Chen Jie, Gu Baohua, Royer Richard A, Burgos William D
Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6036, USA.
Sci Total Environ. 2003 May 20;307(1-3):167-78. doi: 10.1016/S0048-9697(02)00538-7.
Although natural organic matter (NOM) is known to be redox reactive, the roles and effectiveness of specific functional groups of NOM in metal reduction are still a subject of intense investigation. This study entails the investigation of the Fe(III) reduction kinetics and capacity by three fractionated NOM subcomponents in the presence or absence of the dissimilatory metal reducing bacterium Shewanella putrefaciens CN32. Results indicate that NOM was able to reduce Fe(III) abiotically; the reduction was pH-dependent and varied greatly with different fractions of NOM. The polyphenolic-rich NOM-PP fraction exhibited the highest reactivity and oxidation capacity at a low pH (<4) as compared with the carbohydrate-rich NOM-CH fraction and a soil humic acid (soil HA) in reducing Fe(III). However, at a pH>4, soil HA showed a relatively high oxidation capacity, probably resulting from its conformational and solubility changes with an increased solution pH. In the presence of S. putrefaciens CN32, all NOM fractions were found to enhance the microbial reduction of Fe(III) under anaerobic, circumneutral pH conditions. Soil HA was found to be particularly effective in mediating the bioreduction of Fe(III) as compared with the NOM-PP or NOM-CH fractions. NOM-CH was the least effective because it was depleted in both aromatic and polyphenolic organic contents. However, because both soil HA and NOM-PP contain relatively high amounts of aromatic and phenolic compounds, results may indicate that low-molecular-weight polyphenolic organics in NOM-PP were less effective in mediating the bioreduction of Fe(III) at circumneutral pH than the high-molecular-weight polycondensed, conjugated aromatics present in soil HA. These research findings may shed additional light in understanding of the roles and underlying mechanisms of NOM reactions with contaminant metals, radionuclides, and other toxic chemicals in the natural environment.
尽管已知天然有机物（NOM）具有氧化还原活性，但NOM特定官能团在金属还原中的作用和有效性仍是深入研究的课题。本研究旨在考察在存在或不存在异化金属还原菌腐败希瓦氏菌CN32的情况下，三种分级的NOM亚组分对Fe(III)的还原动力学和能力。结果表明，NOM能够非生物还原Fe(III)；这种还原作用依赖于pH值，并且随NOM的不同组分有很大差异。与富含碳水化合物的NOM-CH组分和土壤腐殖酸（土壤HA）相比，富含多酚的NOM-PP组分在低pH值（<4）下还原Fe(III)时表现出最高的反应活性和氧化能力。然而，在pH>4时，土壤HA显示出相对较高的氧化能力，这可能是由于其构象和溶解度随溶液pH值升高而发生变化所致。在存在腐败希瓦氏菌CN32的情况下，发现在厌氧、中性pH条件下，所有NOM组分均能增强Fe(III)的微生物还原作用。与NOM-PP或NOM-CH组分相比，发现土壤HA在介导Fe(III)的生物还原方面特别有效。NOM-CH最无效，因为其芳香族和多酚类有机成分含量均较低。然而，由于土壤HA和NOM-PP都含有相对大量的芳香族和酚类化合物，结果可能表明，在中性pH条件下，NOM-PP中的低分子量多酚类有机物在介导Fe(III)的生物还原方面不如土壤HA中存在的高分子量缩合共轭芳香族化合物有效。这些研究结果可能有助于进一步理解NOM与天然环境中污染金属、放射性核素及其他有毒化学物质反应的作用和潜在机制。
