环境科学  2022, Vol. 43 Issue (12): 5534-5546   PDF    
引用本文
昌盛, 白云松, 涂响, 付青, 张坤锋, 潘杨, 王山军, 杨光, 汪星. 北江中上游地表水和沉积物中PAHs和PCBs污染特征和风险评估[J]. 环境科学, 2022, 43(12): 5534-5546.
CHANG Sheng, BAI Yun-song, TU Xiang, FU Qing, ZHANG Kun-feng, PAN Yang, WANG Shan-jun, YANG Guang, WANG Xing. Pollution Characteristics and Risk Assessment of PAHs and PCBs in Surface Water and Sediments in Middle and Upper Reaches of Beijiang River[J]. Environmental Science, 2022, 43(12): 5534-5546.
北江中上游地表水和沉积物中PAHs和PCBs污染特征和风险评估
昌盛1, 白云松1,2, 涂响1, 付青1, 张坤锋1,3, 潘杨2, 王山军1, 杨光1, 汪星1     
1. 中国环境科学研究院, 国家环境保护饮用水水源地保护重点实验室, 环境基准与风险评估国家重点实验室, 湖泊水污染治理与生态修复技术国家工程实验室, 北京 100012;
2. 苏州科技大学环境科学与工程学院, 苏州 215009;
3. 东北林业大学林学院, 哈尔滨 150040
收稿日期: 2022-02-20; 修订日期: 2022-03-28
基金项目: 国家重点研发计划项目(2021YFC3200804-02)；饮用水水源及重大工程项目区环境监管项目(2110302)
作者简介: 昌盛(1983~), 男, 博士, 副研究员, 主要研究方向为饮用水安全保障, E-mail: changsheng83@163.com
通信作者: 涂响, E-mail: tu_xiang@qq.com
摘要: 采用气相色谱-质谱法(GC-MS)测定了北江中上游流域地表水和沉积物样品中多环芳烃(PAHs)和多氯联苯(PCBs)类污染物的含量，分析了PAHs和PCBs的污染水平和空间分布，并评估了污染物的健康风险和生态风险.结果表明，16种PAHs单体在所有水样和沉积物样品中均被检出，检出范围分别为41.82~443.04 ng·L-1和59.58~635.73 ng·g-1，北江中上游PAHs的污染水平为中、轻度.水中PAHs以二环芳烃和三环芳烃为主，沉积物中以三环芳烃和四环芳烃为主.在水样中检出了17种PCBs，浓度范围0.81~287.50 ng·L-1，以六氯联苯和七氯联苯为主；沉积物中检出了8种PCBs，含量范围0.13~3.96 ng·g-1，以五氯联苯和七氯联苯为主.整个调查区域内地表水中PAHs和PCBs的终生致癌风险指数小于10-4，处于中、低水平；非致癌风险指数均小于1，不存在非致癌风险.采用风险商值(RQ)法对地表水中污染物进行生态风险评价，研究区域内地表水中PAHs和PCBs生态风险总体处于中低风险水平，个别点位存在重度风险的污染物单体，值得引起重视.采用沉积物质量基准法(SQGs)对沉积物中污染物进行生态风险评估，沉积物中PAHs和PCBs均处于较低的生态风险水平.
关键词: 北江      多环芳烃(PAHs)      多氯联苯(PCBs)      污染特征      风险评估     
Pollution Characteristics and Risk Assessment of PAHs and PCBs in Surface Water and Sediments in Middle and Upper Reaches of Beijiang River
CHANG Sheng1 , BAI Yun-song1,2 , TU Xiang1 , FU Qing1 , ZHANG Kun-feng1,3 , PAN Yang2 , WANG Shan-jun1 , YANG Guang1 , WANG Xing1     
1. State Environmental Protection Key Laboratory of Drinking Water Source Protection, State Key Laboratory of Environmental Criteria and Risk Assessment, National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Chinese Research Academy of Environmental Researchs, Beijing 100012, China;
2. School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009, China;
3. School of Forestry, Northeast Forestry University, Harbin 150040, China
Abstract: The contents of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in surface water and sediment samples from the middle and upper reaches of Beijiang River basin were determined using gas chromatography-mass spectrometry (GC-MS). The pollution level and spatial distribution of PAHs and PCBs were analyzed, and the health and ecological risks of pollutants were evaluated. The results showed that 16 PAHs monomers were detected in all surface water and sediment samples, with detection ranges of 41.82-443.04 ng·L-1 and 59.58-635.73 ng·g-1, respectively. The pollution levels of PAHs in the middle and upper reaches of Beijiang River were medium and mild. PAHs in water were mainly composed of bicyclic aromatic hydrocarbons and tricyclic aromatic hydrocarbons, whereas tricyclic aromatic hydrocarbons and tetracyclic aromatic hydrocarbons were mainly in sediments. There were 17 monomers of PCBs detected in the water samples with concentrations in the range of 0.81-287.50 ng·L-1, which mainly consisted of hexachlorobiphenyls and heptachlorobiphenyls. Eight monomers of PCBs were detected in sediments ranging from 0.13 to 3.96 ng·g-1, which were mainly pentachlorobiphenyls and heptachlorobiphenyls. The lifetime carcinogenic risk index of PAHs and PCBs in surface water of the whole survey area was less than 10-4, and the non-carcinogenic risk index was less than 1, indicating that the carcinogenic risk of PAHs and PCBs was at a medium and low level, and there was no non-carcinogenic risk in surface water. The risk quotients (RQ) method was used to evaluate the ecological risk of pollutants in surface water. The ecological risk of PAHs and PCBs in surface waters in the study area was generally at a low to moderate risk level, including individual points with the presence of heavily risky pollutants that deserve attention. The method of sediment quality guidelines (SQGs) was used to assess the ecological risk of pollutants in sediments. The results showed that PAHs and PCBs were at a low ecological risk level in sediments of Beijiang River.
Key words: Beijiang River      polycyclic aromatic hydrocarbons (PAHs)      polychlorinated biphenyls (PCBs)      pollution characteristics      risk assessment     

多环芳烃(polycyclic aromatic hydrocarbons, PAHs)和多氯联苯(polychlorinated biphenyls, PCBs)是两类典型的持久性有机污染物(persistent organic pollutants, POPs), 具有致癌、致畸、致突变效应[1, 2], 其生物毒性可以通过食物链逐渐向顶端富集; 另外, 其半衰期长, 在环境中持续存在, 能够通过各种环境介质(水、大气和生物体等)进行远距离传输[3, 4], 对自然环境和人类健康存在的风险不可忽视.多环芳烃是一类碳氢化合物, 其来源包括森林火灾、细菌合成、石油泄漏和火山喷发等自然来源和焚烧、炼油和车辆尾气排放等人为源, 通过地表径流、大气沉降等方式进入自然水体带来负面影响[5].16种PAHs单体已于1979年被美国环境保护署(EPA)列为优先检测物[6].多氯联苯是一类人工合成的有机氯化物, 是2001年首批进入联合国环境规划署颁布的《关于持久性有机污染物的斯德哥尔摩公约》中12种持久性有机污染物之一, 从20世纪70年代美国等西方国家逐步禁止生产PCBs[7].多氯联苯的来源包括废旧电器产品的拆解和泄漏, 工业排放和垃圾焚烧等.多环芳烃和多氯联苯在环境介质中普遍存在, 对生态环境和人类健康造成严重威胁.

北江是珠江流域第二大水系, 是广东省重要的河流之一.北江拥有众多支流, 包括潖江、大燕河、滨河和漫水河等.位于北江中上游是广东省重要的矿产产地, 冶金和建材是当地的支柱产业, 同时该地区也是我国电子废弃物拆解业的集中地, 快速发展的工农业和繁忙的内河运输使北江流域的水环境问题日益显著, 水环境中有毒有害污染物问题较为突出.在北江河流沿线分布着多个集中式饮用水水源, 如七星岗、观洲坝、飞来峡库区和北江江口等, 研究该流域环境污染水平对当地居民的日常生活和身体健康影响意义重大.目前关于北江流域地表水和沉积物中多环芳烃和多氯联苯类污染物分布特征、污染水平和生态风险的研究较少.本文以北江中上游及其支流为研究对象, 对水和沉积物中16种PAHs单体和28种PCBs同类物进行检测分析, 分析北江流域PAHs和PCBs的污染水平、对人体健康和生态风险做出评价, 以期为北江流域地表水环境质量保障和痕量有机污染物治理提供基础数据.

1 材料与方法 1.1 样品采集

根据前期针对北江中上游周边环境的调研工作, 本研究选择北江干流及其支流(潖江、大燕河、漫水河和滨河)布置采样点34个, 采样点分布如图 1所示.采样时间为2021年11月份(枯水期).使用表层采样器采集水样, 表层水采样深度控制在0.5 m, 放置于1 L棕色玻璃瓶中, 4℃冷藏保存运输, 24 h内运至实验室处理分析.由于当地地质条件和气候变化导致河沙堆积, 此次采样仅采集到BJ1、BJ3、BJ4、BJ12、BJ15、BJ16、BJ25和PJ5共8个点位的沉积物样品.使用抓式采泥器采集0~10 cm深度的沉积物, 取得的样品在4℃下冷藏, 然后在-56℃进行冷冻干燥.干燥后的样品粉碎后过50目筛子.过筛后样品置于玻璃瓶中, 保存在-20℃的环境下.

图 1 北江流域采样点分布示意 Fig. 1 Distribution of sampling sites in Beijiang River basin

1.2 仪器与试剂

仪器：24孔固相萃取装置(美国Mediwax公司)、RE-52B型旋转蒸发仪(上海亚荣生化仪器厂)、KL512型氮吹仪(北京康林科技有限公司)和7890A/5975C型GC-MS联用仪(美国Agilent公司).

试剂：本研究分析测定的16种优控PAHs和28种PCBs见表 1.各物质标准品购自美国Wellington公司, 采用固相萃取-气相色谱-质谱(SPE-GC-MS)内标分析法对其进行定性定量分析, HLB(6 mL, 500 mg)固相萃取小柱购自美国Waters公司; 二氯甲烷(农残级)和甲醇(色谱纯)购自美国Merck公司.测定PAHs选用的替代物为-d12和二萘嵌苯-d12, 测定PCBs的替代物为2, 4, 5, 6-四氯间二甲苯; 测定PAHs和PCBs选用的内标物均为十氯联苯, 所有内标物和替代物均购自美国Supelco公司.

表 1 北江流域检测的PAHs和PCBs种类 Table 1 Types of PAHs and PCBs detected in the Beijiang River Basin

1.3 预处理与分析

水样预处理：①选用HLB固相萃取小柱对水样进行富集, 富集前用6 mL二氯甲烷以及甲醇依次对HLB小柱进行预先淋洗, 用6 mL超纯水对HLB小柱进行活化, 活化后再加入6 mL超纯水, 准备上样.②水样中加入10 ng替代物, 开始固相萃取, 处理后的水样通过活化后的HLB小柱, 使用真空泵抽滤, 控制溶液流速为5 mL·min-1, 水样滴完后, 继续抽滤0.5 h.③用10 mL二氯甲烷洗脱后, 用旋转蒸发仪和氮吹仪浓缩至0.5 mL, 加入内标物后, 置于4℃冰箱冷藏至开始GC-MS分析.

沉积物预处理：取10 g干燥过的样品, 加入一定量的替代物(0.1 mg·kg-1), 搅拌后密闭过夜, 用滤纸包好后放入索氏提取器进行处理, 1∶1(体积比)丙酮和甲醇的混合液220 mL作为提取液.索氏提取12 h后, 把提取液用50 g无水硫酸钠过滤脱水.脱水后的提取液用旋转蒸发仪(50℃)和氮吹仪(50℃)浓缩至0.8~1.5 mL, 经过0.22 μm滤膜过滤后转移至1.5 mL的样品瓶(最后在0.5~1.0 mL之间).

测定PAHs和PCBs时所用GC-MS仪器的分析条件如下：采用DB-5石英毛细管色谱柱(0.25 mm×60 m×0.25 μm), 载气为氮气, 流速恒定为1 mL·min-1, 线速度26 cm·s-1.进样口温度250℃, MSD300℃, 电子能量70 eV, 选择离子模式扫描, 升温程序为: 初始温度60℃, 保持2 min; 以10℃·min-1升至120℃; 再4℃·min-1升至290℃, 保持10 min.最后无分流进样1 μL.通过检索NIST质谱谱库和色谱峰保留时间进行定性分析, 并采用内标峰面积法和6点校正曲线定量.

1.4 质量控制

采用方法空白、回收率实验和精密度对PAHs进行质量控制和保证.在实验过程中, 在每10个样品中增1个方法空白, 相对标准偏差(RSD) <20%(n=6).水样和沉积物中PAHs的加标回收率分别为75%~102%和68%~94%.对PAHs样品分别添加萘d-8、-d12和二萘嵌苯-d12作为回收率指示物, PAHs的回收率范围分别为78%~106%、73%~107%和78%~112%, 水样和沉积物中PAHs的检出限范围分别为0.10~0.99 ng·L-1和0.17~3.63 ng·g-1.对PCBs进行质量控制和保证, 在分析过程中采用样品平行样、内标法定量、空白加标和方法空白, 每10个样品为1组, 分别设置一个空白加标、基质加标、方法空白和溶剂空白.每个样品都有替代标准物, 相对标准偏差(RSD) < 20%(n=6).每个样品均进行3次平行测定, 取平均值为最终结果, 方法空白没有物质检出.PCBs的空白加标回收率、基质加标回收率和替代物回收率分别为66%~111%、74%~98%和64~78%, PCBs的回收率范围水样和沉积物中PCBs的检出限范围分别为0.24~3.76 ng·L-1和0.05~0.09 ng·g-1.

1.5 风险评价 1.5.1 健康风险评价

为将北江水体中污染物对可能造成人类健康风险进行表征, 参考美国环保署健康风险评价方法, 选用终生致癌风险指数(ILCR)和非致癌风险(HI)作为评价指标.水中的污染物进入人体主要由饮用摄入和通过皮肤接触摄入两种方式, 本研究将以上两种暴露途径产生的风险之和作为最终健康风险.具体计算公式如下.

每日饮用暴露剂量ADDdri [mg·(kg·d)-1]：

(1)

每日皮肤接触暴露剂量ADDder [mg·(kg·d)-1]：

(2)

终生致癌风险指数ILCR(无量纲)：

(3)

非致癌风险指数HI(无量纲)：

(4)

对于PAHs, 需要根据苯并(a)芘的毒性当量因子将各PAHs单体浓度换算为等效浓度[(式(5)], 然后代入式(1)和式(2)计算终生致癌风险ILCR和非致癌风险HI.

(5)

式中, Cw为某物质在水中的检出浓度(mg·L-1); IR为日饮水量(L·d-1); EF为暴露频率(d·a-1); ED为暴露持续时间(a); BW为体重(kg); AT为致癌作用发生的平均时间(d); SA为皮肤接触表面积(cm2); PC为皮肤渗透系数(cm·h-1); CF为转化因子(10-9); ET为日均暴露时间(h·d-1), 以上取值均参考中国人群暴露手册.SF为致癌斜率因子[mg·(kg·d)-1], RfD为非致癌参考量[(kg·d)·mg-1], 取值参考EPA综合风险信息系统.TEQ为毒性当量浓度(mg·L-1), Ci为每种PAHs单体浓度(mg·L-1), TEF为毒性当量因子, 无量纲.若ILCR <10-6, 对人体造成的致癌风险可以忽略; 10-6≤ILCR <10-4, 说明对人体可能存在致癌风险; 若ILCR≥10-4, 造成的致癌风险不可忽略.

1.5.2 生态风险评价

本研究采用风险商值法(risk quotients, RQ)评价水中PAHs和PCBs的生态风险, RQ的计算公式如式(6)所示.若RQ < 0.1说明此种污染物的生态风险可忽略; 若0.1≤RQ < 1说明污染物对水环境中的生物存在较低的生态风险; 若1≤RQ < 10说明污染物对水生生物存在中等生态风险; 若RQ≥10, 说明污染物造成重度生态风险, 有必要采取措施加以管控.

(6)

式中, RQ为风险商(无量纲); MEC为污染物在环境中的暴露浓度(ng·L-1); PNEC为预测无效应浓度(ng·L-1).PNEC等于污染物的毒性数据与评估因子(AF)的比值.污染物毒性数据从通过EPA建立的ECOTOX数据库[8]中查找各污染物单体的LC50(半致死浓度)或EC50(最大半效应浓度)和慢性毒性数据NOEC(最大无影响浓度); 评估因子的选取参考欧盟技术导则[9], 本研究中覆盖3个营养级, 故AF取1 000.

采用沉积物质量基准法(SQGs)[10]评价沉积物中PAHs和PCBs的生态风险.通过效应区间低值(effects range low, ERL)和效应区间中值(effects range median, ERM)确定沉积物中污染物潜在的生态风险.含量 < ERL时几乎对生物不产生毒副作用, 污染物含量>ERM时对生物可能产生一定的毒副作用, 污染物含量介于ERL和ERM之间, 偶尔产生毒副作用.

2 结果与讨论 2.1 PAHs污染水平和分布特征

北江流域地表水和沉积物中PAHs的检出情况如表 2所示.在34个水样和8个沉积物样品中均检测到16种PAHs单体, 每种PAHs单体的检出率为100%.从含量水平看, 地表水中ρ(ΣPAHs)范围在41.82~443.04 ng·L-1之间, 平均值为116.90 ng·L-1, 水中检出浓度最高和最低的单体分别为Nap和Acy, 平均值分别为22.93 ng·L-1和1.71ng·L-1; 沉积物中ω(ΣPAHs)范围在59.58~635.73 ng·g-1之间, 平均值为209.32 ng·g-1, 沉积物中检出含量最高和最低单体为分别Phe和Acy, 平均值分别为37.07 ng·g-1和1.24ng·g-1.根据已有的研究结果, 将PAHs的污染水平分为4个污染等级, 对应的含量水平分别为：轻微污染(地表水10~50 ng·L-1, 沉积物0~100 ng·g-1)、轻度污染(地表水50~250 ng·L-1, 沉积物100~1 000 ng·g-1)、中度污染(地表水250~1 000 ng·L-1, 沉积物1 000~5 000 ng·g-1)和重度污染(地表水>1 000 ng·L-1, 沉积物>5 000 ng·g-1), 经比较可以得出本研究除了BJ4和BJ11这2个点位的地表水属于中度污染以外, 其他采样点地表水都属于轻度污染; BJ15、BJ16和PJ5这3个点位的沉积物属于轻微污染, BJ1、BJ3、BJ4、BJ12和BJ25这5个点位的沉积物属于中度污染水平.

表 2 北江流域地表水和沉积物中PAHs检出情况 Table 2 Detection of PAHs in surface water and sediments of Beijiang River basin

表 3列举对比了本研究与国内外其他不同河流湖泊地表水与沉积物中PAHs的检出情况. ρ(ΣPAHs)含量范围与2016年检测情况(41.2~413.8 ng·L-1)相比变化不大, 与武汉长江典型饮用水源(57.04~475.79 ng·L-1)持平, 明显低于太湖(831~2 425 ng·L-1)和埃及尼罗河(1 112.70~4 364.30 ng·L-1), 高于安徽池州升金湖(54.7~148.0 ng·L-1)、俄罗斯莫斯科河(50.60~120.10 ng·L-1)和美国密西西比河(22.20~163.40 ng·L-1).沉积物中ω(ΣPAHs)含量略低于2016年北江枯水期的检测情况(54.8~951.8 ng·g-1), 与黑龙江小兴凯湖(82.1~534.6 ng·g-1)和上海滴水湖(74.03~579.20 ng·g-1)相当, 低于广州饮用水源地(144.55~1 681.0 ng·g-1), 显著低于美国特拉华河(3 749~22 324 ng·g-1), 高于土耳其伊斯坦布尔湖(46.29~403.9 ng·g-1), 显著高于安徽升金湖(0.19~2.43 ng·g-1).总体而言, 北江流域水和沉积物中多环芳烃含量属中、低等水平.

表 3 国内外各河流/湖泊中PAHs检出情况对比1) Table 3 Comparison of PAHs in surface water of lakes and rivers at home and abroad

从空间分布来看(图 2), 采样范围内水中ρ(ΣPAHs)峰值出现在BJ11(443.94 ng·L-1), 该点位于飞来峡上游, 周围分布较多旅游景点和度假村, G240国道和京广铁路从旁经过, 可能是人类活动汽车尾气排放的PAHs经过大气沉降地表径流等方式进入地表水中.另外滨江在BJ18点汇入北江后, 下游PAHs的浓度有短暂地下降(BJ18~22), 推测可能是滨江水体中多环芳烃浓度小于北江从而产生了稀释作用, 在后续研究中将对滨江采样进一步分析与北江多环芳烃含量之间的关系.此次采样中仅采集到8个沉积物样品, BJ4的ω(ΣPAHs)=635.73 ng·g-1, 显著高于其他点位, 且BJ4水中ρ(ΣPAHs)=307.80 ng·L-1也较高, 推测BJ4点位白石窑水力发电站右岸分布众多机械设备和塑料制品等生产企业, 可能是工业生产和大型运输车辆尾气排放的多环芳烃造成该点位地表水和沉积物中PAHs含量较高.

图 2 地表水和沉积物中PAHs单体含量 Fig. 2 Concentrations of PAHs monomers in surface water and sediments

从成分组成来看, 将不同的PAHs根据分子结构的芳香环个数分类(图 3), 北江流域水中二环芳烃的占比明显高于沉积物中的占比.水中PAHs以二环芳烃和三环芳烃为主, 质量分数范围分别为5.31%~45.64%和13.83%~64.34%, 平均值分别为22.59%和28.15%; 沉积物中以三环芳烃和四环芳烃为主, 质量分数范围分别为21.44%~35.80%和38.26%~49.93%, 平均值分别为29.69%和43.01%.造成这种现象可能的原因是低环芳烃与高环芳烃相比, 分子量较小, 亲水性更强, 更易存在于水中.

图 3 北江中上游地表水和沉积物中不同环数PAHs占比 Fig. 3 Proportions of PAHs with different rings in surface water and sediments of Beijiang River Basin

2.2 PCBs污染水平和分布特征

北江流域地表水和沉积物中PCBs检出情况见表 4.从检出含量来看, 在地表水34个点位中共检测到17种PCBs单体.水中ρ(ΣPCBs) 范围在0.81~287.50 ng·L-1, 平均值为38.92 ng·L-1.检出率最高的物质为HexaCBs-128(检出率94.12%); 检出率最低的物质是HexaCBs-153(检出率2.94%), 仅在一个点位中检出. HeptaCBs-180该种物质检出浓度最大, 范围为ND~88.31 ng·L-1, 平均值35.00 ng·L-1; TetraCBs-66检出浓度最小, 范围ND~1.20 ng·L-1, 平均值0.69 ng·L-1.在8个沉积物采样点位中检测到PentaCBs-105、PentaCBs-114、PentaCBs-123、HexaCBs-128、HeptaCBs-170、HeptaCBs-180、HeptaCBs-187和HeptaCBs-189共8种PCBs单体. 沉积物中ω(ΣPCBs)范围为0.13~3.96 ng·g-1, 平均值为0.99 ng·g-1.检出率最高的物质为HeptaCBs-170和HeptaCBs-180, 检出率均为75.00%; 检出率最低的物质是PentaCBs-105和PentaCBs-123, 检出率均为12.50%.在沉积物中PentaCBs-114含量最大, 平均值为1.19 ng·g-1; HeptaCBs-187含量最小, 平均值为0.05 ng·g-1.

表 4 北江流域地表水和沉积物中PCBs检出情况1) Table 4 Detection of PCBs in surface water and sediments of Beijiang River Basin

表 5列举了国内外地表水和沉积物中PCBs检出的浓度范围和平均浓度, 并与本研究对比.在本研究中地表水中ρ(ΣPCBs)范围为0.81~287.50 ng·L-1, 低于汾河流域(8~485 ng·L-1), 显著低于埃及尼罗河三角洲(14 400~20 200 ng·L-1), 略高于美国密西西比河(22.2~163.4 ng·L-1), 高于洞庭湖及入湖河流(0.077~10 ng·L-1)、太湖流域水源地(ND~1.04 ng·L-1)和武汉长江饮用水源地(ND~24.84 ng·L-1); 沉积物中ω(ΣPCBs)范围为0.13~3.96 ng·g-1, 与宁波象山港沉积物ω(ΣPCBs)相当(ND~3.54 ng·g-1), 低于上海市地表水体(0.99~46.11 ng·g-1)、河北白洋淀(ND~37.61 ng·g-1)和海南三亚河(1.75~92.75 ng·g-1), 显著低于尼日利亚的尼日尔三角洲(1 520~3 540 ng·g-1).总体而言, 北江中上游地表水和沉积物中PCBs含量属于中等水平.

表 5 国内外各河流/湖泊中PCBs检出情况对比1) Table 5 Comparison of PCBs in surface water of lakes and rivers at home and abroad

从空间分布来看(图 4), 地表水中ρ(ΣPCBs)最高的点位为PJ3(287.50 ng·L-1), 最低的为MSH(0.81 ng·L-1); 沉积物样品中BJ25的ω(ΣPCBs)最高(3.96ng·g-1), BJ1的ω(ΣPCBs)最低(0.13ng·g-1).

图 4 地表水和沉积物中PCBs单体含量 Fig. 4 Concentrations of PCBs monomers in surface water and sediments

从成分组成来看, 根据分子结构中包含氯原子个数将PCBs进行分类, 不同种类PCBs的占比见图 5.水中PCBs主要以六氯联苯和七氯联苯为主, 沉积物中主要以五氯联苯和七氯联苯为主.由于多氯联苯是半挥发性持久性污染物, 其挥发性随着氯原子数量的增加而降低[40, 41], 因此可以解释水中高(五、六和七)氯代联苯在水相和沉积物中优势.另外根据前人报道[42, 43], 北江中上游流域周边长期以来电子废弃物拆解产业较为密集, 电子废弃物中高氯代PCBs进入水环境可能是造成该种现象的原因之一.

图 5 北江中上游地表水和沉积物中不同氯原子数PCBs占比 Fig. 5 Proportions of PCBs with different chlorine atomic numbers in surface water and sediments of Beijiang River Basin

2.3 PAHs和PCBs风险评价 2.3.1 健康风险评价

北江流域水样中PAHs和PCBs的健康风险(致癌风险指数ILCR和非致癌风险指数HI)见图 6.由图 6(a)可知, PAHs的致癌风险指数范围在2.95×10-7~7.96×10-6之间, 20个点位的致癌风险指数小于EPA规定的致癌风险阈值(1×10-6), 表明这些点位PAHs对人类不存在致癌风险, 其余14个点位致癌风险指数介于10-6~10-4之间, 可能存在潜在的致癌风险; PAHs的非致癌风险指数范围3.36×10-5~3.48×10-4, 均远小于1, 低于EPA规定的非致癌风险阈值, 表明在整个研究区域内PAHs对人类的非致癌风险可以忽略.

图 6 地表水中PAHs和PCBs的致癌风险指数和非致癌风险指数 Fig. 6 Carcinogenic and non-carcinogenic risks of PAHs and PCBs in surface water

由图 6(b)可知, 水中PCBs致癌风险指数范围为3.83×10-8~1.36×10-5, 20个点位的致癌指数小于EPA规定的致癌风险限值(1×10-6), PCBs对人类不足以造成终生致癌风险; 有14个点位的致癌指数介于10-6~10-4之间, 虽然处于可接受范围内, 但是这些点位的PCBs可能对人体存在一定的健康风险.水中PCBs的非致癌风险指数介于4.43×10-1~1.24×10-3, 均小于1, 低于非致癌风险阈值, 说明以当前水中PCBs的浓度对人类造成的非致癌风险可以忽略.

2.3.2 生态风险评价

所有点位地表水中PAHs和PCBs各单体的风险商(RQ)值分布如图 7所示, 总的来看, 研究区域内大多数点位地表水中的PAHs和PCBs单体的RQ < 1.0, 基本处于低风险和无风险范围, 对水生态环境无明显毒害作用.但与此同时存在2种PAHs单体(Fla和BghiP)和3种PCBs单体(PentaCBs-126、HexaCBs-128和HeptaCBs-189)在较多点位(占比>50%)处于中等风险(1.0≤RQ < 10.0); 并且2种多环芳烃(BbF和BkF)和4种多氯联苯(PentaCBs-126、HeptaCBs-170、HeptaCBs-187和HeptaCBs-189)共6种物质在个别点位存在重度生态风险(RQ≥10.0), 值得引起重视.

图 7 水中PAHs和PCBs生态风险分布 Fig. 7 Distributions of ecological risks of PAHs and PCBs in surface water

将北江流域水体沉积物中各PAHs单体含量和ΣPCBs含量与SQGs[10]中相应的ERL和ERM进行比较, 结果见表 6.所有沉积物样品中各PAHs单体(BJ4的Flu除外)和ΣPCBs含量均小于效应区间低值(ERL), 表明不存在负面生态风险.值得补充的是, InP该种单体无效应区间低值, 只要存在于环境中就会产生一定毒害作用, 本次沉积物样品中InP有不同程度地检出, 应当引起重视.总体而言, 北江沉积物中PAHs和PCBs存在生态风险的几率较低, 处于较低的生态风险水平, 建议在以后的工作中加强对Flu和InP的管控.

表 6 沉积物中PAHs和PCBs含量与ERL和ERM的比较/ng·g-1 Table 6 Comparisons of PAHs and PCBs contents in sediments with ERL and ERM/ng·g-1

3 结论

(1) 北江中上游地表水和沉积物中PAHs检出范围分别为41.82~443.04 ng·L-1和59.58~635.73 ng·g-1, 平均值分别为41.82 ng·L-1和209.32 ng·g-1; 水中PAHs以二环芳烃和三环芳烃为主, 沉积物中以三环芳烃和四环芳烃为主.PCBs在地表水和沉积物中的检出范围分别为0.81~287.50 ng·L-1和0.13~3.96 ng·g-1, 平均值分别为116.90 ng·L-1和0.99 ng·g-1; 水中PCBs以六氯联苯和七氯联苯为主, 沉积物中PCBs主要为七氯联苯和五氯联苯.

(2) 健康风险评价结果显示, 北江中上游地表水中PAHs和PCBs致癌风险总体处于中低水平, 地表水中PAHs和PCBs的非致癌风险可以忽略.生态风险评价结果显示, 研究区域内地表水中PAHs和PCBs生态风险总体处于中低风险水平, 个别点位存在重度风险的污染物单体, 值得引起重视; 沉积物中PAHs和ΣPCBs处于较低的生态风险水平, 建议加强对Flu和InP的管控.

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