When using the safety factor approach, confidence intervals are not given and the degree of protection is usually unknown. Because of the somewhat arbitrary nature of safety factors, their application must be appropriate to the particular purpose and documentation describing the logic used in selecting a particular number should always be provided. The use of the same safety factor (e.g., 10) in all cases has been discouraged by several regulatory and scientific bodies in favor of case-specific values. In particular, the scale, frequency, severity, and potential for long-term consequences of the environmental insult must be taken into account. Providing protection against an acute spill that is easily remediated may require less precaution (and therefore smaller safety factors) than the permitted continual release of a pollutant discharge. The decision to use a safety factor approach, and the eventual selection of the appropriate number, is more a management decision than a scientific methodology. The desired level of protection (which is inversely proportional to the degree of risk aversion of the regulatory body) will play a large role in determining how much of a margin of safety to build into a management decision.
There are those who propose that a severe lack of data (e.g., only one or two acute toxicity values) should preclude the use of a risk assessment in favor of a precautionary approach. That is, rather than applying a large safety factor and allowing the action to proceed, no action should be taken until sufficient data are generated to have at least a reasonable estimate of the potential range of sensitivities. While this may have merit within the context of new chemical releases or discharges, it provides no means for establishing remediation or cleanup levels for environments with historic pollution issues, nor does it allow for any means of an assessment of the comparative risk of current practice with proposed new technologies.
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