Regulatory 

Determination 3 

Support Document
Office of Water (4607M)

EPA 815-R-14-003 

April 2014

http://water.epa.gov/drink/
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Disclaimer

This document is designed to provide technical background information for the 

Environmental Protection Agency’s (EPA’s) third Regulatory Determination (RD 3) for drinking 

water contaminants under Safe Drinking Water Act (SDWA) provisions, based on the third 

Contaminant Candidate List (CCL 3).

This document is not a regulation itself, and it does not substitute for the SDWA or 

EPA’s regulations. Mention of trade names or commercial products does not constitute 

endorsement or recommendation for use. 
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Executive Summary

This document provides background information to support the U.S. Environmental 

Protection Agency’s (EPA’s) third Regulatory Determination (RD 3) for drinking water 

contaminants under the Safe Drinking Water Act (SDWA) provisions, based on the third

Contaminant Candidate List (CCL 3). The regulatory determinations are presented formally in 

the Federal Register. This report itself does not constitute a regulation or a formal determination.

This regulatory support document consists of an introductory chapter on the CCL 3 and 

RD 3 process (chapter 1), a chapter on data sources used to evaluate contaminants (chapter 2), 

and four chapters (chapters 3-6) devoted to the five contaminants EPA has selected for 

regulatory determination under RD 3: 1,3-dinitrobenzene, dimethoate, strontium, terbufos, and 

terbufos sulfone. (Terbufos and terbufos sulfone are discussed together in one chapter.)

EPA evaluates contaminants for regulatory determination based on three statutory 

criteria. Regulation with a national primary drinking water regulation (NPDWR) is warranted if: 

(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 (PWSs) 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 PWSs. 

In evaluating contaminants against these criteria, EPA gathered data and information on 

health effects and occurrence in public water systems, as well as physical and chemical 

properties, environmental fate and transport, formation (as applicable, e.g., in the case of 

disinfection by-products), and occurrence in ambient water. EPA also evaluated the availability 

of analytical methods and treatment technologies. The availability of treatment technologies is 

not taken into consideration when deciding whether regulation is warranted, but suitable 

technologies must be developed and available by the time an NPDWR is promulgated.

EPA has preliminarily determined that one of the five contaminants, strontium, meets all 

three criteria and warrants regulation with an NPDWR. EPA has preliminarily determined that 

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

do not satisfy all three criteria and do not warrant regulation at this time. Those decisions are 

presented formally in the Federal Register.

Chapters 3-6 of this document present and summarize the information and data gathered 

and used to evaluate the five contaminants. Since EPA understands that members of the public

with varied concerns might be more interested in certain contaminants and less interested in 

others, the document is designed in such a way that individual chapters are more or less selfcontained and can be distributed separately.

Additional documents produced to support the RD 3 process include a Health Effects 

Support Document for strontium, a UCMR 2 occurrence report, and a Regulatory Determination 

3 Protocol document that explains how the CCL 3 contaminants were evaluated and the five 

contaminants were selected for inclusion in RD 3.
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Contents

Disclaimer..........................................................................................................................................i

Executive Summary...........................................................................................................................iii

Contents.............................................................................................................................................v

Chapter 1: Introduction....................................................................................................1-1

Chapter 2: Evaluation of Health and Occurrence Data ...................................................2-1

Chapter 3: Dimethoate.....................................................................................................3-1

Chapter 4: 1,3-Dinitrobenzene.........................................................................................4-1

Chapter 5: Strontium........................................................................................................5-1

Chapter 6: Terbufos and Terbufos Sulfone .....................................................................6-1
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Chapter 1:

Introduction

A chapter from: 

Regulatory Determination 3 Support Document

EPA Report 815-R-14-003 
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Contents

Chapter 1: Introduction......................................................................................................................1-7

1.1 Purpose and Scope .................................................................................................................1-7

1.2 Background on the CCL and Regulatory Determinations.....................................................1-7

1.2.1 Statutory Requirements for CCL and Regulatory Determinations ................1-7

1.2.2 The First Contaminant Candidate List (CCL 1).............................................1-8

1.2.3 The First Regulatory Determination (RD 1) for CCL 1.................................1-9

1.2.4 The Second Contaminant Candidate List (CCL 2) ........................................1-9

1.2.5 The Second Regulatory Determination (RD 2) for CCL 2 ............................1-9

1.2.6 National Drinking Water Advisory Council (NDWAC) Recommendations.1-10

1.3 The CCL Classification Process and the Third Contaminant Candidate List (CCL 3) .........1-10

1.4 Summary of the Approach Used to Identify and Evaluate Contaminants for Regulatory 

Determination 3 .....................................................................................................................1-12

1.5 Summary of Regulatory Determination 3..............................................................................1-15

1.6 References..............................................................................................................................1-15
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Exhibits

Exhibit 1-1: General Overview of the Approach Used to Establish CCL 3 ......................................1-11

Exhibit 1-2: General Overview of the Approach Used to Evaluate CCL 3 Contaminants for 

Regulatory Determination 3..............................................................................................1-13
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Abbreviations

ATSDR Agency for Toxic Substances and Disease Registry

CCL Contaminant Candidate List

CCL 1 First Contaminant Candidate List

CCL 2 Second Contaminant Candidate List

CCL 3 Third Contaminant Candidate List

CCLCP Work 

Group

Work Group on the Contaminant Candidate List Classification 

Process

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

EPA Environmental Protection Agency

EPTC S-ethyl dipropylthiocarbamate

FR Federal Register

HRL Health Reference Level

IRIS Integrated Risk Information System

MCL Maximum Contaminant Level

MCLG Maximum Contaminant Level Goal

NAS National Academy of Sciences

NCOD National Contaminant Occurrence Database

NDWAC National Drinking Water Advisory Council

NPDWR National Primary Drinking Water Regulation

NRC National Research Council

OGWDW Office of Ground Water and Drinking Water

OPP Office of Pesticide Programs

OW Office of Water

PCCL Preliminary Contaminant Candidate List

PCCL 3 PCCL for the Third Candidate Contaminant List

PWS Public Water System

RD 1 First Regulatory Determination

RD 2 Second Regulatory Determination

RD 3 Third Regulatory Determination

RED Reregistration Eligibility Decisions

SAB Science Advisory Board

SDWA Safe Drinking Water Act

SRMD Standards and Risk Management Division

TT Treatment Technique

UCMR 2 Second Unregulated Contaminant Monitoring Regulation

WHO World Health Organization
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Chapter 1: Introduction

1.1 Purpose and Scope

The 1996 Safe Drinking Water Act (SDWA) Amendments (section 1412(b)(1)) direct 

EPA to publish a list of currently unregulated contaminants that may pose risks for drinking 

water (referred to as the Contaminant Candidate List, or CCL) every five years and to make 

determinations on whether or not to regulate at least five contaminants from the CCL with a 

national primary drinking water regulation (NPDWR).

This document serves to support EPA’s third Regulatory Determination (RD 3), based 

on an evaluation of contaminants on the third Contaminant Candidate List (CCL 3). This 

regulatory determination support document provides:

• A summary of the statutory requirements, previous activities related to the CCL and 

regulatory determinations, and the approach used to select and evaluate CCL 3 

contaminants for RD 3,

• Background information on the data sources used to evaluate physical and chemical 

properties, use and environmental release, environmental fate, and occurrence and 

exposure for CCL 3 contaminants, and

• Detailed information and data on the physical and chemical properties, use and 

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

exposure estimates and a summary of the preliminary regulatory determinations

made by the agency for each of the five CCL 3 contaminant candidates.

The five regulatory determination candidates discussed in this document are: 

1,3-dinitrobenzene, dimethoate, strontium, terbufos, and terbufos sulfone. Additional detail on 

the process used to evaluate CCL 3 contaminants can be found in the Protocol for the Regulatory 

Determination 3 (USEPA, 2014a). Additional detail on the evaluation of health effects for

strontium, the one contaminant receiving a preliminary positive determination, can be found in 

the Health Effects Support Document for Strontium (USEPA, 2014b).

EPA understands that members of the public with varied concerns might be more 

interested in certain contaminants and less interested in others, therefore the document is 

designed in such a way that individual chapters are more or less self-contained and can be 

distributed separately. 

1.2 Background on the CCL and Regulatory Determinations

1.2.1 Statutory Requirements for CCL and Regulatory Determinations 

The statutory requirements for the CCL and regulatory determinations can be found in 

SDWA Section 1412(b)(1). The 1996 SDWA Amendments require EPA to publish the CCL 

every five years. The CCL is a list of contaminants that are not subject to any proposed or 

promulgated NPDWRs, are known or anticipated to occur in PWSs, and may require regulation 

under SDWA to protect public health. SDWA requires consultation with the scientific 

community, including EPA’s Science Advisory Board (SAB); opportunity for public comments; 

and consideration of the National Contaminant Occurrence Database (NCOD), established under 

section 1445(g) of the Act. The 1996 SDWA Amendments also direct EPA to determine whether 

or not to regulate at least five contaminants from the CCL every five years. There are three 
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criteria to be considered in making a regulatory determination. A decision to regulate is 

warranted if:

(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 PWSs 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 PWSs. 

If EPA determines that all three of these statutory criteria are met, it makes a preliminary 

positive regulatory determination that an NPDWR1 is needed. . Following a comment response 

period and a final positive regulatory determination, the agency has 24 months to publish a 

proposed Maximum Contaminant Level Goal2 (MCLG) and an NPDWR. After the proposal, the 

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

1412(b)(1)(E)).3 The agency may determine that there is no need for a regulation when a 

contaminant fails to meet one or more of the criteria. A decision not to regulate is considered a 

final agency action and is subject to judicial review. The agency can choose to publish a Health 

Advisory (a nonregulatory action) or other guidance for any contaminant on the CCL, 

independent of the regulatory determination.

1.2.2 The First Contaminant Candidate List (CCL 1) 

The 1996 SDWA Amendments required EPA to publish the first CCL (CCL 1) 18 

months after the date of enactment. Following the 1996 SDWA Amendments, EPA sought input 

from the National Drinking Water Advisory Council (NDWAC) on the process that should be 

used to identify contaminants for inclusion on CCL 1. For chemical contaminants, the agency 

developed screening and evaluation criteria based on recommendations from NDWAC. For 

microbiological contaminants, NDWAC recommended that the agency seek external expertise to 

identify and select potential waterborne pathogens. As a result, the agency convened an 

international panel of microbiologists and public health experts who developed criteria for 

screening and evaluation and subsequently developed an initial list of potential microbiological 

contaminants.

With the short time frame required, the first CCL was largely based on expert knowledge 

and the evaluation of readily available information. EPA did obtain beneficial input from the 

NDWAC, the scientific community, and the public through stakeholder meetings and the public 

comments received on the draft CCL 1 published on October 6, 1997 (62 FR 52193; USEPA, 

 

1 An NPDWR is a legally enforceable standard that applies to PWSs. 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.

2 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 nonenforceable health goals." (CFR 141.2)

3 The statute authorizes a nine month extension of this promulgation date.
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1997). EPA published the final CCL 1, which contained 50 chemical and 10 microbiological 

contaminants, on March 2, 1998 (63 FR 10273; USEPA, 1998). A more detailed discussion of 

how EPA developed CCL 1 can be found in the 1997 and the 1998 Federal Register notices (62 

FR 52193; USEPA 1997 and 63 FR 10273; USEPA 1998).

1.2.3 The First Regulatory Determination (RD 1) for CCL 1 

EPA published its preliminary regulatory determinations for a subset of contaminants 

listed on CCL 1 on June 3, 2002 (67 FR 38222; USEPA, 2002). The agency published its final 

regulatory determinations on July 18, 2003 (68 FR 42898; USEPA, 2003). EPA identified nine

contaminants from the 60 contaminants listed on CCL 1 that had sufficient data and information 

available to make regulatory determinations. The nine contaminants were Acanthamoeba, aldrin, 

dieldrin, hexachlorobutadiene, manganese, metribuzin, naphthalene, sodium, and sulfate. The 

agency determined that an NPDWR was not necessary for any of these nine contaminants. The 

agency did, however, issue guidance on Acanthamoeba and health advisories for manganese,

sodium, and sulfate.

The decision-making process that EPA used to make its regulatory determinations for 

CCL 1 was based on substantial expert input and recommendations from different groups 

including stakeholders, the National Research Council (NRC), and NDWAC. In June 2002, EPA 

consulted with the SAB Drinking Water Committee and requested its review and comment on 

whether the protocol EPA developed, based on the NDWAC recommendations, was consistently 

applied and appropriately documented. SAB provided verbal feedback regarding the use of the 

NRC and NDWAC recommendations in EPA’s decision criteria for making its regulatory 

determinations. SAB recommended that the agency provide a transparent and clear explanation 

of the process for making regulatory determinations. The agency took SAB’s recommendation 

into consideration and further explained the regulatory determination evaluation process in the 

2003 Federal Register notice (68 FR 42898; USEPA, 2003) and in the supporting 

documentation.

1.2.4 The Second Contaminant Candidate List (CCL 2) 

After completing CCL 1, the agency realized the need to develop an enhanced, more 

robust approach to evaluating the risk of potential drinking water contaminants for future CCLs. 

The agency requested assistance from the NRC for guidance on an approach to develop a more 

rigorous and expansive approach for the CCL. The NRC’s evaluation, and other assessments 

leading to an enhanced process, overlapped with the deadline requirements to produce CCL 2.

Hence, while EPA developed the more rigorous process, CCL 2 was based on the process used 

for CCL 1, and reflected the changes related to RD 1. The CCL 2 carried forward the 51 

chemical and microbial contaminants remaining on CCL 1 after RD 1. The agency published its 

draft CCL 2 Federal Register notice on April 2, 2004 (69 FR 17406; USEPA, 2004) and the final 

CCL 2 Federal Register notice on February 24, 2005 (70 FR 9071; USEPA, 2005).

1.2.5 The Second Regulatory Determination (RD 2) for CCL 2 

The agency published its preliminary regulatory determinations for contaminants listed 

on the CCL 2 Federal Register notice on May 1, 2007 (72 FR 24106; USEPA, 2007). In the May 

1, 2007 notice, EPA made preliminary determinations for 11 of the 51 contaminants listed on the 

CCL 2. These contaminants were: boron, the dacthal mono- and di-acid degradates, 1,1-

dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), 1,3-dichloropropene, 2,4-dinitrotoluene, 

2,6-dinitrotoluene, s-ethyl dipropylthiocarbamate (EPTC), fonofos, terbacil, and 

1,1,2,2-tetrachloroethane. The agency determined that an NPDWR was not necessary for any of 
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these 11 contaminants. EPA finalized those regulatory determinations on CCL 2 on July 30, 

2008 (73 FR 44251; USEPA, 2008a).

1.2.6 National Drinking Water Advisory Council (NDWAC) Recommendations

In March 2000, EPA convened a Working Group under the National Drinking Water 

Advisory Council (NDWAC) to help develop an approach for making regulatory determinations. 

The Working Group developed a protocol for analyzing and presenting the available scientific 

data and recommended methods to identify and document the rationale supporting a regulatory 

determination decision. The NDWAC Working Group report was presented to and accepted by 

the entire NDWAC in July 2000.

The Working Group developed separate but similar protocols for microorganisms and 

chemicals. The approach for chemicals was based on an assessment of the impact of acute, 

chronic, and lifetime exposures, as well as a risk assessment that includes evaluation of 

occurrence, fate, and dose-response. The NDWAC protocol for chemicals provided a semiquantitative, systematic approach for addressing each of the three Regulatory Determination 

criteria. EPA utilized NDWAC suggestions for Regulatory Determinations 1, 2, and 3. The RD 3 

process was formalized in a Protocol document that was reviewed by an expert panel in October, 

2011, and revised in response to reviewer suggestions (USEPA, 2014a).

1.3 The CCL Classification Process and the Third Contaminant Candidate List 

(CCL 3)

As noted, after CCL 1 the agency realized the need to develop an enhanced approach to 

evaluating the risk of potential drinking water contaminants based on occurrence in drinking 

water and adverse health effects – both demonstrated and potential – for future CCLs. The

agency requested assistance from the NRC for guidance on methods and processes to identify 

and narrow a universe of potential contaminants into a smaller, more focused list of 

contaminants in drinking water for the future CCLs. The NRC recommended a multi-step 

process including using prototype classification algorithm(s) that evaluates attributes in 

conjunction with expert judgment to identify contaminants for future CCLs. The approach is 

based on predictive features or attributes that characterize the occurrence in drinking water and 

health effects of each contaminant. The NRC described two health effects attributes, severity and 

potency, and three occurrence attributes: prevalence, magnitude, and persistence/mobility.

The details of the NRC recommendation are available in the report entitled “Classifying 

Drinking Water Contaminants for Regulatory Considerations” (NRC, 2001). It is important to 

emphasize that the NRC report only gives a broad framework for EPA to develop its own 

prototype classification scheme and then to calibrate the scheme using diagnostic contaminants.

With the NRC recommendations in hand, the Office of Water turned to the NDWAC to 

provide advice on whether to pursue the stepped approach recommended in the NRC report and 

to work out how this could be implemented. The NDWAC formed a subcommittee, the Work 

Group on the Contaminant Candidate List Classification Process (CCLCP Work Group), to 

provide advice to the NDWAC.

Based on the deliberations of the CCLCP Work Group, NDWAC released a report in 

June 2004 that found merit in the NRC recommendations, but noted that the EPA may need 

several CCL cycles to fully develop and implement the NRC recommended approach. While the 

NDWAC agreed with the overall approach, the group noted that not all the data and information 

needed to develop the NRC-envisioned CCL were available at the time. The NDWAC also 
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recognized that the agency would be developing a new and powerful tool that could be refined 

and improved in successive efforts; therefore the agency should take advantage of the knowledge 

gained and improve upon the next CCL using an adaptive management approach.

Based on these consultations with expert groups and stakeholders, EPA developed a 

multi-step approach to select contaminants for CCL 3, which includes the following key steps:

(1) The identification of a broad universe of potential drinking water contaminants 

(CCL 3 Universe); 

(2) A screening process that uses readily available information on health effects and 

occurrence in water to narrow the universe of contaminants to a Preliminary CCL 

(PCCL); and 

(3) A structured classification process that “scores” and ranks contaminants, to develop a 

CCL from the PCCL, involving prototype classification models as tools, coupled 

with expert review and assessment.

Exhibit 1-1illustrates the three-step process used to evaluate contaminants for CCL 3.

Exhibit 1-1: General Overview of the Approach Used to Establish CCL 3

Classification 

Tools

Evaluation

Expert Review

Universe

PCCL

Proposed CCL

Surveillance

and

Nomination

STEP 1

Identify the 

Universe

STEP 2

Screen 

to a PCCL

STEP 3

Select the CCL

Final CCL
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To populate the CCL 3 Universe of chemicals, an extensive preliminary list of substances 

was compiled from a wide variety of data sources that met specific criteria. The preliminary list 

was refined by removing chemicals with an existing NPDWR, substances that are considered 

mixtures of chemicals, and “non-chemically defined” entries. The resultant CCL 3 Universe 

included approximately 6,000 chemicals (see USEPA, 2009a, for further details on the CCL 3

Universe process).

The Universe of chemicals was then screened using a framework that took into account 

both health effects and occurrence data. In the case of health effects, EPA evaluated both 

quantitative and qualitative information on the hazard and/or dose-response properties of the 

contaminants. For occurrence, EPA evaluated both quantitative and qualitative information on 

occurrence in water, releases to the environment, and amounts produced. As the result of this

screening process, 561 chemical contaminants were selected to move on to the Preliminary CCL

3 (PCCL 3) from the approximately 6,000 chemicals in the CCL 3 Universe (see USEPA, 2009b, 

for details on the screening process).

To select contaminants for the CCL 3 from among the 561 PCCL 3 contaminants, EPA 

used classification models as a support tool to handle larger, more complex assortments of data 

in a consistent and reproducible manner. The classification models were trained based on past 

expert decisions for a sample of chemicals. To enable numerical scoring of the contaminants, 

using complex data, a scaling system was developed for four attributes: severity, potency, 

magnitude, and prevalence (see USEPA, 2009c, for details). Contaminants were scored for each 

of these attributes, and the scores were run through three calibrated models. The EPA Evaluation 

Team made several post-model refinements to compile the draft list of CCL 3 contaminants. 

EPA also put out a special call for nominations to the CCL 3 (USEPA, 2009d), held expert panel 

consultations, consulted with the SAB, and accepted public comments (USEPA, 2009e). The 

draft CCL 3 was published on February 21, 2008 (73 FR 9628; USEPA, 2008b), and the final 

CCL 3 was published on October 8, 2009 (74 FR 51850; USEPA, 2009f). The final CCL 3

consists of 104 chemicals or chemical groups, and 12 microbiological contaminants.

1.4 Summary of the Approach Used to Identify and Evaluate Contaminants for 

Regulatory Determination 3

Exhibit 1-2 provides a brief overview of the process EPA used to identify which CCL 3

contaminants should be considered for regulatory determinations. The exhibit also summarizes

the SDWA statutory criteria EPA applies when making the regulatory determinations. Details 

about the process of evaluating CCL 3 contaminants for regulatory determination are found in 

the Protocol for the Regulatory Determination 3 (USEPA, 2014a). A brief summary is provided 

in the following paragraphs.
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Exhibit 1-2: General Overview of the Approach Used to Evaluate CCL 3

Contaminants for Regulatory Determination 3

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

Does it 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

Is the 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, 

does regulation of such contaminant 

present a meaningful opportunity for 

health risk reduction for persons served by 

public water systems?

CCL3 

Step 3: Identify 

Contaminants Occurring 

at Levels and Frequencies 

of Public Health Concern

Step 4: Identify 

Contaminants with No or 

Low Occurrence at Levels 

of Public Health Concern

In deciding which CCL 3 contaminants should be considered for RD 3, the agency 

considered whether sufficient information and/or data were available to characterize 

contaminants’ potential health effects and the known/likely occurrence in and exposure from 

drinking water. For health effects, EPA considered whether an agency-approved health risk 

assessment4 was available to identify any potential adverse health effect(s) and derive a Health 

Reference Level (HRL), an estimated concentration threshold below which adverse health effects 

are considered unlikely to occur (for a threshold toxicant), or below which adverse effects have a 

defined low probability of occurrence (for a non-threshold toxicant, such as a carcinogen). For

occurrence, the agency considered whether available information and data provided a

representative picture of known and/or likely occurrence in PWSs. If sufficient information and 

data were available to characterize adverse human health effects and known/likely occurrence in 

PWSs, the agency identified the contaminant as potentially suitable for regulatory 

 

4 Sources of health assessments used to evaluate CCL 3 contaminants for RD 3 eligibility included the 

agency’s Integrated Risk Information System (IRIS), the agency’s Office of Pesticide Programs (OPP) 

Reregistration Eligibility Decisions (REDs), the agency’s Office of Water (OW), the National Academy of Sciences 

(NAS), the World Health Organization (WHO), and the Agency for Toxic Substances and Disease Registry 

(ATSDR). 
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determinations. EPA also gathered information on the availability and adequacy of analytical 

methods (for monitoring) and treatment technologies. The availability of treatment technologies 

is not taken into consideration when deciding whether regulation is warranted, but suitable 

technologies must be developed and available by the time an NPDWR is promulgated. 

In cases where EPA chose a contaminant as suitable for regulatory determination, the 

agency considered the following in evaluating each of the three statutory criteria (see section 

1.2.1). 

(1) First statutory criterion: Is the contaminant likely to cause an adverse effect on the health 

of persons?

The agency evaluated the best available, peer-reviewed assessments and studies to 

characterize the human health effects that may result from exposure to the contaminant 

when found in drinking water. Based on this characterization, the agency estimated an

HRL for each contaminant. Section 2.3 of this document provides more detailed 

information about the approach used to evaluate and analyze the health information. 

(2) Second statutory criterion - Is the contaminant known to occur, or is there a substantial 

likelihood that the contaminant will occur, in PWSs at a frequency and level of public 

health concern?

To evaluate known occurrence in PWSs, the agency compiled, screened, and analyzed 

data from several occurrence data sets to develop representative occurrence estimates for 

public drinking water systems. EPA used the HRL estimates for each contaminant as a 

benchmark against which to conduct an initial evaluation or screening of the occurrence 

data. For each contaminant EPA estimated, when possible, the number of PWSs (and the 

population served by these PWSs) with detections greater than one-half the HRL (> 1⁄2

HRL) and greater than the HRL (> HRL). To further evaluate the likelihood of a 

contaminant occurring in drinking water, the agency considered information on the use 

and release of the contaminant into the environment and supplemental information on 

occurrence in water (e.g. ambient water quality data, special studies performed by other 

agencies, organizations, and/or entities). Section 2.4 provides more details on the 

approach used to analyze the occurrence information/data.

(3) Third statutory criterion - In the sole judgment of the Administrator, does regulation of 

the contaminant present a meaningful opportunity for health risk reduction for persons 

served by PWSs?

EPA evaluated a number of additional factors to determine whether regulation presents a 

meaningful opportunity for health risk reduction among persons served by PWSs, 

including: the total estimated population served by systems contaminated at levels of 

health concern; the estimated contribution of drinking water exposure to total exposure 

(considering alternative routes of exposure such as food, air, soil, etc.); and the existence 

of sensitive subpopulations that might be at special risk.

If EPA determines that all three of these statutory criteria are met, it makes a preliminary 

positive regulatory determination that an NPDWR is needed. Following a comment response 

period and a final positive regulatory determination, the agency has 24 months to publish a 

proposed MCLG and an NPDWR. After the proposal, the agency has 18 months to publish a 

final MCLG and promulgate a final NPDWR. It should be noted that this regulatory 
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determination process is distinct from the more detailed analyses needed to support the 

development of the NPDWR itself. Thus, a decision to regulate is the beginning of the agency

regulatory development process, not the end.

If the answer to any of the three statutory criteria is negative based on the available data, 

then the agency makes a determination that an NPDWR is not necessary for that contaminant at 

that time. A decision not to regulate is considered a final agency action and is subject to judicial 

review. The agency can choose to publish a Health Advisory (a nonregulatory action) or other 

guidance for any contaminant on the CCL, independent of the regulatory determination. If EPA 

has insufficient information/data to evaluate a contaminant according to the statutory criteria, it 

will not make a decision until such data become available.

For more detail on the regulatory determinations process, see the Protocol for the 

Regulatory Determination 3 (USEPA, 2014a).

1.5 Summary of Regulatory Determination 3

EPA identified five CCL 3 contaminants (1,3-dinitrobenzene, dimethoate, strontium, 

terbufos, and terbufos sulfone) as suitable for regulatory determinations based on the available 

data and information on adverse health effects, known and likely occurrence in PWSs, and other 

factors. After evaluating these contaminants against the three SDWA criteria, the agency has 

made a preliminary regulatory determination to regulate one contaminant, strontium, with an 

NPDWR, and to not regulate the remaining four (dimethoate, 1,3-dinitrobenzene, terbufos, and 

terbufos sulfone). The formal preliminary determination for each contaminant can be found in 

the Federal Register notice. Additional information about the preliminary regulatory 

determinations, and the information evaluated for each contaminant, can be found in the series of 

support documents developed for RD 3, including this document, the Health Effects Support 

Document for Strontium (USEPA, 2014b), Occurrence Data from the Second Unregulated 

Contaminant Monitoring Regulation (UCMR 2) (which presents background information and 

findings from the UCMR 2 national drinking water survey) (USEPA, 2014c), and the Protocol 

for the Regulatory Determination 3 (which documents the procedure used to select the five RD 3 

contaminants) (USEPA, 2014a).

1.6 References

National Research Council (NRC). 2001. Classifying Drinking Water Contaminants for 

Regulatory Considerations. Committee on Drinking Water Contaminants, Water Science 

and Technology Board, Board on Environmental Studies and Toxicology, National 

Research Council. National Academies Press.

United States Environmental Protection Agency (USEPA). 1997. Announcement of the Draft 

Drinking Water Contaminant Candidate List; Notice. Federal Register. Vol. 62, No. 193, 

p. 52193. October 6, 1997.

USEPA. 1998. Announcement of the Drinking Water Contaminant Candidate List; Notice. 

Federal Register. Vol. 63, No. 40, p. 10273. March 2, 1998. 

USEPA. 2002. Announcement of Preliminary Regulatory Determinations for Priority 

Contaminants on the Drinking Water Contaminant Candidate List. Federal Register. Vol. 

67, No. 106, p. 38222. June 3, 2002.

USEPA. 2003. Announcement of Regulatory Determinations for Priority Contaminants on the 

Drinking Water Contaminant Candidate List. Federal Register. Vol. 68, No. 138, p. 
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42898. July 18, 2003. 

USEPA. 2004. Drinking Water Contaminant Candidate List 2; Notice. Federal Register. Vol. 69, 

No. 64, p. 17406, April 2, 2004.

USEPA. 2005. Notice—Drinking Water Contaminant Candidate List 2; Final Notice. Federal 

Register. Vol. 70, No. 36, p. 9071, February 24, 2005.

USEPA. 2007. Drinking Water: Regulatory Determinations Regarding Contaminants on the 

Second Drinking Water Contaminant Candidate List—Preliminary Determinations; 

Proposed Rule. Federal Register. Vol. 72, No. 83, p. 24016, May 1, 2007.

USEPA. 2008a. Drinking Water: Regulatory Determinations Regarding Contaminants on the 

Second Drinking Water Contaminant Candidate List. Federal Register. Vol. 73, No. 147, 

p. 44251, July 30, 2008.

USEPA. 2008b. Drinking Water Contaminant Candidate List 3—Draft Notice. Federal Register. 

Vol, 73. No 35. p. 9628, February 21, 2008.

USEPA. 2009a. Final Contaminant Candidate List 3 Chemicals: Identifying the Universe. EPA 

815-R-09-006. August 2009.

USEPA. 2009b. Final Contaminant Candidate List 3 Chemicals: Screening to a PCCL. EPA 815-

R-09-007. August 2009.

USEPA. 2009c. Final Contaminant Candidate List 3 Chemicals: Classification of PCCL to the 

CCL. EPA 815-R-09-008. August 2009.

USEPA. 2009d. Summary of Nominations for the Third Contaminant Candidate List. EPA-815-

R-09-011. August 2009.

USEPA. 2009e. Final Comment Response Document for the Third Drinking Water Contaminant 

Candidate List 3 Categorized Public Comments. EPA 815-R-09-010. August 2009.

USEPA. 2009f. Drinking Water Contaminant Candidate List 3–Final. Federal Register. Vol. 74, 

No. 194, p. 51850, October 8, 2009.

USEPA. 2014a. Protocol for the Regulatory Determinations 3. Including Appendices A-F. April 

2014. EPA-815-R-14-005.

USEPA. 2014b. Health Effects Support Document for Strontium. April 2014. EPA-815-R-14-

003.

USEPA. 2014c. Occurrence Data from the Second Unregulated Contaminant Monitoring 

Regulation (UCMR 2). April 2014. EPA-815-R-14-004.
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Chapter 2:

Evaluation of Health 

and Occurrence Data

A chapter from: 

Regulatory Determination 3 Support Document

EPA Report 815-R-14-003
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Contents

Contents....................................................................................................................................... 2-3

Exhibits........................................................................................................................................ 2-4

Abbreviations............................................................................................................................... 2-5

Chapter 2: Evaluation of Health and Occurrence Data................................................................ 2-7

2.1 Evaluation of Contaminant Background, Chemical, and Physical Properties................. 2-7

2.2 Evaluation of Sources and Environmental Fate............................................................... 2-7

2.3 Evaluation of Adverse Health Effects............................................................................ 2-11

2.3.1 Use of Carcinogenicity Data for the Derivation of a Health Reference Level .. 2-11

2.3.2 Use of Non-carcinogenic Health Effects Data for Derivation of an HRL......... 2-12

2.3.3 Sources of Data/Information for Health Effects................................................ 2-13

2.4 Evaluation of Contaminant Occurrence and Exposure.................................................. 2-15

2.4.1 General Considerations...................................................................................... 2-15

2.4.2 Occurrence in Ambient Water ........................................................................... 2-16

2.4.3 Occurrence in Drinking Water – Primary Data Sources.................................... 2-19

2.4.4 Occurrence in Drinking Water – Secondary Data Sources................................ 2-29

2.5 Evaluation of Analytical and Treatment Methods......................................................... 2-33

2.5.1 Evaluation of Analytical Methods..................................................................... 2-33

2.5.2 Evaluation of Treatment Technologies.............................................................. 2-34

2.6 References...................................................................................................................... 2-34
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Exhibits

Exhibit 2-1: CUS-IUR National Production Volume Ranges .....................................................2-8

Exhibit 2-2: Sources and Dates of Health Effects Assessments................................................2-14

Exhibit 2-3: Primary Sources of Drinking Water Occurrence Data Used to Evaluate RD 3 

Contaminants.....................................................................................................2-20

Exhibit 2-4: Cross-section States for UCM Round 1 and Round 2 ...........................................2-26
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Abbreviations

ADAFs Age Dependent Adjustment Factors

AMWA Association of Metropolitan Water Agencies

AQUA Automated Quantitative Usage Analysis

AWWA American Water Works Association

AwwaRF American Water Works Association Research Foundation

ATSDR U.S. Agency for Toxic Substances and Disease Registry

BW Body Weight

CCL Contaminant Candidate List

CCL 3 Third Contaminant Candidate List

CCR Consumer Confidence Reports

CDR Chemical Data Reporting

CSF Cancer Slope Factor

CUS Chemical Update System

CWS Community Water System

CWSS Community Water System Survey

DBP Disinfection Byproducts

DBP ICR Disinfection Byproducts Information Collection Rule

DL Detection Limit

DOE Department of Energy

DWI Drinking Water Intake

EPA Environmental Protection Agency

EPCRA Emergency Planning and Community Right-to-Know

EWG Environmental Working Group

EXAMS Exposure Analysis Modeling System

FIFRA Federal Insecticide Fungicide and Rodenticide Act

HBSL Health Based Screening Level

HSDB Hazardous Substances Data Bank

HRL Health Reference Level

IOC Inorganic Compound

IRED Interim Reregistration Eligibility Decisions

IRIS Integrated Risk Information System

IUR Inventory Update Reporting

LCMRL Lowest Concentration Minimum Reporting Level

LOAEL Lowest-Observed-Adverse-Effect Level

MCL Maximum Contaminant Levels

MCLG Maximum Contaminant Level Goal

mg/kg-day Milligram per kilogram per day

MDL Method Detection Limit

MRL Minimum Reporting Level

MTBE Methyl Tertiary Butyl Ether
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NAWQA National Water Quality Assessment

NCFAP National Center for Food and Agricultural Policy

NCOD National Drinking Water Contaminant Occurrence Database

NIRS National Inorganics and Radionuclides Survey

NOAEL No-Observed-Adverse-Effect Level

NPDWR National Primary Drinking Water Regulation

NPS National Pesticide Survey

OGWDW Office of Ground Water and Drinking Water

OPP Office of Pesticide Programs

OW Office of Water

PBT Persistence, Bioaccumulation, and Toxicity

PDP Pesticide Data Program

PMP Pilot Monitoring Program

PRZM Pesticide Root Zone Model

PWS Public Water System

QA Quality Assurance

RD 3 Third Regulatory Determination

RED Reregistration Eligibility Decisions

RfD Reference Dose

RSC Relative Source Contribution

SCI-GROW Screening Concentration In GROund Water

SDWA Safe Drinking Water Act

SOC Synthetic Organic Compound

STORET EPA’s Storage and Retrieval

TRED Tolerance Reassessment Progress and Risk Management Decisions

TRI Toxics Release Inventory

TSCA Toxic Substances Control Act

UCM Unregulated Contaminant Monitoring

UCMR Unregulated Contaminant Monitoring Regulation

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

USNLM U.S. National Library of Medicine

VOC Volatile Organic Compound

WHO World Health Organization
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Chapter 2: Evaluation of Health and Occurrence Data

This report provides background information to support the Environmental Protection 

Agency’s (EPA’s) third Regulatory Determination (RD 3) for drinking water contaminants under 

Safe Drinking Water Act (SDWA) provisions, based on the third Contaminant Candidate List 

(CCL 3). Chapter 2 provides a general overview of the sources of data used to evaluate 

contaminants under CCL 3 and RD 3. It includes, where available, information about the quality 

of the data. For more information about the CCL 3 and RD 3 processes, see Chapter 1 of this 

report and the Regulatory Determination 3 Protocol (USEPA, 2014a). For detailed findings on 

individual contaminants, and a summary of EPA’s regulatory determination for each 

contaminant, see Chapters 3-6 of this document. For more detail on EPA’s evaluation of the 

health effects of strontium, the RD 3 contaminant receiving a preliminary positive determination, 

see the Health Effects Support Documents for Strontium (USEPA, 2014b).

This chapter is organized as follows: Section 2.1 describes the sources used to evaluate 

contaminant background information and chemical and physical properties. Section 2.2 covers 

sources of contamination and environmental fate. Section 2.3 describes the process of evaluating 

health effects information, the use of carcinogenic and non-carcinogenic health effects data for 

the derivation of a health reference level (HRL), and the sources of information used for health 

effects evaluations. Section 2.4 describes the primary and supplemental sources of ambient and 

drinking water occurrence information used to evaluate contaminant occurrence and exposure.

Section 2.5 describes the process used to evaluate analytical methods and treatment technologies.

This outline mirrors the organization of the contaminant-specific chapters.

2.1 Evaluation of Contaminant Background, Chemical, and Physical Properties

EPA consulted a number of standard sources for information on contaminant background 

and properties. These sources include the U.S. National Library of Medicine’s (USNLM)

Hazardous Substances Data Bank (HSDB), Toxicity Profiles from the U.S. Agency for Toxic 

Substances and Disease Registry (ATSDR), USNLM’s ChemIDplus website, reports about 

pesticides prepared by EPA’s Office of Pesticide Programs (OPP), chemical-specific parameters 

from the Department of Energy’s (DOE) Risk Assessment Information System (RAIS), and 

standard chemistry reference books. To fill some information gaps, primary literature was 

consulted as well, with preference give to peer-reviewed sources.

2.2 Evaluation of Sources and Environmental Fate

Information about non-anthropogenic sources of contamination and the environmental 

fate of contaminants was assembled from the range of secondary sources and primary literature 

described in Section 2.1. When possible, environmental fate write-ups include estimates of 

partitioning and half-lives in various media from EPA’s Persistence, Bioaccumulation, and 

Toxicity (PBT) Profiler. Descriptions of special topics of concern such as formation through 

chemical reactions in environmental media and formation as disinfection byproducts (DBP) in 

water were prepared by consulting the primary peer-reviewed literature and reports by 

government agencies and other authoritative organizations.

Quantitative data on anthropogenic sources, including data on production, use, and 

industrial releases, comes from specific primary sources and data compilations. The most 

important of these are profiled in the following paragraphs.
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Chemical Update System (CUS) – Inventory Update Reporting (IUR) Program

The Toxic Substances Control Act (TSCA) requires EPA to compile, keep current, and 

publish a Chemical Substance Inventory, a list of chemical substances that are manufactured or 

processed in the United States. Following the promulgation of the 1986 Inventory Update 

Reporting (IUR) rule, chemical manufacturers (including importers) were required to report to 

EPA every four years the identity of and basic manufacturing information for organic chemical 

substances manufactured (including imported) in quantities of 10,000 pounds or more annually 

at individual sites. Modifications of the IUR rule in 2003 and 2005 expanded the range of 

chemicals and plant sites reporting, expanded the type of data reported, raised the production 

volume threshold that triggers reporting from 10,000 pounds to 25,000 pounds, and made certain 

further adjustments. In 2011 the Agency issued the Chemical Data Reporting (CDR) Rule, which 

replaced the IUR Rule and established a somewhat modified program (USEPA, 2012a).

Data on production volumes submitted under IUR are housed in the Chemical Update 

System (CUS). EPA makes certain non-confidential information available to the public. This 

includes aggregated national total annual production volumes for chemicals based on reports 

filed every four years from 1986 to 2006. As a result of the changes in minimum thresholds and 

other program modifications, the results from 2006 might not be directly comparable to results 

from earlier years. The first reporting year under the new CDR Rule is 2012; these data were not 

available at the time of writing.

In making total annual national production volumes for chemicals from 1986 through 

2006 available to the public, the agency assigned one of eight production and importation 

volume ranges. The ranges used for 2006 data differ slightly from those used for 1986-2002 data.

Exhibit 2-1 shows the production volume categories used for 1986-2002 data and for 2006 data. 

If no reports were filed for a chemical in a particular year, the chemical is flagged as having “no 

reports.”

Exhibit 2-1: CUS-IUR National Production Volume Ranges

1986 - 2002 2006

10,000 pounds - 500,000 pounds <500,000 pounds

>500,000 - 1 million pounds 500,000 to <1 million pounds

>1 million - 10 million pounds 1 million to <10 million pounds

>10 million - 50 million pounds 10 million to <50 million pounds

>50 million - 100 million pounds 50 million to <100 million pounds

>100 million - 500 million pounds 100 million to <500 million pounds

> 500 million - 1 billion pounds 500 million to <1 billion pounds

Over 1 billion pounds 1 billion pounds or greater

Sources: USEPA, 2008a; USEPA, 2012b.

Several factors should be considered when interpreting production ranges assigned to 

chemicals. Site-specific production volumes less than 10,000 pounds (25,000 pounds in 2006) 

were not reported and thus are not included in the totals. Production volume ranges for 2006 are 

similar but not identical to production volume ranges for earlier reporting years. Other program 

changes, noted in previous paragraphs, affected reporting in 2006. Furthermore, the data provide 

a snapshot of production (including importation) every four years, and do not capture fluctuation 

from year to year.
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Toxics 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. EPCRA section 313 also requires EPA to 

make this information available to the public through a computer database. The database is 

accessible through EPA’s TRI Explorer. In 1990 Congress passed the Pollution Prevention Act, 

which required that additional data on waste management and source reduction activities be 

reported under TRI. 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, 2002a; USEPA, 2003a). 

Facilities are required to report releases and other waste management activities related to 

TRI chemicals if they manufacture, process, or otherwise use more than established threshold 

quantities of these chemicals. Currently, for most chemicals the 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 so that in 2002 over 24,000 industrial and Federal 

facilities submitted in excess of 93,000 reports on toxic releases. In 2000, special thresholds were 

added for persistent bioaccumulative toxic chemicals, for example dioxin and dioxin-like 

compounds (USEPA, 2002a). Today, TRI includes information on releases of nearly 670 

chemicals.

Although TRI can provide a general idea of release trends, it is far from exhaustive and 

has limitations. For example, small facilities (those with fewer than 10 full-time employees and 

those that do not exceed certain manufacture and use limits) are not required to report releases.

In addition, the reporting threshold for the manufacturing and processing of TRI chemicals 

changed between 1987 and 1989, dropping from 75,000 pounds per year in 1987 to 50,000 in 

1988 to the current 25,000 in 1989; this creates the potential for misleading data trends over time 

(USEPA, 1996a). Finally, TRI data are meant to reflect “releases” and should not be used to 

estimate general public exposure to a chemical (USEPA, 2002a).

Pesticide Usage Estimates from EPA’s Office of Pesticide Programs (OPP) Reregistration 

Documents

OPP sometimes presents estimations of annual U.S. usage of individual pesticides in its 

pesticide reregistration documents (e.g., Reregistration Eligibility Decisions (REDs), Interim 

Reregistration Eligibility Decisions (IREDs), Tolerance Reassessment Progress and Risk 

Management Decisions (TREDs). Many details of pesticide production and use are considered 

confidential business information and are not publically released. OPP relies on an Automated 

Quantitative Usage Analysis (AQUA) program to automatically extract information about 

individual pesticides from relevant agency databases and calculate estimated total annual usage, 

among other figures (e.g., estimates of application rate, number of applications, and amount of 

crops treated). The estimate of total usage represents an approximate maximum annual value: 

“The likely maximum is calculated using statistical procedures that set a usage level below 

which actual usage is expected to fall 95% of the time” (USEPA, 2000a). The values generated 

by AQUA are reviewed, modified as necessary based on additional information not contained in 

the electronic databases, and validated by comparison to other sources within and outside the 

agency. The AQUA methodology has been revised and refined over time since it was introduced 

in 1993 (USEPA, 2000a). 
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EPA Pesticide Industry Sales and Usage Report

EPA’s OPP 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 data presented in EPA’s Pesticide Industry Sales and Usage reports represent “the 

best available information from the public domain and proprietary sources” (USEPA, 2004). 

Publicly available data come from OPP’s Pesticide Data Center, and from a variety of other 

sources, including national data from the United States Department of Agriculture (USDA). 

Proprietary data sources include widely used commercial data compilations produced by “wellknown organizations” (USEPA, 2004).

Certain considerations apply when using or interpreting data presented in the Pesticide 

Industry Sales and Usage reports. OPP cautions that “the numbers in the report represent 

approximate values rather than precise values with known statistical properties” (USEPA, 2004). 

In addition, OPP notes: “We caution the reader not to infer too much from changes in the amount 

of pesticides used from year to year. Changes in the amount of pesticides used are not 

necessarily correlated to changes in the level of pest control or changes in the human health or 

environmental risks associated with pesticide use” (USEPA, 2004).

National Center for Food and Agricultural Policy (NCFAP) Pesticide Use Database

The National Center for Food and Agricultural Policy (NCFAP), a private non-profit 

institution, has assembled a national Pesticide Use Database. NCFAP annual pesticide use 

estimates for circa 1992 and circa 1997 are based on state-level commercial agriculture usage 

patterns for the periods 1990-1993 and 1995-1998, and state-level crop acreage for 1992 and 

1997. The database contains estimates of pounds applied and acres treated in each state for 220 

active 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 NCFAP data are estimates and have several limitations. First, the database only 

includes applications of pesticides to cropland (foliar, soil, and in furrow applications). Noncropland applications, such as uses for homes, greenhouses, livestock, ornamentals, or golf 

courses are not included. The database does not include non-bearing orchards or vineyards, or 

governmental Area-wide Eradication programs. Second, in interpreting the NCFAP database, it 

should be noted that records are compiled from a wide variety of sources. NCFAP states that 

there is no way to determine the accuracy of any of the estimates in the database, adding that 

some are based on surveys of farmers, while others are expert opinions from knowledgeable 

extension service specialists. (As noted, the details of pesticide manufacture, sales, and use are 

confidential business information.) When data for particular states and crops are unavailable, as 

they are in many cases, values are assigned on the basis of data from a nearby state (NCFAP, 

2000).

United States Geological Survey (USGS) Pesticide Use Maps

The United States Geological Survey (USGS, 2014) has produced maps of pesticide use 

for over 200 compounds used in United States crop production, providing insight into the 

regional distribution of the use of many pesticides. The pesticide use maps show the average 

annual pesticide use intensity expressed as average weight (in pounds) of a pesticide applied per 

square mile. 
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USGS used two methods to estimate pesticide usage, since pesticide usage information 

was not available in some districts. “EPestHigh” estimates were generated by projecting usage 

estimates for such districts based on usage in neighboring districts. “EPestLow” estimates were 

generated by assuming no usage in such districts. Note that USGS considers the 2011 maps 

presented in this document “preliminary,” pending updates with crop data from the 2012 Census 

of Agriculture.

USGS notes that the maps are suitable for making national, regional, and watershed 

assessments of annual pesticide use, but that reliability of estimates generally decreases with 

scale (USGS, 2014). 

2.3 Evaluation of Adverse Health Effects

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

contaminant considered for regulatory determination may have an adverse effect on public 

health. This section describes the overall process the agency used 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 RD 3. 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 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. 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 compared to 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; both are described in the 

following sections. If a contaminant has both a cancer HRL and a non-cancer HRL, generally 

the lower (more conservative) one is used in decision-making. For more information on the 

calculation and use of HRLs, see chapters 3-6 and the accompanying Health Effects Support 

Document for Strontium (USEPA, 2014b).

2.3.1 Use of Carcinogenicity Data for the Derivation of a Health Reference Level

Although none of the CCL 3 contaminants with cancer-based HRLs were ultimately 

selected for inclusion in the final RD 3 list, a brief summary of the methodology for carcinogens 

is included here for completeness.

For those contaminants considered to be “likely” or “probable” human carcinogens, EPA 

evaluates data on the mode of action of the chemical to determine the appropriate method of low 

dose extrapolation. When the data do not suggest the use of an alternate extrapolation method, 

EPA uses linear low dose extrapolation to calculate a toxicity value that defines the relationship 

between dose and response (i.e., cancer slope factor or CSF).. Linear low dose extrapolation 

involves the assumption that every dose, no matter how small, is associated with some risk, and 

that the risk of adverse effects from a low dose is proportionate with the size of the dose. The 

CSF is combined with an adult body weight of 70 kg and the 90th percentile adult drinking water 
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intake of 2 L/day to calculate the unit risk, 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. 

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 

If the chemical has a mutagenic mode of action, the U.S. EPA’s 2005 Guidelines for 

Carcinogen Risk Assessment (USEPA, 2005a) requires that the potential increased cancer risk 

due to early-life exposure be taken into account. When chemical-specific data to quantify the 

increased risk are lacking, Age Dependent Adjustment Factors (ADAFs) are applied, in 

conjunction with age-specific drinking water intake values from the U.S. EPA’s Exposure 

Factors Handbook (USEPA, 2011) to estimate age-adjusted unit risks. 

None of the five contaminants receiving a regulatory determination under RD 3 were 

evaluated using a cancer-based HRL. Cancer-based HRLs were used to evaluate numerous CCL 

3 contaminants as part of the RD 3 process, as described in the RD 3 Protocol document 

(USEPA, 2014a). 

2.3.2 Use of Non-carcinogenic Health Effects Data for Derivation of an HRL

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

non-carcinogenic, “not likely” to be carcinogenic to humans or a “possible” carcinogen (Class C, 

in EPA’s former cancer classification system). 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 

the 95% lower confidence bound on a benchmark dose (BMD), known as a BMDL, 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, 2011) 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: 
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• the variation in sensitivity among the members of the human population (i.e., intraspecies 

variability); 

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

• the 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); 

• the uncertainty in extrapolating from a LOAEL rather than from a NOAEL; and/or

• the uncertainty associated with an incomplete database.

For dimethoate, 1,3-dinitrobenzene, strontium1,

terbufos, and terbufos sulfone, EPA derived the 

HRLs using the RfD approach as follows: 

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 a maximum contaminant 

level goal (MCLG) for drinking water. 

Further information about these contaminants can be found in Chapters 3, 4, 5, 6, and in 

the Health Effects Support Document for Strontium (USEPA, 2014b).

2.3.3 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 for CCL 3 chemicals considered for regulatory 

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

Program, the agency’s OPP, the National Academy of Sciences (NAS), the ATSDR, and the 

World Health Organization (WHO). 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. (See the RD 3 

Protocol (USEPA, 2014a) for more detailed information on sources consulted.)

 

1 Since 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 (2011) to derive the HRL for strontium. 
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Exhibit 2-2 summarizes the sources of the health assessment data for each chemical 

under consideration for RD 3. Two of the contaminants receiving a preliminary regulatory 

determination had peer-reviewed health effects assessments available from EPA’s own IRIS 

Program.

2 The remaining three had peer-reviewed health effects assessments available from EPA

OPP’s REDs.

3

Exhibit 2-2: Sources and Dates of Health Effects Assessments

Chemical IRIS Date OPP 

RED Date OW Assessment Date

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

1,3-Dinitrobenzene1 X 1988 --- --- --- ---

Strontium X 1992 --- --- X 2012

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

Terbufos Sulfone2 --- --- X 2006 --- --- 1 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. 

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

effects assessments 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 indicated that a 

change to the existing RfD or cancer assessment was needed, an updated Office of Water (OW)

assessment is prepared and independently peer-reviewed. All quantitative cancer assessments 

conducted under the Guidelines for Carcinogen Risk Assessment (USEPA, 1986) were updated 

using the Guidelines for Carcinogen Risk Assessment (USEPA, 2005a), the Supplemental 

Guidance for Assessing Susceptibility from Early-life Exposures to Carcinogens (USEPA, 

2005b), and the Exposure Factors Handbook (USEPA, 2011). These guidelines include new 

considerations for contaminants with a mutagenic mode of action and potential risks due to early 

childhood exposure.

EPA has prepared a technical health effects support document for strontium, the one 

RD 3 contaminant receiving a preliminary positive regulatory determination. That document 

addresses exposure from drinking water and other media, toxicokinetics, hazard identification, 

and dose-response assessment, and provides an overall characterization of risk from drinking 

water (USEPA, 2014b). 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 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, and slope factors and unit risks for carcinogenic effects.

3 OPP is required under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA) to review all 

pesticides registered prior to 1984 and determine whether to reregister them for continued use. The results of the 

reregistration analysis are included in the REDs. Copies of the REDs are located at the following Web site: 

http://www.epa.gov/oppsrrd1/reregistration/status.htm.
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2.4 Evaluation of Contaminant Occurrence and Exposure

2.4.1 General Considerations

Detection and reporting thresholds

Several types of concentration thresholds are important in the study of chemical 

contaminants in drinking water. This section clarifies some of the terminology used in this 

report. 

Typically, an analytical method allows for low-level detection of a chemical in water at 

concentrations that cannot be quantified with accuracy. Thus there is a distinction between the 

detection limit (the threshold at or above which the presence or absence of a compound can be 

distinguished with a specified degree of confidence) and the quantitation level (a somewhat 

higher threshold, at or above which the concentration of a compound can be measured with a 

specified degree of precision and/or accuracy). Both of these thresholds can vary from method to 

method, contaminant to contaminant, laboratory to laboratory, and even from technician to 

technician, based on method limitations, chemical properties, technician skill, and the quality of 

analytical instrumentation. Published analytical methods specify the standards of precision and 

accuracy that define acceptable laboratory performance, and often estimate “normal” or expected 

detection limits. In practice, the limits vary.

The reporting level is the threshold at or above which a contaminant’s presence or 

concentration is officially quantitated. Reporting levels may be established by the laboratory or 

by those who design and carry out a study. The requirements for precision and accuracy that are 

included in a published analytical method help to dictate where laboratories establish a reporting 

level for a particular analyte.

In the absence of an otherwise established reporting level, laboratories generally report 

results as low as can be reliably measured, i.e., at the quantitation level. Sometimes the terms 

“quantitation level” and “reporting level” are used interchangeably in the laboratory context. 

In a well-designed occurrence study, the investigator will establish a reporting level in 

advance of data collection, based on analytical method(s) chosen, laboratory capabilities, and 

other considerations. Setting a reporting level is a balancing act: A reporting level set too high 

will result in the under-reporting of contaminants that are present, while a reporting level set too 

low may run into data quality problems--e.g., some of the participating laboratories may be 

unable to reliably quantify results at the low threshold. In the case of many of EPA’s nation-wide 

drinking water studies, the selected reporting level is known officially as the Minimum 

Reporting Level (MRL). The MRL for each contaminant in each study is set at a level that EPA 

believes can be achieved with specified confidence by a broad spectrum of certified laboratories 

across the nation.

In some cases, an investigator may establish a “common reporting level,” a high, uniform 

reporting threshold for multiple contaminants that facilitates inter-contaminant comparison. A 

common reporting level may be applied retrospectively. Some studies report results at low 

contaminant-specific thresholds and also at a high common reporting level. Longitudinal studies 

and data compilations sometimes select a high retrospective reporting level to facilitate 

comparison of results from older data collection efforts with results from newer efforts that 

employed more advanced analytical techniques with lower quantitation limits.

Knowing the reporting level(s) associated with a study or data set can help with 

interpretation of the results. For instance, knowing that the reporting level is lower than a health-
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based threshold provides assurance that all exceedances of the threshold were captured in the 

study results. Also, knowledge of reporting levels can help a reader to determine whether data 

from two studies are directly comparable. Compilations of data from multiple sources must be 

interpreted with caution if reporting levels are not documented, as they may have varied widely. 

To facilitate interpretation of occurrence results in the contaminant-specific chapters that 

follow, reporting levels are provided whenever they are available. In many cases reporting levels 

are not known, and this too is documented. In some cases, the lowest reported concentration 

values can give a rough idea of what the reporting threshold(s) might have been. (Generally, the 

reporting level could not have been higher than the lowest reported concentration. If a 

sufficiently large number of detections are reported, the lowest reported concentration is 

probably a good approximation of the reporting level.)

In occurrence studies, the word detection is frequently used as shorthand for a sampling 

result that exceeds a given reporting level, and non-detection for a result that does not exceed the 

reporting level. Thus, even a sample that exhibits measurements that exceed the laboratory 

detection limit could, in the context of a particular study or data compilation, be considered a 

non-detection.

Rounding

In reporting quantitative occurrence findings, EPA is sensitive to the issue of precision 

(i.e., the desirability of presenting numbers with the right number of significant digits, if it can be 

determined), and the challenge of presenting findings in a uniform format. EPA draws data from 

a wide variety of sources, some of which are better-documented than others, and calculates other 

values internally. EPA follows the following guidelines in this support document.

When presenting results obtained from published studies or other sources, EPA reports 

the numbers exactly as given in the source, or retains the level of precision given in the source. 

(All water concentration values are converted to micrograms per liter.)

When calculating new values, EPA follows different procedures for percentages and 

concentration values. With limited exceptions, calculated percentages are presented to two 

decimal places. Calculated concentration values (e.g., median and 99th-percentile concentrations) 

are rounded, if necessary, to have the same number of decimal places as the (actual, reported) 

minimum and maximum values, or whichever of the two has more decimal places.

2.4.2 Occurrence in Ambient Water

This section describes the most important sources EPA consulted to evaluate the 

occurrence of CCL 3 contaminants in U.S. ambient water (e.g., aquifers, rivers, lakes). 

USGS National Water Quality Assessment (NAWQA) – Ambient Water Analysis

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 among study basins across the country and over time. These occurrence 

assessments serve to facilitate interpretation of natural and anthropogenic factors affecting 

national water quality. 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).
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The NAWQA program conducts monitoring and water quality assessments in significant 

watersheds and aquifers referred to as “study units.” The program’s sampling approach is not 

“statistically” designed (i.e., it does not involve random site selection), but it provides a 

representative view of the nation’s waters in its coverage and scope. Together, the 51 study units 

monitored between 1991 and 2001 include the aquifers and watersheds that supply more than 

60% of the nation’s drinking water and water used for agriculture and industry. The NAWQA 

program monitors the occurrence of chemicals such as pesticides, nutrients, volatile organic 

compounds (VOCs), trace elements, and radionuclides, and the condition of aquatic habitats and 

fish, insects, and algal communities (NRC, 2002; Hamilton et al., 2004). NAWQA has collected 

data from over 6,400 surface water and 7,000 ground water sampling points. (The NAWQA Data 

Warehouse can be reached via a link from the following Web site: 

http://water.usgs.gov/nawqa/data.html).

Monitoring of study units occurs in stages. Between 1991 and 2001, approximately onethird of the study units at a time were studied intensively for a period of three to five years, 

alternating with a period of less intensive research and monitoring that lasted between five and 

seven years. Thus, all participating study units rotated through intensive assessment in a ten-year 

cycle (Leahy and Thompson, 1994). The first ten-year cycle was designated Cycle 1. Summary 

reports are available for the 51 study units that underwent intensive monitoring in Cycle 1 

(USGS, 2001). Cycle 2 monitoring, 2002 to 2012, proceeded with 42 study units (Hamilton et 

al., 2004). Other adjustments were made during the course of Cycle 2. Partial analyses of Cycle 2 

data are available.

EPA Analysis of NAWQA Cycle 1 Monitoring Results

Whereas the NAWQA program often uses the most representative data for particular sites

to calculate summary statistics for particular interpretive reports, EPA, with the cooperation of 

USGS, has performed a summary analysis of all Cycle 1 water monitoring data from all study 

units (1991-2001) for many of the CCL 3 contaminants being considered for regulatory 

determination. A summary of the occurrence monitoring data analysis are presented in Part II of 

this document.

The surface water data consist of stream samples; all surface water data were included in 

the EPA summary analysis. For ground water, all well data were used; as with the USGS 

National Pesticide Synthesis Project, data from springs and artificial drains were excluded. For 

each contaminant, EPA calculated detection frequencies simply as the percentage of samples and 

the percentage of sites with at least one detection. (A detection is an analytical result equal to or 

greater than the reporting limit.) EPA used USGS data without any censoring or weighting. From 

samples with detections a number of descriptive statistics were also calculated, including the 

minimum, median, 90th percentile, 99th percentile, and maximum concentrations. In addition to 

summarizing the number of samples/sites with detections, the number and percentage of sites 

with detections greater than the HRL and the 1⁄2 HRL was also included. Note that reporting 

limits for some contaminants varied over time during the NAWQA program. Because reporting 

limits varied, the minimum concentration reported as a detection can sometimes be lower than 

the highest reporting limit.

USGS issues many special reports that are summarized for individual contaminant 

discussions. There can be some overlap in data used in USGS reports. USGS may use only 

selected data for some reports (i.e., related to specific land use), whereas EPA used all data for a 

national overview of ambient occurrence. Selected special USGS programs are noted in 

following paragraphs.
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USGS Analysis: National Synthesis Assessments

Through a series of National Synthesis efforts, the USGS NAWQA program is preparing 

comprehensive analyses of data on topics of particular concern. These National Synthesis 

assessments aggregate NAWQA contaminant occurrence and water quality parameter data from 

individual study units and other sources to provide a national overview.

Pesticide National Synthesis Project

The NAWQA Pesticide National Synthesis Project is a national-scale assessment of the 

occurrence and behavior of pesticides in streams and ground water of the United States and the 

potential for pesticides to adversely affect drinking-water supplies or aquatic ecosystems.

Results from the most recent Pesticide National Synthesis analysis, based on complete 

Cycle 1 (1992-2001) data from NAWQA study units, are posted on the NAWQA Pesticide 

National Synthesis Web site (Gilliom et al., 2007). Data for surface water and ground water are 

presented separately, and results in each category are subdivided by land use category. Land use 

categories include agricultural, urban, mixed (deeper aquifers of regional extent in the case of 

ground water), and undeveloped. The Pesticide National Synthesis analysis is a first step toward 

the USGS goals of describing the occurrence of pesticides in relation to different land use and 

land management patterns, and developing a deeper understanding of the relationship between 

spatial occurrence of contaminants and their fate, transport, persistence, and mobility 

characteristics.

The surface water summary data presented in the Pesticide National Synthesis (Gilliom et 

al., 2007) only includes stream data. Sampling data from a single one-year period, generally the 

year with the most complete data, were used to represent each stream site. Sites with few data or 

significant gaps were excluded from the analysis. NAWQA stream sites were sampled repeatedly 

throughout the year to capture and characterize seasonal and hydrologic variability. 

Ground water data reported in the Pesticide National Synthesis only include samples 

from wells; data from springs and agricultural tile drains were not included. In the National 

Synthesis analysis (Gilliom et al., 2007), USGS uses a single sample to represent each well, 

generally the earliest sample with complete data for the full suite of analytes.

Over the course of Cycle 1 (1992-2001), some NAWQA analytical methods were 

improved or changed. Hence, detection thresholds varied over time for some compounds

(Gilliom et al., 2007).

VOC National Synthesis: Random and Focused VOC Surveys

The VOC National Synthesis began in 1994. The most comprehensive VOC National 

Synthesis reports to date are one random survey and one focused survey funded cooperatively by 

the American Water Works Association Research Foundation (AwwaRF) and carried out by 

USGS in collaboration with the Metropolitan Water District of Southern California and the 

Oregon Health & Science University. The random survey (Grady, 2003) targeted surface and 

ground waters used as source water by community water systems (CWSs). Samples were taken 

from the source waters of 954 CWSs in 1999 and 2000. The random survey was designed to be 

nationally representative of CWS source water. In the focused survey (Delzer and Ivahnenko, 

2003), 451 samples were taken from source waters serving 134 CWSs between 1999 and 2001.

These surface and ground waters were chosen because they were suspected or known to contain 

Methly Tertiary Butyl Ether (MTBE). The focused survey was designed to provide insight into 

temporal variability and anthropogenic factors associated with VOC occurrence. Details of the 
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monitoring plan for these two studies, including detection limits, are provided by Ivahnenko et 

al. (2001). Separately, AwwaRF also published the results of this monitoring effort (AwwaRF, 

2003).

VOC National Synthesis: Compilation of Historical VOC Monitoring Data

Additional products of the VOC National Synthesis include a compilation of historical 

VOC monitoring data from multiple studies (Squillace et al., 1999). The data, collected from 

2,948 wells between 1985 and 1995 by local, state, and federal agencies, were reviewed to 

ensure they met data quality criteria. Most of the data were from early study unit monitoring. The 

samples represent both urban and rural areas, and both drinking water and non-drinking water 

wells. A full analysis of 10 years of study unit monitoring data has not yet been performed by the 

VOC National Synthesis.

Storage and Retrieval (STORET) Data Warehouse

EPA’s Storage and Retrieval (STORET) Data Warehouse is a collaborative database that

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 are finished drinking water data. Users 

began populating the STORET Data Warehouse in 1999. Most data are post-1999, but some 

earlier sampling is included.

STORET data have quality limitations. The extent of national coverage and data 

completeness varies from parameter to parameter. Some (though not all) sample results are 

accompanied by information on sample location (latitude, longitude, state, county, Hydrologic 

Unit Code and a brief site identification), sample date, the medium sampled (e.g., water, 

sediment, fish tissue), and the name of the organization that sponsored the monitoring. In 

addition, there can be information on why the data were gathered; sampling and analytical 

methods used; the laboratory used to analyze the samples; the quality control checks used when 

sampling, handling the samples, and analyzing the data; and the personnel responsible for the 

data. There are few restrictions on submission of data based on analytical methods, quality 

assurance (QA) practices, 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 (USEPA, 2012c). The STORET Data Warehouse also included 

Public Water System (PWS) data from three states (Indiana, Missouri, and Ohio); EPA reviewed 

these as well (USEPA, 2012c). 

2.4.3 Occurrence in Drinking Water – Primary Data Sources

The major or primary sources of the drinking water occurrence data used to support the

RD 3 process, including selection and evaluation of RD 3 contaminants, were the following:

• the First Unregulated Contaminant Monitoring Regulation (UCMR 1)

• the Second Unregulated Contaminant Monitoring Regulation (UCMR 2)

• Rounds 1 and 2 of the Unregulated Contaminant Monitoring (UCM) program 

• the Disinfection Byproducts Information Collection Rule (DBP ICR)
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• the National Inorganics and Radionuclides Survey (NIRS)

All five of these sources are national assessments that were administered or overseen by 

EPA. UCMR 1, UCMR 2, and NIRS are designed to be statistically representative of the nation. 

(NIRS, which does not include surface water systems, is designed to be statistically 

representative of ground water systems.) The UCM program and the DBP ICR are national in 

scope but were not designed to be statistically representative of the nation (see further discussion 

in the sub-sections of the report that follow). In the case of UCM, the agency has developed a 

peer-reviewed cross-section-based approach to elicit national estimates from the data.

Several CCL 3 contaminants, including the RD 3 contaminant strontium, are currently 

being monitored under the third Unregulated Contaminant Monitoring Rule (UCMR 3) (77 FR 

26072; USEPA, 2012d). With data becoming available after 2015, UCMR 3 will be too late to 

inform the preliminary regulatory determinations, but it could support the final regulatory 

determinations and national primary drinking water regulation (NPDWR) development, as well 

as future rounds of Contaminant Candidate List (CCL) regulatory determinations or off-cycle 

decision-making. 

Exhibit 2-3 indicates which RD 3 contaminants have data from which of the primary 

sources. Note that none of the five contaminants receiving a regulatory determination under 

RD 3 have data from UCMR 1 Assessment Monitoring, UCMR 2 Screening Survey, UCM 

Rounds 1 or 2, or the DBP ICR. Data from these sources were used to evaluate CCL 3 

contaminants as part of the RD 3 development process, as described in the RD 3 Protocol 

document (USEPA, 2014a). Although none of the CCL 3 contaminants with UCMR 1 

Assessment Monitoring, UCMR 2 Screening Survey, UCM, or DBP ICR data were ultimately 

selected for inclusion in the final RD 3 list, these data sources were important for the 

development of RD 3 and are included here for completeness.

Exhibit 2-3: Primary Sources of Drinking Water Occurrence Data Used to Evaluate 

RD 3 Contaminants

Contaminant

UCMR 11 UCMR 21 UCM1

DBP ICR1List 1 Assessment MonitoringList 2Screening SurveyList 1 AssessmentMonitoringList 2 Screening SurveyRound 1 

NIRS

Cross Section

Round 2

Cross Section

Dimethoate X

1,3-Dinitrobenzene X

Strontium2 X

Terbufos X

Terbufos sulfone X 1 Data from UCMR 1 Assessment Monitoring, UCMR 2 Screening Survey, UCM, and DBP ICR were used in the RD 3 

development process, but none of the contaminants ultimately selected for regulatory determination have data from 

these sources. They are covered in this chapter for completeness. See the RD 3 Protocol document (USEPA, 2014a) 

for detailed information on the RD 3 development process.

2 Currently being monitored under UCMR 3. 
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Basic occurrence values calculated for contaminants from primary data sources as part of 

the RD 3 process include direct counts of the number and percent of systems, and population 

served by systems, with at least one analytical detection above a given concentration threshold.

EPA considered this to be a straightforward and accurate way to present these data for the 

regulatory determination process.

Where the data from the primary sources permit, national extrapolations are made to 

estimate the number of systems and the population in various size and source categories exposed

to a given level of contamination. The extrapolations are made using figures from the 4th edition 

of the Baseline Handbook (USEPA, 2003b) or other authoritative sources on national PWS 

characteristics and populations served (including census figures from primary occurrence sources 

themselves). 

The analytical approach that is used to evaluate the contaminant occurrence data was 

previously developed for other EPA Office of Ground Water and Drinking Water (OGWDW) 

national occurrence studies, including the first Six-Year Review of National Primary Drinking

Water Regulations (USEPA, 2003c), UCMR 1 (USEPA, 2008b), and previous rounds of the 

regulatory determination process (USEPA, 2002b; USEPA, 2008c). In each case, the data 

analysis process and presentation have been peer-reviewed and subject to public and stakeholder 

review and comment.

Robust data from the UCMR program can support a more involved statistical analysis 

(Stage 2 analysis) to assess and estimate the annual mean concentrations at systems, for 

comparisons with HRLs. The Stage 2 approach, also peer-reviewed, is presented in the reports

Occurrence Estimation Methodology and Occurrence Findings for Six-Year Review of National 

Primary Drinking Water Regulations (USEPA, 2003c) and The Analysis of Regulated 

Contaminant Occurrence Data from Public Water Systems in Support of the Second Six-Year 

Review of National Primary Drinking Water Regulations (USEPA, 2009b). This advanced 

occurrence analysis was not deemed necessary for the four RD 3 contaminants with UCMR 1 

and/or UCMR 2 data, since all four are receiving preliminary negative determinations.

The following sections provide a brief summary of primary data sources and the 

approach used to estimate contaminant occurrence in each case. References are provided to other 

reports that present additional detail. Readers are referred to later chapters and RD 3 companion 

support documents for contaminant-specific results. In the case of UCMR 1, UCM, and NIRS, 

readers are referred to support documents from earlier CCL and Regulatory Determination 

efforts for study details. 

First Unregulated Contaminant Monitoring Regulation (UCMR 1)

In 1999, EPA developed the Unregulated Contaminant Monitoring Regulation (UCMR)

program in coordination with the CCL and the National Drinking Water Contaminant 

Occurrence Database (NCOD) to provide national occurrence information on unregulated 

contaminants (64 FR 50556; USEPA, 1999a; 65 FR 11372; USEPA, 2000b; 66 FR 2273;

USEPA, 2001a). The UCMR is currently EPA’s primary authority for collecting monitoring data 

on the occurrence of unregulated contaminants in PWSs. UCMR 1 data were available for one 

RD 3 contaminant, namely terbufos.

EPA designed the UCMR 1 data collection with three parts (or tiers) for monitoring, 

primarily based on the availability of analytical methods and related analytical laboratory 

capability. Contaminants for which well-established laboratory methods were available were 

scheduled to undergo full UCMR 1 List 1 Assessment Monitoring. Contaminants whose 
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laboratory methods were newly developed and less widely available were placed on List 2; these 

were scheduled for a “Screening Survey” at a smaller group of systems. The purpose of the 

Screening Survey was to develop a preliminary assessment of national occurrence for 

contaminants of concern that may be difficult to monitor at the larger scale of Assessment 

Monitoring. List 3 monitoring (“Pre-Screen Testing”) was intended to address contaminants with 

analytical methods that are in an early stage of development; the analyses would be limited to a 

few special laboratories. The expectation was that Pre-Screen Testing would only involve a 

limited number of systems determined to be most vulnerable to the targeted contaminants. EPA 

did not implement Pre-Screen Testing under UCMR 1 due to the lack of suitable candidate 

methods.

EPA required all large4 PWSs, plus a statistically representative national sample of 800 

small5 PWSs, to conduct Assessment Monitoring of List 1 contaminants.

6 Approximately onethird of the participating small systems were scheduled to monitor for the List 1 contaminants 

during each calendar year from 2001 through 2003. Large systems could conduct one year of 

monitoring anytime during the 2001-2003 UCMR 1 period. EPA specified a quarterly 

monitoring schedule for surface water systems and a twice per year, six-month-interval 

monitoring schedule for ground water systems. Monitoring was scheduled so that one sampling 

event occurred during the most vulnerable season for the water system. The objective of the 

peer-reviewed UCMR 1 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 ensuring the selection of at least two systems from each state. With 

contaminant monitoring data from all large PWSs and a nationally representative sample of 

small PWSs, the UCMR 1 List 1 Assessment Monitoring program provides a contaminant 

occurrence data set suitable for national drinking water estimates.

In total, 372,086 sample results have been collected under the UCMR 1 List 1 

Assessment Monitoring program at 3,090 large systems and 797 small systems. Approximately 

33,800 samples were collected for each contaminant. The UCMR 1 List 1 Monitoring program 

included systems from all 50 states, the District of Columbia, four U.S. territories, and tribal 

lands in five EPA Regions.

UCMR 1 Screening Survey sampling for List 2 contaminants was conducted at 300 

systems (120 large and 180 small PWSs) statistically selected from the pool of systems required 

to conduct Assessment Monitoring. While the statistical design of the UCMR 1 Screening 

Survey provided national data, the small number of systems sampled left concerns about the 

relative uncertainty of the findings. For the RD 3 process, supplemental data were identified and 

compiled to augment the UCMR 1 Screening Survey data. Terbufos was a UCMR 1 Screening 

Survey analyte.

A total of 29,765 sample results have been collected under the UCMR 1 List 2 Screening 

Survey from the participating large and small systems. Approximately 2,300 samples were 

 

4 Systems serving more than 10,000 people.

5 Systems serving 10,000 people or fewer.

6 Large and small systems that purchase 100% of their water supply were not required to participate in the 

UCMR 1 Assessment Monitoring or the UCMR 1 Screening Survey.
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collected for each contaminant. The UCMR 1 List 2 Screening Survey included systems from 48 

states, two U.S. territories, and tribal lands in one EPA Region.

See USEPA (2001b) and USEPA (2008b) for more information on UCMR 1 study design 

and data analysis.

EPA analyzed the UCMR 1 List 1 Assessment Monitoring and List 2 Screening Survey 

data to generate the following occurrence and exposure summary statistics for CCL 3 

contaminants: 

• the total number of systems and the total population served by these systems,

• the number and percentage of systems with detections, the 90th and 99th percentile 

concentrations from samples with detections, and the minimum, median, and 

maximum concentrations from samples with detections,

• the number and percentage of systems with at least one detected concentration greater 

than the 1⁄2 HRL and at least one detected concentration greater than the HRL (or in 

some cases greater than or equal to the MRL), and 

• the number of people and percentage of the population served by systems with at least 

one detected concentration greater than the 1⁄2 HRL and greater than the HRL (or in 

some cases greater than or equal to the MRL).

The UCMR 1 summary occurrence statistics are presented in later chapters of this 

document and in USEPA (2008b).

Note that in some cases, an HRL analysis was not performed because the HRL was lower 

than the MRL. EPA set the MRL for UCMR 1 contaminants based on the capability of analytical 

methods, taking into consideration the relative magnitude of MRLs and health-based thresholds

to the extent possible. In the case of VOCs, the MRL was determined by multiplying by 10 either 

the published minimum detection limit or 0.5 μg/L, whichever was greater. For other 

contaminants, the MRL was determined by multiplying by 10 the least sensitive method’s 

minimum detection limit, or, when available, multiplying by 5 the least sensitive method’s 

estimated detection limit (USEPA, 2000c). MRLs were set approximately an order of magnitude 

higher than detection limits to ensure consistency, accuracy, and reproducibility of results.

Second Unregulated Contaminant Monitoring Regulation (UCMR 2)

UCMR 2 monitoring, designed to provide nationally representative contaminant 

occurrence data, was conducted from 2008 through 2010. Similar in design to UCMR 1, UCMR 

2 required surface water systems to monitor quarterly and ground water systems to monitor twice

per year. Monitoring is scheduled so that one sampling event is during the most vulnerable 

season for the water system. As with UCMR 1, there were multiple tiers of monitoring: 

Assessment Monitoring for contaminants with commonly used analytical method technologies, 

and Screening Survey monitoring for contaminants that require specialized analytical method 

technologies not in wide or common use. (Again, there was no Pre-Screen Testing.)

One difference between the UCMR 1 and UCMR 2 is that the UCMR 2 Screening 

Survey consists of a larger sample of PWSs, as described in following paragraphs, and therefore 

provides monitoring data statistically robust enough to support national contaminant occurrence 

estimates. See USEPA (2005c), USEPA (2007), and USEPA (2014c) for more information on 

the UCMR 2 program, including study design and data analysis.
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For UCMR 2, all large PWSs (serving more than 10,000 people), plus a statistically 

representative national sample of 800 small PWSs (serving 10,000 people or fewer), were

required to conduct Assessment Monitoring during a 12-month period between January 2008 and 

December 2010. UCMR 2 List 1 Assessment Monitoring occurrence data are available for three 

RD 3 contaminants: 1,3-dinitrobenzene, dimethoate, and terbufos sulfone.

For the UCMR 2 Screening Survey, monitoring was required by all PWSs serving more 

than 100,000 people (approximately 400 PWSs, serving a large proportion of the national 

population), 320 representative PWSs serving 10,001-100,000 people, and 480 representative 

PWSs serving 10,000 people or fewer, during a 12-month period between January 2008 and 

December 2010. With approximately 1,200 systems participating in the Screening Survey, 

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). Multiple 

CCL 3 contaminants have UCMR 2 List 2 Screening Survey occurrence data, but none of these 

are receiving a regulatory determination.

The UCMR 2 occurrence analyses used to support RD 3 decision-making are based on 

data collected through June 2011 and released in July 2011. A relatively small amount of 

additional data were received and added to the UCMR 2 data set after June 2011. The UCMR 2 

data set was not considered “final” until December 2011. Through the end of June 2011, data had 

been received from 99.96% of systems (4,618 out of 4,620) that were expected to submit UCMR 

2 data. (The two systems that had not submitted their data by the end of June 2011 were only 

scheduled to participate in Assessment Monitoring, not the Screening Survey.)

EPA analyzed the UCMR 2 List 1 Assessment Monitoring and List 2 Screening Survey 

data to generate the following occurrence and exposure summary statistics for CCL 3 

contaminants: 

• the total number of systems and the total population served by these systems,

• the number and percentage of systems with detections, the 90th and 99th percentile 

concentrations from samples with detections, and the minimum, median, and 

maximum concentrations from samples with detections,

• the number and percentage of systems with at least one detected concentration greater 

than the 1⁄2 HRL and at least one detected concentration greater than the HRL (or in 

some cases greater than or equal to the MRL), and 

• the number of people and percentage of the population served by systems with at least 

one detected concentration greater than the 1⁄2 HRL and greater than the HRL (or in 

some cases greater than or equal to the MRL).

The UCMR 2 summary occurrence statistics used to support RD 3 decision-making for 

pertinent contaminants are presented in Chapters 3, 4, and 6 of this document and in Occurrence 

Data from the Second Unregulated Contaminant Monitoring Regulation (UCMR 2) (USEPA, 

2014c). Analysis of the complete set of UCMR 2 occurrence results is found in the UCMR 2 

Support Document (USEPA, 2014c). 

Unregulated Contaminant Monitoring (UCM) Program Rounds 1 and 2

In 1987, EPA initiated the UCM program to fulfill a 1986 SDWA Amendment 

requirement to monitor for specified unregulated contaminants. The UCM required PWSs 
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serving more than 500 people to conduct the monitoring. The intent of the monitoring was to 

gather information on the occurrence of select contaminants in drinking water for future 

regulatory decision-making purposes.

EPA implemented the UCM program in two phases or rounds. The first round of UCM 

monitoring generally extended from 1988 to 1992 and is referred to as UCM Round 1 

monitoring. The second round of UCM monitoring generally extended from 1993 to 1997 and is 

referred to as UCM Round 2 monitoring.

UCM Round 1 monitoring initially involved 34 required VOCs, 14 VOCs to be 

monitored at states’ discretion, and two synthetic organic compounds (SOCs). Monitoring for 

unregulated compounds was to be conducted alongside monitoring for regulated compounds (52 

FR 25720; USEPA, 1987). The final database for this round of monitoring included 62 regulated 

and unregulated contaminants (USEPA, 2001c). UCM Round 2 involved monitoring for 20 

VOCs from the earlier required list and 14 VOCs from the earlier discretionary list, plus 13 

SOCs and sulfate. The final database for this round of monitoring included 48 unregulated 

contaminants (USEPA, 2001c ). There was no requirement that the monitoring data be reported 

to EPA and individual states maintained the data in different forms and formats. In the context of

various initiatives and information collection requests, many states voluntarily submitted the 

UCM data to EPA. EPA worked to assemble the state data into a composite data set that would 

support national occurrence estimates.

The UCM Round 1 database contains contaminant occurrence data from 38 states, 

Washington, D.C., and the U.S. Virgin Islands. The UCM Round 2 database contains data from 

35 states and several tribes. However, some state data sets were incomplete; hence national 

occurrence estimates based on raw (unedited) UCM Round 1 or Round 2 data could be skewed 

to low-occurrence or high-occurrence settings (e.g., some states only reported detections). In 

addition, certain types of land use and geologic/hydrologic settings could be over- or underrepresented. To address potential biases in the data (including those due to incompleteness and 

lack of representativeness), EPA developed national cross-sections from the UCM Round 1 and 

Round 2 state data using an approach similar to that used for EPA’s 1999 Chemical Monitoring 

Reform (USEPA, 1999b), the first Six-Year Review (USEPA, 2003c), and the first round of

Regulatory Determinations (USEPA, 2002b). This national cross-section approach for 

occurrence analyses was supported by scientific peer reviewers and stakeholders. Using this 

approach, EPA constructed national cross-sections using 24 of the 38 states from the UCM 

Round 1 database and 20 of the 34 states from the UCM Round 2 data base. The support 

document 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, 2008d) provides a description of how the national cross-sections for the Round 1 and 

Round 2 data sets were developed and utilized for regulatory determination.

Since UCM Round 1 and Round 2 data represent different time periods and include 

occurrence data from different states, EPA developed separate national cross-sections for each 

data set. The UCM Round 1 national cross-section, consisting of data from 24 states, includes 

approximately 3.3 million records from approximately 22,000 unique PWSs. The UCM Round 2 

national cross-section, consisting of data from 20 states, includes approximately 3.7 million 

records from slightly more than 27,000 unique PWSs. The UCM Round 1 and 2 national crosssections represent significantly large samples of national occurrence data. Within each crosssection, the actual number of systems and analytical records for each contaminant varies.
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EPA constructed the national cross-sections in a way that provides a balance and range of 

states with varying pollution potential indicators, a wide range of geologic and hydrologic 

conditions, and a very large sample of monitoring data points. While EPA recognizes that some 

limitations exist, the agency believes that the national cross-sections do provide a reasonable 

estimate of the overall distribution and the central tendency of contaminant occurrence across the 

United States. For more information on the development of national cross-sections, refer to 

USEPA (1999b), USEPA (2002b), and USEPA (2003c). See Exhibit 2-4 for a listing of states in 

each national cross-section.

Exhibit 2-4: Cross-section States for UCM Round 1 and Round 2 

UCM Round 1 – 24-State Cross-Section UCM Round 2 – 20-State Cross-Section

Alabama Minnesota* Alaska* New Hampshire

Alaska* Montana Arkansas New Mexico*

Arizona New Jersey Colorado North Carolina*

California New Mexico* Kentucky* North Dakota

Florida North Carolina* Maine Ohio*

Georgia Ohio* Maryland* Oklahoma

Hawaii South Dakota Massachusetts Oregon

Illinois Tennessee Michigan Rhode Island

Indiana Utah Minnesota* Texas

Iowa Washington* Missouri Washington*

Kentucky* West Virginia

Maryland* Wyoming

* States in both Round 1 and Round 2 Cross-sections
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EPA analyzed the UCM Round 1 and 2 National Cross-Section data to generate the 

following initial occurrence and exposure summary statistics for CCL 3 contaminants: 

• the total number of systems and the total population served by these systems,

• the number and percentage of systems with detections, the 90th and 99th percentile 

concentrations from samples with detections, and the minimum, median, and 

maximum concentrations from samples with detections,

• the number and percentage of systems with at least one observed detection that has a 

concentration greater than the 1⁄2 HRL and greater than the HRL (or in some cases 

greater than or equal to the MRL), and 

• the number of people and percentage of the population served by systems with at least 

one detection that has a concentration greater than the 1⁄2 HRL and greater than the 

HRL (or in some cases greater than or equal to the MRL). 

The UCM Round 1 and Round 2 summary occurrence statistics for pertinent 

contaminants are presented in USEPA (2001c), USEPA (2002b), and USEPA (2008d).

Disinfection Byproducts Information Collection Rule (DBP ICR)

The DBP ICR (61 FR 24353; USEPA, 1996b) required PWSs serving at least 100,000 

people to monitor and collect data on DBPs over an 18-month period from July 1997 to 

December 1998. The DBP data were collected from 296 very large water systems (that is, 

systems serving a population of more than 100,000), including both surface water systems and 

ground water systems. These very large systems provided extensive information on the 

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

of a national research project to support development of national drinking water standards. EPA 

used the data to identify national and regional patterns. The data were not intended to support 

conclusions about individual systems or treatment plants. 

DBP ICR monitoring was conducted on a “per plant” basis; most participating systems 

had more than one water treatment plant. Plants using chlorine dioxide were required to monitor 

on a monthly basis. These plants sampled at anywhere between one and four different locations 

in the distribution system. Sampling points generally represented the point of entry into the 

distribution system, a point of maximum residence time, or a point of average residence time. 

Plants monitoring hypochlorite were required to gather samples on a quarterly basis. Monitoring

was conducted at one point in the distribution system, generally the point of entry into the 

distribution system.

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). DBP ICR occurrence data are 

available for one or more CCL 3 contaminants, but none of these contaminants are receiving a 

preliminary regulatory determination.

EPA analyzed the DBP ICR data to generate the following occurrence and exposure 

summary statistics for CCL 3 contaminants: 

• the total number of systems and the total population served by these systems, 
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• the number and percentage of systems with detections, the 90th and 99th percentile 

concentrations from samples with detections, and the minimum, median, and 

maximum concentration s from samples with detections,

• the number and the percentage of systems with at least one concentration greater than 

the 1⁄2 HRL and greater than the HRL,

• the number of people and percentage of the population served by systems with at least 

one concentration greater than the 1⁄2 HRL and greater than the HRL.

In additional to developing system-level results, EPA also analyzed findings at the level 

of the individual treatment plant.

While the DBP ICR only includes 296 systems, this was a census of the largest systems 

in the nation, serving over half of the nation’s population served by PWSs. It has previously been 

vetted for use in regulatory development, and can be used in the regulatory determination 

process.

National Inorganics and Radionuclides Survey (NIRS)

In the mid-1980’s, EPA implemented NIRS to provide a statistically representative 

sample of the national occurrence of inorganic contaminants in CWSs served by ground water.

The survey is stratified based on system size (population served by the system). Most of the 

NIRS data are from smaller systems (92 percent from systems serving 3,300 persons or fewer).

EPA used data from NIRS to evaluate occurrence for one RD 3 contaminant, namely strontium.

The NIRS database includes 36 radionuclides and inorganic compounds (IOCs). NIRS 

provides contaminant occurrence data from 989 ground water CWSs in 49 states (all except 

Hawaii) as well as Puerto Rico. Surface water systems were not included in the study, in part 

because IOCs tend to occur more frequently and at higher concentrations in ground water than in 

surface water. Each of the 989 randomly selected CWSs was sampled once between 1984 and 

1986.

EPA analyzed the NIRS data to generate the following occurrence and exposure 

summary statistics for CCL 3 contaminants: 

• the total number of systems and the total population served by these systems, 

• the number and percentage of systems with detections, the 90th and 99th percentile 

concentrations from samples with detections, and the minimum, median, and 

maximum concentration s from samples with detections,

• the number and the percentage of systems with at least one concentration greater than 

the 1⁄2 HRL and greater than the HRL,

• the number of people and percentage of the population served by systems with at least 

one concentration greater than the 1⁄2 HRL and greater than the HRL.

Because the NIRS data were collected in a randomly designed sample survey, the 

summary statistics are representative of national occurrence in ground water CWSs. Information 

about NIRS monitoring and data analysis is available in Longtin (1988) and USEPA (2008c).

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

provide perspective on the occurrence of the inorganic compounds in surface water systems 

relative to ground water systems EPA also reviewed various supplemental data sources.
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2.4.4 Occurrence in Drinking Water – Secondary Data Sources

The agency evaluated many sources of supplemental drinking water occurrence 

information (including information on occurrence in “source” or “raw” water, e.g., at the 

wellhead in ground water systems) to augment the primary drinking water occurrence data, to 

evaluate the likelihood of contaminant occurrence, and/or to more fully characterize a 

contaminant’s presence in the environment. These data sources are generally narrower in 

geographic scope than the primary drinking water data sources. 

This section provides brief descriptions of many of the supplemental drinking water 

information/data sources cited in contaminant data discussions in this document and in 

companion support documents.

State Monitoring Data 

Since there is no national database that receives and stores all relevant data regarding the 

occurrence of regulated or unregulated contaminants in public drinking water systems, EPA 

conducted a voluntary data call-in from the states, territories, and tribes to obtain regulated 

contaminant occurrence data in support of national occurrence assessments conducted for the 

second Six-Year Review. EPA worked with the states and primacy agencies to receive the states’ 

and agencies’ complete records of compliance monitoring data (public drinking water system 

regulated contaminant occurrence data) for specified contaminants for 1998 through 2005. Using 

these data, EPA established a high quality national contaminant occurrence database consisting 

of data from 47 states/primacy agencies (45 states plus Region 8 and Region 9 tribes) for the 

regulated contaminants requested. For more details on the Six-Year Review Information 

Collection Request (ICR) Dataset, refer to USEPA (2009a).

Six states and the Region 9 tribes submitted PWS occurrence data for unregulated 

contaminants in addition to their data for regulated contaminants. EPA was able to supplement 

these data on unregulated contaminants by downloading additional publicly available monitoring 

data from state Web sites (specifically, from Florida and Wisconsin). The result was a collection 

of unregulated contaminant monitoring data from nine states (eight states and one tribal entity; 

this support document uses the term “state” for SDWA primacy entities for convenience). The 

nine data sets vary in the range of monitoring dates (in some cases extending beyond the 1998-

2005 period of interest for Six-Year Review), the number of contaminants monitored, the 

number of systems reporting monitoring, and the number of samples taken. The number of 

systems varies widely in completeness of coverage relative to all the PWSs in the state. Hence, 

these data are used only to augment and compliment the national drinking water data and to 

assess any unique occurrence that may suggest a need for further review.

2000 Community Water System Survey (2000 CWSS)

The 2000 Community Water System Survey (CWSS) (USEPA, 2002c; USEPA, 2002d) 

gathered data on the financial and operating characteristics of a random sample of CWSs 

nationwide. In addition, the Survey asked all CWSs serving more than 500,000 people (a total of 

83 systems) to provide monitoring results for five regulated compounds (arsenic, atrazine, 2,4-D, 

simazine, and glyphosate) and four unregulated compounds (radon, MTBE, metolachlor, and 

boron), including results from raw water at each intake and from finished water at each treatment 

plant. EPA received completed questionnaires from 58 of the 83 systems. Not all systems 

answered every question. Note that because reported results are incomplete, they are only

illustrative, not statistically representative, and are only used as supplemental information.
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2006 Community Water System Survey (2006 CWSS)

The 2006 CWSS (USEPA, 2009b) gathered data on the financial and operating 

characteristics of a random sample of CWSs nationwide. All systems serving more than 500,000 

people (94 systems in 2006) were included in the sample, and systems in that size category were 

asked questions about concentrations of unregulated contaminants in their raw and finished 

water. Not all systems responded to the survey and, of the systems that responded to the survey, 

not all systems answered every question. EPA supplemented the data set by gathering additional 

information about contaminant occurrence at the systems in this size category from publicly 

available sources (e.g., consumer confidence reports). Note that because reported results are 

incomplete, they are only illustrative, not statistically representative, and are only used as 

supplemental information.

Water Systems’ Consumer Confidence Reports (CCRs)

CCRs are annual water quality reports that CWSs are required to provide to their 

customers. These reports summarize information on water sources, detected contaminants, and 

system compliance with EPA drinking water standards; they may also include general 

educational material. Under the CCR Rule (40 CFR Subpart O), CWSs with 15 or more 

connections or serving at least 25 year-round residents must prepare and distribute a CCR to all 

billing units or service connections every year. Systems serving 100,000 or more residents are 

also required to post their current CCRs on a publicly accessible Internet site. EPA reviewed 

CCRs published by the 26 systems that serve over 1 million customers for unregulated 

contaminant occurrence information. Note that because reported results are incomplete, they are 

more illustrative than statistically representative, and are only used as supplemental information.

United States Department of Agriculture (USDA) Pesticide Data Program (PDP)

The USDA Pesticide Data Program (PDP) has developed a national pesticide residue 

database. PDP was initiated in 1991 to collect data on pesticide residues in food with sampling 

conducted on a statistically defensible representation of pesticide residuals in the United States 

food supply (USDA, 2007). Sampling and testing are conducted on fruits and vegetables, select 

grains, milk, and (as of 2001) drinking water.

The PDP drinking water sampling program was initiated at CWSs in New York and 

California in 2001. Since then the drinking water sampling program has expanded, though a 

somewhat changing mix of states is sampled each year. At one time or another, CWSs in 27 

states and Washington, D.C., have contributed raw and/or finished water data to the program 

(USDA, 2011). The sampling frame is designed to provide coverage in regions of interest for at 

least two years, to reflect the seasonal and climatic variability during growing seasons. PDP 

works with EPA and American Water Works Association (AWWA) to identify specific water 

treatment facilities to be monitored. EPA reviews the PDP data on the occurrence of select 

contaminants in untreated and treated water. The CWSs selected for sampling tend to be smalland medium-sized systems (primarily CWSs serving under 50,000), systems served by surface 

water, and systems located in regions of heavy agriculture. Sampling of untreated water in 

addition to treated water began in 2004 (USDA, 2004).

USGS Pilot Monitoring Program (PMP)

In 1999, the Pilot Monitoring Program (PMP) was initiated by USGS and EPA to provide 

information on pesticide concentrations in drinking water. This study particularly focused on 

small drinking-water supply reservoirs in areas with high pesticide use to test the sampling 
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approach in areas where pesticides are probably present (Blomquist et al., 2001). Sampling sites 

represent a variety of geographic regions, as well as different cropping patterns. The ideal site 

candidates were mostly small reservoirs located in high pesticide-use areas, with a high runoff 

potential. Twelve water-supply reservoirs, considered vulnerable to pesticide contamination, 

were selected from the list of candidates. These 12 sites were located in California, Indiana, 

Ohio, Oklahoma, Louisiana, Missouri, South Carolina, South Dakota, New York, North 

Carolina, Pennsylvania, and Texas.

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 rawwater intake and from the finished drinking-water tap prior to entering the distribution system. 

At some sites, samples were also collected at the reservoir outflow.

USGS NAWQA – Source Water and Drinking Water Studies 

Organic Compounds in Source Water of Selected Community Water Systems (Hopple 

et al., 2009 and Kingsbury et al., 2008)

As part of the NAWQA program, Hopple et al. (2009) and Kingsbury et al. (2008) 

conducted studies to characterize anthropogenic organic compounds in waters used as source 

waters for PWSs in the United States. Hopple et al. (2009) focused on ground water and

Kingsbury et al. (2008) focused on surface water. In Phase 1 of the studies, geographically 

diverse source water samples were collected between October 2002 and July 2005 from 9 CWSs 

served by streams and from 12 aquifers. In Phase 2, USGS collected source and finished water 

samples at a subset of sites between June 2004 and September 2005. 

Water Quality in Public-Supply Wells (Toccalino et al., 2010)

A study by Toccalino et al. (2010), conducted as part of the NAWQA Program, provides 

information about the occurrence of regulated and unregulated contaminants in the environment. 

Water samples were collected from source (untreated) groundwater from 932 public-supply 

wells located in parts of 40 NAWQA Study Units in 41 states. Each well was sampled once 

between 1993 and 2007. Six water-quality properties and 215 chemical contaminants (58 

regulated and 157 unregulated in drinking water) were analyzed. Whenever possible, 

contaminant concentrations were compared to human-health benchmarks: Maximum 

Contaminant Levels (MCLs) for 58 EPA-regulated contaminants and health based screening 

levels (HBSLs) for 96 unregulated contaminants. The public wells sampled in this study 

represented 629 unique PWSs. The 629 PWSs with one or more wells sampled in this study 

represent about 0.5% of the approximately 140,000 groundwater-supplied PWSs but nearly 25% 

of the population served by groundwater PWSs in the United States.

Water Quality in Domestic Wells (DeSimone, 2009)

As part of the NAWQA Program, USGS also conducted an assessment of the quality of

water from domestic wells across the United States (DeSimone, 2009). The program analyzed 

the concentrations of major ions, trace elements, nutrients, radon, and organic compounds 

(pesticides and VOCs) at approximately 2,100 domestic wells (private drinking water wells) 

across 48 states, covering 30 regional aquifers. Water samples were collected between 1991 and 

2004 from domestic wells (private wells used for household drinking water). In addition, USGS 

summarized data from wells sampled for NAWQA agricultural land-use assessment studies to 

provide an indication of the potential effects of agricultural land-use practices on the ground 

water in the aquifers studied.
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Water Quality in Carbonate Aquifers (Lindsey et al., 2008)

A study by Lindsey et al. (2008), conducted as part of the NAWQA Program, provided 

an assessment of the water quality in carbonate aquifers in the United States. Analytical results 

from ground water samples from 865 wells and 177 springs from 14 NAWQA study units (in 20 

states) formed the basis of this study. The study analyzed samples collected between 1993 to 

2005 for major ions, radon, nutrients, pesticides and VOCs. The 12 aquifer systems selected for 

this study represent a wide range of climate, land-use types, and degrees of confinement. The 

water use associated with the sampling sites used in this study fell into four categories: domestic 

water use, public water use, “unused” (e.g., monitoring well or an abandoned domestic well), and 

other (e.g., aquaculture, commercial, dewatering, industrial cooling, etc.). 

USGS National Reconnaissance of Emerging Contaminants (NREC)

For CCL 3, USGS provided EPA with data from various reconnaissance studies looking 

at the occurrence of emerging contaminants in surface waters and ground waters. The data 

represent sites from over 30 states, and include analyses for over 124 contaminants.

National Pesticide Survey (NPS)

In 1990, EPA completed a national survey of pesticides in the source water of drinking 

water wells. The purpose of the National Pesticide Survey (NPS) was to determine the national 

occurrence frequencies and concentrations of select pesticides in the nation’s drinking water 

wells, and to improve EPA’s understanding of how pesticide occurrence in ground water 

correlates with patterns of pesticide usage and ground water vulnerability. The survey included 

approximately 1,300 CWS wells and rural domestic wells. Sampling was conducted between 

1988 and 1990. The survey targeted areas representing a variety of pesticide usage levels and 

ground water vulnerability. The survey was designed to provide a statistically reliable estimate of 

pesticide occurrence in the nation’s drinking water wells. It was not designed to provide 

statistically valid results at the state or local level. Wells were sampled for 101 pesticides, 25 

pesticide degradates, and nitrate (USEPA, 1990).

OPP Estimated Concentrations

EPA’s OPP uses modeling to develop estimated drinking water and environmental 

concentrations for acute and chronic pesticide exposure scenarios involving surface and/or 

ground water (USEPA, 2010a). The Screening Concentration In GROund Water (SCI-GROW) 

model estimates exposure values in vulnerable ground water using the pesticide’s environmental 

fate properties, maximum application rate, and available water monitoring data. These estimates 

are “conservative or high-end exposure values,” and thus should not be used for regional or 

national exposure estimates (USEPA, 2010b). The Pesticide Root Zone Model (PRZM) models 

pesticide migration in soil. The PRZM model can be used in tandem with the Exposure Analysis 

Modeling System (EXAMS) to generate improved exposure estimates. The EXAMS model 

examines the fate, transport, and exposure of pesticides in surface water (USEPA, 2010c).

Environmental Working Group (EWG) Drinking Water Database

In December 2009, the Environmental Working Group (EWG) released its “National 

Drinking Water Database,” which includes data on both regulated and unregulated drinking 

water contaminants collected between 2004 and 2009 from 45 states and the District of 

Columbia (EWG, 2009). (In 2005, EWG had assembled a drinking water compilation covering 

an earlier time period; this older compilation is no longer posted by EWG on its Web site.) EWG 
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states that its 2009 database includes results on 315 contaminants from approximately 48,000 

PWSs; data were obtained primarily from state water offices.

Upon assembly of the database, EWG reviewed the data for inconsistencies, potential 

outliers and other errors. It invited AWWA and the Association of Metropolitan Water Agencies 

(AMWA) to review the data and/or have their constituents, the PWSs, review the data. Some 

corrections apparently were made since the public release of the data in December of 2009. The 

data analyzed in this document were downloaded on January 10, 2010. The information 

presented by EWG on its Web site does not include complete data for assessment; it consists of 

summary reports. These data were used by EPA as supplementary information, and were 

reviewed particularly to assess if there were any unique findings that would warrant additional 

review.

The EWG online data include counts, by state, of the number of systems that had 

detections of each contaminant and the population served by those systems, as well as counts 

(when available) of the number of systems with exceedances of contaminant-specific thresholds

and the associated population served. EWG established the thresholds by surveying health-based 

and legal limits established by state and federal agencies and selecting the most conservative one

for each contaminant. Note that although EWG does provide some data on contaminant 

concentration, the presentation of the concentration data is not complete. Specifically, EWG only 

provides concentration data (study-wide average and range of daily average detected 

concentrations) from the ten water systems with the highest average detected concentrations of 

each contaminant. Hence, the data are not sufficient to estimate the magnitude of occurrence. 

2.5 Evaluation of Analytical and Treatment Methods

2.5.1 Evaluation of Analytical Methods

EPA has evaluated the availability of analytical methods for CCL 3 contaminants. In the 

case of a positive regulatory determination, EPA needs to ensure that laboratories have the 

capacity to measure the newly regulated contaminant with confidence at concentrations of 

concern (generally a health-based threshold) by the time the regulation goes into effect.

The Method Sensitivity Ratio (MSR) provides a measure of analytical method 

performance relative to the HRL for each contaminant. To determine the MSR, a reporting level 

is needed for each contaminant. Reporting levels can be estimated from detection limits or may 

be available in more recent EPA analytical methods as the Lowest Concentration Minimum 

Reporting Level (LCMRL). The “gold standard” for reporting levels is the MRL, which is 

determined by EPA from raw LCMRL data from multiple laboratories. The following quantities 

are used in the MSR calculations in this document:

• Method Detection Limit (MDL) – The MDL is determined over a single day and includes 

an iteration step to optimize the MDL. MDLs are published in EPA analytical methods.

• Detection Limit (DL) – The DL is determined over a three-day period and does not 

include an iteration step to optimize the DL. DLs are published in EPA analytical 

methods where the MDL procedure has not been used. Since DLs are determined over a 

three-day period and their calculation does not include the iterative optimization step, 

DLs are typically not as low as MDLs.

• 5xMDL or DL – A 5x multiplier is applied to the MDL or DL as a surrogate for the 

reporting level based on an MDL or a DL.
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• LCMRL – The LCMRL is a single-laboratory reporting level for selected EPA analytical 

methods. It is determined via a statistical model for future analyte recovery using the 

method. The LCRML is only used for MSR calculation in cases where the analytical 

method has been recently developed and an MRL was not derived for use in EPA’s 

UCMR program;

• MRL – The MRL is the reporting level used for national application in EPA’s UCMR

program. For UCMR 1 analytes, the MRL was established by EPA in light of anticipated 

laboratory capability. For UCMR 2 and UCMR 3 analytes, the MRL has been determined 

via a statistical model from multiple sets of single-laboratory LCMRL data.

The MRL is preferred as the reporting threshold of the best quality, followed by the LCMRL, 

and then 5xMDL and 5xDL. A favorable MSR is one that is greater than ten. That is, it is 

preferable that the concentration at which data can be reliably reported be at least 10 times lower 

than the HRL; this provides a margin of safety for uncertainty in the HRL and/or method 

performance (see USEPA, 2009c).

2.5.2 Evaluation of Treatment Technologies

The availability of treatment technologies is not a factor EPA considers when making a 

regulatory determination. However, suitable treatment technologies must be made available 

before a NPDWR can be promulgated. 

EPA conducted a preliminary review of the literature to investigate which treatment 

technologies have been investigated for their applicability to particular CCL 3 contaminants. The 

review included both peer-reviewed literature and “grey” literature. It was not necessarily 

exhaustive. It was conducted in 2009 and has not been updated since that time.

For most contaminants EPA made some preliminary judgments, within the limits of the 

information available, about which treatment modalities appear to be the most promising. 

A range of traditional and experimental treatment modalities were considered in the 

literature reviewed. When applicable, modification of disinfection practices, pretreatment of 

DBP precursors, and other measures to prevent the formation of DBPs were included in the 

discussion of treatment technologies.

2.6 References 

Agency for Toxic Substances and Disease Registry (ATSDR). 1995. Toxicological Profile for 

1,3-Dinitrobenzene and 1,3,5-Trinitrobenzene (1,3-DNB and 1,3,5-TNB). Available on 

the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp74.pdf. Accessed October 16, 

2012.

American Water Works Association Research Foundation (AwwaRF). 2003. Occurrence of 

MTBE and VOCs in Drinking Water Sources of the United States.

Blomquist, J.D., J.M. Denis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001. 

Pesticides in Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-

2000: Summary of Results from a Pilot Monitoring Survey. U.S. Geological Survey 

Open-File Report 01-456. 65 pp. Available on the Internet at: 

http://md.water.usgs.gov/nawqa/OFR_01-456.pdf.
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Delzer, G.C. and T. Ivahnenko. 2003. Occurrence and Temporal Variability of Methyl tert-Butyl 

Ether (MTBE) and Other Volatile Organic Compounds in Select Sources of Drinking 

Water: Results of the Focused Survey. U.S. Geological Survey Water-Resources 

Investigations Report 02-4084. 65 pp. Available on the Internet at: 

http://sd.water.usgs.gov/nawqa/pubs/wrir/wrir02_4084.pdf.

DeSimone, L.A. 2009. Quality of Water from Domestic Wells in Principal Aquifers of the United 

States, 1991-2004. U. S. Geological Survey Scientific Investigations Report 2008-5227.

139 pp. Available on the Internet at: http://pubs.usgs.gov/sir/2008/5227/. 

Environmental Working Group (EWG). 2009. National Drinking Water Database. Available on 

the Internet at: http://www.ewg.org/tap-water/home. Accessed December 16, 2009.

Gilliom, R.J., J.E. Barbash, C.G. Crawford, P.A. Hamilton, J.D. Martin, N. Nakagaki, L.H. 

Nowell, J.C. Scott, P.E. Stackelberg, G.P. Thelin, and D.M. Wolock. 2007. The Quality 

of Our Nation’s Waters - Pesticides in the Nation’s Streams and Ground Water, 1992–

2001. Appendix 7. Statistical summaries of water-quality data. U.S. Geological Survey 

Circular 1291. 172 pp. Available on the Internet at: 

http://water.usgs.gov/nawqa/pnsp/pubs/circ1291/appendix7/.

Grady, S.J. 2003. A National Survey of Methyl tert-Butyl Ether and Other Volatile Organic 

Compounds in Drinking-Water Sources: Results of the Random Survey. U.S. Geological 

Survey Water-Resources Investigations Report 02-4079. 85 pp. Available on the Internet 

at: http://sd.water.usgs.gov/nawqa/pubs/wrir/wrir02_4079.pdf.

Hamilton, P.A., T.L. Miller, and D.N. Myers. 2004. Water Quality in the Nation’s Streams and 

Aquifers: Overview of Selected Findings, 1991-2001. USGS Circular 1265. Available on 

the Internet at: http://water.usgs.gov/pubs/circ/2004/1265/pdf/circular1265.pdf. 

Hopple, J.A., G.C. Delzer, and J.A. Kingsbury. 2009. Anthropogenic Organic Compounds in 

Source Water of Selected Community Water Systems that Use Groundwater, 2002–05.

U.S. Geological Survey Scientific Investigations Report 2009–5200. 74 pp. Available on 

the Internet at: http://pubs.usgs.gov/sir/2009/5200/pdf/sir2009-5200.pdf.

Ivahnenko, T., S.J. Grady, and G.C. Delzer. 2001. Design of a National Survey of Methyl tertButyl Ether and Other Volatile Organic Compounds in Drinking-Water Sources. U.S. 

Geological Survey Open-File Report 01-271. 42 pp. Available on the Internet at: 

http://sd.water.usgs.gov/nawqa/pubs/ofr/ofr01_271.pdf.

Kingsbury, J.A., G.C. Delzer, and J.A. Hopple. 2008. Anthropogenic Organic Compounds in 

Source Water of Nine Community Water Systems that Withdraw from Streams, 2002–05.

U.S. Geological Survey Scientific Investigations Report 2008–5208. 66 pp. Available on 

the Internet at: http://pubs.usgs.gov/sir/2008/5208/pdf/sir2008-5208.pdf.

Leahy, P.P. and T.H. Thompson. 1994. The National Water-Quality Assessment Program. U.S. 

Geological Survey Open-File Report 94-70. 4 pp. Available on the Internet at: 

http://water.usgs.gov/nawqa/NAWQA.OFR94-70.html. Accessed October 25, 2004.

Lindsey, B.D., M.P. Berndt, B.G. Katz, A.F. Ardis, and K.A. Skach. 2008. Water Quality in 

Carbonate Aquifers in the United States, 1993-2005. U.S. Geological Survey Scientific 

Investigations Report 2008-5240. Available on the Internet at:

http://pubs.usgs.gov/sir/2008/5240/. 
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Longtin, J.P. 1988. Occurrence of Radon, Radium and Uranium in Groundwater. Journal of the 

American Water Works Association. 80(7):84-93.

McGuire, M.J., J.L. McLain, and A. Obolensky. 2002. Information Collection Rule Data 

Analysis. Sponsored by the Microbial/Disinfection By-Products Research Council. 

Jointly funded by AwwaRF and USEPA. Published by by AwwaRF and AWWA.

National Center for Food and Agricultural Policy (NCFAP). 2000. Pesticide Use in U.S. Crop 

Production: 1997. National Summary Report. Available on the Internet at: 

http://www.ncfap.org/documents/nationalsummary1997.pdf.

National Research Council (NRC). 2002. Opportunities to Improve the U.S. Geological Survey 

National Water Quality Assessment Program. National Academy Press. 238 pp.

Available on the Internet at: http://www.nap.edu/catalog/10267.html.

Squillace, P.J., M.J. Moran, W.W. Lapham, C.V. Price, R.M. Clawges and J.S. Zogorski. 1999.

Volatile organic compounds in untreated ambient groundwater of the United States, 

1985-1995. Environmental Science and Technology. 33(23):4176-4187. Available on the 

Internet at: http://sd.water.usgs.gov/nawqa/pubs/journal/EST.voc.squillace.pdf.

Toccalino, P.L., J.E. Norman, and K.J. Hitt. 2010. Quality of Source Water from Public-supply 

Wells in the United States, 1993–2007. U.S. Geological Survey Scientific Investigations 

Report 2010-5024. 206 pp. Available on the Internet at: 

http://pubs.usgs.gov/sir/2010/5024/.

United States Department of Agriculture (USDA). 2004. USDA Pesticide Data Program Water 

Monitoring Survey Overview. 11 March 2004. Available on the Internet at: 

http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=PDPWATOVIEW.

USDA. 2011. Pesticide Data Program, Annual Summary, Calendar Year 2009. May 2011. 

Available on the Internet at: 

http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5091055.

United States Environmental Protection Agency (USEPA). 1986. EPA Guidelines for 

Carcinogen Risk Assessment. Federal Register. Vol. 51, No. 185. p. 33992, September 

24.

USEPA. 1987. National Primary Drinking Water Regulations-Synthetic Organic Chemicals; 

Monitoring for Unregulated Contaminants: Final Rule. Federal Register. Vol. 52, No. 

XXX, p. 25720, July 8, 1987.

USEPA. 1990. National Pesticide Survey: Survey Analytes. EPA 570-9-90-NPS2. Available on 

the Internet at: http://www.epa.gov/nscep/index.html [Search for document number 

570990NPS2.]

USEPA. 1996a. 1996 Toxics Release Inventory: Public Data Release Report. Chapter 3: Yearto-Year Comparison of Toxics Release Inventory Data. Available on the Internet at: 

http://www.epa.gov/tri/tridata/tri96/pdr/chap3.pdf. 

USEPA. 1996b. Monitoring Requirements for Public Drinking Water Supplies. Federal Register. 

Vol. 61, No. 94, p. 24353, May 14, 1996.

USEPA. 1999a. Revisions to the Unregulated Contaminant Monitoring Regulation for Public 

Water Systems; Final Rule. Federal Register. Vol. 64, No. 80, p. 50556, September 17, 

1999.
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USEPA. 1999b. A Review of Contaminant Occurrence in Public Water Systems. EPA-816-R-99-

006, Office of Water.

USEPA. 2000a. The Role of Use-Related Information in Pesticide Risk Assessment and Risk 

Management. August 21, 2000. Office of Pesticide Programs. Available on the Internet 

at: www.epa.gov/oppbead1/use-related.pdf.

USEPA. 2000b. Unregulated Contaminant Monitoring Regulation for Public Water Systems: 

Analytical Methods for Perchlorate and Acetochlor; Announcement of Laboratory 

Approval and Performance Testing (PT) Program for the Analysis of Perchlorate; Final 

Rule and Proposed Rule. Federal Register. Vol. 42, No. 65, p. 11372, March 2, 2000.

USEPA. 2000c. Unregulated Contaminant Monitoring Regulation Analytical Methods and 

Quality Control Manual. EPA 815-R-00-006. 

USEPA. 2001a. Unregulated Contaminant Monitoring Regulation for Public Water Systems; 

Analytical Methods for List 2 Contaminants; Clarifications to the Unregulated 

Contaminant Monitoring Regulation. Federal Register. Vol. 66, No. 8, p. 2273, January 

11, 2001.

USEPA. 2001b. Reference Guide for the Unregulated Contaminant Monitoring Regulation.

Office of Water. EPA 815-R-01-023. 65 pp. Available on the Internet at: 

http://www.epa.gov/ogwdw/ucmr/ucmr1/pdfs/guidance_ucmr1_ref_guide.pdf.

USEPA. 2001c. Occurrence of Unregulated Contaminants in Public Water Systems: An Initial 

Assessment. EPA 815-P-00-001. May, 2001.

USEPA. 2002a. The Toxics Release Inventory (TRI) and Factors to Consider When Using TRI 

Data. EPA 260-F-02-017. November. Available on the Internet at: 

http://www.epa.gov/tri/triprogram/FactorsToConPDF.pdf.

USEPA. 2002b. Analysis of National Occurrence of the 1998 Contaminant Candidate List (CCL) 

Regulatory Determination Priority Contaminants in Public Water Systems. May 2002. 

EPA-815-D-01-002, Office of Water.

USEPA. 2002c. Community Water System Survey 2000. Volume I: Overview. EPA 815-R-02-

005A. December. Available on the Internet at: 

http://www.epa.gov/safewater/consumer/pdf/cwss_2000_volume_i.pdf. 

USEPA. 2002d. Community Water System Survey 2000. Volume II: Detailed Tables and Survey 

Methodology. EPA 815-R-02-005B. December. Available on the Internet at: 

http://www.epa.gov/safewater/consumer/pdf/cwss_2000_volume_ii.pdf. 

USEPA. 2003a. How are the Toxics Release Inventory Data Used? EPA 260-R-002-004. May.

Available on the Internet at:

http://www.epa.gov/tri/guide_docs/pdf/2003/2003_datausepaper.pdf.

USEPA. 2003b. Drinking Water Baseline Handbook, Fourth Edition (Draft). September 4, 2003.

USEPA. 2003c. Occurrence Estimation Methodology and Occurrence Findings for Six-Year 

Review of National Primary Drinking Water Regulations. EPA Report 815-R-03-006, 

Office of Water.

USEPA. 2004. Pesticide Industry Sales and Usage: 2000 and 2001 Market Estimates. Biological 

and Economic Analysis Division, Office of Pesticide Programs. Available on the Internet 

at: http://www.epa.gov/oppbead1/pestsales/index.htm.
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USEPA. 2005a. Guidelines for Carcinogen Risk Assessment. EPA 630-P-03-001B. March.

Available on the Internet at: http://www.epa.gov/ttn/atw/cancer_guidelines_final_3-25-

05.pdf.

USEPA. 2005b. Supplemental Guidance for Assessing Susceptibility to Early-life Exposure to 

Carcinogens. EPA 630-R-03-003F. March. Available on the Internet at: 

http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf.

USEPA. 2005c. Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water 

Systems Revisions; Proposed Rule. Federal Register. Vol. 70, No. 161, p. 49093, August 

22, 2005.

USEPA. 2007. Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water 

Systems Revisions. Federal Register. Vol. 72, No. 2, p. 367, January 4, 2007. 

USEPA. 2008a. 2006 IUR Public Data Background Document. December 2008. Available on 

the Internet at: http://www.epa.gov/iur/pubs/iurdbbackground.pdf

USEPA. 2008b. The Analysis of Occurrence Data from the First Unregulated Contaminant 

Monitoring Regulation (UCMR 1) in Support of Regulatory Determinations for the 

Second Drinking Water Contaminant Candidate List. EPA 815-R-08-012. June 2008.

USEPA. 2008c. Drinking Water: Regulatory Determinations Regarding Contaminants on the 

Second Drinking Water Contaminant Candidate List. Federal Register. Vol. 73, No. 147, 

p. 44251. July 30, 2008.

USEPA. 2008d. 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. EPA 815-R-08-012. June.

USEPA. 2009a. The Analysis of Regulated Contaminant Occurrence Data from Public Water 

Systems in Support of the Second Six-Year Review of National Primary Drinking Water 

Regulations. EPA-815-B-09-006. October 2009.

USEPA. 2009b. Community Water System Survey 2006. Draft 3.5. EPA 815-R-09-001. 

USEPA. 2009c. Final Contaminant Candidate List 3 Chemicals: Classification of the PCCL to 

CCL. Office of Water. EPA 815-R-09-008.

USEPA. 2010a. Water Exposure Models Used by the Office of Pesticide Programs. Available on 

the Internet at: http://www.epa.gov/oppefed1/models/water/models4.htm.

USEPA. 2010b. SCI-GROW Description. Available on the Internet at: 

http://www.epa.gov/oppefed1/models/water/scigrow_description.htm. 

USEPA. 2010c. Water Models. Available on the Internet at: 

http://www.epa.gov/oppefed1/models/water/index.htm#scigrow. 

USEPA. 2011. Exposure Factors Handbook 2011 Edition (Final). U.S. Environmental Protection 

Agency, Washington, DC, EPA/600/R-09/052F. 

USEPA. 2012a. Chemical Data Reporting/Inventory Update Reporting: Basic Information. 

Available on the Internet at: http://www.epa.gov/iur/pubs/guidance/basic.html. Last 

updated August 23, 2012.
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USEPA, 2012b. Non-confidential IUR Production Volume Information. Available on the 

Internet at: http://www.epa.gov/iur/tools/data/2002-vol.html. Last updated February 09, 

2012.

USEPA. 2012c. Storage and Retrieval (STORET) Data Warehouse. Available on the Internet at: 

http://www.epa.gov/storet/index.html. Data Warehouse consulted March 2012.

USEPA. 2012d. Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) 

for Public Water Systems. Federal Register. Vol 77. No. 85, p. 26072, May 2, 2012.

USEPA, 2014a. Protocol for the Regulatory Determinations 3. Including Appendices A-F. April 

2014. EPA-815-R-14-005.

USEPA. 2014b. Health Effects Support Document for Strontium. April 2014. EPA-820-P14-001.

USEPA. 2014c. Occurrence Data from the Second Unregulated Contaminant Monitoring 

Regulation (UCMR 2). April 2014. EPA-815-R-14-004.

United States Geological Survey (USGS). 2001. “Summary publications from 51 NAWQA study 

units sampled in 1991-2001.” Available on the Internet at: 

http://water.usgs.gov/nawqa/nawqasum/. Accessed May 24, 2004. Last updated May 19, 

2004.

United States Geological Survey (USGS). 2014. Pesticide National Synthesis Project, Annual 

Pesticide Use Maps, 2002-2011. Available on the Internet at:

http://water.usgs.gov/nawqa/pnsp/usage/maps/index.php. Accessed April 30, 2014.
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Chapter 3:

Dimethoate

A chapter from: 

Regulatory Determination 3 Support Document

EPA Report 815-R-14-003
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Contents

Contents...........................................................................................................................................3

Exhibits............................................................................................................................................4

Abbreviations...................................................................................................................................5

3.1 Contaminant Background, Chemical and Physical Properties ............................................7

3.2 Sources and Environmental Fate .........................................................................................8

3.2.1 Production, Use, and Release...................................................................................8

3.2.2 Environmental Fate................................................................................................12

3.3 Health Effects.....................................................................................................................13

3.4 Occurrence .........................................................................................................................14

3.4.1 Occurrence in Ambient Water ...............................................................................14

3.4.2 Occurrence in Drinking Water...............................................................................16

3.5 Technology Assessment.....................................................................................................22

3.5.1 Analytical Methods................................................................................................22

3.5.2 Treatment Technologies.........................................................................................23

3.6 Preliminary Regulatory Determination..............................................................................24

3.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL........24

3.6.2 Health Effects (Criterion #1) .................................................................................24

3.6.3 Occurrence in Public Water Systems (Criterion #2)..............................................25

3.6.4 Risk Reduction (Criterion #3)................................................................................26

3.6.5 Regulatory Determination Decision ......................................................................27

3.7 References..........................................................................................................................27
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Exhibits

Exhibit 3-1: Chemical Structure of Dimethoate ..............................................................................7

Exhibit 3-2: Physical and Chemical Properties of Dimethoate .......................................................8

Exhibit 3-3: Annual Production and Importation of Dimethoate in the United States (pounds).....9

Exhibit 3-4: Environmental Releases (in pounds) of Dimethoate in the United States, 1997-

2010....................................................................................................................................10

Exhibit 3-5: Summary of Total Releases and Total Surface Water Discharges of Dimethoate, 

2002, 2004, 2006, 2008, and 2010.....................................................................................10

Exhibit 3-6: Estimated Annual Agricultural Use of Dimethoate, c. 2011.....................................12

Exhibit 3-7: Dimethoate STORET Data – Summary of Detected Concentrations........................15

Exhibit 3-8: Dimethoate STORET Data – Summary of Samples..................................................15

Exhibit 3-9: Dimethoate STORET Data – Summary of Sites .......................................................15

Exhibit 3-10: Dimethoate STORET Data – Summary of States....................................................16

Exhibit 3-11: Dimethoate State Drinking Water Occurrence Data – Summary of Detected 

Concentrations ...................................................................................................................18

Exhibit 3-12: Dimethoate State Drinking Water Occurrence Data – Summary of Samples.........18

Exhibit 3-13: Dimethoate State Drinking Water Occurrence Data – Summary of Systems.........19

Exhibit 3-14: Summary of Dimethoate PDP Data, 2001-2009......................................................20

Exhibit 3-15: Dimethoate Data from Source Water (Hopple et al., 2009 and Kingsbury et al., 

2008) – Summary of Detections from Phase 1 ..................................................................21

Exhibit 3-16: Dimethoate Data from Source Water (Hopple et al., 2009) – Summary of 

Detections from Phase 2 – Ground Water .........................................................................21

Exhibit 3-17: Method Sensitivity Ratio (MSR) for Dimethoate....................................................23
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Abbreviations

a.i. Active Ingredient

AMWA Association of Metropolitan Water Agencies

AWWA American Water Works Association

BMD Benchmark Dose 

BMDL Benchmark Dose Level

CARC Cancer Assessment Review Committee

CAS Chemical Abstracts Service

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

ChE Cholinesterase

CDPR California Department of Pesticide Regulation

CDR Chemical Data Reporting

CUS Chemical Update System

CWS Community Water System

CWSS Community Water System Survey

DL Detection Limit

EDWC Estimated Drinking Water Concentration

EPA Environmental Protection Agency

EPCRA Emergency Planning and Community Right-to-Know Act

EWG Environmental Working Group

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act

FQPA Food Quality Protection Act

GAC Granular Activated Carbon

GC Gas Chromatography

HSDB Hazardous Substance Data Bank

HRL Health Reference Level

ICR Information Collection Request

IRED Interim Reregistration Eligibility Decision

IUR Inventory Update Reporting

LCMRL Lowest Concentration Minimum Reporting Level

MCLG Maximum Contaminant Level Goal

MRL Minimum Reporting Level

MS Mass Spectrometry

MSR Method Sensitivity Ratio

N/A Not Applicable

NAWQA National Water-Quality Assessment

NCFAP National Center for Food and Agricultural Policy

NDWAC National Drinking Water Advisory Council
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NPDWR National Primary Drinking Water Regulation

NTNCWS Non-Transient Non-Community Water System

OPP Office of Pesticide Programs

OPPTS Office of Prevention, Pesticides and Toxic Substances

PBT Persistence, Bioaccumulation, and Toxicity

PDP Pesticide Data Program

PMP Pilot Monitoring Program

PWS Public Water System

QA Quality Assurance

RAIS Risk Assessment Information System

RD 3 Third Regulatory Determination

RED Reregistration Eligibility Decision

RfD Reference Dose

RSC Relative Source Contribution

RSD Relative Standard Deviation

SAP Scientific Advisory Panel

SCI-GROW Screening Concentrations in Ground Water

SDWA Safe Drinking Water Act

STORET Storage and Retrieval

TRI Toxics Release Inventory

TSCA Toxic Substances Control Act

UCM Unregulated Contaminant Monitoring

UCMR 1 First Unregulated Contaminant Monitoring Regulation

UCMR 2 Second Unregulated Contaminant Monitoring Regulation

UF Uncertainty Factor

USDA United States Department of Agriculture

USGS United States Geological Survey

UV Ultraviolet
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Chapter 3: Dimethoate

The Environmental Protection Agency (EPA) is evaluating dimethoate for possible 

regulation as a drinking water contaminant. Dimethoate is listed on the agency’s third 

Contaminant Candidate List (CCL 3) and is being considered for regulation as part of the third

Regulatory Determination (RD 3) under the Safe Drinking Water Act (SDWA) provisions. 

Information on the CCL 3/RD 3 process is found in Chapter 1. Background on data sources used 

to evaluate CCL 3/RD 3 chemicals is found in Chapter 2. This chapter presents information and 

analysis specific to dimethoate, including background information on the contaminant, 

information on sources and environmental fate, an analysis of health effects, an analysis of 

occurrence in ambient and drinking water, and information about the availability of analytical 

methods and treatment technologies. A summary of EPA's decision regarding dimethoate

appears at the end of this chapter. (The decision is presented formally in the associated Federal 

Register notice).

3.1 Contaminant Background, Chemical and Physical Properties

Dimethoate is an organophosphate pesticide, commonly used as an insecticide on field 

crops (e.g., wheat, alfalfa, corn, and cotton), orchard crops, and vegetable crops, and in forestry. 

Synonyms for dimethoate include dimethogen, dimeton, dimevur, and cygon (HSDB, 2009, 

USEPA, 2007b). Dimethoate was first registered for use as a pesticide in 1962 (USEPA, 2007b).

EPA’s Office of Pesticide Programs (OPP) released a Revised Interim Reregistration 

Eligibility Decision (IRED) for dimethoate in 2007 (USEPA, 2007b). Dimethoate is included in 

EPA's Office of Prevention, Pesticides and Toxic Substances (OPPTS) April 2009 list of 67 

chemicals (Pesticide Active Ingredients and Pesticide Inerts) selected for Tier I screening within 

the Endocrine Disruptor Screening Program (EDSP). EDSP consists of a two-tiered screening 

and testing process: Through Tier 1, EPA hopes to identify chemicals that have the potential to 

interact with the endocrine system. Through Tier 2, EPA will determine the endocrine-related 

effects caused by each chemical and obtain information about effects at various doses.

Exhibit 3-1 presents the structural formula for dimethoate. Physical and chemical

properties and other reference information are listed in Exhibit 3-2.

Exhibit 3-1: Chemical Structure of Dimethoate

Source: ChemIDPlus/National Library of Medicine
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Exhibit 3-2: Physical and Chemical Properties of Dimethoate

Property Data

Chemical Abstracts Service (CAS) 

Registry Number 60-51-5

EPA Pesticide Chemical Code Not applicable

Chemical Formula C5H12NO3PS2

Molecular Weight 229.26 g/mol (RAIS, 2009; HSDB, 2009; ChemIDPlus, 2009)

Color/Physical State White crystalline solid (HSDB, 2010)

Boiling Point 361 deg C (HSDB, 2009)

Melting Point 52-52.5 deg C (HSDB, 2010)

Density 1.277 g/mL at 27 deg C (HSDB, 2009)

Freundlich Adsorption Coefficient 1,080 (μg/g)(L/μg)1/n (Speth and Miltner, 1990)

Vapor Pressure 8.25E-06 mm Hg (RAIS, 2009; ChemIDPlus, 2009)

Henry’s Law Constant 2.40E-10 atm-m3/mol (HSDB, 2009; ChemIDPlus, 2009)

Log Kow 0.78 (dimensionless) (RAIS, 2009; HSDB, 2009; ChemIDPlus, 2009)

Koc 5.2-50 L/kg (HSDB, 2010)

Solubility in Water 25,000 mg/L (RAIS, 2009; ChemIDPlus, 2009)

Other Solvents Readily soluble in most organic solvents (HSDB, 2010)

Conversion Factors (at 25 deg C, 

1 atm)

--

Note: “--” indicates that no information was found.

3.2 Sources and Environmental Fate

3.2.1 Production, Use, and Release

Production data for dimethoate are available from EPA’s Inventory Update Reporting 

(IUR) program, and industrial release data are available from EPA’s Toxics Release Inventory 

(TRI). Information on the application of dimethoate as a pesticide is available from several 

sources.

Chemical Update System (CUS) – Inventory Update Reporting (IUR) Program

EPA collects information on chemicals manufactured in or imported into the United 

States from the Toxic Substances Control Act (TSCA) Chemical Substance Inventory. The IUR 

regulation requires manufacturers and importers of chemical substances included on the TSCA 

Chemical Substance Inventory to report site and manufacturing information for chemicals 

manufactured (including imported) in amounts of 25,000 pounds or greater at a single site. 

Additional information on domestic processing and use must be reported for chemicals 

manufactured in amounts of 300,000 pounds or more at a single site. Note that, prior to the 2003 

amendments (i.e., reporting from 2002 or earlier), information was collected for only organic 

chemicals that were manufactured (including imported) in amounts of 10,000 pounds or more, 

and was limited to more basic manufacturing information such as production volume. As a result 

of changes in minimum thresholds and other program modifications, the results from 2006 might 

not be directly comparable to results from earlier years (USEPA, 2010a).

The Chemical Update System – Inventory Update Reporting (CUS-IUR) assigns one of 

eight production and importation volume ranges for each chemical included in the inventory. The 

ranges used for the 2006 reports differ slightly from those used in the 1986 through 2002 reports. 
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Exhibit 3-3 presents the production and importation of dimethoate in the United States from 

1986 to 1990. (Note that no data were reported for 1994, 1998, 2002, or 2006.) Production and 

importation of dimethoate in the United States was between 500,000 and 1 million pounds in 

both 1986 and 1990.

Exhibit 3-3: Annual Production and Importation of Dimethoate in the United 

States (pounds)

Chemical Inventory Update Reporting Cycle

1986 1990 1994 1998 2002 2006

Range of 

Production / 

Importation 

Volume

> 500,000 –

1 million 

pounds

> 500,000 –

1 million 

pounds

No Reports No Reports No Reports No Reports

Toxics Release Inventory (TRI)

EPA established TRI in 1987 in response to section 313 of the Emergency Planning and 

Community Right-to-Know Act (EPCRA). EPCRA section 313 requires the reporting of annual 

information on toxic chemical releases from facilities that meet specific criteria. This reported 

information is maintained in a database accessible through TRI Explorer (USEPA, 2012b).

Although TRI can provide a general idea of release trends, it has limitations. Not all 

facilities are required to report all releases. Facilities are required to report releases if they 

manufacture or process more than 25,000 pounds of a chemical or use more than 10,000 pounds 

per year. Reporting requirements have changed over time (e.g., reporting thresholds have 

decreased); this creates the potential for misleading data trends over time (USEPA, 1996). TRI 

data are meant to reflect releases and should not be used to estimate general public exposure to a 

chemical (USEPA, 2004a).

TRI data for dimethoate from the years 1997 through 2010 are summarized in Exhibit 3-4

(USEPA, 2012b). Total on- and off-site reported releases fluctuated between tens of pounds and 

tens of thousands of pounds during the reporting period, with the majority of these reported 

releases occurring during single years. Reported on-site air emissions were less than 60 pounds 

from 1997 to 2005. From 2006 to 2010, air emissions remained at several thousand pounds, with 

the highest reported emissions of over 15,000 pounds in 2008. Releases via underground 

injection were zero during all years of the reporting period, except in 2004 when reported 

releases exceeded 28,000 pounds. Reported on-site releases to surface water and land also 

generally followed this pattern, peaking at nearly 20,000 pounds released to land in 1998 and 

over 2,000 pounds released to surface water in 2004.
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Exhibit 3-4: Environmental Releases (in pounds) of Dimethoate in the United 

States, 1997-2010

Year

On-Site Releases

Off-Site 

Releases

Total On- &

Off-Site

Releases Air 

Emissions

Surface Water 

Discharges

Underground 

Injection

Releases

to Land

1997 26 0 0 0 0 26

1998 57 5 0 19,975 69 20,106

1999 51 5 0 0 177 233

2000 36 255 0 0 0 291

2001 27 5 0 0 620 652

2002 22 5 0 0 0 27

2003 15 5 0 0 0 20

2004 11 2,615 28,795 29 29 31,480

2005 18 5 0 1,208 17 1,248

2006 6,407 5 0 736 0 7,148

2007 10,419 5 0 1,002 96 11,522

2008 15,549 5 0 5 2 15,561

2009 7,510 5 0 5 2,212 9,732

2010 8,437 5 0 0 0 8,442

Exhibit 3-5 presents the total releases, total surface water discharges, and the count of 

states reporting releases for the years 2002, 2004, 2006, 2008, and 2010 (USEPA, 2012b). Three 

states reported releases of dimethoate in 2002. Four states reported releases of dimethoate in 

2004. Two states reported releases of dimethoate in 2006 and 2008. One state reported releases 

of dimethoate in 2010. The number of states reporting surface water discharges of dimethoate 

ranged from one to two for the years included in Exhibit 3-5. (For the purposes of TRI, “state” 

counts include the District of Columbia and United States territories in addition to the 50 states.)

Exhibit 3-5: Summary of Total Releases and Total Surface Water Discharges of 

Dimethoate, 2002, 2004, 2006, 2008, and 2010

Year Total Releases

(pounds)

Count of States with 

Releases

Total Surface Water 

Discharges

(pounds)

Count of States with 

Surface Water 

Discharges

2002 27 3 5 1

2004 31,480 4 2,615 2

2006 7,148 2 5 1

2008 15,561 2 5 1

2010 8,442 1 5 1

EPA Office of Pesticide Programs (OPP) Reregistration Program

EPA has estimated that the total annual average domestic use of dimethoate (no 

timeframe specified) is approximately 1.8 million pounds (USEPA, 2007b).
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EPA Pesticide Industry Sales and Usage Report

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, 2004b; USEPA, 

2011).

National Center for Food and Agricultural Policy (NCFAP) Pesticide Use Database

The National Center for Food and Agricultural Policy (NCFAP) maintains a national 

Pesticide Use Database, primarily for herbicides. Pesticide use estimates are based on state-level 

commercial agriculture usage patterns and state-level crop acreage. For 1992, NCFAP lists uses 

of dimethoate on 37 crops totaling approximately 2.6 million pounds a.i. per year in 46 states. 

NCFAP lists uses of dimethoate on 33 crops totaling approximately 1.9 million pounds a.i. per 

year in 43 states in 1997 (NCFAP, 2003).

United States Geological Survey (USGS) Pesticide Use Maps

The United States Geological Survey (USGS) has produced maps of pesticide use for 244 

compounds used in United States crop production. The pesticide use maps show the average 

annual pesticide use intensity expressed as average weight (in pounds) of a pesticide applied to 

each square mile of agricultural land in a county. The maps represent pesticide use circa 2002, 

and are based on data from 1999 through 2004. The USGS maps were created using data from 

NCFAP and county-level information on harvested crop acreage from the Census of Agriculture.

Exhibit 3-6 (USGS, 2014) shows the geographic distribution of average annual 

dimethoate use in the United States circa 2011. A breakdown of use by crop is also included.

USGS used two methods to estimate dimethoate usage, since pesticide usage information was 

not available in some districts. At left, the “EPestHigh” estimates were generated by projecting 

usage estimates for such districts based on usage in neighboring districts. At right, the 

“EPestLow” estimates were generated by assuming no usage in such districts. Annual usage

appears to have generally declined over the years, and was somewhere in the range of 0.5 – 1.5 

million pounds in 2011. The maps indicate that dimethoate use is distributed fairly widely in the 

East, Midwest, Great Plains, and West. Note that USGS considers these 2011 maps 

“preliminary,” pending updates with crop data from the 2012 Census of Agriculture.
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Exhibit 3-6: Estimated Annual Agricultural Use of Dimethoate, c. 2011

Source: USGS, 2014

3.2.2 Environmental Fate

Dimethoate is considered highly mobile and relatively non-persistent in the environment 

(USEPA, 2007b). Modeling indicates that if dimethoate is released to the atmosphere it will exist 

in both the vapor and particulate phases. In the vapor phase, dimethoate will undergo oxidation 

reactions in the atmosphere with photochemically produced hydroxyl radicals. The half-life is 

estimated to be 5 hours based on structural estimation (HSDB, 2010). Dimethoate does not 

adsorb ultraviolet (UV) light and is not expected to undergo direct photolysis. Particulate-phase 

dimethoate can also be removed from the atmosphere by wet and dry deposition (HSDB, 2010).

The Koc value of 5.2-50 L/kg indicates that dimethoate is not likely to bind to soil and 

will be mobile in soils (HSDB, 2010). One study found that between 72 and 100 percent of 

dimethoate leached from sandy loam columns (USEPA, 2007b). The Henry’s Law Constant of 

2.40E-10 atm-m3/mol indicates that volatilization from soil is likely to be a slow process. Halflives of between 2 and 122 days validate this assumption (HSDB, 2010). Evaporation may be a 

significant loss mechanism from soil, and one study found dimethoate losses from soil were 

proportional to water losses. Dimethoate is also susceptible to hydrolysis and was found to have 

a half-life of 3.7 days at a pH of 9 (HSDB, 2010); however, hydrolysis half-lives of 68 and 156 

days were observed in sterile buffer solutions at pH 7 and 5, respectively (USEPA, 2007b). 

Biodegradation may also be a significant process as one study found 77% degradation in soil 

after two weeks when an autoclaved sample of the same soil only experienced 18 to 20%

degradation (HSDB, 2010).
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Based on a Koc of 5.2-50 L/kg and a Henry’s Law Constant of 2.40E-10 atm-m3/mol,

dimethoate appears to be very mobile in water. It is not likely to volatilize from water or attach 

to particles (HSDB, 2010). Hydrolysis can be a loss pathway for dimethoate with the process 

being slow at low pH and becoming rapid at higher pH. Half-lives for hydrolysis of dimethoate 

have been reported to be 156 days and 4.4 days in sterile buffer solutions at pH 5 and 9 

respectively (HSDB, 2010). Biodegradation occurs slowly for dimethoate and is dependent on 

temperature. Half-lives between 171 and 219 days were found at 6 deg C and between 29 and 43 

days at 22 degC (HSDB, 2010).

EPA developed the Persistence, Bioaccumulation, and Toxicity (PBT) Profiler to serve as 

a screening tool for estimating the percentage of a contaminant that is predicted to partition to 

water, air, soil, and sediment in a four-compartment system. PBT Profiler (2009) modeling 

predicts that 36% of dimethoate will partition to water, 64% to soil, 0% to air, and 0% to 

sediment. PBT Profiler (2009) modeling also projects biodegradation half-lives in various media. 

For dimethoate, projected half-lives are approximately 15 days in water, 30 days in soil, 0.2 days 

in air, and 140 days in sediment. Note that the PBT Profiler, as a screening tool, provides 

estimated values only and “not . . . definitive PBT determinations” (PBT Profiler, 2009).

3.3 Health Effects

Dimethoate is rapidly metabolized in mammals. Dimethoate affects the proper function 

of the nervous system by inhibiting cholinesterase (ChE), an important enzyme involved in 

neurotransmission. ChE inhibition is mediated by the primary toxic metabolite of dimethoate, 

which is omethoate. ChE inhibition is the most sensitive endpoint described in numerous studies 

with adult and juvenile animals, involving oral, dermal, or inhalation exposure to dimethoate or 

omethoate (USEPA, 2007b).

Dimethoate causes equivocal hemolymphoreticular tumors in male B6C3F1 mice and a 

weak response for combined spleen (hemangioma and hemangiosarcoma), skin 

(hemangiosarcoma), and lymph (angioma and angiosarcoma) tumors in male Wistar rats 

(USEPA, 1990; USEPA, 2007b). Dimethoate is also positive in some mutagenic assays. 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, 1990; 

USEPA, 2007b).

As discussed in the 2007 EPA OPP Reregistration Eligibility Decision (RED) 

assessment, EPA’s Cancer Assessment Review Committee (CARC) classified dimethoate as a 

Group C carcinogen (a possible human carcinogen) in 1991, with concurrence from the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP) on the 

agency’s classification in 1992. The Group C finding was based on equivocal 

hemolymphoreticular tumors in the mouse study, and on the fact that the rat carcinogenicity 

study showed a weak effect of combined spleen (hemangioma and hemangiosarcoma), skin 

(hemangiosarcoma), and lymph (angioma and angiosarcoma) tumors that lacked a dose-response 

effect. 

The 2007, OPP established an acute reference dose (RfD) of 0.013 mg/kg for dimethoate, 

based on a benchmark dose level (BMDL10) of 1.3 mg/kg for inhibition of brain ChE following a 

single oral dose administered to rats on postnatal day 11, using a 100-fold uncertainty factor 

(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). The RfD was derived using the benchmark 
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dose (BMD) method and based on the lower 95% confidence limit (BMDL) of 0.22 mg/kg-day, 

with application of a net uncertainty factor (UF) of 100 (i.e., x10 for intraspecies variability and 

x10 for interspecies variability). EPA’s OPP did not apply any uncertainty factor for database 

deficiencies, nor apply a Food Quality Protection Act (FQPA) factor, indicating that the database 

for dimethoate was considered to be complete. EPA calculated a non-cancer health reference 

level (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 a relative source contribution (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, 1990; USEPA, 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 presents more detailed information about the 

potential health effects for dimethoate (USEPA, 2007b).

3.4 Occurrence

This section presents data on the occurrence of dimethoate in ambient water and drinking 

water in the United States. As described in Section 3.3, an HRL of 15.4 μg/L was calculated for 

dimethoate based on non-carcinogenic effects. This HRL represents the concentration of the 

contaminant in drinking water that is likely to be present without an appreciable risk of 

deleterious effects during a lifetime. Occurrence data from various sources presented in the 

following sections are analyzed with respect to the HRL and the 1⁄2 HRL. When possible, 

estimates of the population exposed at concentrations above the HRL and the 1⁄2 HRL are 

presented.

For additional background information about many of the data sources used to evaluate 

occurrence, please refer to Chapter 2.

3.4.1 Occurrence in Ambient Water

Lakes, rivers, and aquifers are the ambient sources of most drinking water. Contaminant 

occurrence in ambient water provides information on the potential for contaminants to adversely 

affect drinking water supplies. Dimethoate was not included in USGS National Water-Quality 

Assessment (NAWQA) Cycle 1 monitoring (1992-2001). However, dimethoate data are 

available from EPA’s Storage and Retrieval (STORET) Data Warehouse and from a monitoring 

study in California.

Storage and Retrieval (STORET) Data Warehouse

EPA’s STORET Data Warehouse is a collaborative database that 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 are finished drinking water data. Users began populating the STORET Data 

Warehouse in 1999. Most data are post-1999, but some earlier sampling is included.

STORET data have quality limitations. The extent of national coverage and data 

completeness varies from parameter to parameter. There are no restrictions on submission of data 

based on analytical methods, quality assurance (QA) practices, etc. For more general STORET 

data information, please refer to: http://www.epa.gov/storet/index.html.
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EPA reviewed STORET ground water data from wells and surface water data from lakes, 

rivers/streams, and reservoirs (USEPA, 2012c). The STORET Data Warehouse also included 

public water system (PWS) data from three states (Indiana, Missouri, and Ohio); EPA reviewed 

these as well (USEPA, 2012c). (For more data gathered by state drinking water programs, see the 

discussion of state monitoring data in section 3.4.2.)

The results of the STORET analysis are presented in Exhibit 3-7 through Exhibit 3-10.

These STORET data represent dimethoate samples collected between 1989 and 2009. Of 798

sites (211 surface water and 587 ground water) analyzed for dimethoate, 42 (5.26%) had 

detections. These sites all represent ground water and surface water; no PWS data were reported 

for this contaminant. Detected concentrations ranged from 0 μg/L to 0.44 μg/L, with none 

greater than either the 1⁄2 HRL or the HRL. Minimum detected concentrations are reported in 

Exhibit 3-7; these minimum values may be indicative of reporting levels used. No Indiana, 

Missouri, or Ohio PWS data were available for this contaminant.

Exhibit 3-7: Dimethoate STORET Data – Summary of Detected Concentrations

Source Water Type Concentration Value of Detections (μg/L)

Minimum1 Median 90th Percentile Maximum

Ground Water 0 0 0.088 0.44

Surface Water 0 0 0.161 0.268

Total 0 0 0.161 0.44

PWS 2 N/A N/A N/A N/A

N/A = not applicable (no detections in this category).

1

A minimum value of zero may represent a detection that was entered into the database as a non-numerical value 

(e.g., “Present”).

2 It could not be determined from the data in STORET whether the PWS facilities were served by ground water or 

surface water.

Exhibit 3-8: Dimethoate STORET Data – Summary of Samples

Source Water 

Type

Total 

Number of 

Samples

Samples with 

Detections

Samples with 

Detections > 1⁄2 HRL 

(7.7 μg/L)

Samples with 

Detections > HRL 

(15.4 μg/L)

Number Percent Number Percent Number Percent

Ground Water 867 9 1.04% 0 0% 0 0%

Surface Water 4,432 171 3.86% 0 0% 0 0%

Total 5,299 180 3.40% 0 0% 0 0%

PWS1 0 0 0% 0 0% 0 0% 1 It could not be determined from the data in STORET whether the PWS facilities were served by ground water or 

surface water.

Exhibit 3-9: Dimethoate STORET Data – Summary of Sites

Source Water 

Type

Total 

Number of 

Sites

Sites with Detections Sites with Detections

> 1⁄2 HRL (7.7 μg/L)

Sites with Detections 

> HRL (15.4 μg/L)

Number Percent Number Percent Number Percent

Ground Water 587 9 1.53% 0 0% 0 0%
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Source Water 

Type

Total 

Number of 

Sites

Sites with Detections Sites with Detections

> 1⁄2 HRL (7.7 μg/L)

Sites with Detections 

> HRL (15.4 μg/L)

Number Percent Number Percent Number Percent

Surface Water 211 33 15.64% 0 0% 0 0%

Total 798 42 5.26% 0 0% 0 0%

PWS1 0 0 0% 0 0% 0 0% 1 It could not be determined from the data in STORET whether the PWS facilities were served by ground water or 

surface water.

Exhibit 3-10: Dimethoate STORET Data – Summary of States

Source Water 

Type

Total 

Number of 

States

States with Detections States with Detections 

> 1⁄2 HRL (7.7 μg/L)

States with Detections 

> HRL (15.4 μg/L)

Number Percent Number Percent Number Percent

Ground Water 3 2 66.67% 0 0% 0 0%

Surface Water 5 2 40.00% 0 0% 0 0%

Total1 7 4 57.14% 0 0% 0 0%

PWS2 0 0 0% 0 0% 0 0% 1 The number of states with ground water data plus the number of states with surface water data may not equal the 

“Total” number of states providing data because some states provided both ground water and surface water data.

2 It could not be determined from the data in STORET whether the PWS facilities were served by ground water or 

surface water.

Additional Ambient Water Studies

The California Department of Pesticide Regulation (CDPR) undertook a multiyear 

surface water monitoring study. The highest concentration of dimethoate, 2.4 μg/L, was detected 

in the San Joaquin River basin (USEPA, 2007b). This detection did not exceed the 1⁄2 HRL or the 

HRL.

3.4.2 Occurrence in Drinking Water

The agency reviewed a number of data sources for information on contaminant 

occurrence in drinking water. Data and information on dimethoate from the following sources 

are available and are summarized in this section:

• EPA’s Second Unregulated Contaminant Monitoring Regulation (UCMR 2).

• State drinking water monitoring programs.

• Consumer Confidence Reports (CCRs) from PWSs.

• United States Department of Agriculture (USDA) Pesticide Data Program (PDP).

• USGS Pilot Monitoring Program (PMP).

• USGS NAWQA Source Water and Drinking Water Studies.

• Estimated concentrations in environmental media generated by EPA OPP modeling.

• Environmental Working Group (EWG) Drinking Water Database.
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Note that there may be some overlap, as sources with different purposes and audiences 

may have reported the same underlying data.

Reviewed sources that contain no information on dimethoate occurrence included, among 

others, EPA’s First Unregulated Contaminant Monitoring Regulation (UCMR 1), Rounds 1 and 

2 of EPA’s Unregulated Contaminant Monitoring (UCM) program, and EPA’s Community 

Water System Survey (CWSS).

Primary Data Sources

Second Unregulated Contaminant Monitoring Regulation (UCMR 2), 2008-2010

UCMR 2 monitoring, designed to provide nationally representative contaminant 

occurrence data, was conducted from 2008 to 2010. UCMR 2 required surface water systems to 

monitor quarterly and ground water systems to monitor twice per year. There were two tiers of 

monitoring: Assessment Monitoring for contaminants with commonly used analytical method 

technologies, and Screening Survey monitoring for contaminants that require specialized 

analytical method technologies not in wide or common use. 

All very large PWSs (serving more than 100,000 people) and large PWSs (serving 

10,001-100,000 people), plus a statistically representative national sample of 800 small PWSs 

(serving 10,000 people or fewer), were required to conduct Assessment Monitoring during a 12-

month period between January 2008 and December 2010. For the Screening Survey, monitoring 

was required by all very large PWSs, 320 representative large PWSs, and 480 representative 

small PWSs, during a 12-month period between January 2008 and December 2010. See USEPA 

(2007a) and USEPA (2010b) for more information on the UCMR 2 program, including study 

design and data analysis.

Dimethoate was monitored under the UCMR 2 Assessment Monitoring. The minimum 

reporting level (MRL) used for dimethoate in this study was 0.7 μg/L. 

The design of UCMR 2 permits estimation of national occurrence. To calculate national 

extrapolations, the percent of systems (or population served) estimated to exceed a specified 

threshold is multiplied by the total number of systems (or population served) in the nation. (Note 

that because all large and very large systems were required to conduct UCMR 2 Assessment 

Monitoring, survey census figures are used in those size categories.) See Chapter 2 for additional 

information on national extrapolations. 

As of July 2011, a total of 32,013 dimethoate samples have been collected from 4,138

systems. There have not been any detections of dimethoate from the systems that sampled under 

UCMR 2, and thus no exceedances of the HRL or the 1⁄2 HRL. The fact that there have not been 

any detections of dimethoate from systems sampled under UCMR 2 suggests that nation-wide 

occurrence of this compound is likely to be low or negligible.

Supplemental Data Sources

State Monitoring Data, 1995-2007

Because there is no national database that receives and stores all relevant data regarding 

the occurrence of regulated contaminants in public drinking water systems, EPA conducted a 

voluntary data call-in from the states, territories, and tribes to obtain regulated contaminant 

occurrence data in support of national occurrence assessments conducted for the second Six-Year 

Review. For more details on the Six-Year Review-Information Collection Request (ICR)

Dataset, refer to USEPA (2009a). 
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A few states also submitted PWS occurrence data for unregulated contaminants. EPA 

was able to supplement these data on unregulated contaminants by downloading additional 

publicly available monitoring data from state Web sites. The result was a collection of 

unregulated contaminant monitoring data from nine states, representing those states with varying 

degrees of completeness. 

Drinking water occurrence data for dimethoate were submitted from the State of 

California. Dimethoate results from 48% of community water systems (CWSs) and 35% of nontransient non-community water systems (NTNCWSs) in California were included in the data set. 

Results are presented in Exhibit 3-12 through Exhibit 3-13. Since dimethoate data from 

California represent only a small portion of all PWSs in the state, the exhibits do not include 

estimates of population served. Precise information about methods used and reporting levels is 

not available for the state data. Minimum detected concentrations are reported in Exhibit 3-11; 

these minimum values may be indicative of reporting levels used. 

An analysis of the California data set indicates that dimethoate was detected in two

(0.01%) of 21,571 drinking water samples. These detections occurred in two (0.09%) of the 

2,153 systems reporting data. Detected concentrations ranged from 1 μg/L to 2 μg/L; all were 

less than the 1⁄2 HRL and the HRL.

Exhibit 3-11: Dimethoate State Drinking Water Occurrence Data – Summary of 

Detected Concentrations 

State

(Date Range)

Source Water 

Type

Concentration Value of Detections (μg/L)

Minimum Median 90th Percentile 99th Percentile Maximum

California

(1995-2007)

Ground Water 1 1.5 1.9 1.99 2

Surface Water N/A N/A N/A N/A N/A

Unknown N/A N/A N/A N/A N/A

Total 1 1.5 1.9 1.99 2

N/A = not applicable (no detections in this category).

Exhibit 3-12: Dimethoate State Drinking Water Occurrence Data – Summary of 

Samples

State

(Date Range)

Source Water 

Type

Total 

Number 

of 

Samples

Samples with 

Detections

Samples with 

Detections > 1⁄2 HRL 

(7.7 μg/L)

Samples with 

Detections > HRL 

(15.4 μg/L)

Number Percent Number Percent Number Percent

California

(1995-2007)

Ground Water 13,719 2 0.01% 0 0% 0 0%

Surface Water 7,838 0 0% 0 0% 0 0%

Unknown 14 0 0% 0 0% 0 0%

Total 21,571 2 0.01% 0 0% 0 0%
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Exhibit 3-13: Dimethoate State Drinking Water Occurrence Data – Summary of 

Systems

State

(Date Range)

Source 

Water Type

Total 

Number 

of 

Systems

Systems with 

Detections

Systems with 

Detections > 1⁄2 HRL 

(7.7 μg/L)

Systems with 

Detections > HRL 

(15.4 μg/L)

Number Percent Number Percent Number Percent

California

(1995-2007)

Ground Water 1,786 2 0.11% 0 0% 0 0%

Surface Water 356 0 0% 0 0% 0 0%

Unknown 11 0 0% 0 0% 0 0%

Total 2,153 2 0.09% 0 0% 0 0%

Water Systems’ Consumer Confidence Reports (CCRs), 1998-2007

CCRs are annual water quality reports that CWSs are required to provide to their 

customers. These reports summarize information on water sources, detected contaminants, and 

system compliance with EPA drinking water standards; they may also include general 

educational material. Under the CCR Rule (40 CFR Subpart O), CWSs with 15 or more 

connections or serving at least 25 year-round residents must prepare and distribute a CCR to all 

billing units or service connections every year. Systems serving 100,000 or more residents are 

also required to post their current CCRs on a publicly accessible Internet site. EPA reviewed 

CCRs published by the 26 systems that serve over one million customers for unregulated 

contaminant occurrence information. Data on dimethoate were available from CCRs prepared by 

a single CWS in New York, New York. Reporting levels were not specified in this CCR. 

New York City included data on dimethoate in its 1998 through 2007 CCRs. Samples 

were collected from one or more of the city’s three distribution systems (two supplied by surface 

water and one supplied by treated ground water). Dimethoate was not detected in any year. The 

number of samples was not reported.

United States Department of Agriculture (USDA) Pesticide Data Program (PDP), 2001-2009

The USDA PDP maintains a national pesticide residue database. PDP was initiated in 

1991 to collect data on pesticide residues in food with sampling conducted on a statistically 

defensible representation of pesticide residuals in the United States food supply (USDA, 2011). 

Sampling and testing are conducted on fruits and vegetables, select grains, milk, and (as of 2001) 

drinking water.

The PDP drinking water sampling program was initiated at CWSs in New York and 

California in 2001. Since then the drinking water sampling program has expanded, though a 

somewhat changing mix of states is sampled each year. At one time or another, CWSs in 27

states and Washington, D.C. have contributed raw and/or finished water data to the program 

(USDA, 2011). The CWSs selected for sampling tend to be small- and medium-sized systems 

(primarily CWSs serving under 50,000), systems served by surface water, and systems located in 

regions of heavy agriculture. Sampling of raw water in addition to finished water began in 2004 

(USDA, 2004). 

Dimethoate was included in the USDA PDP (see Exhibit 3-14) (USDA, 2012). It was 

detected in three of 5,374 total samples (0.05%) collected between 2001 and 2009, with limits of 

detection ranging from 0.0053 to 0.063 μg/L. Within that set, it was detected in two (0.05%) of 

3,555 finished samples collected. The three detections (0.009, 0.008, and 0.068 μg/L) did not 
OW – OGWDW Regulatory Determination 3 Support Document – Ch 3, Dimethoate April 2014

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exceed the 1⁄2 HRL or the HRL. Note that temporal trends cannot be evaluated based on these 

data since, with the exception of 2002 and 2003, samples were not collected from the same sites 

and states in consecutive years. 

Exhibit 3-14: Summary of Dimethoate PDP Data, 2001-2009

Year Finished/

Raw

Total Number 

of Samples

Number of 

Detections 

Percent of 

Detections

Minimum 

Value of 

Detections 

(μg/L)

Maximum Value 

of Detections 

(μg/L)

2001 Finished 283 0 0% N/A N/A

2002 Finished 659 0 0% N/A N/A

2003 Finished 793 0 0% N/A N/A

2004

Finished 239 0 0% N/A N/A

Raw 239 11 0.4% 0.0088 0.0088

2005

Finished 230 0 0% N/A N/A

Raw 232 0 0% N/A N/A

2006

Finished 368 0 0% N/A N/A

Raw 369 0 0% N/A N/A

2007

Finished 368 0 0% N/A N/A

Raw 364 0 0% N/A N/A

2008

Finished 309 0 0% N/A N/A

Raw 309 0 0% N/A N/A

2009

Finished 306 2 0.7% 0.0075 0.068

Raw 306 0 0% N/A N/A

N/A = not applicable (no detections in this category).

1 Only one distinct detected concentration was reported.

USGS Pilot Monitoring Program (PMP), 1999

In 1999, a PMP was initiated by USGS and EPA to provide information on pesticide 

concentrations in drinking water. This study focused on small drinking water supply reservoirs in 

areas with high pesticide use in order to test the sampling approach in areas where pesticides are 

probably present (Blomquist et al., 2001). Sampling sites represent a variety of geographic 

regions, as well as different cropping patterns. The ideal site candidates were mostly small 

reservoirs located in high pesticide-use areas with a high runoff potential. Twelve water-supply 

reservoirs considered vulnerable to pesticide contamination were selected from the list of 

candidates. These 12 sites were located in California, Indiana, Ohio, Oklahoma, Louisiana, 

Missouri, South Carolina, South Dakota, New York, North Carolina, Pennsylvania, and Texas. 

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 rawwater intake and from the finished drinking water tap prior to entering the distribution system. At 

some sites, samples were also collected at the reservoir outflow.

Dimethoate was an analyte in the PMP. At a method reporting level of 0.005 μg/L, 

dimethoate was detected in four (1.3%) of the 317 samples taken from raw water sites, with a 
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maximum concentration of 0.022 μg/L, less than the 1⁄2 HRL and the HRL. Dimethoate was not 

detected in any of the 221 samples taken from finished water sites (Blomquist et al., 2001).

USGS National Water Quality Assessment (NAWQA) Source Water and Drinking Water 

Studies

Organic Compounds in Source Water of Selected Community Water Systems (Hopple 

et al., 2009 and Kingsbury et al., 2008), 2002-2005

As part of the NAWQA program, Hopple et al. (2009) and Kingsbury et al. (2008) 

conducted studies to characterize anthropogenic organic compounds in U.S. waters used as 

source waters for PWSs. Hopple et al. (2009) focused on ground water and Kingsbury et al.

(2008) focused on surface water. In Phase 1 of the studies (Exhibit 3-15), geographically diverse 

source water samples were collected between October 2002 and July 2005 from nine CWSs 

served by streams and from 221 CWS wells that withdraw from 12 aquifers. Dimethoate was not 

detected in any of the 221 ground water samples and was detected in two (1.4%) of 146 surface 

water samples at levels less than 0.01 μg/L, which is less than the 1⁄2 HRL and the HRL. In Phase 

2 of the studies, USGS collected source and finished water samples at a subset of sites between 

June 2004 and September 2005. In this phase, 48 raw and 48 finished ground water samples were 

analyzed for dimethoate; it was not detected in any of these samples (Hopple et al., 2009). 

Dimethoate was not included in the surface water portion of Phase 2 (Kingsbury et al., 2008).

Phase 2 results are presented in Exhibit 3-16. The reporting level for dimethoate was 0.0061

μg/L in both phases, for both ground and surface water samples.

Exhibit 3-15: Dimethoate Data from Source Water (Hopple et al., 2009 and 

Kingsbury et al., 2008) – Summary of Detections from Phase 1

Ground Water Surface Water

Number of 

Samples

Percent of 

Detections Maximum 

Concentration 

(μg/L)

Number of 

Samples

Percent of 

Detections Maximum 

Concentration 

All (μg/L) > 0.01 μg/

L All > 0.01 μg/L

221 0% 0% N/A 146 1.4% 0% 0.009

N/A = not applicable (no detections in this category).

Exhibit 3-16: Dimethoate Data from Source Water (Hopple et al., 2009) – Summary 

of Detections from Phase 2 – Ground Water

Number of Samples Percent of Detections Maximum Concentration (μg/L)

Raw Water Finished Water Raw Water Finished Water Raw Water Finished Water

48 48 0% 0% N/A N/A

N/A = not applicable (no detections in this category).

OPP Estimated Concentrations

EPA’s OPP used modeling to develop estimated drinking water concentrations (EDWCs) 

for acute and chronic dimethoate exposure scenarios involving ground water (USEPA, 2007b). 

The EDWCs were developed using the Screening Concentrations in Ground Water (SCIGROW) model. In ground water, the EDWC value for dimethoate was 0.04 μg/L for both acute 

and chronic exposures. This value is less than the 1⁄2 HRL and the HRL.
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Environmental Working Group (EWG) Drinking Water Database, 2004-2009

In December 2009, EWG released its “National Drinking Water Database,” which 

includes data on occurrence of drinking water contaminants (regulated and unregulated) 

collected between 2004 and 2009 from 45 states and the District of Columbia (EWG, 2009). The 

2009 EWG database includes results from approximately 48,000 water systems; data were 

obtained primarily from state water offices.

EWG reviewed the data for inconsistencies, potential outliers, and other errors. It also 

invited the American Water Works Association (AWWA) and the Association of Metropolitan 

Water Agencies (AMWA) to review the data and/or have their constituents, the PWSs, review 

the data. Some corrections apparently were made since the public release of the data in 

December, 2009. The data analyzed by EPA were downloaded on December 29, 2010. EPA’s 

analysis is based solely on the data made publicly available by EWG on its Web site. Reporting 

levels are not specified in EWG’s database.

As of November 10, 2010, a total of 1,153 systems reported having tested for dimethoate

between 2004 and 2009. No detections of dimethoate were found.

3.5 Technology Assessment

3.5.1 Analytical Methods

EPA has developed one analytical method for the analysis of dimethoate in drinking 

water: 

• EPA Method 527, Revision 1.0, Determination of Selected Pesticides and Flame 

Retardants in Drinking Water by Solid Phase Extraction and Capillary Column Gas 

Chromatography/Mass Spectrometry (GC/MS), has a Detection Limit (DL) of 0.025 

μg/L. The Lowest Concentration Minimum Reporting Level (LCMRL) is 0.36 μg/L. 

Recoveries range from 78 to 114%, with Relative Standard Deviations (RSDs) of 2.6 

to 7.1% (USEPA, 2005).

Although not listed in EPA Method 527, the MRL for dimethoate is 0.7 μg/L. This value

served as a national benchmark for laboratories that participated in UCMR 2 using EPA Method 

527 (72 FR 367; USEPA, 2007a). The MRL for dimethoate was determined by EPA using data 

generated from EPA Method 527.

An estimated reporting level for the method (calculated as the MRL) was compared to the 

HRL for dimethoate to determine whether the available analytical method is capable of reliable 

quantitation at concentrations of estimated toxicological concern (see Exhibit 3-17). The Method 

Sensitivity Ratio (MSR) is calculated from the following equation:

MSR = HRL (μg/L) / MRL (μg/L)

A favorable MSR is one that is greater than ten. That is, it is preferable that the HRL be 

at least ten times above the concentration at which data can be reliably reported; this provides a 

margin of safety for uncertainty in the HRL and/or method performance (see USEPA, 2009b).
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Exhibit 3-17: Method Sensitivity Ratio (MSR) for Dimethoate

Method MRL (μg/L) HRL (μg/L) MSR

527 0.7 15.4 22

The MSR is greater than ten; hence, the available analytical method is capable of reliable 

quantitation at least ten times below the HRL. 

3.5.2 Treatment Technologies

The availability of treatment technologies is not a factor EPA considers when making a 

regulatory determination. However, suitable treatment technologies must be made available 

before a national primary drinking water regulation (NPDWR) can be promulgated. 

A preliminary review of the literature reveals that the following treatment technologies 

have been investigated empirically for their applicability to this contaminant:

• Granular activated carbon (GAC).

• Powdered activated carbon.

• Conventional (coagulation, flocculation, sedimentation, filtration).

• Chlorine.

• Ozone.

• UV light (including photocatalysis).

• Riverbank filtration.

• Nanofiltration.

• Reverse osmosis.

• Ultrafiltration.

• Softening.

• Advanced oxidation processes (combinations of two or more oxidants including 

UV/peroxide, ozone/peroxide).

• Air stripping.

• Ion exchange.

Based on percentage-removal values reported in the reviewed literature, the most 

promising options appear to be advanced oxidation processes, ozone, reverse osmosis, and 

chlorine. 

Please note that the literature review was not exhaustive, and findings from the reviewed 

studies might not be directly comparable. A full assessment of treatment technology applicability 

will require a more detailed review and analysis of the literature, and possibly additional 

research.
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3.6 Preliminary Regulatory Determination

3.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL

The statutory requirements for the CCL and regulatory determinations can be found in 

SDWA Section 1412(b)(1). The 1996 SDWA Amendments require EPA to publish the CCL 

every five years. The CCL is a list of contaminants that are not subject to any proposed or 

promulgated NPDWRs, are known or anticipated to occur in PWSs, and may require regulation 

under SDWA to protect public health. The 1996 SDWA Amendments also direct EPA to 

determine whether or not to regulate at least five contaminants from the CCL every five years.

There are three criteria to be considered in making a regulatory determination. A decision to 

regulate is warranted if:

(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 PWSs 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 PWSs. 

If EPA determines that all three of these statutory criteria are met, it makes a preliminary 

positive regulatory determination that an NPDWR1 is needed. . Following a comment response 

period and a final positive regulatory determination, the agency has 24 months to publish a 

proposed Maximum Contaminant Level Goal2 (MCLG) and an NPDWR. After the proposal, the 

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

1412(b)(1)(E)).3 The agency may determine that there is no need for a regulation when a 

contaminant fails to meet one or more of the criteria. A decision not to regulate is considered a 

final agency action and is subject to judicial review. The agency can choose to publish a Health 

Advisory (a nonregulatory action) or other guidance for any contaminant on the CCL, 

independent of the regulatory determination. Refer to section 1.4 for a summary of the approach 

used to identify and evaluate contaminants for RD 3. The following section summarizes the 

preliminary RD 3 decision for dimethoate.

3.6.2 Health Effects (Criterion #1)

The first criterion asks if the contaminant may have an adverse effect on the health of 

persons. Since all chemicals have adverse effects at some level of exposure, the challenge is to 

identify an HRL, a dose below which adverse health effects are considered unlikely to occur 

(threshold toxicant), or below which adverse effects have a defined low probability of occurrence 

 

1 An NPDWR is a legally enforceable standard that applies to PWSs. 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.

2 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 nonenforceable health goals." (CFR 141.2)

3 The statute authorizes a nine month extension of this promulgation date.
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(non-threshold toxicant). The key elements that must be considered in evaluating the first 

criterion are the mode of action, the critical effect(s), the dose-response for critical effect(s), the 

RfD for threshold effects, and the slope factor for non-threshold effects.

A full description of the health effects associated with exposure to dimethoate is 

presented in section 3.3 of this document.

Health Criterion Data

Dimethoate is rapidly metabolized in mammals. Dimethoate affects the proper function 

of the nervous system by inhibiting ChE, an important enzyme involved in neurotransmission. 

ChE inhibition is mediated by the primary toxic metabolite of dimethoate, which is omethoate. 

ChE inhibition is the most sensitive endpoint described in numerous studies with adult and 

juvenile animals, involving oral, dermal, or inhalation exposures to dimethoate or omethoate 

(USEPA, 2007b). Dimethoate causes equivocal hemolymphoreticular tumors in male B6C3F1 

mice and a weak response for combined spleen (hemangioma and hemangiosarcoma), skin 

(hemangiosarcoma), and lymph (angioma and angiosarcoma) tumors in male Wistar rats 

(USEPA, 1990; USEPA, 2007b). Dimethoate is also positive in some mutagenic assays. 

A chronic study based on inhibition of brain ChE in rats (American Cyanamid Company, 

1986) was identified as the critical study for establishing a chronic oral RfD of 0.0022 mg/kgday (USEPA, 2007b). The RfD was derived using the BMD method. It is based on the lower 

95% confidence limit (BMDL) of 0.22 mg/kg-day, with a net UF of 100 for 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 a 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, 1990; USEPA, 2007b).

The USEPA’s CARC classified dimethoate as a Group C carcinogen (a possible human 

carcinogen) in 1991, with concurrence from the FIFRA SAP on the agency’s classification in 

1992. The Group C finding was based on equivocal hemolymphoreticular tumors in the mouse 

study and on the fact that the rat carcinogenicity study showed a weak effect of combined spleen 

(hemangioma and hemangiosarcoma), skin (hemangiosarcoma), and lymph (angioma and 

angiosarcoma) tumors that lacked a dose-response effect. 

Health Criterion Conclusion

Toxicological data from animal studies indicate that dimethoate is a ChE inhibitor. Data 

on cholinesterase inhibition in rats support the development of an HRL of 15.4 μg/L for human 

exposure via drinking water. Based on these considerations, EPA concludes that dimethoate 

meets the SDWA statutory criterion #1 for regulatory determination; it may have an adverse 

effect on the health of persons.

3.6.3 Occurrence in Public Water Systems (Criterion #2)

The second criterion asks if the contaminant is known to occur or if there is a substantial 

likelihood that the contaminant will occur in PWSs with a frequency and at levels of public 

health concern. In order to address this question, EPA consulted a variety of information sources, 

including data from the UCMR 2 Screening Survey, a nationally representative survey of PWSs 

conducted from 2008 to 2010. EPA examined the total number of systems that reported 

detections of dimethoate, as well as those that reported concentrations of dimethoate above the 

HRL of 15.4 μg/L.
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Available monitoring data, including data that may shed light on regional and national 

occurrence, are presented in section 3.4. Additional information on production, use, and fate is 

found in section 3.2.

Occurrence Criterion Data

The primary occurrence data for dimethoate are recent (2008-2010) nationallyrepresentative 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 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).

The State of California reported results from testing 24,571 finished drinking water 

samples from 2,153 PWSs; 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 and the HRL. The 

USDA PDP monitored for dimethoate in finished water from 2001 to 2009 and found only two 

detections in 3,555 samples; both detected concentrations were less than the 1⁄2 HRL and the 

HRL. The USGS PMP monitored for dimethoate in finished water in 1999 and found no 

detections greater than 1⁄2 the HRL or the HRL in any of the 221 samples. 

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 

found no detections greater than the 1⁄2 HRL or the HRL in any of the 317 samples. Mixed source 

and finished water data were gathered in a two-phase USGS study conducted between 2002 and 

2005 by Hopple et al. (2009) and Kingsbury et al. (2008). There were 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. There were no Phase 2 surface water results for 

dimethoate. Ambient water data in STORET included no measured results above 0.44 μg/L in 

5,299 samples from 798 sites. Ambient water data reported by the California Department of 

Pesticide Regulation included no measured results above 2.4 μg/L.

Occurrence Criterion Conclusion

Dimethoate was not detected in any of the 32,013 UCMR 2 samples collected by 4,138 

PWSs 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). 

Additional data from states, USDA, and USGS confirm that dimethoate occurrence at levels of 

public health concern is rare. Based on these considerations, EPA concludes that dimethoate 

does not meet the SDWA statutory criterion #2 for regulatory determination; it does not occur 

with a frequency and at levels of public health concern in public water.

3.6.4 Risk Reduction (Criterion #3)

The third criterion asks if, in the sole judgment of the Administrator, regulation presents a 

meaningful opportunity for health risk reduction for persons served by PWSs. In evaluating this 

criterion, EPA looked at several factors.

EPA calculated the total exposed population and the population exposed to levels above 

the HRL. Estimates of the populations exposed and the levels to which they are exposed were 

derived from the monitoring results. These estimates are included in section 3.4 and summarized 

in the “Exposed Population Estimates” section.
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In evaluating the third criterion, EPA also considered effects on potentially sensitive 

populations, including the fetus, infants, and children. Sensitive population considerations are 

discussed in the following “Sensitive Populations” section. 

Exposed Population Estimates

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. 

Sensitive Populations

EPA also evaluated whether 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, 1990, 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. 

Risk Criterion Conclusion 

Based on the estimated exposed population, including sensitive subpopulations, EPA has 

preliminarily determined that dimethoate does not meet the SDWA statutory criterion #3 for 

regulatory determination; regulation of dimethoate does not present a meaningful opportunity 

health risk reduction for persons served by PWSs.

3.6.5 Regulatory Determination Decision

As stated in section 3.6.1, a positive finding for all three criteria is required in order to 

make a determination to regulate a contaminant. EPA has made a preliminary determination that 

dimethoate does not meet all three criteria.

Dimethoate has the potential to cause adverse health effects, including cholinesterase 

inhibition. However, dimethoate does not appear to occur in PWSs with a frequency and at levels 

of public health concern. Dimethoate was not detected in any of the 32,013 UCMR 2 samples 

collected by 4,138 PWSs 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). Due to the relatively small number of people likely exposed to dimethoate 

through drinking water, regulation of dimethoate does not appear to represent a meaningful 

opportunity for health risk reduction for persons served by PWSs. 

Additional information about the preliminary regulatory determination can be found in 

the Federal Register notice.

3.7 References

American Cyanamid Company. 1986. MRID No. 00164177, 40545501. (as cited in USEPA, 

2008).

Blomquist, J.D., J.M. Denis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001. 

Pesticides in Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-

2000: Summary of Results from a Pilot Monitoring Survey. U.S. Geological Survey 
OW – OGWDW Regulatory Determination 3 Support Document – Ch 3, Dimethoate April 2014

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Open-File Report 01-456. 65 pp. Available on the Internet at: 

http://md.water.usgs.gov/nawqa/OFR_01-456.pdf.

ChemIDPlus. 2009. Available on the Internet at: http://chem.sis.nlm.nih.gov/chemidplus/. 

Accessed August 10, 2009. 

Environmental Working Group (EWG). 2009. National Drinking Water Database. Available on 

the Internet at: http://www.ewg.org/tap-water/home. Accessed December 29, 2010.

Hopple, J.A., G.C. Delzer, and J.A. Kingsbury. 2009. Anthropogenic Organic Compounds in 

Source Water of Selected Community Water Systems that Use Groundwater, 2002-05.

U.S. Geological Survey Scientific Investigations Report 2009-5200. 74 pp. Available on 

the Internet at: http://pubs.usgs.gov/sir/2009/5200/pdf/sir2009-5200.pdf.

Hazardous Substances Data Bank (HSDB). 2009. Available on the Internet at: 

http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. Accessed August 10, 2009. 

HSDB. 2010. Available on the Internet at: http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. 

Accessed September 2010.

Kingsbury, J.A., G.C. Delzer, and J.A. Hopple. 2008. Anthropogenic Organic Compounds in 

Source Water of Nine Community Water Systems that Withdraw from Streams, 2002-05.

U.S. Geological Survey Scientific Investigations Report 2008-5208. 66 pp. Available on 

the Internet at: http://pubs.usgs.gov/sir/2008/5208/pdf/sir2008-5208.pdf.

National Center for Food and Agricultural Policy (NCFAP). 2003. National Pesticide Use 

Database. Available on the Internet at: http://www.ncfap.org/pesticideuse.html.

Persistence, Bioaccumulation, and Toxicity (PBT) Profiler. 2009. Available on the Internet at: 

http://www.pbtprofiler.net/. Accessed August 10, 2009. 

Risk Assessment Information System (RAIS). 2009. Available on the Internet at:

http://rais.ornl.gov/. Accessed August 10, 2009. 

Speth, T. and R. Miltner. 1990. Technical note: GAC adsorption capacities for SOCs. Journal of 

the American Water Works Association. 82(2):72.

United States Department of Agriculture (USDA). 2004. USDA Pesticide Data Program Water 

Monitoring Survey Overview. 11 March 2004. Available on the Internet at: 

http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=PDPWATOVIEW.

USDA. 2011. Pesticide Data Program, Annual Summary, Calendar Year 2009. May 2011. 

Available on the Internet at: 

http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5091055.

USDA. 2012. PDP - Databases and Annual Summaries. Available on the Internet at: 

http://www.ams.usda.gov/AMSv1.0/ams.fetchTemplateData.do?template=TemplateG&to

pNav=&leftNav=ScienceandLaboratories&page=PDPDownloadData/Reports&descriptio

n=Download+PDP+Data/Reports&acct=pestcddataprg. Accessed February 15, 2012.

United States Environmental Protection Agency (USEPA). 1990. IRIS Summary for Dimethoate. 

Available on the internet at: http://www.epa.gov/ncea/iris/subst/0044.htm .

USEPA. 1996. 1996 Toxics Release Inventory: Public Data Release Report. Chapter 3: Year-toYear Comparison of Toxics Release Inventory Data. Available on the Internet at: 

http://www.epa.gov/tri/tridata/tri96/pdr/chap3.pdf.
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USEPA. 2004a. The Toxics Release Inventory (TRI) and Factors to Consider When Using TRI 

Data. Available on the Internet at: 

http://www.epa.gov/tri/triprogram/FactorsToConPDF.pdf. File created June 14, 2004. 

Accessed February 22, 2011.

USEPA. 2004b. Pesticides Industry Sales and Usage 2000 and 2001 Market Estimates. 

Available on the Internet at:

http://www.epa.gov/opp00001/pestsales/01pestsales/market_estimates2001.pdf.

USEPA. 2005. Method 527. Determination of Selected Pesticides and Flame Retardants in 

Drinking Water by Solid Phase Extraction and Capillary Column Gas 

Chromatography/Mass Spectrometry (GS/MS). Revision 1.0. Technical Support Center, 

Office of Ground Water and Drinking Water. EPA 815-R-05-005.

USEPA. 2007a. Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water 

Systems Revisions. Federal Register. Vol. 72, No. 2, p. 367, January 4, 2007. 

USEPA. 2007b. Revised Interim Reregistration Decision for Dimethoate. Available on the 

Internet at: 

http://www.epa.gov/pesticides/reregistration/REDs/dimethoate_ired_revised.pdf.

USEPA. 2009a. The Analysis of Regulated Contaminant Occurrence Data from Public Water 

Systems in Support of the Second Six-Year Review of National Primary Drinking Water 

Regulations. EPA-815-B-09-006. October 2009.

USEPA. 2009b. Final Contaminant Candidate List 3 Chemicals: Classification of the PCCL to 

CCL. Office of Water. EPA 815-R-09-008.

USEPA. 2009c. Drinking Water Contaminant Candidate List 3–Final. Federal Register. Vol. 74, 

No. 194, p. 51850, October 8, 2009.

USEPA. 2010a. Non-confidential IUR Production Volume Information. Available on the Internet 

at: http://www.epa.gov/iur/tools/data/2002-vol.html.

USEPA. 2010b. Data Management and Analytical Plan for the Second Unregulated 

Contaminant Monitoring Regulation (UCMR 2) Data. June 2010 Draft Report Submitted 

to EPA.

USEPA. 2011. Pesticide Industry Sales and Usage: 2006 and 2007 Market Estimates. Biological 

and Economic Analysis Division, Office of Pesticide Programs. Available on the Internet 

at: http://www.epa.gov/opp00001/pestsales/.

USEPA. 2012a. Chemical Data Reporting/Inventory Update Reporting: Basic Information. 

http://www.epa.gov/iur/pubs/guidance/basic.html. Last updated August 23, 2012.

USEPA. 2012b. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm.

USEPA. 2012c. Storage and Retrieval (STORET) Data Warehouse. Available on the Internet at: 

http://www.epa.gov/storet/index.html. Data Warehouse consulted March 2012. 

United States Geological Survey (USGS). 2014. Pesticide National Synthesis Project, Annual 

Pesticide Use Maps, 2002-2011. Available on the Internet at:

http://water.usgs.gov/nawqa/pnsp/usage/maps/index.php. Accessed April 30, 2014.
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Chapter 4:

1,3-Dinitrobenzene

A chapter from: 

Regulatory Determination 3 Support Document

EPA Report 815-R-14-003
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Contents

Contents.......................................................................................................................................... 3

Exhibits........................................................................................................................................... 4

Abbreviations.................................................................................................................................. 5

4.1 Contaminant Background, Chemical and Physical Properties ............................................7

4.2 Sources and Environmental Fate .........................................................................................8

4.2.1 Production, Use, and Release...................................................................................8

4.2.2 Environmental Fate................................................................................................10

4.3 Health Effects.....................................................................................................................11

4.4 Occurrence .........................................................................................................................13

4.4.1 Occurrence in Ambient Water ...............................................................................13

4.4.2 Occurrence in Drinking Water...............................................................................15

4.5 Technology Assessment.....................................................................................................16

4.5.1 Analytical Methods................................................................................................16

4.5.2 Treatment Technologies.........................................................................................17

4.6 Preliminary Regulatory Determination..............................................................................17

4.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL........17

4.6.2 Health Effects (Criterion #1) .................................................................................18

4.6.3 Occurrence in Public Water Systems (Criterion #2)..............................................19

4.6.4 Risk Reduction (Criterion #3)................................................................................20

4.6.5 Regulatory Determination Decision ......................................................................21

4.7 References..........................................................................................................................21
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Exhibits

Exhibit 4-1: Chemical Structure of 1,3-Dinitrobenzene ................................................................. 7

Exhibit 4-2: Physical and Chemical Properties of 1,3-Dinitrobenzene .......................................... 8

Exhibit 4-3: Annual Production and Importation of 1,3-Dinitrobenzene in the United States 

(pounds) .......................................................................................................................................... 9

Exhibit 4-4: Environmental Releases (in pounds) of 1,3-Dinitrobenzene in the United States, 

1997-2010 ..................................................................................................................................... 10

Exhibit 4-5: Summary of Total Releases and Total Surface Water Discharges of 1,3-

Dinitrobenzene, 2002, 2004, 2006, 2008, and 2010 ..................................................................... 10

Exhibit 4-6: 1,3-Dinitrobenzene STORET Data – Summary of Detected Concentrations .......... 14

Exhibit 4-7: 1,3-Dinitrobenzene STORET Data – Summary of Samples.................................... 14

Exhibit 4-8: 1,3-Dinitrobenzene STORET Data – Summary of Sites.......................................... 15

Exhibit 4-9: 1,3-Dinitrobenzene STORET Data – Summary of States........................................ 15

Exhibit 4-10: Method Sensitivity Ratio (MSR) for 1,3-Dinitrobenzene ...................................... 17
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Abbreviations

ATSDR Agency for Toxic Substances and Disease Registry

ATSDR MRL ATSDR Minimum Risk Level

CAS Chemical Abstracts Service

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

CUS-IUR Chemical Update System - Inventory Update Reporting

CWSS Community Water System Survey

DL Detection Limit

EPA Environmental Protection Agency

EPCRA Emergency Planning and Community Right-to-Know Act

GAC Granular Activated Carbon

GC Gas Chromatography

HSDB Hazardous Substances Data Bank

HRL Health Reference Level

IRIS Integrated Risk Information System

IUR Inventory Update Reporting

LOAEL Lowest Observed Adverse Effect Level

LCMRL Lowest Concentration Minimum Reporting Level

MCLG Maximum Contaminant Level Goal

MRL Minimum Reporting Level

MS Mass Spectrometry

MSR Method Sensitivity Ratio

NAWQA National Water-Quality Assessment

NDWAC National Drinking Water Advisory Council

NOAEL No Observed Adverse Effect Level

NPDWR National Primary Drinking Water Regulation

PBT Persistence, Bioaccumulation, and Toxicity

PWS Public Water System

QA Quality Assurance

RAIS Risk Assessment Information System

RD 3 Third Regulatory Determination

RfD Reference Dose

RSC Relative Source Contribution

RSD Relative Standard Deviation

SDWA Safe Drinking Water Act

STORET Storage and Retrieval

TRI Toxics Release Inventory

TSCA Toxic Substances Control Act
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UCM Unregulated Contaminant Monitoring

UCMR 1 First Unregulated Contaminant Monitoring

UCMR 2 Second Unregulated Contaminant Monitoring

UF Uncertainty Factor

USGS United States Geological Survey

UV Ultraviolet
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Chapter 4: 1,3-Dinitrobenzene

The Environmental Protection Agency (EPA) is evaluating 1,3-dinitrobenzene for

possible regulation as a drinking water contaminant. 1,3-Dinitrobenzene is listed on the agency’s 

third Contaminant Candidate List (CCL 3) and is being considered for regulation as part of the 

third Regulatory Determination (RD 3) under the Safe Drinking Water Act (SDWA) provisions. 

Information on the CCL 3/RD 3 process is found in Chapter 1. Background on data sources used 

to evaluate CCL 3/RD 3 chemicals is found in Chapter 2. This chapter presents information and 

analysis specific to 1,3-dinitrobenzene, including background information on the contaminant, 

information on sources and environmental fate, an analysis of health effects, an analysis of 

occurrence in ambient and drinking water, and information about the availability of analytical 

methods and treatment technologies. A summary of EPA's decision regarding 1,3-dinitrobenzene

appears at the end of this chapter. (The decision is presented formally in the associated Federal 

Register notice).

4.1 Contaminant Background, Chemical and Physical Properties

1,3-Dinitrobenzene is a nitro aromatic compound that is used as an industrial chemical 

and in the production of munitions and other substances. Synonyms for 1,3-dinitrobenzene 

include m-dinitrobenzene, binitrobenzene, and 1,3-dinitrobenzol (HSDB, 2009).

Exhibit 4-1 presents the structural formula for 1,3-dinitrobenzene. Physical and chemical 

properties and other reference information are listed in Exhibit 4-2.

Exhibit 4-1: Chemical Structure of 1,3-Dinitrobenzene

Source: ChemIDPlus/National Library of Medicine
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Exhibit 4-2: Physical and Chemical Properties of 1,3-Dinitrobenzene

Property Data

Chemical Abstracts Service (CAS) Registry 

Number 99-65-0

EPA Pesticide Chemical Code Not applicable

Chemical Formula C6H4N2O4

Molecular Weight 168.11 g/mol (RAIS, 2009; HSDB, 2009; ChemIDPlus, 2009)

Color/Physical State Pale white or yellow, crystalline solid (HSDB, 2010)

Boiling Point 302.8 deg C (HSDB, 2009)

Melting Point 89-90 deg C (HSDB, 2010)

Density 1.575 at 18 deg C/4 deg C (HSDB, 2010)

Freundlich Adsorption Coefficient 1,080 (μg/g)(L/μg)1/n (Speth and Miltner, 1990)

Vapor Pressure 0.0002 mm Hg at 25 deg C (HSDB, 2012)

Henry’s Law Constant 4.9E-08 atm-m3/mol (HSDB, 2009; ChemIDPlus, 2009)

Log Kow 1.49 (dimensionless) (RAIS, 2009; HSDB, 2009; ChemIDPlus, 2009)

Koc 150 L/kg (HSDB, 2010)

Solubility in Water 533 mg/L (RAIS, 2009; HSDB, 2009; ChemIDPlus, 2009)

Other Solvents Very soluble in acetone and ethanol; soluble in ether (HSDB, 2010)

Conversion Factors (at 25 deg C, 1 atm)

1 ppm (v/v) = 0.145 mg/m3

1 mg/m3 = 6.88 ppm (v/v)

(calculated)

Note: “--” indicates that no information was found.

4.2 Sources and Environmental Fate

4.2.1 Production, Use, and Release

As noted above, 1,3-dinitrobenzene is a nitro aromatic compound that is used as an 

industrial chemical and in the production of munitions and other substances. There are no known 

natural sources of 1,3-dinitrobenzene.

Production data for 1,3-dinitrobenzene are available from EPA’s Inventory Update 

Reporting (IUR) program, and industrial release data are available from EPA’s Toxics Release 

Inventory (TRI), as described below.

Chemical Update System (CUS) – Inventory Update Reporting (IUR) Program

EPA collects information on chemicals manufactured in or imported into the United 

States from the Toxic Substances Control Act (TSCA) Chemical Substance Inventory. The IUR 

regulation requires manufacturers and importers of chemical substances included on the TSCA 

Chemical Substance Inventory to report site and manufacturing information for chemicals 

manufactured (including imported) in amounts of 25,000 pounds or greater at a single site. 

Additional information on domestic processing and use must be reported for chemicals 

manufactured in amounts of 300,000 pounds or more at a single site. Note that, prior to the 2003 

amendments (i.e., reporting from 2002 or earlier), information was collected for only organic 

chemicals that were manufactured (including imported) in amounts of 10,000 pounds or more, 

and was limited to more basic manufacturing information such as production volume. Because of 

changes in minimum thresholds and other program modifications, the results from 2006 might 

not be directly comparable to results from earlier years (USEPA, 2010a).
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The Chemical Update System – Inventory Update Reporting (CUS-IUR) assigns one of 

eight production and importation volume ranges for each chemical included in the inventory. The 

ranges used for the 2006 reports differ slightly from those used in the 1986 through 2002 reports. 

Exhibit 4-3 presents the production and importation of 1,3-dinitrobenzene in the United States 

for 1986. (No data were reported for any other years.) Production and importation of 1,3-

dinitrobenzene in the United States was between 10 and 50 million pounds in 1986.

Exhibit 4-3: Annual Production and Importation of 1,3-Dinitrobenzene in the 

United States (pounds)

Chemical Inventory Update Reporting Cycle

1986 1990 1994 1998 2002 2006

Range of 

Production / 

Importation 

Volume

> 10 million –

50 million 

pounds

No Reports No Reports No Reports No Reports No Reports

Toxics Release Inventory (TRI)

EPA established TRI in 1987 in response to section 313 of the Emergency Planning and 

Community Right-to-Know Act (EPCRA). EPCRA section 313 requires the reporting of annual 

information on toxic chemical releases from facilities that meet specific criteria. This reported 

information is maintained in a database accessible through TRI Explorer (USEPA, 2012a).

Although TRI can provide a general idea of release trends, it has limitations. Not all 

facilities are required to report all releases. Facilities are required to report releases if they 

manufacture or process more than 25,000 pounds of a chemical or use more than 10,000 pounds

per year. Reporting requirements have changed over time (e.g., reporting thresholds have 

decreased); this creates the potential for misleading data trends over time (USEPA, 1996). TRI 

data are meant to reflect releases and should not be used to estimate general public exposure to a 

chemical (USEPA, 2004).

TRI data for 1,3-dinitrobenzene from the years 1997 through 2010 are summarized in 

Exhibit 4-4 (USEPA, 2012a). Total on- and off-site reported releases for most years ranged from 

hundreds of pounds to tens of thousands of pounds, though total reported releases for 2004 were 

greater than 500,000 pounds (primarily as off-site releases). Reported on-site releases to air and 

surface water were both in the range of hundreds of pounds from 1997-2002, after which 

reported air emissions increased to thousands and tens of thousands of pounds, and reported 

surface water releases decreased to below 15 pounds. Releases to land ranged from zero pounds 

to thousands of pounds. There were no reported releases by underground injection over the 

reporting period.
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Exhibit 4-4: Environmental Releases (in pounds) of 1,3-Dinitrobenzene in the 

United States, 1997-2010

Year

On-Site Releases Off-Site 

Releases

Total On- &

Off-Site

Air Emissions Releases

Surface Water 

Discharges

Underground 

Injection

Releases

to Land

1997 421 816 0 451 0 1,688

1998 383 517 0 516 0 1,416

1999 385 442 0 49 100 976

2000 355 466 0 134 0 955

2001 316 412 0 0 0 728

2002 296 438 0 3,774 0 4,508

2003 63 0 0 229 0 292

2004 4,149 2 0 161 524,650 528,962

2005 13,698 8 0 123 1 13,830

2006 8,834 0 0 156 8,755 17,745

2007 7,350 0 0 7,310 0 14,660

2008 19,202 2 0 654 0 19,858

2009 8,815 13 0 575 0 9,403

2010 8,792 0 0 94 1,709 10,595

Exhibit 4-5 presents the total releases, total surface water discharges, and the count of 

states reporting releases for the years 2002, 2004, 2006, 2008, and 2010 (USEPA, 2012a). One 

state reported releases of 1,3-dinitrobenzene in 2002, 2004, 2006, 2008, and 2010. The number 

of states reporting surface water discharges of 1,3-dinitrobenzene ranged from none to one for 

the years included in Exhibit 4-5.

Exhibit 4-5: Summary of Total Releases and Total Surface Water Discharges of 

1,3-Dinitrobenzene, 2002, 2004, 2006, 2008, and 2010

Year Total Releases

(pounds)

Count of States with 

Releases

Total Surface Water 

Discharges

(pounds)

Count of States with 

Surface Water 

Discharges

2002 4,508 1 438 1

2004 528,962 1 2 1

2006 17,745 1 0 0

2008 19,858 1 2 1

2010 10,595 1 0 0

4.2.2 Environmental Fate

A vapor pressure of 0.0002 mm Hg at 25 deg C indicates that 1,3-dinitrobenzene will 

likely be in the vapor phase if it is released to the atmosphere. Vapor-phase 1,3-dinitrobenzene 

undergoes oxidative reactions in the atmosphere. Its degradation by hydroxyl radicals is 

estimated to have a half-life of 526 days (HDSB, 2010). It is known to absorb light greater than 

290 nm and therefore may be susceptible to direct photolysis reactions, but the reaction rates for 

those reactions are unknown. 
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The Koc value of 150 L/kg implies that 1,3-dinitrobenzene is expected to have moderate 

mobility and not strongly adsorb to soil. It is known, however, to bind strongly to clay. Therefore 

it is expected to be less mobile in soils with high clay content over those with high organic 

content (HDSB, 2010). The relatively low Henry’s Law Constant of 4.9E-08 atm-m3/mol

indicates that 1,3-dinitrobenzene is unlikely to volatilize from soil. Biodegradation can occur 

slowly. A half-life of more than 64 days was measured in a silt loam inoculums at 25 deg C

(HDSB, 2010).

Based on a Henry’s Law Constant of 4.9E-08 atm-m3/mol, volatilization is not expected 

to be a major loss pathway in water (HSDB, 2010). A Koc of 150 L/kg (HSDB, 2010) suggests

that 1,3-dinitrobenzene will not bind to suspended solids or sediments and will be mobile in 

water. 1,3-Dinitrobenzene has been found to degrade in acclimated river water with a half-life of 

1 day, but did not degrade in unacclimated river water (HDSB, 2010). It is not expected to 

undergo hydrolysis because it does not have structural groups which are typically susceptible to 

hydrolysis. 

EPA developed the Persistence, Bioaccumulation, and Toxicity (PBT) Profiler to serve as 

a screening tool for estimating the percentage of a contaminant that is predicted to partition to 

water, air, soil, and sediment in a four-compartment system. PBT Profiler (2009) modeling 

predicts that 34% of 1,3-dinitrobenzene will partition to water, 65% to soil, 1% to air, and 0% to 

sediment. PBT Profiler (2009) modeling also projects biodegradation half-lives in various media.

For 1,3-dinitrobenzene, projected half-lives are approximately 38 days in water, 75 days in soil, 

540 days in air, and 340 days in sediment. Note that the PBT Profiler, as a screening tool, 

provides estimated values only and “not . . . definitive PBT determinations” (PBT Profiler, 

2009).

4.3 Health Effects

1,3-Dinitrobenzene is absorbed from the gastrointestinal tract of humans and animals. In 

F-344 rats, the highest levels of radio-labeled 1,3-dinitrobenzene were found in the liver, kidney, 

and sciatic nerve after administration of radio-labeled compound (USEPA, 1988). 1,3-

Dinitrobenzene appears to be highly metabolized through full or partial reduction of the nitrogroups to amine functional groups, and in some cases, via hydroxylation of the benzene ring. In 

one study in rabbits, the major metabolites in the urine were 2,4-diaminophenol and 3-

nitroaniline (Hajjar et al., 1992). Some of the metabolites of 1,3-dinitrobenzene are excreted as 

glucuronide or sulfate conjugates. The urine is the major route of excretion, and unabsorbed 

material is found in the feces.

1,3-Dinitrobenzene has demonstrated adverse health effects in many rodent and 

occupational studies. Occupational studies indicate that humans are more sensitive to the effects 

of 1,3-dinitrobenzene than are rodents because of lower methemoglobin reductase activity in 

some humans, especially neonates (ATSDR, 1995; USEPA, 1988), when compared to rodents 

(Linder et al., 1986, 1988). Methemoglobinemia, hemolytic anemia, and cyanosis are seen in 

workers who experience an acute reaction to 1,3-dinitrobenzene (Hajjar et al., 1992).

The lethal dose of 1,3-dinitrobenzene was estimated to be between 5 and 50 mg/kg 

(Linder et al., 1986, 1988). Primary adverse biological effects from exposure to 1,3-

dinitrobenzene are on red blood cells, spleen, and testes. In a drinking water study, groups of 20 

Carworth Farm rats of each sex were exposed to 0, 3, 8, or 20 mg/L 1,3-dinitrobenzene for 16 

weeks (Cody et al., 1981; USEPA, 1988). Hematocrit, hemoglobin levels, and white cell counts 

were measured on selected males in each group at 5, 10, and 14 weeks after the study 
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commencement. Body weight, food and water consumption were recorded throughout the 

experiment. At study termination, body and organ weights were measured, and all major tissues 

were examined histopathologically. 

At the 20 mg/L dose, 1,3-dinitrobenzene decreased body weight gain in females, 

decreased hemoglobin concentrations and caused testicular atrophy in males, and was associated 

with splenic enlargement and hemosiderin deposits in both sexes of rats. Significantly increased 

spleen weights were also observed in both sexes of rats treated with 8 mg/L 1,3-dinitrobenzene. 

No treatment-related effects were identified at 3 mg/L 1,3-dinitrobenzene. Cody et al. (1981) 

reported that the 3 mg/L concentration no observed adverse effect level (NOAEL) corresponded 

to a mean daily 1,3-dinitrobenzene dose of 0.40 mg/kg in male rats. 

Cody et al. (1981) identified signs of neurotoxicity in the same study. Rats treated with 3 

and 8 mg/L 1,3-dinitrobenzene showed significantly increased running wheel activity in running 

wheel studies, and non-significant increases in recorded movement activity on a platform in 

activity platform count studies. There was no dose-response reported for these observations. 

Hajjar et al. (1992) later expressed concern about whether these effects were test compoundrelated. In another component of the Cody et al. (1981) study, the length of the period of sodium 

hexobarbital-induced sleep time was significantly decreased at concentrations of 50 mg/L or 

higher for females, and at 100 mg/L or higher for males. This was interpreted by the authors to 

suggest induction of hexobarbital-metabolizing enzymes by 1,3-dinitrobenzene in microsomes of 

metabolically active cells primarily in the liver.

There have been many animal studies on the testicular effects (i.e., sperm morphology, 

motility, and fertility) of 1,3-dinitrobenzene, as discussed in Hajjar et al. (1992). Sertoli cells 

appear to be the target for the effects of 1,3-dinitrobenzene on sperm, and older animals appear 

to be more sensitive than younger ones. 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). 

1,3-Dinitrobenzene is mutagenic in several strains of S. typhimurium, both with and 

without activation. There are currently no long-term studies of the tumorigenic effects of 1,3-

dinitrobenzene. The EPA Integrated Risk Information System (IRIS) assessment of the 

carcinogenicity of 1,3-dinitrobenzene currently classifies it in Group D (not classifiable as to 

human carcinogenicity) (USEPA, 1988).

The reference dose (RfD) for 1,3-dinitrobenzene is 0.0001 mg/kg-day (USEPA, 1988; 

Cody et al., 1981), and 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). An 

uncertainty factor (UF) of 3,000 was applied in the RfD derivation (10 for intraspecies 

differences, 10 for interspecies differences, 10 for extrapolating from a subchronic to a chronic 

duration, and 3 for the lack of chronic, developmental, and multigenerational reproductive 

toxicity studies). The EPA calculated a non-cancer Health Reference Level (HRL) of 0.7 μg/L 

for 1,3-dinitrobenzene using the oral RfD of 0.0001 mg/kg-day for a 70 kg adult ingesting 2 L of 

drinking water per day, with the application of a 20% relative source contribution (RSC).

The current EPA oral RfD value is supported by a more recent 1,3-dinitrobenzene 

assessment conducted by the Agency for Toxic Substances and Disease Registry (ATSDR) 

(ATSDR, 1995). An oral intermediate duration ATSDR minimal risk level (MRL) of 0.0005 

mg/kg-day for splenic hemosiderosis in male rats was established using a lowest observed 

adverse effect level (LOAEL) of 0.54 mg/kg-day (animals were dosed by gavage 5 days/week 
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for 12 weeks, and the LOAEL of 0.75 mg/kg-day was normalized for a 7-day/week exposure) 

and a net UF of 1,000 (intraspecies variability and interspecies variability, LOAEL to NOAEL). 

In the same study, adverse testicular effects were also observed at doses ≥1.5 mg/kg-day and 

altered spermatogenesis was noted at ≥3 mg/kg-day (Linder et al., 1986). The observed testicular

effects were at higher doses compared to the splenic hemosiderosis and therefore considered 

secondary. Based on EPA assumptions and a net UF of 3,000 (10 for intraspecies variability, 10 

for interspecies variability, 10 for the use of a LOAEL in place of a NOAEL and 3 for 

subchronic to chronic) 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, 1988) presents more detailed information about the potential health effects 

for 1,3-dinitrobenzene.

Individuals with a genetic predisposition to methemoglobinemia and/or hemosiderosis, 

neonates and those co-exposed to other hemolytic agents, could be sensitive to 

1,3-dinitrobenzene exposure. Males having sperm production complications could also have 

increased sensitivity to 1,3-dinitrobenzene exposure.

4.4 Occurrence

This section presents data on the occurrence of 1,3-dinitrobenzene in ambient water and 

drinking water in the United States. As described in Section 4.3, an HRL of 0.7 μg/L was 

calculated for 1,3-dinitrobenzene based on non-carcinogenic effects. An HRL represents the 

concentration of a contaminant in drinking water that is likely to be present without an 

appreciable risk of deleterious effects during a lifetime. Occurrence data from various sources 

presented below are analyzed with respect to the HRL and 1⁄2 the HRL. When possible, estimates 

of the population exposed at concentrations above the HRL and 1⁄2 the HRL are presented.

For additional background information about many of the data sources used to evaluate 

occurrence, please refer to Chapter 2.

4.4.1 Occurrence in Ambient Water

Lakes, rivers, and aquifers are the ambient sources of most drinking water. Contaminant 

occurrence in ambient water provides information on the potential for contaminants to adversely 

affect drinking water supplies. 1,3-Dinitrobenzene was not included in United States Geological 

Survey (USGS) National Water-Quality Assessment (NAWQA) Cycle 1 monitoring (1992-

2001). However, 1,3-dinitrobenzene data are available from EPA’s Storage and Retrieval 

(STORET) Data Warehouse. 

Storage and Retrieval (STORET) Data Warehouse

EPA’s STORET Data Warehouse is a collaborative database that 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 are finished drinking water data. Users began populating the STORET Data 

Warehouse in 1999. Most data are post-1999, but some earlier sampling is included.

STORET data have quality limitations. The extent of national coverage and data 

completeness varies from parameter to parameter. There are no restrictions on submission of data 

based on analytical methods, quality assurance (QA) practices, etc. For more general STORET 

data information, please refer to: http://www.epa.gov/storet/index.html.
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EPA reviewed STORET ground water data from wells and surface water data from lakes, 

rivers/streams, and reservoirs (USEPA, 2012b). The STORET Data Warehouse also included 

public water system (PWS) data from three states (Indiana, Missouri, and Ohio); EPA reviewed 

these as well (USEPA, 2012b).

The results of the STORET analysis for 1,3-dinitrobenzene are presented in Exhibit 4-6

through Exhibit 4-9. Of the 70 sites (53 surface water and 17 ground water), 53 (75.71%)

reported detections of 1,3-dinitrobenzene. All detections were at surface water sites. Detected 

concentrations ranged from 0 to 0.33 μg/L. No 1,3-dinitrobenzene detections exceeded 1⁄2 the 

HRL or the HRL. Minimum detected concentrations are reported in Exhibit 4-6; these minimum 

values may be indicative of reporting levels used. (A minimum value of zero, on the other hand, 

could represent a detection that was entered into the database as a non-numerical value (e.g., 

“Present”). No Indiana, Missouri, or Ohio PWS data were available for this contaminant.

Exhibit 4-6: 1,3-Dinitrobenzene STORET Data – Summary of Detected 

Concentrations

Source Water Type Concentration Value of Detections (μg/L)

Minimum Median 90th Percentile Maximum

Ground Water N/A N/A N/A N/A

Surface Water 01 0.04 0.31 0.33

Total 01 0.04 0.31 0.33

PWS2 N/A N/A N/A N/A

N/A = not applicable (no detections in this category). 1 A minimum value of zero may represent a detection that was entered into the database as a non-numerical value 

(e.g., “Present”).

2 It could not be determined from the data in STORET whether the public water supply facilities were served by 

ground water or surface water.

Exhibit 4-7: 1,3-Dinitrobenzene STORET Data – Summary of Samples

Source Water 

Type

Total 

Number 

of 

Samples

Samples with 

Detections

Samples with 

Detections > 1⁄2 HRL 

(0.35 μg/L)

Samples with 

Detections > HRL 

(0.7 μg/L)

Number Percent Number Percent Number Percent

Ground Water 48 0 0% 0 0% 0 0%

Surface Water 95 95 100% 0 0% 0 0%

Total 143 95 66.43% 0 0% 0 0%

PWS1 0 0 0% 0 0% 0 0% 1 It could not be determined from the data in STORET whether the public water supply facilities were served by 

ground water or surface water.
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Exhibit 4-8: 1,3-Dinitrobenzene STORET Data – Summary of Sites

Source Water 

Type

Total 

Number 

of Sites

Sites with Detections Sites with Detections 

> 1⁄2 HRL (0.35 μg/L)

Sites with Detections 

> HRL (0.7 μg/L)

Number Percent Number Percent Number Percent

Ground Water 17 0 0% 0 0% 0 0%

Surface Water 53 53 100% 0 0% 0 0%

Total 70 53 75.71% 0 0% 0 0%

PWS1 0 0 0% 0 0% 0 0% 1 It could not be determined from the data in STORET whether the public water supply facilities were served by 

ground water or surface water.

Exhibit 4-9: 1,3-Dinitrobenzene STORET Data – Summary of States

Source Water 

Type

Total 

Number 

of States

States with Detections States with Detections 

> 1⁄2 HRL (0.35 μg/L)

States with Detections 

> HRL (0.7 μg/L)

Number Percent Number Percent Number Percent

Ground Water 1 0 0% 0 0% 0 0%

Surface Water 1 1 100% 0 0% 0 0%

Total1 2 1 50.00% 0 0% 0 0%

PWS2 0 0 0% 0 0% 0 0% 1 The number of states with ground water data plus the number of states with surface water data may not equal the 

“Total” number of states providing data because some states provided both ground water and surface water data. 2 It could not be determined from the data in STORET whether the public water supply facilities were served by 

ground water or surface water.

4.4.2 Occurrence in Drinking Water

The agency reviewed a number of data sources for information on contaminant 

occurrence in drinking water. Data and information on 1,3-dinitrobenzene from the following 

source are available and are summarized in this section:

• EPA’s Second Unregulated Contaminant Monitoring Regulation (UCMR 2).

Reviewed sources that contain no information on 1,3-dinitrobenzene occurrence 

included, among others, EPA’s First Unregulated Contaminant Monitoring Regulation (UCMR 

1), Rounds 1 and 2 of EPA’s Unregulated Contaminant Monitoring (UCM) Program, State 

drinking water monitoring programs, EPA’s Community Water System Survey (CWSS), and 

Consumer Confidence Reports (CCRs) from PWSs.

Primary Data Sources

Second Unregulated Contaminant Monitoring Regulation (UCMR 2), 2008-2010

UCMR 2 monitoring, designed to provide nationally representative contaminant 

occurrence data, was conducted from 2008 to 2010. UCMR 2 required surface water systems to 

monitor quarterly and ground water systems to monitor twice per year. There were two tiers of

monitoring: Assessment Monitoring for contaminants with commonly used analytical method 

technologies, and Screening Survey monitoring for contaminants that require specialized 

analytical method technologies not in wide or common use. 

All very large PWSs (serving more than 100,000 people) and large PWSs (serving 

10,001-100,000 people), plus a statistically representative national sample of 800 small PWSs 
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(serving 10,000 people or fewer), were required to conduct Assessment Monitoring during a 12-

month period between January 2008 and December 2010. For the Screening Survey, monitoring 

was required by all very large PWSs, 320 representative large PWSs, and 480 representative 

small PWSs, during a 12-month period between January 2008 and December 2010. See USEPA 

(2007) and USEPA (2010b) for more information on the UCMR 2 program, including study 

design and data analysis.

1,3-Dinitrobenzene was monitored under the UCMR 2 Assessment Monitoring. The 

Minimum Reporting Level (MRL) used for 1,3-dinitrobenzene in this study was 0.8 μg/L, which 

is slightly greater than the HRL.

The design of UCMR 2 permits estimation of national occurrence. To calculate national 

extrapolations, the percent of systems (or population served) estimated to exceed a specified 

threshold is multiplied by the total number of systems (or population served) in the nation. (Note 

that because all large and very large systems were required to conduct UCMR 2 Assessment 

Monitoring, survey census figures are used in those size categories). See Chapter 2 for additional 

information on national extrapolations. 

As of July 2011, a total of 32,017 1,3-dinitrobenzene samples have been collected from 

4,137 systems. There have not been any detections of 1,3-dinitrobenzene from the systems that 

sampled under UCMR 2. The fact that there have not been any detections of 1,3-dinitrobenzene

from systems sampled under UCMR 2 suggests that nation-wide occurrence of this compound is 

likely to be low or negligible.

4.5 Technology Assessment

4.5.1 Analytical Methods

EPA has developed one analytical method for the analysis of 1,3-dinitrobenzene in 

drinking water:

• EPA Method 529, Revision 1.0, Determination of Explosives and Related 

Compounds in Drinking Water by Solid Phase Extraction and Capillary Column Gas 

Chromatography/ Mass Spectrometry (GC/MS), has Detection Limits (DLs) that 

range from 0.003 to 0.076 μg/L. The Lowest Concentration Minimum Reporting 

Levels (LCMRLs), although not included in EPA Method 529, range from 0.17 to 

1.27 μg/L. Recoveries range from 77.6 to 128%, with Relative Standard Deviations 

(RSDs) of 1.0 to 11% (USEPA, 2002).

Although not listed in EPA Method 529, the MRL for 1,3-dinitrobenzene is 0.8 μg/L.

This value serves as a national benchmark for laboratories that participated in UCMR 2 using 

EPA Method 529 (72 FR 367; USEPA, 2007). The MRL for 1,3-dinitrobenzene was determined 

by EPA using data generated from EPA Method 529.

An estimated reporting level (calculated as MRL) was compared to the HRL for 1,3-

dinitrobenzene in order to determine whether the available analytical method is capable of 

reliable quantitation at concentrations of estimated toxicological concern (see Exhibit 4-10). The 

Method Sensitivity Ratio (MSR) is calculated from the following equation:

MSR = HRL (μg/L) / MRL (μg/L)

A favorable MSR is one that is greater than ten. That is, it is preferable that the HRL be

at least ten times above the concentration at which data can be reliably reported; this provides a 

margin of safety for uncertainty in the HRL and/or method performance (see USEPA, 2009a).
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Exhibit 4-10: Method Sensitivity Ratio (MSR) for 1,3-Dinitrobenzene

Method MRL (μg/L) HRL (μg/L) MSR

529 0.8 0.7 0.875

The MSR is less than ten; hence, the available analytical method is not capable of reliable 

quantitation at least ten times below the HRL.

4.5.2 Treatment Technologies

The availability of treatment technologies is not a factor EPA considers when making a 

regulatory determination. However, suitable treatment technologies must be made available 

before a National Primary Drinking Water Regulation (NPDWR) can be promulgated.

A preliminary review of the literature reveals that the following treatment technologies 

have been investigated empirically for their applicability to this contaminant:

• Granular activated carbon (GAC).

• Ultraviolet (UV) irradiation (including photocatalysis).

• Advanced oxidation processes (a combination of two oxidants such as ozone/UV, 

ozone/peroxide, possibly with the addition of iron).

• Biologically active filtration.

Based on percentage-removal values reported in the reviewed literature, the most 

promising options appear to be GAC and advanced oxidation processes, especially Fenton’s 

reagent (iron/peroxide/UV). 

Please note that the literature review was not exhaustive, and findings from the reviewed 

studies might not be directly comparable. A full assessment of treatment technology applicability 

will require a more detailed review and analysis of the literature, and possibly additional 

research.

4.6 Preliminary Regulatory Determination

4.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL

The statutory requirements for the CCL and regulatory determinations can be found in 

SDWA Section 1412(b)(1). The 1996 SDWA Amendments require EPA to publish the CCL 

every five years. The CCL is a list of contaminants that are not subject to any proposed or 

promulgated NPDWRs, are known or anticipated to occur in PWSs, and may require regulation 

under SDWA to protect public health. The 1996 SDWA Amendments also direct EPA to 

determine whether or not to regulate at least five contaminants from the CCL every five years.

There are three criteria to be considered in making a regulatory determination. A decision to 

regulate is warranted if:

(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 PWSs with a frequency and at levels of public health 

concern; and 
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(c) in the sole judgment of the Administrator, regulation of such contaminant presents a 

meaningful opportunity for health risk reduction for persons served by PWSs. 

If EPA determines that all three of these statutory criteria are met, it makes a preliminary 

positive regulatory determination that an NPDWR1 is needed. . Following a comment response 

period and a final positive regulatory determination, the agency has 24 months to publish a 

proposed Maximum Contaminant Level Goal2 (MCLG) and an NPDWR. After the proposal, the 

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

1412(b)(1)(E)).3 The agency may determine that there is no need for a regulation when a 

contaminant fails to meet one or more of the criteria. A decision not to regulate is considered a 

final agency action and is subject to judicial review. The agency can choose to publish a Health 

Advisory (a nonregulatory action) or other guidance for any contaminant on the CCL, 

independent of the regulatory determination. Refer to section 1.4 for a summary of the approach 

used to identify and evaluate contaminants for RD 3. The following section summarizes the 

preliminary RD 3 decision for 1,3-dinitrobenzene.

4.6.2 Health Effects (Criterion #1)

The first criterion asks if the contaminant may have an adverse effect on the health of 

persons. Because all chemicals have adverse effects at some level of exposure, the challenge is to 

identify an HRL, a dose below which adverse health effects are considered unlikely to occur 

(threshold toxicant), or below which adverse effects have a defined low probability of occurrence 

(non-threshold toxicant). The key elements that must be considered in evaluating the first 

criterion are the mode of action, the critical effect(s), the dose-response for critical effect(s), the 

RfD for threshold effects, and the slope factor for non-threshold effects.

A full description of the health effects associated with exposure to 1,3-dinitrobenzene is 

presented in Section 4.3 of this document.

Health Criterion Data

1,3-Dinitrobenzene is absorbed from the gastrointestinal tract of humans and animals. 

1,3-Dinitrobenzene appears to be highly metabolized through full or partial reduction of the 

nitro- groups to amine functional groups, and in some cases, via hydroxylation of the benzene 

ring. Primary adverse biological effects from exposure to 1,3-dinitrobenzene are on red blood 

cells, spleen, and testes. There have been many animal studies of the testicular effects (i.e., 

sperm morphology, motility, and fertility) of 1,3-dinitrobenzene (Hajjar et al., 1992). Sertoli cells 

appear to be the target for the effects of 1,3-dinitrobenzene on sperm, and older animals appear 

to be more sensitive than younger ones. 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 ). Individuals with a genetic predisposition to 

 

1 An NPDWR is a legally enforceable standard that applies to PWSs. 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.

2 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 nonenforceable health goals." (CFR 141.2)

3 The statute authorizes a nine month extension of this promulgation date.
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methemoglobinemia and/or hemosiderosis, neonates, and those co-exposed to other hemolytic 

agents, could be sensitive to exposure to 1,3-dinitrobenzene. Males having sperm production 

complications could also have increased sensitivity to 1,3-dinitrobenzene exposure.

A subchronic oral study based on increased spleen weight in rats was identified as the 

critical study for establishing an oral RfD of 0.0001 mg/kg-day (USEPA, 1988; Cody et al., 

1981). The RfD was derived by using a NOAEL of 0.4 mg/kg-day, with a net UF of 3,000 (10 

for intraspecies differences, 10 for interspecies differences, 10 for extrapolating from a 

subchronic to a chronic duration, and 3 for the lack of chronic, developmental, and 

multigenerational reproductive toxicity studies). EPA calculated a non-cancer HRL of 0.7 μg/L 

for 1,3-dinitrobenzene using the oral RfD of 0.0001 mg/kg-day for a 70 kg adult ingesting 2 L of 

drinking water per day and a RSC of 20%. The current EPA oral RfD value is supported by a 

recent 1,3-dinitrobenzene assessment (ATSDR, 1995), in which an oral intermediate duration 

ATSDR minimal risk level (MRL) of 0.0005 mg/kg-day for splenic hemosiderosis in male rats 

was established using a LOAEL of 0.54 mg/kg-day and a net UF of 1,000 (10 for intraspecies 

variability, 10 for interspecies variability, and 10 for LOAEL to NOAEL). Based on EPA 

assumptions and a net UF of 3,000 (10 for intraspecies variability, 10 for interspecies variability, 

10 for the use of a LOAEL in place of a NOAEL, and 3 for subchronic to chronic) 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.

1,3-Dinitrobenzene is mutagenic in several strains of S. typhimurium, both with and 

without activation. There are currently no long-term studies of the tumorigenic effects of 1,3-

dinitrobenzene. The EPA IRIS assessment of the carcinogenicity of 1,3-dinitrobenzene currently 

places the chemical in Group D (not classifiable as to human carcinogenicity) (USEPA, 1988).

Health Criterion Conclusion

Toxicological data from animal studies indicate that red blood cells, spleen, and testes are 

targets of 1,3-dinitrobenzene toxicity. Data on increased spleen weight in rats support the 

development of an HRL of 0.7 μg/L for human exposure via drinking water. Based on these 

considerations, EPA concludes that 1,3-dinitrobenzene meets the SDWA statutory criterion #1 

for regulatory determination; it may have an adverse effect on the health of persons.

4.6.3 Occurrence in Public Water Systems (Criterion #2)

The second criterion asks if the contaminant is known to occur or if there is a substantial 

likelihood that the contaminant will occur in PWSs with a frequency and at levels of public 

health concern. In order to address this question, EPA consulted a variety of information sources, 

including data from the UCMR 2 Screening Survey, a nationally representative survey of PWSs 

conducted from 2008 to 2010. EPA examined the total number of systems that reported 

detections of 1,3-dinitrobenzene, as well as those that reported concentrations of 1,3-

dinitrobenzene above the HRL of 0.7 μg/L.

Available monitoring data, including data that may shed light on regional and national 

occurrence, are presented in Section 4.4, and are summarized below. Additional information on 

production, use, and fate is found in Section 4.2.

Occurrence Criterion Data

The primary occurrence data for 1,3-dinitrobenzene are recent (2008-2010) nationallyrepresentative drinking water monitoring data generated through EPA’s UCMR 2. UCMR 2 is 

the only dataset with finished water data for this contaminant. UCMR 2 collected 32,017 samples 
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from 4,137 PWSs. 1,3-Dinitrobenzene was not detected in any sample 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. It should be noted that some occurrence above the 

HRL may have gone undetected since reporting levels are not documented.

Occurrence Criterion Conclusion

1,3-Dinitrobenzene was not detected in any of the 32,017 UCMR 2 samples collected by 

4,137 PWSs using an MRL of 0.8 μg/L, which is only slightly higher than the HRL (0.7 μg/L).

Limited ambient water data confirm that 1,3-dinitrobenzene occurrence does not appear to be 

common at levels of public health concern. Based on these considerations, EPA concludes that 

1,3-dinitrobenzene does not meet the SDWA statutory criterion #2 for regulatory determination; 

it does not occur with a frequency and at levels of public health concern in public water.

4.6.4 Risk Reduction (Criterion #3)

The third criterion asks if, in the sole judgment of the Administrator, regulation presents a 

meaningful opportunity for health risk reduction for persons served by PWSs. In evaluating this 

criterion, EPA looked at several factors.

EPA calculated the total exposed population and the population exposed to levels above 

the HRL. Estimates of the populations exposed and the levels to which they are exposed were 

derived from the monitoring results. These estimates are included in Section 4.4 and summarized 

in the “Exposed Population Estimates” section below.

In evaluating the third criterion, EPA also considered effects on potentially sensitive 

populations, including the fetus, infants, and children. Sensitive population considerations are 

discussed in the “Sensitive Populations” section, below. 

Exposed Population Estimates

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. 

Sensitive Populations

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 (the estimated prevalence in the general population is 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 (Jaffe and Hultquist, 1989; ATSDR, 1995). 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 an UF for this 

database deficiency. The IRIS assessment (USEPA, 1988) presents more detailed information 

about the potential health effects and sensitive populations for 1,3-dinitrobenzene.
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Risk Criterion Conclusion

Based on the estimated exposed population, including sensitive subpopulations, EPA has 

preliminarily determined that 1,3-dinitrobenzene does not meet the SDWA statutory criterion #3 

for regulatory determination; regulation of 1,3-dinitrobenzene does not present a meaningful 

opportunity for health risk reduction for persons served by PWSs.

4.6.5 Regulatory Determination Decision

As stated in the “Criteria for Regulatory Determination” section above, a positive finding 

for all three criteria is required in order to make a determination to regulate a contaminant. EPA 

has made a preliminary determination that 1,3-dinitrobenzene does not meet all three criteria.

1,3-Dinitrobenzene has the potential to cause adverse health effects, including effects in 

red blood cells, spleen, and testes. However, 1,3-dinitrobenzene does not appear to occur in 

PWSs with a frequency and at levels of public health concern. 1,3-Dinitrobenzene was not 

detected in any of the 32,017 UCMR 2 samples collected by 4,137 PWSs using an MRL of 0.8 

μg/L, which is only slightly higher than the HRL (0.7 μg/L). Due to the relatively small number 

of people likely exposed to 1,3-dinitrobenzene through drinking water, regulation of 1,3-

dinitrobenzene does not appear to represent a meaningful opportunity for health risk reduction 

for persons served by PWSs. 

4.7 References

Agency for Toxic Substances and Disease Registry (ATSDR). 1995. Toxicological Profile: 1,3-

dinitrobenzene and 1,3,5-trinitrobenzene. Agency for Toxic Substances and Disease 

Registry, Public Health Service, U.S. Department of Health and Human Services. 

Available on the Internet at: 

http://www.atsdr.cdc.gov/toxprofiles/tp.asp?id=842&tid=164 .

ChemIDPlus. 2009. Available on the Internet at: http://chem.sis.nlm.nih.gov/chemidplus/. 

Accessed August 10, 2009. 

Cody, T.E., S. Witherup, L. Hastings, et al. 1981. 1,3-Dinitrobenzene: Toxic effects in vivo and 

in vitro. J. Toxicol. Environ. Health 7: 829-847.

Hajjar, N.P., M. Brower, P.A. Turck, et al. 1992. 1,3-Dinitrobenzene (DNB). Drinking Water 

Health Advisory: Munitions. Lewis Publishers, Ann Arbor, MI. pp. 49-86.HSDB. 2010. 

Available on the Internet at: http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. 

Accessed September, 2010.

Hazardous Substances Data Bank (HSDB). 2009. Available on the Internet at: 

http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. Accessed August 10, 2009. 

HSDB. 2010. Available on the Internet at: http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. 

Accessed September, 2010.

HSDB. 2012. Available on the Internet at: http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. 

Accessed November, 2012.

Jaffe, E.R. and D. E. Hultquist. 1989. Cytochrome b5 reductase deficiency and enzymopenic 

hereditary methemoglobinemia. In: Metabolic Basis of Inherited Disease. Scriver, C., 

Beaudet, A.L., Sly, W.S., and D. Valle, eds. New York: McGraw Hill Information 

Services Co. pp.2267-2280.
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Linder, R.E., R.A. Hess, and L.F. Strader. 1986. Testicular toxicity and infertility in male rats 

treated with 1,3-dinitrobenzene. J. Toxicol. Environ. Health 19:477-489 (as cited in 

Hajjar et al., 1992).

Linder, R.E., R.A. Hess, S.D. Perreault, et al. 1988. Acute effects and long-term sequelae of 1,3-

dinitrobenzene on male reproduction in the rat. J. Androl. 9:326-327.

Persistence, Bioaccumulation, and Toxicity (PBT) Profiler. 2009. Available on the Internet at: 

http://www.pbtprofiler.net/. Accessed August 10, 2009. 

Risk Assessment Information System (RAIS). 2009. Available on the Internet at: 

http://rais.ornl.gov/. Accessed August 10, 2009. 

Speth, T. and R Miltner. 1990. Technical note: GAC adsorption capacities for SOCs. Journal of 

the American Water Works Association. 82(2):72.

United States Environmental Protection Agency (USEPA). 1988. IRIS Summary: mDinitrobenzene. National Center for Environmental Assessment. Available at 

http://www.epa.gov/ncea/iris/subst/0318.htm.

USEPA. 1996. 1996 Toxics Release Inventory: Public Data Release Report. Chapter 3: Year-toYear Comparison of Toxics Release Inventory Data. Available on the Internet at: 

http://www.epa.gov/tri/tridata/tri96/pdr/chap3.pdf. 

USEPA. 2002. Method 529. Determination of Explosives and Related Compounds in Drinking 

Water by Solid Phase Extraction and Capillary Column Gas Chromatography/Mass 

Spectrometry (GC/MS). Revision 1.0. EPA/600/R-05/052. National Exposure Research 

Laboratory, Office of Research and Development.

USEPA. 2004. The Toxics Release Inventory (TRI) and Factors to Consider When Using TRI 

Data. Available on the Internet at: 

http://www.epa.gov/tri/triprogram/FactorsToConPDF.pdf. File created June 14, 2004. 

Accessed February 22, 2011.

USEPA. 2007. Unregulated Contaminant Monitoring Regulation (UCMR) for Public Water 

Systems Revisions. Federal Register. Vol. 72, No. 2, p. 367, January 4, 2007. 

USEPA. 2009a. Final Contaminant Candidate List 3 Chemicals: Classification of the PCCL to 

CCL. Office of Water. EPA 815-R-09-008. 

USEPA. 2009b. Drinking Water Contaminant Candidate List 3–Final. Federal Register. Vol. 74, 

No. 194, p. 51850, October 8, 2009.

USEPA. 2010a. Non-confidential IUR Production Volume Information. Available on the Internet 

at: http://www.epa.gov/iur/tools/data/2002-vol.html.

USEPA. 2010b. Data Management and Analytical Plan for the Second Unregulated 

Contaminant Monitoring Regulation (UCMR 2) Data. June 2010 Draft Report Submitted 

to EPA.

USEPA. 2012a. TRI Explorer: Trends. Available on the Internet at: 

http://www.epa.gov/triexplorer/trends.htm. 

USEPA. 2012b. Storage and Retrieval (STORET) Data Warehouse. Available on the Internet at: 

http://www.epa.gov/storet/index.html. Data Warehouse consulted March 2012.
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Chapter 5:

Strontium

A chapter from:

Regulatory Determination 3 Support Document

EPA Report 815-R-14-003
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Contents

Contents...........................................................................................................................................3

Exhibits............................................................................................................................................4

Abbreviations...................................................................................................................................5

5.1 Contaminant Background, Chemical and Physical Properties ............................................7

5.2 Sources and Environmental Fate .........................................................................................9

5.2.1 Natural Sources........................................................................................................9

5.2.2 Production, Use, and Release...................................................................................9

5.2.3 Environmental Fate................................................................................................11

5.3 Health Effects.....................................................................................................................12

5.4 Occurrence .........................................................................................................................14

5.4.1 Occurrence in Ambient Water ...............................................................................14

5.4.2 Occurrence in Drinking Water...............................................................................16

5.5 Technology Assessment.....................................................................................................25

5.5.1 Analytical Methods................................................................................................25

5.5.2 Treatment Technologies.........................................................................................26

5.6 Preliminary Regulatory Determination..............................................................................26

5.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL........26

5.6.2 Health Effects (Criterion #1) .................................................................................27

5.6.3 Occurrence in Public Water Systems (Criterion #2)..............................................28

5.6.4 Risk Reduction (Criterion #3)................................................................................30

5.6.5 Regulatory Determination Decision ......................................................................32

5.7 References..........................................................................................................................33
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Exhibits

Exhibit 5-1: Physical and Chemical Properties of Strontium......................................................... 8

Exhibit 5-2: Annual Production and Importation of Strontium Compounds in the United 

States (pounds)...................................................................................................... 10

Exhibit 5-3: Strontium STORET Data – Summary of Detected Concentrations ......................... 15

Exhibit 5-4: Strontium STORET Data – Summary of Samples................................................... 15

Exhibit 5-5: Strontium STORET Data – Summary of Sites......................................................... 16

Exhibit 5-6: Strontium STORET Data – Summary of States....................................................... 16

Exhibit 5-7: Strontium Occurrence Data from the NIRS Database – Summary of Detected 

Concentrations ...................................................................................................... 18

Exhibit 5-8: Strontium Occurrence Data from the NIRS Database – Summary of System and 

Population Served Data – All Detections............................................................. 18

Exhibit 5-9: Strontium Data from the NIRS Database – Summary of System and Population 

Served Data – Detections > 1⁄2 HRL ..................................................................... 18

Exhibit 5-10: Strontium Data from the NIRS Database – Summary of System and 

Population Served Data – Detections > HRL ....................................................... 19

Exhibit 5-11: Strontium State Drinking Water Occurrence Data – Summary of Detected 

Concentrations ...................................................................................................... 20

Exhibit 5-12: Strontium State Drinking Water Occurrence Data – Summary of Samples........... 20

Exhibit 5-13: Strontium State Drinking Water Occurrence Data – Summary of Systems........... 21

Exhibit 5-14: Strontium Data from Public-Supply Wells (Toccalino et al., 2010) – Summary 

of Detected Concentrations................................................................................... 22

Exhibit 5-15: Strontium Data from Public-Supply Wells (Toccalino et al., 2010) – Summary 

of Samples............................................................................................................. 23

Exhibit 5-16: Strontium Data from Northern United States Glacial Aquifer System 

(Groschen et al., 2009) – Summary of Detection Frequencies............................. 24

Exhibit 5-17: Strontium Data from Northern United States Glacial Aquifer System 

(Groschen et al., 2009) – Summary of Concentrations......................................... 24

Exhibit 5-18: Summary of EWG Strontium Data, 2004-2009 ..................................................... 25

Exhibit 5-19: Method Sensitivity Ratios (MSRs) for Strontium .................................................. 26
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Abbreviations

AMWA Association of Metropolitan Water Agencies

AWWA American Water Works Association

BMD Benchmark Dose

BMDL Benchmark Dose Level

CASRN Chemical Abstracts Service Registry Number

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

CDC Center for Disease Control and Prevention

CUS-IUR Chemical Update System - Inventory Update Reporting

CWS Community Water System

CWSS Community Water System Survey

DNA Deoxyribonucleic Acid

EPA Environmental Protection Agency

EWG Environmental Working Group

FDA Food and Drug Administration

GAC Granular Activated Carbon

HESD Health Effects Support Document

HRL Health Reference Level

ICR Information Collection Request

IOC Inorganic Chemical

IUR Inventory Update Reporting

MCLG Maximum Contaminant Level Goal

MDL Method Detection Limit

MRL Minimum Reporting Level

MSR Method Sensitivity Ratio

N/A Not Applicable

NAWQA National Water-Quality Assessment

NDWAC National Drinking Water Advisory Council

NIRS National Inorganics and Radionuclides Survey

NPDWR National Primary Drinking Water Regulation

NTNCWS Non-Transient Non-Community Water System

PWS Public Water System

QA Quality Assurance

RD 3 Third Regulatory Determination

RfD Reference Dose

ROS Regression on Ordered Statistics

RPD Relative Percent Difference

RSC Relative Source Contribution
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SDWA Safe Drinking Water Act

SDWIS Safe Drinking Water Information System

STORET Storage and Retrieval

TNCWS Transient Non-Community Water System

TRI Toxics Release Inventory

TSCA Toxic Substances Control Act

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

USGS United States Geological Survey

VOC Volatile Organic Compound
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5-7

Chapter 5: Strontium

The Environmental Protection Agency (EPA) is evaluating strontium for possible 

regulation as a drinking water contaminant. Strontium is listed on the agency’s third 

Contaminant Candidate List (CCL 3) and is being considered for regulation as part of the third 

Regulatory Determination (RD 3) under the Safe Drinking Water Act (SDWA) provisions. 

Information on the CCL 3/RD 3 process is found in Chapter 1. Background on data sources used 

to evaluate CCL 3/RD 3 chemicals is found in Chapter 2. This chapter presents information and 

analysis specific to strontium, including background information on the contaminant, 

information on sources and environmental fate, an analysis of health effects, an analysis of 

occurrence in ambient and drinking water, and information about the availability of analytical 

methods and treatment technologies. A summary of EPA's decision regarding strontium appears 

at the end of this chapter. (The decision is presented formally in the associated Federal Register

notice.)

5.1 Contaminant Background, Chemical and Physical Properties

Strontium is a naturally-occurring element (atomic number 38) and a member of the 

alkaline earth metals (Group Two of the periodic table), which also include beryllium, 

magnesium, calcium, barium, and radium. Of the many known isotopes of strontium, four are 

stable and found in nature: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.00%), and 88Sr (82.58%) (ATSDR, 

2004).

There are also several radioactive isotopes formed by nuclear fission of uranium or 

plutonium (ATSDR, 2004). Notable among these is 90Sr, a beta particle emitter with a half-life of 

29 years that was released into the atmosphere from above-ground testing of nuclear weapons in 

the period 1945 through 1980. Since drinking water contamination by radioactive isotopes, 

including beta particle emitters, is covered under the existing radionuclides rule, this document 

deals primarily with nonradioactive properties and the occurrence of “total” strontium in the 

environment.

Strontium constitutes approximately 0.02-0.03% of the earth’s crust, and is the fifth most 

abundant metallic ion in seawater (HSDB, 2010). In the earth’s crust strontium occurs 

principally as strontium sulfate (SrSO4) in the mineral celestite (USGS, 2009). The elemental 

form does not exist in nature (ATSDR, 2004). Two common refining methods for extracting 

strontium from celestite ore are the black ash method (calcining) and the soda method. Both 

produce strontium carbonate (SrCO3) (ATSDR, 2004). Strontium may be present as an impurity 

in coal, and may be released to air as strontium oxide from coal-burning (ATSDR, 2004).

Physical and chemical properties and other reference information for select strontium 

compounds are listed in Exhibit 5-1. Exhibit 5-2, in the following section, identifies some 

additional strontium-containing compounds that are produced industrially.
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Exhibit 5-1: Physical and Chemical Properties of Strontium

Property

Information

Elemental 

Strontium

Strontium 

Carbonate

Strontium 

Chromate

Strontium 

Nitrate

Strontium 

Hydroxide

Strontium 

Chloride

Chemical 

Abstracts

Service

Registry

Number

(CASRN)

7440-24-6 1633-05-2 7789-06-2 10042-76-9 18480-07-4 10476-85-4

Chemical 

Formula Sr SrCO3 SrCrO4 Sr(NO3)2 Sr(OH)2 SrCl2

Molecular 

Weight

87.6 g/mol 

(HSDB, 2010; 

RAIS, 2009; 

CRC Press, 

1981)

147.63 g/mol 

(ChemIDPlus, 

2009; HSDB, 

2010; CRC 

Press, 1981)

203.61 g/mol 

(ChemIDPlus, 

2009; HSDB, 

2010; CRC 

Press, 1981)

211.63 g/mol 

(ChemIDPlus, 

2009; HSDB, 

2010; CRC 

Press, 1981)

121.64 g/mol 

(ATSDR, 

2004)

158.53 g/mol 

(ATSDR, 

2004; CRC 

Press, 1981)

Color/ 

Physical State

Pale yellow 

solid (ATSDR, 

2004)

White solid 

(ATSDR, 

2004)

Yellow solid 

(ATSDR, 

2004)

Colorless solid 

(ATSDR,

2004)

Colorless solid 

(ATSDR, 

2004)

White solid 

(ATSDR, 

2004)

Boiling Point 1,390 deg C 

(HSDB, 2010)

Decomposes 

at 1,100 deg C 

(ATSDR, 

2004)

-- 645 deg C 

(HSDB, 2010)

-H20, 710 deg 

C (CRC Press, 

1981)

1,250 deg C 

(ATSDR, 

2004)

Melting Point

777 deg C 

(ATSDR, 

2004)

1,497 deg C at 

69 atm 

pressure 

(ATSDR, 

2004)

--

570 deg C 

(ATSDR, 

2004)

375 deg C 

(ATSDR, 

2004)

875 deg C 

(ATSDR, 

2004)

Density

2.6 g/mL at 4 

deg C (CRC 

Press, 1981)

3.70 g/mL at 4 

deg C (CRC 

Press, 1981)

3.895 g/mL at 

15 deg C 

(CRC Press, 

1981)

2.986 g/mL at 

4 deg C (CRC 

Press, 1981)

3.625 g/mL at 

4 deg C (CRC 

Press, 1981)

3.052 g/mL at 

4 deg C (CRC 

Press, 1981)

Freundlich 

Adsorption 

Coefficient

-- -- -- -- -- --

Vapor 

Pressure -- -- -- -- -- --

Henry’s Law 

Constant -- -- -- -- -- --

Log Kow -- -- -- -- -- --

Koc -- -- -- -- -- --

Solubility in 

Water

Reactive 

(HSDB, 2010)

11 mg/L at 18 

deg C (HSDB, 

2010)

1,200 mg/L at 

15 deg C 

(HSDB, 2010; 

CRC Press, 

1981)

709,000 mg/L 

at 18 deg C 

(HSDB, 2010; 

CRC Press, 

1981)

4,100 mg/L at 

0 deg C (CRC 

Press, 1981)

538,000 mg/L 

at 20 deg C 

(CRC Press, 

1981)

Other 

Solvents

Alcohol 

(ATSDR, 

2004)

Acid, 

ammonium 

salts (CRC 

Press, 1981)

Acetic acid 

(ATSDR, 

2004)

Slightly in 

alcohol and 

acetone 

(ATSDR, 

2004)

Alcohol 

(ATSDR, 

2004)

Alcohol, 

acetone 

(ATSDR, 

2004)

Conversion 

Factors

(at 25 deg C, 

1 atm)

-- -- -- -- -- --

Note: “--” indicates that no information was found.
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5.2 Sources and Environmental Fate

5.2.1 Natural Sources

Naturally occurring strontium in minerals, rocks, soils, and seawater can be mobilized by 

natural weathering, wind, and sea spray. Higher concentrations of atmospheric strontium in 

coastal areas relative to inland areas have been attributed to sea spray (WHO, 2010).

5.2.2 Production, Use, and Release

Strontium mineral mining ceased in the United States in 1959. The United States imports 

celestite for refining as well as refined strontium compounds (USGS, 2009). Imports of 

strontium minerals and compounds stood at approximately 31,000 to 38,500 metric tons from 

1994 to 2001 (ATSDR, 2004). Since then imports have declined substantially. 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. During manufacturing strontium 

carbonate is added to liquid glass and converts to strontium oxide (SrO). Strontium oxide 

constitutes approximately 8% (by weight) of the picture tube glass (ATSDR, 2004). 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 (USGS, 

2009; ATSDR, 2004; HSDB, 2010).

Strontium concentrations of up to 2,718 μg/m3 have been measured in atmospheric

emissions from coal-fired power plants in the western United States, and concentrations of 

approximately 9,800 μg/m3 have been measured in the eastern United States. (It is not clear from 

the source whether this finding is representative of differences between the regions, or whether 

these maximum concentrations are outliers.) Local atmospheric concentrations of strontium in 

the range of 0.009 μg/m3 have been observed following pyrotechnic displays. Strontium may be 

present in phosphate fertilizers, where concentrations are reported to range between 20 μg/g and 

4,000 μg/g (WHO, 2010).

Production data for strontium compounds are available from EPA’s Inventory Update 

Reporting (IUR) program, described below.

No industrial release data for strontium compounds are available from EPA’s Toxics 

Release Inventory (TRI). (More precisely: the list of compounds for which TRI reporting is 

required has never included a compound with “strontium” in its name (USEPA, 2010a)) .

Chemical Update System (CUS) – Inventory Update Reporting (IUR) Program

Production data from the EPA IUR program are available for several strontiumcontaining compounds. EPA collects information on chemicals manufactured in or imported into 

the United States from the Toxic Substances Control Act (TSCA) Chemical Substance 

Inventory. The IUR regulation requires manufacturers and importers of chemical substances 

included on the TSCA Chemical Substance Inventory to report site and manufacturing 
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information for chemicals manufactured (including imported) in amounts of 25,000 pounds or 

greater at a single site. Additional information on domestic processing and use must be reported 

for chemicals manufactured in amounts of 300,000 pounds or more at a single site. Note that, 

prior to the 2003 amendments (i.e., reporting from 2002 or earlier), information was collected for 

only organic chemicals that were manufactured (including imported) in amounts of 10,000 

pounds or more, and was limited to more basic manufacturing information such as production 

volume. Because of changes in minimum thresholds and other program modifications, the results 

from 2006 might not be directly comparable to results from earlier years.

The Chemical Update System - Inventory Update Reporting (CUS-IUR) assigns one of 

eight production and importation volume ranges for each chemical included in the inventory. The 

ranges used for the 2006 reports differ slightly from those used in the 1986 through 2002 reports. 

Exhibit 5-2 presents the reported production and importation of 17 strontium compounds in the 

United States every four years from 1986 to 2006. Not every compound had data reported in 

every cycle. Annual production of strontium carbonate varied considerably over the periods for 

which data were reported, reaching into the tens of millions of pounds. There was an apparent 

increase in strontium nitrate production between 2002 and 2006. The production and importation

of the other fifteen strontium compounds remained relatively constant in years when data were 

reported. Three compounds, strontium carbonate, strontium chromate, and strontium nitrate, 

were produced or imported in quantities greater than one million pounds in at least one cycle 

(USEPA, 2010b).

When considering the strontium contribution from complex compounds, it is important to 

remember that strontium is only a fraction of the total poundage reported. For example, 

strontium distearate (listed in the table below as “octadecanoic acid, strontium salt”) is only 13% 

strontium by weight (88 out of 656 g/mol). Dissociation of strontium and strontium species from 

compounds listed in the table may pose health risks, and some of the compounds themselves may 

be of health concern.

Exhibit 5-2: Annual Production and Importation of Strontium Compounds in the 

United States (pounds)

Chemical Name and CASRN 

in CUS Database

Chemical Inventory Update Reporting Cycle

1986 1990 1994 1998 2002 2006

Carbonic acid, strontium salt 

(1:1)

1633-05-2

> 1 million -

10 million No Reports No Reports > 10 million - 50 million

10,000 -

500,000

10 million –

< 50 million

Chromic acid (H2CrO4), 

strontium salt (1:1)

7789-06-2

> 1 million -

10 million

> 1 million -

10 million No Reports No Reports No Reports < 500,000 

Octadecanoic acid, strontium 

salt

10196-69-7

10,000 -

500,000

10,000 -

500,000 No Reports No Reports No Reports No Reports

Nitric acid, strontium salt

10042-76-9 No Reports No Reports No Reports No Reports 10,000 -500,000

1 million –

< 10 million

2-Naphthalenecarboxylic acid, 

3-hydroxy-4-[(4-methyl-2-

sulfophenyl)azo]-, strontium 

salt (1:1)

73612-29-0

10,000 -

500,000

10,000 -

500,000

10,000 -

500,000

10,000 -

500,000

10,000 -

500,000 No Reports
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Chemical Name and CASRN 

in CUS Database

Chemical Inventory Update Reporting Cycle

1986 1990 1994 1998 2002 2006

1-Naphthalenesulfonic acid, 2-

[(2-hydroxy-1-

naphthalenyl)azo]-, strontium 

salt (2:1)

6371-67-1

No Reports No Reports No Reports No Reports 10,000 -

500,000 No Reports

2-Naphthalenecarboxylic acid, 

3-hydroxy-4-[(4-methyl-2-

sulfophenyl)azo]-, calcium 

strontium salt (2:1:1)

55491-44-6

No Reports No Reports No Reports No Reports 10,000 -

500,000 No Reports

2-Naphthalenecarboxylic acid, 

4-[(5-chloro-4-methyl-2-

sulfophenyl)azo]-3-hydroxy-, 

strontium salt (1:1)

15782-05-5

10,000 -

500,000

10,000 -

500,000

10,000 -

500,000

10,000 -

500,000

10,000 -

500,000 No Reports

2-Naphthalenecarboxylic acid, 

4-[(4-chloro-5-methyl-2-

sulfophenyl)azo]-3-hydroxy-, 

strontium salt (1:1)

67828-72-2

10,000 -

500,000

10,000 -

500,000 No Reports No Reports No Reports No Reports

Strontium oxide (SrO)

1314-11-0 No Reports No Reports No Reports No Reports No Reports < 500,000 

Strontium titanium oxide 

(SrTiO3)

12060-59-2

No Reports No Reports No Reports No Reports No Reports 500,000 to -

1 million

Phosphoric acid, strontium salt 

(1:1)

13450-99-2

No Reports No Reports No Reports No Reports No Reports < 500,000 

Phenol, nonyl-, strontium salt 

(2:1)

31291-42-6

No Reports No Reports No Reports No Reports No Reports < 500,000 

Phosphoric acid, magnesium 

strontium salt, tin-doped

68784-28-1

No Reports No Reports No Reports No Reports No Reports < 500,000 

Strontium fluoride phosphate 

(Sr5F(PO4)3), antimony and 

manganese-doped

68784-78-1

No Reports No Reports No Reports No Reports No Reports < 500,000 

Barium calcium strontium 

chloride phosphate, europiumdoped

109037-74-3

No Reports No Reports No Reports No Reports No Reports < 500,000 

Silicon sodium strontium 

titanium hydroxide oxide

326855-77-0

No Reports No Reports No Reports No Reports No Reports < 500,000 

5.2.3 Environmental Fate

Strontium can exist in oxidation states 0 and +2; under normal environmental conditions 

it is found primarily in the +2 oxidation state (ATSDR, 2004).

Strontium enters the atmosphere via natural weathering and sea spray, and as a result of 

industrial activity, the application of phosphate fertilizers, and the use of pyrotechnics. If 

strontium is released to air as strontium oxide (e.g., from coal-burning), it will react with 

moisture to form strontium hydroxide (Sr(OH)2) or with carbon dioxide to form strontium 
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carbonate. Strontium hydroxide will further interact with moisture to form Sr2+ and SrOH+ ions. 

Strontium ions and compounds in the atmosphere are subject to wet and dry deposition (ATSDR, 

2004).

Strontium is naturally present in most soils, and additional strontium may be added by 

atmospheric deposition and by direct human activity such as application of phosphate fertilizers 

(ATSDR, 2004). Strontium is considered to have moderate or moderate-to-low mobility in soils 

(ATSDR, 2004; HSDB, 2010). Mobility is affected by the type of soil and by the salinity of the 

soil water (ATSDR, 2004; HSDB, 2010). Though strontium is not an essential nutrient for most 

plants, it is taken up by many plants by the same mechanism that these plants take up calcium 

(ATSDR, 2004).

Strontium enters freshwater resources (surface and ground water) from the natural 

weathering of rocks and soils, from atmospheric deposition, from the leaching of strontium 

compounds from soils, and from direct discharge of contaminated waste water. Strontium may 

be present in water in an ionic form such as Sr2+ or SrOH+

, or in the form of undissolved 

compounds such as SrCO3 and SrSO4 (ATSDR, 2004). The mobility of strontium can increase in 

water bodies with high salt concentrations on account of decreased sorption to sediments 

(HSDB, 2010).

5.3 Health Effects

There are several studies that evaluated the relationship between strontium exposure in 

the environment or the body burden of strontium (as a measure of internal dose) and 

development of disease following either occupational or environmental exposures (Curzon and 

Spector, 1977; Dawson et al., 1978; St. Leger et al., 1980; Curzon, 1981; Longerich et al., 1991; 

Özgür et al., 1996; Zerbino and Solomenchuk, 2007). These studies are of limited utility for 

characterizing hazard and assessing dose response due to inadequate control for other factors 

potentially contributing to the endpoint being evaluated.

Strontium has low acute toxicity to rodents via the oral and dermal routes (Woodard and 

Calvery, 1941; Ghosh et al., 1990; Llobet et al., 1991; NIER, 2006a); the low volatility of 

strontium compounds makes inhalation exposure unlikely. 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

(Comar et al., 1957; Sowden and Stitch, 1957; Tipton and Cook, 1963; Schroeder et al., 1972; 

Underwood, 1977; Weast and Astle, 1981; Skoryna, 1981; Rosenthal, 1981; Cabrera et al., 

1999). Subchronic and chronic studies in rats show that strontium can decrease the calcification 

of the cartilaginous portion of bone in the young, and at low doses can increase bone formation

relative to degradation in the elderly (Marie et al., 1985; Grynpas and Marie, 1990; Neufeld and 

Boskey, 1994). Due to the mode of action for strontium toxicity, strontium uptake into bone and 

the resulting toxicity is affected by the stage of bone development and intake of nutrients related 

to bone formation, such as calcium, phosphorous, and vitamin D (Marie et al., 1985; Grynpas 

and Marie, 1990; Clarke, 2008). The results of clinical studies in people administered strontium

ranelate [Sr2(C12H6N2O8)] to treat osteoporosis (McCaslin and James, 1959; Krane, 1977; 

Skoryna, 1981; Skoryna and Fuskova, 1981; ATSDR, 2004) support the conclusion from animal 

studies that the primary target of strontium exposure is bone.

There are no standard one- or two-generation reproductive toxicity studies for any 

strontium compound, but the available data (Kroes et al., 1977; Skoryna, 1981; Shibata and 

Yamashita, 2001; NIER, 2006b) indicate that strontium does not cause structural or functional 
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effects at doses well above those causing bone effects. In a screening test for reproductive and 

developmental toxicity (NIER 2006b), no effects were observed on mating behavior, fertility, 

gestation period, or the histopathology of the reproductive tissues and organs, and no 

developmental or teratogenic effects were observed.

The data relevant to strontium carcinogenicity are very limited. No increase in tumors

was seen in the only available chronic oral study (Skoryna, 1981; Skoryna and Fuskova, 1981),

but this study used a small sample size and was inadequate for evaluation of carcinogenic 

potential. The weight of evidence from the genotoxicity data is that strontium compounds are 

negative for gene mutation (Kanematsu et al., 1980; Yang, 1984; NIER, 2006d), chromosome 

aberrations (Tateno and Kamiguchi, 1997; NIER, 2006c) and deoxyribonucleic acid (DNA)

damage (Loeb et al., 1977; Casto and DiPaolo, 1983). Based on these data, there is inadequate 

information to assess the carcinogenic potential of strontium, due to the lack of adequate studies 

of chronic duration.

The reference dose (RfD) of 0.3 mg Sr/kg-day is based on the critical effect of decreased 

bone calcification during growth and development. In the principal study (Marie et al., 1985), 

male weanling rats (eight per group) were administered strontium in drinking water for nine

weeks at concentrations of 0, 0.19, 0.27, 0.34, or 0.40% strontium chloride (estimated by the 

authors to be equivalent to 0, 316, 425, 525, and 633 mg Sr/kg-day, respectively). The RfD was 

calculated using the benchmark dose (BMD) method, and based on the lower 95% confidence 

limit on the BMD (defined as a one control standard deviation change in the mean), a benchmark 

dose level (BMDL) (1 SD) of 328 mg Sr/kg-day was derived. This value was divided by an 

uncertainty factor of 1000 (10 for human variability, 10 for extrapolation from rats, and 10 for 

database uncertainties).

EPA also evaluated whether health information is available regarding potential effects on 

children and/or other sensitive populations. Since strontium can substitute for calcium in 

growing bone, children and teenagers are expected to be a sensitive population, since they are 

actively growing. Strontium exposure in children and teenagers may result in effects on bone 

structure with a more severe and/or a long-term impact than similar exposures in adults (Storey, 

1961; Özgür et al., 1996). Many of the toxic effects of strontium result from strontium ions 

substituting for calcium ions, therefore, calcium deficiency would also be expected to result in 

increased sensitivity to strontium. Groups with higher risks of becoming calcium deficient 

include: postmenopausal women, amenorrheic women, female athletes, vegans, and individuals 

with lactose intolerance or cow’s milk allergies. People with severely impaired kidney function 

or 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.

For additional health effects information, please refer to the Health Effects Support Document 

(HESD) for strontium (USEPA, 2014a). 
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Derivation of the Health Reference Level

To evaluate the systems and populations exposed to strontium in drinking water from 

public water systems (PWSs), the monitoring data were analyzed against a concentration in 

drinking water that is termed the Health Reference Level (HRL). The HRL is defined as a riskderived concentration against which to compare the occurrence data from PWSs to determine if 

strontium occurs with a frequency and at levels of public health concern. 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.

EPA calculated a non-cancer HRL of 1,500 μg/L for strontium using the RfD of 0.3 

mg/kg-day, a relative source contribution (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. The

RfD was based on changes in bone growth in weanling rats (i.e., comparable to the sensitive time 

period in humans) and therefore, the HRL is expected to be protective of the sensitive 

population. For additional health effects information, please refer to the Health Effects Support 

Document (HESD) for strontium (USEPA, 2014a). 

5.4 Occurrence

This section presents data on the occurrence of strontium in ambient water and drinking 

water in the United States. As described in Section 5.3, an HRL of 1,500 μg/L was calculated 

based on strontium bone development effects in children and adolescents. This HRL represents

the concentration of the contaminant in drinking water that is likely to be without an appreciable 

risk of deleterious effects during a lifetime. Occurrence data from various sources presented 

below are analyzed with respect to the HRL and the 1⁄2 HRL. When possible, estimates of the 

population exposed at concentrations above the various thresholds are presented as well.

For additional background information about many of the data sources used to evaluate 

occurrence, please refer to Chapter 2.

5.4.1 Occurrence in Ambient Water

Lakes, rivers, and aquifers are the ambient sources of most drinking water. Contaminant 

occurrence in ambient water provides information on the potential for contaminants to adversely 

affect drinking water supplies. Strontium was not included in United States Geological Survey 

(USGS) National Water-Quality Assessment (NAWQA) Cycle 1 monitoring (1992-2001)

However, strontium data are available from EPA’s Storage and Retrieval (STORET) Data 

Warehouse.

Storage and Retrieval (STORET) Data Warehouse

EPA’s STORET Data Warehouse is a collaborative database that 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 are finished drinking water data. Users began populating the STORET Data 

Warehouse in 1999. Most data are post-1999, but some earlier sampling is included.

STORET data have quality limitations. The extent of national coverage and data 

completeness varies from parameter to parameter. There are no restrictions on submission of data 
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based on analytical methods, quality assurance (QA) practices, 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 (USEPA, 2012a). The STORET Data Warehouse also included 

PWS data from three states (Indiana, Missouri, and Ohio); EPA reviewed these as well (USEPA, 

2012a). (For more data gathered by state drinking water programs, see the discussion of state 

monitoring data in Section 5.4.2, below.)

The results of the STORET analysis for strontium are presented in Exhibit 5-3 through 

Exhibit 5-6. These STORET data represent strontium samples collected between 1967 and 2011. 

Fewer records are available in the early years. Of the 12,433 sites (11,543 surface water and 890 

ground water), 12,299 (98.92%) reported detections of strontium. A total of 1,541 (12.39%) sites 

reported detections greater than the 1⁄2 HRL, and 653 (5.25%) sites reported detections greater 

than the HRL. Detected concentrations ranged from 0 to 19,034,000 μg/L. Minimum detected 

concentrations are reported; these minimum values may be indicative of reporting levels used. (A 

minimum value of zero, on the other hand, could represent a detection that was entered into the 

database as a non-numerical value (e.g., “Present”)). No Missouri PWS data were available for 

this contaminant.

Exhibit 5-3: Strontium STORET Data – Summary of Detected Concentrations

Source Water Type Concentration Value of Detections (μg/L)

Minimum Median 90th Percentile Maximum

Ground Water 01 240 2,528.40 19,000

Surface Water 01 270 1,300 19,034,000

Total 01 270 1,344.83 19,034,000

PWS (IN, OH)

2 52 567 18,210 66,200 1 A minimum value of zero may represent a detection that was entered into the database as a non-numerical value 

(e.g., “Present”).

2 It could not be determined from the data in STORET whether the Indiana or Ohio PWS facilities were served by 

ground water or surface water.

Exhibit 5-4: Strontium STORET Data – Summary of Samples

Source Water 

Type

Total 

Number of 

Samples

Samples with 

Detections

Samples with Detections 

> 1⁄2 HRL (750 μg/L)

Samples with Detections 

> HRL (1,500 μg/L)

Number Percent Number Percent Number Percent

Ground Water 2,320 2,179 93.92% 555 23.92% 322 13.88%

Surface Water 41,121 39,780 96.74% 8,866 21.56% 3,170 7.71%

Total 43,441 41,959 96.59% 9,421 21.69% 3,492 8.04%

PWS (IN, OH)

1 3,128 3,110 99.42% 1,345 43.00% 1,039 33.22% 1 It could not be determined from the data in STORET whether the Indiana or Ohio PWS facilities were served by 

ground water or surface water.
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Exhibit 5-5: Strontium STORET Data – Summary of Sites

Source Water 

Type

Total 

Number 

of Sites

Sites with Detections Sites with Detections 

> 1⁄2 HRL (750 μg/L)

Sites with Detections 

> HRL (1,500 μg/L)

Number Percent Number Percent Number Percent

Ground Water 890 865 97.19% 208 23.37% 120 13.48%

Surface Water 11,543 11,434 99.06% 1,333 11.55% 533 4.62%

Total 12,433 12,299 98.92% 1,541 12.39% 653 5.25%

PWS (IN, OH)

1 199 199 100% 99 49.75% 75 37.69% 1 It could not be determined from the data in STORET whether the Indiana or Ohio PWS facilities were served by 

ground water or surface water.

Exhibit 5-6: Strontium STORET Data – Summary of States

Source Water 

Type

Total 

Number 

of States

States with Detections States with Detections 

> 1⁄2 HRL (750 μg/L)

States with Detections 

> HRL (1,500 μg/L)

Number Percent Number Percent Number Percent

Ground Water 13 13 100% 7 53.85% 7 53.85%

Surface Water 31 31 100% 19 61.29% 17 54.84%

Total1 33 33 100% 21 63.64% 19 57.58%

PWS (IN, OH)

2 2 2 100% 1 50.00% 1 50.00% 1 The number of states with ground water data plus the number of states with surface water data may not equal the 

“Total” number of states providing data because some states provided both ground water and surface water data.

2 It could not be determined from the data in STORET whether the Indiana or Ohio PWS facilities were served by 

ground water or surface water.

5.4.2 Occurrence in Drinking Water

The agency reviewed a number of data sources for information on contaminant 

occurrence in drinking water. Data and information on strontium from the following sources are 

available and are summarized in this section:

• EPA’s National Inorganics and Radionuclides Survey (NIRS).

• State drinking water monitoring programs.

• EPA’s Community Water System Survey (CWSS).

• Consumer Confidence Reports (CCRs) from PWSs.

• USGS NAWQA – Source Water and Drinking Water Studies.

• Environmental Working Group (EWG) Drinking Water Database.

Note that there may be some overlap, as sources with different purposes and audiences 

may have reported the same underlying data.

Reviewed sources that contain no information on strontium occurrence included, among 

others, EPA’s First Unregulated Contaminant Monitoring Regulation (UCMR 1), EPA’s Second 

Unregulated Contaminant Monitoring Regulation (UCMR 2), and Rounds 1 and 2 of EPA’s 

Unregulated Contaminant Monitoring (UCM) Program.

Strontium has been selected for monitoring from 2013 to 2015 under the Third 

Unregulated Contaminant Monitoring Rule (UCMR 3) (77 FR 26072; USEPA, 2012b). 
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Primary Data Sources

National Inorganics and Radionuclides Survey (NIRS), 1984-1986

NIRS was conducted by EPA to provide data on the occurrence of a select set of 

radionuclides and inorganic chemicals (IOCs). It provides contaminant occurrence data from 989 

community water systems (CWSs) served by ground water sources. Each of these randomly 

selected PWSs was sampled a single time between 1984 and 1986. Selection of the PWSs was 

designed so that the contaminant occurrence results from these PWSs would be representative of 

national occurrence of contaminants in ground water systems. Further description of the NIRS 

survey can be found in Longtin (1988) and USEPA (2008).

NIRS was structured as a stratified, random sampling of the nation’s community ground 

water supplies as they existed in the mid-1980s. A random selection of systems from each of 

several size categories was included, in proportion to the number of PWSs that existed in those 

size categories nationally. The sampling frame used in NIRS was designed to be representative 

of ground water supplies on a national basis, but not necessarily on a state-by-state, regional, or 

other geographic basis. The resulting sample of systems represents approximately 2% of the 

nation’s community ground water supply in each system size category. Since there are many 

more small than large PWSs in the United States, most of the NIRS data are from smaller 

systems. The data are from 49 states (there are no data from Hawaii), as well as Puerto Rico.

Results of the NIRS are presented in Exhibit 5-7 through Exhibit 5-10. The first two 

exhibits summarize all detections. Strontium was monitored with a reporting level of 1 μg/L. 

Approximately 99.1% of ground water PWSs had detections of strontium (i.e., concentrations at 

or above the reporting level). These detections affected about 99.9% of the population served by 

the PWSs. Detected concentrations ranged from 1.53 μg/L to 43,550.2 μg/L. The mean 

concentration among detections (not shown in the tables) was 603 μg/L.

Review of the NIRS data shows that strontium was detected in all 50 states/entities in 

which it was sampled (i.e., in 49 states (all except Hawaii) as well as Puerto Rico). It was 

detected at levels greater than the 1⁄2HRL (750 μg/L) in 34 states and at levels greater than the 

HRL (1,500 μg/L) in 26 states, including states in all regions of the country.

The development of the NIRS data set enables extrapolation of contaminant occurrence 

in ground water on a nationwide scale. To extrapolate, the percentage of ground water systems 

observed to exceed a specified threshold (or percentage of population served) is multiplied by the 

total national number of ground water systems (or the total national population served). The total 

number of ground water systems (and population served) is calculated in two ways in the tables

below: as the total number of CWSs served by ground water, and as the sum of CWSs and nontransient non-community water systems (NTNCWSs) served by ground water. NTNCWSs are 

public water systems that regularly supply water to at least 25 of the same people at least six 

months per year, but not year-round. Some examples are schools, factories, office buildings, and 

hospitals that have their own water systems. See Chapter 2 for additional information on national 

extrapolations. The results of this national extrapolation are presented in Exhibit 5-8 through

Exhibit 5-10.
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Exhibit 5-7: Strontium Occurrence Data from the NIRS Database – Summary of 

Detected Concentrations

Source 

Water 

Type

Total 

Number of 

Samples

Number of 

Detections 

Percent of 

Detections

Concentration Value of Detections (μg/L)

Minimum Median 90th

Percentile

99th

Percentile Maximum

Ground 

Water Only 989 980 99.09% 1.53 178 1,078 7,339 43,550.2

Exhibit 5-8: Strontium Occurrence Data from the NIRS Database – Summary of 

System and Population Served Data – All Detections

Source 

Water Type

Total Number

Detections

Number Percent National Extrapolation1

Systems Population Systems Population Systems Population Systems Population

Ground

Water Only 989 1,482,133 980 1,480,581 99.09% 99.90%

39,741

(CWS only)

93,035,877

(CWS only)

58,864 

(CWS + 

NTNCWS)

98,406,604

(CWS + 

NTNCWS) 1 National extrapolations are generated by multiplying the NIRS national statistical sample findings of 

system/population percentages and national system/population inventory numbers for ground water-sourced PWSs 

developed from EPA’s Safe Drinking Water Information System (SDWIS), the CWSS, and UCMR (see Chapter 2 for 

discussion). The inventory numbers are: 93.1 million people served by 40,106 ground water CWSs, and 98.5 million 

people served by 59,405 CWSs + NTNCWSs.

Exhibit 5-9: Strontium Data from the NIRS Database – Summary of System and 

Population Served Data – Detections > 1⁄2 HRL

Source Water 

Type

Detections > 1⁄2 HRL (750 μg/L)

Number Percent National Extrapolation1

Systems Population Systems Population Systems Population

Ground Water 

Only 141 245,870 14.26% 16.59%

5,718

(CWS only)

15,449,834

(CWS only)

8,469

(CWS + NTNCWS)

16,341,714

(CWS + NTNCWS) 1 National extrapolations are generated by multiplying the NIRS national statistical sample findings of 

system/population percentages and national system/population inventory numbers for ground water-sourced PWSs 

developed from EPA’s SDWIS, the CWSS, and UCMR (see Chapter 2 for discussion). The inventory numbers are: 

93.1 million people served by 40,106 ground water CWSs, and 98.5 million people served by 59,405 CWSs + 

NTNCWSs.
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Exhibit 5-10: Strontium Data from the NIRS Database – Summary of System and 

Population Served Data – Detections > HRL

Source Water

Type

Detections > HRL (1,500 μg/L)

Number Percent National Extrapolation1

Systems Population Systems Population Systems Population

Ground Water 

Only 69 158,557 6.98% 10.70%

2,798

(CWS only)

9,963,311

(CWS only)

4,145

(CWS + NTNCWS)

10,538,468

(CWS + NTNCWS)

1 National extrapolations are generated by multiplying the NIRS national statistical sample findings of 

system/population percentages and national system/population inventory numbers for ground water-sourced PWSs 

developed from EPA’s SDWIS, the CWSS, and UCMR (see Chapter 2 for discussion). The inventory numbers are: 

93.1 million people served by 40,106 ground water CWSs, and 98.5 million people served by 59,405 CWSs + 

NTNCWSs.

Supplemental Data Sources

State Monitoring Data, 1998-2005

Since there is no national database that receives and stores all relevant data regarding the 

occurrence of regulated contaminants in public drinking water systems, EPA conducted a 

voluntary data call-in from the states, territories, and tribes to obtain regulated contaminant 

occurrence data in support of national occurrence assessments conducted for the second Six-Year 

Review. For more details on the Six-Year Review Information Collection Request (ICR) Dataset, 

refer to USEPA (2009a). 

A few states also submitted PWS occurrence data for unregulated contaminants. EPA 

was able to supplement these data on unregulated contaminants by downloading additional 

publicly available monitoring data from state Web sites. The result was a collection of 

unregulated contaminant monitoring data from nine states, representing those states with varying 

degrees of completeness.

Drinking water occurrence data for strontium were submitted from: Illinois, Ohio, and

EPA Region 9 tribes.1 There is a range in completeness from these states and tribes. For 

example, strontium results from approximately 2.5% of CWSs and less than 1% of NTNCWSs 

and transient non-community water systems (TNCWSs) were included in the strontium data 

submitted by Ohio; approximately 1% of CWSs (and no data for NTNCWSs) were included in 

the data from Illinois. One CWS from the EPA Region 9 tribes submitted results for strontium. 

Results are presented in Exhibit 5-11 through Exhibit 5-13. As a result of the differences in 

completeness of the state occurrence data, the exhibits do not include estimates of population 

served. Precise information about methods used and reporting levels is not available for the state 

data. Minimum detected concentrations are reported in Exhibit 5-11; these minimum values may 

be indicative of reporting levels used.

In Illinois, strontium was detected in 100% of 21 drinking water samples collected at 19 

CWSs. Detected concentrations ranged from 71 μg/L to 4,600 μg/L, with 26.32% of systems 

reporting concentrations greater than the HRL. 

 

1 A small amount of strontium data (37 records) was available for download from the State of Wisconsin, 

but it was unclear if some of the data represented “Total strontium” or “Strontium-90” (the radionuclide). Hence, 

those data are not included in this summary.
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The state of Ohio detected strontium in 75 (97.40%) of 77 drinking water samples. These 

detections occurred in 30 (93.75%) of 32 PWSs reporting data. Detected concentrations ranged 

from 4 μg/L to 40,889 μg/L, with 21.88% of sites reporting concentrations greater than the HRL. 

Additional PWS monitoring data, from Ohio, are reported in STORET (see Section 5.4.1). 

Strontium was not detected in the single sample analyzed by tribes in EPA Region 9.

Exhibit 5-11: Strontium State Drinking Water Occurrence Data – Summary of 

Detected Concentrations

State

(Date Range)

Source Water 

Type

Concentration Value of Detections (μg/L)

Minimum Median 90th

Percentile

99th

Percentile Maximum

Illinois

(1998-2005)

Ground Water 71 475 2,360 4,243 4,600

Surface Water 81 270 2,614 3,141 3,200

Total 71 450 2,500 4,320 4,600

Ohio

(2000-2005)

Ground Water 4 262 6,032 40,193 40,889

Surface Water 131 169 7,109 8,863 9,009

Total 4 257 6,950 39,935 40,889

EPA Region 9 

Tribes (2003)

Ground Water N/A N/A N/A N/A N/A

Surface Water N/A N/A N/A N/A N/A

Total N/A N/A N/A N/A N/A

N/A = not applicable (no detections in this category).

Exhibit 5-12: Strontium State Drinking Water Occurrence Data – Summary of 

Samples

State

(Date Range)

Source Water 

Type

Total 

Number

of 

Samples

All Detections Detections > 1⁄2 HRL 

(750 μg/L)

Detections > HRL 

(1,500 μg/L)

Number Percent Number Percent Number Percent

Illinois

(1998-2005)

Ground Water 18 18 100% 4 22.22% 4 22.22%

Surface Water 3 3 100% 1 33.33% 1 33.33%

Total 21 21 100% 5 23.81% 5 23.81%

Ohio

(2000-2005)

Ground Water 57 55 96.49% 13 22.81% 10 17.54%

Surface Water 20 20 100% 8 40.00% 8 40.00%

Total 77 75 97.40% 21 27.27% 18 23.38%

EPA Region 

9 Tribes

(2003)

Ground Water 1 0 0% 0 0% 0 0%

Surface Water 0 0 0% 0 0% 0 0%

Total 1 0 0% 0 0% 0 0%
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Exhibit 5-13: Strontium State Drinking Water Occurrence Data – Summary of 

Systems

State

(Date Range)

Source Water 

Type

Total 

Number

of 

Systems

Systems with 

Detections

Systems with 

Detections

> 1⁄2 HRL (750 μg/L)

Systems with 

Detections

> HRL (1,500 μg/L)

Number Percent Number Percent Number Percent

Illinois

(1998-2005)

Ground Water 16 16 100% 4 25.00% 4 25.00%

Surface Water 3 3 100% 1 33.33% 1 33.33%

Total 19 19 100% 5 26.32% 5 26.32%

Ohio

(2000-2005)

Ground Water 28 26 92.86% 8 28.57% 5 17.86%

Surface Water 4 4 100% 2 50.00% 2 50.00%

Total 32 30 93.75% 10 31.25% 7 21.88%

EPA Region 

9 Tribes

(2003)

Ground Water 1 0 0% 0 0% 0 0%

Surface Water 0 0 0% 0 0% 0 0%

Total 1 0 0% 0 0% 0 0%

Community Water System Survey (CWSS), 2006

The 2006 CWSS (USEPA, 2009b) gathered data on the financial and operating 

characteristics of a random sample of CWSs nationwide. All systems serving more than 500,000 

people (94 systems in 2006) received the survey, and systems in that size category were asked 

questions about concentrations of unregulated contaminants in their raw and finished water. Of 

the 94 systems asked about unregulated contaminants, 62 percent (58 systems) responded to the 

survey, though not all of these systems answered every question. EPA supplemented the data set 

by gathering additional information about contaminant occurrence at the 94 systems from 

publicly available sources (e.g., CCRs).

In the 2006 CWSS, one of the 94 systems serving more than 500,000 people reported 

monitoring data for strontium. This system reported the results of one sample only. The 

concentration of strontium in that sample was 330 μg/L and thus did not exceed the HRL or the

1⁄2 HRL. Reporting levels were not specified in this survey.

Water Systems’ Consumer Confidence Reports (CCRs), 2006-2007

CCRs are annual water quality reports that CWSs are required to provide to their 

customers. These reports summarize information on water sources, detected contaminants, and 

system compliance with EPA drinking water standards; they may also include general 

educational material. Under the CCR Rule (40 CFR Subpart O), CWSs with 15 or more 

connections or serving at least 25 year-round residents must prepare and distribute a CCR to all 

billing units or service connections every year. Systems serving 100,000 or more residents are 

also required to post their current CCRs on a publicly accessible Internet site. EPA reviewed 

CCRs published by the 26 systems that serve over one million customers for unregulated 

contaminant occurrence information. Data on strontium were available from CCRs prepared by 

two CWSs in New York: Suffolk County and New York City. Reporting levels were not 

specified in either of the CCRs.
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The Suffolk County Water Authority included data on strontium-88 in its 2007 CCR. 

Samples were collected from 30 distribution areas supplied by both treated and untreated ground 

water from three major aquifers. The number of strontium samples collected in each distribution 

area varied from 4 to 255. Strontium-88 was detected in 26 of the 30 distribution areas. The 

average annual concentrations calculated for these 26 distribution areas ranged from nondetections to 150 μg/L. The highest detected concentration was 200 μg/L, which is less than the 

HRL and the 1⁄2 HRL.

New York City included data on strontium in its 2006 and 2007 CCRs. The city is served 

by two distribution systems supplied by surface water from 19 reservoirs and three controlled 

lakes, and one distribution system supplied by treated ground water. In 2006, one of the surface 

water systems was off-line; 319 strontium samples were collected from the other surface water 

system and six samples were collected from the ground water system. The number of samples 

with detections was not reported. The average annual strontium concentration calculated for the 

surface water system was 20 μg/L, while that for the ground water system was 40 μg/L. 

Maximum concentrations of 30 μg/L and 50 μg/L were reported from the surface water and 

ground water systems, respectively. In 2007, strontium monitoring was conducted at the two 

surface water systems, but not at the ground water system. Four samples were collected at one 

system and 332 samples were collected at the other system. The number of samples with detects 

was not reported. Average annual concentrations calculated for the two surface water systems 

were 20 μg/L and 70 μg/L. The highest detected concentration was 70 μg/L. No detections 

exceeded the HRL or the 1⁄2 HRL.

United States Geological Survey (USGS) National Water Quality Assessment (NAWQA)

Source Water and Drinking Water Studies 

Water Quality in Public-Supply Wells (Toccalino et al., 2010), 1993-2007

To assess risks posed by contaminants in public-supply wells, water samples were 

collected from source (untreated) ground water from 932 public-supply wells located in parts of 

40 NAWQA Study Units in 41 states (Toccalino et al., 2010). Each well was sampled once 

between 1993 and 2007. Reporting levels for strontium were not specified in this study; 

however, the minimum detected concentration (reported in Exhibit 5-14) may be indicative of 

reporting levels used. Results from this study are presented in Exhibit 5-14 and Exhibit 5-15. 

Strontium was detected in every sample. Of the 503 samples, 126 (25.05%) exceeded the 1⁄2 HRL 

and 61 (12.13%) exceeded the HRL.

Exhibit 5-14: Strontium Data from Public-Supply Wells (Toccalino et al., 2010) –

Summary of Detected Concentrations

Source Water Type Concentration Value of Detections (μg/L)

Minimum Median 90th Percentile 99th Percentile Maximum

Ground Water Only 5.61 385 1,810 7,080 43,950 
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Exhibit 5-15: Strontium Data from Public-Supply Wells (Toccalino et al., 2010) –

Summary of Samples

Source Water 

Type

Number of 

Samples

All Detections Detections > 1⁄2 HRL 

(750 μg/L)

Detections > HRL 

(1,500 μg/L)

Number Percent Number Percent Number Percent

Ground Water Only 503 503 100% 126 25.05% 61 12.13%

Water Quality in Domestic Wells (DeSimone, 2009; Bartholomay, 2007), 1991-2004

and 1991-2006

USGS conducted an assessment of the quality of water from domestic wells across the 

United States using NAWQA data (DeSimone, 2009). The program included the analysis of 

major ions, trace elements, nutrients, radon, and organic compounds (pesticides and volatile 

organic compounds (VOCs)) at approximately 2,100 domestic wells (private drinking water 

wells) across 48 states, covering 30 regional aquifers, between 1991 and 2004. In addition, 

USGS summarized data from wells sampled for NAWQA agricultural land-use assessment 

studies to provide an indication of the potential effects of agricultural land-use practices on the 

ground water in the aquifers studied. Reporting thresholds varied; DeSimone censored the 

strontium data at a common reporting level of 10 μg/L. There were a total of 570 analyses for 

strontium in aquifer and agricultural land-use studies. In 6.49% of wells, detected concentrations 

of strontium exceeded 4,000 μg/L (and, therefore exceeded the strontium HRL).

In a summary of select USGS NAWQA data on domestic well water quality in 16 states

from 1991 to 2006, compiled for the Centers for Disease Control’s (CDC’s) National 

Environmental Public Health Tracking Program, Bartholomay et al. (2007) report that strontium 

was detected in 100 percent of the 446 wells sampled in 16 states. Strontium was detected at 

concentrations in excess of 4,000 μg/L (a screening level used by the USGS) in 2.2% of samples; 

therefore, the frequency of occurrence in excess of the HRL is at least 2.2%. Reporting levels

varied (Bartholomay et al., 2007).

Water Quality in Carbonate Aquifers (Lindsey et al., 2008), 1993-2005

As part of the NAWQA program, Lindsey et al. (2008) conducted an assessment of the 

water quality in carbonate aquifers, which account for 22% of the ground water pumped by the 

country’s PWSs. From 1993 to 2005, the study analyzed 1,042 wells and springs across 12 

aquifer systems and 20 states for major ions, radon, nutrients, pesticides, and VOCs. The study 

reports 425 “observations” of strontium, but does not specify how many of the 1,042 samples 

collected for the study were tested for strontium and does not specify a reporting level for 

strontium. From the 425 observations, the 25th percentile concentration was 92.3 μg/L, the 50th

percentile concentration was 220.0 μg/L, the 75th percentile concentration was 606.1 μg/L, and 

the maximum concentration was 43,950 μg/L. The maximum concentration exceeded the HRL. 

Selected Trace Elements in Ground Water in the Glacial Aquifer System of the 

Northern United States (Groschen et al., 2009), 1991-2003

Using NAWQA data, Groschen et al. (2009) conducted an assessment of the occurrence 

and distribution of several contaminants in ground water of the glacial aquifer system in the 

Northern United States, which underlies portions of New England, the Midwest, the Pacific 

Northwest, and Alaska. The study analyzed data collected from 1,590 monitoring wells and 

water supply wells sampled between 1991 and 2003. Reporting levels ranged from 0.08 μg/L to 
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1.4 μg/L. The results of the USGS analysis are presented in Exhibit 5-16 and Exhibit 5-17.

Strontium was detected in 551 (99.8%) of a total of 552 samples. The maximum detected 

concentration was 9,120 μg/L. Less than 5% of detected concentrations exceeded the HRL, and 

around 10% exceeded the 1⁄2 HRL.

Exhibit 5-16: Strontium Data from Northern United States Glacial Aquifer System 

(Groschen et al., 2009) – Summary of Detection Frequencies

Element

Number of 

Samples 

Analyzed

Number of Samples 

with Concentration

≥ any Reporting 

Level

Percent of 

Samples with 

Detection at any 

Reporting Level

Number of 

Samples with 

Concentration 

≥ 1 μg/L

Percent of 

Samples with 

Detection 

≥ 1 μg/L

Strontium 552 551 99.8% 551 99.8%

Exhibit 5-17: Strontium Data from Northern United States Glacial Aquifer System

(Groschen et al., 2009) – Summary of Concentrations

Element

Minimum 

Concentration 

(μg/L)

Mean 

Concentration 

(μg/L)

Maximum 

Concentration 

(μg/L)

Percentile Concentrations (μg/L) 

Estimated from Regression on Ordered 

Statistics (ROS)

5th 10th 25th 50th 75th 90th 95th

Strontium 1.47 390 9,120 28 37 84 185 438 800 1,300

Note: the minimum, mean and maximum concentrations are measured values. The percentile concentrations are 

estimated statistically. In the report, USGS notes: “Regression on Ordered Statistics (ROS) techniques were used to 

estimate medians, percentiles, and other summary statistics. ROS was used to estimate the descriptive statistics for 

all elements because most elements had substantial portions of results reported as below detection (less than the 

reporting level).” Hence, the ROS-modeled summary statistics are sometimes less than the minimum measured 

concentrations or even the reporting levels. These are estimates based on the modeled probability distributions.

Environmental Working Group (EWG) Drinking Water Database, 2004-2009

In December 2009, EWG released its “National Drinking Water Database” which 

includes data on occurrence of drinking water contaminants (regulated and unregulated) 

collected between 2004 and 2009 from 45 states and the District of Columbia (EWG, 2009). The 

2009 EWG database includes results from approximately 48,000 water systems; data were 

obtained primarily from state water offices.

EWG reviewed the data for inconsistencies, potential outliers and other errors. It also

invited the American Water Works Association (AWWA) and the Association of Metropolitan 

Water Agencies (AMWA) to review the data and/or have their constituents, the PWSs, review 

the data. Some corrections apparently were made since the public release of the data in 

December, 2009. The data included in the table below were downloaded on January 10, 2010. 

EPA’s analysis is based solely on the data made publicly available by EWG on its Web site.

Reporting levels are not specified in EWG’s database.

A total of 370 systems reported having tested for strontium between 2004 and 2009. 

These data showed detections of strontium in 366 (98.9%) of the PWSs, serving almost 2.4 

million people in five states (Exhibit 5-18). EWG found that 16 of the PWSs, in four states, had 

detections of strontium above a threshold of 4,000 μg/L. Thus, at least 16 PWSs had 

exceedances of the HRL of 1,500 μg/L.
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Exhibit 5-18: Summary of EWG Strontium Data, 2004-2009

State

PWSs with Detections of Strontium

Number of PWSs Population Served

Wisconsin 2 64,500

Illinois 340 2,141,804

Ohio 17 117,126

New York 3 9,668

Minnesota 4 32,955

Total 366 2,366,053

5.5 Technology Assessment

5.5.1 Analytical Methods

EPA has developed two analytical methods for the analysis of strontium in drinking 

water: 

• EPA Method 200.7, Revision 4.4, Determination of Metals and Trace Elements in 

Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry, 

has a Method Detection Limit (MDL) of 0.3 μg/L. Recoveries in tap water, pond 

water, and well water range from 94 to 105%, with Relative Percent Differences 

(RPDs) of 0.0 to 2.7% (USEPA, 1994a).

• EPA Method 200.8, Revision 5.4, Determination of Trace Elements in Waters by 

Inductively Coupled Plasma - Mass Spectrometry. No MDL or recovery data are 

available for EPA Method 200.8 because strontium was not included as an analyte 

during method development. However, EPA personnel used EPA Method 200.8 to 

generate a value for the Minimum Reporting Level (MRL) for potential use in UCMR 

3. EPA Method 200.8 was used for strontium so that occurrence data for all four 

elemental contaminants being considered for UCMR 3 can be generated with a single 

analytical method (USEPA, 1994b).

Although not listed in EPA Method 200.8, the MRL for strontium is 0.3 μg/L. This value

serves as a national benchmark for laboratories that may participate in UCMR 3 using EPA 

Method 200.8 (77 FR 26072; USEPA, 2012b). 

An estimated reporting level for each method (calculated as five times the MDL for EPA 

Method 200.7 and as the MRL for EPA Method 200.8) was compared to the HRL for strontium 

to determine whether the available analytical methods are capable of reliable quantitation at 

concentrations of estimated toxicological concern (see Exhibit 5-19). The Method Sensitivity 

Ratio (MSR) is calculated from the following equation:

MSR = HRL (μg/L) / MRL or 5x the MDL (μg/L)

A favorable MSR is one that is greater than ten. That is, it is preferable that the HRL be 

at least ten times above the concentration at which data can be reliably reported; this provides a 

margin of safety for uncertainty in the HRL and/or method performance (see USEPA, 2009c).
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Exhibit 5-19: Method Sensitivity Ratios (MSRs) for Strontium

Method MDL (μg/L) 5x the MDL 

(μg/L) MRL (μg/L) HRL (μg/L) MSR

200.7 0.3 1.5 -- 1,500 1,000

200.8 -- -- 0.3 1,500 5,000

For both methods, the MSRs are greater than ten; hence, the available analytical methods 

are capable of reliable quantitation at least ten times below the HRL.

5.5.2 Treatment Technologies

The availability of treatment technologies is not a factor EPA considers when making a 

regulatory determination. However, suitable treatment technologies must be made available 

before a National Primary Drinking Water Regulation (NPDWR) can be promulgated.

The literature reviewed revealed three technologies that have been tested for strontium 

removal: ion exchange, adsorption, and membranes. Clifford (1990) states that ion exchange or 

adsorption onto activated alumina can remove strontium. Apak et al. (1995) reported on the 

adsorption of radioactive isotopes onto wastes from aluminum production. They reported that 

strontium-90 was adsorbed but less well than cesium-137. Specific removals depended on 

conditions such as temperature and pH. Romano (1997) filed a patent for an adsorption process 

using a zeolite adsorbent, which was reported to reduce strontium concentrations by 99.7% (311 

mg/L to 0.85 mg/L). Selek-Murathan (2004) reported adsorption onto packed beds with various 

adsorbents including sepiolite, diatomite, and pumice. Sepiolite was reported as being the most 

effective for removal of strontium. Bostick et al. (1997) reported adsorption onto a zeolite and a 

resorcinol-formaldehyde resin. Both adsorbed strontium well; the zeolite had a longer period 

before breakthrough. Knappe et al. (2007) mentions that mordenite zeolite is highly specific for 

strontium. Van der Brueggen and Vandecasteele (2003), in a review article, mention 

nanofiltration being used for strontium removal, although specifics were not included with the 

citation. Amy et al. (2003) reported removal of strontium to below detection limits using both 

nanofiltration and reverse osmosis membranes. Ultrafiltration membranes were less effective, 

achieving less than 50 percent removal. Ecowater (2005) reports on a system using a reverse 

osmosis membrane followed by a granular activated carbon (GAC) filter. They report a 94 

percent or greater removal of strontium. The literature shows that both adsorption and membrane 

filtration (nanofiltration or reverse osmosis) can be effective in strontium removal.

Please note that the literature review was not exhaustive, and findings from the reviewed 

studies might not be directly comparable. A full assessment of treatment technology applicability 

will require a more detailed review and analysis of the literature, and possibly additional 

research.

5.6 Preliminary Regulatory Determination

5.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL

The statutory requirements for the CCL and regulatory determinations can be found in 

SDWA Section 1412(b)(1). The 1996 SDWA Amendments require EPA to publish the CCL 

every five years. The CCL is a list of contaminants that are not subject to any proposed or 

promulgated NPDWRs, are known or anticipated to occur in PWSs, and may require regulation 

under SDWA to protect public health. The 1996 SDWA Amendments also direct EPA to 

determine whether or not to regulate at least five contaminants from the CCL every five years.
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There are three criteria to be considered in making a regulatory determination. A decision to 

regulate is warranted if:

(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 PWSs 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 PWSs. 

If EPA determines that all three of these statutory criteria are met, it makes a preliminary 

positive regulatory determination that an NPDWR2 is needed. . Following a comment response 

period and a final positive regulatory determination, the agency has 24 months to publish a 

proposed Maximum Contaminant Level Goal3 (MCLG) and an NPDWR. After the proposal, the 

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

1412(b)(1)(E)).4 The agency may determine that there is no need for a regulation when a 

contaminant fails to meet one or more of the criteria. A decision not to regulate is considered a 

final agency action and is subject to judicial review. The agency can choose to publish a Health 

Advisory (a nonregulatory action) or other guidance for any contaminant on the CCL, 

independent of the regulatory determination. Refer to section 1.4 for a summary of the approach 

used to identify and evaluate contaminants for RD 3. The following section summarizes the 

preliminary RD 3 decision for strontium.

5.6.2 Health Effects (Criterion #1)

The first criterion asks if the contaminant may have an adverse effect on the health of 

persons. Since all chemicals have adverse effects at some level of exposure, the challenge is to 

identify an HRL, a dose below which adverse health effects are considered unlikely to occur 

(threshold toxicant), or below which adverse effects have a defined low probability of occurrence 

(non-threshold toxicant). The key elements that must be considered in evaluating the first 

criterion are the mode of action, the critical effect(s), the dose-response for critical effect(s), the 

RfD for threshold effects, and the slope factor for non-threshold effects.

A full description of the health effects associated with exposure to strontium is presented 

in Section 5.3 of this document and in Chapters 7 and 8 of the HESD for strontium. 

Health Criterion Data

The available toxicological data indicate exposure to strontium has the potential to cause 

adverse health effects in humans and animals; the bone is the primary target. A potential link 

 

2 An NPDWR is a legally enforceable standard that applies to PWSs. 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.

3 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 nonenforceable health goals." (CFR 141.2)

4 The statute authorizes a nine month extension of this promulgation date.
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between high strontium exposures and rickets in Turkish children was reported by Özgür et al. 

(1996), but the data were insufficient for identifying the doses associated with this effect. No 

other epidemiology study was located that evaluated bone effects following strontium exposure. 

Clinical studies evaluating strontium exposure are available (McCaslin and James, 1959; Krane, 

1977; D’Haese et al., 1999, 2000; Vanholder et al., 2002; Cohen-Solal et al., 2002; De Broe and 

D’Haese, 2003). However these studies are limited to patients with bone disorders or chronic 

renal failure; thus, they are considered as part of human variability but are not appropriate for the 

basis of the RfD. Disruption of normal skeletal development, causing effects similar to 

osteomalacia and rickets in rats (young and adult) and mice has been reported following 

subchronic and chronic oral strontium exposure (Storey, 1961, 1962; Kshirsagar, 1976; Johnson 

et al., 1968; Marie et al., 1985; Marie and Hott, 1986; Grynpas and Marie, 1990; Neufeld and 

Boskey, 1994). Data to support the potential for effects on systems other than the skeleton are 

limited. 

Two studies were considered co-critical for development of the strontium RfD (Marie et 

al., 1985; Grynpas and Marie, 1990). The RfD of 0.3 mg Sr/kg-day is derived from the BMDL (1 

SD) of 328 mg Sr/kg-day, for decreased bone calcification rate in male weanling rats (Marie et 

al., 1985), divided by a composite UF of 1,000. The composite UF is based on a factor of 10 for 

interspecies differences, a factor of 10 for protection of sensitive populations, and a factor of 10 

for database uncertainties and deficiencies. EPA calculated a non-cancer HRL of 1,500 μg/L for 

strontium using the RfD of 0.3 mg/kg-day, an 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. 

There is inadequate information to assess the carcinogenic potential of strontium and due to the 

lack of adequate studies of chronic duration no cancer slope factor was calculated.

Health Criterion Conclusion

Toxicological data from human and animal studies indicate that bone is a target of 

strontium toxicity. Data on decreased bone calcification in rats support the development of an 

HRL of 1,500 μg/L for human exposure via drinking water. Based on these considerations, EPA 

concludes that strontium meets the SDWA statutory criterion #1 for regulatory determination; it

may have an adverse effect on the health of persons.

5.6.3 Occurrence in Public Water Systems (Criterion #2)

The second criterion asks if the contaminant is known to occur or if there is a substantial 

likelihood that the contaminant will occur in PWSs with a frequency and at levels of public 

health concern. In order to address this question, EPA consulted a variety of information sources, 

including data from NIRS, a nationally representative survey of ground water systems conducted 

from 1984 to 1986. EPA looked at the total number of systems that reported detections of 

strontium, as well as those that reported concentrations of strontium above the drinking water 

HRL of 1,500 μg/L.

Available monitoring data, including data that may inform regional and national 

occurrence, are presented in Section 5.4 of this document and in Chapter 4 of the HESD, and are 

summarized below. Additional information on production, use, and fate is found in Section 5.2

of this document and in Chapter 3 of the HESD.
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Occurrence Criterion Data

Concentrations of strontium from CWSs supplied from ground water sources were 

obtained from NIRS, a nationally representative survey conducted from 1984 to 1986. Strontium 

was monitored with a reporting level of 1 μg/L. The mean reported level was 603 μg/L and the 

maximum reported level was 43,500 μg/L (a value approximately 30 times the HRL of 1,500 

μg/L). Sixty-nine of 989 systems (6.98%) reported detections greater than the HRL. The national 

extrapolation from these findings suggests an estimated 2,798 ground water CWSs serving 10.0 

million people nationally will have strontium concentrations exceeding the HRL. 

Review of the NIRS data shows that strontium was detected in all 50 states/entities in 

which it was sampled (i.e., in 49 states (all except Hawaii) as well as Puerto Rico). It was 

detected at levels greater than the 1⁄2 HRL (750 μg/L) in 34 states and at levels greater than the 

HRL (1,500 μg/L) in 26 states, including states in all regions of the country.

Finished water data for strontium from Ohio and Illinois are consistent with the NIRS 

data. The State of Illinois reported results from testing 21 drinking water samples from 19 PWSs; 

strontium was detected in all 21 samples (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). The State of Ohio reported results from testing 77 samples 

from 32 PWSs; strontium was detected in 75 samples (97.4%) from 30 systems (93.8%). 

Approximately 27.3% (21 of 77) of samples from 31.3% (10 of 30) of systems had strontium at 

levels greater than the 1⁄2 HRL, and approximately 23.4% (18 of 77) of samples from 21.9% (7 of 

30) of systems had strontium at levels greater than the HRL. Finished water data from Ohio and 

Illinois come from both surface water and ground water systems; rates of strontium detection and 

HRL exceedance from the two source water types are comparable. More limited monitoring data 

gathered from states by the EWG confirm that strontium has been detected in PWSs within 

Wisconsin, Illinois, New York, Minnesota, and Ohio.

Ambient water data also show high levels of occurrence, which is expected since 

strontium 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 to 2007, and strontium 

was detected in 100% of samples (503 of 503). Of the detections, 25.8% (130 of 503) were 

above the 1⁄2 HRL (750 μg/L) and 12.3% (62 of 503) were above the HRL (1,500 μg/L). 

STORET, which includes data on ambient water, records strontium concentrations up to 13,000 

times greater than the HRL. 

Occurrence Criterion Conclusion

NIRS, a nationally representative survey of ground water, indicates that strontium 

concentrations exceed the HRL of 1,500 μg/L in 6.98% of PWSs, and in some cases the 

measured concentrations exceed the HRL by large margins. The national extrapolation from 

these findings suggests an estimated 2,798 ground water CWSs serving 10.0 million people 

nationally will have strontium concentrations exceeding the HRL. In addition, the supplemental 

surface water data for strontium are consistent with groundwater findings and demonstrate the 

potential for high levels of occurrence in surface waters.

Based on these considerations, EPA concludes that strontium meets the SDWA statutory 

criterion #2 for regulatory determination; it does occur with a frequency and at levels of public 

health concern in PWSs
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5.6.4 Risk Reduction (Criterion #3)

The third criterion asks if, in the sole judgment of the Administrator, regulation presents a 

meaningful opportunity for health risk reduction for persons served by PWSs. In evaluating this 

criterion, EPA looked at several factors.

Using the monitoring results, EPA estimated the total exposed population and the 

population exposed to levels above the HRL. These estimates are included in Section 5.4.2 of 

this document and in Chapter 4 of the HESD, and summarized in the “Exposed Population 

Estimates” section, below.

EPA also examined the relative contribution of drinking water exposure and other routes 

of exposure (e.g., in food, via air, etc.) to overall risk. For example, if exposure to a contaminant 

occurs primarily through ambient air, regulation of emissions to air may provide a more 

meaningful opportunity for EPA to reduce risk than regulation of the contaminant in drinking 

water. In making the preliminary regulatory determination, the available information on 

exposure through drinking water (Section 5.4.2 of this document and Chapter 4 of the HESD) 

and information on exposure through other media (Chapter 5 of the HESD) were used to 

estimate the fraction that drinking water contributes to the total exposure. These findings are 

discussed in the “Relative Sources of Exposure” section, below.

In evaluating the third criterion, EPA also considered effects on potentially sensitive 

populations, including the fetus, infants, and children. Sensitive population considerations are 

discussed in Chapter 7 of the HESD and in the “Sensitive Populations” section, below. 

Exposed Population Estimates 

EPA estimated the populations served by CWSs with water containing strontium at any 

level, and at levels in excess of the HRL or the 1⁄2 HRL, based on extrapolation from stratified, 

random sampling of the nation’s community ground water supplies as they existed in the mid1980s, recorded in the NIRS database.

According to NIRS data, among the population served nationally by CWSs relying on 

ground water (93.1 million people served by 40,106 ground water CWSs), a total of 93.0 million 

people (99.9%) may be exposed to strontium in drinking water. A subset of 15.4 million (16.6%) 

may be exposed to concentrations in excess of the 1⁄2 HRL, and 10.0 million (10.7%) may be 

exposed to concentrations in excess of the HRL. These estimates do not include people who may 

be exposed to strontium from CWSs relying on surface water, or from public water supplies 

other than CWSs.

Strontium occurs naturally and is abundant in the environment. Patterns of occurrence at 

varying concentrations may reflect the geologic and geochemical setting of the source waters for 

PWSs. NIRS data indicate that PWSs with strontium at concentrations greater than the HRL and 

the 1⁄2 HRL occur in all regions of the country.

Relative Sources of Exposure

The contribution of drinking water to total strontium exposure can be estimated by

comparing the exposure expected via drinking water to the exposure from intake of strontium in 

other media, such as food, air, and soil.

The intake of strontium from drinking water can be calculated from the NIRS ground 

water data, where the mean concentration among the detections was 603 μg/L. Using a 90th

percentile daily intake of 2 L/day for an adult, the daily exposure would be 1,206 μg/day. For 
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formula fed infants, assuming a 90th percentile daily intake of 1 L/day, the intake would be 603 

μg/day.

Although strontium is known to occur in food, air, and soil, data on levels in those media 

are limited, as are estimates of exposure from those sources. Food appears to be a more 

significant source than air and soil. A Food and Drug Administration (FDA) Total Diet Study by 

Pennington and Jones (1987), which collected 234 individual foods in 1984 from three cities in 

one region of the country, found that dietary intakes range from 493 to 685 μg/day for children 6 

months to 2 years old (493 μg/day for children 6 to 11 months); 928 to 1,388 μg/day for 14- to 

16-year-old adolescents; and 979 to 1,489 μg/day for adults (ages 25-30 and 60-65). Note that 

the 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. Estimated strontium intakes from air and soil are very low compared with those from 

food or drinking water. EPA estimated strontium exposure from non-occupational air to be 0.1 

μg/day for children and 0.3 μg/day for adults (based on data from Dzubay and Stevens, 1975) 

and estimated intake from soil as 24 μg/day for children and 12 μg/day for adults (based on data 

from 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 is dated and some aspects of strontium exposure may have changed. For more 

information on the sources of exposure other than water, refer to Chapter 5 in the HESD.

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 (Storey, 1961; Abrams et al., 2000; Lee et al., 1996; Matkovic et al., 2005). There 

are some data from studies in humans that demonstrate a positive association between low 

trauma fractures in children and low bone density or low calcium intakes (Farr et al. 2014; 

Matkovic et al., 2007). A recent study in embryonic zebrafish found that the relative ration of 

calcium to strontium in water was an important factor influencing strontium’s impact on 

embryonic bone development (Psqualetti et al., 2013); inhibition of bone mineralization 

increased as the strontium: calcium ratio increased. 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); the data do not include the risk during prenatal development and lactation, factors 

considered in the selection of the uncertainty factors. Age-specific exposure factors (USEPA, 

2012c) were used to reflect the sensitive population (birth through 18 years) in derivation of the 

HRL. Exposures from drinking water at or below the HRL (1,500 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.

Since many of the toxic effects of strontium result from strontium ions substituting for 

calcium ions, calcium deficiency would also be expected to result in increased sensitivity to 

strontium. 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). In this respect, it is 
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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).

The major route of elimination of strontium is via the kidneys, therefore, individuals with 

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 20,000,000 people (10%) above the age of 20 with chronic kidney disease (CDC, 

2010) and 547,982 people with kidney end-stage renal disease (USRDS, 2010), who may thus 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 (Schrooten et al., 1998, 2003; D’Haese et al., 1999, 2000; Tothill et al., 

1983). 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 disease is more common in older 

people and those of northern European heritage. Men are about twice as likely as women to have 

the disease. 

For more information on sensitive populations refer to Chapter 7 of the HESD. 

Risk Criterion Conclusion

Based on data from NIRS, an estimated 10.0 million people are exposed nationally to 

levels of strontium greater than the HRL (1500 μg/L). The measured concentrations in NIRS 

exceed the HRL by large margins in some water systems. STORET, which includes data on 

ambient water, records strontium concentrations up to 13,000 times greater than the HRL. Based 

on the available data, strontium exposure predominately comes from drinking water and food. 

Potentially sensitive populations include fetuses, infants and children, as well as calciumdeficient individuals and those with impaired renal function and Paget’s disease.

EPA finds that strontium meets the SDWA statutory criterion #3 for regulatory 

determination; regulation of strontium presents a meaningful opportunity for health risk 

reduction in drinking water based on the estimated exposed population and potential impacts on 

sensitive populations.

5.6.5 Regulatory Determination Decision

As stated in the “Criteria for Regulatory Determination” section above, a positive finding 

for all three criteria is required in order to make a determination to regulate a contaminant. EPA 

has made a preliminary determination that strontium meets all three criteria.

Strontium has the potential to cause adverse health effects to the bone, based on 

toxicological data from animal studies, limited human data, and an understanding of its mode of 

action. Strontium is known to occur in PWSs with a frequency and at levels of public health 

concern. Data from NIRS indicate that strontium concentrations exceed the HRL of 1,500 μg/L 

in 6.98% of ground water CWSs, and suggest that an estimated 10.0 million people nationally 

may be exposed to strontium in drinking water from PWSs at levels of health concern. Due to the 

large number of people exposed to strontium through drinking water and the potentially high 

concentration of strontium measured in these PWSs, regulation of strontium presents a 

meaningful opportunity for health risk reduction for persons served by PWSs, especially for 

those with developing bones (such as infants, children, and adolescents), individuals deficient in 

calcium, and persons with kidney conditions.
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It is important to note that the agency included strontium in UCMR 3. As of January 

2014, a preliminary analysis of the first nine months of the UCMR 3 monitoring data (USEPA, 

2014b) 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 1,500 

μg/L. While EPA believes the occurrence data from NIRS (in concert with the supplemental 

information discussed earlier) is sufficient to make the preliminary regulatory determination, the 

agency believes the additional monitoring results from UCMR 3 will assist EPA in making the 

final regulatory determination for strontium and in developing the proposed NPDWR. Note that 

the 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..

Additional information about the preliminary regulatory determination can be found in 

the Federal Register notice.

5.7 References

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Chapter 6:

Terbufos and Terbufos Sulfone

A chapter from: 

Regulatory Determination 3 Support Document

EPA Report 815-R-14-003
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Contents

Contents...........................................................................................................................................3

Exhibits............................................................................................................................................4

Abbreviations...................................................................................................................................5

6.1 Contaminant Background, Chemical and Physical Properties ............................................7

6.2 Sources and Environmental Fate .........................................................................................9

6.2.1 Production, Use, and Release...................................................................................9

6.2.2 Environmental Fate................................................................................................10

6.3 Health Effects.....................................................................................................................11

6.4 Occurrence .........................................................................................................................14

6.4.1 Occurrence in Ambient Water ...............................................................................14

6.4.2 Occurrence in Drinking Water...............................................................................20

6.5 Technology Assessment.....................................................................................................29

6.5.1 Analytical Methods................................................................................................29

6.5.2 Treatment Technologies.........................................................................................31

6.6 Preliminary Regulatory Determination..............................................................................31

6.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL........31

6.6.2 Health Effects (Criterion #1) .................................................................................32

6.6.3 Occurrence in Public Water Systems (Criterion #2)..............................................33

6.6.4 Risk Reduction (Criterion #3)................................................................................35

6.6.5 Regulatory Determination Decision ......................................................................36

6.7 References..........................................................................................................................36
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Exhibits

Exhibit 6-1: Chemical Structure of Terbufos...................................................................................7

Exhibit 6-2: Chemical Structure of Terbufos Sulfone .....................................................................8

Exhibit 6-3: Physical and Chemical Properties of Terbufos and Terbufos Sulfone ........................8

Exhibit 6-4: Estimated Annual Agricultural Use of Terbufos, c. 2011 .........................................10

Exhibit 6-5: EPA Summary Analysis of Terbufos Data from NAWQA Study Units, 1992-

2001 – Summary of Detected Concentrations...................................................................15

Exhibit 6-6: EPA Summary Analysis of Terbufos Data from NAWQA Study Units, 1992-

2001 – Summary of Samples.............................................................................................16

Exhibit 6-7: EPA Summary Analysis of Terbufos Data from NAWQA Study Units, 1992-

2001 – Summary of Sites...................................................................................................16

Exhibit 6-8: USGS National Synthesis Summary of NAWQA Monitoring of Terbufos in 

Streams, 1992-2001 ...........................................................................................................17

Exhibit 6-9: USGS National Synthesis Summary of NAWQA Monitoring of Terbufos in 

Ground Water, 1992-2001 .................................................................................................18

Exhibit 6-10: Terbufos STORET Data – Summary of Detected Concentrations..........................19

Exhibit 6-11: Terbufos STORET Data – Summary of Samples....................................................19

Exhibit 6-12: Terbufos STORET Data – Summary of Sites..........................................................19

Exhibit 6-13: Terbufos STORET Data – Summary of States........................................................20

Exhibit 6-14: Terbufos Sulfone Occurrence Data from UCMR 2 Assessment Monitoring –

Summary of Detected Concentrations...............................................................................22

Exhibit 6-15: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of Samples ......................................................22

Exhibit 6-16: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of System and Population Served Data –

All Detections ....................................................................................................................23

Exhibit 6-17: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of System and Population Served Data –

Detections > 1⁄2 HRL ..........................................................................................................24

Exhibit 6-18: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of System and Population Served Data –

Detections > HRL ..............................................................................................................25

Exhibit 6-19: Method Sensitivity Ratio (MSR) for Terbufos and Terbufos Sulfone ....................31
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Abbreviations

a.i. Active Ingredient

AMWA Association of Metropolitan Water Agencies

AWWA American Water Works Association

bw Body Weight

CAS Chemical Abstracts Service

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

ChE Cholinesterase

CHO Chinese Hamster Ovary

CWS Community Water System

CWSS Community Water System Survey

DL Detection Limit

DNA Deoxyribonucleic Acid

EEC Estimated Environmental Concentration

EPA Environmental Protection Agency

EWG Environmental Working Group

GC Gas Chromatography

HSDB Hazardous Substances Data Bank

HRL Health Reference Level

ICR Information Collection Request

IRED Interim Reregistration Eligibility Decision

IUR Inventory Update Reporting

LCMRL Lowest Concentration Minimum Reporting Level

LD50 50% Lethal Dose

LOAEL Lowest Observed Adverse Effect Level

LT-MDL Long-Term Method Detection Level

MCLG Maximum Contaminant Level Goal

MDL Method Detection Limit

MRL Minimum Reporting Level

MS Mass Spectrometry

MSR Method Sensitivity Ratio

N/A Not Applicable

NAWQA National Water-Quality Assessment

NCFAP National Center for Food and Agricultural Policy

ND Not Detected

NDWAC National Drinking Water Advisory Council

NOAEL No Observed Adverse Effect Level

NPDWR National Primary Drinking Water Regulation
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NPS National Pesticide Survey

NTNCWS Non-Transient Non-Community Water Systems

OPP Office of Pesticide Programs

PBT Persistence, Bioaccumulation, and Toxicity

PDP Pesticide Data Program

PMP Pilot Monitoring Program

PRZM/EXAMS Pesticide Root Zone Model/Exposure Analysis Modeling System

PWS Public Water System

QA Quality Assurance

RAIS Risk Assessment Information System

RD 3 Third Regulatory Determination

RED Reregistration Eligibility Decision

RfD Reference Dose

RSC Relative Source Contribution

RSD Relative Standard Deviation

SCI-GROW Screening Concentrations in Ground Water

SDWA Safe Drinking Water Act

SDWIS Safe Drinking Water Information System

STORET Storage and Retrieval

TRI Toxics Release Inventory

TSC Technical Support Center

UCM Unregulated Contaminant Monitoring

UCMR 1 First Unregulated Contaminant Monitoring Regulation

UCMR 2 Second Unregulated Contaminant Monitoring Regulation

UF Uncertainty Factor

USDA United States Department of Agriculture

USGS United States Geological Survey

UV Ultraviolet

VOC Volatile Organic Compound
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Chapter 6: Terbufos and Terbufos Sulfone

The Environmental Protection Agency (EPA) is evaluating terbufos and terbufos sulfone

for possible regulation as a drinking water contaminant. Terbufos and terbufos sulfone are listed 

on the agency’s third Contaminant Candidate List (CCL 3) and are being considered for 

regulation as part of the third Regulatory Determination (RD 3) under the Safe Drinking Water 

Act (SDWA) provisions. Information on the CCL 3/RD 3 process is found in Chapter 1. 

Background on data sources used to evaluate CCL 3/RD 3 chemicals is found in Chapter 2. This 

chapter presents information and analysis specific to terbufos and terbufos sulfone, including 

background information on the contaminants, information on sources and environmental fate, an 

analysis of health effects, an analysis of occurrence in ambient and drinking water, and 

information about the availability of analytical methods and treatment technologies. A summary 

of EPA's decision regarding terbufos and terbufos sulfone appears at the end of this chapter. (The 

decision is presented formally in the associated Federal Register notice).

6.1 Contaminant Background, Chemical and Physical Properties

Terbufos is a phosphorodithioate pesticide and is used as an insecticide and nematicide to 

control a variety of pests. Synonyms for terbufos include S-tert-butylthiomethyl O and O-diethyl 

phosphorodithioate (HSDB, 2009). Synonyms for terbufos sulfone include phosphorodithioic 

acid S-(((1,1-dimethylethyl)sulfonyl)methyl) O and O-diethyl ester (HSDB, 2009).

Terbufos was first registered in 1974 to control insect pests on corn, sugar beets, and 

sorghum. Target pests include corn rootworms, wireworms, white grubs, billbugs, sugarbeet root 

maggots, cutworms, and nematodes (USEPA, 2001a). EPA’s Office of Pesticide Programs 

(OPP) released an Interim Reregistration Eligibility Decision (IRED) for terbufos in September 

of 2001 (USEPA, 2001a), and a Reregistration Eligibility Decision (RED) in July of 2006 

(USEPA, 2006). 

Terbufos sulfone is a phosphorodithioate pesticide degradate of terbufos. The degradate 

may co-occur in the environment with the parent compound.

Exhibit 6-1 and Exhibit 6-2 present the chemical structures of terbufos and terbufos 

sulfone, respectively. Physical and chemical properties and other reference information are listed 

in Exhibit 6-3.

Exhibit 6-1: Chemical Structure of Terbufos

Source: ChemIDPlus/National Library of Medicine
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Exhibit 6-2: Chemical Structure of Terbufos Sulfone

Source: ChemIDPlus/National Library of Medicine

Exhibit 6-3: Physical and Chemical Properties of Terbufos and Terbufos Sulfone

Property Information

Terbufos Terbufos Sulfone

Chemical Abstracts Service (CAS) 

Registry Number 13071-79-9 56070-16-7

EPA Pesticide Chemical Code Not applicable Not applicable

Chemical Formula C9H21O2PS3 C9H21O4PS3

Molecular Weight 288.4 g/mol (RAIS, 2009; 

HSDB, 2009; ChemIDPlus, 

2009)

320.43 g/mol 

(ChemIDPlus, 2009)

Color/Physical State Clear, slightly brown liquid 

(HSDB, 2010) --

Boiling Point 332 deg C (RAIS, 2009) --

Melting Point -29 deg C (HSDB, 2010) --

Density 1.105 g/mL (HSDB, 2009) --

Freundlich Adsorption Coefficient 4,420 (μg/g)(L/μg)1/n (Speth et 

al., 2001) 0.4 – 2.93 (USEPA, 2006)

Vapor Pressure 3.2E-04 mm Hg (RAIS, 2009; 

HSDB, 2009; ChemIDPlus, 

2009)

7.88E-06 mm Hg 

(ChemIDPlus, 2009)

Henry’s Law Constant 2.4E-05 atm-m3/mol 

(ChemIDPlus, 2009)

2.21E-08 atm-m3/mol 

(ChemIDPlus, 2009)

Log Kow 4.48 (dimensionless) 

(Speth et al., 2001; HSDB, 2010)

2.48 (dimensionless) 

(ChemIDPlus, 2009)

Koc 979 L/kg (RAIS, 2009; 

Speth et al., 2001)

500-5,000 L/kg (HSDB, 2010)

27.41 L/kg (RAIS, 2009)

Solubility in Water 5.07 mg/L (RAIS, 2009; 

HSDB, 2009; ChemIDPlus, 

2009)

408 mg/L (ChemIDPlus, 2009)

Other Solvents Readily soluble in most organic 

solvents: aromatic hydrocarbons, 

chlorinated hydrocarbons, 

alcohols, acetone (HSDB, 2010)

--

Conversion Factors

(at 25 deg C, 1 atm)

-- --

Note: “--” indicates that no information was found.
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6.2 Sources and Environmental Fate

6.2.1 Production, Use, and Release

Terbufos is a phosphorodithioate pesticide and is used as an insecticide and nematicide to 

control a variety of pests. Information on the application of terbufos as a pesticide is available 

from several sources, described below.

Production data from EPA’s Inventory Update Reporting (IUR) program are not 

available for terbufos. No industrial release data for terbufos are available from EPA’s Toxics 

Release Inventory (TRI). (The list of chemicals for which TRI reporting is required has never 

included terbufos (USEPA, 2010a)).

As a pesticide degradate, terbufos sulfone is neither produced nor used commercially. Its

formation is discussed under “Environmental Fate,” below (Section 6.2.2).

EPA Office of Pesticide Programs (OPP) Reregistration Program

Data available to EPA suggest that approximately 7.5 million pounds of terbufos active 

ingredient (a.i.) were used annually between 1987 and 1996 (USEPA, 2006).

EPA Pesticide Industry Sales and Usage Report

EPA’s most recent Pesticide Industry Sales and Usage report states that between 5 and 7 

million pounds of terbufos a.i. were used in 1999 and between 3 and 5 million pounds of a.i. 

were used in 2001 (USEPA, 2004).

National Center for Food and Agricultural Policy (NCFAP) Pesticide Use Database

National Center for Food and Agricultural Policy (NCFAP) maintains a national 

Pesticide Use Database, primarily for herbicides. Pesticide use estimates are based on state-level 

commercial agriculture usage patterns and state-level crop acreage. NCFAP listed uses of 

terbufos on four crops totaling approximately 8.7 million pounds a.i. per year in 37 states in 

1992. In 1997, NCFAP listed uses of terbufos on four crops totaling approximately 6.5 million 

pounds a.i. per year in 37 states (NCFAP, 2003).

United States Geological Survey (USGS) Pesticide Use Maps

United States Geological Survey (USGS) has produced maps of pesticide use for 244 

compounds used in United States crop production. The pesticide use maps show the average 

annual pesticide use intensity expressed as average weight (in pounds) of a pesticide applied to 

each square mile of agricultural land in a county. The maps represent pesticide use circa 2002, 

and are based on data from 1999 through 2004. The USGS maps were created using data from 

NCFAP and county-level information on harvested crop acreage from the Census of Agriculture.

Exhibit 6-4 (USGS, 2014) shows the geographic distribution of estimated average annual 

terbufos use in the United States circa 2011. A breakdown of use by crop is also included. USGS 

used two methods to estimate dimethoate usage, since pesticide usage information was not 

available in some districts. At left, the “EPestHigh” estimates were generated by projecting 

usage estimates for such districts based on usage in neighboring districts. At right, the 

“EPestLow” estimates were generated by assuming no usage in such districts. Annual usage has 

declined over the years, and was somewhere in the range of roughly 0.5 – 1.5 million pounds in 

2011The maps indicate that terbufos use is heaviest in the Midwest but also common in the other 

parts of the country. Note that USGS considers these 2011 maps “preliminary,” pending updates

with crop data from the 2012 Census of Agriculture.
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Exhibit 6-4: Estimated Annual Agricultural Use of Terbufos, c. 2011

Source: USGS, 2014

6.2.2 Environmental Fate

A vapor pressure of 3.2E-4 mm Hg at 20-25 deg C suggests that terbufos will be present 

only as a vapor in the atmosphere (HSDB, 2010). Terbufos can degrade in the atmosphere by 

reaction with photochemically produced hydroxyl radicals. The half-life for reaction with 

hydroxyl radicals is estimated at 1.6 hours based on structural estimation methods (HSDB, 

2010). Terbufos does not contain functional groups that are expected to absorb light at 

wavelengths >290 nm, and would not be expected to be susceptible to direct photolysis by 

sunlight in air (HSDB, 2010). Terbufos is known to undergo direct photolysis in water, but no 

data are available on its photolysis in air.

Koc values of 500-5,000 L/kg suggests that terbufos is likely to be slightly mobile in soils 

(HSDB, 2010). A Freundlich adsorption coefficient of between 0.4 and 2.93 suggests that 

terbufos sulfone is more mobile than the parent compound in soil (USEPA, 2006). 

A Henry’s Law Constant of 2.4E-05 atm-m3

/mol and a vapor pressure of 3.20E-04 mm 

Hg suggest that volatilization of terbufos will be a significant loss mechanism from both wet and 

dry soils (HSDB, 2010). The corresponding values for terbufos sulfone are much smaller, 

suggesting that volatilization will be a less significant loss mechanism from both wet and dry 

soils. Terbufos has a half-life in soil of 11 to 17 days with biodegradation and hydrolysis being 

the primary loss mechanisms (HSDB, 2010). Biological degradation has an estimated half-life of 

between 14 and 40 days (USEPA, 2006). The half-life for abiotic hydrolysis is estimated at 12.3 

to 13.7 days at typical environmental pH values of 5, 7, and 9 (USEPA, 2006). Terbufos sulfone 
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is more resistant to biological degradation with an estimated half-life of 96 days (USEPA, 2006). 

One study found the half-life of terbufos in a silty clay loam soil was between 11 and 12 days. 

The half-life of terbufos sulfone in the same fields was between 19 and 39 days (HSDB, 2010).

Based on a Koc range of 500-5,000 L/kg, terbufos appears to be only slightly mobile in 

water and will bind to sediments or suspended particles. A Henry’s Law Constant of 2.4E-05 

atm-m3/mol for terbufos suggests that volatilization from water will be a significant loss 

mechanism. Half-lives of terbufos in water have been calculated to be 2.8 days for a model 

stream and 26 days for a model lake (HSDB, 2010). Terbufos was found to biologically degrade 

with a half-life of 3 days at pH 8.8 and 20 deg C (HSDB, 2010). Terbufos may also degrade in 

the presence of sunlight with a half-life of approximately an hour (HSDB, 2010). Based on a Koc

of 27.41 L/kg and a Henry’s Law Constant of 2.21E-08 atm-m3/mol, terbufos sulfone appears to 

be very mobile in water. A log Kow of 2.48 and a water solubility of 408 mg/L suggest that 

terbufos sulfone is moderately mobile in water.

The empirical data indicate, in summary, that 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, 2006).

EPA developed the Persistence, Bioaccumulation, and Toxicity (PBT) Profiler to serve as 

a screening tool for estimating the percentage of a contaminant that is predicted to partition to 

water, air, soil, and sediment in a four-compartment system. PBT Profiler (2009) modeling 

predicts that 14% of terbufos will partition to water, 76% to soil, 0% to air, and 10% to sediment. 

PBT Profiler (2009) modeling also projects biodegradation half-lives in various media. For 

terbufos, projected half-lives are approximately 38 days in water, 75 days in soil, 0.067 days in 

air, and 340 days in sediment. Note that the PBT Profiler, as a screening tool, provides estimated 

values only and “not . . . definitive PBT determinations” (PBT Profiler, 2009).

A biodegradation half-life of 38 days (PBT Profiler, 2009) indicates that terbufos is 

moderately persistent in water.

EPA’s PBT Profiler (2009) predicts that 21% of terbufos sulfone will partition to water

79% to soil, 0% to air, and 0% to sediment. Projected half-lives for terbufos sulfone are identical 

to the predicted half-lives for the parent compound, or approximately 38 days in water, 75 days 

in soil, 0.067 days in air, and 340 days in sediment. Note that the PBT Profiler, as a screening 

tool, provides estimated values only and “not . . . definitive PBT determinations” (PBT Profiler, 

2009). 

As with the parent compound, a biodegradation half-life of 38 days (PBT Profiler, 2009) 

indicates that terbufos sulfone is moderately persistent in water.

6.3 Health Effects

Terbufos has been found to be readily absorbed, with about 83% of the radioactive label 

from a dose of terbufos (0.8 mg/kg) recovered in the urine within 168 hours. The majority (80%) 

is excreted within 48 hours and only 3.5% of the dose is recovered in the feces (North, 1973). 

Terbufos was found to be widely distributed throughout the tissues, with the highest 

concentrations of radioactivity in the liver 6 hours after dosing, and in the kidney 12 hours after 

dosing (North, 1973). The majority of terbufos excreted in the urine was represented by 

metabolites not containing phosphorus (i.e., methane, (t-butylsulfinyl) (methylsulfinyl); 

terbufoxon sulfone; sulfoxide, (t-butylsulfonyl) methyl methyl; sulfone, t-butyl (methyl-sulfonyl) 

methyl; and sulfoxide, t-butyl (methyl-sulfonyl) methyl), while the majority excreted in the feces 

contained phosphorus (i.e., terbufoxon, terbufoxon sulfoxide, terbufos sulfoxide, and terbufos 
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sulfone). The proposed metabolic pathway for terbufos consists of sulfoxidation and 

desulfuration of terbufos, followed by hydrolysis of the thiolophosphorus bond, enzymatic Smethylation, and then additional S-oxidation to final metabolites sulfone, t-butyl (methylsulfonyl) methyl and sulfoxide, (t-butylsulfonyl) methyl methyl (Cheng, 1992). Cheng (1992) 

did not find any sex differential in the absorption or metabolic fate of terbufos in SpragueDawley rats. Although there have been no pharmacokinetic studies identified for the terbufos 

degradate, terbufos sulfone, systemic effects indicate that the compound is absorbed.

There are limited data available for terbufos, terbufos sulfoxide, or terbufos sulfone in 

humans. In animals the acute oral toxicity of terbufos varies with sex, species, and duration of 

exposure. Median lethal dose (LD50) values of 3.5 to 9.2 mg/kg in mice, 1.4 to 9.0 mg/kg in rats, 

and 4.5 to 6.3 mg/kg in dogs have been reported. Clinical signs of cholinergic toxicity were 

noted, and included tremors, salivation, exophthalmos, prostration, decreased activity, 

chromodacryorrhoea, diuresis, piloerection, ataxia, urogenital staining, nasal discharge, anorexia, 

and labored breathing. Death has been noted to occur from within minutes to up to one week 

later after exposure (USEPA, 2003). An acute no observed adverse effect level (NOAEL) of 0.15 

mg/kg-day, based on plasma cholinesterase (ChE) inhibition and clinical signs, was identified in 

an oral neurotoxicity study in rats. Acute neurotoxicity tests did not find any macroscopic or 

microscopic changes, even though there were treatment-related abnormalities in the functional 

observational battery test related to cholinergic toxicity (Mandella, 1998).

In a 14-day study conducted in male dogs, terbufos was administered daily via gelatin 

capsule at doses of 2.5 or 250 μg/kg body weight (bw) per day (Bailey, 1988). Clinical signs and 

statistically significantly inhibited ChE activity (plasma, erythrocyte, and brain, ranging from 

37% (brain) to 79% (erythrocyte) inhibition) were noted at the 250 μg/kg bw per day dose of 

terbufos. ChE activity (plasma and brain) also was significantly reduced with the 2.5 μg/kg bw 

per day dose (ranging from 42% (brain) to 25% (plasma) inhibition); this study lacked a 

NOAEL.

In the same study (Bailey, 1988), the effects of terbufos sulfone were also evaluated 

using doses of 15, 62.5, 250, or 1000 μg/kg bw per day. Three of the dogs administered terbufos 

sulfone died during the course of the study after developing clinical signs of toxicity (i.e., tremor, 

languid behavior, prostration, ataxia, emesis, salivation, dyspnea, cold-to-the-touch, squint eye, 

meiosis, no feces, an increase in soft feces, prolapsed rectum, and sanguineous-appearing 

material in the cage). Plasma ChE activity was statistically significantly inhibited by terbufos 

sulfone at all time-points: by 67–77% at the highest dose of 1000 μg/kg bw per day; by 39–56% 

at 250 μg/kg bw per day; and by 24–37% at 62.5 μg/kg bw per day. At the lowest dose (15 μg/kg 

bw per day), statistically significant inhibition of plasma ChE activity (of 20%) was seen only on 

day 8, but not on day 15, and thus was not clearly related to treatment. Statistically significant 

decreases in erythrocyte ChE activity were observed only at the highest dose, where inhibition, 

ranging from 57% to 93%, was noted at all time-points. Inhibition of brain ChE activity was 

found at the two higher doses (statistically significant only at the highest dose, by 62%). 

Cerebellar ChE activity was inhibited by 23% (not statistically significant) at 250 μg/kg bw per 

day, and by 46% (not statistically significant) at the highest dose (1000 μg/kg bw per day). Gross 

necropsy found treatment-related lesions in the 1,000 μg/kg bw per day group only (Bailey, 

1988). 

ChE inhibition is the critical effect for short term terbufos exposures. This critical effect 

has been evaluated in a 14-day feeding study in rats (Fischer, 1978), a 28-day oral toxicity study 

in dogs (Shellenberger, 1984) and a 29-day capsule study in dogs (Shellenberger, 1987). 
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Depending on the dose tested and duration, these studies also observed death, reduced food 

consumption, reduced body weights, reduced relative organ weights (liver and kidneys), and 

clinical signs.

The terbufos database for animal studies with 85-day to lifetime durations is extensive. 

ChE inhibition was noted in a 30-day feeding study in dogs (Morici, 1972), a 31-day feeding 

study in rats (Morici, 1972), 85-day feeding study in rats (Mandella, 1999), a 3-month feeding 

study in rats (Daly and Knezevich, 1979), a 6-month feeding study in dogs (Morgareidge, 1973), 

a 1-year oral toxicity study in dogs (Shellenberger and Billups, 1986), a 1-year feeding study in 

rats (Daly, 1987), and a 2-year feeding study in rats (Rapp, 1974). The critical dose for ChE 

inhibition was identified as a NOAEL of 0.005 mg/kg-day from a 28-day oral study in dogs 

(Shellenberger, 1984), and a one year oral study in dogs (Shellenberger and Billups, 1986).

There are no subchronic or chronic studies available which describe the effects of the degradate, 

terbufos sulfone.

There are data on reproductive and developmental effects for terbufos but not for its 

degradate, terbufos sulfone. In a two-generation reproductive study in rats, terbufos administered 

in the diet beginning 63 days prior to F0 mating, at concentrations of 0, 0.5, 1.0, or 2.5 mg/kg diet 

(equivalent to daily intakes of 0.035 to 0.22 mg/kg-day in the F0 generation, and 0.04 to 0.24 

mg/kg-day in the F1 generation), caused a decrease in male fertility, the number of pregnant 

females, pup viability, and pup body weight in the highest dose group (Schroeder, 1989). The 

only non-ChE effect observed in the parental animals was a decrease in body weight during 

lactation in the 2.5 mg/kg food dose group. ChE activity was decreased in F0 and F1 adults, even 

with the lowest dose tested. The NOAEL identified in this study for reproductive effects and 

offspring toxicity was 1.0 mg/kg in the diet (equivalent to 0.07 mg/kg-day in males, and 

approximately 0.09 mg/kg-day in females) (Schroeder, 1989). In a 3-generation reproductive 

study conducted by Smith and Kasner (1972), terbufos administered via the diet at doses of 0, 

0.25, or 1 ppm (equivalent to 0, 0.0125, or 0.05 mg/kg-day) to rats during this 6-month study 

period resulted in a reported Lowest Observed Adverse Effect Level (LOAEL) of 0.05 mg/kgday, based on an increased percentage of litters with dead offspring in each of the 3 generations, 

as compared to controls. The NOAEL for this study was 0.0125 mg/kg-day.

Developmental studies with terbufos in rats and rabbits did not find any treatment-related 

effects (USEPA, 2003), although the rat studies were potentially flawed. The rabbit study by 

Hoberman (1988a, 1988b) appears to be well conducted. In this study, the NOAEL of 0.25 

mg/kg-day for terbufos was the same for maternal toxicity and fetal toxicity. Maternal toxicity 

was based on increased number of does with soft or liquid feces, maternal body weight loss 

during gestational days 16 to 20, occurrence of reddened areas in the fundic region of the 

stomach at necropsy, and one abortion at the highest dose. Fetal toxicity was based on decreased 

fetal body weight and an increase in the incidence of does with any resorption sites at the next 

highest dose.

Terbufos has been found to be negative in the majority of mutagenicity tests, both in vivo 

animal studies (chromosomal aberrations in rats) and in vitro studies (i.e., reverse mutation in 

Salmonella typhimurium, point mutations and chromosomal aberrations in Chinese hamster 

ovary (CHO) cells, and unscheduled deoxyribonucleic acid (DNA) synthesis in primary male rat 

hepatocytes) (USEPA, 2003). However, a dominant lethal mutation test in rats had inconclusive 

results (MacKenzie, 1986), and a mitotic gene conversion test in yeast was positive with 

technical-grade terbufos, with or without metabolic activation, and weakly positive with 
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commercial-grade terbufos, without metabolic activation (Gentile et al., 1982). Genotoxicity 

studies of the degradate, terbufos sulfone are lacking.

There has been no evidence that terbufos is carcinogenic in either mice administered 

doses of 0.45 to 1.8 mg/kg terbufos via gavage for 18 months (Silverman et al., 1986), or in rats 

fed 0.0125 to 0.1 mg/kg-day terbufos for 2 years (Rapp, 1974). EPA (USEPA, 1988) determined 

that the data were not adequate to make a determination regarding the potential carcinogenicity 

of terbufos and classified it in Group D, not classifiable as to human carcinogenicity, following 

the agency’s 1986 cancer guidelines (USEPA, 1986). There are no long-term animal studies of 

terbufos sulfone. 

The 2006 EPA OPP RED identifies the reference dose (RfD) for terbufos as 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), respectively, 

with application of a 100-fold uncertainty factor (UF) (10 for interspecies variability and 10 for 

intraspecies variability) (USEPA, 2006). EPA calculated a non-cancer health reference level

(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 a relative source contribution (RSC) of 20%. 

Lacking subchronic or chronic studies, the OPP did not develop an RfD for terbufos 

sulfone in the RED (USEPA, 2006). 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 reasonable. 

The USEPA concluded in 2003 and in 2006 that the existing toxicity database for 

terbufos is sufficient to evaluate its potential hazards to the general population, and adequate to 

characterize its potential hazards to fetuses, infants, and children. Developmental studies with 

terbufos in rats and rabbits did not find any developmental effects (USEPA, 2003) and no 

sensitive populations were identified or characterized. There are no data on reproductive and 

developmental effects for terbufos sulfone. The OPP RED (USEPA, 2006) presents more 

detailed information about the health effects for terbufos and terbufos sulfone.

6.4 Occurrence

This section presents data on the occurrence of terbufos and terbufos sulfone in ambient 

water and drinking water in the United States. As described in section 6.3, an HRL of 0.35 μg/L 

was calculated for terbufos based on non-carcinogenic effects, and the same value was adopted 

as the HRL for terbufos sulfone. This HRL represents the concentration of the contaminant in 

drinking water that is likely to be present without an appreciable risk of deleterious effects 

during a lifetime. Occurrence data from various sources presented below are analyzed with 

respect to the HRL and 1⁄2 the HRL. When possible, estimates of the population exposed at 

concentrations above the HRL and 1⁄2 the HRL are presented.

For additional background information about many of the data sources used to evaluate 

occurrence, please refer to Chapter 2.

6.4.1 Occurrence in Ambient Water

Lakes, rivers, and aquifers are the ambient sources of most drinking water. Contaminant 

occurrence in ambient water provides information for the potential for contaminants to adversely 
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affect drinking water supplies. Occurrence data for terbufos in ambient water are available from 

the USGS National Water-Quality Assessment (NAWQA) program and from EPA’s Storage and 

Retrieval (STORET) database. Terbufos sulfone was not included in NAWQA Cycle 1 

monitoring (1992-2001), and no terbufos sulfone data are available from EPA’s STORET Data 

Warehouse.

United States Geological Survey (USGS) National Water-Quality Assessment (NAWQA)

Ambient Water Analyses

USGS instituted the NAWQA program in 1991 to examine ambient water quality status 

and trends in the United States. The NAWQA program generates high quality contaminant 

occurrence and other water quality parameter data for significant watersheds and aquifers across 

the nation. The program is designed to apply nationally consistent methods to provide a uniform 

basis for contaminant occurrence comparisons and assessments among study basins across the 

country and over time. The occurrence assessments can also serve to facilitate interpretation of 

natural and anthropogenic factors affecting national water quality. For more detailed information 

on NAWQA program design and implementation, refer to Leahy and Thompson (1994) and 

Hamilton et al. (2004).

EPA Analysis of NAWQA Cycle 1 Monitoring Results, 1992-2001

With the cooperation of USGS, EPA performed a summary analysis of all Cycle 1 water 

monitoring data from all study units (1992-2001). EPA’s analysis of the NAWQA data is a 

simple, non-parametric occurrence analysis that provides summary statistics to characterize 

contaminant occurrence.

All surface water data from sampled streams were included in the EPA summary 

analysis. The ground water analysis relied on well data and excluded data from springs and 

drains. EPA calculated detection frequencies as the percentage of samples and the percentage of 

sites with at least one detection, without any censoring or weighting. (A detection is an analytical 

result equal to or greater than the reporting level.) EPA calculated other descriptive statistics as 

well, including the minimum, median, 95th percentile, 99th percentile, and maximum 

concentrations (based only on samples with detections). Reporting levels varied over time during 

the NAWQA program. In most cases, the reporting level for terbufos was 0.013 μg/L. Therefore, 

in some cases the minimum concentration reported as a detection could be lower than the highest 

reporting level.

The results of the EPA analysis of terbufos are presented in Exhibit 6-5 through Exhibit 

6-7. Overall, terbufos was detected in 0.14% of samples and at 0.31% of sites. The median 

concentration based on detections from all sites is 0.02 μg/L. The 99th percentile concentration 

based on detections from all sites is 0.56 μg/L. Of the 20,960 samples from 7,118 sites, one

(0.005%) sample from one (0.01%) site had a detected concentration of terbufos that was greater 

than the terbufos HRL. No data were available for terbufos sulfone.

Exhibit 6-5: EPA Summary Analysis of Terbufos Data from NAWQA Study Units, 

1992-2001 – Summary of Detected Concentrations

Source Water Type Concentration Values of Detections, μg/L

Minimum Median 90th Percentile 99th Percentile Maximum

Ground Water 0.008 0.01 0.012 0.012 0.012

Surface Water 0.0021 0.02 0.23 0.56 0.56
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Source Water Type Concentration Values of Detections, μg/L

Minimum Median 90th Percentile 99th Percentile Maximum

All Sites 0.0021 0.02 0.21 0.56 0.56

Exhibit 6-6: EPA Summary Analysis of Terbufos Data from NAWQA Study Units, 

1992-2001 – Summary of Samples

Source Water 

Type

Total 

Number of 

Samples

Samples with 

Detections

Samples with 

Detections > 1⁄2 HRL 

(0.175 μg/L)

Samples with 

Detections > HRL 

(0.35 μg/L)

Number Percent Number Percent Number Percent

Ground Water 6,080 2 0.03% 0 0% 0 0%

Surface Water 14,880 28 0.19% 4 0.03% 1 0.01%

All Sites 20,960 30 0.14% 4 0.02% 1 0.005%

Exhibit 6-7: EPA Summary Analysis of Terbufos Data from NAWQA Study Units, 

1992-2001 – Summary of Sites

Source Water 

Type

Total 

Number of 

Sites

Sites with Detections Sites with Detections

> 1⁄2 HRL (0.175 μg/L)

Sites with Detections 

> HRL (0.35 μg/L)

Number Percent Number Percent Number Percent

Ground Water 5,211 2 0.04% 0 0% 0 0%

Surface Water 1,907 20 1.05% 4 0.21% 1 0.05%

All Sites 7,118 22 0.31% 4 0.06% 1 0.01%

NAWQA Pesticide National Synthesis Project, 1992-2001

Through a series of National Synthesis efforts, the USGS NAWQA program is preparing 

comprehensive analyses of data on topics of particular concern. These National Synthesis 

assessments aggregate NAWQA contaminant occurrence and water quality parameter data from 

individual study units and other sources to provide a national overview. The NAWQA Pesticide 

National Synthesis Project is a national-scale assessment of the occurrence and behavior of 

pesticides in streams and ground water of the United States and the potential for pesticides to 

adversely affect drinking water supplies or aquatic ecosystems.

Results from the most recent Pesticide National Synthesis analysis, based on complete 

Cycle 1 (1992-2001) data from NAWQA study units, are posted on the NAWQA Pesticide 

National Synthesis Web site (Gilliom et al., 2007). Data for surface water and ground water are 

presented separately, and results in each category are subdivided by land use category. Land use 

categories include agricultural, urban, mixed (deeper aquifers of regional extent in the case of 

ground water), and undeveloped. The Pesticide National Synthesis analysis is a first step toward 

the USGS goals of describing the occurrence of pesticides in relation to different land use and 

land management patterns, and developing a deeper understanding of the relationship between 

spatial occurrence of contaminants and their fate, transport, persistence, and mobility 

characteristics.

The surface water summary data presented in the Pesticide National Synthesis (Gilliom et 

al., 2007) only includes stream data. Sampling data from a single one-year period, generally the 

year with the most complete data, were used to represent each stream site. Sites with few data or 

significant gaps were excluded from the analysis. NAWQA stream sites were sampled repeatedly 
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throughout the year to capture and characterize seasonal and hydrologic variability. Ground 

water data reported in the Pesticide National Synthesis only include samples from wells; data 

from springs and agricultural tile drains were not included. In the National Synthesis analysis 

(Gilliom et al., 2007), USGS uses a single sample to represent each well, generally the earliest 

sample with complete data for the full suite of analytes.

Over the course of Cycle 1 (1992-2001), some NAWQA analytical methods were 

improved or changed. Hence, detection thresholds varied over time for some compounds. USGS 

used the maximum Long-Term Method Detection Level (LT-MDL) for each analyte as a 

uniform reporting threshold. The maximum LT-MDL for terbufos was 0.009 μg/L (Gilliom et 

al., 2007). Terbufos was an analyte in the Pesticide National Synthesis Project, but terbufos 

sulfone was not. 

In NAWQA stream samples (Exhibit 6-8), terbufos was found at frequencies ranging 

from 0% of samples in undeveloped and urban areas to 0.05% of samples in agricultural settings, 

and 0.27% of samples in mixed land use settings. The 95th percentile concentrations were less 

than the maximum LT-MDL in all land use settings. The highest surface water concentration of

0.560 μg/L, which is greater than the terbufos HRL, was detected at an agricultural site.

Exhibit 6-8: USGS National Synthesis Summary of NAWQA Monitoring of 

Terbufos in Streams, 1992-2001

Land Use Type Number of 

Sites

Number of 

Samples 

Detection 

Frequency

(Samples)

Concentration Values (of detections, in μg/L)

Median 95th Percentile Maximum

Agricultural 83 2,004 0.05% ND ND 0.560

Mixed 65 1,386 0.27% ND ND 0.031

Undeveloped 8 144 0% ND ND ND

Urban 30 811 0% ND ND ND

ND = not detected (concentration is less than the maximum LT-MDL and is expected to be less than any higher 

percentile concentration shown in the table).

In NAWQA ground water samples (Exhibit 6-9), terbufos was found at frequencies 

ranging from 0% of samples in undeveloped and agricultural areas to 0.04% of samples in mixed 

land use settings, and 0.12% of samples in urban areas. The 95th percentile concentrations were 

less than the maximum LT-MDL in all land use settings. The highest ground water concentration

of 0.012 μg/L was detected at an urban site. No maximum detected concentrations of ground 

water exceeded the terbufos HRL.
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Exhibit 6-9: USGS National Synthesis Summary of NAWQA Monitoring of 

Terbufos in Ground Water, 1992-2001

Land Use Type Number of 

Wells

Detection 

Frequency

Concentration Values (of detections, in μg/L)

Median 95th Percentile Maximum

Agricultural 1,405 0% ND ND ND

Mixed 2,729 0.04% ND ND 0.008

Undeveloped 34 0% ND ND ND

Urban 856 0.12% ND ND 0.012

ND = not detected (concentration is less than the maximum LT-MDL and is expected to be less than any higher 

percentile concentration shown in the table).

Storage and Retrieval (STORET) Data Warehouse

EPA’s STORET Data Warehouse is a collaborative database that 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 are finished drinking water data. Users began populating the STORET Data 

Warehouse in 1999. Most data are post-1999, but some earlier sampling is included.

STORET data have quality limitations. The extent of national coverage and data 

completeness varies from parameter to parameter. There are no restrictions on submission of data 

based on analytical methods, quality assurance (QA) practices, 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 (USEPA, 2012). The STORET Data Warehouse also included 

public water system (PWS) data from three states (Indiana, Missouri, and Ohio); EPA reviewed 

these as well (USEPA, 2012). (For more data gathered by state drinking water programs, see the 

discussion of state monitoring data in Section 6.4.2, below.)

The results of the STORET analysis for terbufos are presented in Exhibit 6-10 through

Exhibit 6-13. (The STORET database does not contain any information on terbufos sulfone.) 

These STORET data represent terbufos samples collected between 1982 and 2010. Fewer 

records are available in the early years. Of 1,066 (625 surface water and 441 ground water) sites 

that submitted data, 138 (12.95%) surface water sites reported detections of terbufos, with 14 

(1.31%) sites reporting a detection greater than 1⁄2 the terbufos HRL and 2 (0.19%) sites reporting 

a detection greater than the terbufos HRL. All detections were at surface water sites. Detected 

concentrations ranged from 0 μg/L to 3.2 μg/L. The maximum concentration of 3.2 μg/L was 

greater than the HRL. Minimum detected concentrations are reported in Exhibit 6-10; these 

minimum values may be indicative of reporting levels used. (A minimum value of zero, on the 

other hand, could represent a detection that was entered into the database as a non-numerical 

value (e.g., “Present”)). No Missouri or Ohio PWS data were available for this contaminant.
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Exhibit 6-10: Terbufos STORET Data – Summary of Detected Concentrations

Source Water Type Concentration Value of Detections (μg/L)

Minimum Median 90th Percentile Maximum

Ground Water N/A N/A N/A N/A

Surface Water 01 0 0.01 3.2

Total 01 0 0.01 3.2

PWS (IN)

2 0 0 0 0

N/A = not applicable (no detections in this category). 1 A minimum value of zero may represent a detection that was entered into the database as a non-numerical value 

(e.g., “Present”).

2 It could not be determined from the data in STORET whether the Indiana PWS facilities were served by ground

water or surface water.

Exhibit 6-11: Terbufos STORET Data – Summary of Samples

Source Water 

Type

Total 

Number of 

Samples

Samples with 

Detections

Samples with 

Detections > 1⁄2 HRL 

(0.175 μg/L)

Samples with 

Detections > HRL 

(0.35 μg/L)

Number Percent Number Percent Number Percent

Ground Water 699 0 0% 0 0% 0 0%

Surface Water 5,826 457 7.84% 23 0.39% 2 0.03%

Total 6,525 457 7.00% 23 0.35% 2 0.03%

PWS (IN)

1 21 21 100% 0 0% 0 0% 1 It could not be determined from the data in STORET whether the Indiana PWS facilities were served by ground 

water or surface water.

Exhibit 6-12: Terbufos STORET Data – Summary of Sites

Source Water 

Type

Total 

Number of 

Sites

Sites with Detections Sites with Detections 

> 1⁄2 HRL (0.175 μg/L)

Sites with Detections 

> HRL (0.35 μg/L)

Number Percent Number Percent Number Percent

Ground Water 441 0 0% 0 0% 0 0%

Surface Water 625 138 22.08% 14 2.24% 2 0.32%

Total 1,066 138 12.95% 14 1.31% 2 0.19%

PWS (IN)

1 6 6 100% 0 0% 0 0%

1 It could not be determined from the data in STORET whether the Indiana PWS facilities were served by ground 

water or surface water.
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Exhibit 6-13: Terbufos STORET Data – Summary of States

Source Water 

Type

Total 

Number of 

States

States with Detections States with Detections 

> 1⁄2 HRL (0.175 μg/L)

States with Detections 

> HRL (0.35 μg/L)

Number Percent Number Percent Number Percent

Ground Water 3 0 0% 0 0% 0 0%

Surface Water 17 11 64.71% 3 17.65% 2 11.76%

Total1 17 11 64.71% 3 17.65% 2 11.76%

PWS (IN)

2 1 1 100% 0 0% 0 0%

1 The number of states with ground water data plus the number of states with surface water data may not equal the 

“Total” number of states providing data because some states provided both ground water and surface water data.

2 It could not be determined from the data in STORET whether the Indiana PWS facilities were served by ground 

water or surface water.

6.4.2 Occurrence in Drinking Water

The agency reviewed a number of data sources for information on contaminant 

occurrence in drinking water. Data and information on terbufos and/or terbufos sulfone from the 

following sources are available and are summarized in this section:

• EPA’s First Unregulated Contaminant Monitoring Regulation (UCMR 1).

• EPA’s Second Unregulated Contaminant Monitoring Regulation (UCMR 2).

• State drinking water monitoring programs.

• Consumer Confidence Reports (CCRs) from PWSs.

• United States Department of Agriculture (USDA) Pesticide Data Program (PDP).

• USGS Pilot Monitoring Program (PMP).

• USGS NAWQA Source Water and Drinking Water Studies.

• National Pesticide Survey (NPS).

• Monitoring information reviewed by the OPP reregistration program.

• Estimated concentrations in environmental media generated by EPA OPP modeling.

• Environmental Working Group (EWG) Drinking Water Database.

Note that there may be some overlap, as sources with different purposes and audiences 

may have reported the same underlying data.

Reviewed sources that contain no information on terbufos or terbufos sulfone occurrence 

included, among others, Rounds 1 and 2 of EPA’s Unregulated Contaminant Monitoring (UCM) 

program, and EPA’s Community Water System Survey (CWSS).

Primary Data Sources

First Unregulated Contaminant Monitoring Regulation (UCMR 1), 2001-2003

UCMR 1 required the collection of data to support nationally representative estimates of 

contaminant occurrence in PWSs. UCMR 1 monitoring occurred primarily from 2001 to 2003 

and required surface water systems to monitor quarterly and ground water systems to monitor 

twice per year. There were two tiers of monitoring: Assessment Monitoring for contaminants 
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with commonly used analytical method technologies, and Screening Survey monitoring for 

contaminants that require specialized analytical method technologies not in wide or common use. 

All large PWSs serving more than 10,000 people, plus a statistically representative 

national sample of 800 small PWSs (serving 10,000 people or fewer) were required to conduct 

UCMR 1 Assessment Monitoring. For the UCMR 1 Screening Survey, EPA required monitoring 

by a representative sample of 120 large and 180 small PWSs. Monitoring by each PWS was 

required during a 12-month period between January 2001 and December 2003. Due to the small 

sample size, contaminant occurrence estimates based on data from UCMR 1 Screening Survey 

are statistically less robust than those based on data from the UCMR 1 Assessment Monitoring. 

(For more details on all aspects of UCMR 1, refer to USEPA, 2008.)

A total of 2,301 terbufos samples were collected under the UCMR 1 Screening Survey

Monitoring from 295 systems (178 small systems and 117 large systems). There were no 

detections of terbufos from any of the small or large systems that sampled under UCMR 1. The 

minimum reporting level (MRL) for terbufos was 0.5 μg/L. Terbufos sulfone was not an analyte 

in UCMR 1.

The design of UCMR 1 permits estimation of national occurrence. To calculate national 

extrapolations, the percent of systems (or population served) estimated to exceed a specified 

threshold is multiplied by the total number of systems (or population served) in the nation. See 

Chapter 2 for additional information on national extrapolations. Since no detections of terbufos 

were observed among 2,301 samples from 295 systems in the UCMR 1 Screening Survey 

sample, terbufos occurrence in the nation’s small and large systems is likely to be negligible. 

Second Unregulated Contaminant Monitoring Regulation (UCMR 2), 2008-2010

UCMR 2 monitoring, designed to provide nationally representative contaminant 

occurrence data, was conducted from 2008 to 2010. UCMR 2 required surface water systems to 

monitor quarterly and ground water systems to monitor twice per year. There were two tiers of 

monitoring: Assessment Monitoring for contaminants with commonly used analytical method 

technologies, and Screening Survey monitoring for contaminants that require specialized 

analytical method technologies not in wide or common use. 

All very large PWSs (serving more than 100,000 people) and large PWSs (serving 

10,001-100,000 people), plus a statistically representative national sample of 800 small PWSs 

(serving 10,000 people or fewer), were required to conduct Assessment Monitoring during a 12-

month period between January 2008 and December 2010. For the Screening Survey, monitoring 

was required by all very large PWSs, 320 representative large PWSs, and 480 representative 

small PWSs, during a 12-month period between January 2008 and December 2010. See USEPA 

(2007) and USEPA (2010b) for more information on the UCMR 2 program, including study 

design and data analysis.

Terbufos sulfone was monitored under the UCMR 2 Assessment Monitoring, and 

terbufos was not. Monitoring results for terbufos sulfone from the UCMR 2 Assessment 

Monitoring (as of July 2011) are presented in Exhibit 6-14 through Exhibit 6-18. The MRL used 

for terbufos sulfone in this study was 0.4 μg/L, which is slightly greater than the terbufos sulfone 

HRL (0.35 μg/L).

The design of UCMR 2 permits estimation of national occurrence. To calculate national 

extrapolations, the percent of systems (or population served) estimated to exceed a specified 

threshold is multiplied by the total number of systems (or population served) in the nation. (Note 

that because all large and very large systems were required to conduct UCMR 2 Assessment 
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Monitoring, survey census figures are used in those size categories.) See Chapter 2 for additional 

information on national extrapolations. The results of this national extrapolation are presented in 

Exhibit 6-16 through Exhibit 6-18.

As of July 2011, a total of 32,012 samples have been collected from 4,138 systems. Of 

these systems, one reported a detection of 0.42 μg/L, which is slightly greater than the terbufos

sulfone HRL. These findings suggest that an estimated one PWS serving 44,600 people 

nationally has a detection of terbufos sulfone greater than the terbufos sulfone HRL. That 

population of 44,600 represents approximately 0.02% of the national population served by 

PWSs.

Exhibit 6-14: Terbufos Sulfone Occurrence Data from UCMR 2 Assessment 

Monitoring – Summary of Detected Concentrations

Total Number of 

Samples

Concentration Value of Detections (μg/L)

Minimum Median 90th Percentile 99th Percentile Maximum

Small Systems (serving ≤ 10,000 people)

Ground Water N/A N/A N/A N/A N/A

Surface Water N/A N/A N/A N/A N/A

All Small Systems N/A N/A N/A N/A N/A

Large Systems (serving 10,001 - 100,000 people) -- CENSUS

Ground Water 0.42 0.42 0.42 0.42 0.42

Surface Water N/A N/A N/A N/A N/A

All Large Systems 0.42 0.42 0.42 0.42 0.42

Very Large Systems (serving > 100,000 people) -- CENSUS

Ground Water N/A N/A N/A N/A N/A

Surface Water N/A N/A N/A N/A N/A

All Very Large Systems N/A N/A N/A N/A N/A

All Systems

All Water Systems 0.42 0.42 0.42 0.42 0.42

N/A = not applicable (no detections in this category).

Exhibit 6-15: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of Samples

Source Water 

Type

Total Number 

of Samples

Samples with 

Detections

Samples with 

Detections 

> 1⁄2 HRL (0.175 μg/L)

Samples with 

Detections 

> HRL (0.35 μg/L)

Number Percent Number Percent Number Percent

Small Systems (serving ≤ 10,000 people)

Ground Water 2,328 0 0.00% 0 0.00% 0 0.00%

Surface Water 920 0 0.00% 0 0.00% 0 0.00%

All Small 

Systems 3,248 0 0.00% 0 0.00% 0 0.00%
OW – OGWDW Regulatory Determination 3 Support Document– Ch 6, Terbufos and Terbufos Sulfone April 2014

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Source Water 

Type

Total Number 

of Samples

Samples with 

Detections

Samples with 

Detections 

> 1⁄2 HRL (0.175 μg/L)

Samples with 

Detections 

> HRL (0.35 μg/L)

Number Percent Number Percent Number Percent

Large Systems (serving 10,001 - 100,000 people) -- CENSUS

Ground Water 11,680 1 0.01% 1 0.01% 1 0.01%

Surface Water 10,301 0 0.00% 0 0.00% 0 0.00%

All Large 

Systems 21,981 1 0.005% 1 0.005% 1 0.005%

Very Large Systems (serving > 100,000 people) -- CENSUS

Ground Water 2,013 0 0.00% 0 0.00% 0 0.00%

Surface Water 4,770 0 0.00% 0 0.00% 0 0.00%

All Very Large 

Systems 6,783 0 0.00% 0 0.00% 0 0.00%

All Systems

All Water 

Systems 32,012 1 0.003% 1 0.003% 1 0.003%

Exhibit 6-16: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of System and Population Served Data –

All Detections

Source Water 

Type

UCMR 2 Sample

Number (and Percent) 

of Detections in the 

UCMR 2 Sample

National Inventory

National Estimate1 of 

the Number (and 

Percent) of Detections

Systems Population Systems Population Systems Population Systems Population

Small Systems (serving ≤ 10,000 people)

Ground Water 618 1,790,743

0 0

57,818 37,685,557

0 0

(0%) (0%) (0%) (0%)

Surface Water 182 878,262

0 0

3,866 8,928,745

0 0

(0%) (0%) (0%) (0%)

All Small 

Systems 800 2,669,004

0 0

61,684 46,614,302

0 0

(0%) (0%) (0%) (0%)

Large Systems (serving 10,001 - 100,000 people) – CENSUS

Ground Water 1,374 34,828,693

1 44,600

1,374 34,828,693

1 44,600

(0.07%) (0.13%) (0.07%) (0.13%)

Surface Water 1,566 49,720,870

0 0

1,566 49,720,870

0 0

(0%) (0%) (0%) (0%)

All Large 

Systems 2,940 84,549,563

1 44,600

2,940 84,549,563

1 44,600

(0.03%) (0.05%) (0.03%) (0.05%)

Very Large Systems (serving > 100,000 people) – CENSUS

Ground Water 63 17,269,919

0 0

63 17,269,919

0 0

(0%) (0%) (0%) (0%)

Surface Water 335 124,711,765

0 0

335 124,711,765

0 0

(0%) (0%) (0%) (0%)

All Very Large 

Systems 398 141,981,684

0 0

398 141,981,684

0 0

(0%) (0%) (0%) (0%)

All Systems
OW – OGWDW Regulatory Determination 3 Support Document– Ch 6, Terbufos and Terbufos Sulfone April 2014

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All Water 

Systems 4,138 229,200,252

1 44,600

65,022 273,145,549

1 44,600

(0.02%) (0.02%) (0.002%) (0.02%)

1 National estimates for the small systems are extrapolations, generated by multiplying the UCMR 2 national 

statistical sample findings of system/population percentages and national system/population inventory numbers for 

PWSs developed from EPA’s Safe Drinking Water Information System (SDWIS), the CWSS, and UCMR (see Chapter 

2 for discussion). National estimates for the large and very large systems are based directly on the UCMR 2 results, 

since this was a census, i.e., all large and very large systems were required to conduct UCMR 2 Assessment

Monitoring. Due to rounding, some calculations may appear to be slightly off.

Exhibit 6-17: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of System and Population Served Data –

Detections > 1⁄2 HRL

Source Water 

Type

UCMR 2 Sample

Number (and Percent) 

of Detections > 1/2 HRL 

(0.175 μg/L) in the 

UCMR 2 Sample

National Inventory

National Estimate1 of 

the Number (and 

Percent) of Detections 

> 1/2 HRL (0.175 μg/L)

Systems Population Systems Population Systems Population Systems Population

Small Systems (serving ≤ 10,000 people)

Ground Water 618 1,790,743

0 0

57,818 37,685,557

0 0

(0%) (0%) (0%) (0%)

Surface Water 182 878,262

0 0

3,866 8,928,745

0 0

(0%) (0%) (0%) (0%)

All Small 

Systems 800 2,669,004

0 0

61,684 46,614,302

0 0

(0%) (0%) (0%) (0%)

Large Systems (serving 10,001 - 100,000 people) – CENSUS

Ground Water 1,374 34,828,693

1 44,600

1,374 34,828,693

1 44,600

(0.07%) (0.13%) (0.07%) (0.13%)

Surface Water 1,566 49,720,870

0 0

1,566 49,720,870

0 0

(0%) (0%) (0%) (0%)

All Large 

Systems 2,940 84,549,563

1 44,600

2,940 84,549,563

1 44,600

(0.03%) (0.05%) (0.03%) (0.05%)

Very Large Systems (serving > 100,000 people) -- CENSUS

Ground Water 63 17,269,919

0 0

63 17,269,919

0 0

(0%) (0%) (0%) (0%)

Surface Water 335 124,711,765

0 0

335 124,711,765

0 0

(0%) (0%) (0%) (0%)

All Very Large 

Systems 398 141,981,684

0 0

398 141,981,684

0 0

(0%) (0%) (0%) (0%)

All Systems

All Water 

Systems 4,138 229,200,252

1 44,600

65,022 273,145,549

1 44,600

(0.02%) (0.02%) (0.002%) (0.02%)

1 National estimates for the small systems are extrapolations, generated by multiplying the UCMR 2 national 

statistical sample findings of system/population percentages and national system/population inventory numbers for 

PWSs developed from EPA’s SDWIS, the CWSS, and UCMR (see Chapter 2 for discussion). National estimates for 

the large and very large systems are based directly on the UCMR 2 results, since this was a census, i.e., all large and

very large systems were required to conduct UCMR 2 Assessment Monitoring. Due to rounding, some calculations 

may appear to be slightly off.
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Exhibit 6-18: Terbufos Sulfone National Occurrence Measures Based on UCMR 2 

Assessment Monitoring Data – Summary of System and Population Served Data –

Detections > HRL

Source Water 

Type

UCMR 2 Sample

Number (and Percent) 

of Detections > HRL 

(0.35 μg/L) in the UCMR 

2 Sample

National Inventory

National Estimate1 of 

the Number (and 

Percent) of Detections 

> HRL (0.35 μg/L)

Systems Population Systems Population Systems Population Systems Population

Small Systems (serving ≤ 10,000 people)

Ground Water 618 1,790,743

0 0

57,818 37,685,557

0 0

(0%) (0%) (0%) (0%)

Surface Water 182 878,262

0 0

3,866 8,928,745

0 0

(0%) (0%) (0%) (0%)

All Small 

Systems 800 2,669,004

0 0

61,684 46,614,302

0 0

(0%) (0%) (0%) (0%)

Large Systems (serving 10,001 - 100,000 people) -- CENSUS

Ground Water 1,374 34,828,693

1 44,600

1,374 34,828,693

1 44,600

(0.07%) (0.13%) (0.07%) (0.13%)

Surface Water 1,566 49,720,870

0 0

1,566 49,720,870

0 0

(0%) (0%) (0%) (0%)

All Large 

Systems 2,940 84,549,563

1 44,600

2,940 84,549,563

1 44,600

(0.03%) (0.05%) (0.03%) (0.05%)

Very Large Systems (serving > 100,000 people) -- CENSUS

Ground Water 63 17,269,919

0 0

63 17,269,919

0 0

(0%) (0%) (0%) (0%)

Surface Water 335 124,711,765

0 0

335 124,711,765

0 0

(0%) (0%) (0%) (0%)

All Very Large 

Systems 398 141,981,684

0 0

398 141,981,684

0 0

(0%) (0%) (0%) (0%)

All Systems

All Water 

Systems 4,138 229,200,252

1 44,600

65,022 273,145,549

1 44,600

(0.02%) (0.02%) (0.002%) (0.02%)

1 National estimates for the small systems are extrapolations, generated by multiplying the UCMR 2 national 

statistical sample findings of system/population percentages and national system/population inventory numbers for 

PWSs developed from EPA’s SDWIS, the CWSS, and UCMR (see Chapter 2 for discussion). National estimates for 

the large and very large systems are based directly on the UCMR 2 results, since this was a census, i.e., all large and

very large systems were required to conduct UCMR 2 Assessment Monitoring. Due to rounding, some calculations 

may appear to be slightly off.

Supplemental Data Sources

State Monitoring Data, 2002-2007

Since there is no national database that receives and stores all relevant data regarding the 

occurrence of regulated contaminants in public drinking water systems, EPA conducted a 

voluntary data call-in from the states, territories, and tribes to obtain regulated contaminant 
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occurrence data in support of national occurrence assessments conducted for the second Six-Year 

Review. For more details on the Six-Year Review- Information Collection Request (ICR)

Dataset, refer to USEPA (2009a). 

A few states also submitted PWS occurrence data for unregulated contaminants. EPA 

was able to supplement these data on unregulated contaminants by downloading additional 

publicly available monitoring data from state Web sites. The result was a collection of UCM data 

from nine states, representing those states with varying degrees of completeness. 

Drinking water occurrence data for terbufos were submitted by the State of California. 

Terbufos results from 0.7% of community water systems (CWSs) and 0.07% of non-transient 

non-community water systems (NTNCWSs) were included in data submitted from California. 

Precise information about methods used and reporting levels is not available.

An analysis of those data indicates that terbufos was not detected in any of the 191 

drinking water samples collected from 23 systems between 2002 and 2007. No data on terbufos 

sulfone were reported.

Water Systems’ Consumer Confidence Reports (CCRs), 1997

CCRs are annual water quality reports that CWSs are required to provide to their 

customers. These reports summarize information on water sources, detected contaminants, and 

system compliance with EPA drinking water standards; they may also include general 

educational material. Under the CCR Rule (40 CFR Subpart O), CWSs with 15 or more 

connections or serving at least 25 year-round residents must prepare and distribute a CCR to all 

billing units or service connections every year. Systems serving 100,000 or more residents are 

also required to post their current CCRs on a publicly accessible Internet site. EPA reviewed 

CCRs published by the 26 systems that serve over one million customers for unregulated 

contaminant occurrence information. Data on terbufos were available only from the CCR for 

New York City. Reporting levels were not specified in this CCR.

New York City included data on terbufos in its 1997 CCR. The city is served by 2

distribution systems supplied by surface water from 19 reservoirs and 3 controlled lakes, and 1

distribution system supplied by treated ground water. A total of 22 terbufos samples were taken 

at one surface water system, 10 samples at the other surface water system, and 22 at the ground 

water system that year. There were no detections of terbufos.

United States Department of Agriculture (USDA) Pesticide Data Program (PDP), 2001-2009

The USDA PDP maintains a national pesticide residue database. PDP was initiated in 

1991 to collect data on pesticide residues in food with sampling conducted on a statistically 

defensible representation of pesticide residuals in the United States food supply (USDA, 2011). 

Sampling and testing are conducted on fruits and vegetables, select grains, milk, and (as of 2001) 

drinking water.

The PDP drinking water sampling program was initiated at CWSs in New York and 

California in 2001. Since then the drinking water sampling program has expanded, though a 

somewhat changing mix of states is sampled each year. At one time or another, CWSs in 27

states and Washington, D.C., have contributed raw and/or finished water data to the program 

(USDA, 2011). The CWSs selected for sampling tend to be small- and medium-sized systems 

(primarily CWSs serving under 50,000), systems served by surface water, and systems located in 

regions of heavy agriculture. Sampling of raw water in addition to finished water began in 2004 

(USDA, 2004). 
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Terbufos and terbufos sulfone were included in the USDA PDP (USDA, 2012). Neither 

contaminant was detected in any of the 4,168 total terbufos samples (including 2,597 finished

samples), or 4,101 total terbufos sulfone samples (including 2,923 finished samples), collected 

between 2001 and 2009. The number of samples each year ranged from 134 to 612 for terbufos 

and from 238 to 794 for terbufos sulfone. Terbufos had limits of detection ranging from 0.0052

to 0.100 μg/L. Terbufos sulfone had limits of detection ranging from 0.0045 to 0.018 μg/L. Note 

that temporal trends cannot be evaluated based on these data since, with the exception of 2002 

and 2003, samples were not collected from the same sites and states in consecutive years.

United States Geological Survey (USGS) Pilot Monitoring Program (PMP), 1999

In 1999, PMP was initiated by USGS and EPA to provide information on pesticide 

concentrations in drinking water. This study focused on small drinking water supply reservoirs in 

areas with high pesticide use in order to test the sampling approach in areas where pesticides are 

probably present (Blomquist et al., 2001). Sampling sites represent a variety of geographic 

regions, as well as different cropping patterns. The ideal site candidates were mostly small 

reservoirs located in high pesticide-use areas, with a high runoff potential. Twelve water-supply 

reservoirs, considered vulnerable to pesticide contamination, were selected from the list of 

candidates. These 12 sites were located in California, Indiana, Ohio, Oklahoma, Louisiana, 

Missouri, South Carolina, South Dakota, New York, North Carolina, Pennsylvania, and Texas. 

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 rawwater intake and from the finished drinking water tap prior to entering the distribution system. At 

some sites, samples were also collected at the reservoir outflow.

Terbufos was an analyte in the PMP. At a method reporting level of 0.013 μg/L, terbufos 

was not detected in any of the raw or finished water sites from the 12 sites sampled (Blomquist et 

al., 2001).

The PMP did not include terbufos sulfone as an analyte but did include the related 

metabolite terbufos-O-analogue sulfone. At a reporting method level of 0.016 μg/L, terbufos-Oanalogue sulfone was not detected in any of the 317 raw water samples but was detected in two

(0.9%) of the 221 finished water samples. The highest concentration detected was 0.016 μg/L,

which is less than the terbufos HRL.

United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) 

Source Water and Drinking Water Studies 

Organic Compounds in Source Water of Selected Community Water Systems (Hopple 

et al., 2009 and Kingsbury et al., 2008), 2002-2005

Hopple et al. (2009) and Kingsbury et al. (2008) conducted studies, as part of the 

NAWQA program, to characterize anthropogenic organic compounds in U.S. waters used as 

source waters for PWSs. Hopple et al. (2009) focused on ground water and Kingsbury et al. 

(2008) focused on surface water. In Phase 1 of the studies, geographically diverse source water 

samples were collected between October 2002 and July 2005 from nine CWSs served by streams 

and from 221 CWS wells that withdraw from 12 aquifers. In Phase 2 of the studies, USGS 

collected source and finished water samples at a subset of sites between June 2004 and 

September 2005. In Phase 1 of the studies, terbufos was not detected in 221 ground water 

samples or 146 surface water samples. In Phase 2 of the studies, a total of 48 raw and 48 finished 

ground water samples were analyzed for terbufos. It was not detected in any ground water 

samples. Terbufos was not included in the surface water portion of Phase 2 (Hopple et al., 2009; 
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Kingsbury et al., 2008). The reporting level for terbufos was 0.017 μg/L, and was the same for 

both phases and for ground and surface water samples.

Water Quality in Public-Supply Wells (Toccalino et al., 2010), 1993-2007

As a part of the NAWQA program, water samples were collected from source (untreated) 

ground water from 932 public-supply wells located in parts of 40 NAWQA Study Units in 41 

states (Toccalino et al., 2010). Each well was sampled once between 1993 and 2007. The public 

wells sampled in this study represented 629 unique PWSs, representing 0.5% of the 

approximately 140,000 ground-water-supplied PWSs, but nearly 25% of the population served 

by ground water-PWSs in the United States. A total of 898 samples from these wells were 

analyzed for terbufos. Terbufos was not detected in any of the 898 samples collected. Reporting 

limits used for terbufos in this study ranged from 0.006 μg/L to 0.013 μg/L.

Water Quality in Domestic Wells (DeSimone, 2009), 1991-2004

USGS conducted a recent assessment of the quality of water from domestic wells across 

the United States using NAWQA data (DeSimone, 2009). The program included the analysis of 

major ions, trace elements, nutrients, radon, and organic compounds (pesticides and volatile 

organic compounds (VOCs)) at approximately 2,100 domestic wells (private drinking water 

wells) across 48 states, covering 30 regional aquifers, between 1991 and 2004. In addition, 

USGS summarized data from wells sampled for NAWQA agricultural land-use assessment 

studies to provide an indication of the potential effects of agricultural land-use practices on the 

ground water in the aquifers studied. Reporting thresholds varied; thresholds of both 0.009 μg/L 

and 0.013 μg/L are listed. Terbufos was detected in one (0.04%) of the 2,539 samples from 

aquifer and agricultural land-use studies, at an unspecified concentration that was less than 0.01 

μg/L, and therefore also less than the terbufos HRL and 1⁄2 the terbufos HRL.

Water Quality in Carbonate Aquifers (Lindsey et al., 2008), 1993-2005

As part of the NAWQA program, Lindsey et al. (2008) conducted an assessment of the 

water quality in carbonate aquifers, which account for 22% of the ground water pumped by the 

country’s PWSs. From 1993 to 2005, the study analyzed 1,042 wells and springs across 12 

aquifer systems and 20 states for major ions, radon, nutrients, pesticides, and VOCs. Terbufos

was not detected in any of 1,027 samples. Reporting levels were not given. 

National Pesticide Survey (NPS), 1988-1990

In 1990, EPA completed a national survey of pesticides and pesticide degradates in 

drinking water wells. The purpose of the NPS was to determine the national occurrence 

frequencies and concentrations of select pesticides in the nation’s drinking water wells, and to 

improve EPA’s understanding of how pesticide occurrence in ground water correlates with 

patterns of pesticide usage and ground water vulnerability. The survey included 566 CWS wells 

and 783 rural domestic wells. Sampling was conducted between 1988 and 1990. The survey 

targeted areas representing a variety of pesticide usage levels and ground water vulnerability. 

The survey was designed to provide a statistically reliable estimate of pesticide occurrence in the 

nation’s drinking water wells. It was not designed to provide statistically valid results at the state 

or local level. Wells were sampled for 101 pesticides, 25 pesticide degradates, and nitrate 

(USEPA, 1990).

Terbufos was included as an analyte, but could not be quantified or reliably detected with 

the analytical techniques available (USEPA, 1990). Terbufos sulfone was not included in the 

study.
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Monitoring Information Reviewed by the OPP Reregistration Program

EPA OPP gathered monitoring information from various sources in the RED for terbufos 

(USEPA, 2006). Reviewed data on terbufos in ground water came from the registrant, USGS 

NAWQA, EPA’s Pesticides in Ground Water Database, and several states within the major use 

areas. There were 20 confirmed detections of terbufos, plus another seven questionable or 

unconfirmed detections, out of 4,563 ground water samples taken in 13 states. Concentrations of 

terbufos detected in the ground water studies ranged from 0.01 μg/L to a maximum 

concentration of 20.0 μg/L, which is greater than the terbufos HRL and 1⁄2 the HRL. In Iowa, 13 

wells were also sampled for terbufos sulfone; it was not detected in any samples. Reporting 

levels are not provided in the RED (USEPA, 2006). 

OPP Estimated Concentrations 

EPA’s OPP used modeling to develop estimated environmental concentrations (EECs) 

for acute and chronic exposure scenarios for terbufos and its degradates (terbufos sulfone and 

terbufos sulfoxide), in aggregate, in surface water and ground water (USEPA, 2006). The EECs 

were developed using the Pesticide Root Zone Model/Exposure Analysis Modeling System 

(PRZM/EXAMS) and Screening Concentrations in Ground Water (SCI-GROW) model. 

For acute and chronic exposure, the EEC values for terbufos and its degradates, in 

aggregate, range from 4.8 to 7.4 μg/L in ground water. In surface water, EEC values for terbufos 

and its degradates, in aggregate, range from 5.4 to 13.3 μg/L and from 1.3 to 5.5 μg/L for acute 

and chronic exposures, respectively.

Environmental Working Group (EWG) Drinking Water Database, 2004-2009

In December 2009, EWG released its “National Drinking Water Database,” which 

includes data on occurrence of drinking water contaminants (regulated and unregulated) 

collected between 2004 and 2009 from 45 states and the District of Columbia (EWG, 2009). The 

2009 EWG database includes results from approximately 48,000 water systems; data were 

obtained primarily from state water offices.

EWG reviewed the data for inconsistencies, potential outliers, and other errors. It also 

invited the American Water Works Association (AWWA) and the Association of Metropolitan 

Water Agencies (AMWA) to review the data and/or have their constituents, the PWSs, review 

the data. Some corrections apparently were made since the public release of the data in 

December, 2009. The data analyzed by EPA were downloaded on December 29, 2010. EPA’s 

analysis is based solely on the data made publicly available by EWG on its Web site. Reporting 

levels are not specified in EWG’s database.

As of November 10, 2010, a total of 195 systems reported having tested for terbufos

between 2004 and 2009. No detections of terbufos were found.

6.5 Technology Assessment

6.5.1 Analytical Methods

EPA has developed three analytical methods for the analysis of terbufos in drinking 

water:

• EPA Method 507, Revision 2.1, Determination of Nitrogen- and PhosphorusContaining Pesticides in Water by Gas Chromatography with a Nitrogen-Phosphorus 

Detector, has a Method Detection Limit (MDL) of 0.054 μg/L. The method lists 

recoveries ranging from 77 to 97%, with Relative Standard Deviations (RSDs) of 4 to 
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7%. However, personnel from EPA’s Technical Support Center (TSC) have indicated 

that terbufos is not stable by this method (USEPA, 1995a).

• EPA Method 525.2, Revision 2.0, Determination of Organic Compounds in Drinking 

Water by Liquid-Solid Extraction and Capillary Column Gas Chromatography/Mass 

Spectrometry, has MDLs that range from 0.077 to 0.15 μg/L. The method lists 

recoveries ranging from 90 to 123%, with RSDs of 4.2 to 11%. However, personnel 

from EPA’s TSC have indicated that terbufos is not stable by this method (USEPA, 

1995b).

• EPA Method 526, Revision 1.0, Determination of Selected Semivolatile Organic 

Compounds in Drinking Water by Solid Phase Extraction and Capillary Column Gas 

Chromatography/Mass Spectrometry (GC/MS), has MDLs that range from 0.017 to 

0.05 μg/L. Recoveries range from 80.2 to 128%, with RSDs of 1.6 to 4.6% (USEPA, 

2000).

EPA has developed one analytical method for the analysis of terbufos sulfone in drinking 

water:

• EPA Method 527, Revision 1.0, Determination of Selected Pesticides and Flame 

Retardants in Drinking Water by Solid Phase Extraction and Capillary Column Gas 

Chromatography/Mass Spectrometry (GC/MS), has a Detection Limit (DL) of 0.041 

μg/L. The Lowest Concentration Minimum Reporting Level (LCMRL) is 0.27 μg/L. 

The method lists recoveries ranging from 87.3 to 111%, with RSDs of 1.6 to 11%. 

However, personnel from EPA’s TSC have indicated that there are stability problems 

with terbufos sulfone via this method (USEPA, 2005).

Although not included in any analytical methods, the MRL for terbufos is 0.5 μg/L. This 

value served as a national benchmark for laboratories that participated in UCMR 1 using EPA 

Method 526 (66 FR 2273; USEPA, 2001b). The MRL of 0.5 μg/L for use of EPA Method 526 

was obtained from precision and accuracy measurements made during method development. The 

MRL of 0.5 μg/L was also verified by second laboratory validation (66 FR 2273; USEPA, 

2001b). Note that the MRLs established for UCMR 1 were defined and calculated differently 

from those MRLs used in subsequent rounds of UCMR. 

Although not included in any analytical methods, the MRL for terbufos sulfone is 0.4 

μg/L. This value serves as a national benchmark for laboratories participating in UCMR 2 using 

EPA Method 527 (72 FR 367; USEPA, 2007). The MRL of 0.4 μg/L was determined by EPA 

using data generated from EPA Method 527. 

An estimated reporting level for the method (calculated as the MRL) was compared to the 

HRLs for terbufos and terbufos sulfone to determine whether the available analytical methods 

are capable of reliable quantitation at concentrations of estimated toxicological concern (see

Exhibit 6-19). The Method Sensitivity Ratio (MSR) is calculated from the following equation:

MSR = HRL (μg/L) / MRL (μg/L)

A favorable MSR is one that is greater than 10. That is, it is preferable that the HRL be at 

least 10 times above the concentration at which data can be reliably reported; this provides a 

margin of safety for uncertainty in the HRL and/or method performance (see USEPA, 2009b).
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Exhibit 6-19: Method Sensitivity Ratio (MSR) for Terbufos and Terbufos Sulfone

Contaminant Name Method MRL (μg/L) HRL (μg/L) MSR

Terbufos 526 0.5 0.35 0.7

Terbufos Sulfone 527 0.4 0.35 0.88

Both of the MSRs are less than 10; hence, the available analytical methods are not 

capable of reliable quantitation at least 10 times below the HRL.

6.5.2 Treatment Technologies

The availability of treatment technologies is not a factor EPA considers when making a 

regulatory determination. However, suitable treatment technologies must be made available 

before a National Primary Drinking Water Regulation (NPDWR) can be promulgated. 

A preliminary review of the literature reveals that the following treatment technologies 

have been investigated empirically for their applicability to terbufos:

• Ultraviolet (UV) irradiation (photocatalysis with titanium dioxide).

• Chlorine.

• Conventional treatment.

Based on percentage-removal values reported in the reviewed literature, the most 

promising option appears to be UV irradiation (photocatalysis with titanium dioxide).

The preliminary review of the literature revealed no information about the applicability of 

treatment technologies to terbufos sulfone.

Please note that the literature review was not exhaustive, and findings from the reviewed 

studies might not be directly comparable. A full assessment of treatment technology applicability 

will require a more detailed review and analysis of the literature, and possibly additional 

research.

6.6 Preliminary Regulatory Determination

6.6.1 Making Preliminary Regulatory Determinations for Chemicals on the CCL

The statutory requirements for the CCL and regulatory determinations can be found in 

SDWA Section 1412(b)(1). The 1996 SDWA Amendments require EPA to publish the CCL 

every five years. The CCL is a list of contaminants that are not subject to any proposed or 

promulgated NPDWRs, are known or anticipated to occur in PWSs, and may require regulation 

under SDWA to protect public health. The 1996 SDWA Amendments also direct EPA to 

determine whether or not to regulate at least five contaminants from the CCL every five years.

There are three criteria to be considered in making a regulatory determination. A decision to 

regulate is warranted if:

(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 PWSs with a frequency and at levels of public health 

concern; and 
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(c) in the sole judgment of the Administrator, regulation of such contaminant presents a 

meaningful opportunity for health risk reduction for persons served by PWSs. 

If EPA determines that all three of these statutory criteria are met, it makes a preliminary 

positive regulatory determination that an NPDWR1 is needed. . Following a comment response 

period and a final positive regulatory determination, the agency has 24 months to publish a 

proposed Maximum Contaminant Level Goal2 (MCLG) and an NPDWR. After the proposal, the 

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

1412(b)(1)(E)).3 The agency may determine that there is no need for a regulation when a 

contaminant fails to meet one or more of the criteria. A decision not to regulate is considered a 

final agency action and is subject to judicial review. The agency can choose to publish a Health 

Advisory (a nonregulatory action) or other guidance for any contaminant on the CCL, 

independent of the regulatory determination. Refer to section 1.4 for a summary of the approach 

used to identify and evaluate contaminants for RD 3. The following section summarizes the 

preliminary RD 3 decision for terbufos and terbufos sulfone.

6.6.2 Health Effects (Criterion #1)

The first criterion asks if the contaminant may have an adverse effect on the health of 

persons. Since all chemicals have adverse effects at some level of exposure, the challenge is to 

identify a HRL, a dose below which adverse health effects are considered unlikely to occur 

(threshold toxicant), or below which adverse effects have a defined low probability of occurrence 

(non-threshold toxicant). The key elements that must be considered in evaluating the first 

criterion are the mode of action, the critical effect(s), the dose-response for critical effect(s), the 

RfD for threshold effects, and the slope factor for non-threshold effects.

A full description of the health effects associated with exposure to terbufos and terbufos 

sulfone is presented in Section 6.3 of this document.

Health Criterion Data

Terbufos has been found to be readily absorbed. The proposed metabolic pathway for 

terbufos consists of sulfoxidation and desulfuration of terbufos, followed by hydrolysis of the 

thiolophosphorus bond, enzymatic S-methylation, and then additional S-oxidation to final 

metabolites sulfone, t-butyl (methyl-sulfonyl) methyl and sulfoxide, (t-butylsulfonyl) methyl 

methyl (Cheng, 1992). Although there have been no pharmacokinetic studies identified for 

terbufos sulfone, systemic effects indicate that the compound is absorbed. There are limited data 

available on terbufos and terbufos sulfone in humans. Clinical signs of cholinergic toxicity were 

noted in animal studies, and included tremors, salivation, exophthalmos, prostration, decreased 

activity, chromodacryorrhoea, diuresis, piloerection, ataxia, urogenital staining, nasal discharge, 

anorexia, and labored breathing from oral exposure to terbufos. Animal studies have reported 

 

1 An NPDWR is a legally enforceable standard that applies to PWSs. 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.

2 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 nonenforceable health goals." (CFR 141.2)

3 The statute authorizes a nine month extension of this promulgation date.
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ChE inhibition as the critical effect for subchronic and chronic exposures to terbufos. There are 

no subchronic or chronic studies available which describe the effects of terbufos sulfone. 

EPA concluded in 2003 and in 2006 that the existing toxicity database for terbufos is 

sufficient to evaluate its potential hazards to the general population, and adequate to characterize 

its potential hazards to fetuses, infants, and children. Developmental studies of terbufos in rats 

and rabbits did not find any developmental effects (USEPA, 2003) and no sensitive populations 

were identified or characterized. A two-generation reproductive study in rats reported that 

terbufos caused a decrease in male fertility, the number of pregnant females, pup viability, and 

pup body weight in the highest dose group (Schroeder, 1989). There are no data on reproductive 

and developmental effects of terbufos sulfone. Terbufos has been found to be negative in the 

majority of mutagenicity tests, both in vivo animal studies (chromosomal aberrations in rats) and 

in vitro studies (i.e., reverse mutation in Salmonella typhimurium, point mutations and 

chromosomal aberrations in CHO cells, and unscheduled DNA synthesis in primary male rat 

hepatocytes) (USEPA, 2003). Genotoxicity studies of terbufos sulfone are lacking.

Dog studies, by Shellenberger (1984) and Shellenberger and Billups (1986), on ChE 

inhibition were identified as the critical studies for establishing the RfD of 0.00005 mg/kg-day 

for terbufos. The RfD was derived from a NOAEL of 0.005 mg/kg-day and a net UF of 100 for 

interspecies and intraspecies variability (USEPA, 2006). 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 a RSC of 20%. Lacking subchronic or chronic studies, the OPP RED 

did not develop an RfD for terbufos sulfone (USEPA, 2006). Bailey (1988) conducted a 14-day 

study of both terbufos and terbufos sulfone in dogs. Data from the study suggests that terbufos 

sulfone is less toxic than its parent, and that the use of the terbufos HRL of 0.35 μg/L for 

terbufos sulfone is reasonable. 

There has been no evidence that terbufos is carcinogenic in either mice (Silverman et al., 

1986) or in rats (Rapp, 1974). EPA (USEPA, 1988) determined that the data were not adequate 

to make a determination regarding the potential carcinogenicity of terbufos and placed it in 

Group D (not classifiable as to human carcinogenicity), following the agency’s 1986 cancer 

guidelines (USEPA, 1986). There are no long-term animal studies of terbufos sulfone 

carcinogenicity. 

Health Criterion Conclusion

Toxicological data from animal studies indicate that terbufos exposure is associated with 

ChE inhibition and reproductive effects. Data on ChE inhibition in dogs support the development 

of an HRL of 0.35 μg/L for human exposure to terbufos via drinking water. The limited data on 

terbufos sulfone toxicity suggest that it is less toxic than its parent, making an HRL of 0.35 μg/L 

for terbufos sulfone protective of human health. Based on these considerations, EPA concludes 

that terbufos and terbufos sulfone meet the SDWA statutory criterion #1 for regulatory 

determination; they may have an adverse effect on the health of persons.

6.6.3 Occurrence in Public Water Systems (Criterion #2)

The second criterion asks if the contaminant is known to occur or if there is a substantial 

likelihood that the contaminant will occur in PWSs with a frequency and at levels of public 

health concern. In order to address this question, EPA consulted a variety of information sources, 

including data from the UCMR 1 Screening Survey and the UCMR 2 Assessment Monitoring, 

national surveys of PWSs conducted from 2001 to 2003 and from 2008 to 2010, respectively. 

EPA examined the total number of systems that reported detections of terbufos and terbufos 
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sulfone, as well as those that reported concentrations of terbufos and terbufos sulfone above their 

respective HRLs (both 0.35 μg/L).

Available monitoring data, including data that may shed light on regional and national 

occurrence, are presented in Section 6.4, and are summarized below. Additional information on 

production, use, and fate is found in Section 6.2.

Occurrence Criterion Data

The primary occurrence data for terbufos are from the UCMR 1 screening survey (2001-

2003). 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). 

The primary occurrence data for terbufos sulfone are nationally-representative finished 

water monitoring data generated through EPA’s UCMR 2 (2008-2010). UCMR 2 collected 

32,012 finished water samples from 4,138 PWSs. Terbufos sulfone was detected in only one 

sample, at a concentration of 0.42 μg/L. The MRLwas 0.4 μg/L, which is slightly higher than the 

HRL (0.35 μg/L). 

Finished water data for terbufos and terbufos sulfone from California, Iowa, USDA, and 

USGS are consistent with the UCMR 1 and UCMR 2 data. The State of California reported no 

detections of terbufos in 191 samples from 23 PWSs. The State of Iowa reported no detections of 

terbufos sulfone from 13 wells. 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. 

The USGS PMP monitored for terbufos in finished water in 1999 and reported no detections. 

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 1⁄2 

the 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 1⁄2 the 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 1⁄2 the HRL or the HRL in 1,027 and 

2,539 samples, respectively. 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 or the 146 Phase 1 surface water samples. In 

Phase 2, there were no detections of terbufos from 48 raw and 48 finished groundwater samples. 

(Terbufos was not included as an analyte in the Phase 2 surface water study.) Ambient water data 

from a USGS study conducted between 1993-2007 by Toccalino et al. (2010), reported no 

terbufos detections in 898 groundwater samples. Terbufos ambient data reported in the EPA 

OPP’s RED for terbufos included 20 detections in 4,563 groundwater samples from 13 states. 

The detected concentrations ranged from 0.01 to 20 μg/L, a range that extends both above and 

below 1⁄2 the 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. Terbufos ambient data are reported 

in STORET from 17 states. 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 
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sites (22.1%). Of the 457 surface water detections, only 23 samples (0.39%) at 14 sites (2.24%) 

were above 1⁄2 the HRL and only two samples (0.03%) at two sites (0.32%) were above the HRL.

Occurrence Criterion Conclusion

Terbufos was not detected in any of the 2,301 UCMR 1 samples collected by 295 PWSs, 

using an MRL of 0.5 μg/L, which is slightly higher than the HRL (0.35 μg/L). Terbufos sulfone 

was detected in only one out of 32,012 UCMR 2 samples from 4,138 PWSs, using an MRL of 

0.4 μg/L, which was slightly higher than the HRL (0.35 μg/L). The detected terbufos sulfone 

concentration was 0.42 μg/L.

Based on these considerations, EPA concludes that terbufos and terbufos sulfone do not 

meet the SDWA statutory criterion #2 for regulatory determination; they do not occur with a 

frequency and at levels of public health concern in PWSs.

6.6.4 Risk Reduction (Criterion #3)

The third criterion asks if, in the sole judgment of the Administrator, regulation presents a 

meaningful opportunity for health risk reduction for persons served by PWSs. In evaluating this 

criterion, EPA looked at several factors.

EPA calculated the total exposed population and the population exposed to levels above 

the HRL. Estimates of the populations exposed and the levels to which they are exposed were 

derived from the monitoring results. These estimates are included in Section 6.4 and summarized 

in the “Exposed Population Estimates” section below.

In evaluating the third criterion, EPA also considered effects on potentially sensitive 

populations, including the fetus, infants, and children. Sensitive population considerations are 

discussed in the “Sensitive Populations” section, below. 

Exposed Population Estimates

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. 

The estimated population exposed to terbufos sulfone at a level of public health concern 

is 44,600 (0.02% of the population served by PWSs); there was only one detection greater than 

the HRL in 4,138 PWSs (1 of 32,012 samples in UCMR 2).

Sensitive Populations

EPA also evaluated whether 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, 2003). There are no data on reproductive 

and developmental effects for terbufos sulfone. No sensitive populations were identified or 

characterized. The OPP RED (USEPA, 2006) presents more detailed information about the 

potential health effects and sensitive populations for terbufos and terbufos sulfone.

Risk Criterion Conclusion

Based on the estimated exposed populations, including sensitive subpopulations, EPA has 

preliminarily determined that terbufos and terbufos sulfone do not meet the SDWA statutory 

criterion #3 for regulatory determination; regulation of neither terbufos nor terbufos sulfone 

presents a meaningful opportunity for health risk reduction for persons served by PWSs. 
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6.6.5 Regulatory Determination Decision

As stated in the “Criteria for Regulatory Determination” section above, a positive finding 

for all three criteria is required in order to make a determination to regulate a contaminant. EPA 

has made a preliminary determination that terbufos and terbufos sulfone do not meet all three 

criteria.

Terbufos has the potential to cause adverse health effects, including ChE inhibition and 

reproductive effects. The limited toxicity studies for terbufos sulfone suggest that it is less toxic 

than the parent compound. Neither terbufos nor terbufos sulfone appear to occur in PWSs with a 

frequency and at levels of public health concern. Terbufos was not detected in any of the 2,301 

UCMR 1 samples collected by 295 PWSs, using an MRL of 0.5 μg/L, which is slightly higher 

than the HRL (0.35 μg/L). Terbufos sulfone was detected in only one out of 32,012 UCMR 2 

samples from 4,138 PWSs, using an MRL of 0.4 μg/L, which was slightly higher than the HRL 

(0.35 μg/L). The detected terbufos sulfone concentration was 0.42 μg/L. Due to the relatively 

small number of people likely exposed to terbufos and terbufos sulfone through drinking water, 

regulation of terbufos or terbufos sulfone does not appear to represent a meaningful opportunity 

for health risk reduction for persons served by PWSs. 

Additional information about the preliminary regulatory determination can be found in 

the Federal Register notice.

6.7 References

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Open-File Report 94-70. 4 pp. Available on the Internet at: 

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Lindsey, B.D., M.P. Berndt, B.G. Katz, A.F. Ardis, and K.A. Skach. 2008. Factors Affecting 

Water Quality in Selected Carbonate Aquifers in the United States, 1993-2005. U.S. 
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Geological Survey Scientific Investigations Report 2008-5240. Available on the Internet

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America, Inc., Madison, WI, USA (as cited in U.S. EPA, 2003).

Mandella, R.C. 1998. An acute neurotoxicity study with AC 92 100 in the rat via oral gavage 

administration. Unpublished report, Huntingdon study No. 98-4525 (BASF RDI No. TE451-002) from Huntingdon Life Sciences, East Millstone, NJ, USA (as cited in USEPA, 

2003 and 2006).

Mandella, R.C. 1999. 13-week dietary neurotoxicity study with AC 92 100 in the rat. 

Unpublished report, Huntingdon study No. 98-4521 (BASF RDI No. TE-451-004) from 

Huntingdon Life Sciences, East Millstone, NJ, USA (as cited in USEPA, 2003).

Morgareidge, K. 1973. Six-month feeding study in dogs on AC-92 100. Unpublished report, 

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report No. 87019 (BASF RDI No. TE-420-003) from Tegeris Laboratories, Inc., Laurel, 

MD, USA (as cited in USEPA, 2003).
OW – OGWDW Regulatory Determination 3 Support Document– Ch 6, Terbufos and Terbufos Sulfone April 2014

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Shellenberger, T., and L.H. Billups. 1986. One-year oral toxicity study in purebred beagle dogs 

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Drinking Water by Solid Phase Extraction and Capillary Column Gas 
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Chromatography/Mass Spectrometry (GC/MS). Revision 1.0. National Exposure 

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013.

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Systems in Support of the Second Six-Year Review of National Primary Drinking Water 

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