Clemson University, Department of Biological Sciences, Institute of Environmental Toxicology, Pendleton, South Carolina, USA; Department of Zoology, The University of Melbourne, Parkville, Victoria, Australia.
Environ Toxicol Chem. 2014 Apr;33(4):791-7. doi: 10.1002/etc.2488. Epub 2014 Feb 14.
The assumption of the individual effective dose is the basis for the probit method used for analyzing dose or concentration-response data. According to this assumption, each individual has a uniquely innate tolerance expressed as the individual effective dose (IED) or the smallest dose that is sufficient to kill the individual. An alternative to IED, stochasticity suggests that individuals do not have uniquely innate tolerance; deaths result from random processes occurring among similar individuals. Although the probit method has been used extensively in toxicology, the underlying assumption has not been tested rigorously. The goal of the present study was to test which assumption, IED or stochasticity, best explained the response of Daphnia magna exposed to multiple pulses of copper sulfate (CuSO4 ) over 24 d. Daphnia magna were exposed to subsequent age-dependent 24-h median lethal concentrations (LC50s) of copper (Cu). Age-dependent 24-h LC50 values and Cu depuration test were determined prior to the 24-d bioassay. The LC50 values were inversely related to organism age. The Cu depuration of D. magna did not depend on age or Cu concentration, and 5 d was sufficient recovery time. Daphnia magna were exposed to 4 24-h Cu exposures, and surviving organisms after each exposure were transferred to Cu-free culture media for recovery before the next exposure. Stochasticity appropriately explained the survival and reproduction response of D. magna exposed to Cu.
个体有效剂量的假设是用于分析剂量或浓度-反应数据的概率单位法的基础。根据这一假设，每个个体都有一种独特的内在耐受性，表现为个体有效剂量（IED）或足以杀死个体的最小剂量。IED 的替代方案是随机性，它表明个体没有独特的内在耐受性；死亡是由相似个体中发生的随机过程引起的。虽然概率单位法在毒理学中得到了广泛应用，但该假设并未经过严格检验。本研究的目的是检验哪种假设，IED 或随机性，最能解释暴露于硫酸铜（CuSO4）多次脉冲 24 天后大型溞的反应。大型溞暴露于随后的年龄依赖性 24 小时半数致死浓度（LC50）的铜（Cu）。在 24 天生物测定之前，确定了年龄依赖性 24 小时 LC50 值和 Cu 净化试验。LC50 值与生物体年龄成反比。大型溞对 Cu 的净化不依赖于年龄或 Cu 浓度，5 天是足够的恢复时间。大型溞暴露于 4 个 24 小时的 Cu 暴露，每次暴露后的存活生物被转移到无 Cu 的培养基中进行恢复，然后再进行下一次暴露。随机性适当地解释了暴露于 Cu 的大型溞的存活和繁殖反应。
