`[Federal Register Volume 90, Number 9 (Wednesday, January 15, 2025)]
[Notices]
[Pages 3830-3859]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2025-00133]


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ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-OW-2024-0456; FRL-10774-01-OW]


Announcement of Preliminary Regulatory Determinations for 
Contaminants on the Fifth Drinking Water Contaminant Candidate List

AGENCY: Environmental Protection Agency (EPA).

ACTION: Request for public comment.

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SUMMARY: The Safe Drinking Water Act (SDWA), as amended in 1996, 
requires that the U.S. Environmental Protection Agency (EPA) determine 
whether to regulate at least five unregulated contaminants every five 
years. The decision to regulate or not to regulate a contaminant is 
known as a regulatory determination. In most cases, the contaminants 
chosen for regulatory determination are selected from the most recent 
Contaminant Candidate List (CCL), which the SDWA requires the EPA to 
publish every five years. This document presents the preliminary 
regulatory determinations and supporting rationale for contaminants 
listed on the EPA's fifth CCL (CCL 5). Since the fourth round of 
regulatory determinations was published in March 2021, the EPA has made 
determinations to regulate per- and polyfluoroalkyl substances (PFAS), 
including individual determinations for three PFAS: perfluorononanoic 
acid (PFNA), perfluorohexanesulfonic acid (PFHxS), hexafluoropropylene 
oxide dimer acid and its ammonium salt (HFPO-DA, also known as GenX or 
GenX chemicals); and mixtures including two or more of these three PFAS 
and perfluorobutanesulfonic acid (PFBS). In April 2024, the agency 
issued a final National Primary Drinking Water Regulation that includes 
these four PFAS as well as perfluorooctanoic acid (PFOA) and 
perfluorooctanesulfonic acid (PFOS). In this Federal Register Notice 
(FRN), the EPA is making preliminary determinations not to regulate 
nine additional contaminants from CCL 5: 2-aminotoluene, 
cylindrospermopsin, ethoprop, microcystins, molybdenum, permethrin, 
profenofos, tebuconazole and tribufos. The EPA requests public comment 
on these preliminary determinations and other aspects of this FRN. The 
EPA also presents updates on additional contaminants from CCL 5, as 
well as on some of those that have been considered in previous rounds 
of regulatory determinations and for which the EPA has not yet made a 
regulatory determination. The agency is also presenting and requesting 
comment on the process and analyses used for this round of regulatory 
determinations (i.e., RD 5), the supporting information, and the 
rationale used to make these preliminary decisions.

DATES: Comments must be received on or before March 17, 2025.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OW-2024-0456, by any of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov/ 
(our preferred method). Follow the online instructions for submitting 
comments.
     Mail: Water Docket, Environmental Protection Agency, Mail 
Code: [28221T], 1200 Pennsylvania Ave. NW, Washington, DC 20460.
     Hand Delivery: EPA Docket Center, [EPA/DC] EPA West, Room 
3334, 1301 Constitution Ave. NW, Washington DC. Such deliveries are 
only accepted during the Docket's normal hours of operation and special 
arrangements should be made for deliveries of boxed information.
    Instructions: All submissions received must include the Docket ID 
No. for this rulemaking. Comments received may be posted without change 
to https://www.regulations.gov/, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the rulemaking process, see the ``Written Comments'' 
heading of the SUPPLEMENTARY INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: George Gardenier, Standards and Risk 
Management Division, Office of Ground Water and Drinking Water, MC: 
4607M, Environmental Protection Agency, 1200 Pennsylvania Ave. NW, 
Washington, DC 20460; telephone number: (202) 564-3333; email address: 
[email protected].

SUPPLEMENTARY INFORMATION:

I. General Information

A. Written Comments

    Submit your comments, identified by Docket ID No. EPA-HQ-OW-2024-
0456, at https://www.regulations.gov (our preferred method), or the 
other methods identified in the ADDRESSES section. Once submitted, 
comments cannot be edited or removed from the docket. The EPA may 
publish any comment received to its public docket. Do not submit 
electronically any information you consider to be Confidential Business 
Information (CBI) or other information whose disclosure is restricted 
by statute. Multimedia submissions (audio, video, etc.) must be 
accompanied by a written comment. The written comment is considered the 
official comment and should include discussion of all points you wish 
to make. The EPA will generally not consider comments or comment 
contents located outside of the primary submission (i.e., on the web, 
cloud or other file sharing system). For additional submission methods, 
the full EPA public comment policy, information about CBI or multimedia 
submissions, and general guidance on making effective comments, please 
visit https://www.epa.gov/dockets/commenting-epa-dockets.
    When submitting comments, remember to:
     Identify the rulemaking by docket number and other 
identifying information (subject heading, Federal Register date and 
page number).
     Explain why you agree or disagree and suggest 
alternatives.
     Describe any assumptions and provide any technical 
information and data that you used.
     Provide specific examples to illustrate your concerns and 
suggest alternatives.
     Explain your views as clearly as possible.

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     Make sure to submit your comments by the comment period 
deadline identified.

B. Does this action apply to me?

    Neither these preliminary regulatory determinations nor the final 
regulatory determinations, when published, impose any requirements on 
anyone. Instead, this action notifies interested parties of the EPA's 
preliminary regulatory determinations for nine unregulated contaminants 
for comment.

Abbreviations Used in This Document

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            Abbreviation                           Meaning
------------------------------------------------------------------------
AChE...............................  Acetylcholinesterase.
ADAF...............................  Age Dependent Adjustment Factor.
AM.................................  Assessment Monitoring.
ATSDR..............................  Agency for Toxic Substances and
                                      Disease Registry.
ATSDR MRL..........................  ATSDR Minimal Risk Level.
AWIA...............................  America's Water Infrastructure Act.
BAT................................  Best Available Technology.
BMD................................  Benchmark Dose.
BMDL10.............................  Lower 95% Confidence Limit on the
                                      Benchmark Dose Level Associated
                                      with a 10% Response.
BMDL1SD............................  Lower 95% Confidence Limit on the
                                      Benchmark Dose Level Associated
                                      with a Difference of One Standard
                                      Deviation from Controls.
BW.................................  Body Weight.
CBI................................  Confidential Business Information.
CCL................................  Contaminant Candidate List.
CCL 1..............................  First Contaminant Candidate List.
CCL 2..............................  Second Contaminant Candidate List.
CCL 3..............................  Third Contaminant Candidate List.
CCL 4..............................  Fourth Contaminant Candidate List.
CCL 5..............................  Fifth Contaminant Candidate List.
CCR................................  Consumer Confidence Report.
CDR................................  Chemical Data Reporting.
ChE................................  Cholinesterase.
CRL................................  Cancer Risk Level.
CSF................................  Cancer Slope Factor.
CWA................................  Clean Water Act.
CWS................................  Community Water System.
CWSS...............................  Community Water System Survey.
DBP................................  Disinfection Byproduct.
DDE................................  1,1-Dichloro-2,2-bis(p-
                                      chlorophenyl)ethylene.
DWI................................  Drinking Water Intake.
DWI-BW.............................  Drinking Water Intake Adjusted for
                                      Body Weight.
EF.................................  Exposure Factor.
EPA................................  U. S. Environmental Protection
                                      Agency.
EPTC...............................  S-Ethyl dipropylthiocarbamate.
FIFRA..............................  Federal Insecticide, Fungicide and
                                      Rodenticide Act.
FQPA...............................  Food Quality Protection Act.
FR.................................  Federal Register.
FRN................................  Federal Register Notice.
Gen X..............................  Gen X Chemicals (i.e., HFPO dimer
                                      acid and its ammonium salt), also
                                      known as (2,3,3,3-tetrafluoro-2-
                                      (1,1,2,2,3,3,3-
                                      heptafluoropropoxy)propanoic acid
                                      (CASRN 13252-13-6) or
                                      hexafluoropropylene oxide (HFPO)
                                      dimer acid (HFPO-DA) and 2,3,3,3-
                                      tetrafluoro-2-(1,1,2,2,3,3,3-
                                      heptafluoropropoxy)propanoate
                                      (CASRN 62037-80-3) or HFPO-DA
                                      dimer acid and its ammonium salt).
GWUDI..............................  Groundwater Under the Direct
                                      Influence of Surface Water.
HA.................................  Health Advisory.
HAA5...............................  Sum of Five Haloacetic Acids.
HAB................................  Harmful Algal Bloom.
HCl................................  Hydrochloride.
HED................................  Health Effects Division.
HESD...............................  Health Effects Support Document.
HFPO-DA............................  Hexafluoropropylene Oxide Dimer
                                      Acid.
HHRA...............................  Human Health Risk Assessment.
HRL................................  Health Reference Level.
HRRCA..............................  Health Risk Reduction Cost
                                      Analysis.
IUR................................  Inventory Update Reporting.
Koc................................  Organic Carbon Partitioning
                                      Coefficient.
Kow................................  Octanol-Water Partitioning
                                      Coefficient.
LOAEL..............................  Lowest Observed Adverse Effect
                                      Level.
MAC................................  Maximum Acceptable Concentration.
MCL................................  Maximum Contaminant Level.
MCLG...............................  Maximum Contaminant Level Goal.
MOA................................  Mode of Action.
MRL................................  Minimum Reporting Level.
NAS................................  National Academy of Sciences.
NAWQA..............................  National Water-Quality Assessment.
NDBA...............................  N-Nitrosodi-n-butylamine.
NDEA...............................  N-Nitrosodiethylamine.
NDMA...............................  N-Nitrosodimethylamine.

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NDPA...............................  N-Nitroso-di-n-propylamine.
NPYR...............................  N-Nitrosopyrrolidine.
NDWAC..............................  National Drinking Water Advisory
                                      Council.
NIRS...............................  National Inorganics and
                                      Radionuclides Survey.
NOAEL..............................  No Observed Adverse Effect Level.
NPDWR..............................  National Primary Drinking Water
                                      Regulation.
NRC................................  National Research Council.
NRDC...............................  Natural Resources Defense Council.
NWIS...............................  National Water Information System.
OPP................................  Office of Pesticides Program.
OW.................................  Office of Water.
PAD................................  Population-Adjusted Dose.
PCCL...............................  Preliminary Contaminant Candidate
                                      List.
PDP................................  Pesticide Data Program.
PFAS...............................  Per- and Polyfluoroalkyl
                                      Substances.
PFBA...............................  Perfluorobutanoic acid.
PFBS...............................  Perfluorobutanesulfonic acid.
PFHxS..............................  Perfluorohexanesulfonic acid.
PFNA...............................  Perfluorononanoic acid.
PFOA...............................  Perfluorooctanoic acid.
PFOS...............................  Perfluorooctanesulfonic acid.
PMP................................  Pilot Monitoring Program.
PND................................  Postnatal Day.
POD................................  Point of Departure.
PPRTV..............................  Provisional Peer-Reviewed Toxicity
                                      Value.
PST................................  Pre-Screen Testing.
PWS................................  Public Water System.
RBC................................  Red Blood Cell.
RD 1...............................  Regulatory Determination 1.
RD 2...............................  Regulatory Determination 2.
RD 3...............................  Regulatory Determination 3.
RD 4...............................  Regulatory Determination 4.
RD 5...............................  Regulatory Determination 5.
RDX................................  Royal Demolition eXplosive.
RED................................  Reregistration Eligibility
                                      Decision.
RfD................................  Reference Dose.
RSC................................  Relative Source Contribution.
RUP................................  Restricted Use Pesticide.
SDWA...............................  Safe Drinking Water Act.
SS.................................  Screening Survey.
SSCT...............................  Small System Compliance Technology.
STORET.............................  Storage and Retrieval Data System.
TCP................................  Trichloropropane.
TDI................................  Tolerable Daily Intake.
TRI................................  Toxics Release Inventory.
TSCA...............................  Toxic Substances Control Act.
TT.................................  Treatment Technique.
TTHM...............................  Total Trihalomethanes.
UA.................................  Unit Adjustment Factor.
UCM................................  Unregulated Contaminant Monitoring.
UCMR...............................  Unregulated Contaminant Monitoring
                                      Rule.
UCMR 1.............................  First Unregulated Contaminant
                                      Monitoring Rule.
UCMR 2.............................  Second Unregulated Contaminant
                                      Monitoring Rule.
UCMR 3.............................  Third Unregulated Contaminant
                                      Monitoring Rule.
UCMR 4.............................  Fourth Unregulated Contaminant
                                      Monitoring Rule.
UCMR 5.............................  Fifth Unregulated Contaminant
                                      Monitoring Rule.
UF.................................  Uncertainty Factor.
UFA................................  Interspecies Uncertainty Factor.
UFD................................  Database Uncertainty Factor.
UFH................................  Intraspecies Uncertainty Factor.
UFL................................  LOAEL-to-NOAEL Extrapolation
                                      Uncertainty Factor.
UFS................................  Subchronic-to Chronic Exposure
                                      Duration Uncertainty Factor.
USDA...............................  United States Department of
                                      Agriculture.
USEPA..............................  United States Environmental
                                      Protection Agency.
USGS...............................  United States Geological Survey.
WQP................................  Water Quality Portal.
WQX................................  Water Quality Exchange.
------------------------------------------------------------------------

Table of Contents

I. General Information
    A. Written Comments
    B. Does this action apply to me?
II. Purpose and Background
    A. What is the purpose of this action?
    B. Background on the CCL and Regulatory Determinations
    1. Statutory Requirements for CCL and Regulatory Determinations

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    2. The First Contaminant Candidate List (CCL 1) and Regulatory 
Determination (RD 1)
    3. The Second Contaminant Candidate List (CCL 2) and Regulatory 
Determination (RD 2)
    4. The Third Contaminant Candidate List (CCL 3) and Regulatory 
Determination (RD 3)
    5. The Fourth Contaminant Candidate List (CCL 4) and Regulatory 
Determination (RD 4)
    6. The Fifth Contaminant Candidate List (CCL 5)
III. Approach and Overall Outcomes for RD 5
    A. Summary of the Approach and Overall Outcomes for RD 5
    1. Phase 1 (Data Availability Phase)
    2. Phase 2 (Data Evaluation Phase)
    3. Phase 3 (Regulatory Determination Assessment Phase)
    B. Supporting Documentation for the EPA's Preliminary 
Determination
    C. Analyses Used To Support the Preliminary Regulatory 
Determinations
    1. Evaluation of Contaminant Occurrence and Exposure
IV. Contaminant-Specific Discussions for the RD 5 Preliminary 
Determination
    A. Summary of the Preliminary Regulatory Determinations
    B. Contaminant Profiles
    1. 2-Aminotoluene
    2. Cylindrospermopsin
    3. Ethoprop
    4. Microcystins
    5. Molybdenum
    6. Permethrin
    7. Profenofos
    8. Tebuconazole
    9. Tribufos
V. Status of the Agency's Evaluation of 1,2,3-Trichloropropane, 1,4-
Dioxane, Manganese, Quinoline and Strontium
    A. Ongoing Evaluation of Additional Phase 3 Contaminants
    B. Phase 3 Contaminant Updates
    1. 1,2,3-Trichloropropane
    2. 1,4-Dioxane
    3. Manganese
    4. Quinoline
    5. Strontium
VI. The EPA's Request for Comments and Next Steps
VII. References

II. Purpose and Background

A. What is the purpose of this action?

    The purpose of this action is to request comment on the EPA's 
preliminary determinations not to regulate the following nine 
contaminants under the Safe Drinking Water Act: 2-aminotoluene, 
cylindrospermopsin, ethoprop, microcystins, molybdenum, permethrin, 
profenofos, tebuconazole and tribufos. As required by the SDWA, the EPA 
is seeking comment on these preliminary determinations. The agency is 
also presenting and requesting comment on the process and analyses used 
for this round of regulatory determinations (i.e., RD 5), the 
supporting information, and the rationale used to make these 
preliminary decisions. It should be noted that the analyses associated 
with a regulatory determination are distinct from the more detailed 
analyses required to develop a National Primary Drinking Water 
Regulation (NPDWR).

B. Background on the CCL and Regulatory Determinations

1. Statutory Requirements for CCL and Regulatory Determinations
    Section 1412(b)(1)(B)(i) of the SDWA requires the EPA to publish 
the CCL every five years after public notice and an opportunity to 
comment. The CCL is a list of contaminants which are not subject to any 
proposed or promulgated NPDWRs but are known or anticipated to occur in 
public water systems (PWSs) and may require regulation under the SDWA. 
SDWA section 1412(b)(1)(B)(ii) directs the EPA to determine, whether to 
regulate at least five contaminants from the CCL every five years. 
Under section 1412(b)(1)(A) of SDWA, the EPA may regulate a contaminant 
in drinking water if the Administrator determines that:
    (i) the contaminant may have an adverse effect on the health of 
persons;
    (ii) the contaminant is known to occur or there is substantial 
likelihood that the contaminant will occur in PWSs with a frequency and 
at levels of public health concern; and
    (iii) in the sole judgment of the Administrator, regulation of such 
contaminant presents a meaningful opportunity for health risk reduction 
for persons served by PWSs.
    SDWA 1412(b)(1)(C) requires that the Administrator prioritize 
selection of contaminants that present the greatest public health 
concern. The Administrator, in making such selections, shall take into 
consideration, among other factors of public health concern, the effect 
of such contaminants upon subgroups that comprise a meaningful portion 
of the general population (such as infants, children, pregnant women, 
the elderly, individuals with a history of serious illness or other 
subpopulations) that are identifiable as being at greater risk of 
adverse health effects due to exposure to contaminants in drinking 
water than the general population.
    If the EPA determines that these three statutory criteria are met 
and makes a final determination to regulate a contaminant (i.e., a 
positive determination), the agency must publish a proposed Maximum 
Contaminant Level Goal (MCLG) \1\ and NPDWR \2\ within 24 months. After 
a proposal, the agency must publish a final MCLG and promulgate a final 
NPDWR (SDWA section 1412(b)(1)(E)) within 18 months.\3\ The EPA may 
also develop regulatory determinations and associated rulemakings 
outside of the SDWA mandated process.
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    \1\ An MCLG is the maximum level of a contaminant in drinking 
water at which no known or anticipated adverse effect on the health 
of persons would occur, and which allows an adequate margin of 
safety. MCLGs are non-enforceable health goals. (40 CFR 141.2; 42 
U.S.C. 300g-1)
    \2\ An NPDWR is a legally enforceable standard that applies to 
public water systems. An NPDWR sets a legal limit (called a maximum 
contaminant level or MCL) or specifies a certain treatment technique 
(TT) for public water systems for a specific contaminant or group of 
contaminants. The MCL is the highest level of a contaminant that is 
allowed in drinking water and is set as close to the MCLG as 
feasible using the best available treatment technology and taking 
cost into consideration.
    \3\ The statute authorizes a nine-month extension of this 
promulgation date.
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2. The First Contaminant Candidate List (CCL 1) and Regulatory 
Determination (RD 1)
    The EPA published the final CCL 1, which contained 60 chemical and 
microbiological contaminants, in the Federal Register (FR) on March 2, 
1998 (63 FR 10273; USEPA, 1998). The agency published the final 
regulatory determinations for nine of the 60 CCL 1 contaminants in the 
FR on July 18, 2003 (68 FR 42898; USEPA, 2003). The agency determined 
not to regulate the following nine contaminants with NPDWRs: 
Acanthamoeba, aldrin, dieldrin, hexachlorobutadiene, manganese, 
metribuzin, naphthalene, sodium and sulfate. The agency posted 
information about Acanthamoeba \4\ on the EPA's website and issued 
health advisories (HAs) \5\ for manganese, sodium and sulfate.
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    \4\ Consumer information about Acanthamoeba for people who wear 
contact lenses can be found at http://water.epa.gov/action/advisories/acanthamoeba/index.cfm.
    \5\ Health advisories provide information on contaminants that 
can cause human health effects and are known or anticipated to occur 
in drinking water. The EPA's health advisories are non-enforceable 
and provide technical guidance to states agencies and other public 
health officials on health effects, analytical methodologies and 
treatment technologies associated with drinking water contamination. 
Health advisories can be found at http://water.epa.gov/drink/standards/hascience.cfm. See also SDWA Section 1412(b)(1)(F).
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3. The Second Contaminant Candidate List (CCL 2) and Regulatory 
Determination (RD 2)
    The agency published the final CCL 2 in the FR on February 24, 2005 
(70 FR 9071; USEPA, 2005a) and carried

[[Page 3834]]

forward the 51 remaining chemical and microbial contaminants listed on 
CCL 1. The agency published the final regulatory determinations for 11 
of the 51 CCL 2 contaminants in the FR on July 30, 2008 (73 FR 44251; 
USEPA, 2008a). The agency determined not to regulate the following 11 
contaminants: boron, the dacthal mono- and di-acid degradates, 1,1-
dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), 1,3-dichloropropene 
(Telone), 2,4-dinitrotoluene, 2,6-dinitrotoluene, S-ethyl 
dipropylthiocarbamate (EPTC), fonofos, terbacil and 1,1,2,2-
tetrachloroethane. The agency issued new or updated HAs for boron, 
dacthal degradates, 2,4-dinitrotoluene, 2,6-dinitrotoluene and 1,1,2,2-
tetrachloroethane.
4. The Third Contaminant Candidate List (CCL 3) and Regulatory 
Determination (RD 3)
    The agency published the final CCL 3, which listed 116 
contaminants, in the FR on October 8, 2009 (74 FR 51850; USEPA, 2009a). 
In developing CCL 3, the EPA improved and built upon the process that 
was used for CCL 1 and CCL 2. The CCL 3 process was based on 
substantial expert input and recommendations from the National Academy 
of Sciences' (NAS) National Research Council (NRC) and the National 
Drinking Water Advisory Council (NDWAC) as well as input from the 
public. Based on these consultations and input, the EPA developed a 
multi-step process to select candidates for a final CCL, which included 
the following key steps:
    (a) Building a broad universe;
    (b) Screening the universe to select a Preliminary CCL (PCCL); and
    (c) Classification of PCCL chemicals to select a CCL.
    The agency published its preliminary regulatory determinations for 
contaminants listed on the CCL 3 in the FR on October 20, 2014 (79 FR 
62715; USEPA, 2014). In that notice, the EPA made preliminary 
determinations for five of the 116 contaminants listed on the CCL 3, 
including a preliminary positive determination for strontium and 
preliminary negative determinations for dimethoate, 1,3-dinitrobenzene, 
terbufos and terbufos sulfone. On January 4, 2016 (81 FR 13; USEPA, 
2016a), the EPA finalized the negative determinations for dimethoate, 
1,3-dinitrobenzene, terbufos and terbufos sulfone. The EPA announced a 
delay in issuing a final regulatory determination on strontium in order 
to consider additional data. Additional discussion on strontium is 
provided in section V of this document.
    The EPA also published an off-cycle final determination to regulate 
one CCL 3 contaminant, perchlorate, on February 11, 2011 (76 FR 7762; 
USEPA, 2011) during the RD 3 cycle (bringing the total number of final 
determinations to five).
5. The Fourth Contaminant Candidate List (CCL 4) and Regulatory 
Determination (RD 4)
    The final CCL 4 was published on November 17, 2016 (81 FR 81099; 
USEPA, 2016b). The final CCL 4 consisted of 97 chemicals or chemical 
groups and 12 microbiological contaminants. Most CCL 4 contaminants 
were carried over from CCL 3. The EPA added two contaminants (manganese 
and nonylphenol) to the CCL 4 list based on nominations. The EPA 
removed from the list those CCL 3 contaminants that had been subject to 
recent preliminary or final regulatory determinations (perchlorate, 
dimethoate, 1,3-dinitrobenzene, terbufos, terbufos sulfone and 
strontium) and three pesticides with cancelled registrations 
(disulfoton, fenamiphos and molinate).
    The EPA published its preliminary determinations for the fourth CCL 
in the Federal Register on March 10, 2020 (85 FR 14098; USEPA, 2020a). 
In that notice, the EPA made determinations for eight of the 109 
contaminants on the CCL 4. The EPA determined to regulate two PFAS, 
perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), 
and determined not to regulate six additional contaminants: 1,1-
dichloroethane, acetochlor, methyl bromide, metolachlor, nitrobenzene 
and Royal Demolition eXplosive (RDX). The EPA published its final 
regulatory determinations for these contaminants on March 3, 2021 (86 
FR 12272; USEPA, 2021a).
6. The Fifth Contaminant Candidate List (CCL 5)
    The final CCL 5 was published on November 14, 2022 (87 FR 68060; 
USEPA, 2022a). The final CCL 5 consists of 66 chemicals, 3 chemical 
groups (cyanotoxins, disinfection byproducts (DBPs) and PFAS) and 12 
microbial contaminants. The CCL 5 was developed based on the existing 
framework used for CCL 3 and CCL 4. For CCL 5, the EPA updated the CCL 
process to consider a larger number of contaminants, enhance 
transparency in the data evaluation, and improve efficiency of 
information transfer to other SDWA processes, such as regulatory 
determinations.

III. Approach and Overall Outcomes for RD 5

    This section describes (a) the approach the EPA used to identify 
and evaluate contaminants for RD 5 along with the overall outcome of 
applying this approach, (b) the supporting RD 5 documentation and (c) 
the technical analyses and sources of health and occurrence 
information.

A. Summary of the Approach and Overall Outcomes for RD 5

    The approach taken under RD 5 is similar to that used in previous 
rounds of regulatory determination and formalized in a written protocol 
under RD 3. The Regulatory Determination 5 Protocol, found in Appendix 
B of the Regulatory Determination 5 Support Document (USEPA, 2024b), 
like the RD 3 and RD 4 Protocols, describes a three-phase process. The 
three phases are: (1) the Data Availability Phase, (2) the Data 
Evaluation Phase and (3) the Regulatory Determination Assessment Phase. 
Figure 1 provides an overview of the process the EPA uses to identify 
which CCL 5 contaminants are candidates for regulatory determinations 
and the SDWA statutory criteria considered in making the regulatory 
determinations. For more detailed information on the three phases of 
the RD 5 process, refer to the RD 5 Protocol in Appendix B of the 
Regulatory Determination 5 Support Document (USEPA, 2024b).
BILLING CODE 6560-50-P

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[GRAPHIC] [TIFF OMITTED] TN15JA25.049

1. Phase 1 (Data Availability Phase)
    In Phase 1, the Data Availability Phase, the agency identifies 
contaminants that have sufficient health and occurrence data to proceed 
to Phase 2 and be included on a ``short list'' for further evaluation. 
SDWA 1412(b)(1)(B)(ii)(II) requires that the EPA consider the best 
available public health information in making the regulatory 
determination.
    To identify contaminant health effects data that are sufficient to 
make a regulatory determination regarding potential adverse health 
effect(s), the agency considers whether an EPA health assessment or an 
externally peer-reviewed health assessment from another agency is 
available, from which a health reference level (HRL) \6\ sufficient to 
inform a regulatory determination can be derived. See section III.C.1 
of this document for information about how HRLs are derived. To 
identify ``qualifying'' health assessments, the EPA conducted a 
systematic search in January 2023 for the EPA and other authoritative 
sources of human health effects assessments for each drinking water 
chemical contaminant on CCL 5. Health assessments are considered 
qualifying if they (1) derived one or more toxicity values (e.g., oral 
reference value or oral cancer slope factor [CSF]) based on the best 
available science; (2) underwent a documented peer-review process; (3) 
are publicly available and final; (4) were developed using human health 
risk assessments methods that are comparable to current EPA human 
health risk assessment principles and approaches (e.g., a weight of 
evidence approach); and (5) are produced from an authoritative source 
that routinely develops health assessments (e.g., Agency for Toxic 
Substances and Disease Registry [ATSDR]). If a qualifying health 
assessment is not available for a contaminant, the contaminant will not 
proceed to Phase 2. See section B.5.1.1 in Appendix B of the Regulatory 
Determination 5 Support Document for a list of sources of Health 
Effects Assessments (USEPA, 2024b).
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    \6\ A health reference level (HRL) is a health-based 
concentration against which the agency evaluates occurrence data 
when making decisions about preliminary regulatory determinations. 
An HRL is not a final determination on establishing a protective 
level of a contaminant in drinking water for a particular 
population; it is derived prior to development of a complete health 
and exposure assessment.
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    After identifying the qualifying peer-reviewed health assessments 
for a chemical, the EPA followed a structured and transparent process 
to select the assessment(s) for both cancer and noncancer HRL 
derivation. The process included expert evaluations applying specific 
criteria. These criteria are designed to identify the assessment 
relevant to drinking water that was developed using comparable 
approaches to the EPA human health risk assessment methods and based on 
the best available science. The EPA used the results from the expert 
evaluations to select the health assessment used to derive the HRL for 
the chemical. In addition, the EPA applied expert judgement when 
evaluating a set of assessments for a given contaminant because certain 
health assessments and chemicals can present unique challenges. See 
section B.5.1.2 in Appendix B of the Regulatory Determination 5 Support 
Document for

[[Page 3836]]

the decision-logic that was applied for all RD 5 chemicals (USEPA, 
2024b).
    To identify contaminant occurrence data that are sufficient to 
evaluate with respect to the frequency and level of occurrence in PWSs, 
the agency considers nationally representative finished drinking water 
data (samples collected after the water undergoes treatment) when 
available for making regulatory determinations. The following sources, 
administered or overseen by the EPA, include finished drinking water 
occurrence data that are considered nationally representative: (a) the 
fourth Unregulated Contaminant Monitoring Rule (UCMR 4); (b) the third 
Unregulated Contaminant Monitoring Rule (UCMR 3); (c) the second 
Unregulated Contaminant Monitoring Rule (UCMR 2); (d) the first 
Unregulated Contaminant Monitoring Rule (UCMR 1); (e) the Unregulated 
Contaminant Monitoring (UCM) program; and (f) the National Inorganics 
and Radionuclides Survey (NIRS).\7\ If a contaminant has occurrence 
data from a nationally representative source, it passes the Occurrence 
Data Availability Assessment.
---------------------------------------------------------------------------

    \7\ Specific types of UCMR monitoring (e.g., assessment 
monitoring and sometimes the screening survey) are considered 
nationally representative. These are described further in Section 
III.C.2.a.1 of this notice.
---------------------------------------------------------------------------

    If nationally representative drinking water data are not available, 
the EPA identifies and evaluates other sources of finished water data, 
which may include other national assessments, regional data, state data 
and more localized finished water assessments. For more information on 
sources of occurrence that may be evaluated during the regulatory 
determination process, please refer to Chapter 2 of the Regulatory 
Determination 5 Support Document (USEPA, 2024b).
    In Phase 1, the agency assesses whether the non-nationally 
representative finished water occurrence data show at least one 
detection at levels >\1/2\ the HRL \8\ for the critical endpoint. If a 
contaminant without nationally representative finished water occurrence 
data has non-nationally representative finished water occurrence data 
showing at least one detection > \1/2\ HRL, the contaminant passes the 
Occurrence Data Availability Assessment. While there may be robust non-
national data available for certain contaminants which can demonstrate 
substantial likelihood of occurrence at a frequency and level of public 
health concern (e.g., see PFAS Federal Register Notice section III.C), 
the EPA does not rely on non-national data alone to determine that 
there is no or low potential for occurrence in the nation's PWSs 
because these data tend to be limited in scope and do not provide a 
sufficiently accurate picture of occurrence to support a negative 
determination.
---------------------------------------------------------------------------

    \8\ Note that the \1/2\ HRL threshold is based on a 
recommendation from the NDWAC working grouping that provided 
recommendations on the first regulatory determination effort (USEPA, 
2000a).
---------------------------------------------------------------------------

    If a widely available analytical method does not exist for 
monitoring occurrence of a contaminant in water, the contaminant will 
not be a viable candidate for regulation with a Maximum Contaminant 
Level (MCL). In certain limited cases, a contaminant's occurrence data 
may have been gathered using a specialized or experimental method that 
is not in general use. In the Analytical Methods Availability 
Assessment, the EPA determines for each contaminant whether a widely 
available analytical method for monitoring, which employs technology 
that is commonly in use at numerous drinking water laboratories, 
exists. If a widely available analytical method exists, the contaminant 
passes the Analytical Methods Availability Assessment. If a widely 
available analytical method does not exist, the EPA may still advance 
the contaminant to Phase 2 if the agency determines that indicator or 
surrogate monitoring, or use of a treatment technique (TT), could allow 
for effective regulation and there is evidence of occurrence.
    The EPA also may consider issuing a regulatory determination for 
contaminant groups and/or mixtures that are a contaminant. The EPA has 
made final regulatory determinations for contaminant mixtures and 
regulated certain contaminants in drinking water collectively. For 
example, the EPA made a determination to regulate mixture combinations. 
containing two or more of the following PFAS: PFHxS PFNA, HFPO-DA (GenX 
chemicals), and PFBS. Additionally, the EPA has also established NPDWRs 
for groups of contaminants (e.g., DBPs; for total trihalomethanes 
[TTHMs] and the sum of five haloacetic acids [HAA5], as well as 
radionuclides). After conducting the health and occurrence data 
availability assessments, the agency identifies those contaminants and 
contaminant groups that meet the following Phase 1 data availability 
criteria:
    (a) An EPA health assessment or an externally peer-reviewed health 
assessment from another agency that conforms with the current EPA 
guidelines is available, from which an HRL can be derived;
    (b) Either nationally representative finished drinking water 
occurrence data are available or other finished water occurrence data 
show occurrence at levels >\1/2\ the HRL; and
    (c) A widely available analytical method for monitoring is 
available.
    If a contaminant or group meets these three criteria, it is placed 
on a ``short list'' and proceeds to Phase 2. After evaluating the 81 
CCL 5 contaminants/groups of contaminants and strontium in Phase 1, the 
agency identified 35 contaminants to evaluate further in Phase 2 
(contaminants listed in Table 1 of this document). PFHxS, PFNA and 
HFPO-DA received final positive regulatory determinations in 
conjunction with the development of the PFAS NPDWR and therefore are 
not included in the contaminants considered here as part of the 
preliminary RD 5. For RD 5, the EPA set January 31, 2023 as a cutoff 
date for selection of health assessments. Health assessments published 
after this date were not considered in RD 5.

        Table 1--Contaminants Proceeding From Phase 1 to Phase 2
------------------------------------------------------------------------
 
-------------------------------------------------------------------------
1,2,3-Trichloropropane.
1,2,4-Trimethylbenzene.
1,4-Dioxane.
2-Aminotoluene (o-Toluidine).
alpha-Hexachlorocyclohexane.
Boron.
Carbaryl.
Chlorate.
Cobalt.
Cylindrospermopsin.
Dieldrin.
Dimethoate.
Diuron.
Ethoprop.
Legionella pneumophila.
Lithium.
Manganese.
Methomyl.
Microcystins.
Molybdenum.
N-Nitrosodi-n-butylamine (NDBA).
N-Nitrosodiethylamine (NDEA).
N-Nitrosodimethylamine (NDMA).
N-Nitroso-di-n-propylamine (NDPA).
N-Nitrosopyrrolidine (NPYR).
Perfluorobutanoic acid (PFBA).
Permethrin.
Profenofos.
Propachlor.
Quinoline.
Strontium.
Tebuconazole.
Terbufos.
Tribufos.
Vanadium.
------------------------------------------------------------------------

    The remaining CCL 5 contaminants listed in Chapter 2 of the 
Regulatory Determination 5 Support Document (USEPA, 2024b) did not meet 
one or

[[Page 3837]]

more of the Phase 1 data availability criteria described earlier in 
this section and were not considered further for RD 5.
2. Phase 2 (Data Evaluation Phase)
(a) Evaluation of Adverse Health Effects
    This section describes the approach for deriving the HRL for the 
contaminants under consideration for regulatory determinations. HRLs 
are health-based drinking water concentrations against which the EPA 
evaluates occurrence data to determine if contaminants occur at levels 
of potential public health concern in drinking water. HRLs are not 
final values for establishing a protective level of a contaminant in 
drinking water for any particular population and are derived prior to 
the development of a complete health and exposure assessment for 
regulatory determination. More specific information about the potential 
for adverse health effects for each contaminant is presented in section 
IV.B of this action.
(i) Derivation of an HRL
    There are two general approaches to the derivation of an HRL. One 
approach is used for chemicals with a threshold dose-response. For 
noncancer effects and non-linear carcinogens, HRLs are obtained by 
dividing the reference dose (RfD) (or equivalent, such as an ATSDR 
minimal risk level) by an exposure factor (EF) (i.e., drinking water 
intake rate adjusted for body weight [DWI-BW]) relevant to the target 
population and critical effect (USEPA, 2019a) and multiplying by a 20% 
relative source contribution (RSC) (USEPA, 2000a). Consistent with HRL 
development for previous regulatory determinations, HRLs derived for RD 
5 are rounded to one significant figure. The RSC is used to account for 
exposure via non-drinking water routes in deriving health-based 
drinking water concentrations for contaminants with threshold effects 
(noncarcinogens and nonlinear carcinogens). A 20% RSC is used for all 
RD 5 contaminants, consistent with other regulatory determination 
cycles (USEPA, 2021a), to derive the noncancer HRL because (1) HRLs are 
developed prior to completing the exposure assessment; and (2) a 20% 
RSC is the lowest that is applied for deriving health-based drinking 
water concentrations, therefore resulting in the most health protective 
HRL (USEPA, 2000a). Should a contaminant proceed to a NPDWR, a full 
exposure analysis is conducted and an RSC is derived following the 
Exposure Decision Tree approach described in the Methodology for 
Deriving Ambient Water Quality Criteria for the Protection of Human 
Health (USEPA, 2000a).
    HRLs for contaminants with a threshold dose-response (non-cancer 
and nonlinear cancer endpoints) are calculated as follows:
[GRAPHIC] [TIFF OMITTED] TN15JA25.050

    The second general approach is used for chemicals that exhibit a 
linear, non-threshold response to dose as is typical of carcinogens. 
For this approach, the HRL is calculated for one-in-a-million 
(10-6) cancer risk expressed as a drinking water 
concentration. HRLs for contaminants with a linear dose-response 
(typically cancer endpoints) are calculated as follows:
[GRAPHIC] [TIFF OMITTED] TN15JA25.051

    In this second approach, when a carcinogen with a linear dose-
response has a known mutagenic mode of action (MOA), the EPA follows 
the Cancer Guidelines (USEPA, 2005b) when deriving HRLs (USEPA, 2024b). 
For carcinogens with a MOA, the 2005 Cancer Guidelines recommend 
consideration of increased risk due to early-life exposure. When 
chemical-specific data to quantify the increased risk from 
developmental exposure are lacking, Age Dependent Adjustment Factors 
(ADAFs) are applied. The recommended ADAFs are a 10-fold adjustment for 
exposure during the interval from birth to <2 years (infant and 
toddler); a 3-fold adjustment for exposure from 2 to <16 years 
(childhood and adolescence); and no additional adjustment for exposures 
for 16 years to 70 years of age. In cases where the MOA cannot be 
determined, the default low-dose linear extrapolation approach without 
ADAFs (described earlier in this section) is used.
    HRLs for carcinogenic contaminants with a known mutagenic MOA are 
calculated as follows:
[GRAPHIC] [TIFF OMITTED] TN15JA25.052

    The following terms are used in these questions:

    HRL = Health Reference Level (mg/L), a non-regulatory health-
based drinking water concentration levels of a specific contaminant 
at or below which is not anticipated to lead to adverse human health 
effects.
    RfD = Reference Dose (mg/kg/day)--an estimate (with uncertainty 
spanning perhaps an order of magnitude) of a daily oral exposure of 
the human population to a substance that is likely to be without an 
appreciable risk of deleterious effects during a lifetime. The value 
of this parameter is derived in the selected qualifying health 
assessment and is based on the critical effect and study identified 
in that assessment. An RfD is considered an oral reference value for 
RD 5 and can also refer to the maximum acceptable concentration 
(MAC), ATSDR minimal risk level, point of departure (POD)/
uncertainty factor (UF), population-adjusted dose (PAD) or tolerable 
daily intake (TDI).
    DWI-BWi = Drinking water intake (DWI), adjusted for body weight 
(BW), in units of liter per kilogram BW per day (L/kg/day) for each 
age group (i).
    RSC = Relative Source Contribution--the percentage of the total 
exposure attributed to drinking water sources (USEPA, 2000a) where 
the remainder of the exposure is allocated to other routes or 
sources.
    CSF = Cancer Slope Factor (mg/kg/day)-1,--an upper-
bound estimate of risk per increment of dose that can be used to 
estimate cancer risk probabilities for different exposure levels 
(USEPA, 2005b).
    CRL = Cancer risk level,--the target incidence used to establish 
lifetime exposure limits for carcinogens, set at one excess cancer 
case in a population of one million (1 x 10-6).
    ADAFi = the age dependent adjustment factor for each age group 
(i), used when calculating cancer risk concentrations for 
carcinogens that act via a mutagenic MOA; by default, ADAF = 10 from 
birth to two years of age; ADAF = 3 from two to sixteen years of 
age; and ADAF = 1 from 16 to 70 years of age (USEPA, 2005b).
    UA = Unit adjustment factor to convert the dose (i.e., CSF) from 
mg of a chemical to [micro]g of the chemical--ensures the ADAF-
adjusted Unit Risk is in [micro]g/L. This unit adjustment is not 
needed if the CSF is presented in (ug/kg/day)-1 or if the 
desired units of the ADAF-adjusted concentration (i.e., HRL) is mg/
L. A different adjustment factor is needed for other units.
    Fi = the fraction of life spent in each age group (i), used when 
calculating cancer risk concentrations for mutagens (USEPA, 2005b).

    In some cases, the health assessments identified for HRL derivation 
provided both cancer and non-cancer toxicity values (e.g., an oral 
reference value and oral CSF). When this situation occurred, the EPA 
selected the health assessments

[[Page 3838]]

according to the criteria explained earlier in this section, derived a 
noncancer HRL and a cancer HRL based on noncancer and cancer health 
effects information, respectively, and then selected the most health 
protective (i.e., lowest value) to serve as the final HRL (USEPA, 
2000a).
(ii) Exposure Factor Selection Process for HRL Derivation
    In prioritizing the contaminants of greatest public health concern 
for regulatory determination, section 1412(b)(1)(C) of SDWA requires 
the agency to consider ``among other factors of public health concern, 
the effect of such contaminants upon subgroups that comprise a 
meaningful portion of the general population (such as infants, 
children, pregnant women, the elderly or other subpopulations) that are 
identifiable as being at greater risk of adverse health effects due to 
exposure to contaminants in drinking water compared to the general 
population.'' It is also the EPA's policy to ``protect children from 
environmental exposures by consistently and explicitly considering 
early life exposures and lifelong health in human health decisions'' 
(USEPA, 2021b). One way that the EPA considers potentially sensitive 
populations or life stages (i.e., populations or life stages that may 
be more susceptible or sensitive to a chemical exposure) is during the 
selection of EFs for the development of HRLs.
    DWI-BW is the EF used to derive HRLs for RD 5 (USEPA, 2019a). EFs 
are input values intended to protect the general population including 
sensitive populations or life stages from adverse effects resulting 
from exposure to a contaminant. The agency selects an appropriate DWI-
BW for each chemical by reviewing the critical effect and study used 
for HRL derivation and identifying the interval of exposure (for 
examples, see USEPA, 2022b; USEPA, 2022c). The critical effect used as 
the basis for the oral reference value or oral CSF typically represents 
the health outcome at the lowest dose from the critical study among the 
best available studies. Since the critical effect typically represents 
the most sensitive adverse effect observed based on the available 
published data for a given chemical, it is reasonable to assume that 
the interval of exposure in the critical study could inform the 
selection of a DWI-BW protective of sensitive populations. Therefore, 
the EPA uses the interval of exposure in the critical study to identify 
potentially sensitive life stages as the basis for EF selection. When 
multiple potentially sensitive populations or life stages are 
identified based on the interval of exposure in the study used for HRL 
derivation, the EPA selects the population or life stage with the 
highest DWI-BW because it is the most health protective. See section 
B.6.1.2 in Appendix B of the Regulatory Determination 5 Support 
Document for more information regarding the EPA's EF selection process 
(USEPA, 2024b).
(b) Occurrence Data Evaluation
    In Phase 2, the agency collects additional data on occurrence 
(including finished drinking water data; ambient water data; data on 
use, production and release; and information on environmental fate and 
transport) and more thoroughly evaluates this information (based on 
factors enumerated in the following paragraphs) to identify 
contaminants that should proceed to Phase 3.
    In Phase 2, the agency focuses its efforts on identifying those 
contaminants or contaminant groups that are occurring or have 
substantial likelihood to occur at levels and frequencies of public 
health concern in drinking water. As noted in section III.A, SDWA 
1412(b)(1)(C) requires that the Administrator select contaminants that 
present the greatest public health concern. To identify such 
contaminants, the agency considers the following information:
    (a) How many samples (number and percentage) have detections > HRL 
and \1/2\ HRL in the nationally representative and other finished water 
occurrence data?
    (b) How many systems (number and percentage) have detections > HRL 
and \1/2\ HRL in the nationally representative and other finished water 
occurrence data?
    (c) Are there uncertainties or limitations with the data or 
analyses, such as the age of the dataset, the reporting threshold 
(i.e., minimum reporting level [MRL \9\] > HRL), or representativeness 
of the data (e.g., limited to a specific region), that may cause over- 
or underestimation of occurrence in finished water at levels and 
frequency of public health concern?
---------------------------------------------------------------------------

    \9\ The MRL is the minimum concentration that is required to be 
reported quantitatively in a study. The MRL is set at a value that 
takes into account typical laboratory capabilities to reliably and 
cost-effectively detect and quantify a compound.
---------------------------------------------------------------------------

    After identifying contaminants that are occurring at levels and 
frequencies of public health concern in drinking water to proceed to 
Phase 3 for a potential positive determination, the agency evaluates 
the remaining contaminants on the ``short list'' to determine which 
contaminants have no or low occurrence at levels of health concern that 
should proceed to Phase 3 for a potential negative determination. The 
agency considers the following information in selecting contaminants of 
no or low potential for public health concern to proceed to Phase 3:
    (a) Does the contaminant have nationally representative finished 
drinking water data showing no or a low number or percent of detections 
> HRL?
    (b) If a contaminant has other finished water data in addition to 
nationally representative finished water data, do these data suggest 
that there is no or low potential for occurrence in drinking water? 
\10\
---------------------------------------------------------------------------

    \10\ Note that other finished water data (i.e., non-nationally-
representative occurrence data) tend to be limited in scope and the 
EPA does not use these data alone to support a determination that 
the contaminant is not substantially likely to ``occur in PWSs with 
a frequency and at levels of public health concern,'' which would 
therefore be a decision ``not to regulate'' (i.e., negative 
determination).
---------------------------------------------------------------------------

    (c) Does additional high-quality occurrence information support the 
conclusion that there is low or no occurrence or potential for 
occurrence in drinking water? For example, is the occurrence in 
ambient/source water at levels below the HRL? How are releases to the 
environment or use/production changing over time?
    (d) Are critical gaps in health and occurrence information/data 
minimal?
    After evaluating the ``short list'' contaminants (listed in Table 1 
of this document), the agency identified 14 CCL 5 contaminants to 
proceed to Phase 3 (listed in Table 2 of this document). The 
contaminants are within one of the following Phase 2 data evaluation 
categories:
    (a) A contaminant or part of a contaminant group occurring or 
likely to occur at levels and frequencies of public health concern, or
    (b) A contaminant not occurring or not likely to occur at levels 
and frequencies of public health concern and no data gaps.

[[Page 3839]]



        Table 2--Contaminants Proceeding From Phase 2 to Phase 3
------------------------------------------------------------------------
 
------------------------------------------------------------------------
1,2,3-Trichloropropane.                     Molybdenum.
1,4-Dioxane.                                Permethrin.
2-Aminotoluene (o-Toluidine).               Profenofos.
Cylindrospermopsin.                         Quinoline.
Ethoprop.                                   Strontium.
Manganese.                                  Tebuconazole.
Microcystins.                               Tribufos.
------------------------------------------------------------------------

    Note that the agency does not have a threshold for occurrence in 
drinking water that triggers whether a contaminant is occurring with a 
frequency and at levels of public health concern. An evaluation of this 
statutory criterion requires consideration of a number of factors, some 
of which include the health effect(s), the potency of the contaminant, 
the level at which the contaminant is found in drinking water, the 
frequency at which the contaminant is found, the geographic 
distribution (national, regional or local occurrence), other possible 
sources of exposure, and potential impacts on sensitive populations or 
lifestages. Given the many possible combinations of factors, a simple 
threshold is not viable.
    The remaining CCL 5 contaminants did not proceed to Phase 3 and 
were not considered for RD 5 for reasons that may include of one or 
more of the following reasons:
    (a) An updated health assessment completed by January 31, 2023 was 
not identified;
    (b) Critical health effects gap (e.g., lack of data to support 
quantification for the oral route of exposure);
    (c) Lack of nationally representative finished water occurrence 
data and lack of sufficient other data to demonstrate occurrence at 
levels and frequencies of public health concern;
    (d) Critical occurrence data limitation or gap (e.g., inconsistent 
results or trends in occurrence data requiring further research; 
significant uncertainty in occurrence analyses or data);
    or
    (e) The contaminant is being evaluated in other actions by the 
agency.
    The agency continues to conduct research and collect information to 
fill the data and information gaps identified for these contaminants. 
Three contaminants that had previously received negative regulatory 
determinations have been re-listed on CCL 5 based on new health or 
occurrence information or a reevaluation of existing information. The 
EPA made determinations not to regulate dieldrin and manganese in RD 1 
and dimethoate in RD 3. These contaminants were considered in RD 5. 
Based on preliminary RD 5 evaluations of dieldrin and dimethoate, the 
EPA is not proposing a change to its previous negative regulatory 
determinations for these two contaminants at this time. Manganese is 
further discussed in section V. Additionally, all 29 PFAS contaminants 
that have approved analytical methods are being monitored under the 
fifth Unregulated Contaminant Monitoring Rule (UCMR 5). The UCMR 5 
occurrence data collection began in 2023 and ends in 2025.
3. Phase 3 (Regulatory Determination Assessment Phase)
    Phase 3, the Regulatory Determination Assessment Phase, involves a 
complete evaluation of the statutory criteria for each contaminant or 
group of contaminants that proceed from Phase 2 and have sufficient 
information and data for making a regulatory determination. To meet the 
statutory requirement of making at least five regulatory 
determinations, in this phase, the agency evaluates the remaining 
contaminants against the following statutory criteria (SDWA 
1412(b)(1)(A)):
    (a) Statutory Criterion 1--``The contaminant may have an adverse 
effect on the health of persons.'' To evaluate the first criterion, the 
EPA evaluates whether a contaminant has an EPA health assessment, or an 
externally peer-reviewed health assessment from another agency that is 
publicly available and conforms with current EPA guidelines, from which 
an HRL can be derived. The HRL derived in or from the health assessment 
takes into account the MOA, the critical health effect(s), the dose-
response relationship for critical health effect(s) and impacts on 
sensitive population(s) or lifestages.
    If an acceptable health assessment that demonstrates adverse health 
effects is available, the agency answers ``yes'' to the first statutory 
criterion. Otherwise, the agency answers ``no'' to the first statutory 
criterion. (In practice, it is expected that any contaminant that 
reaches Phase 3 would receive a ``yes'' to the first criterion.)
    (b) Statutory Criterion 2--``The contaminant is known to occur or 
there is a substantial likelihood that the contaminant will occur in 
PWSs with a frequency and at levels of public health concern.'' The EPA 
compares the occurrence data for each contaminant to the HRL to 
determine if the contaminant occurs at a frequency and levels of public 
health concern. The types of occurrence data used at this stage are 
described in section III.C.1, Evaluation of Contaminant Occurrence and 
Exposure, and in Appendix B of the Regulatory Determination 5 Support 
Document (USEPA, 2024b). The agency may consider the multiple factors 
when identifying contaminants or contaminant groups that are occurring 
at frequencies and levels of public health concern, including:
     How many samples (number and percentage) have detections > 
HRL in the nationally representative and other finished water 
occurrence data?
     How many systems (number and percentage) have detections > 
HRL in the nationally representative and other finished water 
occurrence data, and, in addition to the number of systems, what type 
of systems does the contaminant occur in? Does the contaminant occur in 
large or small systems? Does the contaminant occur in surface or 
groundwater systems?
     Is the geographic distribution of the contaminant 
occurrence national, regional or localized?
     Are there significant uncertainties or limitations with 
the data or analyses, such as the age of the dataset, the MRL (i.e., 
MRL > HRL), or representativeness of the data (e.g., limited in scope 
to a specific region)?
    (c) Statutory Criterion 3--``In the sole judgment of the 
Administrator, regulation of the contaminant presents a meaningful 
opportunity for health risk reduction for persons served by public 
water systems.'' The EPA evaluates the population exposed at the health 
level of concern along with several other factors to determine if 
regulation presents a meaningful opportunity for health risk reduction. 
Among other things, the EPA may consider the following factors in 
evaluating statutory criterion 3:

[[Page 3840]]

     What is the nature of the health effect(s) identified in 
statutory criterion 1?
     Are there sensitive populations that may be affected 
(evaluated either qualitatively or quantitatively \11\)?
---------------------------------------------------------------------------

    \11\ If appropriate and available, the agency considers 
quantitative exposure data applicable to sensitive populations or 
lifestages when deriving HRLs for regulatory determinations. When 
data are not available on sensitive populations, the derivation of 
the RfD typically includes an uncertainty factor to account for the 
limitation in the database. Additionally, the EPA will use exposure 
factors relevant to the sensitive population in deriving the HRL. 
See Section III.C.1. Sensitive populations are also qualitatively 
considered by providing national prevalence estimates for a 
particular sensitive population, if available.
---------------------------------------------------------------------------

     Based on the occurrence information for statutory 
criterion 2, including the number of systems potentially affected, what 
is the national population exposed or served by systems with levels > 
HRL and >\1/2\ HRL?
     For non-carcinogens, are there other sources of exposure 
that should be considered (i.e., what is the RSC from drinking water)?
     What is the geographic distribution of occurrence (e.g., 
local, regional, national)?
     Are there any uncertainties or limitations in the health 
and occurrence information or analyses that should be considered?
     Are there any limiting considerations related to 
technology (e.g., lack of available treatment or analytical methods)?
    If the Administrator, in their sole judgement, determines that 
there is a meaningful opportunity to reduce risk by regulating the 
contaminant in drinking water, then the agency answers ``yes'' to the 
third statutory criterion.
    The agency may make a positive preliminary determination if the 
agency answers ``yes'' to all three statutory criteria in Phase 3 for a 
particular contaminant. Additionally, after identifying compounds 
occurring at frequencies and levels of public health concern, if any, 
the agency may initiate a systematic literature review to identify new 
studies that may influence the derivation of an RfD or CSF. The list of 
potentially relevant health effect studies that could affect the 
derivation of an RfD or CSF identified through the systematic review 
process would then be placed in the docket at the time of the 
preliminary determination for public comment (discussed further in 
section IV of this document).
    If, after considering public comment on the preliminary regulatory 
determination, the agency again answers ``yes'' to all three statutory 
criteria, the agency then may make a positive final determination that 
regulation is appropriate and proceed to develop an MCLG and NPDWR. If 
a final positive determination is made, the agency has 24 months to 
publish a proposed MCLG and NPDWR and an additional 18 months to 
publish a final MCLG and promulgate a final NPDWR.\12\
---------------------------------------------------------------------------

    \12\ The statute authorizes a nine-month extension of this 
promulgation date.
---------------------------------------------------------------------------

    It should be noted that the analyses associated with a regulatory 
determination process are distinct from the more detailed analyses 
needed to develop an NPDWR. The development and promulgation of an 
NPDWR is a multi-step process, which includes deriving a proposed MCLG 
as well as conducting a statutorily required health risk reduction cost 
analysis (HRRCA) and conducting other analyses required to propose an 
MCL or a TT approach to reduce contaminant levels in water systems. As 
part of the proposal, the agency must identify best available 
technologies (BATs), small system compliance technologies (SSCTs) and 
approved analytical methods if it proposes an enforceable MCL. 
Alternatively, if the EPA proposes a TT instead of an MCL, the agency 
must identify the TT. The EPA must also prepare a HRRCA which includes 
an extensive evaluation of the treatment costs and monitoring costs at 
a system level and aggregated at the national level. Thus, a decision 
to regulate is the beginning of the agency's regulatory development 
process, not the end.
    If a contaminant has sufficient information and the agency answers 
``no'' to any of the three statutory criteria based on the available 
data, then the agency considers making a negative determination that an 
NPDWR is not appropriate for that contaminant at that time. A final 
determination not to regulate a contaminant is, by statute, a final 
agency action and is subject to judicial review. While a negative 
determination is considered a final agency action under SDWA for a 
round of regulatory determinations, the contaminant may be relisted on 
a future CCL based on newly available health or occurrence information.
    If a negative determination or no determination is made for a 
contaminant, the agency may decide to develop an HA, which provides 
non-regulatory concentration values for drinking water contaminants at 
which adverse health effects are not anticipated to occur over specific 
exposure durations (e.g., one day, ten days, or a lifetime). The EPA's 
HAs are non-enforceable and non-regulatory and provide technical 
information to states' agencies and other public health officials on 
health effects, analytical methodologies and treatment technologies 
associated with drinking water contamination. See SDWA section 
1412(b)(1)(F).
    After evaluating the CCL 5 contaminants in Table 3 of this document 
against the three SDWA criteria and considering the factors listed for 
each, the agency is making preliminary negative regulatory 
determinations for nine CCL 5 contaminants. Table 5 of this 
documentprovides a summary of the 14 contaminants evaluated for Phase 3 
and the preliminary regulatory determination outcome for each 
contaminant. The agency seeks comment on the preliminary determination 
not to regulate nine contaminants (2-aminotoluene, cylindrospermopsin, 
ethoprop, microcystins, molybdenum, permethrin, profenofos, 
tebuconazole and tribufos). Section IV.B of this document provides a 
more detailed summary of the information and the rationale used by the 
agency to reach its preliminary decisions for these contaminants. At 
this time, the agency is not making preliminary regulatory 
determinations for five of the 14 contaminants that proceeded to Phase 
3, namely1,2,3-trichloropropane (1,2,3-TCP), 1,4-dioxane, manganese, 
quinoline and strontium (see section V of this document for more 
information).

      Table 3--Contaminants Evaluated in Phase 3 and the Regulatory
                          Determination Outcome
------------------------------------------------------------------------
                                                       Preliminary
       Number                Contaminant          determination outcome
------------------------------------------------------------------------
1...................  2-Aminotoluene (o-        Negative Determination.
                       Toluidine).
2...................  1,2,3-Trichloropropane..  No Determination.
3...................  1,4-Dioxane.............  No Determination.
4...................  Cylindrospermopsin......  Negative Determination.

[[Page 3841]]

 
5...................  Ethoprop................  Negative Determination.
6...................  Manganese...............  No Determination.
7...................  Microcystins............  Negative Determination.
8...................  Molybdenum..............  Negative Determination.
9...................  Permethrin..............  Negative Determination.
10..................  Profenofos..............  Negative Determination.
11..................  Quinoline...............  No Determination.
12..................  Strontium...............  No Determination.
13..................  Tebuconazole............  Negative Determination.
14..................  Tribufos................  Negative Determination.
------------------------------------------------------------------------

    In National Resources Defense Council v. Michael S. Regan, 
Administrator, U.S. Environmental Protection Agency and Environmental 
Protection Agency (NRDC v. EPA), 67 F.4th 397 (D.C. Cir., 2023), the 
D.C. Circuit Court of Appeals ruled that when the EPA finalizes a 
positive regulatory determination for a contaminant under the SDWA, the 
EPA must then promulgate a regulation and the EPA does not have the 
ability to withdraw a final positive determination during the 
development of the proposed rule. This ruling presents a change to the 
EPA's understanding of the flexibilities afforded to the agency under 
the SDWA. Prior to this ruling, the EPA had understood that the agency 
could withdraw a positive determination if, during the more-detailed 
analyses conducted during the development of the proposed rule, for 
example, in the HRRCA, the EPA determined that the potential for 
health-risk reduction was less beneficial than initially predicted. 
Following the NRDC v. EPA ruling and the understanding now of the EPA's 
authorities under the SDWA, the agency will need to be more certain of 
the potential for health-risk reduction through regulation before 
making a determination to regulate a contaminant. As a result, the EPA 
will need to consider preliminary health benefits analysis information 
to support the finding that a positive determination would provide a 
meaningful opportunity for health risk reduction if the agency decides 
to regulate a contaminant under the SDWA. Therefore, the EPA is not 
making a regulatory determination for these five contaminants at this 
time, in order to gain an understanding of the potential for health-
risk reduction by conducting additional analyses of the potential 
benefits and treatment feasibility prior to making positive 
determinations.

B. Supporting Documentation for the EPA's Preliminary Determination

    For this action, the EPA prepared several supporting documents that 
are available for review and comment in the EPA Water Docket. These 
support documents include:
     The comprehensive regulatory support document, Regulatory 
Determination 5 Support Document (USEPA, 2024b), summarizes the 
information and data evaluated by the EPA on the physical and chemical 
properties, uses and environmental release, environmental fate, 
potential health effects, occurrence and exposure estimates, analytical 
methods, treatment technologies and preliminary determinations. 
Additionally, Appendix B of the Regulatory Determination 5 Support 
Document describes the approach implemented by the agency to evaluate 
the CCL 5 contaminants in a three-phase process and select the 
contaminants for preliminary determinations for RD 5.
     A comprehensive technical occurrence support document for 
UCMR 4, Occurrence Data from the Fourth Unregulated Contaminant 
Monitoring Rule (UCMR 4) (USEPA, 2024c). This occurrence support 
document includes more detailed information about UCMR 4, how the EPA 
assessed the data quality, completeness and representativeness, and how 
the data were used to generate estimates of drinking water contaminant 
occurrence in support of these regulatory determinations.

C. Analyses Used To Support the Preliminary Regulatory Determinations

1. Evaluation of Contaminant Occurrence and Exposure
    The EPA uses data from many sources to evaluate occurrence and 
exposure from drinking water contaminants. The discussion in this 
section focuses mainly on the following sources of finished drinking 
water occurrence data:
     Unregulated Contaminant Monitoring Rules (UCMR 1, 2, 3 and 
4);
     UCM-State Program Rounds 1 and 2; and,
     Data collected by states.
    Several of the primary sources of finished water occurrence data 
are designed to be statistically representative of the nation. These 
data sources include Assessment Monitoring (AM) data collected under 
UCMR 1-4 and Screening Survey (SS) data collected under UCMR 2 and 3.
    The agency also evaluates supplemental sources of information on 
occurrence in drinking water, information on occurrence in ambient and 
source water and information on contaminant production and release to 
augment and complement these primary sources of drinking water 
occurrence data. section III.C.1.a of this action provides a brief 
summary of the primary sources of finished water occurrence data and 
sections III.C.1.b and III.C.1.c provide brief summary descriptions of 
some of the supplemental sources of occurrence information and data. 
These descriptions do not cover all the sources that the EPA reviews 
and evaluates. For individual contaminants, the EPA reviews additional 
published reports and peer-reviewed studies that may provide the 
results of monitoring efforts in limited geographic areas. A summary of 
the occurrence data and the results or findings for each of the 
contaminants considered for regulatory determination is presented in 
section IV.B, the contaminant profiles section, and the data are 
described in further detail in the Regulatory Determination 5 Support 
Document (USEPA, 2024b).
(a) Primary Sources of Finished Drinking Water Occurrence Data
    The following section provides a brief summary of the finished 
water occurrence data sources used in RD 5. Table 4 in section IV of 
this document lists the primary data source/finding used to evaluate 
each of the nine contaminants for which the EPA is making preliminary 
determinations in this Federal Register Notice. The

[[Page 3842]]

contaminant-specific discussions in section IV of this document, 
provide more detailed information about the primary data source 
findings as well as any supplemental occurrence information.
    Section V of this document provides more information about the five 
Phase 3 contaminants for which the EPA is not making a preliminary 
regulatory determination at this time: 1,4-dioxane, 1,2,3-TCP, 
manganese, quinoline and strontium.
 The Unregulated Contaminant Monitoring Rules (UCMR 1, UCMR 2, 
UCMR 3 and UCMR 4)
    The UCMR program is the EPA's primary vehicle for collecting 
monitoring data on the occurrence of unregulated contaminants in PWSs. 
SDWA section 1412 (b)(1)(B)(ii)(II) requires that the EPA include 
consideration of the data collected by the UCMR program in making 
regulatory determinations. The UCMR program is designed to collect 
nationally representative occurrence data in coordination with the CCL 
and regulatory determination processes. The UCMR sampling is limited by 
statute to no more than 30 contaminants every five years (SDWA section 
1445(a)(2)). However, the National Defense Authorization Act for Fiscal 
Year 2020 provided a one-time exception to this limit by stating that 
PFAS monitored under UCMR 5 do not count toward the limit of 30 
contaminants. The EPA published the lists and requirements for UCMR 1 
on September 17, 1999 (64 FR 50556; USEPA, 1999), and the monitoring 
was conducted primarily during 2001-2005. The requirements for UCMR 2 
were published on January 4, 2007 (72 FR 367; USEPA, 2007) with 
monitoring conducted primarily during 2008-2010. Requirements for UCMR 
3 were published on May 2, 2012 (77 FR 26072; USEPA, 2012a); with 
monitoring conducted primarily during 2013-2015. Requirements for UCMR 
4 were published on December 20, 2016 (81 FR 92666; USEPA, 2016c) with 
monitoring conducted primarily during 2018-2020. (The complete 
contaminant lists are available at: https://www.epa.gov/dwucmr.) On 
December 27, 2021, the EPA published UCMR 5, requiring certain PWSs to 
collect national occurrence data for 29 PFAS and lithium from 2023 
through 2025 (86 FR 73131; USEPA, 2021c). The final UCMR 5 dataset is 
not complete at the time of these RD 5 preliminary determinations and 
will not conclude until December 31, 2026.
    The UCMR program is designed as a three-tiered approach for 
monitoring contaminants related to the availability and complexity of 
analytical methods, laboratory capacity, sampling frequency, relevant 
PWSs based on contaminants and other considerations (e.g., cost/
burden). AM is the primary tier and the largest in scope. The AM 
generally relies on analytical methods that use more common techniques 
and are expected to be widely available. SS monitoring is smaller in 
scope than the AM and generally pertains to monitoring with less 
established analytical techniques, such that laboratory capacity or 
cost may be a concern. A Pre-Screen Testing (PST) tier can be 
customized to meet specific monitoring objectives for a specific group 
of PWSs.
    The EPA designed the AM sampling frame to ensure that sample 
results would support a high level of confidence and a low margin of 
error (see USEPA, 1999 and 2001a, for UCMR design details). The AM 
program includes PWSs from all 50 states, the District of Columbia, all 
five U.S. territories and Tribal lands across the EPA regions. The AM 
is required for all large and very large PWSs, those serving between 
10,001 and 100,000 people and serving more than 100,000 people, 
respectively (i.e., a census of all large and very large systems) and a 
national statistically representative sample of 800 small PWSs, those 
serving 10,000 or fewer people.\13\ The small system sample is 
stratified and population-weighted and includes some other sampling 
adjustments such as allocating a selection of at least two systems from 
each state for spatial coverage. The design meets the data quality 
objective for overall exposure estimates (99% confidence level with 
1% error tolerance, at 1% exposure) while providing more 
precise occurrence estimates for categories of small systems. The AM, 
the primary tier, has been used for all or a subset of contaminants in 
each UCMR cycle. With contaminant monitoring data from all large PWSs 
and a statistical, nationally representative sample of small PWSs, AM 
provides a robust dataset for evaluating national drinking water 
contaminant occurrence.
---------------------------------------------------------------------------

    \13\ Section 1445 of the Safe Drinking Water Act was recently 
amended by Public Law 115-270, America's Water Infrastructure Act of 
2018 (AWIA), and now specifies that, effective October 23, 2021, 
subject to the availability of appropriations for such purpose and 
appropriate laboratory capacity, the EPA must require all systems 
serving between 3,300 and 10,000 persons to monitor and ensure that 
only a representative sample of systems serving fewer than 3,300 
persons are required to monitor.
---------------------------------------------------------------------------

    Each system conducts monitoring for 12 consecutive months during 
the three-year monitoring period. The rules typically require quarterly 
monitoring for surface water and groundwater under the direct influence 
of surface water (GWUDI) systems and twice-a-year, six-month-interval 
monitoring for groundwater systems, and include flexibilities for 
specialized sampling (e.g., eight sample events for cyanotoxins in UCMR 
4). Samples may be collected at different sampling points or locations 
within the PWS depending on the specific contaminant (e.g., entry point 
to the distribution system). A brief outline of the structure of the 
UCMR efforts is provided in the paragraphs that follow.
    UCMR 1 included both the AM and SS tiers. UCMR1 a.m. was conducted 
by approximately 3,100 large systems and approximately 800 small 
systems and resulted in over 33,900 sample results for each 
contaminant. The UCMR 1 SS design included approximately 640 UCMR1 SS 
PWSs randomly selected from those PWSs required to conduct AM and was 
designed to determine if additional monitoring would be needed. Samples 
from the 639 PWSs from throughout the nation provided over 2,300 
results for each contaminant. While the statistical design of the SS is 
national in scope, the uncertainty in the results for contaminants that 
have low occurrence is relatively high. Therefore, the EPA looked for 
additional data to supplement the SS data for regulatory determinations 
in RD 2. After UCMR 1, the SS design was adapted to include more PWSs 
and to be representative of national occurrence.
    UCMR 2 also included the AM and SS tiers. The UCMR 2 a.m. was 
conducted by approximately3,300 large systems and 800 small systems and 
resulted in over 32,000 sample results for each contaminant. For the 
UCMR 2 SS, the EPA improved the design to include a census of all 
systems serving more than 100,000 people, a nationally representative, 
statistically selected sample of 320 PWSs serving between 10,001 and 
100,000 people, and a nationally representative sample including 
approximately 480 small PWSs serving 10,000 or fewer people (72 FR 367, 
January 4, 2007, USEPA, 2007). With a total of approximately 1,200 
systems participating in the SS, sufficient data were generated to 
provide a confident national estimate of contaminant occurrence and 
population exposure. The UCMR 2 SS PWSs provided between 11,100 to 
18,100 sample results per contaminant (depending on the specific 
sampling design for the contaminant).
    UCMR 3 included the AM, SS and PST tiers. The UCMR 3 a.m. was 
conducted by approximately 4,100 large

[[Page 3843]]

systems and approximately 800 small systems and resulted in between 
36,800 and 63,000 sample results for each contaminant (depending on the 
specific sampling design for the contaminant). The UCMR 3 SS monitoring 
was conducted by all large systems serving more than 100,000 people, a 
nationally representative sample of 320 large systems serving 10,001 to 
100,000 people and a nationally representative sample of approximately 
480 small water systems serving 10,000 or fewer people for a total of 
approximately 1,200 PWSs. The UCMR 3 SS PWSs provided over 11,700 
sample result per contaminant. The UCMR 3 PST monitoring was conducted 
by approximately 800 PWSs including, transient noncommunity water 
systems that purchase all their finished water from another. See USEPA 
(2012a) and USEPA (2019b) for more information on the UCMR 3 study 
design and data analysis.
    UCMR 4 involved only AM and did not include any SS or PST efforts. 
The UCMR 4 a.m. was conducted by approximately 4,200 large systems and 
two separate nationally representative statistical samples of 
approximately 800 small PWSs. One set of 800 small systems monitored 
for cyanotoxins, while the second set of 800 small systems monitored 
for the remaining UCMR 4 contaminants.
    Systems with surface water or GWUDI monitored for cyanotoxins and 
conducted eight sampling events over a period of four consecutive 
months. Cyanotoxin sampling was conducted during the period of March 
through November, when harmful algal bloom (HAB) events are more likely 
to occur in the Northern Hemisphere. Groundwater systems were excluded 
from cyanotoxin monitoring (USEPA, 2016c). Overall, the UCMR 4 a.m. 
resulted in approximately 35,000 to 63,000 sample results per 
contaminant (depending on the specific sampling design for the 
contaminant). (81 FR 92666; USEPA, 2016c)
    The details of the occurrence data and the results or findings for 
each of the contaminants considered for regulatory determination are 
presented in section IV.B of this document, the contaminant profiles 
section, and are described in further detail in the Regulatory 
Determination 5 Support Document (USEPA, 2024b). The national design, 
the statistical sampling frame, any new analytical methods and the data 
analysis approach for the UCMR program have been peer-reviewed at 
different stages of development (see USEPA, 2001b, 2008b, 2015a, 
2019b).
    The fifth UCMR (UCMR 5) FRN, published December 2021, requires 
sample collection and analysis for 29 PFAS, including PFOA, PFOS, 
PFHxS, PFNA, HFPO-DA and PFBS, to occur between January 2023 and 
December 2025 using drinking water analytical methods developed by the 
EPA. Section 2021 of America's Water Infrastructure Act of 2018 (AWIA) 
(Pub. L. 115-270) amended SDWA and specifies that, subject to the 
availability of EPA appropriations for such purpose and sufficient 
laboratory capacity, the EPA must require all PWSs serving between 
3,300 and 10,000 people to monitor and ensure that a nationally 
representative sample of systems serving fewer than 3,300 people 
monitor for the contaminants in UCMR 5 and future UCMR cycles. All 
large water systems continue to be required to participate in the UCMR 
program. As data under the UCMR 5 are being collected concurrently with 
the RD 5 evaluation process, the complete UCMR 5 dataset is not 
available to inform the regulatory determinations in this preliminary 
RD 5 FRN. The EPA intends to evaluate the full UCMR 5 dataset when it 
is available and to consider making regulatory determinations for the 
included contaminants in the future.
    The UCMR program serves as the primary occurrence data source for 
all nine preliminary determinations included in this FRN. Other 
examples of occurrence data sources considered to be nationally 
representative for RD 5 are listed here. These are described in more 
detail in Chapter 2 of the Regulatory Determination 5 Support Document 
(USEPA, 2024b).

 National Inorganics and Radionuclides Survey (NIRS)
 Unregulated Contaminant Monitoring (UCM) Program Rounds 1 and 
2
(b) Supplemental Sources of Finished Drinking and Ambient Water 
Occurrence Data
    The agency evaluates several sources of supplemental information 
related to contaminant occurrence in finished water and ambient and 
source waters to augment the primary drinking water occurrence data. 
Some of these sources were part of other agency information gathering 
efforts or submitted to the agency in public comment or suggested by 
stakeholders during previous CCL and regulatory determination efforts. 
These supplemental data are useful to evaluate the likelihood of 
contaminant occurrence in drinking water, to more fully characterize a 
contaminant's presence in the environment and potentially in source 
water and to evaluate any possible trends or spatial patterns that may 
need further review. In cases where there is a sufficient amount of 
non-national data to illustrate contaminant occurrence at a national 
level, the EPA may use non-national data as the basis for a regulatory 
determination. The descriptions that follow do not cover all the 
sources that the EPA used. For individual contaminants, the EPA 
reviewed additional published reports and peer-reviewed studies that 
may have provided the results of monitoring efforts in limited 
geographic areas. A more detailed discussion of the supplemental 
sources of information/data that the EPA evaluated and the occurrence 
data for each contaminant can be found in the Regulatory Determination 
5 Support Document (USEPA, 2024b).
    Occurrence data were collected from other sources for consideration 
in RD 5 as well. Non-national occurrence data sources are also 
discussed in detail in Chapter 2 of the Regulatory Determination 5 
Support Document and include:

 Individual states' data
 Community Water System Survey (CWSS) Data
 United States Department of Agriculture (USDA) Pesticide Data 
Program (PDP)
 United States Geological Survey (USGS) Pilot Monitoring 
Program (PMP)
 USGS National Water Quality Assessment (NAWQA)
 National Water Information System (NWIS)
 Water Quality Exchange (WQX)/Water Quality Portal (WQP) Data 
System (Formerly the Storage and Retrieval Data System [STORET])
(c) Supplemental Production, Use and Release Data
    The agency reviews various sources of information to assess if 
there are changes or trends in a contaminant's production, use and 
release that may affect its presence in the environment and potential 
occurrence in drinking water. The cancellation of a pesticide or a 
clear increase in production and use of a contaminant are trends that 
can inform the regulatory determination process. Examples of such 
sources are listed here. A more detailed discussion of the supplemental 
sources of information/data that the EPA evaluated and the occurrence 
data for each contaminant can be found in the Regulatory Determination 
5 Support Document (USEPA, 2024b).

 Inventory Update Reporting (IUR) and Chemical Data Reporting 
(CDR) Program (https://www.epa.gov/chemical-data-reporting)

[[Page 3844]]

 Toxics Release Inventory (TRI) (https://www.epa.gov/toxics-release-inventory-tri-program)
 Pesticide Usage Estimates (https://www.epa.gov/pesticides/pesticides-industry-sales-and-usage-2008-2012-market-estimates)

IV. Contaminant-Specific Discussions for the RD 5 Preliminary 
Determinations

A. Summary of the Preliminary Regulatory Determinations

    Based on the EPA's evaluation of the three SDWA criteria (discussed 
in section II.B.1 of this document), the agency is making preliminary 
determinations not to regulate nine contaminants. For each of the nine 
contaminants discussed in this section of this Document, Table 4 of 
this document summarizes information about the qualifying health 
assessment that was selected, the critical study, the critical effect 
and the associated oral reference value or oral CSF used to derive an 
HRL. Following Table 4, Table 5 of this document summarizes the primary 
occurrence information used to make these preliminary regulatory 
determinations. Section IV.B of this document provides a more detailed 
summary of the information and the rationale used by the agency to 
reach its preliminary decisions for these nine contaminants. For more 
information about the five Phase 3 contaminants that are not receiving 
a preliminary regulatory determination, see section Vof this document.

                                      Table 4--Health Effects Information for Contaminants Discussed in Section IV
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                Oral reference
                                                                                                                   value for     Oral CSF,
          RD 5 contaminant              Qualifying health        Critical study           Critical effect          noncancer     in (mg/kg/    HRL, in
                                       assessment selected                                                      effects, in mg/  day) -\1\    [micro]g/L
                                                                                                                    kg/day
--------------------------------------------------------------------------------------------------------------------------------------------------------
2-Aminotoluene.....................  EPA PPRTV, 2012.......  Weisburger et al.,     Subcutaneous fibromas and              n/a        0.016            2
                                                              1978.                  fibrosarcomas in male
                                                                                     rats and mice.
Cylindrospermopsin.................  EPA OW HESD, 2015.....  Humpage and Falconer,  Increased relative kidney           0.0001          n/a          0.6
                                                              2002; Humpage and      weight in male mice.
                                                              Falconer, 2003.
Ethoprop...........................  EPA OPP HHRA, 2015....  Chartier et al., 2005  Inhibition of red blood       6.5 x 10-\5\          n/a         0.09
                                                                                     cell (RBC) cholinesterase
                                                                                     (ChE) in postnatal day
                                                                                     (PND) 11 rat pups.
Microcystins *.....................  EPA OW HESD, 2015.....  Heinze, 1999.........  Liver effects (increased        5 x 10-\5\          n/a          0.3
                                                                                     liver weight, slight to
                                                                                     moderate liver necrosis
                                                                                     lesions and increased
                                                                                     enzyme levels) in rats.
Molybdenum.........................  ATSDR, 2020...........  Murray et al., 2014..  Renal proximal tubule                 0.06          n/a          100
                                                                                     hyperplasia.
Permethrin.........................  EPA OPP HHRA, 2020....  Wolansky et al., 2006  Decreased motor activity              0.44          n/a        3,000
                                                                                     in adult male rats.
Profenofos.........................  EPA OPP HHRA, 2015....  Burdock et al., 1981.  Inhibition of RBC                  0.00012          n/a          0.7
                                                                                     acetylcholinesterase
                                                                                     (AChE) in adult rats.
Tebuconzole........................  EPA OPP HHRA, 2021....  Becker and             Increased incidence of                0.03          n/a          200
                                                              Biedermann, 1995.      skull/neural tube defects
                                                                                     including abnormalities
                                                                                     of the eyes, head and
                                                                                     skull.
Tribufos...........................  EPA OPP HHRA, 2015....  Sheets and Gilmore,    Inhibition of RBC ChE in            0.0002          n/a            1
                                                              2001.                  adult female rats.
--------------------------------------------------------------------------------------------------------------------------------------------------------
* Microcystin LR was used as a surrogate for deriving an oral reference value for all microcystin congeners.


                                                 Table 5--Occurrence Findings From Primary Data Sources
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                            Population served                         Population served
                                       HRL,                            PWSs with at least    by PWSs with at     PWSs with at least    by PWSs with at
         RD 5 contaminant           [micro]g/L    Primary database     1 detection >\1/2\   least 1 detection    1 detection > HRL   least 1 detection >
                                                                              HRL               >\1/2\ HRL                                   HRL
--------------------------------------------------------------------------------------------------------------------------------------------------------
2-Aminotoluene...................            2  UCMR 4 AM...........  0/5,030 (0.00%)....  0/249 M (0.00%)....  0/5,030 (0.00%)....  0/249 M (0.00%).
Cylindrospermopsin...............          0.6  UCMR 4 AM...........  3/3,484 (0.09%)....  30,829/195 M         1/3,484 (0.03%)....  10,174/195 M
                                                                                            (0.02%).                                  (0.01%).
Ethoprop.........................         0.09  UCMR 4 AM...........  3/5,028 (0.06%)....  75,032/249 M         1/5,028 (0.02%)....  14,999/249 M
                                                                                            (0.03%).                                  (0.01%).
Microcystins.....................          0.3  UCMR 4 AM...........  7/3,485 (0.20%)....  119,725/195 M        7/3,485 (0.20%)....  119,725/195 M
                                                                                            (0.06%).                                  (0.06%).
Molybdenum.......................          100  UCMR 3 AM...........  29/4,922 (0.59%)...  600,187/241 M        7/4,922 (0.14%)....  148,678/241 M
                                                                                            (0.25%).                                  (0.06%).
Permethrin.......................         3000  UCMR 4 AM...........  0/5,028 (0.00%)....  0/249 M (0.00%)....  0/5,028 (0.00%)....  0/249 M (0.00%).
Profenofos.......................          0.7  UCMR 4 AM...........  4/5,028 (0.08%)....  85,728/249 M         1/5,028 (0.02%)....  14,999/249 M
                                                                                            (0.03%).                                  (0.01%).
Tebuconazole.....................          200  UCMR 4 AM...........  0/5,028 (0.00%)....  0/249 M (0.00%)....  0/5,028 (0.00%)....  0/249 M (0.00%).
Tribufos.........................            1  UCMR 4 AM...........  0/5,027 (0.00%)....  0/249 M (0.00%)....  0/5027 (0.00%).....  0/249 M (0.00%).
--------------------------------------------------------------------------------------------------------------------------------------------------------

B. Contaminant Profiles

1. 2-Aminotoluene
(a) Background
    2-Aminotoluene (also referred to as o-toluidine or 2-methylaniline) 
is a synthetic aromatic amine and occurs as a colorless or light-yellow 
liquid. It is used in the manufacture of dyes, rubber vulcanization 
accelerators, pharmaceuticals and pesticides.
    Production data for 2-aminotoluene are available from the EPA's IUR 
and CDR programs. Annual production and importation of 2-aminotoluene 
was last reported by IUR for 2005 to be in the range of 10 to <50 
million pounds. From 2012 to 2019, annual production was in the range 
of 50 to 100 million pounds as reported under CDR. Industrial release 
data from TRI indicate that on-

[[Page 3845]]

site surface water discharges have been at just under 200 pounds per 
year since 2009, with no more than six states reporting surface water 
discharges in a given year.
    An overall removal half-life for 2-aminotoluene in Rhine River 
water was estimated to be approximately 1 day (IPCS, 1998). 
Volatilization from water surfaces is expected to be an important fate 
process. Based on these physical and chemical properties, 2-
aminotoluene is unlikely to be environmentally persistent in surface 
water.
(b) Statutory Criterion 1 (Adverse Health Effects)
    The EPA proposes to find that 2-aminotoluene meets the first SDWA 
statutory criterion for regulatory determinations: exposure to 2-
aminotoluene may have an adverse effect on the health of persons. The 
health assessment selected for RD 5 is the 2012 EPA Provisional Peer-
Reviewed Toxicity Value (PPRTV) (USEPA, 2012b) because it is the only 
qualifying peer-reviewed health assessment identified for 2-
aminotoluene that derives an oral CSF based on the best available 
science. In this health assessment, the EPA determined that 2-
aminotoluene is ``likely to be carcinogenic to humans'' by following 
the process described in the EPA's 2005 Guidelines for Carcinogen Risk 
Assessment (USEPA, 2005b; USEPA, 2012b).
    In the 2012 EPA PPRTV (USEPA, 2012b), the EPA selected a chronic 
carcinogenicity diet study in mice and rats (Weisburger et al., 1978) 
as the critical study to derive an oral CSF for 2-aminotoluene (see 
section 3.3 of Chapter 3 in the Regulatory Determination 5 Support 
Document for more details about the critical study). Increased 
subcutaneous fibromas and fibrosarcomas in male rats was the critical 
effect selected for derivation of an oral CSF because it provided the 
most sensitive cancer endpoint (USEPA, 2012b). Because the Weisburger 
et al. (1978) study exposed experimental animals to o-toluidine 
hydrochloride (HCl), the EPA converted the oral CSF of 0.02 (mg/kg-
day)-1 o-toluidine HCl to account for the molecular weight 
difference of o-toluidine, resulting in a computed oral CSF of 0.016 
(mg/kg-day)-1 for o-toluidine (2-aminotoluene) (USEPA, 
2012b).
    Because exposure began during postnatal development (i.e., at six 
to eight weeks of age) in the critical study (Weisburger et al., 1978), 
the EPA used the DWI-BW representing the 90th percentile consumers-
only, two-day average, direct and indirect community water consumption 
for children (birth to <21 years) of 0.0343 L/kg/day (USEPA, 2019a) to 
derive the HRL for 2-aminotoluene (see decision logic provided in 
section B.6.1.2 of the RD 5 Protocol, found in Appendix B of the 
Regulatory Determination 5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 2-
aminotoluene of 2 [micro]g/L after rounding to one significant figure, 
based on a one-in-a-million (10-6) CRL, an oral CSF of 0.016 
(mg/kg/day)-1 (USEPA, 2012b) and a DWI-BW of 0.0343 L/kg/day 
(USEPA, 2019a).
    These analyses formed the basis for the EPA's finding that 2-
aminotoluene may have adverse effect on the health of persons and 
therefore that Statutory Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that 2-aminotoluene does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of the following occurrence information.
    The primary occurrence data for 2-aminotoluene are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). Under UCMR 4 a.m., 37,517 samples collected from 5,030 
PWSs were analyzed for 2-aminotoluene. Of these systems, 86 (1.71%) 
reported detections at or above the MRL of 0.007 [micro]g/L. There were 
no detections greater than the HRL (2 [micro]g/L) or the \1/2\ HRL 
threshold (1 [micro]g/L) (USEPA, 2024b). This comprehensive dataset 
suggests that 2-aminotoluene is not present in public water systems at 
concentrations that would pose a risk to human health.
    Occurrence data for 2-aminotoluene in ambient water are available 
from the NWIS database and STORET. NWIS data show no detections of 2-
aminotoluene in any of the 145 samples at 67 sites. The STORET data set 
had no detections of 2-aminotoluene out of 3 samples collected at 3 
sites in 2021-2022.
    Based on the evaluation of these data sources, the EPA finds that 
2-aminotoluene does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating 2-Aminotoluene under the SDWA does not present a 
meaningful opportunity for health risk reduction for persons served by 
PWSs based on the estimated exposed population, including sensitive 
populations. UCMR 4 data indicate that the estimated population exposed 
to 2-aminotoluene at levels of public health concern is 0%. As a 
result, the agency finds that an NPDWR for 2-aminotoluene does not 
present a meaningful opportunity for health risk reduction.
(e) Preliminary Regulatory Determination for 2-Aminotoluene
    The agency is making a preliminary determination not to regulate 2-
aminotoluene with an NPDWR after evaluating health, occurrence and 
other related information against the three SDWA statutory criteria. 
While data indicate that 2-aminotoluene may have an adverse effect on 
human health, the occurrence data indicate that 2-aminotoluene does not 
occur, nor is it likely to occur in PWSs with a frequency and at levels 
of public health concern.
    Therefore, the agency has determined that regulating 2-aminotoluene 
with an NPDWR would not present a meaningful opportunity to reduce 
health risk for persons served by PWSs. The Regulatory Determination 5 
Support Document (USEPA, 2024b) and the Occurrence Data from the Fourth 
Unregulated Contaminant Monitoring Rule (UCMR 4) (USEPA, 2024c) present 
additional information and analyses supporting the agency's evaluation 
of 2-aminotoluene.
2. Cylindrospermopsin
(a) Background
    Cylindrospermopsin is a toxin naturally produced and released by 
cyanobacteria. Cyanobacteria, sometimes referred to as blue-green 
algae, are photosynthetic bacteria that are nearly ubiquitous in 
freshwater and marine environments. HABs of cyanobacteria in freshwater 
environments can release quantities of cyanotoxins, including 
cylindrospermopsin.
    Cylindrospermopsin is a tricyclic alkaloid (USEPA, 2015b). 
Cylindrospermopsin is naturally produced in the environment by 
cyanobacteria genera including the cylindrospermopsin-producing species 
Aphanizomenon, Dolichospermum (previously Anabaena), Lyngbya, 
Raphidiopsis (previously Cylindrosperopsis) and Umezakia (USEPA, 
2022d). Cyanotoxin production is influenced by environmental conditions 
that favor the growth of particular cyanobacterial species and strains. 
Factors that affect

[[Page 3846]]

cyanobacterial growth, cyanobacteria population dynamics and the 
development of blooms include nutrient concentrations, light intensity, 
water turbidity, temperature, competing bacteria and phytoplankton, pH 
and turbulence (mixing). The concentrations of cyanotoxins released 
from a bloom will depend on the composition of the bloom and 
environmental and ecosystem influences on bloom dynamics (USEPA, 
2015b).
    Cylindrospermopsin may readily leach or be released from intact 
cyanobacterial cells into surrounding water. Field studies have found 
that from 24% to 100% of cylindrospermopsin can be extracellular 
(Chorus and Welker, 2021). Cylindrospermopsin is highly water-soluble 
(WHO, 2020a). Its ability to partition from water to sediments is 
affected by the type of sediment, with some adsorption to organic 
carbon sediments and little adsorption to sandy and silt sediments. 
Bioaccumulation of cylindrospermopsin in freshwater organisms has been 
documented (Kinnear, 2010).
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to cylindrospermopsin may have an adverse effect on the 
health of persons as supported by the health assessments identified for 
RD 5 (USEPA, 2015b; WHO, 2020a). The health assessment selected to 
derive an HRL for cylindrospermopsin is the 2015 EPA Office of Water 
(OW) Health Effects Support Document (HESD) (USEPA, 2015b) because it 
is an EPA peer-reviewed health assessment that derives an oral toxicity 
value and it uses the best available science in its evaluation of 
noncancer risk for cylindrospermopsin.
    In the 2015 EPA OW HESD (USEPA, 2015b), the EPA selected an 11-week 
drinking water toxicity study in mice (Humpage and Falconer, 2002; 
Humpage and Falconer, 2003) as the critical study to derive an oral 
reference value (see section 4.3 of Chapter 4 in the Regulatory 
Determination 5 Support Document for more details about the critical 
study). A No Observed Adverse Effect Level (NOAEL) of 30 mg/kg/day for 
increased relative kidney weight in mice was the critical effect and 
point of departure (POD) selected to derive an oral reference value 
because this was the most sensitive endpoint assessed in the critical 
study (USEPA, 2015b). A total UF of 300 was applied to the POD: an 
interspecies UF (UFA) of 10, an intraspecies UF 
(UFH) of 10 and a database UF (UFD) of 3. After 
applying the total UF of 300 (details can be found in section 4.3 of 
Chapter 4 in the Regulatory Determination 5 Support Document), the oral 
reference value was calculated to be 0.0001 mg/kg/day (USEPA, 2015b) 
and the EPA selected this oral reference value to derive an HRL for RD 
5.
    The critical study does not report how old the mice were at the 
onset of exposure; however, it does report that mice weighed 20 to 25 
grams at the beginning of the experiment (Humpage and Falconer, 2002; 
Humpage and Falconer, 2003). The EPA extrapolated the body weight of 
the rodents to their approximate age to determine the most sensitive 
lifestage exposed (Jackson Labs, 2023). Because exposure was estimated 
to have begun during postnatal development (i.e., at approximately six 
to eight weeks of age), the EPA used the DWI-BW representing the 90th 
percentile consumers-only, two-day average, direct and indirect 
community water consumption for children (birth to <21 years) of 0.0343 
L/kg/day (USEPA, 2019a) to derive the to derive the HRL for 
cylindrospermopsin (see decision logic provided in section B.6.1.2 of 
the RD 5 Protocol, found in Appendix B of the Regulatory Determination 
5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
cylindrospermopsin of 0.6 [micro]g/L after rounding to one significant 
figure, based on an oral reference value of 0.0001 mg/kg/day (USEPA, 
2015b), a DWI-BW of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC 
(USEPA, 2000a). Note that this value differs from the 10-day HA for 
bottle-fed infants and young children (0.7 [micro]g/L) and the 10-day 
HA for school-age children through adults (3 [micro]g/L). These HA 
values are considered protective of non-carcinogenic adverse health 
effects over a ten-day exposure to cylindrospermopsin in drinking 
water.
    Based on these analyses, the EPA finds that cylindrospermopsin may 
have an adverse effect on the health of persons and therefore that 
Statutory Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that cylindrospermopsin does not occur 
with a frequency and at levels of public health concern in PWSs based 
on the EPA's evaluation of the following occurrence information.
    Occurrence data for cylindrospermopsin in ambient water are 
available from the USGS NAWQA program, the USGS NWIS database, the 
EPA's legacy STORET Data System and several published studies. 
Additionally, a total of 18 states voluntarily adopted use of the One 
Health Harmful Algal Bloom System and entered 421 reports during 2016-
2018 (Roberts et al., 2020). The majority of HAB events occurred during 
May-October (98%) and in freshwater bodies (90%). Cylindrospermopsin 
was reported as present in 4 (1%) of the 421 HAB events.
    The primary occurrence data for cylindrospermopsin are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). Under UCMR 4 a.m., 35,425 samples collected from 3,484 
PWSs were analyzed for cylindrospermopsin via EPA Method 545. 
Monitoring consisted of sampling finished drinking water in PWSs that 
use surface water or GWUDI. Groundwater systems were excluded from 
cyanotoxin monitoring. Monitoring occurred twice a month for four 
consecutive months during the period from March through November (for a 
total of eight sampling events). Sampling was conducted at entry points 
to the distribution system.
    In addition to analytical sample results, UCMR 4 required systems 
to provide information related to source water conditions and 
cyanobacteria/cyanotoxin occurrence and treatment, including bloom 
occurrence, possible bloom treatment and details on changes in source 
water quality conditions.
    Reported UCMR 4 cylindrospermopsin concentrations ranged from 0.09 
[micro]g/L (the MRL) to 0.877 [micro]g/L. Of these sampled systems, 12 
(0.34% of systems, serving 0.23% of the PWS-served population) reported 
at least one detection of cylindrospermopsin. Three systems serving 
nearly 31,000 people reported at least one detection of 
cylindrospermopsin greater than the \1/2\ HRL threshold of 0.3 
[micro]g/L and 1 system serving 10,174 people reported at least one 
detection of cylindrospermopsin greater than the HRL of 0.6 [micro]g/L. 
Extrapolating these findings from the population served by the PWSs 
participating in UCMR 4 to the national PWS-served population suggests 
that an estimated 34 PWSs serving around 488,000 people nationally have 
at least one detection of cylindrospermopsin while an estimated 14 PWSs 
serving 40,900 people nationally have at least one detection of 
cylindrospermopsin greater than the \1/2\ HRL threshold and only 1 PWS, 
serving 10,200 people, has at least one detection greater than the HRL.
    Based on the evaluation of these data sources, the EPA finds that 
cylindrospermopsin does not occur in PWSs with a frequency and at 
levels of

[[Page 3847]]

public health concern. Therefore, the EPA finds that Statutory 
Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating cylindrospermopsin under the SDWA does not present a 
meaningful opportunity for health risk reduction for persons served by 
PWSs based on the estimated exposed population, including sensitive 
populations. The estimated PWS-served population exposed to 
cylindrospermopsin at levels of public health concern is 0.01% based on 
UCMR 4 finished water data.
    Conventional water treatment (consisting of coagulation, 
sedimentation, filtration and chlorination) can generally remove intact 
cyanobacterial cells and low levels of cyanotoxins from source waters. 
However, water systems may face challenges in providing drinking water 
during a severe bloom event when there are high levels of cyanobacteria 
and cyanotoxins in source waters. With proactive planning, diligent 
operations and maintenance and active management, PWSs can reduce the 
risks of cyanotoxins breaking through the treatment process and 
occurring in finished drinking water. Because these non-regulatory 
efforts to manage cyanotoxins are effective, the agency finds that an 
NPDWR for cylindrospermopsin does not present a meaningful opportunity 
for health risk reduction.
(e) Preliminary Regulatory Determination for Cylindrospermopsin
    The EPA is making a preliminary determination not to regulate 
cylindrospermopsin with an NPDWR after evaluating health, occurrence 
and other related information against the three SDWA statutory 
criteria. While data suggest that cylindrospermopsin may have an 
adverse effect on human health, the occurrence data indicate that 
cylindrospermopsin is not occurring or not likely to occur in PWSs with 
a frequency and at levels of public health concern. Additionally, 
because conventional water treatment and continued efforts by water 
systems to manage cyanotoxins have proven effective, an NPDWR for 
cylindrospermopsin does not present a meaningful opportunity for health 
risk reduction.
2. Ethoprop
(a) Background
    Ethoprop is an organophosphate (phosphorodithioate) pesticide and 
is used as an insecticide and nematicide. Ethoprop was first registered 
in the U.S. in 1967 (USEPA, 2006a) and is used on vegetables, fruits 
and other plants, including potatoes, sweet potatoes, beans, cucumbers, 
cabbage, pineapples, bananas, plantains, tobacco and ornamentals. 
Environmental fate assessments with organic carbon partitioning 
coefficient (Koc) values of 70-120 L/kg suggest ethoprop is mobile in 
soil and water (NCBI, 2023a).
    USGS estimates the usage of ethoprop has unevenly declined from 
1992 to 2019, with less than 1 million pounds of ethoprop used per year 
since 2012 in the United States. According to USGS, ethoprop usage has 
been limited geographically in recent years, mainly to the Pacific 
Northwest and California.
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to ethoprop may have an adverse effect on the health of 
persons as supported by the health assessment identified for RD 5 
(USEPA, 2015c; USEPA, 2015d). For pesticide chemicals currently 
registered under the Federal Insecticide, Fungicide and Rodenticide Act 
(FIFRA), including ethoprop, toxicity information from the EPA's Office 
of Pesticide Programs (OPP) Human Health Risk Assessments (HHRAs) was 
used as the basis for HRL derivation (USEPA, 2024b).
    The health assessment selected to derive an HRL for ethoprop is the 
2015 EPA OPP HHRA (USEPA, 2015c; USEPA, 2015d), which provided both 
cancer and noncancer toxicity values (i.e., an oral reference value and 
oral CSF) for ethoprop. In 2023, OPP conducted exposure assessments for 
ethoprop to estimate human health risks resulting from registered uses 
(USEPA, 2023a). The cancer classification had then changed from 
``Likely to be Carcinogenic to Humans'' to ``Suggestive Evidence of 
Carcinogenic Potential'' based on the presence of thyroid C-cell tumors 
in male F344 rats (USEPA, 2005b; 2023a). Although the critical study 
showed suggestive cancer effects from exposure to ethoprop, there were 
no concerns for mutagenicity. As a result, OPP recommended using a non-
linear (i.e., RfD) approach as a protective measure of carcinogenic 
risk and did not conduct a new cancer assessment (USEPA, 2023a). 
Therefore, for RD 5 the EPA derived a noncancer HRL based on the oral 
reference value provided in the 2015 EPA OPP HHRA (USEPA, 2015c).
    In the 2015 EPA OPP HHRA, the EPA selected a repeat-dosing gavage 
study in rats (Chartier et al., 2005) as the critical study to derive 
the oral reference value (see section 5.3 of Chapter 5 in the 
Regulatory Determination 5 Support Document for more details about the 
critical study). Benchmark dose (BMD) modeling was used to determine 
the lower 95% confidence limit on the BMD level associated with a 10% 
response (BMDL10), the response in this case being 
inhibition of cholinesterase (ChE) activity (USEPA, 2015c). Inhibition 
of red blood cell (RBC) acetylcholinesterase (AChE) activity in 
postnatal day (PND) 11 males was the critical effect selected for 
derivation of the oral reference value because it was the most 
sensitive endpoint modeled (USEPA, 2015c). Therefore, the corresponding 
BMDL10 of 0.0653 mg/kg/day was selected as the POD for 
ethoprop (USEPA, 2015c). A total uncertainty factor (UF) of 1,000 was 
applied to the POD: an interspecies UF (UFA) of 10, an 
intraspecies UF (UFH) of 10, and a Food Quality Protection 
Act (FQPA) safety factor of 10 to account for uncertainty in the human 
dose-response relationship for neurodevelopmental effects (USEPA, 
2015c). After applying the total UF (for more details about the 
selected UF, see section 5.3 of Chapter 5 in the Regulatory 
Determination 5 Support Document), the oral reference value was 
calculated to be 0.000065 mg/kg/day and the EPA selected this oral 
reference value to derive an HRL for ethoprop.
    Because exposure began during early postnatal development (i.e., 11 
days of age) in the critical study (Chartier et al., 2005), the EPA 
used the DWI-BW representing the 90th percentile consumers-only, two-
day average, of direct and indirect community water consumption for 
infants (birth to <1 year) of 0.143 L/kg/day (USEPA, 2019a) to derive 
the HRL for ethoprop (see decision logic provided in section B.6.1.2 of 
the RD 5 Protocol, found in Appendix B of the Regulatory Determination 
5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
ethoprop of 0.09 [micro]g/L after rounding to one significant figure, 
based on an oral reference value of 0.000065 mg/kg/day (USEPA, 2015c), 
a DWI-BW of 0.143 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000a).
    Based on these analyses, the EPA finds that ethoprop may have an 
adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that ethoprop does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of occurrence information.

[[Page 3848]]

    The primary occurrence data for ethoprop are nationally 
representative drinking water monitoring data from UCMR 4 (2018-2020). 
Ethoprop was found in 0.1% of systems (5 of 5,028) monitored in UCMR 4 
a.m. Of systems that reported results for ethoprop, three systems, or 
0.06%, reported results above the \1/2\ HRL threshold of 0.045 
[micro]g/L, and one system (0.02%) reported a result above the HRL 
(0.09 [micro]g/L). Extrapolating the UCMR 4 data suggests that less 
than 0.01% of the national PWS-served population may be exposed to 
ethoprop in drinking water at levels above the HRL.
    Based on the evaluation of these data sources, the EPA finds that 
ethoprop does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    The EPA proposes to find that ethoprop does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of the occurrence information. Therefore, regulation 
of ethoprop under the SDWA does not present a meaningful opportunity 
for health risk reduction for persons served by PWSs.
(e) Preliminary Regulatory Determination for Ethoprop
    The agency is making a preliminary determination not to regulate 
ethoprop with an NPDWR after evaluating health, occurrence and other 
related information against the three SDWA statutory criteria. While 
data suggest that ethoprop may have an adverse effect on human health, 
the occurrence data indicate that ethoprop is not occurring or not 
likely to occur in PWSs with a frequency and at levels of public health 
concern. The Regulatory Determination 5 Support Document (USEPA, 2024b) 
and the Occurrence Data from the Fourth Unregulated Contaminant 
Monitoring Rule (UCMR 4) (USEPA, 2024c) present additional information 
and analyses supporting the agency's evaluation of ethoprop.
3. Microcystins
(a) Background
    Microcystins are toxins naturally produced and released by 
cyanobacteria. Cyanobacteria, sometimes referred to as blue-green 
algae, are photosynthetic bacteria that are nearly ubiquitous in 
freshwater and marine environments. HABs of cyanobacteria in freshwater 
environments can release quantities of cyanotoxins, including 
microcystins.
    Microcystins exist in multiple forms (congeners), based on 
variations in amino acid composition; there are approximately 100 known 
microcystin congeners (USEPA, 2015e). Microcystins are generally 
distinguished using letters that refer to the two variable amino acids. 
Microcystin-LR, which includes leucine (L) and arginine (R) amino 
acids, is the most common congener and also the most intensively 
studied (USEPA, 2015e). Synonyms for microcystin-LR include 
cyanoginosin LR (NCBI, 2022).
    The cyanobacteria genera Anabaena, Fischerella, Gloeotrichia, 
Microcystis, Nodularia, Nostoc, Oscillatoria and Planktothrix are known 
to include microcystin-producing species (USEPA, 2015e). Microcystins 
are the most common cyanotoxins found worldwide and they have been 
reported in surface waters in most of the U.S. (Funari and Testai, 2008 
as cited in USEPA, 2015e). For the most part, microcystins are not 
released into surrounding waters by healthy living cyanobacterial 
cells. Release of microcystins generally results from senescence or 
lysis. Cyanotoxin production is influenced by environmental conditions 
that favor the growth of particular cyanobacterial species and strains. 
Factors that affect cyanobacterial growth, cyanobacteria population 
dynamics and the development of blooms include nutrient concentrations, 
light intensity, water turbidity, temperature, competing bacteria and 
phytoplankton, pH and turbulence (mixing). The concentrations of 
cyanotoxins released from a bloom will depend on the composition of the 
bloom and environmental and ecosystem influences on bloom dynamics 
(USEPA, 2015f). Microcystins have the potential for bioconcentration 
and bioaccumulation in tissue (Machado et al., 2017).
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to microcystin congeners microcystin-LA, microcystin-LW, 
microcystin-RR, microcystin-YR and microcystin-LR, referred to 
collectively throughout this document as ``microcystins,'' may have an 
adverse effect on the health of persons as supported by the multiple 
health assessments identified for RD 5 (USEPA, 2015e; HC, 2017; WHO, 
2020b). The health assessment selected for RD 5 is the 2015 EPA OW HESD 
(USEPA, 2015e) because it is an EPA peer-reviewed health assessment 
that derives an oral toxicity value and uses the best available science 
in its evaluation of noncancer risk.
    In the 2015 EPA OW HESD (USEPA, 2015e), the EPA selected a 28-day 
drinking water study in 11-week-old male rats (Heinze, 1999) as the 
critical study to derive an oral reference value (see section 6.3 of 
Chapter 6 in the Regulatory Determination 5 Support Document for more 
details about the critical study). A Lowest Observed Adverse Effect 
Limit (LOAEL) of 50 mg/kg/day for liver effects in rats orally exposed 
to microcystin-LR was identified as the critical effect and used to 
derive an oral reference value because this was considered the ``most 
appropriate basis for quantitation as it was a common finding among 
oral toxicology studies'' (USEPA, 2015e). Since microcystin-LR is one 
of the most potent microcystin congeners and the majority of 
microcystin toxicity data comes from studying this congener, 
microcystin-LR was used as a surrogate for deriving an oral reference 
value for all microcystins (USEPA, 2015e). A total UF of 1000 was 
applied to the POD: a UFA of 10, a UFH of 10, a 
LOAEL-to-NOAEL extrapolation UF (UFL) of 3 and a 
UFD of 3. After applying the total UF of 1000, the oral 
reference value was calculated to be 0.00005 mg/kg/day (USEPA, 2015e) 
and the EPA selected this oral reference value to derive an HRL for 
microcystins.
    Because exposure in the critical study started post-adolescence 
(i.e., at 11 weeks of age), the EPA used the DWI-BW EF representing the 
90th percentile consumers-only, two-day average, direct and indirect 
community water consumption for adults (21 years and older) of 0.0336 
L/kg/day (USEPA, 2019a) to derive the HRL for microcystins (see 
decision logic provided in section B.6.1.2 of the RD 5 Protocol, found 
in Appendix B of the Regulatory Determination 5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
microcystins of 0.3 [micro]g/L after rounding to one significant 
figure, based on an oral reference value of 0.00005 mg/kg/day (USEPA, 
2015e), a DWI-BW of 0.0336 L/kg/day (USEPA, 2019a) and a 20% RSC 
(USEPA, 2000a).
    Based on these analyses, the EPA finds that microcystins may have 
an adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that microcystins do not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's

[[Page 3849]]

evaluation of the following occurrence information.
    Occurrence data for microcystins in ambient water are available 
from the USGS NAWQA program, the USGS NWIS database, the EPA's legacy 
STORET Data System and several published studies. Additionally, a total 
of 18 states voluntarily adopted use of the One Health Harmful Algal 
Bloom System and entered 421 reports during 2016-2018 (Roberts et al., 
2020). The majority of HAB events occurred during May-October (98%) and 
in freshwater bodies (90%). Microcystins were reported as present in 
291 of the 421 HABs. Of the 35 HABs where multiple cyanotoxins were 
found, microcystins were present in 33. Ambient water occurrence data 
are also available in the National Lakes Assessment. According to the 
2017 report (USEPA, 2022e), microcystin was found in 21% of lakes. The 
minimum detection level was 0.1 [micro]g/L. The EPA's recreational 
criterion (8 [micro]g/L) was exceeded in 2% of lakes (4,400 lakes).
    The primary occurrence data for microcystins are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). Under UCMR 4 a.m., 35,000 samples were collected from 
3,485 PWSs and analyzed for total microcystins via EPA Method 546.\14\ 
Monitoring consisted of sampling finished drinking water in PWSs that 
use surface water or groundwater under the influence of surface water 
(GWUDI. Groundwater systems were excluded from cyanotoxin monitoring. 
Monitoring occurred twice a month for four consecutive months from 
March through November (for a total of eight sampling events). Sampling 
was conducted at entry points to the distribution system.
---------------------------------------------------------------------------

    \14\ Using EPA Method 546, UCMR 4 systems were required to 
report total microcystins values at or above the EPA-defined MRL of 
0.3 [mu]g/L. If a reporting threshold of 0.3 [mu]g/L for total 
microcystins using EPA Method 546 was exceeded, systems were 
required to report values for the six included microcystin congeners 
at or above the EPA-defined MRLs for each individual congener using 
EPA Method 544. For more details, see USEPA (2024c).
---------------------------------------------------------------------------

    In addition to analytical sample results, UCMR 4 required systems 
to provide information related to source water conditions and 
cyanobacteria/cyanotoxin occurrence and treatment, including bloom 
occurrence, possible bloom treatment and details on changes in source 
water quality conditions.
    Reported UCMR 4 total microcystins concentrations ranged from 0.32 
[micro]g/L to 0.83 [micro]g/L. Seven systems (0.20% of systems, serving 
0.06% of the PWS-served population) reported at least one result at or 
above the MRL for total microcystins. Extrapolating these findings 
suggests that an estimated 29 PWSs serving 0.06% of the PWS-served 
population nationally may have detectable levels of total microcystins. 
While all reported results were above the HRL (0.3 [micro]g/L), only 
eight of the 35,000 samples collected during UCMR 4 contained 
reportable concentrations of microcystins.
    Based on the evaluation of these data sources, the EPA finds that 
microcystins do not occur and are not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating microcystins under the SDWA does not present a 
meaningful opportunity for health risk reduction for persons served by 
PWSs based on the estimated exposed population, including sensitive 
populations. The estimated population exposed to microcystins at levels 
of public health concern is 0.06% based on UCMR 4 finished water data.
    Conventional water treatment (consisting of coagulation, 
sedimentation, filtration and chlorination) can generally remove intact 
cyanobacterial cells and low levels of cyanotoxins from source waters. 
However, water systems may face challenges in providing drinking water 
during a severe bloom event when there are high levels of cyanobacteria 
and cyanotoxins in source waters. With proactive planning, diligent 
operations and maintenance and active management, PWSs can reduce the 
risks of cyanotoxins breaking through the treatment process and 
occurring in finished drinking water. Because these non-regulatory 
efforts are effective, the agency finds that an NPDWR for microcystins 
does not present a meaningful opportunity for health risk reduction.
(e) Preliminary Regulatory Determination for Microcystins
    The agency is making a preliminary determination to not regulate 
microcystins with an NPDWR after evaluating health, occurrence and 
other related information against the three SDWA statutory criteria. 
While data suggest that microcystins may have an adverse effect on 
human health, the occurrence data indicate that microcystins are not 
occurring or not likely to occur in PWSs with a frequency and at levels 
of public health concern. Additionally, because conventional water 
treatment and continued efforts by water systems to manage cyanotoxins 
have proven effective, an NPDWR for microcystins does not present a 
meaningful opportunity for health risk reduction.
5. Molybdenum
(a) Background
    Molybdenum is a naturally occurring element, which, especially in 
the form of molybdenum trioxide, is commonly used in metallurgy, 
including in alloys with cast iron, steel and superalloys. Molybdenum 
compounds are also used in catalysts, lubricants and pigments.
    Molybdenum is naturally present in soils and additional molybdenum 
may be added by weathering and atmospheric deposition and by direct 
human activity such as application of molybdenum and phosphate 
fertilizers (Wong et al., 2021; Smedley and Kinniburgh, 2017). 
Anthropogenic sources of molybdenum in water include effluents from 
molybdenum, uranium and copper mining and milling operations, oil 
production and oil refining operations, and coal-fired power plants. 
Molybdenum is generally more mobile in water under alkaline conditions, 
with a greater potential for bioavailability through water exposure 
(ATSDR, 2020).
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to molybdenum may have an adverse effect on the health of 
persons as supported by the health assessments identified for RD 5 
(USEPA, 1992; WHO, 2011; ATSDR, 2020). The health assessment selected 
for RD 5 is the 2020 ATSDR Toxicological Profile (ATSDR, 2020) because 
it is the most recent peer-reviewed health assessment identified for 
molybdenum that derives an oral toxicity value, it uses the best 
available science in its evaluation of noncancer risk, and its toxicity 
value is based on a more recent critical study (Murray et al., 2014) 
than those of previous health assessments (USEPA, 1992; WHO, 2011).
    In the 2020 ATSDR Toxicological Profile (ATSDR, 2020), ATSDR 
selected a 90-day dietary toxicity study in rats (Murray et al. 2014) 
as the critical study to derive an intermediate-duration oral reference 
value (see section 7.3 of Chapter 7 in the Regulatory Determination 5 
Support Document for more details about the critical study). A NOAEL of 
17 mg/kg/day for renal effects in female rats was identified as the 
critical effect to derive an oral reference value because this was the 
most sensitive endpoint identified (ATSDR,

[[Page 3850]]

2020). After applying the total UF of 100 and a modifying factor of 3, 
the intermediate-duration oral reference value was calculated to be 
0.06 mg/kg/day. Because ATSDR did not derive a chronic-duration oral 
reference value, and the EPA's definition of chronic exposure is 
repeated exposure (oral, dermal or inhalation) for more than 
approximately 90 days to 2 years (USEPA, 2023b), the EPA applied a UF 
for extrapolation from subchronic-to chronic exposure duration 
(UFS) of 3, per agency guidelines (USEPA, 2002), to the 
intermediate-duration oral reference value that was derived using the 
90-day study. Therefore, the resulting oral reference value used to 
derive the HRL for molybdenum was calculated to be 0.02 mg/kg/day.
    Because exposure began during postnatal development (approximately 
nine weeks of age), the EPA used the DWI-BW representing the 90th 
percentile consumers-only, two-day average, direct and indirect 
community water consumption for children (birth to <21 years) of 0.0343 
L/kg/day (USEPA, 2019a) to derive the HRL for molybdenum (see decision 
logic provided in section B.6.1.2 of the RD 5 Protocol, found in 
Appendix B of the Regulatory Determination 5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
molybdenum of 100 [micro]g/L after rounding to one significant figure, 
based on an oral reference value of 0.06 mg/kg/day (ATSDR, 2020), with 
an additional UFS of 3, a DWI-BW of 0.0343 L/kg/day (USEPA, 
2019a) and a 20% RSC (USEPA, 2000a).
    Based on these analyses, the EPA finds that molybdenum may have an 
adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that molybdenum does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of the following occurrence information.
    The primary occurrence data for molybdenum are nationally 
representative drinking water monitoring data from the UCMR 3 program 
(2013-2015). Under UCMR 3 a.m., 62,986 samples were collected from 
4,922 PWSs and analyzed for molybdenum. Of these systems, 52% reported 
results at or above the MRL of 1 [micro]g/L. Seven systems (0.14%) 
reported results above the HRL of 100 [micro]g/L and 29 systems (0.59%) 
reported results above the \1/2\ HRL threshold of 50 [micro]g/L. Based 
on the UCMR 3 occurrence data set, a national estimate of 216 systems 
and 0.06% of the PWS-served population may be exposed to molybdenum in 
drinking water at levels exceeding the HRL.
    Occurrence data for molybdenum in ambient water are available from 
the NAWQA program and NWIS database. Across the three cycles of NAWQA, 
molybdenum was detected in 45% to 100% of samples. The HRL was exceeded 
in a single surface water sample (in Cycle 1) and in 0.12% to 0.26% of 
groundwater samples across the three cycles. Non-NAWQA NWIS data for 
molybdenum include 47 finished water samples from 29 sites. The highest 
reported finished water concentration (52.5 [micro]g/L) exceeds the \1/
2\ HRL threshold but not the HRL. The median concentration of NWIS 
detections was 1.64 [micro]g/L.
    For additional information on occurrence data available for 
molybdenum in drinking water please see section 7.4 of Chapter 7 in the 
Regulatory Determination 5 Support Document (USEPA, 2024b).
    Based on the evaluation of these data sources, the EPA finds that 
molybdenum does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating molybdenum under the SDWA does not present a meaningful 
opportunity for health risk reduction for persons served by PWSs based 
on the estimated exposed population, including sensitive populations. 
UCMR 3 data indicate that the estimated population exposed to 
molybdenum above the HRL is 0.08%. As a result of the low occurrence 
above the HRL, the agency finds that an NPDWR for molybdenum does not 
present a meaningful opportunity for health risk reduction.
(e) Preliminary Regulatory Determination for Molybdenum
    The agency is making a preliminary determination not to regulate 
molybdenum with an NPDWR after evaluating health, occurrence and other 
related information against the three SDWA statutory criteria. While 
data suggest that molybdenum may have an adverse effect on human 
health, the occurrence data indicate that molybdenum is not occurring 
or not likely to occur in PWSs with a frequency and at levels of public 
health concern. The Regulatory Determination 5 Support Document (USEPA, 
2024b) and the Occurrence Data from the Third Unregulated Contaminant 
Monitoring Rule (UCMR 3) (USEPA, 2019b) present additional information 
and analyses supporting the agency's evaluation of molybdenum.
7. Permethrin
(a) Background
    Permethrin is a pyrethroid pesticide primarily used as an 
insecticide, with various synonyms including ambush and corsair. It was 
first registered in the U.S. in 1979.
    Sources of permethrin include agricultural usage and industrial 
activities. TRI provides insight into industrial releases of 
permethrin. There have been no reported surface water discharges since 
2005. Permethrin usage in agriculture has been estimated by USGS to 
have peaked in 1995 with 1.4 million pounds, with a gradual decrease to 
steady usage between around 600,000 and 800,000 pounds annually 
throughout 2001-2019.
    The EPA's assessments of permethrin include its chemical and 
physical properties, such as very low solubility in water (0.006 mg/L) 
and Koc values of 10,471-86,000 L/kg, which suggest that 
permethrin will be of low mobility in soil and less likely to partition 
to water. Biodegradation is expected to be rapid in various 
environmental conditions, since the half-life of permethrin in 
sediment/seawater is <2.5 days, while the half-life of permethrin in a 
model ecosystem at 15-19 degrees Celsius and a pH of 7.7 was 1.1-3.6 
days.
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to permethrin may have an adverse effect on the health of 
persons as supported by the health assessment identified for RD 5 
(USEPA, 2020b; USEPA, 2020c). For pesticide chemicals currently 
registered under FIFRA, including permethrin, toxicity information from 
EPA's OPP HED HHRAs was used as the basis for HRL derivation (USEPA, 
2023c).
    The health assessment selected to derive an HRL for permethrin is 
the 2020 EPA OPP HHRA (USEPA, 2020ba; USEPA, 2020c). Following the 
approach described in the EPA's Guidelines for Carcinogen Risk 
Assessment (USEPA, 2005b), permethrin was classified in the health 
assessment as having ``Suggestive Evidence of Carcinogenic Potential'' 
based on lung adenomas in female mice. However, due to the lack of 
increased hazard from repeated/chronic exposure to permethrin, the 
acute risk estimate derived from the non-linear approach is

[[Page 3851]]

protective of chronic toxicity, including carcinogenicity, that could 
result from permethrin exposure (USEPA, 2020c). Therefore, the EPA 
selected an acute gavage study in rats (Wolansky et al., 2006) as the 
critical study to derive an oral reference value (see section 8.3 of 
Chapter 8 in the Regulatory Determination 5 Support Document for more 
details about the critical study). BMD modeling was performed to derive 
a lower 95% confidence limit on the BMD level associated with a 
difference of one standard deviation from controls (BMDL1SD) 
for decreased motor activity (Wolansky et al., 2006), which was 
identified as the critical effect for dietary exposure, as this was the 
most sensitive endpoint measured (USEPA, 2020c). The BMDL1SD 
was calculated to be 44 mg/kg. A total UF of 100 was applied to the 
POD: a UFH of 10 and a UFA of 10. After applying 
the total UF of 100, the oral reference value was calculated to be 0.44 
mg/kg/day (USEPA, 2020c) and the EPA selected this oral reference value 
to derive an HRL for permethrin.
    Because exposure began during postnatal development (i.e., at 
approximately nine weeks of age) in the critical study (Wolansky et 
al., 2006), the EPA used the DWI-BW representing the 90th percentile 
consumers-only, two-day average, direct and indirect community water 
consumption for children (birth to <21 years) of 0.0343 L/kg/day 
(USEPA, 2019a) to derive the HRL for permethrin (see decision logic 
provided in section B.6.1.2 of the RD 5 Protocol, found in Appendix B 
of the Regulatory Determination 5 Support Document, USEPA, 2024b).
    Following HRL derivation practices, the EPA derived an HRL for 
permethrin of 3,000 [micro]g/L after rounding to one significant 
figure, based on an oral reference value of 0.44 mg/kg/day (USEPA, 
2020b; USEPA, 2020c), a DWI-BW of 0.0343 L/kg/day (USEPA, 2019a) and a 
20% RSC (USEPA, 2000a).
    Based on these analyses, the EPA finds that permethrin may have an 
adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that permethrin does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of occurrence information.
    The primary occurrence data for permethrin are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). Under UCMR 4 a.m., 37,291 samples collected from 5,028 
PWSs were analyzed for permethrin. Permethrin was detected in 0.26% of 
systems at or above the MRL of 0.04 [micro]g/L. There were no reported 
results above the HRL of 3,000 [micro]g/L or above the \1/2\ HRL 
threshold. This comprehensive dataset suggests that permethrin is not 
present in public water systems at concentrations that would pose a 
risk to human health.
    To supplement the data obtained from UCMR 4, the EPA also reviewed 
ambient water data from the USGS NAWQA program. NAWQA Cycle 2 showed no 
detections of permethrin. NAWQA Cycle 3 showed detections of permethrin 
in 2 of 11 sites (18%) with no results above the HRL.
    Based on the evaluation of these data sources, the EPA finds that 
permethrin does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating permethrin under the SDWA does not present a meaningful 
opportunity for health risk reduction for persons served by PWSs based 
on the estimated exposed population, including sensitive populations. 
UCMR 4 findings indicate the estimated population exposed to permethrin 
at levels of public health concern is 0%.
(e) Preliminary Regulatory Determination for Permethrin
    The agency is making a preliminary determination to not regulate 
permethrin with an NPDWR after evaluating health, occurrence and other 
related information against the three SDWA statutory criteria. While 
data suggest that permethrin may have an adverse effect on human 
health, the occurrence data indicate that permethrin is not occurring 
or not likely to occur in PWSs with a frequency and at levels of public 
health concern.
    Therefore, the agency has made the preliminary determination that 
an NPDWR for permethrin would not present a meaningful opportunity to 
reduce health risk for persons served by PWSs. The Regulatory 
Determination 5 Support Document (USEPA, 2024b) presents additional 
information and analyses supporting the agency's evaluation of 
permethrin.
7. Profenofos
(a) Background
    Profenofos is an organophosphate pesticide that is applied as an 
insecticide. Synonyms for profenofos include curacron and selecron 
(NCBI, 2023b). Profenofos was first registered in the U.S. in 1982 
(USEPA, 2008c). Profenofos registration was canceled in 2018 and it 
currently has no active labels in the EPA's Pesticide Product and Label 
System database (USEPA, 2023c). USGS Pesticide Use Maps show cotton is 
the sole crop to which profenofos was applied in the years before 
cancellation; usage diminished since the mid-1990s and ceased around 
2011 according to these records.
    Environmental fate assessments indicate that low to slight mobility 
in soil and transport to water is expected based on Koc 
values. Volatilization from water is not expected to occur based on the 
contaminant's Henry's Law Constant; thus it will remain once present in 
water (NCBI, 2023b). In soil and water, biodegradation may occur, but 
profenofos is stable to photolysis in these media and is not likely to 
degrade with exposure to sunlight.
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to profenofos may have an adverse effect on the health of 
persons as supported by the health assessment identified for RD 5 
(USEPA, 2015d; USEPA, 2015g). For pesticide chemicals currently 
registered under FIFRA, including profenofos, toxicity information from 
EPA OPP HED HHRAs was used as the basis for HRL derivation (USEPA, 
2024b).
    The health assessment selected to derive an HRL for profenofos is 
the 2015 EPA OPP HHRA (USEPA, 2015d; USEPA, 2015g). The EPA selected a 
chronic toxicity and carcinogenicity study in rats (Burdock et al., 
1981) as the critical study to derive an oral reference value for 
profenofos (see section 9.3 of Chapter 9 in the Regulatory 
Determination 5 Support Document for more details about the critical 
study). A BMDL10 of 0.12 mg/kg/day based on RBC AChE 
inhibition was identified as the critical effect and POD for dietary 
exposure, as this was the most sensitive endpoint measured (USEPA, 
2015g). After applying the total UF of 1,000, the oral reference value 
was calculated to be 0.00012 mg/kg/day (USEPA, 2015g) and the EPA 
selected this oral reference value to derive an HRL for profenofos.
    The EPA extrapolated the body weight of the rodents to their 
approximate age at the onset of exposure in the critical study (Burdock 
et al., 1981) to determine the most sensitive lifestage exposed. 
Because exposure was estimated to have begun during postnatal 
development (i.e., at approximately seven to eight weeks of age), the 
EPA used the DWI-BW representing the 90th percentile

[[Page 3852]]

consumers-only, two-day average, direct and indirect community water 
consumption for children (birth to <21 years) of 0.0343 L/kg/day 
(USEPA, 2019a) to derive the HRL for profenofos (see decision logic 
provided in section B.6.1.2 of the RD 5 Protocol, found in Appendix B 
of the Regulatory Determination 5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
profenofos of 0.7 [micro]g/L after rounding to one significant figure, 
based on an oral reference value of 0.00012 mg/kg/day (USEPA, 2015d; 
USEPA, 2015g), a DWI-BW of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC 
(USEPA, 2000a).
    Based on these analyses, the EPA finds that profenofos may have an 
adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that profenofos does not occur with a 
frequency and at levels of public health concern in PWSs after 
evaluation of information from the following sources: UCMR 4, Consumer 
Confidence Reports (CCRs) from PWSs, USDA PDP, USGS PMP.
    The primary occurrence data for profenofos are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). The MRL for profenofos was 0.3 [micro]g/L. Under UCMR AM, 
37,287 samples collected from 5,028 PWSs were analyzed for profenofos 
and profenofos was detected in only four systems (0.08%). One system 
reported a result above the HRL of 0.7 [micro]g/L. This comprehensive 
dataset suggests that profenofos is not present in public water systems 
at concentrations that would pose a risk to human health.
    Ambient water data from the USGS NAWQA program and NWIS database 
were evaluated. In NAWQA Cycle 1, profenofos was not detected in any 
samples at any sites. In Cycle 2, profenofos was detected only once, in 
surface water, and the detection was below the HRL. In Cycle 3, 
profenofos was detected in 0.06% of both groundwater and surface water 
samples. The highest concentration observed in surface water is less 
than the \1/2\ HRL threshold. In NWIS, profenofos was detected in a 
single surface water sample representing 0.2% of surface water sites. 
There were no detections in groundwater. The single surface water 
detection had a profenofos concentration of 0.00019 [micro]g/L, which 
is less than the \1/2\ HRL threshold.
    Based on the evaluation of these data sources, the EPA finds that 
profenofos does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating profenofos under the SDWA does not present a meaningful 
opportunity for health risk reduction for persons served by PWSs based 
on the estimated exposed population. The estimated population exposed 
to profenofos at levels of public health concern in drinking water is 
less than 0.005%.
(e) Preliminary Regulatory Determination for Profenofos
    The agency is making a preliminary determination not to regulate 
profenofos with an NPDWR after evaluating health, occurrence and other 
related information against the three SDWA statutory criteria. While 
data suggest that profenofos may have an adverse effect on human 
health, occurrence data indicate that profenofos is not occurring or 
not likely to occur in PWSs with a frequency and at levels of public 
health concern.
    Therefore, the agency has determined that an NPDWR for profenofos 
would not present a meaningful opportunity to reduce health risk for 
persons served by PWSs. The Regulatory Determination 5 Support Document 
(USEPA, 2024b) presents additional information and analyses supporting 
the agency's evaluation of profenofos.
8. Tebuconazole
(a) Background
    Tebuconazole is a monochlorobenzene, triazole and tertiary alcohol 
that is used as a fungicide. It was first registered by the EPA in 1983 
(USEPA, 2023d). Synonyms for tebuconazole include folicur, 
terbutrazole, ethyltrianol and fenetrazole (NCBI, 2023c).
    The USGS provides estimates for annual usage of U.S. pesticides, 
including tebuconazole. The USGS pesticide use data show that there has 
been an increase in tebuconazole use over the past few decades, peaking 
in 2015 at over 2.5 million pounds and then remaining steady at around 
2.0 million pounds per year from 2016 to 2019 (USGS, 2023).
    Tebuconazole is expected to have a high likelihood of partitioning 
to water based on its Henry's Law Constant, and volatilization from 
water is not expected (NCBI, 2023c). Tebuconazole is expected to be 
persistent in soils and water based on the soil aerobic metabolism 
half-life of approximately 800 days, as well as resistance to 
photolysis in water and soil (USEPA, 2000b; NCBI, 2023c).
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to tebuconazole may have an adverse effect on the health 
of persons as supported by the health assessment identified for RD 5 
(USEPA, 2021d; USEPA, 2021e). For pesticide chemicals currently 
registered under the FIFRA, including tebuconazole, toxicity 
information from EPA OPP HED HHRAs was used as the basis for HRL 
derivation (USEPA, 2024b).
    The health assessment selected to derive an HRL for tebuconazole is 
the 2021 EPA OPP HHRA (USEPA, 2021d; USEPA, 2021e). The EPA selected a 
developmental toxicity study in mice (Becker and Biedermann, 1995) as 
the critical study to derive the oral reference value (see section 10.3 
of Chapter 10 in the Regulatory Determination 5 Support Document for 
more details about the critical study). A NOAEL of 3 mg/kg/day for 
increased incidence of fetal skull and neural tube defects was 
identified as the critical effect and POD, as this was the most 
sensitive endpoint measured after gestational exposure to tebuconazole 
via gavage (USEPA, 2021d). A total UF of 100 was applied to the POD: a 
UFA of 10 and a UFH of 10 (USEPA, 2021d). After 
applying the total UF of 100, the oral reference value was calculated 
to be 0.03 mg/kg/day and the EPA selected this oral reference value to 
derive an HRL for tebuconazole.
    Because the mice in the critical study (Becker and Biedermann, 
1995) were exposed to tebuconazole during gestation only (i.e., 
gestation days 6 through 15), the EPA determined that the critical 
effect in the fetus corresponds with gestational exposure in humans. 
The EPA used the DWI-BW representing the 90th percentile consumers-
only, two-day average, direct and indirect community water consumption 
for females of reproductive age (13 to <50 years) of 0.0354 L/kg/day 
(USEPA, 2019a) to derive the HRL for tebuconazole, as it is more health 
protective (i.e., greater) than the DWI-BW for pregnant women (0.0333 
L/kg/day) (USEPA, 2019a) (see decision logic provided in section 
B.6.1.2 of the RD 5 Protocol, found in Appendix B of the Regulatory 
Determination 5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
tebuconazole of 200 [micro]g/L after rounding to one significant 
figure, based on an oral reference value of 0.03 mg/kg/day

[[Page 3853]]

(USEPA, 2021d; USEPA, 2021e), a DWI-BW of 0.0354 L/kg/day (USEPA, 
2019a) and a 20% RSC (USEPA, 2000a).
    Based on these analyses, the EPA finds that tebuconazole may have 
an adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that tebuconazole does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of the following occurrence information.
    The primary occurrence data for tebuconazole are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). Under UCMR 4 a.m., 37,286 samples collected from 5,028 
PWSs were analyzed for tebuconazole. Tebuconazole was found at or above 
the MRL of 0.2 [micro]g/L in three of the 5,028 systems, or 0.06%. 
However, there were no exceedances of the HRL (200 [micro]g/L) or the 
\1/2\ HRL threshold (USEPA, 2024b). Reported results ranged from 0.21 
to 1.96 [micro]g/L. This comprehensive dataset suggests that 
tebuconazole is not present in public water systems at concentrations 
that would pose a risk to human health.
    To understand the impact of tebuconazole use post UCMR 4, the EPA 
assessed ambient water and limited finished water data collected after 
2020. Sources of such data include CCRs from Community Water Systems 
(CWSs), PWSs, USDA PDP, the NAWQA program, the NWIS database, STORET 
and several published studies. Data on tebuconazole were available from 
CCRs prepared by five CWSs from 2018 to 2021; tebuconazole was not 
detected in any system. Tebuconazole was included in the USDA PDP from 
2001 to 2013, where it was detected in 2.11% of 2,656 raw water samples 
and 2.18% of 3,575 finished water samples, but no detected 
concentrations exceeded the \1/2\ HRL threshold or the HRL (USDA, 
2022). Cycle 2 and Cycle 3 of the NAWQA program found tebuconazole in 
surface water (17.97% to 26.48% of samples) and groundwater (0% to 
0.11% of samples), but no concentrations exceeded the \1/2\ HRL 
threshold or the HRL (WQP, 2023). Non-NAWQA NWIS data (1991-023) show 
no detected concentration greater than the \1/2\ HRL threshold or the 
HRL in ambient water (WQP, 2023). Analysis of STORET data from 2003 to 
2016 shows that in 2,021 samples tested for tebuconazole there were no 
detectable concentrations (WQP, 2023).
    Based on the evaluation of these data sources, the EPA finds that 
tebuconazole does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating tebuconazole under the SDWA does not present a 
meaningful opportunity for health risk reduction for persons served by 
PWSs based on the estimated exposed population, including sensitive 
populations. The estimated population exposed to tebuconazole at levels 
of public health concern is 0%, based on UCMR 4 finished water data 
from 2018-2020.
(e) Preliminary Regulatory Determination for Tebuconazole
    The agency is making a preliminary determination not to regulate 
tebuconazole with an NPDWR after evaluating health, occurrence and 
other related information against the three SDWA statutory criteria. 
While data suggest that tebuconazole may have an adverse effect on 
human health, the occurrence data indicate that tebuconazole is not 
occurring or not likely to occur in PWSs with a frequency and at levels 
of public health concern and that regulation of such contaminant does 
not present a meaningful opportunity for health risk reduction served 
by PWSs. The Regulatory Determination 5 Support Document (USEPA, 2024b) 
and the Occurrence Data from the Fourth Unregulated Contaminant 
Monitoring Rule (UCMR 4) (USEPA, 2024c) present additional information 
and analyses supporting the agency's evaluation of tebuconazole.
9. Tribufos
(a) Background
    Tribufos is a thiophosphate pesticide that is used as an 
insecticide and cotton defoliant. It was first registered for use in 
the United States in 1961 (USEPA, 2009b). The EPA conducted a 
Reregistration Eligibility Decision (RED) for tribufos in July 2006, 
which included a comprehensive review of the available data on its 
environmental and human health effects (USEPA, 2006b). Tribufos is not 
listed on the EPA's most recent list of Restricted Use Pesticides (RUP) 
(USEPA, 2022f). Synonyms for tribufos include butifos, butiphos, butyl 
phosphorotrithioate and tribuphos (NCBI, 2023d).
    According to TRI data for tribufos from the years 1995-2022, on-
site surface water discharges peaked in 1999 at 161 pounds and no 
discharges have been reported since 2007, with specific usage data 
indicating fluctuations based on agricultural demand and cotton acreage 
with an overall reduction in usage since 1999. The reports highlight 
the targeted and seasonal application of tribufos, reflecting its 
specific role in cotton production rather than widespread use 
throughout the year (USEPA, 2024b).
    Environmental fate assessments with organic carbon partitioning 
coefficient (Koc) values of 4,870-12,684 L/kg suggest that 
tribufos will have little to no mobility in soil (NCBI, 2023d). Its 
strong adsorption to soil organic matter suggests limited mobility in 
soil, minimizing leaching into water. Tribufos is less mobile in soil 
and tends to remain near the application site. Persistence depends on 
various factors, including degradation and environmental conditions 
(USEPA, 2024b).
(b) Statutory Criterion 1 (Adverse Health Effects)
    Exposure to tribufos may have an adverse effect on the health of 
persons as supported by the health assessment identified for RD 5 
(USEPA, 2015h; USEPA, 2015i). For pesticide chemicals currently 
registered under FIFRA, including tribufos, toxicity information from 
EPA OPP HED HHRAs was used as the basis for HRL derivation (USEPA, 
2024b).
    The health assessment selected to derive an HRL for tribufos is the 
2015 EPA OPP HHRA (USEPA, 2015h; USEPA, 2015i). The EPA selected a 
subchronic oral neurotoxicity study in rats (Sheets and Gilmore, 2001) 
as the critical study to derive an oral reference value for tribufos 
(see section 11.3 of Chapter 11 in the Regulatory Determination 5 
Support Document for more details about the critical study). BMD 
modeling was performed to determine a BMDL10 for inhibition 
of RBC ChE in adult female rats. The BMDL10 of 0.19 mg/kg/
day was identified as the critical effect and POD, as this was the most 
sensitive endpoint measured (USEPA, 2015h). A total UF of 1,000 was 
applied to the POD: a UFA of 10, a UFH of 10 and 
an FQPA safety factor of 10 to account for uncertainty in the human 
dose-response relationship for neurodevelopmental effects. After 
applying the total UF of 1,000, the oral reference value was calculated 
to be 0.0002 mg/kg/day (USEPA, 2015h) and the EPA selected this oral 
reference value to derive an HRL for tribufos.
    Because exposure began during postnatal development (i.e., at eight 
weeks of age) in the critical study

[[Page 3854]]

(Sheets and Gilmore, 2001), the EPA used the DWI-BW representing the 
90th percentile consumers-only, two-day average, direct and indirect 
community water consumption for children (birth to <21 years) of 0.0343 
L/kg/day (USEPA, 2019a) to derive the HRL for tribufos (see decision 
logic provided in section B.6.1.2 of the RD 5 Protocol, found in 
Appendix B of the Regulatory Determination 5 Support Document).
    Following HRL derivation practices, the EPA derived an HRL for 
tribufos of 1 [micro]g/L after rounding to one significant figure, 
based on an oral reference value of 0.0002 mg/kg/day (USEPA, 2015h; 
USEPA, 2015i), a DWI-BW of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC 
(USEPA, 2000a).
    Based on these analyses, the EPA finds that tribufos may have an 
adverse effect on the health of persons and therefore that Statutory 
Criterion 1 is met.
(c) Statutory Criterion 2 (Occurrence)
    The EPA proposes to find that tribufos does not occur with a 
frequency and at levels of public health concern in PWSs based on the 
EPA's evaluation of the following occurrence information.
    The primary occurrence data for tribufos are nationally 
representative drinking water monitoring data from the UCMR 4 program 
(2018-2020). Tribufos was found at or above the MRL of 0.07 [micro]g/L 
in 3 (0.008%) of the 37,269 a.m. samples analyzed during this 
monitoring period. The estimated population exposed to tribufos at 
levels of public health concern is 0%. Detected concentrations ranged 
from 0.0742 [micro]g/L to 0.4 [micro]g/L. These detections were found 
at three large systems, representing 0.06% of systems participating in 
the monitoring program. There were no exceedances of the HRL or the \1/
2\ HRL threshold. This comprehensive dataset suggests that tribufos is 
not present in PWSs at concentrations that would pose a risk to human 
health.
    Based on the evaluation of the available data, the EPA finds that 
tribufos does not occur and is not likely to occur in PWSs with a 
frequency and at levels of public health concern. Therefore, the EPA 
finds that Statutory Criterion 2 is not met.
(d) Statutory Criterion 3 (Meaningful Opportunity)
    Regulating tribufos under the SDWA does not present a meaningful 
opportunity for health risk reduction for persons served by PWSs based 
on the estimated exposed population, including sensitive populations. 
The agency finds that an NPDWR for tribufos does not present a 
meaningful opportunity for health risk reduction.
    The assessment also took into consideration the use patterns and 
regulatory actions related to tribufos, which have led to a decrease in 
its application and potential release into the environment. These 
factors, combined with the lack of detection in the UCMR 4 program, 
support the conclusion that tribufos does not currently represent a 
risk to public health for persons served by PWSs.
(e) Preliminary Regulatory Determination for Tribufos
    The agency is making a preliminary determination to not regulate 
tribufos after evaluating health, occurrence and other related 
information against the three SDWA statutory criteria. While data 
suggest that tribufos may have an adverse effect on human health, the 
occurrence data indicate that tribufos is not occurring or not likely 
to occur in PWSs with a frequency and at levels of public health 
concern. Therefore, the agency has determined that an NPDWR for 
tribufos would not present a meaningful opportunity to reduce health 
risk for persons served by PWSs. The Regulatory Determination 5 Support 
Document (USEPA, 2024b) presents additional information and analyses 
supporting the agency's evaluation of tribufos.

V. Status of the Agency's Evaluation of 1,2,3-Trichloropropane, 1,4-
Dioxane, Manganese, Quinoline and Strontium

A. Ongoing Evaluation of Additional Phase 3 Contaminants

    In addition to the nine contaminants discussed in section IV of 
this document for which the EPA is making preliminary negative 
determinations, there are five additional contaminants that were 
evaluated according to the RD 5 Protocol and proceeded to Phase 3 based 
on the robust available health effects and occurrence data for finished 
drinking water: 1,2,3-TCP, 1,4-dioxane, manganese, quinoline and 
strontium. As discussed earlier in section III.A.3 of this document, in 
order to make a positive determination, the EPA must show that a 
contaminant meets all three statutory criteria relating to health 
effects, occurrence and meaningful opportunity for health risk 
reduction, while the agency makes a negative determination if any one 
of the criteria is not met.
    The EPA is continuing to analyze the available health and 
occurrence data for these contaminants to evaluate whether they occur 
at levels of public health concern in finished drinking water and to 
characterize the potential meaningful opportunity for health risk 
reduction if they were to be regulated under the SDWA. Therefore, the 
EPA is not making preliminary determinations for these five 
contaminants at this time. As noted in section III.A.3 of this 
document, the 2023 panel ruling from the D.C. Circuit Court of Appeals 
in NRDC v. EPA (D.C. Cir., 2023) established that the agency cannot 
withdraw a positive determination even if evidence identified during 
the rulemaking would change the EPA's conclusion of the potential for 
meaningful opportunity for health risk reduction by regulating a 
contaminant. Prior to this ruling, formal evaluation of the potential 
health benefits and analysis of the availability and feasibility of 
treatment options were conducted during the rule development process as 
part of the HRRCA. Because of the 2023 ruling, however, the EPA now has 
concluded that while the SDWA does not require a full HRRCA as part of 
regulatory determination prior to rule development, the agency will 
need to conduct preliminary benefits analyses, treatment feasibility 
analyses or both prior to making determinations for contaminants that 
may warrant regulation under the SDWA. The EPA will evaluate for each 
contaminant the population exposed at the health level of concern along 
with several other factors to determine if regulation presents a 
meaningful opportunity for health risk reduction. Therefore, the EPA 
intends to conduct such analyses for each of these five contaminants 
prior to making regulatory determinations, in order to better 
understand whether there would be a meaningful opportunity for health 
risk reduction for persons served by PWSs if the contaminant were to be 
regulated.

B. Phase 3 Contaminant Updates

1. 1,2,3-Trichloropropane
    1,2,3-Trichloropropane (1,2,3-TCP) is a synthetic chemical used as 
an industrial solvent, a cleaning and degreasing agent and a synthesis 
intermediate.
    Since the EPA last provided an update on the evaluation of 1,2,3-
TCP in the RD 4 FRN (USEPA, 2021a), the EPA has continued work on the 
evaluation of this contaminant. Work has focused on addressing issues 
related to the analytical method MRL being substantially higher than 
the level of public health concern which presents uncertainty in 
assessing the potential contaminant concentrations and exposure 
analysis. The fact that the MRL is much higher than the HRL

[[Page 3855]]

suggests that there may be a substantial amount of occurrence of 1,2,3-
TCP at levels of public health concern in water systems that would not 
show up in the occurrence data, as any measurement results below the 
MRL would not be reported. The EPA did not make a regulatory 
determination for 1,2,3-TCP during RD 4 due to this analytical method 
limitation, and the agency needs lower-level occurrence information 
prior to making a preliminary regulatory determination for 1,2,3-TCP. 
Method development work is underway to lower the MRL for 1,2,3-TCP 
under Method 524.3, which would enable reporting of concentrations 
closer to levels of public health concern. The EPA intends to consider 
new information related to the improved analytical method in future 
regulatory determination efforts to assess whether there would be a 
meaningful opportunity for health risk reduction if the EPA were to 
regulate 1,2,3-TCP in drinking water.
2. 1,4-Dioxane
    1,4-Dioxane is a cyclic aliphatic ether that is used as a solvent 
and a solvent stabilizer. As a solvent it is used in such products as 
inks, coatings, adhesives, oils, resins, waxes, and dyes (USEPA, 
2024b). The EPA is continuing its efforts to evaluate 1,4-dioxane to 
determine in what manner to regulate this contaminant under SDWA and 
under the Toxic Substances Control Act (TSCA). The EPA evaluated 1,4-
dioxane in RD 4 but did not make a regulatory determination at that 
time (USEPA, 2021a), referencing the status of the TSCA risk evaluation 
and the Health Canada health effects assessment, which had not been 
finalized at that time (Health Canada, 2018). During the timeframe of 
preliminary RD 5 evaluation, the EPA finalized the 2024 Supplement to 
the 2020 Risk Evaluation and a revised Risk Determination for 1,4-
dioxane under the TSCA program. In the TSCA Risk Evaluation, which 
covers all conditions of use of 1,4-dioxane, the EPA found that 1,4-
dioxane presents risk to the general population via drinking water 
sourced from surface water contaminated both by industrial discharges 
of 1,4-dioxane and down-the-drain releases of products that contain 
1,4-dioxane (generated as an unintentional byproduct). Under section 6 
of TSCA, if at the end of the TSCA risk evaluation process, the EPA 
determines that a chemical presents an unreasonable risk to health or 
the environment, the agency must immediately start the risk management 
process to reduce or eliminate these risks. TSCA directs the EPA to 
coordinate actions taken under TSCA with actions taken under other 
federal laws administered by the EPA, such as the Clean Water Act (CWA) 
and the SDWA. TSCA section 9 also provides that, if the EPA 
Administrator determines that a risk to health or the environment 
associated with a chemical substance could be eliminated or reduced to 
a sufficient extent by actions taken under those other Federal laws, 
the EPA must use those other laws unless the Administrator determines, 
in the Administrator's discretion, that it is in the public interest to 
protect against such risk by actions taken under TSCA. Input from all 
stakeholders is critical to the risk management process under TSCA. The 
EPA is committed to developing risk management actions for chemicals in 
a way that is transparent and includes proactive, meaningful outreach 
and education with the public and other stakeholders. The EPA is 
working collaboratively across programs to address the unreasonable 
risk identified under TSCA and has determined that the risk to human 
health associated with 1,4-dioxane exposure via drinking water sourced 
from surface water contaminated with both industrial discharges and 
down-the-drain releases of products containing 1,4-dioxane is best 
managed by coordinating actions under both TSCA and SDWA.
    As described in the EPA Administrator's memorandum ``Coordinated 
Risk Management Action on 1,4-Dioxane under section 9(b) of the Toxic 
Substances Control Act'' released alongside the TSCA's program's final 
2024 Supplement to the 2020 Risk Evaluation and the revised Risk 
Determination for 1,4-dioxane, after the agency's regulatory action to 
address this risk under TSCA is implemented, the EPA will re-evaluate 
under SDWA whether there is any remaining risk that presents a 
meaningful opportunity for health risk reduction by regulating 1,4-
dioxane in drinking water.
3. Manganese
    Manganese is a naturally occurring element and is ubiquitous in the 
environment as a component of over 100 minerals (ATSDR, 2012). 
Manganese compounds are used in a variety of industrial production 
processes and applications--production data from 2011 to 2019 from the 
EPA's CDR Program shows that fifteen manganese substances were produced 
or imported in quantities greater than one million pounds in at least 
one year and that elemental manganese was produced in quantities 
greater than 500 million pounds in 2018 (USEPA, 2024b).
    The EPA made a negative regulatory determination for manganese in 
RD 1 (USEPA, 2003). Since then, new health effects information 
developed for the 2021 World Health Organization's (WHO) Guidelines for 
Drinking Water Quality indicates exposure to elevated levels of 
manganese in drinking water contributes to increased risk for adverse 
neurological effects, such as behavioral and sensorimotor effects (WHO, 
2021). Nationally representative occurrence data in finished drinking 
water were collected for manganese in UCMR 4 (USEPA, 2024c). The EPA 
continues to evaluate the health effects and occurrence data for 
manganese and will conduct preliminary benefits analysis and treatment 
feasibility analysis to inform the potential meaningful opportunity for 
health risk reduction if manganese were to be regulated under the SDWA 
in the future.
4. Quinoline
    Quinoline is an aromatic heterocyclic amine used to make paints, 
dyes and other chemicals. Quinoline is also used as a solvent, 
anatomical specimen preservative, corrosion inhibitor, antimalarial 
drug and flavoring agent.
    Nationally representative finished water occurrence data for 
quinoline was collected under UCMR4. The analytical method MRL for 
quinoline is greater than the level of public health concern thus there 
is uncertainty regarding the frequency at which quinoline occurs at 
levels of public health concern in PWSs. Therefore, the EPA needs more 
information prior to making a preliminary regulatory determination for 
quinoline.
    The EPA continues to evaluate the health effects and occurrence 
data for quinoline and plans to conduct additional analyses of health 
benefits and possible treatment feasibility to inform whether 
regulating quinoline under SDWA would present a meaningful opportunity 
for health risk reduction to persons served by PWSs.
5. Strontium
    Strontium is a naturally occurring element, an alkaline earth metal 
typically found in the form of mineral compounds. Stable strontium 
tends to dissolve in water, and therefore water in contact with 
strontium-laden soils may also contain strontium.
    Since the RD 4 FRN was published in 2021, (USEPA, 2021a) the EPA 
has continued to conduct additional work to evaluate the health risks 
and the potential for health risk reduction if strontium were to be 
regulated with an NPDWR. For the preliminary RD 5 evaluation, the EPA 
identified the 2019

[[Page 3856]]

Health Canada Guidelines for Drinking Water Quality (HC, 2019), because 
it is the most recent health assessment identified for strontium and 
uses the best available science in its evaluation of noncancer risk. 
The EPA continues to evaluate the UCMR 3 occurrence data in light of 
the newer health effects information to determine whether there would 
be a meaningful opportunity for health risk reduction if strontium were 
to be regulated under the SDWA. In addition, the EPA understands that 
strontium may co-occur with beneficial calcium in some drinking water 
systems and treatment technologies that remove strontium may also 
remove calcium. The agency is evaluating the effectiveness of treatment 
technologies under different water conditions, including calcium 
concentrations.
    The EPA continues to evaluate the health effects and occurrence 
data for strontium and plans to conduct additional analyses of health 
benefits and possible treatment feasibility to inform whether 
regulating strontium under SDWA would present a meaningful opportunity 
for health risk reduction to persons served by PWSs.
    In summary, the EPA is not making regulatory determinations at this 
time for these five contaminants in this document. In light of the 
decision announced in NRDC v. EPA (D.C. Cir., 2023), the EPA plans to 
conduct preliminary health benefits analyses to inform whether there 
would be a potential meaningful opportunity for health risk reduction 
through regulation of a contaminant with an NPDWR. In addition, the EPA 
continues to evaluate the effectiveness and feasibility of treatment 
methods to lower concentrations of these contaminants from drinking 
water systems.

VI. The EPA's Request for Comments and Next Steps

    The EPA invites commenters to submit any relevant data or 
information pertaining to the preliminary regulatory determinations 
identified in this document, as well as other relevant comments. The 
EPA will consider the public comments and any new, relevant data 
submitted for the contaminants discussed in this document and in the 
supporting rationale.
    The data and information requested by the EPA include peer-reviewed 
science and supporting studies conducted in accordance with sound and 
objective scientific practices, and data collected by accepted methods 
or best available methods (if the reliability of the method and the 
nature of the review justifies use of the data).
    Peer-reviewed data are studies/analyses that have been reviewed by 
qualified individuals (or organizations) who are independent of those 
who performed the work, but who are collectively equivalent in 
technical expertise (i.e., peers) to those who performed the original 
work. A peer review is an in-depth assessment of the assumptions, 
calculations, extrapolations, alternate interpretations, methodology, 
acceptance criteria and conclusions pertaining to the specific major 
scientific or technical work products and the documentation that 
supports them (USEPA, 2015j).
    Specifically, the EPA is requesting comment and information related 
to the following aspects:
     The health effects information considered by the agency in 
making the preliminary determinations described in this Document. The 
EPA requests commenters identify any additional peer reviewed studies 
that could inform the final regulatory determination.
     Drinking water occurrence information considered by the 
agency in making the preliminary determinations described in this 
document. The EPA requests commenters identify any additional data and 
studies on the occurrence of these contaminants in drinking water.
    The EPA intends to evaluate the public comments received on the 
nine preliminary determinations and issue final regulatory 
determinations. If the agency makes a final determination to regulate 
any of the contaminants, the EPA intends to propose an NPDWR within 24 
months and promulgate a final NPDWR within 18 months following the 
proposal.\15\ In addition, the EPA will also consider information 
provided in public comment about the five contaminants discussed in 
section V of this document to inform potential future regulatory 
determinations.
---------------------------------------------------------------------------

    \15\ The statute authorizes a nine-month extension of this 
promulgation date.
---------------------------------------------------------------------------

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USEPA. 2006a. Reregistration Eligibility Decision for Ethoprop. 
Includes July 31, 2006, finalization memo and EPA 738-R-06-018. 
Office of Prevention, Pesticides, and Toxic Substances. https://archive.epa.gov/pesticides/reregistration/web/pdf/ethoprop_red.pdf.
USEPA. 2006b. Reregistration Eligibility Decision for Tribufos. 
Includes July 31, 2006, finalization memo and EPA 738-R-00-022. 
Office of Prevention, Pesticides, and Toxic Substances. https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/red_PC-074801_31-Jul-06.pdf.
USEPA. 2007. Unregulated Contaminant Monitoring Regulation (UCMR) 
for Public Water Systems Revisions. Federal Register, 72(2): 367, 
January 4, 2007. https://www.govinfo.gov/content/pkg/FR-2007-01-04/pdf/E6-22123.pdf.
USEPA. 2008a. Drinking Water: Regulatory Determinations Regarding 
Contaminants on the Second Drinking Water Contaminant Candidate 
List. Federal Register, 73(147): 44251, July 30, 2008. https://federalregister.gov/a/E8-17463.
USEPA. 2008b. The Analysis of Occurrence Data from the First 
Unregulated Contaminant Monitoring Regulation (UCMR 1) in Support of 
Regulatory Determinations for the Second Drinking Water Contaminant 
Candidate List (CCL 2). EPA 815-R-08-013. https://www.epa.gov/sites/default/files/2014-09/documents/the_analysis_of_occurrence_data_from_ucmr1_in_support_of_rd2.pdf.
USEPA. 2008c. Profenofos Summary Document, Registration Review: 
Initial Docket, June 2008. https://www.regulations.gov/document/EPA-HQ-OPP-2008-0345-0002.
USEPA. 2009a. Drinking Water Contaminant Candidate List 3--Final. 
Federal Register, 74(194): 51850, October 8,

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2009. https://federalregister.gov/a/E9-24287.
USEPA. 2009b. Tribufos Summary Document, Registration Review: 
Initial Docket, March 2009. https://www.regulations.gov/document/EPA-HQ-OPP-2008-0883-0004.
USEPA. 2011. Drinking Water: Regulatory Determination on 
Perchlorate. Federal Register, 76(29): 7762, February 11, 2011. 
https://federalregister.gov/a/2011-2603.
USEPA. 2012a. Revisions to the Unregulated Contaminant Monitoring 
Regulation (UCMR 3) for Public Water Systems. Federal Register, 
77(85): 26071, May 2, 2012. https://www.govinfo.gov/content/pkg/FR-2012-05-02/pdf/2012-9978.pdf.
USEPA. 2012b. Provisional Peer-Reviewed Toxicity Values for o-
Toluidine (CASRN 95-53-4). Office of Research and Development's 
National Center for Environmental Assessment, Superfund Health Risk 
Technical Support Center. EPA/690/R-12/032F. December. https://cfpub.epa.gov/ncea/pprtv/documents/ToluidineoMethylaniline2.pdf.
USEPA. 2014. Announcement of Preliminary Regulatory Determinations 
for Contaminants on the Third Drinking Water Contaminant Candidate 
List. Federal Register, 79(202): 62716, October 20, 2014. https://www.govinfo.gov/content/pkg/FR-2014-10-20/pdf/2014-24582.pdf.
USEPA. 2015a. Occurrence Data from the Second Unregulated 
Contaminant Monitoring Regulation (UCMR 2). Office of Water. EPA-
815-R-15-013. December. https://www.regulations.gov/document/EPA-HQ-OW-2012-0155-0030.
USEPA. 2015b. Health Effects Support Document for the Cyanobacterial 
Toxin Cylindrospermopsin. Office of Water, Health and Ecological 
Criteria Division. EPA-820R15103. June. https://www.epa.gov/sites/default/files/2017-06/documents/cylindrospermopsin-support-report-2015.pdf.
USEPA. 2015c. Ethoprop: Draft Human Health Risk Assessment for 
Registration Review. September 15, 2015, memo from Office of 
Chemical Safety and Pollution Prevention, Office of Pesticide 
Programs, Health Effects Division. DP D410028. https://www.regulations.gov/document/EPA-HQ-OPP-2008-0560-0028.
USEPA. 2015d. Pesticide Registration: Draft Human Health and 
Ecological Risk Assessments for Sulfonylureas and Certain Other 
Pesticides. Federal Register, 80(186): 57812-57816, Sept 25, 2015. 
https://www.federalregister.gov/documents/2015/09/25/2015-24452/pesticide-registration-review-draft-human-health-and-ecological-risk-assessments-for-sulfonylureas.
USEPA. 2015e. Health Effects Support Document for the Cyanobacterial 
Toxin Microcystins. EPA-820R15102. June. https://www.epa.gov/sites/default/files/2017-06/documents/microcystins-support-report-2015.pdf.
USEPA. 2015f. Drinking Water Health Advisory for the Cyanobacterial 
Microcystin Toxins. EPA-820R15100. June. https://www.epa.gov/sites/default/files/2017-06/documents/microcystins-report-2015.pdf.
USEPA. 2015g. Profenofos: Human Health Draft Risk Assessment (DRA) 
for Registration Review. September 15, 2015 memo from Office of 
Chemical Safety and Pollution Prevention. DP D414150. https://www.regulations.gov/document/EPA-HQ-OPP-2008-0345-0024.
USEPA. 2015h. Tribufos: Human Health Draft Risk Assessment for 
Registration Review. September 15, 2015, memo from Office of 
Chemical Safety and Pollution Prevention. DP D357537. https://www.regulations.gov/document/EPA-HQ-OPP-2008-0883-0011.
USEPA. 2015i. Pesticide Registration Review; Draft Human Health and 
Ecological Risk Assessments for Certain Organophosphates; Extension 
of Comment Period. Federal Register, 80(246): 79888-79889, December 
23, 2015. https://www.govinfo.gov/content/pkg/FR-2015-12-23/pdf/2015-32326.pdf.
USEPA. 2015j. Peer Review Handbook, 4th Edition. Science and 
Technology Policy Council. EPA 100-B-15-001. October. https://www.epa.gov/osa/peer-review-handbook-4th-edition-2015.
USEPA. 2016a. Announcement of Final Regulatory Determinations for 
Contaminants on the Third Drinking Water Contaminant Candidate List. 
Federal Register, 81(1): 13, January 4, 2016. https://www.govinfo.gov/content/pkg/FR-2016-01-04/pdf/2015-32760.pdf.
USEPA. 2016b. Drinking Water Contaminant Candidate List 4--Final. 
Federal Register, 81(222): 81099, November 17, 2016. https://www.govinfo.gov/content/pkg/FR-2016-11-17/pdf/2016-27667.pdf.
USEPA. 2016c. Revisions to the Unregulated Contaminant Monitoring 
Rule (UCMR 4) for Public Water Systems and Announcement of Public 
Meeting. Federal Register, 81(224): 92666, December 20, 2016. 
https://www.govinfo.gov/content/pkg/FR-2016-12-20/pdf/2016-30469.pdf.
USEPA. 2019a. Exposure Factors Handbook Chapter 3 (Update): 
Ingestion of Water and Other Select Liquids. Office of Research and 
Development. EPA/600/R-8/259F. https://cfpub.epa.gov/ncea/efp/recordisplay.cfm?deid=343661.
USEPA. 2019b. Occurrence Data from the Third Unregulated Contaminant 
Monitoring Rule (UCMR 3). EPA 815-R-19-007. https://www.regulations.gov/document/EPA-HQ-OW-2019-0583-0005.
USEPA. 2020a. Announcement of Preliminary Regulatory Determinations 
for Contaminants on the Fourth Drinking Water Contaminant Candidate 
List. Federal Register, 85(47): 14098, March 10, 2020. https://www.govinfo.gov/content/pkg/FR-2020-03-10/pdf/2020-04145.pdf.
USEPA. 2020b. Pesticide Registration Review: Interim Decisions for 
Several Pesticides. Federal Register, 85(206): 67538-67540, Oct 23, 
2020. https://www.federalregister.gov/documents/2020/10/23/2020-23504/pesticide-registration-review-interim-decisions-for-several-pesticides-notice-of-availability.
USEPA. 2020c. Permethrin: Human Health Risk Assessment for New Use 
on ``Fruit, Small, Vine Climbing, Except Fuzzy Kiwifruit, Subgroup 
13-07F''; Multiple Crop Group Conversions/Expansions; and the 
Establishment of a Tolerance without a U.S. Registration for Tea, 
and the Revised Draft Risk Assessment (DRA) for Registration Review. 
March 17, 2020, memo from Office of Chemical Safety and Pollution 
Prevention, Office of Pesticide Programs, Health Effects Division. 
DPs D449288, D455545. https://www.regulations.gov/document/EPA-HQ-OPP-2011-0039-0130.
USEPA. 2021a. Announcement of Final Regulatory Determinations for 
Contaminants on the Fourth Drinking Water Contaminant Candidate 
List. Federal Register, 86(40): 12272, March 3, 2021. https://www.govinfo.gov/content/pkg/FR-2021-03-03/pdf/2021-04184.pdf.
USEPA. 2021b. 2021 Policy on Children's Health. October 5, 2021, 
memo from Administrator Michael S. Regan. https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf.
USEPA. 2021c. Revisions to the Unregulated Contaminant Monitoring 
Rule (UCMR 5) for Public Water Systems and Announcement of Public 
Meetings. Federal Register, 86(245): 73131, December 27, 2021. 
https://www.govinfo.gov/content/pkg/FR-2021-12-27/pdf/2021-27858.pdf.
USEPA. 2021d. Registration Review Draft Risk Assessment for the 
Antimicrobial Uses of Tebuconazole. March 24, 2021, memo from Office 
of Chemical Safety and Pollution Prevention. DP 455145. https://downloads.regulations.gov/EPA-HQ-OPP-2015-0378-0020/content.pdf.
USEPA. 2021e. Pesticide Registration Review; Draft Human Health and/
or Ecological Risk Assessments for Several Pesticides; Notice of 
Availability. Federal Register, 86(97): 27593-27594, May 21, 2021. 
https://www.govinfo.gov/content/pkg/FR-2021-05-21/pdf/2021-10715.pdf.
USEPA. 2022a. Drinking Water Contaminant Candidate List 5--Final. 
Federal Register, 87(218): 68060, November 14, 2022. https://www.govinfo.gov/content/pkg/FR-2022-11-14/pdf/2022-23963.pdf.
USEPA. 2022b. Drinking Water Health Advisory: Hexafluoropropylene 
Oxide (HFPO) Dimer Acid (CASRN 13252-13-6) and HFPO Dimer Acid 
Ammonium Salt (CASRN 62037-80-3), Also Known as ``GenX Chemicals.'' 
Office of Water, Office of Science and Technology. EPA/822/R-22/005. 
June. https://www.epa.gov/system/files/documents/2022-06/drinking-water-genx-2022.pdf.
USEPA. 2022c. Drinking Water Health Advisory: Perfluorobutane 
Sulfonic Acid (CASRN 375-73-5) and Related Compound Potassium 
Perfluorobutane Sulfonate (CASRN 29420-49-3). Office of Water, 
Office of Science and Technology. EPA/822/R-22/006. June. https://
www.epa.gov/system/files/documents/2022-06/drinking-water-pfbs-

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2022.pdf.
USEPA. 2022d. Learn about Cyanobacteria and Cyanotoxins. https://www.epa.gov/cyanohabs/learn-about-cyanobacteria-and-cyanotoxins. 
Accessed September 8, 2022.
USEPA. 2022e. National Lakes Assessment 2017 Web Report. https://www.epa.gov/national-aquatic-resource-surveys/reports-and-data-national-lakes-assessment-2017.
USEPA. 2022f. Restricted Use Product Summary Report (October 31, 
2022). https://www.epa.gov/system/files/documents/2022-11/RUP-Report-10-31-2022.pdf.
USEPA. 2023a. Ethoprop. Updated Occupational and Non-Occupational 
Spray Drift Assessment for Registration Review. February 17, 2023, 
memo from Office of Chemical Safety and Pollution Prevention, Office 
of Pesticide Programs. https://www.regulations.gov/document/EPA-HQ-OPP-2008-0560-0058.
USEPA. 2023b. Entry for ``Chronic Exposure'' in the Integrated Risk 
Information System (IRIS) Glossary. https://www.epa.gov/iris/iris-glossary.
USEPA. 2023c. Pesticide Product and Label System Database. https://ordspub.epa.gov/ords/pesticides/f?p=PPLS:1.
USEPA. 2023d. Pesticide Chemical Search for tebuconazole: https://ordspub.epa.gov/ords/pesticides/f?p=CHEMICALSEARCH:3::::21,3,31,7,12,25:P3_XCHEMICAL_ID:3984.
USEPA. 2024a. PFAS National Primary Drinking Water Regulation: Final 
Rule. Federal Register, 89(82): 32532, April 26, 2024. https://www.govinfo.gov/content/pkg/FR-2024-04-26/pdf/2024-07773.pdf.
USEPA. 2024b. Regulatory Determination 5 Support Document. EPA 815-
B-24-017.
USEPA. 2024c. Occurrence Data from the Fourth Unregulated 
Contaminant Monitoring Rule (UCMR 4). EPA 815-B-24-016.
United States Geological Survey (USGS). 2023. Estimated Annual 
Agricultural Pesticide Use. https://water.usgs.gov/nawqa/pnsp/usage/maps/index.php. Last updated June 14, 2023.
Water Quality Portal (WQP). 2023. Water Quality Portal Data 
Warehouse. https://www.waterqualitydata.us/. Data Warehouse 
consulted September 2023.
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E. Boger, C.G. Van Dongen, and K.C. Chu. 1978. Testing of Twenty-One 
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Atmospheric Molybdenum Cycle. Global Biogeochemical Cycles, 35(2): 
e2020GB006787. https://doi.org/10.1029/2020GB006787.

Jane Nishida,
Acting Administrator.
[FR Doc. 2025-00133 Filed 1-14-25; 8:45 am]
BILLING CODE 6560-50-P`