## 1 Introduction  
In recent years, skin cancer has attracted widespread attention owing to a series of risks related to ultraviolet (UV) radiation, sunburn, and premature skin aging [1]. Thereby UV filters are widely used in personal care products (PCPs) as UV-absorbing (shielding) agents that protect against UVA and UVB radiation and protect human health [2]. Most PCPs such as cosmetics, sunscreens, hair care products, detergents, etc., contain one or more UV filters in everyday products that are closely related to our lives. These organic UV filters are prone to the persistent pollution of the environment due to their large dosage, stable physical and chemical properties, and resistance to degradation. Those UV filters have become a new class of contaminants as they continue to enter the environment daily [3]. Residues of organic UV filters have been detected in various media such as surface water, sediment and aquatic organisms [4; 5; 6; 7]. Several studies have shown that UV filters have potential endocrine disrupting effects that adversely affect organisms such as human tissues, mammals, animals, and fish, and cause serious health threats [8; 9; 10; 11]. UV filters are relatively stable in nature and are resistant to biodegradation, making it difficult for municipal wastewater treatment plants (MWTPs) to remove them thoroughly [12; 13; 14]. Among them, \(p\)-aminobenzoic acid (PABA)-type compounds are the earliest and most widely used sunscreen products, thus their exposure characteristics, ecological effects and environmental behavior have become research hotspots in environmental fields in recent years [15; 16]. They can exist for a long time and are dispersed in the environment due to their relatively high photochemical stability and low biodegradability. Thus, it is urgent to find efficient ways to remove PABA-type UV filters thoroughly. In recent years, advanced oxidation technology based on sulfate radicals (SR-AOPs) has become a new research hotspot, and it has some practical applications at home and abroad [17]. Persulfate (PS), used to produce sulfate radicals (SO4\({}^{\bullet-}\)), is new type of oxidant used in in-situ chemical oxidation [18]. PS, including peroxymonosulfate (PMS) and peroxdyisulfate (PDS), can be activated by ultraviolet light (UV) [19], ultrasound, heat [20], transition metal ions or their oxides [21; 22; 23; 24; 25; 26; 27; 28], and nanocarbon [29; 30; 31]. Compared with hydroxyl radicals (\({}^{\bullet}\)OH), SO4\({}^{\bullet-}\) has higher redox potentials (E\({}_{0}\) = 2.60 V) at neutral pH value that can effectively remove organic contaminants in water via an oxidation reaction. UV-based AOPs have great potential due to their high treatment efficiency, non-toxicity and low cost. Many researchers [32; 33] used the UV-activated persulfate process to study the removal of refractory organic pollutants. Since UV technology has been widely used in MWTPs, it is advantageous to use UV to activate persulfate. In this case, UV cannot only disinfect and sterilize the water [34], but also activate persulfate to produce strong oxidizing SO4\({}^{\bullet-}\) to remove organic pollutants, thus it is more practical to study UV-activated persulfate to remove PABA-type UV filters [35]. However, previous studies have been mainly focused on the photocatalytic degradation of PABA [36; 37; 38; 39] or ethyl 4-aminobenzoate (Et-PABA) [40], one of the typical PABA-type UV filters. Information regarding the SO4\({}^{\bullet-}\) degradation process of Et-PABA is limited, which hinders the application of this technique in PABA-type UV filter treatments. In this paper, the UV-activated PDS process was used to remove Et-PABA. The effects of PDS dosage, pH value, humic acid (HA) and other factors on the removal of Et-PABA during the UV/PDS process were investigated. The degradation intermediates of Et-PABA were identified and the possible degradation pathways were proposed.