Alterra, Wageningen UR, P.O. Box 47, 6700 AA Wageningen, The Netherlands.
Chemosphere. 2011 Oct;85(6):1017-25. doi: 10.1016/j.chemosphere.2011.07.025. Epub 2011 Aug 27.
We tested the effects of the herbicide metsulfuron-methyl on growth of the submerged macrophyte Myriophyllum spicatum under laboratory conditions using different exposure scenarios. The exposures of each scenario were comparable in the concentration × time factor, viz., the same 21-d time-weighted average (TWA) concentrations but variable in peak exposure concentrations (ranging from 0.1 to 21000 ng ai L⁻¹) and exposure periods (1, 3, 7, 14 or 21 d). To study recovery potential of the exposed M. spicatum plants we continued the observation on shoot and root growth for another 21 d in herbicide-free medium so that the total observation period was 42 d. Non-destructive endpoints, length and number of new shoots and roots, were determined weekly from day 14 onwards. Destructive endpoints, dry-weight (DW) of main shoots, new shoots and new roots, were measured at the end of the experiment (t=42 d). Metsulfuron-methyl exposure in particular inhibited new tissue formation but was not lethal to main shoots. On days 21 and 42 after start exposure, EC₁₀/EC₅₀ values for new tissues expressed in terms of peak concentration (=measured concentration during exposure periods of different length) showed large differences between exposure scenarios in contrast to EC₁₀/EC₅₀ values for days 21 and 42 expressed in terms of 21-d and 42-d TWA concentrations, respectively. At the end of the experiment (day 42), 42-d TWA EC(x) values were remarkably similar between exposure scenarios, while a similar trend could already be observed on day 21 for 21-d TWA EC(x) values. For the macrophyte M. spicatum and exposure to the herbicide metsulfuron-methyl the TWA approach seems to be appropriate to use in the risk assessment. However, the data from the toxicity experiment suggest that on day 21 also the absolute height of the pulse exposure played a (minor) role in the exposure - response relationships observed.
我们在实验室条件下使用不同的暴露场景测试了除草剂甲磺隆对沉水植物狐尾藻生长的影响。每个场景的暴露在浓度×时间因素方面是可比的，即相同的 21 天时间加权平均（TWA）浓度，但峰值暴露浓度（范围从 0.1 到 21000ng ai L⁻¹）和暴露期（1、3、7、14 或 21 天）不同。为了研究暴露的狐尾藻植物的恢复潜力，我们在无除草剂的培养基中继续观察其茎和根的生长另外 21 天，因此总观察期为 42 天。每周从第 14 天开始，通过非破坏性终点，即新茎和根的长度和数量来确定。在实验结束时（t=42 天）测量主要茎、新茎和新根的干重（DW）等破坏性终点。甲磺隆暴露特别抑制新组织的形成，但对主要茎没有致死作用。在开始暴露后的第 21 天和第 42 天，以峰值浓度（=不同长度暴露期内的实测浓度）表示的新组织的 EC₁₀/EC₅₀值在暴露场景之间差异很大，而以 21 天和 42 天 TWA 浓度表示的第 21 天和第 42 天的 EC₁₀/EC₅₀值则差异较小。在实验结束时（第 42 天），暴露场景之间的 42 天 TWA EC(x)值非常相似，而在第 21 天，21 天 TWA EC(x)值也可以观察到类似的趋势。对于狐尾藻这种大型植物和甲磺隆除草剂的暴露，TWA 方法似乎适用于风险评估。然而，毒性实验数据表明，在第 21 天，脉冲暴露的绝对高度也在观察到的暴露-反应关系中发挥了（次要）作用。
