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Lack of monitoring undermines coatings convention

10 July 2017 IHS Markit Maritime & Trade Expert

This story originally published on

Questions are being asked about the use of organotins in anti-fouling paints. Credit: Withheld

The International Maritime Organization (IMO) has come under fire following its admission that it was not aware of any monitoring taking place under the Anti-Fouling Systems (AFS) Convention.

The AFS Convention, which was introduced by the IMO in 2008, prohibits the use of harmful organotins in anti-fouling paints used on ships. Anti-fouling paints are used to coat the hulls of ships to prevent sealife, such as algae and molluscs, from attaching themselves to the hull - thereby slowing down the ship and increasing fuel consumption.

Part of the convention requires the IMO to monitor the levels of organotins used in paints, as well as to research the effects of anti-fouling systems.

However, when asked by Fairplay if it had any knowledge that such monitoring and research had taken place, the IMO responded, "Not that we know of."

Modern foul release coatings (FRCs) use organotins, such as dibutyltin (DBT), as a catalyst to cure the paint and the catalyst is sealed into the coating using subsequent coatings, which should prevent the poisonous DBT from leaching into the ocean and thereby entering the food chain.

Jan Genzer, professor of chemical engineering at North Carolina State University, told Fairplay, "Monitoring of coatings needs to be done, because without it we won't know what's happening to the coating. The trapped material in the network may be leaching out, and we won't know unless someone is monitoring the situation."

Genzer said that coatings companies had maintained the amount of DBT used to within the limits set by IMO, and that, as long as the catalyst is physically trapped by the outer coating, there should be no problem. However, if the coating is damaged, leaching can occur.

Monitoring FRC systems are crucial as the coatings are considered to be fragile. Scraping the top coat, through cleaning or removal of any fouling that has collected, can damage the system, as can contact with ice in colder regions or contact with harbour walls. Any degrading of the coating could expose the organotin catalyst and allow the compound to seep into the water.

Environmental effects

This has had a dramatic effect on marine life as organisms can deform, such as female dog whelks, which grow penises (imposex) before they die from the effects of the organotin.

According to eminent marine toxicologist Edward Goldberg, who died in 2008 after more than 50 years at Scripps Institution of Oceanography, University of California, San Diego, "Tributyltin (TBT) is perhaps the most toxic substance to have been deliberately introduced into the marine environment." TBT derivatives, such as dibutyltin and monobutyltin, are less toxic, but are still considered to be highly poisonous to marine life.

Some monitoring is currently taking place in Sweden by Åke Granmo, a member of the Marine Monitoring team that constantly scrutinises the Swedish coast for evidence of pollution. Granmo told Fairplay, "In my opinion no organotins should be used in anti-fouling paints. Imposex effects are common everywhere along the coast today, many years after the first ban for small boats, [introduced in] 1989."

Marine Monitoring examines the whole Swedish coast for the effects of pollutants on marine biology and Granmo said the results of historical TBT pollution are still visible.

"[Since 1998] we have seen that the level of tin in the snails has gradually decreased. However, the appearance of different stages of imposex is still found at most of the localities. This means that there is a very slow degradation process in the sea. Furthermore, the remains [of TBT pollution] from pleasure boats are still leaking out from small marinas and dockyards. The levels of DBT are most often lower than TBT."

Dr. Simon Walmsley, a WWF (World Wide Fund for Nature) expert on marine ecotoxicology said that "IMO and its member states must ensure that the AFS Convention is enforced and that the oceans are protected from the potential leaching damage caused by the use of organotins in marine coatings. Monitoring this risk should be part of the Convention and IMO and its member states must fulfil their responsibilities."


Following the emergence of photographs revealing damaged coatings, questions have again arisen regarding the use of organotins in marine coatings and the IMO's monitoring methods in FRCs. Owners are reluctant to reveal the coatings that they use on their vessels, so it is therefore unknown which vessels are at risk of polluting the oceans.

The IMO's response that it does not know if any monitoring has taken place is an admission that the AFS is not being enforced and that means one can only speculate about which ships may be polluting.

Images seen by Fairplay of damaged coatings on vessels operating in sensitive areas, such as the polar regions, raise questions about whether tin pollution is being leached into the marine environment. In particular, photographs of one cruise company's vessel showing significant hull coating damage below the waterline, raising fears of pollution in the seas around the vessels.

The cruise company in question would not say which coating is on its ships, although it did confirm that it has a five-year contract with paint manufacturer Jotun, which produces FRCs.

The cruise operator is just one company, and may well be one of the least polluting, while Maersk, considered to be one of the better operators, is said to have coated 70 of its vessels with FRCs some 10 years ago and found the coatings to be ineffective, before repainting its vessels with conventional coatings.

The company itself would not discuss the issue. A Maersk spokesman told Fairplay, "We do not wish to comment hereon due to competitive reasons. It is a field which we spend a lot [of] resources on, and we do not wish to share our considerations with a wider audience."

Paint problems

Even discounting Maersk's vessels, thousands of ships have been coated with FRCs, including International Paint's Intersleek 970 and Intersleek 1100, Hempel's Hempeguard X5 and X7 or Jotun's Sealion or Sealion Repulse. All of these coatings are known to use DBT as a catalyst at concentrations that are within the IMO's legal limits. However, if the compounds were to seep into the seas it would poison marine life and work its way up the food chain.

Pollution from FRCs has been suspected since 2012 following the release of a number of reports into the use of organotins in marine coatings. The AFS was established because TBT was found to have a severe toxic effect on marine organisms and the compound was banned as a result.

However, a 2013 report into the effects of organotins on the marine environment argued that there is a sustainable alternative to DBT in bismuth neodecanoate, which can act as a catalyst in the coating's curing process, but shows no toxicity to the surrounding environment.

In a 2013 study on DBT alternatives, Carlo Pretti et al found that bismuth neodecanoate was an "effective catalyst for the condensation curing of PDMS [anti-fouling systems] coatings" that exhibited no toxicity against a number of marine organisms while dibutyltin diacetate, even if it is an effective catalyst, showed considerable toxicity.

"This encourages further exploitation of [bismuth neodecanoate] and suggests that it may represent an eco-sustainable alternative to dibutyltin diacetate for the preparation of PDMS coatings incorporating a surface-active polymer to combat marine bio-fouling," the study concluded.

Akzo Nobel, the manufacturers of the Intersleek series of paints, told Fairplay, "We have continually pioneered the development of new hull coatings for the shipping industry.

Over the last 20 years, in particular, we have invested heavily in research and development to create the most sustainable foul release systems that deliver significant fuel and emissions savings as well as reduced waste and raw material consumption, in line with the sustainability challenges shipowners and the wider industry faces.

Bismuth neodecanoate was one of many potential catalysts rigorously tested by our scientists and was found not to be viable for use in foul release systems."

Danish coating manufacturer Hempel said it uses "less than half" the allowable limit of organotin catalyst in its coatings.

Stefan Olsen, fouling release systems and marine technology manager at Hempel, added, "Over the last few years, we have worked closely with suppliers to test other potential alternatives to be used as catalysts, such as bismuth.

"However, it has shown that the available bismuth catalysts are not sufficiently stable against, for example, high humidity and therefore they do not work under the broad application conditions that hull coatings are exposed to. Bismuth could only be a suitable replacement if we could control the temperature and humidity levels in the environment where hull coatings are applied.

However, this is not the case in real life scenarios when applying fouling release coatings."

It is not clear why the IMO has not banned the use of organotins given that there has been awareness of bismuth neodecanoate as an alternative since at least 2013. According to the IMO, "if there is an issue then it is up to member states to raise it at the appropriate meeting, eg MEPC", and no such concerns have been raised.

A long-term problem

Problems with the FRCs in their current form have been voiced by informed sources at environmental organisations, such as WWF and Greenpeace, and academic institutions, but these protests have been largely ignored. For shipowners, that could prove to be disastrous as in some cases they use the coatings in good faith, with the view that they can reduce carbon emissions and are beneficial to the environment.

However, while improving air quality, FRCs could have a significant negative effect on the oceans.

There is a growing body of evidence that organotins, which were banned by the AFS Convention from acting as biocides, are still polluting the oceans and scientists now believe that the increasing levels of these poisonous compounds in FRCs are being seen in marine organisms in regions where few vessels operate.

Dr Simon Bray, a visiting researcher at the University of Southampton, with a background in TBT effects on non-target species and ecological effects of anti-fouling coatings, undertook a review of global TBT pollution for the WWF in 2006 with Dr William Langston of the Marine Biological Association. Research showed that TBT had become an oceanic issue with the compound found in deepsea Pacific Tuna and also recorded in sediments in the Antarctic and in cetaceans in both the Arctic and Antarctic regions.

He pointed out that TBT has decreased significantly since the global ban in 2008, but the TBT breaks down into DBT and monobutyltin. However, he told Fairplay that "there are significant reservoirs of the compound, particularly in some port and harbour sediments" and that he has been helping some harbours manage the issue. In fine harbour sediments, organotins can remain for considerable periods in anoxic environments. While the decline of TBT to less toxic compounds is notable, the reservoir of organotins still requires careful consideration and management.

There is no way of knowing whether the organotins now found in the ocean are newly introduced through leaching from FRCs or from the original pre-2008 pollution of TBT.

The reason for this is that, once in the sediment in conditions where there is little or no oxygen, the compound could lay dormant for decades.

Wildlife experts are calling once again for IMO to research and monitor the use of organotin compounds in marine coatings. However, monitoring is the very least that marine experts require from the authorities. The only way to be certain that organotins are prevented from causing lasting damage to both humans and the environment may be to ban them altogether.

What is the AFS Convention?

The Anti-Fouling Systems (AFS) Convention limits the use of organotins in marine coatings to 2,500mg/kg of dry paint, which is enough to allow dibutyltin (DBT) to be used as a catalyst, but crucially not enough to be a biocide.

Article 8 of the AFS Convention states, "The parties shall take appropriate measures to promote and facilitate scientific and technical research on the effects of AFS, as well as the monitoring of such effects. In particular, such research should include observation, measurement, sampling, evaluation, and analysis of the effects of AFS."

IMO has responded that although the AFS Convention is an IMO regulation it is the 'parties' who are responsible for monitoring and enforcement. However, the parties to the convention are required to report any monitoring that is undertaken and the position remains that no such report of monitoring has been given to the IMO and as such the only known monitoring of the marine environment for the effects of the marine industry on oceanic organisms is the monitoring performed in Sweden as mentioned above. It is understood by Fairplay that Marine Monitoring does not report its findings to IMO.



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