Magnetic Response of Heavy Metal Pollution in Playground Dust of an Industrial Area

Abstract

The use of mineral magnetic measurements as a potential pollution proxy is explored as an alternative means of monitoring heavy metal pollution in playground dust in industrial areas. Dust samples were collected from playgrounds in an industrial area in Nanjing. The magnetic properties of the samples were analyzed, and the total and acid-extractable concentrations of heavy metals were measured.Mineral magnetic concentration parameters[mean magnetic susceptibility (χlf) 939.31×10-8 m3·kg-1 and saturation isothermal remanent magnetization (SIRM) 16618.74×10-5 A·m2·kg-1] indicate that the dust samples contain high concentrations of magnetic minerals when compared to the non-industrial zone of the city. High and stable S-ratio values (mean 0.97, standard deviation 0.01) indicate the prominence of ferromagnetic minerals. Low values of anhysteretic remanent magnetization (χARM)/χlf(2.35) and χARM/SIRM (0.12×10-3 m·A-1) indicate predominantly coarse pseudo single domain (PSD) and multi-domain (MD) magnetic grain size assemblages. The playground dust is considered moderately to highly polluted, and the enrichment factor values for Cd, Zn, Cu, and Pb indicate extremely high contamination levels in the playground dust. Mineral magnetic parameters[χlf, SIRM, hard isothermal remanent magnetization (HIRM), χARM, and χARM/SIRM] reveal significant correlations with total and acid-extractable concentrations of the trace metals, and the correlations with total concentrations are stronger. The most significant correlations were found with mineral magnetic concentrations (χARM and SIRM) and total concentrations of the elements Mn, Ni, and Cr and the Tomlinson pollution load index (PLI) (0.69 ≤ r ≤ 0.86, P<0.01). Consistent spatial characteristics between them were also found, showing that the total concentrations of heavy metals and magnetic parameter values are higher in the playgrounds near and downwind of the power plant. Results of a principal component analysis indicate that anthropogenic activities (mainly from coal consumption by power plants) are the main sources for both heavy metals and magnetic minerals. In summary, significant correlations and consistent spatial characteristics between heavy metal contents and magnetic parameters and the same anthropogenic source for heavy metals and magnetic minerals confirm that magnetic parameters could be considered as efficient indicators for heavy metal contamination in the playground dust in industrial areas.