Center for Health and Environmental Risk Research, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba, Ibaraki, 305-8506, Japan.
Graduate School of Global Environmental Studies, Sophia University, 7-1, Kioicho, Chiyoda-ku, Tokyo, 102-8554, Japan.
Chemosphere. 2018 Mar;195:810-816. doi: 10.1016/j.chemosphere.2017.12.124. Epub 2017 Dec 22.
Short-term pulsed exposure tests have been increasingly used to evaluate the ecotoxicity of pollutants of which concentrations vary over time in the field. In pulsed exposure, time-weighted average (TWA) concentration is often used as an index of exposure. However, there have been few studies to demonstrate whether TWA concentration can be used to evaluate the effect of endocrine-disrupting chemicals on the daphnids. Pyriproxyfen is one of the juvenile hormone analogs that induces daphnids to produce male offspring. To evaluate whether peak or TWA concentration can explain the effects of pyriproxyfen on daphnid reproduction, we measured the number of offspring and the proportion of male offspring produced by Daphnia magna during 21-day under different exposure treatments, constant, single-pulse, and multi-pulse exposure, at an equivalent TWA concentration. Constant exposure of 50 ng/L pyriproxyfen did not affect either the fecundity or the proportion of male offspring, while a single-pulse exposure of 525 ng/L pyriproxyfen over 2 day at four different age did not reduce fecundity, but the proportion of male offspring increased age dependently. Multi-pulses exposure of 131 ng/L pyriproxyfen over two days four times (total eight days) resulted in a decrease in fecundity and the highest proportion of male offspring. Daily observation demonstrated that male offspring was only produced several days after the exposure to a certain concentration of pyriproxyfen. Therefore, neither TWA nor peak concentration accurately evaluated the effects of pulsed exposure of pyriproxyfen on the reproduction of D. magna, particularly its effect on the proportion of male offspring.
短期脉冲暴露试验已越来越多地用于评估污染物的生态毒性，这些污染物在野外的浓度随时间变化。在脉冲暴露中，时间加权平均（TWA）浓度通常用作暴露的指标。然而，很少有研究证明 TWA 浓度是否可用于评估内分泌干扰化学品对水蚤的影响。吡丙醚是一种保幼激素类似物，可诱导水蚤产生雄性后代。为了评估峰值或 TWA 浓度是否可以解释吡丙醚对水蚤繁殖的影响，我们在不同的暴露处理下，即恒定、单次脉冲和多次脉冲暴露下，测量了 21 天内大型溞产生的后代数量和雄性后代的比例，在等效 TWA 浓度下。50ng/L 吡丙醚的恒定暴露既不影响繁殖力，也不影响雄性后代的比例，而 525ng/L 吡丙醚在四个不同年龄的 2 天内的单次脉冲暴露既不降低繁殖力，但雄性后代的比例随年龄依赖性增加。131ng/L 吡丙醚的两次两天四次（共八天）的多次脉冲暴露导致繁殖力下降和雄性后代的比例最高。每日观察表明，雄性后代仅在暴露于一定浓度的吡丙醚几天后才产生。因此，TWA 或峰值浓度都不能准确评估吡丙醚脉冲暴露对 D. magna 繁殖的影响，特别是对雄性后代比例的影响。
