Received: 28 July 2010 Revised: 14 October 2010 Accepted: 15 October 2010 Published online in Wiley Online Library: 00 Month 2010 Investigation of the dissociation pathways of metolachlor, acetochlor and alachlor under electron ionization – application to the identification of ozonation products Ste ´ phane Bouchonnet 1 * , Said Kinani 1 , Yasmine Souissi 1 , Sophie Bourcier 1 , Michel Sablier 1 , Pascal Roche 2 , Ve ´ ronique Boireau 3 and Vale ´ rie Ingrand 3 1 Laboratoire des Me ´ canismes Re ´actionnels UMR-7651, Ecole Polytechnique, 91128 Palaiseau Cedex, France 2 Anjou Recherche – Veolia Environnement Recherche et Innovation, Chemin de la Digue, BP 76, 78603 Maisons-Laffitte Cedex, France 3 Centre d’Analyses Environnementales – Veolia Environnement Recherche et Innovation, 1 Place de Turenne, 94417 Saint Maurice Cedex, France With the future aim of using gas chromatography coupled with mass spectrometry to characterize the transformation products of ozonated herbicides: metolachlor, acetochlor and alachlor, an interpretation of their electron ionization mass spectra is presented. Fragmentation mechanisms are proposed on the basis of isotopic labelling and multi- ple-stage mass spectrometry experiments carried out on an ion trap mass spectrometer. We also give examples in order to demonstrate how the elucidation of such fragmentation mechanisms for herbicides may simplify the character- ization of their ozonation products. Copyright ß 2010 John Wiley & Sons, Ltd. The contamination of soils, ground and/or surface water by chlorinated herbicides, used in agriculture as the principal weapon against pests, disease and weed infestation, is of growing environmental concern. [1–4] Several of these agrochemical compounds are considered to be a threat both to the environment and to human health. Herbicide- contaminated lands and farming areas may require remedia- tion to mitigate the contamination of water resources. Some acetanilide herbicides, metolachlor [2-chloro-N-(2-ethyl-6- methylphenyl)-N-(2-methoxy-1- methylethyl)acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and acetochlor [2-chloro- N-(ethoxymethyl)- N-(2-ethyl-6-methyl- phenyl)acetamide], are widely used to control annual grasses and yellow nutsedge, and to manage small-seeded broad leaf weeds. Their widespread use has resulted in their frequent detection in water sources near agriculture areas [5,6] where those compounds are exposed to leaching and urban runoff. While their control role in agriculture is necessary, their persistence in soil and the emergence of potential breakdown products are undesirable side effects that may lead to serious ecological and human problems. Recently, those herbicides and their degradation products have been demonstrated to be potential endocrine disruptors (EDCs). The routes of human exposure to endocrine disruptor pesticides have been discussed. [7] Herbicides are considered as EDCs of increasing concern as they threaten environmental equilibrium as well as wildlife and human health; cases of birth defect and infertility have been reported. [8,9] Metolachlor, alachlor and acetochlor were shown to interact with the endocrine system. Hladik et al. [10] pointed out that neutral by-products of chloroace- tamide herbicide require closer attention as they are considered to be micropollutants that have to be regulated in drinking water. [11] These compounds have been reported to possess at least a low level of persistency and they may affect organisms because of their toxic or other deleterious effects. [12] The presence of EDCs including trace levels of metolachlor has also been reported in some treated drinking waters. [13,14] Several water treatment procedures for the removal of EDCs with different treatment efficiencies have been reported. [15–19] Ozonation is one of the major methods that has been described for alachlor remediation. [20–25] The toxicity of ozonated alachlor solutions was slightly reduced compared with that of untreated ones. Different degradation pathways of alachlor by ozonation were proposed; they mainly include oxidation of the arylethyl group, N-dealkylation, cyclization and cleavage of the benzene ring. [24] In another study, the ozonation of alachlor resulted in the formation of several organic aromatic intermediates which underwent further oxidation to more refractory and short-chain mono- and dicarboxylic acids such as acetic acid, propionic acid and oxalic acid. [23] Several degradation products of alachlor obtained by other removal process from aqueous systems such as photolysis and photocatalysis, [26–29] photo-Fenton degradation, [30] ultrasonic degradation, [31,32] as well as hydrodynamic cavitation, [33] have been described. In contrast, few studies have reported approaches for the removal of metolachlor and alachlor. For those two herbicides, photodegradation has been found to be the main degradation procedure. [34–39] However, few break- down products and degradation pathways have been described for these compounds. [29,35,39] Two other studies Rapid Commun. Mass Spectrom. 2011, 25, 93–103 (wileyonlinelibrary.com) DOI: 10.1002/rcm.4832 Research Article * Correspondence to: S. Bouchonnet, Laboratoire des Me ´canismes Re ´actionnels UMR-7651, Ecole Polytechnique, 91128 Palaiseau Cedex, France. E-mail: stephane.bouchonnet@dcmr.polytechnique.fr Rapid Commun. Mass Spectrom. 2011, 25, 93–103 Copyright ß 2010 John Wiley & Sons, Ltd. 93