Photolytic degradation of triclosan in freshwater and seawater Kazushi Aranami a,b, * , James W. Readman b a National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-0053, Japan b Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, Devon PL1 3DK, United Kingdom Received 24 November 2005; received in revised form 23 June 2006; accepted 7 July 2006 Available online 22 August 2006 Abstract A 12-days photolysis experiment of triclosan, a widely used bactericide, was performed in freshwater and seawater under a low inten- sity artificial white light source. Photodegradation of triclosan was observed in both the freshwater and seawater samples. Assuming a first-order reaction, half-lives of triclosan in the freshwater and seawater were approximately 8 and 4 days, respectively. 2,8-Dic- hlorodibenzo-p-dioxin (DCDD) was detected in both the freshwater and seawater samples after 3 days of irradiation. The photodegra- dation of triclosan and the production of DCDD suggest that triclosan could be less stable and DCDD might be more stable in seawater than freshwater. As a result, DCDD produced from triclosan survives for a longer time in seawater. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Triclosan; 2,8-Dichlorodibenzo-p-dioxin; Photolysis; Freshwater; Seawater 1. Introduction Triclosan, 5-chloro-2-(2,4-dichlorophenoxy)phenol, com- mercially known as Irgasan DP 300 or Irgacare MP, is a broad-spectrum bactericide used in pharmaceutical and personal care products, e.g. toothpaste, mouthwash, medi- cal skin creams, hand-disinfecting soaps, deodorant, house- hold cleaners and textiles (sportswear, bed clothes, shoes and carpets). Recent studies suggest that triclosan blocks lipid biosynthesis by specifically inhibiting the enzyme enoyl-acyl carrier protein reductase and may induce bacte- rial resistance development (McMurry et al., 1998; Levy et al., 1999). Triclosan is non-volatile (5.3 · 10 4 Pa at 20 °C) and is relatively soluble in water (10 mg/l at 20 °C), in spite of its high octanol–water partition coefficient (log K ow of 4.8). In addition, the compound is quite stable against hydrolysis. Thus, triclosan is often detected in the aquatic environment, e.g. waste water, surface water and sediments (Lopez-Avila and Hites, 1980; Okumura and Nishikawa, 1996; Lindstro ¨m et al., 2002; McAvoy et al., 2002; Singer et al., 2002). Triclosan is acutely and chronically toxic to aquatic organisms. For rainbow trout, a median effective concentration (EC 50 ) of 350 lg/l and a no observed effect concentration (NOEC) of 34 lg/l have been reported (Adolfsson-Erici et al., 2002). For certain algae species, e.g. Scenedesmus subspicatus, the NOEC is 500 ng/l, which leads to a predicted no effect concentration (PNEC) of 50 ng/l (assuming the commonly used safety factor of 10) (Orvos et al., 2002). However, the environmental fate and behaviour of triclosan is not fully understood. Triclosan is a chlorinated phenoxyphenol with a pK a of 8.1 and is photodegradable in its phenolate form, whilst is photostable in its phenolic form. Photolysis of triclosan is a major removal pathway (Lindstro ¨m et al., 2002; Tixer et al., 2002) and is associated with the production of 2,8-DCDD (Latch et al., 2003; Mezcua et al., 2004). The pH of the surface water has a large influence on its speciation and hence on its fate and behaviour. Moreover, in the aquatic environment, the presence of co-solutes, 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.07.010 * Corresponding author. Present address: National Institute for Envi- ronmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-0053, Japan. Tel./fax: +81 29 8502902. E-mail address: arachan4553@hotmail.co.jp (K. Aranami). www.elsevier.com/locate/chemosphere Chemosphere 66 (2007) 1052–1056