In the past, tributyltin (TBT) was commonly used in ship's paint. It is a biocide used to kill barnacles and other marine life such as bacteria, tube-worms and algae that attach to boats. TBT is now banned by the International Maritime Organization due to its severe toxicity, although some shipping companies continue to use it. TBT is known to leach out of the paint into the ocean, adversely effecting sea life by poisoning the food chain.
Cuprous oxide is a red crystalline material that is used as an anti-fouling agent on ships. It is generated through copper's exposure to heat either in a furnace or via electrolyte. When produced in nature, it is known as cuprite. Cuprous oxide is not compatible with aluminum and is therefore not used on boats with an aluminum hull. It is not considered safe to use in the environment because it breaks down over time and becomes dangerous to sea life.
Copper thiocyanate is a white powdery substance that is also used as an anti-fouling agent. Though thought to be more environmentally friendly than cuprous oxide, it is still not generally considered completely safe due to a lack of long-term studies of its effects. Copper thiocyanate is often chosen over cuprous oxide because it lasts longer and because its white color can be readily mixed with various pigments, whereas cuprous oxide's red color limits possible pigmentation choices.
Researchers at North Carolina State University have developed a coating using rubber and an ultraviolet ozone treatment. The coating contains "wrinkles" that do not allow the barnacles to attach to it. The researchers stretched the rubber and then exposed it to an ultraviolet ozone treatment, then released the tension and added a thin layer of semi-fluorinated material. It proved to be barnacle-free after 18 months in the ocean. Typically infestation begins within one month at sea.