Opinion ID: 338705
Heading Depth: 2
Heading Rank: 1

Heading: The Threshold Determination

Text: 19 In making his threshold determination that lead particulate emissions from motor vehicles will endanger the public health or welfare, the Administrator provided his interpretation of the statutory language by couching his conclusion in these words: such emissions present a significant risk of harm to the health of urban populations, particularly to the health of city children. 38 Fed.Reg. 33734. By way of further interpretation, he added that it was his view 20 that the statutory language    does not require a determination that automobile emissions alone create the endangerment on which controls may be based. Rather, the Administrator believes that in providing this authority, the Congress was aware that the public's exposure to harmful substances results from a number of sources which may have varying degrees of susceptibility to control. 21 Id. It is petitioners' first claim of error that the Administrator has erroneously interpreted Section 211(c)(1)(A) by not sufficiently appreciating the rigor demanded by Congress in establishing the will endanger standard. Therefore, petitioners argue, the Administrator's action is short of statutory right, in violation of Section 10(e)(2)(C) of the Administrative Procedure Act (APA), 5 U.S.C. § 706(2)(C) (1970). 22 Petitioners argue that the will endanger standard requires a high quantum of factual proof, proof of actual harm rather than of a significant risk of harm. See supplemental brief of petitioner Ethyl Corporation (hereinafter Ethyl Supp.Br.) at 20. Since, according to petitioners, regulation under Section 211(c)(1)(A) must be premised upon factual proof of actual harm, the Administrator has, in their view, no power to assess risks or make policy judgments in deciding to regulate lead additives. Moreover, petitioners argue, regulation must be based on the danger presented by lead additives in and of themselves, so it is improper to consider, as the Administrator did, the cumulative impact of lead additives on all other sources of human exposure to lead. We have considered these arguments with care and find them to be without merit. 15 It is our view that the Administrator's interpretation of the standard is the correct one. 16 23 1. The Precautionary Nature of Will Endanger. Simply as a matter of plain meaning, we have difficulty crediting petitioners' reading of the will endanger standard. The meaning of endanger is not disputed. Case law and dictionary definition agree that endanger means something less than actual harm. 17 When one is endangered, harm is threatened ; no actual injury need ever occur. Thus, for example, a town may be endangered by a threatening plague or hurricane and yet emerge from the danger completely unscathed. 18 A statute allowing for regulation in the face of danger is, necessarily, a precautionary statute. Regulatory action may be taken before the threatened harm occurs; indeed, the very existence of such precautionary legislation would seem to demand that regulatory action precede, and, optimally, prevent, the perceived threat. As should be apparent, the will endanger language of Section 211(c)(1)(A) makes it such a precautionary statute. 24 The Administrator read it as such, interpreting will endanger to mean presents a significant risk of harm. 38 Fed.Reg. 33734. We agree with the Administrator's interpretation. This conclusion is reached not only by reference to the plain meaning of the statute, but by juxtaposition of Section 211(c)(1)(A) with other sections of the Clean Air Act and by analysis of pertinent precedent. 19 25 Petitioners support their view of the rigorous nature of the will endanger standard by relying on two other sections of the Clean Air Act that also allow for regulation of air pollutants for health reasons. Ethyl Supp.Br. at 18-23; supplemental brief of petitioner Nalco Chemical Company (hereinafter Nalco Supp.Br.) at 20-25; NPRA Supp.Br. at 31-46. However, we find in the same sections relied upon by petitioners firm support for our view of the precautionary nature of Section 211(c)(1)(A). The provisions identified by petitioners are Sections 108 and 202 of the Act. Section 108 directs the Administrator to list, for the purpose of establishing national primary and secondary ambient air quality standards pursuant to Section 109, each air pollutant which in his judgment has an adverse effect on public health or welfare   . Section 108(a)(1)(A), 42 U.S.C. § 1857c-3(a)(1)(A). Section 202 authorizes the Administrator to set standards for each automobile emission which in his judgment causes or contributes to, or is likely to cause or to contribute to, air pollution which endangers the public health or welfare. Section 202(a)(1), 42 U.S.C. § 1857f-1(a)(1). 26 Petitioners suggest that the threshold decision to regulate under both Section 108 and Section 202 can be based on less evidence than required under Section 211 and that, therefore, the proof necessary for action under Section 211 must be particularly firm. Petitioners misread both sections. Section 108 requires an actual adverse effect on health before an air pollutant may be listed for regulation; actual harm must result. 20 This firm threshold finding is reasonable in light of the considerable disruption caused by action under Sections 108-110. After a pollutant is listed under Section 108, the Administrator must issue national ambient air quality standards under Section 109 within a year. Promulgation of standards begins the implementation plan process of Section 110 under which the states must control, on a mandatory timetable, the listed pollutants to the extent necessary to achieve the federal standards. Section 110, 42 U.S.C. § 1857c-5. Sections 108-110 are technology forcing provisions; the attainment of the primary, health-based standards takes precedence over the cost and present technological feasibility of achieving the requisite control. Union Electric Co. v. EPA, 515 F.2d 206, 215-16 (8th Cir.), cert. granted, 423 U.S. 821, 96 S.Ct. 35, 46 L.Ed.2d 38, 44 U.S.L.Week 3200 (1975). Cf. Train v. Natural Resources Defense Council, 421 U.S. 60, 90-91, 95 S.Ct. 1470, 1487-1488, 43 L.Ed.2d 731, 752-753 (1975). See also S.Rep.No.91-1196, 91st Cong., 2d Sess. 1-3 (1970). 27 Thus, before ordering this extensive chain of action to begin, Congress demanded a threshold determination that the pollutant causes actual harm. 21 In this sense Section 108 is not a precautionary statute at all, and so differs sharply from Section 211. However, the effects of such after-the-fact regulation are somewhat ameliorated by the Act; Congress did provide a precautionary element in standard-setting under Sections 108-110. Section 109 expressly requires that the ambient air standards ultimately issued provide for an adequate margin of safety. 42 U.S.C. § 1857c-4(b)(1). Thus, while the threshold decision to regulate under Sections 108-110 is not precautionary but rather requires proof of demonstrable harm caused by the suspect pollutant, once the decision is made the standards promulgated must be preventive in nature. Congress' choice of this scheme is in direct contrast to the procedures it established under Section 211. Under that section the decision to regulate is based on perceived danger. Unless we are to assume Congress chose its language carelessly, regulation in the face of danger rather than in the face of adverse effects must mean that the threshold decision to regulate under Section 211 is precautionary. 22 The contrast between the standards of Sections 108-110 and of Section 211 supports our view of the precautionary nature of the will endanger standard. 23 28 Petitioners also rely on Section 202 to support their strict reading of Section 211. Ethyl suggests that Section 202 is more lenient than Section 211 in that it allows regulation of likely dangers. Ethyl Supp.Br. at 18-19. See also Nalco Supp.Br. at 20-21; NPRA Supp.Br. at 31-36. Section 202 provides that the Administrator may regulate 29 The emission of any air pollutant (from any new motor vehicle) which in his judgment causes or contributes to, or is likely to cause or to contribute to, air pollution which endangers the public health or welfare. 30 42 U.S.C. § 1857f-1(a)(1) (emphasis added). While this language may be unnecessarily opaque, we think a fair reading disproves petitioners' suggestion. The italicized language upon which petitioners rely refers not to the causal relationship between air pollution and health, but to the relationship between automobile emissions and air pollution. 24 Thus regulation may not be premised on a threshold determination of likely danger; rather regulation must be premised on a determination of danger, a finding that air pollution which endangers the public health is the end product of the emission to be regulated. This is essentially the same finding of endangerment as under Section 211. Likely enters the equation only in determining whether the emitted air pollutant, which would be regulated, contributes to the air pollution which is found dangerous. Here the statute allows for a somewhat attenuated chain of causation. Regulation may be premised on a determination that an air pollutant emitted from a new automobile is likely to contribute to air pollution which endangers the public health. In establishing this chain of causation Section 202 is more lenient than Section 211, 25 but in making the threshold determination of danger both sections are the same: 26 air pollution must endanger the public health before regulation is justified. 27 31 Thus the two sections of the Clean Air Act presented by petitioners in support of their stringent reading of the threshold requirement for action under Section 211 turn out, upon analysis, to be of no support at all. Section 108 only bolsters our reading of Section 211 as a precautionary statute while Section 202 includes the same standard as Section 211 and thus is of no guidance one way or the other. While petitioners have little more to offer to prove that the will endanger standard demands proof of actual harm and is not precautionary in nature, we may turn, in support of our interpretation, to the relevant case law. While cases interpreting the meaning of endanger are few in number, 28 at least one recent case is directly on point and fully in accord with our view. 32 In Reserve Mining Co. v. EPA, 514 F.2d 492 (8th Cir. 1975) (en banc ), the Eighth Circuit addressed, among other issues, the meaning of the phrase endangering the health or welfare of persons under Section 112 of the Federal Water Pollution Control Act of 1970 (FWPCA), 33 U.S.C. § 1160. FWPCA and the Clean Air Act together constitute the bulk of this nation's substantive environmental protection legislation. 29 As such, and because of their contemporaneous enactment, interpretations of provisions of one Act have frequently been applied to comparable provisions of the other. See, e. g., Natural Resources Defense Council, Inc. v. Train, 166 U.S.App.D.C. 312, 321-322, 510 F.2d 692, 701-702 (1975). Thus Reserve Mining's interpretation of endangering is relevant to the meaning of the term endanger in the Clean Air Act. Indeed, it is particularly relevant because in construing the language before it the Eighth Circuit borrowed extensively from the interpretation of the will endanger language of Section 211 expressed in the dissent from the division opinion in this case, the same interpretation we adopt here. See Reserve Mining Co. v. EPA, supra, 514 F.2d at 528-529. After analysis of the plain meaning of the FWPCA provision, comparison with other sections of that Act, and reference to our division's dissent, the Eighth Circuit's unanimous conclusion fully supports our view of the will endanger standard: 33 In the context of this environmental legislation, we believe that Congress used the term endangering in a precautionary or preventive sense, and, therefore, evidence of potential harm as well as actual harm comes within the purview of that term. 34 Id. at 528. 35 In sum, based on the plain meaning of the statute, the juxtaposition of Section 211 with Sections 108 and 202, and the Reserve Mining precedent, we conclude that the will endanger standard is precautionary in nature and does not require proof of actual harm before regulation is appropriate. 30 36 Perhaps because it realized that the above interpretation was the only possible reading of the statutory language, petitioner Ethyl addresses this interpretation and argues that even if actual harm is not required for action under Section 211(c)(1)(A), the occurrence of the threatened harm must be probable before regulation is justified. Ethyl Supp.Br. 12. While the dictionary admittedly settles on probable as its measure of danger, we believe a more sophisticated case-by-case analysis is appropriate. 31 Danger, the Administrator recognized, is not set by a fixed probability of harm, but rather is composed of reciprocal elements of risk and harm, or probability and severity. Cf. Carolina Environmental Study Group v. United States, 166 U.S.App.D.C. 416, 419, 510 F.2d 796, 799 (1975); Reserve Mining Co. v. EPA, supra, 514 F.2d at 519-520. That is to say, the public health may properly be found endangered both by a lesser risk of a greater harm and by a greater risk of a lesser harm. 32 Danger depends upon the relation between the risk and harm presented by each case, and cannot legitimately be pegged to probable harm, regardless of whether that harm be great or small. As the Eighth Circuit found in Reserve Mining, these concepts necessarily must apply in a determination of whether any relief should be given in cases of this kind in which proof with certainty is impossible. 33 514 F.2d at 520. 37 In Reserve Mining the issue was whether asbestiform wastes flushed into Lake Superior by the Reserve Mining Company endangered health. 34 The polluted lake waters formed the drinking supply of several surrounding communities, while a medical theory, bolstered only by inconclusive evidence, suggested that ingestion of the wastes caused cancer. See pages --- - --- of --- U.S.App.D.C., pages 45-46 of 541 F.2d infra. Applying the endangering the health or welfare of persons standard of the FWPCA, the court found the wastes to be a danger cognizable under the Act. The court did not find that the danger was probable; rather it found the wastes to be potentially harmful, 514 F.2d at 528, and potential harm to be embraced by the endangering standard, id. See page --- of --- U.S.App.D.C., page 17 of 541 F.2d supra. The court concluded: 38 The record shows that Reserve is discharging a substance into Lake Superior waters which under an acceptable but unproved medical theory may be considered as carcinogenic. As previously discussed, this discharge gives rise to a reasonable medical concern over the public health. We sustain the district court's determination that Reserve's discharge into Lake Superior constitutes pollution of waters endangering the health or welfare of persons within the terms of §§ 1160(c)(5) and (g)(1) of the Federal Water Pollution Control Act and is subject to abatement. 39 514 F.2d at 529 (footnote omitted; emphasis added). The court thus allowed regulation of the effluent on only a reasonable or potential showing of danger, hardly the probable finding urged by Ethyl as the proper reading of the endanger language in Section 211. The reason this relatively slight showing of probability of risk justified regulation is clear: the harm to be avoided, cancer, was particularly great. However, because the risk was somewhat remote, the court did not order the immediate cessation of asbestiform dumping, but rather ordered such cessation within a reasonable time. Id. at 538. 40 Reserve Mining convincingly demonstrates that the magnitude of risk sufficient to justify regulation is inversely proportional to the harm to be avoided. Cf. Carolina Environmental Study Group v. United States, supra. It would be a bizarre exercise in balancing horrors to determine whether cancer or lead poisoning is a greater harm to be avoided, 35 but fortunately such balancing is unnecessary in this case. Undoubtedly, the harm caused by lead poisoning is severe; nonetheless, the Administrator does not rely on a potential risk or a reasonable medical concern to justify the regulations before us. Instead, he finds a significant risk of harm to health. While this finding may be less than the probable standard urged by Ethyl, it is considerably more certain than the risk that justified regulation in Reserve Mining of a comparably fright-laden harm. Cf. Environmental Defense Fund, Inc. v. EPA, 150 U.S.App.D.C. 348, 358, 465 F.2d 528, 538 (1972). Moreover, like the Reserve Mining court, in the face of this still less than certain risk the Administrator did not order the cessation of use of lead additives, but rather directed a phased step-down to a plateau level. Thus we conclude that however far the parameters of risk and harm inherent in the will endanger standard might reach in an appropriate case, they certainly present a danger that can be regulated when the harm to be avoided is widespread lead poisoning and the risk of that occurrence is significant. 36 41 2. The Administrator's Power to Assess Risks. Petitioners argue that Section 211 requires the Administrator to make a threshold factual determination that automobile emissions will endanger the public health, Nalco Supp.Br. at 15-20; Ethyl Supp.Br. at 24-26, and dispute EPA's claim that the Administrator may make an essentially legislative policy judgment, rather than a factual determination, concerning the relative risks of underprotection as compared to overprotection. Industrial Union Department, AFL-CIO v. Hodgson, 162 U.S.App.D.C. 331, 339, 499 F.2d 467, 475 (1974). We must reject petitioners' argument, since the power to assess risks, without relying solely on facts, flows inexorably from the nature of the will danger standard. We have already found that Section 211 allows the Administrator to regulate fuel content when he finds that emissions cause a significant risk of harm to the public health. Yet, how can the Administrator determine that a risk is a significant risk if he cannot assess risks? And how can he assess risks if he cannot make policy judgments? Surely reliance on facts as contemplated by petitioners will provide little guidance. However, sole reliance on facts was not demanded by Congress. 37 42 Originally, it is true, it appeared that Congress would severely restrict the Administrator's ability to assess risks and make policy judgments to protect public health. The bill sent to the floor of the House, and eventually passed by the House, would have allowed EPA to control fuels or fuel additives only if the determination that their emission products would endanger the public health were established 43 on the basis of specific findings derived from relevant medical and scientific evidence, including    a finding that it is not otherwise technologically or economically feasible to achieve the emission standards established pursuant to section 202 of this Act. 44 H.R. 17255, 91st Cong., 2d Sess. § 210(g)(1) (1970) (emphasis added). The specific findings requirement had more than procedural significance. It limited the scope of evidence on which the Administrator could proceed, made alternative action under Section 202 mandatory if possible, and was widely interpreted in the House, as the extracts of debate relied upon by petitioners show, Ethyl Supp.Br. at 24; NPRA Supp.Br. at 30; Nalco Supp.Br. at 15, as requiring that any EPA action be based solely on facts. 38 See also H.R.Rep. No. 91-1146, 91st Cong., 2d Sess., at 13 (1970), U.S.Code Cong. & Admin.News 1970, p. 5356. 45 But the House bill did not become law. The Senate's preference for less restriction of EPA freedom in regulating fuel additives for health reasons 39 was adopted by the conference committee and ultimately enacted into law. 40 Although the legislative history does not expressly discuss the reasons for the change, 41 the contrast in language is stark. As Section 211 now reads, the only finding the Administrator is required to make is that any fuel additive that might replace one that is prohibited does not cause emissions that will pose the same or greater danger to the public health. 42 The substantive impact of the change is clear. All of the requirements for specific findings quoted above are replaced by requirements that the Administrator consider the specified evidence. The mandatory deference to Section 202 is removed. 43 And the Administrator may act based on all information available to him. 44 As we recognized in Amoco, construing a similar change in parallel Section 211(c)(1)(B), the conference committee's decision was a deliberated one and was meant to have significance. Amoco Oil Co. v. EPA, supra, 163 U.S.App.D.C. at 173, 501 F.2d at 733. 46 In this case the decision has even more significance than it did in Amoco, for under Section 211(c)(1)(B), at issue in Amoco, the Administrator was still required to make findings. All the conferees dropped was the adjective specific. For regulation under Section 211(c)(1)(A), at issue here, however, the entire requirement was dropped, and no greater restriction was placed on the Administrator than that required by the basis and purpose statement of Section 4(b) of the APA, 5 U.S.C. § 553(c). We interpreted the meaning of the limited findings requirement for acting under Section 211(c)(1) (B) in Amoco : 47 (W)e read Section 211(c)(2)(B) as incorporating the commonsense approach which the courts have developed in applying Section 4(b) 45 of the APA. Where EPA's regulations turn crucially on factual issues, we will demand sufficient attention to these in the statement to allow the fundamental rationality of the regulations to be ascertained. Where, by contrast, the regulations turn on choices of policy, on an assessment of risks, or on predictions dealing with matters on the frontiers of scientific knowledge, we will demand adequate reasons and explanations, but not findings of the sort familiar from the world of adjudication. 48 Amoco Oil Co. v. EPA, supra, 163 U.S.App.D.C. at 180-181, 501 F.2d at 740-741 (emphasis added). Thus the Amoco court read the limited findings necessary for action under Section 211(c)(1)(B) as a flexible requirement that demanded actual findings for questions of fact and something less adequate reasons and explanations for questions of policy. 49 As petitioners correctly point out, the Amoco court applied this approach by holding that the threshold determination whether to regulate at all under Section 211(c)(1)(B) was essentially a question of fact, for which a factual finding must be offered. In suggesting that such a finding is necessary for action under Section 211(c)(1)(A) as well, however, petitioners completely ignore the fact that a finding is required for action under Section 211(c)(1) (B) and is not required under Section 211(c)(1)(A). By so glossing over the language of the statute, petitioners miss a vital difference between the threshold determinations under Sections 211(c)(1)(A) and (B). Recall what the Administrator must find in order to act under Section 211(c)(1)(B): that the emission products of the fuel or additive to be regulated 50 will impair to a significant degree the performance of any emission control device or system which is in general use, or which the Administrator finds has been developed to a point where in a reasonable time it would be in general use were such regulation to be promulgated. 51 42 U.S.C. § 1857f-6c(c)(1)(B). At its core, this is a peculiarly factual finding. Will the emission impair the performance of a control device? Is the device in general use, or has it the potential to be? These were the questions, highly suitable to factual proof, that the Amoco court construed. Contrary to petitioners' implication, the court did not hold that any threshold determination to regulate must be based on factual proof, but that this threshold determination must be factually based. The Section 211(c)(1)(A) threshold determination, however, is inherently unlike that of its sister section. Endanger, as we have suggested above, is not a standard prone to factual proof alone. Danger is a risk, and so must be decided by assessment of risks as well as by proof of facts. 52 Thus a reason emerges for the deletion of the findings requirement for action under the will endanger standard. The Amoco court held the findings requirement of Section 211(c)(1)(B) no more than reiterated the minimal demands of the basis and purpose statement of the APA. Amoco Oil Co. v. EPA, supra, 163 U.S.App.D.C. at 179, 501 F.2d at 739. What Congress was doing, then, was using the findings requirement to indicate which section demanded a factual threshold determination and which section did not. While inclusion of the phrase was unnecessary in that the APA would have demanded a factual threshold determination under Section 211(c)(1)(B) in any case, the selective use of the findings requirement served to emphasize to the Administrator the demands of the APA and the intent of the Congress. While Congress did not discuss the extent of the Administrator's power under the will endanger standard, its actions the statute it enacted and the one it rejected make the legislative intent clear. We find that deletion of the findings requirement for action under Section 211(c)(1)(A) was a recognition by Congress that a determination of endangerment to public health is necessarily a question of policy that is to be based on an assessment of risks and that should not be bound by either the procedural or the substantive rigor proper for questions of fact. 53 This conclusion follows not only from the language of Section 211(c)(1)(A) and its legislative history, but from the nature of the Administrator's charge: to protect the public from danger. Regulators such as the Administrator must be accorded flexibility, a flexibility that recognizes the special judicial interest in favor of protection of the health and welfare of people, even in areas where certainty does not exist. Environmental Defense Fund, Inc. v. Ruckelshaus, 142 U.S.App.D.C. 74, 88, 439 F.2d 584, 598 (1971). 54 Questions involving the environment are particularly prone to uncertainty. Technological man has altered his world in ways never before experienced or anticipated. The health effects of such alterations are often unknown, sometimes unknowable. While a concerned Congress has passed legislation providing for protection of the public health against gross environmental modifications, 46 the regulators entrusted with the enforcement of such laws have not thereby been endowed with a prescience that removes all doubt from their decisionmaking. Rather, speculation, conflicts in evidence, and theoretical extrapolation typify their every action. How else can they act, given a mandate to protect the public health but only a slight or nonexistent data base upon which to draw? Never before have massive quantities of asbestiform tailings been spewed into the water we drink. 47 Never before have our industrial workers been occupationally exposed to vinyl chloride 48 or to asbestos dust. 49 Never before has the food we eat been permeated with DDT 50 or the pesticides aldrin and dieldrin. 51 And never before have hundreds of thousands of tons of lead emissions been disgorged annually into the air we breathe. Sometimes, of course, relatively certain proof of danger or harm from such modifications can be readily found. But, more commonly, reasonable medical concerns and theory long precede certainty. Yet the statutes and common sense demand regulatory action to prevent harm, even if the regulator is less than certain that harm is otherwise inevitable. 55 Undoubtedly, certainty is the scientific ideal to the extent that even science can be certain of its truth. 52 But certainty in the complexities of environmental medicine may be achievable only after the fact, when scientists have the opportunity for leisurely and isolated scrutiny of an entire mechanism. Awaiting certainty will often allow for only reactive, not preventive, regulation. 53 Petitioners suggest that anything less than certainty, that any speculation, is irresponsible. But when statutes seek to avoid environmental catastrophe, can preventive, albeit uncertain, decisions legitimately be so labeled? 56 The problems faced by EPA in deciding whether lead automotive emissions pose a threat to the public health highlight the limitations of awaiting certainty. First, lead concentrations are, even to date, essentially low-level, so that the feared adverse effects would not materialize until after a lifetime of exposure. Contrary to petitioners' suggestion, however, we have not yet suffered a lifetime of exposure to lead emissions. At best, emissions at present levels have been with us for no more than 15-20 years. 54 Second, lead exposure from the ambient air is pervasive, so that valid control groups cannot be found against which the effects of lead on our population can be measured. Third, the sources of human exposure to lead are multiple, so that it is difficult to isolate the effect of automobile emissions. Lastly, significant exposure to lead is toxic, so that considerations of decency and morality limit the flexibility of experiments on humans that would otherwise accelerate lead exposure from years to months, and measure those results. 55 Cf. Environmental Defense Fund, Inc. v. EPA (Shell), 167 U.S.App.D.C. 71, 78, 510 F.2d 1292, 1299 (1975). 57 The scientific techniques for attempting to overcome these limitations are several: toxicology can study the distribution and effect of lead in animals; epidemiological techniques can analyze the effects of lead emissions on entire populations; clinical studies can reproduce in laboratories atmospheric conditions and measure under controlled circumstances the effects on humans. All of these studies are of limited usefulness, however. Dr. J. H. Knelson, Director of EPA's Human Studies Laboratory, has described, in the context of setting ambient air standards, the limitations of these various investigative tools: 58 Each of these investigative approaches classic toxicology, epidemiology, and clinical research has its advantages and disadvantages. The toxicologist can control the dose and use invasive or destructive techniques in measuring response in the animal, but is always faced with the problem of extrapolating results to humans. Epidemiology is most relevant because it studies phenomena actually occurring in humans under natural conditions, but can only draw inference from observed correlations rather than prove cause and effect relationships. Clinical research can provide the most accurate dose-response relationships in the species of interest. Precisely because the study subjects are humans, however, many experimental design problems are encountered in assuring their safety. Although the dose of an atmospheric pollutant can be carefully controlled and measured in the clinical laboratory, qualitative comparability to the multiplex variable of atmospheric pollution cannot always be assured. 59 The best scientific criteria for establishing air quality standards result from interactions between these disciplines. Clinical studies must be preceded by exhaustive toxicological assessment in other species; observations from population studies should play an important role in the experimental design of clinical research. Biomedical data from all these sources, taken in their entirety, should be used for the prudent definition of air pollution control needs. 60 JA 582-583. The best biomedical evidence will be derived from relating all three research approaches. This EPA did. That petitioners, and their scientists, find a basis to disagree is hardly surprising, since the results are still uncertain, and will be for some time. But if the statute accords the regulator flexibility to assess risks and make essentially legislative policy judgments, as we believe it does, preventive regulation based on conflicting and inconclusive evidence may be sustained. Recent cases have recognized this flexibility in similar situations. 61 In Industrial Union Department, AFL-CIO v. Hodgson, supra, this court considered the Secretary of Labor's delegated power under the Occupational Safety and Health Act (OSHA), 29 U.S.C. § 651 et seq., to protect the health of industrial workers by setting standards for exposure to industrial pollutants. Under review was a standard for exposure to asbestos dust, thought to be carcinogenic. Judge McGowan, writing for the division, laid down the rule: 62 From extensive and often conflicting evidence, the Secretary in this case made numerous factual determinations. With respect to some of those questions, the evidence was such that the task consisted primarily of evaluating the data and drawing conclusions from it. The court can review that data in the record and determine whether it reflects substantial support for the Secretary's findings. But some of the questions involved in the promulgation of these standards are on the frontiers of scientific knowledge, and consequently as to them insufficient data is presently available to make a fully informed factual determination. Decision making must in that circumstance depend to a greater extent upon policy judgments and less upon purely factual analysis. 18 63 18. Where existing methodology or research in a new area of regulation is deficient, the agency necessarily enjoys broad discretion to attempt to formulate a solution to the best of its ability on the basis of available information, Permian Basin Area Rate Cases, 390 U.S. 747, 811, 88 S.Ct. 1344, 20 L.Ed.2d 312 (1968). 64 162 U.S.App.D.C. at 338, 499 F.2d at 474. 65 This rule was likewise applied in Society of the Plastics Industry, Inc. v. OSHA, 509 F.2d 1301 (2d Cir.), cert. denied, 421 U.S. 992, 95 S.Ct. 1998, 44 L.Ed.2d 482 (1975), where the Second Circuit reviewed regulations limiting industrial exposure to vinyl chloride, also considered a carcinogen: 66 As in Industrial Union Department, AFL-CIO v. Hodgson, supra, the ultimate facts here in dispute are on the frontiers of scientific knowledge, and, though the factual finger points, it does not conclude. Under the command of OSHA, it remains the duty of the Secretary to act to protect the workingman, and to act even in circumstances where existing methodology or research is deficient. The Secretary, in extrapolating the MCA study's finding from mouse to man, has chosen to reduce the permissible level to the lowest detectable one. We find no error in this respect. 67 Id. at 1308. And in Reserve Mining the Eighth Circuit agreed. Although reviewing the determination of a District Court, not an expert Administrator, the court recognized that it must nonetheless apply the test of the preventive statute before it: 68 (W)e note that many of the issues in this case do not involve historical facts subject to the ordinary means of judicial resolution. Indeed, a number of the disputes involve conflicting theories and experimental results, about which it would be judicially presumptuous to offer conclusive findings (quoting Amoco Oil Co. v. EPA, 163 U.S.App.D.C. 181, 501 F.2d at 741, which relied on Industrial Union ). In such circumstances, the finder of fact must accept certain areas of uncertainty, and the findings themselves cannot extend further than attempting to assess or characterize the strengths and weaknesses of the opposing arguments. 69 514 F.2d at 507 n.20. See also id. at 529. 70 These cases, recognizing as they do the developing nature of environmental medicine, fortify our analysis of the will endanger language of Section 211. 56 Where a statute is precautionary in nature, 57 the evidence difficult to come by, uncertain, or conflicting because it is on the frontiers of scientific knowledge, the regulations designed to protect the public health, and the decision that of an expert administrator, we will not demand rigorous step-by-step proof of cause and effect. Such proof may be impossible to obtain if the precautionary purpose of the statute is to be served. Of course, we are not suggesting that the Administrator has the power to act on hunches or wild guesses. Amoco makes it quite clear that his conclusions must be rationally justified. Amoco Oil Co. v. EPA, supra, 163 U.S.App.D.C. at 180-181, 501 F.2d at 740-741. However, we do hold that in such cases the Administrator may assess risks. He must take account of available facts, of course, but his inquiry does not end there. The Administrator may apply his expertise to draw conclusions from suspected, but not completely substantiated, relationships between facts, from trends among facts, from theoretical projections from imperfect data, from probative preliminary data not yet certifiable as fact, and the like. We believe that a conclusion so drawn a risk assessment may, if rational, form the basis for health-related regulations under the will endanger language of Section 211. 58 71 All of this is not to say that Congress left the Administrator free to set policy on his own terms. To the contrary, the policy guidelines are largely set, both in the statutory term will endanger and in the relationship of that term to other sections of the Clean Air Act. These prescriptions direct the Administrator's actions. Operating within the prescribed guidelines, he must consider all the information available to him. Some of the information will be factual, but much of it will be more speculative scientific estimates and guesstimates of probable harm, hypotheses based on still-developing data, etc. Ultimately he must act, in part on factual issues, but largely on choices of policy, on an assessment of risks, (and) on predictions dealing with matters on the frontiers of scientific knowledge   . Amoco Oil Co. v. EPA, supra, 163 U.S.App.D.C. at 181, 501 F.2d at 741. A standard of danger fear of uncertain or unknown harm contemplates no more. 72 3. Propriety of the Cumulative Impact Approach. In addition to demanding that the Administrator act solely on facts, petitioner Ethyl insists that those facts convince him that the emission product of the additive to be regulated in and of itself, i. e., considered in isolation, endangers health. The Administrator contends that the impact of lead emissions is properly considered together with all other human exposure to lead. See page --- of --- U.S.App.D.C., page 12 of 541 F.2d supra. We agree. 73 First, Ethyl points to the language of Section 202 allowing regulation of any automobile emission that causes or contributes to, or is likely to cause or to contribute to, air pollution which endangers the public health or welfare. Section 202(a)(1), 42 U.S.C. § 1857f-1(a)(1) (emphasis Ethyl's in its brief at 18). This is contrasted with Section 211's language allowing regulation of fuels or fuel additives whose emission products    will endanger the public health or welfare. By italicizing the contribute to language of Section 202 Ethyl presumably suggests that Section 202 is more lenient, allowing use of the cumulative impact theory while Section 211 does not. This argument is but a variant on Ethyl's already rejected claim that Section 202 allows for regulation of likely dangers while Section 211 does not. As with the earlier argument, this reading of Section 202 must be rejected. While it is possible that Section 202's inclusion of emissions that cause or contribute to air pollution is more encompassing than Section 211's term emission products, it is clear that whatever leniency Section 202 suggests only concerns the makeup of air pollution. This is irrelevant to the cumulative impact theory. However they differ, both Section 202 and Section 211 allow regulation of lead additives only on a determination that the resultant polluted air, however composed, endangers the public health. 59 Both provisions leave open the question whether emissions or air pollution can be found to endanger the public health when the endangerment is not caused by that pollution alone. 60 74 While Ethyl's comparison suggests no answer, the question is directly raised here. The Administrator found endangerment, but recognized that the national lead exposure problem is caused, not by air pollution alone, but by an aggregate of sources, including food, water, leaded paint, and dust. He believed that regulation was justified because the aggregate was dangerous, and because leaded gasoline was a significant source that was particularly suited to ready reduction. 38 Fed.Reg. 33734. To the question whether the Administrator was correct in his belief, comparison with the contribute to language of Section 202 provides no guidance. 75 The only other evidence relied upon by Ethyl for its in and of itself theory is a quotation, taken out of context, from Senator Baker. When the context of Ethyl's partial quotation is revealed the irrelevance of his statement to Ethyl's theory becomes clear. Senator Baker reviewed the Committee bill for the Senate: 76 The (Administrator) is authorized to either control or prohibit the sale of any given fuel when he finds one of two things: 77 First. That the combustion or evaporation of such fuel produces emissions that, in and of themselves, endanger the public health or welfare; or 78 Second. That such emissions prevent the operation of a system that is necessary to reduce automobile emissions to the levels required by standards issued by the (Administrator) under section 202 of the act. 79 116 Cong.Rec. 32920 (1970) (emphasis added). Ethyl relies on the Senator's subsequent repetition of the words in and of themselves, italicized above. Ethyl brief at 16. But the second paragraph makes clear that Senator Baker's meaning is contrary to Ethyl's implication. He is simply emphasizing the different nature of the two provisions and thus uses the words in and of themselves to show that under Section 211(c)(1)(A) the Administrator may act only because of the direct effects of lead additives on a legislative goal, protection of health, while under Section 211(c)(1)(B) he may act because of their indirect effects on another goal, implementation of emission control systems. 61 80 Beyond these two points, Ethyl has nothing more to offer in support of its in and of itself reading. Thus it has made out no case at all, particularly in light of the realities of human exposure to lead and what Congress knew about those realities. Such consideration demonstrates both that, under Ethyl's approach, EPA regulation of lead on health grounds would be impossible and that Congress could not possibly have intended the restrictive by itself reading. As has been discussed more extensively above, see pages --- - --- of --- U.S.App.D.C., pages 8-9 of 541 F.2d supra, lead enters the human body from multiple sources, so that the effect of any one source is meaningful only in cumulative terms. If, for example, airborne lead were the only source of the lead body burden, and it caused, by itself, a blood lead level of 30 ug, there would be no danger to the public health. But if that hypothetical 30 ug is added to a possible 30 ug attributable to dietary ingestion, the blood lead level would be 60 ug, a definite threat to health. Under Ethyl's approach, despite obvious endangerment such a cumulative finding is insufficient to justify regulation. Airborne, lead, in and of itself, may not be a threat. But the realities of human lead exposure show that no one source in and of itself (except possibly leaded paint) is a threat. Thus, under Ethyl's tunnel-like reasoning, even if parallel legislation permitted regulation of other sources of lead exposure, which it does not, no regulation could ever be justified. 81 Such cannot be the case. Congress understood that the body lead burden is caused by multiple sources. It understood that determining the effect of lead automobile emissions, by themselves, on human health is of no more practical value than finding the incremental effect on health of the fifteenth sleeping pill swallowed by a would-be suicide. 62 It did not mean for endanger to be measured only in incremental terms. 63 This the Administrator also understood. He determined that absorption of lead automobile emissions, when added to all other human exposure to lead, raises the body lead burden to a level that will endanger health. He realized that lead automobile emissions were, far and away, the most readily reduced significant source of environmental lead. And he determined that the statute authorized him to reduce those emissions on such a finding. We find no error in the Administrator's use of the cumulative impact approach. 82 4. Summary of the Will Endanger Determination. In sum, we must reject petitioners' cramped and unrealistic interpretation of Section 211(c)(1)(A). Their reading would render the statute largely useless as a basis for health-related regulation of lead emissions. Petitioners' arguments are rebuffed by the plain meaning of the statute and the Administrator's interpretation of it, 64 by the legislative history and the implications that can drawn from other sections of the same statute, by the relevant precedents, and by the established maxim that health-related legislation is liberally construed to achieve its purpose. 65 83 We believe the Administrator may regulate lead additives under Section 211(c) (1)(A) when he determines, based on his assessment of the risks as developed by consideration of all the information available to him, and as guided by the policy judgment inherent in the statute, that lead automobile emissions significantly increase the total human exposure to lead so as to cause a significant risk of harm to the public health. Before so regulating, he must consider the possibility of regulation under Section 202. 66 This interpretation of Section 211 does not allow for baseless or purposeless regulation, but does grant the Administrator the flexibility needed to confront realistically the public health problem presented by massive diffusion of lead emissions from automobiles.