Reactions of hydroxyl radical with humic substances: Bleaching, mineralization, and production of bioavailable carbon substrates
Reactions of hydroxyl radical with humic substances: Bleaching, mineralization, and production of bioavailable carbon substrates
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DOI：
10.1021/es0109646
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发表时间：
2002-02-01
影响因子：
11.4
通讯作者：
Voelker, BM
中科院分区：
文献类型：
--
作者：
Goldstone, JV;Pullin, MJ;Voelker, BM
在这项研究中，我们研究了羟基（OH，）自由基的作用，作为一种机制，在阳光照射的表面沃茨的发色溶解有机物（CDOM）的光分解。使用水的γ-辐解，OH.产生的标准腐殖物质的解决方案中的数量相当的时间尺度上产生的阳光照射表面沃茨。OH的二级速率系数。与Suwannee河富里酸（SRFA; 2.7 x 10（4）s（-1）（mg C/L）（-1））和腐殖酸（SRHA; 1.9 x 10（4）s（-1）（mg C/L）（-1））的反应与天然水样中DOM和其他来源DOM分离物的观察结果相当，但随着OH的增加略有下降。剂量哦与腐殖物质的反应产生溶解无机碳（DIC），具有类似于0.3molCO2/molOH的高效率。从氧化的早期阶段直到DOM完全矿化，这种效率保持大致恒定。通过SRFA和SRHA与OH反应的低分子量（LMW）酸（包括乙酸、甲酸、丙二酸和草酸）的生产速率。使用HPLC测量。SRHA和SRFA的这些酸的产生速率与DIC产生速率的比率与天然水样光解时观察到的比率相似。生物测定表明OH.与腐殖物质的反应不会导致可测量的除LMW酸以外的生物可利用碳基质的形成。腐植酸发色团的OH漂白。是相对缓慢的。我们的研究结果表明，OH。与腐殖物质的反应不太可能对在阳光照射的沃茨中观察到的DOM光矿化和LMW酸产生的速率有显著贡献。它们也不太可能是光漂白的重要机制，除非在具有非常高的OH的沃茨中。光生成速率
In this study, we examine the role of the hydroxyl (OH,) radical as a mechanism for the photodecomposition of chromophoric dissolved organic matter (CDOM) in sunlit surface waters. Using gamma-radiolysis of water, OH. was generated in solutions of standard humic substances in quantities comparable to those produced on time scales of days in sunlit surface waters. The second-order rate coefficients of OH. reaction with Suwannee River fulvic (SRFA; 2.7 x 10(4) s(-1) (mg of C/L)(-1)) and humic acids (SRHA; 1.9 x 10(4) s(-1) (mg of C/L)(-1)) are comparable to those observed for DOM in natural water samples and DOM isolates from other sources but decrease slightly with increasing OH. doses. OH. reactions with humic substances produced dissolved inorganic carbon (DIC) with a high efficiency of similar to0.3 mol of CO2/mol of OH.. This efficiency stayed approximately constant from early phases of oxidation until complete mineralization of the DOM. Production rates of low molecular weight (LMW) acids including acetic, formic, malonic, and oxalic acids by reaction of SRFA and SRHA with OH. were measured using HPLC. Ratios of production rates of these acids to rates of DIC production for SRHA and for SRFA were similar to those observed upon photolysis of natural water samples. Bioassays indicated that OH. reactions with humic substances do not result in measurable formation of bioavailable carbon substrates other than the LMW acids. Bleaching of humic chromophores by OH. was relatively slow. Our results indicate that OH. reactions with humic substances are not likely to contribute significantly to observed rates of DOM photomineralization and LMW acid production in sunlit waters. They are also not likely to be a significant mechanism of photobleaching except in waters with very high OH. photoformation rates.