## 1 Introduction  
Synthetic musk fragances (SMFs) are synthetic aromatic compounds that are used in the perfume industry to mimic the scent of deer and other animals [1, 2]. Synthetic musks are categorized as nitro, macrocyclic, polycyclic, or alicyclic musk according to their chemical structure and the synthesis methods [3, 4]. Nitro musk was synthesized by [PERSON] in 1888, but its use is now restricted due to its proven harmful effects on humans and the environment [5, 6]. Macrocyclic musk is difficult to synthesize, and expensive, because it has a complex chemical structure. In contrast, polycyclic musk is relatively inexpensive to synthesize and is known to be safer than nitro musk; it accounts for more than 90% of all synthetic musk used currently [2, 7]. The amount of polycyclic musk used in Korea in 2006 was reported to be 60.6 tons for 4,6,6,7,8,8-hexamethyl-1,3,4,7-tetrahydrorocyclopent(g)isochromene (HHCB) and 2 tons for 1-(3,5,5,6,8,8-hexamethyl-6,7-dihydronathalen-2-yl)ethanone (AHTN). The most commonly used nitro musks are musk ketone (MK; 1-(4-tert-butyl-2,6-dimethyl-3,5-dinitrophenyl) ethanone) and musk xylene (MX;1-tert-butyl-3,5-dimethyl-2,4,6-trinitropbenzene; 11.6 and 0.9 tons of these musks were used in 2006, respectively [8, 9]. This indicates that on a volume basis, polycyclic musk is more widely used than nitro musk in Korea. Given that the total amount of chemical substances used in 2016 increased by 40% compared to 2010 [10], the amount of SMFs used in personal care products (PCPs) might now be much more than in 2006 when the survey was originally conducted. The annual usage of HHCB increased by more than six times in 2016 compared to 2006 [11]. Because SMFs are difficult to chemically degrade, they can persist in the environment. Synthetic musk fragrances are also lipophilic, so they can accumulate in the adipose tissues of humans and aquatic animals. Several researchers have raised concerns about the safety of HHCB and AHTN following their detection in human fat cells, milk, and even breast milk [7,12]. Other studies have confirmed that nitro musk can act as a weak endocrine disruptor [6]. In a rat study, it was also confirmed that nitro musk compounds can increase the incidence of various cancers, and their toxicity is enhanced when they are present together with other toxic substances, such as benzo-a-pyrene [6]. Additionally, Xenobiotic metabolism on fish, estrogenic effect on zebrafish, and acute toxicity on medaka by SMFs have been reported [13, 14, 15]. Therefore, the European Chemical Agency has determined the predicted no effect concentration (PNEC) values for the aqueous phase (PNECwater) for several SMFs (HHCB, 4.4 \(\mu\)g/L; AHTN, 2.8 \(\mu\)g/L; MX, 1.1 \(\mu\)g/L; and MK, 1.0 \(\mu\)g/L) [16, 17, 18, 19]. The United States Environmental Protection Agency (US EPA) also lists SMFs on the inventory list of the Toxic Substances Control Act (TSCA) because they have negative effects on human health and the environment, including endocrine-disrupting effects [20]. Musk xylene, HHCB, and AHTN are included in the Substances of Very High Concern (SVHC) list as very persistent and very bioaccumulative (vPvB) substances. The European Chemicals Agency (ECHA) has classified HHCB as an acute and chronic aquatic toxic substance, while MX and MK have been classified as acute and chronic aquatic toxic substances and carcinogens [21]. It is therefore important to determine the levels, and the fate and behavior, of SMFs in the aquatic environment. Because SMFs are widely used as scented raw materials in household PCPs, more than 90% of the total amount of SMFs used in households enters domestic sewage treatment plants (STPs). Untreated SMFs in STPs can contaminate surface waters through STP effluents. The SMF concentrations in the receiving water can be affected by the sewage treatment process and their removal efficiencies in STPs. Several studies have reported the occurrence of SMFs in sewage effluents in several STPs [7, 22, 23, 24, 25, 26].