National Academies Press: OpenBook

Issues in Risk Assessment (1993)

Chapter: Discussion

Suggested Citation:"Discussion." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.

areas, particularly in harbors with large marinas. Snails in the vicinity of a marina on the York River, Virginia, were shown to have an abnormally high incidence of imposex (expression of male characteristics by female organisms), an effect previously observed under laboratory conditions in female European oysters, Ostrea edulis (Huggett et al., 1992). EPA began to assess effects of TBT in 1986, but has not yet issued any regulations. Meanwhile, restrictive actions have been taken by states and by the Congress.

A proposal by the U.S. Navy to use TBT paints on its entire fleet was prohibited by Congress in 1986, despite a Navy study that predicted no adverse environmental impact. Virginia enacted legislation and an emergency regulation in 1987, and Maryland, Michigan, and other states have since taken similar actions. Congress enacted national legislation restricting use of TBT paints in 1988. Those actions generally banned or restricted the use of TBT paints on small boats (less than 25 m long) and placed limits on leaching rates from paints used on larger vessels. Studies in Virginia had shown that most TBT releases were from small boats. Small-scale monitoring studies (e.g., in France and Virginia) have shown that the restrictions have been effective in reducing environmental concentrations and adverse impacts of TBT.

Risk management of TBT has been unusual in several ways. The initial basis for concern was field observation of adverse effects, not extrapolation from laboratory bioassays and field chemistry data. Risk assessment and risk management were conducted by state agencies and legislatures, rather than by EPA. Although the risk assessments were made without formalized methods, the results of the independent assessments were the same. Finally, TBT is the first compound banned by the Congress and the first regulated for environmental reasons alone.


(Led by L. Barnthouse, Oak Ridge National Laboratory, and P. F. Seligman, Naval Ocean Systems Center)

The case study addressed, with differing completeness, each of the five recommended steps in risk assessment and management. Hazard identification included the observation of abnormalities in the field and the same effects in experimentally exposed animals. Dose-response identification included data both from the field (correlative) and from the laboratory (experimental). Exposure assessment was based on estimated

Suggested Citation:"Discussion." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
Page 294
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The scientific basis, inference assumptions, regulatory uses, and research needs in risk assessment are considered in this two-part volume.

The first part, Use of Maximum Tolerated Dose in Animal Bioassays for Carcinogenicity, focuses on whether the maximum tolerated dose should continue to be used in carcinogenesis bioassays. The committee considers several options for modifying current bioassay procedures.

The second part, Two-Stage Models of Carcinogenesis, stems from efforts to identify improved means of cancer risk assessment that have resulted in the development of a mathematical dose-response model based on a paradigm for the biologic phenomena thought to be associated with carcinogenesis.

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