Long-term monitoring of Nucella lapillus imposex in Ria de Aveiro (Portugal): When will a full recovery happen?

Abstract Nucella lapillus imposex has been monitored in Ria de Aveiro (Portugal) in order to understand the evolution of organotin (OT) pollution after the EU ban on OT-based antifouling systems (OT-AFS). A rapid decrease of imposex occurred, but a countercurrent tendency upsurged recently (2018–2019) with a slight increase of imposex at some sites, instead of a continuous decline towards a complete recovery. In 2018 the vas deferens sequence index ranged between 0.6 and 1.0 across stations and the percentage of females with imposex varied from 63 to 100%. In 2019 these parameters varied between 0.4 and 1.0 and 37–100%, while the concentration of butyltins (TBT, DBT, MBT) in the dogwhelk tissues were