藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理學(xué)研究進(jìn)展

薛慶舉, 蘇小妹, 謝麗強(qiáng)

1 中國(guó)科學(xué)院南京地理與湖泊研究所湖泊與環(huán)境國(guó)家重點(diǎn)實(shí)驗(yàn)室, 南京 210008 2 中國(guó)科學(xué)院大學(xué), 北京 100049

藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理學(xué)研究進(jìn)展

薛慶舉1,2, 蘇小妹1,2, 謝麗強(qiáng)1,*

1 中國(guó)科學(xué)院南京地理與湖泊研究所湖泊與環(huán)境國(guó)家重點(diǎn)實(shí)驗(yàn)室, 南京 210008 2 中國(guó)科學(xué)院大學(xué), 北京 100049

近年，由于人類活動(dòng)加劇，大量氮磷等營(yíng)養(yǎng)物質(zhì)流入湖泊等緩流水體，導(dǎo)致水體富營(yíng)養(yǎng)化。而由此引起有害藍(lán)藻水華的頻繁爆發(fā)，使生態(tài)環(huán)境和人類健康受到嚴(yán)重威脅。相關(guān)研究表明，藍(lán)藻水華的爆發(fā)不僅能夠使水體水質(zhì)惡化，其中一些產(chǎn)毒藻類還會(huì)產(chǎn)生大量藍(lán)藻毒素，對(duì)水生生物產(chǎn)生重要影響。底棲動(dòng)物作為水體生態(tài)系統(tǒng)的重要組成部分，在食物網(wǎng)中有重要作用，同時(shí)其中的許多種類又與人類息息相關(guān)，因此關(guān)于水華藍(lán)藻毒素對(duì)淡水底棲動(dòng)物的毒理學(xué)研究具有重要意義。在介紹藍(lán)藻毒素概況的基礎(chǔ)上，綜述了藍(lán)藻毒素的致毒機(jī)理和對(duì)底棲動(dòng)物的影響，展望了研究方向。

底棲動(dòng)物; 藍(lán)藻毒素; 食物網(wǎng); 環(huán)境毒理學(xué)

由于人類活動(dòng)的加劇，氮磷等植物營(yíng)養(yǎng)物質(zhì)大量流入水體，造成水體富營(yíng)養(yǎng)化，在與光照、溫度、濁度、pH值、電導(dǎo)率、鹽度和一些水文條件(如水體的流動(dòng)性)等相互影響后[1]，最終使一些光能自養(yǎng)型藻類大量繁殖而導(dǎo)致藻類水華爆發(fā)。淡水水體水華的發(fā)生主要以藍(lán)藻水華為主，藍(lán)藻的大量繁殖不但會(huì)對(duì)水體造成直接影響(如溶解氧降低等)，還能夠產(chǎn)生毒性很強(qiáng)的代謝產(chǎn)物——藍(lán)藻毒素(cyanotoxin)，危及動(dòng)物和人類安全。

底棲動(dòng)物是水體中與藍(lán)藻毒素具有最直接關(guān)系的一類水生生物。底棲動(dòng)物是指生活史的全部或大部分時(shí)間生活于水體底部的水生動(dòng)物類群，是水生態(tài)系統(tǒng)的一個(gè)重要組成部分[2]。底棲動(dòng)物在水生態(tài)系統(tǒng)中發(fā)揮著重要作用。首先，它們可以加速水底物質(zhì)分解，促進(jìn)水體自凈；其次，底棲動(dòng)物是水體生態(tài)系統(tǒng)食物鏈的重要組成部分，不僅是浮游生物的捕食者，還是一些掠食動(dòng)物(Predators)的食物，有的雜食種類還能充當(dāng)分解者；再次，底棲動(dòng)物在水體富營(yíng)養(yǎng)化研究中有重要作用，它們可以通過自身的生命活動(dòng)對(duì)水體中營(yíng)養(yǎng)鹽的含量產(chǎn)生重要影響，其中的一些物種已經(jīng)被用于水體富營(yíng)養(yǎng)化的治理。同時(shí)，底棲動(dòng)物中有許多物種不僅是一些水產(chǎn)品的重要餌料，還是倍受人類歡迎的美食。所以，研究藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理學(xué)具有重要的理論和實(shí)際意義。有鑒于此，本文綜述了藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理學(xué)研究現(xiàn)狀，對(duì)藍(lán)藻毒素的基本性質(zhì)、致毒機(jī)理、在生物體內(nèi)的累積與清除，以及對(duì)底棲動(dòng)物的影響進(jìn)行了綜述，并進(jìn)一步對(duì)未來(lái)研究重點(diǎn)進(jìn)行了展望，以期能夠?yàn)榻窈髮?duì)藍(lán)藻毒素的進(jìn)一步研究提供參考。

1 藍(lán)藻毒素概述

自1878年首次報(bào)道藍(lán)藻毒素導(dǎo)致家禽死亡后，世界范圍內(nèi)關(guān)于藍(lán)藻毒素對(duì)動(dòng)物和人類危害的報(bào)道越來(lái)越多，當(dāng)家畜及野生動(dòng)物飲用含有藻毒素的水之后，一般會(huì)出現(xiàn)肝臟腫大、充血或壞死，腸炎出血、肺水腫等病變，同時(shí)因接觸藍(lán)藻毒素而導(dǎo)致的人類死亡事件也時(shí)有發(fā)生，而有學(xué)者亦指出中國(guó)南方原發(fā)性肝癌的高發(fā)病率與飲用水中含有微囊藻毒素(Microcystin， MC)存在一定的關(guān)系[3-6]。相關(guān)研究發(fā)現(xiàn)，藍(lán)藻毒素為藍(lán)藻的次級(jí)代謝產(chǎn)物，在不同生境都有廣泛的分布[7]。藍(lán)藻毒素根據(jù)化學(xué)結(jié)構(gòu)可以分為三類：環(huán)肽(Cyclic peptide)、生物堿(Alkaloid)和脂多糖內(nèi)毒素(Lipopolysacchride, LPS)；也可根據(jù)毒素作用位置的不同分為肝毒素(Hepatotoxin)、神經(jīng)毒素(neurotoxin)、細(xì)胞毒素(cytotoxin)和皮膚毒素(dermatotoxin)等[8]。而其中微囊藻毒素(MC)是世界各地最為常見且危害最嚴(yán)重的毒素，具有顯著的肝臟毒性，其結(jié)構(gòu)在20世紀(jì)80年代初得到確認(rèn)，為環(huán)狀七肽結(jié)構(gòu)，目前已發(fā)現(xiàn)80余種毒素亞型，最常見的為MC-LR，在世界范圍內(nèi)得到最廣泛的關(guān)注[9-11]。除MC之外，對(duì)其它毒素(如節(jié)球藻毒素(Nodularin)、擬柱孢藻毒素(Cylindrospermopsin，CYN)和生物堿毒素等)的研究相對(duì)較少。

相關(guān)研究發(fā)現(xiàn)，MC的性質(zhì)穩(wěn)定，大多數(shù)MC是親水的，一般在水中的溶解度能達(dá)到1 gL以上，不易沉淀或被沉積物和懸浮顆粒物吸附，易溶于甲醇或丙酮。由于MC分子結(jié)構(gòu)中含有羧基、氨基和酰氨基，所以在不同pH值條件下MC有不同的離子化傾向[12],但蛋白質(zhì)水解酶對(duì)它們卻不起作用。MC還具有熱穩(wěn)定性，在加熱到300 ℃后仍能維持很長(zhǎng)時(shí)間不分解[1]。MC在陽(yáng)光照射下亦非常穩(wěn)定，但是在不同濃度的水可提取色素存在的條件下它的穩(wěn)定性和異構(gòu)化有顯著的變化[8]，同時(shí)在某些條件下MC能夠被生物所降解。

2 致毒機(jī)理

圖1 動(dòng)物細(xì)胞中微囊藻毒素MC的攝取、毒性機(jī)制、生物轉(zhuǎn)化和排泄的路徑[14]

由于MC具有親水性導(dǎo)致其不能以被動(dòng)運(yùn)輸?shù)姆绞酵ㄟ^細(xì)胞膜，而只能依靠相應(yīng)載體的運(yùn)輸，這也是MC器官選擇性毒性的重要原因[13]，MC在動(dòng)物細(xì)胞中的遷移轉(zhuǎn)化過程如圖1[14]所示。MC致毒的分子機(jī)制主要有以下幾個(gè)方面：抑制蛋白磷酸酶的活性、引起氧化應(yīng)激和內(nèi)質(zhì)網(wǎng)應(yīng)激。研究發(fā)現(xiàn)微囊藻毒素和節(jié)球藻毒素可以與蛋白磷酸酶(protein phosphatases, PPs)1和2A的絲氨酸蘇氨酸亞基相結(jié)合，從而抑制它們的活性[15-17]。由于蛋白磷酸酶在催化蛋白分子脫磷酸化和調(diào)控細(xì)胞骨架與細(xì)胞凋亡等過程中具有重要的作用，所以當(dāng)?shù)鞍琢姿崦窹P1和PP2A被抑制時(shí)，會(huì)導(dǎo)致細(xì)胞過度磷酸化，甚至使細(xì)胞凋亡[18]。同時(shí)，蛋白磷酸酶的抑制可使DNA依賴的蛋白激酶(DNA-dependent Protein Kinase, DNA-PK)失活，進(jìn)而造成DNA的損傷[19-20]。MC還能夠引起活性氧簇(Reactive oxygen species, ROS)的快速產(chǎn)生，而ROS的大量產(chǎn)生會(huì)導(dǎo)致脂質(zhì)過氧化、線粒體結(jié)構(gòu)和功能的破壞和DNA損傷等。而MC對(duì)細(xì)胞內(nèi)抗氧化系統(tǒng)的損傷主要是在與OATP(Organic anion transporting polypeptides，有機(jī)陰離子轉(zhuǎn)運(yùn)多肽)載體結(jié)合進(jìn)入細(xì)胞時(shí)谷胱甘肽(Glutathione，GSH)的流出導(dǎo)致的[10,21-23]。目前對(duì)于內(nèi)質(zhì)網(wǎng)應(yīng)激的研究還相當(dāng)少，但已有研究表明，MC可能導(dǎo)致錯(cuò)誤折疊的蛋白質(zhì)在內(nèi)質(zhì)網(wǎng)內(nèi)堆積，從而引起內(nèi)質(zhì)網(wǎng)應(yīng)激[24]。隨著不斷的研究發(fā)現(xiàn)，MC的毒性作用在最后幾乎都能導(dǎo)致細(xì)胞的凋亡，同時(shí)還有一定的促癌作用，而對(duì)于藍(lán)藻毒素在生物體內(nèi)的轉(zhuǎn)化還需要進(jìn)一步深入的研究。

3 藍(lán)藻毒素與底棲動(dòng)物

藍(lán)藻毒素對(duì)淡水水生生物作用的研究較少且大多集中于一些魚類和某些大型的底棲動(dòng)物，原因可能主要有以下幾個(gè)方面：一方面，與海洋藻毒素相比，淡水藻毒素對(duì)人類和一些動(dòng)物產(chǎn)生的急性中毒事件較少；第二，人類對(duì)淡水水產(chǎn)品的消耗量與海洋水產(chǎn)品的消耗量相比要小的多，聯(lián)合國(guó)食品與農(nóng)業(yè)組織調(diào)查發(fā)現(xiàn)，2008年全球捕魚量為9000萬(wàn) t，而內(nèi)陸淡水捕魚量只有1000萬(wàn) t[25]；第三，所研究的淡水水生生物大都是被人類食用的食物(如螺、蚌和蝦等)，對(duì)人類可能存在較大的潛在危害；同時(shí)，研究還會(huì)受生物個(gè)體特征、實(shí)驗(yàn)和檢測(cè)分析條件的限制，如生物食性、生物量大小、存活能力和體內(nèi)毒素含量。目前的研究基本集中在生物體內(nèi)或者不同器官中藻毒素富集和清除的研究，也有一些藻毒素在同一生物不同器官中分布和對(duì)不同成長(zhǎng)階段個(gè)體影響的研究，但對(duì)于藻毒素在生物體內(nèi)的分子生物學(xué)轉(zhuǎn)化及代謝和生物鏈中轉(zhuǎn)移機(jī)制方面的研究則相對(duì)較少。

3.1 藍(lán)藻毒素在底棲動(dòng)物體內(nèi)的富集與清除

底棲動(dòng)物通過不同的方式富集MC后，MC大部分富集于消化道、肝胰腺和性腺三個(gè)器官之內(nèi)，以消化道和肝胰腺中的含量最高，多數(shù)研究結(jié)果都已超過WHO的規(guī)定(0.04 μg kg-1d-1)[26]，關(guān)于藍(lán)藻毒素在底棲動(dòng)物體內(nèi)的富集與清除詳見表1。相對(duì)來(lái)說(shuō)，底棲動(dòng)物的足和肌肉中MC的含量要小的多，所以在只食一些底棲動(dòng)物的足或者肌肉的情況下，MC對(duì)于人類健康的影響相對(duì)較小[27-36]。研究表明，MC在底棲動(dòng)物體內(nèi)的富集與一些環(huán)境因子存在一定的相關(guān)性。如Ozawa[29]等研究淡水田螺(Sinotaiahistrica)肝胰腺和腸道中MC的季節(jié)變化時(shí)發(fā)現(xiàn)，當(dāng)湖泊中浮游植物體內(nèi)MC含量最高時(shí)(10月)，田螺腸道和肝胰腺中的MC的含量也最高，而Yokoyama和Park[37]發(fā)現(xiàn)褶紋冠蚌(Cristariaplicata)在夏季水華時(shí)MC含量很低，但是在水華消失的秋季卻迅速升高；Chen和Xie[31]對(duì)3種雙殼類的研究得出，夏季大部分器官M(fèi)C含量的峰值與懸浮顆粒物和水華藍(lán)藻的MC含量峰值相吻合，同時(shí)，Chen和Xie[33]還指出不同底棲動(dòng)物中不同的MC含量可能與攝取的食物不同有關(guān)。Lance[38]等和Prepas[39]等的研究表明，靜水椎實(shí)螺(Lymnaeastagnalis)和淡水無(wú)齒蚌 (Anodontagrandissimpsoniana)對(duì)MC的富集主要通過攝食含有毒素的浮游植物，而極少通過吸收溶解的毒素，而Zhang[40]等對(duì)橢圓蘿卜螺(Radixswinhoei)和螺獅(Margaryamelanioide)各器官對(duì)MC的生物富集的研究卻發(fā)現(xiàn)，橢圓蘿卜螺中MC濃度與環(huán)境中的溶解MC有關(guān)，而螺獅中的MC濃度與細(xì)胞內(nèi)毒素相關(guān)。Zhang[30]等對(duì)太湖中銅銹環(huán)棱螺(Bellamyaaeruginosa)的研究還發(fā)現(xiàn)，后代體內(nèi)MC含量還與母體性腺中MC的含量有關(guān)。Zhang[9]等對(duì)太湖銅銹環(huán)棱螺肝胰腺中3種最常見的毒素亞型(MC-LR、MC-RR和MC-YR)的時(shí)空分布的研究指出，MC在肝胰腺中濃度的變化與不同點(diǎn)位水體中細(xì)胞內(nèi)毒素的變化一致，且與懸浮顆粒物中MC濃度顯著相關(guān)，同時(shí)結(jié)果表明其它因素(如水溫)對(duì)銅銹環(huán)棱螺肝胰腺內(nèi)的MC富集有重要的影響；當(dāng)?shù)讞珓?dòng)物處于不同的營(yíng)養(yǎng)級(jí)時(shí)，其體內(nèi)MC的含量也會(huì)有很大的差別[35]。Galanti[42]等在室內(nèi)對(duì)淡水蝦Palaemonetesargentinus的研究發(fā)現(xiàn)，將P.argentinus在MC-LR(50 μg/L)中培養(yǎng)3 d后就能檢測(cè)到MC，同時(shí)還指出MC與GSH的結(jié)合是P.argentinus的一種重要的MC解毒機(jī)制。

目前對(duì)擬柱孢藻毒素(CYN)等其它毒素生物富集的研究相對(duì)較少。Seifert[43]的研究顯示CYN在低于100 μg/L情況下就能對(duì)一些水生無(wú)脊椎動(dòng)物產(chǎn)生顯著的影響。Saker和Eaglesham[44]第一次對(duì)紅螯螯蝦(Cheraxquadricarinatus)肌肉和肝胰臟中CYN的濃度進(jìn)行了檢測(cè)，發(fā)現(xiàn)肝胰腺和肌肉組織中含量分別達(dá)到4.3和0.9 mg/kg(干重)，而室內(nèi)研究結(jié)果要比野外低很多。Saker[45]等將淡水無(wú)齒蚌(Anodontacygnea)暴露于不同濃度的CYN中，發(fā)現(xiàn)各器官中所占比例為血淋巴68.1%，內(nèi)臟為23.3%，足和性腺為7.7%，外套膜0.9%，在鰓和肌肉中未發(fā)現(xiàn)，而且在經(jīng)過14 d的清除之后還有大約50%的毒素存留。White[46]等在實(shí)驗(yàn)室內(nèi)對(duì)瘤擬黑螺(Melanoidestuberculata)的研究發(fā)現(xiàn)腹足類亦有富集CYN的能力。而Berry和Lind[47]對(duì)一腹足類(Pomaceapatulacatemacensis)的野外研究發(fā)現(xiàn)，組織中毒素含量為(3.35±1.90)ng/g，但是生物富集系數(shù)卻為157，說(shuō)明CYN濃度非常低時(shí)也會(huì)發(fā)生生物富集。Wood[48]等對(duì)淡水小龍蝦(Paranephropsplanifrons)的研究發(fā)現(xiàn)，其肝胰腺中nodularin-R濃度(9.7—225.3 μg/kg, 濕重)顯著高于尾部組織的濃度(0.5—0.7 μg/kg, 濕重)。Galanti[42]等將P.argentinus放入含有節(jié)球藻毒素的水庫(kù)后發(fā)現(xiàn)，3周后P.argentinus中也能檢測(cè)到節(jié)球藻毒素。Kankaanp??[49]等發(fā)現(xiàn)節(jié)球藻毒素在海產(chǎn)貽貝、斑紋蚌(Dreissenapolymorpha)和波羅的海白櫻蛤(Dreissenapolymorpha)中都有富集現(xiàn)象。除以上幾種毒素的研究外，還有少量對(duì)其它毒素在底棲生物中富集與清除的研究[50-51]。

表1 藍(lán)藻毒素在底棲動(dòng)物體內(nèi)的富集與清除

3.2 藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理作用

藍(lán)藻毒素對(duì)底棲動(dòng)物的毒性作用主要有急性毒性，如存活個(gè)體的減少、攝食的抑制和麻痹等；慢性毒性，如對(duì)生長(zhǎng)和繁殖的影響；生物化學(xué)的變化，如磷酸酶、谷胱甘肽S轉(zhuǎn)移酶和蛋白酶等活性的改變等；還有就是對(duì)動(dòng)物行為的影響[52]。

MC對(duì)腹足類生活史特征的影響因生物年齡、暴露方式(產(chǎn)毒藻類或者溶解性MC)和是否存在無(wú)毒食物的不同而不同，實(shí)驗(yàn)研究發(fā)現(xiàn)MC能夠?qū)е屡咛グl(fā)育變緩，孵化成功率和后代存活率降低[53]。Zhu[54]等用兩種暴露方式(單一有毒藍(lán)藻和有毒藍(lán)藻與無(wú)毒綠藻混合)對(duì)銅銹環(huán)棱螺進(jìn)行處理，然后觀察螺肝胰腺超微結(jié)構(gòu)和生物化學(xué)反應(yīng)的變化，發(fā)現(xiàn)在中毒階段后期肝中酸性磷酸酶、堿性磷酸酶和谷胱甘肽S轉(zhuǎn)移酶活性顯著升高，而在清除階段酶的活性又回到原來(lái)水平，同時(shí)出現(xiàn)細(xì)胞質(zhì)嚴(yán)重液泡化、細(xì)胞核壓縮變形、線粒體膨脹成髓狀、內(nèi)質(zhì)網(wǎng)粗面被破壞和溶酶體增殖等現(xiàn)象，并觀察到細(xì)胞凋亡，放到無(wú)毒藻類處理中這些現(xiàn)象便消失，這些反應(yīng)可能是細(xì)胞用來(lái)減少傷害的適應(yīng)機(jī)制。這與Martins[55]等對(duì)MC與底棲動(dòng)物相互作用所表現(xiàn)出得生物化學(xué)反應(yīng)的研究結(jié)果相似。Puerto[56]等對(duì)擬柱孢藻毒素對(duì)兩種雙殼類細(xì)胞內(nèi)生物化學(xué)反應(yīng)的影響進(jìn)行了研究。毒素對(duì)生物的胚胎發(fā)育也有負(fù)面的影響，而且能夠從受污染的母體性腺中傳遞到后代體內(nèi)[33,57]。Lance[58]等對(duì)淡水螺(Potamopyrgusantipodarum)的研究就發(fā)現(xiàn)，MC不僅能夠影響螺的生存和生長(zhǎng)，而且對(duì)它的繁殖也產(chǎn)生了一定影響。MC對(duì)不同底棲動(dòng)物的群落結(jié)構(gòu)也會(huì)產(chǎn)生顯著的影響，Lance[53]等發(fā)現(xiàn)腹足類前鰓亞綱和肺螺亞綱種群對(duì)MC有不同的反應(yīng)，而肺螺亞綱對(duì)MC的抗性更強(qiáng)；Gérard[59]等的研究指出在受MC嚴(yán)重污染的水體中軟體動(dòng)物豐度和物種豐富度沒有顯著變化，而肺螺亞綱、前鰓亞綱和雙殼綱的相對(duì)多度在藍(lán)藻水華前后卻又顯著的不同。Lance[60]等對(duì)靜水椎實(shí)螺(Lymnaeastagnalis)的研究發(fā)現(xiàn)，MC使螺的生長(zhǎng)變緩，這在幼年個(gè)體中更為顯著，而成年個(gè)體的繁殖能力降低，沒有發(fā)現(xiàn)存活率和遷移的變化，同時(shí)螺體內(nèi)消化腺發(fā)生了一些可逆的變化，在未進(jìn)食有毒藻類3周后變化消失。Gérard[61]等發(fā)現(xiàn)有毒藍(lán)藻的循環(huán)性增殖與腹足類群落生物的減少相吻合。Oberholster[62]等發(fā)現(xiàn)水體中微囊藻毒性的增加伴隨著大型無(wú)脊椎動(dòng)物中蛭綱、搖蚊科和顫蚓科豐度的增加，在遠(yuǎn)離藍(lán)藻浮渣的地方大型無(wú)脊椎動(dòng)物豐度較低但多樣性卻較高，這可能與較細(xì)無(wú)機(jī)顆粒對(duì)生境多樣性的改變、腐殖質(zhì)分解使可利用溶氧降低、大量懸浮顆粒物長(zhǎng)時(shí)間存在使透光性降低、藻類浮渣釋放毒素對(duì)大型無(wú)脊椎動(dòng)物的毒性作用和浮渣對(duì)pH與營(yíng)養(yǎng)鹽濃度等指標(biāo)的影響有關(guān)。

3.3 底棲動(dòng)物對(duì)藍(lán)藻毒素在食物網(wǎng)中的傳播作用

相關(guān)研究得出，MC能夠在食物鏈中遷移，但沒有生物放大現(xiàn)象[63]。Papadimitriou[64]等對(duì)食物網(wǎng)中不同組成部分中MC的分布和累積進(jìn)行了研究，雖然沒發(fā)現(xiàn)生物放大的證據(jù)，但是MC對(duì)動(dòng)物和人類健康的威脅仍然存在。Kozlowsky-Suzuki[65]等研究了食物網(wǎng)中MC消費(fèi)者浮游動(dòng)物、十足目、軟體動(dòng)物、魚類、烏龜和水鳥體內(nèi)MC的濃度，結(jié)果表明大部分的初級(jí)消費(fèi)者表現(xiàn)為生物稀釋，研究中僅有浮游動(dòng)物和以浮游動(dòng)物為食的魚類出現(xiàn)生物放大現(xiàn)象，這與Ibelings[66]等的研究一致。基于對(duì)簡(jiǎn)單食物鏈模型(Microcystisaeruginosa→Daphniapulex→Chaoborus)的研究，Laurén[67]等發(fā)現(xiàn)捕食含有毒微囊藻飼養(yǎng)水蚤的幽蚊死亡率更高。雖然生物鏈幾乎不能累積MC，但是MC卻能夠以底棲動(dòng)物假糞的形式被魚類攝取而進(jìn)入食物鏈[68]。Poste 和Ozersky[69]也發(fā)現(xiàn)貽貝可以通過兩種方式將MC傳遞到更高的營(yíng)養(yǎng)級(jí)，一是被底棲魚類(如蝦虎魚)所捕食，再就是可以通過它們的生物沉積物間接被其它底棲無(wú)脊椎動(dòng)物取食。同時(shí)，Lance[70]等通過喂食魚類靜水椎實(shí)螺消化腺發(fā)現(xiàn)，魚類的各個(gè)器官都會(huì)檢測(cè)到MC，且含量按肝臟、肌肉、腎臟和鰓的順序降低。

4 討論

由于底棲動(dòng)物為水體中有毒物質(zhì)的最直接接觸者，目前關(guān)于底棲動(dòng)物毒理學(xué)的研究已成為水環(huán)境毒理學(xué)研究的一個(gè)熱點(diǎn)，經(jīng)過多年的發(fā)展，已經(jīng)獲得了很多重要成果，但關(guān)于水華藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理學(xué)研究仍然存在許多的問題需要進(jìn)一步的研究，而今后最值得關(guān)注的問題主要有以下幾個(gè)方面：

(1)毒素分析方法等的標(biāo)準(zhǔn)化 在對(duì)毒素近幾十年的研究中，發(fā)展了許多檢測(cè)分析毒素的方法，但由于毒素種類和異構(gòu)體繁多、水體其它有毒物質(zhì)干擾和檢測(cè)儀器設(shè)備等問題，使得各種方法在實(shí)際的應(yīng)用中存在一定的局限性，從而導(dǎo)致目前國(guó)際上還沒有檢測(cè)毒素的標(biāo)準(zhǔn)方法。同時(shí)，由于人類接觸的毒素為各種毒素的混合，而目前對(duì)人體每天攝入量的規(guī)定只限于單一的毒素種類，對(duì)水產(chǎn)品的中含量的限定亦沒有標(biāo)準(zhǔn)，所以對(duì)毒素監(jiān)測(cè)分析方法和攝入量標(biāo)準(zhǔn)的研究仍會(huì)是今后研究的重要方向。

(2)加強(qiáng)藍(lán)藻毒素對(duì)底棲動(dòng)物致毒的分子機(jī)理和急性與慢性中毒反應(yīng)，以及不同毒素之間的協(xié)同關(guān)系的研究 在重點(diǎn)研究微囊藻毒素的同時(shí)，還應(yīng)加大對(duì)其他種類毒素的研究。同時(shí)，還應(yīng)對(duì)藍(lán)藻毒素進(jìn)行長(zhǎng)期的觀測(cè)，進(jìn)一步研究藍(lán)藻毒素在底棲動(dòng)物體內(nèi)富集、轉(zhuǎn)化、代謝以及沿食物鏈的傳遞機(jī)制，并篩選藻毒素污染指示生物，從而為進(jìn)一步監(jiān)測(cè)和評(píng)價(jià)其對(duì)人類健康的威脅提供證據(jù)。

(3)底棲動(dòng)物對(duì)藍(lán)藻毒素清除機(jī)制的研究 目前，相關(guān)研究已經(jīng)證明底棲動(dòng)物中的一些貝類對(duì)藍(lán)藻毒素有很高的富集與清除能力，而貝類具有生物量大、濾食能力強(qiáng)、易于存活等特點(diǎn)，重要的是其中一些貝類具有很高的抗毒能力，所以對(duì)底棲動(dòng)物清除藍(lán)藻毒素機(jī)制的研究，對(duì)有毒藍(lán)藻水華的防范與控制具有重要的意義。

(4)進(jìn)一步加強(qiáng)對(duì)水體富營(yíng)養(yǎng)化的研究 藍(lán)藻毒素都是由藻類所產(chǎn)生，所以控制藍(lán)藻毒素的關(guān)鍵最后還要依靠對(duì)水體富營(yíng)養(yǎng)化的治理，既淡水水體水華各方面的研究仍是今后的熱點(diǎn)。

(5)加強(qiáng)對(duì)一些最新研究方向的研究 主要有兩個(gè)方面，一方面是關(guān)于一些藥物對(duì)藍(lán)藻毒素毒性作用的緩解作用的研究，如已有研究表明抗生素利福平、免疫抑制劑環(huán)孢霉素A[71]和抗氧化劑維生素E[72]對(duì)MC的生物毒性都有一定的緩解作用；二是對(duì)藍(lán)藻毒素的利用，有研究發(fā)現(xiàn)微囊藻毒素能夠促使肝癌細(xì)胞凋亡[73]，這表明一些藻毒素有可能成為重要的抗癌藥物，所以關(guān)于這方面的研究必將成為一個(gè)新的熱點(diǎn)。

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Advances on cyanotoxin toxicology of zoobenthos

XUE Qingju1,2, SU Xiaomei1,2, XIE Liqiang1,*

1StateKeyLaboratoryofLakeScienceandEnvironment,NanjingInstituteofGeographyandLimnology,ChineseAcademyofSciences,Nanjing210008,China2UniversityofChineseAcademyofSciences,Beijing100049,China

In recent years, owing to the intensified human activities, a large number of nutrients, primarily nitrogen and phosphorus, flow into lakes and other water bodies and result in serious eutrophication. However, the cultural eutrophication is often associated with cyanobacteria blooms which can create significant water quality and human health problems. What′s more, some species of cyanobacteria are capable of producing secondary metabolites named cyanotoxins. Mass populations of toxin-producing cyanobacteria are in natural and controlled water bodies include blooms and scums of planktonic species, and mats and biofilms of benthic species. Toxic cyanobacterial populations have been reported in freshwaters in over 45 countries. These toxins can be classified into five main types according to their mechanism of action in vertebrates: hepatotoxins, cytotoxins, dermatotoxins, neurotoxins and irritant toxins. These toxins (microcystins, nodularins, saxitoxins, anatoxin-a, anatoxin-a(s), cylindrospermopsin) are structurally diverse and their effects range from liver damage, including liver cancer, to neurotoxicity. There are more than 80 microcystin congeners, microcystin-LR (L, L-leucine; R, L-arginine) is the best studied cyanobacterial toxin, whereas information for the other toxins is largely lacking. Many studies on the effects of cyanobacteria and their toxins over a wide range of aquatic organisms, including invertebrates and vertebrates, have reported acute effects (e.g., reduction in survivorship, feeding inhibition, paralysis), chronic effects (e.g., reduction in growth and fecundity), biochemical alterations (e.g., activity of phosphatases, GST, AChE, proteases), and behavioral alterations. Research has also focused on the potential for bioaccumulation and transferring of these toxins through the food chain. In general, the toxins can transfer to human bodies by drinking and very little by entertainment or health care products. In some special circumstances, the toxins can also be transferred into human bodies by dialysis. Be the highest level of the food chain, toxins can also transfer to human beings by eating aquatic products. As an important part of the aquatic ecosystem, zoobenthos plays an important role in the aquatic food web. On the one hand, it plays an important part in the material and energy flow process. It is not only the source of the predacity fish, but also the predator of the phytoplankton, zooplankton or organic detritus. On the other hand, some species of the zoobenthos can also be used in water cleaning and influence the formation of the eutrophication. The most important thing is that many of them are even closely related to human beings (directly or indirectly food sources), especially the people leave around the lakes and other water bodies, so the study of the cyanotoxin toxicology of zoobenthos is of great importance. In this review, we first summarized the mechanism of toxicity of cyanotoxin on zoobenthos on the base of a brief introduction of cyanotoxins, with emphasis on microcystins. Secondly, the effects of cyanotoxins on zoobenthos is discussed in details, including the bioaccumulation and elimination of the cyanotoxin, the effects of cyanotoxin and the food web studies about cyanotoxin (mainly microcystis) in zoobenthos. At last, we prospect the further research directions as well as drawbacks and future needs in this field of research.

zoobenthos; cyanotoxin; food web; environmental toxicology

中國(guó)科學(xué)院百人計(jì)劃(y3bro11050); 南京地理與湖泊研究所一三五項(xiàng)目(NIGLAS2012135015)

2013-08-26;

2014-10-09

10.5846/stxb201308262157

*通訊作者Corresponding author.E-mail: lqxie@niglas.ac.cn

薛慶舉, 蘇小妹, 謝麗強(qiáng).藍(lán)藻毒素對(duì)底棲動(dòng)物的毒理學(xué)研究進(jìn)展.生態(tài)學(xué)報(bào),2015,35(14):4570-4578.

Xue Q J, Su X M, Xie L Q.Advances on cyanotoxin toxicology of zoobenthos.Acta Ecologica Sinica,2015,35(14):4570-4578.