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

Abstract

The fungicides Ziram and Maneb (class dithiocarbamate) are organic Zn and Mn complexes in which the trace metal is chelated to organic dithiocarbamate ligands. The resulting organic metal complex is small, neutrally charged, and lipophilic in character. Short-term uptake experiments 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, Cu 2ϩ and Pb 2ϩ ions in seawater solution undergo exchange reactions with Zn and Mn and form lipophilic organic Cu and Pb complexes that also diffuse across the plasma membrane and into the cytosol of the cell. Intracellularly, these trace metals are thought to dissociate from the transport ligand and complex intracellular ligands. Based on these results, the presence of dithiocarbamate fungicides in surface water can inadvertantly enhance the passive uptake of a variety of toxic heavy metals from the water into microorganisms.

When are metal complexes bioavailable?

“…For example, whereas (CH 3 ) 2 their bioaccumulation by a marine alga (Thalassiosira weissflogii) is lower, presumably because elemental mercury and dimethylmercury do not readily form complexes with intracellular ligands. [12] Generally speaking, the observed uptake rates of lipophilic metal complexes are usually at least an order of magnitude higher than their hydrophilic metal counterparts, [10,11,16,17] which makes this mechanism potentially important for certain metals. Furthermore, uptake is sensitive to the pH of the medium, with a decreased bioaccumulation of the lipophilic metal complexes at low pH, potentially due to a reduction in the electrostatic repulsion between adjacent phospholipids, leading to their tighter packing and a decreased membrane permeability.…”

Influences of metal‐ligand complexes on the cadmium and zinc biokinetics in the marine bacterium, Bacillus firmus

“…One likely route for the internalization of lipophilic metal complexes is the passive diffusion pathway. Phinney and Bruland [13,14] suggested that lipophilic organic metal (Cu, Cd, Pb) complexes could enter the coastal diatom Thalassiosira weiss‐flogii via direct passive diffusion. In addition, Croot et al [25] also demonstrated that the uptake of lipophilic complex Cu‐64‐oxine was by passive diffusion across the plasma membrane of five marine phytoplankton species.…”

“…All these ligands can bind with Cd and Zn to form hydrophilic ligand‐metal complexes with relatively low molecular weights (less than 500 Da). Previously, Phinney and Bruland [12,13] reported that lipophilic organic Zn, manganese, copper, and lead complexes could diffuse across the plasma membrane of marine diatoms. To determine whether lipophilic metal complexes are also bioavailable to Bacillus firmus and if they act as other possible metal uptake pathway, lipophilic ligands, 8‐hydroxyquinoline (Ox − ) and diethyldithiocarbamate (DDC) were used to complex with Cd and Zn to form small, neutrally charged, lipophilic organic ligand‐metal complexes in another uptake experiment.…”

Metals as Water Quality Parameters – Role of Speciation and Bioavailability

“…Hydrophobic metal complexes may directly diffuse through the cell membrane and thus may contribute to higher uptake fluxes of metals (Croot et al, 1999;Phinney and Bruland, 1997). Hydrophobic metal complexes may directly diffuse through the cell membrane and thus may contribute to higher uptake fluxes of metals (Croot et al, 1999;Phinney and Bruland, 1997).…”