Solid-Liquid Extraction with Low Temperature Purification Coupled with Gas Chromatography and Mass Spectrometry for Determination of Polychlorinated Biphenyls in Sewage Sludge

Abstract

Sewage sludge is the residue produced by the wastewater treatment plants, which can be used as soil conditioner in agriculture. However, the current legislation recommends monitoring chemical contaminants such as polychlorinated biphenyls (PCBs). In this study, solid-liquid extraction with low temperature purification (SLE-LTP) was optimized and validated for monitoring six PCBs. The analyses were performed by gas chromatography and mass spectrometry. Sulfur interference was removed by 1.5 g of copper metal. The extraction was carried out using 6.50 mL isopropanol, 1.50 mL ethyl acetate, 0.1 g NaCl, 0.8 mL water and 15 min into ultrasound. Extraction percentages were between 82 and 94% and relative standard deviation ≤ 16% for low concentrations. Detection and quantification limits were 3.3 and 10 µg kg -1 , respectively. The method was applied to sludge samples collected monthly in the wastewater treatment plant and PCB 52 was detected in six samples. Keywords: PCB, sewage sludge, SLE-LTP, extraction method IntroductionSewage sludge is the solid residue produced by the wastewater treatment plants (WWTP). This residue can be used in agriculture as a fertilizer complement or soil conditioner. The sludge has a high content of organic matter and essential elements to plants such as nitrogen and phosphorus. 1,2 However, sewage sludge may contain chemical contaminants which can be transferred to soil, plants, animals, rivers and groundwater. [3][4][5][6] Among the contaminants, polychlorinated biphenyls (PCBs) stand out for being highly persistent in soil, for their low biodegradability and high lipophilicity and the proven harmful effects on biota and carcinogenicity on humans.7-10 Although these compounds have been banned by the 2001 Stockholm Convention, recently, 209 polychlorinated biphenyl congeners have been identified in sewage effluents.11 The PCB congeners named 28, 52, 101, 138, 153 and 180 are known as indicators of environmental pollution due to their highly frequent detection in environmental and biological samples. [12][13][14] PCBs are quantified by gas chromatography and mass spectrometric detection (GC-MS) or electron capture detection (ECD).15 Traditional techniques such as shaker table, 16 soxhlet extraction 17 and ultrasound 18 are the most used ones for PCB studies on sewage sludge.19 Accelerated solvent extraction, a more sophisticated technique, has also been used. 20 Recently, solid-liquid extraction with low temperature purification (SLE-LTP) was used for quantification of polycyclic aromatic hydrocarbons (PAHs) and chlorobenzenes in sewage sludge. 21,22 The principle of SLE-LTP is based on the addition of a homogenous mixture composed of water and organic solvent to the sample. The system is homogenized and cooled to −20 °C to freeze the matrix components and the aqueous phase. The organic phase, typically acetonitrile, remains liquid and extracts the compounds of interest. The Solid-Liquid Extraction with Low Temperature Purification Coupled with Gas Chromatography and Mass Spectrometry ...

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