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

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 < 1 ng Sn g-1 dw. Although N. lapillus imposex levels are low they are indicative of OT pollution. The full recovery of N. lapillus imposex in the future is uncertain and a cause for concern.

Automated summary

The study found that after the ban on OT-based antifouling systems by the EU, there was a decrease in Nucella lapillus imposex in Aveiro Estuary, but a recent upsurge was observed with some sites showing a slight increase instead of a continuous decline. The percentage of females with imposex varied greatly, but the vas deferens sequence index did not differ significantly across stations.