Environmental status of TBT pollution in the Portuguese coastline: insights into persistence and regulatory...

This study constitutes the most comprehensive assessment of imposex along the Portuguese coast. It is based on a 22-year biomonitoring program using Nucella lapillus and Tritia reticulata, comparing new measurements from 2022 with historical data collected at the same locations. Since the EU ban on organotin (OT) antifouling (AF) systems in 2003, the intensity of imposex and OT tissue concentrations have declined in both species; however, in 2022, imposex remained widespread, with moderate to high levels still recorded in several areas. N. lapillus met the OSPAR Ecological Quality Objective (EcoQO) at all sampled sites, whereas T. reticulata failed to meet this target at 44% of the locations. This contrast reflects species distribution: T. reticulata inhabits a broader range of habitats, including more contaminated areas, making it a more effective bioindicator of OT pollution along the entire coast. Despite OT-based AF systems being banned on small vessels in 1993 by the Directive 89/677/EEC - nearly three decades before the current survey - and banned on all vessels in 2003 by the Regulation (EC) No. 782/2003, TBT continues to cause imposex, particularly in areas dominated by small-boat activity. These findings indicate spatially heterogeneous recovery patterns and suggest that vessel-size-dependent management and monitoring frameworks may influence post-ban environmental outcomes. Strengthened monitoring strategies targeting small-vessel-dominated areas may therefore support more effective long-term recovery.