Patterns And Magnetic Response To Heavy Metal Pollution Along Urban-rural Gradient, Shanghai

Environmental magnetism has been widely used to characterize the pattern of urban environmental. But, little research has been performed to systematically reveal the spatial pattern of heavy metals and magnetic characters along urban-rural gradient in Shanghai. Nearly no regional magnetic distribution pattern using dust-loaded tree leaves was described in published papers in Shanghai. In this study, a total of97soil and82dust-loaded tree leaves samples was collected spatially from17districts along urban-rural gradient in Shanghai. Magnetic properties, heavy metal contents, scanning electron microscope-energy dispersive X-ray (SEM-EDX) measures, combined with multivariate statistics and GIS methods were used to characterize the spatial pattern of soil and dust-loaded tree leaves along urban-rural gradient of Shanghai. The paper found the significant positive between magnetic parameters and heavy metal contents in soil and dust-loaded tree leaves, identified the source of heavy metal and magnetic particles in a multi-pollution sources area, and established a magnetic evaluation system for assessing soil and atmosphere environment quality. The major results as follows:(1) The average concentrations of heavy metals were increased over the corresponding background values of the soils in Shanghai. The heavy metals contents in soils were differ among various functional areas.(2) Different pollution level was found among four land use types soils in Shanghai. The soils in parks were moderate polluted, while the soils in residential areas, Baoshan Iron and Steel Plant and Longwu roadside were all heavily polluted. Cd in the soils collected from parks and residential areas, Zn and Cd inside the Baoshan Iron and Steel Plant, and Zn, Cd, and Pb along Longwu Road were the most polluted elements.(3) The heavy metal pollution degree in soils of parks and residential areas soils was gradually decreased along urban-rural gradient. Significant difference of heavy metal content between urban and rural, suburban and rural was found in parks and residential areas soils (P＜0.05).(4) The spatial distribution of average contents of heavy metals in dust-loaded tree leaves was different among four land use types. The Cr, Zn, and Cu contents in dust-loaded tree leaves of different functional areas were ranked as Baoshan Iron and Steel Plant＞Longwu Roadside＞residential areas＞parks, and the Pb content was ranked as Longwu Roadside＞Baoshan Iron and Steel Plant＞residential areas> parks. Ni content had no difference in samples from all functional areas except Baoshan Iron and Steel Plant. Average content of Pb was gradually increased along urban-rural gradient in parks leaf, but the average contents of Cr, Ni, Zn, Cu, Pb in residential areas leaves were gradually decreased along urban-rural gradient.(5) The magnetic parameters showed that ferromagnetic/ferrimagnetic particles were the main magnetic carriers in soils and dust-loaded tree leaves, and magnetic grains were predominantly pseudo-single domain (PSD) and multidomain (MD) in size. The soils in each land use type along urban-rural gradient in Shanghai were polluted more or less according to x values.(6) Significant positive correlations (P<0.01) were found between x, xARM, SIRM and Cr, Zn, Cd, Pb in soils, and Ni, Cr, Zn, Cd, Cu, Pb in dust-loaded tree leaves, which indicating the same source of heavy metals and magnetic particles in soils and leaves. The magnetic parameters like x, XARM, SIRM could be used as a proxy for heavy metal contents.(7) Baoshan district is a multi-source of pollution area in Shanghai. In this paper, this area was selected to indentify different sources contributing to observed pollution in Baoshan district, x,xARM, SIRM, Cr, Zn in Baoshan district soil samples were mainly from industrial pollution source; Cu, Cd, Pb were in Baoshan district soil samples mainly from traffic pollution source; HIRM was controlled by multi-source of industrial pollution and Ni was mainly controlled by parent materials in Baoshan district soil samples.x,xasm, SIRM, Cr, Ni, Cu, Zn in dust-loaded tree leaves were mainly from industrial pollution source, and also controlled partly by traffic pollution source. HIRM, Cd, Pb in dust-loaded tree leaves were mainly controlled by traffic pollution source.(8) A magnetic evaluation system for assessing soil and atmosphere environment quality was established according to the significant positive correlations between magnetic parameters and heavy metals contents in soils and dust-loaded leaves.1) In soil samples, when x, SIRM were0-29.1x10-8m3kg-1and0-2371×10-6Am2kg-1, respectively, the soil environment was clean; when x, SIRM were29.1-40×10-8m3kg-1and2371-5228×10-6Am2kg-1, respectively, the soil environment was slightly polluted; when x, SIRM were40-132×10-8m3kg-1and5228-17904×10-6Am2kg-1, respectively, the soil environment was moderate polluted; when x＞132×10-8m3kg-1and SIRM>17904×10-6Am2kg-1, the soil environment was heavily polluted.2) In dust-loaded tree leaves, when SIRM was0-242×10-6Amkg-1, the air environment was clean; when242＜SIRM＜473, the air environment was slightly polluted; when473＜SIRM＜1345, the air environment was moderate polluted; when SIRM＞1345×10-6Am2kg-1, the air environment was heavily polluted.