Conceptual Bases for De Minimis Risks

The concept of de manifestis risk is not controversial because some effects are clearly unacceptable. However, the idea that some exposures to and effects of pollutants are acceptable (de minimis) is controversial. The use of the de minimis concept is based on the following considerations:

1. Some exposures and effects are manifestly trivial. For example, it is absurd to assess effects of exposure to one molecule per organism or to consider restricting a pollutant exposure because it causes a transient physiological response or causes one copepod species to replace another.
2. There are many genuinely significant risks, so it is inappropriate to set them aside while assessing the trivial ones. As Weinberg (1987) remarked, one does not swat gnats while being charged by elephants.
3. Regulatory scientists and decision‐makers do not have infinite time and resources. The benefits from their time and resources should be maximized by quickly setting aside trivial risks.
4. Very low level exposures and effects are very difficult to accurately quantify. Therefore, any attempt to balance their costs against the costs of treatment or prevention, or the benefits of a product are likely to be confusing or misleading rather than enlightening.
5. Small increases in exposure to naturally occurring chemicals or other hazardous agents are likely to have trivial effects, because of adaptation to the background levels. This is particularly true if the increase is also small relative to variation in the naturally occurring background levels.
6. Effects that are small relative to natural temporal or spatial variability of the biological parameter are likely to have trivial implications either at other levels of biological organization or for other components of the same level of organization. For example, an apparently large (e.g. 50%) temporary depression of the decomposition rate is unlikely to significantly affect primary production or abundance of birds because they are adapted to much larger variance in the rate due to wetting and drying cycles and other natural variables.
7. Treating a trivial risk as if it were potentially significant unnecessarily raises public concerns that are not entirely extinguished by a subsequent finding that the risks are small.

Since we cannot prevent all human effects on the environment, and we cannot even carefully assess the benefits and costs of all human actions, it is desirable to develop criteria for eliminating clearly trivial risks from further consideration.