Shah Amisha D, Kim Jae-Hong, Huang Ching-Hua
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Environ Sci Technol. 2006 Dec 1;40(23):7228-35. doi: 10.1021/es060404c.
The potential release of carbadox (CDX), a commonly used antibacterial agent in swine husbandry, into water systems is of a concern due to its carcinogenic and genotoxic effects. Until this study, the reactivity of carbadox (possessing quinoxaline N,N'-dioxide and hydrazone moieties) toward aqueous chlorine has yetto be investigated in depth. Chemical reactivity, reaction kinetics, and transformation pathways of carbadox and structurally related compounds with free chlorine under typical water treatment conditions were determined. This study found that only CDX and desoxycarbadox (DCDX), a main metabolite of CDX with no ring N-oxide groups, react rapidly with free chlorine while other structurally related compounds including olaquindox, quindoxin, quinoxaline N-oxide, quinoxaline, and quinoline N-oxide do not. The reaction kinetics of CDX and DCDX with chlorine are highly pH dependent (e.g., the apparent second-order rate constant, kapp, for CDX ranges from 51.8 to 3.15 x 10(4) M(-1)s(-1) at pH 4-11). The high reactivity of CDX and DCDX to chlorine involves deprotonation of their hydrazone N-H moieties where initial chlorine attack results in a reactive intermediate that is further attacked by nucleophiles in the matrix to yield non-chlorinated, hydroxylated, and larger molecular weight byproducts. All of the CDX's byproducts retain their biologically active N-oxide groups, suggesting that they may remain as active antibacterial agents.
卡巴多司（CDX）是一种在养猪业中常用的抗菌剂，由于其致癌和基因毒性作用，其向水系统中的潜在释放令人担忧。在本研究之前，卡巴多司（具有喹喔啉N，N'-二氧化物和腙部分）与氯水的反应活性尚未得到深入研究。测定了卡巴多司及结构相关化合物在典型水处理条件下与游离氯的化学反应性、反应动力学和转化途径。本研究发现，只有CDX和去氧卡巴多司（DCDX，CDX的一种主要代谢产物，无环N-氧化物基团）能与游离氯快速反应，而其他结构相关化合物，包括喹乙醇、喹烯酮、喹喔啉N-氧化物、喹喔啉和喹啉N-氧化物则不能。CDX和DCDX与氯的反应动力学高度依赖于pH值（例如，CDX的表观二级速率常数kapp在pH 4-11范围内为51.8至3.15×10⁴ M⁻¹s⁻¹）。CDX和DCDX对氯的高反应活性涉及其腙N-H部分的去质子化，初始氯攻击产生一种反应性中间体，该中间体在基质中进一步被亲核试剂攻击，生成非氯化、羟基化和更大分子量的副产物。CDX的所有副产物都保留了其生物活性N-氧化物基团，这表明它们可能仍作为活性抗菌剂存在。
