99184 Federal Register / Vol. 89, No. 237 / Tuesday, December 10, 2024 / Proposed Rules 

Dated: December 4, 2024. 

Ce ́sar Zapata, 

Acting Regional Administrator, Region 4. 

[FR Doc. 2024–28873 Filed 12–9–24; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 180 

[EPA–HQ–OPP–2024–0431; FRL–12415–01– 

OCSPP] 

Chlorpyrifos; Tolerance Revocation 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: EPA is proposing to revoke all 

tolerances for residues of chlorpyrifos, 

except for those associated with the use 

of chlorpyrifos on the following crops: 

alfalfa, apple, asparagus, tart cherry, 

citrus, cotton, peach, soybean, 

strawberry, sugar beet, and spring and 

winter wheat. This proposal also 

addresses the request to revoke all 

chlorpyrifos tolerances contained in the 

September 12, 2007, petition submitted 

by the Natural Resources Defense 

Council (NRDC) and Pesticide Action 

Network North America (PANNA). 

DATES: Comments must be received on 

or before February 10, 2025. 

ADDRESSES: Submit your comments, 

identified by docket identification (ID) 

number EPA–HQ–OPP–2024–0431, 

through the Federal eRulemaking Portal 

at https://www.regulations.gov. Follow 

the online instructions for submitting 

comments. Do not submit electronically 

any information you consider to be 

Confidential Business Information (CBI) 

or other information whose disclosure is 

restricted by statute. Additional 

instructions on commenting and visiting 

the docket, along with more information 

about dockets generally, is available at 

https://www.epa.gov/dockets. 

FOR FURTHER INFORMATION CONTACT: 

Patricia Biggio, Pesticide Re-Evaluation 

Division (7508M), Office of Pesticide 

Programs, Environmental Protection 

Agency, 1200 Pennsylvania Ave. NW, 

Washington, DC 20460–0001; telephone 

number: 202–566–0700; email address: 

OPPChlorpyrifosInquiries@epa.gov. 

SUPPLEMENTARY INFORMATION: 

I. General Information 

A. Does this action apply to me? 

This action is directed to the public 

in general and may be of interest to a 

wide range of stakeholders including 

environmental, human health, and 

agricultural advocates; the chemical 

industry; pesticide users; and members 

of the public interested in the sale, 

distribution, or use of pesticides. Since 

others also may be interested, the 

Agency has not attempted to describe all 

the specific entities that may be affected 

by this action. 

B. How can I get electronic access to 

other related information? 

You may access a frequently updated 

electronic version of 40 CFR part 180 

through the Office of the Federal 

Register’s e-CFR site at https://

www.ecfr.gov/current/title-40. 

C. What action is the Agency proposing? 

EPA is proposing to revoke all 

tolerances for residues of the insecticide 

chlorpyrifos as contained in 40 CFR 

180.342, except for those tolerances 

associated with 11 uses that were 

proposed for retention in the Agency’s 

December 2020 Chlorpyrifos Proposed 

Interim Decision (2020 PID). (Ref. 1) As 

a result of voluntary cancellations and 

label amendments, registrations of 

chlorpyrifos will be limited in terms of 

food uses to these crops within certain 

states, as proposed in the 2020 PID and 

EPA’s Updated Chlorpyrifos Refined 

Drinking Water Assessment for 

Registration Review (September 2020) 

(‘‘2020 DWA’’) as described in Unit III 

below. (Ref. 2) 

Therefore, the Agency is proposing to 

revoke all other tolerances that are not 

needed as a result of the cancellations, 

including uses in food handling 

establishments and food service 

establishments. This proposal will also 

address the request to revoke 

chlorpyrifos tolerances in the pending 

2007 Petition from NRDC and PANNA. 

D. What is EPA’s authority for taking 

this action? 

Pursuant to its authority under 

section 408 of the Federal Food, Drug, 

and Cosmetic Act (FFDCA), 21 U.S.C. 

346a (https://www.govinfo.gov/link/ 

uscode/21/346a), EPA may respond to a 

petition filed with the Agency under 

FFDCA section 408(d) by issuing a 

proposed and final rule under FFDCA 

section 408(e). The 2007 Petition 

requested that EPA revoke chlorpyrifos 

tolerances, as well as cancel 

chlorpyrifos registrations. EPA is 

proposing to revoke chlorpyrifos 

tolerances that will no longer be 

necessary due to the cancellation of 

domestic uses on those commodities. 

Under section 408(e) of the FFDCA, EPA 

may issue a rule revoking tolerances 

after providing notice of a proposed 

rulemaking and a period of not less than 

60 days for public comment. 21 U.S.C. 

346a(e). 

E. What is the expected impact of this 

action? 

The revocations of these tolerances 

are not expected to present 

extraordinary circumstances because the 

registrants have requested, pursuant to 

the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) section 6(f) (7 

U.S.C. 136d(f)), to voluntarily cancel 

uses associated with these tolerances. 

EPA is in the process of approving those 

cancellation requests under FIFRA, 

which means that soon the tolerances 

will no longer be needed to cover 

residues of chlorpyrifos in or on those 

food commodities. 

The revocations of tolerances could 

impact foreign producers who use 

chlorpyrifos to control insect pests and 

importers of those commodities. 

Shipments found to have residues could 

not be sold in the United States, which 

may represent a loss to importers or 

their trading partners. It is possible that 

these effects could have downstream 

effects, such as raising costs to U.S. 

consumers of these commodities. 

Regardless of the potential impacts of 

this action, tolerances can only be 

maintained if they are safe, which is a 

risk-only analysis under the FFDCA. 

F. What can I do if I want the Agency 

to maintain, for import purposes, a 

tolerance that the Agency proposes to 

revoke? 

This proposed rule provides a 60-day 

public comment period. All chlorpyrifos 

registrants have already voluntarily 

requested cancellation of all the uses of 

chlorpyrifos associated with the 

tolerances proposed for revocation in 

this notice. Once those cancellations are 

effective, those uses of chlorpyrifos on 

these commodities will no longer be 

registered in the United States, and once 

use terminates under the applicable 

existing stocks provisions, the 

tolerances will no longer be necessary to 

cover residues from use of the pesticide. 

Any food being moved through 

interstate commerce after tolerances are 

revoked would be covered by the 

FFDCA channels of trade provision, 21 

U.S.C. 346a(l)(5), as described in Unit 

VII.A. The Agency’s typical process, 

e.g., during registration review, is to 

remove tolerances from the regulations 

that are no longer necessary. This avoids 

confusion among the regulated 

community by reflecting registered uses 

and label directions and helps with 

consistency in enforcement under the 

FFDCA and FIFRA. 

The only reason to retain a tolerance 

in such circumstances is for import 

purposes. Any commenter seeking to 

retain tolerances for import purposes 


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must provide a comment to that effect 

and include information demonstrating 

the need for retaining a specific 

tolerance for specific imports, even if 

they have previously provided this 

information; a hypothetical need based 

on the potential for some commodities 

containing chlorpyrifos residues to one 

day be imported into the United States 

is insufficient. 

If any data are necessary to retain the 

tolerances for import purposes, EPA 

will issue an order in the Federal 

Register under FFDCA section 408(f). 

The order would specify data needed 

and the timeframes for submission of 

the data and would require that within 

90 days some person or persons notify 

EPA that they will submit the data. If 

the data are not submitted as required 

in the order, EPA will take appropriate 

action under FFDCA. 

After considering comments that are 

received in response to this proposed 

rule, EPA will issue a final rule. 

G. What should I consider as I prepare 

my comments for EPA? 

1. Submitting CBI. Do not submit CBI 

information to EPA through https://

www.regulations.gov or email. If you 

wish to include CBI in your comment, 

please follow the applicable instructions 

at https://www.epa.gov/dockets/ 

commenting-epa-dockets#rules and 

clearly mark the part or all of the 

information that you claim to be CBI. In 

addition to one complete version of the 

comment that includes information 

claimed as CBI, a copy of the comment 

that does not contain the information 

claimed as CBI must be submitted for 

inclusion in the public docket. 

Information so marked will not be 

disclosed except in accordance with 

procedures set forth in 40 CFR part 2. 

2. Tips for preparing your comments. 

When preparing and submitting your 

comments, see the commenting tips at 

https://www.regulations.gov/faq. 

3. Environmental justice. EPA seeks to 

achieve environmental justice—the just 

treatment and meaningful involvement 

of all people, regardless of income, race, 

color, national origin, Tribal affiliation, 

or disability, in Agency decision-making 

and other Federal activities that affect 

human health and the environment so 

that people are fully protected from 

disproportionate and adverse human 

health and environmental effects 

(including risks). To help address 

potential environmental justice issues, 

the Agency seeks information on any 

groups or segments of the population 

who, as a result of their location, 

cultural practices, or other factors, may 

have atypical or disproportionate and 

adverse human health impacts or 

environmental effects from exposure to 

chlorpyrifos, compared to the general 

population. 

H. What is contained in this proposed 

rule? 

The following provides a brief 

roadmap of the Units in this proposed 

rule. 

• Unit II contains an overview of the 

relevant statutory background under the 

FFDCA and FIFRA as well as the 

regulatory status of chlorpyrifos. This 

Unit also provides a summary of the 

various recent legal challenges to the 

chlorpyrifos tolerances. 

• Unit III describes the Agency’s 

proposal to revoke tolerances that will 

not be needed as a result of the approval 

of registrants’ requests to cancel 

chlorpyrifos uses on certain food 

commodities. 

• Unit IV contains a safety 

determination that supports the 

tolerances that are not proposed for 

revocation. 

• Unit V contains the Agency’s 

responses to specific claims raised in 

the 2007 Petition not otherwise 

addressed in the rest of the proposed 

rule. 

• Units VI, VII, and VIII contain 

EPA’s request for public comment, 

discuss EPA’s intention for phasing out 

the tolerances, and consistency with 

other statutory requirements and 

executive orders. 

II. Background 

A. What is a tolerance? 

A ‘‘tolerance’’ represents the 

maximum level for residues of pesticide 

chemicals legally allowed in or on food, 

which includes raw agricultural 

commodities, processed foods, and feed 

for animals. Under the FFDCA, residues 

of a pesticide chemical that are not 

covered by a tolerance or exemption 

from the requirement of a tolerance are 

considered unsafe. See 21 U.S.C. 

346a(a)(1). Foods containing unsafe 

residues are deemed adulterated and 

may not be distributed in interstate 

commerce. See 21 U.S.C. 331(a), 

342(a)(2)(B). This applies to both food 

treated domestically with a pesticide 

registered in the United States or treated 

in another country and imported into 

the United States. Thus, before 

registering any food-use pesticide (i.e., a 

pesticide use that is likely to result in 

residues in or on food) under FIFRA, 7 

U.S.C. 136 et seq., EPA ensures that any 

necessary tolerances or exemptions are 

in place. 40 CFR 152.112(g). EPA also 

establishes tolerances or exemptions for 

pesticides not registered in the United 

States in order for commodities treated 

with those pesticides to be imported. 

B. FFDCA/FIFRA Background 

1. FFDCA 

FFDCA section 408(b) authorizes EPA 

to establish a tolerance, if the Agency 

determines that a tolerance is safe. See 

21 U.S.C. 346a(b). If EPA determines 

that a tolerance is not safe, EPA must 

modify or revoke that tolerance. The 

FFDCA defines ‘‘safe’’ 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. 

346a(b)(2)(A)(ii). This includes exposure 

through drinking water and in 

residential settings but does not include 

occupational exposure. 

FFDCA section 408(b)(2)(C) requires 

EPA to give special consideration to the 

exposure of infants and children to the 

pesticide chemical residue in 

establishing a tolerance and to ‘‘ensure 

that there is a reasonable certainty that 

no harm will result to infants and 

children from aggregate exposure to the 

pesticide chemical residue[s].’’ 21 

U.S.C. 346a(b)(2)(C). This provision also 

creates a presumption that EPA will use 

an additional safety factor for the 

protection of infants and children. 

Specifically, it directs that ‘‘in the case 

of threshold effects, . . . an additional 

tenfold margin of safety for the pesticide 

chemical residue and other sources of 

exposure shall be applied for infants 

and children to take into account 

potential pre- and post-natal toxicity 

and completeness of the data with 

respect to exposure and toxicity to 

infants and children.’’ (21 U.S.C. 

346a(b)(2)(C)) EPA is permitted to ‘‘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.) Due to Congress’s focus on both 

prenatal and post-natal toxicity, EPA 

has interpreted this additional safety 

factor as pertaining to risks to infants 

and children that arise due to prenatal 

exposure as well as to exposure during 

childhood years. This section providing 

for the special consideration of infants 

and children in section 408(b)(2)(C) was 

added to the FFDCA by the Food 

Quality Protection Act (FQPA) in 1996; 

therefore, this additional margin of 

safety is referred to throughout this 

proposed rule as the FQPA safety factor 

(SF). 

Finally, FFDCA section 408(b)(2)(D) 

contains several factors that EPA 

considers when making determinations 

about establishing, modifying, or 


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revoking tolerances. 21 U.S.C. 

346a(b)(2)(D). 

Any person may file a petition 

requesting that EPA establish, modify, 

or revoke a tolerance. 21 U.S.C. 

346a(d)(1). After publishing notice of 

receipt of that petition and after giving 

due consideration, EPA may issue a 

final or proposed rule establishing, 

modifying, or revoking the tolerances or 

issue an order denying the petition. 21 

U.S.C. 346a(d)(4)(A). 

2. FIFRA 

Under FIFRA (7 U.S.C. 136 et seq.), 

EPA regulates the sale, distribution, and 

use of pesticides. While FFDCA 

authorizes the establishment of legal 

limits for pesticide residues in food, 

FIFRA generally requires the approval 

of pesticides prior to their sale and 

distribution (id. at section 136a(a)) and 

establishes a registration regime for 

regulating the use of pesticides. In order 

for a pesticide to be registered, EPA 

must determine that a pesticide ‘‘will 

not generally cause unreasonable 

adverse effects on the environment,’’ 

among other things. (Id. at section 

136a(c)(5)) The term ‘‘unreasonable 

adverse effects on the environment’’ is 

defined to include ‘‘a human dietary 

risk from residues that results from a 

use of a pesticide in or on any food 

inconsistent with the standard under 

section 346a of Title 21.’’ (Id. at section 

136(bb)) The FFDCA safety standard 

was integrated into the FIFRA 

registration standard through the FQPA, 

which also directed that EPA 

coordinate, to the extent practicable, 

revocations of tolerances with pesticide 

cancellations under FIFRA. (21 U.S.C. 

346a(l)(1)). 

Also under FIFRA, EPA is required to 

re-evaluate existing registered pesticides 

every 15 years in a process called 

‘‘registration review.’’ (7 U.S.C. 

136(a)(g)) The purpose of registration 

review is ‘‘to ensure that each pesticide 

registration continues to satisfy the 

FIFRA standard for registration,’’ (40 

CFR 155.40(a)(1)) taking into account 

changes that have occurred since the 

last registration decision, including any 

new relevant scientific information and 

any changes in the law or regulations, 

policy, risk-assessment procedures or 

methods, and data requirements. (40 

CFR 155.53(a)) To ensure that a 

pesticide continues to meet the standard 

for registration, EPA must determine, 

based on the available data, including 

any additional information that has 

become available since the pesticide 

was originally registered or previously 

re-evaluated, that the pesticide does not 

cause ‘‘unreasonable adverse effects on 

the environment.’’ (7 U.S.C. 136a(c)(1), 

(5); see also 40 CFR 152.50) As part of 

the registration review of a pesticide, 

EPA also evaluates whether existing 

tolerances are safe and whether any 

changes to existing tolerances are 

necessary or appropriate. Pesticide 

products that do not meet the FIFRA 

standard for registration may be 

cancelled pursuant to the procedures in 

FIFRA section 6, 7 U.S.C. 136d. That 

provision of FIFRA also provides a 

mechanism for registrants to request 

voluntary cancellation of registered 

products or to request termination of 

specific uses on any registered product, 

at any time for any reason. 7 U.S.C. 

136d(f). If a registrant requests such 

cancellation or use termination, EPA 

publishes notice of that request and 

allows for a public comment period. 7 

U.S.C. 136d(f)(1)(B) and (C). After the 

public comment period, EPA may 

approve or deny the request. 7 U.S.C. 

136d(f)(1)(D). 

C. Chlorpyrifos Background 

Chlorpyrifos (0,0-diethyl-0-3,5,6- 

trichloro-2-pyridyl phosphorothioate) is 

a broad-spectrum, chlorinated 

organophosphate (OP) insecticide. 

Chlorpyrifos also forms the more toxic 

and potent acetylcholinesterase (AChE) 

inhibitor, chlorpyrifos oxon. 

Chlorpyrifos has been registered for 

use in the United States since 1965. 

These uses have included a wide range 

of food crops (e.g., soybean, wheat) and 

non-food use sites (e.g., tobacco, 

ornamental flowering plants, turf), as 

well as public health uses (e.g., aerial 

and ground-based fogger mosquito 

adulticide treatments) and residential 

uses (e.g., roach bait products, and 

individual fire ant mound treatments). 

In 2000, chlorpyrifos registrants reached 

an agreement with EPA to voluntarily 

cancel all residential use products 

except those registered for ant and roach 

baits in child-resistant packaging and 

fire ant mound treatments. Most 

recently, as discussed later in this 

document, chlorpyrifos registrants have 

voluntarily requested to cancel all food 

uses except the 11 uses described in 

Unit III. Pursuant to those requests, EPA 

has already cancelled most of those 

registered food uses and expects to 

process the remaining cancellation 

requests by the end of this calendar year 

(2024). (Ref. 3–8). 

EPA is currently working to complete 

the registration review of chlorpyrifos. 

As part of that process, EPA has 

completed multiple human health risk 

assessments (HHRAs) since 2011. As 

additional data became available for 

chlorpyrifos and its metabolite of 

concern, chlorpyrifos oxon, EPA 

completed revised draft human health 

risk assessments in 2014, 2016, and 

2020. A refined drinking water 

assessment (DWA) was completed in 

2016 (2016 DWA), and the Updated 

DWA was completed in 2020 (2020 

DWA). In December 2020, EPA issued 

the Chlorpyrifos Proposed Interim 

Decision (2020 PID). (Ref. 1) At this 

time, EPA is working on responding to 

comments received on the 2020 PID and 

supporting risk assessments and on 

preparing an updated human health risk 

assessment and amended proposed 

interim registration review decision. 

EPA anticipates issuing an amended PID 

in 2026 followed by the Chlorpyrifos 

Interim Decision. 

It should be noted that there has been 

an international effort to develop a 

battery of new approach methodologies 

(NAMs) to inform the developmental 

neurotoxicity (DNT) potential for 

individual chemicals. The assays in this 

battery are expected to provide a 

mechanistic understanding of the 

underlying biological processes that 

may be vulnerable to chemicallyinduced disruption. Since the 

integration of data from the DNT NAM 

battery for the chlorpyrifos risk 

assessment is in progress, it has not 

been incorporated into the risk 

assessment that supports this 

rulemaking. It is intended to be 

incorporated into the amended human 

health risk assessment anticipated for 

release in 2025 in support of registration 

review, and the Agency will provide 

any updates on the status of this effort 

through the ongoing registration review 

of chlorpyrifos. 

D. 2007 Petition and Associated 

Litigation 

In September 2007, PANNA and the 

NRDC jointly submitted to EPA a 

petition under FFDCA section 408(d), 

seeking revocation of all chlorpyrifos 

tolerances. The 2007 Petition also 

sought the cancellation of all 

chlorpyrifos pesticide product 

registrations under FIFRA section 6, 7 

U.S.C. 136d. The 2007 Petition raised 

several claims, which are discussed in 

Unit V., regarding both EPA’s 2006 

FIFRA reregistration eligibility decision 

(RED) and active registrations of 

chlorpyrifos in support of the request 

for tolerance revocations and product 

cancellations. 

In March 2009, EPA decided it would 

be appropriate to address these issues 

and the 2007 Petition claims in 

connection with the registration review 

of chlorpyrifos under FIFRA section 3(g) 

and decided to expedite that review, 

intending to finalize it several years in 

advance of the registration review 

deadline at that time, October 1, 2022. 


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On July 16, 2012, EPA denied the one 

FIFRA claim in a letter to the Petitioners 

and offered a partial response on several 

of the FFDCA claims; however, because 

the complexity of these scientific issues 

precluded EPA from finishing its review 

according to EPA’s original timeline, the 

Petitioners brought legal action in the 

U.S. Court of Appeals for the Ninth 

Circuit to compel EPA to either issue an 

order denying the 2007 Petition or to 

grant the 2007 Petition by initiating the 

tolerance revocation process. On August 

10, 2015, the Ninth Circuit ordered EPA 

to ‘‘issue either a proposed or final 

revocation rule or a full and final 

response to the administrative [P]etition 

by October 31, 2015.’’ In re Pesticide 

Action Network N. Am., 798 F.3d 809, 

815 (9th Cir. 2015). 

In response to that 2015 order, EPA 

issued a proposed rule to revoke all 

tolerances for chlorpyrifos on October 

28, 2015 (published in the Federal 

Register on November 6, 2015 (80 FR 

69080)). Although EPA noted that 

further evaluation might enable more 

tailored risk mitigation, EPA was unable 

to conclude, based on the information 

before EPA at the time, that the 

tolerances were safe, since the aggregate 

exposure to chlorpyrifos, driven by 

drinking water exposures, exceeded safe 

levels. In November 2016, EPA issued a 

notice of data availability announcing 

the availability of a revised human 

health risk assessment. (81 FR 81049) 

(Nov. 17, 2016) (Ref. 9) 

In the meantime, the Ninth Circuit 

ordered EPA to take final action on its 

proposed revocation rule and issue its 

final response to the Petition by 

December 30, 2016. In re Pesticide 

Action Network N. Am., 808 F.3d 402 

(9th Cir. 2015). EPA requested an 

extension of the deadline in order to be 

able to fully consider the July 2016 

FIFRA Scientific Advisory Panel (SAP) 

report regarding chlorpyrifos toxicology, 

but the Ninth Circuit ordered EPA to 

complete its final action by March 31, 

2017. In re Pesticide Action Network of 

North America v. EPA, 840 F.3d 1014 

(9th Cir. 2016). 

Accordingly, EPA issued a formal 

denial of the FFDCA claims in the 2007 

Petition in an order issued in March 

2017. (Ref. 10) In that 2017 Petition 

Denial, EPA concluded that it was not 

required to complete—and would not 

complete—any tolerance revocation of 

chlorpyrifos without resolution of those 

issues during the ongoing FIFRA 

registration review of chlorpyrifos. 

Chlorpyrifos; Order Denying PANNA 

and NRDC’s Petition to Revoke 

Tolerances, 82 FR 16581 (April 5, 2017) 

(‘‘2017 Petition Denial’’). EPA also 

denied objections filed in response to 

the 2017 Petition Denial on July 24, 

2019. See Chlorpyrifos; Final Order 

Denying Objections to March 2017 

Petition Denial Order, 84 FR 35555 (July 

24, 2019) (‘‘2019 Objections Denial’’). In 

the 2019 Objections Denial, EPA 

concluded that it was appropriate to 

deny the objections related to new 

issues raised after EPA’s 2006 tolerance 

reassessment and reregistration of 

chlorpyrifos as these issues are being 

addressed according to the schedule for 

EPA’s ongoing registration review of 

chlorpyrifos. 

The 2019 Objections Denial was 

challenged by several farmworker 

advocacy groups and States, and in 

April 2021, the Ninth Circuit issued its 

decision, finding that EPA’s denial was 

arbitrary and capricious based on the 

record before the court. See League of 

United Latin Am. Citizens, et al., v. 

Regan, 996 F.3d 673 (9th Cir. 2021). The 

Ninth Circuit vacated EPA’s petition 

response and ordered EPA to grant the 

2007 Petition; to issue a final rule either 

revoking all chlorpyrifos tolerances or 

modifying the chlorpyrifos tolerances, 

provided EPA could make a 

determination that those modified 

tolerances met the safety standard 

mandated by the FFDCA; and to cancel 

registered chlorpyrifos products or uses 

associated with the revoked tolerances. 

The Ninth Circuit ordered EPA to issue 

that final rule within 60 days of the 

issuance of the mandate and to cancel 

the registered pesticides in a timely 

manner. Frustrated with the ‘‘[then-] 

thirteen years of interminable delay,’’ 

the Ninth Circuit concluded that 

‘‘further factfinding’’ would not be 

reasonable and that ‘‘immediate 

issuance of a final regulation is the only 

reasonable action,’’ citing the FFDCA 

provision authorizing issuance of a final 

rule ‘‘ ‘without further notice and 

without further period for public 

comment.’ ’’ See id. at 702, citing 21 

U.S.C. 136a(d)(4)(A)(i) (emphasis in 

original). 

On August 30, 2021, EPA complied 

with the Ninth Circuit’s ruling by 

granting the 2007 Petition and issuing 

the Final Tolerance Rule for 

Chlorpyrifos, which revoked all 

tolerances for chlorpyrifos. See 86 FR 

48315 (Aug. 30, 2021) (‘‘2021 Final 

Rule’’). EPA explained in the 2021 Final 

Rule that it was unable to determine 

that there was a reasonable certainty of 

no harm for aggregate exposure, 

including food, drinking water, and 

residential exposure, based on the 

available data and the anticipated 

exposures from all of the then-currently 

registered uses of chlorpyrifos. EPA’s 

analysis indicated that risk from 

aggregate exposures from all of the thenregistered uses would exceed the 

Agency’s levels of concern. To satisfy 

international trade considerations, the 

2021 Final Rule allowed the tolerances 

to remain in effect for six months until 

February 28, 2022, at which time the 

tolerances expired. Pursuant to FFDCA 

section 408(g), registrants and grower 

groups, among others, filed objections to 

the 2021 Final Rule, which EPA denied 

on February 28, 2022. See Chlorpyrifos; 

Final Order Denying Objections, 

Requests for Hearings, and Requests for 

a Stay of the August 2021 Tolerance 

Final Rule. 87 FR 11222 (Feb. 28, 2022) 

(‘‘2022 Objections Denial’’). 

The 2021 Final Rule and 2022 

Objections Denial were challenged by a 

chlorpyrifos registrant, Gharda 

Chemicals International, Inc. (Gharda), 

and 19 grower groups in the U.S. Court 

of Appeals for the Eighth Circuit. The 

grower groups included Red River 

Valley Sugarbeet Growers Association, 

U.S. Beet Sugar Association, American 

Sugarbeet Growers Associations, 

Southern Minnesota Better Sugar 

Cooperative, American Crystal Sugar 

Company, Minn-Dak Farmer 

Cooperative, American Farm Bureau 

Federation, American Soybean 

Association, Iowa Soybean Association, 

Minnesota Soybean Growers 

Association, Missouri Soybean 

Association, Nebraska Soybean 

Association, South Dakota Soybean 

Association, North Dakota Soybean 

Growers Association, National 

Association of Wheat Growers, Cherry 

Marketing Institute, Florida Fruit and 

Vegetable Association, Georgia Fruit 

and Vegetable Growers Association, and 

the National Cotton Council of America. 

These petitioners argued, among other 

things, that EPA should have modified 

tolerances by leaving tolerances in place 

consistent with the 11 uses proposed 

the 2020 PID, rather than revoking all 

tolerances. 

On November 2, 2023, the Eighth 

Circuit issued its decision, vacating the 

2021 Final Rule (and EPA’s response to 

the 2007 Petition once again) and 

remanding the matter to EPA for further 

proceedings. See Red River Valley 

Sugarbeet Growers Ass’n, et al. v. 

Regan, 85 F.4th 881 (8th Cir. 2023). The 

Eighth Circuit’s decision noted that the 

Agency had ‘‘identified 11 specific 

candidates’’ of food and feed crop uses 

in the 2020 PID as part of Registration 

Review. Although the 2021 Final Rule 

(and the 2022 Objections Denial) 

explained why EPA was not modifying 

the tolerances consistent with the 2020 

PID, the Eighth Circuit concluded that 

the 2021 Final Rule ignored 

modification of tolerances as an option 

for addressing the Ninth Circuit’s 


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mandate and thus was arbitrary and 

capricious. The Eighth Circuit’s 

mandate issued on December 28, 2023, 

at which time all chlorpyrifos tolerances 

were automatically reinstated. EPA 

amended the Code of Federal 

Regulations on February 5, 2024, to 

reflect the Eighth Circuit’s reinstatement 

of chlorpyrifos tolerances. See 

Chlorpyrifos; Reinstatement of 

Tolerances, 89 FR 7625 (Feb. 5, 2024). 

III. Proposed Rule 

In this document, EPA is proposing to 

revoke tolerances to reflect registrants’ 

requests to voluntarily cancel food uses 

and submission of label amendments 

consistent with the 2020 PID and 

supporting documents. EPA anticipates 

approving all submitted cancellation 

requests by the end of 2024. After 

approval of the cancellation requests 

and label amendments, the only food 

uses that will remain on federally 

registered chlorpyrifos products are 

listed below and will be limited to the 

following States: 

1. Alfalfa: Arizona, Colorado, Iowa, 

Idaho, Illinois, Kansas, Michigan, 

Minnesota, Missouri, Montana, North 

Dakota, Nebraska, New Mexico, Nevada, 

Oklahoma, Oregon, South Dakota, 

Texas, Utah, Washington, Wisconsin, 

and Wyoming. 

2. Apple: Alabama, Delaware, 

Georgia, Idaho, Indiana, Kentucky, 

Maryland, Michigan, New Jersey, New 

York, Ohio, Oregon, Pennsylvania, 

Tennessee, Virginia, Vermont, 

Washington, West Virginia, and 

Washington, DC. 

3. Asparagus: Michigan. 

4. Tart cherry: Michigan. 

5. Citrus: Alabama, Florida, Georgia, 

North Carolina, South Carolina, and 

Texas. 

6. Cotton: Alabama, Florida, Georgia, 

North Carolina, South Carolina, and 

Virginia. 

7. Peach: Alabama, Delaware, Florida, 

Georgia, Maryland, Michigan, North 

Carolina, New Jersey, New York, Ohio, 

Pennsylvania, South Carolina, Texas, 

Virginia, Vermont, West Virginia, and 

Washington, DC. 

8. Soybean: Alabama, Colorado, 

Florida, Georgia, Iowa, Illinois, Indiana, 

Kansas, Kentucky, Minnesota, Missouri, 

Montana, North Carolina, North Dakota, 

Nebraska, New Mexico, Ohio, 

Oklahoma, Pennsylvania, South 

Carolina, South Dakota, Tennessee, 

Texas, Virginia, Wisconsin, West 

Virginia, and Wyoming. 

9. Strawberry: Oregon 

10. Sugar beet: Iowa, Idaho, Illinois, 

Michigan, Minnesota, North Dakota, 

Oregon, Washington, Wisconsin. 

11. Wheat: 

a. Spring wheat: Colorado, Kansas, 

Missouri, Montana, North Dakota, 

Nebraska, South Dakota, and Wyoming. 

b. Winter wheat: Colorado, Iowa, 

Kansas, Minnesota, Missouri, Montana, 

North Dakota, Nebraska, Oklahoma, 

South Dakota, Texas, and Wyoming. 

EPA notes that not all chlorpyrifos 

products are registered for these uses in 

all of the above listed States. If the use 

is not registered on a particular 

chlorpyrifos product, it must be added 

via the FIFRA section 3 registration 

process in order for that product to be 

used in a particular State. Moreover, 

EPA notes that since the issuance of the 

2020 PID, several States have prohibited 

use of chlorpyrifos, including 

California, Hawaii, New York, 

Maryland, and Oregon. States may 

regulate the sale or use of federally 

registered pesticides within their State. 

Although these particular States have 

adopted additional restrictions, the 

voluntary cancellation requests for the 

federally registered uses only reflected 

EPA’s proposal in the 2020 PID and did 

not incorporate any additional 

restrictions at the State level. As a 

result, EPA’s proposed tolerance 

revocations reflect only the adjustments 

to the federal registrations, but the 

continued registration review of 

chlorpyrifos allows for further 

consideration of this issue. 

In addition, the submitted label 

amendments are consistent with the 

reduced application frequency and rates 

for these uses that were used in the 2020 

DWA and support the Estimated 

Drinking Water Concentration (EDWC) 

calculations. (Ref. 2) EPA expects to 

approve the last of these label 

amendments by the end of 2024. 

Consistent with the terms of the 

cancellation orders, use of these 

previously registered chlorpyrifos 

products on any crops beyond the 11 

uses listed above and restricted as 

described herein will be prohibited after 

June 30, 2025. 

To cover residues of chlorpyrifos in 

food from these remaining food uses, 

the following existing tolerances are not 

being revoked: alfalfa, forage; alfalfa, 

hay; apple, apple, wet pomace; beet, 

sugar, dried pulp; beet, sugar, molasses; 

beet, sugar, roots; beet, sugar, tops; 

cattle, fat; cattle, meat; cattle, meat 

byproducts; cherry, tart; citrus, dried 

pulp; citrus, oil; cotton, undelinted 

cotton seed; egg; fruit, citrus, group 10; 

goat, fat; goat, meat; goat, meat 

byproducts; hog, fat; hog, meat; hog, 

meat byproducts; horse, meat; horse, 

meat byproducts; milk, fat (reflecting 

0.01 ppm in whole milk); peach; 

poultry, fat; poultry, meat; poultry, meat 

byproducts; sheep, fat; sheep, meat; 

sheep, meat byproducts; soybean, seed; 

strawberry; wheat, forage; wheat, grain; 

and wheat, straw in section 40 CFR 

180.342(a) and asparagus in 180.342(c). 

EPA is proposing to revoke all other 

tolerances for residues of chlorpyrifos 

on specific food commodities (40 CFR 

180.342(a)(1)); on all food commodities 

treated in food handling and food 

service establishments in accordance 

with prescribed conditions (40 CFR 

180.342(a)(2) and(a)(3)); and on grape 

when used under regional registrations 

(40 CFR 180.342(c)). 

EPA is proposing these tolerance 

revocations because all the registrants 

have submitted voluntary cancellation 

requests for all food uses that trigger the 

need for those tolerances. Moreover, all 

registrants retaining any of the 11 food 

uses listed above have submitted label 

amendments that limit uses to the 

specific States listed above and restrict 

application rates and application 

frequency consistent with the 

assumptions supporting the 2020 DWA. 

As of the publication of this proposed 

rule, 41 products have been cancelled, 

and 12 products have had all food uses 

but the 11 uses identified above 

cancelled. EPA has approved amended 

labels for 15 products. EPA is currently 

working to process and expects to 

complete its issuance of cancellation 

orders by the end of 2024, at which time 

no food uses beyond the 11 identified 

above will remain registered. 

Because of the cancellation of these 

uses, these tolerances will no longer be 

needed to cover residues from use of the 

pesticide within the United States. 

Removing unnecessary tolerances helps 

to avoid confusion among stakeholders 

about where the pesticide can be used 

and improves coordination under 

FIFRA and the FFDCA. EPA’s typical 

practice when tolerances are no longer 

needed due to the cancellation of 

registered uses or products is to remove 

them from the Code of Federal 

Regulations, usually carried out after 

being discovered as not necessary in 

registration review. See, e.g., Pesticide 

Tolerance; Exemptions, Petitions, 

Revocations, etc.: Implementing 

Registration Review Decisions for 

Certain Pesticides; Aluminum tris (Oethylphosphonate), Carbon disulfide, et 

al., (88 FR 46077) (July 19, 2023). (Ref. 

11) There is no requirement, however, 

to wait until the conclusion of 

registration review, and since EPA is 

aware of the lack of necessity of these 

tolerances now, EPA’s current proposed 

rule facilitates a more-timely reflection 

of the actual use status within the 

tolerance regulation to provide greater 

clarity to stakeholders, including 

growers and States, to avoid confusion 


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about what is allowed under the FFDCA 

and FIFRA. Moreover, although the 

EPA’s conclusions and rationale for the 

revocation of these tolerances differ 

from the claims outlined in the 

Petitioner’s 2007 request to revoke all 

tolerances, the EPA is, in part, taking 

the action requested by the 2007 

Petition. 

In some cases, the registrants’ requests 

to terminate these food uses or cancel 

registered chlorpyrifos products 

included requests to continue sale, 

distribution, and use of existing stocks 

for a certain period of time after 

cancellation. Existing stocks are those 

stocks of registered pesticide products 

that were in the United States and that 

were packaged, labeled, and released for 

shipment prior to the effective date of 

the cancellation action. Under those 

applicable cancellation orders, some 

existing stocks of previously registered 

chlorpyrifos products may be used on 

food until June 30, 2025. Therefore, EPA 

is proposing that the final rule revoking 

the unnecessary tolerances set an 

expiration date for those tolerances 

being revoked of July 1, 2025. This 

approach would align the permissible 

use period allowed under the 

cancellation orders with the coverage of 

the existing tolerance to allow for 

clearer coverage under section 408(l)(5) 

of the FFDCA. Under that provision, 

residues of a pesticide chemical in or on 

food will not render that food 

adulterated despite the revocation of a 

tolerance as long as the residue is 

present as a result of a lawful 

application of the pesticide and does 

not exceed the tolerance level that was 

authorized at the time of the 

application. See 21 U.S.C. 346a(l)(5). In 

addition, this approach would provide 

for a reasonable interval for exporting 

countries to adjust to the new tolerance 

restrictions consistent with the United 

States’ obligations under the World 

Trade Organization Agreement on the 

Application of Sanitary and 

Phytosanitary Measures (SPS 

Agreement). 

IV. Safety of the Remaining Tolerances 

As noted in the previous Unit, in a 

typical revocation action following the 

cancellation of registered products or 

uses, EPA would propose to remove 

tolerances that are no longer necessary. 

Those actions typically do not require a 

rationale for justifying retention of the 

tolerances that are not affected by that 

action, as revocation does not impact 

the prior safety determinations made for 

the tolerances left in place. 

Chlorpyrifos, however, presents an 

unusual situation due to the litigation 

history and the pending 2007 Petition. 

The last formal determination that EPA 

made concerning chlorpyrifos 

tolerances was in the 2021 Final Rule, 

in which EPA concluded that aggregate 

exposure to chlorpyrifos, based on all 

registered food uses on chlorpyrifos 

products at that time, was unsafe. That 

rule was issued in response to a Ninth 

Circuit order, which vacated EPA’s 2017 

Petition Denial and 2019 Objections 

Denial in full and ordered EPA to issue 

a final rule revoking all tolerances or 

modifying tolerances, as long as a safety 

determination supported those modified 

tolerances. Then the Eighth Circuit 

reinstated those tolerances through 

vacatur of the 2021 Final Rule, despite 

EPA’s finding that those tolerances were 

unsafe based on uses that were 

registered at that time and noted that 

EPA should have considered the option 

of retaining tolerances for the 11 uses 

proposed in the 2020 PID in its 2021 

Final Rule. In addition, the 2007 

Petition asserted that all chlorpyrifos 

tolerances were unsafe and should be 

revoked. Because EPA’s proposed rule 

does not revoke all chlorpyrifos 

tolerances, EPA is providing an updated 

determination of safety supporting the 

tolerances that are not being revoked. 

This approach and the related FIFRA 

cancellation actions satisfy the Eighth 

Circuit’s remand for further proceedings 

and the Ninth Circuit’s directive to 

ensure that any modified tolerances are 

safe, without further factfinding and 

delay. 

As indicated in Unit III., all 

chlorpyrifos registrants have submitted 

requests to voluntarily cancel all but 11 

food uses of chlorpyrifos and to amend 

labels that limit those food uses in 

several ways, i.e., limiting uses to 

specific States and restricting 

application rates and application 

frequency. After cancellation of all uses 

but the 11 food uses listed in Unit III, 

amendment of those uses on labels as 

described, and the termination of 

existing stocks terms, which EPA 

expects no later than June 30, 2025, EPA 

anticipates that exposure to chlorpyrifos 

in food and drinking water will align 

with the calculations in the 2020 DWA, 

the 2020 human health risk assessment, 

and the proposed determinations in the 

2020 PID. The cancellations and label 

amendments are reducing the amount of 

chlorpyrifos being used—and thus being 

applied to food and getting into 

drinking water. 

The safety determination in this 

document is based on the anticipated 

aggregate exposures expected as a result 

of the cancellation of most of the 

registered food uses and, on the analysis 

conducted in the 2020 HH DRA and the 

2020 DWA. As noted above, the 

registration review process is ongoing, 

and there is a possibility that additional 

information may alter the Agency’s 

conclusions once that process has been 

completed. However, for purposes of 

this rule and in an effort not to further 

delay progress on this rulemaking or in 

responding to the FFDCA petition, EPA 

is relying on the currently available 

scientific documents to conclude that 

the tolerances not being revoked are 

safe, i.e., that there is a reasonable 

certainty that no harm will result from 

the aggregate exposure to chlorpyrifos. 

As noted in this Unit, the aggregate 

exposures assessed reflect the 

anticipated exposures to chlorpyrifos 

residues in drinking water after the 

cancellation of most food uses of 

chlorpyrifos, rather than chlorpyrifos 

residues in drinking water based on the 

wider set of previously registered food 

uses as was done in the 2021 Final Rule. 

EPA’s full risk conclusions supporting 

this proposed response are set forth in 

Chlorpyrifos: Third Revised Human 

Health Risk Assessment for Registration 

Review (September 2020) (‘‘2020 HH 

DRA’’) and the 2020 DWA. (Ref. 12 and 

2) EPA’s assessment supports a 

conclusion that aggregate exposures 

(including residential exposures and 

food and drinking water exposures 

anticipated from the remaining 

registered chlorpyrifos uses after the 

cancellation orders are issued and 

amended labels are approved under 

FIFRA) are safe. 

A. EPA’s Hazard Assessment for 

Chlorpyrifos 

1. General Approach to Hazard 

Identification, Dose-Response 

Assessment, and Extrapolation 

Any risk assessment begins with an 

evaluation of a chemical’s inherent 

properties, and whether those properties 

have the potential to cause adverse 

effects (i.e., a hazard identification). In 

evaluating toxicity or hazard, EPA 

reviews toxicity data, typically from 

studies with laboratory animals, to 

identify any adverse effects on the test 

subjects. Where available and 

appropriate, EPA will also take into 

account studies involving humans, 

including human epidemiological 

studies. The animal toxicity database for 

a conventional, food use pesticide 

usually consists of studies investigating 

a broad range of endpoints including 

potential for carcinogenicity, 

mutagenicity, developmental and 

reproductive toxicity, and neurotoxicity. 

These studies include gross and 

microscopic effects on organs and 

tissues, functional effects on bodily 

organs and systems, effects on blood 


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parameters (such as red blood cell (RBC) 

count, hemoglobin concentration, 

hematocrit, and a measure of clotting 

potential), effects on the concentrations 

of normal blood chemicals (including 

glucose, total cholesterol, urea nitrogen, 

creatinine, total protein, total bilirubin, 

albumin, hormones, and enzymes such 

as alkaline phosphatase, alanine 

aminotransferase and cholinesterase), 

and behavioral or other gross effects 

identified through clinical observation 

and measurement. EPA examines 

whether adverse effects are caused by 

different durations of exposure ranging 

from short-term (acute) to long-term 

(chronic) pesticide exposure and 

different routes of exposure (oral, 

dermal, inhalation). Further, EPA 

evaluates potential adverse effects in 

different age groups (adults as well as 

fetuses and juveniles). (Ref. 13 at 8–10). 

Once a pesticide’s potential hazards 

are identified, EPA determines a 

toxicological level of concern for 

evaluating the risk posed by human 

exposure to the pesticide. In this step of 

the risk assessment process, EPA 

essentially evaluates the levels of 

exposure to the pesticide at which 

effects might occur. An important aspect 

of this determination is assessing the 

relationship between exposure (dose) 

and response (often referred to as the 

dose-response analysis). In evaluating a 

chemical’s dietary risks, EPA uses a 

reference dose (RfD) approach, which 

typically involves a number of 

considerations including: 

• A ‘‘point of departure’’ (PoD): 

Typically, the PoD is the value from a 

dose-response curve that is at the low 

end of the observable data in laboratory 

animals and that is the toxic dose that 

serves as the ‘‘starting point’’ in 

extrapolating a risk to the human 

population, although a PoD can also be 

derived from human data as well. PoDs 

are selected to be protective of the most 

sensitive adverse toxic effect for each 

exposure scenario and are chosen from 

toxicity studies that show clearly 

defined No Observed Adverse Effect 

Levels (NOAELs) or Lowest Observed 

Adverse Effect Levels (LOAELs), doseresponse relationships, and 

relationships between the chemical 

exposure and effect. EPA will select 

separate PoDs, as needed, for each 

expected exposure duration (e.g., acute, 

chronic, short-term, intermediate-term) 

and route of exposure (e.g., oral, dermal, 

inhalation). For chlorpyrifos, as 

discussed later in this Unit, EPA 

derived PoDs based on 10% RBC AChE 

inhibition in the 2020 HH DRA. 

• Interspecies extrapolation: Because 

most PoDs are derived from toxicology 

studies in laboratory animals, there is a 

need to extrapolate from animals to 

humans. In typical risk assessments, a 

default tenfold (10X) uncertainty factor 

is used to address the potential for a 

difference in toxic response between 

humans and animals used in toxicity 

tests. For chlorpyrifos, as described 

further below, EPA used a sophisticated 

model called a physiologically based 

pharmacokinetic-pharmacodynamic 

(PBPK–PD) model that accounts for 

differences in laboratory animals and 

humans, thereby obviating the need for 

the default interspecies factor. 

• Intraspecies extrapolation: To 

address the potential for differences in 

sensitivity in the toxic response across 

the human population, EPA conducts 

intraspecies extrapolation. In typical 

risk assessments, a 10X default 

uncertainty factor is used. For 

chlorpyrifos, the PBPK–PD model used 

to derive PoDs also accounts for 

differences in metabolism and toxicity 

response across the human population 

for some age groups and some 

subpopulations, which allows the 

default factor of 10X to be refined in 

accordance with EPA’s 2014 Guidance 

for Applying Quantitative Data to 

Develop Data-Derived Extrapolation 

Factors for Interspecies and Intraspecies 

Extrapolation. 

• Food Quality Protection Act safety 

factor (FQPA SF): The FFDCA section 

408(b)(2)(C) instructs EPA, in making its 

‘‘reasonable certainty of no harm’’ 

finding, that in ‘‘the case of threshold 

effects, an additional tenfold margin of 

safety for the pesticide chemical residue 

and other sources of exposure shall be 

applied for infants and children to take 

into account potential pre- and postnatal toxicity and completeness of data 

with respect to exposure and toxicity to 

infants and children.’’ Section 

408(b)(2)(C) further states that ‘‘the 

Administrator 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.’’ For 

chlorpyrifos, EPA is retaining the 

default 10X FQPA SF as discussed later 

in this Unit. 

In the human health risk assessment 

process, as indicated above, EPA uses 

the selected PoD to calculate a RfD for 

extrapolating risk. The RfD is calculated 

by dividing the selected PoD by any 

applicable interspecies and intraspecies 

factors and other relevant uncertainty 

factors such as LOAEL to NOAEL factor 

or database uncertainty factor. 

After calculating the RfD, as indicated 

above, EPA retains an additional safety 

factor of 10X to protect infants and 

children (the FQPA SF), unless reliable 

data support selection of a different 

factor, as required under the FFDCA. As 

described in EPA’s policy for 

determining the appropriate FQPA SF, 

this additional safety factor often 

overlaps with other traditional 

uncertainty factors (e.g., LOAEL to 

NOAEL factor or database uncertainty 

factor), but it might also account for 

residual concerns related to pre- and 

post-natal toxicity or exposure. (Ref. 14 

at 13–16) In implementing FFDCA 

section 408, EPA calculates a variant of 

the RfD referred to as a Population 

Adjusted Dose (PAD), by dividing the 

RfD by the FQPA SF. Risk estimates less 

than 100% of the PAD are safe. 

2. Toxicological Effects of Chlorpyrifos 

Consistent with FFDCA section 

408(b)(2)(D), EPA has reviewed the 

available scientific data and other 

relevant information for chlorpyrifos in 

support of this action. For over two 

decades, EPA has evaluated the 

scientific evidence surrounding the 

different health effects associated with 

chlorpyrifos. The Agency has conducted 

extensive reviews of the scientific 

literature on health outcomes associated 

with chlorpyrifos and presented 

approaches for evaluating and using that 

information to the FIFRA Scientific 

Advisory Panel (SAP), on several 

occasions, as discussed in Unit V of the 

2021 Final Rule. See 86 FR at 48320–21. 

(Note: The FIFRA SAP is a federal 

advisory committee created by FIFRA 

section 25(d), 7 U.S.C. 136w(d), and 

serves as EPA’s primary source of 

external, independent, scientific peer 

review for significant regulatory and 

policy matters involving pesticides). 

Chlorpyrifos has been tested in 

toxicological studies for the potential to 

cause numerous different adverse 

outcomes (e.g., reproductive toxicity, 

developmental toxicity, cancer, 

genotoxicity, dermal toxicity, endocrine 

toxicity, inhalation toxicity, and 

immunotoxicity). Chlorpyrifos has an 

established neurotoxic mode of action, 

and neurotoxicity is the most sensitive 

effect in all species, routes, and 

lifestages. The hazard characterization 

for chlorpyrifos and its oxon is based on 

adverse health effects in animals and 

humans related to two different 

neurotoxic endpoints: AChE inhibition 

and potential for neurodevelopmental 

effects. AChE inhibition is being used to 

derive the PODs for risk assessment. 

These PODs are protective for 

neurotoxic effects related to AChE 

inhibition and potential downstream 

neurotoxic effects. A weight-of-theevidence (WOE) analysis on the 

potential for neurodevelopmental effects 

following chlorpyrifos exposure 

considered (1) whether chlorpyrifos 


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causes long-term effects from prenatal 

and/or early lifestage exposure and (2) 

whether adverse effects can be 

attributed to doses lower than those 

which elicit 10% inhibition of RBC 

AChE. (Ref. 12 at 6) The FIFRA SAP 

reports have rendered numerous 

recommendations for additional study 

and sometimes conflicting advice for 

how EPA should consider (or not 

consider) the available data in 

conducting EPA’s registration review 

human health risk assessment for 

chlorpyrifos. 

The remainder of this Unit IV.A.2. 

discusses the Agency’s assessment of 

the science relating to AChE inhibition 

and the potential for 

neurodevelopmental effects. Other 

adverse outcomes besides AChE 

inhibition and neurodevelopment are 

less sensitive and are thus not discussed 

in detail here. Further information 

concerning those effects can be found in 

the 2000 human health risk assessment 

which supported the RED and the 2011 

preliminary human health risk 

assessment. (Ref. 15 and 16). 

a. Acetylcholinesterase (AChE) 

Inhibition 

Chlorpyrifos, like other 

organophosphate pesticides, affects the 

nervous system by inhibiting AChE, an 

enzyme necessary for the proper 

functioning of the nervous system and 

ultimately leading to signs of 

neurotoxicity. This mode of action, in 

which AChE inhibition leads to 

neurotoxicity, is well-established, and 

thus has been used as basis for the PoD 

for organophosphate human health risk 

assessments, including chlorpyrifos. 

This science policy is based on decades 

of work, which shows that AChE 

inhibition is the initial event in the 

pathway to cholinergic neurotoxicity. 

The Agency has conducted a 

comprehensive review of the available 

data and public literature regarding this 

adverse effect from chlorpyrifos. (Ref. 17 

at 24–25, Ref. 16 at 25–27) There are 

many chlorpyrifos studies evaluating 

RBC AChE inhibition or the brain in 

multiple lifestages (gestational, fetal, 

post-natal, and non-pregnant adult), 

multiple species (rat, mouse, rabbit, dog, 

human), methods of oral administration 

(oral gavage with corn oil, dietary, 

gavage via milk) and routes of exposure 

(oral, dermal, inhalation via vapor and 

via aerosol). In addition, chlorpyrifos is 

unique in the availability of AChE data 

from peripheral tissues in some studies 

(e.g., heart, lung, liver). There are also 

literature studies comparing the in vitro 

AChE response to a variety of tissues 

which show similar sensitivity and 

intrinsic activity. Across the database, 

brain AChE tends to be less sensitive 

than RBC AChE or peripheral AChE. In 

oral studies, RBC AChE inhibition is 

generally similar in response to 

peripheral tissues. Thus, the in vitro 

data and oral studies combined support 

the continued use of RBC AChE 

inhibition as the critical effect for 

quantitative dose-response assessment. 

For chlorpyrifos, there are data from 

multiple studies which provide robust 

RBC AChE data, including studies in 

pregnant, lactating, and non-pregnant 

female rats from oral exposure (e.g., 

developmental neurotoxicity (DNT), 

reproductive, and subchronic data). In 

addition, studies are available in 

juvenile pups that show age-dependent 

differences, particularly following acute 

exposures, in sensitivity to chlorpyrifos 

and its oxon metabolite. This sensitivity 

is not derived from differences in the 

AChE enzyme itself but instead are 

derived largely from the immature 

metabolic clearance capacity in the 

juveniles. 

b. Neurodevelopmental Toxicity 

In addition to information on the 

effects of chlorpyrifos on AChE, there is 

an extensive body of information (in the 

form of laboratory animal studies, 

epidemiological studies, and 

mechanistic studies) studying the 

potential effects on neurodevelopment 

in infants and children following 

exposure to organophosphates, 

including chlorpyrifos. 

There are numerous laboratory animal 

studies on chlorpyrifos in the literature 

that have evaluated the impact of 

chlorpyrifos exposure in pre- and postnatal dosing on the developing brain. 

These studies vary substantially in their 

study design, but all involve gestational 

and/or early post-natal dosing with 

behavioral evaluation from adolescence 

to adulthood. The data provide 

qualitative support for chlorpyrifos to 

potentially impact the developing 

mammalian brain with adverse 

outcomes in several neurological 

domains including cognitive, anxiety 

and emotion, social interactions, and 

neuromotor function. It is, however, 

important to note that there is little 

consistency in patterns of effects across 

studies. In addition, most of these 

studies use doses that far exceed EPA’s 

10% benchmark response level for RBC 

AChE inhibition. There are only a few 

studies with doses at or near the 10% 

brain or RBC AChE inhibition levels; 

among these only studies from Carr 

laboratory at Mississippi State 

University are considered by EPA to be 

high quality. In the 2020 HH DRA, EPA 

concluded that the laboratory animal 

studies on neurodevelopmental 

outcomes are not sufficient for 

quantitatively establishing a PoD. EPA 

further concluded that the laboratory 

animal studies do not support a 

conclusion that adverse 

neurodevelopmental outcomes are more 

sensitive than 10% RBC AChE 

inhibition. (Ref. 17 at 25–31, Ref. 12 at 

88–89). 

EPA evaluated numerous 

epidemiological studies on chlorpyrifos 

and other organophosphate pesticides in 

accordance with the ‘‘Framework for 

Incorporating Human Epidemiologic & 

Incident Data in Health Risk 

Assessment.’’ (Ref. 17, 18, and 19) The 

most robust epidemiologic research 

comes from three prospective birth 

cohort studies. These include: (1) The 

Mothers and Newborn Study of North 

Manhattan and South Bronx performed 

by the Columbia Children’s Center for 

Environmental Health (CCCEH) at 

Columbia University; (2) the Mount 

Sinai Inner-City Toxicants, Child 

Growth and Development Study or the 

‘‘Mt. Sinai Child Growth and 

Development Study;’’ and (3) the Center 

for Health Assessment of Mothers and 

Children of Salinas Valley 

(CHAMACOS) conducted by researchers 

at University of California Berkeley. 

(Ref. 17 at 32–43). 

In the case of the CCCEH study, 

which specifically evaluated the 

possible connections between 

chlorpyrifos levels in cord blood and 

neurodevelopmental outcomes on a 

specific cohort, there are a number of 

notable associations. (Ref. 17 at 36–38) 

Regarding infant and toddler 

neurodevelopment, the CCCEH authors 

reported statistically significant deficits 

of 6.5 points on the Psychomotor 

Development Index at three years of age 

when comparing high to low exposure 

groups. Notably, these decrements 

persist even after adjustment for group 

and individual level socioeconomic 

variables. These investigators also 

observed increased odds of mental delay 

and psychomotor delay at age three 

when comparing high to low exposure 

groups. The CCCEH authors also report 

strong, consistent evidence of a positive 

association for attention disorders, 

attention deficit hyperactivity disorder 

(ADHD), and pervasive development 

disorder (PDD) when comparing high to 

low chlorpyrifos exposure groups. 

Moreover, it was reported that for 

children in the CCCEH cohort at age 

seven for each standard deviation 

increase in chlorpyrifos cord blood 

exposure, there is a 1.4% reduction in 

Full-Scale IQ and a 2.8% reduction in 

Working Memory. In addition, the 

CCCEH authors evaluated the 

relationship between pre-natal 


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chlorpyrifos exposure and motor 

development/movement and reported 

elevated risks of arm tremor in children 

around 11 years of age in the CCCEH 

cohort. 

Notwithstanding the observed 

associations, EPA and the 2012 and 

2016 FIFRA SAP reports identified 

multiple uncertainties in the CCCEH 

epidemiology studies. (Ref. 17 and 20) 

Some of these include the relatively 

modest sample sizes, which limited the 

statistical power; exposure at one point 

in pre-natal time with no additional 

information regarding post-natal 

exposures; representativeness of a single 

point exposure where time-varying 

exposures or the ability to define 

cumulative exposures would be 

preferable; lack of specificity of a 

critical window of effect and the 

potential for misclassification of 

individual exposure measures; and lack 

of availability of the raw data from the 

studies that would allow verification of 

study conclusions. 

One of the notable uncertainties in the 

CCCEH epidemiology studies identified 

by EPA and the 2016 FIFRA SAP report 

is the lack of specific exposure 

information on the timing, frequency, 

and magnitude of chlorpyrifos 

application(s) in the apartments of the 

women in the study. Since 2012, despite 

extensive effort by EPA to obtain or 

infer this exposure information from 

various sources, the lack of specific 

exposure data remains a critical 

uncertainty. EPA made efforts in 2014 

and 2016 to develop dose reconstruction 

of the exposures to these women. These 

dose reconstruction activities represent 

the best available information and tools 

but are highly uncertain. In addition, 

the pregnant women and children in the 

CCCEH studies were exposed to 

multiple chemicals, including multiple 

potent AChE-inhibiting 

organophosphates and N-methyl 

carbamates. Moreover, using EPA’s dose 

reconstruction methods from 2014 

suggest that the pregnant women likely 

did not exhibit RBC AChE inhibition 

above 10%. The 2012 and 2016 FIFRA 

SAP reports expressed concern that it is 

likely that the CCCEH findings occurred 

at exposure levels below those that 

result in 10% RBC AChE inhibition. 

(Ref. 17 and 20) However, given the 

limitations of the available CCCEH 

exposure information and the exposures 

to multiple potent AChE inhibiting 

pesticides, EPA has been unable to 

definitively conclude the level of AChE 

inhibition occurring in the CCCEH 

studies. Consistent with the 2016 SAP 

report, EPA remains unable to make a 

causal linkage between chlorpyrifos 

exposure and the outcomes reported by 

CCCEH investigators. (Ref. 12 and 17) 

Given the uncertainties, particularly in 

the exposure information available from 

CCCEH (single timepoints, lack of time 

varying exposure, lack of knowledge 

about application timing), uncertainties 

remain about the dose-response 

relationships from the epidemiology 

studies, which EPA noted in the 2020 

HH DRA. (Ref. 12) 

Finally, there are several lines of 

evidence for modes of action of 

chlorpyrifos distinct from the classical 

mode of action of AChE inhibition. This 

information has been generated from 

model systems representing different 

levels of biological organization and 

provide support for molecular initiating 

events (binding to the morphogenic site 

of AChE, muscarinic receptors, or 

tubulin), cellular responses (alterations 

in neuronal proliferation, 

differentiation, neurite growth, or 

intracellular signaling), and responses at 

the level of the intact nervous system 

(serotonergic tone, axonal transport). 

Among the many in vitro studies on 

endpoints relevant to the developing 

brain available for chlorpyrifos, only 

three have identified outcomes in 

picomole concentrations, including 

concentrations lower than those that 

elicit AChE inhibition in vitro. 

However, as is the case for many other 

developmental neurotoxicants, most of 

these studies have not been designed 

with the specific goal of construction or 

testing an adverse outcome pathway. 

Thus, as discussed in the 2020 HHRA, 

there are not sufficient data available to 

test rigorously the causal relationship 

between effects of chlorpyrifos at the 

different levels of biological 

organization in the nervous system. 

(Ref. 17 at 27–31), so until there are any 

updates to the state of the science for 

chlorpyrifos, the Agency is relying on 

the 2020 HHRA for this rule. 

3. Hazard Identification: Using AChE as 

the Toxicological Endpoint for Deriving 

PADs 

In its 2020 HH DRA assessment, based 

on its review of all available data, EPA 

determined that AChE inhibition has 

the most robust quantitative doseresponse data and, thus, was chosen as 

the critical effect for the quantitative 

risk assessment. The Agency typically 

uses a 10% response level for AChE 

inhibition in human health risk 

assessments. This longstanding 

approach, see 2006 RED, is consistent 

with the advice of the FIFRA SAP from 

2008 and 2012 and has been applied in 

the 2006 OP cumulative risk assessment 

and other single-chemical OP risk 

assessments. (Ref. 21 and 22). 

During the ongoing registration 

review of chlorpyrifos and 

consideration of the 2007 Petition, the 

Agency has received comments 

concerning whether the use of the 10% 

AChE inhibition is sufficiently health 

protective. In one effort to take those 

comments into consideration, EPA 

conducted an additional hazard analysis 

and convened the 2016 FIFRA SAP to 

evaluate a proposal of using cord blood 

data from the CCCEH epidemiology 

studies as the source of data for PoDs. 

The 2016 FIFRA SAP report did not 

support the ‘‘direct use’’ of the cord 

blood and working memory data for 

deriving the regulatory endpoint, due to 

insufficient information about timing 

and magnitude of chlorpyrifos 

applications in relation to cord blood 

concentrations at the time of birth, 

uncertainties about the pre-natal 

window(s) of exposure linked to 

reported effects, and lack of a second 

laboratory to reproduce the analytical 

blood concentrations. (Ref. 17) Despite 

their critiques regarding uncertainties in 

the CCCEH studies, the 2016 FIFRA 

SAP report expressed concern that 10% 

RBC AChE inhibition may not be 

sufficiently protective of human health. 

The 2016 FIFRA SAP report, however, 

did present an alternative approach for 

EPA to consider. This report was 

supportive of EPA’s use of the PBPK–PD 

model as a tool for assessing internal 

dosimetry from typical pesticide 

exposure scenarios. Use of the PBPK–PD 

model coupled with typical exposure 

scenarios provides the strongest 

scientific foundation for chlorpyrifos 

human health risk assessment. Given 

that the window(s) of susceptibility are 

currently not known for the observed 

neurodevelopmental effects, and the 

uncertainties associated with 

quantitatively interpreting the CCCEH 

cord blood data, the 2016 FIFRA SAP 

report recommended that the Agency 

use a time weighted average (TWA) 

blood concentration of chlorpyrifos for 

the CCCEH study cohort as the PoD for 

risk assessment. Thus, in 2016, EPA 

attempted, using the PBPK–PD model, 

to determine the TWA blood level 

expected from post-application 

exposures from the chlorpyrifos indoor 

crack-and-crevice use scenario. Despite 

that effort, EPA concluded in the 2020 

HH DRA that the shortcomings of the 

data with regard to the dose-response 

relationship and lack of exposure 

information discussed above, continue 

to raise issues that make quantitative 

use of the CCCEH data in risk 

assessment not scientifically sound. 

(Ref. 12) 

Thus, taking into consideration the 

robustness of the available data at this 


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time, EPA has determined in the 2020 

HH DRA that the most appropriate 

toxicological endpoint for deriving 

points of departure for assessing risks of 

chlorpyrifos is 10% RBC AChE 

inhibition. The Agency is not ignoring 

or dismissing the extensive data 

concerning the potential for adverse 

neurodevelopmental outcomes. As 

discussed later in this Unit, the Agency 

is addressing the uncertainties 

surrounding the potential for adverse 

neurodevelopmental outcomes by 

retaining the default 10X FQPA SF. 

a. Durations of Exposure 

As noted in Unit IV.A.1., EPA 

establishes PoDs for each expected 

exposure duration likely to result from 

pesticide exposure. For chlorpyrifos, 

exposure can occur from a single event 

or on a single day or from repeated days 

of exposure. With respect to AChE 

inhibition, effects can occur from a 

single exposure or from repeated 

exposures. For organophosphates, 

repeated exposures generally result in 

more AChE inhibition at a given 

administered dose compared to acute 

exposures. Moreover, AChE inhibition 

in repeated dosing guideline toxicology 

studies with most organophosphates 

show a consistent pattern of inhibition 

reaching a ‘‘steady state’’ of inhibition at 

or around 2 to 3 weeks of exposure in 

adult laboratory animals. (Ref. 23) This 

pattern observed with repeated dosing is 

a result of the amount of inhibition 

coming to equilibrium with production 

of new enzyme. As such, AChE studies 

of 2 to 3 weeks generally show the same 

degree of inhibition with those of longer 

duration (i.e., up to two years of 

exposure). Thus, for most of the human 

health risk assessments for the 

organophosphates, the Agency is 

focusing on the critical durations 

ranging from a single day up to 21 days 

(i.e., the approximate time to reach 

steady state for most organophosphates). 

As such, EPA has calculated PoDs for 

the acute and steady-state durations. As 

described below, these PoDs have been 

derived for various lifestages, routes, 

and exposure scenarios. 

b. Deriving PoDs, Interspecies and 

Intraspecies Extrapolation: Use of the 

PBPK Model 

The process for developing RfDs and 

PADs typically involves first deriving 

PoDs directly from laboratory animal 

studies, followed by dividing the PoD 

by the default uncertainty factors of 10X 

each for interspecies extrapolation and 

intraspecies extrapolation, and the 

FQPA safety factor. For chlorpyrifos, 

EPA has developed a sophisticated 

PBPK–PD model to derive PoDs. 

Numerous federal advisory committees 

and external review panels have 

encouraged the use of such a modeling 

approach to reduce inherent uncertainty 

in the risk assessment and facilitate 

more scientifically sound extrapolations 

across studies, species, routes, and dose 

levels. The PBPK–PD model for 

chlorpyrifos has undergone extensive 

peer review by various individual or 

groups, including the FIFRA SAPs. 

Significant improvements have been 

made to the model over the years in 

response to recommendations from the 

2008, 2011, and 2012 FIFRA SAPs and 

comments from both internal and 

external peer reviewers. (Ref. 12 at 20) 

As a result, EPA has concluded that the 

current PBPK–PD model is sufficiently 

robust and is using it for deriving PoDs 

for chlorpyrifos. 

i. Derivation of PoDs 

As noted above, the PoDs for 

chlorpyrifos are based on the levels at 

which 10% RBC AChE inhibition is 

observed. The PBPK–PD model 

accounts for pharmacokinetic and 

pharmacodynamic characteristics to 

derive age, duration, and route-specific 

PoDs. Separate PoDs have been 

calculated for dietary (food, drinking 

water) and residential exposures by 

varying inputs on types of exposures 

and populations exposed. Specifically, 

the following characteristics have been 

evaluated: (1) Duration (24-hour (acute), 

21-day (steady-state)); (2) route (dermal, 

oral, inhalation); (3) body weights 

which vary by lifestage; (4) exposure 

duration (hours per day, days per week); 

and (5) exposure frequency (events per 

day (eating, drinking)). For each 

exposure scenario, the appropriate body 

weight for each age group or sex was 

modeled as identified from the 

Exposure Factors Handbook for 

residential exposures and from the U.S. 

Department of Agriculture’s (USDA) 

National Health and Nutrition 

Examination Survey (NHANES)/What 

We Eat in America (WWEIA) Survey for 

dietary exposures. (Ref. 24). 

Using the PBPK–PD model, the 

Agency evaluated the following 

exposure scenarios: (1) drinking water 

exposures to oxon (chlorpyrifos 

metabolite)—acute and steady-state 

exposures for infants, children, youths, 

and female adults; (2) food exposures to 

chlorpyrifos—acute and steady-state 

exposures for infants, children, youths, 

and female adults; (3) residential dermal 

exposures to chlorpyrifos—steady-state 

exposures for children, youths, and 

female adults; (4) residential hand-tomouth ingestion exposures—steadystate for children 1 to 2 years old; and 

(5) residential inhalation exposures— 

steady-state for children 1 to 2 years old 

and female adults. (Ref. 12 at 22–25). 

Steady-state dietary exposure was 

estimated daily for 21 days. For 

drinking water exposure, infants and 

young children (infants <1 year old, 

children between 1 to 2 years old, and 

children between 6 to 12 years old) were 

assumed to consume water 6 times per 

day, with a total consumption volume of 

0.69 L/day. For youths and female 

adults, they were assumed to consume 

water 4 times per day, with a total 

consumption volume of 1.71 L/day. 

For all residential dermal exposures 

to chlorpyrifos, the dermal PoDs were 

estimated assuming 50% of the skin’s 

surface was exposed. Exposure times for 

dermal exposure assessment were 

consistent with those recommended in 

the 2012 Residential Standard Operating 

Procedures (SOPs). (Ref. 22) For 

residential inhalation exposures 

following public health mosquitocide 

application, the exposure duration was 

set to 1 hour per day for 21 days. The 

incidental oral PoDs for children 1 to <2 

years old for other turf activities were 

estimated assuming that there were six 

events, 15 minutes apart, per day. 

The PBPK-modeled PoDs derived for 

the various lifestages, routes, and 

exposure scenarios discussed above, can 

be found in table 4.2.2.1.2 of the 2020 

HH DRA. (Ref. 12). 

ii. Interspecies Extrapolation 

As indicated above, the PBPK–PD 

model directly predicts human PoDs 

based on human physiology and 

biochemistry; thus, there is no need for 

an interspecies uncertainty factor to 

extrapolate from animal PoDs. 

iii. Intraspecies Extrapolation 

The PBPK–PD model can account for 

variability of critical physiological, 

pharmacokinetic, and 

pharmacodynamic parameters in a 

population to estimate, using the Monte 

Carlo analysis, the distribution of doses 

that result in 10% RBC AChE inhibition. 

Therefore, Data-Derived Extrapolation 

Factors (DDEF) for intraspecies 

extrapolation have been estimated to 

replace the default intraspecies 

uncertainty factor for some groups. (Ref. 

25). 

According to EPA’s DDEF guidance, 

when calculating a DDEF intraspecies 

extrapolation factor, administered doses 

leading to the response level of interest 

(in the case of chlorpyrifos, the 10% 

change in RBC AChE inhibition) are 

compared between a measure of average 

response and response at the tail of the 

distribution representing sensitive 

individuals. The tail of the distribution 


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may be selected at the 95th, 97.5th, and 

99th percentile. 

As for chlorpyrifos, the 99th 

percentile was used in risk assessment 

to provide the most conservative 

measure. (Ref. 26) In addition to 

estimating DDEF using the above 

approach for specific age groups, 

intraspecies DDEF were also calculated 

by comparing average responses 

between adults and 6-month-old infants. 

For the 2020 HHRA, the largest 

calculated DDEFs, 4X for chlorpyrifos 

and 5X for the oxon metabolite, were 

used for intraspecies extrapolation for 

all groups except women of 

childbearing age. There was a slightly 

higher variability between adults and 

infants when considering the 

distributions for the oxon metabolite, 

thus, the slightly higher intraspecies 

factor. For women of childbearing age, 

the Agency is applying the standard 10X 

intraspecies extrapolation factor due to 

limitations in the PBPK–PD model to 

account for physiological, anatomical, 

and biochemical changes associated 

with pregnancy. (Ref. 12 at 21–22). 

iv. Summarizing the PoDs, Interspecies 

and Intraspecies Extrapolation Factors 

In summary, for assessing the risks 

from exposure to chlorpyrifos, the 

human PBPK–PD model has been used 

to derive PoDs based on 10% RBC AChE 

inhibition for various populations, 

durations, and routes. The model, 

which calculates a human PoD directly, 

obviates the need for an interspecies 

extrapolation factor since animal data 

are not used. To account for variations 

in sensitivities, the Agency has 

determined that an intraspecies factor of 

4X for chlorpyrifos and 5X for the oxon 

is appropriate for all groups except 

women of childbearing age. For women 

of childbearing age, the typical 10X 

intraspecies factor is being applied, due 

the lack of appropriate information and 

algorithms to characterize physiological 

changes during pregnancy. 

c. FQPA Safety Factor 

As noted above, the FFDCA requires 

EPA, in making its safety finding, that 

in ‘‘the case of threshold effects, an 

additional tenfold margin of safety for 

the pesticide chemical residue and other 

sources of exposure shall be applied for 

infants and children to take into account 

potential pre- and post-natal toxicity 

and completeness of data with respect 

to exposure and toxicity to infants and 

children.’’ 21 U.S.C. 346a(b)(2)(C). 

Section 408(b)(2)(C) further states that 

‘‘the Administrator 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. 

In applying the FQPA SF provision, 

EPA has interpreted it as imposing a 

presumption in favor of retaining it as 

an additional 10X SF. (Ref. 27 at 4, 11) 

Thus, EPA generally refers to the 10X 

factor as a presumptive or default 10X 

factor. EPA has also made clear, 

however, that this presumption or 

default in favor of the 10X is only a 

presumption. The presumption can be 

overcome if reliable data demonstrate 

that a different factor is safe for 

children. (Id.). In determining whether a 

different factor is safe for children, EPA 

focuses on the three factors listed in 

FFDCA section 408(b)(2)(C)—the 

completeness of the toxicity database, 

the completeness of the exposure 

database, and potential pre- and postnatal toxicity. In examining these 

factors, EPA strives to make sure that its 

choice of a SF, based on a weight-of-theevidence evaluation, does not 

understate the risk to children. (Id. at 

24–25, 35). 

In the 2020 HH DRA, the default 10X 

FQPA SF was retained, and the 

assessment did not adopt or offer 

support for reducing the factor to 1X. 

However, the 2020 HH DRA does 

present potential risks from exposures 

to chlorpyrifos with retention of the 

default 10X FQPA SF and with 

reduction of the FQPA SF to 1X. The 

purpose of presenting both values was 

to provide an indication of what the 

potential risk estimates would be under 

either scenario. To reduce the FQPA SF 

to 1X, the FFDCA requires that EPA 

determine that reliable data demonstrate 

that the 1X would be safe for infants and 

children. The 2020 HH DRA did not 

make that determination. For 

chlorpyrifos, of the three factors 

mentioned in the previous paragraph, 

the primary factor that undercuts a 

determination that a different SF would 

be safe for children is the uncertainty 

around the potential for pre- and postnatal toxicity for infants and children in 

the area of neurodevelopmental 

outcomes. 

Based on the weight of the evidence 

concerning the potential for 

neurodevelopmental outcomes as 

discussed in this Unit above, there is 

ample qualitative evidence of a 

potential effect on the developing brain; 

however, there remains uncertainty 

around the levels at which these 

potential neurodevelopmental outcomes 

occur. Although the laboratory animal 

studies do not support a conclusion that 

neurodevelopmental outcomes are more 

sensitive than AChE inhibition, there 

remains some uncertainty in the doseresponse relationship between 

chlorpyrifos and adverse 

neurodevelopmental outcomes based on 

the epidemiology data, and the 

mechanistic data are, at this time, 

incomplete in their characterization of 

dose-response. Because the data 

available at this time indicate remaining 

uncertainties concerning pre- and postnatal toxicity due to insufficient clarity 

on the levels at which these outcomes 

occur, the Agency is unable to conclude, 

at this time, that a different SF would 

be safe for infants and children. Thus, 

the Agency is retaining the default 10X 

FQPA SF at this time. 

d. Total Uncertainty Factors and PADs 

In conclusion, the Agency used a total 

uncertainty factor of 100X for 

determining the food and drinking 

water PADs for females of childbearing 

age (1X interspecies factor, 10X 

intraspecies factor, and 10X FQPA SF); 

40X for determining the food PADs for 

remaining populations (1X interspecies 

factor, 4X intraspecies factor, and 10X 

FQPA SF); and 50X for determining the 

PADs for drinking water for remaining 

populations (1X interspecies factor, 5X 

intraspecies factor, and 10X FQPA SF). 

Taking into consideration the PoDs, 

intraspecies extrapolation factors, and 

FQPA SF, the Agency calculated acute 

PADs (aPADs) and steady-state PADs 

(ssPADs) for infants (less than 1 year 

old), children (1 to 2 years old), 

children/youth (6 to 12 years old), and 

females (13 to 49 years old); these 

subpopulations will be protective of 

other subpopulations. While PADs were 

calculated for youths (13 to 19 years 

old), these PADs were not used in the 

dietary/aggregate assessments because 

females (13 to 49 years old) are 

considered protective of this subpopulation. (Ref. 12 at 30–32) Risk 

estimates can be found in table 5.0.1 in 

the 2020 HH DRA. 

B. EPA’s Exposure Assessment for 

Chlorpyrifos 

Risk is a function of both hazard and 

exposure. Thus, equally important to 

the risk assessment process as 

determining the hazards posed by a 

pesticide and the toxicological 

endpoints for those hazards is 

estimating human exposure. Under 

FFDCA section 408, EPA must evaluate 

the aggregate exposure to a pesticide 

chemical residue, which includes ‘‘all 

anticipated dietary exposures and all 

other exposures for which there is 

reliable information.’’ 21 U.S.C. 

346a(b)(2)(A)(ii). This means that EPA is 

concerned not only with exposure to 

pesticide residues in food but also 

exposure resulting from pesticide 

contamination of drinking water 


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supplies and from use of pesticides in 

the home or other non-occupational 

settings. (See 21 U.S.C. 

346a(b)(2)(D)(vi)). 

Pursuant to FFDCA section 408(b), 

EPA has evaluated chlorpyrifos’s risks 

based on ‘‘aggregate exposure’’ to 

chlorpyrifos. By ‘‘aggregate exposure,’’ 

EPA is referring to exposure to 

chlorpyrifos by multiple pathways of 

exposure, i.e., food, drinking water, and 

residential. EPA uses available data and 

standard analytical methods, together 

with assumptions designed to be 

protective of public health, to produce 

separate estimates of exposure for a 

highly exposed subgroup of the general 

population, for each potential pathway 

and route of exposure. 

The following analysis reflects a 

summary of the Agency’s exposure 

assessment from the 2020 HH DRA 

unless otherwise specified. (Ref. 2). 

1. Exposure From Food 

a. General Approach for Estimating 

Food Exposures 

There are two critical variables in 

estimating exposure in food: (1) the 

types and amount of food that is 

consumed; and (2) the residue level in 

that food. Consumption is estimated by 

EPA based on scientific surveys of 

individuals’ food consumption in the 

United States conducted by the U.S. 

Department of Agriculture (USDA). (Ref. 

28 at 12) Information on residue values 

can come from a range of sources 

including crop field trials; data on 

pesticide reduction (or concentration) 

due to processing, cooking, and other 

practices; information on the extent of 

usage of the pesticide; and monitoring 

of the food supply. (Id. at 17). 

Data on the residues of chlorpyrifos in 

foods are available from both field trial 

data and monitoring data, primarily the 

USDA’s Pesticide Data Program (PDP) 

monitoring data. Monitoring data 

generally provide a characterization of 

pesticide residues in or on foods 

consumed by the U.S. population that 

closely approximates real-world 

exposures because they are sampled 

closer to the point of consumption in 

the chain of commerce than field trial 

data, which are generated to establish 

the maximum level of legal residues that 

could result from maximum permissible 

use of the pesticide immediately after 

harvest. 

EPA used a computer program known 

as the Dietary Exposure Evaluation 

Model and Calendex software with the 

Food Commodity Intake Database 

(DEEM–FCID version 3.16/Calendex) to 

estimate chlorpyrifos exposure by 

combining data on human consumption 

amounts with residue values in food 

commodities. This version of the model 

incorporated 2003–2008 consumption 

data from USDA’s NHANES/WWEIA. 

The data are based on the reported 

consumption of more than 20,000 

individuals over two non-consecutive 

survey days. Foods ‘‘as consumed’’ (e.g., 

apple pie) are linked to EPA-defined 

food commodities (e.g., apples, peeled 

fruit—cooked; fresh or N/S (Not 

Specified); baked; or wheat flour— 

cooked; fresh or N/S, baked) using 

publicly available recipe translation 

files developed jointly by USDA 

Agricultural Research Service (ARS) and 

EPA. For chronic exposure assessment 

(or in the case of chlorpyrifos, for 

steady-state exposure assessment), 

consumption data are averaged for the 

entire U.S. population and within 

population subgroups; however, for 

acute exposure assessment, 

consumption data are retained as 

individual consumption events. Using 

this consumption information and 

residue data, the exposure estimates are 

calculated for the general U.S. 

population and specific subgroups 

based on age, sex, ethnicity, and region. 

For chlorpyrifos, EPA determined that 

acute and steady-state exposure 

durations were relevant for assessing 

risk from food consumption. EPA 

calculates potential risk by using 

probabilistic techniques to combine 

distributions of potential exposures in 

sentinel populations. The resulting 

probabilistic assessments present a 

range of dietary exposure/risk estimates. 

Because probabilistic assessments 

generally present a realistic range of 

residue values to which the population 

may be exposed, EPA’s starting point for 

estimating exposure and risk for such 

assessments is the 99.9th percentile of 

the population under evaluation. When 

using a probabilistic method of 

estimating acute dietary exposure, EPA 

typically assumes that, when the 99.9th 

percentile of acute exposure is equal to 

or less than the aPAD, the level of 

concern for acute risk has not been 

exceeded. By contrast, where the 

analysis indicates that estimated 

exposure at the 99.9th percentile 

exceeds the aPAD, EPA would generally 

conduct one or more sensitivity 

analyses to determine the extent to 

which the estimated exposures at the 

high-end percentiles may be affected by 

unusually high food consumption or 

residue values. (The same assumptions 

apply to estimates for steady-state 

dietary exposure and the ssPAD.) To the 

extent that one or a few values seem to 

‘‘drive’’ the exposure estimates at the 

high-end of exposure, EPA would 

consider whether these values are 

reasonable and should be used as the 

primary basis for regulatory decision 

making. (Ref. 29). 

b. Estimating Chlorpyrifos Exposures in 

Food 

The residue of concern, for tolerance 

expression and risk assessment, in 

plants (food and feed) and livestock 

commodities is the parent compound 

chlorpyrifos. EPA has determined that 

the metabolite chlorpyrifos oxon is not 

a residue of concern in food or feed, 

based on available field trial data and 

metabolism studies that indicate that 

the oxon is not present in the edible 

portions of the crops. This conclusion is 

supported by USDA PDP monitoring 

data, which did not find residues of 

chlorpyrifos oxon on food samples. 

Furthermore, the oxon metabolite was 

not found in milk or livestock tissues. 

(Ref. 12 at 33). 

Acute and steady-state dietary (food 

only) exposure analyses for chlorpyrifos 

were conducted using the DEEM–FCID 

version 3.16/Calendex software. (Ref. 

30) These analyses were performed for 

the purpose of obtaining food exposure 

values for comparison to the 

chlorpyrifos doses predicted by the 

PBPK–PD model to cause 10% RBC 

AChE inhibition. The acute and steadystate dietary (food only) exposure 

analyses do not include drinking water 

exposures, which were assessed 

separately, as discussed in the next 

section. 

The assessments include exposures to 

residues on all field crops and livestock 

use resulting from uses registered at the 

time of the dietary risk assessment as 

well as residues on imported 

commodities, but the assessments do 

not include potential exposure from 

food handling establishments as those 

were considered negligible. (Ref. 26) 

Both the acute and steady-state dietary 

(food only) exposure analyses are highly 

refined. The large majority of food 

residues used were based upon PDP 

monitoring data except in a few 

instances where no appropriate PDP 

data were available. In those cases, field 

trial data or tolerance-level residues 

were assumed. EPA also used foodprocessing factors from submitted 

studies as appropriate. In addition, 

EPA’s acute and steady-state dietary 

(food only) exposure assessments used 

percent crop treated (PCT) information. 

(Ref. 30). 

The chlorpyrifos acute dietary (food 

only) exposure analysis was conducted 

using the DEEM–FCID, version 3.16. 

The acute risk estimates were presented 

for the sentinel populations for infants 

(less than 1 year old); children (1–2 

years old); youths (6–12 years old); and 


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adults (females 13–49 years old). The 

assessment of these index lifestages is 

protective of other population 

subgroups. 

The chlorpyrifos steady-state dietary 

(food only) exposure analysis was 

conducted using the Calendex 

component of DEEM–FCID (with 2003– 

2008 survey consumption data from 

USDA’s NHANES/WWEIA). Calendex 

provides a focus detailed profile of 

potential exposures to individuals 

across a calendar year. A calendar-based 

approach provides the ability to 

estimate daily exposures from multiple 

sources over time to an individual and 

is in keeping with two key tenets of 

aggregate risk assessment: (1) that 

exposures when aggregated are 

internally consistent and realistic; and 

(2) that appropriate temporal and 

geographic linkages or correlations/ 

associations between exposure scenarios 

are maintained. 

The chlorpyrifos steady-state dietary 

(food only) assessment considers the 

potential risk from a 21-day exposure 

duration using a 3-week rolling average 

(sliding by day) across the year. For this 

assessment, the same food residue 

values used in the acute assessment 

were used for the 21-day duration. In 

the Calendex software, one diary for 

each individual in the WWEIA is 

selected to be paired with a randomly 

selected set of residue values for each 

food consumed. The steady-state 

analysis calculated exposures for the 

sentinel populations for infants (less 

than 1 year old); children (1 to 2 years 

old); youths (6 to 12 years old); and 

adults (females 13 to 49 years old). The 

assessment of these index lifestages is 

protective of other population 

subgroups. 

2. Exposure From Drinking Water 

a. General Approach for Assessing 

Exposure From Drinking Water 

i. Modeling and Monitoring Data 

Monitoring and modeling are both 

important tools for estimating pesticide 

concentrations in water and can provide 

different types of information. 

Monitoring data can provide estimates 

of pesticide concentrations in water that 

are representative of the specific 

agricultural or residential pesticide 

practices in specific locations, under the 

environmental conditions associated 

with a sampling design (i.e., the 

locations of sampling, the times of the 

year samples were taken, and the 

frequency by which samples were 

collected). Although monitoring data 

can provide a direct measure of the 

concentration of a pesticide in water, it 

does not always provide a reliable basis 

for estimating spatial and temporal 

variability in exposures because 

sampling may not occur in areas with 

any pesticide use, with the highest 

pesticide use, when the pesticides are 

being used, and/or at an appropriate 

sampling frequency to detect high 

concentrations of a pesticide that occur 

over the period of a day to several days. 

Because of the limitations in most 

monitoring studies, EPA’s standard 

approach is to use water exposure 

models as the primary means to 

estimate pesticide exposure levels in 

drinking water. Modeling is a useful 

tool for characterizing vulnerable sites 

and can be used to estimate upper-end 

pesticide water concentrations in 

surface water and groundwater. EPA’s 

computer models use detailed 

information on soil properties, crop 

characteristics, and weather patterns to 

estimate water concentrations in 

vulnerable locations where the pesticide 

could be used according to its label. 

(Ref. 31 at 27–28) EPA’s models 

calculate estimated water 

concentrations of pesticides using 

laboratory data that describe how fast 

the pesticide breaks down to other 

chemicals and how it moves in the 

environment at these vulnerable 

locations. Depending on the modeling 

algorithm (e.g., surface water modeling 

scenarios), daily concentrations can be 

estimated continuously over long 

periods of time, and for places that are 

of most interest for any particular 

pesticide. 

EPA relies on models it has developed 

for estimating pesticide concentrations 

in both surface water and ground water. 

The most common model used to 

conduct drinking water assessments is 

the Pesticide in Water Calculator (PWC). 

PWC couples the Pesticide Root Zone 

Model (PRZM) and Variable Volume 

Water Model (VVWM) together to 

simulate pesticide fate and transport 

from the field of application to an 

adjacent reservoir. (Ref. 31 at 27–28). 

The PWC estimates pesticide 

concentrations for an index reservoir 

that is modeled for site-specific 

scenarios (i.e., weather and soil data) in 

different areas of the country. A detailed 

description of the models routinely used 

for exposure assessment is available 

from the EPA OPP Aquatic Models 

website. See EPA’s aquatic models for 

estimating pesticide concentrations in 

food, water, non-target organisms, and 

residential and occupational 

environments. (Ref. 2). 

In modeling potential surface water 

concentrations, EPA models areas of the 

country that are vulnerable to surface 

water contamination. Consequently, 

EPA models exposures occurring in 

small highly agricultural watersheds in 

different growing areas throughout the 

country, over a 30-year period. The 

scenarios are designed to capture 

residue levels in drinking water from 

reservoirs with small watersheds with a 

large percentage of land use in 

agricultural production. EPA believes 

these assessments are likely reflective of 

a small subset of watersheds across the 

country and represent a drinking water 

source generally considered to be the 

most vulnerable to frequent high 

concentrations of pesticides. 

When monitoring data meet certain 

data quantity criteria, EPA has tools 

available to quantify the uncertainty in 

available monitoring data such that it 

can be used quantitively to estimate 

pesticide concentrations in drinking 

water. (Ref. 32) Furthermore, monitoring 

data can be used in a weight of evidence 

approach with model estimated 

concentrations to increase confidence in 

the conclusions of a drinking water 

assessment. 

ii. Drinking Water Level of Comparison 

(DWLOC) 

The drinking water level of 

comparison (DWLOC) is a benchmark 

that can be used to guide refinements of 

the DWA. For a drinking water 

assessment that utilizes a DWLOC, the 

calculated DWLOC is compared to the 

EDWC. When the EDWC is greater than 

the DWLOC, there may be a risk 

concern. Conversely, when the EDWC is 

less than the DWLOC, there are no risks 

of concern. 

The DWLOC relates to the concept of 

the ‘‘risk cup,’’ which EPA developed to 

facilitate risk refinement when 

considering aggregate human health risk 

to a pesticide. (Ref. 33) The risk cup is 

the total exposure allowed for a 

pesticide considering its toxicity and 

required safety factors. The risk cup 

represents the maximum safe exposure 

for the duration and population being 

considered. Exposures exceeding the 

risk cup are of potential concern. There 

are risk cups for each pertinent duration 

of exposure (e.g., acute, short-term, 

chronic). For chlorpyrifos, EPA is using 

exposure durations of acute (single day, 

24 hours) and steady state (21-day). (Ref. 

32). 

In practice, EPA calculates the total 

exposure from food consumption and 

residential (or other non-occupational) 

exposures and subtracts this value from 

the maximum safe exposure level. The 

resulting value is the allowable 

remaining exposure that can come from 

drinking water without the potential for 

adverse health effects. Knowing this 

allowable remaining exposure and the 

water consumption for each population 


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subgroup (e.g., infants), the Agency can 

calculate the DWLOC, which is the 

estimate of safe concentration of 

pesticides in drinking water. Using this 

process of DWLOC calculation allows 

EPA to determine a target maximum 

safe drinking water concentration, 

thereby identifying instances where 

drinking water estimates require 

refinement or estimates that may be 

indicative of risk. (Ref. 31 at 19–20). 

iii. Scale of Drinking Water Assessment 

Although food is distributed 

nationally and pesticide residue values 

on food are therefore not expected to 

vary substantially throughout the 

country, drinking water is locally 

derived and concentrations of pesticides 

in source water fluctuate over time and 

location for a variety of reasons. 

Pesticide residues in water fluctuate 

daily, seasonally, and yearly because of 

the timing of the pesticide application, 

the vulnerability of the water supply to 

pesticide loading through runoff, spray 

drift and/or leaching, and changes in the 

weather. Concentrations are also 

affected by the method of application, 

the location, and characteristics of the 

sites where a pesticide is used, the 

climate, and the type and degree of pest 

pressure, which influences the 

application timing, rate used, and 

number of treatments in a crop 

production cycle. 

EPA may conduct a DWA for a 

national scale depending on the 

pesticide use under evaluation. A 

national scale DWA may use a single 

upper-end pesticide concentration as a 

starting point for assessing whether 

additional refinements are needed or 

estimated pesticide concentrations for 

certain site-specific scenarios that are 

associated with locations in the United 

States vulnerable to pesticide 

contamination based on pesticide use 

patterns. (Ref. 31 at 22). 

EPA may also conduct a regional scale 

DWA to focus on areas where pesticide 

concentrations may be higher than the 

DWLOC. Under this assessment, EPA 

estimates pesticide concentrations 

across different regions in the United 

States that are subdivided into different 

areas called hydrologic units, identified 

by a two-digit hydrologic unit code 

(HUC 2) number. There are 21 HUC 2 

regions in the United States, with 18 of 

them within the contiguous United 

States. These areas contain either the 

drainage area of a major river or a 

combined drainage of a series of rivers. 

See United States Geological Survey 

(USGS) Water Resources of the United 

States. (Ref. 34) Estimated pesticide 

concentrations under this approach 

would be associated with a vulnerable 

pesticide use area somewhere within 

the evaluated region. (Ref. 31 at 23). 

iv. Drinking Water Refinements 

EPA has defined four assessment tiers 

for drinking water assessments. Lowertiered assessments are more 

conservative based on the defaults or 

upper bound assumptions and may 

compound conservatisms, while higher 

tiers integrate more available data and 

provide more realistic estimates of 

environmental pesticide concentrations. 

These four tiers vary in the level of 

resources, the amount of data 

considered, the spatial scale, and the 

refinement in the estimated pesticide 

concentration. Tier 1 requires the least 

amount of resources and the least 

amount of data, whereas Tier 4 is 

resource intensive, considers a wide 

range of sources and types of data, and 

is spatially explicit, resulting in high 

confidence in the reported pesticide 

concentration. Each successive tier 

integrates more focused pesticide, 

spatial, temporal, agronomic, and cropspecific information. The order in 

which refinements are considered (i.e., 

the order in which the assessment is 

refined) is pesticide-specific and 

depends on the nature and quality of the 

available data used to support the 

refinement. Additional information on 

the conduct of drinking water 

assessments can be found in the 

‘‘Framework for Conducting Pesticide 

Drinking Water Assessment for Surface 

Water’’ (USEPA, 2020) (‘‘DWA 

Framework document’’). (Ref. 31). 

As discussed in the DWA Framework 

document, EPA can incorporate several 

refinements in higher tiered modeling. 

Two such refinements are the percent 

cropped area (PCA) and the PCT. These 

are described in the document titled 

‘‘Integrating a Distributional Approach 

to Using Percent Crop Area (PCA) and 

Percent Crop Treated (PCT) into 

Drinking Water Assessment.’’ (Ref. 35) 

The PCA refers to the amount of area in 

a particular community water system 

that is planted with the crop of interest 

(e.g., the default assumption is that the 

entire watershed is planted with a crop 

of interest). The PCT refers to the 

amount of the cropped area that is 

treated with the pesticide of interest 

(e.g., the default is that the entire 

cropped area is treated with the 

pesticide of interest). With additional 

use and usage data, EPA can refine 

assumptions about the application rate 

and PCT for use in modeling to generate 

EDWCs that are appropriate for human 

health risk assessment and more 

accurately account for the contribution 

from individual use patterns in the 

estimation of drinking water 

concentrations. 

b. Drinking Water Assessment for 

Chlorpyrifos 

For the chlorpyrifos drinking water 

assessment, the metabolite chlorpyrifos 

oxon—which forms during water 

treatment, e.g., chlorination, of source 

water containing chlorpyrifos and is 

more toxic than chlorpyrifos—was 

selected as the residue of concern. (Ref. 

36 and 37) The range of conversion from 

parent to oxon depends upon the type 

of water treatment and other conditions. 

Based on available information 

regarding the potential effects of certain 

water treatments (e.g., chlorination 

appears to hasten transformation of 

chlorpyrifos-to-chlorpyrifos oxon), EPA 

assumed that all chlorpyrifos in source 

water is converted to chlorpyrifos oxon 

upon treatment. 

The Agency used a DWLOC approach 

for assessing aggregate risk from 

chlorpyrifos. EPA calculated DWLOCs 

for different age groups for both the 

acute aggregate assessment and the 

steady-state aggregate assessment, taking 

into consideration the food and 

residential contributions to the risk cup. 

These numbers were provided as a 

benchmark for evaluating drinking 

water contributions from uses of 

chlorpyrifos across the United States, 

and whether such concentrations would 

result in aggregate exposures to 

chlorpyrifos that exceeded the Agency’s 

levels of concern. The lowest acute 

DWLOC calculated was for exposure to 

chlorpyrifos oxon to infants (<1 year 

old) at 23 ppb; the lowest steady-state 

DWLOC calculated was also for 

exposure to chlorpyrifos oxon to infants 

(<1 year old) at 4.0 ppb. (Ref. 12 at 45) 

In other words, EDWCs for infants of 

chlorpyrifos oxon greater than 23 ppb 

from a single exposure or 4.0 ppb for a 

21-day average would exceed EPA’s 

DWLOC and present a risk that exceeds 

the Agency’s level of concern. 

In its 2014 DWA, EPA concluded that 

there were multiple uses of chlorpyrifos 

that could lead to exposures to 

chlorpyrifos oxon in drinking water that 

exceed the DWLOC. (Ref. 38) The 2014 

DWA provided the basis for the 

Agency’s proposal to revoke tolerances 

in 2015. (Ref. 39) In 2016, EPA 

conducted a refined DWA that 

estimated drinking water concentrations 

based on modeling of all registered uses, 

as well as all available surface water 

monitoring data. That 2016 DWA 

considered several refinement strategies 

in a two-step process to derive exposure 

estimates for chlorpyrifos and 

chlorpyrifos oxon across the country. 

The first step was an assessment of 


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potential exposure based on the current 

maximum label rates at a national level. 

This indicated that the EDWCs could be 

above the DWLOC. 

Because estimated concentrations at 

the national level exceeded the DWLOC, 

the Agency conducted a more refined 

assessment of uses on a regional level. 

(Ref. 36 at 73–86) This more refined 

analysis derived EDWCs using the PWC 

modeling for maximum labeled rates 

and 1 pound per acre by region for each 

use. The analysis indicated that 

approved uses of chlorpyrifos in certain 

vulnerable watersheds in every region of 

the country would result in EDWCs that 

exceed the DWLOC. For example, table 

25 of EPA’s 2016 DWA, which provides 

the range of estimated concentrations of 

chlorpyrifos in drinking water from uses 

on golf courses and agricultural or 

production crops, shows EDWCs that 

exceed the DWLOC in vulnerable 

watersheds in every region in the 

country. While the lower end of some of 

the ranges provided in that table are 

below the DWLOC, those lower 

numbers reflect a single use (i.e., single 

crop) and do not reflect potential 

exposure from other uses where 

applications occur at higher rates, more 

frequently, or in more locations made 

more vulnerable due to soil type, 

weather, or agronomic practices—all of 

which were permitted by labeling that 

was approved at that time. The relevant 

estimated concentration for risk 

assessment purposes was the highest 

concentration across all uses because it 

reflects concentrations that may occur 

in vulnerable sources of drinking water 

based on approved use instructions. 

(Ref. 36 at 73–74). 

In addition, a robust quantitative 

analysis of the monitoring data was 

conducted resulting in concentrations 

consistent with model-estimated 

concentrations above the DWLOC. (Ref. 

36 at 90–121) Considering both 

monitoring data and modeling estimates 

together supported the conclusion that 

drinking water concentrations in regions 

across the country exceeded the 

DWLOC. (Ref. 36 at 121–123). 

After the EPA’s 2016 DWA showed 

that the DWLOC exceedances are 

possible from several uses, EPA 

developed refinement strategies to 

examine those estimated regional/ 

watershed drinking water 

concentrations to pinpoint community 

drinking water systems where exposure 

to chlorpyrifos oxon as a result of 

chlorpyrifos applications may pose an 

exposure concern. At that time, it was 

anticipated that a more refined drinking 

water assessment might allow EPA to 

better identify where at-risk watersheds 

are located throughout the country to 

support more targeted risk mitigation 

through the registration review process. 

The refinements better account for 

variability in the use area treated within 

a watershed that may contribute to a 

drinking water intake (referred to as 

PCA or percent use area when 

considering non-agricultural uses) and 

incorporate data on the amount of a 

pesticide that is actually applied within 

a watershed for agricultural and nonagricultural uses (referred to as PCT). 

These refinement approaches 

underwent external peer review and 

were issued for public comment in 

January 2020. (Ref. 39 and 40) In 

addition, EPA used average application 

rates, average numbers of annual 

applications for specific crops, and 

estimated typical application timing at 

the state-level based on pesticide usage 

data derived from a statistically reliable 

private market survey database, publicly 

available survey data collected by the 

USDA, and state-specific scientific 

literature from crop extension experts. 

(Ref. 1) 

The refinements were integrated in 

the 2020 DWA. The updated assessment 

applied the new methods for 

considering the entire distribution of 

community water systems, PCA 

adjustment factors, integrated state level 

PCT data, incorporated refined usage 

and application data, and included 

quantitative use of surface water 

monitoring data in addition to 

considering state level usage rate and 

data information. In addition, given the 

2016 DWA calculation of EDWCs 

exceeding the DWLOC of 4.0 ppb, the 

Agency decided to focus its refinements 

for the 2020 DWA on a subset of uses 

in specific regions of the United States. 

The purpose of the focus on this subset 

of uses was to determine if limiting use 

of chlorpyrifos to only certain food uses 

and regions would yield EDWCs below 

the DWLOC. The subset of uses assessed 

were selected because they were 

identified as critical uses by the 

registrant and/or high benefit uses to 

growers. That subset of registered uses 

included the 11 identified crops in the 

specific geographical areas listed in Unit 

III, and the assessment of those uses 

assumed application rate and timing/ 

frequency restrictions based on 

available usage data as described in the 

previous paragraph. The results of this 

analysis indicated that the EDWCs from 

this limited subset of uses are below 

both the acute and chronic DWLOCs. 

(Ref. 2 at 16–17) The 2020 DWA refined 

estimates did not include chlorpyrifos 

exposures from uses beyond that subset 

and expressly noted that a separate 

assessment would be needed in order to 

evaluate whether other uses could be 

added to or substituted for the crops and 

areas already identified and still 

maintain concentrations below the 

DWLOC. 

3. Residential Exposure to Pesticides 

a. General Approach to Assessing 

Residential Exposures 

Residential assessments examine 

exposure to pesticides in nonoccupational or residential settings (e.g., 

homes, parks, schools, athletic fields or 

any other areas frequented by the 

general public), based on registered uses 

of the pesticide. Exposures to pesticides 

may occur to persons who apply 

pesticides (which is referred to as 

residential handler exposure) or to 

persons who enter areas previously 

treated with pesticides (which is 

referred to as post-application 

exposure). Such exposures may occur 

through oral, inhalation, or dermal 

routes and may occur over different 

exposure durations (e.g., short-term, 

intermediate-term, long-term), 

depending on the type of pesticide and 

particular use pattern. 

Residential assessments are 

conducted through examination of 

significant exposure scenarios (e.g., 

children playing on treated lawns or 

homeowners spraying their gardens) 

using a combination of generic and 

pesticide-specific data. EPA has 

prepared SOPs for conducting 

residential assessments on a wide array 

of scenarios that are intended to address 

the most common uses by which 

individuals could be exposed to 

pesticides in a non-occupational 

environment. (Ref. 22) The SOPs 

identify relevant generic data and 

construct algorithms for calculating 

exposure amounts using these generic 

data in combination with pesticidespecific information. The generic data 

generally involve survey data on 

behavior patterns (e.g., activities 

conducted on turf and time spent on 

these activities) and transfer coefficient 

data. Transfer coefficient data measure 

the amount of pesticide that transfers 

from the environment to humans from 

a defined activity (e.g., hand contact 

with a treated surface or plant). Specific 

information on pesticides can include 

information on residue levels as well as 

information on environmental fate such 

as degradation data. 

Typically, once EPA assesses 

potential exposures from all applicable 

exposure scenarios, EPA selects the 

highest exposure scenario for each 

exposed lifestage to calculate 

representative risk estimates for use in 

the aggregate exposure assessment. 


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Those specific exposure values are then 

combined with the lifestage appropriate 

exposure values provided for food and 

drinking water to determine whether a 

safety finding can be made. As 

described above, since EPA used a 

DWLOC approach for assessing risks for 

chlorpyrifos, EPA combined food 

exposures covered by all chlorpyrifos 

tolerances with residential exposures to 

identify the DWLOC and compared the 

DWLOC to EDWCs to determine 

whether a safety finding could be made. 

The end result is the same since both 

methods aggregate food, drinking water, 

and residential exposure estimates to 

determine whether a safety finding can 

be made. 

b. Residential Exposure Assessment for 

Chlorpyrifos 

Most chlorpyrifos products registered 

for residential treatment were 

voluntarily cancelled or phased out by 

the registrants between 1997 and 2001; 

however, some uses of chlorpyrifos 

remain that may result in nonoccupational, non-dietary (i.e., 

residential) exposures, specifically 

roach bait products, fire ant mound 

treatments, and uses on golf courses. 

The roach bait product is designed such 

that the active ingredient is contained 

within a bait station, which eliminates 

the potential for contact with the 

chlorpyrifos containing bait material; 

therefore, residential exposures from the 

roach bait product were determined to 

be negligible. Since the ant mound 

treatments can only be applied 

professionally and direct exposure with 

treated mounds is not anticipated, 

residential exposures from the ant 

mound use were also determined to be 

negligible. (Ref. 12 at 36–44). 

For the golf course use, the Agency 

does not anticipate residential handler 

exposures, although there is a potential 

for residential post-application 

exposures that would aggregate with 

dietary exposures from the registered 

use on golf courses. Based on the 

anticipated use patterns reviewed under 

the SOP, EPA assessed these exposures 

as steady-state residential postapplication exposures, which would be 

protective of shorter durations of 

exposure. There is a potential for dermal 

post-application exposures from the golf 

course uses for adults (females 13 to 49 

years old); youths (11 to less than 16 

years old); and children (6 to less than 

11 years old). Although EPA did not 

identify any post-application risks of 

concern from use on golf courses, EPA 

used the post-application exposures and 

risk estimates resulting from the golfing 

scenarios in EPA’s aggregate exposure 

and risk assessment. 

4. Cumulative Risk 

FFDCA section 408(b)(2)(D)(v), 21 

U.S.C. 346a(b)(2)(D)(v), requires EPA to 

consider ‘‘available information 

concerning the cumulative effects of 

[pesticide chemical] residues and other 

substances that have a common 

mechanism of toxicity.’’ 

Chlorpyrifos belongs to a class of 

pesticides called organophosphates 

(OPs), which share the ability to inhibit 

AChE through phosphorylation of the 

serine residue on the enzyme leading to 

accumulation of acetylcholine and 

ultimately cholinergic neurotoxicity. 

This shared mode of action/adverse 

outcome pathway (MOA/AOP) is the 

basis for the OP common mechanism 

grouping per OPP’s Guidance for 

Identifying Pesticide Chemicals and 

Other Substances that have a Common 

Mechanism of Toxicity (USEPA, 1999). 

The 2006 cumulative risk assessment for 

organophosphates (2006 OP CRA) used 

brain AChE inhibition in female rats as 

the source of dose response data for the 

relative potency factors and PODs for 

each OP, including chlorpyrifos. After 

considering the potential for cumulative 

risks of concern from the OPs, EPA 

concluded that the tolerances were safe. 

(Ref. 21). 

After completion of the singlechemical OP assessments for this round 

of registration review, but prior to the 

issuance of a final registration review 

decision for chlorpyrifos (and the other 

OPs), EPA will determine whether any 

updates to the 2006 OP CRA on AChE 

inhibition are necessary. In the 

meantime, no additional uses have been 

approved since that document was 

completed (i.e., no additional 

exposures), and many uses have been 

(or are in the process of being) cancelled 

or reduced (e.g., the current reduction of 

chlorpyrifos uses). As such, EPA 

expects the potential for cumulative 

risks and any cumulative risk estimates 

will likely be lower than assessed in 

2006, when EPA concluded that the 

results of the cumulative assessment 

support a reasonable certainty of no 

harm finding as required by FQPA. 

C. Aggregate Risk Assessment and 

Determination of Safety for Chlorpyrifos 

The final step in the risk assessment 

is the aggregate exposure assessment 

and risk characterization. In this step, 

EPA combines information from the first 

three steps (hazard identification, level 

of concern (LOC)/dose-response 

analysis, and human exposure 

assessment) to quantitatively estimate 

the risks posed by a pesticide. The 

aggregated exposure assessment process 

considers exposure through multiple 

pathways or routes of exposure (e.g., 

food, water, and residential) for 

different sub-populations (e.g., infants, 

children ages 1–2) and exposure 

duration or types of effects (e.g., acute 

(single dose) noncancer effects, chronic 

noncancer effects, and cancer). The 

aggregated exposure assessments can be 

deterministic (levels of exposure for 

each pathway are point estimates), 

probabilistic (levels of exposure are a 

distribution for a given population), or 

a combination of the two and are 

dependent on the level of refinement or 

assessment tier. 

As noted above, EPA evaluates 

aggregate exposure by comparing 

combined exposure from all relevant 

sources to the safe level. Where 

exposures exceed the safe level (i.e., the 

risk cup), they present potential risks of 

concern. There are risk cups for each 

pertinent duration of exposure for a 

pesticide because the amount of 

exposure that can be incurred without 

adverse health effects will vary by 

duration (e.g., acute, short-term, 

chronic). 

Whether risks will exceed the risk cup 

(i.e., whether exposures are expected to 

exceed safe levels) is expressed 

differently, depending on the type of 

level of concern the Agency has 

identified. For dietary assessments, the 

risk is expressed as a percentage of the 

acceptable dose (i.e., the dose which 

EPA has concluded will be ‘‘safe’’). 

Dietary exposures greater than 100% of 

the acceptable dose are generally cause 

for concern and would be considered 

‘‘unsafe’’ within the meaning of FFDCA 

section 408(b)(2)(B). For non-dietary 

(and combined dietary and non-dietary) 

risk assessments of threshold effects, the 

toxicological level of concern is 

typically not expressed as an RfD/PAD, 

but rather in terms of an acceptable (or 

target) Margin of Exposure (MOE) 

between human exposure and the PoD. 

The ‘‘margin’’ that is being referred to in 

the term MOE is the ratio between the 

PoD and human exposure, which is 

calculated by dividing human exposure 

into the PoD. An acceptable MOE is 

generally considered to be a margin at 

least as high as the product of all 

applicable safety factors for a pesticide. 

For example, when the Agency retains 

the default uncertainty factors for 

dietary or aggregate risk (a 10X 

interspecies uncertainty factor, a 10X 

intraspecies uncertainty factor, and a 

10X FQPA safety factor), the total 

uncertainty factor (or level of concern) 

is 1,000, and any MOE above 1,000 

represents exposures that are not of 

concern. Like RfD/PADs, specific target 

MOEs are selected for exposures of 

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dietary exposures, EPA typically 

examines short-term, intermediate-term, 

and long-term exposures. Additionally, 

target MOEs may be selected based on 

both the duration of exposure and the 

various routes of non-dietary 

exposure—dermal, inhalation, and oral. 

Target MOEs for a given pesticide can 

vary depending on the characteristics of 

the studies relied upon in choosing the 

PoD for the various duration and route 

scenarios. 

In addition, in a DWLOC aggregate 

risk assessment, the calculated DWLOC 

is compared to the EDWC. Where EPA 

has calculated a DWLOC, it can 

determine whether drinking water 

exposures will result in aggregate risks 

of concern by comparing estimated 

pesticide concentrations in drinking 

water to the DWLOC. As noted above, 

an aggregate DWLOC represents the 

amount of allowable safe residues of 

pesticide in drinking water because it 

represents the room remaining in the 

risk cup after accounting for the food 

and residential exposures. The DWLOC 

provides an estimate of the allowable 

safe concentrations of pesticides in 

drinking water for comparison to 

EDWCs. When the EDWC is less than 

the DWLOC, there are no risk concerns 

for aggregate exposures because the 

Agency can conclude that the 

contribution from drinking water when 

aggregated with food and residential/ 

non-occupational exposures will not 

exceed save levels of exposure. 

Conversely, an EDWC at or exceeding 

the DWLOC would indicate a risk of 

concern, as those exposures to 

chlorpyrifos in drinking water, when 

aggregated with exposures from food 

and residential exposures, would 

exceed safe levels of exposure. (Ref. 41). 

1. Dietary Risks From Food Exposures 

As noted above, EPA’s acute and 

steady-state dietary (food only) exposure 

assessments for chlorpyrifos were 

highly refined and incorporated 

monitoring data for almost all foods. 

The Agency assessed food exposures 

based on all food uses of chlorpyrifos 

for which tolerances have been 

established, including all uses registered 

at the time of the 2020 HH DRA. It did 

not include potential exposure from 

food handling establishment uses since 

the Agency did not identify any actual 

usage under the registered food 

handling establishment uses. Previous 

assessments of the food handling 

establishment uses had indicated 

negligible residues. (Ref. 12 at 33–36 

and 31 at 3). 

Considering food exposures alone, the 

Agency did not identify risks of concern 

for either acute or steady-state 

exposures. (Ref. 12 at 34–36) Acute 

dietary (food only) risk estimates, which 

are based on risk from a single exposure 

event in the 2020 HH DRA, were all 

below 100% of the acute population 

adjusted dose for food (aPADfood) at the 

99.9th percentile of exposure and are 

not of concern. The population with the 

highest risk estimate was females (13 to 

49 years old) at 3.2% aPADfood. Steadystate dietary (food only) risk estimates, 

which are based on the potential risk 

from a 21-day exposure duration using 

a 3-week rolling average (sliding by day) 

across the year, were also all below 

100% of the steady-state PAD for food 

(ssPADfood) at the 99.9th percentile of 

exposure and are not of concern. The 

population with the highest risk 

estimate was children (1 to 2 years old) 

at 9.7% ssPADfood. Note: Because the 

Agency has retained the 10X FQPA SF, 

as indicated in Unit VI.C.3., the relevant 

risk estimates are those associated with 

the retention of the 10X FQPA SF. The 

risk estimates associated with a 1X 

FQPA SF were provided solely to 

identify a range of risk estimates to 

characterize the risk in the event that 

EPA identified reliable data to support 

another FQPA SF that would be safe for 

infants and children, but no such data 

has been identified. 

Following the approval of the product 

and use cancellation requests, the 

Agency has not conducted a separate 

quantitative assessment of the 

anticipated risk from food exposures 

from the 11 food uses remaining. Given 

that the cancellation actions will reduce 

exposure from residues in food and the 

current assessment with all currently 

registered food uses indicates there is no 

risk of concern from exposure to 

residues on all food for which there are 

tolerances, the Agency concludes that 

there will still be no risks of concern 

from exposure to residues of 

chlorpyrifos on food after most of the 

food uses are cancelled. 

2. Non-Occupational, Non-Dietary 

(Residential) Risks 

Because there are some uses of 

chlorpyrifos that may result in 

residential exposures, EPA assessed risk 

from those uses. All residential postapplication risk estimates for the 

registered uses of chlorpyrifos were 

below the Agency’s level of concern. 

(Ref. 12 at 38) The residential postapplication LOC for children is 40, and 

the lowest risk estimate for children (11 

to less than 16 years old) was 1,200. The 

residential post-application LOC for 

adults is 100, and the lowest risk 

estimate is 1,000. Because the calculated 

MOEs are above the Agency’s level of 

concern, there are no risks of concern 

from residential exposures. 

3. Risks From Drinking Water 

As noted above, the Agency 

aggregated exposures to chlorpyrifos 

from food and residential exposures and 

calculated the DWLOC, i.e., the amount 

of drinking water exposures that would 

be considered safe, based on how much 

room was left in the risk cup after 

accounting for food and residential/nonoccupational exposures. The Agency 

calculated acute and steady-state 

DWLOCs for infants (less than 1 year 

old); children (1 to 2 years old); youths 

(6 to 12 years old), and adults (females 

13 to 49 years old), which would be 

protective of other subpopulations. The 

most sensitive acute DWLOC was 23 

ppb chlorpyrifos oxon, and the most 

sensitive steady-state DWLOC was 4.0 

ppb chlorpyrifos oxon. 

As indicated above in Unit IV.B.2., 

the Agency estimated drinking water 

contributions from the 11 food uses 

identified in Unit III. above in its 2020 

DWA for both acute and steady-state 

exposure durations. Those estimates 

were based on limiting those uses to 

specific states and were modeled based 

on usage data concerning application 

frequency and application rates. These 

application rate and maximum number 

of application-per-year restrictions vary 

by use site, as specified in the 2020 

DWA. (Ref. 2) That document indicated 

that EDWCs for those food uses with 

those specific limitations would be 

below the acute DWLOC of 23 ppb and 

the steady-state DWLOC of 4.0 ppb. The 

underlying assumption of the 2020 

DWA was that there would be no other 

food uses contributing to drinking water 

exposures. As indicated in Unit III., all 

chlorpyrifos registrants have submitted 

requests to cancel all other food uses 

and to amend products for use on food 

consistent with the restrictions 

identified in Unit III; EPA has 

completed approval of the label 

amendments and expects to finalize the 

cancellations by the end of 2024, prior 

to the time this rule is finalized. Under 

the terms of those cancellation orders, 

use of chlorpyrifos will not be permitted 

on food except on the 11 remaining uses 

in accordance with the new label 

restrictions after June 30, 2025. As a 

result, EPA anticipates that use of 

chlorpyrifos products with the more 

restrictive labeling will result in 

drinking water exposures below the 

DWLOC. 

4. Aggregate Exposure and 

Determination Concerning Safety 

As noted above, in accordance with 

FFDCA section 408(b)(2), EPA must, 


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when establishing or leaving in effect 

tolerances for residues of a pesticide 

chemical, determine that the tolerances 

are safe. That is, EPA must determine 

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. 346a(b)(2)). 

As discussed earlier in this Unit, 

exposures from food and residential/ 

non-occupational exposures, taken 

separately or together, do not exceed 

EPA’s levels of concern. The Agency 

determined that risks from exposures to 

chlorpyrifos residues in food (from all 

food uses registered at the time of the 

2020 HHRA) comprised 3.2% of the 

aPAD for females (13 to 49 years old) 

and 9.7% of the ssPAD for children (1 

to 2 years old), the highest exposed 

subpopulations. Combining those 

exposures with relevant residential 

exposures, which did not exceed the 

Agency’s levels of concern, the Agency 

calculated the levels of drinking water 

concentrations that would be safe, i.e., 

the DWLOCs. The lowest DWLOC for 

acute exposures (for infants) is 23 ppb, 

and the lowest DWLOC for steady-state 

exposures (for infants) is 4.0 ppb; 

therefore, any EDWCs of chlorpyrifos 

oxon exceeding 23 ppb in an acute 

scenario or 4.0 ppb in a steady-state 

exposure scenario indicate that 

aggregate exposures of chlorpyrifos 

would be unsafe. 

The Agency’s 2020 DWA 

demonstrates that the DWLOCs will not 

be exceeded for the 11 uses as assessed 

in that document, i.e., where those uses 

are limited to specific geographic areas 

and with restrictions on application 

rates and frequency. Those restrictions 

are described in Unit III. Because the 

registrants have, under FIFRA, 

requested cancellation of all other food 

uses and have submitted label 

amendments that reflect the necessary 

restrictions on the remaining food uses 

for consistency with the assumptions in 

the 2020 DWA, EPA considers the more 

limited exposure to be reasonably 

anticipated at this time, unlike at the 

time of the 2021 Final Rule when no 

such requests had been submitted. Use 

consistent with the amended labels will 

result in drinking water exposures that 

are below the DWLOC, and 

consequently, there is a reasonable 

certainty that no harm will result from 

aggregate exposure (including food, 

drinking water, and residential/nonoccupational exposures) to chlorpyrifos. 

Therefore, EPA concludes that the 

tolerances remaining in place will be 

safe. 

V. Petition Response 

As noted in Unit II.D., PANNA and 

NRDC submitted a petition to EPA in 

September 2007, seeking revocation of 

all chlorpyrifos tolerances and 

cancellation of all chlorpyrifos 

registrations (‘‘2007 Petition’’). The 2007 

Petition raised the following claims in 

support of that request: 

1. EPA has ignored genetic evidence 

of vulnerable populations. 

2. EPA has needlessly delayed a 

decision regarding endocrine disrupting 

effects. 

3. EPA has ignored data regarding 

cancer risks. 

4. EPA’s 2006 OP CRA 

misrepresented risks and failed to apply 

the 10X FQPA Safety Factor. 

5. EPA has over-relied on registrant 

data. 

6. EPA has failed to properly address 

the exporting hazard in foreign 

countries from chlorpyrifos. 

7. EPA has failed to quantitatively 

incorporate data demonstrating longlasting effects from early life exposure to 

chlorpyrifos in children. 

8. EPA has disregarded data 

demonstrating that there is no evidence 

of a safe level of exposure during prebirth and early life stages. 

9. EPA has failed to cite or 

quantitatively incorporate studies and 

clinical reports suggesting potential 

adverse effects below 10% 

cholinesterase inhibition. 

10. EPA has failed to incorporate 

inhalation routes of exposure. 

In a response dated July 16, 2012, 

EPA explained that all but one of the 

issues raised in the 2007 Petition relate 

to EPA’s establishment of the 

chlorpyrifos tolerances under the 

FFDCA that would be addressed in 

either a rule or an order issued under 

the FFDCA. (Ref. 42) The one issue that 

was not related to the safety of the 

tolerances was claim 6, which EPA 

denied in that July 16, 2012, response. 

EPA expressly noted that its denial of 

claim 6 was a final agency action subject 

to judicial review under section 16 of 

FIFRA; that denial was never 

challenged. 

The only claims remaining in the 

2007 Petition, therefore, are claims 

related to the safety of the chlorpyrifos 

tolerances that must be addressed under 

the FFDCA. Because of the integration 

of the safety standard into the FIFRA 

registration standard, if EPA were to 

determine that the tolerances were 

unsafe, then the corresponding food 

uses would not meet the FIFRA 

standard for registration and must be 

cancelled. If, however, EPA were to 

determine that the 2007 Petition does 

not provide a basis for determining that 

the tolerances associated with the 11 

remaining food uses are unsafe, as EPA 

is proposing to do in this document, 

there would be no separate basis in the 

2007 Petition for a cancellation action 

under FIFRA. Section 408(h)(5) 

prohibits the review of issues under 

other statutes, for which review is 

obtainable under the FFDCA. 21 U.S.C. 

346a(h)(5). Accordingly, EPA intended, 

as indicated in its July 2012 response, 

and intends currently to treat the final 

rule of this rulemaking as its final 

response to the remaining claims in the 

2007 Petition. 

Regarding the remaining claims, 

which must be reviewed under the 

FFDCA, EPA denied the rest of the 

claims in the 2017 Denial Order and 

denied the objections to that order in 

the 2019 Denial Order. (Ref. 10 and 43) 

After the 2017 and 2019 Denial Orders 

were vacated by the Ninth Circuit in 

2021, EPA granted the 2007 Petition as 

part of the 2021 Final Rule, as directed 

by the Ninth Circuit, but that 2021 Final 

Rule (and petition response) was 

subsequently vacated by the Eighth 

Circuit in 2023. 

As noted above, however, EPA is 

taking action in this rulemaking to 

revoke most tolerances, which is 

consistent, in part, with the 2007 

Petition’s request. Based on the 

available data, use of chlorpyrifos has 

been decreasing (also noted in section 

IV.B.4 of this rule). Cancelling all food 

uses but the 11 mentioned in Unit III. 

above—along with geographic 

limitations and additional application 

restrictions—will contribute to the 

decrease of chlorpyrifos applied in the 

United States compared to historical 

usage. In addition, to address concerns 

about whether the rest of the tolerances 

should be revoked as requested by the 

2007 Petition, EPA has provided a safety 

determination in Unit IV. above. To the 

extent the Petition’s request to revoke 

tolerances is not fully addressed above, 

EPA is clarifying its responses to the 

specific claims in this Unit. 

EPA provided responses to the 

specific claims 1–5 and 10 in the 2017 

Denial Order. EPA’s position on those 

issues has not changed, and thus EPA is 

incorporating those responses into this 

document by reference. Those responses 

can be found in Unit V.1–5 and 10 of 

the 2017 Petition Denial. See 82 FR at 

16585–91. 

EPA has grouped claims 7–9 together 

because they fundamentally all raise the 

same issue: Whether the potential exists 

for chlorpyrifos to cause 

neurodevelopmental effects in infants 

and children from exposures (either to 

mothers during pregnancy or directly to 


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infants and children) that are lower than 

those resulting in 10% cholinesterase 

inhibition—the basis for EPA’s longstanding point of departure in regulating 

chlorpyrifos and other OPs. 

The petitioners assert that human 

epidemiology and rodent developmental 

neurotoxicity data suggest that pre-natal 

and early life exposure to chlorpyrifos 

can result in long-lasting, possibly 

permanent damage to the nervous 

system and that these effects are likely 

occurring at exposure levels below 10% 

cholinesterase inhibition, EPA’s existing 

regulatory standard for chlorpyrifos and 

other OPs. They assert that EPA has 

therefore used the wrong endpoint as a 

basis for regulation and that, taking into 

account the full spectrum of toxicity, 

chlorpyrifos does not meet the FFDCA 

safety standard (and thus does not meet 

the FIFRA standard for registration, 

which integrates the FFDCA safety 

standard). 

EPA initiated a science evaluation of 

the potential effects on 

neurodevelopment in 2007 following 

the receipt of the 2007 Petition. EPA has 

three times presented approaches and 

proposals to the FIFRA SAP for 

evaluating epidemiologic, laboratory 

animal, and mechanistic data exploring 

the possible connection between in 

utero and early childhood exposure to 

chlorpyrifos and adverse 

neurodevelopmental effects. The FIFRA 

SAP reports have rendered numerous 

recommendations for additional study 

and sometimes conflicting advice for 

how EPA should consider (or not 

consider) the epidemiology data in 

conducting EPA’s registration review 

human health risk assessment for 

chlorpyrifos. For over two decades, EPA 

has evaluated the scientific evidence 

surrounding the different health effects 

associated with chlorpyrifos. The 

Agency’s position on the strengths and 

weaknesses of the available 

epidemiological, laboratory animal, and 

mechanistic data as laid out in the 2020 

HH DRA is discussed in Unit IV.A.2.b 

above. 

As noted in that section and in Unit 

IV.A.3., EPA concludes that the 

available epidemiological data does not 

provide a sufficient basis for calculating 

a PoD nor does it support a conclusion 

that PoDs based on the 10% AChE 

inhibition are not protective. 

Nevertheless, as discussed in Unit 

IV.A.3.c., EPA has retained the 10X 

FQPA SF to account for the 

uncertainties around the dose-response 

level for neurodevelopmental effects for 

the purpose of this rule. 

Through this proposal, EPA is 

proposing to take action to revoke most 

chlorpyrifos tolerances as requested in 

the 2007 Petition but is not proposing to 

revoke tolerances associated with the 

remaining registered uses because the 

Agency’s analysis in the 2020 HH DRA 

and the 2020 DWA support a conclusion 

that those tolerances are safe. The 

voluntary cancellations will effectuate a 

reduction in exposures, and because 

exposures will be reduced, the 

underlying assessment, even with the 

retention of the default 10X FQPA SF, 

supports the retention of the remaining 

tolerances. 

EPA is proposing that the claims in 

the 2007 Petition do not provide a basis 

for concluding that the tolerances not 

being revoked are unsafe. 

VI. Request for Public Comment 

The Agency is requesting comments 

on this proposal. 

During the lengthy pendency of the 

2007 Petition to revoke tolerances and 

the registration review process for 

chlorpyrifos, the public has had 

numerous opportunities to comment on 

EPA’s scientific conclusions, risk 

assessments, regulatory proposals, and 

rules. Hundreds of thousands of 

comments have been submitted, and 

those comments have informed EPA’s 

subsequent assessments and regulatory 

decision making. 

As this is a proposed rule, EPA is 

providing an opportunity to comment 

on issues related to this proposal, and 

EPA will consider significant comments 

in the final rule. Comments on this 

particular proposal must be submitted at 

this time, even if that person has 

submitted comments at other times 

during the history of chlorpyrifos 

regulatory actions. 

VII. Other Administrative 

Considerations 

A. Tolerance Expiration Date 

EPA is proposing to set an expiration 

date for the chlorpyrifos tolerances 

being revoked so that those tolerances 

will expire on July 1, 2025. This date 

would align with the existing stocks 

provisions for the related cancellation 

actions, which allow use of existing 

stocks of some cancelled chlorpyrifos 

products on food until June 30, 2025. 

This approach is also intended to satisfy 

the U.S. commitments under the SPS 

Agreement, requiring Members to 

provide a ‘‘reasonable interval’’ between 

the publication of a regulation subject to 

the Agreement and its entry into force 

to allow time for producers in exporting 

Member countries to adapt to the new 

requirement. 

Any commodities treated with 

chlorpyrifos that are in the channels of 

trade and impacted by the tolerance 

revocations shall be subject to FFDCA 

section 408(1)(5). That section provides 

that any residues of the subject pesticide 

in or on such food shall not render the 

food adulterated so long as it is shown 

to the satisfaction of the Food and Drug 

Administration that: 

1. The residue is present as the result 

of an application or use of the pesticide 

at a time and in a manner that was 

lawful under FIFRA, and 

2. The residue does not exceed the 

level that was authorized at the time of 

the application or use to be present on 

the food under a tolerance or exemption 

from tolerance. Evidence to show that 

food was lawfully treated may include 

records that verify the dates when the 

pesticide was applied to such food. 

The tolerance revocations in this 

proposed rule are not discriminatory 

and are designed to ensure that both 

domestically produced and imported 

foods meet the food safety standard 

established by the FFDCA. The same 

food safety standards apply to 

domestically produced and imported 

foods. 

B. Severability 

This proposed rule includes two 

distinct actions concerning chlorpyrifos 

tolerances. Specifically, the Agency is 

proposing: (1) to revoke all tolerances 

associated with use cancellations as 

those tolerances are no longer needed 

and (2) that the tolerances not being 

revoked are safe. The Agency intends 

that these two actions be severable from 

each other, although for purposes of 

expediency and to fully address the 

pending 2007 Petition, EPA is proposing 

to include all parts in one rulemaking. 

(21 U.S.C. 346a(l)(1)). However, EPA 

retains the discretion to take each of 

these actions separately, with each 

implementing a portion or portions of 

this proposed rule. 

The revocation of tolerances that are 

no longer needed is an almost entirely 

ministerial action. Because those uses of 

chlorpyrifos on these commodities will 

no longer be registered in the United 

States, the corresponding tolerances are 

considered unnecessary. The Agency’s 

typical process is to automatically 

remove tolerances from the regulations 

that are no longer necessary. The only 

element of agency discretion involved 

in revocation of most tolerances would 

arise from a hypothetical request that 

EPA retain certain tolerances for 

purposes of importing food treated with 

chlorpyrifos. The proposal to revoke all 

tolerances except for those on the 11 

specified crops depends neither on the 

Agency making a safety finding for the 

remaining tolerances nor on the 

Agency’s response to the 2007 Petition. 


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Even if safety of the tolerances not being 

revoked is challenged, the revocation of 

unnecessary tolerances would not be 

affected and would stand on its own 

right; EPA could re-evaluate the safety 

of the remaining tolerances and either 

provide additional justification for its 

safety determination or take other 

action—if needed—to address the safety 

of chlorpyrifos tolerances. The 

tolerances proposed for revocation in 

this document would remain revoked in 

such circumstances. 

This discussion of separate actions 

proposed in this document is not 

intended to be exhaustive and should 

not be viewed as an intention by EPA 

to consider other actions or 

determinations proposed herein as nonseverable from other parts of the 

proposed rule. 

VIII. Statutory and Executive Order 

Reviews 

In this proposed rule, EPA is 

proposing to revoke specific tolerances 

established under FFDCA section 408. 

The Office of Management and Budget 

(OMB) has exempted this type of action 

(e.g., tolerance revocation for which 

extraordinary circumstances do not 

exist) from review under Executive 

Order 12866, entitled ‘‘Regulatory 

Planning and Review’’ (58 FR 51735, 

October 4, 1993). These revocations are 

not expected to present extraordinary 

circumstances because the registrants 

have requested to voluntarily cancel 

uses associated with these tolerances, 

which means that the tolerances will no 

longer be needed to cover residues of 

chlorpyrifos in or on those food 

commodities. Because this proposed 

rule has been exempted from review 

under Executive Order 12866, this 

proposed rule is not subject to Executive 

Order 13211, entitled ‘‘Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use’’ (66 FR 28355, May 

22, 2001). 

This proposed rule does not contain 

any information collections subject to 

OMB approval under the Paperwork 

Reduction Act (PRA) (44 U.S.C. 3501 et 

seq.) or impose any enforceable duty or 

contain any unfunded mandate as 

described under Title II of the Unfunded 

Mandates Reform Act (UMRA) (2 U.S.C. 

1501 et seq.). Nor does it require any 

special considerations as required by 

Executive Order 12898, entitled 

‘‘Federal Actions to Address 

Environmental Justice in Minority 

Populations and Low-Income 

Populations’’ (59 FR 7629, February 16, 

1994); or OMB review or any other 

Agency action under Executive Order 

13045, entitled ‘‘Protection of Children 

from Environmental Health Risks and 

Safety Risks’’ (62 FR 19885, April 23, 

1997). However, EPA considered the 

best available science in order to protect 

children against environmental health 

risks and this proposed rule is 

consistent with EPA’s 2021 Policy on 

Children’s Health (Oct. 5, 2021). (Ref. 

43). 

This proposed rule does not involve 

any technical standards that would 

require Agency consideration of 

voluntary consensus standards pursuant 

to section 12(d) of the National 

Technology Transfer and Advancement 

Act (NTTAA) (15 U.S.C. 272 note). In 

addition, the Agency has determined 

that this proposed rule will not have a 

substantial direct effect on States, on the 

relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132, entitled 

‘‘Federalism’’ (64 FR 43255, August 10, 

1999). This proposed rule directly 

regulates growers, food processors, food 

handlers, and food retailers, not states, 

including a state’s ability to register 

pesticide products. This proposed rule 

does not alter the relationships or 

distribution of power and 

responsibilities established by Congress 

in the preemption provisions of FFDCA 

section 408(n)(4). For these same 

reasons, the Agency has determined that 

this proposed rule does not have any 

‘‘tribal implications’’ as described in 

Executive Order 13175, entitled 

‘‘Consultation and Coordination with 

Indian Tribal Governments’’ (65 FR 

67249, November 9, 2000). 

In addition, pursuant to section 605(b) 

of the Regulatory Flexibility Act (RFA) 

(5 U.S.C. 601 et seq.), the Agency hereby 

certifies that the revocation of these 

tolerances in response to the 

cancellation of associated food uses will 

not have a significant impact on a 

substantial number of small entities. 

The certification presented above is 

based on the following rationale. In the 

case of domestically grown food, the 

tolerance revocations contained in this 

notice, as is generally the case, will have 

no economic impact. The associated 

pesticide registered uses are in the 

process of being canceled at this time, 

as requested by the registrants. By the 

time this rule is finalized, EPA intends 

to have approved all requested 

cancellations, and use will only be 

permitted on food consistent with the 

existing stocks provisions of those 

orders. Pursuant to the cancellation 

orders, U.S. growers will be prohibited 

from using chlorpyrifos on the foods for 

which this rule proposes revoking 

tolerances after June 30, 2025. 

Accordingly, revoking the tolerances 

themselves will have no effect on food 

grown in the United States. As for food 

grown in the United States, it will not 

be considered adulterated if it was 

treated in a way that complied with the 

tolerance in effect at the time of 

treatment and the use is consistent with 

the applicable cancellation order. The 

revocation of a pesticide tolerance 

generally has a greater potential to affect 

foreign-grown food, since the uses of the 

pesticide prohibited in the United States 

may still be lawful in other countries. If 

foreign growers use the pesticide after 

the tolerances are revoked, the food they 

grow will be considered adulterated and 

cannot be imported. 

IX. References 

EPA has established an official record 

for this rulemaking. The official record 

includes all information considered by 

EPA in developing this proposed rule. 

This official record includes all 

information physically located in docket 

ID number EPA–HQ–OPP–2024–0431, 

any documents identified in this 

proposal, and documents referenced in 

documents in the docket. The public 

version of the official record does not 

include any information claimed as CBI. 

1. U.S. EPA (2020). Chlorpyrifos Proposed 

Interim Registration Review Decision. 

Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2008-0850-0971. 

2. U.S. EPA (2020). Chlorpyrifos Updated 

Drinking Water Assessment for 

Registration Review. Available at: 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2008-0850-0941. 

3. U.S. EPA (2022). Cancellation Order for 

Certain Chlorpyrifos Registrations. 

Available at: https://

www.federalregister.gov/documents/ 

2022/08/31/2022-18838/cancellationorder-for-certain-chlorpyrifosregistrations. 

4. U.S. EPA (2023). Final Cancellation Order 

for Certain Chlorpyrifos Registrations 

and Uses. Available at: https://

www.federalregister.gov/documents/ 

2023/11/06/2023-24462/finalcancellation-order-for-certainchlorpyrifos-registrations-and-uses. 

5. U.S. EPA (2023). Cancellation Order for 

Certain Chlorpyrifos Registrations and 

Uses. Available at: https://

www.federalregister.gov/documents/ 

2023/05/04/2023-09396/cancellationorder-for-certain-chlorpyrifosregistrations-and-uses. 

6. U.S. EPA (2023). Final Cancellation Order 

for Certain Chlorpyrifos Registrations 

and Uses. Available at: https://

www.federalregister.gov/documents/ 

2023/11/06/2023-24462/finalcancellation-order-for-certainchlorpyrifos-registrations-and-uses. 

7. U.S. EPA (2024). Final Cancellation Order 

for Certain Chlorpyrifos Registrations 


khammond on DSK9W7S144PROD with PROPOSALS
99204 Federal Register / Vol. 89, No. 237 / Tuesday, December 10, 2024 / Proposed Rules 

and Uses. Available at: https://

www.federalregister.gov/documents/ 

2024/06/24/2024-13779/finalcancellation-order-for-cancelling-certainpesticide-registrations-and-uses. 

8. U.S. EPA (2024) Chlorpyrifos; Final 

Cancellation Order for Certain Pesticide 

Registrations and Amendment of Certain 

Pesticide Registrations to Terminate 

Certain Uses. Available at: https://

www.federalregister.gov/documents/ 

2024/08/07/2024-17453/chlorpyrifosfinal-cancellation-order-for-certainpesticide-registrations-and-amendmentof-certain. 

9. U.S. EPA (2016). Chlorpyrifos: Revised 

Human Health Risk Assessment for 

Registration Review (November 3, 2016). 

Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2015-0653-0454. 

10. U.S. EPA (2017) Chlorpyrifos; Order 

Denying PANNA and NRDC’s Petition to 

Revoke Tolerances. Available at: https:// 

www.regulations.gov/document/EPAHQ-OPP-2007-1005-0100. 

11. U.S. EPA (2023) Pesticide Tolerance; 

Exemptions, Petitions, Revocations, etc.: 

Implementing Registration Review 

Decisions for Certain Pesticides; 

Aluminum tris (O-ethylphosphonate), 

Carbon disulfide, et al. Available at: 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2017-0128-0005. 

12. U.S. EPA (2020) Chlorpyrifos: Third 

Revised Human Health Risk Assessment 

for Registration Review. Available at: 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2008-0850-0944. 

13. A User’s Guide to Available EPA 

Information on Assessing Exposure to 

Pesticides in Food (June 21, 2000). 

Available at: https://www.doh.wa.gov/ 

Portals/1/Documents/4000/PASW_

exposurefood.pdf. 

14. U.S. EPA (2002) Determination of the 

Appropriate FQPA Safety Factor(s) in 

Tolerance Assessment. Available at: 

https://www.epa.gov/sites/default/files/ 

2015-07/documents/determ.pdf. 

15. U.S. EPA (2000). Chlorpyrifos Human 

Health Risk Assessment. Available at: 

https://archive.epa.gov/scipoly/sap/ 

meetings/web/pdf/hed_ra.pdf. 

16. U.S. EPA (2011). Chlorpyrifos: 

Preliminary Human Health Risk 

Assessment for Registration Review. 

Available in docket number EPA–HQ– 

OPP–2008–0850, https://

www.regulations.gov/document/EPAHQ-OPP-2008-0850-0025. 

17. U.S. EPA (2016). Scientific Advisory 

Panel for Chlorpyrifos: Analysis of 

Biomonitoring Data. Available at: https:// 

www.epa.gov/sites/default/files/2016-07/ 

documents/chlorpyrifos_sap_april_

2016_final_minutes.pdf. 

18. U.S. EPA (2016). Summary Reviews for 

Additional Epidemiological Literature 

Studies from Prospective Birth Cohort 

Studies. Available in docket number 

EPA–HQ–OPP–2015–0653 at https://

www.regulations.gov/document/EPAHQ-OPP-2015-0653-0438. 

19. U.S. EPA (2020). The Use of New 

Approach Methodologies (NAMs) to 

Derive Extrapolation Factors and 

Evaluate Developmental Neurotoxicity 

for Human Health Risk Assessment. 

Available in docket number EPA–HQ– 

OPP–2020–0263 at https://

www.regulations.gov/document/EPAHQ-OPP-2020-0263-0033. 

20. FIFRA Scientific Advisory Panel (2012). 

‘‘Scientific Issues Associated with 

Chlorpyrifos’’. Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2012-0040-0029. 

21. U.S. EPA (2006). Revised 

Organophosphorous Pesticide 

Cumulative Risk Assessment. Available 

at https://downloads.regulations.gov/ 

EPA-HQ-OPP-2006-0618-0002/ 

content.pdf. 

22. U.S. EPA (2012). Standard Operating 

Procedures for Residential Pesticide 

Exposure Assessment https://

www.epa.gov/sites/default/files/2015-08/ 

documents/usepa-opp-hed_residential_

sops_oct2012.pdf. 

23. FIFRA Scientific Advisory Panel (2002). 

‘‘Organophosphate Pesticides: 

Preliminary OP Cumulative Risk 

Assessment.’’ Information on how to 

obtain the meeting report is available at 

https://www.epa.gov/sap/fifra-scientificadvisory-panel-meetings. 

24. EPA’s Exposure Factors Handbook. 

Available at: https://www.epa.gov/ 

expobox/about-exposure-factorshandbook. 

25. U.S. EPA (2014). Guidance for Applying 

Quantitative Data to Develop DataDerived Extrapolation Factors for 

Interspecies and Intraspecies 

Extrapolation. Available at: https://

www.epa.gov/sites/default/files/2015-01/ 

documents/ddef-final.pdf. 

26. U.S. EPA (2014). Chlorpyrifos: Revised 

Human Health Risk Assessment for 

Registration Review. Available in docket 

number EPA–HQ–OPP–2008–0850, 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2008-0850-0195. 

27. U.S. EPA (2016). Office of Pesticide 

Programs’ Framework for Incorporating 

Human Epidemiologic & Incident Data in 

Risk Assessments for Pesticides. (2016) 

Available at: https://www3.epa.gov/ 

pesticides/EPA-HQ-OPP-2008-0316- 

DRAFT-0075.pdf. 

28. A User’s Guide to Available EPA 

Information on Assessing Exposure to 

Pesticides in Food (June 21, 2000). 

Available at: https://www.doh.wa.gov/ 

Portals/1/Documents/4000/PASW_

exposurefood.pdf. 

29. U.S. EPA (2000). Choosing a Percentile of 

Acute Dietary Exposure as a Threshold 

of Regulatory Concern. Available at: 

https://www.epa.gov/sites/production/ 

files/2015-07/documents/trac2b054_

0.pdf. 

30. U.S. EPA (2014). Chlorpyrifos Acute and 

Steady Dietary (Food Only) Exposure 

Analysis to Support Registration Review. 

Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2008-0850-0197. 

31. U.S. EPA (2020). Framework for 

Conducting Pesticide Drinking Water 

Assessments for Surface Water. 

Environmental Fate and Effects Division. 

Office of Pesticide Programs. Office of 

Chemical Safety and Pollution 

Prevention. U.S. Environmental 

Protection Agency. Available at: https:// 

www.epa.gov/sites/default/files/2020-09/ 

documents/framework-conductingpesticide-dw-sw.pdf. 

32. FIFRA Scientific Advisory Panel (2019) 

‘‘Approaches for Quantitative Use of 

Surface Water Monitoring Data in 

Pesticide Drinking Water Assessments.’’ 

Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2019-0417-0019. 

33. U.S. EPA (2001). General Principles for 

Performing Aggregate Exposure and Risk 

Assessments. Available at: https://

www.epa.gov/sites/default/files/2015-07/ 

documents/aggregate.pdf. 

34. United States Geological Survey (USGS) 

Water Resources of the United States 

https://water.usgs.gov/GIS/huc.html. 

35. U.S. EPA (2020). Appendix B. Case Study 

for Integrating a Distributional Approach 

to Using Percent Crop Area (PCA) and 

Percent Crop Treated (PCT) into 

Drinking Water Assessment. Available 

at: https://www.regulations.gov/ 

document/EPA-HQ-OPP-2020-0279- 

0002. 

36. U.S. EPA (2016). Chlorpyrifos Refined 

Drinking Water Assessment for 

Registration Review. Available at: 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2015-0653-0437. 

37. U.S. EPA (2014). Chlorpyrifos Updated 

Drinking Water Assessment for 

Registration Review. Available at: 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2008-0850-0198. 

38. U.S. EPA (2015). Proposed Rule: 

Tolerance Revocations: Chlorpyrifos. 

Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2015-0653-0001. 

39. U.S. EPA (2019). Documents on PCA/PCT 

and New Scenario Methods for 

Estimating Pesticide Concentration in 

Drinking Water. Available at https://

www.epa.gov/pesticide-science-andassessing-pesticide-risks/documentspcapct-and-new-scenario-methods. 

40. U.S. EPA (2020). Pesticide Drinking 

Water Assessment Improvements. 

Available at https://

www.regulations.gov/docket/EPA-HQOPP-2020-0279/document. 

41. U.S. EPA (2011). Finalization of Guidance 

on Incorporation of Water Treatment 

Effects on Pesticide Removal and 

Transformations in Drinking Water 

Exposure Assessments. Available at: 

https://www.epa.gov/pesticide-scienceand-assessing-pesticide-risks/ 

finalization-guidance-incorporationwater-treatment. 

42. U.S. EPA (2012) EPA’s Partial Response 

to Chlorpyrifos Petition by NRDC & 

PANNA. Available at: https://

www.regulations.gov/document/EPAHQ-OPP-2007-1005-0095. 

43. U.S. EPA (2019) Chlorpyrifos; Final Order 

Denying Objections to March 2017 

Petition Denial Order. Available at 

https://www.regulations.gov/document/ 

EPA-HQ-OPP-2007-1005-0527. 


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Federal Register / Vol. 89, No. 237 / Tuesday, December 10, 2024 / Proposed Rules 99205 

List of Subjects in 40 CFR Part 180 

Environmental protection, 

Administrative practice and procedure, 

Agricultural commodities, Pesticides 

and pests, Reporting and recordkeeping 

requirements. 

Dated: November 27, 2024. 

Edward Messina, 

Director, Office of Pesticide Programs. 

Therefore, for the reasons stated in the 

preamble the Environmental Protection 

Agency proposes to amend 40 CFR part 

180 as follows: 

PART 180—TOLERANCES AND 

EXEMPTIONS FOR PESTICIDE 

CHEMICAL RESIDUES IN FOOD 

■ 1. The authority citation for part 180 

continues to read as follows: 

Authority: 21 U.S.C. 321(q), 346a and 371. 

■ 2. Revise § 180.342 to read as follows: 

§ 180.342 Chlorpyrifos; tolerances for 

residues. 

(a) General. (1) Tolerances are 

established for residues of the pesticide 

chlorpyrifos per se (O,O-diethyl-O- 

(3,5,6-trichloro-2-pyridyl) 

phosphorothioate) in or on the 

following food commodities: 

TABLE 1 TO PARAGRAPH (a)(1) 

Commodity Parts per 

million 

Tolerance 

expiration 

date 

Alfalfa, forage ........................................................................................................................................... 3.0 None 

Alfalfa, hay ............................................................................................................................................... 13 None 

Almond ..................................................................................................................................................... 0.2 7/1/2025 

Almond, hulls ........................................................................................................................................... 12 7/1/2025 

Apple ........................................................................................................................................................ 0.01 None 

Apple, wet pomace .................................................................................................................................. 0.02 None 

Banana ..................................................................................................................................................... 0.1 7/1/2025 

Beet, sugar, dried pulp ............................................................................................................................ 5.0 None 

Beet, sugar, molasses ............................................................................................................................. 15 None 

Beet, sugar, roots .................................................................................................................................... 1.0 None 

Beet, sugar, tops ..................................................................................................................................... 8.0 None 

Cattle, fat ................................................................................................................................................. 0.3 None 

Cattle, meat ............................................................................................................................................. 0.05 None 

Cattle, meat byproducts ........................................................................................................................... 0.05 None 

Cherry, sweet ........................................................................................................................................... 1.0 7/1/2025 

Cherry, tart ............................................................................................................................................... 1.0 None 

Citrus, dried pulp ..................................................................................................................................... 5.0 None 

Citrus, oil .................................................................................................................................................. 20 None 

Corn, field, forage .................................................................................................................................... 8.0 7/1/2025 

Corn, field, grain ...................................................................................................................................... 0.05 7/1/2025 

Corn, field, refined oil .............................................................................................................................. 0.25 7/1/2025 

Corn, field, stover .................................................................................................................................... 8.0 7/1/2025 

Corn, sweet, forage ................................................................................................................................. 8.0 7/1/2025 

Corn, sweet, kernel plus cob with husk removed ................................................................................... 0.05 7/1/2025 

Corn, sweet, stover .................................................................................................................................. 8.0 7/1/2025 

Cotton, undelinted seed ........................................................................................................................... 0.2 None 

Cranberry ................................................................................................................................................. 1.0 7/1/2025 

Cucumber ................................................................................................................................................ 0.05 7/1/2025 

Egg ........................................................................................................................................................... 0.01 7/1/2025 

Fig ............................................................................................................................................................ 0.01 7/1/2025 

Fruit, citrus, group 10 .............................................................................................................................. 1.0 None 

Food commodities (other than those already covered by a higher tolerance as a result of use on 

growing crops) in food service establishments where food and food products are prepared and 

served, as a result of the application of chlorpyrifos in microencapsulated form ............................... 0.1 7/1/2025 

Goat, fat ................................................................................................................................................... 0.2 None 

Goat, meat ............................................................................................................................................... 0.05 None 

Goat, meat byproducts ............................................................................................................................ 0.05 None 

Hazelnut ................................................................................................................................................... 0.2 7/1/2025 

Hog, fat .................................................................................................................................................... 0.2 None 

Hog, meat ................................................................................................................................................ 0.05 None 

Hog, meat byproducts ............................................................................................................................. 0.05 None 

Horse, fat ................................................................................................................................................. 0.25 None 

Horse, meat ............................................................................................................................................. 0.25 None 

Horse, meat byproducts .......................................................................................................................... 0.25 None 

Kiwifruit .................................................................................................................................................... 2.0 7/1/2025 

Milk, fat (Reflecting 0.01 ppm in whole milk) .......................................................................................... 0.25 None 

Nectarine .................................................................................................................................................. 0.05 7/1/2025 

Onion, bulb .............................................................................................................................................. 0.5 7/1/2025 

Peach ....................................................................................................................................................... 0.05 None 

Peanut ...................................................................................................................................................... 0.2 7/1/2025 

Peanut, refined oil .................................................................................................................................... 0.2 7/1/2025 

Pear ......................................................................................................................................................... 0.05 7/1/2025 

Pecan ....................................................................................................................................................... 0.2 7/1/2025 

Pepper ..................................................................................................................................................... 1.0 7/1/2025 

Peppermint, tops ...................................................................................................................................... 0.8 7/1/2025 

Peppermint, oil ......................................................................................................................................... 8.0 7/1/2025 


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99206 Federal Register / Vol. 89, No. 237 / Tuesday, December 10, 2024 / Proposed Rules 

TABLE 1 TO PARAGRAPH (a)(1)—Continued 

Commodity Parts per 

million 

Tolerance 

expiration 

date 

Plum, prune, fresh ................................................................................................................................... 0.05 7/1/2025 

Poultry, fat ................................................................................................................................................ 0.1 None 

Poultry, meat ............................................................................................................................................ 0.1 None 

Poultry, meat by products ........................................................................................................................ 0.1 None 

Pumpkin ................................................................................................................................................... 0.05 7/1/2025 

Radish ...................................................................................................................................................... 2.0 7/1/2025 

Rutabaga ................................................................................................................................................. 0.5 7/1/2025 

Sheep, fat ................................................................................................................................................ 0.2 None 

Sheep, meat ............................................................................................................................................ 0.05 None 

Sheep, meat byproducts .......................................................................................................................... 0.05 None 

Spearmint, tops ........................................................................................................................................ 0.8 7/1/2025 

Spearmint, oil ........................................................................................................................................... 8.0 7/1/2025 

Sorghum, grain, forage ............................................................................................................................ 0.5 7/1/2025 

Sorghum, grain, grain .............................................................................................................................. 0.5 7/1/2025 

Sorghum, grain, stover ............................................................................................................................ 2.0 7/1/2025 

Soybean, seed ......................................................................................................................................... 0.3 None 

Strawberry ................................................................................................................................................ 0.2 None 

Sunflower, seed ....................................................................................................................................... 0.1 7/1/2025 

Sweet potato, roots .................................................................................................................................. 0.05 7/1/2025 

Turnip, roots ............................................................................................................................................. 1.0 7/1/2025 

Turnip, tops .............................................................................................................................................. 0.3 7/1/2025 

Vegetable, brassica, leafy, group 5 ......................................................................................................... 1.0 7/1/2025 

Vegetable, legume, group 6, except soybean ......................................................................................... 0.05 7/1/2025 

Walnut ...................................................................................................................................................... 0.2 7/1/2025 

Wheat, forage .......................................................................................................................................... 3.0 None 

Wheat, grain ............................................................................................................................................ 0.5 None 

Wheat, straw ............................................................................................................................................ 6.0 None 

(2) Chlorpyrifos [O,O-diethyl O-(3,5,6- 

trichloro-2-pyridyl) phosphorothioate] 

may be safely used up until and 

including June 30, 2025 in accordance 

with the following prescribed 

conditions. On and after July 1, 2025, 

chlorpyrifos may not be used as 

described below: 

(i) Application shall be limited solely 

to spot and/or crack and crevice 

treatment in food handling 

establishments where food and food 

products are held, processed, prepared 

or served. Contamination of food or food 

contact surfaces shall be avoided. Food 

must be removed or covered during 

treatment. 

(ii) Spray concentration for spot 

treatment shall be limited to a 

maximum of 0.5 percent of the active 

ingredient by weight. A course, lowpressure spray shall be used to avoid 

atomization or splashing of the spray. 

(iii) Paint-on application for spot 

treatment shall be limited to a 

maximum of 2 percent of the active 

ingredient by weight. 

(iv) Crack and crevice treatment shall 

be limited to a maximum of 2 percent 

of the active ingredient by weight. 

Equipment capable of delivering a pinstream of insecticide shall be used. 

(v) Application via adhesive strips 

shall contain a maximum of 10% by 

weight of the controlled-release product 

in food-handling establishments where 

food and food products are held, 

processed, prepared, or served. A 

maximum of 36 strips (or 5.15 grams of 

chlorpyrifos) is to be used per 100 

square feet of floor space. The strips are 

not to be placed in exposed areas where 

direct contact with food, utensils, and 

food-contact surfaces would be likely to 

occur. 

(vi) To assure safe use of the 

insecticide, its label and labeling shall 

conform to that registered by the U.S. 

Environmental Protection Agency, and 

it shall be used in accordance with such 

label and labeling. 

(3) A tolerance of 0.1 part per million 

is established for residues of 

chlorpyrifos, per se, in or on food 

commodities (other than those already 

covered by a higher tolerance as a result 

of use on growing crops) in food service 

establishments where food and food 

products are prepared and served, as a 

result of the application of chlorpyrifos 

in microencapsulated form. This 

tolerance expires on July 1, 2025. 

(i) Application of a 

microencapsulated product shall be 

limited solely to spot and/or crack and 

crevice treatment in food handling 

establishments where food and food 

products are prepared and served. All 

treatments shall be applied in such a 

manner as to avoid contamination of 

food or food contact surfaces. 

(ii) Spray concentrations shall be 

limited to a maximum of 0.5 percent of 

the active ingredient by weight. 

(iii) For crack and crevice treatment, 

equipment capable of delivering a pin 

stream of spray directly into cracks and 

crevices or capable of applying small 

amounts of insecticide into cracks and 

crevices shall be used. 

(iv) For spot treatment, an individual 

spot shall not exceed 2 square feet. 

(v) To assure safe use of the 

insecticide, its label and labeling shall 

conform to that registered by the U.S. 

Environmental Protection Agency, and 

it shall be used in accordance with such 

label and labeling. 

(b) [Reserved] 

(c) Tolerances with regional 

registrations. Tolerances with regional 

registration, as defined in 180.1(l), are 

established for residues of the pesticide 

chlorpyrifos per se (O,O-diethyl- O- 

(3,5,6-trichloro-2-pyridyl) 

phosphorothioate) in or on the 

following food commodities: 


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Federal Register / Vol. 89, No. 237 / Tuesday, December 10, 2024 / Proposed Rules 99207 

TABLE 2 TO PARAGRAPH (c) 

Commodity Parts per 

million 

Tolerance 

expiration 

date 

Asparagus ........................................................................................................................................................ 5.0 None 

Grape ............................................................................................................................................................... 0.01 7/1/2025 

(d) [Reserved] 

[FR Doc. 2024–28332 Filed 12–9–24; 8:45 am] 

BILLING CODE 6560–50–P 

DEPARTMENT OF THE INTERIOR 

Fish and Wildlife Service 

50 CFR Part 17 

[Docket No. FWS–R2–ES–2024–0193; 

FXES1111090FEDR–256–FF09E21000] 

Endangered and Threatened Wildlife 

and Plants; 12-Month Not-Warranted 

Finding for the Rio Grande Cutthroat 

Trout 

AGENCY: Fish and Wildlife Service, 

Interior. 

ACTION: Notification of finding. 

SUMMARY: We, the U.S. Fish and 

Wildlife Service (Service), announce a 

12-month finding on a petition to list 

the Rio Grande cutthroat trout 

(Oncorhynchus clarkii virginalis) as an 

endangered or threatened species under 

the Endangered Species Act of 1973, as 

amended (Act). Rio Grande cutthroat 

trout, a subspecies of cutthroat trout 

(Oncorhynchus clarkii), inhabit highelevation streams in New Mexico and 

southern Colorado. After a thorough 

review of the best available scientific 

and commercial information, we find 

that listing the Rio Grande cutthroat 

trout as an endangered or threatened 

species is not warranted at this time. 

However, we ask the public to submit to 

us at any time any new information 

relevant to the status of the Rio Grande 

cutthroat trout or its habitat. 

DATES: The finding in this document 

was made on December 10, 2024. 

ADDRESSES: A detailed description of 

the basis for this finding is available on 

the internet at https://

www.regulations.gov under Docket No. 

FWS–R2–ES–2024–0193. Supporting 

information used to prepare this finding 

is also available for public inspection, 

by appointment, during normal business 

hours at the New Mexico Ecological 

Services Office. Please submit any new 

information, materials, comments, or 

questions concerning this finding to the 

person listed under FOR FURTHER

INFORMATION CONTACT. 

FOR FURTHER INFORMATION CONTACT: 

Shawn Sartorius, Field Supervisor, New 

Mexico Ecological Services Office, 505– 

346–2525, shawn_sartorius@fws.gov. 

Individuals in the United States who are 

deaf, deafblind, hard of hearing, or have 

a speech disability may dial 711 (TTY, 

TDD, or TeleBraille) to access 

telecommunications relay services. 

Individuals outside the United States 

should use the relay services offered 

within their country to make 

international calls to the point-ofcontact in the United States. 

SUPPLEMENTARY INFORMATION: 

Background 

Under section 4(b)(3)(B) of the Act (16 

U.S.C. 1531 et seq.), we are required to 

make a finding on whether or not a 

petitioned action is warranted within 12 

months after receiving any petition that 

we have determined contains 

substantial scientific or commercial 

information indicating that the 

petitioned action may be warranted 

(‘‘12-month finding’’). We must make a 

finding that the petitioned action is: (1) 

Not warranted; (2) warranted; or (3) 

warranted, but precluded by other 

listing activity. We must publish a 

notification of the 12-month finding in 

the Federal Register. 

Summary of Information Pertaining to 

the Five Factors 

Section 4 of the Act (16 U.S.C. 1533) 

and the implementing regulations at 

part 424 of title 50 of the Code of 

Federal Regulations (50 CFR part 424) 

set forth procedures for adding species 

to, removing species from, or 

reclassifying species on the Lists of 

Endangered and Threatened Wildlife 

and Plants (Lists). The Act defines 

‘‘species’’ as including any subspecies 

of fish or wildlife or plants, and any 

distinct population segment of any 

species of vertebrate fish or wildlife 

which interbreeds when mature. The 

Act defines an ‘‘endangered species’’ as 

a species that is in danger of extinction 

throughout all or a significant portion of 

its range and a ‘‘threatened species’’ as 

a species that is likely to become an 

endangered species within the 

foreseeable future throughout all or a 

significant portion of its range. The Act 

requires that we determine whether any 

species is an endangered species or a 

threatened species because of any of the 

following factors: 

(A) The present or threatened 

destruction, modification, or 

curtailment of its habitat or range; 

(B) Overutilization for commercial, 

recreational, scientific, or educational 

purposes; 

(C) Disease or predation; 

(D) The inadequacy of existing 

regulatory mechanisms; or 

(E) Other natural or manmade factors 

affecting its continued existence. 

These factors represent broad 

categories of natural or human-caused 

actions or conditions that could have an 

effect on a species’ continued existence. 

In evaluating these actions and 

conditions, we look for those that may 

have a negative effect on individuals of 

the species, as well as other actions or 

conditions that may ameliorate any 

negative effects or may have positive 

effects. 

We use the term ‘‘threat’’ to refer in 

general to actions or conditions that are 

known to or are reasonably likely to 

negatively affect individuals of a 

species. The term ‘‘threat’’ includes 

actions or conditions that have a direct 

impact on individuals (direct impacts), 

as well as those that affect individuals 

through alteration of their habitat or 

required resources (stressors). The term 

‘‘threat’’ may encompass—either 

together or separately—the source of the 

action or condition or the action or 

condition itself. 

However, the mere identification of 

any threat(s) does not necessarily mean 

that the species meets the statutory 

definition of an ‘‘endangered species’’ or 

a ‘‘threatened species.’’ In determining 

whether a species meets either 

definition, we must evaluate all 

identified threats by considering the 

species’ expected response and the 

effects of the threats—in light of those 

actions and conditions that will 

ameliorate the threats—on an 

individual, population, and species 

level. We evaluate each threat and its 

expected effects on the species, then 

analyze the cumulative effect of all of 

the threats on the species as a whole. 

We also consider the cumulative effect 

of the threats in light of those actions 

and conditions that will have positive 


khammond on DSK9W7S144PROD with PROPOSALS