Langlois Maureen C, Weavers Linda K, Chin Yu-Ping
Environmental Science Graduate Program, The Ohio State University, Columbus, OH 43210, USA.
Environ Sci Process Impacts. 2014 Sep 20;16(9):2098-107. doi: 10.1039/c4em00138a. Epub 2014 May 14.
Photolytic transformation of organic contaminants in wetlands can be mediated by chromophoric dissolved organic matter (CDOM), which in turn can lose its reactivity from photobleaching. We collected water from a small agricultural wetland (Ohio), Kawai Nui Marsh (Hawaii), the Everglades (Florida), and Okefenokee Swamp (Georgia) to assess the effect of photobleaching on the photofate of two herbicides, acetochlor and isoproturon. Analyte-spiked water samples were irradiated using a solar simulator and monitored for changes in CDOM light absorbance and dissolved oxygen. Photobleaching did not significantly impact the indirect photolysis rates of either herbicide over 24 hours of irradiation. Surprisingly, the opposite effect was observed with isoproturon, which accelerated DOM photobleaching. This phenomenon was more pronounced in higher-CDOM waters, and we believe that the redox pathway between triplet-state CDOM and isoproturon may be responsible for our observations. By contrast, acetochlor indirect photolysis was dependent on reaction with the hydroxyl radical and did not accelerate photobleaching of wetland water as much as isoproturon. Finally, herbicide indirect photolysis rate constants did not correlate strongly to any one chemical or optical property of the sampled waters.
湿地中有机污染物的光解转化可由发色溶解性有机物（CDOM）介导，而CDOM又会因光漂白而失去其反应活性。我们从一个小型农业湿地（俄亥俄州）、卡瓦伊努伊沼泽（夏威夷州）、大沼泽地（佛罗里达州）和奥克弗诺基沼泽（佐治亚州）采集了水样，以评估光漂白对两种除草剂乙草胺和异丙隆光降解的影响。用太阳模拟器照射添加了分析物的水样，并监测CDOM吸光度和溶解氧的变化。在24小时的照射过程中，光漂白对两种除草剂的间接光解速率均无显著影响。令人惊讶的是，对于异丙隆观察到了相反的效果，即它加速了DOM的光漂白。这种现象在CDOM含量较高的水体中更为明显，我们认为三重态CDOM和异丙隆之间的氧化还原途径可能是我们观察结果的原因。相比之下，乙草胺的间接光解取决于与羟基自由基的反应，并且对湿地水的光漂白加速作用不如异丙隆。最后，除草剂的间接光解速率常数与所采水样的任何一种化学或光学性质均无强相关性。
