A blast from the (not quite) past – Why Tributytin (TBT) Antifouling should concern us all

8 Aug

The other day I was poking around the paint department of my local recycled materials store when I came across this relic:

That’s an old, old can of antifouling using Tributyltin, or TBT, as an active ingredient. As I mentioned a while back in my antifouling post this stuff has been banned in the US and EU (among others) because of its extreme toxicity to marine life. Still I have to admit that I considered squirreling it away in my shop, visions running through my head of painting the hull in the dead of night in some secret cove away from the prying eyes of ‘the man’. After all, I’m not a fan of regulations, right?

Well obviously I did the ‘right thing’ or else I wouldn’t be telling you this story. When I explained what she had for sale the cashier cheerfully put this can in their disposal pile. Then I went home, feeling a tad silly for wasting such a small can of paint. After all, the stuff is supposed to work really well, and how bad can one can be? I decided to find out. What I learned is rather chilling. It turn out that not only is TBT very long-lasting, it also accumulates, moving up the food chain into all levels of marine life. Nor is it, as I assumed, a relic of the past. Levels are increasing globally and it is still used by a significant percentage of the world’s shipping and government vessels. It is even used, I was surprised to discover, by quite a few recreational boaters, in particular cruising sailors in the Caribbean. It turns out that TBT, being vastly more effective at the job of antifouling than any other product on the market, is not so easy to phase out as we might have hoped. So here I give you some information on the chemical and its history, and I will follow up with a look at why people still use it, and what the alternatives are. For those who are currently using TBT antifouling I want to be clear that my aim here is to inform, not to preach, and at no point am I going to be telling you what you should, or should not, be doing.

A brief history of Tributyltin:

Model of Tributyltin Hydride (Wikipedia)

 Tributyltin actually refers to a group of compounds, also called organotins. These chemically-synthesized compounds have a number of uses but the one which concerns us most directly is as a biocide in antifouling paint. I looked this word up. ‘Biocide’. Lit- ‘A substance (as DDT) that is destructive to many different organisms’). Here the Mirriam-Websters unexpectedly brings up a disturbing comparison to our particular biocide- the story of tributyltin is not unlike that of DDT, the incredibly toxic insecticide which helped birth the contemporary environmental movement.

TBT antifouling paints were widely introduced in the US and Canada in the 1960’s and in the UK in the early 70’s. Being so poisonous TBT makes a very effective antifouling and these paints quickly came to dominate the market worldwide. By the mid-eighties the majority world’s vessels, from personal watercraft to commercial shipping and the military, were coated with some form of TBT antifouling.
The first warnings about TBT were heard from the scientific community in the late sixties but it was not until the seventies and eighties when people began to realize just how nasty this stuff was turning out to be.  In France’s Archaron bay oyster crops failed repeatedly and the damage was traced to TBT. The chemical was, among other things, messing with the reproductive function of the oysters, causing females to grow male sexual organs and leading to sterility. Attention was turned to the unintended effects of worldwide TBT usage and over the next twenty-five years a body of research slowly accumulated which showed just how effective TBT is as a poison. (IMO, WWF)

A normal oyster shell…
and one exposed to TBT (UCSC)

It turned out the mollusks in Archaron Bay were the marine equivalent of a canary in a mineshaft. While mollusks seem to be the least tolerant species research over the past 25 years increasingly indicates that TBT is an effective toxin to far more species and at much lower concentrations than anyone expected. We’ve learned that it can last intact for decades and is able to enter the foodchain at the lowest levels and accumulate. Research has found detectable levels in species ranging from plankton up to cetaceans and pelagic fish and there is growing evidence that it is effecting many species in areas around the globe. Dead zones, particularly of mollusks but possibly including a number of other species, have been convincingly traced to TBT. Nor is TBT distribution limited to ‘hot spots’ in harbors and bays. In global oceanic testing of skipjack tuna “Organotins [TBT] were recorded in all of the samples taken, with particularly high levels recorded off Japan and from the offshore waters around developing Asian nations.” Unusually high levels have been found in the beached bodies of dolphins and whales. There may even be implications for human health. In short, this is very, very, nasty stuff. (IMOEPA, WWF)

As the evidence against TBT became increasingly unassailable there was a global movement to ban it, though it proceeded at a typically glacial pace. Some governments, including France and Japan, were quick to adopt measures against TBT but most dragged their heels. Worse, nearly all countries that initially passed legislation against TBT chose to ban its use only for boats under twenty-five meters in length, unfairly targeting small boat owners whilst doing nothing about the application of millions of gallons on commercial and military shipping. It wasn’t until the late nineties, when even shipping companies and paint manufacturers were calling for increased regulation, that an international ban was finally drafted. It took seven more years before it first came into law in portions of the world.

This treaty, the International Maritime Organisation’s Antifouling System Convention (AFS), bans the use of TBT on any vessel entering the territorial waters of a nation which has ratified it, meaning that it applies also to foreign commercial vessels. I have no idea how, or how well, this clause is enforced. I also, surprisingly, don’t know which countries have ratified it. The most recent number I came across indicated that as of Aug. 1, 2009, 40 countries representing 68 percent of the worlds tonnage have ratified the AFS but nowhere was I able to find a list of these countries (link). You would think this would be prominently listed on, say, the IMO’s website but I suppose international diplomacy is not known for transparency… I do know that the ban is in force in the EU and that, in typical style when it comes to environmental regulation, the United States took a leadership role in drafting the treaty but as of 2009 (and I think at present) had failed to ratify it. There are other laws in place banning the use of TBT in United States waters, though at least one US paint company, Seahawk, is still manufacturing it.

These numbers really surprised me – not only is TBT far more harmful than I realized, but it is only banned in forty countries and still used on up to 30 percent of the world’s shipping? It seems crazy but the heart off the problem is that TBT works better than anything else we’ve ever developed as an antifouling – even paint with high concentrations of copper – generally considered the next-best alternative, provides significantly less protection in tropical waters.. This means that TBT it is still used extensively in many rapidly-developing countries, and still accumulating in our oceans. More on that in my next post, where I’ll look at how this big picture relates to the small boat owner.

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder

Comments

  1. Dr Simon Bray

    Paul, I am the author of the WWF article you cite in your text. TBT mainly persists in harbour sediments where it is projected to have a life of circa 30 years (see Maguire, 2000), thus any disturbance (dredging etc.) can lead to significant pulses of contamination, and toxic effects in some species are induced down to 1 nano-gram per litre of water. As you say, in some areas levels are increasing (possibly due to illegal use – recent work in coastal waters off Egypt. The query re DDT below, it has been used as a cheap antifoul option, particularly in China, though the UN has been working hard to change the ethos and persuade users to switch to alternatives – of which, in China and elsewhere, hopefully non toxic approaches will be the eventual future.

  2. Mike Garside

    There are alternatives to biocidal anti-fouling paint. Most of the current replacements for TBT use copper and zinc with the herbicides diuron and irgarol. All of these components are a threat to marine life – if they weren’t, they wouldn’t do anything to remove the marine life which grows on ship hulls (it’s called ‘fouling’, but if you call it ‘marine life’ instead it changes the perception).
    For an alternative solution, check out Ecospeed, which is completely non-toxic. It doesn’t prevent the growth of marine life on the hull, but it is a hard coating which can be scrubbed clean as often as you want. It has the added advantage that one application will last the lifetime of the ship.

  3. Wendy

    In your research have you come across the company and names of the initial developers of the original DDT paint? How far back does this go? WWII? Further back? Any information would be helpful.

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