Biotransformation in soil of chloroaromatic compounds related to bleach plant effluents

The aim of the study was to examine the biotransformation of 6 chlorodromatic compounds in soil under laboratory conditions simulating the landspreading of sludges from the wastewater treatment of chlorine bleaching effluents. The soil samples were mixed with each of tetrachlorocatechol, -guaiacol, and -veratrole (at 5 ppm concentration) and 4,5-dichlorocatechol, -guaiacol, and -veratrole (at 50 ppm). The samples were kept moist at 25°C. The analytical methodology, directed to the examination of the transformation reactions of O-methylation and O-demethylation,comprised a modified extraction technique which enabled the recovery of chlorocatechols in reasonable yields (53 to 75%). The extracts, collected after 0,5,15, and 30 days of incubation, were analyzed by gas chromatography after acetylation. On kinetic curves, lag phases were observed in most instances. The half-lives (days) of the compounds in the 'fast' stage were: TeCC: 9.6, TeCG: 6.1, TeCV: 24.8, DCC: 24.8, DCG: 4.3, and DCV: 4.1. Detection limits for O-methylation/demethylation products ranged from 0.3 to 4% of the starting concentration. O-Methylation was detected in TeCG (4.0% after 30 days), while O-demethylation was observed in DCV, TeCG and TeCV (45.5, 2.9, and 6.5% after 30 days, respectively). Especially fast and selective was O-demethylation of DCV with 77% recovery of DCC within 15 days. All of the starting compounds and biotransformation products were gradually disappearing from the soil and difference chromatograms showed no permanent accumulation of new chloroaromatic compounds after 30 days. The active role of microorganism in depletion of the test compounds from soil was proven in a control experiment with sterilized soil.