于學(xué)峰，劉曉清，王亞萍

（1.中國科學(xué)院地球環(huán)境研究所 黃土與第四紀(jì)地質(zhì)國家重點(diǎn)實(shí)驗(yàn)室，西安 710061；2.陜西省環(huán)保產(chǎn)業(yè)集團(tuán)有限公司，西安 710075；3.陜西省環(huán)境科學(xué)研究院，西安 710061）

紅堿淖湖泊表層沉積物重金屬生態(tài)風(fēng)險評價

于學(xué)峰1，劉曉清2,3，王亞萍3

（1.中國科學(xué)院地球環(huán)境研究所 黃土與第四紀(jì)地質(zhì)國家重點(diǎn)實(shí)驗(yàn)室，西安 710061；2.陜西省環(huán)保產(chǎn)業(yè)集團(tuán)有限公司，西安 710075；3.陜西省環(huán)境科學(xué)研究院，西安 710061）

為掌握紅堿淖重金屬污染水平及其生態(tài)風(fēng)險，我們對紅堿淖表層沉積物開展了重金屬分析，采用元素富集因子法和潛在生態(tài)風(fēng)險指數(shù)法對沉積物重金屬進(jìn)行生態(tài)風(fēng)險評價。結(jié)果表明：（1）湖心樣品的重金屬元素豐度比湖岸樣品略高；（2）紅堿淖各采樣點(diǎn)重金屬均處于輕度污染狀態(tài)，僅Cd存在一定程度的富集；（3）沉積物重金屬潛在生態(tài)風(fēng)險指數(shù)處于較低水平。

紅堿淖；重金屬；元素富集因子法；潛在生態(tài)風(fēng)險指數(shù)

重金屬在生態(tài)系統(tǒng)中具有富集性和持久性特征，且具有顯著的生物毒性，使之成為嚴(yán)重影響生態(tài)環(huán)境安全的因素（田林鋒等，2012；Varol and ?en，2012）。水體中底泥是重金屬污染的儲存庫和最后的聚居地（弓曉峰等，2006；Peng et al，2009）。湖泊底泥中重金屬以多種形式存在，當(dāng)環(huán)境變化時，重金屬形態(tài)也發(fā)生變化并釋放，造成湖泊水體污染。近年來，已有很多學(xué)者對不同湖泊底泥的重金屬污染特征及其生態(tài)風(fēng)險進(jìn)行了評價（程杰等，2008；焦偉等，2010；李永進(jìn)等，2011；馬婷等，2011；余暉等，2011；劉婉清等，2014；毛志剛等，2014），對指導(dǎo)湖泊生態(tài)治理起到了重要作用。

紅堿淖是我國最大的沙漠淡水湖，處于毛烏素沙漠與黃土高原生態(tài)脆弱區(qū)，被稱為“塞上明珠”。特殊的地理位置使紅堿淖在區(qū)域生態(tài)環(huán)境中具有重要的地位，它具有防風(fēng)固沙、水源涵養(yǎng)、生物多樣性保育等生態(tài)功能。它還是世界瀕危物種遺鷗的主要棲息地。近年來在氣候變化和人類活動等因素作用下，紅堿淖湖泊水域面積正不斷縮減，面臨一系列生態(tài)問題（李登科等，2010；雷忻等，2011；劉曉清和王亞萍，2014）。目前，尚無在紅堿淖開展表層沉積物重金屬污染及其生態(tài)風(fēng)險控制的研究，筆者對紅堿淖湖泊表層沉積物開展了系統(tǒng)采樣與重金屬測試分析，并對重金屬污染生態(tài)風(fēng)險進(jìn)行評估，以期對紅堿淖生態(tài)環(huán)境風(fēng)險控制提供理論支持，也為紅堿淖水環(huán)境保護(hù)提供科學(xué)依據(jù)。

1 樣品采集與測試

1.1 樣品采集

如圖1所示，在紅堿淖布設(shè)了12個采樣點(diǎn)。采樣點(diǎn)布設(shè)盡量考慮平面展布的均勻性，同時又兼顧湖岸、湖心、入湖河口等不同沉積單元的代表性（劉曉清等，2013）。用Van veen采泥器，抓取湖泊底部10 cm×20 cm面積的表層沉積物樣品，采樣深度為10 cm。樣品用密封袋包裝后運(yùn)回實(shí)驗(yàn)室。

圖1 紅堿淖采樣點(diǎn)Fig.1 Sampling sites in Hongjiannao Lake

1.2 樣品分析測定

樣品自然風(fēng)干后，用瑪瑙研缽加工成粒徑為74 μm的粉末，以開展As、Hg、Cr、Cu、Zn、Pb、Cr6+、Cd等測試分析。

1.2.1 ICP-MS檢測Cr、Cd、Cu、Pb、Zn

準(zhǔn)確稱取0.1000 g樣品，105℃烘干2小時后，置于30 mL塑料坩堝中，加入HF、HClO4在200—250℃電熱板加熱，白煙冒盡。加5 mL王水，加熱至干。用稀 HNO3加熱溶解，并用純水稀釋后，用ICP-MS測定Cr、Cd、Cu、Pb、Zn等元素豐度，測量相對誤差分別控制在：Cr（15%）、Cd（30%）、Cu（10%）、Pb（10%）、Zn（12%）以內(nèi)。

1.2.2 原子熒光法測定As、Hg

稱取0.100 g樣品于25 mL比色管中，加入10 mL王水（1+1），水浴中加熱2 h，冷卻，用純水稀釋，放置澄清。

取清液5 mL于25 mL比色管中，加2 mL還原劑（硫脲、VC），放置1h，在原子熒光儀測定As。

取清液5 mL在原子熒光儀測定Hg。

1.2.3 二苯碳酰二肼比色法檢測Cr6+

稱取5.000 g樣品（105℃烘干2小時）于300 mL塑料瓶中，加入50 mL水，震蕩8 h，放置澄清。取清液10 mL于25 mL比色管中，加2.5 mL二苯碳酰二肼顯色劑，加水稀釋至刻度。用分光光度計在540 nm處測定吸光度。

以上測試均在中國地質(zhì)調(diào)查局西安地質(zhì)調(diào)查中心完成。

2 紅堿淖表層沉積物幾種重金屬測試結(jié)果

2.1 測試結(jié)果

表1列出了紅堿淖各點(diǎn)位幾種重金屬含量、變化范圍及其變異系數(shù)。總體上紅堿淖表層沉積物重金屬含量較低。表層沉積物中重金屬平均含量從高到低分別為：Cr ＞ Zn ＞ Pb ＞ Hg ＞ Cu ＞ As ＞ Cd。所測七種重金屬元素在紅堿淖表現(xiàn)出較大的變異性，即不同點(diǎn)位測試結(jié)果差別較大。除Pb、As和Cr外，其他5種元素在12個點(diǎn)位的變異系數(shù)均大于0.55。 Cd的變異系數(shù)最大，達(dá)到0.68。

2.2 與國家土壤環(huán)境質(zhì)量標(biāo)準(zhǔn)的比較

中華人民共和國國家標(biāo)準(zhǔn)土壤環(huán)境質(zhì)量標(biāo)準(zhǔn)（GB 15618—1995）規(guī)定了不同類型土壤中重金屬含量的上限（夏家淇，1996）。本文對比了紅堿淖湖泊表層沉積物均值、極大值和極小值與不同土壤環(huán)境分類的重金屬含量（表2）。

由表2可以看出，紅堿淖重金屬元素含量均值均在國家一類土壤標(biāo)準(zhǔn)上限以內(nèi)，整體上重金屬污染程度較輕。從12個樣點(diǎn)的極值來看，大部分元素的最大值也未超出一類土壤標(biāo)準(zhǔn)上限值，只有Cd的最大值超出了土壤二類標(biāo)準(zhǔn)上限值，說明該湖泊Cd存在一定范圍內(nèi)的富集。

表1 幾種重金屬元素（含六價鉻）測試結(jié)果Tab.1 Heavy metals (including Cr6+) in the surface sediment of Hongjiannao Lake

表2 紅堿淖表層沉積物樣品與國家土壤環(huán)境質(zhì)量標(biāo)準(zhǔn)的對比Tab.2 The comparison of samples in Hongjiannao Lake with the Environmental Quality Standard for Soils

3 紅堿淖重金屬污染生態(tài)風(fēng)險評價

目前重金屬生態(tài)風(fēng)險評估的方法較多，主要有：地質(zhì)累積指數(shù)法（Sutherland，2000；Qu et al，2001；楊麗原等，2003）、富集因子法（Blaser et al，2000；Sutherland，2000；滕彥國等，2003；Hernandez et al，2003；Tania et al，2003）、沉積物質(zhì)量基準(zhǔn)法（Long et al，1995；徐爭啟等，2004）、潛在生態(tài)風(fēng)險指數(shù)法（Hakanson，1980）、污染負(fù)荷指數(shù)法（Long et al，1998）等。由瑞典著名地球化學(xué)家Hakanson（1980）提出的潛在生態(tài)風(fēng)險指數(shù)法，是很多地區(qū)開展重金屬元素潛在風(fēng)險評估的常用方法。該方法涉及到單項(xiàng)污染系數(shù)、重金屬毒性響應(yīng)系數(shù)以及潛在生態(tài)危害系數(shù), 不僅考慮了土壤重金屬的含量, 而且將重金屬的生態(tài)效應(yīng)、環(huán)境效應(yīng)與毒理學(xué)聯(lián)系在一起，采用可比的、等價屬性指數(shù)分級法進(jìn)行評價。

本研究采用元素富集因子法和潛在生態(tài)風(fēng)險指數(shù)法評價紅堿淖湖泊表層沉積物重金屬生態(tài)風(fēng)險。

3.1 元素富集因子法

元素富集因子是指測試體系元素相對于某一參比體系富集情況的一個指標(biāo)。利用元素富集因子法，結(jié)合某地元素背景值資料，可以評估某種元素富集情況，從而判斷重金屬污染情況。

用Al作為參比元素，分別使用《中國土壤元素背景值》中陜西省相關(guān)元素平均值（中國環(huán)境監(jiān)測總站，1990）和上地殼平均元素豐度（Taylor and McClennan，1985），計算紅堿淖表層沉積物中As、Cr、Cd、Hg、Cu、Pb、Zn富集因子（EF）。

EF計算公式如下（Zhang et al，1993）：

其中：Ei為計算富集因子的某種元素，Al為參比元素，m代表元素實(shí)測數(shù)據(jù)與參比元素的比值，c代表比較體系元素與參比元素的比值。

元素富集因子可以用來表示研究體系中某種元素相對于參比體系的富集程度，通常數(shù)值大于1代表研究體系某元素相對參比體系富集，數(shù)值越大富集程度越高，數(shù)值等于1代表研究體系與參比體系元素變化一致，數(shù)值小于1代表研究體系與參比體系元素?zé)o富集。計算結(jié)果如表3和表4所示。

如表3和表4所示，紅堿淖湖泊表層沉積物除Cd和As兩個元素外，其余元素的富集因子均小于1，未表現(xiàn)明顯富集。Cd在1、7、8、9、10、11號樣點(diǎn)無論相對于陜西省A層土壤還是上地殼平均豐度均表現(xiàn)為相對富集；As僅相對于上地殼平均元素豐度的富集因子均大于1，這暗示陜西省土壤As元素背景值本身高于上地殼平均值?？梢姡t堿淖湖泊表層沉積物元素富集因子表明該湖泊未受明顯污染。

表3 紅堿淖底泥重金屬元素相對陜西省土壤平均元素豐度的富集因子Tab.3 The EF of heavy metals in Hongjiannao Lake relative to soils in Shaanxi Province

表4 紅堿淖表層沉積物重金屬元素相對上地殼平均元素豐度的富集因子Tab.4 The EF of heavy metals in Hongjiannao Lake relative to the upper continental crust

3.2 潛在生態(tài)風(fēng)險指數(shù)法

潛在生態(tài)風(fēng)險指數(shù)法是目前常用的評價重金屬污染程度的方法。分為單一元素生態(tài)風(fēng)險評價和多元素生態(tài)風(fēng)險評價，計算公式如下：

沉積物污染程度Cde：

潛在生態(tài)風(fēng)險指數(shù)RI：

其中：Ci為某元素實(shí)測值，為該元素環(huán)境背景值，為某元素毒性響應(yīng)參數(shù)（幾種元素的毒性響應(yīng)系數(shù)通常?。篐g=40，Cd=30，As=10，Pb=5，Cu=5，Cr=2，Zn=1）。采用陜西省A層土壤均值作為元素背景值（中國環(huán)境監(jiān)測總站，1990），計算七種元素潛在生態(tài)風(fēng)險指數(shù)。結(jié)果列于表5。

表5 紅堿淖湖泊表層沉積物重金屬潛在生態(tài)風(fēng)險指數(shù)計算結(jié)果Tab.5 The potential ecological risk index of heavy metals in the surface sediment of Hongjiannao Lake

表6 給出了污染程度（Cde）和生態(tài)風(fēng)險等級（RI）判別區(qū)間。值得注意的是，Hakanson（1980）除了計算本次研究的其中重金屬污染物外，還包含了多氯聯(lián)苯（PCBs），為了更客觀地評價重金屬的生態(tài)危害，本文根據(jù)Hakanson（1980）的數(shù)據(jù)，采用除去PCBs影響的方法，重新計算了分類等級數(shù)值范圍。計算原則如下：

首先將Hakanson（1980）的數(shù)據(jù)中PCBs對應(yīng)的Cfi分為三個等級：較低（1）、中等（2）和較高（4）；然后將相應(yīng)的Cde數(shù)值范圍分別減去1、2、4即得出其中重金屬污染程度（Ci）

f評價標(biāo)準(zhǔn)。將上述Cfi分級分別乘以PCBs的毒性系數(shù)40得到三個級別的PCBs的Eri數(shù)據(jù)40、80和160；然后將相應(yīng)的Eri數(shù)值范圍分別減去40、80、160即得出其中重金屬潛在危害程度（RI）評價標(biāo)準(zhǔn)。

表6 污染程度和潛在生態(tài)風(fēng)險等級Tab.6 Grades for pollution and potential ecological risk assessment

紅堿淖各取樣點(diǎn)重金屬元素的在2.06—9.97變化，均值為6.04，污染程度處于較低的水平，Cf

i值超過7的有五個點(diǎn)（1、7、9、10、11號樣點(diǎn)），但均未超過中等污染的范圍。RI在22.52到179.18之間變化，均值為93.50，有6個樣點(diǎn)RI值高于110，分別是1、7、8、9、10、11樣點(diǎn)，其他點(diǎn)位RI值均小于110，為較低污染水平。

由表5可知，對RI值貢獻(xiàn)最大的元素是Cd。究其原因，一方面是Cd的毒性系數(shù)較高；另一方面，根據(jù)元素富集因子評價結(jié)果，Cd在樣點(diǎn)1、7、8、9、10、11均表現(xiàn)為相對富集（表3，表4），以上兩方面的原因致使RI值在上述幾個樣點(diǎn)超過110，表現(xiàn)為中等危害。

通過不同方法對紅堿淖湖泊表層沉積物重金屬進(jìn)行了生態(tài)風(fēng)評估，其評估結(jié)果具有很強(qiáng)的相似性，顯示紅堿淖重金屬污染程度總體上較低，僅Cd存在一定程度的富集。

4 紅堿淖表層沉積物重金屬元素與其他湖泊的對比

紅堿淖表層沉積物重金屬元素與其他湖泊的比較如表7所示。同其他湖泊相比，紅堿淖所測重金屬污染物均處于較低水平（表7），如紅堿淖湖泊表層沉積物As元素含量僅比巢湖的結(jié)果略高，低于其他湖泊測試結(jié)果；Hg含量為所有對比湖泊中最低的；Cr含量僅比洪澤湖和太湖略高，而低于其他湖泊；Cu、Zn、Pb、Cd含量均為所有參比湖泊中最低的。

表7 紅堿淖表層沉積物重金屬元素與其他湖泊的比較Tab.7 The comparison of heavy metals contents in the surface sediment of Hongjiannao Lake with that in other lakes of China

（續(xù)表7 Continued Tab. 7）

5 結(jié)論

（1）通過兩種方法對紅堿淖湖泊表層沉積物重金屬的生態(tài)危害開展了評估，結(jié)果顯示紅堿淖重金屬污染程度總體上較低，均為低污染水平。由于Cd存在一定程度的富集， 且因Cd毒性系數(shù)較高，致使該湖泊表層沉積物重金屬潛在生態(tài)危害指數(shù)處于中等污染水平下限。

（2）與我國其他淡水湖相比，紅堿淖表層沉積物所測重金屬豐度平均處于較低水平，指示該湖泊受人為污染的影響較小。

（3）盡管多項(xiàng)評價指標(biāo)均顯示紅堿淖湖泊表層沉積物重金屬污染水平屬較低水平，但隨著湖泊退縮和周邊人類活動加劇，保護(hù)紅堿淖生態(tài)環(huán)境仍不容忽視，尤其應(yīng)嚴(yán)格限制污染物直接向湖泊排放。

程 杰, 李學(xué)德, 花日茂, 等. 2008. 巢湖水體沉積物重金屬的分布及生態(tài)風(fēng)險評價[J].農(nóng)業(yè)環(huán)境科學(xué)學(xué)報, 27(4): 1403 – 1408. [Cheng J, Li X D, Hua R M, et al. 2008. Distribution and ecological risk assessment of heavy metals in sediments of Chaohu Lake [J].Journal of Agro-Environment Science, 27(4): 1403 – 1408.]

弓曉峰, 陳春麗, 周文斌, 等. 2006. 鄱陽湖底泥中重金屬污染現(xiàn)狀評價 [J]．環(huán)境科學(xué)，27(4): 732 – 736. [Gong X F, Chen C L, Zhou W B, et al. 2006. Assessment on heavy metal pollution in the sediment of Poyang Lake [J].Environmental Science, 27(4): 732 – 736.]

焦 偉，盧少勇, 李光德, 等. 2010. 滇池內(nèi)湖濱帶重金屬污染及其生態(tài)風(fēng)險評價[J].農(nóng)業(yè)環(huán)境科學(xué)學(xué)報, 29(4): 740 – 745. [Jiao W, Lu S Y, Li G D, et al. 2010. Heavy metals pollution and potential ecological risk assessment of inner lakeside belt of Lake Dianchi [J].Journal of Agro-Environment Science, 29(4): 740 – 745.]

雷 忻, 王文強(qiáng), 廉振民. 2011. 陜西紅堿淖遺鷗研究現(xiàn)狀分析[J].延安大學(xué)學(xué)報（自然科學(xué)版）, 30(4): 93 – 96. [Lei X, Wang W Q, Lian Z M. 2011. A Review of studies on the status ofLarus relictusin Hongjiannao Lake, Shaanxi Province [J].Journal of Yanan University (Natural Science Edition), 30(4)：93 – 96.]

李登科, 何慧娟, 劉安麟. 2010. 人類活動和氣候變化對紅堿淖植被覆蓋變化的影響[J].中國沙漠, 30(4): 831 – 836. [Li D K, He H J, Liu A L. 2010. Impact of human activities and climate change on vegetation around Honhjian Nur Lake in northwestern China [J].Journal of Desert Research, 30(4): 831 – 836.]

李永進(jìn), 湯玉喜, 唐潔袁, 等. 2011. 洞庭湖灘地重金屬分布及其生態(tài)風(fēng)險評價[J].中南林業(yè)科技大學(xué)學(xué)報, 31(2): 55 – 59. [Li Y J, Tang Y X, Tang J Y, et al. 2011. Distribution and ecological risk assessment of heavy metal elements in soils of the beaches in Dongting Lake [J].Journal of Central South University of Forestry & Technology, 31(2): 55 – 59.]

李玉斌, 馮 流, 劉征濤, 等. 2012. 中國主要淡水湖泊沉積物中重金屬生態(tài)風(fēng)險研究[J].環(huán)境科學(xué)與技術(shù), 35(2): 200 – 205. [Li Y B, Feng L, Liu Z T, et al. 2012. Ecological risk assessment of sediment heavy metals in main lakes of China [J].Environmental Science & Technology, 35(2): 200 – 205.]

劉婉清, 倪兆奎, 吳志強(qiáng), 等. 2014. 江湖關(guān)系變化對鄱陽湖沉積物重金屬分布及生態(tài)風(fēng)險影響[J].環(huán)境科學(xué), 35(5): 1750 – 1758. [Liu W Q, Ni Z K, Wu Z Q, et al. 2014. Influence of the river-lake relation change on the distribution of heavy metal and ecological risk assessment in the surface sediment of Poyang Lake [J].Environmental Science, 35(5) : 1750 – 1758.]

劉曉清, 王亞萍. 2014. 陜西紅堿淖湖泊水體富營養(yǎng)化評價[J].人民黃河, 36(12): 76 – 78. [Liu X Q, Wang Y P. 2014. Evaluation of the eutrophication in Hongjiannao Lake [J].Yellow River, 36(12): 76 – 78.]

劉曉清, 王亞萍, 張振文, 等. 2013. 陜西紅堿淖湖底表層沉積物粒度特征[J].地球環(huán)境學(xué)報, 4(4): 1371 – 1378. [Liu X Q, Wang Y P, Zhang Z W, et al. 2013. Grain-size characteristics of the surface deposit in Hongjiannao Lake in northern Shaanxi Province [J].Journal of Earth Environment, 4(4): 1371 – 1378.]

馬 婷, 趙大勇, 曾 巾, 等. 2011. 南京主要湖泊表層沉積物中重金屬污染潛在生態(tài)風(fēng)險評價[J].生態(tài)與農(nóng)村環(huán)境學(xué)報, 27(6): 37 – 42. [Ma T, Zhao D Y, Zeng J, et al. 2011. Potential ecological risk assessment of heavy metal pollutants in surface sediments of the lakes in Nanjing [J].Journal of Ecology and Rural Environment, 27(6): 37 – 42.]

毛志剛, 谷孝鴻, 陸小明, 等. 2014. 太湖東部不同類型湖區(qū)疏浚后沉積物重金屬污染及潛在生態(tài)風(fēng)險評價[J]. 環(huán)

境科學(xué), 35 (1): 186 – 193. [Mao Z G, Gu X H, Lu X M, et al. 2014. Pollution distribution and potential ecological risk assessment of heavy metals in sediments from the different eastern dredging regions of Lake Taihu [J].Environmental Science, 35(1): 186 – 193.]

滕彥國, 倪師軍, 庹先國, 等. 2003. 應(yīng)用標(biāo)準(zhǔn)化方法評價攀枝花地區(qū)表層土壤的重金屬污染[J].土壤學(xué)報, 40(3): 374 – 379. [Teng Y G, Ni S J, Tuo X G, et al. 2003. Application of a normalization procedure in assessing heavy metal pollution in topsoil, Panzhihua region [J].Acta Pedologica Sinica, 40(3): 374 – 379.]

田林鋒, 胡繼偉, 羅桂林, 等．2012. 貴州百花湖沉積物重金屬穩(wěn)定性及潛在生態(tài)風(fēng)險性研究[J]．環(huán)境科學(xué)學(xué)報, 32(4): 885 – 894. [Tian L F, Hu J W, Luo G L, et al. 2012. Ecological risk and stability of heavy metals in sediments from Lake Baihua in Guizhou Province [J].Acta Scientiae Circumstantiae, 32(4): 885 – 894.]

夏家淇. 1996. 土壤環(huán)境質(zhì)量標(biāo)準(zhǔn)詳解[M]. 北京: 中國環(huán)境科學(xué)出版社. [Xia J Q. 1996. Explanation of soil environmental standard in detail [M]. Beijing: China Environmental Science Press.]

徐爭啟, 倪師軍, 張成江, 等. 2004. 應(yīng)用污染負(fù)荷指數(shù)法評價攀枝花地區(qū)金沙江水系沉積物中的重金[J]．四川環(huán)境, 23(3): 64 – 67. [Xu Z Q, Ni S J, Zhang C J, et al. 2004. Assessment on heavy metals in the sediments of Jinsha River in Panzhihua area by pollution load index [J].Sichuan Environment, 23(3): 64 – 67.]

楊麗原, 沈 吉, 張祖陸, 等. 2003. 南四湖表層底泥重金屬污染及其風(fēng)險性評價[J].湖泊科學(xué), 15(3): 252 – 256. [Yang L Y, Shen J, Zhang Z L, et al. 2003. Distribution and ecological risk assessment for heavy metals in super fi cial sediments of Nansihu Lake [J].Journal of Lake Sciences, 15(3): 252 – 256.]

余 輝, 張文斌, 余建平. 2011. 洪澤湖表層沉積物重金屬分布特征及其風(fēng)險評價[J].環(huán)境科學(xué), 32(2): 437 – 444. [Yu H, Zhang W B, Yu J P. 2011. Distribution and potential ecological risk assessment of heavy metals in surface sediments of Hongze Lake [J].Environmental Science, 32(2): 437 – 444.]

中國環(huán)境監(jiān)測總站. 1990. 中國土壤元素背景值[M]. 北京:中國環(huán)境科學(xué)出版社. [China National Environmental Monitoring Centre. 1990. Background values of elements in soils of China [M]. Beijing: China Environmental Science Press.]

Blaser P, Zimmermann S, Luster J, et al. 2000. Critical examination of trace element enrichments and depletions in soils: As, Cr, Cu, Ni, Pb and Zn in Swiss forest soils [J].The Science of the Total Environment, 249: 257 – 280.

Hakanson Lars. 1980. An ecological risk index for aquatic pollution control: A sedimentological approach [J].Water Research, 14(8): 975–1001.

Hernandez L, Probst A, Probst J L, et al. 2003. Heavy metal distribution in some French forest soils: evidence for atmospheric contamination [J].The Science of the Total Environment, 312: 195 – 219.

Long E R,MacDonald D D, Smith S L, et al. 1995. Incidence of adverse biological effects within Ranges of chemical concentrations in marine and estuarine sediments [J].EnvironmentalManagement, 19: 81 – 97.

Long E R, Field L J,MacDonald D D. 1998. Predicting toxicity in marine sediments with numerical sediment quality guidelines [J].Environmental Toxicology and Chemistry, 17(4): 714 – 727.

Peng J F, Song Y H, Peng Y, et al. 2009. The remediation of heavy metals contaminated sediment [J].Journal of HazardousMaterials, 161(2 / 3): 633 – 640.

Qu W, Dickman M, Wang S. 2001. Multivariate analysis of heavy metal and nutrient concentrations in sediments of Taihu Lake, China [J].Hydrobiologia, 450(1 – 3): 83 – 89.

Sutherland R A. 2000. Bed sediment-associated trace metals in an urban stream, Oahu, Hawaii [J].EnvironmentalGeology, 39: 611 – 627.

Tania L, Micaela P,Malcolm C. 2003. Heavy metal distribution and controlling factors within coastal plain sediments, bells creek catchment, southeast Queensland, Australia [J].Environment International, 29: 935 – 948.

Taylor S R, McClennan S. 1985. The continental crust: its composition and evolution [M]. Palo Alto, California: Blackwell Scienti fi c Publications.

Varol M, ?en B. 2012. Assessment of nutrient and heavy metal contamination in surface water and sediments of the upper Tigris River, Turkey [J].Catena, 92: 1 – 10.

Zhang X Y, Arimoto R, An Z S, et al. 1993. Atmospheric trace elements over source regions for Chinese dust: concentrations, sources and atmospheric deposition on the Loess Plateau [J].Atmospheric Environment Part A, 27: 2051 – 2067.

Ecological risk assessment of heavy metals in the surface sediment of Hongjiannao Lake, Shaanxi Province, China

YU Xuefeng1, LIU Xiaoqing2,3, WANG Yaping3
(1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; 2. Shaanxi Environmental Protection Industry Group, Co. Ltd., Xi'an 710075, China; 3. Shaanxi Provincial Academy of Environmental Sciences, Xi'an 710061, China)

Background, aim and scopeAs the biggest desert freshwater lake in China, Hongjiannao Lake, located in the southern margin of Mu Us Desert, plays an important role in the regional ecosystem. It is the habitats ofLarus relictuswhich is classi fi ed as “vulnerable” on the Red List of International Union for the Conservation of Nature (IUCN). However, the degradation of aquatic ecosystem in this region was found to be accelerating in recent years under the context of global warming and the intensi fi ed human activities. The ecological risk of heavy metals in the surface sediment of Hongjiannao Lake remains unknown so far. Therefore, the aim of this study is to provide the basic data for protecting the lake ecosystem by assessing the potential ecological risk of heavy metals in the surface sediment of the lake.Materials and methodsTwelve samples of surface sediment in the lake was taken by the Van veen grab sampler. The distribution of sampling sites in the lake were designed to be even to ensure the representativeness of the samples. Cr, Cd, Cu, Pb and Zn were analyzed by ICP-MS. The relative error of this method was controlled within 15% for Cr, 30% for Cd, 10% for Cu, 10% for Pb, and 12% for Zn. As, Hg were analyzed by atomic fl uorescence spectrometry. The relative error of this method was controlled within 10% for As and 25% for Hg. Cr6+was measured by diphenylcarbonydraide-spectrophotometer method with the relative error controlled within 15%. Three approaches were used in the assessment of the ecological risk of heavy metals in the surface sediment of Hongjiannao Lake: (1) the comparison of samples in Hongjiannao Lake with the Environmental Quality Standard for Soils in China (GB 15618—1995) (EQSS). (2) The enrichment factor (EF) to showthe state of the enrichment for each element relative to the reference system. The reference system is selected respectively as soils in Shaanxi Province to show the enrichment relative to the local environment, and the upper continental crust (UCC) to show the enrichment relative to the global mean content of upper continental crust. And (3) the potential ecological risk index (RI) to assess the potential risk of the toxicity of heavy metals to the lake ecosystem.ResultsThe result shows that the heavy metals in the surface sediment of Hongjiannao Lake are generally at a low level. The order of content from higher to lower is Cr ＞ Zn ＞ Pb ＞ Hg ＞ Cu ＞ As ＞ Cd. Except for Pb, As and Cr, the coef fi cient variations (CV) of other four metals (Cd, Cu, Zn and Hg) among twelve sites are higher than 0.55 with Cd to be the highest in 0.68. Obviously, the contents of heavy metals of the surface sediments in the center of the lake (sites 7 to 12) are higher than those near the lakeshore (sites 1 to 6).DiscussionCompared with the EQSS, the mean value of each heavy metal is within the upper limit value of the fi rst class soil in EQSS, indicating that the risk of heavy metals to this lake is at a lighter degree. Even for the maximum value of each element among the twelve samples, most of them are within the upper limit value of the fi rst class soil in EQSS, except for Cd. There are only two samples with the maximum value of Cd extend the upper limit value of the second class soil in EQSS. For most elements in the surface sediment of Hongjiannao Lake, the values of enrichment factor are lower than 1, indicating that there is no obvious enrichment for most elements, except for Cd and As. Cd assumes obvious enrichment both relative to soils in Shaanxi Province and to UCC at sites 1, 7, 8, 9, 10, 11. For As, it assumes enrichment only relative to UCC, but there is no enrichment relative to soils in Shaanxi Province, implying that the background content of As in soils in Shaanxi Province is higher than that in UCC. Thevalue of heavy metals for each sampling site varies from 2.06 to 9.97, with the mean value of 6.04. The RI value of heavy metals for each sampling site varies from 22.52 to 179.18, with the mean value of 93.50. There are six sites (1, 7, 8, 9, 10, 11) where the RI value are higher than 110, indicating that the risk of heavy metals in the center of the lake is light higher than that near the lakeshore. Generally, both thevalue and the RI value show that the potential risk of heavy metals in the lake is at a low level.ConclusionsThe above results show that: (1) the contents of heavy metals of the surface sediments in the center of the lake are higher than those near the lakeshore; (2) generally, the pollution of heavy metals in the lake is at a very low level, with the mild enrichment of Cd; and (3) the potential ecological risk of heavy metals in the surface sediment of Hongjiannao Lake is at a low level.Recommendations and perspectivesThe assessment provides the basic data for protecting the aquatic ecosystem in Hongjiannao Lake. Although the current risk of heavy metals in the surface sediment is not severe, the strict measures should be taken in the future to forbid the discharge of polluted water into the lake.

Hongjiannao Lake; heavy metal; enrichment factor (EF); risk index (RI)

YU Xuefeng, E-mail: xfyu@loess.llqg.ac.cn

10.7515/JEE201602007

2015-11-04；錄用日期：2016-02-26

Received Date:2015-11-04;Accepted Date:2016-02-26

環(huán)境保護(hù)部“良好湖泊生態(tài)環(huán)境保護(hù)專項(xiàng)”；黃土與第四紀(jì)地質(zhì)國家重點(diǎn)實(shí)驗(yàn)室自主部署課題

Foundation Item:MEP Special Fund for Lake Eco-environmental Protection; MOST Special fund for SKLLQG

于學(xué)峰，E-mail: xfyu@loess.llqg.ac.cn