Pollution Characteristics,Air-soil Exchange And Risk Implications Of Short-and Medium-chain Chlorinated Paraffins Along Typical Riverine In Yangtze River Delta

Chlorinated Paraffins（CPs）are a class of synthetic complex chlorinated n-alkanes that are detected widely in the environmental matrix such as the atmosphere,soils,water bodies,and sediments.Among them,soil is an important"reservoir"and"source of secondary pollution"of Short-Chain Chlorinated Paraffins（SCCPs）and Medium-Chain Chlorinated Paraffins（MCCPs）.The bark as a passive air sampler can reflect the long-term exposure level of pollutants in the atmosphere.Therefore,it is of scientific significance to investigate the residues of SCCPs and MCCPs in soil and bark and to investigate their air-soil exchange behaviors and health risks accordingly.In this study,we collected surface soil and bark samples from the Yangtze River Delta（Dianshan Lake,Taipu River,Huangpu River）,and established a method by ultrasonic extraction,one-step purification of the composite silica gel column,GC-ECNI-LRMS for the qualitative and quantitative analysis of SCCPs and MCCPs in the samples.Based on the spatial distribution characteristics,the fugacity model was used to analyze the direction and flux of air-soil exchange,and the ecological health risk status in the region was assessed.The results of the study provide data support and scientific reference for the future regulation and control of CPs.The results are as follows:（1）The concentrations of SCCPs and MCCPs in the soil in Dianshan Lake were39.73-406（mean 113）ng/g and 273-1.79×10³（mean 805）ng/g,respectively.The concentrations of SCCPs and MCCPs in the bark were 126-1.05×10³（mean 282）ng/g and 944-1.10×10⁴（mean 2.78×10³）ng/g,respectively.The concentrations of CPs in the bark were significantly higher compared to those in the soil in this region.The carbon congeners of SCCPs and MCCPs in both matrices were dominated by C₁₀-CPs and C₁₄-CPs,while Cl₇-CPs and Cl₈-CPs were the main contributors of chloride congeners.Pearson correlation analysis indicated a significant positive correlation between the concentrations of SCCPs and MCCPs in bark（r=0.852,p<0.05）.The fugacity fractions（ff_s）of SCCPs and MCCPs were found to be 3.03×10^-2-0.855 and 2.34×10^-3-0.370,which decreased with the growth of carbon chains and degree of chlorination.The ff_sshowed a significant negative correlation with the Octanol-Air Partition Coefficient(K_OA)（r=-0.974,p<0.01）.The soil to air emission fluxes for SCCPs and MCCPs were6.34×10^-5-32.4 and 2.03×10^-5-1.63 ng/（m²·h）,respectively.The net air-soil exchange fluxes were 3.35×10^-3-0.941 and 2.60×10^-2-3.98 ng/（m²·h）,respectively.SCCPs had higher volatilization and MCCPs had higher net deposition fluxes.The results of Principal Component Analysis（PCA）suggest that the CPs in the Dianshan Lake area may be mainly from atmospheric transport.The exposure levels for children were（5.39±3.65）×10^-3 and（3.37±2.28）×10^-3μg/（kg·d）by ingestion and dermal exposure,respectively,and（2.56±1.73）×10^-4and（3.07±2.08）×10^-4μg/（kg·d）for adults,respectively,which were lower than the tolerable daily intake（TDI,10μg/（kg·d））,indicating a low human health risk due to non-dietary exposure in this area.（2）The concentration of SCCPs and MCCPs in soil in the Taipu River were 191-996（mean 494）ng/g and 2.23×10³-1.38×10⁴（mean 6.99×10³）ng/g,respectively.The concentrations of SCCPs and MCCPs in the bark were 1.23×10³-5.38×10³（mean3.06×10³）ng/g and 2.13×10⁴-8.08×10⁴（mean 5.08×10⁴）ng/g,respectively.The major components of SCCPs in both matrices were C₁₀Cl_7-8,while the major contributors were C₁₄Cl_6-7 and C₁₄Cl_5-7in soil and bark for MCCPs,respectively.Fugacity calculations revealed that the average ff_s of SCCPs and MCCPs congeners were 5.63×10^-3-0.657and 2.40×10^-4-0.216,respectively,and the ff_s showed a significant negative correlation with Octanol-water Partition Coefficient(K_OW)and K_OA.There were 75.6%of the ff_swere less than 0.3,showing significant deposition from air to soil.The exchange flux calculation of CPs showed that the soil to air emission fluxes were 1.50×10^-4-390ng/（m²·h）and the net air-soil exchange fluxes were 2.83×10^-2-192 ng/（m²·h）,which showed a higher air-soil exchange level compared with the Dianshan Lake area.The PCA analysis showed that the source of CPs in the Taipu River was complex,and the combined use of various types of CPs products was mainly considered.The risk quotient（RQ）model indicated that the RQ values of SCCPs and MCCPs in the area ranged from 3.61×10^-2-0.189 and 7.96×10^-2-0.494,respectively.Some points may pose a medium ecological risk to soil organisms in the area.The exposure levels for children were（4.49±2.39）×10^-2 and（2.81±1.49）×10^-2μg/（kg·d）through ingestion and dermal contact,respectively,and for adults were（2.12±1.13）×10^-3 and（2.56±1.36）×10^-3μg/（kg·d）,respectively,which were below the TDI.The non-dietary exposures in this watershed were considered to cause low human health risks.（3）The concentration levels of SCCPs and MCCPs in the soil in Huangpu River were 74.1-1.13×10³（mean 347）ng/g and 237-1.02×10⁴（mean 2.00×10³）ng/g,respectively.The concentration levels of SCCPs and MCCPs in the bark were 584-4.48×10³（mean 1.63×10³）ng/g and 2.28×10³-3.16×10⁴（mean 1.38×10⁴）ng/g,respectively.The concentration of MCCPs was significantly higher than that of SCCPs,reflecting the current trend of the shift in the production of CPs from SCCPs to MCCPs.The Kruskal-Wallis（K-W）test showed significant spatial differences（p<0.01）in the concentrations of both soil and bark SCCPs and MCCPs in different study areas,and the ranking of pollution levels all followed:Taipu River>Huangpu River>Dianshan Lake.Unlike the previously described watersheds,the main composition of CPs congeners in the soil and bark in Huangpu River was C_11-13Cl_7-8 and C_14,16Cl_5-6.The differences in the production and use of CPs between different regions may be the main reason for the differences in the composition of CPs,while environmental processes such as fractionation and deposition of CPs in atmospheric transport may also affect the composition of CPs congeners.The fugacity analysis revealed that 79.2%CPs congeners at the Huangpu River site had ff_s<0.3,showing a significant deposition trend.The mean ff_s values of CPs congeners showed a significant negative correlation with K_OA（r=-0.916,p<0.01）and K_OW（r=-0.487,p<0.01）.Unlike the other watersheds,the net exchange fluxes of SCCPs and MCCPs in this region were 3.81×10^-2-72.4 and7.01×10^-3-29.4 ng/（m²·h）,respectively,indicating a higher net deposition of SCCPs.The RQ values of CPs in soil samples in the Huangpu River ranged from 1.40×10^-2-0.215 and 8.46×10^-3-0.364,and the ecological risk level was between the Taipu River and Dianshan Lake.Exposure model estimates showed that the estimated daily exposure was significantly lower than the TDI for both adults and children,indicating that the exposure levels of CPs do not yet pose a health risk to humans.