used for environmental evaluation and policy, the principal objective of the risk assessment and risk management approach is not to eliminate all risk but to quantify the risk and provide risk managers with tools to balance the level of risk against the cost of risk reduction, against competing risks, or against risks that are generally accepted as trivial or acceptable. Controlling the exposure of human populations to environmental contaminants in biosolids using a risk-based approach requires a definition of both an appropriate metric for assessing the impacts of contaminants on human health and a defensible process for assigning value to the predicted impacts. The end product of a risk-based approach to environmental management is either to identify an acceptable level of exposure or to prescribe the technical controls or political process needed to attain acceptable risk. Intervention can be achieved through technical or political controls.

Components of the Risk-Analysis Process

The NRC (1982, 1994) has divided and continues to divide the practice of risk analysis into two substantially different processes—risk assessment and risk management. Along with these processes are concurrent efforts to communicate and evaluate risk (NRC 1989, 1996). This section explores the evolution of the risk-assessment process over the last decade by considering the component steps in the process.

Risk assessment is the process of selecting and quantifying the adverse consequences that result from an action, such as application of biosolids to soils, or from inaction. A risk assessment begins with efforts to identify the potential hazards associated with a chemical or microbial agent and its use or occurrence. Hazard identification addresses the potential for harm but not the likelihood of harm. Risk characterization establishes the significance of an identified hazard by quantifying the likelihood and severity of exposure scenarios linked to that hazard. As applied to toxic agents, risk characterization has five principal elements: (1) quantification of sources and environmental concentrations in exposure media; (2) quantification of exposure to the target population and distribution of the dose among the population; (3) characterization of a dose-response function for all potential toxic agents that have been identified; (4) estimates of the number of people affected and severity of consequences expected within the population at risk; and (5) an assessment of the magnitude and sources of uncertainty that limit the precision of the estimate of consequences.

Risk management is the process of weighing policy alternatives and selecting the appropriate societal or institutional response. Risk management is

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