Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Gent, Belgium.
Laboratory for Systemic Physiology and Ecotoxicological Research, University of Antwerp, Belgium.
Environ Toxicol Chem. 2019 Apr;38(4):784-793. doi: 10.1002/etc.4352. Epub 2019 Feb 20.
It is well known that temperature can affect the ecotoxicity of chemicals (including metals) to aquatic organisms. It was recently reported that nickel (Ni), a priority substance under the European Water Framework directive, showed decreasing chronic toxicity to Daphnia magna with increasing temperature, between 15 and 25 °C. We performed a toxicokinetic study to contribute to an increased mechanistic understanding of this effect. More specifically, we investigated the effect of temperature on Ni uptake and elimination in D. magna (in 4 clones) using an experimental design that included Ni exposures with different stable isotopic composition and using a one-compartment model for data analysis. Both Ni uptake and elimination were affected by temperature, and some clear interclonal differences were observed. On average (across all clones), however, a similar pattern of the effect of temperature was observed on both Ni uptake and elimination, that is, the uptake rate constant (k ) and elimination rate constant (k ) during 72 h of Ni exposure were lower at 25 than at 19 °C, by 2.6-fold and 1.6-fold, respectively, and they were similar at 19 and 15 °C. This pattern does not correspond to the effects of temperature on chronic Ni toxicity reported previously, suggesting that Ni compartmentalization and/or toxicodynamics may also be affected by temperature. The data gathered with our specific experimental design also allowed us to infer that 1) the k was up-regulated over time, that is, the k after 2 d of Ni exposure was significantly higher than the initial k , by 1.5- to 2.3-fold, and 2) the k decreased significantly when the external Ni exposure was stopped, by 1.2- to 1.9-fold. These 2 findings are in contrast with 2 commonly used assumptions in toxicokinetic models, that is, that k is constant during exposure and k is independent of external exposure. We suggest that future toxicokinetic studies consider these factors in their experimental designs and data analyses. Overall, our study contributes to the growing body of evidence that temperature affects toxicokinetics of metals (and chemicals in general), but at the same time we emphasize that knowledge of toxicokinetics alone is not necessarily sufficient to explain or predict temperature effects on (chronic) toxicity. Environ Toxicol Chem 2019;38:784-793. © 2019 SETAC.
众所周知，温度会影响化学物质（包括金属）对水生生物的生态毒性。最近有报道称，镍（Ni）作为欧洲水框架指令下的优先物质，在 15 至 25°C 之间，随着温度的升高，对大型溞（Daphnia magna）的慢性毒性呈下降趋势。我们进行了一项毒代动力学研究，以帮助增加对这一效应的机制理解。更具体地说，我们使用包括不同稳定同位素组成的 Ni 暴露实验设计，并使用单室模型进行数据分析，研究了温度对大型溞（在 4 个克隆中）Ni 吸收和消除的影响。Ni 的吸收和消除都受到温度的影响，并且观察到了一些明显的克隆间差异。然而，平均而言（在所有克隆中），在 Ni 暴露的 72 小时内，Ni 吸收和消除的温度效应模式相似，即在 25°C 时的吸收速率常数（k）和消除速率常数（k）分别比 19°C 时低 2.6 倍和 1.6 倍，而在 19°C 和 15°C 时则相似。这种模式与先前报道的慢性 Ni 毒性的温度效应不一致，表明 Ni 的区室化和/或毒代动力学也可能受到温度的影响。我们特定实验设计收集的数据还使我们能够推断出 1）k 随着时间的推移而上调，即 Ni 暴露 2 天后的 k 明显高于初始 k ，提高了 1.5 至 2.3 倍，以及 2）当外部 Ni 暴露停止时，k 显著降低，降低了 1.2 至 1.9 倍。这 2 个发现与毒代动力学模型中常用的 2 个假设相反，即 k 在暴露期间是恒定的，并且 k 独立于外部暴露。我们建议未来的毒代动力学研究在其实验设计和数据分析中考虑这些因素。总的来说，我们的研究有助于越来越多的证据表明，温度会影响金属（和一般化学物质）的毒代动力学，但同时我们强调，仅仅了解毒代动力学并不一定足以解释或预测温度对（慢性）毒性的影响。Environ Toxicol Chem 2019；38:784-793。© 2019 SETAC。
