# Announcement of Final Regulatory Determinations for Contaminants on the Fifth Drinking Water Contaminant Candidate List
**AGENCY:**
Environmental Protection Agency (EPA).
**ACTION:**
Regulatory determinations.
**SUMMARY:**
The U.S. Environmental Protection Agency (EPA) is announcing final regulatory determinations for nine contaminants listed on the fifth Contaminant Candidate List. Specifically, the Agency is making final determinations not to regulate 2-aminotoluene, cylindrospermopsin, ethoprop, microcystins, molybdenum, permethrin, profenofos, tebuconazole, and tribufos. The Safe Drinking Water Act (SDWA) requires the EPA to make regulatory determinations every five years on at least five unregulated contaminants. A regulatory determination is a decision about whether or not to begin the process to propose and promulgate- a national primary drinking water regulation (NPDWR) for an unregulated contaminant.
**DATES:**
For the purpose of judicial review, the determinations not to regulate in this document are issued as of March 19, 2026.
**FOR FURTHER INFORMATION CONTACT:**
George Gardenier, Standards and Risk Management Division, Office of Ground Water and Drinking Water (Mail Code 4607M), Environmental Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC 20460; telephone number: (202) 564-3333; email address: *[email protected].*
**SUPPLEMENTARY INFORMATION:**
**Abbreviations Used in This Document**
ATSDR Agency for Toxic Substances and Disease Registry
CCL Contaminant Candidate List
CCL 5 Fifth Contaminant Candidate List
CRL Cancer Risk Level
CSF Cancer Slope Factor
DWI-BW Drinking Water Intake Adjusted for Body Weight
FIFRA Federal Insecticide, Fungicide and Rodenticide Act
HABs Harmful Algal Blooms
HESD Health Effects Support Document
HHRA Human Health Risk Assessment
HRL Health Reference Level
HRRCA Health Risk Reduction Cost Analysis
MRL Minimum Reporting Level
NPDWR National Primary Drinking Water Regulation
NRDC Natural Resources Defense Council
OW Office of Water
PPRTV Provisional Peer-Reviewed Toxicity Value
PWS Public Water System
RD 5 Regulatory Determination 5
RSC Relative Source Contribution
SDWA Safe Drinking Water Act
UCMR Unregulated Contaminant Monitoring Rule
UCMR 3 Third Unregulated Contaminant Monitoring Rule
UCMR 4 Fourth Unregulated Contaminant Monitoring Rule
USEPA United States Environmental Protection Agency
USGS United States Geological Survey
**Table of Contents**
I. General Information
A. Does this action apply to me?
B. How can I get copies of this document and other related information?
II. Purpose and Background
A. What is the purpose of this action?
B. What are the statutory requirements for the SDWA Contaminant Candidate List (CCL) and regulatory determinations?
C. Which contaminants did the EPA consider for regulation?
III. Approach to Identifying and Evaluating Contaminants for Regulatory Determinations
A. How the EPA Identified and Evaluated Contaminants for the Fifth Regulatory Determination
B. Consideration of Public Comments
IV. The EPA's Findings on Specific Contaminants
A. 2-Aminotoluene
B. Cylindrospermopsin
C. Ethoprop
D. Microcystins
E. Molybdenum
F. Permethrin
G. Profenofos
H. Tebuconazole
I. Tribufos
V. The EPA's Considerations for Future Regulatory Determinations
VI. Next Steps
VII. References
**I. General Information**
**A. Does this action apply to me?**
These final regulatory determinations will not impose any requirements on anyone. Instead, this action notifies interested parties of the EPA's final determinations not to regulate nine contaminants under the SDWA.
**B. How can I get copies of this document and other related information?**
*1. Docket.* The EPA has established a docket for this action under Docket ID No. EPA-HQ-OW-2024-0456. Publicly available docket materials are available either electronically through *https://www.regulations.gov* or in hard copy at the EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Ave. NW, Washington, DC. The Docket Center's hours of operations are 8:30 a.m.-4:30 p.m., Monday through Friday (except Federal Holidays). For further information on the EPA Docket Center services and the current status, see: *https://www.epa.gov/dockets.*
*2. Electronic Access.* You may access this *Federal Register* document electronically from *https://www.federalregister.gov/documents/current.*
**II. Purpose and Background**
**A. What is the purpose of this action?**
The purpose of this action is to present a summary of the EPA's final SDWA regulatory determinations for nine contaminants on the fifth Contaminant Candidate List (CCL 5) (87 FR 68060; USEPA, 2022). The Agency is making determinations not to regulate 2-aminotoluene, cylindrospermopsin, ethoprop, microcystins, molybdenum, permethrin, profenofos, tebuconazole, and tribufos. This action summarizes the SDWA statutory requirements for selecting new contaminants in drinking water to regulate, provides an overview of the contaminants that the Agency considered for regulation, and describes the approach used to make the final regulatory determinations. In addition, this action summarizes the public comments received on the Agency's preliminary determinations announcement and the Agency's responses to those comments.
**B. What are the statutory requirements for the SDWA Contaminant Candidate List (CCL) and regulatory determinations?**
The SDWA provides a stepwise process for establishing drinking water standards for unregulated contaminants. First, the SDWA section 1412(b)(1)(B)(i) requires the EPA to publish a list of unregulated contaminants that are candidates for drinking water regulations, referred to as the Contaminant Candidate List (CCL). The statute requires the EPA to publish this CCL every five years after public notice and an opportunity to comment. The SDWA defines the CCL as a list of contaminants which are not subject to any proposed or promulgated National Primary Drinking Water Regulations (NPDWRs) but are known or anticipated to occur in public water systems (PWSs) and may require regulation under the SDWA.
Second, the SDWA section 1412(b)(1)(B)(ii) directs the EPA to determine, after public notice and an opportunity to comment, whether to regulate at least five contaminants from the CCL every five years. Under SDWA section 1412(b)(1)(A), the EPA makes a determination to 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 a substantial likelihood that the contaminant will occur in public water systems 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 public water systems.
If, after considering public comment on a preliminary determination, the Agency makes a final determination to regulate a contaminant, section 1412(b)(1)(E) requires the EPA to propose and promulgate an NPDWR and publish a Maximum Contaminant Level Goal for that contaminant. In that case, the statutory time frame provides for the Agency's proposal of a regulation within 24 months and action on a final regulation within 18 months of proposal (which may be extended by 9 months).
**C. Which contaminants did the EPA consider for regulation?**
The EPA has published five CCLs since 1996. On January 15, 2025, the EPA published preliminary regulatory determinations not to regulate nine contaminants on the fifth Contaminant Candidate List (CCL 5) (90 FR 3830; USEPA, 2025a). The Agency is finalizing the determinations not to regulate 2-aminotoluene, cylindrospermopsin, ethoprop, microcystins, molybdenum, permethrin, profenofos, tebuconazole, and tribufos.
Information further describing the Agency's analyses informing the regulatory determinations for these nine contaminants can be found in the *Final Regulatory Determination 5 Support Document* (USEPA, 2026a). More information is available in the Public Docket at *https://www.regulations.gov* (Docket ID No. EPA-HQ-OW-2024-0456) and also on the EPA's Regulatory Determination 5 website at *https://www.epa.gov/ccl/regulatory-determination-5* .
**III. Approach to Identifying and Evaluating Contaminants for Regulatory Determinations**
**A. How the EPA Identified and Evaluated Contaminants for the Fifth Regulatory Determination**
This section summarizes the Agency's approach to identifying and evaluating contaminants for the Fifth Regulatory Determination (RD 5). As explained in the *Federal Register* document for the preliminary determinations for this fifth cycle of regulatory determinations, the approach taken under RD 5 is similar to that used in previous rounds of regulatory determination and formalized in a written protocol under Regulatory Determination 3 (USEPA 2014; 81 FR 13; USEPA, 2016). For more detailed information on the approach and the analyses performed, please refer to the “Protocol for the Regulatory Determination 5” found in appendix B of the *Final Regulatory Determination 5 Support Document* (USEPA, 2026a) and the *Federal Register* publication for the preliminary regulatory determinations (90 FR 3830; USEPA, 2025a).
The CCL 5 identified 81 contaminants or groups of contaminants that are not currently subject to any proposed or promulgated NPDWR, are known or anticipated to occur in public water systems, and may require regulation under the SDWA (87 FR 68060; USEPA, 2022). The Agency used a three-phase process to identify which of the contaminants are candidates for regulatory determinations and found that many of the CCL 5 contaminants do not have adequate health and/or finished drinking water occurrence data to evaluate against the three statutory criteria necessary to make a regulatory determination (see section II.B. of this document). Priority was given to identifying contaminants known or substantially likely to occur at frequencies and levels of public health concern.
In accordance with the Agency's Policy on Evaluating Health Risks to Children (USEPA, 1995), the EPA has explicitly considered children's health and potential unique vulnerabilities in the RD 5 process by reviewing all available scientific information on children's exposure and health effects from the contaminants the Agency considered.
The three phases of the Fifth Regulatory Determination protocol, like the protocol the Agency used for the Third and Fourth Regulatory Determinations, are (1) the *Data Availability Phase,* (2) the *Data Evaluation Phase* and (3) the *Regulatory Determination Assessment Phase.* Throughout the RD 5 Evaluation process, the EPA conducted its evaluations in a manner consistent with the *U.S. Environmental Protection Agency Implementation of Gold Standard Science* (USEPA, 2025b), including through developing a standardized process for conducting the evaluations of contaminants from RD 5, which can be found in appendix B of the *Regulatory Determination 5 Support Document* (USEPA, 2026a). The overall process is displayed in Exhibit 1.
The purpose of the first phase, the *Data Availability Phase,* is to screen out contaminants that clearly do not have sufficient data to support a regulatory determination. The Agency applies criteria to ensure that any contaminant that potentially has sufficient data to characterize the health effects and known or likely occurrence in drinking water will proceed to the *Data Evaluation Phase,* the second phase of the regulatory determination process. From the 81 CCL 5 contaminants and contaminant groups, the Agency identified 35 CCL 5 contaminants to further evaluate in the second phase of the regulatory determination process. See the *Final Regulatory Determination 5 Support Document* for more details of the *Data Evaluation Phase* (USEPA, 2026a).
During the second phase, the Agency evaluated these 35 contaminants in greater detail to identify those that have sufficient data (or are expected to have sufficient data within the timeframe allotted for the second phase) for the EPA to assess the three statutory criteria. As part of the second phase, the Agency specifically focused 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 based on the best available peer-reviewed data.
The EPA conducted a systematic search for human health effects assessments from EPA and other authoritative sources for each drinking water chemical contaminant on CCL 5 in a manner consistent with the EPA's Scientific Integrity Policy and with the Agency's *Implementation of Gold Standard Science* (USEPA, 2025b). When conducting the literature searches for health effects assessments, the EPA prioritized assessments that are reproducible, transparent, communicative of error and uncertainty, subject to unbiased peer review, and without conflicts of interest. The EPA selected a health effects assessment for each contaminant and derived a Health Reference Level (HRL). 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. HRLs are health-based drinking water concentrations, derived from qualifying health effects assessments based on the best available science, and are not final drinking water values. HRLs are derived using a procedure that is inclusive of sensitive subpopulations. The EPA evaluates the HRLs against the occurrence data to determine if contaminants occur at levels of potential public health concern in drinking water, to inform regulatory determinations. As with the first phase, if the Agency finds in Phase 2 that sufficient data are not available to evaluate the three statutory criteria, then the contaminant is not considered a candidate for regulatory determination.
Often the primary source of nationally representative occurrence data is from the EPA's Unregulated Contaminant Monitoring Rule (UCMR) program. 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 collects nationally representative occurrence data that is considered by the EPA in 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)) and provides information on unregulated contaminants in finished drinking water that is considered in this process. Under UCMR 3 and UCMR 4, the UCMRs relevant to this document, data were collected from all PWSs serving a population of more than 10,000, and from a nationally representative sample of 800 small PWSs serving 10,000 people or fewer.
If sufficient data are available for a contaminant to characterize the potential health effects and known or likely occurrence in drinking water, the contaminant is evaluated against the three SDWA statutory criteria laid out in section 1412(b)(1)(A) in the *Regulatory Determination Assessment Phase,* which is the third phase of the process. Of the 35 contaminants that were evaluated under Phase 2, 14 were designated for evaluation against the three statutory criteria in Phase 3.
Of the 14 CCL 5 contaminants that were evaluated in Phase 3 against the three statutory criteria, the Agency made preliminary regulatory determinations not to regulate nine contaminants (2-aminotoluene, cylindrospermopsin, ethoprop, microcystins, molybdenum, permethrin, profenofos, tebuconazole, and tribufos). These preliminary determinations were published in the *Federal Register* on January 15, 2025, for public comment (90 FR 3830; USEPA, 2025a).
**B. Consideration of Public Comments**
The EPA received comments from eight organizations and individuals on the preliminary regulatory determinations for CCL 5 (90 FR 3830; USEPA, 2025a). Most of these comments were supportive of the Agency's determinations not to regulate the nine contaminants. There were two commenters who urged the EPA to regulate all nine contaminants because each has the potential to cause adverse health effects. While these contaminants may have potential adverse health effects, SDWA section 1412(b)(1)(A) requires the Agency to consider all three statutory criteria, described in section II.B. of this document, of which the potential to have adverse health effects is only one. In order to make a determination to regulate a contaminant under the SDWA, all three criteria must be met: exposure to the contaminant may result in an adverse health effect, the contaminant is known or substantially likely to occur in public water systems with a frequency and at levels of public health concern, and that regulation in public water systems would provide a meaningful opportunity to reduce the public health risks associated with exposure to the contaminant. The potential for adverse health effects alone, therefore, is not a sufficient basis to determine to regulate a contaminant in drinking water under the SDWA.
See the *Responses to Public Comments on Preliminary Regulatory Determinations for Contaminants on the Fifth Drinking Water Contaminant Candidate List* for additional details about the public comments received and the EPA's responses (USEPA, 2026b).
**IV. The EPA's Findings on Specific Contaminants**
After considering the public comments, the EPA is making final determinations not to regulate the nine contaminants listed in table 1. The next sections of this document provide a brief description of the Agency's findings on these contaminants. Details on the background, health and occurrence information, and analyses used to evaluate and make final determinations for these contaminants can be found in the *Final Regulatory Determination 5 Support Document* (USEPA, 2026a), the *Occurrence Data from the Fourth Unregulated Contaminant Monitoring Rule (UCMR 4)* (USEPA, 2024), and the *Federal Register* publication for the preliminary regulatory determination (90 FR 3830; USEPA, 2025a).
| RD 5 contaminant | Minimum | Health | Critical effect | PWSs
with | Population |
| --- | --- | --- | --- | --- | --- |
| 2-Aminotoluene | 0.007 | 2 | Subcutaneous fibromas and fibrosarcomas | 0.0 | 0.0 |
| Cylindrospermopsin | 0.09 | 0.6 | Increased relative kidney weight | 0.03 | 0.01 |
| Ethoprop | 0.03 | 0.09 | Inhibition of red blood cell cholinesterase | 0.02 | 0.01 |
| Microcystins | 0.3 | 0.3 | Liver effects | 0.2 | 0.06 |
| Molybdenum | 1 | 100 | Kidney effects | 0.1 | 0.06 |
| Permethrin | 0.04 | 3,000 | Decreased motor activity | 0.0 | 0.0 |
| Profenofos | 0.3 | 0.7 | Inhibition of red blood cell acetylcholinesterase | 0.02 | 0.01 |
| Tebuconazole | 0.2 | 200 | Increased incidence of skull/neural tube defects | 0.0 | 0.0 |
| Tribufos | 0.07 | 1 | Inhibition of red blood cell cholinesterase | 0.0 | 0.0 |
**A. 2-Aminotoluene**
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. 2-Aminotoluene is used in the manufacture of dyes, rubber vulcanization accelerators, pharmaceuticals and pesticides (NCBI, 2024).
The EPA has found that 2-aminotoluene may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected to derive an HRL for 2-aminotoluene is the 2012 EPA Provisional Peer-Reviewed Toxicity Value (PPRTV) (USEPA, 2012), because it is a qualifying peer-reviewed health assessment that derives an oral cancer slope factor (CSF) based on the best available science. The 2012 EPA PPRTV health assessment for 2-aminotoluene describes multiple adverse health effects. The EPA selected subcutaneous fibromas and fibrosarcomas ( *i.e.,* cancer) in male rats as the critical effect to derive the oral toxicity value (USEPA, 2012). 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, 2005; USEPA, 2012). The EPA derived an HRL for 2-aminotoluene of 2 µg/L based on a one-in-a-million (10 <sub>−6</sub> ) cancer risk level (CRL), oral CSF of 0.016 (mg/kg/day) <sub>−1</sub> (USEPA, 2012), and a drinking water intake adjusted for body weight (DWI-BW) for children (birth to <21 years) of 0.0343 L/kg/day (USEPA, 2019a).
The EPA has determined that 2-aminotoluene does not occur with a frequency and at levels of public health concern in PWSs based on available occurrence information and therefore does not meet SDWA's Statutory Criterion 2 for regulatory determinations. The primary occurrence data for 2-aminotoluene are nationally representative drinking water monitoring data from the UCMR 4 program (2018-2020) (USEPA, 2024). Under UCMR 4 assessment monitoring, there were no measurements of 2-aminotoluene greater than the HRL (USEPA, 2026a).
The UCMR 4 data do not indicate that persons served by public water systems are exposed to 2-aminotoluene at levels of public health concern (USEPA, 2026a). The Agency, therefore, has determined that regulating 2-aminotoluene under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs, as required by SDWA's Statutory Criterion 3 for regulatory determinations.
The Agency has evaluated the best available information on 2-aminotoluene against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate 2-aminotoluene with an NPDWR.
**B. Cylindrospermopsin**
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. Harmful algal blooms (HABs) of cyanobacteria in freshwater environments can release cyanotoxins, including cylindrospermopsin.
The EPA has found that cylindrospermopsin may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected to derive an HRL for cylindrospermopsin is the EPA's 2015 *Health Effects Support Document for the Cyanobacterial Toxin Cylindrospermopsin* (USEPA, 2015a) because it is a 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. The 2015 EPA Health Effects Support Document (HESD) health assessment describes multiple adverse health effects for cylindrospermopsin. The EPA selected increased relative kidney weight in mice as the critical effect to derive the oral toxicity value (USEPA, 2015a). The EPA derived an HRL for cylindrospermopsin of 0.6 µg/L based on an oral reference value of 0.0001 mg/kg/day (USEPA, 2015a), a DWI-BW for children (birth to <21 years) of 0.0343 L/kg/day (USEPA, 2019a) and a 20% relative source contribution (RSC) (USEPA, 2000).
The EPA has determined that cylindrospermopsin does not occur with a frequency and at levels of public health concern in PWSs based on the available occurrence information and therefore does not meet SDWA's Statutory Criterion 2 for regulatory determinations. The primary occurrence data for cylindrospermopsin are nationally representative drinking water monitoring data from the UCMR 4 program (USEPA, 2024). Under UCMR 4 assessment monitoring, 0.03% of PWSs reported at least one measurement of cylindrospermopsin greater than the HRL (USEPA, 2026a).
The EPA has determined that regulating cylindrospermopsin under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs based on the exposed population and therefore does not meet SDWA's Statutory Criterion 3 for regulatory determinations. The PWS-served population exposed to cylindrospermopsin at levels of public health concern is only 0.01%, based on UCMR 4 finished water data (USEPA, 2026a).
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 for this reason as well.
The Agency has evaluated the best available information on cylindrospermopsin against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate cylindrospermopsin with an NPDWR.
**C. Ethoprop**
Ethoprop is an organophosphate pesticide and is used as an insecticide and nematicide on mostly vegetables and fruit crops. Over the past few decades, estimated usage of ethoprop has declined, and in 2019 showed limited geographic usage to the Pacific Northwest and California (USGS, 2023).
The EPA has found that ethoprop may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The EPA used toxicity information from the EPA's Office of Pesticide Programs for ethoprop as the basis for HRL derivation (USEPA, 2015b). The health assessment selected to derive an HRL for ethoprop is the EPA's Office of Pesticide Programs 2015 Human Health Risk Assessment (HHRA) for ethoprop (USEPA, 2015b; USEPA, 2015c). The 2015 EPA HHRA describes multiple adverse health effects for ethoprop. The EPA selected inhibition of red blood cell cholinesterase in male rats as the critical effect to derive the oral toxicity value (USEPA, 2015b). The EPA derived an HRL for ethoprop of 0.09 µg/L based on an oral reference value of 0.000065 mg/kg/day (USEPA, 2015b), a DWI-BW for infants (birth to <1 year) of 0.143 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
The EPA has determined that ethoprop does not occur with a frequency and at levels of public health concern in PWSs based on nationally representative drinking water monitoring data from UCMR 4 (USEPA, 2024). The Agency therefore finds that ethoprop does not meet Statutory Criterion 2 for regulatory determinations. Of the UCMR 4 systems that reported results for ethoprop, only 0.02% reported a result above the HRL (USEPA, 2026a).
The EPA has determined that there is no meaningful opportunity for health risk reduction through regulation of ethoprop with an NPDWR. The PWS-served population exposed to ethoprop at levels of public health concern is only 0.01%, based on UCMR 4 finished water data (USEPA, 2026a). Therefore, Statutory Criterion 3 for regulatory determinations is also not met.
The Agency has evaluated the best available information on ethoprop against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate ethoprop with an NPDWR.
**D. Microcystins**
Microcystins are toxins that are naturally produced and released by cyanobacteria. Microcystins exist in multiple forms (congeners), based on variations in amino acid composition; there are approximately 100 known microcystin congeners (USEPA, 2015d). 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, 2015d).
The EPA has found that microcystins may have an adverse effect on the health of persons and therefore meet SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected for RD 5 is the EPA's 2015 *Health Effects Support Document for the Cyanobacterial Toxin Microcystins* (USEPA, 2015d) because it is a peer-reviewed health assessment that derives an oral toxicity value and uses the best available science in its evaluation of noncancer risk. The 2015 EPA HESD describes multiple adverse health effects for microcystins. The EPA selected liver effects in rats as the critical effect to derive the oral toxicity value (USEPA, 2015d). The EPA derived an HRL for microcystins of 0.3 µg/L based on an oral reference value of 0.00005 mg/kg/day (USEPA, 2015d), a DWI-BW for adults (21 years and older) of 0.0336 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
The EPA has determined that microcystins do not occur in PWSs with a frequency and at levels of public health concern based upon nationally representative drinking water monitoring data from the UCMR 4 program (USEPA, 2024). Only 0.2% of systems reported at least one result above the HRL for total microcystins (USEPA, 2026a). As a result, the EPA finds that SDWA's Statutory Criterion 2 for regulatory determinations is not met.
Regulating microcystins under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs based on the exposed population, including sensitive populations. The population exposed to microcystins at levels of public health concern is only 0.06% based on UCMR 4 finished drinking water data (USEPA, 2026a). Therefore, the EPA finds that SDWA's Statutory Criterion 3 for regulatory determinations is not met.
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 for this reason as well.
The Agency has evaluated the best available information on microcystins against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The Agency is therefore making a final determination not to regulate microcystins with an NPDWR.
**E. Molybdenum**
Molybdenum is a naturally occurring element present in soils. 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 commonly used in metallurgy, including in alloys with cast iron, steel and superalloys. Molybdenum compounds are also used in catalysts, lubricants and pigments (ATSDR, 2020).
The EPA has found that exposure to molybdenum may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected for RD 5 is the 2020 Agency for Toxic Substances and Disease Registry's (ATSDR) 2020 Toxicological Profile for Molybdenum (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). The 2020 ATSDR health assessment describes multiple adverse health effects for molybdenum, and ATSDR selected kidney effects in female rats as the critical effect to derive the oral toxicity value (ATSDR, 2020). The EPA derived an HRL for molybdenum of 100 µg/L based on an oral reference value of 0.06 mg/kg/day (ATSDR, 2020), with an additional uncertainty factor of 3, a DWI-BW for children of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
Based on the Agency's evaluation of the available occurrence information, the EPA has determined that molybdenum does not occur with a frequency and at levels of public health concern in PWSs and therefore does not meet Statutory Criterion 2 for regulatory determinations. The primary occurrence data for molybdenum are nationally representative drinking water monitoring data from the UCMR 3 program (2013-2015) (USEPA, 2019b). Under UCMR 3 assessment monitoring, 0.1% of systems reported results above the HRL (USEPA, 2026a).
The UCMR 3 data indicate that the population exposed to molybdenum above the HRL is only 0.06% (USEPA, 2026a). The Agency, therefore, has determined that regulating molybdenum under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs, and as required by SDWA's Statutory Criterion 3 for regulatory determinations.
The Agency has evaluated the best available information on molybdenum against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate molybdenum with an NPDWR.
**F. Permethrin**
Permethrin is a pyrethroid pesticide primarily used as an insecticide. Sources of permethrin include agricultural usage and industrial activities. 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 (USGS, 2023).
The EPA has found that exposure to permethrin may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected to derive an HRL for permethrin is the EPA's Office of Pesticide Programs 2020 HHRA for permethrin (USEPA, 2020a; USEPA, 2020b). The EPA's 2020 HHRA describes multiple adverse health effects for permethrin. The EPA selected decreased motor activity in male rats as the critical effect to derive the oral toxicity value (USEPA, 2020a; USEPA 2020b). The EPA derived an HRL for permethrin of 3,000 µg/L based on an oral reference value of 0.44 mg/kg/day (USEPA, 2020a; USEPA, 2020b), a DWI-BW for children of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
The EPA has determined that permethrin does not occur with a frequency and at levels of public health concern in PWSs based on available occurrence information and therefore does not meet SDWA's Statutory Criterion 2 for regulatory determinations. The primary occurrence data for permethrin are nationally representative drinking water monitoring data from the UCMR 4 program (2018-2020) (USEPA, 2024). Under UCMR 4 assessment monitoring, there were no measurements of permethrin greater than the HRL (USEPA, 2026a).
The UCMR 4 data indicate persons served by the public water systems are not exposed to permethrin at levels of public health concern (USEPA, 2026a). The Agency has thus determined that regulating permethrin under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs, as required by SDWA's Statutory Criterion 3 for regulatory determinations.
The Agency has evaluated the best available information on permethrin against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate permethrin with an NPDWR.
**G. Profenofos**
Profenofos is an organophosphate pesticide that is applied as an insecticide. Profenofos registration was canceled in 2018, and it currently has no active labels in the EPA's Pesticide Product and Label System database (USEPA, 2023). 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 (USGS, 2023).
The EPA has found exposure to profenofos may have an adverse effect on the health of persons, meeting SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected to derive an HRL for profenofos is the EPA's Office of Pesticide Programs 2015 HHRA for profenofos (USEPA, 2015c; USEPA, 2015e). The EPA's 2015 HHRA describes multiple adverse health effects for profenofos, and the EPA selected inhibition of red blood cell acetylcholinesterase in rats as the critical effect to derive the oral toxicity value (USEPA, 2015c; USEPA, 2015e). The EPA derived an HRL for profenofos of 0.7 µg/L based on an oral reference value of 0.00012 mg/kg/day (USEPA, 2015c; USEPA, 2015e), a DWI-BW for children of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
The EPA has determined that profenofos does not occur with a frequency and at levels of public health concern in PWSs based on available occurrence information and therefore does not meet SDWA's Statutory Criterion 2 for regulatory determinations. The primary occurrence data for profenofos are nationally representative drinking water monitoring data from the UCMR 4 program (USEPA, 2024), during which 0.02% of systems reported a result above the HRL (USEPA, 2026a).
The population exposed to profenofos at levels of public health concern in drinking water is less than 0.01%, based on UCMR 4 finished water data (USEPA, 2026a). Therefore, the EPA has determined that regulating profenofos under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs, as required by SDWA's Statutory Criterion 3 for regulatory determinations.
The Agency has evaluated the best available information on profenofos against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate profenofos with an NPDWR.
**H. Tebuconazole**
Tebuconazole is a triazole that is used as a fungicide. The USGS estimated 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).
The EPA has found that exposure to tebuconazole may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected to derive an HRL for tebuconazole is the EPA's Office of Pesticide Programs 2021 HHRA for tebuconazole (USEPA, 2021a; USEPA, 2021b). The EPA's 2021 HHRA describes multiple adverse health effects for tebuconazole. The EPA selected increased incidence of skull/neural tube defects in mice as the critical effect to derive the oral toxicity value (USEPA, 2021a; USEPA, 2021b). The EPA derived an HRL for tebuconazole of 200 µg/L based on an oral reference value of 0.03 mg/kg/day (USEPA, 2021a; USEPA, 2021b), a DWI-BW for females of reproductive age (13 to < 50 years) of 0.0354 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
The EPA has determined that tebuconazole does not occur with a frequency and at levels of public health concern in PWSs based on available occurrence information and therefore does not meet SDWA's Statutory Criterion 2 for regulatory determinations. The primary occurrence data for tebuconazole are nationally representative drinking water monitoring data from the UCMR 4 program (USEPA, 2024). Under UCMR 4 assessment monitoring there were no measurements of tebuconazole greater than the HRL (USEPA, 2026a).
The UCMR 4 finished water data indicate that there are no persons served by public water systems exposed to tebuconazole at levels of public health concern in drinking water (USEPA, 2026a). Therefore, the EPA has determined that regulating tebuconazole under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs, as required by SDWA's Statutory Criterion 3 for regulatory determinations.
The Agency has evaluated the best available information on tebuconazole against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The EPA is therefore making a final determination not to regulate tebuconazole with an NPDWR.
**I. Tribufos**
Tribufos is a thiophosphate pesticide that is used as an insecticide and cotton defoliant (NCBI, 2023). From 1992 to 2018, tribufos usage has fluctuated between about 1.5 million pounds and 4.5 million pounds. Tribufos has been used almost exclusively on cotton. The maps indicate that tribufos is most intensively used in the South, in particular in the Atlantic coastal states, along the lower Mississippi River, and in Texas (USGS, 2023).
The EPA has found that exposure to tribufos may have an adverse effect on the health of persons and therefore meets SDWA's Statutory Criterion 1 for regulatory determinations. The health assessment selected to derive an HRL for tribufos is the EPA's 2015 HHRA for tribufos (USEPA, 2015f; USEPA, 2015g). The EPA's 2015 HHRA describes multiple adverse health effects for tribufos, and the EPA selected red blood cell cholinesterase inhibition in rats as the critical effect to derive the oral toxicity value (USEPA, 2015h; USEPA, 2015i). The EPA derived an HRL for tribufos of 1 µg/L based on an oral reference value of 0.0002 mg/kg/day (USEPA, 2015f; USEPA, 2015g), a DWI-BW for children of 0.0343 L/kg/day (USEPA, 2019a) and a 20% RSC (USEPA, 2000).
The EPA has determined that tribufos does not occur with a frequency and at levels of public health concern in PWSs based on available occurrence information and therefore does not meet SDWA's Statutory Criterion 2 for regulatory determinations. The primary occurrence data for tribufos are nationally representative drinking water monitoring data from the UCMR 4 program (USEPA, 2024). Under UCMR 4 assessment monitoring there were no measurements of tribufos greater than the HRL (USEPA, 2026a).
The UCMR 4 finished water data indicate that there are no persons served by public water systems exposed to tribufos at levels of public health concern in drinking water (USEPA, 2026a). Therefore, the EPA has determined that regulating tribufos under the SDWA does not present a meaningful opportunity for health risk reduction for persons served by PWSs, as required by SDWA's Statutory Criterion 3 for regulatory determinations.
The Agency has evaluated the best available information on tribufos against the three SDWA section 1412(b)(1)(A) statutory criteria and found that this contaminant does not satisfy the second and third criteria. The Agency is therefore making a final determination not to regulate tribufos with an NPDWR.
**V. The EPA's Considerations for Future Regulatory Determinations**
In a 2023 decision, the D.C. Circuit Court of Appeals in *NRDC* v. *Regan,* 67 F.4th 397 (D.C. Cir. 2023), held that the EPA must proceed to regulate a contaminant after finalizing a determination to regulate even when the Agency later determines that the contaminant no longer satisfies the statutory criteria for regulation. This ruling presented 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, the EPA determined that the potential for health-risk reduction was less beneficial than initially predicted.
In light of this ruling, the EPA continues to consider changes to its approach to making future determinations to regulate contaminants as explained in the preliminary regulatory determination for RD 5 (90 FR 3830; USEPA, 2025a). The EPA is evaluating conducting preliminary benefits analyses and treatment feasibility analysis for some future regulatory determinations. The EPA is considering performing these analyses for future regulatory determinations such as certain of those contaminants that are determined to meet the first two regulatory determination criteria under SDWA section 1412(b)(1)(A)(i) and (ii). The results of these analyses would add to information for the Agency's evaluation under the third regulatory determination criterion (SDWA section 1412(b)(1)(A)(iii)) on whether regulation of the contaminant presents a meaningful opportunity for health risk reduction for persons served by PWSs.
Several commenters expressed support for the EPA's intention to conduct preliminary benefits or treatment feasibility analyses prior to making positive regulatory determinations (USEPA, 2026b). The commenters noted that these analyses will be especially important in light of the 2023 D.C. Circuit Court ruling in *NRDC* v. *Regan* (USEPA, 2026b).
In the preliminary regulatory determination FRN for RD 5 (90 FR 3830; USEPA, 2025a) the EPA stated that the Agency was working collaboratively across programs to address the unreasonable risk from 1,4 -dioxane identified under TSCA. Since that time, the EPA is administratively reconsidering the 2024 supplemental risk evaluation and revised risk determination, as well as the underlying 2020 risk evaluation, focusing on the cancer risk analysis in the hazard assessment and its consistency with the best available science and EPA's 2005 Cancer Guidelines ( *https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/final-risk-evaluation-14-dioxane* ). Results of the reconsideration of the cancer risk analysis may be taken into consideration for future Agency actions, as appropriate, to protect public health based on the best available science.
**VI. Next Steps**
The Agency will not be taking regulatory action under the SDWA for the nine contaminants receiving negative determinations at this time. However, if new information about any of these contaminants becomes available ( *e.g.,* new studies on adverse health effects or new occurrence data), the EPA will evaluate whether to include them on a future CCL.
**VII. References**
Agency for Toxic Substances and Disease Registry (ATSDR). 2020. *Toxicological Profile for Molybdenum.* U.S. Department of Health and Human Services, Public Health Service. *https://www.atsdr.cdc.gov/ToxProfiles/tp212.pdf.*
D.C. Circuit Court (D.C. Cir.). 2023. *National Resources Defense Council* v. *Michael S. Regan, Administrator, U.S. Environmental Protection Agency and Environmental Protection Agency,* 67 F.4th 397. *https://casetext.com/case/nat-res-def-council-v-regan-1.*
Murray F.J., F.M. Sullivan, A.K. Tiwary, and S. Carey. 2014. 90-Day Subchronic Toxicity Study of Sodium Molybdate Dihydrate in Rats. *Regulatory Toxicology and Pharmacology,* 70(3): 579-88. *https://doi.org/10.1016/j.yrtph.2013.09.003.*
National Center for Biotechnology Information (NCBI). 2023. PubChem Compound Summary for CID 5125, Tribufos. Accessed December 11, 2023. *https://pubchem.ncbi.nlm.nih.gov/compound/Tribufos.*
NCBI. 2024. PubChem Compound Summary for CID 7242, o-Toluidine. *https://pubchem.ncbi.nlm.nih.gov/compound/o-Toluidine.* Accessed January 5, 2024.
United States Environmental Protection Agency (USEPA). 1992. Molybdenum; CASRN 7439-98-7. National Center for Environmental Assessment, Integrated Risk Information System, Chemical Assessment Summary. *https://iris.epa.gov/static/pdfs/0425_summary.pdf.*
USEPA. 1995. Policy on Evaluating Health Risks to Children. October 20, 1995. Science Policy Council, Washington, DC. Available on the internet at: *https://www.epa.gov/sites/production/files/2014-05/documents/1995_childrens_health_policy_statement.pdf;* Cover memo at: *https://www.epa.gov/sites/production/files/2014-05/documents/health_policy_cover_memo.pdf.*
USEPA. 2000. *Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000).* Office of Water, Office of Science and Technology. EPA/822/B-00/004. October. *https://www.epa.gov/sites/default/files/2018-10/documents/methodology-wqc-protection-hh-2000.pdf.*
USEPA. 2005. *Guidelines for Carcinogen Risk Assessment.* Risk Assessment Forum. EPA/630/P-03/001F. March. *https://www.epa.gov/sites/default/files/2013-09/documents/cancer_guidelines_final_3-25-05.pdf.*
USEPA. 2012. 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. Protocol for the Regulatory Determinations 3. Including appendices A-F. EPA 815-R14-005. April 2014.
USEPA. 2015a. *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. 2015b. 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. 2015c. 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. 2015d. *Health Effects Support Document for the Cyanobacterial Toxin Microcystins.* EPA-820-R-15-102. June. *https://www.epa.gov/sites/default/files/2017-06/documents/microcystins-support-report-2015.pdf.*
USEPA. 2015e. 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. 2015f. 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. 2015g. 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. 2016. Announcement of Final Regulatory Determinations for Contaminants on the Third Drinking Water Contaminant Candidate List. *Federal Register* 81(1): 13, January 4, 2016.
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.
USEPA. 2020a. 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. 2020b. 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. 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. 2021b. 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. 2022. Drinking Water Contaminant Candidate List 5-Final. *Federal Register* . Vol. 87, No. 218. P. 68060, November 14, 2022.
USEPA. 2023. Pesticide Product and Label System Database. *https://ordspub.epa.gov/ords/pesticides/f?p=PPLS:1.*
USEPA. 2024. *Occurrence Data from the Fourth Unregulated Contaminant Monitoring Rule (UCMR 4).* EPA 815-B-24-016.
USEPA. 2025a. Announcement of Preliminary Regulatory Determinations for Contaminants on the Fifth Drinking Water Contaminant Candidate List. *Federal Register* Vol 90 Number 9 Page 3830. January 15, 2025.
USEPA. 2025b. *U.S. Environmental Protection Agency Implementation of Gold Standard Science. https://www.epa.gov/scientific-leadership/gold-standard-science.*
USEPA. 2026a. *Final Regulatory Determination 5 Support Document.* EPA 815-R-26-002.
USEPA. 2026b. Responses to Public Comments on Preliminary Regulatory Determinations for Contaminants on the Fifth Drinking Water Contaminant Candidate List. EPA-815-R-26-003.
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.
World Health Organization (WHO). 2011. *Molybdenum in Drinking-Water. Background Document for Development of WHO Guidelines for Drinking-Water Quality.* WHO/SDE/WSH/03.04/11/Rev/1. *https://cdn.who.int/media/docs/default-source/wash-documents/wash-chemicals/molybdenum.pdf?sfvrsn=d01920eb_4.*
Lee Zeldin,
Administrator.