Introduction

According to its charter, the Commission is charged with investigating "the policy implications and appropriate uses of risk assessment and risk management in regulatory programs under various Federal laws." Current practices in these areas vary among Federal agencies and even among regulatory programs within the EPA. Some of this variation is attributable to different requirements among the Federal laws authorizing regulatory activity, either in the form of explicit methodologic requirements that assessments must follow or as differently mandated regulatory responsibilities that the assessments must support. Other differences reflect variations in policy among organizations, adopted as a matter of differing scientific and policy judgment or simply because of the independent establishment of varying precedents and preferences.

This array of methods reflects the fact that there is no single, agreed upon scientific procedure for the assessment of health risks from chemical exposures. The primary reason is that the needs of the risk assessment process, to make projections of possible human health risks for the variety of types and levels of exposures that may arise, far outstrip the ability of scientific investigation to give firm answers. The practical need remains, however, to make characterizations of the risk consequences (including the uncertainty about those consequences) of various potential actions and activities by industries, by government, by individuals, and by society as a whole.

Faced with this practical problem, regulatory agencies have arrived at practical methods. These methods include reliance on procedures that, while attempting to embody information from the available data, of necessity rely on uncertainty-bridging principles derived from a combination of general knowledge about chemicals, their behaviors in the environment and their toxic effects, a desire to maintain internal case-by-case consistency in how uncertainties are resolved, and a desire to ensure that regulatory decisions are likely to fulfill the legislative mandates about public health protection.

The basic issues of chemical health risk assessment and the role of risk assessment methods, default assumptions, and conservatism have been discussed in the National Academy of Sciences Report, Science and Judgment in Risk Assessment (NRC, 1994). This document builds on earlier works taking a comprehensive view of risk assessment and the principles underlying its conduct, especially Risk Assessment in the Federal Government: Managing the Process (NRC, 1993), widely known as the "NAS Red Book," and Chemical Carcinogens: A Review of the Science and Its Associated Principles [50 FR 10371-10442], widely known as the "OSTP Principles."

These documents epitomize an ongoing discussion that has largely succeeded in defining a common framework and structure for risk assessment. Within this framework, however, there continues to be vigorous debate about the most appropriate risk assessment approaches, the bearing of various kinds of data on risk projections, and the degree and appropriateness of conservatism in risk assessment methods. Faced with this continuing disagreement about methods, various Federal regulatory agencies have adopted somewhat different procedures. In part, this diversity can be attributed to the different questions being asked of the risk assessment process in different regulatory contexts by different environmental statutes. In part, it reflects different institutional judgments about the most appropriate methods and different scientific judgments about matters with high scientific uncertainty. And in part, it reflects simple policy choices made for the sake of consistency within each organization (which, owing to independent histories, becomes inconsistent among organizations).

The effect of this diversity of methods among Federal regulatory agencies is to make it difficult to compare risks, or the actions taken to mitigate those risks, from one regulatory program to another. One program's concern for a one-in-a-million cancer risk, say, may be based on an upper bound low-dose extrapolation to an average person in the exposed population extrapolated from mice based on a presumption of equal toxicity when daily doses are scaled by surface area, while another program's one-in-a-million is for a hypothetical person exposed to an agent at the regulatory limit for 45 years based on a maximum likelihood low-dose extrapolation and the presumption that equitoxic doses are proportional to body weight.

Although defaults and standard methods are necessary in the face of uncertainty and lack of case-specific knowledge, variation from group to group in these defaults enhances the sense of arbitrariness in risk analyses. In cases where regulatory responsibilities overlap or when different groups have cause to assess the same exposures, differences in assessment outcome can lead to conflict and confusion among the public and the regulated community.

This chapter attempts to sort out some of those sources of confusion by analyzing the public health mandates and regulatory powers of a number of risk-related regulatory programs' enabling statutes (see Table A.6.1), along with risk assessment and risk management practices as they have evolved in response to those statutes. Special attention is focussed on the laws' requirements about who in the exposed population is to be protected, and how sufficiently protective standards are defined. A summary overview of Federal risk-based regulations, mandates, statutory language, and principal differences in risk assessment methods is provided in Table A.6.2.



Table A.6.1. Environmental regulatory statutes addressed in this report.

Table A.6.2. Summary overview of Federal regulation of potentially toxic chemicals, including risk mandates, key statutory language, and principal differences in risk assessment methods among Federal regulatory programs.