Regulating copper-leaching rates of antifouling paints may be better than banning them
Issue 149: March/April 2023
Copper is lethal to many marine organisms. That’s why it works. Antifouling paints release a tiny but steady stream of copper ions, which repel barnacles but also enter the environment, potentially accumulating to sufficient amounts in poorly flushed harbors to levels that can affect the local biome. Washington and California have been wrestling with this issue for decades, and it seems, at least from a regulatory perspective, that a compromise has been struck between clean bottoms, environmental risk, and our understanding of the problem. In 2011, Washington state banned copper-based antifouling paints, effective January 1, 2020.
When working with any bottom paint, remember to protect yourself and contain all materials.
Super-slippery paints have been proposed as an alternative, but in high-fouling areas they are all spectacular failures when applied to sporadically used sailboats; there simply is not enough turbulence to cause the growth to release, and the bottom appears as though no antifouling was used at all. Copper-free paints have been proposed, and in fact, many of them are quite good. I have a test patch of a two-year copper-free paint on my boat right now, alongside test patches of copper-based two-year paints, and at the one-year mark it is among the best performing.
But what about the toxicity of the organic antifouling chemicals used to replace copper, including cybutryne/ irgarol, DCOIT/Sea-Nine, tralopyril/ econea, and zinc pyrithione? Washington commissioned a review of the alternatives and decided that the risks might just be greater than copper, which is naturally occurring and well understood. In 2015, Washington delayed the ban until 2026, pending a study due in 2019. The study revealed that although copper from boats was measurable, only one marina actually exceeded state water quality targets, and it was not clear to what extent the copper was in a form that was bioavailable and thus toxic. The study further concluded that irgarol should be heavily restricted or banned and that control of copperleaching rates is probably the best path forward.
Drew Frye cleans a four-panel paint testing board.
Meanwhile, California had been pursuing a different approach, measuring and then regulating the rate at which copper paints leach. It was determined that paints that leach less than 9.5 μg/ cm2/day (micrograms per square centimeter per day) present minimal risk to the environment. In 2013, the California Department of Pesticide Regulation proposed that effective July 2018, the maximum allowable leach rates depending on hull cleaning practices would be 9.5 μg/cm2/day for boats that were cleaned no more than once per month using best practices (using a soft-pile carpet or something similar) and 13.4 μg/ cm2/day for products that prohibited in-water hull cleaning (ablative paints). All registrants were required to submit proof of testing by a prescribed method.
Make sure to adhere to boatyard and marina rules regarding sanding, scraping, and washing your boat’s bottom.
About the same time, the U.S. Environmental Protection Agency proposed that a 9.5 μg/cm2/day copper leach rate limit should be sufficiently protective, but did not have enough data on the performance of the paints in the marketplace to determine which might be acceptable and what the current leach rates were. In fact, past testing suggests that most multiyear copper paints have met this standard for some time, because if they did not carefully parcel out their copper loads, they would never last the expected two to three years. Singleseason paints, on the other hand, often release copper more quickly and less carefully.
The use of cybutryne/irgarol has been banned in Europe, California, and Washington, and all the major manufacturers have stopped formulating with it. The environmental impact and regulatory fate of other copper alternatives are unknown.
My recommendation is to use multiyear paints when possible, stretch them as far as possible, and minimize (hard paint) or eliminate (ablative paint) in-water cleaning. Keep your ear to the ground for new technical and regulatory developments. I’m not on the copper-free bandwagon, because the safety of the alternatives is not known, and at least one has been banned because it was worse than copper. Let’s not second-guess conservative West Coast agencies.
Most of the major brands have reformulated to the new California limits — check the list to see where you stand. Where does Coppercoat stand on the spectrum? Judging by the copper load, life expectancy, and limited effectiveness in high-fouling waters, it is a low leach-rate product, probably half the 9.5ug/cm2/day standard, but we don’t have the data, and performance (and leach rate) appears to be very application- and maintenance practice-dependent.
Good Old Boat Technical Editor Drew Frye draws on his training as a chemical engineer and pastimes of climbing and sailing to solve boat problems. He cruises Chesapeake Bay and the mid-Atlantic coast in his Corsair F-24 trimaran, Fast and Furry-ous, using its shoal draft to venture into less-explored waters. He is most recently the author of Rigging Modern Anchors (2018, Seaworthy Publications).
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
