Department of Environmental Microbiology, Swiss Federal Institute for Aquatic Science and Technology (Eawag), Dübendorf, Switzerland.
Environ Sci Technol. 2012 Apr 3;46(7):4051-8. doi: 10.1021/es204143x. Epub 2012 Mar 20.
α-, β, γ-, and δ-Hexachlorocyclohexane (HCH), the four major isomers of technical HCH, are susceptible to biotic transformations, whereby only α- and γ-HCH undergo complete mineralization. Nevertheless, LinA and LinB catalyzing HCl elimination and hydrolytic dehalogenations, respectively, as initial steps in the mineralization also convert β- and δ-HCH to a variety of mainly hydroxylated metabolites. In this study, we describe the isolation of two minor components of technical HCH, ε-HCH, and heptachlorocyclohexane (HeCH), and we present data on enzymatic transformations of both compounds by two dehydrochlorinases (LinA1 and LinA2) and a haloalkane dehalogenase (LinB) from Sphingobium indicum B90A. In contrast to reactions with α-, γ-, and δ-HCH, both LinA enzymes converted ε-HCH to a mixture of 1,2,4-, 1,2,3-, and 1,3,5-trichlorobenzenes without the accumulation of pentachlorocyclohexene as intermediate. Furthermore, both LinA enzymes were able to convert HeCH to a mixture of 1,2,3,4- and 1,2,3,5-tetrachlorobenzene. LinB hydroxylated ε-HCH to pentachlorocyclohexanol and tetrachlorocyclohexane-1,4-diol, whereas hexachlorocyclohexanol was the sole product when HeCH was incubated with LinB. The data clearly indicate that various metabolites are formed from minor components of technical HCH mixtures. Such metabolites will contribute to the overall toxic potential of HCH contaminations and may constitute serious, yet unknown environmental risks and must not be neglected in proper risk assessments.
α-、β-、γ-和δ-六氯环己烷(HCH)是技术 HCH 的四个主要异构体,易发生生物转化,其中只有α-和γ-HCH 完全矿化。然而,LinA 和 LinB 分别催化 HCl 消除和水解脱卤,作为矿化的初始步骤,也将β-和δ-HCH 转化为多种主要羟基化代谢物。在这项研究中,我们描述了技术 HCH 的两种次要成分ε-HCH 和七氯环己烷(HeCH)的分离,并介绍了两种脱氯化氢酶(LinA1 和 LinA2)和一种卤代烷烃脱卤酶(LinB)对这两种化合物的酶转化数据,这些酶来自 Sphingobium indicum B90A。与与α-、γ-和δ-HCH 的反应相反,两种 LinA 酶将ε-HCH 转化为 1,2,4-、1,2,3-和 1,3,5-三氯苯的混合物,而没有五氯环己烯作为中间体的积累。此外,两种 LinA 酶都能够将 HeCH 转化为 1,2,3,4-和 1,2,3,5-四氯苯的混合物。LinB 将ε-HCH 羟化为五氯环己醇和四氯环己烷-1,4-二醇,而当 HeCH 与 LinB 孵育时,六氯环己醇是唯一的产物。这些数据清楚地表明,从技术 HCH 混合物的次要成分中形成了各种代谢物。这些代谢物将有助于 HCH 污染的整体毒性潜力,并可能构成严重的、未知的环境风险,在适当的风险评估中不能被忽视。