Biomonitoring of air pollution in SW Finland by magnetic and chemical measurements of moss bags and lichens

摘要

Mosses and lichens are among the best biogenic dust collectors and these can be used in detailed studies of airborne pollutants. In this study, magnetic and chemical measurements were performed on moss bags collected from urban (Turku City) and industrial (Harjavalta City) areas of SW Finland, to study the relationship between concentration of anthropogenic magnetic particles and heavy metals. The main source of air pollution in the urban site is heavy traffic while in the industrial site it is a Cu-Ni smelter. Additionally, the representative lichen samples were selected from the urban site for detailed magnetic and chemical studies, on the basis of volume magnetic susceptibility mapping (κ). The moss bags and lichen samples were collected near the roads and from city parks in the urban site. In the industrial site the moss bags were collected around a Cu-Ni smelter. The significant enhancement of mass magnetic susceptibility (χ) was observed near the main pollution sources (roads, Cu-Ni smelter) in both sites. A decreasing trend in χ and concentration of heavy metals with increasing distance from the pollution source was noticed in the investigated samples. Most of the examined heavy metals show a strong significant correlation with χ. Moreover, the Tomlinson pollution load index (PU) exhibits significant correlation with the χ. The magnetic mineralogy of the samples from both sites is dominated by a magnetite-like phase. Thermo-magnetic analysis revealed stoichiometric and non-stoichiometric magnetite in the samples collected from urban and industrial sites, respectively. Hysteresis parameters and FORCs (first-order reversal curves) of lichen samples indicate a mixture of PSD/MD (pseudo-single domain/multi-domain) magnetite as the main magnetic fraction. The angular-shaped particles prevail in the road dust of Turku city, while the iron-rich spherules are predominant in the fly ash from the Cu-Ni smelter. This study demonstrates that magnetic measurements of moss bags and lichens can be effectively applied to monitor the temporal and spatial distribution of heavy metals and trace the sources of anthropogenic pollutants.