A technique for the separation of the most recently deposited nacreous layer in Mytilus californianus shells for trace metal analysis

Abstract

 A new method to separate a section of the most recently deposited nacreous layer from the rest of the shell of Mytilus californianus was developed. Techniques described for other mussel species proved unsuitable for this species. In this new method, the shells are soaked in 30% hydrogen peroxide for 10–15 min at 80–85ºC to eliminate the periostracum, a potential source of trace metal contamination. Next, the shells are heated in a muffle furnace at 350ºC for 1 h to separate the nacreous layer from the calcite layer. Finally, the nacreous band is easily separated from the rest of the shell by gently tapping it with a stainless steel needle. This is a simple and fast method that is proposed for trace metal monitoring purposes using M. californianus shells. To illustrate the application of the method, results from an experiment performed in our laboratory, in which mussels were exposed to two different Cd concentrations for 60 days and their shells processed by this technique, are included. The most recently deposited nacreous layer showed significant increases in Cd concentrations, which were proportional to the exposed ambient concentrations.