## 4 Conclusions  
Nine SMFs were measured in the influents and effluents of four STPs, 17 tributaries, and five sampling sites in the Han River, and also in 36 different PCPs, including hair care products, perfumes, and detergents. In the PCPs, HHCB was the most abundant SMF, while AHTN, MK, AHMI, DPMI, ATII, and ADBI were detected with a frequency of less than 50%. Among the PCPs, hair care products had the highest SMF content per unit weight, with the highest concentration (median, 395.8 \(\upmu\)g/g) being observed for HHCB. The SMF distribution among the four STP influents was similar to that of PCPs, with a median total SMF concentration of 6.756 \(\upmu\)g/L and median HHCB concentration of 6.130 \(\upmu\)g/L. The median SMF concentration in the effluents was 2.945 \(\upmu\)g/L, while the median HHCB concentration was 2.546 \(\upmu\)g/L, and their distribution pattern was similar to that in the sewage influents, although the MK concentration was slightly higher (0.218 \(\upmu\)g/L) than that of AHTN (0.161 \(\upmu\)g/L). In the sewage treatment process, the removal efficiencies of HHCB, AHTN, and MK were 58.5%, 56.8%, and 38.1%, respectively. In the 17 tributaries and Han River mainstream, five SMFs were detected at levels similar to those in the STP effluents, but the concentrations decreased due to the dilution effect. The HHCB concentration was 0.220 \(\upmu\)g/L in tributaries and 0.105 \(\upmu\)g/L in the mainstream. The highest SMF concentrations in the tributaries were observed at locations close to the STPs,  
Figure 4: The location of the sampling site in the tributaries and the Han River basin and the average concentration of SMFs at each tributary (red circles represent the effluent volume of STP). implying that sewage effluents were the main source of SMFs in the receiving water. The results of this study confirmed that the mainource of SMFs in the receiving water was sewage effluents containing untreated SMFs, which largely originate from household PCPs, especially hair care products (e.g., shampoo) and perfumes. The limitation of this study was that monitoring was not sufficient. More comprehensive monitoring is needed to achieve a clear correlation of SMF levels between the Han River and household personal care products, and to investigate the effect of sewage effluent discharge on SMF concentrations in receiving water. Finally, as a suggestion to reduce the level of SMFs, more effective treatment technologies such as advanced oxidation processes need to be implemented in sewage treatment plants. The following are available online at [[https://www.mdpi.com/2073-4441/13/4/392/s1](https://www.mdpi.com/2073-4441/13/4/392/s1)]([https://www.mdpi.com/2073-4441/13/4/392/s1](https://www.mdpi.com/2073-4441/13/4/392/s1)), Text S1: Quality assurance and quality control (QA/QC) of synthetic musk fragrances (SMFs), Table S1: Basic information of four sewage treatment plants in highly populated urban area, Table S2: Recoveries, MDL and LOQ values for nine synthetic musk fragrances (SMFs), Table S3: Chromatograms and mass spectra of the SMFs, Table S4: Concentration of synthetic musk fragrances in sewage treatment plant (STP) influents and effluents in other countries. Conceptualization, M.-Y.L. and [PERSON]-[PERSON]; methodology, [PERSON]-[PERSON], [PERSON]-[PERSON] and [PERSON]-[PERSON]; software, [PERSON]-H.H. ; validation, H.-J.H. ; investigation, [PERSON]-H.H., [PERSON]-H.J., [PERSON]-Y.L., [PERSON]-[PERSON], [PERSON]-Y.L. and [PERSON]; data curation, J.-H.H. ; writing--original draft preparation, J.-H.H. ; writing--review and editing, [PERSON]-Y.L., [PERSON] and [PERSON]-[PERSON]; visualization, [PERSON]-H.H. and [PERSON]-[PERSON]; supervision, [PERSON]-Y.L. and [PERSON]-[PERSON]; project administration, M.-Y.L. ; funding acquisition, M.-Y.L. All authors have read and agreed to the published version of the manuscript. This study was supported by the Seoul Metropolitan Government Research Institute of Public Health and Environment (SIHE). Not applicable.