Variability of PAH Patterns in Upper Forest Soil (Sub)horizons—A Case Study From South-Central Poland

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a class of contaminants characterized by their persistent and toxic nature. This study examines the variability in PAH distribution patterns in the upper layers of forest soils, focusing on the influence of different characteristics of individual soil (sub)horizons. A total of 130 samples were collected from five forest areas in south-central Poland and analyzed for the 16 priority PAHs. Samples were taken from the organic fermentative-humic (Ofh), humic (A), and humic-eluvial (AE) (sub)horizons. The highest mean concentrations of total PAHs were found in the subhorizon-Ofh (Ofh—1547 μg kg⁻¹, A—1103 μg kg⁻¹, AE—109 μg kg⁻¹). The PAH content was significantly correlated with SOM content and pH, but this correlation was only significant in the horizon-A. The percentage contributions of 3-, 4-, 5-, and 6-ring compounds to the total PAHs varied among the investigated soil (sub)horizons. The subhorizon-Ofh had the highest percentage contribution of 6-ring PAHs, 4- and 5-ring PAHs were most prevalent in the horizon-A, while 3-ring compounds in the horizon-AE. The variability in PAH patterns was also reflected in individual PAH ratios (BaA/BaA+Chr, IcdP/IcdP+BghiP), confirming the different behavior of 4-, 5-, and 6-ring compounds in these (sub)horizons. This suggests that the retention of PAHs in the investigated (sub)horizons is influenced by several factors, including pH, degree of SOM decomposition, and mineral fraction, each to a different extent. Our findings reveal significant knowledge gaps regarding the behavior and accumulation of PAHs in soil (sub)horizons, underscoring the need for further research.