Heavy Metals in Mollusc Shells: A Quick Method for their Detection

Abstract

It is known for a long time that calcified tissues secreted by aquatic or terrestrial invertebrates – such as mollusc shells – have the ability to concentrate large amounts of pollutants, in particular heavy metals. In the present paper, we have found an extremely rapid and easy procedure to qualitatively detect the putative presence of heavy metals in shells, without having to use sophisticated techniques such as Wavelength Dispersive Spectroscopy, atomic adsorption spectroscopy or ICP-MS. Our method rests on the capacity of the silver enhancement chemicals that are traditionally used in immunogold localization experiments to increase the size of heavy metal nanoparticles, whatever the chemical element. It goes as follows: freshly broken pieces of shells that are suspected to contain traces of heavy metals are simply incubated 15 minutes in few drops of a silver enhancement solution (British Biocell International), and, after short rinsing and drying, the shell fragments are directly observed with a tabletop Scanning Electron Microscope, under back scattered electron (BSE) mode without any further preparation. Heavy metals nanoparticles are detected as bright spots. Our method is extremely fast (about half an hour in total), and may be used as a quick check for pre-selecting series of calcified samples prior to the quantitative analysis of their heavy metal content.