United States Prevention, Pesticides EPA 738-R-06-014 

Environmental Protection and Toxic Substances July 2006 

Agency (7509P) 

Reregistration 

Eligibility Decision 

(RED) for Inorganic 

Chlorates 

 
 

 ii

REREGISTRATION ELIGIBILITY 

DECISION 

for 

Inorganic Chlorates

Case No. 4049 

Approved by: 

______________________ 

Debra Edwards, Ph.D. 

Director, Special Review and 

Reregistration Division 

________________________ 

Date 
 

 iii

TABLE OF CONTENTS 

Inorganic Chlorates Reregistration Eligibility Decision Team....................................................v 

Glossary of Terms and Abbreviations.......................................................................................vi 

Abstract..................................................................................................................................viii 

I. Introduction.......................................................................................................................1 

II. Chemical Overview .......................................................................................................3 

A. Regulatory History ........................................................................................................3 

B. Chemical Identification – Sodium Chlorate .................................................................3 

C. Use Profile......................................................................................................................3 

D. Estimated Usage of Sodium Chlorate ...........................................................................4 

III. Summary of Inorganic Chlorates Risk Assessments.......................................................6 

A. Human Health Risk Assessment .....................................................................................6 

1. Toxicity of Sodium Chlorate .......................................................................................6 

2. Carcinogenicity of Sodium Chlorate ...........................................................................9 

3. Sodium Chlorate Endocrine Effects .......................................................................10 

4. Metabolites and Degradates....................................................................................10 

5. Dietary Exposure and Risk (Food)............................................................................11 

6. Dietary Exposure and Risks (Drinking Water)......................................................13 

7. Residential Exposure and Risk ...............................................................................17 

8. Aggregate Risk.........................................................................................................20 

9. Occupational Exposure and Risk............................................................................21 

B. Environmental Fate and Effects Risk Assessment.....................................................27 

1. Environmental Fate and Transport........................................................................27 

2. Ecological Exposure and Risk...................................................................................28 

IV. Risk Management, Reregistration, and Tolerance Reassessment..................................40 

A. Determination of Reregistration Eligibility ...................................................................40 

B. Public Comments and Responses................................................................................40 

C. Regulatory Position.......................................................................................................41 

1. Food Quality Protection Act Findings.......................................................................41 

2. Endocrine Disruptor Effects ...................................................................................42 

3. Cumulative Risks.....................................................................................................42 

4. Endangered Species.................................................................................................43 

D. Tolerance Reassessment Summary.........................................................................44 

E. Regulatory Rationale...................................................................................................46 

1. Human Health Risk Management ..........................................................................46 

2. Non-Target Organism (Ecological) Risk Management..........................................52 

3. Summary of Mitigation Measures ..........................................................................57 

F. Other Labeling Requirements ....................................................................................58 

1. Endangered Species Considerations.......................................................................58 

2. Spray Drift Management ........................................................................................59 

V. What Registrants Need to Do .........................................................................................60 

A. Manufacturing-Use Products......................................................................................60 

1. Generic Data Requirements....................................................................................60 

2. Labeling for Manufacturing-Use Products.............................................................61 

B. End-Use Products........................................................................................................61 

1. Additional Product-Specific Data Requirements...................................................61 
 

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2. Labeling for End-Use Products...............................................................................61 

C. Labeling Changes Summary Table.............................................................................61 

D. Existing Stocks.............................................................................................................61 
 

 v

Inorganic Chlorates Reregistration Eligibility Decision Team

Biological and Economic Analysis Assessment

Rafael Prieto 

Alan Halvorson 

Nicole Zinn 

Andrew Lee 

Environmental Fate and Effects Risk Assessment

Brian Anderson 

Silvia Termes 

Jim Goodyear 

Stephanie Syslo 

 

Health Effects Risk Assessment

Susan Hummel 

Bonnie Cropp-Kohlligian 

Abdullah Khasawinah 

Matthew Crowley 

Thurston Morton 

Gary Otakie 

Registration Support

 Juanita Gilchrist 

 Jim Tompkins 

 

Risk Management

Molly Clayton 

Kimberly Nesci 

Office of General Counsel

 Erin Koch 
 

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Glossary of Terms and Abbreviations 

a.i. Active Ingredient 

aPAD Acute Population Adjusted Dose 

APHIS Animal and Plant Health Inspection Service 

ARTF Agricultural Re-entry Task Force 

BCF Bioconcentration Factor 

CDC Centers for Disease Control 

CDPR California Department of Pesticide Regulation 

CFR Code of Federal Regulations 

ChEI Cholinesterase Inhibition 

CMBS Carbamate Market Basket Survey 

cPAD Chronic Population Adjusted Dose 

CSFII USDA Continuing Surveys for Food Intake by Individuals 

CWS Community Water System 

DCI Data Call-In 

DEEM Dietary Exposure Evaluation Model 

DL Double layer clothing {i.e., coveralls over SL} 

DWLOC Drinking Water Level of Comparison 

EC Emulsifiable Concentrate Formulation 

EDSP Endocrine Disruptor Screening Program 

EDSTAC Endocrine Disruptor Screening and Testing Advisory Committee 

EEC Estimated Environmental Concentration. The estimated pesticide concentration in an environment, 

such as a terrestrial ecosystem. 

EP End-Use Product 

EPA U.S. Environmental Protection Agency 

EXAMS Tier II Surface Water Computer Model 

FDA Food and Drug Administration 

FFDCA Federal Food, Drug, and Cosmetic Act 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FOB Functional Observation Battery 

FQPA Food Quality Protection Act 

FR Federal Register 

GL With gloves 

GPS Global Positioning System 

HIARC Hazard Identification Assessment Review Committee 

IDFS Incident Data System 

IGR Insect Growth Regulator 

IPM Integrated Pest Management 

RED Reregistration Eligibility Decision 

LADD Lifetime Average Daily Dose 

LC50 Median Lethal Concentration. Statistically derived concentration of a substance expected to cause 

death in 50% of test animals, usually expressed as the weight of substance per weight or volume of 

water, air or feed, e.g., mg/l, mg/kg or ppm. 

LCO Lawn Care Operator 

LD50 Median Lethal Dose. Statistically derived single dose causing death in 50% of the test animals 

when administered by the route indicated (oral, dermal, inhalation), expressed as a weight of 

substance per unit weight of animal, e.g., mg/kg. 

LOAEC Lowest Observed Adverse Effect Concentration 

LOAEL Lowest Observed Adverse Effect Level 

LOC Level of Concern 

LOEC Lowest Observed Effect Concentration 

mg/kg/day Milligram Per Kilogram Per Day 

MOE Margin of Exposure 

MP Manufacturing-Use Product 

MRID Master Record Identification (number). EPA's system of recording and tracking studies submitted. 
 

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MRL Maximum Residue Level 

N/A Not Applicable 

NASS National Agricultural Statistical Service 

NAWQA USGS National Water Quality Assessment 

NG No Gloves 

NMFS National Marine Fisheries Service 

NOAEC No Observed Adverse Effect Concentration 

NOAEL No Observed Adverse Effect Level 

NPIC National Pesticide Information Center 

NTP National Toxicology Program 

NR No respirator 

OP Organophosphorus 

OPP EPA Office of Pesticide Programs 

ORETF Outdoor Residential Exposure Task Force 

PAD Population Adjusted Dose 

PCA Percent Crop Area 

PDCI Product Specific Data Call-In 

PDP USDA Pesticide Data Program 

PF10 Protections factor 10 respirator 

PF5 Protection factor 5 respirator 

PHED Pesticide Handler's Exposure Data 

PHI Preharvest Interval 

ppb Parts Per Billion 

PPE Personal Protective Equipment 

PRZM Pesticide Root Zone Model 

RBC Red Blood Cell 

RAC Raw Agricultural Commodity

RED Reregistration Eligibility Decision 

REI Restricted Entry Interval 

RfD Reference Dose 

RPA Reasonable and Prudent Alternatives 

RPM Reasonable and Prudent Measures 

RQ Risk Quotient 

RTU (Ready-to-use) 

RUP Restricted Use Pesticide 

SCI-GROW Tier I Ground Water Computer Model 

SF Safety Factor 

SL Single layer clothing 

SLN Special Local Need (Registrations Under Section 24(c) of FIFRA) 

STORET Storage and Retrieval 

TEP Typical End-Use Product 

TSH Thyroid Stimulating Hormone 

TGAI Technical Grade Active Ingredient 

TRAC Tolerance Reassessment Advisory Committee 

TTRS Transferable Turf Residues 

UF Uncertainty Factor 

USDA United States Department of Agriculture 

USFWS United States Fish and Wildlife Service 

USGS United States Geological Survey 

WPS Worker Protection Standard 
 

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Abstract

 The Environmental Protection Agency (EPA or the Agency) has completed the human 

health and environmental risk assessments for the Inorganic Chlorates and is issuing its risk 

management decision and tolerance reassessment. The risk assessments, which are summarized 

below, are based on the review of the required target database supporting the use patterns of 

currently registered products and additional information received through the public docket. 

After considering the risks identified in the revised risk assessments, comments received, and 

mitigation suggestions from interested parties, the Agency developed its risk management 

decision for uses of inorganic chlorates that pose risks of concern. As a result of this review, 

EPA has determined that inorganic chlorate-containing products are eligible for reregistration, 

provided that risk mitigation measures are adopted and labels are amended accordingly. That 

decision is discussed fully in this document. 

Sodium chlorate is an inorganic salt herbicide that was first registered in 1966. It is a 

defoliant and a desiccant that is primarily used on cotton, but it also has other agricultural and 

non-agricultural uses. As a non-selective herbicide it is used to kill grasses and weeds in 

industrial and non-agricultural sites such as driveways, tennis courts, and recreational areas. The 

initial risk assessment indicated some ecological and occupational risks of concern. Risk 

assessments were revised based on refinements to the assessments as well as mitigation 

measures. Occupational and ecological risks resulting from non-agricultural uses have been 

mitigated by reducing application rates, as well as limiting applications of sodium chlorate to 

spot treatments only. Use on rights-of-way and ditch banks will be cancelled. The Agency may 

require changes to the language of the sodium chlorate label in the future if deemed necessary 

under the Endangered Species Protection Program. 
 

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I. Introduction 

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) was amended in 1988 

to accelerate the reregistration of products with active ingredients registered prior to November 

1, 1984. The amended Act calls for the development and submission of data to support the 

reregistration of an active ingredient, as well as a review of all submitted data by the U.S. 

Environmental Protection Agency (referred to as EPA or “the Agency”). Reregistration involves 

a thorough review of the scientific database underlying a pesticide’s registration. The purpose of 

the Agency’s review is to reassess the potential hazards arising from the currently registered uses 

of the pesticide, to determine the need for additional data on health and environmental effects, 

and to determine whether or not the pesticide meets the “no unreasonable adverse effects” 

criteria of FIFRA. 

 On August 3, 1996, the Food Quality Protection Act (FQPA) was signed into law. This 

Act amends FIFRA and the Federal Food, Drug, and Cosmetic Act (FFDCA) to require 

reassessment of all existing tolerances for pesticides in food. FQPA also requires EPA to review 

all tolerances in effect on August 2, 1996, by August 3, 2006. In reassessing these tolerances, 

the Agency must consider, among other things, aggregate risks from non-occupational sources of 

pesticide exposure, whether there is increased susceptibility of infants and children, and the 

cumulative effects of pesticides with a common mechanism of toxicity. When a safety finding 

has been made that aggregate risks are not of concern and the Agency concludes that there is a 

reasonable certainty of no harm from aggregate exposure, the tolerances are considered 

reassessed. EPA decided that, for those chemicals that have tolerances and are undergoing 

reregistration, tolerance reassessment will be accomplished through the reregistration process. 

Of the inorganic chlorates listed as active ingredients (i.e., sodium chlorate (073301), 

calcium chlorate (073302), potassium chlorate (073303), and magnesium chlorate (530200)), 

only sodium chlorate is present as an active ingredient in currently registered products. As such, 

sodium chlorate is the primary focus of the reregistration eligibility decision. Sodium chlorate is 

a strong oxidizer and may be reduced to a variety of chemical species depending on the 

environmental conditions. As a consequence of its reaction as an oxidant, sodium chlorate 

generates reduced chloro species (i.e., chlorine in lower oxidation states than chlorate), such as 

chlorite and hypochlorite. Since chlorite is also an active ingredient and is being considered in 

the chlorite/chlorine dioxide reregistration eligibility decision (case number 4043). The Agency 

will not consider the tolerances for chlorate reassessed until the assessment of chlorite is 

complete. As mentioned above, FQPA requires EPA to consider available information 

concerning the cumulative effects of a particular pesticide’s residues and “other substances that 

have a common mechanism of toxicity.” Potential cumulative effects of chemicals with a 

common mechanism of toxicity are considered because low-level exposures to multiple 

chemicals causing a common toxic effect by a common mechanism could lead to the same 

adverse health effect as would a higher level of exposure to any one of these individual 

chemicals. 

EPA has not made a common mechanism of toxicity finding as to parent sodium chlorate and 

any other substances, and sodium chlorate does not appear to produce a toxic metabolite that is 

in common with those produced by other substances. For the purposes of this reregistration 

eligibility decision (RED), therefore, EPA has not assumed that the inorganic chlorates have a 

common mechanism of toxicity with other substances. For information regarding EPA’s efforts 
 

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to determine which chemicals have a common mechanism of toxicity and to evaluate the 

cumulative effects of such chemicals, see the policy statements released by EPA’s Office of 

Pesticide Programs concerning common mechanism determinations and procedures for 

cumulating effects from substances found to have a common mechanism on EPA’s website at 

http://www.epa.gov/pesticides/cumulative/. 

 This document presents EPA’s revised human health and ecological risk assessments, its 

progress toward tolerance reassessment, and the reregistration eligibility decision for inorganic 

chlorates. The document consists of six sections. Section I contains the regulatory framework 

for reregistration/tolerance reassessment; Section II provides a profile of the use and usage of the 

chemical; Section III gives an overview of the human health and environmental effects risk 

assessments; Section IV presents the Agency's decision on reregistration eligibility and risk 

management; and Section V summarizes the label changes necessary to implement the risk 

mitigation measures outlined in Section IV. Finally, the Appendices list related information, 

supporting documents, and studies evaluated for the reregistration decision. The revised risk 

assessments for inorganic chlorates are available in the Office of Pesticide Programs (OPP) 

public docket under docket number OPP-2005-0507 available on the Agency’s web page at 

http://www.epa.gov/oppsrrd1/reregistration/inorganicchlorates/. 
 

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II. Chemical Overview 

Of the inorganic chlorates listed as active ingredients (i.e., sodium chlorate (073301), 

calcium chlorate (073302), potassium chlorate (073303), and magnesium chlorate (530200)), 

only sodium chlorate is present as an active ingredient in currently registered products. Sodium 

chlorate, calcium chlorate, and potassium chlorate are present as inert ingredients in currently 

registered products and exposures as a result of those uses are addressed herein. Sodium chlorate 

is a defoliant/desiccant, and is used as an herbicide. 

 A. Regulatory History 

Sodium chlorate was first registered in February 23, 1966 by Value Gardens Supply, 

LLC, for use on both annual and perennial grasses and weeds for the following non-agricultural 

use sites: garage areas, tennis courts, curbs, driveways, walks, and patios. On October 30, 1968, 

Helena Chemical Company registered it for use as a desiccant on agricultural sites (sorghum and 

cotton). Currently, there are 56 active product registrations containing sodium chlorate as an 

active ingredient, including 11 technical (manufacturing use) registrations, and 45 end-use 

products ranging from 2.3% to 99.7% active ingredient. Sodium chlorate is currently 

manufactured by seven companies. The compound may be used in combination with other 

herbicides, such as atrazine, 2,4-D, bromacil, diuron, and sodium metaborate. 

 

 B. Chemical Identification – Sodium Chlorate 

Chemical Structure:

 

Common Names: Sodium chlorate, soda chlorate, chloric acid, sodium salt 

Chemical Name: Sodium chlorate 

Trade Names: Ferti-Lome, Barespot, Tri-Kil, Bareground, Prometon, Pramitol, 

Killsall, TriChlor 

Chemical Family: Inorganic salt 

Case Number: 4049 

CAS Number: 7775-09-9 

PC Code: 073301 

Molecular Weight: 106.5 

Empirical Formula: NaClO3

Technical Registrants: EKA Chemicals, ERCO Chemicals, Kerr-McGee Chemical, 

Nexen Chemical USA, Moore Agricultural Products Company, Inc. 

C. Use Profile 

 The following is information on the currently registered uses of sodium chlorate, 

including an overview of use sites and application methods. A detailed table of the uses of 

sodium chlorate eligible for reregistration is available in Appendix A. 
 

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Type of Pesticide: Herbicide (desiccant/defoliant) 

Target Pest: Broadleaf weeds 

Mode of Action: Non-selective, contact herbicide that penetrates the cuticle causing 

cell death by altering the metabolic processes. 

Use Sites

Agricultural uses: Agriculturally, it is primarily used on cotton; however, it is also 

applied to a wide variety of other crops including, but not limited 

to, rice, corn, soybeans, dry beans, potatoes, sunflowers, flax, 

safflower, chili peppers (for processing only), grain sorghum, and 

wheat. 

Non-agricultural Uses: Sodium chlorate is used on nonagricultural (residential and 

industrial) areas such as rights-of-ways, building perimeters, ditch 

banks, bleachers, airport runways, vacant lots, fire hydrants, or as a 

pre-paving treatment. It is also used by a small percentage of 

water treatment facilities for the generation of chlorine dioxide. 

Use Classification: General Use 

Formulation Types: Agricultural products are all formulated as soluble 

concentrates/liquids; non-crop products are formulated as soluble 

concentrates/liquids and granules or pellets/tablets. 

Application Methods: Sodium chlorate as a defoliant/desiccant in agricultural settings is 

applied using aerial and groundboom equipment. As an herbicide 

in nonagricultural settings, it is applied using handheld equipment 

such as a low-pressure handwands or sprinkling cans; it is also 

applied via groundboom or handgun sprayer application methods 

for larger commercial scenarios. Granular formulations can be 

applied using belly grinders, push-type spreaders, tractor-drawn 

spreaders, or by hand. 

Application Rates: In agriculture, rates range from 6 pounds active ingredient per acre 

(6 lb ai/A) to 12.5 lbs ai/A. Industrial and other noncrop site rates 

range from 132 to 1032 lbs ai/A, based on current labels. Sodium 

chlorate can be applied multiple times per year. 

Application Timing: Sodium chlorate is applied post-emergence. 

D. Estimated Usage of Sodium Chlorate 

 The primary non-pesticidal use for sodium chlorate is as a precursor in chlorine dioxide 

generation through a closed system to bleach wood pulp/paper. The pesticidal uses of sodium 

chlorate, including the agricultural uses as a defoliant/desiccant, are a small percentage 

(approximately 2%) of the total sodium chlorate used in the United States. According to Agency 
 

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data, approximately 2.8 million pounds of sodium chlorate are applied annually to agricultural, 

residential, and commercial use sites. A screening-level usage analysis (SLUA) of sodium 

chlorate from 1998 to 2005 indicates that approximately 2.1 million pounds of sodium chlorate 

are used annually on agricultural use sites in the United States. In terms of pounds applied, the 

greatest use is on cotton (1.9 million lbs ai per year); annually this represents approximately 5 

percent of cotton acreage treated. 

 Exposure to the chlorate may also occur as a result of the drinking water disinfection process. 

This use and resulting exposure are explained in detail in this document. 
 

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III. Summary of Inorganic Chlorates Risk Assessments 

The following is a summary of EPA’s revised human health and ecological risk 

assessments for inorganic chlorates, as presented fully in the documents, revised Inorganic 

Chlorates. HED Chapter of the Reregistration Eligibility Decision Document (RED), dated 

January 26, 2006, and the revised Sodium Chlorate Ecological Risk Assessment, dated June 1, 

2006. The purpose of this summary is to assist the reader by identifying the key features and 

findings of these risk assessments, and to help the reader better understand the conclusions 

reached in the assessments. 

 The human health and ecological risk assessment documents and supporting information 

listed in Appendix C were used to reach the safety finding and regulatory decision for sodium 

chlorate. While the risk assessments and related addenda are not included in this document, they 

are available from the OPP Public Docket, located at http://www.regulations.gov, under docket 

number EPA-HQ-OPP-2005-0507. 

 EPA's use of human studies in the sodium chlorate risk assessment is in accordance with 

the Agency's Final Rule promulgated on January 26, 2006, related to Protections for Subjects in 

Human Research, which is codified in 40 CFR Part 26. 

A. Human Health Risk Assessment 

 The human health risk assessment incorporates potential exposure, hazard, and risks from 

all sources, which include food, drinking water, residential (if applicable), and occupational 

scenarios. Aggregate assessments combine food, drinking water, and any residential or other 

non-occupational (if applicable) exposures to determine potential exposures to the U.S. 

population. The Agency’s human health assessment considers all U.S. populations, including 

infants and young children. For more information on the inorganic chlorates human health risk 

assessment, see Revised Inorganic Chlorates. HED Chapter of the Reregistration Eligibility 

Decision Document (RED) dated June 26, 2006. 

 1. Toxicity of Sodium Chlorate 

 Toxicity assessments are designed to predict whether a pesticide could cause adverse health 

effects in humans (including short-term or acute effects such as skin or eye damage, and lifetime or 

chronic effects such as cancer, developmental effects, or reproductive effects), and the level or dose at 

which such effects might occur. The Agency has reviewed all toxicity studies submitted for sodium 

chlorate and has determined that the toxicological database is complete, reliable, and sufficient for 

reregistration. For more details on the toxicity and carcinogenicity of the inorganic chlorates, see 

Revised Inorganic Chlorates. HED Chapter of the Reregistration Eligibility Decision Document 

(RED) dated January 26, 2006, which is available under docket number EPA-HQ-OPP-2005-0507. 

 a. Acute Toxicity Profile 

In acute toxicity tests, sodium chlorate is slightly toxic by the oral (Toxicity Category 

IV), dermal (Toxicity Category III), and inhalation routes (Toxicity Category IV). Sodium 

chlorate crystals were mildly irritating to the rabbit eye (Toxicity Category III), and were a 
 

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minimal to mild dermal irritant (Toxicity Category III). Incident reports show that ingestion of 

toxic doses of sodium chlorate by humans produces gastritis, hemolysis, methemoglobinemia, 

hemoglobinurea, late toxic nephritis, and acute renal failure. Doses in excess of 100 mg/kg are 

generally fatal to humans. The acute toxicity profile for sodium chlorate is summarized in Table 

1 below. 

Table 1. Acute Toxicity Profile - Sodium Chlorate

Guideline Number Study Type MRID No. Results Toxicity Categorya

870.1100 Acute oral -Rats 41819901 LD50 ≥5000 mg/kg (rat) IV 

870.1200 Acute dermal - Rabbits 42497601 LD50 = > 2000 mg/kg III 

870.1300 Acute inhalation - Rats 41819903 LC50 = 5.59 mg/L IV 

870.2400 Acute eye irritation - Rabbit 

00085090 

00102998 

41819904 

mildly irritating III 

870.2500 Acute dermal irritation - 

Rabbit 42497602 minimally irritating III 

870.2600 Skin sensitization - guinea 

pigs 41819906 not a dermal sensitizer NA 

a. The technical acute toxicity values included in this document are for informational purposes only. The data 

supporting these values may or may not meet the current acceptance criteria. 

b. FQPA Safety Factor Considerations 

The Federal Food, Drug, and Cosmetic Act (FFDCA), as amended by the Food Quality 

Protection Act (FQPA), directs the Agency to use an additional ten fold (10x) safety factor (SF) to 

account for potential pre- and postnatal toxicity and completeness of the data with respect to exposure 

and toxicity to infants and children. FQPA authorizes the Agency to modify the 10x FQPA SF only if 

reliable data demonstrate that the resulting level of exposure would be safe for infants and children. 

For sodium chlorate, based on the hazard data and the exposure data, the FQPA SF was 

reduced to 1x. There was no pre- or postnatal sensitivity or susceptibility observed in the 

submitted developmental studies in rats and rabbits or the 2-generation reproduction study in 

rats. However, there is a concern for developing offspring because of the effects of inorganic 

chlorate on thyroid function in rats. The thyroid hormone system plays a critical role in 

development, and it is therefore important to understand whether the thyroid hormone system in 

the developing young differs in response to thyroid toxicants compared to adults. There exists, 

therefore, an uncertainty regarding information on comparative thyroid response in young versus 

(vs.) adult rats; however, a SF reflecting the uncertainty in comparative response is not necessary 

and the 10x FQPA SF can be removed (reduced to 1x). 

The rationale for removal of the FQPA SF lies in the comparative thyroid physiology of 

rats vs. humans. As a consequence of these dynamic differences, rats are much more sensitive to 

thyroid toxicants, such as chlorate, than humans and non-human primates. As discussed in the 

section below, the chronic reference dose (RfD) for inorganic chlorates is 0.03 mg/kg/day based 

on thyroid hypertrophy in adult rats. There is a study of the effects of chlorate on adult monkeys, 

in which the no observed adverse effects level (NOAEL) for effects on blood thyroxine levels 
 

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was 58 mg/kg/day. If the NOAEL from the monkey study were used to derive a chronic RfD 

with uncertainty factors of 10x for interspecies extrapolation and 10X for intraspecies variability, 

and an FQPA SF of 10x reflecting uncertainties in effects to the young, the chronic RfD would 

be 0.06 mg/kg/day. The chronic RfD selected by the risk assessment team of 0.03 mg/kg/day 

derived from a chronic rat study, conducted by the National Toxicology Program (NTP), is 

therefore protective of thyroid effects in primates (including a 10X factor for uncertainty with 

respect to developing young) without the necessity of an additional uncertainty factor applied to 

the rat data. 

In addition, the moderately refined dietary food assessment uses field trial data and 

percent crop treated estimates for all commodities, and the residential exposure assessment is 

based on reliable data; as such, exposure will not be underestimated. The dietary drinking water 

assessment uses residues in finished drinking water collected from water treatment facilities, 

which use chlorine dioxide or hypochlorite to treat drinking water. See Revised Inorganic 

Chlorates. HED Chapter of the Reregistration Eligibility Decision Document (RED) dated 

January 26, 2006, for additional details. 

c. Toxicological Endpoints 

The toxicological endpoints used in the human health risk assessment for sodium chlorate are 

listed in Table 2 below. Although several studies were considered, an acute reference dose (aRfD) 

was not identified. None of the available studies provided an endpoint of toxicity attributable to a 

single exposure. 

Sodium chlorate is unlikely to be absorbed by the skin based on its high water solubility 

and ionic nature; therefore, a risk assessment for dermal exposure is not needed and a dermal 

endpoint was not selected. For inhalation absorption, a default factor of 100% was used since, per 

Agency policy, the inhalation dose was derived from an oral endpoint. 

The usual interspecies uncertainty factor is 10x, but there are several important 

quantitative dynamic differences between rats and humans with respect to thyroid function that 

permit an interspecies factor of less than 10x for a thyroid toxicant like sodium chlorate. The 

half-life of thyroid hormone T4 in rats is approximately 12 hours, whereas in humans, the halflife is 5-9 days. The shorter half-life in rats is likely related to a high-affinity binding globulin 

for thyroxin that is present in humans, but absent in rodents. In the absence of a functional 

thyroid gland, a rat requires approximately 10-times more T4 than an adult human for full 

reconstitution. Constitutive thyroid stimulating hormone (TSH) levels are nearly 25-times higher 

in rats than in humans, reflecting the increased activity of the thyroid-pituitary axis in rats. 

Therefore, the 10x interspecies factor can be reduced to 3x based on dynamic considerations. 

The uncertainty factors (UF) and safety factors used to account for interspecies extrapolation, 

intraspecies variability, and susceptibility of infants and children (FQPA SF) are also described in 

Table 2. 

 
 

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Table 2. Summary of Toxicological Doses and Endpoints for Chlorate per se for Use in Human Risk Assessments 

for Inorganic Chlorates

Exposure Scenario Dose, Uncertainty 

Factors

FQPA Safety Factor and 

Level of Concern Study and Endpoint for Risk Assessment

Acute Dietary Acute RfD= not 

applicable 

Although several studies were considered, an acute reference dose 

(aRfD) was not identified. None of the available studies provided an 

endpoint of toxicity attributable to a single exposure. 

Chronic Dietary 

(all populations) 

BMDL1

 = 0.9 mg/kg/day 

UF = 30 (3x interspecies 

and 10x intraspecies) 

Chronic RfD = 0.03 

mg/kg/day 

FQPA SF = 1X 

cPAD = Chronic RfD

 FQPA SF 

cPAD= 0.03 mg/kg/day 

Chronic Study in rats (NTP, 2004). 

The LOAEL= 5 mg/kg/day based on 

increased thyroid gland follicular cell 

hypertrophy and follicular cell 

mineralization. 

Short- and 

Intermediate-Term 

Incidental Oral 

Oral NOAEL =30 

mg/kg/day 

UF = 100 

FQPA SF = 1X 

Residential LOC for 

MOE =100 

Subchronic study in rats McCauley et al, 

1995. Pituitary effects (vacuolization) 

and thyroid gland effects (colloid 

depletion), body weight decrease and 

organ weight changes and reduction in 

erythrocyte counts and hemoglobin 

content at the LOAEL of 100 and 150 

mg/kg/day in males and females, 

respectively 

Short-, 

Intermediate-, and 

Long-Term Dermal 

Not applicable Dermal absorption is unlikely due to the ionic nature and water 

solubility of sodium chlorate 

Short-, 

Intermediate-, and 

Long-Term 

Inhalation 

NOAEL =30 mg/kg/day2 

UF = 100 

FQPA SF = 1X 

Residential LOC for 

MOE =100 

Occupational LOC for 

MOE =100 

McCauley et al, 1995 

Cancer (Oral, 

dermal, inhalation) 

Classification: Not likely to be carcinogenic to humans at doses that do not alter thyroid hormone 

homeostasis. 

UF = uncertainty factor, FQPA SF = FQPA safety factor, NOAEL = no observed adverse effect level, LOAEL = lowest 

observed adverse effect level, PAD = population adjusted dose (a = acute, c = chronic), RfD = reference dose, MOE = 

margin of exposure, LOC = level of concern, NA = Not Applicable 

1. A NOAEL was not identified in this study. Therefore a bench mark dose (BMD) analysis was performed and a BMDL 

of 28 mg sodium chlorate/L (22 mg chlorate/L) was calculated. This corresponds to 0.9 mg chlorate/kg/day oral dose. 

2. A 100% inhalation absorption factor is used for extrapolating from an oral endpoint of toxicity. 

2. Carcinogenicity of Sodium Chlorate 

 Sodium chlorate is a thyroid toxicant producing thyroid gland follicular cell hypertrophy 

in rats and mice following chronic exposures. The Agency classified sodium chlorate as not 

likely to be carcinogenic to humans at doses that do not alter thyroid hormone homeostasis in 

accordance with the EPA policy, Assessment of Thyroid Follicular Cell Tumors, dated March 
 

 10

1998. This policy states that nonmutagenic pesticides that induce elevated levels of TSH and 

thyroid follicular cell tumors in the rat are classified as not likely to be carcinogenic to humans at 

doses that do not alter thyroid hormone homeostasis. 

The preliminary results of a draft 2-year National Toxicology Program (NTP) bioassay 

study on sodium chlorate to determine the potential of this chemical to induce tumors in 

laboratory animals (rats and mice) (NTP, 2004) showed evidence of thyroid gland follicular cell 

hyperplasia and follicular cell tumors in male rats. The effects may be attributed to changes in 

levels of thyroid hormones seen after administration of high doses of sodium chlorate. A final 

study report is expected later this year. In female mice there was equivocal and marginal 

evidence of increased pancreatic islet carcinoma. Sodium chlorate was negative in most 

bacterial gene mutation assays and in several cytogenetics tests, including a hypoxanthineguanine phosphoribosyl-transferase (HGPRT) assay in Chinese hamster ovaries and a 

micronucleus assay. 

The Agency selected a chronic endpoint based on the thyroid effects from the NTP 

bioassay study using a benchmark dose analysis approximation of the NOAEL. This endpoint is 

protective for all populations, including children because children are not expected to be more 

susceptible to chlorate-induced thyroid effects than adults. Therefore, the current chronic risk 

assessments presented in this document are protective of any cancer-related effects for all 

populations. For more information, see the document Revised Inorganic Chlorates. HED 

Chapter of the Reregistration Eligibility Decision Document (RED) dated January 26, 2006. 

 3. Sodium Chlorate Endocrine Effects

The EPA is required under the FFDCA, as amended by FQPA, to develop a screening 

program to determine whether certain substances (including pesticides active and other 

ingredients) “may have an effect in humans similar to an effect produced by a naturally 

occurring estrogen, or other such endocrine effects as the Administrator may designate.” 

Following recommendations of its Endocrine Disruptor and Testing Advisory Committee 

(EDSTAC), EPA determined that there was a scientific basis for including, as part of the 

program, the androgen and thyroid hormone systems, in addition to the estrogen hormone 

system. 

 The available toxicity studies on sodium chlorate demonstrate the thyroid gland to be its 

target of toxicity. The endpoints selected to assess chronic dietary risk and short- and 

intermediate-term oral and inhalation risks in this document are protective of the observed 

thyroid effects seen in the available toxicity studies. When additional appropriate screening 

and/or testing protocols being considered under the Agency’s Endocrine Screening Disruption 

Program have been developed, sodium chlorate may be subject to further screening and/or 

testing to better characterize effects related to endocrine disruption. 

 

 4. Metabolites and Degradates 

The Agency reviewed the metabolism of the inorganic chlorates, and concluded that there are 

several residues of concern in food. In plants, the terminal residues of sodium chlorate in/on plants are 

likely chlorate (ClO3

-

), chlorite (ClO2

-

), and chloride (Cl-). Based on published rat metabolism data, 
 

 11

terminal residues of sodium chlorate in animal tissues are also expected to be chlorate (ClO3

-

), chlorite 

(ClO2

-

), and chloride (Cl-). 

 In the environment, because chlorate is a strong oxidizing agent (oxidation state V), it gets 

reduced to chlorine species in lower oxidation states, such as the oxyanions chlorite (ClO2

-

, 

oxidation state III) and hypochlorite (ClO-

, oxidation state I), chlorine dioxide (oxidation state 

IV), and chloride (oxidation state -I). Thus, at least some, and possibly a substantial, reduction 

of the chlorate resulting from the application of sodium chlorate is likely to occur in the field 

prior to any runoff to surface water. Under environmental (terrestrial field) redox conditions, 

and based on chemical equilibria alone, the thermodynamically favored, end reduction product of 

chlorate in soil and in water is the chloride anion. Any intermediate chlorine dioxide that may 

form under environmental conditions will undergo photochemical reactions when exposed to 

sunlight. The chlorine oxyanions, chlorite and hypochlorite (other possible more reduced 

intermediates in the ultimate reduction of chlorate to chloride), are strong oxidizers in 

themselves; thus, they are also reduced and/or undergo disproportionation reactions. Although 

reduction reactions of chlorate, chlorite, and hypochlorite are said to occur very fast, how fast 

they occur is not known (i.e., the actual rate constants in the environment are not known). 

Therefore, at any given time the distribution of reduced species (type and concentration) cannot 

be estimated. However, it is unlikely that a single reduced species would be present. Chlorite is 

being considered in the chlorite/chlorine dioxide reregistration eligibility decision (case number 

4043). (See Revised Inorganic Chlorates. HED Chapter of the Reregistration Eligibility 

Decision Document (RED) dated January 26, 2006, for additional details.) 

5. Dietary Exposure and Risk (Food) 

 Dietary exposure (food only) to inorganic chlorates as the chlorate ion (ClO3

-

) may be 

expected from the following dietary exposure routes: 1) from sodium chlorate as an active 

ingredient in conventional (agricultural) pesticides used on food crops; 2) from sodium chlorate 

and potassium chlorate as inert ingredients in conventional pesticides used on food crops or in 

poultry premises; 3) from secondary residues in meat/milk/poultry/eggs due to residues in animal 

feedstuffs; 4) from sodium chlorate and calcium chlorate as inert ingredients in antimicrobial 

agents used as fruit, vegetable, and egg sanitizing washes, as treatments to mushrooms to control 

bacterial blotch, as treatments to seed used for sprouting, for conditioning live oysters, in poultry 

drinking water, in fish filleting, and in pecan cracking/dyeing; and 5) as a potential redox of 

chlorine dioxide and sodium chlorite in conventional and antimicrobial pesticides; (6) from 

degradation of hypochlorites in antimicrobial agents used as fruit and vegetable washes; and, (7) 

from translocation of very small amounts of chlorate ion (ClO3

-

) by plants (translocation of 

significant amounts would be phytotoxic to plants) from the environment which may be present 

as a result of inorganic chlorate pesticide uses. 

No acute dietary endpoint was selected because effects attributable to a single dose were 

not seen in the available data. Chronic and cancer dietary analyses were conducted for the 

general U.S. population and various population subgroups. 

a. Exposure Assumptions 

A chronic dietary risk assessment was conducted using the Dietary Exposure Evaluation 
 

 12

Model software with the Food Commodity Intake Database (DEEM-FCIDTM, Version 2.03), 

which uses food consumption data from the USDA’s Continuing Surveys of Food Intakes by 

Individuals (CSFII) from 1994-1996 and 1998. No food monitoring data are available for this 

risk assessment; therefore, exposure estimates in food were based on field trial data or, in the 

case of fruit/vegetable/other washes, were derived from a film thickness model. No chemicalspecific livestock metabolism or feeding data are available; exposure estimates in meat, milk, 

poultry, and eggs were derived from rat metabolism data, field trial data, and livestock reference 

information concerning feed consumption, tissue weights, and milk production. Default 

concentration factors (no chemical-specific processing data are available) and the effects of 

washing after foliar treatments were also incorporated into the risk assessment. Percent crop 

treated data were used in this analysis. Exposures were single point estimates; no residue decline 

was utilized. 

b. Population Adjusted Dose 

 A population adjusted dose, or PAD, is the reference dose (RfD) adjusted for the FQPA 

SF. A risk estimate that is less than 100% of the acute PAD (aPAD), the dose at which an 

individual could be exposed over the course of a single day and no adverse health effects would 

be expected, does not exceed EPA’s level of concern. Likewise, a risk estimate that is less than 

100% of the chronic PAD (cPAD), the dose at which an individual could be exposed over the 

course of a lifetime and no adverse health effects would be expected, does not exceed EPA’s 

level of concern. 

 c. Acute Dietary Risk (Food) 

No acute dietary endpoint was selected because effects attributable to a single dose were 

not seen in the available data; therefore, an acute dietary risk assessment was not conducted. 

d. Chronic Dietary Risk (Food) 

A chronic (non-cancer) dietary risk assessment was conducted for all potential chlorate 

dietary exposure routes using food consumption data from 1994-1996 and 1998. The chronic 

dietary exposure and risk estimates resulting from food intake were determined for the general 

U.S. population and various population subgroups. 

The chronic (non-cancer) dietary (food only) risk is below the Agency’s level of concern 

for the general US population and all population subgroups. The most likely highest exposed 

population subgroup, children 1-2 years of age, was at 28% of the cPAD. See Table 3 below for 

details. 

 

Table 3. Results of Chronic Dietary (Food only) Exposure Analysis 

Population Subgroup cPAD 

(mg/kg/day)

Exposure (mg/kg/day) % cPAD

All populations 0.002730 9 

All infants (< 1 year old) 

0.03 

0.004511 15 
 

 13

Table 3. Results of Chronic Dietary (Food only) Exposure Analysis 

Children 1-2 years old 0.008376 28 

Children 3-5 years old 0.006906 23 

A cancer dietary risk assessment was conducted for all potential chlorate dietary exposure 

routes, using the same dietary (food only) exposure estimates used in the chronic (non-cancer) 

dietary risk assessment for the US population. As discussed above, sodium chlorate is a thyroid 

toxicant producing thyroid gland follicular cell hypertrophy in rats and mice following chronic 

exposures, and may be producing follicular cell tumors in rats. The lack of mutagenicity 

indicates that the thyroid tumors are induced by a non-mutagenic mechanism. Children are not 

expected to be more susceptible to chlorate-induced thyroid effects than adults, and the endpoint 

selected for the thyroid effects is protective for all populations, including children. Therefore, as 

shown in Table 3 above, the chronic (food only) dietary risk assessment is protective for cancer 

for the general US population, since the estimated risk does not exceed 100% of the cPAD. 

6. Dietary Exposure and Risks (Drinking Water) 

Drinking water exposure to pesticides can occur through surface and groundwater 

contamination. Chronic dietary (water only) risk assessments were conducted using DEEMFCIDTM Version 2.03 and drinking water consumption data from the USDA’s CSFII from 1994-

1996 and 1998. Exposures were single point estimates; no residue decline was utilized. 

 Drinking water exposure can result from several different uses for sodium chlorate. 

Agriculturally, sodium chlorate is used as a defoliant and dessicant, primarily on cotton; 

however, it is also applied to a wide variety of other crops including, but not limited to, rice, 

corn, soybeans, dry beans, potatoes, sunflowers, flax, safflower, chili peppers (for processing 

only), grain sorghum, and wheat. As a non-selective herbicide, it is applied to industrial/noncrop areas such as rights-of-ways, building perimeters, ditch banks, bleachers, airport runways, 

vacant lots, fire hydrants, or as a pre-paving treatment. Sodium chlorate is also used to generate 

chlorine dioxide, which is then used to bleach wood pulp/paper and, in some cases, treat drinking 

water. All of these uses could result in chlorate reaching water systems. However, the majority 

of chlorate in drinking water is a result of drinking water disinfection treatment practices. 

 In the US, there are two primary methods of drinking water treatment. The first method 

is the generation of chlorine dioxide. In the second method, either gaseous chlorine or 

hypochlorite is used to produce free chlorine. Each of these methods, except the use of gaseous 

chlorine, produce chlorate as a disinfection byproduct (DBP). The American Water Works 

Association (AWWA) Disinfection Systems Committee tracks disinfection practices in US 

community water systems. AWWA’s most recent comprehensive survey (completed in 1998) 

estimated that, of all community water systems (CWS), approximately 20% of CWSs serving 

populations greater than 10,000 use sodium hypochlorite (2% generated it on-site), 8% use 

chlorine dioxide, and <1% use calcium hypochlorite. For CWSs using groundwater and serving 

populations less than 10,000, the survey estimated that approximately 34% use sodium 

hypochlorite, none use chlorine dioxide, and at least 4.5% use calcium hypochlorite. For CWSs 
 

 14

using surface water and serving less than 10,000, the survey estimated that 17% use sodium 

hypochlorite, 6% use chlorine dioxide, and 9% use calcium hypochlorite. 

 For chlorine dioxide generation, both sodium chlorate and sodium chlorite are used as 

precursor materials, and both typically result in chlorate byproduct in finished drinking water. 

Sodium chlorite is more commonly used than sodium chlorate. The free chlorine disinfection 

process involves the use of either gaseous chlorine, or sodium or calcium hypochlorite, as 

precursor materials. Historically, gaseous chlorine has far more widely been used than 

hypochlorite to produce free chlorine. In recent years, primarily as a result of various homeland 

security measures, many drinking water systems are switching from gaseous chlorine to 

hypochlorite. While the use of gaseous chlorine does not result in chlorate byproduct in finished 

drinking water, the use of either sodium or calcium hypochlorite can produce chlorate byproduct, 

and this will be discussed in greater detail later in this section. 

Chlorine Dioxide 

The use of chlorine dioxide can introduce chlorate into the finished water by several 

routes. Drinking water plants generally use sodium chlorite as a starting material (i.e., feedstock) 

in the production of chlorine dioxide. Chlorate ion may be present as a contaminant in the 

sodium chlorite feedstock (usually less than four percent of the active chlorite is chlorate). A 

typical range of chlorate carryover to the finished water from chlorite feedstock contamination is 

about 50 μg/L for a 1 mg/L dose of chlorine dioxide. Technology to generate chlorine dioxide 

using sodium chlorate is now available to the drinking water industry, which introduces the 

possibility of chlorate carryover to the finished water from the chlorate feedstock. However, 

since this method is more technically complicated than the method used with sodium chlorite, 

sodium chlorite is far more commonly used in the generation of chlorine dioxide than sodium 

chlorate. 

 

Chlorate ion (ClO3

-

) may also be produced due to inefficient generation of chlorine 

dioxide. Excess chlorine will favor the production of chlorate over chlorine dioxide, as will 

keeping the generator mixtures at highly alkaline (pH > 11) or acidic (pH < 3) conditions. If the 

concentrations of feedstock reactants are too low, or too much dilution water is added during the 

reaction, chlorate formation is also favored. 

Chlorite ion (ClO2

-

) is a major degradation product resulting from the reaction of chlorine 

dioxide with inorganic and organic constituents in the water. When free chlorine is used after 

the application of chlorine dioxide in the treatment process, chlorite is oxidized to chlorate. This 

conversion will continue over time as the water travels through the distribution system. Chlorate 

ion is also formed by photodecomposition of chlorine dioxide when treated water is exposed to 

bright sunlight in open basins. 

There are ways that water systems can control the levels of chlorate in drinking water, 

and these will be discussed in Section 4 of this document. 
 

 15

Hypochlorite

Chlorine-based disinfectants, such as free chlorine, are also used by drinking water 

treatment systems to treat drinking water. Some of these water systems use sodium hypochlorite 

or calcium hypochlorite as their source of free chlorine. Chlorate ion can be formed in these 

products during the manufacturing process, but the decomposition of hypochlorite solutions 

during storage is the more significant source of chlorate ion in systems using hypochlorite. 

Chlorate ion concentrations increase between the time of manufacture and delivery to the 

water plant. The rate at which hypochlorite ion disproportionates to chlorate is influenced by 

concentration of hypochlorite, pH, and temperature. As with the chlorine dioxide methods, there 

are several ways that water systems using hypochlorite can control the levels of chlorate; these 

will be discussed in Section 4 of this document. 

a. Drinking Water Exposure 

Data on the occurrence of chlorate ion in drinking water were available from two primary 

sources: 1) the Information Collection Rule (ICR) Auxiliary 1 Database, Version 5.0, and 2) the 

American Water Works Association Research Foundation (AwwaRF) study on the control of 

chlorate ion in hypochlorite solutions. The ICR data is the more extensive data set, and the water 

systems represented in the ICR database serve 60% of the total US population. The EPA Office 

of Water (OW) issued the ICR in order to collect data to support future regulation of microbial 

contaminants, disinfectants, and disinfection byproducts. Monitoring for chlorate was included 

in the ICR, since chlorate is a disinfection byproduct. Source water and drinking water were 

monitored for chlorate ion between July 1997 and December 1998. Water systems serving a 

population of at least 100,000 were required to monitor for chlorate ion at treatment plants using 

chlorine dioxide or hypochlorite solutions in the treatment process. Plants using chlorine dioxide 

collected monthly samples of the source water entering the plant, the finished water leaving the 

plant, and at three sample points in the distribution system (near the first customer, an average 

residence time, and a maximum residence time). Plants using hypochlorite solutions were 

required to collect quarterly samples of the water entering and leaving the plant. If chlorine 

dioxide or hypochlorite solutions were used intermittently at a plant, chlorate ion samples were 

only required in sample periods in which they were in use. 

The ICR Database was considered the more appropriate data source for estimating 

average chlorate concentrations in drinking water from individual water treatment plants. The 

AwwaRF study is a less robust data set, consisting of only one sample per utility, whereas the 

ICR database included multiple samples over an 18 month period. Both the AwwaRF study and 

the ICR data reveal high concentrations of chlorate ion to be a local problem affecting a 

relatively small number of systems. 

Based on the ICR monitoring data, the Agency was able to assess exposure to chlorate in 

drinking water. The ICR data confirm the presence of chlorate in untreated source water which 

may be the result of agricultural and other uses of sodium chlorate. However, the chlorate 

concentrations in ambient water are generally very low and are minor compared to those 

observed in drinking water treated with chlorine dioxide or hypochlorite. Table 4 below 
 

 16

summarizes the annual chlorate concentrations calculated for each plant. The data listed for 

hypochlorite plants is the average chlorate concentrations, taken from samples collected at the 

entry point to a distribution system. The figures for chlorine dioxide in the next two columns 

(chlorine dioxide plans and combined hypochlorite and chlorine dioxide plants) represent the 

distribution system average chlorate concentrations. As previously explained, for chlorine 

dioxide plants, samples were collected from three points in the distribution systems; the data 

from these three collection points were used to calculate a distribution system average. 

Monitoring in the distribution system was required by the ICR, since chlorate concentrations are 

expected to change as the water travels through the distribution system. The concentration 

changes, because many of the chlorine dioxide systems use chlorine to maintain a disinfectant 

residual in the distribution system, and chlorine reacts with the chlorite ion to form chlorate ion. 

 Table 4. Distribution of Average Annual Chlorate Concentrations - ICR Data

Hypochlorite 

Plantsa

Chlorine Dioxide 

Plants b

Combined Hypochlorite 

and Chlorine Dioxide 

Plants 

Number of Public Water Systems 44 22 66 

Number of Water Treatment Plants 61 29 90 

Chlorate Concentration (μg/L) 

10th Percentile 23 52 24 

20th Percentile 37 79 53 

50th Percentile (Median) 99 129 108 

80th Percentile 155 217 179 

90th Percentile 239 264 242 

Maximum 502 691 691 

a. Concentrations for hypochlorite plants are an average of samples collected from distribution system entry 

points. 

b. For chlorine dioxide pants, the distribution system average concentration was calculated for each WTP using 

the three distribution system sample points. 

 b. Acute Dietary Risk (Drinking Water)

No acute dietary endpoint was selected because effects attributable to a single dose were 

not seen in the available data; therefore, an acute dietary (drinking water only) risk assessment 

was not conducted. 

 c. Chronic Dietary Risk (Drinking Water) 

 The chronic dietary (water only) risk assessment for chlorate in drinking water, using the 

highest annual average concentration estimated at 0.69 mg/L, is below 100% of the cPAD, and 

therefore, is below the Agency’s level of concern for the general US population and all 

population subgroups except infants (<1 year of age). The highest exposed subgroup, infants, 

was 159% of the cPAD, based on the highest annual average concentration of chlorate in Table 4 

(0.69 mg/L). Using the 90th percentile annual average concentration estimated at 0.24 mg/L, the 

chronic (non-cancer) dietary (water only) risk for infants was 55% of the cPAD. Also for 

infants, using the median annual average concentration estimated at 0.11mg/L, the risk was 25% 
 

 17

of the cPAD. See Table 5 below for details. 

 Table 5. Sum Table 5. Summary of Estimated Chronic Dietary (water only) Exposure and Risk for 

Sodium Chlorate by Average Annual Concentration in Large Drinking Water Systems 

% cPAD 

Population Subgroup cPAD 

mg/kg/day 

Water Estimated 

at the 

Highest Annual 

Average 

(0.69 mg/L) 

Water Estimated 

at the 

90th Percentile 

Annual Average 

(0.24 mg/L) 

Water 

Estimated at the 

Median Annual 

Average 

(0.11 mg/L) 

General U.S. Population 49 17 8 

All Infants (< 1 yr) 159 55 25 

Children 1-2 yrs 72 25 12 

Children 3-5 yrs 67 23 11 

Children 6-12 yrs 47 16 7 

Youth 13-19 yrs 35 12 6 

Adults 20-49 yrs 45 16 7 

Adults 50+ yrs 48 17 8 

Females 13-49 yrs 

0.03 

45 16 7 

 7. Residential Exposure and Risk 

 Residential exposure assessments consider all potential non-occupational pesticide 

exposure, other than exposure due to residues in foods or in drinking water. For sodium 

chlorate, the Agency has evaluated potential exposure and risk to sodium chlorate for 

homeowners who handle (mix, load, and apply) products containing sodium chlorate. The 

Agency also evaluated potential post-application exposure and risk to adults and children 

entering sodium chlorate-treated areas, such as lawns, or patio areas. Since the episodic nature 

of residential exposure for sodium chlorate is inconsistent with the mechanism of chlorate 

carcinogenicity, a residential cancer risk assessment was not conducted. 

To estimate residential non-cancer (dermal and inhalation) risks, the Agency calculates a 

margin of exposure (MOE), which is the ratio of the NOAEL selected for risk assessment to the 

exposure. This MOE is compared to a level of concern which is the same value as the 

uncertainty factor (UF) applied to a particular toxicity study. The standard UF is 100x (10x to 

account for interspecies extrapolation and 10x for intraspecies variation), plus any additional 

FQPA SF retained due to concerns unique to the protection of infants and children. The FQPA 

SF for sodium chlorate is reduced to1x for reasons explained above; thus, the Agency’s LOC is 

100. 

 a. Residential Handler Risks 

 The Agency determined that there is the potential for residential handlers to be exposed 

to sodium chlorate in outdoor residential settings during the application of conventional pesticide 
 

 18

products containing sodium chlorate as the active ingredient. Sodium chlorate can be used as a 

non-selective herbicide in outdoor residential environments as a spot treatment or edging 

treatment around patios, along fence lines, lawn edges, around foundations, underneath or around 

wood decks, and in cracks and crevices of driveways. Although there is the potential for dermal 

exposure by residential handlers, sodium chlorate is an inorganic salt; therefore, significant 

absorption of sodium chlorate through intact skin is not expected. Hence, only a short-term risk 

assessment for residential handlers exposed to sodium chlorate via the inhalation exposure route 

was conducted. 

The risk assessment considered seven residential exposure scenarios based on the types 

of equipment and techniques that can potentially be used to make sodium chlorate applications, 

such as handheld equipment (hand wand sprayers) and ready-to-use (RTU) methods (sprinkler 

cans). The use patterns assessed are representative of the range of sodium chlorate residential 

uses. 

The Agency considered residential handler exposure scenarios to be short-term (1-30 

days) only due to infrequency of use associated with homeowner products. The residential risk 

assessment is also based on estimates of what and how much homeowners would typically treat, 

such as the size of the lawn or garden, based on the Agency’s standard operating procedures for 

residential exposures. For more information on the daily volume handled and the area treated 

used in each residential handler scenarios, refer to Inorganic Chlorates: Residential and 

Occupational Exposure Assessment for the Reregistration Eligibility Decision Document, dated 

January 26, 2006. 

Risk to homeowners handling sodium chlorate products are below the Agency’s LOC. 

The inhalation MOEs for all scenarios assessed are greater than 100 (ranging from 370 to 

710,000). See Table 6 for further detail. 

Table 6. Sodium Chlorate Residential Risk Estimates1

Exposure Scenario (Scenario #) Daily Area 

Treated 

Crop/Target Application 

Rate 

Inhalation 

MOE2

Mixing/loading/applying liquids with a 

low pressure hand wand sprayer 

1000 ft2/day Spot/edging treatment 23.7 

 lb ai/1000 ft2

3000 

Loading/applying RTU liquid with a 

trigger pump sprayer 

1 gallon/day Spot/edging treatment 0.196 

lb ai/gallon 

87000 

Mixing/loading/applying liquids with a 

sprinkler can 

1000 ft2/day Spot/edging treatment 23.7 

lb ai/1000 ft2

5200 

Applying liquid with a RTU sprinkler 

can 

1 gallon /day Spot/edging treatment 0.27 

lb ai/gallon 

710000 

Applying granules by hand 1000 ft2

/day Spot/edging treatment 12 

lb ai/1000 ft2

370 

Loading and applying granules with a 1000 ft2/day Spot/edging treatment 12 2800 
 

 19

Table 6. Sodium Chlorate Residential Risk Estimates1

Exposure Scenario (Scenario #) Daily Area 

Treated 

Crop/Target Application 

Rate 

Inhalation 

MOE2

belly grinder lb ai/1000 ft2

Loading and applying granules with a 

push-type spreader 

1000 ft2

/day Spot/edging treatment 12 

lb ai/1000 ft2

200000 

 1. Residential exposures assessments do not include personal protective equipment (PPE). 

 2. Inhalation MOE = Oral NOAEL (30 mg/kg/day) / Daily Inhalation Dose. The LOC for MOE is 100. 

 b. Residential Post-Application Risks 

The Agency uses the term “post-application” to describe exposures to individuals that 

occur as a result of being in an environment that has been previously treated with a pesticide. 

Unlike residential handler exposure, where the EPA assumed only adults will be handling and 

applying sodium chlorate products, individuals of varying ages can potentially be exposed when 

reentering or performing activities in areas that have been previously treated. For products 

containing sodium chlorate as the active ingredient, a post-application exposure assessment was 

not conducted for the following reasons: 

• Although potential for post-application dermal exposure in residential and occupational 

settings exists, sodium chlorate is an inorganic salt; therefore, significant absorption of 

sodium chlorate through the skin is not expected. 

• Post-application inhalation exposure is not expected due to a negligible vapor pressure. 

• Post-application exposure assessments for residential settings (dermal and incidental oral) 

are not typically performed for spot treatments/edging treatments. 

 However, for products containing sodium chlorate as an inert ingredient, there is the 

potential for post-application exposure in outdoor residential settings from entering areas 

previously treated. Therefore, a residential post-application risk assessment was conducted 

based on this use. As an inert ingredient in herbicide formulations professionally broadcast on 

residential sites, there is potential for children to have incidental oral exposures (i.e., hand-tomouth, object-to-mouth, and soil ingestion). As stated above, residential post-application 

exposures via dermal and inhalation routes are not of concern. Although there is the potential for 

post-application dermal exposure in residential settings, sodium chlorate is an inorganic salt; 

therefore, significant dermal absorption of sodium chlorate through intact skin is not expected. 

Post-application inhalation exposure for sodium chlorate is not expected due to negligible vapor 

pressure. 

A series of conservative assumptions and exposure factors served as the basis for 

completing the residential post-application risk assessment, and those assumptions and factors 

are listed in detail in the previously referenced Inorganic Chlorates: Residential and 

Occupational Exposure Assessment for the Reregistration Eligibility Decision Document, dated 

January 26, 2006. The risk estimates for incidental oral exposures to sodium chlorate as an inert 

ingredient in other pesticide formulations and the highest exposed population subgroup are 
 

 20

shown in Table 7. The combined oral MOE of 23,000 is greater than 100; therefore, the risk is 

below the Agency’s level of concern. 

 

Table 7. Residential Post-application Risk Estimates for Sodium Chlorate as an Inert Ingredient in 

Herbicide Products Applied Professionally to Residential Sites

Population Subgroup Scenario Route MOE Combined MOE 

Hand-to-Mouth Oral 29000 

Object-to-Mouth Oral 110000 

 Child 

Soil Ingestion Oral 8600000 

23000 

8. Aggregate Risk 

 The FQPA amendments to the Federal Food, Drug, and Cosmetic Act (FFDCA, Section 

408(b)(2)(A)(ii)) require “that there is a reasonable certainty that no harm will result from 

aggregate exposure to the pesticide chemical residue, including all anticipated dietary exposures 

and other exposures for which there is reliable information.” Aggregate exposure will typically 

include exposures from food, drinking water, residential uses of a pesticide, and other nonoccupational sources of exposure. 

 In accordance with FQPA, the Agency must consider and aggregate pesticide exposures 

and risks from three major sources: food, drinking water, and if applicable, residential or other 

non-occupational exposures. In an aggregate assessment, exposures from relevant sources are 

added together and compared to quantitative estimates of hazard (e.g., a NOAEL), or the risks 

themselves can be aggregated. When aggregating exposures and risks from various sources, the 

Agency considers both the route and duration of exposure. Aggregate exposure and risk 

assessments for sodium chlorate include the following scenarios: short-term (food + water + 

residential handler) and chronic dietary (food + drinking water). Results of the aggregate risk 

assessment are summarized here, and are discussed more extensively in the document: Revised 

Inorganic Chlorates. HED Chapter of the Reregistration Eligibility Decision Document (RED) 

dated January 26, 2006, which is available in the public docket and on the internet. 

 a. Short-Term Aggregate Risk (food + drinking water) 

Short-term aggregate risk was assessed for adults only, using the highest exposure 

scenario (inhalation exposure while applying granules by hand). Short-term aggregate risk for 

children would be less than the short-term aggregate risk for adults (MOE of 324), because the 

short-term MOE for residential risk to children from the use of sodium chlorate as an inert is 

significantly greater (i.e., lower risk) than the residential handler short-term MOE for adults. 

Thus, all short-term aggregate risks are below the Agency’s level of concern (i.e., MOEs are 

greater than 100), as presented in Table 8. 
 

 21

 

Table 8. Short-Term Aggregate Risk Calculations

Population Target Aggregate 

MOE 

MOE 

Food + 

water 

MOE inhalation Aggregate MOE 

(food + water + residential) 

 Adult 100 1715 400 324 

 

 b. Chronic Aggregate Risk (food + drinking water)

 Since no chronic residential (non-dietary) exposure scenarios have been identified, the 

chronic aggregate risk assessment considers exposure only through food and drinking water. To 

assess aggregate risks from chronic food and drinking water exposure, the Agency used 

conservative Tier 1 chronic food estimates and incorporated drinking water monitoring data 

collected under the Information Collection Rule (ICR). For chronic aggregate dietary risks, 

using the estimated highest annual average of drinking water concentrations, food and drinking 

water chronic exposure estimates were above the Agency’s level of concern for all infants (<1 

year old), the most highly exposed population, at 174% cPAD. Chronic aggregate dietary risks 

were at the Agency’s level of concern (100 % cPAD) for children 1-2 years of age. All other 

population subgroups were <100 % cPAD, and therefore, below the Agency’s level of concern. 

At the 90th percentile and median annual average water concentration, all population subgroups 

are below the Agency’s LOC. The results of this assessment for sodium chlorate are presented 

below in Table 9. 

Table 9. Summary of Chronic Dietary Aggregate (food + drinking water) Risk for Sodium Chlorate 

% cPAD (food + drinking water) 

Population Subgroupa cPAD 

(mg/kg/day) 

Highest Annual 

Average 

(0.69 mg/L) 

90th Percentile 

Annual 

Average 

(0.24 mg/L) 

Median Annual 

Average 

(0.11 mg/L) 

General US Population 58 26 17 

All Infants (< 1 yr) 174 70 40 

Children 1-2 yrs 100 53 39 

Children 3-5 yrs 

0.03 

90 47 34 

 9. Occupational Exposure and Risk 

The occupational risk assessment addresses risks to workers who may be exposed to 

sodium chlorate when mixing, loading, or applying a pesticide (i.e., handlers), and when entering 

treated sites for routine tasks (post-application). Please see Table 2 for the toxicological 

endpoints used in the sodium chlorate occupational assessment. Based on the registered use 

patterns of sodium-chlorate, short-term (1-30 days) and intermediate-term (1-6 months) 

occupational exposures were assessed; long-term (> 6 months) exposure is not expected. 
 

 22

Exposure for workers generally occurs via the dermal or inhalation route; however, since 

sodium chlorate is an inorganic salt, and significant absorption of sodium chlorate through the 

skin is not expected, a dermal toxicological endpoint was not selected. As such, a risk 

assessment for dermal exposure was not performed. Similarly, post-application exposure was 

not assessed due to the physical and chemical characteristics of sodium chlorate as an inorganic 

salt; no significant amount of sodium chlorate is expected to be absorbed through the skin, and 

the vapor pressure is negligible. Further, for the antimicrobial use of sodium chlorate in chlorine 

dioxide generation for drinking water treatment, exposure to chlorate is expected to be negligible 

because of its conversion to chlorine dioxide inside the closed generators. Post-application 

exposure to chlorine dioxide will be addressed in the chlorine dioxide risk assessment and RED. 

The occupational assessment estimates non-cancer risks using the MOE approach. 

MOEs greater than 100 are below the Agency’s level of concern for short- and intermediate-term 

occupational exposure. 

Occupational exposure to sodium chlorate was assessed using data from the Pesticide 

Handler Exposure Database (PHED) and Outdoor Residential Exposure Task Force (ORETF). 

In addition, standard default assumptions pertaining to average body weight, work day, and area 

treated daily were used to calculate risk estimates. Application rates used in this assessment are 

derived directly from current sodium chlorate labels. Worker exposure and risk estimates are 

based on the best data currently available to the Agency. 

 The occupational risk assessment is summarized here. For further detail, see the 

following documents: (1) Revised Inorganic Chlorates. HED Chapter of the Reregistration 

Eligibility Decision Document (RED) dated January 26, 2006; (2) Inorganic Chlorates: 

Occupational and Residential Exposure Assessment for the Reregistration Eligibility Decision 

(RED) Document (Case 4049), dated June 13, 2005; and (3) Sodium Chlorate: Occupational and 

Residential Exposure Assessment of Antimicrobial Uses for the Reregistration Eligibility 

Decision Document dated January 24, 2005. 

 

a. Handler Risks

 Occupational handler exposure assessments are conducted by the Agency using different 

levels of protection. The Agency typically evaluates all exposures with minimal protection and 

then adds protective measures in a tiered approach to determine the level of protection necessary 

to obtain appropriate MOEs. The lowest level (baseline) includes long sleeve shirts, long pants, 

shoes, and socks. A single layer of PPE includes the addition of chemical-resistant gloves to the 

baseline attire of long sleeves, long pants, shoes, and socks. A respirator may also be added if 

there is a concern for inhalation exposure. If MOEs at that level of PPE are less than 100, 

increasing levels of PPE are applied (i.e., coveralls are added to provide a double layer of 

protective clothing or respirators). If MOEs are still less than 100 with maximum PPE, then 

engineering controls are applied (i.e., enclosed cabs or cockpits and closed mixing/loading 

systems). Note that the lower levels of PPE protect against dermal exposure, and dermal 

exposure is not anticipated for sodium chlorate. The types of protection, including PPE and 

engineering controls, which were used to calculate inhalation occupational exposure from 

sodium chlorate are as follows: 
 

 23

 • Baseline: No respirator 

 • PPE: Dust/mist respirator with an 80% reduction factor 

 • Engineering Controls: Enclosed cockpits or enclosed cabs 

 Anticipated use patterns and current labeling for sodium chlorate indicate several major 

occupational exposure scenarios that can result in handlers receiving inhalation exposures to 

sodium chlorate, including the antimicrobial use of sodium chlorate to generate chlorine dioxide 

for drinking water treatment. These exposure scenarios are based on the chemical formulations, 

equipment, and techniques that handlers can use to make sodium chlorate applications. 

Exposures are also considered based on their duration. The Agency assessed short- (1 to 30 

days) and intermediate-term (30 days to several months) exposures to sodium chlorate, though 

the results were essentially the same because the toxicological endpoints for short- and 

intermediate-term exposures are the same in the case of sodium chlorate. For short and 

intermediate-term exposures, MOEs greater than 100 are not of concern to the Agency. 

 Risks to handlers treating water systems are below the Agency’s level of concern, with 

inhalation MOEs of 800 to 95,000 depending on the size of the generator. All sodium chlorate 

applications to chlorine dioxide generators occur in closed delivery systems. In addition, risk for 

most occupational handler scenarios do not exceed the Agency’s level of concern of 100 (i.e, 

most scenarios had MOEs > 100) at the baseline level of protection. However, risks for the 

following occupational scenarios did exceed the Agency’s level of concern at baseline level of 

protection: 

• Mixing/Loading liquids for groundboom application to industrial/non-crop sites at 

1032 lb ai per acre (MOE = 42) and 523 lb ai per acre (MOE = 84); 

• Loading granules for tractor-drawn spreader applications to industrial/non-crop 

sites at 523 lb ai per acre (MOE = 59); 

• Applying sprays to industrial/non-crop sites using groundboom equipment (open 

cab) at 1032 lb ai per acre (MOE = 69); at 523 lb ai per acre (MOE = 140); 

• Mixing/Loading/Applying liquids for low pressure handwand applications to 

industrial/non-crop sites at 1032 lb ai per acre (MOE = 34) and 523 lb ai per acre 

(MOE = 67); and 

• Loading/Applying granules to industrial/non-crop sites using a belly grinder at 

523 lb ai per acre (MOE = 65); 

 Inhalation handler risk for these scenarios did not exceed the Agency’s level of concern 

with the addition of a dust/mist respirator (with an 80% reduction factor). Additionally, risks for 

certain scenarios were below the Agency’s level of concern, without the application of PPE or 

engineering controls, once lower application rates were used. All risks of concern were at the 

high end of application rates (>523 lb ai per acre), whereas at lower rates the risks were not of 

concern. Table 10 summarizes the risk results for short-term and intermediate-term occupational 

handlers. 
 

 24

Table 10. Sodium Chlorate: Short- and Intermediate-Term Occupational Inhalation Exposure 

Exposure 

Scenario 

Daily 

Area 

Treated1 

Crop/Target 

Application 

Rate 

(lb ai/A) 

Baseline 

Inhalation 

MOE2

PPE3 Engineering 

Controls 

Mixer/Loaders 

Cotton, Corn, Rice, Dry 

Beans, Grain Sorghum, 

Flax, Safflower, 

Sunflower, Soybeans 

7.5 190 ------- -------- 

1200 

Fallow Land, Wheat 6 240 ------- -------- 

Chili Peppers (for 

processing only), Potatoes 12.5 400 ------- -------- 

Ornamental Gourds, 

Cucurbits (grown for seed) 6 830 ------- -------- 

Mixing/Loading 

liquids for aerial 

application 

350 

Guar Beans, Southern Peas 7.5 670 ------- -------- 

Cotton, Corn, Rice, Dry 

Beans, Grain Sorghum, 

Flax, Safflower, 

Sunflower, Soybeans 

7.5 1200 ------- -------- 

200 

Fallow Land, Wheat 6 1500 ------- -------- 

Chili Peppers (for 

processing only), Potatoes 12.5 1800 ------- -------- 

Ornamental Gourds, 

Cucurbits (grown for seed) 

80 6 3600 ------- -------- 

Guar Beans, Southern Peas 7.5 2900 ------- -------- 

1032 42 210 -------- 

523 84 420 -------- 

Mixing/Loading 

liquids for 

groundboom 

application 

40 Industrial/Non-Crop Sites 

132 330 ------- -------- 

1032 340 ------- -------- 

523 670 ------- -------- 

Mixing/Loading 

liquids for rightsof-way sprayer 

application 

5 Rights-of-Way & 

Industrial/Non-Crop Sites 

132 2700 ------- -------- 

523 59 300 -------- 

240 130 ------- -------- 

Loading granules 

for tractor-drawn 

spreader 

application 

40 Industrial/Non-Crop Sites 

161 190 ------- -------- 

Applicators 

Aerial spray 

applications 

(enclosed cockpit) 

1200 

Cotton, Corn, Rice, Dry 

Beans, Grain Sorghum, 

Flax, Safflower, 

Sunflower, Soybeans 

7.50 -------- ------- 3400 
 

 25

Table 10. Sodium Chlorate: Short- and Intermediate-Term Occupational Inhalation Exposure 

Exposure 

Scenario 

Daily 

Area 

Treated1 

Crop/Target 

Application 

Rate 

(lb ai/A) 

Baseline 

Inhalation 

MOE2

PPE3 Engineering 

Controls 

Fallow Land, Wheat 6 -------- ------- 4300 

Guar Beans, Southern Peas 7.5 -------- ------- 12000 

Chili Peppers (for 

processing only), Potatoes 350 12.5 -------- ------- 7100 

Ornamental Gourds, 

Cucurbits (grown for seed) 6 -------- ------- 15000 

Cotton, Corn, Rice, Dry 

Beans, Grain Sorghum, 

Flax, Safflower, 

Sunflower, Soybeans 

7.5 1900 ------- -------- 

1200 

Fallow Land, Wheat 6 2400 ------- -------- 

Guar Beans, Southern Peas 7.5 4700 ------- -------- 

Chili Peppers (for 

processing only), Potatoes 350 12.5 2800 ------- -------- 

Ornamental Gourds, 

Cucurbits (grown for seed) 6 5900 ------- -------- 

1032 69 340 1200 (closed 

cab) 

523 140 ------- 2300 (closed 

cab) 

Groundboom 

spray applications 

40 Industrial/Non-Crop Sites 

132 540 ------- 9200 (closed 

cab) 

1032 110 ------- -------- 

Rights-of-way 523 210 ------- -------- 

sprayer 

applications 

5 Rights-of-Way & 

Industrial/Non-Crop Sites 

132 820 ------- -------- 

523 84 420 460 (closed 

cab) 

240 180 ------- 990 (closed 

cab) 

Tractor-drawn 

spreader 

applications 

40 Industrial/Non-Crop Sites 

161 270 ------- 1500 (closed 

cab) 

Flaggers 

Flagging for 

aerial spray 

applications 

350 Various Agricultural 

Crops 12.5 1400 ------- -------- 

Mixer/Loader/Applicators & Loader/Applicators 

1032 34 170 -------- 

523 67 330 -------- 

M/L/A liquids 

with a low 

pressure 

handwand sprayer 

2 Industrial/Non-Crop Sites 

132 270 ------- -------- 
 

 26

Table 10. Sodium Chlorate: Short- and Intermediate-Term Occupational Inhalation Exposure 

Exposure 

Scenario 

Daily 

Area 

Treated1 

Crop/Target 

Application 

Rate 

(lb ai/A) 

Baseline 

Inhalation 

MOE2

PPE3 Engineering 

Controls 

1032 230 ------- -------- 

523 450 ------- -------- 

M/L/A liquids 

with a handgun 

sprayer 

5 Industrial/Non-Crop Sites 

132 1800 ------- -------- 

523 65 320 -------- 

240 140 ------- -------- L/A granules with 

a belly grinder 1 Industrial/Non-Crop Sites 

161 210 ------- -------- 

523 110 ------- -------- 

240 240 ------- -------- 

L/A granules with 

a push-type 

spreader 

5 Industrial/Non-Crop Sites 

161 360 ------- -------- 

1. Amount treated is presented in acres/day. 

2. Inhalation MOE = Oral NOAEL (30 mg/kg/day) / Daily Inhalation Dose. LOC for MOE is 100. 

3. PPE dust/mist respirator with an 80% reduction factor. 

a. Incident Reports 

 Available sources of incident data in humans were reviewed for the active 

ingredients sodium chlorate and calcium chlorate (not currently registered). No data were 

found in any of the available databases on calcium chlorate, so this review exclusively 

addresses sodium chlorate. Data were available from the following sources: OPP Incident Data 

System (IDS) consisting of reports submitted to EPA by registrants, other federal and state 

health and environmental agencies, and the public, since 1992; Poison Control Centers (1993-

2001); California Department of Pesticide Regulation for pesticide poisoning since 1982; 

National Pesticide Telecommunications Network (NPTN) for ranking of the top 200 active 

ingredients for which phone calls were received during calendar years 1984-1991; and National 

Institute of Occupational Safety and Health’s Sentinel Event Notification System for 

Occupational Risks (NIOSH SENSOR) from 1998-2002. 

A total of 21 cases were recorded by the Poison Control Center from 1993 through 2001. 

Seven reported minor symptoms, and two reported moderate medical outcomes, primarily due to 

dermal effects such as swelling and rash. It is difficult to draw any conclusions from these 

reports because of the small number of cases. 

 Detailed descriptions of 36 cases submitted to the California Pesticide Illness 

Surveillance Program (1982-2002) were reviewed. However, sodium chlorate was determined to 

be the primary cause of illness in just four of these cases, and all four occurred in an agricultural 

setting (three in cotton fields and one unknown). Two of these cases were classified as systemic 

and one each involved skin or eye effects. The two systemic cases involved applicators; one 

with nausea and the other with nausea, headache, and itching skin after spraying for one week. 
 

 27

Both of these cases were classified as “possibly” due to sodium chlorate. The skin case involved 

a worker exposed to drift from an adjacent field and the eye case occurred when a worker 

bumped into a spray nozzle while getting off the tractor and was splashed in the face. The skin 

case was classified as “probably,” and the eye case as “definitely,” due to sodium chlorate. 

 A number of suicidal ingestions of sodium chlorate have been reported in the literature, 

and many of these have led to death. The chance of ingesting a fatal dose accidentally is small 

unless the compound is mistaken for a drug and taken purposely. However, a near-fatal 

poisoning occurred when a 13-year-old boy “tasted” crystals of this weed killer which he found 

in his father’s shed. In spite of intensive treatment, recovery did not begin until about the 15th

day and required a little over 40 days. 

Dermal absorption associated with agricultural use of sodium chlorate is not sufficient to 

cause systemic poisoning. Even by mouth, a large dose is required to produce illness. A 6.35% 

solution of potassium chlorate was long used as a gargle, or a 300-mg tablet was allowed to 

dissolve slowly in the mouth to treat pharyngitis before modern antibiotics became available. 

The toxicities of the sodium and potassium salts are similar. It was considered that a dose of 

10,000 mg was fatal. The smallest recorded fatal dose was 7500 mg. However, vigorous 

treatment saved one person who had ingested about 40,000 mg. 

 B. Environmental Fate and Effects Risk Assessment 

 A summary of the Agency’s environmental fate and effects risk assessment is presented 

below. For detailed discussion of all aspects of the environmental risk assessment, please see the 

Revised Environmental Fate and Ecological Risk Assessment of Sodium Chlorate, dated June 1, 

2006; it is available on the internet and in the public docket. This risk assessment was refined 

and updated to incorporate public comments and data received during the phase 3 public 

comment period. 

 

 1. Environmental Fate and Transport 

 Sodium chlorate, an inorganic salt, is not a naturally occurring chemical. It is made by 

electrolysis of brine under controlled temperature and pH conditions to optimize the efficiency of 

the process and yield. Since targeted, guideline studies designed to understand the 

environmental fate of chlorate are not available, open, peer-reviewed chemical literature and 

descriptive chemistry of the chlorine system were used as the basis for understanding the redox 

behavior of chlorate (at least on a qualitative basis) and for generating a screening-level 

environmental fate assessment. 

 Physical and chemical properties of a chemical can be used to identify potential routes of 

exposure. For example, the vapor pressure and Henry’s Law Constant provide an indication of 

the potential to volatilize from soil and water (partitioning into air), and the n-octanol/water 

partition coefficient provides an indication of the potential to bioaccumulate in fish or other 

aquatic organisms. Based on the very low vapor pressure and very high solubility of sodium 

chlorate in water, sodium chlorate is not expected to volatilize from soil or water. In addition, 

the low log n-octanol/water partition coefficient indicates that sodium chlorate has low potential 
 

 28

to bioaccumulate. 

 As stated above, sodium chlorate is highly soluble. In addition, sodium chlorate is 

completely ionized in water, thus producing sodium (Na+

) and the chlorate (ClO 3

-

) anion. 

Anions do not bind readily to soil or sediment particulates1

 and, therefore, are expected to be 

very mobile. Assuming that chlorate does not undergo any redox reactions, it is expected to be 

very mobile and to partition predominantly into the water. However, extensive redox reactions 

are expected to occur in the environment that will reduce the concentration of chlorate in the 

water column. 

 The redox chemistry2

 of chlorate affects its behavior in soils and natural water. 

Therefore, identification of the conditions under which chlorate and other oxyanions of chlorine 

may predominate is an important consideration in the environmental fate and risk assessment of 

chlorate. The oxidation-reduction reactions of chlorate with organic matter and other inorganic 

chemical species are very complex and depend on the redox conditions of the media, nature and 

concentration of reductants, chlorate concentration, temperature, pH, and degree of moisture 

(soils). For example, chlorate is generally more stable under alkaline than acidic conditions; 

however, when a chemical element (chlorine) can exist in two or more oxidation states (i.e., 

chlorite and chlorate), the redox potential of the media also effects the predominance of the 

reduction products. Nitrate concentrations in soil and water (as well as other physical and 

chemical properties of soil and water) play an important role in the redox chemistry of chlorate 

in the environment. 

 2. Ecological Exposure and Risk 

 To estimate potential ecological risk, EPA integrates the results of exposure and 

ecotoxicity studies using the risk quotient method. Risk quotients (RQs) are calculated by 

dividing acute and chronic estimated environmental concentrations (EECs) by ecotoxicity values 

for various wildlife and plant species. RQs are then compared to levels of concern (LOCs), and 

when the RQ exceeds the level of concern for a particular category, the Agency presumes a risk 

of concern to that category. See Table 11 below for the Agency’s ecological LOCs. Risk 

characterization provides further information on potential adverse effects and the possible impact 

of those effects by considering the fate of the chemical and its degradates in the environment, 

organisms potentially at risk, and the nature of the effects observed. 

 

1 Unless they chemisorb to soil or sediment particulates. Chemisorption of chlorate is unlikely. 

2

The term “redox chemistry” is used as an overall term for oxidation and reduction reactions. Other terms that are frequently 

used for oxidizers are “oxidants,” “oxidizing agents.” Reductants are frequently referred to as “reducing agents.” All redox 

reactions require an oxidant and a reductant. Reductants are electron donors, while oxidants are electron acceptors. 
 

 29

Table 11. EPA’s Ecological Levels of Concern (LOCs) and Risk Presumptions 

If a calculated RQ is greater than the LOC presented, then the Agency presumes 

that...

LOC 

terrestrial 

animals

LOC 

aquatic 

animals

LOC 

plants

Acute Risk ...there is potential for acute risk; regulatory action may be warranted in 

addition to restricted use classification 0.5 0.5 1.0 

Acute Endangered Species ...endangered species may be adversely affected 0.1 0.05 1.0 

Chronic Risk ...there is potential for chronic risk 1 1 NA 

 

a. Terrestrial Organisms 

1. Birds and Mammals 

a. Exposure 

Sodium chlorate may be applied as a spray (agricultural and nonagricultural uses) or as 

granules (nonagricultural uses only). The Agency’s methods for assessing exposure to terrestrial 

organisms are different for each of these application methods and are discussed below. 

 For spray applications, the Agency’s terrestrial exposure model (ELL-FATE) was used to 

estimate exposures and risks to avian and mammalian species. Input values on avian and 

mammalian toxicity, as well as chemical application and foliar dissipation half-life data, are 

required to run the model. The model provides estimates of both exposure concentrations and 

RQs. Specifically, the model provides estimates of concentrations (maximum and average) of 

chemical residues on the surface of different types of foliage that may be sources of exposure to 

avian, mammalian, reptilian, or terrestrial phase amphibian receptors. The surface residue 

concentration (ppm) is estimated by multiplying the application rate (pounds active ingredient 

per acre) by a value specific to each food item. In all screening-level assessments, the organisms 

are assumed to consume 100% of their diet as one food type. These exposure estimates are only 

applicable to the applied pesticide, sodium chlorate. It is uncertain to what extent exposure to 

reduced species of chlorate, such as chlorite, may occur. 

 ELL-FATE was run for sodium chlorate for use on agricultural crops using the inputs 

provided in Table 12 below. In the absence of foliar dissipation half-life data for sodium 

chlorate, the Agency’s default half-life value of 35 days was used for all scenarios. 

Table 12. Input Parameters for Sodium Chlorate Used in ELL-FATE 

Crop

Maximum labeled 

application rate 

No. of 

applications 

Application 

interval 

Chili peppers; white/Irish potatoes 12.5 lbs ai/A 1 N/A 

Cotton 7.5 lbs ai/A 2 30 days 

Corn; flax, guar; southern peas; rice; 

safflower; sorghum; soybeans; sunflower 7.5 lbs ai/A 1 N/A 
 

 30

Table 12. Input Parameters for Sodium Chlorate Used in ELL-FATE 

Crop

Maximum labeled 

application rate 

No. of 

applications 

Application 

interval 

Agricultural fallow land; dried beans; corn; 

cucurbits, flax, gourds; guar; southern peas; 

white/Irish potatoes; rice; safflower; sorghum; 

soybeans; sunflower 

6 lbs ai/A 1 N/A 

 

 The predicted upper 90th percentile and mean chlorate EECs (agricultural and nonagricultural uses) on various wild animal food items are presented in Table 13 below. 

Table 13. EECs (mg ai/kg-food item) for Terrestrial Animal Risk Assessment for Sodium Chlorate 

Crops Predicted 90th Percentile Residue Levels Predicted Mean Residue Levels

short 

grass tall grass

broadleaf 

forage, 

small 

insects

fruit, 

pods, 

seeds, 

small 

insects

short 

grass tall grass

broadleaf 

forage, 

small 

insects

fruit, 

pods, 

seeds, 

small 

insects

Agricultural Uses (Spray Applications) 

Chili peppers; 

white/Irish potatoes 3000 1400 1700 190 1100 450 560 88 

Cotton 2800 1300 1600 170 990 420 520 81 

Corn; flax, guar; 

southern peas; rice; 

safflower; sorghum; 

soybeans; sunflower 

1800 830 1000 110 640 270 340 53 

Agricultural fallow 

land; dried beans; corn; 

cucurbits, flax, gourds; 

guar; southern peas; 

white/Irish potatoes; 

rice; safflower; 

sorghum; soybeans; 

sunflower 

1400 660 810 90 510 220 270 42 

Non-Agricultural Uses (Spray Applications)

Industrial sites such as 

driveways, paths, brick 

walks, cobble gutters, 

tennis courts 

12500 5700 7000 780 4400 1900 2300 360 
 

 31

Table 13. EECs (mg ai/kg-food item) for Terrestrial Animal Risk Assessment for Sodium Chlorate 

Crops Predicted 90th Percentile Residue Levels Predicted Mean Residue Levels

short 

grass tall grass

broadleaf 

forage, 

small 

insects

fruit, 

pods, 

seeds, 

small 

insects

short 

grass tall grass

broadleaf 

forage, 

small 

insects

fruit, 

pods, 

seeds, 

small 

insects

Parking lots, fence 

lines, building 

perimeters, ditch banks, 

picnic areas, vacant 

lots, wood decks, 

bleachers, cemeteries, 

fuel tanks, runways, 

helo pads, etc. 

125,000 57,000 70,000 7800 44,000 19,000 23,000 3600 

 For granular applications, estimation of chlorate loading per unit area (mg/ft2

) is 

calculated. This approach, which is intended to represent exposure via multiple routes (e.g., 

incidental ingestion of contaminated soil, dermal contact with treated seed surfaces and soil 

during activities in the treated areas, preening activities, and ingestion of drinking water 

contaminated with pesticide) and not just direct ingestion, considers observed effects in toxicity 

studies and relates them to the amount of pesticide applied to surface area. The maximum labeled 

application rate for the active ingredient is the basis for the exposure estimate. The terrestrial 

EECs for sodium chlorate’s non-agricultural use granular applications are presented in Table 14 

below. 

Table 14. Range of Terrestrial EECs (Granular Applications) for Sodium Chlorate 

 Non-Agricultural Uses

Use Application Rate 

(lbs ai/A) EEC (mg/ft2

)

a

Parking lots, under asphalt paving, fence lines, building perimeters, 

ditch banks, picnic areas, vacant lots, wood decks, bleachers, 

cemeteries, fuel tanks, runways, helo pads, etc. 

520 5400 

Around buildings, storage areas, fences, pumps, machinery, fuel 

tanks, recreational areas, roadways, guard rails, airports, rights of 

ways. 

160 1700 

 a. EEC = Application rate (lbs/Acre) x 453,000 mg/lb ÷ 43,600 sq ft/Acre 

 b. Toxicity 

 Effects characterization describes the potential effects a pesticide can produce in a 

terrestrial organism, and is based on registrant-submitted studies that describe acute and chronic 

toxicity effects for various terrestrial animals. Table 15 summarizes the toxicity effects and 

reference values used to assess risks for sodium chlorate to mammals and birds. 
 

 32

Table 15. Toxicity Reference Values for Mammals and Birds for Sodium Chlorate. 

Exposure 

Scenario Species Toxicity Value Used in 

Risk Assessment Effect 

Mammals 

Acute Rat LD50 = > 5000 mg/kg-bw At 5000 mg/kg-bw, 1/10 animals died. 

Chronic Rat 

NOAEC = 500 mg/kg-bw, 

highest dose tested 

(approx. 10,000 ppm) 

No reproductive effects 

Birds 

Acute Mallard duck LD50 > 2510 mg/kg-bw No mortality and no clinical signs of toxicity 

were observed. 

Chronic Bobwhite 

quail NOAEC = 271 ppm 

The LOAEC was 964 ppm based on effects on 

egg production and thickness, embryonic 

survival, and hatchling body weight. 

 c. Avian Risk Estimates 

 Acute RQs for birds were not calculated, because no mortality or signs of toxicity were 

observed in the submitted subacute or acute toxicity studies at concentrations that are above the 

limit for these types of studies. 

 Avian chronic RQs for agricultural crops, at the estimated upper 90th percentile residue levels, 

are presented in Table 16 below. RQ values for all crops and all avian food items assessed, except 

the fruits, pods, seeds, and small insects category, marginally exceeded the Agency’s chronic 

LOC of 1.0. The highest chronic avian RQ was 11 (chili pepper/potato and short grass scenario). 

Chronic RQs based on mean EECs, although not presented here, would be approximately three 

times lower for most food items than those based on the 90th percentile residue levels shown 

below. 

 Table 16. Avian Chronic Risk Quotients for Sodium Chlorate Agricultural Uses

Crops Short grass Tall grass Broadleaf forage, 

small insects

Fruit, pods, seeds, 

small insects

Chili peppers; white/Irish potatoes 11.0 5.2 6.3 0.7 

Cotton 10.0 4.8 5.9 0.63 

Corn; flax, guar; southern peas; rice; 

safflower; sorghum; soybeans; 

sunflower 

6.6 3.1 3.7 0.41 

Agricultural fallow land; dried beans; 

corn; cucurbits, flax, gourds; guar; 

southern peas; white/Irish potatoes; 

rice; safflower; sorghum; soybeans; 

sunflower 

5.2 2.4 3.0 0.33 

 Chronic RQs for birds are not presented for chlorate’s non-agricultural uses (granular or 
 

 33

spray). However, RQs would be considerably higher for birds foraging where chlorate is applied 

at the rates assessed for the non-agricultural uses. EECs ranged from 12,500 to 125,000 (short 

grass food item), which would result in chronic avian RQs of 46 to 460. The size of the treated 

areas for these uses is uncertain, and this will be discussed further in Section IV of this 

document; therefore, the likelihood that a bird would consume 100% of its diet from a nonagricultural area treated with sodium chlorate is uncertain. 

 d. Mammalian Risk Estimates 

Acute RQs were not calculated for mammals. The LD50 from a core acute oral toxicity 

study in rats was >5000 mg/kg-bw. In this study, 10% (1/10) of the rats administered 5000 

mg/kg died. Mortality was not observed at any other dose. Therefore, the data were not 

sufficient to allow for characterization of the dose-response relationship and the proximity of the 

LD50 to 5000 mg/kg-bw is uncertain. For this reason, acute RQs were not calculated. However, 

Tables 17 and 18 below present a comparison of the body weight adjusted LD50s to the 

agricultural and non-agricultural EECs, respectively, based on current use rates and the spray 

application method. These ratios can be used to estimate high-end acute risk to exposed 

mammals. Actual RQs would be lower than the values in Tables 17 and 18. 

Table 17. Proximity of the lowest observed acute toxic dose in mammals to the upper 90th percentile EEC 

(mg/kg-bw) for the range of maximum application rates for all agricultural uses

Food item Size of mammal 

(grams)

Adjusted lowest 

observed toxic dose 

(mg/kg-bw)

Range of EECs 

(mg/kg-bw)a

Ratio of lowest 

observed toxic dose 

to the upper 90th 

percentile EEC 

(unitless)

15 10,989 1400 - 2900 0.13 - 0.26 

Short grass 35 8891 950 - 2000 0.11 - 0.22 

1000 3846 200 - 450 0.052 - 0.12 

15 10,989 630 - 1300 0.057 - 0.12 

Tall grass 35 8891 440 - 910 0.049 - 0.10 

1000 3846 99 - 210 0.026 - 0.055 

15 10,989 770 - 1600 0.070 - 0.15 

35 8891 540 - 1100 0.061 - 0.12 Broadleaf 

plants/small insects 

1000 3846 120 - 250 0.031 - 0.065 

15 10989 86 - 180 <0.01 - 0.016 

35 8891 59 - 120 <0.01 - 0.013 Fruits, pods, large 

insects 

1000 3846 14 - 28 <0.01 - <0.01 

a. EECs were calculated by assuming that small, medium, and large mammals consume 95%, 66%, and 15% of 

their body weight daily. Only the highest and lowest EECs from chlorate’s agricultural uses are used in this 

assessment.

For sodium chlorate’s agricultural uses, all of the acute ratios are below the Agency’s 

acute and endangered species LOC of 1.0 and 0.1, respectively, with the exception of small 
 

 34

mammals eating short grass. The highest exceedence is for 15 gram mammals eating short grass 

(ratio = 0.26). 

 Based on current non-agricultural use application rates, the only group that does not 

exceed the Agency’s acute mammalian LOC of 1.0 is animals eating fruits, pods, or large insects 

(ratios range from 0.3 to 0.7). The Agency’s acute mammalian endangered species LOC of 0.1 

is potentially exceeded for all size animals and food items. While the ratios presented in Table 

18 suggest that there could be risk to mammals of all sizes that forage in the area where chlorate 

is used for the non-agricultural spray applications, the risk was likely over-estimated, since an 

LD50 has not been established. The highest dose tested in the available toxicity studies (5000 

mg/kg-bw) induced 10% mortality. The proximity of the LD50 to 5000 mg/kg-bw is uncertain. 

Furthermore, many of the non-agricultural uses will likely result in small contiguously treated 

areas; therefore, the likelihood that an animal will consume 100% of its diet from the areas 

treated with sodium chlorate is low for some of these uses. Nonetheless, the EECs were 

predicted to be up to 11 times higher than 5000 mg/kg-bw for the non-agricultural uses. 

Therefore, there may be some acute risk to mammals at levels of concern to the Agency for nonagricultural uses. 

Table 18. Proximity of the lowest observed acute toxic dose in mammals to the predicted EEC (mg/kg-bw) 

for the range of maximum application rates for all non-agricultural uses (spray applications)

Food item

Size of 

mammal 

(grams)

Adjusted lowest observed 

toxic dose 

(mg/kg-bw)

Range of EECs 

(mg/kg-bw)a

Ratio of lowest observed toxic 

dose to the upper 90th 

percentile EEC (unitless)

15 10989 11,900 - 119,000 1.1 - 11 

Short grass 35 8891 8200 - 82,000 0.93 - 9.3 

1000 3846 1900 - 19,000 0.49 - 4.9 

15 10989 5400 - 54,000 0.49 - 4.9 

Tall grass 35 8891 3800 - 38,000 0.43 - 4.3 

1000 3846 860 - 8600 0.22 - 2.2 

15 10989 6700 - 67,000 0.61 - 6.1 

35 8891 4600 - 46,000 0.52 - 5.2 

Broadleaf 

plants/small 

insects 

1000 3846 1100 - 11,000 0.27 - 2.7 

15 10989 740 - 7400 0.07 - 0.7 

35 8891 520 - 5200 0.06 - 0.6 Fruits, pods, 

large insects 

1000 3846 120 - 1200 0.03 - 0.3 

a. EECs were calculated by assuming that small, medium, and large mammals consume 95%, 66%, and 15%, 

respectively, of their body weight daily, and were calculated using the lowest and highest labeled application rates 

(52 lbs ai/A and 520 lbs ai/A) that are most likely to result in exposure

RQs were not calculated for acute risk for non-agricultural granular applications for 

reasons previously discussed. However, Table 19 below presents a comparison of the body 

weight adjusted lowest observed toxic dose in rats (5000 mg/kg-day) to the granular application 
 

 35

EECs (mg/ft2). These ratios indicate a potential acute risk to mammals of all size classes, as the 

lowest ratio (0.43 for large mammals and the building and storage area perimeter scenario) 

exceeds the acute endangered species LOC of 0.1. 

Table 19. Range of ratios of chlorate’s body weight adjusted LD50 to granular EECs (mg/ft2) for sodium 

chlorate’s non-agricultural uses (granular formulations)

Use Body Weight 

(g)

Rat LD50

mg/kg-bw EEC (mg/ft2

)

a Ratio of LD50 

to EEC

15 10,989 5400 33 

35 8891 5400 17 

Parking lots, under asphalt paving, fence 

lines, building perimeters, ditch banks, 

picnic areas, vacant lots, wood decks, 

bleachers, cemeteries, fuel tanks, runways, 

helo pads, etc. 

1000 3846 5400 1.4 

15 10,989 1700 10 

35 8891 1700 5.4 

Around buildings, storage areas, fences, 

pumps, machinery, fuel tanks, recreational 

areas, roadways, guard rails, airports, 

rights of ways. 

1000 3846 1700 0.43 

a. EEC = Application rate (lbs/Acre) x 453,000 mg/lb ÷ 43,600 sq ft/Acre 

For mammals, the Agency typically evaluates the mammalian reproductive effects for 

exposures greater than 30 days. Interpretation of the RQs resulting from the NOAEL of 500 

mg/kg-day observed in a 2-generation rat study is difficult in this respect. Although the study 

did indicate some chronic effects, reproduction effects were not observed at any dose level 

tested. Because 500 mg/kg was the highest dose tested, it is uncertain whether there is a NOAEL 

for reproductive effects. In addition, if there is an actual NOAEL for reproductive effects, it 

could be much greater than 500 mg/kg. 

However, the Agency calculated RQs based on the 500 mg/kg-day NOAEL as a 

conservative estimate of risk, as presented in Table 20. Based on this conservative estimate, 

chronic mammalian LOC of 1.0 was only slightly exceeded for the smallest weight classes of 

mammals for most food items and the largest weight class of mammals feeding on short grass. 

Based on the lack of observed reproductive effects in the chronic study and the slight RQs 

exceedances for agricultural uses, the Agency does not anticipate a chronic risk of concern to 

mammals from agricultural uses of sodium chlorate. 

Table 20. Mammalian Chronic Risk Quotients for Sodium Chlorate’s Agricultural Uses (Spay Application)

Use Food Item 15-gram mammal 35-gram mammal 1000-gram mammal

Single application of 12.5 lbs ai/A 

Chili peppers; white/Irish 

potatoes Short Grass 2.6 2.2 1.2 
 

 36

Table 20. Mammalian Chronic Risk Quotients for Sodium Chlorate’s Agricultural Uses (Spay Application)

Use Food Item 15-gram mammal 35-gram mammal 1000-gram mammal

Single application of 12.5 lbs ai/A 

Tall Grass 1.2 1.0 0.55 

Broadleaf 

plants/small 

insects 

1.5 1.3 0.67 

Chili peppers; white/Irish 

potatoes 

Fruits/pods/large 

insects 0.16 0.14 0.07 

Multiple applications (7.5 lbs ai/A, 2 applications, 30-day interval)

Short Grass 2.4 2.1 1.1 

Tall Grass 1.1 0.95 0.51 

Broadleaf 

plants/small 

insects 

1.4 1.2 0.62 

Cotton 

Fruits/pods/large 

insects 0.15 0.13 0.07 

Single application (7.5 lbs ai/A)a

Short Grass 1.6 1.3 0.72 

Tall Grass 0.72 0.61 0.33 

Broadleaf 

plants/small 

insects 

0.88 0.75 0.40 

Corn; flax, guar; southern peas; 

rice; safflower; sorghum; 

soybeans; sunflower 

Agricultural fallow land; dried 

beans; corn; cucurbitsa, flax, 

gourds; guar; southern peas; 

white/Irish potatoes; rice; 

safflower; sorghum; soybeans; 

sunflower 

Fruits/pods/large 

insects 0.10 0.08 0.04 

a. EECs and RQs are similar for the 7.5lbs a.i/A (corn, et al.) and 6.0 lbs a.i./A (agricultural fallow land, et al.) and 

single applications, and LOC exceedances are equivalent; therefore, only results from the single application of 7.5 

lbs ai/A are presented. 

Reproduction RQs were not calculated for chlorate’s non-agricultural uses (spray or 

granular applications). However, based on the high application rates and resulting high potential 

EECs, risks from chlorate’s non-agricultural uses could be considerably higher than risks 

presented for agricultural uses. 

 2. Non-Target Insects 

 EPA currently does not estimate RQs for terrestrial non-target insects. Furthermore, the 

Agency has no insect toxicity data for sodium chlorate. 
 

 37

 3. Non-Target Terrestrial Plants 

 Based on chlorate’s non-selective mode of action and lack of adequate toxicity data, the 

Agency presumes risk to non-target terrestrial plants at levels above the Agency’s level of 

concern for all uses. The risks to plants cannot be quantified at this time due to lack of data; 

however, the Agency will require data to address this uncertainty. 

b. Aquatic Organisms 

At the present time, there is no methodology to estimate exposure concentrations in water 

for non-metal inorganic chemical species that can be found in different oxidation states (e.g., for 

inorganic chemical species that can exhibit extensive pH-pE dependent redox chemistry, such as 

the chlorine system). As an approximation on the impact of chlorate on surface water quality, 

the Tier I GENEEC-2 simulation model was used to estimate exposure concentrations in aquatic 

systems. Extreme assumptions in the environmental persistence of chlorate were made that 

resulted in high-end exposure concentrations in the standard ecological pond scenario. The 

predicted chlorate concentrations are believed to be high because the chemical speciation of 

chlorate was not considered in the assessment. As previously discussed, under thermodynamic 

equilibrium conditions, chloride is likely the predominant species in natural environments. This 

analysis, however, indicates that chlorate can be reduced to chloride, but not how fast the 

reduction will occur. Since there are no input parameters for the model that take into account the 

redox behavior of chlorate, it was assumed that unchanged chlorate runs off into surface water, 

where it remains as chlorate. 

 Unlike the drinking water assessment described in the human health risk assessment 

section of this document, the exposure values used in the ecological risk assessment do not 

include the Index Reservoir (IR) and Percent Cropped Area (PCA) factor refinements. These 

factors represent a drinking water reservoir, not the variety of aquatic habitats relevant to a risk 

assessment for aquatic animals, such as ponds adjacent to treated fields. Therefore, the EEC 

values used to assess exposure and risk to aquatic animals are not the same as those used to 

assess exposure and risk to humans from pesticides in drinking water. 

 1. Fish 

 

Acute toxicity studies for both freshwater and marine/estuarine fish were consistent with 

a “practically non-toxic” designation for fish. No effects were observed in sheepshead minnows 

(estuarine/marine) or bluegill (freshwater) fish at up to 1000 mg/L. For inorganic chlorates, RQs 

were not calculated for freshwater or estuarine/marine fish, since the proximity of the LC50 to the 

highest concentration tested (1000 mg/L) could not be estimated. Although 1000 mg/L is not an 

LC50, which is the toxicity value usually used to derive RQs, this value was used only to estimate 

high-end risk to exposed fish. EECs for both agricultural and nonagricultural uses of sodium 

chlorate were more than 20-fold lower than the toxic concentration observed in fish of 1000 

mg/L (all RQs would be less than 0.05, and below the Agency’s acute LOC of 0.5 and the acute 

endangered species LOC of 0.05). Therefore, acute risk to freshwater and estuarine/marine fish 

is not of concern to the Agency. 

 No chronic toxicity studies in fish have been submitted to the Agency, nor were any 
 

 38

identified in the ECOTOX database. However, the Agency will require data to address this area 

of uncertainty. 

 

2. Aquatic Invertebrates 

For freshwater invertebrates, acute RQs are based on the EC50 of 920 mg/L (daphnids) 

and EECs calculated by GENEEC-2; these are presented in Table 21 below. All RQs are below 

the acute LOC of 0.5 and the endangered species acute LOC of 0.05; therefore, acute risk to 

freshwater invertebrates is not of concern to the Agency. 

Table 21. Acute Freshwater Aquatic Invertebrate Risk Quotients 

Use Application Rate Range Maximum EEC EC50 RQ

Agricultural uses 4.5–7.5 lb ai/A 0.91 mg/L 920 mg/L <0.01 

Non-agricultural uses 132–520 lb ai/A 39 mg/L 920 mg/L <0.042 

For saltwater invertebrates, acute RQs were not calculated, because the proximity of the 

LC50 from a supplemental 96-hr study (mysid shrimp) to the highest concentration tested (1000 

mg/L), could not be estimated. However, the ratios of chlorate’s EECs (agricultural and 

nonagricultural uses) to the concentration of 1000 mg/L were calculated, and the highest 

resulting value was 0.04. As this is well below the acute LOC of 0.5, in addition to the 

endangered species acute LOC of 0.05, acute risk to saltwater invertebrates is not of concern to 

the Agency. 

 Chronic risk to invertebrates was not assessed, since treatment-related effects were not 

observed at any concentration in available studies. 

 3. Aquatic Plants 

Toxicity (EC50) and exposure (EEC) values, as well as RQs, for non-endangered aquatic 

plants are shown in Tables 22. For non-endangered aquatic plants, the Agency calculates RQs 

by dividing EECs by EC50 values.. For sodium chlorate, the LOC (1.0) was not exceeded for 

either the agricultural or nonagricultural uses of chlorate; therefore, risk to non-endangered 

aquatic plants is not of concern to the Agency. 

 Table 22. Risk Quotients for Non-endangered Aquatic Plants 

Use Maximum Peak 

EEC Algal EC50 Duckweed EC50 Algal RQ Duckweed RQ

Agricultural Up to 0.9 mg/L 133 mg/L 43 mg/L <0.01 0.02 

Non-agricultural Up to 39 mg/L 133 mg/L 43 mg/L Up to 0.29 0.91 

The RQs for endangered aquatic plants are presented in Table 23. The Agency calculates 
 

 39

RQs for endangered aquatic plants by dividing EECs by NOAECs. For endangered aquatic 

plants, the Agency’s LOC (1.0) was exceeded for sodium chlorate’s non-agricultural uses (RQ = 

12.6). However, the EECs for the non-agricultural use sites are likely conservative; therefore, 

additional information on use patterns would allow for characterization of potential risks to 

aquatic plants. Also, testing on three additional required plant species is required for herbicides. 

Overall, additional data are needed to allow for a full characterization of potential risk to aquatic 

plants. 

 Table 23. Endangered Species Algal Risk Quotients Agricultural and Non-Agricultural Uses 

Use Maximum Peak 

EEC Algal EC50 Duckweed EC50 Algal RQ Duckweed RQ

Agricultural Up to 0.9 mg/L 62.5 mg/L 3.1 mg/L Up to 0.014 Up to 0.29 

Non-Agricultural Up to 39 mg/L 62.5 mg/L 3.1 mg/L Up to 0.62 Up to 12.6 

 c. Endangered Species 

 

The Agency’s screening level assessment results in the determination that sodium 

chlorate will have no acute risks to birds, no acute risks to fish (freshwater and estuarine/marine), 

and no acute or chronic risks to aquatic invertebrates (freshwater and estuarine/marine). 

 However, the preliminary risk assessment for endangered species indicates that RQs 

exceed endangered species LOCs for chronic risks to birds (RQs up to 11 for agricultural uses 

and greater for non-agricultural uses); acute risks to mammals (RQs up to 33); chronic risks to 

mammals (RQs up to 1.2 for agricultural uses and greater for non-agricultural uses); and risks to 

aquatic plants (RQs up to 13). Risks could not be calculated for terrestrial plants and for chronic 

risks to fish; however, the Agency will be requiring data. 

 Further, potential indirect effects to any species dependent upon a species that 

experiences effects from use of sodium chlorate can not be precluded based on the screening 

level ecological risk assessment. These findings are based solely on EPA’s screening level 

assessment and do not constitute “may affect” findings under the Endangered Species Act. 

 d. Ecological Incidents 

 A review of the Ecological Incident Information System (EIIS) database for ecological 

incidents involving chlorate was completed on October 25, 2004. There were no chlorate incidents in 

the database 
 

 40

IV. Risk Management, Reregistration, and Tolerance Reassessment 

 A. Determination of Reregistration Eligibility 

 Section 4(g)(2)(A) of FIFRA calls for the Agency to determine, after submission of 

relevant data concerning an active ingredient, whether or not products containing the active 

ingredient are eligible for reregistration. The Agency has previously identified and required the 

submission of the generic (i.e., active ingredient-specific) data required to support reregistration 

of products containing sodium chlorate as an active ingredient. The Agency has completed its 

review of these generic data, and has determined that the data are sufficient to support 

reregistration of all products containing sodium chlorate. 

 The Agency has completed its assessment of the dietary, occupational, residential, and 

ecological risk associated with the use of pesticide products containing the active ingredient 

sodium chlorate. Based on a review of these data and on public comments on the Agency’s 

assessments for the active ingredient sodium chlorate, the Agency has sufficient information on 

the human health and ecological effects to make decisions as part of the tolerance reassessment 

process under FFDCA and reregistration process under FIFRA, as amended by FQPA. The 

Agency has determined that sodium chlorate-containing products are eligible for reregistration 

provided that: (i) the risk mitigation measures outlined in this document are adopted, (ii) label 

amendments are made to reflect these measures, and (iii) a safety finding can be made for 

sodium chlorite. Label changes are described in Section V. Appendix A summarizes the uses of 

sodium chlorate that are eligible for reregistration. Appendix B identifies the generic data 

requirements that the Agency reviewed as part of its determination of reregistration eligibility of 

sodium chlorate, and lists the submitted studies that the Agency found acceptable. Data gaps are 

identified as generic data requirements that have not been satisfied with acceptable data. 

 Based on its evaluation of sodium chlorate, the Agency has determined that sodium 

chlorate products, unless labeled and used as specified in this document, would present risks 

inconsistent with FIFRA. Accordingly, should a registrant fail to implement any of the risk 

mitigation measures identified in this document, the Agency may take regulatory action to 

address the risk concerns from the use of sodium chlorate. If all changes outlined in this 

document are incorporated into the product labels, then all current risks for sodium chlorate will 

be adequately mitigated for the purposes of this determination under FIFRA. Once an 

Endangered Species assessment is completed, further changes to these registrations may be 

necessary as explained in Section III.B.2.c. of this document.

 

B. Public Comments and Responses

 Through the Agency’s public participation process, EPA worked with stakeholders and 

the public to reach the regulatory decisions for sodium chlorate. EPA released its sodium chlorate 

preliminary risk assessments for public comment on February 1, 2006, for a 60-day public comment 

period (Phase 3 of the public participation process). During the public comment period on the risk 

assessments, which closed on April 3, 2006, the Agency received comments from the sodium 

chlorate task force, technical registrants, and private citizens. These comments in their entirety, 
 

 41

responses to the comments, as well as the preliminary and revised risk assessments, are available 

in the public docket (OPP-2005-0507) at http:www.regulations.gov. 

 C. Regulatory Position

1. Food Quality Protection Act Findings 

 a. “Risk Cup” Determination 

 As part of the FQPA tolerance reassessment process, EPA assessed the risks associated 

with this pesticide. The Agency has determined that, if the mitigation described in this document 

is adopted and labels are amended, and a safety finding can be made for sodium chlorite, human 

health risks as a result of exposures to sodium chlorate are within acceptable levels. In other 

words, EPA has concluded that the exemptions from tolerances for sodium chlorate meet FQPA 

safety standards. In reaching this determination, EPA has considered the available information 

on the special sensitivity of infants and children, as well as exposures to sodium chlorate from all 

possible sources. 

 b. Determination of Safety to U.S. Population 

 The Agency has determined that provided a safety finding can be made for sodium 

chlorite, the Agency has determined that the established tolerance exemptions for sodium 

chlorate, with amendments and changes as specified in this document, meet the safety standards 

under the FQPA amendments to section 408(b)(2)(D) of the FFDCA, and that there is a 

reasonable certainty no harm will result to the general population or any subgroup from the use 

of sodium chlorate. In reaching this conclusion, the Agency has considered all available 

information on the toxicity, use practices and exposure scenarios, and the environmental 

behavior of sodium chlorate. As discussed in Section III, the acute, chronic, and cancer dietary 

(food and drinking water) risks from sodium chlorate are below the Agency’s acute and chronic 

LOC, provided that mitigation measures outlined in this document are adopted and labels are 

amended. 

 c. Determination of Safety to Infants and Children 

 EPA has determined that the established tolerance exemptions for sodium chlorate, with 

amendments and changes as specified in this document, and provided that a safety finding can be 

made for sodium chlorite, meet the safety standards under the FQPA amendments to section 

408(b)(2)(C) of the FFDCA, that there is a reasonable certainty of no harm for infants and 

children. The safety determination for infants and children considers factors on the toxicity, use 

practices and environmental behavior noted above for the general population, but also takes into 

account the possibility of increased dietary exposure due to the specific consumption patterns of 

infants and children, as well as the possibility of increased susceptibility to the toxic effects of 

sodium chlorate residues in this population subgroup. 

In determining whether or not infants and children are particularly susceptible to toxic 

effects from exposure to residues of sodium chlorate, the Agency considered the completeness of 
 

 42

the hazard database for developmental and reproductive effects, the nature of the effects 

observed, and other information. On the basis of this information, the FQPA SF has been 

reduced to 1X for sodium chlorate. The rationale for the decisions on the FQPA SF can be found 

in Section III and the following document: HED Chapter of the Reregistration Eligibility 

Decision Document (RED), dated January 26, 2006. 

 2. Endocrine Disruptor Effects 

 EPA is required under the FFDCA, as amended by FQPA, to develop a screening 

program to determine whether certain substances (including all pesticide active and other 

ingredients) “may have an effect in humans that is similar to an effect produced by a naturally 

occurring estrogen, or other endocrine effects as the Administrator may designate.” Following 

recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee 

(EDSTAC), EPA determined that there was a scientific basis for including, as part of the 

program, the androgen and thyroid hormone systems, in addition to the estrogen hormone 

system. EPA also adopted EDSTAC's recommendation that EPA include evaluations of 

potential effects in wildlife. For pesticides, EPA will use FIFRA and, to the extent that effects in 

wildlife may help determine whether a substance may have an effect in humans, FFDCA 

authority to require the wildlife evaluations. As the science develops and resources allow, 

screening for additional hormone systems may be added to the Endocrine Disruptor Screening 

Program (EDSP). 

 The available toxicity studies on sodium chlorate demonstrate the thyroid gland to be its 

target of toxicity. The endpoints selected to assess chronic dietary risk and short- and 

intermediate-term oral and inhalation risks in this document are protective of the observed 

thyroid effects seen in the available toxicity studies. When additional appropriate screening 

and/or testing protocols being considered under the Agency’s EDSP have been developed, 

sodium chlorate may be subjected to further screening and/or testing to better characterize effects 

related to endocrine disruption. 

 3. Cumulative Risks 

The FFDCA, as amended by the FQPA, requires that the Agency consider “available 

information” concerning the cumulative effects of a particular pesticide’s residues and “other 

substances that have a common mechanism of toxicity.” The reason for consideration of other 

substances is due to the possibility that low-level exposures to multiple chemical substances that 

cause a common toxic effect by a common toxic mechanism could lead to the same adverse 

health effect as would a higher level of exposure to any of the substances individually. The EPA 

has not made a common mechanism of toxicity finding as to sodium chlorate and any other 

substances. For the purposes of this reregistration eligibility decision (RED), therefore, EPA has 

not assumed that the inorganic chlorates have a common mechanism of toxicity with other 

substances. For information regarding EPA’s efforts to determine which chemicals have a 

common mechanism of toxicity and to evaluate the cumulative effects of such chemicals, see the 

policy statements released by EPA’s Office of Pesticide Programs concerning common 

mechanism determinations and procedures for cumulating effects from substances found to have 

a common mechanism on EPA’s website at http://www.epa.gov/pesticides/cumulative/. 
 

 43

 4. Endangered Species 

 The Agency’s screening-level assessment results in the determination that sodium 

chlorate will have no acute risks to birds, no acute risks to fish (freshwater and estuarine/marine), 

and no acute or chronic risks to aquatic invertebrates (freshwater and estuarine/marine). 

 However, the preliminary risk assessment for endangered species indicates that RQs 

exceed endangered species LOCs for chronic risks to birds (RQs up to 11 for agricultural uses 

and greater for non-agricultural uses); acute risks to mammals (RQs up to 33); chronic risks to 

mammals (RQs up to 1.2 for agricultural uses and greater for non-agricultural uses); and risks to 

aquatic plants (RQs up to 13). Risks could not be calculated for terrestrial plants and for chronic 

risks to fish; however, the Agency will be requiring data. 

 Further, potential indirect effects to any species dependent upon a species that 

experiences effects from use of sodium chlorate cannot be precluded based on the screeninglevel ecological risk assessment. These findings are based solely on EPA’s screening-level 

assessment and do not constitute “may affect” findings under the Endangered Species Act. 

 The Agency has developed the Endangered Species Protection Program to identify 

pesticides whose use may cause adverse impacts on endangered and threatened species, and to 

implement mitigation measures that address these impacts. The Endangered Species Act (ESA) 

requires federal agencies to ensure that their actions are not likely to jeopardize listed species or 

adversely modify designated critical habitat. To analyze the potential of registered pesticide uses 

that may affect any particular species, EPA uses basic toxicity and exposure data developed for 

the REDs and considers it in relation to individual species and their locations by evaluating 

important ecological parameters, pesticide use information, geographic relationship between 

specific pesticide uses and species locations, and biological requirements and behavioral aspects 

of the particular species, as part of a refined species-specific analysis. When conducted, this 

species-specific analysis will take into consideration any regulatory changes in this RED that are 

being implemented at that time. 

 Following this future species-specific analysis, a determination that there is a likelihood 

of potential impact to a listed species or its critical habitat may result in: limitations on the use 

of sodium chlorate, other measures to mitigate any potential impact; or consultations with the 

Fish and Wildlife Service or the National Marine Fisheries Service as necessary. If the Agency 

determines use of sodium chlorate “may affect” listed species or their designated critical habitat, 

EPA will employ the provisions in the Services regulations (50 CFR Part 402). Until that 

species-specific analysis is completed, the risk mitigation measures being implemented through 

this RED will reduce the likelihood that endangered and threatened species may be exposed to 

sodium chlorate at levels of concern. EPA is not requiring specific sodium chlorate label 

language at the present time relative to threatened and endangered species. If, in the future, 

specific measures are necessary for the protection of listed species, the Agency will implement 

them through the Endangered Species Protection Program. 
 

 44

 D. Tolerance Reassessment Summary 

Table 24 summarizes the reassessment of the sodium chlorate tolerance exemptions 

pending a safety finding can be made for sodium chlorite. 40 CFR must be updated to reflect the 

tolerance exemptions in the table below. The tolerance exemptions listed in 40 CFR must be 

reorganized in order to: (i) incorporate the recommendations made by the Agency concerning the 

sodium chlorate residues of concern that need to be regulated for plant and animal commodities; 

(ii) include tolerance exemptions that are needed to cover sodium chlorate residues of concern 

in/on the raw agricultural commodities and processed commodities of rotational crops; and (iii) 

conform with the requirements of FQPA. 

 

Table 24. Tolerance Reassessment Summary for Sodium Chlorate 

Listed under 40 CFR 180.1020(a)

Commodity 

Current 

Tolerance 

(ppm) 

Tolerance 

Reassessment 

(ppm) 

[Correct Definition] 

Comments 

Beans, dry, edible Exempt Exempt [Bean, dry, seed] 

Corn, fodder Exempt 

Corn, forage Exempt 

Corn, grain Exempt 

Exempt 

[Corn, field, stover; Corn, field, forage; Corn, field, 

grain; Corn, sweet, stover; Corn, pop, stover; Corn, 

pop, grain; Corn, sweet, forage] 

Cottonseed Exempt Exempt [Cotton, undelinted seed] 

Flaxseed Exempt Exempt [Flax, seed] 

Flax, straw Exempt Revoke Flax straw is not listed in Table 1 of OPPTS 

860.1000 

Guar beans Exempt Exempt [Guar, seed] 

Peas, southern Exempt Exempt [Pea, southern, seed] 

Potatoes Exempt Exempt [Potato] 

Peppers, chili Exempt Exempt [Pepper, nonbell] 

Rice Exempt 

Rice, straw Exempt 

Exempt [Rice, grain; Rice, straw] 

Safflower, grain Exempt Exempt [Safflower, seed] 

Sorghum, grain Exempt 

Sorghum, fodder Exempt 

Sorghum, forage Exempt 

Exempt 

[Sorghum grain, grain; Sorghum, grain, stover; 

Sorghum, grain, forage] 

Soybeans Exempt Exempt [Soybean, seed] 
 

 45

Table 24. Tolerance Reassessment Summary for Sodium Chlorate 

Listed under 40 CFR 180.1020(a)

Sunflower seed Exempt Exempt [Sunflower, seed] 

Wheat None Exempt [Wheat, grain] 

Listed under 40 CFR 180.1020(b)

Wheat Exempt Revoke [Wheat, grain] Time-limited exemption currently 

expires on 12/31//2006 

Existing Exemptions 

 Sodium chlorate is currently registered for preharvest and foliar applications as a 

defoliant or desiccant to the following food/feed crops: beans, corn, cotton, flax, guar, chili 

peppers, potatoes, rice, safflower, sorghum (grain), southern peas (i.e., cowpeas), soybeans, and 

sunflowers. 

 Sodium chlorate exemptions under 40 CFR 180.1020(a) from the requirement of a 

tolerance should be amended as follows to: (1) specify defoliant and desiccant use only, (2) 

specify use on crops rather than raw agricultural commodities, and (3) include an exemption for 

wheat (grain). 

40 CFR 180.1020(a) Sodium chlorate is exempt from the requirement of a tolerance for residues 

when used as a defoliant or desiccant in accordance with good agricultural practice on the 

following crops: Bean (dry, seed), Corn (field, stover), Corn (field, forage), Corn (field, grain), 

Corn (sweet, stover), Corn (pop, stover), Corn (pop, grain); Corn (sweet, forage), Cotton 

(undilented seed), Flax (seed), Guar (seed), Peas (southern, seed), Peppers (nonbell), Potatoes,

Rice (grain), Rice (straw), Safflower (seed), Sorghum (grain, grain), Sorghum (grain, stover), 

Sorghum (grain, forage), Soybean (seed), and Sunflower (seed). 

 Under 40 CFR 180.1020(b), a time-limited exemption from the requirement of a 

tolerance is established for residues of the defoliant/desiccant in connection with use of the 

pesticide under section 18 emergency exemptions granted by EPA. This exemption was granted 

for wheat and expires 12/31/06. The use of sodium chlorate on wheat is also addressed herein 

with the intention to convert the time-limited exemption status to a permanent exemption from 

the requirement of a tolerance under 40 CFR.1020 (a). The proposed use rate is for a single 

application of sodium chlorate to wheat at 6 lbs ai/A with a 3-day PHI. 

Needed Exemptions

 Sodium chlorate (873301) as an inert ingredient in herbicide formulation products can be 

applied professionally to agricultural (corn, guava, macadamia nuts, sorghum grain, sugarcane, 

wheat), commercial (non-agricultural), and residential sites. These conventional pesticide 

products contain < 1 % sodium chlorate and can be applied at rates no greater than 0.07 lb (as 

sodium chlorate) per acre. 
 

 46

 Potassium chlorate (900583) as an inert ingredient in fungicide products can be applied in 

poultry premises. These conventional pesticide products contain < 20% potassium chlorate and 

can be applied at rates not greater than 0.01 lb (as potassium chlorate) per 500 ft3

. See Table 25 

below for the tolerance exemptions needed for sodium chlorate. 

Table 25. Tolerance Exemptions Needed for sodium chlorate

Tolerance Exemption 

Expression

PC Code CAS Reg No. 40 CFR § Use 

(Pesticidal)

List 

Classification

Sodium chlorate 873301 7775-09-9 180.920 1 Stabilizer 3 

Potassium chlorate 900583 3811-04-9 180.930 2 Oxidizer 3 

1. Residues listed in 40 CFR §180.920 [formerly 40 CFR§ 180.100(d)] are exempted from the requirement of a 

tolerance when used in accordance with good agricultural practice as inert (or occasionally active) ingredients in 

 pesticide formulations applied to growing crops only. 

2. Residues listed in 40 CFR §180.930 [formerly 40 CFR§ 180.100(e)] are exempted from the requirement of a 

tolerance when used in accordance with good agricultural practice as inert (or occasionally active) ingredients in 

pesticide formulations applied to animals. 

Codex/International Harmonization

 There are no Codex maximum residue limits (MRLs) for sodium chlorate. 

E. Regulatory Rationale 

 The following is a summary of the rationale for managing risks associated with the use of 

sodium chlorate for sodium chlorate products to be eligible for reregistration. Where labelling 

revisions are warranted, specific language is set forth in Table 28 of Section V. 

 1. Human Health Risk Management 

 a. Dietary (Food) Risk Mitigation 

Acute Dietary (Food) Risk

 No acute dietary endpoint was selected for sodium chlorate, because effects attributable 

to a single dose were not seen in the available data. Therefore, dietary acute risk is not of 

concern to the Agency, and no mitigation measures are required to address acute risk. 

Chronic Dietary (Food) Risk

The chronic dietary risk assessment for food only is below the Agency’s level of concern 

(LOC) for the general US population and all population subgroups. The most highly exposed 

population subgroup, children 1-2 years of age, was at 28% of the chronic Population Adjusted 

Dose (cPAD). Since this is less than 100% of the cPAD, no mitigation is needed. 
 

 47

b. Residential Risk Mitigation 

 

All residential (non-occupational) handler and post-application risk estimates for 

inorganic chlorates, as active or inert ingredients in conventional pesticide products used in 

residential environments, are below the Agency’s LOC (i.e., MOEs are greater than the LOC of 

100). The handler inhalation MOEs ranged from 370 to 710,000. The post-application 

combined MOE (for inert ingredients) was 23,000 for all potential routes of exposure to children; 

therefore, no residential mitigation is necessary. 

 c. Aggregate Risk Mitigation 

As discussed in Section III of this RED, aggregate risk refers to the combined risk from 

food, drinking water, and residential exposures. Aggregate risk can result from one-time (acute), 

short-term and/or chronic exposures. 

Acute Aggregate Risk 

For sodium chlorate, acute aggregate risk was not assessed, because effects attributable to 

a single dose were not seen in the available data. Therefore, acute aggregate risk is not of 

concern to the Agency. 

Short-Term Aggregate Risk 

Short-term aggregate risk was quantitatively assessed for adults only, using the highest 

exposure scenario (inhalation exposure while applying granules by hand) resulting in an MOE of 

324. Short-term aggregate risk for children was qualitatively assessed and not of concern to the 

Agency because the short-term residential risk to children from the use of sodium chlorate as an 

inert is minimal (MOE of 23,000). All short-term aggregate risks are below the Agency’s LOC 

(i.e., MOEs are greater than 100); therefore, no mitigation is necessary. 

Chronic Aggregate Risk 

Since no chronic residential (non-dietary) exposure scenarios have been identified for 

sodium chlorate, the chronic aggregate risk assessment considers exposure only through food 

and drinking water. The Agency believes there is no chronic risk of concern, for the US general 

population or any subpopulation group, for the reasons described below. 

The chronic dietary (water only) risk assessment for chlorate in drinking water, using the 

highest annual average concentration from ICR data of 0.69 mg/L, is below the Agency’s level 

of concern for the general US population and all subgroups except all infants <1 year of age. 

The highest exposed population subgroup, all infants <1 year of age, was 159% of the cPAD. 

Using the 90th percentile annual average concentration of 0.24 mg/L, the chronic dietary (water 

only) risk for all infants <1 year of age was <55% of the cPAD; using the median annual average 

concentration estimated at 0.11 mg/L, estimated chronic risk from drinking water was 25% of the 

cPAD. The contribution of exposure from food sources increases total dietary risk (food + 

drinking water) to 174% of the cPAD for infants <1 year of age at the highest annual average, 
 

 48

but remains below EPA’s level of concern at the 90th percentile (70% of the cPAD). 

 Data on the occurrence of chlorate ion in drinking water were available from two primary 

sources: the Information Collection Rule (ICR) Auxiliary 1 Database, Version 5.0, and the 

AwwaRF research study on the control of chlorate ion in hypochlorite solutions. The most 

extensive data are from the ICR where source water and drinking water were monitored for 

chlorate ion between July 1997 and December 1998. Water systems serving a population of at 

least 100,000 were required to monitor for chlorate ion at treatment plants using chlorine dioxide 

or hypochlorite solutions in the treatment process. Although the ICR water systems represent 

roughly one percent of the total number of drinking water systems in the United States, these 

systems serve almost 60% of the population. Under the ICR, plants using chlorine dioxide 

collected monthly samples of the source water entering the plant, the finished water leaving the 

plant, and at three sample points in the distribution system (near the first customer, an average 

residence time, and a maximum residence time). Samples were taken throughout the distribution 

systems for plants using chlorine dioxide, since the concentration of chlorate is expected to 

change within the system due to the conversion of chlorine dioxide to chlorate that occurs in the 

presence of chlorine. Plants using hypochlorite solutions were required to collect quarterly 

samples of the water entering and leaving the plant. 

 The AwwaRF data consists of samples collected in 1993 by 111 water treatment plants 

using hypochlorite. The majority of the systems in the AwwaRF project serve populations less 

than 100,000, and a large subset of those serve populations less than 10,000. Samples of source 

water, hypochlorite solution, and finished drinking water from 111 of water systems were 

analyzed for chlorate. Only one set of samples was collected for each system, and samples were 

not collected at plants using chlorine dioxide. Furthermore, the background information on the 

111 water systems that participated in the project was not linked to the samples they provided; 

therefore, the chlorate concentrations can not be directly related to the size of the water system or 

type of hypochlorite solution in use. 

 The AwwaRF samples were typically found to have higher concentrations of chlorate 

than the samples collected from the larger ICR systems. The difference in chlorate 

concentrations could be the result of a number of factors, such as: 1) The AwwaRF data 

represents a single point in time, while the ICR data reflects an average over 18 months; 2) most 

of the AwwaRF samples were collected from utilities that served populations of less that 

100,000, while all of the ICR samples were from utilities serving at least 100,000; and 3) 

hypochlorite treatment plant practices may have changed between when the AwwaRF samples 

were collected (1993) and the ICR samples were collected (1997-1998). When the AwwaRF 

study was conducted, utilities were just becoming aware of the formation of chlorate ion in 

hypochlorite solutions. The AwwaRF project was funded in order to provide water treatment 

facilities with information on how to minimize the formation of chlorate byproduct; it is possible 

that facilities consequently revised their treatment practices. 

 The ICR Database was considered the more appropriate source for estimating exposure 

averages from individual water treatment plants, primarily because the AwwaRF study is a less 

robust data set consisting of only one sample per utility, whereas the ICR database collected 

multiple samples over an 18 month period, from plants using both hypochlorite and chlorine 
 

 49

dioxide. Both the AwwaRF study and the ICR data reveal high concentrations of chlorate ion to 

be a local situation affecting a relatively small number of systems. Of the ICR data set, only four 

water treatment plants had average chlorate ion concentrations that exceeded the Agency’s level 

of concern (i.e., 370 ppb or 0.37 mg/L, for the infant subpopulation) including one treatment 

plant serving 218,000 people that had the highest annual average (0.69 mg/L). Of the four plants 

that exceeded, two treatment plants used chlorine dioxide, and two used hypochlorite. The total 

number of people served by the four water treatment plants exceeding 0.37 mg/L represents 

0.5% of the ICR population, or 621,000 people. All three exposure ranges (highest average, 90th

percentile, and median) are presented in Section III. Only the “highest average” exposures 

resulted in potential chronic risk estimates that were above the Agency’s LOC, and only for 

infants. Over 99% of the ICR population receives finished water below the Agency’s LOC of 

0.37 mg/L. 

 

The chlorate ion (ClO 3

-

) is a disinfection byproduct (DBP) of water treatment which can 

be formed during the on-site generation of chlorine dioxide (ClO 2

-

), the decomposition of 

chlorine dioxide in the water treatment system, the decomposition of hypochlorite (OCl-) during 

storage, and the interaction of chlorite ion and free chlorine. Treatment of public water supplies 

is necessary to kill pathogens that may exist in the drinking water, such as cholera, typhoid, and 

dysentery. Outbreaks of these diseases decreased significantly when disinfection of the water 

systems was introduced in the early 1900s. While there are many important public functions of 

water treatment, the Agency is taking steps to limit the exposure of chlorate ion as a DBP to the 

public. 

In order to help reduce potential exposure to chlorate, the Agency’s Office of Pesticide 

Programs (OPP), in conjunction with the Office of Water (OW), is working with the American 

Water Works Association (AWWA), the Chlorine Institute, and individual water communities to 

provide community water systems with information on Best Management Practices (BMPs) for 

use in drinking water treatment. BMPs may include measures such as production modifications, 

operational changes, materials substitution, materials and water conservation, and other such 

measures. For example, water systems that use hypochlorite solutions can minimize the levels of 

chlorate ion by purchasing high quality hypochlorite solutions and through careful storage during 

use. While decomposition of hypochlorite solutions cannot be avoided, the rate of 

decomposition can be managed. Among the major factors affecting stability are the following: 

concentration of the hypochlorite solution, temperature of the solution, pH of the solution, and 

exposure to light sources. The pH of the solution should be in the 12 to 13 range to minimize 

decomposition. Hypochlorite solutions should be protected from high temperatures and sunlight, 

and storage time should be minimized, both from the time of manufacture to delivery, and from 

the time of delivery to use. The solutions can also be diluted to control decomposition as long as 

the proper pH is maintained and high quality dilution water is used. The primary ways in which 

water systems using chlorine dioxide can control the levels of chlorate in the finished water is 

through high efficiency operation of their chlorine dioxide generators and by reducing chlorite 

ion concentrations prior to the addition of free chlorine. The BMPs could also include additional 

training of the water systems employees on the proper handling of these chemicals. 

The Agency believes that sodium chlorate does not constitute a risk of concern to the 

general population or any population subgroups, since the LOC exceedances are associated with 
 

 50

a small number of water treatment facilities and inappropriate treatment practices. Furthermore, 

the Agency anticipates that the community water system outreach strategy previously discussed 

will greatly reduce potential drinking water byproduct exposure. 

 d. Occupational Risk Mitigation 

With the consideration of mitigation measures proposed by registrants and the use of 

engineering controls (enclosed cockpits or cabs), all occupational handler risks for the use of 

inorganic chlorates as an active or inert ingredient in conventional pesticides are below the 

Agency’s LOC (i.e., MOEs are greater than the LOC of 100). For sodium chlorate, occupational 

exposure durations are short- (1-30 days) and intermediate term (1-6 months) only. Long-term 

(> 6 months) exposure is not expected based on the use pattern for sodium chlorate. Postapplication dermal and inhalation exposures are negligible due to the chemical’s physical and 

chemical characteristics as an inorganic salt. No significant amount of sodium chlorate is 

expected to be absorbed through the skin and the vapor pressure is negligible; therefore, a postapplication exposure assessment was not conducted. 

Antimicrobial Uses of Sodium Chlorate

 Risks to handlers treating water systems are below the Agency’s LOC; therefore, no 

mitigation measures are necessary. 

Agricultural Uses of Sodium Chlorate

 With the exception of aerial applications, for which enclosed cockpits are required, the 

handler and flagger MOEs for sodium chlorate’s agricultural uses are below the Agency LOC at 

baseline level of protection (long sleeve shirt, long pants, shoes, and socks). MOEs range from 

190 (mixing/loading liquids for aerial application on cotton, corn, et al.) to 3600 (mixing/loading 

liquids for groundboom application on ornamental gourds and cucurbits). Further, the maximum 

application rate for use on cotton will be reduced from 7.5 lbs ai/A to 6 lbs ai/A, with a limitation 

of one application (except for California, where two applications will be allowed). No additional 

mitigation is required for occupational risk resulting from the agricultural uses of sodium 

chlorate. 

Non-agricultural Uses of Sodium Chlorate

 The Agency’s review of sodium chlorate labels, in addition to discussions with 

registrants, indicates that the current non-agricultural use labels are not reflective of actual use 

practices. The non-agricultural use labels currently allow for larger application rates than are 

necessary for efficacy, as well as allow for unlimited treatment areas, although sodium chlorate’s 

non-agricultural formulations are typically used as spot treatments. 

Mitigation measures for sodium chlorate’s non-agricultural uses to be included on 

product labels will reduce risk from the occupational and ecological exposures to sodium 

chlorate. The registrants have agreed to the following non-agricultural use mitigation measures 

for sodium chlorate: 
 

 51

• All non-agricultural uses will be limited to spot treatments only (with the exception of the 

granular formulation for use under asphalt, although this use will be limited to an 8000 ft2 

treatment area). The uses limited to spot treatments include, but are not limited to: 

building perimeters (including farm buildings), driveways, parking lots, fence rows, 

military installations, pipelines, railroads, lumberyards, industrial sites (transformers, 

generators, utility poles, etc.), tennis court perimeters, picnic areas, bleachers, cemeteries, 

fuel tanks, airport runways, helo pads, wood decks, guard rails, highway medians, 

sidewalks/walkways, vacant lots, fire hydrants, recreational areas, and other similar areas. 

• Use on rights-of-way and ditch banks will be cancelled. 

• The label will specify a maximum application rate of 0.9 lb ai/100 ft2 

The Agency generally converts application rates to a per acre basis for assessment 

purposes; therefore, the rate of 0.9 lb ai/100 ft2

 is referred to as 392 lb ai/A in this document. 

However, because all non-agricultural uses will be limited to spot treatment applications only, all 

392 pounds of a.i. will not be applied on any one given acre. Assuming only one acre is 

considered for treatment, sodium chlorate can only be applied to up to 8000 ft2

, which equates to 

up to approximately 78 lbs ai being applied to any given acre. It is assumed that more than one 

acre will be treated. 

Risk calculations have been developed to better represent the current, actual use pattern 

for sodium chlorate, and occupational risk was reassessed based on the revised use pattern 

discussed above (i.e., application rates, target sites, and amount treated). Following is a 

summary of the Inorganic Chlorates: Addendum to the Occupational and Residential Exposure 

Assessment for the Reregistration Eligibility Decision (RED) Document, dated May 18, 2006. 

 

All data, factors, and assumptions used in the addendum are the same as those used in the 

previous occupational risk assessment. These include, but are not limited to: 

• body weight (70 kg representing adult handlers); 

• toxicological endpoints (short-/intermediate-term oral NOAEL of 30 mg/kg/day) and 

uncertainty factors (Level of Concern (LOC) for the MOE is 100); 

• application rates (in lb ai/A – presented as a range to encompass the various registered 

products); and, 

• unit exposures (from PHED and/or ORETF database, both of which have undergone 

appropriate review by the Human Studies Review Board). 

However, factors regarding application equipment used and daily area treated were 

revised based on updated use pattern information and proposed product label revisions. The 

previous assessment, summarized in Section III, was based on applications with larger, industrial 

equipment such as tractor spreaders or groundboom sprayers. As a result of mitigation measures 

agreed to by the technical registrants, sodium chlorate applications to non-agricultural areas (i.e., 

building perimeters, ditch banks, bleachers, airport runways, vacant lots, fire hydrants, or as a 

pre-paving treatment) will be limited to “handheld” equipment such as rotary spreaders and 
 

 52

pump or power sprayers. In addition, the standard Agency assumptions for the amount applied 

per work day is based on the application equipment used to determine exposure and risk. Since 

submitted information indicates that no more than 8,000 ft2

 of an acre (approximately 20%) will 

be treated with sodium chlorate, the Agency has adjusted the standard assumptions for acres 

treated per day to reflect this spot treatment-type scenario. 

Based on the revised assumptions for the daily area treated and on application methods 

suitable for spot treatments (low-pressure handwand sprayers, belly grinders, push-type 

spreaders), the risks for all non-agricultural uses, even at the currently labeled application rate 

(523 lbs ai/A instead of 392 lb ai/A), are below the Agency LOC. The higher application rate of 

523 lb ai/A was used, because at the time the Inorganic Chlorates: Addendum to the 

Occupational and Residential Exposure Assessment for the Reregistration Eligibility Decision 

(RED) Document, dated May 18, 2006, was prepared, the 392 lb ai/A maximum application rate 

mitigation measure was not yet finalized. The mitigation measures outlined above reduce the 

occupational risk from all of sodium chlorate’s non-agricultural uses to below the Agency’s level 

of concern at baseline level of protection (long sleeve shirt, long pants, shoes, and socks). The 

risks based on the revised non-agricultural use patterns for sodium chlorate are summarized in 

Table 26 below. 

Table 26: Sodium Chlorate: Short- and Intermediate-Term Occupational Inhalation Exposure 

Exposure Scenario 

Daily Area 

Treated 

(Acres/day) 

Crop/Target 

Application 

Rate 

(lbs ai/Acre)a

Inhalation 

MOE 

(at baseline) 

Mixer/Loader/Applicators & Loader/Applicators 

523 330 Mixing/Loading/Applying 

liquids with a lowpressure handwand 

sprayer 

0.4 Industrial/Non-Crop Sites 

132 1300 

523 2200 M/L/A liquids with a 

handgun sprayer 1 Industrial/Non-Crop Sites 

132 8800 

523 320 

240 710 L/A granules with a belly 

grinder 0.2 Industrial/Non-Crop Sites 

161 1100 

523 550 

240 1200 L/A granules with a pushtype spreader 1 Industrial/Non-Crop Sites 

161 1800 

a. Application rate will be reduced to 0.9 lb ai/100 ft2 (392 lb ai/A). 

 2. Non-Target Organism (Ecological) Risk Management 

 Chlorate is a strong oxidizer and may be reduced to other chemically related species 

under some environmental conditions. The extent and rate to which this occurs will depend on 

the redox chemical species (including organic matter) in the water or soil. Extensive spatial and 
 

 53

temporal variability is expected for the reactions of chlorate in the environment. However, the 

currently available simulation models do not allow for a quantitative evaluation of the potential 

exposure levels of each the reduced products of chlorate (i.e., speciation and predominance) and 

how fast these chemical species may form. Therefore, there is a high degree of uncertainty in the 

ecological exposure and risk assessment. This is important because a reduction product of 

chlorate (chlorite) is expected to be more toxic to most aquatic and terrestrial species, 

particularly aquatic invertebrates. 

 a. Terrestrial Organisms 

 1. Birds and Mammals

 EPA’s screening-level risk assessment, based on currently labelled maximum application 

rates, for both agricultural and non-agricultural uses for sodium chlorate, suggests potential acute 

and chronic risk for birds 

 

Avian Acute Risk

 Avian acute risk was not calculated, since no mortality or signs of toxicity were observed 

in the submitted subacute or acute toxicity studies at concentrations that are above the limit for 

these types of studies; therefore, acute risk to birds is not expected. However, the Agency cannot 

preclude acute or subacute risk from the non-agricultural uses. Some labels have maximum 

application rates up to 1032 lbs ai/A, and the ecological assessment for risk from nonagricultural uses was based on rates ranging from 52 to 523 lbs ai/A, with corresponding EECs 

from 12,500 and 125,000 ppm, respectively. These EECs are approximately 2.5 to 25-fold 

higher than the highest concentration tested in the subacute bird toxicity studies. The nonagricultural use mitigation outlined above, including the reduction of the maximum application 

rate to 392 lbs ai/A, and a limitation to spot treatments only (except for use under asphalt, 

although this use is limited to no more than an 8000 ft2

 area). Reducing the maximum 

application rate from 520 lbs ai/A to 392 lbs ai/A will reduce the estimated environmental 

concentrations of chlorate by approximately 25%. Further, to the extent that there is any 

potential acute risk to birds from the non-agricultural uses, the fact that these uses will result in 

small contiguously treated areas could limit avian exposure. 

Avian Chronic Risk

 Maximum chronic RQs, based on EECs derived with 90th percentile residue estimates 

from the Kenaga nomogram, exceed the Agency’s avian LOC of 1.0 for all agricultural uses 

assessed for birds eating short grass, tall grass, broadleaf forage, and small insects. Chronic RQs 

based on EECs derived with mean residue estimates from the Kenaga nomogram, although not 

presented in Section III, would be approximately three times lower for any single application of 

sodium chlorate. The highest agricultural use chronic RQ was 11 (chili peppers/white, Irish 

potatoes and the short grass food category). The second highest RQs were for cotton (ranging 

from 10.0 for the short grass food category, to 0.63 for fruits, pods, seeds, and small insects). 

Cotton is also by far the most common agricultural use of sodium chlorate, with approximately 

1,900,000 lbs ai applied annually. 
 

 54

 To address the chronic risk to birds from use on cotton, the maximum application rate 

will be reduced from 7.5 lbs ai/A to 6 lbs ai/A, and applications will be limited to a single 

applications in all states except California, where a second application will be allowed. This 

mitigation measure will reduce chronic risk to birds from use on cotton by approximately onehalf, with RQs ranging from 5.31 (on the short grass food category), to 0.33 (on fruits, pods, 

seeds, and small insects) for all states except California. In California, the chronic avian RQs 

based on the reduced maximum application rate of 6 lbs ai/A, and two applications, will be 

reduced to a range of 8.25 (on the short grass food category) to 0.52 (on fruits, pods, seeds, and 

small insects). 

 Chronic avian RQs for sodium chlorate were based on a NOAEC of 271 ppm from the 

bobwhite quail chronic reproductive toxicity test. However, maximum EECs for a majority of 

the uses and classes of food items were also higher than the LOAEC in bobwhite quail of 964 

ppm. At the LOAEC, reproductive effects occurred, including a 67% reduction in eggs laid and 

64% reduction in number of hatchlings per egg laid. Therefore, if actual exposure is equivalent 

to the maximum values calculated with the T-REX model, there is a greater certainty that frank 

reproductive effects in birds might occur. 

 However, the duration of exposure needed to produce reproductive effects in birds is an 

uncertainty. This uncertainty is significant in the case of sodium chlorate, because as a broadspectrum herbicide, its toxic effects on plants are visible within several days. Since the 

vegetation in the treated area will die, it is uncertain whether or not this vegetation will be 

attractive to birds as a feed item long enough for the chronic effects to occur. 

Chronic RQs were not calculated for sodium chlorate’s non-agricultural uses. However, 

based on the high application rates and resulting high potential EECs, risks from sodium 

chlorate’s non-agricultural uses could be considerably higher than those described in Section III 

for the agricultural uses. The non-agricultural use mitigation outlined above, including a 

reduction in the maximum labeled application rate to 0.9 lbs ai/100 ft2 (392 lbs ai/A), would 

reduce the EECs of chlorate by approximately 25% in the areas treated. Furthermore, the 

limitation of most non-agricultural uses to spot treatments only is expected to reduce the 

likelihood that a terrestrial organism will come into contact and consume all of its diet from a 

treated area. However, RQs still exceed the chronic LOC for birds (1.0). See the Analysis of 

proposed changes to sodium chlorate’s application rates and maximum treated area on potential 

ecological risks presented in EFED’s reregistration eligibility decision (RED) document, dated 

June 13, 2006 for further detail. 

Mammalian Acute Risk 

Acute RQs were not calculated for mammals. The LD50 from a core acute oral toxicity 

study in rats was >5000 mg/kg-bw. In this study, 10% (1/10) of the rats administered 5000 

mg/kg died. Mortality was not observed at any other dose. Therefore, the data were not 

sufficient to allow for characterization of the dose-response relationship and the proximity of the 

LD50 to 5000 mg/kg-bw is uncertain. Although RQs were not calculated for mammals, Tables 

17, 18 and 19 in Section III present a comparison of the body weight adjusted LD50s to EECs for 
 

 55

agricultural spray, and the non-agricultural spray and granular, formulations, respectively. These 

ratios can be used to estimate high-end risk to exposed mammals. Risk quotients would be lower 

than the values in Section III. 

For sodium chlorate’s agricultural uses, all of the mammalian acute risk estimates are 

below the Agency’s acute and endangered species LOC of 1.0 and 0.1, respectively, with the 

exception of small mammals eating short grass. The highest exceedence is for 15 gram 

mammals eating short grass (risk ratio = 0.26); therefore, no mitigation is necessary. 

For sodium chlorate’s non-agricultural uses, the ratios indicate a potential acute concern 

to mammals for both spray and granular formulations, with the highest ratios calculated for small 

mammals (ratios =11 and 33 for spray and granular formulations, respectively). While the ratios 

presented in Section III suggest that there could be acute risk to mammals of all sizes that forage 

in the area where sodium chlorate is applied to non-agricultural use sites, the risk was likely 

over-estimated, since an LD50 has not been established. Furthermore, as previously explained, a 

reduction in the maximum application rate for the non-agricultural uses to 392 lbs ai/A would 

reduce the EEC’s of chlorate in treated areas by approximately 25%. Limitation of the 

treatments to spot treatments only would be expected to further reduce the likelihood that a 

terrestrial organism will come into contact and consume all of its diet from that area. 

Mammalian Chronic Risk

 

For mammals, the Agency typically evaluates the mammalian reproductive effects for 

exposures greater than 30 days. The interpretation of the effects seen in the 2-generation rat 

reproduction toxicity study, used to derive the mammalian reproduction toxicity endpoint for 

sodium chlorate, is difficult in this respect. While effects were observed at 70 mg/kg-bw and 

above, the effects are not clearly associated with reduced reproductive success or survival. The 

mammalian reproductive NOAEC is based on the highest dose tested in this study (500 mg/kgbw), although no toxic or reproductive effects were observed at this level. Therefore, the 

NOAEC could be higher than 500 mg/kg-bw, which would result in lower mammalian 

reproduction risk estimates. However, the Agency calculated risk ratios based on the 500 mg/kgday NOAEL as a conservative estimate of risk, as presented in Section III. For the agricultural 

uses of sodium chlorate, the chronic mammalian LOC of 1.0 was only slightly exceeded for the 

smallest weight classes of mammals for most food items and the largest weight class of 

mammals feeding on short grass (RQs range from 2.6 to 0.07). The mitigation measures 

previously outlined for sodium chlorate use on cotton (maximum application rate reduced from 

7.5 lbs ai/A to 6 lbs ai/A, with the limitation of a single application, except in California, where a 

second application will be allowed), will further reduced chronic mammalian risk. Furthermore, 

based on the lack of observed reproductive effects in the chronic study and the slight LOC 

exceedances for agricultural uses, the Agency does not anticipate a chronic risk of concern to 

mammals from these uses. 

As with the agricultural uses, mammalian reproduction RQs were not calculated for 

sodium chlorate’s non-agricultural uses. However, the higher application rates for the nonagricultural uses, and the resulting higher EECs, suggest that the risk for these uses would be 

higher than the risk estimates presented for the agricultural uses. Note that the mammalian 
 

 56

reproduction RQs for the agricultural uses of sodium chlorate, presented in Section III, are a 

conservative estimate of risk. Furthermore, as previously explained, to reduce risk from sodium 

chlorate’s non-agricultural uses, the maximum application rate will be reduced to 0.9 lb ai/100 

ft2

. This mitigation measure will reduce the EECs by approximately 25%. In addition, the 

limitation to spot treatments will reduce the likelihood that mammals will come into contact and 

consume all of its diet from a treated area. See the Analysis of proposed changes to sodium 

chlorate’s application rates and maximum treated area on potential ecological risks presented in 

EFED’s reregistration eligibility decision (RED) document, dated June 13, 2006, for further 

detail. 

2. Non-Target Insects 

 EPA currently does not estimate RQs for terrestrial non-target insects. In addition, the Agency 

has no toxicity data for sodium chlorate. Therefore, EPA will require data to address this uncertainty. 

 3. Non-Target Terrestrial Plants 

 Based on chlorate’s non-selective mode of action and lack of adequate toxicity data, the 

Agency presumes risk to non-target terrestrial plants at levels above the Agency’s level of 

concern for all uses. The risks to plants cannot be quantified at this time due to lack of data; 

however, the Agency will require data to address this uncertainty. 

b. Aquatic Organisms 

 1. Fish

 

There is no acute risk of concern, from either the agricultural or non-agricultural uses of 

sodium chlorate, to freshwater or estuarine/marine fish. All risk ratios are less than 0.05, which 

is below the Agency’s acute LOC of 0.5 and below the acute endangered species LOC of 0.05. 

However, some data suggest that brown trout (freshwater fish) could be substantially more 

sensitive than other fish species tested to chlorate’s toxicity. It is uncertain if these data are 

reliable; therefore, the Agency will require additional testing in brown trout to address this area 

of uncertainty. 

No chronic fish toxicity studies are available to allow for chronic risk to fish to be 

quantified. Therefore, the Agency will require data to address this uncertainty.

2. Aquatic Invertebrates 

For freshwater invertebrates, acute RQs are below the acute LOC of 0.5 and the 

endangered species acute LOC of 0.05, for both agricultural and non-agricultural uses of sodium 

chlorate. Therefore, acute risk to freshwater invertebrates is not of concern to the Agency, and 

no mitigation is required. 

For saltwater invertebrates, the acute risk ratios for sodium chlorate’s agricultural and 

nonagricultural uses were below the Agency’s acute LOC of 0.5, in addition to the endangered 

species acute LOC of 0.05 (highest ratio = 0.04 for non-agricultural uses). Therefore, acute risk 
 

 57

to saltwater invertebrates is not of concern to the Agency. 

 Chronic risk to invertebrates (freshwater and saltwater) was not assessed, since treatmentrelated effects were not observed at any concentration in available studies. 

 3. Aquatic Plants 

For non-endangered aquatic plants, the Agency’s LOC of 1.0 was not exceeded for either 

the agricultural or nonagricultural uses of sodium chlorate (highest RQ = 0.91 for nonagricultural uses). Therefore, risk to non-endangered aquatic plants is not of concern to the 

Agency. 

For endangered aquatic plants, the Agency’s LOC of 1.0 was not exceeded for sodium chlorate’s 

agricultural uses (highest RQ = 0.29), but the LOC was exceeded for sodium chlorate’s nonagricultural uses (highest RQ = 12.6). However, the mitigation measures listed above for the 

non-agricultural uses of sodium chlorate, including a reduction in the application rate and treated 

area, result in a reduction of the endangered vascular plant RQ from 12.6 to 1.5. While this is a 

significant improvement, it is still above the Agency’s endangered plant LOC of 1.0. 

Furthermore, because of a lack of submitted data, there is uncertainty remaining on sodium 

chlorate’s toxicity to aquatic plants. The Agency will require data to address this area of 

uncertainty. 

 3. Summary of Mitigation Measures

 The following mitigation measures are necessary for sodium chlorate to be eligible for 

reregistration. These include use restrictions, voluntary cancellations and/or use deletions, and 

personal protective equipment. 

Agricultural use mitigation: 

• Engineering controls (enclosed cockpits) for aerial applications on agricultural crops. 

• For cotton, the maximum application rate will be reduced from 7.5 lbs ai/A to 6 lbs ai/A, 

and applications will be limited to a single applications in all states except California, 

where a second application will be allowed. 

Non-agricultural use mitigation: 

• All non-agricultural uses will be limited to spot treatments only (with the exception of the 

granular formulation for use under asphalt, although this use will be limited to an 8000 ft2 

treatment area). The uses limited to spot treatments include, but are not limited to: 

building perimeters (including farm buildings), driveways, parking lots, fence rows, 

military installations, pipelines, railroads, lumberyards, industrial sites (transformers, 

generators, utility poles, etc.), tennis court perimeters, picnic areas, bleachers, cemeteries, 

fuel tanks, airport runways, helo pads, wood decks, guard rails, highway medians, 

sidewalks/walkways, vacant lots, fire hydrants, recreational areas, and other similar areas. 
 

 58

• Use on rights-of-way and ditch banks will be cancelled. 

• The label will specify a maximum application rate of 0.9 lb ai/100 ft2. 

F. Other Labeling Requirements 

 To be eligible for reregistration, various use and safety information will be included in 

the labeling of all end-use products containing sodium chlorate. For the specific labeling 

statements and a list of outstanding data, refer to Section V of this RED document. 

 1. Endangered Species Considerations

The Agency’s screening level assessment results in the determination that sodium 

chlorate will have no acute risks to birds, no acute risks to fish (freshwater and estuarine/marine), 

and no acute or chronic risks to aquatic invertebrates (freshwater and estuarine/marine). 

 However, the preliminary risk assessment for endangered species indicates that RQs 

exceed endangered species LOCs for chronic risks to birds (RQs up to 11 for agricultural uses 

and greater for non-agricultural uses); acute risks to mammals (RQs up to 33); chronic risks to 

mammals (RQs up to 1.2 for agricultural uses and greater for non-agricultural uses); and risks to 

aquatic plants (RQs up to 13). Risks could not be calculated for terrestrial plants and for chronic 

risks to fish; however, the Agency will be requiring data. 

 Further, potential indirect effects to any species dependent upon a species that 

experiences effects from use of sodium chlorate can not be precluded based on the screening 

level ecological risk assessment. These findings are based solely on EPA’s screening level 

assessment and do not constitute “may affect” findings under the Endangered Species Act. 

 The Agency has developed the Endangered Species Protection Program to identify 

pesticides whose use may cause adverse impacts on endangered and threatened species, and to 

implement mitigation measures that address these impacts. The Endangered Species Act (ESA) 

requires federal agencies to ensure that their actions are not likely to jeopardize listed species or 

adversely modify designated critical habitat. To analyze the potential of registered pesticide uses 

that may affect any particular species, EPA uses basic toxicity and exposure data developed for 

the REDs and considers it in relation to individual species and their locations by evaluating 

important ecological parameters, pesticide use information, geographic relationship between 

specific pesticide uses and species locations, and biological requirements and behavioral aspects 

of the particular species, as part of a refined species-specific analysis. When conducted, this 

species-specific analysis will take into consideration any regulatory changes recommended in 

this RED that are being implemented at that time. 

 Following this future species-specific analysis, a determination that there is a likelihood 

of potential impact to a listed species or its critical habitat may result in: limitations on the use of 

sodium chlorate, other measures to mitigate any potential impact, or consultations with the Fish 

and Wildlife Service or the National Marine Fisheries Service as necessary. If the Agency 

determines use of sodium chlorate “may affect” listed species or their designated critical habitat, 
 

 59

EPA will employ the provisions in the Services regulations (50 CFR Part 402). Until that 

species-specific analysis is completed, the risk mitigation measures being implemented through 

this RED will reduce the likelihood that endangered and threatened species may be exposed to 

sodium chlorate at levels of concern. EPA is not requiring specific sodium chlorate label 

language at the present time relative to threatened and endangered species. If, in the future, 

specific measures are necessary for the protection of listed species, the Agency will implement 

them through the Endangered Species Protection Program. 

 

 2. Spray Drift Management 

 The Agency has been working closely with stakeholders to develop improved approaches 

for mitigating risks to human health and the environment from pesticide spray and dust drift. As 

part of the reregistration process, EPA will continue to work with all interested parties on this 

important issue. 

 From its assessment of sodium chlorate, as summarized in this document, the Agency 

concludes that certain drift mitigation measures are needed to address the risks from off-target 

drift for sodium chlorate, including a requirement for medium to coarse droplet size. Label 

statements implementing these measures are listed in the "spray drift management" section of the 

label table (Table 28 in Section V of this RED document. In the future, sodium chlorate product 

labels may need to be revised to include additional or different drift label statements. 
 

 60

V. What Registrants Need to Do

 A. Manufacturing-Use Products 

 1. Generic Data Requirements 

 The generic data base supporting the reregistration of sodium chlorate has been reviewed 

and determined to be substantially complete. However, there are a few data gaps remaining, and 

these data, presented in Table 27, must be submitted or the Agency may take regulatory action 

on registrations of pesticide products containing sodium chlorate. 

Table 27. Guideline Requirements for Sodium Chlorate 

Data Requirement Old Guideline 

Number 

New OPPTS 

Guideline No. 

Magnitude of the Residue- Meat/Milk/Poultry/Eggs 171-4j 860.1480 

Submittal of Analytical Reference Standards 171-13 860.1650 

28-Day Inhalation Toxicity 82-4 870.3465 

Terrestrial Field Dissipation or Retrospective Monitoring Study 164-1 835.6100 

Freshwater Fish Early Life Stage 72-4 (a) 850.1400 

Avian Reproduction (1-Generation, Duck) 71-4b 850.2300 

Seedling Emergence (Tier II only) 123-1 (a) 850.4225 

Vegetative Vigor (Tier II only) 123-1 (b) 850.4250 

Aquatic Plant Toxicity, using Lemna spp. (Tier II) 123-2 850.4400 

Honey Bee Acute Contact Toxicity 141-1 850.3020 

While the terrestrial field dissipation (835.6100) guideline study may not be appropriate 

for sodium chlorate, the Agency is still concerned about the prolonged use of sodium chlorate on 

cotton (about 50 years). Terrestrial field dissipation data are not available for sodium chlorate, 

and the guideline requirement for this study was never waived. There are some reports that 

sodium chlorate can be persistent in the field (ranging from 6 months to 5 years, depending on 

application rate, soil type, fertility, organic matter, moisture, and weather conditions). Also, 

several labels report that sodium chlorate is effective for the control of weeds for up to a year, 

which indicates that chlorate may persist for up to a year. Therefore, the range of persistence of 

sodium chlorate in the field remains a major uncertainty in the environmental fate behavior of 

this chemical. Use of sodium chlorate in the field requires that it be applied in conjunction with 

a fire retardant to minimize fire incidents. It is unclear how the fire retardant could influence the 

persistence in the field. Even though the persistence of chlorate in the field is uncertain, a 

terrestrial field dissipation data from a study conducted as per guideline 835.6100 may not 

provide adequate data because of the complexity of the chlorine oxyanion system and analytical 

chemistry methodology. Given that chloride is the end chemical species of chlorate, it poses the 
 

 61

question of increased chloride from year-after-year usage (i.e., salinization), and leaching of 

chloride to ground water, particularly in areas where chloride is not a significant, natural 

component in soil and/or ground water. Therefore, the Agency recommends a retrospective 

monitoring study (soil; ground water) aimed to address the effect of prolong use of sodium 

chlorate on cotton. The study must be conducted upon agreement of a protocol, but monitoring 

sites in coastal areas should not be included. 

 2. Labeling for Manufacturing-Use Products 

 To ensure compliance with FIFRA, manufacturing-use product (MUP) labeling should be 

revised to comply with all current EPA regulations, PR Notices, and applicable policies. The 

MUP labeling should bear the labeling contained in Table 28. 

B. End-Use Products 

 1. Additional Product-Specific Data Requirements 

 Section 4(g)(2)(B) of FIFRA calls for the Agency to obtain any needed product-specific 

data regarding the pesticide after a determination of eligibility has been made. The registrant 

must review previous data submissions to ensure that they meet current EPA acceptance criteria 

and if not, commit to conduct new studies. If a registrant believes that previously submitted data 

meet current testing standards, then the study MRID numbers should be cited according to the 

instructions in the Requirement Status and Registrants Response Form provided for each 

product. The Agency intends to issue a separate product-specific data call-in (PDCI) outlining 

specific data requirements. 

2. Labeling for End-Use Products 

 To be eligible for reregistration, labeling changes are necessary to implement measures 

outlined in Section IV above. Specific language to incorporate these changes is provided in 

Table 28. Generally, conditions for the distribution and sale of products bearing old 

labels/labeling will be established when the label changes are approved. However, specific 

existing stocks time frames will be established case-by-case, depending on the number of 

products involved, the number of label changes, and other factors. 

C. Labeling Changes Summary Table 

For sodium chlorate to be eligible for reregistration, all sodium chlorate labels must be 

amended to incorporate the risk mitigation measures outlined in Section IV. Table 28 describes 

how language on the labels should be amended. 

D. Existing Stocks 

Registrants may generally distribute and sell products bearing old labels/labeling for 18 

months after the date of approval of revised labels implementing the changes described in this 

RED. Registrants and all other persons remain obligated to meet pre-existing label requirements 
 

 62

and existing stocks requirements applicable to stocks they sell or distribute. 
 63

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

Manufacturing Use Products 

For all Manufacturing Use Products 

“Only for formulation as a defoliant/dessicant applied to agricultural crops [Registrant insert crops supported], as an herbicide applied in nonagricultural settings (residential, commercial, and industrial) or as an antimicrobial for the following uses: - [Registrant, please insert].” 

Direc

Environmental Hazards Statements 

“ENVIRONMENTAL HAZARDS” “Do not discharge effluent containing this product into lakes, streams, ponds, estuaries, oceans, or other waters unless in accordance with the requirements of a National Pollutant Discharge Eliminations System (NPDES) permit and the permitting authority has been notified in writing prior to discharge. Do not discharge effluent containing this product to sewer systems without previously notifying the local sewage treatment plant authority. For guidance, contact your State Water Board or Regional Office of the Environmental Protection Agency.” 

PrecaEnvi
 64

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

End-Use Products Intended for Occupational Use (WPS and Non-WPS)

PPE Requirements for All Formulations 

“Personal Protective Equipment (PPE)” “Some materials that are chemical-resistant to this product are [registrant inserts correct material(s)].” For more options, follow the instructions for category [insert A, B, C, D, E, F, G or H] on the chemical-resistance category selection chart. “All mixers, loaders, applicators, and other handlers must wear: 

- long-sleeved shirt and long pants, and 

- shoes and socks” 

“See engineering controls for additional requirements.” Note: this statement should be placed on labels containing agricultural crop scenarios. It should not be placed on labels where the sole uses are in nonagricultural settings, including commercial, industrial, or residential. 

ImmfolloPrecaHazaDom

Engineering Controls for products within the scope of the Worker Protection Standard (WPS) 

Enclosed Cockpits/Cabs “Applicators must use an enclosed cockpit or enclosed cab that meets the requirements listed in the Worker Protection Standard (WPS) for agricultural pesticides [40 CFR 170.240(d)(6)]. 

PrecaHazaDomimmPPE 
 65

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

User Safety Requirements 

 “Follow manufacturer’s instructions for cleaning/maintaining PPE. If no such instructions for washables exist, use detergent and hot water. Keep and wash PPE separately from other laundry.”  “Discard clothing or other absorbent materials that have been drenched or heavily contaminated with this product’s concentrate. Do not reuse them.” 

PrecaHazaDomimmPPE 

User Safety Recommendations 

“User Safety Recommendations” “Users should wash hands before eating, drinking, chewing gum, using tobacco, or using the toilet.” “Users should remove clothing/ PPE immediately if pesticide gets inside, then wash thoroughly and put on clean clothing.” “Users should remove PPE immediately after handling this product. Wash the outside of gloves before removing. As soon as possible, wash thoroughly and change into clean clothing.” 

Precaundeand D(Mus

Environmental Hazards Statements 

“ENVIRONMENTAL HAZARDS” “Do not apply directly to water, or to areas where surface water is present, or to inter-tidal areas below the mean high water mark. Do not contaminate water when cleaning equipment or disposing of equipment washwater or rinsate.” 

PrecaHazaDom

Restricted-Entry Interval For products within the scope of the Worker Protection Standard (WPS)

“Do not enter or allow worker entry into treated areas during the restricted entry interval (REI) of 12 hours.” 

DirecAgriRequ
 66

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

Early Reentry Personal Protective Equipment For Products Subject to WPS as required by Supplement 3 of PR Notice 93-7 

“PPE required for early entry to treated areas that is permitted under the Worker Protection Standard and that involves contact with anything that has been treated, such as soil or water, is 

- coveralls, 

- shoes and socks, and 

- chemical-resistant gloves made of any waterproof material.” 

DirecAgriRequ

Entry Restrictions for Non WPS Uses 

Product applied as a spray: “Do not enter of allow others to enter until treated areas have dried” Products applied dry: “Do not enter or allow other to enter until dusts have settled.” 

If no prodapproDirecGeneRestralso then AgriRequdirecand pstate

General Application Restrictions 

“Do not apply this product in a way that will contact workers or other persons, either directly or through drift. Only protected handlers may be in the area during application.” 

Place Use dAgri

Application RestrictionsAgricultural Uses For cotton, the maximum application rate is 6 lbs ai/A per application. A maximum of one application per year is permitted, except in California, where a maximum of two applications per 

year is permitted. 

Place Use fcotto

Application RestrictionsNon-agricultural Uses Application rates for products labeled for non-agricultural use must be amended to reflect the maximum application rate: 0.9 lb ai/100 ft2. 

Liquid formulations: “Non-agricultural uses are limited to spot treatments only. Broadcast applications are prohibited.” 

Place UndeResr
 67

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

Use on rights-of-way and ditch banks is prohibited. Granular formulations: “Non-agricultural uses are limited to spot treatments with the exception of applications under asphalt. Applications under asphalt may only be applied with handheld equipment such as a rotery spreader and are limited to 8,000 square feet per site”. Use on rights-of-way and ditch banks is prohibited. 
 68

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

Spray Drift Label Language for Products Applied as a Spray to Agricultural Sites 

"Spray Drift Management” 

“A variety of factors including weather conditions (e.g., wind direction, wind speed, temperature, relative humidity) and method of application can influence pesticide drift. The applicator must evaluate all factors and make appropriate adjustments when applying this product.” Wind Speed

“Do not apply at wind speeds greater than 15 mph.” Droplet Size

“Apply as a medium or coarser spray (ASAE Standard 572)” Temperature Inversions

“If applying at wind speeds less than 3 mph, the applicator must determine if a) conditions of temperature inversion exist, or b) stable atmospheric conditions exist at or below nozzle height. Do not make applications into areas of temperature inversions or stable atmospheric conditions.” Other State and Local Requirements

“Applicators must follow all state and local pesticide drift requirements regarding application of sodium chlorate. Where states have more stringent regulations, they must be observed.” Equipment

“All application equipment must be properly maintained and calibrated using appropriate carriers or surrogates.” Additional requirements for aerial applications: 1. “The boom length must not exceed 75% of the wingspan or 90% of the rotor blade diameter.” 2. “Release spray at the lowest height consistent with efficacy and flight safety. Do not release spray at a height greater than 10 feet above the crop canopy unless a greater height is required for aircraft safety.” 3. “When applications are made with a crosswind, the swath must be displaced downwind. The applicator must compensate for this displacement at the up and downwind edge of the application area by adjusting the path of the aircraft upwind.” 

DirecGeneRestrAppl
 69

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

Additional requirement for groundboom application: “Do not apply with a nozzle height greater than 4 feet above the crop canopy.” 

End Use Products Primarily Used by Consumers/Homeowners 

Environmental Hazards Statement 

“ENVIRONMENTAL HAZARDS” “This product is toxic to fish and shrimp. Do not apply directly to water. Do not contaminate water when cleaning equipment or disposing of equipment washwaters or rinsate.” “Drift and runoff may be hazardous to aquatic organisms in water adjacent to treated areas.” 

PrecaundeHaza

Entry Restrictions Products applied as a spray: 

“Do not allow adults, children, or pets to enter the treated area until sprays have dried.” Products applied dry: “Do not allow adults, children, or pets to enter the treated area until dusts have settled.” 

DirecGeneRestr

General Application Restrictions 

“Do not apply this product in a way that will contact adults, children, or pets, either directly or through drift.” 

Place Use 
 70

Table 28. Summary of Labeling Changes for Sodium Chlorate 

Description Amended Labeling Language P

Application Restrictions Liquid Formulations 

“Use is limited to spot treatments only. Broadcast applications are prohibited Use on ditch banks is prohibited.” Granular Formulations “Use is limited to spot treatments only, with the exception of applications under asphalt. Applications under asphalt are limited to 8,000 square feet per site. Use on ditch banks is prohibited. “ Application rates for products labeled for non-agricultural use must be amended to reflect the maximum application rate: 0.9 lb ai/100 ft2. 

Place undeRestr