Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, Colorado 80523, United States.
Environ Sci Technol. 2013 Jul 2;47(13):7506-13. doi: 10.1021/es401255h. Epub 2013 Jun 17.
Field surveys of metal-contaminated streams suggest that some aquatic insects, particularly mayflies (Ephemeroptera) and stoneflies (Plecoptera), are highly sensitive to metals. However, results of single species toxicity tests indicate these organisms are quite tolerant, with LC50 values often several orders of magnitude greater than those obtained using standard test organisms (e.g., cladocerans and fathead minnows). Reconciling these differences is a critical research need, particularly since water quality criteria for metals are based primarily on results of single species toxicity tests. In this research we provide evidence based on community-level microcosm experiments to support the hypothesis that some aquatic insects are highly sensitive to metals. We present results of three experiments that quantified effects of Cu and Zn, alone and in combination, on stream insect communities. EC50 values, defined as the metal concentration that reduced abundance of aquatic insects by 50%, were several orders of magnitude lower than previously published values obtained from single species tests. We hypothesize that the short duration of laboratory toxicity tests and the failure to evaluate effects of metals on sensitive early life stages are the primary factors responsible for unrealistically high LC50 values in the literature. We also observed that Cu alone was significantly more toxic to aquatic insects than the combination of Cu and Zn, despite the fact that exposure concentrations represented theoretically similar toxicity levels. Our results suggest that water quality criteria for Zn were protective of most aquatic insects, whereas Cu was highly toxic to some species at concentrations near water quality criteria. Because of the functional significance of aquatic insects in stream ecosystems and their well-established importance as indicators of water quality, reconciling differences between field and laboratory responses and understanding the mechanisms responsible for variation in sensitivity among metals and metal mixtures is of critical importance.
野外调查表明，受金属污染的溪流中的一些水生昆虫，特别是蜉蝣目（Ephemeroptera）和石蝇目（Plecoptera），对金属非常敏感。然而，单一物种毒性测试的结果表明，这些生物具有很强的耐受性，LC50 值通常比使用标准测试生物（如桡足类和黑头呆鱼）获得的值高出几个数量级。协调这些差异是一个关键的研究需求，特别是因为金属的水质标准主要基于单一物种毒性测试的结果。在这项研究中，我们提供了基于群落水平的微宇宙实验的证据，以支持一些水生昆虫对金属高度敏感的假设。我们介绍了三个实验的结果，这些实验量化了 Cu 和 Zn 单独和组合对溪流昆虫群落的影响。EC50 值定义为使水生昆虫丰度减少 50%的金属浓度，其数量级比以前从单一物种测试中获得的文献值低几个数量级。我们假设，实验室毒性测试的持续时间短，以及未能评估金属对敏感早期生命阶段的影响，是导致文献中 LC50 值过高的主要因素。我们还观察到，尽管暴露浓度代表了理论上相似的毒性水平，但 Cu 对水生昆虫的毒性比 Cu 和 Zn 的混合物要大得多。我们的结果表明，Zn 的水质标准对大多数水生昆虫具有保护作用，而 Cu 在接近水质标准的浓度下对某些物种具有高度毒性。由于水生昆虫在溪流生态系统中的功能重要性及其作为水质指标的既定重要性，协调野外和实验室反应之间的差异以及了解金属和金属混合物敏感性变化的机制至关重要。
