Distribution of magnetic susceptibility of surface dust in Xining City and its indicative significance to heavy metal pollution

^a Key Laboratory of Surface Processes and Ecological Conservation on the Qinghai-Tibetan Plateau, Qinghai Normal University, Xining 810008, China
^b Qinghai Normal University, School of Geographic Sciences, Key Laboratory of Natural Geography and Environmental Processes of Qinghai Province, Xining 810008, China
^c Qinghai Provincial People's Government - Institute of Plateau Science and Sustainable Development, Beijing Normal University Xining 810008, China

^* echongyi@163.com

Abstract

The establishment of heavy metal pollution grade standards based on the magnetic susceptibility of surface dust can provide a simpler magnetic method for the evaluation of heavy metal pollution of surface dust. A total of 251 urban soil surface samples were collected in Xining City, and As, Cd, Cr, Cu, Ni, and Pb were determined V and Zn contents, as well as low-frequency magnetic susceptibility (χ_LF) and high-frequency magnetic susceptibility (χ_HF). The common Kriging interpolation method was used to explore the spatial distribution of χ_LF, and the pollution load index (PLI) was used to evaluate the degree of soil heavy metal pollution, and the correlation analysis between PLI and χ_LF was established。 The results showed that the average PLI of the seven heavy metals in the urban soil samples of Xining City was 2 34. Moderate pollution, Zn is the most important pollution factor. The average value of soil χ_LF was 125. 7 × 10^-8m³ kg^-1, which decreased from “northwest-southeast”, and the high-value area appeared in the northwest near Xining Special Steel along the line. The regression equation between soil heavy metal PLI and χ_LF was y=3.36E-06x2+0.01x+0.9092, showing a significant positive correlation (p<0.01). The χ_LF of surface dust can be used to evaluate the degree of heavy metal pollution of surface dust in Xining City: when the χLF of surface dust is ≤66.05 × 10-8m3 kg-1, it is pollution-free; When 66.05 × 10^-8m³ kg^-1<χ_LF≤437.332 × 10^-8m³ kg^-1, it is slightly polluted. When 437.332 × 10^-8m³ kg^-1<χ_LF≤652.02 × 10^-8m³ kg^-1, it is moderately polluted. When χ_LF > 652.02 × 10^-8m³ kg^-1, it is an intensity pollution.