Magnetic Responses To Heavy Metal Pollution In Urban Topsoil In Typical Industrial Belt In Arid Regions In Northwest China

With the rapid development of industrialization and urbanization, the problem of soil pollution becomes more and more serious and has aroused public attention both at home and abroad. Soil is not only the physical basis and support for city development but also is the central part connecting the organic and inorganic world. Soil is also an important part of diffusion and transformation of matter and energy in the system of earth’s surface. Depending on the characteristics of simplicity, rapidity, non-destructivity and high sensitivity, environmental magnetism has received much progress in monitoring and governance in soil pollution. Based on the environmental magnetism and geochemical method, we carry out an investigation on topsoil samples in Wuhai and Shizuishan along the Yellow River in arid regions in northwest China. In this study, the correlation between magnetic parameters and heavy metal concentration is discussed and the mechanism of environmental magnetism applied in urban topsoil pollution is further explored in order to monitor the pollution condition and assess the origin of contaminant. The results are as follows.Magnetic susceptibility is generally high. The main magnetic mineral is magnetite and the main magnetic grain sizes are multi-domain(MD) and pseudo single domain(PSD). The concentration and grain sizes of magnetic minerals show differences in different functional zones and magnetic parameters show obvious spatial difference. In industrial zone, the concentration is higher and the grain size is coarser, but obviously lower and finer in agricultural zone and raw coal zone.The high magnetic susceptibility is controlled by human activity. Environmental magnetic measurements are efficient to monitor pollution caused by burned fossil fuel, but are not sensitive to unburned fuel.χlf SIRM and SOFT are effective indicators to reflect urban soil pollution. The results of heavy metal concentration show that the concentration of heavy metal in industrial zone is higher than agricultural zone and raw coal zone. Three zones are all affected by light pollution but the industrial zone is the most serious. It is very important to reduce pollution emission and have a rational industrial distribution plan.In different functional zone, different magnetic parameters have different environmental significance. The correlation analysis between magnetic parameters and heavy metal concentration, the cluster analysis and principal component analysis indicate that magnetic parameters reflecting the concentration of magnetic minerals can be used as indicators of heavy metal pollution in industrial zone, magnetic parameters reflecting the grain size of magnetic minerals can be used as indicators of heavy metal pollution in agricultural zone, the correlation between magnetic parameters and heavy metal pollution is not obvious in raw coal zone. Environmental magnetism is an effective method to evaluate heavy metal pollution in urban soil.