Destruction of Man-Made Materials by Marine Microbes
An important aspect of microbial activity in the sea, at least from the economic point of view, has to do with the corrosion and destruction of man-made structures, including ships, steel and concrete pilings, rope, wharf pilings and similar things.l Bacteria are believed to form a primary film on steel ships; this coating prevents or delays the copper or mercury of the antifouling paint from keeping off the larger fouling organisms such as barnacles or tube-worms. Dr. Hendey, in Britain, has found that some diatoms have a higher resistance than others to both copper and mercury, the poisons actually used in antifouling paints for the control of growths or ships bottoms.2 Microbes of several kinds can, therefore, reduce the effectiveness of antifouling paints and shorten their active life. They also play a part in the destruction of antifouling and anticorrosive paints used on the hulls of ships, mainly by attacking the vehicle — the part of the paint that causes it to flow and to adhere to the surface. Very important in the corrosion of hulls and steel structures are the bacteria which reduce sulphates to sulphides. Sometimes a blister in the metal of a hull, or a small ‘holiday’ or gap in the paint film, will allow bacteria to collect against the steel, while the decomposition of organic detritus sticking to the hull removes most of the oxygen. As a result, a small area has a lower electrode potential than the rest of the hull, that is a lower redox potential, and a small electricurrent passes from one area to another; part of the metal then goes into solution by electrolysis. The reaction spreads, the paint sloughs off, and cracks appear, allowing further attack by the bacteria. When the mothball fleet of the United States Navy in San Diego harbour was activated for the Korean war, it was found that this kind of corrosion had occurred on a number of ships, just below the waterline and all around the hulls, so there was a band of partly removed and altered metal right round the ship. Considerable repairs were necessary before the fleet could put to sea.
KeywordsPaint Film Antifouling Paint Botulinus Toxin Lower Redox Potential Organic Detritus
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