Benzo[a]pyrene sourcing and abundance in a coal region in transition reveals historical pollution, rendering soil screening levels impractical.

Benzo[a]pyrene (BaP) is a hazardous compound for human health and for environmental compartments. Its transfer and deposition through the atmosphere affects soil quality. In this context, we quantified the content of BaP and other Polycyclic Aromatic Hydrocarbons (PAHs) in the soils of a prominent Coal Region in Transition to test whether the soil screening levels in force are realistic and whether they reflect the complexity of regions closely linked to heavy industries and mining. In this regard, soil screening levels are thresholds often established without considering historical anthropogenic activities that affect soil (diffuse pollution). The 150 soil samples studied showed a notable content of high molecular weight PAHs, and BaP surpassed the threshold levels in practically the entire area. PAH-parent diagrams revealed a relatively homogenous fingerprint of four clusters obtained in a multivariate statistical study. In addition, molecular diagnostic ratios pointed to coal combustion as the main pollution source, whereas only some outliers appeared to be related to specific spills. A BaP threshold was calculated to be 0.24 mg kg, over 10 times the limit established in Spain. Finally, a factor analysis revealed a positive correlation of BaP with elements usually emitted in coal combustion processes, such as Tl and V. This observation fosters the hypothesis of a historical and indelible pollution fingerprint in soils whose sources, characteristics and potential environmental and health concerns deserve further attention. All things considered, caution should be taken when using soil screening levels in regions associated with coal exploitation and heavy industry.