Laserfiche WebLink
4 <br />In order to compare the risks associated with different antifouling <br />paints, each risk assessment component should be evaluated similarly <br />and be based on similar types of data. <br />This paper first discusses some of the key issues and types of data <br />that are necessary for a comparative assessment of antifoulant risks <br />to be valid and scientifically defensible. Second, the availability of <br />exposure and effects data for TBT-self-polishing copolymer (SPC) <br />paints is discussed, along with the results of aquatic risk life <br />assessments that have been conducted at multiple sites in the United <br />States. Third, the availability of exposure and effects data for <br />alternative antifoulants is compared to that of TBT. The paper <br />concludes with a summary on the state-of--the-science with regards to <br />the comparative risks posed by TBT and alternative antifoulants. <br />Key Issues/Data Requirements <br />The following highlights the key issues and data requirements that <br />must be addressed in comparing the risks posed by TBT-SPC and <br />alternative antifoulants in the marine environment: <br />Problem Formulation. Assessment endpoints define the measurable <br />ecosystem characteristics that are to be evaluated in the risk <br />assessment (USEPA 1998), such as survival, growth, and <br />reproduction of the marine community. Using this example, the <br />measure of exposure may be antifoulant concentrations in surface <br />water and the measure of effect may be the toxic response of marine <br />organisms to antifoulants. For a comparative risk assessment to be <br />meaningful, therefore, the assessment endpoints and measures of <br />exposure and effects must be the same or comparable for the <br />different antifouling systems. <br />Exposure Characterization. As discussed above, the measure of <br />exposure in an antifoulant risk assessment may be antifoulant <br />concentrations in surface water. In a comparative risk assessment, <br />these exposure concentrations should be based on comparable data <br />sources. For TBT, surface water concentrations have been well <br />characterized in many locations throughout the world (e.g., CEFIC <br />1994; Dowson et al. 1994; Russell et al. 1996; Tolosa et al. 1996). As <br />discussed later, however, surface water data for most other <br />antifouling biocides are limited or non-existent because they are still <br />in the developmental phase, they have had little use, or they just <br />simply have not been measured. Accordingly, environmental <br />concentrations of alternative antifoulants typically need to be <br />modeled. In a comparative risk assessment between antifouling <br />biocides and TBT-SPC, therefore, TBT concentrations should also be <br />modeled to ensure consistency. It should also be noted that chronic <br />(i.e., long-term) exposure durations are probably the most relevant <br />