Küstenbiologie - Coastal Biology

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Shipworm countermeasures chemical impregnation

chemical impregnation

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Teredolarvae are quite small and delicate (see: biology), so theoretically (!) it should be easy to keep them from penetrating the wood surface. All you need is a thin layer to separate the larva from wood, and it does not necessarily need to be poisonous.

In practice it seem to be harder to find the right coating for wood in sea water. Wood expands or contracts, it takes up water or cracks appear. Close to the water surface  you also get UV radiation, wave action, ice and flotsam, that could damage the coating. A ship may scrape along in deeper regions. And even a small damage may be quite fatal, because larvae will "smell"´the free wood surface and aggregate there, weakening the piling more than if they spread evenly. One would need a very elastic coating. AFAIK the L.A. port authority did extensive testing with polurethane coating, but I failed to find the results.

Poisonous preparations are supposed to balance out this shortcoming, especially for wooden ships. They may cover little damages by leaking their substances into wood and water. Also, they will reduce not only shipworms, but also fouling organisms. However, the leakage of substances like copper or TBT into water and food chain is no longer tolerated, at least not in the Baltic Sea, and traditional anti-foulings slowly go out of fashion.

This leaves us with impregnations. If you are able to move the "coating" under the wood surface, the leakage is reduced and only has to work when the shipworm actually ingests it. One could develop chemicals that are less noxious or work specifically with wood borers, but so far the industry relies on the "chemical mace". Earlier the perfect chemical used to be creosote, the stuff you used to see in telegraph poles. It is very effective against teredinids, but also very carcinogenic. It has long been banned, along with CCA-salt (copper-chromium-arsenic), which was especially popular in the US, it seems. In Germany and Danmark we used to have the very similar CKB-salt (copper-chromium-borate). These pilings are still in use and can be recognized by their greenish color. "Marine impregnation" with CKB takes up to 80 kg of salt per cubic meter, but even this amount will not last forever. Over twenty years it leaks out of the wood so that pilings finally are attacked, while the heavy metals end up in the environment. So CKB is banned now as well.

Next in line are "copper-organic" solutions, which are likely to be banned as well by the EU bureaucracy. Especially in the Baltic the introduction of all kinds of chemical is restricted, so that the development of environmentally friendly impregnations should be encouraged. Here Coastal Biology can help with research and testing.

Last Updated on Thursday, 22 February 2018 09:51