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AntiFoulings add microplastic danger to oceans

Following the widespread international concern over the effects of plastic pollution in the world’s oceans, a new report published by the International Maritime Organisation suggests that anti-fouling hull coatings may be an overlooked source of particularly dangerous microplastics.

Anti-fouling coatings typically contain biocides embedded within a polymer (plastic) resin, designed to continually lose their surface layer during the course of a a five-year drydocking cycle. The volume of biocides thus released has been estimated to be on the order of a million tons per annum across the world’s commercial fleet of over 50,000 ships.

Previous investigations have concentrated on the toxic effects of the biocides, often copper oxides mixed with ‘booster’ biocides such as weed-killers that are subject to far stricter restriction on land.  The new IMO report highlights the additional dangers posed by the plastic compounds carrying the biocides.

As the coatings are abraded by passage through the wat, the plastic elements of the coatings are released in the form of microplastics and are thus easily ingested by marine organisms. Whilethe specific level of danger this represents to different species has had only limited research the levels are certainly high enough to cause major concern.

The report is titled “HULL SCRAPINGSAND MARINE COATINGS AS A SOURCE OF MICROPLASTICS” and was published earlier this year by the International Maritime Organization.

It begins: “The impacts of marine plastics and microplastics upon species and communities are increasingly recognised with concomitant regulation and public attention. Accordingly, through its mandate on the protection of the marine environment from shipping operations, the International Maritime Organization (IMO) conducted a literature review to assess current knowledge and data regarding marine coatings as microplastics sources.…It is now recognised that uptake of plastics can impact species and communities directly and that they may bioaccumulate or be directly taken up by humans.

“Whilst plastics suffer limited microbial degradation, over time they are known to break down to monomers with potential toxic effects. They can also be taken up by planktivorous and particulate filter feeding species where they may affect biophysical processes (e.g. respiration, growth, etc.). Microplastics (generally agreed to be of a size less than 5 mm) have also been shown to sorb contaminants such as heavy metals and organic pollutants, with some organism guts having higher contaminant levels than the surrounding sediment.”


The report highlights hull coatings as a source of the microplastics: “It is known that anti-fouling systems and marine coatings in general commonly contain a relatively high content of a polymer material (e.g. epoxy or acrylic). Nonetheless, while the release of biocides and heavy metals from marine anti-fouling systems and, to a lesser extent, other coatings has been considered, the issue of plastics has seen limited attention. Some research has identified microplastics from marine paints in sediment, and other work identified that shipyard maintenance may transport microplastics by air or runoff but in-water hull cleaning was not considered. Further, work shows that general operation emits copper and biocides from vinyl and epoxy coatings, which increases significantly during cleaning maintenance. However, the research reviewed did not consider microplastics release.

“Limited work does begin to recognize marine coatings as a source of possible microplastics, particularly self-polishing anti-fouling products, which are designed to slough off during a ship’s normal operations.

“With specific regard to anti-fouling systems, the AFS Convention regulates the use of harmful anti-fouling systems on ships. The AFS Convention initially included controls on tributyltin anti- fouling paints, but the Convention also incorporates a mechanism for adding controls on further substances and, at present, there is an ongoing consideration of cybutryne. It is noted that, in addition to the AFS Convention, some individual nations have additional restrictions. For example, these include the United Kingdom ban on the biocides Irgarol 1051 and Diuron, Sweden’s strict biocidal paint regulations for use on recreational vessels (Swedish Environmental Protection Agency, 2015) and the intended (initially scheduled for 1 January 2018 though currently delayed) ban on copper-based antifouling paint use on recreational boats in Washington State, United States (Washington State Legislature, 2011).


Toxic compounds

The report continues: “Many (though not all) modern anti-fouling paints follow a co-polymer approach where a toxic metallic / biocide compound is embedded within a polymer (plastic) resin by which, through interaction with water, a constant release rate of settlement-inhibiting organo-metals and biocide is achieved,” and notes that anti-fouling compounds “include co-polymer compounds. These may be alkyls, epoxies, polyesters, vinylesters (e.g. acrylates see Zhou et al., 2015), etc., which are, in general, defined as plastics (Dyckman, 1974).”

The issue of underwater cleaning of anti-fouling coatings is also taken up: “Aggressive cleaning has also been shown to reduce the efficacy of AFS coatings through excessive loss of metals / biocides and through roughening of the coating, potentially providing a surface at the microscopic scale to which organisms can attach (Oliveira and Granhag, 2016). In addition Oliveira and Granhag (2016) show that attachment of macro-foulers to epoxy based coatings is very strong and they recommend not cleaning such macro-fouling underwater due to coating damage and loss of biological material through shell shattering. This aspect acknowledges that there is coating damage and indicates that, as this is realised, there is a concomitant loss of polymer material potentially becoming biologically available microplastics.”

See the full IMO report here:





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