categories.” By using definitions of risk and hazard established in previous National Research Council reports, the committee attempted to rank those concerns. In these two ways, the committee attempted to put those concerns in perspective and to provide a balanced viewpoint.

Any analysis of GE organisms and their potential impact on the environment needs to distinguish between organisms engineered for deliberate release and those that are engineered with the intention of confinement but escape or are inadvertently released. The discussion in this report focuses primarily on the latter category, but the committee recognized the possibility of intentional release of GE organisms into the environment and expressed a high level of concern about it. This chapter also focuses primarily on risks as a result of genetically engineered (GE) animals entering natural environments and transgene spread through vertical gene transmission (the sexual transfer of genetic information between genomes) followed by natural selection. The risk of horizontal gene transfer (the nonsexual transfer of genetic information between genomes; Kidwell, 1993) is discussed primarily in Chapter 2.

This chapter, therefore, is organized into a discussion of: (1) general principles of risk analysis, (2) general aspects of the organism, transgene, or transgene function that can be used a priori to prioritize GE animals for level of environmental concern, (3) risks posed by key classes of GE animals, and (4) the need for further research directed at improving our understanding of hazards and estimating risks posed by genetically engineered animals.

GENERAL PRINCIPLES OF RISK ANALYSIS

Consideration of environmental concerns posed by GE animals must be based on an understanding of key concepts underlying the science and practice of ecologic risk assessment. A seminal review of risk assessment methodology (NRC, 1983) states, “Regulatory actions are based on two distinct elements, risk assessment, and risk management. Risk assessment is the use of the factual base to define the health effect of exposure of individuals or populations to hazardous material and situations.” Risk management is “the process of weighing policy alternatives and selecting the most appropriate regulatory action, integrating the results of risk assessment with engineering data and with social, economic, and political concerns to reach a decision.” Clearly, risk management is beyond the purview of this committee, while elements of risk assessment are needed to prioritize concerns.

Understanding Risk: Informing Decisions in a Democratic Society (NRC, 1996) updated the 1983 NRC study and provided two important definitions: Hazard: an act or phenomenon that has the potential to produce harm, and Risk: the likelihood of harm resulting from exposure to the hazard. While the earlier study describes risk assessment as containing some or all of the following steps:



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