Join Date: Feb 2000
Location: Annapolis, Md
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LaBatt, it is a mistake to say, " Tributyl-Tin based paints were not outlawed in the US due to quantitative scientific measurement " or suggest that there wasn't adequate research on TBT before it was eliminated from bottom paint.
Much of that research was done here on the Chesapeake and was pretty well known to the sailing community locally. The original research looked at densely populated creeks like Back Creek in and around Annapolis. Creek bottom soil samples taken both near marinas with haul- out facilities but also at marinas without haul-out facilities and surprisingly, all of the samples showed extremely high concentrations of the TBT. It was also well known that TBT has a very long lifespan in the environment. Decades and not days.
Crustations and Mollusks harvested within several miles of these populated creeks were shown to have above the then legal concentrations of TBT. In alter research other popular but less densely populated boating anchorages were shown to have very high TBT levels as well.
It is important to understand that TBT was added to bottom paint because it was a potent anti-herbicide. It did very little extra in preventing barnacle build-up as compared to the copper based anti-fouling paints then in use.
To continue, as TBT was further researched, data showed that on the Chesapeake, bottom grasses were greatly reduced in areas with high TBT levels in the soil and that these areas of high TBT content, even when adjusted for other environmental factors were shown to be far more prone to sand bottom syndrome, and the research further showed that localized sand bottom syndrome occurred where there were elevated TBT content in areas where anchorages were limited to small areas within a bigger body of water, and that even within these bodies of water where TBT levels were lower, sand bottom was far less likely to occur.
Similar research in Florida showed that samples from popular anchorages had high TBT content and that even at low concenrtation levels TBT was able to kill coral reefs and that even comparatively small areas with higher TBT concentrations experienced localized eco-system failures.
It was primarily on the basis of that research that the US eliminated TBT from bottom paint. These factors have little to do with the more complicated issue of TBT's danger to humans. TBT and heavy metals have been shown to be a threat to humans in high enough concentrations. It could be argued that we do not really know what those dangerous concentrations really are or how these materials act a lower levels, but it would be hard to argue that higher levels of these materials haven't entered the food chain over a comparatively short period of time and that mankind did not play a predominant role in that, or that mankind, and we, as sailors need to try to responsiblibly reduce these levels where we can.
And this comes back to the last point that I want to make, even the long lifespan argument to use TBT paints is specious. TBT even more than copper based paints, is very dependent on the vehicle (type of paint that it is suspended in). Unlike copper based paints, it does not corrode and create passages that allow fresh metal to reach the surface and so TBT only works well in ablative paints where the paint sloughs away revealing fresh TBT. The lifespan of an abblative paint is solely related to its thickness and its hardness. Using a moderately hard, moderately thick coating of an ablative can result in a very long lifespan bottom paint. That lifespan is the same whether the paint is copper or TBT based. It is also important to understand that TBT does not inherently add to the lifespan of that paint.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies
Last edited by Jeff_H; 06-05-2009 at 09:20 AM.