Modifications in Crassostrea gigas shell composition exposed to high concentrations of lead

Oysters Crassostrea gigas were exposed to two different lead concentrations, 470 and 790 mu g l(-1), with the main objective of finding any alterations on shell biochemical composition, namely amino acids and metal ions. Whole shell elemental composition showed that Pb levels are higher and Ca, Na and Co levels are lower in contaminated than in control oysters. Elemental analyses using Proton induced X-ray emission (PIXE) showed lower Zn levels in the foliated layer and higher Cl in the prismatic layer in contaminated rather than in the control oysters. Mantle Pb content seems to be proportional to foliated shell layer Pb content. Pb levels of the whole soft tissue showed that this trace metal is similar for both concentrations, suggesting a possible regulatory mechanism that sends the excess Pb to the shell through the mantle. Shell amino acid composition is altered in treated oysters, mainly in the ones submitted to 470 mu g l(-1), having higher asparagine, glycine and cystine and lower threonine, proline, valine, isoleucine, leucine, phenylalanine and arginine. Pb seems to affect shell amino acids secretion. (C) 1998 Elsevier Science B.V. All rights reserved.