Study On Pollution Characteristics And Ecological Risks Of Steroid Hormones In Taihu Lake

Steroids are widely used in aquaculture,animal husbandry,daily health care,disease treatment and other fields as muscle growth promoters and effective components of many drugs.The residual steroidal active substances can be continuously discharged into the natural environment from municipal sewage treatment plants,livestock farms or pharmaceutical factories.As a kind of potent endocrine disrupting chemicals,although the detected concentration is only at trace level,steroids of environment related concentrations can still cause significant endocrine disrupting effects in vertebrates,affecting their growth,development and reproduction,and even causing more serious consequences such as imbalance of sex ratio and reduction of population number.Taihu Lake is located in the Yangtze River Delta,which is very important in the Yangtze River economic belt.It plays an important role in supplying water for many surrounding provinces and cities,developing agricultural and fishery resources,and improving the downstream water quality.Understanding the occurrence trend and potential ecological risks of steroids in Taihu Lake is of great significance to protect the ecological security and residents’health in the surrounding areas.Therefore,this paper studies the occurrence level and spatial-temporal distribution of steroids in Taihu Lake;Three kinds of sediments of Taihu Lake with different properties were selected to carry out adsorption experiments on steroids,and the adsorption rules and mechanisms of steroids in the sediment-water system were analyzed through different kinetics and isotherm models;Risk quotient method was used to assess the risk of steroid hormones detected in Taihu Lake.Dexamethasone and humic acid were used as the representative of typical steroid and natural organic matter to study the toxicological effects of single and combined action on red tilapia(Oreochromis niloticus),so as to preliminarily explore the effect of natural organic matter on the bioavailability of steroids.The main conclusions are as follows:(1)Eleven steroids were detected in the surface water of Taihu Lake.Among them,estrogens estriol and androgen androstenedione were the main detected hormones,with the detection frequency of 43%and 41%,respectively.The average concentrations of androgen androstenedione and progesterone levonorgestrel were relatively high,which were 1.02 and1.25 ng/L,respectively.Six steroids were detected in the sediments,of which the detection frequency of progestogen levonorgestrel was 91%,and the average concentrations of cortisone and dexamethasone were 1.95 and 1.26μg/kg dw,respectively.In temporal distribution,the total average concentrations of steroids in water of spring were significant higher than those of summer;the total average concentrations in sediments of winter were significant higher than those of summer.In spatial distribution,the total average concentrations of steroids in water and sediment of Gonghu Bay were both the highest,while Wulihu Lake was at a low level.In-situ organic carbon-normalized partition coefficient showed that steroids might not reach equilibrium in Taihu Lake,and the adsorption might be related to the organic matter content in sediments.(2)The pseudo second-order kinetic equation is more suitable for the adsorption of 12steroids in three sediments in this study.The adsorption process conforms to the principle of"fast adsorption,slow equilibrium".Increasing the initial concentration of steroids is conducive to the adsorption.The adsorption rate of steroids in three sediments was androgens>progestogens>estrogens.The equilibrium adsorption capacity of estrogen estrone and progestogen progesterone was the highest,and estrogen ethinylestradiol was the lowest.The commonly used Langmuir,Freundlich and linear partition adsorption isotherm models are suitable for the adsorption analysis of steroids in three sediments.The maximum adsorption capacity Q_m value of S3 was higher than that of S1 and S2 with significant difference,indicating that the higher the organic carbon content in sediment,the stronger the adsorption capacity of steroids.The K_d values of 12 steroids in three sediments showed the same trend,indicating that the nature property of steroids was also an important factor affecting the adsorption.(3)The conclusion is obtained by formula calculation.Most of the target steroids detected in Taihu Lake are at a low risk level to the lower aquatic organisms,but there are still some steroids that may cause high risk to some aquatic organisms.For different kinds of aquatic organisms,molluscs may be the most sensitive to steroids,while worms and algae may be more tolerant to steroids.Different from the lower aquatic organisms,most of the steroids showed medium to high risk to the higher aquatic organism-fish;ethinylestradiol and17α-methyltestosterone in the water environment,and dexamethasone in the sediments may have reached the level of potential risk to the dominant species Cyprinidae in Taihu Lake.(4)There was no significant change in the expression of steroid receptor gene in the liver of red tilapia exposed to 50μg/L or lower concentration of dexamethasone,SOD,LDH and BFCOD increased significantly after exposure to 50μg/L dexamethasone.The results showed that in the presence of DEX,red tilapia could enhance superoxide scavenging mechanism,glycolysis and steroid hormone synthesis.Fulvic acid has different effects on the bioavailability of DEX.Its existence weakens the feminization effect of DEX on red tilapia,but promotes the enhancement effect of DEX on glycolysis and steroid hormone synthesis.