The surfaces of vessels under the waterline are prone to fouling; hence, antifouling is needed for reducing the friction between ship hulls and the surrounding water. An adequate coating will improve ship efficiency, save fuel and reduce running and maintenance costs. Antifouling paints prevent parasites from attaching to the hull under water and may play a role in preventing invasive aquatic species from being transported from one part of the world to another. The antifouling substances leach into the water and subsequently the bottom. This leaching process presents danger, as a number of these compounds are found to be highly toxic, such as biocide antifoulings. Historically, antifouling products have contained heavy metals, such as copper and tin. As these compounds constantly leach into the water, they present a real environmental risk, with possibly severe adverse effects on oysters, whelks, shell-fishes, sea mammals and fish. Next to the leaching process, the compounds can also be released into the environment through ship maintenance (sanding and grinding).
Biocide antifoulings are not the only antifouling types that have negative side effects. Other substances still used also affect the environment, for example the ones that use heavy metals, such as copper. Despite the ban on the use of antifouling containing biocide, already applied substances can still impact nature.
TBT (organotin tributylin) has been widely used by the shipping industry as an antifouling product. TBT is not only a problem in large commercial ports, but also in leisure boat marinas. Research carried out in Sweden shows the concentration of TBT in the top layer of the sediments of some natural harbours frequently visited by leisure boats to be three times higher than the concentration found in the sediments of the Port of Rotterdam and 3 000 times that of the ambient limit value. The concentration was 10 times higher in
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