Photodegradation of the fungicide thiram in aqueous solutions. Kinetic studies and identification of the photodegradation products by HPLC–MS/MS O.M.S. Filipe a , Sónia A.O. Santos b , M. Rosário M. Domingues c , M.M. Vidal a , A.J.D. Silvestre b , C.P. Neto b , E.B.H. Santos d,⇑ a CERNAS, Department of Basic Sciences, ESAC, Bencanta, 3040-316 Coimbra, Portugal b CICECO, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal c Mass Spectrometry Center, QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal d CESAM, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal highlights " The photodegradation of thiram followed a pseudo-first order kinetics. " Formulation components have a significant effect on the photodegradation of thiram. " Organic matter enhance the photodegradation rate of thiram. " In natural water other natural components can influence thiram photodegradation. " Three products of the photodegradation of thiram were identified by HPLC–MS n . article info Article history: Received 21 September 2012 Received in revised form 10 January 2013 Accepted 20 January 2013 Available online 7 March 2013 Keywords: Thiram Photodegradation Humic substances Kinetics HPLC–MS/MS abstract In this study, the relevance of photodegradation processes on the persistence of the fungicide thiram in waters was investigated. The photodegradation of thiram in Milli-Q water and in aqueous solutions of humic and fulvic acids, as well as the photodegradation in spiked river water were studied. Both pure thi- ram and one of its commercial formulations were used to prepare the solutions which were irradiated in a solar light simulator. In general, thiram photodegradation follows pseudo-first order kinetics. The half-life time of thiram 2 mg L 1 in Milli-Q water was 28 min. However, the degradation rate of thiram was signif- icantly increased (p = 0.02) by the inert components of the thiram commercial formulation as well as by commercial humic acids and by fulvic acids isolated from river water (p < 0.004). Thus, the half-life time of thiram decreased to 24 min in the presence of the inert formulation components, while, in the presence of both humic and fulvic acids (10 mg L 1 ) it decreased to 22 min. Furthermore, thiram photodegradation in natural river water showed that there is a significant enhancement of the degradation rate constant of thiram relatively to Milli-Q water, corresponding to a decrease of about 38% in its half-life time. This increase of the degradation rate in river water seems to be higher than that observed in the presence of FA, suggesting that beyond organic matter, other natural river components can increase the thiram photo- degradation rate. These results allow us to conclude that photodegradation by solar radiation can be an important degradation pathway of thiram in natural waters. HPLC–MS/MS allowed to identify, for the first time, three products of the photodegradation of thiram in aqueous solution. Three compounds were iden- tified and their structure was corroborated by the MS n spectra fragmentation profile. Pathways for the for- mation of the products from thiram photodegradation are proposed and discussed. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The environmental impact of organic pollutants, such as pesti- cides, has raised a growing concern over the years, mainly due to the world wide application of intensive agriculture methods and to the development of the agrochemical industry. Thus, informa- tion about possible degradation pathways of pesticides in the envi- ronment is important in order to understand their transport and fate in surface and ground waters and to identify the degradation products to which they can give rise. Photodegradation is one of the factors that can affect the environmental behaviour and 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.01.092 ⇑ Corresponding author. Tel.: +351 234370725. E-mail address: edsantos@ua.pt (E.B.H. Santos). Chemosphere 91 (2013) 993–1001 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere