Cedergreen Nina, Andersen Lone, Olesen Charlotte Frihauge, Spliid Hans Henrik, Streibig Jens Carl
Department of Agricultural Sciences, The Royal Veterinary and Agricultural University (KVL), Højbakkegård Allé 9, DK-2630 Taastrup, Denmark.
Aquat Toxicol. 2005 Feb 10;71(3):261-71. doi: 10.1016/j.aquatox.2004.11.010. Epub 2004 Dec 28.
The highest concentrations of herbicides measured in flowing surface waters are often only present for short periods of time. These herbicide pulses can reach concentrations that would affect aquatic plants if present over a long time. The aim of this study was to assess the effect of a 3-h herbicide pulse relative to the effects of long-term (4 and 7 days) exposure of six herbicides with different sites of action and different K(ow) on the growth of the floating macrophyte Lemna minor. The herbicides were the two photosynthetic inhibitors: diquat and terbuthylazine, the inhibitors of acetolactate syntase (ALS), imazamox and metsulfuron-methyl and the microtubule assembly inhibitors propyzamide and pendimethalin. The log K(ow) ranged from -4.6 to 5.2. For imazamox, metsulfuron-methyl, propyzamide and pendimethalin a 3-h pulse induced the effect on area-specific growth as did a 4-day exposure at an approximate 10-fold higher concentration. For diquat and terbuthylazine a concentration closer to a factor of 100 or more was needed for a 3-h pulse to induce an effect similar to that of a 4-day exposure. For diquat, the low pulse-effect was most likely due to a slow uptake of the hydrophilic ion (log K(ow) = -4.6), as no effect was observed on chlorophyll fluorescence within 8 h after exposure. The chlorophyll fluorescence parameters are expected to respond quickly to a PSI inhibitor as diquat. For terbuthylazine, fluorescence measurements showed an effect on photosynthesis within 1h of exposure, and reached a minimum after 3 h. Recovery was fast, and initial fluorescence was restored within 24 h. Hence, the small pulse effect on area-specific growth was due to rapid recovery of photosynthesis. In contrast to terbuthylazine, the stop in area-specific growth observed for the ALS-and microtubule assembly inhibitors, took up to 4 days to recover from. Such a long recovery time after a pulse of only 3 h indicate that at realistic pulse exposures of up to a day or two, pulse-effects will approach the effects obtained in long-term studies. When investigating the effects of pulse exposures on aquatic plants, we should therefore focus more on non-photosynthetic inhibitors, which might not appear in pulses in as large concentrations as the PSII inhibitors investigated up till now, but whose effect, even in a shorter pulse, can be more damaging.
在流动地表水测得的除草剂最高浓度通常仅在短时间内出现。这些除草剂脉冲所达到的浓度若长期存在，会对水生植物产生影响。本研究的目的是评估3小时除草剂脉冲相对于六种作用位点不同、辛醇-水分配系数（K(ow)）不同的除草剂长期（4天和7天）暴露对漂浮大型植物浮萍生长的影响。这些除草剂包括两种光合抑制剂敌草快和特丁津、乙酰乳酸合成酶（ALS）抑制剂咪唑乙烟酸和甲磺隆，以及微管组装抑制剂丙草胺和二甲戊灵。其log K(ow)范围为-4.6至5.2。对于咪唑乙烟酸、甲磺隆、丙草胺和二甲戊灵，3小时脉冲诱导的面积特异性生长效应与4天暴露在约高10倍浓度下诱导的效应相同。对于敌草快和特丁津，3小时脉冲要诱导出与4天暴露相似的效应，所需浓度要接近100倍或更高。对于敌草快，低脉冲效应很可能是由于亲水性离子（log K(ow) = -4.6）吸收缓慢，因为暴露后8小时内未观察到对叶绿素荧光的影响。叶绿素荧光参数预计会对像敌草快这样的PSI抑制剂迅速做出反应。对于特丁津，荧光测量显示暴露1小时内光合作用就受到影响，3小时后达到最小值。恢复很快，初始荧光在24小时内恢复。因此，对面积特异性生长的小脉冲效应是由于光合作用的快速恢复。与特丁津不同，ALS抑制剂和微管组装抑制剂导致的面积特异性生长停止需要长达4天才能恢复。仅3小时脉冲后如此长的恢复时间表明，在实际长达一两天的脉冲暴露情况下，脉冲效应将接近长期研究中获得的效应。因此，在研究脉冲暴露对水生植物的影响时，我们应更多地关注非光合抑制剂，它们在脉冲中出现的浓度可能不像迄今研究的PSII抑制剂那么高，但其效应即使在较短脉冲中也可能更具破坏性。
