FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

LEAGUE OF UNITED LATIN 

AMERICAN CITIZENS; PESTICIDE 

ACTION NETWORK NORTH AMERICA;

NATURAL RESOURCES DEFENSE 

COUNCIL; CALIFORNIA RURAL 

LEGAL ASSISTANCE FOUNDATION;

FARMWORKERS ASSOCIATION OF 

FLORIDA; FARMWORKER JUSTICE;

LABOR COUNCIL FOR LATIN 

AMERICAN ADVANCEMENT;

LEARNING DISABILITIES 

ASSOCIATION OF AMERICA;

NATIONAL HISPANIC MEDICAL 

ASSOCIATION; PINEROS Y 

CAMPESINOS UNIDOS DEL NOROESTE;

UNITED FARM WORKERS;

GREENLATINOS,

Petitioners,

v.

MICHAEL S. REGAN, Administrator, 

United States Environmental 

Protection Agency; U.S.

ENVIRONMENTAL PROTECTION 

AGENCY,

Respondents.

No. 19-71979

EPA No.

EPA-HQ-OPP2007-1005
2 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

STATE OF NEW YORK; STATE OF 

CALIFORNIA; STATE OF 

WASHINGTON; STATE OF 

MARYLAND; STATE OF VERMONT;

COMMONWEALTH OF 

MASSACHUSETTS,

Petitioners,

DISTRICT OF COLUMBIA; STATE OF 

HAWAII; STATE OF OREGON,

Intervenors,

v.

MICHAEL S. REGAN, Administrator, 

United States Environmental 

Protection Agency; U.S.

ENVIRONMENTAL PROTECTION 

AGENCY,

Respondents.

No. 19-71982

EPA No.

EPA-HQ-OPP2007-1005

OPINION

On Petition for Review of an Order of the

Environmental Protection Agency

Argued and Submitted July 28, 2020

San Francisco, California

Filed April 29, 2021
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 3

Before: Jay S. Bybee and Jacqueline H. Nguyen, Circuit 

Judges, and Jed S. Rakoff,* District Judge.

Opinion by Judge Rakoff;

Dissent by Judge Bybee

SUMMARY**

Environmental Protection Agency

The panel granted petitions for review, vacated the 

Environmental Protection Agency (“EPA”)’s 2017 Order 

and 2019 Order, and remanded with instructions to the EPA 

in cases challenging the EPA’s regulation of the pesticide 

chlorpyrifos.

The EPA has recognized that when pregnant mothers are 

exposed to chlorpyrifos residue, this likely harms infants in 

utero. This proceeding began in 2007, when two 

environmental non-profit organizations filed a petition 

asking the EPA to prohibit foods that contain residue of the 

insecticide chlorpyrifos. The EPA declined to take final 

action on the 2007 Petition for more than a decade. This 

Court issued multiple writs of mandamus requiring the EPA 

to move forward. In 2017, the EPA denied the 2007 Petition, 

and in 2019 denied all objections to that decision.

* The Honorable Jed S. Rakoff, United States District Judge for the 

Southern District of New York, 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.
4 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

The panel held that the EPA had abdicated its statutory 

duty under the Federal Food, Drug and Cosmetic Act 

(“FFDCA”). The panel held that the EPA spent more than a 

decade assembling a record of chlorpyrifos’s ill effects and 

repeatedly determined, based on that record, that it could not 

conclude, to the statutorily required standard of reasonable 

certainty, that the present tolerances caused no harm. Rather 

than ban the pesticide or reduce the tolerances to levels that 

the EPA could find were reasonably certain to cause no 

harm, the EPA sought to evade through delay tactics its plain 

statutory duty. Because the FFDCA permitted no further 

delays, the panel ordered the EPA within 60 days after 

issuance of the mandate either to modify chlorpyrifos’s 

tolerances and concomitantly publish a finding that the 

modified tolerances are safe, including for infants and 

children – or to revoke all chlorpyrifos tolerances. The panel 

also ordered the EPA to correspondingly modify or cancel 

related Federal Insecticide, Fungicide and Rodenticide Act 

(“FIFRA”) regulations for food use in a timely fashion 

consistent with the requirements of 21 U.S.C. § 346a(a)(1).

Specifically, the panel first considered whether the EPA

lawfully denied the 2007 Petition. The panel rejected the 

EPA’s argument that it could leave in effect tolerances, 

without a new safety finding, when the EPA concluded the 

petition contained insufficient evidence for the EPA to 

undertake proceedings to revoke or modify tolerances. The 

panel held, first, once the EPA became aware, through a 

petition or otherwise, of genuine questions about the safety 

of an existing tolerance, the EPA had its own continuing 

duty under the FFDCA to determine whether a tolerance that 

was once thought to be safe still is. Here, the EPA’s own 

studies and pronouncements still in effect showed that it 

regarded chlorpyrifos as harmful at levels below the existing 

tolerances. Second, the 2007 Petition, under the EPA’s own 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 5

regulations, contained more than sufficient evidence to 

undertake a safety review, and the EPA recognized as much. 

The panel held that when the EPA publishes a petition 

seeking revocation of a tolerance and later takes final action 

denying that petition, the EPA leaves that tolerance in effect. 

The EPA can only do so if it finds the tolerance to be safe 

for the general population and for infants and children. The 

EPA failed to make such findings, directly contrary to the 

FFDCA.

The panel held that even if the FFDCA did not require a 

safety finding here, the EPA’s denial of the 2007 Petition 

was arbitrary and capricious. The panel rejected the EPA’s 

four objections to the data.

The panel held that its remand with specific instructions 

did not raise due process concerns. On this record, 

immediate issuance of a final regulation was the only 

reasonable action, and the panel ordered the EPA to do so. 

The panel clarified that this was not an open-ended remand, 

or a remand for further factfinding.

Dissenting, Judge Bybee wrote that the majority opinion 

erred by misreading the FFDCA, and misallocating the risk 

of nonpersuasion; overruling the EPA’s judgment on the 

validity and weight to be given technical evidence within the 

EPA’s expertise; and, by its decision to give the EPA 60 days 

to issue a final decision, likely predetermining EPA’s option.
6 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

COUNSEL

Patti A. Goldman (argued), Marisa C. Ordonia, and Kristen 

L. Boyles, Earthjustice, Seattle, Washington, for Petitioners

League of United Latin American Citizens, Pesticide Action 

Network North America, Natural Resources Defense 

Council, California Rural Legal Assistance Foundation,

Farmworkers Association of Florida, Farmworker Justice,

Labor Council for Latin American Advancement, Learning 

Disabilities Association of America, National Hispanic 

Medical Association, Pineros y Campesinos Unidos del 

Noroeste, United Farm Workers, and GreenLatinos.

Frederick A. Brodie (argued), Assistant Solicitor General Of 

Counsel; Andrea Oser, Deputy Solicitor General; Barbara D. 

Underwood, Solicitor General; Letitia James, Attorney 

General; Office of the Attorney General, Albany, New York;

Xavier Becerra, Attorney General; Christie Vosburg, 

Supervising Deputy Attorney General; Reed Sato, Deputy 

Attorney General; Office of the Attorney General, 

Sacramento, California; Robert W. Ferguson, Attorney 

General; William R. Sherman, Counsel for Environmental 

Protection; Attorney General’s Office, Seattle, Washington;

Brian E. Frosh, Attorney General; Steven M. Sullivan, 

Solicitor General; Joshua M. Segal, Special Assistant 

Attorney General; Office of the Attorney General, 

Baltimore, Maryland; Thomas J. Donovan Jr., Attorney 

General; Nichols F. Persampieri, Assistant Attorney 

General; Office of the Attorney General, Montpelier, 

Vermont; Clare E. Connors, Attorney General; Wade H. 

Hargrove III, Deputy Attorney General; Department of the 

Attorney General, Honolulu, Hawaii; Ellen F. Rosenblum, 

Attorney General; Benjamin Gutman, Solicitor General; 

Office of the Attorney General, Salem, Oregon; Maura 

Healey, Attorney General; I. Andrew Goldberg, Assistant 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 7

Attorney General; Environmental Protection Division, 

Office of the Attorney General, Boston, Massachusetts; Karl 

A. Racine, Attorney General; Loren L. Alikhan Solicitor 

General; Caroline S. Van Zile, Principal Deputy Solicitor 

General; Brian R. Caldwell, Assistant Attorney General, 

Public Integrity Unit; Office of the Attorney General, 

Washington, D.C.; for Petitioners States of New York,

California, Washington, Maryland, Vermont, Hawaii, 

Oregon, the Commonwealth of Massachusetts, and the 

District of Columbia.

Mark L. Walters (argued) and Jessica O’Donnell,

Environmental Defense Section, United States Department 

of Justice, Washington, D.C.; Angela Huskey, Office of 

General Counsel, United States Environmental Protection 

Agency, Washington, D.C.; for Respondents.

Shaun A. Goho, Emmett Environmental Law & Policy 

Clinic, Harvard Law School, Cambridge, Massachusetts, for 

Amici Curiae American Academy of Pediatrics, Alliance of 

Nurses for Healthy Environments, American Public Health 

Association, Migrant Clinicians Network, Physicians for 

Social Responsibility, and Union of Concerned Scientists.

Edward Lloyd, Jacob Elkin, Claire MacLachlan, and Basil 

Oswald, Columbia Environmental Clinic, Morningside 

Heights Legal Services, New York, New York, for Amicus 

Curiae Congressman Henry Waxman.

Kathryn E. Szmuszkovicz and Andrew C. Stilton, Beveridge 

& Diamond P.C., Washington, D.C.; Rachel Lattimore, 

Senior Vice President & General Counsel; Ashley Boles, 

Counsel; CropLife America, Washington, D.C.; for Amicus 

Curiae CropLife America.
8 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

David Y. Chung, Kirsten L. Nathanson, and Elizabeth B. 

Dawson, Crowell & Moring LLP, Washington, D.C., for 

Amici Curiae Agribusiness Council of Indiana, Agricultural 

Retailers Association, American Farm Bureau Federation, 

AmericanHort, American Seed Trade Association, 

American Soybean Association, American Sugarbeet 

Growers Association, Beet Sugar Development Foundation, 

California Alfalfa and Forage Association, California Citrus 

Mutual, California Cotton Ginners and Growers 

Association, California Seed Association, California 

Specialty Crops Council, California Walnut Commission, 

Florida Fruit and Vegetable Association, National 

Agricultural Aviation Association, National Association of 

Wheat Growers, National Corn Growers Association,

National Cotton Council, National Onion Association, 

National Sorghum Producers, North Dakota Grain Growers 

Association, Oregonians for Food and Shelter, Washington 

Friends of Farms & Forests, Western Agricultural 

Processors Association, Western Growers, and Western 

Plant Health Association.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 9

OPINION

RAKOFF, District Judge:

This dispute concerning the documented health risks 

posed by a widely used pesticide, chlorpyrifos, has been 

before this Court more than a half-dozen times. The 

Environmental Protection Agency (“EPA” or the “Agency”) 

has recognized that when pregnant mothers are exposed to 

chlorpyrifos residue, this likely harms infants in utero. 

Nevertheless, in derogation of the statutory mandate to ban 

pesticides that have not been proven safe, the EPA has failed 

to act, requesting extension after extension. The Agency’s 

present position is effectively more of the same.

The proceeding began in 2007, when two environmental 

non-profit organizations – Pesticide Action Network North 

America (“PANNA”) and the Natural Resources Defense 

Council, Inc. (“NRDC”) – filed a petition (the “2007 

Petition”) asking the EPA to prohibit foods that contain any 

residue of the insecticide chlorpyrifos. Then, and now, the 

EPA has permitted distribution of food containing 

chlorpyrifos residue as long as the residue is less than a limit 

known as a “tolerance,” which varies depending on the food. 

The 2007 Petition argued that, even at levels beneath these 

tolerances, chlorpyrifos poses neurodevelopmental risks, 

especially to infants and children.

The Federal Food, Drug and Cosmetic Act (“FFDCA”) 

provides that the EPA’s “Administrator may establish or 

leave in effect a tolerance for a pesticide chemical residue in 

or on a food only if the Administrator determines that the 

tolerance is safe. The Administrator shall modify or revoke 
10 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

a tolerance if the Administrator determines it is not safe.”1 

The statute also requires that the EPA “ensure that there is a 

reasonable certainty that no harm will result to infants and 

children from aggregate exposure to the pesticide chemical 

residue” and “publish a specific determination regarding the 

safety of the pesticide chemical residue for infants and 

children.”2

Since 2007, the evidence of harm has continued to build, 

primarily through two kinds of studies: experimental studies 

on live mice and rats and epidemiological studies tracking 

humans who were exposed to chlorpyrifos in utero. 

Between 2007 and 2016, the EPA published several Human 

Health Risk Assessments regarding chlorpyrifos and 

convened its Scientific Advisory Panel (“SAP”) several 

times. Those assessments and SAP reviews increasingly 

recognized the persuasiveness of the studies showing 

chlorpyrifos’s risks. Nevertheless, the EPA declined to take 

final action on the 2007 Petition for more than a decade. 

Eventually, PANNA, NRDC, and others sought judicial 

relief, and this Court issued multiple writs of mandamus 

requiring the EPA to move forward. But, festina lente, the 

EPA continued to delay ruling on the 2007 Petition. This, 

moreover, was despite the fact that in November 2015, the 

EPA published a Notice of Proposed Rulemaking that 

proposed to revoke all chlorpyrifos tolerances because the 

EPA could not find them to be safe. Similarly, in 2016, the 

EPA issued a Revised Human Health Risk Assessment 

1 21 U.S.C. § 346a(b)(2)(A)(i).

2 Id. § 346a(b)(2)(C)(i)–(ii).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 11

finding that the present tolerances are “not sufficiently health 

protective.”3

In 2017, the EPA, pursuant to a court-set deadline, 

finally ruled on the 2007 Petition. But in the very face of its 

own prior acknowledgements of the health risks posed by 

chlorpyrifos, the EPA denied the 2007 Petition, and in 2019 

denied all objections to that decision. In reality, however, 

this was just one more attempt at delay, because the EPA did 

not conclude that the tolerances were safe, but simply denied 

the Petition on the ground that the EPA would forgo further 

consideration of the question of safety until chlorpyrifos 

underwent a registration re-review under a separate statute, 

which could be as late as 2022. As explained below, this 

delay tactic was a total abdication of the EPA’s statutory 

duty under the FFDCA.

In short, the EPA has spent more than a decade 

assembling a record of chlorpyrifos’s ill effects and has

repeatedly determined, based on that record, that it cannot 

conclude, to the statutorily required standard of reasonable 

certainty, that the present tolerances are causing no harm. 

Yet, rather than ban the pesticide or reduce the tolerances to 

levels that the EPA can find are reasonably certain to cause 

no harm, the EPA has sought to evade, through one delaying 

tactic after another, its plain statutory duties. The FFDCA 

permits no further delay. Accordingly, for the reasons that 

follow, the Court grants the petitions for review and orders 

the EPA within 60 days after the issuance of the mandate 

either to modify chlorpyrifos tolerances and concomitantly 

publish a finding that the modified tolerances are safe, 

3 Chlorpyrifos; Tolerance Revocations; Notice of Data Availability 

and Request for Comment, 81 Fed. Reg. 81,049, 81,050 (Nov. 17, 2016) 

(hereinafter “2016 Notice of Data Availability”).
12 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

including for infants and children – or to revoke all 

chlorpyrifos tolerances. The Court also orders the EPA to 

correspondingly modify or cancel related FIFRA 

registrations for food use in a timely fashion consistent with 

the requirements of 21 U.S.C. § 346a(a)(1).

BACKGROUND

I. The EPA’s Duty to Regulate Pesticides

Congress requires the EPA to regulate the use of 

pesticides on food pursuant to the FFDCA. Congress also 

requires the EPA to regulate the use of pesticides more 

generally under the Federal Insecticide, Fungicide and 

Rodenticide Act (“FIFRA”). This case principally concerns 

the FFDCA.

The FFDCA begins with a general rule that food 

containing pesticide residue is unsafe and prohibited.4 

Congress empowered the EPA to make exceptions to that 

rule by promulgating “tolerances” for a pesticide – i.e., 

threshold levels of pesticide residue that the EPA is 

reasonably certain will cause no harm.5

 If the EPA 

promulgates a tolerance for a pesticide, then food may 

contain residue of that pesticide in an amount not exceeding 

the applicable tolerance.

6

The EPA’s discretion to set such tolerances is 

circumscribed, however, by an uncompromisable limitation: 

4 Id. §§ 331, 342(a)(2)(B), 346a(a)(1). The FFDCA applies only to 

food and other products in interstate commerce. See 21 U.S.C. § 331.

5 Id. § 346a(b)(1), (b)(2)(A).

6 Id. § 346a(a)(4).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 13

the pesticide must be determined to be safe for human 

beings. The EPA “may establish or leave in effect a 

tolerance for a pesticide chemical residue in or on a food only

if the Administrator determines that the tolerance is safe.”7 

Furthermore, following enactment of the Food Quality 

Protection Act of 1996 (“FQPA”), it is now clear that the 

EPA must look beyond food to consider all of the ways 

someone might be exposed to a pesticide, “including all 

anticipated dietary exposures and all other exposures for 

which there is reliable information.”8 The EPA can 

determine that a tolerance is safe only if “there is a 

reasonable certainty that no harm will result from aggregate

exposure to the pesticide chemical residue.”9

In addition to requiring this general safety finding, the 

FFDCA also conditions the EPA’s authority to set or leave 

in effect a tolerance on its determination that the tolerance is 

safe for infants and children. “In establishing, modifying, 

leaving in effect, or revoking a tolerance . . . , the 

Administrator . . . shall . . . ensure that there is a reasonable 

certainty that no harm will result to infants and children from 

aggregate exposure to the pesticide chemical residue,” and 

shall “publish a specific determination regarding the safety 

of the pesticide chemical residue for infants and children.”10 

If a tolerance is not safe – in other words, if the EPA cannot 

determine that there is a reasonable certainty of no harm 

across all sources of exposure for infants, children, and 

adults – then the EPA no longer has discretion. Rather, the 

7 Id. § 346a(b)(2)(A)(i) (emphasis added).

8 Id. § 346a(b)(2)(A)(ii).

9 Id. (emphases added).

10 Id. § 346a(b)(2)(C)(ii).
14 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

law commands that the EPA “shall modify or revoke [the] 

tolerance.”11

The FFDCA authorizes “[a]ny person [to] file . . . a 

petition proposing the issuance of a regulation establishing, 

modifying, or revoking a tolerance.”12 The EPA, by 

regulation, may dictate what a petition seeking revocation of 

a tolerance must contain.13 Pursuant to that authority, the 

EPA requires that a petition state “reasonable grounds for the 

action sought,” including “an assertion of facts.”14 If the 

EPA determines that a petition has met the threshold 

requirements, then it must publish the petition within 

30 days.15 “[A]fter giving due consideration to a petition . . .

and any other information available to the Administrator,”

the EPA “shall” do one of three things: “issue a final 

regulation (which may vary from that sought by the petition) 

establishing, modifying, or revoking a tolerance . . . (which 

final regulation shall be issued without further notice and 

without further period for public comment),” “issue a 

proposed regulation . . . and thereafter issue a final 

regulation,” or “issue an order denying the petition.”16 If the 

EPA denies a petition, “any person may file objections 

11 Id. § 346a(b)(2)(A)(i).

12 Id. § 346a(d)(1).

13 Id. § 346a(d)(2)(B).

14 40 C.F.R. § 180.32(b).

15 21 U.S.C. § 346a(d)(3).

16 Id. § 346a(d)(4)(A).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 15

thereto with the Administrator.”17 The Administrator “shall 

issue an order stating the action taken upon each . . .

objection” “[a]s soon as practicable.”18 Those affected may 

seek “judicial review . . . in the United States Court of 

Appeals.”19

Separately, the EPA also regulates pesticides pursuant to 

FIFRA. Under FIFRA, pesticides must be registered by the 

EPA before they can be distributed or sold.20 To register a 

pesticide, the EPA must determine, among other things, that 

it does not have “unreasonable adverse effects on the 

environment.”21 FIFRA defines “unreasonable adverse 

effects” to include “a human dietary risk from residues that 

result from a use of a pesticide in or on any food inconsistent 

with” the standards of the FFDCA.22 In other words, FIFRA 

incorporates the FFDCA safety standard for food uses, 

among other considerations. FIFRA requires the EPA to 

reevaluate pesticides as part of a registration review every 

fifteen years.23

17 Id. § 346a(g)(2)(A).

18 Id. § 346a(g)(2)(C).

19 Id. § 346a(h)(1).

20 See 7 U.S.C. § 136a(a).

21 Id. § 136a(c)(5)(C)–(D).

22 Id. § 136(bb).

23 See id. §§ 136a(c)(1)(F)(iii), (g)(1)(A), 136a-1(a).
16 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

II. This Administrative Proceeding and Related 

Litigation

This administrative proceeding began with the filing of 

the 2007 Petition, which sought revocation of all tolerances 

and registrations for chlorpyrifos. Chlorpyrifos is an 

organophosphate pesticide. Organophosphates were first 

developed as toxic nerve agents for potential use in chemical 

warfare during World War II, and chlorpyrifos was initially 

registered as a pesticide in the United States in 1965. Since 

then, farmers have used chlorpyrifos to protect dozens of 

types of crops. As of 2017, “[b]y pounds of active 

ingredient, it [was] the most widely used conventional 

insecticide in the country.”24 Nevertheless, in 2019, 

California (and the European Union) announced they would 

ban the sale of chlorpyrifos.25

Chlorpyrifos disrupts the functioning of 

acetylcholinesterase (“AChE”), a crucial enzyme that breaks 

down the neurotransmitter acetylcholine.26 In setting 

24 Chlorpyrifos; Order Denying PANNA and NRDC’s Petition to 

Revoke Tolerances, 82 Fed. Reg. 16,581, 16,584 (Apr. 5, 2017) 

(hereinafter “2017 Order”).

25 Press Release, Cal. Env’t Prot. Agency & Cal. Dep’t of Pesticide 

Regul., Agreement Reached to End Sale of Chlorpyrifos in California 

by February 2020 (Oct. 9, 2019), https://www.cdpr.ca.gov/docs/pressrl

s/2019/100919.htm; Stephen Gardner, EU to Ban Chlorpyrifos Pesticide 

Starting in February, Bloomberg L. News (Dec. 6, 2019, 6:43 AM), 

https://news.bloomberglaw.com/environment-and-energy/eu-to-banchlorpyrifos-pesticide-starting-in-february.

26 See EPA, Office of Prevention, Pesticides, and Toxic Substances, 

EPA 738-R-01-007, Interim Reregistration Eligibility Determination for 

Chlorpyrifos 2 (Feb. 2002) (“Chlorpyrifos can cause [AChE] inhibition 

in humans; that is, it can overstimulate the nervous system causing 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 17

chlorpyrifos tolerances, the EPA must determine the greatest 

exposure amount that poses no risk of harm, which is known 

as a “point of departure.” Since enactment of the FQPA, the 

EPA has tied the chlorpyrifos point of departure directly to 

acute AChE inhibition, finding that exposure to chlorpyrifos 

residue on food would be unsafe if aggregate exposure 

across all sources caused more than 10% acute AChE 

inhibition.

However, for decades, the EPA has itself expressed 

concerns that chlorpyrifos might also be causing harm 

through a different mechanism: neurotoxic effects that are 

especially harmful to infants and children.27 The 2007 

Petition was partly based on these concerns. Yet, despite the 

EPA’s expressed concerns, the EPA repeatedly failed to act 

on the 2007 Petition until this Court compelled it to do so. 

The following is a chronological summary both of the EPA’s 

assessment of chlorpyrifos’s safety and of this dispute.

A. 2000–2006: The EPA Finds Certain Chlorpyrifos 

Tolerances Safe, Despite Concerns

Between 2000 and 2006, even before the Petition was 

filed, the EPA began taking steps to reduce exposure to 

chlorpyrifos as part of its reevaluation of chlorpyrifos’s 

safety, as required by the FQPA. The FQPA imposed the 

requirements, still included in the FFDCA today, that the 

nausea, dizziness, confusion, and at very high exposures (e.g., accidents 

or major spills), respiratory paralysis and death.”).

27 This different mechanism of harm might still relate to AChE 

inhibition; the EPA has considered the possibility that chronic AChE 

inhibition at levels of less than 10% might cause permanent damage. 

Herein, unless stated otherwise, AChE inhibition means acute AChE 

inhibition of 10% or more.
18 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

EPA (1) consider proof of safety as an absolute prerequisite 

to establishing or leaving in effect a tolerance, without 

balancing it against other factors; (2) assess a pesticide’s 

cumulative exposure from multiple sources (e.g., drinking 

water as well as food); and (3) specifically assess the 

pesticide’s potential risks to children. The FQPA also 

required the EPA to reassess the safety of all then-authorized 

pesticides using this new standard.

During this period, the EPA began to express concerns 

that chlorpyrifos might be causing harms through a 

mechanism other than AChE inhibition. For example, in a 

2000 Human Health Risk Assessment, the EPA recognized 

that studies had preliminarily shown that AChE inhibition 

might not be the only mechanism of harm.28

The EPA also began acting on its concerns about 

chlorpyrifos safety, in collaboration with the pesticide 

industry. In 2000, the EPA and the chlorpyrifos technical 

registrants entered into an agreement regarding chlorpyrifos 

that eliminated or phased out its use for virtually all 

residential and termiticide purposes, and on tomatoes and, 

during the growing season, grapes and apples.29 In 2002, the 

28 EPA, Office of Pesticide Programs, Human Health Risk 

Assessment-Chlorpyrifos 4 (June 8, 2000), https://archive.epa.gov/scip

oly/sap/meetings/web/pdf/hed_ra.pdf (discussing live animal studies and 

explaining that “new data in the literature also gave rise to uncertainties 

such as the suggestion that the inhibition of [AChE] may not be essential 

for adverse effects on brain development”).

29 Letter to Aaron Colangelo, NRDC, & Margaret Reeves, PANNA, 

from Steven Bradbury, EPA, re: Chlorpyrifos Petition Dated September 

12, 2007 (hereinafter “2007 Petition”), at 6 (July 16, 2012).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 19

EPA announced certain risk mitigation measures, especially 

for people exposed to chlorpyrifos through their work.30

Subject to these changes, however, the EPA determined 

in February 2002, based upon the evidence then available, 

that “[d]ietary exposures from eating food crops treated with 

chlorpyrifos are below the level of concern for the entire 

U.S. population, including infants and children,” and that 

“[d]rinking water risk estimates . . . are generally not of 

concern.”31 The EPA reiterated its safety finding in July 

2006, stating that chlorpyrifos tolerances “meet the safety 

standard under Section 408(b)(2) of the FFDCA.”32

B. 2007: PANNA and NRDC File a Petition to Revoke 

Tolerances, Citing Mounting Evidence of Harm

In September 2007, PANNA and NRDC filed an 

administrative petition with the EPA seeking revocation of 

all chlorpyrifos tolerances under the FFDCA and the 

cancellation of all of chlorpyrifos’s FIFRA registrations. 

The 2007 Petition asserted that scientific evidence now 

available showed that the current chlorpyrifos tolerances 

were not safe, especially for infants and children; indeed, 

they argued, “no safe level of early-life exposure to 

30 Interim Reregistration Eligibility Decision for Chlorpyrifos, supra

note 26.

31 Id. at 2.

32 EPA, Office of Prevention, Pesticides and Toxic Substances, 

Memo to Jim Jones from Debra Edwards, Finalization of Interim 

Reregistration Eligibility Decisions and Interim Tolerance Reassessment 

and Risk Management Decisions for the Organophosphate Pesticides, 

and Completion of the Tolerance Reassessment and Reregistration 

Eligibility Process for the Organophosphate Pesticides 2 (July 31, 2006).
20 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

chlorpyrifos can be supported.”33 They cited “[m]any 

studies published since 2001 [that] report that fetal exposure 

to chlorpyrifos is more damaging than adult exposure.”34

The 2007 Petition relied in part upon certain experiments 

performed on live mice and rats. They were exposed in utero

to levels of chlorpyrifos below those previously known to 

cause AChE inhibition. The scientists found marked 

declines in thinking and movement, indicative of

neurological effects. The declines were sex-linked, harming 

males more than females.

The 2007 Petition also relied upon an epidemiological 

study, known as the “Columbia Study.” Researchers worked 

with a cohort of pregnant women and their children, 

collecting data on the mothers’ organophosphate exposure 

(including chlorpyrifos) during pregnancy, and then 

following the development of the children for many years. 

Some of the participating children were born before the EPA 

and the registrants agreed to end residential use of 

chlorpyrifos, and others were born after. Over time, the 

researchers found a correlation between prenatal 

chlorpyrifos exposure and several negative outcomes:

• at age three, lower performance in motor and mental 

development tests and higher incidences of attentiondeficit hyperactivity disorder and autism spectrum 

disorder;

33 Marc S. Wu et al., NRDC, & Susan E. Kegley, PANNA, Petition 

to Revoke All Tolerances and Registrations for the Pesticide 

Chlorpyrifos 5 (Sept. 12, 2007).

34 Id. at 6.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 21

• at age seven, changes in brain morphology and lower 

IQ scores; and

• at age eleven, a greater likelihood of mild or 

moderate tremors.

Like the live animal experiments, the Columbia Study found 

that in utero exposures were harmful even beneath the levels 

thought to cause notable AChE inhibition and that harms 

were sex-linked, disproportionately affecting boys.

Two other groups of researchers also conducted 

epidemiological studies similar to the Columbia Study (the 

“Mount Sinai Study” and the “CHAMACOS Study”; 

collectively with the Columbia Study, the “Human Cohort 

Studies”). The Mount Sinai and CHAMACOS Studies 

looked at exposure to organophosphate pesticides and, like 

the Columbia Study, found a correlation between prenatal 

organophosphate exposure and cognitive impairments in 

early childhood.35

C. 2008–2011: The EPA Preliminarily Links 

Chlorpyrifos to Neurotoxic Harms in Infants and 

Children

Within a year of the 2007 Petition, the EPA, in August 

2008, published a Science Issue Paper, which reviewed 

existing scientific studies and “preliminarily concluded that 

chlorpyrifos likely played a role” in the low birth rate and 

delays in infant mental development observed in the Human 

35 Although the Mount Sinai Study and the CHAMACOS Study 

were not cited in the 2007 Petition, they later became part of the 

administrative record.
22 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

Cohort Studies.36 The EPA recognized that some of these 

studies found these effects despite lesser AChE inhibition, 

suggesting there was a different mechanism of harm.37 

However, the paper also noted that it was “not a full and 

complete risk assessment/characterization,” and that the 

EPA “ha[d] not developed any final conclusions regarding 

updates to the chlorpyrifos hazard assessment.”38

In September 2008, the EPA convened a committee of 

experts known as a Scientific Advisory Panel (“SAP”) to 

peer-review its findings. The 2008 SAP considered “the 

results of the three [Human Cohort Studies] (with an 

emphasis on the Columbia [S]tudy) . . . along with the 

findings from experimental studies in animals,” and 

concluded that “maternal chlorpyrifos exposure would likely 

be associated with adverse neurodevelopmental outcomes in 

humans.”39 The SAP “agreed with [the EPA’s] conclusion 

that chlorpyrifos likely played a role in the birth and 

neurodevelopmental outcomes noted in the three [Human 

Cohort Studies].”40

36 Health Effects Division, Office of Pesticide Programs, EPA, 

Science Issue Paper: Chlorpyrifos Hazard and Dose Response 

Characterization 52 (Aug. 21, 2008).

37 Id. at 40–41 & fig.5.

38 Id. at 7.

39 SAP Minutes No. 2008-04, A Set of Scientific Issues Being 

Considered by the Environmental Protection Agency Regarding: The 

Agency’s Evaluation of the Toxicity Profile of Chlorpyrifos 13 (Sept. 

16–18, 2008) (hereinafter “2008 SAP Minutes”).

40 Id. at 37.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 23

However, the SAP also posited that the effects might not 

be entirely attributable to chlorpyrifos; rather, they might 

also reflect exposure to other AChE-inhibiting insecticides. 

A majority of SAP members agreed that the adverse 

outcomes of the Columbia Study were concerning, 

especially “in light of evidence demonstrating that low levels 

of exposure to toxicants once thought to have adverse 

neurodevelopmental effects only at high levels (i.e. lead, 

mercury, and PCBs) are now known to produce significant 

effects at lower levels.”41 Nevertheless, the 2008 SAP found 

that the Human Cohort Studies had “utility for risk 

characterization, but not as the principal basis for 

establishing the point of departure.”42

About three years later, in 2011, the EPA published a 

Preliminary Human Health Risk Assessment. The EPA 

discussed the three Human Cohort Studies and noted the 

2008 SAP’s conclusion that those studies, “in concert with 

the animal studies[,] indicate that ‘maternal chlorpyrifos 

exposure would likely be associated with adverse 

41 Id. at 43–44.

42 2007 Petition, supra note 29, at 6–7. The Dissent notes that the 

2008 SAP expressed “concerns that the Columbia Study—the most 

robust of the three—did not provide sufficient data to be the sole factor

for risk assessment or modifying tolerances and produced uncertainty 

through its measurement method.” Dissent, infra, at 91. In fact, 

although the 2008 SAP recognized that “there were limitations . . . that 

precluded [the Human Cohort Studies] from being used to directly derive 

the [point of departure] or the uncertainty factor,” it also concluded that 

the Columbia Study “could be used to determine bounding values for the 

levels of chlorpyrifos that might cause a measurable effect.” 2008 SAP 

Minutes, supra note 39, at 46. Thus, even as early as 2008, the SAP 

recognized the utility of the Columbia Study for risk assessment.
24 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

neurodevelopmental outcomes in humans.’”43 While the 

Preliminary Human Health Risk Assessment asserted that 

the EPA could not yet identify the mechanism of action for 

neurotoxic harm, nevertheless, it viewed the Human Cohort 

Studies favorably, describing the Columbia Study as a 

“natural experiment” since some participants were pregnant 

before the EPA banned residential use of chlorpyrifos and 

some were pregnant after the ban.44 The EPA “intend[ed] to 

carefully consider the strengths and limitations of the 

epidemiology studies along with the available empirical data 

in a full weight of evidence analysis in the final [Human 

Health Risk Assessment].”45 Thus, while the EPA continued 

to use 10% AChE inhibition to set a point of departure, it 

explained that “ongoing analyses will ensure that [the points 

of departure] in [its] preliminary assessment are [also] 

human health protective for neurodevelopmental toxicity 

that may arise from pre- or postnatal exposure.”46

43 Memo from Danette Drew et al. to Tom Myers re: Chlorpyrifos: 

Preliminary Human Health Risk Assessment for Registration Review, 

EPA, at 28 (June 30, 2011).

44 Id. at 31.

45 Id. at 34.

46 Id. at 42.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 25

D. 2012–2015: The EPA Expresses Increasing 

Certainty That Chlorpyrifos Causes Neurotoxic 

Effects in Infants and Children

In April 2012, having received no response from the 

EPA on the pertinent arguments raised in the 2007 Petition,47

PANNA and NRDC petitioned this Court for a writ of 

mandamus.

Meanwhile, also in April 2012, the EPA convened 

another SAP. The 2012 SAP opined with more certainty 

than the 2008 SAP that multiple “lines of evidence suggest 

that chlorpyrifos can affect neurodevelopment at levels 

lower than those associated with AChE inhibition, and that 

the use of AChE inhibition data may not be the most 

appropriate for . . . [assessing] the neurodevelopmental risks 

of chlorpyrifos.”48 The 2012 SAP paid particular attention 

to the Human Cohort Studies and identified “nine strengths”

of them, including, among others, the longitudinal design, 

the use of biomarkers of exposure (rather than only selfreported exposure), and “the relative consistency of findings 

in different populations while using similar standardized 

exposure and outcome measures.”49 The 2012 SAP also 

identified some shortcomings of the Human Cohort Studies, 

such as a relatively small sample size and uncertainty 

47 The 2007 Petition raised several other claims, some of which the 

EPA addressed at earlier points in time, but here petitioners only press 

the claims related to neurotoxic effects.

48 SAP Minutes No. 2012-04, A Set of Scientific Issues Being 

Considered by the Environmental Protection Agency Regarding 

Chlorpyrifos Health Effects 53 (Apr. 10–12, 2012) (hereinafter “2012 

SAP Minutes”).

49 Id. at 18.
26 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

regarding whether harms could be attributed to chlorpyrifos 

alone. Overall, though, it found that “[t]he strengths of the 

three studies support the Panel’s conclusion.”50

Specifically, the 2012 SAP, based on its review of all the 

evidence available at the time, “concur[red] with the 2008 

SAP and the Agency in concluding that chlorpyrifos likely 

plays a role in impacting the neurodevelopmental outcomes 

examined in the three cohort studies.”51 It noted that the 

Human Cohort Studies showed potentially serious harms to 

infants and children, including “abnormal reflexes in the 

newborn, pervasive development disorder at 24 or 

36 months, mental development at 7–9 years, and attention 

and behavior problems at 3 and 5 years of age.”52

Despite all this, the EPA, following issuance of the 2012 

SAP report, still did not take final action on the 2007 

Petition; but it represented in the mandamus proceedings that 

it had “a concrete timeline for final agency action that would 

resolve the 2007 Petition by February 2014.”53 In light of 

that representation, this Court, in July 2013, denied PANNA 

and NRDC’s petition for a writ of mandamus.

February 2014 came and went, but the EPA did not take 

final action on the 2007 Petition. PANNA and NRDC 

50 Id.

51 Id.

52 Id. at 17.

53 PANNA v. EPA (In re PANNA), 532 F. App’x 649, 651 (9th Cir. 

2013).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 27

returned to this Court in September 2014 with a second 

petition for a writ of mandamus.

Shortly thereafter, in December 2014, the EPA published 

a Revised Human Health Risk Assessment. It expressed 

greater certainty both that chlorpyrifos was causing the 

neurotoxic harms seen in the cohort studies and that it was 

doing so through a mechanism other than AChE inhibition.54

Because the EPA concluded that chlorpyrifos could 

cause harm even if exposure was below the AChE 

inhibition-related point of departure, the EPA proposed a 

new method for calculating a point of departure. But with 

all this, the EPA still did not act on the 2007 Petition.

In August 2015, this Court therefore granted the second 

mandamus petition.55 The EPA had offered an “ambiguous 

plan to possibly issue a proposed rule nearly nine years after 

receiving the administrative petition,” and the Court found 

this to be “too little, too late.”56 The Court found the EPA’s 

delay “egregious” and ordered the EPA “to issue a full and 

54 Memo from Danette Drew et al. to Tom Myers et al. re: 

Chlorpyrifos: Revised Human Health Risk Assessment for Registration 

Review, EPA (Dec. 29, 2014) (hereinafter “2014 Revised Human Health 

Risk Assessment”), at 43 (“[C]hlorpyrifos likely played a role in the 

neurodevelopmental outcomes observed in these epidemiology 

studies.”); id. at 46 (“[The] EPA believes it is unlikely mothers enrolled 

in the [Human Cohort Studies] experienced [red blood cell] AChE 

inhibition”); see also id. (“Given the differences across laboratory 

animal and epidemiology studies, the qualitative similarity in research 

findings is striking.”).

55 PANNA v. EPA (In re PANNA), 798 F.3d 809, 811 (9th Cir. 2015).

56 Id.
28 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

final response to the petition no later than October 31,

2015.”57

E. 2015–2016: The EPA Finds That Chlorpyrifos 

Tolerances Are Unsafe

Once again, this Court’s deadline came and went, and the 

EPA still did not take final action on the 2007 Petition. But 

in November 2015, the EPA published in the Federal 

Register a Notice of Proposed Rulemaking “proposing to 

revoke all tolerances for residues of the insecticide 

chlorpyrifos.”58 It wrote: “The agency is proposing to 

revoke all of these tolerances because [the] EPA cannot, at 

this time, determine that aggregate exposure to residues of 

chlorpyrifos, including all anticipated dietary exposures and 

all other non-occupational exposures for which there is 

reliable information, are safe.”59 Specifically, the EPA 

found that “contributions to dietary exposures to 

chlorpyrifos from food and residential exposures are safe,”

but “when those exposures are combined with estimated 

exposures from drinking water, as required by the FFDCA,

. . . safe levels of chlorpyrifos in the diet may be exceeded 

for people whose drinking water is derived from certain 

vulnerable watersheds throughout the United States.”60

57 Id.

58 Chlorpyrifos; Tolerance Revocations, 80 Fed. Reg. 69,080, 

69,081 (Nov. 6, 2015) (hereinafter “2015 Notice of Proposed 

Rulemaking”).

59 Id.

60 Id.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 29

The EPA adhered to the findings of the 2014 Revised 

Human Health Risk Assessment. It relied upon “a 

considerable and still-growing body of literature on the 

effects of chlorpyrifos on the developing brain of laboratory 

animals (rats and mice) indicating that gestational and/or 

postnatal exposure may cause persistent behavioral effects 

into adulthood.”61 It also relied upon the three Human 

Cohort Studies:

[The] EPA has considered the strengths and 

limitations of these studies, and believes that 

random or systematic errors in the design, 

conduct or analysis of these studies were 

unlikely to fully explain observed positive 

associations between in utero

[organophosphate] exposure and adverse 

neurodevelopmental effects observed at birth 

and through childhood (age 7 years). [The] 

EPA believes these are strong studies which 

support a conclusion that [organophosphates] 

likely played a role in these outcomes.62

The EPA acknowledged “significant uncertainties . . . about 

the actual exposure levels experienced by mothers and infant 

participants in the three children’s health cohorts,” but found 

that the measured exposures “are likely low enough that they 

were unlikely to have resulted in AChE inhibition.”63

61 Id. at 69,090.

62 Id. at 69,091.

63 Id. at 69,093.
30 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

Since, however, the proposed rule did not constitute a 

final response to the 2007 Petition, this Court, in December 

2015, ordered the EPA “to take final action by December 30, 

2016 on its proposed revocation rule and its final response 

to . . . [the] 2007 [P]etition.”64 In other words, this Court, 

despite the EPA’s repeated disregard of this Court’s orders, 

most leniently gave the EPA yet another year to rule on the 

2007 Petition.

In April 2016, the EPA convened another SAP, which 

peer-reviewed the 2014 Revised Human Health Risk 

Assessment. The 2016 SAP “agree[d] that both 

epidemiology and toxicology studies suggest there is 

evidence for adverse health outcomes associated with 

chlorpyrifos exposures below levels that result in 10% red 

blood cell [AChE] inhibition.”65

However, the 2016 SAP disagreed with the EPA’s 

method for calculating a new point of departure. 

Specifically, “with the exception of one Panel member, the 

Panel stated that using [umbilical] cord blood chlorpyrifos 

concentrations for derivation of the [point of departure] 

could not be justified by any sound scientific evaluation.”66 

“Many Panel members” also objected to the specific 

threshold of harm that the EPA used to replace 10% AChE 

inhibition – a 2% decline in working memory – saying that 

64 PANNA v. EPA (In re PANNA), 808 F.3d 402 (9th Cir. 2015).

65 SAP Minutes No. 2016-01, A Set of Scientific Issues Being 

Considered by the Environmental Protection Agency Regarding: 

Chlorpyrifos: Analysis of Biomonitoring Data 18 (Apr. 19–21, 2016) 

(hereinafter “2016 SAP Minutes”).

66 Id. at 26.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 31

such a change in working memory was “of questionable 

biological significance.”67

On the other hand, the 2016 SAP explained that, in 

general, it “support[ed] the use of measured maternal 

chlorpyrifos blood concentrations as a surrogate for fetal 

exposure . . . .”68 And the SAP offered some guidance on 

how to proceed. “Multiple panel members noted that 

[physiologically based pharmacokinetic (“PBPK”)] 

modeling is a valuable tool,”69 and the SAP recommended 

that the EPA “consider determination and characterization 

of time-weighted average blood concentrations for different 

exposure scenarios,”70 rather than measurements based upon 

umbilical cord blood concentrations at a single point in time.

The EPA returned to this Court in June 2016, claiming 

that it once again could not meet the much-extended 

deadline for final action on the 2007 Petition. In August 

2016, the Court denied the EPA’s request for an additional 

six months.71 The Court did, however, grant the EPA a 

three-month extension, to March 31, 2017. The Court 

acknowledged that “evidence may be imperfect . . . [,] the 

feasibility inquiry is formidable, and . . . premature 

rulemaking is undesirable,” but the Court found that “at this 

stage, a claim of premature rulemaking has come and 

67 Id. at 27.

68 Id. at 18.

69 Id.

70 Id. at 70.

71 NRDC v. EPA (In re PANNA), 840 F.3d 1014, 1015 (9th Cir. 

2016).
32 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

gone.”72 The Court warned that this was “the final 

extension” and that the Court would “not grant any further 

extensions.”73

In November 2016, the EPA revised its Human Health 

Risk Assessment again. The 2016 Revised Human Health 

Risk Assessment remains the EPA’s most recent 

comprehensive assessment of the risks of chlorpyrifos. In 

the assessment, the EPA “continue[d] to conclude that the 

[Human Cohort Studies] provide the most robust available 

epidemiological evidence.”74 The EPA “acknowledge[d] 

the lack of [an] established” mechanism of action that would 

explain the neurotoxic effects and also recognized “the 

inability to make strong causal linkages, and the unknown 

window(s) of susceptibility.”75 The EPA concluded, 

nevertheless, that “[t]hese uncertainties do not undermine or 

reduce the confidence in the findings of the epidemiology 

studies. The epidemiology studies . . . represent different 

investigators, locations, points in time, exposure assessment 

procedures, and outcome measurements.”76 “In summary,”

the EPA concluded that “the [Columbia Study], with 

supporting results from the other [two Human Cohort 

Studies] and the seven additional epidemiological studies 

72 Id. (quoting Public Citizen Health Rsch. Grp. v. Chao, 314 F.3d 

143, 154–55 (3d Cir. 2002)).

73 Id.

74 Memo from Wade Britton to Dana Friedman re: Chlorpyrifos: 

Revised Human Health Risk Assessment for Registration Review, EPA 

(Nov. 3, 2016) (hereinafter “2016 Revised Human Health Risk 

Assessment”), at 12.

75 Id.

76 Id.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 33

reviewed in 2015, provides sufficient evidence that there are 

neurodevelopmental effects occurring at chlorpyrifos 

exposure levels below that required for AChE inhibition.”77 

Based on this finding, the EPA continued to conclude that it 

was necessary to adopt an approach “protective of both the 

AChE inhibition and any adverse effects that could occur at 

lower doses.”78

The EPA acknowledged that “the 2016 SAP did not 

support using the [Columbia Study] cord blood” to derive a 

new point of departure.79 Responsive to those comments, 

the EPA adopted a different approach.80 It accepted the 2016 

SAP’s statement that the “EPA should use estimated peak 

blood concentrations or [time-weighted average] blood 

concentrations within the prenatal period” rather than 

umbilical cord blood concentrations at the time of delivery.81 

Also, consistent with the 2016 SAP’s comments, the EPA 

77 Id. at 13.

78 Id.

79 Id.

80 Id. at 4 (“Given that the window(s) of susceptibility are currently 

not known for the observed neurodevelopmental effects, and the 

uncertainties associated with quantitatively interpreting the [Columbia 

Study] cord blood data, the SAP recommended that the agency use a time 

weighted average . . . blood concentration of chlorpyrifos for the 

[Columbia] [S]tudy cohort as the [point of departure] for risk assessment. 

[The] EPA has chosen to follow that advice in this assessment.”).

81 Id. at 14.
34 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

estimated blood concentrations using a PBPK model devised 

by a chlorpyrifos registrant.82

When the EPA compared the resulting safety thresholds 

against typical pesticide exposure scenarios, it determined 

that chlorpyrifos tolerances were not safe – even considering 

food alone, without aggregating other exposure sources, like 

drinking water.83 For example, the EPA found that expected 

food exposure for children 1–2 years of age was 14,000% of 

the threshold level of risk concern.84

The EPA announced the findings of the 2016 Revised 

Human Health Risk Assessment through a Notice of Data 

Availability published in the Federal Register,85 and it 

reopened the comment period on its 2015 Notice of 

Proposed Rulemaking. In the Notice of Data Availability, 

the EPA reiterated that the present tolerances are “not 

82 Id.

83 Id. at 24.

84 Id. at 6.

85 2016 Notice of Data Availability, supra note 3, 81 Fed. Reg. at 

81,050 (“After careful consideration of public comments and the SAP’s 

recommendations, [the] EPA has concluded the most appropriate path 

for reconciling the SAP’s concerns is to follow through on the SAP’s 

recommendation to use a time weighted average approach. The agency 

agrees with the 2016 FIFRA SAP (and previous SAPs) that there is a 

potential for neurodevelopmental effects associated with chlorpyrifos 

exposure to occur at levels below 10% RBC AChE inhibition, and that 

[the] EPA’s existing point of departure (which is based on 10% AChE 

inhibition), is therefore not sufficiently health protective.”).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 35

sufficiently health protective.”86 The Agency explained that 

its

revised analyses do not result in a change to 

the EPA’s proposal to revoke all tolerances 

but it does modify the methods and risk 

assessment used to support that finding in 

accordance with the advice of the SAP. The 

revised analysis indicates that expected 

residues of chlorpyrifos on most individual 

food crops exceed the ‘reasonable certainty 

of no harm’ safety standard under the 

[FFDCA].

The EPA adhered to its proposal to revoke chlorpyrifos 

tolerances, rather than modify them, explaining that the 

“EPA has not identified a set of currently registered uses that 

meets the FFDCA safety standard because it is likely only a 

limited number of food uses alone, and in combination with 

predicted drinking water exposures, would meet the 

standard.”87 The EPA has never retracted the findings in its 

2016 Revised Human Health Risk Assessment.88

86 Id.

87 Id.

88 Today, the EPA’s website continues to warn about chlorpyrifos, 

citing the 2016 Revised Human Health Risk Assessment:

What does [the] EPA’s revised human health risk 

assessment show?

This assessment shows dietary and drinking water 

risks for the current uses of chlorpyrifos. Based on 
36 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

F. 2017–Present: The EPA Denies the 2007 Petition

Faced with this Court’s statement that it would brook no 

further delays in the EPA’s ruling on the 2007 Petition, the 

EPA finally in April 2017 ruled on the 2007 Petition. 

Notwithstanding the findings in its own 2016 Revised 

Human Health Risk Assessment, however, the EPA’s order 

denying the 2007 Petition (the “2017 Order”) stated that, 

“despite several years of study, the science addressing 

neurodevelopmental effects remains unresolved.”89 

Therefore, the EPA concluded that “further evaluation of the 

science during the remaining time for completion of 

[FIFRA] registration review is warranted to achieve greater 

certainty as to whether the potential exists for adverse 

neurodevelopmental effects to occur from current human 

exposures to chlorpyrifos.”90

current labeled uses, the revised analysis indicates that 

expected residues of chlorpyrifos on food crops 

exceed the safety standard under the [FFDCA]. In 

addition, the majority of estimated drinking water 

exposure from currently registered uses, including 

water exposure from non-food uses, continues to 

exceed safe levels . . . .

EPA, Revised Human Health Risk Assessment on Chlorpyrifos, 

available at https://www.epa.gov/ingredients-used-pesticideproducts/revised-human-health-risk-assessment-chlorpyrifos (last 

accessed Apr. 17, 2021).

89 2017 Order, supra note 24, 82 Fed. Reg. at 16,583.

90 Id.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 37

The EPA further explained that it was denying the 2007 

Petition only because this Court had ordered it to make a 

decision, but that

[the] EPA has . . . concluded that it will not 

complete the human health portion of the 

registration review or any associated 

tolerance revocation of chlorpyrifos without 

first attempting to come to a clearer scientific 

resolution . . . . Because the [Ninth] Circuit’s 

August 12, 2016 order has made clear, 

however, that further extensions to the March 

31, 2017 deadline for responding to the 

Petition would not be granted, [the] EPA is 

today also denying all remaining petition 

claims.

PANNA, NRDC, and others objected to the EPA’s 

denial of the 2007 Petition, both by filing objections with the 

EPA and by seeking relief from this Court. The Court denied 

mandamus relief on the ground that the EPA had “now 

complied with our orders” to issue a decision, and 

“substantive objections must first be made through the 

administrative process.”91

But even though the statute required the EPA to rule on 

petitioners’ objections “[a]s soon as practicable after 

receiving the arguments of the parties,” 21 U.S.C. 

§ 346a(g)(2)(C), and even though these objections were 

simply reiterations of the positions petitioners had 

consistently taken since 2007, the EPA had still not 

responded to petitioners’ objections 14 months later, when 

91 PANNA v. EPA (In re PANNA), 863 F.3d 1131, 1132 (9th Cir. 

2017).
38 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

the Court heard oral argument on petitioners’ petition for 

review of the 2017 Order.

The EPA objected to this Court’s consideration of the 

merits of the decision on the ground that, until the EPA ruled 

on petitioners’ administrative objections, this Court lacked 

jurisdiction. A panel of this Court concluded that “the EPA 

is engaging in yet more delay tactics to avoid our reaching 

the merits of . . . whether chlorpyrifos must be banned from 

use on food products because the EPA has not determined 

that there is a ‘reasonable certainty’ that no harm will result 

from its use, even under the established tolerances.”92 The 

panel held that, under these circumstances, the Court had 

jurisdiction and that, on the merits, “the EPA bears a 

continuing obligation to revoke tolerances that it can no 

longer find with a ‘reasonable certainty’ are safe,” and 

because the Agency could not make such a finding, the 

tolerance must be revoked.93 The panel vacated the 2017 

Order and remanded to the EPA with instructions to revoke 

all chlorpyrifos tolerances within 60 days after issuance of 

the mandate.94

Subsequently, however, a majority of nonrecused active 

judges voted to rehear the case en banc. The en banc Court 

did not address the jurisdictional question, but instead issued 

a writ of mandamus requiring the EPA to rule on the 

objections to the 2017 Order within 90 days.95 In July 2019, 

92 LULAC v. Wheeler, 899 F.3d 814, 827 (9th Cir. 2018), vacated on 

reh’g en banc, 914 F.3d 1189 (9th Cir. 2019).

93 Id. at 829.

94 Id.

95 LULAC v. Wheeler, 922 F.3d 443, 445 (9th Cir. 2019) (en banc).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 39

the EPA issued a final order (the “2019 Order”) denying 

petitioners’ objections and thereby completing the 

administrative denial of the 2007 Petition. The 2019 Order 

again relied upon the need for greater scientific certainty, but 

went further and held that “the objections and the underlying 

Petition are not supported by valid, complete, and reliable 

evidence sufficient to meet the Petitioners’ burden under the 

FFDCA, as set forth in [the] EPA’s implementing 

regulations.”96

With the Court’s jurisdiction now clear, petitioners 

petitioned for review of the 2017 and 2019 Orders. Several 

states moved to intervene. The en banc Court granted the 

motion to intervene, consolidated the cases, and returned the 

matter to this panel as a “comeback case.”97

STANDARD OF REVIEW

The Administrative Procedure Act (“APA”) authorizes 

the Court to “hold unlawful and set aside agency action, 

findings, and conclusions” if they are “arbitrary, capricious, 

an abuse of discretion, or otherwise not in accordance with 

law,”98 and to “compel agency action unlawfully withheld 

or unreasonably delayed.”99 Agency action is arbitrary and 

capricious where the agency has “offered an explanation for 

96 Chlorpyrifos; Final Order Denying Objections to March 2017 

Petition Denial Order, 84 Fed. Reg. 35,555, 35,557 (July 24, 2019) 

(hereinafter “2019 Order”).

97 LULAC v. Wheeler, 940 F.3d 1126, 1126–27 (9th Cir. 2019) (en 

banc); see 9th Cir. Gen. Order 3.6(b).

98 5 U.S.C. § 706(2)(A).

99 Id. § 706(1).
40 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

its decision that runs counter to the evidence before the 

agency.”100

ANALYSIS

I. Merits

The Court first considers whether the EPA lawfully

denied the 2007 Petition. Petitioners argue that the EPA’s 

2017 and 2019 Orders were ultra vires under the FFDCA 

and arbitrary and capricious under the APA.

A. Whether the EPA Left in Effect a Tolerance Without 

Determining That It Is Safe

As noted above, the FFDCA provides that the EPA “may 

establish or leave in effect a tolerance for a pesticide 

chemical residue in or on a food only if the Administrator 

determines that the tolerance is safe. The Administrator 

shall modify or revoke a tolerance if the Administrator 

determines it is not safe.”101 The statute also specifically 

requires that the EPA “ensure that there is a reasonable 

certainty that no harm will result to infants and children from 

aggregate exposure to the pesticide chemical residue” and 

“publish a specific determination regarding the safety of the 

pesticide chemical residue for infants and children.”102

Courts “normally interpret[] a statute in accord with the 

ordinary public meaning of its terms at the time of its 

100 Motor Vehicle Mfrs. Ass’n of the U.S., Inc. v. State Farm Mut. 

Auto. Ins. Co., 463 U.S. 29, 43 (1983).

101 21 U.S.C. § 346a(b)(2)(A)(i).

102 Id. § 346a(b)(2)(C)(ii)(I)–(II).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 41

enactment.”103 Furthermore, the FFDCA must be “given a 

liberal construction consistent with the Act’s overriding 

purpose to protect the public health.”104

The EPA admits that the 2017 and 2019 Orders left in

effect tolerances without determining that they are safe, 

claiming that it could delay this determination for several 

more years until it had resolved safety-related issues in the 

15-year FIFRA registration review. Since, as discussed 

below, the EPA’s duty to engage in a periodic FIFRA 

registration review is separate from its continuous obligation 

to ensure safety under the FFDCA, this concession is 

effectively dispositive in favor of petitioners.

FIFRA aside, the EPA argues that it may leave in effect

tolerances, without a new safety finding, “when [the] EPA 

concludes the petition contains insufficient evidence for 

[the] EPA to undertake proceedings to revoke or modify 

tolerances.” This argument fails for two reasons. First, once 

the EPA has become aware, through a petition or otherwise, 

of genuine questions about the safety of an existing 

tolerance, the EPA has its own continuing duty under the 

FFDCA to determine whether a tolerance that was once 

thought to be safe still is, and here the EPA’s own studies 

and pronouncements still in effect show that it regards 

chlorpyrifos as harmful at levels below the existing 

tolerances. Second, in any case, the 2007 Petition, under the 

EPA’s own regulations, contained more than sufficient 

evidence to undertake a safety review, and the EPA 

recognized as much, began such a review, and only now, 

103 Bostock v. Clayton County, 140 S. Ct. 1731, 1738 (2020).

104 United States v. An Article of Drug . . . Bacto-Unidisk, 394 U.S. 

784, 798 (1969).
42 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

13 years later, claims for the first time that the 2007 Petition 

was somehow inadequate.

1. The EPA’s Duty to Ensure Human Safety

The FFDCA imposes a continuous duty upon the EPA 

by permitting it to “leave in effect” a tolerance “only” if it 

finds it is safe. To “leave” something in effect means “to 

cause or allow [it] to be or remain in a specified 

condition.”105 Denying the 2007 Petition caused the 

chlorpyrifos tolerances to remain in place; as the EPA itself 

wrote in its brief, it “le[ft] the existing tolerances in place 

pending . . . registration review.” But in so doing, the EPA 

did not “determine[] that the tolerance is safe.”106 Rather, 

the EPA’s own pronouncements show that it has already 

concluded that it can no longer be reasonably certain that 

chlorpyrifos is safe at current tolerances.

It should be noted in this respect that, because of the 

FQPA, assurance of safety for human health is the primary 

issue the EPA must consider. Before 1996, when Congress 

unanimously passed the FQPA, the EPA interpreted the 

FFDCA to permit the balancing of safety against other 

considerations, such as economic factors. Congress was 

105 Merriam Webster, “Leave,” available at https://www.merriamwebster.com/dictionary/leave (last accessed Apr. 17, 2021). The Dissent 

quibbles with our use of the dictionary, arguing that the phrase “leave in 

effect” is unambiguous. But then the Dissent ascribes to that term a 

meaning of the Dissent’s own creation: that the EPA leaves in effect a 

tolerance only when it conducts FIFRA registration review. The statute 

imposes no such limitation on the phrase.

106 21 U.S.C. § 346a(b)(2)(A)(i).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 43

aware of this,107 and the FQPA largely abrogated that 

approach.108 Congress made the explicit decision to 

prioritize safety over all else. This makes the FFDCA a 

remedial statute, which, as noted, must be “given a liberal 

construction consistent with the Act’s overriding purpose to 

protect the public health.”109 Reading the EPA’s duty 

narrowly would undermine the statute’s health-protective 

purpose.

The EPA argues that one of Congress’s purposes was to 

provide the EPA with regulatory discretion. The EPA points

to the fifteen-year registration review cycle under FIFRA110

as evidence that “Congress recognized that [reregistration] 

would be a complex and potentially burdensome 

proceeding”; thus, by contrast, Congress must have intended 

“a different” – and less burdensome – obligation “[w]hen 

[the] EPA responds to a petition to revoke pesticide 

tolerances” under the FFDCA. This contention is 

unpersuasive because of the differences between FIFRA and 

107 H.R. Rep. No. 104-669, pt. 2, at 40 (1996) (noting that under the 

prior procedure for setting tolerances, the EPA was authorized to 

consider “factors including the necessity for production of an adequate, 

wholesome, and economical food supply”).

108 Notwithstanding the safety standard, in certain circumstances the 

EPA may leave a tolerance in effect if “[u]se of the pesticide chemical

. . . is necessary to avoid a significant disruption in domestic production 

of an adequate, wholesome, and economical food supply.” 21 U.S.C. 

§ 346a(b)(2)(B)(iii)(II). However, this is permitted only where the risk 

of harm from a “nonthreshold effect,” such as cancer, is not significantly 

greater than would be allowed for threshold effects. See id.

§ 346a(b)(2)(B)(iv). Nonthreshold effects are not at issue here.

109 Bacto-Unidisk, 394 U.S. at 798.

110 See 7 U.S.C. § 136a(g)(1)(A)(iii)–(iv).
44 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

the FFDCA. The statutes impose different duties that require 

different assessments. Under FIFRA, the EPA has a 

discretionary power to cancel registrations for a variety of 

reasons.111 Specifically, FIFRA requires the EPA to balance 

several factors in determining whether a pesticide should be 

registered. For example, although FIFRA review includes 

an assessment of safety under the FFDCA,112 it also requires 

a more general assessment of a pesticide’s “economic, 

social, and environmental costs and benefits,”113 including 

“the impact of [any proposed] action . . . on production and 

prices of agricultural commodities, retail food prices, and 

otherwise on the agricultural economy.”114 Given these 

differences, Congress’s decision to give the EPA discretion 

to set FIFRA priorities does not translate to the FFDCA. The 

EPA’s obligations under the FFDCA are linked to a single 

issue, safety, but they are mandatory.115 The whole point of 

the FQPA would be destroyed if the EPA could exercise 

unfettered discretion to defer safety considerations until it 

111 7 U.S.C. § 136d(b).

112 See id. § 136(bb). The Dissent accuses us of “repeatedly 

miss[ing] this point,” Dissent, infra, at 83 n.6, but the fact that FIFRA 

reregistration review includes, as one component, an assessment of 

safety under the FFDCA does not gainsay the many other factors FIFRA 

review also encompasses. FIFRA’s wider scope justifies that statute’s 

periodic rereview timeline and the greater agency discretion that 

approach entails. By contrast, the FFDCA’s singular focus on safety 

corresponds with the EPA’s continuous duty to leave in effect a tolerance 

only if it finds that the tolerance is safe.

113 7 U.S.C. § 136(bb).

114 Id. § 136d(b).

115 See 21 U.S.C. § 346a(b)(2)(A)(i) (“The Administrator shall

modify or revoke [an unsafe tolerance].” (emphasis added)).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 45

was prepared to engage in the full multi-factor balancing 

assessment required for FIFRA registration.

Our dissenting colleague reaches a different conclusion 

regarding the EPA’s obligations, or lack thereof, when 

confronted with a petition for revocation of tolerances. The 

Dissent focuses upon two sentences in the FFDCA:

The Administrator may establish or leave in 

effect a tolerance for a pesticide chemical 

residue in or on a food only if the 

Administrator determines that the tolerance is 

safe. The Administrator shall modify or 

revoke a tolerance if the Administrator 

determines it is not safe.116

We think that these two simple sentences are – with their 

emphasis on the word “only” – remarkably straightforward. 

As here explained, they mean that the EPA can lawfully 

deny the 2007 Petition and thereby “leave in effect” a 

tolerance “only if the Administrator determines that the 

tolerance is safe.” The Dissent’s more strained reading of 

these sentences is to the effect that there are three possible 

scenarios, one in which the EPA “determines that a tolerance 

is safe,” one in which the EPA “determines it is not safe,”

and one in which the EPA is unwilling or unable to make a 

safety determination at this time. In this latter, middle world, 

the Dissent continues, the statute is silent as to the EPA’s 

obligations, leaving the EPA with the discretion to leave in 

116 Id. The EPA and the Dissent also contend that our reading 

renders the second sentence superfluous, but it does not. The second 

sentence limits the EPA’s discretion by explaining that when it finds that 

a tolerance is not safe, it may not, for example, convene a SAP or wait 

15 years pending further research; its only options are to revoke or 

modify the tolerance.
46 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

effect a tolerance based on its prior safety finding (here, the 

2006 safety finding).

One problem (among others) with the Dissent’s 

imaginative reading is that other statutory provisions are not 

silent. The FFDCA imposes an overarching obligation that 

the EPA protect human safety, and particularly the safety of 

infants and children:

In establishing, modifying, leaving in effect, 

or revoking a tolerance or exemption for a 

pesticide chemical residue, the Administrator 

shall assess the risk of the pesticide chemical 

residue . . . and shall ensure that there is a 

reasonable certainty that no harm will result 

to infants and children from aggregate 

exposure to the pesticide chemical residue.117

Congress has excluded the middle, not this Court. The 

EPA can only lawfully take agency action to establish or 

leave in effect a tolerance (e.g., denying the 2007 Petition) if 

the EPA finds that the tolerance is safe.

2. The Burdens of Production and Persuasion

The EPA claims that the issue of safety as it bears on an 

existing tolerance need not be addressed unless a petitioner 

meets a threshold burden to come forward with evidence that 

the existing tolerance is unsafe. In this regard, the EPA 

points to the fact that the FFDCA gives the EPA the 

authority to “establish the requirements for information and 

117 21 U.S.C. § 346a(b)(2)(C) (punctuation and section lettering 

omitted).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 47

data to support a petition to modify or revoke a tolerance.”118 

In a regulation promulgated pursuant to that authority, the 

EPA requires such a petition to “furnish reasonable grounds 

for the action sought.”119 Reasonable grounds “include . . .

an assertion of facts (supported by data if available) showing

. . . that new data are available as to toxicity of the chemical, 

or that experience with the application of the tolerance . . .

may justify its modification or revocation.”120

We do not doubt that the EPA has gatekeeping authority 

to reject a wholly frivolous petition – i.e., a petition that fails 

even to “furnish reasonable grounds for the action sought” –

without publishing a notice of its filing if the petition is 

deficient on its face, and in such circumstances we can 

assume the EPA need not address the concerns raised by the 

petition. But the record here unequivocally shows both that 

the 2007 Petition met all relevant requirements and that, in 

fact, it caused the EPA to re-evaluate the safety of the 

chlorpyrifos tolerances, thus triggering the EPA’s duty to 

ensure a reasonable certainty of no harm.

The FFDCA requires the EPA to determine whether a 

petition satisfies the threshold requirements prior to 

publishing a notice of the filing of the petition.121 Here, the 

EPA published a notice of the filing of the 2007 Petition in 

118 21 U.S.C. § 346a(d)(2)(B).

119 40 C.F.R. § 180.32(b).

120 Id.

121 See 21 U.S.C. § 346a(d)(3) (“A notice of the filing of a petition 

that the Administrator determines has met the [data and information] 

requirements . . . shall be published by the Administrator within 30 days 

after such determination.” (emphasis added)).
48 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

October 2007,122 thereby finding that it met the data and 

information requirements in the FFDCA and the EPA’s 

regulations promulgated thereunder. The EPA cannot now 

be heard, more than a dozen years later, to claim that the 

petition did not, in fact, meet those threshold requirements.

Independently, even if the EPA had raised this issue 

thirteen years ago when the 2007 Petition was filed, the EPA 

offers no specific way in which the petition failed to comply 

with the EPA’s technical requirements and no plausible 

argument for why the 2007 Petition does not contain 

“reasonable grounds” for revocation. The EPA points to the 

continued scientific uncertainty regarding how chlorpyrifos 

harms infants and children and the fact that the 2007 Petition 

did not attach complete underlying data for the studies that 

it cited. But the regulation does not say that the petition must 

prove that revocation is required; it requires only that the 

petition state “reasonable grounds” for revocation. And the 

grounds listed in the 2007 Petition meet any definition of 

“reasonable”; indeed, the EPA has implicitly acknowledged 

as much by reacting to the 2007 Petition with years of 

deliberation, hundreds of pages of analysis, several 

convenings of the SAP, and a Notice of Proposed 

Rulemaking and further Notice of Data Availability 

proposing to grant the requested relief, all substantially 

based on grounds cited in the 2007 Petition.

The Dissent contends that a petitioner who seeks 

revocation of a pesticide tolerance bears not only a burden 

of production, i.e., to provide “reasonable grounds” for 

revocation, but also a burden of persuasion, i.e., to offer 

valid, complete, and reliable data that affirmatively 

demonstrate that the tolerances are unsafe. However, as 

122 72 Fed. Reg. 58,845 (Oct. 17, 2007).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 49

previously explained, the Dissent’s reading is inconsistent 

with the FQPA’s health protective purpose and the FFDCA’s 

overarching command that the EPA, whenever leaving in 

effect a tolerance, “assess the risk of the pesticide chemical 

residue . . . and . . . ensure that there is a reasonable certainty 

that no harm will result to infants and children from 

aggregate exposure . . . .”123 The Dissent’s reading is also 

inconsistent with the EPA’s regulations, which only impose 

a burden of production on the petitioner.124 Indeed, in its 

brief the EPA relies upon the burden-setting regulation that 

would apply if the EPA conducted an evidentiary hearing on 

the 2007 Petition. Although there was no evidentiary 

hearing here, the regulation is illustrative. Ordinarily, “[t]he 

party whose request for an evidentiary hearing was granted 

has the burden of going forward in the hearing with evidence 

as to the issues relevant to that request for a hearing.”125 

However, when section 408 of the FFDCA is at issue, the 

section pertaining to “safety,” then “[t]he party or parties 

who contend that a regulation satisfies the criteria of section 

408 of the FFDCA has the burden of persuasion in the 

hearing on that issue, whether the proceeding concerns the 

establishment, modification, or revocation of a tolerance or 

exemption from the requirement for a tolerance.”126 Put 

simply, on the question of safety, while the burden of 

production is on the petitioners, the burden of persuasion 

always rests on the party claiming that a tolerance is safe. 

For these reasons, the Court concludes that when the EPA 

123 21 U.S.C. § 346a(b)(2)(C).

124 40 C.F.R. § 180.32(b).

125 40 C.F.R. § 179.91(a).

126 Id. § 179.91(b).
50 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

publishes a petition seeking revocation of a tolerance and 

later takes final action denying that petition, the EPA leaves 

that tolerance in effect. The EPA can only do so if it finds 

the tolerance to be safe for the general population and for 

infants and children.127 Here, the EPA did not make such 

findings, so it acted directly contrary to the FFDCA.

B. Whether Denying the 2007 Petition Was Arbitrary 

and Capricious

Separately, in light of the present record and the EPA’s 

assessment of that record, petitioners argue that, even if the 

FFDCA does not require a safety finding here (which we 

find it does), the EPA’s denial of the 2007 Petition was 

arbitrary and capricious. The Court agrees.

An agency has a baseline obligation to “articulate a 

satisfactory explanation for its action including a ‘rational 

connection between the facts found and the choice 

made.’”128 The EPA has not done so because none of the 

reasons proffered in the 2017 and 2019 Orders provides “a 

satisfactory explanation for” denying the 2007 Petition.

The EPA has not retracted the 2016 Revised Human 

Health Risk Assessment indicating that chlorpyrifos is not 

safe at current tolerances and has not issued a new Human 

127 This is not to say, of course, that the EPA must perform a new 

Human Health Risk Assessment in response to every petition. The EPA 

might consider the issues raised by the petition alongside all the other 

evidence considered in its most recent safety determination and conclude 

that it need not conduct further review before reaffirming its prior 

findings.

128 Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43 (quoting Burlington 

Truck Lines v. United States, 371 U.S. 156, 168 (1962)).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 51

Health Risk Assessment or SAP report since 2016. Rather, 

the 2017 Order denied the 2007 Petition on purely 

discretionary grounds, relying upon the EPA’s purported 

authority to demand more study through at least 2022. After 

13 years of delay, a desire for yet more delay does not 

rationally support denial of a petition that the EPA’s own 

prior studies indicate raises a genuine issue of ongoing harm 

to infants and children.

The EPA asserted in the 2017 Order that it “may lawfully 

re-prioritize the registration review schedule developed by 

earlier [presidential] administrations.”129 In other words, 

more delay. Furthermore, while the EPA recognized that the 

2007 Petition was filed under the FFDCA and raised 

arguments concerning human safety, the EPA found in its 

2017 Order that it had to be permitted to synchronize its 

review of the petition with FIFRA registration review. To 

find otherwise “would effectively give petitioners under the 

FFDCA the authority to re-order scheduling decisions 

regarding the FIFRA registration review process that 

Congress has vested in the Administrator.”130

But the FIFRA registration review, as already noted, is a 

different animal, in that it permits a balancing of multiple 

factors, whereas a FFDCA review is limited to the sole issue 

of safety but allows no balancing as far as that factor is 

concerned. Chlorpyrifos’s wide use and the significance of 

this issue to the Administration are not valid legal 

considerations, as the EPA recognized in its 2017 Order.131 

129 2017 Order, supra note 24, 82 Fed. Reg. at 16,590.

130 Id.

131 Id.
52 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

As already noted, the FQPA amended the FFDCA to 

explicitly prohibit the EPA from balancing safety against 

other considerations, including economic or policy 

concerns, in most instances. Thus, the EPA’s citation to 

these admittedly extralegal factors in its denial of the 2007 

Petition is telling. It strongly suggests that the EPA’s aboutface in 2017 was motivated by factors unrelated to human 

safety, contrary to the FFDCA’s commands.

The reference in the denial to the FIFRA 15-year period 

of review is, instead, nothing but a red herring, as the 2007 

Petition does not concern FIFRA registration review. It 

concerns a petition under the FFDCA that contends that 

chlorpyrifos is unsafe. The EPA’s position would largely 

strip FFDCA petitions of meaning, converting them into 

comments for the EPA to consider whenever it gets around 

to the next FIFRA registration review. The EPA offers no 

statutory support for this – because there is none. When, as 

here, a petitioner files a detailed petition identifying new 

evidence providing reasonable grounds to believe that 

exposure at less than a pesticide’s current tolerances may be 

unsafe, the EPA has a duty to “giv[e] due consideration to 

[the] petition . . . and any other information available”132 and 

to act on that petition with reasonable dispatch to protect 

human health – not fifteen years later. For these reasons, 

consistent with what this Court has said for years, the EPA’s 

desire for delay is not a satisfactory explanation for denying 

the 2007 Petition.

The 2019 Order (unlike the 2017 Order) relied upon a 

second ground for denial of the 2007 Petition. The EPA 

found that PANNA and the NRDC bore an initial burden of 

production that, according to the EPA, they did not meet. 

132 21 U.S.C. § 346a(d)(4)(A).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 53

The EPA pointed out that the FFDCA requires it to consider 

“the validity, completeness, and reliability of the available 

data”133 and authorizes it to promulgate regulations stating 

what a petition must contain.134 As noted above, under this 

authority, the EPA promulgated a regulation requiring a 

petition to include “reasonable grounds” for revocation, 

which include an “assertion of facts (supported by data if 

available).”135 Given this initial burden of production, the 

“EPA conclude[d] that the information . . . presented by 

Petitioners is not sufficiently valid, complete, and reliable to 

support abandoning the use of AChE inhibition as the critical 

effect for regulatory purposes under the FFDCA section 

408.”136 Thus, the EPA concluded that the FFDCA safety 

issue was not before it.

For reasons already stated, this finding is unreasonable 

and inconsistent with the petition itself. The 2007 Petition 

claimed in detail that chlorpyrifos posed a risk of neurotoxic 

harm, especially to infants and children, and it invoked the 

live animal studies and the Columbia Study as evidence. 

The EPA acknowledges that it “has, since [2006], 

consistently concluded that the available data support a 

conclusion of increased sensitivity of the young to the 

neurotoxic effects of chlorpyrifos and for the susceptibility 

of the developing brain to chlorpyrifos.”137 Therefore, under 

any reasonable construction, the 2007 Petition met the low 

133 21 U.S.C. § 346a(b)(2)(D)(i).

134 Id. § 346a(d)(2)(B).

135 40 C.F.R. § 180.32.

136 2019 Order, supra note 96, 84 Fed. Reg. at 35,563.

137 Id.
54 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

bar of stating “reasonable grounds” for revocation with an 

“assertion of facts” in support. Also, as noted above, the 

time for finding that the petition did not meet the burden of 

production was in 2007, before the EPA published the 

petition in the Federal Register.

Because the Court rejects both of the EPA’s 

justifications for refusing to make a safety finding, the Court 

concludes that the EPA’s denial of the 2007 Petition was 

arbitrary and capricious.138

Although not necessary for this determination, the Court,

for completeness, also considers the EPA’s four objections 

to the data.

First, the EPA objects, in general, that “the science on 

this question is not resolved and would benefit from 

additional inquiry.”139 It will always be possible to conduct 

additional studies or to reach a greater degree of certainty, 

but a generalized concern that the science is not resolved is 

not a rationale sufficient to support denying a revocation 

petition. The FFDCA requires that the EPA make a safety 

determination based on whatever “information” is 

138 The Dissent takes great umbrage at this conclusion, reminding us 

that “[w]hen an agency makes determinations ‘within its area of special 

expertise, at the frontiers of science . . . a reviewing court must generally 

be at its most deferential.’” Dissent, infra, at 109 (alteration in original) 

(quoting Balt. Gas & Elec. Co. v. NRDC, 462 U.S. 87, 103 (1983)). If 

the 2019 Order had found that existing chlorpyrifos tolerances were safe, 

then such deference would be appropriate. But no such finding was 

made. It is the Order’s utter failure to make a required safety 

determination that this Court finds was arbitrary and capricious. This 

has nothing to do with deference or non-deference to expertise and 

everything to do with simple compliance with the law.

139 Id. at 35,560.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 55

“available.”140 And, as this Court has said before, a statutory 

mandate to rely on “available” scientific data “does not mean 

‘the best scientific data possible.’”141

Second, the EPA argues that it does not know how

chlorpyrifos’s neurotoxic effects harm infants and children. 

But that is not the question before the EPA. The question is 

whether chlorpyrifos causes such harms. Even if the 

mechanism is unknown, if a tolerance is unsafe, then the 

EPA must revoke it.142

Third, the EPA argues that the studies of rats and mice 

applied a “dosing regimen . . . that differs from 

internationally accepted protocols.”143 The EPA says:

[T]he in vivo laboratory animal studies 

generally use fewer days of dosing that are 

aimed at specific periods of rodent fetal or 

early post-natal development compared to 

internationally adopted guideline studies 

which are intended to cover both pre- and 

post-gestational periods. The degree to 

which these shorter dosing periods coincide 

140 21 U.S.C. § 346a(d)(4)(A).

141 San Luis & Delta-Mendota Water Auth. v. Jewell, 747 F.3d 581, 

602 (9th Cir. 2014) (quoting Building Indus. Ass’n v. Norton, 247 F.3d 

1241, 1246 (D.C. Cir. 2001)).

142 Cf. Am. Trucking Ass’ns, Inc. v. EPA, 175 F.3d 1027, 1055 (D.C. 

Cir. 1999) (finding the EPA was not required to prove “how particles 

actually interact with cells and organs to cause sickness and death”), 

aff’d in part and rev’d in part on other grounds sub nom. Whitman v. 

Am. Trucking Assn’s, 531 U.S. 457 (2001).

143 2019 Order, supra note 96, 84 Fed. Reg. at 35,563.
56 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

with comparable windows of susceptibility in 

human brain development is unclear.144

This argument, apparently raised for the first time in the 

2019 Order, is stated in cursory fashion. The EPA does not 

identify these “internationally accepted protocols” or 

explain why the EPA did not find deviations from these 

protocols to be troubling in the 2015 Notice of Proposed 

Rulemaking, the 2016 Notice of Data Availability, the 2016 

Revised Human Health Risk Assessment, or the many other 

publications by the EPA that relied upon the animal studies. 

In any event, however, even if the Court were convinced, for 

the sake of argument, that divergence from these 

internationally accepted dosing protocols might somewhat 

diminish the value of these studies, it would not change the 

result, for reasons described below.

Fourth and finally, the EPA objects that it has been 

unable to get the raw data, as well as information concerning 

how residential pesticides were applied, from the Columbia 

Study. (Columbia, for its part, has expressed reasonable 

concerns about the subjects’ privacy, especially given that 

the study covered a small geographic radius. Nevertheless, 

Columbia suggested to the EPA that it could make at least 

144 Id. The EPA also explains that “except for some studies 

conducted recently, most of the in vivo laboratory studies use doses that 

are higher than doses that cause 10% [red blood cell] AChE inhibition. 

These studies are therefore are [sic] not useful quantitatively to evaluate 

whether [the] EPA’s current regulatory standard is or is not sufficient to 

preclude the potential for neurodevelopmental effects.” Id. This 

objection is, of course, valid as far as it goes: studies that apply pesticide 

at doses above the current tolerance are less helpful in showing whether 

the tolerance is safe. But the EPA concedes that “some studies” use 

lower doses. The EPA offers no justification for refusing to consider 

these studies.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 57

some of the datasets available for viewing in a secure data 

center.145) The EPA has changed its position over time 

regarding the value of this data. It initially requested the 

data, but after meeting with the Columbia researchers in 

2014, the EPA abandoned its request for this data.146 Later, 

when the EPA sought to develop a point of departure based 

upon the umbilical cord blood measurements in the 

Columbia Study, it sought the data again. However, the 

2016 SAP took issue with an approach based upon those 

cord blood measurements, so, as explained above, the EPA 

moved to a time-weighted average approach based upon a 

registrant’s PBPK model. As a result, the EPA once again 

determined that it did not need the Columbia data, explaining 

that its new approach “does not directly rely on quantitative 

measures of chlorpyrifos in cord blood obtained from 

[Columbia], and thus, the lack of access to the raw data from 

[Columbia] is less of an uncertainty.”147 The EPA has now 

reversed position yet again, reiterating its desire for the data.

145 See Chlorpyrifos Epidemiology Study Data De-identification 

Discussion (July 31, 2018).

146 2014 Revised Human Health Risk Assessment, supra note 54, 

at 391 (“As a result of this meeting and additional discussions with 

[Columbia] staff, [the] EPA concluded that access to the raw data would 

either not provide answers to [the] EPA’s questions or that the 

information [the] EPA sought could be obtained without analyzing the 

raw data. Indeed, based on discussions in that meeting as well as further 

work conducted by agency staff, [the] EPA has gained additional 

information to better clarify and characterize the major issue areas 

identified as uncertainties. For these reasons, [the] EPA decided that it 

would not further pursue its request for the analytic data file from the 

[Columbia] researchers.”) (emphasis added).

147 2016 Revised Human Health Risk Assessment, supra note 74, 

at 14.
58 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

The EPA’s flip-flopping suggests the weakness of this 

objection. Nevertheless, even if the Court were to assume 

for the sake of argument that the underlying data, and 

information concerning the method of residential pesticide 

application, would be of some use and that the EPA’s 

inability to access it might diminish the value of the 

Columbia Study, it would not change the result in this case.

This is because, while the EPA might reasonably 

conclude that divergences from international protocols and 

lack of access to raw data might affect the weight the EPA 

accords to these studies, they are nowhere near enough to 

show that the studies are entirely unreliable. The FFDCA 

requires the EPA to consider the “information” that is 

“available”148 and to make a safety determination based on 

that information. In this case, live animal studies showing 

sex-linked, neurotoxic harms from in utero chlorpyrifos 

exposure are available – even if such studies are supposedly 

not perfectly aligned with (unspecified) international 

standards. And peer-reviewed cohort studies showing harms 

to infants’ neurological development following their 

mothers’ exposure to chlorpyrifos are available – even if the 

underlying data is not. The EPA speculates that it might find 

an error if the unspecified international standards were 

applied to the animal studies or if the data from the Human 

Cohort Studies were available. But that is all it is: 

speculation. Such speculation “runs counter to the evidence 

before the agency,”149 so it cannot form the basis for denying 

the 2007 Petition.

148 21 U.S.C. § 346a(d)(4)(A).

149 See Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 59

II. Remedy

The Court concludes that the EPA lacked power to deny 

the 2007 Petition without making the safety findings 

required by the FFDCA and that the EPA’s decision was 

arbitrary and capricious. Therefore, the Court must, at least, 

“set aside the order or regulation complained of”150 and 

remand to the EPA. Petitioners argue that the Court should 

also order the EPA to revoke the current chlorpyrifos 

tolerances and registrations by a date certain. Under the 

APA, the Court has the power to “compel agency action 

unlawfully withheld or unreasonably delayed.”151 The Court 

returns once more to the two sentences of the FFDCA that 

are key to assessing whether the Court should order the relief 

petitioners request:

The Administrator may establish or leave in 

effect a tolerance for a pesticide chemical 

residue in or on a food only if the 

Administrator determines that the tolerance is 

safe. The Administrator shall modify or 

revoke a tolerance if the Administrator 

determines it is not safe.152

The second sentence is more than a mere gloss on the 

first because the command inherent in the second sentence 

150 21 U.S.C. § 346a(h)(2).

151 5 U.S.C. § 706(1).

152 21 U.S.C. § 346a(b)(2)(A)(i).
60 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

is important.153 To be sure, the “only if” clause in the first 

sentence, standing alone, limits what the EPA may do when 

it determines that a tolerance is unsafe: it may not leave it in 

effect. But what are the EPA’s options? May it order 

additional study? Convene another SAP? Wait for fifteen 

years to see if further evidence appears? No. The second 

sentence makes clear that, once the EPA has determined that 

a tolerance is not safe, it has no discretion to temporize 

pending additional research; it must modify or revoke the 

tolerance. For these reasons, if the EPA has determined that 

the present chlorpyrifos tolerances are not safe – or if that is 

the only conclusion the EPA could reasonably draw on this 

record – then the EPA has unlawfully withheld the relief that 

petitioners request.

On the present record, the only reasonable conclusion the

EPA could draw is that the present tolerances are not safe 

within the meaning of the FFDCA. The EPA can find a 

tolerance safe only if there is “a reasonable certainty” of “no 

harm,”154 and for nearly a decade, the EPA and its SAPs 

have concluded that there is not a reasonable certainty of no 

harm:

• 2012 SAP: “[E]vidence suggest[s] that chlorpyrifos 

can affect neurodevelopment at levels lower than 

those associated with AChE inhibition, and that the 

use of AChE inhibition data may not be the most 

appropriate for dose-response modeling and 

153 For this reason, the EPA and the Dissent are also incorrect to 

contend that petitioners’ reading of the statute contains surplusage. See 

Dissent, infra, at 80.

154 21 U.S.C. § 346a(b)(2)(A)(ii).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 61

derivation of a point of departure for assessment of 

the neurodevelopmental risks of chlorpyrifos.”155

• 2014 Revised Human Health Risk Assessment:

“[C]hlorpyrifos likely played a role in the 

neurodevelopmental outcomes observed in these 

epidemiology studies.”156 Moreover, “it is unlikely 

mothers enrolled in the [Human Cohort Studies] 

experienced [red blood cell] AChE inhibition.”157

• 2015 Notice of Proposed Rulemaking: “[The] EPA 

cannot, at this time, determine that aggregate 

exposure to residues of chlorpyrifos, including all 

anticipated dietary exposures and all other nonoccupational exposures for which there is reliable 

information, are safe.”158

• 2016 SAP: “[B]oth epidemiology and toxicology 

studies suggest there is evidence for adverse health 

outcomes associated with chlorpyrifos exposures 

155 2012 SAP Minutes, supra note 48, at 53.

156 SAP Minutes No. 2008-04, A Set of Scientific Issues Being 

Considered by the Environmental Protection Agency Regarding: The 

Agency’s Evaluation of the Toxicity Profile of Chlorpyrifos 43 

(Sept. 16–18, 2008).

157 Id. at 46.

158 2015 Notice of Proposed Rulemaking, supra. note 58, 80 Fed. 

Reg. at 69,081.
62 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

below levels that result in 10% red blood cell [AChE] 

inhibition.”159

• 2016 Revised Human Health Risk Assessment:

The Columbia Study, “with supporting results from 

the other [Human Cohort Studies] and the seven 

additional epidemiological studies reviewed in 2015, 

provides sufficient evidence that there are 

neurodevelopmental effects occurring at 

chlorpyrifos exposure levels below that required for 

AChE inhibition.”160

• 2016 Notice of Data Availability: “[E]xpected 

residues of chlorpyrifos on most individual food

crops exceed the ‘reasonable certainty of no harm’ 

safety standard under the [FFDCA] . . . . [The] EPA 

has not identified a set of currently registered uses 

that meets the FFDCA safety standard . . . .

161

Even in its brief here, the EPA, though it purports to 

withhold judgment on chlorpyrifos’s safety, admits that it 

cannot conclude there is a reasonable certainty of no harm. 

Rather, the EPA represents that there are “uncertainties

concerning the impact of chlorpyrifos on children”

(emphasis added).

The EPA has not determined, and on this record 

reasonably could not determine to a “reasonable certainty”

159 2016 SAP Minutes, supra note 65, at 18.

160 2016 Revised Human Health Risk Assessment, supra note 74, 

at 13.

161 Id.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 63

that aggregate chlorpyrifos exposures under the current 

tolerances pose no risk of harm. Therefore, by statutory 

definition, the present tolerances are not safe. Accordingly, 

the EPA’s obligation is clear: it must modify or revoke 

chlorpyrifos tolerances and modify or cancel chlorpyrifos 

registrations.

The EPA cites cases counseling that upon reversal of 

agency action, an open-ended remand is the correct 

approach, “[g]enerally speaking”162 and “except in rare 

circumstances.”163 But this is not a typical case. On the 

present record the EPA has limited legal discretion: its only 

options are to modify or revoke the tolerances. Nor would it 

be reasonable to remand for further factfinding after thirteen 

years of interminable delay. Indeed, further delay would 

make a mockery, not just of this Court’s prior rulings and 

determinations, but of the rule of law itself. This is precisely 

the sort of “rare circumstance” where yet another openended remand would only frustrate the purpose of the 

FFDCA.

Finally, the EPA argues that “any order by this Court 

unilaterally ordering [the] EPA to revoke the existing 

tolerances for chlorpyrifos or cancel the existing 

registrations would raise serious due process concerns” for 

registrants and “violate Congress’s procedures.” Here, 

however, the Court is not unilaterally ordering the EPA to 

revoke existing tolerances; as explained below, it may 

instead modify such tolerances if it can make the requisite 

safety findings.

162 INS v. Orlando Ventura, 537 U.S. 12, 16 (2002).

163 Fla. Power & Light Co. v. Lorion, 470 U.S. 729, 744 (1985).
64 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

In any event, remanding with specific instructions does 

not raise due process concerns. In responding to a petition, 

the FFDCA explicitly authorizes the EPA to “issue a final 

regulation modifying or revoking a tolerance . . . (which 

final regulation shall be issued without further notice and 

without further period for public comment).”164 On this 

record, immediate issuance of a final regulation is the only 

reasonable action, and the Court orders the EPA to do so.

Such a final regulation could take one of two forms: 

either it could revoke all chlorpyrifos tolerances or it could 

modify chlorpyrifos tolerances and conclude that under the 

new tolerances there is a “reasonable certainty that no harm 

will result” due to “aggregate exposure to the pesticide 

chemical residue” that would result from such modified 

tolerances, including “to infants and children.”165 To be 

clear, the EPA may only choose to modify chlorpyrifos 

tolerances, rather than to revoke them, if at the same time it 

publishes such a safety determination.166 On this record, it 

164 21 U.S.C. § 346a(d)(4)(A)(i) (emphasis added) (comma 

omitted).

165 Id. § 346a(b)(2)(A)(ii), (b)(2)(C)(ii)(I).

166 The Dissent opines that the Court “may have effectively 

foreclosed other options Congress made available,” Dissent, infra, at 112

n.11, such as the exceptional steps the EPA may take when “the residue 

protects consumers from adverse effects on health that would pose a 

greater risk than the dietary risk” or when the tolerance “is necessary to 

avoid a significant disruption in domestic production of an adequate, 

wholesome, and economical food supply.” 21 U.S.C. 

§ 346a(b)(2)(B)(iii). These provisions offer alternatives to the FFDCA’s 

general safety requirement for certain “eligible pesticide chemical 

residues,” but only for adults. While subparagraph (b)(2)(B) provides an 

exception to “subparagraph [(b)(2)(A)(i)],” the general safety rule, it 

expressly requires compliance with subsection (b)(2)(C), which 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 65

may well be that the EPA cannot make such a determination. 

In 2016, the EPA explained that it “ha[d] not identified a set 

of currently registered uses that meets the FFDCA safety 

standard,”167 a finding consistent with more than a decade of 

EPA issue papers, revised human health risk assessments, 

and SAP proceedings.

Nevertheless, during the pendency of this proceeding, in 

December 2020, the EPA issued a Proposed Interim 

Registration Review Decision proposing to modify certain 

chlorpyrifos tolerances. The EPA also convened another 

SAP in 2020. If, based upon the EPA’s further research the 

EPA can now conclude to a reasonable certainty that 

modified tolerances or registrations would be safe, then it 

may modify chlorpyrifos registrations rather than cancelling 

them.168

mandates that the EPA assure a reasonable certainty of no harm to 

children specifically. Id. § 346a(b)(2)(B)(vi). Thus, these provisions are 

irrelevant because regardless of whether chlorpyrifos is an “eligible”

pesticide for purposes of § 346a(b)(2)(B) – a question not briefed by the 

parties and raised sua sponte by the Dissent – the EPA may only leave 

in effect chlorpyrifos tolerances that are safe for children.

167 2016 Notice of Data Availability, supra note 3, 81 Fed. Reg. 

at 81,050.

168 Whichever path the EPA chooses to take, the FFDCA also 

provides that within 60 days after the EPA publishes a final response to 

the 2007 Petition, either modifying chlorpyrifos tolerances and 

publishing a safety finding or revoking chlorpyrifos tolerances, anyone 

may object to the EPA’s final order, 21 U.S.C. § 346a(g)(2)(A), and the 

EPA must then “issue an order stating the action taken” on those 

objections, id. § 346a(g)(2)(C). It is hard to imagine that registrants will 

have much to add, given the many opportunities they have already 

received to comment on the 2015 Notice of Proposed Rulemaking and 

the 2016 Notice of Data Availability, as well as to participate as amici 
66 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

 To be clear, however, this is not an open-ended remand 

or a remand for further factfinding. The EPA must act based 

upon the evidence and must immediately revoke or modify 

chlorpyrifos tolerances.

For these reasons, the Court remands this matter to the 

EPA with instructions to publish a legally sufficient final 

response to the 2007 Petition within 60 days of the issuance 

of the mandate. That response must be a final regulation that 

either revokes all chlorpyrifos tolerances or modifies 

chlorpyrifos tolerances and makes the requisite safety 

findings based on aggregate exposure, including with respect 

to infants and children.

While the Dissent effectively views this as a “tight 

deadline[],”169 it agrees that the “EPA dithered far too 

long.”170 The EPA has had nearly 14 years to publish a 

legally sufficient response to the 2007 Petition. During that 

time, the EPA’s egregious delay exposed a generation of 

American children to unsafe levels of chlorpyrifos. By 

remanding back to the EPA one last time, rather than 

compelling the immediate revocation of all chlorpyrifos 

tolerances, the Court is itself being more than tolerant. But 

the EPA’s time is now up.

curiae before this Court. But, in any event, registrants’ 60-day period to 

object will follow the EPA’s final revocation of chlorpyrifos tolerances 

(or modification with concomitant safety findings). If registrants ask the 

EPA to promulgate new chlorpyrifos tolerances or revert to higher 

tolerances, they must provide proof of safety, and the EPA can approve 

registrants’ request only if the EPA concludes that there is a reasonable 

certainty of no harm, including for infants and children.

169 Dissent, infra, at 115.

170 Dissent, infra, at 67.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 67

CONCLUSION

We GRANT the petitions for review. The 2017 Order 

and the 2019 Order are vacated, and the matter is remanded 

to the EPA, with instructions to (1) grant the 2007 Petition; 

(2) issue a final regulation within 60 days following issuance 

of the mandate that either (a) revokes all chlorpyrifos 

tolerances or (b) modifies chlorpyrifos tolerances and

simultaneously certifies that, with the tolerances so 

modified, the EPA “has determined that there is a reasonable 

certainty that no harm will result from aggregate exposure to 

the pesticide chemical residue, including all anticipated 

dietary exposures and all other exposures for which there is 

reliable information,”171 including for “infants and 

children”;

172 and (3) modify or cancel related FIFRA 

registrations for food use in a timely fashion consistent with 

the requirements of 21 U.S.C. § 346a(a)(1).

VACATED AND REMANDED, WITH 

INSTRUCTIONS.

BYBEE, Circuit Judge, dissenting:

This is a consequential proceeding. EPA has before it a 

petition to revoke the tolerances for chlorpyrifos, one of the 

most important pesticides in the United States. This is a very 

complicated statute and I agree with the majority that EPA 

dithered far too long before ruling on the petition. Beyond 

that, I disagree with the majority opinion and judgment. In 

171 21 U.S.C. § 346a(b)(2)(A)(ii).

172 Id. § 346a(b)(2)(C)(ii)(I).
68 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

my view it has misread EPA’s obligations to review 

pesticide chemical residue tolerances EPA has previously 

found to be “safe” under the Federal Food, Drug, and 

Cosmetic Act (FFDCA), 21 U.S.C. § 346a(b)(2)(A)(i). 

Further, the majority has substituted its own judgment for 

EPA’s decision and then concluded that, because there is a 

difference of opinion, EPA’s decision must be arbitrary and 

capricious. See 5 U.S.C. § 706(2)(A). Difference is not 

caprice. Finally, among the options Congress entrusted to 

EPA when an existing tolerance is determined to be unsafe, 

the majority effectively mandates the option that EPA will 

enforce.

As to the first point, I part with the majority over EPA’s 

duty with respect to the petition. According to the majority, 

EPA must find that chlorpyrifos is safe for human use, and 

EPA did not do so here. Maj. Op. at 41–46. EPA did find 

chlorpyrifos safe. That was the result of the proceedings in 

2006, made final shortly before the present petition was 

filed. The question EPA had to answer in this proceeding is 

whether new scientific evidence is sufficient to require EPA 

to “modify or revoke” its prior determination. Under the 

FFDCA, EPA must do so “if the Administrator determines it 

is not safe.” 21 U.S.C. § 346a(b)(2)(A)(i) (emphasis added). 

Because EPA found that chlorpyrifos was safe when it 

concluded its prior rulemaking in 2006, EPA properly 

determined here that there was insufficient evidence to 

conclude that chlorpyrifos is “not safe” and thus it was not 

required to “modify or revoke” those tolerances. EPA does 

not start from scratch when it is reviewing a petition to 

revoke or modify, but may rely on its prior finding. The 

majority would require, contrary to the FFDCA, that EPA 

start all over again. I take this point up in Part I.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 69

As to the second point, the majority cherry-picks EPA’s 

careful and honest questions about the safety of chlorpyrifos 

in light of various studies produced in the petition. 

Admittedly, it feels like EPA had this question under review 

for far too long—through three administrations—but the 

majority then assumes EPA’s tentative conclusions are 

proven and concludes that it was arbitrary and capricious for 

EPA to determine otherwise. However, EPA never 

concluded that the studies presented to it were scientifically 

established. At every step of its overly cautious proceedings, 

EPA referred these studies to its Scientific Advisory Panel 

(SAP), which ultimately advised EPA that it could not verify 

the studies’ conclusions. When EPA requested the 

underlying data, the studies’ authors declined to produce it. 

Left without means of authenticating the studies, EPA 

concluded there was insufficient verifiable evidence to 

conclude that chlorpyrifos was “not safe” and to require EPA 

to modify or revoke its prior approval. The petition failed 

for lack of scientifically verifiable evidence. EPA explained 

all of this in detail, explained why it needed additional time 

to conduct the appropriate inquiries, and advised how it 

would proceed through the reregistration required by the 

statute. There is nothing arbitrary and capricious about that. 

I address this problem in Part II.

Not only do we decide that EPA’s decision was arbitrary 

and capricious, but we have effectively decided the 

appropriate remedy. By ordering EPA either to revoke all 

tolerances or modify the tolerances with the requisite safety 

findings within 60 days, our order virtually guarantees the 

EPA will revoke chlorpyrifos tolerances. This is a vast 

overreach, a clear abuse of our discretion, as I discuss in Part 

III.
70 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

We can be unhappy with EPA’s dilatory proceedings, 

but the remedy for that is a writ of mandamus, which we 

issued in League of United Latin American Citizens v. 

Wheeler (LULAC III), 922 F.3d 443 (9th Cir. 2019) (en 

banc). Now that EPA has complied fully with our directions, 

we don’t get to set aside EPA’s decision “simply because 

[we are] unhappy with the result reached.” Vt. Yankee 

Nuclear Power Corp. v. NRDC, 435 U.S. 519, 558 (1978). 

Nor do we get to “second-guess[] the [agency’s] weighing 

of risks and benefits.” Dep’t of Com. v. New York, 139 S. Ct. 

2551, 2571 (2019). “[A] reviewing court must remember 

that” when an agency is acting “within its area of special 

expertise, at the frontiers of science,” we “must generally be 

at [our] most deferential.” Balt. Gas & Elec. Co. v. NRDC, 

462 U.S. 87, 103 (1983). I respectfully dissent.

I

For starters, I fundamentally disagree with the majority 

over its construction of the FFDCA. The majority reads 

§ 346a(b)(2)(A)(i), which is the critical section of the 

FFDCA for setting standards for pesticide use, as creating a 

binary choice for EPA: either a tolerance is “safe” or it is 

“not safe.” The majority concludes that because EPA did 

not conclude that the chlorpyrifos tolerances were “safe”

when it denied the petition, EPA must have concluded that 

they were “not safe” and the petition should have been 

granted. See Maj. Op. at 41 (EPA “left in effect tolerances 

without determining that they are safe . . . .”). With respect, 

the majority has misread the statute and its logic. I will start 

with some background on the statutes, then turn to how the 

majority has misread the statute, and conclude by addressing 

two additional arguments the majority makes.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 71

A

Let’s start with some background. EPA regulates 

pesticides pursuant to two statutes: the Federal Food, Drug, 

and Cosmetic Act (FFDCA), 21 U.S.C. § 346a, and the 

Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA), 7 U.S.C. §§ 136a–136y. The provisions relevant 

here were adopted as amendments to those Acts in the Food 

Quality Protection Act of 1996 (FQPA), Pub. L. No. 104-

170, 110 Stat. 1489 (Aug. 3, 1996). See Nw. Coal. for Alts. 

to Pesticides v. EPA, 544 F.3d 1043, 1046 (9th Cir. 2008). 

The FFDCA authorizes EPA to regulate pesticides used on 

food that pose safety risks to humans and to establish 

pesticide tolerance levels “necessary for the protection of 

public health.” 21 U.S.C. § 346. FIFRA authorizes EPA to 

“limit the distribution, sale, or use” of pesticides “[t]o the 

extent necessary to prevent unreasonable adverse effects on 

the environment” and issue registrations for distribution or 

sale of pesticides. 7 U.S.C. § 136a(a).

The FFDCA begins with a presumption that all 

“pesticide chemical residue in or on a food . . . [is] unsafe.” 

21 U.S.C. § 346a(a)(1)(A). If the EPA Administrator 

determines that a pesticide is “safe,” the Administrator may 

establish a regulatory “tolerance.”1

 A pesticide may be 

deemed “safe” if EPA has found “that there is a reasonable 

1 EPA may also exempt a pesticide from the FFDCA, where either 

(1) use of the pesticide protects consumers from greater adverse health 

effects than the dietary risk of the pesticide or (2) the pesticide is 

necessary to avoid significant disruption in the food supply chain, so 

long as aggregate risk is not too high. 21 U.S.C. § 346a(b)(2)(B)(ii)–

(iv).

Although some of the statutes I will cite here refer to exemptions, 

EPA did not consider exemption of chlorpyrifos in this proceeding.
72 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

certainty that no harm will result from aggregate exposure to 

the pesticide.” Id. § 346a(b)(2)(A)(i), (ii). The FFDCA has 

a separate requirement protecting infants and children. EPA 

must separately assess the risk of the pesticide based on 

available information concerning consumption patterns, 

special susceptibility, and cumulative effects unique to 

infants and children. Id. § 346a(b)(2)(C)(i). Based on this 

assessment, EPA must “ensure that there is a reasonable 

certainty that no harm will result to infants and children from 

aggregate exposure” and “publish a specific determination 

regarding safety” of the pesticide for infants and children. 

Id. § 346a(b)(2)(C)(ii). In making these determinations, 

EPA “shall consider . . . the validity, completeness, and 

reliability of the available data” and “available information 

concerning the relationship of the results of such studies to 

human risk.” Id. § 346a(b)(2)(D)(i), (iii).

In addition to establishing safe tolerance levels for 

pesticides under the FFDCA, EPA regulates pesticides under 

FIFRA by issuing registrations required for distribution or 

sale. 7 U.S.C. § 136a(a). EPA may register a pesticide 

where, in addition to other requirements, “it will perform its 

intended function without unreasonable adverse effects on 

the environment” and “when used in accordance with 

widespread and commonly recognized practice it will not 

generally cause unreasonable adverse effects on the 

environment.” Id. § 136a(c)(5)(C), (D). “Unreasonable 

adverse effects on the environment” are unreasonable risks 

to man or the environment, including “human dietary risk

. . . inconsistent with the standard under section 346a of Title 

21.” Id. § 136(bb). Thus, FIFRA incorporates the FFDCA 

safety determination into its registration assessment.

At the time the FQPA was passed in 1996, there were a 

number of existing tolerances in effect. The use of 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 73

chlorpyrifos, for example, has been federally authorized 

since 1965. See Chlorpyrifos; Final Order Denying 

Objections to March 2017 Petition Denial Order, 84 Fed. 

Reg. 35,555, 35,558 (July 24, 2019) (Final Order). The 

FFDCA, as amended by the FQPA, provided that 

“[r]egulations that establish tolerances” issued on or before 

August 3, 1996, “shall remain in effect unless modified or 

revoked.” 21 U.S.C. § 346a(j)(3). The Act also instructed 

EPA to “review tolerances and exemptions for pesticide 

chemical residues in effect on [August 2, 1996],” and to 

determine whether to leave in effect, “modify or revoke”

those tolerances in accordance with the new standards. Id.

§ 346a(q)(1).2

 The FFDCA provided that EPA “shall . . .

modify or revoke the tolerance or exemption if the tolerance 

or exemption does not meet such requirements.” Id. The 

FFDCA further provided that at any time EPA could, on its 

own initiative, issue regulations “establishing, modifying, 

. . . or revoking a tolerance for a pesticide . . . .” Id.

§ 346a(e)(1)(A). Once a pesticide has been approved and 

registered, FIFRA requires EPA to reevaluate the 

registration within 15 years, in this case no later than 

October 2022. 7 U.S.C. § 136a(g)(1)(A)(iii), (iv). During 

FIFRA reregistration, EPA must decide whether to leave a 

tolerance in effect or revoke or modify it. Id.

§ 136a(g)(1)(A).

The general standards for establishing, leaving in effect, 

modifying, or revoking tolerances are found in 

§ 346a(b)(2)(A)(i):

2 The FQPA required EPA to review tolerances in existence in 1996 

according to a priority schedule. 21 U.S.C. § 346a(q)(1), (2). EPA 

placed chlorpyrifos in its first priority group and completed its review in 

2006. Final Order, 84 Fed. Reg. at 35,558.
74 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

The Administrator may establish or leave in 

effect a tolerance for a pesticide chemical 

residue in or on a food only if the 

Administrator determines that the tolerance is 

safe. The Administrator shall modify or 

revoke a tolerance if the Administrator 

determines it is not safe.

These sentences are awkwardly written. For readability we 

can transpose them as follows:

Only if the Administrator determines that a 

tolerance for a pesticide chemical residue in 

or on a food is safe may the Administrator 

establish or leave in effect the tolerance.3 If 

the Administrator determines a tolerance is 

not safe, the Administrator shall modify or 

revoke the tolerance.

These standards are consistent with the presumption against 

the use of pesticides in food. If EPA determines a pesticide 

is safe, then EPA may establish a new tolerance or leave in 

place a tolerance previously established. However, if EPA 

determines a tolerance is not safe, then EPA shall modify or 

revoke the tolerance. Establishing or leaving a tolerance in 

place is not mandatory, even if EPA determines that a 

pesticide is safe; but if EPA determines a tolerance is not 

safe, it must modify or revoke the tolerance.

3 This sentence could also be written as “If the Administrator 

establishes or leaves in effect a tolerance, then he has determined that the 

tolerance is safe.”
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 75

When acting on its own initiative or in response to a 

petition,4 the FFDCA requires EPA to consider “the validity, 

completeness, and reliability of the available data from 

studies of the pesticide” as well as other available 

information concerning risks and effects. § 346a(b)(2)(D). 

The statute also authorizes EPA to adopt regulations 

governing “requirements for information and data to support 

a petition to modify or revoke a tolerance.” § 346a(d)(1), 

(d)(2)(B). EPA has issued regulations establishing these 

requirements and mandating supporting data and studies. 

40 C.F.R. § 180.32(b). A petition must be supported by 

“reasonable grounds for the action sought,” including “an 

assertion of facts (supported by data if available)” that “may 

justify [the tolerance’s] modification or revocation.” Id.

§ 180.32(b). The regulations also specify the form and 

content required for a petition. Id. § 180.7(b). Under its 

regulations, EPA may deny a petition when it finds that a 

petition is not supported by “reasonable grounds” for 

revocation. Id. § 180.32(b).

B

Now to the majority’s errors. The majority reads 

§ 346a(b)(2)(A)(i) as creating a binary choice, an “either/or”

scenario: either a tolerance is “safe” or it is “not safe.” For 

the majority, there is no middle ground. See Maj. Op. at 13,

(“If a tolerance is not safe—in other words, if the EPA 

cannot determine that there is a reasonable certainty of no 

harm across all sources of exposure for infants, children, and 

adults—then the EPA no longer has discretion.”), 62–63

4 The FFDCA provides a mechanism for interested persons to 

petition EPA to “propos[e] the issuance of a regulation establishing, 

modifying, or revoking a tolerance for a pesticide chemical residue in or 

on a food.” Id. § 346a(d)(1)(A).
76 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

(“EPA has not determined . . . that aggregate chlorpyrifos 

exposures under the current tolerances pose no risk of harm. 

Therefore, by statutory definition, the present tolerances are 

not safe.”). The majority’s logic is irrefutable because the 

statement is, of course, a tautology. But as a tautology it is 

not helpful, because it doesn’t tell us anything about the 

actual state of affairs. As Ludwig Wittgenstein once 

commented, “I know nothing about the weather when I know 

that it rains or does not rain.”5 The problem with the 

majority’s reasoning is, in a phrase, the fallacy of the 

excluded middle. See Wall v. Mich. Rental, 852 F.3d 492, 

496 (6th Cir. 2017) (“[A] statement of two contradictory 

facts [is] a statement of nothing at all under a venerable 

principle of logic—the law of the excluded middle.”); Miller 

v. Henman, 804 F.2d 421, 426 (7th Cir. 1986) (rejecting the 

“Law of the Excluded Middle” in favor of “a third 

alternative”). It is true that § 346a(b)(2)(A)(i) uses the terms 

“safe” and “not safe.” But the context for the terms is 

different. The terms are opposites, but they do not exhaust 

the possible outcomes.

We should be familiar with the problem of the excluded 

middle from other areas of law and life. For example, 

“guilty” and “not guilty,” as logical opposites, describe the 

universe, so long as we don’t care about factual innocence. 

But if we do, we have to consider a third alternative. Thus, 

we have examples where courts have gone beyond the binary 

thinking of guilty/not guilty to declare persons “factually 

innocent.” See Humphries v. Cnty. of L.A., 554 F.3d 1170, 

1181–82 & nn. 6, 8 (9th Cir. 2009) (discussing the legality 

and effect of findings of “factually innocent” by a California 

criminal court and “not true” by a California juvenile court 

5 Ludwig Wittgenstein, Tractatus Logico-Philosophicus, quoted in

Joseph G. Brennan, A Handbook of Logic 160 (2d ed. 1961).
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 77

in a child abuse case), rev’d in part on other grounds, Cnty. 

of L.A. v. Humphries, 562 U.S. 29 (2010). Other countries 

offer juries the option of a third verdict. See Samuel L. Bray, 

Comment, Not Proven: Introducing a Third Verdict, 72 U. 

Chi. L. Rev. 1299, 1299–1300 (2005) (“Not proven and not 

guilty are both acquittals, indistinguishable in legal 

consequence but different in connotation. Not guilty is for a 

defendant the jury thinks is innocent; not proven, for a case 

with insufficient evidence of guilt”; citing Scottish law as an 

example). In football, a ruling may be overturned only if 

there is indisputable evidence that it was wrong. But what if 

the ruling is not indisputably wrong? Do we care if it was 

correct, or just “not wrong”? Turns out that we do. The 

presumption will lie with the official who made the call. If 

the ruling cannot be overturned, “the ruling on the field 

stands.” But if the ruling on the field is correct, then “the 

ruling on the field is confirmed.” See NCAA Football Rules 

Book R. 12, § 6, art. 1.d (2019) (distinguishing three options: 

“the ruling on the field is confirmed,” “the ruling on the field 

stands,” and reversing a ruling). There is no practical 

difference in the immediate effect on the game between “the 

ruling on the field stands” and “the ruling on the field is 

confirmed,” but there are collateral consequences for 

officials and for the lively debates among the fans that 

inevitably follow in close games.

The majority’s premise that a pesticide is either “safe” or 

“not safe” ignores an important alternative—namely, that 

there is insufficient information to reach either of those 

conclusions. That is why Congress instructed EPA to 

consider “the validity, completeness, and reliability of the 

available data”—it understood that the evidence might be 

inconclusive. 21 U.S.C. § 346a(b)(2)(D)(i). That is also 

why § 346a(b)(2)(A)(i) allocates a burden of persuasion. I 

hesitate to use the term “burden of proof” because it suggests 
78 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

that EPA and petitioners are adverse to each other; they are 

not. EPA is responsible for regulating pesticide use and, as 

a court, we assume that it has developed an expertise. We 

also assume that EPA will be an honest broker in assessing 

the safety of a pesticide; after all, agency employees have to 

eat the same food we do. So instead of “burden of proof,” I 

am going to use the term “risk of nonpersuasion.”

Here is how the risk of nonpersuasion figures into the 

FFDCA. When EPA receives a petition, it has a duty of 

inquiry, but it is a different duty depending on whether the 

decision on the table is whether to establish or leave in effect

a tolerance (the first sentence of § 346a(b)(2)(A)(i)) or to 

modify or revoke a tolerance (the second sentence in that 

subsection). EPA (or a petitioner) has the initial burden to 

show that a proposed tolerance can be safely established. If

the proposal does not satisfy that standard, EPA cannot adopt 

the proposed tolerance. EPA has the same burden when it 

considers an existing tolerance for reregistration. Recall that 

when the FQPA was adopted in 1996, that Act tightened the 

standards for pesticides. Because EPA had approved 

pesticides in use, the FQPA required EPA to review and 

reregister all existing tolerances to determine whether to 

“leave in effect” those tolerances. 21 U.S.C. §§ 346a(j)(3), 

(q)(1). Additionally, the FQPA, amending FIFRA, 

mandated that following that reregistration, EPA must 

review existing tolerances no less frequently than every 

15 years. 7 U.S.C. § 136a(a), (g)(1)(A)(iv). In these 

reregistration proceedings, EPA must conclude that the 

existing tolerance is “safe” before it can “leave [it] in effect.” 

21 U.S.C. § 346a(b)(2)(A)(i). What happens if the evidence 

is inconclusive? Since there is a presumption that all 

pesticides are “unsafe,” id. § 346a(a)(1), the risk of 

nonpersuasion means that EPA must either approve the 

tolerance or exempt it under other provisions of the FFDCA, 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 79

see id. § 346a(a)(1)(A), (B). As I transposed 

§ 346a(b)(2)(A)(i) for readability, “only if the Administrator 

determines that the tolerance is safe may [the Administrator] 

establish or leave in effect a tolerance.”

By contrast, when a petitioner requests modification or 

revocation of an existing tolerance, the risk of nonpersuasion 

cuts in the opposite direction. EPA has previously found the 

tolerance to be “safe.” If EPA subsequently determines that 

the pesticide is “not safe,” then it must modify or revoke the 

tolerance. What happens if the evidence is inconclusive? 

The risk of nonpersuasion means that EPA may, but does not 

have to, modify or revoke the tolerance. Section 

346a(b)(2)(A)(i) is clear (as I have revised it for readability): 

“If the Administrator determines a tolerance is not safe, the 

Administrator shall modify or revoke the tolerance.” 

Accordingly, when a petitioner files an appropriate petition 

claiming that a tolerance is not safe, EPA assumes a duty of 

inquiry, but not a duty of declaring anew that the tolerance 

is “safe.” Here is the crucial distinction: determining that a 

tolerance is “not safe” is not the same as not determining 

that a tolerance is “safe.” The majority’s either/or approach 

has excluded the middle. As the First Circuit explained, 

albeit in a different context:

Confronted by such conflict a reasonable 

person investigates matters further; he 

receives assurances or clarification before 

relying. A reasonable person does not 

gamble with the law of the excluded middle, 

he suspends judgment until further evidence 

is obtained. Explicit conflict engenders 

doubt, and to rely on a statement the veracity 

of which one should doubt is unreasonable. 

The law does not supply epistemological 
80 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

insurance. Nor does it countenance reliance 

on one of a pair of contradictories simply

because it facilitates the achievement of 

one’s goal.

Trifiro v. Nw. York Life Ins. Co., 845 F.2d 30, 33–34 (1st Cir. 

1988).

The majority’s either/or treatment of § 346a(b)(2)(A)(i) 

has two important consequences. First, it effectively reads 

the second sentence of that subsection out of the statute 

because, in the majority’s understanding, EPA always has 

the burden to show that a tolerance is “safe,” which means 

that it is, by definition, not “not safe.” Or, to put it another 

way, in the majority’s view, if at any time EPA does not 

affirmatively declare that a tolerance is “safe,” the tolerance 

is, again by definition, “not safe.” Under the majority’s 

reading, the second sentence of § 346a(b)(2)(A)(i) doesn’t

do any work because in order to determine that a tolerance 

is “not safe” EPA must decide that it is not “safe.” In other 

words, for the majority, in every case EPA has a duty of 

reregistration. The reason the majority has committed this 

error of logic is that it fails to appreciate the different context 

for the two sentences in § 346(b)(2)(A)(i). In the first 

sentence, the presumption runs against the tolerance because 

EPA is required to establish or reregister (“leave in effect”) 

the tolerance. In the second sentence, EPA has already 

determined that the tolerance is “safe,” so the question is 

whether there is enough evidence to show that it is “not 

safe.” When EPA denies a petition for insufficient evidence, 

it may rely on its prior determination that the tolerance is 

“safe.” The two sentences operate in different contexts.

Second, the majority’s reading means that petitioners can 

seize control of the statutory schedule for reviewing existing 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 81

tolerances. Under the FQPA, EPA had to review all existing

tolerances, such as chlorpyrifos, under the new standard. 

And it had to do so “as expeditiously as practicable,” but no 

later than 2006. 21 U.S.C. § 346a(q)(1). This EPA did in 

2006, leaving in effect the chlorpyrifos tolerance. Under the 

FIFRA and the FFDCA, EPA would have to reevaluate 

chlorpyrifos for reregistration no later than October 2022. 

See 7 U.S.C. § 136a(g)(1)(A)(iv); Final Order, 84 Fed. Reg. 

at 35,558. In the interim, any interested person may petition 

EPA to modify or revoke the tolerance. Under the majority’s 

reading of the FFDCA, to respond to the petition, EPA must 

either reregister chlorpyrifos as “safe” or modify or revoke 

the tolerance—but in either case the petition has altered the 

statutory review process for chlorpyrifos. Since petitioners 

can file petitions at will, EPA has lost control over its docket, 

and the statutory schedule has been derailed. As EPA put it, 

if 

EPA were required to truncate its ongoing 

registration review process to make a new 

FFDCA safety finding every time it received 

a petition to modify or revoke tolerances, 

petitioners would effectively have the 

authority to re-order the Administrator’s 

scheduling of registration review decisions 

under FIFRA and dictate the extent of inquiry 

EPA may put to a matter before reaching a 

resolution.

Final Order, 84 Fed. Reg. at 35,565.

C

Despite the (relative) clarity of these provisions, the 

majority makes two arguments to get around this reading of 

§ 346a(b)(2)(A)(i). First, the majority holds that any time 
82 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

EPA considers a petition to modify or revoke an existing 

tolerance (which is governed by the second sentence of 

§ 346a(b)(2)(A)(i)), it is “leav[ing] in effect” the tolerance 

(which is governed by the first sentence). Maj. Op. at 41–

42. It concludes that EPA has “a continuous duty” under the 

FFDCA “to ‘leave in effect’ a tolerance ‘only’ if it finds it is 

safe.” Id. at 42. Second, the majority claims that once EPA 

accepted the petition, because it was not “wholly frivolous,”

EPA had an independent duty to determine whether 

chlorpyrifos is “safe” and cannot now claim that the petition 

was “somehow inadequate.” Id. at 42, 47. Neither point 

withstands scrutiny.

The majority’s focus on EPA “leaving in effect” the 

chlorpyrifos tolerance misconceives the proceedings. Under 

the FFDCA, any petitioner had the right to petition EPA to 

“establish[], modify[] or revok[e]” a tolerance. 21 U.S.C. 

§ 346a(d)(1)(A). “Leave in effect” is not mentioned as an 

option in the petition subsection, and for good reason: “leave 

in effect” has a particular context and meaning in the 

FFDCA. As I have explained, prior to the adoption of the 

FQPA in 1996, which established the current statutory 

standards in the FFDCA, there were tolerances in place for 

pesticides such as chlorpyrifos. The FQPA imposed a duty 

and a schedule on EPA to review all existing tolerances and 

to decide whether to “leave in effect” those tolerances. 

21 U.S.C. § 346a(q)(1). See also id. § 346a(l)(3)(B) 

(explaining if EPA suspends a tolerance it “shall not be 

considered to be in effect,” but if the suspension is 

terminated, “leaving the registration of the pesticide for such 

use in effect,” EPA must rescind the suspension). Because 

the prior tolerances were not established under the same 

standards demanded by the FFDCA, as amended by the 

FQPA, EPA had to determine afresh that the preexisting 

tolerances were “safe.” With respect to that review, EPA 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 83

could “leave in effect a tolerance . . . only if the 

Administrator determines that the tolerance is safe.” Id.

§ 346a(b)(2)(A)(i). Under FIFRA, EPA must also re-certify 

its tolerances no less than every 15 years and decide whether 

to leave a tolerance in effect or modify or revoke it. 7 U.S.C. 

§ 136a(g)(1)(A).6 The majority has conflated EPA’s 

responsibility with respect to the preexisting tolerances with 

its responsibility when it reviews a petition.

The majority reaches its conclusion because it reads 

§ 346a(b)(2)(A)(i) in isolation from the rest of the statute. 

That leads the majority to consider a dictionary definition of 

the phrase. Maj. Op. at 42. Dictionaries can be useful for 

understanding terms. Here, recurring to a dictionary is 

neither necessary nor useful, because the term “leave in 

effect” is not ambiguous when it is read in context with the 

remainder of the statute. See Carson Harbor Vill., Ltd. v. 

Unocal Corp., 270 F.3d 863, 878 (9th Cir. 2001) (en banc) 

6 Contrary to the majority’s statements, FIFRA incorporates the 

FFDCA’s standards. See 7 U.S.C. § 136(bb) (referring to “the standard 

under Section 346a of Title 21”). As part of its reregistration 

requirements for licensing, FIFRA requires EPA to review its FFDCA 

standards no less than every 15 years. See Final Order, 84 Fed. Reg. 

at 35,557 (“In the FQPA, Congress integrated action under the two 

statutes by requiring that the safety standard under the FFDCA be used 

as a criterion in FIFRA registration actions for pesticide uses that result 

in residues in or on food.”). Because FIFRA requires periodic 

recertification under FFDCA, the FFDCA standard governs 

chlorpyrifos’s use, independent of anything required for licensing under 

FIFRA. The majority repeatedly misses this point. See Maj. Op. at 43–

44 (“[EPA’s claim that reregistration is required by FIFRA] is 

unpersuasive because of the differences between FIFRA and the 

FFDCA. The statutes impose different duties that require different 

assessments.”), 51 (“FIFRA registration review . . . is a different animal, 

in that it permits a balancing of multiple factors, whereas a FFDCA 

review is limited to the sole issue of safety . . . .”).
84 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

(“Where the language is plain and admits of no more than 

one meaning the duty of interpretation does not arise, and the 

rules which are to aid doubtful meanings need no 

discussion.” (quoting Caminetti v. United States, 242 U.S. 

470, 485 (1917)); see also Hughes Aircraft Co. v. Jacobson, 

525 U.S. 432, 438 (1999) (“[W]here the statutory language 

provides a clear answer, [the inquiry] ends there . . . .”); 

Robinson v. Shell Oil Co., 519 U.S. 337, 340 (1997) (“Our 

inquiry must cease if the statutory language is unambiguous 

and the statutory scheme is coherent and consistent.”

(internal quotation marks and citations omitted)); United 

States v. Williams, 659 F.3d 1223, 1225 (9th Cir. 2011) (“If 

the plain meaning of the statute is unambiguous, that 

meaning is controlling . . . .”). When the statute offers a 

definition of a term, the statutory definition—even if it is a 

functional usage—governs. Carson Harbor Vill., 270 F.3d 

at 878 (“When a statute includes an explicit definition, 

however, we must follow that definition, even if it varies 

from that term’s ordinary meaning.” (quoting Stenberg v. 

Carhart, 530 U.S. 914, 942 (2000) (alteration omitted)); see 

also United States v. Havelock, 664 F.3d 1284, 1289 (9th 

Cir. 2012) (en banc) (“Statutory construction must begin 

with the language employed by Congress and the assumption 

that the ordinary meaning of that language accurately 

expresses the legislative purpose. That assumption, 

however, does not apply where Congress provides a 

statutory definition.” (internal citations and quotation marks 

omitted)). The FFDCA, as amended by the FQPA, is quite 

clear that “leave in effect” refers to a particular kind of 

proceeding mandated by Congress.

That brings us to the majority’s second point. The 

majority attempts to shift the risk of nonpersuasion through 

a contorted reading of EPA’s regulations regarding the filing 

of a petition. According to the majority, EPA has a 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 85

“gatekeeping authority to reject a wholly frivolous petition.” 

Maj. Op. at 47. But if EPA accepts a petition, it “trigger[s] 

the EPA’s duty to ensure a reasonable certainty of no harm”

by re-evaluating chlorpyrifos and, if it decides to “leave in 

effect” the tolerance, it must certify chlorpyrifos as “safe.” 

Id. According to the majority, accepting a petition flips the 

risk of nonpersuasion. But EPA’s regulations say nothing of 

the kind.

In an exercise of its “gatekeeping authority,” EPA has 

adopted “Procedure for modifying and revoking tolerances 

or exemptions from tolerances.” 40 C.F.R. § 180.32. That 

regulation provides in relevant part:

Any person may file with the Administrator a 

petition proposing the issuance of a 

regulation modifying or revoking a tolerance 

or exemption from a tolerance for a pesticide 

chemical residue. The petition shall furnish 

reasonable grounds for the action sought. 

Reasonable grounds shall include . . . an 

assertion of facts (supported by data if 

available) showing that new uses for the 

pesticide chemical have been developed or 

old uses abandoned, that new data are 

available as to toxicity of the chemical, or 

that experience with the application of the 

tolerance or exemption from tolerance may 

justify its modification or revocation.

Id. § 180.32(b). There is not a word in the regulation that 

would affect the risk of nonpersuasion. The regulation 

requires little to be a qualifying petition: “reasonable 

grounds,” including “an assertion of facts” which shall be 

“supported by data if available.” Id. (emphasis added). That 
86 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

is the most modest of rules. EPA will generously accept 

such petitions and consider them. Accepting a petition—

which in the majority’s phrase means that they are not 

“wholly frivolous”7—is the lowest of bars. This is as it 

should be. We want interested persons—“any person”—to 

be able to go to EPA and suggest that it take a second look 

at a tolerance for a pesticide going on our food. But the 

majority takes EPA’s decision to accept the petition as 

nullifying EPA’s prior decision to approve the tolerance; 

effectively, EPA must start all over again. That’s not how 

administrative law usually works. Under the FFDCA, EPA 

must modify or revoke the tolerance if it is “not safe.” The 

majority would require EPA to prove that the tolerance is 

“safe.”

Although EPA’s Final Order was overdue, there was 

nothing improper in its form. EPA denied the petition and 

instead relied upon its 2006 safety determination for 

chlorpyrifos tolerances because it found that the data and 

studies supporting the petition were “not sufficiently valid, 

complete, and reliable” to support revocation. Final Order, 

84 Fed. Reg. at 35,562–63. In other words, the data 

supporting the petition was not sufficient to support a 

determination that chlorpyrifos tolerances are “not safe.” 

21 U.S.C. § 346a(b)(2)(A)(i).

The FFDCA does not require EPA to make a new safety 

determination in response to a petition supported solely by 

studies that EPA has already considered and found 

insufficient for revocation while conducting its FIFRA 

review. Here, EPA considered the petition’s cited studies at 

multiple instances during its own review and found that they 

7 So far as I can tell, the phrase “wholly frivolous” belongs to the 

majority.
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 87

were not reliable enough to support revocation without more 

information. See Final Order, 84 Fed. Reg. at 35,563. The 

agency’s determination that the petition did not present 

sufficiently valid, complete, or reliable information to 

support revocation is thus supported by the record. See

§ 346a(b)(2)(D). Because the 2007 petition did not present 

reasonable grounds for modification or revocation, EPA was 

entitled to rely upon its 2006 safety finding while it engaged 

in its FIFRA review of chlorpyrifos tolerances. The 

tolerance had already been deemed “safe,” and the petition 

did not raise sufficient grounds to overcome that 

presumption.

Under a correct reading of the statute, and proper 

allocation of the risk of nonpersuasion, we should be 

reviewing EPA’s determination that the petition, and the 

evidence it mustered, was insufficient to determine that the 

chlorpyrifos tolerance is “not safe.” That is not the inquiry 

the majority conducts, so in Part II I will review the 

proceedings before EPA, as punctuated by our orders, and 

its Final Order, which is the only decision we have authority 

to review. 5 U.S.C. § 704.

II

EPA’s denial of the 2007 petition was not arbitrary or 

capricious. The denial of the petition did not conflict with 

any final agency findings or conclusions and, to the contrary, 

was supported by the extensive record of EPA’s concerns 

with the petition’s supporting studies over the course of 

nearly a decade. The only final agency action in effect for 

chlorpyrifos tolerances is the 2006 safety determination, and 

EPA’s denial of the petition comports with this 

determination.
88 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

I will begin with a brief review of EPA’s 2006–17 

proceedings, with some emphasis on the questions and 

qualifications EPA raised at each step of those proceedings. 

I will then turn to the Final Order and our review under the 

APA.

A

In 2006, pursuant to the FFDCA, EPA completed a 

tolerance reassessment of chlorpyrifos and found that 

chlorpyrifos was eligible for reregistration and met the 

standard of 21 U.S.C. § 346a(b)(2). EPA, Office of 

Prevention, Pesticides and Toxic Substances, Memo to Jim 

Jones from Debra Edwards, Finalization of Interim 

Reregistration Eligibility Decisions and Interim Tolerance 

Reassessment and Risk Management Decisions for the 

Organophosphate Pesticides, and Completion of the 

Tolerance Reassessment and Reregistration Eligibility 

Process for the Organophosphate Pesticides (July 31, 2006) 

(2006 Reregistration Decision); see also Final Order, 

84 Fed. Reg. at 35,558. In doing so, EPA found that 

chlorpyrifos tolerances were safe and left them in effect.

1. The Petition is filed; EPA conducts various studies 

for reregistration

In September 2007, the Pesticide Action Network North 

America (PANNA) and the National Resources Defense 

Council (NRDC) filed a petition with EPA to revoke all 

tolerances for chlorpyrifos based on new studies purporting 

to show that current chlorpyrifos tolerances were not safe. 

See Petition to Revoke All Tolerances and Cancel All 

Registrations for the Pesticide Chlorpyrifos; Notice of 

Availability, 72 Fed. Reg. 58,845 (Oct, 17, 2007); see also 

Final Order, 84 Fed. Reg. at 35,556. Petitioners raised ten 

claims alleging numerous errors in the 2006 Reregistration 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 89

Decision, including claims that EPA ignored or 

misinterpreted data.8 EPA was able to resolve seven of the 

ten claims relatively quickly. In July 2012 and July 2014, 

EPA issued interim responses indicating its intent to deny all 

but the three claims at issue here (grounds 7–9 in the 

petition), and it informed Petitioners of its intent to finalize 

all interim conclusions (grounds 1–6, and 10) when it 

resolved the remaining three claims, a decision to which 

Petitioners did not object. Final Order, 84 Fed. Reg. at 

35,556; see also In re Pesticide Action Network North 

America (PANNA I), 532 F. App’x 649 (9th Cir. 2013) 

(denying petition for mandamus). The three claims not 

addressed by EPA in those responses were interrelated and 

concerned the potential for chlorpyrifos exposure at current 

tolerance levels to cause neurodevelopmental effects in 

children. Final Order, 84 Fed. Reg. at 35,556. However, 

EPA did not give these claims short shrift. Instead, early in 

its review, in 2009, the agency found the issues raised 

important enough questions that they should be addressed as 

part of an accelerated reregistration review of chlorpyrifos. 

Id. at 35,556 (noting that these claims “raised novel, highly 

complex scientific issues” that should be addressed in EPA’s 

8 Petitioners alleged that EPA: (1) “ignored genetic evidence of 

vulnerable populations”; (2) “needlessly delayed a decision regarding 

endocrine disrupting effects”; (3) “ignored data regarding cancer risks”; 

(4) “misrepresented risks and failed to apply FQPA 10X safety factor” 

in its 2006 cumulative risk assessment; (5) “over-relied on registrant 

data”; (6) “failed to properly address the exporting hazard in foreign 

countries from chlorpyrifos”; (7) “failed to quantitatively incorporate 

data demonstrating long-lasting effects from early life exposure to 

chlorpyrifos in children”; (8) “disregarded data demonstrating that there 

is no evidence of a safe level of exposure during pre-birth and early life 

stages”; (9) “failed to cite or quantitatively incorporate studies and 

clinical reports suggesting potential adverse effects below 10% 

cholinesterase inhibition”; and (10) “failed to incorporate inhalation 

routes of exposure.” Final Order, 84 Fed. Reg. at 35,556.
90 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

expedited reregistration review). Despite its 2022 statutory 

deadline, EPA announced that it planned to prioritize review 

of chlorpyrifos and complete reevaluation by 2015, years 

ahead of schedule. Id. at 35,558. However, this review 

proved to be complex, particularly with regard to the 

potential human health risks and neurodevelopmental effects 

of chlorpyrifos tolerances. Id.

In the interim, EPA convened scientific panels to 

evaluate the evidence and published reports. In 2008, as part 

of its reregistration review, EPA published a Science Issue 

Paper addressing chlorpyrifos hazards. EPA, Office of 

Pesticide Programs, Science Issue Paper: Chlorpyrifos 

Hazard and Dose Response Characterization (Aug. 21, 

2008). The paper summarized “data relevant to infants, 

children, and pregnant women,” interpreted this data, and 

suggested alternatives for updating the mechanism used to 

assess chlorpyrifos tolerance safety. Id. at 7. The paper 

“preliminarily concluded that chlorpyrifos likely played a 

role in” adverse health effects in children. Id. at 52. 

However, the paper specifically noted that there had not been 

“a full and complete risk assessment/characterization” of the 

human health risks of chlorpyrifos and that “the [EPA] has 

not developed any final conclusions regarding updates to the 

chlorpyrifos hazard assessment.” Id. at 7.

Later that year, EPA convened a Science Advisory Panel 

(SAP or the Panel), a federal advisory committee 

“established under the provisions of FIFRA” that “serves as 

the [EPA’s] primary scientific peer review mechanism” for 

pesticide matters, to peer review the paper. EPA, SAP 

Minutes No. 2008-04: A Set of Scientific Issues Being 

Considered by the Environmental Protection Agency 

Regarding: The Agency’s Evaluation of the Toxicity Profile 

of Chlorpyrifos 2 (Sept. 16–18, 2008). The SAP also 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 91

considered several new studies concerning the risk of 

chlorpyrifos to pregnant women and children. The SAP’s 

evaluation noted that “Panel members were concerned that a 

high degree of uncertainty is evident in the available data

. . . .” Id. at 10. First, the Panel expressed concerns about 

several laboratory studies involving live rodents and the 

meaning of phrases used and experimental methods 

employed, and concluded that this data was “insufficient.” 

Id. at 11–12. The Panel also considered three epidemiology 

studies, referred to as the Mt. Sinai, CHAMACOS, and 

Columbia University studies. The Columbia Study, which 

assessed chlorpyrifos risk to pregnant women, infants, and 

children, commanded particular attention. Id. at 12. The 

Panel found defects in all three of the studies, including 

concerns that the Columbia Study—the most robust of the 

three—did not provide sufficient data to be the sole factor 

for risk assessment or modifying tolerances and produced 

uncertainty through its measurement method. Id. at 12–13, 

32–35, 43–44. Although the SAP found that the studies 

“raise concerns,” the SAP also agreed that the studies were 

inconclusive. Id. at 13–14. The SAP concluded that 

“chlorpyrifos could have contributed to the birth and 

neurodevelopmental outcomes” indicated in the studies, but 

“that due to their limitations, the epidemiological data 

currently available are useful primarily for hazard 

identification.” Id. at 13.

In 2011, EPA published a Preliminary Human Health 

Risk Assessment (PHHRA) for chlorpyrifos as part of its 

forthcoming FIFRA review. EPA, Office of Chemical 

Safety & Pollution Prevention, Chlorpyrifos: Preliminary 

Human Health Risk Assessment for Registration Review 1–

2 (June 30, 2011). This assessment again considered the 

laboratory and epidemiology studies evaluated by the 2008 

SAP and similarly noted their limitations. Id. at 29–34. The 
92 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

PHHRA also considered developments since the 2008 SAP, 

including new data and follow-up analysis on the Columbia 

Study that had been recommended by the Panel. Id. at 34. 

EPA came to no definitive conclusion in the PHHRA, instead 

stating that analyses were ongoing and the final assessment 

would

be based on a full scientific weight of 

evidence approach that considers the best 

available science and integrates all key lines 

of evidence, from empirical animal 

toxicology to observational human 

epidemiology studies, in an integrated 

framework analysis and will transparently 

address and clearly characterize the strength 

of the evidence and areas of remaining 

uncertainty and variability.

Id. at 42.

In April 2012, EPA again convened the SAP to consider 

the health effects of chlorpyrifos. EPA, SAP Minutes 2012-

04: A Set of Scientific Issues Being Considered by the 

Environmental Protection Agency Regarding Chlorpyrifos 

Health Effects (April 10–12, 2012). The SAP recognized “a 

growing body of literature with laboratory animals (rats and 

mice) indicating that gestational and/or early postnatal 

exposure to chlorpyrifos may cause persistent effects into 

adulthood” and epidemiology studies “that have reported 

associations with birth outcomes, childhood 

neurobehavioral and neurodevelopment outcomes.” Id.

at 10. In addition to nine new laboratory studies, the 2012 

SAP reviewed the same laboratory studies evaluated by the 

2008 SAP, again noting the laboratory studies’ limitations 

and “recommend[ing] these experimental outcomes be 
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regarded as exploratory, and hypothesis-generating, as 

opposed to being evidence of toxicity.” Id. at 15. However, 

the Panel found that, despite concerns about the studies, “the 

collective weight of evidence from these studies demonstrate 

that it is probable that there are significant long-term adverse 

effects from chlorpyrifos exposure.” Id. at 16. The 2012 

SAP likewise considered the same epidemiology studies 

analyzed by the 2008 SAP, recognizing their strengths and 

limitations. Id. at 17–18, 48–50. The Panel noted that the 

epidemiological studies indicated “that chlorpyrifos likely 

plays a role in impacting the neurodevelopmental outcomes 

examined in the three cohort studies” but proposed further 

study because “the data generated from these studies alone 

are not adequate enough” to make a definitive risk 

assessment. Id. at 18–19. The SAP advised EPA to “explore 

additional ways of using these studies” and conduct 

additional research. Id. at 19–20.

In December 2014, EPA published a Revised Human 

Health Risk Assessment (2014 RHHRA) for chlorpyrifos. 

EPA, Office of Chemical Safety & Pollution Prevention, 

Chlorpyrifos: Revised Human Health Risk Assessment for 

Registration Review (Dec. 29, 2014). This revised 

assessment incorporated comments on the preliminary 

assessment and included assessment of new data. Id. at 5. 

The 2014 RHHRA found that data, including the laboratory 

and epidemiology studies, “indicate that chlorpyrifos likely 

played a role in the neurodevelopmental outcomes reported 

by the epidemiologic study (Columbia University) 

investigators” but that “uncertainties . . . preclude definitive 

causal inference.” Id. at 6. Yet again, EPA noted that the 

studies reflected both strengths and “notable limitations.” 

Id. at 43. In this assessment, EPA also revised its approach 

to calculating chlorpyrifos “points of departure,” or the 
94 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

ceiling for safe exposure to a pesticide based on these 

studies. Id. at 40, 62–70, 131.

In January 2015, EPA announced the availability of the 

2014 RHHRA and sought public comments on “the Agency’s 

risk assessment methodologies and assumptions . . . [and] 

suggestions for mitigating any risks identified in the [2014 

RHHRA].” Chlorpyrifos Registration Review; Revised 

Human Health Risk Assessment; Notice of Availability, 

80 Fed. Reg. 1,909, 1,910 (Jan. 14, 2015). Additionally, in 

March 2015, EPA advised counsel for the petitioners by 

letter that it intended to deny the three unresolved claims in 

the 2007 Petition—the claims at issue in this appeal. EPA, 

Office of Chemical Safety & Pollution Prevention, Re: 

Chlorpyrifos Petition Dated September 12, 2007; March 

2015 Provisional Response (Mar. 26, 2015). EPA 

incorporated its prior partial petition responses from 2012 

and 2014, which denied seven of the ten claims raised in the 

petition. Id. With respect to the three remaining claims, 

which were those related to infants and children and based 

on the Columbia, Mount Sinai, and CHAMACOS studies, 

EPA advised counsel that “EPA does not believe the claims 

raised in your petition establish a basis to revoke all 

chlorpyrifos tolerances and cancel all chlorpyrifos 

registrations.” Id. at 3. The letter noted that EPA had “risk 

concerns” with exposure to chlorpyrifos in drinking water, 

but it was seeking comment on its 2014 RHHRA and would 

“take appropriate action under the FFDCA and/or FIFRA to 

ensure that exposures to chlorpyrifos are consistent with the 

requirements of those statutes.” Id. at 3–4.

2. We issue mandamus; EPA proposes to revoke the 

tolerances

Six months later, in August 2015, we issued a writ of 

mandamus ordering EPA “to issue either a proposed or final 
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revocation rule or a full and final response to the 

administrative petition.” In re Pesticide Action Network 

North America (PANNA II), 798 F.3d 809, 815 (9th Cir. 

2015). In response, EPA issued a proposed rule to revoke 

all chlorpyrifos tolerances because “EPA cannot, at this 

time, determine that aggregate exposure to residues of 

chlorpyrifos, including all anticipated dietary exposures and 

all other non-occupational exposures for which there is 

reliable information, are safe.” Chlorpyrifos; Tolerance 

Revocations, 80 Fed. Reg. 69,080, 69,080–81 (Nov. 6, 2015) 

(2015 Proposed Rule). EPA advised that it was issuing the 

proposed rulemaking because of our mandamus order and 

that the proposal was “in advance of [EPA] completing its 

refined drinking water assessment.” Id. at 69,083. EPA 

explained that it “believe[d] that acute dietary risk from food 

only does not present a significant risk” and that “EPA 

would therefore not be proposing the revocation of 

chlorpyrifos if dietary exposures were confined to food.” Id.

at 69,096–97. The basis for the proposed revocation was 

instead new data indicating that “for some portions of the 

country, food exposures, when aggregated with residential 

exposures and potentially more significant drinking water 

exposures, do present a significant risk concern and support 

revocation of all chlorpyrifos tolerances.” Id. at 69,097. At 

the same time, EPA stated that it had “insufficient time to 

address comments received on the [2014] RHHRA,” and it 

would “update this action . . . as EPA completes additional 

work.” Id. at 69,083. EPA also cautioned that its analysis 

was incomplete and that it might yet modify the proposed 

rule based on the completed analysis and comments. Id. We 

then ordered EPA to take final action on the proposed rule 

and on PANNA and NRDC’s petition no later than 

December 30, 2016. In re Pesticide Action Network North 

America (PANNA III), 808 F.3d 402, 403 (9th Cir. 2015).
96 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

In March 2016, EPA published a new Chlorpyrifos Issue 

Paper and solicited comment from the SAP regarding 

changing points of departure based solely on 

neurodevelopmental effects measured by the Columbia 

Study. EPA, Office of Pesticide Programs, Chlorpyrifos 

Issue Paper: Evaluation of Biomonitoring Data from 

Epidemiology Studies 9 (Mar. 11, 2016) (2016 Issue Paper). 

At the time EPA had proposed to revoke chlorpyrifos

tolerances, “EPA had not completed a refined drinking water 

assessment or additional analysis of the hazard from 

chlorpyrifos that was suggested by several commenters.” 

EPA, Office of Chemical Safety & Pollution Prevention, 

Chlorpyrifos: Revised Human Health Risk Assessment for 

Registration Review 3 (Nov. 3, 2016) (2016 RHHRA). After 

engaging in additional research, EPA—in this Issue Paper—

proposed using different “toxicological points of departure”

based on data from the Columbia Study, and sought the 

advice of the 2016 SAP on this new approach. 2016 Issue 

Paper at 9.

In April 2016, the SAP convened to review the Issue 

Paper. EPA, SAP Minutes No. 2016-01: A Set of Scientific 

Issues Being Considered by the Environmental Protection 

Agency Regarding: Chlorpyrifos: Analysis of Biomonitoring 

Data (April 19–21, 2016) (2016 SAP Minutes). The SAP 

expressed significant disagreement with the substance of the 

paper, including a lack of confidence that the Columbia 

Study “c[ould] accurately be used” in determining new 

points of departure. Id. at 18. The panel “thought the quality 

of the [Columbia Study] data is hard to assess when raw 

analytical data have not been made available, and the study 

has not been reproduced.” Id. The SAP noted that review 

of the raw data from the Columbia Study could resolve some 

uncertainty regarding the study’s conclusions. Id. at 20.
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By mid-2016, claiming “extraordinary circumstances,”

EPA requested a six month extension on our order of final 

action. In re Pesticide Action Network North America

(PANNA IV), 840 F.3d 1014, 1015 (9th Cir. 2016). EPA 

advised us that it had “issued its proposed rule before 

completing two studies that may bear on the Agency’s final 

rule.” Id. at 1015. We characterized EPA’s request as 

“another variation on a theme ‘of partial reports, missed 

deadlines, and vague promises of future action.’” Id.

(quoting PANNA II, 798 F.3d at 811). We denied EPA’s 

request and ordered final action by March 31, 2017. Id.

In November 2016, EPA released yet another Revised 

Human Health Risk Assessment, responding to the 2016 

SAP’s concerns. EPA, Office of Chemical Safety & 

Pollution Prevention, Chlorpyrifos: Revised Human Health 

Risk Assessment for Registration Review (Nov. 3, 2016) 

(2016 RHHRA). EPA recounted that in 2013 it had sought 

the raw data used in the Columbia Study, and although the 

researchers would not agree to provide EPA with the data, 

EPA “gained valuable insight into the conduct of the study.” 

Id. at 9–10. EPA concluded that the SAP had rejected both 

the approach in the 2015 Proposed Rule and the new method 

based on the Columbia Study. Id. at 3. EPA agreed with the 

SAP that, despite uncertainties in the studies, there was 

“sufficient evidence that there are neurodevelopmental 

effects occurring at chlorpyrifos exposure levels” below the 

tolerances. Id. at 13. As a result, EPA proposed following 

the 2016 SAP’s recommendation to use a hybrid point of 

departure, rather than relying solely on the data from the 

Columbia Study. Id. at 13–14.

Within two weeks of issuing the 2016 RHHRA, EPA 

reopened the comment period on the 2015 Proposed Rule. 

Chlorpyrifos; Tolerance Revocations; Notice of Data 
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Availability and Request for Comment, 81 Fed. Reg. 81,049 

(Nov. 17, 2016) (2016 Request for Comments). EPA noted 

that it was not proposing “a change to the EPA’s proposal to 

revoke all tolerances but it does modify the methods and risk 

assessment used to support that finding in accordance with 

the advice of the SAP.” Id. at 81,050; see also id. (“[T]he 

agency’s analysis provided in this notice continues to 

indicate that the risk from the potential aggregate exposure 

does not meet the FFDCA safety standard.”). At the same 

time, EPA expressed frustration with the process, and 

advised that “the timing of EPA’s issuance of the proposal 

was dictated” by our order in PANNA II. Id. EPA was clear 

that the basis for its proposed revocation depended on 

studies that were incomplete. It observed that EPA had 

completed a water assessment, but “[b]ecause of the court 

decision . . . EPA was not able to complete a more refined 

drinking water assessment for chlorpyrifos in advance of the 

proposed rule” and that with additional time it conducted the 

assessment to provide “a more tailored approach to risk 

mitigation.” Id. at 81,051. EPA admitted that

In the proposal, EPA proposed revoking all 

tolerances largely because the agency could 

not make a safety finding based on drinking 

water exposure in highly-vulnerable 

watersheds. EPA reasoned if it could better 

identify where such vulnerable areas might 

be, it could be possible for registrants to 

amend product labeling in ways that might 

make unnecessary some number of the 

proposed tolerance revocations.

Id. Importantly, EPA warned that its proposed course of 

conduct was not fixed:
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Since EPA is still in the process of 

deliberating the provisions of a final rule, 

EPA cannot definitively state whether this 

information will provide support for any 

provision of the final rule, or that the agency 

has determined that it is appropriate to rely on 

this information in developing the final rule.

Id.

3. EPA denies the petition; we issue mandamus

In April 2017, EPA reversed course, issuing a final 

response to the 2007 petition, which denied it in full. 

Chlorpyrifos; Order Denying PANNA and NRDC’s Petition 

to Revoke Tolerances, 82 Fed. Reg. 16,581 (April 5, 2017) 

(2017 Denial). The order stated:

Following a review of comments on both the 

November 2015 proposal and the November 

2016 notice of data availability, EPA has 

concluded that, despite several years of 

study, the science addressing 

neurodevelopmental effects remains 

unresolved and that further evaluation of the 

science during the remaining time for 

completion of registration review is 

warranted to achieve greater certainty as to 

whether the potential exists for adverse 

neurodevelopmental effects to occur from 

current human exposures to chlorpyrifos. 

EPA has therefore concluded that it will not 

complete the human health portion of the 

registration review or any associated 

tolerance revocation of chlorpyrifos without 
100 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

first attempting to come to a clearer scientific 

resolution on those issues.

Id. at 16,583. EPA thus denied the petition without resolving 

all scientific uncertainty concerning the tolerances 

“[b]ecause the 9th Circuit’s August 12, 2016 order has made 

clear, however, that further extensions to the March 31, 2017 

deadline for responding to the Petition would not be 

granted.” Id. (referring to PANNA IV, 840 F.3d at 1015). 

EPA explained that the comments received in response to the 

2015 Proposed Rule “suggest that there continue to be 

considerable areas of uncertainty with regard to what the 

epidemiology data show and deep disagreement over how 

those data should be considered in EPA’s risk assessment.” 

Id. at 16,590. It then explained why it was denying the 

petition, rather than continuing its prior course:

As the 9th Circuit has made clear . . . EPA 

must provide a final response to the Petition 

by March 31, 2017, regardless of whether the 

science remains unsettled and irrespective of 

whatever options may exist for a more 

complete resolution of these issues . . . .

Although past EPA administrations had 

chosen to attempt to complete [FIFRA] 

review several years in advance of the 

statutory deadline (and respond to the 

Petition on the same time frame), it has 

turned out that it is not possible to fully 

address these issues early in the registration 

review period . . . . Accordingly, EPA is 

denying these Petition claims and intends to 

complete a full and appropriate review of the 

neurodevelopmental data before either 
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finalizing the [2015] proposed rule . . . or 

taking an alternative regulatory path.

Id. EPA concluded that “given the importance of this matter 

and the fact that critical questions remain regarding the 

significance of the data addressing neurodevelopmental 

effects, EPA believes there is good reason to extend the 

registration review of chlorpyrifos and therefore to deny the 

Petition.” Id.

Various organizations petitioned our court for review of 

EPA’s order. On review of EPA’s 2017 Denial, the panel 

ordered EPA to revoke the chlorpyrifos tolerances. League 

of United Latin American Citizens v. Wheeler (LULAC I), 

899 F.3d 814, 829 (9th Cir. 2018). Judge Fernandez 

dissented on the grounds that the 2017 Denial was not a final 

action. Id. at 830–32 (Fernandez, J., dissenting). We 

granted en banc review, vacated the panel opinion, and 

ordered EPA to issue a final order. League of United Latin 

American Citizens v. Wheeler (LULAC II), 922 F.3d 443, 

445 (9th Cir. 2019) (en banc). EPA issued its Final Order

in July 2019, and we referred the petition back to the threejudge panel. League of United Latin American Citizens v. 

Wheeler (LULAC III), 940 F.3d 1126, 1127 (9th Cir. 2019).

B

EPA’s Final Order responded to the two objections 

raised in LULAC I: (1) that the “EPA has unlawfully left 

chlorpyrifos tolerances in place without making the safety 

finding required by the FFDCA”; and (2) that EPA must 

revoke the tolerances because it “has previously found that 

chlorpyrifos tolerances are unsafe and has not disavowed 

those findings.” Final Order, 84 Fed. Reg. at 35,561.
102 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

1. Failure to find that chlorpyrifos is “safe”

EPA first addressed Petitioners’ argument that EPA was 

required to make a new safety finding to deny the petition. 

EPA found that it was not required to make a new safety 

determination in response to every revocation petition, the 

FFDCA did not require revocation in the absence of a new 

safety determination for each petition, and even if a new 

safety determination was required, both the FFDCA and 

EPA implementing regulations “require petitioners seeking 

withdrawal of a tolerance to support this request with valid, 

complete and reliable data that set forth why the tolerances 

are unsafe.” Id. at 35,562.

The agency found that petitioners had not met their 

burden of presenting evidence that the tolerances must be 

revoked because “the information yet presented by 

Petitioners is not sufficiently valid, complete, and reliable.” 

Id. at 35,562–63. EPA had already considered, during its 

2006 review, the laboratory and epidemiological studies 

cited by Petitioners and had “consistently concluded” these 

studies did not warrant revocation based on “an evaluation 

across multiples lines of evidence.” Id. at 35,563. EPA 

determined these studies were deficient because they lacked 

a “mechanistic understanding for effects on the developing 

brain,” which precluded EPA from having a “valid or 

reliable way[] to bridge the scientific interpretation” of the 

studies with chlorpyrifos; the dosing regimen of the in vivo 

studies presented problems for “quantitative interpretation 

and extrapolation of the results” because they did not align 

with “internationally accepted protocols”; and EPA had been 

unable to obtain the raw data underlying the epidemiological 

studies, despite numerous efforts, to allow for verification of 

validity and reliability as well as replication. Id. EPA 

candidly acknowledged that its conclusion was “at odds”
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with its 2016 RHHRA but ultimately asserted that it had 

“undertaken considerable efforts to assess the available 

chlorpyrifos data.” Id. at 35,564; see also id. (“EPA 

acknowledges this conclusion differs from the position 

supported in the 2016 revised human health risk 

assessment.”). The agency concluded that “the 

shortcomings of the data identified raise issues of validity, 

completeness and reliability under the FFDCA that direct 

against using the data for risk assessment at this time.” Id.

EPA explained that a majority of the 2016 SAP had 

concluded that use of the scientific studies under review for 

developing points of departure “could not be justified by any 

sound scientific evaluation.” Id. at 33,564. The SAP 

“expressed significant reservations” about using the studies 

as the sole source of revised points of departure and “noted 

the incompleteness of the information,” including the 

“reproducibility” of the data. Id. EPA concluded that 

“[b]ased on the uncertainties identified by the 2016 SAP,”

the data were “not complete.” Id. EPA further laid out its 

requests to obtain the raw data underlying the studies and 

“visit[] [to] Columbia University in an attempt to better 

understand their study results and what raw data exist.” Id.

at 33,565. Although the university initially had pledged to 

share its data, it failed to produce it, citing “privacy 

concerns.” Id. As a result, “EPA cannot validate or confirm 

the data analysis performed, the degree to which the 

statistical methods employed were appropriate, or the extent 

to which (reasonable or minor) changes in assumptions may 

have changed any final results or conclusions.” Id. As a 

consequence, EPA concluded petitioners had “failed to meet 

their initial burden of providing sufficiently valid, complete, 

and reliable evidence that neurodevelopmental effects may 

be occurring at levels below EPA’s current regulatory 

standard.” Id.
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EPA further concluded that denying the 2007 petition 

was appropriate because the claims in the petition would be 

subject to FIFRA registration review, which is a “more upto-date, thorough and methodical” review. Id. EPA 

reiterated its commitment to complete FIFRA and FFDCA 

review of chlorpyrifos tolerances in advance of the October 

2022 deadline, anticipating some updates “by summer of 

2020.” Id. at 35,566.

2. EPA’s prior finding that chlorpyrifos is “not safe”

EPA also addressed petitioners’ objection that the 

agency had already found chlorpyrifos to be unsafe in its 

2015 proposed tolerance revocation. Id. at 35,566. EPA, 

however, was quite clear that “EPA has not made any 

findings that chlorpyrifos tolerances are not safe.” Id. EPA 

pointed out that its last final action regarding the safety of 

chlorpyrifos tolerances—and the only regulatory finding in 

effect—was its 2006 reregistration and safety determination. 

Id. The 2015 Proposed Rule was not a final agency action, 

and “EPA made clear it was issuing the proposal because of”

the Ninth Circuit’s order, “without having resolved many of 

the issues critical to EPA’s FFDCA determination and 

without having fully considered comments previously 

submitted to the Agency.” Id. It was up to EPA to “choose 

to finalize, modify or withdraw the proposal based on the 

comments received.” Id. Accordingly, its prior proposed 

findings were “not binding pronouncements.” Id.

C

EPA’s decision to deny the petition in its entirety in 

response to our writ of mandamus is entirely reasonable. We 

ordered EPA to grant or deny the petitions; EPA did as we 

ordered. It has explained why it did so and explained how it 

will proceed with the chlorpyrifos reregistration, in which it 
LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN 105

will have to decide whether it is “safe.” There is nothing 

arbitrary or capricious in EPA’s decision.

Although petitioners can argue that the denial of the 

petition conflicts with EPA’s prior proposal, the 2015 

Proposed Rule is just that—a proposed rule. 2015 Proposed 

Rule, 80 Fed. Reg. at 69,083 (“EPA may update this 

[proposed rule] with new or modified analyses as EPA 

completes additional work after this proposal.”). “Agencies 

are entitled to change their minds.” Defenders of Wildlife v. 

Zinke, 856 F.3d 1248, 1262 (9th Cir. 2017) (citation 

omitted); see also Nat’l Ass’n of Home Builders v. Defenders 

of Wildlife, 551 U.S. 644, 658–59 (2007) (“[T]he only 

‘inconsistency’ respondents can point to is the fact that the 

agencies changed their minds—something that, as long as 

the proper procedures were followed, they were fully 

entitled to do.”). “The federal courts ordinarily are 

empowered to review only an agency’s final action, see 

5 U.S.C. § 704, and the fact that a preliminary determination

. . . is later overruled . . . does not render the decisionmaking 

process arbitrary and capricious.” Nat’l Ass’n of Home 

Builders, 551 U.S. at 659. Agencies that change their mind 

are not “subjected to more searching review.” FCC v. Fox 

Television Stations, Inc., 556 U.S. 502, 514 (2009). What is 

important is that the agency “display awareness that it is 

changing position” and has explained itself. Id. at 515. EPA 

did not act arbitrarily and capriciously merely because it 

reversed course from its 2015 Proposed Rule—a reversal 

that EPA explained.

Nor was the 2016 RHHRA a final agency action. Human 

Health Risk Assessments are part of FIFRA reregistration 

review but are not in themselves safety determinations. 2016 

RHHRA at 3. It is the final Reregistration Eligibility 

Decision—which in this case was issued in 2006—that 
106 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

serves as the final EPA action for determining safety 

pursuant to the FFDCA. 2006 Reregistration Decision at 1–

2. Although the 2016 RHHRA stated that the studies cited 

by the petition provided “sufficient evidence that there are 

neurodevelopmental effects occurring at chlorpyrifos 

exposure levels below” current tolerances, this conclusion is 

tentative until the agency adopts it as part of a final order or 

rule. 2016 RHHRA at 13. The 2016 RHHRA remains part 

of a broader review process that will culminate in another 

Registration Eligibility Decision no later than 2022. In the 

meantime, however, relying on its Scientific Advisory 

Panel, EPA has explained why that study is flawed. The 

methodology used in the 2015 Proposed Rule was rejected 

by the SAP, and the 2016 RHHRA attempted to address the 

SAP’s concerns by using a different approach. Id. at 3–4.

As it is entitled to do, EPA has sufficiently explained its 

rationale for reversing course from the 2015 Proposed Rule

and 2016 RHHRA and denying the petition. EPA was 

required to “examine the relevant data and articulate a 

satisfactory explanation for its action including a rational 

connection between the facts found and the choice made.” 

Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. 

Ins. Co., 463 U.S. 29, 43 (1983) (quotations marks and 

citation omitted). EPA did articulate an explanation for its 

departure from the 2015 Proposed Rule and the 2016 

RHHRA in its 2017 Denial and Final Order. In its 2017 

Denial of the petition, EPA explained that responses from 

the 2016 SAP and comments received in response to the 

2015 Proposed Rule raised “considerable areas of 

uncertainty” regarding the studies. 2017 Denial, 82 Fed. 

Reg. at 16,590. Based on this uncertainty, EPA concluded 

that it should instead “explore approaches raised by the SAP 

and commenters on the proposed rule, and possibly seek 

additional authoritative peer review of EPA’s risk 
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assessment prior to finalizing any regulatory action in the 

course of registration review.” Id.

EPA again explained the rationale for its departure from 

the 2016 RHHRA in its Final Order. EPA explicitly 

recognized its denial of the petition was “at odds with” the 

2016 RHHRA, but it explained that it had “undertaken 

considerable efforts to assess the available chlorpyrifos 

data,” summarizing its longstanding concerns about the 

studies relied on by petitioners. Final Order, 84 Fed. Reg. 

at 35,564. EPA discussed its decision to convene the SAP 

in 2016 to specifically consider the EPA’s proposal to use 

information derived from the Columbia Study to develop a 

point of departure—a meeting EPA noted “was unique in 

focus compared to the previous meetings”—and the SAP’s 

rejection of using that data alone as the basis for the new 

point of departure. Id. EPA explained that the 2016 SAP’s 

feedback on the proposal based on the Columbia Study data 

was “consistent with concerns raised in public comments 

EPA received on the use of the epidemiology data 

throughout the course of registration review.” Id. EPA 

further noted that, although the 2008 and 2012 SAPs 

recognized strengths in the Columbia Study, neither 

recommended changing points of departure based on the 

study, and the 2016 SAP expressed even more reservation 

about using the study in this way. Id. Thus, despite 

preliminary assessments that recognized potential in the 

Columbia Study data, EPA ultimately concluded that “the 

shortcomings of the data identified raise issues of validity, 

completeness and reliability under the FFDCA that direct 

against using the data for risk assessment at this time.” Id. 

EPA also noted that this was not its final conclusion 

regarding the validity of the studies and that it “intends to 

continue its exploration of the uncertainty” with regards to 

the studies’ conclusions. Id. Because these studies—which 
108 LEAGUE OF UNITED LATIN AM. CITIZENS V. REGAN

met the threshold requirements for consideration on the 

merits—were not sufficiently valid, complete, and reliable

to support revocation, EPA decided not to modify or revoke 

the chlorpyrifos tolerances.

Nothing in EPA’s explanations is arbitrary or capricious. 

It is clear that the agency has struggled with the scientific 

studies before it. But nothing in either the procedure or the 

substance of EPA’s actions—aside from playing Hamlet—

suggests that the agency has been irresponsible. To the 

contrary, at every step of the way, EPA has conscientiously 

examined the evidence. In 2015, it told petitioners it would 

deny the petition outright. This was not surprising because 

EPA had long advised the petitioners and other interested 

persons of the flaws in the studies. It changed course later 

that year when it was forced to make a decision in response 

to our writ of mandamus. EPA then proposed revoking the 

chlorpyrifos tolerances based on a novel measure of the 

effect on infants and children—only to have the SAP 

disapprove of the measure in 2016 and recommend further 

study. EPA requested further comments on the science—

and an extension of time to make a decision. When we told 

EPA that there would be no further extensions, EPA called 

for additional comments and repeated that the studies were 

inconclusive, but EPA continued to believe it had no choice 

but to revoke the tolerances. But even as it called for last 

comments, EPA advised that it was “still in the process of 

deliberating the provisions of a final rule.” 2016 Request for 

Comments, 81 Fed. Reg. at 81,051.

So how do we assess this convoluted history? It is 

certainly true that the agency had some stops and starts along 

the way, but that is evidence of deliberate decisionmaking, 

not dereliction of duty. We, of all institutions, should respect 

that there will be give-and-take in complicated matters of 
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consequence. The FFDCA does not demand unanimity 

within EPA, any more than it requires unanimity from this 

court before we may issue a judgment in this case.

In my view, the majority has intervened in ongoing 

debates within EPA over what the evidence proves and how 

it should be weighed. It is not our place to second-guess 

EPA’s scientific assessment of laboratory and 

epidemiological studies supporting the petition. “Deference 

to an agency’s technical expertise and experience is 

particularly warranted with respect to questions involving

. . . scientific matters.” United States v. Alpine Land & 

Reservoir Co., 887 F.2d 207, 213 (9th Cir. 1989). When an 

agency makes determinations “within its area of special 

expertise, at the frontiers of science . . . a reviewing court 

must generally be at its most deferential.” Balt. Gas & Elec. 

Co. v. NRDC, 462 U.S. 87, 103 (1983). The majority 

improperly makes its own assessment of the reliability of the 

studies and whether EPA’s concerns are sufficient to 

determine that chlorpyrifos tolerances are “not safe.” Maj. 

Op. 54–58, 60–63. But EPA’s assessment of the scientific 

strength of the studies supporting the petition is precisely the 

type of analysis that should be given deference. FFDCA 

safety determinations are within EPA’s area of expertise. 

We should not second-guess EPA’s scientific conclusions 

with regards to the value of these studies. EPA’s denial of 

the 2007 petition was neither arbitrary nor capricious.

* * *

The FFDCA does not require EPA to engage in a fullblown FFDCA safety evaluation in response to every 

petition filed with the agency. Instead, where a petition 

presents reasonable grounds for revocation, EPA must 

consider whether the petition puts forth data that supports a 

determination that a pesticide tolerance is not safe. Where 
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the data supporting a petition are not sufficiently valid, 

reliable, or complete, EPA may deny the petition and rest on 

its operative safety determination. Here, EPA complied with 

its statutory obligation: the agency considered the petition on 

the merits and determined that the data supporting the 

petition was insufficient to support revocation. Based on this 

determination, EPA denied the petition and relied on its 2006 

finding that chlorpyrifos tolerances are safe. EPA explained 

the deficiencies in the underlying petition’s supporting 

studies and its rationale for departing from its prior 

preliminary determinations. EPA did all that the FFDCA 

required.

III

Even if I thought the majority had read the statute 

correctly and had a clear-eyed view of the validity and 

weight to be given to the scientific evidence, the remedy 

ordered by the majority is an abuse of our discretion. 

Assuming that petitioners have demonstrated that 

chlorpyrifos is “not safe,” the FFDCA gives EPA the 

discretion to decide whether to modify or to revoke the 

tolerance. See 21 U.S.C. § 346a(b)(2)(A)(i); Maj. Op. at 60

(“[O]nce the EPA has determined that a tolerance is not safe,

. . . it must modify or revoke the tolerance.”). Concluding 

that on this record “the present tolerances are not safe,” Maj. 

Op. at 63, the majority orders EPA to “modify or revoke 

chlorpyrifos tolerances and modify or cancel chlorpyrifos 

registrations,”9 Maj. Op. at 63, and gives EPA 60 days to do 

9 In ordering the modification or cancellation of FIFRA 

registrations, Maj. Op. at 67, the majority has exceeded the scope of what 

a petition under the FFDCA allows: modification or cancellation of 

chlorpyrifos tolerances under the FFDCA. See 21 U.S.C. 

§ 346a(d)(1)(A) (allowing petitions “proposing the issuance of a 
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so, Maj. Op. at 67. It is more than a little ironic that this 

court will have taken over a year since the filing of the last 

brief to decide this case, but we will expect EPA to make an 

informed decision in the next 60 days.

The 60 days the majority gives EPA is not a number 

drawn from the statutes, but one made up by the majority, 

and it may well foreordain the option EPA must choose. In 

my view, the stakes in this case are too high for the majority 

to take upon itself to decide what the United States will do 

with respect to chlorpyrifos. “By pounds of active 

ingredient, [chlorpyrifos] is the most widely used 

conventional insecticide in the country” and for some crops 

it is “currently the only cost-effective choice for control of 

certain insect pests.” Final Order, 84 Fed. Reg. at 35,558.10 

That, of course, is not an argument for finding chlorpyrifos 

safe, as EPA recognized, but it should sharpen our focus on 

what we are doing. See 2017 Denial, 82 Fed. Reg. at 16,590 

(“Although not a legal consideration, it is important to 

recognize that for many decades chlorpyrifos has been and 

remains one of the most widely used pesticides in the United 

States, making any decision to retain or remove this pesticide 

from the market an extremely significant policy choice.”). 

That is why EPA should be considering the options Congress 

regulation establishing, modifying or revoking a tolerance” under that 

statute (emphasis added)). Although modification of revocation of a 

tolerance under the FFDCA will necessarily impact registrations under 

FIFRA, the FFDCA does not afford this court authority to order 

modification or cancellation under FIFRA.

10 Chlorpyrifos tolerances are classified by crop (e.g., alfalfa, 

almonds, apples, corn, cotton, grapes, oranges, pears, soybeans, walnuts, 

and wheat) and usage (e.g., cockroach and fire ant control, mosquito 

abatement, utility pole treatments) and are region specific. The 

complexity of the tolerances is difficult to overstate.
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made available, not us. And we have not given anything but 

the most fleeting consideration to the options.11

It is far from clear that EPA will be able to do anything 

in the next 60 days other than revoke the tolerances. Yet, 

between argument and the issuing of this decision, EPA 

advised us that it has issued an interim decision to reregister 

chlorpyrifos, with modifications. Pesticide Registration 

Review; Proposed Interim Decision for Chlorpyrifos; Notice 

of Availability, 85 Fed. Reg. 78,849 (Dec. 7, 2020) (2020 

Proposed Interim Decision) (inviting comments on EPA, 

Chlorpyrifos: Proposed Interim Registration Review 

Decision (Dec. 3, 2020) (2020 Proposed Interim 

Registration)). In the 2020 Proposed Interim Registration, 

EPA explained that it was proceeding with suggested 

modifications, but that it still faced “numerous novel 

scientific issues, notably the potential for neurodevelopment 

effects on the young.” 2020 Proposed Interim Registration 

Decision at 10. Candidly, EPA stated:

Despite several years of study, the science 

addressing neurodevelopmental effects 

remains unresolved. . . . Notwithstanding, 

11 The majority may have effectively foreclosed other options 

Congress made available to EPA. Under the FFDCA, if a petitioner can 

show that it not safe, EPA must modify or revoke the tolerance; or, in its 

periodic statutory review, if EPA cannot determine chlorpyrifos is safe, 

it cannot leave the tolerance in place. But if EPA arrives at that point, 

there is yet an additional option: EPA has the power to leave in effect or 

modify a tolerance if it concludes that certain consequences will 

follow—if “the residue protects consumers from adverse effects on 

health that would pose a greater risk than the dietary risk” or if the 

tolerance “is necessary to avoid a significant disruption in domestic 

production of an adequate, wholesome, and economical food supply.” 

21 U.S.C. § 346a(b)(2)(B)(iii). These contingencies would still require 

EPA to certify that the tolerances modified or left in effect satisfy the 

“no harm” to infants and children criteria in 21 U.S.C. § 346a(b)(2)(C).
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EPA recognizes that the science is evolving 

on this topic, and that there may be new 

information available prior to the completion 

of registration review that may impact the 

agency’s conclusions about these effects.

Id. It further advised that it had convened a SAP in 

September 2020 “to assess new approval methodologies that 

might used to evaluate developmental neurotoxicity in 

EPA’s assessment of risks to human health.” Id.; see also 

id. at 40, 63. The SAP’s report was issued a week later in 

December 2020. EPA, FIFRA Scientific Advisory Panel 

Meeting Minutes and Final Report No. 2020-02: Peer 

Review of the Use of New Approach Methodologies (NAMs) 

to Derive Extrapolation Factors and Evaluate 

Developmental Neurotoxicity for Human Health Risk 

Assessment (Sept. 15–18, 2020) (report released Dec. 15, 

2020). For the reasons I have explained, in this latest 

proceeding, the risk of nonpersuasion runs against the 

existing tolerances. That means that EPA will have to decide 

the issues reserved in its interim proceedings—and, 

specifically, the question of safe tolerances for children and 

youth—and it must do so by 2022, the deadline set by 

Congress.

What effect the majority’s order will have on EPA’s 

latest proceeding is unclear, but the majority’s order presents 

it with two unsatisfactory choices: either issue modified 

tolerances outside the procedure required by the FFDCA, 

FIFRA, and APA, or revoke the tolerances. Given the 2020 

Proposed Interim Registration Decision, maybe EPA will be 

comfortable issuing modified tolerances, but in order to do 

so it will have to accelerate its schedule, and that may mean 

skipping some steps. See 2020 Proposed Interim

Registration Decision at 4, 8–9 (explaining that EPA is 
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awaiting revised biological opinions from the National 

Marine Fisheries Service and the U.S. Fish & Wildlife 

Service). Alternatively, EPA may be forced to revoke 

tolerances that it has tentatively concluded it will reregister 

or reregister with modifications. Perhaps EPA will again 

approve registration of chlorpyrifos at some future date once 

it completes full FIFRA and FFDCA review, but our 

precipitous order will have imposed tremendous costs on 

various sectors of the economy without waiting for the 

system to work.

Finally, I have to comment on the artificial schedule that 

our court has imposed on EPA, not only in this case, but time 

and again in these proceedings. EPA took the 2007 petition 

to revoke chlorpyrifos very seriously. Unlike reregistration 

under FIFRA, there is no statutory deadline for dealing with 

a petition, although in principle twelve years seems like 

more than enough time. The extraordinary delay, however, 

makes more sense in context: EPA initially believed that it 

could accelerate the FIFRA reregistration due in 2022 and 

address both the petition and the reregistration at the same 

time and well before that date. In the meantime, the 

petitioners asked us to intervene and order EPA to rule on its 

petition. EPA repeatedly advised us that it could not meet 

those demands if it was to complete the reregistration 

process properly. We insisted. Eventually, but reluctantly, 

EPA proposed to revoke the tolerances—even as it stated 

that it was doing so without complete information. See, e.g., 

2016 Request for Comments, 81 Fed. Reg. at 81,050; 2015 

Proposed Rule, 80 Fed. Reg. at 69,080. After further 

proceedings, EPA concluded that it was better to deny the 

petitions outright because the petitioners had failed to show 

that the tolerances were not safe, and then complete the 

FIFRA reregistration process, where it would have a full 

record. EPA’s decision is consistent with the FFDCA, as 
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amended by the FQPA. Although in hindsight the process 

took much longer than EPA anticipated, that was a 

reasonable decision on EPA’s part at the time.

When we intervene in scientific inquiries with 

impatience and impose artificial deadlines, we bear some 

responsibility for the confusion that results. In San Luis & 

Delta-Mendota Water Authority v. Jewell, 747 F.3d 581 (9th 

Cir. 2014), the district court ordered the U.S. Fish & Wildlife 

Service to produce a complex, 400-page biological opinion 

in less than a year. The resulting biological opinion was

a jumble of disjointed facts and analyses. It 

appears to be the result of exactly what we 

would imagine happens when an agency is 

ordered to produce an important opinion on 

an extremely complicated and technical 

subject matter covering multiple federal and 

state agencies and affecting millions of acres 

of land and tens of millions of people.

Id. at 605; see also id. at 605 n.15 (noting that “the FWS had 

less time to produce its opinion than either the district court 

or we will have had to review it”). We “wonder[ed] whether 

anyone was ultimately well-served by the imposition of tight 

deadlines in a matter of such consequence.” Id. at 606. 

When we interject ourselves into technical proceedings, our 

“[d]eadlines become a substantive constraint on what an 

agency can reasonably do. . . . Such scientific tasks may not 

be as well suited to deadlines as producing written copy; the 

final product will necessarily reflect the time allotted to the 

agency.” Id. We can only hope that “[f]uture analyses [will] 

be given the time and attention that these serious issues 

deserve.” Id.
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In any event, our order is an abuse of any discretion the 

APA confers on us. We have the power to “compel agency 

action . . . unreasonably delayed,” 5 U.S.C. § 706(1), but we 

do not have the power to choose among the options available 

to EPA. Our deadline may effectively make the choice for 

EPA.

IV

There are manifest errors in the majority opinion. It has 

misread the FFDCA and misallocated the risk of 

nonpersuasion. It has overruled EPA’s judgment on the 

validity and weight to be given technical evidence within 

EPA’s expertise. And by its decision to give EPA 60 days 

to issue a final decision in this case, the majority has likely 

predetermined EPA’s option. I respectfully, but firmly, 

dissent.