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Copper (Cu) is the most commonly used biocide in antifouling paints and is often used in 
combination with organic biocides which are commonly referred to as secondary, or booster, 
organic co-biocides. These booster biocides aim to enhance the efficacy of the formulation by 
broaden the spectrum of antifouling effectiveness to more-copper tolerant organisms (Department 
af the Environment and MPI 2015). In this matter zinc (Zn) is commonly used as an additional 
compound (Tamburri et al. 2020). The fraction of copper and zinc in the paint differs thereby and 
so do their leaching rates (Keep the Archipelago Tidy Finland 2020). 
Previous studies also demonstrated that some aggressive cleaning techniques can significantly 
increase biocide emissions (Schiff et al. 2004) not only by the direct release during cleaning but 
also indirect by a passive leaching of biocides afterwards until it becomes steady again (Morrisey 
et al. 2013). During IWC, there is a distinct increase of dissolved copper concentrations in close- 
by waters. Dissolved copper will pass through a 0.45 um filter per definition (Morrisey et al. 2013). 
The passive leaching rates after cleaning have been monitored to return to steady state after ca. 
3 days (Brown & Schottle 2006). Other factors affecting the concentration of released biocides 
from the paint include the ship’s area being cleaned, the number of ships cleaned per day as well 
as the cleaning method used (Scianni & Georgiades 2019). 
If the coating is ablative, these studies observed that released contaminants during cleaning could 
also result from paint particles or paint flakes. Disintegrated paint particles by water-blasting 
typically had a size of about 5-30 um, consisting of 2-30% of copper (10% on average). In addition 
to the great loss of paint particles, the hull’s surface area grew by water-blasting and sanding 
(Williamson et al. 1995). Paint particles therefore predicted lost their copper rapidly, within less 
than a day to a few weeks (Department of the Environment and MPI 2015). For the techniques of 
brush cleaning systems and probably also hand scrubbing, the dislodgement of paint chips (along 
with biofouling organisms) has been found, particularly if the biofouling included calcareous 
arganisms such as barnacles (Conway & Locke 1994). In general, calcareous fouling can 
accelerate paint system failure (Department of the Environment and MPI 2015). 
The rates of biocide release from antifouling coatings can vary with water parameters such as 
temperature, salinity, pH and water movement over the surface and copper concentration in the 
water (de la Court & de Vries 1973). The amount of released copper raises with increasing 
temperature and salinity and decreases with a pH elevation (Finnie 2006). Copper release rates 
of antifouling paints might vary during the coating’s service-life depending on several factors such 
as the formulation and the environment. Additionally, differences in berthing locations, operating 
schedules, vessel speed, length of service, and condition of paint film surface might also play a 
role (Department of the Environment and MPI 2015). 
2.1.2 Biocide-free AFS 
As mentioned in chapter 2.1 biocide-free AFS’s are either fouling-release coatings that are 
silicone-based to minimise adhesion strengths or mechanically resistant coatings with no active 
measures to prevent biofouling attachment but a physically durable surface. Mechanically 
resistant coatings can thus withstand regular cleaning. However, there are certain factors that