Common Environmental Hormones And Their Conjugates In Water And Milk: Analytical Methods,Concentration Levels And Risk Evaluation

Environmental hormones can cause the adverse effects on human body and wildlife;therefore,have become one of the main hotspots in the field of environmental research.Since last 30 years,many research studies focused on environmental hormones;however,there are few studies have dealt with their conjugates.Hence,the important role of these conjugates in environmental matrix and the estimation of exposure levels in human has been ignored.Therefore,four estrogens and ten bisphenols and their conjugates were chosen as the target research entities in this study emphasizing on the systematic clarification of the importance of environmental hormone conjugates in environmental matrix and human exposure risk assessment by studying their removal in urban sewage systems.Further,the concentration levels and distribution of target compounds in river as well as the concentration levels and human exposure risk assessment in milk were also assessed.The main research contents and conclusions of this doctoral dissertation are as follows:(1)Due to the shortcomings of low recovery and sensitivity of the existing analytical methods for natural estrogens and their conjugates,a method based on the solid phase extraction(SPE)combined with ultra-high performance liquid chromatography tandem mass spectrometry(UPLC-MS/MS)was established and optimized for the determination of three natural estrogens,i.e.,estrone(E1),17β-estradiol(E2),estriol(E3)and six conjugated natural estrogens.The established method was successfully applied to determine the target estrogens from the samples of urban sewage and river water.The limits of detection(LODs)and limits of quantitation(LOQs)of 9 target entities in ultrapure water,influent and effluent of wastewater treatment plants(WWTPs)and river water were 0.02-0.39 ng/L and 0.05-1.29ng/L.The spiked recoveries were between 81.0% and 116.1%;while,the relative standard deviations(RSDs)were lower than 20.0%.The method has obtained satisfactory recoveries and the sensitivity is superior to previous works.(2)It is assumed that the main reason behind ineffective removal of 17α-ethynylestradiol(EE2)in WWTPs is the existence of conjugates in urban sewage.Therefore,an analytical method based on SPE-UPLC-MS/MS for the determination of EE2 and its sulphate conjugate(EE2-3S)and glucuronide conjugate(EE2-3G)was established and successfully applied for the analysis of urban sewage samples.The results showed that the detection frequencies of EE2,EE2-3S and EE2-3G in the influents of seven WWTPs were all 100%;while,the concentration ranged from 0.17 to 50.10 ng/L.The average concentrations of EE2-3G in the influent and effluent accounted for 83.7% and 79.6%;respectively,which not only indicates that EE2-3G was the main form in urban sewage but also confirms for first time that the existence of EE2 conjugates is important reason for the poor removal of EE2 in current WWTPs.At the same time,the concentration of EE2-3G in the effluent was 8 times higher than that of EE2 indicating that the potential ecological risk of EE2 in the effluent to the receiving water has been seriously underestimated.(3)Based on the fact that natural estrogens and EE2 conjugates existed in the urban sewage and the inference that they are most likely to exist in the river water,the concentration levels of E1,E2,E3 and EE2 as well as their eight main conjugates in Guangzhou section of Pearl River Basin were also investigated.Except for E3-3-glucuronide sodium salt,the remaining 11 targets were detected;where,the proportion of conjugates in the total concentration was high with an average of 81.0%.Since the conjugated hormones can be converted into the corresponding active environmental hormones under the action of the corresponding enzyme,its environmental risk in river water cannot be ignored.By comparing the concentrations of target compounds in the upstream and downstream of seven WWTPs in Guangzhou,it was confirmed that the WWTPs effluent was the main source of environmental hormones in surface water.(4)In order to verify the important role of environmental hormone conjugates in human exposure risk assessment,the differences between enzymatic hydrolysis and non-enzymatic hydrolysis of 10 bisphenol substances(BPs)were studied in milk.In the absence of enzyme hydrolysis,the concentrations of BPs in 13 brands of fresh milk were between not detected-12.75 ng/m L.After enzymatic hydrolysis,the average concentration of the targets increased by 6.8%-107.1%.These results confirmed that the proportion of BPs conjugates in fresh milk is relatively high,which cannot be ignored.Since the current human exposure risk assessment of BPs in milk is mostly based on themselves,the human exposure risk of BPs in milk is seriously underestimated.In this thesis,four estrogens and ten BPs as well as their conjugates were taken as examples to confirm the proportion of high concentrations of environmental hormone conjugates in urban sewage,Pearl River water and milk samples.Further,it also systematically illustrated the important role of environmental hormone conjugates in water environment and human exposure risk assessment.Compared with environmental hormones,there are few studies on environmental hormone conjugates.In view of the important role of environmental hormone conjugates in environmental matrix,the research on their environmental behavior needs to be further deepened.This study also shows that during the evaluation of human exposure risk,ignoring the environmental hormone conjugates will inevitably lead to underestimation,which should be paid proper attention.