Triclosan breakdown by Fenton-like oxidation Macarena Munoz ⇑ , Zahara M. de Pedro, Jose A. Casas, Juan J. Rodriguez Ingenieria Quimica, Universidad Autonoma de Madrid, Crta. Colmenar km 15, 28049 Madrid, Spain highlights " Fenton-like process is an efficient alternative for triclosan breakdown. " Triclosan is more susceptible to Å OH attack than chlorophenols. " Aromatic byproducts formed during reaction evolved rapidly to organic acids. " All the reaction products obtained showed lower ecotoxicity values than triclosan. " Fenton oxidation of triclosan leads to a dramatic decrease of ecotoxicity. article info Article history: Received 27 February 2012 Received in revised form 17 May 2012 Accepted 18 May 2012 Available online 5 June 2012 Keywords: Advanced oxidation Fenton-like process Emerging pollutants Triclosan Ecotoxicity abstract Fenton-like oxidation has proved to be highly efficient for the removal of triclosan, a highly toxic emerg- ing water pollutant. From 10 mg/L starting aqueous solutions complete conversion of triclosan was achieved in less than 1 h at 25 °C and around 20 min at 50 °C with 1 mg/L Fe 3+ and H 2 O 2 at the theoretical stoichiometric amount (25 mg/L). From the evolution of byproducts a reaction pathway has been pro- posed according to which oxidation of triclosan gives rise to several aromatic intermediates (mainly, p-hydroquinone of triclosan and 2,4-dichlorophenol) which evolve to short-chain organic acids. These compounds are mineralized except oxalic acid. A dramatic decrease of ecotoxicity was achieved in a rel- atively short time (more than 95% in 15 min at 35 °C). The evolution of ecotoxicity is intimately related to the disappearance of triclosan, much more toxic than the aromatic oxidation intermediates. This disap- pearance was successfully described by a simple pseudo-first order rate equation with an apparent acti- vation energy value close to 27 kJ/mol. The apparent rate constant at 25 °C was several orders of magnitude higher than the reported in the literature for other chlorophenolic compounds indicating a higher susceptibility of triclosan to OH radical attack. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction In recent years, there has been increasing concern regarding the emerging pollutants such as pharmaceuticals and personal care products, surfactants, flame retardants, industrial additives, ste- roids and hormones and disinfection by-products. These pollutants correspond in many cases to unregulated contaminants, which may be candidates for future regulation depending on research on their potential health effects and monitoring data regarding their occurrence. These hardly biodegradable products, resistant to conventional biological treatment in sewage plants, have been found in their effluents at concentrations ranging 0.1–20 lgL 1 [1,2]. A particularly relevant example of such emerging pollutants is triclosan, 5-chloro-2-(2,4-dichlorophenoxy)phenol, commer- cially known as Irgasan DP 300 or Irgacare MP [3], a synthetic broad-spectrum antimicrobial agent. Its antibacterial activity is associated to its capacity to block lipid biosynthesis by specifically inhibiting the enzyme enoyl-acyl carrier protein reductase [4,5]. Due to its high antimicrobial action, triclosan has been incorpo- rated into a vast array of products (toothpaste, mouthwash, soaps and household cleaners), especially in the last 15 years and thus has been detected in municipal wastewater, where in spite of its low levels has been reported as refractory to conventional biolog- ical treatments [3,6,7] thus being usually discharged to surface water bodies. This can involve serious environmental implications derived from its toxicity to several water-living organisms such as fish (LC 50 rainbow trout = 0.35 mg/L) [8], algae i.e., Scenedesmus subspicatus [3] or microorganisms like Daphnia magna (EC 50 = 0.39 mg/L) [8]. Evidences of estrogenic effects have also been observed by several authors [9,10]. Moreover, the presence of triclosan in water can lead to the formation of chloroform and related trihalomethanes as well as chlorinated dioxins from chlorine disinfection [7,11]. In order to complete the treatment of urban wastewaters con- taining triclosan, several works in the literature have proposed 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.05.097 ⇑ Corresponding author. Tel.: +34 91 497 3991; fax: +34 91 497 3516. E-mail address: macarena.munnoz@uam.es (M. Munoz). Chemical Engineering Journal 198–199 (2012) 275–281 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej