Concentrations and distribution of synthetic musks and siloxanes in sewage sludge of wastewater treatment plants in China

• High levels and detection frequencies of SMs and siloxanes were found in sludge.
• SM levels were correlated with the TOC of the sludge and serving population of WWTPs.
• Cyclic siloxane levels had a positive correlation with the treatment capacity of WWTPs.
• Linear siloxane concentrations had correlation with the TOC of the sludge in WWTPs.
• When using treated sewage sludge as bio-solids, negligible effect was observed.

In this study, we assessed the occurrence and distribution patterns of seven synthetic musks (SMs) and 17 siloxanes in anaerobic digested sludge samples collected at the dewatering process from 42 wastewater treatment plants (WWTPs) in China. SMs in sludge from different WWTPs exhibited similar composition profiles, and their total concentrations ranged from 47.3 ng/g to 68.2 μg/g dry weight (dw). On average, galaxolide (HHCB, 63.8%) and tonalide (AHTN, 31.7%) accounted for 95.5% of ∑ SMs. The total concentrations of cyclic siloxanes ranged from < LOQ (limit of quantitation) to 36.1 μg/g dw (mean: 1.98 μg/g), while from < LOQ to 13.2 μg/g dw (mean: 0.937 μg/g) for linear siloxanes. On average, cyclic siloxanes accounted for 68% of the total siloxanes. High concentrations and detection frequencies of SMs and siloxanes in sewage sludge indicated that both of them were widely used in China. Among the sludge samples from 42 WWTPs, the concentrations of both ∑ SMs and ∑ siloxanes had considerable variations. We investigated the influence of potential factors (wastewater and sludge characteristics, the treatment capacity, serving population, and the treatment techniques of WWTPs) on the levels of target compounds in sludge, and found that SMs were significantly (p < 0.05) correlated with the total organic carbon (TOC) of the sludge and the serving population of WWTP. There were also strong correlations (p < 0.05) between the treatment capacity of WWTPs and cyclic siloxanes, as well as between the TOC of the sludge and linear siloxanes. In addition, the ecological risks of SMs and siloxanes in sewage sludge addressed to land application were assessed, which suggested that there was a low risk to the soil environment.