## 3 Results and Discussion
### Synthetic Musk Fragrances in the STP Effluents  
The total SMF concentrations in the sewage effluents were in the range 0.949-5.880 \(\upmu\)g/L, and the median value was 2.945 \(\upmu\)g/L (Table 3). The SMF detection frequencies in the STP effluents were similar to those in the STP influents. Among the SMFs, HHCB, AHTN, MK, DPMI, and ATII were detected in most of the samples, while ADBI, AHMI, MA, and MX were not detected. The SMF with the highest concentration was HHCB, with a median value of 2.546 \(\upmu\)g/L, and a range of 0.701-5.390 \(\upmu\)g/L. Based on the median value, HHCB accounted for almost 90% of the total SMFs, and its concentration was several tens of times higher than those of AHTN, MK, and DPMI.  
The HHCB concentrations measured in this study were slightly higher than previously reported values in Germany [37], Thailand [24], USA [28], and China [26] (Table S4). The distribution of SMFs in the STP effluents was dependent on the SMF concentrations in the STP influents, removal efficiency, and the chemical properties of each SMF. The relatively higher level of HHCB in the sewage effluents was a consequence of the high concentration in the sewage influents.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Category** & **ug/L** & **DPMI** & **ADBI** & **AHMI** & **HHCB** & **ATII** & **AHTN** & **MA** & **MX** & **MK** & **Sum** \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} STP \\ Influent \\ (n = 27) \\ \end{tabular} } & Range & 0.034-0.393 & N.D.\(-\)0.015 & N.D. & 3.200-10.110 & N.D.\(-\)0.090 & 0.012-0.572 & N.D. & N.D. & 0.148-1.056 & 3.532-11.08 \\ \cline{2-11}  & Median & 0.166 & N.D. & N.D. & 6.130 & 0.058 & 0.373 & N.D. & N.D. & 0.352 & 6.756 \\ \cline{2-11}  & Frequency (\%) & 100 & 28 & 0 & 100 & 92 & 100 & 0 & 0 & 100 & \\ \hline \multirow{3}{*}{
\begin{tabular}{c} STP \\ Influent \\ (n = 37) \\ \end{tabular} } & Range & 0.015-0.129 & N.D. & N.D. & 0.701-5.390 & N.D.\(-\)0.059 & N.D.\(-\)0.306 & N.D. & N.D. & 0.085-0.423 & 0.949-5.880 \\ \cline{2-11}  & Median & 0.071 & N.D. & N.D. & 2.546 & 0.028 & 0.161 & N.D. & N.D. & 0.218 & 2.945 \\ \cline{2-11}  & Frequency (\%) & 100 & 0 & 0 & 100 & 82.9 & 97.1 & 0 & 0 & 100 & \\ \cline{2-11}  & Range & N.D.-0.131 & N.D. & N.D. & 0.017-2.825 & N.D.\(-\)0.040 & N.D.-0.169 & N.D. & N.D. & 0.085-0.258 & 0.034-3.392 \\ \cline{2-11}  & Median & 0.007 & N.D. & N.D. & 0.220 & N.D. & 0.019 & N.D. & N.D. & 0.022 & 0.304 \\ \cline{2-11}  & Frequency (\%) & 52.3 & 0 & 0 & 100 & 46.4 & 82.4 & 0 & 0 & 100 & \\ \cline{2-11}  & Range & N.D.-0.045 & N.D. & N.D. & 0.026-0.705 & N.D.\(-\)0.016 & N.D.-0.046 & N.D. & N.D. & N.D.-0.074 & N.D.-0.844 \\ \cline{2-11}  & Median & N.D. & N.D. & N.D. & 0.105 & N.D. & 0.010 & N.D. & N.D. & 0.016 & 0.141 \\ \cline{2-11}  & Frequency (\%) & 37.5 & 0 & 0 & 100 & 15.0 & 62.5 & 0 & 0 & 87.5 & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Concentration of synthetic mask fragames in the in the sewage treatment plant (STP) influent, effluent, tributary, and the Han River.  
The average removal rate of SMFs in the four STPs using the MLE and A2O processes (Table S2) was 58.5% for HHCB and 56.8% for AHTN. The HHCB and AHTN removal efficiencies were lower than the values reported in previous studies [23; 24; 37; 38].