Abstract:Wastewater irrigation was adopted in irrigation district in southeastern suburb of Beijing from 1950s to 2003, the main source of wastewater was industrial and domestic wastewater from Beijing. Reclaimed water was used for irrigation since 2003 in the irrigation district. To investigate the residual levels of polycyclic aromatic hydrocarbons (PAHs) in topsoil and crops in the irrigation district, totally 31 samples of soil and 38 samples of crops were collected, and the concentrations of 16 US EPA (United States Environmental Protection Agency) priority PAHs were determined by gas chromatography equipped with a mass spectrometry detector (GC-MS) in 2015. Results showed that the PAHs in topsoil in the district were ranged from 113.5μg/kg to 449.8μg/kg, with a mean value of 258.5μg/kg. And 80% of the collected soil samples were slightly polluted by PAHs. The sums of 10 PAHs were 83~307μg/kg, which were lower than the standard of Netherlands (the intervention value was 40mg/kg). The average value of bap toxic equivalence quantity (TEQBap) for 10 PAHs in topsoil was 19.0μg/kg, which was lower than the standard of Netherland (33.0μg/kg), indicating that there was no remarkable potential ecological risk. The concentrations of winter wheat grain, summer maize grain and vegetables were 368.7~389.9μg/kg, 87.7~113.5μg/kg and 51.8~291.8μg/kg, respectively. Benzo(g,h,i)perylene was the dominant component in winter wheat grain and summer maize grain, which accounted for 36.6%~41.6% of the 16 PAHs concentrations. For vegetables, the highest individual PAH was phenanthrene, which represented 24.0% of the 16 PAHs. The concentrations of benzo(a)pyrene in cereal grains were lower than the Chinese standard limits of 5μg/kg in food. The high temperature combustion was the major pollution source for PAHs in topsoil and cereal grains, while the mixed sources of fossil fuel combustion and oil source were the pollution source for PAHs in vegetables. The carcinogenic risk of adult and child caused by PAHs were 4.02×10-5 and 1.76×10-5, respectively;the non-carcinogenic hazard index of PAHs for adult and child were 2.72×10-2 and 4.78×10-2, respectively;all of them were lower than the threshold values. Dietary intake was the major route of human exposure, which accounted for 98.39%~99.64% of carcinogenic risk and 99.8%~99.9% of non-carcinogenic hazard index, respectively. The carcinogenic risk caused by benz（a）pyrene and dibenzo（a,h）anthracene were relatively higher, which accounted for 42.89%~46.72% and 22.15%~26.36% of the total carcinogenic risk, respectively. The non-carcinogenic hazard index of benzo(g,h,i)perylene and phenanthrene were relatively higher, which accounted for 44.28%~46.28% and 29.14%~29.60% of the total non-carcinogenic hazard index, respectively.
