Transplanted common whelk (Buccinum undatum) (Mollusca, Gastropoda) accumulated fairly high levels of organotins (tributyltin (TBT) and triphenyltin (TPT)) during exposure in three harbours with different TBT contamination. This did not though lead to an increase in imposex frequency in the adult females studied. Simulating harbour dredging in an experiment using suspended sediment from one of the harbours only resulted in a low concentration of TBT in the tissues of the common whelk and subsequently no changes in the occurrence and degree of imposex. The common whelk seemed to receive the main part of TBT from the water column and the limited bioaccumulation in the experiment indicates that desorption of TBT from the suspended sediment was slow. After TBT has been totally banned, dredging of contaminated sediments will cause increased exposure of the biota to TBT. Due to slow desorption the increase may however, be slight and temporary to pelagic and epibenthic species unless the settled particles are resuspended.