Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, Madison, WI 53706, United States.
Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI 53706, United States.
Aquat Toxicol. 2021 May;234:105806. doi: 10.1016/j.aquatox.2021.105806. Epub 2021 Mar 10.
We studied the temperature dependence of accumulation and elimination of two polychlorinated biphenyls (PCBs; PCB-70 and PCB-126) and a commercial mixture of congeners of polybrominated diphenyl ethers (PBDEs; DE-71™)) in Northern leopard frog (Lithobates pipiens) tadpoles. We reared tadpoles at 18, 23, or 27 °C for 5.3 or up to 13.6 weeks (longer at cooler temperature where development is slower) on diets containing the toxicants, each at several different toxicant concentrations, and compared tissue concentrations as a function of food concentration and rearing temperature. Following > 1 month of accumulation, tissue concentrations of all three toxicants in exposed tadpoles were linearly related to dietary concentrations as expected for first order kinetics, with no significant effect of rearing temperature.We also raised free-swimming L. pipiens tadpoles for 14 days on foods containing either toxicant at 18 or 27 °C during an accumulation phase, and then during depuration (declining toxicant) phase of 14 days we provided food without toxicants and measured the decline of toxicants in tadpole tissue. All the congeners were eliminated faster at warmer rearing temperature, as expected. Using Arrhenius' equation, we calculated that the apparent activation energy for elimination of both PCB congeners by tadpoles was 1.21 eV (95% confidence interval 0.6-1.8 eV). We discuss how this value was within the range of estimates for metabolic reactions generally (range 0.2 - 1.2 eV), which might include metabolic pathways for biotransformation and elimination of PCBs. Furthermore, we discuss how the lack of an effect of rearing temperature on tadpole near-steady-state tissue residue levels suggests that faster elimination at the warmer temperature was balanced by faster uptake, which is plausible considering the similar temperature sensitivities (i.e., activation energies) of all these processes. Although interactions between toxicants and temperature can be complex and likely toxicant-dependent, it is plausible that patterns observed in tadpoles might apply to other aquatic organisms. Published data on depuration in 11 fish species eliminating 8 other organic toxicants indicated that they also had similar apparent activation energy for elimination (0.82 ± 0.12 eV; 95% confidence interval 0.56 - 1.08 eV), even though none of those studied toxicants were PCBs or PBDEs. Additional research on toxicant-temperature interactions can help improve our ability to predict toxicant bioaccumulation in warming climate scenarios.
我们研究了两种多氯联苯（PCBs；PCB-70 和 PCB-126）和一种商用多溴二苯醚（PBDEs；DE-71™）混合物在北方豹蛙（Lithobates pipiens）蝌蚪中的积累和消除随温度的变化。我们将蝌蚪在 18、23 或 27°C 下饲养 5.3 或长达 13.6 周（在发育较慢的低温下饲养时间更长），饮食中含有这些毒物，每种毒物浓度不同，并比较了组织浓度与食物浓度和饲养温度的关系。在积累阶段持续 1 个月以上后，暴露于毒物的蝌蚪体内所有三种毒物的组织浓度均与饮食浓度呈线性关系，符合一级动力学预期，而饲养温度无显著影响。我们还在 18 或 27°C 的食物中饲养自由游动的 L. pipiens 蝌蚪 14 天，进行积累阶段，然后在 14 天的消除阶段（毒物浓度下降）期间，提供不含毒物的食物，并测量蝌蚪组织中毒物的下降情况。所有同系物在温暖的饲养温度下的消除速度都更快，这是意料之中的。使用阿仑尼乌斯方程，我们计算出 PCB 同系物被蝌蚪消除的表观活化能为 1.21eV（95%置信区间 0.6-1.8eV）。我们讨论了这个值如何在代谢反应的一般估计范围内（范围 0.2-1.2eV），这可能包括生物转化和消除 PCB 的代谢途径。此外，我们还讨论了为什么饲养温度对蝌蚪的近稳态组织残留水平没有影响，这表明在温暖温度下更快的消除速度被更快的吸收所平衡，这是合理的，因为所有这些过程的温度敏感性（即活化能）相似。尽管毒物和温度之间的相互作用可能很复杂，并且可能取决于毒物，但在蝌蚪中观察到的模式可能适用于其他水生生物。11 种鱼类消除 8 种其他有机毒物的消除数据表明，它们的消除也具有相似的表观活化能（0.82±0.12eV；95%置信区间 0.56-1.08eV），尽管研究中没有一种毒物是 PCBs 或 PBDEs。关于毒物-温度相互作用的进一步研究可以帮助提高我们在变暖气候情景下预测毒物生物累积的能力。
