Determination of nonylphenol polyethoxylates and their carboxylic acid metabolites in sewage treatment plant sludge by supercritical carbon dioxide extraction

Abstract

A supercritical fluid extraction (SFE) method was developed for the extraction of nonylphenol polyethoxylate (NPnEO) non-ionic surfactants from dried sewage treatment plant sludge. Extraction was carried out at 80°C and 5100 p.s.i. with carbon dioxide using water as a modifier. The ethoxylates were analyzed by gradient high-performance liquid chromatography (HPLC) with an APS Hypersil column and a fluorescence detector (230 nm excitation and 300 nm emission). This SFE method was more time-efficient and it produced higher recovery than the traditional Soxhlet extraction and steam distillation techniques used for NPnEO in sewage sludge. The same procedure was also applicable to the coextraction of nonylphenoxyacetic (NP1EC) and nonylphenoxyethoxyacetic (NP2EC) acids, which were metabolites of the ethoxylates under aerobic conditions. Following an off-line methylation, analysis of the acids was achieved by GC-MS in selected ion monitoring mode. In a brief survey of sludge samples collected from nine sewage treatment plants across Canada, very high levels of nonylphenol mono- (NP1EO, 28–304 μg/g) and di-ethoxylates (NP2EO, 4–118 μg/g) were found. In contrast, the total polyethoxylate concentration (from 3 to 17 ethoxy units) was generally less than 50% of the sum of NP1EO and NP2EO in the same sample. NP1EC and NP2EC were found in only three of the seven samples tested, with concentrations ranging from 4 to 38 μg/g.