Distribution and transport of PAHs in soil profiles of different water irrigation areas in Beijing, China.

Vertical distribution characteristics and transport mechanisms of polycyclic aromatic hydrocarbons (PAHs) in soil profiles (0-5.5 m) of different water irrigation areas in the southeast suburb of Beijing were analyzed and compared. 16 priority PAHs on the United States Environmental Protection Agency (US EPA) list were analyzed using gas chromatography and mass spectrometry (GC-MS). The relationship between the properties of soil and PAHs was also studied by statistical analyses. The results showed that total PAH concentrations in the topsoils of the wastewater irrigation (WWI) area, reclaimed water irrigation (RWI) area, groundwater irrigation (GWI) area were much higher than those in the deep soils, with the concentrations of 726.0, 206.8 and 42.8 μg kg(-1) (dry wt), respectively. The low molecular weight (LMW) PAHs (2-3 ring) including naphthalene (Nap), phenanthrene (Phe), fluorene (Fl) dominated the layers (0.5-5.5 m) underneath the surfaces. The migration of LMW PAHs was faster than that of high molecular weight (HMW) PAHs and LMW PAHs were transported in dissolved matter. The different soil textures of three sites caused the differences in the variation ranges of PAHs in the profiles. The statistical analyses showed a significant linear positive correlation between PAHs and total organic carbon (TOC). The 2-4 ring PAHs were detected in the wastewater and reclaimed waters, which was consistent with those in the soil profiles. The presence of PAHs in the soil profiles was mainly due to the irrigation of wastewater. Wastewater reuse guidelines and standards for irrigation should be established urgently.