The re-emergence of organotin in marine hull coatings is of increasing concern, with academics and environmentalists calling on IMO to investigate the use of tin in silicone-based foul release systems and other hull coatings While use of the organotin tributyltin (TBT) was outlawed as an active biocide almost ten years ago, the International Maritime Organisation (IMO) is claimed to “have left the door open” for tin as a catalyst. Indeed, according to some academics the amount of organotin used suggests it could be being used as the active agent.
Dr Rik Bruer, a former researcher at Netherlands research institute TNO and now managing director of Finsulate, a manufacturer of a non-toxic antifouling wrap, claims that ‘something strange’ has happened with regard to the formulation of many foul release coatings. He says: “Until 2002 I worked at TNO and at that time the chemistry of the silicone foul release coatings seemed to be in order. There was some organotin in there, but this is known to be a catalyst for curing these coatings. About a year ago, I studied the Materials Safety Data Sheets of recent versions of these foul release coatings and it turns out that the amount of ‘catalyst’ added is more than ten times higher compared to 2005. For me there is no debate that there is a purpose beside the catalyst activity and that the risk of spreading tin compounds again to kill marine life is evident.”
While shipowners may have thought the use of organotins in marine hull coatings was completely outlawed in 2008 with the ban on tributyltin (TBT), they can still be used as a catalyst if organotin content does not exceed the allowable limit of 250mg/1kg of paint. Dibutyltin and dioctyltin are the organotins under most scrutiny.
The question being raised is why are organotins still being used when there are much safer chemicals available that are just as effective as catalysts for curing hull coatings? Even small amounts of organotin leaching into the sea can impact marine fauna in the same way as TBT.
Boud Van Rompay, chairman of Subsea Industries, which manufactures the Ecospeed toxin-free hull coating system, says: “Only a proper and independent investigation will determine whether some paints exceed the permitted levels. Like most people in the industry, we had thought the days of toxic tin in hull coatings was long gone. It is very worrying to hear this may not be so.”
There are claims that silicone-based hull coatings are relying on the presence of organotins as an active ingredient to prevent fouling, rather than a catalyst to deliver ‘non-stick’ properties to the coating. Van Rompay suggests action needs to be taken to assess whether such claims are correct. He says: “It is important that independent laboratories assess the biofouling on these hulls, underwater or in drydock, to measure the levels of toxicity. We need to have clear evidence on how these silicone-based coatings are affecting marine organisms, which are vital to the marine ecosystem.”
Since 1993, Subsea Industries has gathered more than 500 references for its coating system. Van Rompay adds: “We have successfully squared optimum hull performance with effective, environmentally-safe ship hull protection and solved the cardinal problems of paint degradation, corrosion and cavitation erosion. The coatings range represents a major breakthrough in the market for non-toxic, environmentally-sustainable coatings.”