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EO12866_SDWA Part 141 RIN 2040-ZA20 STAGE FRN_20130722 

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 141 

[EPA-HQ-OW-____-____ ;FRL-_______-_______]

Announcement of Preliminary Regulatory Determinations for Contaminants on the Third 

Drinking Water Contaminant Candidate List 

AGENCY: Environmental Protection Agency (EPA). 

ACTION: Notice and Request for Public Comment 

_______________________________________________________________________ 

SUMMARY: The Safe Drinking Water Act (SDWA), as amended in 1996, requires the 

Environmental Protection Agency (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. These unregulated contaminants are chosen from the 

Contaminant Candidate List (CCL), which SDWA requires the agency to publish every five 

years. EPA published the third CCL (CCL 3) in the Federal Register on October 8, 2009. This 

notice presents the preliminary regulatory determinations and supporting rationale for 5 of the 

116 contaminants listed on CCL 3. The agency is making preliminary determinations to regulate 

one contaminant (i.e., strontium) and to not regulate four contaminants (i.e., 1,3-dinitrobenzene, 

dimethoate, terbufos and terbufos sulfone). EPA seeks comment on these preliminary 

determinations.
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DATES: Comments must be received on or before [INSERT DATE 60 DAYS AFTER DATE 

OF PUBLICATION IN THE FEDERAL REGISTER], 60 days after publication in the Federal 

Register. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-____-____, 

by one of the following methods: 

• www.regulations.gov: Follow the online instructions for submitting comments. 

 • Mail: Water Docket, Environmental Protection Agency, Mailcode: [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: Direct your comments to Docket ID No. EPA-HQ-OW-____-____]. EPA's policy 

is that all comments received will be included in the public docket without change and may be 

made available online at www.regulations.gov, including any personal information provided, 

unless the comment includes information claimed to be Confidential Business Information (CBI) 

or other information whose disclosure is restricted by statute. Do not submit information that you 

consider to be CBI or otherwise protected through www.regulations.gov. The 

www.regulations.gov website is an “anonymous access” system, which means EPA will not 
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know your identity or contact information unless you provide it in the body of your comment. If 

you send an e-mail comment directly to EPA without going through www.regulations.gov your 

e-mail address will be automatically captured and included as part of the comment that is placed 

in the public docket and made available on the Internet. If you submit an electronic comment, 

EPA recommends that you include your name and other contact information in the body of your 

comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to 

technical difficulties and cannot contact you for clarification, EPA may not be able to consider 

your comment. Electronic files should avoid the use of special characters, any form of 

encryption, and be free of any defects or viruses. For additional information about EPA’s public 

docket visit the EPA Docket Center homepage at http://www.epa.gov/epahome/dockets.htm. For 

additional instructions on submitting comments, go to Section I.B of the SUPPLEMENTARY 

INFORMATION section of this document. 

Docket: All documents in the docket are listed in the www.regulations.gov index. Although 

listed in the index, some information is not publicly available, e.g., CBI or other information 

whose disclosure is restricted by statute. Certain other material, such as copyrighted material, 

will be publicly available only in hard copy. Publicly available docket materials are available 

either electronically in www.regulations.gov or in hard copy at the Water Docket, EPA/DC, EPA 

West, Room 3334, 1301 Constitution Ave., NW, Washington, DC. The Public Reading Room is 

open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The 

telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for 

the Water Docket is (202) 566-2426. 
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FOR FURTHER INFORMATION CONTACT: Zeno Bain, Standards and Risk Management 

Division, Office of Ground Water and Drinking Water, Office of Water (Mailcode 4607M), 

Environmental Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460; 

telephone number: (202) 564-5970; e-mail address: bain.zeno@epa.gov. For general 

information, contact the Safe Drinking Water Hotline, telephone number: (800) 426-4791. The 

Safe Drinking Water Hotline is open Monday through Friday, excluding legal holidays, from 10 

a.m. to 4 p.m. Eastern time. 

SUPPLEMENTARY INFORMATION: 

I. General Information

A. 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 EPA’s preliminary regulatory determinations for five unregulated 

contaminants for comment. 

B. Tips for Preparing Your Comments. 

When submitting comments, remember to: 

• Identify the rulemaking by docket number and other identifying information 

(subject heading, Federal Register date and page number). 
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• Explain why you agree or disagree and suggest alternatives. 

• Describe any assumptions and provide any technical information and/or data that 

you used. 

• Provide specific examples to illustrate your concerns, and suggest alternatives. 

• Explain your views as clearly as possible, avoiding the use of profanity or 

personal threats. 

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

Abbreviations Used in This Document 

Abbreviation Meaning 

 

μg/L Micrograms per liter 

ADAF Age Dependent Adjustment Factor 

AM Assessment Monitoring 

AMWA Association of Metropolitan Water Agencies 

ATSDR Agency For Toxic Substances And Disease Registry 

AWWA American Water Works Association 

BATs Best Available Technologies 

BMD Benchmark Dose 

BMDL Benchmark Dose (95% Lower Confidence Bound) 

BW Body Weight 

CARC Cancer Assessment Peer Review Committee 

CAS Chemical Abstracts Service 

CASRN Chemical Abstract Service Registry Number 

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 

CCR Consumer Confidence Report 
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CFR Code of Federal Regulations 

ChE Cholinesterase 

CMR Chemical Monitoring Reform 

CSF Cancer Slope Factor 

CUSIUR Chemical Update System/Inventory Update Rule 

cVOC Carcinogenic Volatile Organic Compounds 

CW Concentration in Water 

CWS Community Water System 

CWSS Community Water System Survey 

DBP Disinfection Byproduct 

DBP ICR Disinfection Byproduct Information Collection Rule 

DDE 1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene 

DSMRT Distribution System Maximum Residence Time 

DWI Drinking Water Intake 

DWS Drinking Water Strategy 

EFSA European Food Safety Authority 

ELCD Electrolytic Conductivity Detection 

EPA Environmental Protection Agency 

EPCRA Emergency Planning And Community Right-To-Know Act 

EPTC S-Ethyl propylthiocarbamate 

EPTDS Entry Point to the Distribution System 

ESA Ethanesulfonic Acid 

EWG Environmental Working Group 

F Fraction of a 70 year lifetime applicable to the age period 

FFQ Food Frequency Questionnaire 

FIFRA Federal Insecticide, Fungicide, And Rodenticide Act 

FR Federal Register 

GAC Granular Activated Carbon 

GAO Government Accountability Office 

GC Gas Chromatography 

GW Ground Water 

HA Health Advisory 

HRL Health Reference Level 

ICR Information Collection Rule 

IOC Inorganic Compound 

IREDs Interim Eligibility Decisions 

IRIS Integrated Risk Information System 

Kg Kilogram 

LOAEL Lowest Observed Adverse Effect Level 

MCLG Maximum Contaminant Level Goal 

MDL Method Detection Limit 
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mg/L Milligrams per liter 

mg/kg/day Milligrams per kilogram per day

MDBP Microbial Disinfection Byproduct 

MOA Mode of Action 

MRL Minimum Reporting Limit 

MS Mass Spectrometry 

MTBE Methyl Tertiary Butyl Ether 

NAS National Academy of Sciences 

NAWQA National Water Quality Assessment 

NCFAP National Center for Food and Agricultural Policy 

NCI National Cancer Institute 

NCOD National Drinking Water Contaminant Occurrence Database 

NDBA N-Nitroso-di-n-butylamine 

NDEA N-Nitrosodiethylamine 

NDMA N-Nitrosodimethylamine 

NDPA N-Nitroso-di-n-propylamine 

NDPhA N-Nitrosodiphenylamine 

NDWAC National Drinking Water Advisory Council 

NIRS National Inorganics And Radionuclides Survey 

NMEA N-Nitrosomethylethylamine 

NOAEL No Observed Adverse Effect Level 

NPDES National Pollutant Discharge Elimination System 

NPDWR National Primary Drinking Water Regulation 

NPYR N-Nitrosopyrrolidine 

NRC National Research Council 

NREC National Reconnaissance of Emerging Contaminants 

NTP National Toxicology Program 

OA Oxanilic Acid 

OPP Office of Pesticides Program 

OW Office of Water 

PCCL Preliminary Contaminant Candidate List 

PCE Tetrachloroethylene 

PDP Pesticide Data Program 

PFOA Perfluorooctanoic Acid 

PFOS Perfluorooctanesulfonic Acid 

PHA Provisional Health Advisory 

PID Photoionization Detection 

PMP Pesticide Monitoring Program 

PWS Public Water System 

QA Quality Assurance 

RD 1 Regulatory Determinations 1 
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RD 2 Regulatory Determinations 2 

RD 3 Regulatory Determinations 3 

RED Reregistration Eligibility Decision 

RfD Reference Dose 

RL Reporting Limit 

RSC Relative Source Contribution 

SAP Scientific Advisory Panel 

SDWA Safe Drinking Water Act 

SEPW U.S. Senate Committee on Environment and Public Works 

SS Screening Survey 

SSCTs Small System Compliance Technologies 

STORET Storage And Retrieval (STORET) Data System 

SW Surface Water 

SY Six Year Review 

SY3 Six Year Review 3 

TCE Trichloroethylene 

TPTH Triphenyltin Hydroxide 

TRED Tolerance Reassessment Progress And Risk Management Decision 

TRI Toxic Release Inventory 

TT Treatment Technique 

UCM Unregulated Contaminant Monitoring 

UCMR 1 First Unregulated Contaminant Monitoring Regulation 

UCMR 2 Second Unregulated Contaminant Monitoring Regulation 

UCMR 3 Third Unregulated Contaminant Monitoring Regulation 

UF Uncertainty Factor 

USDA United States Department of Agriculture 

USGS United States Geological Survey 

VOC Volatile Organic Compound 

 

WHO World Health Organization 

Formatted: Font: Not Bold

Formatted: Level 1, Line spacing: Double, No

widow/orphan control, Don't adjust space between

Latin and Asian text, Don't adjust space between Asian

text and numbers
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Table of Contents 

I. General Information 

A. Does this Action Apply to Me? 

B. Tips for Preparing Your Comments 

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 

2. The First Contaminant Candidate List (CCL 1) and Regulatory Determinations (RD 

1) 

3. The Second Contaminant Candidate List (CCL 2) and Regulatory Determinations 

(RD 2) 

4. The Third Contaminant Candidate List (CCL 3) and Regulatory Determinations (RD 

3) 

5. The Drinking Water Strategy 

6. Outreach for RD 3 (Stakeholder Meeting and Expert Review) 

III. Approach and Overall Outcome for RD 3 

A. Summary of the Approach and Overall Outcome for RD 3 
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1. Phase 1 (Data Availability Phase) 

2. Phase 2 (Data Evaluation Phase) 

3. Phase 3 (Regulatory Determination Assessment Phase) 

B. Supporting Documentation for EPA’s Preliminary Determinations 

C. Analyses Used To Support the Preliminary Regulatory Determinations 

1. Evaluation of Adverse Health Effects 

2. Evaluation of Contaminant Occurrence and Exposure 

IV. Contaminant-Specific Discussions for the RD 3 Preliminary Regulatory Determinations 

A. Summary of the Preliminary Regulatory Determination 

B. Contaminant Profiles 

1. Dimethoate 

2. 1,3-Dinitrobenzene 

3. Strontium 

 4-5. Terbufos and Terbufos Sulfone 

V. What is the Status of the Agency’s Evaluation of Chlorate and the Nitrosamines? 

VI. What About the Remaining CCL 3 Contaminants? 

VII. EPA's Next Steps 

VIII. References 
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II. Purpose and Background 

 This section briefly summarizes the purpose of this action, the statutory requirements, 

and previous activities related to the CCL and regulatory determinations. 

A. What is the Purpose of This Action? 

 The purpose of this action is to present and request comment on EPA’s preliminary 

regulatory determinations for five unregulated contaminants. The five contaminants include: 

dimethoate, 1,3-dinitrobenzene, strontium, terbufos, and terbufos sulfone. The agency is making 

preliminary determinations to regulate one contaminant (strontium) and to not regulate the 

remaining four contaminants (dimethoate, 1,3-dinitrobenzene, terbufos, and terbufos sulfone). 

EPA seeks comment on these preliminary determinations. The agency is also presenting and 

requesting comment on the process used for this round of regulatory determinations (i.e., RD 3), 

the supporting information, and the rationale used to make these preliminary decisions. 

B. Background on the CCL and Regulatory Determinations 

1. Statutory Requirements for CCL and Regulatory Determinations. Section 

1412(b)(1)(B)(i) of the 1996 Safe Drinking Water Act Amendments (SDWA) requires EPA to 

publish the CCL every five years. The CCL is a list of contaminants which are not subject to any 

proposed or promulgated national primary drinking water regulations (NPDWRs,), are known or 

anticipated to occur in public water systems (PWSs), and may require regulation under SDWA. 

SDWA section 1412(b)(1)(B)(ii) directs EPA to determine whether to regulate at least five 

contaminants from the CCL every five years. For EPA to make a determination to regulate a 

contaminant, SDWA requires the Administrator to determine that: 
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 (a) the contaminant may have an adverse effect on the health of persons; 

(b) the contaminant is known to occur or there is substantial likelihood that the 

contaminant will occur in public water systems with a frequency and at levels of public 

health concern; and 

(c) 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 EPA determines that these three statutory criteria are met and makes a final 

determination to regulate a contaminant, the agency has 24 months to publish a proposed 

Maximum Contaminant Level Goal1

 (MCLG) and NPDWR2. After the proposal, the agency has 

18 months to publish and promulgate a final MCLG and NPDWR (SDWA section 

1412(b)(1)(E))3

. 

2. The First Contaminant Candidate List (CCL 1) and Regulatory Determinations (RD 

1). 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 made and published the final regulatory determinations for 9 of the 60 CCL 1 

 

1

 The 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. Maximum contaminant 

level goals are non-enforceable health goals." (40 C.F.R. 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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contaminants in the FR on July 18, 2003 (68 FR 42898; USEPA, 2003a).. The agency 

determined that NPDWRs were not necessary for any of these nine contaminants: 

Acanthamoeba, aldrin, dieldrin, hexachlorobutadiene, manganese, metribuzin, naphthalene, 

sodium, and sulfate. (68 FR 42898; USEPA, 2003a). The agency issued guidance on posted 

information about Acanthamoeba4 on the EPA website and issued health advisories5 for 

manganese, sodium, and sulfate. 

3. The Second Contaminant Candidate List (CCL 2) and Regulatory Determinations (RD 

2). The agency published the final CCL 2 in the FR on February 24, 2005, (70 FR 9071; USEPA, 

2005a) and carried forward the 51 remaining chemical and microbial contaminants listed on 

CCL 1. The agency made and 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 that NPDWRs were not necessary for any of these 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 propylthiocarbamate 

(EPTC), fonofos, terbacil, and 1,1,2,2-tetrachloroethane. (73 FR 44251; USEPA, 2008a). The 

agency issued new or updated health advisories6 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 Determinations (RD 

 

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

 The health advisories for CCL 1 can be found at http://water.epa.gov/drink/standards/hascience.cfm 

6

 The health advisories for CCL 2 can be found at http://water.epa.gov/drink/standards/hascience.cfm 

Formatted: Font: 11 pt
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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, EPA improved and built upon the 

process that was used for CCL 1 and CCL 2. The new CCL 3 process was based on substantial 

expert input and recommendations from the National Academy of Science’s (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, EPA developed a multi-step 

process to select candidates for the final CCL 3, which included the following key steps: 

(a) identification of a broad universe of ~7,500 potential drinking water contaminants 

(the CCL 3 Universe); 

(b) screening the CCL 3 Universe to a preliminary CCL (PCCL) of ~600 contaminants 

based on the potential to occur in PWSs and the potential for public health concern; and 

(c) evaluation of the PCCL contaminants based on a more detailed review of the 

occurrence and health effects data to identify a final list of 116 CCL 3 contaminants. 

The development of the CCL, regulatory determinations, and any subsequent rulemaking 

should be viewed as a progression where each process builds upon the previous process, 

including the collection of data and analyses conducted. The agency’s improvements in 

developing CCL 3 provide an excellent foundation for RD 3 by enhancing EPA’s ability to 

identify contaminants of concern for drinking water. 

While this notice focuses on the preliminary regulatory determinations for 5 of the 116 

CCL 3 contaminants, it is important to note that the agency made and published a final 

determination to regulate one CCL 3 contaminant, perchlorate, on February 11, 2011 (76 FR 
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7762; USEPA, 2011a). Additional information about CCL 3 and the perchlorate final 

determination can be found in the October 8, 2009 (74 FR 51850; USEPA, 2009a) and February 

11, 2011 (76 FR 7762; USEPA, 2011a) Federal Register notices, respectively. Sections III and 

IV in this notice provide more detailed information about the approach and outcome used for RD 

3 and the contaminant-specific regulatory determinations. 

5. The Drinking Water Strategy. In March 2010, EPA announced the agency’s new 

Drinking Water Strategy (DWS)7

, which is aimed at finding ways to strengthen the protection of 

public health from contaminants in drinking water. The new vision is intended to streamline 

decision-making, expand protection under existing laws, and promote cost-effective new 

technologies to meet the needs of rural, urban, and other water-stressed communities. The four 

principles underlying the DWS are: 

(a) Address contaminants as groups rather than one at a time so that enhancement of 

drinking water protection can be achieved cost-effectively. 

(b) Foster development of new drinking water technologies to address health risks posed 

by a broad array of contaminants. 

(c) Use the authority of multiple statutes to help protect drinking water. 

(d) Partner with States to develop shared access to all PWSs monitoring data. 

The first principle (i.e., addressing contaminants as groups) has a direct bearing on RD 3 

and how to designate the contaminants for analysis, determination and subsequent regulation; 

 

7

 More information about the DWS can be found at water.epa.gov/lawsregs/rulesregs/sdwa/dwstrategy/ 
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that is, should they be considered individually or as a group. Although the agency has previously 

regulated contaminants as groups (e.g., total trihalomethanes, total haloacetic acids, gross alpha 

radionuclides, gross beta and photon emitters, etc.), all of the determinations for RD 1 and RD 2 

were made on individual contaminants. As part of the DWS, the agency identified several factors 

to evaluate which contaminants might effectively be regulated as a group and considered these 

factors in evaluating contaminant groups for RD 3. All the factors do not have to be met, but the 

more factors that are met, the more suitable it may be to regulate the contaminants as a group. 

These factors include whether the contaminants in the group: 

(a) have a similar health endpoint, 

(b) can be measured by the same analytical methods, 

(c) can be treated using the same technology or treatment technique approach and/or 

(d) have been shown to occur individually (and possibly co-occur if data are available). 

EPA conducted extensive national outreach to solicit input from stakeholders on the DWS and 

how best to address groups of contaminants. Stakeholders generally agreed that while public 

health protection is of paramount importance, the grouping factors previously listed were some 

of the other important factors to consider in evaluating which contaminants would work best in a 

group regulation. Several CCL 3 contaminants (as well as non-CCL 3 contaminants) belong to 

contaminant groups that underwent consideration for regulation during the RD 3 process. 

In February 20118

, the agency decided to address carcinogenic volatile organic 

 

8

 http://water.epa.gov/lawsregs/rulesregs/sdwa/dwstrategy/ 
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compounds (cVOCs) as a group in a separate and concurrent regulatory process. (which the 

agency expects to release in late 2014). Some of the cVOCs being considered include 

unregulated cVOCs listed on CCL 3 (e.g., 1,2,3-trichloropropane). While the cVOC group is 

being evaluated in a separate regulatory process, the same factors used to group cVOCs (i.e., 

similar health endpoint, measured by the same analytical method, similar treatment technique 

approach, etc.) were used to evaluate groups of contaminants for RD 3 as well (e.g., 

nitrosamines, chloroacetanilides, etc.). Although EPA hasevaluated the nitrosamines and 

chloroacetanilides groups as part of the RD 3 process, in the end, EPA decided not to 

includemake any groups of contaminants in the preliminary determinations for these groups

under RD 3. 

The SDWA requires EPA to review each existing NPDWR at least once every six years 

and revise them, if appropriate. The purpose of the review, called the Six Year Review (SY), is 

to identify those NPDWRs for which current health effects assessments, changes in technology, 

and/or other factors provide a health or technical basis to support a regulatory revision that will 

maintain or provide for greater protection of the health of persons. In contrast, the RD process is 

intended to address currently unregulated contaminants. The agency will review the existing 

Microbial Disinfection Byproduct (MDBP) regulations as part of the third Six Year Review 

(SY3). Because chlorate and nitrosamines are disinfection byproducts (DBPs) that can be 

introduced or formed in public water systems partly because of disinfection practices, the agency 

 
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believes it is important to evaluate these unregulated DBPs in the context of the review of the 

existing DBP regulations. DBPs need to be evaluated collectively, because the potential exists 

that the chemical disinfection used to control a specific DBP could affect the concentrations of 

other DBPs. Therefore, the agency is not making a regulatory determination for chlorate and 

nitrosamines at this time. The agency expects to complete the review of these DBPs by the end 

of 2015. 

6. Outreach for RD 3 (Stakeholder Meetings and Expert Review) 

EPA sought external advice and expert input for RD 3 by convening two public 

stakeholder meetings and conducting an Expert Review panel. On March 3, 2011, EPA held an 

Environmental Justice (EJ) Stakeholder meeting in Washington, D.C. to solicit input on RD 3 

and environmental justice issues. Approximately 90 stakeholders participated (either by phone or 

in person) including representatives of children's advocacy groups, environmental organizations, 

community action groups, the drinking water industry, and State drinking water and public 

health programs. Stakeholders did not identify any EJ issues specific to RD 3. On June 16, 2011, 

EPA held another public Stakeholder Meeting in Washington, D.C., to disseminate information 

on the progress of RD 3 and solicit input from stakeholders, the public, and other interested 

groups. Forty-six participants attended including representatives from States, environmental and 

public health organizations, drinking water systems, chemical manufacturers, local governments, 

and academia. EPA presented and discussed: (a) the approach used to narrow the contaminants 

listed on CCL 3 and identify potential candidates for RD 3 (with a focus on those occurring at 

levels of health concern in drinking water) and (b) the background, health, and occurrence 
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information for a “short list” of 329 contaminants being evaluated as potential RD 3 candidates. 

Stakeholders asked questions and provided comments about the approach as well as the health 

and occurrence information presented on several contaminants. One stakeholder provided 

additional health information on the chloroacetanilides and submitted a letter requesting that 

EPA regulate these compounds with an NPDWR (USEPA, 2011b). A summary of the June 16, 

2011, meeting is provided in the docket for this action (USEPA, 2011c). 

 In May 2011, the Government Accountability Office (GAO) released a report entitled, 

“EPA Should Improve Implementation of Requirements on Whether to Regulate Additional 

Contaminants” (GAO, 2011). Specifically for regulatory determinations, GAO recommended 

that the agency develop criteria to identify contaminants of greatest public health concern and be 

more transparent, clear, and consistent by developing policies/guidance to interpret the SDWA 

criteria and make determinations (i.e., include thresholds for positive findings, factors for 

determining adequacy of occurrence/health data to make determinations, an approach for 

evaluating health effects on sensitive subpopulations, a process for presenting key information in 

documents, etc). In response to questions regarding the GAO report at a July 2011 U.S. Senate 

Committee on Environment and Public Works (SEPW) hearing10, EPA committed to consulting 

 

9

 Subsequent to the June 2011 stakeholder meeting and before the October 2011 Expert Review, EPA identified two 

additional contaminants for the shortlist, bringing the total to 34. In response to the Expert Review comments, an 

additional contaminant was added to the short list, bringing the final total to 35 CCL 3 contaminants. 10 The U.S. Senate Committee on Environment and Public Works full committee hearing, entitled “Oversight 

Hearing on the Environmental Protection Agency’s Implementation of the Safe Drinking Water Act’s Unregulated 

Drinking Water Contaminants Program” can be found at 

(http://www.epw.senate.gov/public/index.cfm?FuseAction=Hearings.Hearing&Hearing_ID=fc5a8756-802a-23ad454a-b9eeb7bf1c36). 
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with an independent panel of scientists on the RD 3 process to determine how SDWA criteria 1 

and 2 are evaluated11, how the best available science is used to make decisions, how the 

contaminants of greatest public health risk are assessed, and how vulnerable populations 

(especially children) are considered. EPA also committed to making the process used for 

regulatory determinations publicly available and to review the process every five years as EPA 

conducts the regulatory determination cycle. 

To addressimplement the commitment, EPA convened a panel of experts in October 2011 

to provide an unbiasedindependent review of the approach used for RD 3, which EPA described 

in a draft of the document entitled, “Protocol for the Regulatory Determinations 3” (USEPA, 

2012a2014a). The Expert Review panel included seven experts representing one or more of the 

following areas of expertise: health effects evaluation, drinking water occurrence/exposure 

information evaluation, State drinking water perspective, PWS perspective, and/or some 

familiarity with the RD 3 process (including the Contaminant Candidate List). The review 

involved a three-week paper review of the October 2011 Draft RD 3 Protocol document and an 

in-person meeting held in Washington D.C., on October 26 and 27, 2011. Panel members were 

encouraged to provide comments as individuals based upon their expertise and background, not 

as representatives of any respective organizational affiliation. The information and input 

provided by the expert reviewers assisted the agency in revising and clarifying the approach used 

for the RD 3 process. A summary of the October 26-27, 2011, meeting and the expert reviewers’ 

 

11 Under the statute, SDWA criterion 3 of Section 1412(b)(1)(A) is solely the Administrator’s decision. 
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comments (USEPA, 2011d), as well as the protocol document (USEPA, 2012a2014a), are 

provided in the docket for this action. 

III. Approach and Overall Outcome for RD 3

This section describes (a) the approach EPA uses to identify and evaluate contaminants for the 

agency’s third round of Regulatory Determinations (RD 3) along with the overall outcome of 

applying this approach, (b) the supporting RD 3 documentation, and (c) the technical analyses 

and sources of health and occurrence information. 

A. Summary of the Approach and Overall Outcome for RD 3 

The three phases of the RD 3 Process are (1) the Data Availability Phase, (2) the Data Evaluation 

Phase, and (3) the Regulatory Determination Assessment Phase. Figure 1 provides a brief 

overview of the process EPA uses to identify which CCL 3 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 3 process please 

refer to the “Protocol for the Regulatory Determinations 3” (USEPA, 2012a2014a). 
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Figure 1: The Three Primary Phases of the RD 3 Process 

Formatted: Line spacing: Double

Formatted: Centered, Tab stops: 0.75", Left
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Health Data Availability

Assessment

•Health Assessment

available or in process

Occurrence Data

Availability Assessment

•Nationally representative  

finished water data “or”

•Other finished water data

with detects greater than

CCL3 derived HRL

Evaluation of Outcomes of Health &

Occurrence Data Availability Assessments

Doesit potentially have sufficient health and

occurrence data available?

Phase 1: Data Availability

Phase 2: Data Evaluation

Phase 3:

Regulatory Determination Assessment

Step 1: Collect &

Evaluate Health

Information and Derive

a Draft HRL

Step 2: Gather &

Evaluate Additional

Occurrence Data

Sources Relative to the  

Draft HRL

Evaluate Statutory Criterion #2:

Occurrence Assessment

Isthe contaminant known to occur or is

there substantial likelihood that the

contaminant will occur above the HRL at a

frequency and level of public health

concern?

Evaluate Statutory Criterion #1:  

Health Assessment

May the contaminant have an

adverse effect on the health of

persons?

Evaluate Statutory Criterion #3:

Meaningful Opportunity Assessment

(Administrator’s Decision)

In the sole judgment of the Administrator,

doesregulation of such contaminant

present a meaningful opportunity for

health risk reduction for personsserved by

public water systems?

CCL3

Step 3: Identify

ContaminantsOccurring

at Levels and Frequencies

of Public Health Concern

Step 4: Identify

Contaminants with No or

Low Occurrence at Levels

of Public Health Concern

Health Data Availability

Assessment

•Health Assessment

available or in process

Occurrence Data

Availability Assessment

•Nationally representative  

finished water data “or”

•Other finished water data

with detects greater than

CCL3 derived HRL

Evaluation of Outcomes of Health &

Occurrence Data Availability Assessments

Doesit potentially have sufficient health and

occurrence data available?

Phase 1: Data Availability

Phase 2: Data Evaluation

Phase 3:

Regulatory Determination Assessment

Step 1: Collect &

Evaluate Health

Information and Derive

a Draft HRL

Step 2: Gather &

Evaluate Additional

OccurrenceData

Sources Relative to the  

Draft HRL

Evaluate Statutory Criterion #2:

Occurrence Assessment

Isthe contaminant known to occur or is

there substantial likelihood that the

contaminant will occur above the HRL at a

frequency and level of public health

concern?

Evaluate Statutory Criterion #1:  

Health Assessment

May the contaminant have an

adverse effect on the health of

persons?

Evaluate Statutory Criterion #3:

Meaningful Opportunity Assessment

(Administrator’s Decision)

In the sole judgment of the Administrator,

doesregulation of such contaminant

present a meaningful opportunity for

health risk reduction for persons served by

public water systems?

CCL 3

Step 3: Identify

ContaminantsOccurring

at Levels and Frequencies

of Public Health Concern

Step 4: Identify

Contaminants with No or

Low Occurrence at Levels

of Public Health Concern

Field Code Changed
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1. Phase 1 (Data Availability Phase)

In Phase 1, the Data Availability Phase, the agency identifies contaminants that may have 

sufficient health and occurrence data to proceed to Phase 2 and be listed on a “short list” for 

further evaluation. With regard to sufficient health effects data used to identify potential adverse 

health effect(s), the agency considers whether a peer-reviewed health risk assessment is available 

or in process from one of the following sources: (a) the agency’s Integrated Risk Information 

System (IRIS); (b) the agency’s Office of Water (OW); (c) the agency’s Office of Pesticide 

Programs (OPP); (d) the National Academy of Sciences (NAS); (e) the Agency for Toxic 

Substances and Disease Registry (ATSDR); and/or (f) the World Health Organization (WHO). 

For a non-EPA health assessment (i.e., NAS, ATSDR, WHO) to be utilized for regulatory 

determinations, the health assessment must use comparable methods, standards, and guidelines to 

an EPA health assessment. If a health assessment is not available from one of these sources, then 

the contaminant is not considered for RD 3. 

In regard to sufficient occurrence data, the agency considers the availability of nationally 

representative finished water data and whether other finished water data are available that 

indicate known and/or likely occurrence in PWSs. Occurrence data from the following sources, 

administered or overseen by EPA, is considered nationally representative: (a) the Second 

Unregulated Contaminant Monitoring Regulation (UCMR 2); (b) the First Unregulated 

Contaminant Monitoring Regulation (UCMR 1) Assessment Monitoring; (c) the Unregulated 

Contaminant Monitoring (UCM) program; and/or (d) the National Inorganics and Radionuclides 

Survey (NIRS). 
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If nationally representative data are not available, EPA identifies and evaluates other 

finished water data, which may include other national assessments as well as regional, State, and 

more localized finished water assessments. These other national finished water data include 

assessments that are geographically distributed across the nation but not intended to be 

statistically representative of the nation. These other finished water data include the following 

sources for consideration in the regulatory determination process: (a) finished water assessments 

for Federal agencies (e.g., EPA and the United States Geological Survey (USGS))12; (b) statelevel finished water monitoring data; (c) research performed by institutions and universities 

(e.g., scientific literature); and/or (d) other supplemental finished water monitoring surveys (e.g., 

Pesticide Monitoring Program (PMP), National Reconnaissance of Emerging Contaminants 

(NREC), and other targeted surveys or localized State/Federal monitoring surveys). 

EPA prefers to have nationally representative data available when making regulatory 

determinations but may also use these other sources of finished water occurrence data to 

evaluate the contaminant and determine if there is “substantial likelihood that the contaminant 

will occur in PWSs with a frequency and at levels of public health concern.” If there is sufficient 

occurrence in these other finished water data sources, EPA uses this information to address the 

occurrence-related aspects of the statutory criteria when deciding to regulate a contaminant. 

However, it is difficult to determine that a contaminant is not occurring or not likely to occur 

based on these other sources of finished water data because the data are limited in scope and the 

 

12 These may be assessments that are geographically distributed across the nation but not intended to be statistically 

representative of the nation. Examples include EPA’s Disinfection By Product Information Collection Request and 

various USGS water quality surveys. 
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contaminant could be occurring in other parts of the country that were not monitored. 

EPA also considers the availability of analytical methods for monitoring, and whether the 

contaminant is part of a contaminant group based on factors defined by the Drinking Water 

Strategy (DWS) (see section II.B.5). 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) A peer-reviewed health assessment is available or in process, and 

(b) A widely available analytical method for monitoring is available, and 

(c) Either nationally representative finished water occurrence data are available, or other 

finished water occurrence data shows occurrence at levels ≥> 1⁄2 CCL 3 health reference 

level (HRL)

13. 

If a contaminant meets these three criteria, it is placed on a “short list” and proceeds to Phase 2. 

EPA also evaluated whether the contaminant could be considered as part of a group using the 

DWS factors discussed earlier in section II.B.5. After evaluating the 116 CCL 3 contaminants in 

Phase 1, the agency identified 35 CCL 3 contaminants and two non-CCL 3 contaminants (listed 

in Table 1) to evaluate further in Phase 2. The non-CCL 3 contaminants were included because 

they are part of a larger group (nitrosamines) that also includes a number of CCL 3 

 

13 See section III.C for a discussion about how EPA derives an HRL. EPA developed the CCL 3 HRLs using the 

most recent health data available during the CCL 3 process. EPA uses 1⁄2 CCL 3 HRL as a conservative value to 

identify contaminants with potential occurrence of concern. during Phase 1 of the RD process. The CCL 3 HRLs for 

the 116 contaminants can be found at (http://water.epa.gov/scitech/drinkingwater/dws/ccl/upload/Final-CCL-3-

Contaminant-Information-Sheets.pdf ). After updating, completing and peer-reviewing health assessments as 

necessary, the final HRL used for RD 3 may be different than the CCL 3 HRL. 
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contaminants.

 
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Table 1. Contaminants Proceeding from Phase 1 to Phase 2 

1, 1, 1, 2-Tetrachloroethane1,3 Metolachlor oxanilic acid (OA)1,3

1, 2, 3-Trichloropropane1,3 Molinate1

1, 3-Dinitrobenzene1 Molybdenum1

1, 4-Dioxane2 Nitrobenzene1,3

Acephate2 N-Nitroso-di-n-butylamine (NDBA)1,3,5

Acetochlor1,3 N-Nitrosodiethylamine (NDEA)1,3

Acetochlor ethanesulfonic acid (ESA)1,3 N-Nitrosodimethylamine (NDMA)1,3

Acetochlor oxanilic acid (OA)1,3 N-Nitroso-di-n-propylamine (NDPA)1,3

Alachlor ethanesulfonic acid (ESA)1,3 N-Nitrosodiphenylamine (NDPhA)3

Alachlor oxanilic acid (OA)1,3 N-Nitrosomethylethylamine (NMEA)1,3,5

Chlorate2 N-Nitrosopyrrolidine (NPYR)1,3

Cobalt1 Perfluorooctanesulfonic acid (PFOS)2

Dimethoate1 Perfluorooctanoic acid (PFOA)2

Disulfoton4 RDX1

Diuron4 Strontium1

Methyl bromide (Bromomethane)1 Terbufos2,3

Methyl tert-butyl ether1 Terbufos sulfone1,3

Metolachlor1,3 Vanadium1

Metolachlor ethanesulfonic acid (ESA)1,3 

1

 Has nationally representative finished water data and available or in process health assessment 

2

 Has other finished water data (occurrence at levels ≥> 1⁄2 CCL 3 HRL) and available or in process health 

assessment 

3 Component of a contaminant group and will be further evaluated in Phase 2 

4

 One exception to the criterion of having available nationally representative drinking water data applies 

to contaminants monitored in the UCMR 1 Screening Survey (SS). As noted in section 5, the UCMR 1 

SS is a statistically defined, national sample of 300 PWSs. Because this survey only includes 300 

systems, the agency identified and compiled additional supplemental data to compliment the UCMR 1 SS 

data for these contaminants that proceed to Phase 2 for further evaluation. 

5

A non-CCL 3 contaminant that is part of the nitrosamine group. 

The remaining 81 CCL 3 contaminants (listed in Table 2) did not meet either or both of the 

Phase 1 data availability criteria above and were not considered further for RD 3. 
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Table 2. Contaminants Not Proceeding from Phase 1 to Phase 2 

Has nationally representative finished water data but no health assessment 

1,1-Dichloroethane 

Halon 1011 (Bromochloromethane)nPropylbenzene

3-Hydroxycarbofuran n-Propylbenzenesec-Butylbenzene

Chloromethane (Methyl chloride) sec-ButylbenzeneTellurium

GermaniumHalon 1011 

(Bromochloromethane) Tellurium

Has available or in process health assessment and other finished drinking water data 

but no occurrence at levels ≥> 1⁄2 CCL 3 HRL 

1-Butanol Formaldehyde 

Acrolein Methamidophos Germanium

alpha-Hexachlorocyclohexane Oxydemeton-methylMethamidophos

Bensulide OxyfluorfenOxydemeton-methyl

Benzyl chloride PermethrinOxyfluorfen

Captan ProfenofosPermethrin

Dicrotophos TebuconazoleProfenofos

Ethoprop TribufosTebuconazole

Ethylene glycol VinclozolinTribufos

Ethylene thiourea (Maneb) ZiramVinclozolin

Fenamiphos Ziram

Has other finished drinking water data but no health assessment 

17-alpha-Estradiol Estriol 

Acetaldehyde Estrone 

Anatoxin-aAniline 

Ethinyl Estradiol (17-alpha-Ethynylethynyl

estradiol) 

Aniline HCFC-22

Butylated hydroxyanisole HCFC-22Hexane

Cyanotoxins (Anatoxin-a, 

Cylindrospermopsin, Microcystin-LR) HexaneMestranol

Equilenin MestranolMicrocystin-LR

Equilin Norethindrone (19-Norethisterone) 

Erythromycin Naegleria fowleri*

Estradiol (17-beta-Estradiol) 

Does not have nationally representative or other finished water data 

1,3-Butadiene Quinoline 

2-Methoxyethanol Tebufenozide 

Formatted Table
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Table 2. Contaminants Not Proceeding from Phase 1 to Phase 2 

2-Propen-1-ol Thiodicarb 

4,4'-Methylenedianiline Thiophanate-methyl 

Acetamide Toluene diisocyanate 

Clethodim Triethylamine 

Cumene hydroperoxide Triphenyltin hydroxide (TPTH) 

Dimethipin Urethane 

Ethylene oxide Campylobacter jejuni

Hydrazine Escherichia coli (0157)

Methanol Helicobacter pylori

Nitroglycerin Hepatitis A virus 

N-Methyl-2-pyrrolidone Salmonella enteric

o-Toluidine Shigella sonnei

Oxirane, methylDoes not have a widely available analytical method for occurrence monitoring 

Adenovirus Legionella pneumophila 

Caliciviruses Mycobacterium avium 

Enterovirus 

Not within scope of this RD 3 since regulatory determination made in February 2011 

Perchlorate 

* Does not have a widely available analytical method for occurrence monitoring 

2. Phase 2 (Data Evaluation Phase) 

 Contaminants that meet the minimum health and occurrence data availability 

requirements in Phase 1 are advanced to the Phase 2 evaluation. In addition to health and 

occurrence information data assessed in Phase 1, the agency collects additional health and 

occurrence data and more thoroughly evaluates this information to identify a list of contaminants 

that should proceed to Phase 3. The agency uses the following steps to develop this list: (a) 
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derive a draft HRL14 (See section III.C) for each contaminant, (b) compare all occurrence data 

against the draft HRL (along with the analytical method minimum reporting limit (MRL)), (c) 

identify contaminants that occur at levels and frequencies of public health concern, and (d) 

identify contaminants that have no or low occurrence at levels of public health concern. 

Using the available health effects assessments, the agency derives a draft HRL and then 

evaluates this HRL value (along with the analytical method MRL), against the concentration 

values compiled for the nationally representative or other finished water occurrence information 

identified in Phase 1. The agency also gathers additional occurrence data and information on 

monitoring in ambient or source water (relative to the draft HRL and the analytical method 

MRL), production, use, release to the environment, and persistence and mobility. The agency’s 

highest priority is In Phase 2, the agency specifically focuses its efforts to identify those 

contaminants or contaminant groups that are occurring or have substantial likelihood to occur at 

levels and frequencies of public health concern. To identify thesesuch contaminants, the agency 

considers the following information: 

(a) How many samples (# and %) have detections ≥> draft HRL and 1⁄2 draft HRL in the 

nationally representative and other finished water occurrence data? 

(b) How many systems (# and %) have detections ≥> draft HRL and 1⁄2 draft HRL in the 

nationally representative and other finished water occurrence data? and 

 

14 HRLs are not final determinations about the level of a contaminant in drinking water that is necessary to protect 

any particular population and are derived prior to development of a complete exposure assessment. HRLs are risk 

derived concentrations against which to evaluate the occurrence data to determine if contaminants occur at levels of 

potential public health concern. 
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(c) Is the contaminant associated with a contaminant group that is of public health 

concern and is being considered as part of the DWS?15 

(d) Are there uncertainties or limitations with the data and/or analyses, such as the age of 

the dataset, limitation of the detection limit (i.e., MRL > draft HRL) and/or 

representativeness of the data (e.g., limited scope to a specific region) that may cause 

underestimationmisestimation of occurrence in finished water at levels and frequency of 

public health concern? 

After identifying contaminants that are occurring at levels and frequencies of public 

health concern to proceed to Phase 3, 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 could also proceed to Phase 3 by considering the following factors: 

(a) Does the contaminant have nationally representative finished water data showing no 

or low # or % of detections ≥> draft HRL?16 

(b) If a contaminant has other finished water data in addition to nationally representative 

finished water data, does it support no or low potential for occurrence in drinking water? 

(c) Does additional occurrence information of known quality support low or no 

occurrence or potential for occurrence in drinking water? For example, is the occurrence 

 

15 Carcinogenic Volatile Organic Compounds (including 1,2,3-trichloropropane) are being evaluated in a separate 

regulatory effort. 

16 Note that the non-national data tend to be limited in scope and EPA does not use these data alone to support a 

determination that the contaminant is not or is not substantially likely to “occur in PWSs with a frequency and at 

levels of public health concern” and,” which would therefore be a decision “not to regulate” (i.e., negative 

determination). 
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in ambient/source water at levels below the draft HRL? Are releases to the environment 

or use/production decreasing over time? 

 (d) There are no critical information/data gaps after evaluating the available health or 

occurrence data; and 

(e) The contaminant is not included or evaluated with a group of contaminants based on 

the factors defined by the DWS. 

If a contaminant meets all or most ofAfter evaluating these factors and whether a 

contaminant appears to have sufficient data to evaluate the statutory criteria for regulatory 

determination, the agency determines if the contaminant proceedsshould proceed to Phase 3. 

After evaluating the 35 “short list” contaminants, (listed in Table 1), the agency identified 10 

CCL 3 contaminants and 2 non-CCL 3 contaminants (listed in Table 3) that were within one of 

the following Phase 2 data evaluation categories to proceed to Phase 3: 

(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 likely to occur at levels and frequencies of public 

health concern and no data gaps. 
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Table 3. Contaminants Proceeding from Phase 2 to Phase 3 

Chlorate1,3 N-Nitrosodiethylamine (NDEA)1

Dimethoate2 N-Nitrosomethylethylamine (NMEA)1,4

1,3-Dinitrobenzene2 N-Nitrosopyrrolidine (NPYR)1

N-Nitroso-di-n-butylamine (NDBA)1,4 Strontium1,3

N-Nitrosodimethylamine (NDMA)1 Terbufos2

N-Nitroso-di-n-propylamine (NDPA)1 Terbufos Sulfone2

1 A contaminant or part of a contaminant group occurring or likely to occur at levels and frequencies of 

public health concern

2 A contaminant not occurring or likely to occur at levels and frequencies of public health concern and no 

data gaps 

3 The UCMR 3 includes sampling at both the entry point to the distribution system (EPTDS) and 

distribution system maximum residence time (DSMRT) for this contaminant (77 FR 26071, May 2, 2012). 

For some contaminants, including disinfection byproducts and inorganics, occurrence values may differ 

between the EPTDS and the DSMRT due to dynamics within the distribution system such as contaminant 

degradation, formation, accumulation and release. 4

 A non-CCL 3 contaminant that is part of the nitrosamine group.

Note that the agency does not have a threshold or a bright line for occurrence in drinking 

water that triggers whether a contaminant is of public health concern. There are a number of 

factors to consider in developing thresholds, some of which include the health effect(s), the 

potency of the contaminant, the level at which the contaminant is found in drinking water, how 

frequently 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, etc. Given the many possible combinations of factors and the constantly evolving 

science, EPA believes it is better to analyze each contaminant and characterize and present the 

best available information that helps identify whether the occurrence of a contaminant is of 

public health concern. In the end, the determination of whether there is a meaningful opportunity 

for health risk reduction by regulation of a contaminant in drinking water is a highly 
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contaminant-specific one that takes into consideration a large number of factors. 

The remaining 25 CCL 3 contaminants (listed in Table 4) did not proceed to Phase 3 and 

were not considered for RD 3 because of one or more of the following critical health, occurrence, 

and/or other data gaps: 

(a) An updated health assessment is needed, but was not completed by fall 2011; 

(b) A health assessment is in process, but was not completed by fall 2011; 

(c) Critical health effects gap (e.g., health valueslack of data to support quantification for 

the oral route of exposure are not available for critical health endpoint); 

(d) Lacked nationally representative occurrence data; 

(e) Insufficient other finished water occurrence data to demonstrate occurrence at levels 

and frequencies of public health concern (although it may have some levels of public 

health concern); 

(f) Individual contaminants that were part of a group but lacked a widely available 

analytical method for occurrence monitoring; and 

(g) Critical occurrence data gap (e.g., inconsistent results and/or trends in occurrence 

data, significant uncertainty in occurrence analyses and/or data). 

Table 4 identifies the health, occurrence, and/or other data gaps that prevented the 

following 25 contaminants from moving forward for RD 3. The agency continues to conduct 

research, collect information or find other avenues to fill the data and information gaps identified 

in Table 4. 
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Table 4. Data and Rationale Summary of the 25 Contaminants Not Proceeding to Phase 3 

# Contaminant Health Data 

Available 

Occurrence 

Data Available 

Rationale 

1 1,4-Dioxane Yes No1 Occurrence data gaps (no nationally 

representative finished water data or 

sufficient other finished water data) 

2 Acephate Yes No Occurrence data gaps (no nationally 

representative finished water data or 

sufficient other finished water data) 

3 Acetochlor No Yes Health data gap (no health assessment 

for the degradates) and no detections in 

nationally representative finished water 

data 

4 Acetochlor 

ethanesulfonic 

acid (ESA) 

No Yes Health data gap (no health assessment 

for the ESA degradate) and no or low 

detections based on nationally 

representative finished water data

5 Acetochlor 

oxanilic acid 

(OA) 

No Yes Health data gap (no health assessment 

for the OA degradate) and no or low 

detections based on nationally 

representative finished water data 

6 Alachlor 

ethanesulfonic 

acid (ESA) 

No Yes Health data gap (no health assessment 

for the ESA degradate) and no or low 

detections based on nationally 

representative finished water data 

7 Alachlor 

oxanilic acid 

(OA) 

No Yes Health data gap (no health assessment 

for the OA degradate) and no or low 

detections based on nationally 

representative finished water data 

8 Cobalt No Yes2 Health data gap (health assessment not 

updated by fall 2011) and no detections 

in nationally representative or other 

finished water data at levels of public 

health concern 

9 Disulfoton Yes No Occurrence data gap (no nationally 

representative finished water data and no 

detections in other finished water data) 

10 Diuron Yes No Occurrence data gap (no nationally 

representative finished water data and no 
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detections in other finished water data) 

11 Methyl 

Bromide 

No Yes1 Health data gap (health assessment not 

updated by fall 2011) 

12 Methyl tertbutyl ether No Yes Health data gap (IRIS health assessment 

not completed by fall 2011) and no or 

low detections based on nationally 

representative finished water data 

13 Metolachlor No Yes Health data gap (no health assessment 

for degradates) and few detections in 

nationally representative finished water 

data 

14 Metolachlor 

ethanesulfonic 

acid (ESA) 

No Yes Health data gap (no health assessment 

for ESA degradate) and no or low 

detections based on nationally 

representative finished water data 

15 Metolachlor 

oxanilic acid 

(OA) 

No Yes Health data gap (no health assessment 

for OA degradate) and no or low 

detections based on nationally 

representative finished water data 

16 Molinate No Yes Health data gap (OPP health assessment 

not completed by fall 2011 due to 

cancellation of molinate) and no 

detections in nationally representative or 

other finished water data at levels of 

public health concern 

17 Molybdenum No Yes Health data gap (health assessment not 

updated by fall 2011) and no detections 

in nationally representative or other 

finished water data at levels of public 

health concern 

18 NNitrosodiphen

ylamine 

(NDPhA) 

Yes No Health data gap (health assessment not 

updated by fall 2011) and occurrence 

data gaps (no EPA approved analytical 

method for monitoring) 

19 Perfluorooctan

esulfonic acid 

(PFOS) 

No No1 Health data gap (health assessment not 

completed by fall 2011) and occurrence 

data gaps (limited other finished water 

data available) 

20 Perfluorooctan

oic acid 

(PFOA) 

No No1 Health data gap (health assessment not 

completed by fall 2011) and occurrence 

data gaps (limited other finished water 

data available) 
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21 RDX No Yes Health data gap (IRIS health assessment 

not updated by fall 2011) and no 

detections in nationally representative or 

other finished water data at levels of 

public health concern 

22 Vanadium No Yes2 Health data gap (health assessment not 

updated by fall 2011) and no to low 

detections in nationally representative 

finished water data at levels of public 

health concern 

23 1,1,1,2-

Tetrachloroeth

ane 

 ---- ----- Will be evaluated and considered for the 

Carcinogenic Volatile Organic 

Compounds (cVOCs) group rule 

addressed in a separate process 

24 1,2,3-

Trichloropropa

ne 

 ----- -----1 Will be evaluated and considered for the 

Carcinogenic Volatile Organic 

Compounds (cVOCs) group rule 

addressed in a separate process 

25 Nitrobenzene ---- ----- Will be evaluated and considered for the 

Carcinogenic Volatile Organic 

Compounds (cVOCs) group rule 

addressed in a separate process 1

 The UCMR 3 includes sampling at the EPTDS for this contaminant (77 FR 26071, May 2, 2012).

2 The UCMR 3 includes sampling at both the EPTDS and DSMRT for this contaminant (77 FR 26071, May 

2, 2012). For some contaminants, including disinfection byproducts and inorganics, occurrence values may 

differ between the EPTDS and the DSMRT due to dynamics within the distribution system such as 

contaminant degradation, formation, accumulation and release.
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3. Phase 3 (Regulatory Determination Assessment Phase)

Phase 3, the Regulatory Determination Assessments 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. In 

this phase, the agency evaluates the following statutory criteria: 

(a) Statutory Criterion #1 - The contaminant may have an adverse effect on the health of 

persons. To evaluate statutory criterion #1, EPA completes any health assessment that needs to 

be updated and externally peer-reviewed, and derives a final HRL. The derivation of the final 

HRL, further described in the section III.C.1, Evaluation of Adverse Health Effects, takes into 

account many of the key elements that are considered when evaluating criterion #1, which 

includes the mode of action, the critical health effect(s), the dose-response for critical health 

effect(s), impacts on sensitive populations(s) or lifestages, the RfD, and/or the cancer slope 

factor. HRLs are not final determinations about the level of a contaminant in drinking water that 

is necessarymust not be exceeded to protect any particular population and are derived prior to the 

development of a complete exposure assessment. HRLs are risk derived concentrations against 

which to evaluate the occurrence data to determine if contaminants may occur at levels of 

potential public health concern. With this information, EPA determines whether the contaminant 

“may have an adverse effect.” While CCL 3 contaminants are generally expected to meet 

statutory criterion #1 because their adverse health effects were analyzed as part of the 

determination to list them on the CCL, the availability of a final HRL is derived as part of the 

first statutory criterion and is necessary to evaluate the second statutory criterion. 
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 (b) Statutory Criterion #2 - 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. EPA compares the occurrence data for each contaminant to the final 

peer-reviewed 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.2, 

Evaluation of Contaminant Occurrence and Exposure. The agency considers the following 

factors when identifying contaminants or contaminant groups that are occurring at frequencies 

and levels of public health concern: 

 How many samples (# and %) have detections ≥> final HRL in the nationally 

representative and other finished water occurrence data? 

 How many systems (# and %) have detections ≥> final HRL in the nationally 

representative and other finished water occurrence data? 

 Is the contaminant associated with a contaminant group that is of public health concern 

and is being considered as part of the DWS? 

 Is the geographic distribution of the contaminant occurrence national, regional, or 

localized? 

 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 ground water systems? 

 Are there significant uncertainties or limitations with the data and/or analyses, such as the 
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age of the dataset, limitation of the detection limit (i.e., MRL > final HRL) and/or 

representativeness of the data (e.g., limited in scope to a specific region)? 

Additional, less important factors that the agency considers when identifying contaminants or 

contaminant groups that are of public health concern also include: 

 How many samples (# and %) have detections ≥> 1⁄2 final HRL17 in the nationally 

representative and other finished water occurrence data? 

 How many systems (# and %) have detections ≥> 1⁄2 final HRL in the nationally 

representative and other finished water occurrence data? 

 How many samples (# and %) have detections ≥> final HRL and 1⁄2 final HRL in the 

ambient/source water occurrence data? 

 How many monitoring sites (# and %) have detections ≥> final HRL and 1⁄2 final HRL in 

the ambient/source water occurrence data? 

 Are production and use trends for the contaminant increasing or decreasing? 

 How many pounds are discharged annually to surface water and/or released to the 

environment? 

 Do the environmental fate and transport parameters indicate that the contaminant would 

persist and/or be mobile in water? 

 Are there other uncertainties or limitations with the data and/or analyses for these 

additional factors that should be considered? 

 

17 Note that the 1⁄2 HRL threshold is based on a recommendation from the NDWAC working grouping that provided 

recommendations on the first regulatory determinations effort. (USEPA, 2000b) 
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 Is the contaminant introduced by water treatment processes (e.g., disinfection 

byproducts)? 

If a contaminant is known to occur or substantially likely to occur at a frequency and level of 

health concern in public water systems based on the factors listed above, then the agency 

answers “yes” to the second statutory criterion. 

 (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. 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. EPA considers the following factors in evaluating statutory criterion #3: 

 Based on the occurrence information for statutory criterion #2 (and the potential number 

of systems impacted), what is the national population exposed or served by systems with 

levels > HRL and 1⁄2 HRL (provide actual and estimated # and %)? 

 What is the nature of the adverse health effect ((s) identified in statutory criterion #1) and 

are there sensitive populations that may be impacted (either qualitative or quantitative18)? 

 For non-carcinogens, are there other sources of exposure that should be considered (i.e., 

what is the relative source contribution) that should be considered?)? 

 What is the geographic distribution of occurrence (e.g., local, regional, national)? 

 

18 If appropriate and if available, the agency quantitatively takes into account exposure data applicable to sensitive 

populations or lifestages when deriving HRLs for regulatory determinations. When data is not available on sensitive 

populations, the derivation of the RfD typically includes an uncertainty factor to account for the weakness in the 

database. See section B.1III.C.1. Sensitive populations are also qualitatively considered by providing national 

prevalence estimates for a particular sensitive population if available. 
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 Are there any uncertainties and/or limitations in the health and occurrence information or 

analyses that should be considered? 

 What other factors or other pieces of information should be considered that may have 

direct bearing on any decision to regulate the contaminant (e.g., treatment, analytical 

methods19, etc.)? 

After evaluating these factors, if the Administrator 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. 

 If the agency answers “yes” to all three statutory criteria in Phase 3 for a particular 

contaminant, then the agency makes a “positive” preliminary determination and requests public 

comment. 

 If after the public comment period, the agency answers “yes” to all three statutory 

criteria, the agency then makes a “positive” final determination that regulation is necessary and 

proceeds to develop an MCLG and NPDWR. 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. It should be noted that this regulatory determination process is distinct from the 

 

19 If the agency decides to regulate a contaminant, SDWA requires that EPA issue a proposed regulation within two 

years of the final determination (with the possibility of a 9 month extension). As part of the proposal, the agency 

must list the best available technologies (BATs), small system compliance technologies (SSCTs), and approved 

analytical methods if it proposes an enforceable MCL. Alternatively, if EPA proposes a treatment technique (TT) 

instead of an MCL, the agency must identify the TT. EPA must also prepare a health risk reduction and cost 

analysis. This analysis includes an extensive evaluation of the treatment costs and monitoring costs at both system 

level and aggregated at the national level. To date, treatment information and approved analytical methods have not 

been a significant factor in regulatory determinations but are important considerations for regulation development. 
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more detailed analyses needed to develop a national primary drinking water regulation. 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 necessary for that contaminant at that time. The 

agency may decide to develop a Health Advisory (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 (one-day, ten-days, several years, and a 

lifetime). HAs serve as informal technical guidance to assist Federal, State, and local officials, 

and managers of public or community water systems (CWSs) in protecting public health when 

emergency spills or contamination situations occur. 

 While a negative determination is considered a final agency action for this round of 

regulatory determinations, the contaminant is reconsidered for inclusion on the next CCL. If new 

health or occurrence information becomes available on contaminants with negative regulatory 

determinations, the agency considers whether the contaminant(s) should be listed on the next 

CCL and further evaluated in the next regulatory determinations process. 

Of the twelve contaminants that proceeded to Phase 3, the agency is not making 

preliminary regulatory determinations for seven contaminants at this time. The seven 

contaminants include chlorate and the six nitrosamines (i.e., NDBA, NDMA, NDPA, NDEA, 

NPYR, and NMEA). As discussed in section V, chlorate and the six nitrosamines are DBPs and 
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the agency plans to consider these contaminants as part of the regulatory review of existing 

MDBP regulations. DBPs need to be evaluated collectively, because the potential exists that the 

control of one DBP could affect the concentrations of other DBPs or the necessary treatment. 

After evaluating the five remaining CCL 3 contaminants in Table 3 (i.e., dimethoate, 1,3-

dinitrobenzene, strontium, terbufos, and terbufos sulfone) against the three SDWA criteria and 

considering the factors listed for each, the agency is making preliminary regulatory 

determinations for these five CCL 3 contaminants. Table 5 provides a summary of the five 

contaminants evaluated for Phase 3 and the preliminary regulatory determination outcome. The 

agency seeks comment on the preliminary determination to regulate one contaminant (i.e., 

strontium) and to not regulate the remaining four contaminants (i.e., dimethoate, 1,3-

dinitrobenzene, terbufos, and terbufos sulfone). Section IV.B of this notice provides a more 

detailed summary of the information and the rationale used by the agency to reach its 

preliminary decisions for these five contaminants. 

Table 5. Contaminants Evaluated in Phase 3 and the Regulatory Determination 

Outcome 

# RD 3 Contaminants Preliminary Determination 

Outcome 

1 Dimethoate Do not regulate 

2 1,3-Dinitrobenzene Do not regulate 

3 Strontium Regulate 

4 Terbufos Do not regulate 

5 Terbufos Sulfone Do not regulate 

 B. Supporting Documentation for EPA’s Preliminary Determinations

 For this action, EPA prepared several support documents that are available for review and 
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comment in the EPA Water Docket. These support documents include: 

 The comprehensive regulatory support document entitled, “Regulatory 

DeterminationsDetermination 3 Support Document” (USEPA, 2012b2014b), summarizes 

the information and data on the physical and chemical properties, uses and environmental 

release, environmental fate, potential health effects, occurrence and exposure estimates, 

the preliminary determinations, and the agency’s rationale for these determinations.

 A separate health effects support document for strontium, entitled “Health Effects 

Support Document for Strontium” (USEPA, 2012c2014c), that addresses exposure from 

drinking water and other media, toxicokinetics, hazard identification, and dose-response 

assessment, and provides an overall characterization of the risk from drinking water 

containing strontium. For the contaminants with negative determinations, the agency 

refers the reader to the IRIS or OPP assessments for more detailed information regarding 

health effects. (USEPA, 1990a, 1990b, 2003c). These documents serve as the basis for 

the health information provided in the regulatory support documents.

• A comprehensive technical occurrence support document for UCMR 2 entitled, 

“Occurrence Data from the Second Unregulated Contaminant Monitoring Rule (UCMR 

2)” (USEPA, 2012d2014d). This occurrence support document includes more detailed 

information about UCMR 2, how 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. 
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• A comprehensive protocol document, entitled “Protocol for the Regulatory 

DeterminationsDetermination 3” (USEPA, 2012a2014a). This protocol document 

describes the approach implemented by the agency to evaluate 116 CCL 3 contaminants 

in a three phase process and select the contaminants for preliminary determinations for 

RD 3. The protocol underwent expert review and the comments received were addressed 

by the agency. 

 C. Analyses Used To Support the Preliminary Regulatory Determinations 

 Sections III.C.1 and 2 of this action outline the health effects and occurrence/exposure 

evaluation process EPA used to support these preliminary determinations. 

 1. Evaluation of Adverse Health Effects 

Section 1412(b)(1)(A)(i) of SDWA requires EPA to determine whether each candidate 

contaminant may have an adverse effect on public health. This section describes the overall 

process the agency uses to evaluate health effects, hazard and dose-response information, and the 

approach for deriving the health reference level (HRL) for the contaminants under consideration 

for regulatory determinations. HRLs are not final determinations about the level of a contaminant 

in drinking water that is necessarymust not be exceeded to protect any particular population and. 

HRLs are derived prior to the development of a complete exposure assessment. HRLs are risk 

derived concentrations against which to evaluate the occurrence data to determine if 

contaminants occur at levels of potential public health concern. More specific information about 

the potential for adverse health effects for each contaminant is presented in section IV.B of this 

action. 
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In evaluating contaminants for regulatory determination, Section 1412 (b)(1)(C) of 

SDWA also 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, individuals with a history of 

serious illness, or other subpopulations” that are identifiable as being at greater risk of adverse 

health effects duecompared to exposure to contaminants in drinking water than the general 

population. If appropriate and if available, the agency quantitatively takes into account data from 

sensitive populations and lifestages when deriving HRLs for regulatory determinations. 

There are two general approaches to the derivation of an HRL. One approach is used for 

chemicals that cause cancer and exhibit a linear response to dose and the other applies to noncarcinogens and carcinogens evaluated using a non-linear approach. The derivation of HRLs for 

carcinogens and non-carcinogens are described below. 

a. Derivation of an HRL for Carcinogens 

For those contaminants that are considered to be likely or probable human carcinogens by 

a mutagenic or unknown mode of action (MOA), the agency calculates a toxicity value that 

defines the linear relationship between dose and response (i.e., the cancer slope factor or CSF). 

 (1) MOA: Unknown 

In cases where the data on the mode of action are lacking, EPA typically uses a default 

low dose linear extrapolation to calculate a CSF from risk-specific doses.. The unit risk is the 

estimated upper-bound excess lifetime cancer risk from a continuous exposure to a chemical at a 

concentration of 0.001 mg/L in drinking water. The exposure estimate assumes an adult body 
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weight of 70 kg and the 90th percentile adult drinking water intake of 2 L/day. 

Unit Risk (μg/L)-1 = CSF x [(DWI x CW)/BW] 

where: 

CSF = Cancer Slope Factor (mg/kg-/day)-1

DWI = Drinking Water Intake for an adult, assumed to be 2 L/day (90th 

percentile) 

CW = Unit risk concentration in drinking water of 0.001 mg/L (1 μg/L) 

BW = Body Weight for an adult, assumed to be 70 kilograms (kg) 

The cancer HRL is the concentration of a contaminant in drinking water corresponding to an 

excess estimated lifetime cancer risk of one-in-a-million (1x 10-6), calculated as follows: 

HRL (μg/L) = Risk Level of 10-6 ÷ Unit Risk (μg/L)-1 

As noted above, HRLs are not final determinations about the level of a contaminant in drinking 

water that must not be exceeded to protect any particular population. Rather, HRLs are risk 

derived concentrations against which to evaluate the occurrence data during the RD process to 

determine if contaminants occur at levels of potential public health concern. 

 (2) MOA: Mutagenic 

 If the chemical has a mutagenic mode of action, low dose linear extrapolation is used to 

calculate the CSF as described in the preceding paragraph. The U.S. EPA’s 2005 Guidelines for 

CarcinogenicCarcinogen Risk Assessment (USEPA, 2005b) requires that the potential increased 

cancer risk due to early-life exposure be taken into account for chemicals with a mutagenic mode 

of action. When chemical-specific data to quantify the increased risk are lacking, Age Dependent 

Adjustment Factors (ADAFs) are applied to estimate age-adjusted unit risks. The age-adjusted 

Formatted: Superscript
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unit risk is determined by using the sum of the unit risks for each of the three ADAF 

developmental groups (birth to < 2 yrs; 2 yrs to < 16 yrs; 16 yrs to 70 yrs). The age-adjusted unit 

risks include a ten-fold adjustment for early life (birth to < 2 yrs) exposures, a three-fold 

adjustment for childhood/adolescent (2 yrs to < 16 yrs) exposures, and no additional adjustment 

for exposures later in life (16 yrs to 70 yrs), in conjunction with age-specific drinking water 

intake values derived from the U.S. EPA’s 2011 Exposure Factors Handbook (USEPA, 2011e), 

and the fraction of a 70 year lifetime applicable to each age period. The increase in risk during 

early life results from active tissue growth resulting in limited time for repair of DNA replication 

errors. The age-adjusted unit risk is the upper-bound excess lifetime cancer risk estimated to 

result from continuous postnatal exposure to a chemical at a concentration of 0.001 mg/L in 

drinking water. 

Age-Adjusted Unit Risk (μg/L)-1 = ∑(CSF x ADAF x DWI/BWR x CW x F) 

where: 

CSF = Cancer Slope Factor (mg/kg-/day)-1

ADAF = The Age Dependent Adjustment Factor for the age group birth to 

two-years (ADAF=10), two years to sixteen years (ADAF=3), and 

sixteen to seventy years (ADAF=1) 

DWI/BWR = Drinking Water Intake Body Weight Ratio (DWI/BWR) expressed 

as liters per kg body weight for the age-specific group (90th

percentile, consumers only)20

CW = Unit risk concentration in drinking water of 0.001 mg/L (1 μg/L) 

F = The fraction of a 70 year lifetime applicable to the age period: 2/70 

 

20 The drinking water intake values were derived from the data in the U.S. EPA’s Exposure Factors Handbook 

(USEPA, 2011e). The procedure used for the data normalization is described in the OW Policy paper for 

determining lifetime cancer risks involving early life exposures (USEPA, 2012g2012c). 

 
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for the birth to two- years, 14/70 for two years to sixteen years and 

54/70 for sixteen years to seventy year periodsyears 

 The cancer HRL is the concentration of a contaminant in drinking water corresponding to 

an excess estimated lifetime cancer risk of one-in-a-million (1x 10-6), calculated as follows: 

HRL (μg/L) = Risk Level of 10-6 ÷ Age-Adjusted Unit Risk (μg/L)-1 

 

 The six nitrosamines discussed in section V had data available to classify them as known 

or likely human carcinogens with a mutagenic mode of action. Low-dose linear extrapolations 

and ADAFs were applied to all four of the CCL 3 nitrosamines: NDMA, NDPA, NDEA and 

NYPR, as well as the two non-CCL 3 nitrosamines, NMEA and NDBA. The five contaminants 

for which the agency is making preliminary regulatory determinations (dimethoate, 1,3-

dinitrobenzene, strontium, terbufos and terbufos sulfone) are non-carcinogens and were therefore 

evaluated using the RfD approach (discussed in the following section). 

 b. Derivation of an HRL for Non-carcinogens 

EPA generally calculates a reference dose (RfD) for those chemicals considered to be 

non-carcinogenic or not likely to be carcinogenic to humans. An RfD is an estimate of a daily 

oral exposure to the human population (including sensitive populations or lifestages) that is 

likely to be without an appreciable risk of deleterious effects during a lifetime. The RfD can be 

derived from either a no-observed-adverse-effect level (NOAEL), a 

lowest-observed-adverse-effect level (LOAEL), or a benchmark dose (BMD) - the 95% lower 

confidence bound (on a benchmark dose (BMD), known as a BMDL) typically 10% above the 
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control response, with uncertainty factors applied to reflect limitations of the data used. In 

addition, if the critical health endpoint has high quality data associated with exposure for a 

specific developmental group or period of sensitivity, age-specific drinking water intake to body 

weight ratio values from the Exposure Factors Handbook (USEPA, 2011e) may be included in 

deriving an HRL from the RfD. 

The agency uses uncertainty factors (UFs) to address uncertainty resulting from 

incompleteness of the toxicological database (e.g., lacking sensitive population data). The 

individual UFs (usually applied as integers of one, three, or ten) are multiplied together and used 

to derive the RfD from experimental data. Individual UFs are intended to account for: 

(1) variation in sensitivity among the members of the human population (i.e., intraspecies 

variability); 

(2) uncertainty in extrapolating animal data to humans (i.e., interspecies variability); 

(3) uncertainty in extrapolating from data obtained in a study with less-than-lifetime 

exposure to lifetime exposure (i.e., extrapolating from subchronic to chronic exposure); 

(4) uncertainty in extrapolating from an LOAEL rather than from an NOAEL; and/or 

(5) uncertainty associated with an incomplete database. 

For chlorate, dimethoate, 1,3-dinitrobenzene, strontium21, terbufos, and terbufos sulfone, EPA 

derived the HRLs using the RfD approach as follows: 

 

21 Because the critical health endpoint had dose-response data associated with exposure during a specific period of 

sensitivity (i.e., sensitive population), EPA used age-specific drinking water intake to body weight ratio values 

(DWI/BWR) from the Exposure Factors Handbook (2011USEPA, 2011e) to derive the HRL for strontium. 
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HRL (mg/L) = [(RfD x BW)/DWI] x RSC 

Where: 

RfD = Reference Dose (mg/kg/-day) 

BW = Body Weight for an adult, assumed to be 70 kilograms (kg); for a child, 

assumed to be 10 kg 

DWI = Drinking Water Intake for an adult, assumed to be 2 L/day (90th percentile); 

for child, assumed to be 1L/day (90th percentile) 

RSC = Relative Source Contribution, or the level of exposure believed to result 

from drinking water when compared to other sources (e.g., food, ambient 

air). In all cases, a 20% RSC is used for HRL derivation because (1) HRLs 

are developed prior to a complete exposure assessment and (2) 20% is the 

most conservative RSC used in the derivation of an MCLG for drinking 

water. 

 

 c. Sources of Data/Information for Health Effects 

 EPA uses the best available peer-reviewed data and analyses in evaluating adverse health 

effects. Peer-reviewed health-risk assessments are available for all chemicals considered for 

regulatory determinations from the agency’s Integrated Risk Information System (IRIS) 

Program22, the agency’s Office of Pesticide Programs (OPP)23, the National Academy of 

Sciences (NAS), the Agency for Toxic Substances and Disease Registry (ATSDR)24, and/or the 

 

22 IRIS is an electronic EPA data base (www.epa.gov/iris/index.html) containing peer-reviewed information on 

human health effects that may result from exposure to various chemicals in the environment. These chemical files 

contain descriptive and quantitative information on hazard identification and dose response, RfDs for chronic 

noncarcinogenic health effects, as well as slope factors and unit risks for carcinogenic effects. 

23 The OPP is required under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA) to periodically review 

the health effects data on all registered pesticides and reregister them for continued use. The results of the 

reregistration analysis are published in the Reregistration Eligibility Decision (RED) documents. Copies of the 

REDs are located at the following EPA web site (http://www.epa.gov/oppsrrd1/reregistration/status.htm)

24 ATSDR establishes oral minimal risk levels for non-neoplastic endpoints for acute (14 days or less), intermediate 

(15 – 364 days), and chronic (365 days or more) exposure durations. Minimal risk levels for oral chronic exposure 
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World Health Organization (WHO)25. For a non-EPA health assessment (i.e., NAS, ATSDR, 

WHO) to be considered for regulatory determinations, the health assessment must use 

comparable methods, standards, and guidelines to an EPA health assessment. Table 6 

summarizes the sources of the health assessment data for each chemical under consideration for 

RD 3. 

 The agency performs a literature search for studies published after the available health 

assessment is completed to determine if new information suggests a different outcome. The 

agency collects and evaluates any peer-reviewed publications identified through the literature 

search for their impact on the RfD and/or cancer assessment. In cases where the recent data 

indicate that a change to the existing RfD or cancer assessment is needed, the updated OW 

assessment is preparedEPA Office of Water prepares and independently peer-reviewedreviews 

an “OW Assessment” of the data. EPA updates all quantitative cancer assessments conducted 

under the Guidelines for Carcinogen Risk Assessment (USEPA, 1986) using the Guidelines for 

Carcinogen Risk Assessment (USEPA, 2005b), the Supplemental Guidance for Assessing 

Susceptibility from Early-life Exposures to Carcinogens (USEPA, 2005c), and the Exposure 

Factors Handbook (USEPA, 2011e). These guidelines include considerations for contaminants 

 

are similar to EPA’s RfDs. However, ATSDR and EPA use different approaches when the database is limited to 

subchronic studies and no adequate chronic study is available. ATSDR derives an intermediate duration minimal 

risk level that protects against exposures up to 10% of a lifetime, and it does not incorporate an uncertainty factor to 

account for using a less-than-lifetime study. ATSDR does not perform quantitative cancer assessments or assign 

formal cancer classifications or descriptors. 

25 WHO establishes a “guideline value”, a drinking water concentration that uses different default assumptions than 

EPA for estimating water concentration from doses, including a 60 kg adult body weight, daily water consumption 

of 2 L/day, and a data derived or default RSC of 10%. WHO develops one guideline value that is based either on 

cancer or non cancer. 
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with a mutagenic mode of action and potential risks due to early childhood exposure. 

Table 6. Sources and Dates of EPA Health Risk Assessments 

Chemical IRIS 

(Date) 

Date OPP 

RED

(Date) 

Date OW 

Assessme

nt (Date)

Date

Dimethoate --- --- X 2007 --- ---

1,3-

Dinitrobenze

ne1

X

1988 --- --- 

--- ---

Strontium X 1992 --- --- X 2012 

Terbufos --- --- X 2006 --- ---

Terbufos Sulfone2

--- --- X 2006 --- ---

1 The1

The agency also reviewed a non-EPA source (ATSDR, 1995) for 1,3-dinitrobenzene to corroborate the 

IRIS assessment. 

2

The OPP RED for the parent compound (terbufos) was used.

 As noted in section III.B, EPA prepared a technical Health Effects Support Document for 

strontium (USEPA, 2012c2014c). This document addresses the exposure from drinking water 

and other media, toxicokinetics, hazard identification, and dose-response assessment, and 

provides an overall characterization of risk from drinking water. For the contaminants with a 

preliminary negative determination (i.e., a decision not to regulate), refer to the EPA health risk 

assessments online from OPP or IRIS for additional health effect information. 

 2. Evaluation of Contaminant Occurrence and Exposure 

EPA uses data from many sources to evaluate occurrence and exposure from drinking 

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water contaminants. The following comprise the primary sources of finished drinking water 

occurrence data discussed in this Federal Register notice: 

• the Unregulated Contaminant Monitoring Regulation (UCMR 1 and 2), 

• the National Inorganic and Radionuclide Survey (NIRS), and 

• Disinfection Byproducts Information Collection Rule (DBP ICR). 

 Several of the primary sources of finished water occurrence data are designed to be 

statistically representative of the nation. These data sources include UCMR 1, UCMR 2, and 

NIRS26. The DBP ICR is geographically distributed across the country and national in scope but 

is not intended to be statistically representative of the nation. 

 The agency also evaluates supplemental sources of information on occurrence in drinking 

water, occurrence in ambient and source water, and information on contaminant use and release 

to augment and compliment these primary sources of drinking water occurrence data. Section 

III.C.2.a. of this action provides a brief summary of the primary sources of finished water 

occurrence data, and sections III.C.2.b and II.C.2.c provide brief summary descriptions of some 

of the supplemental sources of occurrence information and/or data. These descriptions do not 

cover all the reports that EPA reviews and evaluates. For individual contaminants 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 

 

26 NIRS is designed to be statistically representative of groundwater systems and does not include surface water 

systems. 
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IV.B, the contaminant profiles section, and the data are described in further detail in the support 

documents for the RD 3 process (see USEPA, 2012a2014a, b, c and d). 

 a. Primary Sources of Finished Drinking Water Occurrence Data. 

 As previously mentioned, the primary national sources of the drinking water occurrence 

data discussed in this Federal Register notice are UCMR 1, UCMR 2, NIRS, and the DBP ICR. 

The following sections provide a brief summary of these data sources. Table 7 in section IV lists 

the primary data source/finding used to evaluate each of the five contaminants considered for 

regulatory determinations. The contaminant-specific discussions in section IV provide more 

detailed information about the primary data source findings as well as any supplemental 

occurrence information. 

(1) The Unregulated Contaminant Monitoring Regulation (UCMR 1 and UCMR 2) 

The UCMR is currently EPA’s primary vehicle for collecting monitoring data on the 

occurrence of unregulated contaminants in PWSs. The UCMR is designed to collect nationally 

representative occurrence data and is developed in coordination with the CCL and Regulatory 

Determination process and the National Drinking Water Contaminant Occurrence Database 

(NCOD). The UCMR sampling is limited by statute to 30 contaminants during any five year 

cycle (SDWA section 1445(a)(2)) and the PWSs and State primacy agencies are required to 

report the data to EPA. EPA published the list and requirements for the first Unregulated 

Contaminant Monitoring Regulation cycle (i.e., UCMR 1) in September 17, 1999 (64 FR 50556, 

September 17, 1999, USEPA, 1999; see also 65 FR 11372, March 2, 2000, USEPA, 2000a; and 

66 FR 2273, January 11, 2001, USEPA, 2001a), and the monitoring was conducted primarily 
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during 2001-2003. UCMR 2 was published on January 4, 2007 (72 FR 367; USEPA, 

20072007a), with monitoring conducted during 2008-2010. (The complete analytical monitoring 

lists are available at: http://water.epa.gov/lawsregs/rulesregs/sdwa/ucmr/.) 

 The UCMR was designed as a three-tiered approach for monitoring contaminants related 

to the availability of analytical methods and related analytical laboratory capacity. Assessment 

Monitoring (AM), the largest sampling tier, typically relies on analytical methods that are in 

common use in drinking water laboratories. The Screening Survey (SS), the second tier, uses 

newly developed analytical methods that may not be as commonly used in drinking water 

laboratories. The SS has involved a smaller number of PWSs because laboratory capacity is 

expected to be limited. The third tier, Pre-Screen Testing was designed to address contaminants 

with analytical methods that are in an early stage of development and the analyses would be 

limited to a few special laboratories. The expectation was that it would only involve the limited 

number of systems determined to be most vulnerable to the targeted contaminants. No PreScreen Testing was conducted during UCMR 1 or UCMR 2. 

 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 2001b, for UCMR design 

details). AM is required for all large PWSs, those serving more than 10,000 people (i.e., a census 

of all large systems) and a national statistically representative sample of 800 small PWSs, those 

serving 10,000 or fewer people (for a total sample of approximately 4,000 systems). PWSs that 

purchase 100% of their water were not required to participate. 

 Each system conducts UCMR assessment monitoring for one year (during the three-year 
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monitoring period). The rules require quarterly monitoring for surface water systems and twicea-year, six-month interval monitoring for ground water systems. At least one sampling event 

must occur during a specified vulnerable period. Differing sampling points within the PWS may 

be specified for each contaminant related to the contaminants source(s). 

 The objective of the UCMR sampling approach for small systems was to collect 

contaminant occurrence data from a statistically selected, nationally representative sample of 

small systems. The small system sample was stratified and population-weighted, and included 

some other sampling adjustments such as allocating a selection of at least two systems from each 

State for spatial coverage. The UCMR AM program includes systems from all 50 States, the 

District of Columbia, four U.S. Territories, and Tribal lands in five EPA Regions. With 

contaminant monitoring data from all large PWSs – a census of large systems – and a statistical, 

nationally representative sample of small PWSs, the UCMR AM program provides a robust 

dataset for evaluating national drinking water contaminant occurrence. 

 UCMR 1 AM was conducted by approximately 3,090 large systems and 797 small 

systems. Approximately 33,800 samples were collected for each contaminant. In UCMR 2, 

sampling was conducted by over 3,300 large systems and 800 small systems, and resulted in over 

32,000 sample results for each contaminant. 

 As noted, in addition to AM, SS monitoring was required for contaminants. For UCMR 

1, the SS was conducted at 300 PWSs (120 large and 180 small systems) selected at random 

from the pool of systems required to conduct AM. Samples from the 300 PWSs from throughout 

the nation provided approximately 2,300 analyses for each contaminant. While the statistical 
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design of the SS is national in scope, the uncertainty in the results for contaminants that have low 

occurrence is relatively high. Therefore, EPA looked for additional data to supplement the SS 

data for regulatory determinations. 

 For the UCMR 2 SS, EPA improved the design to include a census of all systems serving 

more than 100,000 people (approximately 400 PWSs – but the largest portion of the national 

population served by PWSs) and a nationally representative, statistically selected sample of 320 

PWSs serving between 10,001 and 100,000 people, and 480 small PWSs serving 10,000 or fewer 

people (72 FR 367, January 4, 2007, USEPA, 20072007a). With approximately 1,200 systems 

participating in the SS, sufficient data were generated to provide a confident national estimate of 

contaminant occurrence and population exposure. In UCMR 2, the 1,200 PWSs provided more 

than 11,000 to 18,000 analyses (depending on the sampling design for the different 

contaminants). 

 As previously noted, the details 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 is described in further detail in the support documents for the 

RD 3 process (USEPA, 2012a2014a and 2012b2014b). The national design, statistical sampling 

frame, any new analytical methods, and the data analysis approach for the UCMR program has 

been peer-reviewed at different stages of development (see, USEPA, 2001b, 2008c, 2012d2014d, 

for example.)

 (2) National Inorganics and Radionuclides Survey (NIRS)

EPA conducted the NIRS to provide a statistically representative sample of the national 
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occurrence of 36 selected inorganic compounds (IOCs) and radionuclides in CWSs served by 

ground water. The sample was stratified by system size and 989 ground water CWSs were 

selected at random representing 49 States (all except Hawaii) as well as Puerto Rico. The survey 

focused on ground water systems, in part because IOCs tend to occur more frequently and at 

higher concentrations in ground water than in surface water. Each of the selected CWSs was 

sampled at a single time between 1984 and 1986. 

 One limitation of the NIRS is a lack of occurrence data for surface water systems. EPA 

also reviews additional finished water data from State datasets and other sources, as well as data 

from ambient and source surface waters, to augment the NIRS data. Information about NIRS 

monitoring and data analysis is available in The Analysis of Occurrence Data from the 

Unregulated Contaminant Monitoring (UCM) Program and National Inorganics and 

Radionuclides Survey (NIRS) in Support of Regulatory Determinations for the Second Drinking 

Water Contaminant Candidate List (USEPA, 2008b). 

(3)  Disinfection Byproducts Information Collection Rule (DBP ICR)

The DBP ICR (61 FR 24353, May 14, 1996 (USEPA, 1996)) required PWSs serving at 

least 100,000 people to monitor and collect data on DBPs from July 1997 to December 1998. 

The DBP ICR data were collected from 296 water systems that provided extensive information 

on the occurrence of DBPs and on water treatment methods. The DBP ICR data were collected 

as part of a national project to support development of national disinfection by-products and 

microbial drinking water standards. EPA used the data to identify national and regional patterns 

and overall water quality, not to reach system-by-system or treatment plant-by-treatment plant 
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conclusions. Additional details on the data collection process for the DBP ICR, along with an 

independent analysis of the data, can be found in a report sponsored by the 

Microbial/Disinfection Products Council (McGuire et al., 2002). 

 The DBP ICR provided a census of the largest systems that serve the largest proportion 

of the population served by PWSs at that time. It has previously been vetted for use in regulatory 

development, and EPA determined it can be used in the regulatory determination process. 

 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 and/or 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. The descriptions 

that follow do not cover all the reports that EPA used. For individual contaminants 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 EPA evaluated and the occurrence data for each 

contaminant can be found in the comprehensive regulatory determination support documents 

(USEPA, 2012a2014a and 2012b2014b). 
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(1) Individual States’ Data

To support the second Six-Year Review of regulated contaminants (see USEPA, 2009b), 

EPA issued an ICR to collect compliance monitoring data from PWSs for the time period 

covering 1998-2005. After issuing the ICR, EPA received monitoring data from 45 States plus 

Region 8 and Region 9 Tribes. Six States and Region 9 Tribes also provided monitoring data for 

unregulated contaminants along with their compliance monitoring data. EPA further collected 

additional unregulated contaminant data from two additional States that provide monitoring data 

through their websites. EPA reviews these datasets during the RD 3 process. These datasets vary 

from State to State in the contaminants included, the number of samples, and the completeness of 

monitoring. They are reviewed and used to augment the national data and assess if they provide 

supportive observations or any unique occurrence results that might warrant further review. 

(2) Community Water System Survey (CWSS)

EPA periodically conducts the CWSS to collect data on the financial and operating 

characteristics from a nationally representative sample of CWSs. As part of the CWSS, all 

systems serving more than 500,000 people receive the survey. In the 2000 and 2006 CWSS, 

these very large systems were asked questions about the occurrence and concentration of 

unregulated contaminants in their raw and finished water. The 2000 CWSS (USEPA, 2002a, 

2002b) requested data from 83 very large CWSs and the 2006 CWSS (USEPA, 2009c, 2009d) 

requested data from 94 very large CWSs. Not all systems answered every question or provided 

complete information on the unregulated contaminants. Because reported results are incomplete, 

they are illustrative, not representative, and are only used as supplemental information. 
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 (3) United States Department of Agriculture (USDA) Pesticide Data Program (PDP) 

Since 1991, the USDA PDP has gathered data on pesticide residues in food. In 2001 the 

program expanded to include sampling of pesticide residues in treated drinking water, and in 

2004 some sampling of raw water was incorporated as well (USDA, 2004). The CWSs selected 

for sampling tend to be small and medium-sized water surface water systems (serving under 

50,000 people) located in regions of heavy agriculture. The sampling frame is designed to 

monitor in regions of interest for at least two years to reflect the seasonal and climatic variability 

during growing seasons. PDP works with EPA and the American Water Works Association 

(AWWA) to identify specific water treatment facilities where monitoring data are collected. The 

number of sites and samples have varied among different sampling periods. EPA reviewed the 

PDP data on the occurrence of select contaminants in untreated and treated water (USDA, 2004). 

(4) United States Geological Survey (USGS) Pilot Monitoring Program (PMP) 

In 1999, USGS and EPA conducted the PMP to provide information on pesticide 

concentrations in small drinking water supply reservoirs in areas with high pesticide use 

(Blomquist et al., 2001). The study was undertaken, in part, to test and refine the sampling 

approach for pesticides in such reservoirs and related drinking water sources. Sampling sites 

represent a variety of geographic regions, as well as different cropping patterns. Twelve water 

supply reservoirs considered vulnerable to pesticide contamination were included in the study. 

Samples were collected quarterly throughout the year and at weekly or biweekly intervals 

following the primary pesticide-application periods. Water samples were collected from the raw 

water intake and from the finished drinking water prior to entering the distribution system. At 
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some sites, samples were also collected at the reservoir outflow. 

(5). United States Geological Survey (USGS) National Water Quality Assessment 

(NAWQA) 

The USGS instituted the National Water Quality Assessment (NAWQA) program in 

1991 to examine ambient water quality status and trends in the United States. The NAWQA 

program is designed to apply nationally consistent methods to provide a consistent basis for 

comparisons over time nationally and among significant watersheds and aquifers across the 

country. These occurrence assessments serve to facilitate interpretation of natural and 

anthropogenic factors affecting national water quality. The NAWQA program monitors the 

occurrence of chemicals such as pesticides, nutrients, VOCs, trace elements, and radionuclides, 

and the condition of aquatic habitats and fish, insects, and algal communities. For more detailed 

information on the NAWQA program design and implementation, please refer to Leahy and 

Thompson (1994), Hamilton et al. (2004), and NRC (2002). 

The NAWQA program has been designed in ten-year cycles to enable national coverage 

that can be used for trends and causal assessments. In the Cycle 1 monitoring period, which was 

conducted from 1991 through 2001, NAWQA collected data from over 6,400 surface water and 

7,000 ground water sampling points. Cycle 2 monitoring covers the period from 2002 through 

2012, with various design changes from Cycle 1 (see Hamilton et al., 2004). 

EPA, with the cooperation of USGS, performed a summary analysis of all Cycle 1 water 

monitoring data for the CCL 3 and Regulatory Determination process. The surface water data 

consisted of stream samples; all surface water data were included in the EPA summary analysis. 
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For ground water, all well data were used and data from springs and drainage systems were 

excluded. 

For RD 3, EPA used and evaluated many USGS NAWQA reports to review causal or 

spatial factors that USGS may have presented in their interpretations. In particular, EPA 

evaluated many reports from the Pesticide National Synthesis Programs (e.g., Gilliom et al., 

2007) and the VOC National Synthesis (e.g., Delzer and Ivahnenko, 2003). While there is 

overlap in the data used in the USGS reports and the EPA analysis, the USGS reports can 

provide unique observations related to their synthesis of additional data. 

For RD 3, EPA also supplemented these data with information from recent special USGS 

reports that also used additional data from other programs, particularly reports that focused on 

contaminant occurrence in source waters for PWSs, such as: Organic Compounds in Source 

Water of Selected Community Water Systems (Hopple et al., 2009 and Kingsbury et al., 2008), 

and Water Quality in Public-Supply Wells (Toccalino et al., 2010). 

 (6). Storage and Retrieval (STORET) Data System

EPA’s STORET database contains raw biological, chemical, and physical data from 

surface and ground water sampling conducted by Federal, State and local agencies, Indian 

Tribes, volunteer groups, academics, and others. A wide variety of data relating to water quality 

from all 50 States as well as multiple territories and jurisdictions of the United States are 

represented in this data system. These are primarily ambient water data, but in some cases they 

include finished drinking water data. STORET data have quality limitations. There are few 

restrictions on submission of data based on analytical methods, quality assurance (QA) practices, 
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etc. For more general STORET data information, please refer to: 

http://www.epa.gov/storet/index.html. EPA reviewed STORET ground water data from wells 

and surface water data from lakes, rivers/streams, and reservoirs. 

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. A more detailed discussion of the supplemental sources of 

information/data that EPA evaluated and the occurrence data for each contaminant can be found 

in the comprehensive regulatory determination support documents (USEPA, 2012a2014a and 

2012b2014b). Several sources are described in more detail below. 

(1). Chemical Update System/Inventory Update Rule (CUS IUR)

The IUR regulation requires manufacturers and importers of certain chemical substances, 

included on the Toxic Substances Control Act (TSCA) Chemical Substance Inventory, to report 

site and manufacturing information and the amount of chemicals produced or imported in 

amounts of 25,000 pounds or more at a single site. Additional information on domestic 

processing and use must be reported for chemicals produced or imported in amounts of 300,000 

pounds or more at a single site. Prior to the 2003 TSCA Amendments (i.e., reporting from 2002 

or earlier), information was collected for only organic chemicals that were produced or imported 

in amounts of 10,000 pounds or more, and was limited to more basic manufacturing information 
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such as production volume. Because of changes in reporting rules, contaminants may have 

reports for some years but not others (USEPA, 2010a). 

(2). Toxic Release Inventory (TRI) 

EPA established the Toxics Release Inventory (TRI) in 1987 in response to Section 313 

of the Emergency Planning and Community Right-to-Know Act (EPCRA). EPCRA Section 313 

requires facilities to report to both EPA and the States annual information on toxic chemical 

releases from facilities that meet reporting criteria. The TRI database details not only the types 

and quantities of toxic chemicals released to the air, water, and land by facilities, but also 

provides information on the quantities of chemicals sent to other facilities for further 

management (USEPA, 2002c, 2003b). Currently, for most chemicals the reporting thresholds are 

25,000 pounds for manufacturing and processing and 10,000 pounds for use. Both the number 

and type of facilities required to report has increased over time. 

Although TRI can provide a general idea of release trends, it has limitations because of 

the reporting changes over time. Finally, TRI data are meant to reflect “releases” and should not 

be used to estimate general public exposure to a chemical (USEPA, 2002c). 

(3). Pesticide Usage Estimates

For the regulatory determinations process, the agency reviews various sources of 

information about pesticide usage. SDWA directs EPA to consider pesticides in the CCL 

process. Pesticide use and manufacturing information is considered confidential business 

information and therefore, accurate measures of production and use are not publically available. 

As a result, the agency reviews various estimates of use as supplemental information in the 
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deliberative process. 

Occasionally, EPA presents estimations of annual U.S. usage of individual pesticides in 

its pesticide reregistration documents (e.g., Reregistration Eligibility Decisions or (REDs), 

Interim Reregistration Eligibility Decisions (IREDs), Tolerance Reassessment Progress and Risk 

Management Decisions (TREDs)). EPA also periodically issues Pesticides Industry Sales and 

Usage reports. The reports provide contemporary and historical information on U.S. pesticide 

production, imports, exports, usage, and sales, particularly with respect to dollar values and 

quantities of active ingredient. The most recent report presents data from the years 2000 and 

2001 (USEPA, 2004). 

The National Center for Food and Agricultural Policy (NCFAP), a private non-profit 

institution, has also produced national pesticide use estimates based on USDA State-level 

statistics and surveys for commercial agriculture usage patterns and State-level crop acreage. The 

database contains estimates of pounds applied and acres treated in each State for 220 active 

(pesticide) ingredients and 87 crops. The majority of the chemicals monitored are herbicides, but 

the database also follows significant numbers of fungicides and insecticides (NCFAP, 2000). 

The USGS produced usage estimates and maps for over 200 pesticides used in United 

States crop production, providing spatial insight to the regional use of many pesticides (USGS, 

2007). These pesticide use estimates were generated by the USGS through State-level estimates 

of pesticide usage rates for individual crops that were compiled by the CropLife Foundation and 

the Crop Protection Research Institute, combined with county-level data on harvested crop 

acreage obtained from the 2002 Census of Agriculture. 
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IV. Contaminant-Specific Discussions for the RD 3 Preliminary Regulatory 

Determinations

 A. Summary of the Preliminary Regulatory Determination 

Based on EPA’s evaluation of the three SDWA criteria (discussed in section II.B.1), the 

agency is making preliminary determinations to regulate one contaminant and to not regulate 

four contaminants. Table 7 summarizes the primary health and occurrence information used to 

make these preliminary regulatory determinations. Section IV.B of this notice provides a more 

detailed summary of the information and the rationale used by the agency to reach its 

preliminary decisions for these five contaminants. 
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Table 7. Summary of the Health and Occurrence Information and the Preliminary Determinations 

for the Five Contaminants Considered for Regulatory Determinations 3 

 # RD 3 Contaminants 

Health 

Reference 

Level 

(HRL) 

Occurrence Findings from Primary Data Sources

Preliminary 

Determination Primary 

Database 

PWSs with at 

least 1 detection 

> 1⁄2 HRL 

Population served 

by PWSs with at 

least 1 detection > 1⁄2 

HRL 

PWSs with at least 

1 detection > HRL 

Population served by 

PWSs with at least 1 

detection > HRL 

1 Dimethoate 15.4 μg/L UCMR 2 0% (0 of 4138) 0% (0 of 229M) 0% (0 of 4138) 0% (0 of 229M) Do not regulate 2 1,3-Dinitrobenzene 0.7 μg/L UCMR 2 0% (0 of 4137) 0% (0 of 229M) 0% (0 of 4137) 0% (0 of 229M) Do not regulate 3 Strontium 1,500 μg/L NIRS 14.3% (141 of 989) 16.6% (246K of 1.5M) 6.98% (69 of 989) 10.7% (158.5K of 1.5M) Regulate 4 Terbufos 0.35 μg/L UCMR 1 0% (0 of 295) 0% (0 of 41M) 0% (0 of 295) 0% (0 of 41M) Do not regulate 5 Terbufos Sulfone 0.35 μg/L UCMR 2 0.02% (1 of 4138) 0.01% (44.6K of 229M) 0.02% (1 of 4138) 0.01% (44.6K of 229M) Do not regulate 
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 B. Contaminant Profiles. 

 This section provides further information on the background, health, and occurrence data 

that the agency uses to evaluate each of the five candidate contaminants considered for 

regulatory determinations. For each candidate, the agency evaluates the available human and 

toxicological data, derives a health reference level, and evaluates the potential and/or likely 

occurrence and exposed population for the contaminant in public water systems. The agency also 

considers whether information is available on sensitive populations. The agency uses the 

findings from these evaluations to determine whether the three SDWA statutory criteria are 

satisfied. The agency also prepares a regulatory support document (USEPA, 2012b2014b) that 

provides more details on the background, health, and occurrence information/analyses used to 

evaluate and make preliminary determinations for these five contaminants. 

 1. Dimethoate 

a. Background 

Dimethoate is an organophosphate pesticide, commonly used as an insecticide on field 

crops (e.g., wheat, alfalfa, corn, and cotton), orchard crops, vegetable crops, and in forestry. 

Synonyms for dimethoate include dimethogen, dimeton, dimevur, and cygon (HSDB, 2009; 

USEPA, 2008d2007b). EPA has estimated that the total annual average domestic use of 

dimethoate is approximately 1.8 million pounds (USEPA, 2007b). EPA’s most recent Pesticide 

Industry Sales and Usage reports indicate that the amount of dimethoate active ingredient (a.i.) 

used in the United States was between 1 and 2 million pounds in 1999 and 2001, and less than 1 

million pounds in 2005 and 2007 (USEPA, 2004: USEPA, 2011f). TRI data from the years 1997 

to 2010 show that annual releases to various sources range from tens of pounds to tens of 

thousands of pounds, with the larger releases occurring only occasionally and in no clear pattern 
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(USEPA, 2012e2012a). For example, reported on-site air emissions were in the range of tens of 

pounds for 1997-2005 but increased to the range of thousands of pounds in 2006-2010. The only 

reported non-zero release by underground injection was in 2004 and was over 28,000 pounds. 

Reported on-site releases to surface water and land were low or non-existent in most years, but 

peaked suddenly at nearly 20,000 pounds in 1998 (land) and over 2,000 pounds in 2004 (surface 

water). Dimethoate is considered highly mobile and relatively non-persistent in the environment 

(USEPA, 2007b). 

b. Statutory Criterion #1 (Adverse Health Effects) 

 Dimethoate meets the SDWA statutory criterion #1 for regulatory determinations; it may 

have an adverse effect on the health of persons. Dimethoate belongs to a group of pesticides 

called organophosphates, which share a common MOA. Organophosphates affect the proper 

function of the nervous system by inhibiting cholinesterase (ChE), an important enzyme 

involved in neurotransmission. Inhibition of ChE in the brain, plasma, and red blood cells is the 

most sensitive endpoint described in numerous studies with adult and juvenile animals, following 

oral, dermal, or inhalation exposures of dimethoate or its primary toxic metabolite omethoate 

(USEPA, 2007b). As discussed in the 2007 OPP assessment, the U.S. EPA’s Cancer Assessment 

Review Committee (CARC) classified dimethoate as a Group C carcinogen (a possible human 

carcinogen) in 1991, with concurrence from the FIFRA Scientific Advisory Panel (SAP) on the 

agency’s classification in 1992 (USEPA, 2007b). 

The 2007 OPP assessment established a chronic oral RfD for dimethoate of 0.0022 

mg/kg/day based on a 2-year feeding study in rats with inhibition of brain ChE as the critical 

effect (American Cyanamid Company, 1986).USEPA, 2007b). The RfD was derived using the 

BMD method and based on the lower 95% confidence limit (BMDL) of 0.22 mg/kg/day, with 
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application of a composite UF of 100 (i.e., intraspecies and interspecies variability). EPA 

calculated a non-cancer HRL of 15.4 μg/L for dimethoate using the RfD of 0.0022 mg/kg/day for 

a 70 kg adult ingesting 2 L of drinking water per day and an RSC of 20%. The chronic RfD and 

subsequent HRL of 15.4 μg/L for dimethoate are considered to be protective of any potential 

cancer risk or acute ChE effects (USEPA, 1990a, 2007b). The OPP RED (USEPA, 2007b) 

presents more detailed information about the potential health effects for dimethoate. 

c. Statutory Criterion #2 (Occurrence at frequency and levels of public health concern) 

Dimethoate does not meet the SDWA statutory criterion #2 for regulatory 

determinations; it does not occur with a frequency and at levels of public health concern in 

public water systems based on EPA’s evaluation of the following occurrence information. 

The primary data for dimethoate are recent (2008-2010) nationally-representative 

drinking water monitoring data, generated through EPA’s UCMR 2. Dimethoate was not 

detected in any of the 32,013 UCMR 2 samples collected by 4,138 PWSs (serving ~ 230 million 

people) at levels greater than the 1⁄2 HRL (7.7 μg/L), the HRL (15.4 μg/L), or the MRL (0.7 

μg/L) (USEPA, 2012d2014d). 

The State of California reported results from testing more than 20,000 finished drinking 

water samples from over 2,000 PWSs and dimethoate was detected in two samples from two 

different PWSs. The detected concentrations (1 μg/L and 2 μg/L) were less than the 1⁄2 HRL (7.7 

μg/L) and the HRL (15.4 μg/L) (see USEPA, 2012b2014b). The USDA PDP monitored for 

dimethoate in finished water from 2001 to 2009 and had only two detections in 3,555 samples; 

both detected concentrations were less than the 1⁄2 HRL and the HRL (USDA, 2012). The USGS 

PMP monitored for dimethoate in finished water in 1999 and had no detections greater than 1⁄2 

the HRL or the HRL in any of the 221 samples (Blomquist et al., 2001). 
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 Dimethoate occurrence data for ambient water are consistent with those for finished 

drinking water. The USGS PMP also monitored for dimethoate in ambient water in 1999 and had 

no detections greater than the 1⁄2 HRL (7.7 μg/L) or the HRL (15.4 μg/L) in any of the 317 

samples (Blomquist et al., 2001). Ambient water data from a two-phase USGS study conducted 

between 2002 and 2005 by Hopple et al. (2009) and Kingsbury et al. (2008) reported no 

detections in the 221 Phase 1 groundwater samples. Only two detections were reported from 146 

Phase 1 surface water samples at nine PWSs. The highest concentration detected was 0.009 

μg/L, which is less than the 1⁄2 HRL and the HRL. In Phase 2, there were no detections of 

dimethoate from 48 raw and finished water groundwater samples (Hopple et al., 2009; 

Kingsbury et al., 2008). Ambient water data in STORET included no measured results above 

0.44 μg/L in 5,299 samples from 798 sites (USEPA, 2012f2012b). Ambient water data reported 

by the California Department of Pesticide Regulation included no measured results above 2.4 

μg/L (USEPA, 2007b). 

d. Statutory Criterion #3 (Meaningful Opportunity) 

 EPA finds that dimethoate does not meet the SDWA statutory criterion #3 for regulatory 

determinations; regulation of dimethoate does not present a meaningful opportunity health risk 

reduction for persons served by PWSs based on the estimated exposed population, including 

sensitive populations. The estimated population exposed to dimethoate at levels of public health 

concern is 0%; it was not found to occur at levels above the HRL (or the 1⁄2 HRL) in 4,138 PWSs 

and 32,013 samples from the UCMR 2 monitoring. In addition, other supplementary sources of 

finished water and ambient water data indicate that the occurrence of dimethoate in PWSs is 

likely to be low to non-existent. As a result, the agency finds that an NPDWR for dimethoate 

does not present a meaningful opportunity for health risk reduction. 
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EPA also evaluated whether health information is available regarding the potential health 

effects on children and other sensitive populations. The database for dimethoate includes a 3-

generation reproductive study in mice, developmental (teratology) studies in rats and rabbits, and 

a neurodevelopmental toxicity study (USEPA, 1990a, 2007b). The critical effect of ChE 

inhibition is a more sensitive endpoint compared to the reproductive and developmental 

endpoints (USEPA, 2007b); therefore no sensitive populations were identified or characterized. 

The OPP RED (USEPA, 2007b) presents more detailed information about the potential health 

effects and sensitive populations for dimethoate. 

e. Preliminary Regulatory Determination

The agency is making a preliminary determination to not regulate dimethoate with an 

NPDWR after evaluating health, occurrence, and other related information against the three 

SDWA statutory criteria. While data suggests that dimethoate may have an adverse effect on 

human health, the occurrence data indicate that dimethoate is not occurring or not likely to occur 

in PWSs with a frequency and at levels of public health concern. Therefore, the agency finds that 

an NPDWR would not present a meaningful opportunity to reduce health risk for persons served 

by PWSs. The Regulatory Determinations 3 Support Document (USEPA, 2012d2014d) and the 

Occurrence Data from the Second Unregulated Contaminant Monitoring Regulation (UCMR 2) 

(USEPA, 2012a2014a) present additional information and/or analyses supporting the agency’s 

evaluation of dimethoate. 

 2. 1,3-Dinitrobenzene 

a. Background 

 1,3-Dinitrobenzene is a nitro aromatic compound that is used as an industrial chemical 

and formed as a by-product in the manufacture of munitions as well as in the production of other 
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substances (HSDB, 2009). There are no known natural sources of 1,3-dinitrobenzene. Annual 

production and importation of 1,3-dinitrobenzene in the United States was last reported by CUSIUR in 1986 to be between 10-50 million pounds (USEPA, 2010b). TRI data indicate 19,858 

pounds were released to the environment by industry in 2008 and 10,595 pounds in 2010 

(USEPA, 2012e2012a). 1,3-dinitrobenzene appears to be moderately persistent in environmental 

media and moderately mobile in soil and water, though in soils with high clay content it will be 

less mobile (USEPA, 2012b2014b). 

b. Statutory Criterion #1 (Adverse Health Effects) 

1,3-dinitrobenzene meets the SDWA statutory criterion #1 for regulatory determinations; 

it may cause adverse effect on the health of persons. 1,3-Dinitrobenzene has demonstrated 

adverse health effects in many rodent and occupational studies. Occupational studies indicate 

that methemoglobinemia, hemolytic anemia, and cyanosis are seen in workers who experience an 

acute reaction to 1,3-dinitrobenzene (Hajjar et al., 1992). The EPA IRIS assessment (USEPA, 

1990b) of the carcinogenicity of 1,3-dinitrobenzene currently lists it as Group D (not classifiable 

as to human carcinogenicity). 

The primary adverse biological effects from exposure to 1,3-dinitrobenzene are on red 

blood cells, spleen, and testes. The RfD for 1,3-dinitrobenzene is 0.0001 mg/kg/day (Cody et al., 

1981). The RfD was derived from a NOAEL of 0.4 mg/kg/day in a subchronic oral study in rats 

where increased spleen weight was identified as the critical effect (Cody et al., 1981). A 

composite UF of 3,000 (intraspecies variability, interspecies variability, subchronic to chronic 

duration, and lack of chronic, developmental, and multigenerational reproductive toxicity 

studies) was applied to the NOAEL to obtain the RfD. EPA calculated a non-cancer HRL of 0.7 

μg/L for 1,3-dinitrobenzene using the RfD of 0.0001 mg/kg/day for a 70 kg adult ingesting 2 L 
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of drinking water per day and an RSC of 20%. 

The current EPA oral RfD value is supported by a more recent 1,3-dinitrobenzene 

assessment that was conducted by ATSDR, in which an oral intermediate duration minimal risk 

level of 0.0005 mg/kg/day for splenic hemosiderosis in male rats was established using a 

LOAEL of 0.54 mg/kg/day (Linder et al., 1986; dose adjusted for a 7-day/week exposure) and a 

composite UF of 1,000 (intraspecies variability and interspecies variability, LOAEL to NOAEL). 

Based on EPA assumptions and a composite UF of 3,000 (intraspecies variability, interspecies 

variability, LOAEL to NOAEL and subchronic to chronic duration) applied to the LOAEL of 

0.54 mg/kg/day, the resultant HRL value of 1 μg/L supports the HRL value of 0.7 μg/L derived 

from the IRIS RfD (ATSDR, 1995). The IRIS assessment (USEPA, 1990b) presents more 

detailed information about the potential health effects for 1,3-dinitrobenzene. 

c. Statutory Criterion #2 (Occurrence at frequency and levels of public health concern) 

1,3-dinitrobenzene does not meet the SDWA statutory criterion #2 for regulatory 

determinations; it does not occur with a frequency and at levels of public health concern in 

public water systems based on EPA’s evaluation of the following occurrence information. 

 The primary data for 1,3-dinitrobenzene are recent (2008-2010) nationally-representative 

drinking water monitoring data generated through EPA’s UCMR 2 (USEPA, 2012d2014d). 

UCMR 2 is the only dataset with finished water data for this contaminant. UCMR 2 collected 

32,017 samples from 4,137 PWSs and 1,3-dinitrobenzene was not detected above the MRL (0.8 

μg/L), which is only slightly higher than the HRL (0.7 μg/L). 

Findings from the available ambient water data for 1,3-dinitrobenzene are consistent with 

the results in finished water. Ambient water data in STORET included no measured results 

above 0.33 μg/L in 143 samples from 70 sites (USEPA, 2012f2012b). It should be noted that 
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some occurrence above the HRL may have gone undetected since reporting levels are not 

documented. 

d. Statutory Criterion #3 (Meaningful Opportunity) 

EPA finds that 1,3-dinitrobenzene does not meet the SDWA statutory criterion for 

regulatory determinations; regulation of 1,3-dinitrobenzene 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 1,3-

dinitrobenzene at or above the MRL is 0%; it was not found to occur in finished drinking water 

at levels ≥> MRL (0.8 μg/L), which is only slightly higher than the HRL (0.7 μg/L), in 32,017 

samples and 4,137 PWSs from the UCMR 2 monitoring. As a result, the agency finds that an 

NPDWR for 1,3-dinitrobenzene does not present a meaningful opportunity for health risk 

reduction. 

EPA also evaluated whether information is available regarding the potential health effects 

on children and other sensitive populations. Individuals with a genetic predisposition to 

methemoglobinemia (estimated prevalence in the general population = 1% or 1 per 100) and/or 

hemosiderosis, neonates, and those co-exposed to other hemolytic agents, could be more 

sensitive to exposure to 1,3-dinitrobenzene (ATSDR, 1995; Jaffe and Hultquist, 1989). Males 

having sperm production complications could also have increased sensitivity to 1,3-

dinitrobenzene exposure (Hajjar et al., 1992). There is currently no multigenerational animal 

study available for 1,3-dinitrobenzene, and no data available from studies of 1,3-dinitrobenzene 

developmental toxicity (Hajjar et al., 1992 ). However, the RfD incorporated a UF for this 

database deficiency. The IRIS assessment (USEPA, 1990b) presents more detailed information 

about the potential health effects and sensitive populations for 1,3-dinitrobenzene. 
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e. Preliminary Regulatory Determination for 1,3-dinitrobenzene

The agency is making a preliminary determination to not regulate 1,3-dinitrobenzene 

with an NPDWR after evaluating health, occurrence, and other related information against the 

three SDWA statutory criteria. While data suggest that 1,3-dinitrobenzene may have an adverse 

effect on human health, the occurrence data indicate that 1,3-dinitrobenzene 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 1,3-dinitrobenzene would not present a 

meaningful opportunity to reduce health risk for persons served by PWSs. The Regulatory 

Determinations 3 Support Document (USEPA, 2012b2014b) and the Occurrence Data from the 

Second Unregulated Contaminant Monitoring Regulation (UCMR 2) (USEPA, 2012d2014d)

present additional information and analyses supporting the agency’s evaluation of 1,3-

dinitrobenzene. 

 3. Strontium 

a. Background 

Strontium is a naturally occurring element (atomic number 38) and a member of the 

alkaline earth metals (ANL, 2007). There are several radioactive strontium isotopes formed by 

nuclear fission of uranium or plutonium. The best known is 90Sr, a legacy from above ground 

testing of the atomic bomb (half-life 29 years). Since drinking water contamination by 

radioactive isotopes, including beta particle emitters, is covered under the existing radionuclides 

rule, this FR notice deals primarily with the stable 88Sr isotope which represents 83% of total 

environmental strontium (ATSDR, 2004). 

Strontium mineral mining ceased in the United States in 1959. The United States imports 

both strontium minerals for refining and refined strontium containing compounds (USGS, 2009). 
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Imports of strontium minerals and compounds were approximately 31,000 to 38,500 metric tons 

from 1994 to 2001 and have declined since 2001 (ATSDR, 2004; USGS, 2009). In the United 

States, total consumption of strontium minerals and compounds was 16,700 metric tons of 

strontium content in 2004 and approximately 7,750 metric tons in 2008 (USGS, 2009). 

Historically, the most important commercial use of strontium has been in the faceplate 

glass of cathode-ray tube televisions to block x-ray emissions (ATSDR, 2004). Conversely, flat 

panel televisions incorporating LCD or Plasma displays are not capable of emitting x-radiation; 

therefore, they do not require strontium (FDA, 2011). As flat panel technology has become 

widespread in the United States in the last decade, demand for strontium for this application has 

fallen (USGS, 2009). In 2008, approximately 30% of commercial strontium consumption was in 

pyrotechnics and signals (as strontium nitrate and other compounds), 30% in ferrite ceramic 

magnets (as strontium ferrite), 10% in master alloys (as strontium metal), 10% in pigments and 

fillers (as strontium chromate), 10% in electrolytic production of zinc (as strontium carbonate), 

and 10% in other applications such as fluorescent lights (strontium phosphate), toothpaste 

(strontium chloride), and medicines (strontium chloride and strontium peroxide). The feed 

material for most applications is strontium carbonate (ATSDR, 2004; HSDB, 2010; USGS, 

2009). Strontium may becan exist in oxidation states 0 and +2; under normal environmental 

conditions it is found in the environment in the elemental state (+2 oxidation state 0) or in 

various ionic or salt forms (oxidation state +2).. Strontium is considered to have moderate or 

moderate-to-low mobility in soils. The mobility of strontium in water can increase with increased 

salt concentrations due to a decrease in sorption to sediments (USEPA, 20102b20104b). The 

Regulatory Determination 3 Support Document (USEPA, 2012b2014b) for this notice presents 

more detailed background information on strontium. 
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b. Statutory Criterion #1 (Adverse Health Effects) 

Strontium meets the SDWA statutory criterion #1 for regulatory determinations; it may 

have an adverse effect on the health of persons. The primary target of strontium exposure is the 

bone. The chemical similarity of strontium to calcium allows it to exchange imperfectly for 

calcium in a variety of biological processes; the most important of these is the substitution of 

calcium in bone, affecting skeletal development. Due to the MOA for strontium toxicity, 

strontium uptake into bone is affected by the intake of nutrients related to bone formation, such 

as calcium, phosphorous, and vitamin D (Clarke, 2008; Grynpas and Marie, 1990; Marie et al., 

1985). The decreased calcification in bones results in increased width of the epiphyseal 

cartilage, changes in the pattern of calcification, abnormally long metaphyses, reduction in bone 

mineralization, and active osteoclasts in young rats (Marie and Hott, 1986; Matsumoto, 1976; 

Neufeld and Boskey, 1994; Storey, 1961). Due to this effect on growing bones, infants, children, 

and adolescents are of particular concern as a sensitive population. 

A study based on decreased bone calcification rate in male weanling rats (i.e., 

comparable to the sensitive time period in humans), which administered strontium chloride in 

drinking water for nine weeks (Marie et al., 1985), was identified by EPA as the critical study for 

RfD determination. The RfD was established by using the BMD method and based on the lower 

95% confidence limit (BMDL) of 328 mg/kg/day for a one standard deviation decrease in bone 

calcification compared to control. Using a composite UF of 1000 (10 for intraspecies variability, 

10 for interspecies variability, and 10 for database uncertainties) the RfD for strontium is 

calculated to be 0.3 mg/kg/day. This RfD is supported by additional studies reporting bone 

effects on weanling rats at similar dose levels (Grynpas and Marie, 1990; Storey, 1961). EPA 

calculated a non-cancer HRL of 1500 μg/L for strontium using the RfD of 0.3 mg/kg/day, ana 
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default RSC of 20% and age-specific exposure factors (i.e., drinking water intake expressed as 

liters per kg of body weight) for the sensitive population of birth through 18 years to reflect the 

most active period of bone growth and development (see section IV.B.10.d.3). 

EPA released an IRIS assessment for strontium in 1992 and developed an RfD of 0.6 

mg/kg/day based on the Storey, 1961 study. The IRIS assessment was completed before the 1998 

changes to the IRIS program wherein the agency develops and peer reviews a detailed 

Toxicological Review before posting an IRIS summary. The point of departure for the 1992 IRIS 

RfD of 0.6 mg/kg/day is a NOAEL of 190 mg Sr/kg-day with a composite UF of 300 (10 for 

interspecies variability, 3 for intraspecies variability, and 10 for database uncertainties). This 

would yield an HRL of 3000 μg/L, using the same age-specific exposure adjustment factors 

described above. If the age-specific exposure adjustment factors were not used, the HRL would 

be 2000 μg/L based on the OW assessment, or 4000 μg/L based on the IRIS assessment. As 

noted in section III.C.1.c, EPA evaluates the existing data and performs a literature search for 

studies published after the available health assessment is completed to determine if new 

information suggests a different outcome. In cases where the review suggests that a change the 

existing RfD or cancer assessment is needed, the EPA Office of Water prepares and 

independently peer-reviews an OW Assessment of the data. In the case of strontium and because 

newer information provided additional support for the 1985 Marie et al. study, EPA chose to use 

the BMDL of 328 mg/kg/day from Marie et al., (over the 1961 Storey study) for the following 

reasons: (a) Marie et al., (1985) reported the doses rather than estimated the doses; (b) the study 

duration was longer (63 days for Marie as compared to 20 days for Storey); (c) the monitoring of 

the bone effects for Marie et al., (1985) was more quantitative than the photomicrographs 

evaluated by Storey (1961); (d) dosing was provided via drinking water, the medium of interest 
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(rather than a weakly soluble SrCO3 in the diet); (e) Marie et al., (1985) reported the strain of 

rats and the age of the animals, at the time that dosing was initiated and completed; (f) the data 

were amenable to dose-response modeling to identify the BMD and BMDL; and (g) the dietary 

calcium provided in the Storey study was three times higher than that in the Marie study, making 

those rats less at risk due to the calcium and strontium competition for uptake, as verified by a 

comparison of serum data from the two studies. The OW assessment uses a 10x uncertainty 

factor for intraspecies variability, rather than the 3x factor used in the 1992 IRIS assessment 

because it is not clear if the window of vulnerability was adequately captured, since the weanling 

rats were exposed only for 28-63 days, a period that did not include exposure during gestation, 

lactation, and through young adulthood. EPA requests comment on its revised RfD calculation 

and on its proposal to use the OW assessment in lieu of the RfD from the 1992 IRIS assessment. 

There is inadequate information to assess the carcinogenic potential of strontium due to 

the lack of adequate studies of chronic duration. The Health Effects Support Document (USEPA, 

2012c2014c) for this determination presents more detailed analysis of the health effects of 

strontium. 

c. Statutory Criterion #2 (Occurrence at frequency and levels of public health concern?) 

Strontium meets the SDWA statutory criterion #2 for regulatory determinations; it does 

occur with a frequency and at levels of public health concern in public water systems based on 

EPA’s evaluation of the following occurrence information. 

EPA used the National Inorganics and Radionuclides Survey (NIRS) (USEPA, 2008b) as 

the primary data source to evaluate the occurrence of strontium in PWSs. It provides 

contaminant occurrence data from 989 CWSs served by ground water sources. Each of these 

randomly selected PWSs was sampled a single time between 1984 and 1986. Of the 989 systems 
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in NIRS, 980 (99%) had detectable levels of strontium ranging from 1.53 to 43,550 μg/L. The 

mean concentration was 603 μg/L. Approximately 7.0% (69 of 989) of the NIRS PWSs detected 

strontium at a level greater than the HRL (1500 μg/L) and 14.3% (141 of 989) detected strontium 

at a level greater than 1⁄2 HRL (750 μg/L). Extrapolated by the total number of ground water 

CWSs found nationally, this represents 2,798 and 5,718 groundwater CWSs that could have 

strontium at a level greater than the HRL and the 1⁄2 HRL, respectively. These figures are 

summarized in Table 8 (USEPA, 2012b2014b). 

Table 8 – Estimates of Population Exposed to Strontium, Observed 

and Extrapolated from NIRS 

Threshold 

National Inorganics and 

Radionuclides Survey (NIRS)

Extrapolation of NIRS Data to 

Groundwater Systems Nationwide

Systems Population Systems Population 

Systems with 

Detectable 

Concentrations 

99.1% 

(980 of 989) 

99.9% 

(1.481M of 

1.482M) 

99.1% 

(39.7K of 40.1K) 

99.9% 

(93.0M of 93.1M) 

Systems detecting 

strontium above 

one half the HRL 

( > 750 μg/L) 

14.3% 

(141 of 989) 

16.6% 

(246K of 1.5M)

14.3% 

(5.7K of 40.1K) 

16.6% 

(15.4M of 93.1M) 

Systems detecting 

strontium above 

the HRL 

( > 1500 μg/L) 

7.0% 

(69 of 989) 

10.7% 

(159K of 1.5M)

7.0% 

(2.8K of 40.1K) 

10.7% 

(10.0M of 93.1M) 
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As a point of reference to the earlier IRIS assessment, if EPA used the HRL derived from this 

assessment of 3000 μg/L, 30/989 systems (3%) would have finished water samples that exceed 

the HRL using the NIRS data, compared to 69/989 (7%) using the HRL of 1500 μg/L derived 

from the more recent OW assessment. 

Finished water data, analyzed between 1998 and 2005, from Ohio and Illinois are also 

consistent with the NIRS data. The State of Illinois reported results from testing 21 drinking 

water samples from 19 PWSs and strontium was detected in all 21 samples (100%) from all 19 

systems (100%). Approximately 23.8% (5 of 21) of samples from five systems (26.3%) had 

strontium at levels greater than the 1⁄2 HRL (750 μg/L) and approximately 23.8% (5 of 21) of 

samples from five systems (26.3%) had strontium at levels greater than the HRL (1500 μg/L) 

(USEPA, 2012b). The State of Ohio reported results from testing 77 samples from 32 PWSs and 

strontium was detected in 75 samples (97.4%) from 30 different systems (93.8%). 

Approximately 27.3% (21 of 77) of samples from 10 systems (31.3%) had strontium at levels 

greater than the 1⁄2 HRL and approximately 23.4% (18 of 77) of samples from seven systems 

(21.9%) had strontium at levels greater than the HRL (USEPA, 2012b2014b). 

Although there are limited surface water data available for strontium, the available data 

are consistent and demonstrate high occurrence in surface waters. Ambient water data for 

strontium are also consistent with high occurrence in finished water, which is expected since it is 

a naturally occurring element. The NAWQA Quality of Public Supply Wells (Toccalino et al., 

2010) study collected water samples from source (untreated) groundwater public supply wells in 

41 states. Each well was sampled once from 1993-2007 and 100% of samples (503 of 503) had a 

strontium detection. Of the detections, 25.8% (1301% (126 of 503) were above the 1⁄2 HRL (750 

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μg/L) and 12.3% (621% (61 of 503) were above the HRL (1500 μg/L). Additional occurrence 

information on strontium can be found in the Regulatory Determinations 3 Support Document 

(USEPA, 2012b2014b). 

d. Statutory Criterion #3 (Meaningful Opportunity?) 

EPA findsmakes a preliminary finding that strontium meets the SDWA statutory criterion 

#3 for regulatory determinations; regulation of strontium in drinking water presents a meaningful 

opportunity for health risk reduction in drinking water based on the estimated exposed 

population, potential impacts on sensitive populations and estimated exposure from other sources 

(e.g., food). 

1. National Population Exposed: In the NIRS dataset 989 ground water systems were 

sampled serving a population of 1.48 million. The NIRS data indicates that the population 

exposed to strontium at a level greater than the HRL (1500 μg/L) is 158,557 (11%) and the 1⁄2 

HRL (750 μg/L) is 245,870 (17%) (USEPA, 2012b). EPA also performed national extrapolations 

generated by multiplying the NIRS findings of system/population percentages and the national 

system/population inventory numbers for PWSs developed from EPA’s Safe Drinking Water 

Information System, the CWSS, and UCMR. Out of the 93.1 million people served by 40,106 

ground water CWSs in the nation, the national extrapolation indicates that 10.0 million may be 

exposed to concentrations greater than the HRL (1500 ug/L) and 15.4 million may be exposed to 

concentrations greater than the 1⁄2 HRL (750 ug/L). The system and population estimates are 

summarized in Table 8. 

Strontium occurs naturally and is abundant in the environment (as is apparent in its 

detections in 98-100% of water samples (e.g., NIRS).. Its occurrence in water at concentrations 

>HRL may be a reflection of the geologic and geochemical setting of the source waters for 
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PWSs. The NIRS drinking water data showed that strontium was detected in one or more 

systems sampled in all 48 continuous states, Alaska and Puerto Rico (Hawaii was not included in 

NIRS). The occurrence data (e.g., NIRS) show that PWSs with strontium at concentrations 

greater than the HRL and the 1⁄2 HRL occur in all regions of the country26 states and 34 states, 

respectively (USEPA, 2012b2014b). 

2. Exposure from media other than water: EPA has determined that there is a meaningful 

opportunity to regulate strontium in drinking water to reduce the public’s overall exposure after 

evaluating the available exposure data from media other than water. Although strontium is 

known to occur in food, air, and soil, data on levels in those media are limited as are estimates of 

intake from those sources. The dietary intakes based on anTherefore, EPA used the default 20% 

RSC to calculate the HRL. This section provides a summary of the available exposure data. 

An FDA Total Diet Study by Pennington and Jones (1987) collected 234 individual foods 

in 1984 from three cities in one region of the country and indicated dietary intakes of 493 μg/day 

for young children (6 to 11 months), 928 to 1,388 μg/day for 14 to 16 year old adolescents, and 

979-1,489 μg/day for adults. Using the mean detection water concentrationThe FDA Total Diet 

Study foods are prepared with distilled water and do not reflect any contributions from the 

cooking water during preparation of foods that absorb water such as rice and pasta. Thus, the 

strontium in many foods will be impacted by the strontium levels in the local water supply. 

Using the mean of the detected water concentrations from the NIRS dataset (603 μg/L), the 

estimated water intake for young children (90th percentile water intake of 1L/day) is 603 μg/day 

and 1,206 μg/day for adults (90th percentile water intake of 2L/day). The estimated strontium 

intakes from air and soil are very low compared with those from food and drinking water. The 

estimated air exposure for children from air is 0.1 μg/day and for adults is 0.3 μg/day for adults
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(Dzubay and Stevens, 1975) and the). The estimated exposure from soil is 24 μg/day for children 

and 12 μg/day for adults (Shacklette and Boerngen, 1984). No data were identified on consumer 

products, such as toothpaste that contain strontium as an ingredient or impurity. 

The exposure data for food, air and soil are dated and some aspects of strontium exposure 

may have changed, but with the available strontium exposure dataset it is possible to estimate the 

approximate contribution of drinking water from PWS to total strontium exposure. Strontium 

exposure from drinking water represents approximately 40% to 50% of total strontium exposure 

for adults and young children respectively (USEPA, 2012c). 
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3. Sensitive populations: Children are expected to be a sensitive population, since they are 

actively growing and strontium can substitute for calcium in growing bone. This means that 

changes in bone structure and homeostasis may have more severe and/or a long-term impact than 

similar changes in adults. These effects would be expected to have the greatest impact during 

periods of rapid growth in the developing fetus, during childhood and adolescence, particularly if 

their calcium intake is insufficient (Abrams et al., 2000; Lee et al., 1996; Matkovic et al., 2005; 

Storey, 1961). The estimated populations of pregnant women (and thus fetuses) and of children 

(<17 years old) are 6 and 75 million, respectively (O’Day et al., 1998). The RfD was based on 

changes in bone growth in weanling rats (i.e., the sensitive population). As a result, the data do 

not include the risk during prenatal development and lactation so these factors were considered 

when selecting the UFs used to derive the RfD. Age-specific exposure factors (USEPA, 

2012g2012c) were also used to reflect the sensitive population (birth through 18 years) in 

derivation of the HRL. Exposures from drinking water at or below the HRL (1500 μg/L) are 

expected to be protective of the sensitive population, assuming that 80% of exposure comes from 

other sources such as air, soil and food. 

The toxic effects of strontium result from strontium ions substituting for calcium ions, 

therefore calcium deficiency would be expected to result in increased risk among sensitive 

populations. In this respect, it is important to note that recent NHANES data indicate that about 

50% of females, nine years and older, fail to receive adequate calcium from diet and supplements 

on a daily basis (IOM, 2010). Groups with higher risks of becoming calcium deficient include:

adolescent girls, postmenopausal women, amenorrheic women, female athletes, vegans, and 

individuals with lactose intolerance or cow’s milk allergies (IOM, 2010; NIH, 2011a). 

The major route of elimination of strontium is via the kidneys, therefore individuals with 

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impaired renal function are another sensitive population. This population may potentially have 

impaired strontium clearance, as has been shown in renal failure patients. There are 

approximately 20 million people (10%) above the age of 20 with chronic kidney disease (CDC, 

2010) and 548,000 people with kidney end-stage renal disease (USRDS, 2010), who may be at 

an increased risk. People with disorders affecting the normal equilibrium between the breakdown 

of old bone and the formation of new bone (such as Paget’s disease) might also be sensitive to 

strontium exposure (D’Haese et al., 1999, 2000; Schrooten et al., 1998, 2003; Tothill et al., 

1983). According to the National Institute of Arthritis and Musculoskeletal and Skin 

Diseases,According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases,

there are approximately 1 million people (1.2 people per 100 men and women age 45 to 74) 

diagnosed with Paget’s disease of the bone (NIH, 2011b). The Health Effects Support Document 

(USEPA, 2012c2014c) for strontium presents more detailed information about the potential 

health effects and sensitive populations. Because the RfD includes an uncertainty factor of 10 

for intraspecies variability, the RfD is also expected to be protective of these sensitive 

populations. 

d. Preliminary Regulatory Determination 

 The At this time, the agency is making a preliminary determination to regulate strontium 

with an NPDWR after evaluating the available health, occurrence, and other related information 

against the three SDWA statutory criteria. Specifically, EPA has foundit is EPA’s preliminary 

determination that (a) strontium may have an adverse effect on the health of persons, (b) it is 

known to occur or there is substantial likelihood that strontium will occur in public water 

systems with a frequency and at levels of public health concern, (c) regulation of strontium with 

an NPDWR presents a meaningful opportunity to reduce health risks for persons served by 
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PWSs. 

It is important to note that the agency included strontium in UCMR 3. The agency 

believes the additional data collected under As of January 2014, a preliminary analysis of the 

first nine months of the UCMR 3 will assist the agency in developing the NPDWR formonitoring 

data (USEPA, 2014e) indicate that 4.9% (70 of 1,432) of systems, 3.8% (175 of 4,547) of entry 

points, and 3.9% (274 of 7,061) of samples have detects of strontium. at levels greater than the 

HRL of 1500 μg/L. While EPA believes the occurrence data from NIRS (in concert with the 

supplemental information discussed earlier) are sufficient to make the regulatory determination, 

the agency will considerbelieves the availableadditional monitoring results from UCMR 3 will 

assist EPA in making the final regulatory determination for strontium and in developing the 

proposed NPDWR. As noted in section III.A.3., this regulatory determination process is distinct 

from the more detailed analyses needed to develop a national primary drinking water regulation. 

Thus a decision to regulate is the beginning of the agency’s regulatory development process, not 

the end. As the agency collects additional information about drinking water and other sources of 

exposure (and performs more detailed analyses), this information will inform the agency’s 

opinion as to whether strontium should be regulated. The agency asks the public to submit any 

data or information that may be useful in evaluating drinking water and other sources of 

exposure (e.g., food, food prepared in drinking water, air, soil, etc.).

 4 and 5. Terbufos and Terbufos Sulfone 

a. Background 

Terbufos is a phosphorodithioate pesticide (i.e., an organophosphate) used as an 

insecticide-nematicide to control a variety of insect pests, primarily used on corn and sugar beets 

(USEPA, 2006c). Terbufos sulfone is a degradate of terbufos. EPA’s most recent Pesticide 
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Industry Sales and Usage report states that between 5 and 7 million pounds of terbufos active 

ingredient were used in 1999 and between 3 and 5 million pounds of active ingredient were used 

in 2001 (USEPA, 2004). There are no industrial release data available for terbufos from TRI. As 

a pesticide degradate, terbufos sulfone is neither produced nor used commercially. Total toxic 

residues of terbufos and degradates are highly mobile and persistent in the environment, with 

terbufos sulfone being more mobile and substantially more persistent than terbufos (USEPA, 

2006c).

b. Statutory Criterion #1 (Adverse Health Effects?) 

Terbufos and its degradate, terbufos sulfone, meet the SDWA statutory criterion #1 for 

regulatory determinations; they may cause an adverse effect on the health of persons. Terbufos 

and terbufos sulfone belong to a group of pesticides called organophosphates, which share a 

common mechanism of toxicity. Organophosphates affect the proper function of the nervous 

system by inhibiting ChE, an essential enzyme in neurotransmission. There has been no evidence 

that terbufos is carcinogenic in animal studies (Rapp, 1974; Silverman et al., 1986) and it is 

classified as a class D carcinogen (inadequate evidence of carcinogenicity) (USEPA, 1988). 

Overall, health effects information for the terbufos sulfone degradate is lacking; there are no 

long-term studies or cancer classification for terbufos sulfone. 

The 2006 OPP RED assessment (USEPA, 2006c) established an oral RfD for terbufos of 

0.00005 mg/kg/day, derived from the NOAEL of 0.005 mg/kg/day for ChE inhibition in the 28-

day and 1-year dog studies by Shellenberger (1984) and Shellenberger and Billups (1986). A 

composite UF of 100 (interspecies and intraspecies variability) was applied to the NOAEL to 

obtain the RfD. EPA calculated a non-cancer HRL of 0.35 μg/L for terbufos using the RfD of 

0.00005 mg/kg/day for a 70 kg adult ingesting 2 L of drinking water per day and an RSC of 
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20%. The agency has not developed an RfD for terbufos sulfone because subchronic and chronic 

studies are not available. However, Bailey (1988) conducted a 14-day study of both terbufos and 

its sulfone degradate in dogs. The NOAEL based on ChE activity for terbufos sulfone was 

greater than the LOAEL of 2.5 mg/kg/day for the same endpoint following 14-day dosing with 

the parent compound terbufos. This suggests that the terbufos sulfone degradate is less toxic than 

its parent, and that the use of the terbufos HRL of 0.35 μg/L for the degradate, terbufos sulfone, 

is acceptable. The OPP RED (USEPA, 2006c) presents more detailed information about the 

health effects for terbufos and terbufos sulfone. 

c. Statutory Criterion #2 (Occurrence at frequency and levels of public health concern?) 

Terbufos and terbufos sulfone do not meet the SDWA statutory criterion #2 for 

regulatory determinations; they do not occur with a frequency and at levels of public health 

concern in public water systems based on EPA’s evaluation of the following occurrence 

information. 

The primary data for terbufos sulfone are nationally-representative finished water 

monitoring data generated through EPA’s UCMR 2 (2008-2010) (USEPA, 2012d2014d). UCMR 

2 collected 32,012 finished water samples from 4,138 PWSs (serving ~ 230 million people) and 

terbufos sulfone was detected in only one sample, at a concentration of 0.42 μg/L. The MRL was 

0.4 μg/L, which is slightly higher than the HRL (0.35 μg/L) (USEPA, 2012d). The primary data 

for terbufos are from the UCMR 1 screening survey (2001-2003) (USEPA, 2008c). The UCMR 

1 screening survey collected 2,301 finished water samples from 295 PWSs. Terbufos was not 

detected at levels at or above the MRL (0.5 μg/L), which is slightly higher than the HRL (0.35 

μg/L) (USEPA, 2008c). Finished water data for terbufos and terbufos sulfone from California, 

Iowa, USDA, and USGS are also consistent with the UCMR 1 and UCMR 2 data. The State of 
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California reported no detections of terbufos in 191 samples from 23 PWSs (see USEPA, 

2012b2014b). The State of Iowa reported no detections of terbufos sulfone from 13 wells (see 

USEPA, 2012b2014b). The USDA PDP monitored for terbufos (2,597 samples) and terbufos 

sulfone (2,923 samples) in finished water from 2001 to 2009 and reported no detections at or 

above method reporting levels ranging from 0.005 μg/L to 0.1 μg/L (USDA, 2012: USEPA, 

2012b2014b). The USGS PMP monitored for terbufos in finished water in 1999 and reported no 

detections, at or above their method reporting level of 0.013 μg/L (Blomquist et al., 2001). 

Terbufos and (very limited) terbufos sulfone occurrence data for ambient water from 

EPA, STORET, and several USGS programs or studies are consistent with those for finished 

water. The USGS NAWQA Program (1992-2001) reported no groundwater detections above the 

1⁄2 HRL (0.175 μg/L) or the HRL (0.35 μg/L) for terbufos in 20,960 samples at 7,118 sites. 

NAWQA reported surface water detections for terbufos in 28 of 14,480 samples (0.19%) at 20 of 

1,907 sites (1.05%). Of the 28 surface water detections for terbufos, only four samples (0.03%) 

at four sites (0.21%) were above the 1⁄2 HRL and only one sample (0.01%) at one site (0.05%) 

was above the HRL (Gilliom et al., 2007). The NAWQA Carbonate Aquifer Study (1993-2005; 

Lindsey et al., 2008) and the NAWQA Domestic Well Water Quality Study (1991-2004; 

DeSimone, 2009) reported no detections for terbufos above the 1⁄2 HRL or the HRL in 1,027 and 

2,539 samples, respectively. The NAWQA National Synthesis Program (1992-2001) reported no 

groundwater detections for terbufos above the 1⁄2 HRL or the HRL and one surface water 

detection (0.56 μg/L), from agricultural sites, above the HRL (Gilliom et al., 2007). 

Ambient water data from a two phase USGS study conducted between 2002 and 2005 by 

Hopple et al. (2009) and Kingsbury et al. (2008) reported no terbufos detections in the 221 Phase 

1 groundwater samples nor the 146 Phase 1 surface water samples. In Phase 2, there were no 
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detections of terbufos from 48 raw and 48 finished groundwater samples. Ambient water data 

from a USGS study conducted between 1993 and 2007 by Toccalino et al. (2010) reported no 

terbufos detections in 898 groundwater samples. 

Terbufos ambient data reported in EPA’s OPP RED for Terbufos (USEPA, 2006c) 

document included 20 detections in 4,563 groundwater samples from 13 States. The detections 

ranged from 0.01 to 20 μg/L, a range that extends both above and below the 1⁄2 HRL (0.175 

μg/L) and the HRL (0.35 μg/L). The USGS PMP monitored for terbufos in ambient water in 

1999 and reported no detections (Blomquist et al., 2001). 

Terbufos ambient data are reported in STORET from 17 States (USEPA, 2012f2012b). 

No groundwater detections were reported in 699 samples at 441 sites. STORET reported surface 

water detections in 457 of 5,826 samples (7.84%) at 138 of 625 sites (22.1%). Of the 457 surface 

water detections, only 23 samples (0.39%) at 14 sites (2.24%) were above the 1⁄2 HRL and only 

two samples (0.03%) at two sites (0.32%) were above the HRL. 

d. Statutory Criterion #3 (Meaningful Opportunity?) 

 Terbufos and terbufos sulfone do not meet the SDWA statutory criterion #3 for 

regulatory determinations; regulation of terbufos and terbufos sulfone do not present a 

meaningful opportunity for health risk reduction based on the estimated population exposed, 

including sensitive populations. The estimated population exposed to terbufos at or above the 

MRL is 0%; the compound was not found to occur in finished water at levels greater than or 

equal to the MRL (0.4 μg/L), which is slightly higher than the HRL (0.35 μg/L), in 2,301 

samples from 295 PWSs in UCMR 1 (USEPA, 2008c). The estimated population exposed to 

terbufos sulfone at a level of public health concern (based on the HRL for terbufos) is 44,600 

(0.02% of the population served by PWSs); there was only one detection greater than the HRL in 
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4,138 PWSs (1 of 32,012 samples in UCMR 2) (USEPA, 2012d2014d). As a result, the agency 

finds that an NPDWR does not present a meaningful opportunity for health risk reduction. 

EPA also evaluated whether health information is available regarding the potential health 

effects on children and other sensitive populations. Developmental studies with terbufos in rats 

and rabbits did not find any developmental effects (USEPA, 2003c). There are no data on 

reproductive and developmental effects for terbufos sulfone. No sensitive populations were 

identified or characterized. The OPP RED (USEPA, 2006c) presents more detailed information 

about the potential health effects and sensitive populations for terbufos and terbufos sulfone. 

e. Preliminary Regulatory Determination 

The agency is making preliminary determinations to not regulate terbufos and terbufos 

sulfone with NPDWRs after evaluating health, occurrence, and other related information against 

the three SDWA statutory criteria. While the data suggests that terbufos and terbufos sulfone 

may have adverse effects on human health, the occurrence data indicate there is no substantial 

likelihood that terbufos or terbufos sulfone will occur in PWSs with a frequency and at levels of 

public health concern. Therefore, the agency finds that NPDWRs for terbufos and terbufos 

sulfone would not present meaningful opportunities to reduce health risk for persons served by 

PWSs. The Regulatory Determinations 3 Support Document (USEPA, 2012b2014b) presents 

additional information and/or analyses supporting the agency’s evaluation of terbufos and 

terbufos sulfone. 

V. What is the Status of the Agency’s Evaluation of Chlorate and Nitrosamines? 

 The agency will review the existing MDBP regulations as part of the SY3. Because 

chlorate and nitrosamines are DBPs that can be introduced or formed in public water systems 

partly because of disinfection practices, the agency believes it is important to evaluate these 
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unregulated DBPs in the context of the review of the existing DBP regulations. DBPs need to be 

evaluated collectively, because the potential exists that the chemical disinfection used to control 

a specific DBP could affect the concentrations of other DBPs. Therefore, the agency is not 

making a regulatory determination for chlorate and nitrosamines at this time. The agency expects 

to complete the review of these DBPs by the end of 2015. 

A. Chlorate 

 The following sections provide the background, health and occurrence information/data 

that the agency has collected to date for chlorate. If the public has any additional health and 

occurrence information that may be useful as the agency evaluates chlorate in the context of the 

existing MDBP rules, please provide this information to the docket. 

1. Background 

The chlorate anion (ClO3

-

) forms a variety of salts (e.g., sodium chlorate, calcium 

chlorate, potassium chlorate, and magnesium chlorate) collectively known as chlorates, which 

are powerful oxidizers. Chlorate compounds (especially sodium chlorate) are used as herbicides 

and to generate chlorine dioxide (ClO2) as a bleaching agent (USEPA, 2006a). Disinfection 

practices are the most important source of chlorate in drinking water; this includes formation as a 

DBP from use of chlorine dioxide and its presence in hypochlorite disinfectants as an impurity 

(USEPA, 2006a). 

Chlorate can be formed during decomposition of hypochlorite (ClO-

) solutions, which are 

used as a disinfectant and/or oxidant in water treatment. Hypochlorite solutions that are more 

aged are generally less effective and require higher doses to achieve the treatment (disinfection) 

objectives, which can result in more chlorate to be introduced into the chlorinated water. In 

addition to being a DBP (along with chlorite) formed from the use of chlorine dioxide as a 
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disinfectant, chlorate ion may also be present as an impurity in the chlorine dioxide (Gates et al., 

2009; USEPA, 2006a). Chlorate can also form by the reaction of chlorite with free chlorine 

applied as a residual disinfectant in the distribution system (Gallagher et al., 1994). In addition, 

chlorite can be oxidized by a strong oxidant (such as ozone) to produce chlorate in the water 

(von Gunten, 2003). Chlorate salts readily dissolve in water and are highly mobile because of the 

absence. In the absence of redox reactions, the chlorate ion would be expected to partition 

predominantly into water and to be highly mobile in water. However, under most environmental 

conditions chlorate is subject to redox reactions, which are expected to reduce the concentration 

of chlorate in the water column (USEPA, 2006a). 

2. Health Effects Information 

Acute ingestion of high levels of sodium chlorate has resulted in acute kidney failure and 

hemolysis among other effects based on numerous case reports of individuals accidently 

ingesting high levels of chlorate compounds (USEPA, 2006b; WHO, 2005). A population-based 

case-control study of chlorate as a DBP at concentrations >200 μg/L identified significantly 

increased odds ratios for obstructive urinary defects, cleft palate, and spina bifida (Righi et al., 

2012). The median chlorate exposure for the study population was 280 μg/L. In a case-control 

study of the same population in Italy, Aggazzotti et al. (2004) found no association between 

preterm births and exposure to chlorate. 

 The animal studies provide clear and consistent evidence that subchronic and chronic 

exposure to chlorate results in effects on blood and thyroid. Subchronic studies in rats have 

reported decreased hemoglobin, hematocrit, and red blood cell (RBC) counts (Abdel-Rahman et 

al., 1984; Barrett, 1987; McCauley et al., 1995) and thyroid colloid depletion, follicular cell 

hypertrophy and hyperplasia (Hooth et al., 2001). 
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 A chronic study based on increased thyroid gland follicular cell hypertrophy in male rats 

(NTP, 2005a) was identified as the critical study for establishing an RfD of 0.03 mg/kg/day 

(USEPA, 2006b). The RfD was derived by using the BMD method and based on the lower 95% 

confidence limit (BMDL) of 28 mg/L as sodium chlorate (22 mg/L as chlorate), corresponding to 

0.9 mg/kg/day (USEPA, 2006b), with a composite UF of 30 for intraspecies (i.e., sensitive 

populations) and interspecies variability (i.e., thyroid hormone differences between humans and 

rats). EPA calculated a non-cancer HRL of 210 μg/L for chlorate using the RfD of 0.03 

mg/kg/day for a 70 kg adult ingesting 2 L of drinking water per day and an RSC of 20%. 

A cancer risk assessment was not conducted for chlorate because sodium chlorate is 

classified as not likely to be carcinogenic to humans at doses that do not alter thyroid hormone 

homeostasis under the USEPA (2005b) Cancer Guidelines. The RfD is protective against acute 

alterations in thyroid homeostasis and therefore considered to also be protective of 

tumorigenicity as well as other chronic and subchronic adverse health effects discussed in the 

literature (Hooth et al., 2001; Khan et al., 2005; NTP, 2005a). 

 EPA also evaluated whether health information is available regarding sensitive 

populations. According to the OPP RED, there was no pre- or postnatal sensitivity or 

susceptibility observed in the submitted developmental studies in rats and rabbits or the 2-

generation reproduction study in rats. However, there is a concern for developing offspring 

because of the effects of inorganic chlorate on thyroid function in rats (USEPA, 2006a). Chlorate 

is one of a number or inorganic ions that may interfere with iodine uptake by the thyroid, but 

chlorate is not highly potent in this respect (Van Sande et al., 2003). 

Chlorate may also cause hemolysis, thus persons with low red blood cell counts such as 

those with anemia may be particularly sensitive to sodium chlorate. Data from the 1994 National 
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Health Interview Survey (O’Day et al., 1998) indicate that there were about 5 million people in 

the U.S. who suffered from some form of anemia. About 3 to 5 % of the population may have an 

inherited glucose-6-phosphate dehydrogenase (G6PD) deficiency, with males more sensitive 

than females (Luzzatto and Mehta, 1989), and about 1% may have a form of hereditary 

methemoglobinemia (Jaffe and Hultquist, 1989). Each one of these conditions is a contributor to 

low red blood cell counts within the population. Individuals co-exposed to other ions that 

decrease iodine uptake by the thyroid or have low RBC counts may be more sensitive to chlorate 

exposure.

3. Occurrence Data and Information 

a. Drinking Water 

The 1997-1998 DBP ICR is currently the best available data source for characterizing the 

national occurrence baseline for chlorate. The DBP ICR, which included monitoring data for 296 

water systems serving 100,000 people or more (representing a total population of 130 million), 

required water systems that use hypochlorite solutions or chlorine dioxide for disinfection to 

monitor for chlorate (USEPA, 1996). Subsequently, 82 water systems serving approximately 40 

million people monitored and reported chlorate occurrence under the DBP ICR (using a 

detection limitan MRL of 20 μg/L). Table 9 presents the number and percentage of samples and 

systems (along with the population served) that measured chlorate at levels exceeding the 

specified threshold concentrations (i.e., HRL and 1⁄2 HRL). These samples were associated with 

41.5% (34 of 82) of the ICR systems using hypochlorite solutions or chlorine dioxide for 

disinfection and 11.5% (34 of 296) of all of the ICR systems. EPA assumes there was no 

occurrence of chlorate among the ICR systems that were not required to monitor for it, since they 

use disinfection techniques not expected to produce chlorate. Approximately 51.1% (878 of 
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1,719) of ICR samples from the finished water or distribution system of the systems required to 

monitor had chlorate at levels greater than the 1⁄2 HRL (105 μg/L) and 19.3% (332 of 1,719) had 

chlorate at levels greater than the HRL (210 μg/L). The samples greater than the 1⁄2 HRL were 

associated with 73.2% (60 of 82) of the ICR systems using hypochlorite solutions or chlorine 

dioxide for disinfection and 20.3% (60 of 296) of all ICR systems (including those that were not 

required to monitor for chlorate). The samples greater than the HRL were associated with 41.5% 

(34 of 82) of the ICR systems using hypochlorite solutions or chlorine dioxide for disinfection 

and 11.5% (34 of 296) of all ICR systems (including those that were not required to monitor for 

chlorate) (McGuire et al., 2002). 

Since the DBP ICR was completed in 1998, these data likely underestimate current 

(2012) chlorate occurrence among the systems serving 100,000 people or more for the following 

two reasons: (1) some of these systems may have changed the disinfectant type from chlorine gas 

to chlorine dioxide for compliance with the existing Stage 1 or Stage 2 DBP rules; and/or (2) 

some systems may have switched from chlorine gas to hypochlorite solution due to a security 

concern (i.e., a concern of safety of transportation and storage for chlorine gas). Disinfection 

surveys conducted by the AWWA Disinfection Systems Committee in 1998 and 2007 have 

confirmed that chlorine dioxide and hypochlorite use has increased (AWWA Disinfection 

Systems Committee, 2008a, 2008b; Connell et al., 2000a, 2000b). 

Table 9. Summary of Chlorate Monitoring Results under the DBP ICR

Chlorate 

Threshold 

Of DBP ICR PWSs that monitored 

for Chlorate, Samples and PWSs 

with at Least One Detection > 

Threshold* 

Of All DBP ICR PWSs, PWSs with 

at Least One Detection > 

Threshold and Estimated 

Population Served** 
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Number 

(Percentage) of 

DBP ICR 

Samples with 

Detection > 

Threshold 

Number 

(Percentage) of 

DBP ICR PWSs 

with at Least 

One Detection > 

Threshold 

Number 

(Percentage) of 

DBP ICR PWSs 

with at Least 

One Detection > 

Threshold* 

Population 

Served by DBP 

ICR PWSs with 

at Least One 

Detection > 

Threshold* 

HRL 

(210 μg/L) 

332 of 1,719 

(19.3%) 

34 of 82 

(41.5%) 

34 of 296 

(11.5%) 

11.8 of 130 

million 

(9.1%) 

1⁄2 HRL 

(105 μg/L) 

878 of 1,719 

(51.1%) 

60 of 82 

(73.2%) 

60 of 296 

(20.3%) 

31.7 of 130 

million 

(24.4%) 

* 82 PWSs that used hypochlorite or chlorine dioxide were required to monitor for chlorate during the DBP 

ICR monitoring period, based on their potential to form chlorate. Number and percentage of samples and 

PWSs are based on those 82 PWSs that monitored for chlorate. 

** The number and percentage of PWSs and population served > threshold is based on all 296 systems. EPA 

assumes that the 214 systems not required to monitor do not have chlorate concentrations above the 

thresholds.

Finished water data for chlorate from California collected between 2001 and 2007 show 

lower occurrence compared to the DBP ICR. The State of California reported results from testing 

more than 1,200 drinking water samples from 45 PWSs and chlorate was detected in 945 

samples (78.4 %) from 24 different systems (53.3 %) (Ranalli, B., 2013). Approximately 41.6 % 

(501 of 1,205) of samples from 17 systems (37.8 %) had chlorate at levels greater than the 1⁄2 

HRL (105 μg/L) and approximately 12.4 % (149 of 1,205) of samples from 10 systems (22.2 %) 

had chlorate at levels greater than the HRL (210 μg/L) (Ranalli, B., 2013). 

It is important to note that the agency included chlorate in the UCMR 3, which is 

currently in process. UCMR 3 will provide a national dataset of chlorate occurrence in drinking 

water and will update the occurrence data provided by the DBP ICR. 

Ambient water data for chlorate are limited, but chlorate could be present in areas where 

it is used as an herbicide or discharged from paper plants where it is used as a bleaching agent. 
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Since chlorate is a DBP, higher concentrations are expected in finished water than in ambient 

water. 

b. Exposure from media other than water 

There is very little quantitative information available on the occurrence of chlorate in 

food, air, and soil or other products resulting in residential exposures. Without reliable estimates 

of intakes, it is not possible to estimate the contribution of drinking water to total exposure. 

However, based on modeling results, the agency estimated that the chlorate intake from food (as 

a result of sodium chlorate use as a pesticide) for the overall population is approximately 3

μg/kg-day, with somewhat higher intakes for children under five years old of approximately 5 to 

8 μg/kg-day (USEPA, 2006a). Additional food exposure from use of sanitizing solutions in food 

preparation plants (e.g., equipment and contact surfaces) and processing (e.g., bleaching agent) 

may also be a source of exposure (21CFR section 178.1010). Intake for adults from dietary 

supplements containing chlorate may range from 0.001 to 0.29 μg/kg-day. 

 B. Nitrosamines group (6 nitrosamines)

 The following sections provide the background, health and occurrence information/data 

that the agency has collected to date for nitrosamines. If you have any additional health and 

occurrence information that may be useful as the agency evaluates nitrosamines in the context of 

the regulatory review of existing MDBP rules, please provide this information to the docket. 

1. Background 

Nitrosamines are a class of nitrogen-containing organic compounds that share a common 

nitrosamino functional group (HSDB, 2010). EPA included five nitrosamine compounds on the 

CCL 3: N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodi-npropylamine (NDPA), N-nitrosopyrrolidine (NPYR), and N-nitrosodiphenylamine (NDPhA). 
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EPA monitored six nitrosamines under UCMR 2 using EPA Analytical Method 521, four of 

which are CCL 3 compounds (i.e., NDMA, NDEA, NDPA, NPYR), and two non-CCL 3 

nitrosamines [i.e., N-nitrosomethylethylamine (NMEA) and N-nitrosodi-n-butylamine (NDBA)]. 

The fifth CCL 3 nitrosamine compound, NDPhA, was not monitored under UCMR 2 due to lack 

of a reliable analytical method. Although other nitrosamines (e.g., N-nitrosomorpholine, Nnitrosopiperidine) have been identified in finished water (Mitch et al., 2009), they were also not 

included in UCMR 2 for similar analytical reasons. The nitrosamines from the UCMR 2 thus 

comprise the list of six nitrosamines that moved forward to the data evaluation phase of 

regulatory determination and are the focus of the information that follows below. 

All six nitrosamines may be produced in small quantities for research purposes, but only 

one (NDEA) is currently produced commercially in the United States. NDEA is used as an 

additive in gasoline and in lubricants, as an antioxidant, and as a stabilizer in plastics, though no 

data are available about quantities used (HSDB, 2010). NDMA was once used in the production 

of rocket fuel, as a solvent, and as a rubber accelerator. It was also used or proposed for use as an 

antioxidant, an additive for lubricants, and a softener for copolymers (ATSDR, 1989). There are 

no production data on any of the nitrosamine compounds from EPA’s Inventory Update 

Reporting (IUR) program. 

NDMA can be formed as an unintended byproduct of manufacturing processes that 

involve the use of nitrite or nitrate and amines, including tanneries, fish processing plants, 

foundries, and pesticide, dye, rubber or tire manufacturing plants (ATSDR, 1989). Nitrosamines 

have been found in tobacco products, cured meats, ham, bacon, beer, whiskey, fish, cheese, 

soybean oil, toiletries, household cleaners, pesticides, rubber baby bottle nipples and pacifiers 
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(ATSDR, 1989; Drabik-Markiewicz et al,. 2009; Fine et al., 1977; NTP, 2011; Pérez et al., 2008; 

Yurchenko and Mölder, 2007). 

NDMA is commonly present in municipal sewage sludge (ATSDR, 1989). NPYR has 

also been detected in municipal sewage sludge (HSDB, 2010). ATSDR (1989) cites several 

studies indicating that nitrosamine formation in sewage sludge appears to be the result of 

biological and chemical transformation of alkylamines in the presence of nitrite. In addition, 

nitrosamines may form in air, soil, water, sewage, food, animal systems and other media where 

precursors (e.g., amines and nitrite) are present (HSDB, 2010). NDMA can be produced 

endogenously in humans from the interaction of nitrates and nitrites with amines in the stomach 

(Mirvish 19741975, 1992; Tricker et al., 1994). 

 As described in the following occurrence section, nitrosamines in finished water are 

commonly considered as DBPs because most of the literature indicates that the main source of 

nitrosamines in finished water is associated with water treatment, particularly from disinfection 

with chloramines. NDMA is the predominant species of nitrosamines found in finished water; 

other nitrosamines are detected less frequently. Based on their physical and chemical properties, 

the nitrosamines appear to be moderately to very mobile in the environment (the exception being 

NDBA, which is of low mobility). The nitrosamines are subject to a variety of removal mechanisms 

when present in soil and water, including volatilization (particularly NDMA), photodegradation, and 

microbial degradation, although the rates and extent of biodegradation are highly variable (HSDB, 

2010).

2. Health Effects Information 

As the more thoroughly studied nitrosamine compared to the other nitrosamine 

compounds, NDMA provides epidemiological case-control and other evidence that human 
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nitrosamine exposure is associated with an increased risk of several types of cancer, including 

cancer of the stomach, esophagus, oral cavity, and pharynx (La Vecchia et al., 1995; Larsson et 

al., 2006; Loh et al., 2011; Straif et al., 2000). In accordance with the most recent Guidelines for 

Carcinogen Risk Assessment (USEPA, 2005b), EPA has categorized the six nitrosamine 

compounds as likely to be carcinogenic to humans based on sufficient evidence of 

carcinogenicity in animal studies with multiple tumor types (predominately liver and esophageal) 

in multiple animal species (e.g., rats, mice, and hamsters) (Clapp et al., 1968, 1971; Druckrey et 

al., 1967; Lijinsky, 1987a, 1987b; Peto et al., 1991a, 1991b;). TheAll of the six nitrosamines 

have also been determined to cause cancer through a mutagenic MOA because of DNA adduct 

formation leading to errors in DNA replication, altered cell proliferation and ultimately tumors 

(Diaz Gomez et al., 1986; Goto et al., 1999; Jarabek et al., 2009; Souliotis et al., 1998). The 

mutagenic MOA is supported by positive findings from mutagenicity and genotoxicity in vitro

and in vivo studies (Gollapudi et al., 1998; Kushida et al., 2000; Martelli et al., 1988, Robbiano 

et al., 1996, Tinwell et al., 1994). 

With a mutagenic MOA, Age Dependent Adjustment Factors (ADAFs) are used to 

account for the potential increased cancer risk due to early-life exposure for infants and children 

(USEPA, 2005c). The age-adjusted unit risk is determined by summing up each of the timeweighted unit risks for the three ADAF developmental groups. The age-adjusted unit risks 

include a ten-fold adjustment for birth to < 2 years, a three-fold adjustment for 2 years to < 16 

years, and no additional adjustment for exposures later in life, in conjunction with age-specific 

drinking water intake values (USEPA. 2012g2012c), and the fraction of a 70-year lifetime 

applicable to each age period. The main cancer risk values used to derive the HRLs are further 

explained in section III.C.1 and are also summarized for nitrosamines in Table 10 below. 
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Table 10. EPA Derived Risk Values and HRLs for the Six Individual Nitrosamines

Nitrosamines 

Studies for 

Establishing a 

Slope Factor 

Cancer Slope 

Factor 

(mg/kg-/day)-

1

1

AgeAdjusted 

Unit 

Risk 

(μg/L)-1

2

HRL 

(μg/L) 

3

HRL 

(ng/L)

NDBA Liver and 

esophageal tumors 

in rats 

(Druckrey et al., 

1967) 

0.4 3.0 x 10-5 3 x 10-2 30 

NDEA Liver and 

esophageal tumors 

in rats (Peto et al., 

1991a,b) 

30 2.3 x 10-3 4 x 10-4 0.4 

NDMA Liver tumors in rats 

(Peto et al., 

1991a,b) 

21 1.6 x 10-3 6 x 10-4 0.6 

NDPA Liver and 

esophageal tumors 

in rats (Druckrey et 

al., 1967) 

2 1.5 x 10-4 7 x 10-3 7 

NMEA Liver tumors in rats 

(Druckrey et al., 

1967) 

4 3.0 x 10-4 3 x 10-3 3 

NPYR Liver tumors in rats 

(Peto et al., 1984) 

7 5.3 x 10-4 2 x 10-3 2 

1

 Based on the recommendations of the U. S EPA’s 2005 Supplemental Guidance for Assessing 

Susceptibility from Early-Life Exposure to Carcinogens, the Unit Risk applicable to exposures 

beginning in early-life was adjusted with ADAFs and age-specific drinking water intakes resulting 

in a lifetime value of unit risk for exposure to 1 μg/L of a contaminant. The calculation for AgeAdjusted Unit Risk = ∑(CSF x ADAF x DWI/BWR x CW x F). The risk calculations for each 

individual nitrosamine can be found in the HESDs. 

2

 The cancer HRL is determined by dividing the population risk level, one-in a million (10-6), by 

the age-adjusted unit risk. 

3

 The nitrosamine HRL values are converted to ng/L units by multiplying the μg/L values by 1000. 

 As shown in table 10, the available data indicate a range of cancer risk values for the 

individual nitrosamines. Moreover, when multiple nitrosamines from this group are present in 

finished water together, their individual cancer risks are additive (Berger et al., 1987). 
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EPA also evaluated whether health information is available regarding sensitive 

populations. The fetus, newborns, and infants may be potentially sensitive to the carcinogenic 

effects of nitrosamines due to the mutagenic MOA and evidence of transplacental 

carcinogenicity (Althoff et al., 1977; Donovan and Smith, 2008;).). Studies have found that 

younger rats were more susceptible to the development of liver tumors compared to rats exposed 

later in life to nitrosamines (Gray et al., 1991; Peto et al., 1984; Vesselinovitch et al., 1984). 

EPA’s Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to 

Carcinogens (USEPA, 2005c) indicates that potential increased cancer risk due to early-life 

exposure should be taken into account for such compounds when there is the potential for greater 

susceptibility for structural changes to DNA leading to tumors when the exposures occur in 

infancy or childhood. Thus, the Supplemental Guidance (USEPA, 2005c) recommends using 

CSF estimates from chronic studies with ADAFs when chemical-specific data that quantify the 

potential increased risk are lacking. All of the HRLs are based on lifetime exposure and include 

application of ADAFs, which adjust for the increased risk from early life exposure (see section 

III.C.1). 

 In addition, habitual consumers of alcoholic beverages may be more susceptible to 

carcinogenic effects of nitrosamines because alcohol increases the metabolism of nitrosamines 

via a metabolic pathway that leads to the formation of mutagenic DNA adducts. Co-exposure to 

ethanol has been shown to exacerbate the cancer effects of nitrosamines in animal studies 

(Anderson et al., 1993; Kamataki et al., 2002; McCoy et al., 1986). There are approximately five 

million people in the U.S. who suffer from alcoholism (O’Day et al., 1998) that may have an 

increased risk if co-exposed to nitrosamines (Amelizad et al., 1989; Verna et al., 1996). 
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3. Occurrence Data and Information 

The data collected under UCMR 2 (USEPA, 2012d2014d) are currently the best available 

data for characterizing the national occurrence baselines for the six nitrosamines. Under UCMR 

2, PWSs were required to collect a sample at each entry point to the distribution system as well 

as at the maximum residence time locations within the distribution system associated with each 

entry point, and to report the disinfectant type in use at these locations at the time that the 

samples were being taken. The agency was unable to measure at the HRL for some of the 

nitrosamines. Therefore, Table 11 presents all of the monitoring results for each of the six 

nitrosamines relative to the MRLs. 

Table 11. Summary of UCMR 2 Monitoring Results for Six Nitrosamines 

Nitrosamines 

Considered 

Under RD 3 

 MRL 

Percentages 

(Number) of 

Samples with 

Detection 

Percentages 

(Number) of 

UCMR 2 PWSs 

with at Least 

One Detection 

Percentages 

(Number) of Actual 

UCMR 2 Population 

Served with at Least 

One Detection* 

Nitrosamine 

Group 

2 to 7 

ng/L 

 10.6% 

(1,907 of 18,053) 

 28.6% 

(343 of 1,198) 

46.43% 

(73 of 157 million) 

NDBA 4 ng/L 0.05% 

(9 of 18,043) 

0.4% 

(5 of 1,198) 

1.07% 

(1.7 of 157 million) 

NDEA 5 ng/L 0.3% 

(46 of 18,038) 

2.2% 

(26 of 1,198) 

7.14% 

(11.2 of 157 million) 

NDMA 2 ng/L 10.2% 

(1,841 of 18,040) 

 27.0% 

(324 of 1,198) 

41.54% 

(65.3 of 157 million) 

NDPA 7 ng/L 

0% 

(0 of 18,049) 

0% 

(0 of 1,198) 

0% 

(0 of 157 million) 

NMEA 3 ng/L 0.02% 

(3 of 18,043) 

 0.3 

(3 of 1,198) 

0.003% 

(0.004 of 157 million) 

NPYR 2 ng/L 0.2% 

(41 of 18,043) 

 1.8% 

(21 of 1,198) 

4.73% 

(7.4 of 157 million) 

* The population-served values have been adjusted to include both the population served directly by 

a system and also the estimated attributable proportion of the population served by other systems 

that purchase water from the system. These adjustments are described in the UCMR 2 support 

document. 
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Finished water data for the nitrosamines from California (Ranalli, B., 2013) are 

consistent with the UCMR 2 data. The State of California reported NDMA detections in 23.8% 

(24 of 101) of PWSs and NDEA detections in 7.1% (1 of 14) of PWSs. There were no NPYR, 

NDPA, NMEA, or NDBA detections reported. Reporting levels are not known. For California 

data on NDMA and NDEA, the minimum reported detections were 1 ng/L and 30 ng/L, 

respectively. NDBA, NDPA, NMEA, and NPYR had no detections and thus no minimum 

reported value in the dataset (Ranalli, B., 2013). While ambient water data for the nitrosamines 

are limited, because they are DBPs, it is expected that in general there would be higher 

concentrations in finished water than in ambient water. 

V. What About the Remaining CCL 3 Contaminants? 

 For the remaining CCL 3 contaminants, the agency lacked adequate health and/or 

occurrence information needed to address the three SDWA statutory criteria to make a regulatory 

determination. Table 2 and Table 4 of this notice provide information about the data or 

information gap(s) that prevented the contaminant from moving forward for this regulatory 

determination effort. The agency continues to conduct research, collect information or find other 

avenues to fill the data and information gaps identified in Table 2 and 4. One mechanism the 

agency plans to continue to use to fill occurrence gaps for several of these contaminants is the 

UCMR. 

VI. EPA's Next Steps
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 EPA intends to carefully evaluate and respond to the public comments received on the 

five preliminary determinations and issue its final regulatory determinations in 2015. If the 

agency makes a final determination to regulate any of the contaminants, EPA will begin the 

process to propose an NPDWR within 24 months and promulgate a final NPDWR within 18 

months following the proposal. 

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between Asian text and numbers, Tab stops: Not at 

-0.88" + -0.5" + 0" + 0.5" + 0.88" + 1.5" + 2" + 2.5"

+ 3" + 3.5" + 4" + 4.5" + 5" + 5.5" + 6" + 6.5" + 7"

+ 7.5" + 8" + 8.5" + 9" + 9.5" + 10" + 10.5" + 11" + 

11.5" + 12" + 12.5" + 13"
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for the Third Contaminant Candidate List Stakeholder Meeting, June 16, 2011. 

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Protection Agency, Washington, DC, EPA/600/R-09/052F. 

 

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February 2012.

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Regulation (UCMR 2).

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February 2012.

USEPA. 2014b. Regulatory Determinations 3 Support Document. 

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USEPA. 2014c. Health Effects Support Document for Strontium.

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United States Geological Survey (USGS). 2007. Pesticide National Synthesis Project, 2002 

Pesticide Use Maps. Available on the Internet at: 

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symporter. Endocrinology. 144(1): 247-252. 

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Vesselinovitch, S.D., M. Koka, N. Mihailovich, and K.V.N. Rao. 1984. Carcinogenicity of 

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Dated: 

Gina A. McCarthy, 

Administrator. 

Appendix A: HRL Derivation with Age‐Related Exposure Factors

Derivation of the Health Reference Level (HRL) for Strontium using AgeSpecific Exposure Factors 

Age Range 

DWI/BWR 

(L/kg/day) 

Age-Specific Fractions 

of a 19-Year Exposure 

Duration 

Time-Weighted 

DWI/BWR 

(L/kg/day) 

Birth to < 1 month 0.235 0.004 0.001 

1 to <3 months 0.228 0.009 0.002 

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3 to <6 months 0.148 0.013 0.002 

6 to <12 months 0.112 0.026 0.003 

1 to <2 years 0.056 0.053 0.003 

2 to <3 years 0.052 0.053 0.003 

3 to <6 years 0.043 0.158 0.007 

6 to <11 years 0.035 0.263 0.009 

11 to <16 years 0.026 0.263 0.007 

16 to <18 years 0.023 0.105 0.002 

18 to <21 years# 0.026 0.053 0.001 

Summation of the Time-Weighted DWI/BWRs = 0.040 L/kg/day* 

Reference Dose= 0.3 mg/kg/day 

RSC= 20% +HRL = (0.3 mg/kg/day ÷ 0.040 L/kg/day) x .20 = 1.500 mg/L 

Final child specific HRL: 1500 μg/L 

*Rounded; # includes 18th year; DWI/BWR = drinking water intake to body weight ratio; HRL= health 

reference level; RSC = relative source contribution 

+ HRL = (RfD / ∑(DWI/BWR x F)) x RSC

The age-specific data on drinking water intakes in units of L/kg/day from birth through age 3 are 

from Table 3-19 in the EPA Exposures Factors Handbook (2011e) and from Table 3-38 for ages 

3 to <19 . The exposure duration adjustment was calculated by dividing the age-specific fraction 

of a 19 year exposure by the total exposure in months or years as appropriate (e.g., birth to <1 

month = (1/12)/19 years = 0.00439; 6 to <11 years = 5/19 years = 0.26316). The time-weighted 

DWI/BWR values are the product of the age-specific DWI/BWR multiplied by the age–specific 

fraction of a 19 year exposure. The time-weighted DWI/BWRs are summed to obtain the 

normalized value.