Winter Anna R, Fish Terry Anne E, Playle Richard C, Smith D Scott, Curtis P Jefferson
Wilfrid Laurier University, Department of Biology, Waterloo, Ontario, Canada N2L 3C5.
Aquat Toxicol. 2007 Aug 30;84(2):215-22. doi: 10.1016/j.aquatox.2007.04.014. Epub 2007 Jun 16.
Natural organic matter (NOM) is significant in determining fate, transport and toxicity of metals in aqueous systems but NOM is not a static component; NOM can undergo photochemical changes in chemical structure. These changes will modify NOM quality and in turn influence how metals are transported in the environment, as well as their toxicity to aquatic organisms. Natural organic matter was collected from five freshwater sources using a portable reverse osmosis unit, diluted to about 10 mg CL(-1), then exposed for 13 days to summer temperatures either in the dark or exposed to sunlight. Light exposed NOM had decreases in total organic carbon (TOC) of 8-35% compared to samples kept in a refrigerator (dark, 4 degrees C), and the NOM became optically lighter, as shown by specific absorbance coefficients (SAC) taken at 340 nm (55-76% decreases in SAC(340)). In contrast, dark exposed NOM showed much smaller decreases in TOC (< or = 3%) or SAC(340) (</=32%). For light exposed samples fluorescence excitation-emission matrix spectroscopy showed loss of fluorescence mainly in the 330 nm excitation, 420-450 nm emission range, consistent with loss of fulvic- and humic-like, aromatic groups in the NOM. Commercial (Aldrich) humic acid showed similar changes when exposed to light, with decreases in fulvic and humic fluorescence peaks. Finely ground fish food, used as a source of protein-rich organic matter, showed similar decreases in TOC and SAC(340) when exposed to light, but showed increased SAC(340) in the foil wrapped samples, presumably because bacteria were involved in decomposition of the food organic matter. Overall, these results indicate photodegradation of terrestrially derived, aromatic functional groups (e.g., from lignin) in natural organic matter from various freshwater sources.
天然有机物（NOM）在决定水体系中金属的归宿、迁移和毒性方面具有重要意义，但NOM并非一个静态成分；NOM的化学结构会发生光化学变化。这些变化会改变NOM的性质，进而影响金属在环境中的迁移方式及其对水生生物的毒性。使用便携式反渗透装置从五个淡水水源采集天然有机物，将其稀释至约10 mg CL(-1)，然后在黑暗中或暴露于阳光下，于夏季温度下放置13天。与保存在冰箱中的样品（黑暗，4℃）相比，暴露于光照下的NOM总有机碳（TOC）降低了8 - 35%，并且NOM在光学上变浅，如在340 nm处测得的比吸收系数（SAC）所示（SAC(340)降低了55 - 76%）。相比之下，黑暗中放置的NOM的TOC（≤3%）或SAC(340)（≤32%）降低幅度要小得多。对于暴露于光照的样品，荧光激发 - 发射矩阵光谱显示荧光主要在330 nm激发、420 - 450 nm发射范围内损失，这与NOM中类富里酸和类腐殖酸芳香基团的损失一致。商业（Aldrich）腐殖酸在光照下也表现出类似变化，富里酸和腐殖酸荧光峰降低。用作富含蛋白质的有机物质来源的精细研磨鱼食，在光照下TOC和SAC(340)也有类似降低，但在铝箔包裹的样品中SAC(340)增加，推测是因为细菌参与了食物有机物的分解。总体而言，这些结果表明来自各种淡水水源的天然有机物中源自陆地的芳香官能团（如来自木质素）发生了光降解。
