Nrdc v. Usepa ( 2017 )


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  •                      FOR PUBLICATION
    UNITED STATES COURT OF APPEALS
    FOR THE NINTH CIRCUIT
    NATURAL RESOURCES DEFENSE                         No. 15-72308
    COUNCIL,
    Petitioner,
    v.
    U.S. ENVIRONMENTAL PROTECTION
    AGENCY,
    Respondent.
    CENTER FOR FOOD SAFETY;                           No. 15-72312
    INTERNATIONAL CENTER FOR
    TECHNOLOGY ASSESSMENT,
    Petitioners,                    OPINION
    v.
    U.S. ENVIRONMENTAL PROTECTION
    AGENCY; SCOTT PRUITT,* in his
    official capacity as Administrator of
    the Environmental Protection
    Agency,
    Respondents.
    *
    Scott Pruitt, Administrator of the Environmental Protection
    Agency, is substituted for his predecessor, Gina McCarthy. Fed. R. App.
    P. 43(c)(2).
    2                         NRDC V. USEPA
    On Petition for Review of an Order of the
    Environmental Protection Agency
    Argued and Submitted November 17, 2016
    San Francisco, California
    Filed May 30, 2017
    Before: Michael J. Melloy,** Richard R. Clifton,
    and Paul J. Watford, Circuit Judges.
    Opinion by Judge Melloy
    SUMMARY***
    Pesticides / EPA
    The panel vacated the United States Environmental
    Protection Agency’s (“EPA”) conditional registration of the
    pesticide NSPW-L30SWS – an antimicrobial materials
    preservative that uses nanosilver as its active ingredient –
    because the EPA failed to support its requisite finding that
    NSPW was in the public interest under 7 U.S.C.
    § 136a(c)(7)(C).
    **
    The Honorable Michael J. Melloy, United States Circuit Judge for
    the U.S. Court of Appeals for the Eighth Circuit, sitting by designation.
    ***
    This summary constitutes no part of the opinion of the court. It has
    been prepared by court staff for the convenience of the reader.
    NRDC V. USEPA                            3
    The Federal Insecticide, Fungicide, and Rodenticide Act
    governs the sale, use, and distribution of pesticides, and the
    Act requires that pesticides generally must be registered with
    the EPA before being sold or distributed. The EPA may grant
    a temporary, conditional registration if it first determines that
    use of a pesticide was in the public interest.
    The panel held that substantial evidence supported the
    EPA’s findings that NPSW has lower application and
    mobility rates than conventional-silver pesticides.
    The panel held, however, that substantial evidence did not
    support the EPA’s finding that use of NPSW was in the
    public interest because it had the “potential” to reduce the
    amount of silver released into the environment. The panel
    held that the EPA’s finding was based on two unsubstantiated
    assumptions: first, that current users of conventional-silver
    pesticides would replace those pesticides with NSPW; and
    second, that NSPW would not be incorporated into new
    products to the extent that such incorporation would actually
    increase the amount of silver released into the environment.
    The panel concluded that without evidence in the record to
    support the assumptions, it could not find that the EPA’s
    public-interest finding was supported by substantial evidence
    as required by the Act.
    COUNSEL
    Jaclyn H. Prange (argued), San Francisco, California; Aaron
    Colangelo, Washington, D.C.; as and for Petitioner Natural
    Resources Defense Council.
    4                    NRDC V. USEPA
    George A. Kimbrell and Sylvia Wu, Center for Food Safety,
    San Francisco, California, for Petitioners Center for Food
    Safety and International Center for Technology Assessment.
    Sue Chen (argued), Attorney, and John C. Cruden, Assistant
    Attorney General, Environmental Defense Section,
    Environment & Natural Resources Division, United States
    Department of Justice, Washington, D.C.; Amber Aranda, Of
    Counsel, Office of General Counsel, United States
    Environmental Protection Agency, Washington, D.C.; for
    Respondent.
    OPINION
    MELLOY, Circuit Judge:
    The Federal Insecticide, Fungicide, and Rodenticide Act
    (“FIFRA”), 7 U.S.C. §§ 136–136y, governs the sale, use, and
    distribution of pesticides. Under FIFRA, a pesticide
    generally must be registered with the Environmental
    Protection Agency (“EPA”) before it is sold or distributed.
    
    Id. § 136a(a).
    In order to obtain pesticide registration, an
    applicant must submit sufficient data “concerning the
    product’s health, safety, and environmental effects.”
    Pollinator Stewardship Council v. EPA, 
    806 F.3d 520
    , 523
    (9th Cir. 2015). The registration requirement thus enables the
    EPA to prohibit pesticides that will cause “unreasonable
    adverse effects on the environment.” 
    Id. (quoting 7
    U.S.C.
    § 136a(c)(5)). Sometimes, however, the EPA may receive
    sufficient data to determine that short-term use of a pesticide
    is reasonable, but not enough data regarding its long-term
    use. See 7 U.S.C. § 136a(c)(7)(C). If the EPA lacks this data
    “because a period reasonably sufficient for generation of the
    NRDC V. USEPA                            5
    data has not elapsed since the [EPA] first imposed the data
    requirement,” the EPA may grant a temporary, conditional
    registration. 
    Id. But, to
    issue the conditional registration, the
    EPA must first determine “that use of the pesticide is in the
    public interest.” 
    Id. This case
    involves the pesticide NSPW-L30SS
    (“NSPW”). Manufactured by Nanosilva LLC, NSPW is an
    antimicrobial materials preservative that uses nanosilver as its
    active ingredient. Petitioners—the Natural Resources
    Defense Council, the Center for Food Safety, and the
    International Center for Technology Assessment—opposed
    the EPA’s conditional registration of NSPW during public
    notice and comment. Petitioners argued the EPA failed to
    support its findings that (1) use of NPSW is in the public
    interest; and (2) Nanosilva LLC had insufficient time to
    submit the required data.          The EPA, nonetheless,
    conditionally registered NSPW in May 2015. Petitioners
    filed a timely petition for review and now renew their
    arguments before this Court. We have jurisdiction for direct
    review of the agency action pursuant to 7 U.S.C. § 136n(b).
    After reviewing the conditional registration for substantial
    evidence, we conclude the EPA failed to support its finding
    that NSPW is in the public interest. We therefore vacate the
    registration in whole and need not reach Petitioners’
    insufficient-time arguments.
    I
    NSPW is a materials preservative incorporated into
    plastic and textile products. When so incorporated, the EPA
    explains, NSPW can help “suppress the growth of bacteria,
    algae, fungus, mold[,] and mildew, which cause odors,
    6                          NRDC V. USEPA
    discoloration, stains, and deterioration.”1 NSPW may be used
    in products such as trash cans, mops, window blinds,
    furniture, baseboards, light switches, plastic decking, carpet,
    toilet seats, shower curtains, tubs, cell phones, computers,
    plastic components in humidifiers, vacuums, combs, brushes,
    electric razors, blow dryers, beds, wall coverings,
    wheelchairs, linens, golf bags, exercise equipment, life
    preservers, sportswear, nursing uniforms, watch bands,
    restaurant uniforms, litter boxes, swimming pool equipment,
    ink pens, portable toilets, office supplies, and luggage.
    NSPW may not be used, however, in products designed for
    food contact, food packaging, or drinking water.
    The active ingredient in NSPW is nanosilver. Simply put,
    nanosilver is a version of “conventional” silver that is
    engineered to have a much smaller particle size.
    Conventional silver has long been recognized as an
    antimicrobial agent and is the active ingredient in a number
    of currently registered pesticides used as materials
    preservatives. Nanosilver, due to its much smaller particle
    size, can have significantly different properties than
    conventional silver. These different properties provide new
    benefits and opportunities to industry.
    But with these new benefits come new risks. After
    companies seeking to market nanosilver and other
    nanomaterials began approaching the EPA for pesticide
    1
    Under FIFRA, pesticides include “any substance or mixture of
    substances intended for preventing, destroying, repelling, or mitigating
    any pest.” 7 U.S.C. § 136(u). Pests include, with some exceptions,
    “(1) any insect, rodent, nematode, fungus, weed, or (2) any other form of
    terrestrial or aquatic plant or animal life or virus, bacteria, or other micro-
    organism.” 
    Id. § 136(t).
                         NRDC V. USEPA                        7
    registration, the EPA convened a meeting of the FIFRA
    Scientific Advisory Panel (“the Panel”) in November 2009 to
    discuss potential hazards. In part, the Panel summarized its
    meeting as follows:
    The Panel was not aware of any
    information that suggested that silver ions
    released from silver nanomaterials would
    behave differently than silver ions generated
    by any other source. However, the Panel
    believed that the rate of silver ion production,
    as well as the distribution of silver in
    [biological] tissue, may differ substantially
    between silver nanomaterials and other forms
    of silver. Nanomaterials can deliver ions
    directly to specific tissues, cell membranes or
    inside cells. The biological effects of silver
    nanomaterials (including temporal pattern for
    ion delivery), as well as their environmental
    fate, can be affected by other materials
    present in the preparation (e.g., surfactants).
    Nanosilver can also potentially act as a carrier
    for other toxic chemicals. These issues led
    the Panel to suggest that the hazard profile of
    silver nanomaterials may differ from other
    forms of silver.
    The Panel thus recommended that the “EPA treat nanosilver
    differently from its conventional silver counterpart.” The
    Panel also “cautioned about extrapolating from one
    nanosilver formulation to another when assessing hazards.”
    After the Panel convened, the EPA evaluated and
    conditionally registered two pesticides containing a form of
    8                         NRDC V. USEPA
    nanosilver: AGS-20 and NSPW. Like NSPW, AGS-20 is a
    nanosilver-based antimicrobial pesticide used as a materials
    preservative. However, unlike NSPW, which is a liquid
    suspension incorporated into plastics and textiles, AGS-20 is
    a powder which may be used as a surface coating or by
    incorporation with textiles only. The nanosilver in AGS-20
    also “has different size range and surface coatings than the
    nanosilver in NSPW[ ].” The EPA conditionally registered
    AGS-20 in December 2011, approximately three years after
    its manufacturer submitted its application for registration.2
    Granting conditional registration to NSPW, however, took
    longer. While Nanosilva LLC submitted an application to
    register NSPW in 2009, the EPA did not conditionally
    register NSPW until May 2015. This conditional registration
    is for a four-year period.
    In granting conditional registration, the EPA found, as
    required by 7 U.S.C. § 136a(c)(7)(C), that NSPW contained
    a new active ingredient and would not cause unreasonable
    adverse effects on the environment. The EPA also made two
    findings relevant to Petitioners’ arguments in the present
    case. The EPA, first, found that granting conditional
    registration was in the public interest. Specifically, it found
    that NSPW had a lower application rate (i.e., it uses less
    silver) and a lower mobility rate (i.e., it is less likely to
    release silver into the environment in detectable quantities)
    when compared to conventional-silver pesticides. Therefore,
    the EPA reasoned, using NSPW has the “potential” to reduce
    2
    This Court partially vacated the conditional registration of AGS-20
    because the EPA did not satisfy its own rule for determining particular risk
    concerns requiring mitigation. Nat. Res. Def. Council v. EPA (NRDC),
    
    735 F.3d 873
    , 886–87 (9th Cir. 2013).
    NRDC V. USEPA                                   9
    “environmental loading” and risk caused by silver release.
    Second, the EPA found that Nanosilva LLC had insufficient
    time to generate the data required for unconditional
    registration.
    Petitioners, who had opposed the conditional registration
    of NSPW during public notice and comment, filed a timely
    petition for review in this Court. They argue the EPA failed
    to support its public-interest and insufficient-time findings.3
    II
    The following principles guide our review of the EPA’s
    conditional registration of NSPW. First, we must sustain the
    conditional registration “if it is supported by substantial
    evidence when considered on the record as a whole.”
    7 U.S.C. § 136n(b). “Substantial evidence means more than
    a mere scintilla but less than a preponderance; it is such
    relevant evidence as a reasonable mind might accept as
    adequate to support a conclusion.” 
    NRDC, 735 F.3d at 877
    (quoting Vasquez v. Astrue, 
    572 F.3d 586
    , 591 (9th Cir.
    2009)). “Under the substantial evidence standard, we must
    affirm the [EPA’s] finding ‘where there is “such relevant
    evidence as a reasonable mind might accept as adequate to
    support a conclusion” even if it is possible to draw two
    inconsistent conclusions from the evidence.’” 
    Id. (quoting Nw.
    Food Processors Ass’n v. Reilly, 
    886 F.2d 1075
    ,
    1079–80 (9th Cir. 1989)). “When, as in this case, the agency
    ‘is making predictions, within its area of special expertise, at
    3
    Petitioners do not directly challenge the EPA’s no-adverse-effects
    finding (i.e., that NSPW will not have any unreasonable adverse effect on
    the environment during the conditional-registration period), but Petitioners
    do not concede that NSPW is “safe.”
    10                    NRDC V. USEPA
    the frontiers of science . . . a reviewing court must generally
    be at its most deferential.’” 
    Id. (alteration in
    original)
    (quoting Balt. Gas & Elec. Co. v. NRDC, 
    462 U.S. 87
    , 103
    (1983)). But, “[a]lthough we must give due deference to
    EPA’s findings, ‘[i]t is well-established that an agency’s
    action must be upheld, if at all, on the basis articulated by the
    agency itself.’” 
    Id. (quoting Motor
    Vehicle Mfrs. Ass’n of the
    U.S., Inc. v. State Farm Mut. Auto. Ins. Co., 
    463 U.S. 29
    , 50
    (1983)).
    Second, “[w]hen interpreting a statute, we are guided by
    the fundamental canons of statutory construction and begin
    with the statutory text.” United States v. Neal, 
    776 F.3d 645
    ,
    652 (9th Cir. 2015). “The words of a statute should be
    accorded their plain meaning, as considered in light of ‘the
    particular statutory language at issue, as well as the language
    and design of the statute as a whole.’” Preap v. Johnson,
    
    831 F.3d 1193
    , 1200 (9th Cir. 2016) (quoting K Mart Corp.
    v. Cartier, Inc., 
    486 U.S. 281
    , 291 (1988)). And, where a
    statute is ambiguous, “we may turn to legislative history for
    guidance.” United States v. Thomsen, 
    830 F.3d 1049
    , 1058
    (9th Cir. 2016).
    III
    We are unaware of any prior decision considering the
    public-interest requirement under 7 U.S.C. § 136a(c)(7)(C).
    Accordingly, to illuminate the requirement’s role in FIFRA’s
    regulatory scheme, we begin with the statutory background.
    We then turn to whether the EPA supported its public-interest
    finding in the present case with substantial evidence.
    NRDC V. USEPA                          11
    A
    Generally, “no person . . . may distribute or sell to any
    person any pesticide that is not registered” with the EPA.
    7 U.S.C. § 136a(a). In order for the EPA to evaluate an
    application for pesticide registration, an application must
    “describ[e] how the pesticide will be used, the claims made
    of its benefits, the ingredients, and a description of all tests
    and studies done and the results thereof, concerning the
    product’s health, safety, and environmental effects.”
    Pollinator Stewardship 
    Council, 806 F.3d at 523
    . The EPA
    “shall publish guidelines specifying the kinds of information
    which will be required to support the registration of a
    pesticide and shall revise such guidelines from time to time.”
    7 U.S.C. § 136a(c)(2)(A).
    After an applicant submits sufficient data for pesticide
    registration, the EPA may grant “unconditional registration”
    under § 136a(c)(5). “Unconditional registration necessarily
    requires sufficient data to evaluate the environmental risks.”
    Pollinator Stewardship 
    Council, 806 F.3d at 523
    ; see also
    7 U.S.C. § 136a(c)(5) (listing the findings required for
    unconditional registration). If an applicant has not submitted
    sufficient data to support unconditional registration, however,
    the EPA may conditionally register the pesticide under
    limited circumstances. See 7 U.S.C. § 136a(c)(7). As
    relevant here,
    [t]he [EPA] may conditionally register a
    pesticide containing an active ingredient not
    contained in any currently registered pesticide
    for a period reasonably sufficient for the
    generation and submission of required data
    (which are lacking because a period
    12                   NRDC V. USEPA
    reasonably sufficient for generation of the
    data has not elapsed since the [EPA] first
    imposed the data requirement) on the
    condition that by the end of such period the
    [EPA] receives such data and the data do not
    meet or exceed risk criteria enumerated in
    regulations issued under this subchapter, and
    on such other conditions as the [EPA] may
    prescribe. A conditional registration under
    this subparagraph shall be granted only if the
    [EPA] determines that use of the pesticide
    during such period will not cause any
    unreasonable adverse effect on the
    environment, and that use of the pesticide is in
    the public interest.
    
    Id. § 136a(c)(7)(C)
    (emphasis added).
    The public-interest requirement reflects an important
    distinction between conditional registration and unconditional
    registration. Conditional registration under § 136a(c)(7)(C)
    does not require all the risk data that unconditional
    registration requires. Cf. 7 U.S.C. § 136a(c)(5). Instead,
    § 136a(c)(7)(C) allows the EPA to temporarily register a
    pesticide with less-than-complete risk data so long as the
    EPA, among other additional requirements, determines “that
    use of the pesticide is in the public interest.”
    The statute does not further define the public-interest
    requirement, but the legislative history of conditional
    registration provides some insight. For example, a report by
    the Senate Committee on Agriculture, Nutrition, and Forestry,
    stated:
    NRDC V. USEPA                            13
    No new-chemical conditional registration
    [under § 136a(c)(7)(C)] could be issued unless
    the [EPA] determined that use of the pesticide
    during the period required to complete the
    testing would not cause any unreasonable
    adverse effect on the environment, and that
    use of the pesticide was required in the public
    interest, as for example, in a situation in
    which there is a significant pest control
    problem which cannot satisfactorily be
    handled by use of products which have been
    fully registered.
    S. Rep. No. 95-334, at 21 (1977).
    On the Senate floor, Senator Leahy, who sponsored the
    bill that created the conditional registration provision, stated
    that the Senate committee carefully considered the statutory
    requirements so conditional registration “would be reserved
    to the truly exceptional case.” 123 Cong. Rec. 25,706 (1977).
    The public-interest requirement, he stated, was “a more
    stringent test” than that required for unconditional
    registration. 
    Id. (“[A]s with
    all other registrations, the [EPA]
    has to find the pesticide would not have an unreasonable
    adverse effect on the environment. Finally, a more stringent
    test also applies. The [EPA] must be shown evidence
    sufficient to find that this confidential [sic] registration is ‘in
    the public interest.’” (emphasis added)). Senator Leahy
    continued:
    Suppose we have a serious pest problem for
    which this new pesticide would be an
    alternative to other chemicals. The [EPA] is
    14                    NRDC V. USEPA
    sure that this pesticide is as safe as any
    pesticide already registered for that use. . . .
    . . . However, in the best case there may be
    gaps in the safety data which supports the
    registration. . . . Clearly the objectives of the
    Act are best served with the added flexibility
    to permit a new product to be used which will
    meet the stringent test of being “in the public
    interest.”
    
    Id. The EPA
    Administrator, while testifying before the
    Senate committee, made statements to similar effect. See S.
    Rep. No. 95-334, at 74 (Statement of Douglas Costle, Adm’r,
    Environmental Protection Agency) (“[T]here may be a real
    need for use of the pesticide to avoid pest outbreaks. It is our
    opinion that in some of these cases it would be proper to
    allow conditional registration . . . if the public interest would
    be served by issuance of a conditional registration, bearing in
    mind the benefits as well as the likely scope of the risk.
    Although we think that the exercise of this conditional
    registration authority for new chemicals would be rare, we
    feel that it should be available in appropriate cases.”).
    B
    In the present case, the EPA found that use of NSPW is in
    the public interest because it has the “potential” to reduce the
    amount of silver released into the environment. Petitioners
    do not dispute that reducing the amount of silver in the
    environment is in the public interest. Rather, Petitioners
    dispute the factual premises underlying the EPA’s public-
    NRDC V. USEPA                                15
    interest finding: (1) that NSPW has a lower application rate
    (i.e., it uses less silver) than conventional-silver pesticides;
    (2) that NSPW has a lower mobility rate (i.e., it is less likely
    to release silver into the environment in detectable
    quantities); and (3) that current users of conventional-silver
    pesticides will switch to NSPW and/or that NSPW will not be
    incorporated into new products. Although we conclude that
    the first two premises are supported by substantial evidence,
    we hold that the third premise impermissibly relies on
    unsubstantiated assumptions.4
    1
    The EPA found that NSPW has a lower application rate
    than conventional-silver pesticides. Petitioners make several
    arguments as to why this finding is not supported by
    substantial evidence. First, Petitioners argue that the
    increased toxicity of nanosilver5 outweighs any benefits that
    may be gained from its lower application rate. We conclude,
    however, that the EPA presented substantial evidence to
    support its conclusion regarding these toxicity risks. In its
    response to public comments, the EPA agreed that the
    evidence suggests “nano-scale silver can potentially be more
    toxic than ionic silver alone.” But the EPA also concluded
    that the evidence suggests nanosilver would not be
    4
    The EPA argues that Petitioners waived their arguments regarding
    EPA’s assumptions. After reviewing Petitioners’ comments, however, we
    conclude Petitioners more than adequately raised the issue during the
    public notice-and-comment period. See Portland Gen. Elec. Co. v.
    Bonneville Power Admin., 
    501 F.3d 1009
    , 1023–24 (9th Cir. 2007).
    5
    For ease of reference and at the risk of conflating different
    formulations of nanosilver, our references to “nanosilver” from this point
    forward pertain only to the formulation in NSPW.
    16                    NRDC V. USEPA
    “sufficiently more toxic to raise risk concerns when taking
    into account leaching rates for the proposed uses.” For
    NSPW incorporated into plastics, the EPA specifically
    concluded that nanosilver would have to be “on the order of
    5 to 53 times more toxic” than conventional silver to raise
    concerns. And for textiles, the EPA concluded that
    nanosilver would need to be “on the order of 19 to 190 times
    more toxic.”
    Petitioners appear to attack these conclusions as too
    probabilistic. Nevertheless, on substantial evidence review,
    the EPA need not present evidence to support an outcome
    with certainty; it only needs to present “such relevant
    evidence as a reasonable mind might accept as adequate to
    support a conclusion.” 
    NRDC, 735 F.3d at 877
    (quoting
    
    Vasquez, 572 F.3d at 591
    ). We defer to the EPA on this
    matter as it “is making predictions, within its area of special
    expertise, at the frontiers of science.” 
    Id. (quoting Balt.
    Gas
    & Elec. 
    Co., 462 U.S. at 103
    ).
    Second, Petitioners argue the EPA failed to explain why,
    given the different risks that nanosilver poses, total mass of
    silver applied (i.e., the application rate) is a relevant point of
    comparison. We disagree. The EPA acknowledged in its
    response to public comments that there was an “ongoing
    debate within the scientific community that metrics other than
    mass (such as particle number or surface area) may be more
    suitable for assessing nanosilver risks.” But the EPA also
    considered its use of mass in light of NSPW’s “low release[ ]
    [levels], the available toxicity data, use of multiple risk
    uncertainty factors . . . [,] and required risk-mitigation
    measures on the product label.” Under these circumstances,
    we conclude that the EPA’s qualified use of application rate
    NRDC V. USEPA                        17
    is supported by substantial evidence and defer to the EPA’s
    expertise.
    Finally, Petitioners argue that the EPA failed to support
    its finding that conventional-silver pesticides have higher
    application rates than NSPW. While the EPA did not list
    every conventional-silver pesticide’s application rate, the
    EPA listed 16 different conventional-silver pesticides and
    their application rates in its response to public comments.
    These rates are many times higher than the permitted
    application rate of NSPW. As a result, we cannot say the
    EPA’s lower-application rate finding is unsupported by
    substantial evidence.
    2
    The EPA next found that the nanosilver in NSPW has a
    lower mobility rate than conventional-silver pesticides.
    Petitioners argue this finding relied on a plastic-leaching
    study the EPA had previously found deficient. But the EPA’s
    finding does not rely solely on the plastic-leaching study.
    The EPA also relied on an undisputed textile-leaching study
    which also demonstrated low release levels. Further, the EPA
    noted, the nanosilver in NSPW “is complexed to a larger
    particle that is then embedded into a polymer. The submitted
    leaching studies show that nanosilver is unlikely to be
    released in quantities above the detection limit from this
    polymer. Absent release from the polymer, the mobility of
    nanosilver in [NSPW] is greatly reduced.” The EPA then
    compared this structure to “silver salts,” which are in “most
    silver-based pesticide products” and          “immediate[ly]
    dissol[ve].” We therefore cannot say the EPA’s lower-
    mobility finding is unsupported by substantial evidence.
    18                       NRDC V. USEPA
    3
    Our inquiry cannot end with the EPA’s findings that
    NSPW has lower application and mobility rates than
    conventional-silver pesticides. The EPA ultimately found
    that, based on these comparatively lower rates, use of NSPW
    is in the public interest because it has the “potential” to
    reduce the amount of silver released into the environment.
    This finding, however, also requires two interrelated and
    unstated assumptions. It assumes, first, that current users of
    conventional-silver pesticides will replace those pesticides
    with NSPW (“the substitution assumption”). It also assumes
    that NSPW will not be incorporated into new products to the
    extent that such incorporation would actually increase the
    amount of silver released into the environment (“the no-new-
    products assumption”).6 Because the substitution and no-
    new-products assumptions are unsubstantiated, Petitioners
    argue that the EPA’s public-interest finding is not supported
    by substantial evidence. We agree.
    The EPA cites no evidence in the record to support its
    substitution assumption. In briefing before this Court, the
    EPA contends that substitution will occur as a “logical
    matter.” To support this proposition, the EPA cites a 1983
    entry in the Federal Register, stating that “the pesticide
    market in general is finite, relatively ‘saturated’ and inelastic”
    and that increased competition may “shift the user’s purchase
    6
    New “products” should not be confused with new “use pattern.”
    When referring to new products, we refer to new incorporations of NSPW
    within current registered use patterns. In other words, we base our
    analysis on the understanding that NSPW is not registered for use in a
    greater range of products than conventional-silver pesticides. We provide
    an example below of how NSPW may be used in new products.
    NRDC V. USEPA                          19
    from one company to another.” See Regulations for the
    Enforcement of FIFRA; Conditional Registration, 48 Fed.
    Reg. 34000, 34003 (July 26, 1983). We cannot, however,
    “accept appellate counsel’s post-hoc rationalizations for
    agency action.” Hernandez-Cruz v. Holder, 
    651 F.3d 1094
    ,
    1109 (9th Cir. 2011) (quoting Nw. Envtl. Def. Ctr. v.
    Bonneville Power Admin., 
    477 F.3d 668
    , 688 (9th Cir. 2007)).
    And even if we did consider the general description of the
    pesticide market as it existed in 1983, we have no way of
    knowing from the record whether that description is
    applicable to the current and narrower markets for silver-
    based pesticides and materials preservatives.
    The lack of evidence supporting the substitution
    assumption may not be inherently problematic: if no
    manufacturer adopts NSPW, then NSPW will not present any
    environmental risk through those manufacturers’ products.
    The substitution assumption is certainly problematic,
    however, in light of the no-new-products assumption, which
    the EPA also fails to support. In response, the EPA argues
    that there is no evidence to suggest that NSPW will be
    incorporated into new products. It also contends that it need
    not prove a negative proposition. But, as a logical matter, the
    EPA’s no-new-products assumption must be weighed against
    its substitution assumption. On the one hand, the EPA
    assumes that current users of conventional-silver pesticides
    will switch to NSPW. On the other hand, however, it
    assumes that the benefits of NSPW will not also invite
    manufacturers to incorporate NSPW into new products. The
    EPA assumes, moreover, that the costs of switching to NSPW
    are not prohibitive, while it also assumes that the costs of
    adding NSPW will discourage new incorporations during the
    conditional-registration period.
    20                    NRDC V. USEPA
    We do not foreclose the possibility that the EPA could
    have proved these assumptions. Nevertheless, without
    evidence in the record to support the assumptions, we cannot
    find that the EPA’s public-interest finding is supported by
    substantial evidence as required by FIFRA. Requiring
    substantial evidence for public-interest findings, moreover, is
    not just a statutory technicality as this case demonstrates.
    Here, if the EPA’s substitution and no-new-products
    assumptions are incorrect, NSPW may increase the amount
    of silver released into the environment and contravene the
    identified public interest. For example, the EPA permits
    NSPW and conventional-silver pesticides to be incorporated
    into certain plastic furniture under their current registrations.
    That does not mean, however, that every plastic furniture
    product actually incorporates a silver-based pesticide.
    Furniture A may use a conventional-silver pesticide as a
    materials preservative, but Furniture B may not. If NSPW is
    added to Furniture B, but Furniture A continues to use the
    conventional-silver pesticide, there would be a net increase in
    the amount of silver incorporated into Furniture A and B.
    The EPA argues that its public-interest finding allows for
    the possibility that NSPW could be added to new products.
    It points out, again, that the maximum application rate for the
    nanosilver in NSPW “is a fraction of what is permitted in
    pesticides containing conventional silver.” The EPA also
    states that it used “worst-case scenarios” when assessing how
    much nanosilver from NSPW will leach from products and
    end up in the environment. The maximum-application-rate
    argument, however, still requires the assumption that a new
    product would have used a conventional-silver pesticide if
    NSPW was not available or that there will be an offsetting
    switch from conventional-silver pesticides to NSPW in other
    products. Regardless of whether the NSPW in new products
    NRDC V. USEPA                               21
    only releases a minimal amount of silver in the “worst-case
    scenario,” the public interest that the EPA identified—
    reducing silver in the environment—will not be met unless
    one of these two conditions occurs. In short, these arguments
    do nothing to address the core flaw in the EPA’s public-
    interest finding: it assumed, without citing evidence, that
    NSPW would be used enough by some, but not too much by
    others, to reduce the amount of silver released into the
    environment.
    The EPA is capable of evaluating the kind of evidence
    that would have substantiated these assumptions. In its own
    guidance document, the EPA listed several factors it may
    consider in determining whether a pesticide is in the public
    interest. See Pesticide Programs; Conditional Registration of
    New Pesticides, 51 Fed. Reg. 7628-02, 7632–33 (Mar. 5,
    1986).7 These include economic factors, such as the
    “[c]omparative estimated costs and savings if the new
    pesticide is used instead of equivalent registered pesticides or
    alternative non-pesticide methods.” 
    Id. at 7633.
    NSPW,
    moreover, is not the first registered nanosilver-based
    materials preservative on the market—it is the second. While
    there are important differences between AGS-20 and NSPW,
    we have to imagine that at least some data about AGS-20’s
    use and adoption were ascertainable and would have been
    useful in evaluating the EPA’s assumptions.
    7
    We acknowledge that the EPA is not bound to follow this guidance
    document and do not base our decision on the EPA’s failure to follow this
    guidance. The guidance is only relevant to the extent it illustrates the
    EPA’s capability to evaluate and consider the kind of evidence that would
    have supported its public-interest finding in the present case.
    22                    NRDC V. USEPA
    To be clear, the EPA need not “ferret out every possible
    alternative” scenario that may occur when determining that a
    conditional registration is in the public interest. Vermont
    Yankee Nuclear Power Corp. v. Nat. Res. Def. Council, 
    435 U.S. 519
    , 551 (1978). Nor is the EPA required to support a
    public-interest finding with “scientific certainty.” ASARCO,
    Inc. v. Occupational Safety & Health Admin., 
    746 F.2d 483
    ,
    490 (9th Cir. 1984) (citation omitted). But the EPA must
    support its predicted public-interest scenario with “substantial
    evidence when considered on the record as a whole.” See
    7 U.S.C. § 136n(b). Further, § 136a(c)(7)(C) does not
    presume, as the EPA argues, that the EPA may collect
    missing data related to its public-interest finding after
    granting a conditional registration. To the contrary,
    § 136a(c)(7)(C) only presumes the EPA needs more data to
    make a risk determination regarding use of the pesticide
    beyond the conditional-registration period. The statute
    instead requires the EPA to find, before granting conditional
    registration, “that use of the pesticide is in the public
    interest.” 7 U.S.C. § 136a(c)(7)(C) (emphasis added).
    In sum, the public-interest requirement of § 136a(c)(7)(C)
    is an additional, “more stringent test” that distinguishes
    conditional registration from unconditional registration. See
    123 Cong. Rec. at 25,706; see also 
    Preap, 831 F.3d at 1200
    (stating that a statute’s words must be considered in light of
    the “design of the statute as a whole” (citation omitted)). To
    pass this test, the EPA must support its finding with
    substantial evidence. The EPA may not satisfy the
    requirement by simply finding that a pesticide has the
    “potential” to be in the public interest—especially where the
    pesticide also has the “potential” to contravene the public
    interest. Accordingly, where an essential premise of a public-
    interest finding is only supported by bare assumptions, as in
    NRDC V. USEPA                          23
    the present case, we will find substantial evidence lacking.
    See Pollinator Stewardship 
    Council, 806 F.3d at 538
    (N.R.
    Smith, J., concurring in judgment) (“Although the EPA
    certainly has authority to rely on its well-founded beliefs,
    scientifically-derived knowledge, and experience-driven
    professional judgment, it must support the beliefs,
    knowledge, and judgment with evidence.”).
    IV
    The public-interest finding is an essential prerequisite to
    conditional registration under § 136a(c)(7)(C). With respect
    to NSPW, the EPA failed to support that finding with
    substantial evidence. We therefore vacate the conditional
    registration in whole, see 7 U.S.C. § 136n(b), and need not
    reach the remaining grounds for vacatur raised by Petitioners,
    see Pollinator Stewardship 
    Council, 806 F.3d at 532
    –33.
    VACATED and REMANDED.
    Costs are awarded to the Petitioners.