02-04-2002 Port of Houston Expansion Review Committee Minutes

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5 type of exposure to evaluate because chemicals leaching from the hull of a ship represent along-term continuous source. Effects Characterization. Atypical aquatic community in a marine environment is comprised of a wide variety of organisms, including copepods, amphipods, polychaetes, decapods, bivalves, and fish. The physiology of these organisms is quite variable, and accordingly, they have very different sensitivities to chemicals such as antifoulants. Because toxicity data will not be available for all species in the marine community being evaluated, the sensitivities of a diverse group of test organisms are assumed to represent the sensitivities of a natural marine community. Ideally, toxicity data from chronic studies would be available, but it is sometimes necessary to estimate the chronic sensitivities from acute toxicity data. The toxicity tests should be based on ecologically relevant endpoints such as survival, reproduction, development, and growth. For most alternative antifouling biocides chronic toxicity data are very limited, and for several antifouling biocides acute toxicity data are also limited. The paucity of toxicity data for several antifouling biocides may be the limiting factor in comparing the risks posed by a variety of antifoulants. Risk Characterization. The risk characterization combines the information compiled in the exposure and effects characterizations in order to estimate potential risk. The risk characterization may simply be deterministic where a point estimate of exposure is compared to a point estimate of effects (e.g., the concentration protective of 95 percent of the species) or probabilistic where the distribution of exposure data is compared to the distribution of effects data and risk is reported as the percent species in the aquatic community expected to be affected. Regardless of approach, the point estimates or distributions must be calculated using the same methods. In addition to direct chemical risks posed by an antifoulant, other issues must be considered in a comparative risk assessment. For example, increased fouling could result in introduction of foreign species, increased emissions of greenhouse gases caused by greater ship drag, and greater consumption of fossil fuels due to reduced fuel efficiency. Tributyltin The following summarizes the availability of exposure and effects data for TBT, as well as the results of a TBT risk assessment at three marine locations in the U. S. Exposure Data. Tributyltin concentrations in the aquatic environment have been heavily studied at many locations throughout the world, including the North Sea, the Mediterranean Sea, the Black Sea, and Japanese water bodies (e.g., CEFIC 1994; Tolosa et al. 1996; Suzuki