Research On The Pollution Features, Dating, Source And Risk Assessment Of Soil Polycyclic Aromatic Hydrocarbons In Hunpu Wastewater-irrigated Area, Old Industrial Base In Northeast

Northeast area of China is a major base of agriculture as well as an important old industrial one.Organic pollution is one of the primary factors in environmental pollution.Soil organic pollution has always been an old and big environmental problem in this area.Persistent organic pollutants have become a huge potential threat to ecological environment safety,public health and social economy development.The major sources of soil organic pollutants include fuel burning,factory fume, automotive exhaust,etc.Wastewater irrigation is another important source.Therefore it will be very helpful to research on soil organic pollution for soil restoration and for ecological safety and public health.In this research,the agricultural soils of the typical wastewater-irrigated area in Northeast China,Hunpu wastewater-irrigated area,were selected.Eight soil profiles were sampled,four upland and four paddy soils respectively,numbering H1 upland, H1 paddy,H2 upland,H2 paddy,H3 upland,H3 paddy,H4 upland,H4 paddy.The depth of soil profile was 1 m,including 10 layers,0～5,5～10,10～15,15～20,20～25, 25～30,30～40,40～50,50～60,60～100 cm respectively.One control profile located in Qingyuan area,Liaoning province.Soil samples were distilled with accelerated solvent extraction(ASE),purified by silica gel column.The 16 priority PAHs by USEPA were determined by gas chromatography with mass spectrum(GC/MS).In this paper,the pollution feature,dating,source and risk assessment of PAHs in soils of Hunpu wastewater-irrigated area were studied.The main results are as follows:(1) The PAHs concentrations in Hunpu upland soils ranged from 7.91 to 2231.42μg·kg^-1,while paddy soils from 7.88 to 1592.05μg·kg^-1.H1 upland,H1 paddy,H3 upland soils were heavily polluted by PAHs.(2) The peak concentrations of PAHs were within upper 20 cm soils.The concentrations of PAHs were lower below 20 cm layers.This indicated that PAHs were mainly from human activities.PAHs entered into soils,then collected in upper layers.(3) In the cultivated 0～20 cm layers,the concentrations of PAHs in upland soil layers were generally higher than the same paddy ones.This was maybe caused by clean water irrigation from 2002.Because of bigger water irrigation in paddy soils, more PAHs were dissolved than upland soils.So the bigger amount of PAHs was degraded by microorganism or migrated to deep layers with colloid.(4) In upper soils,median and high benzene tings PAHs generally accounted for more than 50%,while the percentage of low benzene rings PAHs grew in deeper layers.(5) PAHs had highly positive correlations with soil organic matter and clay.PAHs had highly negative correlations with soil pH values.PAHs had positive correlations with silt,having little correlations with sand.(6) ²¹⁰pb isotope dating technique was used to date the PAHs below the 20 cm soil layers.The results showed that in the 60～100 cm layers of H1 upland and H4 paddy profiles,the concentrations of PAHs were a little high.This may be related to the rapid development of military industry.In the 25-50 cm layers of HI upland profile, 25～30 cm and 40～50 cm layers of H2 paddy profile,40～50 cm layers of H4 paddy profile,the concentrations of PAHs increased.PAHs formed between 20cn 50era and 70era.PAHs entered soil through wet and dry deposition or wastewater irrigation.(7) The abound degree of PAHs with different benzene rings and the ratio of isomer PAHs were used to identify the source of soil PAHs in Hunpu wastewater-irrigated area.Both pyrogenic and petrogenic PAHs were the major source. PAHs in upper soils were mainly from fuel burning,factory fume,automotive exhaust and wastewater irrigation.The percentage of petrogenic source grew in deeper layers, and this was mainly caused by wastewater irrigation.Hunpu wastewater irrigated area lied in oil region.The petrogenic source PAHs may be related to the geological factor.(8) The concentrations of PAHs in groundwater Hunpu wastewater-irrigated area were in accordance with the degree of PAHs in soil sampling sites,having no relation with the distance from Xi River.This indicated that the PAHs in groundwater were mainly from soil migration. (9) The ecological risk are higher in upland soils than in paddy ones.Ecological risk more possibly occurred in H1 upland and H3 upland soils.Fluorene and dibenzo [a,h]anthrancene were common pollutants to bring on adverse biological effects. Totally,the level of soil ecological risk was median or low.(10) PAHs had potential threat to local resident health.PAHs in H1 paddy,H3 upland,H3 paddy,H4 upland soils brought on high cancer possibility,especially in H4 upland soils.