Trace Analysis Of Environmental Corticosteroids (ECs) In Suspended Particulate Matter And Sediment Samples And Its Application In Monitoring The ECs In Rivers Of The Pearl River Delta

Environmental corticosteroids（ECs）,as a class of“emerging”environmental endocrine disruptors,have increasingly received extensive attention from the international community for their pollution problem.Most of current studies on ECs pollution are focusing on surface water and sewage samples.There are few reports on the occurrence and spatial distribution of the ECs in environmental solid mediums such as suspended particulate matters（SPM）and sediments.Due to the complex matrix of SPM and sediment samples,it is difficult to implement effective environmental monitoring.Therefore,it is significant to develop an efficient and sensitive trace analysis method for simultaneously measuring various glucocorticoids and mineralocorticoids in these environmental solid samples.This will be helpful to the supervision and prevention of these emerging endocrine disruptors.In this study,the pretreatment of the solid samples were developed and the instrumental analysis conditions were optimized.A novel method was achieved for the simultaneous determination of the 24 ECs in sediment and SPM samples using ultra performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS）.The correlation coefficients of linear calibration curves were greater than 0.995 in the range of 1.0-100μg/L.The recoveries of the 24 ECs at 5,20,50 ng/g spiked levels ranged from 64.9%to 125.1%with relative standard deviations of 0.4%-12.6%.For the sediment sample,the limits of detection（LODs）and limits of quantification（LOQs）of all the 24 compounds were 0.14-1.25 ng/g and 0.26-2.26ng/g,respectively,and the relative standard deviations（RSDs）were 0.4%-12.6%.For the SPM sample,the LODs and LOQs were 0.28-0.97 ng/g and 0.51-2.48 ng/g,respectively,and the RSDs were 0.7%-9.4%.The method is sensitive,accurate,and reliable.Moreover,the developed method was applied and analyze ECs in SPM and sediment samples from the rivers of the Pearl River Delta.The specific results are as follows:（1）The concentrations of total ECs（ΣECs）in the SPM from the rivers of the Pearl River Delta ranged from<LOQ to 1724 ng·g^-1.The pollution was mainly derived from amcinonide,deoxycorticosterone acetate and clobetasone butyrate.The average SPM concentrations ofΣECs in the four rivers occurred in the following order:the tributaries of the Guangzhou section of the Pearl River(238.1 ng·g^-1)>Dongguan section of the Dongjiang River(74.7 ng·g^-1)>Foshan section of the Beijiang River(69.5 ng·g^-1)>the main stream of the Guangzhou section of the Pearl River(42.4 ng·g^-1).The concentrations ofΣECs in SPM presents a spatial trend of increasing first and then decreasing from upstream to downstream.TheΣECs concentration levels of tributaries of the Guangzhou section were higher than those of the mainstream,and the concentrations ofΣECs in the dry season were generally higher than those in the wet season.（2）Total organic carbon（TOC）,dissolved oxygen（DO）and chlorophyll a（Chl a）were correlated with ECs concentrations.It implied that these environmental factors are important factors affecting the occurrence and distribution of the ECs in SPM of the Pearl River.According to the distribution characteristics of ECs between SPM and surface water,it is found that a considerable proportion of ECs is existing in the water phase（80.2%±19.7%）.The relationship between the ECs log K_d values of SPM/water with TOC and DO indicated that TOC and DO were playing an important role in controlling the distribution of ECs between the SPM and surface water.（3）The concentration ranges（average/median）of theΣECs in the sediments of the main stream,tributaries of the Guangzhou section of the Pearl River and the Dongguan section of the Dongjiang River were<LOQ(0.63 ng·g^-1)-3.35 ng·g^-1(1.4/1.3 ng·g^-1),<LOQ(0.73 ng·g^-1)-5.28 ng·g^-1(1.77/0.99 ng·g^-1)and<LOQ(0.17 ng·g^-1)-5.40 ng·g^-1(1.10/0.61 ng·g^-1),respectively.In the north channel of the Guangzhou section of the Pearl River,the concentrations ofΣECs of the sediments increased firstly and then decreased from the upstream to the downstream,and theΣECs concentrations in the tributaries were higher than those in the main stream.Regarding the Dongguan section of the Dongjiang River,a general trend was shown in which lower ECs levels were found in the upper reach,and the contaminant concentrations gradually increased from upstream to the middle and lower reaches.The spatial distribution of ECs is mainly affected by human activities,point source pollution and hydrodynamics.The multiphase distribution of the ECs revealed that most of the ECs are enriched in the sediments,followed by the water phase,and the lowest proportion of them is associated with the SPM.Risk assessment inferred that the pollution of ECs in the sediments of the tributaries of the Guangzhou section of the Pearl River is at a high risk level.The main stream of the Guangzhou section of the Pearl River and the Dongguan section of the Dongjiang River are at a medium to high risk level.These might have posed a serious threat to benthic organisms and benthic fishes in the rivers.（4）According to the vertical distribution profiles of the ECs,it was found that the concentration of those corticosteroids with higher hydrophobicity and lower water solubility rose with the increasing of depth.These compounds tend to migrate from the surface to the tidal flat of the rivers,and finally accumulate in the deep riverbed.The sediment/water log K_d value of each selected compound is larger than the SPM/water log K_dvalue,indicating stronger interactions of ECs with the sediment.The log K_d values of the sediment/water were negatively correlated with DO and Chl a,and positively correlated with TOC,suggesting that DO,Chl a and TOC are important factors controlling the partitioning of ECs between the sediment and water phases.