Effect of metal complexation on the degradation of dithiocarbamate fungicides

When dithiocarbamate fungicides are released to the environment, it is assumed that they degrade within days to weeks via acid-catalyzed hydrolysis. However, the formation of complexes between dithiocarbamates and trace elements can slow transformation reactions. Experiments performed with a component of the fungicide Ziram, dimethydithiocarbamate (DMDC), indicate that complexation by cadmium, copper, or zinc inhibit acid-catalyzed hydrolysis. Evaluation of the stability constant for the complexes between the metal and DMDC indicate that copper is the only metal that is most likely to inhibit the transformation reactions under conditions encountered in the environment. Measurement of the transformation of DMDC and ethylenebis(dithiocarbamate) (EBDC) in the presence of trace amounts of Cu(II) yielded half lives greater than 2 weeks, irrespective of pH. Experiments performed in surface water samples indicate that, when DMDC is discharged to natural waters in an uncomplexed form, it may not be stabilized by the Cu(II) present in the water, possibly because natural organic matter outcompetes DMDC for Cu(II). When DMDC is complexed by Cu(II) before it is released to natural waters, the compound is more persistent because acid-catalyzed hydrolysis is inhibited.