Shell layers of Ostrea edulis as an environmental indicator of TBT pollution: the contribution of surface techniques

X-ray powder diffraction (XRD) was used to study the mineral composition of the shells and shell layers of the European flat oyster Ostrea edulis (Linnaeus) collected at two localities in the East Adriatic Sea of the coast of Croatia. The variations of the shell element chemistry between two different shell layers were determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) with an energy dispersive X-Ray (EDX) microprobe. XRD showed that the dominant component of the outer prismatic foliated shell layers was calcite with traces of aragonite and halite. The newly formed chambers of the inner nacreous shell layers were mainly built of magnesium calcite. Chemical element analysis given by XPS and SEM confirmed that besides carbonates other minor elements could be incorporated in the oyster shells. Silicon was present from 0.1 to almost 1.5 atomic percentage (at.%) in the outer shell layers, whereas its amount was lower and difficult to quantify in the inner shell layers. On the contrary, tin was detected only in the chambers of the newly formed inner nacreous layers, in a concentration that could be estimated, according to both XPS and SEM, to be of the order of 0.1-0.2 at.%. In the chambers of the oyster shells, tin is environmentally induced. A possible formation mechanism and specific ecological factors that could influence the precipitation of tin in the different shell layers of Copyright © 2006 John Wiley & Sons, Ltd.