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/comp lexation with organic ligands. The most dominating ligand is 2-mercaptobenz othiazole (MBT), which binds with a 2 : 1 ligand to metal stoichiometric ra tio. MBT has the highest concentrations at the vicinity of the redoxcline w here the oxidation of sulfide to elemental sulfur and sulfate is most exten sive. 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 met als 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.