Opinion ID: 365968
Heading Depth: 1
Heading Rank: 5

Heading: EVIDENTIARY BASIS FOR REGULATION OF LESS CHLORINATED PCBs.

Text: 49
50 The principal claim of industry petitioners is that EPA's regulations lack an adequate basis in the record to the extent that they cover less chlorinated PCBs because the record consists, in large part, of studies of related, but different substances (more chlorinated PCBs). In order to rule on this claim, we have no alternative except to venture into a difficult realm of chemistry and toxicology, for, however deferential may be our review, we cannot rule on an issue without a firm grasp of it. 59 51 PCBs are a group of related chemicals that have two aspects in common. First, they share a basic chemical structure known as the biphenyl structure, consisting of two rings of carbon atoms with hydrogen atoms attached. 60 Second, instead of a simple biphenyl structure PCBs have one or more chlorine atoms substituting for one or more hydrogen atoms. From these two aspects comes the name polychlorinated biphenyls. PCBs vary with respect to how much chlorine is substituted for hydrogen, ranging from one to ten chlorine atoms per molecule of PCBs. 61 52 Commercially, PCBs are manufactured and sold in the form of mixtures. Some mixtures contain predominantly PCBs with few chlorine atoms per molecule; these are termed less chlorinated PCBs. 62 Other PCBs mixtures contain predominantly PCBs with more chlorine atoms per molecule; these are termed more chlorinated PCBs. 63 53 As we have discussed, more chlorinated PCBs were the main PCBs in use from 1929 until the early 1970's. 64 In the early 1970's, under public and government pressure, PCBs manufacturers and users shifted from more chlorinated to less chlorinated PCBs. 65 The chemical and electrical industries were able to shift relatively rapidly from use of one PCBs mixture to another. However, this shift created the knowledge gap that underlies the principal issue in this proceeding. As a practical matter, scientific knowledge about the effects of chemicals cannot keep up with the ability of industrial laboratories to create new ones. Most of the available scientific studies on PCBs concern more chlorinated PCBs, either because the studies were conducted over the decades when more chlorinated PCBs were the main PCBs in use, or because, even after the early 1970's, scientists continued to study the more chlorinated PCBs. 66 54 Accordingly, EPA faced a familiar choice in this proceeding. On one hand, it could regulate a substance whose properties were incompletely understood (less chlorinated PCBs) by relying, in major part, upon its knowledge about more familiar substances (more chlorinated PCBs), despite the uncertainties of extrapolation from one substance to another. On the other hand, it could delay regulation until science could more fully explore the risks of the new substance. 55 Industry petitioners contend that EPA lacked an adequate basis for regulation because of this incompleteness in the scientific knowledge about less chlorinated PCBs mixtures. They argue that EPA could not have reasonably hoped to regulate Aroclors 1016 and 1242 (less chlorinated PCBs) without commissioning extensive studies on comparative mammalian toxicity. The Agency failed to commission such studies. . . . It is the failure of the Administrator to present studies relating to Aroclors 1016 and 1242 which has led to his attempt to build an elaborate evidentiary house of cards. Brief for Industry Petitioners at 53. Petitioners assert, in effect, that EPA cannot rely upon merely suggestive evidence or upon extrapolation from data concerning related substances to justify regulation of the less chlorinated PCBs. They insist that EPA must trace a line of direct causation from each substance it regulates to the danger requiring regulation. 56 In response, EPA disputes that it must produce such direct proof concerning the danger posed by every regulated substance. EPA notes that the statutory standard calls for setting discharge levels at the level that will provide an ample margin of safety, and cites prior authority, particularly Ethyl Corp. v. EPA, 176 U.S.App.D.C. 373, 541 F.2d 1 (en banc), Cert. denied, 426 U.S. 941, 96 S.Ct. 2663, 49 L.Ed.2d 394 (1976), to support its position. In EPA's view, action need not be delayed while a risky situation persists that is, until the extent of the danger is fully ascertained. EPA contends that ample evidence showing the danger of more chlorinated PCBs together with scientific reasoning and evidence that less chlorinated PCBs share some dangerous qualities of more chlorinated PCBs, constitutes an adequate basis for regulation. 57
58 Section 307(a)(2) sets forth the relevant factors for setting toxic effluent standards. It requires EPA to take into account six factors in proposing such standards: the toxicity of the pollutant, its persistence, degradability, the usual or potential presence of the affected organisms in any waters, the importance of the affected organisms and the nature and extent of the effect of the toxic pollutant on such organisms. 59 The six factors consist of two groups. The first three factors, toxicity, persistence, and degradability, constitute a carefully drafted tripartite division of the relationship between a toxic substance and the environment. Toxicity concerns the adverse biological effects of toxic substances on life in the environment. 67 Persistence concerns the physical and chemical effects of the nonliving environment (such as sunlight and water) on toxic substances. 68 Degradability concerns the effects of the living environment on toxic substances. 69 Taken together, the three factors were intended to cover comprehensively the fate of toxic substances in the environment and their effects on living organisms. 70 60 The last three factors concern affected organisms : their presence (usual or potential) in any waters, their importance, and the effect on them of the toxic substance. Inclusion of these factors requires EPA to focus on specific effects on specific important organisms as well as on the general toxicity, persistence, and degradability of the substance. On the list of affected organisms is, of course, man, 71 although other organisms may certainly trigger the last three factors. 61 Based on these factors, section 307(a)(4) directs EPA to set discharge standards at a level providing an ample margin of safety. The parties dispute the significance of this important subsection. EPA argues that this subsection gives it latitude to protect against risks that are incompletely understood, in essence to err on the side of overprotection with respect to known risks in order to provide safety from unknown dangers. Industry petitioners disagree. 62 On examination of the wording of the statute and the legislative background, we find ourselves in agreement with EPA, whose interpretation of the complex statutes it administers is, of course, entitled to some deference. E. I. du Pont de Nemours & Co. v. Train, 430 U.S. 112, 134-35, 97 S.Ct. 965, 51 L.Ed.2d 204 (1977); Union Electric Co. v. EPA, 427 U.S. 246, 256, 96 S.Ct. 2518, 49 L.Ed.2d 474 (1976); Train v. NRDC, 421 U.S. 60, 75, 87, 95 S.Ct. 1470, 43 L.Ed.2d 731 (1975). Despite the problems associated with estimating the scale of incompletely understood dangers, Congress required EPA to set standards that would protect against them. 63 The ample margin of safety standard was taken originally from technical jargon for use in section 112 of the Clean Air Act Amendments of 1970, the hazardous pollutants provision. See note 28 Supra. One academic commentator has traced the history of the use of this term: 64 The term (margin of safety) seems to have been borrowed in the first instance from the field of engineering. It is a common engineering practice to incorporate a factor of safety into the design of a structure to ensure that under full working loads the stress will nowhere exceed a safe working limit. The safety factor is meant to compensate for uncertainties and variabilities in design, materials workmanship, and so forth; the greater the variability, the larger the factor of safety. 65 That the use of the term margin of safety in section 307(a) was similarly meant by Congress to take into account and compensate for uncertainties and lack of precise predictions in the area of forecasting the effects of toxic pollutants is confirmed by reference to the Clean Air Act. FWPCA section 307(a) is very similar to section 112 of the Clean Air Act. Among the similarities is the requirement in both that any standard set should provide an ample margin of safety. 66 Congress . . . provided in section 307(a) of the FWPCA, as in section 112 of the Clean Air Act, that the margin of safety be ample. This is in contrast to the requirement of section 109 of the Clean Air Act that primary air standards assure an Adequate margin of safety ; the requirement of the Safe Drinking Water Act that contaminant levels for public water supplies be set at a level to assure an Adequate margin of safety ; or the requirement of section 303(d)(1)(C) of the (1972 Act) that waste load allocations be established at simply a margin of safety. 67 Ample is defined as abundant; plentiful; more than adequate. Clearly Congress intended that in dealing with toxic pollutants that pose a threat to human health, margins of safety should be generous to ensure protection of human health and aquatic ecosystems to the greatest extent possible. 68 Hall, The Control of Toxic Pollutants Under the Federal Water Pollution Control Act Amendments of 1972, 63 Iowa L.Rev. 609, 629-30 (1978) (footnotes omitted) (emphasis in original). The foregoing analysis demonstrates that the term margin of safety was intended to provide protection against hazards which research has not yet identified. 72 Moreover, the public and the environment were not to be exposed to anything resembling the maximum risk. Not only was EPA to provide a margin of safety, but the margin was to be greater than normal or adequate : the margin was to be ample. If administrative responsibility to protect against unknown dangers presents a difficult task, indeed, a veritable paradox calling as it does for knowledge of that which is unknown then, the term margin of safety is Congress's directive that means be found to carry out the task and to reconcile the paradox. Addition of a generous measure ample is Congress's recognition that the EPA would need great latitude in meeting its responsibility. 73 C. Scope of Review. 69 EPA's decision is reviewed under the substantial evidence test. Three leading Supreme Court opinions have elaborated the nature of the substantial evidence test in review of nonscientific adjudications. In Consolidated Edison Co. v. NLRB, 305 U.S. 197, 229, 59 S.Ct. 206, 217, 83 L.Ed. 126 (1938), Chief Justice Hughes described substantial evidence as more than a mere scintilla. It means such relevant evidence as a reasonable mind might accept as adequate to support a conclusion. In Universal Camera Corp. v. NLRB, 340 U.S. 474, 488, 71 S.Ct. 456, 465, 95 L.Ed. 456 (1951), the Supreme Court instructed that under this standard, (a) court may (not) displace the (agency's) choice between two fairly conflicting views, even though the court would justifiably have made a different choice had the matter been before it de novo. In Consolo v. FMC, 383 U.S. 607, 620, 86 S.Ct. 1018, 1026, 16 L.Ed.2d 131 (1966), the Court added that the standard of substantial evidence means something less than the weight of the evidence, and the possibility of drawing two inconsistent conclusions from the evidence does not prevent an administrative agency's finding from being supported by substantial evidence. 70 Recent lower court decisions have elucidated a significant aspect of the substantial evidence test in review of scientific rulemaking. Recently, in Industrial Union Department, AFL-CIO v. Hodgson, 162 U.S.App.D.C. 331, 499 F.2d 467 (1974) (Cited with approval, FCC v. National Citizens Committee for Broadcasting, 436 U.S. 775, 814, 98 S.Ct. 2096, 56 L.Ed.2d 697 (1978) ), this court construed a section of the Occupational Safety and Health Act of 1970 that provides for judicial review of rulemaking under the substantial evidence test. The court distinguished between those administrative determinations that were factual, and those that were legislative I. e., involved policy judgments: 71 The Secretary's task thus contains elements of both a legislative policy determination and an adjudicative resolution of disputed facts. Mobil Oil Corp. v. FPC, 157 U.S.App.D.C. 235, 254, 483 F.2d 1238, 1257 (1973). Although in practice these elements may so intertwine as to be virtually inseparable, they are conceptually distinct and can only be regarded as such by a reviewing court. 72 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. Thus, in addition to currently unresolved factual issues, the formulation of standards involves choices that by their nature require basic policy determinations rather than resolution of factual controversies. Judicial review of inherently legislative decisions of this sort is obviously an undertaking of different dimensions. 73 162 U.S.App.D.C. at 338-39, 499 F.2d at 474-75 (footnotes omitted) (emphasis added). The central conclusion of Industrial Union when an agency must resolve issues on the frontiers of scientific knowledge, the reviewing court will uphold agency conclusions based on policy judgments in lieu of factual determinations has gained acceptance in many statutory contexts. See, e. g., American Iron & Steel Institute v. OSHA, 577 F.2d 825, 833-834 (3d Cir. 1978); Ethyl Corp. v. EPA, 176 U.S.App.D.C. at 392-400, 541 F.2d at 20-28; National Asphalt Pavement Association v. Train, 176 U.S.App.D.C. 296, 304-05, 539 F.2d 775, 783-84 (1976); Society of the Plastics Industry v. OSHA, 509 F.2d 1301, 1308 (2d Cir.), Cert. denied, 421 U.S. 992, 95 S.Ct. 1998, 44 L.Ed.2d 482 (1975); Cf. FCC v. National Citizens Committee for Broadcasting, 436 U.S. at 814, 98 S.Ct. 2096 (broadcast licensing); Superior Oil Co. v. FERC, 563 F.2d 191, 201 (5th Cir. 1977) (information disclosure). 74 D. Adequacy of the Basis for EPA Regulations. 75
76 Industry petitioners contend that EPA lacked an adequate basis for the regulations under review because of the incomplete scientific knowledge about less chlorinated PCBs. In effect, they assert that EPA must demonstrate the toxicity of each chemical it seeks to regulate through studies demonstrating a clear line of causation between a particular chemical and harm to public health or the environment. We do not agree. 77 The principal basis for rejecting petitioners' views is the wording of the statute. As we stated, the ample margin of safety provision directs EPA to guard against incompletely known dangers. EPA, in its expert policy judgment, relied on its knowledge about a known substance to assess the danger of one about which less is known. Petitioners suggest no alternative approach for the agency short of waiting for conclusive proof about the danger posed by a less understood substance. However, by requiring EPA to set standards providing an ample margin of safety, Congress authorized and, indeed, required EPA to protect against dangers before their extent is conclusively ascertained. The statute thus does not deny EPA the authority that petitioners would have us withhold. Indeed, the legislative history indicates that Congress intended EPA to take into account the availability of data on similar substances or compounds. 74 Moreover, the Clean Water Act of 1977 supports the notion that extrapolation from data about related substances is a valid approach. In 1977, Congress did not list individual substances, but rather listed families of substances, 75 recognizing that similarities among substances render them susceptible to regulation by group. 76 78 Proper deference in judicial review to the scientific expertise of the Administrator also militates against precluding EPA from regulating less chlorinated PCBs on the basis of what is known about related substances. Industrial Union Department, AFL-CIO v. Hodgson, 162 U.S.App.D.C. at 338-39, 499 F.2d at 474-75. 77 The risks posed by toxic substances, and the extent to which one substance has effects similar to those of related substances, are matters on the frontiers of scientific knowledge. EPA, not the court, has the technical expertise to decide what inferences may be drawn from the characteristics of related substances and to formulate policy with respect to what risks are acceptable. 78 79 Moreover, we are currently in a period of rapid change in assessing and regulating toxic substances. TSCA has established new regulatory mechanisms that may well lead to wholesale estimation of the risks of toxic substances. 79 A holding from this court that only one technique of risk assessment (such as extensive studies on comparative mammalian toxicity, Brief of Industry Petitioners at 53) is acceptable to the detriment of others would unnecessarily inhibit EPA from evaluating new approaches and formulating appropriate policy. 80 Finally, in reviewing EPA's policy of regulating less chlorinated PCBs in part on the basis of what is known about more chlorinated PCBs, we must recognize considerations of administrative feasibility. 80 The number of toxic substances subject to regulation seems very large. 81 Regulation of so many substances could well be extremely difficult if EPA were precluded from drawing inferences from available data on well-known, related substances. Moreover, requiring proof of causation for each chemical would force EPA to expend resources in areas that are well-enough known so that inference is acceptable, when those resources could be otherwise employed in areas where knowledge is inadequate. In ruling on the type of proof and procedure required for making individual determinations, the Supreme Court has construed statutes protecting the environment and public health in light of considerations of administrative feasibility. See E. I. du Pont de Nemours & Co. v. Train, 430 U.S. at 132, 97 S.Ct. 965 (type of proof); 82 Weinberger v. Hynson, Westcott & Dunning, Inc., 412 U.S. 609, 62-22, 93 S.Ct. 2469, 37 L.Ed.2d 207 (1973) (procedure). 83 See also United States v. Storer Broadcasting Co., 351 U.S. 192, 202-05, 76 S.Ct. 763, 100 L.Ed. 1081 (1956). 81
82 We now review the evidence presented by EPA, industry petitioners, and others. EPA did not rely on a single approach or study, but acted on the basis of a variety of studies and types of evidence. Under the substantial evidence test, it is not necessary that all the evidence, or even most of the evidence, point in one direction. The evidence supporting the agency's conclusion must be such, in light of all of the evidence on the record as a whole, that a reasonable mind might accept (it) as adequate to support (the) conclusion. Consolidated Edison Co. v. NLRB, 305 U.S. at 229, 59 S.Ct. at 217. The evidence on scientific matters need not consist of one dispositive study, but may be varied and cumulative. 84 83 We have structured our review under the substantial evidence test according to the primary factors of section 307(a)(2): toxicity (including carcinogenicity), persistence, and degradability as they relate to affected organisms. 85 84
85 The evidence presented concerning toxicity may be divided into (i) evidence bearing on aquatic organisms, (ii) evidence bearing on man, and (iii) evidence concerning the special quality of carcinogenicity.i. Aquatic organisms 86 EPA's Criteria Document, See App. II, and evidentiary affidavits summarized studies concerning adverse effects of all PCBs on a wide range of aquatic organisms. PCBs showed some variation in toxicity: sometimes less chlorinated PCBs were more toxic than more chlorinated PCBs, and sometimes vice-versa, with few systematic tendencies. 42 Fed.Reg. 6534, 6541. 86 87 Petitioners contended that EPA's evidence as to aquatic effects does not support a prohibition. They pointed out that EPA found that aquatic organisms could live with a minimal level of PCBs in the water. 87 Indeed, EPA originally proposed a low effluent standard for PCBs rather than a prohibition. New evidence concerning effects on mammals, not effects on aquatic organisms, led to the prohibition. However, this is not to say that EPA's prohibition is unsupported by the aquatic evidence. Although mammalian evidence appears to have tipped the scales, the evidence concerning aquatic dangers lent support to a prohibition. That evidence showed that, even at low levels of discharge, PCBs might build up over time to levels that would menace aquatic organisms. 88 88 ii. Man 89 EPA's Criteria Document and evidentiary affidavits summarized studies concerning adverse effects of PCBs on a wide range of mammals. EPA deemed the animal studies relevant, in part because some mammals are exposed to PCBs in their fish diet, E. g., domesticated mink, but mainly because mammalian data reflect risks to humans that cannot be readily determined through studies about humans. For the reasons previously discussed, the Criteria Document summarized many studies on more chlorinated PCBs, 89 but almost none on less chlorinated PCBs. See note 66 Supra & accompanying text. After the preparation of the Criteria Document, during the hearings EPA brought forth a few recent studies about the effects of less chlorinated PCBs. These studies lacked the wealth of detail of the studies on more chlorinated PCBs, but did show ill effects. 90 90 In addition to animal studies, EPA summarized some studies on humans, relating to occupational diseases 91 and poisoning incidents. 92 These studies dealt only with effects of more chlorinated PCBs. 91 In opposition, industry petitioners criticized EPA's studies of less chlorinated PCBs. 93 They sought to minimize evidence of the effects of more chlorinated PCBs by asserting that less chlorinated PCBs were different. 94 92 We hold that EPA's toxicity evidence provided support for the prohibition. It is well established that evidence concerning toxic effects on mammals is probative of dangers to man. Although extrapolation of data from mice to men may be quantitatively imprecise, it is sufficient to establish a 'substantial likelihood' that harm will result. EDF v. EPA (aldrin and dieldrin), 167 U.S.App.D.C. 71, 78, 510 F.2d 1292, 1299 (1975). Similarly, evidence concerning occupational diseases and incidents of poisoning appears to be very probative of dangers to man. 95 93 As we have held, EPA did not err in using data generated in studies of more chlorinated PCBs in dealing with less chlorinated PCBs. Industry petitioners' criticisms of EPA's studies of less chlorinated PCBs, while relevant, do not preclude EPA from considering the studies to be support for a prohibition. 94 iii. Carcinogenicity 95 In the EPA proceedings, as in the public debate over PCBs, 96 an issue of considerable importance was whether PCBs cause cancer. EPA introduced studies showing that exposure to more chlorinated PCBs produces cancer and cancer-like growths in rats. App. II 251-53 & Appendix D. EPA also introduced studies showing that more chlorinated PCBs are mutagenic, App. II 254, which, according to commentators, suggests that they may be carcinogenic. 97 Finally, EPA introduced studies that PCBs, including less chlorinated PCBs, are enzyme inducers, 98 indicating that they may be co-carcinogenic that is, that they may produce cancer when they act in combination with other substances. 99 EDF introduced evidence showing that on-the-job exposure to more chlorinated PCBs decades ago resulted eventually in a high incidence of cancer. App. I 168. 96 Industry petitioners respond that the evidence that less chlorinated PCBs are carcinogenic is far from conclusive. Again, they earnestly contend that evidence concerning more chlorinated PCBs fails to support regulation of less chlorinated PCBs. In response to the studies showing that less chlorinated PCBs are enzyme inducers, they introduced expert testimony disputing that enzyme inducers are necessarily carcinogenic or co-carcinogenic. The role of enzyme induction, especially in chemical carcinogenesis, is not as yet very well understood. . . . (I)t must remain highly speculative to deduce enhancement of chemical carcinogenesis by enzyme induction by PCBs. App. I 234 (testimony of Dr. Mueller). 97 After review of the authorities on the difficult issue of carcinogenic effect, we conclude that EPA's evidence furnishes adequate support for its prohibition. An administrator has a heavy burden to explain the basis for his decision to permit the continued use of a chemical known to produce cancer in experimental animals. EDF v. Ruckelshaus (DDT), 142 U.S.App.D.C. 74, 86, 439 F.2d 584, 596 n. 41 (1971); Accord, EDF v. EPA (heptachlor and chlordane), 179 U.S.App.D.C. 43, 50, 548 F.2d 998, 1005 (1976), Cert. denied, 431 U.S. 925, 97 S.Ct. 2199, 53 L.Ed.2d 239 (1977); EDF v. EPA (aldrin and dieldrin), 167 U.S.App.D.C. at 74, 510 F.2d at 1302; See EDF v. Department of Health, Education and Welfare, 138 U.S.App.D.C. at 388-90, 428 F.2d at 1090-92. When firm evidence establishes that a chemical is a carcinogen, statutes generally leave an administrator no alternative but to step in to protect the public. 98 On the other hand, when the evidence is less than firm, but merely suggests that a chemical may be a carcinogen, the same heavy burden may not attend administrative inaction. The decision to act in such a case has been held to fall within the discretion of the Administrator. For example, in Reserve Mining Co. v. EPA, 514 F.2d 492 (8th Cir. 1975) (en banc), EPA sought to abate discharge of mining refuse into Lake Superior under an acceptable but unproved medical theory, that the discharges were carcinogenic. 514 F.2d at 529. The court concluded that the discharges should be abated, even though there would be a heavy cost, including possible loss of many jobs, to the local economy. Id. at 514-20, 535-40. Similarly, in Certified Color Manufacturers Association v. Mathews, 177 U.S.App.D.C. 137, 150, 543 F.2d 284 (1976), the Food and Drug Administration (FDA) terminated its provisional approval of a color additive used to dye food on the basis of a vigorously debated study of the additive's carcinogenic effects. This court concluded that the FDA action should be upheld, based upon FDA's scientific judgment that the study was not conclusive, but was merely suggestive of carcinogenicity. Id. 177 U.S.App.D.C. at 150, 543 F.2d at 297. Courts have traditionally recognized a special judicial interest in protecting the public health, particularly where 'the matter involved is as sensitive and fright-laden as cancer.' Where the harm envisaged is cancer, courts have recognized the need for action based upon lower standards of proof than otherwise applicable. Id. 177 U.S.App.D.C. at 150, 543 F.2d at 297-98 (footnotes omitted) (quoting EDF v. EPA (DDT), 150 U.S.App.D.C. 348, 358, 465 F.2d 528, 538 (1972)). The courts have frequently upheld regulations based on evidence of carcinogenic effects. See, e. g., American Iron & Steel Institute v. OSHA, 577 F.2d at 840, 841 (coke oven emissions); Society of the Plastics Industry v. OSHA, 509 F.2d at 1311 (vinyl chloride); Synthetic Organic Chemical Manufacturers Association v. Brennan, 506 F.2d 385, 387 (3d Cir. 1974) (industrial chemicals), Cert. denied, 423 U.S. 830, 96 S.Ct. 50, 46 L.Ed.2d 48 (1975); Synthetic Organic Chemical Manufacturers Association v. Brennan, 503 F.2d 1155, 1159-60 (3d Cir.) (same), Cert. denied, 420 U.S. 973, 95 S.Ct. 1396, 43 L.Ed.2d 653 (1974). 99 These cases demonstrate the inevitable tension attending regulation of carcinogens. Frequently, such regulations have severe economic impact. Indeed, sometimes, as alleged by industry petitioners in this case, such regulations may jeopardize plants or whole industries, and the jobs depending on them. In such circumstances, the temptation to demand that the agency furnish conclusive proof of carcinogenicity as support for the regulations is great. However, the decision to delegate authority to an agency to control suspected carcinogens is a legislative judgment that is not open to question in this court. Congress's direction to EPA to protect against incompletely understood dangers could not be carried out if we were to adopt the proof requirements advocated by industry petitioners. 100 What scientists know about the causes of cancer is how limited is their knowledge. 100 The record in this case demonstrates that it may take decades for human exposure to carcinogens to result in cancer; 101 in the meantime, the case for inferring a cancer danger with respect to an incompletely understood substance is vigorously disputed. If regulation were withheld until the danger was demonstrated conclusively, untold injury to public health could result. Accordingly, we find that Congress has allowed EPA to support a prohibition on the basis of strongly contested and merely suggestive proof. We conclude that the evidence in this case is at least suggestive of carcinogenicity and thus supports EPA's decision. 101
102 EPA summarized studies showing that PCBs tend to accumulate in the environment over many years, are mobile, and adhere to sediments. 102 This court has noted before that such characteristics intensify the dangers posed by toxic substances, because they increase the exposure of persons and vulnerable organisms of all kinds to those substances. See EDF v. EPA (heptachlor and chlordane), 179 U.S.App.D.C. at 53, 548 F.2d at 1008; EDF v. EPA (aldrin and dieldrin), 167 U.S.App.D.C. at 73, 510 F.2d at 1301. 103 Accordingly, these studies provide support for EPA's prohibition. 103
104 EPA summarized a number of studies concerning the degradation of both less and more chlorinated PCBs by living organisms. PCBs were shown to resist degradation, to bioaccumulate (build up) to high levels in simple organisms, and then to bioaccumulate further as those simple organisms are consumed by higher organisms. 104 42 Fed.Reg. 6539-41. When degradation does occur, it may result in creation of other harmful substances, either as intermediates, or as end products of degradation. 105 Industry petitioners disputed EPA's evidence, and produced their own evidence that less chlorinated PCBs are more easily metabolized and eliminated, and less likely to bioaccumulate than more chlorinated PCBs. They also contended that these substances degrade by safe routes into non-dangerous substances. App. I 209-12, 237-39. 105 However, the conclusions advanced by industry petitioners do not necessarily weaken the support for EPA's prohibition. It was not necessary for EPA to prove that less chlorinated PCBs were as dangerous as more chlorinated PCBs in order to justify a prohibition. The central issue is not whether less chlorinated PCBs are less degradable than more chlorinated PCBs, but whether less chlorinated PCBs are insufficiently degradable. Our task in reviewing the record is not to choose between these conflicting studies, but rather to determine whether EPA's decision had substantial evidence on the whole record. Viewed as a whole, the record provided substantial support for EPA's conclusions. 106
107 Under the substantial evidence standard of review, EPA is not required to prove its case in the reviewing court in some sense of weight of the evidence. EDF v. EPA (heptachlor and chlordane), 179 U.S.App.D.C. at 50, 548 F.2d at 1005. Its policy decisions are subject to deferential review, and its factual conclusions are upheld although they may not be supported by all the evidence, or even by most of it. It suffices that EPA's conclusions are supported by such relevant evidence as a reasonable mind might accept as adequate to support (the) conclusion(s). Consolidated Edison Co. v. NLRB, 305 U.S. at 229, 59 S.Ct. at 217. On this record, it is clear that EPA's prohibition on discharges of PCBs must be upheld. 108