The Case Against TBT Antifouling

10 Aug

Much of the antifouling used in the Caribbean is still TBT-based

Ok, my last post gave you some (rather long-winded) background information. I’ll try to make this a bit shorter. Having thought Tributyltin (TBT) was something of relic off the past I was quite surprised to learn that it is not uncommonly used by cruising sailors, particularly those in the Caribbean. This post is a look at the arguments for and against such use.

First a quick recap. TBT, which used to be the number one antifouling compound, is a ‘pervasive marine pollutant’ (per the EPA). It is particularly damaging to shellfish but can be toxic to many other marine animals. It is also an accumulator, meaning that the toxin does not dissipate but enters the food chain and works its way up. Testing of skipjack tuna and oceanic shellfish populations has shown that TBT is now globally present, even offshore and far from shipping channels (WWF). Though there is currently an international ban in effect which is enforced by 40 countries representing 68 percent of the worlds tonnage but TBT is still the antifouling of choice in quite a few countries including some large, rapidly-developing Asian nations. It is also available in many Caribbean nations and seems to be used by quite a few cruising sailors in this area.

It is this last thing, the use of TBT antifouling by cruisers, that I want to look at. I should mention that my knowledge of this is anecdotal at best, mostly coming from a handful of forum posts that I stumbled across in my research. After a quick tally I was surprised to find these posts split more or less evenly between those who used or approved of TBT antifouling, and those who did not. This isn’t to say that these numbers can be translated to ‘all cruisers’ (whatever that might mean) just that this seems a not-insignificant number. The ‘pro-TBT’ camp put forward arguments which roughly fell into three categories.

Argument #1 – Here’s an example (with slight grammatical editing) “I am looking forward to using TBT paint– wont get my paint job done until I get to Caribbean…. morally reprehensible??/ Maybe. Functional?? YES!!!!!! “
 This justification was the most prominent and though this example is a bit callous it is understandable. A lot of the antagonism I saw in these discussions came from cold-water sailors hurling accusations at warm-water sailors based on a misunderstanding of just how difficult it can be to keep a clean hull in the Caribbean. While other types of antifoulings have mixed reputations TBT is both cheap and known to be highly effective.

SeaHawk paints, a US company, still produces TBT antifouling though they cannot sell it domestically. Other prominent paint manufacturers such as Interlux have ceased production of TBT paints and actively discourage their use.

Argument #2
 ‘All the big boys are using it, so what’s the difference with my little boat?’ At the root of this argument is some truly absurd legislation passed in the eighties. This was a period when the scientific evidence against TBT was fast becoming unassailable yet it was used by the majority of the world’s vessels. The ‘solution’ put forward by quite a few governments was to ‘phase out’ TBT use starting with all vessels under twenty-five meters in length. This effectively banned TBT for recreational and small-boat owners while allowing its use for government vessels and commercial shipping. To a lot of people this looked less like a ‘phasing out’ and more like unfairly penalizing pleasureboat owners while doing little to reduce the amounts of TBT actually going into our oceans. In the words of one poster “One 300 foot super tanker has a 35,000 square metre bottom. A 30 foot yacht has 30. The tanker is OK. The yottie banned. Can some one work that out for me?.” This meant that for many years small-boat owners could argue not only that the principle of the thing was grating but that the amount of TBT they put into the oceans was merely a drop in the bucket compared to the big players.
Argument #3 goes something like this –
‘All antifouling is poison anyway, so I don’t see the big difference between using TBT or a copper-based paint which is also poisonous. Aren’t the same people trying to ban copper?’ This one is more or less self-explanatory, and again pretty understandable. There are certainly those who would like to ban all anti-foulings with any hint of biocide. I am not one of them. In fact I expect many of these people come from that camp of blissfully innocent cold-water sailors who think that all your hull needs to stay fresh is a quick wipe-down every few months. That said, I think many people in this camp fail to realize just how toxic TBT is compared to other ‘toxic’ antifoulings.

Lets get to that, then. I titled this post ‘The case against…’ because I believe there is a strong counterpoint to each of these arguments in favor.

Counterpoint #1:
 Look, I’m not going to lie to you, or sugarcoat it. Despite what some press releases may tell you, nothing on the market seems to work as well as TBT. That’s an unfortunate fact. However, the situation is much better than it was in the past. When TBT was first being phased out paint manufacturers were really struggling to come up with an effective alternative. There are many stories during this time of less than stellar results or even complete failure from expensive non-TBT paints. Sometimes this was due to inadequacy in the paint, others it seems to have been a particular batch which was bad but the end result was a lot of frustrated boatowners who lightened their checkbooks for promised results that never materialised. Fortunately this situation is changing. In my experience, and that of many others, the current top-of-the-line paints, while no less expensive, at least work as intended. While sailing in the Caribbean my family found that with regular (approx every two years) coats of Petit Trinidad our boat required only light and occasional scrubbing. However, we were sailing nearly every day. For boats which sit for long periods and in particularly high-growth areas non-TBT paints may still require regular cleaning. At least the water is warm, right?

Counterpoint #2:
This argument became largely moot on 17 September 2008 when the International Maritime Organisation treaty against TBT came into force in much of the world (IMO). Granted there are still plenty of ships in, say, China, which have TBT paint but it’s a bit of a stretch to justify using an environmental toxin because the Chinese are still doing it… The greater point of course is a very valid feeling of outrage by small-boat owners who were scapegoated by governments not wanting to own up to their own heavy use of yet another pollutant. As for this I might point out that this is nothing new and that historically almost every nasty pollutant we have pumped into our environment and bodies has been banned not by governments or corporations feeling a sudden moral twinge but by the pressure of individuals.

TBT antifouling is no longer used on the majjority of the world’s shipping

Of course the Caribbean, and some other areas, are a special case. In places where TBT paint is still legal one might make the argument that if all the other boats use it one more small hull isn’t going to make much of a difference. I think that this discounts the power of individuals. While I can’t give you exact numbers I suspect that the majority, or at least a significant percentage, of TBT entering Caribbean waters is coming not from large ships but from fleets of small boats. I mean aside from commercial shipping and cruise liners how many large ships have you seen in the Caribbean? Nearly all the traffic, both locals and tourists, is small boats and put together these small boats add up to a lot of surface area. This is particularly true when all of the cruise liners and most of the commercial shipping is either coming from or going to countries which have banned TBT antifouling. Sure, TBT is still legal in much of the Caribbean but these countries are rapidly becoming small holdouts in a TBT-free world and as such the impact of each individual is becoming increasingly important.

Argument #3:
This argument, that TBT can’t be that much worse than the other poisons (primarily copper) which we use for antifouling, seems to be largely due to misconception. Let me give you some numbers.

In 1992 the California State Board set its water quality objectives for San Francisco Bay at 4.9
micrograms per liter (ug/L) for Copper while for TBT it was set at 0.005 ug/L. Meaning the California EPA decided that TBT is nearly one thousand times more toxic than copper. (CA EPA)

Here’s another one:
A 1994 study of shellfish showed that “an LC50 (concentration killing 50% of the population considered) could be set for TBT at < 1.3 ug […] while exposure to up to 80 ug Cu1 [Copper].’ did not result in increased mortalities with respect to the controls.” (Gibbs et al.) In other words exposing these shellfish to a minute amount of TBT killed half of them while eighty times that amount of copper killed not a one.
Now, what was that about TBT being just another poison?

TBT has been found worldwide in pelagic skipjack tuna populations

Sure, there is some evidence that copper-based antifouling may be an issue where it is being shed in great quantities into bays and estuaries, but the jury is still out on that one. Regardless, there can be no comparison between copper and TBT. TBT is not only many times more toxic than copper but where copper is a naturally occurring metal that settles out and eventually dissipates into the environment TBT is a man-made compound which does not dissipate and only deteriorates after a great many years.

This, my friends, is why I think it is imperative that we all cease using TBT antifouling, even though it makes for a little more work and expense keeping the hull growth-free. This stuff is just too nasty to be putting into our oceans any longer!

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


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