It has been estimated that every year, a mean of 340 tonnes of copper (from antifouling) and 900 tonnes of zinc (from anodes) is released into UK coastal waters from recreational vessels (article 1 below).
Almost all antifouling paints in current use contain copper (along with a range of other substances) as the primary biocide, and this is released into the marine environment.
Most yacht anodes are still made of zinc alloy, despite the less harmful aluminium alloy being of equal efficacy.
Metals build up in sediment on the seabed and affect organisms at all levels in the food chain. Generally, copper is more harmful than zinc, which in turn is thought to be more harmful than aluminium.
Legislation relating to copper in antifouling and zinc in anodes has been tightened in some countries, and this is likely to become more widespread.
What can we do to reduce metal release into the sea?
Copper
At present, in the UK, there are two alternatives to copper antifouling that have comparable efficacy with evidence of better safety concerning marine life:
Second & third generation silicone foul release coatings (FRCs)
These preparations produce a surface on the hull that is difficult for marine life to adhere to.
In a study in Sweden (Article 2 below), their efficacy was found to be as good or slightly better than copper antifouling. They appear to have much lower environmental toxicity, though this needs to be evaluated as they gain in popularity. They do not release microplastics.
Experience of using FRCs on recreational vessels is at an early stage. If you have any, we would appreciate it if you could share it with us by emailing james@cleanharbours.co.uk
Coppercoat
Coppercoat still uses copper as the biocide. The rate of release of copper is claimed to be less than with antifouling paint. It lasts many seasons, making it cost effective.
The most cost effective way of changing to Silicone or Coppercoat is to wait until a full scrape back of all paint to bare hull is next done.
Conventional Antifouling
For boat owners who want to continue using conventional paint, Hard Racing antifouling releases less copper into the water than Self-Polishing (Ablative or Eroding) antifouling.
Scraping Off
Physically scraping antifouling paint off the hull produces large volumes of copper waste. It should be done ashore, and the scrapings carefully collected and disposed of appropriately.
Further information about choosing an antifouling can be found on the Green Blue website https://thegreenblue.org.uk/you-and-your-boat/info-and-advice/water-pollution-prevention/choosing-an-antifoul/
2. Zinc
Aluminium anodes are as effective as zinc (more so in brackish water), as well as being cheaper.
When changing from zinc to aluminium, all external anodes should be replaced at the same time. This does not apply to zinc anodes in the engine water cooling system, if the two bodies of water are separate.
If an anode is eroding more quickly than expected, it’s worth looking for an electrical problem causing stray current. Addressing this would reduce the amount of metal shed by the anodes into the environment. Prolonged connection to shore power without a galvanic isolator can have the same effect.
Boat owners should check that they are using the right amount of anode material for their vessel: Enough to be effective, without causing unnecessary release into the sea.
Useful information on aluminium vs zinc anodes can be found on the websites of MG Duff and Cathwell, suppliers of boat anodes.
- Richir et al, Three decades of trace element sediment contamination: The mining of Governmental databases and the need to address hidden sources for clean and healthy seas. Apr 2021
https://www.sciencedirect.com/science/article/pii/S0160412020323163?via%3Dihub - Lagerström et al, Are silicone foul-release coatings a viable and environmentally sustainable alternative to biocidal antifouling coatings in the Baltic Sea? Nov 2022
https://www.sciencedirect.com/science/article/pii/S0025326X22007846
Photo by David Clode on Unsplash
Clean Harbours Partnership 