Study On The Migration And Transformation Of The Typical Endocrine Disrupting Chemicals In Soil

Endocrine disrupting chemicals (EDCs) are harmful to wildlife even atconcentrations as low as1ng/L. The effluent of wastewater treatment plants, as well asthe reclaimed water originated from it, is considered as a major source of EDCs.The reclaimed water can transfer EDCs into soil and groundwater when it is usedfor irrigation and groundwater recharge. The purpose of this study was to investigate thespatial and seasonal variation of concentrations of EDCs in aquifers recharged byreclaimed water, meanwhile, select the typical EDCs, and then investigate the influenceof adsorption, biodegradation and recharge conditions on the fate of the typical EDCs,thus simulating and predicting the migration and transformation processes in aquifersrecharged by reclaimed water, so as to provide a technical support for risk assessment ofreusing the reclaimed water.An analytical method of separating and determining seven selected EDCs inwastewater and reclaimed water was developed. The method was based on solid-phaseextraction and ultra-performance liquid chromatography tandem mass spectrometry.The limit of detections for selected EDCs, namely, estrone (E1),17β-estradiol (E2),17α-ethinyl estradiol (EE2), estriol (E3), bisphenol A (BPA),4-n-nonylphenol, and4-t-octylphenol, ranged from0.01ng/L to0.06ng/L for reclaimed water andgroundwater.The detection rate of E1, E2, EE2, E3and BPA was100%among the64reclaimedwater samples in the Chaobai River, Beijing, where reclaimed water is used to rechargegroundwater through the permeable bed. The detection rate of EDCs was80.4%amongthe51groundwater samples. The highest detection frequency of BPA indicated thatBPA can be used as a sewage tracer in groundwater. The concentrations of EE2in23groundwater samples exceeded its predicted no-effect concentrations which indicatedthat EE2is the major compound causing the estrogenic activity of groundwater. Thus,BPA and EE2are selected as two typical EDCs in the studied aquifers recharged byreclaimed water.The saturated sorption capacity of EDCs in soil was influenced by the total organiccarbon and specific surface area of soil and molecular diameters of EDCs. The rate-limiting step of EDCs sorption was the diffusion in micropores. Sorptionnonlinearity was influenced by hard carbon content. The content and locationdifferences of hard carbon could explain various degrees of desorption hysteresis. BPAsignificantly suppressed the sorption of EE2, which could be attributed to the specificsorption on the hard carbon. The strong competitive sorption of BPA can enhance themobility of EE2.The aerobic biodegradation rates of EDCs in the soil-water system could bedescribed by a pseudo-first-order kinetic equation. The half-lives of EDCs in allcombinations were1.4-2.9times prolonged in the binary-chemical system than in thesingle chemical system. The following biotransformation pathway of estrogen wasproposed: E2/EE2â†'E1â†'E3. The desorption hysteresis suppressed the biodegradationrates of EDCs.In soil column under continual recharging, the migration rates of EE2and BPAdecreased45%after mixing0.5%black carbon with the packing soil. Theconcentrations of EE2and BPA in the effluent of soil column under intermittentrecharging were only0-44.5%of that under continual recharging. The parameters ofconvection-dispersion model were calculated by measuring the breakthrough curves ofEE2and BPA in the lab-scale column packed with the river sand obtained from theChaobai River. The convection-dispersion model fitted well with the measuredconcentrations of EE2and BPA in the unconfined aquifer with good uniformity. In thisaquifer, the migration rates of EE2and BPA were21.4m/a and28.5m/a, respectively.The half-lives were21.7d for EE2and20.4d for BPA. After ten years of continualrecharging, EE2and BPA will be detected in the groundwater with the distance of337mand734m to the bank of the Chaobai River.