Delineation of heavy metal uptake pathways (seawater and food) in the variegated scallop Chlamys varia, using radiotracer techniques

The bioaccumulation and depuration kinetics of selected metals (Ag, Co, Hg, Mn and Zn) were determined in the European variegated scallop Chlamys varia following exposures via seawater and food, using highly sensitive radiotracer techniques (Ag-110m, Co-57, Hg-203, Mn-54 and Zn-65). Body distribution of Ag, Co, Mn and Zn was similar for both waterborne and dietary metals. Ag was mainly present in the digestive gland (>80%), Co and Mn were generally localized in similar proportions in the digestive gland and kidneys, and Zn was mainly found in the kidneys (>40%). In contrast, Hg was mainly present in gills during seawater exposure whereas, after exposure through food, it was primarily distributed in the digestive gland. The results from all experiments were integrated into a bioaccumulation model in order to delineate the relative contribution of each metal uptake route in C. varia. Computation indicated that food is the main uptake route of Ag, Co, Mn, and Zn in scallop, whereas waterborne and dietary pathways were shown to contribute similarly in the global bioaccumulation of Hg in C. varia. Except for Hg, dietary transfer was investigated using 2 different phytoplankton species, Isochrysis galbana and Skeletonema costatum. For Mn and Zn, the dietary contribution was not influenced by the phytoplankton species used. In contrast, food quality played a major role for Ag and Co intake. For example, when S. costatum was used as food, the dietary pathway contributed 97% of the global Ag bioaccumulation, while it contributed only 58% when Ag was ingested with I. galbana.