TOXICOLOGICAL PROFILE FOR 

CHLORINE DIOXIDE AND CHLORITE 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Public Health Service 

Agency for Toxic Substances and Disease Registry
 

September 2004 
CHLORINE DIOXIDE AND CHLORITE ii 

DISCLAIMER 

The use of company or product name(s) is for identification only and does not imply endorsement by the 

Agency for Toxic Substances and Disease Registry. 
CHLORINE DIOXIDE AND CHLORITE iii 

UPDATE STATEMENT 

Toxicological Profile for Chlorine Dioxide and Chlorite, Draft for Public Comment was released in 

September 2002. This edition supersedes any previously released draft or final profile. 

Toxicological profiles are revised and republished as necessary. For information regarding the update 

status of previously released profiles, contact ATSDR at: 

Agency for Toxic Substances and Disease Registry
 

Division of Toxicology/Toxicology Information Branch 

1600 Clifton Road NE, 

Mailstop F-32 

Atlanta, Georgia 30333 


CHLORINE DIOXIDE AND CHLORITE vi 

*Legislative Background 

The toxicological profiles are developed in response to the Superfund Amendments and Reauthorization 

Act (SARA) of 1986 (Public law 99-499) which amended the Comprehensive Environmental Response, 

Compensation, and Liability Act of 1980 (CERCLA or Superfund). This public law directed ATSDR to 

prepare toxicological profiles for hazardous substances most commonly found at facilities on the 

CERCLA National Priorities List and that pose the most significant potential threat to human health, as 

determined by ATSDR and the EPA. The availability of the revised priority list of 275 hazardous 

substances was announced in the Federal Register on November 17, 1997 (62 FR 61332). For prior 

versions of the list of substances, see Federal Register notices dated April 29, 1996 (61 FR 18744); April 

17, 1987 (52 FR 12866); October 20, 1988 (53 FR 41280); October 26, 1989 (54 FR 43619); October 17, 

1990 (55 FR 42067); October 17, 1991 (56 FR 52166); October 28, 1992 (57 FR 48801); and February 

28, 1994 (59 FR 9486). Section 104(i)(3) of CERCLA, as amended, directs the Administrator of ATSDR 

to prepare a toxicological profile for each substance on the list. 
 

 

CHLORINE DIOXIDE AND CHLORITE vii 

QUICK REFERENCE FOR HEALTH CARE PROVIDERS 

Toxicological Profiles are a unique compilation of toxicological information on a given hazardous 

substance. Each profile reflects a comprehensive and extensive evaluation, summary, and interpretation 

of available toxicologic and epidemiologic information on a substance. Health care providers treating 

patients potentially exposed to hazardous substances will find the following information helpful for fast 

answers to often-asked questions. 

Primary Chapters/Sections of Interest 

Chapter 1: Public Health Statement: The Public Health Statement can be a useful tool for educating 

patients about possible exposure to a hazardous substance. It explains a substance’s relevant toxicologic 

properties in a nontechnical, question-and-answer format, and it includes a review of the general health 

effects observed following exposure. 

Chapter 2: Relevance to Public Health: The Relevance to Public Health Section evaluates, interprets, 

and assesses the significance of toxicity data to human health. 

Chapter 3: Health Effects: Specific health effects of a given hazardous compound are reported by type 

of health effect (death, systemic, immunologic, reproductive), by route of exposure, and by length of 

exposure (acute, intermediate, and chronic). In addition, both human and animal studies are reported in 

this section. 

NOTE: Not all health effects reported in this section are necessarily observed in the clinical 

setting. Please refer to the Public Health Statement to identify general health effects observed following 

exposure. 

Pediatrics: Four new sections have been added to each Toxicological Profile to address child health 

issues: 

Section 1.6 How Can (Chemical X) Affect Children? 

Section 1.7 How Can Families Reduce the Risk of Exposure to (Chemical X)? 

Section 3.7 Children’s Susceptibility 

Section 6.6 Exposures of Children 

Other Sections of Interest: 

Section 3.8 Biomarkers of Exposure and Effect 

Section 3.11 Methods for Reducing Toxic Effects 

ATSDR Information Center 

Phone: 1-888-42-ATSDR or (404) 498-0110 Fax: (404) 498-0093 

E-mail: atsdric@cdc.gov Internet: http://www.atsdr.cdc.gov 

The following additional material can be ordered through the ATSDR Information Center: 

Case Studies in Environmental Medicine: Taking an Exposure History—The importance of taking an 

exposure history and how to conduct one are described, and an example of a thorough exposure history is 

provided. Other case studies of interest include Reproductive and Developmental Hazards; Skin Lesions 

and Environmental Exposures; Cholinesterase-Inhibiting Pesticide Toxicity; and numerous chemicalspecific case studies. 
CHLORINE DIOXIDE AND CHLORITE viii 

Managing Hazardous Materials Incidents is a three-volume set of recommendations for on-scene 

(prehospital) and hospital medical management of patients exposed during a hazardous materials incident. 

Volumes I and II are planning guides to assist first responders and hospital emergency department 

personnel in planning for incidents that involve hazardous materials. Volume III—Medical Management 

Guidelines for Acute Chemical Exposures—is a guide for health care professionals treating patients 

exposed to hazardous materials. 

Fact Sheets (ToxFAQs) provide answers to frequently asked questions about toxic substances. 

Other Agencies and Organizations 

The National Center for Environmental Health (NCEH) focuses on preventing or controlling disease, 

injury, and disability related to the interactions between people and their environment outside the 

workplace. Contact: NCEH, Mailstop F-29, 4770 Buford Highway, NE, Atlanta, GA 30341-3724 • 

Phone: 770-488-7000 • FAX: 770-488-7015. 

The National Institute for Occupational Safety and Health (NIOSH) conducts research on occupational 

diseases and injuries, responds to requests for assistance by investigating problems of health and safety in 

the workplace, recommends standards to the Occupational Safety and Health Administration (OSHA) and 

the Mine Safety and Health Administration (MSHA), and trains professionals in occupational safety and 

health. Contact: NIOSH, 200 Independence Avenue, SW, Washington, DC 20201 • Phone: 800-356­

4674 or NIOSH Technical Information Branch, Robert A. Taft Laboratory, Mailstop C-19, 4676 

Columbia Parkway, Cincinnati, OH 45226-1998 • Phone: 800-35-NIOSH. 

The National Institute of Environmental Health Sciences (NIEHS) is the principal federal agency for 

biomedical research on the effects of chemical, physical, and biologic environmental agents on human 

health and well-being. Contact: NIEHS, PO Box 12233, 104 T.W. Alexander Drive, Research Triangle 

Park, NC 27709 • Phone: 919-541-3212. 

Referrals 

The Association of Occupational and Environmental Clinics (AOEC) has developed a network of clinics 

in the United States to provide expertise in occupational and environmental issues. Contact: AOEC, 

1010 Vermont Avenue, NW, #513, Washington, DC 20005 • Phone: 202-347-4976 • FAX: 202-347­

4950 • e-mail: AOEC@AOEC.ORG • Web Page: http://www.aoec.org/. 

The American College of Occupational and Environmental Medicine (ACOEM) is an association of 

physicians and other health care providers specializing in the field of occupational and environmental 

medicine. Contact: ACOEM, 55 West Seegers Road, Arlington Heights, IL 60005 • Phone: 847-818­

1800 • FAX: 847-818-9266. 
CHLORINE DIOXIDE AND CHLORITE ix 

CONTRIBUTORS 

CHEMICAL MANAGER(S)/AUTHOR(S): 

Jessilynn B. Taylor, M.S. 

ATSDR, Division of Toxicology, Atlanta, GA 

David W. Wohlers, Ph.D. 

Richard Amata, M.S. 

Syracuse Research Corporation, North Syracuse, NY 

THE PROFILE HAS UNDERGONE THE FOLLOWING ATSDR INTERNAL REVIEWS: 

1. Health Effects Review. The Health Effects Review Committee examines the health effects 

chapter of each profile for consistency and accuracy in interpreting health effects and classifying 

end points. 

2.	 Minimal Risk Level Review. The Minimal Risk Level Workgroup considers issues relevant to 

substance-specific Minimal Risk Levels (MRLs), reviews the health effects database of each 

profile, and makes recommendations for derivation of MRLs. 

3. Data Needs Review. The Research Implementation Branch reviews data needs sections to assure 

consistency across profiles and adherence to instructions in the Guidance. 

 

CHLORINE DIOXIDE AND CHLORITE xi 

PEER REVIEW 

A peer review panel was assembled for chlorine dioxide and chlorite. The panel consisted of the 

following members: 

1. Dr. Mohamed S. Abdel-Rahman, Professor of Pharmacology and Physiology, Director of 

Toxicology, New Jersey Medical School, Newark, New Jersey; 

2.	 Dr. Syed M. GhiasUddin, Toxicologist and Section Chief, Environmental Toxicology and 

Chemistry Section, Indiana Department of Environmental Management, Indianapolis, Indiana; 

and 

3. Dr. John S. Reif, Professor and Chairman, Department of Environmental Health, Colorado State 

University, Ft. Collins, Colorado. 

These experts collectively have knowledge of chlorine dioxide's and chlorite’s physical and chemical 

properties, toxicokinetics, key health end points, mechanisms of action, human and animal exposure, and 

quantification of risk to humans. All reviewers were selected in conformity with the conditions for peer 

review specified in Section 104(I)(13) of the Comprehensive Environmental Response, Compensation, 

and Liability Act, as amended. 

Scientists from the Agency for Toxic Substances and Disease Registry (ATSDR) have reviewed the peer 

reviewers' comments and determined which comments will be included in the profile. A listing of the 

peer reviewers' comments not incorporated in the profile, with a brief explanation of the rationale for their 

exclusion, exists as part of the administrative record for this compound. A list of databases reviewed and 

a list of unpublished documents cited are also included in the administrative record. 

The citation of the peer review panel should not be understood to imply its approval of the profile's final 

content. The responsibility for the content of this profile lies with the ATSDR. 

 

CHLORINE DIOXIDE AND CHLORITE xiii 

CONTENTS 

DISCLAIMER ..............................................................................................................................................ii 

UPDATE STATEMENT .............................................................................................................................iii 

FOREWORD ................................................................................................................................................v 

QUICK REFERENCE FOR HEALTH CARE PROVIDERS....................................................................vii 

CONTRIBUTORS.......................................................................................................................................ix 

PEER REVIEW ...........................................................................................................................................xi 

CONTENTS...............................................................................................................................................xiii 

LIST OF FIGURES ..................................................................................................................................xvii 

LIST OF TABLES.....................................................................................................................................xix 

1. PUBLIC HEALTH STATEMENT..........................................................................................................1 

1.1 WHAT ARE CHLORINE DIOXIDE AND CHLORITE?..............................................................1 

1.2 WHAT HAPPENS TO CHLORINE DIOXIDE AND CHLORITE WHEN THEY ENTER 

THE ENVIRONMENT?..................................................................................................................2 

1.3 HOW MIGHT I BE EXPOSED TO CHLORINE DIOXIDE AND CHLORITE? .........................2 

1.4 HOW CAN CHLORINE DIOXIDE AND CHLORITE ENTER AND LEAVE MY BODY? ......3 

1.5 HOW CAN CHLORINE DIOXIDE AND CHLORITE AFFECT MY HEALTH? .......................3 

1.6 HOW CAN CHLORINE DIOXIDE AND CHLORITE AFFECT CHILDREN?...........................4 

1.7 HOW CAN FAMILIES REDUCE THE RISK OF EXPOSURE TO CHLORINE DIOXIDE 

AND CHLORITE............................................................................................................................5 

1.8 IS THERE A MEDICAL TEST TO DETERMINE WHETHER I HAVE BEEN EXPOSED 

TO CHLORINE DIOXIDE AND CHLORITE? .............................................................................5 

1.9 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH?.....................................................................................................5 

1.10 WHERE CAN I GET MORE INFORMATION?............................................................................6 

2. RELEVANCE TO PUBLIC HEALTH ...................................................................................................9 

2.1 BACKGROUND AND ENVIRONMENTAL EXPOSURES TO CHLORINE DIOXIDE 

AND CHLORITE IN THE UNITED STATES...............................................................................9 

2.2 SUMMARY OF HEALTH EFFECTS ............................................................................................9 

2.3 MINIMAL RISK LEVELS............................................................................................................11 

3. HEALTH EFFECTS..............................................................................................................................15 

3.1 INTRODUCTION .........................................................................................................................15 

3.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE.......................................15 

3.2.1 Inhalation Exposure ..............................................................................................................17 

3.2.1.1 Death.................................................................................................................................17 

3.2.1.2 Systemic Effects ...............................................................................................................18 

3.2.1.3 Immunological and Lymphoreticular Effects...................................................................24 

3.2.1.4 Neurological Effects .........................................................................................................24 

3.2.1.5 Reproductive Effects.........................................................................................................24 

3.2.1.6 Developmental Effects......................................................................................................24 

3.2.1.7 Cancer...............................................................................................................................24 

3.2.2 Oral Exposure........................................................................................................................25 

3.2.2.1 Death.................................................................................................................................25 

3.2.2.2 Systemic Effects ...............................................................................................................26 

3.2.2.3 Immunological and Lymphoreticular Effects...................................................................37 

3.2.2.4 Neurological Effects .........................................................................................................38 
CHLORINE DIOXIDE AND CHLORITE xiv 

3.2.2.5 Reproductive Effects.........................................................................................................38 

3.2.2.6 Developmental Effects......................................................................................................39 

3.2.2.7 Cancer...............................................................................................................................45 

3.2.3 Dermal Exposure...................................................................................................................47 

3.2.3.1 Death.................................................................................................................................47 

3.2.3.2 Systemic Effects ...............................................................................................................47 

3.2.3.3 Immunological and Lymphoreticular Effects...................................................................48 

3.2.3.4 Neurological Effects .........................................................................................................48 

3.2.3.5 Reproductive Effects.........................................................................................................48 

3.2.3.6 Developmental Effects......................................................................................................48 

3.2.3.7 Cancer...............................................................................................................................48 

3.3 GENOTOXICITY .........................................................................................................................49 

3.4 TOXICOKINETICS ......................................................................................................................50 

3.4.1 Absorption.............................................................................................................................50 

3.4.1.1 Inhalation Exposure ..........................................................................................................50 

3.4.1.2 Oral Exposure ...................................................................................................................50 

3.4.1.3 Dermal Exposure ..............................................................................................................51 

3.4.2 Distribution ...........................................................................................................................51 

3.4.2.1 Inhalation Exposure ..........................................................................................................51 

3.4.2.2 Oral Exposure ...................................................................................................................51 

3.4.2.3 Dermal Exposure ..............................................................................................................52 

3.4.3 Metabolism............................................................................................................................52 

3.4.3.1 Inhalation Exposure ..........................................................................................................52 

3.4.3.2 Oral Exposure ...................................................................................................................52 

3.4.3.3 Dermal Exposure ..............................................................................................................53 

3.4.4 Elimination and Excretion.....................................................................................................53 

3.4.4.1 Inhalation Exposure ..........................................................................................................53 

3.4.4.2 Oral Exposure ...................................................................................................................53 

3.4.4.3 Dermal Exposure ..............................................................................................................53 

3.4.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models .............54 

3.5 MECHANISMS OF ACTION.......................................................................................................55 

3.5.1 Pharmacokinetic Mechanisms............................................................................................... 55 

3.5.2 Mechanisms of Toxicity........................................................................................................57 

3.5.3 Animal-to-Human Extrapolations.........................................................................................58
 

3.6 TOXICITIES MEDIATED THROUGH THE NEUROENDOCRINE AXIS ..............................58 

3.7 CHILDREN’S SUSCEPTIBILITY ...............................................................................................59 

3.8 BIOMARKERS OF EXPOSURE AND EFFECT.........................................................................61 

3.8.1 Biomarkers Used to Identify or Quantify Exposure to Chlorine Dioxide and Chlorite ........62 

3.8.2 Biomarkers Used to Characterize Effects Caused by Chlorine Dioxide and Chlorite ..........63 

3.9 INTERACTIONS WITH OTHER CHEMICALS.........................................................................63 

3.10 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE ...................................................63 

3.11 METHODS FOR REDUCING TOXIC EFFECTS.......................................................................64 

3.11.1 Reducing Peak Absorption Following Exposure ..................................................................64 

3.11.2 Reducing Body Burden .........................................................................................................64 

3.11.3 Interfering with the Mechanism of Action for Toxic Effects................................................65 

3.12 ADEQUACY OF THE DATABASE............................................................................................65 

3.12.1 Existing Information on Health Effects of Chlorine Dioxide and Chlorite...........................65 

3.12.2 Identification of Data Needs .................................................................................................67 

3.12.3 Ongoing Studies ....................................................................................................................71 

4. CHEMICAL AND PHYSICAL INFORMATION................................................................................73 
CHLORINE DIOXIDE AND CHLORITE xv 

4.1 CHEMICAL IDENTITY...............................................................................................................73 

4.2 PHYSICAL AND CHEMICAL PROPERTIES............................................................................73 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL............................................................77 

5.1 PRODUCTION..............................................................................................................................77 

5.2 IMPORT/EXPORT........................................................................................................................79 

5.3 USE................................................................................................................................................79 

5.4 DISPOSAL ....................................................................................................................................82 

6. POTENTIAL FOR HUMAN EXPOSURE ...........................................................................................85 

6.1 OVERVIEW ..................................................................................................................................85 

6.2 RELEASES TO THE ENVIRONMENT ......................................................................................85 

6.2.1 Air .........................................................................................................................................85 

6.2.2 Water.....................................................................................................................................87 

6.2.3 Soil ........................................................................................................................................87 

6.3 ENVIRONMENTAL FATE..........................................................................................................90 

6.3.1 Transport and Partitioning.....................................................................................................90 

6.3.2 Transformation and Degradation ..........................................................................................90 

6.3.2.1 Air.....................................................................................................................................91 

6.3.2.2 Water.................................................................................................................................91 

6.3.2.3 Sediment and Soil .............................................................................................................95 

6.3.2.4 Other Media ......................................................................................................................95 

6.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT .....................................95 

6.4.1 Air .........................................................................................................................................95 

6.4.2 Water.....................................................................................................................................96 

6.4.3 Sediment and Soil .................................................................................................................98 

6.4.4 Other Environmental Media..................................................................................................99 

6.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE............................................99 

6.6 EXPOSURES OF CHILDREN ...................................................................................................100
 

6.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES................................................101 

6.8 ADEQUACY OF THE DATABASE..........................................................................................101 

6.8.1 Identification of Data Needs ...............................................................................................101 

6.8.2 Ongoing Studies ..................................................................................................................104 

7. ANALYTICAL METHODS ...............................................................................................................105 

7.1 BIOLOGICAL MATERIALS .....................................................................................................105 

7.2 ENVIRONMENTAL SAMPLES................................................................................................105 

7.3 ADEQUACY OF THE DATABASE..........................................................................................110 

7.3.1 Identification of Data Needs ...............................................................................................110 

7.3.2 Ongoing Studies ..................................................................................................................111 

8. REGULATIONS AND ADVISORIES ...............................................................................................113 

9. REFERENCES ....................................................................................................................................117 

10. GLOSSARY ......................................................................................................................................137 
CHLORINE DIOXIDE AND CHLORITE xvi 

APPENDICES 

A. ATSDR MINIMAL RISK LEVELS AND WORKSHEETS .............................................................A-1 

B. USER'S GUIDE ..................................................................................................................................B-1 

C. ACRONYMS, ABBREVIATIONS, AND SYMBOLS......................................................................C-1 

D. INDEX ................................................................................................................................................D-1 
 

CHLORINE DIOXIDE AND CHLORITE xvii 

LIST OF FIGURES 

3-1 Levels of Significant Exposure to Chlorine Dioxide and Chlorite—Inhalation ............................ 21 

3-2 Levels of Significant Exposure to Chlorine Dioxide and Chlorite—Oral ..................................... 31 

3-3 Conceptual Representation of a Physiologically Based Pharmacokinetic (PBPK) Model for a 

Hypothetical Chemical Substance .................................................................................................56 

3-4 Existing Information on Health Effects of Chlorine Dioxide and Chlorite ...................................66 

6-1 Frequency of NPL Sites with Chlorine Dioxide and Chlorite Contamination...............................86 

6-2 Percentage of POTW Facilities Reporting to ICR vs. Level of Chlorite in Distribution System

 Water..............................................................................................................................................97 

CHLORINE DIOXIDE AND CHLORITE xix 

LIST OF TABLES 

3-1 Levels of Significant Exposure to Chlorine Dioxide and Chlorite—Inhalation ............................ 19 

3-2 Levels of Significant Exposure to Chlorine Dioxide and Chlorite—Oral ..................................... 27 

4-1 Chemical Identity of Chlorine Dioxide and Sodium Chlorite .......................................................74 

4-2 Physical and Chemical Properties of Chlorine Dioxide and Sodium Chlorite ..............................75 

5-1 Facilities that Produce, Process, or Use Chlorine Dioxide ............................................................78 

5-2 Publicly Owned Treatment Works (POTW) Utilizing Chlorine Dioxide for Water Treatment 

in 1995 ...........................................................................................................................................81 

6-1 Releases to the Environment from Facilities that Produce, Process, or Use Chlorine Dioxide.....88 

6-2 Chlorine Speciation in Aqueous Solutions ....................................................................................92 

7-1 Analytical Methods for Determining Chlorine Dioxide and Chlorite in Environmental 

 Samples........................................................................................................................................107 

8-1 Regulations and Guidelines Applicable to Chlorine Dioxide and Chlorite .................................114 

CHLORINE DIOXIDE AND CHLORITE 1 

1. PUBLIC HEALTH STATEMENT 

This public health statement tells you about chlorine dioxide and chlorite and the effects of 

exposure to them. 

The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in 

the nation. These sites are then placed on the National Priorities List (NPL) and are targeted for 

long-term federal clean-up activities. Chlorine dioxide and chlorite have not been found in any 

of the 1,647 current or former NPL sites. Although the total number of NPL sites evaluated for 

these substances is not known, the possibility exists that chlorine dioxide and chlorite may be 

found in the future as more sites are evaluated. This information is important because these sites 

may be sources of exposure and exposure to these substances may harm you. 

When a substance is released either from a large area, such as an industrial plant, or from a 

container, such as a drum or bottle, it enters the environment. Such a release does not always 

lead to exposure. You can be exposed to a substance only when you come in contact with it. 

You may be exposed by breathing, eating, or drinking the substance, or by skin contact. 

If you are exposed to chlorine dioxide or chlorite, many factors will determine whether you will 

be harmed. These factors include the dose (how much), the duration (how long), and how you 

come in contact with them. You must also consider any other chemicals you are exposed to and 

your age, sex, diet, family traits, lifestyle, and state of health. 

1.1 WHAT ARE CHLORINE DIOXIDE AND CHLORITE? 

Chlorine dioxide is a yellow to reddish-yellow gas that can decompose rapidly in air. Because it 

is a hazardous gas, chlorine dioxide is always made at the location where it is used. Chlorine 

dioxide is used as a bleach at pulp mills, which make paper and paper products, and in public 

water-treatment facilities, to make water safe for drinking. It has also been used to 

decontaminate public buildings. Chlorine dioxide is soluble in water and will react rapidly with 

other compounds. When it reacts in water, chlorine dioxide forms chlorite ion, which is also a 
CHLORINE DIOXIDE AND CHLORITE 2 

1. PUBLIC HEALTH STATEMENT 

very reactive chemical. Because chlorine dioxide is very reactive, it is able to kill bacteria and 

microorganisms in water. About 5% of large water-treatment facilities (serving more than 

100,000 persons) in the United States use chlorine dioxide to treat drinking water. An estimated 

12 million persons may be exposed in this way to chlorine dioxide and chlorite ions. In 

communities that use chlorine dioxide to treat drinking water, chlorine dioxide and its byproduct, chlorite ions, may be present at low levels in tap water. 

In this profile, the term “chlorite” will be used to refer to “chlorite ion,” which is a water-soluble 

ion. Chlorite ion can combine with metal ions to form solid salts (e.g., sodium chlorite). Sodium 

chlorite dissolves in water and forms chlorite ions and sodium ions. More than 80% of all 

chlorite (present as sodium chlorite) is used to make chlorine dioxide to disinfect drinking water. 

Sodium chlorite is also used as a disinfectant to kill germs. 

1.2 WHAT HAPPENS TO CHLORINE DIOXIDE AND CHLORITE WHEN THEY 

ENTER THE ENVIRONMENT? 

Chlorine dioxide is a very reactive compound. In air, sunlight quickly breaks chlorine dioxide 

apart into chlorine gas and oxygen. In water, chlorine dioxide reacts quickly to form chlorite 

ions. When chlorine dioxide reacts with dissolved organic compounds in water-treatment 

systems, it forms disinfection by-products, such as chlorite and chlorate ions. 

Like chlorine dioxide, chlorite is very reactive. Since chlorite is an ionic compound, it will exist 

primarily in water. Chlorite ions are mobile in water, and may move into groundwater. 

However, the reaction of chlorite ions with soils and sediments may reduce the concentration of 

chlorite ions capable of reaching groundwater. For additional information about what happens to 

chlorine dioxide and chlorite when they enter the environment, see Chapter 6. 

1.3 HOW MIGHT I BE EXPOSED TO CHLORINE DIOXIDE AND CHLORITE? 

Chlorine dioxide is added to drinking water to protect people from harmful bacteria and other 

microorganisms. Most people will be exposed to chlorine dioxide and its disinfection by­
CHLORINE DIOXIDE AND CHLORITE 3 

1. PUBLIC HEALTH STATEMENT 

product, chlorite ions, when they drink water that has been treated with chlorine dioxide. The 

EPA has set the maximum concentration in the drinking water at 0.8 milligrams per liter (mg/L) 

for chlorine dioxide and 1.0 mg/L for chlorite ion. The concentrations of chlorine dioxide and 

chlorite ion in your drinking water, however, may be lower or higher than these levels. For 

additional information about how you might be exposed to chlorine dioxide and chlorite, see 

Chapter 6. 

1.4 HOW CAN CHLORINE DIOXIDE AND CHLORITE ENTER AND LEAVE MY 

BODY? 

Chlorine dioxide and chlorite usually enter the body when people drink water that has been 

disinfected with chlorine dioxide. Because chlorine dioxide rapidly breaks down in air to 

chlorine gas and oxygen, you would not likely breathe air containing dangerous levels of 

chlorine dioxide, but if you did, it could be absorbed across your lungs. You are not likely to 

encounter chlorite in the air you breathe. Whether chlorine dioxide or chlorite on your skin 

would be absorbed to any great extent is not known. 

Both chlorine dioxide and chlorite act quickly when they enter the body. Chlorine dioxide 

quickly changes to chlorite ions, which are broken down further into chloride ions. The body 

uses these ions for many normal purposes. Some chloride ions leave the body within hours or 

days, mainly in the urine. Most chlorite that is not broken down also leaves the body in the urine 

within a few days after exposure to chlorine dioxide or chlorite. 

1.5 HOW CAN CHLORINE DIOXIDE AND CHLORITE AFFECT MY HEALTH? 

Both chlorine dioxide and chlorite react quickly in water and moist body tissues. If you were to 

breathe air containing chlorine dioxide gas, you might experience irritation in your nose, throat, 

and lungs. If you were to eat or drink large amounts of chlorine dioxide or chlorite, you might 

experience irritation in the mouth, esophagus, or stomach. Most people will not be exposed to 

chlorine dioxide or chlorite in amounts large enough to damage other parts of the body, but if 
CHLORINE DIOXIDE AND CHLORITE 4 

1. PUBLIC HEALTH STATEMENT 

you were, you might experience shortness of breath and other respiratory problems because of 

damage to the substances in blood that carry oxygen throughout the body. 

Scientists use many tests to protect the public from harmful effects of toxic chemicals and to find 

ways for treating persons who have been harmed. 

One way to learn whether a chemical will harm people is to determine how the body absorbs, 

uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal 

testing may also help identify health effects such as cancer or birth defects. Without laboratory 

animals, scientists would lose a basic method for getting information needed to make wise 

decisions that protect public health. Scientists have the responsibility to treat research animals 

with care and compassion. Scientists must comply with strict animal care guidelines because 

laws today protect the welfare of research animals. 

Animal studies have shown effects of chlorine dioxide and chlorite that are similar to those seen 

in people exposed to very high amounts of these chemicals. In addition, exposure to high levels 

of chlorine dioxide and chlorite in animals both before birth and during early development after 

birth may cause delays in brain development. The levels to which the animals were exposed 

were much higher than levels that would likely be found in drinking water that has been 

disinfected with chlorine dioxide. 

1.6 HOW CAN CHLORINE DIOXIDE AND CHLORITE AFFECT CHILDREN? 

This section discusses potential health effects in humans from exposures during the period from 

conception to maturity at 18 years of age. 

Children exposed to large amounts of chlorine dioxide or chlorite would likely be affected in the 

same manner as adults. Exposure to chlorine dioxide gas in young children, however, might 

more quickly reduce the ability of blood to carry oxygen than in adults, making breathing more 

difficult. If infants or babies still in their mother’s womb were exposed to large amounts of 
CHLORINE DIOXIDE AND CHLORITE 5 

1. PUBLIC HEALTH STATEMENT 

chlorine dioxide, it might cause parts of their brains to develop more slowly. This has been seen 

in young animals, but has not actually been seen in humans. 

1.7 HOW CAN FAMILIES REDUCE THE RISK OF EXPOSURE TO CHLORINE 

DIOXIDE AND CHLORITE 

If your doctor finds that you have been exposed to substantial amounts of chlorine dioxide or 

chlorite, ask whether your children might also have been exposed. Your doctor might need to 

ask your state health department to investigate. 

Families that drink water treated with chlorine dioxide may reduce the risk of exposure to 

chlorine dioxide and chlorite ions by drinking bottled water that has not been treated with 

chlorine dioxide or chlorite ions. 

1.8 IS THERE A MEDICAL TEST TO DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO CHLORINE DIOXIDE AND CHLORITE? 

Although no medical tests are available to determine whether you have been exposed to chlorine 

dioxide or chlorite, exposure to very large amounts may result in damage to red blood cells that 

can be observed through routine blood tests. 

1.9 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

The federal government develops regulations and recommendations to protect public health. 

Regulations can be enforced by law. The EPA, the Occupational Safety and Health 

Administration (OSHA), and the Food and Drug Administration (FDA) are some federal 

agencies that develop regulations for toxic substances. Recommendations provide valuable 

guidelines to protect public health, but cannot be enforced by law. The Agency for Toxic 

Substances and Disease Registry (ATSDR) and the National Institute for Occupational Safety 
CHLORINE DIOXIDE AND CHLORITE 6 

1. PUBLIC HEALTH STATEMENT 

and Health (NIOSH) are two federal organizations that develop recommendations for toxic 

substances. 

Regulations and recommendations can be expressed as “not-to-exceed” levels, that is, levels of a 

toxic substance in air, water, soil, or food that do not exceed a critical value that is usually based 

on levels that affect animals; they are then adjusted to levels that will help protect humans. 

Sometimes these not-to-exceed levels differ among federal organizations because they used 

different exposure times (an 8-hour workday or a 24-hour day), different animal studies, or other 

factors. 

Recommendations and regulations are also updated periodically as more information becomes 

available. For the most current information, check with the federal agency or organization that 

provides it. Some regulations and recommendations for chlorine dioxide and chlorite include the 

following: 

OSHA regulates the level of chlorine dioxide in workplace air. The occupational exposure limit 

for an 8-hour workday, 40-hour workweek is 0.1 parts per million (0.28 milligrams per cubic 

meter [mg/m3

]). The EPA has set a maximum contaminant level of 1 mg/L for chlorite in 

drinking water and a goal of 0.8 mg/L for both the maximum residual disinfectant level for 

chlorine dioxide and the maximum contaminant level for chlorite in drinking water that has been 

treated with chlorine dioxide as a disinfectant. 

For more information on regulations and guidelines, see Chapter 8. 

1.10 WHERE CAN I GET MORE INFORMATION? 

If you have any more questions or concerns, please contact your community or state health or 

environmental quality department, or contact ATSDR at the address and phone number below. 
 

 

 

 

CHLORINE DIOXIDE AND CHLORITE 7 

1. PUBLIC HEALTH STATEMENT 

ATSDR can also tell you the location of occupational and environmental health clinics. These 

clinics specialize in recognizing, evaluating, and treating illnesses that result from exposure to 

hazardous substances. 

Toxicological profiles are also available on-line at www.atsdr.cdc.gov and on CD-ROM. You 

may request a copy of the ATSDR ToxProfilesTM CD-ROM by calling the toll-free information 

and technical assistance number at 1-888-42ATSDR (1-888-422-8737), by e-mail at 

atsdric@cdc.gov, or by writing to: 

Agency for Toxic Substances and Disease Registry 

 Division of Toxicology 

1600 Clifton Road NE 

 Mailstop F-32 

 Atlanta, GA 30333 

 Fax: 1-770-488-4178 

Organizations for-profit may request copies of final Toxicological Profiles from the following: 

National Technical Information Service (NTIS) 

5285 Port Royal Road 

 Springfield, VA 22161 

 Phone: 1-800-553-6847 or 1-703-605-6000 

 Web site: http://www.ntis.gov/ 

 

CHLORINE DIOXIDE AND CHLORITE 9 

2. RELEVANCE TO PUBLIC HEALTH 

2.1 BACKGROUND AND ENVIRONMENTAL EXPOSURES TO CHLORINE DIOXIDE 

AND CHLORITE IN THE UNITED STATES 

Chlorine dioxide is a yellow to reddish-yellow gas that can decompose rapidly in air if it is present at high 

concentrations. Because it is a hazardous gas, chlorine dioxide is always made at the place where it is 

used. Chlorine dioxide is used as a bleach at pulp mills to make paper and paper products, and in 

publicly-owned treatment works (POTW) as a disinfectant for drinking water. In 2001, chlorine dioxide 

was used to decontaminate a number of public buildings following the release of anthrax spores in the 

United States. Chlorine dioxide is a very reactive compound and will not exist in the environment for 

long periods of time. In air, chlorine dioxide will dissociate in sunlight into chlorine gas and oxygen. 

Chlorine dioxide, a strong oxidizer, will react quickly in water to form by-products such as chlorite ions. 

EPA has set the maximum concentration of chlorine dioxide and chlorite ion for drinking waters at 

0.8 and 1.0 mg/L, respectively. However, the concentrations of chlorine dioxide and chlorite ion in 

drinking water may be higher or lower than these levels. 

Human exposure to chlorine dioxide and its by-products (e.g., chlorite ion) occurs primarily by ingestion 

of drinking water. People who live in communities where chlorine dioxide is used in drinking water 

treatment have a greater probability of exposure to chlorine dioxide and chlorite ions than individuals 

who do not. About 5% of the water treatment facilities serving more than 100,000 people in the United 

States use chlorine dioxide to treat drinking water. This would translate to about 12 million people who 

may be exposed to chlorine dioxide and chlorite ions in the United States. However, the total number 

people exposed will be higher if smaller facilities (i.e., those serving less than 50,000 people) are also 

included in this value. 

2.2 SUMMARY OF HEALTH EFFECTS 

Available human and animal data indicate that airborne chlorine dioxide (ClO2) primarily acts as a 

respiratory tract and ocular irritant. Chlorite (ClO2

-

) does not persist in the atmosphere either in ionic 

form or as chlorite salt, and is not likely to be inhaled. Potential for human exposure to chlorine dioxide 

or chlorite may be greatest via the oral exposure route because chlorine dioxide is sometimes used as a 
CHLORINE DIOXIDE AND CHLORITE 10 

2. RELEVANCE TO PUBLIC HEALTH 

disinfectant for drinking water. Available human and animal data indicate that oral exposure to relatively 

large amounts of chlorine dioxide or chlorite may result in irritation of the digestive tract, the severity of 

which is likely to be dose-dependent. In addition, high-level oral exposure results in increased levels of 

methemoglobin in the blood, which reduces the ability of oxygen to bind with hemoglobin. 

Other hematological changes have been observed in animals exposed to chlorine dioxide and chlorite. 

However, the degree of reported changes does not appear to be dependent upon the amount of exposure, 

and the toxicological significance of such changes is not clear. Nor has the toxicological significance of 

changes in thyroid hormone levels in the blood been established. 

Both chlorine dioxide and chlorite appear to induce delays in neurodevelopment, as evidenced by delayed 

brain growth, decreased locomotor and exploratory behavior, and altered auditory startle response in 

animals exposed during critical periods of neurodevelopment. It is not known whether similar chlorine 

dioxide- or chlorite-induced neurodevelopmental effects might occur in humans. 

Limited carcinogenicity data for chlorine dioxide and chlorite do not indicate a particular cancer concern, 

but adequate animal cancer bioassays have not been performed. Genotoxicity testing has produced mixed 

results. Chlorine dioxide and chlorite do not appear to be reproductive toxicants. 

Animal studies indicate that the lowest observed adverse-effect level (LOAEL) is approximately 

5 mg/kg/day for repeated oral exposure to chlorite. Assuming that the average human male (70 kg 

reference bodyweight) drinks 2 liters of water per day, the dose of chlorite would be approximately 

0.03 mg/kg/day from drinking water containing the maximum level of 1 mg chlorite/L that is allowed by 

EPA. It is not likely that humans would be exposed to levels of chlorine dioxide or chlorite in the 

drinking water that would approach adverse effect levels reported in animal studies. 

Neurodevelopmental effects appear to be of greatest toxicological concern, particularly in light of the fact 

that chlorine dioxide and chlorite may be used as disinfectants for drinking water. Therefore, the 

following brief discussion includes only developmental effects. The reader is referred to Section 3.2, 

Discussion of Health Effects by Route of Exposure, for additional information regarding the potential for 

other chlorine dioxide- or chlorite-induced health effects. 

Developmental Effects. Neurodevelopmental effects, such as decreases in brain weight, brain cell 

number, exploratory behavior, and locomotor activity, have been observed in rat pups whose mothers 
 

CHLORINE DIOXIDE AND CHLORITE 11 

2. RELEVANCE TO PUBLIC HEALTH 

were exposed to chlorine dioxide before mating and during gestation and lactation and other rat pups that 

were directly exposed via oral gavage only during postnatal development. Decreases in exploratory 

behavior and amplitude of auditory startle response have been reported in rat pups whose mothers were 

orally exposed to chlorite during gestation and lactation. Perinatal exposure to chlorine dioxide or 

chlorite has also resulted in altered serum thyroid hormone levels or activity. Although mechanisms of 

action responsible for mediating these chlorine dioxide- and chlorite-mediated thyroid hormone effects 

have not been identified, it is widely understood that the thyroid hormone, T3, is essential for normal 

development of the nervous system, and that T3 is synthesized from the deiodination of T4. 

2.3 MINIMAL RISK LEVELS 

Inhalation MRLs 

An acute-duration inhalation MRL was not derived for chlorine dioxide because adequate human or 

animal data are not available. 

No inhalation MRLs were derived for chlorite. The only available information regarding health effects 

following inhalation exposure to chlorite was limited to a single study of lethality in rats exposed to 

aerosols of sodium chlorite, an exposure scenario not likely to be encountered in environmental or 

occupational settings. Furthermore, lethality is a serious effect, and therefore cannot be used as the basis 

for deriving an MRL. 

•	 An MRL of 0.001 ppm (0.003 mg/m3

) has been derived for intermediate-duration inhalation 

exposure (15–365 days) to chlorine dioxide. 

This MRL is based on a lowest-observed-adverse-effect-level (LOAEL) of 1 ppm for respiratory effects 

in rats. Paulet and Desbrousses (1970) exposed groups of 10 rats/sex (strain not specified) to chlorine 

dioxide vapors at concentrations of 0 or 2.5 ppm, 7 hours/day for 30 days. Chlorine dioxide-exposed rats 

exhibited respiratory effects that included lymphocytic infiltration of the alveolar spaces, alveolar 

vascular congestion, hemorrhagic alveoli, epithelial erosions, and inflammatory infiltrations of the 

bronchi. The study authors also reported slightly decreased body weight gain, decreased erythrocyte 

levels, and increased leukocyte levels, relative to controls. Recovery from the pulmonary lesions was 

apparent in rats examined after a 15-day recovery period. In a follow-up study designed to examine a 

lower exposure level (Paulet and Desbrousses 1972), eight Wistar rats (sex not reported) were exposed to 

chlorine dioxide vapors at a concentration of 1 ppm, 5 hours/day, 5 days/week for 2 months. The authors 
CHLORINE DIOXIDE AND CHLORITE 12 

2. RELEVANCE TO PUBLIC HEALTH 

stated that weight gain and erythrocyte and leukocyte levels were not affected. Chlorine dioxide-induced 

respiratory effects included peribronchiolar edema and vascular congestion in the lungs. No alterations in 

epithelium or parenchyma were seen. 

Collectively, these studies adequately identify a LOAEL for respiratory effects associated with 

intermediate-duration inhalation exposure to chlorine dioxide. The intermediate-duration inhalation MRL 

for chlorine dioxide was based on the LOAEL of 1 ppm identified in the Paulet and Desbrousses (1972) 

study, which was adjusted to 0.15 ppm (LOAELADJ) to compensate for intermittent exposure, converted 

to the human equivalent concentration (LOAELHEC) of 0.3 ppm, and then divided by an uncertainty factor 

of 300 (3 for interspecies extrapolation using dosimetric adjustments, 10 for the use of a LOAEL, and 

10 to account for sensitive populations). 

A chronic-duration inhalation MRL was not derived for chlorine dioxide because chronic inhalation 

exposure studies in humans or animals are not available. An approach using an uncertainty factor for 

extrapolating from intermediate- to chronic-duration exposure was not used because it is not known 

whether respiratory irritation, observed during intermediate-duration inhalation exposure to chlorine 

dioxide, might result in more persistent effects in cases of chronic-duration exposure. Furthermore, it is 

not likely that humans would be chronically exposed to significant concentrations of chlorine dioxide 

vapors in environmental or occupational settings. 

Oral MRLs 

Acute-duration oral MRLs were not derived for chlorine dioxide or chlorite because adequate human or 

animal data are not available. 

•	 An MRL of 0.1 mg/kg/day has been derived for intermediate-duration oral exposure (15–
 

364 days) to chlorite. 

This MRL is based on a no-observed-adverse-effect-level (NOAEL) of 2.9 mg chlorite/kg/day and a 

LOAEL of 5.7 mg chlorite/kg/day for neurodevelopmental effects (lowered auditory startle amplitude) in 

rat pups that had been exposed throughout gestation and lactation via their mothers (Gill et al. 2000). 

Groups of 30 male and 30 female Sprague-Dawley rats (F0) received sodium chlorite in the drinking 

water at concentrations of 35, 70, or 300 mg/L (approximate chlorite doses of 3, 5.7, and 21 mg/kg/day 

for males and 3.9, 7.6, and 29 mg/kg/day for females) for 10 weeks prior to mating and during mating, 

after which exposure of females continued throughout gestation and lactation. Groups of F1 pups were 
CHLORINE DIOXIDE AND CHLORITE 13 

2. RELEVANCE TO PUBLIC HEALTH 

continued on the same treatment regimen as their parents (chlorite doses of 2.9, 6, and 23 mg/kg/day and 

3.9, 7.6, and 29 mg/kg/day for F1 males and females, respectively). Low-dose female pups exhibited 

slight, but statistically significant differences in some hematological parameters, relative to controls. No 

other effects were seen in pups of this exposure level, and the hematological effects were not considered 

to be adverse. A significant decrease in maximum response to an auditory startle stimulus was noted in 

mid-dose pups on postnatal day 24, but not on postnatal day 60. Mid-dose F1 pups also exhibited reduced 

liver weight. Significant effects at high dose included reduced absolute and relative liver weight in F1 

males and females, reduced pup survival, reduced body weight at birth and throughout lactation in F1 and 

F2 rats, lower thymus and spleen weight in both generations, lowered incidence of pups exhibiting normal 

righting reflex and with eyes open on postnatal day 15, decreased in absolute brain weight for F1 males 

and F2 females, delayed sexual development in F1 and F2 males (preputial separation) and F1 and F2 

females (vaginal opening), and lowered red blood cell parameters in F1 rats. The NOAEL of 

2.9 mg/kg/day was divided by an uncertainty factor of 30 (10 for interspecies extrapolation and 3 to 

account for sensitive populations). An uncertainty factor of 3 rather than 10 was used for sensitive 

populations because the critical effect (neurodevelopmental delay) occurred in a sensitive population 

(perinatal rat pups). 

Chlorine dioxide in drinking water rapidly degrades, predominately to chlorite (Michael et al. 1981). In 

laboratory animals, orally administered chlorine dioxide is rapidly converted to chlorite and chloride ion 

(Abdel-Rahman et al. 1980b). Being both a strong oxidizer and water soluble, chlorine dioxide is not 

likely absorbed in the gastrointestinal tract to any great extent. Chlorite is the most likely source of 

systemic toxicity resulting from oral exposure to either chlorine dioxide or chlorite. Therefore, the 

intermediate-duration oral MRL derived for chlorite should also be applicable to chlorine dioxide. 

Chronic-duration oral MRLs were not derived for chlorine dioxide or chlorite. No human studies were 

available in which chronic oral exposure to chlorine dioxide or chlorite was evaluated, and available 

chronic-duration oral studies in animals identified LOAELs that were higher than those observed for 

developmental effects following exposures of significantly shorter duration. 

CHLORINE DIOXIDE AND CHLORITE 15 

3. HEALTH EFFECTS 

3.1 INTRODUCTION 

The primary purpose of this chapter is to provide public health officials, physicians, toxicologists, and 

other interested individuals and groups with an overall perspective on the toxicology of chlorine dioxide 

and chlorite. It contains descriptions and evaluations of toxicological studies and epidemiological 

investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic 

data to public health. 

A glossary and list of acronyms, abbreviations, and symbols can be found at the end of this profile. 

3.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE 

To help public health professionals and others address the needs of persons living or working near 

hazardous waste sites, the information in this section is organized first by route of exposure (inhalation, 

oral, and dermal) and then by health effect (death, systemic, immunological, neurological, reproductive, 

developmental, genotoxic, and carcinogenic effects). These data are discussed in terms of three exposure 

periods: acute (14 days or less), intermediate (15–364 days), and chronic (365 days or more). 

Levels of significant exposure for each route and duration are presented in tables and illustrated in 

figures. The points in the figures showing no-observed-adverse-effect levels (NOAELs) or lowestobserved-adverse-effect levels (LOAELs) reflect the actual doses (levels of exposure) used in the studies. 

LOAELs have been classified into "less serious" or "serious" effects. "Serious" effects are those that 

evoke failure in a biological system and can lead to morbidity or mortality (e.g., acute respiratory distress 

or death). "Less serious" effects are those that are not expected to cause significant dysfunction or death, 

or those whose significance to the organism is not entirely clear. ATSDR acknowledges that a 

considerable amount of judgment may be required in establishing whether an end point should be 

classified as a NOAEL, "less serious" LOAEL, or "serious" LOAEL, and that in some cases, there will be 

insufficient data to decide whether the effect is indicative of significant dysfunction. However, the 

Agency has established guidelines and policies that are used to classify these end points. ATSDR 

believes that there is sufficient merit in this approach to warrant an attempt at distinguishing between 

"less serious" and "serious" effects. The distinction between "less serious" effects and "serious" effects is 
CHLORINE DIOXIDE AND CHLORITE 16 

3. HEALTH EFFECTS 

considered to be important because it helps the users of the profiles to identify levels of exposure at which 

major health effects start to appear. LOAELs or NOAELs should also help in determining whether or not 

the effects vary with dose and/or duration, and place into perspective the possible significance of these 

effects to human health. 

The significance of the exposure levels shown in the Levels of Significant Exposure (LSE) tables and 

figures may differ depending on the user's perspective. Public health officials and others concerned with 

appropriate actions to take at hazardous waste sites may want information on levels of exposure 

associated with more subtle effects in humans or animals (LOAELs) or exposure levels below which no 

adverse effects (NOAELs) have been observed. Estimates of levels posing minimal risk to humans 

(Minimal Risk Levels or MRLs) may be of interest to health professionals and citizens alike. 

Estimates of exposure levels posing minimal risk to humans (Minimal Risk Levels or MRLs) have been 

made for chlorine dioxide and chlorite. An MRL is defined as an estimate of daily human exposure to a 

substance that is likely to be without an appreciable risk of adverse effects (noncarcinogenic) over a 

specified duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the 

target organ(s) of effect or the most sensitive health effect(s) for a specific duration within a given route 

of exposure. MRLs are based on noncancerous health effects only and do not consider carcinogenic 

effects. MRLs can be derived for acute, intermediate, and chronic duration exposures for inhalation and 

oral routes. Appropriate methodology does not exist to develop MRLs for dermal exposure. 

Although methods have been established to derive these levels (Barnes and Dourson 1988; EPA 1990), 

uncertainties are associated with these techniques. Furthermore, ATSDR acknowledges additional 

uncertainties inherent in the application of the procedures to derive less than lifetime MRLs. As an 

example, acute inhalation MRLs may not be protective for health effects that are delayed in development 

or are acquired following repeated acute insults, such as hypersensitivity reactions, asthma, or chronic 

bronchitis. As these kinds of health effects data become available and methods to assess levels of 

significant human exposure improve, these MRLs will be revised. 

A User's Guide has been provided at the end of this profile (see Appendix B). This guide should aid in 

the interpretation of the tables and figures for Levels of Significant Exposure and the MRLs. 
CHLORINE DIOXIDE AND CHLORITE 17 

3. HEALTH EFFECTS 

3.2.1 Inhalation Exposure 

Available human and animal data indicate that airborne chlorine dioxide (ClO2) primarily acts as a 

respiratory tract and ocular irritant. Chlorite (ClO2

-

) does not persist in the atmosphere either in ionic 

form or as chlorite salt. Available information concerning health effects associated with inhalation 

exposure is limited to chlorine dioxide. 

3.2.1.1 Death 

Information regarding death in humans exposed to atmospheres of chlorine dioxide is limited to a single 

case in which a bleach tank worker died after being exposed for an unspecified amount of time (Elkins 

1959). A chlorine dioxide vapor concentration of 19 ppm (52.4 mg/m3

) was measured inside the tank. 

Limited information is available regarding death in laboratory animals exposed to atmospheres of 

chlorine dioxide. Death resulted from the exposure of a single guinea pig for 44 minutes to an airborne 

chlorine dioxide concentration of 150 ppm (420 mg/m3

); at the same concentration, exposure for 5 or 

15 minutes was not lethal (Haller and Northgraves 1955). 

Dalhamn (1957) exposed four rats to approximately 260 ppm (728 mg/m3

) of chlorine dioxide for 

2 hours. One of the rats died during exposure and the remaining three rats were sacrificed immediately 

following the 2-hour exposure period. Microscopic examination revealed pulmonary edema and 

circulatory engorgement. Dalhamn (1957) also reported death in three of five rats exposed to 

approximately 10 ppm (28 mg/m3

) of chlorine dioxide, 4 hours/day for up to nine exposures in a 13-day 

period; clinical signs of toxicity included rhinorrhea and altered respiration. 

In another study, rats were repeatedly exposed for 1 month (15 minutes/exposure, 2 or 4 times/day) to 

atmospheres containing 15 ppm (42 mg/m3

) of chlorine dioxide (Paulet and Desbrousses 1974). Death 

was noted in 1/10 and 1/15 rats exposed 2 or 4 times/day, respectively. Histological examination of the 

exposed rats revealed nasal and ocular inflammation, bronchitis, and alveolar lesions. No deaths occurred 

in rats similarly exposed to 10 ppm (28 mg/m3

) of chlorine dioxide. 
CHLORINE DIOXIDE AND CHLORITE 18 

3. HEALTH EFFECTS 

3.2.1.2 Systemic Effects 

The highest NOAEL values and all LOAEL values from each reliable study for each systemic effect in 

each species and duration are recorded in Table 3-1 and plotted in Figure 3-1. 

No reports were located in which gastrointestinal, musculoskeletal, endocrine, dermal, or metabolic 

effects were associated with inhalation exposure of humans or animals to chlorine dioxide or chlorite. 

Respiratory Effects. Limited human data indicate that airborne chlorine dioxide is a primary 

respiratory tract irritant. In a case of accidental inhalation exposure to chlorine dioxide in the paper 

industry, exposure to 5 ppm (14 mg/m3

) for an unspecified amount of time was reported to be irritating 

(Elkins 1959). In another case report, a woman experienced coughing, pharyngeal irritation, and 

headache while mixing a bleach solution that was then used to bleach dried flowers (Exner-Freisfeld et al. 

1986). The mixing process resulted in the release of chlorine dioxide. Increasing cough caused the 

woman to abandon the bleaching process. Seven hours later, the woman began experiencing intensified 

coughing and dyspnea that resulted in hospitalization (16 hours after the exposure) with clinical findings 

of cough, dyspnea, tachypnea, and rales. Pulmonary function tests revealed reduced VC (vital capacity) 

and FEV1 (forced expiratory volume in 1 second) values and increased resistance. Blood gas analysis and 

blood chemistry revealed hypoxemia and leukocytosis, respectively. Corticosteroid treatment resulted in 

the alleviation of clinical signs and improved lung function, which was in the normal range at the 2-year 

follow-up examination. 

Nasal abnormalities (including injection, telangectasia, paleness, cobblestoning, edema, and thick mucus) 

were observed in 13 individuals (1 man and 12 women) who had been accidentally exposed to chlorine 

dioxide from a leak in a water purification system pipe 5 years earlier (Meggs et al. 1996). These 

individuals also exhibited sensitivity to respiratory irritants. Nasal biopsies revealed chronic 

inflammation in the lamina propria of 11/13 chlorine dioxide-exposed individuals, compared with 

1/3 control individuals. The severity of inflammation was significantly increased in the chlorine dioxide 

exposed group, compared to controls. 

Several investigators examined the respiratory health of workers who had been occasionally exposed to 

increased levels of chlorine dioxide resulting from equipment failure (Ferris et al. 1967, 1979; Gloemme 

and Lundgren 1957; Kennedy et al. 1991). Since the results of these studies are confounded by 

concurrent exposure to chlorine gas and/or sulfur dioxide, the reported respiratory effects (such as 
104

10

103

10

105

760

0.1

106108

101010

Table 3-1 Levels of Significant Exposure to Chlorine Dioxide And Chlorite - Inhalation 

Exposure/ LOAEL

Duration/

a

Key to Species Frequency NOAEL Less Serious Serious 

(Specific Route) figure (Strain) System (ppm) (ppm) (ppm) 

ACUTE EXPOSURE Death 

1 Rat 2 hr/d for 9 of 13 d 

10 100% mortality by day 14 

Systemic 

2 Rat 2 hr/d for 9 of 13 d 

Resp 10 rhinorrhea and embarrased 

respiration 

INTERMEDIATE EXPOSURE Systemic 

3 Rat 3 min/d, 1d/wk, for 3 wk 

Resp 760 bronchopneumonia 

4 Rat 5 hr/d for 10 wk 

Resp 0.1 

5 Rat 2 hr/d for 30 d 

Resp 10 bronchopneumonia 

Hemato 10 increased RBC and WBC 

counts 

Ocular 10 irritation 
109

5

111

2.5

113

1

5

115

10

110

5

112

2.5

a

Key to 

figure 

Species 

(Strain) 

LOAEL 

NOAEL Less Serious Serious 

System 

Table 3-1 Levels of Significant Exposure to Chlorine Dioxide And Chlorite - Inhalation 

(ppm) (ppm) (ppm) 

Exposure/ 

Duration/ 

Frequency 

(Specific Route) 

(continued) 

6 Rat 2 hr/d for 30 d 

Resp 5 bronchopneumonia 

7 Rat 7 hr/d for 30 d 

Resp 2.5 slight respiratory irritation 

8 

(Wistar) Rat 5 hr/d 5 d/wk for 2 mo 

Resp 1 

b

minimal peribronchiolar edema 

and vascular congestion in the lungs 

9 Rat 15 min 2 x/d (or 4 x/d) 

for 1 mo Resp 5 10 alveolar irritation 

10 Rabbit 2 hr/d for 30 d 

Resp 5 slight bronchopneumonia 

11 Rabbit 4 hr/d for 45 d 

Resp 2.5 slight pulmonary irritation 

a The number corresponds to entries in Figure 3-1. b An intermediate-duration inhalation MRL of 0.001 ppm was derived from a LOAEL of 1 ppm and adjusted to 0.15 ppm (LOAELADJ) to compensate for interconverted to the human equivalent concentration (LOAELHEC) of 0.3 ppm, and then divided by an uncertainty factor of 300 (3 for interspecies extrapolation usadjustments, 10 for the use of a LOAEL, and 10 to account for sensitive populations). d = day(s); hemato = hematological; hr = hour(s); LOAEL = lowest-observed-adverse-effect level; mo = month(s); NOAEL = no-observed-adverse-effect level= week(s) 
1000 

Death Respiratory Respiratory Hematological Ocula

Figure 3-1. Levels of Significant Exposure to Chlorine Dioxide And Chlorite- Inhalation 

Acute (≤14 days) Intermediate (15-364 days) 

Systemic Systemic 

ppm 

3r 

100 

10 1r 2r 5r 9r 5r 5r 

6r 9r 10h 

7r 11h 

1 8r 

0.1 4r 

0.01 

0.001 

c-Cat -Humans f-Ferret n-Mink Cancer Effect Level-Animals Cancer Effect Level-Humans 

d-Dog k-Monkey j-Pigeon o-Other LOAEL, More Serious-Animals LOAEL, More Serious-Humans 

r-Rat m-Mouse e-Gerbil LOAEL, Less Serious-Animals LOAEL, Less Serious-Humans 

p-Pig h-Rabbit s-Hamster NOAEL - Animals NOAEL - Humans 

q-Cow a-Sheep g-Guinea Pig 
CHLORINE DIOXIDE AND CHLORITE 22 

3. HEALTH EFFECTS 

coughing, wheezing, shortness of breath, and excess phlegm) could not be specifically attributed to 

chlorine dioxide. 

Animal studies also indicate that the respiratory system is a major target of toxicity following inhalation 

exposure to chlorine dioxide. Dalhamn (1957) reported the results of several inhalation studies in 

laboratory animals. In one study, a single 2-hour inhalation exposure of four rats to a chlorine dioxide 

concentration of 260 ppm (728 mg/m3

) resulted in pulmonary edema and nasal bleeding. Respiratory 

distress was reported in three other rats subjected to 3 weekly 3-minute exposures to decreasing 

concentrations of airborne chlorine dioxide from 3,400 to 800 ppm (from 9,520 to 2,240 mg/m3

); 

bronchopneumonia was observed in two of these rats. In a third rat study, repeated exposure to 

approximately 10 ppm (28 mg/m3

) of chlorine dioxide (4 hours/day for 9 days in a 13-day period) 

resulted in rhinorrhea, altered respiration, and respiratory infection. No indications of adverse effects 

were seen in rats exposed to approximately 0.1 ppm (0.28 mg/m3

) of chlorine dioxide 5 hours/day for 

10 weeks. 

Paulet and Desbrousses (1970, 1972, 1974) conducted a series of studies in which laboratory animals 

were exposed to atmospheres of chlorine dioxide. Nasal discharge and localized bronchopneumonia 

(with desquamation of alveolar epithelium) were noted in rats exposed to an airborne concentration of 

10 ppm (28 mg/m3

), 2 hours/day for 30 days. Similar, but less severe, respiratory tract effects were 

observed in another group of rats exposed to a concentration of 5 ppm (14 mg/m3

), 2 hours/day for 

10 days. Bronchial inflammation and alveolar congestion and hemorrhage were observed in rats exposed 

to 2.5 ppm (7 mg/m3

), 7 hours/day for 30 days. Alveolar congestion and hemorrhage were also seen in 

rabbits following inhalation exposure to 2.5 ppm (7 mg/m3

), 4 hours/day for 45 days. In a group of rats 

and rabbits sacrificed 15 days after exposure termination, recovery from the pulmonary lesions was 

apparent (Paulet and Desbrousses 1970). Vascular congestion and peribronchiolar edema were noted in 

the lungs of rats exposed to a concentration of 1 ppm (2.8 mg/m3

), 5 hours/day, 5 days/week for 2 months 

(Paulet and Desbrousses 1972). The LOAEL of 1 ppm for respiratory effects, identified in this study, 

served as the basis for the derivation of an intermediate-duration inhalation MRL for chlorine dioxide (see 

Section 2.3). In another rat study, exposure to concentrations of 10 or 15 ppm (28 or 42 mg/m3

) for 

periods as short as 15 minutes (2 or 4 times/day for 1 month) resulted in nasal, bronchial, and alveolar 

inflammation. These effects had subsided in a 15 ppm (42 mg/m3

) group of rats sacrificed 15 days 

following exposure termination. This study identified a NOAEL of 5 ppm (14 mg/m3

) for respiratory 

effects (Paulet and Desbrousses 1974). 
 

CHLORINE DIOXIDE AND CHLORITE 23 

3. HEALTH EFFECTS 

Cardiovascular Effects. Information regarding cardiovascular effects in humans following 

inhalation exposure to chlorine dioxide is limited to a single account of tachycardia that developed in a 

woman several hours after having been exposed to an unknown concentration of chlorine dioxide that had 

triggered respiratory effects severe enough to force her to leave the area where she had been bleaching 

dried flowers (Exner-Freisfeld et al. 1986). The tachycardia was likely secondary to the primary 

respiratory effects. 

Circulatory engorgement was observed in rats that had been exposed to atmospheres containing a chlorine 

dioxide concentration of approximately 260 ppm (728 mg/m3

) for 2 hours (Dalhamn 1957). This effect 

was likely secondary to respiratory distress. 

Hematological Effects. Information regarding hematological effects in humans following inhalation 

exposure to chlorine dioxide is limited to a single account of marked leukocytosis diagnosed in a woman 

several hours after she had been exposed to an unknown concentration of chlorine dioxide that triggered 

respiratory effects severe enough to force her to leave the area where she had been bleaching dried 

flowers (Exner-Freisfeld et al. 1986). 

Significantly increased blood erythrocyte and leukocyte levels were reported in rats exposed to 

atmospheres containing a chlorine dioxide level of approximately 10 ppm (28 mg/m3

), 2 hours/day for 

30 days (Paulet and Desbrousses 1970). These effects were not seen in a group of rats exposed to 5 ppm 

(14 mg/m3

), 2 hours/day for 10 days. 

Hepatic Effects. No information was located regarding hepatic effects in humans following 

inhalation exposure to chlorine dioxide. 

Paulet and Desbrousses (1974) found no signs of liver effects in rats exposed to atmospheres containing 

chlorine dioxide levels as high as 10 ppm (28 mg/m3

), 2 hours/day for 30 days. On the other hand, 

Dalhamn (1957) reported acute liver congestion in rats that had been exposed to atmospheres of 

approximately 10 ppm of chlorine dioxide for 4 hours/day over 9 days in a 13-day period. However, the 

liver congestion may have been secondary to primary respiratory effects. 

Renal Effects. No information was located regarding renal effects in humans following inhalation 

exposure to chlorine dioxide. 
CHLORINE DIOXIDE AND CHLORITE 24 

3. HEALTH EFFECTS 

Evidence of renal effects in animals is limited to a single report of renal hyperemia in two of three rats 

subjected to 3 weekly 3-minute exposures to decreasing concentrations of airborne chlorine dioxide from 

3,400 to 800 ppm (from 9,520 to 2,240 mg/m3

); however, two of three control rats similarly exhibited 

renal hyperemia (Dalhamn 1957). 

Ocular Effects. Workers employed at a sulfite-cellulose production facility reported ocular 

discomfort that was associated with periods when equipment failure resulted in relatively high air 

concentrations of chlorine dioxide (Gloemme and Lundgren 1957). However, this finding was 

confounded by concurrent exposure to chlorine gas and sulfur dioxide. 

Animal studies indicate that exposure to chlorine dioxide at airborne concentrations ≥10 ppm (28 mg/m3

) 

may result in ocular irritation (Dalhamn 1957; Paulet and Desbrousses 1970, 1974). 

Body Weight Effects. No information was located regarding body weight effects in humans 

following inhalation exposure to chlorine dioxide. 

Limited animal data indicate that repeated inhalation exposure to chlorine dioxide concentrations 

≥10 ppm (28 mg/m3

) may result in depressed body weight gain (Dalhamn 1957; Paulet and Desbrousses 

1970); however, this effect may be secondary to primary respiratory effects. 

No reports were located in which the following health effects in humans or animals could be associated 

with inhalation exposure to chlorine dioxide: 

3.2.1.3 Immunological and Lymphoreticular Effects 

3.2.1.4 Neurological Effects 

3.2.1.5 Reproductive Effects 

3.2.1.6 Developmental Effects 

3.2.1.7 Cancer 
CHLORINE DIOXIDE AND CHLORITE 25 

3. HEALTH EFFECTS 

3.2.2 Oral Exposure 

3.2.2.1 Death 

No information was located regarding death in humans following oral exposure to chlorine dioxide or 

chlorite. 

Shi and Xie (1999) indicated that an acute oral LD50 value (a dose expected to result in death of 50% of 

the dosed animals) for stable chlorine dioxide was >10,000 mg/kg in mice. In rats, acute oral LD50 values 

for sodium chlorite (NaClO2) ranged from 105 to 177 mg/kg (equivalent to 79–133 mg chlorite/kg) 

(Musil et al. 1964; Seta et al. 1991; Sperling 1959). 

No exposure-related deaths were observed in rats receiving chlorine dioxide in the drinking water for 

90 days at concentrations that resulted in approximate doses as high as 11.5 mg/kg/day in males and 

14.9 mg/kg/day in females (Daniel et al. 1990). 

In a 14-day range-finding study of rats administered gavage doses of sodium chlorite in the range of 25– 

200 mg/kg/day (equivalent to 18.6–149.2 mg chlorite/kg/day), one exposure-related death was observed 

in each sex (Harrington et al. 1995a). The deaths occurred in the 200 mg/kg/day group on treatment 

days 2 and 3. No treatment-related deaths occurred in the groups receiving chlorite doses ≤56 mg/kg/day. 

In the 13-week main study performed by these investigators, treatment-related mortality was noted 

between exposure weeks 10 and 13 in 4/30 rats (3 males and 1 female) receiving sodium chlorite by 

gavage at a level resulting in a chlorite dose of 80 mg/kg/day. No treatment-related mortality was 

observed at chlorite dose levels 18.6 mg/kg/day. Death was noted in all four female rats that were 

administered sodium chlorite by gavage at a dose level of 200 mg/kg/day (equivalent to 150 mg 

chlorite/kg/day) on gestation days 8–10 (Couri et al. 1982b). 

Haag (1949) exposed groups of rats to chlorine dioxide in the drinking water for 2 years at concentrations 

that resulted in estimated doses of 0.07, 0.13, 0.7, 1.3, or 13 mg/kg/day. The results did not indicate any 

significant differences in mortality between controls and treated groups up to the highest exposure level 

tested. Survival was not significantly decreased in groups of rats exposed to chlorite (as sodium chlorite) 

in the drinking water for 2 years at concentrations that resulted in estimated chlorite doses as high as 

81 mg/kg/day (Haag 1949). In another chronic study (Kurokawa et al. 1986), survival was not adversely 

affected in rats given sodium chlorite in the drinking water at concentrations that resulted in estimated 

chlorite doses as high as 32.1 mg/kg/day in males and 40.9 mg/kg/day in females. This study was 
 

CHLORINE DIOXIDE AND CHLORITE 26 

3. HEALTH EFFECTS 

terminated after 85 weeks of treatment, due to widespread Sendai viral infection in both treatment groups 

and controls. Exposure of mice to sodium chlorite for up to 85 weeks at concentrations resulting in 

estimated chlorite doses as high as 90 mg/kg/day did not appear to adversely affect survival. However, 

control males exhibited markedly reduced survival after 30 weeks of exposure, which was attributed to 

severe fighting (Kurokawa et al. 1986). 

The only available LD50 value for chlorite is recorded in Table 3-2 and plotted in Figure 3-2. 

3.2.2.2 Systemic Effects 

The highest NOAEL values and all LOAEL values from each reliable study for each systemic effect in 

each species and duration are recorded in Table 3-2 and plotted in Figure 3-2. 

No reports were located in which cardiovascular, musculoskeletal, dermal, ocular, or metabolic effects 

were associated with oral exposure of humans or animals to chlorine dioxide or chlorite. 

Respiratory Effects. Extremely limited information is available regarding respiratory effects in 

humans following oral exposure to chlorine dioxide or chlorite. Respiratory distress was diagnosed in a 

patient who had ingested 10 g of sodium chlorite dissolved in 100 mL of water (Lin and Lim 1993). 

However, the respiratory distress was likely secondary to other effects such as severe methemoglobinemia. No adverse effects on respiration rate were seen in healthy adult males who ingested 

chlorine dioxide or chlorite every 3 days (for 16 days) at increasing doses of 0.1, 1, 5, 10, 18, and 

24 mg/day or 0.01, 0.1, 0.5, 1.0, 1.8, and 2.4 mg/day, respectively (Lubbers et al. 1981). Assuming an 

average body weight of 70 kg, the individual doses were approximately 0.0014, 0.014, 0.070, 0.140, 0.26, 

and 0.34 mg/kg/day, respectively, for chlorine dioxide and a factor of 10 lower for respective chlorite 

doses. No adverse effects on respiration rate were observed in other healthy adult males who ingested 

chlorine dioxide or chlorite in daily amounts of 2.5 mg (0.04 mg/kg/day) for 12 weeks (Lubbers et al. 

1981). 

Information regarding respiratory effects in orally-exposed animals is limited to a report of a significantly 

increased incidence of nasal lesions (goblet cell hyperplasia and inflammation of nasal turbinates) 

following 90 days of exposure to chlorine dioxide in the drinking water at concentrations that resulted in 

estimated doses as low as 2 mg/kg/day in males and 8 mg/kg/day in females (Daniel et al. 1990). These 
128

140

25

12

19

4

19

0.9

137

9

10

139

Table 3-2 Levels of Significant Exposure to Chlorine Dioxide And Chlorite - Oral 

a

Key to 

figure 

Exposure/ 

Duration/ 

Frequency 

(Specific Route) Species (Strain) 

ACUTE EXPOSURE Death 

1 1x 

(GW) 

Rat 

System 

NOAEL 

(mg/kg/day) 

Less Serious 

(mg/kg/day) 

LOAEL 

Serious 

(mg/kg/day) 

140 M (LD50) 

2 

INTERMEDIATE EXPOSURE Systemic 

12 hrs d 30 d (W) 

A/J 

Mouse 

Hemato 25 

3 

A/J 

Mouse 12 hrs/d 

30 d (W) 

Hemato 19 Increased average corpuscular 

volume and osmotic fragility 

4 

C57L/J Mouse 12 hrs/d 

30 d (W) 

Hemato 19 Increased average corpuscular 

volume and osmotic fragility 

5 

Reproductive 

66-76 d 

(Long- Evans) (W) Rat 

0.9 M 9 M decreased progressive sperm 

movement 

6 1x/d for 9 wk 

(Long- Evans) (GW) Rat 

10 
29

131

1.3

146

13

0.9

135

9

2.9

129

5.7

132

13

2.6

133

5.2

Table 3-2 Levels of Significant Exposure to Chlorine Dioxide And Chlorite - Oral (continued) 

Exposure/ LOAEL

Duration/

a

Key to Species Frequency NOAEL Less Serious Serious 

(Specific Route) figure (Strain) System (mg/kg/day) (mg/kg/day) (mg/kg/day) 

7 Rat 16 wk 

29

(Sprague- (W) 

Dawley)

8 Rat 13 wk 

1.3 13 decreased number of implants (Sprague- (W) 

Dawley)

Developmental 

9 Rat 8 wk 

0.9 M 9 M decreased serum T3 and T4 

(Long- Evans) (W) 

levels 

10 Rat 16 wk b 

2.9 M 5.7 M lowered auditory startle (Sprague- (W) 

response amplitude on Dawley) postnatal day 24 

11 Rat 9 wk 

13 M decreased litter weight and (Sprague- (W) 

exploratory activity Dawley) 

12 Rat 9 wk 

2.6 M 5.2 M decreased exploratory activity (Sprague- (W) 

on postnatal days 36-39 Dawley) 
2.6

140

13

141

14

1.3

145

13

1.3

147142

13

143

14

144

14

Table 3-2 Levels of Significant Exposure to Chlorine Dioxide And Chlorite - Oral (continued) 

Exposure/ LOAEL

Duration/

a

Key to Species Frequency NOAEL Less Serious Serious 

(Specific Route) figure (Strain) System (mg/kg/day) (mg/kg/day) (mg/kg/day) 

13 Rat 8 wk 

2.6 F 13 F altered serum thyroid hormone (Sprague- (W) 

levels

Dawley) 

14 Rat ppd 5-20 

14 decreased activity, decreased (Sprague- (W) 

serum T4

Dawley) 

15 Rat 13 wk 

1.3 13 decreased number of live

(Sprague- (W) fetuses 

Dawley)

16 Rat 13 wk 

1.3

(Sprague- (W) 

Dawley)

17 Rat 8 wk 

13 M decreased activity, decreased (Sprague- (W) 

brain weight and cell number Dawley) 

18 Rat ppd 5-20 

14 M decreased activity, decreased (Sprague- (GW) 

brain weight and DNA content Dawley) 

19 Rat ppd 1-20 

14 decreased brain weight and (Long- Evans) (GW) 

protein content 
148

23

Table 3-2 Levels of Significant Exposure to Chlorine Dioxide And Chlorite - Oral (continued) 

Exposure/ LOAEL

Duration/

a

Key to Species Frequency NOAEL Less Serious Serious 

(Specific Route) figure (Strain) System (mg/kg/day) (mg/kg/day) (mg/kg/day) 

20 Mouse 6 wk 

23 decreased average pupweaning A/J (W) weight and birth-to-weaning 

growth rate 

aThe number corresponds to entries in Figure 3-2. b An intermediate-duration oral MRL of 0.1 mg/kg/d was derived from a NOAEL of 2.9 mg/kg/day and divided by an uncertainty factor of 30 (10 for interspecieaccount for sensitive populations). d = day(s); F = Female; G = gavage; hr = hour(s); GW = gavage in water; LOAEL = lowest-observed-adverse-effect level; M = male; NOAEL = no-observed-ad= post parturition day; (W) = drinking water; wk = week(s) 
1000 

Death Hematological Reproductive Developmental 

Figure 3-2. Levels of Significant Exposure to Chlorine Dioxide And Chlorite- Oral 

Acute (≤14 days) Intermediate (15-364 days) 

Systemic 

mg/kg/day 

1r 

100 

7r 2m 20m 

3m 4m 

14r 

8r 11r 13r 15r 17

10 6r 5r 9r 

10r 12r 10r 12r 13r 

8r 15r 16r 

1 5r 9r 

0.1 

c-Cat -Humans f-Ferret n-Mink Cancer Effect Level-Animals Cancer Effect Level-Humans 

d-Dog k-Monkey j-Pigeon o-Other LOAEL, More Serious-Animals LOAEL, More Serious-Humans 

r-Rat m-Mouse e-Gerbil LOAEL, Less Serious-Animals LOAEL, Less Serious-Humans 

p-Pig h-Rabbit s-Hamster NOAEL - Animals NOAEL - Humans 

q-Cow a-Sheep g-Guinea Pig 
CHLORINE DIOXIDE AND CHLORITE 32 

3. HEALTH EFFECTS 

nasal effects were likely caused by inhalation of chlorine dioxide vapors released from the water rather 

than a systemic respiratory effect following oral exposure. 

Gastrointestinal Effects. Information in humans is limited to a single account of abdominal cramps, 

nausea, and vomiting within a few minutes after a 25-year-old Chinese male had consumed 10 g of 

sodium chlorite dissolved in 100 mL of water in an apparent suicide attempt (Lin and Lim 1993). 

Information regarding gastrointestinal effects in animals following oral exposure to chlorine dioxide or 

chlorite is also limited. Bercz et al. (1982) reported erythema and ulceration of the oral mucosa in adult 

African green monkeys exposed to chlorine dioxide in the drinking water for between 30 and 60 days at a 

concentration that resulted in a dose of approximately 9 mg/kg/day. Dose-related increased severity of 

salivation and histopathologic alterations in the stomach (including squamous epithelial hyperplasia, 

hyperkeratosis, ulceration, chronic inflammation, and edema) were observed in groups of rats 

administered sodium chlorite in gavage doses of 25 or 80 mg/kg/day (equivalent to 19 or 60 mg 

chlorite/kg/day, respectively) for 13 weeks; these effects were not seen at a dose level of 7.4 mg 

chlorite/kg/day (Harrington et al. 1995a). 

Hematological Effects. Profound methemoglobinemia was diagnosed in a 25-year-old Chinese male 

after he had consumed 10 g of sodium chlorite dissolved in 100 mL of water in an apparent suicide 

attempt (Lin and Lim 1993). Other hematological effects, including ensuing intravascular coagulation, 

were likely secondary to the methemoglobinemia that persisted despite treatment with methylene blue. 

No indications of altered hematological parameters were seen in adult male subjects consuming chlorine 

dioxide in aqueous solution that resulted in a single dose of approximately 0.34 mg/kg of chlorine dioxide 

(Lubbers et al. 1981) or in other adult males consuming approximately 0.04 mg/kg/day for 12 weeks 

(Lubbers et al. 1981, 1984a). The same investigators tested chlorite for adverse effects in healthy adult 

males, and found no evidence of hematological effects after each subject consumed of a total of 1,000 mL 

of a solution containing 2.4 mg/L chlorite (approximately 0.068 mg/kg) in two doses (separated by 

4 hours), or in other healthy normal or glucose-6-phosphate dehydrogenase (G6PD) deficient male 

subjects who consumed approximately 0.04 mg/kg/day for 12 weeks (Lubbers et al. 1981, 1984a, 1984b). 

No chlorine dioxide- or chlorite-induced hematological effects were seen among the inhabitants of a rural 

village who were exposed for 12 weeks via chlorine dioxide in the drinking water at weekly measured 

concentrations ranging from 0.25 to 1.11 mg/L (chlorine dioxide) or from 3.19 to 6.96 mg/L (chlorite) 

(Michael et al. 1981). In this epidemiological study, levels of chlorine dioxide in the drinking water 

before and after the treatment period were <0.05 mg/L. The chlorite level in the drinking water was 
CHLORINE DIOXIDE AND CHLORITE 33 

3. HEALTH EFFECTS 

0.32 mg/L prior to chlorine dioxide treatment. At 1 and 2 weeks following cessation of treatment, 

chlorite levels dropped to 1.4 and 0.5 mg/L, respectively. 

Some animal studies include reports of hematological effects following oral exposure to chlorine dioxide 

or chlorite. Abdel-Rahman and coworkers (Abdel-Rahman et al. 1984b; Couri and Abdel-Rahman 1980) 

exposed groups of male rats to chlorine dioxide in the drinking water, 20 hours/day for 11 or 12 months, 

at concentrations that resulted in estimated doses of 0.1, 1, 10, and 100 mg/kg/day. Abdel-Rahman et al. 

(1984b) noted that several hematological parameters were significantly altered in exposed rats, relative to 

controls, and included decreased osmotic fragility in the 10 and 100 mg/kg/day groups after 2, 4, 7, or 

9 months of exposure, and in the 1 mg/kg/day group after 9 months of exposure; decreased erythrocyte 

counts in the 0.1 mg/kg/day and 100 mg/kg/day groups after 9 months of exposure, but not after 

7 months; reduced hematocrit and hemoglobin levels in all groups at 9 months that did not exhibit clear 

dose-response patterns; increased hematocrit levels in the 10 and 100 mg/kg/day groups at 7 months; and 

increased mean corpuscular hemoglobin concentrations in the 10 and 100 mg/kg/day groups after 

9 months. The study authors suggested that the decreased osmotic fragility may have been related to the 

disulfide bond between hemoglobin and the cell membrane as the result of oxidative stress. Couri and 

Abdel-Rahman (1980) found significant increases in blood glutathione reductase levels in rats of the 

1, 10, and 100 mg/kg/day groups after 6 months of exposure. At 12 months of exposure, the blood 

glutathione reductase levels in all exposure groups were similar to those of controls, but the levels of 

blood glutathione peroxidase were significantly increased at 10 and 100 mg/kg/day. Blood catalase levels 

were increased in the 100 mg/kg/day group after 6 and 12 months of exposure and decreased in the 

0.1 and 1 mg/kg/day groups after 6 months of exposure. The results of Couri and Abdel-Rahman (1980) 

generally indicate that chlorine dioxide and chlorite may induce increased blood glutathione oxidase 

activity and resulting decreased blood glutathione levels, which is consistent with the protective role of 

glutathione against oxidative cellular damage. 

Abdel-Rahman and coworkers (Abdel-Rahman et al. 1984b; Couri and Abdel-Rahman 1980) also 

exposed male rats to sodium chlorite in the drinking water, 20 hours/day for up to 1 year, at 

concentrations that resulted in estimated doses of 1 or 10 mg/kg/day. Both dose levels resulted in 

increased mean corpuscular hemoglobin concentration (after 7, but not 9 months) and decreased osmotic 

fragility after 7–9 months). Erythrocyte glutathione levels were significantly decreased at dose levels 

0.1 mg/kg/day by the end of the 1-year exposure period. No consistent treatment-related alterations in 

erythrocyte count, hematocrit, or hemoglobin levels were observed. 
 

CHLORINE DIOXIDE AND CHLORITE 34 

3. HEALTH EFFECTS 

Harrington et al. (1995a) administered sodium chlorite to rats by gavage for 13 weeks, resulting in 

chlorite doses of 7.4, 19, or 60 mg/kg/day. Relative to controls, significant treatment-related 

hematological effects included decreased hematocrit and hemoglobin levels (high-dose males), increased 

methemoglobin and neutrophil levels (mid- and high-dose males), decreased lymphocyte count (mid-dose 

males), decreased mean erythrocyte count (high-dose males and females), morphological changes in 

erythrocytes (high-dose males and females), and increased spleen weights (high-dose males and mid- and 

high-dose females). An unexplained decrease in methemoglobin was observed in high-dose females. 

No consistent alterations in hematological parameters (erythrocyte and total and differential leukocyte 

counts, hemoglobin levels, hematocrit, mean corpuscular volume) were observed in groups of male and 

female rats given chlorine dioxide in the drinking water for 90 days at concentrations that resulted in 

doses as high as 12 and 15 mg/kg/day for males and females, respectively (Daniel et al. 1990). 

No significant alterations in hematological parameters were seen in adult African green monkeys given 

chlorine dioxide in the drinking water for up to 60 days at rising concentrations that resulted in estimated 

doses as high as 9 mg/kg/day (Bercz et al. 1982). Bercz and coworkers later exposed these same 

monkeys to sodium chlorite in the drinking water in rising concentrations that resulted in estimated 

chlorite doses as high as 58.4 mg/kg/day. Statistically significant dose-related hematological alterations 

in these monkeys included decreased erythrocyte levels and cell indices, decreased hemoglobin levels, 

and slight increases in reticulocyte and methemoglobin levels. However, the data were not presented in a 

manner that would allow identification of threshold doses for these effects. 

Moore and Calabrese (1982) found no significant alterations in hematological parameters within groups 

of mice exposed to chlorine dioxide in the drinking water for 30 days, at a concentration that resulted in 

an estimated dose of 25 mg/kg/day. However, when similarly examining the hematotoxicity of chlorite, 

Moore and Calabrese (1982) found significant increases in mean corpuscular volume and osmotic 

fragility at a dose level of 19 mg/kg/day. 

Heffernan et al. (1979b) observed significant methemoglobinemia within 1–2 hours in cats that had been 

administered chlorite in single doses of 20 or 64 mg/kg. These same investigators found no signs of 

methemoglobinemia in rats exposed to sodium chlorite in the drinking water for 30–90 days at 

concentrations that resulted in estimated chlorite doses as high as 50 mg/kg/day. Doses ≥10 mg/kg/day 

resulted in slight anemia at 30 days, but this condition appeared to improve at 60 and 90 days. 
CHLORINE DIOXIDE AND CHLORITE 35 

3. HEALTH EFFECTS 

Hepatic Effects. No indications of adverse hepatic effects (assessed in tests of serum chemistry) were 

seen in adult male subjects consuming chlorine dioxide in aqueous solution that resulted in a dose of 

approximately 0.34 mg/kg (Lubbers et al. 1981) or in other adult males consuming approximately 

0.04 mg/kg/day for 12 weeks (Lubbers et al. 1984a). The same investigators administered chlorite to 

healthy adult males, and found no evidence of adverse hepatic effects after each subject had consumed of 

a total of 1,000 mL of a solution containing 2.4 mg/L chlorite (approximately 0.068 mg/kg) in two doses 

(separated by 4 hours), or in other healthy normal or G6PD deficient male subjects who had consumed 

approximately 0.04 mg/kg/day for 12 weeks (Lubbers et al. 1984a, 1984b). No chlorine dioxide- or 

chlorite-induced signs of altered liver function were seen among the inhabitants of a rural village who 

were exposed for 12 weeks via chlorine dioxide in the drinking water at weekly measured concentrations 

ranging from 0.25 to 1.11 mg/L (chlorine dioxide) or from 3.19 to 6.96 mg/L (chlorite) (Michael et al. 

1981). In this epidemiological study, levels of chlorine dioxide in the drinking water before and after the 

treatment period were <0.05 mg/L. The chlorite level in the drinking water was 0.32 mg/L prior to 

chlorine dioxide treatment. At 1 and 2 weeks following cessation of treatment, chlorite levels dropped to 

1.4 and 0.5 mg/L, respectively. 

Limited information is available regarding hepatic effects in animals following oral exposure to chlorine 

dioxide or chlorite. Daniel et al. (1990) exposed male and female rats to chlorine dioxide in the drinking 

water for 90 days at concentrations that resulted in estimated doses of 1.9, 3.6, 6.2, or 11.5 mg/kg/day for 

males and 2.4, 4.6, 8.2, or 14.9 mg/kg/day for females. Significantly depressed mean absolute liver 

weights were observed in males at doses ≥3.6 mg/kg/day and females of the 8.2 mg/kg/day dose group. 

However, these groups also exhibited decreased water consumption. Moore and Calabrese (1982) found 

significant increases in G6PD activity in mice receiving sodium chlorite in the drinking water for 30 days 

at a concentration that resulted in a chlorite dose of 19 mg/kg/day. 

Renal Effects. No chlorine dioxide- or chlorite-induced signs of altered renal function were seen 

among the inhabitants of a rural village who were exposed for 12 weeks via chlorine dioxide in the 

drinking water at weekly measured concentrations ranging from 0.25 to 1.11 mg/L (chlorine dioxide) or 

from 3.19 to 6.96 mg/L (chlorite) (Michael et al. 1981). In this epidemiological study, levels of chlorine 

dioxide in the drinking water before and after the treatment period were <0.05 mg/L. The chlorite level in 

the drinking water was 0.32 mg/L prior to chlorine dioxide treatment. At 1 and 2 weeks following 

cessation of treatment, chlorite levels dropped to 1.4 and 0.5 mg/L, respectively. Acute renal failure 

developed in a 25-year-old Chinese male some days after he had consumed 10 g of sodium chlorite 
 

CHLORINE DIOXIDE AND CHLORITE 36 

3. HEALTH EFFECTS 

dissolved in 100 mL of water in an apparent suicide attempt (Lin and Lim 1993), but this effect followed 

earlier signs of profound methemoglobinemia and respiratory distress. 

Information regarding renal effects in animals is limited. Moore and Calabrese (1982) found no evidence 

of renal effects in mice exposed to sodium chlorite in the drinking water for up to 180 days at a 

concentration that resulted in an estimated chlorite dose of 25 mg/kg/day. Haag (1949) reported 

treatment-related pathological effects (distension of the glomerular capsule and appearance of a pale 

pinkish staining material in the renal tubules) in the kidneys of rats exposed to chlorite in the drinking 

water for 2 years at concentrations that resulted in estimated doses of 7 or 13 mg/kg/day. Increased 

relative kidney weights, in the absence histopathological renal effects, were observed in rats administered 

sodium chlorite in gavage doses of 80 mg/kg/day (equivalent to 60 mg chlorite/kg/day) for 13 weeks 

(Harrington et al. 1995a). 

Endocrine Effects. No reports were located in which endocrine effects could be associated with oral 

exposure to chlorine dioxide or chlorite in humans. 

Information from animal studies is limited to accounts of significantly reduced serum levels of the T4 

thyroid hormone in African green monkeys consuming approximately 9 mg chlorine dioxide/kg/day from 

the drinking water for 6 weeks or approximately 58.4 mg chlorite/kg/day for 8 weeks (Bercz et al. 1982), 

and a single report of significantly increased adrenal weight in female rats administered sodium chlorite 

gavage doses ≥25 mg/kg/day (≥19 mg chlorite/kg/day) for 13 weeks (Harrington et al. 1995a). Refer to 

Section 3.2.2.6 for information regarding altered serum hormone levels in laboratory animals that had 

been exposed via their mothers during prenatal and postnatal development. 

Body Weight Effects. No reports were located in which body weight effects could be associated 

with oral exposure to chlorine dioxide or chlorite in humans. 

Abdel-Rahman et al. (1984b) reported significantly reduced body weight gain (up to 18% lower than 

controls) in male rats exposed to chlorine dioxide in the drinking water for 11 months at concentrations 

resulting in estimated doses ranging from 0.12 to 120 mg/kg/day. The same authors reported similar, but 

less pronounced, reduced body weight gain in rats exposed to sodium chlorite at concentrations that 

resulted in chlorite doses of approximately 1.2 and 12 mg/kg/day. Although this effect appeared earlier at 

the highest concentration, mean terminal body weight after 11 months of exposure was lower in low-dose 

rats than in high-dose rats. Furthermore, the authors did not provide information regarding water and 
CHLORINE DIOXIDE AND CHLORITE 37 

3. HEALTH EFFECTS 

food consumption. Kurokawa et al. (1986) reported slightly decreased body weight gain (<10% lower 

than controls) in male and female rats exposed to sodium chlorite in the drinking water for up to 85 weeks 

at concentrations that resulted in estimated chlorite doses of 13.5 and 24 mg/kg/day in males and 21 and 

31 mg/kg/day in females. The results of Kurokawa et al. (1986) are of questionable toxicological 

significance because water intake among sodium chloride treatment groups was lower than that of 

controls and the study had to be terminated early due to a Sendai virus infestation within all study groups. 

Harrington et al. (1995a) found no significant adverse body weight effects in rats administered up to 

60 mg chlorite/kg/day (via gavage) for 13 weeks. No treatment-related effects on body weight were seen 

in male rats that were administered chlorine dioxide in gavage doses of 2.5, 5, or 10 mg/kg/day for 

56 days prior to mating and 10 more days during mating, or in female rats administered the same doses 

for 14 days prior to mating and throughout mating, gestation, and lactation (Carlton et al. 1991). No 

significant adverse body weight effects were seen in mice given sodium chlorite in the drinking water for 

up to 180 days at concentrations resulting in estimated chlorite doses as high as 25 mg/kg/day (Moore and 

Calabrese 1982) or in other mice exposed to sodium chlorite for 80 weeks at a concentration that resulted 

in an estimated chlorite dose of 90 mg/kg/day (Kurokawa et al. 1986). 

3.2.2.3 Immunological and Lymphoreticular Effects 

No reports were located in which immunological or lymphoreticular effects could be associated with oral 

exposure to chlorine dioxide or chlorite in humans. 

Animal data are restricted to limited accounts of treatment-related altered thymus and spleen weights. 

Daniel et al. (1990) observed reduced spleen weights in female, but not male, rats exposed to chlorine 

dioxide in the drinking water for 90 days at concentrations that resulted in estimated doses ranging from 

2 to 15 mg/kg/day, but the basis for this effect was not discussed. Harrington et al. (1995a) found 

significantly increased spleen weights in male rats administered sodium chlorite by gavage at a dose level 

of 80 mg/kg/day (60 mg chlorite/kg/day) for 13 weeks and in female rats similarly treated with 10 or 

60 mg chlorite/kg/day. In this study, increased spleen weights were attributed to morphological changes 

in erythrocytes. Significantly lower spleen and thymus weights were seen in F1 and F2 rats that had been 

exposed to sodium chlorite via their mothers during gestation and lactation and via the drinking water 

after weaning (Gill et al. 2000). 
CHLORINE DIOXIDE AND CHLORITE 38 

3. HEALTH EFFECTS 

3.2.2.4 Neurological Effects 

No reports were located in which neurological effects could be associated with oral exposure to chlorine 

dioxide or chlorite in humans or animals. Refer to Section 3.2.2.6 for information regarding 

neurodevelopmental effects. 

3.2.2.5 Reproductive Effects 

No reports were located in which reproductive effects could be associated with oral exposure to chlorine 

dioxide or chlorite in humans. 

A paucity of evidence exists for reproductive effects in animals following oral exposure to chlorine 

dioxide or chlorite. Slight, but significantly altered sperm morphology and motility were observed in 

male rats exposed to sodium chlorite in the drinking water for 66–76 days at concentrations that resulted 

in estimated chlorite doses of 9 and 37 mg/kg/day. No dose-related alterations in fertility rates or 

reproductive tissues (both gross and histopathological examination) were seen and no adverse effects 

were observed at a chlorite dose level of 0.9 mg/kg/day (Carlton and Smith 1985; Carlton et al. 1987). 

Significantly decreased testicular deoxyribonucleic acid (DNA) synthesis was noted in male rats given 

chlorine dioxide or chlorite (as sodium salt) in the drinking water for 3 months at concentrations that 

resulted in estimated chlorine dioxide and chlorite doses ≥1.3 and 0.13 mg/kg/day, respectively (AbdelRahman et al. 1984b), and other male rats exposed for 3 weeks to a concentration that resulted in a 

chlorine dioxide dose of 13 mg/kg/day or a chlorite dose of 1.3 mg/kg/day (Suh et al. 1983). A treatmentrelated decreased number of implants was noted in untreated females that had been mated with chlorine 

dioxide-treated males of the 13 mg/kg/day level (Suh et al. 1983). No significant increases in abnormal 

sperm-head morphology were seen in mice given chlorine dioxide or chlorite in gavage doses as high as 

16 and 40 mg/kg/day, respectively, for 5 days followed by 3 weeks without treatment prior to testing 

(Meier et al. 1985). Carlton et al. (1991) found no significant treatment-related effects on fertility rates or 

sperm parameters in rats following the administration of chlorine dioxide in gavage doses as high as 

10 mg/kg/day for 56 days prior to mating and throughout a 10-day mating period (males) and 14 days 

prior to mating and throughout mating, gestation, and lactation (females). 

The highest NOAEL values and all LOAEL values from each reliable study for reproductive effects in 

each species and duration are recorded in Table 3-2 and plotted in Figure 3-2. 
CHLORINE DIOXIDE AND CHLORITE 39 

3. HEALTH EFFECTS 

3.2.2.6 Developmental Effects 

Information regarding developmental effects in humans following oral exposure to chlorine dioxide or 

chlorite is limited. 

Tuthill et al. (1982) retrospectively compared infant morbidity and mortality data for a community that 

had utilized chlorine dioxide as a drinking water disinfectant in the 1940s with data of a neighboring 

community that used conventional drinking water chlorination practices. Exposure to chlorine dioxidetreated water did not adversely affect fetal or perinatal mortality, or birth weight, maximum weight loss, 

weight loss at 6 days, sex ratio, or birth condition. The authors reported a significantly greater proportion 

of premature births in the community using chlorine dioxide, as judged by physician assessment. 

However, other measures of premature birth, such as birth weight and gestational age, did not support the 

results based on physician assessment. Infants from the community using chlorine dioxide exhibited 

statistically significantly greater maximum weight loss after birth and smaller weight gain in 6 days, 

although these effects appeared to be partially linked to the mode of feeding practiced by the mother. 

Kanitz et al. (1996) followed 548 births at Galliera Hospital, Genoa, Italy, and 128 births at Chiavari 

Hospital, Chiavari, Italy, during 1988–1989. Data on infant birth weight, body length, cranial 

circumference, and neonatal jaundice and on maternal age, smoking, alcohol consumption, education, and 

preterm delivery were collected from hospital records. Women in Genoa were exposed to filtered water 

disinfected with chlorine dioxide, sodium hypochlorite, or both; trihalomethane levels varied from 8 to 

16 ppb in sodium hypochlorite-treated water and from 1 to 3 ppb in chlorine dioxide-disinfected water. 

Levels of chlorine dioxide in the water immediately after treatment were <0.3 mg/L, while chlorine 

residue was <0.4 mg/L. Women residing in Chiavari used water pumped from wells, without any 

disinfection treatment, and served as the comparison group (controls). Odds ratios (ORs) were 

determined for the somatic parameters by comparison of groups exposed to chlorine dioxide, sodium 

hypochlorite, or both with controls and adjusted for maternal education level, income, maternal age, 

alcohol consumption, and smoking, as well as for sex of the child. Neonatal jaundice occurred more 

frequently (OR=1.7; 95% confidence interval [CI]=1.1–3.1) in infants whose mothers resided in the area 

where surface water was disinfected with chlorine dioxide, when compared with infants with mothers 

using nondisinfected well water. Infants born to mothers residing in areas where surface water was 

disinfected had smaller cranial circumference (≤35 cm) (OR=2.2, 95% CI=1.4–3.9 for chlorine dioxide; 

OR=3.5, 95% CI=2.1–8.5 for sodium hypochlorite vs. untreated well water; OR=2.4, 95% CI=1.6–5.3 for 
CHLORINE DIOXIDE AND CHLORITE 40 

3. HEALTH EFFECTS 

both vs. untreated well water). In addition, these infants had a smaller body length (≤49.5 cm) (OR=2.0, 

95% CI=1.2–3.3 for chlorine dioxide vs. untreated well water; OR=2.3, 95% CI=1.3–4.2 for sodium 

hypochlorite vs. untreated well water). Risks for low birth weight (≤2,500 g) were reported to be 

increased among mothers residing in areas using water disinfected with chlorine dioxide, but these 

associations were not statistically significant. For preterm delivery (≤37 weeks), small but not 

statistically significant increased risks were found among mothers residing in the area using chlorine 

dioxide. The study authors concluded that infants of women who consumed drinking water treated with 

chlorine compounds during pregnancy were at higher risk for neonatal jaundice, cranial circumference 

≤35 cm, and body length ≤49.5 cm. 

Interpretability of the results of Kanitz et al. (1996) is limited by lack of consideration of exposure and 

potential confounding variables such as lack of quantitative exposure information, exposure to other 

chemicals in the water, and nutritional habits of the women. In addition, baseline values for the infant sex 

ratio and percentage of low-weight births for the comparison group deviate from values presented by the 

World Health Organization for Italy. For example, the sex ratio (male/female live births x100) used in 

the study for the comparison group was 86, but most recent data (1996; as cited in WHO 2002) for Italy 

indicate a sex ratio value of 106. Although the percentage of low-weight births in the control group for 

the Kanitz et al. (1996) study was 0.8%, the percentage of low-weight births (<2,500 g) in Italy for 1994 

was 6%. The quality of the untreated well water is not known (i.e., whether it contained any chemical or 

biological contaminants). 

Källén and Robert (2000) found no adverse effects on congenital malformations, childhood cancer, infant 

mortality, low Apgar score, neonatal jaundice, or neonatal hypothyroidism among infants and children 

who lived in areas where drinking water was disinfected with chlorine dioxide, compared to controls 

living in areas where chlorination of drinking water was not practiced. This study is limited because 

levels of chlorination products and byproducts in the drinking water were not monitored. 

Numerous animal studies are available in which developmental end points have been evaluated following 

oral exposure to chlorine dioxide or chlorite. Some studies cited effects such as decreases in brain 

weight, brain cell number, exploratory behavior, locomotor activity, and serum thyroxine levels in rat 

pups whose mothers were exposed to chlorine dioxide before mating and during gestation and lactation 

and other rat pups that were directly exposed via oral gavage only during postnatal development. Effects 

such as decreases in serum thyroxine levels, body weight and growth, exploratory behavior, and 
 

CHLORINE DIOXIDE AND CHLORITE 41 

3. HEALTH EFFECTS 

amplitude of auditory startle response were reported in rat pups whose mothers were exposed to chlorite 

before mating and during gestation and lactation. 

Chlorine Dioxide. Mobley et al. (1990) administered chlorine dioxide in the drinking water of female 

rats for 10 days prior to mating with unexposed males, and during gestation and lactation (until 

postconception days 35–42) at a concentration that resulted in an estimated dose of 13 mg/kg/day. No 

treatment-related effects were seen in litter size at birth, pup weight gain, or day of eye opening. Litter 

weight at birth was significantly lower (5%) than controls. At ages 36 through 39 days postconception, 

exploratory activity was significantly depressed, relative to controls, but not on day 40. On 

postconception days 37 and 38, no significant treatment-related effects were seen in serum T3 or T4 

levels in male pups (serum thyroid hormone levels were not tested in female pups), but T3 uptake was 

significantly decreased. By postconception day 42, T3 uptake in the exposed male pups was no longer 

significantly different from controls. The authors suggested that reduced T3 uptake may be the source of 

delay in exploratory activity. 

Orme et al. (1985) exposed rat dams to chlorine dioxide in the drinking water for 2 weeks prior to mating 

and throughout gestation and lactation at concentrations resulting in estimated doses of 0.26, 2.6, or 

13 mg/kg/day. Maternal body weights were not significantly affected by treatment. No significant 

treatment-related effects were seen in pup body weights or age at eye opening. Consistent, but not 

significantly lower activity levels were observed in 13 mg/kg/day pups, relative to controls, on 

postpartum days 15–20. At 13 mg/kg/day, pups also exhibited significantly depressed serum T4 and 

elevated T3 levels, relative to controls, when tested on postpartum day 21. A significant correlation was 

noted between T4 levels and locomotor activity. In the same report, pups of unexposed rat dams were 

administered chlorine dioxide in a gavage dose of 14 mg/kg/day on postnatal days 5–20. Relative to 

controls, treated pups exhibited lower body weights at 14 and 21 days (17 and 33% lower, respectively), 

lower activity levels at days 18 and 19 (but not days 15–17 and 20), and lower serum T4 levels on 

postpartum day 21. Age at eye opening and serum T3 levels were not significantly different from 

controls. A significant correlation was noted between T4 levels and locomotor activity. 

Taylor and Pfohl (1985) found no significant treatment-related effects on body weights of male rat pups 

whose mothers had been exposed to chlorine dioxide in the drinking water for 14 days prior to mating and 

throughout gestation and lactation at a concentration that resulted in an estimated dose of 13 mg/kg/day. 

Female rat pups were not assessed in this study. Compared with controls, the treated pups exhibited 

consistently (but not significantly) lower activity levels (assessed at 10–20 days of age), significantly 
CHLORINE DIOXIDE AND CHLORITE 42 

3. HEALTH EFFECTS 

decreased whole brain weight (primarily because of a decrease in cerebellar weight) and cerebellar total 

DNA content (due to a decrease in total cell number) in 21-day-old pups, and decreased exploratory 

activity at 60 days of age. Other pups were exposed to chlorine dioxide only during postnatal days 5–20 

at a daily gavage dose of 14 mg/kg. At 21 days of age, these pups exhibited significant decreases in body 

weight, absolute and relative whole brain and forebrain weights, and forebrain DNA content and total cell 

number, compared with controls. Decreased DNA content and total cell number were seen in the 

cerebellum and forebrain when tested at 11 days of age. 

Toth et al. (1990) administered chlorine dioxide to male and female rat pups at a daily gavage dose of 

14 mg/kg on postnatal days 1–20. Examinations were performed on selected pups at ages 11, 21, and 

35 days, and results were compared to control pups. Significantly lower (5–7% lower) body weights and 

decreased ratio of forebrain content to cerebellum weight were noted at all three examination times. 

Significantly lower forebrain weights were seen on days 21 and 35, along with accompanying reductions 

in protein content (days 21 and 35) and reduced DNA content (day 35). Serum T3 and T4 levels were not 

affected by chlorine dioxide treatment. A slight, but statistically significant decrease in free T4 was 

reported at day 21, but the toxicological significance is not clear. 

Suh et al. (1983) administered chlorine dioxide in the drinking water of female rats for 2.5 months prior to 

mating with unexposed males, and during gestation days 1–20 at levels that resulted in estimated doses of 

0.13, 1.3, or 13 mg/kg/day. The only reported maternal effect was a slight (but not significantly) 

decreased maternal body weight gain in 1.3 and 13 mg/kg/day dams, relative to controls. Fetal effects 

included a significant dose-response trend for decreasing number of implants per litter and number of live 

fetuses per dam, and significantly increased total fetal weights and male fetal weights in the 13 mg/kg/day 

group, compared with controls. No significant effects were seen in crown-rump length or skeletal 

anomalies. 

Carlton et al. (1991) administered chlorine dioxide to rats in gavage doses of 2.5, 5, or 10 mg/kg for 

56 days prior to mating and during 10 days of mating (males) and 14 days prior to mating and throughout 

mating, gestation, and lactation (females). Relative to controls, pups in the exposure groups exhibited no 

significant differences in death before weaning, mean litter size, or mean body weight. Significantly 

lower absolute vaginal weight and vagina-to-body weight ratio were seen in F1 females of the 

10 mg/kg/day exposure group; no significant changes in reproductive organ weights were observed in F1 

males. 
CHLORINE DIOXIDE AND CHLORITE 43 

3. HEALTH EFFECTS 

Chlorite. Gill et al. (2000; results previously published in CMA 1996) conducted a 2-generation study to 

examine reproductive, developmental, neurological, and hematological end points in rats exposed to 

sodium chlorite. Male and female rats (F0) received sodium chlorite in the drinking water at 

concentrations that resulted in estimated chlorite doses of 3, 5.7, or 21 mg/kg/day for males and 3.9, 7.6, 

and 29 mg/kg/day for females. The treatment period lasted for 10 weeks prior to mating and during 

mating, after which males were sacrificed; exposure of females continued throughout gestation and 

lactation. Sodium chlorite concentrations were adjusted during lactation to maintain a constant intake 

during a period of increased water intake. F1 generation pups were continued on the same treatment 

regimen as their parents (chlorite doses of 2.9, 6, or 23 mg/kg/day and 3.9, 8, or 29 mg/kg/day for F1 

males and females, respectively). Mating commenced at approximately 14 weeks of age to produce F2a 

rats that were maintained through weaning on postnatal day 21. Due to a reduced number of litters in the 

mid-dose F1-F2a generation, the F1 animals were remated following weaning of the F2a rats to produce an 

F2b generation. Significant alterations related to treatment at high-dose included reduced absolute and 

relative liver weight in F1 males and females, reduced pup survival (increase in number of pups found 

dead and/or killed prematurely during lactation) and reduced body weight at birth and throughout 

lactation in F1 and F2 rats, lower thymus and spleen weight in both generations, decreased absolute brain 

weight for F1 males and F2 females, delayed sexual development in F1 and F2 males (preputial separation) 

and females (vaginal opening), and lowered red blood cell parameters and white blood cell counts in F1 

rats. In the mid-dose groups, reduced absolute and relative liver weight in F1 males was observed. In 

addition, a significant decrease in maximum response to an auditory startle stimulus was noted in midand high-dose groups on postnatal day 24, but not on postnatal day 60. The NOAEL of 2.9 mg/kg/day, 

identified in this study, served as the basis for the derivation of an intermediate-duration oral MRL for 

chlorite. A LOAEL was 5.7 mg/kg/day for lowered auditory startle response amplitude and 

hematotoxicity on postnatal day 24. 

Mobley et al. (1990) exposed female rats to chlorite in the drinking water for 10 days prior to mating with 

unexposed males and during gestation and lactation until postnatal days 42–53 at concentrations that 

resulted in estimated chlorite doses of 2.6 or 5.2 mg/kg/day. Chlorite exposure did not adversely affect 

litter size or pup weight gain. Significant, consistent decreases in exploratory activity were observed in 

the 5.2 mg/kg/day group on postnatal days 36–39, but not on days 39–41. In the 2.6 mg/kg/day group, 

there were significant decreases in activity on days 36 and 37, but not on days 38–40. No significant 

alterations in serum T3 or T4 levels or free T4 levels were observed in male pups (female pups were not 

assessed for thyroid hormone levels). The day of eye opening in the treatment groups was similar to that 

of controls. 
CHLORINE DIOXIDE AND CHLORITE 44 

3. HEALTH EFFECTS 

Carlton et al. (1987) exposed groups of 12 male rats to sodium chlorite in the drinking water for 56 days 

prior to mating and throughout a 10-day mating period. Groups of 24 female rats were also exposed to 

sodium chlorite for 14 days prior to mating, during the mating period, and throughout gestation and 

lactation. Estimated chlorite doses were 0.09, 0.9, or 9 mg/kg/day for males and 0.1, 1, or 10 mg/kg/day 

for females. No significant alterations in litter survival rates, median day of eye opening, or median day 

of observed vaginal patency were observed. Significant decreases in serum T3 and T4 levels were 

consistently observed in high-dose groups of F1 males and females at postnatal days 21 and 40. 

Couri et al. (1982b) exposed pregnant rats to sodium chlorite in the drinking water during gestational 

days 8–15 at concentrations that resulted in estimated chlorite doses of 70, 440, or 610 mg/kg/day. The 

litters were either delivered at term or by cesarean section on gestational day 22. Significant decreases in 

crown-rump length were observed at all doses in term-delivered litters and in the 70 mg/kg/day group that 

was cesarean-delivered. Fetal weights were not adversely affected. An increase in the number of 

resorbed and dead fetuses was observed in cesarean-delivered litters of all exposure levels; two litters out 

of five were totally resorbed in the high-dose group. Postnatal growth and the incidences of soft tissue 

and skeletal malformations were not adversely affected. 

Suh et al. (1983) administered chlorite in the drinking water of female rats for 2.5 months prior to mating 

with unexposed males and during gestational days 0–20 at chlorite concentrations that resulted in 

estimated doses of 0.13 or 1.3 mg/kg/day; the dams were killed on gestational day 20. No treatmentrelated effects were seen regarding resorptions, dead fetuses, or fetal body weights. Crown-rump length 

was significantly higher in the high-dose group compared with controls, but the difference was very small 

and is probably not biologically significant. Chlorite exposure did not significantly alter incidence of 

skeletal anomalies. 

Moore and coworkers (Moore and Calabrese 1982; Moore et al. 1980b) exposed pregnant mice to sodium 

chlorite in the drinking water throughout gestation and lactation at a concentration that resulted in an 

estimated chlorite dose of 23 mg/kg/day. A decrease in the conception rate (number of females positive 

for vaginal plug/number of females producing litters; 39 vs. 56% in controls) was observed; the statistical 

significance was not reported. No significant alterations in gestation length, litter size, number of pups 

dead at birth, or number of pups alive at weaning were observed. Pup growth was adversely affected, as 

shown by significant decreases in average pup weaning weight and birth-to-weaning growth rate. 
 

CHLORINE DIOXIDE AND CHLORITE 45 

3. HEALTH EFFECTS 

Harrington et al. (1995b) treated rabbits with sodium chlorite via their drinking water on gestation 

days 7–20 at levels that resulted in estimated chlorite doses of 10, 26, or 40 mg/kg/day. Dams were 

sacrificed on gestation day 28. Although the number and mean percentage of major external and visceral 

and skeletal abnormalities were increased in the 26 and 40 mg/kg/day groups (external/visceral: 6.6 and 

2.9%, respectively, vs. 1.5% in controls; skeletal: 5.4 and 0%, respectively, vs. 0% in controls), the 

authors did not consider these to be treatment-related adverse effects. Mean fetal weights in the 26 and 

40 mg/kg/day groups were slightly decreased (<9%, relative to controls). In the 26 and 40 mg/kg/day 

groups, the incidence of minor skeletal abnormalities (13.9 and 14.2% for the 26 and 40 mg/kg/day 

groups, respectively, vs. 7.7% in controls) and skeletal variants related to incomplete fetal bone 

ossification was higher than for controls. The authors state in their discussion that these alterations in 

fetal body weight and delayed ossification indicate embryonic growth retardation. Decreases in maternal 

food and water consumption and body weight gain may be responsible, at least in part, for some of the 

fetal effects. 

Skowronski et al. (1985) administered Alcide (a liquid sterilizer consisting of sodium chlorite and lactic 

acid that form chlorine dioxide) to mice and rats in gavage doses of 1 and 0.1 mL, respectively, on 

gestation days 6–15. No signs of maternal toxicity were observed, and there were no statistically 

significant adverse fetal effects. 

The highest NOAEL values and all LOAEL values from each reliable study for developmental effects in 

each species and duration are recorded in Table 3-2 and plotted in Figure 3-2. 

3.2.2.7 Cancer 

No reports were located in which cancer could be associated with oral exposure to chlorine dioxide or 

chlorite in humans. 

Kurokawa et al. (1986) performed a cancer bioassay on rats and mice that were exposed to sodium 

chlorite in the drinking water. Rats were exposed to concentrations that resulted in estimated chlorite 

doses of 13.5 or 24 mg/kg/day in males and 21 or 31 mg/kg/day in females. All groups of rats became 

infected with the Sendai virus, causing a premature termination of the study after 85 weeks of exposure. 

Mice were exposed for 80 weeks to concentrations that resulted in estimated doses of 45 or 90 mg/kg/day. 

Mice received distilled water only for an additional 5 weeks following the 80-week treatment period. 

Yokose et al. (1987) also published a report of the mouse data presented in Kurokawa et al. (1986). The 
CHLORINE DIOXIDE AND CHLORITE 46 

3. HEALTH EFFECTS 

two accounts vary slightly in exposure duration information and in reported numbers of tumor-bearing 

mice at study end. Yokose et al. (1987) indicated that exposure of mice was terminated at 80 weeks 

according to a guideline for carcinogenicity studies from the Ministry of Health and Welfare of Japan. 

No chlorite-related increased tumor incidences were observed in rats. Significant increases in liver and 

lung tumors were observed in the male mice. Incidence of hyperplastic nodules in the liver was 

significantly increased in the low- and high-dose groups relative to controls (3/35 [reported as 6/35 in 

Yokose et al. 1987], 14/47, and 11/43, in the control, low-, and high-dose groups, respectively) and 

combined incidence of liver hyperplastic nodules and hepatocellular carcinoma was increased in the lowdose group (7/35, 22/47, and 17/43, respectively). Incidence of lung adenoma (0/35, 2/47, and 5/43, 

respectively) and combined incidence for lung adenoma and adenocarcinoma (0/35, 3/47, and 7/43, 

respectively) were significantly increased in the high-dose group compared with controls. The study 

authors noted that incidences of liver hyperplastic nodules and lung adenomas in the treated animals were 

within the range of historical controls in their laboratory and in the National Toxicology Program 

laboratories. In addition, high mortality in the control males because of fighting reduced the sample size, 

making statistical comparisons between controls and treated animals difficult to interpret. In the female 

mice, the only significant alteration in tumor incidence was a significantly lower incidence of malignant 

lymphoma/leukemia in the high-dose group (7/47, 5/50, and 1/50, respectively). The exposure durations 

of both rat and mouse studies were considerably less-than-lifetime exposure guidelines for adequate 

carcinogenicity studies. 

Using three short-term assays, Miller et al. (1986) found no evidence of carcinogenic potential of drinking 

water disinfected with chlorine dioxide. In an initiation-promotion assay, water was disinfected with 

chlorine dioxide, after which water samples containing chlorine dioxide residue were concentrated and 

administered orally to mice 3 times/week for 2 weeks. The mice were then exposed to 12-tetradecanylphorbal-13-acetate (a known cancer promoter) in acetone by dermal applications 3 times/week for 

20 weeks. No significant increases in the number of skin tumors or the number of tumors per animal 

were observed, compared with vehicle controls. In a lung adenoma assay, groups of female Strain A mice 

received 0.25 mL gavage doses of the concentrated water samples 3 times/week for 8 weeks, followed by 

a 16-week observation period. The number of animals with lung adenomas and the number of adenomas 

per animal were not significantly altered compared with vehicle controls. In the third assay, partially 

hepatectomized rats were exposed to a single oral dose of the concentrated water samples followed 

1 week later by administration of 500 mg/L sodium phenobarbital (a known cancer promoter) in drinking 
CHLORINE DIOXIDE AND CHLORITE 47 

3. HEALTH EFFECTS 

water for 56 days. Examination of livers in the treated rats did not reveal significant treatment-induced 

increases in gamma glutamyl transpeptidase-positive foci (an indicator of preneoplastic liver changes). 

3.2.3 Dermal Exposure 

The database for health effects related to dermal exposure to chlorine dioxide or chlorite is extremely 

limited. No reports were located regarding adverse effects in humans following dermal exposure to 

chlorine dioxide or chlorite. Available information in animals is restricted to a report that a solution 

containing chlorine dioxide concentrations of approximately 9.7–11.4 mg/L was nonirritating to the skin 

of mice in a 48-hour test. Dermal exposure to high concentrations would be expected to result in 

irritation, due to the oxidizing properties of chlorine dioxide and chlorite. Sodium chlorite was not 

carcinogenic in mice treated dermally for 51 weeks. Nor did sodium chlorite appear to be a cancer 

promoter in mice initiated with a single dermal dose of dimethylbenzanthracene followed by 51 weeks of 

dermal exposure to sodium chlorite. 

The toxicity of Alcide, an antimicrobial compound consisting of solutions of sodium chlorite and lactic 

acid that produce chlorine dioxide when mixed, was assessed in laboratory animals following repeated 

exposure and in fetuses of pregnant animals following in utero exposure during critical periods of 

organogenesis (Abdel-Rahman et al. 1987a, 1987b; Gerges et al. 1985). However, levels of exposure to 

sodium chlorite and chlorine dioxide were not known and uncertainty exists regarding the potential for 

the formation of other reactive substances that could trigger toxic responses. 

3.2.3.1 Death 

No reports were located regarding death in humans or animals following dermal exposure to chlorine 

dioxide or chlorite. 

3.2.3.2 Systemic Effects 

No reports were located in which respiratory, cardiovascular, gastrointestinal, hematological, 

musculoskeletal, hepatic, renal, endocrine, ocular, or body weight effects could be associated with dermal 

exposure to chlorine dioxide or chlorite in humans or animals. 
CHLORINE DIOXIDE AND CHLORITE 48 

3. HEALTH EFFECTS 

Dermal Effects. No reports were located regarding dermal effects in humans following dermal 

exposure to chlorine dioxide or chlorite. 

A solution containing chlorine dioxide concentrations of approximately 9.7–11.4 mg/L was nonirritating 

to the skin of mice in a 48-hour test (Shi and Xie 1999). Moderate to severe erythema was observed in 

rabbits following repeated daily applications of Alcide, an antimicrobial compound consisting of 

solutions of sodium chlorite and lactic acid that produce chlorine dioxide when mixed (Abdel-Rahman et 

al. 1987b). However, levels of exposure to sodium chlorite or chlorine dioxide could not be quantified. 

No reports were located in which the following health effects in humans or animals could be associated 

with dermal exposure to chlorine dioxide or chlorite: 

3.2.3.3 Immunological and Lymphoreticular Effects 

3.2.3.4 Neurological Effects 

3.2.3.5 Reproductive Effects 

3.2.3.6 Developmental Effects 

No reports were located regarding developmental effects in humans following dermal exposure to 

chlorine dioxide or chlorite. 

Animal data are limited to studies of laboratory rodents exposed to Alcide, an antimicrobial compound 

consisting of solutions of sodium chlorite and lactic acid that produce chlorine dioxide when mixed 

(Abdel-Rahman et al. 1987a; Gerges et al. 1985). No statistically significant treatment-related 

developmental effects were observed in the offspring of rats, mice, and rabbits treated daily with dermal 

applications of Alcide gel (as high as 2 g/kg) during the critical period of organogenesis. However, levels 

of exposure to sodium chlorite or chlorine dioxide could not be quantified. 

3.2.3.7 Cancer 

Kurokawa et al. (1984) conducted two dermal carcinogenicity assays on chlorite. In an assay designed to 

assess the ability of chlorite to act as a complete carcinogen, female mice were treated with dermal 

applications of sodium chlorite (in acetone) twice weekly for 51 weeks. Compared with controls, sodium 
 

CHLORINE DIOXIDE AND CHLORITE 49 

3. HEALTH EFFECTS 

chlorite exposure did not result in increased tumor incidence. To test the ability of chlorite to act as a 

tumor promoter, a single initiating dose of dimethylbenzanthracene (DMBA) was applied to the skin of 

mice. The DMBA application was followed by dermal applications of sodium chlorite (in acetone) twice 

weekly for 51 weeks. Although incidences of tumors were higher in the chlorite/acetone-exposed mice 

than in those receiving acetone only, the differences were not statistically significant. 

3.3 GENOTOXICITY 

No reports were located regarding the genotoxicity of chlorine dioxide or chlorite in humans. 

The genotoxic potential of chlorine dioxide and chlorite has been assessed in a number of standard 

genotoxicity test systems, resulting in both positive and negative results. Chlorine dioxide was not 

mutagenic (either with or without metabolic activation) in one Ames assay of Salmonella typhimurium 

strains TA 97, TA98, TA100, and TA102 (Wang et al. 2002a), but a weakly positive response (without 

metabolic activation) in strain TA100 was noted in another Ames assay (Ishdate et al. 1984). Chlorine 

dioxide did not increase chromosomal aberrations in Chinese hamster fibroblast cells (Ishidate et al. 

1984). Samples of water that had been disinfected with chlorine dioxide did not induce reverse mutations 

in S. typhimurium with or without activation (Miller et al. 1986). Negative results were obtained from in 

vivo assays for micronuclei and bone marrow chromosomal aberrations in Swiss CD-1 mice, as well as 

sperm-head abnormalities in B6C3F1 mice, following gavage administration of chlorine dioxide doses 

ranging from 0.1 to 0.4 mg/mouse/day for 5 consecutive days (Meier et al. 1985). Chlorine dioxide did 

not induce micronuclei in the bone marrow of mice that had been exposed via the drinking water at a 

concentration of 624 mg/L (Wang et al. 2002b). Hayashi et al. (1988) reported positive results in the 

micronucleus assay in ddY mice following single intraperitoneal injection of chlorine dioxide at dose 

levels of 3.2–25 mg/kg. 

Sodium chlorite induced reverse mutations in S. typhimurium (with activation) and chromosomal 

aberrations in Chinese hamster fibroblast cells (Ishidate et al. 1984). Negative results were obtained from 

in vivo assays for micronuclei and bone marrow chromosomal aberrations in Swiss CD-1 mice, as well as 

sperm-head abnormalities in B6C3F1 mice, following gavage administration of sodium chlorite at doses 

ranging from 0.25 to 1 mg/mouse/day for 5 consecutive days (Meier et al. 1985). Hayashi et al. (1988) 

reported negative results for induction of micronuclei in ddY mice that were administered sodium chlorite 

in single oral gavage doses ranging from 37.5 to 300 mg/kg, but positive results were obtained in mice 

subjected to single or multiple intraperitoneal injection of 7.5 to 60 mg sodium chlorite/kg. 
 

CHLORINE DIOXIDE AND CHLORITE 50 

3. HEALTH EFFECTS 

3.4 TOXICOKINETICS 

Although no data were located regarding absorption following inhalation exposure to chlorine dioxide, 

little absorption of parent compound across lung tissue would be expected due to the highly reactive 

nature of chlorine dioxide. The rapid appearance of 36Cl in plasma following oral administration of 

chlorine dioxide (36ClO2) or chlorite (36ClO2

-

) has been shown in laboratory animals. Using 72-hour 

urinary excretion rates for 36Cl, absorption rates of 30–35% of intragastrically administered chlorine 

dioxide or chlorite have been estimated. Limited animal data indicate the presence of 36Cl in plasma 

following dermal application of Alcide, an antimicrobial compound containing sodium chlorite and lactic 

acid that rapidly form chlorine dioxide when mixed together. In rats, absorbed 36Cl (from 36ClO2 or 

36 - ClO2 exposure sources) is slowly cleared from the blood and is widely distributed throughout the body. 

Chlorine dioxide rapidly dissociates, predominantly into chlorite (which itself is highly reactive) and 

chloride ion (Cl-

), ultimately the major metabolite of both chlorine dioxide and chlorite in biological 

systems. Urine is the primary route of 36Cl elimination, predominantly in the form of chloride ion. 

3.4.1 Absorption 

3.4.1.1 Inhalation Exposure 

No information was located regarding absorption following inhalation exposure to chlorine dioxide or 

chlorite in humans or animals. 

3.4.1.2 Oral Exposure 

No information was located regarding absorption following oral exposure to chlorine dioxide or chlorite 

in humans. 

In rats, a single gavage dose of 36ClO2 resulted in the rapid appearance of 36Cl in the plasma, which 

peaked 1 hour after dosing (Abdel-Rahman et al. 1980a). Based on 72-hour urinary excretion of 30% of 

the 36Cl in the administered dose, it can be assumed that absorption was at least 30%. The absorption rate 

constant and half-time were 3.77/hour and 0.18 hours, respectively (Abdel-Rahman et al. 1982). Similar 

- results were reported following single gavage dosing of rats with 36ClO2 (Abdel-Rahman et al. 1982). In 
CHLORINE DIOXIDE AND CHLORITE 51 

3. HEALTH EFFECTS 

this study, peak plasma levels of 36Cl were reached within 2 hours following dosing and 72-hour urinary 

excretion data indicated that at least 35% of the radiolabel had been absorbed. The absorption rate 

constant and half-time were 0.198/hour and 3.5 hours, respectively. 

3.4.1.3 Dermal Exposure 

No information was located regarding absorption following dermal exposure to chlorine dioxide or 

chlorite in humans. 

Dermal absorption of 36Cl was measured in rats following 10 daily applications of Alcide, an 

antimicrobial compound consisting of solutions of sodium chlorite and lactic acid that produce chlorine 

dioxide when mixed (Scatina et al. 1984). Maximal levels of plasma 36Cl were reached after 72 hours. 

The absorption rate constant and half-life were 0.0314/hour and 22.1 hours, respectively. 

3.4.2 Distribution 

3.4.2.1 Inhalation Exposure 

No information was located regarding distribution of chlorine dioxide, chlorite, or their metabolites 

following inhalation exposure in humans or animals. 

3.4.2.2 Oral Exposure 

No information was located regarding distribution of chlorine dioxide, chlorite, or their metabolites 

following oral exposure in humans. 

Animal data indicate that 36Cl, absorbed from the gastrointestinal tract following single oral (gavage) 

administration of 36ClO2, is cleared from the blood with a half-time of elimination of 43.9 hours (AbdelRahman et al. 1982) and is widely distributed throughout the body (Abdel-Rahman et al. 1980a, 1980b, 

1982, 1984a). At 72 hours following dosing, highest concentrations were found in the blood, stomach, 

and small intestines. Relatively high concentrations were also seen in the lung, kidney, liver, testes, 

spleen, thymus, and bone marrow. A shorter elimination half-time (31.0 hours) was noted in rats that had 

been exposed to chlorine dioxide in the drinking water for 2 weeks prior to receiving a single gavage dose 
CHLORINE DIOXIDE AND CHLORITE 52 

3. HEALTH EFFECTS 

of 36ClO2 (Abdel-Rahman et al. 1980a). Single oral (gavage) administration of chlorite (36ClO2

-

) resulted 

in an elimination half-time of 35.2 hours from the blood and widespread distribution of 36Cl (AbdelRahman et al. 1982, 1984a), similar to that observed following oral exposure to chlorine dioxide. 

3.4.2.3 Dermal Exposure 

No information was located regarding distribution of chlorine dioxide, chlorite, or their metabolites 

following dermal exposure in humans or animals. However, 36Cl has been measured in plasma of rats 

following 10 daily applications of Alcide, an antimicrobial compound consisting of solutions of sodium 

chlorite and lactic acid that produce chlorine dioxide when mixed (Scatina et al. 1984). 

3.4.3 Metabolism 

3.4.3.1 Inhalation Exposure 

No information was located regarding metabolism of chlorine dioxide or chlorite following inhalation 

exposure in humans or animals. 

3.4.3.2 Oral Exposure 

Both chlorine dioxide and chlorite are primarily metabolized to chloride ion. At 72 hours following 

single oral (gavage) administration of radiolabeled chlorine dioxide in rats, chloride ion accounted for 

approximately 87% of the radioactivity that had been collected in the urine and 80% of the radioactivity 

in a plasma sample (Abdel-Rahman et al. 1980b). Chlorite was the other major metabolite, accounting 

for approximately 11 and 21% of the radioactivity in the urine and plasma samples, respectively. 

Chlorate was a minor component of the radioactivity in the urine. Similarly, chloride ion accounted for 

approximately 85% of the radioactivity in the 72-hour urine collection of rats that had been orally 

administered radiolabeled chlorite; the remainder in the form of chlorite (Abdel-Rahman et al. 1984a). 

Both chlorine dioxide and chlorite, being strong oxidizing agents, are most likely rapidly reduced in 

biological systems mainly to chloride ion. Bercz et al. (1982) demonstrated this reduction for chlorine 

dioxide that was introduced into saliva obtained from anesthetized monkeys. 
CHLORINE DIOXIDE AND CHLORITE 53 

3. HEALTH EFFECTS 

3.4.3.3 Dermal Exposure 

No information was located regarding metabolism of chlorine dioxide or chlorite following dermal 

exposure in humans or animals. 

3.4.4 Elimination and Excretion 

3.4.4.1 Inhalation Exposure 

No information was located regarding elimination or excretion following inhalation exposure to chlorine 

dioxide or chlorite in humans or animals. 

3.4.4.2 Oral Exposure 

The urine is the primary route of excretion of orally administered radioactivity from radiolabeled chlorine 

dioxide or chlorite. In rats, 72 hours following single oral (gavage) administration of 36ClO2, 31 and 4.5% 

of the radiolabel had been excreted in the urine and feces, respectively, mainly in the form of the chloride 

- ion. The ratio of 36Cl- to 36ClO2 was 4 to 1, and no parent compound was detected (Abdel-Rahman et al. 

1980a, 1980b). In rats administered a single oral (gavage) dose of radiolabeled chlorite, 35 and 5% of the 

radiolabel were excreted in the urine and feces, respectively, in the first 72 hours after dosing. 

Approximately 90% of the urinary label was in the form of chloride ion (Abdel-Rahman et al. 1984a). 

3.4.4.3 Dermal Exposure 

Urinary excretion of 36Cl was observed in rats that had been administered Alcide, an antimicrobial 

compound consisting of sodium chlorite and lactic acid that form chlorine dioxide when mixed (Scatina et 

al. 1984). The rats had received 10 daily dermal applications, followed by an application of radiolabeled 

Alcide. Urinary excretion was greatest in the first 24 hours post application; the half-time of urinary 

elimination was 64 hours. The excreted radioactivity consisted of approximately equal portions of 

chloride ion and chlorite. No radioactivity was detected in feces or expired air. 
CHLORINE DIOXIDE AND CHLORITE 54 

3. HEALTH EFFECTS 

3.4.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models 

Physiologically based pharmacokinetic (PBPK) models use mathematical descriptions of the uptake and 

disposition of chemical substances to quantitatively describe the relationships among critical biological 

processes (Krishnan et al. 1994). PBPK models are also called biologically based tissue dosimetry 

models. PBPK models are increasingly used in risk assessments, primarily to predict the concentration of 

potentially toxic moieties of a chemical that will be delivered to any given target tissue following various 

combinations of route, dose level, and test species (Clewell and Andersen 1985). Physiologically based 

pharmacodynamic (PBPD) models use mathematical descriptions of the dose-response function to 

quantitatively describe the relationship between target tissue dose and toxic end points. 

PBPK/PD models refine our understanding of complex quantitative dose behaviors by helping to 

delineate and characterize the relationships between: (1) the external/exposure concentration and target 

tissue dose of the toxic moiety, and (2) the target tissue dose and observed responses (Andersen et al. 

1987; Andersen and Krishnan 1994). These models are biologically and mechanistically based and can 

be used to extrapolate the pharmacokinetic behavior of chemical substances from high to low dose, from 

route to route, between species, and between subpopulations within a species. The biological basis of 

PBPK models results in more meaningful extrapolations than those generated with the more conventional 

use of uncertainty factors. 

The PBPK model for a chemical substance is developed in four interconnected steps: (1) model 

representation, (2) model parametrization, (3) model simulation, and (4) model validation (Krishnan and 

Andersen 1994). In the early 1990s, validated PBPK models were developed for a number of 

toxicologically important chemical substances, both volatile and nonvolatile (Krishnan and Andersen 

1994; Leung 1993). PBPK models for a particular substance require estimates of the chemical substancespecific physicochemical parameters, and species-specific physiological and biological parameters. The 

numerical estimates of these model parameters are incorporated within a set of differential and algebraic 

equations that describe the pharmacokinetic processes. Solving these differential and algebraic equations 

provides the predictions of tissue dose. Computers then provide process simulations based on these 

solutions. 

The structure and mathematical expressions used in PBPK models significantly simplify the true 

complexities of biological systems. If the uptake and disposition of the chemical substance(s) is 

adequately described, however, this simplification is desirable because data are often unavailable for 
CHLORINE DIOXIDE AND CHLORITE 55 

3. HEALTH EFFECTS 

many biological processes. A simplified scheme reduces the magnitude of cumulative uncertainty. The 

adequacy of the model is, therefore, of great importance, and model validation is essential to the use of 

PBPK models in risk assessment. 

PBPK models improve the pharmacokinetic extrapolations used in risk assessments that identify the 

maximal (i.e., the safe) levels for human exposure to chemical substances (Andersen and Krishnan 1994). 

PBPK models provide a scientifically sound means to predict the target tissue dose of chemicals in 

humans who are exposed to environmental levels (for example, levels that might occur at hazardous waste 

sites) based on the results of studies where doses were higher or were administered in different species. 

Figure 3-3 shows a conceptualized representation of a PBPK model. 

No PBPK models for exposure to chlorine dioxide or chlorite were identified. 

3.5 MECHANISMS OF ACTION 

3.5.1 Pharmacokinetic Mechanisms 

Absorption. No information was located regarding mechanisms of absorption of chlorine dioxide or 

chlorite. Being a strong oxidizer, chlorine dioxide is likely to undergo rapid redox reactions within 

biological tissues rather than to be absorbed as parent compound. Chlorite levels have been measured in 

urine following oral exposure to chlorine dioxide or chlorite, indicating that some degree of chlorite 

absorption occurs across the digestive tract. Due to the highly reactive nature of chlorite, itself a strong 

oxidizer, absorption would be expected to occur via passive diffusion rather than active transport 

mechanisms. 

Distribution. No information was located regarding the transport of chlorine dioxide or chlorite in the 

blood. However, based on the fact that the strong oxidizing property of chlorine dioxide likely results in 

rapid conversion to chlorite (also a strong oxidizer) in biological systems, and ultimately to chloride ion, 

it would be expected that distribution would follow normal ionic distribution patterns. 

Metabolism. Although no information was located regarding mechanisms of chlorine dioxide and 

chlorite metabolism, ultimate transformation to chloride ions is likely achieved via redox reactions with a 

variety of substances in biological systems that are readily oxidized. 
Lungs 

Liver 

Fat 

S low ly 

perfused 

tissues 

Richly 

perfused 

tissues 

K idney 

Skin 

V 

E 

N 

O 

U 

S 

B 

L 

O 

O 

D 

A 

R 

T 

E 

R 

I 

A 

L 

B 

L 

O 

O 

D 

V max K m 

Ingestion 

Inhaled chem ical E xhaled chem ical 

GI 

Tract 

Feces 

Urine

 C hem icals in air 

contacting skin 

CHLORINE DIOXIDE AND CHLORITE 56 

3. HEALTH EFFECTS 

Figure 3-3. Conceptual Representation of a Physiologically Based 

Pharmacokinetic (PBPK) Model for a 

Hypothetical Chemical Substance 

Source: adapted from Krishnan et al. 1994 

Note: This is a conceptual representation of a physiologically based pharmacokinetic (PBPK) model for a 

hypothetical chemical substance. The chemical substance is shown to be absorbed via the skin, by 

inhalation, or by ingestion, metabolized in the liver, and excreted in the urine or by exhalation. 
 

CHLORINE DIOXIDE AND CHLORITE 57 

3. HEALTH EFFECTS 

Excretion. No information was located regarding specific mechanisms of excretion of chlorine 

dioxide, chlorite, or their metabolites. However, since chloride ion is the primary excretory product of 

chlorine dioxide and chlorite, excretory mechanisms would be expected to be similar to those responsible 

for excretion of other ions. 

3.5.2 Mechanisms of Toxicity 

Chlorine dioxide and chlorite are strong oxidizing agents that readily react upon direct contact with 

biological tissues, resulting in local irritation. Mechanisms whereby chlorine dioxide and chlorite exert 

hematological effects such as methemoglobinemia in humans (Lin and Lim 1993; Michael et al. 1981) 

and animals (Bercz et al. 1982; Harrington et al. 1995a; Heffernan et al. 1979b) and alterations in other 

blood factors are not presently known, but may be related to their properties as oxidants. Due to its 

highly reactive nature, it is unlikely that chlorine dioxide would be absorbed in quantities large enough to 

produce systemic toxicity directly. Chlorite is produced and absorbed following oral exposure to chlorine 

dioxide in animals (Abdel-Rahman et al. 1980b), and may be more likely to be involved in observed 

hematological effects than chlorine dioxide itself. Chlorite has been shown to be more efficient than 

chlorine dioxide in the production of methemoglobin, in decreasing blood glutathione, and in alteration of 

erythrocytes (Abdel-Rahman et al. 1980a, 1984b; Couri and Abdel-Rahman 1980; Heffernan et al. 1979a, 

1979b). In vitro studies have further shown that sufficient amounts of glutathione may prevent chlorine 

dioxide-induced osmotic fragility, presumably by the prevention of the formation of disulfide bonds 

between hemoglobin and components of the cell membrane (Abdel-Rahman et al. 1984b). A recent in 

vitro study demonstrated that sodium chlorite readily depleted glutathione in mammalian cells, but 

treatment of phospholipids with chlorite yielded only low levels of hydroperoxides (Ingram et al. 2003). 

These findings indicate that chlorite-induced cellular damage may be more likely due to interaction with 

thiol compounds than with cell membrane lipids. 

Although changes in thyroid hormones have been reported in laboratory animals that were either directly 

exposed to chlorine dioxide or exposed to chlorine dioxide or chlorite via their mothers during pre and 

postpartum development (Bercz et al. 1982; Carlton and Smith 1985; Carlton et al. 1987, 1991; Mobley et 

al. 1990; Orme et al. 1985), possible mechanisms that might mediate such effects have not been 

elucidated. Increased levels of iodine have been noted in esophagus and small intestine of rats up to 

24 hours after administration of gavage doses of radiolabeled iodine followed by chlorine dioxide 

(Harrington et al. 1985). However, no concurrent treatment-related alterations in blood or thyroid gland 

iodine level were seen. Because the extent of thyroid uptake of bioavailable iodine does not appear to 
 

CHLORINE DIOXIDE AND CHLORITE 58 

3. HEALTH EFFECTS 

decrease following oral exposure to chlorine dioxide, Bercz et al. (1986) speculated that indications of 

altered hormonogenesis, such as altered serum thyroid hormone, could be the result of absorption of 

iodinated molecules having thyromimetic or thyroid inhibitory properties. These results, however, do not 

imply that the effect is mediated through a hormonal pathway. 

Likewise, mechanisms responsible for the developmental effects observed in laboratory animals exposed 

to chlorine dioxide or chlorite are not known. They might be related to the oxidative properties of these 

chemicals. Although overt signs of neurodevelopmental effects (delays in exploratory activity and 

general locomotor activity) and altered serum thyroid hormone have been observed concurrently in 

animals that had been exposed via their mothers during pre and postpartum development, a mechanistic 

basis has not been investigated. 

3.5.3 Animal-to-Human Extrapolations 

Mechanisms involved in chlorine dioxide- and chlorite-induced oxidative stress, such as 

methemoglobinemia in humans and animals, would be expected to be similar across species. However, 

the database of pharmacokinetic and health effects information for chlorine dioxide or chlorite does not 

include studies in which interspecies comparisons were made. 

3.6 TOXICITIES MEDIATED THROUGH THE NEUROENDOCRINE AXIS 

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine 

system because of the ability of these chemicals to mimic or block endogenous hormones. Chemicals 

with this type of activity are most commonly referred to as endocrine disruptors. However, appropriate 

terminology to describe such effects remains controversial. The terminology endocrine disruptors, 

initially used by Colborn and Clement (1992), was also used in 1996 when Congress mandated the 

Environmental Protection Agency (EPA) to develop a screening program for “...certain substances 

[which] may have an effect produced by a naturally occurring estrogen, or other such endocrine 

effect[s]...”. To meet this mandate, EPA convened a panel called the Endocrine Disruptors Screening and 

Testing Advisory Committee (EDSTAC), which in 1998 completed its deliberations and made 

recommendations to EPA concerning endocrine disruptors. In 1999, the National Academy of Sciences 

released a report that referred to these same types of chemicals as hormonally active agents. The 

terminology endocrine modulators has also been used to convey the fact that effects caused by such 
CHLORINE DIOXIDE AND CHLORITE 59 

3. HEALTH EFFECTS 

chemicals may not necessarily be adverse. Many scientists agree that chemicals with the ability to disrupt 

or modulate the endocrine system are a potential threat to the health of humans, aquatic animals, and 

wildlife. However, others think that endocrine-active chemicals do not pose a significant health risk, 

particularly in view of the fact that hormone mimics exist in the natural environment. Examples of 

natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995; Livingston 1978; Mayr et 

al. 1992). These chemicals are derived from plants and are similar in structure and action to endogenous 

estrogen. Although the public health significance and descriptive terminology of substances capable of 

affecting the endocrine system remains controversial, scientists agree that these chemicals may affect the 

synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body responsible 

for maintaining homeostasis, reproduction, development, and/or behavior (EPA 1997). Stated differently, 

such compounds may cause toxicities that are mediated through the neuroendocrine axis. As a result, 

these chemicals may play a role in altering, for example, metabolic, sexual, immune, and neurobehavioral 

function. Such chemicals are also thought to be involved in inducing breast, testicular, and prostate 

cancers, as well as endometriosis (Berger 1994; Giwercman et al. 1993; Hoel et al. 1992). 

Treatment-related altered serum thyroid hormone levels indicate that chlorine dioxide and chlorite may 

exert toxic effects that are mediated through the neuroendocrine axis. Changes in thyroid hormones have 

been reported in laboratory animals that were either directly exposed to chlorine dioxide (repeated doses 

as low as 9 mg/kg/day), or exposed to chlorine dioxide or chlorite via their mothers (maternal doses of 

chlorine dioxide and chlorite as low as 13 and 9 mg/kg/day, respectively) during pre- and postpartum 

development (Bercz et al. 1982; Carlton and Smith 1985; Carlton et al. 1987, 1991; Mobley et al. 1990; 

Orme et al. 1985). 

Altered sperm morphology has been associated with oral exposure of rats to sodium chlorite at doses as 

low as 9 mg chlorite/kg/day for 66–76 days of exposure (Carlton and Smith 1985; Carlton et al. 1987). 

However, available data do not indicate that the endocrine pathway might be involved in this effect. 

3.7 CHILDREN’S SUSCEPTIBILITY 

This section discusses potential health effects from exposures during the period from conception to 

maturity at 18 years of age in humans, when all biological systems will have fully developed. Potential 

effects on offspring resulting from exposures of parental germ cells are considered, as well as any indirect 

effects on the fetus and neonate resulting from maternal exposure during gestation and lactation. 

Relevant animal and in vitro models are also discussed. 
CHLORINE DIOXIDE AND CHLORITE 60 

3. HEALTH EFFECTS 

Children are not small adults. They differ from adults in their exposures and may differ in their 

susceptibility to hazardous chemicals. Children’s unique physiology and behavior can influence the 

extent of their exposure. Exposures of children are discussed in Section 6.6 Exposures of Children. 

Children sometimes differ from adults in their susceptibility to hazardous chemicals, but whether there is 

a difference depends on the chemical (Guzelian et al. 1992; NRC 1993). Children may be more or less 

susceptible than adults to health effects, and the relationship may change with developmental age 

(Guzelian et al. 1992; NRC 1993). Vulnerability often depends on developmental stage. There are 

critical periods of structural and functional development during both prenatal and postnatal life and a 

particular structure or function will be most sensitive to disruption during its critical period(s). Damage 

may not be evident until a later stage of development. There are often differences in pharmacokinetics 

and metabolism between children and adults. For example, absorption may be different in neonates 

because of the immaturity of their gastrointestinal tract and their larger skin surface area in proportion to 

body weight (Morselli et al. 1980; NRC 1993); the gastrointestinal absorption of lead is greatest in infants 

and young children (Ziegler et al. 1978). Distribution of xenobiotics may be different; for example, 

infants have a larger proportion of their bodies as extracellular water and their brains and livers are 

proportionately larger (Altman and Dittmer 1974; Fomon 1966; Fomon et al. 1982; Owen and Brozek 

1966; Widdowson and Dickerson 1964). The infant also has an immature blood-brain barrier (Adinolfi 

1985; Johanson 1980) and probably an immature blood-testis barrier (Setchell and Waites 1975). Many 

xenobiotic metabolizing enzymes have distinctive developmental patterns. At various stages of growth 

and development, levels of particular enzymes may be higher or lower than those of adults, and 

sometimes unique enzymes may exist at particular developmental stages (Komori et al. 1990; Leeder and 

Kearns 1997; NRC 1993; Vieira et al. 1996). Whether differences in xenobiotic metabolism make the 

child more or less susceptible also depends on whether the relevant enzymes are involved in activation of 

the parent compound to its toxic form or in detoxification. There may also be differences in excretion, 

particularly in newborns who all have a low glomerular filtration rate and have not developed efficient 

tubular secretion and resorption capacities (Altman and Dittmer 1974; NRC 1993; West et al. 1948). 

Children and adults may differ in their capacity to repair damage from chemical insults. Children also 

have a longer remaining lifetime in which to express damage from chemicals; this potential is particularly 

relevant to cancer. 

Certain characteristics of the developing human may increase exposure or susceptibility, whereas others 

may decrease susceptibility to the same chemical. For example, although infants breathe more air per 
CHLORINE DIOXIDE AND CHLORITE 61 

3. HEALTH EFFECTS 

kilogram of body weight than adults breathe, this difference might be somewhat counterbalanced by their 

alveoli being less developed, which results in a disproportionately smaller surface area for alveolar 

absorption (NRC 1993). 

Developmental effects have been observed in animals following exposure of their mothers to chlorine 

dioxide or chlorite during gestation and/or lactation (Gill et al. 2000; Harrington et al. 1995b; Mobley et 

al. 1990; Moore and Calabrese 1982; Orme et al. 1985; Taylor and Pfohl 1985; Toth et al. 1990). In the 

absence of apparent maternal toxicity, these findings suggest that parent compound or toxic metabolite 

can cross the placenta and that infants and children may be particularly vulnerable to chlorine dioxideand chlorite-mediated toxic effects. It is well recognized that neurological development continues after 

birth and that gastrointestinal uptake of many nutrients and chemicals is greater in the neonate than in the 

adult. 

Infants may exhibit a greater degree of methemoglobinemia than adults following oral exposure to 

chlorine dioxide or chlorite because infants form methemoglobin more readily than adults, due at least in 

part to the presence of hemoglobin F at birth, which is readily oxidized to methemoglobin. Additional 

indications that infants may exhibit increased susceptibility to chlorine dioxide- or chlorite-induced 

hematological effects include a lower capacity to enzymatically reduce methemoglobin and a 

characteristically lower level of vitamin E (an important antioxidant) at birth. However, actual data were 

not found to support such speculation. 

No information was located regarding age-related differences in toxicokinetic parameters for chlorine 

dioxide or chlorite. 

3.8 BIOMARKERS OF EXPOSURE AND EFFECT 

Biomarkers are broadly defined as indicators signaling events in biologic systems or samples. They have 

been classified as markers of exposure, markers of effect, and markers of susceptibility (NAS/NRC 

1989). 

Due to a nascent understanding of the use and interpretation of biomarkers, implementation of biomarkers 

as tools of exposure in the general population is very limited. A biomarker of exposure is a xenobiotic 

substance or its metabolite(s) or the product of an interaction between a xenobiotic agent and some target 

molecule(s) or cell(s) that is measured within a compartment of an organism (NAS/NRC 1989). The 
CHLORINE DIOXIDE AND CHLORITE 62 

3. HEALTH EFFECTS 

preferred biomarkers of exposure are generally the substance itself or substance-specific metabolites in 

readily obtainable body fluid(s), or excreta. However, several factors can confound the use and 

interpretation of biomarkers of exposure. The body burden of a substance may be the result of exposures 

from more than one source. The substance being measured may be a metabolite of another xenobiotic 

substance (e.g., high urinary levels of phenol can result from exposure to several different aromatic 

compounds). Depending on the properties of the substance (e.g., biologic half-life) and environmental 

conditions (e.g., duration and route of exposure), the substance and all of its metabolites may have left the 

body by the time samples can be taken. It may be difficult to identify individuals exposed to hazardous 

substances that are commonly found in body tissues and fluids (e.g., essential mineral nutrients such as 

copper, zinc, and selenium). Biomarkers of exposure to chlorine dioxide and chlorite are discussed in 

Section 3.8.1. 

Biomarkers of effect are defined as any measurable biochemical, physiologic, or other alteration within an 

organism that, depending on magnitude, can be recognized as an established or potential health 

impairment or disease (NAS/NRC 1989). This definition encompasses biochemical or cellular signals of 

tissue dysfunction (e.g., increased liver enzyme activity or pathologic changes in female genital epithelial 

cells), as well as physiologic signs of dysfunction such as increased blood pressure or decreased lung 

capacity. Note that these markers are not often substance specific. They also may not be directly 

adverse, but can indicate potential health impairment (e.g., DNA adducts). Biomarkers of effects caused 

by chlorine dioxide and chlorite are discussed in Section 3.8.2. 

A biomarker of susceptibility is an indicator of an inherent or acquired limitation of an organism's ability 

to respond to the challenge of exposure to a specific xenobiotic substance. It can be an intrinsic genetic or 

other characteristic or a preexisting disease that results in an increase in absorbed dose, a decrease in the 

biologically effective dose, or a target tissue response. If biomarkers of susceptibility exist, they are 

discussed in Section 3.10 “Populations That Are Unusually Susceptible”. 

3.8.1 Biomarkers Used to Identify or Quantify Exposure to Chlorine Dioxide and 

Chlorite 

Chlorine dioxide is a strong oxidizing agent that is not likely to be widely distributed in biological 

systems or excreted as parent compound. Chlorite may be detected in tissues, blood, urine, and feces, 

which may serve as an indication of exposure to chlorine dioxide or chlorite. However, no information 
 

CHLORINE DIOXIDE AND CHLORITE 63 

3. HEALTH EFFECTS 

was located regarding the quantification of exposure based on measured levels of chlorite in biological 

samples. 

3.8.2 Biomarkers Used to Characterize Effects Caused by Chlorine Dioxide and Chlorite 

Exposure to relatively high levels of chlorine dioxide or chlorite may result in increased methemoglobin 

levels. However, this effect is not unique to chlorine dioxide or chlorite. Presently, no chemical-specific 

biomarkers of effect are known to exist for chlorine dioxide or chlorite. 

3.9 INTERACTIONS WITH OTHER CHEMICALS 

No information was located regarding interactions of chlorine dioxide or chlorite with other chemicals 

that might impact toxicity. 

3.10 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE 

A susceptible population will exhibit a different or enhanced response to chlorine dioxide or chlorite than 

will most persons exposed to the same level of chlorine dioxide or chlorite in the environment. Reasons 

may include genetic makeup, age, health and nutritional status, and exposure to other toxic substances 

(e.g., cigarette smoke). These parameters result in reduced detoxification or excretion of chlorine dioxide 

and chlorite or compromised function of organs affected by chlorine dioxide or chlorite. Populations who 

are at greater risk due to their unusually high exposure to chlorine dioxide and chlorite are discussed in 

Section 6.7, Populations With Potentially High Exposures. 

Individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency may be more sensitive to 

chlorine dioxide or chlorite (Michael et al. 1981) because of a reduced capacity for maintaining 

significant levels of glutathione, which can lead to destruction of red blood cells and hemolytic anemia. 

Approximately 10% of the African American population expresses G6PD deficiency. Moore and 

Calabrese (1980a) demonstrated that G6PD-deficient human red blood cells exposed to chlorite exhibited 

markedly greater decreased glutathione and G6PD activity and increased methemoglobin levels than red 

blood cells from humans with normal G6PD activity. Abdel-Rahman and coworkers (Abdel-Rahman et 

al. 1984b; Couri and Abdel-Rahman 1980) noted decreased glutathione levels in rats chronically exposed 

to chlorite in the drinking water. Additionally, individuals who are deficient in NADH-dependent 
CHLORINE DIOXIDE AND CHLORITE 64 

3. HEALTH EFFECTS 

methemoglobin reductase, the principal means by which methemoglobin is reduced to hemoglobin, may 

exhibit a decreased ability to reduce methemoglobin. 

Refer to Section 3.7 for information regarding age-related differences in susceptibility to chlorine dioxide 

and chlorite. 

3.11 METHODS FOR REDUCING TOXIC EFFECTS 

This section will describe clinical practice and research concerning methods for reducing toxic effects of 

exposure to chlorine dioxide and chlorite. However, because some of the treatments discussed may be 

experimental and unproven, this section should not be used as a guide for treatment of exposures to 

chlorine dioxide and chlorite. When specific exposures have occurred, poison control centers and 

medical toxicologists should be consulted for medical advice. No texts were located that provide specific 

information about treatment following exposures to chlorine dioxide or chlorite. 

3.11.1 Reducing Peak Absorption Following Exposure 

No information was located regarding methods to reduce peak absorption following exposure to 

potentially toxic levels of chlorine dioxide or chlorite. 

3.11.2 Reducing Body Burden 

No information was located regarding methods to reduce body burden following exposure to potentially 

toxic levels of chlorine dioxide or chlorite. Chlorine dioxide is rapidly converted to chlorite and chloride 

ion in biological systems. Chlorite is fairly rapidly excreted in the urine following exposure to chlorine 

dioxide or chlorite. Increasing urinary output might be an effective method for reducing body burden 

shortly following exposure. 
 

CHLORINE DIOXIDE AND CHLORITE 65 

3. HEALTH EFFECTS 

3.11.3 Interfering with the Mechanism of Action for Toxic Effects 

Intravenous administration of methylene blue may be an effective method for reducing chlorine dioxideor chlorite-induced increases in methemoglobin. However, this treatment is not effective in G6PDdeficient individuals. 

3.12 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the 

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of chlorine dioxide and chlorite is available. Where adequate 

information is not available, ATSDR, in conjunction with the National Toxicology Program (NTP), is 

required to assure the initiation of a program of research designed to determine the health effects (and 

techniques for developing methods to determine such health effects) of chlorine dioxide and chlorite. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will be 

evaluated and prioritized, and a substance-specific research agenda will be proposed. 

3.12.1 Existing Information on Health Effects of Chlorine Dioxide and Chlorite 

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to 

chlorine dioxide and chlorite are summarized in Figure 3-4. The purpose of this figure is to illustrate the 

existing information concerning the health effects of chlorine dioxide and chlorite. Each dot in the figure 

indicates that one or more studies provide information associated with that particular effect. The dot does 

not necessarily imply anything about the quality of the study or studies, nor should missing information in 

this figure be interpreted as a “data need”. A data need, as defined in ATSDR’s Decision Guide for 

Identifying Substance-Specific Data Needs Related to Toxicological Profiles (Agency for Toxic 

Substances and Disease Registry 1989), is substance-specific information necessary to conduct 

comprehensive public health assessments. Generally, ATSDR defines a data gap more broadly as any 

substance-specific information missing from the scientific literature. 
Existing Studies 

Inhalation 

Oral 

Dermal 

Animal 

Inhalation 

Oral 

Dermal 

Human 

Death

Acute 

Intermediate 

Chronic 

Immunologic/Lymphoretic 

Neurologic 

Reproductive 

Developmental 

Genotoxic 

Cancer 

Systemic 

Death

Acute 

Intermediate 

Chronic 

Immunologic/Lymphoretic 

Neurologic 

Reproductive 

Developmental 

Genotoxic 

Cancer 

Systemic 

CHLORINE DIOXIDE AND CHLORITE 66 

3. HEALTH EFFECTS 

Figure 3-4. Existing Information on Health Effects of Chlorine Dioxide and 

Chlorite 
CHLORINE DIOXIDE AND CHLORITE 67 

3. HEALTH EFFECTS 

3.12.2 Identification of Data Needs 

Acute-Duration Exposure. Chlorine dioxide and chlorite are strong oxidizing agents that readily 

react upon direct contact with biological tissues, resulting in local irritation. Information regarding health 

effects in acutely exposed humans is limited to cases of accidental exposure to concentrated chlorine 

dioxide vapors (Elkins 1959; Exner-Freisfeld et al. 1986; Meggs et al. 1996) and a single case of 

intentional ingestion of sodium chlorite in an apparent suicide attempt (Lin and Lim 1993). Reports of 

acute toxicity in animals primarily concern lethality following relatively high-level inhalation or oral 

exposure to chlorine dioxide or chlorite (Couri et al. 1982b; Dalhamn 1957; Haller and Northgraves 1955; 

Harrington et al. 1995a; Musil et al. 1964; Seta et al. 1991; Shi and Xie 1999; Sperling 1959). Additional 

acute toxicity studies should focus on oral and inhalation exposures that result in less serious critical 

effects. Results of such studies might serve as bases for establishing acute-duration oral and inhalation 

MRLs. 

Intermediate-Duration Exposure. Information regarding chlorine dioxide- or chlorite-induced 

adverse health effects in humans following intermediate-duration exposure is restricted to a single report 

in which no adverse effects were seen in 198 persons of a rural village following 3 months of exposure to 

approximately 5 ppm of chlorite in drinking water that had been disinfected with chlorine dioxide 

(Michael et al. 1981). Animal studies indicate that the respiratory system is the major target of toxicity 

following inhalation exposure (Dalhamn 1957; Paulet and Desbrousses 1970, 1972, 1974). The studies of 

Paulet and Desbrousses served as the basis for an intermediate-duration inhalation MRL. Additional 

animal studies are needed to assess the effects of chlorine dioxide vapors on upper respiratory tissues, 

which may be more sensitive than pulmonary tissues. Intermediate-duration oral studies identified 

neurodevelopmental delay and thyroid hormone effects as the most sensitive chlorine dioxide- or chloriteinduced end points (Carlton and Smith 1985; Carlton et al. 1987; Gill et al. 2000; Mobley et al. 1990; 

Orme et al. 1985; Taylor and Pfohl 1985; Toth et al. 1990). Additional studies are needed to further 

assess these critical end points and to determine whether they might be interrelated. See Section 3.12.2 

for additional information concerning potential for chlorine dioxide- or chlorite-induced 

neurodevelopmental effects following intermediate-duration oral exposure to chlorine dioxide or chlorite. 

Chronic-Duration Exposure and Cancer. No information was located regarding health effects in 

humans following chronic-duration exposure to chlorine dioxide or chlorite; however, information is 

available from animal studies. Results of animal carcinogenicity testing are available for oral (Kurokawa 
 

CHLORINE DIOXIDE AND CHLORITE 68 

3. HEALTH EFFECTS 

et al. 1986; Miller et al. 1986) and dermal exposure (Kurokawa et al. 1984). These results generally do 

not indicate a carcinogenic effect, with the exception of a report of significantly higher incidences of liver 

and lung tumors in male mice exposed to 250 and 500 ppm of chlorite, respectively, in the drinking water 

(Kurokawa et al. 1986). However, high mortality in the control males (due to fighting) reduced the 

sample size, making statistical comparisons between controls and treated animals difficult to interpret. A 

well-designed cancer bioassay that includes noncancer end points might provide valuable information 

concerning the effects of long-term exposure to chlorine dioxide or chlorite. 

Genotoxicity. No reports were located regarding the genotoxicity of chlorine dioxide or chlorite in 

humans. Genotoxicity tests using standard in vivo and in vitro test systems have produced mixed results 

(Hayashi et al. 1988; Ishidate et al. 1984; Meier et al. 1985; Wang et al. 2002a, 2002b). Both chlorine 

dioxide and chlorite induced reverse mutations in S. typhimurium (with activation). Chlorite, but not 

chlorine dioxide, induced chromosomal aberrations in Chinese hamster fibroblast cells. Negative results 

were obtained in tests for micronuclei and chromosomal aberrations in bone marrow of mice orally 

administered chlorine dioxide or chlorite during a period of 5 days. However, both chlorine dioxide and 

chlorite produced positive results for micronuclei in mice following intraperitoneal injection. The 

database for chlorine dioxide and chlorite genotoxicity is not extensive and testing has produced mixed 

results; additional genotoxicity testing is not warranted. 

Reproductive Toxicity. No information was located regarding chlorine dioxide- or chlorite-induced 

reproductive effects in humans. Slightly altered sperm morphology and motility were observed in rats 

administered sodium chlorite in the drinking water, but treatment did not result in significant alterations 

in fertility rates or reproductive tissues (Carlton and Smith 1985; Carlton et al. 1987). Repeated oral 

exposure of male rats to chlorine dioxide or chlorite resulted in significantly decreased testicular DNA 

synthesis (Abdel-Rahman et al. 1984b; Suh et al. 1983). No significant treatment-related effects on 

fertility rates or sperm parameters were seen in other rats following repeated oral exposure to chlorine 

dioxide (Carlton et al. 1991). Additional reproductive toxicity studies are needed to further investigate 

the potential for chlorine dioxide or chlorite to induce reproductive effects. 

Developmental Toxicity. Epidemiological reports have focused on human populations exposed to 

chlorine dioxide-treated drinking water (Kanitz et al. 1996; Tuthill et al. 1982). However, study 

limitations preclude making definitive conclusions regarding the potential for chlorine dioxide- or 

chlorite-induced developmental toxicity in humans. Results from rat studies indicate that perinatal 

exposure to chlorine dioxide or chlorite may result in delayed neurodevelopment, observed as decreases 
CHLORINE DIOXIDE AND CHLORITE 69 

3. HEALTH EFFECTS 

in brain size and exploratory and locomotor activities (Mobley et al. 1990; Orme et al. 1985; Taylor and 

Pfohl 1985; Toth et al. 1990) or decreased auditory startle response (Gill et al. 2000). In some studies, 

postnatal changes in serum thyroid hormone levels have also been observed (Carlton and Smith 1985; 

Carlton et al. 1987; Mobley et al. 1990; Orme et al. 1985). These effects have been observed at maternal 

doses of approximately 6–14 mg/kg/day. Neither chlorine dioxide nor chlorite appears to induce 

significant gross soft tissue or skeletal abnormalities (Couri et al. 1982b; Harrington et al. 1995b; Suh et 

al. 1983). Additional developmental toxicity studies in animals are needed, which include a mechanistic 

approach designed to investigate the basis of the observed neurodevelopmental delays and a possible 

relationship between thyroid hormone effects and neurodevelopmental delays. 

Immunotoxicity. Reports of immunotoxicity are restricted to the findings of treatment-related altered 

thymus and spleen weights in animals exposed to chlorine dioxide or chlorite (Daniel et al. 1990; Gill et 

al. 2000; Harrington et al. 1995a). Neither chlorine dioxide nor chlorite appears to be of particular 

immunotoxicity concern. Additional immunotoxicity studies are not needed at this time. 

Neurotoxicity. With the exception of neurodevelopmental effects, chlorine dioxide and chlorite do 

not appear to present a significant neurotoxicity concern. Additional studies should focus on 

neurodevelopmental end points (refer to Section 3.12.2). 

Epidemiological and Human Dosimetry Studies. Limited information is available regarding 

health effects in humans following exposure to chlorine dioxide or chlorite. Respiratory effects were 

reported among individuals who were accidentally exposed to concentrated chlorine dioxide vapors 

(Elkins 1959; Exner-Freisfeld et al. 1986; Ferris et al. 1967, 1979; Gloemme and Lundgren 1957; 

Kennedy et al. 1991; Meggs et al. 1996). A single case report was located in which an individual ingested 

approximately 10 g of sodium chlorite in an apparent suicide attempt (Lin and Lim 1993). In a set of 

controlled studies, male volunteers consumed chlorine dioxide in aqueous solution and submitted blood 

samples for analysis (Lubbers et al. 1981, 1984a, 1984b). Three epidemiological studies were designed to 

investigate the potential for adverse effects in communities that utilized chlorine dioxide as a drinking 

water disinfectant (Kanitz et al. 1996; Michael et al. 1981; Tuthill et al. 1982). However, these studies 

had limitations in their designs that affect their interpretability. Well-designed epidemiological studies of 

populations orally exposed to chlorine dioxide in the drinking water could provide valuable information 

regarding safe levels. 
CHLORINE DIOXIDE AND CHLORITE 70 

3. HEALTH EFFECTS 

Biomarkers of Exposure and Effect. 

Exposure. No known biomarkers of exposure exist for chlorine dioxide. Being a water-soluble, strong 

oxidizing agent, chlorine dioxide is not likely to be absorbed as parent compound, but rather quickly 

reduced to chlorite and ultimately chloride ion. Chlorite levels can be measured in biological tissues and 

fluids, and may serve as an indication of recent exposure to chlorine dioxide or chlorite. Studies could be 

designed to quantify chlorite levels in various body tissues and fluids; however, it is not known whether 

such measurements could be used to quantify exposure levels. 

Effect. No known chlorine dioxide- or chlorite-specific biomarkers of effect exist. Additional studies of 

mechanisms of toxicity might provide information that could aid in the search for biomarkers of effect. A 

human study of methemoglobinemia among persons (especially children and nursing infants) exposed to 

higher concentrations of chlorine dioxide and chlorite in the drinking water might be beneficial. 

Absorption, Distribution, Metabolism, and Excretion. Information regarding the 

pharmacokinetics of chlorine dioxide and chlorite is predominantly derived from oral studies in 

laboratory animals. Chlorite (ClO2

-

) does not persist in the atmosphere either in ionic form or as chlorite 

salt. The rapid appearance of 36Cl in plasma following oral administration of chlorine dioxide (36ClO2) or 

chlorite (36ClO2

-

) has been shown in laboratory animals (Abdel-Rahman et al. 1980a, 1982, 1984a). 

Limited animal data indicate the presence of 36Cl in plasma following dermal application of Alcide, an 

antimicrobial compound containing sodium chlorite and lactic acid which rapidly form chlorine dioxide 

- when mixed together (Scatina et al. 1983). In rats, absorbed 36Cl (from 36ClO2 or 36ClO2 sources) is 

slowly cleared from the blood and is widely distributed throughout the body (Abdel-Rahman et al. 1980a, 

1980b, 1982, 1984a). Chlorine dioxide rapidly dissociates, predominantly into chlorite (which itself is 

highly reactive) and chloride ion (Cl-

), ultimately the major metabolite of both chlorine dioxide and 

chlorite in biological systems (Abdel-Rahman et al. 1980b, 1984a). Urine is the primary route of 

elimination, predominantly in the form of chloride ion (Abdel-Rahman et al. 1980a, 1980b, 1984a). 

Additional pharmacokinetic studies of chlorine dioxide and chlorite should be designed to examine 

mechanisms of absorption and metabolic changes that might account for observed neurodevelopmental 

effects. Such studies might also elucidate mechanisms underlying alterations in various hematological 

and thyroid hormone parameters of currently unknown significance. 

Comparative Toxicokinetics. No studies were located in which toxicokinetics of chlorine dioxide 

or chlorite were examined in humans. Chlorine dioxide is used as a drinking water disinfectant and 

readily forms chlorite (ClO2

-

) in aqueous environments. Therefore, humans would be most likely to 
 

CHLORINE DIOXIDE AND CHLORITE 71 

3. HEALTH EFFECTS 

encounter chlorine dioxide or chlorite via the oral exposure route. Currently, available toxicokinetic 

information is restricted to animal studies. Additional studies could be designed to examine 

toxicokinetics in humans orally exposed to chlorine dioxide or chlorite. Results of human and animal 

studies could then provide a basis for development of PBPK models for species extrapolation. 

Methods for Reducing Toxic Effects. No information was located regarding methods for reducing 

the toxic effects of chlorine dioxide or chlorite. Increasing urinary output might be an effective method 

for reducing body burden shortly following exposure. Intravenous administration of methylene blue 

might reduce chlorine dioxide- or chlorite-induced increases in methemoglobin. Future studies should be 

designed to evaluate mechanisms of chlorine dioxide- and chlorite-mediated toxicity. Results of such 

mechanistic studies might elucidate methods to reduce the toxic effects. 

Children’s Susceptibility. Neurodevelopmental delays and postnatal changes in serum thyroid 

hormone levels have been observed in animals following exposure of their mothers to chlorine dioxide or 

chlorite during gestation and/or lactation (Carlton and Smith 1985; Carlton et al. 1987; Gill et al. 2000; 

Mobley et al. 1990; Orme et al. 1985; Taylor and Pfohl 1985; Toth et al. 1990). It is not known whether 

age-related differences in toxicokinetic parameters exist for chlorine dioxide or chlorite. Additional 

studies should be designed to further examine neurodevelopmental toxicity and underlying mechanisms. 

A human study of methemoglobinemia among children and nursing infants exposed to higher 

concentrations of chlorine dioxide and chlorite in the drinking water might provide valuable information 

regarding age-related susceptibility. 

Child health data needs relating to exposure are discussed in 6.8.1 Identification of Data Needs: 

Exposures of Children. 

3.12.3 Ongoing Studies 

No ongoing studies pertaining to the toxicity or pharmacokinetics of chlorine dioxide or chlorite were 

located in a search of the Federal Research in Progress database (FEDRIP 2003). 

CHLORINE DIOXIDE AND CHLORITE 73 

4. CHEMICAL AND PHYSICAL INFORMATION 

4.1 CHEMICAL IDENTITY 

Information regarding the chemical identity of chlorine dioxide and sodium chlorite is located in 

Table 4-1. Table 4-1 lists common synonyms, trade names, and other pertinent identification information 

for chlorine dioxide and sodium chlorite. 

4.2 PHYSICAL AND CHEMICAL PROPERTIES 

Information regarding the physical and chemical properties of chlorine dioxide and sodium chlorite is 

located in Table 4-2. Table 4-2 lists important physical and chemical properties of chlorine dioxide and 

sodium chlorite, but is not intended to be all inclusive. 
Table 4-1. Chemical Identity of Chlorine Dioxide and Sodium Chlorite 

Characteristic Information 

Chemical name 

Synonym(s) 

Registered trade name(s) 

Chemical formula 

Chemical structure 

Identification numbers: 

 CAS Registry 

 NIOSH RTECS 

EPA Hazardous Waste 

OHM/TADS 

DOT/UN/NA/IMCO 

HSDB 

NCI 

Chlorine dioxide Sodium chlorite 

Alcide; Anthium dioxcide; Chlorine(IV) Chlorous acid, sodium salt; Textone 

oxide; Chlorine oxide; Chlorine peroxide; Chloroperoxide; Chloriperoxyl; 

Chloryl radical; Dioxide de cloro 

[Spanish]; Dioxide de chlore [French]; 

Caswell No. 179A; Doxcide 50 

No data No data 

ClO2 NaClO2 

+

O Cl O Na O

Cl O 

10049-04-4 7758-19-2 

FO3000000 VZ4800000 

No data No data 

No data No data 

NA 9191 (Frozen Solution) UN 1496 (solid)/UN 1908 (solution) 

517 733 

No data No data 

CAS = Chemical Abstracts Services; CIS = Chemical Information System; DOT/UN/NA/IMCO = Department of 

Transportation/United Nations/North America/International Maritime Dangerous Goods Code; EPA = Environmental 

Protection Agency; HSDB = Hazardous Substance Data Bank; NCI = National Cancer Institute; NIOSH = National 

Institute for Occupational Safety and Health; OHM/TADS = Oil and Hazardous Materials/Technical Assistance Data 

System; RTECS = Registry of Toxic Effects of Chemical Substances 

CHLORINE DIOXIDE AND CHLORITE 74 

4. CHEMICAL AND PHYSICAL INFORMATION 
 

CHLORINE DIOXIDE AND CHLORITE 75 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Chlorine Dioxide and Sodium 

Chlorite 

Property 

Molecular weight (g/mol) 

Color 

Physical state 

Melting point 

Boiling point 

Density 

Odor 

Chlorine dioxide 

67.452a

Yellow to reddish-yellowc

Gasc

-59 °Cc

11 °Cc

1.640 g/mL (0 °C; liquid)a 

1.614 g/mL (10 °C; liquid)a 

Pungent, distinctive from chlorinea

Sodium chlorite 

90.45b 

Whiteb 

Solidc 

 180–200° C 

(decomposes)c 

 Decomposesc 

2.468 g/mL (solid)d 

 No data 

Odor threshold: 

Water No data No data 

Air No data No data 

Taste No data No data 

Solubility: 

Water 3.01 g/L at 25 °C and 34.5 mm Hgc 390 g/L at 30 °Cc 

Other solvents No data No data 

Partition coefficients: 

 Log Kow No data No data 

 Log Koc 

Vapor pressure at 25 °C 

Photolysis 

No data 

>1 atm (gas)e

Unstable in lighte

No data 

 No data 

 No data 

Henry's law constant at 25 °C No data No data 

Autoignition temperature No data No data 

Flashpoint No data No data 

Flammability limits at 25 °C No data No data 

Incompatibilities 

Conversion factors 

(25 °C and 1 atm) 

Organic materials, heat, phosphorus, 

potassium hydroxide, sulfur, mercury, 

carbon monoxide; unstable in light; a 

powerful oxidizere 

1 ppm=2.76 mg/m3e

Organic matter, sulfur, 

powdered coal; a powerful 

oxidizerb 

 No data 
CHLORINE DIOXIDE AND CHLORITE 76 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Chlorine Dioxide and Sodium 

Chlorite 

Property Chlorine dioxide Sodium chlorite 

Explosive limits Explosive at temperatures >-40 °Ca and No data 

concentrations in excess of 10% v/v at 

1 atmf 

a

Kaczur and Cawfield 1993 

b

Vogt et al. 1986 

c

O'Neil 2001 

d

HSDB 2002 

e

NIOSH 2002 

f

Dobson and Cary 2002 
CHLORINE DIOXIDE AND CHLORITE 77 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

5.1 PRODUCTION 

Chlorine dioxide is always manufactured on site because of the risk of rapid decomposition. In all 

processes, chlorine dioxide is produced in strong acid solutions from either sodium chlorite or sodium 

chlorate. Small- and medium-scale industrial production of chlorine dioxide utilizes sodium chlorite as 

the raw material. This is typical of water treatment and disinfection applications that require high purity 

(i.e., chlorine-free) waters. Other applications not requiring high purity waters utilize sodium chlorate. 

This is typical of pulp bleaching where large quantities of chlorine dioxide are necessary. There are 

several processes used to generate chlorine dioxide from sodium chlorate. In the R2 process, chlorine 

dioxide is produced from sodium chlorate and sulfuric acid, with sodium chloride as the reducing agent. 

Chlorine dioxide is absorbed from the gas phase in packed towers in cold water, and chlorine leaves the 

system as a by-product. In the Mathieson process, a sulfur dioxide-air mixture is diffused into a solution 

of sodium chlorate and sulfuric acid. Sulfur dioxide is used as the reductant to produce chlorine dioxide 

with a much lower chlorine content. The process also produces sulfuric acid, reducing the overall acid 

requirement. Exit gases from the Mathieson process are passed through a scrubber to remove any 

unreacted sulfur dioxide. The Solvay process uses sodium chlorate and sulfuric acid, with methanol as 

the reducing agent. Products from this process are chlorine dioxide, formic acid, and carbon dioxide. In 

improved Solvay processes, sulfuric acid demand is reduced by crystallizing out the by-products sodium 

sulfate, sodium sesquisulfate, or sodium bisulfate (Kaczur and Cawlfield 1993; Vogt et al. 1986). 

The production volume of chlorine dioxide can be accurately estimated from the total sodium chlorate 

consumption for chemical pulp bleaching because this accounts for >95% of all chlorine dioxide 

production. The annual production of chlorine dioxide in the United States was estimated to be 79, 81, 

146, 226, and 361 kilotons for the years 1970, 1975, 1980, 1985, and 1990, respectively (Kaczur and 

Cawlfield 1993). 

Table 5-1 lists the facilities in each state that manufacture or process chlorine dioxide, the intended use, 

and the range of maximum amounts of chlorine dioxide that are stored on-site. There are 118 facilities 

that produce or process chlorine dioxide in the United States. Current estimates for the amounts of 

chlorine dioxide stored on-site as a by-product or impurity range from 99 to 9,999,999 pounds/year (45– 
CHLORINE DIOXIDE AND CHLORITE 78 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

Table 5-1. Facilities that Produce, Process, or Use Chlorine Dioxide 

Number Minimum Maximum 

of amount on site amount on site 

Statea facilities in poundsb in poundsb Activities and usesc 

AL 9 10,000 999,999 1, 3, 6, 10, 11, 12 

AR 4 10,000 9,999,999 1, 3, 10, 11 

CA 3 0 99,999 1, 3, 10, 12 

CO 1 1,000 9,999 1, 3, 12 

FL 7 0 9,999,999 1, 3, 10, 11, 12 

GA 8 100 999,999 1, 3, 5, 10, 11, 12 

ID 1 10,000 99,999 1, 3, 10 

IL 1 0 99 1, 3, 12 

KY 3 10,000 999,999 1, 3, 6, 12 

LA 5 1,000 999,999 1, 3, 6, 10, 11 

MA 1 0 99 1, 3, 12 

MD 1 10,000 99,999 1, 3, 10 

ME 6 10,000 9,999,999 1, 3, 6, 10, 11, 12 

MI 3 10,000 99,999 1, 3, 7, 10, 11 

MN 2 10,000 99,999 1, 3, 10 

MS 4 10,000 999,999 1, 3, 8, 10 

NC 8 0 9,999,999 1, 3, 5, 6, 10, 12 

NY 2 1,000 99,999 1, 3, 10, 12 

OH 1 10,000 99,999 1, 3, 10 

OR 3 10,000 999,999 1, 3, 10 

PA 6 1,000 999,999 1, 2, 3, 10, 11, 12 

SC 6 0 99,999 1, 3, 6, 10, 11, 12 

TN 2 10,000 99,999 1, 3, 6, 10 

TX 4 1,000 99,999 1, 3, 5, 10, 11 

VA 3 1,000 999,999 1, 3, 10, 12 

VT 1 0 99 1, 3, 12 

WA 7 0 99,999 1, 3, 6, 10, 11, 12 

WI 3 100 99999 1, 3, 4, 10, 11, 12 

Source: TRI01 2003 

a

Post office state abbreviations used 

b

Amounts on site reported by facilities in each state 

c

Activities/Uses: 

1. Produce 6. Impurity 11. Chemical Processing Aid 

2. Import 7. Reactant 12. Manufacturing Aid 

3. Onsite use/processing 8. Formulation Component 13. Ancillary/Other Uses 

4. Sale/Distribution 9. Article Component 14. Process Impurity 

5. Byproduct 10. Repackaging 
CHLORINE DIOXIDE AND CHLORITE 79 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

4,500,000 kg/year) (TRI01 2003). The data from the Toxics Release Inventory (TRI) listed in Table 5-1 

should be used with caution, however, since only certain types of facilities were required to report (EPA 

1995). This is not an exhaustive list. 

The commercial manufacture of sodium chlorite is based almost entirely on the reduction of chlorine 

dioxide gas in a sodium hydroxide solution containing hydrogen peroxide as the reducing agent. The 

chlorine dioxide is generated from the chemical or electrochemical reduction of sodium chlorate under 

acidic conditions. The product is a 33 weight percent solution of sodium chlorite, which is then converted 

to a dry solid containing approximately 80% of sodium chlorite with other added salts (e.g., sodium 

chloride), which act as diluents for increased safety in storage and handling (Kaczur and Cawlfield 1993; 

Vogt et al. 1986). 

In 1991, the production capacity of sodium chlorite was 7,700 metric tons for 80% assay basis sodium 

chlorite (Kaczur and Cawlfield 1993). In the United States, sodium chlorite is produced by International 

Dioxcide, Inc. (North Kingstown, Rhode Island) and Vulcan Materials Co. (Wichita, Kansas) (SRI 2001). 

5.2 IMPORT/EXPORT 

In all cases, chlorine dioxide is produced at the point of use. No import or export of this chemical occurs 

(Kaczur and Cawlfield 1993; Vogt et al. 1986). 

Import/export data on chlorites from the U.S. Department of Commerce are combined with data for 

hypochlorites and hypobromites (ITA 2002). Separate data on the import/export of chlorite were not 

located. 

5.3 USE 

Wood-pulp bleaching is the largest use of chlorine dioxide, which is a uniquely selective oxidizer for 

lignin. In general, the trend in the pulp industry has been to eliminate chlorine and hypochochlorite as 

bleaching agents and replace them with chlorine dioxide. Since chlorine dioxide functions via an 

oxidative reaction rather than a chlorinating reaction, the formation of chlorinated organic compounds is 

limited. Also, unlike other oxidizing agents, chlorine dioxide does not attack cellulose, and thus 

preserves the mechanical properties of bleached pulp. In the final stages of the pulp-bleaching processes, 
CHLORINE DIOXIDE AND CHLORITE 80 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

chlorine dioxide is the most frequently used bleaching chemical. A unique whiteness can be achieved 

using chlorine dioxide in kraft pulp, sulfite pulp, and soda pulp processes. In the United States, the firststage of the pulp-bleaching process makes use of mixtures of chlorine and chlorine dioxide to reduce the 

formation of organic chlorine compounds (EPA 2002c; Kaczur and Cawlfield 1993; Vogt et al. 1986). 

In the textile industry, chlorine dioxide is used as a bleaching agent and produces high-quality textile 

fibers with additional qualities. For example, “shrinkproof” wool owes its qualities to the reaction of 

chlorine dioxide with the cross-linking sulfur atoms of the wool. 

In industrial and municipal waste-water treatment, chlorine dioxide is more effective than chlorine as a 

biocide over a wide pH range. It is also less corrosive and more compatible with some construction 

materials. Some municipal water systems use chlorine dioxide to eliminate taste and odor problems from 

drinking waters (EPA 2002c; Kaczur and Cawlfield 1993; Vogt et al. 1986). The advantage of using 

chlorine dioxide, rather than chlorine or ozone, is that chlorine dioxide does not react with organic matter 

to form trihalomethanes (THMs); it also does not transform bromide into hypobromite (OBr-

), which 

could react with organic matter to form bromoform (CHBr3) or bromate (BrO3

-

) (Aieta and Berg 1986; 

Stevens 1982; WHO 2000). As part of the EPA Information Collection Rule (ICR), 5.1% of the water 

treatment facilities serving more than 100,000 people in the United States reported that chlorine dioxide 

was used in 1995 (Hoehn et al. 2000). Table 5-2 summarizes the number of facilities utilizing chlorine 

dioxide for water treatment in each state. However, the percentage of facilities using chlorine dioxide 

would be higher if smaller facilities (i.e., those serving less than 50,000 people) were also included in this 

value. 

Chlorine dioxide has been recognized for its disinfectant properties since the early 1900s. Chlorine 

dioxide kills microorganisms by disrupting the transport of nutrients across the cell wall. In 1967, EPA 

first registered the liquid form of chlorine dioxide for use as a disinfectant and sanitizer. Liquid 

formulations are used as disinfectants in a variety of applications (e.g., on pets and farm animals; in 

bottling plants; and in food processing [fruit and vegetable washing, meat and poultry disinfection, 

disinfection of food processing equipment], handling, and storage plants). In industrial processes, 

chlorine dioxide is used as a disinfectant in water treatment (cooling systems/towers), ammonia plants, 

pulp mills (slime control, paper machines), oil fields, scrubbing systems, odor-control systems, and the 

electronics industry. In 1988, EPA registered chlorine dioxide gas as a sterilant. Chlorine dioxide gas is 
CHLORINE DIOXIDE AND CHLORITE 81 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

Table 5-2. Publicly Owned Treatment Works (POTW) Utilizing Chlorine Dioxide 

for Water Treatment in 1995 

Number of facilities Statesa 

0 AK, DE, FL, HI, ID, MD, MN, MS, ND, NV, OR, UT, VT, WI, WV 

1–5 AL, AR, AZ, CA, CO, CT, IN, KS, LA, ME, MI, MT, NE, NH, NJ, NM, NY, OK, 

PA, RI, SD, TN, WA, WY 

6–10 IA, KY, MA, NC, VA 

11–15 GA, MO, SC 

21–25 OH 

72 TX 

Source: Hoehn et al. 2000 

a

Post office state abbreviations used 
CHLORINE DIOXIDE AND CHLORITE 82 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

registered for sterilizing manufacturing and laboratory equipment, environmental surfaces, tools, and 

clean rooms. (EPA 2002c; Kaczur and Cawlfield 1993; Vogt et al. 1986). 

Chlorine dioxide is one of many antimicrobial agents being considered for use in some anthrax 

decontamination efforts because of its effectiveness against spore-forming bacteria. Section 18 of the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) authorizes EPA to allow certain state and 

federal agencies to use a pesticide for an unregistered use for a limited time if EPA determines that 

emergency conditions exist. On November 9, 2001, EPA issued a crisis exemption for the limited sale, 

distribution, and use of EPA-registered pesticide products containing aqueous chlorine dioxide for 

cleaning surfaces contaminated with anthrax. Under the crisis exemption, only registered stabilized 

chlorine dioxide products may be sold or distributed to employees of EPA, other federal, state, or local 

government agencies, and the U.S. Postal Service. Application of the pesticide products under crisis 

exemption are limited to specific buildings or treatment sites identified by EPA, other federal, state, or 

local government agencies, and the U.S. Postal Service (EPA 2002c). 

More than 80% of all sodium chlorite produced is used for the generation of chlorine dioxide. Sodium 

chlorite is also used in disinfectant formulations and for sterilization. Like chlorine dioxide, it must be 

registered with EPA under FIFRA for each specific application use as a disinfectant. Sodium chlorite is 

used in other industrial settings (e.g., in scrubber systems used to remove NOx and SOx from combustion 

flue gas; in the treatment and removal of toxic and odorous gases such as hydrogen sulfide and 

mercaptans; and as an aqueous formulation used to oxidize copper surfaces in multilayer circuit boards) 

(Kaczur and Cawlfield 1993). 

5.4 DISPOSAL 

Chlorine dioxide is a strong oxidizer and will not persist in the open environment for long periods. At 

concentrations >10%, chlorine dioxide is easily detonated by sunlight (O’Neil et al. 2001). It can remain 

for short periods of time in clean distribution systems (Kaczur and Cawlfield 1993; NRC 1980; Vogt et 

al. 1986). No further information on the disposal of chlorine dioxide was located. 

Chlorite ions and salts are strong oxidizers. Responsible care should be undertaken during disposal of 

chlorite ion solutions and salts. For example, solid sodium chlorite is unstable and can form explosive 

mixtures with oxidizable materials, such as organic compounds. Chlorite ion solutions should not be 

allowed to dry on textiles because this may result in a flammable combination (Kaczur and Cawlfield 
CHLORINE DIOXIDE AND CHLORITE 83 

5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

1993; Vogt et al. 1986). No further information on the disposal of chlorite ions and chlorite salts were 

located. 

 

CHLORINE DIOXIDE AND CHLORITE 85 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.1 OVERVIEW 

Chlorine dioxide and chlorite have not been identified in any of the 1,647 waste sites that have been 

proposed for inclusion on the EPA National Priorities List (NPL) (HazDat 2004). However, the number 

of sites evaluated for chlorine dioxide and chlorite are not known. The frequency of these sites can be 

seen in Figure 6-1. 

Chlorine dioxide is a highly reactive chemical (see Section 6.3.2) that will exist only in the immediate 

vicinity of where it is produced or used. In the United States, the primary route of exposure to chlorine 

dioxide and chlorite (ions and salts) is from the consumption of drinking water. Chlorine dioxide is 

added to drinking water as a disinfectant in some municipal water-treatment systems in the United States. 

In 1995, 5.1% of community water-treatment systems in the United States reported that chlorine dioxide 

was used (Hoehn et al. 2000). However, the total number people exposed will be higher if smaller 

facilities (i.e., those serving less than 50,000 people) are also included in this value (see Section 5.3). As 

regulated by EPA (as of January 1, 2002), the maximum residual disinfectant levels in drinking water for 

chlorine dioxide and chlorite ion are 0.8 and 1.0 mg/L, respectively (EPA 2002e, 2002g). 

6.2 RELEASES TO THE ENVIRONMENT 

Releases of chlorine dioxide are required to be reported under Superfund Amendment Reauthorization 

Act (SARA) Section 313; consequently, data are available for this compound in the Toxics Release 

Inventory (TRI) (EPA 1995). According to the TRI, a total of 582,315 pounds (264,134 kg) of chlorine 

dioxide was released to the environment in 2001 (TRI01 2003). The TRI data should be used with 

caution because only certain types of facilities are required to report. This is not an exhaustive list. 

6.2.1 Air 

The estimated release of 582,005 pounds (263,993 kg) of chlorine dioxide to the atmosphere from over 

100 manufacturing, processing, and waste-disposal facilities in 2001 accounted for about 99.9% of the 
CHLORINE DIOXIDE AND CHLORITE 86 

6. POTENTIAL FOR HUMAN EXPOSURE 

Figure 6-1. Frequency of NPL Sites with Chlorine Dioxide and Chlorite 

Contamination 

Frequency of 

NPL Sites

Derived from HazDat 2004 

*No data are available in HazDat 2004
CHLORINE DIOXIDE AND CHLORITE 87 

6. POTENTIAL FOR HUMAN EXPOSURE 

estimated total environmental releases (TRI01 2003). These releases are summarized in Table 6-1. The 

data from the TRI listed in Table 6-1 should be used with caution, however, since only certain types of 

facilities are required to report (EPA 1995). This is not a comprehensive list. 

No other information was found in the literature about the releases of chlorine dioxide and chlorite (ions 

or salts) into air. 

6.2.2 Water 

The estimated release of 310 pounds (141 kg) of chlorine dioxide to water from one electric power 

facility in Florida accounted for <0.1% of the estimated total environmental releases in 2001 (TRI01 

2003). No releases (0 pounds) of chlorine dioxide occurred via underground injection (TRI01 2003). 

These releases are summarized in Table 6-1. The data from the TRI listed in Table 6-1 should be used 

with caution, however, since only certain types of facilities are required to report (EPA 1995). This is not 

a comprehensive list. 

No other information was found in the literature about the releases of chlorine dioxide and chlorite (ions 

or salts) into water. 

6.2.3 Soil 

One manufacturing facility reported releases of chlorine dioxide to the environment in 2001; no chlorine 

dioxide was reportedly released to land (TRI01 2003). Releases to the environment from facilities that 

produce, process, or use chlorine dioxide are summarized in Table 6-1. The data from the TRI should be 

used with caution since only certain types of facilities are required to report (EPA 1995). This is not a 

comprehensive list. 

No other information was found in the literature about the releases of chlorine dioxide and chlorite (ions 

and salts) to soils and sediment. 
CHLORINE DIOXIDE AND CHLORITE 88 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-1. Releases to the Environment from Facilities that Produce, Process, or 

Use Chlorine Dioxidea
 

Reported amounts released in pounds per yearb 

Number Under- Total on and 

Statec 

of 

facilities Aird

 Water 

ground 

injection Land 

Total on-site 

releasee 

Total offsite releasef 

off-site 

release 

AL 9 53,789 0 0 0 53,789 0 53,789 

AR 5 18,848 0 0 0 18,848 0 18,848 

CA 3 3,391 0 0 0 3,391 0 3,391 

CO 1 255 No data 0 0 255 0 255 

FL 8 110,496 310 0 0 110,806 0 110,806 

GA 8 6,924 0 0 0 6,924 0 6,924 

ID 1 6,105 No data 0 0 6,105 0 6,105 

IL 2 9,714 No data 0 0 9,714 0 9,714 

KY 3 5,147 0 0 0 5,147 0 5,147 

LA 6 19,861 0 0 0 19,861 0 19,861 

MA 1 0 No data 0 0 0 0 0 

MD 1 19,005 No data 0 0 19,005 0 19,005 

ME 6 8,936 0 0 0 8,936 0 8,936 

MI 3 1,563 0 0 0 1,563 0 1,563 

MN 2 23,229 0 0 0 23,229 0 23,229 

MS 4 35,758 0 0 0 35,758 0 35,758 

NC 8 66,695 0 0 0 66,695 0 66,695 

NY 2 6,560 0 0 0 6,560 0 6,560 

OH 1 22,005 0 0 0 22,005 0 22,005 

OR 3 15,295 No data 0 0 15,295 0 15,295 

PA 6 34,555 0 0 0 34,555 0 34,555 

SC 6 56,967 0 0 0 56,967 0 56,967 

TN 2 13,403 No data 0 0 13,403 0 13,403 

TX 4 6,259 0 0 0 6,259 0 6,259 

VA 3 14,105 0 0 0 14,105 0 14,105 

VT 1 0 0 0 0 0 0 0 

WA 7 15,846 0 0 0 15,846 0 15,846 

WI 5 7,294 No data 0 0 7,294 0 7,294 

Total 111 582,005 310 0 0 582,315 0 582,315 

Source: TRI01 2003 

a

The TRI data should be used with caution since only certain types of facilities are required to report. This is not an 

exhaustive list. Data are rounded to nearest whole number.
 b

Data in TRI are maximum amounts released by each facility.
 c

Post office state abbreviations are used. 

d

The sum of fugitive and stack releases are included in releases to air by a given facility.
 e

The sum of all releases of the chemical to air, land, water, and underground injection wells. 

f

Total amount of chemical transferred off-site, including to publicly owned treatment works (POTW). 
 

 

CHLORINE DIOXIDE AND CHLORITE 89 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.3 ENVIRONMENTAL FATE 

6.3.1 Transport and Partitioning 

Chlorine dioxide is a very reactive compound and may exist in the environment for only short periods of 

time (see Section 6.3.2). Chlorine dioxide is readily soluble as a gas. However, chlorine dioxide can be 

easily driven out of aqueous solutions with a strong stream of air. The partition coefficient between water 

and ClO2 (g) is about 21.5 at 35 °C and 70.0 at 0 °C (Aieta and Berg 1986; Kaczur and Cawlfield 1993; 

Stevens 1982). Transport and partition of chlorine dioxide in soils and sediments will not be significant. 

Chlorine dioxide is expected to be reduced to chlorite ions in aqueous systems (see Section 6.3.2.2). 

Like chlorine dioxide, the chlorite ion is a strong oxidizer (Rav-Acha 1998). Since chlorite is an ionic 

species, it is not expected to volatilize and will not exist in the atmosphere in the vapor phase. Thus, 

volatilization of chlorite ions from moist soil and water surfaces or dry soil surfaces will not occur. 

Because chlorite is an anion, sorption of chlorite ions onto suspend particles, sediment, or clay surfaces is 

expected to be limited under environmental conditions. Thus, chlorite ions will be mobile in soils and 

leach into groundwater. However, chlorite (ions and salts) will undergo oxidation-reduction reactions 

with components in soils, suspend particles, and sediments (e.g., Fe2+, Mn2+ ions; see Section 6.3.2.2). 

Thus, oxidation-reduction reactions may reduce the concentration of chlorite ions capable of leaching into 

groundwater. 

No additional information was located in the literature on the transport and partitioning of chlorine 

dioxide and chlorite (ions and salts). 

6.3.2 Transformation and Degradation 

Chlorine dioxide is an unstable gas that rapidly decomposes in air. In water, chlorine dioxide is a strong 

oxidizer; 50–70% of the chlorine dioxide that reacts with organic and inorganic compounds will 

immediately appear as chlorite (ClO2

-

) and chloride (Cl-) ions. Chlorine dioxide does not form trihalomethanes as disinfection by-products (DBPs). However, chlorine dioxide does result in the formation of 

other DBPs (e.g., lower chlorinated organics, chlorate, and chlorite) which may be found in drinking 

water treated with chlorine dioxide (Aieta and Berg 1986; Chang 1982; Stevens 1982). Suh and Abdel­
 

CHLORINE DIOXIDE AND CHLORITE 90 

6. POTENTIAL FOR HUMAN EXPOSURE 

Rahman (1985) reported that the presence of ClO2 and HOCl (Cl2 dissolved in water) inhibit the 

formation of trihalomethanes, and the degree of inhibition depends on the ratio of ClO2 to HOCl. 

6.3.2.1 Air 

Chlorine dioxide gas is unstable and can rapidly decompose at high concentrations (>40 kPa partial 

pressure). It also decomposes to chlorine and oxygen with exposure to mild heat, noise, flame, and a 

minor pressure wave at low concentrations (Dobson and Cary 2002). Chlorine dioxide will decompose 

upon exposure to sunlight (Vogt et al. 1986). The gas-phase absorption spectrum for chlorine dioxide is 

the same as in aqueous solution (Kaczur and Cawfield 1993). The primary photochemical reaction of 

ClO2 in the gas phase corresponds to homolytic scission of one of the chlorine-oxygen bonds (i.e., 

ClO26ClO + O). Products of this initial reaction generate secondary products including doublet-state 

oxygen (O2

*

), chlorine (Cl2), and chlorine trioxide (Cl2O3) (Griese et al. 1992; Zika et al. 1984). If 

chlorine dioxide gas is diluted in air to <15 volume percent, it can be relatively stable in darkness (Vogt et 

al. 1986). 

6.3.2.2 Water 

Chlorine dioxide is readily soluble in water, forming a greenish-yellow solution. It is not unusual to 

simultaneously have multiple chlorine species present in chlorine dioxide solutions originating from byproducts or unreacted precursors. Table 6-2 lists the various chlorine species that might be present in 

solutions of chlorine dioxide (Gordon 2001). 

Chlorine dioxide alone will not hydrolyze in solution to any appreciable extent between pH 2 and 10. 

Dilute neutral or acidic aqueous solutions of chlorine dioxide are stable if kept cool, well sealed, and 

protected from sunlight. In the absence of oxidizable substances and in the presence of hydroxyl ions, 

chlorine dioxide will dissolve in water and then decompose with the slow formation of chlorite and 

chlorate ions (e.g., 2ClO2 + 2OH- X ClO2- + ClO3- + H2O). At chlorine dioxide concentrations in the 5– 

10 mg/L range at pH 12, the decomposition half-life of chlorine dioxide in solution ranges from 20 to 

180 minutes (Aieta and Berg 1986; Stevens 1982; WHO 2000). Lee et al. (2004) found that the 

concentration of chlorate ions formed from chlorine dioxide were higher at low pHs. For example, 
CHLORINE DIOXIDE AND CHLORITE 91 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-2. Chlorine Speciation in Aqueous Solutions 

Oxidation State Species Formula 

+7 Perchlorate ion ClO4 

-

+5 Chlorate ion ClO3 

-

+4 Chlorine dioxide ClO2 

+3 Chlorite ion ClO2 

-

+3 Hypochlorous acid HClO2 

+1 Hypochlorite ion OCl-

+1 Hypochlorous acid HOCl 

0 Chlorine Cl2 

-1 Chloride ion Cl-
CHLORINE DIOXIDE AND CHLORITE 92 

6. POTENTIAL FOR HUMAN EXPOSURE 

10 and 15% chlorate ions were formed from chlorine dioxide at pHs 4 and 7, respectively. At pH 10, 

chlorate ions were not formed at all. 

Chlorine dioxide has a positive chlorine-oxidation state of four (+4), which is intermediate between 

chlorite (+3) and chlorate (+5) ions. Reduction of chlorine dioxide usually results in the formation of 

chlorite ions (e.g., ClO2 + e- X ClO2

-

; EpH=7=0.95 volts). Chlorite ions (ClO2

-

) are also effective oxidizing 

agents, although they react much slower than chlorine dioxide. The reduction of chlorite results in the 

- formation of chloride ions (e.g., ClO2 + 4H+

 + 4e- X Cl- + 2H2O; EpH=7=0.37 volts). The redox potential 

at pH 7 (i.e., EpH=7) indicates that chlorine dioxide is a stronger oxidizer than chlorite ions (Rav-Acha 

1998). During water-treatment, approximately 50–70% of the chlorine dioxide reacted will immediately 

appear as chlorite and chloride (Aieta and Berg 1986; Stevens 1982). 

Chlorine dioxide, like other strong oxidants, will oxidize manganese (II), iron (II), iodide (I-

), and sulfide 

(S2-), forming insoluble manganese dioxide (MnO2), iron hydroxides precipitates, iodine (I2), and sulfate 

(SO4

2-), respectively (Dernat and Pouillot 1992). In the absence of sunlight, bromide (Br-

) is not oxidized 

by chlorine dioxide. Thus, chlorine dioxide will not transform bromide into hypobromite (OBr-

), which 

could react with organic matter to form bromoform (CHBr3) or bromate (BrO3

-

). This is a significant 

difference between the use of chlorine dioxide as an oxidant and the use of chlorine or ozone as oxidants 

in water-treatment systems (Aieta and Berg 1986; Stevens 1982; WHO 2000). 

Since chlorine dioxide reacts generally as an electron acceptor, hydrogen atoms present in activated 

organic CH or NH bonds do not react by electrophilic substitution with chlorine (Hoigne and Bader 

1994). As a result, chlorine dioxide will form fewer chlorinated compounds compared to Cl2 when it 

reacts with organic matter. In contrast, chlorine (Cl2) reacts not only by oxidation, but also by 

electrophilic substitution, resulting in a variety of volatile and nonvolatile chlorinated organic products; 

for example, trihalomethanes (THMs). It has been well established that “chlorine-free” chlorine dioxide 

in reaction with both humic and fulvic acids does not form THMs. However, some other types of 

chlorinated organics may be formed from the reaction of chlorine dioxide with humic and fulvic acids 

(Aieta and Berg 1986; Stevens 1982). The reactions of chlorine dioxide with olefin compounds in wastewater are apparently very complex and produce a host of chlorinated and nonchlorinated products. No 

evidence exists that chlorine dioxide undergoes reactions with saturated aliphatic hydrocarbons under 

mild conditions. Chlorine dioxide does not seem to cause the formation of odorous compounds with 

phenol. Chlorine dioxide treatment of phenols can cause chlorine substitution, ring cleavage, or both, 

depending on the particular phenol reacted and the conditions of the reaction. Through complex 
CHLORINE DIOXIDE AND CHLORITE 93 

6. POTENTIAL FOR HUMAN EXPOSURE 

mechanisms, chlorine dioxide reacts rapidly with phenols and phenoxide anions to form quinones and 

chloroquinones, and when in excess, oxalic and maleic acids. Chlorine substitution in the products, 

however, is not entirely absent (Aieta and Berg 1986; Rav-Acha and Choshen 1987; Stevens 1982). 

Chlorine dioxide reacts with natural organic matter (NOM; i.e., humic and fulvic acids) mainly on the 

aromatic part. Formaldehyde and acetaldehyde are the main byproducts of oxidation of NOM by chlorine 

dioxide; pH does not have any significant influence on this reaction (Dąbrowska et al. 2003). 

At a waste water-treatment pilot plant in Evansville, Indiana, which used chlorine dioxide as a primary 

disinfectant, more than 40 different organic disinfection by-products (DBPs) were identified at very low 

concentrations. Eleven of these DBPs are regulated chemicals by EPA (i.e., bromodichloromethane, 

carbon tetrachloride, dibromochloromethane, 1,1,1-trichloro-2-propanone, maleic anhydride, bromoform, 

1,4-dichlorobenzene, benzyl cyanide, benzoic acid, naphthalene, and decylphenol) (Richardson et al. 

1994). Chlorine dioxide will not react with ammonia and reacts only slowly with primary amines. In 

general, amines produce the respective aldehyde upon reaction with chlorine dioxide in the following 

order of reactivity: tertiary>seconary>primary (Aieta and Berg 1986; Stevens 1982). 

Chlorine dioxide readily degrades in aqueous solutions under ultraviolet light. It has a broad UV 

absorption band with a maximum near 360 nm and a molar extinction coefficient of about 

1,150 (M x cm)

-1 (Aieta and Berg 1986). It is postulated that the reaction in solution proceeds as in the 

gas phase, to give ClO and O. The initial photodissociation reaction is followed by rapid dark and light 

reactions to produce chlorate (ClO3

-

), hypochlorite (OCl-), and chloride (Cl-) (Zika et al. 1984). Solution 

speciation can have a marked effect on the mechanism and products generated from photolysis of chlorine 

dioxide. In the absence of light, chlorine dioxide will not oxidize bromide ion into hypobromite (OBr-

) 

and will not form of bromoform (CHBr3) or bromate (BrO3

-

). However, under sunlight, some photolysis 

intermediates of chlorine dioxide with long half-lives are capable of oxidizing bromide to hypobromite, 

which will result in the formation of bromate. Thus, if labile organic materials are present during 

illumination, bromoform may be generated by the reaction of organic matter with hypobromite formed by 

intermediates of chlorine dioxide photolysis (Aieta and Berg 1986; Bolyard et al. 1993; Griese et al. 1992; 

Stevens 1982; WHO 2000; Zika et al. 1984). 

Chlorite and chlorate ions have been shown to undergo reduction by bacteria under anaerobic conditions. 

Anaerobic degradation is an important process in anoxic groundwater, sediments, and some soils. It has 

been known for over 40 years that chlorate ions can be reduced by mixed cultures under anaerobic 

conditions (Logan 1998). Chlorate-respiring bacteria are widely distributed in the environment and 
CHLORINE DIOXIDE AND CHLORITE 94 

6. POTENTIAL FOR HUMAN EXPOSURE 

utilize electron acceptors (e.g., chlorate ions) in lieu of oxygen to generate energy and produce carbonbased building blocks. The reduction of chlorate ions occurs in two steps; chlorate reduction with 

chlorate reductase enzyme followed by chlorite disproportionation catalyzed by chlorite dismutase (a nonrespiratory enzyme). Oxygen and chloride are formed as the end products (Danielsson et al. 2003; Xu et 

al. 2004). Although oxygen is produced during reduction processes, it is rapidly consumed by the 

bacteria such that oxygen does not accumulate to high levels. Chlorate dismutase activity is unaffected 

by oxygen, but expression of this enzyme does not occur under aerobic conditions even in the presence of 

perchlorate or chlorate ion (Xu et al. 2004). Several dinitrifying bacteria reduce chlorate but, in general, 

this reduction is not coupled to microbial growth (Wolterink et al. 2002). Moreover, these organisms lack 

chlorite dismutase enzyme, which is required for reduction of chlorite. Thus, it is likely that the nitrate 

and chlorate pathways for chlorate-reduction are not necessarily related (Wolterink et al. 2002). No 

quantitative information was located on the biodegradation rate of chlorate or chlorite ions in the 

environment. However, the rate of chlorate ion degradation appears to be rapid under anaerobic 

conditions in waste-water treatment facilities (Logan 1998). 

6.3.2.3 Sediment and Soil 

No information was located in the literature on the transformation and degradation of chlorine dioxide or 

chlorite (ions and salts) in sediment and soils. 

6.3.2.4 Other Media 

No information was located in the literature on the transformation and degradation of chlorine dioxide or 

chlorite (ions and salts) in other environmental media. 

6.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT 

6.4.1 Air 

Chlorine dioxide degrades rapidly in air (see Section 6.3.2.1) and should be measurable only near its 

source of production or use (e.g., pulp and paper-mill plants, water-treatment facilities). As part of an 

international study of workers in the pulp and paper industry, the concentration of chlorine dioxide was 

measured in the workplace air of pulp and paper mills in 19 countries. The concentration of chlorine 

dioxide was measured in the following work areas: steam and power generation (range, <1–60 ppb); 
CHLORINE DIOXIDE AND CHLORITE 95 

6. POTENTIAL FOR HUMAN EXPOSURE 

effluent water-treatment (range, not detected to 3 ppb); and maintenance (range, <detection limit to 

5.8 ppb) (Kauppinen et al. 1997; Teschke et al. 1999). In another study, the concentration of chlorine 

dioxide was measured in the workplace air at a pulp mill in British Columbia, Canada between May and 

June, 1988. The concentration of chlorine dioxide was <10 ppb in area samples and personal full-shift 

samples. The exception was in the bleach/chemical preparation area sample in which the concentration of 

chlorine dioxide ranged from <10 to 300 ppb (Kennedy et al. 1991). 

The formation of offensive odors in indoor air, such as “kerosene-like” and “cat-urine-like” odors, have 

been attributed to drinking water treated with chlorine dioxide. The “kerosene-like” and “cat-urine-like” 

odors are produced by reactions between chlorine dioxide escaping from water and volatile organic 

compounds found in homes, primarily from new carpeting. This has been ascribed to over-dosing 

drinking water with residual chlorine dioxide (or chlorite ions), which is used as a postdisinfectant to 

prevent microbial growth in water-distribution systems (Dluzniewski 2002; Hoehn et al. 1990, 2003). 

No other information was located in the literature on the concentrations of chlorine dioxide or chlorite 

(ions and salts) in air. 

6.4.2 Water 

Chlorine dioxide is added to drinking water as a disinfectant in some municipal water-treatment systems 

in the United States. In 1995, 5.1% of community water-treatment systems in the United States reported 

that chlorine dioxide was used (Hoehn et al. 2000). This would translate to about 12 million people who 

may be exposed to chlorine dioxide and chlorite ions in the United States. However, the total number of 

people exposed will be higher if smaller facilities (i.e., those serving <50,000 people) are also included in 

this value. 

As regulated by EPA (as of January 1, 2002), the maximum residual-disinfectant level (MRDL) for 

chlorine dioxide is 0.8 mg/L (EPA 2002g); the maximum contaminant level (MCL) for its oxidation 

product, chlorite ion, in drinking water is 1.0 mg/L (EPA 2002e). The levels of chlorite ion in 

distribution system waters have been reported as part of the Information Collection Rule (ICR), a research 

project used to support the development of national drinking-water standards in the United States (EPA 

2002d). Figure 6-2 illustrates the levels of chlorite ion in drinking waters sampled from distribution 

systems versus the percentage of publicly-owned treatment works (POTW) facilities in the United States 
% of POTW facilities reporting to IC

R

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

0.0-0.1 0.1-0.2 0.2-0.3 0.3-0.4 0.4-0.5 0.5-0.6 0.6-0.7 0.7-0.8 0.8-0.9 0.9-1.0 above 

1.0 

Level of ClO2 

- (ppm) in distribution system water 

CHLORINE DIOXIDE AND CHLORITE 96 

6. POTENTIAL FOR HUMAN EXPOSURE 

Figure 6-2. Percentage of POTW Facilities Reporting to ICR vs. Level of Chlorite 

in Distribution System Water* 

Source: EPA 2002d 

*Samples were taken from the distribution system of POTW facilities that utilized chlorine dioxide. 

ClO2

-

 = chlorite; ICR = Information Collection Rule; POTW = publicly owned treatment works 
CHLORINE DIOXIDE AND CHLORITE 97 

6. POTENTIAL FOR HUMAN EXPOSURE 

that reported as part of the ICR in 1998. Approximately 16% of this group had levels of chlorite ion over 

the MCL of 1 mg/L. 

In a 12-week epidemiological study conducted in a small town in Ohio, the ranges of concentrations of 

chlorine dioxide, chlorite ion, and chlorate ion in drinking water were 0.3–1.1, 3.2–7.0, and 0.3–1.1 mg/L, 

respectively (Lykins et al. 1990; Michael et al. 1981). In one study using a sensitive analytical method, 

the average concentration of chlorine dioxide in tap water from the city of Brest, France was 

1.8x10-7 mol/L (0.012 mg/L) (Quentel et al. 1994). 

Bolyard et al. (1993) analyzed samples from four water-treatment facilities in the United States that use 

chlorine dioxide as a disinfectant. Source water samples were also analyzed from each facility and no 

chlorite or chlorate ions were detected. At these water-treatment facilities, additional gaseous Cl2 was 

added to provide a residual disinfectant in the distribution systems. Water taken from these distribution 

systems (i.e., water sampled at water-treatment plant) had measurable concentrations of both chlorite and 

chlorate ions. The ranges of concentrations were 15–740 and 21–330 μg/L for chlorite and chlorate, 

respectively (Bolyard et al. 1993). In general, chlorite ion was the predominate disinfection by-product. 

However, at two sites where water was chlorinated prior to passing through secondary sedimentation 

basins containing activated carbon, concentrations of chlorate ion concentrations were higher than 

chlorite ions. At these sites, residual Cl2 and activated carbon likely oxidized chlorite to chlorate, which 

resulted in elevated levels of chlorate in finish water samples (Bolyard et al. 1993). 

No other information was located in the literature on the concentrations of chlorine dioxide or chlorite 

(ions and salts) in water. 

6.4.3 Sediment and Soil 

No information was located in the literature on the concentrations of chlorine dioxide or chlorite (ions and 

salts) in sediments and soil. Due to the high reactivity of chlorine dioxide and chlorite (ions and salts), 

however, concentrations of these compounds are expected to be small or nil. 
CHLORINE DIOXIDE AND CHLORITE 98 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.4.4 Other Environmental Media 

No information was located in the literature on the concentrations of chlorine dioxide or chlorite (ions and 

salts) in other environmental media. 

6.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE 

The general population may be exposed to chlorine dioxide and chlorite (ions or salts) by the ingestion of 

drinking water. As part of the ICR, 5.1% of the water-treatment facilities serving more than 

100,000 people in the United States reported that chlorine dioxide was used in 1995 (Hoehn et al. 2000). 

However, the percentage of facilities using chlorine dioxide would be higher if smaller facilities (i.e., 

those serving <50,000 people) were also included in this value. Individuals who live in communities with 

water-treatment facilities using chlorine dioxide will have a higher exposure to chlorine dioxide and 

chlorite ions than other segments of the population. 

For communities that utilize chlorine dioxide as a drinking-water disinfectant, an exposure estimate may 

be calculated based on the maximum residual-disinfectant levels for chlorine dioxide and chlorite ion. If 

the concentration of chlorine dioxide in U.S. drinking water is assumed to be 0.8 mg/L (the maximum 

residual disinfectant level [EPA 2002g]) and the consumption rate of drinking water by a normal adult is 

assumed to be 2 L/day, then the exposure to chlorine dioxide from drinking water would be 1.6 mg/day. 

Similarly, if the concentration of chlorite ion in U.S. drinking water is assumed to be 1.0 mg/L (the 

maximum contaminant level [EPA 2002e]), and the consumption rate of drinking water by a normal adult 

is assumed to be 2 L/day, then the exposure from drinking water would be 2.0 mg/day. However, the 

exposure to chlorine dioxide and chlorite ion may be much lower than these estimated levels depending 

on individual conditions for each community. Other sources of exposure to chlorine dioxide and chlorite 

(ions and salts) are not significant for the general population. 

Occupational exposure to chlorine dioxide and chlorite may occur at facilities that utilize these chemicals 

as bleaching agents (e.g., pup and paper mills) or water disinfectants (e.g., water-treatment facilities). 

The primary route of occupational exposure will be by inhalation of these compounds in the immediate 

vicinity of their use. As part of an international study of workers in the pulp and paper industry, the 

concentration of chlorine dioxide was measured in the workplace air of pulp and paper mills from 

19 countries. The concentration of chlorine dioxide was measured in the following work areas: steam 

and power generation (range, <1–60 ppb); effluent water-treatment (range, not detected to 3 ppb); and 
CHLORINE DIOXIDE AND CHLORITE 99 

6. POTENTIAL FOR HUMAN EXPOSURE 

maintenance (range, <detection limit to 5.8 ppb) (Kauppinen et al. 1997; Teschke et al. 1999). In another 

study, the concentration of chlorine dioxide was measured in the workplace air at a pulp mill in British 

Columbia, Canada between May and June in 1988. The concentration of chlorine dioxide was <10 ppb in 

area samples and personal full-shift samples. The exception was in the bleach/chemical preparation area 

sample, in which the concentration of chlorine dioxide ranged from <10 to 300 ppb (Kennedy et al. 

1991). 

6.6 EXPOSURES OF CHILDREN 

This section focuses on exposures from conception to maturity at 18 years in humans. Differences from 

adults in susceptibility to hazardous substances are discussed in 3.7 Children’s Susceptibility. 

Children are not small adults. A child’s exposure may differ from an adult’s exposure in many ways. 

Children drink more fluids, eat more food, breathe more air per kilogram of body weight, and have a 

larger skin surface in proportion to their body volume. A child’s diet often differs from that of adults. 

The developing human’s source of nutrition changes with age: from placental nourishment to breast milk 

or formula to the diet of older children who eat more of certain types of foods than adults. A child’s 

behavior and lifestyle also influence exposure. Children crawl on the floor, put things in their mouths, 

sometimes eat inappropriate things (such as dirt or paint chips), and spend more time outdoors. Children 

also are closer to the ground, and they do not use the judgment of adults to avoid hazards (NRC 1993). 

Specific information on the exposure of children to chlorine dioxide and chlorite (ions and salts) was not 

located. Like adults, the primary route of exposure for children will be from drinking water. Water 

consumption among children is higher on a proportional body weight basis than for adults. Therefore, 

children may have a higher exposure to chlorine dioxide and chlorite (ions and salts). Other sources of 

exposure to chlorine dioxide and chlorite (ions and salts) will not be significant. Chlorine dioxide and 

chlorite (ions and salts) are reactive chemicals and will not be found in amniotic fluid, meconium, 

neonatal blood, or breast milk. 
 

 

CHLORINE DIOXIDE AND CHLORITE 100 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES 

Individuals who are employed at pulp and paper mills, municipal water-treatment facilities, and other 

facilities that use chlorine dioxide as a disinfectant may have high exposures to chlorine dioxide and 

chlorite (ions and salts) (see Section 6.5). 

6.8 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the 

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of chlorine dioxide and chlorite are available. Where adequate 

information is not available, ATSDR, in conjunction with the National Toxicology Program (NTP), is 

required to assure the initiation of a program of research designed to determine the health effects (and 

techniques for developing methods to determine such health effects) of chlorine dioxide and chlorite. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will be 

evaluated and prioritized, and a substance-specific research agenda will be proposed. 

6.8.1 Identification of Data Needs 

Physical and Chemical Properties. The relevant physical and chemical properties of chlorine 

dioxide and chlorite (ions and salts) are well known and permit estimation of its environmental fate. 

Physical and chemical properties are presented in Table 4-2 (Dobson and Cary 2002; HSDB 2002; 

Kaczur and Cawfield 1993; O'Neil 2001; NIOSH 2002; Vogt et al. 1986). 

Production, Import/Export, Use, Release, and Disposal. Data regarding the production of 

chlorine dioxide and chlorite (ions and salts) are available, but are limited (Kaczur and Cawlfield 1993). 

Annual production of chlorine dioxide in the United States has increased from 79 to 361 kilotons between 

the years 1970 and 1990 (Kaczur and Cawlfield 1993). Additional production information for chlorite 

(ions and salts) specifically whether the production amount (7,700 metric tons in 1991; Kaczur and 

Cawlfield 1993) is larger or smaller than in the past would be useful. Information on future production of 
 

CHLORINE DIOXIDE AND CHLORITE 101 

6. POTENTIAL FOR HUMAN EXPOSURE 

chloride dioxide and chlorite (ions and salts) would also be helpful. Chlorine dioxide and chlorite (ions 

and salts) are not widely used in the home or environment. Some municipal waste water-treatment 

facilities use chlorine dioxide or chlorite (ions and salts) to disinfect drinking water (EPA 2002c; Kaczur 

and Cawlfield 1993; Vogt et al. 1986). Wood-pulp bleaching is the largest industrial use of chlorine 

dioxide (EPA 2002c; Kaczur and Cawlfield 1993; Vogt et al. 1986). Air is the medium most likely 

contaminated with chlorine dioxide near facilities where it is used (TRI01 2003). Additional information 

on disposal methods is not warranted since chlorine dioxide and chlorite (ions and salts) are reactive and 

will not exist for long periods of time in the environment (see Section 6.3). 

According to the Emergency Planning and Community Right-to-Know Act of 1986, 42 U.S.C. Section 

11023, industries are required to submit substance release and off-site transfer information to the EPA. 

TRI, which contains this information for 2001, became available in July of 2003. This database is 

updated yearly and should provide a list of industrial facilities and emissions. 

Environmental Fate. Chlorine dioxide and chlorite (ions and salts) are strong oxidizers and will not 

exist in the environment for long periods of time (Dobson and Cary 2002); therefore, transport and 

partitioning of chlorine dioxide and chlorite (ions and salts) are not important. Chlorine dioxide reacts 

immediately in water to form chlorite and chlorate ions, and in air to form chlorine and oxygen (Dobson 

and Cary 2002). Information on the half-life of chlorite (ions and salts) in environmental media would be 

useful. 

Bioavailability from Environmental Media. Chlorine dioxide and chlorite (ions and salts) are 

strong oxidizers. Chlorine dioxide is highly reactive and will not be bioavailable in environmental media. 

Additional information concerning the bioavailability of chlorite (ions and salts) would be helpful. 

Food Chain Bioaccumulation. Chlorine dioxide and chlorite (ions and salts) are strong oxidizers 

and will not bioconcentrate or biomagnify in plants, aquatic organisms, or animals. 

Exposure Levels in Environmental Media. Chlorine dioxide and chlorite (ions and salts) are 

strong oxidizers and react quickly in air, water, soil, plant material, and foodstuffs. No environmental 

monitoring studies are available. The general population may be exposed to chlorine dioxide and chlorite 

(ions and salts) by the ingestion of drinking water. As part of the ICR, 5.1% of the water-treatment 

facilities serving more than 100,000 people in the United States reported that chlorine dioxide was used in 

1995 (Hoehn et al. 2000). Using the maximum contaminant level (EPA 2002e) for chlorine dioxide and 
 

CHLORINE DIOXIDE AND CHLORITE 102 

6. POTENTIAL FOR HUMAN EXPOSURE 

chlorite, exposure from drinking water for these populations would be 1.6 and 2.0 mg/day, respectively. 

Additional monitoring data are needed for populations exposed to chlorine dioxide and chlorite (ions and 

salts) from drinking water. Reliable monitoring data for the levels of chlorine dioxide and chlorite (ions 

and salts) in contaminated media at hazardous waste sites are needed so that the information obtained on 

levels chlorine dioxide and chlorite (ions and salts) in the environment can be used in combination with 

the known body burden of chlorine dioxide and chlorite (ions and salts) to assess the potential risk of 

adverse health effects in populations living in the vicinity of hazardous waste sites. 

Exposure Levels in Humans. Chlorine dioxide and chlorite (ions and salts) are strong oxidizers 

and react quickly in water or moist body tissues to form chloride ions. Consequently, chlorine dioxide 

and chlorite (ions and salts) are not detected in human tissues (e.g., blood, urine, fat, or breast milk). 

Biological monitoring studies are not available for these compounds near hazardous waste sites. This 

information is necessary for assessing the need to conduct health studies on these populations. 

Exposures of Children. There are no unique exposure pathways for children. Children will be 

exposed to chlorine dioxide and chlorite (ions and salts) in the same manner as adults in the general 

population (i.e., ingestion of water). Studies focusing on the exposure of children to drinking waters 

containing chlorine dioxide and chlorite (ions and salts) would be useful. Additional information on 

whether children are different in their weight-adjusted intake of chlorine dioxide and chlorite (ions and 

salts) is needed. Data on childhood specific means to decrease exposure would also be useful. Chlorine 

dioxide and chlorite (ions and salts) are strong oxidizers and react quickly in water or moist body tissues 

to form chloride ions. Consequently, chlorine dioxide and chlorite (ions and salts) will not be detected in 

tissues of children (e.g., blood, urine, or fat). 

Child health data needs relating to susceptibility are discussed in 3.12.2 Identification of Data Needs: 

Children’s Susceptibility. 

Exposure Registries. No exposure registries for chlorine dioxide and chlorite (ions and salts) were 

located. These substances are not currently compounds for which a sub-registry has been established in 

the National Exposure Registry. These substances will be considered in the future when chemical 

selections are made for sub-registries to be established. The information that is amassed in the National 

Exposure Registry facilitates the epidemiological research needed to assess adverse health outcomes that 

may be related to exposure to this substance. 
CHLORINE DIOXIDE AND CHLORITE 103 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.8.2 Ongoing Studies 

The Federal Research in Progress (FEDRIP 2003) database provides additional information obtainable 

from a few ongoing studies that may fill in some of the data needs identified in Section 6.8.1. A National 

Science Foundation study exploring the photochemistry of chlorine dioxide relevant to stratospheric 

ozone depletion is currently being conducted by Dr. Prezhdo at the University of Washington. No other 

studies on the environmental fate of chlorine dioxide or chlorite (ions and salts) are reported to be 

currently in progress (FEDRIP 2003). 

 

CHLORINE DIOXIDE AND CHLORITE 105 

7. ANALYTICAL METHODS 

The purpose of this chapter is to describe the analytical methods that are available for detecting, 

measuring, and/or monitoring chlorine dioxide and chlorite, its metabolites, and other biomarkers of 

exposure and effect to chlorine dioxide and chlorite. The intent is not to provide an exhaustive list of 

analytical methods. Rather, the intention is to identify well-established methods that are used as the 

standard methods of analysis. Many of the analytical methods used for environmental samples are the 

methods approved by federal agencies and organizations such as EPA and the National Institute for 

Occupational Safety and Health (NIOSH). Other methods presented in this chapter are those that are 

approved by groups such as the Association of Official Analytical Chemists (AOAC) and the American 

Public Health Association (APHA). Additionally, analytical methods are included that modify previously 

used methods to obtain lower detection limits and/or to improve accuracy and precision. 

7.1 BIOLOGICAL MATERIALS 

No methods for determining chlorine dioxide in biological materials were located. Most studies 

concerning human health effects measure the concentrations of chlorine dioxide in the air or in water. 

The measurement of chlorine dioxide in biological materials is not commonly used because of the rapid 

conversion of chlorine dioxide to chlorine-containing metabolites, such as chlorite and chloride ions. 

Abdel-Rahman et al. (1980b) developed a method to quantitatively and qualitatively measure the 

metabolites of chlorine dioxide (e.g., ClO2

-

, and ClO-) in biological fluids. These biomarkers can be used 

to indirectly measure chlorine dioxide exposure. 

The concentration of residual chlorite ion in vegetables and eggs treated with sodium chlorite was 

determined by UV-ion chromatography (Suzuki et al. 1997). Sodium chlorite was extracted with water 

and cleaned-up using C18 cartridge. The detection limit of sodium chlorite in vegetables and eggs was 

1 mg/kg with recoveries of 90–100%. 

7.2 ENVIRONMENTAL SAMPLES 

Chlorine dioxide has been measured in air and water. Methods for determining levels in the air include 

spectrophotometry and ion chromatography. Environmental analyses of chlorine dioxide in water are 
CHLORINE DIOXIDE AND CHLORITE 106 

7. ANALYTICAL METHODS 

performed using electrochemical, chromatographic, or spectrophotometric methods. Analytical methods 

for the determination of chlorine dioxide in environmental samples are given in Table 7-1. Ion 

chromatography may also be used to analyze the inorganic disinfection by-products of chlorine dioxide 

(i.e., chlorite ions) in an analogous manner using EPA Method 300.0 (Pfaff and Brockhoff 1990). 

Atmospheric chlorine dioxide may be sampled by pulling a given volume of air through a toxic gas vapor 

detector tube. The tube contains chemicals that react only with chlorine dioxide. If chlorine dioxide is 

present, the indicator chemical in the tube will change color. The concentration of the gas or vapor may 

be estimated by either the length-of-stain compared to a calibration chart or the intensity of the color 

change compared to a set of standards (EMMI 1997). Diffusive samplers have been used to monitor 

chlorine dioxide and chlorine in workplace air. In this technique, workplace air is diffused into an 

absorbing solution of neutrally buffered potassium iodide. In the absorbing solution, chlorine dioxide and 

chlorine are reduced by iodide ions to chlorite and chloride ions, respectively. The formed ions are then 

separated and quantified by ion chromatography. The analytical detection limits have been found to be 

0.02 and 0.07 ppm for chloride and chlorite ions, respectively (Björkholm et al. 1990). 

Spectrophotometry (or colorimetry) has been used to measure chlorine dioxide in water using indicators 

that change colors when oxidized by chlorine dioxide. Spectrophotometric analyzers determine the 

concentration of chlorine dioxide by measuring the optical absorbance of the indicator in the sample 

solution. The absorbance is proportional to the concentration of the chlorine dioxide in water. Indicators 

used for this technique include N,N-diethyl-p-phenylenediamine, chlorophenol red, and methylene blue 

(APHA 1998; Fletcher and Hemming 1985; Quentel et al. 1994; Sweetin et al. 1996). For example, 

chlorophenol red selectively reacts with chlorine dioxide at pH 7 with a detection limit of 0.12 mg/L. The 

interferences from chlorine may be reduced by the addition of oxalic acid, sodium cyclamate, or 

thioacetamide (Sweetin et al. 1996). 

APHA Method 4500-CLO2-B, iodometric titration analysis, measures the concentration of chlorine 

dioxide in water by titration with iodide, which is reduced to form iodine. Iodine is then measured 

colorimetrically when a blue color forms from the production of a starch-iodine complex. The detection 

limit for this method is 20 μg/L (APHA 1998). 
 

 

CHLORINE DIOXIDE AND CHLORITE 107 

7. ANALYTICAL METHODS 

Table 7-1. Analytical Methods for Determining Chlorine Dioxide and Chlorite in 

Environmental Samples 

Sample Analytical Sample Percent 

matrix Preparation method method detection limit recovery Reference 

Air None. 

Work- Diffusion of air into potasplace air sium iodide solution at pH 7. 

Water None. 

Water To 100 mL sample, add 2 

mL glycine solution and mix. 

In a separate flask, place 

5 mL buffer reagent and 

N,N-diethyl-p-phenylenediamine indicator solution 

and mix. Add 200 mg 

EDTA, disodium salt, and 

then add glycine-treated 

sample and mix. 

Water Add buffer and indicator. 

Water/ Measure initial temperature 

waste and pH and protect sample 

water from light throughout the 

procedure. Phenylarsine 

oxide is used as standard 

titrant. 

Water None. 

Toxic gas vapor 

detector tube 

Ion chromatography (of 

chlorite ion in 

solution) 

Ion chromatography with 

conductivity 

detector 

UV/VIS 

spectrometry 

UV/VIS 

spectrometry 

Amperometric 

titration 

Flow injection 

using redox 

electrode 

detector 

0.05 ppm 

0.02 ppm of 

chlorine dioxide 

0.01 mg/L (as 

chlorite ion) 

0.03 mg/L (as 

chlorite ion) 

>0.1 mg/La 

Indicator 

(detection limit); 

acid chrome 

violet K 

(0.02 mg/L); 

amaranth 

(0.005 mg/L); 

lissamine green 

B (0.03 mg/L); 

methylene blue 

(0.02 mg/L); 

chlorophenol 

red (0.12 mg/L) 

0.5 mg/La 

3.4 ppb (as 

chlorite ion) 

No data EPA 1997 

No data Björkholm et al. 

1990; Hekmat et 

al. 1994 (OSHA 

Method 202) 

No data Hoehn et al. 

2000 (EPA 

Method 300.0) 

 Pfaff and 

Brockhoff 1990 

No data APHA 1998 

(Method 4500­

CLO2-D) 

No data Fletcher and 

Hemmings 

1985; Hofmann 

et al. 1998; Hui 

et al. 1997; 

Sweetin et al. 

1996 

No data APHA 1998 

(Method 2350­

C), (Method 

4500-CLO2-C) 

(Method 4500­

CLO2-E) 

No data Ohura et al. 

1999 
CHLORINE DIOXIDE AND CHLORITE 108 

7. ANALYTICAL METHODS 

Table 7-1. Analytical Methods for Determining Chlorine Dioxide and Chlorite in 

Environmental Samples 

Sample 

matrix Preparation method 

Analytical 

method 

Sample 

detection limit 

Percent 

recovery Reference 

Water Transfer 5 mL acetic acid, or 

enough to adjust sample pH 

between 3 and 4, and 1 g 

KI, and 1 mL starch solution; 

Iodometric 

titration 

20 μg/L No data APHA 1998 

(Method 4500­

CLO2-B) 

pour in sample and mix. 

Water, 

drinking 

Add sample to 1,2-dihydroxy-anthraquinone-3-sulphonic acid in 

phosphate buffer. 

Polarographic 

analyser 

2 μg/L No data Quentel et al. 

1994 

a

Hofmann et al. (1998) 

APHA = American Public Health Association; EDTA = ethylene diamine tetraacetic acid; EPA = Environmental 

Protection Agency; KI = potassium iodide; OSHA = Occupational Safety and Health Administration; 

UV/VIS = ultraviolet/visible light 
CHLORINE DIOXIDE AND CHLORITE 109 

7. ANALYTICAL METHODS 

For APHA Methods 2350-C and 4500-CLO2-E, amperometric analyzers are used to measure chlorine 

dioxide in water. Amperometric analyzers measure the current that is necessary to maintain a constant 

concentration of titrant as chlorine dioxide reduces the titrant (e.g., phenylarsine oxide). This method is 

limited by interference from compounds that might react with the titrant (e.g., chlorine and chloroamine) 

(APHA 1998). 

Because of its sensitivity and precision, ion chromatography (EPA Method 300.0) is a good technique for 

analyzing chlorine dioxide in water. Ion chromatography utilizes the ability of certain ion exchange 

resins to separate a mixture of anionic species. A liquid mobile phase (e.g., eluant) is used to carry the 

sample through the system either by isocratic (using same eluant) or gradient (varying concentration or 

flow rate) elution. After separation is achieved, the separated anions are measured using a detector (e.g., 

conductometric, ultraviolet/visible, or fluorescence). Typically, chlorine dioxide is indirectly analyzed as 

chlorite ions (Hoehn et al. 2000). Detection limits for chlorite ions range from 0.01 to 0.03 mg/L (Hoehn 

et al. 2000; Pfaff and Brockhoff 1990). Other detection methods used with ion chromatography, such as 

ion-spray mass spectrometry, have been developed and offer greater ion selectivity and sensitivity 

(Charles and Pépin 1998). Precolumn sample treatments using tetraborate/boric acid to separate analytes 

from common interfering ions (e.g., chloride, carbonate, and nitrate) result in lower detection limits on the 

order of 10 μg/L for chlorite ions (Hautman and Bolyard 1992a). With postcolumn derivatization of 

chlorite ions to tribromate ions, detection limits on the order of 0.4 μg/L have been achieved for chlorite 

ions (Weinberg and Yamada 1998). 

Gas-diffusion flow injection analysis is capable of detecting very low concentrations of chlorine dioxide 

in water (i.e., detection limit is 5 μg/L). A chemiluminescence flow-through detector cell is used to 

measure the concentration chlorine dioxide as a function of chemiluminescence intensity. A gas diffusion 

membrane separates the donor stream from the detecting stream and removes ionic interferences from 

iron and manganese compounds, as well as from other oxychlorinated compounds, such as chlorate and 

chlorite (Hollowell et al. 1986; Saksa and Smart 1985). 

A rapid potentiometric flow inject technique for the simultaneous determination of oxychlorine species 

(e.g., ClO2

-

) was developed by Ohura et al. (1999). The analytical method is based on the detection of a 

large transient potential change of the redox electrode due to chlorine generated via the reaction of the 

oxychlorine species (e.g., ClO2

-

). The detection limit for ClO2

-

 is 3.4 ppb. 
 

 

CHLORINE DIOXIDE AND CHLORITE 110 

7. ANALYTICAL METHODS 

7.3 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the 

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of chlorine dioxide and chlorite are available. Where adequate 

information is not available, ATSDR, in conjunction with the National Toxicology Program (NTP), is 

required to assure the initiation of a program of research designed to determine the health effects (and 

techniques for developing methods to determine such health effects) of chlorine dioxide and chlorite. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will be 

evaluated and prioritized, and a substance-specific research agenda will be proposed. 

7.3.1 Identification of Data Needs 

Methods for Determining Biomarkers of Exposure and Effect. 

Exposure. Metabolites of chlorinated phenoloic compounds in fish bile have been found to be sensitive 

biomarkers of bleach pulp mill effluent exposure (Brumley et al. 1996). Analysis of metabolites of 

chlorinated syringaldehydyes in fish bile can provide a biomarker of effluent exposure that is sensitive to 

low levels of exposure and correlates well with exposure concentrations. Methods for determining 

biomarkers of exposure in human were not located. Abdel-Rahman et al. (1980b) developed a method to 

quantitatively and qualitatively measure the metabolites of chlorine dioxide (e.g., ClO2

-

, and ClO-) in 

biological fluids. These biomarkers may be used to indirectly measure chlorine dioxide exposure. 

Methods for determining biomarkers of exposure in humans are needed to determine background levels in 

the population and levels at which biological effects occur. 

Effect. Methods for determining biomarkers of effect in human were not located. Methods for 

determining biomarkers of effect in humans are needed to determine background levels in the population 

and levels at which biological effects occur. 
CHLORINE DIOXIDE AND CHLORITE 111 

7. ANALYTICAL METHODS 

Methods for Determining Parent Compounds and Degradation Products in Environmental 

Media. Methods for determining chlorine dioxide and chlorite in air and water, the media of most 

concern for human exposure, are reliable, but may not be sensitive enough to measure background levels 

in the environment. 

No data are available on methods for determining chlorine dioxide and chlorite in soil and other solid 

media. In addition, there is insufficient information on the methods for determining chlorine dioxide and 

chlorite in media such as shellfish, fish, and plants. Some exposure to chlorine dioxide and chlorite may 

occur via ingestion of food, and thus, standardized methods for foods are needed. Methods with 

sufficient sensitivity for measuring background levels in foods are needed as well. 

7.3.2 Ongoing Studies 

No ongoing studies were located as a result of a search of Federal Research in Progress (FEDRIP 2003). 

CHLORINE DIOXIDE AND CHLORITE 113 

8. REGULATIONS AND ADVISORIES 

The international, national, and state regulations and guidelines regarding chlorine dioxide and chlorite in 

air, water, and other media are summarized in Table 8-l. 

ATSDR has derived an intermediate-duration inhalation MRL of 0.001 ppm (0.003 mg/m3

) for chlorine 

dioxide based on a LOAEL of 1 ppm for respiratory effects (peribronchiolar edema and vascular 

congestion in the lungs) in rats exposed to chlorine dioxide vapors 5 hours/day, 5 days/week for 2 months 

(Paulet and Desbrousses 1972). The LOAEL was converted to a LOAELHEC of 0.3 ppm and divided by 

an uncertainty factor of 300 (3 for interspecies extrapolation using dosimetric adjustments, 10 for the use 

of a LOAEL, and 10 to account for sensitive populations). 

ATSDR has derived an intermediate-duration oral MRL of 0.1 mg/kg/day for chlorite based on a NOAEL 

of 2.9 mg chlorite/kg/day and a LOAEL of 5.7 mg chlorite/kg/day for neurodevelopmental effects 

(lowered auditory startle amplitude) in rat pups that had been exposed throughout gestation and lactation 

via their mothers (CMA 1996; Gill et al. 2000). The NOAEL of 2.9 mg chlorite/kg/day was divided by 

an uncertainty factor of 30 (10 for interspecies extrapolation and 3 to account for sensitive populations). 

ATSDR considered the intermediate-duration oral MRL for chlorite to be applicable to chlorine dioxide 

as well. 

EPA (IRIS 2002) has derived an RfC of 2x10-4 mg/m3

 for chlorine dioxide based on a LOAEL of 

2.76 mg/m3

 (1 ppm) for respiratory effects (peribronchiolar edema and vascular congestion in the lungs) 

in rats exposed to chlorine dioxide vapors 5 hours/day, 5 days/week for 2 months (Paulet and Desbrousses 

1972). The LOAEL was converted to a LOAEL HEC of 0.64 mg/m3

 and divided by an uncertainty factor 

of 3,000 (10 for extrapolation of a chronic RfC from a subchronic study, 3 for interspecies extrapolation 

using dosimetric adjustments, 10 for intrahuman variability, and 10 to account for extrapolation from a 

LOAEL for mild effects and for the lack of inhalation developmental and reproductive toxicity studies). 

EPA (IRIS 2002) has derived an RfD of 3x10-2 mg/kg/day for chlorite based on a NOAEL of 3 mg/kg/day 

for neurodevelopmental effects in rat pups that had been exposed throughout gestation and lactation via 

their mothers (CMA 1996; Gill et al. 2000). The NOAEL of 3 mg chlorite/kg/day was divided by an 

uncertainty factor of 100 (10 for interspecies extrapolation and 10 to account for sensitive populations). 

EPA (IRIS 2002) considered the RfD for chlorite to be applicable to chlorine dioxide as well. 
 

 

 

 

 

CHLORINE DIOXIDE AND CHLORITE 114 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Chlorine Dioxide and 

Chlorite 

Agency Description Information Reference 

INTERNATIONAL 

Guidelines: 

IARC Carcinogenicity classification IARC 2002 

Sodium chlorite Group 3a 

NATIONAL 

Regulations and 

Guidelines: 

a. Air 

ACGIH TLV (8-hour TWA) 0.1 ppm ACGIH 2001 

TLV-STEL (15-minute TWA) 0.3 ppm 

EPA Chemical accident prevention 

Toxic end point 2.8x10-3 mg/L 

EPA 2002b 

40CFR68, 

Appendix A 

Regulated toxic substance for 

accidental release preventionb

 EPA 2002a 

40CFR68.130, 

Table 1 

Threshold quantity 1,000 pounds 

NIOSH TWA-REL (10-hour TWA) 0.1 ppm NIOSH 2002 

STEL (15-minute TWA) 0.3 ppm 

IDLH 5 ppm 

OSHA PEL (8-hour TWA) for general 

industry 

0.1 ppm OSHA 2002b 

29CFR1910.1000 

Highly hazardous chemical for 

general industry 

 OSHA 2002c 

29CFR1910.119, 

Appendix A 

Threshold quantity 1,000 pounds 

PEL (8-hour TWA) for construction 

industry 

0.1 ppm OSHA 2002a 

29CFR1926.55 

Highly hazardous chemical for 

construction industry 

 OSHA 2002d 

29CFR1926.64, 

Appendix A 

Threshold quantity 1,000 pounds 

b. Water 

EPA Maximum contaminant level EPA 2002e 

40CFR141.64(a) 

Chlorite 1.0 mg/L 
 

 

 

 

 

 

 

 

 

CHLORINE DIOXIDE AND CHLORITE 115 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Chlorine Dioxide and 

Chlorite 

Agency Description Information Reference 

NATIONAL (cont.) 

EPA Maximum contaminant level goal EPA 2002f 

40CFR141.53 

Chlorite 0.8 mg/L 

Maximum residual disinfectant 0.8 mg/L EPA 2002g 

level 40CFR141.65(a) 

Maximum residual disinfectant 0.8 mg/L EPA 2002h 

level goal 40CFR141.54 

c. Food 

EPA Exemption from the requirement of For residues as a seed - EPA 2002j 

a tolerance—sodium chlorite soak treatment in 40CFR180.1070 

growing Brassica (cole) 

leafy vegetables and 

radishes 

FDA Direct food additive permitted in Not to exceed 3 ppm FDA 2001e 

food for human consumption; used 21CFR173.300 

as an antimicrobial agent in water 

used in poultry processing and to 

wash fruits and vegetables 

Direct food additive permitted in Used at levels from 50– FDA 2001d 

food for human consumption; used 1,500 ppm 21CFR173.325 

as an antimicrobial agent— 

acidified sodium chlorite 

Indirect food additive; adjuvants, FDA 2001b 

production aids, and sanitizers 21CFR178.1010 

Indirect food substance affirmed as 

generally recognized as safe; used 

as a slimicide in the manufacture of 

paper and paperboard that contact 

food—sodium chlorite 

Used at levels from 125– 

250 ppm 

FDA 2001c 

21CFR186.1750 

Substance for use only as 

components of adhesives— 

sodium chlorite 

 FDA 2001a 

21CFR175.105 

(c)(5) 

d. Other 

EPA Chlorine dioxide IRIS 2002 

Carcinogenicity classification 

RfC 

RfD 

Group Dc 

2x10-4 mg/m3 

3x10-2 mg/kg/day 

Chlorite IRIS 2002 

Carcinogenicity classification Group Dc 

RfC No data 

RfD 3x10-2 mg/kg/day 
 

 

 

 

 

 

CHLORINE DIOXIDE AND CHLORITE 116 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Chlorine Dioxide and 

Chlorite 

Agency Description Information Reference 

NATIONAL (cont.)

 EPA 

Toxic chemical release reporting; 01/01/87 EPA 2002k 

community right-to-know; effective 40CFR372.65(a) 

date for reporting 

STATE 

Regulations and 

Guidelines: 

a. Air 

Louisiana Toxic air pollutantd BNA 2001 

Minimum emission rate 25 pounds/year 

New Mexico Toxic air pollutant BNA 2001 

OEL 0.3 mg/m3
 

Emissions 0.02 pounds/hour 

Vermont Hazardous air contaminant BNA 2001 

b. Water 

Maine Drinking water guideline HSDB 2002 

Chlorine dioxide 60 μg/L 

Chlorite 7 μg/L 

c. Food No data 

d. Other 

Florida Toxic substance in the workplace BNA 2001 

a

Group 3: not classifiable as to its carcinogenicity to humans

b

Basis for listing: toxic gas 

c

Group D: not classifiable as to human carcinogenicity

d

Class II: suspected human carcinogen and known or suspected human reproductive toxin 

ACGIH = American Conference of Governmental Industrial Hygienists; BNA = Bureau of National Affairs; 

CFR = Code of Federal Regulations; EPA = Environmental Protection Agency; FDA = Food and Drug 

Administration; HSDB = Hazardous Substances Data Bank; IARC = International Agency for Research on Cancer; 

IDLH = immediately dangerous to life and health; IRIS = Integrated Risk Information System; NIOSH = National 

Institute for Occupational Safety and Health; OEL = occupational exposure limit; OSHA = Occupational Safety and 

Health Administration; PEL = permissible exposure limit; ppm = parts per million; REL = recommended exposure 

limit; RfC = inhalation reference concentration; RfD = oral reference dose; STEL = short-term exposure limit; 

TLV = threshold limit value; TWA = time-weighted average 
 

 

 

_______________________ 

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*Weinberg HS, Yamada H. 1998. Post-ion-chromatography derivatization for the determination of 

oxyhalides at sub-ppb levels in drinking water. Anal Chem 70:1-6. 

*West JR, Smith HW, Chasis H. 1948. Glomerular filtration rate, effective renal blood flow, and 

maximal tubular excretory capacity in infancy. J Pediatr 32:10-18. 
CHLORINE DIOXIDE AND CHLORITE 135 

9. REFERENCES 

Wheeler GL, Lott PF. 1978. A rapid microdetermination of chlorine dioxide in the presence of active 

chlorine compounds. Microchem J 23:160-164. 

*WHO. 2000. Disinfectants and disinfectant by-products. World Health Organization. 

http://www.inchem.org. April 24, 2000. 

*WHO. 2002. Health for All Statistical Database. European Public Health Information Network for 

Eastern Europe. World Health Organization. http://www.euphin.dk/hfa/Phfa.asp. April 24, 2002. 

*Widdowson EM, Dickerson JWT. 1964. Chemical composition of the body. In: Comar CL, Bronner 

F, eds. Mineral metabolism: An advanced treatise. Volume II: The elements Part A. New York: 

Academic Press. 

*Wolterink AFWM, Jonker AB, Kengen SWM, et al. 2002. Pseudomonas chloritidismutans sp. nov., a 

non-denityifying, chlorate-reducing bacterium. Int J Syst Evol Microbiol 52:2183-2190. 

Wondergem E, Van Dijk-Looijaard AM. 1991. Chlorine dioxide as a post-disinfectant for Dutch 

drinking water. Sci Total Environ 102:101-112. 

*Xu J, Trimble JJ, Steinberg L, et al. 2004. Chlorate and nitrate reduction pathways are separately 

induced in the perchlorate-respiring bacterium Dechlorosoma sp. KJ and the chlorate-respiring bacterium 

Pseudomonas sp. PDA. Water Res 38:673-680. 

*Yokose Y, Uchida K, Nakae D, et al. 1987. Studies of carcinogenicity of sodium chlorite in B6C3F1 

mice. Environ Health Perspect 76:205-210. 

Zhang X, Echigo S, Minear RA, et al. 1999. Characterization and comparison of disinfection byproducts from using four major disinfectants. Am Chem Soc Abstr Pap 39:251-254. 

*Ziegler EE, Edwards BB, Jensen RL, et al. 1978. Absorption and retention of lead by infants. Pediatr 

Res 12:29-34. 

*Zika RG, Moore CA, Gidel LT, et al. 1984. Sunlight-induced photodecomposition of chlorine dioxide. 

In: Jolley RL, Bull RJ, Davis WP, et al. eds., Water chlorination-Chemistry, environmental impact and 

health effects. Vol. 5. Williamsburg, VA: Lewis Publishers, Inc., 1041-1063. 

Zoeteman BCJ, Hrubec J, de Greef E, et al. 1982. Mutagenic activity associated with by-products of 

drinking water disinfection by chlorine, chlorine dioxide, ozone and UV-irradiation. Environ Health 

Perspect 46:197-205. 

CHLORINE DIOXIDE AND CHLORITE 137 

10. GLOSSARY 

Absorption—The taking up of liquids by solids, or of gases by solids or liquids. 

Acute Exposure—Exposure to a chemical for a duration of 14 days or less, as specified in the 

Toxicological Profiles. 

Adsorption—The adhesion in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the 

surfaces of solid bodies or liquids with which they are in contact. 

Adsorption Coefficient (Koc)—The ratio of the amount of a chemical adsorbed per unit weight of 

organic carbon in the soil or sediment to the concentration of the chemical in solution at equilibrium. 

Adsorption Ratio (Kd)—The amount of a chemical adsorbed by sediment or soil (i.e., the solid phase) 

divided by the amount of chemical in the solution phase, which is in equilibrium with the solid phase, at a 

fixed solid/solution ratio. It is generally expressed in micrograms of chemical sorbed per gram of soil or 

sediment. 

Benchmark Dose (BMD)—Usually defined as the lower confidence limit on the dose that produces a 

specified magnitude of changes in a specified adverse response. For example, a BMD10 would be the 

dose at the 95% lower confidence limit on a 10% response, and the benchmark response (BMR) would be 

10%. The BMD is determined by modeling the dose response curve in the region of the dose response 

relationship where biologically observable data are feasible. 

Benchmark Dose Model—A statistical dose-response model applied to either experimental toxicological 

or epidemiological data to calculate a BMD. 

Bioconcentration Factor (BCF)—The quotient of the concentration of a chemical in aquatic organisms 

at a specific time or during a discrete time period of exposure divided by the concentration in the 

surrounding water at the same time or during the same period. 

Biomarkers—Broadly defined as indicators signaling events in biologic systems or samples. They have 

been classified as markers of exposure, markers of effect, and markers of susceptibility. 

Cancer Effect Level (CEL)—The lowest dose of chemical in a study, or group of studies, that produces 

significant increases in the incidence of cancer (or tumors) between the exposed population and its 

appropriate control. 

Carcinogen—A chemical capable of inducing cancer. 

Case-Control Study—A type of epidemiological study that examines the relationship between a 

particular outcome (disease or condition) and a variety of potential causative agents (such as toxic 

chemicals). In a case-controlled study, a group of people with a specified and well-defined outcome is 

identified and compared to a similar group of people without outcome. 

Case Report—Describes a single individual with a particular disease or exposure. These may suggest 

some potential topics for scientific research, but are not actual research studies. 
CHLORINE DIOXIDE AND CHLORITE 138 

10. GLOSSARY 

Case Series—Describes the experience of a small number of individuals with the same disease or 

exposure. These may suggest potential topics for scientific research, but are not actual research studies. 

Ceiling Value—A concentration of a substance that should not be exceeded, even instantaneously. 

Chronic Exposure—Exposure to a chemical for 365 days or more, as specified in the Toxicological 

Profiles. 

Cohort Study—A type of epidemiological study of a specific group or groups of people who have had a 

common insult (e.g., exposure to an agent suspected of causing disease or a common disease) and are 

followed forward from exposure to outcome. At least one exposed group is compared to one unexposed 

group. 

Cross-sectional Study—A type of epidemiological study of a group or groups of people that examines 

the relationship between exposure and outcome to a chemical or to chemicals at one point in time. 

Data Needs—Substance-specific informational needs that if met would reduce the uncertainties of human 

health assessment. 

Developmental Toxicity—The occurrence of adverse effects on the developing organism that may result 

from exposure to a chemical prior to conception (either parent), during prenatal development, or 

postnatally to the time of sexual maturation. Adverse developmental effects may be detected at any point 

in the life span of the organism. 

Dose-Response Relationship—The quantitative relationship between the amount of exposure to a 

toxicant and the incidence of the adverse effects. 

Embryotoxicity and Fetotoxicity—Any toxic effect on the conceptus as a result of prenatal exposure to 

a chemical; the distinguishing feature between the two terms is the stage of development during which the 

insult occurs. The terms, as used here, include malformations and variations, altered growth, and in utero 

death. 

Environmental Protection Agency (EPA) Health Advisory—An estimate of acceptable drinking water 

levels for a chemical substance based on health effects information. A health advisory is not a legally 

enforceable federal standard, but serves as technical guidance to assist federal, state, and local officials. 

Epidemiology—Refers to the investigation of factors that determine the frequency and distribution of 

disease or other health-related conditions within a defined human population during a specified period. 

Genotoxicity—A specific adverse effect on the genome of living cells that, upon the duplication of 

affected cells, can be expressed as a mutagenic, clastogenic, or carcinogenic event because of specific 

alteration of the molecular structure of the genome. 

Half-life—A measure of rate for the time required to eliminate one half of a quantity of a chemical from 

the body or environmental media. 

Immediately Dangerous to Life or Health (IDLH)—The maximum environmental concentration of a 

contaminant from which one could escape within 30 minutes without any escape-impairing symptoms or 

irreversible health effects. 
CHLORINE DIOXIDE AND CHLORITE 139 

10. GLOSSARY 

Incidence—The ratio of individuals in a population who develop a specified condition to the total 

number of individuals in that population who could have developed that condition in a specified time 

period. 

Intermediate Exposure—Exposure to a chemical for a duration of 15–364 days, as specified in the 

Toxicological Profiles. 

Immunologic Toxicity—The occurrence of adverse effects on the immune system that may result from 

exposure to environmental agents such as chemicals. 

Immunological Effects—Functional changes in the immune response. 

In Vitro—Isolated from the living organism and artificially maintained, as in a test tube. 

In Vivo—Occurring within the living organism. 

Lethal Concentration(Lo) (LCLo)—The lowest concentration of a chemical in air that has been reported 

to have caused death in humans or animals. 

Lethal Concentration(50) (LC50)—A calculated concentration of a chemical in air to which exposure for 

a specific length of time is expected to cause death in 50% of a defined experimental animal population. 

Lethal Dose(Lo) (LDLo)—The lowest dose of a chemical introduced by a route other than inhalation that 

has been reported to have caused death in humans or animals. 

Lethal Dose(50) (LD50)—The dose of a chemical that has been calculated to cause death in 50% of a 

defined experimental animal population. 

Lethal Time(50) (LT50)—A calculated period of time within which a specific concentration of a 

chemical is expected to cause death in 50% of a defined experimental animal population. 

Lowest-Observed-Adverse-Effect Level (LOAEL)—The lowest exposure level of chemical in a study, 

or group of studies, that produces statistically or biologically significant increases in frequency or severity 

of adverse effects between the exposed population and its appropriate control. 

Lymphoreticular Effects—Represent morphological effects involving lymphatic tissues such as the 

lymph nodes, spleen, and thymus. 

Malformations—Permanent structural changes that may adversely affect survival, development, or 

function. 

Minimal Risk Level (MRL)—An estimate of daily human exposure to a hazardous substance that is 

likely to be without an appreciable risk of adverse noncancer health effects over a specified route and 

duration of exposure. 

Modifying Factor (MF)—A value (greater than zero) that is applied to the derivation of a Minimal Risk 

Level (MRL) to reflect additional concerns about the database that are not covered by the uncertainty 

factors. The default value for a MF is 1. 

Morbidity—State of being diseased; morbidity rate is the incidence or prevalence of disease in a specific 

population. 
CHLORINE DIOXIDE AND CHLORITE 140 

10. GLOSSARY 

Mortality—Death; mortality rate is a measure of the number of deaths in a population during a specified 

interval of time. 

Mutagen—A substance that causes mutations. A mutation is a change in the DNA sequence of a cell’s 

DNA. Mutations can lead to birth defects, miscarriages, or cancer. 

Necropsy—The gross examination of the organs and tissues of a dead body to determine the cause of 

death or pathological conditions. 

Neurotoxicity—The occurrence of adverse effects on the nervous system following exposure to a 

chemical. 

No-Observed-Adverse-Effect Level (NOAEL)—The dose of a chemical at which there were no 

statistically or biologically significant increases in frequency or severity of adverse effects seen between 

the exposed population and its appropriate control. Effects may be produced at this dose, but they are not 

considered to be adverse. 

Octanol-Water Partition Coefficient (Kow)—The equilibrium ratio of the concentrations of a chemical 

in n-octanol and water, in dilute solution. 

Odds Ratio (OR)—A means of measuring the association between an exposure (such as toxic substances 

and a disease or condition) which represents the best estimate of relative risk (risk as a ratio of the 

incidence among subjects exposed to a particular risk factor divided by the incidence among subjects who 

were not exposed to the risk factor). An odds ratio of greater than 1 is considered to indicate greater risk 

of disease in the exposed group compared to the unexposed group. 

Organophosphate or Organophosphorus Compound—A phosphorus-containing organic compound 

and especially a pesticide that acts by inhibiting cholinesterase. 

Permissible Exposure Limit (PEL)—An Occupational Safety and Health Administration (OSHA) 

allowable exposure level in workplace air averaged over an 8-hour shift of a 40-hour workweek. 

Pesticide—General classification of chemicals specifically developed and produced for use in the control 

of agricultural and public health pests. 

Pharmacokinetics—The dynamic behavior of a material in the body, used to predict the fate 

(disposition) of an exogenous substance in an organism. Utilizing computational techniques, it provides 

the means of studying the absorption, distribution, metabolism, and excretion of chemicals by the body. 

Pharmacokinetic Model—A set of equations that can be used to describe the time course of a parent 

chemical or metabolite in an animal system. There are two types of pharmacokinetic models: data-based 

and physiologically-based. A data-based model divides the animal system into a series of compartments, 

which, in general, do not represent real, identifiable anatomic regions of the body, whereas the 

physiologically-based model compartments represent real anatomic regions of the body. 

Physiologically Based Pharmacodynamic (PBPD) Model—A type of physiologically based doseresponse model that quantitatively describes the relationship between target tissue dose and toxic end 

points. These models advance the importance of physiologically based models in that they clearly 

describe the biological effect (response) produced by the system following exposure to an exogenous 

substance. 
CHLORINE DIOXIDE AND CHLORITE 141 

10. GLOSSARY 

Physiologically Based Pharmacokinetic (PBPK) Model—Comprised of a series of compartments 

representing organs or tissue groups with realistic weights and blood flows. These models require a 

variety of physiological information: tissue volumes, blood flow rates to tissues, cardiac output, alveolar 

ventilation rates, and possibly membrane permeabilities. The models also utilize biochemical information 

such as air/blood partition coefficients, and metabolic parameters. PBPK models are also called 

biologically based tissue dosimetry models. 

Prevalence—The number of cases of a disease or condition in a population at one point in time. 

Prospective Study—A type of cohort study in which the pertinent observations are made on events 

occurring after the start of the study. A group is followed over time. 

q1*—The upper-bound estimate of the low-dose slope of the dose-response curve as determined by the 

multistage procedure. The q1* can be used to calculate an estimate of carcinogenic potency, the 

incremental excess cancer risk per unit of exposure (usually μg/L for water, mg/kg/day for food, and 

μg/m3

 for air). 

Recommended Exposure Limit (REL)—A National Institute for Occupational Safety and Health 

(NIOSH) time-weighted average (TWA) concentrations for up to a 10-hour workday during a 40-hour 

workweek. 

Reference Concentration (RfC)—An estimate (with uncertainty spanning perhaps an order of 

magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) 

that is likely to be without an appreciable risk of deleterious noncancer health effects during a lifetime. 

The inhalation reference concentration is for continuous inhalation exposures and is appropriately 

expressed in units of mg/m3 or ppm. 

Reference Dose (RfD)—An estimate (with uncertainty spanning perhaps an order of magnitude) of the 

daily exposure of the human population to a potential hazard that is likely to be without risk of deleterious 

effects during a lifetime. The RfD is operationally derived from the no-observed-adverse-effect level 

(NOAEL-from animal and human studies) by a consistent application of uncertainty factors that reflect 

various types of data used to estimate RfDs and an additional modifying factor, which is based on a 

professional judgment of the entire database on the chemical. The RfDs are not applicable to 

nonthreshold effects such as cancer. 

Reportable Quantity (RQ)—The quantity of a hazardous substance that is considered reportable under 

the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Reportable 

quantities are (1) 1 pound or greater or (2) for selected substances, an amount established by regulation 

either under CERCLA or under Section 311 of the Clean Water Act. Quantities are measured over a 

24-hour period. 

Reproductive Toxicity—The occurrence of adverse effects on the reproductive system that may result 

from exposure to a chemical. The toxicity may be directed to the reproductive organs and/or the related 

endocrine system. The manifestation of such toxicity may be noted as alterations in sexual behavior, 

fertility, pregnancy outcomes, or modifications in other functions that are dependent on the integrity of 

this system. 
 

CHLORINE DIOXIDE AND CHLORITE 142 

10. GLOSSARY 

Retrospective Study—A type of cohort study based on a group of persons known to have been exposed 

at some time in the past. Data are collected from routinely recorded events, up to the time the study is 

undertaken. Retrospective studies are limited to causal factors that can be ascertained from existing 

records and/or examining survivors of the cohort. 

Risk—The possibility or chance that some adverse effect will result from a given exposure to a chemical. 

Risk Factor—An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or 

inherited characteristic that is associated with an increased occurrence of disease or other health-related 

event or condition. 

Risk Ratio—The ratio of the risk among persons with specific risk factors compared to the risk among 

persons without risk factors. A risk ratio greater than 1 indicates greater risk of disease in the exposed 

group compared to the unexposed. 

Short-Term Exposure Limit (STEL)—The American Conference of Governmental Industrial 

Hygienists (ACGIH) maximum concentration to which workers can be exposed for up to 15 minutes 

continually. No more than four excursions are allowed per day, and there must be at least 60 minutes 

between exposure periods. The daily Threshold Limit Value - Time Weighted Average (TLV-TWA) may 

not be exceeded. 

Standardized Mortality Ratio (SMR)—A ratio of the observed number of deaths and the expected 

number of deaths in a specific standard population. 

Target Organ Toxicity—This term covers a broad range of adverse effects on target organs or 

physiological systems (e.g., renal, cardiovascular) extending from those arising through a single limited 

exposure to those assumed over a lifetime of exposure to a chemical. 

Teratogen—A chemical that causes structural defects that affect the development of an organism. 

Threshold Limit Value (TLV)—An American Conference of Governmental Industrial Hygienists 

(ACGIH) concentration of a substance to which most workers can be exposed without adverse effect. 

The TLV may be expressed as a Time Weighted Average (TWA), as a Short-Term Exposure Limit 

(STEL), or as a ceiling limit (CL). 

Time-Weighted Average (TWA)—An allowable exposure concentration averaged over a normal 8-hour 

workday or 40-hour workweek. 

Toxic Dose(50) (TD50)—A calculated dose of a chemical, introduced by a route other than inhalation, 

which is expected to cause a specific toxic effect in 50% of a defined experimental animal population. 

Toxicokinetic—The absorption, distribution, and elimination of toxic compounds in the living organism. 
CHLORINE DIOXIDE AND CHLORITE 143 

10. GLOSSARY 

Uncertainty Factor (UF)—A factor used in operationally deriving the Minimal Risk Level (MRL) or 

Reference Dose (RfD) or Reference Concentration (RfC) from experimental data. UFs are intended to 

account for (1) the variation in sensitivity among the members of the human population, (2) the 

uncertainty in extrapolating animal data to the case of human, (3) the uncertainty in extrapolating from 

data obtained in a study that is of less than lifetime exposure, and (4) the uncertainty in using lowestobserved-adverse-effect level (LOAEL) data rather than no-observed-adverse-effect level (NOAEL) data. 

A default for each individual UF is 10; if complete certainty in data exists, a value of 1 can be used; 

however, a reduced UF of 3 may be used on a case-by-case basis, 3 being the approximate logarithmic 

average of 10 and 1. 

Xenobiotic—Any chemical that is foreign to the biological system. 

CHLORINE DIOXIDE AND CHLORITE A-1 

APPENDIX A. ATSDR MINIMAL RISK LEVELS AND WORKSHEETS 

The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) [42 U.S.C. 

9601 et seq.], as amended by the Superfund Amendments and Reauthorization Act (SARA) [Pub. L. 99– 

499], requires that the Agency for Toxic Substances and Disease Registry (ATSDR) develop jointly with 

the U.S. Environmental Protection Agency (EPA), in order of priority, a list of hazardous substances most 

commonly found at facilities on the CERCLA National Priorities List (NPL); prepare toxicological 

profiles for each substance included on the priority list of hazardous substances; and assure the initiation 

of a research program to fill identified data needs associated with the substances. 

The toxicological profiles include an examination, summary, and interpretation of available toxicological 

information and epidemiologic evaluations of a hazardous substance. During the development of 

toxicological profiles, Minimal Risk Levels (MRLs) are derived when reliable and sufficient data exist to 

identify the target organ(s) of effect or the most sensitive health effect(s) for a specific duration for a 

given route of exposure. An MRL is an estimate of the daily human exposure to a hazardous substance 

that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration 

of exposure. MRLs are based on noncancer health effects only and are not based on a consideration of 

cancer effects. These substance-specific estimates, which are intended to serve as screening levels, are 

used by ATSDR health assessors to identify contaminants and potential health effects that may be of 

concern at hazardous waste sites. It is important to note that MRLs are not intended to define clean-up or 

action levels. 

MRLs are derived for hazardous substances using the no-observed-adverse-effect level/uncertainty factor 

approach. They are below levels that might cause adverse health effects in the people most sensitive to 

such chemical-induced effects. MRLs are derived for acute (1–14 days), intermediate (15–364 days), and 

chronic (365 days and longer) durations and for the oral and inhalation routes of exposure. Currently, 

MRLs for the dermal route of exposure are not derived because ATSDR has not yet identified a method 

suitable for this route of exposure. MRLs are generally based on the most sensitive chemical-induced end 

point considered to be of relevance to humans. Serious health effects (such as irreparable damage to the 

liver or kidneys, or birth defects) are not used as a basis for establishing MRLs. Exposure to a level 

above the MRL does not mean that adverse health effects will occur. 

MRLs are intended only to serve as a screening tool to help public health professionals decide where to 

look more closely. They may also be viewed as a mechanism to identify those hazardous waste sites that 
CHLORINE DIOXIDE AND CHLORITE A-2 

APPENDIX A 

are not expected to cause adverse health effects. Most MRLs contain a degree of uncertainty because of 

the lack of precise toxicological information on the people who might be most sensitive (e.g., infants, 

elderly, nutritionally or immunologically compromised) to the effects of hazardous substances. ATSDR 

uses a conservative (i.e., protective) approach to address this uncertainty consistent with the public health 

principle of prevention. Although human data are preferred, MRLs often must be based on animal studies 

because relevant human studies are lacking. In the absence of evidence to the contrary, ATSDR assumes 

that humans are more sensitive to the effects of hazardous substance than animals and that certain persons 

may be particularly sensitive. Thus, the resulting MRL may be as much as 100-fold below levels that 

have been shown to be nontoxic in laboratory animals. 

Proposed MRLs undergo a rigorous review process: Health Effects/MRL Workgroup reviews within the 

Division of Toxicology, expert panel peer reviews, and agency-wide MRL Workgroup reviews, with 

participation from other federal agencies and comments from the public. They are subject to change as 

new information becomes available concomitant with updating the toxicological profiles. Thus, MRLs in 

the most recent toxicological profiles supersede previously published levels. For additional information 

regarding MRLs, please contact the Division of Toxicology, Agency for Toxic Substances and Disease 

Registry, 1600 Clifton Road NE, Mailstop F-32, Atlanta, Georgia 30333. 
 

 

CHLORINE DIOXIDE AND CHLORITE A-3 

APPENDIX A 

MINIMAL RISK LEVEL (MRL) WORKSHEET 

Chemical Name: Chlorine dioxide 

CAS Number: 10049-04-4 

Date: July 2, 2004 

Profile Status: Final Post Public Comment 

Route: [X] Inhalation [ ] Oral 

Duration: [ ] Acute [X] Intermediate [ ] Chronic 

Graph Key: 8 

Species: Rat 

Minimal Risk Level: 0.001 [ ] mg/kg/day [X] ppm 

Reference: Paulet G, Desbrousses S. 1972. On the toxicology of chlorine dioxide. Arch Mal Prof 33(1­

2):59-61. 

Experimental design and effects noted: The intermediate-duration inhalation MRL is based on results of 

a study in which the most significant finding was respiratory effects in adult rats exposed to chlorine 

dioxide vapors. Groups of eight Wistar rats (sex not reported) were exposed to chlorine dioxide vapors at 

a concentration of 1 ppm (2.8 mg/m3

), 5 hours/day, 5 days/week for 2 months. The authors stated that 

weight gain and erythrocyte and leukocyte levels were not affected, but concurrent control data were not 

presented. Chlorine dioxide-induced respiratory effects included peribronchiolar edema and vascular 

congestion in the lungs. No alterations in epithelium or parenchyma were seen. This study identified a 

LOAEL of 1 ppm (2.8 mg/m3

) for mild respiratory effects. 

Dose and end point used for MRL derivation: 1 ppm; respiratory effects. 

[ ] NOAEL [X] LOAEL 

Uncertainty Factors used in MRL derivation: 

[X] 10 for use of a LOAEL 

[X] 3 for interspecies extrapolation since the exposure concentration was dosimetrically adjusted 

[X] 10 for human variability 

Was a conversion factor used from ppm in food or water to a mg/body weight dose? NA 

Was a conversion used from intermittent to continuous exposure? Yes 

LOAELADJ = LOAEL (1 ppm) x 5 hours/24 hours x 5 days/7 days = 0.15 ppm 
 

 

CHLORINE DIOXIDE AND CHLORITE A-4 

APPENDIX A 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: 

The human equivalent concentration (HEC) for the LOAEL (LOAELHEC) was calculated by multiplying 

the LOAELADJ by the regional gas ratio for the pulmonary region of the respiratory tract (RGDRPU) 

according to the equation: 

(RGDPU 

= ) A =

Q 

SA 

alv 

PU 







& 



 A 

e



  −











VE

&

SATB 







A 

KgTB 











e



  −











VE

&

SAET 







A 

 KgET 











(RGD PU

RGDR PU ) H Qalv 

&   ⋅  − SATB 

V&   −

⋅ SAET 

V& 






   




  



 
 

(EPA 1994, Equation 4-28 to be used for pulmonary effects of a Category 1 gas) 

RGD = Regional Gas Dose 

RGDR = Regional Gas Dose Ratio 

Qalv = alveolar ventilation rate (cm3

/minute) 

SA = surface area (cm2

) 

VE = minute volume (cm3

/minute) 

Kg = overall mass transport coefficient (cm/minute) 

ET = extrathoracic (nose and mouth) 

TB = tracheobronchial (trachea, bronchi, bronchioles to terminal bronchioles) 

PU = pulmonary (respiratory bronchioles, alveolar region) 

A = animal
 

H = human 

The following values were used for respiratory parameters in the equation above: 

Surface area (SA) (EPA 1994, Table 4-4) 

Species ET (cm2

) TB (cm2) PU (cm2) 

Rat 15.0 22.5 3,400 

Human 200 3,200 540,000 

Species Alveolar ventilation rate (Qalv, in cm3

/minute) Minute volume (VE, in cm3/minute) 

Rat 111 (67% of VE per EPA 1988) 165* (Equation 4-4, EPA 1994) 

Human 9,250 (67% of VE per EPA 1988) 13,800 (EPA 1994) 

* Average body weight of the treated rats in the critical study (Paulet and Desbrousses 1972) was 0.225 kg. 

Since the overall mass transport coefficient (Kg) is not available, the value has been assumed to equal 1. 

H 

E e e 

H 

E 

SAPU H 
CHLORINE DIOXIDE AND CHLORITE A-5 

APPENDIX A 

Therefore: 

1 1 2 2

        22 5 . cm 15cm 111cm

3 

3400 

9250cm 







/ min 

2 

/ min 







− − 3 3










 











⋅




















 




 

165cm /min 


 




 

165 /min 


 

cm e
 e
 cm 

3 

rat 



rat rat RGDR PU =
 ⋅ 2 2

     3200 

[

[

cm 200 cm − − 3 3



  



]

]
 

13800 /min 


 




 

13800 /min 


 

cm cm e
 e 540 000 cm

2 , 

0 03265 rat . [

[

H   

]rat 

]

H H 

1 1

 0 1364 . 

0 2319 . 

  0 09091 . 

0 01449 . 

 −

−

e
 

e
 

−

− [

[

]



] e
 

e
 

rat 

 H



 





⋅





 



 RGDRPU = ⋅ 0 01713 . H H 

1 1 

]

]

[

08725 . [0 9131 . rat rat 

] 0 9856 .

]

RGDRPU = 1.9060x1.1003x0.9093=1.9070 

Therefore: LOAELHEC = 0.15 ppm x1.9=0.3 ppm 

Other additional studies or pertinent information that lend support to this MRL: 

Paulet and Desbrousses (1970) exposed groups of 10 rats/sex (strain not specified) to chlorine dioxide 

vapors at a concentrations of 0 or 2.5 ppm (6.9 mg/m3

), 7 hours/day for 30 days. The weekly exposure 

frequency was not reported. Chlorine dioxide-exposed rats exhibited respiratory effects that included 

lymphocytic infiltration of the alveolar spaces, alveolar vascular congestion, hemorrhagic alveoli, 

epithelial erosions, and inflammatory infiltrations of the bronchi. The study authors also reported slightly 

decreased body weight gain and decreased erythrocyte and increased leukocyte levels, relative to controls. 

Recovery from the pulmonary lesions was apparent in rats examined after a 15-day recovery period. 

A set of other inhalation studies supports the finding of the respiratory system as a major target of toxicity 

following exposure to chlorine dioxide vapors, although these studies are limited in design (Dalhamn 

1957). A single 2-hour inhalation exposure of four rats to a chlorine dioxide concentration of 260 ppm 

(728 mg/m3

) resulted in pulmonary edema and nasal bleeding. Respiratory distress was reported in three 

other rats subjected to 3 weekly 3-minute exposures to decreasing concentrations of airborne chlorine 

dioxide from 3,400 to 800 ppm (from 9,520 to 2,240 mg/m3

); bronchopneumonia was observed in two of 

these rats. In a third rat study, repeated exposure to approximately 10 ppm (28 mg/m3

) of chlorine 

dioxide (4 hours/day for 9 days in a 13-day period) resulted in rhinorrhea, altered respiration, and 

respiratory infection. No indications of adverse effects were seen in rats exposed to approximately 

0.1 ppm (0.28 mg/m3

) of chlorine dioxide 5 hours/day for 10 weeks. 

[

[


 





⋅ 

RGDRPU 19060 . 



⋅ 

 
 = 0 7930 . H H
CHLORINE DIOXIDE AND CHLORITE A-6 

APPENDIX A 

Human data support the animal findings. In a case of accidental inhalation exposure to chlorine dioxide 

in the paper industry, exposure to 5 ppm (14 mg/m3

) for an unspecified amount of time resulted in signs 

of respiratory irritation (Elkins 1959). In another case report, a woman experienced coughing, pharyngeal 

irritation, and headache while mixing a bleach solution that was then used to bleach dried flowers (ExnerFreisfeld et al. 1986). Nasal abnormalities (including injection, telangectasia, paleness, cobblestoning, 

edema, and thick mucus) were observed in 13 individuals (1 man and 12 women) who had been 

accidentally exposed to chlorine dioxide from a leak in a water purification system pipe 5 years earlier 

(Meggs et al. 1996). 

Agency Contact (Chemical Manager): Jessilynn B. Taylor, M.S. 
 

 

CHLORINE DIOXIDE AND CHLORITE A-7 

APPENDIX A 

MINIMAL RISK LEVEL WORKSHEET 

Chemical Name: Chlorite (as sodium salt) 

CAS Number: 7758-19-2 

Date: July 2, 2004 

Profile Status: Final Post Public Comment 

Route: [ ] Inhalation [X] Oral 

Duration: [ ] Acute [X] Intermediate [ ] Chronic 

Graph Key: 10 

Species: Rat 

Minimal Risk Level: 0.1 [X] mg/kg/day [ ] ppm 

Reference: Gill MW, Swanson MS, Murphy SR, et al. 2000. Two-generation reproduction and 

developmental neurotoxicity study with sodium chlorite in the rat. J Appl Toxicol 20:291-303. 

Experimental design and effects noted: The intermediate-duration oral MRL is based on results of a study 

in which the most significant finding was neurodevelopmental delays (lowered auditory startle amplitude, 

decreased brain weight) in rat pups that had been exposed throughout gestation and lactation via their 

mothers. Groups of 30 male and 30 female Sprague-Dawley rats (F0) received sodium chlorite in the 

drinking water at concentrations of 35, 70, or 300 mg/L (approximate chlorite doses of 3, 5.7, and 

21 mg/kg/day and 3.9, 7.6, and 29 mg/kg/day for males and females, respectively) for 10 weeks prior to 

mating and during mating; exposure of females continued throughout gestation and lactation. Groups of 

F1 pups were continued on the same treatment regimen as their parents (chlorite doses of 2.9, 6.0, and 

23 mg/kg/day and 3.9, 8.0, and 29 mg/kg/day for F1 males and females, respectively). Low-dose female 

pups exhibited slight, but statistically significant differences in some hematological parameters, relative to 

controls. No other effects were seen in pups of this exposure level, and the hematological effects were 

not considered to be adverse. Mid-dose pups exhibited a significant decrease in maximum response to an 

auditory startle stimulus on postnatal day 24, but not on postnatal day 60. At this exposure level, F1 pups 

also exhibited reduced liver weight. At the high dose, significant effects included reduced absolute and 

relative liver weight in F1 males and females, reduced pup survival, reduced body weight at birth and 

throughout lactation in F1 and F2 rats, lowered thymus and spleen weight in both generations, lowered 

incidence of pups exhibiting normal righting reflex and with eyes open on postnatal day 15, decreased 

absolute brain weight for F1 males and F2 females, delayed sexual development in males (preputial 

separation) and females (vaginal opening) in F1 and F2 rats, and lowered red blood cell parameters in F1 

rats. 

Dose and end point used for MRL derivation: 2.9 mg/kg/day 

[X] NOAEL [ ] LOAEL 

Uncertainty Factors used in MRL derivation: 

[X] 10 for interspecies extrapolation 

[X] 3 for human variability 

Was a conversion factor used from ppm in food or water to a mg/body weight dose? The study authors 

calculated sodium chlorite intakes (in mg/kg/day) from measured water consumption and body weight 

data. These intakes were multiplied by a factor of 0.75 to adjust for the fraction of chlorite in sodium 

chlorite, resulting in calculated doses of chlorite in units of mg/kg/day. 
 

CHLORINE DIOXIDE AND CHLORITE A-8 

APPENDIX A 

Was a conversion used from intermittent to continuous exposure? NA 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: NA 

Other additional studies or pertinent information that lend support to this MRL: The principal study is 

supported by the developmental studies of Orme et al. (1985), Taylor and Pfohl (1985), Mobley et al. 

(1990), and Toth et al. (1990), in which rats administered chlorite (as sodium salt) or chlorine dioxide at 

similar dosages in drinking water showed alterations in exploratory and locomotor behavior and reduced 

brain weights. These studies supported NOAELs and LOAELs of approximately 3 and 14 mg/kg/day, 

respectively. 

Chlorine dioxide in drinking water rapidly degrades to chlorite (Michael et al. 1981). In laboratory 

animals, orally administered chlorine dioxide is rapidly converted to chlorite and chloride ion (AbdelRahman et al. 1980b). Being a strong oxidizer and water soluble, chlorine dioxide is not likely absorbed 

in the gastrointestinal tract to any great extent. Chlorite is the most likely source of systemic toxicity 

resulting from oral exposure to either chlorine dioxide or chlorite (soluble salts). Therefore, the 

intermediate-duration oral MRL derived for chlorite should also be applicable to chlorine dioxide. 

Agency Contact (Chemical Manager): Jessilynn B. Taylor, M.S. 
CHLORINE DIOXIDE AND CHLORITE B-1 

APPENDIX B. USER'S GUIDE 

Chapter 1 

Public Health Statement 

This chapter of the profile is a health effects summary written in non-technical language. Its intended 

audience is the general public, especially people living in the vicinity of a hazardous waste site or 

chemical release. If the Public Health Statement were removed from the rest of the document, it would 

still communicate to the lay public essential information about the chemical. 

The major headings in the Public Health Statement are useful to find specific topics of concern. The 

topics are written in a question and answer format. The answer to each question includes a sentence that 

will direct the reader to chapters in the profile that will provide more information on the given topic. 

Chapter 2 

Relevance to Public Health 

This chapter provides a health effects summary based on evaluations of existing toxicologic, 

epidemiologic, and toxicokinetic information. This summary is designed to present interpretive, weightof-evidence discussions for human health end points by addressing the following questions. 

1. What effects are known to occur in humans? 

2. What effects observed in animals are likely to be of concern to humans? 

3. What exposure conditions are likely to be of concern to humans, especially around hazardous 

waste sites? 

The chapter covers end points in the same order that they appear within the Discussion of Health Effects 

by Route of Exposure section, by route (inhalation, oral, and dermal) and within route by effect. Human 

data are presented first, then animal data. Both are organized by duration (acute, intermediate, chronic). 

In vitro data and data from parenteral routes (intramuscular, intravenous, subcutaneous, etc.) are also 

considered in this chapter. 

The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using 

existing toxicokinetic, genotoxic, and carcinogenic data. ATSDR does not currently assess cancer 

potency or perform cancer risk assessments. Minimal Risk Levels (MRLs) for noncancer end points (if 

derived) and the end points from which they were derived are indicated and discussed. 

Limitations to existing scientific literature that prevent a satisfactory evaluation of the relevance to public 

health are identified in the Chapter 3 Data Needs section. 

Interpretation of Minimal Risk Levels 

Where sufficient toxicologic information is available, ATSDR has derived MRLs for inhalation and oral 

routes of entry at each duration of exposure (acute, intermediate, and chronic). These MRLs are not 

meant to support regulatory action, but to acquaint health professionals with exposure levels at which 

adverse health effects are not expected to occur in humans. 
 

 

 

CHLORINE DIOXIDE AND CHLORITE B-2 

APPENDIX B 

MRLs should help physicians and public health officials determine the safety of a community living near 

a chemical emission, given the concentration of a contaminant in air or the estimated daily dose in water. 

MRLs are based largely on toxicological studies in animals and on reports of human occupational 

exposure. 

MRL users should be familiar with the toxicologic information on which the number is based. Chapter 2, 

"Relevance to Public Health," contains basic information known about the substance. Other sections such 

as Chapter 3 Section 3.9, "Interactions with Other Substances,” and Section 3.10, "Populations that are 

Unusually Susceptible" provide important supplemental information. 

MRL users should also understand the MRL derivation methodology. MRLs are derived using a 

modified version of the risk assessment methodology that the Environmental Protection Agency (EPA) 

provides (Barnes and Dourson 1988) to determine reference doses (RfDs) for lifetime exposure. 

To derive an MRL, ATSDR generally selects the most sensitive end point which, in its best judgment, 

represents the most sensitive human health effect for a given exposure route and duration. ATSDR 

cannot make this judgment or derive an MRL unless information (quantitative or qualitative) is available 

for all potential systemic, neurological, and developmental effects. If this information and reliable 

quantitative data on the chosen end point are available, ATSDR derives an MRL using the most sensitive 

species (when information from multiple species is available) with the highest no-observed-adverse-effect 

level (NOAEL) that does not exceed any adverse effect levels. When a NOAEL is not available, a 

lowest-observed-adverse-effect level (LOAEL) can be used to derive an MRL, and an uncertainty factor 

(UF) of 10 must be employed. Additional uncertainty factors of 10 must be used both for human 

variability to protect sensitive subpopulations (people who are most susceptible to the health effects 

caused by the substance) and for interspecies variability (extrapolation from animals to humans). In 

deriving an MRL, these individual uncertainty factors are multiplied together. The product is then 

divided into the inhalation concentration or oral dosage selected from the study. Uncertainty factors used 

in developing a substance-specific MRL are provided in the footnotes of the levels of significant exposure 

(LSE) Tables. 

Chapter 3 

Health Effects 

Tables and Figures for Levels of Significant Exposure (LSE) 

Tables and figures are used to summarize health effects and illustrate graphically levels of exposure 

associated with those effects. These levels cover health effects observed at increasing dose 

concentrations and durations, differences in response by species, MRLs to humans for noncancer end 

points, and EPA's estimated range associated with an upper- bound individual lifetime cancer risk of 1 in 

10,000 to 1 in 10,000,000. Use the LSE tables and figures for a quick review of the health effects and to 

locate data for a specific exposure scenario. The LSE tables and figures should always be used in 

conjunction with the text. All entries in these tables and figures represent studies that provide reliable, 

quantitative estimates of NOAELs, LOAELs, or Cancer Effect Levels (CELs). 

The legends presented below demonstrate the application of these tables and figures. Representative 

examples of LSE Table 3-1 and Figure 3-1 are shown. The numbers in the left column of the legends 

correspond to the numbers in the example table and figure. 
CHLORINE DIOXIDE AND CHLORITE B-3 

APPENDIX B 

LEGEND 

See Sample LSE Table 3-1 (page B-6) 

(1) Route of Exposure. One of the first considerations when reviewing the toxicity of a substance 

using these tables and figures should be the relevant and appropriate route of exposure. Typically 

when sufficient data exists, three LSE tables and two LSE figures are presented in the document. 

The three LSE tables present data on the three principal routes of exposure, i.e., inhalation, oral, 

and dermal (LSE Table 3-1, 3-2, and 3-3, respectively). LSE figures are limited to the inhalation 

(LSE Figure 3-1) and oral (LSE Figure 3-2) routes. Not all substances will have data on each 

route of exposure and will not, therefore, have all five of the tables and figures. 

(2) Exposure Period. Three exposure periods—acute (less than 15 days), intermediate (15– 

364 days), and chronic (365 days or more)—are presented within each relevant route of exposure. 

In this example, an inhalation study of intermediate exposure duration is reported. For quick 

reference to health effects occurring from a known length of exposure, locate the applicable 

exposure period within the LSE table and figure. 

(3) Health Effect. The major categories of health effects included in LSE tables and figures are 

death, systemic, immunological, neurological, developmental, reproductive, and cancer. 

NOAELs and LOAELs can be reported in the tables and figures for all effects but cancer. 

Systemic effects are further defined in the "System" column of the LSE table (see key number 

18). 

(4) Key to Figure. Each key number in the LSE table links study information to one or more data 

points using the same key number in the corresponding LSE figure. In this example, the study 

represented by key number 18 has been used to derive a NOAEL and a Less Serious LOAEL 

(also see the two "18r" data points in sample Figure 3-1). 

(5) Species. The test species, whether animal or human, are identified in this column. Chapter 2, 

"Relevance to Public Health," covers the relevance of animal data to human toxicity and 

Section 3.4, "Toxicokinetics," contains any available information on comparative toxicokinetics. 

Although NOAELs and LOAELs are species specific, the levels are extrapolated to equivalent 

human doses to derive an MRL. 

(6) Exposure Frequency/Duration. The duration of the study and the weekly and daily exposure 

regimen are provided in this column. This permits comparison of NOAELs and LOAELs from 

different studies. In this case (key number 18), rats were exposed to “Chemical x” via inhalation 

for 6 hours/day, 5 days/week, for 13 weeks. For a more complete review of the dosing regimen 

refer to the appropriate sections of the text or the original reference paper (i.e., Nitschke et al. 

1981). 

(7) System. This column further defines the systemic effects. These systems include respiratory, 

cardiovascular, gastrointestinal, hematological, musculoskeletal, hepatic, renal, and 

dermal/ocular. "Other" refers to any systemic effect (e.g., a decrease in body weight) not covered 

in these systems. In the example of key number 18, one systemic effect (respiratory) was 

investigated. 

(8) NOAEL. A NOAEL is the highest exposure level at which no harmful effects were seen in the 

organ system studied. Key number 18 reports a NOAEL of 3 ppm for the respiratory system, 

which was used to derive an intermediate exposure, inhalation MRL of 0.005 ppm (see 

footnote "b"). 
CHLORINE DIOXIDE AND CHLORITE B-4 

APPENDIX B 

(9) LOAEL. A LOAEL is the lowest dose used in the study that caused a harmful health effect. 

LOAELs have been classified into "Less Serious" and "Serious" effects. These distinctions help 

readers identify the levels of exposure at which adverse health effects first appear and the 

gradation of effects with increasing dose. A brief description of the specific end point used to 

quantify the adverse effect accompanies the LOAEL. The respiratory effect reported in key 

number 18 (hyperplasia) is a Less Serious LOAEL of 10 ppm. MRLs are not derived from 

Serious LOAELs. 

(10) Reference. The complete reference citation is given in Chapter 9 of the profile. 

(11) CEL. A CEL is the lowest exposure level associated with the onset of carcinogenesis in 

experimental or epidemiologic studies. CELs are always considered serious effects. The LSE 

tables and figures do not contain NOAELs for cancer, but the text may report doses not causing 

measurable cancer increases. 

(12) Footnotes. Explanations of abbreviations or reference notes for data in the LSE tables are found 

in the footnotes. Footnote "b" indicates that the NOAEL of 3 ppm in key number 18 was used to 

derive an MRL of 0.005 ppm. 

LEGEND 

See Sample Figure 3-1 (page B-7) 

LSE figures graphically illustrate the data presented in the corresponding LSE tables. Figures help the 

reader quickly compare health effects according to exposure concentrations for particular exposure 

periods. 

(13) Exposure Period. The same exposure periods appear as in the LSE table. In this example, health 

effects observed within the acute and intermediate exposure periods are illustrated. 

(14) Health Effect. These are the categories of health effects for which reliable quantitative data 

exists. The same health effects appear in the LSE table. 

(15) Levels of Exposure. Concentrations or doses for each health effect in the LSE tables are 

graphically displayed in the LSE figures. Exposure concentration or dose is measured on the log 

scale "y" axis. Inhalation exposure is reported in mg/m3

 or ppm and oral exposure is reported in 

mg/kg/day. 

(16) NOAEL. In this example, the open circle designated 18r identifies a NOAEL critical end point in 

the rat upon which an intermediate inhalation exposure MRL is based. The key number 18 

corresponds to the entry in the LSE table. The dashed descending arrow indicates the 

extrapolation from the exposure level of 3 ppm (see entry 18 in the Table) to the MRL of 

0.005 ppm (see footnote "b" in the LSE table). 

(17) CEL. Key number 38r is one of three studies for which CELs were derived. The diamond 

symbol refers to a CEL for the test species-mouse. The number 38 corresponds to the entry in the 

LSE table. 

(18)	 Estimated Upper-Bound Human Cancer Risk Levels. This is the range associated with the upperbound for lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. These risk levels are derived 
CHLORINE DIOXIDE AND CHLORITE B-5 

APPENDIX B 

from the EPA's Human Health Assessment Group's upper-bound estimates of the slope of the 

cancer dose response curve at low dose levels (q1*). 

(19) Key to LSE Figure. The Key explains the abbreviations and symbols used in the figure. 
1 3 4 

SAMPLE 

→ Table 3-1. Levels of Significant Exposure to [Chemical x] – Inhalation 

LOAEL (effect) Exposure Less serious Serious (ppm) frequency/ NOAEL (ppm) Key to figurea Species duration System (ppm) Re

2 → INTERMEDIATE EXPOSURE 

5 6 7 8 9 10 

→ Systemic ↓ ↓ ↓ ↓ ↓ 

→

18 Rat 13 wk 

5 d/wk 6 hr/d 

Resp 3b 10 (hyperplasia) 

N

CHRONIC EXPOSURE Cancer 11 

↓

38 Rat 18 mo 

5 d/wk 7 hr/d 

20 (CEL, multiple 

organs) 

W

39 Rat 89-104 

5 d/wk 6 hr/d 

wk 10 (CEL, lung tumors, 

nasal tumors) 

NT

40 Mouse 79-103 

5 d/wk 

wk 10 (CEL, lung tumors, 

hemangiosarcomas) 

NT

6 hr/d 

12 → a The number corresponds to entries in Figure 3-1. 

b Used to derive an intermediate inhalation Minimal Risk Level (MRL) of 5x10-3 ppm; dose adjusted for intermittent e

by an uncertainty factor of 100 (10 for extrapolation from animal to humans, 10 for human variability). 


CHLORINE DIOXIDE AND CHLORITE C-1 

APPENDIX C. ACRONYMS, ABBREVIATIONS, AND SYMBOLS 

ACGIH American Conference of Governmental Industrial Hygienists 

ACOEM American College of Occupational and Environmental Medicine 

ADI acceptable daily intake 

ADME absorption, distribution, metabolism, and excretion 

AED atomic emission detection 

AFID alkali flame ionization detector 

AFOSH Air Force Office of Safety and Health 

ALT alanine aminotransferase 

AML acute myeloid leukemia 

AOAC Association of Official Analytical Chemists 

AOEC Association of Occupational and Environmental Clinics 

AP alkaline phosphatase 

APHA American Public Health Association 

AST aspartate aminotransferase 

atm atmosphere 

ATSDR Agency for Toxic Substances and Disease Registry 

AWQC Ambient Water Quality Criteria 

BAT best available technology 

BCF bioconcentration factor 

BEI Biological Exposure Index 

BMD benchmark dose 

BMR benchmark response 

BSC Board of Scientific Counselors 

C centigrade 

CAA Clean Air Act 

CAG Cancer Assessment Group of the U.S. Environmental Protection Agency 

CAS Chemical Abstract Services 

CDC Centers for Disease Control and Prevention 

CEL cancer effect level 

CELDS Computer-Environmental Legislative Data System 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CFR Code of Federal Regulations 

Ci curie 

CI confidence interval 

CL ceiling limit value 

CLP Contract Laboratory Program 

cm centimeter 

CML chronic myeloid leukemia 

CPSC Consumer Products Safety Commission 

CWA Clean Water Act 

DHEW Department of Health, Education, and Welfare 

DHHS Department of Health and Human Services 

DNA deoxyribonucleic acid 

DOD Department of Defense 

DOE Department of Energy 

DOL Department of Labor 

DOT Department of Transportation 
 

 

CHLORINE DIOXIDE AND CHLORITE C-2 

APPENDIX C 

DOT/UN/ Department of Transportation/United Nations/ 

NA/IMCO North America/International Maritime Dangerous Goods Code 

DWEL drinking water exposure level 

ECD electron capture detection 

ECG/EKG electrocardiogram 

EEG electroencephalogram 

EEGL Emergency Exposure Guidance Level 

EPA Environmental Protection Agency 

F Fahrenheit 

F1 first-filial generation 

FAO Food and Agricultural Organization of the United Nations 

FDA Food and Drug Administration 

FEMA Federal Emergency Management Agency 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FPD flame photometric detection 

fpm feet per minute 

FR Federal Register 

FSH follicle stimulating hormone 

g gram 

GC gas chromatography 

gd gestational day 

GLC gas liquid chromatography 

GPC gel permeation chromatography 

HPLC high-performance liquid chromatography 

HRGC high resolution gas chromatography 

HSDB Hazardous Substance Data Bank 

IARC International Agency for Research on Cancer 

IDLH immediately dangerous to life and health 

ILO International Labor Organization 

IRIS Integrated Risk Information System 

Kd adsorption ratio 

kg kilogram 

kkg metric ton 

Koc organic carbon partition coefficient 

Kow octanol-water partition coefficient 

L liter 

LC liquid chromatography 

LC50 lethal concentration, 50% kill 

LCLo lethal concentration, low 

LD50 lethal dose, 50% kill 

LDLo lethal dose, low 

LDH lactic dehydrogenase 

LH luteinizing hormone 

LOAEL lowest-observed-adverse-effect level 

LSE Levels of Significant Exposure 

LT50 lethal time, 50% kill 

m meter 

MA trans,trans-muconic acid 

MAL maximum allowable level 

mCi millicurie 

MCL maximum contaminant level 
 

 

CHLORINE DIOXIDE AND CHLORITE C-3 

APPENDIX C 

MCLG maximum contaminant level goal 

MF modifying factor 

MFO mixed function oxidase 

mg milligram 

mL milliliter 

mm millimeter 

mmHg millimeters of mercury 

mmol millimole 

mppcf millions of particles per cubic foot 

MRL Minimal Risk Level 

MS mass spectrometry 

NAAQS National Ambient Air Quality Standard 

NAS National Academy of Science 

NATICH National Air Toxics Information Clearinghouse 

NATO North Atlantic Treaty Organization 

NCE normochromatic erythrocytes 

NCEH National Center for Environmental Health 

NCI National Cancer Institute 

ND not detected 

NFPA National Fire Protection Association 

ng nanogram 

NHANES National Health and Nutrition Examination Survey 

NIEHS National Institute of Environmental Health Sciences 

NIOSH National Institute for Occupational Safety and Health 

NIOSHTIC NIOSH's Computerized Information Retrieval System 

NLM National Library of Medicine 

nm nanometer 

nmol nanomole 

NOAEL no-observed-adverse-effect level 

NOES National Occupational Exposure Survey 

NOHS National Occupational Hazard Survey 

NPD nitrogen phosphorus detection 

NPDES National Pollutant Discharge Elimination System 

NPL National Priorities List 

NR not reported 

NRC National Research Council 

NS not specified 

NSPS New Source Performance Standards 

NTIS National Technical Information Service 

NTP National Toxicology Program 

ODW Office of Drinking Water, EPA 

OERR Office of Emergency and Remedial Response, EPA 

OHM/TADS Oil and Hazardous Materials/Technical Assistance Data System 

OPP Office of Pesticide Programs, EPA 

OPPT Office of Pollution Prevention and Toxics, EPA 

OPPTS Office of Prevention, Pesticides and Toxic Substances, EPA 

OR odds ratio 

OSHA Occupational Safety and Health Administration 

OSW Office of Solid Waste, EPA 

OTS Office of Toxic Substances 

OW Office of Water 
CHLORINE DIOXIDE AND CHLORITE C-4 

APPENDIX C 

OWRS Office of Water Regulations and Standards, EPA 

PAH polycyclic aromatic hydrocarbon 

PBPD physiologically based pharmacodynamic 

PBPK physiologically based pharmacokinetic 

PCE polychromatic erythrocytes 

PEL permissible exposure limit 

pg picogram 

PHS Public Health Service 

PID photo ionization detector 

pmol picomole 

PMR proportionate mortality ratio 

ppb parts per billion 

ppm parts per million 

ppt parts per trillion 

PSNS pretreatment standards for new sources 

RBC red blood cell 

REL recommended exposure level/limit 

RfC reference concentration 

RfD reference dose 

RNA ribonucleic acid 

RQ reportable quantity 

RTECS Registry of Toxic Effects of Chemical Substances 

SARA Superfund Amendments and Reauthorization Act 

SCE sister chromatid exchange 

SGOT serum glutamic oxaloacetic transaminase 

SGPT serum glutamic pyruvic transaminase 

SIC standard industrial classification 

SIM selected ion monitoring 

SMCL secondary maximum contaminant level 

SMR standardized mortality ratio 

SNARL suggested no adverse response level 

SPEGL Short-Term Public Emergency Guidance Level 

STEL short term exposure limit 

STORET Storage and Retrieval 

TD50 toxic dose, 50% specific toxic effect 

TLV threshold limit value 

TOC total organic carbon 

TPQ threshold planning quantity 

TRI Toxics Release Inventory 

TSCA Toxic Substances Control Act 

TWA time-weighted average 

UF uncertainty factor 

U.S. United States 

USDA United States Department of Agriculture 

USGS United States Geological Survey 

VOC volatile organic compound 

WBC white blood cell 

WHO World Health Organization 
CHLORINE DIOXIDE AND CHLORITE C-5 

APPENDIX C 

> ≥

= 

< ≤

% αβγδ

μm

μg q1

* 

– 

+ 

(+) 

(–) 

greater than 

greater than or equal to 

equal to 

less than 

less than or equal to 

percent 

alpha 

beta 

 gamma 

delta 

 micrometer 

microgram 

cancer slope factor 

negative 

positive 

weakly positive result 

weakly negative result 

CHLORINE DIOXIDE AND CHLORITE D-1 

APPENDIX D. INDEX 

absorbed dose..............................................................................................................................................62 

active transport............................................................................................................................................55 

adenocarcinoma ..........................................................................................................................................46 

aerobic.........................................................................................................................................................95 

alveolar...................................................................................................................................... 11, 17, 22, 61

anaerobic.....................................................................................................................................................94 

anemia................................................................................................................................................... 34, 63

auditory startle response ..................................................................................................... 10, 11, 41, 43, 69
 

bioavailability ...........................................................................................................................................102 

biodegradation.............................................................................................................................................95 

biomarker ...................................................................................................................................... 61, 62, 110

biomarkers ................................................................................................................ 61, 62, 63, 70, 105, 110 

birth weight .................................................................................................................................................39 

blood cell count...........................................................................................................................................43 

blood cell counts.........................................................................................................................................43 

body weight............................................. 11, 13, 24, 26, 36, 37, 40, 41, 42, 43, 44, 45, 47, 60, 61, 100, 101 

body weight effects ................................................................................................................... 24, 36, 37, 47 

body weight gain................................................................................................................. 11, 24, 36, 42, 45 

bone marrow ................................................................................................................................... 49, 51, 68

breast milk................................................................................................................................. 100, 101, 103

bronchial .....................................................................................................................................................22 

bronchitis .............................................................................................................................................. 16, 17

bronchopneumonia......................................................................................................................................22 

cancer .................................................................................................................. 4, 10, 40, 45, 46, 47, 60, 68

carcinogen........................................................................................................................................... 48, 116 

carcinogenic ........................................................................................................................ 15, 16, 46, 47, 68 

carcinogenicity.................................................................................................................. 10, 46, 48, 67, 116 

carcinoma....................................................................................................................................................46 

cardiovascular ................................................................................................................................. 23, 26, 47

cardiovascular effects..................................................................................................................................23 

catalase........................................................................................................................................................33 

cerebellar.....................................................................................................................................................42 

cerebellum...................................................................................................................................................42 

chromosomal......................................................................................................................................... 49, 68

chromosomal aberrations ...................................................................................................................... 49, 68

congenital....................................................................................................................................................40 

corpuscular............................................................................................................................................ 33, 34 

crown-rump length................................................................................................................................ 42, 44 

death.................................................................................................................................... 15, 17, 25, 42, 47

delayed ossification.....................................................................................................................................45 

deoxyribonucleic acid (see DNA)...............................................................................................................38 

dermal effects..............................................................................................................................................48 

DNA (see deoxyribonucleic acid)............................................................................................. 38, 42, 62, 68 

dyspnea .......................................................................................................................................................18 

edema ................................................................................................................................ 12, 18, 22, 32, 113

elimination half-time...................................................................................................................................51 

endocrine............................................................................................................................. 18, 36, 47, 58, 59

endocrine effects .........................................................................................................................................36 
 

CHLORINE DIOXIDE AND CHLORITE D-2 

APPENDIX D 

erythema................................................................................................................................................ 32, 48 

erythrocyte ................................................................................................................................ 11, 23, 33, 34 

erythrocytes..................................................................................................................................... 34, 37, 57 

exploratory .............................................................................................................. 10, 40, 41, 42, 43, 58, 69 

eye opening ..................................................................................................................................... 41, 43, 44 

fertility .................................................................................................................................................. 38, 68 

fetus.............................................................................................................................................................59 

forebrain......................................................................................................................................................42 

gastrointestinal ........................................................................................................ 13, 18, 32, 47, 51, 60, 61 

gastrointestinal effects ................................................................................................................................32 

general population................................................................................................................. 61, 99, 100, 103 

genotoxic............................................................................................................................................... 15, 49 

genotoxicity........................................................................................................................................... 49, 68 

gestation ................................................................ 11, 12, 25, 37, 38, 40, 41, 42, 43, 44, 45, 59, 61, 71, 113
 

glomerular............................................................................................................................................. 36, 60 

glutathione ...................................................................................................................................... 33, 57, 63 

groundwater ...................................................................................................................................... 2, 90, 94 

growth retardation.......................................................................................................................................45 

half-life.................................................................................................................................... 51, 62, 91, 102 

hematocrit ............................................................................................................................................. 33, 34 

hematological effects .............................................................................................. 13, 23, 32, 33, 34, 57, 61 

hematotoxicity....................................................................................................................................... 34, 43 

hemoglobin ................................................................................................................... 10, 33, 34, 57, 61, 64
 

hemorrhage .................................................................................................................................................22 

hepatic effects ....................................................................................................................................... 23, 35 

hepatocellular..............................................................................................................................................46 

hyperemia....................................................................................................................................................24 

hyperkeratosis .............................................................................................................................................32 

hyperplasia ............................................................................................................................................ 26, 32 

hyperplastic.................................................................................................................................................46 

hypoxemia...................................................................................................................................................18 

immunological ...................................................................................................................................... 15, 37 

inflammation....................................................................................................................... 17, 18, 22, 26, 32 

irritant................................................................................................................................................ 9, 17, 18 

jaundice................................................................................................................................................. 39, 40 

kidney.................................................................................................................................................... 36, 51 

Kow.............................................................................................................................................................75 

lactation............................................................................. 11, 12, 37, 38, 40, 41, 42, 43, 44, 59, 61, 71, 113 

LD50 ..................................................................................................................................................... 25, 26 

leukemia......................................................................................................................................................46 

leukocyte......................................................................................................................................... 11, 23, 34 

liver ....................................................................................................... 13, 23, 35, 43, 46, 47, 51, 56, 62, 68 

locomotor ............................................................................................................................ 10, 40, 41, 58, 69 

lymphoreticular...........................................................................................................................................37 

metabolic effects ................................................................................................................................... 18, 26 

methemoglobinemia.................................................................................... 26, 32, 34, 36, 57, 58, 61, 70, 71 

methylene blue................................................................................................................ 32, 65, 71, 106, 107
 

micronuclei ........................................................................................................................................... 49, 68 

morbidity............................................................................................................................................... 15, 39 

mortality........................................................................................................................ 15, 25, 39, 40, 46, 68 

motility.................................................................................................................................................. 38, 68 
CHLORINE DIOXIDE AND CHLORITE D-3 

APPENDIX D 

nasal .......................................................................................................................................... 17, 22, 26, 32 

nasal turbinates............................................................................................................................................26 

neonatal......................................................................................................................................... 39, 40, 101 

neurobehavioral...........................................................................................................................................59 

neurodevelopmental.................................................................................. 10, 12, 38, 58, 67, 69, 70, 71, 113 

neutrophil ....................................................................................................................................................34 

ocular .................................................................................................................................... 9, 17, 24, 26, 47 

oral mucosa .................................................................................................................................................32 

organogenesis........................................................................................................................................ 47, 48 

osmotic fragility.............................................................................................................................. 33, 34, 57 

oxidative stress...................................................................................................................................... 33, 58 

peribronchiolar.............................................................................................................................. 12, 22, 113 

pharmacodynamic.......................................................................................................................................54 

pharmacokinetic.................................................................................................................. 54, 55, 56, 58, 70 

pharmacokinetics ............................................................................................................................ 60, 70, 71 

pharyngeal...................................................................................................................................................18 

photolysis ....................................................................................................................................................94 

placenta .......................................................................................................................................................61 

postpartum ................................................................................................................................ 41, 57, 58, 59 

preputial ................................................................................................................................................ 13, 43 

pulmonary edema.................................................................................................................................. 17, 22 

rales.............................................................................................................................................................18 

rate constant .......................................................................................................................................... 50, 51 

renal effects................................................................................................................................ 23, 24, 35 36 

Renal Effects......................................................................................................................................... 23, 35 

resorbed.......................................................................................................................................................44 

resorptions...................................................................................................................................................44 

respiration ....................................................................................................................................... 17, 22, 26 

respiratory ..................................................... 4, 9, 11, 12, 15, 17, 18, 22, 23, 24, 26, 32, 36, 47, 67, 95, 113
 

respiratory tract ........................................................................................................................... 9, 17, 18, 22 

reticulocyte..................................................................................................................................................34 

reverse mutations .................................................................................................................................. 49, 68 

rhinorrhea.............................................................................................................................................. 17, 22 

salivation.....................................................................................................................................................32 

skeletal ...................................................................................................................................... 42, 44, 45, 69 

sperm morphology .......................................................................................................................... 38, 59, 68 

sperm-head morphology .............................................................................................................................38 

spleen ............................................................................................................................ 13, 34, 37, 43, 51, 69 

survival...................................................................................................................................... 13, 25, 43, 44 

T3........................................................................................................................................ 11, 41, 42, 43, 44 

T4.................................................................................................................................. 11, 36, 41, 42, 43, 44 

tachypnea ....................................................................................................................................................18 

testicular.......................................................................................................................................... 38, 59, 68 

thymus................................................................................................................................. 13, 37, 43, 51, 69 

thyroid....................................................................................... 10, 11, 36, 41, 43, 57, 58, 59, 67, 69, 70, 71 

thyroxine .....................................................................................................................................................40 

toxicokinetic.................................................................................................................................... 15, 61, 71 

toxicokinetics ..............................................................................................................................................70 

tumor promoter ...........................................................................................................................................49 

tumors ............................................................................................................................................. 46, 49, 68 

ulceration ....................................................................................................................................................32 
CHLORINE DIOXIDE AND CHLORITE D-4 

APPENDIX D 

vaginal....................................................................................................................................... 13, 42, 43, 44 

vapor phase .................................................................................................................................................90 

visceral ........................................................................................................................................................45 

vital capacity ...............................................................................................................................................18 

volatilization ...............................................................................................................................................90