Soil-Water Interfacial Migration And Transformation Behavior Of Typical Endocrine Disrupting Chemicals In The Water-Level Fluctuation Zone Of The Three Gorges Reservoir

The ecological and environmental effects of the Three Gorges Reservoir?TGR?have received increased attention,and the immediate need for ecological civilization and ecological security has highlighted the urgency of these concepts.Endocrine disrupting chemicals?EDCs?have been proven to cause serious effects at even the lowest?e.g.,ng/L?levels.EDCs can cause reproductive disorders,birth defects,developmental abnormalities;they may also affect the occurrence and development of some cancers.EDCs exhibit strong hydrophobicity,low volatility,and natural photolysis.The adsorption/desorption behavior of EDCs in the Water-Level Fluctuation Zone?WLFZ?of the TGR directly affects the water ecological security of the reservoir.However,the environmental behavior of EDCs in the WLFZ of the TGR remains unreported.Existing research data are closely related to the properties of the soil,and the environmental conditions during research differ markedly from those in the WLFZ of the TGR.Large variations in water-level conditions and highly dense population distributions along the coast,for example,have been found.In this study,several typical EDCs were screened,and soil samples were collected from different water level gradients in the fluctuation zone as test materials.The adsorption,degradation,and release behaviors of EDCs at the soil�water interface in the TGR fluctuation zone were studied through controlled-condition experiments,and the effects of important environmental conditions on the migration and transformation of these chemicals were analyzed.The effects of biochar?BC?as a soil additive on the migration and transformation of EDCs were preliminarily discussed,thereby providing theoretical guidance and technical support for the ecological risk assessment and regulation of EDCs in the TGR.This research may be summarized as follows:?1?An analytical method for the simultaneous determination of five EDCs,namely,estrone?E1?,17?-estradiol?E2?,17?-ethinylestradiol?EE2?,estriol?E3?,and bisphenol A?BPA?,in water and soil samples was established by optimizing the conditions of the pretreatment of float liquid�liquid microextraction and high-performance liquid chromatography tandem mass spectrometry.The limits of detection for the selected EDCs ranged from 0.41?g/L to 7.50?g/L.?2?The adsorption process of EDCs in soil samples could be best described by a quasi-second-order kinetic equation.The adsorption rate of EDCs in soil samples with a long drying period is high but the equilibrium adsorption capacity is low.EDC adsorption and desorption isotherm data in soil samples from the fluctuation zone could be well fitted by the Freundlich model.The adsorption capacity of EDCs in soil samples positively correlated with soil organic matter content.In all water-level gradient soil samples,the adsorption capacity of EDCs showed the order EE2>E2>E1>BPA.Moreover,hydrophobic partitioning considerably influenced adsorption.The adsorption of EDCs in soil samples showed different degrees of non-linear adsorption?n:0.588�0.976?,and the desorption hysteresis index?HI?values of EE2,E2,and E1 were 0.576�0.682,0.652�0.862,and 0.676�0.819,respectively,thus indicating a certain desorption hysteresis.BPA showed no obvious desorption lags in all soil samples and strong migrability.?3?Environmental conditions significantly influenced the adsorption and desorption behaviors of EDCs in the soil�water system of the TGR fluctuation zone.The adsorption coefficient K_F of EDCs increased with decreasing temperature.Adsorption of EDCs into the soil of the WLFZ at low temperature was more advantageous.Increases in ionic strength contributed to the adsorption capacity of EDCs in the soil of the WLFZ.The amount of EDCs adsorbed in the experimental range increased significantly at first and then increased slowly with increasing ionic strength.The amount of EDCs adsorbed in the soil samples of the TGR fluctuation zone decreased with increasing pH,and alkaline conditions were not conducive to EDC adsorption.Under strongly alkaline conditions?pH>8?,the amount of EDCs adsorbed in the soil samples decreased sharply,and the amount of EDCs desorbed increased substantially.?4?After addition of BC,the adsorption kinetics and isothermal data of EDCs in the soil samples of the WLFZ could be fitted by a quasi-second-order kinetic equation and the Freundlich model,respectively.Addition of BC greatly enhanced the adsorptive capacity of soil samples for several types of EDCs,and the degree of non-linearity of adsorption was enhanced.With increasing proportion of BC,the contribution rate of the material to EDC adsorption increased.The contribution rate reached 51.1%�91.1%when 0.1%BC was added and further increased to 88.7%�97.8%when 0.2%BC was added.Before and after addition of BC,EDC adsorption in the soil samples in the WLFZ of the TGR involved an entropy reduction process with spontaneous heat release??G<0,?S<0?,and physical adsorption was the dominant mechanism observed.The absolute enthalpy of the EDC adsorption of soil samples treated with BC(20.43�40.95 kJ�mol^-1)was significantly higher than that of soil samples without BC(12.369�22.40 kJ�mol^-1).BC addition enhanced bonding between the soil and EDCs.With increasing BC addition,the desorption lag coefficient HI first decreased and then increased.Addition of BC of a certain range of concentrations could improve the adsorption capacity of soil and enhance the desorption hysteresis effect,such that EDCs could be well retained in soil.?5?The degradation rate of EDCs in the WLFZ of the TGR revealed the order E2>E3>E1>BPA>EE2,and the degradation process could be fitted by a pseudo-first-order dynamic model.Under the same experimental conditions,EE2 and BPA were quickly degraded in long-term flooded soil samples,and the half-life of EDCs was longer in soil samples with a long dry-up period.The degradation rate of EDCs decreased significantly at low temperature.Compared with their rates at 25 and35?,the degradation rates of EE2 and BPA at 10?decreased by 51.6%and 19.8%and by 77.3%and 24.7%,respectively;moreover,their half-lives under 10?were prolonged to 10.44 and 12.25 days,respectively.The degradation rates of EE2 and BPA at 40%W were 1.35 and 1.75 times higher than those at 15%W,respectively.In the flooded system,the EDC content in soil affected by desorption decreased rapidly in the first two days,after which the degradation rate became lower than that at 15%water content.The half-life of EDCs in soil with 0.1%BC addition was shorter than that in the original soil;indeed,the degradation of EDCs was inhibited by further addition of BC.During operation of the TGR,the large soil area in the WLFZ simultaneously functions as a sink and source of EDCs from a wide range of sources in the reservoir.The sink effect is significant during the impoundment period under the condition of low temperature and flooding,while the source effect is strong during the dry period under high temperature and frequent rainstorm conditions.During the drying-up period of the TGR,a feasible means to reduce the ecological risk of EDCs involves enhancing the coupling effect of fixation and degradation by addition of a certain amount of BC to the soil in the WLFZ.However,the optimal BC species,dosage,and application method deserve further investigation.