University of Coimbra, Centre for Functional Ecology, Department of Life Sciences, Calçada Martim de Freitas, 3000-456, Coimbra, Portugal.
University of Coimbra, Centre for Functional Ecology, Department of Life Sciences, Calçada Martim de Freitas, 3000-456, Coimbra, Portugal.
Chemosphere. 2021 Feb;264(Pt 1):128403. doi: 10.1016/j.chemosphere.2020.128403. Epub 2020 Sep 24.
Natural populations are commonly exposed to sequential pulses of contaminants. Accordingly, this study aimed at testing the existence of an association between the tolerance to lethal levels of copper (Cu) and the survival recovery ability from pulsed partially lethal copper exposures in six clonal lineages of Daphnia longispina. It was hypothesized that the most tolerant genotypes would be the ones exhibiting a faster survival recovery from a pulsed contaminant exposure. For each clonal lineage, the intensity of pulses corresponded to the respective concentration of Cu causing 30% of mortality after 24h of exposure (LC). The initial hypothesis was not corroborated: obtained results showed no association between survival recovery and lethal tolerance to Cu. Nevertheless, some patterns could be detected. Firstly, the most sensitive lineages to lethal levels of copper revealed a faster survival recovery from a first Cu pulse comparatively to the most tolerant ones, though they were the most sensitive to a second pulse exposure. Secondly, the most tolerant lineages, though being more tolerant to a second exposure, exhibited the lowest survival recovery capacity after exposure to a first pulse of Cu. However, differences in the survival recovery capacity of the six clonal lineages after the exposure to the two pulses of Cu were not observed. Increasing the duration of the recovery period from 24h to 72h did not significantly alter mortality rates, except for the most sensitive and most tolerant clonal lineages. The results here obtained suggests that standard lethality assays may sub-estimate the toxicity of chemicals under realistic exposure scenarios, since sequential pulses are not infrequent in natural conditions.
自然种群通常会暴露于连续的污染物脉冲中。因此，本研究旨在测试六个长额溞（Daphnia longispina）克隆系对致死水平铜（Cu）的耐受性与从脉冲式部分致死铜暴露中恢复生存能力之间是否存在关联。假设最耐受的基因型将是那些在脉冲污染物暴露后更快恢复生存的基因型。对于每个克隆系，脉冲的强度对应于导致暴露 24 小时后死亡率为 30%的相应铜浓度（LC）。最初的假设没有得到证实：结果表明，生存恢复与 Cu 的致死耐受性之间没有关联。然而，还是可以发现一些模式。首先，对致死水平铜最敏感的谱系在第一次 Cu 脉冲后表现出比最耐受的谱系更快的生存恢复能力，尽管它们对第二次脉冲暴露最敏感。其次，尽管最耐受的谱系在第二次暴露时更耐受，但在第一次 Cu 脉冲暴露后，它们的生存恢复能力最低。然而，在暴露于两次 Cu 脉冲后，六个克隆系的生存恢复能力没有差异。将恢复期从 24 小时延长至 72 小时并没有显著改变死亡率，除了最敏感和最耐受的克隆系。这里获得的结果表明，标准致死率测定可能会低估化学物质在实际暴露情况下的毒性，因为在自然条件下连续脉冲并不罕见。
