Investigation of critical copper release rates for dose optimization of antifouling coatings

Antifouling coatings are applied to ship and boat hulls to prevent the unwanted attachment of marine organisms known as biofouling. Most antifouling coatings do so through toxic means by continuously releasing copper from the paint film to the surrounding water and are thus of environmental concern. Few studies have investigated the minimum dose of copper from an antifouling coating required to inhibit biofouling, commonly referred to as the critical release rate. This study presents a comprehensive investigation into the critical release rates of copper from commercial antifouling coatings in European coastal waters, with study sites in the Atlantic (Arcachon, France), Kattegat (Hundested, Denmark) and Skagerrak (Tjärnö, Sweden). Employing a combination of X-ray Fluorescence (XRF) analysis and visual inspection, this six-month field study has evaluated the efficacy of various antifouling coatings with differing copper contents. The findings of this study indicate that a release rate of 7 μg cm⁻² d⁻¹ was sufficient to inhibit macrofoulers at all three sites during static conditions. Results also indicate that the critical release rate is a parameter that coating manufacturers can optimize, as the performance of the coatings was not solely dependent on the copper release rates. The general critical release rate of 7 μg cm⁻² d⁻¹ could serve as a benchmark for dose optimization of coatings for both the yacht and ship sectors in the studied waters to reduce their environmental impact. It can also be used as support for decision-makers to phase out coatings with unnecessarily high copper release rates from the market.