engleski

Influence of environmental pollution on the shell layers of oysters Ostrea edulis

Antifouling systems release into the water toxicants that inhibit the fixation of fouling organisms. Since 1970s, tributyltin (TBT) has been used in anti-fouling ship paints. TBT leaches from the paint and enters the marine environment, accumulates in the sediments, in particular in areas with many ships like harbors and ports. TBT is responsible for the disruption of the endocrine system of marine mollusks, leading to the development of male sex characteristics in female marine snails, and causes harmful effects on other marine organisms. An extremely low level of TBT in the seawater significantly affects shellfish larval growth impairs the immune system of organisms and causes malformations in the shells of the adult shellfish. Shell calcification anomalies, consisting of stacked "chambers" filled with a gelatinous substance, giving the shell a ball-like shape, were observed in the oyster Crassostrea gigas sampled at the French Atlantic coast and in California [C. Alzieu, J. Sanjuan, P. Michel, M. Borel, J.P. Dreno, Marine Pollution Bulletin 20 (1989) 22 ; M. Stephenson, Marine Environmental Research 32 (1991) 51]. Similar deformation effects showed the shells of adult oysters C.gigas and European flat oyster Ostrea edulis sampled at several localities along the East Adriatic coast [D. Medaković, Ph.D. Thesis. University of Zagreb and R. Boskovic Institute, Zagreb, 1995. p. 216]. 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 (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). XRD showed that the dominant component of the outer prismatic foliated shell layer was calcite with traces of aragonite and halite. The newly formed chambers of the inner nacreous shell layers were built mainly of magnesium calcite. Chemical element analysis given by XPS and SEM confirmed that, beside carbonates, other minor elements could be incorporated in the oyster shells. Silicon was present from 0.1 to almost 1.5 atomic % (A %) 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 layer, in a concentration that can be estimated, according to both XPS and SEM, of the order of 0.1-0.2 A %. 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 O.edulis is discussed.

XRD; XPS; SEM; Tin; Silica; Chamber; Oyster

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