Environmental impact and efficacy of different antifouling coatings in the Atlantic and Baltic Transition marine regions

Abstract

This thesis evaluates the environmental impact and efficacy of various antifouling (AF) coatings under field conditions across three marine sites in the Baltic Transition and Atlantic regions. The AF paints tested in the study included five copper-based coatings with varying copper content (6 – 32 wt% Cu2O), one alternative biocidal coating containing tralopyril and one biocide-free silicone foul release coating. Biocide release was quantified using X-ray fluorescence spectrometry (XRF) and environmental risk was assessed through Marine Antifouling Model to Predict Environmental Concentrations (MAMPEC) via Risk Characterisation Ratios (RCRs).

The results demonstrate that in-situ XRF measurements, when integrated into the new environmental risk assessment (ERA) tool, provide a robust basis for estimating biocide release and assessing environmental risk. Applying this method revealed that most copper-based coatings exceed acceptable environmental thresholds, particularly in Baltic Transition sites, suggesting that they could face challenges under current approval frameworks if evaluated using this method. The tralopyril-based coating exhibited alarmingly high RCRs at all test locations, raising serious environmental concerns about its continued marketing.

When the coatings were compared by performance and environmental risk, the silicone coating emerged as the most promising option, achieving high antifouling efficacy with minimal environmental impact. Additionally, low copper-content coatings demonstrated a favourable balance of acceptable efficacy and lower environmental impact than coatings with higher copper content. Site-specific differences also influenced both fouling intensity and environmental risk, with Baltic Transition sites experiencing heavier fouling but greater copper efficacy. Lower RCRs were generally observed in the Atlantic region for the copper-based coatings, likely due to enhanced water exchange assumed in the MAMPEC model. However, this may lead to an underestimation of environmental risk in sensitive areas like Arcachon Bay.

A case study of Arcachon Bay was performed to model the annual metal loads resulting from using either of the five studied copper-based AF coatings. The model estimated that continued use of copper coatings, similar to those currently in use in the area, could result in annual copper emissions of up to 8 tonnes per year, posing considerable risks to the local marine ecosystem, particularly to oyster populations. However, this load could be reduced to around 2 tonnes annually if boaters switch to a low-copper alternative, or even eliminated entirely by adopting biocide-free silicone coatings. These findings highlight the potential environmental benefits of transitioning to more sustainable antifouling strategies without compromising fouling control.