RAMAN AND SURFACE-ENHANCED RAMAN-SPECTROSCOPY OF DITHIOCARBAMATE FUNGICIDES

The Fourier transform Raman and surface-enhanced Raman spectra on silv er colloid of the dithiocarbamate fungicides thiram, ziram, metiram, z ineb and mancozeb are reported. Surface-enhanced Raman spectroscopy (S ERS) affords good quality vibrational spectra of these fungicides at v ery low aqueous concentrations. A degradation of these fungicides when interacting with the silver surface can be deduced: thiram and metira m 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 manco zeb, as deduced from their weaker SERS. These results have a significa nt importance as regards the understanding of the potential environmen tal impact of these molecules. According to our findings, these fungic ides 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 concentr ations and different excitation wavelengths, revealing that two differ ent coordination complexes having different geometries (monodentate an d bidentate) are possible on the silver surface. (C) 1998 Elsevier Sci ence B.V. All rights reserved.