Geographical impact on the distribution of polycyclic aromatic hydrocarbons (PAHs) in hilly terrain topsoil: A case study at Chongqing, SW, China

The distribution and transport of polycyclic aromatic hydrocarbons (PAHs) in urban environments are influenced by both anthropogenic sources and natural landscape features. While previous research has primarily focused on human activities as drivers of PAH pollution, the role of terrain-especially in cities with complex topographies-remains underexplored. To investigate the effect of terrain features on PAH distribution and transport, we analyzed topsoil samples evenly distributed in Chongqing, a city with hilly terrain (elevation: 48-2300 m). PAH concentrations (Σ₁₆PAHs) ranged from 170.3 to 4426.4 ng/g (mean: 688.3 ng/g). Low-molecular-weight (LMW) PAHs were the most prevalent pollutants, with high-molecular-weight (HMW) PAHs predominantly accumulating in valleys formed by the hilly terrain. Multivariate receptor model methods identified fossil fuel combustion as the primary source of PAHs. Redundancy Analysis (RDA) revealed that elevation changes in the terrain significantly affect PAH accumulation, amplifying the influence of human activities. Integrating principal component analysis multiple linear regression (PCA-MLR) with ARCGIS kriging interpolation provided a novel approach to visualizing source apportionment and mapping the spatial distribution of PAH pollution. These findings highlight that hilly terrain plays a significant role in PAH distribution, with valleys acting as key sinks and obstructing transport, particularly in urbanized areas. Combustion sources tend to accumulate near their origin, while petroleum-derived PAHs are transported over longer distances and accumulate in areas with significant elevation changes. The TEQ_BaP and optimized ILCR model, with a regional cancer risk of 3.69 × 10⁻⁵, indicate a low overall health risk. Most health risks arise from oral ingestion and dermal exposure, with risk increasing with age.