| Nitrated polycyclic aromatic hydrocarbons(NPAHs)are nitrated derivatives of PAHs with higher mutagenic,carcinogenic and teratogenic effects than that of the corresponding parent PAHs.NPAHs are widely distributed in various environmental media.They have been aroused extensive attention in recent years due to their persistence and long-distance transport abilities.Soil is known as a source and sink of pollutants,so NPAHs in the soil may cause the pollution of the atmosphere,surface water and groundwater through volatilization,surface runoff and soil leaching,respectively.NPAHs can also be accumulated in the organism by bioconcentration and biomagnification,posing potential harm or influences to the ecological environment and human health.However,the research on the occurrence of NPAHs in soil around the world is still limited.Investigating the occurrence levels,sources and risks of NPAHs in soil in different regions can provide basic data support for the pollution characteristics and control of NPAHs.The Taige Canal is located in the economically developed area of the Taihu Lake Basin,twith 31°20??31°54? north latitude and 119°40??120°12? east longitude.Due to the population density,intensive industrial and agricultural production,the targeted area has good regional representation.It is speculated that the soil in the area has been contaminated by NPAHs,posing a threat to the health and ecological environment of the surrounding residents.Therefore,it is urgent to carry out relevant investigations.In this study,60 soil samples were collected in the Taige Canal valley and 15 NPAHs and 16 PAHs were selected as the target compounds.The occurrence,concentration levels,spatial distribution characteristics,possible sources of pollution,potential ecological risks and human health risks of NPAHs and PAHs were comprehensively investigated.The aim of this study is to figure out the pollution status and potential risks of PAHs and their nitro derivatives in the surface soil of Taige Canal valley,which can provide data support and theoretical basis for regional pollution control and management of related authority.The main results are as follows:(1)ASE-SPE pretreatment technique and GC-MS instrumental analytical method were combined to determine NPAHs and PAHs in this study.The detection rates of NPAHs and PAHs were between 73% to 97% and 77% to 100%,respectively.Theresults showed that the total concentration of 15 NPAHs in the soil in the study area ranged from 14.3 to 137.9 ng/g with the average concentration of 37.9 ng/g.1,8-DNPYR,1,3-DNPYR and 5-NACE were the most abundant NPAHs.The total concentration of 16 PAHs ranged from 117.4 to 1487.0 ng/g with an average concentration of 451.8 ng/g.FLA,PHE and PYR were the most abundant PAHs.PAHs in the soil were one order higher than NPAHs.Both NPAHs and PAHs had a composition characteristic of high-ring(4-6 rings)pollutants,which might be because the low-ring NPAHs and PAHs are mostly volatile and their concentrations are easily affected by environmental conditions,such as atmospheric movement,temperature and illumination,resulting in low levels in the soil.Comparing NPAHs and PAHs in the Taige Canal valley with relevant domestic and foreign studies and relevant evaluation standards,it was found that the pollution levels of NPAHs and PAHs in the soil were relatively serious.(2)The spatial distribution map of NPAHs and PAHs pollution in the soil of the study area was drawn using the inverse distance weighted interpolation method of the geostatistical analysis module of Arc GIS software.The results indicated that 15 NPAHs showed a higher concentration in the northeast and a relatively lower concentration in the middle and northwest study area.The spatial distribution of 16 PAHs was similar to that of 15 NPAHs.The sites with high concentrations were mainly concentrated in the northeast and southeast regions,while relatively low concentrations were found in the middle and northwestern areas.(3)The analysis of the correlation between NPAHs,PAHs and the physicochemical indexes of soil was studied.There was no significant correlation of p H between neither NPAHs nor PAHs in soil.TOC and TN were significantly correlated with high-ring PAHs(4-6 rings),which is mainly because the high-ring PAHs are relatively less volatile than the low-ring PAHs(2-3 rings)and can enter the soil slowly,reaching equilibrium after being adsorbed by TOC in the soil.Therefore,TOC and TN may be important factors affecting the residue and distribution of PAHs in soil.Most NPAHs were not significantly correlated with TOC and TN,which may be due to relatively low concentrations of NPAHs in the soil.In addition,soil microorganisms also have a certain effect on the concentration of NPAHs and physicochemical indexes of soil.(4)There was a good correlation between the corresponding monomers of PAHs and NPAHs through Pearson's correlation coefficients analysis,which confirmedtheir homologies.The isomer ratio method and principal component analysis combined with multiple linear regression(PCA-MLR)analysis was used for source apportionment.The results showed that the NPAHs in the soil of the study area were mainly from direct emission including diesel exhaust emissions and incomplete combustion of coal with their contribution rates were 76.1% and 23.9%,respectively.PAHs were mainly derived from combustion sources including petroleum and coal combustion,biomass combustion,petroleum source and coke oven emissions from their contribution rates were 64.0%,18.9% and 17.1%,respectively.(5)The lifetime carcinogenic risk(ILCR)increase model was used to calculate the carcinogenic risk of NPAHs and PAHs in the soil of the study area to adults and children through three exposure pathways.The results showed that ingestion and dermal were the main pathways for the two sub-populations exposed to NPAHs.Inhalation exposure to NPAHs and PAHs produced the negligible ILCR values.For NPAHs,the ILCR values calculated by ingestion and dermal pathways in children were both greater than those of adults;in the case of PAHs,the total ILCR values for adults were greater than those of children.In general,NPAHs and PAHs in our study presented high health risks to the human health referring to the US EPA evaluation standards.(6)The ecological risk of PAHs in the soil of the study area was evaluated by the biological toxicity evaluation method and risk quotient method.The analysis results based on the biological toxicity evaluation method showed that most PAHs monomers rarely produced negative ecological effects in all sampling sites.However,due to the high detection rates of Bb F,Bk F,Icd P and Bghi P,PAHs in the soil of the study area still had some potential ecological risks.According to the analysis of risk quotient method,each kind of PAHs and ?PAHs had the medium risk.Combining the two methods,it can be concluded that there was a moderate ecological risk for PAHs in the soil of the Taige Canal valley. |
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