Global patterns of polycyclic aromatic hydrocarbons (PAHs) in soil

Abstract

Recent findings suggest a higher natural contribution to PAH concentrations in soil than previously thought. I hypothesized that the PAH pattern in soil is dominated by two main types, which are indicative of background conditions on the one side (i.e., by biological and diffuse PAHs) and a strong impact by atmospheric deposition of anthropogenic emissions on the other side. To test this hypothesis, concentrations of 20 PAHs in 225 topsoil samples from 12 geographic regions were evaluated. The Σ20PAHs concentrations ranged between 4.8 and 186,000 μg kg − 1 . In soils with low concentrations of Σ20PAHs, naphthalene (NAPH), phenanthrene (PHEN), and perylene (PERY), together defined as Σbackground, dominated. In soils with high concentrations of Σ20PAHs, 11 high-molecular weight PAHs (HMPAHs) were most abundant. Regressing the means of the contributions of Σ11HMPAHs to the sum of 20 PAHs on those of Σbackground for the 12 regions resulted in a linear function typical for simple mixing of two end members ( r = − 0.98). To validate this model, published results of PAH measurements from 15 more geographic regions were used. In spite of methodological differences, there was again a close significant correlation ( r = − 0.79) between the contributions of NAPH + PHEN and of 8 HMPAHs to the sum of the 16 PAHs identified as priority pollutants by the U.S. Environmental Protection Agency. NAPH + PHEN contributions correlated negatively with mean Σ16PAHs concentrations, taken as indication of anthropogenic impact. These results support the hypothesis that PAH mixtures in soils are dominated by two major source patterns, a background and a human-made one.