Fouling is the successive build up of bacteria, macroalgae, mussels, barnacles and other invertebrates on underwater surfaces. In order to prevent or reduce such fouling, paints containing biocides are applied to ship and boat hulls and other underwater structures to prevent or reduce fouling. These paints are known as antifoulants. Antifoulant paints contain biocides which are released slowly over a period of time minimising fouling. As they are by their very nature toxic to aquatic organisms, antifouling biocides could have an impact on non-target organisms.

In the past, organotins and copper were used. However, while copper is still used, the legal use of tributyltin is now limited to vessels greater than 25 m in length.

Some common algae (e.g. Enteromorpha and Amphora sp) are tolerant to copper. Consequently, manufacturers have introduced additional biocides for use on vessels less than 25 m and on certain larger vessels. These biocides are generally used in combination with copper and are termed booster biocides.

Organotins

Booster biocides in antifoulant paints

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