Effect of copper ions on the degradation of thiram in aqueous solution: Identification of degradation products by HPLC–MS/MS

doi:10.1016/j.jhazmat.2014.06.051

Journal of Hazardous Materials

Volume 279, 30 August 2014, Pages 125-132

https://doi.org/10.1016/j.jhazmat.2014.06.051 Get rights and content

Highlights

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Cu(II) in excess accelerates the degradation of thiram in aqueous solutions.
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The [CuThi]²⁺ complex degrades into [(DMDTC)Cu]⁺ which readily decomposes.
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New degradation products of [CuThi]²⁺ were identified for the 1st time by HPLC–MSⁿ.
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Some degradation products are quite persistent, at least during 2 months.

Abstract

The aim of this work was to examine the effect of Cu(II) on the degradation of thiram (Thi) in aqueous solutions, since the literature focused on this effect is scarce and copper based fungicides can be applied together with thiram or during the same season to agricultural crops. The effect of Cu(II) on the degradation of thiram was followed by both UV–vis and HPLC–MS/MS. When thiram is dissolved in pure water its degradation occurs very slowly, being negligible during the first 7 days. However, the presence of Cu(II) has a strong influence on the thiram degradation in aqueous solutions along time. In the presence of an excess of Cu(II), a [CuThi]²⁺ complex is initially formed which degrades into a complex formed between the dimethyldithiocarbamate anion (DMDTC) and Cu(II) ion, [Cu(DMDTC)]⁺. This complex further degrades leading to other copper complexes which were identified for the first time, by MSⁿ. The results obtained in the present work also demonstrated that a redox reaction involving DMDTC anions and Cu(II) ions gives rise to the formation of a Thi–Cu(I) complex. Finally, some of the complexes resulting from the degradation of [CuThi]²⁺ are quite persistent in solution for long periods of time (>1 month).

Graphical abstract

Introduction

Pesticides are intensively used in agriculture and much effort is devoted to control and reduce possible damaging effects on the environment, such as contamination of soil and leaching to ground and surface waters, with the possible contamination of aquatic organisms, and, ultimately, contamination of water and food consumed by human beings, with the consequent toxic effects. The fate of a pesticide is determined by processes that affect mobility, such as sorption or volatilization, and those that affect persistence, including photo-, chemical and microbial degradation. According to the literature, the degradation products of some pesticides may be more toxic and persistent, representing a higher environmental risk than the parent compounds [1], [2]. To understand the fate of a pesticide in soil and water systems an accurate knowledge of its environmental behavior is essential.

Thiram, tetramethylthiuramdisulfide, is a dithiocarbamate compound that has been used as a contact fungicide with preventive action, worldwide applied not only in agriculture, but also in rubber industry as an accelerator and vulcanization agent [3], [4]. In Portugal, thiram was considered the second most popular contact fungicide of the dithiocarbamate group, after manconzeb. Dithiocarbamates contributed with ∼12% of the total sales of fungicides, followed by the copper-based fungicides (∼10%) [5].

Because of the worldwide use of Cu(II) based fungicides, copper effects on the behavior of some organic pesticides in environmental matrices have been object of attention [6], [7], [8], [9], [10]. However, the literature dealing with the effect of Cu(II) on the behavior of thiram in the environment is scarce [11], despite the fact that Cu(II) based fungicides are frequently applied in the same season and/or in the same crops as thiram, increasing the effectiveness of thiram fungicidal action. Recently, Gupta et al. [12], [13] studied the persistence of thiram in water and soil, under controlled conditions. However, in both studies there is no reference to the possible effect of metal ions, namely copper ions.

In our previous work [14], data about thiram recovery from natural waters showed fast thiram degradation in environmental matrices. Thiram was completely recovered (>80%) from river water samples when analyzed immediately after spiking but scarcely recovered when analyzed after one or two days. Several thiram recovery experiences in the presence of EDTA suggested that metal ions, namely copper ions, were involved in thiram degradation. This mechanism might be environmentally relevant since, as referred above, copper based fungicides are often applied either in the same season or in the same crops as thiram.

Thus, the aim of this work was to examine the effect of copper ions on the degradation of thiram in aqueous solutions. The effect of copper ions was studied during 1 or 2 months, following the UV–vis spectral changes of different thiram–Cu(II) mixtures. The identification of complexes formed over time was also studied by HPLC–MS/MS.

Section snippets

Chemicals and solutions

All chemicals used were of analytical grade and ultra-pure water was obtained using a Milli-Q water purification system (Millipore). Thiram (Thi, 97%) and acetonitrile (HPLC grade) were obtained from Aldrich and LabScan, respectively. Sodium dimethyldithiocarbamate solution (DMDTC, purum, ∼ 40% in H₂O) and cupric perchlorate hexahydrate were purchased from Fluka. Cupric acetate, used in the solutions preparation for MS analysis, was from May and Baker LTD. Aqueous thiram stock solutions 20 mg L⁻¹

Evaluation of thiram stability in aqueous solution

To evaluate thiram stability in aqueous solution, UV–vis spectra and pH values of a 2.0 mg L⁻¹ thiram aqueous solution were monitored during 1 month (Fig. S1A and S1B, respectively of the Supplementary data). The spectrum of a fresh thiram solution exhibits two absorption maxima, at 220 nm and at 272 nm, showing no significant changes up to the 7th day (Fig. S1A, curve a). For longer periods, the absorbance maximum at 272 nm begins to decrease and a new maximum appears at 207 nm (Fig. S1A, curve c).

Acknowledgments

O. Filipe wishes to acknowledge the PhD grant (SFRH/BD/39551/2007) from the Portuguese Science and Technology Foundation (FCT). S. A. O. Santos wishes to thank FCT and POPH/FSE for the postdoctoral grant (SFRH/BPD/84226/2012).

This work was supported by European Funds through COMPETE and by National Funds through the FCT within project PEst-C/MAR/LA0017/2013.

The authors also thank the financial support provided to CERNAS (PEst-OE/AGR/UI0681/2014), CICECO (PEst-C/CTM/LA0011/2013) and QOPNA

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Effect of copper ions on the degradation of thiram in aqueous solution: Identification of degradation products by HPLC–MS/MS

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals and solutions

Evaluation of thiram stability in aqueous solution

Acknowledgments

J. Environ. Sci.

Chemosphere

Environm. Poll.

J. Hydrol.

Sci. Total Environ.

Polyhedron