| Chongqing is the traditional industrial city in Western China with the largest economic center,land and water transportation hub in the upper reaches of the Yangtze River.With the rapid development of the economy,human activities have led to an increase in the input of organic pollutants,and the accumulation of persistent organic pollutants will undoubtedly make the potential damage of urban ecosystems increasingly serious.As one of the indicators of urban pollution,urban soil is often the carrier of organic pollutants.Therefore,understanding the characteristics of organic pollutants in urban soil and exploring their adsorption characteristics in water-soil system are of great significance to the research and prevention of persistent organic pollutants in urban soil.In view of this,we investigated the occurrence,distribution and source of two typical organic pollutants–organophosphate esters?OPEs?with 12 monomers and phthalates esters?PAEs?with 7monomers in the soil of the main urban areas in Chongqing.The adsorption characteristics of seven OPEs monomers in water-soil system were also studied,in order to provide basic data and background information on OPEs and PAEs for urban soil environment in this region.A total of 66 soil samples were collected from five different urban functional areas in Chongqing,and the concentration levels of PAEs and OPEs in soil were analyzed using ultra high performance liquid chromatography-quadrupole-time of flight mass spectrometry?UPLC-Q-TOF-MS?.Meanwhile,the composition and characteristics of PAEs and OPEs were discussed along with the possible sources of PAEs and OPEs through correlation analysis and principal component analysis.In addition,the adsorption characteristics of OPEs in water-soil system were studied.We discussed the adsorption isotherms of different OPEs monomers and the effects of temperature and dissolved organic carbon?DOC?on OPEs adsorption.The results showed that the concentrations of?PAEs ranged from 93.1-312ng·g-1 dry weight,which lay at a low end of the worldwide figure.DEHP,DBP and DIBP were dominated compounds,contributing to 87.4%-92.9%of the total?PAEs.DEHP was the most abundant PAEs congener,responsible for 52.4%of the total?PAEs.Through the correlation analysis,it was noted that the PAEs with similar molecular weight were more likely to show a significant relationship among each other,which suggested that these PAEs may share similar source.According to the principal component analysis,DBP,DIBP and DEHP had a similar source,while BBP and DnOP strongly correlated with each other.The concentrations of?OPEs ranged from 10.7-108ng·g-1 dry weight,with the mean concentration of 46.4 ng·g-1,which laid at a low level end of the worldwide figure,and the average concentration was 55.6ng·g-1 in the industrial area,55.5ng·g-1 in the residential area,41.8ng·g-1 in the commercial area and 34.1ng·g-1 in the city park.TCPP and EHDPP were dominated compounds,with contributing to 31.5%in industrial area for TCPP and 23.4%,24.7%in commercial area and city park respectively for EHDPP.Significant relationship between concentrations of SOM and?OPEs?P<0.05?,TCP?P<0.01?respectively,indicated SOM was a factor affecting the concentration and distribution of the OPEs.The PCA?Principal Component Analysis?suggested the sources of OPEs in urban soil were not single.Sewage irrigation,road runoff,indoor source pollution and sludge reuse could become potential sources of soil OPEs.The soil isothermal adsorption of OPEs showed that the five monomers could reach the adsorption equilibrium after 12 hours of adsorption.TBEP and TDCP had the largest adsorption capacity,and TCPP had the smallest adsorption capacity,and the difference in adsorption amount was mainly related to the solubility and the lgKow of the monomer.The five monomers can well conform to the Freundlich adsorption isotherm equation,and the R2 ranged from 0.963 to 0.995.The n values of the three chlorinated OPEs?TCEP,TCPP,TDCP?Freundlich adsorption isotherms were 1.455,2.049 and 1.368,respectively,indicated that the adsorption of the test soils was preferential adsorption,while TBEP with non-preferential adsorption?n<1?,indicated that TBEP was rapidly adsorbed and less affected by the competition of other adsorbates in the system.The n=0.92 in the Freundlich isotherm equation of TBEP was slightly less than 1,which indicated that TBEP tended to be linear adsorption.It showed that TBEP was mainly partitioned and took the lead in occupying the high adsorption point of the adsorbent in the adsorption process.Whereas,n=2.049 for TCPP was much larger than 1,and the degree of nonlinearity was higher,which indicated that the competition for high adsorption sites was weak.In the process of adsorption with other monomers,because the high adsorption sites on the adsorbent were occupied by other monomers,TCPP was mainly adsorbed by the lower adsorption sites,so it was mainly characterized by non-linear adsorption.The correlation analysis showed that the Kd values of structurally similar monomers were significantly correlated?P<0.05?,indicating that in addition to physical and chemical properties,molecular structure was also one of the factors affecting Kd values.Temperature had a significant effect on the Kd.For the adsorption reaction was an exothermic process,higher temperature would reduce the adsorption of OPEs on soil.The difference among the properties leaded to different adsorption effects of DOC on different monomers.The adsorption capacity of TCEP and TCPP were the two most significant monomers affected by DOC.Due to the high solubility of TCEP and TCPP,they were more easily distributed in the aqueous phase,Adding exogenous DOC made the concentration of DOC in liquid phase increase,which led to the more distribution of TCEP and TCPP in liquid phase.As for TDCP and TBP,they had extremely low solubility and were typical of two highly hydrophobic monomers,which tended to be distributed in the soil,therefore,although DOC concentration increased,it had no significant effect on their adsorption capacity. |
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