Those charged with risk management for human health are fully aware that some risks have consequences so dire that they must be avoided no matter what the cost. Risks so obviously unacceptable are called de manifestis. The companion concept, de minimis, which we shall explore shortly, points to the existence of risks with consequences so harmless that they are not worth treating, no matter how little the cost. Whipple (1987) has written about de minimis risks, and Travis et al. (1987) and Kocher and Hoffman (1991) have discussed both concepts in relation to cancer prevention.
Risk levels between the de manifestis and de minimis bounds are balanced against costs, technical feasibility of remediation, and other considerations to determine their acceptability. Because there have been no standard assessment endpoints for ecological effects, there have been no de minimis or de manifestis ecological risk levels. However, the protection provided to endangered species in the United States provides one basis for de manifestis risk levels because it ostensibly precludes economic and sociopolitical considerations. Establishment of de manifestis and de minimis risks would allow assessors to quickly dispense with clearly unacceptable or trivial risks after minimal assessments that do not establish the exact expected risk level, or balance costs and benefits. Consideration of what levels and types of ecological effects are clearly and invariably acceptable, and which are clearly and invariably unacceptable would provide risk assessors and risk managers with a good basis for working out the relation between societal values and ecological principles.
A final consideration in risk characterization and management is the need for audiences other than the risk manager to understand the risks and the bases for the decision. These include the public, environmental advocacy groups, and regulated parties. Risk communication to the nonprofessional has been a major topic of research and discussion with respect to health risks, but not ecological risks (NRC 1989). This is understandable because the average citizen is more concerned with personal and family health than with ecological effects. However, when outside parties become concerned about potential ecological effects, the diversity of ecological endpoints and the uncertainty of their valuation make risk communication highly complex. Earlier we cited a hypothetical situation in which a nonpesticide approach to eliminating crop‐destroying insects that would harm some wildlife was likely to be acceptable to groups opposed on principle to pesticides. Under different circumstances, there might be scientific support for replacing a pesticide with another substance that posed a higher risk to avian populations but a lower risk to zooplankton. Yet arguments for accepting more dead birds in exchange for fewer dead zooplankton would not be easily conveyed to a diverse audience.
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