public health gains and costs would yield a more effective use of resources for public health (or other) purposes. 2. Designation of a Significant Risk At the initia) stage in its standard-setting process, EPA determines whether the emissions from a source category pose a “significant” public health risk. In doing so, EPA considers whether the substance emitted is a human car- cinogen and whether individuais or larger populations are significantly exposed to the substance. However, EPA re- ports that it has not used a “numerical target level” of significant exposures because of the uncertainties associated with its risk estimates."’ There is indeed no pattern in EPA's proposed rules that suggests the use of a systematic cutoff in regulating source categories emitting hazardous pollutants. In Its proposed rules for source categories emitting radionuclides and inorganic arsenic, EPA propose standards for seven source categories. In addition, EPA specifically considered and decided not to propose standards for ten other source categories it had identified at the time of listing these pollu- tants." EPA reached its decision on whether to propose standards for these source categories only after making a BAT determination and a residual risk assessment for each source category. By deferring to a later stage in the standard-setting process the decision whether to propose standards, EPA was able to consider a variety of other factors, including the potential for further reductions in emissions (taking into account current regulatory requirements), the likely reduction in public health risk, and the costs and other economic effects of requiring more stringent contro! of these source categories. The deferral of a decision whether to propose a Standard until a later stage in the standard-setting process represents, in our view, a tacit recognition that an informed - 748 FT 33116. "EPA has taken no action for one source category —~ fossil fuel- fired combustion ~— identified in the listing of inorganic arsenic as a hazardous pollutant. : decision on the neead tor tui ics wepe - only after weighing the likely public health gains with the costs and other economic effects (e.g., plant closures) of further regulation. In general, this appears to be a good way to proceed. It is dificult to establish a priori a cutoff point that distin guishes “significant” public health risks from “acceptable” risks. The health risks posed by the various source categories identified by EPA as emitting inorganic arsenic and radionuclides illustrate the problem. There is no pronounced gap or clustering in the risks posed by the various source categories identified by EPA—rather, there appears to be a continuum from the highest risk sources to those sources posing lower risks. (See Figure 1.) Webelieveit is difficult to identify a de minimis level of public health risk without considering other factors influencing the likely public health gains of further regulation. However, EPA may find that there are administrative advantages to establishing a de minimis risk level. This would allow EPA to direct its attention toward those source categories posing the greatest public health risks. In addition, if EPA finds that it is precluded by statute from directly weighing the likely public health gains with the costs of regulation, an explicit de minimis threshold for public health risk at an initial stage in the standard-setting process could serve to screen out a numberof cases where regulation would achieve only negligible gains in public health. We encourage EPA to review the role of this initial stage in its standard-setting process. If EPA decides that an initial step of designating source categories posing significant public health risks serves a useful administrative role, we believe EPA should establish explicit criteria identifying levels of public health risk warranting further regulatory consideration. If EPA should do so, we would suggest the following as de mintmis levels of public health risk: EPA would consider further regulatory action for a source category if the aggregate annual cancer incidence at current emission Jevels for the source category is one likely cancer or more per year. In addition, EPA might want to consider regulatory action where annual risks to the most exposed ingiyidual are relatively high—for example, on the order of one in ten thousand or more. -~ g 1-13-84 Environment Reporter ates:ah eee sysSeA a eeSek ‘ - a bapa ed ay ee . + - ee ee Pa z3s aa w A ry Pe . . “4 See ran “ 7 a” . ”bef? eB ee ai Os