Mapping dust distribution around an industrial site by measuring magnetic parameters of tree leaves

In recent years magnetic measurements were increasingly used as a proxy for the heavy metal content in soils and sediments influenced by industrial emissions. But sometimes it is difficult to judge if the measured distribution really reflects the present situation or if it is a product of past industrial activities. Therefore, we tested in how far magnetic measurements of tree leaf samples can give information on the current spread of magnetic dusts. We sampled maple leaves at 102 locations in and around the industrial city of Leoben in Austria and determined magnetic susceptibility, isothermal remanent magnetization (IRM) at 1 Telsa(T), the S-ratio (IRM−100mT/IRM1T) and the ratio of IRM to susceptibility (IRM/κ). The distributions of S-ratio and IRM/κ showed that one soft ferrimagnetic phase is dominant over the whole investigated area. This finding was corroborated by scanning electron microscopy (SEM) analysis of the leaves. A comparison with a map of soil magnetic susceptibility revealed that the location of the main source has been the same over a long-time span. The correspondence of the soil map and the leaf map is a convincing proof of the suitability of the method to monitor ongoing emissions.