Occurrence And Distribution Of The Phthalate Esters And The Organophosphate Esters In The Fluctuating Zone Soil Of The Three Gorges Reservoir And Release Characteristics Of Organophosphate Esters During The Flooding

The Three Gorges reservoir?TGR?is the most important strategic water resources and aquatic ecosystem in China.However,the TGR used a special water level scheduling method of "winter storage and summer draining" to form a fluctuating zone with an area about 440 km²,and its ecological environment is sensitive and fragile.In recent years,the slather of phthalate esters?PAEs?and organophosphate esters?OPEs?brings us lots of austere environment and social problems.The periodic water level change of the TGR made the fluctuating zone in wet and dry alternation for a long time.PAEs and OPEs in the fluctuating zone soil were used as a source release to the overlying water,and they also were used as a sink to enter the fluctuating zone soil.Therefore,we investigated the occurrence,distribution and health risk of the PAEs and OPEs in the fluctuating zone soil of the TGR,which was the basis for solving the environmental hazard.It was of great significance to study and control the persistent organic pollutants in the TGR.In the present study,we selected the fluctuating zone of the TGR as our studying area and collected surface soils to analyze the concentrations and distribution of PAEs and OPEs using ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry?UPLC-Q-TOF-MS?in the fluctuating zone soil.Meanwhile,the interrelationship among the congers of PAEs and OPEs was also analyzed,and the potential sources of the PAEs and OPEs in soil samples were understood through correlation analysis and principal component analysis.According to the content and distribution of PAEs and OPEs in soil,the health risk assessment of PAEs and OPEs in the fluctuating zone soil was evaluated using the health risk assessment model,and simulated the migration and release characteristics of OPEs during the flooding.The results showed that the concentrations of ?₈PAEs ranged from 322.0-737.3 ng·g^-1 dry weight,with a mean value of 497.2 ng·g^-1 dry weight,which lie at the low end of worldwide figures.DIBP was the most abundant PAEs congeners,followed by DBP and DEHP,contributed to 94.5%of the total PAEs.However,DEHP was not the main pollutants compared with other studies,which might ascribe to the DEHP releasing from the flooded soil to surrounded water,but the degradation by the microorganism in the soil can not be completely ruled out.Significantly interrelationships were observed among DMP,DEP,DBP and DIBP,according to the principal component analysis,DMP,DEP,DBP and DIBP may have a similar source.The mean values of OPEs were 272 ng·g^-1 in farmland soil,while 486 and 498 ng·g^-1 in riparian soil,respectively,which lie at the middle range of the worldwide figures.The hydrodynamic conditions might be an important factors contributing to the slightly different spatial distribution of OPEs.The concentrations of OPEs in riparian soil exceed those in farmland soil,which could partly ascribe to the complete operation of the Three Gorges Dam?TGD?.Of particular note is the elevated contribution of TCP,followed by EHDPP,accounting for more than 90%of the total OPEs,and the degradation of TBEP by microorganisms in the soil could not be ruled out for the low occurrence of TBEP.Significant correlation between OPEs concentrations in farmland and riparian soil were obtained,indicating that OPEs in farmland and riparian soil originated from the same source.The principal component analysis showed that the OPEs in farmland soil might largely come from the construction and decoration materials and the OPEs in riparian soil may derived from the combination of construction materials and vehicular traffic emission.The health risk assessment results showed that the daily intake dose was lower than the reference dose?RfD?proposed by USEPA,and the carcinogenic risk of the 6 PAEs congeners was far below the tolerable values proposed by USEPA.Nevertheless,the daily intake dose of DBP occupied 60%to 84%of the total PAEs,more attention should be paid to the potential health risk caused by DBP.Comprehensive considered the content levels of the OPEs in soil,which health risk quotient was still far less than 1,so the health risks of human was not caused by the OPEs in soils.Since only the health risks of people passing through the soil medium in the farming environment were taken into account,the risk of food enrichment and diets were not taken into account at the same time.This showed that the health risks of PAEs and OPEs were underestimated.Therefore,the health risks of PAEs and OPEs should not be negligible.We also investigated the effects of OPEs concentrations,temperature,soil organic matter and microbial on the migration and release of several common OPEs from the fluctuating zone soil in the TGR to the overlying water by the simulation experiments in the lab.The results indicated that the release of OPEs was determined by its concentrations in soil.The release of OPEs from soil to the overlying water decreased with increasing content of organic matter,which indicated the presence of organic matter could inhibit the migration of OPEs.However,the inhibition of organic matter on the release of OPEs was not significantly enhanced when the organic content was greater than 30 g·kg^-1.The average migration amount of OPEs was 1077.3 ng·mL-1 at 27? which was higher than that at 7 ?,indicating that high temperature promoted the release of OPEs.The effect of microorganisms was not obvious.The chlorine-based OPEs including Tris?2-chloroethyl?phosphate?TCEP?,Tris?1-chloro-2-propyl?phosphate?TCPP?and Tris?1,3-Dichloro-2-Propyl?Phosphate?TDCP?were main monomers in the overlying water.The main reason was that both the Octanol-Water Partition Coefficient?Kow?and the Organic Carbon Partition Coefficient?Koc?of chlorine-based OPEs were lower than that of alkane-based OPEs and aromatic-based OPEs,thus chlorine-based OPEs were more easily dissolved in water and not easily adsorbed by organic matter in the soil.Therefore,the chlorine-based OPEs were more likely to migrate from the soil and release into the overlying water than other OPEs,becoming the main mononer types of OPEs in the overlying water of the TGR.