Concentrations of Fe, Zn, Cu, Pb and Cd were measured in four surface sediments, whole worm tissues and faeces collected along Aguas de Moura channel in Sado estuary. Six wet-weight worm classes were used to analyze the influence of weight. The metal concentration in colonized sediments is high for Fe and Cu, moderate for Pb and Zn, and low for Cd. The analyses of whole worm tissues show that Zn, Cd and Cu are accumulated. Considering the elevated sediment concentrations to which this species is exposed, the high levels of Zn and Cu suggest sequestration and Cu adaptation. However, the low Fe concentration indicates that this metal is not readily available. The similar Pb behaviour also suggests low availability or Fe interference. The high correlation in the sediment between Pb and Fe reinforces this suggestion. The results obtained show that Pb, Zn and Fe are the most important metals in the different weight classes. The overall results of this study show: (1) that this worm is able to adapt physiologically to elevated levels of metals; and (2) that the weight of the worms needs to be taken into account in environmental management programmes.