CHLOROBIPHENYLS IN SEWAGE-SLUDGE - COMPARISON OF EXTRACTION METHODS

Six extraction methods for the analysis of PCBs (CB-28, CB-52, CB-101, CB-118, CB-138, CB-153 and CB-180) in sewage sludge were tested. A ce rtified reference material (CRM 392) was used for the evaluation of th e performance of the methods. Soxhlet-Dean-Starch with toluene as solv ent, Soxhlet with hexane:acetone (2:3), cold digestion/saponification with 2 mol/L KOH in methanol followed by partition with hexane, and so nication liquid-solid extraction with hexane:acetone (1:1) produced ac curate results (97%, 93%, 104%, and 88%, respectively) with acceptable precisions (6.2%, 6.8%, 15% and 12%, respectively). Results in close agreement with the certified value for all congeners were obtained by treatment with BF3-methanol prior to partition with dichloromethane. H owever, this is a tedious procedure and involves the use of hazardous compounds. Cyclic steam distillation produced results with an accuracy of around 80% and a good precision (5.2%). The very low consumption o f solvents and other expensive chemicals by this technique and the pos sibility of analyzing the extract directly without clean-up make it an interesting alternative to the mor sophisticated methods. Column elut ion with dichloromethane was found to br les efficient (61%), but it i s a rapid, direct method with a low consumption of solvents and it may therefore serve as screening method.