Zhang Huichun, Huang Ching-Hua
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Environ Sci Technol. 2003 Jun 1;37(11):2421-30. doi: 10.1021/es026190q.
The antibacterial agents triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) and chlorophene (4-chloro-2-(phenylmethyl)phenol) show similar susceptibility to rapid oxidation by manganese oxides (delta-MnO2 and MnOOH) yielding Mn(II) ions. Both the initial reaction rate and adsorption of triclosan to oxide surfaces increase as pH decreases. The reactions are first-order with respect to the antibacterial agent and MnO2. The apparent reaction orders to H+ were determined to be 0.46 +/- 0.03 and 0.50 +/- 0.03 for triclosan and chlorophene, respectively. Dissolved metal ions (Mn(II), Zn(II), and Ca(II)) and natural organic matter decrease the reaction rate by competitively adsorbing and reacting with MnO2. Product identification indicates that triclosan and chlorophene oxidation occurs at their phenol moieties and yields primarily coupling and p-(hydro)quinone products. A trace amount of 2,4-dichlorophenol is also produced in triclosan oxidation, suggesting bond-breaking of the ether linkage. The experimental results support the mechanism that after formation of a surface precursor complex of the antibacterial agent and the surface-bound Mn(IV), triclosan and chlorophene are oxidized to phenoxy radicals followed by radical coupling and further oxidation to form the end products. Compared to several structurally related substituted phenols (i.e., 2-methyl-4-chlorophenol, 2,4-dichlorophenol, 3-chlorophenol, and phenol), triclosan and chlorophene exhibit comparable or higher reactivities toward oxidation by manganese oxides. The higher reactivities are likely affected by factors including electronic and steric effects of substituents and compound hydrophobicity. Once released into the environment, partitioning of triclosan and chlorophene to soils and sediments is expected because of their relatively hydrophobic nature. Results of this study indicate that manganese oxides in soils will facilitate transformation of these antibacterial agents.
抗菌剂三氯生（5-氯-2-(2,4-二氯苯氧基)苯酚）和氯酚（4-氯-2-(苯甲基)苯酚）对被氧化锰（δ-MnO₂和MnOOH）快速氧化生成Mn(II)离子表现出相似的敏感性。随着pH值降低，三氯生的初始反应速率和在氧化物表面的吸附均增加。这些反应对抗菌剂和MnO₂而言是一级反应。对于三氯生和氯酚，H⁺的表观反应级数分别确定为0.46±0.03和0.50±0.03。溶解的金属离子（Mn(II)、Zn(II)和Ca(II)）以及天然有机物通过与MnO₂竞争性吸附和反应降低反应速率。产物鉴定表明，三氯生和氯酚的氧化发生在它们的酚基部分，主要生成偶联产物和对（氢）醌产物。三氯生氧化过程中还产生微量的2,4-二氯苯酚，这表明醚键发生了断裂。实验结果支持这样的机制：在抗菌剂与表面结合的Mn(IV)形成表面前体络合物后，三氯生和氯酚被氧化为苯氧基自由基，随后自由基偶联并进一步氧化形成最终产物。与几种结构相关的取代酚（即2-甲基-4-氯苯酚、2,4-二氯苯酚、3-氯苯酚和苯酚）相比，三氯生和氯酚对氧化锰氧化表现出相当或更高的反应活性。较高的反应活性可能受到包括取代基的电子和空间效应以及化合物疏水性等因素的影响。由于它们相对疏水的性质，一旦释放到环境中，预计三氯生和氯酚会分配到土壤和沉积物中。本研究结果表明，土壤中的氧化锰将促进这些抗菌剂的转化。
