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Even Darker Waters – Fluoropolymers in Marine Antifouling Coatings

If you’ve not seen DARK WATERS, we highly recommend it.

With a dark dive into chemical giant DuPont’s murky netherworld, the film documents the exposure of PFOA. PFOA, also known as C8, is perfluorooctanoic acid, a chemical used for decades by DuPont to produce Teflon and a disturbingly wide range of water-repellent, non-stick, stain resistant coatings that are almost certainly in your house right now.

PFOA is part of the larger PFAS family, chemicals that contain a certain number of carbon-fluorine chemical bonds. Because of the strength of the carbon-fluorine bond, this family of chemicals demonstrates remarkable environmental persistence, sticking around in the environment and living creatures for decades, if not centuries. PFOA also has widespread commercial and industrial utility, including fire-fighting foams, nonstick cookware, stain-resistant carpeting, water-resistant clothing, food packaging, compostable plates, some cosmetics, and many other consumer products that repel oil, grease, or water.

The film portrays machiavellean attempts by Dupont to cover up the disastrous results of dumping PFOA near its Parkersburg, West Virginia plant, while throwing some light on the ongoing dangers of a ‘forever’ chemical which is now pervasive across the world. A US Environmental Protection Agency (EPA) report that 110 million Americans may be contaminated with PFAS, is now seen as far too low.

Potentially linked chemicals are now being promoted for even broader use as “foul release” coatings for ships and touted as more effective than the already environmentally compromised silicone coatings. Perhaps more worryingly the coatings are still being presented as ‘green’ alternatives.

A new biocide-free, advanced fluoropolymer ‘fouling-release’ coating developed by AkzoNobel claims to deter the formation of both macro- and microfouling on marine structures.  In an interview with Materials Performance magazine Lyndsey Tyson, team leader—fouling control with AkzoNobel’s team  admits that their silicone-based coatings are less than successful in preventing microfouling build-up and are susceptible to moderately heavy microfouling. “These fouling release technologies have not been 100% fouling free,” Fletcher says. “They have good resistance to growth of weed and barnacle types of fouling, but slime fouling is something that nobody had managed to really deter, and any type of fouling will have an impact on the hydrodynamic efficiency of a surface.” She also accepts a criticism that has been widely made by ship owners that the Silicone hydrogel coatings are highly hydrophilic (show a strong affinity for water), which limits their service life because of film dissolution in the surrounding environment.

While the long molecular chains associated with fluoropolymers have been viewed as making them different to and unlikely to degrade into versions of the PFOA/PFAS chemicals, the chemicals are currently being used in combination with silicones:  AkzoNobel’s Intersleek 1100SR, promoted as a fluoropolymer coating, also contains the silicone octamethylcyclotetrasiloxane and the organic tin compound dioctyltin dilaurate.

Silicone-based coatings, presented as ‘biocide-free’ green alternatives,  have been revealed on this website and elsewhere to contain a small but significant element of highly toxic dibutyltin, and have only escaped the ban on tin in hull coatings through what many consider a thin loophole: the tin in the silicone coatings is classed by the manufacturers as a leftover catalyst, not a deliberately included biocide.

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