Association of soil polycyclic aromatic hydrocarbon levels and anthropogenic impacts in a rapidly urbanizing region: Spatial distribution, soil–air exchange and ecological risk

The occurrence of polycyclic aromatic hydrocarbons (PAHs) in soil of the Pearl River Delta (PRD) and surrounding areas was examined on a basis of six land-use types and four geographic regions, from which the impacts of anthropogenic events on the terrestrial environment were evaluated. No significant difference in the concentrations of Σ28PAH and Σ15PAH (sums of 28 and 15 PAHs, respectively) was found among the land-use types of industry, landfill and residency. On the other hand, higher soil PAH concentrations occurred in the central PRD characterized by dense population and high urbanization level, compared to other geographic regions. Source diagnostics implicated the combustions of coal and refined petroleum as the major input sources of anthropogenic PAHs. Furthermore, low molecular weight PAHs tended to volatilize from soil to air while the opposite was prevailing for high molecular weight PAHs. The mean annual diffusive flux of Σ15PAH (852μgm−2yr−1) from the soil to the atmosphere in the central PRD was greater than those in the PRD's periphery (195μgm−2yr−1), West region (322μgm−2yr−1) and East region (84.9μgm−2yr−1), suggesting that the central PRD may have become a secondary source of PAHs to the surrounding areas. Finally, ecological risk assessment based on the classification from Maliszewska-Kordybach showed that 3.5% of soil within the central PRD was heavily contaminated by PAHs and 5.2million residents may be subjected to high health risk. •Land use types are less relevant in defining the spatial distribution of soil PAHs.•Anthropogenic impacts play a major role in the spatial pattern of soil PAHs.•Soil has become a secondary source of individual PAHs to the atmosphere.•Contaminated soil is concentrated in populated areas, subjecting more residents to higher risk.