Characterization, source apportionment, and risk assessment of polycyclic aromatic hydrocarbons in urban soil of Nanjing, China

Polycyclic aromatic hydrocarbons (PAHs) are widespread in the urban environment, particularly in urban soil, which are affected by intensive human activities. The purpose of this study was to determine the levels of PAHs in urban areas of Nanjing, China, apportion their sources, and evaluate their health risk. One hundred eighty topsoil samples (0-10 cm) were collected from 180 grids of 1 km x 1 km in the main urban area of Nanjing, China, which was divided into four different land use classes. All the soil samples were analyzed for 16 US Environmental Protection Agency (US EPA) priority PAHs by HPLC. Source of PAHs was explained by isomer ratios and principal component analysis, and health risk of PAHs was assessed by benzo[a]pyrene (BaP) toxic equivalency factors. The average concentration of PAHs ranged from 41.19 to 7016.65 mu g kg(-1), with an average of 979.59 mu g kg(-1). PAHs in soil characterized by different land uses, in decreasing order, were as follows: university (UN) > traffic area (TA) > forest park (FP) > residential area (RA). PAHs in FP soils were mainly attributed to biomass combustion, while TA soils exhibited clear traffic emission characteristics. PAHs for UN and RA came from mixed sources. A principle component analysis (PCA) and ordinary kriging map indicated coal combustion and vehicle emissions as the major contributors to PAHs in Nanjing urban soils, respectively. A health risk assessment based on the BaP toxic equivalency approach indicated a potential risk level of PAHs. The mean value of PAH concentrations in UN was the highest. However, the maximum was detected in TA. The PAHs in soil samples originated mainly from coal combustion and petroleum combustion sources. There was a potential health risk level of PAHs in Nanjing urban areas.