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DEALING WITH UNCERTAINTY ABOUT RISK IN RISK MANAGEMENT 57 original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. Multiple Sources of Risk The definition of a de minimis risk should reflect the possibility that multiple de minimis exposures could result in a large aggregate risk. For instance, one could conceivably be exposed to the same hazardous material in drinking water, in the air, or in a variety of foods as in exposure to a pesticide in a rural area. As a practical matter, one or two pathways are likely to dominate exposures, and it is unlikely that total exposures could be greater than several times the exposure received through the most significant pathway. Given the uncertainties in the estimate of low-level risks, this difference seems trivial. A far more troubling question is posed by the sheer number of risk agents. It would hardly be comforting to learn that although no single chemical in drinking water poses a cancer risk greater than 10-7/yr, there are hundreds of such chemicals. The problem this issue poses for the use of de minimis as a regulatory threshold is the degree to which risks are examined and managed singly rather than aggregated. The prevalent chemical-specific approach to risk analysis seems to support a de minimis concept on an agent-by-agent basis. Other approaches to risk analysis support a de minimis definition for an aggregation of agents and provide confidence that the sum of de minimis risks any individual sees is limited in the aggregate. Of course there are many ways to aggregate risks: one could consider all effluents from a single facility or those found only in the air, in drinking water, or in food. Clearly the approach taken under a de minimis philosophy to avoid excessive accumulations of risk can take many forms, depending on the specific context. The Food and Drug Administration treats this issue through stringent criteria that consider the potential for accumulation of risk. Proposed de minimis risk levels for radiation are typically higher than the levels considered by FDA for food additives, reflecting the fact that there are far fewer sources of radiation than of food additives. Applying the De Minimis Concept Many issues must be resolved to develop a workable de minimis policy. Contextual issues such as multiple exposures, the population at risk, and the degree of confidence in a risk estimate suggest that a basic de minimis risk philosophy will have to be flexible to specific considerations. Proposed de minimis approaches have dealt with aspects of the problem, notably with the comparative logic that justifies selection of a de minimis level in a specific context. More effort is needed, however, if the de minimis approach to risk
