Nationwide occurrence and distribution of liquid crystal monomers in municipal sewage sludge of China

Abstract

Environmental pollution and the fate of liquid crystal monomers (LCMs) in different matrices have received increasing attention owing to their potential persistence and toxicity. Sewage sludge, a representative environmental matrix, may be an important sink for LCMs. However, the contamination status of LCMs in sewage sludge remains unknown, especially on a large scale. In this study, a robust method was developed using GC–MS/MS analysis to determine 65 LCMs in sewage sludge. The occurrence of 65 LCMs in municipal sewage sludge in China was investigated for the first time. Among the 65 target LCMs, 48 were detectable, including 14 biphenyls/bicyclohexyls and their analogs (BAs) and 34 fluorobiphenyls and their analogs (FBAs). Six LCMs were detected at a rate >50 %. These results demonstrate the ubiquity of this class of synthetic chemicals in China. The total concentrations of LCMs in sludge ranged from 17.2 to 225 ng/g, with a median concentration of 46.4 ng/g. BAs were the major components of LCMs contamination in the sludge, with total BAs concentrations accounting for approximately 75 % of the total LCMs concentrations. A comparative analysis of sludge samples from different regions revealed significant regional distribution differences in LCMs: the concentrations of LCMs in sludge from East and Central China were significantly higher than those from West China (p < 0.05). Correlation and principal component analyses of the concentrations of LCMs revealed that LCMs in sludge share similar contamination sources and environmental behaviors. E-waste dismantling, domestic releases, and industrial releases may be sources of LCMs in sludge. Furthermore, the results of the degradation prediction implied that the plausible transformation products exhibited the same or even stronger persistence as the parent LCMs. Our study will be beneficial for LCMs regulation and offer suggestions for its development and safe application.