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Leaching from the anti-fouling paints used to prevent the build-up of micro-organisms, algae or plants (known as biofouling) on ships’ hulls can have negative consequences for marine habitats, and is a source of water pollution.

Anti-fouling paints may contain biocides (chemical substances or microorganisms) that are harmful to the marine environment.

One of the most effective anti-fouling paints, developed in the 1960s, contained tributyltin (TBT). However, it soon became clear that the use of TBT coatings had negative consequences for the wider marine habitat, including an adverse impact on many non-target organisms, like oysters and whelks.

Moreover, TBT deposited in sediments and dredged material from affected areas (e.g. near ports, dockyards and marinas) became a serious concern. On account of such harmful effects, many countries eventually prohibited or restricted the use of TBT.

Following the entry into force of the International Convention on the Control of Harmful Anti-Fouling Systems (AFS Convention) in 2008 and its transposition into EU rules banning the use of organotin compounds, copper-based compounds containing organic booster biocides started to be used. Copper has anti-fouling properties against organisms such as barnacles and tube worms. However, some species show some tolerance to copper, and therefore booster biocides are used in conjunction with copper (principal biocide) to develop a broad spectrum of anti-fouling paints.

Cybutryne is a booster biocide used as an additive in anti-fouling paints for protection against ‘soft fouling’(e.g. due to algae). It inhibits the photosynthesis of marine algae, preventing fouling to the ship’s hull. However scientific research shows that cybutryne has the potential to have adverse effects on non-target organisms, e.g. corals and other non-target organisms on which other species feed. It also persists in the environment (sea- and freshwater sediments) once released from painted surfaces.

In 2017, this adverse effect on the environment prompted an initial proposal by the EU Member States and the European Commission to include cybutryne in the AFS Convention and ban its use in ships’ anti-fouling systems internationally.