湖泊科学   2021, Vol. 33 Issue (2): 483-493.  DOI: 10.18307/2021.0214.
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研究论文——水环境保护与修复

引用本文 [复制中英文]

张亚茹, 张国栋, 王永强, 刘晓晖, 毕斌, 刘宪斌, 卢少勇, 新疆赛里木湖近岸表层水典型抗生素的赋存与风险评价. 湖泊科学, 2021, 33(2): 483-493. DOI: 10.18307/2021.0214.
[复制中文]
Zhang Yaru, Zhang Guodong, Wang Yongqiang, Liu Xiaohui, Bi Bin, Liu Xianbin, Lu Shaoyong. Occurrence and ecological risk of typical antibiotics in surface water of the Lake Sayram, Xinjiang. Journal of Lake Sciences, 2021, 33(2): 483-493. DOI: 10.18307/2021.0214.
[复制英文]

基金项目

国家自然科学基金项目(41877409)和科技基础性工作专项重点项目(2015FY110900)联合资助

通信作者

卢少勇, E-mail:lusy@craes.org.cn

文章历史

2020-02-13 收稿
2020-05-23 收修改稿

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新疆赛里木湖近岸表层水典型抗生素的赋存与风险评价
张亚茹1,2 , 张国栋2 , 王永强2 , 刘晓晖2 , 毕斌2 , 刘宪斌1 , 卢少勇2     
(1: 天津科技大学海洋与环境学院, 天津 300457)
(2: 中国环境科学研究院湖泊水污染治理与生态修复技术国家工程实验室, 环境基准与风险评估国家重点实验室, 国家环境保护洞庭湖科学观测研究站, 北京 100012)
摘要:利用超高效液相色谱-串联质谱联用技术(UPLC-MS/MS)检测了2019年3月份和7月份新疆赛里木湖近岸表层水中12种抗生素的浓度水平,分析了赛里木湖表层水中典型抗生素的时空分布特征及生态风险.结果表明,氧氟沙星和磺胺甲恶唑为赛里木湖中主要抗生素污染物,春季最高检出浓度分别为2.7×104和1.8×103 ng/L,其次为红霉素(71.7 ng/L)和土霉素(15.9 ng/L),其余抗生素浓度均小于10.0 ng/L.与其他湖泊或河流地表水相比,赛里木湖抗生素浓度除磺胺甲恶唑和氧氟沙星外,基本处于中等或低水平.由于人类活动和水力流动等因素,抗生素浓度存在时空分布差异,夏季抗生素浓度比春季低2~4个数量级;位于养殖区内的S1点位抗生素总浓度明显高于其他点位.风险评估结果表明,春季红霉素、氧氟沙星和磺胺甲恶唑对赛里木湖生态环境持高风险(RQ>1).
关键词赛里木湖    抗生素    赋存特征    生态风险    
Occurrence and ecological risk of typical antibiotics in surface water of the Lake Sayram, Xinjiang
Zhang Yaru1,2 , Zhang Guodong2 , Wang Yongqiang2 , Liu Xiaohui2 , Bi Bin2 , Liu Xianbin1 , Lu Shaoyong2     
(1: School of Ocean and Environment, Tianjin University of Science and Technology, Tianjin 300457, P. R. China)
(2: National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, State Key Laboratory of Environmental Criteria Risk Assessment, State Environmental Protection Scientific Observation and Research Station for Lake Dongtinghu(SEPSORSLD), Chinese Research Academy of Environmental Sciences, Beijing 100012, P. R. China)
Abstract: Occurrence characteristic of antibiotics in the surface water of Lake Sayram in Xinjiang were analyzed by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Ofloxacin and sulfamethoxazole were the main antibiotic pollutants in Lake Sayram. The highest concentrations of ofloxacin and sulfamethoxazole were 2.7×104 ng/L and 1.8×103 ng/L, respectively, followed by erythromycin (71.7 ng/L) and oxytetracycline (15.9 ng/L). Others were less than 10.0 ng/L. The antibiotic concentration of Lake Sayram, except for sulfamethoxazole and ofloxacin, were basically at a medium or low level compared with most surface water. Due to human activities and hydraulic flow or other factors, the concentration of antibiotics in summer was 2-4 orders of magnitude lower than that in spring, and the total concentration of antibiotics in aquaculture area (S1 site) was higher than that in other points. The risk assessment showed that erythromycin, ofloxacin and sulfamethoxazole had a high risk to the ecological environment of the lake in spring(RQ>1).
Keywords: Lake Sayram    antibiotics    occurrence characteristics    ecological risk    

近年来,随着抗生素的大量使用,其归趋与危害引起人们广泛注意.中国作为抗生素的最大生产国和消费国,2013年总使用量为1.6×105 t,人均用量是欧美国家的6~10倍[1].但由于生物体的不完全吸收和代谢,部分抗生素在摄入后有25 % ~75 %以母体化合物或代谢物的形式排出,而传统污水处理厂和牲畜饲养场中对抗生素的去除效率较低,一般为36 % ~79 % [2],Thai等[3]研究发现制药污水处理厂中抗生素的残留浓度范围为41~250 μg/L,其中磺胺类和喹诺酮类的浓度最高;在一些亚洲国家,污水处理厂中部分抗生素的残留量甚至达到mg/L水平[4].残留的抗生素会通过废水排放等途径进入天然水环境,大量的研究调查表明[5],我国天然地表水中的抗生素污染物浓度为ng/L~μg/L,且不平衡的区域发展使抗生素残留浓度空间分布差异明显,且磺胺类(磺胺甲恶唑、磺胺嘧啶等)、四环素类(四环素、土霉素)、大环内酯类(红霉素和罗红霉素)及喹诺酮类(氧氟沙星等)抗生素在湖水和湖底沉积物中检测浓度较高(10~100 ng/L)[5].湖泊作为(半)封闭的水体,湖水流动性低,长期暴露其中的抗生素会对水相中典型微生物(硝化、反硝化细菌等)的生物量、活性及功能产生影响,抑制硝化、反硝化等作用,扰乱水环境中的氮磷循环过程[6],导致水质恶化并破坏湖泊稳态.此外,抗生素长期处于湖泊中可通过吸附、解吸等过程在水/沉积物界面迁移,诱导抗性基因的产生[7],而湖泊是淡水的重要饮用来源,抗生素或抗性基因可通过食物链富集,进而对水生生物、动物产生毒害作用甚至威胁人体健康.目前我国不断升级抗生素在临床及畜牧业中使用的管控措施并开展抗生素生产使用和环境中残留情况的调查,对于控制污染源,保护水生态健康有着重要的指导意义.

根据我国第一份抗生素污染地图[8],目前抗生素调查关注的重点区域多在东部,而对于西北部的关注较少.赛里木湖位于新疆博尔塔拉州博乐市境内北天山山脉中,是第五批国家级风景名胜区[9],旅游业较为发达;且在1998年引入冷水鱼养殖后,经过10年的发展,销往全国各地甚至是国外市场,已成为新疆重要的冷水鱼生产基地.但水产养殖和人体抗生素用药可能会使赛里木湖的敏感菌耐药性增强,对其它生物也可能产生一定的毒性进而对生态环境及人类健康造成潜在威胁[10],而目前对于新疆赛里木湖抗生素的赋存特征、风险水平等研究还未有报道.因此,本研究以新疆赛里木湖表层水为研究区域,选取畜牧养殖和临床中常用的四类抗生素(大环内酯类、磺胺类、喹诺酮类和四环素类)作为目标污染物,分析赛里木湖抗生素的赋存状况,并初步评价其生态风险,以期为赛里木湖的污染防治及环境保护提供科学的参考依据,丰富新疆地区有毒有害污染物的研究数据.

1 材料与方法 1.1 试剂与仪器

仪器:超高效液相色谱三重四级杆质谱联用仪(UPLC-MS/MS-8060,日本岛津);氮吹仪(NEVAP-111,南京铭奥仪器设备有限公司)、固相萃取装置(Agilent 5982-9110,12孔)、循环式真空泵(SHB-IIIA,上海振捷实验设备有限公司)、溶剂过滤器(T-50,天津市津腾市实验设备有限公司)、Waters HLB固相萃取柱(500 mg,6 mL)、酸碱pH计(上海雷磁PHS-25数显台式酸度计)、玻璃纤维滤膜(美国的Millipore公司,孔径0.45 μm)、涡旋混合器(VORTEX-5,海门市其林贝尔仪器制造有限公司),稀释标配仪(HAMILTON, USA).

12种抗生素标准品包括大环内酯类:罗红霉素(ROX)、红霉素(ERY);磺胺类:磺胺嘧啶(SDZ)、磺胺甲恶唑(SMX)、磺胺二甲嘧啶(SMZ);喹诺酮类:诺氟沙星(NOR)、环丙沙星(CIP)、恩诺沙星(ENR)、氧氟沙星(OFLO);四环素类:四环素(TC)、土霉素(OTC)、金霉素(CTC),以上12种抗生素均购自Dr. Ehrenstorfer GmbH (Germany),纯度大于99 %.实验所用的甲醇购自Fisher ChERYicals (Fair Lawn, NJ, USA)(色谱纯)、Na2-EDTA、氨水、甲酸和甲酸铵购自Sigma-Aldrich (St. Louis, MO, USA) (色谱纯),盐酸购自国药集团化学试剂有限公司(优级纯),实验中用水为超纯水(Millipore超纯水系统,USA).

1.2 样品采集

2019年3月和7月在新疆赛里木湖设点采样,共设置8个采样点(S1~S8)(图 1).使用不锈钢水样采集器采集表层水,采集深度为0~1 m,置于用甲醇和超纯水清洗过并用水样润洗3次的1 L棕色瓶中,然后加入5 mL甲醇,运到实验室于0~4℃冰箱保存,样品于15 h内进行预处理.

图 1 赛里木湖采样点位 Fig.1 Sampling sites in Lake Sayram
1.3 样品预处理与仪器分析

样品预处理:准确量取1 L水样,过0.45 μm的玻璃纤维滤膜(Whatman GF/F, 0.45 μm, USA),调节pH值为3并加入Na2-EDTA,水样以一定的流速通过已预先活化过的Waters Oasis HLB(500 mg,6 mL)固相萃取柱,后在真空下抽2 h至干.用甲醇和5 %氨水-甲醇溶液洗脱抗生素,在温和的氮气流动条件下,40℃水浴条件下将洗脱液用氮吹仪吹至近干,用1 mL 10 %的甲醇复溶,过0.22 μm膜过滤,将提取液转移到2 mL样品瓶中进行分析,待测.具体方法详见本课题组以前研究[11-12].

仪器分析:UPLC测定采用InertSustainTM Bio C18色谱柱(2.1×100 mm(UP),1.9 μm)对抗生素进行分析.流动相为A相-0.1 %甲酸;B相-乙腈.样品分析时,色谱柱保持在40℃.流速为0.4 mL/min,进样量2 μL,洗脱方式为梯度洗脱,B相初始浓度为10 %,洗脱程序见表 1.质谱采用离子源为电喷雾离子源(ESI)多反应监测(MRM)的扫描模式,接口温度为300℃,雾化气流速为3.0 L/min,加热气流速为10.0 L/min,干燥气流速为10.0 L/min,驻留时间为17.0 ms.

表 1 梯度洗脱程序 Tab. 1 Gradient eluting procedure
1.4 质量控制

采用外标法定量分析. 12种抗生素标准品分别用甲醇配成1 g/L的标准储备液,以7个不同梯度的标准物质溶液作定量曲线,混合标准溶液的浓度0.5~100 μg/L,相关性系数R2均大于0.99.分别以比S/N≥3和S/N≥10的信噪比计算方法的检测限和定量限分别为0.06~0.47和0.25~1.88 μg/L.回收率指示物为13C3-咖啡因,加入浓度为50 ng/L,抗生素的回收率分别为大环内酯类91.3 % ~95.6 %;磺胺类95.2 % ~98.7 %;喹诺酮类90.3 % ~ 94.8 %;四环素类80.5 % ~86.7 %.相对标准偏差为1.3 % ~6.7 % (表 2).设置3个平行样品,定期检测溶剂空白、程序空白和工作标准溶液,以监测系统性能和可能的污染.具体方法见本课题组以前研究[11-12].

表 2 12种抗生素的回收率、标准偏差、检测限及定量限 Tab. 2 Antibiotic recoveries of antibiotics, relative standard deviation, limits of detection and limits of quantification (water)
1.5 生态风险评价

本文采用了生态风险熵(RQ)的方法对赛里木湖水生环境中残留抗生素的生态风险进行评价[7, 13].基于最坏情况考虑(点位抗生素浓度最大值),筛选最敏感的物种作为测试生物种,毒性数据均来自于国内研究文献,且均选取标准实验的急性毒性结果.对于慢性毒性数据,筛选的原则是当同一物种有多个毒理数据可用时,选取暴露时间最长的NOEC,具体每种抗生素的毒性数据见表 3.计算公式如下:

$ RQ = MEC/PNEC $ (1)
$ PNEC = (NOEC\;{\rm{or}}\;L\left( E \right){C_{50}})/AF $ (2)
表 3 抗生素对最敏感物种的毒理学数据 Tab. 3 Toxicological data of antibiotics to the most sensitive species

式中,MEC为所测抗生素的最大环境浓度(ng/L),PNEC为预测的无效应浓度(ng/L). EC50LC50是最敏感物种的急性半致死浓度,NOEC为最敏感物种的慢性(长期)未观察到的影响浓度,AF为评估因子,基于EC(2003)[14]AF的值为1000(急性毒性数据)或100(慢性毒性数据).采用3个风险水平:RQ < 0.1表示风险可忽略,0.1≤RQ < 1表示低风险,RQ≥1表示高风险.

2 结果与讨论 2.1 赛里木湖近岸表层水抗生素的污染状况

赛里木湖共检出4类(大环内酯类、四环素类、磺胺类、喹诺酮类)7种抗生素,浓度和检出频率见图 2表 4.抗生素浓度范围为ND~2.7×104 ng/L,其中红霉素、磺胺甲恶唑和氧氟沙星残留浓度较高,检出率分别为100 %、100 %和64 %,且最大浓度均在3月份检出,分别为71.7、1.8×103和2.7×104 ng/L,是赛里木湖中主要的抗生素污染物.罗红霉素的检出率(57.1 %)高于土霉素(16.7 %),但其浓度水平与检出率呈现相反的结果,其余抗生素浓度均处于较低水平(低于10 ng/L).

图 2 赛里木湖采样点抗生素的累积浓度 Fig.2 Accumulative concentration of antibiotics in sampling sites of Lake Sayram
表 4 赛里木湖春季和夏季的抗生素检测频率及浓度(ng/L) Tab. 4 Summary of antibiotic detection frequencies and concentrations in Lake Sayram in Spring and Summer

磺胺类抗生素仅检出磺胺甲恶唑,总浓度范围为31.5~1.8×103 ng/L,平均浓度为2.8×102 ng/L,总检出率达100 %,这可能与赛里木湖冷水鱼养殖基地季节用药特性有关.此外,磺胺甲恶唑具有良好的化学稳定性和环境迁移能力,不易被降解[20]. Grenni等[21]研究发现磺胺甲恶唑及其主要转化产物N4-乙酰磺胺甲恶唑是被测河流水样中的持久性化合物,且添加磺胺甲恶唑后河流中的微生物群落丰度降低,不利于其通过微生物被降解.

喹诺酮类抗生素中氧氟沙星、诺氟沙星和恩诺沙星均有不同程度的检出,总检出率分别为100 %、14.3 %和28.6 %,其中诺氟沙星仅在春季S1检出,浓度为10.7 ng/L;恩诺沙星的总浓度范围在0.5~4.6 ng/L之间,而氧氟沙星平均浓度为2.0×103 ng/L,远高于新疆博斯腾湖中氧氟沙星的平均浓度(32.2 ng/L)[22].排入赛里木湖的抗生素可能受到水的稀释、扩散等作用较弱,加之氧氟沙星对水解不敏感且生物降解过程受硝化过程共代谢的影响较大[23],因此排入天然水体的氧氟沙星主要通过光解降解,但光解受到水中溶解性物质、pH以及光敏剂等多种因素的影响[24],降解速率缓慢,这可能是造成氧氟沙星浓度较高的重要原因.

罗红霉素和红霉素均属于大环内酯类抗生素,春季红霉素浓度处于11.5~71.7 ng/L,检出率为100 %,夏季红霉素仅在S5点位检测出,浓度为0.4 ng/L,检出率为16.7 %.大环内酯类抗生素低检出浓度与其在地表水中的低持久性与高生物可降解性相关[25],Vione等[26]研究发现3月份晴天照射的条件下大环内酯类抗生素半衰期一般为10 d,且地表水中其他污染物对光降解大环内酯类抗生素的影响较小.

四环素类抗生素中仅有土霉素在春季S5点位检出,浓度为15.9 ng/L.四环类抗生素在水环境为酸性或碱性条件下均不稳定,土霉素和金霉素均具有光解特性[27],而赛里木湖海拔高,日照时间长,有利于四环类抗生素的降解.同时四环类抗生素具有较高的Kow,容易被沉积物或土壤吸附,因此四环类抗生素在湖中检出浓度较低,但仍需进一步调查湖泊沉积物中的抗生素浓度以确定其迁移转化途径.

2.2 赛里木湖近岸表层水抗生素的时空分布特征

根据红霉素、磺胺甲恶唑和氧氟沙星在S1~S6点位的浓度变化对赛里木湖典型抗生素污染物进行时空分布分析(图 3).夏季(7月份)磺胺甲恶唑和氧氟沙星的平均浓度分别为1.8和27.4 ng/L;春季磺胺甲恶唑和氧氟沙星的平均检出浓度分别为2.8×102和3.4×103 ng/L,比夏季高出2~3个数量级.春季浓度检出高的原因与低温季节赛里木湖区域水产养殖业中投加抗生素量大及降解速率低有关,春季是投放鱼苗及药物的最佳时期,磺胺甲恶唑和氧氟沙星是杀菌效果好的广谱抑菌剂,在兽用和人体治疗方面使用较为广泛[11].同时低温季节微生物活性低、赛里木湖区域光照弱,不利于抗生素的生物和光降解[28].此外,赛里木湖雨季通常在6-7月,坡面径流量大,对湖表层水中抗生素浓度具有一定稀释作用.

图 3 赛里木湖抗生素浓度的时间变化 Fig.3 Temporal variation of antibiotic concentration in Lake Sayram

夏季红霉素仅在S5检出,浓度为0.4 ng/L;春季红霉素的平均检出浓度为30.7 ng/L,远高于夏季.红霉素用于水产养殖可预防鱼类白嘴病等疾病,因此当鱼类受这些疾病影响时,红霉素使用量会增加[29].同时,光和生物降解是自然环境中去除抗生素的两条重要途径,而温度明显会影响抗生素的降解速率,Alexy等[30]研究了光照和温度对抗生素降解速率的影响,发现在15℃时抗生素的降解效率要远高于5℃,因此夏季水环境中红霉素的残留浓度较低.

赛里木湖各采样点的平均浓度在27.2~5.8×103 ng/L之间(图 4).春季各采样点的抗生素浓度存在空间差异,其中S1点位累计浓度最高(29.1 μg/L),其次为S5点位,累计浓度为3.3×102 ng/L,两点位主要贡献因子为磺胺甲恶唑和氧氟沙星,贡献率达到98 %.由图 4可知,各采样点的中位线基本处于30~50 ng/L之间,但S1累计抗生素浓度高出其他点位3~4个数量级.从S1点位所处位置来看,近岸的样品受到人为活动的影响很大,污染物可能受到水的稀释、扩散作用等较弱[31],排入湖内的抗生素不易被降解稀释.同时S1点位处于冷水鱼养殖区,磺胺类和喹诺酮类抗生素既能够抑制疾病的产生,又可作为促生长剂促进鱼的生长[32],因此一般在越冬后大量使用.从抗生素本身的性质来看,尽管抗生素的持久性低于POPs,但若持续大量排入会造成抗生素在环境中呈现“假持久性”的情况[33],磺胺类抗生素具有较低的Kd和Koc值,对土壤和沉积物吸附亲和力较低[34],在水生环境中具有较高的稳定性,不利于其在水环境中的自然降解.氧氟沙星亲水性较强,易溶于水但其光降解受到pH和溶解性有机质(DOM)的显著影响,3月赛里木湖平均pH为7.7,电导率为2.1×102 s/m,而研究表明[35]pH为8且水中DOM较低时氧氟沙星光降解速率较大,这可能是导致氧氟沙星残留浓度的另一原因. S5点位抗生素残留浓度较大,但残留量最大的药物不一定仅与其绝对使用量相关,还可能与其在水环境中的吸附、迁移、降解等环境行为有关[34]. S7点位抗生素累计浓度最低,原因可能为S7位于坡面径流入湖口的交汇处,水流通量较大,对抗生素浓度有一定稀释作用.赛里木湖作为新疆最大的冷水鱼养殖基地及著名的旅游景点,部分区域养鱼密集、旅游区污染较为分散可能是导致不同点位浓度不一样的另一原因;部分区域虽未作为景点或养鱼基地,但由于抗生素在水体中的迁移等,这些区域会出现一定程度的抗生素积累.后续应加强对赛里木湖抗生素使用和排放的调查,追溯其来源,为湖泊中抗生素污染控制提供依据.

图 4 春季赛里木湖8个采样点的7种目标抗生素的空间分布 (分割框上下分别表示25和75百分位数.横线代表中位值,正方形代表均值,黑点代表异常值) Fig.4 Spatial distributions of 7 target antibiotics at 8 sampling sites in Lake Sayram in Spring (The upper and lower sides of the split box represent 25 and 75 percentiles, respectively. The horizontal line represents the median value, the square represents the mean value, and the black spot represents the abnormal value)
2.3 与国内外部分湖泊及河流比较

国内外部分河流湖泊中均存在不同程度的抗生素污染(表 5),磺胺类和喹诺酮类抗生素是湖泊和河流中普遍存在的污染因子[36].赛里木湖磺胺类药物中仅检测出磺胺甲恶唑,平均浓度为1.6×102 ng/L,与白洋淀(平均浓度2.4×102 ng/L)同处于较高污染水平;最高浓度为1.8×103 ng/L,低于肯尼亚内罗比流域(最高浓度1.4×104 ng/L).渭河、洪湖和汉江(韩国)的磺胺甲恶唑最高污染浓度均大于1.0×102 ng/L,低于赛里木湖和内罗比流域,高于国内松花江、巢湖(<50 ng/L)等湖泊.喹诺酮类抗生素中氧氟沙星在赛里木湖水体中的最高浓度为2.7×104 ng/L,高于滇池(7.1×102 ng/L)和渤海湾(5.1×103 ng/L)[36],而辽河与洪湖氧氟沙星浓度水平一致(<3.0×102 ng/L),东洞庭湖、新疆的博斯腾湖、白洋淀和松花江氧氟沙星最高浓度<1.0×102 ng/L,均显著低于赛里木湖氧氟沙星浓度.巴河、辽河及白洋淀诺氟沙星平均浓度在20~50 ng/L范围内,处于较高污染水平,而赛里木湖诺氟沙星春季检出浓度为10.7 ng/L,略高于松花江和大通湖春季检出浓度,处于中等污染水平.赛里木湖恩诺沙星的平均浓度为2.0 ng/L,与松花江相似,低于巢湖、洞庭湖、大通湖及博斯腾湖等湖泊,处于较低污染水平.恩诺沙星和诺氟沙星在水产养殖中的使用率较氧氟沙星少,这可能是导致它们在水中浓度较低的原因.

表 5 国内外典型河流、湖泊中抗生素的浓度(ng/L)水平* Tab. 5 Concentration level of antibiotics in typicalriver and lakes in China and foreign

罗红霉素在赛里木湖中的平均检出浓度为2.2 ng/L,红霉素平均检出浓度为30.7 ng/L,低于国内湖泊中大环内酯类抗生素的平均污染浓度[34],与松花江等河流污染水平相似.大环内酯类抗生素广泛用于治疗动物和人类的细菌感染疾病,赛里木湖周围居住者较少,且春季游客量较少,大环内酯类抗生素污染水平较低.四环素和金霉素在赛里木湖均未有检出,土霉素检出最高浓度为15.9 ng/L,略高于巢湖、东洞庭湖,博斯腾湖等(<10.0 ng/L),但明显低于巴河、洪湖及汉江(韩国)等地表水体.

总体来说,赛里木湖抗生素检出种类较少,抗生素浓度除磺胺甲恶唑和氧氟沙星之外均低于国内外大部分河流及湖泊,S1点位的磺胺甲恶唑和氧氟沙星浓度较高甚至达到微克每升的级别,这与当地抗生素的使用情况及环境中抗生素的存在形态有关,因而会呈现出较大差异.

2.4 生态风险评价

基于RQ风险熵值法对3月份赛里木湖水体中7种抗生素——罗红霉素、土霉素、磺胺甲恶唑、氧氟沙星、恩诺沙星、诺氟沙星和红霉素的潜在环境风险进行评价.计算的RQ值见图 5.磺胺甲恶唑、氧氟沙星及红霉素的最高浓度在S1~S8点位分别表现出聚球藻(Synechococcus leopoliensis)和近头状尖胞藻(Pseudokirchnerella subcapitata)具有高急性风险(1.2<RQ<2.4×103).诺氟沙星和恩诺沙星的RQ范围在0.02~0.1之间,对Vibrio fischeri分别表现为中等慢性风险和较低急性风险.大环内酯类和四环素类抗生素风险值在10-2~10-3数量级之间,对敏感的水生生物构成的急性风险可忽略不计(RQ<0.01). 3月份赛里木湖被冰雪覆盖,不仅水汽界面交换量小,水面也难以接受到足够的太阳光,磺胺甲恶唑和氧氟沙星在温度较低的自然环境下很难依靠生物降解或光降解在短时间内去除[48].更为重要的是,赛里木湖以养殖冷水鱼为主,大量使用养殖用的抗生素可能会导致食用性鱼类产生耐药性,进而可能对长期食用具有耐药性肉类的人类健康产生潜在威胁[49].

图 5 春季赛里木湖采样点抗生素RQ值分布 Fig.5 Distribution of antibiotic RQ in sampling sites of Lake Sayram in Spring

本研究利用单化合物的急性或慢性毒性数据,初步评价了抗生素污染对赛里木湖可能存在的潜在风险,但LC50EC50忽略了抗生素的协同毒性作用[42],在此基础上评估的风险可能比实际环境中低.此外,由于缺乏实际环境长期的生物毒性数据,利用常规敏感物种对赛里木湖抗生素污染风险水平进行慢性研究可能影响风险评估结果的有效性.因此,在此基础上可以进一步应用物种敏感度分布(SSD, species sensitive distribution)方法来根据不同物种对某一环境胁迫不同的敏感度构建累积概率分布模型,从而得出在某一暴露浓度水平下的物种潜在受影响比例,定量反映风险水平[50].同时,考虑到长期暴露于低浓度抗生素造成的抗生素耐药性的生态风险,赛里木湖地区在使用抗生素和向环境排放抗生素方面需要更好的环境管理或管制.

3 结论

赛里木湖近岸表层水共检出7种抗生素,其中氧氟沙星的平均浓度最高(2.0×103 ng/L),其次为磺胺甲恶唑(1.6×102 ng/L)和红霉素(17.6 ng/L),检出率均为100 %,磺胺甲恶唑和氧氟沙星为赛里木湖主要抗生素污染因子,土霉素、诺氟沙星、罗红霉素和恩诺沙星浓度范围为0.06~16.0 ng/L,且检出率均低于50 %.与国内外部分河流相比,赛里木湖抗生素污染情况处于中等水平,但局部采样点(S1和S5)氧氟沙星和磺胺甲恶唑抗生素检出浓度较高,应引起重视.赛里木湖抗生素分布存在明显的时空差异,S1~S8点位夏季抗生素平均浓度为29.2 ng/L,低于春季2个数量级(3.8×103 ng/L).在空间分布上,S1点位浓度最高(累计浓度为29.1 μg/L),S7最低(累计浓度为81.6 ng/L),其中氧氟沙星和磺胺甲恶唑贡献率达99 %以上.通过RQ法评价春季检出的7种抗生素对湖泊水环境的风险,处于高风险的(RQ>1)的抗生素为红霉素、氧氟沙星和磺胺甲恶唑,其余抗生素污染处于较低的风险水平.

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