IRON AND MANGANESE DEPOSITION IN THE PERIOSTRACA OF SEVERAL BIVALVE MOLLUSCS

¹ Department of Chemistry, University of California, Davis, California 95616

The iron (Fe) and managanese (Mn) contents of the periostraca of specimens of the freshwater molluscs Anodonta californiensis and Unio novahollandae, and marine mollusc Mytilus californianus were determined. The freshwater molluscs concentrate Fe and Mn. The manganese being concentrated in regions high in Ca and P, which regions appear to be amorphous Ca₃(PO₄)₂ in a proteinaceous matrix. Iron appears in these Ca-P regions but also occurs elsewhere in the periostracum. Electron spin resonance (ESR) measurements indicate the oxidation states of the Mn to be +2 and +4, while chemical experiments suggest Fe is present in the +3 oxidation state. The levels of Mn and Fe in the periostracum can be several per cent. Local concentrations, determined by electron microprobe measurement, are as high as 15% and 5%, respectively for A. californiensis, and 40 and 13%, respectively for U. novahollandae. It is postulated that the Mn and Fe are removed directly from muds rich in these metals. Iron and Mn levels in the marine mollusc M. californianus do not locally exceed 0.05%.

Manganese and iron in the periostracum of a mollusc can act as a defensive buffer against degradation from acidic conditions. The concentration of these metals, in the presence of phosphate and protein, produces a condition which can maximize nutritive value to microorganisms.