Anti-fouling systems are used on ships’ hulls to limit the effect fouling can have on drag, fuel consumption, and the emission of combustion products.
They may contain pesticides or be pesticide-free. The pesticides tributyltin (TBT) and copper are the most common anti-fouling biocides, although the shipping industry is moving away from TBT systems.
The most effective biocidal anti-fouling systems are formulated as self-polishing polymer coatings that wear away as the ship is propelled through the water, to expose a fresh layer of biocide.
Biocides that leach into water from ship hulls may adversely affect non-target organisms. Anti-fouling coating removal activities can be another major source for the release of TBT to the environment.
The choice of anti-fouling system, and collection, treatment, and disposal of spent coatings have an impact on the release of biocides into the environment, and may result in high concentrations of biocides in the marine sediments in areas close to where application and removal activities are conducted.
The adoption of sound management practices for the application and removal of anti-fouling systems can reduce the release of biocides into the natural environment.
By their nature, all anti-fouling biocides are toxic and can affect a broad range of organisms beyond those that cause fouling. TBT causes reproductive anomalies and population effects in certain species of marine snails at concentrations in the parts-per-trillion range, and has been implicated in endocrine effects on other organisms.
Oysters exposed to low levels of TBT can develop shell deformities that reduce their value as seafood. TBT is associated with immune suppression and other adverse effects in other marine species, is slow to degrade, and is very persistent in sediments, where many affected species live and feed.
As a consequence, ships will have to either replace or overcoat their existing organotin-based anti-fouling systems. If the large amount of TBT containing waste that is expected to be generated at shipyards and other facilities as owner/operators attempt to achieve compliance is not properly managed, it will adversely affect the quality of bottom sediments in nearby waters.
Future amendments to the Convention could result in requirements for removal of other anti-fouling paints from vessel hulls, and methods to control organotin-based waste are largely transferable to other anti-fouling wastes.
For these reasons, in 2006, the Scientific Groups established under the London Convention and Protocol began to develop guidance on Best Management Practices (BMPs) for removal of anti-fouling coatings from ships. The Scientific Groups discussed an initial report of BMPs.
Types of waste associated with removal of TBT hull coatings include:
- Surface cleanings to remove fouling organisms which have the potential to remove TBT paint along with the organisms themselves;
- Paint chips and other paint remnants, either dry from scraping, sanding, etc.; or in washwater, water used in wet blasting;
- Dissolved TBT and degradation products, in washwater and water used in wet blasting;
- Contaminated sand or grit used in blasting; and
- TBT removed from waste materials by physical means, such as filtration or water treatment.