The determination of polychlorinated biphenyls in municipal sewage sludges using microwave-assisted extraction and gas chromatography-mass spectrometry
The presence of organic micropollutants [such as poly(chlorobiphenyls)] in municipal sewage sludges is a major problem on account of risks associated with the agricultural valorisation of the sludges. In France, since January 1998, maximum values for trace organic pollutants are imposed [0.8 mg kg–1 dry matter for the sum of seven poly(chlorobiphenyls)]. The aim of this study was to develop a reliable, accurate and fast analytical procedure (extraction, clean-up, quantification) in order to determine polychlorinated biphenyls in municipal sewage sludges. Such pollutants could be efficiently extracted from dried sewage sludge samples using microwave-assisted extraction. This technique affords several advantages as compared to the classical Soxhlet extraction, mainly rapidity and reduction in solvent consumption. Extractions (10 min under 30 W with 30 ml hexane–acetone 1:1) were conducted in the presence of copper to avoid sulfur interferences in the extracts. The latter were further concentrated and purified onto disposable silica cartridges. After final concentration and addition of the internal standard, they were analysed by gas chromatography coupled to mass spectrometry (in the selected ion monitoring mode). Two types of sludges (from Achères and Valenton sewage treatment plants near Paris, France) were analysed, whose polychlorobiphenyl concentrations differed largely (Achères sludge being the most contaminated). The microwave extraction compared favourably with the classical Soxhlet extraction. In addition, the sludge concentrations found with our experimental procedure were close to the analyses made by another laboratory, even though some discrepancy was noted.