Mexico City topsoils: Heavy metals vs. magnetic susceptibility

The degree of anthropogenic impact in the urban environments can be evaluated in terms of metal concentration of soils, often established in terms of integrated pollution index (IPI). Detailed geochemical investigations on urban soils require a great amount of chemical analyses, which are time consuming and expensive. The magnetic susceptibility signal detected in some urban topsoils is mainly attributed to the ferromagnetic components of anthropogenic origins, which include in their molecules a portion of heavy metals. Therefore, the application of susceptibility measurements of soils allows the assessment of polluted areas reducing the amount of chemical analyses. The magnetic survey reported here for first time on Mexico City's topsoils tries to establish the link between magnetic proprieties and the content of heavy metals (Fe, Pb, Cu, Zn, Ni, Cr and V). The best correlation between susceptibility values and the heavy metal content was found for highly contaminated samples yielding susceptibility values higher than 400 χ × 10− 8 SI. In contrast, low contamination levels (metals contents near to background values) don't have significant correlation with magnetic susceptibility. The results show that magnetic susceptibility has a significant correlation with IPI, Fe, Cu and Zn. It is concluded that magnetic susceptibility can be used as a first approach for heavy metal contamination in terms of IPI, allowing to recognize areas that would require a detailed chemical study.