| Extractable organochlorine (EOCl) was measured in fish taken from two regions: the Moose River Basin in northern Ontario and the Northern River Basins Study area in northern Alberta, in particular downstream from bleached kraft pulp mills and at relevant reference sites. Statistical analysis of the survey data showed that technology upgrades at the mills such as elemental chlorine-free bleaching, oxygen delignification, and biological treatment have led to a significant decrease in EOCl in downstream fish, eventually resulting in levels close to the background in the regions.; A study of the chemical nature of fish EOCl started with gel permeation chromatography, which indicated that the major EOCl compounds were chlorinated fatty acids, probably present in fish in the form of glycerolipids including triglycerides and phosphoglycerides. Several analytical methods were developed for the analysis of traces of chlorinated fatty acids in a matrix of nonchlorinated fatty acids: (1) gas chromatography using a halogen specific detector; (2) high performance liquid chromatographic fractionation for efficient enrichment of target analytes; (3) negative chemical ionization mass spectrometry of pentafluorobenzyl esters for identifying unknowns; and (4) mass spectrometry of 4,4-dimethyloxazoline derivatives for locating the chlorine in dichloro fatty acids. The study shows that threo-5,6-dichlorotetradecanoic, threo-7,8-dichlorohexadecanoic and threo-9,10-dichlorooctadecanoic acids are predominant components in fish collected downstream from bleached kraft pulp mills, while they are undetectable in reference fish samples. The EOCl mass balance indicates that these three components represent about 30% of total EOCl in extracts, of which threo-5,6-dichlorotetradecanoic acid accounts for 60--70%, threo-9,10-dichlorooctadecanoic acid for 19--24%, and threo-7,8-dichlorohexadecanoic acid for 11--16%. The findings support the working hypothesis that, among chlorinated compounds discharged from bleached kraft pulp mills, threo-9,10-dichlorooctadecanoic acid, presumably generated in chlorine-based bleaching processes, is the most bio-accumulative in fish, and that it can be biodegraded by fish into dichlorohexadecanoic and dichlorotetradecanoic acids, presumably via beta-oxidative metabolism. These three dichloro fatty acids were identified in suspended solids isolated from biologically treated final effluent discharged from a pulp mill using 50% ClO2 substitution. The effluent-related source of chlorinated fatty acids in downstream fish was thus confirmed. |
