Raman and surface-enhanced Raman spectroscopy of dithiocarbamate fungicides

The Fourier transform Raman and surface-enhanced Raman spectra on silver colloid of the dithiocarbamate fungicides thiram, ziram, metiram, zineb and mancozeb are reported. Surface-enhanced Raman spectroscopy (SERS) affords good quality vibrational spectra of these fungicides at very low aqueous concentrations. A degradation of these fungicides when interacting with the silver surface can be deduced: thiram and metiram are cleaved at their disulphide bonds, while the metallic complexes ziram, zineb and mancozeb could undergo metal exchange with the silver on the surface. Decomposition is lower in the case of zineb and mancozeb, as deduced from their weaker SERS. These results have a significant importance as regards the understanding of the potential environmental impact of these molecules. According to our findings, these fungicides can be decomposed in the environment and could be converted into dimethyldithiocarbamate and ethylenebisdithiocarbamate ions. The SERS study of these compounds was carried our at several adsorbate concentrations and different excitation wavelengths, revealing that two different coordination complexes having different geometries (monodentate and bidentate) are possible on the silver surface. (C) 1998 Elsevier Science B.V. All rights reserved.