Polycyclic aromatic hydrocarbons in urban Greenland soils of Nanjing, China: concentration, distribution, sources and potential risks.

In order to better study the influence of land use on the concentration and distribution of organic contaminants in urban areas, the concentrations of 16 principal polycyclic aromatic hydrocarbons (PAHs) were determined on soil samples collected at three depths (0~10 cm, 10~20 cm and 20~30 cm) from urban greenland areas of 6 functional zones: residential zone (RZ), business zone (BZ), industrial zone (IZ), cultural and educational zone (CZ), urban park (UP) and urban rural forest (URF) of Nanjing, China. Results showed that the average concentration of ∑PAHs in the urban greenland of Nanjing (499.47 ng/g) was comparable to the value reported for other cities under similar conditions. Acenaphthene was the dominant compound (46.2% of the ∑PAHs), and low molecular weight PAHs (LPAHs) represented the largest share of ∑PAHs. Concentrations of ∑PAHs in 6 function zones were different, with the highest value in IZ (954.33 ng/g) and lowest value in URF (147.81 ng/g). The soil showed the highest ∑PAHs contamination in the layer 10~20 cm in all zones (on average 547.01 ng/g). ∑PAHs of IZ showed the highest values in all soil layers. Isomer ratio and factor analysis were used to determine the source of PAHs in soil. Petroleum combustion (PC), coal and biomass combustion (CBC), mixed (M) and petroleum (P) sources were finally identified as the four main sources of PAHs in Nanjing urban greenland soil, accounting for 50.2%, 14.9%, 8.4% and 6.6%, respectively. Bap toxic equivalent (TEQ) was used to analyze the ecological risk. TEQ was 20.59 ng/g in total zones (TZ), below the threshold for multipurpose soil of Dutch legislation (32.96 ng/g), but 69% of samples exceeded this threshold. TEQ of different functional zones is ordered as: IZ (43.62 ng/g)>RZ (23.89 ng/g) > BZ (20.62 ng/g) > CZ (19. 93 ng/g) > UP (12.97 ng/g) > URF (2.01 ng/g). In the industrial area, more than 97% of TEQ depended on seven carcinogenic PAHs (∑PAH), which indicated that IZ had high ecological risk. Lifetime risk of cancer (ILCR) model was used to assess the health risk of ∑PAHs. ILCRs ranked as following: children > youth > adults, with soil oral intake determining the highest cancer risk, followed by skin contact and breath intake. ILCRs of children were in high cancer risk range, with values of 3.77 × 10 (for boy) and 3.87 × 10 (for girl), while ILCRs of youth and adults were in an acceptable range; ILCRs were highest in IZ, followed by RZ, BZ, CZ, UP and URF. The soil PAHs analysis in different function greenland zones of Nanjing showed that land use influenced the concentration and distribution of PAHs in soils. This difference should be taken into account in the urban greenland planning and management to reduce the risks for the environment and human health.