摘要
为了解重金属镉在鱼体内的累积情况,给鱼体内重金属镉富集问题提供经济、安全、快速的解决方法,以我国常见养殖鱼类鲫(Carassius auratus)为试验对象,确定镉对鲫的安全浓度后将鲫暴露在含有不同浓度镉的水体中14 d,使用电感耦合等离子体质谱仪对重金属污染物镉在鱼体各组织内的累积和分布情况进行检测,之后将鲫转移至不同流速的清水中14 d,比较不同水流流速对鱼体中镉的清除效果,同时分别在暴露试验和清除试验后对鲫可食用部位进行非致癌膳食风险评估。结果显示:镉对鲫96 h的安全质量浓度为1.528 mg/L;镉在鲫鱼头和肝脏中累积较多,肌肉中较少,镉富集程度与水环境中镉浓度和镉暴露时间呈正相关;鲫肌肉、胆中的镉排出较快,而肝脏、肾脏中的镉排出较慢,在水流流速为0.1~0.2 m/s时的清除效果最佳;水体镉暴露14 d后鲫鱼头、肌肉存在潜在的非致癌食用风险,流水清除14 d后肌肉可达到食用标准,但鱼头仍具有食用风险。综上所述,鲫各组织器官对镉的累积能力及清除能力具有显著性差异,适宜的水流流速有利于鲫体内镉的排出,对于镉污染后的鲫需进行重金属的清除后才可食用。
重金属元素包括必需金属和非必需金属,其中镉、铅、汞等非必需金属在低浓度时也具有较强的毒性,是对水生态系统和人类危害最大的污染源之
水环境中的镉可通过生物富集和生物放大作用在鱼体内不断累
本研究所用鲫购自湖北省武汉市白沙洲水产市场,在华中农业大学水产学院实验室的500 L聚乙烯塑料桶中暂养14 d,使其适应实验室养殖环境:水温(21.2±1.0) ℃、溶解氧>6.0 mg/L、pH (7.1±0.2),暂养期间对试验鱼投喂商业饲料(鲫、暂养水体、商业饲料中均不含镉)。暂养完成后从中选取180尾体质量(150.0±5.0) g、体长(20.0±1.5) cm规格相近的鲫,随机转移至18个养殖缸中,每组3个平行,每缸10尾鱼。参照文献[
取经驯养的体质量为(150.0±5.0) g的鲫240尾随机分为4组,分别暴露于镉质量浓度0.000、0.764、1.528、3.054 mg/L的水体中,每组3个平行,每缸20尾鱼,在镉暴露0、4、7、14 d时取样研究镉在鲫各组织中的累积分布规律。同时将另240尾鲫放置于镉质量浓度为1.528 mg/L的水体中暴露96 h后,转移至不同流速(0.0、0.1、0.2、0.4 m/s)的无镉清水中继续养殖,每组3个平行,每缸20尾鱼,在流水清除1、4、7、14 d时取样并测定各组织中镉含量,研究不同水流流速对于鲫体内镉的清除效果。
本试验所用流水装置为自行设计的环形循环水流装置,如

图1 环形循环水流装置
Fig.1 Circulating water device
1.水流方向; 2.增氧气泡石; 3.集污器; 4.潜水泵。1.Water flow direction; 2.Oxygen device; 3.Waste collecting device; 4.Submerged pump.
1)水体中镉浓度测定。使用滴管直接吸取适量水样于15 mL塑料离心管中,摇匀,采用美国珀金埃尔默公司的电感耦合等离子体质谱仪(ICP-MS)测定。
2)组织中镉浓度测定。将鲫放入含MS-222(100 mg/L)的水中进行麻醉,使用手术剪从鲫的泄殖孔插入并剪至下颌处,打开体腔,分离肝、肾、肠、胆,去除皮肤后取背部、腹部肌肉,剪取头部两侧鳃丝,以及去除鳃后的整体头部。取上述各组织适量于15 mL塑料离心管中,加入适量硝酸浸泡12 h,待样本完全溶解后转入石英管,加入1.0 mL硝酸,将其放入石墨消解仪,经低温消解至溶液清亮,取出冷却后加入三蒸水,定容至10 mL摇匀,静置过夜后采用ICP-MS进行测定。
参考文献[
安全浓度=LC50×0.1 | (1) |
生物累积系数(bioaccumulation factor,BAF)通常用于指示重金属在鱼体内的累积情
BAF | (2) |
其中,Ct为时间t时对应的组织中重金属含量,mg/kg;Ccon为对照组组织中的重金属含量,mg/kg;Cwater为暴露溶液中的重金属含量,mg/kg。
清除率(depuration rate,K)表示为清除一段时间后的重金属含量相对于暴露试验后的重金属浓度减少的百分比,计算公式如下:
K×100% | (3) |
其中,Cexp为暴露后组织中重金属含量,mg/kg;Cdep为清除后组织中重金属含量,mg/kg。
目标风险系数(target hazard quotient,THQ)被用于评估重金属对鱼类的非致癌健康风险。当THQ≥1时,认为该重金属对人体存在潜在的非致癌风
THQ= | (4) |
其中,F(food ingestion rate)为鱼肉日均摄入量,根据2016年中国居民膳食指南,我国居民人均每天水产品摄入量为40~75 g,取平均值57.5 g/
随着镉暴露浓度的升高,鲫呈现出紧张不安,剧烈游泳,上下窜动,甚至撞击桶壁等行为。鲫在高浓度组暴露数小时后丧失游泳能力,体表出现白色絮状物,鳃处有大量黏液,鳃丝粘连且呈暗红色,肌肉失去弹性,解剖后发现其肝脏颜色变深。试验期间记录其死亡数并计算平均死亡率、LC50及安全质量浓度(

图2 急性镉暴露下鲫的死亡率
Fig.2 Mortality of crucian carp of acute cadmium exposure
在含不同质量浓度(0.000、0.764、1.528、3.054 mg/L)镉的水体中暴露4、7、14 d后,鲫各组织(肝、肾、鳃、肠、胆、背肌、腹肌、鱼头)中镉含量如

图3 不同质量浓度镉暴露下鲫各组织中的镉累积含量
Fig.3 The cumulative content of cadmium in various tissues of crucian carp exposed to different cadmium mass concentrations
A:肝Liver;B:肾Kidney; C:肠Intestine; D:胆Gallbladder; E:鳃Gill; F:背肌Dorsal muscle; G:腹肌Ventral muscle; H:鱼头Fish head.柱上不同字母表示同一组织的镉含量在不同暴露时间下存在显著性差异。 Different letters on the column indicate significant differences in cadmium content of the same tissue at different exposure times.
不同暴露时间及不同暴露浓度下鲫对镉的生物累积系数如
在不同流速(0.0、0.1、0.2、0.4 m/s)的水体中进行清除试验1、4、7、14 d后,鲫各组织(肝、肾、鳃、肠、胆、血清、背肌、腹肌、鱼头)中镉含量如

图4 不同流速流水清除后鲫各组织中镉含量
Fig.4 The content of cadmium in various tissues of crucian carp after removal at different flow rates
A:肝Liver;B:肾Kidney; C:肠Intestine; D:胆Gallbladder; E:鳃Gill; F:背肌Dorsal muscle; G:腹肌Ventral muscle; H:鱼头Fish head.柱上不同字母表示同一组织的镉含量在不同水流流速清除后存在显著性差异。 Different letters on the column indicate that the cadmium content of the same tissue differs significantly after removal at different water flow rates.
注: 表中同行数据不同字母表示同一清除时间不同流速间有显著性差异(P<0.05)。Note: Different letters indicate significant differences between different water velocities of the same day(P<0.05).
在含不同质量浓度镉的水体中暴露14 d后,将可食用部分(背肌、腹肌、鱼头)进行风险评估,根据体质量及鱼肉摄入量的不同分为成人组和儿童组,结果如

图5 镉暴露后鲫背肌(A、B)、腹肌(C、D)和鱼头(E、F)目标风险系数
Fig.5 The target hazard quotient for crucian carp dorsal muscle(A,B),ventral muscle(C,D),and fish head(E,F) after cadmium exposure
A:成人Adult; B:儿童Children; C:成人Adult; D:儿童Children; E:成人Adult; F:儿童Children.
在不同流速的水体中清除14 d后,鲫可食用部分的风险评估结果如

图6 流水清除后鲫背肌(A、B)、腹肌(C、D)和鱼头(E、F)目标风险系数
Fig.6 The target hazard quotient for crucian carp dorsal muscle(A,B),ventral muscle(C,D),and fish head(E,F) after water clearance
A:成人Adult; B:儿童Children; C:成人Adult; D:儿童Children; E:成人Adult; F:儿童Children.
鱼类吸收镉或通过鳃与水体中的镉直接接
镉作为一种毒性重金属,对人体的肝脏、肾脏等都有严重的危害作
鱼类通过自身排出重金属的途径主要有排泄、胆汁分泌、体表黏液分泌、解毒机制及其他生理过程。一般来说,鱼体内镉的累积和清除始终处于相对平衡的状
鱼类在较低水速下可利用的溶氧水平较
流水清除试验后,对鲫的可食用部分(鱼头、背肌、腹肌)再次进行风险评估,结果显示各处理组中背肌和腹肌的风险系数均小于1,证明经过流水清除之后的鲫肌肉部分不存在潜在的食用风险,然而直至清除试验结束,鱼头部分的风险系数仍大于1,说明鱼头仍然存在食用风险。
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