Bala_2012_Environ.Sci.Technol_46_4051

alpha-, beta, gamma-, and delta-Hexachlorocyclohexane (HCH), the four major isomers of technical HCH, are susceptible to biotic transformations, whereby only alpha- and gamma-HCH undergo complete mineralization. Nevertheless, LinA and LinB catalyzing HCl elimination and hydrolytic dehalogenations, respectively, as initial steps in the mineralization also convert beta- and delta-HCH to a variety of mainly hydroxylated metabolites. In this study, we describe the isolation of two minor components of technical HCH, sigma-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 alpha-, gamma-, and delta-HCH, both LinA enzymes converted sigma-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 sigma-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.