TRACE-METAL EXCHANGE IN SOLUTION BY THE FUNGICIDES ZIRAM AND MANEB (DITHIOCARBAMATES) AND SUBSEQUENT UPTAKE OF LIPOPHILIC ORGANIC ZINC, COPPER AND LEAD COMPLEXES INTO PHYTOPLANKTON CELLS

The fungicides Ziram and Maneb (class dithiocarbamate) are organic Zn and Mn complexes in which the trace metal is chelated to organic dithi ocarbamate ligands. The resulting organic metal complex is small, neut rally charged, and lipophilic in character. Short-term uptake experime nts using a coastal diatom demonstrated that these lipophilic organic Zn and Mn complexes diffuse across the lipid bilayer that constitutes the plasma membrane. In addition, Cu2+ and Pb2+ ions in seawater solut ion undergo exchange reactions with Zn and Mn and form lipophilic orga nic Cu and Pb complexes that also diffuse across the plasma membrane a nd into the cytosol of the cell. Intracellularly, these trace metals a re thought to dissociate from the transport ligand and complex intrace llular ligands. Based on these results, the presence of dithiocarbamat e fungicides in surface water can inadvertantly enhance the passive up take of a variety of toxic heavy metals from the water into microorgan isms.