New paint: no harm, no foul?

The hulls of oceangoing ships traditionally have been coated with toxic paints containing heavy metals such as copper and tributyltin, active ingredients that work by poisoning hull-hugging marine organisms such as barnacles, tube worms, and algae. Nontoxic silicone-based alternatives are available, but they still foul, yet are harder to clean. They are also more expensive and less durable. Now, however, scientists at Cornell University in Ithaca, New York, have developed what may prove to be a more effective nontoxic hull paint.

The toxic metals in hull paints leach into water during normal use, maintenance, and application. They can work their way into the food chain, killing marine life and, because they bioaccumulate, possibly contaminating food fish, says David Guggenheim, vice president for conservation policy at The Ocean Conservancy, a Washington, D.C.-based environmental organization. Studies have further shown that tributyltin can disrupt the endocrine systems of marine shellfish.

Starting in 2003, worldwide law established by the International Maritime Organization forbids new application of tributyltin paint, the most potent of the common toxic hull paints and the type most often used on commercial vessels. By 2008 all ships must remove the material. And countries such as Canada and Denmark are starting to restrict copper paints, the kind most commonly used on recreational boats and the type used on virtually all U.S. Navy watercraft.

Yet some sort of hull treatment is vital to a ship's fuel efficiency, according to Stephen McElvany, an environmental quality program officer with the Office of Naval Research. Additional drag can waste 15-30% of the fuel used to power a ship. The additional drag also reduces ships' top speed and range. For the Navy fleet, that adds up to $50-70 million dollars per year in wasted fuel. Guggenheim adds that, although antifouling paint can pollute, it also serves an important environmental role--preventing invasive species from hitchhiking into new waters attached to a vessel's hull. This potential conflict between protecting sea life and slowing invasive species presents what Guggenheim calls "an environmental tradeoff that will no doubt need to be examined further."

The Cornell group, led by materials science and engineering professor Christopher Ober, has developed a layered coating that may be more durable and more effective than currendy available nontoxic hull paints. "There are really two parts of the fouling process," Ober says. "There's the accumulation, and there's how easy it is to remove it. The reason our material seems so promising is that it does both well." Ober says that the challenge of an antifouling coating that works through physical--rather than chemical--processes is to be able to address the arsenal of adhesives that marine bacteria, animals, and plants use for sticking to surfaces.

Ober's solution is a bilayer coating that can be sprayed on or applied as a film. The base is a commercial copolymer rubber that provides a firm structural foundation. For the surface layer, Ober's group developed two types of liquid crystalline structures, both of which appear to work equally well, he says. One is a hydrophobic, fluorinated material, which repels water and so prevents fouling life from gaining a foothold. The other is a polyethylene glycol-based hydrophilic material, which forms a thin barrier of water that protects the surface and appears to discourage marine organisms from settling in. Both types also make it easier to clean off persistent organisms that do manage to stick.

Both variations of the coating are currently being tested on panels submerged in Hawaiian and Florida waters that teem with sea life, and patents are pending. If the paint performs as well as Ober predicts, it could be commercially manufactured within 12 months, he says.

"Although the challenge remains to produce a nontoxic coating that is more effective than copper-based materials, our results to date are promising," Ober says. "However, there's nothing like a zone of death to make something fouling release."