Pollution Characteristics,source Analysis And Risk Assessment Of Typical Persistent Organic Pollutants In Soil From Hexi Corridor

Hexi corridor,located in the west of Gansu province,is the key area of the northwest of the"silk road economic belt",and it is also a main commercial grain base and economic crop production area in the northwestern China.In recent years,the rapid development of industry and agriculture has caused the soil pollution by organic pollutants in this area.Furthermore,the Hexi Corridor is an ecologically sensitive area,and the soil quality has a great impact on the sustainable development of economy and human health in this region.In this paper,soil samples collected from five cities in Hexi corridor?Jiuquan,Jiayuguan,Zhangye,Wuwei and Jinchang?are taken as the research districts,and the occurrence characteristics,spatial distribution,source analysis and potential risks of three typical organic pollutants,such as PAHs,PCBs,OCPs and PBDEs in the soil of Hexi corridor were studied through experimental analysis methods such as low-temperature ultrasonic extraction,rotary evaporator concentration,glass chromatography column purification,gas chromatography mass spectrometry analysis and data processing methods such as isomeric ratio analysis,correlation analysis,factor analysis and cluster analysis.The following results have been obtained:?1?PAHs were widely distributed in the soil collected from Hexi Corridor.The contents of?₁₈PAHs were in a range of 69.57-1300.19 ng/g with an average value of 505.58 ng/g.The order from high to low of PAHs contents in the soil from different regions was:Jinchang>Jiayuguan>Jiuquan>Wuwei>Zhangye.The lower levels of PAHs in the study area were found compared with other regions.Correlation analysis showed that PAHs in the soil were correlated with TOC,indicating TOC was a key factor affecting PAHs retention in soil in the study area.The significant of correlation between soil pH and individual PAHs was small,indicating that the pH value of soil was not an important factor affecting soil retention of PAHs.PAHs in soil of Hexi Corridor were mainly dominated by carcinogenic PAHs with high molecular weight,of which BbF,BkF,BjF,Ba P,DBA,In P and BP were the dominated pollutants.PCA and isomer ratio method were used to analyze the sources of PAHs in soil.The results showed that PAHs pollution mainly came from combustion sources of petroleum,coal and biomass.The potential carcinogenic risk of PAHs in soil from Hexi corridor was evaluated and analyzed by TEQ_BaP.The results showed that 32.2%sampling sites in the study area exceeded the Dutch soil standard target reference value?33.00 ng/g?.The contribution of7 carcinogenic PAHs accounted for 87.17%of the total 18 TEQ_BaP,indicating that carcinogenic PAHs are the major contributors to the total TEQ_BaP.Health risk assessment showed that the carcinogenic risk value of PAHs in soil in Hexi corridor was less than 10-4,which indicates that it has less potential carcinogenic risk to human beings,and non-carcinogenic risk assessment,HI<1 indicates that PAHs in soil from Hexi corridor were had no obvious non-carcinogenic health effects on human beings.?2?The contents of OCPs in soil in Hexi Corridor was ranged from 23.07 to 392.55 ng/g with a mean value of 94.65 ng/g.The contents of?HCHs was in a range of 3.40-97.48 ng/g with a mean of 16.03 ng/g.The contents of?DDTs was ranged from 4.96 to 166.97 ng/g,with an average of 35.76 ng/g.The results indicated that OCPs in soil from Hexi Corridor were dominated by HCHs and DDTs.Compared the contents of HCHs and DDTs in soil with other region in China,the residual level of HCHs is relatively high,while the residual level of DDTs is relatively low in soil of Hexi Corridor.Generally speaking,the residual levels of HCHs and DDTs in soil of Hexi Corridor are lower than the secondary standard?500 ng/gdw?of Soil Environmental Quality Standard of China?GB15618-1995?,which could not be caused adverse effects on agricultural production and population living.Correlation analysis showed that the correlation coefficient between OCPs and TOC in soil from Hexi corridor was high,while the correlation between pH and individual OCPs was not significant,which indicated that TOC had a important impact on the distribution of OCPs in soil from Hexi corridor.Source analysis showed that HCHs came from recent input of pesticide use activities,DDTs mainly came from residues of early pesticide application,and aerobic conditions in metabolic environment used to be dominant.The pollution assessment of single factor index and Nemerow index showed that the single factor index of HCHs and DDTs were both less than 1,indicating that the contents of HCHs and DDTs in soil samples met the secondary standard.From the point of Nemerow comprehensive index,PN was both less than 0.7,and the soil environmental quality was safe.Ecological risk assessment showed that there was a certain ecological risk of OCPs pollution in soil from Hexi corridor,which may cause harm to the ecological environment.Health risk assessment showed that the health risks of HCHs and DDTs in different areas of Hexi Corridor were the largest in the ingestion contribution of human exposure,followed by skin contact,while the effect of inhalation was negligible.From a comprehensive perspective,HCHs and DDTs in Jiuquan City in different soils from Hexi Corridor have certain carcinogenic risks to local residents,which need to be paid attention.?3?The concentration of?PCBs in the soil from Hexi corridor was in a range of2.00-148.47 ng/g with a mean of 21.34 ng/g.The order from high to low of PCBs contents in different regions was Jiuquan>Jiayuguan>Wuwei>Zhangye>Jinchang.The residual amount of PCBs in soil in the study area was higher than that in agriculture in some countries and regions,but far lower than that in typical polluted countries and regions.In a word,the residual level of PCBs in soil from Hexi corridor was relatively high,which indicated that the industrial activities such as mining,heavy industry and other enterprises have an important input impact on the residual of PCBs in soil.Correlation analysis showed that the correlation between individual PCB and TOC was high,indicating that TOC had certain influence on the residue of PCBs in soil,and soil pH and water contents were basically irrelevant to PCBs.The proportions of Tetra-CBs,penta-CBs,Hexa-CBs and heptachlor-CBs in total PCBs in soil were contributed to 30.41%,15.96%,35.61%and 18.02%,respectively.Tetra-CBs and Hexa-CBs were the dominated components,and the major individual monomers were PCB-81,PCB-77,PCB-169,PCB-167,PCB-156 and PCB-157.PCA showed that the main sources of PCBs may be leakage of vehicles?locomotives,lubricating oils,etc.?,production of automobile parts and automobile exhaust,paint additives,insulating materials and other industrial products.Health risk assessment showed that the carcinogenic health risk level of PCBs in soil from Hexi corridor was within the acceptable range.However,the exposure risk of PCBs to children was greater than that to adults,which needs more attention.?4?The PBEDs content in the soil of Hexi corridor was not detected due to its low content in the sampling area,thus,this part of the content will be omitted in the following discussion.