Lopes Isabel, Baird Donald J, Ribeiro Rui
Instituto do Ambiente e Vida, Departamento de Zoologia da Universidade de Coimbra, Largo Marquês de Pombal, 3004-517 Coimbra, Portugal.
Environ Toxicol Chem. 2004 Jul;23(7):1702-8. doi: 10.1897/03-231.
Almost all terrestrial and aquatic assays that are accepted as standardized, or that have been proposed, involve the exposure of confined organisms to toxicants. If avoidance (sensu evasion, displacement) of contaminants occurs in real situations, then bioassays involving forced exposure severely underestimate pernicious effects of contamination. Two main objectives were achieved in this study: To verify the occurrence of avoidance of copper by cladocerans; to determine the association between avoidance and other toxicity endpoints (lethality and feeding depression), and therefore, to ascertain if fully acclimated individuals from a reference field population exhibited a genetically determined avoidance markedly different from those belonging to a historically metal-stressed population. Twelve cloned lineages of the cladoceran Daphnia longispina, collected from two field populations, were selected according to their lethal sensitivity to copper and acclimated to controlled conditions for more than 30 generations. A 1.1-m test chamber with five compartments was built, allowing the establishment of a dissolved toxicant gradient and the free movement of individuals. In the absence of any toxicant, juveniles from each cloned lineage distributed themselves randomly along the test chamber and furthermore, no significant differences were observed between the two replicates, attesting the repeatability of this novel assay. All lineages showed significant avoidance to copper when exposed to a gradient from 3 to 87 microg/L. The most sensitive lineages to lethal levels of copper began avoiding this metal earlier than resistant ones. An intense association was observed between other endpoints and avoidance; furthermore, avoidance was determined to be much more sensitive than lethality. Therefore, avoidance assays should be recommended as a complementary tool in ecological risk assessments and effluent biomonitoring because such assays can provide cost-effective and ecologically relevant information.
几乎所有被认可为标准化的或已被提议的陆生和水生生物测定，都涉及将受限生物暴露于有毒物质中。如果在实际情况中发生了对污染物的回避（从逃避、迁移的意义上来说），那么涉及强制暴露的生物测定会严重低估污染的有害影响。本研究实现了两个主要目标：验证枝角类动物对铜的回避现象是否存在；确定回避与其他毒性终点（致死率和摄食抑制）之间的关联，从而确定来自参考野外种群的完全适应环境的个体是否表现出与历史上受金属胁迫种群的个体显著不同的遗传决定的回避行为。从两个野外种群收集的枝角类长刺溞的12个克隆谱系，根据它们对铜的致死敏感性进行选择，并在受控条件下驯化了30多代。建造了一个带有五个隔室的1.1米测试室，以建立溶解有毒物质的梯度并允许个体自由移动。在没有任何有毒物质的情况下，每个克隆谱系的幼体在测试室内随机分布，此外，两个重复样本之间未观察到显著差异，证明了这种新测定方法的可重复性。当暴露于3至87微克/升的梯度时，所有谱系对铜都表现出显著的回避。对铜致死水平最敏感的谱系比抗性谱系更早开始回避这种金属。在其他终点和回避之间观察到强烈的关联；此外，确定回避比致死率更敏感。因此，应推荐回避测定作为生态风险评估和废水生物监测的补充工具，因为这种测定可以提供具有成本效益且与生态相关的信息。
