FOR PUBLICATION

UNITED STATES COURT OF APPEALS

FOR THE NINTH CIRCUIT

NORTHWEST COALITION FOR 

ALTERNATIVES TO PESTICIDES

(NCAP),

Petitioner,

No. 05-75255

v.  EPA No. UNITED STATES ENVIRONMENTAL Clear Air Act PROTECTION AGENCY,

Respondent,

CROPLIFE AMERICA,

Intervenor. 

NATURAL RESOURCES DEFENSE 

COUNCIL, INC., No. 05-76807 Petitioner,

EPA No.

v.  70 Fed Reg 46706

UNITED STATES ENVIRONMENTAL OPINION PROTECTION AGENCY,

Respondent. 

On Petition for Review of an Order of the

Environmental Protection Agency

Argued and Submitted

June 6, 2007—Seattle, Washington

Filed September 19, 2008

13239
Before: Harry Pregerson and Sandra S. Ikuta, Circuit Judges,

and Barry T. Moskowitz,* District Judge.

Opinion by Judge Pregerson;

Partial Concurrence and Partial Dissent by Judge Ikuta

*The Honorable Barry T. Moskowitz, District Judge for the Southern

District of California, sitting by designation. 

13240 NORTHWEST COALITION v. EPA
COUNSEL

Aaron Colangelo and Erik D. Olsen, National Resource

Defense Council, Washington, D.C.; Shelley Davis, Farmworker Justice Fund, Washington, D.C.; Patti Goldman,

Earthjustice, Seattle, Washington, for petitioners-appellants

Northwest Coalition for Alternatives to Pesticides and

National Resources Defense Council. 

Jonathan J. Fleuchaus, Environmental Protection Agency,

Washington, D.C.; Sue Ellen Woodridge, Attorney General,

John C. Cruden, Deputy Assistant Attorney General, and Kent

E. Hanson, Environment and Natural Resources Division,

United States Department of Justice, Washington, D.C., for

respondent-appellee Environmental Protection Agency. 

Kenneth W. Weinstein, Claudia M. O’Brien, and Cassandra

Sturkie, Latham & Watkins LLP, Washington, D.C., for

respondent-intervenor CropLife America. 

13242 NORTHWEST COALITION v. EPA
OPINION

PREGERSON, Circuit Judge: 

Petitioners are two environmental groups challenging the

Environmental Protection Agency’s (“EPA”) establishment of

tolerances for seven pesticides used mostly on fruit and vegetable crops. We grant the petition in part, deny it in part, and

remand to the EPA.

BACKGROUND

I.

The EPA regulates pesticides under two statutes: the Federal Insecticide, Fungicide, and Rodenticide Act (“FIFRA”),

7 U.S.C. § 136-136y, and the Federal Food, Drug, and Cosmetic Act (“FDCA”), 21 U.S.C. § 346a. 

Under FIFRA, pesticides sold in the United States must be

registered by the EPA. 7 U.S.C. § 136a. The EPA may not

register a pesticide unless the pesticide will perform its

intended function without causing “any unreasonable adverse

effects on the environment.” 7 U.S.C. § 136a(c)(5)(C). 

The FDCA authorizes the EPA to set “tolerances” for pesticide residues in food. 21 U.S.C. § 346a(b). “A tolerance is the

maximum allowable amount of pesticide that may remain in

or on a commodity.” Nader v. EPA, 859 F.2d 747, 748 (9th

Cir. 1988). The EPA may “establish or leave in effect a tolerance for a pesticide chemical residue in or on a food only if

[the EPA] determines that the tolerance is safe.” 21 U.S.C.

§ 346a(b)(2)(A)(i). The term “safe” is defined to mean 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.” 21 U.S.C.

NORTHWEST COALITION v. EPA 13243
§ 346a(b)(2)(A)(ii). Any tolerance that is not “safe” must be

modified or revoked. 21 U.S.C. § 346a(b)(2)(A)(i). 

Tolerances are established by rulemaking. 21 U.S.C.

§ 346a(d). Pesticide manufacturers initiate the rulemaking

process by petitioning the EPA to set a tolerance. 21 U.S.C.

§ 346a(d)(1). The EPA publishes notices of these petitions in

the Federal Register. 21 U.S.C. § 346a(d)(3). After reviewing

a petition and any comments received on it, the EPA may

issue: (1) a final rule establishing a tolerance, (2) a proposed

rule, or (3) an order denying the petition. 21 U.S.C.

§ 346a(d)(4). 

Once the EPA takes final action on a petition, any affected

party has sixty days to file objections with the EPA and to

seek an evidentiary hearing on those objections. 21 U.S.C.

§ 346a(g)(2). The EPA’s final order in response to those

objections is subject to judicial review. 21 U.S.C.

§ 346a(h)(1). 

II.

In 1996, Congress amended the FDCA by enacting the

Food Quality Protection Act (“FQPA”), Pub. L. No. 104-170,

110 Stat. 1489. One of the key provisions of the FQPA

requires the EPA to give special consideration to risks posed

to infants and children when establishing pesticide tolerances.

Specifically, the FQPA directs the EPA to use “an additional1

tenfold margin of safety . . . to take into account potential preand post-natal toxicity and completeness of the data with

respect to exposure and toxicity to infants and children.” 21

1This margin of safety is “additional” to two safety factors that the EPA

has long used to account for other uncertainties: a tenfold factor for interspecies differences (to account for the possibility that people are more susceptible than animals studied in laboratory experiments), and a tenfold

safety factor for intra-species differences (to account for the wide range

of sensitivities in the human population). 

13244 NORTHWEST COALITION v. EPA
U.S.C. § 346a(b)(2)(C). This tenfold (or “10x”) child safety

factor is presumptively applied to all tolerances. Thus, in

making tolerance decisions, the EPA must assume that the

risk to children from the use of a particular pesticide on food

is ten times greater than for adults. The EPA may “use a different margin of safety for the pesticide chemical residue only

if, on the basis of reliable data, such margin will be safe for

infants and children.” Id. (emphasis added). 

Unfortunately, the FQPA does not define “reliable data.”

The dispute before us turns on the definition of this term. 

Between December 2001 and April 2002, the EPA published seven regulations establishing tolerances for the pesticides acetamiprid, fenhexamid, halosulfuron-methyl,

isoxadifen-ethyl, mepiquat, pymetrozine, and zetacypermethrin used on many foods, including fruits, vegetables, nuts, cereal grains, milk, and eggs.2

 Each regulation was

promulgated in response to an industry petition to establish

tolerances. 

The EPA did not apply the presumptive 10x child safety

factor to any of these seven pesticides. The EPA reduced the

10x child safety factor to 3x for four of the pesticides

(acetamiprid, fenhexamid, isoxadifen-ethyl, and pymetrozine). For the remaining three pesticides (halosulfuron,

mepiquat, and zeta-cypermethrin), the EPA did not apply a

child safety factor at all. 

2For the EPA’s individual tolerance rulings, see Acetamiprid; Pesticide

Tolerance, 67 Fed. Reg. 14,649 (Mar. 27, 2002); Fenhexamid; Pesticide

Tolerance, 67 Fed. Reg. 19,114 (Apr. 18, 2002); Halosulfuron-methyl;

Pesticide Tolerance, 66 Fed. Reg. 66,333 (Dec. 26, 2001); Isoxadifenethyl; Pesticide Tolerance, 67 Fed. Reg. 12,875 (Mar. 20, 2002);

Mepiquat; Pesticide Tolerance, 67 Fed. Reg. 3,113 (Jan. 23, 2002);

Pymetrozine; Pesticide Tolerance, 66 Fed. Reg. 66,786 (Dec. 27, 2001);

Zeta-cypermethrin and its Inactive R-isonomers; Pesticide Tolerance, 67

Fed. Reg. 6,422 (Feb. 15, 2002). 

NORTHWEST COALITION v. EPA 13245
In 2002, Natural Resources Defense Council, Inc.

(“NRDC”) filed objections to each of the tolerances based on

the EPA’s decision to reduce or remove the child safety factor.3

NRDC argued that the EPA did not have “reliable data”

allowing it to deviate from the child safety factor. 

On August 10, 2005, the EPA issued its final order rejecting NRDC’s objections. See Order Denying Objections to

Issuances of Tolerances, 70 Fed. Reg. 46,706 (Aug. 10, 2005)

(hereinafter “Final Order”). The Final Order upheld the 3x

child safety factor for acetamiprid, fenhexamid, isoxadifenethyl, and pymetrozine, and a 1x child safety factor (i.e., no

safety factor) for halosulfuron, mepiquat, and zetacypermethrin. Id. at 46,711-13, 46,736. 

NRDC and the Northwest Coalition for Alternatives to Pesticides (“NCAP”) each petitioned for review of the Final

Order. 

JURISDICTION

We have jurisdiction under the FDCA, which provides that

“any person who will be adversely affected” by an EPA order

denying tolerance objections may file a petition for review in

the Court of Appeals within 60 days of the EPA’s order. 21

U.S.C. § 346a(h)(1). 

NRDC filed administrative objections to the tolerances in

2002. The EPA published its Final Order denying those objections on August 10, 2005. Within 60 days, NRDC filed a petition for review in the Second Circuit, and NCAP filed a

petition for review in this court. The Judicial Panel on Multidistrict Litigation transferred NRDC’s petition for review to

this court pursuant to 28 U.S.C. § 2112, and NRDC and

NCAP filed joint briefs on appeal. 

3NRDC did not request an evidentiary hearing on its objections. 

13246 NORTHWEST COALITION v. EPA
STANDARD OF REVIEW

The FDCA does not establish a standard for reviewing pesticide tolerances that are established without a public evidentiary hearing. See 21 U.S.C. § 346a(h)(2). In the absence of

such a standard, our review is governed by section 706 of the

Administrative Procedure Act (“APA”). See 5 U.S.C. § 706;

City of Sausalito v. O’Neill, 386 F.3d 1186, 1205-06 (9th Cir.

2004). 

Under the APA, we must set aside an agency’s decision if

it is “arbitrary, capricious, an abuse of discretion, or otherwise

not in accordance with law.” 5 U.S.C. § 706(2)(A). An

agency decision would normally be arbitrary and capricious

if “the agency has relied on factors which Congress has not

intended it to consider, entirely failed to consider an important

aspect of the problem, offered an explanation for its decision

that runs counter to the evidence before the agency, or is so

implausible that it could not be ascribed to a difference in

view or the product of agency expertise.” Mfrs’ Ass’n v. State

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

“The scope of review under the ‘arbitrary and capricious’

standard is narrow and a court is not to substitute its judgment

for that of the agency.” Id. “Nevertheless, the agency must

examine the relevant data and articulate a satisfactory explanation for its action including a ‘rational connection between

the facts found and the choice made.’ ” Id. (citation omitted).

“In reviewing that explanation, [the court] must consider

whether the decision was based on a consideration of the relevant factors and whether there has been a clear error of judgment.” Id. (citation omitted). 

Although we will “uphold a decision of less than ideal clarity if the agency’s path may be reasonably discerned,” we

“may not supply a reasoned basis for the agency’s action that

the agency itself has not given.” Id. (citations omitted).

NORTHWEST COALITION v. EPA 13247
ANALYSIS

Petitioners challenge seven tolerances (acetamiprid, fenhexamid, halosulfuron-methyl, isoxadifen-ethyl, mepiquat,

pymetrozine, and zeta-cypermethrin) based on the EPA’s failure to gather drinking water data as part of its exposure analysis. Petitioners also challenge three tolerances (acetamiprid,

mepiquat, and pymetrozine) based on the absence of certain

toxicity studies, and based on the EPA’s failure to explain

why it had reliable data in the absence of those toxicity studies.4

We address these challenges in turn. 

I.

[1] The FQPA directs the EPA to use an additional tenfold

margin of safety to take into account completeness of data

with respect to pesticide “exposure to infants and children.”

21 U.S.C. § 346a(b)(2)(C) (emphasis added). 

As required by the FQPA, the EPA monitors whether

infants and children will be exposed to unsafe levels of pesticides in drinking water. However, the EPA lacks sufficient

drinking water exposure data for several pesticides, including

the ones at issue in this case. Therefore, the EPA used computer modeling to determine drinking water exposure for the

seven pesticides. Because the modeling results revealed littleto-no risk of pesticide exposure in drinking water, the EPA

reduced or removed the child safety factor for each of the pesticide tolerances. 

Petitioners argue that because the EPA used modeling

instead of actual sampling data to determine drinking water

exposure to these pesticides, the EPA does not have “reliable

4Petitioners also initially challenged the tolerances for halosulfuronmethyl and zeta-cypermethrin on these grounds. They now acknowledge,

however, that subsequent agency actions have rendered those challenges

moot. 

13248 NORTHWEST COALITION v. EPA
data” justifying its use of a lower than 10x margin of safety

for the pesticide tolerances. See 21 U.S.C. § 346a(b)(2)(C). In

short, Petitioners argue that modeling results can never constitute reliable data within the meaning of the FQPA. 

[2] We disagree. Petitioners have presented no evidence

that modeling does not yield reliable data. There is nothing

inherently unreliable about the use of models in scientific

assessments. See, e.g., Small Refiner Lead Phase-Down Task

Force v. EPA, 705 F.2d 506, 535 (D.C. Cir. 1983)

(“[A]dministrative agencies have undoubted power to use predictive models.”). Moreover, because of the difficulty in sampling the entire nation’s water supply, modeling is necessary

to determine whether drinking water has been contaminated

by pesticides. Topography, geology, and hydrology differ

greatly across the nation and constantly change. In many

cases, computer modeling can more accurately incorporate

these elements and provide more reliable data than actual

water sampling data can provide.5

[3] Therefore, we are unwilling to adopt the narrow construction of “reliable data” that Petitioners advance. Although

the FQPA does not define “reliable data,” we are confident

that modeling results can satisfy this statutory requirement. 

[4] Furthermore, in this case, the EPA provided a specific,

detailed explanation of why its drinking water exposure models do yield reliable data. The Final Order states: 

Lack of comprehensive drinking water (DW) monitoring data. NRDC contends that, because EPA

used a model for calculating drinking water expo5

See FIFRA Scientific Advisory Panel, A Set of Scientific Issues Being

Considered by the Agency in Connection with Estimating Drinking Water

Exposure as a Component of Dietary Risk Assessment, 4-7 (Dec. 1997),

available at http://epa.gov/scipoly/sap/meetings/1997/december/

finaldec.pdf. 

NORTHWEST COALITION v. EPA 13249
sure, EPA does not have, as a definitional matter,

“reliable data” for choosing a factor different than

the 10X default value. Similar comments were made

during the development of EPA’s Children’s Safety

Policy. This issue was addressed at length in the

response to the imidacloprid objections. That

response is incorporated herein and is summarized

below. 

Although the availability of drinking water monitoring data has increased dramatically in the last several years, EPA still finds it necessary to rely for

most pesticides upon various exposure models to

estimate exposure levels in drinking water. These

models are based on generic data regarding fate and

transport of pesticides in the environment, and they

operate by combining this generic data with

pesticide-specific data on chemical properties to estimate exposure. EPA has primarily used its drinking

water models to “screen” those pesticides that may

pose unacceptable risks due to exposures in drinking

water from pesticides not likely to result in such

exposures. To accomplish this goal, the models are

based on data from studies at sites that are highly

vulnerable to runoff of pesticides to surface water or

leaching of pesticides to ground water. If a pesticide

fails this conservative (health-protective) screen,

EPA would investigate whether the model is significantly overstating the residue levels that actually

occur. 

EPA has developed models for estimating exposure in both surface water and ground water. EPA

uses a two-tiered approach to modeling pesticide

exposure in surface water. In the initial tier, EPA

uses the FQPA Index Reservoir Screening Tool

(FIRST) model. FIRST replaces the Generic Estimated Environmental Concentrations (GENEEC)

13250 NORTHWEST COALITION v. EPA
model that was used as the first tier screen by EPA

from 1995-1999. If the first tier model suggests that

pesticide levels in water may be unacceptably high,

a more refined model is used as a second tier assessment. The second tier model is actually a combination of the models, Pesticide Root Zone Model

(PRZM) and the Exposure Analysis Model System

(EXAMS). For estimating pesticide residues in

groundwater, EPA uses the Screening Concentration

In Ground Water (SCI-GROW) model. Currently,

EPA has no second tier groundwater model. 

Whether EPA assesses pesticide exposure in

drinking water through monitoring data or modeling, EPA uses the higher of the two values from surface and ground water in assessing overall exposure

to the pesticide. In most cases, pesticide residues in

surface water are significantly higher than in ground

water.

In the Imidacloprid Order, EPA analyzed each of

its water models extensively. Based on the results of

design characteristics of the models, outside peer

review of the models, validation of the models, and

comparison between the models’ predictions and

extensive water monitoring data, EPA concluded

that the models are based on reliable data and will

produce estimates that are unlikely to underestimate

exposure to pesticides in drinking water. 

Accordingly, EPA reaffirms its earlier conclusion

that its drinking water models provide a reliable

basis for finding that exposure to pesticide residues

in water are not underestimated. 

Final Order at 46,726-29 (internal citations omitted) (emphasis added). Thus, the EPA addressed at length the reliability

of its models. The EPA explained that the models yield conNORTHWEST COALITION v. EPA 13251
servative data because the models incorporate the higher of

the two values from surface and ground water in assessing the

overall risk of exposure to the pesticides. Petitioners have not

established that the EPA’s explanation regarding the reliability of its models is faulty or suspect. 

[5] Accordingly, we conclude that the computer modeling

used by the EPA to calculate the safety of drinking water was

neither contrary to law nor arbitrary and capricious.6 We

affirm this aspect of the Final Order.

II.

In addition to NRDC’s challenge to the completeness of

exposure data, Petitioners also raise two arguments regarding

whether reliable toxicity data supported a reduction in the

child safety factor. 

A.

NRDC first challenges the EPA’s failure to wait for the

results of certain developmental neurotoxicity studies (“DNT

studies”) before establishing tolerances for acetamiprid,

mepiquat, and pymetrozine. The EPA specifically required

the registrants of these pesticides to conduct DNT studies.

However, the EPA did not wait for the results of the DNT

studies before making its tolerance determinations. 

6Our conclusion, of course, is not meant to suggest that the EPA’s models are flawless. Petitioners have raised some concerns about the EPA’s

water exposure models that may warrant further scrutiny. To give one

example, the EPA first performs a model-based water exposure test using

conservative criteria; if the test results reveal unacceptable exposure

levels, the EPA runs a second test to ensure that the first result was accurate. The EPA does not run a second test, however, if the initial test results

reveal acceptable exposure levels. Although we are required to defer to

the EPA’s technical expertise in this area, see, e.g., Envtl Def. Ctr., Inc.

v. EPA, 344 F.3d 832, 869 (9th Cir. 2003), we note that the EPA may wish

to revisit this methodology. 

13252 NORTHWEST COALITION v. EPA
Petitioners contend that DNT studies are essential for

assessing pesticide effects. Petitioners explain that DNT

studies are the best available studies for examining neurological effects in children because DNT studies are more sensitive

than other studies, address areas that are not covered by other

studies, and sometimes reveal developmental harm that is significant enough to require more stringent regulation. Petitioners argue that the EPA acted arbitrarily and capriciously by

requesting DNT studies but failing to wait for the results of

those studies before removing the child safety factor. 

[6] Petitioners’ position, however, is inconsistent with the

Supreme Court’s decision in National Ass’n of Home Builders

v. Defenders of Wildlife, 127 S. Ct. 2518 (2007). In Home

Builders, our court rejected a final order of the EPA as “arbitrary and capricious” because the EPA had relied on “legally

contradictory positions” before arriving at its final administrative decision. 127 S. Ct. at 2529. The Supreme Court, however, reversed our opinion. The Court held that the mere fact

that the EPA might have adopted “internally inconsistent”

positions throughout the decision-making process did not render the EPA’s final decision arbitrary and capricious. 127

S. Ct. at 2530. The Court explained that as long as agencies

follow the proper administrative procedures, they have the

authority to change their minds before issuing a final order.

Id.

[7] Thus, Home Builders appears to foreclose Petitioners’

argument. Even though the EPA initially thought that the

DNT studies were needed, the EPA later determined that the

DNT studies were not needed. Under Home Builders, the

EPA’s later determination does not automatically render the

EPA’s Final Order arbitrary and capricious. Notably, Petitioners have not identified any procedures that were violated

when the EPA decided not to wait for the requested DNT

studies before setting the tolerances. Moreover, the Final

Order provided a reasoned explanation of why DNT studies

are not actually required in every case where there is a reducNORTHWEST COALITION v. EPA 13253
tion of the 10x child safety factor. Final Order at 46,711-12,

46,723-24. 

[8] Therefore, we reject Petitioner’s argument that the EPA

acted arbitrarily and capriciously by establishing the pesticide

tolerances for acetamiprid, mepiquat, and pymetrozine before

receiving the DNT studies. While Petitioners’ concerns about

the EPA’s apparent change of heart are understandable, on

such questions of scientific judgment, we are required to defer

to the EPA.

B.

[9] NRDC also disputes that the EPA’s decision to deviate

from the 10x presumptive child safety factor imposed by Congress was supported by reliable data establishing, with reasonable certainty, that the lower margin of safety for acetamiprid,

mepiquat, and pymetrozine would not harm infants and children. 21 U.S.C. § 346a(b)(2)(A), (C). Even though the EPA

was not necessarily required to wait for the results of the DNT

studies, the decision to reduce the 10x child safety factor for

these three pesticides must still be based on reliable data.

Moreover, the EPA must tell the public why its data are reliable. 

[10] The problem in this case is that the EPA’s Final Order

is vague, making it impossible for us to determine whether the

EPA’s deviations from the 10x child safety factor for acetamiprid, mepiquat, and pymetrozine were in fact supported by

reliable data, even in the absence of the DNT studies. For

example, with respect to pymetrozine, the Final Order states:

NRDC challenged a December 27, 2001 action

establishing tolerances for pymetrozine on cotton

seed, cotton gin byproducts, the fruiting vegetables

crop group, the cucurbit vegetables crop group, the

leafy vegetables crop group (except Brassica), head

and stem Brassica, leafy Brassica, turnip greens,

13254 NORTHWEST COALITION v. EPA
dried hops, and pecans. (66 FR 66786, December 27,

2001). Given pymetrozine’s exposure pattern and

toxicological characteristics, EPA determined that

pymetrozine potentially presented acute, chronic,

short-term, and cancer risks and EPA quantitatively

assessed these risks in making its safety determination. (66 FR at 66791-66792). All of these risks were

found to be below the Agency’s level of concern.

(Id.). Although a DNT study was outstanding, EPA

determined that the additional 10X children’s safety

factor could generally be reduced to 3X because the

toxicological data showed no evidence of greater

sensitivity to the young and there was no evidence of

abnormalities in the development of the fetal nervous system. (64 FR 52438, 52444, September 29,

1999). 

Final Order at 46,711. 

The Final Order recites that the “toxicological data”

showed no evidence of increased sensitivity for developing

fetuses or the “young.” However, the Final Order does not

explain the connection between the toxicological data and the

3x margin of safety selected by the EPA in place of the 10x

standard. This same critique applies to the Final Order’s reasoning with respect to acetamiprid and mepiquat. As a result,

it is entirely unclear why the EPA chose safety factors of 3x

for pymetrozine and acetamiprid, and 1x for mepiquat, as

opposed to 4x or 5x or 8x or 9x. As far as we can tell from

the record, it appears that the EPA chose these lower safety

levels arbitrarily—to acknowledge certain concerns about

each pesticide, but with no specific evidence that these lower

safety factors would actually account for the risks to infants

and children. 

[11] In sum, the Final Order does not provide enough information to demonstrate a rational connection between the factors that the EPA examined and the conclusions it reached.

NORTHWEST COALITION v. EPA 13255
See State Farm, 463 U.S. at 43. We are therefore unable to

determine whether there was reliable data supporting the

EPA’s reductions of the 10x child safety factor. Although on

remand the EPA may be able to explain why a 3x or 1x factor

is appropriate, we cannot conclude it is appropriate on this

record. To do so would abdicate our responsibility to ensure

compliance with Congress’s expressed desire to have a presumptive 10x child safety factor. Accordingly, we remand the

tolerance regulations for acetamiprid, mepiquat, and pymetrozine to the EPA. See, e.g., State Farm, 463 U.S. at 57

(remanding where the agency failed to supply the requisite

“reasoned analysis”); Safe Food & Fertilizer v. EPA, 350 F.3d

1263, 1271 (D.C. Cir. 2003) (remanding for the EPA to provide “further explanation” of an exemption level for chromium found in zinc fertilizers).7

7While we are aware that the scope of our review under the APA is narrow, we are also mindful that we should not endorse the removal of the

statutorily presumed child safety factor if we cannot determine that the

EPA’s conclusions are rationally supported. As Judge J. Skelly Wright of

the D.C. Circuit elucidated, there is an important difference between the

depth of our review of an agency’s action and the scope of that review:

Judicial review of agency action requires that the reviewing

court consider whether the [agency’s] decision was based on a

consideration of the relevant factors and whether there has been

a clear error of judgment. As noted by this court in International

Ladies Garment Workers Union v. Donovan, 722 F.2d 795, 815

(D.C. Cir. 1983), cert. denied, 469 U.S. 820 (1984), such review

“is not merely perfunctory. We are to engage in a ‘searching and

careful’ inquiry, the keystone of which is to ensure that the

[agency] engaged in reasoned decisionmaking.” 

This formulation points to an acknowledged disparity between

the depth of our review and the ultimate scope of that review:

Although the ultimate scope may be narrow, the depth must be

sufficient for us to be able to comprehend the agency’s handling

of the evidence cited or relied upon. The purpose of this in-depth

review is to educate ourselves so that we can properly perform

our reviewing function: determining whether the agency’s conclusions are rationally supported. For, although data interpretation and analysis are functions that often lie within an agency’s

13256 NORTHWEST COALITION v. EPA
The EPA and the dissent argue that Petitioners did not raise

this argument below and therefore cannot assert it now. We

disagree. In its administrative objections, NRDC challenged

the basis for the reduced safety levels as inadequate. In particular, NRDC argued that, absent the DNT studies, the EPA had

no reliable data to reduce the 10x child safety factor. NRDC’s

objection was a direct challenge to the lower child safety

levels set by the EPA. To justify its decision to set a 3x or 1x

child safety factor without the DNT studies, the EPA needed

to explain why the data in its possession was reliable and supported such reductions. As noted above, the EPA explained

why the absence of the DNT studies does not necessarily

mean that there is a lack of reliable data justifying a downward deviation from the 10x child safety factor. However, the

EPA failed to explain why, in the case of the three pesticides

at issue, the available information justified the specific safety

reductions. Because the NRDC challenged the EPA to provide that explanation, the EPA’s failure to do so is properly

before us for review. 

CONCLUSION

Because the EPA failed to adequately explain the basis for

its deviations from the 10x child safety factor for acetamiprid,

realm of expertise, it is our duty to review those functions to

ascertain whether the agency’s actions were complete, reasoned,

and adequately explained. The mere fact that an agency is operating in a field of its expertise does not excuse us from our customary review responsibilities. And, where the agency’s reasoning,

although complex, is rational, clear, and complete, we must

affirm. Contrarily, where the agency’s reasoning is irrational,

unclear, or not supported by the data it purports to interpret, we

must disapprove the agency’s action. 

Center for Auto Safety v. Peck, 751 F.2d 1336, 1373 (D.C. Cir. 1985)

(Wright, J., dissenting) (internal citations and quotation marks omitted).

See also Riverkeeper, Inc. v. United States Environmental Protection

Agency, 475 F.3d 83, 103-04 (2d Cir. 2007) (“In a technical area of this

sort, it is difficult for judges or interested parties to determine the propriety of the Agency’s action without a justification for the action supported

by clearly identified substantial evidence whose import is explained.”). 

NORTHWEST COALITION v. EPA 13257
mepiquat, and pymetrozine, we grant the petitions for review

in part and remand to the EPA for further proceedings consistent with this opinion. On all other issues, we deny the petitions for review. 

Each side to bear its own costs on appeal. 

GRANTED IN PART, DENIED IN PART, AND

REMANDED.

IKUTA, Circuit Judge, concurring in part and dissenting in

part: 

I agree with the majority’s conclusion that “the computer

modeling used by the EPA to calculate the safety of drinking

water was neither contrary to law nor arbitrary and capricious.” Maj. Op. at 13252; see also The Lands Council v.

McNair, ___ F.3d ___, 2008 WL 2640001, at *6-10 (9th Cir.

2008) (en banc). I also agree with the majority’s holding that

National Ass’n of Home Builders v. Defenders of Wildlife,

127 S. Ct. 2518, 2529-30 (2007), forecloses petitioners’ argument “that the EPA acted arbitrarily and capriciously by

establishing the pesticide tolerances for acetamiprid,

mepiquat, and pymetrozine before receiving . . . DNT

studies.” Maj. Op. at 13254. 

I disagree, however, with the majority’s conclusion that the

tolerance regulations for acetamiprid, mepiquat, and pymetrozine must be remanded to the EPA because “it is entirely

unclear why the EPA chose safety factors of 3x for pymetrozine and acetamiprid, and 1x for mepiquat,” and therefore

“the Final Order [did] not provide enough information to

demonstrate a rational connection between the factors the

EPA examined and the conclusions it reached.” Maj. Op. at

13255. The petitioners failed to raise this argument in their

objections to the EPA prior to the issuance of the Final Rule.

13258 NORTHWEST COALITION v. EPA
See Order Denying Objections to Issuances of Tolerances, 70

Fed. Reg. 46,706 (Aug. 10, 2005) [hereinafter, Final Rule],

and therefore the EPA was given no opportunity to explain its

rationale for adopting the 3x and 1x safety factors. Because

we may review only the objections raised before the EPA, see

21 U.S.C. § 346a(g)-(h); 40 C.F.R. §§ 178.25(a)(2),

180.30(b), the issue is not properly before us. Even if the petitioners had raised this objection, there is no doubt the EPA

could have provided information sufficient to demonstrate a

rational basis for selecting these safety factors. Indeed, the

record establishes that the EPA drew upon its expertise to

select uncertainty factors based on principles well established

in the scientific community. There is no basis for the majority’s conclusion that the agency’s path is not reasonably discernable in this case. See, e.g., Motor Vehicle Mfrs. Ass’n v.

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

Accordingly, I dissent from Part IIB of the majority opinion.1

A

As noted by the majority, the tolerance rules at issue in this

appeal have substantially similar histories.2 While the development of its safety factor policy was in process, the EPA

received pesticide petitions requesting the issuance of toler1

I also dissent from footnote 6 of the majority opinion. The majority’s

suggestion that the “EPA may wish to revisit [its] methodology” regarding

its “model-based water exposure test[s]” conflicts directly with the teaching of our en banc panel in Lands Council. Lands Council emphasized that

it “is not a proper role for a federal appellate court” to “act as a panel of

scientists that instructs the [agency] how to validate its hypotheses,”

“chooses among scientific studies,” and requires the agency to “explain

every possible scientific uncertainty.” 2008 WL 2640001, at *4. The

majority errs in this case by doing that which Lands Council expressly forbids. 

2The three pesticides at issue are acetamiprid, mepiquat, and pymetrozine. For the individual tolerance rulings, see Acetamiprid; Pesticide Tolerance, 67 Fed. Reg. 14,649 (Mar. 27, 2002); Mepiquat; Pesticide

Tolerance, 67 Fed. Reg. 3,113 (Jan. 23, 2002); Pymetrozine; Pesticide

Tolerance, 66 Fed. Reg. 66,786 (Dec. 27, 2001). 

NORTHWEST COALITION v. EPA 13259
ances under the FFDCA for the three pesticides at issue. As

required in the FFDCA, the EPA reviewed the scientific data

and other information, evaluated their completeness and reliability, and considered “the relationship of the results of such

studies to human risk.” 21 U.S.C. § 346a(b)(2)(D)(iii); see,

e.g., Pymetrozine; Pesticide Tolerance, 66 Fed. Reg. 66,786,

66,787 (Dec. 27, 2001). The EPA determined that the child

safety factor was not necessary, or could be reduced to 3x, for

each of the pesticides based on its analysis of potential exposure levels for the given pesticide, the extent to which the pesticide affected fetal development, and the effects, if any, on

infants as observed in multi-generational studies of mammals.

In each case, the EPA provided a reasoned explanation for

eliminating or reducing the child safety factor.3

3

In its order establishing the tolerance for acetamiprid, the EPA

explained: 

[T]he safety factor could be reduced to 3x for acetamiprid

because the toxicology database is complete; there is no quantitative or qualitative evidence of increased susceptibility following

in utero exposure of rat and rabbit fetuses; the dietary (food and

water) and residential exposure assessments will not underestimate the potential exposures for infants, children, and/or women

of childbearing age; and the requirement of a developmental neurotoxicity study is not based on criteria reflecting special concern

for the developing fetuses or young which are generally used for

requiring a DNT study and a safety factor. 

Acetamiprid; Pesticide Tolerance, 67 Fed. Reg. at 14,655. 

The EPA removed the additional child safety factor for mepiquat

(reducing it to 1x) because it had already satisfied itself of the safety of

another “salt” of mepiquat that it determined was identical in terms of its

environmental distribution and toxicology. Mepiquat; Pesticide Tolerance,

67 Fed. Reg. at 3,115-16. It explained: 

The Agency published a risk assessment for mepiquat chloride on

January 12, 2000, that discusses use on cotton as well as all other

registered uses of mepiquat chloride. In that analysis risk estimates for exposure to mepiquat chloride were below the Agency’s level of concern. The Agency has reviewed a dissociation

study for mepiquat pentaborate that demonstrates that mepiquat

pentaborate dissociates in an identical physical manner to

13260 NORTHWEST COALITION v. EPA
In 2002, the NRDC filed objections to the final rules for

each of the pesticides based on the EPA’s decision to reduce

the 10x safety factor to 3x or 1x. The NRDC’s objections

were based on the theory that the EPA did not have “reliable

data” which would allow it to reduce the child safety factor

because the EPA had not yet received the results of a DNT

study for each pesticide, and because the EPA relied on drinking water exposure models rather than on pesticide-specific

mepiquat chloride in water. Therefore, the analysis performed for

mepiquat chloride or the “chloride salt,” also pertains to this

mepiquat “pentaborate salt” use because the use rate, maximum

seasonal use rate and other pertinent use factors remain the same

for mepiquat chloride or the “chloride salt.” . . . 

Margins of safety are incorporated into EPA risk assessments

either directly through use of a margin of exposure (MOE) analysis or through using uncertainty (safety) factors in calculating a

dose level that poses no appreciable risk to humans. 

The Agency has determined that the FQPA safety factor for

mepiquat is 1X. See the Agency’s risk assessment for mepiquat

chloride dated January 12, 2000, for details. The facts are that

mepiquat pentaborate is another “salt” of mepiquat and that

mepiquat pentaborate disassociates to mepiquat and therefore the

basic toxicology data base for mepiquat chloride pertains to

mepiquat pentaborate. 

Id.

In establishing the tolerance for pymetrozine, the EPA stated: 

There is a complete toxicity database for pymetrozine and exposure data are complete or are estimated based on data that reasonably accounts for potential exposures. EPA determined that the

10X safety factor to protect infants and children could be reduced

to 3. The FQPA factor is reduced after assessing the potential for

additional sensitivity of infants and children to residues of

pymetrozine in the following studies: developmental toxicity

studies in rabbit and rat and two-generation reproduction study in

the rat. There was no evidence of increased susceptibility in these

studies. The FQPA safety factor was not reduced to one due to

the need for a developmental neurotoxicity study. 

Pymetrozine; Pesticide Tolerance, 66 Fed. Reg. at 66,791. 

NORTHWEST COALITION v. EPA 13261
drinking water monitoring data.4

 Notably, the NRDC did not

object on the ground that the EPA failed to justify its choice

of a safety factor of 3x or 1x relative to some other safety factor, such as “4x or 5x or 8x or 9x.” Maj. Op. at 13255.5

 The

EPA rejected NRDC’s objections in the Final Rule, and provided a detailed explanation of its basis for concluding that it

had reliable data notwithstanding the absence of certain DNT

studies and the use of exposure models, and why such reliable

data supported the EPA’s conclusion that it could safely

reduce the child safety factor. See generally 70 Fed. Reg.

46,706. The Final Rule upheld the 3x child safety factor for

acetamiprid and pymetrozine, and the 1x child safety factor

for mepiquat. Id. at 46,711-13, 46,736. 

B

In concluding that remand is required because the EPA

failed to explain why it chose a 3x uncertainty factor for

acetamiprid and pymetrozine and a 1x uncertainty factor for

mepiquat instead of “4x or 5x or 8x or 9x,” Maj. Op. at

4Natural Resources Defense Council, Objections to the Establishment of

Tolerances for Pesticide Chemical Residues: Halosulfuron-methyl and

Pymetrozine Tolerances (filed Feb. 25, 2002); Natural Resources Defense

Council, Objections to the Establishment of Tolerances for Pesticide

Chemical Residues: Imidacloprid, Mepiquat, Bifenazate, Zetacypermethrin, and Diflubenzuron Tolerances (filed May 19, 2002); Natural Resources Defense Council, Objections to the Establishment of Tolerances for Pesticide Chemical Residues: Isoxadifen-ethyl, Acetamiprid,

Propiconazole, Furilazole, Fenhexamid, and Fluazinam Tolerances (filed

May 20, 2002). 

5The NRDC also objected to the three tolerances on a number of other

grounds, including the failure to consider farm children adequately, a failure to consider worker risk adequately, an inadequate aggregate risk

assessment, an improper reliance on a “lowest observed adverse effect

level” (LOAEL) rather than a “no observed adverse effect level”

(NOAEL), a residue “percentile” assumption that inadequately protected

infants and children, and an improper assessment of chronic dietary exposure, among others. The NRDC did not raise these issues to us on appeal.

See supra Note 4; Final Rule, 70 Fed. Reg. at 46,713-14, 46,717-36.

13262 NORTHWEST COALITION v. EPA
13255, the majority is reaching an argument not properly

before us. The regulations applicable to the FFDCA require

exhaustion of administrative remedies. See 40 C.F.R.

§ 180.30(b) (providing that “judicial review is not available

unless an adversely affected party exhausts the[ ] objection

procedures, and any petition procedures preliminary thereto”).

In order to exhaust the objection procedure provided by the

FFDCA, petitioners must raise their objections to the agency

with specificity. See 21 U.S.C. § 346a(g)(2)(A) (requiring

objections to an EPA order establishing a tolerance to specify

“with particularity the provisions of the regulation or order

deemed objectionable”); 40 C.F.R. § 178.25(a)(2) (“To be

considered by the Administrator, an objection must: Specify

with particularity the provision(s) of the order, regulation, or

denial objected to, the basis for the objection(s), and the relief

sought.”). The purpose of this administrative exhaustion

requirement is to give notice to an agency of specific errors

or issues, so the agency can “bring the Agency’s experience

to bear on a contested question,” Nader v. EPA, 859 F.2d 747,

754 (9th Cir. 1988), and either correct the error or provide a

reasoned explanation. 

The NRDC objected to the EPA’s decision that a 10x safety

factor was not required for each of the three pesticide tolerances, and based this objection on the ground that the EPA

lacked reliable data because it had failed to obtain a DNT

study and had relied on drinking water exposure models. The

majority rests its decision that the tolerances for acetamiprid,

mepiquat, and pymetrozine must be remanded to the EPA on

a different ground, namely that the EPA failed to explain why

it chose a 3x uncertainty factor for acetamiprid and pymetrozine and a 1x uncertainty factor for mepiquat instead of “4x

or 5x or 8x or 9x,” Maj. Op. at 13255. Because the NRDC did

not object to the EPA’s decision on the ground that the EPA

had failed to give a clear explanation of the 3x or 1x safety

factor in lieu of “4x or 5x or 8x or 9x,” id., the issue identified

by the majority is not exhausted, and we are precluded from

reviewing it. 

NORTHWEST COALITION v. EPA 13263
The majority attempts to justify addressing issues that the

NRDC did not raise to the EPA by turning the administrative

exhaustion requirement on its head. As noted above, under the

regulations requiring exhaustion of administrative remedies,

parties objecting to proposed regulations bear the initial burden, and must raise their specific objections to the agency;

any issues not raised are waived and need not be considered

by the agency or by the court on appeal. 40 C.F.R.

§§ 178.25(a)(2), 180.30. Here, the majority shifts the burden

to the EPA to identify, raise, and resolve additional issues that

petitioners failed to raise at all, let alone frame with the requisite “particularity.” Id. § 178.25(a)(2). 

The majority first notes that “the NRDC argued that, absent

the DNT studies, the EPA had no reliable data to reduce the

10x child safety factor.” Maj. Op. at 13257. This is indeed the

specific objection raised by the NRDC. The majority then

recharacterizes this specific objection as being a more general

“challenge to the lower child safety levels set by the EPA.”

Maj. Op. at 13257.6 From this generalization, the majority

leaps to the conclusion that the NRDC’s specific objection

places a burden on the EPA to “explain why the data in its

possession” supported its decision to set a 3x or 1x child

safety factor for the pesticides at issue “as opposed to 4x or

5x or 8x or 9x.” Maj. Op at 13255, 13257. There is no basis

in our case law for taking such a leap or placing such a burden

on the EPA. We have never required an agency to interpret a

specific objection as being, at some level of generality, a different, broader objection, and responding to that different

objection. See, e.g., High Country Resources v. FERC, 255

F.3d 741, 745-46 (9th Cir. 2001) (stating that a petitioner cannot “implicitly” raise an issue to a regulatory agency in order

to exhaust administrative remedies, but must provide “much

6As noted supra, however, a valid objection cannot be this general; it

must “[s]pecify with particularity the provision(s) of the order, regulation

or denial objected to, the basis for the objection(s), and the relief sought.”

40 C.F.R. § 178.25. 

13264 NORTHWEST COALITION v. EPA
more specificity in the statement of objection” and present the

issue “squarely” to the agency.). Nor would it be reasonable

or consistent with the purpose of the administrative exhaustion requirement to do so. Here, the EPA responded to the

NRDC’s specific objection by carefully explaining why the

absence of DNT studies did not require the retention of the

10x safety factor. The EPA satisfied its burden, and had no

additional obligation to make a further response. 

In short, we have no authority to reverse an agency decision based on an objection that was not raised. The Supreme

Court has long warned us not to invent new issues as part of

our review of objections raised to an administrative agency.

“A reviewing court usurps the agency’s function when it sets

aside the administrative determination upon a ground not

theretofore presented and deprives the [administrative agency]

of an opportunity to consider the matter, make its ruling, and

state the reasons for its action.” Unemployment Comp. Com’n

v. Aragon, 329 U.S. 143, 155 (1946); see also Woodford v.

Ngo, 548 U.S. 81, 89 (2006). The EPA addressed, with adequate thoroughness and detail, see, e.g., Balt. Gas and Elec.

Co., 462 U.S. at 105-06, each of the objections filed by the

NRDC. These objections create the compass of our limited

review. 21 U.S.C. § 346a(h)(1), (5); 40 C.F.R. § 178.25(a)(2).7

(Text continued on page 13267)

7The majority also relies in part upon the dissent of Judge Wright in

Center for Auto Safety v. Peck, 751 F.2d 1336, 1373 (D.C. Cir. 1985)

(Wright, J., dissenting). Maj. Op. at 13256-57 n.7. However, Judge (now

Justice) Scalia’s opinion for the majority in that case captures the dissent’s

error, and, concomitantly, the majority’s mistake in this case when it

warns that “we must be implacably skeptical of belated recognition at the

appellate stage that elements of scientific analysis unchallenged during a

contested proceeding are incomprehensible without further explanation.

To credit such post-appeal pleas of inadequate information is to threaten

the integrity of all rulemaking in fields beyond our own limited scientific

ken.” Id. at 1361. The entirety of the passage bears repeating: 

The dissent’s response is equally unsatisfactory, consisting essentially of the assertion that late presentation of the issue must be

disregarded because validity of the [data] curves is essential to

NORTHWEST COALITION v. EPA 13265
validity of the agency’s conclusion. It is simply not the case,

however, that all of the essential postulates for an agency rule

must be contained in the record. Every judgment of any consequence is constructed upon an infinitude of other judgments, of

greater or lesser certitude, in a progression of logical dependency

terminating in a first principle the equivalent of 1 + 1 = 2. They

cannot all possibly be included in the statement of basis and purpose for a rulemaking. We do not have authority to require that

all elements underlying a rule be set forth in a fashion “understandable to a layman,” see Vermont Yankee Nuclear Power

Corp. v. Natural Resources Defense Council, Inc., 435 U.S. 519,

557, 98 S. Ct. 1197, 1218, 55 L. Ed. 2d 460 (1978). And it may

as well be disclosed that in scientific fields we judges ourselves

are laymen, ill equipped to determine where the line falls

between requisite explanation of problematic analysis and useless

replication of what for the cognoscenti amounts to a textbook on

basic physics. Thus, our “feel” for the adequacy of an analysis in

such cases is necessarily governed by the reaction that it elicits

from knowledgeable commenters. From the point at which it

reaches common ground we can reasonably assume that no further explication is required. We will hear on appeal assertions

that needful elaborations fairly requested were not provided; but

we must be implacably skeptical of belated recognition at the

appellate stage that elements of scientific analysis unchallenged

during a contested proceeding are incomprehensible without further explanation. To credit such post-appeal pleas of inadequate

information is to threaten the integrity of all rulemaking in fields

beyond our own limited scientific ken. The present challenge to

the effectiveness curves presents the threat in a particularly flagrant form. NHTSA specifically asked the petitioners (and other

rulemaking participants) in 1979: “Do the existing analyses represent the most appropriate methods of approaching a study of

bumper standards at different impact speeds and levels of damage

resistance? If not, what method should be used?” Though State

Farm and IIHS, among others, responded with substantial comments there was not even a suggestion that the effectiveness

curves represented a fundamentally invalid methodology. The

dissent provides a list of reasons why petitioners might not have

raised these objections during the rulemaking proceeding, Dissent

at 1387-88 all of which boil down to petitioners’ probable reluctance to upset favorable determinations. Even if that were the

13266 NORTHWEST COALITION v. EPA
C

Even were it proper for us to address the adequacy of the

EPA’s consideration of an issue not raised, the record provides an adequate basis for us to conclude that the EPA’s

selection of a 3x and 1x uncertainty factor was not arbitrary,

as the majority erroneously concludes. Maj. Op. at 13255. 

The record in this case contains the EPA’s published guidance for determination of an appropriate FQPA safety factor.

See Office of Pesticide Programs, EPA, Determination of the

only consideration, it would be of questionable wisdom to reward

their tactical decision to leave the agency in the dark—and thus

encourage benighted agency action in the future. But in any

event, the dissent’s speculations do not explain why the proponents of the 2.5 mph standard did not raise these arguments. In

fact, some commenters on the June 1979 Final Assessment

(which supported the 5.0 mph standard) did object that the “effectiveness ratios for 5.0 mph systems are overstated to a considerable extent,” but that objection was based upon the lack of

correspondence with repair cost data rather than theoretical inadequacy of the effectiveness curves. 

We conclude that the curves were considered part of the common ground of expert analysis that required no further explanation. Petitioners’ objections on this score put us in mind of the

Supreme Court’s injunction in Vermont Yankee that administrative proceedings should not be a game or a forum to engage in

unjustified obstructionism by making cryptic and obscure reference to matters that “ought to be” considered and then, after failing to do more to bring the matter to the agency’s attention,

seeking to have that agency determination vacated on the ground

that the agency failed to consider matters “forcefully presented.”

435 U.S. at 553-54, 98 S. Ct. at 1217. These instructions are even

more appropriate when cryptic and obscure reference to theoretical inadequacy—or in fact, even less than that, mere assertion of

lack of explanation of theoretical adequacy—is first made on

appeal. 

Id. at 1361-62 (emphases in original, internal citations to the record omitted). 

NORTHWEST COALITION v. EPA 13267
Appropriate FQPA Safety Factor(s) in Tolerance Assessment

10 (Feb. 28, 2002). As explained in this guidance document,

“when evaluating whether reliable data are available to support a FQPA safety factor different from the default 10x

FQPA safety factor and what level of ‘different’ FQPA safety

factor would be safe for infants and children,” id. at 19, the

EPA may, in the exercise of its scientific judgment, consider

the 3x uncertainty factor that has traditionally been used for

evaluating risks posed by pesticide exposure in a related context. See id. at 26; see also id. at 9-10 (noting that in evaluating the risks posed by pesticide exposure, “often a value of 3x

is used to address database deficiencies . . . .”). However, in

“the optimal case” in “which there is a high level of confidence that the hazard and exposure assessments are sufficiently conservative[,] and there are no residual uncertainties

in the assessment,” the EPA will remove the safety factor, i.e.,

it will apply a “safety factor of 1X,” deeming the existing

threshold “sufficient to protect infants and children.” Id. at

51-52. See also Office of Pesticide Programs, EPA, Office of

Pesticide Programs’ Policy on The Determination of The

Appropriate FQPA Safety Factor(s) For Use in The

Tolerance-setting Process: Response to Public Comments

OPP Docket OPP-00610 97 (Feb. 28, 2002) (internal citation

omitted) (further explaining the long-standing basis for “imposing a database uncertainty factor of 3X if one key study is

missing from the database and a factor of 10X if more than

one is missing.”). 

Other EPA tolerance-setting regulations reflect the

approach described in its guidance documents for selecting a

FQPA safety factor different from the default 10x FQPA

safety factor. See, e.g., Fenarimol; Pesticide Tolerance, 71

Fed. Reg. 32,841, 32,844-45 (June 7, 2006) (noting that the

EPA originally reduced the FQPA Safety factor from 10x to

3x subject to receiving additional data, and subsequently recommended reducing the 3x FQPA Safety factor to 1x when

it obtained adequate data); Thiacloprid; Pesticide Tolerances,

68 Fed. Reg. 55,503, 55,509 (Sept. 26, 2003) (“Although the

13268 NORTHWEST COALITION v. EPA
lack of morphometric assessments in the DNT raised some

uncertainty, EPA determined that there were sufficient reliable data to select an additional safety factor of 3X instead of

10X.”). The EPA relied on this long-established approach in

setting the safety factors for the three pesticides at issue here,

see supra at nn.2 & 3. 

Because the petitioners did not challenge the absence of an

explanation as to why the EPA picked a 3x or 1x factor rather

than a “4x or 5x or 8x or 9x” factor, we are deprived of the

EPA’s more detailed explanation as to why the scientific

community relies on the 3x uncertainty factor when database

deficiencies are identified. Nevertheless, the record indicates

that use of the 3x uncertainty factor is generally accepted by

the scientific community. See Michael L. Dourson et al., Evolution of Science-Based Uncertainty Factors in Noncancer

Risk Assessment, 24 Regulatory Toxicology and Pharmacology 108 (1996) (generally discussing the science underlying

the use of 10x and 3x default uncertainty factors). Indeed, the

lack of any controversy regarding the rationale underlying the

selection of a 3x safety factor rather than a “4x or 5x or 8x

or 9x” factor may explain why the NRDC did not argue in its

objections to the EPA that the agency needed a special justification for selecting a 3x safety factor, once the EPA determined that the additional 10x factor was not required. In light

of the EPA’s reliance on a long-established and widely

accepted protocol, the majority’s statement that “the EPA

chose these lower safety levels arbitrarily” is not supported by

the record, and is contrary to our obligation to defer to the scientific analysis and judgments made by an agency operating

within its area of special expertise. Balt. Gas and Elec. Co.,

462 U.S. at 103. 

As we have recently emphasized, “[w]e are to be most deferential when the agency is making predictions, within its area

of special expertise, at the frontiers of science.” Lands Council, 2008 WL 2640001, at *9 (internal quotation marks and

alterations omitted). Lands Council prohibits us from indulgNORTHWEST COALITION v. EPA 13269
ing the temptation to “act as a panel of scientists.” Id. at *4.

Nor can we require the agency “to always demonstrate the

reliability of its scientific methodology or the hypotheses

underlying the [agency’s] methodology.” Id. at *7 (internal

quotation marks omitted). Lands Council teaches that our

proper role is simply to ensure that the agency, in its expertise, made no clear error of judgment rendering its action arbitrary and capricious. See id. at *9-10. The EPA’s choices in

this case were neither arbitrary nor capricious and we must

defer to its judgment. See 5 U.S.C. § 706(2)(A); Balt. Gas and

Elec. Co., 462 U.S. at 103-05. Accordingly, I would deny the

petition for review in its entirety. 

13270 NORTHWEST COALITION v. EPA