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

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! ~ 6 1994). In the U. S., TBT concentrations have been continuously monitored in three marine water bodies since 1991. Each of these water bodies consist of commercial harbors, shipyards, marinas, and proximal fish/shellfish habitat. This monitoring program provides current concentrations that can be used in risk assessment and also allows for a temporal comparison of risk since passage of TBT regulations in the late 1980s. The results of a risk assessment using these data are summarized below. Effects Data. The toxicity of TBT to aquatic organisms has been heavily studies since the 1970s. Standard acute toxicity data suitable for community-level risk assessments are available for 29 marine species, including echinoderms, bivalves, copepods, amphipods, crabs, shrimp, polychaete worms, and fish (Cardwell et al. 1999). Chronic toxicity data based on appropriate endpoints (e.g., survival, reproduction, development, growth) are available for seven marine species, including copepods, bivalve larvae, gastropods (e.g., snails), and fish (Cardwell et al. 1999; Manning et al. 1999). Risk Assessments. The following summarizes the results of a risk assessment conducted by Cardwell et al. (1999). Cardwell et al. (1999) conducted a risk assessment at four regions across the U. S. at which TBT has been heavily monitored since 1991 (three marine, one freshwater). In each of these regions, TBT concentrations were measured in four different site types: marinas, commercial harbors, shipyards, and fish/shellfish habitat. For each year, probability functions were fit to the TBT surface water data for each site type by region and all marine regions combined. These probability distributions of exposure concentrations were then mathematically integrated with probability distributions of effects data for the 29 different aquatic taxa described above. Risk is then expressed in terms of the average percentage of taxa that are expected to be affected due to TBT toxicity. Using the U. S. TBT monitoring data and acute and chronic toxicity data described above, the percentage of species at chronic risk from TBT in marinas declined from 25 percent in 1989 to <_ 5 percent by 1997. Similarly, chronic risks in commercial harbors and shipyards were also <_ 5 percent by 1997. Chronic risks were negligible (< 1 percent) in fish/shellfish habitat proximal to marinas, harbors, and shipyards by 1996. The sensitive species potentially at risk include some species of bivalves (such as clams and oysters) and copepods. None of these species are at risk in fish/shellfish habitat, however, and no species are at acute risk. These results demonstrate that chronic risks due to TBT are declining to acceptable levels (affecting less than 5 percent of the species is generally considered acceptable [e.g., Aldenberg and Slob 1993; Stephan et al. 1985]) and that risks