EN
Invertebrates are widely used as sentinels of metal bioavailability in water quality monitoring programmes due to their capability to accumulate bioavailable metals water and sediments. Several factors, for instance changes in flesh weight, may affect metal concentration in soft tissues and hence metal bioavailability estimations. The estimation of bioavailability by means of metal/shell-weight indices may provide an alternative approach. Here, it has been applied to a clean estuary (Urdaibai) which receives occasional metal inputs and where mussels Mytilus galloprovincialis exhibit different growth patterns at different geographical sites. Metal/shell-weight indices calculated over a one-year period did not change with the season since they do not depend on changes in flesh weight. In addition, these indices did not differ between sentinel populations of mussels with different growth patterns. The metal/shell-weight indices appear to be sensitive to changes in the bioavailability of metals since they reflect changes in Cd, Cr and Pb bioavailability in the Urdaibai estuary. Thus, the use of these indices is highly recommended for environmental monitoring programmes in coastal and estuarine waters because they offer an easily calculated indication of metal bioavailability.