Magnetic properties as indicators of heavy metals pollution in urban topsoils: a case study from the city of Luoyang, China

This paper deals with the magnetic properties [magnetic susceptibility, saturation isothermal remanent magnetization (SIRM), magnetomineralogicl parameters], the contents of heavy metals (Fe, Mn, Cd, Cr, Cu, Pb and Zn) and their mutual relationship in the urban topsoils of Luoyang, China. Magnetic susceptibility measured on 215 urban topsoil samples ranged from 31 x 10(-8) to 1128 x 10(-8) m(3) kg(-1) (average 215 x 10(-8) m(3) kg(-1)) and showed that high magnetic susceptibility values were obtained on topsoil samples from industrial areas (average 313 x 10(-8) m(3) kg(-1)) and roadside (236 x 10(-8) m(3) kg(-1)), whereas lower susceptibility values were observed in parks and green areas (123 x 10(-8) m(3) kg(-1)). The urban topsoils were enriched with Cd, Cr, Cu, Pb and Zn, with average contents of 1.71, 30.51, 85.40, 65.92 and 215.75 mg kg(-1), respectively. The heavy metals Cr, Cu, Pb and Zn show a statistically significant correlation with magnetic susceptibility and SIRM. The Tomlinson Pollution Load Index (PLI) also shows significant correlation with magnetic susceptibility and SIRM, indicating that the magnetic parameters can provide a proxy method for identifying the heavy metal pollution in urban topsoils. Rock magnetism and X-ray diffraction analyses revealed that the dominant magnetic mineral in the urban topsoils is anthropogenic pseudo-single domain (PSD)-multidomain (MD) magnetite. These magnetic particles are associated with the industrial activities, traffic exhaust and deposition of atmospheric particulate.