| Reclaimed water irrigation (RWI) is an important way to relieve the shortage of water resources. Water Quality Standards or control guidelines have been established in developed countries and areas to ensure the safety of agriculture irrigation. But RWI was at the initial stage in our country. With the increasing of irrigation areas, its safety and impact on the environment has become a matter of great concern. Based on analyzing the soil samples of on-site drilling, irrigation water and groundwater in typical wastewater irrigation (WWI) area, RWI area and groundwater irrigation (GWI) area, the distribution characteristics of typical polycyclic aromatic hydrocarbons (PAHs) which belong to persistent organic pollutants (POPs) were studied and compared in different areas in this paper. The adsorption– desorption of PAHs in different soils, the cumulative effect and the migration and transformation of PAHs in soil aerated zone were discussed through the combination of laboratory batch experiments and column simulation experiments. In this study, the main conclusions were as follows:1. From the soil profiles of field drilling, we found that the content of silt were highest of the three different irrigation areas, followed by clay, while the sand had the smallest percentage of all. The variation of lithology in profiles of WWI area and RWI area were greater than groundwater irrigation (GWI) area. Compared WWI area with RWI area, the contents of silt and clay in RWI area were less than WWI area, but the content of sand was much higher than WWI area.2. The vertical distribution patterns of total PAHs and the single PAH were almost the same in profiles of three irrigation areas. The highest total contents of PAHs appeared in the surface layer, and they declined dramatically along the soil profiles. The PAHs contents ranked as follows: WWI area > RWI area > GWI area. PAHs in WWI area occur at a moderate pollution level, and RWI area at a light pollution level. GWI area was unpolluted. So the results had much to do with the water quality of irrigation. The low weight molecular PAHs were the main pollutants at the whole profiles in WWI area. The high weight molecular PAHs were the main pollutants in the topsoil, and the low weight molecular PAHs were the main pollutants under the surface layer in RWI and GWI area.3. The low weight molecular PAHs were the main pollutants in soil profiles, surface water and groundwater samples. The total PAHs of groundwater in three areas did not exceed the limit of standard for drinking water quality in china(GB5749-2006). In addition, the components and contents of PAHs of effluent varied with the time in different sewage treatment plants. The PAHs with 2 and 3 rings were the main pollutants, which were consistent with those of the surface water in the RWI area. But the contents of pollutants were much lower than those of sewage treatment plants, which indicated that the contents of pollutants were effectively decreased by the long distance transportation.4. Multiple regression analysis between the total PAHs and the physicochemical properties of soils showed that the total organic carbon (TOC) content was the common factor impacting the total PAHs content in the three irrigation areas. Ratio method and principal component analysis were applied to source apportionment of PAHs in soils of three areas, and the results showed that PAHs in WWI area mainly come from oil, while the other two areas mainly from combustion sources.5. From the batch experiments, we can conclude that the adsorption-desorption isotherms of naphthalene in the three typical soils were well described by Freundlich adsorption model, and the soil adsorption capacity of naphthalene increased with increasing TOC content in soils. Desorption hysteresis were observed in the three soils, and much obviously at low concentrations of naphthalene.6. The column leaching experiments showed that the vertical migration of low weight molecular PAHs were much better than the high weight molecular PAHs. Naphthalene and phenanthrene had the sampling holes penetrated in the homogeneous and non-homogeneous columns. The curves fit the theoretical model well.
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