   The Food and Drug Administration’s Discretion to Approve
   Methods of Detection and to Define the Term “ No Residue”
     Pursuant to the Federal Food, Drug, and Cosmetic Act

The Food and Drug Administration has the discretionary authority under the DES proviso to the
   Delaney Clause of the Federal Food, Drug, and Cosmetic Act to prohibit the use of an additive
   in animal feed if the FDA concludes that there is no method that can “ reliably measure and
   confirm” whether the additive contains residues o f carcinogenic concern at or above the “ no res­
   idue” level.

Where the FDA has already approved a method for detecting the presence o f residues of carcinogenic
  concern, the DES proviso does not require the FDA to revise its regulations to adopt the “ best
  available” such method.

The FDA lacks the discretion to determine that an edible tissue contains “ no residue” when a method
   of detection reveals the presence of residues of carcinogenic concern that is below the “ no signifi­
   cant risk” level.

                                                                                                     October 13, 1995

  M e m o r a n d u m O p in io n   fo r th e   A s s is t a n t A d m in is t r a t o r   and   G en era l C oun sel
                                E 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
                                                       and the

                                                G en era l C oun sel
                          D epa rtm en t        of   H ealth    and    H u m a n S e r v ic e s


   This memorandum responds to the Environmental Protection Agency’s
(“ EPA” ) and the Food and Drug Administration’s (“ FDA” ) request for our
opinion regarding the FDA’s regulations implementing what is known as the
“ DES proviso” to the Delaney Clause of the Federal Food, Drug, and Cosmetic
Act, 21 U.S.C. §§301-393 (the “ Act” ) . 1 Both agencies have certain responsibil­
ities under the Act, which establishes federal regulatory authority over the safety
of food additives, human and animal drugs, certain pesticides, and cosmetics.

                                                 I. Background

   The Act requires that a food additive (including additives to animal feed) be
found to be “ safe” before the FDA authorizes its use. The Delaney Clause pro­
hibits such a finding of safety with respect to a substance found to induce cancer
in man or animal. The DES proviso carves out an exception to the Delaney Clause,
allowing cancer-inducing agents to be added to animal feed if the FDA finds that
the additive will not harm the animals, and that no residue of the additive will

  1 Letter for W alter Dellinger, Assistant Attorney General, Office of Legal Counsel, from Jean C. Nelson, General
Counsel, Environmental Protection Agency, and Harriet S. Rabb, General Counsel, Department o f Health and Human
Services (Dec. 8, 1994).


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be found in any edible portion of the animal after slaughter or in any food from
the animal. The presence of residue is to be determined by “ methods of examina­
tion prescribed or approved by the Secretary by regulations.” Id. § 348(c).2
   The proviso was enacted in 1962 to allow substances such as the animal drug
diethylstilbestrol, abbreviated as DES, to be used in appropriate situations. Pub.
L. No. 87-781, § 104(f), 76 Stat. 780, 785 (1962). Under the Delaney Clause
without the proviso, new applications for the use of drugs like DES, a carcinogen,
would ordinarily have been kept from the market. However, because drugs like
DES, when used properly, pass quickly out of the treated animal’s system, may
leave no detectable residue in edible tissue, and do not harm the animal, Congress
permitted the use of such substances. See Hess & Clark, Div. o f Rhodia, Inc.
v. FDA, 495 F.2d 975, 979 (D.C. Cir. 1974).
   Over the years since the DES proviso was enacted, the FDA has implemented
its terms through a series of regulatory decisions. Its current regulations, which
embody the sensitivity of method (“ SOM” ) approach, contain several discrete
elements. The central feature of the regulations is the FDA’s operational defmition
of the statutory term “ no residue.” Under the definition, the FDA determines
a level of residue for any given food additive that will be considered to satisfy
the “ no residue” finding required under the proviso. This “ no residue” level
is calculated in several steps. See 21 C.F.R. § 500.84(c) (1995). First, the FDA
determines a maximum level o f concentration of any “ residue of carcinogenic
concern” from the additive in question that poses no significant increase in the
risk of cancer to people (the “ no significant risk” level). Id. § 500.84(c)(1). Next,
the FDA evaluates the different foods through which a human might consume
some of the additive and estimates the amount of such foods that are consumed
in the human diet. Based on these estimates of food intake, the FDA then des­

  2 The Delaney Clause with the DES proviso states:
     (1) The Secretary shall —
       (A ) by order establish a regulation . . . prescribing, with respect to one or more proposed uses of the
     food additive involved, the conditions un d er which such additive may be safely used. . . .


     (3) No such regulation shall issue if a fair evaluation o f the data before the Secretary —
        (A)    fails to establish that the proposed use o f the food additive, under the conditions o f use to be specified
     in the regulation, will be safe: Provided, That no additive shall be deem ed to be safe if it is found to
     induce cancer when ingested by man o r animal, o r if it is found, after tests which are appropriate for
     the evaluation o f the safety o f food additives, to induce cancer in m an or animal, except that this proviso
     shall not apply with respect to the use o f a substance as an ingredient o f feed for animals which are
     raised for food production, if the Secretary finds (i) that, under the conditions o f use and feeding specified
     in proposed labeling and reasonably certain to be followed in practice, such additive will not adversely
     affect the animals for which such feed is intended, and (ii) that no residue o f the additive will be found
     (by methods o f exam ination prescribed o r approved by the Secretary by regulations, which regulations
     shall not be subject to subsections (f) an d (g) o f this section) in any edible portion o f such animal after
     slaughter o r in any food yielded by or derived from the living a ni mal ; . . . .

21 U.S.C. § 348(c). The Delaney Clause w ith the DES proviso quoted above is similar to the provisions in 21
U.S.C. § 3 6 0 b (d )(l)(I), which governs the approval o f new animal drugs, and 21 U.S.C. § 379e(b)(5)(B), which gov­
erns the approval o f color additives.


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            Term "No Residue” Pursuant to the Federal Food, Drug, and Cosmetic A ct

ignates a level of concentration for each edible tissue in which the additive might
be found such that the “ no significant risk” level for the total diet is not exceeded.
Id. § 500.84(c)(2). So long as concentrations in an edible tissue are below the
maximum level of concentration for that tissue, the FDA considers the edible
tissue to contain “ no residue.” Id . 3
   The FDA requires the sponsor of any additive seeking relief under the DES
proviso to submit a “ regulatory method” of detection that can “ reliably measure
and confirm” the presence of any residue of carcinogenic concern equal to or
above the “ no residue” level for that compound. Id. §§500.86, 500.88. However,
the FDA does not necessarily require a sponsor to employ the most sensitive
detection method available.
   The EPA and the FDA (collectively “ the agencies” ) have posed three separate
questions with respect to the FDA’s current approach to implementing the DES
proviso. The first two raise issues concerning the FDA’s discretion to approve
a method of detection, the results of which will be accepted by the FDA for
purposes of the proviso. The third question concerns the FDA’s discretion to
define “ no residue” as set forth above. Specifically, we address the following
questions: (1) whether the FDA has the discretion to refuse to permit the use
of an additive in animal feed if it finds that there is no method that can “ reliably
measure and confirm” the presence of residues of carcinogenic concern at and
above the “ no residue” level for such residues; (2) whether the FDA must revise
its regulations to adopt more sensitive methods when they become available once
it has approved a method of detection; and (3) whether the FDA has the discretion
to determine that an edible tissue contains “ no residue” when a method of detec­
tion reveals the presence of residues of carcinogenic concern that is below the
“ no significant risk” level. We discuss our answers to each of these questions
below.

              II. The FDA’s Discretion to Approve Methods of Detection

A. Must the FDA Approve a Method of Detection?

  The DES proviso authorizes the use of a cancer-inducing additive in animal
feed if the FDA finds “ that no residue of the additive will be found (by methods
of examination prescribed or approved by the [FDA] by regulations . . .) in any
edible portion of such animal.” 21 U.S.C. §348(c)(3)(A)(ii). The agencies have
  3 As explained by the FDA:
     CTlhe [SOM] procedures provide for a quantitative estimation o f the risk o f cancer presented by the residues
     of a carcinogenic compound proposed for use in food-producing animals. “ No residue" remains in food
     products when conditions o f use, including any required preslaughter withdrawal period or m ilk discard
     time, ensure that the concentration o f the residue o f carcinogenic concern in the total diet o f people will
     not exceed the concentration that has been determined to present an insignificant risk.
52 Fed. Reg. 49.572 (1987). Thus, the SOM regulations base a “ no residue” finding on a determ ination that the
additive creates " n o significant risk.”


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asked whether the FDA may use a method’s inability to detect residues at the
FDA’s “ no significant risk” level (that is, the method’s sensitivity) as a basis
for not approving that method, where the approval of at least one method is nec­
essary in order for an additive itself to be approved. This phrasing of the issue
suggests two questions that can usefully be separated.
   The first is whether the proviso contemplates that at least one method of detec­
tion be approved by the FDA; in other words, whether the FDA lacks the discre­
tion to decide that at present no satisfactory method exists with respect to a spe­
cific additive. If the proviso were read to require the approval of at least one
method, notwithstanding its lack of sufficient sensitivity, this would be equivalent
to reading the proviso as imposing a nondiscretionary duty on the FDA to approve
some method.4 The proviso contains no language explicitly imposing such a duty
on the FDA. Finding one would require inferring it from elsewhere in the statute,
either because of express language found elsewhere or because of the structure
of the statute as a whole. In fact, however, far from undermining the initial view
that the FDA is under no such duty, the rest of the statutory scheme reinforces
this conclusion.
   The Delaney Clause and its DES proviso are subparts of the comprehensive
statutory scheme under which the FDA approves proposed uses of food additives.
See 21 U.S.C. § 348(c)(3). Under this scheme the FDA may not issue a regulation
approving the use of any food additive if “ a fair evaluation of the data before
the [FDA] fails to establish that the proposed use of the food additive . . . will
be safe.” 21 U.S.C. § 348(c)(3). The statute, in other words, requires that safety
is not to be presumed, but rather must rest on an affirmative showing of the predi­
cate facts necessary to support such a conclusion.5
   Before the sponsor of a cancer-inducing additive is even put to the task of
proving safety, however, that additive must satisfy the DES proviso, because if
it does not satisfy the proviso, the Delaney Clause will apply to it, and the Delaney
Clause imposes a required finding of “ not safe” with respect to cancer-inducing
additives. As a necessary condition for satisfying the proviso, the FDA has stated
that a food additive must not be present in an edible tissue in concentrations above
the “ no significant risk” level for that tissue. See 21 C.F.R. §500.84. This means

   4 O n occasion, the FDA will withdraw its marketing approval o f anim al drugs, which are also governed by the
Delaney C lause and the DES proviso, because, among other reasons, there is no approved method o f detection
and, hence, no m eans to demonstrate that the proviso is satisfied. In the sole instance we found o f this position
being raised in litigation, the couit affirmed the FD A ’s action without reaching the propriety o f the FD A ’s basing
its determ ination on the absence of any approved method o f detection. See Rhone-Poulenc, Inc. v. FDA , 636 F.2d
7 5 0 ,7 5 2 n.2 (D.C. Cir. 1980).
   5 That the statute generally requires an affirmative showing o f safety— the absence o f evidence of risk o f harm
is insufficient to satisfy the statute— is reinforced by placing the burden o f proving safety on the sponsor. As one
court sum m arized the m atter “ (I]f the substance is deem ed a food additive, it is presumed to be unsafe . . .
United States v. Two Plastic Drums, More or Less o f an Article o f Food, Labeled in Part: Viponte Ltd. Black
Currant Oil Batch No. BOOSF 039, 984 F.2d 814, 816 (7th Cir. 1993). “ The thmst o f the [Food Additives A mend­
ment A ct o f 1958] was to put upon processors rather than the government the burden of proving that a newly
discovered substance added to food is safe if used within specified quantities.” Id. at 819.


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 The Food and Drug Administration s Discretion to Approve Methods o f Detection and to Define the
           Term "No R esidue" Pursuant to the Federal Food, Drug, and Cosmetic Act

that a finding of “ no significant risk” is also a necessary predicate to FDA’s
potential ultimate conclusion that the additive is “ safe.”
   It would be odd for Congress to have written a statute whose basic requirement
is that the predicate facts for a finding of safety must be affirmatively established
by the sponsor of any additive, and subsequently to have amended that statute
by inserting a new subpart in which the requirement of an affirmative showing
was eliminated, without any indication in the text that such a fundamental change
was intended. Yet, just such an odd outcome would result here if the FDA were
compelled to approve an insufficiently sensitive method. The requirement that
safety be proven, not presumed, was at the very heart of the legislative changes
codified in the Food Additives Amendment Act of 1958, of which § 348(c)(3)
is a key provision. See, e.g.. Two Plastic Drums, More or Less, 984 F.2d at 816-
 19. However, if the FDA were required to apply the proviso based solely on
results from a method inadequate to confirm “ no significant risk,” the FDA would
be in the position of presuming a predicate fact — the absence of significant risk —
 that it considered necessary to its ultimate safety determination. There is
absolutely no evidence in either the statutory text or the legislative history that
such a reversal was intended, and by far the more natural reading of the statute
is that the same requirement of an affirmative showing applies throughout.
   In sum, the DES proviso does not impose an obligation on the FDA to approve
at least one method. To the contrary, the FDA has discretion to refuse to permit
the use of unsatisfactory detection methods.
   The analysis to this point has assumed that it is within the FDA’s discretion
to use levels of risk as one determinant in implementing the method selection
portion of the DES proviso. This issue presents the second question we must
explicitly examine: acknowledging that the FDA has discretion to reject a detec­
tion method for some reason, is the method’s inability to detect no significant
risk levels one of the permissible reasons for the exercise of that discretion? This
question arises because an agency’s exercise of discretion will not be sustained
if the agency considers factors that are either impermissible or irrelevant under
the statute under which the agency is acting. Motor Vehicle Mfrs. A ss’n v. State
Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983) (“ Normally, an agency rule
would be arbitrary and capricious if the agency has relied on factors which Con­
gress has not intended it to consider . . . .” ); Citizens to Preserve Overton Park,
Inc. v. Volpe, 401 U.S. 402, 416 (1971) (The question is “ whether the decision
was based on a consideration of the relevant factors.” ).
   As an initial matter, a method’s ability to detect the “ no significant risk” level
seems to be a permissible reason for exercising discretion under a statute that
requires an affirmative showing of safety, because a finding that an additive does
not pose a significant risk is directly relevant to a determination of safety. See,
e.g.. Industrial Union Dep’t v. American Petroleum Inst., 448 U.S. 607, 642
(1980) (“ ‘[S]afe’ is not the equivalent of ‘risk free.’. . . [A] workplace can

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hardly be considered ‘unsafe’ unless it threatens the workers with a significant
risk of harm.” ). As plausible as this conclusion appears, two court of appeals
decisions interpreting the Delaney Clause may cast doubt on it and cause us to
consider a possible counter argument. See Les v. Reilly, 968 F.2d 985 (9th Cir.
 1992), cert, denied, 507 U.S. 950 (1993); Public Citizen v. Young, 831 F.2d 1108
(D.C. Cir. 1987), cert, denied, 485 U.S. 1006 (1988). Both Public Citizen and
Les hold that the fact that an additive produces extremely low levels of risk (de
minimis levels) does not provide the FDA or the EPA with a basis for refusing
to ban a cancer-inducing additive under the Delaney Clause. The courts reach
this result by concluding that Congress precluded taking risk levels into account
in reaching that decision under the Delaney Clause. Les, 968 F.2d at 989 (“ Thus,
the legislative history supports the conclusion that Congress intended to ban all
carcinogenic food additives, regardless of amount or significance of risk, as the
only safe alternative.” ); accord Public Citizen, 831 F.2d at 1122.
   In Public Citizen, the court did not conclude that the FDA completely lacked
discretion in implementing the Delaney Clause. Specifically, it confirmed that the
FDA did indeed have discretion to determine whether a color additive was cancer-
inducing in the first place. 831 F.2d at 1112. The government sought to use the
existence of this discretion to support its argument that the FDA had discretion
to approve carcinogens that posed merely a de minimis risk by claiming that the
FDA’s decision could be justified as an exercise of the FDA’s admitted discretion
to make that prior determination. The court rejected that argument, concluding
that there was nothing in the record that could support the exercise of such discre­
tion in this instance, where studies done under accepted agency protocols had
produced results that the agency had routinely found supported a finding of
carcinogenicity. Id. at 1122. In particular, the court held that the FDA could not
use the fact that risk was de minimis as the basis for a finding that the substance
does not induce cancer.

       Congress did not intend the FDA to be able to take a finding that
       a substance causes only trivial risk in humans and work back from
       that to a finding that the substance does not “ induce cancer in . . .
       animals.” This is simply the basic question— is the operation of
       the clause automatic once the FDA makes a finding of carcino­
       genicity in animals?— in a new guise.

Id. at 1121 (alteration in original).
  A broad reading of Public Citizen might suggest that levels of risk associated
with a substance may not inform any discretionary judgments made under the
Delaney Clause, because Congress did not intend the FDA to be able to take
a finding about the relative risk of a substance and “ work back” from that to
answer any question under the Clause where it could admittedly exercise discre­

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            Term ' 'No Residue" Pursuant to the Federal Food, Drug, and Cosmetic Act

tion. We believe this reasoning is unsound as applied to the FDA’s using risk
as a factor in selecting detection methods under the DES proviso, on two grounds.
   First, both Public Citizen and Les were concerned with situations in which the
agencies sought to approve the use of substances by escaping from the categorical
ban on the Delaney Clause, even though the necessary conditions for triggering
the Clause had been found to be present. Once those conditions have been found,
both courts held, the operation of the Clause is automatic. Using a “ no significant
risk” benchmark as a basis for rejecting detection methods does not present such
a situation, because the absence of a detection method does not provide an escape
hatch to the Clause. Rather, it presents the opposite situation: if the DES proviso
does not apply, then the Delaney Clause will. Thus, the FDA is not “ working
back” from a finding of “ no significant risk” to a discretionary judgment that
stops the automatic bar of the Delaney Clause from taking effect. Instead, accept
the results of a detection method means that the automatic ban of the Delaney
Clause will apply. As a consequence, the logic of Public Citizen’s limitation on
the use of risk as a factor upon which to base a discretionary judgment does
not apply to this particular situation.
   The second reason we believe the no-discretion argument based on Public Cit­
izen and Les is unsound is more fundamental. The DES proviso and the Delaney
Clause are separate provisions, and there is no a priori reason to believe that
the limitations on factors permitted to influence the exercise of specific discre­
tionary authority under the Clause should also govern the exercise of discretion
under the proviso. In fact, the respective legislative histories of the two provisions
exhibit significant differences that tend to reinforce the conclusion that the FDA
can take the sensitivity of a method into account in deciding whether to approve
that method.6
   The text of the DES proviso and the structure of the statute support the conclu­
sion that the FDA has discretion to employ a method’s sensitivity as a criterion
in method selection. The statute supports that view by granting the FDA the
discretion to prescribe and approve methods of detection. 21 U.S.C.
§ 348(c)(3)(A). However, it is completely silent on explicit criteria the FDA may
employ in the exercise of this discretion. When Congress has failed to speak
directly to the precise question at issue, the implementing agency’s interpretation
  6   Before highlighting those differences, we note that our methodology is the same as that used by the court in
Public Citizen. Like that court, we begin with the statutory text and structure, and then look to the legislative history
to see whether it supports or undermines our preliminary conclusion. In Public Citizen's case, the court first concluded
(hat the best reading o f the Delaney Clause was that the Clause did not permit a de minimis exception to its otherwise
categorical, or automatic, ban on cancer-inducing additives. Public Citizen, 831 F.2d at 1113. This result, seemingly
so contrary to common sense in the case o f trivial risks, might have been resisted by the court were it not for
the very strong and consistent legislative history o f the Delaney Clause, which supported the view that Congress
indeed intended the “ zero tolerance" result for carcinogenic compounds that the Clause announces on its face.
In discussing the color additives version o f the Delaney Clause, Judge W illiams concluded that “ (t]he House com ­
mittee gave considerable attention to the degree o f discretion permitted under the provision. The discussion points
powerfully against any de minimis exception, and is not contradicted either by consideration on the House floor
or by a post-enactment colloquy in the S enate." Id.; accord Les, 968 F.2d at 989. “ [T)his is perhaps as strong
as [legislative history] is likely to g et.” Public Citizen, 831 F.2d at 1117.


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will be sustained as long as it is reasonable. See Chevron, U.S.A., Inc. v. Natural
Resources Defense Council, 467 U.S. 837, 842-44 (1984). We believe that the
use of significant risk levels as a criterion for exercising that discretion is reason­
able in light of the statute’s basic requirement of an affirmative showing of
“ safety.” See discussion supra pp. 250-51. Accordingly, the FDA’s use of levels
of risk as a screening criteria for method approval should be sustained as a
“ reasonable interpretation” o f the statute.
   The statute's silence on this issue means that the Congress has not spoken in
statutory language to this question. That Congress intended to leave this issue
to the discretion of the FDA is reinforced by an examination of the pertinent
legislative history. The history of the DES proviso displays considerable equivo­
cation on the criteria the FDA should employ in implementing the discretionary
portions of the statute. On the one hand, some of the legislative history asserts
that the “ basic principle” of the Delaney Clause itself— its zero tolerance posi­
tion with respect to carcinogens— would be unaffected by the passage of the pro­
viso. A principal piece of evidence of this view is a letter from Secretary Ribicoff
to the chairman of the House Committee on Interstate and Foreign Commerce
in 1962, the year the food additives version of the proviso was enacted.7 The
Secretary’s section-by-section analysis of the proviso stated:

          Section 302(a) would correct a needless and unintentional inequity
          in the application of the food-additive anticancer proviso[8] (sec.
          409(c)(3) of the basic act) to additives for animal feed, while pre­
          serving in its full vigor the consumer protection now afforded by
          that provision. The basic principle of the anticancer provision,
          which would remain unimpaired, is that no tolerance for the addi­
          tion of carcinogenic chemicals to food shall be granted in any
          amount . . . .

Letter for Hon. Oren Harris, Chairman, Committee on Interstate and Foreign Com­
merce, from Abe Ribicoff, Secretary, Department of Health, Education, and Wel­
fare (July 21, 1962), reprinted in Drug Industry A ct o f 1962: Hearings on H.R.
11581 Before the House Committee on Interstate and Foreign Commerce, 87th
Cong. 49 (1962), reprinted in 21 Leg. Hist, at 227.
   7 The DES proviso was first suggested by the Department o f Health, Education and W elfare ( “ HEW ” ) in 1960.
H EW drafted the pertinent provisions o f th e language that were eventually enacted in 1962, and transmitted its
proposal to this same House Committee via another letter from then Secretary Flemming to the chairman, expressing
H E W ’s views on how the proviso would operate. Letter for Hon. Oren Harris, Chairman, Committee on Interstate
and Foreign Com m erce, from Arthur S. Flem m ing, Secretary, Department o f Health, Education, and Welfare (May
 13, I960) ( “ Flemming L etter” ), reprinted in H.R. Rep. No. 86-1761, at 88-89 (I960), reprinted in 16 Legislative
H istory o f the Federal Food, Drug, and C osm etic Act and Its Amendments at 757-58 (1979) ( “ Leg. Hist.” ). Under
these circumstances, the views o f the executive branch with respect to language it requested and initially drafted
are significant sources o f statutory meaning.
   8 Secretary R ibicoff refers to the ‘‘Delaney proviso” or the “ anticancer proviso” where subsequent usage refers
to the “ Delaney C lause.” Secretary Flemming, R ib ico ff s predecessor, employs the same terminology.


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  On the other hand, the proviso has an operational structure that is undeniably
different from that of the Clause, such that it would be impossible for the zero
tolerance principle of the Clause to be completely unaffected, and some elements
of the legislative history reflect an awareness of that fact. A long-time student
and expert on the Act and the Delaney Clause, Professor Richard Merrill, has
succinctly stated the difference: “ By contrast with the Delaney Clause itself, the
DES proviso makes the detection of residues in edible animal tissues, rather than
the addition of the compound to animals or their feed, the critical inquiry.”
Richard A. Merrill, Regulating Carcinogens in Food: A Legislator’s Guide to the
Food Safety Provisions o f the Federal Food, Drug, and Cosmetic Act, 77 Mich.
L. Rev. 171, 233 (1978). In other words, the proviso contemplates that a com­
pound will be approved as long as an approved method detects no residue, even
though this does not affirmatively mean that no residue was present at all. In
fact, there might be a residue remaining, one at a level of concentration below
the sensitivity of the approved method. Consequently, because the operation of
the proviso is linked to detection, and because methods of detection are limited
in their sensitivity, the inclusion of the proviso could not literally leave the “ basic
principle” of the Clause unimpaired.
   Elements of the legislative history demonstrate an awareness that the operation
of the proviso would not guarantee that a zero tolerance policy would be carried
out with full vigor. A principal piece of evidence plainly pointing out the
inconsistency between the proviso and the Delaney Clause is Representative
Leonor Sullivan’s floor statement when the proviso was being considered in 1962,
shortly before actual passage. Representative Sullivan, who introduced another bill
on food and drug safety, H.R. 1235, conveyed her doubts about any weakening
of the Delaney Clause whatsoever based on her belief that new testing methods
would disclose residues that could not be detected in 1962:

        However, I have strong doubts, I must admit, over the retreat on
        the Delaney anticancer clause on feed additives, as contained in
        H.R. 11582, particularly in view of the Government’s experience
        several years ago with hormone-treated chickens. It cost us $10 mil­
        lion to remove from the market the fowl treated with a drug consid­
        ered safe for the purpose — after it was learned that there were resi­
        dues of the cancer-inducing substance in the skin of the chickens.
        Too often for complacency, new testing methods disclose the exist­
        ence of harmful residues which had not shown up in earlier tests,
        but by then the damage is done.

Drug Industry Act o f 1962: Hearings on H.R. 11581 Before the House Committee
on Interstate and Foreign Commerce, 87th Cong. 98 (1962) (Statement of Rep.
Sullivan), reprinted in 21 Leg. Hist, at 276. In order to forestall such weakening,

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Representative Sullivan introduced an amendment to eliminate the DES proviso,
so as to protect consumers from undetectable levels of carcinogenic residues. 108
Cong. Rec. 21,077 (1962) (Statement of Rep. Sullivan), reprinted in 23 Leg. Hist,
at 29. Her amendment was defeated.9
   Representative Sullivan’s statement recounts an actual historical example of sub­
sequent improvements in testing sensitivity that revealed a residue where none
had been detected earlier. No member of Congress disputed the factual accuracy
of her description of the proviso’s operation, although several rose to comment
on her statement. See 108 Cong. Rec. at 21,079-83, reprinted in 23 Leg. Hist,
at 31-35. This sequence reveals very clearly the tension between the proviso and
the original Delaney Clause: in all likelihood the proviso would permit the pres­
ence of physical residues of carcinogenic compounds, because testing methods
would not be sensitive enough to detect them, while the Clause advocates a zero
tolerance approach to the presence of any residue.
   Finally, the tension between the idea that the proviso would preserve the ‘‘basic
principle” of the Clause and the idea that detection methods would most likely
become more sensitive over time, so that a failure to detect residue with any
given method could not be taken to show the complete absence of the compound,
is evident in the major statement of the administration’s understanding of the pro­
viso, Secretary Flemming’s letter of May 13, 1960, which transmitted the language
of the proviso to the House committee considering the Color Additives Amend­
ments.

             There is, however, one respect in which the anticancer proviso
          has proved to be needlessly stringent as applied to the use of addi­
          tives in animal feed. For example, in the case of various animals
          raised for food production, certain drugs are used in animal feed
          which will leave no residue in the animal after slaughter or in any
          food product (such as milk or eggs) obtained from the living
          animal, and which are therefore perfectly safe for man. If this is
          demonstrated with respect to any particular additive intended for
          animal feed, and the additive will not adversely affect the animal
          itself during its expected or intended life cycle, we can see no rea­
          son for not permitting such a use of an additive which could be
          highly useful and beneficial in the raising of animals for food. . . .
             We therefore have included in the enclosed draft bill an amend­
          ment to permit use of an additive animal feed under the above-
          mentioned conditions.
             It may aid public understanding of the Delaney proviso and allay
          unnecessary apprehension regarding it, to touch here on the pro-
   9 The am endm ent failed by voice vote. 108 Cong. Rec. at 21,081, reprinted in 23 Leg. Hist, at 33. Her amendment
to elim inate the DES proviso permitting carcinogenic color additives in animal feed was also rejected. Id. at 21,083,
reprinted in 23 Leg. Hist, at 35.

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          Term "N o R esidue" Pursuant to the Federal Food, Drug, and Cosmetic A ct

      viso’s operation where its application, under present law and the
      proposed modification, depends on whether a residue of the chem­
      ical additive involved is left in the edible tissue or other food prod­
      ucts of an animal. This question may arise in two types of case.
      In the first, a veterinary drug is directly administered — by injec­
      tion, implantation, or otherwise — to the animal, instead of being
      mixed with its feed. In that event, the Delaney proviso can have
      application only if a residue of the added drug occurs in food prod­
      ucts (such as milk or eggs) of the living animal or in some edible
      portion or product of the animal after slaughter. In the second type
      of case, the drug is mixed with feed consumed by the animal. In
      that event, it is necessarily a food additive (since animal feed is
      food within the meaning of the act), but it will nevertheless be taken
      out of the Delaney proviso’s application by the above-proposed
      amendment even if it is cancer inciting (at particular feeding levels)
      in test animals, provided that it satisfies the above-mentioned
      requirements as to the absence of adverse effect on the animals
      for which the feed is intended and as to the absence of any residue
      in the food products or edible portions of the animal.
         In both these instances, where the question of the possibility of
      a residue is crucial, it is desirable that industry laboratory techni­
      cians, and enforcement officers have a common understanding with
      the Food and Drug Administration as to the methods of assay that
      will be recognized by us, and on which we want to rely, in
      resolving the question of residue. We have, therefore, in the pro­
      posed amendment to the Delaney proviso (and likewise in the pro­
      posed modification of the anticancer clause of H.R. 7624) provided
      that, under the amendment, the assay methods applicable in deter­
      mining whether there will be a residue shall be those prescribed
      or approved by us by regulations. This will give reasonable cer­
      tainty in that regard, although, of course, such regulations may from
      time to time be changed as new scientific developments dem­
      onstrate a need for change. It should be clearly understood that the
      industry still would have the responsibility of developing adequate
      analytical methods for detecting residues and furnishing them to
      the Government with a petition for approval of an additive.
        During the hearings on color additives legislation, some wit­
      nesses expressed a concern because of their fear that the Depart­
      ment intends to press a never-ending search for more and more
      delicate methods of analysis, so that it may, without regard to sci­
      entific reason, rescind permissions granted earlier for use of various

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        additives judged to leave no residues in food. This fear is not justi­
        fied.
          The Department applies sound scientific judgment and the rule
       of reason in determining the sensitivity and precision required in
       an analytical procedure used to detect residues of added chemi­
       cals— even before an additive is approved. And when it has been
       determined that a given degree of sensitivity and precision is appro­
       priate, based upon sound scientific facts, it has no intention of
       requiring change in the analytical procedure until new scientific
       developments clearly demonstrate the need.

Flemming Letter, reprinted in H.R. Rep. No. 86-1761, at 88-89, reprinted in
16 Leg. Hist, at 757-58.
   Secretary Flemming’s letter contains some passages that point in the same direc­
tion as the section-by-section analysis of Secretary Ribicoff quoted above, namely
toward the idea that the proviso is entirely consistent with the Clause. Its claim,
for instance, that the proviso would apply to chemicals that leave “ no residue”
in edible tissue, might be read to adopt the zero tolerance position of the Clause,
as might the claim that the Clause is “ needlessly” stringent in case to which
the proviso would apply. However, in the last three paragraphs quoted above,
the Secretary also acknowledges that the application of the proviso would depend
upon sensitivity of the method. The portions responding to concerns expressed
in the hearing make this point clear.
   The sole basis upon which “ a never-ending search for more and more delicate
methods of analysis, so that [the FDA] may, without regard to scientific reason,
rescind permissions granted earlier for use of various additives judged to leave
no residues in food,” Flemming Letter, reprinted in H.R. Rep. No. 86-1761, at
89, reprinted in 16 Leg. Hist, at 758, could be a concern to the industry is if
it were possible to grant permissions on the basis of methods not sensitive enough
to guarantee literally no residue, such that it was then conceivable that more sen­
sitive methods might later be developed that could detect a residue. That is pre­
cisely the scenario painted later on the House floor by Representative Sullivan,
in the passage quoted earlier. See supra p. 255. As was also the case with respect
to Representative Sullivan’s concerns, the Secretary’s response is not that this
scenario is strictly impossible — which it would be if the proviso only operated
in situations where literally no residue remained. Instead, he assures the Com­
mittee that the FDA will exercise “ sound scientific judgment and the rule of rea­
son in determining the sensitivity and precision required in an analytical procedure
used to detect residues of added chemicals — even before an additive is approved.
And when it has been determined that a given degree of sensitivity and precision
is appropriate, based upon sound scientific facts, [the FDA] has no intention of

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            Term “No Residue" Pursuant to the Federal Food, Drug, and Cosmetic Act

requiring change in the analytical procedure until new scientific developments
clearly demonstrate the need.” Id.
   In sum, by permitting approvals to be based on detection methods that cannot
confirm that no additions of the compound to edible tissue will occur, the proviso
articulates a different principle from the one animating the Delaney Clause.
Significant pieces of legislative history confirm an awareness by Congress that
the proviso would operate in a manner significantly different from the Clause,
although other pieces of that history suggest the opposite. The amendments offered
by Representative Sullivan to prevent the weakening of the Clause seem to have
put the choice of continuing a strict zero tolerance approach or not squarely to
the Congress, and Congress voted to adopt the proviso in the form proposed by
the administration.10
   The court in Public Citizen based its conclusion that risk could not enter into
the FDA’s determination of whether a compound “ induces cancer” on its concern
that to do so would permit the consideration of a factor that the Delaney Clause
prohibits the FDA from taking into account in the ultimate decision whether to
ban the substance. For the most part, it based its conclusion that risk could not
be taken into account in that ultimate decision on a consistent and strong legisla­
tive history rejecting the use of risk as a factor. The court’s concern that risk
might work its way back into the agency’s judgment so as to undermine
Congress’s prohibition does not apply here, because rejecting methods on the basis
of risk does not have that effect. See discussion supra p. 253. Even if this decision
did have that effect, the legislative history of the proviso fails to support the
conclusion that Congress meant the same zero tolerance policy of the Clause to
be fully applicable in implementing the proviso. As a whole, the legislative history
amply confirms what the statute suggests on its face: Congress has not clearly
spoken to the question whether the FDA could take risk into account in selecting
methods of detection, thus permitting the FDA to adopt a reasonable interpretation
of the relevant criteria.11
   In retrospect, it is not possible to conclude with confidence why Congress failed
to specify the precise criteria that the FDA ought to employ in selecting detection
methods. Chevron identifies a number of possible reasons that an agency may
be given discretion to interpret a statute:

   10 See supra note 9.
   11 To the extent the legislative history speaks at all to what might cabin the exercise o f discretion in selecting
methods of testing, it is only suggestive. Secretary Flem m ing's letter speaks o f using “ sound scientific judgment
and the rule of reason in determining the sensitivity and precision required.” H.R. Rep. No. 86-1761, at 89, reprinted
in 16 Leg. Hist, at 758. These concepts are nowhere further defined in the subsequent discussions o f the proviso,
which are not numerous in a legislative history dominated by more contentious issues. If anything, they suggest
that levels o f risk might well be a consideration in the decision to require more sensitive methods, because the
need for greater sensitivity, which might be indicated by the significance o f the risks involved, would seem to
be one o f the most obvious factors triggering a “ rule o f reason” decision to seek more sensitive methods, if not
the most obvious factor.


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          Congress [may have] intended to accommodate [competing]
          interests, but did not do so itself on the level of specificity [nec­
          essary to resolve the precise question being litigated]. Perhaps that
          body consciously desired the Administrator to strike the balance
          at this level, thinking that those with great expertise and charged
          with responsibility for administering the provision would be in a
          better position to do so; perhaps it simply did not consider the ques­
          tion at this level; and perhaps Congress was unable to forge a coali­
          tion on either side of the question, and those on each side decided
          to take their chances with the scheme devised by the agency.

Chevron, 467 U.S. at 865. In light of the language of the statute, the structure
of the statute, and the legislative history of the proviso, we conclude that one
of these three conditions obtained here— probably the first or the second, although
“ for judicial purposes, it matters not which of these occurred.” Id. Whatever the
reason may have been, the result is that the FDA’s “ reasonable interpretation”
of its authority — that method sensitivity down to the level of significant risk can
be used as a criterion in method selection — is within its discretion to adopt.

B. M ust the FDA Adopt the M ost Sensitive M ethod of Detection?

   The agencies’ second question is whether the FDA must revise its regulations
to adopt more sensitive methods when they become available once it has adopted
a method that detects the residue. Essentially, this question asks whether the pro­
viso requires the FDA to revise its regulations to adopt the “ best available” detec­
tion methods for a compound, or whether it has discretion to continue to accept
results from less sensitive methods. At one time in the FDA’s implementation
of the proviso, the agency did take the position that it generally should adopt
the best available detection m ethods.12 While that interpretation may be one
permissible interpretation of the proviso, the narrow question we must resolve
is whether the statute compels that course of action. We conclude the answer
to this question is also no.
   The proviso itself is completely silent with respect to what criteria the FDA
must employ in deciding whether to approve a method of detection. It is also
completely silent as to any affirmative obligation on the FDA to revisit or revise
approved methods. Any case in favor of a “ best available” obligation, therefore,
must rely heavily on the zero tolerance principle for carcinogens under the
Delaney Clause itself, coupled with those portions of the legislative history of
the proviso that assert that the proviso maintains this “ basic principle” of the

   12For a history o f the FD A ’s approach to implementing the proviso up to that time, see Chemical Compounds
in Food-Producing Animals, Criteria and Procedures for Evaluating Assays for Carcinogenic Residues in Edible
Products o f A nimals, 42 Fed. Reg. 10,412 (1977).


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Clause. Under this theory, if the method of detection approved by the FDA could
not detect residues at levels achievable by the best available methods, and such
levels were in fact detected by a more sensitive method, then failing to adopt
the best available method as the required method under the proviso seems tanta­
mount to approving a tolerance for the compound.13 Flemming Letter, reprinted
in H.R. Rep. No. 86-1761, at 89, reprinted in 16 Leg. Hist, at 758.
   As we have already discussed, however, the proviso itself does not contain any
language from which an affirmative obligation to use best available methods could
be derived. The plain language of the proviso stands in tension with the basic
principle of the Clause, and the legislative history of the proviso in several places
reflects an awareness that the proviso depends upon detection in its operation.
In fact, some of the legislative history suggests the FDA intended from the begin­
ning not to adopt best available methods, at least under some circumstances, and
that Congress acquiesced in that understanding. First, the history acknowledges
that an approach depending on detection will most likely result in approved uses
of compounds where in fact residues are present in food. See, e.g.. Representative
Sullivan’s statement, supra p. 255. Second, Secretary Flemming’s influential May
13, 1960 letter seeks explicitly to quell industry concerns that the FDA will engage
in a “ never-ending search” for more sensitive methods, without regard to sci­
entific reason. The Secretary’s rejoinder that HEW will not engage in such a
search plainly argues against a requirement to always adopt best available detec­
tion methods. To repeat, Secretary Hemming wrote:

          The Department applies sound scientific judgment and the rule of
          reason in determining the sensitivity and precision required in an
          analytical procedure used to detect residues of added chemicals —
          even before an additive is approved. And when it has been deter­
          mined that a given degree of sensitivity and precision is appropriate,
          based upon sound scientific facts, it has no intention of requiring

   13 The House Committee that first received Secretary Flemming’s request for enacting the DES proviso reported
the Secretary’s views on whether the Delaney Clause itself permitted the FDA to establish tolerances for carcinogens.
The committee report quotes him as stating:
         W henever a sound scientific basis is developed for the establishment o f tolerances for carcinogens, we
      will request the Congress to give us that authority. We believe, however, that the issue is so important
      that the elected representatives o f the people should have the opportunity o f examining the evidence and
      determining whether o r not the authority should be granted.


        This, I believe, is as far as our discretion should go in the light o f present scientific knowledge. W e
     have no basis for asking Congress to give us discretion to establish a safe tolerance for a substance which
    definitely has been shown to produce cancer when added to the diet o f test animals. W e simply have
    no basis on which such discretion could be exercised because no one can tell us with any assurance at
     all how to establish a safe dose o f any cancer-producing substance.
H.R. Rep. No. 86-1761, at 12-13, (quoting Statement by Hon. Arthur S. Flemming, Secretary of HEW , before
the House Committee on Interstate and Foreign Commerce, January 26, 1960), reprinted in 16 Leg. Hist, at 68 1 -
82.


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                     Opinions o f the Office o f Legal Counsel in Volume 19


        change in the analytical procedure until new scientific develop­
        ments clearly demonstrate the need.

Flemming Letter, reprinted in H.R. Rep. No. 86-1761, at 89, reprinted in 16
Leg. Hist, at 758. In the last sentence of this quotation, the Secretary contemplates
a situation in which a more sensitive method is available, but not needed, by
acknowledging as possible a situation in which the agency could change to more
sensitive methods and yet refrains from doing so. Such a situation is possible
only if a superior method were available. This passage, in short, suggests that
the FDA must have some discretion to decline to adopt the best available method.
   Once again, however, the statute itself provides no guidance at all on what fac­
tors the FDA may consider in exercising such discretion, and the legislative history
provides only suggestive guidance. While “ sound scientific judgment and the rule
of reason” is not further defined, the level of risk already capable of being
detected is certainly one plausible factor that might bear on the FDA’s assessment
of whether “ new scientific developments clearly demonstrate the need.” This is
because, as just discussed, the Secretary’s letter contemplates the case in which
a more sensitive method is available, yet determined by the agency not to be
needed. Of all the considerations that might support a conclusion that a better
test is not “ needed,” as opposed, say, to being too expensive, or too time-con-
suming, the consideration that current tests are adequate to detect significant risk
is perhaps the most straightforward and appropriate. This interpretation, thus, ties
the FDA’s discretion in method selection directly to some appraisal of the need
to detect low levels of risk, and the significant risk level is certainly a reasonable
benchmark for assessing adequacy.
   Thus, the Secretary’s letter defines two points that are important for our pur­
poses. As the FDA contemplated the operation of the proviso, it would (1) some­
times refrain from requiring the best available detection method; and (2) base
its decision on method approval on undefined “ sound scientific judgment and
the rule of reason,” which might well incorporate considerations of the risks asso­
ciated with the compound. While turning these points into statutory commands
probably makes too much of Secretary Flemming’s letter, it and the other pieces
of legislative history acknowledging that the proviso’s operation is linked to detec­
tion do refute arguments that such a reading is precluded by the statute. The his­
tory is simply too contradictory to support that result.
   In this section of our opinion, however, the narrow question under review is
whether the statute compels the FDA to push beyond currently approved methods
to require more sensitive methods when they become available. As to this ques­
tion, we are confident the answer is no.


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           Term "N o Residue" Pursuant to the Federal Food, Drug, and Cosmetic A ct

                            III. Definition of “ No Residue”

   Under the SOM regulations, the FDA accepts a finding of some residue as satis­
fying the statutory requirement of “ no residue,” if the level of residue detected
poses no significant risk of increased cancer to people. In other words, it considers
the detected presence of small amounts of residue as satisfying the statutory
requirement of no residue. The final question the agencies have presented is
whether this construction is permissible under the statute. While the first two ques­
tions dealt with the FDA’s discretion to approve methods of detection, this one
deals with the FDA’s possible discretion in interpreting the statutory requirement
that the FDA find “ no residue” by means of whatever methods of detection the
FDA has chosen. The question of what action may be taken when the method
prescribed or approved by the Secretary by regulations detects a residue demands
a different answer.
   Once again, we start with the statute. If Congress has “ directly spoken to the
precise question at issue” in the statute, that instruction must be followed.
Chevron, 461 U.S. at 842-44; see also Connecticut Nat’l Bank v. Germain, 503
U.S. 249, 254 (1992) (“ When the words of a statute are unambiguous, then, the
first canon of construction is also' the last: ‘judicial inquiry is complete.’ ” )
(quoting Rubin v. United States, 449 U.S. 424, 430 (1981)). In this instance, Con­
gress has clearly spoken. The DES proviso states that the Delaney Clause will
not apply “ if the Secretary finds . . . that no residue of the additive will be
found (under methods of examination prescribed or approved by the Secretary
by regulations).” 21 U.S.C. § 348(c)(3)(A). The interpretation of this language
seems straightforward and unambiguous. Giving “ no residue” its ordinary
meaning, the detected presence of any residue by an approved method would be
incompatible with a finding of “ no residue,” and thus would preclude a finding
that the proviso applies.
   Investigation of the legislative history substantiates this reading of the statute.
Previous inquiries into the legislative history of the proviso supported the conclu­
sion that the FDA enjoys considerable discretion to select methods of detection.
That conclusion was initially based on a reading of the statute itself, and subse­
quently reinforced by the findings that Congress’s deliberations reflected no single
clear view either on precisely how the proviso was consistent with the zero toler­
ance principle of the Delaney Clause or on the criteria the FDA should use in
selecting such methods of detection. As to the question at issue here, the legisla­
tive history also reinforces the initial reading of the statute, but this time by
revealing a consistent record. There is nothing in that record to suggest that a
finding of “ no residue” could be based upon the detected presence of residue,
however insignificant, and the most pertinent items in the record on this issue
in fact support the plain reading of the statute.
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  Consider first Secretary Flemming’s May 13, 1960 letter initially proposing the
proviso’s language, which states in part:

           There is, however, one respect in which the anticancer proviso has
           proved to be needlessly stringent as applied to the use of additives
           in animal feed. For example, in the case of various animals raised
           for food production, certain drugs are used in animal feed which
           will leave no residue in the animal after slaughter or in any food
           product (such as milk or eggs) obtained from the living animal,
           and which are therefore perfectly safe for man.

Flemming Letter, reprinted in H.R. Rep. No. 86-1761, at 88, reprinted in 16
Leg. Hist, at 757. It is impossible to read the Secretary’s reference to “ no residue”
as implying that the administration was proposing a statutory revision that would
knowingly permit some residue to remain in food products. This is the same letter,
after all, that endorses the Delaney Clause’s standard of zero tolerance as the
only acceptable public health policy with respect to carcinogens.14 The letter only
proposes a proviso that would operate when the Clause was “ needlessly strin­
gent” ; that is, the proviso will apply in situations where a compound had been
added to animal feed— and came within the scope of the food additive statute’s
Delaney Clause for that reason— but left “ no residue” in food to be composed
by humans. The operating supposition of the Delaney Clause, endorsed by Sec­
retary Flemming, is that no exposure, no matter how small, to a known carcinogen
was then considered “ safe.” On that supposition, the only residue that could be
considered “ perfectly safe” for humans, where the Clause’s application would
be “ needlessly stringent,” would be zero residue.
   That this was Secretary’s Flemming’s view, and Congress’s understanding of
it, is reinforced by the Secretary’s earlier statement:

           We have no basis for asking Congress to give us discretion to estab­
           lish a safe tolerance for a substance which definitely has been
           shown to produce cancer when added to the diet of test animals.
           We simply have no basis on which such discretion could be exer­
           cised because no one can tell us with any assurance at all how
           to establish a safe dose o f any cancer-producing substance.

H.R. Rep. No. 86-1761, at 13 (quoting Statement by Hon. Arthur S. Flemming,
Secretary of HEW, before the Committee on Interstate and Foreign Commerce,
Jan. 26, 1960), reprinted in 16 Leg. Hist, at 682. Having proof of the presence
of a residue but nonetheless exempting a compound from the Delaney Clause’s
   14Id. ( “ [T]he principle o f the [Delaney C lause] reflects, basically, the current state o f scientific knowledge, and
w e w ould therefore, except [as applied to situations governed by the proposed DES proviso] feel constrained to
apply the same principle even in the absence o f [the Delaney C lause].’’).


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prohibition, as the SOM’s construction of “ no residue” does, seems indistinguish­
able from treating that level of residue as a safe tolerance — precisely the result
that Secretary Flemming denies in his statement to the Committee. Likewise, Sec­
retary Ribicoff’s assertion that “ no tolerance for the addition of carcinogenic
chemicals to food shall be granted in any amount,” seems to require the conclu­
sion that permitting a detected residue of a carcinogenic chemical to be present
in food to be consumed by humans would not be permitted. Letter for Hon. Oren
Harris, Chairman, Committee on Interstate and Foreign Commerce, from Abe
Ribicoff, Secretary, Department of Health, Education, and Welfare (July 21,
1962), reprinted in Drug Industry Act of 1962: Hearings on H.R. 11581 Before
the House Committee on Interstate and Foreign Commerce, 87th Cong. 49 (1962),
reprinted in 21 Leg. Hist, at 227.
   There is nothing in the legislative history to suggest that Congress meant to
authorize carcinogenic residue to be detected by the FDA and yet to have the
proviso operate to exempt that compound from the Delaney Clause’s prohibition.
We believe that the statutory language of “ no residue . . . will be found (under
methods of examination prescribed or approved by the Secretary by regulations),”
21 U.S.C. § 348(c)(3)(A), means that whatever approved method of detection is
used must return a negative finding in order for the proviso to operate. Congress
may not have been of one mind in realizing that reliance on detection could well
result in actual, but undetected, residues in cancer-inducing additives being
approved, but the case of actual, undetected, residues is quite distinguishable from
the case of actual, detected ones. The legislative history consistently supports the
conclusion that Congress did not intend for any additive for which a residue was
actually detected to have the benefit of the DES proviso. The statute being clear,
the FDA has no discretion to deviate from it.
   It may be argued that the meaning of “ no residue” is not clear, because the
clearest literal meaning of “ no residue” would preclude the FDA from ever
employing the proviso once one acknowledges the considered scientific view that
one can never be sure that not even a single molecule of a compound remains
in edible tissue. Because it is doubtful that Congress meant “ no residue” to be
given a meaning that would render the proviso nugatory, the argument would
run, what Congress meant by the term is ambiguous, and hence the door is open
for the FDA to exercise a reasonable discretion in interpreting it.
   As already discussed, we agree that the legislative history displays equivocation
on how the proviso was meant to operate, that there are inconsistences in state­
ments concerning its ultimate effect, and that the FDA enjoys some interpretive
discretion as a result. In determining the scope of that discretion, however, one
must keep in mind the particular discretionary judgment at issue. Here the “ pre­
cise question at issue” is whether the FDA may treat a detected presence of res­
idue as “ no residue” within the meaning of the proviso. As to that precise ques­
tion, the foregoing argument does not change the analysis. Had Congress insisted

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upon an affirmative showing of “ no residue,” the current scientific understanding
would indeed render the proviso a dead letter. That, however, is not the proviso
Congress drafted. Instead, the proviso relies upon an affirmative showing that an
approved method o f detection finds “ no residue,” and that finding can still be
made consistent with the belief that a yet more sensitive method might show a
physical residue where the approved method does not.
  In this regard, our analysis finds the proviso to be structurally similar to the
Delaney Clause as interpreted by Judge Williams in Public Citizen. Both provi­
sions contain some administrative discretion, but they also both contain some
“ automatic” elements. To paraphrase Judge Williams, our conclusion is that the
proviso requires that if A [an approved method of detection detects the presence
of any residue], then B [the proviso is not applicable]. See Public Citizen, 831
F.2d at 1112. There is language permitting administrative discretion, but it relates
only to the selection of detection methods.15 Once any residue is detected by
an approved method, the compound cannot be listed, because the proviso does
not apply, and hence the Delaney Clause itself does.

                                                 IV. Conclusion

   Under the DES proviso, the FDA may choose to disapprove methods of detec­
tion because they are not sufficiently sensitive to detect the presence of an additive
at the “ no significant risk” level. Further, the FDA need not revise its regulatory
approval of a method simply because a more sensitive method of detection may
be available. However, it is a necessary condition to the application of the DES
proviso that an FDA approved method of detection return a finding that no residue
has been detected. The FDA may not accept a finding that residue is present,
but below the “ no significant risk” level, as satisfying the statutory requirement
of “ no residue.”

                                                                     CHRISTOPHER SCHROEDER
                                                                   Deputy Assistant Attorney General
                                                                       Office of Legal Counsel

    15 O f course, the exercise o f the FDA’s discretion in selecting a method o f detection might result in an approved
m ethod failing to detect residues that more sensitive methods could detect. The practical consequences o f a finding
o f no residue by such a less sensitive method might well be indistinguishable from the consequences o f following
the F D A ’s current SOM approach, if the less sensitive method were sensitive down to the level of no significant
risk, but no further. Indeed, by giving the Secretary discretion in method selection, Congress may well have con­
tem plated that the risk associated with a com pound might be a factor in the Secretary’s exercise of that discretion.
See discussion supra pp. 2 61-62. Insofar as the FDA’s approach takes no significant risk levels into account, it
can be seen as one plausible methodology fo r accomplishing the purposes o f the DES proviso, at least on one
possible reading o f those purposes.
   N evertheless, the Supreme Court has been quite clear in recent years that where Congress’s statutory command
is unam biguous as to the precise question at issue. Chevron , 467 U.S. at 842, that command must be followed.
E.g., Connecticut Nat’l Bank, 503 U.S. at 254. The proviso structures the FD A ’s decision making in a particular
way, and the fact that an alternative decision making structure might produce a similar ultimate decision does not
justify failing to follow the proviso’s instructions.

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