fifteen years of imposex and tributyltin pollution monitoring along the portuguese coast imos antifouling systems convention banned the use of organotinbased antifouling systems in 2008 as the ultimate effort to stop tributyltin tbt inputs into the marine environment one of the hazardous effects of tbt is imposex the superimposition of male sexual characters onto gastropod females a phenomenon that may cause female sterility and the gastropod populations decline despite previous european union legislation had already been shown effective in reducing the imposex levels along the portuguese coast this study intends to confirm these decreasing trends after 2008 and describe the global evolution in the last 15 years imposex levels were assessed in two bioindicators the dogwhelk nucella lapillus and the nettedwhelk nassarius reticulatus gastropoda prosobranchia in 2011 and 2014 and the results were compared with previous years both species showed progressive decreasing trends in imposex levels over the last 15 years median values of the vas deferens sequence index vdsi fell from 396 to 078 in n lapillus and from 339 to 029 in n reticulatus the temporalspatial evolution of imposex suggests an apparent shift of tbt hotspots being now restricted to fishing ports and marinas in detriment of large commercial harbours where tbt levels fell rapidly butyltins were measured in the whole tissues of n lapillus females collected in 2014 monobutyltin mbt varied from dl detection limit 1 ng sng to 13 ng sng dw dibutyltin dbt from 22 to 27 ng sng dw and tbt from 15 to 55 ng sng dw although tbt body burden has declined over time the butyltin degradation index mbtdbttbt exhibited values 1 in c a 90 of the sites assessed suggesting that recent tbt inputs are still widespread in the portuguese coast eventually due to illegal use of tbt antifouling systems and tbt desorption from sediments