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Photolytic and Photocatalytic Degradation of Organic UV Filters

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Photolytic and Photocatalytic Degradation of Organic UV Filters ACCEPTED MANUSCRIPT UV filters Removal technologies Use in personal care products formulations Biological Physical treatment Chemical treatment treatment processes e.g. reverse Hybrid processes processes processes osmosis, adsorption, Personal use on skin membrane separation Degradation by ozonation, catalysis, halogination, hypochlorite treatments, free Protect from UV radical treatments such as hydroxyl etc. Associated secondary irradiation risks/ impacts/ n environmental fate Advanced chemical o i t processes such as a d Transport to aquatic photolysis, photocatalysis , a r Degradation byproducts environment g photolysis in H 2O2 e d o t o h Associated risks/ impact/ P Future research need environmental fate MANUSCRIPT ACCEPTED ACCEPTED MANUSCRIPT 1 Photolytic and Photocatalytic Degradation of Organic UV Filters 2 in Contaminated Water 3 4 5 Mohammad Boshir Ahmed, Md Abu Hasan Johir, John L Zhou*, Huu Hao Ngo, Wenshan 6 Guo, Kireesan Sornalingam 7 8 9 School of Civil and Environmental Engineering, University of Technology Sydney, 15 10 Broadway, NSW 2007, Australia 11 12 13 14 MANUSCRIPT 15 16 17 Corresponding author: 18 Prof John L Zhou 19 School of Civil and Environmental Engineering 20 University of Technology Sydney 21 15 Broadway, NSWACCEPTED 2007 22 Australia 23 Email: [email protected] 24 1 ACCEPTED MANUSCRIPT 25 Abstract 26 UV filters as emerging contaminants are of great concern and their wide detection in aquatic 27 environments indicates their chemical stability and persistence. This review summarized the 28 photolytic and photocatalytic degradation of UV filters in contaminated water. The findings 29 indicated that limited research has been conducted on the photolysis and photocatalysis of UV 30 filters. Photolysis of UV filters through UV irradiation in natural water was a slow process, 31 which was accelerated by the presence of photosensitisers e.g. triplet state of chromaphoric 32 dissolved organic matter ( 3CDOM*) and nutrients but reduced by salinity, dissolved organic 33 matter (DOM) and divalent cations. UV Photocatalysis of 4-methylbenzylidene camphor and 34 2-phenylbenzimidazole-5-sulfonic acid was very effective with 100% removal within 30 min 35 and 90 min using medicated TiO 2/H 2O2 and TiO 2, respectively. The radiation source, type of 36 catalyst and oxygen content were key factors. Future research should focus on improved 37 understanding of photodegradation pathways and by-products of UV filters. 38 MANUSCRIPT 39 Keywords : Photodegradation products; Photocatalysis; BP-3; BP-4; 4-MBC 40 ACCEPTED 2 ACCEPTED MANUSCRIPT 41 1. Introduction 42 Different classes of UV filters (Table A1), extensively and increasingly used in recent years, 43 are vital formulations of sunscreens products [1-3]. UV filters have unique properties as they 44 can absorb, reflect and/or scatter UV radiation and thereby protecting our health. They are 45 also used as sun-blocking agents for the protection of materials such as plastics, adhesives and 46 rubber [2, 3]. UV filters are gaining growing interest due to their increased production and 47 consumption [4], and are considered emerging contaminants due to their increasing 48 concentrations in the aquatic environment and also for unknown risks associated with their 49 presence [5-7]. The main concern about these compounds is their potential toxicity and 50 adverse effects, namely as xenohormone affecting reproductive activity [8-11]. For example, 51 camphor derivative 4-MBC, as well as benzophenone derivative 2-hydroxy-4- 52 methoxybenzophenone (BZ-3) and 3,3,5-trimethylciclohexyl salicylate (Homosalate) have 53 shown multiple hormonal activities including estrogenic and antiestrogenic effects [12]. 54 Although recreational activities are direct input pathwaysMANUSCRIPT of UV-filters into the environment, 55 they can also come from washing, showering, rub-off to cloths, and subsequent laundering. 56 The occurrence of UV filters has been detected in river water, lake and sea water, 57 groundwater, sediments and even biota [13-26]. The concentrations of different organic UV 58 filters such as benzophenone-3 (BP-3), octocrylene, octyl-dimethyl-p-aminobenzoic acid 59 (ODPABA), 4-methylbenzylidene camphor (4-MBC), octyl methoxycinnamate, and butyl 60 methoxydibenzoyl methane are presented in Table 1 [27]. 61 Different methods have already been applied for the removal of UV filters. For example, 62 adsorptive removalACCEPTED of 4-tert -butil-4’-methoxydibenzoylmethane (avobenzone), homosalate, 63 4-MBC, ODPABA, octocrylene and 2-ethylhexyl 4-methoxycinnamate (EMC) (log Kow > 4.0) 64 onto primary sludge showed 30-70% removal efficiencies [16,28,29]. Coagulation and 65 flocculation were not found to be effective methods for the removal of 2,4- 66 dihydroxybenzophenone (BP-1) and 2-hydroxy-4-methoxy benzophenone-5-sulfonic acid 3 ACCEPTED MANUSCRIPT 67 (BP-4) [16, 17]. Balmer et al. [30] showed moderate to lower concentrations of 4-MBC, 68 octocrylene and EMC in the effluent after mechanical, biological, chemical and sand 69 filtration. Liu et al. [28] investigated 6 UV filters (BP-3, 4-MBC, EMC, UV-326, UV-329, 70 octocrylene) in a full-scale municipal wastewater treatment plant (WWTP) which consisted of 71 primary sedimentation and secondary activated sludge treatment in South Australia; after 72 extended period of application they observed the removal efficiencies of 5-82% [29]. 73 Disinfection process also showed poor removal efficiencies (17-25%) of BP-3, 4-MBC, EMC 74 and octocrylene [31]. Ozonation of BP-3 generated seven intermediate products (Figure A1) 75 [32]. Further, chlorination process was not efficient in removing most compounds from 76 wastewater [16, 17]. Moreover, halogenation of BP-3 and BP-4 generated halogenated by- 77 products which may be of additional concern (Figure A2) [33, 34]. In comparison, reverse 78 osmosis showed the highest efficiencies (> 99%) in removing some UV filters [16,17]. 79 Membrane bioreactor showed excellent removal of BP-3 (> 96%) and octocrylene (67-96%) 80 with a hydraulic retention time of 26 h and sludge MANUSCRIPTretention time of 88 days [35]. 81 Thus, it can be stated that different physical and biological processes may not be effective 82 to remove UV filters from contaminated water. A few review articles on UV filters have been 83 published which mainly focused on the occurrence and fate of the UV filters in different water 84 [6, 29, 36-39]. However, no comprehensive review on the photolytic and photocatalytic 85 degradation of UV filters has been conducted. It is therefore necessary to understand the 86 photolytic and photocatalytic degradation mechanism of UV filters in contaminated water. In 87 this review we assess recent findings on the removal of UV filters through photolytic and 88 photocatalytic degradation,ACCEPTED focusing on the degradation pathways and effectiveness in 89 removing UV filters from contaminated water together with future perspectives. 90 4 ACCEPTED MANUSCRIPT 91 2. Photolytic and photocatalytic degradation of UV filters 92 Photodecomposition is one of the most important abiotic processes affecting the fate of UV 93 absorbing compounds in the aquatic environment and photocatalysis has been suggested as an 94 effective method to degrade UV filters [40]. However, UV filters transformation appears to be 95 a complex process, barely addressed to date as they designed not to be degraded in UV light. 96 The photodegradation of UV filters may produce transformation products which pose 97 additional environmental stress. The mechanisms of photodegradation of UV filters include 98 (i) direct or indirect photolysis by the dissociation of adsorbing molecule and produced free 99 radicals or reactive fragments, and (ii) photo-isomerization which yields species that probably 100 absorb less UV light than the parent species [27]. 101 Among different classes of UV filters, photodegradation and photo-stability of 102 benzophenone derivatives UV filters has been studied extensively using OH • [40, 41]. Typical 103 surface-water conditions, direct photolysis and reactions with OH • and 3CDOM* would be the 104 main processes of BP-3 photo-transformation. TheMANUSCRIPT reaction with OH • would prevail at low 105 dissolved organic carbon (DOC) concentration, direct photolysis at intermediate DOC 106 concentration (5 mg L−1), and reaction with excited 3CDOM* at high DOC concentration. 107 Furthermore, two methylated derivatives were tentatively identified which were probably 108 produced by reactions between BP-3 and fragments arising from photodegradation [42]. In 109 another study, other intermediates such as benzoic acid (maximum concentration ~10% of 110 initial BP-3) and benzaldehyde (1%) were identified [34]. Gago-Ferrero et al. [40] reported 111 that after 24 h of UV irradiation, BP-3 was not photodegraded but BP-1 was readily 112 photodegraded. ACCEPTEDSimilarly, Rodil et al. [41] observed high stability of BP-3, which was further 113 confirmed under UV and artificial solar light [43]. Liu et al. [43] also observed solar radiation 114 exposure of 50 days resulted in 8% loss of BP-3 in pure water; however, the loss was almost 115 31% in solution containing 50 mg L -1 of humic acid. They identified one major photoproduct 116 as 2,4-dimethylanisole, formed by the loss of hydroxyl and benzoyl groups (Figure A3). 5 ACCEPTED MANUSCRIPT 117 Laboratory-scale irradiation experiments revealed that photodegradation of benzophenones 118 [benzophenone (BP), 4-hydroxybenzophenone (4H-BP), BP-3, BP-1 and 2,2'-dihydroxy-4-
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