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A detailed magnetic study of urban soils in Hangzhou City, China, was carried out using combined environmental magnetism and rock magnetism techniques. Magnetic measurements showed that those urban soils have a significant magnetic enhancement, which were characterized by higher magnetic susceptibility (average 128 × 10–8 m3·kg–1) and magnetic remanence, and low frequency-dependent susceptibility (average 3.6%, N=182). Magnetic susceptibility values of urban soils showed highly significant negative correlation with frequency-dependent susceptibility, indicating that the mechanism of the magnetic enhancement of urban soils is different from contribution of pedogenic ferrimagnetic minerals in nature soils. Magnetic susceptibility values of urban soils, on the other hand, have significantly positive correlation with Soft IRM (IRM20mT) and saturation isotherm remanent magnetization (SIRM), suggesting that ferrimagnetic minerals are the main magnetic carriers. The combined rock magnetism (acquisition curves of IRM, temperature-dependent susceptibility and hysteresis measurement) and SEM/EDX (scanning electron microscopy and energy dispersive X-ray analysis) revealed that magnetic mineralogy of urban soils is dominated by magnetite-like and hematite-like phases. The hysteresis parameters suggested that they are present mainly in the pseudo-single domain (PSD) and multidomain (MD) grains, which is attributed to input of anthropogenic magnetic grains from industrial activity, fuel combustion and traffic pollution. This finding suggested that magnetic measurements could be used as potential tools for monitoring soil pollution, mapping spatial distribution of pollution, and differentiating source of pollutants in urban soils. |
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