Decoupling natural and anthropogenic polycyclic aromatic hydrocarbons in the soil environment

Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic organic pollutants that originate from the incomplete combustion of organic matter. Due to lipophilic and hydrophobic properties, PAHs tend to be adsorbed by soil particles. Source apportionment of soil-bound PAHs contributes to controlling emissions and protecting the ecological environment. This research investigated source and distribution characteristics of PAHs in soils from Campania region of Italy, especially the natural sources. The total PAH concentrations ranged from N.D. to 4191 ng/g soil (dry weight). The data do not follow either a normal or lognormal distribution, but rather absolutely the multifractal distribution. Spatially distributed PAHs have experienced different degrees of superposition on the basis of multifractal spectrums curves with asymmetric upper convex. In addition, multifractal spectrum curves are all in a right hook shape, representing that low-values are dominant in the Campania area. The local singularity analysis shows an enrichment phenomenon that is not identified by the spatial interpolation method. The singularity values of PAHs were significantly correlated with TOC, but not significant with pH and population density. As opposed to concentrations, singularity indexes mainly reflecting the influence of soil properties. The fractal method was successfully used to separate the natural sources from the anthropogenic contributions of PAHs. Our results indicate that PAHs mixing distributions may be decomposed into natural background, anthropogenic background, and point source pollution. The background field was attributed to the thermal effects of geological processes, whereas anthropogenic anomaly was associated with anthropogenic activities. In sum, our study provides evidence of natural sources evidence that volcanic events have key effects on the distribution of PAHs, and shows that anthropogenic sources of PAHs are related to regional industrialization and urbanization status.