABSTRACT
It is important to understand the spatial distribution characteristics and health risks of soil heavy metals for the implementation of soil pollution control measures in different levels and regions. Based on the data of 706 core studies in the last 20 years, the spatial distribution characteristics, accumulation degree, and health risks of soil heavy metals in China were analyzed at the provincial level. The results showed that the soil heavy metals had obvious spatial differences on the provincial scale, with an overall trend of "high in the south and low in the north and high in the east and low in the west." The content of heavy metals in the soil of agricultural land and construction land was high, and the rate of exceeding the standard was higher than that of other land types. Soil heavy metal concentrations in most areas of China were higher than the regional background values and were highly cumulative. The accumulation indices were:Cd(1.80)>Pb(0.23)>Cu(0.17)>Zn(-0.05)>As(-0.56)>Cr(-0.69), with more than 85% of the provincial soils reaching moderate levels of Cd pollution. Non-ferrous metal resource-based provinces such as Yunnan, Guizhou, Guangxi, Hunan, and Jiangxi generally had higher soil heavy metal levels than those in other provinces, and local children faced higher cancer risks. Soil pollution in coastal areas such as Fujian, Zhejiang, Jiangsu, and Tianjin mainly originated from industrial production and urbanization construction. High intensity agricultural utilization was an important cause of soil heavy metal accumulation in Henan, Shandong, and Anhui.
ABSTRACT
In this study, we analyzed 247 soil and 20 groundwater samples from a typical chemical site in the Guangdong-Hong Kong-Macau Greater Bay Area and simulated the solute transport of pollutant benzene with the GMS software, in order to reconstruct the distribution and migration mechanism of benzene series (BTX) pollutants. The detected concentrations of benzene, ethylbenzene, m,p-xylene, and o-xylene exceeded the screening values in some soil and groundwater samples, indicating that the pollution of BTX in shallow groundwater was serious. Our simulation indicated an elliptical flow of benzene in groundwater (from northwest to southeast), mainly through convection, dispersion, and molecular diffusion. Along the vertical direction, the BTX was mainly distributed in the form of floating benzene, and some of the constituents were dissolved in the groundwater. Due to hydrodynamic mechanisms, the dissolved benzene tended to migrate faster and had hence a greater impact on the downstream groundwater. Through the model validation and analysis, we obtained a linear fitting correlation coefficient (R2) of 0.995 between the simulated and actual monitoring values, which indicates a good agreement between these two sets of data. The model had a high prediction accuracy, and could hence accurately determine the migration and distribution characteristics of benzene. Therefore, it provides a scientific basis for the accurate control and remediation of chemical contaminated sites in the Guangdong-Hong Kong-Macao Greater Bay Area.
