Trace metals in mussel shells and corresponding soft tissue samples: a validation experiment for the use of Perna perna shells in pollution monitoring.

The uptake of Cr, Mn, Ni, Cu, Zn, Cd and Pb in soft tissue of Perna perna mussels and their shells has been studied in aquarium experiments in which mussels were exposed for 30 or 60 days to seawater spiked with different concentrations of these contaminants (125 and 500 microg L(-1)). Tissue samples were analyzed after acid digestion by conventional solution nebulization ICP-MS. Laser ablation ICP-MS was used for the quantitative determination of trace elements in different areas of the corresponding shells. With the exception of Mn and Zn, all other elements studied showed a significant concentration enhancements in soft tissue, with the magnitude of this enhancement following the order: Cr > Ni > Cd > Cu > Pb. A corresponding increase in most contaminants, although less pronounced, was also observed in the newly formed growth rings of mussel shells, contributing to the validation of Perna perna mussel shell as a bioindicator of toxic elements.

Improvements in calibration procedures for the quantitative determination of trace elements in carbonate material (mussel shells) by laser ablation ICP-MS.

A better repeatability and accuracy in the quantitative determination of trace elements in mussel shells or carbonate-based materials by LA-ICP-MS was achieved by using a series of multielement calibration standards prepared by co-precipitation of twelve elements into a CaCO3 matrix in order to improve the homogeneity of the resulting powder samples. Pressed powder discs of good mechanical stability could be obtained at a pressure of 50 MPa, without the addition of a binder. An UV laser (modified Nd:YAG, 266 nm) was used in the Q-switched mode at a repetition rate of 10 Hz and an energy level of 3.5 mJ. Correlation coefficients (R) for the linear calibration graphs (concentration range: 1.5-400 microg/g) for Cr, Mn, Co, Cu, Zn, As, Cd, Sn, Ba, and Pb are generally better than 0.997. The detection limits for all elements investigated are in the sub-microg/g range. Incorporation of elements into the matrix by co-precipitation has shown as a superior method for producing calibration standards than the simple mixture of the analytes (in carbonate or oxide form) with the matrix (CaCO3) or addition of standard solutions to a carbonate powder base. Two examples of the quantitative determination of toxic elements in mussel shells will be presented.