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Volume 39 Issue 5
Oct.  2020
Article Contents

Citation:

The vertical distribution patterns of heavy metals in a sediment core of the Jiaozhou bay and their controlling factors

  • Received Date: 2019-04-15
    Accepted Date: 2019-06-17
  • A sediment core was collected in the Jiaozhou bay in 2011. The concentrations of eight heavy metals [mercury (Hg), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn)] in the sediment core from 0 m to 1 m were measured. These raw data were then utilized to calculate the enrichment factors (enrichment factors, EFs, represents the enrichment status of elements) of these metals. The results showed that both concentrations and EFs of these heavy metals presented a peak or had the highest value in the subsurface layer (at around 20 cm) of the sediment core. The age of sediment at such depth was estimated to be around 20 years using the reported sediment settlement rate. This indicates that the contamination of heavy metals in Jiaozhou bay sediment may be significantly affected by the high-intensity anthropogenic discharge of heavy metals into the Jiaozhou bay in the late 1980s and 1990s. Pearson correlation and multiple regression analyses were further performed to investigate the primary controlling factors for heavy metals in Jiaozhou bay sediment. The results suggest that the inter-annual variations of the eight common heavy metals may be controlled by different environmental factors in Jiaozhou bay sediment. In addition, the potential ecological risk index was calculated to evaluate the potential risks of these heavy metals in Jiaozhou Bay sediment and their historical variation trends. Mercury generally had a moderate risk in the Jiaozhou bay, and its risk has been increasing in recent years. This finding suggests that Hg should be put in the priority metal to be controlled in the Jiaozhou bay.
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    [2] 张乃星, 曹丛华, 任荣珠, 等. 胶州湾外海洋倾倒区表层沉积物中的重金属及其潜在生态风险[J]. 环境科学, 2011, 32(5): 1315-1320.
    [3] 郭军辉, 殷月芬, 陈发荣, 等. 胶州湾表层沉积物重金属污染分布特征及其生态风险评价[J]. 环境污染与防治, 2012, 34(3): 13-21. doi: 10.3969/j.issn.1001-3865.2012.03.004
    [4] 籍宇科. 胶州湾重要渔业水域环境质量状况及评价[D]. 青岛: 中国海洋大学, 2008.
    [5] 肖彩玲, 陈路锋, 李雁宾. 胶州湾沉积物重金属分布特征及生态风险评价[J]. 中国科技论文, 2017, 12(9): 1079-1086. doi: 10.3969/j.issn.2095-2783.2017.09.019
    [6] 王修林, 李克强, 石晓勇, 等. 胶州湾主要化学污染物海洋环境容量: 中国近海海域污染物排海总量控制理论与应用[M]. 北京: 科学出版社, 2006.
    [7] 徐晓达, 林振宏, 李绍全. 胶州湾的重金属污染研究[J]. 海洋科学, 2005, 29(1): 48-53. doi: 10.3969/j.issn.1000-3096.2005.01.010
    [8] WANG C Y, LIANG S K, LI Y B, et al. The spatial distribution of dissolved and particulate heavy metals and their response to land-based inputs and tides in a semi-enclosed industrial embayment: Jiaozhou Bay, China[J]. Environmental Science and Pollution Research, 2015, 22(14): 10480-10495. doi: 10.1007/s11356-015-4259-3
    [9] 毕世普, 孔祥淮, 张 勇, 等. 胶州湾浅表地层沉积物粒度特征及其环境意义[J]. 海洋地质前沿, 2015, 31(10): 1-7.
    [10] Method 200.2, Sample preparation procedure for spectrochemical analyses of total recoverable elements[S].
    [11] Method 200.7, Determination of metals and trace elements in water and wastes by inductively coupled plasma-atomic emission spectrometry[S].
    [12] Method 7474, Mercury in sediment and tissue samples by atomic fluorescence spectrometry[S].
    [13] XIAO C L, JIAN H M, CHEN L F, et al. Toxic metal pollution in the Yellow Sea and Bohai Sea, China: distribution, controlling factors and potential risk[J]. Marine Pollution Bulletin, 2017, 119(1): 381-389. doi: 10.1016/j.marpolbul.2017.03.027
    [14] TUREKIAN K K, WEDEPOHL K H. Distribution of the elements in some major units of the earth's crust[J]. GSA Bulletin, 1961, 72(2): 175-192. doi: 10.1130/0016-7606(1961)72[175:DOTEIS]2.0.CO;2
    [15] HAKANSON L. An ecological risk index for aquatic pollution control:a sedimentological approach[J]. Water Research, 1980, 14(8): 975-1001. doi: 10.1016/0043-1354(80)90143-8
    [16] WANG Y, YANG Z F, SHEN Z Y, et al. Assessment of heavy metals in sediments from a typical catchment of the Yangtze River, China[J]. Environmental Monitoring and Assessment, 2011, 172(1/2/3/4): 407-417.
    [17] ZHANG J F, GAO X L. Heavy metals in surface sediments of the intertidal Laizhou Bay, Bohai Sea, China: distributions, sources and contamination assessment[J]. Marine Pollution Bulletin, 2015, 98(1/2): 320-327.
    [18] LI Y B, DUAN Z W, LIU G L, et al. Evaluation of the possible sources and controlling factors of toxic metals/metalloids in the Florida everglades and their potential risk of exposure[J]. Environmental Science & Technology, 2015, 49(16): 9714-9723.
    [19] 秦延文, 孟 伟, 郑丙辉, 等. 渤海湾天津段潮间带沉积物柱状样重金属污染特征[J]. 环境科学, 2006, 27(2): 268-273. doi: 10.3321/j.issn:0250-3301.2006.02.014
    [20] JAMSHIDI-ZANJANI A, SAEEDI M. Metal pollution assessment and multivariate analysis in sediment of Anzali international wetland[J]. Environmental Earth Sciences, 2013, 70(4): 1791-1808. doi: 10.1007/s12665-013-2267-5
    [21] 汪亚平, 高 抒. 胶州湾沉积速率: 多种分析方法的对比[J]. 第四纪研究, 2007, 27(5): 787-796. doi: 10.3321/j.issn:1001-7410.2007.05.020
    [22] WANG C Y, GUO J Q, LIANG S K, et al. Long-term variations of the riverine input of potentially toxic dissolved elements and the impacts on their distribution in Jiaozhou Bay, China[J]. Environmental Science and Pollution Research, 2018, 25(9): 8800-8816. doi: 10.1007/s11356-017-1118-4
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    沈阳化工大学材料科学与工程学院 沈阳 110142

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The vertical distribution patterns of heavy metals in a sediment core of the Jiaozhou bay and their controlling factors

  • 1. College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China
  • 2. Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
  • 3. College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
  • 4. Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China

Abstract: A sediment core was collected in the Jiaozhou bay in 2011. The concentrations of eight heavy metals [mercury (Hg), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn)] in the sediment core from 0 m to 1 m were measured. These raw data were then utilized to calculate the enrichment factors (enrichment factors, EFs, represents the enrichment status of elements) of these metals. The results showed that both concentrations and EFs of these heavy metals presented a peak or had the highest value in the subsurface layer (at around 20 cm) of the sediment core. The age of sediment at such depth was estimated to be around 20 years using the reported sediment settlement rate. This indicates that the contamination of heavy metals in Jiaozhou bay sediment may be significantly affected by the high-intensity anthropogenic discharge of heavy metals into the Jiaozhou bay in the late 1980s and 1990s. Pearson correlation and multiple regression analyses were further performed to investigate the primary controlling factors for heavy metals in Jiaozhou bay sediment. The results suggest that the inter-annual variations of the eight common heavy metals may be controlled by different environmental factors in Jiaozhou bay sediment. In addition, the potential ecological risk index was calculated to evaluate the potential risks of these heavy metals in Jiaozhou Bay sediment and their historical variation trends. Mercury generally had a moderate risk in the Jiaozhou bay, and its risk has been increasing in recent years. This finding suggests that Hg should be put in the priority metal to be controlled in the Jiaozhou bay.

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  • 自上世纪80年代以来,随着我国经济快速发展,大量重金属污染物通过河流、污水处理厂和大气沉降等进入海洋。例如,2017年我国55条监测河流入海重金属总量超过一万吨[1]。由于泥沙等颗粒物的吸附沉降作用,大部分入海重金属沉降在河口、海湾等近海海域,导致河口、海湾等区域重金属污染严重。胶州湾是我国污染最严重的七个海湾之一,其重金属污染状况和风险问题已引起一些学者的关注。例如,张乃星、郭军辉、籍宇科[2-4]等人采用潜在生态风险指数法评估了胶州湾沉积物中重金属生态风险程度状况,发现胶州湾重金属风险相对较低。肖彩玲等[5]的风险评价结果表明镉(Cd)、铬(Cr)、铜(Cu)和镍(Ni)是胶州湾污染较为严重的重金属,且主要污染区域位于海泊河和李村河口等东部河口附近。目前关于胶州湾重金属污染及风险虽然已有一些相关研究,但对于其重金属含量和生态风险的历史演变趋势还缺乏清楚认识,需要开展相关研究。

    本研究分析了胶州湾沉积物柱状样中汞(Hg)、砷(As)、Cd、Cr、Cu、Ni、铅(Pb)和锌(Zn)八种重金属含量垂向分布特征,利用富集因子指数法和多元线性回归等统计方法探讨了人为活动和沉积物性质对胶州湾重金属污染的控制作用,并进一步采用沉积物潜在生态风险指数法分析了胶州湾重金属生态风险的历史演变趋势,该研究有助于增进对胶州湾重金属污染历史变化及控制因素的了解,也将为胶州湾重金属污染防治提供理论依据和数据支持。

1.   材料与方法

    1.1.   研究区域概况

  • 胶州湾位于中国黄海中部,是一个典型的半封闭海湾(图1),水域面积约340 km2,水深平均约为7 m。随着胶州湾畔青岛市经济高速发展,大量工业废水和生活污水排入胶州湾,再加上近岸养殖、围海造地等人为活动的影响,湾内面积急剧减少,水质恶化严重[6],局部海域也存在重金属浓度超标的情况,有潜在环境风险[7-8]

    Figure 1.  A map of the Jiaozhou bay with the sampling site

  • 1.2.   样品采集与预处理

  • 2011年在胶州湾Z26站采集沉积物柱状样一根[9],该站位位于岛耳河水道(图1)。取0~100 cm沉积物柱按2 cm间隔分样。样品冷冻干燥后,手工剔除明显的动植物残片,研磨并过240目标准检验筛(筛框材质为聚氯乙烯,筛网材质为聚酰胺纤维)后常温保存待测。

  • 1.3.   重金属及其他参数测定

  • 沉积物As、Cd、Cr、Cu、Ni、Pb和Zn七种重金属总量测定方法参照EPA 200.2[10]和EPA 200.7[11]方法。称取0.5 g过筛后的沉积物样品,置于60 mL聚四氟乙烯消化管中,加入4 mL HNO3/H2O (vv=1∶1) 和10 mL HCl/H2O (vv=1∶4)。85 ℃下消解12 h后,定容至40 mL。离心取上清液并采用电感耦合等离子体原子发射光谱仪(Thermo公司ICAP-6300型)测定消解液中重金属浓度。沉积物总Hg测定参照EPA 7474[12]方法,称取0.2 g样品于10 mL安瓿瓶中。分别加入1 mL纯水和2 mL HNO3后,105 ℃(灭菌锅中)消解1 h。消解液中总Hg浓度测定采用总汞自动分析仪(BROOKS RAND公司MERX)。沉积物粒径和210Pb测定见毕世普等已发表文章[9]

    为保证数据质量,每批样品(最多20个)同时测定两个方法空白和两个沉积物标准物质(总Hg标准物质为ERM-CC580;As、Cd、Cr、Cu、Ni、Pb和Zn标准物质为PACS-3)。As、Cd、Cr、Cu、Ni、Pb、Zn和Hg空白皆满足低于样品浓度10%的要求。As、Cd、Cr、Cu、Ni、Pb、Zn和Hg回收率分别为79%~90%、95%~112%、88%~99%、90%~95%、83%~111%、78%~94%、85%~110%和90%~116%,满足EPA方法测定要求(回收率为70%~130%)。

  • 1.4.   富集因子(EF)计算

  • 富集因子(EF)计算如公式(1)所示[13],本研究选用 Mg 作为参考元素。根据 EF 值的大小可以将重金属人为污染程度分为7级:EF<1为不富集;1≤EF<3为轻度富集;3≤EF<5为中度富集;5≤EF<10为重度富集;10≤EF<25为高度富集;25≤EF<50为极高度富集;EF>50为超高度富集。

    式中:CiCMg 分别为重金属i和 Mg 在沉积物中的实测浓度 (×10−6);BiBMg 分别为重金属 i和 Mg 在研究海域沉积物中的背景值 (×10−6)[13-14]BAsBCdBCrBCuBNiBPbBZnBHgBMg分别为6.26×10−6、0.42×10−6、57.77×10−6、15.34×10−6、31.48×10−6、13.43×10−6、69.12×10−6、0.019×10−6和13327×10−6)。

  • 1.5.   沉积物潜在生态风险指数(Eri)计算

  • 本研究中沉积物生态风险评价采用Hakanson沉积物潜在生态风险指数法[15]。计算公式如下:

    式中:Eiri种重金属的潜在生态风险指数;Tri为毒性系数 (Hg=40、Cd=30、As=10、Pb=Cu=Ni=5、Cr=2、Zn=1)[16-17]Cfi为金属浓度(Ci)与环境背景值(Bi)的比值。

2.   结果与讨论

    2.1.   胶州湾沉积物柱状样重金属浓度分布特征

  • 胶州湾沉积物柱状样As、Cd、Cr、Cu、Ni、Pb、Zn和Hg浓度见图2,平均值分别为6.89×10−6(未检出~11.80×10−6)、0.72×10−6(未检出~1.24×10−6)、86.93×10−6(33.70×10−6~157.69×10−6)、37.00×10−6(4.41×10−6~100.92×10−6)、43.79×10−6(15.16×10−6~63.91×10−6)、28.70×10−6(5.64×10−6~58.02×10−6)、65.10×10−6(26.07×10−6~87.41×10−6)和0.025×10−6(0.011×10−6~0.046×10−6)。垂直分布上,Cu含量由表层向深层总体呈先降低后升高的趋势,在10 cm左右出现第一个高值,最高值位于90 cm左右;Cr含量整体呈先增加后降低的趋势,峰值位于20 cm左右,此外,在90 cm以深浓度也较高;Hg含量整体呈波动降低的趋势;Zn、Pb和Ni含量在60 cm以浅呈先增加后降低的趋势,峰值也位于20 cm左右,此外在60 cm以深浓度也较高;Cd浓度整体呈先增加,后降低,再增加的趋势,分别在20 cm和50 cm有两个高值;As的峰值也位于20 cm左右,之后逐渐降低到60 cm左右,再呈一定的升高趋势。沉积物重金属含量受人为输入和地质条件共同控制[18],多数金属并未表现出自上而下一直降低的趋势,说明除人为污染物输入外,沉积物理化性质的改变也可能是影响胶州湾沉积物重金属含量的重要因素,这也与之前一些研究沉积物柱状样的报道一致[19]。毕世普等[9]的研究也发现我们采用的Z26站沉积物类型从上到下有明显变化。

    Figure 2.  Vertical distribution of heavy metal concentrations in a sediment core of the Jiaozhou bay

  • 2.2.   胶州湾沉积物柱状样重金属富集因子分布特征

  • 重金属富集因子常用来表征重金属分布受人为影响程度[20]。胶州湾沉积物柱状样As、Cd、Cr、Cu、Ni、Pb、Zn和Hg富集因子变化如图3所示,几种金属EF平均值分别为2.13(0.66~4.10)、3.24(0.35~7.07)、2.97(1.06~6.74)、4.05(1.12~9.26)、2.63(1.10~5.09)、3.89(1.53~9.33)、1.78(0.85~3.18)和2.72(0.89~5.45)。结果表明,胶州湾As和Zn为轻度富集,为弱污染;而其他金属的EF值均有大于5的情况出现,为高度富集甚至极高度富集,表明胶州湾沉积物重金属受人为影响明显。垂直分布上,Cr、Zn、As、Pb、Ni五种金属分布趋势基本类似,呈“单峰形”分布,峰值基本都位于20 cm左右;Cu的富集因子除在20 cm左右有一峰值外,在90 cm左右也有一峰值存在;Hg整体也呈先升高后降低的趋势,在20 cm,40 cm和60 cm各有一个峰值;Cd富集因子呈“双峰形”分布,峰值分别位于20 cm左右和60 cm左右。总结可知,胶州湾多数重金属EF值都在次表层20 cm左右达到峰值或有一个高值。该柱子210Pb测定数据呈典型的“三段模式”,在0~56 cm有明显衰变规律,而在56~100 cm无明显变化[9],无法通过210Pb数据测定结果确定20 cm处沉积物的具体年代。根据文献报道,胶州湾百年尺度沉积速率在1 cm/a量级[21],我们粗略估算20 cm沉积物大约可以反映20世纪80年代末90年代初的重金属污染状况,显示沉积物重金属污染状况受人为排污强度增大影响明显。而在表层浓度的降低也显示近年来随着对工业排污等的控制,青岛市重金属等污染物排放有降低的趋势[22]

    Figure 3.  Vertical distribution of heavy metal enrichment factors in a sediment core of the Jiaozhou bay

  • 2.3.   影响胶州湾沉积物柱状样重金属垂向分布的控制因素

  • 进一步分析了影响胶州湾沉积物柱状样重金属垂向分布的关键因素,首先采用Pearson相关性分析得到与8种重金属浓度显著相关的环境因子(表1),然后进一步通过多元线性回归分析这些相关因子的相对重要性(表1)。其中EF 代表人为源输入影响,Fe/Mn含量和不同类型沉积物占比代表沉积物理化性质影响。Pearson相关性分析结果表明,Hg与Fe/Mn含量、沉积物类型和EF显著相关;As、Cd和Cr的主要相关因子为沉积物类型和EF;Fe/Mn含量和EF是Cu和Pb两个金属的主要相关因子;Ni和Zn仅与Fe/Mn含量表现出显著相关性。

    Pearson 相关分析(R多元线性回归(β
    AsCdCrCuNiPbZnHgAsCdCrCuNiPbZnHg
    Fe0.220.010.190.690.560.530.710.28
    Mn0.33−0.330.220.450.520.490.630.540.540.660.530.690.94
    砾/(%)−0.560.67−0.520.340.140.190.23−0.64
    砂/(%)−0.400.74−0.330.27−0.20−0.07−0.29−0.69
    粉砂/(%)0.66−0.690.60−0.250.02−0.07−0.050.72
    黏土/(%)0.64−0.670.60−0.32−0.01−0.14−0.090.650.340.790.290.19
    EF0.560.700.670.680.380.75−0.180.560.370.100.490.840.660.87
    r20.410.730.500.870.430.740.480.86
    p<0.05<0.001<0.05<0.001<0.05<0.001<0.001<0.001
    注:加粗代表p<0.05

    Table 1.  Pearson correlation and multiple linear regression analyses of heavy metals in a sediment core of the Jiaozhou bay with various environmental factors

    进一步通过多元线性回归分析识别了控制胶州湾重金属垂向分布的关键因素。首先判定各自变量间是否有共线性,结果表明Fe与Mn存在共线性,为避免共线性影响结果,仅选取Mn、黏土和EF作为自变量进行多元回归分析,如表1所示。结果表明,胶州湾8种常见重金属的年际变化控制因素不同,其中,Ni和Zn主要受Fe/Mn含量控制;Cr和Cu主要受人为输入控制;Pb和Hg受Fe/Mn含量和人为源输入共同控制;沉积物类型是控制Cd的主要因素;As含量受人为源输入和沉积物类型共同控制。之前的一些研究也表明人为源输入和沉积物理化性质是控制沉积物重金属水平的关键因素,且不同金属的控制因素不同[13,18]。其中,重金属含量与Fe/Mn含量呈正相关关系,原因在于Fe、Mn的水合氧化物是沉积物中重要的无机胶体,它们通过吸附、共沉淀等作用影响沉积物中重金属的含量[19]。沉积物粒度越小,颗粒越细,其比表面积越大,越容易吸附重金属离子。黏土相较其他颗粒物质更易吸附重金属,因此多数重金属含量与黏土占比呈正相关关系(表1)。分析结果也表明人为输入是影响胶州湾重金属年际变化的最关键因素,河流监测结果[22]也表明,自1981到1990年青岛市河流输入胶州湾的As、Hg、Cr、Pb、Cd 和 Cu 等金属的净输入量分别增加了41、21680、7878、487、687 和 159 倍。

  • 2.4.   胶州湾重金属生态风险演变特征

  • 沉积物柱状样重金属潜在生态风险指数结果如图4所示,Zn、Cr、Ni、Cu、As和Pb所有层次样品中风险指数均小于40,为低风险。Cd和Hg有一定风险,尤其是近年来Hg风险还处于高值区,需要引起一定关注。联合国环境规划署《关于汞的水俣公约》于2017年8月正式开始实施,Hg排放量的减少将有利于汞风险的降低。需要注意的是,该沉积物柱采自近湾口深水区,受污染相对较轻,不能代表胶州湾近岸海域的污染情况。垂直分布上,各金属生态风险变化趋势与重金属含量变化趋势基本一致,生态风险并未表现出自上而下一致的变化规律,这也主要是由于除受人为排放影响外,生态风险也受沉积物理化性质控制,表明除外源输入外,海域沉积物本身的类型也是控制重金属风险的关键因素[19]

    Figure 4.  Vertical distribution of heavy metal Eir (potential ecological risk index) in a sediment core of the Jiaozhou bay

3.   结 论
  • (1)本文研究的沉积物柱状样中8种重金属(Hg、As、Cd、Cr、Cu、Ni、Pb和Zn)的含量大都在次表层20 cm左右达到峰值或有一个高值,结合文献报道沉积速率结果分析表明胶州湾沉积物重金属污染程度可能显著受到上世纪八九十年代高强度人为排污的影响。

    (2)统计分析结果表明胶州湾8种常见重金属的年际变化控制因素不同,其中,Ni和Zn主要受Fe/Mn含量控制;Cr和Cu主要受人为输入控制;Pb和Hg受Fe/Mn含量和人为源输入共同控制;沉积物类型是控制Cd的主要因素;As含量受人为源输入和沉积物类型共同控制。总体来看,人为输入是影响胶州湾重金属年际变化的最关键因素。

    (3)沉积物潜在生态风险指数法评价结果表明:Zn、Cr、Ni、Cu、As和Pb六种金属为低风险;Cd和Hg有一定风险,尤其是Hg,整体处于中度污染水平,且近年来风险还呈一定增大趋势,为胶州湾优先控制重金属。

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