Summer is upon us, and for many that means getting out on the water. Sailboats, powerboats, canoes, all are great choices for enjoying the open blue and we're not the only species that enjoys our boats. There are a host of organisms that love the underside of boats (algae, seaweed, barnacles, diatoms), but unfortunately most boat enthusiasts don't love these organisms. As this marine life builds homes on the boat hull the drag on the boat increases and the speed decreases, causing for greater fuel use, emissions to the atmosphere, and costs. To address these concerns, antifouling chemicals were introduced.
Antifoulants are any chemical used to inhibit the growth of this marine life on boats, and they are typically incorporated with the paint. Fifty years ago, a compound called tributyltin oxide (TBTO) came in to prominence in the antifouling scene. While wildly effective for the function it was to serve, over time it was determined that TBTO is quite persistent (with a half-life of more than 6 months in seawater) and chronically toxic to marine life. In the 1980’s many countries and organizations began to ban or severely restrict the use of TBTO as an antifoulant. In the United States, TBTO got its very own restrictive act, the Organotin Antifoulant Paint Control Act of 1988, and the US EPA and US Navy were charged with researching alternatives.
With this kind of history and these restrictions coming into play, it comes as no surprise that green chemistry and antifoulants have a bit of a relationship. TBTO was soon eliminated from all antifouling products and some replacements involving copper hit the market. Though this has since become what many consider to be a “regrettable substitution,” a replacement that has equal or worse effect compared to what it was replacing. Washington State in United States is now phasing out the use of copper as an antifoulant due to its toxicity effect on marine life.
Fortunately innovation is never too far away in the green chemistry space. There are several categories of alternative technologies including biocide-based (zinc or organic based), non-biocide-based (many are silicone based), and physical removal (ultrasonic sound). In the mid-1990’s the US EPA awarded one of its Presidential Green Chemistry Awards to a company (Rohm and Haas Company, now a subsidiary of The Dow Chemical Company) that developed an organic alternative (,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI)) that has essentially zero bioaccumulation threat. DCOI has a half-life in seawater of one day, a stark contrast to TBTO’s six-month half-life, and is also significantly less bioavailable compared to earlier technologies in sediment and water.
Water is an important resource, both to us as scientists and as residents of Earth. As chemists we have a huge opportunity in many research areas to not only improve our interactions with our planet’s water in terms of toxicity impact (using the antifoulant story as an example), but in every aspect of our use of water as chemists. Green chemistry is the lens through which we can identify these opportunities for sustainable water-related innovation, and since every chemist uses water in one way or another, you can start looking through the lens today.
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