Preliminary Study On The Distribution Characteristics And Migration Behavior Of Environmental Corticosteroids And Estrogens In Tidal Flat Of The Pearl River Delta

A global concern about environmental endocrine disrupting chemicals（EDCs）pollution and its ecological and health impacts have attracted increasing attention in recent years.As typical EDCs,environmental corticosteroids（ECs）and environmental estrogens（EEs）are ubiquitous in the environment,and their adverse effects on the ecosystem are becoming increasingly prominent.Although the research on the occurrence of EDCs in terrestrial and aquatic environments has been gradually carried out,their speciation,geochemical behavior,and fate in some critical zones of surface environment are still in lack of systematic and in-depth understanding currently.The drying-wetting riverine tidal flat,as a transitional zone between water and land is an important component of the aquatic and terrestrial ecosystem.It plays an important role in the migration and transformation of pollutants.This study focuses on the composition,distribution,and migration of selected typical ECs and EEs in the riverine tidal flat of the Pearl River Delta（PRD）.A novel method based on ultrasonic extraction coupled with solid-phase extraction（SPE）for sample pretreatment was developed for the simultaneous determination of the 24 ECs and8 EEs including 3 phenolic estrogens（PEs）and 5 steroid estrogens（SEs）in water,sediment,and biofilm samples using ultra performance liquid chromatography-mass spectrometry（UPLC-MS/MS）and gas chromatography-mass spectrometry（GC-MS）for qualitative and quantitative analysis.The ECs average recoveries（relative standard deviation,RSD）of water,sediment,and biofilm samples were 73.9%-119%（1.2%-12.8%）,70.0%-127%（1.9%-12.5%）,and 71.4%-117%（1.0%-11.9%）,respectively,and those recoveries of the EEs were67.0%-127%（6.2%-12.2%）,73.8%-127%（1.0%-12.6%）,and 72.7%-126%（2.3%-11.6%）,respectively.The limit of quantitation（LOQ）of the ECs in the water,sediment,and biofilm samples were 0.50-1.43 ng/L,0.57-1.64 ng/g and 0.62-1.78 ng/g,respectively,and those LOQs of the EEs were 1.54-38.0 ng/L,1.79-39.6 ng/g and 4.48-41.0 ng/g,respectively.The method is efficient,sensitive,and reliable.Using this method,the pollution level,distribution characteristics,and multi-media partitioning of the ECs and EEs in the overlying water,biofilm,sediments of the riverine tidal flat and river bed sediments from the Guangzhou section of the Pearl River,the Dongguan section of the Dongjiang River,the Shiziyang Waterway,and three estuaries in the PRD were investigated.It was found that:（1）PEs:nonylphenol（NP）,octylphenol（OP）,and bisphenol A（BPA）were detected in all samples.SEs and ECs were detected in partial samples.The concentration ranges（mean/median）of the total ECs（ΣECs）in overlying water,tidal flat biofilm,tidal flat sediment,and bed sediment samples were not found（ND）-47.5 ng/L（1.59/0.95 ng/L）,ND-7.27 ng/g（3.89/1.79 ng/g）,ND-26.0 ng/g（1.46/0.71 ng/g）,and ND-2.49 ng/g（0.81/0.63ng/g）,respectively.The dominant pollutants include prednisone,clobetasol propionate,cortisone,and triamcinolone acetonide.The average concentrations of EEs in overlying water,tidal flat biofilm,tidal flat sediment,and bed sediment samples were ranging in<LOQ（estrone:E1）-38.0 ng/L（NP）（8571 ng/L,NP）,<LOQ（estradiol:E2）-39.6 ng/g（NP）（5535ng/g,NP）,<LOQ（E1）-7744 ng/g（NP）（10815 ng/g,NP）,and<LOQ（E1）-5006 ng/g（NP）（34642 ng/g,NP）,respectively.NP,OP,BPA,and E1 were the main pollutants among the EEs.（2）The ECs concentrations in the tidal flat overlying water of some reaches of the PRD were higher in the wet season than in the dry season.It might be due to the increasing direct discharging of untreated domestic sewage from the urban areas in the wet season.Spatially theΣECs concentration levels in the overlying water of the PRD occurred in the following order,the tributaries of Guangzhou section of the Pearl River>the main stream of Guangzhou section of the Pearl River>the Dongguan section of the Dongjiang River≈the Shiziyang waterway≈the estuaries.The main factors affecting its spatial distribution might be the municipal wastewater discharged along the river and the hydrologic conditions.The content of dissolved oxygen（DO）in the water and theΣECs concentrations in tidal flat overlying water were negatively correlated,suggesting that DO may be a key factor to regulate the distribution of ECs in the riverine tidal flat of the PRD.Higher concentrations of OP,NP,BPA,and E1 in the wet season were mostly found in the tidal flat overlying water,this might be related to massive amount of rainwater that had washed the sewage-irrigated soil and the untreated domestic sewage in the receiving rivers.The concentrations of EEs in the overlying water decreased in the order of the tributaries of Guangzhou section of the Pearl River>the main stream of Guangzhou section of the Pearl River>the Dongguan section of the Dongjiang Rive≈the Shiziyang waterway>the estuaries.In the tidal flat environment of the PRD rivers,water temperature,p H,and concentration of Chlorophyll a（Chl a）were the main factors affecting the distribution of EEs.（3）The solid-liquid partition coefficient（K_d）and normalized organic carbon partition coefficient(K_oc)of EEs between tidal flat sediments/biofilm and overlying water were correlated with DO,Chl a,total organic carbon（TOC）,and water temperature,suggesting that the above environmental factors may affect the occurrence and distribution of EEs among multimedia.The field-measured log K_ocvalues of EEs（OP,NP,and BPA）decreased in the order as follows:river bed sediment-overlying water>tidal flat sediment-overlying water>tidal flat biofilm-overlying water.It implies that EEs tend to be adsorbed by the biofilm and sediment on the tidal flat under the drying and wetting shifting conditions and tidal effects,and then gradually migrate to the riverbed from the nearshore zones with the growth and fall of biofilms and the re-suspension of tidal flat sediments.Finally they can accumulate in the bed sediment.Compared to the river bed sediment,higher proportions of ECs were found in the tidal flat sediment and biofilm.It was inferred that ECs were prone to adsorbed on the tidal flat biofilm and sediment.However,the frequent disturbance of multiple factors in the tidal flat environment could substantially facilitate the hydrophilic ECs to be desorbed back to the river water from the tidal flat biofilm and sediment.Besides those adsorbed in suspended particles might partially be degraded before transferring to the river bed sediment.For ECs and EEs,obviously the tidal flat biofilm possesses relatively strong adsorption capacity,which may depend on its organic carbon contents and characteristics.In summary,the biofilm and sediment on the tidal flat are both playing the role of temporary"sinks".Compared to the relatively stable environmental conditions at river bottom,the dry-wet shifting characteristic of the tidal flat environment would lead to the re-release of these pollutants.（4）Based on limited toxicological data,the ecological risk of a part of EEs in the tidal flat sediments of the PRD rivers was preliminarily assessed.Risk quotients（RQs）were found in the rage of 0.016-68.9 for EEs with an average of 19.6,indicating that the EEs could have posed high risks to aquatic organisms in the PRD rivers（ΣRQ>1）.Much higher risks level of the EEs were observed in the Guangzhou section of the Pearl River than those in the Dongguan section of the Dongjiang River,and the risk level of the estuaries was the lowest.The risks were mainly derived from NP,BPA,and OP.