TOXICOLOGICAL PROFILE FOR
 

TOLUENE
 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
 

Public Health Service
 

Agency for Toxic Substances and Disease Registry
 

September 2000 
TOLUENE 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. 
TOLUENE iii 

UPDATE STATEMENT
 

Toxicological profiles are revised and republished as necessary, but no less than once every three years. 

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, E-29
 

Atlanta, Georgia 30333
 


TOLUENE 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 prepared 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 October 21, 1999 (64 FR 

56792). For prior versions of the list of substances, see Federal Register notices dated 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); February 28, 1994 (59 FR 

9486); April 29, 1996 (61 FR 18744); and November 17, 1997 (62 FR 61332). Section 104(i)(3) of 

CERCLA, as amended, directs the Administrator of ATSDR to prepare a toxicological profile for each 

substance on the list. 
 

 

TOLUENE 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: Health Effects: Specific health effects of a given hazardous compound are reported by route 

of exposure, by type of health effect (death, systemic, immunologic, reproductive), 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 Toluene Affect Children? 

Section 1.7 How Can Families Reduce the Risk of Exposure to Toluene? 

Section 2.7 Children’s Susceptibility 

Section 5.6 Exposures of Children 

Other Sections of Interest: 

Section 2.8 Biomarkers of Exposure and Effect 

Section 2.11 Methods for Reducing Toxic Effects 

ATSDR Information Center 

Phone: 1-888-42-ATSDR or (404) 639-6357 Fax: (404) 639-6359 

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 chemical-specific case studies. 
TOLUENE 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@dgs.dgsys.com • AOEC Clinic Director: http://occ-envmed.mc.duke.edu/oem/aoec.htm. 

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: 847-228-6850 • FAX: 847-228-1856. 
TOLUENE ix 

CONTRIBUTORS 

CHEMICAL MANAGER(S)/AUTHORS(S): 

Alfred Dorsey, D.V.M.
 

ATSDR, Division of Toxicology, Atlanta, GA
 

Peter R. McClure, Ph.D., D.A.B.T.
 

Syracuse Research Corporation, North Syracuse, NY
 

A. Rosa McDonald, Ph.D.
 

Syracuse Research Corporation, North Syracuse, NY
 

Mona Singh, Ph.D.
 

Syracuse Research Corporation, Arlington, VA
 

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. 

TOLUENE xi 

PEER REVIEW
 

A peer review panel was assembled for Toluene. The panel consisted of the following members: 

1. Dr. Clint Skinner, Skinner Associates, 3985 Shooting Star Road, Creston, CA 93432; and 

2. Dr. Robert G. Tardiff, 1423 Trapline Court, Vienna, VA 22189. 

These experts collectively have knowledge of Toluene’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. 

TOLUENE xiii 

CONTENTS
 

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

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

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

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

LIST OF FIGURES ................................................................ xviii 
 

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx 
 

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

1.1 WHAT IS TOLUENE? ....................................................... 1 
 

1.2 WHAT HAPPENS TO TOLUENE WHEN IT ENTERS THE ENVIRONMENT? ......... 2 
 

1.3 HOW MIGHT I BE EXPOSED TO TOLUENE? ................................... 3 
 

1.4 HOW CAN TOLUENE ENTER AND LEAVE MY BODY? .......................... 4 
 

1.5 HOW CAN TOLUENE AFFECT MY HEALTH? .................................. 4 
 

1.6	 HOW CAN TOLUENE AFFECT CHILDREN? .................................... 6 
 

1.7 	 HOW CAN FAMILIES REDUCE THE RISK OF EXPOSURE TO TOLUENE? .......... 8 
 

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

EXPOSED TO TOLUENE? .................................................... 8 
 

1.9	 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO
 

PROTECT HUMAN HEALTH? ................................................ 9 
 

1.10 WHERE CAN I GET MORE INFORMATION? .................................. 10 
 

2. HEALTH EFFECTS .............................................................. 11 
 

2.1 INTRODUCTION .......................................................... 11 
 

2.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE ................. 11 
 

2.2.1 Inhalation Exposure .................................................. 12 
 

2.2.1.1 Death ..................................................... 12 
 

2.2.1.2 Systemic Effects ............................................ 13 
 

2.2.1.3 Immunological and Lymphoreticular Effects ...................... 55 
 

2.2.1.4 Neurological Effects ......................................... 57 
 

2.2.1.5 Reproductive Effects ......................................... 70 
 

2.2.1.6 Developmental Effects ....................................... 72 
 

2.2.1.7 Genotoxic Effects ........................................... 75 
 

2.2.1.8 Cancer .................................................... 76 
 

2.2.2 Oral Exposure ...................................................... 78 
 

2.2.2.1 Death ..................................................... 79 
 

2.2.2.2 Systemic Effects ............................................ 79 
 

2.2.2.3 Immunological and Lymphoreticular Effects ...................... 92 
 

2.2.2.4 Neurological Effects ......................................... 93 
 

2.2.2.5 Reproductive Effects ......................................... 94 
 

2.2.2.6 Developmental Effects ....................................... 94 
 

2.2.2.7 Genotoxic Effects ........................................... 95 
 
TOLUENE	 xiv 

2.2.2.8 Cancer .................................................... 95 
 

2.2.3	 Dermal Exposure .................................................... 96 
 

2.2.3.1 Death ..................................................... 96 
 

2.2.3.2 Systemic Effects ............................................ 96 
 

2.2.3.3 Immunological and Lymphoreticular Effects ...................... 98 
 

2.2.3.4 Neurological Effects ......................................... 98 
 

2.2.3.5 Reproductive Effects ......................................... 98 
 

2.2.3.6 Developmental Effects ....................................... 98 
 

2.2.3.7 Genotoxic Effects ........................................... 98 
 

2.2.3.8 Cancer .................................................... 99 
 

2.3 TOXICOKINETICS ......................................................... 99 
 

2.3.1 	 Absorption ........................................................ 100 
 

2.3.1.1 Inhalation Exposure ......................................... 100 
 

2.3.1.2 Oral Exposure ............................................. 100 
 

2.3.1.3 Dermal Exposure ........................................... 101 
 

2.3.2 	 Distribution ....................................................... 102 
 

2.3.2.1 Inhalation Exposure ......................................... 102 
 

2.3.2.2 Oral Exposure ............................................. 105 
 

2.3.2.3 Dermal Exposure ........................................... 105 
 

2.3.3 	 Metabolism ........................................................ 106 
 

2.3.4 	 Elimination and Excretion ............................................ 110 
 

2.3.4.1 Inhalation Exposure ......................................... 110 
 

2.3.4.2 Oral Exposure ............................................. 112 
 

2.3.4.3 Dermal Exposure ........................................... 113 
 

2.3.5	 Physiologically based Pharmacokinetic (PBPK)/Pharmacodynamic 

(PD) Models ....................................................... 113 
 

2.4 MECHANISMS OF ACTION ................................................ 119 
 

2.4.1 	 Pharmacokinetic Mechanisms ......................................... 119 
 

2.4.2 	 Mechanisms of Toxicity .............................................. 120 
 

2.4.3 	 Animal-to-Human Extrapolations ...................................... 124 
 

2.5 RELEVANCE TO PUBLIC HEALTH ......................................... 125 
 

2.6 ENDOCRINE DISRUPTION ................................................ 138 
 

2.7 CHILDREN’S SUSCEPTIBILITY ............................................ 142 
 

2.8 BIOMARKERS OF EXPOSURE AND EFFECT ................................. 147 
 

2.8.1	 Biomarkers Used to Identify or Quantify Exposure to Toluene ............... 148 
 

2.8.2 	 Biomarkers Used to Characterize Effects Caused by Toluene ................. 149 
 

2.9 INTERACTIONS WITH OTHER CHEMICALS ................................. 149 
 

2.10 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE ...................... 153 
 

2.11 METHODS FOR REDUCING TOXIC EFFECTS ................................ 154 
 

2.11.1	 Reducing Peak Absorption Following Exposure ........................... 154 
 

2.11.2 	 Reducing Body Burden .............................................. 155 
 

2.11.3 	 Interfering with the Mechanism of Action for Toxic Effects .................. 155 
 

2.12 ADEQUACY OF THE DATABASE ........................................... 156 
 

2.12.1 	 Existing Information on Health Effects of Toluene ......................... 156 
 

2.12.2 	 Identification of Data Needs .......................................... 158 
 

2.12.3	 Ongoing Studies .................................................... 166 
 

3. CHEMICAL AND PHYSICAL INFORMATION ...................................... 169 
 

3.1 CHEMICAL IDENTITY .................................................... 169 
 

3.2 PHYSICAL AND CHEMICAL PROPERTIES ................................... 169 
 
TOLUENE xv 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL ............................ 173 
 

4.1 PRODUCTION ........................................................... 173 
 

4.2 IMPORT/EXPORT ........................................................ 176 
 

4.3 USE ..................................................................... 176 
 

4.4 DISPOSAL ............................................................... 176 
 

5. POTENTIAL FOR HUMAN EXPOSURE ........................................... 179 
 

5.1 OVERVIEW .............................................................. 179 
 

5.2 RELEASES TO THE ENVIRONMENT ........................................ 180 
 

5.2.1 Air .............................................................. 185 
 

5.2.2 Water ............................................................ 185 
 

5.2.3 Soil .............................................................. 186 
 

5.3 ENVIRONMENTAL FATE .................................................. 186 
 

5.3.1 Transport and Partitioning ............................................ 186 
 

5.3.2 Transformation and Degradation ....................................... 188 
 

5.3.2.1 Air ...................................................... 188 
 

5.3.2.2 Water .................................................... 188 
 

5.3.2.3 Sediment and Soil .......................................... 189 
 

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT ............... 190 
 

5.4.1 Air .............................................................. 190 
 

5.4.2 Water ............................................................ 193 
 

5.4.3 Sediment and Soil .................................................. 194 
 

5.4.4 Other Environmental Media ........................................... 194 
 

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE .................. 194 
 

5.6 EXPOSURES OF CHILDREN ............................................... 198 
 

5.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES ...................... 200 
 

5.8 ADEQUACY OF THE DATABASE ........................................... 201 
 

5.8.1 Identification of Data Needs .......................................... 201 
 

5.8.2 Ongoing Studies .................................................... 205 
 

6. ANALYTICAL METHODS ....................................................... 207 
 

6.1 BIOLOGICAL SAMPLES ................................................... 207 
 

6.2 ENVIRONMENTAL SAMPLES .............................................. 210 
 

6.3 ADEQUACY OF THE DATABASE ........................................... 216 
 

6.3.1 Identification of Data Needs .......................................... 217 
 

6.3.2 Ongoing Studies .................................................... 218 
 

7. REGULATIONS AND ADVISORIES .............................................. 219 
 

8. REFERENCES ................................................................. 229 
 

9. GLOSSARY ................................................................... 307 
 

APPENDICES 

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

D. USER’S GUIDE ........................................................... B-1 
 

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

TOLUENE xvii 

LIST OF FIGURES
 

2-1 Levels of Significant Exposure to Toluene - Inhalation ................................. 38 
 

2-2 Levels of Significant Exposure to Toluene - Oral ..................................... 87 
 

2-3 Scheme for Toluene Metabolism in Humans and Animals ............................. 107 
 

2-4 Conceptual Representation of a Physiologically Based Pharmacokinetic (PBPK) Model
 

for a Hypothetical Chemical Substance ............................................ 115 
 

2-5 Existing Information on Health Effects of Toluene ................................... 157 
 

5-1 Frequency of NPL Sites with Toluene Contamination ................................. 181 
 
.
 
TOLUENE xix 

LIST OF TABLES
 

2-1 Levels of Significant Exposure to Toluene - Inhalation ................................. 14 
 

2-2 Levels of Significant Exposure to Toluene - Oral ..................................... 80 
 

2-3 Levels of Significant Exposure to Toluene - Dermal ................................... 97 
 

2-4 Genotoxicity of Toluene In Vivo ................................................. 139 
 

2-5 Genotoxicity of Toluene In Vitro ................................................. 140 
 

2-6 Ongoing Research for Toluene ................................................... 167 
 

3-1 Chemical Identity of Toluene .................................................... 170 
 

3-2 Physical and Chemical Properties of Toluene ....................................... 171 
 

4-1 Facilities that Manufacture or Process Toluene ...................................... 174 
 

5-1 Releases to the Environment from Facilities that Manufacture or Process Toluene .......... 182 
 

5-2 Median Toluene Levels in Ambient Air ............................................ 191 
 

5-3 Ongoing Studies on the Potential for Human Exposure to Toluene ....................... 206 
 

6-1 Analytical Methods for Determining Toluene in Biological Materials .................... 208 
 

6-2 Analytical Methods for Determining Biomarkers of Toluene in Biological Samples ......... 211 
 

6-3 Analytical Methods for Determining Toluene in Environmental Samples .................. 212 
 

7-1 Regulations and Guidelines Applicable to Toluene ................................... 222 
 

TOLUENE 1 

1. PUBLIC HEALTH STATEMENT 

This public health statement tells you about toluene and the effects of exposure. 

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

the nation. These sites make up the National Priorities List (NPL) and are the sites targeted for 

long-term federal cleanup activities. Toluene has been found in at least 959 of the 1,591 current 

or former NPL sites. However, the total number of NPL sites evaluated for this substance is not 

known. As more sites are evaluated, the sites at which toluene is found may increase. This 

information is important because exposure to this substance may harm you and because these 

sites may be sources of exposure. 

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

such as a drum or bottle, it enters the environment. This release does not always lead to 

exposure. You are 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 toluene, many factors determine whether you’ll be harmed. These factors 

include the dose (how much), the duration (how long), and how you come in contact with 

it/them. You must also consider the other chemicals you’re exposed to and your age, sex, diet, 

family traits, lifestyle, and state of health. 

1.1 WHAT IS TOLUENE? 

Toluene is a clear, colorless liquid with a distinctive smell. It is a good solvent (a substance that 

can dissolve other substances). It is added to gasoline along with benzene and xylene. Toluene 

occurs naturally in crude oil and in the tolu tree. It is produced in the process of making gasoline 

and other fuels from crude oil, in making coke from coal, and as a by-product in the manufacture 

of styrene. Toluene is used in making paints, paint thinners, fingernail polish, lacquers, 

adhesives, and rubber and in some printing and leather tanning processes. It is disposed of at 

hazardous waste sites as used solvent or at landfills where it is present in discarded paints, paint 
TOLUENE 2 

1. PUBLIC HEALTH STATEMENT 

thinners, and fingernail polish. You can begin to smell toluene in the air at a concentration of 

8 parts of toluene per million parts of air (ppm), and taste it in your water at a concentration of 

between 0.04 and 1 ppm. More information on the properties, production, and uses of toluene 

can be found in Chapters 3 and 4. 

1.2 WHAT HAPPENS TO TOLUENE WHEN IT ENTERS THE ENVIRONMENT? 

Toluene enters the environment when you use materials that contain it, such as paints, 

paint thinners, adhesives, fingernail polish, and gasoline. As you work with these materials, the 

toluene evaporates and becomes mixed with the air you breathe. Toluene enters surface water 

and groundwater (wells) from spills of solvents and petroleum products as well as from leaking 

underground storage tanks at gasoline stations and other facilities. Leaking underground storage 

tanks also contaminate the soil with toluene and other petroleum-product components. 

When toluene-containing products are placed in landfills or waste disposal sites, the toluene can 

enter the soil and water near the waste site. Toluene does not usually stay in the environment; it 

is readily broken down to other chemicals by microorganisms in soil and evaporates from 

surface water and surface soils. Toluene dissolved in well water does not break down quickly 

while the water is under the ground because there are few microorganisms in underground water. 

Once the water is brought to the surface, the toluene will evaporate into the air. 

Toluene can be taken up into fish and shellfish, plants, and animals living in water containing 

toluene, but it does not concentrate or build up to high levels because most animal species can 

break down the toluene into other compounds that are excreted. 

More information on how toluene enters the environment and what happens to it can be found in 

Chapters 4 and 5. 
TOLUENE 3 

1. PUBLIC HEALTH STATEMENT 

1.3 HOW MIGHT I BE EXPOSED TO TOLUENE? 

You may be exposed to toluene from many sources, including drinking water, food, air, and 

consumer products. You may also be exposed to toluene through breathing the chemical in the 

workplace or during deliberate glue sniffing or solvent abuse. Automobile exhaust also puts 

toluene into the air. People who work with gasoline, kerosene, heating oil, paints, and lacquers 

are at the greatest risk of exposure. Printers are also exposed to toluene in the workplace. 

Because toluene is a common solvent and is found in many consumer products, you can be 

exposed to toluene at home and outdoors while using gasoline, nail polish, cosmetics, rubber 

cement, paints, paintbrush cleaners, stain removers, fabric dyes, inks, adhesives, carburetor 

cleaners, and lacquer thinners. Smokers are exposed to small amounts of toluene in cigarette 

smoke. 

You can be exposed to toluene at some hazardous waste sites. EPA reported in 1998 that toluene 

was found in well water or surface water at 99% of the hazardous waste sites surveyed and in 

soil at 77% of the sites surveyed. If you live near a waste site and get your drinking water from a 

well, toluene may be in the water. Toluene vapors might also be present in the air. 

Federal and state surveys do not show toluene to be commonly found in drinking water supplies. 

Toluene was found in about 1% of the groundwater sources (wells) at amounts lower than 2 parts 

per billion (ppb). It was found more frequently in surface water samples at similar concentrations. If toluene is in your drinking water you can be exposed by drinking the water or by eating 

cold foods prepared with the water. Evaporation during cooking tends to decrease the amount of 

toluene found in hot foods or water. Additional exposure will occur when you breathe in the 

toluene that evaporates from water while you shower, bathe, clean, or cook with the water. 

The toluene level in the air outside your home is usually less than 1 ppm in cities and suburbs 

that are not close to industry. The toluene inside your house is also likely to be less than 1 ppm. 

The amount of toluene in food has not been reported, but is likely to be low. Traces of toluene 

were found in eggs that were stored in polystyrene containers containing toluene. 
TOLUENE 4 

1. PUBLIC HEALTH STATEMENT 

Unless you smoke cigarettes or work with toluene-containing products, you are probably 

exposed to only about 300 micrograms (μg) of toluene a day. A microgram is one-millionth of a 

gram. If you smoke a pack of cigarettes per day, you add another 1,000 μg to your exposure. 

People who work in places where toluene-containing products are used can be exposed to 

1,000 milligrams of toluene a day when the average air concentration is 50 ppm and they breathe 

at a normal rate and volume. A milligram is one-thousandth of a gram. 

More information on how you can be exposed to toluene can be found in Chapter 5. 

1.4 HOW CAN TOLUENE ENTER AND LEAVE MY BODY? 

Toluene can enter your body when you breathe its vapors or eat contaminated food or drink 

contaminated water. When you work with toluene-containing paints or paint thinners, or use nail 

polish or nail polish remover containing toluene, the toluene can also pass through your skin into 

your bloodstream. You are exposed to toluene when you breathe air containing toluene. When 

this occurs the toluene is taken directly into your blood from your lungs. Where you live, work, 

and travel and what you eat affects your daily exposure to toluene. Factors such as your age, 

sex, body composition, and health status affect what happens to toluene once it is in your body. 

After being taken into your body, more than 75% of the toluene is removed within 12 hours. It 

may leave your body unchanged in the air you breathe out or in your urine after some of it has 

been changed to other chemicals. Generally, your body turns toluene into less harmful 

chemicals such as hippuric acid. More information on how toluene can enter and leave your 

body can be found in Chapter 2. 

1.5 HOW CAN TOLUENE AFFECT MY HEALTH? 

To protect the public from the harmful effects of toxic chemicals and to find ways to treat people 

who have been harmed, scientists use many tests. 

One way to see if a chemical will hurt people is to learn how the chemical is absorbed, used, and 

released by the body; for some chemicals, animal testing may be necessary. Animal testing may 
TOLUENE 5 

1. PUBLIC HEALTH STATEMENT 

also be used to identify health effects such as cancer or birth defects. Without laboratory 

animals, scientists would lose a basic method to get information needed to make wise decisions 

to protect public health. Scientists have the responsibility to treat research animals with care and 

compassion. Laws today protect the welfare of research animals, and scientists must comply 

with strict animal care guidelines. 

A serious health concern is that toluene may have an effect on your brain. Toluene can cause 

headaches and sleepiness, and can impair your ability to think clearly. Whether or not toluene 

does this to you depends on the amount you take in, how long you are exposed, and your genetic 

susceptibility and age. Low to moderate, day-after-day exposure in your workplace can cause 

tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, and loss of appetite. 

These symptoms usually disappear when exposure is stopped. You may experience some 

hearing and color vision loss after long-term daily exposure to toluene in the workplace. 

Researchers do not know if the low levels of toluene you breathe at work will cause any 

permanent effects on your brain or body after many years. 

If you are exposed to a large amount of toluene in a short time because you deliberately sniff 

paint or glue, you will first feel light-headed. If exposure continues, you can become dizzy, 

sleepy, or unconscious. You might even die. Toluene causes death by interfering with the way 

you breathe and the way your heart beats. When exposure is stopped, the sleepiness and 

dizziness will go away and you will feel normal again. If you choose to repeatedly breathe in 

toluene from glue or paint thinners, you may permanently damage your brain. You may also 

experience problems with your speech, vision, or hearing, have loss of muscle control, loss of 

memory, poor balance, and decreased mental ability. Some of these changes may be permanent. 

Toluene (at high levels) could possibly damage your kidneys. If you drink alcohol and are 

exposed to toluene, the combination can affect your liver more than either compound alone. 

Combinations of toluene and some common medicines like aspirin and acetaminophen may 

increase the effects of toluene on your hearing. 
TOLUENE 6 

1. PUBLIC HEALTH STATEMENT 

Some studies in people have shown reproductive effects, such as an increased risk of spontaneous abortions, from exposure to toluene in the workplace. However, other factors, such as 

exposure to other chemicals, smoking and alcohol use, may have affected the results of the 

studies, so it is not possible to say whether toluene has reproductive effects in people. 

The effects of toluene on animals are similar to those seen in humans. The main effect of 

toluene is on the brain and nervous system, but animals exposed to moderate or high levels of 

toluene may also show harmful effects in their liver, kidneys, and lungs. 

Studies in workers and animals exposed to toluene generally indicate that toluene does not cause 

cancer. The International Agency for Research on Cancer (IARC) and the Department of Health 

and Human Services (DHHS) have not classified toluene for carcinogenic effects. The EPA has 

determined that toluene is not classifiable as to its human carcinogenicity. 

More information on the health effects of toluene in humans and animals can be found in 

Chapter 2. 

1.6 HOW CAN TOLUENE AFFECT CHILDREN? 

This section discusses potential health effects from exposures during the period from conception 

to maturity at 18 years of age in humans. 

Children may breathe air contaminated with toluene by family use of glues, paints, or cleaning 

solvents, or by accidents involving products containing toluene. Toluene vapors are heavier than 

air and since young children are closer to the ground or floor because of their height, they may 

breathe more toluene than adults during accidental exposures. Older children and adolescents 

may be exposed to toluene if they breathe household products containing it to get high. Nursing 

mothers who breathe toluene in workplace air may transfer some toluene in breast milk to their 

infants. Toluene is not stored in the body. Toluene in the body either rapidly leaves or is turned 

into less harmful chemicals. Thus, nursing mothers, who do not currently work in jobs with 
TOLUENE 7 

1. PUBLIC HEALTH STATEMENT 

toluene and who do not deliberately breathe large amounts of toluene, are expected to transfer 

very little toluene in breast milk. 

The effects of toluene on children have not been studied very much, but toluene is likely to 

produce the same types of effects on the brain and nervous system in children as it does in 

adults. Some older children and adolescents who have repeatedly breathed large amounts of 

toluene to get high have developed loss of muscle control, loss of memory, poor balance, and 

decreased mental ability. Some of these changes may last for a long time after toluene has left 

the body. Young animals exposed to toluene have shown changes in behavior, hearing loss, and 

chemical changes in their brains. 

Human fetuses and newborn babies may be more sensitive to toluene than adults, because their 

bodies may not be as able to turn toluene into less harmful chemicals. Some animal studies 

suggest that young animals might be more susceptible to toluene effects on health, but, shortly 

after birth, human babies begin to develop the ability to turn toluene into less harmful chemicals. 

By the time children are 1–3 years of age, they may be equal to adults in this ability. 

Some mothers who breathed large amounts of toluene during pregnancy to get high have had 

children with birth defects, including retardation of mental abilities and growth. Results from 

animal studies have found similar effects in new born animals that had mothers that breathed 

large amounts of toluene during pregnancy. However, when the animal mothers breathed small 

amounts of toluene during pregnancy, no birth defects were found in their newborn animals. 

When pregnant animals breathe small amounts of toluene during pregnancy, studies show that 

very little toluene reaches the developing fetus. 

More information on the effects of toluene on children can be found in Chapter 2. 
TOLUENE 8 

1. PUBLIC HEALTH STATEMENT 

1.7	 HOW CAN FAMILIES REDUCE THE RISK OF EXPOSURE TO TOLUENE? 

If your doctor finds that you have been exposed to significant amounts of toluene, ask whether 

your children might also be exposed. Your doctor might need to ask your state health 

department to investigate. 

Families can reduce their risk of exposure to toluene by only using consumer products 

containing it (such as paints, glues, inks, and stain removers) in well ventilated areas. When not 

in use, toluene-containing products should be tightly covered to prevent evaporation into the air. 

Household chemicals should be stored out of reach of young children to prevent accidental 

poisonings. Always store household chemicals in their original labeled containers. Never store 

household chemicals in containers that children would find attractive to eat or drink from, such 

as old soda bottles. Keep your Poison Control Center’s number next to the phone. Sometimes 

older children sniff household chemicals in an attempt to get high. Your children may be 

exposed to toluene by inhaling products containing it. Talk with your children about the dangers 

of sniffing chemicals. 

See Chapter 5 for more information on how families can reduce the risk of exposure to toluene. 

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

EXPOSED TO TOLUENE? 

You can find out if you have been exposed to toluene by having your exhaled air, blood, and 

urine tested for toluene or its breakdown products. These tests may not be available at a doctor's 

office, but are easily done by special laboratories. To determine if you have been exposed to 

toluene, your blood and urine must be checked within 12 hours of exposure for the presence of 

toluene or its breakdown products. Several other chemicals are also changed to the same 

breakdown products as toluene in the body, so some of these tests are not specific for toluene. 

Other factors, such as your weight and body fat, your sex, and the exposure conditions, may also 

influence the amount of the chemicals in your urine. More information on testing for exposure 

to toluene can be found in Chapters 2 and 6. 
TOLUENE 9 

1. PUBLIC HEALTH STATEMENT 

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. Federal agencies that develop regulations for toxic 

substances include the Environmental Protection Agency (EPA), the Occupational Safety and 

Health Administration (OSHA), and the Food and Drug Administration (FDA). 

Recommendations provide valuable guidelines to protect public health but cannot be enforced by 

law. Federal organizations that develop recommendations for toxic substances include the 

Agency for Toxic Substances and Disease Registry (ATSDR) and the National Institute for 

Occupational Safety and Health (NIOSH). 

Regulations and recommendations can be expressed in not-to-exceed levels in air, water, soil, or 

food that are usually based on levels that affect animals; then they are adjusted to help protect 

people. Sometimes these not-to-exceed levels differ among federal organizations because of 

different exposure times (an 8-hour workday or a 24-hour day), the use of different animal 

studies, or other factors. 

Recommendations and regulations are also periodically updated 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 toluene include the following: 

The federal government has developed regulatory standards and guidelines to protect you from 

the possible health effects of toluene in the environment. OSHA has set a limit of 200 ppm of 

toluene for air in the workplace, averaged for an 8-hour exposure per day over a 40-hour work 

week. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends 

that toluene in workplace air not exceed 50 ppm, and NIOSH recommends that toluene in 

workplace air not exceed 100 ppm (both as average levels over 8 hours). 

EPA has set a maximum contaminant level (MCL) for toluene in drinking water of 1 milligram 

per liter of water (1 mg/L). Any release of more than 1,000 pounds of this chemical to the 
TOLUENE 10 

1. PUBLIC HEALTH STATEMENT 

environment must be reported to the National Response Center. More information on federal 

and state government regulations and guidelines for toluene in air and water can be found in 

Chapter 7. 

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 

Agency for Toxic Substances and Disease Registry
 

Division of Toxicology
 

1600 Clifton Road NE, Mailstop E-29
 

Atlanta, GA 30333
 

* Information line and technical assistance 

Phone: 1-888-42-ATSDR (1-888-422-8737)
 

Fax: (404) 639-6359
 

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

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

hazardous substances. 

* To order toxicological profiles, contact 

National Technical Information Service
 

5285 Port Royal Road
 

Springfield, VA 22161
 

Phone: (800) 553-6847 or (703) 605-6000
 
TOLUENE 11 

2. HEALTH EFFECTS 

2.1 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 toluene. 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. 

2.2 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 

lowest-observed-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 

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 
TOLUENE 12 

2. HEALTH EFFECTS 

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

effects to human health. 

2.2.1 Inhalation Exposure 

Adverse effects on the nervous system are the critical effects of concern from inhalation exposure to 

toluene as evidenced by results from studies of workers acutely or chronically exposed to toluene in 

workplace air, studies of volunteers under controlled acute exposure conditions, and studies of chronic 

solvent abusers predominantly exposed to toluene. Observed effects include reversible neurological 

symptoms from acute exposure progressing from fatigue, headache, and decreased manual dexterity to 

narcosis with increasing exposure level, degenerative changes in white matter in chronic solvent abusers, 

and subtle changes in neurological functions including cognitive and neuromuscular performance, 

hearing, and color discrimination in chronically exposed workers. Studies of toluene-exposed animals 

provide supporting data showing changes in behavior, hearing loss, and subtle changes in brain structure, 

brain electrophysiology, and brain chemistry. Case reports of birth defects and developmental delays in 

children of mothers who abused solvents, including toluene, during pregnancy suggest that exposure to 

high levels of toluene may be toxic to the developing fetus. A number of developmental toxicity studies 

with rats, mice, and rabbits exposed to airborne toluene indicate that toluene is not a potent teratogenic 

agent at exposure levels below those inducing maternal toxicity, but can retard fetal growth and skeletal 

development and alter development of behavior in offspring. 

2.2.1.1 Death 

Limited data are available on toluene-associated deaths due to solvent abuse or occupational exposure and 

these studies do not indicate exposure concentrations. Paterson and Sarvesvaran (1983) reported on a 

teenager who died following an episode of glue sniffing. In Japan, a man died of cardiac arrest after 

painting a bathroom using a sealer containing 65% toluene (Shibata et al. 1994) and a woman died of 

adrenal hemorrhage after sniffing thinner containing 67% toluene (Kamijo et al. 1998). In Great Britain, 

approximately 80 deaths per year have been associated with solvent abuse (Anderson et al. 1985). 

Approximately half these cases were attributed to cardiac arrhythmias, central nervous system depression, 

asphyxia, and hepatic and renal failure (Anderson et al. 1982). Among the 52 cases with a toxicological 

report, 42 mentioned toluene(Anderson et al. 1982). 
 

TOLUENE 13 

2. HEALTH EFFECTS 

There are only a few animal inhalation studies that have examined the lethality of toluene, and there is 

evidence from an intermediate-duration study suggesting that mice may be more sensitive than rats. An 

inhalation LC50 value (concentrations causing death in of 50% of the animals) of 5,320 ppm has been 

reported for mice (Svirbely et al. 1943). In 14 to 15 week studies, exposure to 3,000 ppm toluene for 

6.5 hours/day, 5 days/week, caused 80% mortality in male rats, 60% mortality in male mice, and 100% 

mortality in female mice, but no deaths among female rats (NTP 1990). Death also occurred among 

female mice exposed to 625 (10%), 1,250 (10%), and 2,500 (40%) ppm toluene (NTP 1990). 

LOAEL values for deaths in the NTP (1990) study and the LC50 from the Svirbely et al. (1943) report are 

recorded in Table 2-1 and plotted in Figure 2-1. 

2.2.1.2 Systemic Effects 

Data are available pertaining to respiratory, cardiovascular, hematological, musculoskeletal, hepatic, 

renal, endocrine and ocular effects in humans and animals after inhalation exposure to toluene. In 

addition, there are data on gastrointestinal, dermal, body weight, and other systemic effects in animals 

after inhalation exposure to toluene. All systemic effects are discussed below. The highest NOAEL 

values and all LOAEL values from each reliable study for systemic effects in each species and duration 

category are recorded in Table 2-1 and plotted in Figure 2-1. 

Respiratory Effects. In humans, respiratory tract irritation is experienced from exposure to toluene. 

Irritation of the upper airways and degeneration of the nasal epithelium have been observed in animal 

studies. 

Exposure of volunteers to 40 ppm of toluene for 6 hours did not produce statistically significant 

differences in the results of tests measuring nasal mucus flow and lung function or in subjective 

evaluations of air quality, but irritation of the nose was noted at 100 ppm (Andersen et al. 1983). No 

changes in lung function were reported for volunteers exposed to 100 ppm toluene for 6 hours, 

30 minutes of which were spent exercising (Rahill et al. 1996). Individuals exposed to 800 ppm toluene 

for 3 hours (von Oettingen et al. 1942) or 1,862 ppm for 2 hours (Meulenbelt et al. 1990) had no selfreported respiratory effects. However, irritation of the nose and throat was reported in printers exposed to 

100 ppm toluene for 6.5 hours (Baelum et al. 1985), and in volunteers exposed to 200 ppm toluene for 

7–8 hours (Carpenter et al. 1944). Eight workers from a print factory exposed to <200 ppm toluene for 































TOLUENE 45 

2. HEALTH EFFECTS 

more than 18 months had normal chest roentgenograms and did not report breathing difficulty (Guzelian 

et al. 1988). 

Ten paint-sprayers exposed to 13 detected solvents (primarily 0.8–4.8 ppm toluene and isobutylacetate) 

and dusts had morphological changes in the nasal mucosa (Hellquist et al. 1983). However, there was no 

conclusive association between duration of exposure and mucosal abnormalities. Forty-two workers 

exposed to mixtures of solvents, of which toluene was generally a major component, reported symptoms 

of nasal irritation, in addition to eye irritation, nausea, skin conditions, dizziness, and headaches 

(Winchester and Madjar 1986). The concentrations of toluene to which the workers were exposed ranged 

from 1 to 80 ppm (mean of 15 ppm). However, concurrent exposure to a mixture of solvents and dusts in 

these studies precludes establishing an unequivocal causal relationship between exposure to toluene and 

mucosal irritation. 

Rats exposed to 30 or 300 ppm toluene 6 hours/day, 5 days/week for 4 weeks showed histopathological 

changes in the tracheal epithelium (Poon et al. 1994). Rats exposed to 600 ppm for 5 weeks, 7 hours/day 

showed irritation of the lung and rats exposed to 2,500 and 5,000 ppm had pulmonary lesions (von 

Oettingen et al. 1942). No signs of respiratory distress or histological abnormalities were observed in the 

lungs of mice exposed to 4,000 ppm 3 hours/day, for 8 weeks, or in rats and mice exposed to12,000 ppm 

for seven 10-minute periods per day separated by a 20-minute recovery period (Bruckner and Peterson 

1981b). However, this study did not include a histological examination of the upper respiratory tract and 

may therefore not have observed damage to this region. Alternatively, the different results reported by 

von Oettingen et al. (1942) and Bruckner and Peterson (1981b) may be explained by differences in the 

daily exposure duration with the shorter duration causing the less severe effects. 

Significantly increased relative lung weights were reported in rats and male mice exposed to 2,500 and 

3,000 ppm (6.5 hours/day, 5 days/week for 14–15 weeks) and in female mice exposed to >100 ppm 

toluene (NTP 1990). Mild-to-moderate degeneration of the olfactory and respiratory epithelium were 

observed in rats exposed to 600 ppm or 1,200 ppm 6.5 hours/day, 5 days/week for 15 months (NTP 

1990). Minimal hyperplasia of the bronchial epithelium was seen in 4/10 mice exposed to 1,200 ppm, but 

no other treatment-related damage to the respiratory tract was observed (NTP 1990). 

Inflammation of the nasal mucosa, erosion and metaplasia of the olfactory epithelium, and degeneration 

of the respiratory epithelium were reported in rats exposed to 600 or 1,200 ppm for 2 years 

(6.5 hours/day, 5 days/week) (NTP 1990). These effects were not observed in mice exposed to the same 
 

TOLUENE 46 

2. HEALTH EFFECTS 

concentrations for 2 years. No histopathological lesions were observed in the upper respiratory tract or 

lungs of rats exposed for 2 years to 300 ppm toluene (CIIT 1980). 

Cardiovascular Effects. Cardiac arrhythmia is a cause of death that has been associated with some 

solvent abuse fatalities. However, studies in laboratory animals do not provide convincing support for a 

direct effect of toluene on the cardiovascular system (Bruckner and Peterson 1981b; CIIT 1980; NTP 

1990). One study of acute exposure to a lethal concentration of toluene reported the induction of 

arrhythmia, but the authors suggest that this was due to a predisposing arrhythmia-producing heart 

abnormality (Ikeda et al. 1990). Other studies of acute exposure to near-lethal concentrations have 

reported a non significant increase in heart rate (Vidrio et al. 1986) or a reduction of experimentallyinduced arrhythmia (Magos et al. 1990). Chronic exposure to toluene concentrations up to 1,200 ppm did 

not induce cardiovascular system lesions in two well-conducted animal studies (CIIT 1980; NTP 1990) 

and did not appear to be directly toxic to the cardiovascular system. 

Cardiac arrhythmias were noted in two adult males who were found semi-conscious after suffering from 

toluene intoxication (>7,000 mg/m3

 toluene, 1,862 ppm) while removing glue from tiles in a swimming 

pool (Meulenbelt et al. 1990). Response seemed to be variable between these individuals. One man was 

exposed for 2 hours and exhibited a rapid heartbeat (sinus tachycardia), while the second man, exposed 

for 3 hours, exhibited a slow heartbeat (bradycardia) (Meulenbelt et al. 1990). Severe sinus bradycardia 

was also reported in a comatose man with severe toluene intoxication who had sniffed approximately 

250 mL of thinner containing more than 50% toluene (Einav et al. 1997). No effects on systolic or 

diastolic blood pressure or pulse rate were reported in volunteers exposed to 800 ppm toluene for 3 hours 

(von Oettingen et al. 1942). 

Cardiovascular response was assessed in 25 dogs killed by rebreathing 1 L of air containing 30,000 ppm 

toluene via an endotracheal tube (Ikeda et al. 1990). In most cases, death was due to hypoxia, but four of 

the dogs developed transient arrhythmia and in one case, death was due to ventricular fibrillation. The 

authors suggested that toluene had a direct effect on the septal and ventricular muscles of the heart, which 

permitted the development of fatal arrhythmias in sensitive dogs (Ikeda et al. 1990). Inhalation by 

anesthetized rats of 66,276 ppm toluene for 30 minutes (35 minutes inhalation of this concentration was 

fatal) produced a non significant increase in heart rate and changes in electrocardiographs indicative of 

depressed ventricular conduction (Vidrio et al. 1986). However, in rats with arrhythmias induced by 

aconitine injection or coronary ligation, a 15-minute exposure to 6,867 ppm toluene, 10 minutes before 

aconitine treatment significantly reduced the number of ventricular ectopic beats (Magos et al. 1990). 
 

 

TOLUENE 47 

2. HEALTH EFFECTS 

No histological abnormalities were observed in the hearts of mice exposed to 4,000 ppm for 3 hours/day, 

for 8 weeks or to mice and rats exposed to 12,000 ppm for 70 minutes/day for 8 weeks (Bruckner and 

Peterson 1981b). There were also no histopathological lesions of the heart that could be attributed to 

toluene in rats exposed to 300 ppm for 24 months (6 hours/day) (CIIT 1980) or in rats and mice exposed 

to up to 1,200 ppm for 24 months (6.5 hours/day) (NTP 1990). However, there were increased heart 

weights in rats and female mice exposed to 2,500 ppm toluene for 14–15 weeks (6.5 hours/day) (NTP 

1990). 

Gastrointestinal Effects. No studies were located regarding gastrointestinal effects in humans after 

inhalation exposure to toluene. 

The incidence of ulcers of the forestomach was marginally, but not significantly, increased in male rats 

exposed to concentrations of 600–1,200 ppm toluene for 2 years (NTP 1990). These effects were not 

reported in mice or female rats exposed under the same conditions. There were no gastrointestinal effects 

in rats and mice exposed to up to 2,500–3,000 ppm toluene for 14–15 weeks(NTP 1990). 

Hematological Effects. Hematological effects were not reported after inhalation exposure to toluene 

in the majority of recent human and animal studies. However, before the mid-1950s, chronic 

occupational exposure to toluene was associated with hematological effects in the same studies 

(Greenburg et al. 1942; Wilson 1943). These effects are now attributed to concurrent exposure to 

benzene, a common contaminant of toluene at that time (EPA 1985c). More recent studies of workers 

exposed to toluene or to mixed solvents containing toluene have not found consistent evidence for 

abnormal hematological parameters(Banfer 1961; Matsushita et al. 1975; Tahti et al. 1981; Ukai et al. 

1993; Yin et al. 1987). Decreased leukocyte counts were observed in some animal studies (Hobara et al. 

1984a; Horiguchi and Inoue 1977; NTP 1990; von Oettingen et al. 1942), but not in others (Ono et al. 

1996; Poon et al. 1994). There is evidence, however, that the decrease is a reversible phenomenon (von 

Oettingen et al. 1942). The toxicological significance of transitory decreases in leukocyte counts is not 

clear. It appears that toluene affects the blood, but blood is probably not a critical target tissue following 

toluene exposure. 

No effects on leukocyte counts were observed in volunteers exposed to 800 ppm toluene for 3 hours (von 

Oettingen et al. 1942). Two workers accidentally exposed to about 1,862 ppm for three hours had normal 

values for hematological and blood chemistry variables with the exception of an elevated union gap 

(Meulenbelt et al. 1990). 
TOLUENE 48 

2. HEALTH EFFECTS 

Ukai et al. (1993) reported no hematologic effects in 452 toluene-exposed shoemakers and printers 

(average exposure of 24.7 ppm) compared with unexposed controls from the same factories. Exposure 

was estimated from personal monitoring data, and at least 90% of total solvent exposure was due to 

toluene. Workers involved in printing, shoemaking, and audio equipment production, and exposed to 

41 ppm toluene had significantly decreased lymphocyte counts when compared to controls (Yin et al. 

1987). However, total leukocyte counts were not different from controls since the decrease in 

lymphocytes was counterbalanced by an increase in eosinophils. No significant hematological effects 

were observed in workers engaged in shoe-making (Matsushita et al. 1975) or printing (Banfer 1961) who 

were exposed to toluene for several years. The studies were limited by small cohort size and a lack of 

historical exposure data. Workers were exposed to atmospheric concentrations of toluene up to 600 ppm, 

but individual exposure monitoring was generally not performed. As a result, the studies had only limited 

power to detect adverse hematological effects in toluene-exposed workers. 

In contrast, workers exposed for several years to toluene (benzene concentration <0.01%) in a tarpaulin 

factory had increased blood leukocyte counts (Tahti et al. 1981). Toluene exposure concentrations, which 

ranged from 20 to 200 ppm were similar to those reported by Banfer (1961). However, this study is 

limited by small cohort size, a lack of historical exposure monitoring, and the probability that workers 

were exposed to mixtures of chemicals. 

Results of animal studies support the observation of decreased leukocyte counts following exposure to 

toluene. Decreased leukocyte counts were observed in dogs exposed acutely to 500 ppm of toluene 

(Hobara et al. 1984a). Throughout a 20-day exposure to 10, 100, and 1,000 ppm of toluene, mice 

exhibited a concentration-related decrease in thrombocyte counts (Horiguchi and Inoue 1977). The 

100 and 1,000 ppm groups were reported to have decreased erythrocyte counts; but the authors did not 

provide analysis of the results or discuss the findings further. Both studies are limited by small numbers 

of animals in the treatment groups. Slight hypoplasia of the bone marrow was observed in mice exposed 

to 1,000 ppm (Horiguchi and Inoue 1977), but the effect was not statistically significant and was not 

found in mice or rats exposed to up to 1,200 ppm for 2 years (NTP 1990). Rats exposed to 2,500 and 

5,000 ppm of toluene for 5 weeks had a daily, temporary decrease in leukocyte counts, but counts had 

normalized by the next day (von Oettingen et al. 1942). Decreased leukocyte counts were also reported in 

female rats exposed to 1,250 ppm toluene for 15 weeks, but not in mice or male rats exposed to up to 

2,500 ppm (NTP 1990). 
 

 

TOLUENE 49 

2. HEALTH EFFECTS 

Increased hematocrit and blood glucose levels were observed in male rats exposed to 2,000 ppm toluene 

for 48 hours (Tahti et al. 1983). Erythrocyte membranes were stronger and less susceptible to lysis in rats 

exposed to 2,000 ppm of toluene than in controls (Korpela et al. 1983). This was demonstrated to be a 

reversible phenomenon since membrane strength returned to normal after toluene had dissipated from the 

system (Korpela and Tahti 1984). Other lipophilic agents such as anesthetics, tranquilizers, narcotics, and 

steroids have a similar effect on membrane strength (Magos et al. 1990). 

No significant changes in hematological variables were observed in male rats exposed to 2,000 ppm 

6 hours/day for 90 days (Ono et al. 1996), or in rats exposed to 300 ppm 6 hours/day, 5 days/week for 

4 weeks (Poon et al. 1994). 

In one chronic study, rats exposed to 100 or 300 ppm of toluene had significantly reduced hematocrit 

levels (CIIT 1980). However, in another study, no consistent effects on hematological variables were 

reported for mice or rats exposed to toluene at levels up to 1,200 ppm for 2 years (NTP 1990). 

Musculoskeletal Effects. A 29-year-old man who had been sniffing glue containing toluene 

(concentration not specified) for 18 years and complained of severe muscle weakness was diagnosed with 

rhabdomyolysis (an acute disease of the skeletal muscles evidenced by myoglobin in the blood and urine) 

(Hong et al. 1996). 

No histological effects on bone were reported in mice or rats exposed to toluene at concentrations up to 

1,200 ppm for 2 years (NTP 1990). 

Hepatic Effects. Studies of chronic toluene abusers or occupationally-exposed humans, have 

provided little evidence for serious liver damage due to inhaled toluene. Some studies of workers who 

were occupationally exposed to average concentrations between about 30 and 350 ppm toluene reported 

liver effects such as increased serum levels of enzymes (Guzelian et al. 1988; Svensson et al. 1992b), but 

others recorded no adverse effects (Lundberg and Hakansson 1985; Seijii et al. 1987; Ukai et al. 1993). A 

number of animal studies have reported increased liver sizes or minor ultrastructural changes in rats 

exposed to concentrations of toluene ranging from 150 ppm for 30 days to 4,000 ppm 3 hours/day for 

8 weeks (Bruckner and Peterson 1981b; Kjellstrand et al. 1985; NTP 1990), but other studies have 

recorded no adverse effects in rats and mice exposed to concentrations of up to 1,200 ppm for 2 years 

(CIIT 1980; Kyrklund et al. 1987; NTP 1990). 
TOLUENE 50 

2. HEALTH EFFECTS 

No effects on blood levels of bilirubin, alkaline phosphatase activity, serum aspartate aminotransferase 

activity or serum alanine aminotransferase activity were reported for two workers accidentally exposed to 

1,862 ppm toluene for three hours (Meulenbelt et al. 1990). Eight men from a printing factory employing 

289 workers exposed to toluene at concentrations of less than 200 ppm, exceeded the upper end of the 

normal range for blood levels of bilirubin, alanine aminotransferase (ALT), aspartate aminotransferase 

(AST), and alkaline phosphatase (AP) and had an ALT/AST ratio greater than 1 (Guzelian et al. 1988). 

Liver biopsies showed centrilobular and periportal fat accumulation and Kupffer cell hyperplasia. None 

of the men reported drinking alcohol to excess, but they may have had minimal occupational exposure to 

methyl alcohol, ethyl alcohol, diethyl ether, trichloroethylene, and lacquer thinners which could have 

confounded the results. 

An early study of 106 painters exposed to toluene in an airplane factory reported enlargement of the liver 

in 30.2% of the exposed men, versus 7% of the control group (Greenburg et al. 1942). However, before 

the mid-1950s, chronic occupational exposure to toluene was associated with exposure to benzene, a 

common contaminant of toluene at that time (EPA 1985c), and this is a confounding factor for this study. 

Serum alkaline phosphatase values were significantly greater than controls in a group of 47 rotogravure 

workers occupationally exposed to a time-weighted-average (TWA) toluene concentration of 11–47 ppm 

(midpoint 29 ppm) for 3–39 years than in controls (Svensson et al. 1992b). The difference in alkaline 

phosphatase values remained significant even when the data were corrected to eliminate nine workers 

who reported consumption of alcoholic beverages. 

In contrast, no significant elevations in serum liver enzymes were found in another group of 

452 shoemakers and printers (exposed to average concentrations of 24.7 ppm toluene) compared with 

unexposed workers from the same factories (Ukai et al. 1993). Women working in a shoe factory for an 

average of more than 3 years and exposed to toluene concentrations which varied from 65 ppm 

(15-100 ppm) in winter and 100 ppm (10-200 ppm) in summer showed no changes in several serum 

variables indicative of liver damage compared with a control group of unexposed workers from the same 

factory (Matsushita et al. 1975). 

A group of 157 female shoemakers exposed for 2–14 months to toluene (7–324 ppm) had decreased 

serum levels of lactate-dehydrogenase (LDH) as compared to controls, but levels of 8 other serum 

enzymes monitored as indices of liver damage were normal (Seiji et al. 1987). These workers were also 

exposed to n-hexane, cyclohexane, and methyl ethyl ketone at concentrations generally 1/10th of the 

toluene concentration. Because LDH is present in almost all body tissues, this finding cannot be 
TOLUENE 51 

2. HEALTH EFFECTS 

attributed to an effect in the liver with any certainty. A group of 47 Swedish paint industry workers 

exposed for more than 10 years to mixed organic solvents (xylene, toluene, isobutanol, n-butanol, 

ethanol, ethylacetate, n-butylacetate, mineral spirits, methylacetate, methylene chloride, methyl ethyl 

ketone, and isopropanol) did not have elevated serum concentrations of liver enzymes when compared to 

nonexposed controls (Lundberg and Hakansson 1985). Each of these studies is limited by small cohort 

size, exposure to multiple solvents, and by a lack of historical exposure monitoring data. As a result, the 

studies had only limited power to detect adverse effects caused by toluene. 

Several case studies have reported effects on the liver from toluene exposure. Acute fatty liver during 

pregnancy was reported in a 26-year-old woman exposed for at least 2 months to toluene in glue. A liver 

biopsy done 9 days postpartum showed cytoplasmic change in the hepatocytes; however, there was no 

clinical or biochemical evidence of liver disease 1 month later (Paraf et al. 1993). A painter who had 

been exposed to toluene for 5 years exhibited hepatotoxicity, with fatty degeneration of hepatocytes and 

infiltration by lymphocytes (Shiomi et al. 1993). 

Acute exposure to toluene has been reported to produce biochemical and ultrastructural changes in the 

livers of experimental animals. Mice, rats, and rabbits exposed to 795 ppm of toluene for 7 days showed 

increased liver weights and cytochrome P450 levels compared to unexposed controls (Ungvary et al. 

1982). Electron microscopy revealed ultrastructural changes (increased rough or smooth endoplasmic 

reticulum) in the livers of all three species (Ungvary et al. 1982). Cytochrome b5 levels were also 

increased in exposed rats and rabbits but were not measured in mice (Ungvary et al. 1982). Male rats 

exposed to 2,000 ppm toluene for 48 hours had increased serum levels of alanine aminotransferase and 

aspartate aminotransferase (Tahti et al. 1983). Exposure of rats to 4,000 ppm toluene for 6 hours resulted 

in a significant increases in hepatic levels of cytochrome P450 (CYP) 2E1, increased hepatic activities of 

nitrosodimethylamine demethylase and 7-pentoxyresorufin O-depentylase and decreased levels of 

CYP2C11 (Wang et al. 1996). 

Intermediate exposure of animals to toluene has generally produced liver responses similar to those 

reported for acute exposure. Increased liver weights were reported for male mice exposed to12,000 ppm 

toluene, 3 hours/day, 5 days/week for 8 weeks (Bruckner and Peterson 1981b), female mice exposed to 

150 ppm continuously for 30 days (Kjellstrand et al. 1985), rats exposed to $1,200 ppm (males) or 

$2,500 ppm (females), or mice exposed to $625 ppm for 14 or 15 weeks (NTP 1990). However, male 

rats and mice exposed to 12,000 ppm toluene for 8 weeks (seven 10-minute exposures separated by 

20-minute recovery periods) had decreased liver weights (Bruckner and Peterson 1981b), and no change 
 

TOLUENE 52 

2. HEALTH EFFECTS 

in liver weight was observed in rats exposed to 320 ppm (Kyrklund et al. 1987), male mice exposed to 

150 ppm (Kjellstrand et al. 1985) continuously for 30 days, or rats exposed to 30 or 300 ppm toluene 

6 hours/day, 5 days/week for 4 weeks (Poon et al. 1994). No effect on the liver was reported for rats 

exposed to 200–5,000 ppm toluene for 7 hours/day for 5 weeks (Von Oettingen et al. 1942). 

Alkaline phosphatase activity was significantly elevated in male rats exposed to 300 ppm for 6 hours/day, 

5 days/week for 4 weeks (Poon et al. 1994) and centrilobular hepatocellular hypertrophy was noted in 

male mice exposed to 2,500–3,000 ppm toluene for 14 weeks (NTP 1990). 

No significant gross or histpathological liver changes or liver weight changes were found in rats exposed 

to toluene at 300 ppm (CIIT 1980) or rats or mice exposed to up to 1,200 ppm 6–6.5 hours/day, 

5 days/week for up to 2 years (NTP 1990). 

Renal Effects. Studies of chronic toluene abusers, occupationally exposed workers, and laboratory 

animals have provided little support for serious kidney damage due to inhaled toluene. Chronic abuse of 

toluene can produce acidosis, but in most cases, renal dysfunction is transient and normal function returns 

when exposure ceases (Goodwin 1988; Kamijo et al. 1998; Meulenbelt et al. 1990; Patel and Benjamin 

1986). In general, studies of workers occupationally exposed to 100–200 ppm toluene, which assessed 

changes in tests of kidney function, have not shown significant effects (Askergren et al. 1981a; Nielsen et 

al. 1985; Stengel et al. 1998). Animal studies indicate that inhalation of toluene causes concentrationdependent kidney damage in rats, but only after chronic exposure to concentrations $600 ppm for at least 

6 hours/day (Bruckner and Peterson 1981b; CIIT 1980; NTP 1990; Ono et al. 1996; Poon et al. 1994). 

Several cases have been reported where occupational exposure to toluene or toluene abuse was associated 

with acidosis (Gerkin and LoVecchio 1998; Goodwin 1988; Jone and Wu 1988; Meulenbelt et al. 1990; 

Patel and Benjamin 1986). Acidosis generally reflects the inability of the kidneys to maintain the pH 

balance of the blood either due to saturation of kidney transport of hydrogen ion or a defect in tubular 

function. Severe renal tubular acidosis was observed in five pregnant women who were chronic abusers 

of paints containing toluene (Goodwin 1988). When paint-sniffing ended, normal acid-base balance 

returned within 72 hours, indicating that permanent damage to the tubules had not occurred. However, 

one 19-year-old male chronic solvent abuser was found, through a renal biopsy, to have severe tubular 

interstitial nephritis and focal tubular necrosis indicative of prolonged irritation of the kidney (Taverner 

et al. 1988). This patient required hemodialysis to correct hematuria and oliguria which was present at 

the time of his hospital admission. Hemodialysis was also required for a 22-year-old male chronic 
TOLUENE 53 

2. HEALTH EFFECTS 

solvent abuser with acidosis and hypokalemia (Gerkin and LoVecchio 1998). A 22-year-old woman, who 

had sniffed approximately 6 L of toluene during the previous month, was found to have metabolic 

acidosis and histological evidence of tubular injury. The acidosis normalized, but both proximal and 

distal tubular dysfunction persisted (Kamijima et al. 1994). Proteinuria, hematuria, and urinary calculi 

were reported in three solvent abuse case studies (Kaneko et al. 1992); the abused product was primarily 

toluene in one case. Autopsy of a 19-year-old woman, who had sniffed thinner containing 67% toluene 

for 5 years, revealed severe renal tubular degeneration and necrosis (Kamijo et al. 1998). 

A group of 43 printing trade workers exposed to inks containing toluene, alcohols, and ethyl acetate for 

9–25 years were experimentally exposed to 382 mg/m3

 (102 ppm) of toluene for 6.5 hours (Nielsen et al. 

1985). No significant differences in excretion of albumin and β-2-microglobulin were observed either 

before or after exposure when the workers were compared to controls matched by age, educational level, 

and smoking habits (Nielsen et al. 1985). 

In a longitudinal study of 92 printers exposed to 97–232 mg/m3

 (26–62 ppm) toluene, markers of early 

renal damage (microalbumin, N-acetyl-b-D-glucosaminidase, and alanine-aminopeptidase) were not 

significantly elevated in urine, but creatinine clearance was higher among exposed workers than 

unexposed controls (Stengel et al. 1998). Comparison of a group of 42 printers, occupationally exposed 

to 300–400 mg/m3

 toluene (80–107 ppm), with a group of age-matched, unexposed controls showed that 

printers excreted significantly more albumin than controls, but no increase in the excretion of 

β-2-microglobulin was observed (Askergren et al. 1981a). Glomerular filtration rate in a group of 

34 printers (toluene exposure level not stated) was slightly increased compared with unexposed controls, 

but the difference was not significant (Askergren et al. 1981b). 

In an early animal study, toluene produced pathological changes in the kidneys of rats. Inhalation of 

600–5,000 ppm of toluene 7 hours per day for 5 weeks caused the formation of renal casts within the 

collecting tubules of exposed rats (von Oettingen et al. 1942). In a recent study (Ono et al. 1996), an 

increase in kidney weights and necrosis of kidney tubules were seen in male rats exposed to 2,000 ppm 

toluene for 90 days. No histological abnormalities were observed in the kidneys of mice exposed to 

4,000 ppm for daily 3-hour periods or mice and rats exposed to 12,000 ppm for 70 minutes/day, 

5 days/week for 8 weeks, but kidney weights were significantly decreased in rats and mice exposed to 

12,000 ppm (Bruckner and Peterson 1981b). Increased relative kidney weights, but no histological 

lesions were seen in rats exposed for 15 weeks and female mice exposed to toluene for 14 weeks at 
 

 

TOLUENE 54 

2. HEALTH EFFECTS 

1,250 ppm (6.5 hours per day) (NTP 1990). No effects on the kidneys were observed in rats exposed to 

30 or 300 ppm toluene for 4 weeks (Poon et al. 1994). 

Gross and microscopic pathological examination of rats chronically exposed to 300 ppm of toluene for 

24 months found no treatment-related renal effects (CIIT 1980). Nephropathy was observed in most 

(96–98%) of the rats (including controls) from a 2-year inhalation study; the severity increased with 

concentration (600–1,200 ppm) (NTP 1990). The incidence of renal tubular cysts increased with 

concentration level in males. No renal lesions were reported in mice exposed under the same conditions 

(NTP 1990). Since the only essential difference between the CIIT and NTP studies was the concentration 

level used, it appears that the occurrence of renal tubular cysts was concentration-related. 

Endocrine Effects. A 29-year-old man who had been sniffing glue containing toluene 

(concentration not specified) for 18 years was diagnosed with hypothyroidism (Hong et al. 1996). 

Autopsy of a 19-year-old woman who had been sniffing thinner (67% toluene) for 5 years revealed 

histological evidence of massive bilateral adrenal hemorrhage with severe degeneration and necrosis of 

the adrenal cortex (Kamijo et al. 1998). Plasma levels of follicle stimulating hormone, lutenizing 

hormone, and testosterone were reduced in printers exposed to median toluene levels of 36 ppm for an 

average of 25 years compared with unexposed controls (Svensson et al. 1992a). 

Female rats exposed to 30 or 300 ppm toluene for 6 hours/day, 5 days/week for 4 weeks showed a 

treatment-related reduction in follicle size of the thyroid (Poon et al. 1994). No effect on the adrenal 

glands was reported for rats exposed to 200–5,000 ppm toluene for 7 hours/day for 5 weeks (Von 

Oettingen et al. 1942). No gross morphological abnormalities on the pancreas, adrenal, or thyroid glands 

were observed in rats exposed to 100–2,000 ppm toluene for 95 days (API 1985). Mice exposed to up to 

2,500 ppm for 14 weeks (NTP 1990), rats exposed to up to 3,000 ppm for 15 weeks, and mice and rats 

exposed to up to 1,200 ppm for 2 years (NTP 1990) showed no histological abnormalities in the pancreas, 

adrenal, or thyroid glands. 

Dermal Effects. No studies were located regarding dermal effects in humans after inhalation 

exposure to toluene. 

No effects on the skin were observed in rats exposed to 100–2,000 ppm toluene for 95 days (API 1985). 
 

 

 

TOLUENE 55 

2. HEALTH EFFECTS 

Ocular Effects. Humans exposed for 6–8 hours to toluene concentrations of 100 ppm and greater 

developed irritation of the eyes (Andersen et al. 1983; Baelum et al. 1985; Carpenter et al. 1944; 

Meulenbelt et al. 1990). No irritation was reported with 6 hours of exposure to 40 ppm toluene 

(Andersen et al. 1983). Reports of color vision deficits in occupationally exposed workers have linked 

increased color confusion with chronic exposure to <100 ppm toluene (Zavalic et al. 1998a, 1998b, 

1998c). These studies are discussed in the Section 2.2.1.4, Neurological Effects. 

Pregnant rats exposed to 2,000 ppm 6 hours/day for 21 days showed lacrimation (Ono et al. 1996), but no 

lacrimation or discharge was reported for male, female, or pregnant female rats exposed to 

100–2,000 ppm, 6 hours/day for 95 days (API 1985). 

Body Weight Effects. No studies were located regarding body weight effects in humans after 

inhalation exposure to toluene. 

Body weights in rats decreased compared with controls following inhalation exposure to toluene 

concentrations of 2,000 ppm for 48 hours (Tahti et al. 1983), 2,000 ppm, 8 hours/day, 7 days/week for 

11 weeks (Pryor 1991), 320 ppm, 24 hours/day for 30 days (Kyrklund et al. 1987), 8,000 ppm 

2–2.5 hours/day, 5 days/week for 13 weeks (Mattsson et al. 1990), 12,000 ppm 70 minutes/day, 

5 days/week for 8 weeks (Bruckner and Peterson 1981b), 2,500 ppm, or 6.5 hours/day for 15 weeks (NTP 

1990). In contrast, no effects on body weights were observed in rats or mice exposed to 1,000 ppm 

toluene for 6 hours/day, 5 days/week, for 20 or 42 days (API 1997; Horiguchi and Inoue 1977), in rats 

exposed to up to 2,000 ppm toluene 6 hours/day for 90 or 95 days (API 1985; Ono et al. 1996), or in rats 

or mice exposed to up to 1,200 ppm toluene 6–6.5 hours/day for 2 years (CIIT 1980; NTP 1990). 

Decreased body weights were seen in female and male mice exposed 6.5 hours/day to concentrations 

$100 and 2,500 ppm, respectively (NTP 1990), and in male mice exposed to 4,000 ppm, 3 hours/day or 

12,000 ppm 70 minutes/day for 8 weeks (Bruckner and Peterson 1981b). 

Other Systemic Effects. No studies were located regarding other systemic effects in humans after 

inhalation exposure to toluene. 

2.2.1.3 Immunological and Lymphoreticular Effects 

Only limited data are available on the immunological or lymphoreticular effects of inhalation exposure to 

toluene. Studies in exposed workers are confounded to varying degrees by exposure to multiple solvents, 
TOLUENE 56 

2. HEALTH EFFECTS 

but indicate that there may be slight effects of toluene on immunoglobins, leukocytes, and lymphocytes, 

but the significance of these effects in humans is uncertain. A single mouse study reported that exposure 

to concentrations >100 ppm, 3 hours/day for 4 weeks decreased resistance to respiratory infection (Aranyi 

et al. 1985). 

No differences in serum IgG, IgA and IgM values were noted when rotogravure printers exposed to 

concentrations of 104–1,170 ppm for an average of 13 years were compared to office workers at the same 

facility (Pelclova et al. 1990). Blood IgE levels in 92 printers exposed to 97–232 mg/m3

 (26–62 ppm) 

toluene for an average of 16 years were significantly elevated compared to unexposed controls, and a 

dose-response relation was observed between cumulative toluene exposure and IgE levels (Stengel et al. 

1998). Total lymphocytes were significantly decreased in workers involved in shoemaking, printing, and 

audio equipment production (Yin et al. 1987). Mean toluene exposures were 41 ppm for females and 

46 ppm for males over an average of 82 months. 

A decrease in the T lymphocyte count of workers occupationally exposed to a mixture of benzene 

(0–116 ppm), toluene (0–160 ppm), and xylene (0–85 ppm) was observed (Moszczynsky and Lisiewicz 

1984). However, no signs of diminished immunological function or disturbances in immune skin 

reactions against such antigens as tuberculin or distreptase were observed in the subjects studied. The 

reduction of T lymphocytes may have been the result of the depressive effect of benzene on the 

lymphocyte system. Workers exposed to a mixture of 0.8–40 ppm toluene (0.003–0.16 mg/L), 

56–940 ppm benzene (0.18–3.0 mg/L), and 40–609 ppm xylene (0.18–3.0 mg/L) had significantly lower 

serum IgG and IgA levels than unexposed controls (Lange et al. 1973). Leukocyte agglutinins for 

autologous leukocytes and increased leukoagglutination titer in human sera after incubation with the 

solvents were also observed (Lange et al. 1973). The results of these studies are confounded by mixed 

exposure and their significance is therefore uncertain. 

A single 3-hour exposure of mice to 2.5–500 ppm toluene produced a significant increase in susceptibility 

to respiratory infections compared to unexposed controls when mice were challenged by Streptococcus 

zooepidemicus (Aranyi et al. 1985). Exposure to 1 ppm for 3 hours, 5 days (3 hours/day), or 4 weeks 

(3 hours/day) produced no significant difference in susceptibility compared to controls. Pulmonary 

bactericidal activity was decreased at concentrations of 2.5 ppm and 100–500 ppm, but not at 

concentrations of 5–50 ppm. The bactericidal activity of the lung was decreased during the 5-day 

treatment but not with the 4-week treatment. The authors hypothesized that toluene exerted an adverse 

effect on alveolar macrophage function, thereby decreasing disease resistance. 
TOLUENE 57 

2. HEALTH EFFECTS 

No changes in weight or histology of the spleen were recorded for rats exposed to 30–5,000 ppm toluene, 

6–7 hours/day for 4–5 weeks (Poon et al. 1994; von Oettingen et al. 1942), or for the spleen or thymus of 

rats and mice exposed to toluene concentrations up to 3,000 ppm for 14–15 weeks (NTP 1990). Exposure 

of mice and rats to up to 1,200 ppm, 6.5 hours/day for 2 years produced no histological changes in the 

thymus, but there was an increased incidence of pigmentation of the spleen in male mice exposed to 

concentrations $120 ppm (NTP 1990). 

Decreased thymus weights were observed in male rats exposed to 2,000 ppm 6 hours/day for 90 days 

(Ono et al. 1996) and in dams exposed to 600 ppm 6 hours/day during gestation days 7–17 (Ono et al. 

1995). However, no effects on the thymus were reported in rats and mice exposed 6 hours/day to up to 

1,200 ppm for 2 years or up to 3,000 ppm toluene for 14–15 weeks (NTP 1990) or in male rats exposed to 

1,000 ppm toluene for 6 hours/day for up to 42 days (API 1997). 

The highest NOAEL values and all LOAEL values for each reliable study for immunological effects in 

each species and duration category are recorded in Table 2-1 and plotted in Figure 2-1. 

2.2.1.4 Neurological Effects 

Dysfunction of the central nervous system is a critical human health concern following acute, 

intermediate, or chronic inhalation exposure to toluene. Chronic toluene abuse in humans has been 

associated with neurotoxic symptoms, narcosis, and death (Byrne et al. 1991; Caldemeyer et al. 1996; 

Devathasan et al. 1984). Case reports from chronic abusers indicate that prolonged exposure to toluene 

results in permanent damage to the central nervous system (Byrne et al. 1991; King et al. 1981; 

Rosenberg et al. 1988b). Neurotoxic symptoms and reduced ability in tests of cognitive and 

neuromuscular function have been observed in humans occupationally exposed to average concentrations 

as low as 80–150 ppm (Boey et al. 1997; Murata et al. 1993; Orbaek and Nise 1989; Vrca et al. 1995, 

1997b; Yin et al. 1987). Performance deficits in tests of neurobehavior have also been observed in 

volunteers acutely exposed to controlled concentrations >50 ppm (Andersen et al. 1983; Baelum et al. 

1985; Echeverria et al. 1991; EPA 1985c; Iregren 1986; Rahill et al. 1996; von Oettingen et al. 1942) and 

in laboratory animals repeatedly exposed to >500 ppm toluene (Larsby et al. 1986; Lorenzana-Jimenez 

and Salas 1990; Miyagawa et al. 1998; Pryor 1991). Studies of occupationally exposed workers also 

indicate that chronic exposure to average concentrations as low as 30–130 ppm damages hearing and 

color vision presumably involving, at least in part, effects on neurological components of these systems 

(Abbate et al. 1993; Morata et al. 1997; Zavalic et al. 1998a, 1988b, 1988c). Hearing loss has also been 
TOLUENE 58 

2. HEALTH EFFECTS 

reported in laboratory animals exposed to 700–1,500 ppm toluene (Campo et al. 1997; Johnson and 

Canlon 1994; Lataye and Campo 1997; Pryor et al. 1984b). 

Experimental studies in volunteers show that acute exposure to toluene concentrations below 50 ppm 

results in few, if any, observable effects, but signs of neurological impairment have been observed with 

acute exposure to concentrations greater than 50 ppm. For example, exposure to 40 ppm of toluene for 

6 hours did not produce statistically significant differences in the results of tests measuring psychometric 

performance and subjective evaluations of well being when compared to controls (Andersen et al. 1983). 

In contrast, 6–6.5-hour exposures to 100 ppm toluene caused fatigue, sleepiness, headaches, nausea, 

decreased manual dexterity, decreased color discrimination, decreased accuracy in visual perception, and 

decreased accuracy in multiplication tests (Andersen et al. 1983; Baelum et al. 1985). An acute inhalation 

MRL of 1 ppm was calculated as described in the footnote in Table 2-1 and Appendix A, based on the 

NOAEL (40 ppm) from the study by Andersen et al. (1983). 

Several other human studies support the derivation of the acute inhalation MRL and the hypothesis that 

subtle neurological effects can occur with acute exposure to concentrations in the 75–150 ppm range. 

Exposure of volunteers to 0, 75, or 150 ppm toluene for 7 hours caused a concentration-related 

impairment of function on digit span, pattern recognition, the one-hole test, and pattern memory 

(Echeverria et al. 1991). There was an effect on the results of the symbol digit test, but the effect was not 

concentration-related. Tests were administered to each subject before exposure and at the end of the 

exposure period. The treatment effect between groups was smaller than the variation of subjects within 

the group, thus each subject was used as their own control to more accurately assess the changes in 

performance due to exposure. There were no differences in the results on simple reaction time, mood 

(profile on mood scale), visual memory, hand-eye coordination, verbal short-term memory (Sternberg 

test), finger tapping, reaction time, continuous performance test, and critical tracking test. Six volunteers 

exposed to 100 ppm toluene for 6 hours, followed by exercise, showed significantly lower results on 

neuropsychological tests than volunteers exposed to clean air only (Rahill et al. 1996). Exposure of 

26 painters to controlled amounts of toluene (5 or 80 ppm) for 4 hours did not change their performance 

in tests of reaction time, color-word vigilance, or memory reproduction (Iregren 1986). Workers in a 

printing factory (exposed to <200 ppm toluene) returning to work after a 4-day vacation reported a feeling 

of mild intoxication to which they became tolerant within 1 or 2 days (Guzelian et al. 1988). At 

concentrations of 200–800 ppm, acute exposures initially resulted in excitatory effects such as 

exhilaration and lightheadedness. These effects were followed by the development of narcosis, 
TOLUENE 59 

2. HEALTH EFFECTS 

characterized by impaired intellectual, psychomotor, and neuromuscular effects with increased duration 

of exposure (EPA 1985c; von Oettingen et al. 1942). 

Humans exposed to high levels of toluene as a result of solvent abuse or industrial accidents have 

displayed serious central nervous system dysfunction. Accurate exposure data are not available for these 

individuals, but the concentrations inhaled by chronic abusers have been estimated to range from 4,000 to 

12,000 ppm (Gospe et al. 1994). In some cases, the degree of central nervous system depression was 

sufficient to result in death. Prolonged abuse has been reported to cause permanent damage resulting in 

abnormal electroencephalogram (EEG) activity, ataxia, tremors, temporal lobe epilepsy, paranoid 

psychosis, hallucinations, nystagmus (involuntary eye movement), cerebral atrophy, and impaired speech, 

hearing, and vision (Byrne et al. 1991; Devathasan et al. 1984; Hunnewell and Miller 1998; King et al. 

1981; Maas et al. 1991; Meulenbelt et al. 1990; Miyagi et al. 1999; Ryu et al. 1998; Suzuki et al. 1983). 

In two hospitalized patients with a history of solvent abuse, there was a decrease in intelligence quotient 

when the results of tests administered before solvent abuse began were compared to those measured 

during hospitalization for long-term abuse (Byrne et al. 1991). Examination of 19 children (ages 

8–14 years) hospitalized with acute encephalopathy due to toluene exposure indicated that 5 of the 

children retained psychological impairment and personality change when discharged from the hospital, 

while one child had a persistent cerebellar ataxia 1 year after cessation of toluene abuse (King et al. 

1981). 

In general, results from case studies of toluene abusers suggest that some of the neurological symptoms 

associated with chronic toluene abuse may be the result of permanent structural changes in the brain. 

Evaluation of chronic toluene abusers by magnetic resonance imaging (MRI) and single photon emission 

computed tomography (SPECT) has shown an increase in the white matter signal, a loss of gray and white 

matter differentiation, and decreased perfusion in the cerebral cortex, basal ganglia, and thalami 

(Caldemeyer et al. 1996; Filley et al. 1990; Ikeda and Tsukagoshi 1990; Kamran and Bakshi 1998; 

Rosenberg et al. 1988a; Ryu et al. 1998; Yamanouchi et al. 1995). Cerebral, cerebellar, and brainstem 

atrophy were also present (Kamran and Bakshi 1998; Rosenberg et al. 1988b). Correlations between 

clinical signs of neurological impairment and damage visible in MRI images have also been reported 

(Caldemeyer et al. 1996; Hormes et al. 1986; Rosenberg et al. 1988b). Abnormalities in MRI and 

brainstem auditory evoked response (BAER) results were still present in chronic abusers who had 

refrained from toluene exposure for two to nine months (Rosenberg et al. 1988b). 
TOLUENE 60 

2. HEALTH EFFECTS 

Toluene had an effect on pattern-visual evoked potentials in 32 males and 2 females who abused thinner 

containing toluene for 5–10 years. Statistical differences between controls and toluene abusers were seen 

on latencies of waves P-100 and N-145 (Poblano et al. 1996). 

Murata et al. (1993) compared cardiac autonomic function in printers exposed to 83 ppm airborne toluene 

for 1–36 years with matched controls. Autonomic function was evaluated from measurements of heart 

rate, the coefficient of variation in electrocardiographic R-R intervals, the distribution of nerve 

conduction velocities, and the maximal motor and sensory nerve conduction velocities in the median 

nerve. Some printers reported subjective symptoms such as fatigue, headache, and irritation. Heart rate 

was not significantly different in exposed individuals and controls. However, there were statistically 

significant reductions in electrocardiographic R-R intervals, indicating possible dysfunction of the 

autonomic nervous system. There was a significant decrease in the motor and sensory conduction 

velocity in the palm segment of the median nerve in toluene-exposed workers, but there was no 

significant difference in the distribution of the nerve conductance velocities between exposed and control 

subjects (Murata et al. 1993). 

Several studies of workers repeatedly exposed predominantly to toluene in workplace air have found 

evidence for increased incidence of self-reported neurological symptoms (Orbaek and Nise 1989; Yin et 

al. 1987); performance deficits in neurobehavioral tests (Boey et al. 1997; Foo et al. 1990; Orbaek and 

Nise 1989); hearing loss (Abbate et al. 1993; Morata et al. 1997); changes in visual evoked potentials 

(Vrca et al. 1995, 1997a, 1997b), and color vision loss (Zavalic et al. 1998a, 1998b, 1998c). 

A group of 95 workers exposed to TWA of 41–46 ppm toluene during shoemaking, printing, and audio 

equipment production were evaluated for symptoms and signs of exposure when compared to 130 control 

subjects (Yin et al. 1987). The incidence of health-related complaints among the toluene exposed 

workers was 2–3 times that of the controls. Dizziness was reported by about two-thirds of the toluene 

exposed respondents. These subjects also complained of headaches, sore throats, eye irritation, and 

difficulty with sleep. When the exposed subjects were divided into 2 groups, one with TWA exposures of 

less than 40 ppm and the other with exposures greater than or equal to 40 ppm, the incidence of headache 

and sore throat, but not dizziness, showed a concentration-response pattern (Yin et al. 1987). Tests of 

postural sway carried out on 27 United States Air Force workers exposed to jet fuel (mean cumulative 

exposure 23.8±6.1 ppm toluene) found a significant association between toluene exposure and increased 

postural sway (Smith et al. 1997). However, the results of this study are confounded by concurrent 

exposure to other chemicals, including benzene and xylene. 
TOLUENE 61 

2. HEALTH EFFECTS 

Thirty rotogravure printers from two plants and 72 unexposed workers completed a questionnaire 

designed to record their neurasthenic complaints and were given a series of tests designed to evaluate 

psychometric function (Orbaek and Nise 1989). At the time of the study (1985), 19 of the printers were 

exposed to TWA toluene levels of 11.6 ppm, and the remainder were exposed to 42.4 ppm. However, the 

printers had been exposed to solvents for at least 10 years (employment ranged 4–43 years), and 

estimated air concentrations at earlier times were much higher (as high as 453 ppm prior to 1970). 

Taking the midpoints in the ranges of concentration estimates for 1970–1985 for the two factories and 

calculating their mean yields, a representative exposure concentration of 140 ppm was determined. 

Significantly more printers reported neurasthenic symptoms than controls, but no significant differences 

were found between printers and controls for 10 of 11 psychometric tests and in the remaining test 

(Cylinder Board test of motor skill), printers performed better than controls. 

A stronger correlation between impaired neurobehavioral performance and toluene exposure was seen in 

30 female workers exposed to 88 ppm toluene as compared to 30 workers in the same facility exposed to 

only 13 ppm (Foo et al. 1990). The higher exposure group received poorer test scores in tests of visual 

retention, visual reproduction, trail making, grooved peg board, digit span, and digit symbol, but not on 

tests of simple reaction time and finger tapping. 

Another group of 29 exposed workers in Singapore (average TWA toluene exposure of 90.9 ppm) 

performed more poorly than a control group (average TWA exposure of 12.2 ppm) on 8 neurobehavioral 

tests. The exposed group performed significantly more poorly in verbal and nonverbal memory as 

measured by the digit span and visual reproduction tests (Boey et al. 1997). 

Low-level occupational exposure to an average of 97 ppm toluene for 12–14 years had an apparent effect 

on hearing in 40 rotogravure workers when brainstem auditory evoked potential (BAEP) results were 

compared to a group of 40 workers who were of comparable age but were not exposed to toluene (Abbate 

et al. 1993). Workers were carefully screened to eliminate slight hearing abnormalities or exposure to 

other chemicals. Two series of stimuli were used, one with 11 repetitions/second and one with 

90 repetitions/second. In both cases the intensity was 80 dB/nHL. Mean latencies were significantly 

higher for the exposed group than the control group for each BAEP wave evaluated (I, III, and V). 

Discernment mean values for the exposed and control groups were distributed homogeneously with very 

little overlap of exposed and control responses for both the 11-repetition and 90-repetition cycles. Wave I 

showed the most pronounced increase in latency. According to the authors, the effects on Wave I could 
 

TOLUENE 62 

2. HEALTH EFFECTS 

be due to either a change in the membrane of the peripheral receptor, a modification of the structure of the 

junction, or a change in the stimulus transduction mechanism. 

In two other studies, BAEPs in workers exposed to average concentrations of about 50 ppm for an 

average of 21.4 years were found to be affected, with a significant decrease in all wave amplitudes and a 

significant increase in all wave latencies except P2 (Vrca et al. 1995, 1997a). 

In a cross-sectional examination of 124 Brazilian workers exposed to various levels of noise and a variety 

of organic solvents, including toluene at TWA concentrations ranging from 0.037 to 244 ppm, 

(midpoint=122 ppm), 49% of workers experienced hearing loss (Morata et al. 1997). Toluene exposure 

(and exposure to a number of other solvents including ethanol and ethyl acetate) was estimated by 

personal monitoring and measurement of hippuric acid in urine samples. Confidence in the study is 

limited because of exposure to multiple solvents and possible confounding from noise exposure. 

However, logistic regression analysis showed hippuric acid concentration to be significantly associated 

with hearing loss and the odds ratio estimates for hearing loss were 1.76 times greater for each gram of 

hippuric acid per gram creatinine (95% CI 1.00–2.98). 

Occupational exposure to toluene may also affect other sensory-evoked potentials. Visual evoked 

potentials ( P300, N75, N145, and P100 waves) in printers occupationally exposed to average 

concentrations of 50 ppm toluene for an average of 21 years were compared to those of unexposed 

controls (matched for alcohol and coffee consumption, smoking, age, years of work, education, and head 

injuries) (Vrca et al. 1995, 1997a, 1997b). Individual exposure was estimated by measuring toluene 

levels in blood (0.036 mg/L in exposed workers, 0.0096 mg/L in controls) and hippuric acid levels in 

urine (0.426 g/g creatine in exposed workers, 0.338 g/g creatine in controls). There was a significant 

increase in the number of exposed individuals displaying reduced amplitude of P300R waves and 

prolonged latency of the accompanying spontaneous wave P300F (Vrca et al. 1997b). The amplitudes of 

the N75, P100, and N145 waves (Vrca et al. 1995, 1997a), and the latency of the P100 wave, were 

significantly increased in exposed subjects compared with controls (Vrca et al. 1995). 

Chronic exposure to toluene may also cause color vision loss. Zavalic et al. (1998a) examined color 

vision in 83 controls, 41 shoemakers, and 32 printers exposed respectively to geometric mean toluene 

concentrations of 0, 35, or 156 ppm. Toluene exposure was estimated by measuring toluene levels in the 

air and in the blood of workers, and by measuring the amount of hippuric acid and orthocresol in their 

urine at the end of the work shift. The technology, ventilation, and types of workplaces included in the 

study had not changed in the preceding 30 years. Color confusion was significantly higher in printers 
TOLUENE 63 

2. HEALTH EFFECTS 

compared with both shoemakers and controls. Color confusion index was increased in shoemakers 

compared with controls, but the difference was not significant (Zavalic et al. 1998a). Regression analysis 

established a significant correlation between color confusion as a dependent and alcohol intake and age as 

independent variables for the control group. Age- and alcohol-adjusted color confusion index was 

significantly increased in printers compared with shoemakers and controls, and in shoemakers compared 

with controls. After age and alcohol adjustments, individual color confusion indices were significantly 

correlated with individual exposure estimates (air, blood, or urine) in printers, but in shoemakers, the 

correlation was not statistically significant. The significantly increased color confusion index for the 

shoemakers in this study was assessed as a less-serious adverse effect and the LOAEL of 32 ppm served 

as the basis for the chronic-duration inhalation MRL, 1 ppm, for toluene (see footnote of Table 2.1, 

Section 2.5 and Appendix A). 

Further analysis of color vision loss in the same groups of workers described above (Zavalic et al. 1998a) 

was carried out to compare loss in the blue-yellow and red-green ranges (Zavalic et al. 1998c). Both 

blue-yellow and red-green color confusion were significantly increased in printers, but there was no 

significant difference in the prevalence of either type of color confusion between exposed and unexposed 

workers (Zavalic et al. 1998c). 

Color vision impairment was also evaluated in another group of 45 male workers exposed to mean 

concentrations of about 120 ppm toluene (Zavalic et al. 1998b). Color vision was significantly impaired 

in exposed workers compared with unexposed controls. A comparison of color vision assessments made 

on Monday and Wednesday mornings showed no significant difference. This suggests that color vision 

impairment results from chronic rather than acute exposure to toluene. 

Muttray et al. (1995, 1999) also attempted to distinguish between effects on vision due to chronic and 

acute exposure to toluene. Color vision was assessed in 59 male rotogravure workers occupationally 

exposed to unspecified levels of toluene for periods of 1 month to 36 years (mean of 10 years) (Muttray et 

al. 1995). Results of vision testing at the beginning and end of the work week were compared and no 

difference was recorded. A second study compared color vision in eight printers (occupationally exposed 

to toluene) and eight workers previously unexposed to toluene, before and after cleaning a print machine 

with toluene (Muttray et al. 1999). The task took 28–41 minutes and involved exposure to 300–362 ppm 

toluene (1,115–1,358 mg/m3

). No impairment in color vision was recorded for either group. However, a 

comparison of the precleaning performance of the printers with that of a group of matched controls 
TOLUENE 64 

2. HEALTH EFFECTS 

showed a non significant decrease in color vision for the printers, which may indicate a chronic effect of 

toluene exposure on color vision (Muttray et al. 1999). 

Studies of human color vision impairment suggest that vision impairment results from chronic, rather than 

acute, exposure to toluene (Muttray et al. 1995, 1999; Zavalic et al. 1998a, 1998b, 1998c). The 

mechanism by which toluene exposure influences color vision is not known. Visual evoked potentials are 

affected in chronically exposed individuals and show exposure-related changes in amplitude and latency 

(Poblano et al. 1996; Vrca et al. 1995, 1997a, 1997b). However, it is not clear whether the impairment of 

color vision produced by toluene exposure is due solely to neurological damage or also involves damage 

to the eyes. Toluene exposure causes eye irritation in humans (Andersen et al. 1983; Baelum 1990; 

Carpenter et al. 1944; Meulenbelt et al. 1990) and animals (Ono et al. 1976), but no studies were located 

that examined eyes for structural damage due to chronic toluene exposure. 

A number of studies of humans chronically exposed to mixtures of solvents containing toluene provide 

supporting evidence for the neurotoxicity of toluene, but concurrent exposure to other solvents limits the 

conclusions that can be drawn from the results. Painters (100 individuals) exposed to toluene and other 

solvents for 1–40 years had poorer performance on the block design of visual cognitive ability (Hanninen 

et al. 1976). Another study of 325 painters exposed to mixed solvents (including toluene) for an average 

of 5 years found that reduced ability in tests of pattern comparison and memory was correlated with 

solvent-exposure (Tsai et al. 1997). Shoemakers exposed to toluene (20 or 71 ppm) and other solvents for 

more than 10 years showed a significant reduction in the Santa Ana dexterity test and a non significant 

reduction in visual retention (Lee et al. 1998a). Workers exposed to mixed solvents (including toluene) 

during a spraying process showed a significant impairment of color vision with errors of the blue-yellow 

type (Muttray et al. 1997). A study of chronic petrol sniffers found that petrol sniffing was associated 

with neurological and cognitive abnormalities such as tremors, abnormal reflexes, and deficits of visual 

attention and memory (Maruff et al. 1998). However, significant correlations were recorded for the 

magnitude of neurological and cognitive defects and blood lead levels, but not for neurological and 

cognitive defects and blood hydrocarbon levels (Maruff et al. 1998). A group of workers exposed to 

mixed solvents and admitted to the hospital due to suspicion of solvent-induced chronic toxic 

encephalopathy had reduced scores in tests of distorted speech and cortical response audiometry 

compared to unexposed controls (Niklasson et al. 1998). 

In laboratory animals, acute exposure to toluene has both excitatory and depressant effects on the central 

nervous system. A high correlation between the extent of central nervous system depression and brain 
 

TOLUENE 65 

2. HEALTH EFFECTS 

toluene levels was observed in both mice and rats exposed to 2,600–12,000 ppm toluene for varying 

periods of time (Bruckner and Peterson 1981a, 1981b). Acute exposure to toluene concentrations 

between 500 and 15,000 ppm produced an initial increase in locomotor activity in rats and mice followed 

by a decrease in activity with longer exposure (Bowen and Balster 1998; Bushnell et al. 1985; Hinman 

1987). Exposure of mice to 300 ppm for 6, 1-hour exposures with 3–4 days between exposures, had no 

effect on animal movements. Movements were increased at concentrations of 560–1,780 ppm, but were 

decreased at concentrations of 3,000 ppm (Wood and Colotla 1990). This study clearly indicates a 

biphasic response with low-concentration stimulation and high-concentration depression of motor 

activity. 

Monkeys exposed to concentrations of 2,000–4,500 ppm toluene (head only) for 50 minutes on 2 days 

separated by 3 days without exposure, showed significantly increased response time and decreased 

accuracy on a test of conditioned response to a reward stimulus for concentrations (Taylor and Evans 

1985). Exposure to toluene concentrations of 2,000 ppm or less did not cause overt signs of neurological 

impairment such as ataxia and tremors. Exposure to 100 and 200 ppm toluene had no effect on 

performance, but exposure to 500 and 1,000 ppm toluene caused nonsignificant decreases in response 

time and accuracy. 

Exposure to 1,500 ppm toluene 1 hour/day for 14 days produced nystagmus (involuntary movement of 

the eyeballs) in rats with disturbances in the vestibular and opto-oculomotor systems (Larsby et al. 1986). 

These findings suggest that the cerebellum is a target site for toluene, and confirm an earlier report that 

toluene caused nystagmus in rats when arterial blood levels were greater than 75 ppm (Tham et al. 1982). 

In several animal studies, acute toluene exposure diminished the ability of rats to perform trained 

neuromuscular responses. Exposure of rats to 125, 250, or 500 ppm toluene for 4 hours caused a decline 

in lever-press shock avoidance performance 20 minutes after exposure, but recovery was complete 

2 hours later (Kishi et al. 1988). A single 4-hour exposure to concentrations of 810–6,250 ppm toluene 

caused a concentration-related impairment of performance by rats in tests designed to measure 

neuromuscular performance (Mullin and Krivanek 1982). Exposure to $480 ppm toluene for 4 hours 

decreased the ability of trained rats to perform a sequence of lever press actions associated with a reward 

(milk) (Wood et al. 1983). 

In animals, changes in the levels of brain neurotransmitters in rodents exposed to toluene have been 

observed. Significant localized changes in dopamine (DA) or norepinephrine (NE) brain levels were 
TOLUENE 66 

2. HEALTH EFFECTS 

noted in rats exposed to 400 ppm toluene 24 hours/day for 30 days (Ikeda et al. 1986) and in newborn 

male rats 7 weeks after a 10-day exposure to 80 ppm toluene for 6 hours per day (von Euler et al. 1989b). 

Neurotransmitter levels in some areas of the brain were increased, in some areas were decreased, and in 

other areas remained the same. Toluene exposure at 80 ppm for 4 weeks was found to affect dopamine D2 

agonist binding in the rat caudate-putamen (Hillefors-Berglund et al. 1995; von Euler et al. 1993). 

Dopamine levels were increased in the cerebellum and striatum of rats exposed to 1,000– 4,000 ppm 

toluene for 20 minutes, while norepinephrine and 5-hydroxytryptamine were significantly increased in the 

cerebellum and cortex (Kim et al. 1998). Several significant changes in the activities of enzymes 

responsible for neurotransmitter synthesis (glutamic acid decarboxylase, choline acetyltransferase and 

aromatic amino acid decarboxylase) in different areas of the brain were seen in male rats exposed to 

toluene at concentrations of 50–1,000 ppm for 4 weeks or 500 ppm for 12 weeks (Bjornaes and Naalsund 

1988). Concentration-response trends were not apparent in the data and there were variant responses by 

different areas of the brain. There was also some evidence of change in glutamate and gamma amino 

butyric acid (GABA) binding. Binding increased in most of the brain areas studied, but decreased in 

some areas. Because of the variability in response, these data are difficult to evaluate. Von Euler et al. 

(1994) reported that rats exposed to 80 ppm for 6 hours per day for 4 weeks, had increased serum 

prolactin levels. However, no significant changes in serum prolactin levels were reported at 

concentrations up to 320 ppm, also for 4 weeks exposure (Hillefors-Berglund et al. 1995). Exposure to 

400 ppm toluene 7 hour/day for 10 days produced a statistically significant increase in the total 

dehydrogenase activity in the brains of female mice (Courtney et al. 1986). 

Changes in brain levels of glial fibrillary acidic protein (GFAP), a structural marker for astrocytes, have 

been found in toluene-exposed rats. Rats exposed to 1,000 ppm toluene for 3 or 7 days exhibited a 

significant decrease in GFAP levels in the thalamus (Little et al. 1998). Rats exposed to 100–3,000 ppm 

toluene 6 hours/day, 5 days/week for up to 42 days exhibited changes in the concentration of GFAP in the 

cerebellum, hippocampus, and thalamus (API 1997). For the first week of exposure, GFAP concentration 

of exposed animals was significantly increased in the cerebellum and hippocampus, and decreased in the 

thalamus compared with unexposed controls (API 1997). After 21 days, the concentration of GFAP in 

the hippocampus was significantly decreased in rats exposed to 1,000 ppm compared with controls, while 

at 42 days, rats exposed to 300 ppm had significantly higher concentrations of GFAP in the cerebellum 

compared with controls, but rats exposed to 1,000 ppm did not (API 1997). In mice exposed to 

500–2,000 ppm for 8 hours, no significant alterations in c-fos, c-jun, or GFAP mRNA in the cerebrum 

were found (Matsuoka et al. 1997). 
TOLUENE 67 

2. HEALTH EFFECTS 

Rats continuously exposed to toluene at 320 ppm for 30 days had decreased total brain weight and 

decreased weight of the cerebral cortex (Kyrklund et al. 1987). There was a decrease in the total 

phospholipid content of the cerebral cortex accompanied by a small increase in phosphatidic acid levels. 

These data suggest a breakdown of phospholipids resulting in a loss of gray matter (Kyrklund et al. 

1987). The mechanism of action for this effect is uncertain. Increased relative brain weights and ataxia 

in rats were reported after 15-week exposures to toluene at 2,500 and 3,000 ppm 6.5 hours/day, 

5 days/week (NTP 1990). No gross or microscopic tissue changes or changes in brain weights were 

observed in mice exposed to concentrations up to 2,500 ppm for 14 weeks or in rats or mice exposed by 

the same protocol to toluene at concentrations up to 1,200 ppm for 2 years (NTP 1990). 

Animal studies have demonstrated that intermediate exposure to toluene can produce subtle changes in 

the auditory system. Intermediate exposure to toluene produced a permanent loss of hearing in the high 

frequency range (approximately 16 kHz) in rats exposed 14 hours/day to 1,200 ppm for 5–9 weeks or 

1,000 ppm for 2 weeks (Pryor and Rebert 1992; Pryor et al. 1984a, 1984b). The threshold concentration 

for hearing loss was between 700 and 1,000 ppm (Johnson et al. 1988; Pryor et al. 1984b). Hearing loss 

occurred independent of whether or not exposure was continuous or episodic with many short exposures 

during the day (Pryor 1991); it was compounded by postexposure high noise levels (Johnson et al. 1988). 

Lataye and Campo (1997) demonstrated that combined exposure to toluene and noise produced a greater 

loss of hearing function in rats than exposure to toluene alone or noise alone. In another study, hearing 

loss was produced in rats after exposure to 1,750 ppm toluene for 6 hours/day, 5 days/week for 4 weeks 

and loss of hair cells in the organ of corti was observed after exposure to 1,000 ppm (Campo et al. 1997, 

1998). Johnson and Canlon (1994) showed loss of outer hair cells in the cochleae of rats exposed to 

1,400 ppm 14 hours/day for 8 days. Outer hair cell loss was observed after 5 days of exposure, and loss 

progressed to the inner hair cells after 6 weeks postexposure. Pryor et al. (1984a) demonstrated that high 

frequency hearing loss is more severe in weanling rats than in young adult rats, after exposure to 

1,200 ppm for 14 hours/day for 5 weeks. Hearing loss due to toluene exposure was also exacerbated by 

simultaneous treatment with ethanol (Campo et al. 1998) or high doses of acilyl solicylicacid (aspirin) 

(Johnson 1992). 

When rats were preexposed to phenobarbital to stimulate liver metabolism of toluene and then exposed to 

levels of 1,929 ppm 8 hours/day for 1 week, hearing was not affected as measured by the BAER test 

(Pryor et al. 1991). However, rats not pretreated with phenobarbital did experience hearing loss. This 

observation is consistent with the idea that toluene itself, and not one of its metabolites, is responsible for 

the hearing loss. 
TOLUENE 68 

2. HEALTH EFFECTS 

Toluene had more of an effect on hearing loss in mice that had a genetic predisposition for early onset 

spontaneous auditory degeneration than on mice that were predisposed to late onset moderate hearing loss 

(Li et al. 1992). Thus, the severity of toluene-induced hearing loss appears to be influenced by genetic 

susceptibility. 

Impaired motor functions have been observed in animals following repeated exposure to toluene. Daily 

exposure of neonate rats to 10,000, 20,000, or 40,000 ppm toluene for 15 minutes from postpartum days 

2–30 resulted in a concentration-related increase in the time taken for the righting-reflex to occur 

(Lorenzana-Jimenez and Salas 1990). At each concentration, the time taken for the righting-reflex to 

occur decreased over the first 4 weeks of exposure then increased over the last 4 weeks of exposure, but 

did not regain the level of latency observed in the first week of the experiment. These data suggest that 

these animals were developing tolerance to some neurobehavioral effects of toluene. However, it is not 

clear whether this is due to metabolic induction by continued exposure or an age related effect. 

Tilting plane and rotarod test performances did not differ significantly between control rats and rats 

exposed to 1,000 ppm toluene for 8 hours/day, 7 days/week for 13 weeks (Tahti et al. 1983). Rats 

exposed to 2,500 ppm toluene 7 hours/day for 5 weeks showed a lack of coordination (Von Oettingen et 

al. 1942). Exposure of rats to concentrations of 2,273 ppm 8 hours per day for 16 weeks or to 

2,200–6,200 ppm intermittently (8 hours/day, 15–60 minutes/hour) for 23 weeks caused a shortening and 

widening of the gait (Pryor 1991). Increased nose-poking was reported in rats exposed to 178–300 ppm 

toluene for 3 weeks (2 times/week, 2 hours/day) (Wood and Cox 1995). Latency of escape from an 

electric shock was reduced in both young rats (50 days old) and older rats (120 days old) exposed to 

30,000–40,000 ppm toluene for 15 minutes/day for 30 days (Castilla-Serna et al. 1991). Exposure of 

male weanling rats (23 days old) to 1,200 ppm 14 hours/day for 9 weeks produced a significant reduction 

in a tone-induced multisensory conditioned avoidance response (Pryor and Rebert 1992). 

Circadian rhythms apparently have an effect on toluene metabolism and, thus, on its neurological effects. 

Rats that were exposed to 4,000 ppm toluene for 4 hours during daylight demonstrated poorer shock 

avoidance than animals exposed during the dark (Harabuchi et al. 1993). There was a correlation of 

shock avoidance with toluene levels in the brain; the higher the brain toluene level, the poorer the ability 

of the animal to properly respond to stimuli and press the lever that prevented the electrical shock. 

Flash evoked potential (FEP) responses were abnormal in rats exposed to single 30-minute exposures to 

500–16,000 ppm toluene (Rebert et al. 1989a, 1989b) or 15 to 35 minute exposures to 8,000 ppm, 
TOLUENE 69 

2. HEALTH EFFECTS 

4–9 times/day, 5 days/week for 13 weeks (Mattsson et al. 1990). This technique measures the electrical 

response of the visual components of the nervous system to a high intensity flashing strobe light. 

Distortion of the FEP waveform is indicative of impaired visual response to light. In both the acute and 

subchronic testing situations, the toluene caused changes in the amplitude of several components of the 

FEP waveform, suggesting that impaired visual response can result from both short and long term 

exposure to high concentrations of toluene. 

Toluene exposure also changes sleep patterns in animals. Both single 4- or 8-hour episodes of toluene 

exposure (900–4,000 ppm) and repeated exposures, 8 hour/day for 3 weeks (900 and 2,700 ppm), 

changed patterns of sleep and wakefulness in rats (Arito et al. 1988; Takeuchi and Hisanaga 1977). After 

the single exposures, there was a decrease in wakefulness and an increase in slow-wave sleep; a 

prolonged sleep latency was apparent for the 2 days following exposure. Latency was defined as the time 

interval between the end of the exposure period and the beginning of a particular phase of the sleep cycle. 

Following the 3-week exposures, there was an increase in wakefulness during the dark period on the 

2 days after exposure and a decrease in slow wave sleep on the first day. Exposure to concentrations of 

100–700 ppm for 2 hours increased the duration of the wake cycle and decreased both rapid-eye 

movement and nonrapid eye movement sleep in a concentration-related fashion in young and adult male 

rats (Ghosh et al. 1989, 1990). 

Toluene may affect memory in rats. Rats exposed to 600 ppm toluene for 50 days, starting at 23 days old, 

were trained in a radial-arm maze and their performance was compared with air-exposed control animals. 

No significant effects were observed for working memory errors (reentries into “already-entered” areas) 

(Miyagawa et al. 1995). However, rats exposed to 1,600 or 3,200 ppm toluene for 4 hours showed a 

concentration-related decrease in accuracy in a neurological test of short-term memory (Miyagawa et al. 

1998). Exposure to 1,500 ppm toluene 6 hours/day, 5 days/week for 6 months followed by a 4-month 

exposure-free period was found to reduce the number of neurons in the rat hippocampus, an important 

area in the brain for memory and learning processes (Korbo et al. 1996). 

The highest NOAEL values and all LOAEL values for each reliable study for neurological effects in each 

species and duration category are recorded in Table 2-1 and plotted in Figure 2-1. 
TOLUENE 70 

2. HEALTH EFFECTS 

2.2.1.5 Reproductive Effects 

Current data do not provide convincing evidence that toluene causes reproductive effects in humans. 

Reports that occupational exposure to toluene may lead to an increased incidence of spontaneous abortion 

(Ng et al. 1992b; Taskinen et al. 1989) have not been supported by the results of animal testing. Studies 

in rats have shown no evidence of adverse effects on mating or fertility (API 1985; NTP 1990; Ono et al. 

1996). Toluene exposure produced microscopic changes in ovarian structure and a reduction in sperm 

count and the weight of epididymides in rats (Ono et al. 1996; Tap et al. 1996). However, changes in 

sperm count and epididymus weight were not accompanied by any change in indices of reproductive 

performance (Ono et al. 1996). 

Ng et al. (1992b) reported a significant increase in spontaneous abortion for women employed in an audio 

speaker factory and exposed to 50–150 ppm (mean of 88 ppm) for 10 years (12.4%), compared with 

controls exposed to 0–25 ppm toluene from the same factory (2.9%) and unexposed controls from the 

general population (4.5%). The majority of women examined did not smoke or drink and were of similar 

socioeconomic status (Ng et al. 1992b). Exposed workers did not report increased incidence for 

menstrual cycle irregularities, altered extent of uterine bleeding, or occurrence of dysmenorrhea (Ng et al. 

1992a). Other possible confounding factors such as exposure to chemicals other than toluene were 

minimized by inclusion of controls who carried out similar types of work, but did not use toluene-based 

adhesives (Ng et al. 1992b). 

The incidence of spontaneous abortions exceeded population norms among 5 female workers (Lindbohm 

et al. 1992) and among the wives of 28 or 48 male workers (Lindbohm et al. 1992; Taskinen et al. 1989) 

exposed to toluene; however, exposure levels were not reported in these studies and only a small number 

of cases were included. A study of time to pregnancy among the wives of 316 men occupationally 

exposed to mixed organic solvents found that paternal exposure to organic solvents was significantly 

correlated with decreased fecundability of primagravida, but not among couples with at least one previous 

pregnancy (Sallmen et al. 1998). The significance of these studies is limited by the failure to account for 

the large number of possible confounding factors such as smoking, alcohol consumption, and exposure to 

mixed chemicals. 

Changes in human gonadotropic hormone levels have been associated with toluene exposure. A single 

case report of testicular atrophy involving chronic solvent abuse was located (Suzuki et al. 1983). 

Exposure to increasing concentrations of toluene (8–<111 ppm) was associated with decreased plasma 
TOLUENE 71 

2. HEALTH EFFECTS 

levels of the luteinizing hormone, follicular stimulating hormone, and testosterone levels in 20 or 

47 males occupationally exposed for 0.5–39 years to average toluene concentrations of 36 or 29 ppm 

(Svensson et al. 1992a, 1992b). It is not clear how changes of this sort would affect reproductive success. 

Interpretation of these data is complicated by the lack of data on male reproductive function. It is 

generally considered that effects of this sort may be the result of effects of toluene on the catecholamine 

hormones of the hypothalamus or a consequence of toluene or a metabolite having a dopamine-like 

activity. Thus, it appears that any potential toluene-induced hormonal effects on reproductive success 

which may occur may be secondary to effects on the central nervous system. 

Significantly decreased sperm counts (26%) and decreased weights of the epididymides (15%) were 

reported in male rats exposed to 2,000 ppm 6 hours/day for a total of 90 days, including 60 days before 

mating to females that were exposed for 14 days before and 7 days after mating (Ono et al. 1996). A 

slight decrease in sperm count (13%) was also observed at 600 ppm, but histological examination of the 

testes and epididymes found no abnormalities at either concentration. No significant exposure-related 

effects on mating behavior or fertility indices were found in this study (Ono et al. 1996). Exposure of 

female rats to 3,000 ppm toluene for 7 days produced abundant vacuoles, lytic areas, and mitochondrial 

degeneration in the antral follicles of the ovaries (Tap et al. 1996). 

The administration of toluene to male mice at concentrations of 100 or 400 ppm for 8 weeks did not 

induce dominant lethal mutations or cause pre- and postimplantation losses (API 1981). There were no 

treatment-related histopathological lesions in the testes of rats and mice exposed to up to 3,000 ppm 

toluene for 14–15 weeks although rats showed a 15% increase in testis weight (NTP 1990). Similarly, 

toluene did not cause histopathological lesions of the ovaries or testes in rats exposed to toluene 

(300 ppm) for 24 months (CIIT 1980) or in rats and mice at concentrations of 1,200 ppm for 2 years (NTP 

1990). Continuous exposure of pregnant rabbits to 267 ppm during days 7–20 of pregnancy produced 

maternal toxicity (decreased weight gain) and abortions in 4/8 does, but no effect was observed with 

exposure to 133 ppm (Ungvary and Tatrai 1985). Exposure of mice to 267 ppm, 3–4 hours/day on days 

6–15 of gestation produced no increase in fetal mortality (Ungvary and Tatrai 1985). 

In 2-generation reproduction studies in rats, exposure to 2,000 ppm 6 hours/day for up to 95 days did not 

adversely affect reproductive parameters or offspring survival compared with unexposed controls (API 

1985). Another rat study found no effects on mating, fertility, or pregnancy indices for F1 rats that had 

been exposed in utero to 1,200 ppm toluene for 6 hours/day during gestation days 9–21 (Thiel and 

Chahoud 1997). 
TOLUENE 72 

2. HEALTH EFFECTS 

The highest NOAEL values and all LOAEL values for each reliable study for reproductive effects in each 

species and duration category are recorded in Table 2-1 and plotted in Figure 2-1. 

2.2.1.6 Developmental Effects 

Case reports of birth defects in children of mothers who abused toluene during pregnancy and a report of 

nervous system defects in Finnish women exposed to mixed solvents in their workplace suggest that 

exposure to high levels of toluene may be toxic to the developing fetus, but cannot support definitive 

conclusions because of the lack of exposure data and the inability to adjust for confounding exposures to 

other potential developmental toxicants. 

A retrospective study of 14 women in Finland occupationally exposed to mixed solvents, some of which 

included toluene, and also exposed to various drugs including aspirin, vasodilators, and diuretics 

suggested that solvent exposure may increase the risk of central nervous system anomalies and defects of 

neural tube closure in children exposed in utero (Holmberg 1979). However, the sample size was too 

small to be truly meaningful. 

Microcephaly, central nervous system dysfunction, attentional deficits, minor craniofacial and limb 

anomalies, developmental delay, and variable growth have been described in case reports of children who 

were exposed to toluene in utero as a result of maternal solvent abuse during pregnancy (Arnold and 

Wilkins-Haug 1990; Arnold et al. 1994; Hersh 1988; Hersh et al. 1985; Lindemann 1991; Pearson et al. 

1994; Wilkins-Haug and Gabow 1991a). Growth retardation and dysmorphism were reported in five 

infants born to women who were chronic paint sniffers (Goodwin 1988). 

Children born to toluene abusers have exhibited renal tubular acidosis immediately after birth that is 

thought to be due to alterations in ion gradient maintenance in the renal tubules. The kidney effects are 

often associated with hyperchloremia (Erramouspe et al. 1996; Goodwin 1988; Lindemann 1991). In one 

report (Goodwin 1988) the acidosis was resolved within 3 days of birth, while in the other two reports, it 

took about 2 weeks for the resolution of the metabolic acidosis. There were no abnormalities in the 

urinary tract of two children born to chronic toluene abusers based on results of a renal ultrasound 

evaluation (Hersh 1988). 

A number of developmental toxicity studies with rats, mice, and rabbits involving toluene exposure 

during gestation have been conducted to further describe developmentally toxic effects from toluene and 
TOLUENE 73 

2. HEALTH EFFECTS 

exposure-response relationships. In general, the results indicate that toluene is not a potent teratogenic 

agent at exposure levels below those inducing maternal toxicity, but can retard fetal growth and skeletal 

development and alter development of behavior in offspring. 

In pregnant rats exposed to 399 ppm, 24 hours/day on gestation days 1–8 or 9–14, no statistically 

significantly increased incidences of fetuses with visceral or skeletal malformations were found (Hudak 

and Ungvary 1978). However, 5/14 dams died, fetal body weight was decreased, and retardation of fetal 

skeletal development occurred with the days 1–8 exposure protocol, and 2/21 dams died and increased 

incidence of skeletal anomalies (extra ribs, fused sternebrae) were found with the days 9–14 protocol 

(Hudak and Ungvary 1978). No maternal mortality, fetal weight loss, or fetal malformations were found 

in another group of rats exposed to 266 ppm, 8 hours/day on gestation days 1–21, but significantly 

increased incidence of fetuses with skeletal retardation occurred (Hudak and Ungvary 1978). In other 

groups of rats exposed to 250, 750, 1,500, or 3,000 ppm, 6 hours/day on gestation days 6–15, no effects 

were found on maternal or fetal survival, but mean fetal body weights were significantly decreased by 

about 8–14% at 1,500 and 3,000 ppm and the percentage of fetuses with unossified sternebrae was 

significantly increased at 3000 ppm (60 versus 37% in controls) (Huntingdon Research Centre 1992b). 

Incidences of fetuses or litters with skeletal or visceral malformations were slightly increased to a 

statistically significant extent in the 250-, 1,500-, and 3,000-ppm groups, but the response did not increase 

with exposure level, indicating that it was not exposure-related (Huntingdon Research Centre 1992b). A 

preliminary gestational exposure study that did not include comprehensive examination for skeletal and 

visceral fetal variations and malformations found extreme maternal toxicity and marked resorption of 

fetuses in pregnant rats exposed to 5,000 ppm 6 hours/day on gestation days 6–15, and significantly 

decreased mean fetal body weight in a 3,500-ppm exposed group (by about 20% compared with controls) 

(Huntingdon Research Centre 1992a). No statistically significant effects on maternal or fetal survival, 

implantation, numbers or incidences of fetuses or litters with skeletal or visceral malformations, 

anomalies, or variations were found in pregnant rats exposed to 600 or 2,000 ppm, 6 hours/day on 

gestation days 7–17, but maternal and fetal body weights were reduced in the 2,000 ppm group compared 

with controls (Ono et al. 1995). Offspring of rats exposed to 1,200 ppm toluene, 6 hours/day on gestation 

days 9–21 showed a significant reduction in fetal weight, a delay in physical development (vaginal 

opening) and higher mortality until weaning compared to unexposed controls (Thiel and Chahoud 1997). 

Rats exposed to 1,000 ppm, 6 hours/day on gestation days 9–21 also had significantly reduced body 

weights at birth and developmental delay, but no effect on fetal weight or development was recorded for 

rats exposed to 300 or 600 ppm. 
TOLUENE 74 

2. HEALTH EFFECTS 

In mice exposed to 133 ppm, 24 hours/day on gestation days 6–13, no effects on maternal survival or 

incidences of fetuses with malformations were found, but fetal body weight was significantly decreased 

(Hudak and Ungvary 1978). All 15 pregnant mice died that were exposed to 399 ppm, 24 hours/day on 

gestation days 6–13 (Hudak and Ungvary 1978). Exposure of pregnant mice to 133 or 266 ppm, 

3–4 hours/day on gestation days 6–15, did not significantly affect maternal or fetal survival, or incidences 

of fetuses with visceral or skeletal anomalies or malformations, but, in the group exposed to 266 ppm, 

incidences of fetuses with decreased body weight and skeletal retardations were significantly increased 

(Ungvary and Tatrai 1985). Other groups of pregnant mice exposed to 200 or 400 ppm, 7 hours/day on 

gestation days 7–16 showed no statistically significant differences from controls in maternal or fetal 

survival, maternal or fetal body weights, and the number of implantation sites or live fetuses (Courtney et 

al. 1986). Significantly increased incidence of fetuses or litters with visceral or skeletal anomalies or 

malformations were restricted to increased litters with fetuses with enlarged renal pelves in the 200-ppm 

group (but not in the 400-ppm group) and a difference in the distribution of fetuses with varying numbers 

of ribs in the 400-ppm group compared with the control group. Courtney et al. (1986) suggested that 

these effects may be due to toluene-induced “desynchronization of growth and maturation” of the 

developing fetus. Offspring, evaluated 21 days after birth, of a separate group of pregnant mice exposed 

to 400 ppm toluene by the same protocol showed no significant differences from control offspring in 

body or organ weights or activities of lactate dehydrogenase in several tissues, except that brain activities 

of this enzyme were elevated (Courtney et al. 1986). 

In rabbits exposed to 133 ppm, 24 hours/day on gestation days 7–20, no significant effects were found on 

maternal or fetal survival, fetal body weight, or incidences of fetuses with skeletal retardation, minor 

anomalies, or skeletal or visceral malformations (Ungvary and Tatrai 1985). Following exposure to 

266 ppm by the same protocol, 2/8 dams died, 4/8 dams aborted, and no live fetuses were found at 

sacrifice (Ungvary and Tatrai 1985). In other groups of rabbits exposed to 30, 100, 300, or 500 ppm, 

6 hours/day on gestation day 6–18, no signs of maternal toxicity occurred and no significant effects, 

compared with controls, were found on fetal weight or survival, pre- or postimplantation losses, or 

incidences of fetuses with external, soft-tissue, or skeletal variations or malformations (Klimisch et al. 

1992). 

Results from studies of neurobehavioral end points in rats following in utero exposure to toluene suggest 

that maternal exposure to concentrations above 1,200 ppm, 6 hours/day during late embryonic and fetal 

development can impair behavioral development of rat offspring. Rat pups, that were evaluated on 

postnatal days 1–20 and whose mothers were exposed to 2,000 ppm for 60 minutes, 3 times/day on 
TOLUENE 75 

2. HEALTH EFFECTS 

gestation days 12–17, gained less weight and displayed significant performance deficits in 

neurobehavioral tests of reflex development, muscle strength, and motor coordination (Jones and Balster 

1997). These effects were not observed in offspring of dams exposed to 200 or 400 ppm by the same 

protocol (Jones and Balster 1997). Rat offspring of dams exposed to 600 or 2,000 ppm, 6 hours/day on 

gestation days 7–17 showed no significant differences from control rats in tests of reflexes, locomotor 

activity, balance on a rotating rod, learning ability, or in physical development (e.g., eye opening) during 

the first 5 days after birth (Ono et al. 1995). No consistent and concentration-dependent performance 

deficits were found in tests of reflexes, balance on a rotating rod, locomotor activity, or discrimination 

learning in rat offspring, evaluated at several ages, of dams exposed to 300, 600, 1,000, or 1,200 ppm, 

6 hours/day on gestation days 9–21 compared with controls (Thiel and Chahoud 1997). 

In groups of rat pups exposed to toluene (100 or 500 ppm, 12 hours/day) from postnatal days 1–28, the 

volumes of the granular cell layer of the area dentate of the hippocampus were smaller (6 and 13%, 

respectively) compared to unexposed controls (Slomianka et al. 1990). However, when animals in the 

500 ppm group were allowed to recover for 92 days after exposure ceased, these effects were reversible 

(Slomianka et al. 1992). The authors attributed this response to desynchronization in growth and 

maturation. 

The highest NOAEL values and all LOAEL values for each reliable study for developmental effects in 

each species and duration category are recorded in Table 2-1 and plotted in Figure 2-1. 

2.2.1.7 Genotoxic Effects 

Human data are inconclusive with regard to the genotoxicity of toluene. Studies of exposed workers are 

limited by concurrent exposure to other chemicals, small cohort size, and a lack of historical exposure 

monitoring, and it is likely that they are not sufficiently sensitive to detect small, but significant, 

manifestations of genetic toxicity in toluene exposed workers. Genotoxicity testing of laboratory animals 

in vivo has been limited and has produced mostly negative results. Negative results were also reported in 

the in vitro studies discussed in Section 2.5. 

An analysis of chromosome abnormalities in peripheral lymphocytes of printers exposed to 104 to 

1,170 ppm toluene and unexposed workers from the same and nearby sites found an increase in 

chromosome breaks and aberrant cells in lymphocytes of exposed workers (Pelclová et al. 1990). 

Hammer et al. (1998) reported a concentration-related increase in sister chromatid exchange in 
TOLUENE 76 

2. HEALTH EFFECTS 

lymphocytes of printers exposed to 141–328 mg/m3 (38–87 ppm) airborne toluene (measured by personal 

monitor). Chromosome analysis of lymphocytes of workers exposed to 200–300 ppm toluene in a 

rotogravure printing plant found a significantly increased frequency of sister chromatid exchanges and 

chromatid breaks compared to unexposed controls (Bauchinger et al. 1982). Re-examination of workers 

from the same plant after cessation of exposure to toluene found that more than 2 years without exposure 

was necessary to remove a significantly higher incidence of chromatid-aberrations in workers than in 

never-exposed controls (Schmid et al. 1985). Lymphocytes from printers exposed to a median timeweighted air level of 150 mg/m3

 (40 ppm) toluene per week were found to be significantly more sensitive 

to the production of micronuclei after stimulation with pokeweed mitogen than lymphocytes from 

unexposed controls (Nise et al. 1991). 

A study of DNA damage in Bulgarian shoe workers exposed to factory air containing 96.0–412.3 mg/m3 

toluene (28–121 ppm) found no exposure related differences in DNA damage in leukocytes as assessed 

by the Comet assay (Pitarque et al. 1999). Toluene did not induce sister chromatid exchanges in 

lymphocytes of volunteers exposed to 50 ppm airborne toluene for 7 hours/day for 3 days on 3 occasions 

at 2 week intervals (Richer et al. 1993). Other investigators have also found no correlation between 

chronic occupational exposure to toluene and increased frequencies of either chromosome aberrations 

(Haglund et al. 1980; Maki-Paakkanen et al. 1980) or sister chromatid exchanges (Haglund et al. 1980). 

In vivo tests of toluene in laboratory animals have produced mixed results. Exposure to toluene vapor 

induced mitotic arrest (C-mitosis) in embryos of the grasshopper, Melanoplus sanguinipes (Liang et al. 

1983). Toluene was reported to induce chromosomal aberrations in the bone marrow cells of rats 

following exposure by inhalation (Dobrokhotov and Enikeev 1977). Toluene did not induce DNA 

damage in the blood, bone marrow, or liver of mice exposed to 500 ppm toluene for 6 hours/day, 

5 days/week for eight weeks (Plappert et al. 1994). Toluene did not induce dominant lethal mutations in 

sperm cell of mice exposed to 400 ppm for 6 hours/day, 5 days/week for 8 weeks, but female mice were 

not assessed for genotoxic effects (API 1981). Other genotoxicity studies are discussed in Section 2.5. 

2.2.1.8 Cancer 

Eleven human epidemiology studies were located that assessed toluene exposure as a possible risk factor 

for cancer. Cancers of most sites were not significantly associated with toluene exposure in any study 

and there was weak consistency in the findings of those studies that did find association of a particular 

cancer type with toluene exposure. Three cohort studies involved occupationally exposed workers 
TOLUENE 77 

2. HEALTH EFFECTS 

exposed predominantly to toluene (Antilla et al. 1998; Svensson et al. 1990; Walker et al. 1993), whereas 

the remainder of the human studies primarily involved subjects exposed to mixtures of solvents including 

toluene (Austin and Schnatter 1983; Blair et al. 1998; Carpenter et al. 1988; Gérin et al. 1998; Lundberg 

and Milatou-Smith 1998; Olsson and Brand 1980; Wen et al. 1985; Wilcosky et al. 1984). The 

information from these studies is inadequate to assess the carcinogenic potential of toluene, 

predominantly because of the lack of consistent findings across the studies and the likelihood that many 

of the studied groups were exposed to multiple chemicals. 

Svensson et al. (1990) compared cancer incidence and mortality in a cohort of Swedish printers, exposed 

primarily to toluene and employed for at least 3 months between 1925 and 1985, to mortality and cancer 

incidence for the region. Current and historical monitoring data were used to estimate yearly average 

concentrations of toluene in the air. Concentrations had declined from about 450 ppm in the 1940s to 

30 ppm by the mid-1980s. There were indications of excess risk of morbidity (standardized incidence 

ratio, SIR) and mortality (standardized morbidity ratios, SMR) for respiratory tract cancer (SMR, 1.4; 

95% CI, 0.7–2.5; n=11; SIR, 1.8; 95% CI, 1.0–2.9; n=16), stomach cancer (SMR, 2.7; 95% CI, 1.1–5.6; 

n=7; SIR, 2.3; 95% CI, 0.9–4.8; n=7) and colo-rectal cancer (SMR, 2.2; 95% CI, 0.9–4.5; n=7; SIR, 1.5; 

95% CI, 0.7–2.8; n=9), but there was no significant association between increased risk and cumulative 

exposure. 

Walker et al. (1993) conducted a cohort mortality study among 7,814 shoe-manufacturing workers 

(2,529 men and 5,285 women) from two plants in Ohio in operation since the 1930s. Workers were 

exposed to solvents and solvent-based adhesives. Based on results of a hygiene survey (1977–1979), 

exposure was thought to be primarily to toluene (10–72 ppm), but other chemicals (e.g., 2-butanone, 

acetone, and hexane) were also recorded at similar concentrations. IARC (1999) noted that benzene may 

have been present as an impurity of toluene. Mortality follow up was from 1940 to 1982 and relative risk 

estimates (SMRs) were derived using the general population of the United States as controls. There were 

excess risks of lung cancer for both men (SMR, 1.6; 95% CI, 1.2–2.0; n=68) and women (SMR, 1.3; 95% 

CI, 0.9–1.9; n=31), but smoking may have been a confounding factor and relative risk of lung cancer did 

not increase with increasing duration of employment. There was a slight excess risk for colon cancer 

among men (SMR, 1.3; 95% CI, 0.8–2.1; n=18) and women (SMR, 1.2; 95% CI, 0.8–1.8; n=28). Other 

cancers showed no excess risk. 

Antilla et al. (1998) carried out a retrospective cohort analysis of 5,301 workers (3,922 male and 

1,379 female) monitored for biological markers of occupational exposure to styrene, toluene or xylene 
TOLUENE 78 

2. HEALTH EFFECTS 

over the period 1973–1992. No increase in overall cancer risk or risk for cancers at specific tissue sites 

was associated with exposure to toluene, except for a non significant increase in the incidence of lung 

cancer in individuals exposed to toluene for more than 10 years (SIR, 1.62; 95% CI, 0.33–4.73; 3 cases). 

Antilla et al. (1998) noted, however, that these workers may also have been exposed to benzene. 

Many of the other human epidemiological cancer studies showed positive associations between exposure 

to toluene and cancer at one or more tissue site, but individuals were exposed to multiple chemicals in all 

of these studies (Austin and Schnatter 1983; Blair et al. 1998; Carpenter et al. 1988; Gérin et al. 1998; 

Lundberg and Milatou-Smith 1998; Olsson and Brandt 1980; Wen et al. 1985; Wilcosky et al. 1984). 

Nested case-control studies included studies of prostate and brain cancer within cohorts of Texas 

petrochemical plant workers (Austin and Schnatter 1983; Wen et al. 1985), of lung cancer, stomach 

cancer, and leukemia among U.S. rubber workers (Wilcosky et al. 1984), cancer of the central nervous 

system among a group of Tennessee nuclear facility workers (Carpenter et al. 1988), prostate cancer and 

multiple myeloma among Swedish paint industry workers (Lundberg and Milatou-Smith 1998), and 

multiple myeloma, nonHodgkin’s lymphoma, and breast cancer among aircraft maintenance facility 

workers (Blair et al. 1998). Community-based case-control studies examined possible associations 

between Hodgkin’s disease in Swedish patients and controls (Olsson and Brandt 1980) and several cancer 

types in Canadian patients and controls (Gérin et al. 1998). 

Inhalation cancer bioassays carried out in experimental animals have produced no evidence to support 

toluene as a potential carcinogen. No increased incidences of treatment-related neoplastic lesions were 

observed in Fischer 344 rats or B6C3F1 mice exposed to toluene concentrations up to 1,200 ppm for 

6.5 hours/day, 5 days/week for 2 years (NTP 1990). Similar results were reported for another study in 

which Fischer 344 rats were exposed to toluene concentrations up to 300 ppm 6 hours/day, 5 days/week 

for 2 years, but the maximum exposure concentration in this study was likely below that necessary to 

approach a maximum tolerated dose (CIIT 1980). The NTP (1990) study was well conducted, achieved 

the maximum tolerated dose, and provides evidence suggesting a lack of carcinogenicity of toluene in 

experimental animals. 

2.2.2 Oral Exposure 

Studies of the effects of oral exposure to toluene are limited. Only one study was located regarding health 

effects in humans after oral exposure to toluene and there are only a minimal number of animal studies. 
TOLUENE 79 

2. HEALTH EFFECTS 

2.2.2.1 Death 

Ingestion of approximately 60 mL (625 mg/kg) of toluene proved fatal for a 51-year old male (Ameno 

et al. 1989). Death occurred within 30 minutes of ingestion. The autopsy results revealed constriction 

and necrosis of the myocardial fibers, a markedly swollen liver, congestion and hemorrhage of the lungs, 

and acute tubular kidney necrosis. The probable cause of death was determined to be severe depression 

of central nervous system function. 

The limited number of studies on the acute oral toxicity of toluene in animals have focused on lethal 

effects. The acute oral LD50 of toluene in adult rats ranged from 5.5 to 7.4 g/kg (Kimura et al. 1971; 

Smyth et al. 1969; Withey and Hall 1975; Wolf et al. 1956). Age may play a role in determining the 

lethal dose for toluene. The LD50 value for 14-day-old rats was 3.0 g/kg, which is markedly lower than 

the adult values (Kimura et al. 1971). 

Mice were more sensitive than rats to the lethal effects of toluene in 13-week gavage studies. All rats and 

mice that received 5,000 mg/kg died within the first week. Mortality was also high for groups receiving 

2,500 mg/kg with eight out of ten male rats, one out of ten female rats, and with four out of ten male and 

female mice dying before the end of the study. A dose of 1,250 mg/kg/day was lethal in 10% of female 

mice but no deaths occurred in male mice or in rats of either sex (NTP 1990). LOAEL values from each 

reliable study for death in each species and duration category are recorded in Table 2-2 and plotted in 

Figure 2-2. 

2.2.2.2 Systemic Effects 

Human data pertaining to the systemic effects of oral exposure to toluene are limited to two case studies 

(Ameno et al. 1989; Einav et al. 1997). Animal data are also limited, but include cardiovascular, 

hematological, hepatic, and renal effects in animals exposed orally to toluene at dosage levels up to 

2,500 mg/kg/day for 13 weeks, or 590 mg/kg/day for 6 months (Hsieh et al. 1989; NTP 1990; Wolf et al. 

1956). Exposure of rats or mice to toluene doses #2,500 mg/kg/day for 13 weeks was not found to 

produce any musculoskeletal, gastrointestinal or respiratory effects (NTP 1990). All systemic effects are 

discussed below. The highest NOAEL values and all LOAEL values from each reliable study for 

systemic effects in each species and duration category are recorded in Table 2-2 and plotted in Figure 2-2. 










 

 

 

 

TOLUENE 90 

2. HEALTH EFFECTS 

Respiratory Effects. Except for lung congestion and hemorrhage in one case report involving 

lethality (Ameno et al. 1989), no studies were located regarding respiratory effects in humans after oral 

exposure to toluene. 

No respiratory effects were reported in mice or rats after oral exposure to toluene at dosage levels up to 

2,500 mg/kg/day for 13 weeks (NTP 1990) or 650 mg/kg/day for 6 months (Wolf et al. 1956). 

Cardiovascular Effects. One case study involving lethality in humans reported necrosis of 

myocardial fibers after oral exposure to 625 mg/kg toluene (Ameno et al. 1989). Severe sinus 

bradycardia was reported in a man who accidently ingested 30 mL of an organic solvent containing 

toluene and other chemicals, the patient was drowsy and complained of dizziness and gastric pain (Einav 

et al. 1997). 

Increased relative heart weights were noted in rats exposed to toluene at 1,250 mg/kg/day for 13 weeks 

and myocardial degeneration was present in mice exposed to 5,000 mg/kg/day (NTP 1990). All of the 

mice receiving 5,000 mg/kg/day died during the first weeks of exposure. No effects on the weight or 

gross morphology of the heart were noted in rats receiving 590 mg/kg/day for 6 months (Wolf et al. 

1956). 

Gastrointestinal Effects. A case report in humans did not reveal gastrointestinal effects even after 

oral exposure to a lethal dose of toluene (Ameno et al. 1989). 

No gastrointestinal effects were reported in mice or rats after oral exposure to toluene at dosage levels up 

to 2,500 mg/kg/day for 13 weeks (NTP 1990). 

Hematological Effects. No studies were located regarding hematological effects in humans after 

oral exposure to toluene. 

There were no changes in total erythrocytes in male mice administered 5–105 mg/kg/day toluene in their 

drinking water for 28 days, although there was a nonsignificant decrease in the concentrations of 

leukocytes, lymphocytes, and neutrophils (Hsieh et al. 1989). No effect on erythrocyte counts, leukocyte 

counts, or hemoglobin concentrations resulted in rats exposed to 590 mg/kg/day for 6 months (Wolf et al. 

1956). Neither rats nor mice given doses of 312–2,500 mg/kg/day for 13 weeks displayed any 

compound-related differences in hematological parameters (NTP 1990). 
 

 

 

TOLUENE 91 

2. HEALTH EFFECTS 

Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans after 

oral exposure to toluene. 

No musculoskeletal effects were reported in mice or rats after oral exposure to toluene at dosage levels up 

to 2,500 mg/kg/day for 13 weeks (NTP 1990). 

Hepatic Effects. The liver of an adult male who died from toluene ingestion (625 mg/kg) was found 

to be enlarged on autopsy (Ameno et al. 1989). 

In mice, there was a significant increase in liver weight after 28 days of ingestion of 105 mg/kg/day 

toluene in drinking water, but not at doses of 22 mg/kg/day or lower (Hsieh et al. 1989). Relative liver 

weights increased significantly over control levels in mice administered toluene by gavage for 13 weeks 

with doses of 312 mg/kg/day and greater in females and 1,250 mg/kg/day and greater in males (NTP 

1990). In female rats, the liver weights were increased by exposure to doses of 1,250 mg/kg/day or 

greater and in male rats by exposure to doses of 625 mg/kg/day or greater. No treatment-related gross or 

histopathological lesions of the liver were reported (NTP 1990). When rats were exposed for a longer 

duration, liver weights were not affected and there were no treatment-related lesions in rats that received 

590 mg/kg/day toluene by gavage for 6 months (Wolf et al. 1956). 

Renal Effects. Data in humans are limited to one case report noting acute tubular necrosis after a 

lethal exposure to 625 mg/kg (Ameno et al. 1989) and acidosis in another nonlethal case report of thinner 

consumption (Caravati and Bjerk 1997). 

There were no changes in kidney weight for male mice administered doses from 5 to 105 mg/kg/day in 

drinking water for 28 days (Hsieh et al. 1989), or in female mice given doses of 312–2,500 mg/kg/day by 

gavage for 13 weeks (NTP 1990). There was a significant decrease in the absolute kidney weight for 

male mice administered 2,500 mg/kg/day for 13 weeks but no change in the relative kidney weight (NTP 

1990). There were significant increases in the relative kidney weights in male rats administered toluene 

doses of 625 mg/kg/day or greater by gavage for 13 weeks and in females administered doses of 

1,250 mg/kg/day (NTP 1990). In addition, lethal exposures of the rats to 5,000 mg/kg/day resulted in 

hemorrhages of the urinary bladder. No effects on the weight or gross morphology of the kidney were 

recorded for rats receiving 590 mg/kg/day toluene for months (Wolf et al. 1956). 
 

 

 

 

TOLUENE 92 

2. HEALTH EFFECTS 

Endocrine Effects. No studies were located regarding endocrine effects in humans after oral 

exposure to toluene. 

Microscopic examination revealed no effects on the adrenal or thyroid glands in rats and mice 

administered 312–2,500 mg/kg/day toluene by gavage for 13 weeks (NTP 1990). 

Dermal Effects. No studies were located regarding dermal effects in humans or animals after oral 

exposure to toluene. 

Ocular Effects. No studies were located regarding ocular effects in humans or animals after oral 

exposure to toluene. 

Body Weight Effects. No studies were located regarding body weight effects in humans after oral 

exposure to toluene. 

There were no changes in body weight for male mice administered 5–105 mg/kg/day toluene in their 

drinking water for 28 days (Hsieh et al. 1989, 1990b). There was also no significant difference in body 

weights for female rats and female mice given gavage doses of up to 2,500 mg/kg/day for 13 weeks. 

However, body weights were 16% lower in male mice given 1,250 mg/kg/day and 19% lower in male rats 

given 2,500 mg/kg/day by gavage for 13 weeks (NTP 1990). Maternal weight gain was 24% lower in rats 

given 520 mg/kg/day toluene by gavage during gestation days 6–19, compared with control rats (Gospe et 

al. 1994). 

2.2.2.3 Immunological and Lymphoreticular Effects 

No studies were located regarding immunological effects in humans after oral exposure to toluene. 

Thymus weights, mixed lymphocyte culture responses, and antibody plaque-forming cell responses were 

decreased in male mice administered doses of 105 mg/kg/day in their drinking water for 28 days (Hsieh 

et al. 1989). Mitogen-stimulated lymphocyte proliferation and interleukin-2 immunity were depressed by 

doses of 22 and 105 mg/kg/day. A dose of 5 mg/kg/day had no effect upon any of these indicators of 

immune system function. No effects on the histology or weight of the spleen or thymus were reported in 

rats and mice given gavage doses of up to 2,500 mg/kg/day toluene for 13 weeks (NTP 1990). 
TOLUENE 93 

2. HEALTH EFFECTS 

The highest NOAEL values and all LOAEL values for each reliable study for immunological effects in 

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

2.2.2.4 Neurological Effects 

Severe depression of central nervous system function was the probable cause of death for a 51-year-old 

man who ingested approximately 60 mL (625 mg/kg) of toluene (Ameno et al. 1989). No other studies 

were located regarding neurological effects in humans after oral exposure to toluene. 

Male and female rats exposed to single gavage doses of 2,610, 3,915, or 5,220 mg/kg exhibited changes 

on a variety of neurological tests (Mehta et al. 1998). Significantly greater increases in motor activities 

were seen at all doses in both male and female rats on day 1; by day 14 after exposure, there were no 

significant differences, except for vertical motor activity in female rats was significantly reduced at the 

2,620 and 3,915 mg/kg/day doses. A dose-dependent increase in abnormal gait was seen on day 1 for 

male rats at all doses, while female rats exhibited abnormal gait at 3,915 and 5,220 mg/kg. A dosedependent increase in lacrimation and salivation was seen on day 1 for both males and females at all 

doses (Mehta et al. 1998). 

Single doses of 250–1,000 mg/kg administered by gavage to male rats caused a decrease in the flash 

evoked potential wave pattern amplitudes (Dyer et al. 1988). This suggests that toluene may have an 

effect on the visual system at high doses. The LOAEL of 250 mg/kg/day for the effects of the flash 

evoked potential waveform was used as the basis for the acute-duration oral MRL (0.8 mg/kg/day) (see 

Section 2.5 and Appendix A). 

Brain levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), and their respective metabolites, 

vanillylmandelic acid (VMA), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA) were 

altered in 6 areas of the brain in male CD-1 mice administered toluene (5–105 mg/kg/day) in their 

drinking water for a 28-day period (Hsieh et al. 1990b). Significant increases of NE, DA, and 5-HT were 

present in the hypothalamus at all dose levels. The maximum increase occurred with the 22 mg/kg/day 

dose and there were lesser increases for both the 5 and 105 mg/kg/day doses. Roughly similar fluctuations were seen in the concentrations of VMA and HVA, which are metabolites of DA and NE and 

5-HIAA, a serotonin metabolite. In the corpus striatum, the levels of DA and 5-HT were significantly 

increased at the two highest doses. The level of VMA was also increased significantly at the same doses. 

In the medulla oblongata, the concentrations of NE, VMA, and 5-HIAA were significantly increased at 
TOLUENE 94 

2. HEALTH EFFECTS 

the 22 mg/kg/day dose, but not at the other doses, while the levels of 5-HT were significantly increased at 

the 22 and 105 mg/kg/day doses. NE concentrations were elevated in the midbrain. The 5 mg/kg/day 

LOAEL from this study was used as the basis for the intermediate-duration oral MRL (0.02 mg/kg/day) 

(see Section 2.5 and Appendix A). 

Exposure to 1,250 and 2,500 mg/kg/day for 13 weeks resulted in increased relative brain weights in male 

mice (NTP 1990). Necrosis of the brain was present in rats exposed to 1,250 and 2,500 mg/kg/day, but 

increases in brain weight were only apparent with the 2,500 mg/kg/day dose (NTP 1990). Clinical signs 

in rats and mice exposed to 2,500 and 5,000 mg/kg/day included ataxia, hypoactivity, prostration, and 

tremors. No neurological effects were seen in mice or rats at dose levels of 625 mg/kg/day. 

The highest NOAEL values and all LOAEL values for each reliable study for neurological effects in each 

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

2.2.2.5 Reproductive Effects 

No studies were located regarding reproductive effects in humans after oral exposure to toluene. 

There was no effect on the number of mice producing viable litters following oral administration of 

2,350 mg/kg on gestational days 7–14 (Smith 1983). Increased relative testicular weights were reported 

in male mice exposed to 1,250 and 2,500 mg/kg/day by gavage for 13 weeks. However, no effects on the 

or weight of the prostate, testes, uterus, or ovaries were observed in rats and female mice exposed to 

312–2,500 mg/kg/day (NTP 1990). 

The highest NOAEL values and all LOAEL values for reproductive effects in mice following acute 

duration exposure are recorded in Table 2-2 and plotted in Figure 2-2. 

2.2.2.6 Developmental Effects 

No studies were located regarding developmental effects in humans after oral exposure to toluene. 

Toluene was not a developmental toxicant when administered orally to pregnant mice during the period of 

organogenesis at doses of 1,800 or 2,350 mg/kg/day (Seidenberg et al. 1986; Smith 1983). Effects on 

neurological function were observed in mice exposed from 4 to 106 mg/kg/day toluene through their 
TOLUENE 95 

2. HEALTH EFFECTS 

dams during gestation and lactation and thereafter through their drinking water. Open-field activity was 

impaired in mice receiving 106 mg/kg/day toluene when measured on postnatal day 35 (Kostas and 

Hotchin 1981). There was a distinct effect on rotorod performance during the first 2 of 4 consecutive 

trials in all exposed mice when measured on postnatal days 45–55. However, the effect on rotorod 

performance was not dose-related. 

Following exposure of pregnant rats to gavage doses of 520 or 650 mg/kg/day toluene in corn oil on 

gestation days 6–19, fetuses showed significantly reduced body weight, delayed skeletal ossification, 

smaller brain volumes, and decreases in forebrain myelination per cell compared with controls (Gospe 

and Zhou 1998; Gospe et al. 1994, 1996). The difference in forebrain myelination was the only 

difference that remained between exposed and control offspring by postnatal day 21 (Gospe and Zhou 

1998). 

The highest NOAEL values and all LOAEL values for developmental effects in mice following acute and 

intermediate duration exposures are recorded in Table 2-2 and plotted in Figure 2-2. 

2.2.2.7 Genotoxic Effects 

No studies were located regarding genotoxic effects in humans or animals after oral exposure to toluene. 

Genotoxicity studies are discussed in Section 2.5. 

2.2.2.8 Cancer 

No studies were located regarding carcinogenic effects in humans after oral exposure to toluene. 

There is one oral study on the carcinogenic effects of toluene in animals. Toluene was administered at 

doses of 500 and 800 mg/kg/day to male and female rats for 104 weeks (Maltoni et al. 1997). A nondoserelated increase in total malignant tumors in both males and females at all dose levels, in mammary gland 

tumors in females at the lower dose, in head cancers in males at the higher dose and females at the lower 

dose, in lymphomas and leukemias in males at the higher dose and females at both doses, were observed 

(Maltoni et al. 1997). However, the increased incidences were not dose-related and confidence in the 

study is low. 
 

 

TOLUENE 96 

2. HEALTH EFFECTS 

2.2.3 Dermal Exposure 

There are limited data on the effects of dermal exposure to toluene. There are studies describing 

occupational exposure of humans to toluene (see Section 2.2.1). Toxicokinetic data (Section 2.3) indicate 

that humans and animals can absorb toluene across the skin. Studies of dermal exposure to toluene in 

humans and animals are discussed below. 

2.2.3.1 Death 

No studies were located regarding lethal effects in humans or animals after dermal exposure to toluene. 

2.2.3.2 Systemic Effects 

Data are available regarding dermal effects in humans and animals after dermal exposure to toluene. No 

studies were located regarding respiratory, cardiovascular, gastrointestinal, hematological, or musculoskeletal effects in humans or animals after dermal exposure to toluene. In addition, there are data on 

hepatic, renal, and ocular effects in animals after dermal exposure to toluene. The highest NOAEL values 

and all LOAEL values for each reliable study for systemic effects in each species and duration category 

are recorded in Table 2-3. 

Hepatic Effects. No studies were located regarding hepatic effects in humans after dermal exposure 

to toluene. 

Application of 1 mL toluene to the skin of guinea pigs for 16 hours did not alter liver morphology 

(Kronevi et al. 1979). Because only one dose of toluene was applied and more sensitive indicators of 

liver toxicity were not monitored, conclusions cannot be derived regarding the hepatic effects of toluene 

following dermal exposure. 

Renal Effects. No studies were located regarding renal effects in humans after dermal exposure to 

toluene. 

Application of toluene to the skin of guinea pigs for 16 hours did not alter renal morphology (Kronevi et 

al. 1979). The limitations of this study were discussed in the previous section. 

 

 

TOLUENE 98 

2. HEALTH EFFECTS 

Dermal Effects. In humans, dermal contact with toluene may cause skin damage because it removes 

skin lipids (EPA 1983a). Workers exposed to mixtures of solvents, of which toluene was generally the 

major component, reported problems with the skin of their hands (Winchester and Madjar 1986). The 

specific symptoms associated with the reported skin abnormalities were not reported. Eye irritation in 

humans occupationally exposed to toluene vapors has also been reported (Meulenbelt et al. 1990). 

Repeated application of undiluted toluene (amount unstated) to the rabbit ear or shaved skin produced 

slight to moderate irritation (Wolf et al. 1956). In guinea pigs, continuous contact with toluene resulted in 

shrinkage and dissolution of the cell nuclei, cellular edema, and cellular infiltration of the dermis 

(Kronevi et al. 1979). Application of toluene to the skin of guinea pigs, 3 times a day for 3 days, resulted 

in redness and an increase in epidermal thickness (Anderson et al. 1986). These data suggest that toluene 

is slightly to moderately irritating to the skin. 

Ocular Effects. No studies were located regarding ocular effects in humans after dermal exposure to 

toluene. 

Slight irritation of the conjunctival membranes, but no corneal injury, was observed in rabbit eyes 

following direct application of toluene (Hazleton Laboratories 1962; M B Research Labs 1975; Wolf et 

al. 1956). Moderately severe injury to the eyes of rabbits following direct application of a 40% solution 

of toluene has also been reported (Carpenter and Smyth 1946). These data suggest that toluene is slightly 

to moderately irritating to the eyes. 

No studies were located regarding the following effects in humans or animals after dermal exposure to 

toluene: 

2.2.3.3 Immunological and Lymphoreticular Effects 

2.2.3.4 Neurological Effects 

2.2.3.5 Reproductive Effects 

2.2.3.6 Developmental Effects 

2.2.3.7 Genotoxic Effects 

Genotoxicity studies are discussed in Section 2.5. 
TOLUENE 99 

2. HEALTH EFFECTS 

2.2.3.8 Cancer 

No studies were located for cancer effects in humans after dermal exposure to toluene. 

Dermally administered toluene markedly inhibits skin tumorigenesis in the two-stage mouse model 

utilizing phorbol-12-myristate-13-acetate (PMA) as a promoter (Weiss et al. 1986). The reduction in 

tumorigenesis was observed in mice initiated with dermal applications of benzo(a)pyrene or 

7,12-dimethylbenz(a)anthracene. The pattern of inhibition indicated that the observed effect was not 

likely to be due to a direct chemical effect on the promoter. The authors speculated that toluene competed 

for a PMA receptor site, interfered with a biochemical process within the cell membrane, or affected the 

intracellular cascade between the membrane and the nucleus. 

2.3 TOXICOKINETICS 

Studies with volunteers and laboratory animals indicate that toluene is readily absorbed from the 

respiratory and gastrointestinal tracts and, to a lesser extent, through the skin. Animals given toluene 

orally or by inhalation had high concentrations of toluene in their adipose tissue, brain, and bone marrow, 

and moderately high concentrations of toluene and its metabolites in liver and kidney. The primary initial 

steps in toluene metabolism in humans and laboratory animals are side-chain hydroxylation (to form 

benzyl alcohol) catalyzed predominately by the cytochrome P450 (CYP) isozyme, CYP2E1 (Nakajima 

and Wang 1994; Nakajima et al. 1991, 1992a, 1992b, 1993, 1997; Tassaneeyakul et al. 1996) followed by 

oxidation to benzoic acid. Most of the benzoic acid is then conjugated with glycine to form hippuric acid, 

but a small portion can be conjugated with UDP-glucuronate to form the acyl-glucuronide. Studies with 

volunteers and human liver microsomes indicate that a very small portion (<1–5%) of absorbed toluene 

can be converted by CYP1A2, CYP2B2, or CYP2E1 to ortho- or para-cresol, which are excreted in the 

urine as sulfate or glucuronate conjugates (Baelum et al. 1993, Nakajima et al. 1997; Tassaneeyakul et al. 

1996). In both humans and rats, up to about 75–80% of inhaled toluene that is absorbed can be accounted 

for as hippuric acid in the urine (Lof et al. 1993; Wang and Nakajima 1992). Much of the remaining 

toluene is exhaled unchanged. In humans exposed by inhalation, rates of urinary excretion of orthocresol were about 1,000-fold lower than excretion rates for hippuric acid (Baelum et al. 1993). The 

excretion of toluene and its metabolites is rapid, with the major portion occurring within 12 hours of 

exposure. 
TOLUENE 100 

2. HEALTH EFFECTS 

2.3.1 Absorption 

2.3.1.1 Inhalation Exposure 

In humans exposed to 80 ppm toluene, uptake was rapid as shown by the appearance of toluene 

(2–5 μmol/L) in the blood within 10–15 minutes of exposure (Hjelm et al. 1988) and by a high correlation 

between the alveolar and arterial concentrations of toluene both during and after exposure (Carlsson 

1982). About 50% of deuterium labeled toluene was absorbed from the lungs in volunteers exposed to 

53 ppm for 2 hours during a period of light exercise (Lof et al. 1993). Seven humans exposed to 50 ppm 

toluene in a closed chamber showed an average retention of 83% of the inspired concentration (Benoit et 

al. 1985). 

Toluene was rapidly absorbed via the lungs of rats; the log concentrations of toluene in the blood and 

brain were linear functions of the log concentration of toluene in the air (Benignus et al. 1984). In dogs, 

toluene was found in the arterial and venous blood 2 minutes after the start of exposure (Hobara et al. 

1984b). 

No information was located regarding possible differences in absorption of inhaled toluene by humans or 

animals with differences in age. 

2.3.1.2 Oral Exposure 

Complete gastrointestinal absorption of toluene in human subjects was indicated by monitoring exhaled 

air for toluene and urine for toluene metabolites (hippuric acid and ortho-cresol) following oral administration of toluene as a 2 mg/min infusion for 3 hours through a feeding tube into the stomach (Baelum et 

al. 1993). Complete absorption of orally administered toluene has also been observed in rats, but oral 

absorption rates appear to be slower than pulmonary absorption (Pyykko et al. 1977). In this rat study, 

maximum blood concentrations were observed 1.5–3 hours after administration, whereas maximum blood 

levels following inhalation were reached in 15–30 minutes. 

Ingestion of soil contaminated with toluene can be a concern at hazardous waste sites. Binding to soil 

does not prevent absorption. The time course for absorption of toluene mixed with sandy soil or clay soil 

was increased when compared to the time course for pure toluene, but the total amount absorbed was the 

same based on the area under the blood toluene concentration curve (Turkall et al. 1991). 
TOLUENE 101 

2. HEALTH EFFECTS 

Studies with brush border membrane vesicles isolated from rat intestines and exposed to toluene indicate 

that toluene absorption occurs through the lipophilic matrix of the membrane (Alcorn et al. 1991). The 

removal of proteins from the membrane surface had no effect upon the toluene partition coefficient, but 

factors affecting the nonesterified membrane fatty acids reduced absorption. In this same in vitro study of 

membrane partitioning, vesicles harvested from the proximal, middle, and distal intestinal segments 

showed no differences, indicating that concentration and surface area, rather than membrane structure, are 

the factors determining the amount of toluene absorbed from each portion of the small intestines. Since 

toluene absorption occurs through the lipid matrix of the membrane, absorption can occur through the 

mouth and stomach, as well as the small intestines. The amount of toluene absorbed from each organ of 

the gastrointestinal tract will depend on residence time, absorptive surface area, and partitioning between 

membrane lipids and lipids in the gastrointestinal tract. 

No information was located regarding possible differences in absorption of ingested toluene by humans or 

animals with differences in age. 

2.3.1.3 Dermal Exposure 

Toluene is absorbed through human skin slowly (Dutkiewicz and Tyras 1968). The rate of absorption of 

toluene in human forearm skin was found to range from 14 to 23 mg/cm2

/hour. Based on these estimates, 

Brown et al. (1984) calculated that bathing in water containing 0.005–0.5 mg toluene/L (15 minutes/day) 

would result in absorbed dermal dose ranges of 0.0002–0.02 mg/kg/day for a 70-kg adult and 

0.0004–0.04 mg/kg/day for a 10.5-kg infant. 

Soaking the skin of 2 volunteers with toluene for 5 minutes resulted in a maximum concentration of 

toluene in blood of 5.4 μmol/L (Aitio et al. 1984). Individual differences were marked, and dramatic 

changes in blood concentrations were observed over short periods of time. Similar individual differences 

and highly variable results were reported by Sato and Nakajima (1978) in a study using five volunteers. 

Monster et al. (1993) investigated dermal absorption of toluene in 6 rotogravure printing workers. The 

workers washed their hands with toluene for 5 minutes, and alveolar air samples were collected up to 

24 hours after exposure. The concentrations measured the next morning in exhaled air ranged between 

0.5 and 10 mg/m3

, clearly demonstrating dermal absorption of toluene. 
TOLUENE 102 

2. HEALTH EFFECTS 

Toluene in aqueous solution and neat toluene were absorbed through the skin of rats (Morgan et al. 1991). 

Three solution strengths (0.162, 0.333, and 0.448 mg/L) were tested. Although the blood toluene levels 

for each strength were near the analytical detection limits, the results of this study indicate that toluene 

absorption was significant, since only 1% of the body surface was exposed. 

Dermal absorption also occurs when animals are exposed to toluene vapors. In nude mice exposure to 

300, 1,000, or 3,000 ppm toluene under conditions where there was no respiratory intake of toluene, led 

to a dose-related and duration-related increase in whole body toluene levels (Tsuruta 1989). The 

calculated skin absorption coefficient was 1.24 cm/hour. The skin absorption rate for the 300 ppm 

concentration was 0.0009 mg/cm2

/hour; for the 1,000 ppm concentration, it was 0.0046 mg/cm2/hour; and 

for the 3,000 ppm concentration, it was 0.0144 mg/cm2

/hour. Exposure of guinea pigs to an unspecified 

concentration of toluene for 1 minute, with the skin wiped dry and 1 minute exposures continuing every 

30 minutes, for 4 hours, resulted in lower levels of toluene absorption than with continuous exposure for 

4 hours (Boman et al. 1995). 

No information was located regarding possible differences in absorption of dermally applied toluene by 

humans or animals with differences in age. 

2.3.2 Distribution 

2.3.2.1 Inhalation Exposure 

There is a positive correlation between the levels of toluene in alveolar air and the levels in blood in both 

humans and animals (Hjelm et al. 1988; Lof et al. 1990; Ovrum et al. 1978). With an exposure in humans 

of 80 ppm toluene for 4 hours, toluene levels in the blood reached a plateau of 6–7 μmol/L at 

approximately 2 hours (Hjelm et al. 1988; Lof et al. 1990). In humans, the toluene is distributed between 

the plasma and red blood cells at approximately a 1:1 ratio according to in vitro data; in rats, the ratio is 

1:2 based on in vivo data (Lam et al. 1990). In the red blood cells, the toluene appears to be associated 

with the hemoglobin rather than the cell membrane. It is hypothesized that toluene interacts with the 

hydrophobic core of the heme protein. The interaction of the toluene with the red blood cell increases the 

amount of toluene that can be accommodated by the aqueous blood medium and facilitates transport of 

toluene to all areas of the body (including the brain) at a rate that is greater than if toluene was transported 

only in the plasma. 
TOLUENE 103 

2. HEALTH EFFECTS 

Autopsies of toluene-exposed humans indicate that absorbed toluene is distributed to lipid-rich and highly 

vascular tissues such as the brain. For example, toluene levels in the brain and liver of a 16-year-old male 

who died following an episode of glue sniffing were 297 and 89 μg/mg, respectively (Paterson and 

Sarvesvaran 1983). Concentrations in the blood were 20.6 μg/mL of toluene and 3.0 μg/mL of acetone. 

In a man who died following a fall while exposed to toluene during painting, tissue levels of toluene in 

blood, lung, liver, and brain were 48, 35, 65, and 80 μg/g, respectively (Takeichi et al. 1986). 

Within the human brain, toluene has a greater affinity for areas of the brain that contain lipid-rich white 

matter, such as the brain stem, rather than the areas with larger amounts of gray matter (Ameno et al. 

1992). The hippocampus and cerebellum had lower brain: blood toluene ratios than the spinal cord, 

midbrain, medulla oblongata, and pons. The brain stem controls many involuntary aspects of cardiac, 

respiratory, and vasomotor function. 

Concentrations of toluene in subcutaneous adipose tissue of male subjects exposed during rest or physical 

exercise to 300 mg/m3

 of toluene were determined (Carlsson and Ljungquist 1982). After exposure at rest 

for 2 hours, the mean concentration of toluene in adipose tissue was 0.7 mg/kg. The corresponding value 

after 2 hours of work was 9.9 mg/kg. Linear regression analysis indicated that toluene concentrations in 

adipose tissue were lower in subjects with large amounts of body fat. 

The human data are supported by autoradiography studies using mice. Immediately after inhalation, a 

high level of radioactivity was found in the body fat, bone marrow, spinal nerves, spinal cord and white 

matter of the brain of exposed mice (Bergman 1979). Radioactivity was also observed in the blood, 

kidney, and liver at lower levels. Autoradiography of mice sacrificed immediately after the cessation of 

exposure revealed a very high concentration of nonvolatile radioactivity in the kidney, particularly the 

medullary region. Nonvolatile radiation found in the liver and kidney suggests rapid formation and 

excretion of toluene metabolites. 

A one-compartment model was developed for blood and whole-brain toluene levels based on data from 

rats exposed to 575 ppm toluene for up to 240 minutes (Benignus et al. 1981). Estimated saturation 

asymptotes were 10.5 ppm for venous blood and 18.0 ppm for brain, respectively. Blood and brain levels 

achieved 95% of their estimated asymptotes in 53 and 58 minutes, respectively. The distribution half-life 

for a 30-minute exposure of rats to 2,000 ppm toluene was 0.34 hours, while that for exposure to 

10,000 ppm was 0.6 hours (Ameno et al. 1992). 
TOLUENE 104 

2. HEALTH EFFECTS 

Toluene was rapidly distributed to the tissues in rats after 1, 2, or 3 days of exposure to 100 ppm for 

12 hours per day (Zahlsen et al. 1992). Homeostasis was attained in 1 day for the kidney, brain, and liver, 

whereas toluene concentrations continued to increase in perirenal fat deposits. Once exposures ceased, 

toluene concentrations declined within 12 hours to near baseline levels for all tissues except in fat. The 

toluene in rat brains was distributed to the brain stem and midbrain (Ameno et al. 1992), a distribution 

that parallels that observed in humans and mice (Ameno et al. 1992; Bergman 1979). These regions have 

a high concentration of white matter. 

Toluene distribution to several tissues was followed in dogs exposed through inhalation of 30,000 ppm 

toluene from a plastic bag for 10 minutes. The toluene level in the arterial blood was 129±54.8 μg/mL 

while that in the venous blood was 112±48.5 μg/mL. The liver and brain contained roughly equivalent 

concentrations of toluene (184 and 191 μg/g), while the toluene in the kidneys was 99 μg/g (Ikeda et al. 

1990). 

Distribution of toluene (assayed by autoradiography and tissue concentrations of radioactivity) in 

pregnant mice was also characterized by preferential uptake in maternal lipid-rich tissues (brain and fat) 

immediately after 10-minute inhalation exposures to 14C-labeled toluene at approximately 2,000 ppm 

(Ghantous and Danielsson 1986). It was thought that toluene, due to its high lipid solubility and low 

molecular weight, might easily transfer across the placenta, but concentrations of radioactivity in fetal 

tissues were only about 4% of concentrations in maternal brain and adipose tissue immediately after 

exposure, and rapidly decreased within 4 hours of cessation of exposure. These results suggest that 

absorbed toluene is preferentially distributed to maternal adipose tissues in pregnant mice and that 

distribution to the developing fetus is limited with short-term exposure to the relatively high (compared 

with occupational exposures) concentration of 2,000 ppm. This concentration, however, is low 

compared with concentrations experienced by toluene abusers (4,000–12,000 ppm as cited by Gospe et al. 

1994). Ghantous and Danielsson (1986) suggested that the lower lipid content in fetal tissue compared 

with maternal tissue could explain the low uptake of toluene into fetal tissue. 

No studies were located that examined in vivo distribution of toluene into breast milk in humans or 

animals. Although breast milk is high in lipid content, it is unknown if there may be preferential uptake 

of toluene into other maternal lipid-rich tissues. A published estimate of the human milk/blood partition 

coefficient for toluene, 2.68, was lower than estimates of coefficients for partitioning of toluene between 

other tissues and human blood, including liver or highly perfused tissues/blood (4.91) and fat/blood 

(60.01) (Fisher et al. 1997). Transfer from blood to a tissue, however, is also dependent on the rate of 
TOLUENE 105 

2. HEALTH EFFECTS 

perfusion of the tissue with blood. Fisher et al. (1997) used these partition coefficient values in a 

physiologically-based pharmacokinetic (PBPK) model designed to predict transfer of volatile chemicals 

into breast milk, but human or animal pharmacokinetic data for lactational transfer of toluene were not 

available to validate or modify the model. 

Coexposure of rats to xylene increased the concentrations of toluene in the blood and brain in the 

19 hours after exposure as compared to exposure to toluene alone (Tardif et al. 1992). This was, 

apparently, the result of suppressed toluene metabolism because of competition between toluene and 

xylene for active sites on enzymes responsible for metabolizing both compounds. Pulmonary excretion of 

toluene was also decreased when exposure to both compounds occurred. As a result, the half-lives for 

both toluene and xylene were increased. 

Blood and brain toluene levels in rats exposed to 2000 or 4000 ppm for 4 hours during daylight were 

significantly higher at the end of exposure and 40 minutes after the cessation of exposure than in animals 

exposed in the dark (Harabuchi et al. 1993). This suggests that circadian rhythms may have an influence 

on toluene absorption, distribution, and excretion. 

2.3.2.2 Oral Exposure 

In one human who died 30 minutes after ingestion of 625 mg/kg toluene, the liver was found to have the 

highest concentration of toluene (433.5 μg/g) followed by the pancreas (88.2 μg/g), brain (85.3 μg/g), 

heart (62.6 μg/g), blood (27.6 μg/g), body fat (12.2 μg/g), and cerebrospinal fluid (11.1 μg/g) (Ameno 

et al. 1989). The short interval between toluene exposure and death limited the distribution of the toluene 

to the peripheral body tissues. 

When rats were orally exposed to 400 mg/kg toluene, the peak concentration in the blood occurred 

1.5 hours after exposure (Ameno et al. 1992). In the brain, the highest brain: blood toluene ratios were 

found in the pons and caudate-putamen, as opposed to the hippocampus (Ameno et al. 1992). Toluene 

distribution in the brain was similar with inhalation and oral exposure (Ameno et al. 1992). 

2.3.2.3 Dermal Exposure 

No studies were located regarding the distribution of toluene in humans or animals after dermal exposure. 
TOLUENE 106 

2. HEALTH EFFECTS 

2.3.3 Metabolism 

Studies of urinary metabolites in toluene-exposed humans (Andersen et al. 1983; Angerer 1979; Angerer 

et al. 1998a; Baelum et al. 1987, 1993; Dossing et al. 1983b; Inoue et al. 1986; Jonai and Sato 1988; 

Kawai et al. 1992a, 1992b, 1993, 1996; Lof et al. 1990, 1993; Maestri et al. 1997; Ng et al. 1990) and rats 

(Bray et al. 1949; Van Doorn et al. 1980; Wang and Nakajima 1992) have identified hippuric acid (the 

glycine conjugate of benzoic acid) as the major urinary metabolite of toluene. Minor urinary metabolites 

(in approximate order of decreasing abundance) include: the glucuronyl conjugate of benzoic acid; 

sulfate and glucuronide conjugates of ortho- and para-cresol; S-benzylmercapturic acid; and 

S-p-toluylmercapturic acid. Based on these results and the results from in vitro studies, including recent 

studies with human and rat liver microsomes (Nakajima and Wang 1994; Nakajima et al. 1991,1992a, 

1992b, 1993, 1997; Tassaneeyakul et al. 1996), a scheme for toluene metabolism in humans and animals 

is presented in Figure 2-3. 

The initial steps are methyl and ring hydroxylations that are catalyzed by cytochrome P450 (CYP) 

isozymes. Methyl hydroxylation to form benzyl alcohol was the predominant first step in human 

(Nakajima et al. 1997; Tassaneeyakul et al. 1996) and rat (Nakajima et al. 1991, 1992a, 1992b, 1993) 

liver microsomes. Ring hydoxylation to form ortho- or para-cresols in these studies usually represented 

less than 5% of total metabolite formation. 

Results from in vitro studies indicate that CYP2E1 is the most active CYP isozyme in forming benzyl 

alcohol and CYP1A2 is the most active in forming ortho- and para-cresols. Using monoclonal antibodies 

to CYP isozymes as in vitro metabolic inhibitors in rat microsome preparations, Nakajima et al. (1991) 

demonstrated that CYP2E1 (at low toluene concentrations) contributes to the formation of benzyl alcohol 

and para-cresol, CYP1A1/2 contributes to ortho- and para-cresol formation, and CYP2B1/2 and 

CYP2C11/6 (at higher toluene concentrations) contribute to the formation of benzyl alcohol and orthoand para-cresol. Biphasic enzyme kinetics for the formation of benzyl alcohol from toluene were 

observed in human liver microsomes, supporting the concept that at least two isozymes with differing 

affinity for toluene can catalyze benzyl alcohol formation (Tassaneeyakul et al. 1996). The high-affinity 

component in human liver microsomes was markedly inhibited (about 90% inhibition) by 50 μM 

diethyldithiocarbamate, an inhibitor of CYP2E1, whereas inhibitors of other CYP isozymes produced 

generally less than 10% inhibition of the high affinity component (Tassaneeyakul et al. 1996). Other 

inhibitors tested (and the CYP forms that they are expected to inhibit) were: furafylline (CYP1A2), 

coumarin (CYP2A6), mephenytoin (CYP2C19), quinidine (CYP2D6), sulfaphenazole (CYP2D6), and 
Figure 2-3. Scheme for Toluene Metabolism in Humans and Animals 

CH3 CH3 CH3 (CYP1A2 

CYP2E1 CYP2B6) 

O GSH 

Toluene O 

2,3-Toluene 3,4-Toluene (CYP2E1 epoxide epoxide (GSH-S-transferase) CYP2B6 

CYP2C8 CYP1A2) CH3 

CH CH3 CH 3 H 2OH 2C SG GSH 

OH 

(GSH-S-transferase) SG 

Benzyl alcohol o-Cresol OH S-p-Toluyl glutathione 

S-Benzylglutathione p-Cresol 

(Alcohol DH 

Aldehyde DH) 

Conjugation glutamic acid 

Acyl-CoA COOH

Acyl-CoA glutamic acid UDP-glucuronate Sulfates glycine (sulfotransferase) 

Glucuronides glycine (UDP-Glucuronyl transferase) 

(gamma-Glutam

(gamma-Glutamyl

Benzoic acid glycine transpeptidas

 transpeptidase, Aminopeptidas

(UDP-glucuronyl Aminopeptidase M, N-Acetyl transfe

transferase) (Acyl-CoA synthase, N-Acetyl transferase) Acyl-CoA: Amino acid N­

 acyl transferase) NHCOCH3 CH3

H2C S C CH CO-glucuronide CONHCH2COOH H2

COOH

NHCOCH

S C CH 

S-Benzyl Hippuric acid H2 mercapturic acid COOH S-p-Toluylmercaptic ac

Proposed enzymes are noted in parentheses. Sources: Angerer et al. 1998a; IARC 1999; Nakajima and Wang 1994; Nakajima et al. 1997; Tassaneeyakul et al. 1996 CoA = coenzyme A; CYP = cytochrome P-450; DH = dehydrogenase; GSH = glutathione; UPD = uridine 5'-diphosphate 
TOLUENE 108 

2. HEALTH EFFECTS 

troleandomycin (CYP3A) (Tassaneeyakul et al. 1996). Using microsomes from cells in which cDNAs for 

eleven different human CYP isozymes were expressed, Nakajima et al. (1997) demonstrated that CYP2E1 

was the most active in forming benzyl alcohol, followed in order by CYP2B6, CYP2C8, CYP1A2, and 

CYP1A1. The activities of CYP2A6, CYP2C9, CYP2D6, CYP3A3, CYP3A4, and CYP3A5 in 

metabolizing toluene were negligible. CYP1A2 also was active in forming ortho- and para-cresol 

(22 and 35% of total metabolites) and CYP2E1 and CYP2B6 catalyzed the formation of para-cresol 

(11–12% of total metabolites) (Nakajima et al. 1997). 

Benzyl alcohol is thought to be converted to benzoic acid in two steps by alcohol dehydrogenase and 

aldehyde dehydrogenase (see Figure 2-3). Conjugation with glycine to form hippuric acid can represent 

83–94% of urinary metabolites of toluene in rats (Nakajima and Wang 1994). Hippuric acid formation 

from benzoic acid (a common component of the diet) is catalyzed by acyl-CoA synthetase and 

acyl-CoA: amino acid N-acyltransferase. Conjugation of benzoic acid with glucuronic acid to form 

benzoyl glucuronide is catalyzed by UDP-glucuronyl transferase and can account for 3–9% of urinary 

metabolites in rats (Nakajima and Wang 1994). 

The 2,3- and 3,4-epoxide intermediates, precursors of ortho- and para-cresol, are thought to be oxidation 

products of the catalytic actions of CYP1A2, CYP2E1, and CYP2B6 (Nakajima et al. 1997). Ortho- and 

para-cresol and their conjugates have been reported to account for 0.5–1.1% and 2.5–14.2%, 

respectively, of urinary metabolites in rats (Nakajima and Wang 1994). S-benzyl mercapturic acid, a 

minor urinary metabolite identified in humans, is thought to be formed via conjugation of benzyl alcohol 

with glutathione (catalyzed by glutathione-S-transferases), followed by the concerted catalytic actions of 

γ-glutamyltranspeptidase, amino peptidase M, and N-acetyltransferase to release glutamic acid and 

glycine and add an acetyl group (Angerer et al. 1998a) (see Figure 2-3). The formation of another minor 

human urinary metabolite, S-p-toluylmercapturic acid, is thought to proceed by a similar series of 

reactions from the proposed intermediate, 3,4-toluene epoxide (Angerer et al. 1998a). 

The liver is expected to be the prime site of toluene metabolism, based on the high concentration of CYP 

isozymes in the liver relative to other tissues. For example, levels of CYP2E1 in human lung microsomes 

were 10.5% of liver activities (Wheeler et al. 1992). Studies with rats indicate that toluene exposure 

causes changes in CYP-associated enzyme activities and CYP isozymes themselves in the liver (see 

Nakajima and Wang 1994 for review). For example, single 6-hour exposures to toluene induced hepatic 

CYP2E1 levels and associated nitrosodimethylamine demethylase activities (at concentrations 

$1,000 ppm), induced CYP2B1/2 and CYP3A1/2 levels (at concentrations >2,000 ppm), decreased 
TOLUENE 109 

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CYP2C11/6 levels (at 4,000 ppm), and did not change CYP1A1/2 levels (Wang et al. 1993). Other rat 

experiments involving longer durations of exposure and potentially higher dose levels have consistently 

observed induction of hepatic activities of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin 

O-deethylase (EROD), activities associated with CYP1A1/2 (see Nakajima and Wang 1994). Rats given 

single intraperitoneal injections of 5 mmol toluene/kg showed induction of ethoxycoumarin O-deethylase 

(ECOD) and EROD activities in liver, but no induction was apparent in lung or kidney tissues (Pyykko et 

al. 1987). Exposure of rats to 375 ppm toluene, 6 hours/day for up to 5 days or 125 ppm for 6 hours did 

not significantly change activities of AHH, EROD, or benzyloxyresorufin (BROD) in liver microsomes 

compared with activities in nonexposed controls, but significantly decreased activities of AHH (by up to 

about 50%), BROD (by 30–70%), and 2-aminofluorene N-hydroxylase (by up to about 50%) in lung 

microsomes without altering EROD activities (Furman et al. 1998). The results from these rat studies 

suggest that toluene at exposure concentrations $1,000 ppm, but not at lower concentrations, induces 

hepatic CYP enzymes involved in its own metabolism and metabolism of other xenobiotics, and that 

exposure to 125 or 375 ppm may cause a decrease in pulmonary activities of certain CYP mixed function 

oxidases. Consistent with the idea of no CYP induction with low-level exposure is the report that 

workers exposed to 100 ppm toluene did not display increased ability to clear antipyrine (Dossing et al. 

1983c). 

Levels of CYP isozymes in rat fetal livers are very low, but increase rapidly after birth (Nakajima and 

Wang 1994). By 10 days after birth, rats of both sexes are capable of responding to toluene exposure by 

inducing hepatic CYP-associated enzyme activities (Pyykko 1983b). Comparison of rates of metabolism 

in liver microsomes from male and female rats at 3 weeks (immature) and 18 weeks of age (mature) and 

in pregnant female rats on gestations days 10 and 21 indicate that age, gender, and pregnancy can 

influence rates of hepatic toluene metabolism and induction of CYP isozymes (Nakajima et al. 1992b). 

Rates (on a mg protein basis) of high-affinity toluene metabolism were not statistically significantly 

different between immature and mature male rats, but rates of low-affinity toluene metabolism were fourfold higher in mature rats compared with immature rats (Nakajima et al. 1992b). In contrast, rates of 

high-affinity toluene metabolism were lower in mature than in immature female rats, but rates of lowaffinity toluene metabolism were not statistically different between immature and mature female rats. 

Rates of high- and low-affinity toluene metabolism were significantly lower in pregnant rats compared 

with nonpregnant rats. 

Given the lack or low levels of several CYP isozymes in the developing human fetus (Leeder and Kearns 

1997), it is expected that the capacity for metabolic detoxification of toluene is low in the developing 
TOLUENE 110 

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fetus. Rat studies indicate that levels of CYP isozymes involved in toluene metabolism, however, are 

rapidly increased following birth, and suggest that capabilities to carry out Phase I toluene metabolism at 

low exposure levels during neonatal periods may exceed those at sexual maturity and pregnancy 

(Nakajima et al. 1992b). CYP2E1, one of the principal CYP isozymes involved in the major toluene 

pathway (Nakajima et al. 1997; Tassaneeyakul et al. 1996), is reported to be expressed several hours after 

birth in humans and continues to increase during the first year of life (Vieira et al. 1996). Phase II 

enzymes involved in toluene metabolism (e.g., N-acetyl transferases, UDP-glucuronyl transferases, and 

sulfotransferases) also show changes during human neonatal development with adult activities reported to 

be present by 1–3 years of age (Leeder and Kearns 1997). Although no studies were located directly 

comparing toluene metabolic capacity in children and adults, the limited available information suggest 

that children past early neonatal periods may be equally able as adults in metabolically disposing of 

toluene at low exposure levels expected to be found in the general environment or at sites adjacent to 

waste sites. 

2.3.4 Elimination and Excretion 

2.3.4.1 Inhalation Exposure 

Studies with humans and laboratory animals indicate that following acute periods of inhalation exposure 

to toluene, absorbed toluene is excreted predominately in the urine as metabolites (hippuric acid, benzoyl 

glucuronide, ortho- and para-cresol and their sulfate and glucuronide conjugates, S-benzyl mercapturic 

acid, and S-p-toluyl mercapturic acid, as discussed in Section 2.3.3) and, to a lesser extent, as nonmetabolized toluene in exhaled air (Lof et al. 1993; Ogata 1984; Tardif et al. 1998). For example, 

following a 2-hour exposure with light physical exercise to deuterium-labeled toluene at a concentration 

of 200 mg/m3

 (53 ppm), an average 78% of retained label was excreted as urinary hippuric acid within 

20 hours by a group of nine volunteers (Lof et al. 1993). A significant portion of absorbed toluene in this 

and other studies has been estimated to be exhaled as nonmetabolized toluene (7–20% of absorbed 

toluene) (Carlsson 1982; Leung and Paustenbach 1988; Lof et al. 1993). 

Analyses of kinetic data for toluene concentrations in blood, exhaled breath, or adipose tissue following 

inhalation exposure of humans (Leung and Paustenbach 1988; Lof et al. 1993; Pellizzari et al. 1992; 

Pierce et al. 1996, 1999) and rats (Rees et al. 1985) indicate that most absorbed toluene is rapidly 

eliminated from the body and that a smaller portion (that which gets into adipose tissues) is slowly 

eliminated. Using three-phase exponential mathematical models to describe curves of human blood 
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concentration as a function of time up to 3–5 hours after 2-hour exposures to 100 or 53 ppm toluene, 

calculated half-lives (the time to decrease the amount in the phase by one-half) were 1.5 and 3 minutes for 

the initial phase, 26 and 40 minutes for the second phase, and 3.7 and 12.3 hours for the final phase (Lof 

et al. 1993; Sato et al. 1974). Elimination half-lives ranged from about 12 to 65 hours (0.5 to 2.7 days) in 

subcutaneous adipose tissue samples taken from 12 subjects at several times within 8 days of cessation of 

exposure to about 80 ppm toluene for four consecutive 30-minute periods (Carlsson and Ljungquist 

1982). Increasing elimination half-lives were significantly correlated with increasing amounts of body fat 

(Carlsson and Ljungquist 1982). Using PBPK models, mean terminal half-lives of about 30–38 hours 

were calculated for changes in blood toluene concentrations between 50 and 100 hours after cessation of 

2-hour inhalation exposures of male subjects to 50 ppm 1

H8-toluene and 50 ppm 2H8-toluene (Pierce et al. 

1996, 1999). During this terminal phase of disposition, >95% of toluene is expected to be in adipose 

tissue and the release of toluene from adipose tissues has been proposed to be the rate-limiting step 

(Pierce et al. 1999). In studies with rats exposed for 2 hours to 1,000, 1,780, or 3,000 ppm toluene, twophase exponential models were used to calculate average elimination half-lives of approximately 6 and 

90 minutes, but blood toluene concentrations were monitored in this study for no more than 2 hours 

following exposure (Rees et al. 1985). 

Investigators have reported a correlation between occupational exposure to toluene and urinary excretion 

of hippuric acid, o-cresol, and p-cresol (De Rosa et al. 1985, 1987; Foo et al. 1991; Kono et al. 1985; Lof 

et al. 1993; Ogata 1984). However, experts caution that there are individual differences in the amounts of 

these excreted metabolites, and monitoring of urinary excretion of metabolites can only serve as a 

qualitative indication of exposure to toluene (Andersen et al. 1983; Baelum et al. 1987; Hasegawa et al. 

1983; Kawai et al. 1996; Nise 1992). When volunteers were exposed to 50 ppm deuterium-labeled 

toluene plus 50 ppm nonlabeled toluene, there was very little variation of labeled hippuric acid excretion 

between subjects (Lof et al. 1993). After 20 hours, 78% of the absorbed labeled toluene was excreted as 

labeled hippuric acid. However, unlabeled hippuric acid excretion varied widely between subjects and 

the total amount of hippuric acid excreted was about 4 times greater than what would have been generated 

by toluene exposure alone. This indicates that there are a number of hippuric acid precursors present in 

the environment (e.g., benzoic acid in food) and exposure to these compounds varies, making hippuric 

acid excretion a poor indicator of toluene exposure. 

Studies of workers exposed to low levels of airborne toluene (TWA concentrations below 50 ppm) 

indicated that correlation coefficients between end-of-shift levels of ortho-cresol and hippuric acid in 

urine and toluene concentrations in breathing zone air, although statistically significant, were not above 
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0.7, indicating a fair amount of variation not explained by toluene air concentrations (Kawai et al. 1996; 

Nise 1992). In a study of 17 workers exposed to 8-hour TWA breathing zone toluene concentrations 

ranging from about 5 to 70 ppm, end-of-shift levels of S-benzylmercapturic acid in urine were correlated 

with toluene concentrations with a coefficient of 0.74 (Maestri et al. 1997). In addition to the individual 

differences for urinary metabolites, possible ethnic differences in the excretion of hippuric acid and 

o-cresol have also been reported in Chinese, Turkish, and Japanese solvent workers (Inoue et al. 1986). 

Significant differences in o- and p-cresol/hippuric acid ratios in the urine were also seen in four different 

strains of rats exposed to toluene (Inoue et al. 1984). 

The American Conference of Governmental Industrial Hygienists (ACGIH 1999) recommends using a 

combination of three biological exposure indices to assess exposure of workers to toluene in the 

workplace: ortho-cresol and hippuric acid levels in urine at the end of a workshift and toluene levels in 

blood immediately prior to the last shift of a workweek. Angerer et al. (1998a) proposed that 

S-p-toluylmercapturic acid levels in urine may also be useful as a biological indicator of toluene 

exposure. 

2.3.4.2 Oral Exposure 

Following oral administration of toluene to eight male subjects by a 2 mg/minute infusion for 3 hours 

through a feeding tube into the stomach, nonmetabolized toluene was detected in alveolar air samples for 

up to 4 hours after cessation of exposure and rates of urinary excretion of hippuric acid and ortho-cresol 

were elevated compared with values under nonexposed conditions (Baelum et al. 1993). A 6 mg/minute 

infusion for 30 minutes did not change the rates of urinary excretion of hippuric acid and ortho-cresol, but 

increased, by four-fold, the area-under-the-curve (AUC) for alveolar toluene concentration compared with 

the values for the 2-mg/minute exposure protocol. Accompanying the 2-mg/minute exposure protocol 

with oral doses of ethanol (0.32 g/kg, corresponding to two alcoholic drinks) decreased hippuric acid 

urinary excretion and dramatically increased the AUC for alveolar toluene concentration (by about 

850-fold in one experiment and 56-fold in another). These data indicate that orally administered toluene 

is eliminated similarly to inhaled toluene, (i.e., by urinary excretion of metabolites and exhalation of 

nonmetabolized toluene), and that ingestion of ethanol can have a dramatic effect on metabolism and 

subsequent elimination of toluene. The results are consistent with other studies showing that ethanol 

inhibits the major toluene metabolic pathway, side-chain oxidation (Dossing et al. 1984; Wallen et al. 

1984). 
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No other studies were located regarding the excretion of toluene in humans or animals after oral 

exposure. 

2.3.4.3 Dermal Exposure 

Following a 5-minute episode of hand-washing in toluene while wearing an airstream helmet to limit 

inhalation exposure, toluene concentrations in exhaled air from human subjects peaked at about 1 ppm at 

22 minutes and declined to about 0.03 ppm at 24 hours (Monster et al. 1993). The results from this study 

indicate that dermally absorbed toluene can be eliminated as the parent compound in exhaled breath, but 

provide no information concerning the possible urinary excretion of metabolites. 

No other studies were located regarding elimination of toluene following dermal exposure. 

2.3.5 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. 
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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 

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 2-4 shows a conceptualized representation of a PBPK model. 

PBPK models are available that describe the kinetics of toluene after inhalation exposure; two for humans 

(Fisher et al. 1997; Pierce et al. 1996, 1999) and two for rats ( DeJongh and Blaauboer 1996, 1997; Tardif 

et al. 1993). These models are all modifications of the standard four-compartment PBPK model 

developed for styrene (Ramsey and Andersen 1984) in which: 

(1) absorption into the lung blood is assumed to be dependent on the inhaled concentration of 

toxicant, the concentration of toxicant in alveolar air, blood flow to the lung, the blood/air partition 

coefficient, and alveolar ventilation rates, 

(2) exchange of toxicant between arterial blood and tissue compartments is flow-limited, 
Skin 

Kidney 

Richly 

perfused 

tissues 

Slowly 

perfused 

tissues 

Fat 

Liver 

Lungs 

A 

R 

T 

E 

R 

I 

A 

L 

B 

L 

O 

O 

D 

V 

E 

N 

O 

U 

S 

B 

L 

O 

O 

D 

GI 

Tract 

Vmax Km 

Urine 

Chemicals in air 

Inhaled chemical Exhaled chemical 

Ingestion 

Feces 

contacting skin 

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Figure 2-4. 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. 
 

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(3) changes in the amount of toxicant in three nonmetabolizing tissue compartments (adipose 

tissue, slowly perfused tissues, and rapidly perfused tissues) are described by mass transfer 

differential equations with tissue volume, blood flow through the tissue (i.e., tissue perfusion rate), 

arterial blood toxicant concentration, and tissue/blood partition coefficients as explanatory 

variables, and 

(4) changes in toxicant amount in the liver (the fourth compartment) are described by similar 

differential equations that additionally include a Michaelis-Menten term for overall rates of toxicant 

metabolism. 

The five-compartment human model for toluene developed by Pierce et al. (1996) includes an additional 

equation describing mass balance across the lung that has a Michaelis-Menten metabolic term (Pierce et 

al. 1996). The model assumes that toluene metabolism in the liver and lung are adequately described by 

subject-specific maximal rate constants for liver and lung (“Vmax-h and Vmax-p” of 

52.1xBW0.7 μmol/hour and 0–0.7x52.1xBW0.7 μmol/hour, respectively) and a common Km (5.97 μmol/L). 

The Km and Vmax-h values were based on those derived by fitting a Ramsey and Andersen-type fourcompartment PBPK model (in which all parameters were constant except Vmax and Km) to toluene 

uptake data for rats placed in closed chambers at several initial toluene concentrations (Tardif et al. 1993). 

The human Vmax-h was estimated for each subject by multiplying the rat Vmax-h by the subject’s body 

weight to the 0.7 power; the rat Km was taken as the human value (Pierce et al. 1996). The lung Vmax 

(Vmax-p) was estimated by model-fitting for each subject, allowing the value to range between 0 and 

70% of the liver Vmax, Vmax-h. This procedure was based on observations that levels of CYP2E1 in 

human lung microsomes were 10.5% of liver activities (Wheeler et al. 1992), and 12 human liver samples 

showed a seven-fold range of CYP2E1 contents (Thummel et al. 1993). 

Another singular feature of the Pierce human model is that subject-specific parameters such as age, 

height, weight, alveolar ventilation rate, adipose tissue fraction, and blood/air partition coefficient are put 

into the model (Pierce et al. 1996). Volumes of the tissue compartments in the model were scaled to each 

subject’s body weight. Blood flows to the slowly and rapidly perfused tissues and the liver were taken as 

fractions of a standard human cardiac output scaled to body weight to the 0.74 power (in units of literhour), whereas subject-specific blood flows to the adipose tissue were estimated by model fitting (holding 

other parameters constant) allowing the fraction of cardiac output that perfuses adipose tissue to range 

between 0.06 and 0.18. The decision to “model-fit” this parameter within these bounds was based on 

published observations that adipose blood flows among individuals range widely from about 0.06 to 
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0.18 of total cardiac output. Tissue/blood partition coefficients used in the model for the slowly and 

rapidly perfused tissue, the liver, and adipose tissue were 1.54, 4.64, 4.64, and 55.9, respectively. 

The initial development and validation of the human model involved comparing model fits with measured 

data (blood concentrations ) for a group of 26 male volunteers who were exposed to 100 ppm toluene 

(50 ppm 1

H8-toluene and 50 ppm 2H8-toluene) for a 2-hour period (Pierce et al. 1996). Venous blood 

concentrations of 1

H8- and 2H8-toluene were measured at intervals for 120 hours post exposure. Prior to 

exposure, information on age, body weight, and adipose tissue fraction were obtained. During exposure, 

individual ventilation rates and blood/air partition coefficients for toluene were measured. Measures of 

the goodness-of-fit of the model predictions to the data were compared using subject-specific values, 

average values from the 26 subjects, and average literature values for: body weight, adipose tissue 

fraction, ventilation rate, blood/air partition coefficient, maximum velocity of pulmonary metabolism, and 

fraction of cardiac output to adipose tissue. The measured concentrations of toluene in blood showed a 

ten-fold interindividual range of variation. Subject-specific modeling explained 91% of the data 

variability, compared with 53% using literature values for model parameters (Pierce et al. 1996). 

Pierce et al. (1998) used the human model to estimate toluene concentrations in alveolar breath reflective 

of exposure to 50 ppm toluene for 8 hours/day (the current ACGIH 8-hour TWA threshold limit value 

(TLV) for toluene). Calculated values were #10 μmol/m3

 for samples taken just before the final shift of a 

workweek and #150 μmol/m3

 postexposure. It was proposed that toluene breath sampling would be a 

rapid, noninvasive biomarker of toluene exposure in workers that is not contaminated by endogenous 

sources. Pierce et al. (1999) also used the human model as a research tool to ascribe differences in 

toxicokinetic behavior of 1

H8- and 2H8-toluene to underlying physiological mechanisms. 

Another human PBPK model has been developed for volatile organic compounds that models transfer of 

toxicant via lactation from a mother to a nursing infant, but in vivo pharmacokinetic data for toluene in 

breast milk were not available to validate this model (Fisher et al. 1997). This model is an adaptation of 

the Ramsey and Andersen design with the addition of a fifth compartment, a nonmetabolizing milk 

compartment with a varying volume. The model includes equations describing the rate of change in the 

amount of toxicant ingested by a nursing infant from the milk compartment, the rate of change in the 

amount of milk in the mammary tissue lumen, and the rate of change in the amount of toxicant in breast 

milk. The model used Michaelis-Menten kinetic constants for toluene metabolism in the liver estimated 

for rats (Vmax 7.5 mg/kg/hour; Km 0.3 mg/L); the rat Vmax was scaled for use in the model by 

multiplying it by a reference body weight (60 kg) to the 0.74 power. Human milk/blood partition 
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coefficients for 19 volatile organic chemicals were experimentally determined using samples from 

volunteers; the coefficient for toluene was 2.68. Other tissue/blood partition coefficients for toluene used 

in the model included 4.91 for rapidly perfused tissue and for liver, 1.61 for slowly perfused tissue, and 

60.01 for adipose tissue. 

Fisher et al. (1997) used the model to estimate the amount of toluene an infant would ingest via milk if 

the mother was occupationally exposed to toluene at the ACGIH (1999) Threshold Limit Value 

(TLV=50 ppm) throughout a workday. The model predicted that such an infant would have a daily intake 

of 0.46 mg toluene/day, which is below the U.S. EPA Health Advisory, 2.0 mg/day, for chronic ingestion 

of 1 L/day of toluene-contaminated water by a 10-kg child. 

The four-compartment rat PBPK model for toluene developed by Tardif et al. (1993) restricted 

metabolism to the liver compartment. As described before, the Km (0.55 mg/L) and Vmax 

(4.8 mg/hour/kg) values were derived by fitting the model (in which all parameters were held constant 

except Vmax and Km) to toluene uptake data for rats housed in closed chambers for 5 hours at several 

initial toluene concentrations (75, 150, or 225 ppm) (Tardif et al. 1993). The model used 18.0 as the 

blood/air toluene partitioning coefficient, and the following for partitioning between blood and tissue 

groups: 4.64 for liver and rapidly perfused tissue, 1.54 for slowly perfused tissue, and 56.7 for adipose 

tissue. Reference rates for alveolar ventilation (15 L/hour/kg) and cardiac output (15 L/hour/kg) were 

scaled by a factor of body weight to the 0.74 power. Model predictions of venous blood concentrations in 

rats during and after 5-hour exposures to toluene concentrations of 75, 150, or 225 ppm compared 

favorably (by visual inspection) with empirical data. 

Tardif et al. (1993) linked the rat PBPK model for toluene to a similar PBPK model for xylene via the 

metabolism term in the liver compartment to test if there was no metabolic interaction between these 

compounds or if a metabolic interaction existed that could be described by competitive, noncompetitive, 

or uncompetitive inhibitory interaction. A model with a competitive inhibition metabolic term provided 

the best visual fit to empirical data for air concentrations of toluene and xylene during 5-hour exposures 

of rats in a closed chamber to mixtures of toluene and xylene at several initial concentrations. 

A five-compartment rat PBPK model developed by DeJongh and Blaauboer (1996) is similar in design to 

the Tardif rat PBPK model except that it contains an additional compartment, (i.e., the brain, which is 

assumed to be nonmetabolizing). The model used the same toluene partition coefficients used in the 

Tardif et al. (1993) rat model; the brain/blood partition coefficient, 2.0, was estimated from a published 
 

 

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value for the human brain/air coefficient and the rat blood/air coefficient. Reference rates for alveolar 

ventilation (14 L/hour/kg) and cardiac output (14 L/hour/kg) were scaled by a factor of body weight to 

the 0.74 power. With other parameters in the model held constant, models with different published values 

of Vmax and Km for toluene metabolism in rat liver from two in vivo and six in vitro rat studies were 

compared for their ability to fit empirical data from several studies for toluene blood concentrations or 

toluene brain concentrations in rats exposed to inhaled toluene. DeJongh and Blaauboer (1996) judged 

that a Vmax of 4.31 mg/kg/hour and Km of 0.26 mg/L gave the overall best fit to the empirical data, but 

noted that differences were generally small among predictions from models with the various values of 

Vmax and Km. 

Dejongh et al. (1998) used their rat PBPK model for toluene and similar models for 14 other volatile 

organic chemicals to examine a hypothesis that the acute lethality of volatile organic chemicals is related 

to their ability to distribute into the brain. Using these models to calculate the dose in the brain associated 

with the LC50 for the compounds, it was noted that the products of the LC50 and their respective exposure 

durations ranged by about 60-fold, whereas the PBPK-derived brain doses associated with the 

LC50 ranged by about 6-fold. Dejongh et al. (1998) concluded that this observation supports the 

hypothesis that the acute lethality of volatile organic chemicals, including toluene, is directly related to 

the extent of their distribution into the brain. 

2.4 MECHANISMS OF ACTION 

2.4.1 Pharmacokinetic Mechanisms 

Absorption. In humans and animals, toluene is rapidly absorbed by inhalation exposure (Benignus et 

al. 1984; Hjelm et al. 1988; Hobara et al. 1984b; Lof et al. 1993). Animal studies have shown that 

toluene is absorbed less rapidly by the oral route (Ameno et al. 1992; Pyykko 1983b), while toluene is 

absorbed slowly through human skin (Dutkiewicz and Tyras 1968). Studies with brush border membrane 

vesicles isolated from rat intestines and exposed to toluene indicate that toluene absorption occurs 

through the lipid matrix of the membrane (Alcorn et al. 1991). 

Distribution. Toluene has been identified in brain, liver, lung, and blood in humans following toluene 

exposure (Paterson and Sarvesvaran 1983; Takeichi et al. 1986). Within the human brain, toluene has a 

greater affinity for areas of the brain that contain lipid-rich white matter, such as the brain stem, rather 

than the areas with larger amounts of grey matter (Ameno et al. 1992). The human data are supported by 
 

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animal studies where distribution of toluene was found to be characterized by uptake in lipid tissues 

(brain and fat) immediately following inhalation exposure (Ghantous and Danielsson 1986). 

Excretion. In both humans and rats, up to about 75–80% of inhaled toluene that is absorbed can be 

accounted for by urinary excretion of the principal metabolite, hippuric acid (Lof et al. 1993; Ogata 1984; 

Tardif et al. 1998). Excretion of minor metabolites including S-benzyl mercapturic acid, S-p-tolulyl 

mercapturic acid, and conjugates of ortho- and para-cresol account for less than 5% of absorbed toluene. 

Excretion of nonmetabolized toluene in exhaled air can represent from 7 to 20% of absorbed toluene 

(Carlsson 1982; Leung and Paustenbach 1988; Lof et al. 1993). Although the liver is expected to be the 

main site of metabolism of toluene, CYP2E1, one of the principal isozymes catalyzing the initial reaction 

in the principal toluene metabolic pathway, has been detected in human lung microsomes at 

concentrations about 10-fold less than in liver microsomes (Wheeler et al. 1992). Under conditions in 

which the main pathway of toluene metabolism is inhibited by co-exposure with ethanol, exhalation of 

nonmetabolized toluene can become a principal route of excretion (Baelum et al. 1993). 

2.4.2 Mechanisms of Toxicity 

The mechanism by which acute exposure to toluene brings about neurological effects such as central 

nervous system depression and narcosis is generally thought to involve, at least in part, reversible 

interactions between toluene (the parent compound and not its metabolites) and components (lipids or 

proteins) of nervous system membranes. Support of parent-material involvement comes from the 

observation that pretreatment of rats with phenobarbital increased the rate of in vivo toluene metabolism 

and shortened the time of recovery from narcosis from single intraperitoneal doses of toluene (Ikeda and 

Ohtsuji 1971). Other support for this hypothesis includes the transient nature of anesthesia from acute 

high level exposure to toluene and the rapidity with which toluene-induced changes in brain biochemical 

variables can be measured. For example, within 0.25–1 hour of intraperitoneal injection of 1-g/kg doses 

of toluene into rats, brain synaptosomes showed decreased phosphatidylethanolamine content, altered 

phospholipid methylation activities, altered outer membrane fluidity, and increased Na+-K+-ATPase 

activities (Lebel and Schatz 1988, 1989, 1990). Decreased Mg++-ATPase activities were measured in 

brain synaptosomes isolated from rat brains immediately following a 2-hour exposure to 2,000 ppm 

toluene (Korpela and Tahti 1988). Average whole brain concentrations of several biogenic amines 

(dopamine, norepinephrine, and 5-hydoxytrytamine) were increased in rats immediately following an 

8-hour exposure to 1,000 ppm toluene (Rea et al. 1984). On a molecular scale, the acute anaesthetic 

actions of toluene and other agents have been postulated to involve intercalation of toluene into the lipid 
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bilayer of nerve membranes and/or reversible interactions with proteins in the membrane (Franks and 

Lieb 1985, 1987). 

Clinically obvious neurological impairment (e.g., gait and speech abnormalities) and brain atrophy have 

been observed in several cases of chronic toluene-inhalation abuse. MRI of the brain of solvent abusers 

(Filley et al. 1990; Rosenberg et al. 1988a, 1988b) suggest preferential atrophy in lipid-rich regions of the 

brain. Rosenberg et al. (1988a,1988b) found MRI evidence of diffuse central nervous system 

demyelination in 6 toluene abusers with clinically obvious neurological impairment, whereas Filley et al. 

(1990) noted that the degree of MRI-detected white matter abnormality in 14 solvent abusers was 

correlated with neurological impairment. The observed changes in MRI signals may be related to lipid 

compositional changes in the white matter, since these regions are more lipid-rich than gray matter 

(Ameno et al. 1992). These observations are consistent with a hypothesis that chronic exposure to high 

concentrations of toluene brings about structural changes in the brain related to lipid compositional 

changes. Supporting evidence for this hypothesis includes observations of changed phospholipid 

composition of rat brain synaptosomes following acute exposure to toluene (Lebel and Schatz 1988, 

1989, 1990), decreased phospholipid concentrations in the cerebral cortex of rats following 30 days of 

continuous exposure to 320 ppm (Kyrklund et al. 1987), and decreased number of neurons in the 

hippocampus of rats, 4 months after exposure to 1,500 ppm toluene, 6 hours/day, 5 days/week for 

6 months (Korbo et al. 1996). It is uncertain if toluene-induced changes in membrane phospholipid 

content may be caused by increased breakdown of phospholipids or inhibition of synthesis. 

Mechanistic understanding is poor of effects that have been associated with intermediate and chronic 

exposure to toluene in workplace air such as increased symptoms of mild neurological impairment (Boey 

et al. 1997; Orbaek and Nise 1989; Ukai et al. 1993; Yin et al. 1987), performance deficits on 

neurobehavioral tests (Foo et al. 1990; Iregren 1982), hearing loss and changes in brainstem auditoryevoked potentials (Abbate et al. 1993; Morata et al. 1997; Vrca et al. 1996), and color vision impairment 

and changes in brainstem visual-evoked potentials (Muttray et al. 1997, 1999; Vrca et al. 1995, 1997a, 

1997b; Zavalic et al. 1998a, 1998b, 1998c), but several mechanistic actions have been postulated. 

One mechanistic hypothesis postulates that repeated interaction of toluene with membrane proteins and/or 

phospholipids in brain cells can change activities of enzymes involved in the synthesis and/or degradation 

of neurotransmitters and that levels of neurotransmitters at particular sites in the brain may be involved in 

producing subtle neurological effects. Some evidence for this hypothesis comes from observations of 

increased concentrations of dopamine, norepinephrine, and 5-hydroxytryptamine in rats exposed to 
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1,000 ppm for 8 hours (Rea et al. 1984) and in rats exposed to up to 105 mg/kg/day in drinking water for 

28 days (Hsieh et al. 1990b), decreased dopamine levels and rates of turnover in several areas of the 

nucleus caudate in the brain of rats exposed to 80 ppm toluene, 6 hours/day for 3 days (Fuxe et al. 1982), 

increased levels of dopamine and noradrenaline in several brain regions in rats exposed to 80–3,000 ppm, 

6 hours/day for 3 days (Andersson et al. 1983), and decreased activities of aromatic acid decarboxylase, 

an enzyme involved in synthesis of neurotransmitters, in the brain stem of rats exposed to 250 or 

1,000 ppm, 8 hours/day, 5 days/week for 4 weeks (Bjornaes and Naalsund 1988). 

Another mechanistic hypothesis postulates that repeated exposure to toluene may cause neurological 

effects by changing the binding of neurotransmitters to membrane receptors. In support of this 

hypothesis, persistent changes in brain-tissue dopamine D2 receptor binding and increased serum 

prolactin levels were found in rats 17 days after exposure to 80 ppm toluene 6 hours/day, 5 days/week for 

4 weeks (von Euler et al. 1993, 1994). It was speculated that the increase in serum prolactin level could 

be related to a possible interaction between toluene and the pituitary dopamine D2 receptor; this receptor 

normally inhibits the release of prolactin into serum. Correlated with these biochemical changes were a 

significantly increased locomotor activity (approximately 2-fold) in response to injections of apomorphine (a dopamine) and a significantly increased escape latency (indicating impaired spatial learning and 

memory) in a water maze task, both observed 14–17 days after the 4-week toluene exposure (von Euler 

et al. 1994). Whether or not this hypothesis is related to effects observed in occupationally exposed 

humans is uncertain; Svensson et al. (1992b) did not find changes in serum prolactin levels in tolueneexposed printing workers compared with controls. 

Significant decreases (28 or 47%) in rat brain glial fibrillary acidic protein (GFAP) induced by exposure 

to 1,000 ppm toluene, 6 hours/day for 3 or 7 days have been associated with increased serum levels of 

corticosterone (Little et al. 1998). The decreases in GFAP were observed in the thalamus and 

hippocampus, regions of the brain that are reported to be involved in controlling serum glucocorticoid 

levels and have high concentrations of glucocorticoid receptors, respectively (Little et al. 1998). Little et 

al. (1998) postulated that decreases in brain GFAP may be a consequence of toluene disruption of the 

hypothalamic-pituitary-adrenal axis and/or hormonal homeostasis, but noted that the available evidence is 

inadequate to firmly establish cause and effect. The possible mechanistic connections of these 

observations to toluene-induced changes in neurobehavior are uncertain. 

There is evidence that hearing loss in animals induced by inhalation exposure to toluene is produced by 

toluene itself and not by its metabolites. Phenobarbital pretreatment, which increases the rate of in vivo 
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metabolism of toluene, prevented hearing loss in rats exposed to 1,500–2,000 ppm toluene, 8 hours/day 

for 7 days (Pryor et al. 1991). Rats that were given large gavage doses of ethanol (4 g/kg/day) and daily 

inhalation exposure to toluene concentrations of 1,750 ppm, 6 hours/day, 5 days/week for 4 weeks 

showed significantly greater hearing loss (as measured by auditory-evoked brainstem potentials) and 

outer hair cell loss in the ear than those exposed to toluene alone (Campo et al. 1998). Co-exposure to 

ethanol caused a significant decrease in hippuric acid urinary excretion rates compared with exposure to 

toluene alone, indicating that these large doses of ethanol inhibited the metabolism of toluene (Campo et 

al. 1998). Since exposure to ethanol alone in this study did not affect hearing or outer hair cell loss in the 

ear, ethanol inhibition of toluene metabolism and subsequent potentiation of toluene-induced loss of 

hearing are consistent with the idea that toluene itself is responsible for these effects. Mechanistic 

understanding at the molecular and cellular level is poor regarding how toluene exposure leads to a loss of 

outer hair cells in the ear and the degree to which toluene effects on neural cell membranes may be 

involved. 

The molecular mechanism and pathogenesis of color vision impairment (dyschromatopsia) associated 

with occupational and intentional abusive exposure to toluene and other organic solvents are not clearly 

understood, but it has been postulated that toluene interference with dopaminergic mechanisms of retinal 

cells or toxic demylelinizaton of optic nerve fibers may be involved (Muttray et al. 1997, 1999; Zavalic 

et al. 1998a, 1998b, 1998c). 

The postulated arene oxide intermediates formed in the metabolic pathway from toluene to ortho- or 

para-cresol are highly reactive and expected to bind to cell proteins and RNA, thereby potentially leading 

to cellular dysfunction and degeneration. Studies with human and rat liver microsomes and tissue slices 

showed that incubation with labeled toluene leads to incorporation of the label into microsomal proteins 

and RNA in an NADP-requiring reaction (Chapman et al. 1990). It does not appear likely, however, that 

this mechanism of action is the primary mode of toluene’s toxicity, especially at air concentrations below 

100 ppm that are of occupational and public health concern, because: 

(1) the liver is expected to be the main site of toluene metabolism, 

(2) the pathway to the cresol isomers accounts for less than 1–5% of metabolized toluene (see 

Section 2.3.3), 

(3) results from animals studies and studies of toluene-exposed workers do not identify the liver as 

the most sensitive target organ (see Section 2.2.1.), and 
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(4) degenerative lesions in nervous tissues have not been detected by light microscopy in rats and 

mice exposed to concentrations as high as 1,200 ppm 6.5 hours/day, 5 days/week for up to 2 years 

(CIIT 1980; NTP 1990). 

The available evidence, however, is not sufficient to discard the hypothesis that this mode of action (i.e., 

cellular degeneration caused by reactive metabolic intermediates) may play some role in toluene toxicity, 

especially with high-level exposures such as those experienced by toluene abusers. 

2.4.3 Animal-to-Human Extrapolations 

Many laboratory animal species have been used to describe toluene toxicity, but the most commonly used 

species is the rat. Generally, the toxicokinetic data gathered from rat studies compare favorably with the 

information available from human studies. In addition, neurological effects observed in rats including 

changes in locomotor activity, changes in visual- and auditory-evoked brainstem potentials, hearing loss, 

and changes in brain chemistry appear to be related to critical neurological effects observed in humans 

after acute or repeated exposure to toluene including self-reported neurological symptoms, impaired 

performance in neurobehavioral tests, hearing loss, and color vision impairment. Given the availability of 

data for humans exposed by inhalation, MRLs for inhaled toluene are derived without extrapolating from 

the available animal toxic-effects data. In contrast, acute and intermediate MRLs for oral exposure to 

toluene are based on extrapolating neurological effects in rats to humans (see Section 2.5 and Appendix 

A). 

As discussed in Section 2.3.5, PBPK models describing the kinetics of toluene after inhalation exposure 

have been developed for humans (one with four compartments— adipose tissue, liver, and rapidly and 

slowly perfused tissues, and another with a fifth compartment—breast milk) and rats (one with the basic 

four compartments and another model with a fifth compartment—the brain). Further development of a 

human PBPK model that includes partitioning of inhaled and ingested toluene to the brain and a similarly 

designed rat PBPK model may be useful in improving extrapolation from the oral exposure rat data and in 

comparing model-based predictions of human effect levels based on neurological effects in inhalationally 

exposed rats with observed effect levels in humans exposed to airborne toluene. 
 

 

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2.5 RELEVANCE TO PUBLIC HEALTH 

Overview. 

Adverse effects on the nervous system are the critical effects of concern from acute, intermediate, or 

chronic exposure to toluene. Acute exposure is associated with reversible neurological symptoms 

progressing from fatigue, headaches, and decreased manual dexterity to narcosis with increasing exposure 

levels. Reversible neurological impairment from acute exposure likely involves the direct interaction of 

toluene with nervous system membranes. Degenerative changes in white matter regions of the brain have 

been correlated with the severity of persistent neurological impairment in individuals who abused 

solvents and have repeatedly inhaled toluene at high exposure levels (4,000–12,000 ppm). Results from 

studies of groups of occupationally exposed workers suggest that chronic exposure to toluene at lower 

exposure levels (from about 50 to 200 ppm) can produce subtle changes in neurological functions 

including cognitive and neuromuscular performance, hearing, and color discrimination. Supporting data 

come from studies of toluene-exposed animals showing changes in behavior, hearing loss, and subtle 

changes in brain structure, electrophysiology, and levels of neurotransmitters. Case reports of birth 

defects in children of mothers who abused toluene during pregnancy suggest that exposure to high levels 

of toluene may be toxic to the developing fetus. However, results from animal studies indicate that 

toluene is not a teratogenic agent, but can retard fetal growth and skeletal development and adversely 

influence behavior of offspring at exposure levels that overwhelm maternal mechanisms protecting the 

developing fetus from exposure. Other adverse health effects, including cancer or effects on reproductive 

performance, do not appear to be of concern for persons who may experience low exposures to toluene by 

living or working near hazardous waste sites containing toluene. 

Issues relevant to children are explicitly discussed in Section 2.7, Children’s Susceptibility and 

Section 5.6, Exposures of Children. 

Minimal Risk Levels for Toluene. 

Inhalation MRLs. 

C An MRL of 1 ppm (3.8 mg/m3

) has been derived for acute-duration (14 days or less) inhalation 

exposure to toluene. 
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This MRL is based on a study by Andersen et al. (1983) in which the effects of toluene on 16 healthy 

young subjects with no previous regular exposure to organic solvents were investigated (see Appendix 

A). Groups of 4 subjects were in a chamber for 6 hours a day on 4 consecutive days. The concentration 

of toluene was 0, 10, 40, or 100 ppm, with the subjects exposed to a different concentration each day. 

Physiological measurements were performed, including nasal mucociliary flow, and subjective 

measurements of discomfort. Eight different performance assessment tests were carried out. There was a 

statistically significant increase (P<0.05%) in the occurrence of headaches, dizziness, and feelings of 

intoxication during the 100 ppm exposure, but not during exposure to the other concentrations. No 

statistically significant effects of toluene occurred in the eight performance tests. For 3 of the tests, there 

was borderline significance (P<0.10%): the subjects felt that the tests were more difficult and strenuous 

during the 100 ppm exposure. No adverse effects were reported at the 10 and 40 ppm levels. The 

NOAEL of 40 ppm was adjusted to continuous exposure basis 

(40 ppmx5 days/daysx8 hour/24 hour=9.5 ppm) and divided by an uncertainty factor of 10 (to account for 

human variability) to derive the MRL of 1 ppm. 

C No MRL has been derived for intermediate-duration (15–364 days) inhalation exposure to 

toluene. 

No data were considered suitable for use in deriving an intermediate-duration MRL for inhalation 

exposures. ATSDR believes that the chronic inhalation MRL would also be protective for intermediateduration exposures. 

C An MRL of 0.08 ppm (0.3 mg/m3

) was derived for chronic-duration (365 days or more) inhalation 

exposure to toluene. 

The chronic inhalation MRL is based on a LOAEL of 35 ppm toluene for color vision impairment in a 

group of toluene-exposed shoemakers studied by Zavalic et al. (1998a) and an uncertainty factor of 

100 (10 for the use of a LOAEL and 10 to account for human variability). The study examined color 

vision abilities in three groups of workers: (1) 46 shoemakers exposed for an average of 16 years to a 

median toluene concentration of 32 ppm; (2) 37 rotogravure printing workers exposed for an average of 

18 years to a median toluene concentration of 132 ppm; and (3) 90 control workers without any known 

exposure to solvents or neurotoxic agents. Average scores in a color confusion index (based on results of 

color vision tests and adjusted for age and alcohol intake) were significantly increased in the tolueneexposed shoemakers and printers compared with scores for control workers. The chronic LOAEL of 

32 ppm is supported by observations of other subtle neurological effects in other groups of toluene­
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exposed workers including altered visual-evoked brainstem potentials in printing press workers exposed 

to 50 ppm for 30 years (Vrca et al. 1995, 1996, 1997a, 1997b), altered auditory-evoked brainstem 

potentials in printers exposed to 97 ppm for 12–14 years (Abbate et al. 1993), hearing loss in printers 

exposed to 0.04–245 ppm toluene (Morata et al. 1997), changes in electro cardiographic R-R intervals in 

printers exposed to 83 ppm for 1–36 years (Murata et al. 1993), performance deficits in neurobehavioral 

tests in electronics workers exposed to 88–90 ppm (Boey et al. 1997; Foo et al. 1990), and increased 

incidence of self-reported neurasthenic symptoms in printers exposed to an average concentration of 

about 140 ppm over a 29-year period (Orbaek and Nise 1989). 

Most of the data on health effects in humans exposed to toluene come from occupational studies or 

medical reports of solvent abusers. In both situations, concurrent exposure to other chemicals can limit 

the usefulness of the data for development of guidelines or standards. In addition, there are other 

confounding variables, especially in the occupational setting, such as alcohol consumption patterns, 

employment history, diet, use of medications, noise, and fluctuations in atmospheric toluene levels during 

different portions of the day, all of which complicate evaluation of dose-response patterns. These 

limitations were considered in selecting the studies for derivation of the MRLs. 

ACGIH has recommended a TLV of 50 ppm toluene based on reports of headache and irritation 

associated with 4–6 hours continuous inhalation of toluene (Andersen et al. 1983; Baelum et al. 1985; 

Echeverria et al. 1989; Wilson 1943). This value is designed to be protective for healthy adult workers 

exposed 8 hours/day, 5 days/week for up to 45 years. Adjusting the value for a continuous exposure 

lasting up to 70 years yields a value of 8 ppm (50 ppm x 5 days/7 days x 8 hours/24 hours 

x 45 years/70 years=8 ppm). This figure is somewhat higher than the current chronic-duration MRL, but 

does not include an uncertainty factor to protect susceptible populations. Use of an uncertainty factor of 

100 (10 for human variability and 10 for use of a LOAEL) would arrive at a value to 0.08 ppm, which is 

identical to the current MRL. 

Oral MRLs. 

C An MRL of 0.8 mg/kg has been derived for acute (14 days or less) oral exposure to toluene. 

This MRL was based on a LOAEL of 250 mg/kg from a study of flash-evoked potential (FEP) wave 

forms in male Long-Evans rats administered doses of 0, 250, 500, or 1,000 mg/kg toluene by gavage 

(Dyer et al. 1988). Flash-evoked potential tests were administered 45 minutes later as a test of the ability 
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2. HEALTH EFFECTS 

of the nervous system to process visual information. The amplitude of the N3 peak of the FEP was 

decreased by toluene exposure at all doses (P<0.0001). This decrease in peak amplitude was not doserelated. Dyer et al. (1988) also carried out a time-course study in which toluene was administered to male 

Long-Evans rats (16 per group) at doses of 0 and 500 mg/kg by gavage and flash-evoked potential tests 

were performed 4, 8, 16, and 30 hours later. In the time course study, 500 mg/kg also decreased the 

amplitude of the flash-evoked potential; at this dose, little change in magnitude of peak N3 depression 

had occurred 8 hours posttreatment; by 16 hours recovery was complete. An uncertainty factor of 

300 was used for this determination (3 for use of a minimally adverse LOAEL, 10 for interspecies 

extrapolation, and 10 for intraspecies variability). 

C An MRL of 0.02 mg/kg/day has been derived for intermediate-duration (15–364 days) oral 

exposure to toluene. 

This MRL was derived from a LOAEL of 5 mg/kg/day based on regional increases in monoamine 

neurotransmitters in the brains of CD1 mice exposed to toluene through their drinking water for 28 days 

(Hsieh et al. 1990b). Based on water consumption and average toluene concentrations, the authors 

calculated toluene doses for the 4 treatment doses of 0, 5, 22, and 105 mg/kg/day over this period. Brain 

levels of norepinephrine, dopamine, serotonin (5-hydroxytryptamine), and their metabolites 

vanillylmandelic acid, 3,4-dihydroxy-phenylacetic acid, homovanillic acid, and 5-hydroxyindolacetic acid 

were measured in six areas of the brain in the mice. Significant increases (P<0.05) in neurotramsmitter 

levels were seen in all six regions of the brain of animals gavaged with toluene; in general, the increase 

was maximal at 22 mg/kg/day. Significantly increased norepinephrine levels were present in the 

hypothalamus, midbrain, and medulla oblongata. Serotonin levels were significantly increased in the 

hypothalamus, midbrain, and cerebral cortex. The maximum increase of serotonin (P<0.005), dopamine 

(P<0.05), and norepinephrine (P<0.05) in the hypothalamus occurred at 22 mg/kg/day. In the corpus 

striatum, the levels of dopamine and serotonin were significantly increased at the two highest doses. In 

the medulla oblongata, significant toluene increases of norepinephrine and homovanillic acid were seen 

only at 22 mg/kg/day. It should be noted that these are minimal effects, and it is unclear how they are 

related to neurobehavioral changes. An uncertainty factor of 300 was used for this determination (3 for 

the use of a minimally adverse LOAEL, 10 for interspecies extrapolation, and 10 for intraspecies 

variability). 

No MRL was derived for chronic-duration oral exposures because there were no suitable data for toluene. 
 

 

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Death. Case studies that reported on deaths in humans due to exposure to toluene have generally not 

provided information on dose and thus, do not provide a basis for quantitative estimates. In one instance, 

intake of 625 mg/kg resulted in death within 30 minutes (Ameno et al. 1989). 

It has been suggested that the mechanism for death due to solvent abuse might be apparent sensitization 

of the myocardium and consequent sudden and severe arrhythmia resulting from mild anesthesia, and 

intensified by hypercapnia (excess of carbon dioxide) (Bass 1970). Studies in dogs further suggest that 

some individuals may be more sensitive to arrhythmic responses to toluene than others (Ikeda et al. 1990). 

In a single report of human death following oral ingestion of toluene, the cause of death appeared to be 

profound disruption of central nervous system function (Ameno et al. 1989). Exposure to toluene at a 

hazardous waste site is not likely to be of lethal magnitude. 

Systemic Effects. 

Respiratory Effects. The primary effect of toluene on the respiratory tract following inhalation is 

irritation. Studies with volunteers (Andersen et al. 1983; Carpenter et al. 1944; Baelum et al. 1985) and 

exposed workers (Parmeggiani and Sassi 1954) have demonstrated that toluene is a mild-to-moderate 

respiratory irritant. Early animal studies by von Oettingen et al. (1942) reported respiratory irritation and 

pulmonary lesions in rats exposed to high concentrations of toluene. The findings of von Oettingen et al. 

(1942) are supported by more recent observations of nasal lesions (including metaplasia of olfactory 

epithelium and degeneration of respiratory epithelium) in rats exposed to concentrations ranging from 

600 to 1,200 ppm, 6.5 hours/day, 5 days/week for 2 years (NTP 1990). Mice exposed by the same 

exposure protocol to a similar range of concentrations, however, did not display upper or lower 

respiratory tract lesions (NTP 1990). Acute, intermediate, or chronic inhalation exposure to toluene at a 

hazardous waste site might result in respiratory tract irritation, especially if release of toluene is into an 

enclosed space where higher concentrations may develop, but other adverse effects on the lungs or 

breathing passages are not expected. 

Cardiovascular Effects. Inhalation exposure to toluene at concentrations above 1,000 ppm has been 

associated with alterations of the heart rhythm in both humans and animals (Anderson et al. 1982; Einav 

et al. 1997; Ikeda et al. 1990; Magos et al. 1990; Meulenbelt et al. 1990; Vidrio et al. 1986), but exposure 

of rats or mice to concentrations as high as 12,000 ppm (3 hours/day) for intermediate durations or 

1,200 ppm (6.5 hours/day) for chronic durations produced no histological changes in heart tissue 

(Bruckner and Peterson 1981b; CIIT 1980; NTP 1990). There may be intraspecies differences in the 
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cardiac response to toluene that make some individuals more susceptible than others to potentially fatal 

arrhythmias; the degree of hypoxia may also be important (Ikeda et al. 1990). 

The exposure scenarios associated with cardiac rhythm disturbances were of the short-term, high-level 

type experienced by substance abusers. Accordingly, cardiovascular responses are not expected to occur 

following toluene exposure at or near a hazardous waste site, unless some occurrence releases a high 

concentration of toluene into an enclosed space. 

Gastrointestinal Effects. The only gastrointestinal effect reported after exposure to toluene was 

ulceration of the forestomach of rats exposed to 600 and 1,200 ppm by inhalation for 2 years (NTP 1990). 

Similar effects were not seen in mice exposed under the same conditions or to rats or mice orally exposed 

to 2,500 mg/kg/day for 13 weeks (NTP 1990). There is a slight possibility that long-term toluene 

exposure resulting from the contamination of hazardous waste sites would cause gastrointestinal irritation 

in the exposed population. 

Hematological Effects. Before the mid-1950s, chronic occupational exposure to toluene was associated 

with hematological effects (Greenburg et al. 1942; Wilson 1943). However, these effects are now 

attributed to benzene, a common contaminant of toluene at that time (EPA 1985c). In several recent 

studies, no significant effects of toluene on hematological parameters in workers exposed to toluene or a 

to mixture of solvents has been observed (Banfer 1961; Capellini and Alessio 1971; Ukai et al. 1993; Yin 

et al. 1987). In contrast, Tahti et al. (1981) reported a slight positive correlation between exposure and 

decreased blood leukocyte counts in workers. However, the authors did not report whether the workers 

were also exposed to other organic solvents. Therefore, effects that were observed cannot be attributed 

solely to toluene. Decreased leukocyte and white blood cell counts were observed in dogs and rats 

repeatedly exposed to airborne toluene (Hobara et al. 1984a; Horiguchi and Inoue 1977; von Oettingen 

et al. 1942), but have not been observed consistently in other studies of rats and mice exposed by 

inhalation (NTP 1990; Ono et al. 1996; Poon et al. 1994) or by oral administration ( Hsieh et al. 1989; 

NTP 1990; Wolf et al. 1956). In the study by von Oettingen et al. (1942), rats exposed to high 

concentrations (2,500 or 5,000 ppm) of toluene for 7 hours each day had decreased leukocyte counts 

following exposure; however, the leukocyte numbers generally returned to normal by the next day. The 

toxicological significance of a transitory decrease in numbers of leukocytes is not apparent. Since effects 

on hematological variables have not been observed consistently in studies of occupationally exposed 

humans or in animals exposed to toluene, they are not expected to occur from acute, intermediate, or 

exposures at or near hazardous waste sites. 
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Musculoskeletal Effects. There is one case report of a man who had been sniffing glue containing 

toluene for 18 years. He complained of severe muscle weakness and was diagnosed with rhabdomyolysis 

(an acute disease of the skeletal muscles evidenced by myoglobin in the blood and urine) (Hong et al. 

1996). However, it is not expected that any such effects would result from toluene exposure at or near a 

hazardous waste site. 

Hepatic Effects. Studies of chronic toluene abusers or occupationally exposed humans have provided 

little evidence for serious liver damage due to inhaled toluene. Some studies of workers occupationally 

exposed to average concentrations between about 30 and 350 ppm toluene have reported liver effects such 

as increased serum levels of enzymes leaked from the liver (Guzelian et al. 1988; Svensson et al. 1992b), 

but others have recorded no adverse effects (Lundberg and Hakansson 1985; Seijii et al. 1987; Ukai et al. 

1993). Results from studies of animals exposed by inhalation for acute (Ungvary et al. 1982; Wang et al. 

1996), intermediate (Bruckner and Peterson 1981b; Kjellstrand et al. 1985; Kyrklund et al. 1987; NTP 

1990; Poon et al. 1994), or chronic (NTP 1990) durations indicate that daily 6- to 8-hour exposures to 

concentrations above 300 ppm, but not below, can lead to increased liver weights (Bruckner and Peterson 

1981b; NTP 1990; Poon et al. 1994; Ungvary et al. 1982) and induction of hepatic cytochrome P450 

levels (Ungvary et al. 1982; Wang et al. 1996). There are a few reports of toluene-induced effects that 

may be associated with liver damage [e.g., increased serum levels of liver enzymes in rats exposed to 

2,000 ppm for 48 hours (Tahti et al. 1983) and in rats exposed to 300 ppm, 6 hours/day for 4 weeks (Poon 

et al. 1994) and increased endoplasmic reticulum in hepatocytes after exposure of rats, mice, and rabbits 

to 795 ppm 8 hours/day for 7 days (Ungvary et al. 1982)], but no significant histopathological liver 

changes or liver weight changes were observed in well-conducted chronic-duration studies in which rats 

and mice were exposed to concentrations as high as 1,200 ppm, 6.5 hours/day, 5 days/week for 2 years 

(CIIT 1980; NTP 1990). Results from intermediate-duration oral-exposure studies in rats and mice 

support the idea that toluene does not cause degenerative liver effects, but, at sufficiently high doses, 

produces liver weight increases that are likely associated with enzyme induction (Hsieh et al. 1989; NTP 

1990; Wolf et al. 1956). It is possible that exposure of the general population to toluene at hazardous 

waste sites may increase the ability of the liver to metabolize xenobiotics, but other hepatic effects are not 

expected if exposure levels are at or below those normally experienced in workplaces using toluene. 

Renal Effects. The kidney may be a target of toluene toxicity in humans exposed to very high levels of 

toluene. Renal acidosis has been observed in solvent abusers exposed to toluene, but, in most cases, renal 

dysfunction is transient and normal function returns when exposure ceases ( Gerkin and LoVecchio 

1998; Goodwin 1988; Kamijima et al. 1994; Kamijo et al. 1998; Kaneko et al. 1992; Patel and Benjamin 
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2. HEALTH EFFECTS 

1986; Taverner et al. 1988). These cases, however, are frequently confounded by probable exposure to 

multiple solvents. Renal effects have not been observed in workers exposed to levels of toluene up to 

100–200 ppm for long durations (Askergren et al. 1981a; Nielsen et al. 1985). Animal studies indicate 

that inhalation of toluene causes kidney damage in rats (e.g., renal tubular casts), but only after 

intermediate or chronic exposure to concentrations $600 ppm for at least 6 hours/day (CIIT 1980; NTP 

1990; von Oettingen et al. 1942). Histological evidence of kidney damage was not found in rats and mice 

exposed to gavage doses as high as 5,000 mg/kg/day for 14 or 15 weeks (NTP 1990). In general, the 

available human and animal data suggest that kidney damage is not likely to occur with acute, 

intermediate, or chronic exposure at toluene levels likely to be experienced by people who may live close 

to, but not work at, hazardous waste sites containing toluene. 

Endocrine Effects. As discussed in more detail in Section 2.6, Endocrine Disruption, current data for 

toluene-exposed humans or animals provide suggestive, but not conclusive, evidence that toluene may 

cause some effects that may involve endocrine disruption including reports of increased abortions among 

female electronics workers (Ng et al. 1992b), changed levels of luteinizing hormone, follicular 

stimulating hormone, and testosterone in male printers exposed to toluene (Svensson et al. 1992a, 1992b), 

and increased serum levels of prolactin in rats exposed to 80 ppm toluene 6 hours/day, 5 days/week for 

4 weeks (Andersson et al. 1983; Hillefors-Berglund et al. 1995; von Euler et al. 1993, 1994). 

Other results from animal studies regarding possible endocrine disruption from toluene include decreased 

sperm counts and epididymides weight in male rats that were exposed to 2,000 ppm, 6 hours/day for 

90 days but showed no exposure-related changes in mating behavior or fertility indices when mated after 

60 days of exposure (Ono et al. 1996) and abundant vacuoles and mitochondrial degeneration in antral 

follicles of the ovaries of female rats exposed to 3,000 ppm, 8 hours/day for 7 days (Tap et al. 1996). 

Histopathological lesions in male or female reproductive organs, however, were not found in rats and 

mice exposed to gavage doses up to 2,500 mg/kg/day for 13 weeks or exposed (6–6.5 hours/day, 

5 days/week) to concentrations up to 2,500 ppm for 14–15 weeks or 1,200 ppm for 2 years (NTP 1990). 

Assessment of reproductive performance was not consistently affected by toluene in several other animal 

studies. Increased fetal mortality occurred after exposure of pregnant rats to 2,000 ppm, but not 600 ppm, 

6 hours/day on gestation days 7–17 or 14 days before through 7 days after mating (Ono et al. 1995, 

1996), and increased abortions occurred in pregnant rabbits exposed to 267 ppm, but not 133 ppm, 

24 hours/day on gestation days 7–20 (Ungvary and Tatrai 1985). However, the number of pregnant mice 

producing viable litters was not affected following oral administration of 2,350 mg/kg/day on gestation 
 

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days 7–14 (Smith 1983). In addition, reproductive performance variables and offspring survival were not 

significantly affected in two generations of rats exposed to 2,000 ppm, 6 hours/day for up to 95 days (API 

1985) or in rats exposed in utero to 1,200 ppm, 6 hours/day on gestation days 9–21 (Thiel and Chahoud 

1997). 

Dermal Effects. Skin irritation can occur in humans and animals dermally exposed to toluene (EPA 

1983a; Winchester and Madjar 1986; Wolf et al. 1956). This appears to be due to the degreasing action 

of toluene and its removal of protective skin oils. It is uncertain if toluene dissolved in water at or near 

hazardous waste sites would have an effect on the skin of individuals who come in contact with the 

contaminated water. 

Ocular Effects. Humans have reported eye irritation following exposure to toluene vapors (Andersen 

et al. 1983; Baelum et al. 1985; Carpenter et al. 1944, 1976; Meulenbelt et al. 1990). This is probably the 

result of direct contact of toluene vapor with the outer surface of the eye and thus, is not a true systemic 

effect. Slight to moderately severe irritation of rabbit eyes has been reported following direct application 

of toluene to the conjunctiva (Carpenter and Smyth 1946; Hazleton Laboratories 1962; Wolf et al. 1956). 

Reports of color vision deficits in occupationally exposed workers have been postulated to involve 

toluene interference with dopaminergic mechanisms of retinal cells or toxic demylelinizaton of optic 

nerve fibers (Muttray et al. 1997, 1999; Zavalic et al. 1998a, 1998b, 1998c). 

Body Weight Effects. Weight loss has been reported to occur in rats exposed to toluene for periods of 

11–23 weeks (Mattsson et al. 1990; Pryor 1991). 

Immunological and Lymphoreticular Effects. Only limited data are available on the immunological effects of toluene. The studies by Lange et al. (1973) and Moszczynski and Lisiewicz (1985) 

report decreased T lymphocyte counts and decreased serum IgG and IgA levels in occupationally exposed 

workers, but no signs of diminished immunological function or disturbances in immune skin reactions 

against such antigens as tuberculin or distreptase. However, because the specific solvent(s) responsible 

for the effects observed in these studies was not identified, the significance of the findings for humans 

exposed to toluene are unclear. 

Mice exposed to toluene for 4 weeks exhibited an increased susceptibility to infections (Aranyi et al. 

1985). Ingestion of doses of 22 mg/kg/day toluene caused adverse effects on lymphocyte proliferation 

and interleukin-2 immunity in mice exposed through their drinking water. At higher doses 
 

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(105 mg/kg/day), additional effects upon the immune system were observed (decreased thymus weight, 

lymphocyte culture responses, and antibody plaque-forming cell responses) (Hsieh et al. 1989, 1990b). 

There are no data to suggest that these same responses occur in humans. 

Neurological Effects. The nervous system is the critical target of toluene toxicity following acute, 

intermediate, or chronic inhalation or oral exposure to toluene. Studies with volunteers under controlled 

acute (6–8 hours) exposure conditions indicate that subtle neurological impairment is detectable in most 

subjects at concentrations in the 75–150 ppm range (Andersen et al. 1983; Baelum et al. 1985; Echeverria 

et al. 1991; Guzelian et al. 1988; Iregren 1986; Rahill et al. 1996). Concentrations of 200–800 ppm can 

produce exhilaration and light-headedness, and, at higher acute exposure concentrations, intellectual, 

psychomotor, and neuromuscular abilities are obviously impaired followed by development of narcosis 

(EPA 1985c; von Oettingen et al. 1942). 

Numerous case studies have associated chronic inhalation exposure to toluene at levels inducing narcosis 

and euphoria (4,000 to 12,000 ppm as estimated by Gospe et al. 1994) with residual or permanent 

neurological damage as evidenced by abnormal electroencephalograms, structural changes in the brain 

detected by MRI and SPECT, tremors, paranoid psychosis, recurrent hallucinations, and impaired speech, 

hearing, and vision (Byrne et al. 1991; Caldemeyer et al. 1996; Devathasan et al. 1984; Filley et al. 1990; 

Hunnewell and Miller 1998; Ikeda and Tsukagoshi 1990; Kamran and Bakshi 1998; King et al. 1981; 

Maas et al. 1991; Meulenbelt et al. 1990; Miyagi et al. 1999; Rosenberg et al. 1988a, 1988b; Ryu et al. 

1998; Suzuki et al. 1983; Yamanouchi et al. 1995). Studies of workers repeatedly exposed to toluene in 

workplace air at concentrations ranging from about 30 to 150 ppm have found evidence for increased 

incidence of self-reported neurological symptoms (Orbaek and Nise 1989; Yin et al. 1987), performance 

deficits in neurobehavioral tests (Boey et al. 1997; Foo et al. 1990; Orbaek and Nise 1989), hearing loss 

(Abbate et al. 1993: Morata et al. 1997), changes in visual-evoked brainstem potentials (Vrca et al. 1995, 

1997a, 1997b), and color vision impairment (Zavalic et al. 1998a, 1998b, 1998c). 

Studies with laboratory animals provide supporting evidence that the nervous system is the critical target 

of toluene toxicity. Acute (1 to 2 hours) inhalation exposure studies of behavior in rats, mice, and 

monkeys found evidence for stimulatory effects (e.g., increased locomotor activity, significantly 

increased response times) at concentrations ranging from 500 to 2,000 ppm, and central nervous system 

depression (e.g., decreased accuracy in conditioned response tests, decreased locomotor activity, and 

ataxia) at concentrations greater than 2,000 ppm ( Bowen and Balster 1998; Bruckner and Peterson 

1981a, 1981b; Bushnell et al. 1985; Hinman 1987; Taylor and Evans 1985). Rats exposed for 4 hours to 
 

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concentrations as low as 125 ppm toluene showed performance deficits in several trained neuromuscular 

responses (Kishi et al. 1988; Mullin and Krivanek 1982; Wood et al. 1983). Acute- and intermediateduration inhalation exposure studies reported changes in several brain biochemical variables (e.g., 

dopamine levels, dopamine D2 receptor binding, changes in glial fibrillary acidic protein) in rats at 

exposure levels as low as 50–80 ppm for 6–8 hours/day (API 1997; Hillefors-Bergllund et al. 1995; Ikeda 

et al. 1986; Little et al. 1998; von Euler et al. 1989b, 1993, 1994). Neurological effects observed in 

animals after acute- or intermediate-duration oral exposure include changed flash-evoked potentials in 

rats given single gavage doses of toluene as low as 250 mg/kg (Dyer et al. 1988), changes in levels of 

several neurotransmitters (e.g., norepinephrine, dopamine, serotonin) in several brain regions of mice 

exposed to 5–105 mg/kg/day in drinking water for 28 days (Hsieh et al. 1990b), and clinical signs of 

central nervous system dysfunction including ataxia, prostration, and tremors in rats and mice exposed to 

gavage doses $2,500 mg/kg/day for 13 weeks (NTP 1990). Other toluene-induced neurological effects 

reported in studies of animals with intermediate to chronic inhalation exposure include hearing loss in rats 

exposed to concentrations as low as 700–1000 ppm, 6–14 hours/day for 2–9 weeks (Campo et al. 1997, 

1998; Johnson et al. 1988; Pryor and Rebert 1992; Pryor et al. 1984a, 1984b, 1991;), abnormal flashevoked brain potential responses in rats exposed to 8,000 ppm for 15–35 minutes, 4–9 times/days for 

13 weeks (Mattson et al. 1990), decreased weight of the total brain and the cerebral cortex, associated 

with decreased phospholipid content, in rats continuously exposed to 320 ppm for 30 days (Kyrklund et 

al. 1987), and decreased number of neurons in the hippocampus of rats, 4 months after exposure to 

1,500 ppm toluene, 6 hours/day, 5 days/week for 6 months (Korbo et al. 1996). 

Reproductive Effects. There is some evidence that women occupationally exposed to toluene, or 

wives of men similarly exposed, have an increased risk of spontaneous abortions (Lindbohm et al. 1992; 

Ng et al. 1992b; Taskinen et al. 1989). However, interpretation of these results is limited due to small 

sample size evaluated, an inability to define accurate exposure levels, failure to account for all possible 

confounding variables, and the difficulty in validating self-reported data. The occurrence of testicular 

atrophy (Suzuki et al. 1983) in one case of chronic solvent abuse cannot be specifically attributed to 

toluene exposure. Occupational exposure to increasing concentrations of toluene (8–<111 ppm) has been 

associated with decreased plasma levels of the luteinizing hormone, follicle stimulating hormone and 

testosterone levels in males (Svensson et al. 1992a, 1992b). 

Results from the moderate number of animal studies examining reproductive end points following toluene 

exposure were discussed in detail in the Endocrine Effects portion of this section. These studies found 

some evidence for minor toluene-induced changes in male and female reproductive organs [e.g., 
 

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decreased sperm count in male rats (Ono et al. 1995, 1996) and ultra structural changes in antral follicles 

in ovary of female rats (Tap et al. 1996)], but no histological evidence of structural damage to the 

reproductive organs in rats and mice exposed orally for intermediate durations or by inhalation for 

intermediate or chronic durations (NTP 1990). No evidence for impaired reproductive performance was 

found in several assays (Ono et al. 1995, 1996; Smith 1983; Thiel and Chahoud 1997), including a 

2-generation study of rats exposed to up to 2,000 ppm, 6 hours/day (API 1985), except that exposure 

during pregnancy produced increased fetal mortality in rats exposed to 2,000 ppm, but not 600 ppm, 

6 hours/day, on gestation days 7–17 or for 14 days before through 7 days after mating (Ono et al. 1995, 

1996), and increased abortions in pregnant rabbits exposed to 267 ppm, but not 133 ppm, 24 hours/day on 

gestation days 7–20 (Ungvary and Tatrai 1985). 

In general, the available results from studies of humans and animals suggest that toluene is not a potent 

reproductive toxicant, but may cause some reproductive problems, especially with repeated inhalation 

exposure during pregnancy to concentrations above 200 ppm. 

Developmental Effects. There are a number of published reports of birth defects, similar to those 

associated with fetal alcohol syndrome, that have been described in children born to women who 

intentionally inhaled large quantities of toluene or other organic solvents during pregnancy (Arnold et al. 

1994; Erramouspe et al. 1996; Goodwin 1988; Hersch 1988; Hersch et al. 1985; Lindemann 1991; 

Pearson et al. 1994). Defects described include microcephaly, central nervous system dysfunction, 

growth deficiency, cranofacial and limb abnormalities, and reversible renal tubular acidosis. Studies of 

women exposed during pregnancy to much lower concentrations of toluene in the workplace are restricted 

to a retrospective study of 14 women in Finland occupationally exposed to mixed solvents that suggested 

that solvent exposure may increase risk for central nervous system anomalies and neural tube closure 

defects (Holmberg 1979). 

The reports of birth defects in solvent abusers suggest that high-level exposure to toluene during 

pregnancy can be toxic to the developing fetus. The available human data, however, do not establish 

causality between low-level or occupational exposure to toluene and birth defects, because of the small 

sample size and the mixed solvent exposure experienced by the subjects in the Holmberg (1979) study, 

the lack of other studies of possible birth defects in children of occupationally exposed women, and the 

likelihood that the high exposure levels experienced by pregnant solvent abusers (4,000–12,000 ppm) 

overwhelm maternal protection of the developing fetus from absorbed toluene. Experiments with 

pregnant mice demonstrated that 10-minute exposures to 2,000 ppm resulted in low uptake of toluene into 
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2. HEALTH EFFECTS 

fetal tissue and suggest that, at lower exposure levels, absorbed toluene is preferentially distributed to 

maternal adipose tissue before distribution to the developing fetus (Ghantous and Danielsson 1986). 

Studies of animals exposed during pregnancy found evidence for toluene-induced fetal resorptions and 

abortions in rabbits (Ungvary and Tatrai 1985) and skeletal retardation and anomalies in rats (Hudak and 

Ungvary 1978) at 24-hour/day exposure levels associated with maternal toxicity and mortalities (399 and 

266 ppm for rabbits and rats, respectively). Other developmentally toxic effects in animals associated 

with less than continuous inhalation exposure to toluene (3–8 hours/day) during pregnancy include 

retarded skeletal development in rat fetuses at 266 ppm, 8 hours/day (Hudak and Ungvary 1978), 

decreased body weight in rat fetuses at 2,000 ppm, 6 hours/day (Ono et al. 1995), decreased body weight 

and increased incidence of unossified sternebrae in rat fetuses at $1500 ppm, 6 hours/day (Huntingdon 

Research Centre 1992a, 1992b), decreased fetal body weight and delayed vaginal opening in rat offspring 

at 1,000 ppm, 6 hours/day and increased preweaning offspring mortality at 1,200 ppm (Thiel and 

Chahoud 1997), decreased body weight and retarded skeletal development in mouse fetuses at 266 ppm, 

3–4 hours/day (Ungvary and Tatrai 1985), and increased mouse litters with fetuses with enlarged renal 

pelves at 200 ppm, 6 hours/day (Courtney et al. 1986). Several inhalation studies have identified 

no-effect levels for toluene effects on standard developmental end points (e.g., implantations, resorptions, 

fetal body weight, and fetal visceral and skeletal malformations and variations) including 750 ppm, 

6 hours/day on gestation days 6–15 for rats (Huntingdon Research Centre 1992b), 600 ppm, 6 hours/day 

on gestation day 7–17 for rats (Ono et al. 1995), 600 ppm, 6 hours/day on gestation days 9–21 for rats 

(Thiel and Chahoud 1997), 133 ppm, 3–4 hours/day on gestation days 6–15 for mice (Ungvary and Tatrai 

1985), 133 ppm, 24 hours/day on gestation days 7–20 for rabbits (Ungvary and Tatrai 1985), and 

500 ppm, 6 hours/day on gestation days 6–18 for rabbits (Klimisch et al. 1992). 

In animal studies of oral exposure during gestation, developmentally toxic effects were not observed in 

pregnant mice exposed to oral doses of 1,800 or 2,350 mg/kg/day (Seidenberg et al. 1986; Smith 1983), 

but exposure of pregnant rats to gavage doses of 650 mg/kg /day toluene in corn oil on gestation days 

6–19 produced offspring with decreased body weights, delayed ossification, smaller brain volumes, and 

decreased forebrain myelination per cell compared with controls (Gospe and Zhou 1998; Gospe et al. 

1996). 

Results from studies of neurobehavioral end points in rats following in utero exposure to toluene suggest 

that maternal exposure to airborne toluene concentrations above 1,200 ppm, 6 hours/day during late 

embryonic and fetal development can impair behavioral development of rat offspring (Jones and Balster 
 

 

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1997; Ono et al. 1995; Thiel and Chahoud 1997) and that drinking water exposure during gestation and 

lactation at doses of 106 mg/kg/day changes postweaning open-field locomotor activity in rat offspring 

(Kostas and Hotchin 1981). 

The available animal studies suggest that toluene is not a potent teratogenic agent with in utero exposure, 

but can retard fetal growth and skeletal development and adversely influence development of behavior of 

offspring at exposure levels above those that form the basis of the inhalation and oral MRLs for toluene. 

Genotoxic Effects. Results of in vivo studies of exposed humans (see Table 2-4) and in vitro 

microbial assays and other in vitro systems generally indicate that toluene is nonmutagenic and 

nongenotoxic (see Table 2-5). Richer et al. (1993) reported no significant effects on sister chromatid 

exchanges, cell cycle delay, and cell mortality in lymphocytes following exposure of 5 men to 50 ppm 

toluene over 3 consecutive days. However, an increase in the incidence of chromatid breaks, micronuclei, 

and sister chromatid exchanges in lymphocytes of workers exposed to toluene along with other chemicals 

has been reported (Bauchinger et al. 1982; Nise et al. 1991; Pelclova et al. 1990; Schmid et al. 1985). 

These studies of workers are confounded by concurrent exposure to other organic chemicals, small cohort 

size, and a lack of historical exposure monitoring data. 

Cancer. Human and animal studies generally do not support a concern for the carcinogenicity of 

toluene. The only available human epidemiological studies were negative but inconclusive due to 

limitations in design. The validated animal inhalation bioassays were negative (CIIT 1980; NTP 1990); 

however, one available oral study showed a nondose-related increase in a variety of tumors (Maltoni et al. 

1997). Thus, the data do not support a firm conclusion regarding the carcinogenicity of toluene. 

2.6 ENDOCRINE DISRUPTION 

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, or otherwise 

interfere with the normal function of the endocrine system. Chemicals with this type of activity are most 

commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to 

disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. 

Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in 

light 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 
Table 2-4. Genotoxicity of Toluene In Vivo 

Species (tests system) End point Results Reference Non-Mammalian cells: Grasshopper Mitotic arrest + Liang et al. 1983 

Mammalian cells: Rats Chromosomal aberrations in bone marrow cells + Dobrokhotov and 

 Mice Dominant lethal mutations in sperm cells – API 1981 

Mice DNA damage in blood, bone marrow and liver – Plappert et al. 199

Humana Chromatid breaks, gaps, and exchanges + Bauchinger et al. 

Humana Chromosome changes – Forni et al. 1971 Humana Sister chromatid exchange – Haglund et al. 198

Humana Chromosome changes – Maki-Paakkenen e

 Human

b DNA damage Pitarque et al. 199

Humana Micronuclei and chromosome breaks + Nise et al. 1991 Humana Aberrant cells and chromosome breaks + Pelclova et al. 199

Humana Sister chromatid exchange, cell cycle delay, cell mortality – Richer et al. 1993 

Humana Chromosome aberrations + Schmid et al. 1985 

Humana Sister chromatid exchange – Schmid et al. 1985 

aDetected in peripheral lymphocytes bDetected in leukocytes + = positive result; – = negative result 
Table 2-5. Genotoxicity of Toluene In Vitro 

Results 

Species (test system) End point 

With activation 

Without activation 

Prokaryotic organisms: 

Salmonella typhimurium (TA98, TA100, TA1535, 

TA1537, TA1538) 

Gene mutation – – 

S. typhimurium (TA98, TA100, UTH8413, 8414) Gene mutation – – 

S. typhimurium (TA1535, PSK1002) Gene mutation No data – S. typhimurium Gene mutation No data – 

S. typhimurium (TA98, TA100, TA1535, TA1537) 

Gene mutation – – 

Escherichia coli (P3478) Gene mutation No data – 

Mammalian cells: 

Human lymphocytes 

Sister chromatid exchange and chromosomal aberrations 

No data – 

Human lymphocytes Sister chromatid 

exchange and chromosomal aberrations 

No data – 

– = negative result 
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compounds are derived from plants and are similar in structure and action as endogenous estrogen. While 

there is some controversy over the public health significance of endocrine disrupting chemicals, it is 

agreed that the potential exists for these compounds to affect the synthesis, secretion, transport, binding, 

action, or elimination of natural hormones in the body that are responsible for the maintenance of 

homeostasis, reproduction, development, and/or behavior (EPA 1997g). As a result, endocrine disruptors 

may play a role in the disruption of sexual function, immune suppression, and neurobehavioral function. 

Endocrine disruption is also thought to be involved in the induction of breast, testicular, and prostate 

cancers, as well as endometriosis (Berger 1994; Giwercman et al. 1993; Hoel et al. 1992). 

Current data provide suggestive, but not conclusive, evidence that toluene may cause some endocrine 

effects. Most case studies of chronic abusers of toluene and other solvents have not reported effects on 

endocrine organs, but there are reports of effects that may be associated with endocrine disruption in 

groups of toluene-exposed workers including changed plasma levels of luteinizing hormone, follicular 

stimulating hormone, and testosterone in male printers exposed to toluene (Svensson et al. 1992a, 1992b), 

delayed time to pregnancy among wives of men exposed to mixed organic solvents including toluene 

(Sallmen et al. 1998), increased incidence of spontaneous abortions in female toluene-exposed 

electronics workers (Ng et al. 1992b), and incidences of spontaneous abortion above population norms in 

other small groups of toluene-exposed female workers or wives of male workers (Lindbohm et al. 1992; 

Taskinen et al. 1989). However, small numbers and lack of adjustment for possible confounding factors 

in some of these studies precludes drawing definite conclusions. 

In animal studies, female rats exposed to 30 or 300 ppm, 6 hours/day, 5 days/week for 4 weeks showed a 

mild reduction in follicle size of the thyroid in one study (Poon et al. 1994), but results from several other 

studies in rats and mice found no histological evidence of toluene-induced changes in endocrine organs 

including the thyroid, adrenal glands, or pancreas following intermediate or chronic, oral, or inhalation 

exposure (API 1985, NTP 1990, Von Oettingen et al. 1942). 

Exposure to toluene may damage the reproductive organs in animals, but whether this affects reproductive performance is unclear. Decreased sperm counts and decreased weights of the epididymides have 

been reported in male rats exposed to 2,000 ppm, 6 hours/day for 90 days (Ono et al. 1996). Exposure of 

female rats to 3,000 ppm, 8 hours/day for 7 days produced abundant vacuoles, lytic areas, and 

mitochondrial degeneration in the antral follicles of the ovaries (Tap et al. 1996). Increased relative 

testicular weights were reported in male mice exposed to 1,250 and 2,500 mg/kg/day by gavage for 

13 weeks. However, no effects on the prostate, testes, uterus, or ovaries were observed in rats and female 
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mice gavaged with 312–2,500 mg/kg/day (NTP 1990), and no treatment-related histopathological lesions 

were found in the testes or ovaries of rats and mice exposed (for 6–6.5 hours/day) to concentrations up to 

2,500 ppm toluene for 6.5 hours/day for 14–15 weeks or up to 1,200 ppm for 6–6.5 hours/day for 2 years 

(CIIT 1980; NTP 1990). 

Assessment of reproductive performance was not consistently affected by toluene in several other animal 

studies. Increased fetal mortality was reported for rats exposed to 2,000 ppm for 6 hours/day from days 

7–17 of gestation or from 14 days before mating until day 7 of gestation (Ono et al. 1995, 1996). 

Increased abortion was seen in rabbits continuously exposed to 267 ppm on days 7–20 of gestation, but 

not in mice exposed to 267 ppm for 3–4 hours/day on gestational days 6–15 (Ungvary and Tatrai 1985). 

However, the number of pregnant mice producing viable litters was not affected following oral 

administration of 2,350 mg/kg/day on gestation days 7–14 (Smith 1983). In addition, reproductive 

performance variables and offspring survival were not significantly affected in two generations of rats 

exposed to 2,000 ppm 6 hours/day for up to 95 days (API 1985) or in rats that had been exposed in utero 

to 1,200 ppm 6 hours/day on gestation days 9–21 (Thiel and Chahoud 1997). 

There is evidence that toluene exposure can perturb the hypothalamic-pituitary axis in rats leading to 

persistent increases in serum levels of prolactin, but a study of toluene-exposed workers found no 

evidence for changed prolactin levels compared with control subjects (Svensson et al. 1992a, 1992b). 

Acute-to-intermediate duration exposure to 80 ppm toluene (6 hours/day for 4 weeks) increased serum 

levels of prolactin in rats 17 days after cessation of exposure, but not 29–40 days after exposure 

(Andersson et al. 1983; Hillefors-Berglund et al. 1995; von Euler et al. 1993, 1994). Von Euler et al. 

(1993, 1994) speculated that the increase in serum prolactin level could be related to a possible interaction 

between toluene and the pituitary dopamine D2 receptor which inhibits the release of prolactin into 

serum. 

2.7 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. 
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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 5.6 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 while others may 

decrease susceptibility to the same chemical. For example, although infants breathe more air per 

kilogram of body weight than adults breathe, this difference might be somewhat counterbalanced by their 
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2. HEALTH EFFECTS 

alveoli being less developed, which results in a disproportionately smaller surface area for alveolar 

absorption (NRC 1993). 

Data from controlled-exposure studies of volunteers, studies of occupationally exposed humans, case 

reports of toluene abuse, and studies of animals after inhalation or oral exposure indicate that the nervous 

system is the critical target of toluene toxicity (see Sections 2.2, 2.3.4, and 2.5 for more details). The 

effects of toluene have not been thoroughly studied in children, but the limited available data suggest that 

the nervous system is also the most likely target of toluene toxicity in children. There are numerous 

reports of adolescents who repeatedly inhaled high levels (4,000–12,000 ppm) of toluene and developed 

persistent central nervous system dysfunction (e.g., Byrne et al. 1991; Devasthasan et al. 1984; King et 

al. 1981). Neurological effects associated with toluene exposure in juvenile animals include changed 

levels of brain neurotransmitters in rats, 7 weeks after 10-day exposure as newborns to 80 ppm, 

6 hours/day (von Euler et al. 1989b); high frequency hearing loss in rats after exposure to 1,200 ppm for 

14 hours/day for 5 or 9 weeks starting at weaning (Pryor and Rebert 1992; Pryor et al. 1984a); and 

decreased latency of escape from an electric shock in young rats (50 days old) exposed to 

30,000–40,000 ppm toluene for 15 minutes/day for 30 days (Castilla-Serna et al. 1991). 

Available information regarding age-related differences in toluene metabolism suggests that developing 

fetuses and children at very early stages of development may be more susceptible to toluene toxicity than 

adults, and that children past early neonatal periods may have the same capability as adults to dispose of 

toluene at low exposure levels . The capacity for metabolic detoxification of toluene is expected to be 

low in the developing human fetus because several CYP isozymes are either absent or expressed at very 

low levels (Leeder and Kearns 1997). However, rat studies indicate that levels of CYP isozymes involved 

in toluene metabolism are rapidly increased following birth and suggest that capabilities to carry out 

Phase I toluene metabolism at low exposure levels during neonatal periods may exceed those at sexual 

maturity and pregnancy (Nakajima et al. 1992b). CYP2E1, one of the principal CYP isozymes involved 

in the major toluene metabolic pathway (Nakajima et al. 1997; Tassaneeyakul et al. 1996), is expressed 

several hours after birth in humans and continues to increase during the first year of life (Vieira et al. 

1996). Phase II enzymes involved in toluene metabolism (e.g., N-acetyl transferases, UDP-glucuronyl 

transferases, and sulfotransferases) also show changes during human neonatal development with adult 

activities present by 1–3 years of age (Leeder and Kearns 1997). There are other physiological 

differences between adults and children (e.g., children have higher brain mass per unit of body weight, 

higher cerebral blood flow per unit of brain weight, and higher breathing rates per unit of body weight: 
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see Snodgrass [1992]), but their contributions to possible age-related differences in susceptibility to 

toluene toxicity are currently uncertain. 

Results from animal studies indicating that younger animals may be more susceptible to toluene toxicity 

than adults are restricted to markedly lower LD50 values for 14-day-old rats compared with adult rat 

values (Kimura et al. 1971) and more severe high frequency hearing loss in young rats exposed to toluene 

compared with adult rats (Pryor et al. 1984a). The human brain grows rapidly for the first 2 years life and 

continues more slowly until full brain cell numbers, complete myelination of subcortical white matter, 

and complete elaboration of dendrites and axons are attained at adulthood (Snodgrass 1992). It is 

unknown if the relatively long period of development of the human brain may make juvenile humans 

more susceptible to toluene toxicity than juvenile non primate animals. 

Case reports of birth defects in solvent abusers suggest that high-level exposure to toluene during 

pregnancy can be toxic to the developing fetus (Arnold et al. 1994; Erramouspe et al. 1996; Goodwin 

1988; Hersch 1988; Hersch et al. 1985; Lindemann 1991; Pearson et al. 1994). It is likely that the high 

exposure levels experienced by pregnant solvent abusers (4,000 to 12,000 ppm) overwhelm maternal 

mechanisms that protect the developing fetus from absorbed toluene at lower exposure levels. 

Experiments with pregnant mice demonstrated that 10-minute exposures to 2,000 ppm resulted in low 

uptake of toluene into fetal tissue and suggest that, at lower exposure levels, absorbed toluene is 

preferentially distributed to maternal adipose tissue before distribution to the developing fetus (Ghantous 

and Danielsson 1986). 

Studies of pregnant rats, mice, and rabbits found no effects on standard developmental end points such as 

number of resorptions, fetal body weights, and incidences of fetuses or litters with malformations, after 

exposure during gestation to inhaled concentrations as high as 500–750 ppm, 6 hours/day (Huntingdon 

Research Centre 1992b; Klimisch et al. 1992; Ono et al. 1995; Thiel and Chahoud 1997; Ungvary and 

Tatrai 1985) and 133 ppm, 24 hours/day (rabbits only) (Ungvary and Tatrai 1985) or to oral doses as 

high as 1,800 or 2,350 mg/kg/day (Seidenberg et al. 1986; Smith 1983). Observed effects on fetal 

development in the available animal studies, at higher exposure levels that were not fatal to the fetuses or 

the mothers, were generally restricted to fetal body weight decrease, retardation of skeletal development, 

or minor skeletal or visceral anomalies without increased incidences of malformations (Courtney et al. 

1986; Hudak and Ungvary 1978; Huntingdon Research Centre 1992a, 1992b; Ono et al. 1995; Thiel and 

Chahoud 1997; Ungvary and Tatrai 1985). Neurological effects observed in animal offspring following 

gestational exposure to toluene include smaller brain volumes and decreased forebrain myelination per 
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cell in offspring of pregnant rats exposed to 650 mg/kg/day during gestation (Gospe and Zhou 1998; 

Gospe et al. 1996) and behavioral changes in offspring of pregnant rats exposed by to airborne 

concentrations above 1,200 ppm, 6 hours/day (Jones and Balster 1997; Ono et al. 1995; Thiel and 

Chahoud 1997) or to drinking water doses of 106 mg/kg/day (Kostas and Hotchin 1981). 

In general, available information suggests that toluene is not a potent teratogenic agent with in utero 

exposure, but can retard fetal growth and skeletal development and adversely influence development of 

behavior of offspring at exposure levels above those that form the basis of the inhalation and oral MRLs 

for toluene. 

Transfer of toluene to nursing infants from breast milk of currently exposed mothers is expected to be a 

possibility because of the lipophilicity of toluene and the relatively high lipid content of breast milk. 

Elimination kinetics data for nonpregnant or nonlactating humans and rats following toluene exposure, 

however, indicate that most absorbed toluene is rapidly eliminated from the body and that a much smaller 

portion (that which gets into adipose tissues) is slowly eliminated (Leung and Paustenbach 1988; Lof et 

al. 1993; Pierce et al. 1996, 1999; Pellizzari et al. 1992; Rees et al. 1985; see Section 2.3.4). Thus, 

mobilization during pregnancy or lactation of stored toluene from pre conception exposure does not 

appear to be a major concern. 

Fisher et al. (1997) developed a human PBPK model that predicts transfer of toxicant via lactation from a 

mother to a nursing infant and used the model to estimate the amount of toluene an infant would ingest 

via milk if the mother was occupationally exposed to toluene at the ACGIH (1999) Threshold Limit 

Value (TLV=50 ppm) throughout a workday. The model predicted that such an infant would have a daily 

oral intake of 0.46 mg toluene/day. This value is below the U.S. EPA Health Advisory, 2.0 mg/day, for 

chronic ingestion of 1 L/day of toluene-contaminated water by a 10-kg child and a daily oral intake for a 

10-kg child (8 mg/day) associated with the acute oral MRL for toluene (0.8 mg/kg/day). However, this 

value is above the daily oral intake for a 10-kg child (0.2 mg/day) associated with the intermediate oral 

MRL for toluene (0.02 mg/kg/day), suggesting there may be some concern for neurological effects in 

suckling infants exposed for more than 14 days to breast milk from mothers exposed during lactation to 

concentrations of 50 ppm in workplace air. It should be noted, however, that no human (or animal) 

studies were located regarding in vivo distribution of toluene into breast milk or elimination kinetics from 

breast milk, and the Fisher et al. (1997) PBPK model has not been validated with in vivo data. 
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2.8 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 

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 toluene are discussed in Section 2.8.1. 

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 toluene are discussed in Section 2.8.2. 

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 
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the biologically effective dose, or a target tissue response. If biomarkers of susceptibility exist, they are 

discussed in Section 2.10 “Populations That Are Unusually Susceptible”. 

2.8.1 Biomarkers Used to Identify or Quantify Exposure to Toluene 

The biological exposure indices recommended by ACGIH (1999) to assess exposure of workers to 

toluene in the workplace are ortho-cresol and hippuric acid levels in urine at the end of a workshift and 

toluene levels in blood immediately prior to the last shift of a workweek. However, there are no markers 

of toluene exposure that persist in the body for an extended period of time after exposure has ceased. 

The most accurate biomarker of toluene exposure is the presence of toluene in serum or blood, but 

measurements of toluene or its metabolites in urine are often preferred as urine sampling is less invasive. 

Measurements of toluene in serum, blood, and urine taken at the end of shift were significantly correlated 

with measurements of toluene concentrations from personal air monitors (Kawai et al. 1992a, 1992b, 

1996). Measurement of toluene in blood was more sensitive than measurement of toluene in urine for 

detecting toluene at low concentrations (Kawai et al. 1992a). It is not necessary to draw large quantities 

of blood for analysis since toluene concentrations from capillary blood samples were also highly 

correlated (r=0.94) with toluene concentrations in exhaled air (Foo et al. 1991). 

Although measurement of urinary excretion of toluene metabolites (hippuric acid, mercapturic acids, 

ortho-cresol and para-cresol) is a less invasive method than blood sampling for determining toluene 

exposure, the presence of these compounds in the urine is not definitive proof of toluene exposure since 

they are also produced by metabolism from the normal diet (Baelum 1990; Hjelm et al. 1988; Lof et al. 

1993; Maestri et al. 1997). It has also been reported that the presence of toluene in urine is a more 

sensitive biomarker for toluene exposure than the presence of hippuric acid or ortho-cresol (Kawai et al. 

1996). In addition, the background levels of these metabolites may be affected by individual variability 

(Lof et al. 1993), ethnic differences (Inoue et al. 1986), or other factors such as alcohol consumption and 

smoking (Kawamoto et al. 1996; Maestri et al. 1997). Despite these limitations, a number of authors have 

shown a correlation between the levels of these metabolites in urine and toluene exposure (Angerer and 

Kramer 1997; Angerer et al. 1998a; Kawai et al. 1992a, 1992b, 1996; Nise 1992; Truchon et al. 1996) 

and they have been widely used as biomarkers of toluene exposure. 
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2.8.2 Biomarkers Used to Characterize Effects Caused by Toluene 

There are no specific biomarkers used to characterize the effects from toluene exposure. Changes in the 

brain, which are detected through magnetic resonance imaging (MRI) or brainstem auditory evoked 

response (BAER) techniques in combination with an exposure history, can be used to evaluate the degree 

of central nervous system damage experienced by a known toluene abuser. This approach does not 

appear to offer potential as a method of measuring the effects of short- or long-term minimal exposures as 

are likely to occur with environmental releases. A detailed discussion of the effects of toluene exposure is 

included in Section 2.2. 

Additional information concerning biomarkers for effects on the immune, renal, and hepatic systems can 

be found in the CDC/ATSDR Subcommittee Report on Biological Indicators of Organ Damage 

(CDC/ATSDR 1990), and on the neurological system in the Office of Technology Assessment Report on 

Identifying and Controlling Poisons of the Nervous System (OTA 1990). 

2.9 INTERACTIONS WITH OTHER CHEMICALS 

Alteration of toluene metabolism may influence toluene’s toxic effects because toluene metabolism 

predominately represents a detoxification process (see Section 2.4.2). Hypothetically, compounds that 

stimulate or inhibit metabolism of toluene may respectively decrease or increase toluene toxicity, 

although the possible exhalation of unmetabolized toluene represents an alternate dispositional pathway 

that may be utilized under conditions inhibiting mainstream toluene metabolism. Several metabolic 

interactions between toluene and other chemicals have been studied. The results present evidence that 

alteration of toluene metabolism may influence toluene toxicity and that toluene can influence the toxicity 

of other chemicals. 

Phenobarbital pretreatment, which increases the rate of in vivo metabolism of toluene by inducing CYP 

isozymes, prevented hearing loss in rats exposed to 1,500–2,000 ppm toluene, 8 hours/day for 7 days 

(Pryor et al. 1991). Conversely, rats that were given large gavage doses of ethanol (4 g/kg/day) and daily 

inhalation exposure to toluene concentrations of 1,750 ppm, 6 hours/day, 5 days/week for 4 weeks 

showed significantly greater changes in auditory-evoked brainstem potentials and outer hair cell loss in 

the ear than those exposed to toluene alone (Campo et al. 1998). Co-exposure to ethanol caused a 

significant decrease in hippuric acid urinary excretion rates compared with exposure to toluene alone, 

indicating that these large doses of ethanol inhibited the metabolism of toluene (Campo et al. 1998). 
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Consistent with the idea that co-exposure to ethanol inhibits toluene metabolism are observations that 

ingestion of ethanol prolongs the presence of toluene in blood in humans (Imbriani and Ghittori 1997; 

Wallen et al. 1984) and rats (Romer et al. 1986). These results indicate that toluene-induced hearing loss 

is caused by toluene itself and not its metabolites, and that workers exposed to toluene who regularly 

drink alcohol may be at greater risk of developing toluene-related neurological problems than non 

drinkers. 

Concurrent chronic ethanol ingestion and acute toluene inhalation in rats was associated with a modest 

elevation in plasma aspartate aminotransferase and increases in relative liver weight and liver 

triglycerides (Howell et al. 1986). Toluene also antagonized the hypertriglyceridemia associated with 

chronic ethanol ingestion. This study suggests that combined ethanol and chronic occupational toluene 

exposure may have the potential to augment alcohol-induced fatty liver. 

Benzene, xylene, and toluene are metabolized through cytochrome P-450 oxidation. Benzene is 

converted to phenol, hydroquinone, catechol, and phenyl mercapturic acid; xylene is converted to methyl 

hippuric acids, and toluene forms hippuric acid, o-cresol, and p-cresol. The excretion of metabolites was 

investigated in four groups of workers who were exposed in the workplace to benzene and toluene, to a 

mixture of both solvents, or to no solvents (Inoue et al. 1988). Analysis of the data on excretion of 

urinary metabolites indicated that simultaneous exposure to both benzene and toluene inhibited the 

microsomal metabolism of both compounds through the cytochrome P-450 system. Toluene had more of 

an inhibitory effect on benzene metabolism than benzene had on toluene metabolism. This observation 

was confirmed in rodent studies using 6-hour inhalation exposures to benzene, toluene, or a mixture of 

both compounds, with pharmacokinetic modeling of the exposure data (Purcell et al. 1990). 

Combinations of either 200 ppm toluene with 1,000 ppm benzene or 1,000 ppm toluene with 200 ppm 

benzene were tested. The fit of the actual closed chamber concentrations for the individual chemicals 

with the model results, suggests that the interaction of benzene and toluene are noncompetitive. The data 

from studies of the benzene-toluene interaction may indicate that workers exposed to mixtures of both 

solvents have a lower risk of benzene-induced leukopenia than workers exposed to benzene alone (Purcell 

et al. 1990). 

Toluene and xylene are also often found together in mixtures such as paint thinners. Human exposure to 

low levels of both solvents (50 ppm xylene, 40 ppm toluene) did not modify the conversion of either 

substance to its urinary metabolites (Kawai et al. 1992b; Tardif et al. 1991). However, at higher 

concentrations (80 or 150 ppm xylene, 95 or 150 ppm toluene), the blood and exhaled air concentrations 
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of both solvents were increased compared to the controls exposed to either solvent alone, indicating that 

metabolism of both solvents was decreased by the coexposure paradigm (Tardif et al. 1991, 1992). 

Similarly, coexposure of toluene, methyl ethyl ketone and isopropyl alcohol at low concentrations in rats 

had no effect on the urinary excretion of hippuric acid, while high concentrations resulted in decreased 

levels of hippuric acid (Uaki et al. 1995). Tardif et al. (1993) reported that a linked PBPK model for 

toluene and xylene with a competitive inhibition metabolic term provided the best visual fit (compared 

with non- or competitive inhibition metabolic terms) to empirical data for air concentrations of toluene 

and xylene during 5-hour exposures of rats in a closed chamber to mixtures of toluene and xylene at 

several initial concentrations. 

Toluene and n-hexane, which are used together in some glues and paints, are neurotoxic chemicals that 

act by different modes at different sites. Toluene effects on the central nervous system are thought to be 

facilitated by toluene itself, whereas n-hexane affects the peripheral nervous system through the 

production of a toxic metabolite, 2,5-hexanedione (Ali and Tardif 1999). The initial metabolism of both 

compounds has been demonstrated to principally involve CYP isozymes including CYP2E1 and CYP2B6 

(Ali and Tardif 1999). Under in vitro conditions with rat liver microsomes, a noncompetitive inhibition 

of each other’s metabolism was demonstrated (Perbellini et al. 1982). In studies comparing urinary 

excretion of metabolites in rats exposed to mixtures of toluene and n-hexane or to each solvent alone, 

co-exposure inhibited the urinary excretion of 2,5-hexanedione to a larger extent than the urinary 

excretion of toluene metabolites, hippuric acid, and ortho-cresol (Ali and Tardif 1999; Iwata et al. 1983; 

Perbellini et al. 1982). The results from these studies suggest that toluene is a more effective inhibitor of 

n-hexane metabolism than is n-hexane of toluene metabolism. Co-exposure of rats to 1,000 ppm toluene 

and 1,000 ppm n-hexane (12 hours/day for 16 weeks) decreased toxic effects of n-hexane on the 

peripheral nervous system compared with exposure to 1,000 ppm n-hexane alone (Takeuchi et al. 1981). 

Another rat study found confirming results in that co-exposure to 1,200 ppm toluene and 4,000 ppm 

n-hexane (14 hours/day for 9 weeks) decreased n-hexane-induced effects on the peripheral nervous 

system compared with n-hexane alone, and had only slight effects on toluene-induced hearing loss and 

motor dysfunction compared with toluene alone (Pryor and Rebert 1992). Human and rat PBPK models 

have been developed to model the combined exposure and disposition of inhaled toluene and n-hexane 

(Ali and Tardif 1999; Yu et al. 1998). Model simulations predicted that co-exposure to n-hexane and 

toluene at constant concentrations corresponding to their occupational exposure limits (50 ppm) would 

lead to only a slight effect on the kinetics of their respective metabolism and disposition, but that the 

interaction could change with fluctuations in worker activity loads and workplace air concentrations (Ali 

and Tardif 1999; Yu et al. 1998). 
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An individual's drug therapy can have an influence on toluene toxicity. Haloperidol (an antipsychotic) 

functions by blocking dopamine receptors in the brain. The combination of haloperidol with toluene 

exacerbates dopamine depletion in several areas of the brain, thus changing the pharmacodynamics of the 

haloperidol. Individuals who take haloperidol should be counseled by their physician if environmental or 

occupational exposure to toluene is possible (von Euler et al. 1988b). 

Studies in humans and rats indicate that the common analgesics, acetaminophen and aspirin, may inhibit 

toluene metabolism and influence toluene toxicity. CYP2E1 is involved in the initial step of the principal 

metabolic pathway for toluene and acetaminophen, and represents a potential site for a competitive 

metabolic interaction. Aspirin and one of the principal downstream metabolites of toluene, benzoyl 

coenzyme A, are conjugated with glycine. When glycine pools are depleted by competition for glycine 

by aspirin metabolism, toluene metabolism may be inhibited. In volunteers exposed for 4 hours to 

300 mg/m3

 toluene (80 ppm) with or without doses (1,000 mg/70 kg=14.3 mg/kg) of acetaminophen 

(paracetamol) or acetyl salicylic acid (aspirin), co-exposures with these analgesics increased the 

concentration of toluene in the blood compared with exposure to toluene alone (Lof et al. 1990). 

Acetaminophen co-exposure also significantly increased the area under the blood concentration versus 

time curve and the apparent blood clearance of toluene, consistent with an inhibition of toluene 

metabolism. Co-exposure of rats for 10 days to higher oral doses of aspirin (acetyl salicylic acid: 

100 mg/kg, twice daily ) and inhalation exposure to toluene (1,000 ppm, 14 hours/day) caused a more 

severe loss of hearing (assessed 2–5 days or 4 months after cessation of exposure) compared with 

exposure to toluene alone (Johnson 1992). Treatment with aspirin alone at these doses did not cause 

hearing loss in the rats. These results are consistent with the hypothesis that high doses of aspirin may 

potentiate toluene effects on hearing by inhibiting toluene metabolism. 

The benzoic acid metabolite of toluene is conjugated with glycine to produce hippuric acid. Toluene 

potentiation of developmentally toxic effects in rats from high doses of aspirin has been attributed to 

metabolic competition for glycine pools (Ungvary et al. 1983). Pregnant rats that were given 250 mg/kg 

acetyl salicylic acid on gestation day 12 and exposed to toluene at concentrations of 1,000, 2,000, or 

3,600 mg/m3 (265, 531, or 956 ppm) on gestation days 10–13 showed maternal effects (decreased food 

consumption and body weight gain and increased relative liver weight) and fetal effects (retardation of 

skeletal development and increased incidence of fetal malformations) that were more severe than those 

observed in rats exposed to 250 mg/kg acetyl salicylic acid alone. The effects were comparable in 

severity to those observed in rats exposed to 500 mg/kg salicylic acid alone. In this study, no maternal or 

fetal effects were observed in a group of rats exposed to 956 ppm toluene on gestation days 
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10–13 without coexposure to acetyl salicylic acid. The maternal and fetal effects of co-exposure to acetyl 

salicylic acid and toluene were diminished to the severity of the 250-mg/kg acetyl salicylic acid alone 

level when the administration of the acetyl salicylic acid dose was preceded by two hours with a gavage 

dose of 5,000 mg/kg glycine. 

2.10 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE 

A susceptible population will exhibit a different or enhanced response to toluene than will most persons 

exposed to the same level of toluene 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 toluene, or compromised function of organs 

affected by toluene. Populations who are at greater risk due to their unusually high exposure to toluene 

are discussed in Section 5.7, Populations With Potentially High Exposures. 

The main target organ of toluene is the central nervous system, and it is generally thought to be due at 

least in part, to reversible interactions between toluene (the parent compound, not its metabolite) and the 

lipid or protein components of nervous system membranes (mechanisms of toxicity are discussed in detail 

in Section 2.4.2). The main pathway of toluene metabolism leads to the production of hippuric acid, 

which is excreted in the urine. The predominant first step in human and rat metabolism of toluene is 

catalyzed primarily by the CYP 2E1 isozyme. Later steps in this pathway involve the enzymes alcohol 

dehydrogenase, aldehyde dehydrogenase, acyl-coenzyme A synthase, and acyl-coenzyme A:amino acid 

N-acyl transferase (metabolism is discussed in detail in Section 2.2.3). 

Environmental or genetic factors that decrease the capacity for metabolic detoxification of toluene are 

likely to increase susceptibility. This is supported by experiments in which inhibiting or enhancing 

toluene metabolism respectively enhanced of inhibited toluene-induced hearing loss in rats (Campo et al. 

1998; Pryor et al. 1991). Chronic consumers of alcohol, and users of any medication that interfered with 

toluene metabolism, would be likely to have an increased risk for this reason. Differences in the relative 

efficiency of enzymes found in ethnic populations may also lead to differences in toluene susceptibility. 

For instance, ethnic variations in the occurrence of CYP isozymes, alcohol dehydrogenase, and aldehyde 

dehydrogenase are known to exist (Kawamoto et al. 1995, 1996; Kim et al. 1997). 

Nutritional status may also affect susceptibility to toluene. Liver metabolism of toluene in rats fasted for 

1 day was significantly increased compared with rats that had been fed (Nakajima and Sato 1979). 
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However, long-term malnutrition may increase susceptibility to the developmental effects of toluene. 

Skeletal development in the fetuses of rats that were malnourished throughout pregnancy and injected 

with 1.2 g/kg/day toluene was retarded to a significantly greater extent than in the fetuses of wellnourished dams injected with toluene (da Silva et al. 1990). 

Individuals with pre-existing medical conditions may also be more susceptible to the effects of toluene. 

Individuals with pre-existing defects in heart rhythm may have a greater risk than healthy individuals for 

experiencing tachycardia or cardiac fibrillation following exposure to high levels of toluene. The 

presence of toluene in the air reduces the concentration of oxygen and can lead to hypoxia when exposure 

concentrations are high. Thus, individuals with asthma or other respiratory difficulties may be at 

increased risk with exposure to high atmospheric concentrations of toluene. Genetic predisposition for 

hearing loss may increase the risk for toluene-induced ototoxicity (Johnson 1992; Li et al. 1992). 

2.11 METHODS FOR REDUCING TOXIC EFFECTS 

This section will describe clinical practice and research concerning methods for reducing toxic effects of 

exposure to toluene. 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 toluene. When specific 

exposures have occurred, poison control centers and medical toxicologists should be consulted for 

medical advice. The following texts provide specific information about treatment following exposures to 

toluene: 

Aaron, CK and Howland, MA (eds.). 1994. Goldfrank’s Toxicologic Emergencies. Appleton and 

Lange, Norwalk, CT. 

Dreisbak, RH (ed.). 1987. Handbook of Poisoning. Appleton and Lange, Norwalk, CT. 

Ellenhorn, MJ and Barceloux, DG, (eds.). 1988. Medical Toxicology: Diagnosis and Treatment of 

Human Poisoning. Elsevier Publishing, New York, NY. 

Haddad, LM and Winchester, JF (eds.). 1990. Clinical Management of Poisoning and Drug Overdose. 

2nd edition, WB Saunders, Philadelphia, PA. 

2.11.1 Reducing Peak Absorption Following Exposure 

The absorption of toluene is rapid and virtually complete following inhalation and oral exposures. 

Toluene appeared in the blood of 10 human subjects within 10–15 minutes of exposure to 78 ppm toluene 
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in the air, signifying rapid absorption through the lungs. When exposure occurs by the oral route, uptake 

into the blood is expected to be slightly slower due to the time needed for transit to the small intestines. 

Since toluene is absorbed across the lipid matrix of the cell membrane (Alcorn et al. 1991) some 

absorption can occur from the mouth and stomach. However, most of the toluene will be absorbed 

through the intestines due to large exposed surface area of the villi and microvilli. Other factors that will 

influence uptake from the gastrointestinal tract are lipid content of the gastrointestinal contents and the 

magnitude of the toluene exposure. Absorption of inhaled toluene is increased by exercise and so a 

reduction of physical activity during exposure is likely to reduce absorption (Rahill et al. 1996). 

However, there is really no effective way to reduce peak absorption following inhalation exposure. 

Emesis is contraindicated in cases of toluene ingestion due to the risk of aspiration. The use of activated 

charcoal and lavage may help to reduce oral exposure and rapid rinsing of the skin with water or washing 

with soap and water will reduce the opportunity for dermal absorption. If the eyes are affected, proper 

rinsing procedures should be followed. 

2.11.2 Reducing Body Burden 

The total body burden of toluene is reduced by measures that increase the rate of metabolism and 

excretion. Oxygen therapy and positive-pressure ventilation have been used as emergency treatments 

following episodes of toluene abuse (Graham 1990). This procedure promotes the loss of unmetabolized 

toluene from the lungs. Increased oxygen availability also has a positive effect on the rate of oxidative 

metabolism in the liver, lungs, intestines, and other tissues. 

Increased fluid consumption, which increases the rate of urine production and excretion, will help to 

decrease the toluene body burden since toluene metabolites are water soluble and excreted in the urine. In 

cases where kidney function has been impaired, renal dialysis has been used to remove toluene 

metabolites from the body (Graham 1990). 

2.11.3 Interfering with the Mechanism of Action for Toxic Effects 

In cases where toluene has caused cardiac arrhythmias, antiarrhythmic medications have been used to 

control the heart beat (Graham 1990). No other medical practices for ameliorating the toxic effects of 

toluene were identified in the available literature. When toluene exposures are unavoidable, as in the 

workplace, avoidance of alcohol or medications that may inhibit metabolic disposition of toluene is 

another measure that can be taken to reduce health risks from exposure. 
TOLUENE 156 

2. HEALTH EFFECTS 

2.12 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 toluene 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 toluene. 

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. 

2.12.1 Existing Information on Health Effects of Toluene 

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to 

toluene are summarized in Figure 2-5. The purpose of this figure is to illustrate the existing information 

concerning the health effects of toluene. 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 (ATSDR 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. 

As shown in Figure 2-5, there is a considerable body of data on the health effects of toluene in humans 

following acute, intermediate, and chronic inhalation exposures. It appears that clinical effects of high 

concentrations on the major target organ, the central nervous system, have been well characterized. 

However, many of the available reports lack quantitative information on exposure levels and there is still 

much that must be learned about the ultra structural molecular level of toxicity. There are some oral, but 

essentially no dermal, data available; however, these are not primary routes by which humans are exposed 
TOLUENE 157 

2. HEALTH EFFECTS 
 

 

TOLUENE 158 

2. HEALTH EFFECTS 

to toluene. Figure 2-5 also shows that considerable animal toxicity data for inhalation exposure are 

available. However, there are limited oral and dermal data from animal studies. 

2.12.2 Identification of Data Needs 

Acute-Duration Exposure. Several studies are available regarding the effects of single exposures to 

toluene, both in humans and animals (Andersen et al. 1983; Baelum et al. 1985; Echeverria et al. 1991; 

von Oettingen et al. 1942). These studies clearly identify the nervous system as the critical toxicity target 

of toluene, and describe dose-response relationships between neurological end points and exposure levels. 

Supporting data are provided by studies of animals after inhalation (Bowen and Balster 1998; Bruckner 

and Peterson 1981a, 1981b; Bushnell et al. 1985; Hinman 1987; Kishi et al. 1988; Mullin and Krivanek 

1982; Taylor and Evans 1985; Wood et al. 1983) or oral (Dyer et al. 1988) exposure. Further studies of 

orally-exposed animals involving a range of exposure levels (including low levels) and employing 

sensitive, behavioral, ultra structural, and biochemical measurements may be useful. Data for the dermal 

exposure route are limited; however, this is not a primary route of human exposure. Sufficient data for 

the oral and inhalation routes were available to derive an acute inhalation MRL based on a lack of 

neurological effects in volunteers exposed to 40 ppm toluene for 6 hours (Anderson et al. 1983) and an 

acute oral MRL based on changes in flash-evoked brain potentials observed in mice exposed to 

250 mg/kg toluene (Dyer et al. 1988). 

Intermediate-Duration Exposure. Several studies are available on repeated-dose exposure of 

humans and animals to toluene after inhalation exposure (Bjornaes and Naalsund 1988; Kyrklund et al. 

1987; Mattsson et al. 1990; Pryor 1991; von Oettingen et al. 1942). These studies have elucidated the 

effects of repeated exposure of toluene on the primary target organ, the central nervous system. No-effect 

levels for intermediate, low-level inhalation exposure in air have not been thoroughly investigated. 

Determination of these values would be valuable in evaluating the human health risk. Studies on repeated 

intermediate-duration exposure of humans and animals to toluene by the oral route are adequate (Hsieh 

et al. 1989, 1990b; Kostas and Hotchin 1981; NTP 1990), and sufficient data were available to derive an 

intermediate-duration oral MRL based on toluene-induced changes in brain levels of biogenic 

monoamines in mice (Hsieh et al. 1990b). Studies following dermal exposure are lacking, however, this 

is not a primary route by which humans are exposed to toluene. 
 

 

 

TOLUENE 159 

2. HEALTH EFFECTS 

Chronic-Duration Exposure and Cancer. Numerous case reports have associated chronic 

inhalation exposure to toluene at levels inducing narcosis and euphoria (4,000 to 12,000 ppm as estimated 

by Gospe et al. 1994) with persistent neurological damage (Byrne et al. 1991; Caldemeyer et al. 1996; 

Devathasan et al. 1984; Filley et al. 1990; Hunnewell and Miller 1998; Ikeda and Tsukagoshi 1990; 

Kamran and Bakshi 1998; King et al. 1981; Maas et al. 1991; Meulenbelt et al. 1990; Miyagi et al. 1999; 

Rosenberg et al. 1988a, 1988b; Ryu et al. 1998; Suzuki et al. 1983; Yamanouchi et al. 1995). Studies of 

workers repeatedly exposed to toluene in workplace air at concentrations ranging from about 30 to 

150 ppm have found evidence for increased incidence of self-reported neurological symptoms (Orbaek 

and Nise 1989; Yin et al. 1987), performance deficits in neurobehavioral tests (Boey et al. 1997; Foo et 

al. 1990; Orbaek and Nise 1989), hearing loss (Abbate et al. 1993; Morata et al. 1997), changes in visualevoked brainstem potentials (Vrca et al. 1995, 1997a, 1997b), and color vision impairment (Zavalic et al. 

1998a, 1998b, 1998c). Two animal studies have investigated the effects of toluene following chronic 

inhalation exposure (CIIT 1980; NTP 1990). Multiple end points of toxicity were investigated, including 

carcinogenicity, and the data indicate that toluene is not a carcinogen. Sufficient data for the inhalation 

route were available to derive a chronic MRL based on color vision impairment in toluene exposed 

workers (Zavalic et al. 1998a). Additional prospective studies of hearing, color vision ability, and 

performance in neurobehavioral tests of groups of occupationally exposed workers may decrease 

uncertainty in the chronic inhalation MRL for toluene. The chronic effects of toluene have not been 

investigated following oral or dermal exposures, and the carcinogenic potential has not been studied 

following dermal exposure; however, these are not considered major routes of toluene exposure. 

Genotoxicity. To evaluate the potential of toluene to cause chromosomal damage, well designed in 

vivo studies using test material of known purity may be valuable. These tests would aid in determining 

whether toluene itself has clastogenic potential or whether the positive results that have been reported are 

due to impurities in the test material (animal studies) or multiple solvent exposures (human studies) (API 

1981; Bauchinger et al. 1982; Nise et al. 1991; Pelclova et al. 1990; Schmid et al. 1985). Because it is 

believed that toluene toxicity may be mediated, at least in part, through a highly reactive and short-lived 

arene oxide intermediate, which interacts with cellular proteins and RNA (Chapman et al. 1990), further 

studies of this interaction would provide useful information. 

Reproductive Toxicity. In general, available results from studies of toluene-exposed workers and 

animals suggest that toluene is not a potent reproductive toxicant, but may cause some reproductive 

problems, especially with repeated inhalation exposure during pregnancy to concentrations above 

200 ppm. There are a few reports that women occupationally exposed to toluene, or wives of men 
 

TOLUENE 160 

2. HEALTH EFFECTS 

similarly exposed, have an increased risk of spontaneous abortions (Lindbohm et al. 1992; Ng et al. 

1992b; Taskinen et al. 1989), but a causal relationship is not established by these studies due to small 

sample sizes evaluated, inability to define accurate exposure levels, failure to account for potentially 

important confounding variables, and difficulty in validating self-reported data. In addition, one study 

reported that toluene-exposed male workers showed decreasing plasma levels of the luteinizing hormone, 

follicle stimulating hormone and testosterone levels with increasing concentrations of toluene 

(8–<111 ppm) (Svensson et al. 1992a, 1992b). Animal studies found some evidence for minor tolueneinduced changes in male and female reproductive organs (Ono et al. 1995, 1996; Tap et al. 1996), but no 

histological evidence of structural damage to the reproductive organs in rats and mice exposed orally for 

intermediate durations or by inhalation for intermediate or chronic durations (NTP 1990). No evidence 

for impaired reproductive performance was found in several assays (API 1985; Smith 1983; Ono et al. 

1995, 1996; Thiel and Chahoud 1997) (including a 2-generation study of rats exposed to up to 2,000 ppm, 

6 hours/day [API 1985]), except that exposure to concentrations above 200 ppm during pregnancy 

produced increased fetal mortality in pregnant rats (2,000 ppm, 6 hours/day) (Ono et al. 1995, 1996) and 

increased abortions in pregnant rabbits (267 ppm, 24 hours/day) (Ungvary and Tatrai 1985). Additional 

studies of reproductive end points in groups of occupationally exposed workers may be useful in 

discerning the possible reproductive hazards of toluene in the workplace, if large enough groups of 

workers are examined, exposure levels can be accurately monitored, and confounding variables are 

accounted for or minimalized. Another 2-generation reproductive study in another animal species (e.g., 

rabbits) may also help to decrease uncertainty in defining no-effect levels for reproductive effects from 

toluene. 

Developmental Toxicity. Published reports of birth defects described in children born to women 

who abused toluene or other organic solvents during pregnancy suggest that high-level exposure to 

toluene during pregnancy can be toxic to the developing fetus (Arnold et al. 1994; Erramouspe et al. 

1996; Goodwin 1988; Hersch 1988; Hersch et al. 1985; Lindemann 1991; Pearson et al. 1994). Studies of 

developmentally toxic effects in children of women exposed during pregnancy to much lower 

concentrations are restricted to a small study of 14 Finnish women exposed to mixed solvents suggesting 

that solvent exposure may increase risk for central nervous system anomalies and neural tube closure 

defects (Holmberg 1979). The available human data do not establish causality between low-level or 

occupational exposure to toluene and birth defects, because of the small sample size and the mixed 

solvent exposure experienced by the subjects in the Holmberg (1979) study and the lack of other studies 

of possible birth defects in children of women exposed to toluene in the workplace. Additional studies of 
 

TOLUENE 161 

2. HEALTH EFFECTS 

developmental end points in offspring of mothers exposed to toluene in the workplace may help to clarify 

the potential for human health risk. 

Results from several inhalation exposure studies of animals indicate that exposure to levels of toluene that 

begin to produce maternal toxicity can cause fetal effects, including reduced fetal survival and retardation 

of growth and skeletal development (Courtney et al. 1986; Hudak and Ungvary 1978; Huntingdon 

Research Centre 1992a, 1992b; Ono et al. 1995; Thiel and Chahoud 1997; Ungvary and Tatrai 1985). 

No-effect levels in animals for toluene effects on standard developmental end points range from about 

133 ppm for a 24 hour/day exposure protocol (Ungvary and Tatrai 1985) to 133–750 ppm with 

3–6 hours/day protocols (Huntingdon Research Centre 1992b; Klimisch et al. 1992; Thiel and Chahoud 

1997; Ungvary and Tatrai 1985). In animal studies of oral exposure during gestation, no developmental 

effects were observed in pregnant mice exposed to oral doses of 1,800 or 2,350 mg/kg/day (Seidenberg et 

al. 1986; Smith 1983), but exposure of pregnant rats to gavage doses of 650 mg/kg /day produced 

offspring with decreased body weights, delayed ossification, smaller brain volumes, and decreased 

forebrain myelination per cell compared with controls (Gospe and Zhou 1998; Gospe et al. 1996). 

Results from studies of neurobehavioral end points in rats following in utero exposure to toluene suggest 

that maternal exposure to airborne concentrations above 1,200 ppm, 6 hours/day gestation can impair 

behavioral development of rat offspring (Jones and Balster 1997; Ono et al. 1995; Thiel and Chahoud 

1997) and that drinking water exposure during gestation and lactation at doses of 106 mg/kg/day changes 

postweaning open-field locomotor activity in rat offspring (Kostas and Hotchin 1981). 

Additional studies of sensitive neurological end points, including neurobehavioral end points, in offspring 

of toluene-exposed pregnant animals may better determine no-effect levels for toluene effects on 

neurodevelopment. Inhalation exposure studies are likely to be of more relevance to human exposures of 

concern than oral exposure studies. Developmental effects have not been investigated following dermal 

exposure; however, this is not a primary route of human exposure. 

Immunotoxicity. The only inhalation data available on possible immunological effects of toluene are 

from studies of exposed workers (Lange et al. 1973; Moszczynsky and Lisiewicz 1984; Yin et al. 1987). 

In all cases, the workers were exposed to several solvents (toluene, benzene, and xylene), thus making it 

difficult to associate the effects on the immune system specifically with toluene. Animal data using the 

oral route of exposure provide some evidence of immunotoxicity from toluene exposure (Hsieh et al. 

1989). Accordingly, oral and inhalation studies in animals designed to clarify the effect of toluene on the 
 

TOLUENE 162 

2. HEALTH EFFECTS 

immune system, particularly on lymphocyte production and function, antibodies, and interferons, may 

help determine if toluene was involved in the effects on immunity observed in occupationally exposed 

workers. Additional studies of the impact of toluene on disease resistance, building on the work of 

Aranyi et al. (1985), may also be valuable. 

Neurotoxicity. Effects on the human nervous system from inhalation exposure to toluene are well 

documented (Andersen et al. 1983; Baelum et al. 1985; Byrne et al. 1991; Devathasan et al. 1984; 

Echeverria et al. 1991; Filley et al. 1990; Foo et al. 1990; Hanninen et al. 1976; Ikeda and Tsukagoshi 

1990; Orbaek and Nise 1989; Rosenberg et al. 1988a, 1988b; Vrca et al. 1995, 1996, 1997a, 1997b; 

Zavalic et al. 1998a, 1998b, 1998c) and are the basis for the inhalation exposure MRLs. The central 

nervous system effects of toluene in animals have also been studied in detail via the inhalation route of 

exposure (Arito et al. 1988; Bruckner and Peterson 1981a; Bushnell et al. 1985; Hinman 1987; Ikeda 

et al. 1986; Mattsson et al. 1990; Pryor 1991; Pryor et al. 1991; Rebert et al. 1989a; Taylor and Evans 

1985; Wood and Colotla 1990). Available data clearly indicate that the central nervous system is a target, 

but the molecular mechanisms of toxicity have yet to be elucidated with certainty. Dose-response 

relationships for central nervous system effects in humans and animals (rats and mice) have been 

established, but more information concerning the reversibility of effects (especially when exposure is 

chronic) may be useful. The effects of toluene on neurobehavioral function were used to derive an MRL 

of 4 ppm for acute inhalation exposure (based on a study by Andersen et al. 1983) and a chronic-duration 

MRL of 1 ppm (based on a study by Zavalic et al. 1998a). Additional studies concerning the progression 

of subtle, toluene-induced nervous system defects, such as diminished auditory responses, changes in 

flash evoked visual responses, and impaired color vision discrimination, may decrease uncertainties in the 

MRLs. 

The neurological effects of toluene via the oral route have not been extensively investigated, but the 

available data support the inhalation data in identifying the nervous system as the critical target of toluene 

toxicity. An acute MRL of 0.8 mg/kg/day was developed based on a change in flash-evoked potential 

waveforms in rats exposed to a single dose of toluene (Dyer et al. 1988). The intermediate-duration MRL 

(0.02 mg/kg/day) was based on a regional increase in the levels of selected neurotransmitters in the brains 

of exposed mice (Hsieh et al. 1990b). Additional studies may help define the functional manifestation of 

regional alterations in levels of neurotransmitters in the brain and of changes in FEP waveforms. No data 

on dermal exposure are available, but this is not the primary route of human exposure. 
 

 

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2. HEALTH EFFECTS 

Epidemiological and Human Dosimetry Studies. Additional studies of neurological and 

reproductive end points in groups of toluene-exposed workers may decrease uncertainty in the chronic 

MRL and may help determine if toluene represents a reproductive health hazard in humans at low 

exposure levels. These studies will be most useful if groups of workers can be identified whose exposure 

to other chemicals in the workplace is minimal, if adjustments for lifestyle confounding factors can be 

made, and if personal air monitoring data are available. Earlier reports of increased risk of spontaneous 

abortions (Lindbohm et al. 1992; Ng et al. 1992b; Taskinen et al. 1989) and altered plasma levels of male 

sexual hormones (Svensson et al. 1992a, 1992b) in groups of toluene-exposed workers await confirmation 

from further research. 

Biomarkers of Exposure and Effect. 

Exposure. Toluene and its metabolites are easily detected in the blood and urine (DeRosa et al. 1985; 

Hjelm et al. 1988; Kono et al. 1985; Lof et al. 1990; Ogata et al. 1970). However, many toluene 

metabolites are also produced by other naturally occurring or xenobiotic materials and, thus, are not 

specific for toluene. The presence of toluene in exhaled air and blood is the most reliable biomarker of 

exposure (Foo et al. 1991; Kawai et al. 1992a). The ACGIH (1999) recommends using a combination of 

three biological exposure indices to assess exposure of workers to toluene in the workplace: ortho-cresol 

and hippuric acid levels in urine at the end of a workshift and toluene levels in blood immediately prior to 

the last shift of a workweek. 

Angerer et al. (1998a) proposed that S-p-toluylmercapturic acid levels in urine may also be useful as a 

biological indicator of toluene exposure. Maestri et al. (1997) reported that end-of-shift levels of 

S-benzylmercapturic acid in urine of workers were correlated with toluene concentrations with a 

coefficient of 0.74. Additional studies may help determine whether these are reliable biomarkers of 

exposure that can improve the accuracy of monitoring workers’ exposure to toluene. 

Effect. There are no suitable biomarkers of effect except for changes in the brain found in chronic 

solvent abusers with obvious neurological dysfunction (Filley et al. 1990; Rosenberg et al. 1988a). 

Additional information on the mechanism of neurotoxicity may suggest a useful biomarker of either 

exposure or effect. However, at this time, there is little to suggest that such biomarkers are present for 

anything other than the abuse paradigm. 
 

 

TOLUENE 164 

2. HEALTH EFFECTS 

Absorption, Distribution, Metabolism, and Excretion. The absorption, distribution, 

metabolism, and excretion of toluene in humans and animals following inhalation exposure are well 

characterized (Ameno et al. 1992; Andersen et al. 1983; Angerer 1979; Angerer et al. 1998a; Baelum 

et al. 1987, 1993; Benignus et al. 1981; Benoit et al. 1985; Bergman 1979; Bray et al. 1949; Carlsson 

1982; Carlsson and Ljungquist 1982; Chand and Clausen 1982; Dossing et al. 1983c; Furman et al. 1998; 

Ghantous and Danielsson 1986; Hjelm et al. 1988; Ikeda et al. 1990; Kawai et al. 1992a, 1992b, 1993, 

1996; Lof et al. 1990a, 1990b, 1993; Maestri et al. 1997; Nakajima and Wang 1994; Nakajima et al. 1991, 

1992a, 1992b, 1993, 1997; Ng et al. 1990; Ogata 1984; Pellizzari et al. 1992; Pierce et al. 1996, 1999; 

Paterson and Sarvesvaran 1983; Takeichi et al. 1986; Tassaneeyakul et al. 1996; Van Doorn et al. 1980; 

Wang and Nakajima 1992; Zahlsen et al. 1992). 

Sufficient pharmacokinetic data have been generated to support the development of PBPK models that 

describe the kinetics of toluene after inhalation exposure; two for humans (Fisher et al. 1997; Pierce et al. 

1996, 1999) and two for rats (DeJongh and Blaauboer 1996, 1997; Tardif et al. 1993). Further 

development of a human PBPK model that includes partitioning of inhaled and ingested toluene to the 

brain and a similarly designed rat PBPK model may be useful in improving extrapolation from the oral 

exposure rat data and in comparing model-based predictions of human effect levels based on neurological 

effects in inhalationally-exposed rats with observed effect levels in humans exposed to airborne toluene. 

Additional studies of the appearance and elimination kinetics of toluene in breast milk may help to 

validate the human PBPK model developed by Fisher et al. (1997) to estimate transfer of toluene to a 

nursing infant. It is unlikely that such studies would be done with volunteers, but studies of nursing 

animals may provide pertinent information if a similar rat PBPK was developed. 

Limited data are available on the quantitative absorption and excretion of toluene by the oral and dermal 

routes. Studies of humans and animals indicate that dermal absorption of toluene is slow (Aitio et al. 

1984; Dutkiewicz and Tyras 1968), but can be significant (Aitio et al. 1984; Monster et al. 1993; Morgan 

et al. 1991; Sato and Nakajima 1978). Additional studies of dermal uptake of toluene from solution may 

help to further quantify exposure by this pathway. 

Comparative Toxicokinetics. Available data suggest that there are species, age, gender, and strain 

differences in the metabolism of toluene (Chapman et al. 1990; Inoue et al. 1984, 1986; Nakajima et al. 

1992b). Further evaluation of these differences, and comparison of metabolic patterns in humans with 

those of animals, may help determine the most appropriate species and strain of animal to use in 
 

 

TOLUENE 165 

2. HEALTH EFFECTS 

evaluating the risk of human exposure to toluene. Additional evaluation of human variability in 

disposition of toluene is also warranted. 

Methods for Reducing Toxic Effects. Oxygen therapy and positive pressure ventilation have been 

used to reduce the toluene body burden (Graham 1990). Washing of toluene from exposed body surfaces 

is beneficial. Other than these general guidelines, there is very little information available on methods of 

mitigating the toxic effects of toluene. Additional data on the outcome of emergency response procedures 

would be beneficial. Studies of the benefit of diet, ethanol absence, and controlled exposure to 

prescription or nonprescription drugs on blood levels of toluene and its metabolites could provide 

information that would be helpful in understanding the impact of these factors on the risks from 

occupational exposure. 

Children’s Susceptibility. The effects of toluene have not been thoroughly studied in children or 

immature animals, but the effects observed in juvenile toluene abusers (Byrne et al. 1991; Devasthasan et 

al. 1984; King et al. 1981) and immature animals exposed to toluene (Castilla-Serna et al. 1991; Pryor 

and Rebert 1992; Pryor et al. 1984a; von Euler et al. 1989b) are consistent with effects observed in adults. 

Information regarding age-related differences in toluene metabolism suggests that developing fetuses and 

children at very early stages of development may be more susceptible to toluene toxicity than adults due 

to lower capabilities to metabolically detoxify toluene, but, by 1–3 years of age, adult capabilities may be 

attained (Leeder and Kearns 1997; Nakajima et al. 1992b, 1997; Tassaneeyakul et al. 1996; Vieira et al. 

1996). An oral lethality study in rats (Kimura et al. 1971) and a study of toluene-induced hearing loss in 

young rats (Pryor et al. 1984a) provide the only health effect data suggesting that immature animals may 

be more susceptible than adult animals. Additional research on the development of metabolic capabilities 

in newborn and very young children, coupled with animal studies examining relevant neurological end 

points in toluene-exposed animals of varying ages, may lead to better understanding of the susceptibility 

of children to toluene toxicity. 

Studies with pregnant mice suggest that distribution of inhaled toluene to fetal tissue is limited due to 

maternal metabolic detoxification and preferential distribution of nonmetabolized toluene to maternal 

adipose tissue (Ghantous and Danielsson 1986). Data needs relating to both prenatal and childhood 

exposures, and developmental effects expressed either prenatally or during childhood, are discussed in 

detail in the Developmental Toxicity subsection above. 
TOLUENE 166 

2. HEALTH EFFECTS 

Transfer of toluene to infants from breast milk of nursing mothers who are concurrently exposed to 

toluene in the workplace is expected to be a possibility and a concern (see Section 2.7). As discussed in 

the Absorption, Distribution, Metabolism, and Excretion subsection above, additional studies of the 

kinetics of elimination of toluene from nursing animals may provide pertinent information to better 

predict the degree to which toluene may be transferred in breast milk from a toluene-exposed working 

mother to her nursing infant. Monitoring studies of toluene in breast milk in groups of toluene-exposed 

lactating women may also provide some pertinent information. 

2.12.3 Ongoing Studies 

There are several ongoing research efforts that will provide data related to the toxic actions of toluene 

(FEDRIP 1998). These projects are summarized in Table 2-6. Some of this research will supply 

information identified in the preceding section on research needs. Three of the investigators are studying 

the effects of toluene in humans, focusing on different end points. Dr. M. Utell of the University of 

Rochester is studying the effects of toluene on neurological and respiratory end points in humans, while 

Dr. E. Faustman of the University of Washington is examining the effects of toluene on the endocrine 

system. Dr. D.M. Christiani of Harvard University is assessing the reproductive outcomes of 

occupational exposure to aromatic solvents, including toluene, in the oil refinery system in China. 

Two investigators are using animal models to study the effects of toluene. Dr. R. Balster of Virginia 

Commonwealth University is investigating the abuse of inhalants, including toluene, using behavioral test 

procedures in mice. D.N. Kurtzman of Texas Tech University is investigating the relationship between 

ATPase activity and tubular function in rat and rabbit kidneys. 
 

TOLUENE 

2. HEALTH EFFECTS 

167 

Investigator 

Table 2-6. Ongoing Research for Toluene 

Affiliation Research description Sponsor 

Backes, W 

Balster, RL 

Branch, S 

Christiani, DM 

Cunningham, ML 

Faustman, EM 

Fechter, LD 

Greenberg, A 

Kalman, DA 

Karol, MH 

Kurtzman, DN 

Lee, L 

Stern, S 

Louisiana State University 

Medical Center, 

New Orleans, LA 

Virginia Commonwealth 

University, Richmond, VA 

North Carolina State University, 

Raleigh, NC 

Harvard University 

National Institute of 

Environmental Health Sciences, 

Research Triangle Park, NC 

University of Washington, 

Seattle, WA 

University of Oklahoma 

Health Science Center, OK 

University of North Carolina, 

Charlotte, NC 

University of Washington, 

Seattle, WA 

University of Pittsburgh, 

Pittsburgh, PA 

Texas Tech University 

University of Kentucky, 

Lexington, KY 

University of Rochester, 

Rochester, NY 

Toxicological significance 

of alkylbenzene 

metabolism 

Behavioral pharmacology 

of abused solvents 

DNA methylation effects on 

mammalian development 

Reproductive outcomes of 

occupational exposure to 

aromatic solvents in the oil 

refinery system in China 

Metabolism and genotoxicity of genotoxic noncarcinogens 

Human reproductive 

endocrine effects of solvent 

exposure 

Mechanisms of organic 

solvent ototoxicity 

2,3 Eposyoxepins as 

benzene ring opening 

metabolities 

Human dosimetry for 

assessment of exposure to 

volatile compounds 

Chemically induced chronic 

allergic lung disease 

Relationship between 

ATPase activity and tubular 

function in rat and rabbit 

kidneys 

Pulmonary afferents in 

regulation of airway 

functions 

Inhalant abuse during 

gestation 

National Institute of 

Environmental Health 

Sciences 

National Institute on Drug 

Abuse 

National Institute of 

Environmental Health 

Sciences 

National Institute of 

Environmental Health 

Sciences 

National Institute for 

Occupational Safety and 

Health 

National Institute of 

Environmental Health 

Sciences 

National Institute of 

Environmental Health 

Sciences 

National Institute of 

Environmental Health 

Sciences 

National Institute of 

Environmental Health 

Sciences 

National Heart, Lung, and 

Blood Institute 

National Institute on Drug 

Abuse 
TOLUENE 

2. HEALTH EFFECTS 

168 

Table 2-6. Ongoing Research for Toluene (continued) 

Investigator 

Turtletaub, KW 

Utell, M 

Affiliation 

University of California Berkeley, 

Berkeley, CA 

University of Rochester, 

Rochester, NY 

Research description 

Protein and DNA adducts 

following low dose 

exposure by accelerator, 

MS 

Effects of toluene on 

performance in healthy 

humans 

Sponsor 

National Institute of 

Environmental Health 

Sciences 

National Center for 

Research Resources 
TOLUENE 169 

3. CHEMICAL AND PHYSICAL INFORMATION 

3.1 CHEMICAL IDENTITY 

Information regarding the chemical identity of toluene is located in Table 3-1. 

3.2 PHYSICAL AND CHEMICAL PROPERTIES 

Information regarding the physical and chemical properties of toluene is located in Table 3-2. 
TOLUENE 170 

3. CHEMICAL AND PHYSICAL INFORMATION 

Table 3-1. Chemical Identity of Toluene 

Characteristic Information Reference 

Chemical name Toluene Weast 1989 

Synonym(s) Methylbenzene; phenylmethane; 

benzene, methyl-; toluol; methylbenzol 

Weast 1989; 

Budavari et al. 

1989; RTECS 

1998; HSDB 1998 

Registered trade name(s) Methacide WHO 1985 

Chemical formula C6H5CH3 Weast 1989 

Chemical structure CH3 

EPA 1983b 

Identification numbers: 

CAS registry 108-88-3 RTECS 1998 

NIOSH RTECS XS5250000 RTECS 1998 

EPA hazardous waste U220 HSDB 1998 

OHM/TADS 7216928 NFPA 1994 

DOT/UN/NA/IMCO shipping UN 1294 HSDB 1998 

IMCO 3.2 HSDB 1998 

HSDB 131 HSDB 1998 

NCI CO7272 HSDB 1998 

CAS = Chemical Abstracts Services; DOT/UN/NA/IMCO = Department of Transportation/United Nations/North 

America/International Maritime Dangerous Goods Code; EPA = Environmental Protection Agency; HSDB = 

Hazardous Substances Data Bank; NCI = National Cancer Institute; NIOSH = National Institute for Occupational 

Safety and Health; NFPA = National Fire Protection Association; OHM/TADS = Oil and Hazardous 

Materials/Technical Assistance Data System; RTECS = Registry of Toxic Effects of Chemical Substances 
TOLUENE 171 

3. CHEMICAL AND PHYSICAL INFORMATION 

Table 3-2. Physical and Chemical Properties of Toluene 

Property Information Reference 

Molecular weight 92.14 Weast 1989 

Color Colorless NFPA 1994 

Physical state Liquid NFPA 1994 

Melting point -95 EC Weast 1989 

Boiling point 110.6 EC Weast 1989 

Density: 

at 20 EC 0.8669 g/mL Weast 1989 

Vapor density 3.2 (air=1) HSDB 1999 

Odor Benzene-like NFPA 1994 

Odor threshold: 

Water 0.04–1 ppm EPA 1987a 

Air 8 ppm HSDB 1998 

Solubility: 

Water at 25 EC 534.8 mg/L Howard 1990 

Organic solvent(s) Miscible Budavari et al. 1989 

Partition coefficients: 

Log Kow 2.72 Howard 1990 

Log Koc 1.57–2.25 Howard 1990 

Vapor pressure at 25 EC 28.4 mm/Hg Howard 1990 

Henry's law constant: 5.94x10-3 atm-m3

/mol Howard 1990 

Autoignition temperature 480 EC (896 EF) NFPA 1994 

Flashpoint 4 EC (40 EF) NFPA 1994 

Flammability limits 1.2–7.1% NFPA 1994 

Conversion factors ppm (v/v) to mg/m3 

in air (20 EC) 1 ppm=3.75 mg/m3 NIOSH 1986 

Explosive limits 1.3% lower limit Sax and Lewis 1989 

v/v = volume for volume 

TOLUENE 173 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

4.1 PRODUCTION 

Table 4-1 lists the facilities in each state that manufacture or process toluene, the intended use, and the 

range of maximum amounts of toluene that are stored on site. There are currently 3,062 facilities that 

produce or process toluene in the United States. The data listed in Table 4-1 are derived from the Toxics 

Release Inventory (TRI97 1999). Only certain types of facilities were required to report. Therefore, this 

is not an exhaustive list. 

About 11% of the total toluene produced in the United States is isolated by distillation of reformed or 

pyrolyzed petroleum and coal-tar oil. The remainder is added as a mixture, known as benzene-toluenexylene (BTX), to gasoline (EPA 1990a). One estimate of domestic 1978 production of both isolated and 

nonisolated toluene was 3 million metric tons (EPA 1981). Most data available, however, are for isolated 

toluene. According to the latest available data, the domestic capacity has been estimated at 6 million 

metric tons (1,774 million gallons) (SRI 1988). There are 41 major U.S. producers of toluene (SRI 1999). 

Production of isolated toluene in the United States from all sources except for distillers and coke oven 

operators was estimated at 6.7 billion pounds (927 million gallons) in 1995 (C&EN 1996). As of 

October 1, 1996, the International Trade Commission ceased to collect or publish annual synthetic 

organic chemicals data. The National Petroleum Refiners Association, which currently collects such data, 

does not include toluene on its list of organic chemicals. 

Toluene is widely used and is produced by a large number of domestic chemical and petroleum 

companies. In 1979, there were 201 locations in the United States that produced toluene by catalytic 

reformation, 9 locations where it was produced by petroleum pyrolysis, and six where toluene was 

produced from coal tar (IARC 1988). The 10 companies which currently produce or supply toluene in the 

United States are: BP Amoco Corporation; Chevron Chemical Company; CITGO Petroleum Corporation; 

Coastal Eagle Point Oil Co., Coastal Refining and Marketing, Inc.; Dow Chemical U.S.A.; Equilon 

Enterprises LLC; Equistar Chemicals LP; Exxon Chemical Company; Fina Oil and Chemical Company, 

Hovensa, LLC.; Koch Petroleum Group LP; Lyondell-Citgo Refining Company Ltd.; Marathon Ashland 

Chemical, Inc.; Mobil Chemical Company; Phillips Petroleum Company; Shell Chemical Company; 

Sunoco, Inc.; Ultramar Diamond Shamrock Corporation; and Valero Energy Corporation(SRI 1999). 
TOLUENE 174 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

Table 4-1. Facilities that Manufacture or Process Toluene 

Number of Range of maximum 

Statea facilities amounts on site in poundsb Activities and usesc 

AK 2 1,000,000–49,999,999 1, 3, 4, 8 

AL 75 0–999,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

AR 59 0–9,999,999 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 13 

AZ 9 0–999,999 8, 9, 10, 11, 12, 13 

CA 125 100–99,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

CO 22 100–49,999,999 1, 4, 5, 6, 8, 10, 11, 12, 13 

CT 33 1000–9,999,999 8, 9, 11, 12, 13 

DE 10 1,000–49,999,999 1, 3, 8, 9, 11, 12, 13 

FL 47 100–9,999,999 2,3, 8, 9, 10, 11, 12, 13 

GA 79 100–49,999,999 1, 2, 3, 6, 8, 9, 10, 11, 12, 13 

HI 2 1,000,000–9,999,999 1, 2, 6, 8 

IA 51 0–9,999,999 1, 2, 3, 4,7, 8, 9, 10, 11, 12, 13 

ID 3 1000–99,999 2, 3, 8, 10,11, 12 

IL 198 0–99,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

IN 171 100–999,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

KS 51 0–999,999,999 1, 2, 3, 4, 7, 8, 9, 10, 11, 12, 13 

KY 57 100–49,999,999 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13 

LA 75 0–999,999,999 1, 2, 3, 4, 5, 6, 7 ,8, 9, 10, 11, 12, 13 

MA 74 0–999,999 1, 3, 8, 9, 10, 11, 12, 13 

MD 20 1,000–999,999 2, 3, 4, 7, 8, 9, 10, 11, 12, 13 

ME 7 100–999,999 1, 2, 3, 6, 8, 11, 12, 13 

MI 150 0–49,999,999 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13 

MN 65 0–99,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

MO 81 100–9,999,999 2, 3, 4, 7, 8, 9, 10, 11, 12, 13 

MS 61 0–49,999,999 1, 2, 3, 6, 7, 8, 9, 11, 12, 13 

MT 6 1,000–49,999,999 1, 3, 4, 6, 7, 8, 9, 13 

NC 156 0–999,999 1, 2, 3, 5, 7, 8, 9, 10, 11, 12, 13 

ND 3 100–9,999,999 1, 2, 3, 4, 7, 9, 11, 13 

NE 19 100–99,999 2, 3, 8,10, 11, 12, 13 
TOLUENE 175 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

Table 4-1. Facilities that Manufacture or Process Toluene (continued) 

Number Range of maximum 

Statea of Facilities amounts on site in poundsb Activities and usesc 

NH 12 100–999,999 8, 11, 12, 13 

NJ 107 100–99,999,999 1, 2, 3, 4, 7, 8, 9, 10, 11, 12, 13 

NM 10 100–9,999,999 1, 3, 4, 6, 7, 8, 9, 12, 13 

NV 2 1,000,000–9,999,999 9 

NY 87 0–9,999,999 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13 

OH 203 0–99,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

OK 36 1000–49,999,999 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13 

OR 32 0–9,999,999 2, 3, 8, 9, 10, 11, 12, 13 

PA 148 0–99,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

PR 28 1,000–10,000,000,000 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

RI 16 100–999,999 8, 10, 11, 12, 13 

SC 63 0–9,999,999 1, 2, 3, 5, 7, 8, 9, 11, 12, 13 

SD 10 100–99,999 2, 3, 8, 9, 11, 12, 13 

TN 115 100–49,999,999 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13 

TX 208 100–999,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

UT 22 100–49,999,999 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13 

VA 83 100–9,999,999 1, 2, 3, 6, 7, 8, 9, 10, 11, 12, 13 

VI 1 100,000,000–999,999,999 1, 2, 3, 4, 7, 8 

VT 6 1,000–99,999 8, 11, 12, 13 

WA 39 100–99,999,999 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13 

WI 94 0–49,999,999 1, 2, 3, 5, 6, 8, 9, 10, 11, 12, 13 

WV 21 100–49,999,999 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13 

WY 8 0–9,999,999 1, 3, 4, 5, 6, 7, 8, 10, 13 

Source: TRI97 1999 

a

Post office state abbreviations used 

b

Range represents maximum amounts on site reported by facilities in each state c

Activities/Uses: 

1. Produce 6. Impurity 10. Repackaging 

2. Import 7. Reactant 11. Chemical Processing Aid 

3. Onsite use/processing 8. Formulation Component 12. Manufacturing Aid 

4. Sale/Distribution 9. Article Component 13. Ancillary/Other Uses 

5. Byproduct 
TOLUENE 176 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

4.2 IMPORT/EXPORT 

United States imports of toluene in 1984 were estimated at 602 million pounds (273,000 metric tons) 

(U.S. Department of Commerce 1985a). Exports during the same year were estimated at 289 million 

pounds (131,000 metric tons) (U.S. Department of Commerce 1985b). No data on recent import/export 

volume for toluene are available. 

4.3 USE 

All nonisolated toluene is used in a BTX mixture added to gasoline to improve octane ratings 

(EPA 1990a). Nearly half of the isolated toluene is used to produce benzene (IARC 1988). About onethird of the isolated toluene is used as a solvent in paints, coatings, adhesives, inks, and cleaning agents. 

A portion of the isolated toluene goes into the production of polymers used to make nylon, plastic soda 

bottles, and polyurethanes. Toluene is also used as a starting material in the synthesis of trinitrotoluene 

(TNT). The remainder is used for pharmaceuticals, dyes, nail polish, and the synthesis of organic 

chemicals (Cosmetic Ingredient Review Panel 1987). Toluene was once used as an anthelminthic agent 

against roundworms and hookworms (Krinsky 1980). 

4.4 DISPOSAL 

Toluene is regulated by the Resource Conservation and Recovery Act (RCRA) as a hazardous waste 

(F005-spent solvents including toluene) and is therefore subject to RCRA regulations (see Chapter 7). 

These regulations include standards for storage, transport, and disposal of toluene. 

Industrial wastes containing spent solvents may not be disposed of on land if extracts of the waste contain 

more than 0.33 ppm of toluene. Waste waters containing spent solvents may not be land-disposed if they 

contain greater than 1.12 ppm of toluene (EPA 1994d). 

Consumer products containing toluene are typically disposed of in landfills as municipal waste. No 

information was available on total disposal of toluene to solid waste landfills. There are no data 

concerning disposal of toluene by municipal incineration. However, high-temperature incineration 

(>1,600 EF) probably is very efficient for toluene destruction. 
TOLUENE 177 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

In 1996, it was estimated that about 0.6 million pounds (272 metric tons) of waste toluene was disposed 

of in publicly owned treatment works (POTW) and about 125 million pounds (5,679 metric tons) of waste 

toluene was transported from production facilities or points of usage for disposal (TRI97 1999). 

Toluene is listed as a toxic substance under Section 313 of the Emergency Planning and Community 

Right to Know Act (EPCRA) under Title III of the Superfund Amendments and Reauthorization Act 

(SARA) (EPA 1995j). Disposal of wastes containing toluene is controlled by a number of federal 

regulations (see Chapter 7). 

TOLUENE 179 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.1 OVERVIEW 

Large amounts of toluene enter the environment each year, almost entirely as direct releases to the 

atmosphere. The largest source of toluene release is during the production, transport, and use of gasoline, 

which contains about 5–7% toluene by weight. Significant quantities are also released in association with 

the production, use, and disposal of industrial and consumer products that contain toluene. Small 

amounts are released in industrial waste water discharges and land disposal of sludges and petroleum 

wastes. 

Toluene in the atmosphere is degraded by reaction with hydroxyl radicals, with a typical half-life of 

approximately 13 hours. Toluene in soil or water rapidly volatilizes to air, and that which remains is 

subject to microbial degradation. As a consequence of the volatilization and degradation occurring in air, 

soil, and water, there is little tendency for toluene levels to build up in the environment over time. 

The concentrations of toluene in air have been found to be quite low in remote areas, but levels of 

1.3–6.6 ppb are common in suburban and urban areas. The automobile emissions are the principal source 

of toluene in ambient air, with levels fluctuating in proportion to automobile traffic. Toluene is also a 

common indoor contaminant, and indoor air concentrations are often several times higher (averaging 

8 ppb) than outside air. This is likely due to release of toluene from common household products (paints, 

paint thinners, adhesives, and nail polish in which it is used as a solvent) and from cigarette smoke. 

Toluene is occasionally detected in drinking water supplies, but occurrence is not widespread and levels 

are generally below 3 ppb. In contrast, toluene is a very common contaminant of water and soil in the 

vicinity of hazardous waste sites, with average concentrations in water of 7–20 ppb, and average 

concentrations in soil of over 70 ppb. 

The most likely pathway by which people may be exposed to toluene is by breathing contaminated air. 

Since most people spend a large fraction of the day indoors, indoor air levels are likely to be the dominant 

source. Moreover, indoor levels generally exceed outdoor levels because of volatilization of toluene from 

household products. Based on a typical concentration of 8 ppb in indoor air, inhalation of air at 

20 m3

/day, and absorption of 50% of the inhaled dose of toluene, a typical absorbed dose is about 

300 μg/day. Intake from food and water may contribute substantially smaller amounts. By comparison, 
TOLUENE 180 

5. POTENTIAL FOR HUMAN EXPOSURE 

smoking may contribute 1,000 μg/day or more. Higher exposure levels might occur for individuals living 

near a hazardous waste site or an industrial source of toluene emissions, but these exposures can be 

estimated only on a site-by-site basis. 

Toluene exposure may also occur in the workplace, especially in occupations such as printing or painting, 

where toluene is used as a solvent. A workplace air level of 100 ppm (equivalent to a dose of 

3,750 mg/day) has been established by the Occupational Safety and Health Administration (OSHA) as the 

8-hour TWA Permissible Exposure Limit (PEL) for toluene (OSHA 1989a). The American Conference 

of Governmental Industrial Hygienists (ACGIH 1999) recommends an 8-hour TWA concentration of 

50 ppm as the Threshold Limit Value for workplace air to protect against central nervous system effects. 

Toluene has been identified in at least 959 of the 1,591 hazardous waste sites that have been proposed for 

inclusion on the EPA National Priorities List (NPL) (HazDat 2000). However, the number of sites 

evaluated for toluene is not known. The frequency of these sites can be seen in Figure 5-1. Of these 

sites, 959 are located within the United States and none are located in the Commonwealth of Puerto Rico 

(not shown). 

5.2 RELEASES TO THE ENVIRONMENT 

According to the Toxics Release Inventory (TRI), in 1997 a total of 114 million pounds (251 million kg) 

of toluene was released to the environment from 3,118 manufacturing or processing facilities (TRI97 

1999). Table 5-1 lists the amounts released from these facilities to air, water, land, and publicly owned 

treatment works (POTWs). Table 5-1 also shows that less that 1% of the total released was injected deep 

underground and that about 3.3 million pounds of toluene were transferred off-site (TRI97 1999). The 

relative proportions of the material transferred off-site that were recycled or entered environmental media 

are not stated. The TRI data should be used with caution because only certain types of facilities are 

required to report. This is not an exhaustive list. 

Toluene has been identified in a variety of environmental media (air, surface water, groundwater, soil, 

and sediment) collected at 959 of the 1,591 NPL hazardous waste sites (HazDat 2000). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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....... 1-7 ....... 8-14 

15-2

 

27-3

 

43-7

 95 

Frequency o

NPL Sites

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Derived from HazDat 2000 

Figure 5-1. Frequency of NPL Sites with Toluene contamination 
Table 5-1. Releases to the Environment from Facilities that Manufacture or Process 

Range of reported amounts released in pounds per yeara 

Stateb 

Number of facilities Airc Water Land 

Underground injection 

Total environmentd 

POTW trans

AK 2 88,176 0 265 0 88,441 0 AL 75 3,001,377 1,331 0 5 3,002,713 1,046 

AR 59 2,209,387 68 3,250 106,107 2,318,812 5 AZ 9 126,923 0 0 0 126,923 0 

CA 125 1,553,654 242 122 500 1,554,518 61,77CO 22 343,136 0 0 0 343,136 10 

CT 33 668,010 5 0 0 668,015 1,155 DE 10 38,727 72 0 0 38,799 50,54

FL 47 1,429,964 0 3,302 0 1,433,266 899 

GA 79 3,118,819 689 0 0 3,119,508 1,080 HI 2 18,375 0 0 0 18,375 0 

IA 51 1,968,830 66 5 0 1,968,901 9 

ID 3 353,942 0 0 0 353,942 0 

IL 198 5,228,891 611 10,252 0 5,239,754 19,13

IN 171 7,710,949 399 33,703 0 7,745,051 2,883 

KS 51 1,579,396 307 3,296 420 1,583,419 10 

KY 57 5,602,482 613 6,432 0 5,609,527 2,898 

LA 75 1,968,292 553 4,120 157,705 2,130,670 0 
Table 5-1. Releases to the Environment from Facilities that Manufacture or Process Toluen

Range of reported amounts released in pounds per yeara 

Stateb 

Number of facilities Airc Water Land 

Underground injection 

Total environmentd 

POTW trans

MA 74 1,625,237 0 7 0 1,625,244 1 

MD 20 403,263 3 0 0 403,266 79 

ME 7 302,348 0 0 0 302,348 0 MI 150 6,770,172 387 3,022 6,142 6,779,723 13,54MN 65 2,235,464 107 0 0 2,235,571 15 

MO 81 1,990,918 48 911 0 1,991,877 27,91

MS 61 4,489,512 6,278 421 5,120 4,501,331 254 

MT 6 104,600 16 255 0 104,871 5 NC 156 6,404,347 33 5 0 6,404,385 36,97ND 3 80,337 0 1 0 80,338 0 

NE 19 776,949 5 0 0 776,954 250 

NH 12 186,830 0 0 0 186,830 5 

NJ 107 1,110,539 85 4,616 0 1,115,240 63,04

NM 10 317,538 0 1,010 0 318,548 0 

NV 2 619,855 0 0 0 619,855 11 

NY 87 4,074,714 575 5 0 4,075,294 5,121 

OH 203 3,400,247 3,598 760 0 3,404,605 4,579 

OK 36 1,283,992 1,238 439 2,200 1,287,869 726 

OR 32 663,051 0 0 0 663,051 171 
Table 5-1. Releases to the Environment from Facilities that Manufacture or Process Toluen

Range of reported amounts released in pounds per yeara 

Stateb 

Number of facilities Airc Water Land 

Underground injection 

Total environmentd 

POTW trans

PA 148 6,447,689 1,671 251 0 6,449,611 55,63

PR 28 1,130,850 13 0 0 1,130,863 43,14

RI 16 761,923 1 2,089 0 764,013 5 

SC 63 4,931,964 604 1,405 0 4,933,973 510 SD 10 155,429 0 3 0 155,432 0 

TN 115 8,955,221 2,365 0 0 8,957,586 18,46

TX 208 5,519,497 4,899 655,161 235,436 6,414,993 72,06

UT 22 336,598 62 620 0 337,280 9,252 

VA 83 5,191,139 1,020 0 0 5,192,159 116,4

VI 1 151,479 48 0 0 151,527 0 

VT 6 61,159 0 0 0 61,159 250 

WA 39 1,187,149 110 1,480 0 1,188,739 15 WI 94 2,788,125 0 21 0 2,788,146 2,018 

WV 21 1,246,059 2,606 1,429 0–0 1,250,094 0 

WY 8 113,513 10 696 0–250 114,219 0 

Totals 3062 112,827,037 30,738 739,354 513,635 114,110,764 611,9

Source: TRI97 1999 aData in TRI are maximum amounts released by each facilitybPost office state abbreviations used 

dThe sum of all releases of the chemical to air, land, water, a

wells cThe sum of fugitive and stack releases are included in releases to air by a given facility POTW = publicly owned treatment works 
TOLUENE 185 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.2.1 Air 

Nearly all toluene entering the environment is released directly to air. The largest source of emissions is 

gasoline, which typically contains 5–7% toluene by weight (Verschueren 1977). In 1978, air emissions 

associated with gasoline use were estimated to be 1.5 billion pounds (6.8x105

 metric tons), the bulk of this 

(6.4x105

 metric tons) was released through automobile exhaust (EPA 1981). Toluene used in paints, 

solvents, adhesives, inks, and similar products is also released to air upon use. The total release from 

these sources not associated with gasoline was estimated to be about 3.7x105

 metric tons in 1978 (EPA 

1981). 

Toluene may also be released during disposal processes. Based on information from 40 medical waste 

incinerators in the United States and Canada, emission factors for toluene were reported to range from 

37.3 to 178 (mean=113) ppb waste for uncontrolled emissions and 177–3,000 (mean=1,920) ppb waste 

for controlled emissions (Walker and Cooper 1992). Toluene emissions from coal-fired power stations 

(119 μg/Nm3

) were reported to be far less than toluene emissions from diesel engines (167–287 μg/Nm3) 

and automobiles (15,700–370,000 μg/Nm3

, where N denotes 20 EC and 1 atmosphere pressure) (Garcia et 

al. 1992). 

According to the Toxics Release Inventory, in 1997, the estimated releases of toluene of 113 million 

pounds (249 million kg) to air from 3,118 manufacturing or processing facilities accounted for about 50% 

of total environmental releases (TRI97 1999). Table 5-1 lists amounts released from these facilities. The 

TRI data should be used with caution because only certain types of facilities are required to report. This 

is not an exhaustive list. 

Toluene has been identified in air samples collected at 187 of the 959 NPL hazardous waste sites where it 

was detected in some environmental media (HazDat 2000). 

5.2.2 Water 

Toluene may be released to water from industrial discharges and urban wastes, or by spills and leaks of 

gasoline. However, these releases are believed to comprise only a small fraction of the amount of toluene 

released to air (EPA 1981). In a survey of toluene levels in industrial waste waters, EPA (1982a) found 

values ranging from 1 to 2,000 ppb. 
TOLUENE 186 

5. POTENTIAL FOR HUMAN EXPOSURE 

According to the Toxics Release Inventory, in 1997, the estimated releases of toluene of 30,378 pounds 

(166,832 kg) to water from 3,062 manufacturing or processing facilities accounted for about 0.03% of 

total environmental releases (TRI97 1999). The majority of the releases to water are due to spills of 

gasoline and oil to surface water (TRI97 1999). Another 611,931 pounds were transferred to POTWs. 

The TRI data should be used with caution because only certain types of facilities are required to report. 

This is not an exhaustive list. 

Toluene has been identified in 243 surface water and 1,063 groundwater samples collected from 959 NPL 

hazardous waste sites, where it was detected in some environmental media (HazDat 2000). 

5.2.3 Soil 

Toluene has been identified in 807 soil and 220 sediment samples collected from 959 NPL hazardous 

waste sites, where it was detected in some environmental media (HazDat 2000). 

Release of toluene to land may occur in association with gasoline spills, leaking underground gasoline 

storage tanks, or land disposal of municipal sludges or refinery wastes. Although, in some cases, releases 

might be significant on a local scale, the total amount of toluene released to the environment in soil is 

considered to be negligible (EPA 1981). 

According to the Toxics Release Inventory, in 1997, the estimated releases of toluene of 739,354 pounds 

(1.6 million kg) to soil from 3,062 manufacturing or processing facilities accounted for about 0.65% of 

total environmental releases (TRI97 1999). Table 5-1 lists amounts released from these facilities. 

Another 3.3 million pounds were transferred off-site. The TRI data should be used with caution since 

only certain types of facilities are required to report. 

5.3 ENVIRONMENTAL FATE 

5.3.1 Transport and Partitioning 

Although toluene is a liquid at room temperature, it is sufficiently volatile (vapor pressure = 28.4 mmHg 

at 25 EC) that the majority of toluene released to the environment partitions to air. As discussed in 

Section 5.2, most toluene is released directly into air, and that which is released to surface water or soil 
TOLUENE 187 

5. POTENTIAL FOR HUMAN EXPOSURE 

tends to volatilize quickly. The rate of toluene volatilization from surface waters depends on whether the 

water is static (half-life of 1–16 days) or turbulent (half-life of 5–6 hours) (Mackay and Leinonen 1975; 

Wakeham et al. 1983). Laboratory studies indicate that surfactants can affect volatilization of toluene 

from water (Anderson 1992). The rate of volatilization from soils depends on temperature, humidity, and 

soil type, but under typical conditions, more than 90% of the toluene in the upper soil layer volatilizes to 

air within 24 hours (Balfour et al. 1984; Thibodeaux and Hwang 1982). Toluene present in deep soil 

deposits, however, is much less likely to volatilize. Calculations of toluene volatilization for deposits 

1–1.3 m below the soil surface suggest that only 0.1–2.6% will volatilize over a 1-year period (Jury et al. 

1990). The higher volatilization value allows for a soil water evaporation rate of 0.1 cm/day and the 

lower value assumes no water evaporation. 

Because toluene is moderately soluble in water (534.8 ppm at 25 EC), it is likely that toluene is scrubbed 

from air by rainfall, but no quantitative estimate of the rate of this transport process was located. Toluene 

removed from the atmosphere by this process is likely to be rapidly volatilized. 

The rate of toluene transport to groundwater depends on the degree of adsorption to soil. The log organic 

carbon-water partition coefficient is 2.25, which indicates that toluene will be moderately retarded by 

adsorption to soils rich in organic matter, but will be readily leached from soils with low organic content 

(Wilson et al. 1981). Soil desorption can be slow. Distilled water removed 9–40% of the toluene 

adsorbed to samples of five different soils of low organic content within 24 hours (Pavlostathis and 

Mathavan 1992), but after 7 days some of the toluene still remained adsorbed to the soil samples. Studies 

of the sorption mechanism when biological activity is minimized show that the primary, or partitioning 

process, is very fast, but the adsorption process is much slower (Wojtenko et al. 1996). A gravimetric 

method shows that adsorption of gas phase toluene on loam or clay occurs in two stages: fast diffusion 

and adsorption in macropores, followed by slower diffusion and adsorption in intragrain micropores 

(Arocha et al. 1996). Although the organic carbon content of aquifer materials is an important 

determinant of toluene migration in groundwater, other factors may be important as well (Larsen et al. 

1992). For example, information from waste sites and U.S. coastal plain aquifers indicates that many sitespecific hydro geologic factors can have unpredictable effects on toluene migration (Adams and Golden 

1992). In addition, the presence of other gasoline components (benzene, xylene) can impact toluene 

migration. Competitive sorption between these gasoline components decreases the interaction between 

toluene and soil, thereby allowing it to move more quickly through the aquifer (Stuart et al. 1991). 
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5. POTENTIAL FOR HUMAN EXPOSURE 

Based on its lipophilic properties, toluene is expected to have a low tendency to bioconcentrate in the 

fatty tissues of aquatic organisms (Franke et al. 1994). The bioconcentration factor was estimated to be 

about 10.7 in fish (EPA 1980a) and about 4.2 in mussels. The levels that accumulate in the flesh of 

aquatic species also depend on the degree to which the species metabolize toluene. The highest tissue 

levels of toluene tend to occur in species such as eels, crabs, and herring that have a low rate of toluene 

metabolism (EPA 1981). Metabolism of toluene limits its tendency to biomagnify in the food chain. 

5.3.2 Transformation and Degradation 

5.3.2.1 Air 

Toluene in the atmosphere is rapidly degraded by reaction with hydroxyl radicals to yield cresol and 

benzaldehyde, which in turn undergo ring cleavage to yield simple hydrocarbons (Davis et al. 1979; 

Hoshino et al. 1978; Kenley et al. 1973). The estimated rate constant for this process is about 

0.6–2.4x10-5 sec-1, which corresponds to an atmospheric half-life of around 13 hours. The actual half-life 

may range from 10 to 104 hours depending on atmospheric conditions (Howard et al. 1991). Toluene is 

also oxidized by reaction with nitrogen dioxide, oxygen, and ozone, but the rates of these reactions are 

two or more orders of magnitude less than for the hydroxyl radical (Altshuller et al. 1971; Dilling et al. 

1976; Wei and Adelman 1969). Benzyl nitrate and nitrotoluene are formed through the reaction of 

atmospheric toluene with nitrogen oxides (Atkinson 1990). Photolysis is not a significant degradation 

pathway for toluene (EPA 1981). Smog chamber experiments with hydroxyl radical oxidation of toluene 

under simulated atmospheric conditions produce numerous carbonyl products. 

5.3.2.2 Water 

Although toluene may be oxidized in water by reactions similar to those that occur in air, the rates of 

these reactions in water are very slow (EPA 1979). The half-life for benzene in reaction with aqueous 

hydroxyl radicals has been estimated to range from 13 to 54 days (Howard et al. 1991). Degradation of 

toluene in water occurs primarily by microbial action. The rate of biodegradation is a function of many 

parameters (temperature, duration of microbial acclimation, etc.). The degradation half-life is less than 

1 day under favorable conditions (Wakeham et al. 1983). In surface waters, the biodegradation half-life 

of toluene was estimated to range from 4 to 22 days, whereas the biodegradation half-life of toluene in 

groundwater was estimated to range from 7 to 28 days (Howard et al. 1991). The biodegradation of 

toluene in groundwater can be enhanced by the presence of sulfate, nitrate, potassium, and phosphate 
TOLUENE 189 

5. POTENTIAL FOR HUMAN EXPOSURE 

(Acton and Barker 1992; Armstrong et al. 1991; Hutchins 1991). Sulfate enhances toluene 

biodegradation by acting as an alternate electron acceptor (Acton and Barker 1992). The rate of toluene 

mineralization was estimated to range from 0.032 to 0.055 ppb hour (Armstrong et al. 1991). Rapid 

biodegradation (over 90% loss within 7 days) occurs in shallow groundwater (Wilson et al. 1983) and in 

sludge waste water (Davis et al. 1981). In-situ degradation is the most important sink for toluene in 

contaminated streams. Dilution, volatilization, and biodegradation account for 8, 26, and 66% of toluene 

loss in a small stream in Massachusetts (Kim et al. 1995). Laboratory studies of in-situ toluene 

biodegradation show results comparable to the stream studies and indicate that the streambed surfaces 

(sediments and rocks) are responsible for virtually all biodegradation (Cohen et al. 1995). Reduced, but 

still considerable, rates of toluene microbial degradation were reported in salt water, as compared to fresh 

water (Price et al. 1974). Bacteria are unable to degrade toluene in water when toluene concentration falls 

below a threshold value were the metabolism of the compound is too slow to provide cells with energy at 

a rate needed to maintain metabolism (Roch and Alexander 1997). 

5.3.2.3 Sediment and Soil 

Toluene can be degraded in soil by a number of bacterial species of the genera Pseudomonas and 

Achromobacter (Fewson 1981). The biodegradation process appears to occur in two phases. The first 

phase produces benzoic acid and is, in this respect, parallel to the metabolism of toluene by mammalian 

microsomes. In the second phase, the aromatic ring undergoes metabolic cleavage to produce the Krebs 

cycle intermediates, which are degraded to carbon dioxide or incorporated into bacterial biomolecules 

(Harayama et al. 1989). Addition of large numbers of bacterial cells to toluene-contaminated soils may 

have no benefit if the concentration of toluene is too low for the bacteria to maintain metabolic activity 

(Roch and Alexander 1997). Toluene degradation rates were proportional to the initial substrate 

concentration, and these rates reached a maximum at a concentration of 200 ppm (Davis and Madsen 

1996). In aerobic soils, oxygen acts as the terminal electron acceptor in degradation of the ring cleavage 

products. Under anaerobic conditions, nitrogen or sulfate can act as the terminal electron acceptor (Beller 

et al. 1992a, 1992b; Dolfing et al. 1990; Evans et al. 1991). Under favorable conditions (presence of 

electron acceptors, nutrients, and oxidizable compounds), laboratory studies show that BTEX (benzenetoluene-ethylbenzene-xylene) compounds (which include toluene) are also degraded by bacteria in 

anaerobic (Langenhoff et al. 1996) or oxygen-limited environments (Lovley 1997; Olsen et al. 1995). 

Under sulfate-reducing conditions, less than 10% of the toluene carbon was metabolized to 

benzylsuccinic acid and benzylfumaric acid, whereas >80% was mineralized to carbon dioxide (Beller et 

at. 1992a). The half-life for biodegradation in soil under laboratory conditions may be as short as 1 hour 
TOLUENE 190 

5. POTENTIAL FOR HUMAN EXPOSURE 

(Claus and Walker 1964), whereas half-lives of 1–7 days are typical in the environment (API 1984). 

Based on data from the aerobic degradation of toluene in water, the biodegradation half-life of toluene in 

soils is expected to range from 4 to 22 days (Howard et al. 1991). Soil biodegradation is not impeded by 

adsorption (Robinson et al. 1990). The wood-degrading, white-rot fungus, Phanerochaete chrysoporium, 

mineralizes 50% of 2 ppm aqueous solutions of toluene or benzene, toluene, ethylbenzene, and xylenes 

(BTEX) compounds to carbon dioxide within 5 days. Nonlignindytic conditions are favored (Yadav and 

Reddy 1993). 

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT 

Reliable evaluation of the potential for human exposure to toluene depends in part on the reliability of 

supporting analytical data from environmental samples and biological specimens. In reviewing data on 

toluene levels monitored or estimated in the environment, it should also be noted that the amount of 

chemical identified analytically is not necessarily equivalent to the amount that is bioavailable. 

5.4.1 Air 

The concentration of toluene in air has been measured in a number of studies. Table 5-2 summarizes the 

average concentration as a function of sampling location (EPA 1988b). Background levels of toluene in 

remote areas were found to be quite low (0.05 ppb), but levels of 0.27–7.98 ppb were observed in 

suburban and urban areas. Other studies have reported toluene concentrations of 0.9–70.1 ppb, 

0.06–195 ppb, and 2.2–751.5 ppb in rural (Khalil and Rasmussen 1992), urban (Chan et al. 1991b; EPA 

1991c; Evans et al. 1992; Kelly et al. 1993), and source dominated air samples (Guldberg 1992; Kelly et 

al. 1993). There are multiple sources of this atmospheric toluene, with vehicle emissions being a major 

contributor (Altshuller et al. 1971; EPA 1981; Garcia et al. 1992). The emission rate of toluene from 

motor vehicle traffic in a Los Angeles roadway tunnel was found to be 748 ppm (Fraser et al. 1998). 

Concentrations of toluene in air from the inside of vehicles have been reported to range from 0.56 to 

42.0 ppb (Chan et al. 1991a; Lawryk and Weisel 1996; Weisel et al. 1992). 

High air concentrations of toluene were nearly always found indoors (Lebret et al. 1986; Otson et al. 

1983; Wallace et al. 1986). In several studies, indoor (home or office) toluene concentrations ranged 

from 0.7 to 24.2 ppb due mostly to infiltration from auto emissions (Chan et al. 1991b; Hodgson et al. 

1991; Kelly et al. 1993; Michael et al. 1990b; Shields and Weschler 1992). Toluene was among the 

volatile organic compounds detected in the emissions from sponge rubber carpet cushions (Schaeffer et 
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5. POTENTIAL FOR HUMAN EXPOSURE 

Table 5-2. Median Toluene Levels in Ambient Air 

Number of Daily mean Concentration 

Sampling location samples concentration (ppb) (μg/m3

) 

Remote 225 0.049 0.18 

Rural 248 0.35 1.3 

Suburban 958 0.195 0.731 

Urban 2,519 2.883 10.81 

Source dominated 104 6.314 23.67 

Indoor 101 8.4 31.5 

Workplace 80 0.865 3.24 

Personal 1,650 0.000 0.000 

Adapted from EPA 1988b 
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5. POTENTIAL FOR HUMAN EXPOSURE 

al. 1996). Indoor toluene can also originate from household products (paints, thinners, glues, etc.) and 

smoking. The indoor toluene concentrations in a household with smoking residents were found to be 

greater than those in a nonsmoking household (Montgomery and Kalman 1989). 

Volatilization from contaminated tap water is another source of indoor toluene. Efficiencies of toluene 

volatilization have been estimated for sources such as the kitchen sink (13–26%), residential washing 

machines (8.2–99%), residential dishwashers (96–98%), and household showers (61–77%) (Howard and 

Corsi 1996, 1998; Howard-Reed et al. 1999; Moya et al. 1999). Toluene was found to be emitted at a rate 

of 40,000 ppb during the charbroiling of hamburger meat over a natural gas fired grill (Schauer et al. 

1999a). Higher levels of toluene were detected in indoor air during the spring (4.8 ppb) than in the 

summer (7.70 ppb) (Mukerjee et al. 1997). Indoor and in-vehicle toluene levels appear to be affected by 

seasonal changes (Montgomery and Kalman 1989; Weisel et al. 1992). 

Shields et al. (1996) compared volatile organic compounds measured in three types of commercial 

buildings (telecommunication offices, data centers, and administrative offices) across the United States 

The highest amount of toluene was detected in the data centers with a geometric mean concentration of 

2.68 ppb. Geometric mean concentrations of toluene measured in telecommunications offices, 

administrative offices, and outdoor air were 1.3, 1.5, and 0.7 ppb, respectively. The presence of aromatic 

compounds was found to be independent of occupant density and was attributed to presence of adhesives, 

building materials, floor and wall coverings, architectural coatings, and cleaning products. 

Very high concentrations of toluene (53.2–38,038 ppb) were detected in gas from municipal landfills in 

Finland (Assmuth and Kalevi 1992). Toluene can enter nearby homes by diffusion and pressure-driven 

transport from soil (Hodgson et al. 1988). 

al. 1996). Indoor toluene can also originate from household products (paints, thinners, glues, etc.) and 

smoking. The indoor toluene concentrations in a household with smoking residents were found to be 

greater than those in a nonsmoking household (Montgomery and Kalman 1989). 

Volatilization from contaminated tap water is another source of indoor toluene. Efficiencies of toluene 

volatilization have been estimated for sources such as the kitchen sink (13–26%), residential washing 

machines (8.2–99%), residential dishwashers (96–98%), and household showers (61–77%) (Howard and 

Corsi 1996, 1998; Howard-Reed et al. 1999; Moya et al. 1999). Toluene was found to be emitted at a rate 
TOLUENE 193 

5. POTENTIAL FOR HUMAN EXPOSURE 

of 40,000 ppb during the charbroiling of hamburger meat over a natural gas fired grill (Schauer et al. 

1999a). Higher levels of toluene were detected in indoor air during the spring (4.8 ppb) than in the 

summer (7.70 ppb) (Mukerjee et al. 1997). Indoor and in-vehicle toluene levels appear to be affected by 

seasonal changes (Montgomery and Kalman 1989; Weisel et al. 1992). 

Shields et al. (1996) compared volatile organic compounds measured in three types of commercial 

buildings (telecommunication offices, data centers, and administrative offices) across the United States 

The highest amount of toluene was detected in the data centers with a geometric mean concentration of 

2.68 ppb. Geometric mean concentrations of toluene measured in telecommunications offices, 

administrative offices, and outdoor air were 1.3, 1.5, and 0.7 ppb, respectively. The presence of aromatic 

compounds was found to be independent of occupant density and was attributed to presence of adhesives, 

building materials, floor and wall coverings, architectural coatings, and cleaning products. 

Very high concentrations of toluene (53.2–38,038 ppb) were detected in gas from municipal landfills in 

Finland (Assmuth and Kalevi 1992). Toluene can enter nearby homes by diffusion and pressure-driven 

transport from soil (Hodgson et al. 1988). 

5.4.2 Water 

A number of surveys have been conducted to investigate the occurrence of toluene in water. Although 

there is wide variation from location to location, toluene appears to be a relatively infrequent contaminant 

of drinking water, especially for systems utilizing groundwater sources. For example, in 2 surveys 

performed between 1977 and 1981, toluene was detected in only 2 of 289 and 11 of 929 samples, at 

concentrations ranging from 0.5 to 2.9 ppb (EPA 1981). The frequency of detection of toluene in 

drinking water drawn from surface water sources was somewhat higher (3 of 97 and 20 of 99, 

respectively), although concentration ranges were similar (0.1–1.6 ppb). Toluene was detected in less 

than 20% of the samples of groundwater taken from alluvial aquifers beneath Denver, Colorado, a major 

urban center, at a maximum concentration of 1 ppb (Bruce and McMahon 1996). 

Toluene was found in 60 water samples in 48 private wells in the state of Rhode Island. The total number 

of wells sampled and the number of samples taken was not provided. The concentrations detected ranged 

from 1 to 3,500 ppb (RIDH 1989). Characteristics of the well sites, such as proximity to a waste site, 

were not described. Toluene was detected at concentrations of 6,400 and 6,900 ppb in two groundwater 

sampling wells at a hazardous waste site (Armstrong et al. 1991). 
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5. POTENTIAL FOR HUMAN EXPOSURE 

5.4.3 Sediment and Soil 

No studies were located regarding levels of toluene in typical urban, suburban, or rural soils. Toluene has 

been occasionally detected in sediments of surface waters at concentrations averaging 5 ppb (Staples et al. 

1985). Toluene was detected in the sediment of lower Passaic River, New Jersey, in the vicinity of 

combined sewer overflow outfalls (Iannuzzi et al. 1997). The concentrations ranged from 4.0 to 250 ppb. 

In the absence of continuous releases from a waste site, it is expected that toluene would not persist for 

long periods in soil, due to its volatility, susceptibility to biodegradation, and water solubility. 

5.4.4 Other Environmental Media 

Toluene was detected at average levels of 20 ppb in 23% of 150 samples of aquatic biota recorded in the 

STORET data base (Staples et al. 1985). The concentration of toluene in commercial foodstuffs has not 

been thoroughly studied. Although the data are limited, the levels of toluene in food are not likely to be 

significant (EPA 1981). Toluene was detected in eggs stored in polystyrene containers that contained 

toluene (Matiella and Hsieh 1991). Cigarette smoke is a significant source of toluene, estimated to be 

about 80 μg/cigarette (Grob 1965). Toluene was detected in a variety of household items including 

automotive products, household cleaners/polishes, paint-related products, fabric and leather treatments, 

lubricants and adhesives (Sack et al. 1992). The levels of toluene in these products varied from 1.8 to 

23.3% by weight. 

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE 

Available data indicate that for the general population, inhalation of toluene is likely to be the main route 

of exposure. Assuming an average concentration in indoor and outdoor air of 2.12 ppb (EPA 1988b), and 

assuming inhalation of 20 m3

/day and 50% absorption of inhaled toluene (EPA 1981), the typical dose by 

this route would be about 300 μg/day. Exposure could be higher near heavily traveled roadways or point 

sources of toluene, and could also be increased by frequent use of home products containing toluene. For 

example, in an industry-sponsored study, personal inhalation exposures to toluene during the application 

of nail lacquers in residences ranged from approximately 1,030 to 2,820 μg/person/day (Curry et al. 

1994). The mean toluene levels measured in air during the nail laquer application ranged from 0.85 to 

2.45 ppm, while the post-application concentrations ranged from 0.05 to 0.27 ppm. No toluene was 

detected in air prior to the nail laquer application. 
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5. POTENTIAL FOR HUMAN EXPOSURE 

Blood concentrations of toluene have been measured in 604 non-occupationally exposed people in the 

United States who participated in the Third National Health and Nutrition Examination Survey 

(NHANES III). Participants were selected on the basis of age, race, gender, and region of residence. 

Toluene was detected in 75% or more of the blood samples and was present at a mean concentration of 

0.52 ppb, a median concentration of 0.28 ppb, a 5th percentile concentration of 0.11 ppb, and a 95th 

percentile concentration of 1.5 ppb (Ashley et al. 1994). Buckley et al. (1997) compared the amount of 

toluene detected in the blood samples of residents of the Lower Rio Grande Valley to that detected in the 

NHANES III study. Toluene was found in 81% of the blood samples. The amount of toluene was found 

to be lower than that observed in NHANES III, the median concentration being 0.17 ppb. 

Cigarette smoking may also significantly increase exposure. Assuming inhalation of about 80–100 μg of 

toluene per cigarette and 50% absorption (EPA 1981; Grob 1965), smoking one pack per day would 

contribute an absorbed dose of about 1,000 μg/day. 

Toluene is a volatile component of wood smoke. Emission rates of toluene during wood combustion in 

home heating units have been reported in the range of 0.15–1 g/kg of wood (Larson and Koenig 1994). 

Based on average values of toluene in water, exposure by ingestion of contaminated drinking water is 

likely to be relatively small compared to inhalation. The concentration of toluene in drinking water 

drawn from surface water sources is 0.15–0.25 ppb (EPA 1981), and daily intake by this route (based on 

ingestion of 2 L/day) would be approximately 0.3–0.5 μg/day. In a survey of bottled drinking water sold 

in Canada, only 20 (or 11%) of 182 samples analyzed contained measurable amounts of toluene, with an 

average concentration of 6.92 ppb and a range of 0.5–63 ppb (Page et al. 1993). Toluene is also known to 

volatilize from various household sources of water such as the kitchen sink, dishwashers, washing 

machines, and showers water into air; thus, its presence in tap water may ultimately result in inhalation 

exposure (Howard and Corsi 1996, 1998; Howard-Reed et al. 1999; Moya et al. 1999). 

Exposure to gasoline (which contains toluene) has been estimated for a household using gasolinecontaminated water (Beavers et al. 1996). In this house, $694 ppb of toluene was found in the water, 

664 ppb in shower air, and 14.9 ppb in non-shower air. Dermal absorption during shower-related 

activities accounted for 30% of the total dose. Inhalation during shower-related activities represented 

25%. Ingestion represented 30%, and non-shower household inhalation 16%. The authors note that 

personal habits limit the general applicability of these results (Beavers et al. 1996). 
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5. POTENTIAL FOR HUMAN EXPOSURE 

Data are not available to estimate intake of toluene from ingestion of food, but these routes are likely to 

be minor (EPA 1981). A number of studies have indicated significant accumulations of toluene in 

products for human consumption. For example, escaping gasoline vapors from internal combustion 

engines used or stored near olives during the growing, harvesting, storage, and processing steps in the 

production of virgin olive oil can cause significant contamination of the product with toluene and other 

hydrocarbons (Biedermann et al. 1996). Significant concentrations of toluene have also been measured in 

8 of 10 species of fruit tested in a European study, which showed higher concentrations of toluene in the 

peel than in the pulp of the fruit (Górna-Binkul et al. 1996). Dermal absorption of toluene is not a 

significant route of exposure. Uptake of toluene via skin has been estimated to contribute 1–2% of the 

body burden received following whole body (including inhalation) exposure (Brooke et al. 1998). 

Although toluene has been found to be a common contaminant at hazardous waste sites, it is not possible 

to estimate human exposure levels that might occur near waste sites without detailed site-specific 

information on concentration values in air, water, and soil, and on human intake of these media. 

Pathways that might be of significance include inhalation of toluene vapors, ingestion of toluenecontaminated water (surface water and/or groundwater), volatilization and inhalation from contaminated 

water, and dermal contact with toluene-contaminated soil. 

Based on average (0.19–0.7 ppm) and maximum (0.26–2.4 ppm) concentrations of toluene in air at 

service stations, inhalation exposures of self-serve customers, gas station attendants, and downwind 

residents were estimated to be 0.057 to 0.49, 38, and 0.062 to 0. 29 ppb/day, respectively (Guldberg 

1992). An Alaskan study compared the concentration of toluene in blood before and after pumping of 

regular and oxygenated gasoline in February (Backer et al. 1997). The median concentration of toluene 

in blood before pumping gasoline was found to be 0.38 ppb. A greater increase was detected in the blood 

concentration of toluene after pumping oxygenated gasoline (0.85 ppb) than after pumping regular 

gasoline (0.74 ppb). Other transportation-related toluene exposure pathways include: inhalation of 

volatile organic compounds from contaminated air in aircraft cabins (2–135 ppb for toluene) (Dechow et 

al. 1997), and breathing air in long road tunnels (97–167.6 ppb) (Barrefors 1996). 

Toluene exposure may also occur in the work place, especially in the printing industry where toluene is 

used as a solvent for inks and dyes. Occupational exposure may also occur during paint stripping 

operations (Vincent et al. 1994). Concentrations of 5–50 ppm are common in the workplace with some 

values as high as 250 ppm (1,000 mg/m3

) (NCI 1985). Assuming that a worker inhales 10 m3 of air while 

on the job, and that 50% of the inhaled toluene is absorbed, a workplace concentration of 53.2 ppm would 
TOLUENE 197 

5. POTENTIAL FOR HUMAN EXPOSURE 

correspond to an exposure level of 1,000 mg/day. The toluene burden of rotogravure workers measured 

with personal monitoring tubes was found to be higher (ranging from 14.9 to 120 ppm, 

median=60.9 ppm) than the air concentration in the workplace (ranging from 37.5 to 87.2 ppm, 

median=62.8 ppm) (Hammer et al. 1998). In another study, the blood of rotogravure workers was tested 

before and after the use of toluene to clean containers for the primary printing colors (Muttray et al. 

1999). The concentration of toluene in their blood was found to increase from 0.87 to 4.9 ppm. In 

addition, dermal exposure might also occur from contact with toluene-containing materials, contributing 

perhaps 20 mg/use (EPA 1981). Personnel working with various types of fuel may be at a risk of toluene 

exposure. A Finnish study determined the exposure of gasoline tanker drivers to toluene during loading 

and delivery to be 0.4–2.9 ppm (Hakkola and Saarinen 1996; Saarinen et al. 1998). The exposure level of 

aircraft maintenance personnel to toluene in raw JP-8 jet fuel vapor was found to be 6.3±1.6 ppm (Smith 

et al. 1997). 

Art materials, especially painting supplies, represent another potential source for exposure to toluene for 

people of all ages and to people who spend time near an artist's work area or studio, which for about 50% 

of professional artists is in the home (McCann 1992). Case reports on acute toluene poisoning of workers 

installing a parquet floor in Singapore (Tan and Seow 1997) and on excessive exposure to toluene in a 

wood furniture manufacturing facility in the U.S. (Paulson and Kilens 1996) have also been reported. A 

group of Dutch carpet-layers using water-based adhesives were exposed to an 8-hour average 

concentration of toluene in the range of 0.27–76.87 ppm, while carpet-layers using contact adhesives 

were exposed to an 8-hour average concentration of 4.25–161.2 ppm (Muijser et al. 1996). Measurement 

data for fire-fighters occupationally exposed to combustion products in three separate building fires 

indicated they were exposed to an average concentration of 0.23 ppm toluene during the time they were 

fighting the fires (McDiarmid et al. 1991). 

Workplace exposure to toluene and other volatiles is associated with the plastics industry (Socie et al. 

1997), emissions from waste waters in municipal sewage treatment plants (Bianchi and Varney 1997), 

with sculptured nail manicure salons (Hiipakka and Samimi 1987), and with hair salons (Hollund and 

Moen 1998). Combinations of solvents can enhance the dermal penetration of toluene. Methanol 

enhances the skin absorption of toluene. Special precautions need to be taken against the skin absorption 

of toluene when handling paint thinners that contain methanol (Tsuruta 1996). 
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5. POTENTIAL FOR HUMAN EXPOSURE 

5.6 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 Section 2.7 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, and 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, they put things in their 

mouths, sometimes eat inappropriate things (such as dirt or paint chips), and they spend more time 

outdoors. Children also are closer to the ground, and they do not have the judgment of adults to avoid 

hazards (NRC 1993). 

Exposures of the embryo or fetus to volatile organic compounds such as toluene may occur if the 

expectant mother is exposed to high levels that overwhelm maternal protective mechanisms including 

metabolic detoxification and disposition of toluene and possible preferential distribution of toluene to 

maternal adipose tissues (see Sections 2.3 and 2.5). A newborn infant may be exposed by breathing 

contaminated air and through ingestion of mother’s milk that can contain small amounts of toluene. 

Children may be exposed through accidental ingestion of products containing toluene. Older children and 

adolescents may be exposed to toluene in their jobs or hobbies, or through deliberate solvent abuse by 

“sniffing.” Human epidemiological studies and case reports discussing reproductive and/or 

developmental toxicity of toluene in humans have been reviewed. Exposure routes included occupational 

duties and sniffing of paints, paint reducers, and paint thinners (Donald et al. 1991b). Inhalant abuse 

during pregnancy poses significant risks to the pregnancy and endangers both the mother and the fetus. 

Solvent abuse of toluene for euphoric effects results in exposure levels that equal of exceed those 

producing adverse effects in animals. 

Transfer of toluene to nursing infants from breast milk of currently exposed mothers is expected to be a 

possibility because of the lipophilicity of toluene and the relatively high lipid content of breast milk. 

Mobilization during pregnancy or lactation of stored toluene from pre-conception exposure, however, 

does not appear to be a major concern because most toluene is rapidly eliminated from the body (see 

Sections 2.3.4 and 2.7). There is also a risk for an adverse effect on the lactation process itself and the 
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5. POTENTIAL FOR HUMAN EXPOSURE 

nutritional content of the milk. Women should be counseled about the effects of workplace exposure 

while breast-feeding (Byczkowski et al. 1994). A physiologically based pharmacokinetic model (PBPK) 

has been developed to estimate the amount of chemical that an infant ingests for a given nursing schedule 

and daily maternal occupational exposure to 50 ppm toluene for 8 hours (Fisher et al. 1997). This PBPK 

model predicted an ingestion rate of 0.460 mg/day for such an infant. 

Young children often play close to the ground and frequently play in dirt, which increases their dermal 

exposure to toxicants in dust and soil. They also tend to ingest soil, either intentionally through pica or 

unintentionally through hand-to-mouth activity. Children may be orally and dermally exposed to toluene 

present as a contaminant in soil and dust, but toluene is not expected to persist for long periods in soil (in 

the absence of continuous release) due to its volatility, susceptibility to bacterial degradation, and water 

solubility. It has been demonstrated that the toluene adsorbed on soil is absorbed by the body (Turkall et 

al. 1991). Toluene in both aqueous solution and vapor phase has also been shown to be absorbed through 

the human skin, albeit slowly (Brooke et al. 1998; Dutkiewicz and Tyras 1968; Tsuruta 1989). Toluene 

has a log organic carbon-water partition coefficient of 2.25, indicating moderate adsorption to soil, 

especially to soil with high organic matter (Wilson et al. 1981). Most of the toluene present in the upper 

layers of the soil is volatilized to air within 24 hours (vapor pressure=28.4 mmHg at 25 EC) (Balfour et al. 

1984; Thibodeaux and Hwang 1982). The degradation half-life of toluene is 1–7 days in soil (API 1984). 

Loss of toluene from the soil decreases the potential of dermal and oral exposure to children, but its rapid 

volatilization results in inhalation being the most likely route of exposure. 

Children breathe in more air per kilogram of body weight than an adult. Therefore, a child in the same 

micro-environment as an adult may be exposed to more toluene from ambient air. Young children are 

closer to the ground or floor because of their height. The toluene vapors being heavier than air (vapor 

density=3.14 g/mL) tend to concentrate near the ground. The children, therefore, may be at greater risk of 

exposure than adults during accidental spills of toluene. 

Children may also be exposed to fumes of toluene and other hydrocarbons by working with or playing 

near sources of gasoline. Children’s exposure also occurs through accidental ingestion and inspiration of 

the chemicals into the lungs. Asthma, pneumonia, pulmonary damage, and death can result. Most 

accident victims are one- and two-year olds and are about evenly divided between males and females. 

Most incidents occur in the children’s homes and the products are in their normal storage areas. Childresistant packaging is recommended (Journal of Environmental Health 1997). Children are also exposed 

to higher concentrations of toluene in central urban areas with high traffic density, where children's blood 
TOLUENE 200 

5. POTENTIAL FOR HUMAN EXPOSURE 

toluene concentrations are, on average, 56% higher than those of children living in rural areas (Jermann et 

al. 1989; Raaschou-Nielson et al. 1997). 

Children are also exposed through hobbies and art activities involving glues, adhesives, and paints 

(McCann 1992). Abuse of toluene-containing products among young people by inhalation (“sniffing”) is 

a social and clinical concern (Young 1987). 

5.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES 

In addition to individuals who are occupationally exposed to toluene (see Section 5.5), there are several 

groups within the general population that have potentially high exposures (higher than background levels) 

to toluene. These populations include individuals living in proximity to sites where toluene was produced 

or sites where toluene was disposed, and individuals living near one of the 959 NPL hazardous waste sites 

where toluene has been detected in some environmental media (HazDat 2000). 

The population most likely to experience high levels of exposure to toluene are workers in the printing 

industry or other industries employing toluene as a solvent. In addition, workers exposed to gasoline 

vapors are also likely to have higher than average exposure to toluene. Individuals may also be exposed 

to high levels at home in association with the use of toluene-containing consumer products. Smokers 

have a considerably higher exposure to toluene than nonsmokers. 

Toluene has been frequently identified as a water contaminant in the proximity of hazardous waste sites. 

Drinking water sources for populations living near a hazardous waste site containing toluene should be 

evaluated for toluene. If groundwater wells are contaminated, exposure to toluene can occur when the 

well-water is used for showering, cleaning, cooking, and drinking purposes. Exposure can also occur 

through contact with contaminated soil. 

A troublesome route of exposure to toluene is through deliberate inhalation of fumes from paint thinners, 

gasoline, glues contact adhesives, and aromatic solvents. Inhalant abuse can affect pregnancy outcome 

(Jones and Balster 1998). Inhalant abuse is an urgent health care problem among youth, including 

American Indians (Young 1987). Contact adhesives often contain toluene, heptane, and methyl ethyl 

ketone. Although toluene is more toxic than the other ingredients, it evaporates more slowly. Thus the 

vapors inhaled when “sniffing” such adhesives will contain less toluene and should be less toxic than 

would be expected from its liquid composition (Midford et al. 1993). 
 

 

TOLUENE 201 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.8 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 toluene 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 toluene. 

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. 

5.8.1 Identification of Data Needs 

Physical and Chemical Properties. The physical and chemical properties of toluene that are 

needed to evaluate its behavior in the environment are available (Table 3-2). It does not appear that 

further research in this area is essential. 

Production, Import/Export, Use, Release, and Disposal. As of October 1, 1996, the 

International Trade Commission ceased to collect or publish annual synthetic organic chemicals data. 

The National Petroleum Refiners Association, which currently collects such data, does not include 

toluene on its list of organic chemicals. The available production data of toluene are out of date. It is 

essential that these data be updated regularly to allow a more accurate determination of the potential for 

human exposure. 

According to the Emergency Planning and Community Right-to-Know Act of 1986, 42 U.S.C. 

Section 11023, industries are required to submit chemical release and off-site transfer information to the 

EPA. This database, Toxic chemical Release Inventory (TRI), will be updated yearly and should provide 

a list of industrial production facilities and emissions. Available information appears to be adequate for 

assessing industrial production and the potential for release of toluene at this time. Additional 

information concerning home-use products containing toluene and their disposal are needed. Household 
 

 

TOLUENE 202 

5. POTENTIAL FOR HUMAN EXPOSURE 

hazardous waste disposal programs are in their infancy and there are few data on the amounts of waste 

processed through these programs. 

According to the Emergency Planning and Community Right-to-Know Act of 1986, 42 U.S.C. 

Section 11023, industries are required to submit chemical release and off-site transfer information to the 

EPA. The Toxics Release Inventory (TRI), which contains this information for 1996, became available in 

May of 1998. This database will be updated yearly and should provide a list of industrial production 

facilities and emissions. 

Environmental Fate. Existing information indicates that volatilization, followed by reaction with 

hydroxyl radicals in air, is the principal fate process for toluene in the environment (Davis et al. 1979; 

Hoshino et al. 1978; Howard et al. 1991; Kenley et al. 1973). The rate constants for this process have 

been established, although further refinements would improve the ability to model the fate of toluene 

emissions. Although toluene is not a common contaminant in water, it has been found to occur in both 

groundwater and surface water near waste sites (HazDat 2000). Additional studies on the rate of 

volatilization, degradation, and transport of toluene in groundwater, surface water, and soils would be 

useful for assessing potential human exposure near hazardous waste sites. 

Considerable data are available concerning the genetics of toluene-degrading microorganisms (Fewson 

1981; Harayama et al. 1989), but distinctions need to be made between the activities of microorganisms 

found naturally in the soil and water, and those that are genetically engineered for use in bioremediation 

projects. Quantitative characterization of the end products of biodegradation and information concerning 

this fate would also be helpful. 

Bioavailability from Environmental Media. On the basis of the available data, toluene appears to 

be highly bioavailable when it is released to the environment. Inhalation, oral, and dermal absorption 

occur due to toluene solubility in the lipid matrix of the cell membrane (Alcorn et al. 1991). Absorption 

is rapid and virtually complete at low exposure concentrations when exposures are oral or respiratory 

(Alcorn et al. 1991; Carlsson and Ljungqvist 1982; Hjelm et al. 1988). Adsorption also occurs through 

contact with the skin (Dutkiewicz and Tyras 1968). Additional research on bioavailability of toluene 

from the environment does not appear to be needed. 
 

 

 

TOLUENE 203 

5. POTENTIAL FOR HUMAN EXPOSURE 

Food Chain Bioaccumulation. Very little information was identified pertaining to the 

bioaccumulation of toluene in the food chain. Despite its lipid solubility, the bioconcentration factor for 

toluene is expected to be relatively low due to its rapid metabolism to more polar molecules with a lower 

affinity for lipids, and it has little tendency to bind to biomolecules. Additional research efforts 

pertaining to bioaccumulation of toluene would be justified for cold water fish with relatively high fat 

content and for plants used as a source of vegetable oils. It would be helpful to know if toluene becomes 

incorporated in the lipid deposits of these organisms. Although there has been little data collected 

concerning the tendency for toluene to biomagnify in the environment, available data on bioconcentration 

suggest that research on this topic is not needed. 

Exposure Levels in Environmental Media. The concentration of toluene in ambient air and in 

drinking water has been the subject of numerous studies (Bruce and McMahon 1996; EPA 1981, 1988b, 

1991c; HazDat 2000; Kelly et al. 1993; Lebret et al. 1986; Michael et al. 1990b; Montgomery and 

Kalman 1989; Otson et al. 1983; RIDH 1989), but there is a need to maintain the currency of the data. 

Further studies on toluene levels in food and soil would be useful, since quantitative data for these media 

are limited. The potential exists for toluene to be present in human and bovine milk due to its lipid 

solubility, but studies of exposure through these media were not identified. In view of the observation 

that the highest levels of toluene likely to be encountered by an average citizen occur in the home, studies 

that identify the sources of toluene in indoor air would be valuable in reducing or eliminating this 

pathway of exposure. 

Reliable monitoring data for the levels of toluene in contaminated media at hazardous waste sites are 

needed. The information thus obtained on levels of toluene in the environment can be used in 

combination with the known body burdens of toluene to assess the potential risk of adverse health effects 

in populations living in the vicinity of hazardous waste sites. 

Exposure Levels in Humans. Data from the Total Exposure Assessment Methodology study (EPA 

1987c) provide information on the concentration of toluene in the expired air of humans in relation to 

levels in the air breathed by the individual. Exposure of the general population to toluene in air has been 

monitored for a variety of scenarios (Backer et al. 1997; Beavers et al. 1996; Biedermann et al. 1996; 

Curry et al. 1994; EPA 1981; Grob 1965; Guldeberg 1992; Larson and Koenig 1994; Page et al. 1993). 

Amounts of toluene volatilizing from the household sources such as the kitchen sink, dishwashers, 

washing machines, and showers have also been estimated (Howard and Corsi 1996, 1998; Howard-Reed 

et al. 1999; Moya 1999). Combination of this data with appropriate toxicokinetic models of toluene 
 

 

TOLUENE 204 

5. POTENTIAL FOR HUMAN EXPOSURE 

absorption, distribution, and excretion in humans would allow for improved estimates of exposure levels 

in humans. Toluene exposure in the workplace is well documented (Hammer et al. 1998; Hiipakka and 

Samimi 1987; McCann 1992; McDiarmid et al. 1991; Muijser et al. 1996; Muttray et al. 1999; NCI 1985; 

Paulson and Kilens 1996; Smith et al. 1997; Tan and Seow 1997; Vincent et al. 1994). Continued 

monitoring will help to minimize exposure of workers. A study of toluene in human milk of 

occupationally exposed women may be useful in evaluating the risks to this population of mothers and 

infants. This information would be useful to assess the desirability of conducting health studies on 

exposed populations. 

Exposures of Children. A study on the usefulness of intervention methods in cases of inhalant 

abuse by pregnant women may help to develop better means of preventing high-level exposure to toluene 

and other solvents. More research is needed to rule out concomitant risk factors and to identify specific 

chemicals and patterns of use associated with adverse effects. 

Children may be at a greater risk of inhalation exposure to toluene as they breathe in more air per 

kilogram of body weight than an adult. They also spend more time closer to ground because of their 

height. Toluene vapors, being heavier than air, tend to concentrate closer to the ground, thereby 

increasing the risk of exposure for children. No data are available on the exposure of the children to 

toluene present in the air. 

Means of protecting young children from ingestion of home products containing toluene need study and 

action. Child-proof containers and clearer warnings to parents should be considered to avoid unwanted 

exposure. 

Child health data needs relating to susceptibility are discussed in Section 2.12.2, Identification of Data 

Needs: Children’s Susceptibility. 

Exposure Registries. No exposure registries for toluene were located. This substance is not 

currently one of the compounds for which a subregistry has been established in the National Exposure 

Registry. The substance will be considered in the future when chemical selection is made for 

subregistries 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. 
 

TOLUENE 205 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.8.2 Ongoing Studies 

As part of the Third National Health and Nutrition Evaluation Survey (NHANES III), the Environmental 

Health Laboratory Sciences Division of the National Center for Environmental Health, Centers for 

Disease Control and Prevention, will be analyzing human blood samples for toluene and other volatile 

organic compounds. These data will give an indication of the frequency of occurrence and background 

levels of these compounds in the general population. 

A number of ongoing research efforts will provide data regarding the potential for human exposure to 

toluene. These projects are summarized in Table 5-3. The EPA is also sponsoring the National Human 

Adipose Tissue Survey (NHATS), and this will provide additional data on the range of concentrations of 

toluene found in human fat samples taken during surgery or autopsy. 
TOLUENE 206 

5. POTENTIAL FOR HUMAN EXPOSURE 

Table 5-3. Ongoing Studies on the Potential for Human Exposure to Toluene 

Investigator Affiliation Research description Sponsor 

Christiani, D.C. Harvard School of 

Public Health 

Effects on reproductive outcome of 

occupational exposure to aromatic 

solvents in the oil industry 

NIOSH 

Alexander, M. Cornell University Effects of aging of pollutants for soil 

on bioavailability 

NIEHS 

Rappaport, S.M. University of North 

Carolina, Chapel Hill 

Development and application of 

biomarkers of exposure 

NIEHS 

Abroila, L.M. Michigan State 

University 

Persistence of NAPL contaminants 

in natural subsurface systems 

NIEHS 

Balster, R.L. Texas Tech University Behavioral pharmacology of 

abused solvents 

NIDA 

Spormann, A.M. Stanford University Enzymatic studies on the initial 

steps of anaerobic toluene and 

xylene metabolism 

NSF 

NIDA = National Institute of Drug Abuse; NIEHS = National Institutes of Health Science; NIOSH = National Institute 

for Occupational Safety and Health; NSF = Nation Science Foundation 
TOLUENE 207 

6. ANALYTICAL METHODS 

The purpose of this chapter is to describe the analytical methods that are available for detecting, 

measuring, and/or monitoring toluene, its metabolites, and other biomarkers of exposure and effect to 

toluene. 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. 

6.1 BIOLOGICAL SAMPLES 

Toluene can be determined in biological fluids and tissues and breath using a variety of analytical 

methods. Representative methods are summarized in Table 6-1. Most analytical methods for biological 

fluids use headspace gas chromatographic (GC) techniques. Breath samples are usually collected on 

adsorbent traps or in sampling bags or canisters, and then analyzed by GC. 

Because of its volatility, toluene is lost from biological samples, such as plant and animal tissue and body 

fluids, relatively easily. Therefore, samples must be collected and stored with care (e.g., at low 

temperatures in sealed containers) to prevent analyte loss. Blood samples are best stored at 4 EC or 

below, in full containers made from glass, Teflon, or aluminum components (Gill et al. 1988; Saker et al. 

1991). Storage time must be limited to minimize losses. Contamination can occur during sampling or 

analysis since toluene is widely used as a solvent. Care must be taken to monitor for contamination. 

Headspace techniques are usually used to separate toluene from biological fluids such as blood and urine. 

The headspace method involves equilibrium of volatile analytes such as toluene between a liquid and 

solid sample phase and the gaseous phase. The gaseous phase is then analyzed by GC. There are two 

main types of headspace methodology: static (equilibrium) headspace and dynamic headspace which is 

usually called the "purge and trap" method (Seto 1994). The static headspace technique is relatively 

simple, but may be less sensitive than the purge-and-trap method. The purge-and-trap method, while 

providing increased sensitivity, requires more complex instrumentation and may result in artifact 
Table 6-1. Analytical Methods for Determining Toluene in Biological Materials 

Analytical Sample Percent 

Sample matrix Preparation method method detection limit recovery Ref

Blood Lyse; extraction with carbon disulfide GC/FID No data No data Ben

Blood Purge and trap No data 7.5 μg/L No data Coc

Whole blood Purge and trap GC/MS 0.088 μg/L 91–147 AshBlood Purge and trap cap. GC/FID 50 ng/L 50 Fus

Blood Headspace extraction cap. GC/ITD 0.04 μmol/L No data Sch

Mother’s milk Purge and trap cap. GC/FID No data 63 (chloro- Mic

benzene) Pell

Urine Purge and trap cap. GC/FID 50 ng/L 59 FusUrine Heated headspace extraction cap. GC/FID 1 ng/mL 42.3 Lee Biofluids Headspace extraction GC/FID No data No data SuitAdipose tissue Evaporation at 150 EC into GC/FID No data 88–112 Car

nitrogen, direct gas injection Ljun

Brain tissue Extraction with carbon disulfide; GC/FID No data No data Ben

homogenization; centrifugation 

Breath Collection in modified Haldane- cap. GC/MS 1 nmole No data Dyn

Priestly tube; transfer to adsorptiontube; thermal desorption

Breath Collection via spirometer into cap. GC/MS low μg/m3 80–136 Tho

passivated canisters

Breath Collection via spirometer into 1.8 L cap. GC/MS ~2 μg/m3 91–104 Tho

passivated canisters

Breath Collection via spirometer onto cap. GC/MS- 3 μg/m3 No data Ried

charcoal traps; microwave desorption SIM

cap. = capillary; FID = flame ionization detector; GC = gas chromatography; ITD = ion trap detection; MS = mass spectrometry; SIM = s
TOLUENE 209 

6. ANALYTICAL METHODS 

formation (Seto 1994). Packed columns and capillary columns are used for chromatographic separation, 

followed by identification and quantitation using various detectors; flame ionization detection (FID), 

photoionization detection (PID), and mass spectrometry (MS) are used most often. Other sample 

preparation methods have been used, but less frequently. Solvent extraction permits concentration, 

thereby increasing sensitivity, but the extraction solvent can interfere with analysis. Direct aqueous 

injection is a very rapid method, but sensitivity is low and matrix effects can be a serious problem. 

A sensitive and reliable method for identification and quantitation of toluene in samples of whole blood 

taken from humans following exposure to volatile organic compounds (VOCs) has been developed by 

Ashley and coworkers at the Centers for Disease Control and Prevention (Ashley et al. 1992, 1996). The 

method involves purge-and-trap of a 10 mL blood sample with analysis by capillary GC/MS. Anti-foam 

procedures were used, as well as special efforts to remove background levels of VOCs from reagents and 

equipment (Ashley et al. 1992). The method is sensitive enough (ppt levels) to determine background 

levels of VOCs in the population and provides adequate accuracy (91–147% recovery) and precision 

(12% RSD) for monitoring toluene in the population. Most modern purge and trap methods provide 

detection limits in the ppt range for toluene in both blood and urine (Ashley et al. 1992; Fustinoni et al. 

1996). 

Few methods are available for the determination of methylbenzene in other body fluids and tissues. 

Toluene may be extracted from biological materials using solvents such as carbon disulfide (Benignus et 

al. 1981); homogenization of tissue with the extractant and lysing of cells improves extraction efficiency. 

Care must be taken to avoid loss of low-boiling compounds. Highly purified solvents may be used to 

minimize problems with solvent impurities. A modified dynamic headspace method for urine, mother’s 

milk, and adipose tissue has been reported (Michael et al. 1980). Volatiles swept from the sample are 

analyzed by capillary GC/FID. Acceptable recovery was reported for model compounds, but detection 

limits were not reported (Michael et al. 1980). Supercritical fluid extraction using pure carbon dioxide or 

carbon dioxide with additives has good potential for the extraction of organic analytes such as toluene 

from biological samples. 

Sensitive, reliable methods are available for measuring toluene in breath. Exhaled breath is collected in 

modified Haldane-Priestly tubes (Dyne et al. 1997), into passivated canisters (Thomas et al. 1992), or 

directly onto adsorbent traps (Riedel et al. 1996). The detection limits are in the low μg/m3

 range (Riedel 

et al. 1996; Thomas et al. 1991, 1992); accuracy, where reported, is good ($80%) (Riedel et al. 1996; 

Thomas et al. 1991, 1992). 
TOLUENE 210 

6. ANALYTICAL METHODS 

Representative methods for determination of biomarkers of exposure to toluene are shown in Table 6-2. 

Measurement of toluene in blood (Kawai et al. 1993), urine (Kawai et al. 1996) and exhaled air (Lapare et 

al. 1993) provide reliable markers of exposure to toluene. Measurement of toluene metabolites is also 

utilized for monitoring toluene exposure in humans. Hippuric acid is formed in the body by the 

metabolism of toluene, and it is the glycine conjugate of benzoic acid. High performance liquid 

chromatography (HPLC) with ultraviolet (UV) detection is usually used for determination of hippuric 

acid in urine (Kawai et al. 1993; NIOSH 1984a). Other metabolites such as o-cresol (Kawai et al. 1996), 

benzylmercapturic acid (BMA) (Maestri et al. 1997), or S-p-toluylmercapturic acid (Angerer 1998a, 

1998b) may also be measured. o-Cresol is a sensitive marker, but may arise from compounds other than 

toluene; the usefulness of BMA may be limited by variability among individuals. 

6.2 ENVIRONMENTAL SAMPLES 

Methods are available for determining toluene in a variety of environmental matrices. A summary of 

representative methods is shown in Table 6-3. Validated methods, approved by agencies and 

organizations such as EPA, ASTM, APHA, and NIOSH, are available for air, water, and solid waste 

matrices. GC is the most widely used analytical technique for quantifying concentrations of toluene in 

environmental matrices. Various detection devices used for GC include FID, MS, and photoionization 

detection (PID). Because of the complexity of the sample matrix and the usually low concentrations of 

VOCs in environmental media, sample preconcentration is generally required prior to GC analysis. Air 

samples may be collected and concentrated on adsorbent or in canisters for subsequent analysis. Methods 

suitable for determining trace amounts of methylbenzene in aqueous and other environmental media 

include three basic approaches to the pretreatment of the sample: gas purge-and-trap technique, headspace 

gas analysis, and extraction with organic solvent. Purge-and-trap is the most widely used method for the 

isolation and concentration of VOCs in environmental samples (Lesage et al. 1993). The purge and trap 

technique offers advantages over other techniques in that it allows facile isolation and concentration of 

target compounds, thereby improving overall limits of detection and recovery of sample. 

Sampling techniques for air include collection in sample loops, on adsorbent, in canisters, and by 

cryogenic trapping. The analysis is normally performed by GC/FID, GC/PID, or GC/MS. Detection 

limits depend on the amount of air sampled, but values in the ppt range have been reported (Dewulf and 

Van Langenhover 1997). 
Table 6-2. Analytical Methods for Determining Biomarkers of Toluene in Biological S

Sample matrix Preparation method Analytical method 

Sample detection limit 

Percent recovery Refe

Blood (Toluene) 

Headspace GC No data No data Kawa

Urine (Toluene) 

Headspace GC/FID 2 μg/L No data Kawa

Urine (HA) Extraction with ethyl acetate; 

evaporation; redissolve in water 

HPLC/UV 30 mg/L No data NIOS

Urine Extraction with MTBE, elution with 

phosphate buffer/methanol/ formaldehyde 

HPLC 0.1 mmol 101 Tard

Urine (o-Cresol) 

Hydrolysis; solvent extraction HPLC/UV 0.5 mg/L 95a Kawa

Urine (BMA) Adsorbent column cleanup; 

derivatization 

HPLC/Fl 0.5 μg/L No data Maes

Breath Collection in Tedlar bags GC/FID No data No data Lapa

aExtraction efficiency BMA = benzylmercapturic acid; FID = flame ionization detector; Fl = fluorescence detector; GC = gas chromatography; HA = hippuric aciperformance liquid chromatography; MTBE = methyl tertiary butyl ether; UV = ultraviolet detection 
Table 6-3. Analytical Methods for Determining Toluene in Environmental Samp

Sample matrix Preparation method 

Analytical method 

Sample detection limit 

Percent recovery Refe

Workplace air Sorption on activated carbon; extraction 

with carbon disulfide 

GC/FID 0.01 mg ±11.4a NIOS

Meth

Air Sorption onto Tenax®; solvent extraction; 

thermal desorption 

GC/MS <0.88 ppb 111–163 Crist 

Air Sorption onto Tenax®; thermal 

desorption 

GC/MS No data 93–94 EPA 

MethKrost 

Air Collection in passivated canisters GC/MS low ppb No data EPA 

Meth

Air Collection on multisorbent tubes; 

thermal desorption 

GC/MS No data No data EPA 

Meth

Air Collection in sorbent sampler tubes GC/FID 0.01 

mg/sample 

94 USE

NIOS

Air Sorption on activated charcoal; 

extraction with carbon disulfide 

GC/FID 0.01 

mg/sample 

No data USE

NIOS

Stack gas effluents 

Sorption onto Tenax®; thermal 

desorption 

GC/MS No data 50–150 USE

OSW 

Vehicle exhaust Direct GC/FID 0.5 ppb No data Dear

Drinking water Purge and trap cap. GC/PID 0.01–0.02 ppb 98–99 EPA 

Meth

Drinking water Purge and trap GC/PID 0.02 ppb 94 EPA 

Meth

Drinking water Purge and trap cap. GC/MS 0.08–0.11 ppb 100–126 EPA 

Meth
Table 6-3. Analytical Methods for Determining Toluene in Environmental Samples (co

Sample matrix Preparation method 

Analytical method 

Sample detection limit 

Percent recovery Refe

Water/ waste water 

Purge and trap GC/PID 0.2 ppb 77 EPA 

Meth

Water/ waste water 

Purge and trap GC/MS 6.0 ppb 98–101 EPA 

Meth

Water/ waste water 

Addition of isotopically labeled analog; purge and trap 

GC/MS 10 ppb No data EPA 

Meth

Industrial effluents Purged with inert gas onto Tenax®; 

thermally desorbed 

GC/IDMS 20 ppb No data Colby 

Drinking water, waste water 

Purged with inert gas onto Tenax®; 

thermally desorbed, cryofocused 

GC/MS 1 ppb 74–107 Mich

Groundwater Solid-phase microextraction GC/FID 2 ppb No data Arthu

Water Purge and trap GC/MS 0.047 ppb 106 USE

APHA 

Water Direct aqueous injection GC 1.0 ppm No data USE

ASTM 

Water Purge and trap GC 0.5 ppb 80–120 USE

APHA 

Water Dilution in appropriate solvent FS 2.1 ppm No data USE

ASTM 

Groundwater, aqueous sludges, waste solvents, acid and caustic liquors, soils, sediments 

Purge and trap GC/MS 5 ppb 47–150 USE

OSW
Table 6-3. Analytical Methods for Determining Toluene in Environmental Samples (co

Sample matrix Preparation method 

Analytical method 

Sample detection limit 

Percent recovery Refe

Groundwater, aqueous sludges, waste solvents, acid and caustic liquors, soils, sediments 

Purge and trap or direct injection GC/EC or 

GC/PID 

0.01 ppb 99 USE

OSW 

Solid waste Purge-and-trap cap. GC/PID 0.01 ppb 99 EPA 

Meth

Solid waste Purge-and-trap GC/PID 0.08–0.11 ppb 100–102 EPA 

Meth

Soil Methanol extraction; SPE cap. GC sub-ppm >90 MeneSoil (screening) Filter immunoassay 7 ppm No data EPA 

Meth

Soils and sediments 

Headspace extraction GC/PID 0.2 ppb 46–148 USE

OSW 

Soids and other solid matrices 

Headspace extraction GC/FID 

GC/PID/ELCD 

No data No data USE

OSW 

Solid waste matrices 

Purge and trap or direct aqueous injection or concentration by azeotropic distillation or automated static headspace 

GC/MS 0.11 ppb 102 USE

OSW 

Plant cuticle Headspace extraction GC/FID No data No data Keym

Food Headspace extraction, 1 hour at 90 EC GC No data No data Walte
Table 6-3. Analytical Methods for Determining Toluene in Environmental Samples (co

Sample matrix Preparation method 

Analytical method 

Sample detection limit 

Percent recovery Refe

Foods Purge and trap cap. GC/MS 8 ppb 54–76b Heike

Bottled water Headspace extraction GC/MS 0.5-1 ppb No data Page Olive oil Homogenization; headspace cap. GC/MS No data No data Biede

aReported accuracybIntralaboratory accuracy. Single lab accuracy is reported as 100–106% recovery.

cap. = capillary; FID = flame ionization detector; FS = fluorescence spectroscopy, ELCD; GC = gas chromatography; IDMS 

mass spectrometry; MS = mass spectrometry; PID = photoionization detector; SPE = solid-phase extraction
TOLUENE 216 

6. ANALYTICAL METHODS 

Toluene may be determined in occupational air using collection on adsorbent tubes, solvent desorption 

and GC/FID analysis (NIOSH 1994). Detection limits depend upon the amount of air sampled; accuracy 

is very good (11.4% bias) (NIOSH 1994). Passive samplers are also used (Ballesta et al. 1992; Periago et 

al. 1997); however, little performance data are available. 

Gas purge and trap is the most widely used method for the isolation and concentration of VOCs in 

environmental samples (Lesage et al. 1993). The purge and trap technique offers advantages over other 

techniques in that it allows facile isolation and concentration of target compounds, thereby improving 

overall limits of detection and recovery of sample. Detection limits of less than 1 μg of methylbenzene 

per liter of sample have been achieved. Very low detection limits for drinking water are reported for the 

purge and trap method with GC/PID (0.01–0.02 ppb) (EPA 1991a, 1991b). Accuracy is very good 

(94–99% recovery) (EPA 1991a, 1991b). While the analytical method is selective, confirmation using a 

second column or GC/MS is recommended (EPA 1992a). Good sensitivity (0.08–0.11 ppb) and 

accuracy (100–126% recovery) can also be obtained using capillary GC/MS detection (EPA 1992a). 

Purge-and-trap methodology may be applied to waste water as well (EPA 1982b, 1982c, 1984). 

Sensitivity is in the low ppb range and recovery is good (77–101%) (EPA 1982b, 1982c, 1984). 

Soil, sediment, and solid waste are more difficult to analyze. Volatilization during sample handling and 

homogenization can result in analyte loss. Purge-and-trap methods with capillary GC/PID or GC/MS 

analysis provide detection limits of approximately 0.5 ppm for wastes and 5 μg/g for soil and sediment 

(EPA 1982b, 1982c, 1984). 

No methods were found for the determination of toluene in fish and biota. Few methods are available for 

the determination of toluene in food. A purge and trap extraction method is available for determining 

toluene in a variety of foods. The quantitation limit is 8 ppb; single lab recovery is very good 

(100–106%) and precision is good (9.8–25% RSD). Both intra- and inter-laboratory studies were 

conducted, and precision was found to be #25% RSD (Heikes et al. 1995). 

6.3 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 toluene is available. Where adequate information is not 

available, ATSDR, in conjunction with the National Toxicology Program (NTP), is required to assure the 
 

TOLUENE 217 

6. ANALYTICAL METHODS 

initiation of a program of research designed to determine the health effects (and techniques for developing 

methods to determine such health effects) of toluene. 

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. 

6.3.1 Identification of Data Needs 

Methods for Determining Biomarkers of Exposure and Effect. Although toluene and its 

metabolites can be measured in body fluids using a number of techniques (Kawai et al. 1993, 1996; 

NIOSH 1984a,), the metabolites have limited value as biomarkers. A number of common food materials 

produce the same metabolites, thus measurement of toluene metabolites can be used to confirm a known 

exposure but cannot be used to determine whether or not exposure occurred in a poorly defined situation. 

It is also very difficult to quantify the magnitude of exposure from levels of either toluene or its 

metabolites in biological samples. Despite these limitations, end-of-shift concentrations of 2.5 g hippuric 

acid/g creatinine and 1.0 mg/L toluene in venous blood have been established as biological exposure 

indices for toluene (ACGIH 1992a). A technique that could accurately quantify exposure to toluene 

would be useful. 

For occupational health monitoring and animal studies, there is also a need for improved and more 

sensitive methods to determine toluene metabolites. Additional work to develop sensitive methods for 

analysis of the cresol metabolites and to correlate these metabolites with specific exposure conditions 

would be valuable. 

It is equally difficult to monitor the effects of toluene exposure. Magnetic resonance imaging (MRI) and 

BAER evaluations of the brain have some value in determining the neurological damage resulting from 

long-term exposures to high levels of toluene, but have no known value for determining the effects of 

low-level and/or short-term exposures. 
 

TOLUENE 218 

6. ANALYTICAL METHODS 

Methods for Determining Parent Compounds and Degradation Products in Environmental 

Media. There are methods available for the determination of toluene and its metabolites in 

environmental samples. Sensitive techniques for air allow detection of toluene at levels as low as 

0.88 ppb (Crist and Mitchell 1986). In drinking water, detection limits of 0.01–0.02 μg/L are possible 

using GC/MS or GC/PID (EPA 1991a, 1991b). For waste water, detection limits in the low ppb range 

are achievable (EPA 1982b, 1982c, 1984). These techniques are adequate to measure both background 

toluene levels and the levels of toluene in environmental media that could cause health effects. However, 

when toluene is present in combination with other volatile materials, interference from the companion 

volatiles often raises the detection limit and decreases the accuracy and precision of the technique. 

Improved methods for separation of toluene from other volatiles would be useful. 

Very little work has been conducted on measuring the levels of toluene metabolites in the environment. 

Although techniques for measuring these substances exist, they have not routinely been applied to 

environmental media. Research on measuring the levels of metabolites in soil and water would be 

valuable especially in studying the end products of microbial degradation. Few methods are available for 

monitoring toluene in foods; reliable methods are needed for evaluating the potential for human exposure 

that might result from toluene ingestion. 

6.3.2 Ongoing Studies 

The Environmental Health Laboratory Sciences Division of the National Center for Environmental 

Health, Centers for Disease Control and Prevention, is developing methods for the analysis of toluene and 

other volatile organic compounds in blood. These methods use purge-and-trap methodology, highresolution GC, and magnetic sector mass spectrometry which gives detection limits in the low parts per 

trillion (ppt) range. 

The U.S. EPA is conducting a pilot program for comprehensive monitoring of human exposure. The 

National Human Exposure Assessment Study (NHEXAS) is being conducted in three regions of the 

United States in order to establish relationships between environmental concentrations, exposure, dose, 

and health response and to determine the incidence and causes of high exposures, especially for 

biologically susceptible persons. One of the aims of the pilot study is to test measurement methodology 

for a variety of pollutants, including toluene, in air and water. As an adjunct to this pilot study, the U.S. 

EPA and the State of Minnesota are conducting a study of children’s exposure to toxic chemicals, 

including toluene. 
TOLUENE 219 

7. REGULATIONS AND ADVISORIES
 

The international, national, and state regulations and guidelines regarding toluene in air, water, and other 

media are summarized in Table 7-1. 

ATSDR has derived an acute-duration inhalation MRL of 1 ppm (3.8 mg/m3

) for toluene based on a 

NOAEL for neurological effects in humans (Andersen et al. 1983). 

ATSDR has derived a chronic-duration inhalation MRL of 0.08 ppm (0.3 mg/m3

) for toluene based on a 

LOAEL for neurological effects in humans in a study by Zavalic et al. (1998a). 

ATSDR has derived an acute-duration oral MRL of 0.8 mg/kg/day for toluene based on a LOAEL for 

neurological effects in rats (Dyer et al. 1988). 

ATSDR has derived an intermediate-duration oral MRL of 0.02 mg/kg/day for toluene based on a 

LOAEL for neurological effects in mice (Hsieh et al. 1990b). 

The EPA's reference concentration (RfC) for toluene is 0.4 mg/m3

 and the EPA's reference dose (RfD) is 

0.2 mg/kg/day (IRIS 2000). 

The International Agency for Research on Cancer (IARC) classifies toluene as a Group 3 carcinogen (the 

agent is not classifiable as to its carcinogenicity to humans) based on inadequate evidence in humans for 

carcinogenicity of toluene and evidence suggesting lack of carcinogenicity of toluene in experimental 

animals (IARC 1999). The EPA and the American Conference of Governmental Industrial Hygienists 

(ACGIH) also state that there are inadequate data on which to classify toluene in terms of its 

carcinogenicity in humans or animals (ACGIH 1997; IRIS 2000). Therefore, toluene is assigned the 

cancer classification of “Group D” by the EPA and given the cancer category “A4" by the ACGIH 

(ACGIH 1997; IRIS 2000). 

Toluene is listed as a chemical which must meet the requirements of Section 313 of Title III of the 

Superfund Amendments and Reauthorization Act (SARA) (EPA 1996a). Title III of SARA, also known 

as "The Emergency Planning and Community Right-to-Know Act of 1986," requires owners and 

operators of certain facilities that manufacture, import, process, or otherwise use the chemicals on this list 

to report annually any release of those chemicals to any environmental media over a specified threshold 

level. 
TOLUENE 220 

7. REGULATIONS AND ADVISORIES 

Toluene has been designated as a hazardous substance pursuant to the Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA) of 1980 (EPA 1995a). The statutory source for 

this designation is Section 311(b)(4) of the Clean Water Act (CWA), Section 307 (a) of the CWA, 

Section 112 of the Clean Air Act (CAA), and Section 300 of the Resource Conservation and Recovery 

Act (RCRA) (EPA 1995a). The owner and operator of any facility that produces, uses, or stores a 

CERCLA hazardous substance is required to immediately report releases to any environmental media, if 

the amount released is equal to or exceeds the specified “reportable quantity” assigned to the substance. 

The reportable quantity for toluene is 1,000 pounds (454 kg) (EPA 1995a). 

The Occupational Safety and Health Administration (OSHA) sets permissible exposure limits (PELs) to 

protect workers against adverse health effects resulting from exposure to hazardous substances. The 

PELs determined for hazardous substances are enforceable, regulatory limits on allowable air 

concentrations in the workplace. OSHA requires employers of workers who are occupationally exposed 

to these hazardous substances to institute engineering controls and work practices to reduce and maintain 

employee exposure at or below permissible exposure limits (PEL). Between June 27, 1974 and 

January 18, 1989, the Occupational Safety and Health Administration (OSHA) had promulgated 

protective, permissible exposure limits (PELs) for approximately 264 toxic substances (OSHA 1993). On 

January 18, 1989, OSHA promulgated more protective PELs for approximately 376 toxic substances. 

Toluene was included among the 212 toxic substances for which the PEL was lowered (OSHA 1989a). 

The new PELs for toluene were set at 50 ppm (TWA) and 100 ppm for the 15-minute, short-term 

exposure limit (STEL) (OSHA 1989a). Because the 1989 promulgation was rescinded by the 11th Circuit 

Court Appeals in July 1992, only those PELs in place prior to the 1989 rule are currently enforced by 

OSHA. On June 30, 1993, OSHA published in the Federal Register a final rule announcing the 

revocation of the 1989 exposure limits, including the newly established limits for toluene (OSHA 1993). 

An employer must ensure that an employee’s exposure to toluene in any 8-hour work shift of a 40-hour 

week does not exceed the 8-hour time-weighted average (TWA) of 200 ppm (OSHA 1974). The 

acceptable ceiling concentration for toluene which shall not be exceeded at any time during an 8-hour 

shift is 300 ppm (OSHA 1974). The acceptable maximum peak above the ceiling for an 8-hour shift is 

500 ppm. The maximum exposure duration for this level is 5 minutes in any 2-hour period (OSHA 

1974). The ACGIH (1999) recommends an 8-hour TWA Threshold Limit Value of 50 ppm toluene to 

protect against central nervous system effects. 

Toluene is regulated as a hazardous air pollutant (U.S. Congress 1990) and is subject to the emission 

limitations for various processes and operations in the synthetic organic chemicals manufacturing 
TOLUENE 221 

7. REGULATIONS AND ADVISORIES 

industry (EPA 1983a, 1993b, 1995i). Source categories such as wood furniture manufacturing operations 

(EPA 1995g), polymer and resin producers (EPA 1996c) and petroleum refineries (EPA 1996b) that could 

release toluene to the atmosphere must meet the national emissions standards for hazardous air pollutants 

(NESHAPs). 

Because of its potential to cause adverse health effects in exposed people, toluene is also regulated by the 

drinking water standards set by the EPA. Toluene generally gets into drinking water by improper waste 

disposal or leaking underground storage tanks. In order to protect humans from the risk of developing 

adverse health effects from exposure to toluene through drinking water, the EPA Drinking Water 

Regulations and Health Advisories (1996) lists the Maximum Contaminant Level and the Maximum 

Contaminant Level Goal for toluene as 1 mg/L. 
TOLUENE	 222 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene 

Agency Description	 Information Reference 

INTERNATIONAL 

Guidelines: 

IARC	 Cancer Classification Group 3 IARC 1998 

WHO	 Drinking-water guideline values 700 μg/L WHO 1996
 

for health-related organics
 

NATIONAL 

Regulations and 

Guidelines: 

a. Air: 

ACGIH	 TLV—TWA 50 ppm ACGIH 1999 

EPA Listed as a Hazardous Air Yes Clean Air Act 

Pollutant Amendment, Title III, 

Section 112 (b) 

U.S. Congress 1990 

NIOSH Recommended Exposure Limit: NIOSH 1999
 

TWA 100 ppm
 

STEL 150 ppm
 

OSHA 8-hour time weighted average 200 ppm	 29 CFR 1910.1000 

OSHA 1999a 

Acceptable ceiling 300 ppm 29 CFR 1910.1000 

concentration OSHA 1999a 

Acceptable maximum peak 500 ppm 29 CFR 1910.1000 

above the acceptable ceiling OSHA 1999a 

concentration for an 8-hour 

shift for a maximum duration of 

10 minutes 

Vacated 1989 OSHA PELa OSHA 1989a 

TWA 100 ppm 

STEL 150 ppm 

8-hour time weighted average 200 ppm 29 CFR 1915.1000 

for shipyard workers OSHA 1999b 

8-hour-time weighted average 200 ppm 29 CFR 1926.55 

for construction workers OSHA 1999c 

b. Water 
TOLUENE	 223 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene (continued) 

Agency Description	 Information Reference 

EPA (cont.)	 MCLG 

EPA	 MCL 

MCL for community and nontransient, non-community water 

systems 

Health Advisories 

One-day (10-kg child) 

Ten-day (10-kg child) 

Longer-term (child) 

Longer-term (adult) 

Lifetime (adult) 

Cancer Classification 

Water Quality Criteria: 

water and organisms 

organisms only 

Universal treatment standards 

waste water 

non-waste water 

FDA Bottled water limit for toluene 

c. Food 

EPA	 Residue exempt from the 

requirement of a tolerance 

when used in accordance 

with good agricultural practice 

in pesticide formulations 

applied 

to growing crops or to raw 

agricultural commodities after 

harvest 

FDA	 Indirect Food Additive— 

component of adhesives 

Indirect food additive— 

component of resinous and 

polymeric coatings 

Indirect food additive— residual 

solvent in finished 

polycarbonate resins 

1 mg/L 

1 ppm 

1 mg/L 

20 mg/L 

2 mg/L 

2 mg/L 

7 mg/L 

1 mg/L 

Group Db 

6,800 μg/L 

200,000 μg/L 

0.080 mg/L2 

10 mg/kg3 

1 mg/L 

Used as a solvent or 

co-solvent 

Yes 

Yes 

Not to exceed 800 

ppm 

40 CFR 141.50 

EPA 1999g 

40 CFR 141.32 

EPA 1999f 

40 CFR 141.61 

EPA 1999h 

EPA 1996a 

EPA 1999j 

40 CFR 268.48 

EPA 1999e 

21 CFR 165.110 

FDA 1999e 

40 CFR 180.1001 

EPA 1999i 

21 CFR 175.105 

FDA 1999a 

21 CFR 175.320 

FDA 1999c 

21 CFR 177.1580 

FDA 1999d 
TOLUENE 224 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene (continued) 

Agency Description Information Reference 

FDA (cont.) Used as an adjuvant in the 

manufacturing of foam plastics 

intended for use in contact with 

foods— subject to the following 

limitations: 

Use only as a 

blowing agent 

adjuvant to 

polystyrene at a 

level not to exceed 

21 CFR 178.3010 

FDA 1999b 

0.35% by weight of 

finished foam 

polystyrene 

Indirect food additive— Residue limit of 21 CFR 177.1200 

component of cellophane used 

for food packaging 

0.1% FDA 1999f 

d. other 

ACGIH Cancer classification A4c ACGIH 1999 

Biological Exposure Index: 

o-Cresol in urine 

Hippuric acid in urine 

Toluene in blood 

0.5 mg/L 

1.6 g/g creatinine 

0.05 mg/L 

EPA RfD 

RfC 

Cancer Classification 

0.2 mg/kg/day 

0.4 mg/m3 

Dd 

IRIS 2000 

Reportable quantity for toluene 

regarded as a CERCLA 

hazardous substance under 

1,000 lb 40 CFR 302.4 

EPA 1999b 

section 311(b)(4), 307(a) 

and 112 of the Clean Water 

Act; and by RCRA section 

3001 

Identification and Listing of 

toluene as a Hazardous Waste 

Yes 40 CFR 261.33 

EPA 1999a 

Toxic pollutant designated 

pursuant to section 307(a)(1) of 

the Act 

Yes 40 CFR 401.15 

EPA 1998a 

Toxic Chemical Release 

Reporting— effective date 

1/1/87 40 CFR 372.65 

EPA 1999d 

EPA (cont.) Designated hazardous 

substance in accordance with 

Yes 40 CFR 116.4 

EPA 1998b 

section 311(b)(2)(a) of the Act 

Health and Safety Data 

Reporting Rule 

Yes 40 CFR 716.120 

EPA 1995f 
 

TOLUENE	 225 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene (continued) 

Agency Description	 Information Reference 

STATE 

a. Air: 

Arizona 

Connecticut 

Florida 

Idaho 

Indiana 

Kansas 

Louisiana 

Massachusetts 

Maine 

North Carolina 

North Dakota 

Nevada 

New York 

Acceptable concentration 

1-hour 

24-hour 

8-hour acceptable 

concentration 

Acceptable concentration 

Fort Lauderdale

 8-hour 

Pinella
 

8-hour
 

24-hour
 

Annual
 

Acceptable concentration 

Occupational exposure level 

8-hour acceptable 

concentration 

Concentration limits for 

hazardous air emissions 

8-hour acceptable 

concentration 

24-hour and annual acceptable 

concentration 

Acceptable concentration

 24-hour 

Annual 

Acceptable concentration 

15-minute 

24-hour 

Acceptable concentration 

8-hour 

1-hour 

8-hour acceptable 

concentration 

Annual Acceptable 

concentration 

1 ppm 

0.796 ppm 

7,500 μg/m3

7.5 mg/m3 

3,750 μg/m3 

900 μg/m3 

300 μg/m3 

18.75 mg/m3 

375 mg/m3 

1,880 μg/m3 

10 tons/year 

8,900 μg/m3 

10.20 μg/m3 

260 μg/m3 

180 μg/m3 

56 mg/m3 

4.7 mg/m3 

3.77 mg/m3 

5.65 mg/m3 

8.93 mg/m3

7,500 μg/m3 

NATICH 1992 

 NATICH 1992 

NATICH 1992 

ID Dept Health 

Welfare 1999a 

NATICH 1992 

KS Dept. Health Env 

1998b 

NATICH 1992 

NATICH 1992 

NATICH 1992 

NATICH 1992 

NATICH 1992 

 NATICH 1992 

NATICH 1992 

Oklahoma 24-hour acceptable 37,500 μg/m3 NATICH 1992 

concentration 
TOLUENE	 226 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene (continued) 

Agency Description	 Information Reference 

STATE (cont.) 

Rhode Island Acceptable concentration 

24-hour 

Annual 

South Dakota	 8-hour acceptable
 

concentration
 

Texas	 0.5-hour acceptable
 

concentration
 

Virginia	 24-hour acceptable
 

concentration
 

Vermont	 24-hour acceptable
 

concentration
 

Washington	 24-hour acceptable
 

concentration
 

Wisconsin Acceptable emission levels 

<25 feet 

25 feet 

EPA Region 9e	 Preliminary remedial goal (non 

cancer) 

b. Water 

Alabama Human health criteria for 

consumption of: 

water and fishf 

fish onlyf 

Alaska	 Maximum contaminant level 

Arizona	 Human health based guidance 

levels (HBGLS)for ingestion of 

contaminents in drinking water 

Oral HBGL 

MCL 

Aquifer water quality standarddrinking water protected use 

California Drinking water guideline 

2,000 μg/m3 

400 μg/m3 

7,500 μg/m3

3,750 μg/m3 

6,300 μg/m3 

8,930 μg/m3 

1,250 μg/m3 

31 lbs/hour 

131 lbs/hour 

4.0 x 10+2 μg/m3 

6 mg/L 

43.6 mg/L 

1 mg/L 

1400 μg/L 

1000 μg/L 

1 mg/L 

100 μg/L 

RI Dept Env 

Management 1992 

 NATICH 1992 

NATICH 1992 

NATICH 1992 

NATICH 1992 

NATICH 1992 

WI Dept Natural 

Resources 1997 

EPA 1998a 

AL Dept Env 

Management 1998 

AK Dept Env 

Conserv 1999 

AR Dept Health 

Services 1999 

BNA 1998 

FSTRAC 1995 
TOLUENE 227 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene (continued) 

Agency Description Information Reference 

STATE (cont.) 

Colorado Aquatic life based criteria for 

surface waters: 

CO Dept Public 

Health Env 1999 

acute 

chronic 

Human health based for 

17,500 μg/L 

Not given 

surface water: 

water and organism 

water only 

1000 μg/L 

1000 μg/L 

Connecticut Drinking water guideline 1,000 μg/L FSTRAC 1995 

Surface-water protection 

criteria for substances in 

4x10+6 μg/L BNA 1998 

ground water 

Delaware Freshwater fish ingestion 

Freshwater fish and water 

Marine fish ingestion 

370 mg/L 

10 mg/L 

52 mg/L 

BNA 1998 

Florida Criteria for resource protection 

and recovery 

freshwater 

marine 

475 μg/L 

475 μg/L 

BNA 1998 

Hawaii Health guidelines applicable to 

all water: 

HI Dept Health 

1999a 

Freshwater 

acute 

chronic 

5,800 μg/L 

NSg 

Saltwater 

acute 

chronic 

2,100 μg/L 

NSg 

Fish consumption 140,000 μg/L 

MCL applicable to community 

and non-transient, noncommunity water systems 

1 mg/L HI Dept Health 

1999b 

Idaho Ground water quality 1 mg/L ID Dept Health 

Welfare 1999a 

Illinois Human health standards 51.0 mg/L IL Env Protec 

Agency 1999 

Kansas Guideline 2,000 μg/L FSTRAC 1990 

Kansas Surface water quality standards 

for aquatic life: 

acute 

chronic 

17,500 mg/L 

Not given 

KS Dept Health 

Envment 1998a 

Maine Guideline 1400 FSTRAC 1995 
TOLUENE	 228 

7. REGULATIONS AND ADVISORIES 

Table 7-1. Regulations and Guidelines Applicable to Toluene (continued) 

Agency Description	 Information Reference 

STATE (cont.) 

Massachusetts Guideline 2,000 μg/L FSTRAC 1995 

Minnesota Guideline 1,000 μg/L FSTRAC 1995 

New Hampshire Guideline 2,000 μg/L FSTRAC 1990 

New Jersey Ground water quality standards 1000 μg/L	 NJ Dept Env Protec 

1993 

Oklahoma Aquatic life Criteria OK Dept Env Quality 

acute Not given 1997 

chronic 875.0 μg/L 

Rhode Island	 Accepted level - annual 2,000 μg/m3 RI Dept Env 

average Management 1992 

South Dakota	 Maximum contaminant levels— 1 mg/L SD Dept Env Natural 

apply to community and non- Resources 1998 

transient and non-community 

water systems 

Vermont Guideline 2,420 μg/L FSTRAC 1995 

Wisconsin Standard 1,000 μg/L FSTRAC 1995 

EPA Region 9e Preliminary remedial goal 7.2x10+2 μg/m3 EPA 1998a 

(noncancer) 

a

OSHA set more protective PELs for 212 substances in 1989. However, in July 1992, the 11th Circuit Court Appeals rescinded the

 1989 PELs promulgated by OSHA. Only PELs in place prior to the 1989 rule are currently allowed as OSHA standards. b

Not classifiable; Inadequate or no human and animal evidence of carcinogenicity c

A4-Not classifiable as a human carcinogen.

d

D-substances are unclassifiable as to their carcinogenicity e

The preliminary remediation goals (PRGs) are tools used by EPA Region 9 for evaluating and cleaning up contaminated sites.

 They are being used to streamline and standardize all stages of the risk decision-making process for soil remediation. 

f

The following equations were used to calculate the values as given in the Alabama State laws: 

Consumption of water and fish: Concentration (mg/L) = (HBW X RfD) / [(FCR X BCF) + WCR] 

Consumption of water only:	 FCR = fish consumption rate, set at 0.030 kg/day 

Concentration (mg/L) = (HBW X RfD) / (FCR X BCF) BCF = bioconcentration factor, 10.7 L/kg for toluene 

HBW = human body weight, set at 70 kg	 WCR = water consumption rate, set at 2 L/day 

RfD = reference dose, 0.2 mg/(kg-day) for toluene 

g

NS: no standard has been developed 

ACGIH=American Conference of Governmental Industrial Hygienists; CFR=code of federal regulations; CPSC=Consumer Product 

Safety Commission; EPA=Environmental Protection Agency; FDA=Food and Drug Administration; FR=federal register; 

FSTRAC=Federal-State Toxicology and Regulatory Alliance Committee; IARC=International Agency for Research on Cancer; 

IRIS=Integrated Risk Information System; MCL=maximum contaminant level; MCLG=maximum contaminant level goal; 

NIOSH=National Institute for Occupational Safety and Health; NPDES=national pollutant discharge elimination system; 

OSHA=Occupational Safety and Health Administration; PEL=permissible exposure limit; RfC=inhalation reference concentration; 

RfD=oral reference dose; STEL=short term exposure limit; TLV=threshold limit value; TWA=time-weighted average; WHO=World 

Health Organization 
TOLUENE 229 

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TOLUENE 230 

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TOLUENE 307 

9. 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 a 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)—is 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—is 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—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. 

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 which 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. 

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. 
TOLUENE 308 

9. GLOSSARY 

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 which 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. 

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. 
TOLUENE 309 

9. GLOSSARY 

Intermediate Exposure—Exposure to a chemical for a duration of 15-364 days, as specified in the 

Toxicological Profiles. 

Immunological Effects—are functional changes in the immune response. 

Immunologic Toxicity—The occurrence of adverse effects on the immune system that may result from 

exposure to environmental agents such as chemicals. 

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 which 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 which 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. 

Mortality—Death; mortality rate is a measure of the number of deaths in a population during a specified 

interval of time. 
TOLUENE 310 

9. GLOSSARY 

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—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. 

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—is the science of quantitatively predicting 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—is 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 whereby the 

physiologically-based model compartments represent real anatomic regions of the body. 

Physiologically Based Pharmacodynamic (PBPD) Model—is a type of physiologically-based doseresponse model which 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. 
TOLUENE 311 

9. GLOSSARY 

Physiologically Based Pharmacokinetic (PBPK) Model—is 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 

4such 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. 

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 casual factors that can be ascertained from existing 

records and/or examining survivors of the cohort. 
TOLUENE 312 

9. GLOSSARY 

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 min 

continually. No more than four excursions are allowed per day, and there must be at least 60 min 

between exposure periods. The daily Threshold Limit Value - Time Weighted Average (TLV-TWA) may 

not be exceeded. 

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 study of the absorption, distribution and elimination of toxic compounds in the 

living organism. 

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 one can be 

used; however a reduced UF of three may be used on a case-by-case basis, three being the approximate 

logarithmic average of 10 and 1. 

Xenobiotic—any chemical that is foreign to the biological system. 
TOLUENE 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. 
TOLUENE A-2 

APPENDIX A 

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 

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 a hundredfold 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, Mailstop E-29, Atlanta, Georgia 30333. 
TOLUENE A-3 

APPENDIX A 

MINIMAL RISK LEVEL (MRL) WORKSHEET(S) 

Chemical name: Toluene 

CAS number: 108-88-3 

Date: June 8, 2000 

Profile status: Post-public Draft 3/Camera Ready 

Route: [X] Inhalation [ ] Oral 

Duration: [X] Acute [ ] Intermediate [ ] Chronic 

Key to figure: 17 

Species: human 

MRL: 1 [ ] mg/kg/day [X] ppm [ ] mg/m3 

Reference: Andersen I, Lundqvist GR, Molhave L et al. 1983. Human response to controlled levels of 

toluene in six-hour exposures. Scand J Work Environ Health 9: 405-418. 

Experimental design: The effects of toluene on 16 healthy young male subjects with no previous regular 

exposure to organic solvents were investigated. Groups of four subjects were in a chamber for 6 hours a 

day on 4 consecutive days. After 1 hour of exposure to clean air in the chamber, the concentration of 

toluene was steadily increased during 30 minutes to the concentration intended for the day. After hour of 

exposure, all subjects went through all physiological, discomfort, and performance measurements for the 

next 1.5 hours. After a 1 hour lunch, a similar series of measurements were made during the 5th and 6th 

hours of exposure. The concentration of toluene was 0, 10, 40, or 100 ppm with each group exposed to a 

different toluene concentration each day. Physiological measurements were performed, including nasal 

mucociliary flow, FVC, FEV, and FEF25-75, and subjective measurements of discomfort. Eight different 

performance assessment tests (five-choice serial reaction test, rotary pursuit test, screw-plate test, 

Landolt’s ring test, Bourdon Wiersma test, multiplication test, sentence comprehension test, and word 

memory test) were carried out. 

Effects noted in study and corresponding doses: There was a significant change in nasal mucus flow from 

control values during all of the toluene exposures. During the 100 ppm exposure, statistically significant 

increased irritation was experienced in the eyes and in the nose, but not in the throat or lower airways. 

There was also a statistically significant increase in the occurrence of headaches, dizziness, and feelings 

of intoxication during the 100 ppm exposure, but not during the other concentrations. No statistically 

significant effects of toluene occurred in the eight performance tests. For three of the tests, multiplication 

test, Landolt’s rings, and the screw plate test, there was a borderline correlation between toluene and the 

test results. The subjects felt that the tests were more difficult and strenuous during the 100 ppm 

exposure, for which headache, dizziness, and feelings of intoxication were more often reported. No 

adverse effects were reported at the 10 and 40 ppm levels. 

Dose endpoint used for MRL derivation: 40 ppm for neurological effects 

[X ] NOAEL [ ] LOAEL 
TOLUENE A-4 

APPENDIX A 

Uncertainty factors used in MRL derivation: 

[ ] 1 [ ] 3 [ ] 10 (for use of a LOAEL)
 

[ ] 1 [ ] 3 [ ] 10 (for extrapolation from animals to humans)
 

[ ] 1 [ ] 3 [X] 10 (for human variability)
 

MRL = 40 ppm x 5 days/7 days x 8 hours/24 hours ÷10 = 1 ppm (3.8 mg/m3

) 

Was a conversion factor used from ppm in food or water to a mg/body weight dose? No. 

If so, explain: 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: Not 

applicable 

Was a conversion used from intermittent to continuous exposure? Exposure concentration was adjusted to 

continuous exposure basis as shown above. 

Other additional studies or pertinent information that lend support to this MRL: The primary effect of 

toluene is on the central nervous system. There are several other human studies for which the central 

nervous system is the major end point and could have been used to derive an acute inhalation MRL. 

However, the Andersen et al. (1983) study was chosen as the basis for the MRL because this was the only 

human study which reported a NOAEL. Baelum et al.(1985) also reported a LOAEL of 100 ppm for 

neurological effects in humans. In this study, 43 occupationally-exposed subjects and 43 controls were 

exposed to either clean air or air containing 100 ppm toluene for 6.5 hours in a climate chamber. A 

battery of ten tests of visuomotor coordination, visual performance, and cortical function were 

administered during the 6.5 hour period. For both the controls and toluene exposed subjects, there were 

complaints of air quality, irritation of the nasal passages, and increased feelings of fatigue and sleepiness. 

Subjects also complained of headaches and dizziness. Toluene exposure decreased performance on four 

of the neurobehavioral tests; three of these were tests of visual perseverance. The fourth test affected was 

the simple peg board test of visuomotor function, where the effect was noted in toluene-exposed workers 

to a much greater extent than controls. Escheverria et al. (1991) reported a LOAEL of 75 ppm for 

neurological effects in humans. In this study, two groups of 42 students were exposed to 0, 75, and 

150 ppm toluene for a 7 hour period. A complete battery of 12 tests was administered before and at the 

end of each exposure. Toluene caused a dose-related impairment of function on digit span pattern 

recognition, the one hole test, and pattern memory. Rahill et al. (1996) reported a LOAEL of 100 ppm for 

neurological effects in humans. In this study, six volunteers were exposed for 6 hours a day to either 

100 ppm toluene or clean air. Three repetitions of two computerized neuropsychological tests were 

performed, with the composite score on the multitasking test being significantly lower with toluene 

exposure than with clean air. 

Agency Contact (Chemical Manager): Alfred Dorsey 
TOLUENE A-5 

APPENDIX A 

MINIMAL RISK LEVEL (MRL) WORKSHEET 

Chemical name: Toluene 

CAS number: 108-88-3 

Date: June 8, 2000 

Profile status: Post-public Draft 3/Camera Ready 

Route: [X] Inhalation [ ] Oral 

Duration: [ ] Acute [ ]Intermediate [X] Chronic 

Key to figure: 160 

Species: human 

MRL: 0.08 [ ] mg/kg/day [X ] ppm [ ] mg/m3 

References: Zavalic, M, Mandic, Z, Turk, R et al. 1998a. Quantitative assessment of color vision 

impairment in workers exposed to toluene. Am J Ind Med 32: 297-304. 

Zavalic, M, Mandic, Z, Turk, R et al. 1988c. Assessment of colour vision impairment in male workeres 

exposed to toluene generally above occupational exposure limits. Occup Med 48(3):175-180 

Experimental design: Three groups of Croatian workers were examined by means of interviews, medical 

examination, and color vision testing using the Lanthony 15 Hue desaturated panel in standard conditions. 

Workers were excluded from the study if they met any of the following criteria: less than 6 months 

employment, congenital color vision loss, a medical condition which can affect color vision, visual acuity 

below 6/10, use of medications which can affect color vision or a hobby that involved solvent exposure. 

Alcohol intake and smoking were also assessed for each individual. The first group consisted of 46 

workers (43 women and 3 men) employed in manually glueing shoe soles and exposed to median levels 

of 32 ppm and geometric mean levels of 35 ppm toluene. The second group consisted of 37 workers (34 

men and 3 women) employed in a rotogravure printing press and exposed to median levels of 132 ppm 

and geometric mean levels of 156 ppm toluene. The third group consisted of 90 workers (61 men and 29 

women) not occupationally exposed to any solvents or known neurotoxic agents. The average age of the 

workers was 41 years. The technology, ventilation and types of workplaces included in the study had not 

changed in the preceding 30 years. Toluene exposure was evaluated by mid-week environmental and 

biological monitoring of toluene. Samples of air were collected at 11 stations in the shoe factory and 8 

locations in the printing press. Toluene levels were measured in blood samples taken at the beginning of 

the work shift (all workers). Orthocresol and hippuric acid levels in urine were measured (for printers 

only) at the end of the work shift. 

Effects noted in study and corresponding doses: Comparison of mean values between groups was 

assessed by t-test or Mann-Whitney U-test. Correlations between variables were determined using linear 

multiple regression analyses. Analyses were performed using CCI or AACCI as dependent factors and 

age, alcohol intake, exposure duration, work service, toluene in air, toluene in blood, and biological 

markers of toluene in urine (printers only) as independent factors. A p-value <0.05 was regarded as 

significant. The mean CCI was significantly higher in printers compared to both shoemakers and 

controls. The Mean CCI for shoemakers was increased compared with controls, but the difference was 

not significant. Regression analysis of the control data indicated that alcohol intake and age were 

significant explanatory variables for changes in CCI. The age- and alcohol-adjusted color confusion 

index was significantly increased in printers (156 ppm) compared with both shoemakers (35 ppm) and 

controls, and in shoemakers (35 ppm) compared with controls. Regression analyses of the data from 

printers showed significant correlations between CCI as a dependent variable and age, alcohol intake, 

toluene in air, toluene in blood, hippuric acid in urine, or orthocresol in urine as independent variables. 
TOLUENE A-6 

APPENDIX A 

Significant correlation was also found for AACCI as dependent variable and exposure to toluene or 

biomarkers of toluene exposure. In contrast, the shoemaker data showed a significant correlation between 

CCI and age, but did not establish any significant correlation between CCI or AACCI and any marker of 

toluene exposure. This study demonstrated a statistically significant impairment of color vision in 

workers chronically exposed to 156 ppm toluene compared with controls. When the data were adjusted to 

allow for the confounding effects of alcohol consumption and age, a significant difference due to toluene 

exposure was also reported for workers exposed to 35 ppm toluene compared with controls. 

Dose endpoint used for MRL derivation: 35 ppm for alcohol-and age-adjusted color vision impairment 

[ ] NOAEL [x] LOAEL 

Uncertainty factors used in MRL derivation: 

[ ] 1 [ ] 3 [x] 10 (for use of a minimal LOAEL)
 

[ ] 1 [ ] 3 [ ] 10 (for extrapolation from animals to humans)
 

[ ] 1 [ ] 3 [x] 10 (for human variability)
 

MRL = 35 ppm x 5 days/7 days x 8 hours/24 hours ÷ 100 = 0.08 ppm (0.3 mg/m3

) 

Was a conversion factor used from ppm in food or water to a mg/body weight dose? No. 

If so, explain: 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: Not 

applicable. 

Was a conversion used from intermittent to continuous exposure? Exposure concentration was adjusted 

to continuous expsoure basis as shown above. 

Other additional studies or pertinent information that lend support to this MRL: There are several other 

reports of subtle neurological impairments in toluene-exposed workers that support this MRL. Another 

group of printers exposed to mean concentrations of 120 ppm toluene had a significantly increased mean 

alcohol-and age-adjusted color confusion index compared with unexposed controls (Zavalic et al. 1998b). 

A group of printing press workers (exposed to average toluene concentrations of 50 ppm for an average of 

30 years) had significantly reduced wave amplitude of visual evoked potentials and increased latency of 

auditory evoked potentials (Vrca et al. 1995, 1996, 1997a, 1997b). Significant changes in auditory 

evoked potentials were also reported for printers exposed to 97 ppm toluene for 12–14 years (Abbate et 

al. 1993). A study of hearing loss in Brazilian printers exposed to multiple solvents (toluene 

concentrations in air were reported as 0.14–919 mg/m3

 or 0.04–245 ppm) found that the odds ratio for 

hearing loss increased 1.76 times with each gram of hippuric acid/gram creatinine (Morata et al. 1997). 

Ten rotogravure printers (average exposure of 83 ppm for 1–36 years) examined for neurological effects 

were found to have a lower coefficient of variation in electrocardiographic R-R intervals than 10 agematched controls (Murata et al. 1993). Significant deficits in 28 of 30 neurobehavioral tests were found 

for a group of electronics workers exposed to TWA concentrations of 88 ppm toluene for an average of 6 

years compared with unexposed controls (Foo et al. 1990). Boey et al. (1997) also found significant 

deficits in neurological tests for electronics workers (exposed to TWA concentrations of 90.9 ppm 

toluene) compared with unexposed controls. Orbaek and Nise (1989) reported increased neurasthenic 

symptoms and performance deficits in psychometric tests for printers from two plants exposed to toluene 

for 4–43 years (median 29 years). At the time of the study (1985), TWA levels in the two plants were 

11.4 and 41.7 ppm, but previous concentrations were higher, with estimated midpoints for each plant of 

132 and 147 ppm and the mean of these midpoints, 140 ppm, can be taken as a representative exposure 
TOLUENE A-7 

APPENDIX A 

concentration for the overall group. In general, these studies corroboratively demonstrate that subtle 

neurological effects can occur from repeated exposure to toluene concentrations within the range of 

32–150 ppm. 

Agency Contact (Chemical Manager): Alfred Dorsey 
 

TOLUENE A-8 

APPENDIX A 

MINIMAL RISK LEVEL (MRL) WORKSHEET 

Chemical name: Toluene 

CAS number: 108-88-3 

Date: June 8, 2000 

Profile status: Post-public Draft 3/Camera Ready 

Route: [ ] Inhalation [X] Oral 

Duration: [X] Acute [ ]Intermediate [ ] Chronic 

Key to figure: 10 

Species: rat 

MRL: 0.8 [X] mg/kg/day [ ] ppm [ ] mg/m3 

Reference: Dyer RS, Bercegeay MS, Mayo LM. 1988. Acute exposures to p-xylene and toluene alter 

visual information processing. Neurotoxicol Teratol 10: 147–153. 

Experimental design: Male Long-Evans rats (12 per group) were administered doses of toluene in corn 

oil of 0, 250, 500, and 1,000 mg/kg/day by gavage. Flash-evoked potential tests were administered 

45 minutes later as a test of the ability of the nervous system to process visual information. In another 

study (time-course), toluene was administered to male Long-Evans rats (16 per group) at doses of 0 and 

500 mg/kg/day by gavage and flash-evoked potential tests were performed 4, 8, 16, and 30 hours later. 

Effects noted in study and corresponding doses: The amplitude of the N3 peak of the flash-evoked 

potential was significantly decreased (P<0.05) by toluene exposure at all doses. This decrease in peak 

amplitude was not dose-related. In the time course study, 500 mg/kg/day also decreased the amplitude of 

the flash-evoked potential; at this dose, little change in magnitude of peak N3 depression had occurred 

8 hours post treatment; by 16 hours recovery was complete. 

Dose endpoint used for MRL derivation: 250 mg/kg/day for neurological effects 

[ ] NOAEL [x] LOAEL 

Uncertainty factors used in MRL derivation: 

[ ] 1 [x ] 3 [ ] 10 (for use of a minimal LOAEL)
 

[ ] 1 [ ] 3 [ x] 10 (for extrapolation from animals to humans)
 

[ ] 1 [ ] 3 [x] 10 (for human variability)
 

MRL = 250 mg/kg/day ÷ 300 = 0.8 mg/kg/day
 

Was a conversion factor used from ppm in food or water to a mg/body weight dose? No.
 

If so, explain: 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: Not 

applicable. 

Was a conversion used from intermittent to continuous exposure? No. 
TOLUENE A-9 

APPENDIX A 

Other additional studies or pertinent information that lend support to this MRL: Although no additional 

acute oral animal studies are available on the neurological effects of toluene, a number of animal 

inhalation studies have reported neurological effects from toluene (Arito et al. 1988; Bushnell et al. 1994; 

Carpenter et al. 1986; Harabuchi et al. 1993; Hinman 1987). Human inhalation studies have shown the 

central nervous system to be the major end point for toluene exposure (Andersen et al. 1983; Baelum et 

al. 1985; Escheverria et al. 1991; Rahill et al. 1996). 

Agency Contact (Chemical Manager): Alfred Dorsey 
TOLUENE A-10 

APPENDIX A 

MINIMAL RISK LEVEL (MRL) WORKSHEET 

Chemical name: Toluene 

CAS number: 108-88-3 

Date: June 8, 2000 

Profile status: Post-public Draft 3/Camera Ready 

Route: [ ] Inhalation [X] Oral 

Duration: [ ] Acute [X ]Intermediate [ ] Chronic 

Key to figure: 29 

Species: mouse 

MRL: 0.02 [X] mg/kg/day [ ] ppm [ ] mg/m3 

Reference: Hsieh GC, Sharma RP, Parker RDR et al. 1990b. Evaluation of toluene exposure via drinking 

water on levels of regional brain biogenic monoamines and their metabolites in CD-1 mice. Ecotox 

Environ Safety 20: 175–184. 

Experimental design: Male CD-1 mice (5 per group) were administered toluene in their drinking water for 

a 28-day period. Based on water consumption and average toluene concentrations, the authors calculated 

toluene doses for the four treatment doses of 0, 5, 22, and 105 mg/kg/day over this period. Brain levels of 

norepinephrine, dopamine, serotonin, 3-methoxy-4-hydroxymandelic acid, 3,4-dihydroxyphenylacetic 

acid, homovanillic acid, and 5-hydroxyindolacetic acid were measured in six areas of the brain in the 

mice. A level of P<0.05 was considered statistically significant unless otherwise stated. 

Effects noted in study and corresponding doses: Significant increases in norepinephrin were present in the 

hypothalamus and in the midbrain in groups treated with 5, 22, and 105 mg/kg/day toluene. Toluene also 

increased serotonin levels, with the increase being maximal at 22 mg/kg/day in the midbrain (P<0.005) 

and cerebral cortex (P<0.005). A significant increase was also seen in the hypothalamus with 

norepinephrine, dopamine, and serotonin (P<0.005). In the corpus striatum, the levels of dopamine and 

serotonin were significantly increased at the two highest doses. In the medulla oblongata, significant 

toluene increases of norepinephrine and homovanillic acid were seen only at 22 mg/kg/day. 

Dose endpoint used for MRL derivation: 5 mg/kg/day for neurological effects 

[ ] NOAEL [x] LOAEL 

Uncertainty factors used in MRL derivation: 

[ ] 1 [x ] 3 [ ] 10 (for use of a minimal LOAEL)
 

[ ] 1 [ ] 3 [ x] 10 (for extrapolation from animals to humans)
 

[ ] 1 [ ] 3 [x] 10 (for human variability)
 

MRL = 5 mg/kg/day ÷ 300 = 0.02 mg/kg/day
 

Was a conversion factor used from ppm in food or water to a mg/body weight dose? No.
 

If so, explain: 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: Not 

applicable. 
TOLUENE A-11 

APPENDIX A 

Was a conversion used from intermittent to continuous exposure? No. 

Other additional studies or pertinent information that lend support to this MRL: The effects reported in 

the Hsieh et al. (1990b) study are minimal effects, and it is unclear how they are related to 

neurobehavioral changes. These results support the possible involvement of monoamine metabolism in 

the reported behavioral and neurophysiological effects of toluene. Alterations in the brain concentrations 

of neurotransmitters and their metabolites have been correlated with abnormal behavioral and 

physiological functions. 

Although no additional intermediate oral animal studies are available on the neurological effects of 

toluene, a number of animal inhalation studies have reported neurological effects from toluene (Arito et 

al. 1988; Bushnell et al. 1994; Carpenter et al. 1986; Harabuchi et al. 1993; Hinman 1987). Human 

inhalation studies have shown the central nervous system to be the major endpoint for toluene exposure 

(Andersen et al. 1983; Baelum et al. 1985; Escheverria et al. 1991; Rahill et al. 1996). 

An additional study that lends support to the MRL is a developmental study in which impaired rotorod 

performance and motor coordination were reported in the offspring of mice exposed to 4, 21, and 

106 mg/kg/day (Kostas and Hotchin 1981). Pregnant mice were exposed to toluene in their drinking water 

throughout pregnancy and lactation. From weaning at 21 days of age until postnatal day 55, the pups were 

exposed to toluene in their drinking water. The dose levels received by the pups cannot be accurately 

determined because the exposure occurred in utero, during lactation, and also via drinking water. The 

neurobehavioral effects reported in the offspring support the MRL; however, the impairment of rotorod 

performance was not dose-related. 

Agency Contact (Chemical Manager): Alfred Dorsey 

TOLUENE 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 

Tables and figures for Levels of Significant Exposure (LSE) 

Tables (2-1, 2-2, and 2-3) and Figures (2-1 and 2-2) 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, minimal risk levels 

(MRLs) to humans for noncancer end points, and EPA's estimated range associated with an upper- bound 

individual lifetime cancer risk of 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 No-Observed-Adverse- Effect Levels 

(NOAELs), Lowest-Observed-Adverse-Effect Levels (LOAELs), or Cancer Effect Levels (CELs). 

The legends presented below demonstrate the application of these tables and figures. Representative 

examples of LSE Table 2-1 and Figure 2-1 are shown. The numbers in the left column of the legends 

correspond to the numbers in the example table and figure. 

LEGEND 

See LSE Table 2-1 

(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. 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 2-1, 2-2, and 2-3, respectively). LSE figures are limited to the inhalation (LSE Figure 2-1) 

and oral (LSE Figure 2-2) routes. Not all substances will have data on each route of exposure and 

will not therefore have all five of the tables and figures. 
TOLUENE B-2 

APPENDIX B 

(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 2 

"18r" data points in Figure 2-1). 

(5)	 Species The test species, whether animal or human, are identified in this column. Section 2.5, 

"Relevance to Public Health," covers the relevance of animal data to human toxicity and 

Section 2.3, "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 1,1,2,2-tetrachloroethane via 

inhalation for 6 hours per day, 5 days per week, for 3 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, 1 systemic effect (respiratory) was investigated. 

(8)	 NOAEL A No-Observed-Adverse-Effect Level (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"). 

(9)	 LOAEL A Lowest-Observed-Adverse-Effect Level (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 endpoint 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 8 of the profile. 

(11)	 CEL A Cancer Effect Level (CEL) is the lowest exposure level associated with the onset of 

carcinogenesis in experimental or epidemiologic studies. CELs are always considered serious 
TOLUENE B-3 

APPENDIX B 

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 the NOAEL of 3 ppm in key number 18 was used to derive an 

MRL of 0.005 ppm. 

LEGEND 

See Figure 2-1 

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 intermediate and chronic 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, 18r NOAEL is the critical endpoint for which an intermediate inhalation 

exposure MRL is based. As you can see from the LSE figure key, the open-circle symbol indicates 

to a NOAEL for the test species-rat. 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 1 of 3 studies for which Cancer Effect Levels were derived. The diamond 

symbol refers to a Cancer Effect Level 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 

upper-bound for lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. These risk levels are derived 

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. 
2 

SAMPLE

6 TABLE 2-1. Levels of Significant Exposure to [Chemical x] – Inhalation 1 

3 4 

Exposure LOAEL (effect)

Key to frequency/ NOAEL Less serious (ppm) Serious (ppm) figurea Species duration System (ppm) 

6 INTERMEDIATE EXPOSURE 

5 6 7 8 9 

6 Systemic 9 9 9 9 9 

6 18 Rat 13 wk Resp 3b 10 (hyperplasia) 

5d/wk 6hr/d 

CHRONIC EXPOSURE 

11 

Cancer 938 Rat 18 mo 20 (CEL, multiple 

5d/wk organs) 7hr/d 

39 Rat 89–104 wk 10 (CEL, lung tumors, 

5d/wk nasal tumors) 6hr/d 

40 Mouse 79–103 wk 10 (CEL, lung tumors, 

5d/wk hemangiosarcomas6hr/d 

a The number corresponds to entries in Figure 2-1. 

6 b Used to derive an intermediate inhalation Minimal Risk Level (MRL) of 5 x 10-3 ppm; dose adjusted for intermittent exposure 

uncertainty factor of 100 (10 for extrapolation from animal to humans, 10 for human variability). 

CEL = cancer effect level; d = days(s); hr = hour(s); LOAEL = lowest-observed-adverse-effect level; mo = month(s); NOAEL = effect level; Resp = respiratory; wk = week(s) 

12 

TOLUENE B-6 

APPENDIX B 

Chapter 2 (Section 2.5) 

Relevance to Public Health 

The Relevance to Public Health section provides a health effects summary based on evaluations of 

existing toxicologic, epidemiologic, and toxicokinetic information. This summary is designed to present 

interpretive, weight-of-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 section covers end points in the same order they appear within the Discussion of Health Effects by 

Route of Exposure section, by route (inhalation, oral, 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 section. If data are located in the scientific literature, a table of genotoxicity information is 

included. 

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 Data Needs section. 

Interpretation of Minimal Risk Levels 

Where sufficient toxicologic information is available, we have derived minimal risk levels (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. They 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 2.5, "Relevance to Public Health," contains basic information known about the substance. Other
 

sections such as 2.8, "Interactions with Other Substances,” and 2.9, "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 the Environmental Protection Agency (EPA)
 

provides (Barnes and Dourson 1988) to determine reference doses for lifetime exposure (RfDs). 
TOLUENE B-7 

APPENDIX B 

To derive an MRL, ATSDR generally selects the most sensitive endpoint which, in its best judgement, 

represents the most sensitive human health effect for a given exposure route and duration. ATSDR 

cannot make this judgement 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 endpoint are available, ATSDR derives an MRL using the most sensitive 

species (when information from multiple species is available) with the highest 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 LSE tables. 

TOLUENE C-1 

APPENDIX C 

ACRONYMS, ABBREVIATIONS, AND SYMBOLS 

ACGIH American Conference of Governmental Industrial Hygienists 

ADI Acceptable Daily Intake 

ADME Absorption, Distribution, Metabolism, and Excretion 

AFID alkali flame ionization detector 

AFOSH Air Force Office of Safety and Health 

AML acute myeloid leukemia 

AOAC Association of Official Analytical Chemists 

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 

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 

CL ceiling limit value 

CLP Contract Laboratory Program 

cm centimeter 

CML chronic myeloid leukemia 

CNS central nervous system 

CPSC Consumer Products Safety Commission 

CWA Clean Water Act 

d day 

Derm dermal 

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 

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 
 

TOLUENE C-2 

APPENDIX C 

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 

ft foot 

FR Federal Register 

g gram 

GC gas chromatography 

Gd gestational day 

gen generation 

GLC gas liquid chromatography 

GPC gel permeation chromatography 

HPLC high-performance liquid chromatography 

hr hour 

HRGC high resolution gas chromatography 

HSDB Hazardous Substance Data Bank 

IDLH Immediately Dangerous to Life and Health 

IARC International Agency for Research on Cancer 

ILO International Labor Organization 

in inch 

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 

LCLo lethal concentration, low 

LC50 lethal concentration, 50% kill 

LDLo lethal dose, low 

LD50 lethal dose, 50% kill 

LT50 lethal time, 50% kill 

LOAEL lowest-observed-adverse-effect level 

LSE Levels of Significant Exposure 

m meter 

MA trans,trans-muconic acid 

MAL Maximum Allowable Level 

mCi millicurie 

MCL Maximum Contaminant Level 

MCLG Maximum Contaminant Level Goal 

mg milligram 

min minute 

mL milliliter 
TOLUENE C-3 

APPENDIX C 

mm millimeter 

mm Hg millimeters of mercury 

mmol millimole 

mo month 

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 

NCI National Cancer Institute 

NIEHS National Institute of Environmental Health Sciences 

NIOSH National Institute for Occupational Safety and Health 

NIOSHTIC NIOSH's Computerized Information Retrieval System 

NFPA National Fire Protection Association 

ng nanogram 

NLM National Library of Medicine 

nm nanometer 

NHANES National Health and Nutrition Examination Survey 

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 

OPPTS Office of Prevention, Pesticides and Toxic Substances, EPA 

OPPT Office of Pollution Prevention and Toxics, EPA 

OSHA Occupational Safety and Health Administration 

OSW Office of Solid Waste, EPA 

OTS Office of Toxic Substances 

OW Office of Water 

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 

PID photo ionization detector 
TOLUENE C-4 

APPENDIX C 

pg picogram 

pmol picomole 

PHS Public Health Service 

PMR proportionate mortality ratio 

ppb parts per billion 

ppm parts per million 

ppt parts per trillion 

PSNS Pretreatment Standards for New Sources 

REL recommended exposure level/limit 

RfC Reference Concentration 

RfD Reference Dose 

RNA ribonucleic acid 

RTECS Registry of Toxic Effects of Chemical Substances 

RQ Reportable Quantity 

SARA Superfund Amendments and Reauthorization Act 

SCE sister chromatid exchange 

sec second 

SIC Standard Industrial Classification 

SIM selected ion monitoring 

SMCL Secondary Maximum Contaminant Level 

SMR standard 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 Compound 

TPQ Threshold Planning Quantity 

TRI Toxics Release Inventory 

TSCA Toxic Substances Control Act 

TRI Toxics Release Inventory 

TWA time-weighted average 

U.S. United States 

UF uncertainty factor 

VOC Volatile Organic Compound 

yr year 

WHO World Health Organization 

wk week 

> greater than 

> greater than or equal to 

= equal to 

< less than 

< less than or equal to 

% percent α alpha β beta γ gamma δ delta 

μm micrometer 
TOLUENE C-5 

APPENDIX C 

μg microgram q1

* cancer slope factor 

– negative 

+ positive 

(+) weakly positive result 

(–) weakly negative result