Biotransformations of chloroguaiacols, chlorocatechols, and chloroveratroles in sediments

Abstract

The occurrence of trichloro- and tetrachloroguaiacols, -catechols, and -veratroles and their transformation was studied in freshwater and brackish water sediments putatively exposed to bleachery discharge. The samples contained both chloroguaiacols and chlorocatechols, of which >90% could not be removed by simple extraction. The bound concentrations varied and ranged from 550 μg kg of organic C-1 for 3,4,5-trichloroguaiacol to 8,250 μg kg of organic C-1 for tetrachlorocatechol. Chlorinated substrates added to the aqueous phase were rapidly bound to the sediment with K(p) values between 1.3 and 2.8 ml kg of organic C-1 for the chloroguaiacols and chloroveratroles and 22 to 36 ml kg of organic C-1 for the chlorocatechols. Sediment samples incubated aerobically brought about O-methylation of 4,5,6-trichloroguaiacol to 3,4,5-trichloroveratrole in a yield of ca. 25%. Under anaerobic conditions, however, de-O-methylation of both the chloroguaiacols and chloroveratroles took place with synthesis of the corresponding chlorocatechols. In separate experiments, the chlorocatechols were not completely stable under anaerobic conditions, but their ultimate fate has not yet been resolved. Sediment which had been autoclaved twice at 121°C for 20 min was unable to bring about any of these transformations; we therefore conclude that they were mediated by biological processes. These results emphasize that, in determining the fate of chloroguaiacols and related compounds discharged into the aquatic environment, the cardinal roles of sorption to the sediment phase and of the oxygen tension must be taken into account. We propose a hypothetical guaiacol cycle to accommodate our observations.