4.10.2 Non-Toxic Alternatives 



These materials either repel the fouling organisms or interfere with the 

 attachment process (Ghanem et al., 1982) . A repellant compound of cellu- 

 lose acetate and metyl siloxane loaded with silica has been devised and is 

 being tested. When an organic acid such as tannic acid or benzoic acid is 

 combined with acrylamid polymers, a surface treating material is obtained 

 which has the effect of repelling fouling bacteria, without being toxic to 

 them. 



During the recent period of extremely high world oil prices, the U.S. Navy 

 experimented with underwater removal of fouling organisms using divers and 

 motorized hull cleaning brushes on ships painted with conventional copper 

 based antifouling paints, to extend antifoulant life (Cologer, 1984) . A 

 commercial towing firm in England is testing the use of a non-toxic low 

 energy surface such as fluoropolymers (teflon) or silicon polymers which 

 resist adhesion by fouling organisms and release the organisms rea d ily 

 when frequently (intervals as short or shorter than 6 months) scrubbed in 

 the water using the divers and motorized in situ cleaning equipment. To 

 date in the U.S., only the State of Maryland has indicated any concern 

 over the ecological effects of the scrubbing of vessels in coastal 

 waters. Recent TBT control legislation in Maryland also mandated a study 

 of the environmental effects of under-water hull cleaning using motorized 

 brushes (MD General Assembly, 1987) . 



When the surface being scrubbed is coated with conventional antifouling 

 paints there exists the potential to remove a portion of the paint film by 

 abrasion and introduce it directly into the water or sediments. Whether 

 the introduction of fluoropolymers from a teflon coated surface will intro- 

 duce new ecological problems remains to be investigated. 



4.10.3 Disruption of Fouling Succession 



The single most promising line of investigation to develop alternative 

 antifouling materials, is the inquiry into the successional stages of 

 biofouling. When a clean smooth surface is immersed in seawater the first 

 organisms to settle are bacteria. The bacterial attachment to the surface 

 is at first reversible by the bacterium but after a period of time the 

 attachment becomes permanent. On surfaces where the bacterial film is 

 periodically removed, further settlement by other organisms is strongly 

 inhibited. This process is well known to sailboat racers who clean their 

 antifouling paint with a sponge or brush, on weekly intervals during the 

 racing season. 



An undisturbed bacterial film soon embeds the bacterial cells in a matrix 

 of polysaccharides secreted by the bacteria themselves (Madelyn Fletcher, 

 personal coroinunication) . Current investigations by NBS and several 

 researchers at U.S. universities are focusing on the roll of this 

 polysaccharide as an attractant to further settlement by other organisms. 



IV-53 



