Biochelates as a Cause of Metal Cycling Across the Redoxcline

The sharp concentration peak of the metals Cu, Cd and Zn at the redoxcline of the Framvaren Fjord, Norway, is described as an effect of chelation/complexation with organic ligands. The most dominating ligand is 2-mercaptobenzothiazole (MBT), which binds with a 2 : 1 ligand to metal stoichiometric ratio. MBT has the highest concentrations at the vicinity of the redoxcline where the oxidation of sulfide to elemental sulfur and sulfate is most extensive. We suggest the production being caused by sulfide oxidizing bacteria as we have not been able to detect MBT in pure cultures of sulfate reducing bacteria. Ni does not exhibit the same distribution as the other three metals due to lower preference for coordination with S and N donor atoms and a much lower rate for loss of water than Cu, Cd and Zn.