【作者】 王蕾；

【导师】 王文雄；

【作者基本信息】 厦门大学 ， 海洋生物学， 2017， 博士

【摘要】 重金属是我国近海水体和沉积物中重要的污染物,能够在海洋生物体内累积和富集,对我国的海洋环境、海水养殖安全具有非常巨大的危害。双壳类动物在河口生态系统功能维持和重金属污染监测中有重要作用。基于对我国近岸河口地区重金属污染日益加剧、贝类资源衰退现象的关注,本论文以福建省九龙江沿岸典型的双壳类动物—熊本牡蛎(Crassostrea sikamea)和香港牡蛎(C.hongkongensis)为研究对象。首先,研究熊本牡蛎对Cd和Zn的生物动力学的差异,并测定它们体内金属硫蛋白的转化的不同。其次,观察研究了“绿牡蛎”-熊本牡蛎重金属的净化能力。最后,观察研究了“蓝牡蛎”-香港巨牡蛎对重金属的净化。本研究系统研究了河口重金属污染对牡蛎的生态毒理学效应,可望为我国河口环境重金属污染的生物监测,近海贝类生物资源的保护提供重要的科学依据和理论参考。1.我们采集了白礁、宫前和旧镇3个不同重金属污染程度的地点的熊本牡蛎样本,用放射性同位素示踪技术测定不同污染程度的牡蛎对Cd和Zn的生物动力学的差异。采自旧镇的牡蛎,重金属含量相对较低,作为对照,其对Cd和Zn的吸收速率常数明显高于其他无脊椎动物。采集白礁的牡蛎受多种重金属共同污染暴露,Cd、Cu和Zn尤其严重,其对Cd的吸收明显减少,对Zn的吸收与对照组无差别。采自宫前的“绿牡蛎”(Cu和Zn含量高)对Cd的吸收与对照组无差别,对Zn的吸收速率常数低于对照组。我们测定了牡蛎对3种微藻和白礁的沉积物的重金属的同化率,发现对Cd和Zn的同化率分别为14.5-62.6%和36.5-60.6%。3组牡蛎之间没有明显差别。对Cd和Zn的排出速率常数分别为0.013-0.020d-1,0.025-0.031 d-1。白礁的“绿牡蛎”对Zn的排出明显比其他组慢。根据我们的结果推断,污染的牡蛎体内的重金属之所以能达到极高的水平,是牡蛎的高摄食率、被摄食物含有的高重金属浓度和牡蛎的高水相吸收率共同作用的结果。从重金属的亚细胞分布情况看,细胞碎片和类金属硫蛋白两个组分是所测重金属的主要结合位点;MRG对Ag、Ni和Pb同样有很好的结合能力。对被污染的牡蛎来说,快速的金属硫蛋白合成可能将其他亚细胞组分中结合的重金属重新利用,从而降低重金属的排出速率。这也可能是牡蛎能在体内储存极高含量的重金属的原因之一。2.“绿牡蛎”是牡蛎体内含有高浓度的重金属尤其是Cu而使组织颜色改变,在我国的污染河口时有发现。本实验研究采集自由于工业排放造成严重污染的河口熊本牡蛎对8种重金属的净化能力。这些牡蛎在实验室进行16周的排出实验,测定体内重金属的浓度以及重金属的亚细胞分布。结果表明经过16周的净化,“绿牡蛎”的软组织颜色由深绿色褪色呈淡黄色,接近正常牡蛎的颜色。重金属的排出符合一级动力学过程。几种重金属的排出速率为0.008-0.024 d-1,生物半衰期为30-70 d。“绿牡蛎,”对Cd、Cr、Cu和Ni的排出速率远高于对照组,而Ag、Co、Pb和Zn的排出速率在两组牡蛎之间没有显著差别。到实验终点时,“绿牡蛎”对Ag、Cr和Ni的排出量超过初始值的95%,排出最少的Cu和Zn也达到75%。而对照组的排出量明显低于“绿牡蛎”,Cu是最少的被排出,仅有55%。细胞碎片和MTLP组分是牡蛎结合重金属的最重要的亚细胞组分。经过16周的净化,Ag、Cd、Cu和Zn的亚细胞分布变化明显。随净化过程的进行,重金属浓度的降低,结合在细胞碎片组分的重金属逐渐减少,MTLP对重金属的区隔分布的作用逐渐增强。3.九龙江流域发现的受严重污染的香港巨牡蛎,其软组织由于富集超高浓度的重金属,尤其是Cu和Zn而呈蓝色。本实验中,以白礁的香港巨牡蛎——“蓝牡蛎”,和旧镇湾的野生的相对干净的香港巨牡蛎为对象,在实验室条件下观察牡蛎的6种重金属的净化。在16周的实验周期中,于设定的时间点取样,对牡蛎不同组织的重金属含量和重金属的亚细胞分布进行测定。实验终点时,“蓝牡蛎”明显褪色,但鳃的部分仍呈现肉眼可见的不健康的浅蓝色。几种测定的重金属中,Cr的排出速率最快,为0.49-0.61 d-1;Cu和Zn的排出速率最慢,均小于0.3 d-1。重金属之间的排出速率有快慢,但每种重金属在不同组织的排放没有明显差别。经过16周的净化,“蓝牡蛎”体内Ag的浓度降低到与旧镇牡蛎的初始浓度相差不大,内脏中的Cd和Pb也接近旧镇的初始浓度水平,而Cr、Cu和Zn仍远高于对照组。作为对照的旧镇的牡蛎,其体内重金属浓度并未随时间有明显的降低趋势,反而呈无规律的波动,各组织的反应无差别。细胞碎片、MRG和MTLP是香港巨牡蛎主要的重金属结合位点。不同于旧镇牡蛎体内重金属的亚细胞的分布变化,在净化过程中,“蓝牡蛎”体内重金属的亚细胞分布并未呈现一定的可循的规律。在净化实验中,结合到BDM和MSF中的重金属含量显著变化,却是随时间呈强烈的波动趋势。从我们的结果可以看出,16周的净化远不够“蓝牡蛎”将重金属排出或转化,需要更长时间的净化排出,结合长时间的累积实验来推测香港巨牡蛎对体内超高量的重金属的调控机制。而使重金属在生物体内快速的排出和在亚细胞组分之间转移的方法的研究也是今后工作的一大挑战,这对贝类的养殖,对健康需求有重要的现实意义。更多还原

【Abstract】 Heavy metals have long been recognized as one of the most important pollutants in the Chinese coastal waters because of their potentials for accumulation in marine organisms.Thus,they can pose a great threat to marine environments and mariculture of China.Bivalves as the dominant filter-feeders play an important role in keeping the ecological balance of esturine ecosystem and in the biomonitoring of trace metal pollution.Given the increasing pollution of heavy metals in the estuary of China and the phenomenon of deterioration of shellfish resources,we studied two common oyster speices,Crassostrea hongkongensis and Crassostrea sikamea in estuarine environments of China in this study.Firstly,we studied the biokinetics of Cd and Zn as well as the turnover of metallothioneins(MTs)in the oysters collected from different locations with different contamination histories.We then quantified the depuration of 8 metals in the green colored oysters.Finally,we determined the tissue-specific depuration patterns of 6 metals in the blue-colored oysters.Our results have great implications for the biological monitoring,ecological risk assessment of trace metal pollution in esturine environment,as well as the protection of shellfish resources.1.We collected three groups of oysters from estuaries with different contaminated histories and contrasted their differences in the biokinetis of Cd and Zn,coupled with metallothionein turnover measurements.The oysters from the contaminated estuaries were enriched with a suite of toxic metals,specifically Cd,Cu,Zn.The uptake rate constants quantified for Cd and Zn were higher than those of most invertebrates.The assimilation efficiencies(AEs)of metals,determined for four species of phytoplankton and natural sediment,were in the range of 14.5-62.6%for Cd and 36.5-60.6%for Zn,respectively.The measured efflux rate constants in the oysters were in the range of 0.013-0.020 d-1 for Cd and 0.025-0.031 d-1 for Zn.Our measurements suggested that oysters collected from the contaminated sites had a high metal concentration in the estuarine oysters may be achieved by a high ingestion rate,a high concentration of metals in the natural seston and a high uptake rate from the dissolved phase.Cellular debris and MTLPs fractions were the main subcellular fraction binding the metals,but metal-rich granules were important for Cr,Ni,Ag and Pb.In the contaminated oysters,the faster MTLP synthesis could recycle more metals from other intracellular pools,effectively reducing the efflux rate.Our study explored the strategies of the estuarine oysters in accumulating high metal concentration in their tissues.2.Oysters are the hyper-accumulators of several toxic metals,and green colored oysters are now found in Chinese contaminated estuary due to their accumulation of toxic metals(especially copper).In this study,we specifically quantified the depuration of eight toxic metals(Ag,Cd,Co,Cr,Cu,Ni,Pb,and Zn)in Crassostrea sikamea collected from an estuary heavily contaminated by metals due to industrial effluent releases.The oysters were depurated under the laboratory conditions for 16 weeks,and the accumulated concentrations as well as the subcellular distribution of metals were measured at different time intervals.Results showed that the green color of oysters fade to light yellow(nearly normal)after four months of depuration.Depuration of metals could be described by a first-order kinetic process.The calculated efflux rate constants of metals were in the range of 0.008-0.024 d-1,with a biological retention half-life of 30-70 days.The efflux rates of green colored contaminated oysters were significantly higher for Cd,Cu,Cr,and Ni than those from a less contaminated site,whereas the efflux rates of Ag,Co,Pb and Zn were comparable between the two populations.The cellular debris and metallothionein-like proteins were the important fractions binding with the metals in the oysters.Significant changes of metal subcellular distribution were observed during the 4-month depuration for Ag,Cd,Cu,and Zn.Metallothionein-like protein became more important in sequestering the metals during the depuration period,with concomitant decrease of metals associated with the cellular debris fraction.3.Blue oysters are now found in Chinese contaminated estuary due to their hyper-accumulation of toxic metals(especially copper and zinc).In this study,we specifically quantified the depuration of six toxic metals(Ag,Cd,Cr,Cu,Pb and Zn)in Crassostrea hongkongensis collected from an estuary heavily contaminated by metals(Baijiao)and relatively uncontaminated site(Jiuzhen).The oysters were depurated under the laboratory conditions for 16 weeks,and the accumulated concentrations as well as the subcellular distribution of metals were measured at different time intervals.Results showed that the color of oysters fade to light blue but still be unhealthy at the end of experiment.The efflux rates of Cr were the fastest(0.49-0.61 d-1),and Cu and Zn were the slowest,the rates being less than 0.3 d-1(Cu 0.16-0.29 d-1,Zn 0.13-0.24 d-1).The efflux rates varied among metals,but were comparable among different tissues for a metal.At the end of 16-week depuration,the concentrations of Ag in the oysters from Baijiao decreased nearly to the initial levels of Jiuzhen;Cd and Pb in viscera were also close to the initial levels of referenced oysters.However,the concentrations of Cr,Cu and Zn were still higher than those of controls.Cellular debris,MRG and MTLP were the important fractions binding with the metals in the contaminated oysters.Different from the subcellular distributions in oysters from Jiuzhen,there were not consistent trends in the oysters from Baijiao.The percentages of metals in TAM increased during the 16-week depuration.The temporal trends also fluctuated.These results suggested that long-term accumulation and elimination experiments should be carried out to better understand the "regulation" in C.hongkongensis.The challenge is to develop methods facilitating the elimination of metals and transfer in subcellular fractions in bivalves,thus to meet the permissible levels for shellfish consumption.更多还原