Bioaccumulation and retention of 210Pb in the Mediterranean mussel Mytilus galloprovincialis

Pb is commonly reported as a pollutant of concern in the marine environment. Although severely regulated in the industrialised countries, global emissions are not showing a significant downward trend. Therefore Pb will still cause problems because of its conservative nature and its increasing use in some industrial applications. It is therefore important to develop tools to monitor the occurrence and abundance of Pb in coastal waters, particularly those in less-developed regions of the world where its use is not yet, or only poorly, regulated. Thus, the purpose of this study was to quantify Pb bioaccumulation in a widely distributed and abundant species along the Mediterranean coasts of North Africa, i.e. the mussel Mytilus galloprovincialis, in order to assess the relevance of its use as a bioindicator species of Pb contamination. The experimental approach used highly sensitive nuclear detection techniques to investigate uptake and loss kinetics of the radiotracer 210Pb in the mussels. Individuals were exposed experimentally to the radiotracer for 14 d via seawater (uptake phase). At the end of the exposure period, non-contaminated conditions were restored (clean flowing sea water) for 22 d and loss kinetics of 210Pb from mussel tissues were determined (depuration phase) during that time. 210Pb was found to be readily taken up according to linear uptake kinetics. At the end of the exposure period (14 d of exposure), calculated concentration factors reached values as high as 300. When mussels were exposed to increasing 210Pb activities (0.25 to 2.5 Bq ml-1), it was found that Pb bioaccumulation in the mussel tissues was directly proportional to ambient Pb concentrations in sea water. Retention of the metal in mussel tissues was high with ca. 50% of incorporated Pb remaining in the tissues after 3 weeks of depuration. Mussels displayed similar loss kinetics regardless the 210Pb activity (0.25 to 2.5 Bq ml-1) to which they were previously exposed. Estimated biological half- life (Tb1/2) of 210Pb ranged between 23 and 28 days. Overall, our results indicate that M. galloprovincialis could be a useful monitoring tool to assess Pb contamination of North African coastal waters and, thus, could be considered as a suitable bioindicator species for heavy metal monitoring programmes in this region. (author)