and inhibits the release of biocide, then the surface becomes biofouled. 

 This leaves a quantity of biocide that remains unused on the vessel hull, 

 which must be removed prior to the next painting. The removed paint film 

 must be properly disposed of or it may then be a source of environmental 

 contamination. The usual response of the recreational boater and small 

 commercial operator to calcarious fouling of the paint film is to abrade 

 the surface or remove the paint film and reapply. There may be a 

 significant amount of TBT remaining in the film when the fouled film is 

 removed. There have been few studies directed to the extent to which the 

 old paint film is a source of TBT to the environment. The British Royal 

 Yachting Association, in close consultation with other concerned fisheries 

 associations and the Department of the Environment, produced a public 

 education document directed at controlling the introduction of old paint 

 into the coastal waters. 



In about one half of the 1987 registered paint formulations, tributyltin 

 is mixed with copper compounds. By the nature of the mixture, these 

 paints are free association types. An example of this is a vinyl copper 

 formulation which uses a very low (1%) TBT in the film as an 

 antibacterial-antislime agent which increases the effectiveness of the 

 copper oxide, the primary antifouling material. Other example mixed free 

 association formulations include: 



a) a formula having — 2.5% TBT and 16% copper. 



b) a series of blue and green paints having — TBT content ranging 

 from 13.3% to 15.7% depending on the paint color selected. 

 Tributyltin is colorless and is used in higher percentages in 

 colors other than the red shades which copper produces. 



On the basis of paint surface exposure to the environment, the painted 

 areas covered with free association paints account for a little more than 

 one third of the total bottoms painted (Lucas & Williams, 1987) . 



Type 2 is commonly referred to as an "ablative" (or shedding) paint. It 

 is a slightly seawater-soluble matrix paint that sheds during use — as the 

 paint surface roughens, paint particles (very thin microlayers) peel off, 

 exposing a fresh supply of biocide (Figure 1.4). The biocides are added 

 in the free association form, leaching exponentially over time. The 

 release of biocide also is inhibited by the formation of surface 

 insoluble. The lifetime of this paint is about 2 years. 



Type 3 antifouling paint is commonly referred to as "self-polishing" 

 copolymer paint. Developed in the early 1970 's, the paint is hydrophobic 

 (i.e. , seawater does not enter into the paint matrix) . The seawater/paint 

 reaction layer occurs at the surface of the paint; the paint has an 

 unstable release layer that gradually erodes (Figure 1.5). The paint 

 formulation has biocide at very low levels, which are released at the 

 surface layer. 



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