夏天翔,劉雪華,趙孟彬
1.清華大學(xué)環(huán)境科學(xué)與工程系,北京100084
2.中關(guān)村海淀園北京錦繡大地農(nóng)業(yè)股份有限公司博士后工作站,北京100049
單獨(dú)與混合暴露條件下褶紋冠蚌對(duì)Cu、Zn的積累與分布
夏天翔1,2,劉雪華1,*,趙孟彬2
1.清華大學(xué)環(huán)境科學(xué)與工程系,北京100084
2.中關(guān)村海淀園北京錦繡大地農(nóng)業(yè)股份有限公司博士后工作站,北京100049
采用室內(nèi)模擬方法,在單獨(dú)與混合暴露條件下研究了褶紋冠蚌(Cristaria plicata)對(duì)Cu、Zn的積累與分布特征.結(jié)果表明:褶紋冠蚌對(duì)水環(huán)境中的Cu、Zn具有良好的積累能力,持續(xù)暴露8d內(nèi),體內(nèi)各組織重金屬積累量基本呈線性上升,其中鰓與外套積累速率最快(p<0.05).Cu在褶紋冠蚌鰓、內(nèi)臟團(tuán)和生殖腺中的積累速率與Zn之間存在顯著差異(p<0.05),且Cu、Zn之間在各組織中的積累拮抗作用明顯.暴露前,Cu含量在褶紋冠蚌體內(nèi)依次為:生殖腺>外套、內(nèi)臟團(tuán)>鰓、足>肌肉(p<0.05),變化幅度為10倍左右;Zn含量依次為:鰓>內(nèi)臟團(tuán)>生殖腺>足、外套>肌肉(p<0.05),變化幅度為4倍左右.暴露后,外套和鰓對(duì)Cu、Zn的積累量最高,且Cu、Zn含量在不同組織間的變化幅度明顯增加.暴露前后,Cu含量在不同組織間的變化幅度均高于Zn.不同暴露條件下,褶紋冠蚌不同組織對(duì)Zn的濃縮系數(shù)(BCF)明顯高于Cu.
褶紋冠蚌;積累速率;組織;銅;鋅;濃縮系數(shù)
雙殼綱軟體動(dòng)物由于具有高濾水速率以及較強(qiáng)的重金屬富集能力,因此常被用來進(jìn)行重金屬水體污染生物監(jiān)測研究(Lecoeur et al.,2004),尤其是海水生態(tài)系統(tǒng)中的某些貽貝和牡蠣(Boening,1999),而淡水生態(tài)系統(tǒng)中雙殼綱軟體動(dòng)物相關(guān)研究卻較為少見.淡水與海水生態(tài)系統(tǒng)中的水生動(dòng)物在滲透調(diào)節(jié)能力、重金屬吸收速率、同化效率等方面具有明顯差異(Wang and Rainbow,2008).近年來的研究表明,淡水生態(tài)系統(tǒng)中斑馬貽貝(Dreissena polymorpha)(Roditi and Fisher,1999)、三角帆蚌(Hyriopsis cumingii)(項(xiàng)黎新和邵繼光,2002)、河蜆(Corbicula fluminea)(曾麗璇等,2004)對(duì)模擬水環(huán)境中的重金屬同樣具有良好的積累能力,包括Cd、Ag、Hg、Pb等有毒重金屬.褶紋冠蚌(Cristaria plicata),屬軟體動(dòng)物門,雙殼綱,蚌科,過濾性取食,是我國分布廣泛的優(yōu)良淡水育珠蚌之一.目前,針對(duì)褶紋冠蚌的重金屬積累相關(guān)研究還鮮見報(bào)道.Cu、Zn是水生動(dòng)物生命活動(dòng)的必需元素,在水生動(dòng)物體內(nèi)的生物化學(xué)過程中扮演重要角色,特別是作為輔酶存在(Harrison and Hoare,1980),但其富集濃度一旦超過適宜范圍,同樣會(huì)引起毒害作用(Herkovits and Helguero,1998).隨飼料進(jìn)入水生生物食物鏈的重金屬已成為一些水生動(dòng)物重金屬積累的主要來源(Ojo et al.,2008),Cu、Zn是水產(chǎn)養(yǎng)殖過程中隨飼料輸入水體的重金屬主要種類.野外水體中水生動(dòng)物對(duì)Cu、Zn的積累差異明顯,Zn含量一般約為Cu的10倍以上(Herkovits and Helguero,1998),且在混合暴露條件下兩者在生物體內(nèi)的積累存在一定的交互作用,但交互作用結(jié)果明顯受暴露濃度與生物種類的影響(Philips,1976;Ahsannullah et al.,1981;Elliott et al.,1986).目前大部分研究仍以雙殼綱軟體動(dòng)物軟體組織整體積累為主,而重金屬在體內(nèi)不同組織間的分布對(duì)于重金屬生物積累機(jī)制、水生生態(tài)系統(tǒng)重金屬污染生物監(jiān)測與修復(fù)均具有重要意義(Yap et al.,2003;Gundacker,1999;Kádár et al.,2006).Widdows等(1992)認(rèn)為:預(yù)測和判斷重金屬或其他環(huán)境脅迫條件下的生態(tài)學(xué)和生物學(xué)反應(yīng)影響因素是生態(tài)毒理學(xué)研究的最終目的,因此必須建立:(1)環(huán)境中重金屬濃度與生物組織中重金屬含量之間的關(guān)系;(2)生物組織中重金屬含量與其生物效應(yīng)之間的關(guān)系.為此,本文現(xiàn)針對(duì)關(guān)系(1),在單獨(dú)和混合暴露條件下,對(duì)褶紋冠蚌體內(nèi)Cu、Zn的積累與分布進(jìn)行初步試驗(yàn),以期為重金屬生物積累機(jī)制以及我國淡水生態(tài)系統(tǒng)重金屬污染監(jiān)測與管理提供參考.
2008年10 月,3齡左右褶紋冠蚌購于北京水產(chǎn)市場,蚌體重400~500g,殼長16cm左右.用軟毛刷小心除去蚌表面附著物,放入經(jīng)2d以上曝氣自來水中馴化,期間不投食物,早晚曝氣,4d后選擇活力強(qiáng)的褶紋冠蚌進(jìn)行重金屬暴露試驗(yàn),實(shí)驗(yàn)期間室內(nèi)溫度在22℃左右.
污染物來源為CuSO4·5H2O(分析純)和ZnSO4·7H2O(分析純).
將實(shí)驗(yàn)蚌放入8L左右鋼化半透明塑料實(shí)驗(yàn)桶中,每桶一只,加入5L曝氣自來水.每天早晚曝氣半小時(shí).參照Loayza-Muro和Elías-Letts(2007)研究結(jié)果,以及我國地表水環(huán)境質(zhì)量標(biāo)準(zhǔn)(GB 3838-2002)(國家環(huán)境保護(hù)總局,2002)Ⅴ類限值(Cu 1000μg·L-1,Zn 2000μg·L-1)并在預(yù)備實(shí)驗(yàn)基礎(chǔ)上設(shè)置相等Cu、Zn暴露濃度以便觀察兩種重金屬在褶紋冠蚌體內(nèi)積累的差異及其交互作用的結(jié)果.具體設(shè)置如下,單獨(dú)暴露條件分別設(shè)置為:Cu(2000μg·L-1)、Zn(2000μg·L-1);混合暴露條件設(shè)置為Cu+Zn(2000μg·L-1+2000μg·L-1);以不加重金屬組作為對(duì)照(CK).各處理及CK分別設(shè)置12次重復(fù),合計(jì)48只實(shí)驗(yàn)桶(蚌).分別于第2、4、6、8d采集各處理中的實(shí)驗(yàn)蚌(3次重復(fù)),解剖后取出足、鰓、外套、內(nèi)臟團(tuán)、肌肉和生殖腺,每次采集蚌組織樣品后(第8d除外)為剩余處理及對(duì)照更換同樣重金屬濃度的新鮮實(shí)驗(yàn)水體.試驗(yàn)結(jié)束后(第8d),絕大部分供試實(shí)驗(yàn)蚌(對(duì)照組除外)活力出現(xiàn)不同程度下降,少數(shù)出現(xiàn)殼關(guān)閉緩慢現(xiàn)象,但無死亡發(fā)生.另于馴化過程結(jié)束后,暴露實(shí)驗(yàn)開始前,取3只蚌解剖,并取下各組織進(jìn)行測定,作為實(shí)驗(yàn)蚌Cu、Zn含量背景值.
用吸水紙吸去蚌組織樣品表面水分,放入潔凈的塑料杯中,60℃烘干至恒重(Ruelas-Inzunza and Páez-Osuna,2000).將烘干樣品粉碎后,稱取0.1~0.2g,以5mL 70%硝酸消解,稀釋至25mL,過濾,使用原子吸收分光光度計(jì)(PE AA-300,USA)進(jìn)行測定(Liu and Deng,2007).Cu、Zn的加標(biāo)回收率分別為93.7%、95.5%.
采用以EXCEL及SPSS 13.0對(duì)實(shí)驗(yàn)數(shù)據(jù)進(jìn)行處理和分析.不同組織間重金屬積累速率的差異采用一元方差分析,并進(jìn)行多重比較.不同暴露條件下各組織重金屬積累速率差異分別進(jìn)行獨(dú)立t檢驗(yàn).各組織重金屬生物濃縮系數(shù)(BCF,Bioconcentration factor)采用公式(1)計(jì)算:
其中,Ce——暴露后組織中重金屬含量(mg·kg-1);Cs——水體中重金屬暴露濃度(mg·L-1)
單獨(dú)及混合暴露條件下,隨著暴露時(shí)間的延長,褶紋冠蚌各組織對(duì)Cu、Zn的積累,基本呈線性上升(圖1,圖2).一般而言,在可溶性污染物暴露條件下,雙箱動(dòng)力學(xué)模型能夠很好地描述水生動(dòng)物對(duì)污染物的吸收與釋放過程,且隨著時(shí)間的延長,不呈現(xiàn)簡單的線性關(guān)系(張少娜等,2004).但雙箱動(dòng)力學(xué)模型基本假設(shè)為污染物在水相和生物體內(nèi)的兩相分配過程,在低暴露濃度條件、較長時(shí)間的監(jiān)測條件下,往往能夠較好地解釋生物對(duì)重金屬的動(dòng)態(tài)富集情況(張少娜等,2004;Clason et al.,2003;2004;陳海剛等,2008),因此該模型并不完全適合較高暴露濃度下的重金屬的短期積累研究.許多實(shí)驗(yàn)室模擬研究均表明,對(duì)重金屬的積累隨暴露時(shí)間的延長而增加是雙殼綱軟體動(dòng)物共同的特性(蔡立哲等,1999),本實(shí)驗(yàn)表明:褶紋冠蚌對(duì)Cu、Zn的短期積累與暴露時(shí)間基本符合正線性關(guān)系,以一元線性方程斜率(K值)表示不同組織對(duì)重金屬的積累速率(表1),其中各組織對(duì)Cu的積累速率線性模擬結(jié)果R2范圍為0.67~0.97,略優(yōu)于Zn(R2范圍為0.46~0.97).雙殼綱軟體動(dòng)物對(duì)Zn的吸收具有調(diào)節(jié)能力,與Cu相比,其積累更慢,釋放更快(Yap et al.,2003),因此對(duì)Zn的積累時(shí)間效應(yīng)關(guān)系應(yīng)更為復(fù)雜.
一元方差分析結(jié)果表明:不同暴露條件下,褶紋冠蚌鰓與外套中Cu、Zn的積累速率最高(p<0.05),肌肉中積累速率最低(表1),可見鰓與外套對(duì)Cu、Zn的積累能力強(qiáng)于其他組織.獨(dú)立t檢驗(yàn)結(jié)果表明:單獨(dú)與混合暴露條件下,Cu在褶紋冠蚌鰓、內(nèi)臟團(tuán)、生殖腺中的積累速率與Zn相比均存在顯著差異(p<0.05),但積累速率的高低并不具有一致性(K1-K2和K3-K4).與單獨(dú)暴露條件相比,混合暴露條件下,褶紋冠蚌各組織(除足外)對(duì)Cu、Zn的積累速率均有所下降(K1-K3和K2-K4),表明Cu、Zn的積累具有拮抗作用.Cu、Zn在雙殼綱軟體動(dòng)物體內(nèi)均能被金屬硫蛋白(MT)所固定,從而引起拮抗作用(Kǎgi and Kojima,1987).一般認(rèn)為MT作為生物重金屬污染指示蛋白,能夠代表生物對(duì)重金屬污染的初期反應(yīng),其在生物重金屬固定與釋放動(dòng)態(tài)平衡過程中扮演重要角色(Lecoeur et al.,2004),是雙殼綱軟體動(dòng)物解毒機(jī)制的關(guān)鍵所在(Roesijadi,1994).與單獨(dú)暴露條件相比,混合暴露條件下褶紋冠蚌生殖腺對(duì)Cu的積累差異(K1-K3)達(dá)到顯著水平(p<0.05),鰓與外套對(duì)Zn的積累差異(K2-K4)達(dá)到極顯著水平(p<0.01),而在其他組織中則無顯著差異(p>0.05).交互作用在不同組織中表現(xiàn)有所不同,應(yīng)由雙殼綱軟體動(dòng)物體內(nèi)不同組織間MT固定重金屬能力差異所引起(Yap et al.,2003).
表1 單獨(dú)及混合暴露條件下褶紋冠蚌不同組織中Cu、Zn的積累速率K(mg·kg-1·d-1)Table 1Bioaccumulation rates K(mg·kg-1·d-1)of Cu and Zn in each tissue of Cristaria plicata exposed to individual and mixed metals
重金屬暴露前后各組織中Cu、Zn的含量與濃縮系數(shù)見表2.結(jié)果表明:暴露前褶紋冠蚌各組織中Cu含量依次為:生殖腺>外套、內(nèi)臟團(tuán)>鰓、足>肌肉(p<0.05);Zn含量依次為:鰓>內(nèi)臟團(tuán)>生殖腺>足、外套>肌肉(p<0.05).暴露后,各組織中Cu、Zn含量均明顯增加,其中鰓、外套中Cu、Zn含量最高,這一結(jié)果與前文所述的鰓與外套對(duì)Cu、Zn的積累速率顯著高于其他組織相對(duì)應(yīng).雙殼綱軟體動(dòng)物鰓積累重金屬能力較強(qiáng)已有不少報(bào)道(Yap et al.,2003;Gundacker,1999;Kádár et al.,2006),主要原因在于鰓與水體的接觸面積較大,易化擴(kuò)散作用明顯(Philips et al.,1993).而外套組織中Cu、Zn積累量較高則較為少見,我們?cè)诹硪谎芯恐邪l(fā)現(xiàn):褶紋冠蚌在300μg·L-1Cu、300μg·L-1Zn混合暴露條件下外套中Cu、Zn的積累量同樣遠(yuǎn)高于其他組織(尚未公開發(fā)表),其可能原因在于重金屬脅迫條件下褶紋冠蚌外套組織中MT含量更高以及Zn由其他組織(鰓和內(nèi)臟團(tuán))向外套轉(zhuǎn)移.
表2 單獨(dú)及混合暴露前后褶紋冠蚌不同組織中Cu、Zn的含量(mg·kg-1)及濃縮系數(shù)(BCF)Table 2Contents and bioconcentration factor(BCF)of Cu and Zn in each tissue of Cristaria Plicata before and after exposure to individual and mixed metals
暴露前各組織中的Zn含量約為Cu含量的7~30倍,其中Cu含量和Zn含量在不同組織間的變化幅度約為10倍和4倍.單獨(dú)和混合暴露后,Cu含量在不同組織間的變化幅度分別增加到20倍和16倍;Zn含量在不同組織間的變化幅度分別增加到6倍和5倍左右.由此可見:暴露后Cu、Zn在不同組織間分布的差異均有所增加;且暴露前后,Cu在體內(nèi)不同組織間的變化幅度均高于Zn,這與之前的研究結(jié)果相類似(Yap et al.,2003;Philips,1985;Rees et al.,1999),Zn在雙殼綱軟體動(dòng)物體內(nèi)移動(dòng)性強(qiáng)于Cu、Cd等其他重金屬離子(Yap et al.,2003),可能是導(dǎo)致這一結(jié)果的主要原因.生物濃縮系數(shù)(BCF)由于其直觀性而在生物重金屬積累研究領(lǐng)域被廣泛使用(McGeer et al.,2003),其大小表明受檢生物對(duì)環(huán)境中的重金屬的富集能力.單獨(dú)與混合暴露后,蚌體內(nèi)各組織重金屬富集現(xiàn)象明顯,不同組織中Cu、Zn的濃縮系數(shù)分別為:4.35~88.95、40.10~245.45,可見褶紋冠蚌對(duì)Zn的富集能力應(yīng)高于Cu,這與Shi和Wang(2004)在Cu、Zn暴露濃度相近條件下針對(duì)海水模擬系統(tǒng)中的翡翠貽貝(Perna viridis)的研究結(jié)果相符合,由于BCF大小受暴露濃度影響很大,褶紋冠蚌對(duì)Cu,Zn的積累能力與其他雙殼綱軟體動(dòng)物之間尚無法直接比較.
綜上所述,褶紋冠蚌各組織對(duì)較高暴露濃度條件下Cu、Zn的短期積累,隨著時(shí)間的延長,基本呈現(xiàn)線性增長.不同組織對(duì)Cu、Zn的積累存在明顯差異,其中鰓與外套對(duì)Cu、Zn的積累速率以及積累量均顯著高于其他組織(足、外套、內(nèi)臟團(tuán)、生殖腺).Cu、Zn在褶紋冠蚌體內(nèi)的積累存在拮抗作用.不同暴露條件下,褶紋冠蚌不同組織對(duì)Zn的富集能力明顯高于Cu,但Cu在蚌體內(nèi)不同組織間的分布差異更大.
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Accumulation and Distribution of Copper and Zinc in the Freshwater Mussel,Cristaria Plicata,Exposed to Individual and Mixed Metals
XIA Tian-xiang1,2,LIU Xue-hua1,*,ZHAO Meng-bin2
1.Department of Environmental Science and Engineering,Tsinghua University,Beijing 100084
2.Beijing Glorious Land Agricultural Co.,LTD Enterprise Postdoctoral Workstation of Zhongguancun(Haidian)Science Park,Beijing 100049
Characteristics of accumulation and distribution of Cu and Zn in the freshwater mussel,Cristaria plicata,exposed to individual and mixed metals were investigated under the laboratory conditions.Results showed that the Cristaria plicata mussel could concentrate Cu and Zn in each soft tissue,the contents in which linearly increased with exposure times from 0 to 8 days.The tissues of gill and mantle accumulated Cu and Zn more rapidly than the other tissues(p<0.05).Significant differences in accumulation rates between Cu and Zn were found at the tissues of gill,viscera and gonad(p<0.05)and the interaction of the two metals during accumulation was antagonistic.Before the metal exposure,metal contents in different tissues were with the sequences of gonad>mantle,viscera>gill,foot>muscle and the contents varied 10-fold range for Cu(p<0.05),and gill>viscera>gonad>foot,mantle>muscle and the contents varied 4-fold range for Zn(p<0.05).The metal exposures caused Cu and Zn contents reached the highest values in the mantle and gill respectively and the differences in Cu contents and Zn contents among each tissue were improved.The ranges of Cu contents varied in different tissues were higher than that of Zn contents varied before and after the exposure.At the different metal exposures,the bioconcentration factor(BCF)of Zn is higher than that of Cu obviously in each tissue of the test mussel.
Cristaria plicata;accumulation rate;tissue;copper;zinc;bioconcentration factor(BCF)
8 January 2009accepted2 March 2009
1673-5897(2010)2-169-07
X52
A
2009-01-08錄用日期:2009-03-02
中國博士后科學(xué)基金(No.20080430453);北京市海淀區(qū)科委資助項(xiàng)目(No.K2008199)
夏天翔(1979—),男,清華大學(xué)環(huán)境科學(xué)與工程系博士后;*通訊作者(Corresponding author),E-mail:xuehuahjx@mail.tsinghua.edu.cn
劉雪華(1964—),女,清華大學(xué)副教授,主要從事生態(tài)評(píng)價(jià)與生態(tài)規(guī)劃,遙感和地理信息系統(tǒng)應(yīng)用以及水環(huán)境污染治理等方面的研究.