环境科学  2024, Vol. 45 Issue (9): 5244-5253   PDF    
北京市再生水补水河流中抗生素的赋存特征及生态风险评估
武亚林 , 徐井旭 , 刘桂中 , 方瑶瑶 , 蒋宝 , 孙成一 , 孙长虹 , 凌文翠     
北京市生态环境保护科学研究院, 国家城市环境污染控制工程技术研究中心, 北京 100037
摘要: 以北京市再生水补水河流凉水河为研究区域, 检测了水体和沉积物中16种抗生素的种类、检出率和浓度(含量)水平, 探讨其时空变化和赋存特征. 在水体和沉积物中分别检测到9种和13种抗生素, 抗生素的浓度(含量)范围分别为ND~116.68 ng·L-1和ND~235.42 ng·g-1. 水体中的主要抗生素为氧氟沙星和克拉霉素, 沉积物中的主要抗生素为氧氟沙星. 凉水河水体和沉积物中的抗生素总浓度(含量)表现为自上游至下游逐渐降低的趋势, 其支流浓度(含量)高于干流. 支流汇入对凉水河水体抗生素水平有明显影响, 但对沉积物则影响不大. 枯水期水体和沉积物中的抗生素总浓度(含量)整体高于丰水期. 丰水期水体中检出浓度最高的是喹诺酮类抗生素, 枯水期则为大环内酯类抗生素;沉积物在两季中检出含量最高的均为喹诺酮类抗生素. 生态风险评价结果表明, 水体中克拉霉素在枯水期表现为低风险, 克拉霉素在两季沉积物中具有低风险, 其余抗生素均表现为无风险. 联合生态风险及最敏感营养级生态风险表明, 所有点位生态风险表现为低风险和无风险, 枯水期整体大于丰水期. 部分点位在枯水期时接近中风险阈值, 需引起重视.
关键词: 抗生素      再生水      城市河流      赋存特征      生态风险     
Occurrence Characteristics and Ecological Risk Assessment of Antibiotics in Reclaimed Water-receiving Rivers in Beijing
WU Ya-lin , XU Jing-xu , LIU Gui-zhong , FANG Yao-yao , JIANG Bao , SUN Cheng-yi , SUN Chang-hong , LING Wen-cui     
National Engineering Research Center of Urban Environmental Pollution Control, Beijing Municipal Research Institute of Eco-Environmental Protection, Beijing 100037, China
Abstract: Taking Liangshui River, the reclaimed water-receiving river in Beijing, as the research area, the types, detection frequencies, and concentrations of 16 antibiotics in water and sediment were analyzed, and their temporal-spatial variation and occurrence characteristics were discussed. The results showed that nine and 13 target antibiotics were detected in the water and sediment of Liangshui River, with the antibiotic concentration ranges of ND-116.68 ng·L-1 and ND-235.42 ng·g-1, respectively. The main antibiotics in water were ofloxacin and clarithromycin, and the main antibiotic in sediment was ofloxacin. The total concentration of antibiotics in water and sediment showed a gradual decrease from the upstream to the downstream in the Liangshui River mainstream, and the concentration of antibiotics in tributaries was higher than that in the mainstream. The inflow of tributaries had an obvious impact on the antibiotic concentration in water for the Liangshui River but had little impact on its sediment. The total concentration of antibiotics in water and sediment during the dry season was generally higher than that during the wet season. The detected antibiotics with the highest concentration were quinolones in water during the wet season and macrolides in the dry season. Quinolones had the highest concentration in sediment in both seasons. The ecological risk assessment results showed that clarithromycin had a low risk in water in the dry season and sediment in both seasons, whereas the other antibiotics had no risk. The combined ecological risk and the most sensitive trophic level ecological risk assessment showed that all sampling sites had low risk or no risk, and the risk of the dry season was generally greater than that of the wet season. The risk values of some sampling points were close to the medium risk threshold during the dry season, which requires further attention.
Key words: antibiotics      reclaimed water      urban rivers      occurrence characteristics      ecological risk     

再生水作为一种稳定的补充水源, 在节约水资源, 保障城市用水需求, 维持河湖景观等方面发挥了重要作用[1~3]. 然而, 再生水普遍含有重金属、抗生素、全氟化合物、内分泌干扰物和个人护理产品等有毒有害污染物[4, 5]. 其中, 抗生素作为一种新兴污染物是国内外研究热点[6]. 我国是世界上最大的抗生素生产和使用国, 抗生素被广泛用于治疗、预防人类和动物疾病, 然而抗生素进入人体和动物体内后, 30%~90%的抗生素以原药或药物活性成分的形式通过粪尿排泄, 进而通过污水处理厂尾水、医疗废水、养殖废水和农业径流等排放进入各类环境介质, 发生不同形式的降解及迁移转化, 但由于环境中持续不断的抗生素输入, 致使环境中抗生素残留累积, 形成了伪持久性, 其生态风险不容忽视[7~12]. 相关研究表明, 抗生素对土壤微生物和动植物, 水生生物如藻类、枝角类和鱼类具有生态毒性效应[13]. 此外, 抗生素也会诱导产生耐药菌, 由此导致的抗性基因问题和人体健康影响也备受关注[14, 15]. 目前, 已在地表水、地下水、沉积物、土壤和农田等多种环境介质中检测到多类抗生素[16~19], 以再生水补给类河流为研究对象, 系统分析评估多种抗生素在水体和沉积物两种介质赋存特征及多种生态风险非常必要.

凉水河属于典型平原河网城市河流, 具有水深浅、流速慢, 河流自净能力差且底泥容易沉积等特点[20]. 该流域境内人口密集, 污水处理厂数量较多, 非汛期凉水河其水源补给以流域内污水处理厂退水为主, 是北京市城区南部重要的防洪、排水和景观河流. 本文选取凉水河下游作为研究区域, 考察凉水河水体和沉积物中16种抗生素的种类和浓度(含量)水平, 探讨水体和沉积物中抗生素的时空差异和赋存特征, 并通过生态风险评价方法识别出抗生素的生态风险, 以期为水环境抗生素污染研究以及制定经济有效的抗生素污染管控措施提供建议和科学支持.

1 材料与方法 1.1 实验材料

本研究选取磺胺类(sulfonamides, SAs)、大环内酯类(macrolides, MLs)、喹诺酮类(quinolones, QNs)和β-内酰胺类(β-lactams, β-Ls)这4类共16种抗生素作为目标抗生素. 其中磺胺类8种, 分别为磺胺吡啶(sulfapyridine, SPD)、磺胺醋酰(sulfacetamide, SA)、磺胺多辛(sulfadoxine, SDO)、磺胺二甲异嘧啶(sulfisomidine, SM2)、磺胺对甲氧嘧啶(sulfameter, SMT)、磺胺氯哒嗪(sulfachloropyridazine, SCPD)、磺胺间二甲氧嘧啶(sulfadimethoxine, SDM)和磺胺苯吡唑(sulfaphenazolum, SPP);大环内酯类3种, 分别为罗红霉素(roxithromycin, ROX)、克拉霉素(clarithromycin, CLA)和阿奇霉素(azithromycin, AZM);喹诺酮类3种, 分别为氧氟沙星(ofloxacin, OFL)、加替沙星(gatifloxacin, GAT)和洛美沙星(lomefloxacin, LOM);β-内酰胺类2种, 分别为青霉素V钾(penicillin V potassium, PV)和苯唑西林钠(oxacillin sodium, OXS). 抗生素检测内标物为磺胺间二甲氧嘧啶-D6(SDM-D6)、磺胺氯哒嗪-13C(SCPD-13C)、青霉素G钠-D7(penicillin G sodium, PG-D7)和盐酸双氟沙星-D3(difluoxacin hydrochloride, DIF-D3).

抗生素标准品与内标物分别购自德国Dr.Ehrenstorfer和天津阿尔塔公司, 实验溶剂甲醇和乙腈为色谱纯, 其它溶剂如甲酸、柠檬酸、乙二胺四乙酸二钠和磷酸氢二钠等为分析纯.

1.2 样品采集与前处理

于2022年6月和10月两次采样, 分别代表丰水期和枯水期情况. 采样范围为凉水河中下段干流(S1~S8)和支流(S9和S10), 及其小红门再生水厂(W1)与槐房再生水厂(W2), 具体位置如图 1所示. 使用采水器在河流中心和两岸分别采集表层水, 混合均匀, 保存于棕色玻璃瓶中冷藏, 24 h内完成预处理. 使用抓泥斗采集表层沉积物样品, 装入自封袋, 冷藏当天运回实验室, -20 ℃保存. 所有河流点位均采集水体和沉积物进行检测, 再生水厂退水点位仅采集水样.

图 1 采样点分布示意 Fig. 1 Distribution schematic of sampling sites

水样经0.45 μm玻璃纤维滤膜过滤后, 调节[pH =(3 ± 0.05)], 加入Na2EDTA和内标物混合溶液. 而后依次使用10 mL甲醇和10 mL超纯水活化HLB小柱(Waters, 6 mL, 150 mg), 水样以3~5 mL·min-1的流速通过HLB小柱. 抽干后使用10 mL甲醇进行洗脱, 35℃水浴氮气吹干, 加入甲醇定容至1 mL, 涡旋振荡1 min, 过0.22 μm针式滤膜, 上机检测.

沉积物样品冷冻干燥72 h, 去杂质研磨后过200目筛. 准确称取2 g沉积物样品于玻璃离心管中, 添加内标物混合溶液, 于4 ℃黑暗环境中静置24 h. 第一次提取加入5 mL柠檬酸提取液[pH =(4 ± 0.05)]和5 mL甲醇, 涡旋混匀1 min, 超声15 min, 4 000 r·min-1离心10 min, 提取上清液. 第二次和第三次提取使用EDTA提取液[pH =(4 ± 0.05)]和甲醇进行提取, 并重复上述步骤. 合并3次上清液, 超纯水定容至300 mL, 调节[pH =(3 ± 0.05)]后加入0.5 g粉末状Na2EDTA;剩余固相萃取、洗脱、氮吹和定容步骤与水样预处理流程相同.

1.3 样品检测分析

抗生素定量分析使用超高效液相色谱(Waters, Acquity)串联三重四级杆质谱仪(Waters, Xevo-TQD), 色谱柱采用Waters ACQUITY UPLC BEH C18(2.1 mm×50 mm×1.7 μm)色谱柱. 洗脱方式为梯度洗脱, 有机相为含0.1%甲酸的甲醇/乙腈(1∶1, 体积比)溶液, 水相为0.1%甲酸-水溶液. 色谱柱柱温为40 ℃, 进样体积10 μL, 流速设置为0.2 mL·min-1, 质谱采用多反应选择监测(multiple reaction monitoring, MRM)模式检测, 离子源温度为150℃;毛细管电压为3.2 V;碰撞气和脱溶剂气流量分别为50 L·h-1和550 L·h-1, 去溶剂温度为500 ℃. 目标抗生素及内标物质谱检测条件如表 1所示.

表 1 目标抗生素及内标物质谱检测条件 Table 1 Mass spectrometry detection conditions of target antibiotics and internal standard

1.4 质量控制与回收率

本实验使用内标法定量检测, 配制浓度为:1、2、5、10、20、50、100和200 μg·L-1的16种抗生素混合标准溶液, 建立标准曲线. 以3倍信噪比下的最低浓度作为检出限(LOD), 以10倍信噪比下的最低浓度作为定量限(LOQ). 16种抗生素在水体和沉积物中的检出限分别为0.01~2.0 ng·L-1和0.005~1.05 ng·g-1, 定量限分别为0.02~2.9 ng·L-1和0.01~1.15 ng·g-1. 在处理检测数据时, 低于LOD的按照未检出计, 低于LOQ的按照一半定量限值计.

16种目标抗生素在水样和沉积物样品中的回收率分别为56%~103%和73%~120%.

1.5 生态风险评价方法

采用风险商值法(risk quotient, RQ)对目标抗生素的生态风险进行评价, 当RQ < 0.01时表明无潜在生态风险, RQ为0.01~0.1时表明具有低风险, RQ为0.1~1时表明具有中等风险, RQ > 1时表明具有高风险[21, 22], 风险商(RQ)的计算方法如下:

式中, MEC与PNEC分别为抗生素实测浓度与预测无效应浓度, 预测无效应浓度由半致死浓度(EC50)或半数抑制浓度(LC50)和评价因子(AF)计算得出, 评价因子(AF)通常为:1000. PNECSediment为目标抗生素在沉积物中的预测无效应浓度, 由目标抗生素在水中的预测无效应浓度(PNECWater)乘以目标抗生素沉积物-水分配系数(Kd)计算得出.

然而, 环境中多种化合物的共存可能通过协同作用或拮抗作用增加整体的风险[23~25]. 因此, 为了评估混合毒性, 通常采用混合浓度模型进行评价, 如下所示:

式中, MRQMEC/PNEC为联合生态风险商值, MRQSTU为最敏感营养级生态风险商值, MECi和PNECi分别为第i种抗生素的实测浓度与预测无效应浓度, ECAlage、ECInvertebrate和ECFish分别为藻类、无脊椎动物和鱼类的半致死浓度, AF意义与前式相同. 由于计算混合风险商的参数同单一风险商的参数取值相同, 因此二者的风险等级评定相同.

2 结果与讨论 2.1 水体与沉积物抗生素检出情况与浓度(含量)水平

北京市凉水河及其支流水体中共检测出9种目标抗生素, 其中丰水期8种, 枯水期8种, 包括磺胺类3种, 大环内酯类3种, 喹诺酮类3种. 沉积物中共检测到目标抗生素13种, 其中丰水期10种, 枯水期12种. 包括磺胺类7种, 大环内酯类3种, 喹诺酮类3种. 水体和沉积物目标抗生素检出情况与浓度(含量)水平见表 2.

表 2 水体和沉积物中目标抗生素检出频率和检出浓度(含量)1) Table 2 Detection frequencies and concentrations of target antibiotics in river water and sediment

综合两季采样结果[图 2(a)], 发现所有点位的水样中均检测到了SPD、ROX、CLA、AZM和OFL;其余检出的抗生素按照平均检出率大小依次为:LOM(45%)= SCPD(45%) > GAT(10%) > SDO(5%);而SA和SM2等7种抗生素在两季中均未检出. 检出浓度较高的是OFL和CLA, 浓度范围分别为10.36~90.26 ng·L-1和3.43~116.68 ng·L-1;其次是SPD、ROX、AZM和LOM, 浓度最低的是SDO、SCPD和GAT.

图 2 凉水河水体和沉积物中目标抗生素浓度(含量)水平 Fig. 2 Concentrations of target antibiotics in water and sediment of Liangshui River

图 2(b)所示, 沉积物样本中在所有采样点位均检测到了ROX、CLA、OFL和GAT;LOM(95%)、SPD(85%)和AZM(65%)的平均检出率高于50%;其余检出的抗生素按照平均检出率大小依次为:SDM(45%) > SMT(35%) > SPP(10%)= SM2(10%)= SCPD(10%) > SDO(5%);OXS和PV在两季中均未检出. 3种喹诺酮类在沉积物中的检出含量最高, 含量范围分别为OFL(2.69~235.42 ng·g-1)、GAT(8.31~141.41 ng·g-1)和LOM(ND~45.64 ng·g-1), 其次是3种大环内酯类, 含量范围分别为ROX(0.21~8.51 ng·g-1)、CLA(0.23~4.69 ng·g-1)和AZM(ND~4.47 ng·g-1), 含量最低的是磺胺类和β-内酰胺类.

以上结果可以看出, 水体中喹诺酮类和大环内酯类的检出浓度高于磺胺类和β-内酰胺类. 大环内酯类抗生素是一种广泛用于治疗人类疾病的大分子化合物, 在我国常用的几类抗生素中使用量最大, 占比为26%[26]. 喹诺酮类用量同样较大, 占比为17%, 特别是氧氟沙星, 用于治疗呼吸道、咽喉、扁桃体和肠道等部位的急、慢性感染[27]. 凉水河流经北京市中心城区, 中下段的主要水源为再生水, 来自小红门再生水厂和槐房再生水厂, 两者主要处理生活污水, 每天处理量分别约为50万t和40万t. 由此可推测, 凉水河抗生素污染主要来自居民生活污染源. 磺胺类主要用于畜禽疾病防治, 相对于喹诺酮类和大环内酯类, 用量较少, 占比为5%[26]. 另外凉水河流域内养殖较少, 且根据入河排口的排查, 发现并无养殖废水直接入河, 因此整体检出率和检出浓度较低. β-内酰胺类在人兽疾病中均应用广泛, 是我国使用量较大的一类抗生素, 占使用总量的21%[26]. β-内酰胺类抗生素性质活跃, 在水环境中受光照和微生物等多方面作用极易发生降解, 特别是β-内酰胺易被β-内酰胺酶降解[28~30], 造成其在水体中未检出. 对比北京及国内其他地区, 该类抗生素检出率均低于喹诺酮类和大环内酯类[31~33].

沉积物中抗生素的含量受多种因素影响, 如抗生素本身理化性质、水体中抗生素的浓度和水力条件等[31, 34]. 从检出率看, 沉积物中喹诺酮类和大环内酯类的检出率高于磺胺类和β-内酰胺类, 这与水体中目标抗生素的检出情况类似. 从检出含量看, 沉积物中磺胺类、大环内酯类和β-内酰胺类均处于较低的含量水平或未检出;而喹诺酮类的含量水平则明显高于上述3类抗生素. 与大环内酯类和磺胺类相比, 喹诺酮类易被沉积物吸附, 且不易被微生物降解, 加剧了喹诺酮类在沉积物上的积累. 本文研究中的3种喹诺酮类抗生素均带有羧基(—COOH, pKa值约为5~6)和氨基(—NH2, pKa值约为7~10), 即有两个pKa值. 凉水河pH值在7~8之间, 3种喹诺酮类的存在形式以阴离子和两性化合物为主. 有研究表明, 污泥对环丙沙星的吸附以两性化合物为主[35], 由此推断凉水河的水环境条件有利于喹诺酮类抗生素在沉积物上的吸附. 喹诺酮类抗生素在自然水体中降解包括水解、光解和微生物降解, 但是研究表明, 氟喹诺酮类抗生素在水中很难发生水解[8, 36], 且光解和微生物降解过程相当缓慢[37, 38]. 另有研究表明, 喹诺酮类抗生素与阳离子螯合以及与颗粒物结合的能力较强, 这也会加剧其在沉积物中的累积[27, 39~41].

在众多的研究当中, 喹诺酮类在沉积物上的浓度都是比较显著的. 如陈丽红等[17]从全国尺度上调查了几类抗生素在江河沉积物中的浓度, 发现喹诺酮类诺氟沙星是主要污染物;山东省济南市南四湖沉积物中首要污染物是喹诺酮类和四环素类[42];在海河流域河流的沉积物中, 喹诺酮类含量最高, 如在白洋淀中的含量达到65.5~1 166 μg·kg-1[43].

2.2 水体与沉积物抗生素空间分布

凉水河及其支流水体和沉积物, 再生水厂退水中抗生素的空间分布如图 3所示, 可以看出凉水河干流(S1~S8)从上游往下, 水体和沉积物抗生素浓度(含量)整体呈现出逐渐降低的趋势. 两条支流新凤河(S9)与萧太后河(S10)的抗生素浓度(含量)明显高于凉水河干流.

图 3 凉水河水体和沉积物抗生素浓度(含量)空间分布 Fig. 3 Spatial distribution of antibiotic concentrations in water and sediment of Liangshui River

近年来, 北京市大力整治污染源和入河排口, 凉水河干流排口主要以雨水排口和污水处理设施排口为主, 河流抗生素主要来自污水处理设施和支流汇入. 图 1显示S1和S2点位之间分布有小红门再生水厂和槐房再生水厂的设施排口与支流北小龙河, S4与S5、S7与S8点位之间则分别有新凤河和萧太后河汇入. 图 3(a)显示, S2、S5和S8点位抗生素浓度明显高于各自上游的邻近点位. 从S9和S10点位可以看出新凤河和萧太后河水体中抗生素浓度范围处于较高水平, 整体高于凉水河干流. 对比其他研究中污水处理厂的抗生素检出水平[44~48], 小红门再生水厂和槐房再生水厂设施排口出水中抗生素浓度处于较低水平, 分别为59.47 ng·L-1和42.66 ng·L-1. 因此可以推测, 支流汇入是导致S2、S5和S8等点位抗生素浓度升高的主要原因之一, 而再生水厂出水中抗生素浓度较低, 对水体中抗生素浓度可以起到稀释作用.

与水体空间分布类似, 凉水河干流(S1~S8)从上游往下, 沉积物中抗生素含量呈现出较为规律的下降趋势. 同时, 与水体中规律存在两点不同. 首先, 相比水体, 沉积物中抗生素含量随河流沿程梯度变化更为明显. 从S1~S8, 凉水河干流长度为34 km, 沉积物中抗生素含量从309.76 ng·g-1降至86.05 ng·g-1, 衰减比例为72.2%, 而水体中浓度从177.16 ng·L-1降至79.92 ng·L-1, 衰减比例为54.9%. 其次, 再生水厂出水与支流汇入没有引起凉水河干流沉积物抗生素含量的明显变化. 水样更多反映抗生素在水体中的瞬时浓度, 易受来水的稀释和混合影响. 而沉积物中抗生素不仅受到水体浓度的影响, 还与河流泥沙运动有关, 同时沉积物中基质和微生物群落更为复杂, 对外界的输入和冲击表现出更强的缓冲能力[49, 50].

2.3 水体与沉积物抗生素季节性差异

综合季节的检测结果(表 2), 发现枯水期抗生素的检出种类、检出频率和浓度(含量)水平均高于丰水期. 从检出种类看, 水体丰水期为8种, 枯水期为8种;沉积物丰水期为10种, 枯水期为12种. 从检出频率看, 水体中除两季全部检出和全部未检出的种类外, SDO、SCPD和LOM在枯水期的检出率高于丰水期, GAT则情况相反. 对沉积物而言, 除两季全部检出和全部未检出的种类外, 大部分抗生素在枯水期的检出率高于丰水期, 如SPD、SMT、SDM、SPP和LOM等. 从浓度(含量)水平看, 水体与沉积物大部分抗生素在枯水期的浓度(含量)中位值和平均值明显高于丰水期(图 4).

图 4 不同季节凉水河水体和沉积物中抗生素浓度(含量)分布 Fig. 4 Distribution of antibiotic concentrations in Liangshui River water and sediment in different seasons

不同抗生素在两季中的浓度(含量)呈现出不同的规律. 对于水体来说, 丰水期检出浓度最高的是喹诺酮类, 如OFL, 浓度平均值为51.14 ng·L-1, 浓度范围为10.36~88.18 ng·L-1;其次是大环内酯类和磺胺类, β-内酰胺类未检出;而枯水期检出浓度最高的是大环内酯类, 如CLA, 浓度平均值为55.82 ng·L-1, 浓度范围为23.51~116.68 ng·L-1, 其次是喹诺酮类和磺胺类, β-内酰胺类未检出. 对沉积物来说, 两季含量最高的均为喹诺酮类, 磺胺类和大环内酯类处于较低水平, β-内酰胺类未检出. 丰水期和枯水期含量最高的均为OFL, 含量平均值分别为85.26 ng·g-1和86.52 ng·g-1;其次是GAT和LOM, 含量平均值分别为47.08 ng·g-1和20.69 ng·g-1(丰水期), 59.48 ng·g-1和18.67 ng·g-1(枯水期).

综上可知, 16种抗生素在枯水期的检出种类、频率和浓度(含量)均整体高于丰水期. 在水环境中抗生素受到光照、温度、pH和水力条件等多种因素影响[51]. 丰水期河流水量较大, 对抗生素浓度的稀释作用较强. 另外丰水期温度高且光照强, 有利于抗生素发生光解和微生物降解等, 使得水体与沉积物中抗生素累积量较少[37, 52~54].

2.4 目标抗生素的生态风险评价

根据水体与沉积物的抗生素浓度(含量)数据, 计算出两介质中抗生素对于不同营养级水生生物的生态风险商值(RQ)以及联合生态风险商值(MRQMEC/PNEC)和最敏感营养级生态风险商值(MRQSTU). 图 5表明, CLA在枯水期时对水蚤和绿藻的RQ值分别为0.017和0.027, 存在低风险;对于沉积物, CLA在丰水期时对绿藻有低风险, 枯水期时对水蚤和绿藻有低风险. 其余抗生素没有风险.

图 5 水体和沉积物抗生素RQ值 Fig. 5 RQ values of antibiotics in water and sediment

为了预测16种抗生素的联合生态风险, 计算了它们的MRQMEC/PNEC和MRQSTU. 结果表明(图 6), 所有点位水体与沉积物抗生素在两季的联合生态风险商值与最敏感营养级生态风险商值表现为低风险和无风险, 枯水期整体大于丰水期. 特别是点位S2、S9和S10水体中的抗生素, 在枯水期时其MRQMEC/PNEC分别为0.080、0.090和0.072, 接近中风险阈值, 需引起重视. 由于本文检测抗生素种类有限, 其他未被检测的抗生素生态风险无法预测, 因此本研究中预测的风险可能会低估真实的风险值.

图 6 水体和沉积物抗生素MRQMEC/PNEC与MRQSTU Fig. 6 MRQMEC/PNEC and MRQSTU values of antibiotics in water and sediment

3 结论

(1)凉水河水体和沉积物中分别检测到9种和13种抗生素, 检出浓度(含量)平均值范围为0.16~55.82 ng·L-1和0.04~86.52 ng·g-1. 水体中浓度最高的是喹诺酮类和大环内酯类, 氧氟沙星和克拉霉素为主要抗生素;沉积物中含量最高的是喹诺酮类, 氧氟沙星为主要抗生素. 喹诺酮类和大环内酯类的检出率和检出含量均高于磺胺类和β-内酰胺类.

(2)凉水河干流水体和沉积物中的抗生素浓度(含量)水平表现为自上游至下游逐渐降低的趋势, 两条支流高于干流. 同时, 干流沉积物中抗生素含量水平沿河衰减比例高于水体. 此外, 支流汇入会造成干流水体抗生素浓度升高, 对沉积物则无明显影响.

(3)枯水期的抗生素检出种类、频率和浓度(含量)整体高于丰水期. 丰水期水体浓度最高的是喹诺酮类, 枯水期为大环内酯类;沉积物在两季中含量最高的均为喹诺酮类抗生素.

(4)除SPD和CLA表现为低风险外, 大部分目标抗生素表现为无生态风险. 联合生态风险及最敏感营养级生态风险预测表明, 枯水期风险高于丰水期, 所有点位抗生素表现为低风险或无风险. 但是部分点位风险值接近中风险阈值, 需引起重视.

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