Copper occurs naturally in all waters around the world. While high concentration levels can be harmful to humans and the environment, copper is an essential micronutrient to life and a certain amount is essential for the well-being of animals, including humans. 

The use of copper in antifouling coatings must go through an exhaustive review by the regulatory authorities before being approved. Copper has been allowed for this use because the authorities have determined that copper in antifouling paints is safe for the environment and for users when used as directed. 

Copper is an effective and safe antifouling active ingredient and the use of copper has allowed the effective removal of tributyltin (TBT) from the market and from the environment as required by International Maritime Organisation (IMO) Treaty, which fully entered into force in September 2008. In discussing the treaty, the IMO stated that one study had found that copper was 1,000 times less harmful than TBT. 

Copper is internationally recognized and registered as a safe and effective compound to control fouling by organisms such as barnacles, mussels and tube worms. There is no proposal to ban or restrict the use of copper by the IMO at this time. 

On a global scale, the copper level in the aquatic environment resulting from antifouling paints is miniscule and insignificant. For example, it has been calculated that it would take over 100,000 years of use of copper in antifouling paints at the current level to double the copper content of the world’s oceans and this doubled absolute amount would still be minuscule. Another source of copper is plumbing such as the water pipes in homes. 

On a micro-scale, there are a small number of enclosed environments where copper from antifouling paints can contribute a higher proportion of the total copper present. However, the total copper level in these environments has to be high before measured negative effects to the environment occur. The vast majority of marina waters and marinas will not experience any problems related to the use of copper-containing antifouling coatings. 

Copper does not bio-accumulate in the environment because organisms have mechanisms to regulate the amount of copper in their bodies and because the majority of it is quickly detoxified when it leaves the paint film surface. 

This happens in two ways – by entering and binding to the sediment and also by becoming bound to organic matter in the water. Copper is effective as an antifouling biocide because it provides an elevated concentration of bio-available copper ion at the hull surface, which has a deterrent effect, thus inhibiting the attachment of organisms. After accomplishing this task, it becomes benign as outlined above. When metallic copper or cuprous oxide leaches into marine water with oxygen present the predominant form of the copper is the cupric ion Cu²⁺. At the hull of the vessel where the copper is released, the cupric ion is both concentrated and bio-available and thus overwhelms the natural biological processes of the fouling organisms that under normal conditions can utilize the copper as a micronutrient or expel excess copper. However, this concentrated cupric ion, after repelling organisms, quickly complexes and becomes dilute as it moves away from the hull. Because of the way it works, organisms can safely exist in close proximity to vessels with copper-containing coatings, such as on pilings of piers and docks