Occurrence, seasonal variation and spatial distribution of EDCs in the water of Taihu Lake
Detection frequencies and levels of concentrations
Table 1 shows the average, median, maximum and minimal concentrations as well as detection frequencies of the 31 EDCs at all the nine sampling sites in both sampling events. Except four compounds including Epite, Corti, Prednl and Noreth were not detected in both summer and winter, other 27 compounds were detected at varied frequencies (11-100%). A highest detection frequency of 100% is observed for three EDCs including DES, BPA and BPS in both June and December at all the nine sampling sites. This suggests the wide applications of these three EDCs in Taihu area. Nan-phen, TES-pro, E2-ben and BPF were detected at frequency of 100% in winter, and E2-ben and BPF were also detected at high frequency of 89% and 44% in summer. Four EDCs including TES-pro, Dexa, Predn, and Hexe were not detected in the wet season (summer),however, higher detection frequencies of 100%, 11%, 44% and 89% were observed in the dry season (winter), respectively. In contrast, Tren and Norges were not detected in the dry season (winter), but higher detection frequencies in the range of 22% and 11% were observed in the wet season (summer). As for the categories of the EDCs, three out of five individual compounds and all seven estrogens were detected at high frequency in both June and December (44-100%), except for OP and NP (11-22%) and Hexe in Summer (0%). Seven out of eight Androgens were detected at low frequencies (0-22%, except 56 % for Bold ) in summer; however, four out of eight androgens were detected at high frequencies in winter (44%-100%, Nan-phen and TES-pro 100%; Me-TES 67% and TES 44%). Five out of six progesterones were detected at low frequencies in both summer (0-22%) and winter (0-56%), whereas higher detection frequencies were observed for Proges (89% in winter and 56% in summer). In general, adrenocortical hormones were detected at the lowest frequencies. In summer, only one out of five adrenocortical hormones (Me-prednl) were detected ; in winter, low detection frequencies (0%-44%) were also observed for four out of five adrenocortical hormones, and only a higher detection frequency was observed for Me-prednl (56%). In general, the detection frequency of EDCs in Taihu Lake is higher in dry season than that in the wet season.
The highest concentrations of all 31 detected EDCs were typically below 10 ng/L in both summer and winter (Table 1), except five compounds including BPA (102.89 ng/L in summer; 291.70 ng/L in winter ), BPS (45.35 ng/L in summer; 230.45 ng/L in winter), BPF (7.44 ng/L in summer; 114.03 ng/L in winter), Me-prednl (14.3 ng/L in summer) and Nan-phen (13.78 ng/L in winter). In June, the average concentrations were in the range of 0.19 to 28.57 ng/L, the median concentrations were in the range of 0.19 to 22.8 ng/L, and the maximum concentration was 102.89 ng/L (BPA). The average concentrations were below 1 ng/L for estrogens (except E3), androgens (except Tren), progesterones, and adrenocortical hormones (except Me-prednl) in summer. In December, the average concentrations were in the range of 0.33 to 84.87 ng/L, the median concentrations were in the range of 0.3 to 42.15 ng/L, and the maximum concentration was 291.7 ng/L (BPA). BPA showed the highest average concentrations in both June and December (28.57 and 84.87 ng/ L, respectively ), followed by BPS (10.2 and 37.35 ng/L, respectively ) and BPF (3.62 and 21.98 ng/L, respectively). Progesterones showed low concentrations (< 1 ng/L) in both June and December. Individual compounds were predominant and the total concentrations accounted for 44% to 96% of all the five categories of EDCs in each sampling sites.
Seasonal variation and spatial distribution
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It can be seen from Figure 2 that the total concentration of each type of EDCs in the water samples of each sampling point is higher in winter (1-20 times) than that in summer as a whole, except for the progesterones at S1 and S2, the glucocorticoids at S2 and S4, and the industrial substances at S8 and S9. The results show that the concentration of phenolics EDCs is affected by many factors with the changes of high and low water periods. Water flow pattern, industrial wastewater discharge, discharge source distance, dilution effect, temperature, production consumption and other factors will affect pollutant residues[26]. When the temperature increases, the activity of microorganisms in the water will also increase. Some of the biodegradable substances will be consumed by microorganism metabolism, resulting in the decrease of their concentration in the water [27] . In addition, in the wet season, affected by continuous rainfall and other factors, the water volume and flow rate of rivers and lakes are not stable, and the flow pattern changes greatly. In the wet season, aquatic plants in the water can absorb phenol at the same time. Based on the above factors, the concentration of EDCs in Taihu Lake water in summer is significantly lower than that in winter. However, in the dry season, there is less rainfall, the dilution effect of water flow in winter is weakened, the mobility of water flow is poor, and the flow pattern is relatively stable. Therefore, the concentration of pollutants in water in winter will increase relatively, which is the same as the conclusion of kin et al. [28] in the study of seasonal changes of alkylphenol in Seine River. The detected numbers of EDCs at each sampling point in winter and summer were compared, as shown in Figure S1. It can be seen that the number of EDCs detected at each sampling point in winter is higher than that in summer, which proves that the concentration of substances detected in low water period is higher than that in high water period on the whole.
Industrial compounds and estrogens are the main pollutants in surface water of Taihu Lake. BPA, BPS and BPF are the main detected substances of industrial compounds, and BPA > BPS > BPF. In winter, Taihu Lake is more seriously polluted by industrial compounds. The species and concentration of EDCs in different sampling points were different. Yan et al. [29] tested the EDCs in Taihu Lake water. The detection frequency of E2, E3 and BPA was 100%. The concentration of EDCs in different spatial sampling points also varied greatly, which may be caused by the different hydrological conditions of the lake water in different periods. In the nine sampling points, the concentrations of four kinds of substances in the north of Taihu Lake (S1-S5) were higher than those in the East (s6-s9), no matter in summer or in winter. Further work including more sampling events would be required to give a definitive seasonality.
For the spatial distribution, as a whole, the EDC concentrations in Wuxi Taihu Lake (North Taihu Lake, S1-S5) is higher than that in the Suzhou Taihu Lake (East Taihu Lake, S6-S9), which is consistent with our previous drug research results [30]. S1, S2 and S3 sampling points are located in Meiliang Bay and Zhushan Bay of Wuxi, which are economically developed and have serious industrial pollution. Meiliang Bay and Zhushan Bay, as receiving water bodies, receive a large number of sewage from sewage treatment plants in surrounding towns and untreated domestic sewage [31]. Meiliang Bay has been polluted seriously over the years. The water quality of the lake is generally V-type or inferior V-type, and the water exchange is slow, basically in a semi closed state. There are many chemical plants along the main river flowing into Zhushan Bay (S3), about 26000 tons of BPA are put into use as raw materials or standby materials every year, and the industrial wastewater discharged into the river by the chemical plant can reach 23400000 tons every year. Liu et al. [13] measured the EDCs in the tributary water of Taihu Lake, and found that the concentration of industrial compounds detected in Caohe was the highest (1380 ng/ L), which increased the concentration of S1 after flowing into Taihu Lake. S4 is located near Lihu bridge. Lihu lake is the inner lake of Taihu Lake stretching into Wuxi. It is the closest to the downtown of Wuxi City among all sampling points. The surrounding population is dense. There are about 50 hospitals and clinics. The discharge of a large number of municipal wastewater and domestic sewage may be the main reason for the high concentration of EDCs in S4 point [32]. S5 is located in Gonghu Bay and at the entrance of Wangyu River. As shown in Figure 2, the total detected concentration of estrogen in S5 is relatively high (3.75 ng / L in summer and 11.9 ng / L in winter). Wangyu River is a project river of "diverting the river to the Taihu Lake". Liu et al. [33] measured the EDCs in the Yangtze River water of Nanjing section, and found that the concentration level of phenol EDCs in the Yangtze River water was higher than that in Taihu Lake. Hu et al. [34] Detected a high concentration of estrogen in the Yangtze River, which entered Taihu Lake with the branch water of the Yangtze River (S5), which may be one of the reasons for the high concentration of estrogen in S5 [34]. According to Jiang et al. [35], both the activity of estrogen and the concentration of estrogen in the Yangtze River water are at the forefront of China. S6 is close to Suzhou, where the population is dense and animal husbandry and aquaculture are prevalent. Therefore, there are more estrogens discharged, resulting in higher concentration of four kinds of EDCs except industrial compounds in winter. A small amount of estrogen and androgen were detected in S7, S8 and S9. S7 is close to the center of the lake, most of which are villages and scenic spots, with relatively less pollution. S8 is close to Xukou. Xukou town has a rapid economic development in recent years. At the same time, S8 is located at the Hukou of Xujiang river. There are many villages and fishing villages along the Xujiang river. Most of the discharged domestic sewage and aquaculture wastewater are directly discharged into the river, and finally into Taihu Lake. S9 are close to Wuqi farm, with developed aquaculture and untreated wastewater. The aquaculture wastewater is directly discharged into Taihu Lake, which results in the detection of estrogen and androgen concentrations in S7, S8 and S9. In a word, the spatial distribution of EDCs is affected by hydrology, population density, industrial wastewater discharge, aquaculture, and river diversion project.
Comparison of EDCs pollution level with domestic and foreign water environment
The concentration of EDCs in the water phase of Taihu Lake was compared with that at home and abroad, see Table S5 for details. In general, the concentration of EDCs detected in Taihu Lake is relatively high in winter. The concentration range of 31 kinds of EDCs detected in Taihu Lake is 18.6-338.05 ng / L in winter and 16.22-112.69 ng / L in summer. In addition, BPA, BPS and BPF are the main EDCs detected in the water phase. The other two substances with relatively high detection frequency and concentration in Taihu Lake are estrogen (3.55-14.19 ng / L) and androgen (1.22-15.5 ng / L), respectively. Taking the BPA with the highest concentration (2.38-291.7 ng /L) detected in Taihu Lake as an example, which is lower than that in Yangtze River (Nanjing section) (nd-563 ng / L) [33], Pearl River (4-377 ng / L) [36], Liaohe River (12.3-755.6 ng / L)[37], slightly higher than that in Yellow River (12.5-171.5 ng / L) [38], and the same concentration level as Chaohu Lake (7.3-224.9 ng / L) [13]. Compared with foreign studies, it is lower than the concentration levels in Iberia (0.11-649 ng / L) and Singapore (nd-2470 ng / L) [5], and higher than those in Italy (nd-145) [39], Spain (6-126) [40] , Australia (4-59) [41], and Nigeria (not detected) [42]. It can be seen that BPA in surface water of Taihu Lake shows moderate pollution level. Compared with the detected concentrations of EDCs in surface water at home and abroad, the EDCs in Taihu Lake is in the moderate and low pollution level.
Distribution characteristics of EDCs in plasma of wild fish
Concentration levels and detection frequencies of EDCs in wild fish plasma
The detection concentration levels and detection frequencies of 31 EDCs in the plasma of five wild fishes was shown in Table 2. The detection frequencies of 31 EDCs in the plasma of five kinds of wild fish was between 0% and 100%, 8 EDCs including 1 androgen (Tren), 3 glucocorticoids (Dexa, Prednl, and Prednl), 1 estrogen (E2), 1 progestogen (Me-ace) and 2 industrial compounds (OP and NP) were not detected in all plasma samples, and the other 23 EDCs were detected in varying degrees. The total detection frequency (n=20) of androgen was between 5% (Noreth) to 35% (Nortes), except for tren (0%). For glucocorticoids, only Corti (100%) and me - prednl (10%) was detected. For estrogens, the detection frequency was between 5% (Dieno) to 100% (E2 Ben), except that E2 was not detected. For progesterones, except for Me -ACE (0%), other compounds were detected in the range of 5% (TES-pro) to 55% (hydrop). For industrial compounds, only BPA (45%), BPS (40%), BPF (20%) were detected. In terms of the maximum detected concentration in plasma of Carp (n=8) and silver carp (n=5), except Corti (43.61 μg / L in Carp and 37.24 μ g / L in silver carp), the highest detected concentration of other substances is no more than 10 μg / L, and the lowest detected concentration of 25 EDCs is less than 1 μg / L. The total concentrations of the five categories of EDCs varied, with the values of 17.31 μg/L (androgens), 10.55 μg/L (progesterone) , 41.5 μg / L (estrogens), 37.6 μ g /L (industrial compounds) and 351.15 μ g / L (glucocorticoids), respectively. Compared the distribution of EDCs in the plasma of different kinds of wild fish, the detection frequencies of tes (63%), nortes (63%), and hydrop (75%) in the plasma of carp was higher than that in the plasma of other four kinds of fish. The detection frequencies of Norges was 100% in the plasma of silver carp and 0% in the other four kinds of fish. The detection frequencies of industrial compounds (BPA, BPS) in carp, crucian carp, silver carp and plasma was higher, while that in silver carp was 0%. The average concentration of EDCs (10.15 μg / L to 27.53 μ g / L) in the plasma of five kinds of wild fish is not significantly different
It is worth noting that the detection frequency of E2-ben in plasma is 100%, which is consistent with the detection of E2-ben in water phase. E2-ben is more easily enriched in organism due to its high LogKow value (5.47). BPF was detected in water with high concentration and frequency, but rarely in fish plasma. Yu et al. [22] determined the EDCs in the plasma of sea bass, and found that the concentration range of E1 was 2.98-7.52 μ g /L, and the detection range of BPA was 1.18-6.21 μ g / L, which was similar to the detection level of BPA in the plasma in this study. Eight of the 31 EDCs were natural hormones, including Epite, TES, Corti, E1, E2, E3, Hydrop and Proges. Corti as a natural glucocorticoid was detected in all plasma, and the concentration of Corti was very high, ranging from 1.59-43.61 μg / L. In addition, the detection frequency of Corti, Epite and Tes-pro in water was 0%, but they were detected in fish plasma to different degrees, which may be due to the low content of this pollutant in water (lower than the detection limit of the instrument and cannot be quantified) and bioaccumulation of these compounds in fish. Also, because this kind of EDCs can be secreted and metabolized by a certain organ (adrenocortical fat) in vivo, the possibility of endogenous compounds cannot be excluded. In addition, the more frequent detection of Hydrop in all plasma samples may be related to it’s a natural synthetized hormone in the fish.
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Distribution of EDCs in plasma of different species of wild fish
The distribution of five categories of EDCs in the plasma of five kinds of wild fishes in Taihu Lake is shown in Figure 3. Except for glucocorticoids, the concentrations of other four kinds of EDCs (Estrogens, androgens, progesterones and industrial compounds) in fish plasma were generally low (< 10 μ g / L). The detection level of androgens in carp plasma (0.43-2.95 μg/L) is generally higher than that in crucian carp and silver carp (0.13-0.6 μ g /L), and the detection level of glucocorticoids in silver carp plasma is generally lower (1.59-21.44 μ g / L) than that in other four kinds of fish. The concentrations of estrogens in the plasma of crucian carp and silver carp (0.3-10.58 μ g / L) were higher than those of other kinds of fishes. The concentrations of progesterones in the plasma of spotted silver carp were slightly higher than those of other kinds of fish. The concentrations in the plasma of crucian carp and silver carp were comparable. The concentrations of industrial compounds in the plasma of crucian carp (0-7.19 μ g / L), carp (0.5-9.6 μ g / L), and silver carp (0.35-7.19 μ g / L) were comparable, but not detected in the plasma of spotted silver carp. In general, except for glucocorticoids and progesterones, there were no significant difference of the concentrations among the varied fishes for androgens, estrogens, glucocorticoids and industrial compounds.
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The total concentrations of each category of EDCs in the plasma of five kinds of wild fishes are shown in Fig.4. In general, glucocorticoids were detected at highest concentrations in all kinds of fishes, followed by industrial compounds and estrogens. The total concentrations of androgens in the plasma of carp range from 0.43 to 2.95 μ g / L, estrogen from 0.15 to 3.4 μ g / L, industrial compounds from 0.5 to 9.6 μ g / L. The total concentrations of glucocorticoids in the plasma of silver carp range from 0.44 to 37.24 μ g / L, estrogens from 0.3 to 10.58 μ g / L, and industrial compounds is 0.35-7.19 μ g / L. These differences may be due to the differences between carp and silver carp, including the physiological differences in the absorption, metabolism and elimination of pollutants. The result indicates that the distribution of EDCs in fish plasma is species-specific and compound-dependent.
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Bioaccumulation fators (BAFs) of EDCs in fish plasma
The study of bioaccumulation is of great significance in clarifying the migration and transformation of substances in the ecosystem and evaluating the possible impact of pollutants on the environment. It provides a scientific basis for the determination of environmental capacity and environmental standards. At present, BAFs have been used to quantitatively describe bioaccumulation, which is defined as the ratio of target pollutant concentration in fish to concentration in water. In the EU risk assessment system, compounds with BAF > 2000 are considered to show bioaccumulation, while compounds with BAF > 5000 are considered to show high bioaccumulation [43-44]. In order to evaluate the bioaccumulation capacity of EDCs in fish plasma, the BAF value in fish plasma of each EDCs was calculated. However, 11 compounds neither detected in the water (Epite, Corti, Predn, Noreth) nor detected in the fishes (Tren, Dexa, Predn, Prednl, E2, Me-ace, OP and NP) were excluded for BAF calculation. For the undetected substances in serval water or fish samples, take half of the value of each self-inspection limit [20]. Table 3 shown the calculated average BAF values of 20 EDCs in five kinds of fish plasma.
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From Table 3, it can be seen that the measured BAF values of 20 kinds of EDCs varied (0-5626). Most of the measured BAF values of EDCs in the plasma of five kinds of fishes are comparable, and most of EDCs do not show bioaccumulation, no significant interspecific difference is observed, and no relationship with fish weight / body length is observed. This result is consistent with previous study [20] which investigated the absorption of human use drugs in the plasma of Carassius auratus (Crucian carp) and Cyprinus carpio (Carp). The highest mean BAF value was observed for E3 (575 to 5626, LogKow 2.45), flowed by TES (373 to 3093, LogKow 2.99), Norges (250 to 2460, LogKow 3.8), Hexe (625 to 1400, LogKow 4.98), E2-ben (104 to 1572, LogKow 5.47), Hydrop (60 to 1390, LogKow 3.16) and Me-pro (1474 in Carb, LogKow 3.5). Only 3 compounds including E3, TES and Norges show bioaccumulation capacity (BAF>2000) in different kinds of fishes. The BAF value (5626) of E3 in crucian carp plasma is higher than that of the other four kinds of fishes, showing a high bioaccumulation. At the same time, E3 shows bioaccumulation in silver carp plasma (BAF 2632), while Norges only shows bioaccumulation (BAF 2460) in spotted silver carp plasma. The BAFs of 13 out of the 20 EDCs were below 1000, of which the lowest BAFs (<100) were observed for Nan-phen (LogKow 2.62), Proges (LogKow 3.87)), BPA (LogKow 3.32) and BPF (LogKow 2.97). The BAF of BPA in the plasma of crucian carp (45-116), carp (15-129), silver carp (19-23) and white streaked carp (44) was found to be comparable, which is consistent with the results of Liu et al. [45] in the bioaccumulation of BPA in wild carp (29) and wild crucian carp (18) in Dianchi Lake. However, the BAF value of BPA in our study is slightly higher than that of crucian carp and carp in Dianchi Lake, which also reflects the difference of water quality between Taihu Lake and Dianchi Lake. At the same time, the lower BAF value indicates that the bioaccumulation ability of BPA in fish is weak, which is also reflected in other fish (medaka 20-68, rainbow trout 1.7-38.4) [46-47]. As shown in Figure 5(a), the overall trend of measured logBAF increased linearly with the increase of LogKow values of EDCs, although the linear correlation is not significant (P>0.05, R2=0.0428 to 0.1520). This result indicated that the bioaccumulation of EDCs in fish plasma is not only hydrophobicity dependent. The bioaccumulation of EDCs in fish plasm is both fish species-specific and compound dependent, which is consistent with previous work[45]. Further work considering the tissue distribution and metabolism of the EDCs in the fish should be conducted.
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Application of the fish-plasma model
The classical fish plasma model (formula (2)) proposed by Huggett et al. [16] and the improved model (formula (3)) proposed by Fu et al .[24] and Schreiber et al.[25] were tested, and the PBlood:Water, i.e. the theoretical BCF value, was calculated and compared with the measured BAF value. The theoretical BCF values and average measured BAF values of 20 EDCs (other 11 EDCs indulging Epite, Corti, Predn, Noret, Tren, Dexa, Predn, E2, Me-ace, OP and NP were neither detected in the water or in the fish were emitted for the calculation) in five kinds of fish plasma were shown in Table 3. It is found that the theoretical BCFs calculated by the classical FPM (Formula 2, BCF0) are close to the measured BAFs for seven EDCs, including Nan-phen (LogKow 2.62), ME-TES(LogKow 3.61), E2-ben(LogKow 5.47), DES(LogKow 5.07), Hexe(LogKow 4.98), BPA(LogKow 3.32), and BPS(LogKow 2.91). In general, both the classical FPM and the improved FPM underestimate the BAFs of 11 EDCs, including TES (LogKow 2.99), Bold(LogKow 3.0), Nortes (LogKow 2.78), TES-pro (LogKow 2.97), Me-prednl (LogKow 1.5), E1(LogKow 3.13), E3(LogKow 2.45), Me-pro(LogKow 3.5), Hydrop (LogKow 3.16), Norges (LogKow 3.8) and BPF (LogKow 2.91). The BAFs of E2-ben(LogKow 4.98)and Dieno (LogKow 5.9) were overestimated by the classical FPM, whereas the BAFs of five EDCs including E2-ben(LogKow 4.98), Dieno (LogKow 5.9), DES (LogKow 5.07), Hexe (LogKow 4.98), proges (LogKow 3.87) were overestimated by the improved FPM. This results suggested it should be carefully to use the FPM models, since it either underestimated the BAFs of hydrophilic EDCs (logKOW <3.87) or overestimated the BAFs of high hydrophobic EDcs (LogKow >3.87) in fish plasma. The relationship between measured logBAF and the theoretical logBCF calculated by the FPM are clearly displayed in Figure 5(b) and Figure 5 (c). The overall trend was that the measured logBAF increased with the increasing of the theoretical logBCF, although the linearity was not significant (P >0.05). From the 1:1 line in Figure 5(b) and Figure 5(c), we can conclude that the FPM underestimate the LogBAFs of most hydrophilic EDCs (logKow <3.87) and overestimated the LogBAFs of several high hydrophobic EDcs (LogKow >3.87) in fish plasma. The good coincide of measured logBAF and the theoretical logBCF are only observed for limited EDCs. Compared with the classical FPM and the improved FPM, the former model seems superior to the latter which greatly overestimated the BAFs of high hydrophobic EDCs (LogKow >3.87). In general, although the present FPM is barely satisfactory, it is still promising for predicating the accumulation of EDCs in fish plasma and for further environmental risk assessment.
Fish plasma model is a risk assessment tool that can quickly screen out priority control pollutants. Based on the ratio of the therapeutic effect data of the existing drugs in mammalian plasma to the theoretical data of fish plasma predicted by the model, the effect ratio (ER) can be calculated, and the environmental risk of the drugs can be quickly determined according to the value of ER. Therefore, the establishment of a prediction model suitable for a variety of pollutants is the key to promote the risk assessment work, and will greatly simplify the risk assessment work. However, at present, there is a lack of data on the treatment of EDCs in human plasma, and the model is only applicable to a few compounds. Its universality needs to be continuously verified, and a large number of plasma and field data are still needed to improve the existing fish plasma model.