Use of non-radioactive, mono-isotopic metal tracer for studying metal (Zn, Cd, Pb) accumulation in the mussel Mytilus galloprovincialis

The aim of this experimental study was to investigate the usefulness of non-radioactive mono-isotopic metal tracer “spikes” for studying metallic contamination in the environment. These spikes are commonly used in Earth Sciences. Because of their unique non-natural isotopic composition, these tracers are readily distinguishable from the metals initially present in an organism and hence, the evolution of both the “natural” and the “added” metals can be quantified during the same measurement by ICP-MS. The concentrations used in this study allow us to simulate conditions similar to those found in nature, but without the potential dangers associated with the use of radioactive tracers. Mussels Mytilus galloprovincialis, commonly used in environmental surveys, were collected in a lagoon (Thau, S. France) and kept for 14 days in clean seawater tanks, to which 66Zn (20 μg l−1), 111Cd (1 μg l−1), 207Pb (1 μg l−1) tracers were added. The concentrations of these metals and their isotopic compositions were regularly analyzed in the mantle, gills and digestive gland of the mussels. Even though the tracer concentrations were relatively low in the tanks, a significant uptake by the 3 organs was observed from the first day. The dynamics of this uptake are similar in all 3 organs but specific for each metal. The spikes are found to be superimposed on metals initially present and could be stored or excreted by the mussels. At the end of the experiment, the tracer concentrations reached 17% of the total Zn, 67% of the Cd, and 36-58% of Pb in the studied organisms. The differing reponse of the mussels to each metal contamination suggests the possibility of using various biomonitoring strategies in environmental surveys.