b'The Food and Drug Administration\xe2\x80\x99s Discretion to Approve\nMethods of Detection and to Define the Term \xe2\x80\x9c No Residue\xe2\x80\x9d\nPursuant to the Federal Food, Drug, and Cosmetic Act\nThe Food and Drug Administration has the discretionary authority under the DES proviso to the\nDelaney Clause of the Federal Food, Drug, and Cosmetic Act to prohibit the use of an additive\nin animal feed if the FDA concludes that there is no method that can \xe2\x80\x9c reliably measure and\nconfirm\xe2\x80\x9d whether the additive contains residues o f carcinogenic concern at or above the \xe2\x80\x9c no res\xc2\xad\nidue\xe2\x80\x9d level.\nWhere the FDA has already approved a method for detecting the presence o f residues of carcinogenic\nconcern, the DES proviso does not require the FDA to revise its regulations to adopt the \xe2\x80\x9c best\navailable\xe2\x80\x9d such method.\nThe FDA lacks the discretion to determine that an edible tissue contains \xe2\x80\x9c no residue\xe2\x80\x9d when a method\nof detection reveals the presence of residues of carcinogenic concern that is below the \xe2\x80\x9c no signifi\xc2\xad\ncant risk\xe2\x80\x9d level.\n\nOctober 13, 1995\nM e m o r a n d u m O p in io n\n\nfo r th e\n\nA s s is t a n t A d m in is t r a t o r\n\nand\n\nG en era l C oun sel\n\nE n v ir o n m e n t a l P r o t e c t io n A g e n c y\nand the\n\nG en era l C oun sel\nD epa rtm en t\n\nof\n\nH ealth\n\nand\n\nH u m a n S e r v ic e s\n\nThis memorandum responds to the Environmental Protection Agency\xe2\x80\x99s\n(\xe2\x80\x9c EPA\xe2\x80\x9d ) and the Food and Drug Administration\xe2\x80\x99s (\xe2\x80\x9c FDA\xe2\x80\x9d ) request for our\nopinion regarding the FDA\xe2\x80\x99s regulations implementing what is known as the\n\xe2\x80\x9c DES proviso\xe2\x80\x9d to the Delaney Clause of the Federal Food, Drug, and Cosmetic\nAct, 21 U.S.C. \xc2\xa7\xc2\xa7301-393 (the \xe2\x80\x9c Act\xe2\x80\x9d ) . 1 Both agencies have certain responsibil\xc2\xad\nities under the Act, which establishes federal regulatory authority over the safety\nof food additives, human and animal drugs, certain pesticides, and cosmetics.\nI. Background\nThe Act requires that a food additive (including additives to animal feed) be\nfound to be \xe2\x80\x9c safe\xe2\x80\x9d before the FDA authorizes its use. The Delaney Clause pro\xc2\xad\nhibits such a finding of safety with respect to a substance found to induce cancer\nin man or animal. The DES proviso carves out an exception to the Delaney Clause,\nallowing cancer-inducing agents to be added to animal feed if the FDA finds that\nthe additive will not harm the animals, and that no residue of the additive will\n1 Letter for W alter Dellinger, Assistant Attorney General, Office of Legal Counsel, from Jean C. Nelson, General\nCounsel, Environmental Protection Agency, and Harriet S. Rabb, General Counsel, Department o f Health and Human\nServices (Dec. 8, 1994).\n\n247\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nbe found in any edible portion of the animal after slaughter or in any food from\nthe animal. The presence of residue is to be determined by \xe2\x80\x9c methods of examina\xc2\xad\ntion prescribed or approved by the Secretary by regulations.\xe2\x80\x9d Id. \xc2\xa7 348(c).2\nThe proviso was enacted in 1962 to allow substances such as the animal drug\ndiethylstilbestrol, abbreviated as DES, to be used in appropriate situations. Pub.\nL. No. 87-781, \xc2\xa7 104(f), 76 Stat. 780, 785 (1962). Under the Delaney Clause\nwithout the proviso, new applications for the use of drugs like DES, a carcinogen,\nwould ordinarily have been kept from the market. However, because drugs like\nDES, when used properly, pass quickly out of the treated animal\xe2\x80\x99s system, may\nleave no detectable residue in edible tissue, and do not harm the animal, Congress\npermitted the use of such substances. See Hess & Clark, Div. o f Rhodia, Inc.\nv. FDA, 495 F.2d 975, 979 (D.C. Cir. 1974).\nOver the years since the DES proviso was enacted, the FDA has implemented\nits terms through a series of regulatory decisions. Its current regulations, which\nembody the sensitivity of method (\xe2\x80\x9c SOM\xe2\x80\x9d ) approach, contain several discrete\nelements. The central feature of the regulations is the FDA\xe2\x80\x99s operational defmition\nof the statutory term \xe2\x80\x9c no residue.\xe2\x80\x9d Under the definition, the FDA determines\na level of residue for any given food additive that will be considered to satisfy\nthe \xe2\x80\x9c no residue\xe2\x80\x9d finding required under the proviso. This \xe2\x80\x9c no residue\xe2\x80\x9d level\nis calculated in several steps. See 21 C.F.R. \xc2\xa7 500.84(c) (1995). First, the FDA\ndetermines a maximum level o f concentration of any \xe2\x80\x9c residue of carcinogenic\nconcern\xe2\x80\x9d from the additive in question that poses no significant increase in the\nrisk of cancer to people (the \xe2\x80\x9c no significant risk\xe2\x80\x9d level). Id. \xc2\xa7 500.84(c)(1). Next,\nthe FDA evaluates the different foods through which a human might consume\nsome of the additive and estimates the amount of such foods that are consumed\nin the human diet. Based on these estimates of food intake, the FDA then des\xc2\xad\n2 The Delaney Clause with the DES proviso states:\n(1) The Secretary shall \xe2\x80\x94\n(A ) by order establish a regulation . . . prescribing, with respect to one or more proposed uses of the\nfood additive involved, the conditions un d er which such additive may be safely used. . . .\n(3) No such regulation shall issue if a fair evaluation o f the data before the Secretary \xe2\x80\x94\n(A)\nfails to establish that the proposed use o f the food additive, under the conditions o f use to be specified\nin the regulation, will be safe: Provided, That no additive shall be deem ed to be safe if it is found to\ninduce cancer when ingested by man o r animal, o r if it is found, after tests which are appropriate for\nthe evaluation o f the safety o f food additives, to induce cancer in m an or animal, except that this proviso\nshall not apply with respect to the use o f a substance as an ingredient o f feed for animals which are\nraised for food production, if the Secretary finds (i) that, under the conditions o f use and feeding specified\nin proposed labeling and reasonably certain to be followed in practice, such additive will not adversely\naffect the animals for which such feed is intended, and (ii) that no residue o f the additive will be found\n(by methods o f exam ination prescribed o r approved by the Secretary by regulations, which regulations\nshall not be subject to subsections (f) an d (g) o f this section) in any edible portion o f such animal after\nslaughter o r in any food yielded by or derived from the living a ni mal ; . . . .\n21 U.S.C. \xc2\xa7 348(c). The Delaney Clause w ith the DES proviso quoted above is similar to the provisions in 21\nU.S.C. \xc2\xa7 3 6 0 b (d )(l)(I), which governs the approval o f new animal drugs, and 21 U.S.C. \xc2\xa7 379e(b)(5)(B), which gov\xc2\xad\nerns the approval o f color additives.\n\n248\n\n\x0cThe Food and Drug Administration\'s Discretion to Approve Methods o f Detection and to Define the\nTerm "No Residue\xe2\x80\x9d Pursuant to the Federal Food, Drug, and Cosmetic A ct\n\nignates a level of concentration for each edible tissue in which the additive might\nbe found such that the \xe2\x80\x9c no significant risk\xe2\x80\x9d level for the total diet is not exceeded.\nId. \xc2\xa7 500.84(c)(2). So long as concentrations in an edible tissue are below the\nmaximum level of concentration for that tissue, the FDA considers the edible\ntissue to contain \xe2\x80\x9c no residue.\xe2\x80\x9d Id . 3\nThe FDA requires the sponsor of any additive seeking relief under the DES\nproviso to submit a \xe2\x80\x9c regulatory method\xe2\x80\x9d of detection that can \xe2\x80\x9c reliably measure\nand confirm\xe2\x80\x9d the presence of any residue of carcinogenic concern equal to or\nabove the \xe2\x80\x9c no residue\xe2\x80\x9d level for that compound. Id. \xc2\xa7\xc2\xa7500.86, 500.88. However,\nthe FDA does not necessarily require a sponsor to employ the most sensitive\ndetection method available.\nThe EPA and the FDA (collectively \xe2\x80\x9c the agencies\xe2\x80\x9d ) have posed three separate\nquestions with respect to the FDA\xe2\x80\x99s current approach to implementing the DES\nproviso. The first two raise issues concerning the FDA\xe2\x80\x99s discretion to approve\na method of detection, the results of which will be accepted by the FDA for\npurposes of the proviso. The third question concerns the FDA\xe2\x80\x99s discretion to\ndefine \xe2\x80\x9c no residue\xe2\x80\x9d as set forth above. Specifically, we address the following\nquestions: (1) whether the FDA has the discretion to refuse to permit the use\nof an additive in animal feed if it finds that there is no method that can \xe2\x80\x9c reliably\nmeasure and confirm\xe2\x80\x9d the presence of residues of carcinogenic concern at and\nabove the \xe2\x80\x9c no residue\xe2\x80\x9d level for such residues; (2) whether the FDA must revise\nits regulations to adopt more sensitive methods when they become available once\nit has approved a method of detection; and (3) whether the FDA has the discretion\nto determine that an edible tissue contains \xe2\x80\x9c no residue\xe2\x80\x9d when a method of detec\xc2\xad\ntion reveals the presence of residues of carcinogenic concern that is below the\n\xe2\x80\x9c no significant risk\xe2\x80\x9d level. We discuss our answers to each of these questions\nbelow.\nII. The FDA\xe2\x80\x99s Discretion to Approve Methods of Detection\nA. Must the FDA Approve a Method of Detection?\nThe DES proviso authorizes the use of a cancer-inducing additive in animal\nfeed if the FDA finds \xe2\x80\x9c that no residue of the additive will be found (by methods\nof examination prescribed or approved by the [FDA] by regulations . . .) in any\nedible portion of such animal.\xe2\x80\x9d 21 U.S.C. \xc2\xa7348(c)(3)(A)(ii). The agencies have\n3 As explained by the FDA:\nCTlhe [SOM] procedures provide for a quantitative estimation o f the risk o f cancer presented by the residues\nof a carcinogenic compound proposed for use in food-producing animals. \xe2\x80\x9c No residue" remains in food\nproducts when conditions o f use, including any required preslaughter withdrawal period or m ilk discard\ntime, ensure that the concentration o f the residue o f carcinogenic concern in the total diet o f people will\nnot exceed the concentration that has been determined to present an insignificant risk.\n52 Fed. Reg. 49.572 (1987). Thus, the SOM regulations base a \xe2\x80\x9c no residue\xe2\x80\x9d finding on a determ ination that the\nadditive creates " n o significant risk.\xe2\x80\x9d\n\n249\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nasked whether the FDA may use a method\xe2\x80\x99s inability to detect residues at the\nFDA\xe2\x80\x99s \xe2\x80\x9c no significant risk\xe2\x80\x9d level (that is, the method\xe2\x80\x99s sensitivity) as a basis\nfor not approving that method, where the approval of at least one method is nec\xc2\xad\nessary in order for an additive itself to be approved. This phrasing of the issue\nsuggests two questions that can usefully be separated.\nThe first is whether the proviso contemplates that at least one method of detec\xc2\xad\ntion be approved by the FDA; in other words, whether the FDA lacks the discre\xc2\xad\ntion to decide that at present no satisfactory method exists with respect to a spe\xc2\xad\ncific additive. If the proviso were read to require the approval of at least one\nmethod, notwithstanding its lack of sufficient sensitivity, this would be equivalent\nto reading the proviso as imposing a nondiscretionary duty on the FDA to approve\nsome method.4 The proviso contains no language explicitly imposing such a duty\non the FDA. Finding one would require inferring it from elsewhere in the statute,\neither because of express language found elsewhere or because of the structure\nof the statute as a whole. In fact, however, far from undermining the initial view\nthat the FDA is under no such duty, the rest of the statutory scheme reinforces\nthis conclusion.\nThe Delaney Clause and its DES proviso are subparts of the comprehensive\nstatutory scheme under which the FDA approves proposed uses of food additives.\nSee 21 U.S.C. \xc2\xa7 348(c)(3). Under this scheme the FDA may not issue a regulation\napproving the use of any food additive if \xe2\x80\x9c a fair evaluation of the data before\nthe [FDA] fails to establish that the proposed use of the food additive . . . will\nbe safe.\xe2\x80\x9d 21 U.S.C. \xc2\xa7 348(c)(3). The statute, in other words, requires that safety\nis not to be presumed, but rather must rest on an affirmative showing of the predi\xc2\xad\ncate facts necessary to support such a conclusion.5\nBefore the sponsor of a cancer-inducing additive is even put to the task of\nproving safety, however, that additive must satisfy the DES proviso, because if\nit does not satisfy the proviso, the Delaney Clause will apply to it, and the Delaney\nClause imposes a required finding of \xe2\x80\x9c not safe\xe2\x80\x9d with respect to cancer-inducing\nadditives. As a necessary condition for satisfying the proviso, the FDA has stated\nthat a food additive must not be present in an edible tissue in concentrations above\nthe \xe2\x80\x9c no significant risk\xe2\x80\x9d level for that tissue. See 21 C.F.R. \xc2\xa7500.84. This means\n4 O n occasion, the FDA will withdraw its marketing approval o f anim al drugs, which are also governed by the\nDelaney C lause and the DES proviso, because, among other reasons, there is no approved method o f detection\nand, hence, no m eans to demonstrate that the proviso is satisfied. In the sole instance we found o f this position\nbeing raised in litigation, the couit affirmed the FD A \xe2\x80\x99s action without reaching the propriety o f the FD A \xe2\x80\x99s basing\nits determ ination on the absence of any approved method o f detection. See Rhone-Poulenc, Inc. v. FDA , 636 F.2d\n7 5 0 ,7 5 2 n.2 (D.C. Cir. 1980).\n5 That the statute generally requires an affirmative showing o f safety\xe2\x80\x94 the absence o f evidence of risk o f harm\nis insufficient to satisfy the statute\xe2\x80\x94 is reinforced by placing the burden o f proving safety on the sponsor. As one\ncourt sum m arized the m atter \xe2\x80\x9c (I]f the substance is deem ed a food additive, it is presumed to be unsafe . . .\nUnited States v. Two Plastic Drums, More or Less o f an Article o f Food, Labeled in Part: Viponte Ltd. Black\nCurrant Oil Batch No. BOOSF 039, 984 F.2d 814, 816 (7th Cir. 1993). \xe2\x80\x9c The thmst o f the [Food Additives A mend\xc2\xad\nment A ct o f 1958] was to put upon processors rather than the government the burden of proving that a newly\ndiscovered substance added to food is safe if used within specified quantities.\xe2\x80\x9d Id. at 819.\n\n250\n\n\x0cThe Food and Drug Administration s Discretion to Approve Methods o f Detection and to Define the\nTerm "No R esidue" Pursuant to the Federal Food, Drug, and Cosmetic Act\n\nthat a finding of \xe2\x80\x9c no significant risk\xe2\x80\x9d is also a necessary predicate to FDA\xe2\x80\x99s\npotential ultimate conclusion that the additive is \xe2\x80\x9c safe.\xe2\x80\x9d\nIt would be odd for Congress to have written a statute whose basic requirement\nis that the predicate facts for a finding of safety must be affirmatively established\nby the sponsor of any additive, and subsequently to have amended that statute\nby inserting a new subpart in which the requirement of an affirmative showing\nwas eliminated, without any indication in the text that such a fundamental change\nwas intended. Yet, just such an odd outcome would result here if the FDA were\ncompelled to approve an insufficiently sensitive method. The requirement that\nsafety be proven, not presumed, was at the very heart of the legislative changes\ncodified in the Food Additives Amendment Act of 1958, of which \xc2\xa7 348(c)(3)\nis a key provision. See, e.g.. Two Plastic Drums, More or Less, 984 F.2d at 81619. However, if the FDA were required to apply the proviso based solely on\nresults from a method inadequate to confirm \xe2\x80\x9c no significant risk,\xe2\x80\x9d the FDA would\nbe in the position of presuming a predicate fact \xe2\x80\x94 the absence of significant risk \xe2\x80\x94\nthat it considered necessary to its ultimate safety determination. There is\nabsolutely no evidence in either the statutory text or the legislative history that\nsuch a reversal was intended, and by far the more natural reading of the statute\nis that the same requirement of an affirmative showing applies throughout.\nIn sum, the DES proviso does not impose an obligation on the FDA to approve\nat least one method. To the contrary, the FDA has discretion to refuse to permit\nthe use of unsatisfactory detection methods.\nThe analysis to this point has assumed that it is within the FDA\xe2\x80\x99s discretion\nto use levels of risk as one determinant in implementing the method selection\nportion of the DES proviso. This issue presents the second question we must\nexplicitly examine: acknowledging that the FDA has discretion to reject a detec\xc2\xad\ntion method for some reason, is the method\xe2\x80\x99s inability to detect no significant\nrisk levels one of the permissible reasons for the exercise of that discretion? This\nquestion arises because an agency\xe2\x80\x99s exercise of discretion will not be sustained\nif the agency considers factors that are either impermissible or irrelevant under\nthe statute under which the agency is acting. Motor Vehicle Mfrs. A ss\xe2\x80\x99n v. State\nFarm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983) (\xe2\x80\x9c Normally, an agency rule\nwould be arbitrary and capricious if the agency has relied on factors which Con\xc2\xad\ngress has not intended it to consider . . . .\xe2\x80\x9d ); Citizens to Preserve Overton Park,\nInc. v. Volpe, 401 U.S. 402, 416 (1971) (The question is \xe2\x80\x9c whether the decision\nwas based on a consideration of the relevant factors.\xe2\x80\x9d ).\nAs an initial matter, a method\xe2\x80\x99s ability to detect the \xe2\x80\x9c no significant risk\xe2\x80\x9d level\nseems to be a permissible reason for exercising discretion under a statute that\nrequires an affirmative showing of safety, because a finding that an additive does\nnot pose a significant risk is directly relevant to a determination of safety. See,\ne.g.. Industrial Union Dep\xe2\x80\x99t v. American Petroleum Inst., 448 U.S. 607, 642\n(1980) (\xe2\x80\x9c \xe2\x80\x98[S]afe\xe2\x80\x99 is not the equivalent of \xe2\x80\x98risk free.\xe2\x80\x99. . . [A] workplace can\n251\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nhardly be considered \xe2\x80\x98unsafe\xe2\x80\x99 unless it threatens the workers with a significant\nrisk of harm.\xe2\x80\x9d ). As plausible as this conclusion appears, two court of appeals\ndecisions interpreting the Delaney Clause may cast doubt on it and cause us to\nconsider a possible counter argument. See Les v. Reilly, 968 F.2d 985 (9th Cir.\n1992), cert, denied, 507 U.S. 950 (1993); Public Citizen v. Young, 831 F.2d 1108\n(D.C. Cir. 1987), cert, denied, 485 U.S. 1006 (1988). Both Public Citizen and\nLes hold that the fact that an additive produces extremely low levels of risk (de\nminimis levels) does not provide the FDA or the EPA with a basis for refusing\nto ban a cancer-inducing additive under the Delaney Clause. The courts reach\nthis result by concluding that Congress precluded taking risk levels into account\nin reaching that decision under the Delaney Clause. Les, 968 F.2d at 989 (\xe2\x80\x9c Thus,\nthe legislative history supports the conclusion that Congress intended to ban all\ncarcinogenic food additives, regardless of amount or significance of risk, as the\nonly safe alternative.\xe2\x80\x9d ); accord Public Citizen, 831 F.2d at 1122.\nIn Public Citizen, the court did not conclude that the FDA completely lacked\ndiscretion in implementing the Delaney Clause. Specifically, it confirmed that the\nFDA did indeed have discretion to determine whether a color additive was cancerinducing in the first place. 831 F.2d at 1112. The government sought to use the\nexistence of this discretion to support its argument that the FDA had discretion\nto approve carcinogens that posed merely a de minimis risk by claiming that the\nFDA\xe2\x80\x99s decision could be justified as an exercise of the FDA\xe2\x80\x99s admitted discretion\nto make that prior determination. The court rejected that argument, concluding\nthat there was nothing in the record that could support the exercise of such discre\xc2\xad\ntion in this instance, where studies done under accepted agency protocols had\nproduced results that the agency had routinely found supported a finding of\ncarcinogenicity. Id. at 1122. In particular, the court held that the FDA could not\nuse the fact that risk was de minimis as the basis for a finding that the substance\ndoes not induce cancer.\nCongress did not intend the FDA to be able to take a finding that\na substance causes only trivial risk in humans and work back from\nthat to a finding that the substance does not \xe2\x80\x9c induce cancer in . . .\nanimals.\xe2\x80\x9d This is simply the basic question\xe2\x80\x94 is the operation of\nthe clause automatic once the FDA makes a finding of carcino\xc2\xad\ngenicity in animals?\xe2\x80\x94 in a new guise.\nId. at 1121 (alteration in original).\nA broad reading of Public Citizen might suggest that levels of risk associated\nwith a substance may not inform any discretionary judgments made under the\n\nDelaney Clause, because Congress did not intend the FDA to be able to take\na finding about the relative risk of a substance and \xe2\x80\x9c work back\xe2\x80\x9d from that to\nanswer any question under the Clause where it could admittedly exercise discre\xc2\xad\n252\n\n\x0cThe Food and Drug Administration\'s Discretion to Approve Methods o f Detection and to Define the\nTerm \' \'No Residue" Pursuant to the Federal Food, Drug, and Cosmetic Act\n\ntion. We believe this reasoning is unsound as applied to the FDA\xe2\x80\x99s using risk\nas a factor in selecting detection methods under the DES proviso, on two grounds.\nFirst, both Public Citizen and Les were concerned with situations in which the\nagencies sought to approve the use of substances by escaping from the categorical\nban on the Delaney Clause, even though the necessary conditions for triggering\nthe Clause had been found to be present. Once those conditions have been found,\nboth courts held, the operation of the Clause is automatic. Using a \xe2\x80\x9c no significant\nrisk\xe2\x80\x9d benchmark as a basis for rejecting detection methods does not present such\na situation, because the absence of a detection method does not provide an escape\nhatch to the Clause. Rather, it presents the opposite situation: if the DES proviso\ndoes not apply, then the Delaney Clause will. Thus, the FDA is not \xe2\x80\x9c working\nback\xe2\x80\x9d from a finding of \xe2\x80\x9c no significant risk\xe2\x80\x9d to a discretionary judgment that\nstops the automatic bar of the Delaney Clause from taking effect. Instead, accept\nthe results of a detection method means that the automatic ban of the Delaney\nClause will apply. As a consequence, the logic of Public Citizen\xe2\x80\x99s limitation on\nthe use of risk as a factor upon which to base a discretionary judgment does\nnot apply to this particular situation.\nThe second reason we believe the no-discretion argument based on Public Cit\xc2\xad\nizen and Les is unsound is more fundamental. The DES proviso and the Delaney\nClause are separate provisions, and there is no a priori reason to believe that\nthe limitations on factors permitted to influence the exercise of specific discre\xc2\xad\ntionary authority under the Clause should also govern the exercise of discretion\nunder the proviso. In fact, the respective legislative histories of the two provisions\nexhibit significant differences that tend to reinforce the conclusion that the FDA\ncan take the sensitivity of a method into account in deciding whether to approve\nthat method.6\nThe text of the DES proviso and the structure of the statute support the conclu\xc2\xad\nsion that the FDA has discretion to employ a method\xe2\x80\x99s sensitivity as a criterion\nin method selection. The statute supports that view by granting the FDA the\ndiscretion to prescribe and approve methods of detection. 21 U.S.C.\n\xc2\xa7 348(c)(3)(A). However, it is completely silent on explicit criteria the FDA may\nemploy in the exercise of this discretion. When Congress has failed to speak\ndirectly to the precise question at issue, the implementing agency\xe2\x80\x99s interpretation\n6\n\nBefore highlighting those differences, we note that our methodology is the same as that used by the court in\n\nPublic Citizen. Like that court, we begin with the statutory text and structure, and then look to the legislative history\nto see whether it supports or undermines our preliminary conclusion. In Public Citizen\'s case, the court first concluded\n(hat the best reading o f the Delaney Clause was that the Clause did not permit a de minimis exception to its otherwise\ncategorical, or automatic, ban on cancer-inducing additives. Public Citizen, 831 F.2d at 1113. This result, seemingly\nso contrary to common sense in the case o f trivial risks, might have been resisted by the court were it not for\nthe very strong and consistent legislative history o f the Delaney Clause, which supported the view that Congress\nindeed intended the \xe2\x80\x9c zero tolerance" result for carcinogenic compounds that the Clause announces on its face.\nIn discussing the color additives version o f the Delaney Clause, Judge W illiams concluded that \xe2\x80\x9c (t]he House com \xc2\xad\nmittee gave considerable attention to the degree o f discretion permitted under the provision. The discussion points\npowerfully against any de minimis exception, and is not contradicted either by consideration on the House floor\nor by a post-enactment colloquy in the S enate." Id.; accord Les, 968 F.2d at 989. \xe2\x80\x9c [T)his is perhaps as strong\nas [legislative history] is likely to g et.\xe2\x80\x9d Public Citizen, 831 F.2d at 1117.\n\n253\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nwill be sustained as long as it is reasonable. See Chevron, U.S.A., Inc. v. Natural\nResources Defense Council, 467 U.S. 837, 842-44 (1984). We believe that the\nuse of significant risk levels as a criterion for exercising that discretion is reason\xc2\xad\nable in light of the statute\xe2\x80\x99s basic requirement of an affirmative showing of\n\xe2\x80\x9c safety.\xe2\x80\x9d See discussion supra pp. 250-51. Accordingly, the FDA\xe2\x80\x99s use of levels\nof risk as a screening criteria for method approval should be sustained as a\n\xe2\x80\x9c reasonable interpretation\xe2\x80\x9d o f the statute.\nThe statute\'s silence on this issue means that the Congress has not spoken in\nstatutory language to this question. That Congress intended to leave this issue\nto the discretion of the FDA is reinforced by an examination of the pertinent\nlegislative history. The history of the DES proviso displays considerable equivo\xc2\xad\ncation on the criteria the FDA should employ in implementing the discretionary\nportions of the statute. On the one hand, some of the legislative history asserts\nthat the \xe2\x80\x9c basic principle\xe2\x80\x9d of the Delaney Clause itself\xe2\x80\x94 its zero tolerance posi\xc2\xad\ntion with respect to carcinogens\xe2\x80\x94 would be unaffected by the passage of the pro\xc2\xad\nviso. A principal piece of evidence of this view is a letter from Secretary Ribicoff\nto the chairman of the House Committee on Interstate and Foreign Commerce\nin 1962, the year the food additives version of the proviso was enacted.7 The\nSecretary\xe2\x80\x99s section-by-section analysis of the proviso stated:\nSection 302(a) would correct a needless and unintentional inequity\nin the application of the food-additive anticancer proviso[8] (sec.\n409(c)(3) of the basic act) to additives for animal feed, while pre\xc2\xad\nserving in its full vigor the consumer protection now afforded by\nthat provision. The basic principle of the anticancer provision,\nwhich would remain unimpaired, is that no tolerance for the addi\xc2\xad\ntion of carcinogenic chemicals to food shall be granted in any\namount . . . .\nLetter for Hon. Oren Harris, Chairman, Committee on Interstate and Foreign Com\xc2\xad\nmerce, from Abe Ribicoff, Secretary, Department of Health, Education, and Wel\xc2\xad\nfare (July 21, 1962), reprinted in Drug Industry A ct o f 1962: Hearings on H.R.\n11581 Before the House Committee on Interstate and Foreign Commerce, 87th\nCong. 49 (1962), reprinted in 21 Leg. Hist, at 227.\n7 The DES proviso was first suggested by the Department o f Health, Education and W elfare ( \xe2\x80\x9c HEW \xe2\x80\x9d ) in 1960.\nH EW drafted the pertinent provisions o f th e language that were eventually enacted in 1962, and transmitted its\nproposal to this same House Committee via another letter from then Secretary Flemming to the chairman, expressing\nH E W \xe2\x80\x99s views on how the proviso would operate. Letter for Hon. Oren Harris, Chairman, Committee on Interstate\nand Foreign Com m erce, from Arthur S. Flem m ing, Secretary, Department o f Health, Education, and Welfare (May\n13, I960) ( \xe2\x80\x9c Flemming L etter\xe2\x80\x9d ), reprinted in H.R. Rep. No. 86-1761, at 88-89 (I960), reprinted in 16 Legislative\nH istory o f the Federal Food, Drug, and C osm etic Act and Its Amendments at 757-58 (1979) ( \xe2\x80\x9c Leg. Hist.\xe2\x80\x9d ). Under\nthese circumstances, the views o f the executive branch with respect to language it requested and initially drafted\nare significant sources o f statutory meaning.\n8 Secretary R ibicoff refers to the \xe2\x80\x98\xe2\x80\x98Delaney proviso\xe2\x80\x9d or the \xe2\x80\x9c anticancer proviso\xe2\x80\x9d where subsequent usage refers\nto the \xe2\x80\x9c Delaney C lause.\xe2\x80\x9d Secretary Flemming, R ib ico ff s predecessor, employs the same terminology.\n\n254\n\n\x0cThe Food and Drug Administration\xe2\x80\x99s Discretion to Approve Methods o f Detection and to Define the\nTerm \xe2\x80\x98 \'No R esidue\'\' Pursuant to the Federal Food, Drug, and Cosmetic A ct\n\nOn the other hand, the proviso has an operational structure that is undeniably\ndifferent from that of the Clause, such that it would be impossible for the zero\ntolerance principle of the Clause to be completely unaffected, and some elements\nof the legislative history reflect an awareness of that fact. A long-time student\nand expert on the Act and the Delaney Clause, Professor Richard Merrill, has\nsuccinctly stated the difference: \xe2\x80\x9c By contrast with the Delaney Clause itself, the\nDES proviso makes the detection of residues in edible animal tissues, rather than\nthe addition of the compound to animals or their feed, the critical inquiry.\xe2\x80\x9d\nRichard A. Merrill, Regulating Carcinogens in Food: A Legislator\xe2\x80\x99s Guide to the\nFood Safety Provisions o f the Federal Food, Drug, and Cosmetic Act, 77 Mich.\nL. Rev. 171, 233 (1978). In other words, the proviso contemplates that a com\xc2\xad\npound will be approved as long as an approved method detects no residue, even\nthough this does not affirmatively mean that no residue was present at all. In\nfact, there might be a residue remaining, one at a level of concentration below\nthe sensitivity of the approved method. Consequently, because the operation of\nthe proviso is linked to detection, and because methods of detection are limited\nin their sensitivity, the inclusion of the proviso could not literally leave the \xe2\x80\x9c basic\nprinciple\xe2\x80\x9d of the Clause unimpaired.\nElements of the legislative history demonstrate an awareness that the operation\nof the proviso would not guarantee that a zero tolerance policy would be carried\nout with full vigor. A principal piece of evidence plainly pointing out the\ninconsistency between the proviso and the Delaney Clause is Representative\nLeonor Sullivan\xe2\x80\x99s floor statement when the proviso was being considered in 1962,\nshortly before actual passage. Representative Sullivan, who introduced another bill\non food and drug safety, H.R. 1235, conveyed her doubts about any weakening\nof the Delaney Clause whatsoever based on her belief that new testing methods\nwould disclose residues that could not be detected in 1962:\nHowever, I have strong doubts, I must admit, over the retreat on\nthe Delaney anticancer clause on feed additives, as contained in\nH.R. 11582, particularly in view of the Government\xe2\x80\x99s experience\nseveral years ago with hormone-treated chickens. It cost us $10 mil\xc2\xad\nlion to remove from the market the fowl treated with a drug consid\xc2\xad\nered safe for the purpose \xe2\x80\x94 after it was learned that there were resi\xc2\xad\ndues of the cancer-inducing substance in the skin of the chickens.\nToo often for complacency, new testing methods disclose the exist\xc2\xad\nence of harmful residues which had not shown up in earlier tests,\nbut by then the damage is done.\nDrug Industry Act o f 1962: Hearings on H.R. 11581 Before the House Committee\non Interstate and Foreign Commerce, 87th Cong. 98 (1962) (Statement of Rep.\nSullivan), reprinted in 21 Leg. Hist, at 276. In order to forestall such weakening,\n255\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nRepresentative Sullivan introduced an amendment to eliminate the DES proviso,\nso as to protect consumers from undetectable levels of carcinogenic residues. 108\nCong. Rec. 21,077 (1962) (Statement of Rep. Sullivan), reprinted in 23 Leg. Hist,\nat 29. Her amendment was defeated.9\nRepresentative Sullivan\xe2\x80\x99s statement recounts an actual historical example of sub\xc2\xad\nsequent improvements in testing sensitivity that revealed a residue where none\nhad been detected earlier. No member of Congress disputed the factual accuracy\nof her description of the proviso\xe2\x80\x99s operation, although several rose to comment\non her statement. See 108 Cong. Rec. at 21,079-83, reprinted in 23 Leg. Hist,\nat 31-35. This sequence reveals very clearly the tension between the proviso and\nthe original Delaney Clause: in all likelihood the proviso would permit the pres\xc2\xad\nence of physical residues of carcinogenic compounds, because testing methods\nwould not be sensitive enough to detect them, while the Clause advocates a zero\ntolerance approach to the presence of any residue.\nFinally, the tension between the idea that the proviso would preserve the \xe2\x80\x98\xe2\x80\x98basic\nprinciple\xe2\x80\x9d of the Clause and the idea that detection methods would most likely\nbecome more sensitive over time, so that a failure to detect residue with any\ngiven method could not be taken to show the complete absence of the compound,\nis evident in the major statement of the administration\xe2\x80\x99s understanding of the pro\xc2\xad\nviso, Secretary Flemming\xe2\x80\x99s letter of May 13, 1960, which transmitted the language\nof the proviso to the House committee considering the Color Additives Amend\xc2\xad\nments.\nThere is, however, one respect in which the anticancer proviso\nhas proved to be needlessly stringent as applied to the use of addi\xc2\xad\ntives in animal feed. For example, in the case of various animals\nraised for food production, certain drugs are used in animal feed\nwhich will leave no residue in the animal after slaughter or in any\nfood product (such as milk or eggs) obtained from the living\nanimal, and which are therefore perfectly safe for man. If this is\ndemonstrated with respect to any particular additive intended for\nanimal feed, and the additive will not adversely affect the animal\nitself during its expected or intended life cycle, we can see no rea\xc2\xad\nson for not permitting such a use of an additive which could be\nhighly useful and beneficial in the raising of animals for food. . . .\nWe therefore have included in the enclosed draft bill an amend\xc2\xad\nment to permit use of an additive animal feed under the abovementioned conditions.\nIt may aid public understanding of the Delaney proviso and allay\nunnecessary apprehension regarding it, to touch here on the pro9 The am endm ent failed by voice vote. 108 Cong. Rec. at 21,081, reprinted in 23 Leg. Hist, at 33. Her amendment\nto elim inate the DES proviso permitting carcinogenic color additives in animal feed was also rejected. Id. at 21,083,\nreprinted in 23 Leg. Hist, at 35.\n\n256\n\n\x0cThe Food and Drug Administration\xe2\x80\x99s Discretion to Approve Methods o f Detection and to Define the\nTerm "N o R esidue" Pursuant to the Federal Food, Drug, and Cosmetic A ct\n\nviso\xe2\x80\x99s operation where its application, under present law and the\nproposed modification, depends on whether a residue of the chem\xc2\xad\nical additive involved is left in the edible tissue or other food prod\xc2\xad\nucts of an animal. This question may arise in two types of case.\nIn the first, a veterinary drug is directly administered \xe2\x80\x94 by injec\xc2\xad\ntion, implantation, or otherwise \xe2\x80\x94 to the animal, instead of being\nmixed with its feed. In that event, the Delaney proviso can have\napplication only if a residue of the added drug occurs in food prod\xc2\xad\nucts (such as milk or eggs) of the living animal or in some edible\nportion or product of the animal after slaughter. In the second type\nof case, the drug is mixed with feed consumed by the animal. In\nthat event, it is necessarily a food additive (since animal feed is\nfood within the meaning of the act), but it will nevertheless be taken\nout of the Delaney proviso\xe2\x80\x99s application by the above-proposed\namendment even if it is cancer inciting (at particular feeding levels)\nin test animals, provided that it satisfies the above-mentioned\nrequirements as to the absence of adverse effect on the animals\nfor which the feed is intended and as to the absence of any residue\nin the food products or edible portions of the animal.\nIn both these instances, where the question of the possibility of\na residue is crucial, it is desirable that industry laboratory techni\xc2\xad\ncians, and enforcement officers have a common understanding with\nthe Food and Drug Administration as to the methods of assay that\nwill be recognized by us, and on which we want to rely, in\nresolving the question of residue. We have, therefore, in the pro\xc2\xad\nposed amendment to the Delaney proviso (and likewise in the pro\xc2\xad\nposed modification of the anticancer clause of H.R. 7624) provided\nthat, under the amendment, the assay methods applicable in deter\xc2\xad\nmining whether there will be a residue shall be those prescribed\nor approved by us by regulations. This will give reasonable cer\xc2\xad\ntainty in that regard, although, of course, such regulations may from\ntime to time be changed as new scientific developments dem\xc2\xad\nonstrate a need for change. It should be clearly understood that the\nindustry still would have the responsibility of developing adequate\nanalytical methods for detecting residues and furnishing them to\nthe Government with a petition for approval of an additive.\nDuring the hearings on color additives legislation, some wit\xc2\xad\nnesses expressed a concern because of their fear that the Depart\xc2\xad\nment intends to press a never-ending search for more and more\ndelicate methods of analysis, so that it may, without regard to sci\xc2\xad\nentific reason, rescind permissions granted earlier for use of various\n257\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nadditives judged to leave no residues in food. This fear is not justi\xc2\xad\nfied.\nThe Department applies sound scientific judgment and the rule\nof reason in determining the sensitivity and precision required in\nan analytical procedure used to detect residues of added chemi\xc2\xad\ncals\xe2\x80\x94 even before an additive is approved. And when it has been\ndetermined that a given degree of sensitivity and precision is appro\xc2\xad\npriate, based upon sound scientific facts, it has no intention of\nrequiring change in the analytical procedure until new scientific\ndevelopments clearly demonstrate the need.\nFlemming Letter, reprinted in H.R. Rep. No. 86-1761, at 88-89, reprinted in\n16 Leg. Hist, at 757-58.\nSecretary Flemming\xe2\x80\x99s letter contains some passages that point in the same direc\xc2\xad\ntion as the section-by-section analysis of Secretary Ribicoff quoted above, namely\ntoward the idea that the proviso is entirely consistent with the Clause. Its claim,\nfor instance, that the proviso would apply to chemicals that leave \xe2\x80\x9c no residue\xe2\x80\x9d\nin edible tissue, might be read to adopt the zero tolerance position of the Clause,\nas might the claim that the Clause is \xe2\x80\x9c needlessly\xe2\x80\x9d stringent in case to which\nthe proviso would apply. However, in the last three paragraphs quoted above,\nthe Secretary also acknowledges that the application of the proviso would depend\nupon sensitivity of the method. The portions responding to concerns expressed\nin the hearing make this point clear.\nThe sole basis upon which \xe2\x80\x9c a never-ending search for more and more delicate\nmethods of analysis, so that [the FDA] may, without regard to scientific reason,\nrescind permissions granted earlier for use of various additives judged to leave\nno residues in food,\xe2\x80\x9d Flemming Letter, reprinted in H.R. Rep. No. 86-1761, at\n89, reprinted in 16 Leg. Hist, at 758, could be a concern to the industry is if\nit were possible to grant permissions on the basis of methods not sensitive enough\nto guarantee literally no residue, such that it was then conceivable that more sen\xc2\xad\nsitive methods might later be developed that could detect a residue. That is pre\xc2\xad\ncisely the scenario painted later on the House floor by Representative Sullivan,\nin the passage quoted earlier. See supra p. 255. As was also the case with respect\nto Representative Sullivan\xe2\x80\x99s concerns, the Secretary\xe2\x80\x99s response is not that this\nscenario is strictly impossible \xe2\x80\x94 which it would be if the proviso only operated\nin situations where literally no residue remained. Instead, he assures the Com\xc2\xad\nmittee that the FDA will exercise \xe2\x80\x9c sound scientific judgment and the rule of rea\xc2\xad\nson in determining the sensitivity and precision required in an analytical procedure\nused to detect residues of added chemicals \xe2\x80\x94 even before an additive is approved.\nAnd when it has been determined that a given degree of sensitivity and precision\nis appropriate, based upon sound scientific facts, [the FDA] has no intention of\n258\n\n\x0cThe Food and Drug Administration\'s Discretion to Approve Methods o f Detection and to Define the\nTerm \xe2\x80\x9cNo Residue" Pursuant to the Federal Food, Drug, and Cosmetic Act\n\nrequiring change in the analytical procedure until new scientific developments\nclearly demonstrate the need.\xe2\x80\x9d Id.\nIn sum, by permitting approvals to be based on detection methods that cannot\nconfirm that no additions of the compound to edible tissue will occur, the proviso\narticulates a different principle from the one animating the Delaney Clause.\nSignificant pieces of legislative history confirm an awareness by Congress that\nthe proviso would operate in a manner significantly different from the Clause,\nalthough other pieces of that history suggest the opposite. The amendments offered\nby Representative Sullivan to prevent the weakening of the Clause seem to have\nput the choice of continuing a strict zero tolerance approach or not squarely to\nthe Congress, and Congress voted to adopt the proviso in the form proposed by\nthe administration.10\nThe court in Public Citizen based its conclusion that risk could not enter into\nthe FDA\xe2\x80\x99s determination of whether a compound \xe2\x80\x9c induces cancer\xe2\x80\x9d on its concern\nthat to do so would permit the consideration of a factor that the Delaney Clause\nprohibits the FDA from taking into account in the ultimate decision whether to\nban the substance. For the most part, it based its conclusion that risk could not\nbe taken into account in that ultimate decision on a consistent and strong legisla\xc2\xad\ntive history rejecting the use of risk as a factor. The court\xe2\x80\x99s concern that risk\nmight work its way back into the agency\xe2\x80\x99s judgment so as to undermine\nCongress\xe2\x80\x99s prohibition does not apply here, because rejecting methods on the basis\nof risk does not have that effect. See discussion supra p. 253. Even if this decision\ndid have that effect, the legislative history of the proviso fails to support the\nconclusion that Congress meant the same zero tolerance policy of the Clause to\nbe fully applicable in implementing the proviso. As a whole, the legislative history\namply confirms what the statute suggests on its face: Congress has not clearly\nspoken to the question whether the FDA could take risk into account in selecting\nmethods of detection, thus permitting the FDA to adopt a reasonable interpretation\nof the relevant criteria.11\nIn retrospect, it is not possible to conclude with confidence why Congress failed\nto specify the precise criteria that the FDA ought to employ in selecting detection\nmethods. Chevron identifies a number of possible reasons that an agency may\nbe given discretion to interpret a statute:\n10 See supra note 9.\n11 To the extent the legislative history speaks at all to what might cabin the exercise o f discretion in selecting\nmethods of testing, it is only suggestive. Secretary Flem m ing\'s letter speaks o f using \xe2\x80\x9c sound scientific judgment\nand the rule of reason in determining the sensitivity and precision required.\xe2\x80\x9d H.R. Rep. No. 86-1761, at 89, reprinted\nin 16 Leg. Hist, at 758. These concepts are nowhere further defined in the subsequent discussions o f the proviso,\nwhich are not numerous in a legislative history dominated by more contentious issues. If anything, they suggest\nthat levels o f risk might well be a consideration in the decision to require more sensitive methods, because the\nneed for greater sensitivity, which might be indicated by the significance o f the risks involved, would seem to\nbe one o f the most obvious factors triggering a \xe2\x80\x9c rule o f reason\xe2\x80\x9d decision to seek more sensitive methods, if not\nthe most obvious factor.\n\n259\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nCongress [may have] intended to accommodate [competing]\ninterests, but did not do so itself on the level of specificity [nec\xc2\xad\nessary to resolve the precise question being litigated]. Perhaps that\nbody consciously desired the Administrator to strike the balance\nat this level, thinking that those with great expertise and charged\nwith responsibility for administering the provision would be in a\nbetter position to do so; perhaps it simply did not consider the ques\xc2\xad\ntion at this level; and perhaps Congress was unable to forge a coali\xc2\xad\ntion on either side of the question, and those on each side decided\nto take their chances with the scheme devised by the agency.\nChevron, 467 U.S. at 865. In light of the language of the statute, the structure\nof the statute, and the legislative history of the proviso, we conclude that one\nof these three conditions obtained here\xe2\x80\x94 probably the first or the second, although\n\xe2\x80\x9c for judicial purposes, it matters not which of these occurred.\xe2\x80\x9d Id. Whatever the\nreason may have been, the result is that the FDA\xe2\x80\x99s \xe2\x80\x9c reasonable interpretation\xe2\x80\x9d\nof its authority \xe2\x80\x94 that method sensitivity down to the level of significant risk can\nbe used as a criterion in method selection \xe2\x80\x94 is within its discretion to adopt.\n\nB. M ust the FDA Adopt the M ost Sensitive M ethod of Detection?\nThe agencies\xe2\x80\x99 second question is whether the FDA must revise its regulations\nto adopt more sensitive methods when they become available once it has adopted\na method that detects the residue. Essentially, this question asks whether the pro\xc2\xad\nviso requires the FDA to revise its regulations to adopt the \xe2\x80\x9c best available\xe2\x80\x9d detec\xc2\xad\ntion methods for a compound, or whether it has discretion to continue to accept\nresults from less sensitive methods. At one time in the FDA\xe2\x80\x99s implementation\nof the proviso, the agency did take the position that it generally should adopt\nthe best available detection m ethods.12 While that interpretation may be one\npermissible interpretation of the proviso, the narrow question we must resolve\nis whether the statute compels that course of action. We conclude the answer\nto this question is also no.\nThe proviso itself is completely silent with respect to what criteria the FDA\nmust employ in deciding whether to approve a method of detection. It is also\ncompletely silent as to any affirmative obligation on the FDA to revisit or revise\napproved methods. Any case in favor of a \xe2\x80\x9c best available\xe2\x80\x9d obligation, therefore,\nmust rely heavily on the zero tolerance principle for carcinogens under the\nDelaney Clause itself, coupled with those portions of the legislative history of\nthe proviso that assert that the proviso maintains this \xe2\x80\x9c basic principle\xe2\x80\x9d of the\n12For a history o f the FD A \xe2\x80\x99s approach to implementing the proviso up to that time, see Chemical Compounds\nin Food-Producing Animals, Criteria and Procedures for Evaluating Assays for Carcinogenic Residues in Edible\nProducts o f A nimals, 42 Fed. Reg. 10,412 (1977).\n\n260\n\n\x0cThe F ood and Drug Administration\xe2\x80\x99s Discretion to Approve M ethods o f Detection and to Define the\nTerm "N o Residue" Pursuant to the Federal Food, Drug, and Cosmetic A ct\n\nClause. Under this theory, if the method of detection approved by the FDA could\nnot detect residues at levels achievable by the best available methods, and such\nlevels were in fact detected by a more sensitive method, then failing to adopt\nthe best available method as the required method under the proviso seems tanta\xc2\xad\nmount to approving a tolerance for the compound.13 Flemming Letter, reprinted\nin H.R. Rep. No. 86-1761, at 89, reprinted in 16 Leg. Hist, at 758.\nAs we have already discussed, however, the proviso itself does not contain any\nlanguage from which an affirmative obligation to use best available methods could\nbe derived. The plain language of the proviso stands in tension with the basic\nprinciple of the Clause, and the legislative history of the proviso in several places\nreflects an awareness that the proviso depends upon detection in its operation.\nIn fact, some of the legislative history suggests the FDA intended from the begin\xc2\xad\nning not to adopt best available methods, at least under some circumstances, and\nthat Congress acquiesced in that understanding. First, the history acknowledges\nthat an approach depending on detection will most likely result in approved uses\nof compounds where in fact residues are present in food. See, e.g.. Representative\nSullivan\xe2\x80\x99s statement, supra p. 255. Second, Secretary Flemming\xe2\x80\x99s influential May\n13, 1960 letter seeks explicitly to quell industry concerns that the FDA will engage\nin a \xe2\x80\x9c never-ending search\xe2\x80\x9d for more sensitive methods, without regard to sci\xc2\xad\nentific reason. The Secretary\xe2\x80\x99s rejoinder that HEW will not engage in such a\nsearch plainly argues against a requirement to always adopt best available detec\xc2\xad\ntion methods. To repeat, Secretary Hemming wrote:\nThe Department applies sound scientific judgment and the rule of\nreason in determining the sensitivity and precision required in an\nanalytical procedure used to detect residues of added chemicals \xe2\x80\x94\neven before an additive is approved. And when it has been deter\xc2\xad\nmined that a given degree of sensitivity and precision is appropriate,\nbased upon sound scientific facts, it has no intention of requiring\n13 The House Committee that first received Secretary Flemming\xe2\x80\x99s request for enacting the DES proviso reported\nthe Secretary\xe2\x80\x99s views on whether the Delaney Clause itself permitted the FDA to establish tolerances for carcinogens.\nThe committee report quotes him as stating:\nW henever a sound scientific basis is developed for the establishment o f tolerances for carcinogens, we\nwill request the Congress to give us that authority. We believe, however, that the issue is so important\nthat the elected representatives o f the people should have the opportunity o f examining the evidence and\ndetermining whether o r not the authority should be granted.\nThis, I believe, is as far as our discretion should go in the light o f present scientific knowledge. W e\nhave no basis for asking Congress to give us discretion to establish a safe tolerance for a substance which\ndefinitely has been shown to produce cancer when added to the diet o f test animals. W e simply have\nno basis on which such discretion could be exercised because no one can tell us with any assurance at\nall how to establish a safe dose o f any cancer-producing substance.\nH.R. Rep. No. 86-1761, at 12-13, (quoting Statement by Hon. Arthur S. Flemming, Secretary of HEW , before\nthe House Committee on Interstate and Foreign Commerce, January 26, 1960), reprinted in 16 Leg. Hist, at 68 1 82.\n\n261\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nchange in the analytical procedure until new scientific develop\xc2\xad\nments clearly demonstrate the need.\nFlemming Letter, reprinted in H.R. Rep. No. 86-1761, at 89, reprinted in 16\nLeg. Hist, at 758. In the last sentence of this quotation, the Secretary contemplates\na situation in which a more sensitive method is available, but not needed, by\nacknowledging as possible a situation in which the agency could change to more\nsensitive methods and yet refrains from doing so. Such a situation is possible\nonly if a superior method were available. This passage, in short, suggests that\nthe FDA must have some discretion to decline to adopt the best available method.\nOnce again, however, the statute itself provides no guidance at all on what fac\xc2\xad\ntors the FDA may consider in exercising such discretion, and the legislative history\nprovides only suggestive guidance. While \xe2\x80\x9c sound scientific judgment and the rule\nof reason\xe2\x80\x9d is not further defined, the level of risk already capable of being\ndetected is certainly one plausible factor that might bear on the FDA\xe2\x80\x99s assessment\nof whether \xe2\x80\x9c new scientific developments clearly demonstrate the need.\xe2\x80\x9d This is\nbecause, as just discussed, the Secretary\xe2\x80\x99s letter contemplates the case in which\na more sensitive method is available, yet determined by the agency not to be\nneeded. Of all the considerations that might support a conclusion that a better\ntest is not \xe2\x80\x9c needed,\xe2\x80\x9d as opposed, say, to being too expensive, or too time-consuming, the consideration that current tests are adequate to detect significant risk\nis perhaps the most straightforward and appropriate. This interpretation, thus, ties\nthe FDA\xe2\x80\x99s discretion in method selection directly to some appraisal of the need\nto detect low levels of risk, and the significant risk level is certainly a reasonable\nbenchmark for assessing adequacy.\nThus, the Secretary\xe2\x80\x99s letter defines two points that are important for our pur\xc2\xad\nposes. As the FDA contemplated the operation of the proviso, it would (1) some\xc2\xad\ntimes refrain from requiring the best available detection method; and (2) base\nits decision on method approval on undefined \xe2\x80\x9c sound scientific judgment and\nthe rule of reason,\xe2\x80\x9d which might well incorporate considerations of the risks asso\xc2\xad\nciated with the compound. While turning these points into statutory commands\nprobably makes too much of Secretary Flemming\xe2\x80\x99s letter, it and the other pieces\nof legislative history acknowledging that the proviso\xe2\x80\x99s operation is linked to detec\xc2\xad\ntion do refute arguments that such a reading is precluded by the statute. The his\xc2\xad\ntory is simply too contradictory to support that result.\nIn this section of our opinion, however, the narrow question under review is\nwhether the statute compels the FDA to push beyond currently approved methods\nto require more sensitive methods when they become available. As to this ques\xc2\xad\ntion, we are confident the answer is no.\n\n262\n\n\x0cThe Food and Drug Administration\xe2\x80\x99s Discretion to Approve Methods o f Detection and to Define the\nTerm "N o Residue" Pursuant to the Federal Food, Drug, and Cosmetic A ct\n\nIII. Definition of \xe2\x80\x9c No Residue\xe2\x80\x9d\nUnder the SOM regulations, the FDA accepts a finding of some residue as satis\xc2\xad\nfying the statutory requirement of \xe2\x80\x9c no residue,\xe2\x80\x9d if the level of residue detected\nposes no significant risk of increased cancer to people. In other words, it considers\nthe detected presence of small amounts of residue as satisfying the statutory\nrequirement of no residue. The final question the agencies have presented is\nwhether this construction is permissible under the statute. While the first two ques\xc2\xad\ntions dealt with the FDA\xe2\x80\x99s discretion to approve methods of detection, this one\ndeals with the FDA\xe2\x80\x99s possible discretion in interpreting the statutory requirement\nthat the FDA find \xe2\x80\x9c no residue\xe2\x80\x9d by means of whatever methods of detection the\nFDA has chosen. The question of what action may be taken when the method\nprescribed or approved by the Secretary by regulations detects a residue demands\na different answer.\nOnce again, we start with the statute. If Congress has \xe2\x80\x9c directly spoken to the\nprecise question at issue\xe2\x80\x9d in the statute, that instruction must be followed.\nChevron, 461 U.S. at 842-44; see also Connecticut Nat\xe2\x80\x99l Bank v. Germain, 503\nU.S. 249, 254 (1992) (\xe2\x80\x9c When the words of a statute are unambiguous, then, the\nfirst canon of construction is also\' the last: \xe2\x80\x98judicial inquiry is complete.\xe2\x80\x99 \xe2\x80\x9d )\n(quoting Rubin v. United States, 449 U.S. 424, 430 (1981)). In this instance, Con\xc2\xad\ngress has clearly spoken. The DES proviso states that the Delaney Clause will\nnot apply \xe2\x80\x9c if the Secretary finds . . . that no residue of the additive will be\nfound (under methods of examination prescribed or approved by the Secretary\nby regulations).\xe2\x80\x9d 21 U.S.C. \xc2\xa7 348(c)(3)(A). The interpretation of this language\nseems straightforward and unambiguous. Giving \xe2\x80\x9c no residue\xe2\x80\x9d its ordinary\nmeaning, the detected presence of any residue by an approved method would be\nincompatible with a finding of \xe2\x80\x9c no residue,\xe2\x80\x9d and thus would preclude a finding\nthat the proviso applies.\nInvestigation of the legislative history substantiates this reading of the statute.\nPrevious inquiries into the legislative history of the proviso supported the conclu\xc2\xad\nsion that the FDA enjoys considerable discretion to select methods of detection.\nThat conclusion was initially based on a reading of the statute itself, and subse\xc2\xad\nquently reinforced by the findings that Congress\xe2\x80\x99s deliberations reflected no single\nclear view either on precisely how the proviso was consistent with the zero toler\xc2\xad\nance principle of the Delaney Clause or on the criteria the FDA should use in\nselecting such methods of detection. As to the question at issue here, the legisla\xc2\xad\ntive history also reinforces the initial reading of the statute, but this time by\nrevealing a consistent record. There is nothing in that record to suggest that a\nfinding of \xe2\x80\x9c no residue\xe2\x80\x9d could be based upon the detected presence of residue,\nhowever insignificant, and the most pertinent items in the record on this issue\nin fact support the plain reading of the statute.\n263\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nConsider first Secretary Flemming\xe2\x80\x99s May 13, 1960 letter initially proposing the\nproviso\xe2\x80\x99s language, which states in part:\nThere is, however, one respect in which the anticancer proviso has\nproved to be needlessly stringent as applied to the use of additives\nin animal feed. For example, in the case of various animals raised\nfor food production, certain drugs are used in animal feed which\nwill leave no residue in the animal after slaughter or in any food\nproduct (such as milk or eggs) obtained from the living animal,\nand which are therefore perfectly safe for man.\nFlemming Letter, reprinted in H.R. Rep. No. 86-1761, at 88, reprinted in 16\nLeg. Hist, at 757. It is impossible to read the Secretary\xe2\x80\x99s reference to \xe2\x80\x9c no residue\xe2\x80\x9d\nas implying that the administration was proposing a statutory revision that would\nknowingly permit some residue to remain in food products. This is the same letter,\nafter all, that endorses the Delaney Clause\xe2\x80\x99s standard of zero tolerance as the\nonly acceptable public health policy with respect to carcinogens.14 The letter only\nproposes a proviso that would operate when the Clause was \xe2\x80\x9c needlessly strin\xc2\xad\ngent\xe2\x80\x9d ; that is, the proviso will apply in situations where a compound had been\nadded to animal feed\xe2\x80\x94 and came within the scope of the food additive statute\xe2\x80\x99s\nDelaney Clause for that reason\xe2\x80\x94 but left \xe2\x80\x9c no residue\xe2\x80\x9d in food to be composed\nby humans. The operating supposition of the Delaney Clause, endorsed by Sec\xc2\xad\nretary Flemming, is that no exposure, no matter how small, to a known carcinogen\nwas then considered \xe2\x80\x9c safe.\xe2\x80\x9d On that supposition, the only residue that could be\nconsidered \xe2\x80\x9c perfectly safe\xe2\x80\x9d for humans, where the Clause\xe2\x80\x99s application would\nbe \xe2\x80\x9c needlessly stringent,\xe2\x80\x9d would be zero residue.\nThat this was Secretary\xe2\x80\x99s Flemming\xe2\x80\x99s view, and Congress\xe2\x80\x99s understanding of\nit, is reinforced by the Secretary\xe2\x80\x99s earlier statement:\nWe have no basis for asking Congress to give us discretion to estab\xc2\xad\nlish a safe tolerance for a substance which definitely has been\nshown to produce cancer when added to the diet of test animals.\nWe simply have no basis on which such discretion could be exer\xc2\xad\ncised because no one can tell us with any assurance at all how\nto establish a safe dose o f any cancer-producing substance.\nH.R. Rep. No. 86-1761, at 13 (quoting Statement by Hon. Arthur S. Flemming,\nSecretary of HEW, before the Committee on Interstate and Foreign Commerce,\nJan. 26, 1960), reprinted in 16 Leg. Hist, at 682. Having proof of the presence\nof a residue but nonetheless exempting a compound from the Delaney Clause\xe2\x80\x99s\n14Id. ( \xe2\x80\x9c [T]he principle o f the [Delaney C lause] reflects, basically, the current state o f scientific knowledge, and\nw e w ould therefore, except [as applied to situations governed by the proposed DES proviso] feel constrained to\napply the same principle even in the absence o f [the Delaney C lause].\xe2\x80\x99\xe2\x80\x99).\n\n264\n\n\x0cThe Food and Drug Administration\'s Discretion to Approve Methods o f Detection and to Define the\nTerm \xe2\x80\x9cNo Residue \xe2\x80\x9dPursuant to the Federal Food, Drug, and Cosmetic A ct\n\nprohibition, as the SOM\xe2\x80\x99s construction of \xe2\x80\x9c no residue\xe2\x80\x9d does, seems indistinguish\xc2\xad\nable from treating that level of residue as a safe tolerance \xe2\x80\x94 precisely the result\nthat Secretary Flemming denies in his statement to the Committee. Likewise, Sec\xc2\xad\nretary Ribicoff\xe2\x80\x99s assertion that \xe2\x80\x9c no tolerance for the addition of carcinogenic\nchemicals to food shall be granted in any amount,\xe2\x80\x9d seems to require the conclu\xc2\xad\nsion that permitting a detected residue of a carcinogenic chemical to be present\nin food to be consumed by humans would not be permitted. Letter for Hon. Oren\nHarris, Chairman, Committee on Interstate and Foreign Commerce, from Abe\nRibicoff, Secretary, Department of Health, Education, and Welfare (July 21,\n1962), reprinted in Drug Industry Act of 1962: Hearings on H.R. 11581 Before\nthe House Committee on Interstate and Foreign Commerce, 87th Cong. 49 (1962),\nreprinted in 21 Leg. Hist, at 227.\nThere is nothing in the legislative history to suggest that Congress meant to\nauthorize carcinogenic residue to be detected by the FDA and yet to have the\nproviso operate to exempt that compound from the Delaney Clause\xe2\x80\x99s prohibition.\nWe believe that the statutory language of \xe2\x80\x9c no residue . . . will be found (under\nmethods of examination prescribed or approved by the Secretary by regulations),\xe2\x80\x9d\n21 U.S.C. \xc2\xa7 348(c)(3)(A), means that whatever approved method of detection is\nused must return a negative finding in order for the proviso to operate. Congress\nmay not have been of one mind in realizing that reliance on detection could well\nresult in actual, but undetected, residues in cancer-inducing additives being\napproved, but the case of actual, undetected, residues is quite distinguishable from\nthe case of actual, detected ones. The legislative history consistently supports the\nconclusion that Congress did not intend for any additive for which a residue was\nactually detected to have the benefit of the DES proviso. The statute being clear,\nthe FDA has no discretion to deviate from it.\nIt may be argued that the meaning of \xe2\x80\x9c no residue\xe2\x80\x9d is not clear, because the\nclearest literal meaning of \xe2\x80\x9c no residue\xe2\x80\x9d would preclude the FDA from ever\nemploying the proviso once one acknowledges the considered scientific view that\none can never be sure that not even a single molecule of a compound remains\nin edible tissue. Because it is doubtful that Congress meant \xe2\x80\x9c no residue\xe2\x80\x9d to be\ngiven a meaning that would render the proviso nugatory, the argument would\nrun, what Congress meant by the term is ambiguous, and hence the door is open\nfor the FDA to exercise a reasonable discretion in interpreting it.\nAs already discussed, we agree that the legislative history displays equivocation\non how the proviso was meant to operate, that there are inconsistences in state\xc2\xad\nments concerning its ultimate effect, and that the FDA enjoys some interpretive\ndiscretion as a result. In determining the scope of that discretion, however, one\nmust keep in mind the particular discretionary judgment at issue. Here the \xe2\x80\x9c pre\xc2\xad\ncise question at issue\xe2\x80\x9d is whether the FDA may treat a detected presence of res\xc2\xad\nidue as \xe2\x80\x9c no residue\xe2\x80\x9d within the meaning of the proviso. As to that precise ques\xc2\xad\ntion, the foregoing argument does not change the analysis. Had Congress insisted\n265\n\n\x0cOpinions o f the Office o f Legal Counsel in Volume 19\n\nupon an affirmative showing of \xe2\x80\x9c no residue,\xe2\x80\x9d the current scientific understanding\nwould indeed render the proviso a dead letter. That, however, is not the proviso\nCongress drafted. Instead, the proviso relies upon an affirmative showing that an\napproved method o f detection finds \xe2\x80\x9c no residue,\xe2\x80\x9d and that finding can still be\nmade consistent with the belief that a yet more sensitive method might show a\nphysical residue where the approved method does not.\nIn this regard, our analysis finds the proviso to be structurally similar to the\nDelaney Clause as interpreted by Judge Williams in Public Citizen. Both provi\xc2\xad\nsions contain some administrative discretion, but they also both contain some\n\xe2\x80\x9c automatic\xe2\x80\x9d elements. To paraphrase Judge Williams, our conclusion is that the\nproviso requires that if A [an approved method of detection detects the presence\nof any residue], then B [the proviso is not applicable]. See Public Citizen, 831\nF.2d at 1112. There is language permitting administrative discretion, but it relates\nonly to the selection of detection methods.15 Once any residue is detected by\nan approved method, the compound cannot be listed, because the proviso does\nnot apply, and hence the Delaney Clause itself does.\nIV. Conclusion\nUnder the DES proviso, the FDA may choose to disapprove methods of detec\xc2\xad\ntion because they are not sufficiently sensitive to detect the presence of an additive\nat the \xe2\x80\x9c no significant risk\xe2\x80\x9d level. Further, the FDA need not revise its regulatory\napproval of a method simply because a more sensitive method of detection may\nbe available. However, it is a necessary condition to the application of the DES\nproviso that an FDA approved method of detection return a finding that no residue\nhas been detected. The FDA may not accept a finding that residue is present,\nbut below the \xe2\x80\x9c no significant risk\xe2\x80\x9d level, as satisfying the statutory requirement\nof \xe2\x80\x9c no residue.\xe2\x80\x9d\nCHRISTOPHER SCHROEDER\nDeputy Assistant Attorney General\nOffice of Legal Counsel\n15 O f course, the exercise o f the FDA\xe2\x80\x99s discretion in selecting a method o f detection might result in an approved\nm ethod failing to detect residues that more sensitive methods could detect. The practical consequences o f a finding\no f no residue by such a less sensitive method might well be indistinguishable from the consequences o f following\nthe F D A \xe2\x80\x99s current SOM approach, if the less sensitive method were sensitive down to the level of no significant\nrisk, but no further. Indeed, by giving the Secretary discretion in method selection, Congress may well have con\xc2\xad\ntem plated that the risk associated with a com pound might be a factor in the Secretary\xe2\x80\x99s exercise of that discretion.\nSee discussion supra pp. 2 61-62. Insofar as the FDA\xe2\x80\x99s approach takes no significant risk levels into account, it\ncan be seen as one plausible methodology fo r accomplishing the purposes o f the DES proviso, at least on one\npossible reading o f those purposes.\nN evertheless, the Supreme Court has been quite clear in recent years that where Congress\xe2\x80\x99s statutory command\nis unam biguous as to the precise question at issue. Chevron , 467 U.S. at 842, that command must be followed.\nE.g., Connecticut Nat\xe2\x80\x99l Bank, 503 U.S. at 254. The proviso structures the FD A \xe2\x80\x99s decision making in a particular\nway, and the fact that an alternative decision making structure might produce a similar ultimate decision does not\njustify failing to follow the proviso\xe2\x80\x99s instructions.\n\n266\n\n\x0c'