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3 <br />TBT-based paints to ships over 25 meters and controlled the release rate of the <br />antifoulant from the paint. These restrictions have been very effective and TBT in US <br />waters has declined so dramatically that there has been no risk of adverse effects to <br />aquatic life from acute (short-term) exposure to TBT since 1994 (Cardwell et al. 1999). <br />Since 1996, risks to aquatic life from chronic (long-term) exposures to TBT are below the <br />US EPA recommended level for protection of an aquatic community at all sites <br />monitored except for some commercial locations in Galveston Bay, Texas (Cardwell <br />et al. 1999). Since at least 1992, areas critical to fish and shellfish communities have not <br />been at risk from exposure to TBT. These declines in TBT concentrations and <br />elimination/reduction of risk to aquatic life are likely associated with the 1988 regulations <br />and changes in the type of TBT-based paint used. Use of free-association ap ints <br />predominated until the late 1980's, at which time they were replaced by TBT self- <br />polishing copolymer (SPC) based ap ints. SPC paints include the TBT biocide chemically <br />bonded throughout the coating, and allow application of thicker paint coatings. This <br />results in a uniform release of biocide, and reduces the amount of biocide entering the <br />environment (particularly during harbor activities). <br />Comparative Aquatic Life Risk Assessment <br />of Tributyltin and Tin-Free Biocides <br />Introduction <br />Based on recommendations of the Marine Environmental Protection <br />Committee (MEPC), the International Maritime Organization (IMO) <br />has developed a global initiative that will eventually result in the ban <br />of all antifouling systems exhibiting harmful effects on the marine <br />environment. In the interim, antifoulants expected to have the fewest <br />impacts on the marine environment will be required. Tributyltin <br />(TBT) is currently the only antifoulant subject to the regulations <br />under this initiative. Alternative antifouling paints are aggressively <br />being developed as potential replacements for TBT. Given the <br />number of alternative antifouling paints being developed, a process is <br />necessary to determine the antifoulant expected to have the fewest <br />impacts on the environment. <br />The most appropriate process for comparing the potential impacts of <br />antifoulants on the marine environment is risk assessment. Risk <br />assessment considers both the exposure potential and the effects <br />potential of the antifoulant to biota in order to assess the potential to <br />cause adverse impacts. A risk assessment consists of the following <br />phases: <br />Source: US EPA Risk Assessment Guidance for <br />Superfund. Vol. 1. 1989 <br />