Journal of Molecular Catalysis A: Chemical 401 (2015) 13–17 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical jou rn al hom epage: www.elsevier.com/locate/molcata Heterogeneous catalysis Alkaline hydrolysis of vinclozolin: Effect of humic acids aggregates in water J. Morales a,∗ , A. Cid b , J.C. Mejuto a a Department of Physical Chemistry, Faculty of Sciences, University of Vigo, 32004 Ourense, Spain b Chemistry Department, REQUIMTE-CQFB, Faculty of Science and Technology, New University of Lisbon, 2829-51-6 Monte da Caparica, Portugal a r t i c l e i n f o Article history: Received 25 September 2014 Received in revised form 15 February 2015 Accepted 16 February 2015 Available online 19 February 2015 Keywords: Vinclozolin Humate aggregates Colloids Humic substances Hydrolysis a b s t r a c t The influence of natural organic substances as humate colloidal aggregates in water solutions upon the chemical stability of vinclozolin has been investigated in basic media. A large inhibition (9 times- fold) has been observed and it has been rationalized in terms of a micellar pseudophase model. The observed behaviour could increase significantly the half-life of this fungicide. Moreover, these experi- mental results have been compared with the corresponding ones of other substances in these natural colloidal aggregates. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Vinclozolin (V) is a dicarboxamide non-systemic pesticide (Scheme 1) used to control fungal diseases, blights, rots and moulds in vineyards (grapes), fruits (strawberries, raspberries and kiwi), vegetables (snap beans, lettuce and onions) or dif- ferent types of ornamentals [1–5]. It may also be used on turf grass for golf courses [6]. Being highly effective against common fungi caused by Botrytis spp., Sclerotinia spp. or Monilinia spp. [7–9]. It is well known that this fungicide is moderately per- sistent in soil [10] and it is only partially broken down by soil microorganisms [11–13]. Vinclozolin may degrade [14] to 3 ′ ,5 ′ - dichloro-2-hydroxy-2-methylbut-3-enanilide (see Scheme 1A) or 2-[(3,5-dichlorophenyl)-carbamoyl]oxy-2-methyl-3-butenoic acid (see Scheme 1B). Both reactions will continue to degrade to a third degradation product, 3,5-dichloroaniline (see Scheme 1C). In water, it can be degraded by photolysis and/or hydrolysis processes, which are favoured under neutral or basic conditions [15]. The acute median lethal dose (LD 50 ) for V is greater than 15,000 mg kg −1 in rats [10]. Humic substances, and more specifically humate colloidal aggregates (HCAs), represent a large portion of organic matter ∗ Corresponding author. Tel.: +34 988 387031; fax: +34 988 387001. E-mail addresses: morales@uvigo.es (J. Morales), acids@uvigo.es (A. Cid), xmejuto@uvigo.es (J.C. Mejuto). in natural environments and soils [16,17]. In fact, these organic colloids include highly decomposed organic matter generally more known as humus. Their nature as colloids and their behaviour in solution is quite similar to the micellar aggregates [18–20]. Their ability to absorb or adsorb different types of pollutants, both organic and inorganic, made reconsider the use of these substances from a chemical point of view, since traditionally they were considered carriers. The adsorption properties and the respective compart- mentalization of different substrates by humic substances cause changes in the chemical reactivity when a reaction occurs in the presence of these kind of colloidal aggregates [21]. Therefore, to understand the role that humate aggregates currently have in envi- ronmental processes, it requires the knowledge of their role from a chemical kinetic view [22] because they can act as solvents, and toxic reagents scavengers or natural catalysers. Furthermore, it has been considered that the primary route of elimination of organic xenobiotics such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pesticides or other substances is related to the microorganism activity found in soil, neglecting the essential importance of humus. However, the properties of these humate aggregates and their catalytic capacity can be assumed the need to consider other means of disposal [23–29]. New insights in the V reactivity, which is widely used in agricul- ture, on the basis of a pseudophase model, were carried out because the major composition of the organic matter in soils is HCAs [30] and, moreover these compounds are also present in some condi- tions in the natural waters [31]. Thus, the aim of the present work http://dx.doi.org/10.1016/j.molcata.2015.02.017 1381-1169/© 2015 Elsevier B.V. All rights reserved.