Electrolyte Conductivity Through the Shell of the Eastern Oyster Using a Four-Electrode Measurement

Abstract

The bioceramic shell of the Eastern oyster was investigated to determine its physical and chemical compositions. Resistance and electrolyte conductivity measurements through the shell using a four-electrode cell configuration were made. The scanning electron microscopy/energy-dispersive spectroscopy analysis of oyster shell cross sections revealed that this multilayered biocomposite material is composed of numerous incongruent “chalky” and “nonchalky” layers, each containing similar chemical elements but having different overall chemical compositions and porosities, with the chalky layers being quite porous and voluminous, whereas the nonchalky layers appear to be nonporous, more dense, and compact. The electrolyte conductivity within the pores of the shell was dependent on the ionic concentration of the electrolyte, suggesting that the tortuosity across the shell material via the various chalky and nonchalky layers has an effect on the transport of ions. Rather, consideration of the data in terms of the space charge model indicates that the surface charges within the porous biocomposite facilitate the conduction of ions, much like a ceramic membrane. These findings suggest that the oyster shell may function not only as a protective physical structure, but also as a ceramic membrane allowing for the exchange of ions from the external environment.

Electrochemical characterization of a bioceramic material: The shell of the Eastern oyster Crassostrea virginica

“…The full frequency EIS scans were made to determine the impedance behavior of the shell specimen as a function of time and specimen thickness. Since the limiting impedance at low frequencies is the sum of the pore resistance (R pore ), the solution resistance (R s ) and the polarization resistance (R p ), the absolute impedance measured at 10 mHz was used to represent the total impedance of the cell (R cell ) for comparison between the various shell thickness used in 3.5 wt.% NaCl solution [6].…”

“…The resistance measurement using EIS to obtain information about the structure of porous materials has been described previously [6,[16][17][18] The resistance of the oyster shells was measured using a four electrode configuration using both EIS and DC polarization in 3.5 wt.% NaCl solution [6]. The whole intact oyster shell was positioned between two independent flat cells on either side of the shell.…”

“…Between the outer prismatic layer and the innermost foliated layer, there are numerous incongruent foliated layers, each containing similar chemical elements but of differing porosities (i.e. dense vs. foliated chalky) [6]. Fig.…”

“…One such organism is the Eastern oyster, Crassostrea virginica, a bivalve mollusc composed of a soft body protected by two hard shell sections that are jointed at one end by a hinge ligament. Oyster shell valves are composed primarily of calcite, a calcium carbonate polymorph; calcite crystals are integrated within an organic protein matrix in a layer-by-layer arrangement to form the bioceramic [4][5][6][7].…”

“…In an earlier study, we explored the effect of varying electrolyte concentration on the ionic conductivity of bulk oyster shell and found that the shell behaves as a selectively permeable ceramic membrane [6].…”