TOXICOLOGICAL PROFILE FOR 

CYANIDE 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Public Health Service 

Agency for Toxic Substances and Disease Registry

July 2006 
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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. 
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UPDATE STATEMENT 

A Toxicological Profile for Cyanide, Draft for Public Comment was released in September 2004. This 

edition supersedes any previously released draft or final profile. 

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

status of previously released profiles, contact ATSDR at: 

Agency for Toxic Substances and Disease Registry

Division of Toxicology and Environmental Medicine/Applied Toxicology Branch 

1600 Clifton Road NE 

Mailstop F-32 

Atlanta, Georgia 30333 
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v 

FOREWORD 

This toxicological profile is prepared in accordance with guidelines developed by the Agency for Toxic 

Substances and Disease Registry (ATSDR) and the Environmental Protection Agency (EPA). The 

original guidelines were published in the Federal Register on April 17, 1987. Each profile will be revised 

and republished as necessary. 

The ATSDR toxicological profile succinctly characterizes the toxicologic and adverse health effects 

information for the hazardous substance described therein. Each peer-reviewed profile identifies and 

reviews the key literature that describes a hazardous substance’s toxicologic properties. Other pertinent 

literature is also presented, but is described in less detail than the key studies. The profile is not intended 

to be an exhaustive document; however, more comprehensive sources of specialty information are 

referenced. 

The focus of the profiles is on health and toxicologic information; therefore, each toxicological profile 

begins with a public health statement that describes, in nontechnical language, a substance’s relevant 

toxicological properties. Following the public health statement is information concerning levels of 

significant human exposure and, where known, significant health effects. The adequacy of information to 

determine a substance’s health effects is described in a health effects summary. Data needs that are of 

significance to protection of public health are identified by ATSDR and EPA. 

Each profile includes the following: 

(A) The examination, summary, and interpretation of available toxicologic information and 

epidemiologic evaluations on a hazardous substance to ascertain the levels of significant human 

exposure for the substance and the associated acute, subacute, and chronic health effects; 

(B) A determination of whether adequate information on the health effects of each substance 

is available or in the process of development to determine levels of exposure that present a 

significant risk to human health of acute, subacute, and chronic health effects; and 

(C) Where appropriate, identification of toxicologic testing needed to identify the types or 

levels of exposure that may present significant risk of adverse health effects in humans. 

The principal audiences for the toxicological profiles are health professionals at the Federal, State, and 

local levels; interested private sector organizations and groups; and members of the public. 

This profile reflects ATSDR’s assessment of all relevant toxicologic testing and information that has been 

peer-reviewed. Staff of the Centers for Disease Control and Prevention and other Federal scientists have 

also reviewed the profile. In addition, this profile has been peer-reviewed by a nongovernmental panel 

and was made available for public review. Final responsibility for the contents and views expressed in 

this toxicological profile resides with ATSDR. 
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*Legislative Background 

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

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

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

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

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

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

substances was announced in the Federal Register on December 7, 2005 (70 FR 72840). 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); November 17, 1997 (62 FR 61332); October 21, 1999(64 FR 56792); 

October 25, 2001 (66 FR 54014) and November 7, 2003 (68 FR 63098). Section 104(i)(3) of CERCLA, 

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

the list. 
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QUICK REFERENCE FOR HEALTH CARE PROVIDERS 

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

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

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

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

answers to often-asked questions. 

Primary Chapters/Sections of Interest 

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

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

toxicologic properties in a nontechnical, question-and-answer format, and it includes a review of 

the general health effects observed following exposure. 

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

and assesses the significance of toxicity data to human health. 

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

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

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

reported in this section. 

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

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

following exposure. 

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

issues: 

Section 1.6 How Can (Chemical X) Affect Children? 

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

Section 3.7 Children’s Susceptibility 

Section 6.6 Exposures of Children 

Other Sections of Interest: 

Section 3.8 Biomarkers of Exposure and Effect 

Section 3.11 Methods for Reducing Toxic Effects 

ATSDR Information Center 

Phone: 1-888-42-ATSDR or (404) 498-0110 Fax: (770) 488-4178 

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 
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Hazards; Skin Lesions and Environmental Exposures; Cholinesterase-Inhibiting Pesticide 

Toxicity; and numerous chemical-specific case studies. 

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

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

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

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

Medical Management Guidelines for Acute Chemical Exposures—is a guide for health care 

professionals treating patients exposed to hazardous materials. 

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

Other Agencies and Organizations 

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

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

workplace. Contact: NCEH, Mailstop F-29, 4770 Buford Highway, NE, Atlanta, 

GA 30341-3724 • Phone: 770-488-7000 • FAX: 770-488-7015. 

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

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

safety in the workplace, recommends standards to the Occupational Safety and Health 

Administration (OSHA) and the Mine Safety and Health Administration (MSHA), and trains 

professionals in occupational safety and health. Contact: NIOSH, 200 Independence Avenue, 

SW, Washington, DC 20201 • Phone: 800-356-4674 or NIOSH Technical Information Branch, 

Robert A. Taft Laboratory, Mailstop C-19, 4676 Columbia Parkway, Cincinnati, OH 45226-1998 

• Phone: 800-35-NIOSH. 

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

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

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

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

Referrals 

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

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

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

• FAX: 202-347-4950 • e-mail: AOEC@AOEC.ORG • Web Page: http://www.aoec.org/. 

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

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

environmental medicine. Contact: ACOEM, 25 Northwest Point Boulevard, Suite 700, Elk 

Grove Village, IL 60007-1030 • Phone: 847-818-1800 • FAX: 847-818-9266. 
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CONTRIBUTORS 

CHEMICAL MANAGER(S)/AUTHOR(S): 

Jessilynn Taylor, M.S. 

Nickolette Roney, MPH 

Carolyn Harper, Ph.D. 

ATSDR, Division of Toxicology and Environmental Medicine, Atlanta, GA 

Margaret E. Fransen, Ph.D. 

Steven Swarts, Ph.D. 

Syracuse Research Corporation, North Syracuse, NY 

THE PROFILE HAS UNDERGONE THE FOLLOWING ATSDR INTERNAL REVIEWS: 

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

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

end points. 

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

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

profile, and makes recommendations for derivation of MRLs. 

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

consistency across profiles and adherence to instructions in the Guidance. 

4. Green Border Review. Green Border review assures the consistency with ATSDR policy. 
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PEER REVIEW 

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

1. Dr. Arthur Gregory, President, Techto Enterprises, Luray, Virginia; 

2. Dr. Maryce Jacobs, President, Health Sciences Institute, Incorporated, Solomons, Maryland; and 

3. Dr. James Withey, Environmental Health Center Canada, Retired, Ottawa, Ontario, Canada. 

These experts collectively have knowledge of cyanide'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. 

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. 
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CONTENTS 

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

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

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

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

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

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

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

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

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

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

1.1 WHAT IS CYANIDE?................................................................................................................1 

1.2 WHAT HAPPENS TO CYANIDE WHEN IT ENTERS THE ENVIRONMENT?...................3 

1.3 HOW MIGHT I BE EXPOSED TO CYANIDE? .......................................................................4 

1.4 HOW CAN CYANIDE ENTER AND LEAVE MY BODY? ....................................................6 

1.5 HOW CAN CYANIDE AFFECT MY HEALTH? .....................................................................6 

1.6 HOW CAN CYANIDE AFFECT CHILDREN? ........................................................................ 8 

1.7 HOW CAN FAMILIES REDUCE THE RISK OF EXPOSURE TO CYANIDE? ....................9 

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

TO CYANIDE? ...........................................................................................................................9 

1.9 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH?...............................................................................................10 

1.10 WHERE CAN I GET MORE INFORMATION? .....................................................................11 

2. RELEVANCE TO PUBLIC HEALTH .................................................................................................13 

2.1 BACKGROUND AND ENVIRONMENTAL EXPOSURES TO CYANIDE IN THE 

UNITED STATES.....................................................................................................................13 

2.2 SUMMARY OF HEALTH EFFECTS......................................................................................14 

2.3 MINIMAL RISK LEVELS (MRLs) .........................................................................................18 

3. HEALTH EFFECTS..............................................................................................................................25 

3.1 INTRODUCTION.....................................................................................................................25 

3.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE ..................................25 

3.2.1 Inhalation Exposure ..............................................................................................................27 

3.2.1.1 Death ............................................................................................................................27 

3.2.1.2 Systemic Effects...........................................................................................................28 

3.2.1.3 Immunological and Lymphoreticular Effects...............................................................39 

3.2.1.4 Neurological Effects.....................................................................................................40 

3.2.1.5 Reproductive Effects....................................................................................................42 

3.2.1.6 Developmental Effects .................................................................................................42 

3.2.1.7 Cancer...........................................................................................................................42 

3.2.2 Oral Exposure........................................................................................................................42 

3.2.2.1 Death ............................................................................................................................42 

3.2.2.2 Systemic Effects...........................................................................................................43 

3.2.2.3 Immunological and Lymphoreticular Effects...............................................................59 

3.2.2.4 Neurological Effects.....................................................................................................59 

3.2.2.5 Reproductive Effects....................................................................................................63 
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3.2.2.6 Developmental Effects .................................................................................................64 

3.2.2.7 Cancer...........................................................................................................................65 

3.2.3 Dermal Exposure...................................................................................................................66 

3.2.3.1 Death ............................................................................................................................66 

3.2.3.2 Systemic Effects...........................................................................................................66 

3.2.3.3 Immunological and Lymphoreticular Effects...............................................................71 

3.2.3.4 Neurological Effects.....................................................................................................71 

3.2.3.5 Reproductive Effects....................................................................................................72 

3.2.3.6 Developmental Effects .................................................................................................72 

3.2.3.7 Cancer...........................................................................................................................72 

3.3 GENOTOXICITY .....................................................................................................................72 

3.4 TOXICOKINETICS..................................................................................................................75 

3.4.1 Absorption.............................................................................................................................75 

3.4.1.1 Inhalation Exposure......................................................................................................75 

3.4.1.2 Oral Exposure...............................................................................................................76 

3.4.1.3 Dermal Exposure ..........................................................................................................77 

3.4.2 Distribution ...........................................................................................................................77 

3.4.2.1 Inhalation Exposure......................................................................................................77 

3.4.2.2 Oral Exposure...............................................................................................................78 

3.4.2.3 Dermal Exposure ..........................................................................................................79 

3.4.3 Metabolism............................................................................................................................80 

3.4.4 Elimination and Excretion.....................................................................................................84 

3.4.4.1 Inhalation Exposure......................................................................................................84 

3.4.4.2 Oral Exposure...............................................................................................................84 

3.4.4.3 Dermal Exposure ..........................................................................................................85 

3.4.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models .............85 

3.5 MECHANISMS OF ACTION .................................................................................................. 87 

3.5.1 Pharmacokinetic Mechanisms...............................................................................................88 

3.5.2 Mechanisms of Toxicity........................................................................................................90 

3.5.3 Animal-to-Human Extrapolations.........................................................................................98 

3.6 TOXICITIES MEDIATED THROUGH THE NEUROENDOCRINE AXIS ..........................99 

3.7 CHILDREN’S SUSCEPTIBILITY.........................................................................................100 

3.8 BIOMARKERS OF EXPOSURE AND EFFECT ..................................................................103 

3.8.1 Biomarkers Used to Identify or Quantify Exposure to Cyanide .........................................104 

3.8.2 Biomarkers Used to Characterize Effects Caused by Cyanide ...........................................106 

3.9 INTERACTIONS WITH OTHER CHEMICALS ..................................................................107 

3.10 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE............................................. 111 

3.11 METHODS FOR REDUCING TOXIC EFFECTS................................................................. 112 

3.11.1 Reducing Peak Absorption Following Exposure ............................................................113 

3.11.2 Reducing Body Burden...................................................................................................113 

3.11.3 Interfering with the Mechanism of Action for Toxic Effects .........................................114 

3.12 ADEQUACY OF THE DATABASE......................................................................................118 

3.12.1 Existing Information on Health Effects of Cyanide........................................................118 

3.12.2 Identification of Data Needs ...........................................................................................120 

3.12.3 Ongoing Studies..............................................................................................................128 

4. CHEMICAL AND PHYSICAL INFORMATION..............................................................................130 

4.1 CHEMICAL IDENTITY.........................................................................................................131 

4.2 PHYSICAL AND CHEMICAL PROPERTIES......................................................................131 
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5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL..........................................................141 

5.1 PRODUCTION .......................................................................................................................141 

5.2 IMPORT/EXPORT .................................................................................................................146 

5.3 USE..........................................................................................................................................146 

5.4 DISPOSAL..............................................................................................................................149 

6. POTENTIAL FOR HUMAN EXPOSURE .........................................................................................153 

6.1 OVERVIEW............................................................................................................................153 

6.2 RELEASES TO THE ENVIRONMENT................................................................................157 

6.2.1 Air .......................................................................................................................................158 

6.2.2 Water...................................................................................................................................159 

6.2.3 Soil ......................................................................................................................................165 

6.3 ENVIRONMENTAL FATE....................................................................................................166 

6.3.1 Transport and Partitioning...................................................................................................166 

6.3.2 Transformation and Degradation ........................................................................................169 

6.3.2.1 Air...............................................................................................................................169 

6.3.2.2 Water ..........................................................................................................................172 

6.3.2.3 Sediment and Soil.......................................................................................................176 

6.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT...............................177 

6.4.1 Air .......................................................................................................................................178 

6.4.2 Water...................................................................................................................................178 

6.4.3 Sediment and Soil ...............................................................................................................181 

6.4.4 Other Environmental Media................................................................................................182 

6.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE .....................................186 

6.6 EXPOSURES OF CHILDREN...............................................................................................191 

6.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES ...........................................192 

6.8 ADEQUACY OF THE DATABASE......................................................................................193 

6.8.1 Identification of Data Needs ...............................................................................................194 

6.8.2 Ongoing Studies ..................................................................................................................199 

7. ANALYTICAL METHODS ...............................................................................................................201 

7.1 BIOLOGICAL MATERIALS.................................................................................................201 

7.2 ENVIRONMENTAL SAMPLES............................................................................................ 206 

7.3 ADEQUACY OF THE DATABASE......................................................................................217 

7.3.1 Identification of Data Needs ...............................................................................................217 

7.3.2 Ongoing Studies ..................................................................................................................219 

8. REGULATIONS AND ADVISORIES ...............................................................................................220 

9. REFERENCES ....................................................................................................................................229 

10. GLOSSARY ......................................................................................................................................291 
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APPENDICES 

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

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

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

D. INDEX ................................................................................................................................................D-1 
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LIST OF FIGURES 

3-1. Levels of Significant Exposure to Cyanide—Inhalation .................................................................... 33 

3-2. Levels of Significant Exposure to Cyanide—Oral ............................................................................. 50 

3-3. Basic Processes Involved in the Metabolism of Cyanide ...................................................................81 

3-4. Minor Path for the Removal of Cyanide from the Body .................................................................... 83 

3-5. Conceptual Representation of a Physiologically Based Pharmacokinetic (PBPK) Model for a 

Hypothetical Chemical Substance......................................................................................................87 

3-6. Existing Information on Health Effects of Cyanide .........................................................................119 

6-1. Frequency of NPL Sites with Cyanide Contamination.....................................................................154 
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LIST OF TABLES 

3-1. Levels of Significant Exposure to Cyanide—Inhalation .................................................................... 29 

3-2. Levels of Significant Exposure to Cyanide—Oral ............................................................................. 44 

3-3. Levels of Significant Exposure to Cyanide—Dermal ........................................................................ 67 

3-4. Genotoxicity of Cyanide In Vitro .......................................................................................................74 

4-1. Chemical Identity of Cyanide and Compounds................................................................................132 

4-2. Physical and Chemical Properties of Cyanide and Compounds.......................................................135 

5-1. Facilities that Produce, Process, or Use Hydrogen Cyanide.............................................................143 

5-2. Facilities that Produce, Process, or Use Cyanide Compounds.........................................................144 

5-3. Import and Export Volumes of Cyanide Compounds in 2004 ......................................................... 147 

6-1. Releases to the Environment from Facilities that Produce, Process, or Use Hydrogen Cyanide .....160 

6-2. Releases to the Environment from Facilities that Produce, Process, or Use Cyanide 

Compounds.......................................................................................................................................162 

6-3. Environmental Transformation Products of Cyanide Compounds by Medium ...............................170 

6-4. Cyanide and Thiocyanate Concentrations (μg/mL) in Smokers and Nonsmokers...........................190 

7-1. Analytical Methods for Determining Cyanide in Biological Samples .............................................202 

7-2. Analytical Methods for Determining Biomarkers for Cyanide ........................................................207 

7-3. Analytical Methods for Determining Cyanide in Environmental Samples......................................208 

7-4. Analytical Methods for Determining Environmental Degradation Products of Cyanide.................215 

8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide Compounds................................222 
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CYANIDE 1 

1. PUBLIC HEALTH STATEMENT 

This public health statement tells you about cyanide and the effects of exposure to it. 

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

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

long-term federal clean-up activities. Cyanide has been found in at least 471 of the 1,662 current 

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

known, the possibility exists that the number of sites at which cyanide is found may increase in 

the future as more sites are evaluated. This information is important because these sites may be 

sources of exposure and exposure to this substance may harm you. 

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

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

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

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

If you are exposed to cyanide, many factors will determine whether you will be harmed. These 

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

it. You must also consider any other chemicals you are exposed to and your age, sex, diet, 

family traits, lifestyle, and state of health. 

1.1 WHAT IS CYANIDE? 

Cyanide is a chemical group consisting of one atom of carbon connected to one atom of nitrogen 

by three molecular bonds (C≡N) and cyanides are compounds (substances formed by the joining 

of two or more atoms) that contain a cyanide group (typically shown as CN). Cyanides can both 

occur naturally or be man-made and many are powerful and rapid-acting poisons. Hydrogen 

cyanide (HCN), which is a gas, and the simple cyanide salts (sodium cyanide and potassium 

cyanide) are common examples of cyanide compounds. Certain bacteria, fungi, and algae can 
CYANIDE 2 

1. PUBLIC HEALTH STATEMENT 

produce cyanide, and cyanide is found in a number of foods and plants. In certain plant foods, 

including almonds, millet sprouts, lima beans, soy, spinach, bamboo shoots, and cassava roots 

(which are a major source of food in tropical countries), cyanides occur naturally as part of 

sugars or other naturally-occurring compounds. However, the edible parts of plants that are 

eaten in the United States, including tapioca which is made from cassava roots, contain relatively 

low amounts of cyanide. 

Many of the cyanides in soil and water come from industrial processes. The major sources of 

cyanides in water are discharges from some metal mining processes, organic chemical industries, 

iron and steel plants or manufacturers, and publicly owned wastewater treatment facilities. Other 

cyanide sources include vehicle exhaust, releases from certain chemical industries, burning of 

municipal waste, and use of cyanide-containing pesticides. Much smaller amounts of cyanide 

may enter water through storm water runoff where road salts are used that contain cyanide. 

Cyanide in landfills can contaminate underground water. Hydrogen cyanide, sodium cyanide, 

and potassium cyanide are the forms of cyanide most likely to be in the environment as a result 

of industrial activities. Hydrogen cyanide is a colorless gas with a faint, bitter, almond-like odor. 

Sodium cyanide and potassium cyanide are both white solids with a slight, bitter, almond-like 

odor in damp air. Cyanide salts and hydrogen cyanide are used in electroplating, metallurgy, 

organic chemicals production, photographic developing, manufacture of plastics, fumigation of 

ships, and some mining processes. Hydrogen cyanide has also been used in gas-chamber 

executions and as a war gas. Chlorination of water contaminated with cyanide produces the 

compound cyanogen chloride. Four incidents of cyanide in soil resulted from disposal of 

cyanide-containing wastes in landfills and use of cyanide-containing road salts. See 

Chapters 4 and 5 for more information about physical and chemical properties and about 

production and use of cyanide. 

Thiocyanates are a group of compounds formed from a combination of sulfur, carbon, and 

nitrogen. Thiocyanates are found in various foods and plants; they are produced primarily from 

the reaction of free cyanide with sulfur. This reaction occurs in the environment (for example, in 

industrial waste streams that contain cyanide) and in the human body after cyanide is swallowed 

or absorbed. Thiocyanate is the major product formed from cyanide that passes into the body as 
CYANIDE 3 

1. PUBLIC HEALTH STATEMENT 

the body attempts to rid itself of cyanide. Although thiocyanates are less harmful than cyanide in 

humans, they are known to affect the thyroid glands, reducing the ability of the gland to produce 

hormones that are necessary for the normal function of the body. 

Ammonium thiocyanate is used in antibiotic preparations, pesticides, liquid rocket fuels, 

adhesives, and matches. It also is used in photographic processes, to improve the strength of 

silks, and as a weed killer. 

Thiocyanates are present in water primarily because of discharges from coal processing, 

extraction of gold and silver, and mining industries. Thiocyanates in soil result from direct 

application of herbicides (weed killers), insecticides, and rodenticides and from disposal of 

byproducts from industrial processes. Less important sources include release from damaged or 

decaying tissues of certain plants, such as mustard, kale, and cabbage. 

1.2 WHAT HAPPENS TO CYANIDE WHEN IT ENTERS THE ENVIRONMENT? 

Cyanide enters air, water, and soil from both natural processes and industrial activities. Airborne 

cyanide is generally far below levels that would cause concern. In air, cyanide is present mainly 

as gaseous hydrogen cyanide. A small amount of cyanide in air is present as fine dust particles. 

This dust eventually settles over land and water. Rain and snow help remove cyanide particles 

from air. The gaseous hydrogen cyanide is not easily removed from the air by settling, rain, or 

snow. The half-life (the time needed for half of the material to be removed) of hydrogen cyanide 

in the atmosphere is about 1–3 years. Most cyanide in surface water will form hydrogen cyanide 

and evaporate. However, the amount of hydrogen cyanide formed is generally not enough to be 

harmful to humans. Some cyanide in water will be transformed into less harmful chemicals by 

microorganisms (plants and animals of very small size), or will form a complex with metals, 

such as iron. The half-life of cyanide in water is not known. Cyanide in water does not build up 

in the bodies of fish. 

Cyanides are fairly mobile in soil. Once in soils, cyanide can be removed through several 

processes. Some cyanide compounds in soil can form hydrogen cyanide and evaporate, whereas 
CYANIDE 4 

1. PUBLIC HEALTH STATEMENT 

some cyanide compounds will be transformed into other chemical forms by microorganisms in 

soil. Consequently, cyanides usually do not seep into underground water. However, cyanide has 

been detected in underground waters of a few landfills and industrial waste disposal sites. At the 

high concentrations found in some landfill leachates (water that seeps through landfill soil) and 

in the wastes stored in some disposal sites, cyanide becomes toxic to soil microorganisms. 

Because these microorganisms can no longer change cyanide to other chemical forms, cyanide is 

able to passes through soil into underground water. See Chapters 5 and 6 for more information 

about what happens to cyanide in the environment. 

Less is known about what happens to thiocyanate when it enters the environment. In soil and 

water, thiocyanate is changed into other chemical forms by microorganisms. This occurs in soil 

mainly at temperatures up to 86 °F (30 °C). At these temperatures, thiocyanate in soil does not 

undergo much evaporation or sorption (binding to soil). See Chapters 5 and 6 for more 

information about what happens to thiocyanate in the environment. 

1.3 HOW MIGHT I BE EXPOSED TO CYANIDE? 

You can be exposed to cyanides by breathing air and drinking water, touching soil or water 

containing cyanide, or eating foods that contain cyanide. Many plant materials, such as cassava 

roots, lima beans, and almonds, naturally contain low-to-moderate levels of cyanide. The 

concentration of hydrogen cyanide in unpolluted air is less than 0.2 parts of hydrogen cyanide 

per million (ppm; 1 ppm is equivalent to 1 part by volume of hydrogen cyanide in a million parts 

by volume of air). The concentration of cyanide in drinking water ranges from 0.001 to 

0.011 ppm (1 ppm is equivalent to 1 part by weight in 1 million parts by volume of water) in the 

United States and Canada. Cyanogen chloride, which can be formed in the process of water 

chlorination, has been found at concentrations ranging from 0.00045 to 0.0008 ppm in drinking 

water from 35 U.S. cities. We do not know how many people in the general population of the 

United States are exposed to significant amounts of cyanide from eating foods that naturally 

contain it. Smoking is probably one of the major sources of cyanide exposure for people who do 

not work in cyanide-related industries. Breathing smoke-filled air during fires also may be a 
CYANIDE 5 

1. PUBLIC HEALTH STATEMENT 

major source of cyanide exposure. People who live near hazardous waste sites that contain 

cyanide may be exposed to higher amounts of cyanide than the general population. 

Cyanide is used or produced in various occupational settings where activities include 

electroplating, some metal mining processes, metallurgy, metal cleaning, certain pesticide 

applications, tanning, photography and photoengraving, firefighting, and gas works operations. 

Cyanide also is used in some dye and pharmaceutical industries. The National Occupational 

Exposure Survey (NOES) has estimated the numbers of workers potentially exposed to the 

following cyanides: 4,005 to hydrogen cyanide; 66,493 to sodium cyanide; 64,244 to potassium 

cyanide; 3,215 to potassium silver cyanide; 3,606 to calcium cyanide; 22,339 to copper (I) 

cyanide; and 1,393 to cyanogen chloride. See Chapter 6 for more information about exposure to 

cyanide. 

You can be exposed to thiocyanate in the same ways that you can be exposed to cyanide. 

Exposure to cyanide will expose you to thiocyanate because your body changes toxic cyanide to 

the much less toxic thiocyanate. Many foods (plants, dairy products, meat) contain thiocyanate. 

People who work in cyanide-related industries, such as the manufacture of electronic computing 

equipment, commercial printing, photographic processes, hospitals, production of adhesives, and 

construction and furniture manufacture, may be exposed to thiocyanate. No information is 

available about the concentrations of thiocyanate in unpolluted air or drinking water. We do not 

know how many people in the general U.S. population are exposed to significant amounts of 

thiocyanate from eating foods that contain thiocyanate. People who smoke or breathe tobacco 

smoke in the environment can be exposed to high levels of thiocyanate. People who live near 

hazardous waste sites that contain thiocyanate potentially can be exposed to higher amounts of 

thiocyanate compared with nonsmokers in the general population. The National Occupational 

Exposure Survey (NOES) estimates that 90,599 workers potentially are exposed to ammonium 

thiocyanate. 
CYANIDE 6 

1. PUBLIC HEALTH STATEMENT 

1.4 HOW CAN CYANIDE ENTER AND LEAVE MY BODY? 

Cyanide can enter your body if you breathe air, eat food, or drink water that contains it. Cyanide 

can enter your body through the skin, but this may occur only in people who work in cyaniderelated industries without adequate protective gear. You can be exposed to contaminated water, 

air, or soil at hazardous waste sites. Once it is in your lungs or stomach, cyanide can quickly 

enter the bloodstream. Some of the cyanide is changed to thiocyanate, which is less harmful and 

leaves the body in the urine. A small amount of cyanide is converted in the body to carbon 

dioxide, which leaves the body in the breath. At low levels of exposure to cyanide compounds, 

most of the cyanide and its products leave the body within the first 24 hours after exposure. The 

way cyanide enters and leaves the body is similar in people and animals. You can find more 

information about the movement of cyanide in the body in Chapter 3. 

1.5 HOW CAN CYANIDE AFFECT MY HEALTH? 

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

ways for treating persons who have been harmed. 

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

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

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

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

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

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

laws today protect the welfare of research animals. 

Exposure to small amounts of cyanide can be deadly regardless of the route of exposure. The 

severity of the harmful effects depends in part on the form of cyanide, such as hydrogen cyanide 

gas or cyanide salts. Exposure to high levels of cyanide for a short time harms the brain and 

heart and can even cause coma and death. Cyanide produces toxic effects at levels of 

0.05 milligrams of cyanide per deciliter of blood (mg/dL) or higher, and deaths have occurred at 
CYANIDE 7 

1. PUBLIC HEALTH STATEMENT 

levels of 0.3 mg/dL and higher (a deciliter equals 100 milliliters). People who breathed 546 ppm 

of hydrogen cyanide have died after a 10-minute exposure; 110 ppm of hydrogen cyanide was 

life-threatening after a 1-hour exposure. People who eat small amounts of cyanide compounds in 

a short time may die unless they quickly receive antidote therapy. 

Some of the first indications of cyanide poisoning are rapid, deep breathing and shortness of 

breath, followed by convulsions (seizures) and loss of consciousness. These symptoms can 

occur rapidly, depending on the amount eaten. The health effects of large amounts of cyanide 

are similar, whether you eat, drink, or breathe it; cyanide uptake into the body through the skin is 

slower than these other types of exposure. Skin contact with hydrogen cyanide or cyanide salts 

can irritate and produce sores. Workers who breathed in amounts of hydrogen cyanide as low as 

6–10 ppm over a period of time developed breathing difficulties, chest pain, vomiting, blood 

changes, headaches, and enlargement of the thyroid gland. 

Use of cassava roots as a primary food source has led to high blood cyanide levels in some 

people in tropical countries. Some of them suffered harmful effects to the nervous system, 

including weakness of the fingers and toes, difficulty walking, dimness of vision, and deafness, 

but chemicals other than cyanide also could have contributed to these effects. Cyanide exposure 

from cassava was linked to poor functioning and later enlargement of the thyroid gland; this is 

because in the body, cyanide is converted to thiocyanate, which is toxic to the thyroid gland. 

These effects have not been seen at levels of cyanide usually found in foods in the United States. 

Cyanide has not been reported to directly cause reproductive problems in people. Harmful 

effects on the reproductive system occurred in rats and mice that drank water containing sodium 

cyanide. Other cyanide effects in animal studies were similar to those observed in people. 

Cyanide has not been reported to cause cancer in people or animals. EPA has determined that 

cyanide is not classifiable as to its human carcinogenicity (ability to cause cancer in humans). 

Vitamin B12, a natural chemical containing cyanide, is beneficial to your body because it 

prevents anemia (iron-poor blood). The cyanide binds in vitamin B12 so that it does not serve as 

a source of cyanide exposure and cannot harm you. You can find more information about the 

harmful effects of cyanide in Chapter 3. 
CYANIDE 8 

1. PUBLIC HEALTH STATEMENT 

1.6 HOW CAN CYANIDE AFFECT CHILDREN? 

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

conception to maturity at 18 years of age. 

Like adults, children can be exposed to cyanide by breathing air, drinking water, touching soil or 

water, or eating foods that contain cyanide, but the amounts are usually low. Breathing secondhand tobacco smoke is a more important source of cyanide exposure for children. Serious 

exposures can occur when children accidentally eat certain fruit pits, such as apricot kernels, 

containing a cyanide-releasing substance. A high blood level of thiocyanate is a sign of cyanide 

exposure in children, as well as adults. If a pregnant mother is exposed to cyanide, for example, 

by exposure to tobacco smoke, the fetus will be exposed to both cyanide and thiocyanate 

crossing the placenta. Animal studies show that cyanide and thiocyanate can be transferred into 

milk and pass to nursing baby animals, and suggest that this may also occur in humans. 

Effects reported in exposed children are like those seen in exposed adults. Children who ate 

large quantities of apricot pits, which naturally contain cyanide as part of complex sugars, had 

rapid breathing, low blood pressure, headaches, and coma, and some died. Cyanide has not been 

reported to directly cause birth defects in people. However, among people in the tropics who eat 

cassava root, children have been born with thyroid disease because of the mothers' exposure to 

cyanide and thiocyanate during pregnancy. Birth defects occurred in rats that ate cassava root 

diets, and harmful effects on the reproductive system occurred in rats and mice that drank water 

containing sodium cyanide. 

More information on the effects of cyanide exposure in children can be found in Section 3.7. 
CYANIDE 9 

1. PUBLIC HEALTH STATEMENT 

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

If your doctor finds that you have been exposed to cyanide, ask whether your children might also 

have been exposed. Your doctor might need to ask your state health department to investigate. 

Families can reduce their exposure to cyanide by not breathing in tobacco smoke, which is the 

most common source of cyanide exposure for the general population. In the event of a building 

fire, families should evacuate the building immediately, because smoke from burning plastics 

contains cyanide (and carbon monoxide). Breathing this smoke can lead to unconsciousness or 

death. Cyanide in smoke can arise from the combustion of certain plastics (e.g., polyacrylamines, polyacrylics, polyurethane, etc.). 

Compounds that release cyanide are naturally present in plants. The amounts are usually low in 

the edible portion but are higher in cassava. Pits and seeds of common fruits, such as apricots, 

apples, and peaches, may have substantial amounts of cyanide-releasing chemicals, so people 

should avoid eating these pits and seeds to prevent accidental cyanide poisoning. Parents should 

teach their children not eat fruit pits and seeds. People should be aware that taking high levels of 

vitamin C may increase the danger of cyanide poisoning from fruit pits, because more cyanide is 

released from the pits. 

Studies have shown that the effects of cyanide are worse in humans and animals with poor 

nutrition. Diets containing adequate amounts of protein should improve recovery from cyanide 

exposure incidents. 

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

EXPOSED TO CYANIDE? 

Blood and urine levels of cyanide and thiocyanate can be measured, and small amounts of these 

compounds are always detectable in blood and urine because of natural processes. After cyanide 

poisoning, increased blood levels of cyanide and thiocyanate are detectable. Harmful effects can 

occur when blood levels of cyanide are higher than 0.05 parts per million (ppm), but some 
CYANIDE 10 

1. PUBLIC HEALTH STATEMENT 

effects can occur at lower levels. Tissue levels of cyanide can be measured if cyanide poisoning 

is suspected. However, cyanide and thiocyanate are cleared rapidly from the body in urine or 

exhaled breath; for that reason, blood measurements are only useful for detecting recent 

exposure. A bitter, almond-like odor in the breath may alert a physician that a person was 

exposed to cyanide, but this is not always found. In general, if cyanide exposure is suspected, 

treatment should be started immediately without waiting for the results of blood cyanide 

measurements. For more information about the health effects of cyanide and how it can be 

detected in the environment, see Chapters 3 and 7. 

1.9 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

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

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

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

agencies that develop regulations for toxic substances. Recommendations provide valuable 

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

Substances and Disease Registry (ATSDR) and the National Institute for Occupational Safety 

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

substances. 

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

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

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

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

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

factors. 

Recommendations and regulations are also updated periodically as more information becomes 

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

provides it. Some regulations and recommendations for cyanide include the following: 
CYANIDE 11 

1. PUBLIC HEALTH STATEMENT 

EPA sets regulations for the amount of cyanide allowed in drinking water. The highest amount 

allowed is 200 micrograms of cyanide per liter of water (μg/L or 0.2 ppm). EPA also sets limits 

for amounts of hydrogen cyanide in stored foods that have been treated with cyanide to control 

pests. The maximum amount allowed on citrus fruits is 50 ppm. EPA also requires industries to 

report spills of 1 pound or more of potassium silver cyanide and 10 pounds or more of hydrogen 

cyanide, potassium cyanide, sodium cyanide, calcium cyanide, or copper cyanide. 

OSHA sets levels of cyanide that are allowable in workplace air. The permissible exposure limit 

for hydrogen cyanide (HCN) and most cyanide salts is 10 ppm or 11 milligrams of cyanide per 

cubic meter of air (mg/m3) averaged over an 8-hour workday and 40-hour workweek. NIOSH 

sets guidelines (recommended exposure limits or RELs) for chemicals in workplace air. The 

short-term REL for hydrogen cyanide is 4.7 ppm or 5 mg/m3, averaged over 15 minutes and not 

to be exceeded at any time in the workday. There is a 10-minute ceiling limit for most cyanide 

salts of 4.7 ppm or 5 mg/m3. NIOSH also determines levels that are immediately dangerous to 

life and health (IDLH) if a worker is exposed for more than half an hour. IDLH levels are 

50 ppm for hydrogen cyanide or 25 mg/m3 as cyanide for most cyanide salts. 

For more information about regulations and advisories for cyanide in the environment or 

workplace, see Chapter 8. 

1.10 WHERE CAN I GET MORE INFORMATION? 

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

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

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

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

hazardous substances. 
CYANIDE 12 

1. PUBLIC HEALTH STATEMENT 

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

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

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

atsdric@cdc.gov, or by writing to: 

Agency for Toxic Substances and Disease Registry 

 Division of Toxicology and Environmental Medicine 

1600 Clifton Road NE 

 Mailstop F-32 

 Atlanta, GA 30333 

 Fax: 1-770-488-4178 

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

National Technical Information Service (NTIS) 

5285 Port Royal Road 

 Springfield, VA 22161 

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

 Web site: http://www.ntis.gov/ 
CYANIDE 13 

2. RELEVANCE TO PUBLIC HEALTH 

2.1 BACKGROUND AND ENVIRONMENTAL EXPOSURES TO CYANIDE IN THE UNITED 

STATES 

Cyanides, a diverse family of compounds containing the highly reactive cyanide anion (CN–

), are 

produced from both anthropogenic and natural sources. The cyanide compounds most commonly found 

in the environment include sodium cyanide, potassium cyanide, and gaseous hydrogen cyanide, the latter 

being the main form present in air. The use of the term ‘cyanide’ in this section refers to the cyanide ion 

or the cyanogen radical (CN) in a compound. Cyanides may be released into the environment during the 

course of industrial usage or from smoke or vehicle exhaust containing the incomplete combustion 

products of nitrogen-containing organic polymers. Numerous plant species contain cyanogen glycosides 

that can release hydrogen cyanide upon biodegradation or ingestion. The edible portions of dietary plant 

species commonly used in the United States contain relatively low levels of cyanogen glycosides, 

although some pits and seeds of common fruits (e.g., apple, apricot, peach) contain significantly higher 

concentrations. The cassava root (tapioca), which is a major dietary staple in tropical countries, contains 

a sufficient amount of cyanogen glycosides to require special processing to reduce the danger of toxicity. 

The general population is exposed to cyanides primarily by ingestion of food and water, and to a lesser 

degree, by inhalation. The cyanide content in unpolluted air averages 0.160–0.166 ppm (0.180– 

0.187 mg/m3

). Cyanide levels in smoke from U.S. commercial cigarettes range from 10 to 

400 μg/cigarette for mainstream (inhaled) smoke and from 0.006 to 0.27 μg/cigarette for sidestream 

smoke. The cyanide content in 99.8% of public water systems using groundwater in the United States 

between 1993 and 1998 did not exceed the maximum concentration limit of 0.2 mg/L. Mean cyanide 

concentrations have been reported for some food products: cereal grains (0.002–0.45 μg/g), soy protein 

products (0.07–0.3 μg/g), canned unpitted fruits (0–4 μg/g), commercial fruit juices (1,900–4,600 μg/L), 

and U.S. lima beans (100–170 μg/g). There are no comprehensive data on the cyanide content of total 

diet samples in the United States, so it is not possible to estimate the average daily intake from foods. 

See Chapter 6 for more detailed information regarding concentrations of cyanide and cyanogenic 

compounds in environmental media. 
CYANIDE 14 

2. RELEVANCE TO PUBLIC HEALTH 

2.2 SUMMARY OF HEALTH EFFECTS 

The toxicity of individual cyanide compounds is dependent on the ease with which they release cyanide 

anion (CN–

). For example, cyanide radicals have a low affinity for alkali metals and a high affinity for 

ferric iron (Fe3+) and other metals; therefore, simple cyanide salts (for example, sodium cyanide or 

potassium cyanide) are toxic, whereas certain iron-containing cyanide compounds do not release CN– 

readily and are nearly nontoxic. Cyanide exerts its primary toxicological effects by binding to the 

metallic cofactor in metalloenzymes, thereby impairing enzyme and cell function. Cytochrome c oxidase 

(an enzyme in the mitochondrial respiratory chain) is the most significant target of cyanide exposure since 

its inhibition prevents tissues from using oxygen. The result is a reduction in oxygen sufficient to cause 

tissue damage (histiotoxic hypoxia) throughout the body, with the most vulnerable tissues being those 

with high oxygen demands and/or a deficiency in detoxifying enzymes such as rhodanese. The inhibition 

of oxygen use by cells causes oxygen tensions to rise in peripheral tissues; this results in a decrease in the 

unloading gradient for oxyhemoglobin. Thus, oxyhemoglobin is carried in the venous blood, which is 

one biomarker of cyanide exposure. In addition to binding to cytochrome c oxidase, cyanide inhibits 

catalase, peroxidase, hydroxocobalamin, phosphatase, tyrosinase, ascorbic acid oxidase, xanthine oxidase, 

and succinic dehydrogenase activities, which may also contribute to the signs of cyanide toxicity. 

Although the entire body is affected by cyanide exposure, adverse effects on the central nervous system 

are of the most consequence to the organism because of the high metabolic demand for oxygen in neurons 

and its control of respiratory function. Initial stimulation of carotid and aortic bodies and effects on the 

central nervous system adversely affect the function of the respiratory system, which contributes to the 

global histiotoxic hypoxia leading to death. Thus, the adverse affect of cyanide on respiration operates on 

both the cellular and physiological levels. High inhalation, oral, or dermal exposure levels result in 

convulsions, unconsciousness, and death due to inactivation of the centers controlling respiration. Lower 

exposures may result in headache or dizziness. 

The signs of cyanide toxicity at concentrations leading to death in humans are well described. 

Intoxication at ≥2,000 ppm hydrogen cyanide is characterized by a brief sensation of dryness and burning 

in the throat due to local irritation, a suffusing warmth, and a hunger for air. Hyperpnea, and sometimes a 

brief outcry, follows the first breath. In <1 minute, apnea, a few gasps, loss of consciousness, and 

convulsions occur. Cardiovascular failure may also occur, although the heart may continue to beat for 3– 

4 minutes after the last breath. Reported signs sometimes include a bitter almond-like odor on the breath 

and (in light-toned individuals) a rose-colored hue of the skin. The total absorbed dose of hydrogen 
CYANIDE 15 

2. RELEVANCE TO PUBLIC HEALTH 

cyanide in such rapid deaths can be as low as 0.7 mg/kg. Dyspnea has been observed in survivors of 

inhalation poisoning incidents, and renal dysfunction (anuria followed by polyuria) was observed in one 

fatal inhalation exposure case. Similar signs of respiratory distress and renal dysfunction (albuminuria) 

were reported following ingestion of high doses of cyanide salts. Within a few minutes after swallowing 

the toxicant, the victim collapses, frequently with a scream. Dyspnea, convulsions, and death from 

asphyxia follow. Dermal exposure to cyanide results in comparable effects, but at higher doses. Based 

on case report studies, the following acute median lethal exposure levels for humans were estimated: an 

LC50 of 524 ppm for a 10-minute inhalation exposure to hydrogen cyanide, an LD50 of 1.52 mg/kg for the 

oral route, and an LD50 of 100 mg/kg for the dermal route, assuming that CN–

 is readily released from the 

compound. Animal studies also report dyspnea, convulsions, and asphyxiation as effects of high-acute 

exposure to cyanide by any route of exposure. 

Nonlethal exposures to hydrogen cyanide gas produces upper respiratory irritation, cough, altered sense 

of smell, nasal congestion, epistaxis, hemoptysis, and dyspnea in exposed workers. Workers acutely 

exposed to cyanogen, which dissociates into hydrogen cyanide and hydrocyanic acid, experienced nasal 

irritation. Other effects observed at nonlethal exposure levels include hypotension, heart palpitations, 

precordial pains, nausea and vomiting resulting from central nervous system stimulation or direct contact 

with cyanide, and albinuria. Animal studies also report bradycardia, arrhythmia, and T-wave 

abnormalities, vomiting, increased blood urea nitrogen, and histopathology of the renal proximal tubular 

epithelium and glomeruli. Hepatic effects have not been reported in humans, but have been observed in 

some animal studies. 

Thyroid effects following cyanide exposure result from the interference of thiocyanate, a metabolite of 

cyanide, with iodine uptake and utilization in the thyroid gland. Reduced thyroid hormone levels, 

increasingly elevated levels of thyroid stimulating hormone, and goiter are typical sequelae of chronic 

cyanide exposure observed in tropical populations reliant on cassava as the main staple of the diet. The 

effects in these populations are intensified since cassava is a poor source of dietary protein. These 

conditions may not apply to populations in the United States since the varied diets provide levels of 

protein intake and general nutrition that are much higher than in countries using cassava as a food staple. 

Enlargement of the thyroid gland and increased levels of thyroid stimulating hormone were observed in 

workers exposed by inhalation to 6.4–15 ppm hydrogen cyanide. Thyroid toxicity was also reported in 

intermediate-duration oral studies in rats and pigs, but not in dogs because they are deficient in the 

enzyme rhodanese, which promotes thiocyanate formation. 
CYANIDE 16 

2. RELEVANCE TO PUBLIC HEALTH 

In tropical countries, maternal ingestion of cassava during pregnancy has been associated with congenital 

hypothryoidism in some of the offspring. No other conclusive studies were located regarding 

developmental and reproductive effects in humans after exposure to cyanide or ingestion of foods 

containing cyanogenic plant material. Oral studies in animals indicate adverse effects on male 

reproduction (discussed below) and possible developmental toxicity. Studies in goats indicate that 

maternal exposure to cyanide can result in the transfer of cyanide and its metabolite, thiocyanate, through 

milk to offspring, but the relevance of goat data for humans is not established. 

There is no evidence that cyanide exposure is correlated with carcinogenicity in humans or animals. 

Cyanide has only an indirect genotoxic effect in vitro and in vivo in that dying cells release endonucleases 

into the cytosol, ultimately resulting in DNA fragmentation. 

The following sections discuss significant neurotoxic and reproductive effects resulting from exposure to 

cyanide in greater detail. 

Neurological Effects. The most significant effects of cyanide exposure occur in the nervous system, 

especially in the brain (encephalopathy). Acute-duration inhalation of high concentrations of cyanide 

provokes a brief central nervous system stimulation followed by depression, convulsions, coma, and 

death in humans and animals. The effects are probably due to rapid biochemical changes in the brain, 

such as changes in ion flux, neurotransmitter release, and possibly peroxide formation. Death in acute 

cases is associated with effects on neurological centers controlling respiration. Convulsions and coma 

were also reported in humans and animals following acute dermal exposure to cyanide. It is likely that 

absorption of hydrogen cyanide vapor by the inhalation route also occurred in the human cases. 

Pathological changes that may occur in the central nervous system during acute exposure to high doses 

may complicate recovery. Severe Parkinsion-like symptoms have been noted in several cases of severe 

acute oral exposure to lethal amounts of cyanide (after antidotes were administered), often becoming 

more severe in the weeks following the initial exposure. Tremor and headache are milder symptoms of 

neurotoxicity in humans. Extensive degenerative changes have been produced experimentally in the brain 

by cyanide treatment, at 149–633 ppm for 2–10 minutes for dogs, the most sensitive species, and at 

higher levels in other species. In rats, cyanide-induced histopathological damage was observed in deep 

cerebral white matter, the corpus callosum, hippocampus, corpora striata, pallium, and substantia nigra 

following acute inhalation exposures to hydrogen cyanide lasting less than 2 hours. Partial remyelination 

after cessation of exposure has been reported, but it is apparent that this process is slow and incomplete. 

The topographic selectivity of cyanide-induced encephalopathy may be related to the depth of acute 
CYANIDE 17 

2. RELEVANCE TO PUBLIC HEALTH 

intoxication and the distribution of the blood flow, which may result in selected regions of vascular 

insufficiency. 

No data were available for cyanide-induced neurotoxicity in humans following intermediate-duration 

exposures by any route, but a number of animal studies are available, none of which, however, 

systematically evaluated neurotoxicity using a neurobehavioral test battery. Following repeated 

inhalation exposure to cyanide, transitory neurobehavioral effects (increased response rates without 

encephalopathy) were observed in monkeys at 12.5 ppm and more serious effects (tremors, rigidity, 

ataxia, atrophy of Purkinje cells, and vasodilation and hemorrhage in the brain) were observed in dogs, 

the most sensitive species tested, at 45 ppm. Oral exposure studies administered cyanide salts by oral 

gavage, in drinking water, or diet. In oral gavage studies in pigs or rats, behavioral changes (reduced 

activity) were observed at doses between 0.14 and 0.8 mg cyanide/kg/day and more serious effects 

(tremors, convulsions) were observed at 7.8 mg CN–

/kg/day, a lethal dose. No encephalopathy or overt 

signs of neurotoxicity were observed following repeated exposure via drinking water to doses as high as 

12.5 mg CN–

/kg/day in rats or 28.8 mg CN–/kg/day in mice. Myelin degeneration of spinal cord tracts 

was observed in rats receiving 30 mg CN–

/kg/day via dietary exposure. 

Chronic exposure to lower cyanide concentrations in occupational settings causes a variety of symptoms 

from fatigue, dizziness, and headaches to ringing in the ears, paresthesias of extremities, and syncopes, or 

even hemiparesis and hemianopia. In addition, behavioral changes were reported following prolonged 

cyanide exposure in workers and animals, and loss of memory and decreases in visual acuity, 

psychomotor ability, and visual learning were reported in workers. It is possible, however, that during 

occupational exposure, such as electroplating operations, chemicals other than cyanide may have 

contributed to the effects observed. Chronic neurological effects are exacerbated by nutritional 

deficiencies or other disorders that provide inadequate levels of thiosulfate needed to detoxify cyanide. 

Chronic exposure to cyanogenic glycosides in certain cassava diets may lead to multiple neuropathies in 

exposed populations. Among those observed were hyperreflexia or spastic paraparesis of the extremities, 

spastic dysarthria, visual and hearing difficulties, and cerebellar signs. In addition, epidemics of Konzo, a 

neurological disease characterized by the sudden onset of varying degrees of symmetric, isolated, 

nonprogressive spastic paraparesis, have occurred in Africa and have been associated with high dietary 

cyanide exposure from “bitter” cassava that was not fully processed. Scopoletin, a potent hypotensive 

and spasmolytic agent, has been isolated from cassava roots and may contribute to the tropical ataxic 

neuropathy observed among cassava eaters. No chronic-duration data were available for neurotoxicity in 

exposed animals. 
CYANIDE 18 

2. RELEVANCE TO PUBLIC HEALTH 

Reproductive Effects. No studies were located regarding reproductive effects in humans after any 

route of exposure, but a few studies reported reproductive effects in animals exposed via the oral route. 

Reproductive effects were the only adverse effects observed in rats and mice ingesting, respectively, 

12.5 or 24.3 mg CN–

/kg/day as sodium cyanide in the drinking water for 13 weeks. In male rats, 

decreases in the caudal epididymal weight, epididymis weight, testis weight, spermatid heads, and 

spermatid counts were noted, whereas in male mice, significant decreases in the epididymal and caudal 

epididymal weights were noted without changes in sperm parameters. Alterations in the estrus cycle 

(longer duration of proestrus and diestrus stages compared to estrus and metestrus stages) were observed 

in female rats, but were not considered biologically significant. Several other studies support the 

observation of effects on the male reproductive system. Increased gonadal weight was observed in male 

rats exposed by oral gavage to copper cyanide or potassium silver cyanide for 90 days. A reduction in 

the spermatogenic cycle, testicular germ cell sloughing and degeneration, and occasional abnormal cells 

were noted in dogs ingesting 1.04 mg CN–

/kg/day as sodium cyanide in a rice diet or as the equivalent 

cassava diet. In contrast, no effects on reproductive organs were reported in hamsters exposed to cassava 

during gestation. Increased resorptions were noted following oral exposure of rats to cyanogenic 

glycosides in a cassava diet. The results of one study suggest that exposure to cyanide could lead to 

reproductive effects in humans. 

2.3 MINIMAL RISK LEVELS (MRLs) 

Estimates of exposure levels posing minimal risk to humans (MRLs) have been made for cyanide. An 

MRL is defined as an estimate of daily human exposure to a substance that is likely to be without an 

appreciable risk of adverse effects (noncarcinogenic) over a specified duration of exposure. MRLs are 

derived when reliable and sufficient data exist to identify the target organ(s) of effect or the most sensitive 

health effect(s) for a specific duration within a given route of exposure. MRLs are based on 

noncancerous health effects only and do not consider carcinogenic effects. MRLs can be derived for 

acute, intermediate, and chronic duration exposures for inhalation and oral routes. Appropriate 

methodology does not exist to develop MRLs for dermal exposure. 

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

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

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

example, acute inhalation MRLs may not be protective for health effects that are delayed in development 
CYANIDE 19 

2. RELEVANCE TO PUBLIC HEALTH 

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

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

significant human exposure improve, these MRLs will be revised. 

In the discussions of available toxicity data, results for dogs are included as supporting data, but these 

studies were not considered for MRL derivations because their intrinsic levels of the detoxifying enzyme 

rhodanese are lower than in other mammals, resulting in relatively greater sensitivity to cyanide 

exposures than in humans. 

Inhalation MRLs 

No MRLs were derived for inhalation exposure to cyanide because the available data indicated serious 

adverse effects occurring even at the lowest reported exposure levels. The acute inhalation toxicity 

database for humans includes case reports of lethality, serious neurological effects (coma with slight loss 

of peripheral vision after recovery, brain death), and/or metabolic effects (lactic acidosis indicative of 

impaired respiration) following brief exposure to 200–452 ppm hydrogen cyanide (Bonsall 1984; Singh et 

al. 1989). Acute hydrogen cyanide inhalation studies in laboratory rodents reported nonlethal acute 

inhalation effects following 30-minute exposures to hydrogen cyanide, including a 50% reduction in the 

respiratory rate in mice exposed at 63 ppm (Matijak-Schaper and Alarie 1982) and neurological 

(semiconsciousness, changes in electroencephalograph results), respiratory (severe dyspnea), and 

cardiological effects (bradycardia, arrhythmia, and T-wave abnormalities) in cynomolgous monkeys at 

100 ppm (Purser et al. 1984). Cynomolgous monkeys exposed at 60 ppm for 30 minutes exhibited 

abnormal delta wave activity in electroencephalograms but no other abnormalities (Purser et al. 1984). A 

study of auditory function and histology in rats reported a no-observed-adverse-effect level (NOAEL) of 

50 ppm hydrogen cyanide for a 3.5-hour exposure, but these data are not suitable for derivation of an 

MRL because the ear was the only organ evaluated in this study (Fechter et al. 2002). As none of these 

acute-duration studies observed the animals after the day of exposure, it is not known whether effects 

would have persisted or worsened over time. Since human case reports have mentioned increasing 

degradation of neurological status over a period of weeks (Carella et al. 1988; Chin and Calderon 2000; 

Feldman and Feldman 1990; Grandas et al. 1989; Rachinger et al. 2002; Rosenberg et al. 1989; Rosenow 

et al. 1995; Uitti et al. 1985), the available animal data showing minimal or no effects (Fechter et al. 

2002; Purser 1984) are not reliable as points of departure for the derivation of an acute-duration inhalation 

MRL for cyanide. 
CYANIDE 20 

2. RELEVANCE TO PUBLIC HEALTH 

No data are available for the intermediate-duration inhalation toxicity of cyanide in humans and only 

inadequate data are available for animals. One study reported 25% lethality, and serious neurological 

effects (tremors, ataxia, and atrophy of Purkinje and glial cells), respiratory effects (dsypnea), and 

gastrointestinal effects (vomiting, tenesmus, and diarrhea) in dogs exposed to 45 ppm hydrogen cyanide 

for 30 minutes/day, every other day for 28 days (Valade 1952). Another study reported increased creatine 

phosphokinase activity in the hearts of rats exposed to 200 ppm for 12.5 minutes/day, every fourth day for 

20 days, but did not find evidence of cardiac histopathology or evaluate effects in other organ systems 

(O'Flaherty and Thomas 1982). As these studies reported serious effects in dogs, a sensitive species, or 

were limited in scope, neither are adequate for the derivation of an intermediate-duration MRL for 

cyanide. 

The database for chronic-duration inhalation toxicity of cyanide consists of several occupational studies 

in workers in electroplating jobs. These studies described serious neurological effects (paresthesia, 

hallucination, weakness) as well as respiratory (dyspnea), cardiovascular (palpitations and chest pain), 

and thyroid effects (enlargement of thyroid gland or increased levels of thyroid stimulating hormone) 

following exposure to 6.4–15 ppm (Blanc et al. 1985; El Ghawabi et al. 1975). These studies were 

limited in either the lack of information about exposure levels, the small size of the cohorts, or the 

probable dermal contact with cyanide in liquid. Neurological effects were noted in workers who received 

multiple exposures (to gasoline, hydrochloric acid, and copper cyanide) (El Ghawabi et al. 1975). These 

studies are not adequate for deriving a chronic-duration inhalation MRL for cyanide because the lowestobserved-adverse-effect level (LOAEL) effects were serious, and because of the likelihood of multiple 

exposures and possible skin contact with liquid cyanide. 

Oral MRLs 

The database for acute-duration oral toxicity of cyanide consists of a few studies on human poisoning 

incidents and a limited number of studies in laboratory animals exposed to single doses of cyanide salts. 

In humans ingesting 4.6–15 mg CN–

/kg as potassium cyanide, serious adverse effects were observed in 

the nervous system (brain lesions, Parkinsonian-like signs, decreased verbal fluency, reduced information 

processing, coma), respiratory system (hyperventilation), cardiovascular system (shallow pulse, enlarged 

heart, and inaudible heart sounds), gastrointestinal system (nausea and vomiting), renal system 

(albinuria), and musculoskeletal system (generalized muscular rigidity) (Feldman and Feldman 1990; 

Liebowitz and Scharetz 1948; Rosenow et al. 1995). In rodents, single doses of 4–22 mg CN–

/kg as 

potassium, sodium, or calcium cyanide resulted in 50–90% lethality (Ferguson 1962; Smyth et al. 1969). 
CYANIDE 21 

2. RELEVANCE TO PUBLIC HEALTH 

Developmental effects (delayed ossification and 23% reduction in fetal weight) were observed in the 

offspring of hamsters that ingested 1 mg CN–

/kg/day in cassava on gestational days 3–14 (Frakes et al. 

1986a). Fetal effects occurred despite the absence of overt toxicity in dams at doses as high as 

10.4 mg/kg/day. The presence of other chemicals such as scopoletin in cassava (Obidoa and Obasi 1991; 

see Section 3.2.2.4) confound the assessment of the dose-response for cyanide toxicity from the Frakes et 

al. (1986a) developmental toxicity study. No acute-duration oral MRL was derived for cyanide because 

of the serious effects observed at the lowest doses or because of uncertainties as to the dose-response for 

cyanide following ingestion of cassava. 

• An MRL of 0.05 mg CN–/kg/day has been derived for intermediate-duration oral exposure (15– 

364 days) to cyanide compounds. 

There are no data for the intermediate-duration oral toxicity of cyanide in humans, but there are a number 

of studies in animals exposed to sodium or potassium cyanide. As discussed in Section 3.2.2, a number 

of animal studies examined the toxicity of cyanide following intermediate-duration oral exposure. 

However, not all studies are suitable for establishing dose-response relationships. Several studies 

(Gerhart 1986, 1987; Jackson 1988: Soto-Blanco et al. 2002a) in rats and pigs report neurological, 

thyroid, and gastrointestinal effects following gavage administration of cyanide; however, their usefulness 

for dose-response assessment is limited because the bolus dosing may overwhelm the detoxification 

process and is not characteristic of typical general population exposures to cyanide in drinking water. 

Similarly, although a toxicity study in dogs receiving sodium cyanide reported effects in the male 

reproductive system, adrenal gland, and kidney, the lower levels of the detoxifying enzyme rhodanese in 

this species both increases the sensitivity to cyanide and prevents the production of the metabolite 

thiosulfate to levels that would be toxic to the thyroid as seen in humans and other animals (Kamalu 

1993). Additionally, studies involving exposure to cyanide via a cassava diet (Tewe and Maner 1981a, 

1981b) were not considered as the basis of an MRL because there is evidence suggesting that other toxic 

compounds, such as scopoletin, may contribute to the observed toxic effects (Kamalu 1993). 

In rat and mice exposed to sodium cyanide in drinking water for 13 weeks (NTP 1993), reproductive 

effects in males were the only adverse effects observed. Effects on male reproduction included reductions 

in epididymal weights (13%), testicular weights (8%), and spermatid counts (13.6%) in F344 rats exposed 

to 12.5 mg CN–

/kg/day, and 10–18% reductions in epididymal/caudal epididymal weights in B6C3F1 

mice exposed to 24.3 mg CN–

/kg/day. In rabbits exposed to sodium cyanide in the diet at doses of 15 mg 

CN–

/kg/day for 4 weeks or 20 mg CN–/kg/day for 40 weeks, hepatic toxicity (fatty degeneration and 

necrosis of the liver, increased serum levels of succinate dehydrogenase, alanine aminotransferase, and 
CYANIDE 22 

2. RELEVANCE TO PUBLIC HEALTH 

alkaline phosphatase) and renal toxicity (tubular necrosis) were observed (Okolie and Iroanya 2003; 

Okolie and Osagie 1999). Neurotoxicity (myelin degeneration in the spinal cord) was observed in rats 

exposed at 30 mg CN–

/kg/day as potassium cyanide in food for 11.5 months (Philbrick et al. 1979). 

Effects on male reproduction were severe in dogs (germ cell sloughing and degeneration, reduced 

spermatogenesis cycle) (Kamalu 1993) and also observed in rats and mice in studies in which no other 

systemic effects were observed. Hepatic, renal, and body weight effects were reported in Wistar rats that 

received doses of 3.6 mg CN–

/kg/day as potassium cyanide in drinking water for 15 days (Sousa et al. 

2002a). However, the reliability of these findings is questionable because of the lack of incidence data 

for the histopathological lesions and because no body weight effects were noted in other rat studies with 

exposures for longer durations and at higher doses. On the basis of these considerations, reproductive 

toxicity in males is selected as the critical effect of cyanide toxicity. The NTP (1993) bioassay in rats is 

selected as the principal study because it provided the lowest LOAEL and a NOAEL for the critical effect 

and examined the full range of tissues with extensive interim hematological, clinical chemistry, and 

urinalyses. 

The intermediate-duration oral MRL was based on a NOAEL of 4.5 mg CN–

/kg/day and a LOAEL of 

12.5 mg CN–

/kg/day in rats exposed for 13 weeks (NTP 1993). In this study, groups of 10 male and 

10 female F344/N rats were given sodium cyanide in drinking water at concentrations of 0, 3, 10, 30, 100, 

or 300 ppm. The reported average cyanide intakes were 0, 0.2, 0.5, 1.4 (males), 1.7 (females), 4.5 

(males), 4.9 (females), or 12.5 mg/kg/day, respectively). At the end of the study, the animals were 

evaluated for histopathology, hematology, clinical chemistry, urine chemistry, and reproductive toxicity; 

a satellite set of 10 males/group were also evaluated for hematology, clinical chemistry, and urinalyses at 

about 1, 3, 6, and 11 weeks. Exposure to cyanide had no significant effect on survival, body weight gain, 

the incidence of clinical signs, nonreproductive organ weights (absolute or relative to body weight), 

hematology, or clinical chemistry parameters, or histopathology. Dose-related reduced water intake and 

concomitant increased urine density were attributed to palatability effects at the higher doses. Some 

cyanide-related effects were observed in the study of reproductive parameters. Statistically significant 

decreases, compared to controls, were observed in the absolute weights of the left epididymis (7%), left 

cauda epididymis (13%), and left testis (7.6%) of rats treated at 12.5 mg/kg/day. In addition, 13.6% 

reductions compared to controls were observed in spermatid heads per testis and spermatid counts per mL 

suspension in rats treated at 12.5 mg/kg/day. The authors considered these to be evidence of a mild 

adverse effect of cyanide on the male reproductive system. The statistically significant reductions (7.4– 

8.6% lower than controls) in left cauda epididymis weights observed at 1.4 and 4.5 mg/kg/day were not 

considered biologically significant in the absence of any other significant effect. The small (<4%), 
CYANIDE 23 

2. RELEVANCE TO PUBLIC HEALTH 

statistically significant, but not dose-related, reductions observed in spermatozoa motility in the 1.4, 4.5, 

and 12.5 mg/kg/day groups were within the range of normal values and were not considered biologically 

significant by the study investigators. For females, significantly (p=0.03, Wilk’s Criterion) more time 

was spent in proestrus and diestrus stages and less time in estrus and metestrus stages in the 4.9 and 

12.5 mg/kg/day dose groups than in controls, but a dose-relationship was not observed. For this reason, 

the study investigators did not consider these results unequivocal proof that cyanide adversely affects the 

female reproductive system. The intermediate-duration oral MRL of 0.05 mg/kg/day is based on a 

NOAEL of 4.5 mg/kg/day and a LOAEL of 12.5 mg/kg/day for reductions in the number of spermatid 

heads and sperm counts. The NOAEL was divided by an uncertainty factor of 100 (10 for extrapolation 

from animals to humans and 10 for human variability) to derive the MRL. 

A chronic oral MRL was not derived for cyanides because of the lack of suitable data in humans and 

animals. Studies of populations that customarily eat cassava are not appropriate for MRL derivations 

because some neurological effects may have resulted from scopoletin rather than released cyanide 

(Obidoa and Obasi 1991). One chronic-duration oral study found no significant cyanide-dependent 

effects in rats exposed to hydrogen cyanide in the diet for 2 years at doses as high as 7.8 mg/kg/day for 

males or 10.4 mg/kg/day for females (Howard and Hanzal 1955). However, the reliability of this study is 

low because evaporation of the cyanide from the feed resulted in unstable cyanide levels throughout the 

experiment and uncertainties as to the dose-response for cyanide. Since the human data are confounded 

by exposure to cassava and no LOAEL was identified in the only available animal study, no MRL was 

derived for chronic-duration oral exposure to cyanide. 
CYANIDE 24 

2. RELEVANCE TO PUBLIC HEALTH 

This page is intentionally blank. 
CYANIDE 25 

3. HEALTH EFFECTS 

3.1 INTRODUCTION 

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

other interested individuals and groups with an overall perspective on the toxicology of cyanide. It 

contains descriptions and evaluations of toxicological studies and epidemiological investigations and 

provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health. 

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

3.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

"less serious" and "serious" effects. The distinction between "less serious" effects and "serious" effects is 
CYANIDE 26 

3. HEALTH EFFECTS 

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

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

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

effects to human health. 

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

3-1 to 3-3) and figures (Figures 3-1 and 3-2) may differ depending on the user's perspective. Public 

health officials and others concerned with appropriate actions to take at hazardous waste sites may want 

information on levels of exposure associated with more subtle effects in humans or animals (LOAELs) or 

exposure levels below which no adverse effects (NOAELs) have been observed. Estimates of levels 

posing minimal risk to humans (Minimal Risk Levels or MRLs) may be of interest to health professionals 

and citizens alike. 

This section provides information regarding known health effects of cyanide exposure. Exposure to 

hydrogen cyanide gas is most common by inhalation. In the discussion below, inhalation exposures are 

expressed as ppm hydrogen cyanide for a defined period of time. Exposure to cyanide can also occur by 

inhalation of cyanogen gas, a dimer of cyanide. However, cyanogen breaks down in aqueous solution 

into cyanide ion (CN–1) and OCN– ions (Cotton and Wilkinson 1980). The rate of the breakdown depends 

on pH and is faster in basic media (e.g., hydrogen cyanide is in equilibrium as H+

 and CN– in blood with a 

pH of 7.38–7.44) than in acidic media (e.g., hydrogen cyanide is the only species in stomach contents at a 

pH of 3). The amount of cyanide ion formed within a body tissue or fluid as a result of exposure to 

cyanogen has been reported; however, the amount varies with type of body tissue and fluid. Thus, it is 

difficult to estimate cyanide levels in body tissues after cyanogen exposure. Therefore, studies regarding 

exposure to cyanogen are discussed in the text as ppm cyanogen, but are not included in LSE tables or 

figures. 

Oral exposure to cyanide usually results from accidental, homicidal, or suicidal ingestion of cyanide salts. 

Sodium cyanide and potassium cyanide are the most frequently studied cyanide compounds. Copper 

cyanide, potassium silver cyanide, silver cyanide, and calcium cyanide are other compounds that humans 

could encounter through oral or dermal exposure; some data for cyanide compounds containing copper or 

silver are omitted from the LSE tables and figures because the toxicological effects may have been caused 

by the metal, rather than or in addition to CN–

. Similarly, toxicological data for ferricyanide compounds 

are omitted from the LSE tables and figures because CN–

 remains tightly bound to iron and is therefore 

much less bioavailable than CN– in soluble cyanide compounds. Cassava roots and certain fruit pits 
CYANIDE 27 

3. HEALTH EFFECTS 

contain compounds that can be broken down in the gastrointestinal tract to form cyanide. Cassava roots 

form the staple diet of some populations in Africa, Central and South America, and Asia. However, it 

must be noted that cassava roots are notoriously deficient in protein and other nutrients and contain many 

other compounds, in addition to cyanide, that could be responsible for some of the observed toxic effects. 

Thiocyanate, a metabolite of cyanide that is formed in the body after exposure to cyanide compounds, is 

responsible for toxic effects to the thyroid gland. When possible, all oral exposures are expressed as mg 

CN–

/kg/day. 

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

the interpretation of the tables and figures for Levels of Significant Exposure and the MRLs. 

3.2.1 Inhalation Exposure 

3.2.1.1 Death 

Inhalation of sufficient concentrations of hydrogen cyanide gas can rapidly cause death, which has led to 

the use of hydrogen cyanide in gas chamber executions (Wexler et al. 1947). An average fatal 

concentration for humans was estimated as 546 ppm hydrogen cyanide after a 10-minute exposure (DOA 

1976, as cited in Ballantyne 1988). In one case, a worker exposed to 200 ppm hydrogen cyanide in a 

silver plating tank became unconscious and eventually died even though he had received antidotal therapy 

in a hospital (Singh et al. 1989). In other cases, exposure to 270 ppm hydrogen cyanide led immediately 

to death, 181 ppm hydrogen cyanide exposure was fatal after 10 minutes, and 135 ppm hydrogen cyanide 

was fatal after 30 minutes in humans (Dudley et al. 1942). Three deep-sea trawler men died when 

exposed to toxic fumes (containing lethal concentrations of hydrogen cyanide, carbon dioxide and 

hydrogen sulfide) from spoiled fish (Cherian and Richmond 2000); all three men collapsed within 

1 minute of exposure, and cyanide exposure was confirmed in one man post-mortem by a blood cyanide 

concentration of 0.05 mg/L. 

Levels of acute exposure resulting in animal deaths were reported in numerous studies and LC50 (lethal 

concentration, 50% death) values were provided for several species. Inhalation LC50 values of hydrogen 

cyanide in rats ranged from 143 ppm for 60 minutes to 3,417 ppm for 10 seconds (Ballantyne 1983a). 

Five-minute LC50 values of 503 ppm for the rat and 323 ppm for the mouse were reported by DiPasquale 

and Davis (1971). At lethal concentrations, animals exhibited hyperactivity and asphyxial convulsions 

with death occurring within 20 minutes of exposure; gross pathology findings included pulmonary 
CYANIDE 28 

3. HEALTH EFFECTS 

hemorrhage and congestion of the liver and kidney. Exposure to cyanide resulted in similar LC50 values 

in mice (Higgins et al. 1972; Matijak-Schaper and Alarie 1982). LC50 values for hydrogen cyanide in 

rabbits ranged from 188 ppm for 30 minutes to 2,200 ppm for 45 seconds (Ballantyne 1983a). Lethal 

concentrations were also reported in experiments with dogs exposed for acute (Haymaker et al. 1952) and 

intermediate durations (Valade 1952). Both studies used a small number of dogs for different exposure 

regimens so that statistical significance could not be evaluated. 

The LC50 values in each species and LOAEL values for death in humans in the acute-, and intermediateduration category are recorded in Table 3-1 and plotted in Figure 3-1. Lethality data for dogs have been 

omitted from Table 3-1 and Figure 3-1 because that species has a relatively low amount of the detoxifying 

enzyme rhodanese and is unusually susceptible to cyanide exposure compared to humans or other 

mammals (see Sections 3.4.3 and 3.5.3). 

3.2.1.2 Systemic Effects 

The systemic effects observed in humans and animals after inhalation exposure to cyanide are discussed 

below. The highest NOAEL values and all reliable LOAEL values for each systemic effect in each 

species and duration category are recorded in Table 3-1 and plotted in Figure 3-1. Systemic toxicity data 

for dogs have been omitted from Table 3-1 and Figure 3-1 because that species has a relatively low 

amount of the detoxifying enzyme rhodanese and is unusually susceptible to cyanide exposure compared 

to humans or other mammals (see Sections 3.4.3 and 3.5.3). 

Respiratory Effects. Initially, respiration is stimulated, but later, dyspnea occurs in patients admitted 

to a hospital after acute hydrogen cyanide exposure (Chen and Rose 1952; Peden et al. 1986; Potter 

1950). The levels of exposure in these accidental poisonings were not provided. Nasal irritation was 

reported in volunteers exposed to 16 ppm cyanogen (8 ppm cyanide) for 6–8 minutes (McNerney and 

Schrenk 1960). No effects were reported at 8 ppm cyanogen (4 ppm cyanide). 

Dyspnea was observed in workers chronically exposed (5–15 years) to 6.4–10.4 ppm of an unspecified 

cyanide form evolved from sodium cyanide and copper cyanide during electroplating (El Ghawabi et al. 

1975) and in workers exposed to 15 ppm hydrogen cyanide in a silver-reclaiming facility (Blanc et al. 

1985). Other complaints included cough, sore throat, altered sense of smell, nasal congestion, epistaxis, 

and hemoptysis. However, exposure to other chemicals such as cleaners and cutting oils also occurs in 

electroplating operations. 
a

Key to

Figure

Table 3-1 Levels of Significant Exposure to Cyanide - Inhalation

Species

(Strain)

LOAEL

System 

NOAEL

(ppm)

Less Serious

(ppm)

Serious

(ppm)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

ACUTE EXPOSUREDeath

1

191

DOA 1976HCN

546 (LC50)

546

Human 10 min

2

99

Singh et al. 1989HCN

200 M (fatal after 3 days)

200

Human NS

3

954

AMRL 1971

HCN

503 M (5-min LC50)

503

Rat(Wistar)

5 min

4

36

Ballantyne 1983aHCN

143 (LC50 in 60 min)

143

Rat(NS)

60 min

5

222

Higgins et al. 1972HCN

503 (LC50)

503

Rat(Wistar)

5 min

6

955

AMRL 1971

HCN

323 M (5-min LC50)

323

Mouse(ICR)

5 min

7

223

Higgins et al. 1972HCN

323 (LC50)

323

Mouse(ICR)

5 min

8

905

Hume et al. 1995HCN

400 M (90% lethality)

400

Mouse(ICR)

3 min

9

161

Matijak-Schaper and Al1982HCN

166 M (LC50)

166

Mouse(SwissWebster)

30 min

10

37

Ballantyne 1983aHCN

188 (LC50 in 35 min)

188

Rabbit(NS)

35 min
a

Key to

Figure

Table 3-1 Levels of Significant Exposure to Cyanide - Inhalation (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(ppm)

Less Serious

(ppm)

Serious

(ppm)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

Systemic

11

43

Bonsall 1984HCN

Ocular 452 M (slight loss of peripheral

vision after recovery)

452

Human 13 min

12

228

Purser et al. 1984HCN

Resp 100 (severe dyspnea)

100

Monkey(Cynomolgus)

30 min

Cardio 100 (bradycardia, arrhythmia,

T-wave abnormalities)

100

13

162

Matijak-Schaper and Al1982HCN

Resp 63 M (DC50)

63

Mouse(SwissWebster)

30 min

Neurological

14

42

Bonsall 1984HCN

452 M (coma)

452

Human 13 min

15

131

Purser et al. 1984HCN

100 (semiconsciousness,

disrupted respiration,EEG changes)

100

Monkey(Cynomolgus)

30 min

16

956

Fechter et al. 2002HCN

50 M

50

Rat(Long- Evans)

3.5 hr

INTERMEDIATE EXPOSURESystemic

17

127

O'Flaherty and Thomas HCN

Cardio 200 M (increased creatine

phosphokinase activity)

200

Rat(Long- Evans)

20 d4 d intervals12.5 min/d
a

Key to

Figure

Table 3-1 Levels of Significant Exposure to Cyanide - Inhalation (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(ppm)

Less Serious

(ppm)

Serious

(ppm)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

CHRONIC EXPOSURESystemic

18

49

Blanc et al. 1985HCN

Resp 15 M (dyspnea)

15

Human NS

(occup)

Cardio 15 M (palpitations, chest pain)

15

Gastro 15 M (nausea)

15

Endocr 15 M (increased mean thyroid

stimulating hormonelevels)

15

Dermal 15 M (rash)

15

Ocular 15 M (eye irritation)

15

Bd Wt 15 M (approximately 8%

weight loss)

15

19

55

El Ghawabi et al. 1975NaCN

Resp 6.4 M (dyspnea, irritation of

throat)

6.4

Human 5-15 yr (occup)

Cardio 6.4 M (precordial pain)

6.4

Gastro 6.4 M (vomiting)

6.4

Hemato 6.4 M (increased hemoglobin

and lymphocytes)

6.4

Endocr 6.4 M (thyroid enlargement)

6.4

Dermal 10.4 M

10.4

Ocular 6.4 M (lacrimation)

6.4
a

Key to

Figure

Table 3-1 Levels of Significant Exposure to Cyanide - Inhalation (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(ppm)

Less Serious

(ppm)

Serious

(ppm)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

Neurological

20

48

Blanc et al. 1985HCN

15 M (persistent headache,

dizziness, paresthesia)

15

Human NS

(occup)

21a The number corresponds to entries on Figure 3-1.Bd Wt = body weight; Cardio = cardiovascular; d = day(s); DC50 = concentration that resulted in 50% decrease in average respiratory rate; EEG = electroencephalendocrine; F = female; Gastro = gastrointestinal; HCN = hydrogen cyanide; Hemato = hematological; LC50 = lethal concentration, 50%kill; LOAEL = lowest-observelevel; M = male; min = minutes; NaCN = sodium cyanide; NOAEL = no-observed-adverse-effect level; NS = not specified; (occup) = occupational; Resp = respiratosecond(s); yr = year(s); x = time(s)

54

El Ghawabi et al. 1975NaCN

6.4 M (confusion, hallucination,

headache, dizziness,weakness)

6.4

Human 5-15 yr (occup)
10

100

1000

Death

1

2

6m 7m

8m

9m

3r

4r

5r

10h

Respiratory

12k

13m

Cardiovascular

12k

Ocular

11

Neurological

14

15k

16r

ppm

Figure 3-1 Levels of Significant Exposure to Cyanide - Inhalation

Acute (≤14 days)

c-Cat

d-Dog

r-Rat

p-Pig q-Cow

 -Humans

k-Monkey

m-Mouse

h-Rabbit

a-Sheep

f-Ferret

j-Pigeon

e-Gerbil

s-Hamster

g-Guinea Pig

n-Mink

o-Other

 Cancer Effect Level-Animals

 LOAEL, More Serious-Animals

 LOAEL, Less Serious-Animals

 NOAEL - Animals

 Cancer Effect Level-Humans

 LOAEL, More Serious-Humans

 LOAEL, Less Serious-Humans

 NOAEL - Humans

 LD50/LC50

 Minimal Risk Level

 for effects

 other than

 Cancer

Systemic

CYANIDE

 3. HEALTH EFFECTS

33
10

100

1000

Cardiovascular

17r

ppm

Figure 3-1 Levels of Significant Exposure to Cyanide - Inhalation (Continued)

Intermediate (15-364 days)

c-Cat

d-Dog

r-Rat

p-Pig q-Cow

 -Humans

k-Monkey

m-Mouse

h-Rabbit

a-Sheep

f-Ferret

j-Pigeon

e-Gerbil

s-Hamster

g-Guinea Pig

n-Mink

o-Other

 Cancer Effect Level-Animals

 LOAEL, More Serious-Animals

 LOAEL, Less Serious-Animals

 NOAEL - Animals

 Cancer Effect Level-Humans

 LOAEL, More Serious-Humans

 LOAEL, Less Serious-Humans

 NOAEL - Humans

 LD50/LC50

 Minimal Risk Level

 for effects

 other than

 Cancer

Systemic

CYANIDE

 3. HEALTH EFFECTS

34
1

10

100

Respiratory

18

19

Cardiovascular

18

19

Gastrointestinal

18

19

Hematological

19

Endocrine

18

19

Derm al

18

19

Ocular

18

19

Body Weight

18

Neurological

20

21

ppm

Figure 3-1 Levels of Significant Exposure to Cyanide - Inhalation (Continued)

Chronic (≥365 days)

c-Cat

d-Dog

r-Rat

p-Pig q-Cow

 -Humans

k-Monkey

m-Mouse

h-Rabbit

a-Sheep

f-Ferret

j-Pigeon

e-Gerbil

s-Hamster

g-Guinea Pig

n-Mink

o-Other

 Cancer Effect Level-Animals

 LOAEL, More Serious-Animals

 LOAEL, Less Serious-Animals

 NOAEL - Animals

 Cancer Effect Level-Humans

 LOAEL, More Serious-Humans

 LOAEL, Less Serious-Humans

 NOAEL - Humans

 LD50/LC50

 Minimal Risk Level

 for effects

 other than

 Cancer

Systemic

CYANIDE

 3. HEALTH EFFECTS

35
CYANIDE 36 

3. HEALTH EFFECTS 

Asphyxia has been observed in rats exposed to 250 ppm cyanogen (125 ppm cyanide) for 7.5– 

120 minutes (McNerney and Schrenk 1960), asphyxia and pulmonary edema were observed in dogs 

exposed to concentrations ranging from 149 to 633 ppm hydrogen cyanide for 2–10 minutes (Haymaker 

et al. 1952), while severe dyspnea was observed in monkeys exposed to 100 ppm hydrogen cyanide for 

30 minutes (Purser et al. 1984). Exposure to 63 ppm hydrogen cyanide for 30 minutes resulted in a 50% 

decrease in respiratory rate of mice due to depression of the respiratory center (Matijak-Schaper and 

Alarie 1982). 

In intermediate-duration studies, no respiratory effects were reported in rats exposed to 25 ppm cyanogen 

(12.5 ppm cyanide) for 6 months, and a decrease in total lung moisture content was the only finding in 

monkeys exposed to 11 ppm cyanogen (5.5 ppm cyanide), also for 6 months (Lewis et al. 1984). 

Dyspnea was found in dogs exposed to 45 ppm hydrogen cyanide for 30 minutes a day at 2–8-day 

intervals for 28–96 days (Valade 1952). 

Cardiovascular Effects. Wexler (1947) reported on four men who were executed by inhalation of 

hydrogen cyanide gas (concentration not reported). He reported a distinct slowing of the heart rate within 

1–3 minutes of exposure, with further changes in the heart rate, sinus irregularities, and audio-visual 

dissociation. Palpitations and hypotension were the most frequently reported cardiovascular effects in 

patients after accidental inhalation poisoning with cyanide; however, exact exposure levels were not 

known (Peden et al. 1986). Workers occupationally exposed to 6.4–10.4 ppm cyanide for 5–15 years, 

which evolved from sodium cyanide and copper cyanide during electroplating, complained of precordial 

pain (El Ghawabi et al. 1975). About 14% of workers exposed to 15 ppm hydrogen cyanide in a silverreclaiming facility reported palpitations and 31% reported chest pain (Blanc et al. 1985). Exposure to 

other chemicals such as cleaners and cutting oils may have also occurred during electroplating operations. 

Bradycardia, arrhythmias, and T-wave abnormalities were observed in monkeys exposed to 100 ppm 

hydrogen cyanide for 30 minutes (Purser et al. 1984). Increased cardiac-specific creatinine 

phosphokinase activity was measured in blood samples from rats 2 hours after 12.5 minutes of exposure 

to 200 ppm hydrogen cyanide for 20 days at 4-day intervals (O'Flaherty and Thomas 1982). However, no 

treatment-related changes were found in the hearts at histopathology. In addition, no cardiovascular 

effects were reported at necropsy in rats and monkeys exposed to 25 ppm cyanogen (12.5 ppm cyanide) 

for 6 months (Lewis et al. 1984). 
CYANIDE 37 

3. HEALTH EFFECTS 

Gastrointestinal Effects. Nausea or vomiting was reported in 69% of workers exposed to 15 ppm 

hydrogen cyanide in a silver reclaiming facility (Blanc et al. 1985). Vomiting was also reported in 

workers exposed to 6.4–10.4 ppm cyanide evolved from sodium cyanide and copper cyanide during 

electroplating (El Ghawabi et al. 1975), but exposure to other chemicals such as cleaners and cutting oils 

may have also contributed to the effects. The gastrointestinal effects resulting from cyanide exposure are 

probably provoked by central nervous system effects and/or by irritation of the gastric mucosa in cases in 

which the gas is swallowed during breathing. 

Information regarding gastrointestinal effects in animals is limited to a report of vomiting in dogs exposed 

to 45 ppm hydrogen cyanide for 28–96 days (Valade 1952). 

Hematological Effects. Increased hemoglobin and lymphocyte count were observed in workers 

exposed to 6.4–10.4 ppm of an unspecified cyanide form during electroplating (El Ghawabi et al. 1975). 

The results were significantly different from controls. Furthermore, punctate basophilia of erythrocytes, 

which indicated toxic poisoning, was present in 28 of 36 subjects. However, exposure to copper, a known 

hematotoxic agent, also occurred during the electroplating operations. In another study (Kumar et al. 

1992), an increase in neutrophil values, an increase in erythrocyte sedimentation rate, and a decrease in 

hemoglobin levels were noted in male workers exposed to unspecified concentrations of cyanide for an 

unspecified duration during case hardening and electroplating. 

In animals, no hematological effects were found in rats and monkeys exposed to 25 ppm cyanogen 

(12.5 ppm cyanide) 6 hours/day, 5 days/week, for 6 months (Lewis et al. 1984). 

Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans after 

inhalation exposure to cyanide. 

No musculoskeletal effects were observed in rats or monkeys exposed to 25 ppm cyanogen (12.5 ppm 

cyanide) for 6 hours/day, 5 days/week for 6 months (Lewis et al. 1984). 

Hepatic Effects. An increase in serum alkaline phosphatase was noted in workers exposed to 

unspecified levels of cyanide; however, serum bilirubin was found to be within the normal range in these 

workers (Kumar et al. 1992). 
CYANIDE 38 

3. HEALTH EFFECTS 

Only one study reported on pathological and histopathological examinations of the liver in animals. No 

changes were found in rats and monkeys exposed to 25 ppm cyanogen (12.5 ppm cyanide) for 6 months 

(Lewis et al. 1984). 

Renal Effects. One study was located regarding renal effects in humans after inhalation exposure to 

cyanide. Singh et al. (1989) reported anuria followed by polyuria in a man who was occupationally 

exposed to 200 ppm hydrogen cyanide) for an unspecified length of time. 

No histopathological changes were observed in kidneys of rats and monkeys exposed to 25 ppm cyanogen 

(12.5 ppm cyanide) 6 hours/day, 5 days/week for 6 months (Lewis et al. 1984). 

Endocrine Effects. Mean thyroid stimulating hormone (TSH) levels were significantly higher 

(although within normal limits) in a group of 36 workers exposed to 15 ppm hydrogen cyanide for an 

unspecified duration in a silver-reclaiming facility than in unexposed individuals (p<0.05). T3 levels in 

high exposure workers were also elevated relative to unexposed workers (p<0.01). Data for T4 were not 

presented, but the investigators indicated that the absence of T4 abnormalities could be accounted for by 

the time lapse between exposure and examination (median 10.5 months) (Blanc et al. 1985). Similarly, 

thyroid enlargement was present in 20 of 36 workers exposed for 5–15 years to 6.4–10.4 ppm cyanide 

evolved from sodium cyanide and copper cyanide. The endocrine effect may be due to formation of 

thiocyanate, a metabolite of cyanide. However, exposure to other chemicals such as cleaners and cutting 

oils also occurs during electroplating operations. Thyroid 131

I uptake was significantly higher when 

compared with the control group. This may be due to thiocyanate's ability to block iodine uptake and also 

compete with I–

 as a substrate for the thyroid peroxidase, resulting in less "organification" of I2 

(decreasing the iodination of tyrosine to form iodotyrosine) by the thyroid gland. Since the workers were 

away from work on the 2 days preceding the test, the results may be explained on the basis of acute 

cyanide withdrawal, as with other anti-thyroid agents, where sudden cessation of the drug leads to rapid 

accumulation of iodine in the iodine-depleted gland (El Ghawabi et al. 1975). 

No studies were located regarding endocrine effects in animals after inhalation exposure to cyanide. 

Dermal Effects. Cyanide caused a rash in 42% of workers exposed to 15 ppm hydrogen cyanide 

(Blanc et al. 1985). Brick-red chemical burns on the skin were observed in a man who was 

occupationally exposed to 200 ppm hydrogen cyanide for an unspecified length of time (Singh et al. 
CYANIDE 39 

3. HEALTH EFFECTS 

1989). No dermatitis was reported in workers exposed to 6.4–10.4 ppm cyanide evolved from sodium 

cyanide and copper cyanide (El Ghawabi et al. 1975). 

No studies were located regarding dermal effects in animals after inhalation exposure to cyanide. 

Ocular Effects. Cyanogen caused eye irritation in volunteers during acute exposure to 16 ppm (8 ppm 

cyanide) (McNerney and Schrenk 1960). No effect was observed in those exposed to 8 ppm cyanogen 

(4 ppm cyanide). Slight loss of peripheral vision was the only persistent finding from a case report of a 

man who had been exposed to 452 ppm hydrogen cyanide (for 13 minutes while cleaning a chemical tank 

(Bonsall 1984). During chronic occupational exposure, eye irritation occurred in workers of two 

electroplating factories (exposure levels not specified) (Chandra et al. 1988). In other studies, cyanide 

caused eye irritation in 58% of workers exposed to 15 ppm hydrogen cyanide (Blanc et al. 1985) and 

lacrimation in workers exposed to 6.4 ppm cyanide (El Ghawabi et al. 1975). The eye irritation may not 

be due solely to cyanide exposure, as electroplating workers may be exposed to a variety of chemicals 

that are irritating to the eyes. 

Information regarding ocular effects in animals after inhalation exposure is limited to a report of eye 

irritation in rats acutely exposed (7.5–120 minutes) to 250 ppm cyanogen (125 ppm cyanide) (McNerney 

and Schrenk 1960). 

Body Weight Effects. In an occupational setting, loss of appetite was reported in 58% and weight 

loss (approximately 8%) in 50% of workers exposed to 15 ppm hydrogen cyanide (for an unspecified 

duration in a silver-reclaiming facility (Blanc et al. 1985). 

Decreased body weight was reported in rats exposed to 25 ppm cyanogen (12.5 ppm cyanide) 

6 hours/day, 5 days/week for 6 months (Lewis et al. 1984). 

3.2.1.3 Immunological and Lymphoreticular Effects 

No studies were located regarding immunological effects in humans or animals after inhalation exposure 

to cyanide. 
CYANIDE 40 

3. HEALTH EFFECTS 

3.2.1.4 Neurological Effects 

The central nervous system is a primary target for cyanide toxicity. Acute exposure of humans to fatal 

levels of hydrogen cyanide causes a brief stage of central nervous system stimulation followed by 

depression, convulsions, coma with abolished deep reflexes and dilated pupils, paralysis, and in some 

cases, death (Bonsall 1984; Chen and Rose 1952; Peden et al. 1986; Potter 1950; Singh et al. 1989). 

Though clinical symptoms of cyanide poisoning are well recognized, specific dose-response data are 

generally not known. Acute exposure to lower concentrations can cause lightheadedness, breathlessness, 

dizziness, numbness, and headaches (Lam and Lau 2000; Peden et al. 1986). Impaired short-term 

memory was reported as a delayed effect in a female 1 year after treatment for convulsions following 

acute exposure to cyanide gas (Lam and Lau 2000). 

Chronic exposure of humans to potassium cyanide and other chemicals may have produced severe 

neurological effects such as hemiparesis and hemianopia (Sandberg 1967). During chronic occupational 

exposure, workers exposed to 15 ppm hydrogen cyanide for an unspecified duration reported fatigue, 

dizziness, headaches, disturbed sleep, ringing in ears, paresthesias of extremities, and syncopes (Blanc et 

al. 1985). A dose-effect was demonstrated on high- and low-exposure jobs; however, exact cyanide 

concentrations in the air were not known. Neurological effects persisted in some workers even after a 

10-month nonexposure period. Similar effects were observed in workers exposed to 6.4 ppm cyanide (El 

Ghawabi et al. 1975). Clinical symptoms included headaches, weakness, changes in taste and smell, 

dizziness, disturbances of accommodation, and psychosis. Loss of delayed and immediate memory and 

decreases in visual ability, psychomotor ability, and visual learning were reported in workers exposed to 

unspecified levels of hydrogen cyanide for an unspecified duration (Kumar et al. 1992). In another study, 

chronic occupational exposure of workers (5–19 years) to hydrogen cyanide (exposure levels not 

specified) resulted in headaches and dizziness in workers (Chandra et al. 1988). Furthermore, when 

behavioral functions were tested in this cohort, an alteration of delayed memory and/or visual impairment 

was found in 31.5% of workers. However, exposure to other chemicals, such as cleaners and cutting oils, 

also occurs during electroplating operations. 

The central nervous system is also a primary target for cyanide toxicity in animals. Following acute 

exposure, neurological effects before death included restless and panic movements, poor coordination, 

tremor, and lethargy in rats exposed to 250 ppm cyanogen (125 ppm cyanide) for 1.5–120 minutes 

(McNerney and Schrenk 1960). When rats were exposed to unspecified concentrations of hydrogen 

cyanide and kept unconscious for 20–60 minutes, lesions of various degrees developed in the brain 
CYANIDE 41 

3. HEALTH EFFECTS 

(Hirano et al. 1967; Levine 1969; Levine and Stypulkowski 1959a). Necrosis was found mainly in the 

mid-sagittal sections of the brain. Demyelination was also reported and morphological signs indicative of 

remyelination were reported in rats several months after cyanide intoxication (Hirano et al. 1968), but it 

was apparent that this process was slow and incomplete. Acute exposure of dogs for 2–10 minutes, each 

to a different concentration ranging from 149 to 633 ppm hydrogen cyanide resulted in motor 

incoordination, muscular rigidity, and coma (Haymaker et al. 1952). Extensive necrosis in the grey 

matter of the neural system was observed at necropsy. After acute exposure (up to 30 minutes) to 60– 

100 ppm hydrogen cyanide, increased delta activity was observed in electroencephalograms of 

cynomolgus monkeys, but those exposed at the higher level experienced semiconsciousness within 

20 minutes (Purser 1984; Purser et al. 1984). Cyanide exposure levels in most acute-duration studies 

were relatively high and usually caused death in some animals. Only transitory behavioral changes were 

reported in monkeys exposed to 25 ppm cyanogen (12.5 ppm cyanide) for 6 months (Lewis et al. 1984). 

No effects were found at 11 ppm cyanogen (5.5 ppm cyanide) exposure. Exposure of dogs to 45 ppm 

hydrogen cyanide for 28–96 days caused tremors, convulsions, and coma (Valade 1952). Vascular and 

cellular lesions were found in the central nervous system. 

In rats exposed to 10–50 ppm hydrogen cyanide for 3.5 hours, there was no adverse effect 4 weeks later 

on hearing or the histology of cochlear hair cells (Fechter et al. 2002). However, co-administration for 

2 hours of 100 dB broadband noise (13.6 kHz) caused an hydrogen cyanide-dose-related increase in 

auditory compound action potential thresholds compared with noise administered alone that was 

statistically significant at 30 ppm hydrogen cyanide; a loss of outer hair cells of the cochlea was noted in 

rats exposed to hydrogen cyanide and noise. 

The highest NOAEL value and all reliable LOAEL values for neurological effects in each species and 

duration category are recorded in Table 3-1 and plotted in Figure 3-1. Neurotoxicity data for dogs have 

been omitted from Table 3-1 and Figure 3-1 because that species has a relatively low amount of the 

detoxifying enzyme rhodanese and is unusually susceptible to cyanide exposure compared to humans or 

other mammals (see Sections 3.4.3 and 3.5.3). 
CYANIDE 42 

3. HEALTH EFFECTS 

No studies were located regarding the following health effects in humans or animals after inhalation 

exposure to cyanide: 

3.2.1.5 Reproductive Effects 

3.2.1.6 Developmental Effects 

3.2.1.7 Cancer 

3.2.2 Oral Exposure 

3.2.2.1 Death 

An average fatal dose of 1.52 mg/kg cyanide for humans has been calculated from case report studies of 

intentional or accidental poisonings (EPA 1987a). The lowest fatal oral dose reported in humans was 

estimated as 0.56 mg/kg cyanide (form not specified) (Gettler and Baine 1938). However, these data 

were obtained from the case history; furthermore, analytical measurements of the time lack the precision 

of current technology. 

Oral LD50 (lethal dose, 50% death) values for sodium cyanide were calculated as 3 mg CN–

/kg for 

unfasted rats, and 2.7 mg CN–

/kg/day for rats that fasted for 24 hours before exposure and for unfasted 

rabbits (Ballantyne 1988); initial signs of toxicity appeared sooner in rats (1 minute for both groups) than 

in rabbits (4 minutes) and the time to death was shorter in the fasted rats than in the unfasted rats or 

rabbits (17 rather than 22 minutes). In rats, the acute LD50 was 8 mg CN–

/kg as sodium cyanide, but 

22 mg CN–

/kg as calcium cyanide (Smyth et al. 1969). Acute LD50 values in rabbits were similar (2.34– 

2.7 mg CN–

/kg/day) regardless of whether the source was hydrocyanic acid, sodium cyanide, or 

potassium cyanide (Ballantyne 1983a). Mortality was 95% in rats and mice that received a single dose of 

4 and 6 mg CN–

/kg, respectively, in the form of potassium cyanide in a volume of water equivalent to 5% 

of body weight (Ferguson 1962); mortality was lower (50% in rats and 35% in mice) when the same 

doses were delivered in a volume of water equivalent to 1.25% of body weight. Increased mortality was 

observed in rats exposed to 14.5 mg CN–

/kg/day as copper cyanide for 90 days (Gerhart 1986) and to 

2.6 mg CN–

/kg/day as potassium silver cyanide for 90 days (Gerhart 1987); these data are omitted from 

Table 3-2 because of the possible confounding effect of the metals. Hemolytic anemia, which probably 

resulted from copper toxicity, caused death in rats exposed to copper cyanide (Gerhart 1986). No deaths 
CYANIDE 43 

3. HEALTH EFFECTS 

were reported in male and female rats exposed to 0.2–12.5 mg CN–/kg/day in the drinking water for 

13 weeks (NTP 1993). 

The LD50 and minimum lethal dose (LDLO) values in each species and all reliable LOAEL values for 

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

3.2.2.2 Systemic Effects 

The systemic effects observed in humans and animals after oral exposure to cyanide are discussed below. 

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

duration category are recorded in Table 3-2 and plotted in Figure 3-2. Studies on dogs have been omitted 

because that species has a relatively low amount of the detoxifying enzyme rhodanese and is unusually 

susceptible to cyanide exposure compared to humans or other mammals (see Sections 3.4.3 and 3.5.3). 

Studies involving ingestion of cassava have also been omitted because of the confounding effects of 

malnutrition noted in human studies and because of the presence of other toxic compounds besides 

cyanogenic glycosides that might contribute to toxicity (e.g., scopoletin; see Section 3.10). Intermediateduration studies that employed oral gavage dosing are omitted because bolus administration may 

overwhelm detoxification processes in a manner not typical of gradual exposures in drinking water for the 

general population. 

Respiratory Effects. Breathing irregularities occur after cyanide poisoning through oral exposure. 

Stertorous, deep, and rapid breathing was reported in a man who ingested ≈15 mg CN–

/kg as potassium 

cyanide in a suicide attempt (Liebowitz and Schwartz 1948). Shortness of breath and dyspnea were 

observed in two reports of suicide attempts; one man ingested 7.6 mg CN–

/kg (Goodhart 1994) and the 

other man ingested 0.57 mg CN–

/kg (Saincher et al. 1994), both as potassium cyanide. A man admitted to 

a hospital after ingesting an unknown amount of sodium cyanide ceased breathing (Grandas et al. 1989). 

A woman who ingested an unknown amount of cyanide developed acute respiratory distress syndrome 

and arteriolization (elevated oxyhemoglobin saturation) of the ventral venous blood (Martin-Bermudez et 

al. 1997). Dyspnea developed in a woman 20 minutes after eating 30 apricot pits (~15 g), resulting in an 

estimated cyanide exposure between 0.026 and 0.234 mg CN–

/kg (Suchard et al. 1998). Tachypnea was 

also reported in children who were poisoned by cyanide after ingesting apricot pits (Lasch and El Shawa 

1981). 
a

Key to

Figure

Table 3-2 Levels of Significant Exposure to Cyanide - Oral

Species

(Strain)

LOAEL

System 

NOAEL

(mg/kg/day)

Less Serious

(mg/kg/day)

Serious

(mg/kg/day)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

ACUTE EXPOSUREDeath

1

91

Ferguson 1962KCN

4 (19/20 died)

4

Rat(SpragueDawley)

once(GW)

2

92

Smyth et al. 1969Ca(CN)2

22 (LD50)

22

Rat(NS)

once(GW)

3

93

Smyth et al. 1969NaCN

8 (LD50)

8

Rat(NS)

once(GW)

4

90

Ferguson 1962KCN

6 (19/20 died)

6

Mouse(SwissWebster)

once(GW)

Systemic

5

8

Liebowitz and Schwartz KCN

Resp 15 M (hyperventilation)

15

Human once

(IN)

Cardio 15 M (shallow pulse, inaudible

heart sounds, enlargedheart)

15

Gastro 15 M (vomiting and nausea)

15

Hemato 15 M

15

Musc/skel 15 M (generalized muscular

rigidity)

15

Renal 15 M (albuminuria)

15
a

Key to

Figure

Table 3-2 Levels of Significant Exposure to Cyanide - Oral (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(mg/kg/day)

Less Serious

(mg/kg/day)

Serious

(mg/kg/day)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

Neurological

6

7

Liebowitz and Schwartz KCN

15 M (coma)

15

Human once

(IN)

7

930

Rosenow et al. 1995KCN

7.4 M (brain lesions,

Parkinsonian-like signs,decreased verbal fluencyand speed of informationprocessing)

7.4

Human once

(IN)

INTERMEDIATE EXPOSURESystemic

8

301

NTP 1993NaCN

Resp 12.5

12.5

Rat(Fischer- 344)

13 wk(W)

Cardio 12.5

12.5

Hemato 12.5

12.5

Hepatic 12.5

12.5

Renal 12.5

12.5

Endocr 12.5

12.5

Bd Wt 12.5

12.5

9

129

Philbrick et al. 1979KCN

Endocr 30 M (decreased plasma

thyroxine at 4 months,increased thyroid weightat 11 months)

30

Rat(NS)

11.5 mo(F)

Bd Wt 30 M (38% decreased weight

gain)

30
a

Key to

Figure

Table 3-2 Levels of Significant Exposure to Cyanide - Oral (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(mg/kg/day)

Less Serious

(mg/kg/day)

Serious

(mg/kg/day)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

10

352

Philbrick et al. 1979KSCN

Endocr 67 M (decreased plasma

thyroxine and thyroxinesecreting rate, increasedthyroid weight at 11 mo)

67

Rat(NS)

11.5 mo(F)

Bd Wt 67 M

67

11

303

NTP 1993NaCN

Cardio

b

24.3 M

24.3

28.8 F

28.8

Mouse(B6C3F1)

13 wk(W)

Hemato

b

24.3 M

24.3

28.8 F

28.8

Hepatic

b

24.3 M

24.3

28.8 F

28.8

Renal

b

24.3 M

24.3

28.8 F

28.8

Endocr 28.8 F

28.8

Bd Wt

b

24.3 M

24.3

28.8 F

28.8
a

Key to

Figure

Table 3-2 Levels of Significant Exposure to Cyanide - Oral (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(mg/kg/day)

Less Serious

(mg/kg/day)

Serious

(mg/kg/day)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

12

960

Okolie and Iroanya 200NaCN

Resp 15 M (pulmonary edema)

15

Rabbit(NewZealand)

4 wk(F)

Hepatic 15 M (fatty degneration and

necrosis)

15

Renal 15 M (tubular necrosis)

15

Bd Wt 15 M

15

13

958

Okolie and Osagie 1999KCN

Hepatic 20 M (focal congestion and

necrosis, increasedserum SDH, ALT, AP)

20

Rabbit(NewZealand)

40 wk(F)

Renal 20 M (tubular/glomerular

necrosis)

20

Bd Wt 20 M

20

14

959

Okolie and Osagie 2000KCN

Resp 20 M (focal pulmonary edema

and necrosis)

20

Rabbit(NewZealand)

40 wk(F)

Cardio 20 M

20

Endocr 20 M

20

Immuno/ Lymphoret

15

603

NTP 1993NaCN

12.5

12.5

Rat(Fischer- 344)

13 wk(W)
a

Key to

Figure

Table 3-2 Levels of Significant Exposure to Cyanide - Oral (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(mg/kg/day)

Less Serious

(mg/kg/day)

Serious

(mg/kg/day)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

16

604

NTP 1993NaCN

b

24.3 M

24.3

28.8 F

28.8

Mouse(B6C3F1)

13 wk(W)

Neurological

17

605

NTP 1993NaCN

12.5

12.5

Rat(Fischer- 344)

13 wk(W)

18

128

Philbrick et al. 1979KCN

30 M (modest myelin

degeneration in spinalcord)

30

Rat(NS)

11.5 mo(F)

19

353

Philbrick et al. 1979KSCN

67 M (modest myelin

degeneration in spinalcord)

67

Rat(NS)

11.5 mo(F)

20

606

NTP 1993NaCN

b

24.3 M

24.3

28.8 F

28.8

Mouse(B6C3F1)

13 wk(W)
a

Key to

Figure

Table 3-2 Levels of Significant Exposure to Cyanide - Oral (continued)

Species

(Strain)

LOAEL

System 

NOAEL

(mg/kg/day)

Less Serious

(mg/kg/day)

Serious

(mg/kg/day)

ReferenceChemical Form

Exposure/

Duration/

Frequency

(Route)

Reproductive

21

304

NTP 1993NaCN

b,c

4.5 M

4.5

12.5 F

12.5

12.5 M (decreased left

epididymal [7%], leftcaudal epididymal [13%],and testes weights [8%],number of spermatidheads per testis [14%],and spermatid count[14%])

12.5

Rat(Fischer- 344)

13 wk(W)

22a The number corresponds to entries on Figure 3-2.b Differences in levels of health effects and cancer effects between male and females are not indicated in Figure 3-2. Where such differences exist, only the levels most sensitive gender are presented.c Used to derive intermediate oral minimal risk level (MRL) of 0.05 mg/kg/day; dose divided by an uncertainty factor of 100 (10 for extrapolation from animals to humhuman variability).ATP = adenosine triphosphate; Bd Wt = body weight; BUN = blood urea nitrogen; Cardio = cardiovascular; Ca(CN)2 = calcium cyanide; d = day(s); Endocr = endoc

(G) = gavage; Gastro = gastrointestinal; Gd = gestation day; (GW) = gavage in water; HCN = hydrogen cyanide; Hemato = hematological; (IN) = ingestion; KAgCNsilver cyanide; KCN = potassium cyanide; KSCN = potassium thiocyanate; LD50 = lethal dose, 50% kill; Ld = lactation day; LDlo = lowest lethal dose; LOAEL =lowest-observed-adverse-effect level; M = male; mo = month(s); NaCN = sodium cyanide; NOAEL = no-observed-adverse-effect level; NS = not specified; NTP = NProgram; prox = proximal; Resp = respiratory; SDH = sorbital dehydrogenase; T3 = triiodothyronine; T4 = thyroxine; (W) = water; wk = week(s); x = time(s)

305

NTP 1993NaCN

b

8.6 M

8.6

28.8 F

28.8

24.3 M (10 and 18% decrease in

left epididymus andcaudal epididymusweights)

24.3

Mouse(B6C3F1)

13 wk(W)
1

10

100

Death

4m

1r

2r

3r

Respiratory

5

Cardiovascular

5

Gastrointestinal

5

Hematological

5

Musculoskeletal

5

Renal

5

Neurological

6

7

mg/kg/day

Figure 3-2 Levels of Significant Exposure to Cyanide - Oral

Acute (≤14 days)

c-Cat

d-Dog

r-Rat

p-Pig q-Cow

 -Humans

k-Monkey

m-Mouse

h-Rabbit

a-Sheep

f-Ferret

j-Pigeon

e-Gerbil

s-Hamster

g-Guinea Pig

n-Mink

o-Other

 Cancer Effect Level-Animals

 LOAEL, More Serious-Animals

 LOAEL, Less Serious-Animals

 NOAEL - Animals

 Cancer Effect Level-Humans

 LOAEL, More Serious-Humans

 LOAEL, Less Serious-Humans

 NOAEL - Humans

 LD50/LC50

 Minimal Risk Level

 for effects

 other than

 Cancer

Systemic

CYANIDE

 3. HEALTH EFFECTS

50
0.01

0.1

1

10

100

Respiratory

8r

12h

14h

Cardiovascular

11m

8r

14h

Hematological

11m

8r

Hepatic

11m

8r

12h

13h

Renal

11m

8r

12h

13h

Endocrine

11m

8r

9r

10r

14h

Body Weight

11m

8r

9r

10r

12h

13h

Immuno/Lymphor

16m

15r

Neurological

20m

17r

18r

19r

Reproductive

22m

22m

21r

21r

mg/kg/day

Figure 3-2 Levels of Significant Exposure to Cyanide - Oral

Intermediate (15-364 days

c-Cat

d-Dog

r-Rat

p-Pig q-Cow

 -Humans

k-Monkey

m-Mouse

h-Rabbit

a-Sheep

f-Ferret

j-Pigeon

e-Gerbil

s-Hamster

g-Guinea Pig

n-Mink

o-Other

 Cancer Effect Level-Animals

 LOAEL, More Serious-Animals

 LOAEL, Less Serious-Animals

 NOAEL - Animals

 Cancer Effect Level-Humans

 LOAEL, More Serious-Humans

 LOAEL, Less Serious-Humans

 NOAEL - Humans

 LD50/LC50

 Minimal Risk Level

 for effects

 other than

 Cancer

)

Systemic

(Continued)

CYANIDE

 3. HEALTH EFFECTS

51
CYANIDE 52 

3. HEALTH EFFECTS 

Respiratory effects were also observed in animals exposed to cyanide. Alveolar congestion, pulmonary 

edema, and significant decreases in activities of superoxide dismutase, catalase, and alkaline phosphatase 

were observed in the lungs of male rabbits that ingested 15 mg/kg/day of cyanide from sodium cyanide in 

feed for 4 weeks (Okolie and Iroanya 2003). Labored respiration was reported in rats treated with 

4.35 mg CN–

/kg/day as copper cyanide by gavage for 90 days (Gerhart 1986). No effects were reported 

at 1.45 mg CN–

/kg/day. Labored respiration occurred in rats exposed at a lower dose of 0.8 mg CN– 

/kg/day when administered in a form of potassium silver cyanide for 90 days (Gerhart 1987). Lung 

congestion and hemorrhage seen at necropsy were attributed to asphyxia rather than to a direct effect of 

cyanide. In another study, rats were exposed to 0.2–12.5 mg CN–

/kg/day as sodium cyanide in the 

drinking water for 13 weeks. Changes in absolute lung weight were seen, but they were minor and 

sporadic, and the authors did not consider them to be treatment related (NTP 1993). No respiratory 

effects were reported in rats exposed to a target dose of 10.4 mg CN–

/kg/day as hydrogen cyanide in their 

feed for 2 years (Howard and Hanzal 1955). The actual dose, however, may have been considerably 

lower than 10.4 mg/kg/day due to evaporation of hydrogen cyanide from the food. 

Cardiovascular Effects. Several case studies reported cardiovascular effects in humans after oral 

exposure to cyanide. Weak, shallow pulse and inaudible heart sounds were observed in a comatose man 

on hospital admission after ingestion of ≈15 mg CN–

/kg as potassium cyanide (Liebowitz and Schwartz 

1948). Following gastric lavage and glucose infusion, the pulse rate and blood pressure became elevated. 

An enlarged heart was noted. No cardiovascular effects were reported during the recovery. In another 

study, children poisoned by apricot pits had hypotension upon hospital admission (Lasch and El Shawa 

1981). 

After intermediate- or chronic-duration oral exposure to inorganic cyanides, cardiovascular effects in 

animals, if any, are minimal. No significant histopathological changes were observed in rats exposed to 

2.6 or 7.8 mg CN–

/kg/day as potassium silver cyanide for 90 days (Gerhart 1987). No treatment-related 

effects on heart histopathology or tissue levels of aspartate aminotransferase (AST) or alkaline 

phosphatase were observed in male rabbits that ingested 20 mg CN–

/kg/day as potassium cyanide via the 

diet for 10 months (Okolie and Osagie 2000). Changes in absolute heart weight were seen in male and 

female mice exposed to 0.3–28.8 mg CN–

/kg/day as sodium cyanide in the drinking water for 13 weeks, 

but they were minor and sporadic, and the authors did not consider them to be treatment related (NTP 

1993). Dogs fed a diet of cassava ingested an estimated 1.04 mg CN–

/kg/day for 14 weeks and exhibited 

hemorrhage, pyknotic nuclei, and swelling of muscle fibers in the myocardium, while dogs fed rice to 

which 1.04 mg CN–

/kg food was added as sodium cyanide did not show any cardiovascular effects 
CYANIDE 53 

3. HEALTH EFFECTS 

(Kamalu 1993). Furthermore, no cardiovascular effects were observed in rats exposed to an estimated 

dose of 10.4 mg CN–

/kg/day as hydrogen cyanide in their feed for 2 years (Howard and Hanzal 1955). 

The actual dose, however, may have differed from 10.4 mg/kg/day due to evaporation of hydrogen 

cyanide from the food. 

Gastrointestinal Effects. Vomiting was reported in children who ingested a large number of apricot 

pits (Lasch and El Shawa 1981) and in a man who ingested 7.6 mg CN–

/kg in a suicide attempt (Goodhart 

1994). Gastrointestinal spasms were reported in a man who accidentally ingested (and inhaled) an 

unknown amount of potassium cyanide (Thomas and Brooks 1970). Gastric surgery for extensive 

necrosis had to be performed in a man after he ingested an unknown amount of sodium cyanide (Grandas 

et al. 1989). The alkaline properties of solutions of sodium and potassium cyanide cause the corrosive 

responses in the stomach following ingestion. 

Diarrhea was observed in rats treated orally with 14.5 mg CN–

/kg/day copper cyanide for 90 days 

(Gerhart 1986). No effects were observed at 4.35 mg/kg/day. However, as the diarrhea was probably due 

to the toxicity of copper, these data are omitted from Table 3-2. No gastrointestinal effects were found in 

rats exposed to 7.8 mg CN–

/kg/day as potassium silver cyanide for 90 days (Gerhart 1987). However, 

increased vomiting was reported in pigs in a dose as low as 0.7 mg CN–

/kg/day given as potassium 

cyanide for 24 weeks by gavage (Jackson 1988). Chronic intestinal inflammation occurred in dogs 

exposed to ≥0.27 mg CN–

/kg/day for 14.5 months (Hertting et al. 1960). 

Hematological Effects. Information regarding hematological effects in humans after oral exposure 

to cyanide is limited. No adverse hematologic effects were reported in a man who ingested 15 mg 

CN–

/kg as potassium cyanide (Liebowitz and Schwartz 1948). 

In animals, hematological effects were observed in studies with copper cyanide, potassium cyanide, 

potassium silver cyanide, and sodium cyanide. Hemolytic anemia was diagnosed in the group of rats 

treated by gavage for 90 days with 14.5 mg CN–

/kg/day as copper cyanide (Gerhart 1986). Decreased 

erythrocytes were reported together with decreased hemoglobin concentrations and decreased hematocrit. 

The diagnosis of anemia was supported by microscopic findings of pigmentation of the spleen and liver, 

presence of hemoglobin in the cytoplasm of the renal convoluted tubule epithelium, and by hyperplasia of 

hematopoietic tissue (spleen and bone marrow). Decreased hemoglobin was observed also at 4.35 mg 

CN–

/kg/day after 90 days. Since hemolytic anemia is characteristic of copper toxicity; the hematological 

effects can be partially attributed to copper toxicity rather than to cyanide toxicity, and the data are 
CYANIDE 54 

3. HEALTH EFFECTS 

omitted from Table 3-2; other anions of tested cyanide compounds are not known to contribute to 

hematological effects. Increased mean corpuscular volume, mean corpuscular hemoglobin concentration, 

and spleen weight indicated hematological effects in rats exposed to 7.8 mg CN–

/kg/day as potassium 

silver cyanide for 90 days by gavage. No effects were found at 2.6 mg CN–

/kg/day (Gerhart 1987). The 

contribution of silver to the hematological effects is not known. In another study, minimal changes were 

observed in hematology in rats and mice exposed to sodium cyanide in the drinking water for 13 weeks 

and the authors did not consider them to be treatment related (NTP 1993). 

Musculoskeletal Effects. Muscular rigidity was observed in humans after acute cyanide poisoning 

(Grandas et al. 1989) and rhabdomyolysis, a clinical syndrome characterized by skeletal muscle injury, 

was observed in a man who ingested 0.57 mg CN–

/kg as potassium cyanide in a suicide attempt (Saincher 

et al. 1994). 

No studies were located regarding musculoskeletal effects in animals after oral exposure to cyanide. 

Hepatic Effects. Increased serum creatinine and serum creatinine kinase were observed in a man who 

ingested 0.57 mg CN–

/kg as potassium cyanide in a suicide attempt (Saincher et al. 1994). 

In animals, hepatotoxicity was observed after ingestion of copper cyanide. Male rats treated for 90 days 

by gavage with 14.5 mg CN–

/kg/day as copper cyanide had increased levels of serum glutamic 

oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT) levels, increased 

bilirubin and alkaline phosphatase, and decreased globulin levels in the blood (Gerhart 1986). Liver 

necrosis was observed in the group of female rats treated with 4.35 mg CN–

/kg/day. However, blood 

chemistry did not reveal any changes. The hepatic effects of copper cyanide are possibly due to the 

toxicity of copper rather than of cyanide and are therefore omitted from Table 3-2. 

Changes in absolute and relative liver weights were reported in rats exposed to 0.2–12.5 mg CN–

/kg/day 

and mice exposed to 0.3–28.8 mg CN–

/kg/day, both as sodium cyanide in the drinking water for 

13 weeks, but they were minor and sporadic, and the authors did not consider them to be treatment related 

(NTP 1993). Severe cytoplasmic vacuolization of hepatocytes was observed in male rats that ingested 

3.6 mg CN–

/kg/day as potassium cyanide in drinking water for 15 days (Sousa et al. 2002); hepatic effects 

were minimal at 0.36–1.2 mg CN–

/kg/day and absent at 0.12 mg CN–/kg/day. In this study, serum AST 

was significantly higher than the control (by 21–33%) at the three lower doses, but was lower than the 

control at the highest dose. The hepatic toxicity data from Sousa et al. (2002) are omitted from Table 3-2 
CYANIDE 55 

3. HEALTH EFFECTS 

and Figure 3-2 because no incidence data were provided for the lesions and the elevation in AST occurred 

with an inverse dose response in treated groups. Liver histopathology (necrosis, fatty degeneration, and 

congestion), decreased hepatic enzyme activities (for superoxide dismutase, catalase, and alkaline 

phosphatase), and increased serum enzyme activities (lactate dehydrogenase and alanine 

aminotransferase) indicative of liver damage were observed in male rabbits that ingested 15 mg 

CN–

/kg/day from sodium cyanide in feed for 4 weeks (Okolie and Iroanya 2003). In another study, 

periportal vacuolation and congestion were observed in the livers of dogs fed 1.04 mg CN–

/kg/day, as 

cassava, while no hepatic effects were observed in dogs fed rice containing the same concentration of 

cyanide, as sodium cyanide, for 14 weeks (Kamalu 1993). Focal congestion and necrosis were observed 

in the livers of male rabbits that ingested 20 mg CN–

/kg/day as potassium cyanide via the diet for 10 

months (Okolie and Osagie 1999). No hepatic effects were reported in rats exposed by gavage to 7.8 mg 

CN–

/kg/day as potassium silver cyanide for 90 days (Gerhart 1987) or in rats exposed to an estimated 

dose of 10.4 mg CN–

/kg/day as hydrogen cyanide in their feed for 2 years (Howard and Hanzal 1955). 

The actual dose, however, may have differed from 10.4 mg/kg/day due to evaporation of hydrogen 

cyanide from the food. 

Renal Effects. Information regarding renal effects of cyanide in humans is limited to one report. 

Albuminuria was found in a man during the first 2 days after ingestion of 15 mg CN–

/kg as potassium 

cyanide in a suicide attempt (Liebowitz and Schwartz 1948). 

In male rabbits that ingested 15 mg CN–

/kg/day from sodium cyanide in feed for 4 weeks, renal 

histopathology (tubular and glomerular necrosis) and decreases in renal activities of superoxide dismutase 

and catalase were observed (Okolie and Iroanya 2003). In rats, decreased kidney weight was observed in 

rats treated with 14.5 mg CN–

/kg/day as copper cyanide for 90 days (Gerhart 1986); no changes were 

reported at 4.35 mg/kg/day exposure. However, as copper toxicity was probably responsible for the 

kidney effects, these data are omitted from Table 3-2. Increased blood urea nitrogen was found at 7.8 mg 

CN–

/kg/day, but not at 2.6 mg CN–/kg/day, as potassium silver cyanide (Gerhart 1987). The contribution 

of silver to this effect is not known. No significant changes indicating renal effects were found on 

analysis of blood samples taken at the end of the experiment. Changes in absolute and relative kidney 

weights were observed in rats and mice exposed to 0.2–12.5 mg CN–

/kg/day and mice exposed to 0.3– 

28.8 mg CN–

/kg/days sodium cyanide in the drinking water for 13 weeks, but they were minor and 

sporadic, and the authors did not consider them to be treatment related (NTP 1993). 
CYANIDE 56 

3. HEALTH EFFECTS 

Histopathological lesions of the kidney have been reported in animals exposed to cyanide. Congestion 

and cytoplasmic vacuolization of the proximal tubular epithelium (moderate-to-severe) were observed in 

male rats exposed to 1.2–3.6 mg CN–

/kg/day as potassium cyanide in drinking water for 15 days (Sousa et 

al. 2002); lesions were minimal in severity at 0.3 mg CN–

/kg/day and absent at 0.12 mg CN–/kg/day. 

However, as no incidence data were provided for these lesions, they are omitted from Table 3-2 and 

Figure 3-2. Proliferation of glomerular cells in the kidney was observed in pigs exposed to 0.64 mg 

CN–

/kg/day in cassava feed for 110 days (Tewe and Maner 1981b). In another study, vacuolation, 

swelling, and proximal tubule damage with desquamation of the epithelium and casts were observed in 

kidneys of dogs fed 1.04 mg CN–

/kg/day as cassava, while increased urinary protein, casts, and some 

desquamation, but no damage in proximal tubules, were observed in dogs fed rice with the same 

concentration of cyanide, as sodium cyanide, for 14 weeks (Kamalu 1993). Renal tubular and glomerular 

necrosis were observed in male rabbits that were exposed to 20 mg CN–

/kg/day as potassium cyanide via 

the diet for 10 months (Okolie and Osagie 1999). However, no renal effects were observed in rats 

exposed to an estimated dose of 10.4 mg CN–

/kg/day as hydrogen cyanide in their feed for 2 years 

(Howard and Hanzal 1955); in this study, however, the actual dose may have been different due to 

evaporation of hydrogen cyanide from the food. Cloudy swelling of epithelial cells of renal tubules was 

reported in three dogs; each dog was exposed to a different dose of sodium cyanide (ranging from 0.27 to 

1.68 mg CN–

/kg/day) for 14.5 months (Hertting et al. 1960). 

Endocrine Effects. Cyanide occurs naturally in several plants, such as cassava, soybeans, spinach, 

and bamboo shoots, in which it is generated after ingestion from cyanogenic glycosides. Chronic oral 

exposure to cyanide in humans who eat cassava as a main carbohydrate source of their diet has been 

associated with thyroid toxicity. The effects are probably caused by thiocyanate, a metabolite of cyanide 

that reduces iodine uptake by the thyroid. The incidence of endemic goiter correlated with cassava intake 

in the Congo, where thyroid uptake of radioiodine was decreased in the goitrous area, compared with the 

controls (Delange and Ermans 1971). In another study, altered thyroid hormone parameters were 

measured in a village in Mozambique where an epidemic of spastic paraparesis was found, which was 

related to ingestion of cassava (Cliff et al. 1986). Increases in thyroid stimulating hormone levels and the 

ratio of triiodothyronine to thyroxine (T3/T4) were detected in serum; consistent with these measurements, 

the authors calculated a decrease in the index of free thryroxine (FT4I) and an increase in free 

triiodothyronine (FT3I). However, the incidence of endemic goiter was not elevated in this village. 

Examined individuals also had very high levels of thiocyanate in serum and urine (Cliff et al. 1986). 
CYANIDE 57 

3. HEALTH EFFECTS 

Thyroid effects were also found in animals exposed to cyanide. Dose-related increases in the number of 

histological lesions of the thyroid gland (reabsorption vacuoles) were observed in all male rats that 

ingested 0.12–3.6 mg CN–

/kg/day as potassium cyanide in drinking water for 15 days (Sousa et al. 2002). 

These data are omitted from Table 3-2 and Figure 3-2 because plasma levels of T3 and T4 were unaffected 

by treatment and longer exposures in other studies found no effect on the thyroid. For example, daily 

exposure of male rats by gavage to 0.02–0.24 mg CN–

/kg/day as potassium cyanide for 3 months had no 

effect on plasma a levels of T3 and T4 or thyroid histology (Soto-Blanco et al. 2002a). Rats fed a diet 

containing 30 mg CN–

/kg/day as potassium cyanide for 4 months had a significant decrease in plasma 

thyroxine levels and thyroxine secretion rates; at 11 months, treated rats showed no significant decreases 

in thyroxine concentrations, but had significant increases in relative thyroid weight (Philbrick et al. 1979). 

When pigs were fed cassava diets with or without additional potassium cyanide during pregnancy, an 

increase in the maternal thyroid weight and thyroid gland hypofunction were observed after ingestion of 

11.3 mg CN–

/kg/day, but not at 5.6 mg CN–/kg/day (Tewe and Maner 1981b). This study is omitted from 

Table 3-2 and Figure 3-2 because it did not include a control group fed a cyanide-free diet. In another 

study, no effects on the thyroid gland were noted at 12.5 mg CN–

/kg/day in rats given sodium cyanide in 

drinking water for 13 weeks or in mice given 24.3–28.8 mg CN–

/kg/day (NTP 1993). However, thyroid 

effects have been reported at low doses in another study. Decreased thyroid function was found in pigs 

exposed to 0.4 mg CN–

/kg/day as potassium cyanide for 24 weeks by gavage (Jackson 1988). The 

pancreas showed no histopathology in this study. The histology of the pancreas was unaffected in male 

rabbits that ingested 20 mg CN–

/kg/day as potassium cyanide via the diet for 10 months (Okolie and 

Osagie 2000). 

Effects on the adrenal gland, including swelling of the adrenal cortex, hemorrhage, and fibrosis, were 

observed in dogs fed 1.04 mg CN–

/kg/day as cassava, as well as in dogs fed rice with the same 

concentration of cyanide, as sodium cyanide, for 14 weeks (Kamalu 1993). 

Dermal Effects. No studies were located regarding dermal effects in humans after oral exposure to 

cyanide. 

During intermediate-duration exposure, discolored inguinal fur was found in rats exposed for 90 days to 

14.5 mg CN–

/kg/day by gavage as copper cyanide (Gerhart 1986) and to 2.6 mg CN–/kg/day as potassium 

silver cyanide (Gerhart 1987). As no dermal effects were described in animals exposed to cyanide 

compounds that did not include heavy metals, these data are omitted from Table 3-2 and Figure 3-2. 
CYANIDE 58 

3. HEALTH EFFECTS 

Ocular Effects. Macular degeneration and optic atrophy were reported in 20 West Africans who 

ingested cassava over an unspecified period (van Heijst et al. 1994). The mean levels of thiocyanate and 

cyanide in these patients were elevated, but were not statistically different from controls (hospital staff). 

Individuals with other neurological lesions in addition to ocular effects had significantly elevated serum 

levels of thiocyanate and cyanide. The authors indicated that nutritional deficiencies contributed to 

neuropathy. 

Ocular opacity was noted in rats exposed to 2.6 mg CN–

/kg/day as potassium silver cyanide for 90 days 

(Gerhart 1987); since it is likely that opacity resulted from deposition of silver, these data are omitted 

from Table 3-2 and Figure 3-2. No pathological findings were observed during ophthalmological 

examination of rats exposed to 14.5 mg CN–

/kg/day as copper cyanide for 90 days (Gerhart 1986). 

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

exposure to cyanide. 

Decreased body weight gain was cited as one of the effects of exposure to copper cyanide, potassium 

cyanide, and potassium silver cyanide. Terminal body weights were significantly reduced by 18% in 

male rats that ingested 3.6 mg CN–

/kg/day as potassium cyanide in drinking water for 15 days, but were 

unaffected at 0.12–1.2 mg CN–

/kg/day (Sousa et al. 2002); the effect in high dose rats was significant as 

early as the first week of treatment. The significance of these results are uncertain given the lack of body 

weight effects in other studies. For example, no effect on body weight gain was observed in male rats 

exposed by gavage to 0.02–0.24 mg CN–

/kg/day as potassium cyanide for 3 months (Soto-Blanco et al. 

2002a). In addition, there was no statistically significant or dose-related effect on body weight gain in 

rats exposed to doses as high as 12.5 mg CN–

/kg/day or in mice exposed to doses as high as 

28.8 mg CN-/kg/day as sodium cyanide in drinking water for 13 weeks (NTP 1993). Reduced body 

weight gain was reported in male rats exposed for 90 days to 4.35 mg CN–

/kg/day as copper cyanide, but 

not in those exposed to 1.45 mg CN–

/kg/day for 90 days (Gerhart 1986). Furthermore, decreased weight 

gain was found in male rats exposed to 2.6 mg CN–

/kg/day as potassium silver cyanide for 90 days 

(Gerhart 1987). Since the presence of the copper or silver may have contributed to the observed 

decreased body weight, these data are omitted from Table 3-2 and Figure 3-2. Pregnant hamsters fed 

1.0 mg CN–

/kg/day in cassava for 10 days during gestation had decreased body weight gain (Frakes et al. 

1986a). No body weight effects were noted in male rabbits that ingested 15 mg CN–

/kg/day from sodium 

cyanide in the diet for 4 weeks (Okolie and Iroanya 2003). Body weight gain was significantly reduced in 
CYANIDE 59 

3. HEALTH EFFECTS 

male rabbits that ingested 20 mg CN–/kg/day as potassium cyanide via the diet for 10 months (Okolie and 

Osagie 1999). 

Metabolic Effects. Yen et al. (1995) reported metabolic acidosis in 67% of patients acutely poisoned 

by unknown concentrations of cyanide. Metabolic acidosis was observed in a woman who received an 

estimated dose of cyanide between 0.026 and 0.234 mg CN–

/kg from ingesting 30 apricot kernels 

(approximately 15 g) (Suchard et al. 1998). An apparent attempted homicide victim developed metabolic 

acidosis after ingesting an unknown quantity of cyanide (Chin and Calderon 2000). 

In one animal study mentioning metabolic effects, decreased serum albumin and lowered calcium and 

potassium levels were observed in dogs fed 1.04 mg CN–

/kg/day as cassava or sodium cyanide for 

14 weeks (Kamalu 1993). Statistically significant reductions in mitochondrial respiratory control ratios 

(by 17–22%) and tissue ATP levels (by 23–28%) were reported in the liver and heart, but not the brain of 

female rats receiving 3.7 mg CN–

/kg/day as potassium cyanide in drinking water for 30 days (Pritsos 

1996). As no data were provided to confirm whether these biochemical findings were mirrored by 

adverse effects on oxygen usage at the physiological level, these data are omitted from Table 3-2 and 

Figure 3-2. 

3.2.2.3 Immunological and Lymphoreticular Effects 

No studies were located regarding immunological effects in humans after oral exposure to cyanide. 

No significant changes in absolute or relative thymus weight were noted in rats and mice exposed to up to 

12.5 and 28.8 mg CN–

/kg/day as sodium cyanide, respectively, in drinking water for 13 weeks (NTP 

1993). 

3.2.2.4 Neurological Effects 

Neurologic toxicity following cyanide ingestions differs depending on length of exposure and the rate at 

which treatment is administered. Neurological effects of cyanide poisoning in humans may correlate with 

the amount ingested; however, the exact doses consumed by the victims are usually not known. Tremors 

were reported in a patient who accidentally ingested an unknown amount of fluid containing 2.3% silver 

cyanide and 6.9% sodium cyanide (Chen and Rose 1952). Children who ingested a large number of 
CYANIDE 60 

3. HEALTH EFFECTS 

apricot pits experienced various neurological effects ranging in severity from headaches to coma (Lasch 

and El Shawa 1981). The severity of effects corresponded with the amount of ingested pits. Comatose 

patients were admitted to a hospital after ingesting 15 mg CN–

/kg (Liebowitz and Schwartz 1948), 7.6 mg 

CN–

/kg (Goodhart 1994), 114–229 mg CN–/kg (Kasamo et al. 1993), and 5.7 mg CN–/kg (Valenzuela et 

al. 1992), all as potassium cyanide. A cancer patient who ingested 3,000 mg of amygdalin soon became 

comatose and had two general tonic-clonic seizures (Bromley et al. 2005). Although the dose is generally 

nontoxic, hydrolysis would potentially release 180 mg of cyanide. It was suggested that the patient’s high 

daily intake of ascorbic acid (4,800 mg/day) may have elevated the rate of hydrolysis in the gut, resulting 

in increased release of cyanide. Histopathological effects in the brain were noted in an individual who 

died 4 days after being poisoned with potassium cyanide (Riudavets et al. 2005). Effects included 

autolysis in several regions of the brain (basal ganglia, thalamus, hypothalamus, and cerebellum), acute 

hypoxic/ischemic changes (neuronal necrosis) in the cerebellum (Purkinje and granule cells), basal 

ganglia, hypothalamus, and deep cortical layers (manifest as pseudolaminar necrosis), and apoptosis of 

glial cells in the white matter. 

Several reports were located regarding development of Parkinsonism-like signs in patients after cyanide 

ingestion. A man who received emergency treatment for ingestion of 320 mg CN–

 as potassium cyanide 

in a suicide attempt developed extrapyramidal signs in the weeks following his medical discharge, 

including drooling, marked micrographia, masked facies, mild intention tremor, and cogwheel rigidity. 

Magnetic resonance imaging of the brain revealed bilateral, symmetrical abnormalities of the basal 

ganglia, particularly the globus pallidus (Feldman and Feldman 1990). A woman in a light coma had 

positive Babinski's sign on the right with slight right hemiparesis and dysphonia within 2 weeks after 

acute cyanide poisoning (dose and form of cyanide not reported) (Carella et al. 1988). Within 5 years, 

progressive Parkinsonism, dystonia, and apraxia of the right eye opening was present. Atrophy of the 

cerebellum and distinct ventricular enlargement in cerebral hemispheres were revealed by computed 

tomography and magnetic resonance image examinations. Another female developed Parkinsonian-like 

signs (intermittent stiffness with bradykinesia of the limbs) 5 months after ingesting an unknown amount 

of an unspecified cyanide compound (Chin and Calderon 2000). In another case, a man went into a coma 

after ingesting an unknown amount of sodium cyanide (Grandas et al. 1989). He later regained 

consciousness, but was apathetic with reduced speech and a loss of balance; dystonia and severe 

Parkinsonism developed during subsequent years. Computed tomography scan revealed bilateral 

luciencies in the putamen and external globus pallidus. Similar effects were observed in a 35-year-old 

female who was promptly treated after ingestion of a potentially lethal dose of potassium cyanide 

(Zaknun et al. 2005). Five days after an initial period of coma, she presented with agitation and 
CYANIDE 61 

3. HEALTH EFFECTS 

involuntary movements of the trunk and extremities, but in the third week, she developed akinetic mutism 

and loss of muscle strength; damage to central axonal auditory and somatosensory signal propagation was 

detected. Other effects included alterations in signalling in the superior pre-central cortex, disruptions of 

the blood-brain barrier, pseudolaminar cortical necrosis, and progressive loss (between days 18 and 54) of 

nigro-striatal dopaminergic neurons. Severe Parkinsonism also developed in two men who ingested 

≈5.57 mg CN–

/kg (Uitti et al. 1985) and 8.57 mg CN–/kg (Rosenberg et al. 1989), respectively, as 

potassium cyanide in suicide attempts. Lesions were reported in the globus pallidus and putamen in both 

cases. Parkinsonian-like symptoms, including severe bradykinesia, postural instability, delay in initiating 

movement, hypokinetic dysarthria, axial cogwheel rigidity, or hand tremor, developed in two men several 

weeks after ingesting potassium cyanide—amounts unknown in one and 7.4 mg CN–

/kg in the other 

(Rosenow et al. 1995). The latter individual exhibited delays in information processing and motor 

reactions as well as reduced verbal fluency when examined 5 weeks after the incident. Magnetic 

resonance imaging detected lesions of the pallidum, posterior putamen, and substantia nigra in both 

patients; deficits in subthalamic nucleus, temporal and occipital cortex, and cerebellum were noted in the 

patient who ingested 7.4 mg CN–

/kg. Reduced uptake of labeled dopamine in the putamen and caudate 

and in glucose metabolism in the temporo-parieto-occipital cortex, cerebellum, and posterior putamen 

were detected by positron emission tomography in this patient. In another study, enhanced magnetic 

resonance imaging detected lesions in the brain of a woman who became comatose after ingesting an 

unknown quantity of an unspecified cyanide compound (Rachinger et al. 2002). Three weeks after the 

suicide attempt, pseudolaminar necrosis was detected along the sensorimotor cortex and lesions were 

detected in the lentiform nuclei and caudate nuclei. Six weeks after the poisoning incident, hemorrhagic 

necrosis was detected in the striatum and globus pallidus, as well as in the basal ganglia and sensorimotor 

cortex. It must be noted that these studies do not necessarily demonstrate a true cause and effect 

relationship between cyanide exposure and Parkinsonism. However, these nine reports of such a 

relationship are indicative of the need for further research on the subject. In addition, other chemicals, 

such as manganese and carbon monoxide, and therapy with certain drugs may result in Parkinsonism. 

Memory impairment has been reported as a delayed effect in individuals who survived a cyanide 

poisoning incident with antidotal treatment. A female developed difficulties with short-term memory 

5 months after ingesting an unknown amount of an unspecified cyanide compound (Chin and Calderon 

2000). 

The effects of chronic oral exposure of humans to cyanogenic glucosides were studied in regions of 

Africa with populations that consume a high level of cassava roots (Howlett et al. 1990; Ministry of 
CYANIDE 62 

3. HEALTH EFFECTS 

Health, Mozambique 1984; Monekosso and Wilson 1966; Money 1958; Osuntokun 1968, 1972; 

Osuntokun et al. 1969; Tylleskar et al. 1994). In some cases, the diet consisted almost exclusively of 

cassava roots, due to failure of other food crops (Howlett et al. 1990). A variety of neuropathies have 

been observed in these regions and the findings correlated with increased blood thiocyanate levels, all 

collectively termed “tropical ataxic neuropathy” (Osuntokun 1973). Symmetrical hyperreflexia of the 

upper limbs, symmetrical spastic paraparesis of the lower limbs, spastic dysarthria, diminished visual 

acuity, peripheral neuropathy, cerebellar signs, and deafness were among the clinical findings (Ministry 

of Health, Mozambique 1984). Decreased plasma vitamin B12 levels were also detected in affected 

individuals (Monekosso and Wilson 1966). Konzo, a distinct upper motor neuron disease characterized 

by the sudden onset of varying degrees of symmetric, isolated, nonprogressive spastic paraparesis, has 

occurred in rural areas of Africa and has been associated with high dietary cyanide exposure from the 

consumption of insufficiently processed bitter cassava (Tylleskar et al. 1994). However, scopoletin, a 

potent hypotensive and spasmolytic agent, has also been isolated from cassava roots (Obidoa and Obasi 

1991). This substance, which remains in cassava during processing, rather than cyanide, was suggested to 

be the etiological agent in the tropical ataxic neuropathy observed among cassava eaters (Obidoa and 

Obasi 1991). In addition, protein and vitamin deficiencies may subject people in the tropics who eat 

cassava to increased risks of tropical neuropathies (Makene and Wilson 1972; Osuntokun 1972; 

Osuntokun et al. 1969). Until it can be shown that scopoletin is the etiological agent, cyanide must be 

considered the primary cause of these neuropathies. 

The central nervous system is also a primary target of orally administered cyanide in animals. Tremors, 

convulsions, recumbency, and lethargy were observed in rats exposed to 7.8 mg CN–

/kg/day as potassium 

silver cyanide for 90 days by gavage (Gerhart 1987). Since 28 of 40 rats died at this dose level, some of 

the effects described may represent nonspecific signs that precede death. Hypoactivity was observed in 

all exposed groups starting at a dose of 0.8 mg CN–

/kg/day. Similarly, hypoactivity was reported in rats 

exposed to ≥0.14 mg CN–

/kg/day as copper cyanide for 90 days by gavage (Gerhart 1986). At 4.35 mg 

CN–

/kg/day, fixed posture occurred, while pronounced lethargy was noted at 14.5 mg CN–/kg/day. 

Decreased brain weight was reported at 14.5 mg CN–

/kg/day cyanide (Gerhart 1987). The severity of 

effects increased as the dose increased in both of these studies and males seemed to be more sensitive to 

cyanide toxicity than females. 

Male rats receiving 0.24 mg CN–

/kg/day as potassium cyanide by gavage for 3 months showed increases 

in histopathological lesions of the spinal cord (axonal "spheroids" or swellings), hippocampus (neuronal 

loss), and cerebellum (damage to Purkinje cells and loss of white matter) (Soto-Blanco et al. 2002a). 
CYANIDE 63 

3. HEALTH EFFECTS 

Since the original study did not report results quantitatively, this study is omitted from Table 3-2 until 

dose-incidence data can be obtained from the study authors. Rats fed a diet containing 30 mg CN–

/kg/day 

as potassium cyanide and 67 mg CN–

/kg/day as potassium thiocyanate for 11.5 months had myelin 

degeneration in the spinal cord (Philbrick et al. 1979). The authors mentioned that tissues from exposed 

animals were more subject to autolysis, so the strength of the association between neurological 

histopathology and cyanide exposure in this study is uncertain; vitamin B12 deficiency was ruled out as a 

cause in this study. In a behavioral study, exposure to 0.4 mg CN–

/kg/day as potassium cyanide by 

gavage for 24 weeks in pigs led to slower reaction time, reduced exploratory behavior, and increased 

victimization behavior in pigs (Jackson 1988). In contrast, no neurological effects were reported in rats 

fed an estimated dose of 10.4 mg CN–

/kg/day as hydrogen cyanide in their feed for 2 years (Howard and 

Hanzal 1955). The actual dose, however, may have been considerably lower than 10.4 mg/kg/day due to 

evaporation of hydrogen cyanide from the food. No histopathological changes to the brain were noted in 

rats and mice exposed to up to 12.5 and 28.8 mg CN–

/kg/day, as the sodium salt, respectively, in the 

drinking water for 13 weeks (NTP 1993); the spinal cord was not examined for histopathology in this 

study. Degenerative changes in ganglion cells were reported in three dogs that were exposed to 0.27– 

1.68 mg CN–

/kg/day as sodium cyanide in capsules for 14.5 months (Hertting et al. 1960). 

The highest NOAEL value and all reliable LOAEL values for neurological effects in each species and 

duration category are recorded in Table 3-2 and plotted in Figure 3-2. Studies that employed oral gavage 

dosing are omitted because bolus administration may overwhelm detoxification processes in a manner not 

typical of gradual exposures in drinking water for the general population 

3.2.2.5 Reproductive Effects 

No studies were located regarding reproductive effects in humans after oral exposure to cyanide. 

Increased early embryonic deaths were reported in rats fed a diet containing 80% cassava powder during 

gestation, but no reproductive effects were found in a group fed with 50% cassava powder (Singh 1981). 

Furthermore, no changes were observed in the number of implantations or resorptions in hamsters fed a 

cassava diet that provided 10.4 mg CN–

/kg/day during gestation (Frakes et al. 1986a). Increased gonadal 

weight was observed in male rats exposed by oral gavage to 14.5 mg CN–

/kg/day as copper cyanide 

(Gerhart 1986) or 2.6 mg CN–

/kg/day, as potassium silver cyanide, for 90 days (Gerhart 1987). The 

NOAEL values were 4.35 mg CN–

/kg/day (Gerhart 1986) and 0.8 mg CN–/kg/day (Gerhart 1987), 

respectively. No effects were observed in female rats in either study. A reduction in the spermatogenic 
CYANIDE 64 

3. HEALTH EFFECTS 

cycle, testicular germ cell sloughing and degeneration, and occasional abnormal cells were noted in dogs 

fed 1.04 mg CN–

/kg/day as cassava and in dogs fed rice containing the same concentration of cyanide, as 

sodium cyanide, for 14 weeks (Kamalu 1993). 

A number of reproductive effects were observed following exposure of rats and mice to sodium cyanide 

in the drinking water for 13 weeks (NTP 1993). This study was used as the basis for the intermediateduration oral MRL as described in the footnote to Table 3-2 and Appendix A. In male rats, reproductive 

effects including decreased left epididymis weight, left cauda epididymis weight, left testis weight, 

spermatid heads, and spermatid counts were observed at 12.5 mg CN–

/kg/day. In female rats, 

significantly more time was spent in proestrus and diestrus stages, and less time was spent in estrus and 

metestrus stages in the 4.9 and 12.5 mg CN–

/kg/day groups, but these effects were not considered to be 

adverse. In male mice, a significant decrease in the left epididymal and caudal epididymal weights was 

noted at 24.3 mg CN–

/kg/day, but no changes in sperm motility or spermatid head density were observed. 

No changes were noted on the estrus cycle length in female mice. 

The highest NOAEL value and all reliable LOAEL values for reproductive effects in each species and 

duration category are recorded in Table 3-2 and plotted in Figure 3-2. Studies on dogs have been omitted 

because that species has a relatively low amount of the detoxifying enzyme rhodanese and is unusually 

susceptible to cyanide exposure compared to humans or other mammals (see Sections 3.4.3 and 3.5.3). 

Studies involving ingestion of cassava have also been omitted because of the confounding effects of 

malnutrition noted in human studies and because of the presence of other toxic compounds besides 

cyanogenic glycosides that might contribute to toxicity (e.g., scopoletin; see Section 3.10). Studies that 

employed oral gavage dosing are omitted because bolus administration may overwhelm detoxification 

processes in a manner not typical of gradual exposures in drinking water for the general population. 

3.2.2.6 Developmental Effects 

No studies were located regarding developmental effects in humans after oral exposure to cyanide. 

Developmental abnormalities (microcephaly with open eyes, limb defects, and growth retardation) were 

observed in 28% of the fetuses of rats exposed to feed containing 80% cassava powder during gestation 

(Singh 1981). Teratogenic effects (encephalocele and rib abnormalities) were reported in hamsters 

exposed to a single oral dose of amygdalin during gestation, but these changes were found only at 

maternally toxic doses (Willhite 1982). Fetotoxicity (reduced fetal weight and ossification) were found in 
CYANIDE 65 

3. HEALTH EFFECTS 

the offspring of hamsters fed a cassava diet providing 1.0 mg CN–/kg/day during pregnancy (Frakes et al. 

1986a) or to the cyanogenic glucoside linamarin at 120 or 140 mg/kg (Frakes et al. 1985). Blood cyanide 

increased to a peak of 110 nmol/mL at 3 hours after such a dose of linamarin or to 140 nmol/mL after 

amygdalin (Frakes et al. 1986b). In contrast, no major developmental effects were observed in rats that 

were fed a basal cassava diet providing ≈1.2 mg CN–

/kg/day or in rats whose cassava feed was 

supplemented with potassium cyanide bringing the total dose to 51 mg CN–

/kg/day (assuming young 

growing rats and pregnant rats consume food each day equivalent to 10% of their body weight) (Tewe 

and Maner 1981a). The rats were exposed to cyanide during gestation days 16–20 and then for 21 days 

during lactation. When their offspring were exposed to similar diets providing doses of ≈1.2 and 51 mg 

CN–

/kg/day, decreased growth was observed in the higher dosed weanlings regardless of the exposure in 

utero. When pigs were fed a cassava diet alone or one supplemented with potassium cyanide for 

110 gestation days, no effects on number of fetuses or upon fetal weight were observed in the 11.3 mg 

CN–

/kg/day cyanide exposed group (Tewe and Maner 1981b). The rat and pig studies by Tewe and 

Maner (1981a, 1981b) are not presented in Table 3-2 or Figure 3-2 because they did not include control 

groups fed cyanide-free diets. 

The highest NOAEL value and all reliable LOAEL values for developmental effects in each species and 

duration category are recorded in Table 3-2 and plotted in Figure 3-2. Studies for dogs have been omitted 

because that species has a relatively low amount of the detoxifying enzyme rhodanese and is unusually 

susceptible to cyanide exposure compared to humans or other mammals (see Sections 3.4.3 and 3.5.3). 

Studies involving ingestion of cassava have also been omitted because of the confounding effects of 

malnutrition noted in human studies and because of the presence of other toxic compounds besides 

cyanogenic glycosides that might contribute to toxicity (e.g. scopoletin; see Section 3.10). Studies that 

employed oral gavage dosing are omitted because bolus administration may overwhelm detoxification 

processes in a manner not typical of gradual exposures in drinking water for the general population. 

3.2.2.7 Cancer 

No studies were located regarding cancer effects in humans or animals after oral exposure to cyanide. 
CYANIDE 66 

3. HEALTH EFFECTS 

3.2.3 Dermal Exposure 

Chronic dermal exposure of humans to cyanide can occur in occupational settings. However, the main 

route of exposure is considered to be inhalation and, therefore, the occupational exposure studies are 

discussed in Section 3.2.1. Studies involving conjunctival exposure are discussed in this section, 

although not strictly involving the dermal route. 

3.2.3.1 Death 

An average LD50 value for dermal exposure of 100 mg CN–

/kg as hydrogen cyanide was estimated for 

humans (Rieders 1971). 

LD50 values calculated for dermal exposure to cyanides in rabbits were 6.7 mg CN–

/kg when applied as 

hydrogen cyanide, 7.7 mg CN–

/kg as sodium cyanide, and 8.9 mg CN–/kg as potassium cyanide 

(Ballantyne 1983a). The dermal LD50 of cyanide as sodium cyanide was slightly lowered by moistening 

the skin and substantially lowered by abrading the skin (Ballantyne 1988). Similar differences in toxicity 

of various chemical forms of cyanide were observed after cyanide was applied to the inferior conjunctival 

sac of one eye (Ballantyne 1983a, 1983b, 1988). Transocular LD50 values were 1.0 mg CN–

/kg as 

hydrogen cyanide, 2.68 mg CN–

/kg as sodium cyanide, and 3.2 mg CN–/kg as potassium cyanide. The 

deaths occurred within 3–12 minutes. Deaths occurred also in guinea pigs when their skin was exposed to 

hydrogen cyanide; however, the doses could not be quantified (Fairley et al. 1934; Walton and 

Witherspoon 1926). The LD50 values for death are recorded in Table 3-3. 

It should be noted that none of the studies in this section reported the surface area to which the cyanide 

was applied. 

3.2.3.2 Systemic Effects 

No studies were located regarding hematological, musculoskeletal, hepatic, endocrine, or body weight 

effects in humans or animals after dermal exposure to cyanide. The systemic effects observed in humans 

and animals after dermal exposure to cyanide are discussed below. The highest NOAEL values and all 

reliable LOAEL values for each systemic effect in each species and duration category are recorded in 

Table 3-3. 
Table 3-3 Levels of Significant Exposure to Cyanide - Dermal

Species

(Strain)

Exposure/

Duration/

Frequency

(Route) System NOAEL Less Serious 

LOAEL

Serious

ReferenceChemical Form

ACUTE EXPOSURE

Death

(NS)Rabbit

18

once

7.7 F (dermal LD50)

mg/kg

mg/kg

Ballantyne 1983aNaCN

(NS)Rabbit

28

once

6.7 F (dermal LD50)

mg/kg

mg/kg

Ballantyne 1983aHCN

(NS)Rabbit

9

once

8.9 F (dermal LD50)

mg/kg

mg/kg

Ballantyne 1983aKCN

(albino)Rabbit

146

once

1 F (transocular LD50)

mg/kg

mg/kg

Ballantyne 1983a, 1983HCN

(albino)Rabbit

149

once

3.2 F (transocular LD50)

mg/kg

mg/kg

Ballantyne 1983a, 1983KCN

(NewZealand)Rabbit

135

once

2.4 F (transocular LD50)

mg/kg

mg/kg

Ballantyne 1988NaCN

(NewZealand)Rabbit

140

once

4.1 F (dermal LD50 -abraded

skin)

mg/kg

mg/kg

Ballantyne 1988NaCN

(NewZealand)Rabbit

142

once

6.3 F (dermal LD50 -moist

skin)

mg/kg

mg/kg

Ballantyne 1988NaCN
Table 3-3 Levels of Significant Exposure to Cyanide - Dermal (continued)

Species

(Strain)

Exposure/

Duration/

Frequency

(Route) System NOAEL Less Serious 

LOAEL

Serious

ReferenceChemical Form

Systemic

Human

227

8-10 min Cardio 20000 M (palpitations)

ppm

ppm

Drinker 1932HCN

(albino)Rabbit

148

once Resp 0.9 F (rapid breathing)

mg/kg

mg/kg

Ballantyne 1983bHCN

Ocular 0.9 F (corneal opacity,

keratitis)

mg/kg

mg/kg

(albino)Rabbit

151

once Resp 2.5 F (rapid breathing)

mg/kg

mg/kg

Ballantyne 1983bKCN

Ocular 2.5 F (corneal opacity,

keratitis)

mg/kg

mg/kg

(albino)Rabbit

154

once Resp 1.69 F

mg/kg

mg/kg

2.1 F (rapid breathing)

mg/kg

mg/kg

Ballantyne 1983bNaCN

Ocular 1.69 F

mg/kg

mg/kg

2.1 F (corneal opacity,

keratitis)

mg/kg

mg/kg

Neurological

Human

53

8-10 min

20000 M (dizziness, weakness,

headache)

ppm

ppm

Drinker 1932HCN
Table 3-3 Levels of Significant Exposure to Cyanide - Dermal (continued)

Species

(Strain)

Exposure/

Duration/

Frequency

(Route) System NOAEL Less Serious 

LOAEL

Serious

ReferenceChemical Form

(albino)Rabbit

147

once

0.9 F (convulsions and loss of

consciousness)

mg/kg

mg/kg

Ballantyne 1983bHCN

(NewZealand)Rabbit

150

once

2.5 F (convulsions and loss of

consciousness)

mg/kg

mg/kg

Ballantyne 1983bKCN

(albino)Rabbit

Cardio= cardiovascular; d = day(s); F = female; HCN = hydrogen cyanide; KCN = potassium cyanide; LD50 = lethal dose, 50% kill; LOAEL = lowest-observed-advM = male; min = minutes; NaCN = sodium cyanide; NOAEL = no-observed-adverse-effect level; NS = not specified; Resp = respiratory

153

once

1.7 F

mg/kg

mg/kg

2.1 F (convulsions and loss of

consciousness)

mg/kg

mg/kg

Ballantyne 1983bNaCN
CYANIDE 70 

3. HEALTH EFFECTS 

Respiratory Effects. Breathing irregularities including Cheyne-Stokes respiration developed in two 

persons who fell into cisterns containing copper cyanide or potassium cyanide (Dodds and McKnight 

1985; Trapp 1970) and one person whose hands were exposed to hydrogen cyanide (Potter 1950). The 

effects reflect the central nervous system toxicity of cyanide. 

Rapid breathing was reported as the first sign of toxicity in rabbits that received 0.9 mg CN–

/kg as 

hydrogen cyanide, 1.69 and 2.1 mg CN–

/kg as sodium cyanide, and 2.5 mg CN–/kg as potassium cyanide 

in their conjunctival sacs (Ballantyne 1983b, 1988). Similarly, labored or rapid breathing preceded coma 

and death in guinea pigs exposed dermally to unknown doses of hydrogen cyanide (Fairley et al. 1934; 

Walton and Witherspoon 1926). 

Cardiovascular Effects. Peripheral vasoconstriction and gross plasma extravasation were reported 

in a man who accidentally fell into a cistern with hot copper cyanide (Dodds and McKnight 1985). 

Palpitations were recorded in three men who wore respiratory masks while working in an atmosphere 

containing 20,000 ppm hydrogen cyanide for 8–10 minutes (Drinker 1932). The masks were reported to 

give excellent respiratory protection. Therefore, the effects seen in these men may have been due to 

dermal exposure. 

No studies were located regarding cardiovascular effects in animals after dermal exposure to cyanide. 

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

dermal exposure to cyanide. 

Acute dermal exposure of guinea pigs to an unknown concentration of hydrogen cyanide resulted in 

submucous hemorrhages in the stomach as observed at necropsy (Fairley et al. 1934). 

Renal Effects. The information regarding renal effects following dermal exposure to cyanide in 

humans is limited to one case report. Transitory oliguria (scanty urination) was observed in a patient who 

accidentally fell into a cistern containing 1,000 gallons of hot copper cyanide and remained there for 

3 minutes before being rescued (Dodds and McKnight 1985). 

No studies were located regarding renal effects in animals after dermal exposure to cyanide. 
CYANIDE 71 

3. HEALTH EFFECTS 

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

cyanide. 

When the skin of rabbits was exposed to 5,000 ppm cyanide as cyanogen for 8 hours, no dermal lesions 

were found (McNerney and Schrenk 1960). Vascular congestion was reported in the skin of guinea pigs 

after exposure to unknown doses of hydrogen cyanide for 65 minutes (Fairley et al. 1934). 

Ocular Effects. No studies were located regarding ocular effects in humans after dermal exposure to 

cyanide. 

Cyanide toxicity was tested in rabbits by applying 1.69–5.28 mg CN–

/kg/day as sodium cyanide to the 

inferior conjunctival sac of one eye (Ballantyne 1983b, 1988). Irritation, lacrimation, and conjunctival 

hyperemia were present immediately after the treatment. Keratitis developed in some rabbits after a 

cyanide application of 0.9 mg CN–

/kg as hydrogen cyanide, 2.1 mg CN–/kg as sodium cyanide, and 

2.5 mg CN–

/kg as potassium cyanide. 

3.2.3.3 Immunological and Lymphoreticular Effects 

No studies were located regarding immunological effects in humans or animals after dermal exposure to 

cyanide. 

3.2.3.4 Neurological Effects 

Deep coma developed in two persons who accidentally fell into cisterns containing copper cyanide 

(Dodds and McKnight 1985) and potassium cyanide, respectively (Trapp 1970). Similarly, a worker, 

whose hand was exposed to liquid hydrogen cyanide, fell into a coma, lost deep reflexes, and showed 

dilated pupils within 5 minutes (Potter 1950). Men working in an atmosphere containing 20,000 ppm 

hydrogen cyanide for 8–10 minutes experienced dizziness, weakness, and headaches (Drinker 1932). The 

workers wore masks that were reported to give excellent respiratory protection. However, exposure to 

such high concentrations is not safe because the gas is absorbed through the unprotected skin. The effects 

seen in these men may have been due to dermal exposure. 
CYANIDE 72 

3. HEALTH EFFECTS 

Weakness and ataxic movements, convulsions, and coma developed in rabbits that received 

0.9 mg CN-

/kg as hydrogen cyanide, 2.1 mg CN–/kg as sodium cyanide, and 2.5 mg CN–/kg as potassium 

cyanide into their conjunctival sacs (Ballantyne 1983b, 1988). Rabbits exposed dermally to 1.92 mg 

CN–

/kg as hydrogen cyanide, 4.0 mg CN–/kg as potassium cyanide or 2.6 mg CN–/kg as sodium cyanide 

exhibited tremors, retrocolic spasms, and convulsions (Ballantyne 1994). Similarly, convulsions and 

coma preceded death in guinea pigs exposed dermally to unknown doses of hydrogen cyanide (Fairley et 

al. 1934; Walton and Witherspoon 1926). 

All reliable LOAEL values for neurological effects in each species for acute duration are recorded in 

Table 3-3. 

No studies were located regarding the following health effects in humans or animals after dermal 

exposure to cyanide: 

3.2.3.5 Reproductive Effects 

3.2.3.6 Developmental Effects 

3.2.3.7 Cancer 

3.3 GENOTOXICITY 

In vivo. No studies were located regarding genotoxic effects in humans after oral or inhalation exposure 

to cyanide. 

A single oral dose of 1 mg CN–

/kg as potassium cyanide did not inhibit testicular deoxyribonucleic acid 

(DNA) synthesis in mice (Friedman and Staub 1976). 

Increased DNA fragmentation was electrophoretically detectable in mitochondria isolated from the brains 

of male ddy mice that had received a subcutaneous injection of 2.8 mg CN (as potassium cyanide) per kg 

(Yamamoto and Mohanan 2002). DNA fragmentation was detected by in situ terminal deoxynucleotide 

transferase nick-end labeling (TUNEL) in the parietal and suprrhinal regions of the motor cortex in mice 

injected with potassium cyanide (2.4 mg CN/kg/day) for 1–12 days (Mills et al. 1999). 
CYANIDE 73 

3. HEALTH EFFECTS 

In vitro. In vitro genotoxicity studies are summarized in Table 3-4. Cyanide in the form of potassium 

cyanide tested negative in Salmonella typhimurium strains TA1535, TA1537, TA1538, TA98, TA100 (De 

Flora 1981), TA97, and TA102 (De Flora et al. 1984). A positive mutagenic response was reported for 

hydrogen cyanide in strain TA100 without metabolic activation (Kushi et al. 1983). Adding S-9 mix to 

the culture decreased the induction of reverse mutations by cyanide to 40% of the nonactivated reaction. 

Negative results were also obtained in the DNA repair test in Escherichia coli WP67, CM871, and WP2 

with potassium cyanide (De Flora et al. 1984). Cyanide in the form of sodium cyanide tested negative in 

S. typhimurium strains TA97, TA98, TA100, and TA1535, with and without metabolic activation (NTP 

1993). Potassium cyanide tested at 0.01 or 1.0 mM failed to induce reverse mutations in S. typhimurium 

strains TA98 or TA100 with or without metabolic activation (Kubo et al. 2002). 

The Vitotox test is a screening assay for genotoxicity and cytotoxicity (Meriläinen and Lampinen 2004). 

The genotoxicity component is based on a recombinant S. typhimurium TA104 with a reporter luciferase 

operon under control of a recN promoter. In this system, damaged DNA interacts with the recA regulator 

protein, initiating the SOS response that derepresses the recN promoter, allowing luciferase expression. 

Sodium cyanide tested at concentrations up to 0.8 mM without metabolic activation yielded negative 

results for genotoxicity in this system. 

Potassium cyanide did not inhibit DNA synthesis in cultured HeLa cells (Painter and Howard 1982). 

In cultured A549 human epithelial-like lung carcinoma cells, ≥1 mM potassium cyanide induced doserelated reductions in cell viability by 8 hours and dose-dependent increases in electrophoreticallydetectable double-strand DNA breaks by 24 hours (Vock et al. 1998). Based on this temporal relationship 

and the fact that the induced DNA fragments were smaller than 0.5 Mbp, the authors concluded that the 

genotoxic effect of cyanide was indirect and based on the activation of endonucleases by calcium entering 

the damaged cells. Dose-related increases in DNA breaks were induced in rat thymocytes treated for 

6 hours with ≥1.25 mM potassium cyanide or in baby hamster kidney (BHK-21) cells at 5 mM 

(Bhattacharya and Lakshmana Rao 1997). Incubation of cells in calcium-free medium significantly 

reduced the level of DNA damage, supporting the hypothesis that a cytotoxic-related calcium-influx 

contributes to this fragmentation of DNA. 

Storer et al. (1996) evaluated 81 chemicals for genotoxicity in an in vitro alkaline elution assay for DNA 

strand breaks in primary cultures of rat hepatocytes. The study included a battery of assays for 
CYANIDE 74 

3. HEALTH EFFECTS 

Table 3-4. Genotoxicity of Cyanide In Vitro 

Results 

Species (test With Without 

system) End point activation activation Reference Form 

Prokaryotic organisms: 

Salmonella 

typhimurium 

TA82, TA102 Reverse mutation – Not tested De Flora et al. 1984 KCN 

S. typhimurium 

TA98, TA100, Reverse mutation – – De Flora 1981 KCN 

TA1535, TA1537, 

TA1538 

S. typhimurium 

TA98 Reverse mutation – – Kushi et al. 1983 HCN 

TA100 (+) + 

 S. typhimurium 

TA98, TA100 Reverse mutation – – Kubo et al. 2002 KCN 

Escherichia coli 

WP67, CM871, DNA repair test – – De Flora et al. 1984 KCN 

WP2 

 S. typhimurium 

TA97, TA98, Reverse mutation – – NTP 1993 NaCN 

TA 100, TA 1535 

 Eukaryotic 

organisms: 

HeLa cells DNA synthesis – – Painter and Howard KCN 

inhibition 1982 

Human A549 lung DNA breakage +cyt Vock et al. 1998 KCN 

carcinoma cells 

Human TK6 DNA breakage +cyt Henderson et al. 1998 KCN 

lymphoblastoma 

cells 

Rat thymocytes DNA breakage +cyt Bhattacharya and KCN 

Lakshmana Rao 1997 

Hamster BHK-21 DNA breakage +cyt Bhattacharya and KCN 

cells Lakshmana Rao 1997 

Rat hepatocytes DNA breakage +cyt Storer et al. 1996 KCN 

Mitochondrial Mitochondrial DNA + Yamamoto and KCN 

fraction from brain breakage Mohanan 2002 

of male ddy mice 

– = negative result; + = positive result; (+) = weakly positive result; +cyt

 = DNA breakage associated with cytotoxicity; 

DNA = deoxyribonucleic acid; HCN = hydrogen cyanide; KCN = potassium cyanide; NaCN = sodium cyanide 
CYANIDE 75 

3. HEALTH EFFECTS 

cytotoxicity (including tetrazolium dye reduction, trypan blue dye exclusion after 3 hours of recovery, 

ATP content, K+ content, and cell blebbing) to distinguish between genotoxicity and false-positive results 

resulting from the loss of membrane integrity in damaged cells. DNA strand breakage following 

treatment with ≥6 mM potassium cyanide was determined to be associated with the induction of 

endonucleolytic DNA degradation caused by cytotoxicity (ATP content ≤5% of control, increased cell 

blebbing). Henderson et al. (1998) electrophoretically detected significant DNA breakage (DNA 

migration) in TK6 human lymphoblastoma cells treated with potassium cyanide at 2 mg CN–

/mL a 

concentration reducing cell survival (as measured by trypan blue exclusion) by 30%. 

Dose-related increases in electrophoretically detectable DNA breaks were induced by potassium cyanide 

(0.1–2 mM) in a crude mitochondrial fraction isolated from the brains of male ddy mice (Yamamoto and 

Mohanan 2002). 

3.4 TOXICOKINETICS 

Cyanide gas and salts such as sodium cyanide or potassium cyanide are rapidly absorbed following 

inhalation or oral exposure, but are more slowly absorbed by dermal exposure. Following inhalation, 

cyanide is rapidly distributed throughout the body, with measurable levels detected in all organs studied 

to date. Cyanide can be distributed in the body within seconds and death can occur within minutes. 

Following oral exposure, the highest levels have been detected in the lungs and blood. Animal studies 

have shown that cyanide does not accumulate in the blood and tissues following chronic oral exposure. 

Cyanide is transformed to thiocyanate in the body, with a plasma half-life of 20 minutes to 1 hour. 

Cyanide metabolites are excreted primarily in the urine, with small amounts excreted through the lungs. 

3.4.1 Absorption 

3.4.1.1 Inhalation Exposure 

Cyanide as hydrogen cyanide is rapidly absorbed (within seconds) following inhalation exposure. 

Humans retained 58% of hydrogen cyanide in the lungs after inhaling the gas through normal breathing 

(Landahl and Herrmann 1950). 

Quantitative data on the absorption of hydrogen cyanide by inhalation were reported in dogs (Gettler and 

Baine 1938). During exposure to an unknown concentration of hydrogen cyanide, one dog reportedly 
CYANIDE 76 

3. HEALTH EFFECTS 

absorbed 16.0 mg (1.55 mg/kg); the other dog absorbed 10.1 mg (1.11 mg/kg). These doses were fatal to 

the dogs in 15 and 10 minutes, respectively. More recent quantitative data were not available. 

3.4.1.2 Oral Exposure 

Information regarding the rapid lethal effects following oral intake of cyanide as soluble cyanide salts in 

humans indicates that cyanide is rapidly absorbed from the gastrointestinal tract. In a case study, an 

80-kg male ingested an estimated 15–25 mg CN–

/kg as potassium cyanide in a suicide attempt (Liebowitz 

and Schwartz 1948). Based on a concentration of 200 mg hydrogen cyanide/L in the blood 2 hours after 

ingestion, it was estimated that the patient had 1.2 g hydrogen cyanide in the blood, with ≈2.3 g CN–

 in 

the body, after 2 hours. 

The gastrointestinal absorption of cyanide following ingestion of certain complex iron-containing cyanide 

compounds is low because cyanide binds with high affinity to iron. In three volunteers (study authors), 

each of whom ingested a capsule containing 500 mg labeled potassium ferric hexacyanoferrate 

(KFe[Fe(CN)6]), equivalent to a lethal dose of 3.14–3.64 mg CN–

/kg, only 0.03 mg of free CN–/kg were 

absorbed (Nielsen et al. 1990). From the mild toxicological effects, minimal absorption of free cyanide 

was suspected to have occurred in a woman who attempted suicide by ingesting a coffee spoonful of 

potassium ferricyanide (K3Fe(CN)6 or Prussian red) (Hantson et al. 1996). Low bioavailability of cyanide 

was deduced in the case of a man who attempted suicide by ingesting an unknown amount of cyanide in 

the form of potassium ferrocyanide (Laforge et al. 1999). Despite an initial toxic blood cyanide 

concentration of 0.3 mg/100 mL, there were no clinical signs of toxicity and blood chemistry was 

otherwise normal. (Since free cyanide absorption and toxicity is unusually low for these iron compounds, 

the data are not discussed in Section 3.2.2). 

Three dogs were given lethal doses of hydrogen cyanide by gavage. The amount of cyanide absorbed was 

determined by the difference between the cyanide given and the cyanide left in the stomach and intestines 

(Gettler and Baine 1938). The dogs dosed with 8.4, 4.4, or 1.6 mg HCN/kg, died 8, 21, and 155 minutes 

after treatment and had absorbed 17, 24, and 72%, respectively, of the dose given. Rats excreted 47% of 

a dose of radioactivity in the urine during 24 hours following gavage treatment with 2 mg CN–

/kg as 

radiolabeled potassium cyanide (Farooqui and Ahmed 1982), indicating that at least 53% of the cyanide 

was absorbed in 24 hours. 
CYANIDE 77 

3. HEALTH EFFECTS 

Sousa et al. (2003) compared the absorption of cyanide in male Wistar rats and Landrace-Large White 

pigs that were given a single dose of 1.2 mg CN–

/kg as potassium cyanide by aqueous gavage. The peak 

blood concentration (Cmax) of cyanide was reached within 15 minutes in rats and by 30 minutes in pigs. 

The peak plasma cyanide concentrations were 0.23 and 0.15 mg/100 mL for rats and pigs, respectively. 

In this study, the peak blood concentration of thiocyanate was reached within 6 hours in rats and pigs. 

The peak plasma thiocyanate concentrations were 42.8 and 58.1 μmol/L for pigs and rats, respectively. 

More detail on the mechanism of absorption is provided in Section 3.5.1. 

3.4.1.3 Dermal Exposure 

No studies were located regarding quantitative absorption in humans after dermal exposure to cyanide 

gases or common inorganic salts. Evidence that cyanide can be absorbed through the skin of humans is 

provided in case reports of toxic effects in humans after accidental dermal contact with cyanide (see 

Section 3.2.3). 

Information regarding dermal absorption of cyanide in animals was provided in studies of guinea pigs and 

dogs (Walton and Witherspoon 1926). When a small area of the shaved abdomen of guinea pigs was 

exposed to hydrogen cyanide vapor for 30–60 minutes, signs of cyanide toxicity observed included rapid 

respiration followed by general twitching of muscles, convulsions, and death. In a similar experiment, 

shaved and unshaved dogs were placed in a chamber in which their bodies, with the exception of the head 

and neck, were exposed to hydrogen cyanide vapor. No signs of toxicity were reported after exposure to 

4,975 ppm hydrogen cyanide for 180 minutes. Deaths occurred after exposure to 13,400 ppm hydrogen 

cyanide for 47 minutes and suggested dermal absorption. Further indirect evidence regarding dermal 

absorption of cyanide as hydrogen cyanide or its salts (Ballantyne 1983a, 1983b, 1988) can be found in 

Section 3.2.3. 

3.4.2 Distribution 

3.4.2.1 Inhalation Exposure 

Once cyanide is absorbed, it is rapidly distributed by the blood throughout the body. Tissue levels of 

hydrogen cyanide were 0.75, 0.42, 0.41, 0.33, and 0.32 mg/100 g of tissue in the lung, heart, blood, 

kidney, and brain, respectively, in a man who died following inhalation exposure to hydrogen cyanide 

gas. In one case of death due to cyanide oral exposure, it was estimated that 30 mg of hydrogen cyanide 
CYANIDE 78 

3. HEALTH EFFECTS 

had been ingested and that 3 hours had elapsed before death (Gettler and Baine 1938). In another case, 

tissue cyanide levels from a man who died from inhalation of hydrogen cyanide were reported as 0.5 mg 

per 100 mL of blood and 0.11, 0.07, and 0.03 mg/100 g in the kidney, brain, and liver, respectively. 

Urinary cyanide levels were reported as 0.2 mg/100 mL, and 0.03 mg/100 g were found in the gastric 

contents (Finck 1969). Following chronic occupational exposure to 0.19–0.75 ppm hydrogen cyanide, 

56.0 and 18.3 μg CN–

/100 mL were found in the blood of smokers and nonsmokers, respectively 

(Chandra et al. 1980). The cyanide levels in control groups were 4.8 μg/mL for smokers and 3.2 μg/mL 

for nonsmokers. 

In two dogs exposed to unspecified fatal concentrations of hydrogen cyanide, the highest cyanide levels 

were found in the lungs, blood, and heart (Gettler and Baine 1938). Rats exposed to hydrogen cyanide 

gas at 356 or 1,180 ppm died within 10 and 5 minutes, respectively (Yamamoto et al. 1982). Samples 

taken immediately after respiration stopped showed that the pattern of tissue distribution of cyanide did 

not vary with the concentration used. In averaging data for both dose groups, tissue concentrations, 

reported as μg/g wet weight (ww), were 4.4 in the lungs, 3.0 in the blood, 2.15 in the liver, 1.4 in the 

brain, and 0.68 in the spleen. Thus, the highest cyanide concentrations were observed in the lung. 

Rabbits exposed to hydrogen cyanide at 2,714 ppm for 5 minutes had cyanide levels of 170/100 mL in 

blood and 48 μg/100 mL in plasma, and tissue levels (in units of μg/100 g) of 0 in the liver, 6 in the 

kidney, 50 in the brain, 62 in the heart, 54 in the lung, and 6 in the spleen (Ballantyne 1983a). 

3.4.2.2 Oral Exposure 

Small but significant levels of cyanide are present in normal blood plasma at concentrations of 0–14 μg % 

(Feldstein and Klendshoj 1954). Vitamin B12 contains cyanide, with the source of cyanide attributed to 

breakdown of cyanogenic foods by bacteria in the gut. 

Cyanide levels in a woman who died 30 minutes after ingesting ≈1,325 mg cyanide as sodium cyanide 

were, in mg %: stomach contents, 3.2; brain, 0.7; urine, 0.5; blood, 0.4; kidney, 0.2; stomach wall, 0.2; 

and liver, 0.1 (Ansell and Lewis 1970). The mean organ levels of cyanide ion in cases of fatal poisoning 

in 17–58 cases were, in mg %: stomach contents, 160; spleen, 3.77; blood, 2.39; liver, 1.62; brain, 1.2; 

kidney, 0.61; and urine, 0.06 (Ansell and Lewis 1970). Brain cyanide levels ranged from 0.06 to 1.37 mg 

hydrogen cyanide/100 g of tissue in four humans who ingested fatal doses of cyanide (Gettler and Baine 

1938). Cyanide levels in the livers of six humans ranged from 0.22 to 0.91 mg hydrogen cyanide/100 g 

of tissue. In two cases in which men died from ingestion of unknown quantities of unspecified cyanide 
CYANIDE 79 

3. HEALTH EFFECTS 

salts, cyanide levels were highest in the gastric contents, and next highest in the lungs and blood (Finck 

1969). 

Combined data from 9 to 10 rats that died 3.3 and 10.3 minutes after gavage doses of 7 or 21 mg CN–

/kg 

as sodium cyanide showed average tissue concentrations of cyanide in μg/g of: liver, 8.9; lung, 5.8; 

blood, 4.9; spleen, 2.1; and brain, 1.5 (Yamamoto et al. 1982). When six rats were treated with 4 mg 

CN–

/kg as potassium cyanide, signs of central nervous system toxicity were observed (Ahmed and 

Farooqui 1982), and cyanide levels 1 hour after exposure were 3,380 μg/g in liver, 748 μg/g in brain, and 

550 μg/g in kidney. Forty minutes after male Wistar rats received an oral dose of 1.2 mg CN–

/kg as 

potassium cyanide, the tissue levels of cyanide were 1.04 μg/mL in blood, 0.54 μg/g in liver, 0.20 μg/g in 

brain, 0.29 μg/g in kidney, and 0.07 μg/g in stomach (Saito et al. 2000). Two-fold increases in the 

administered dose (2.4 or 4.8 mg CN–

/kg) resulted in approximate 2-fold increases in the cyanide content 

of these tissues, except for the liver, which showed 3-fold increases. In a study using orally administered 

radioactively labeled potassium cyanide, the radioactivity detected in whole blood or plasma decreased 

rapidly within 6 hours. Of the low levels of radioactivity detected in red blood cells, about 94% of the 

radioactivity recovered was found in the hemolysate, of which 70, 14–25, and 5–10% was detected in the 

heme fraction, globin, and cell membranes, respectively (Farooqui and Ahmed 1982). Rabbits treated by 

gavage with 11.9–20.3 mg CN–

/kg as hydrogen cyanide had cyanide levels of 480 μg/100 mL in blood, 

252 μg/100 mL in serum, and tissue levels (μg/100 g wet tissue) of 512 in liver, 83 in kidney, 95 in brain, 

105 in the heart, 107 in the lung, and 72 in the spleen at necropsy (Ballantyne 1983a). 

Cyanide has not been shown to accumulate in the blood and tissues following chronic oral exposure to 

inorganic cyanides. Following the treatment of groups of 10 male and 10 female rats with hydrogen 

cyanide in the diet at ≤10.4 mg CN–

/kg/day for 2 years, virtually no cyanide was found in plasma or 

kidneys (Howard and Hanzal 1955). Low levels were found in erythrocytes (mean of 1.9 μg/100 g). 

Levels of thiocyanate, the less toxic primary metabolite of cyanide, increased 3.5-fold in plasma, 3.3-fold 

in erythrocytes, 1.3-fold in liver, and 2.5-fold in kidney. Evaporation of hydrogen cyanide from the feed 

was thought to have occurred in this study, resulting in lower exposure levels than stated. 

3.4.2.3 Dermal Exposure 

No studies were located regarding distribution in humans after dermal exposure to cyanide. 
CYANIDE 80 

3. HEALTH EFFECTS 

Six rabbits exposed dermally (area not reported) to 33.75 mg CN–/kg as hydrogen cyanide had blood and 

serum cyanide levels of 310 and 144 μg/dL, respectively, and tissue levels (μg/100 g) of 26 in liver, 66 in 

kidney, 97 in brain, 110 in heart, 120 in lungs, and 21 in the spleen (Ballantyne 1983a). Cyanide 

concentrations were measured immediately after rabbits died, 3–12 minutes after administration of 

5.25 mg CN–

/kg as hydrogen cyanide, sodium cyanide, or potassium cyanide to their conjunctival sac 

(Ballantyne 1983b). Higher cyanide levels were observed in whole blood than in serum in all three 

groups. However, blood and serum cyanide levels were significantly lower in sodium cyanide and 

potassium cyanide groups than in the hydrogen cyanide group. Hydrogen cyanide-treated rabbits also had 

higher concentrations of cyanide in myocardium, lungs, and brain than rabbits from the other two groups. 

In all groups, the least amount of cyanide was found in the liver and kidney. 

3.4.3 Metabolism 

Reports of ingestion of cyanides by humans and reports of occupational exposure (see Section 3.8.1) 

indicate that cyanide is transformed into thiocyanate. A plasma half-life of 20 minutes to 1 hour has been 

estimated for cyanides in humans after nonlethal exposures (Hartung 1982). 

Sousa et al. (2003) conducted a toxicokinetic study in male Wistar rats and Landrace-Large White pigs 

that were given a single dose of 1.2 mg CN–

/kg as potassium cyanide by aqueous gavage. In this study, 

the peak blood concentration of thiocyanate, the main metabolite of cyanide, was reached within 6 hours 

in rats and pigs. The peak plasma thiocyanate concentrations were 0.11 and 0.15 mg/100 mL for pigs and 

rats, respectively. 

The metabolism of cyanide has been studied in animals. The proposed metabolic pathways shown in 

Figure 3-3 are (1) the major pathway, conversion to thiocyanate by either rhodanese or 3-mercaptopyruvate sulfur transferase; (2) conversion to 2-aminothiazoline-4-carboxylic acid (Wood and Cooley 

1956); (3) incorporation into a 1-carbon metabolic pool (Boxer and Richards 1952); or (4) combining 

with hydroxocobalamin to form cyanocobalamin (vitamin B12) (Ansell and Lewis 1970). Thiocyanate has 

been shown to account for 60–80% of an administered cyanide dose (Blakley and Coop 1949; Wood and 

Cooley 1956) while 2-aminothiazoline-4-carboxylic acid accounts for about 15% of the dose (Wood and 

Cooley 1956). The conversion of cyanide to thiocyanate was first demonstrated in 1894. Conversion of 

cyanide to thiocyanate is enhanced when cyanide poisoning is treated by intravenous administration of a 

sulfur donor (Smith 1996; Way 1984). The sulfur donor must have a sulfane sulfur, a sulfur bonded to 

another sulfur (e.g., sodium thiosulfate). During conversion by rhodanese, a sulfur atom is transferred 
CYANIDE 81 

3. HEALTH EFFECTS 

Figure 3-3. Basic Processes Involved in the Metabolism of Cyanide 

Cyanide 

Major path (80%) Thiocyanate 

(SCN-

) Urinary excretion 

Cyanocobalamin

 (Vitamin B12) 

2-Aminothiazoline-4-carboxylic acid and 

2-Iminothiazolidine-4-carboxylic acid 

Minor Path 

H++

 CN­

(Pool) 

Metabolism of onecarbon compounds 

Formates 

HCOOH 

HCNO 

CO2 

HCN 

(in expired air) 

Some 

excreted

 in urine 
CYANIDE 82 

3. HEALTH EFFECTS 

from the donor to the enzyme, forming a persulfide intermediate. The persulfide sulfur is then transferred 

from the enzyme to cyanide, yielding thiocyanate. Thiocyanate is then readily excreted in the urine as the 

major metabolite. Once thiocyanate is formed, it is not converted back to cyanide. 

Radioisotopic studies showed that albumin interacts with the sulfane pool and that the serum albuminsulfane sulfur carrier complex can react with cyanide (Schneider and Westley 1969). Higher hepatic 

rhodanese and lower serum albumin levels were found in mice fed a protein-free diet for 14 days 

compared with mice fed a control diet (Rutkowski et al. 1985). Despite the higher rhodanese levels, 

mortality following an intraperitoneal injection of sodium cyanide was higher in mice fed the protein-free 

diet both with and without thiosulfate pretreatment. In mice fed the control diet in reduced amounts, 

serum albumin levels were higher than controls. Mortality in food-deprived mice was also higher 

compared with controls, but only at high cyanide doses when thiosulfate was also administered. 

However, the pharmacokinetic studies in dogs, in which thiosulfate administration increased the rate of 

elimination of cyanide, suggest that the sulfane sulfur pool may play an important role as the central 

compartment for cyanide detoxification (Sylvester et al. 1983; Way 1984). 

The species and tissue distribution of rhodanese is highly variable (Himwich and Saunders 1948). In 

dogs, the highest activity (conversion of cyanide to thiocyanate) of rhodanese was found in the adrenal 

gland, ≈2.5 times greater than the activity in the liver. Monkeys, rabbits, and rats had the highest 

rhodanese activity in the liver and kidney, with relatively low levels in the adrenals. It should be noted 

that total rhodanese activity in other species was higher than in dogs, which is consistent with the greater 

susceptibility of dogs to the acute effects of cyanide. Similar low levels of activity of the enzyme were 

found for the brain, testes, lungs, spleen, and muscle among various species. 

In vitro studies with rat tissues indicated that rhodanese activity was ≈7 times higher in the nasal mucosa 

than in the liver (Dahl 1989). Furthermore, kinetic constants for rhodanese in mitochondria were higher 

in nasal than in liver tissue. 

Figure 3-4 illustrates the minor pathway for metabolism of cyanide in mammalian systems in which 

cyanide chemically combines with the amino acid cystine. This chemical reaction yields cysteine and 

β-thiocyanoalanine that is further converted to form 2-aminothiazoline-4-carboxylic acid and its tautomer, 

2-iminothiazolidiene-4-carboxylic acid (Wood and Cooley 1955). 
CYANIDE 83 

3. HEALTH EFFECTS 

Figure 3-4. Minor Path for the Removal of Cyanide from the Body 

NH2 

S C C COOH NH2 

H2 H S C C COOH 

S C C 

H 

COOH 

H2 H 

H2 CN 

NH2 

Cystine Beta-Thiocyanoalanine 

NH2

NH 

C C

N S NH S 

C C COOH C C COOH 

H2 H H2 H 

2-Aminothiazoline-4-carboxylic acid 2-Imino-4-thiazolidine-carboxylic acid 

Source: Ansell and Lewis 1970 
CYANIDE 84 

3. HEALTH EFFECTS 

Reactions of cyanide with the salts or esters of some amino acids (e.g., pyruvate, α-ketoglutarate, 

oxaloacetate) lead to formation of cyanohydrin intermediates and their incorporation into intermediary 

metabolism. 

The ability of cyanide to form complexes with some metallic ions such as cobalt is the basis for the 

reaction with hydroxocobalamin that yields cyanocobalamin. Cyanocobalamin (vitamin B12), which 

contains cyanide and cobalt, is essential for the health of mammalian organisms. 

3.4.4 Elimination and Excretion 

3.4.4.1 Inhalation Exposure 

Following chronic occupational exposure to 0.19–0.75 ppm hydrogen cyanide, 24-hour urinary levels of 

thiocyanate were 6.23 (smokers) and 5.4 μg/mL (nonsmokers) in exposed workers as compared with 

3.2 (smokers) and 2.15 μg/mL (nonsmokers) in the controls (Chandra et al. 1980). This study 

demonstrates that tobacco smoking contributes to higher thiocyanate levels excreted in the urine. No 

studies were located regarding excretion of cyanide in animals after inhalation exposure to cyanide. 

3.4.4.2 Oral Exposure 

Cyanide metabolites are normally excreted in urine (Vassel et al. 1944) with small amounts eliminated 

through the lungs. Urinary excretion of thiocyanate was monitored in a man after ingestion of ≈3–5 g 

potassium cyanide (15–25 mg CN–

/kg) (Liebowitz and Schwartz 1948). The results indicated that the 

patient excreted 237 mg of thiocyanate over a 72-hour period. This quantity was substantially more than 

the normal average amount of thiocyanate in urine, which varies between 0.85 and 14 mg/24 hours. 

Thirty-one children who had consumed flour made from insufficiently processed cassava had mean 

urinary thiocyanate levels of 757 μmol/L, compared with 50 μmol/L in those children who had consumed 

sufficiently processed cassava (Tylleskar et al. 1992). In another study (Mlingi et al. 1993), mean urinary 

thiocyanate was 490 μmol/L in a village affected by Konzo disease and 350 μmol/L in an unaffected 

village, with the villages being comparable in all other respects. 

When male Sprague-Dawley rats were given 2 mg CN–

/kg [14C] potassium cyanide, urinary excretion of 

radioactivity reached 47% of the dose within 24 hours following administration (Farooqui and Ahmed 

1982). When [14C] sodium cyanide was injected subcutaneously into rats at a level of 8.3 μmol, no 
CYANIDE 85 

3. HEALTH EFFECTS 

difference in radioactivity eliminated was observed between the group pretreated for 6 weeks with a diet 

containing 0.7 mg CN–

/kg as potassium cyanide and their matching controls (Okoh 1983). Most of the 

radioactivity was detected in the urine (89% by 24 hours). Thiocyanate was the major metabolite. About 

4% of the radioactivity was expired, mostly as carbon dioxide. 

Sousa et al. (2003) compared toxicokinetic parameters in male Wistar rats and Landrace-Large White 

pigs that were given 1.2 mg CN–

/kg as potassium cyanide by aqueous gavage. The half-lives of 

elimination of cyanide from the blood were 0.54 hours for pigs and 0.64 hours for rats. The half-lives of 

elimination of thiocyanate from the blood were 4.95 hours in pigs and 5.8 hours in rats. The overall 

clearance of cyanide from the blood was reported as 0.367, and 0.379 mL/minute per kg for pigs and rats, 

respectively; the clearance of thiocyanate was reported as 0.135 and 0.061 mL/minute per kg for pigs and 

rats, respectively. 

Orally administered cyanide and its metabolite thiocyanate were eliminated in the breast milk of lactating 

goats (Soto-Blanco and Gorniak 2003). The relevance of the goat data to humans is not established. 

3.4.4.3 Dermal Exposure 

No studies were located regarding excretion in humans or animals after dermal exposure to cyanide. 

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

Physiologically based pharmacokinetic (PBPK) models use mathematical descriptions of the uptake and 

disposition of chemical substances to quantitatively describe the relationships among critical biological 

processes (Krishnan et al. 1994). PBPK models are also called biologically based tissue dosimetry 

models. PBPK models are increasingly used in risk assessments, primarily to predict the concentration of 

potentially toxic moieties of a chemical that will be delivered to any given target tissue following various 

combinations of route, dose level, and test species (Clewell and Andersen 1985). Physiologically based 

pharmacodynamic (PBPD) models use mathematical descriptions of the dose-response function to 

quantitatively describe the relationship between target tissue dose and toxic end points. 

PBPK/PD models refine our understanding of complex quantitative dose behaviors by helping to 

delineate and characterize the relationships between: (1) the external/exposure concentration and target 
CYANIDE 86 

3. HEALTH EFFECTS 

tissue dose of the toxic moiety, and (2) the target tissue dose and observed responses (Andersen and 

Krishnan 1994; Andersen et al. 1987). These models are biologically and mechanistically based and can 

be used to extrapolate the pharmacokinetic behavior of chemical substances from high to low dose, from 

route to route, between species, and between subpopulations within a species. The biological basis of 

PBPK models results in more meaningful extrapolations than those generated with the more conventional 

use of uncertainty factors. 

The PBPK model for a chemical substance is developed in four interconnected steps: (1) model 

representation, (2) model parameterization, (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) are 

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 3-5 shows a conceptualized representation of a PBPK model. 

No PBPK models were located for cyanide. 
CYANIDE 87 

3. HEALTH EFFECTS 

Figure 3-5. Conceptual Representation of a Physiologically Based 

Pharmacokinetic (PBPK) Model for a 

Hypothetical Chemical Substance 

Lungs 

Liver 

Fat 

S low ly 

perfused 

tissues 

R ichly 

perfused 

tissues 

K idney 

S kin 

V 

E 

N 

O 

U 

S 

B 

L 

O 

O 

D 

A 

R 

T 

E 

R 

I 

A 

L 

B 

L 

O 

O 

D 

V max K m 

Ingestion 

Inhaled chem ical E xhaled chem ical 

GI 

Tract 

Feces 

U rine

 C hem icals in air 

contacting skin 

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. 
CYANIDE 88 

3. HEALTH EFFECTS 

3.5 MECHANISMS OF ACTION 

This section presents a brief overview of any known mechanisms of metabolism, absorption, distribution, 

and excretion including substance reactions or physiological processes that lead to or comprise the 

mechanism(s) of toxic effect. 

3.5.1 Pharmacokinetic Mechanisms 

Absorption. Absorption of cyanide across the gastrointestinal mucosa depends on the pH of the gut 

and the pKa and lipid solubility of the particular cyanide compound. Hydrogen cyanide is a weak acid 

with a pKa of 9.2 at 25 °C. The acidic environment in the stomach favors the non-ionized form of 

hydrogen cyanide and facilitates absorption. Information regarding the rapid lethal effects following oral 

intake of cyanide in humans (Gosselin et al. 1984) indicates that cyanide is rapidly absorbed from the 

gastrointestinal tract. 

Hydrogen cyanide is moderately lipid-soluble, which, along with its small size, allows it to rapidly cross 

mucous membranes and to be taken up instantly across the alveolar epithelium of the lung after 

inhalation; penetration across the epidermis is less rapid. In addition, some cyanide compounds, such as 

potassium cyanide, have a corrosive effect on the skin that can increase the rate of percutaneous 

absorption (NIOSH 1976). Information regarding dermal absorption in animals and evidence that cyanide 

can be absorbed through the skin of humans is provided in Sections 3.4.1.3 and 3.2.3, respectively. 

Distribution. Cyanide is rapidly distributed by the blood throughout the body. In a study using orally 

administered radioactively labeled potassium cyanide, radioactivity detected in whole blood or plasma 

decreased rapidly within 6 hours. Of the low levels of radioactivity detected in the red blood cells, about 

94% of the radioactivity recovered was found in the hemolysate; of which 70% was detected in the heme 

fraction, 14–25% in globin, and only 5–10% in cell membranes (Farooqui and Ahmed 1982). Yamamoto 

et al. (1982) determined that the pattern of distribution of cyanide did not vary with the concentration 

used. Ballantyne (1983b) observed higher cyanide levels in whole blood than in serum in rabbits exposed 

dermally to hydrogen cyanide, potassium cyanide, and sodium cyanide. See Section 3.4.2.1 for specific 

studies on cyanide tissue distribution. 
CYANIDE 89 

3. HEALTH EFFECTS 

Cyanide is a reactive chemical substance and has the potential to form a variety of adducts in biological 

systems. A study of radiolabeled cyanide binding to mouse brain parts revealed that the hypothalamus 

accumulated more label than cerebral cortex, hippocampus, or cerebellum (Borowitz et al. 1994). 

Similarly, Baskin et al. (1987) found that the left ventricle of the guinea pig heart contained nearly twice 

as much as the right ventricle after a brief exposure to cyanide. Binding to certain tissue constituents may 

be important for decreasing the actions of cyanide and protecting cells from cyanide toxicity (Devlin et al. 

1989b). 

Storage. Cyanide does not accumulate in blood and tissues following chronic oral exposure. In a 

study with rats administered hydrogen cyanide in the diet at <10.4 mg CN–

/kg/day for 2 years, virtually 

no cyanide was found in plasma or kidneys (Howard and Hanzal 1955). 

Metabolism. See Section 3.4.5. 

Excretion. Cyanide metabolites (of which thiocyanate is the major component) are excreted primarily 

in urine, with small amounts of the metabolites eliminated through the lungs. When radioactively labeled 

cyanide is administered, most of the radioactivity is detected in the urine within 24 hours (Farooqui and 

Ahmed 1982; Okoh 1983). Boxer and Richards (1952) were the first to show that cyanide was oxidized 

to CO2 and in the Okoh (1983) study, about 4% of the radioactivity was expired, mostly as carbon 

dioxide. See Section 3.4.3.4 for information on studies examining elimination and excretion. 

Effect of Dose and Duration of Exposure on Toxicity. The severity of neurological effects in 

humans and animals after acute oral exposure to cyanide is dose-related (Chen and Rose 1952; Lasch and 

El Shawa 1981). Central nervous system effects have been observed following acute-duration exposures 

(Levine and Stypulkowski 1959a) and chronic-duration exposures (Hertting et al. 1960), via the 

inhalation and oral routes. Necrosis is the most prevalent central nervous system effect following acuteduration exposure to high concentrations of cyanide, whereas demyelination is observed in animals that 

survive repeated exposure protocols (Bass 1968; Ibrahim et al. 1963). 

Increased duration of exposure to inhaled cyanide in mice resulted in lower LC50 values (Higgins et al. 

1972; Matijak-Schaper and Alarie 1982). Additionally, cyanide toxicity was influenced by dilution of the 

gavage dose. Greater dilution resulted in higher mortality for the same total dose (Ferguson 1962). 
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Tylleskar et al. (1992) studied a population in rural Zaire that was affected with Konzo. Konzo is 

characterized by symmetric isolated bilateral involvement of upper motor neurons of abrupt onset; the 

damage is permanent, but not progressive. The Konzo patients had serum thiocyanate concentrations 

below those of the controls. The authors suggest that the combination of high exposure and a decreased 

conversion rate because of a deficiency in suitable sulfur substrates might explain this difference. Thus, 

daily exposure and decreased conversion rates may lead to high blood concentrations of cyanide that may 

then lead to upper motor neuron damage. It has been suggested that defects in the metabolic conversion 

of cyanide to thiocyanate, as well as nutritional deficiencies of protein and vitamin B12, play a role in the 

development of central nervous system disorders such as tropical ataxic neuropathy, tobacco amblyopia, 

and Leber's hereditary optic atrophy. 

Route-Dependent Toxicity. A great similarity exists among cyanide-induced effects following 

inhalation, oral, and dermal exposure. Signs of toxicity in target organs from acute cyanide exposure 

(primarily central nervous system and heart), and chronic exposure (including central nervous system and 

thyroid gland), are similar in both humans and animals regardless of route. In general, the latency of 

effects is shortest by the inhalation route, similar for the oral route, but longer for the dermal route, since 

the skin is a thicker barrier to penetration. The rate of cyanide absorption and, therefore, latency of toxic 

effects is decreased in fasting animals. 

3.5.2 Mechanisms of Toxicity 

Effects of Metabolism on Toxicity. Cyanide (as hydrogen cyanide), originating in vivo by dissociation of 

potassium cyanide, sodium cyanide, and other cyanogenic compounds or arising from catabolism of 

cyanogenic glycosides, exerts its acute toxic effects by complexing with the ferric iron atom in 

metalloenzymes, resulting in histotoxic anoxia through inhibition of cytochrome c oxidase (Rieders 1971; 

Way 1984), metalloenzymes that function as the terminal oxidase of the inner mitochondrial membrane 

respiratory chain. A two-step process has been proposed: cyanide as hydrogen cyanide first penetrates a 

protein crevice of cytochrome c oxidase and binds to the protein (Stannard and Horecker 1948). 

Hydrogen cyanide then binds to the trivalent iron ion of the enzyme, forming a relatively stable (but 

reversible) coordination complex. One mole of hydrogen cyanide is bound to one mole of cytochrome c 

oxidase (Van Buuren et al. 1972). As a result, the enzyme becomes unable to catalyze the reactions in 

which electrons would be transferred from reduced cytochrome to oxygen. Cellular oxygen utilization is 

thus impaired, with resultant reduction in or cessation of aerobic metabolism (Rieders 1971; Way 1984). 

Glucose catabolism then shifts from the aerobic pathway to anaerobic metabolism including the pentose 
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phosphate pathway, resulting in increased blood glucose, pyruvic acid, lactic acid, and nicotinamide 

adenine dinucleotide (NADPH) levels, and a decrease in the adenosine triphosphate/adenosine 

diphosphate (ATP/ADP) ratio (Rieders 1971; Way 1984). Wilson et al. (1994) suggest that it is the 

binding of cyanide to oxidized CuB, the copper ion that is part of the dioxygen binding-site that leads to 

the inhibition of cytochrome c oxidase. 

The inhibition of oxygen use by cells (termed histoxic hypoxia) causes oxygen tensions to rise in 

peripheral tissues (Smith 1996). This results in a decrease in the unloading gradient for oxyhemoglobin; 

thus, oxyhemoglobin is carried in the venous blood (Rieders 1971). Inhibition of oxygen utilization is 

thought to occur rapidly after cyanide exposure. Tadic (1992) determined that inhibition of cytochrome c 

oxidase activity in rat brains was most pronounced between 15 and 20 minutes after administration of 

sodium cyanide (12 mg/kg or 1.3xLD50). In addition to binding to cytochrome c oxidase, cyanide also 

binds to catalase, peroxidase, methemoglobin, hydroxocobalamin, phosphatase, tyrosinase, ascorbic acid 

oxidase, xanthine oxidase, and succinic dehydrogenase. These reactions may also contribute to the 

classic signs of cyanide toxicity (Ardelt et al. 1989; Rieders 1971). Information on mechanisms of 

toxicity in target organs is presented below. 

Target Organ Toxicity. The central nervous system is the primary target for cyanide toxicity in humans 

and animals. Acute inhalation of high concentrations of cyanide provokes a brief central nervous system 

stimulation followed by depression, convulsions, coma, and death in humans (Bonsall 1984; Chen and 

Rose 1952; Peden et al. 1986; Potter 1950; Singh et al. 1989) and in animals (Haymaker et al. 1952; 

McNerney and Schrenk 1960; Purser et al. 1984). The effects are probably due to rapid biochemical 

changes in the brain, such as changes in ion flux, neurotransmitter release, and possibly peroxide 

formation (Johnson and Isom 1985; Kanthasamy et al. 1991a, 1994; Persson et al. 1985). In both in vivo 

and in vitro studies using brain tissue, the sensitivity of mitochondrial cytochrome c oxidase activity to 

inhibition by cyanide was greater than the inhibition of mitochondrial respiratory activity. Only after 

cytochrome c oxidase activity was depressed by >50% was a large decrease in respiratory activity 

detected, suggesting that a large portion of cytochrome c oxidase may serve as a functional reserve. 

Cyanide poisoning likely involves mechanisms in addition to inhibition of cytochrome c oxidase activity 

(Pettersen and Cohen 1993). Cyanide is a strong nucleophile with multiple effects including release of 

secondary neurotransmitters, release of catecholamines from adrenal glands and adrenergic nerves, and 

inhibition of antioxidant enzymes in the brain (Smith 1996). However, the extremely low concentration 

of cyanide required to inhibit the oxidase, the rapid interaction of hydrogen cyanide with the enzyme, and 

the key role of cytochrome c oxidase in aerobic metabolism all combine to make cyanide inhibition of the 
CYANIDE 92 

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terminal step of electron transport (Chance and Erecinsk 1971; Gibson and Greenwood 1963), the key 

molecular target in cyanide poisoning. 

Inhalation and oral studies in animals have shown that acute or chronic cyanide exposure leads to 

encephalopathy in both white and gray matter. In particular, damage has been observed in regions such 

as the deep cerebral white matter, corpus callosum, hippocampus, corpora striata, pallium, and substantia 

nigra. White matter may be more sensitive because of its relatively low cytochrome c oxidase content. 

Rats injected subcutaneously with daily maximal doses between >3.7 and 9.2 mg CN–

/kg/day (not 

averaged) 3 days/week for 3 months developed necrotic lesions of the corpus callosum and optic nerve, 

but there was not a consistent dose-response (Lessell 1971); this may reflect variability in diffusion of 

cyanide into the systemic circulation by the subcutaneous injection route. High mortality was observed 

among exposed animals. These effects have been observed following acute-duration exposures (Levine 

and Stypulkowski 1959a) and chronic-duration exposures (Hertting et al. 1960). Necrosis is a prevalent 

central nervous system effect following acute exposure to high concentrations of cyanide, whereas 

demyelination is observed in animals that survive repeated exposure protocols (Bass 1968; Ibrahim et al. 

1963). The mechanism of cyanide-induced demyelination is not completely understood, but the evidence 

suggests that a direct effect of cyanide on white matter may not be necessary. It has been suggested that 

local edema affecting the oligodendrocytes and caused by vascular changes triggered by cyanide 

represent a primary event in demyelination (Bass 1968; Ibrahim et al. 1963). Aitken and Braitman (1989) 

determined that cyanide has a direct effect on neurons not mediated by its inhibition of metabolism. 

Consistent with the view that cyanide toxicity is due to the inability of tissue to utilize oxygen is a report 

that in cyanide-intoxicated rats, arterial pO2 levels rose, while carbon dioxide levels fell (Brierley et al. 

1976). The authors suggested that the low levels of carbon dioxide may have led to vasoconstriction and 

reduction in brain blood flow; therefore, brain damage may have been due to both histotoxic and anoxic 

effects. Partial remyelination after cessation of exposure has been reported, but it is apparent that this 

process, unlike that in the peripheral nervous system, is slow and incomplete (Hirano et al. 1968). The 

topographic selectivity of cyanide-induced encephalopathy may be related to the depth of acute 

intoxication and distribution of blood flow, which may result in selected regions of vascular insufficiency 

(Levine 1969). 

Several studies have suggested that a disruption in neuronal calcium regulation may be an important 

factor in the manifestation of cyanide-induced neurotoxic events following acute exposure. The 

predominance of anaerobic metabolism in a cyanide-poisoned cell decreases the ATP/ADP ratio, or 

energy charge (Isom et al. 1975), and thus alters energy-dependent processes such as cellular calcium 
CYANIDE 93 

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homeostasis (Johnson et al. 1986). Elevated levels of intracellular calcium in a cyanide-exposed, 

presynaptic squid neuron were observed in an in vitro study (Adams et al. 1985). Elevated levels of 

neuronal calcium may initiate release of neurotransmitters from the presynaptic terminal, which can 

activate the nervous system (Maduh et al. 1990a). Levels of whole-brain calcium increased when 

potassium cyanide was administered subcutaneously to mice. These increases were correlated with 

cyanide-induced tremors (Johnson et al. 1986). Brain injury may be associated with cyanide-induced 

endogenous glutamate release, mediated by both calcium dependent and independent mechanisms, which 

in turn produce excitotoxic responses in select brain areas (Patel et al. 1991, 1992, 1993). In examining 

receptor subtypes involved in mediating cyanide-induced toxicity, sodium cyanide-induced cytotoxicity 

was found to be mediated primarily by activation of the N-methyl-D aspartate (excitatory amino acid) 

receptor. Sturm et al. (1993) examined the ability of adenosine to attenuate the excitotoxicity secondary 

to glutamate receptor activation following potassium cyanide exposure in hippocampal neuronal cell 

cultures. The authors concluded that neuronal cell death was mediated at least in part by glutamate and 

that the cell death was attenuated by adenosine via the A1-specific receptor. Increases in intracellular 

calcium have also been associated with cyanide-induced effects on vascular smooth muscle and cardiac 

muscle, possibly inducing cell damage (Allen and Smith 1985; Robinson et al. 1985a). These effects may 

result from ischemia-induced increases in extracellular potassium, which in turn enhance cellular 

permeabilities to calcium (Robinson et al. 1985b). Furthermore, changes in cytosolic pH and dysfunction 

of hydrogen ion handling mechanisms were observed in neuronal cells exposed in vitro to cyanide 

(Maduh et al. 1990b). Pazdernik et al. (1994) reported an increase of local cerebral glucose utilization 

(LCGU) in many regions of the brain within a minute after sublethal exposure to 2.7–5 mg CN–

/kg as 

sodium cyanide by controlled intravenous infusion over 1 hour. However, by 1 hour, there was a global 

increase in LCGU in almost every region of the brain. LCGU values returned to normal in all regions 

except the choroid plexus by 6 hours and in that region as well by 24 hours. These results support the 

expectation that cyanide causes a shift from aerobic to anaerobic metabolism, as illustrated by increases in 

extracellular lactate and pyruvate and in LCGU. 

When cyanide blocks oxidative metabolism in mitochondria, cells shift their metabolism and enhanced 

glucose utilization occurs. One consequence of this altered metabolic pattern is accumulation of 

nicotinamide adenine dinucleotide (NADH), which is a powerful stimulant of calcium mobilization from 

cell stores through "inositol triphosphate receptors." Elevated calcium damages cells. Increase in cellular 

NADH, therefore, is an important event in the toxic action of cyanide (Kaplin et al. 1996). 
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Studies have shown that cyanide releases catecholamines from rat pheochromocytoma cells and brain 

slices (Kanthasamy et al. 1991b), from isolated bovine adrenal glands (Borowitz et al. 1988), and from 

adrenals of mice following subcutaneous injection of high doses of potassium cyanide (Kanthasamy et al. 

1991b). Thus, it was proposed that the cardiac and peripheral autonomic responses to cyanide are 

partially mediated by an elevation of plasma catecholamines (Kanthasamy et al. 1991b). Dopamine levels 

in potassium cyanide-treated animals were significantly decreased in striatum and hippocampus, and 

somewhat decreased in cerebral cortex of mice (Kanthasamy et al. 1994), while extracellular levels of 

dopamine and homovanillic acid were increased in the brain of rats treated with sodium cyanide (Cassel 

et al. 1995). Kiuchi et al. (1992) suggested that suppression of ATP production by sodium cyanide 

induces an abrupt and remarkable increase in dopamine release from the nerve terminal in the striatum. 

Kanthasamy et al. (1994) also observed that in striatal and hippocampal tissues, but not in cerebral cortex, 

malondialdehyde levels increased indicating the occurrence of lipid peroxidation in these brain regions. 

In addition, reduced numbers of tyrosine hydroxylase (TH) positive cells indicated a loss of dopaminergic 

neurons (Kanthasamy et al. 1994). Behavioral effects seen in the mice were reversed by administration of 

l-DOPA (treatment for dopamine-deficiency). Ardelt et al. (1994) also evaluated hydroperoxide 

generation as a potential mechanism of cyanide neurotoxicity. Increased lipid peroxidation was observed 

in brain and kidney, but not in liver or heart. It was also determined that calcium plays a critical role in 

lipid peroxidation in neuronal cells. Subcellular fractionation of brain tissue showed an increase in lipid 

peroxidation in the microsomal but not mitochondrial fraction. Matsumoto et al. (1993) evaluated the 

involvement of extracellular calcium in dopamine release from rat striatum resulting from cyanide 

exposure. A gradual increase in intracellular calcium was observed during incubation of sodium cyanide 

with striatal slices. The excessive influx of extracellular calcium during sodium cyanide perfusion may 

contribute to the changes in dopamine levels in striatum and to the observed suppression of dopamine 

release in response to high potassium stimulation. Release of dopamine was not suppressed by perfusion 

with a calcium-free solution; thus, additional mechanisms other than the opening of calcium channels 

must also be involved in dopamine release by cyanide. Decreased dopamine uptake has been suggested 

as an explanation for this increase in dopamine, since dopamine uptake is driven by a sodium gradient 

that is maintained by the Na/K ATPase and could be reduced if ATP is depleted. Cyanide did not affect 

monamine oxidase or catechol-o-methyl transferase, suggesting that a disturbance in dopamine 

metabolism did not lead to extracellular dopamine elevation (Matsumoto et al. 1993). 

Mills et al. (1999) reported that there is more than one mode of cell death operating in the brains of mice 

injected with potassium cyanide. Extensive DNA fragmentation, pyknosis, and chromosome 

condensation, all characteristics of apoptosis, were observed in the parietal and suprarhinal regions of the 
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motor cortex of treated mice. However, necrotic lesions with astrocytic gliosis were found in the 

substantia nigra. Pretreatment with the antioxidant alpha-phenyl-tert-butyl nitrone reduced cortical DNA 

fragmentation, but had no effect on the necrotic lesions produced in the substantia nigra. 

Prabhakaran et al. (2002) similarly reported different modes of death induced by cyanide in primary 

cultures of rat cortical or mesencephalic neurons; the mode of cell death and the reactive oxygen species 

generated differed in the two kinds of cells. Cortical neurons exhibited apoptosis, with increases in 

hydrogen peroxide and superoxide, and a moderate change in mitochondrial membrane potential, leading 

to release of cytochrome c and activation of caspase-3-like protease (a cysteine protease associated with 

apoptosis). Mesencephalic neurons exhibited necrosis involving excess nitric oxide and superoxide, with 

a more pronounced reduction in mitochondrial membrane potential. Additional studies demonstrated that 

necrosis of exposed mesencephalic cells or cortical neurons exposed to 0.5–0.6 mM KCN was induced by 

the upregulation of uncoupling protein 2 (UCP-2), a protein of the inner mitochondrial membrane (Li et 

al. 2005; Prabhakaran et al. 2005). UCP-2 increases proton leak across the inner mitochondrial 

membrane, dissociating respiration from ATP synthesis. In experiments preventing the expression of 

UCP-2, the necrotic death of cultured mesencephalic cells exposed to cyanide was also prevented 

(Prabhakaran et al. 2005). 

The mediation of cyanide-induced apoptosis has been studied in cultured cortical neurons exposed to 

0.3 mM cyanide (Shou et al. 2002, 2003). Treatment with cyanide activated p38 mitogen-activated 

protein (MAP) kinase within 30 minutes, an upstream event necessary for the translocation of Bax protein 

from the cytosol to mitochondria 2.5 hours later (Shou et al. 2003). Translocation of Bax protein to 

mitochondria is a required step in the release of cytochrome c from mitochondria as well as the caspase 

cascade that regulates apoptosis. Cyanide treatment of cortical neurons also results in the activation of 

the redox-sensitive transcription factor NF-κB, and its translocation to the nucleus, where it upregulates 

expression of the pro-apoptotic proteins Bax and Bcl-XS (Shou et al. 2002). Increased cytosolic calcium 

levels also contribute to apoptosis of cyanide-treated cortical neurons (Shou et al. 2004). Increased 

calcium activates cellular calcineurin, which stimulates the activation of the protein known as BAD (Bcl2/Bcl-XL-antagonist, causing cell death) and its translocation to mitochondria within 1 hour of treatment 

with cyanide. The net effect of BAD is to selectively inhibit proteins (Bcl-1/Bcl-XL) that are antagonists 

to apoptosis (Shou et al. 2004). 

It has been noted that survivors of cyanide poisoning incidents may develop Parkinsonian-like signs, with 

lesions in the substantia nigra, a dopaminergic center, confirmed by MRI (Carella et al. 1988; Chin and 
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Calderon 2000; Grandas et al. 1989; Feldman and Feldman 1990; Rachinger et al. 2002; Rosenberg et al. 

1989; Rosenow et al. 1995; Uitti et al. 1985; Zaknun et al. 2005). Jones et al. (2000, 2003) have 

presented evidence based on experiments on PC12 cells (a pheochromocytoma cell line that can be 

induced to differentiate as neurons) and fetal rat mesencephalic cells indicating that cyanide toxicity is 

exacerbated by the oxidation of dopamine. Increases in apoptosis and reactive oxygen species occurred at 

higher levels in PC12 cells incubated in dopamine plus potassium cyanide compared to those incubated in 

either chemical separately; concentrations of potassium cyanide that had no effect on fetal rat midbrain 

cells significantly increased the adverse effects of added dopamine. Toxicity in one or both systems was 

reduced by preincubation with antioxidants (superoxide dismutase, glutathione catalase), an inhibitor to 

nitric oxide synthase (Nomega-nitro-L-arginine methyl ester), and the peroxynitrite scavenger uric acid. 

The authors suggest that the inactivation of antioxidant enzymes by cyanide as described by Ardelt et al. 

(1989) may render neurons more vulnerable to the adverse effects of dopamine oxidation. Dopaminergic 

brain centers would therefore be more sensitive to cyanide neurotoxicity. In cultured cerebellar granule 

cells taken from 8-day-old rat pups, cyanide treatment generated nitric oxide and reactive oxygen species 

concurrently, resulting in lipid peroxidation (Gunasekar et al. 1996). 

Chao et al. (1996) investigated the possibility that cyanide had an effect on motor neurons that was 

independent of respiratory impairment. In mouse triangularis sterni and diaphragm nerve-muscle 

preparations under glucose-free conditions, 10 μM sodium cyanide increased spontaneous transmitter 

release. This was correlated with a depression of ATP-sensitive potassium currents, an effect that was 

antagonized by diazoxide, an opener of ATP-sensitive K+

 channels. The authors suggest that cyanide 

causes depolarization of motor nerve terminals via its effect on the ATP-sensitive K+

 channels. Cassel et 

al. (1994) examined the in vitro effects of sodium cyanide on two forms of monoamine oxidase (MAO), 

an enzyme important in regulation of biogenic amines in the brain and peripheral tissue. In striatal tissue, 

cyanide produced a dose-dependent increase in the activity of MAO-A but not MAO-B. Greer and Carter 

(1995) investigated the effects of hydrogen cyanide on the neural mechanisms controlling breathing. 

Cyanide, at concentrations considered lethal in vivo, caused a modest depression of the frequency and 

amplitude of inspiratory rhythmic discharge. The neuronal network underlying respiration continued to 

function for hours in the presence of very high concentrations of cyanide. The authors hypothesized that 

the rapid suppression of breathing caused by cyanide in vivo is due to changes in neuronal excitability in 

respiratory centers in the central nervous system. 

Results of in vitro studies suggest an interaction between calcium ions and cyanide in cardiovascular 

effects (Allen and Smith 1985; Robinson et al. 1985a). It has been demonstrated that exposure to cyanide 
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in metabolically depleted ferret papillary muscle eventually results in elevated intracellular calcium 

levels, but only after a substantial contracture develops (Allen and Smith 1985). The authors proposed 

that intracellular calcium may precipitate cell damage and arrhythmias. The mechanism by which 

calcium levels are raised was not determined. Franchini and Krieger (1993) produced selective 

denervation of the aortic and carotid bifurcation areas, and confirmed the carotid body chemoreceptor 

origin of cardiovascular, respiratory, and certain behavioral responses to cyanide in rats. Bradycardia and 

hyperventilation induced by cyanide are typical responses evoked by carotid body chemoreceptor 

stimulation (Franchini and Krieger 1993). 

The respiratory effects of cyanide include dyspnea, asphyxia, and a decrease in respiratory rate (Blanc et 

al. 1985; Matijak-Schaper and Alarie 1982; McNerney and Schrenk 1960). A recent study (Bhattacharya 

et al. 1994) demonstrated an initial increased air flow, transthoracic pressure, and tidal volume 

accompanied by a significant decrease in pulmonary phospholipids following inhalation of hydrogen 

cyanide in rats. This study also showed that hydrogen cyanide exhibited a direct effect on pulmonary 

cells in rats. 

Cyanide-induced effects on the thyroid gland are particularly important in chronic cyanide exposures and 

are discussed in several studies. Thiocyanate markedly inhibits accumulation of iodine by the thyroid 

gland, thus decreasing the ability of the gland to maintain a concentration of iodine above that of blood 

(VanderLaan and Bissell 1946). In addition, thiocyanate may inhibit the iodination process, thus 

interfering with the binding of glandular iodine and reducing the formation of thyroxine (Ermans et al. 

1972). Changes in thyroid chemistry reported in individuals chronically exposed to cyanide have not 

been accompanied by manifestations of hypothyroidism. Fukayama et al. (1992) studied the antithyroid 

action of thiocyanate in a culture system of thyroid follicles. Thiocyanate concentrations equivalent to 

serum levels in smokers showed three independent antithyroid actions, including inhibition of iodide 

transport, inhibition of binding of iodide in the thyroid, and increased iodide efflux. The discrepancy in 

the potency of the antithyroid activity of thiocyanate in vivo and in vitro appears to be due to the presence 

of iodide and moieties such as the perchlorate ion, which is known to alter the effect of thiocyanate on the 

thyroid (Van Middlesworth 1986). 

Persons with a metabolic disturbance in the conversion of cyanide to thiocyanate may be at greater risk 

from the toxic effect of cyanide. A defect in the rhodanese system and vitamin B12 deficiency have been 

noted in persons with tobacco amblyopia and Leber's hereditary optic atrophy exposed to tobacco smoke 

which contains cyanide (Wilson 1983). Iodine deficiency, along with excess chronic exposure to cyanide, 
CYANIDE 98 

3. HEALTH EFFECTS 

may, in certain cases, be involved in the etiology of such thyroid disorders as goiter and cretinism 

(Delange and Ermans 1971; Ermans et al. 1972). Also, protein deficiencies and vitamin B12 and 

riboflavin, and other deficiencies may subject people who eat foods high in cyanogenic glycosides to 

increased risk of neuropathies (Makene and Wilson 1972; Osuntokun 1972; Osuntokun et al. 1969). 

Patients with motor neuron disease (amyotrophic lateral sclerosis) possess a disorder in cyanide 

metabolism that may result in higher susceptibility to cyanide (Kato et al. 1985). 

Carcinogenesis. No studies were located regarding carcinogenic effects of cyanide exposure in humans 

or animals following any route of exposure. Therefore, no mechanism of carcinogenesis can be 

discussed. 

Caveat Regarding in vitro Studies. During a study of the effect of sodium cyanide on cultured SH-SY5Y 

human neuroblastoma cells, Arun et al. (2005) observed that no significant toxicity was observed up to 

concentrations of 10 mM and conducted further experiments to determine the cause of the apparent 

resistance to cyanide. Culturing at 37 °C for 2 hours resulted in variable depletion of cyanide from the 

medium, depending on the type of vessel: by 3.9% using 15-mL capped polypropylene tubes, by 22.4% 

using vented cap 25-cm2

 culture flasks, and by 57.2–86.7% using unsealed multiwell plates (12-, 24-, or 

96-well). Cyanide loss from standard Dulbecco’s monified Eagle’s/Ham’s F12 medium (DMEM) with 

10% fetal bovine serum (FBS) was compared to the loss from individual constituents of medium tested 

after 2-hour culturing at room temperature. Cyanide loss from solution was 68.6% from an amino acid 

mixture, 47.9% from glucose solution, 36.3% from phenol red (typically included as a pH indicator), and 

81.1% from standard DMEM plus 10% FBS. Arun et al. (2005) measured a 10% loss of sodium cyanide 

from deionized water (0.2 mL volume) over a 2-hour period at room temperature and higher losses when 

a protein donor (alanine) was present. Release of HCN by outgassing accompanied cyanide depletion 

from the medium. The results of these experiments indicate there is measurable loss of cyanide from 

solution where vessels are not sealed. This may result in an underestimate of the toxicity of cyanide in in 

vitro culture experiments. 

3.5.3 Animal-to-Human Extrapolations 

Biological effects of cyanide in humans have been demonstrated (Smith 1996; Wexler et al. 1947). 

However, no studies directly comparing the cytotoxicity of similar animal and human cells were 

available. However, a difference in species susceptibility to cyanide poisoning was indicated by slightly 

lower lethal concentrations in rabbits compared to rats (Ballantyne 1983a). Additionally, mortality from 

cyanides applied dermally varied depending on the cyanide compound used. In the Ballantyne (1983a) 
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study, dermal application resulted in cyanide levels in blood and serum that were lower after topical 

sodium cyanide and potassium cyanide exposure than from hydrogen cyanide; however, oral exposure in 

rabbits produced an LD50 of 2.3–2.7 mg CN–

/kg/day, regardless of whether the source was hydrocyanic 

acid, sodium cyanide, or potassium cyanide (Ballantyne 1983a). 

Species and tissue distribution of rhodanese (thiosulfate sulfurtransferase), an enzyme important in 

metabolizing cyanide, is highly variable (Drawbaugh and Marrs 1987; Himwich and Saunders 1948). In 

dogs, the highest activity of rhodanese was found in the adrenal gland, ≈2.5 times greater than the activity 

in the liver (Himwich and Saunders 1948). Monkeys, rabbits, and rats had the highest rhodanese activity 

in liver and kidney, with relatively low levels in adrenals. It should be noted that total rhodanese activity 

in other species was higher than in dogs, which is consistent with the greater susceptibility of dogs to the 

acute effects of cyanide. Thus, dogs may not be a good model from which to extrapolate the toxicity of 

cyanide to humans. Similar activities of the enzyme among the species were found for the brain, testes, 

lungs, spleen, and muscle. Plasma activities of rhodanese in rats, hamsters, rabbits, and guinea pigs 

ranged from 14 to 20 Units/mL compared to 31 Units/mL for Beagle dogs (Drawbaugh and Marrs 1987). 

In an effort to identify appropriate animal models for testing the efficacy of methemoglobin-forming 

cyanide antidotes, Rockwood et al. (2003) compared the endogenous activities of the erythrocyte NADHdependent enzyme methemoglobin reductase (ferricyanide reductase) in several species. Two strains of 

beagles had enzyme activities roughly 40–50% lower than the mean for humans and with no overlap to 

the range for the human data. The enzyme activities of the other tested species had higher means than the 

human, but the ranges for the Rhesus and Aotus monkeys were similar to the human, indicating that these 

would be appropriate models. Data for the marmoset, Cynomolgus monkey, and African green monkey 

showed less overlap to the human data, whereas data for the ferret, chimpanzee, and baboon showed no 

overlap. 

3.6 TOXICITIES MEDIATED THROUGH THE NEUROENDOCRINE AXIS 

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine 

system because of the ability of these chemicals to mimic or block endogenous hormones. Chemicals 

with this type of activity are most commonly referred to as endocrine disruptors. However, appropriate 

terminology to describe such effects remains controversial. The terminology endocrine disruptors, 

initially used by Thomas and Colborn (1992), was also used in 1996 when Congress mandated the EPA to 

develop a screening program for “...certain substances [which] may have an effect produced by a 
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naturally occurring estrogen, or other such endocrine effect[s]...”. To meet this mandate, EPA convened a 

panel called the Endocrine Disruptors Screening and Testing Advisory Committee (EDSTAC), and in 

1998, the EDSTAC completed its deliberations and made recommendations to EPA concerning endocrine 

disruptors. In 1999, the National Academy of Sciences released a report that referred to these same types 

of chemicals as hormonally active agents. The terminology endocrine modulators has also been used to 

convey the fact that effects caused by such chemicals may not necessarily be adverse. Many scientists 

agree that chemicals with the ability to disrupt or modulate the endocrine system are a potential threat to 

the health of humans, aquatic animals, and wildlife. However, others think that endocrine-active 

chemicals do not pose a significant health risk, particularly in view of the fact that hormone mimics exist 

in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens 

(Adlercreutz 1995; Livingston 1978; Mayr et al. 1992). These chemicals are derived from plants and are 

similar in structure and action to endogenous estrogen. Although the public health significance and 

descriptive terminology of substances capable of affecting the endocrine system remains controversial, 

scientists agree that these chemicals may affect the synthesis, secretion, transport, binding, action, or 

elimination of natural hormones in the body responsible for maintaining homeostasis, reproduction, 

development, and/or behavior (EPA 1997). Stated differently, such compounds may cause toxicities that 

are mediated through the neuroendocrine axis. As a result, these chemicals may play a role in altering, 

for example, metabolic, sexual, immune, and neurobehavioral function. Such chemicals are also thought 

to be involved in inducing breast, testicular, and prostate cancers, as well as endometriosis (Berger 1994; 

Giwercman et al. 1993; Hoel et al. 1992). 

Nishihara et al. (2000) screened a large number of industrial chemicals for estrogenic activity in vitro 

using a two-hybrid expression system: Saccharomyces cerivisiae Y190 containing expression plasmids 

for the estrogen receptor alpha and the coactivator TIF-2. At concentrations as high as 1 mM, potassium 

cyanide did not induce estrogenic expression in this assay (defined as 10% of the agonist activity of 

10-7 M 17-beta-estradiol). No other reports of cyanides modulating estrogen hormonal levels were 

located. 

3.7 CHILDREN’S SUSCEPTIBILITY 

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

maturity at 18 years of age in humans, when all biological systems will have fully developed. Potential 

effects on offspring resulting from exposures of parental germ cells are considered, as well as any indirect 
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effects on the fetus and neonate resulting from maternal exposure during gestation and lactation. 

Relevant animal and in vitro models are also discussed. 

Children are not small adults. They differ from adults in their exposures and may differ in their 

susceptibility to hazardous chemicals. Children’s unique physiology and behavior can influence the 

extent of their exposure. Exposures of children are discussed in Section 6.6, Exposures of Children. 

Children sometimes differ from adults in their susceptibility to hazardous chemicals, but whether there is 

a difference depends on the chemical (Guzelian et al. 1992; NRC 1993). Children may be more or less 

susceptible than adults to health effects, and the relationship may change with developmental age 

(Guzelian et al. 1992; NRC 1993). Vulnerability often depends on developmental stage. There are 

critical periods of structural and functional development during both prenatal and postnatal life, and a 

particular structure or function will be most sensitive to disruption during its critical period(s). Damage 

may not be evident until a later stage of development. There are often differences in pharmacokinetics 

and metabolism between children and adults. For example, absorption may be different in neonates 

because of the immaturity of their gastrointestinal tract and their larger skin surface area in proportion to 

body weight (Morselli et al. 1980; NRC 1993); the gastrointestinal absorption of lead is greatest in infants 

and young children (Ziegler et al. 1978). Distribution of xenobiotics may be different; for example, 

infants have a larger proportion of their bodies as extracellular water, and their brains and livers are 

proportionately larger (Altman and Dittmer 1974; Fomon 1966; Fomon et al. 1982; Owen and Brozek 

1966; Widdowson and Dickerson 1964). The infant also has an immature blood-brain barrier (Adinolfi 

1985; Johanson 1980) and probably an immature blood-testis barrier (Setchell and Waites 1975). Many 

xenobiotic metabolizing enzymes have distinctive developmental patterns. At various stages of growth 

and development, levels of particular enzymes may be higher or lower than those of adults, and 

sometimes unique enzymes may exist at particular developmental stages (Komori et al. 1990; Leeder and 

Kearns 1997; NRC 1993; Vieira et al. 1996). Whether differences in xenobiotic metabolism make the 

child more or less susceptible also depends on whether the relevant enzymes are involved in activation of 

the parent compound to its toxic form or in detoxification. There may also be differences in excretion, 

particularly in newborns who all have a low glomerular filtration rate and have not developed efficient 

tubular secretion and resorption capacities (Altman and Dittmer 1974; NRC 1993; West et al. 1948). 

Children and adults may differ in their capacity to repair damage from chemical insults. Children also 

have a longer remaining lifetime in which to express damage from chemicals; this potential is particularly 

relevant to cancer. 
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Certain characteristics of the developing human may increase exposure or susceptibility, whereas others 

may decrease susceptibility to the same chemical. For example, although infants breathe more air per 

kilogram of body weight than adults breathe, this difference might be somewhat counterbalanced by their 

alveoli being less developed, which results in a disproportionately smaller surface area for alveolar 

absorption (NRC 1993). 

From the few oral studies available, the effects of cyanide on children appear to be like those of similarly 

exposed adults. This is expected based on cyanide's inhibition of mitochondrial respiration in all cells. 

Neurological (headache and coma), respiratory (tachypnea), cardiovascular (hypotension), and 

gastrointestinal effects (vomiting) have been reported in children who have been poisoned by eating 

apricot pits (Lasch and El Shawa 1981). Congenital hypothyroidism has been observed in some children 

who were exposed to increased thiocyanate levels because of the maternal cassava diet during pregnancy 

(Ermans et al. 1980). 

Developmental studies in animals (rats or hamsters) orally exposed to potassium cyanide, cassava diets, 

or one of the cyanogenic glycosides (amygdalin, linamarin) reported fetal toxicity (reduced fetal weight, 

delayed ossification) and developmental anomalies (microcephaly, limb defects, encephalocele, and rib 

abnormalities) in offspring (Frakes et al. 1986a; Singh 1981; Tewe and Maner 1981a; Willhite 1982). 

These effects occurred at exposure levels that were toxic to the dam. A developmental study in pigs 

indicates that this species is less sensitive than rodents to gestational exposure to cyanide (Tewe and 

Maner 1981b). Results of a study in lactating goats indicate that cyanide and thiocyanate can be 

transferred through milk to nursing offspring (Soto-Blanco and Gorniak 2003). 

It is likely that the observed adverse effects on fetal growth and the timing of ossification following 

maternal exposure to cyanide has multiple sources. In addition to a direct action of cyanide on 

mitochondrial respiration in fetal cells, the reduction in oxygen-carrying capacity of the maternal blood 

would also be expected to result in lower metabolic rates in fetuses. Furthermore, hypothyroidism, 

characterized by reductions in thyroid hormone levels, would also adversely affect rates of cell 

metabolism. 

In goats, maternal co-administration of sodium thiocyanate prevented the rise in erythrocyte cyanide 

levels caused by sodium nitroprusside (Curry et al. 1997). Sodium nitroprusside is infused intravenously 

as a vasodilator for the treatment of hypertensive emergencies (Agarwal and Kumari 2003; Curry et al. 

1997; Przybylo et al. 1995; Randall and St. Louis 1996; Sipe et al. 2001). In the blood, sodium 
CYANIDE 103 

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nitroprusside nonenzymatically receives one electron from oxyhemoglobin, forming the nitroprusside 

radical, which dissociates to nitric oxide (the vasodilator) and five cyanide ions (Przybylo et al. 1995). In 

practice, sodium thiocyanate is co-administered to prevent cyanide toxicity. Curry et al. (1997) infused 

sodium nitroprusside into gravid ewes, resulting in elevations of erythrocyte cyanide concentrations that 

caused the death of one ewe and one fetus from cardiac toxicity. Co-administration of sodium 

thiocyanate to gravid ewes prevented the elevation in erythrocyte cyanide levels in ewes and fetuses. 

Curry et al. (1997) conclude that sodium thiocyanate, like cyanide and sodium nitroprusside, cross the 

placenta in goats. The relevance of the goat study to humans is not known. 

3.8 BIOMARKERS OF EXPOSURE AND EFFECT 

Biomarkers are broadly defined as indicators signaling events in biologic systems or samples. They have 

been classified as markers of exposure, markers of effect, and markers of susceptibility (NAS/NRC 

1989). 

Due to a nascent understanding of the use and interpretation of biomarkers, implementation of biomarkers 

as tools of exposure in the general population is very limited. A biomarker of exposure is a xenobiotic 

substance or its metabolite(s) or the product of an interaction between a xenobiotic agent and some target 

molecule(s) or cell(s) that is measured within a compartment of an organism (NAS/NRC 1989). The 

preferred biomarkers of exposure are generally the substance itself, 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 cyanide are discussed in Section 3.8.1. 

Biomarkers of effect are defined as any measurable biochemical, physiologic, or other alteration within an 

organism that, depending on magnitude, can be recognized as an established or potential health 

impairment or disease (NAS/NRC 1989). This definition encompasses biochemical or cellular signals of 

tissue dysfunction (e.g., increased liver enzyme activity or pathologic changes in female genital epithelial 
CYANIDE 104 

3. HEALTH EFFECTS 

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 cyanide are discussed in Section 3.8.2. 

A biomarker of susceptibility is an indicator of an inherent or acquired limitation of an organism's ability 

to respond to the challenge of exposure to a specific xenobiotic substance. It can be an intrinsic genetic or 

other characteristic or a preexisting disease that results in an increase in absorbed dose, a decrease in the 

biologically effective dose, or a target tissue response. If biomarkers of susceptibility exist, they are 

discussed in Section 3.10, Populations That Are Unusually Susceptible. 

3.8.1 Biomarkers Used to Identify or Quantify Exposure to Cyanide 

Methods are available to measure levels of cyanide and its metabolite, thiocyanate, in blood and urine. 

High blood cyanide levels of 250–300 μg/100 mL were reported in cases of death from cyanide poisoning 

(Vogel et al. 1981). The relationship between increased exposure and increased urine levels of 

thiocyanate was demonstrated in workers exposed occupationally to 6.4–10.3 ppm cyanide in air (El 

Ghawabi et al. 1975). In another study, blood cyanide concentrations varied from 0.54 to 

28.36 μg/100 mL in workers exposed to ≈0.2–0.8 ppm cyanide in air and from 0.0 to 14.0 μg/100 mL in 

control workers (Chandra et al. 1988). Correspondingly, blood thiocyanate concentrations were 0.05– 

2.80 mg/100 mL in exposed workers and 0.02–0.88 mg/100 mL in control workers, respectively. Data 

obtained from the controls indicate that cyanide can be detected in populations exposed to low cyanide 

levels in the environment. Cyanide-containing food, metabolism of certain drugs, and combustion of 

nitrogenous polymers are among several sources of cyanide exposure. Furthermore, industrially polluted 

air, soil, and water may contribute to higher environmental cyanide levels. 

Several studies showed increased cyanide and thiocyanate levels in body fluids of smokers. The 

difference between smokers and nonsmokers can be quite distinct (Maliszewski and Bass 1955). Mean 

thiocyanate levels in smokers and nonsmokers, respectively, were found to be 7.1 and 2.0 μg/mL in 

plasma, 75.7 and 20.3 μg/mL in saliva, and 12.3 and 2.1 μg/mL in urine. A more recent study also 

reported on mean thiocyanate levels in smokers and nonsmokers, respectively (Jarvis 1989). Levels 

reported were 7.1 and 2.9 μg/mL in plasma, 142 and 76 μg/mL in saliva, and 9.0 and 5.8 μg/mL in urine. 

Another study found a correlation between the number of cigarettes smoked per day and the thiocyanate 

levels in plasma and in saliva (Yamanaka et al. 1991). Based on changes in salivary thiocyanate in six 
CYANIDE 105 

3. HEALTH EFFECTS 

smokers who stopped smoking, this study estimated the half-life of salivary thiocyanate to be 9.5 days. In 

addition, infants living in homes with family members who smoked heavily were found to have 

significantly higher serum thiocyanate levels than those infants who were not exposed to cigarette smoke 

in the home (Chen et al. 1990). It is unclear whether passive smoking (exposure of a nonsmoker to air 

contaminated with tobacco smoke) is a factor in elevated fetal serum thiocyanate levels. In one study, 

fetal thiocyanate levels were increased in association with passive smoking in the home (Bottoms et al. 

1982), while another study did not report an association (Hauth et al. 1984). 

Whether it is more appropriate to use whole blood or plasma for measuring cyanide concentrations has 

been the subject of several reports. Cyanide plasma levels are usually about one-third to one-half, 

depending on the species, those found in whole blood (Ballantyne 1983a). However, they can more 

closely reflect the actual tissue dose. Furthermore, cyanide was found to attach more readily to plasma 

albumin than to hemoglobin (McMillan and Svoboda 1982). It was suggested that hemoglobin in 

erythrocytes binds cyanide molecules, but does not play any role in their metabolism. Some authors 

argue that cyanide in red blood cells may be biologically active (Way 1984). In addition, it is known that 

cyanide rapidly leaves serum and plasma, especially in the first 20 minutes. It may be appropriate to 

measure cyanide in both whole blood and plasma. Whole blood samples can be stored at 4 °C for several 

weeks with little change in cyanide content. 

In cyanide-poisoning cases, any blood levels of cyanide >0.02 mg/100 mL indicate a toxic situation 

(Berlin 1977). However, because cyanide binds tightly to cytochrome c oxidase, serious effects can also 

occur at lower levels; therefore, the clinical condition of the patient should be considered when 

determining proper therapy. Linden and Lovejoy (1998) presented a rough estimate of blood cyanide 

levels at which symptoms appear: flushing and tachycardia at 0.05–0.1 mg/100 mL, obtundation (dulled 

sensibility) at 0.1–0.25 mg/100 mL, coma and respiratory depression at 0.25–0.3 mg/100 mL, and death 

at >0.3 mg/100 mL. 

An almond-like smell in the breath of a poisoned patient can warn a physician that the individual may be 

suffering from cyanide poisoning. Approximately 60–70% of the population can detect the bitter almond 

odor of hydrogen cyanide. The odor threshold for those sensitive to the odor is estimated to be 1–5 ppm 

in the air. However, even at high toxic concentrations, up to 20% of all individuals are genetically unable 

to smell hydrogen cyanide (Snodgrass 1996). Some effects of cyanide that can also be used to monitor 

exposure are discussed in Section 3.8.2. 
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3. HEALTH EFFECTS 

3.8.2 Biomarkers Used to Characterize Effects Caused by Cyanide 

Cyanide can inhibit enzymatic activity by binding to some metallic moieties in metalloenzymes (Ardelt et 

al. 1989; Way 1984) and cytochrome c oxidase is especially sensitive to cyanide inhibition. Dose-related 

reductions in cytochrome c oxidase activity were detected in various organs of rats exposed to oral doses 

of potassium cyanide (Ikegaya et al. 2001); this marker was suggested as a method of diagnosis for 

samples taken within 2 days post-mortem. Consequent to the inhibition of cytochrome c oxidase, 

theoretically, oxygen cannot be used and histotoxic anoxia occurs. Elevated plasma lactate 

concentrations, resulting from the shift to anaerobic metabolism, have been used to assess the severity of 

cyanide poisoning in humans (Baud et al. 1996, 2002). Death is caused by respiratory failure. Dyspnea, 

palpitations, hypotension, convulsions, and vomiting are among the first effects of acute cyanide 

poisoning (see Section 3.2). Ingestion of amounts ≥50–100 mg sodium or potassium cyanide may be 

followed by almost instantaneous collapse and cessation of respiration (Hartung 1982). Data summarized 

by Hartung (1982) indicate that exposure to a concentration in air of 270 ppm causes immediate death; 

concentrations of 181 and 135 ppm are fatal after 10 and 20 minutes of exposure, respectively; 

concentrations between 45 and 55 ppm can be tolerated for 30–60 minutes with immediate or late effects; 

and 18–36 ppm may produce slight symptoms after several hours of exposure. Following chronic 

exposure, cyanide has been associated with the development of tropical neuropathy, tobacco amblyopia, 

and Leber's hereditary optic atrophy (Wilson 1965). Chronic exposure to cyanide arising from 

consumption of cyanogenic plant foods has also been connected with the occurrence of endemic goiter 

(Delange and Ermans 1971). 

Neuropathological sequelae of acute cyanide poisoning have been detected in the brain by magnetic 

resonance imaging (MRI) and positron emission tomography (PET). MRI techniques identified brain 

lesions that developed in the weeks following a poisoning event, typically in the globus pallidus, 

putamen, substantia nigra, and cerebellum (Rosenberg et al. 1989; Rosenow et al. 1995). PET has been 

used to localize deficiencies in dopa uptake in the striatum and reduced glucose metabolism in the 

cerebral cortex and other brain regions affected by cyanide (Rosenow et al. 1995). These imaging 

methods cannot determine that cyanide was the cause of the lesions, but provide a means of monitoring 

changes in the extent of brain lesions following cyanide exposure. 

In the development of antidotes to cyanide, the following neurochemical biomarkers of cyanide toxicity 

have been considered (Isom and Borowitz 1995): inhibition of cytochrome c oxidase, activation of 

voltage sensitive calcium channels, activation of receptor operated calcium channels, elevation of 
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cytosolic free Ca2+, activation of intracellular calcium cascades, inhibition of antioxidant enzymes 

(superoxide dismutase, catalase, and glutathione peroxidase), peroxidation of membrane lipids, and 

generation of reactive oxygen species. 

Genetic markers for cyanide-induced hypoxia have been identified in several human cell lines (human 

intestinal epithelial T84 cells and Jurkat T cells) exposed to sodium cyanide in vitro (Kiang et al. 2003). 

Cyanide treatment upregulated the expression of inducible nitric oxide synthase (iNOs) and heat shock 

protein-70 (HSP-70) in both cell types, p53 in T84 cells and the protooncogene Bcl-2 in Jurkat T cells. 

Cellular caspase-3 activity, indicative of apoptosis, was also significantly increased in both cell types. An 

inhibitor to iNOs (Nomega

-nitro-L-arginine or LNNA) abolished the cyanide-induced increase in iNOs, 

HSP-70, and Bcl-2 and the increase in caspase-3 activity. These studies indicate genetic responses to 

cyanide exposure in vitro and could provide a strategy for comparing tissue-specific responses to cyanide 

and developing therapeutic interventions following cyanide exposure in vivo. 

For more information on biomarkers for renal and hepatic effects of chemicals see ATSDR/CDC 

Subcommittee Report on Biological Indicators of Organ Damage (1990) and for information on 

biomarkers for neurological effects see OTA (1990). 

3.9 INTERACTIONS WITH OTHER CHEMICALS 

Interactions in the context of this profile refer to modifications in toxic responses when an organism is 

exposed to another compound in addition to cyanide. A number of compounds act in synergy with 

cyanide to produce toxic effects. In smoke, both hydrogen cyanide and carbon monoxide would 

potentially increase central nervous system effects in exposed individuals (Birky and Clarke 1981). High 

blood cyanide levels were found in fire victims; however, the carboxyhemoglobin levels were also high. 

Thus, it is difficult to assess the relative significance of hydrogen cyanide in the toxicity from smoke 

inhalation. 

In an investigation to examine toxicological interactions of the primary fire gases, the additive, 

synergistic, or antagonistic effects of combinations of hydrogen cyanide with carbon monoxide or with 

carbon dioxide on the 30-minute LC50 value for hydrogen cyanide alone were determined in rats (Levin et 

al. 1987). Co-exposure of rats to hydrogen cyanide (LC50=110 ppm) and carbon monoxide 

(LC50=4,600 ppm) resulted in lethal effects of these two gases that were additive. In contrast, coexposure to hydrogen cyanide and 5% carbon dioxide (not lethal by itself) resulted in an increase in 
CYANIDE 108 

3. HEALTH EFFECTS 

lethality of hydrogen cyanide, reflected as a decrease of the hydrogen cyanide LC50 value to 75 ppm. 

Dodds et al. (1992) also investigated the effect of simultaneous exposure to cyanide and carbon monoxide 

in rats, and found an additive effect on certain parameters, including lactate elevation and neurologic 

index. Norris et al. (1986) reported a synergistic effect on lethality in mice that were injected with 

potassium cyanide and exposed to carbon monoxide atmospheres. 

Synergism has also been observed between cyanide and ascorbic acid. Guinea pigs exhibited increased 

toxic effects when treated with ascorbic acid prior to oral administration of potassium cyanide (Basu 

1983). When guinea pigs were treated solely with 3.2 mg CN–

/kg as potassium cyanide, 38% exhibited 

slight tremors, whereas 100% of those pre-treated on 3 consecutive days with 1.3 g/kg ascorbic acid 

before potassium cyanide was administered exhibited severe tremors, ataxia, muscle twitches, paralysis, 

and convulsions. It has been suggested that this synergistic effect results from the ability of ascorbic acid 

to compete with cyanide for cysteine, thus diminishing the detoxication of cyanide. 

Antidotes for cyanide poisoning have been intensively studied and reviewed (Way 1984). Cyanide 

antagonists can be classified into two general groups: those that act as sulfane sulfur donors for 

rhodanese-catalyzed cyanide detoxification and those that induce chemical binding of cyanide. Sulfur 

donors include sodium thiosulfate, polythionates, and thiosulfates. Sodium thiosulfate has been 

successfully used as an antidote against cyanide poisoning in humans for decades (Way 1984). A 

pharmacokinetic study in dogs demonstrated that intravenous administration of thiosulfate increased the 

detoxification rate of intravenously given cyanide to thiocyanate over 30 times (Sylvester et al. 1983). In 

this study, pretreatment with thiosulfate decreased the biological half-life of cyanide from ≈39 to 

≈15 minutes and also decreased the volume of distribution of cyanide from 498 to 204 mL/kg. 

Thiosulfate pretreatment had prophylactic effects in guinea pigs exposed to cyanide by intravenous 

infusion (Mengel et al. 1989). The protection lasted for several hours depending on the dose of 

thiosulfate administered. 

Antagonists that induce the chemical binding of cyanide to sites other than cytochrome c oxidase include 

sodium nitrite, amyl nitrite, and hydroxylamine. These compounds generate methemoglobin, which 

competes with cytochrome c oxidase for cyanide to form cyanmethemoglobin (Way 1984). Sodium 

nitrite has been effectively used in the therapy of cyanide intoxication in humans especially in 

combination with sodium thiosulfate (Smith 1996; Way 1984). Studies in mice demonstrated that 

intraperitoneal pretreatment with sodium nitrite more than doubled the LD50 value of intraperitoneally 

administered sodium cyanide from 3.18 to 7.95 mg CN–

/kg (Kruszyna et al. 1982). Peak 
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3. HEALTH EFFECTS 

methemoglobinemia was 35% at 40 minutes. Other methemoglobin generating agents seemed to be less 

effective. 4-Dimethylaminopropiophenol enhanced the LD50 value to 6.36 mg CN–

/kg and 

hydroxylamine to 4.66 mg CN–

/kg with peak methemoglobinemia being 40 and 36%, respectively, at 

7 minutes. The data suggested that sodium nitrite, a slow methemoglobin former, gave prolonged 

protection against cyanide, while animals treated with fast methemoglobin formers died later on, probably 

due to the cyanide release from the cyanmethemoglobin pool. An improvement of cyanide-altered 

cerebral blood flow was observed in dogs treated with sodium nitrite or 4-dimethylaminophenol 

following intravenous injection of hydrogen cyanide (Klimmek et al. 1983). However, neither treatment 

prevented the progression of lactic acidosis. 

Cobalt-containing compounds may also function as binders by forming a stable complex with cyanide. A 

dramatic antagonism of the lethal effects of potassium cyanide was reported when cobaltous chloride was 

administered to mice along with sodium thiosulfate (Isom and Way 1973). The authors suggested that 

this synergistic antidotal effect of cobaltous chloride may be associated with the physiological disposition 

of the cobaltous ion and its ability to chelate both thiocyanate and cyanide ions. This ability is also 

utilized when dicobalt ethylenediamine tetra-acetate acid (Co2EDTA) is used as a cyanide antidote. An 

improvement of cerebral aerobic metabolism and blood flow was observed in dogs treated with 10 mg/kg 

Co2EDTA intravenously following intravenous application of 1.6 mg CN–

/kg as potassium cyanide 

(Klimmek et al. 1983). A lower molecular weight porphyrin cobalt compound than hydroxocobalamin 

(CoTPPS) was used as an antidote to the lethal effects of cyanide (McGuinn et al. 1994). The interaction 

with hydroxocobalamin (see Section 3.4.3) was also proposed as a mechanism for cyanide detoxification 

in cases of acute poisoning. It was demonstrated that intravenous administration of hydroxocobalamin 

(50–250 mg/kg) prior to or after intraperitoneal injection of potassium cyanide prevented lethality and 

decreased cyanide-induced toxic effects in mice (Mushett et al. 1952). 

Pretreatment of rats with chlorpromazine (10 mg/kg intramuscularly) and sodium thiosulfate 

(1,000 mg/kg intraperitoneally) greatly decreased or abolished the increase in plasma creatine kinase 

observed in rats exposed to hydrogen cyanide at 200 ppm for 12.5 minutes (O'Flaherty and Thomas 

1982). In an in vitro study, chlorpromazine and 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid reduced 

cyanide-induced contractions in vascular smooth muscle (Robinson et al. 1985a). It was suggested that 

chlorpromazine prevents cyanide-induced calcium influx and reduces peroxidation of membrane lipids 

(Maduh et al. 1988). 
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3. HEALTH EFFECTS 

The ability of cyanide to combine with carbonyl groups of some intermediary metabolites (e.g., sodium 

pyruvate, α-ketoglutarate) to form cyanohydrin has been used for antidotal purposes. Pretreatment of 

mice with 1 g/kg sodium pyruvate intraperitoneally prior to subcutaneous injection of potassium cyanide 

caused a statistically significant increase in the LD50 values from 3.1 to 5 mg CN–

/kg (Schwartz et al. 

1979). Sodium pyruvate also prevented the development of convulsions in cyanide-exposed mice. 

Similarly, intraperitoneal pretreatment of mice with 2 g/kg α-ketoglutarate before the intraperitoneal 

injection of potassium cyanide increased the LD50 value from 2.68 to 13.32 mg CN–

/kg (Moore et al. 

1986). It was further demonstrated that both sodium pyruvate and α-ketoglutarate enhanced the antidotal 

effects of other cyanide antagonists (e.g., sodium thiosulfate, sodium nitrite) (Moore et al. 1986; Schwartz 

et al. 1979). 

A striking protection against cyanide can be elicited by a new conceptual approach, employing carrier 

erythrocytes containing highly purified rhodanese (thiosulfate sulfur transferase). Several studies have 

shown that resealed erythrocytes containing rhodanese and sodium thiosulfate rapidly metabolize cyanide 

to the less toxic thiocyanate (Cannon et al. 1994; Petrikovic et al. 1995). Maduh and Baskin (1994) 

showed that rhodanese may be regulated by protein phosphorylation and treatments that alter the 

phosphorylation state of rhodanese may affect cyanide detoxification via formation of thiocyanate. 

Several papers discuss the effects of oxygen alone or with other compounds on cyanide toxicity. Oxygen 

alone results in minimal antagonism in mice injected with potassium cyanide and only slightly enhances 

the antagonistic effects of sodium nitrite on cyanide (Sheehy and Way 1968). The antidotal effect of 

sodium thiosulfate alone or in combination with sodium nitrite, was enhanced by oxygen. Oxygentreated mice did not show behavioral signs of cyanide intoxication below doses of 2.4 mg CN–

/kg as 

potassium cyanide, whereas air-treated animals showed effects such as gasping, irregular breathing, and 

convulsions at levels as low as 1.2 mg CN–

/kg as potassium cyanide (Isom et al. 1982). When mice were 

pretreated with sodium nitrite and sodium thiosulfate and either air or oxygen, the dose of potassium 

cyanide needed to cause a 59% inhibition of brain cytochrome c oxidase more than doubled in mice in an 

oxygen atmosphere; all points on the oxygen curve differed significantly from the air-treatment curve. 

A striking enhancement of the oxidation of glucose to carbon dioxide was observed when oxygen, sodium 

nitrite, and sodium thiosulfate were given to mice dosed at 18 mg CN–

/kg as potassium cyanide; no 

enhancement was noticed at 4 or 6 mg CN–

/kg as potassium cyanide (Isom and Way 1974). These studies 

indicate that oxygen can be used in supporting classical cyanide antagonists in the therapy of cyanide 

poisoning, but even hyperbaric oxygen alone had no effect on cyanide poisoning in mice (Way et al. 
CYANIDE 111 

3. HEALTH EFFECTS 

1972). The mechanism of the action is not known, since cyanide inhibits the cellular utilization of 

oxygen through inhibiting cytochrome c oxidase and, theoretically, the administration of oxygen should 

have no effect or useful purpose (Smith 1996). 

Propargylglycine, which is an inhibitor of the enzyme cystathionine gamma-lyase, significantly lowered 

the LD50 for sodium cyanide intraperitoneally injected into rats (Porter et al. 1996). The authors 

suggested that the enzyme contributes to cyanide detoxification, possibly through the pathway that 

provides sulfur donors for the enzyme rhodanese. 

3.10 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE 

A susceptible population will exhibit a different or enhanced response to cyanide than will most persons 

exposed to the same level of cyanide 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 cyanide, or compromised function of organs 

affected by cyanide. Populations who are at greater risk due to their unusually high exposure to cyanide 

are discussed in Section 6.7, Populations with Potentially High Exposures. 

Persons with a metabolic disturbance in the conversion of cyanide to thiocyanate may be at greater risk. 

A defect in the rhodanese system and vitamin B12 deficiency have been associated with tobacco 

amblyopia and Leber's hereditary optic atrophy in persons exposed to cyanide in tobacco smoke (Wilson 

1983). Individuals with preterminal chronic renal failure have elevated serum thiocyanate levels because 

of impaired clearance of thiocyanate, increasing their vulnerability to cyanide exposure (Koyama et al. 

1997). 

A number of dietary deficiencies may increase the risk of deleterious cyanide effects. Iodine deficiency is 

involved in the etiology of such thyroid disorders as goiter and cretinism. These disorders may be 

exacerbated by excess exposure to cyanide (Delange and Ermans 1971; Ermans et al. 1972). Protein 

deficiencies and vitamin B12, riboflavin, and other vitamin and elemental deficiencies may subject people 

in the tropics who eat cassava to increased risks of tropical neuropathies (Makene and Wilson 1972; 

Osuntokun 1972; Osuntokun et al. 1969). However, a recent study reported that scopoletin, a potent 

hypotensive and spasmolytic agent found in cassava roots, may be the etiological agent in the tropical 

neuropathies observed among cassava eaters, rather than cyanide (Obidoa and Obasi 1991). Furthermore, 

children and women seem to be more susceptible to the endemic spastic paraparesis in the cassava-
CYANIDE 112 

3. HEALTH EFFECTS 

consumption regions (Rosling 1988). Studies that have uncovered more severe effects from cyanides in 

nutritionally deprived animals provide support to the observations in humans (Kreutler et al. 1978; 

Rutkowski et al. 1985). 

In areas where cassava is a staple food, congenital hypothyroidism is present in 15% of newborns 

(Ermans et al. 1980), indicating that fetuses may be at a higher risk. Animal studies provide further 

evidence that fetuses may be at a higher risk than the general population. Developmental toxicity has 

been observed in rodents following inhalation, oral, and parenteral exposure to cyanide-containing 

compounds (Doherty et al. 1982, 1983; Frakes et al. 1985, 1986a; Singh 1981; Willhite 1982). 

One group of people who may be at greater risk are those who are exposed to cyanide but are unable to 

smell the chemical (Kirk and Stenhouse 1953; Snodgrass 1996). Patients with motor neuron disease 

(amyotrophic lateral sclerosis) possess a disorder in cyanide detoxification that may result in their higher 

susceptibility to cyanide (Kato et al. 1985). 

3.11 METHODS FOR REDUCING TOXIC EFFECTS 

This section will describe clinical practice and research concerning methods for reducing toxic effects of 

exposure to cyanide. 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 cyanide. 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 

cyanide: 

Ellenhorn MJ, Barceloux DG. 1997. Medical toxicology, diagnosis and treatment of human poisoning. 

New York, NY: Elsevier Publishing. 

Goldfrank LR, Flomenbaum NE, Lewin NA, et al., eds. 1998. Goldfranks toxicologic emergencies. 6th 

edition. Stamford, CT: Appleton and Lange, 1569-1585. 

Gosselin RE, Smith RP, Hodge HC. 1984. Clinical toxicology of commercial products. 5th edition. III123-130. Baltimore, MD: Williams and Wilkins. 

IPCS/CEC. 1993. Evaluation of antidotes series. Vol. 2. Antidotes for poisoning by cyanide. 

International Program on Chemical Safety/Commission of the European Communities 

http://www.inchem.org/documents/antidote/antidote/ant02.htm. June 16, 2004. 
CYANIDE 113 

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3.11.1 Reducing Peak Absorption Following Exposure 

Human exposure to cyanide may occur by inhalation, ingestion, or by dermal contact, but the general 

population is more likely to be exposed by inhaling air or ingesting food or water contaminated with 

cyanide. General recommendations for reducing absorption of cyanide from inhalation and dermal 

exposure include removing the exposed individual from the contaminated area and removing the 

contaminated clothing (Ellenhorn and Barceloux 1997; Goldfrank et al. 1990; Stutz and Janusz 1988). If 

the eyes and skin are exposed, they should be flushed with water. However, in order not to become 

secondary victims, rescuers may enter potentially contaminated areas only with self-contained breathing 

apparatus and protective clothing. Speed is essential during a rescue operation. 

In order to reduce absorption of ingested cyanide, gastric lavage with activated charcoal may be 

performed immediately after ingestion. Individuals exposed by any route are commonly administered 

100% oxygen and assisted ventilation, including endotracheal intubation, as needed. Hyperbaric oxygen 

has been advocated when patients do no respond to standard therapy (Litovitz et al. 1983); however, 

studies in laboratory animals suggest that hyperbaric oxygen is no more effective than normobaric oxygen 

(Way 1984). An antidotal combination of inhaled amyl nitrate and intravenous sodium nitrite and sodium 

thiosulfate are often indicated. The IPCS/CEC (1993) review of antidotes for cyanide poisoning noted 

that individuals deficient in glucose-6-phosphate-dehyrogenase are at risk of severe hemolysis from 

sodium nitrite therapy because of the resulting high plasma methemoglobin concentrations. Monitoring 

for metabolic acidosis, cardiac dysrhythmias, and possible pulmonary edema is suggested. 

3.11.2 Reducing Body Burden 

The primary target for cyanide toxicity is the central nervous system following both acute and chronic 

exposure. Exposure to high doses of cyanide can rapidly lead to death (see Section 3.2). Cyanide is not 

stored in the organism and one study indicates that, under the stated parameters, >50% of the received 

dose can be eliminated within 24 hours (Okoh 1983). However, because of the rapid toxic action of 

cyanide, therapies that enhance metabolism and elimination of cyanide are warranted immediately. 

Cyanide is metabolized in the body by two metabolic pathways that have been identified (Ansell and 

Lewis 1970). The first and major metabolic pathway involves the transfer of sulfane sulfurs from a donor 

to cyanide to yield thiocyanate (see Section 3.4). The reaction employs the enzyme rhodanese as a 

catalyst. Thiocyanate is a fairly stable compound and is excreted predominately in urine. Serum proteins 
CYANIDE 114 

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(especially albumin) are a major internal pool of sulfane sulfurs. Their protective role against cyanide 

toxicity was confirmed in tests with laboratory animals (Rutkowski et al. 1985; Tewe and Maner 1980, 

1982). Cyanide antagonists help convert cyanide to thiocyanate. Sodium thiosulfate is commonly used in 

cases of cyanide poisoning (Bonsall 1984; Mengel et al. 1989; Schubert and Brill 1968; Sylvester et al. 

1983). Sodium thiocyanate is also used to prevent toxicity resulting from the cyanide released from 

sodium nitroprusside during infusion therapy for hypertensive emergencies (see Section 3.7) (Agarwal 

and Kumari 2003; Curry et al. 1997; Przybylo et al. 1995; Randall and St. Louis 1996; Sipe et al. 2001). 

This usage has been shown to be effective in preventing cyanide toxicity in the fetuses of gravid ewes 

infused with sodium nitroprusside (Curry et al. 1997). An increase in antidotal effect was noted when 

rhodanese was combined with thiosulfate (Frankenberg 1980). Similarly, other sulfane sulfur donors and 

disulfides such as 2-aminoethyl-4-methoxyphenyl disulfide hydrochloride have protective effects against 

cyanide toxicity (Baskin et al. 1999; Petrikovics et al. 1995; Ternay et al. 2000). 

The second and minor metabolic pathway consists of the reaction of cyanide with cystine to yield cysteine 

and β-thiocyanoalanine (Wood and Cooley 1955). The latter is then converted to 2-imino-4-thiazolidinecarboxylic acid and excreted in urine. Cystine has not been used for the purpose of mitigation of cyanide 

effects because its contribution to detoxification via this pathway is minor. 

3.11.3 Interfering with the Mechanism of Action for Toxic Effects 

The mechanism of acute cyanide toxicity is well understood (see Section 3.5). Cyanide inhibits the 

activity of some enzymes by binding to their metallic moiety. By blocking the action of cytochrome c 

oxidase, histotoxic hypoxia/anoxia develops rapidly in exposed organisms (Smith 1996). The ability of 

cyanide to bind to some metallic ions is utilized with antidotes that induce methemoglobinemia in 

exposed organisms. Cyanide binds to the ferric ion of methemoglobin to form inactive cyanmethemoglobin (see Section 3.9). Antidotes utilized for this purpose either clinically or experimentally include 

amyl nitrite, sodium nitrite, hydroxylamine, p-aminopropiophenone, p-aminoheptanophenone, 8-[(4-

amino-1-methylbutyl)amino]-5-1-hexyloxy)-6-methoxy-4-methylquinoline-DL-tartrate (WR242511), 

4-dimethylaminophenol, and primaquine (Bhattacharya 1995; Bhattacharya et al. 1991, 1993; Bright and 

Marrs 1987; Hall et al. 1987; Kampe et al. 2000; Kruszyna et al. 1982; Menton et al. 1996, 1997; Scharf 

et al. 1992; Schubert and Brill 1968; USAMRICD 1994; Vick and Von Bredow 1996). The disadvantage 

of these antidotes is that the methemoglobinemia further aggravates the depletion of oxygen from tissues; 

therefore, antidote-induced methemoglobin levels need to be closely followed in clinical practice. 

Prophylactic administration of stroma-free methemoglobin preserved cardiovascular and metabolic 
CYANIDE 115 

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function in dogs exposed to cyanide intravenously (Breen et al. 1996); the additional methemoglobin 

traps cyanide in the blood, thereby protecting tissues. Experimentally, the antagonistic effect of sodium 

nitrite is improved by co-administration with atropine, an effect attributed to the suppression of 

bradycardia (Vick and Von Bredow 1996; Yamamoto 1995). A complex of diethylamine/nitric oxide 

reduced the toxicity of cyanide in mice (Baskin et al. 1996); the beneficial effect was attributed to 

methemoglobin-forming activity at higher doses and the vasodilation activity of nitric oxide. 

Cyanide's binding to metallic ions is also employed in a reaction with cobalt-containing compounds that 

yields cyanocobalamin (see Section 3.9). Cobalt compounds generally are not used because of their 

toxicity; however, Co2EDTA (Klimmek et al. 1983) and hydroxocobalamin (Benabid et al. 1987; 

Mannaioni et al. 2002; Mengel et al. 1989; Mushett et al. 1952) have been used as antidotes both in 

clinical and laboratory trials. Cardiac toxicity from Co2EDTA use under clinical conditions has raised 

caution in its clinical use, as the cardiac toxicity of cobalt is well known (Way 1984). Both of these 

antidotes have the advantage of not inducing methemoglobinemia. One study (McGuinn et al. 1994) used 

a lower molecular weight cobalt porphyrin compound (CoTPPS) as an antidote to the lethal effects of 

cyanide. This compound was found to have a high affinity for cyanide due to its low molecular weight, 

and it allows administration in 3-fold molar excess of binding sites over a lethal dose of cyanide. 

Similarly, cyanide forms stable complexes with selenite (Palmer and Olson 1979). 

In an effort to find additional antidotes that would not produce methemoglobinemia, compounds such as 

sodium pyruvate, dihydroxyacetone, α-ketoglutarate (Niknahad and O'Brien 1996), oxaloacetate, 

pyridoxal 5'-phosphate, chlorpromazine, and naloxone (Way 1984) have been introduced (see 

Section 3.9). Interactions of cyanide with carbonyl groups of these compounds lead to formation of inert 

cyanohydrin intermediates (Bhattacharya and Vijayaraghavan 2002; Hume et al. 1995; Keniston et al. 

1987; Moore et al. 1986; Schwartz et al. 1979; Yamamoto 1989). Niknahad et al. (1994) demonstrated 

that dihydroxyacetone and glyceraldehyde are much more effective than pyruvate and α-ketoglutarate as 

cyanide antagonists. Dihydroxyacetone and sodium thiosulfate together had synergistic effects against 

potassium cyanide (Niknahad and Ghelichkani 2002); a combination of pretreatment with 

dihydroxyacetone and post-treatment with sodium thiosulfate increased the LD50 of potassium cyanide 

(subcutaneous) in mice by nearly 10-fold. In rabbits injected (subcutaneous) with high doses of 

potassium cyanide, the beneficial effect of dihydroxyacetone and sodium thiosulfate diminished after 

1 hour, which the authors attributed to metabolism of dihydroxyacetone with concomitant release of 

bound cyanide; additional treatment with dihydroxyacetone was needed to prevent the death of the 

animals. Several studies have shown that α-ketoglutaric acid has a synergistic antidotal effect against 
CYANIDE 116 

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hydrogen cyanide, sodium cyanide, or potassium cyanide when administered with sodium nitrite and/or 

sodium thiosulfate. These studies did not address the problem of lactic acidosis that follows cyanide 

exposure. 

Pharmacological approaches to finding antidotes for cyanide are also under investigation. Maduh et al. 

(1995) examined the effects of a protein kinase C inhibitor, 1-5-(isoquinolinesulfonyl)-2 methylpiperazine 

(H-7), on cellular energy depletion caused by sodium cyanide. They reported that H-7 partially prevented 

cellular energy depletion and increased the number of surviving cells. 

Neurological damage following exposure to cyanide has been associated with an influx of calcium ions 

and the subsequent release of biogenic amines. Accordingly, calcium channel blockers have been tested 

for their efficacy in preventing typical cyanide-induced changes. Diltiazem pretreatment, but not cotreatment prevented a cyanide-induced decrease in dopamine (and increase in L-dopa) in the corpus 

striatum of rats (Mathangi and Namasivayam 2004b). The calcium channel blockers procaine (also an 

anesthetic) and verapamil antagonized the toxicity of potassium cyanide in mice (Jiang et al. 1998). Both 

compounds extended the time to death of a lethal dose of potassium cyanide and prevented the cyanideinduced rise in total brain calcium. Procaine increased the LD50 for potassium cyanide and its protective 

effect was synergistic in mice treated with sodium nitrite and/or sodium thiosulfate. The antioxidants, 

Trolox® (6-hydroxy-2,5,7,8-tetramethylchroman 2-carboxylic acid) and EGTA, and the Ca2+/Mg2+-

dependent endonuclease inhibitor, aurintricarboxylic acid, all increased the LD50 for potassium cyanide 

subcutaneously injected into mice (Bhattacharya and Lakshamana Rao 2001). However, mean survival 

time was not significantly increased compared to mice receiving a lethal dose (LD50x8). 

Several antioxidants have been shown to reduce some effects of cyanide toxicity. Dietary 

supplementation with antioxidant vitamins A, C, and E partially antagonized cyanide-induced reductions 

in superoxide dismutase in the liver, kidney, and lung and catalase in the kidney and lung of rabbits 

(Okolie and Iroanya 2003). Cyanide-induced histopathology was ameliorated by vitamin treatment; 

vitamin supplementation eliminated hepatic congestion in the liver (but not necrosis or fatty 

degeneration), eliminated glomerular, but not tubular necrosis in the kidney, and eliminated alveolar 

congestion and pulmonary edema in cyanide-treated rabbits. These results, along with the study by Basu 

(1983, see Section 3.9) that employed "megadoses" of vitamin C, suggest that the effect of vitamins on 

cyanide toxicity may be sensitive to dose and may be tissue-specific. Vitamin C reduced peroxide 

accumulation and cell death in rat pheochromocytoma cells (PC12 cells) exposed to potassium cyanide 

(Kanthasamy et al. 1997). Ibuprofen (Lambat et al. 2000) and aspirin (Daya et al. 2000) reduced the 
CYANIDE 117 

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production of superoxide radicals in rat brain homogenates treated with potassium cyanide. Melatonin 

and 6-hydroxymelatonin protect against cyanide-induced neurotoxicity (seizures, neuronal cell death) by 

suppressing the formation of superoxide anion radicals and lipid peroxidation (Choi and Han 2002; 

Maharaj et al. 2003; Yamamoto and Tang 1996a, 1996b, 1996c, 1998). 

Some antidotes have been tested in cultured hepatocytes. Glycine reduces cyanide-induced mortality of 

hepatocytes in vitro by countering the influx of sodium ions that occurs from metabolic acidosis as ATP 

is depleted by mitochondrial poisoning (Carini et al. 1997); sodium overload can lead to irreversible cell 

injury from osmotic swelling. L- and D-cysteine reduce the toxicity of cyanide to hepatocytes by 

increasing the pool of thiosulfate available for thiocyanate formation (Huang et al. 1998). 

Dexamethasone retarded hepatocyte toxicity by reducing the hydrolysis of membrane phospholipids 

induced by cyanide (Pastorino et al. 1995). 

Sun et al. (1995) reported that the nitric oxide generator, isosorbide dinitrate, is an effective cyanide 

antidote in mice. They showed that the mechanism does not involve methemoglobin formation and 

suggested that nitric oxide might antagonize the respiratory depressant effects of cyanide. Other more 

efficient nitric oxide generators may be very useful cyanide antidotes. 

Myers et al. (1995) investigated the effect of transfection with the protooncogene Bcl-2 on survival of 

GT1-7 hypothalamic tumor cells exposed to potassium cyanide under aglycemic conditions in vitro. 

Transfectants were protected against delayed (24–72-hour) cell death, ATP depletion, lipid oxidation, and 

impaired mitochondrial respiration. The authors suggest that Bcl-2 may operate by an antioxidant 

mechanism. 

Fructose, but not glucose, protected primary cultures of rat hepatocytes against time-dependent toxicity of 

2.5 mM sodium cyanide for up to 4 hours (Thompson et al. 2003). The difference in efficacy between the 

two glycolytic substrates was attributed to fact that fructokinase has a low Km for the phosphorylation of 

fructose compared to the relatively high Km for hepatic glucokinase. Therefore, fructose, but not glucose, 

provides an alternate source of ATP during cyanide exposure in vitro. 

In addition, other chemicals such as α-adrenergic blocking agents like chlorpromazine (O'Flaherty and 

Thomas 1982; Way and Burrows 1976) or oxygen (Burrows et al. 1973; Sheehy and Way 1968; Way et 

al. 1966) may be used to enhance the protective action of other antidotes. However, the mechanism of 
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their action is not well understood. Further research for a potent and safe antidote to mitigate cyanide 

toxicity is desirable, particularly among smoke inhalation victims who have carbon monoxide poisoning. 

In summary, the efficacy and safety of experimental treatments discussed in this section have not been 

compared systematically and therefore, do not replace the current therapeutic practice. It must be stressed 

that the therapeutic value of the antidotes mentioned above is heavily dependent on the time lapse 

between exposure and their use, since the usual course of inorganic cyanide poisoning is acute and 

proceeds at very high rates. 

3.12 ADEQUACY OF THE DATABASE 

Section 104(I)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the 

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of cyanide 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 cyanide. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will be 

evaluated and prioritized, and a substance-specific research agenda will be proposed. 

3.12.1 Existing Information on Health Effects of Cyanide 

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to 

cyanide are summarized in Figure 3-6. The purpose of this figure is to illustrate the existing information 

concerning the health effects of cyanide. Each dot in the figure indicates that one or more studies provide 

information associated with that particular effect. The dot does not necessarily imply anything about the 

quality of the study or studies, nor should missing information in this figure be interpreted as a “data 

need”. A data need, as defined in ATSDR’s Decision Guide for Identifying Substance-Specific Data 

Needs Related to Toxicological Profiles (Agency for Toxic Substances and Disease Registry 1989b), is 
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3. HEALTH EFFECTS 

Figure 3-6. Existing Information on Health Effects of Cyanide 

Death

Acute 

Intermediate 

Chronic 

Immunologic/Lymphoretic 

Neurologic 

Reproductive 

Developmental 

Genotoxic 

Cancer 

Systemic 

Human 

Inhalation 

Oral 

Dermal 

Death

Acute 

Intermediate 

Chronic 

Immunologic/Lymphoretic 

Neurologic 

Reproductive 

Developmental 

Genotoxic 

Cancer 

Systemic 

Animal 

Inhalation 

Oral 

Dermal 

Existing Studies 
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3. HEALTH EFFECTS 

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. 

In the section that follows, data needs are identified for cyanide forms for which toxicity data were 

available and were, therefore, summarized in Section 3.2. These forms include primarily sodium cyanide, 

potassium cyanide, and hydrogen cyanide. As seen from Figure 3-6, information is available regarding 

death, systemic effects of acute exposure, and neurological effects in humans after inhalation, oral, and 

dermal exposure to cyanide. In addition, information is available regarding chronic systemic effects in 

humans after inhalation and oral exposure. 

Data regarding death, systemic effects of acute exposure, and neurological effects were obtained for 

animals following inhalation, oral, and dermal exposure to cyanide. Furthermore, information was 

obtained regarding systemic effects after intermediate-duration inhalation and oral exposure, and chronic 

oral exposure. In addition, information exists regarding developmental and reproductive effects after oral 

exposure of animals to cyanide. Studies involving cassava are omitted from consideration in this figure 

because they do not provide quantitative dose-response information for cyanide. 

3.12.2 Identification of Data Needs 

Acute-Duration Exposure. The target organs of acute cyanide exposure are the central nervous 

system, respiratory system, and cardiovascular system. Exposure to high levels of cyanide leads rapidly 

to death. Lethality data are available in humans for acute inhalation (Dudley et al. 1942; Singh et al. 

1989), oral (Gettler and Baine 1938), and dermal (Rieders 1971) exposures to hydrogen cyanide; 

however, specific exposure levels are often not available. Neurological sequelae (see Neurotoxicity 

below) were reported as long-term, sometimes delayed effects such as Parkinsonism in survivors of acute 

poisoning incidents following inhalation (Lam and Lau 2000) or oral exposure (Carella et al. 1988; Chin 

and Calderon 2000; Rachinger et al. 2002; Rosenberg et al. 1989; Rosenow et al. 1995). Lethality studies 

were performed in several animal species, and LC50 and LD50 values were derived for inhalation 

(hydrogen cyanide and cyanogen) (Ballantyne 1983a), oral (potassium cyanide and sodium cyanide) 

(Ballantyne 1983a, 1988), and dermal (hydrogen cyanide, potassium cyanide, and sodium cyanide) 

(Ballantyne 1983a, 1988) exposures. The systemic effects observed in animals included serious 

impairments in the central nervous system (semiconsciousness), lung (dyspnea), and heart (arrhythmia). 

These effects were also seen in humans regardless of route of cyanide exposure. Since most of the animal 
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studies only reported lethality as an end point and the only other effects were serious, there is no suitable 

NOAEL or LOAEL values to serve as the basis for acute MRLs. Additional acute studies by all routes 

using several dose levels and examining comprehensive end points would help to determine thresholds for 

known target organs and for any new target organs that might be identified. The information would be 

useful to populations living near hazardous waste sites that can be exposed to cyanide in contaminated 

water or soil for a short time. 

Intermediate-Duration Exposure. No intermediate-duration studies were located regarding 

cyanide effects in humans. A few inhalation (Valade 1952) and oral (Jackson 1988; Kamalu 1993; 

Okolie and Osagie 1999; Philbrick et al. 1979; Sousa et al. 2002; Tewe and Maner 1981b) studies in 

animals indicated the central nervous system is an important target organ of intermediate-duration 

exposure to cyanide toxicity (potassium cyanide and hydrogen cyanide). In addition, hematological, 

hepatic, renal, and reproductive effects may be caused by oral exposure. Studies on cyanide compounds 

containing metals such as copper and silver (Gerhart 1986, 1987) are inappropriate for establishing doseresponses for cyanide because the metals may contribute to toxicity. An oral rat study by Soto-Blanco et 

al. (2002a), which employed the lowest exposure levels, did not report dose-response results in sufficient 

detail to serve as a basis for an MRL. The extensive oral study on sodium cyanide by NTP (1993) did not 

evaluate neurohistopathology in the spinal cord. No intermediate-duration dermal studies were available. 

It is known, however, that cyanides can rapidly penetrate the skin and similar toxic effects are presumed. 

No intermediate-duration inhalation MRL could be derived because of the lack of data. An intermediate 

oral MRL of 0.05 mg/kg/day was derived from a study showing reproductive effects in rats exposed in 

drinking water to 12.5 mg CN–

/kg/day as sodium cyanide for 3 months (NTP 1993). This study is further 

described in the Reproductive Toxicity section below. Additional intermediate-duration inhalation 

studies using several dose levels would be useful to determine threshold levels for neurotoxicity. The 

information would be useful to populations living near hazardous waste sites that can be repeatedly 

exposed to cyanide in contaminated water or soil for periods of <1 year. 

Chronic-Duration Exposure and Cancer. Some reports of occupationally exposed workers 

indicated that low concentrations of hydrogen cyanide may have caused neurological, respiratory, and 

cardiovascular effects (Blanc et al. 1985; Chandra et al. 1980, 1988; El Ghawabi et al. 1975; Kumar et al. 

1992). The route of exposure was predominantly inhalation, although dermal exposure can also occur in 

the work place. The studies, however, lacked either information about exposure levels or used small 

cohorts of workers. Studies in populations that used cassava roots as a main source of their diet described 

the neurological effects of cyanide consumption (Osuntokun 1972, 1980). However, these effects may be 
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due to a recently identified substance, scopeletin, rather than to cyanide (Obidoa and Obasi 1991). For 

chronic exposure in animals, only one oral study in rats (hydrogen cyanide) was located (Howard and 

Hanzal 1955). However, the reliability of this study is low because of the unstable cyanide levels in their 

feed throughout the experiment due to evaporation of cyanide. Furthermore, no effects were found in the 

study besides nondose-related changes in weight gain in female rats, but not in male rats. No chronic 

studies in animals were located for the inhalation and dermal routes. Therefore, data are not sufficient to 

derive MRL values for chronic exposure. Additional chronic-duration studies in animals would be 

helpful to determine thresholds for target organs. 

No studies were located regarding carcinogenicity of cyanide in humans or animals. The chronic toxicity 

studies suggested above should be designed to also analyze the carcinogencity of cyanide. 

The results of chronic toxicity and carcinogenicity studies would be useful to populations living near 

hazardous waste sites that can be repeatedly exposed to cyanide in contaminated water or soil for periods 

exceeding 1 year. 

Genotoxicity. No human data are available on the genotoxicity of cyanide. No genotoxicity was 

found in one in vivo study in mice exposed orally to potassium cyanide (Friedman and Staub 1976). 

However, DNA fragmentation has been detected in DNA from the brains of mice injected with potassium 

cyanide (Mills et al. 1999; Yamamoto and Mohanan 2002). The relevance of this fragmentation to 

genotoxicity is not known. In vitro studies with cyanide in the form of potassium cyanide did not show 

any mutagenic activity in S. typhimurium or E. coli (De Flora 1981; De Flora et al. 1984; Kubo et al. 

2002), and cyanide in the form of sodium cyanide tested negative in Salmonella strains TA97, TA98, 

TA100, and TA1535, with and without metabolic activation (NTP 1993). One study in S. typhimurium 

suggested that hydrogen cyanide may be mutagenic (Kushi et al. 1983); an increase in the induction of 

reverse mutations was noted without metabolic activation. A number of in vitro studies on cultured cells, 

including A549 human epithelial-like lung carcinoma cells, as well as various animal cell types, reported 

DNA fragmentation following exposure to potassium cyanide (Bhattacharya and Lakshmana Rao 1997; 

Henderson et al. 1998; Storer et al. 1996; Vock et al. 1998). These studies indicate that the DNA 

fragmentation is secondary to the general cytotoxicity of cyanide, which results in the release of 

endonucleases by the dying cells. As there are no structural reasons to suggest that cyanide may be 

genotoxic and fragmentation is secondary to cytotoxicity, it does not appear that further genotoxicity 

studies are needed at this time, until the Kushi reverse mutation data can be replicated independently. 
CYANIDE 123 

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Reproductive Toxicity. No data were located regarding reproductive effects of cyanide in humans. 

One animal study reported increased resorptions in rats following oral exposure to a cassava diet (Singh 

1981). Because some human populations use cassava roots as the main source of their diet, further 

information regarding this observation would be useful for these populations, but this is probably not a 

concern for people living in the United States. Increased gonadal weight was found in male rats in 90-day 

oral studies of copper cyanide and potassium silver cyanide (Gerhart 1986, 1987), but the possible 

contribution of the metals to the dose-response cannot be discounted. A number of reproductive effects, 

including decreases in left cauda epididymal weight, left testis weight, spermatid heads, and spermatid 

counts were noted in rats exposed to sodium cyanide in the drinking water for 13 weeks (NTP 1993). 

This study was used as the basis for the intermediate oral MRL (see Intermediate-Duration Exposure 

above and Appendix A). Thus, it appears that only limited value would be associated with further 

reproductive studies at this time. 

Developmental Toxicity. No studies were located regarding teratogenic effects in humans exposed 

to cyanide by any route, although hypothyroidism, attributed to elevated thiocyanate levels, has been 

observed in offspring as a result of maternal dietary consumption of cassava during pregnancy (Ermans et 

al. 1980). Developmental studies in animals were performed only following oral exposure and 

contradictory results were obtained. Teratogenic effects of cyanide exposure were observed in rats and 

hamsters fed a cassava diet (Frakes et al. 1986a; Singh 1981), while no effects were found in rats and pigs 

fed cassava diets alone or supplemented with potassium cyanide (Tewe and Maner 1981a, 1981b). 

However, the latter studies are flawed in that they did not include a control group not exposed to cyanide. 

Furthermore, growth retardation was the only effect in weanling rats in the second generation of a twogeneration oral exposure study with potassium cyanide. More data regarding developmental toxicity in 

experimental animals would be useful to identify the possible risk for humans. Studies on developmental 

neurotoxiocology, including postnatal behavior analysis, would provide significant information relative to 

child development for populations living near hazardous waste sites containing cyanide. 

Immunotoxicity. No data were located regarding immunological effects in humans or animals after 

inhalation, oral, or dermal exposure to cyanide. A battery of immune function tests has not been 

performed in humans or animals; testing in animals under low-level exposure conditions would be useful 

to clarify whether cyanide is an immunotoxicant. 

Neurotoxicity. The central nervous system is an important target for cyanide toxicity in humans and 

animals following exposure by all three routes. Acute inhalation exposure to high levels of cyanide, 
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regardless of the form, leads quickly to death that is preceded by dyspnea, convulsions, and central 

nervous system depression (Bonsall 1984; Chen and Rose 1952; Peden et al. 1986; Potter 1950; Singh et 

al. 1989). Neurological and behavioral effects were observed in humans after chronic inhalation exposure 

to hydrogen cyanide in the workplace (Blanc et al. 1985; Chandra et al. 1988; El Ghawabi et al. 1975; 

Lam and Lau 2000). Oral exposure to cyanide led to the development of severe peripheral neuropathies, 

and hearing and visual problems in those who used cassava as a staple in the diet (Osuntokun 1980). 

However, these effects may be due to a recently identified substance, scopeletin, rather than due to 

cyanide (Obidoa and Obasi 1991). Some neurological effects (memory loss and a Parkinsonian-type 

syndrome have been reported as delayed effects following accidental acute ingestion of soluble cyanide 

compounds (Chin and Calderon 2000; Grandas et al. 1989; Rachinger et al. 2002; Rosenberg et al. 1989; 

Rosenow et al. 1995; Uitti et al. 1985). Experimental studies in animals exposed to hydrogen cyanide or 

cyanide compounds by the inhalation (Purser et al. 1984; Valade 1952), oral (Philbrick et al. 1979), or 

dermal routes (Ballantyne 1983b), have found neurological effects similar to those seen in humans. 

Behavioral changes were reported in pigs after oral exposure to potassium cyanide (Jackson 1988). 

Additional studies for neurological effects for all routes and durations would be useful for determining the 

NOAEL values for this most sensitive end point. Of particular value would be studies in animals that 

correlate morphological changes, such as demyelination, with changes in higher functions, such as 

learning and memory. 

Epidemiological and Human Dosimetry Studies. Human exposure to low levels of cyanide is 

quite common. Cigarette and fire smoke contain cyanide (EPA 1981e); cyanide is used as a postharvest 

pesticide fumigant (Jenks 1979) and can be detected at low levels in drinking water supplies (EPA 

1981e). Workers are exposed to cyanide in several industries, but usually only when not using personal 

protective gear (Blanc et al. 1985). Although several studies reported neurological and thyroid effects in 

workers chronically exposed occupationally, dose relationships of these effects are not known, and the 

effects may have been confounded by simultaneous exposure to other chemicals. Similarly, exact 

correlations between environmental exposures and cyanide levels in blood or urine were not established. 

Therefore, occupational and environmental studies that would provide data on exposure levels and 

concentrations found in body fluids would be useful. These studies might be useful for establishing 

cause/effect relationships that might lead to future monitoring of populations exposed to low levels of 

cyanide from dietary sources or contaminated waste sites. Furthermore, studies regarding the health 

status, including significant elevations in urinary thiocyanate as a biomarker, of such populations would 

be informative. Studies examining exposure to cyanide via cassava consumption would not be useful, 
CYANIDE 125 

3. HEALTH EFFECTS 

since cassava is not normally consumed in the United States and it contains another substance rather than 

cyanide which may contribute to neurotoxicity (Obidoa and Obasi 1991). 

Biomarkers of Exposure and Effect. 

Exposure. Concentrations of cyanide can be measured in the blood, urine, and tissues, and the metabolite 

thiocyanate can be measured in blood and urine (Ballantyne 1983a; Berlin 1977; Chandra et al. 1988; El 

Ghawabi et al. 1975; Jarvis 1989; Maliszewski and Bass 1955; Vogel et al. 1981; Yamanaka et al. 1991). 

Since certain amounts of cyanide can always be found in the human tissues, urine, and expired air, only 

exposure to high doses can be detected by this way. Cyanide is metabolized in the body to thiocyanate in 

a reaction that is catalyzed by the enzymes rhodanese and mercaptopyruvate sulfur transferase (Ansell 

and Lewis 1970). Significant elevations in thiocyanate levels have been detected in cassava-eating 

populations (Ermans et al. 1980; Mlingi et al. 1993; Tylleskar et al. 1992) and in animals (Blakely and 

Coop 1949; Himwich and Saunders 1948; Howard and Hanzal 1955; Okoh 1983; Smith 1996; Sousa et 

al. 2003; Way 1984; Wood and Cooley 1956) and can serve as a reasonable marker of exposure. Since 

cyanide is eliminated from the body relatively rapidly, but thiocyanate levels are sustained for longer 

periods, other biomarkers of low-level exposure would be useful. 

Effect. The target organs of cyanide toxicity are the central nervous system and the cardiovascular 

system, but exposure to other chemicals may have similar effects. Reductions in cytochrome c oxidase 

activity in specific organs and elevations in plasma lactate concentrations have been used as measures of 

cyanide toxicity following acute exposure (Baud et al. 1996, 2002; Ikegaya et al. 2001). Imaging 

techniques, such as MRI and PET, have been use to follow the course of brain injury or monitor changes 

in glucose utilization by specific brain regions, respectively, following acute exposure to cyanide (Carella 

et al. 1988; Chin and Calderon 2000; Grandas et al. 1989; Feldman and Feldman 1990; Rachinger et al. 

2002; Rosenberg et al. 1989; Rosenow et al. 1995; Uitti et al. 1985; Zaknun et al. 2005). The features 

examined in these studies are not specific to cyanide exposure. Thus, there is a need for studies 

evaluating characteristic changes in the brain following exposure to cyanide under different exposure 

conditions (routes of exposure, dose levels, frequency, durations, and form administered). Evaluating 

differences in the effect of metal cyanide compounds (copper cyanide or silver cyanide) versus the 

soluble cyanides would help evaluate the contribution of the metal to toxicity. These kinds of studies 

could also serve as a basis for evaluating the efficacy of antidotes. 
CYANIDE 126 

3. HEALTH EFFECTS 

Some genetic markers for cyanide-induced hypoxia have been identified in some human cell lines with or 

without the use of biologically relevant inhibitors (Kiang et al. 2003). These kinds of studies could be 

expanded to evaluate tissue-specific (cell-type-specific) differences in responses to cyanide exposure. 

More studies to identify subtle biochemical changes to serve as biomarkers of effects of low cyanide 

exposure would be useful and could also serve as a platform for the development of new antidotes. 

Absorption, Distribution, Metabolism, and Excretion. Hydrogen cyanide, sodium cyanide, and 

potassium cyanide are readily absorbed following inhalation, oral, and dermal exposures (Ballantyne 

1983a; Sousa et al. 2003). Inhalation exposure provides the most rapid route of entry. Cyanide is 

distributed throughout the body and detoxified by a mitochondrial enzyme, rhodanese (Ansell and Lewis 

1970). Other minor detoxification pathways include spontaneous reaction with cystine and the reaction 

with hydroxo-cobalamin (Ansell and Lewis 1970). The severity and rapidity of the onset of effects 

depend on the route, dose, duration of exposure, and the cyanide compound administered. Certain ironcontaining cyanide compounds exhibit very low bioavailability by the oral route (Nielsen et al. 1990) as 

suggested by the absence of toxicity among attempted suicides of people who ingested these compounds 

(Hantson et al. 1996; Laforge et al. 1999). Once cyanides have been absorbed, excretion is similar in 

humans (Chandra et al. 1980; Liebowitz and Schwartz 1948) and animals (Farooqui and Ahmed 1982; 

Okoh 1983; Sousa et al. 2003). Cyanide metabolites are excreted primarily in urine, and small amounts 

of hydrogen cyanide are eliminated through the lungs (Farooqui and Ahmed 1982; Okoh 1983). 

Additional quantitative data on the toxicokinetics of cyanide would be useful, because there are few 

studies available that quantitate absorption, distribution and excretion following acute inhalation 

exposure. The only studies reporting the transfer of cyanide or thiocyanate into breast milk or across the 

placenta were conducted in goats (Soto-Blanco and Gorniak 2003), which are not an appropriate animal 

model for humans. Such studies need to be conducted in a more appropriate animal model. No data were 

found that dealt with saturation kinetics in cyanide metabolism, since cyanide is fatal long before 

saturation is reached. 

Comparative Toxicokinetics. Several studies on cyanide lethality and toxicity indicate that the 

central nervous system (Blanc et al. 1985; Bonsall 1984; Chandra et al. 1988; Chen and Rose 1952; 

Dodds and McKnight 1985; El Ghawabi et al. 1975; Fairley et al. 1934; Haymaker et al. 1952; Hirano et 

al. 1967; Jackson 1988; Kumar et al. 1992; Lasch and El Shawa 1981; Levine 1969; Levine and 

Stypulkowski 1959a; Lewis et al. 1984; McNerney and Schrenk 1960; Peden et al. 1986; Potter 1950; 

Purser et al. 1984; Singh et al. 1989; Trapp 1970; Valade 1952; Walton and Witherspoon 1926), the 

reproductive system (Kamalu 1993; NTP 1993; Singh 1981), and the thyroid gland (Blanc et al. 1985; El 
CYANIDE 127 

3. HEALTH EFFECTS 

Ghawabi et al. 1975; Gerhart 1986, 1987; Jackson 1988; Philbrick et al. 1979; Soto-Blanco et al. 2002a; 

Tewe and Maner 1981a, 1981b) are target organs in both humans and animals. Toxicokinetic studies 

cannot be performed in humans; however, data regarding cyanide distribution have been obtained during 

autopsies in several lethal cases of poisoning following inhalation or oral exposure to hydrogen cyanide, 

sodium cyanide, or potassium cyanide (Finck 1969; Gettler and Baine 1938). A large proportion of the 

toxicokinetic studies in animals was published between 1935 and 1965 (Blakely and Coop 1949; Boxer 

and Rickards 1952; Gettler and Baine 1938; Howard and Hanzal 1955; Walton and Witherspoon 1926; 

Wood and Cooley 1956). As a result, much of the information is descriptive rather than quantitative, and 

the quantitative data presented were generated with inaccurate analytical equipment and methodologies. 

However, more recent studies in rats with hydrogen cyanide, sodium cyanide, and potassium cyanide 

indicate a pattern of distribution that is similar to that in humans (Ballantyne 1983a, 1983b; Sousa et al. 

2003; Yamamoto et al. 1982). Furthermore, a study regarding transocular exposure showed that tissue 

concentrations of cyanide in rabbits varied depending on the cyanide compound used (Ballantyne 1983a, 

1983b). Detailed pharmacokinetic studies on cyanide and its interaction with thiosulfate have been 

conducted in dogs (Sylvester et al. 1983). A comparative quantitative toxicokinetic study in male rats and 

pigs exposed to a single dose of potassium cyanide focused on the plasma concentration of cyanide and 

thiocyanate (Sousa et al. 2003). Additional toxicokinetic data in several species would be needed to 

identify the best model for assessing human risk. On account of the relatively low hepatic content of the 

detoxifying enzyme rhodanese compared to other species (Drawbaugh and Marrs 1987; Himwich and 

Saunders 1948), dogs do not appear to be the optimal model species for extrapolation to humans. 

Methods for Reducing Toxic Effects. This discussion presumes that cyanide exposure was not 

prevented by the use of protective gear, which, if possible, should be the major strategy for avoiding toxic 

effects. The mechanism by which cyanide enters the blood stream in humans is not known, but due to the 

relatively small size of the molecule, it is likely that cyanide simply follows a concentration gradient. 

Some of the mechanisms of toxic action of cyanide are known: the compound inhibits the activity of 

various enzymes by binding to their metallic moiety. Cyanide antagonists, such as sodium thiosulfate, 

have been used as antidotes to cyanide poisoning by aiding in the conversion of the cyanide ion to 

thiocyanate (Bonsall 1984; Mengel et al. 1989; Schubert and Brill 1968; Sylvester et al. 1983). Other 

antidotes such as amyl nitrite, sodium nitrite, hydroxylamine, p-aminopropiophenone, 4-dimethylaminophenol, and primaquine work by binding to iron ions and increase the levels of methemoglobin to 

which cyanide can bind (Bright and Marrs 1987; Kruszyna et al. 1982; Schubert and Brill 1968). In 

practice, antidote therapy is continued until serum parameters (blood oxygen and serum pH) indicate that 

no additional cyanide is impairing mitochondrial function. Additional research has been carried out on 
CYANIDE 128 

3. HEALTH EFFECTS 

antidotes that would not produce methemoglobinemia (Bhattacharya and Vijayaraghavan 2002; Keniston 

et al; 1987; Moore et al. 1986; Klimmek et al. 1983; Niknahad and O'Brien 1996; Schwartz et al. 1979; 

Yamamoto 1989). Synergistic effects of supplemental therapies such as alpha-ketoglutaric acid along 

with conventional antidotes have been examined (Hume et al. 1995; Niknahad et al. 1994). 

Pharmacological approaches have been employed to find antidotes for cyanide (Isom and Borowitz 1995; 

Maduh et al. 1995). Other types of compounds that have been tested include calcium-channel blockers 

(Jiang et al. 1998; Mathangi and Namisivayam 2004a), antioxidants (Choi and Han 2002; Kanthasamy et 

al. 1997; Maharaj et al. 2003; Okolie and Iroanya 2003; Yamamoto and Tang 1996a, 1996b, 1996c, 

1998), anti-inflammatory drugs (Daya et al. 2000; Lambat et al. 2000), and certain amino acids (Carini et 

al. 1997). Evaluations of antidotes need to consider the progression of lactate acidosis. 

Children’s Susceptibility. 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. 

There is some evidence from the cassava-eating populations that hypothyroidism may occur from 

gestational exposure to cyanide (Ermans et al. 1980) and from lactating ewes that cyanide can be 

transferred in milk of exposed goats (Soto-Blanco and Gorniak 2003). In general, the effects in children 

are not expected to differ from adults. However, there is no study that has yet examined possible 

neurological or neurobehavioral deficits in offspring following gestational exposure to cyanide. This 

would appear to be a significant issue, given the report suggesting that neurohistopathology is the most 

sensitive effect in rats (Soto-Blanco et al. 2002a). Studies evaluating the different sensitivity of young 

organisms to side effects of cyanide antidotes would be useful in establishing suitable dose levels of 

antidotes for children. 

Child health data needs relating to exposure are discussed in Section 6.8.1, Identification of Data Needs: 

Exposures of Children. 

3.12.3 Ongoing Studies 

A number of ongoing studies concerning health effects and mechanisms of action associated with cyanide 

have been identified in the 2005 version of the Federal Research In Progress (FEDRIP) database 

(FEDRIP 2005). 
CYANIDE 129 

3. HEALTH EFFECTS 

In a project supported by the National Institute for Occupational Safety and Health, Dr. Laurence D. 

Fechter, of the Loma Linda Veterans Association, Redlands, California, is investigating the effect of 

hydrogen cyanide exposure on noise-induced hearing loss in rats. 

Dr. Gary E. Isom of Purdue University, West Lafayette, Indiana, is evaluating necrotic and apoptopic 

mechanisms of neuronal cell death caused by cyanide in a project supported by the National Institute of 

Environmental Health Sciences. 

Under the auspices of the National Cancer Institute, Dr. Timothy R. Fennell, of Research Triangle 

Institute, North Carolina, is investigating methods for the analysis of adducts formed between hemoglobin 

and reactive chemicals, including cyanide. The study aims to understand the basis for selective 

vulnerability of specific brain regions to cyanide. 

Dr. Julia A. Kovacs of the University of Washington, Seattle, Washington, is evaluating the inhibitory 

effect of cyanide on superoxide reductases as part of a project on structure-reactivity relationships for 

metalloenzymes; this project is supported by the National Institute of General Medical Sciences. 

Dr. Herbert T. Nagasawa of the Department of Veterans Affairs, Medical Center, Minneapolis, 

Minnesota, is evaluating the efficacy of derivatives of 2-mercaptopyruvic acid as antidotes for cyanide in 

mice. 

Dr. Arne Slungaard of the University of Minnesota, is investigating the effect of thiocyanate on 

eosinophil peroxidase-mediated oxidative damage, inflammation, and apoptosis. The study is supported 

by the National Heart, Lung and Blood Institute. 

Dr. Patricia Sonsalla of the University of Medicine and Dentistry of New Jersey, R.W. Johnson Medical 

School, is investigating a number of mitochondrial toxins, including cyanide, to establish their effect on 

dopamine homeostasis, the function of dopamine vesicles, and the role of dopamine in modulating 

neurodegeneration. This study is supported by the National Institute of Neurological Disorders and 

Stroke. 
CYANIDE 130 

3. HEALTH EFFECTS 

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CYANIDE 131 

4. CHEMICAL AND PHYSICAL INFORMATION 

4.1 CHEMICAL IDENTITY 

Information regarding the chemical identity of the most common cyanides is located in Table 4-1. 

Hydrogen cyanide is a toxic gas that may enter the environment from both natural processes and human 

industrial activities. It may exist in polymeric forms. The cyanide compounds in which cyanide can be 

obtained as CN–

 are classified as simple and complex cyanides. Some simple cyanides are soluble in 

water (sodium cyanide, NaCN; potassium cyanide, KCN; and calcium cyanide, Ca(CN)2), while others 

are sparingly soluble or almost insoluble (copper (I) cyanide, CuCN). Cyanogen (NC-CN) and cyanogen 

chloride (CNCl) are highly toxic gases that are soluble in water. At neutral pH, cyanogen undergoes a 

slow hydrolysis to form hydrogen cyanide, cyanic acid (HOCN), and other products. At alkaline pH, 

CNCl hydrolyzes to CNO–

, which has only limited toxicity. Alkaline chlorination of water containing 

cyanide produces cyanogen chloride. Thiocyanate (SCN–

) is an oxidation product of the cyanide anion 

(CN–

), produced in the presence of a sulfur donor. 

4.2 PHYSICAL AND CHEMICAL PROPERTIES 

Information regarding the physical and chemical properties of cyanide is located in Table 4-2. Cyanides 

form strong complexes with many metals, particularly those of the transition series. One example of such 

complex formation is the reaction of cyanide with iron in the formation of ferrocyanide and ferricyanide 

complexes. Solutions of ferrocyanides and ferricyanides can form hydrogen cyanide and cyanide ions 

when exposed to sunlight or ultraviolet radiation. Cyanogenic glycosides are cyanide compounds 

produced naturally in many plants (Jones 1998). These glycosides produce hydrogen cyanide when 

hydrolyzed (EPA 1978c) or digested (Ellenhorn and Barceloux 1997; WHO 2004b). For example, in the 

human gut, the cyanogenic glycoside amygdalin, which is found in bitter almonds and in apricot pits and 

is the active ingredient in the drug Laetrile, undergoes two enzymatically catalyzed hydrolysis steps 

(Ellenhorn and Barceloux 1997). The first step involves the removal of one of the two β-D-glucopyranosyl groups from amygdalin through the action of beta-glucosidase to form the cyanogenic 

glycoside, prunasin. The enzyme, emulsion, then hydrolyzes prunasin to form hydrogen cyanide, 

glucose, and benzaldehyde. 
CYANIDE 132 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-1. Chemical Identity of Cyanide and Compoundsa 

Characteristic 

Synonym(s) 

Registered trade 

name(s) 

Chemical formula 

Hydrogen cyanide 

Formonitrile; 

hydrocyanic acid; 

prussic acid 

Cyclone B; Cyclonb

HCN 

Sodium cyanide 

Cyanide of sodium; 

hydrocyanic acid; 

sodium salt 

 Cyanogranc 

NaCN 

Potassium cyanide 

Cyanide of potassium; 

hydrocyanic acid; potassium 

salt 

Carswell No. 688A 

KCN 

Chemical structure H+C N Na+C N K+C N 

Identification numbers: 

 CAS registry 74-90-8 143-33-9 151-50-8 

 NIOSH RTECS MW6825000 VZ7530000 TS8750000 

EPA hazardous waste P063; D003 P106; D003 P098; D003 

 OHM/TADS 7216749 7216892 7216862 

 DOT/UN/NA/IMCO 

shipping 

HSDB 

UN1051; IMO 6.1 

UN1614; NA 1051 

165 

UN1689; IMO 6.1 

734 

UN1680; IMO 6.1 

1245 

NCI No data No data No data 
CYANIDE 133 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-1. Chemical Identity of Cyanide and Compoundsa 

Characteristic Calcium cyanide Copper(l) cyanide Potassium silver cyanide 

Synonym(s) Calcid; calcyan; cyanide Cuprous cyanidec; Potassium argentocyanide; 

of calcium cupricinc potassium dicyanoargentate 

Registered trade Caswell No. 142; AI3–28745 No data 

name(s) Cyanogasc 

Chemical formula Ca(CN)2 CuCN KAg(CN)2 

Chemical structure -

N C Ca+2C N Cu+C N K+[Ag(CN)2]­

Identification numbers: 

 CAS registry 592-01-8 544-92-3 506-61-6 

 NIOSH RTECS EW0700000 GL7150000 TT5775000 

EPA hazardous waste P021; D003 P029; D003 P099; D003; D011 

OHM/TADS 7216626 No data No data 

 DOT/UN/NA/IMCO UN1575; IMO 6.1 UN1587; IMO 6.1 No data 

shipping 

HSDB 242 1438 6053 

NCI No data No data No data 
CYANIDE 134 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-1. Chemical Identity of Cyanide and Compoundsa 

Characteristic Cyanogen Cyanogen chloride Ammonium thiocyanate 

Synonym(s) Carbon nitride; Chlorine cyanide; Thiocyanic acid, ammonium 

dicyanogen; 

ethanedinitrile 

chlorocyan salt; ammonium rhodanide; 

ammonium sulfocyanatec 

Registered trade No data Caswell No. 267 Trans-Aidb 

name(s) 

Chemical formula (CN)2 CNCl NH4SCN 

Chemical structure NC C N Cl C N C N 

Identification numbers: 

 CAS registry 460-19-5 506-77-4 1762-95-4 

 NIOSH RTECS GT1925000 GT2275000 XK7875000 

EPA hazardous waste P031; D003 P033; D003 No data 

 OHM/TADS 7216656 7216658 721218 

 DOT/UN/NA/IMCO UN1026; IMO 2.3 UN1589; IMO 2.3 NA9092 

shipping 

HSDB 2130 917 701 

NCI No data No data No data 

NH4 

+S 

a

All data are from HSDB 2004 unless otherwise noted. b

Crop Protection Handbook 2004 c

Budavari 1989 

CAS = Chemical Abstracts Service; DOT/UN/NA/IMO = 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; OHM/TADS = Oil and Hazardous Materials/Technical Assistance Data System; 

RTECS = Registry of Toxic Effects of Chemical Substances 
CYANIDE 135 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Cyanide and Compounds 

Property Hydrogen cyanide Sodium cyanide 

Molecular weight 27.03a 49.01a 

Color Colorlessb Whiteb; colorlessa 

Physical state Gas or liquidb

 Solidb 

Melting point, °C -13.4b

 563.7a 

Boiling point, °C 25.70c

 1496a 

Density, g/cm3 0.6884 (liquid at 20 °C)c 1.60 (for cubic form)

c 

Odor Faint bitter almond odord Odorless when dry, emits slight odor of 

HCN in damp airb 

Odor threshold: 

Water 0.17 ppm (w/v)

e

 No data 

Air 0.58 ppm (v/v)e

; 0.8–4.4 ppmf No data 

Solubility: 

 Water Misciblea 48 g/100 mL at 10 °Cc 

Organic solvent(s) Soluble in ethanol, ethera Slightly soluble in ethanola

 and 

formamidec 

Partition coefficients: 

 Log Kow 0.66g

; 1.07 (calc.)h 0.44g

 Log Koc No data No data 

Vapor pressure, mm Hg 630 (at 20 °C)f 0.76 at 800 °Cc 

Henry's law constant 5.1x10-2 atm-m3

/moli No data 

Autoignition temperature 538c

 No data 

Flashpoint, °C -17.8 (closed cup)

c

 No data 

Flammability limits 5.6–40%j

 Not combustiblej 

Conversion factors: 

mg/m3

 to ppm in air, 1 mg/m3 = 0.890 ppm NAk 

20 °C 

ppm to mg/L in water ppm (w/v) = mg/L = μg/mL ppm (w/v) = mg/L = μg/mL 

ppm to mg/kg in soluble ppm (w/w) = mg/kg = μg/g ppm (w/w) = mg/kg = μg/g 

samples 

Explosive limits Upper, 40%; lower, 5.6%f

 No data 
CYANIDE 136 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Cyanide and Compounds 

Property Potassium cyanide Calcium cyanide 

Molecular weight 65.12a 92.12a 

Color Whiteb; colorlessa Whitea 

Physical state Solidb

 Solida 

Melting point, °C 634.5a Decomposes at >350 °Ca 

Boiling point, °C No data No data 

Density, g/cm3 1.553 (for cubic form)

c 1.8–1.9 (commercial product)c 

Odor Faint bitter almond odorb Faint bitter almond odorb 

Odor threshold: 

Water No data No data 

Air No data No data 

Solubility: 

Water 71.6 g/100 mL at 25 °Cc Soluble in water with gradual liberation 

of HCNb 

Organic solvent(s) Slightly soluble in ethanolc

 and 

methanolb 

Partition coefficients: 

 Log Kow No data No data 

 Log Koc 3.0 (calculated)l

 No data 

Vapor pressure, mm Hg No data No data 

Henry's law constant No data No data 

Autoignition temperature No data No data 

Flashpoint, °C No data No data 

Flammability limits Not combustiblej

 Not combustiblej 

Conversion factors: 

mg/m3

 to ppm in air, NAk NAk 

20 °C 

ppm to mg/L in water ppm (w/v) = mg/L = μg/mL ppm (w/v) = mg/L = μg/mL 

ppm to mg/kg in soluble ppm (w/w) = mg/kg = μg/g 

samples 

Explosive limits No data No data 
CYANIDE 137 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Cyanide and Compounds 

Property Potassium silver cyanide Cyanogen 

Molecular weight 199.01b 52.04a 

Color Whiteb Colorlessa 

Physical state Solidb

 Gasa 

Melting point, °C No data -27.9a 

Boiling point, °C No data -20.7a 

Density, g/cm3

 2.36a 0.9577 at -21.17 °Ca 

Odor No data Almond-like odorb 

Odor threshold: 

Water No data No data 

Air No data 230 ppm; irritating at 15 ppmf 

Solubility: 

 Water Solubleb

; 250 g/L (25 °C)

m 450 cc/100 cc (20 °C)a 

Organic solvent(s) Slightly soluble in ethanola Soluble in ethanol and ethyl ethera 

Partition coefficients: 

 Log Kow No data 0.07n 

 Log Koc No data No data 

Vapor pressure, mm Hg No data 3,800 at 20 °Co 

Henry's law constant No data No data 

Autoignition temperature No data No data 

Flashpoint, °C No data No data 

Flammability limits No data 6.6–32% in air

j 

Conversion factors: 

mg/m3

 to ppm in air, NAk 1 mg/m3 = 0.462 ppm 

20 °C 

ppm to mg/L in water ppm (w/v) = mg/L = μg/mL ppm (w/v) = mg/L = μg/mL

ppm to mg/kg in soluble ppm (w/w) = mg/kg = μg/g ppm (w/w) = mg/kg = μg/g

samples 

Explosive limits No data No data 
CYANIDE 138 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Cyanide and Compounds 

Property Cyanogen chloride Copper(l) cyanide 

Molecular weight 61.47a 89.56a 

Color Colorlessd White to cream-coloredb 

Physical state Gasd

 Solida 

Melting point, °C -6a

 473 (in N2)

a 

Boiling point, °C 13.8b

;12.7a Decomposesa 

Density, g/cm3

 1.186b 2.92a 

Odor Highly irritatingh

 No data 

Odor threshold: 

Water No data No data 

Air 1 ppmf

 No data 

Solubility: 

 Water Solubleb

; 27.5 mg/L (25 °C)

m 2.6 mg/L (25°C)m 

Organic solvent(s) Soluble in ethanol and ethyl etherb Insoluble in alcoholf 

Partition coefficients: 

 Log Kow No data No data 

 Log Koc No data No data 

Vapor pressure, mm Hg 760 at 13.8 °C No data 

Henry's law constant 3.2x10-3 atm-m3

/molm No data 

Autoignition temperature No data No data 

Flashpoint, °C No data No data 

Flammability limits Not combustiblef Does not readily ignitef 

Conversion factors: 

mg/m3

 to ppm in air, 1 mg/m3 = 2.5 ppm NAk

20 °C 

ppm to mg/L in water ppm (w/v) = mg/L = μg/mL ppm (w/v) = mg/L = μg/mL 

ppm to mg/kg in soluble ppm (w/w) = mg/kg = μg/g ppm (w/w) = mg/kg = μg/g 

samples 

Explosive limits No data No data 
CYANIDE 139 

4. CHEMICAL AND PHYSICAL INFORMATION 

Table 4-2. Physical and Chemical Properties of Cyanide and Compounds 

Property Ammonium thiocyanate 

Molecular weight 76.12a 

Color Colorlessa 

Physical state Solida 

Melting point, °C 149.6a 

Boiling point, °C 170 decomposesa 

Density, g/cm3

 1.305a 

Odor Odorlessb 

Odor threshold: 

 Water No data 

Air No data 

Solubility: 

Water 128 g/100 cc at 0 °Ca

; 

Very soluble in hot watera

; 

181 g/100 cc at 25 °Cp 

Organic solvent(s) Very soluble in ethanol; soluble in 

acetone and methanol; insoluble in 

ethyl acetate and chloroformb 

Partition coefficients: 

 Log Kow No data 

 Log Koc No data 

Vapor pressure, mm Hg No data 

Henry's law constant No data 

Autoignition temperature No data 

Flashpoint, °C No data 

Flammability limits May be combustiblef 

Conversion factors: 

mg/m3

 to ppm in air, NAk

20 °C 

ppm to mg/L in water ppm (w/v) = mg/L = μg/mL

ppm to mg/kg in soluble ppm (w/w) = mg/kg = μg/g

samples 

Explosive limits No data 

a

Lide 1990 b

Budavari 1989 c

Jenks 1979 d

Hawley 1981 e

Amoore and Hautala 1983 f

HSDB 2004 

g

EPA 1984a 

h

Verschueren 1983 i

Yoo et al. 1986; value at 25 °C and saturation 

pressure 

j

NFPA 1994 k

Since these compounds do not exist in the atmosphere in 

the vapor phase, their concentrations are always expressed 

in weight by volume unit (e.g., mg/m3

). l

Kenaga 1980 mEPA 1985f 

n

Hansch et al. 1995 o

EPA 1978c 

p

Lide 2005 

EPA = Environmental Protection Agency; HCN = hydrogen cyanide; HSDB = Hazardous Substances Data Bank; 

NA = not applicable 
CYANIDE 140 

4. CHEMICAL AND PHYSICAL INFORMATION 

Hydrogen cyanide has a pKa of 9.2 (Smith and Martell 1989); therefore, solutions of cyanide compounds 

in water (such as from sodium cyanide and potassium cyanide) can form hydrogen cyanide at acid and 

neutral pHs. Alkaline solutions with pH >12 are practical for preventing significant outgassing of 

hydrogen cyanide. 

Hydrogen cyanide is a fire hazard and may be explosive when an excess of a strong acid is added to 

confined hydrogen cyanide. Solutions of some cyanide compounds are not stable and may decompose 

upon exposure to air or light. 
CYANIDE 141 

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

5.1 PRODUCTION 

The demand for hydrogen cyanide in the United States during 2000 was 1.615 billion pounds, up slightly 

from 1.605 billion pounds in 1999 (CMR 2001). Production of hydrogen cyanide in 2003 was 2.019 

billion pounds in the United States (FAS 2005). The demand for hydrogen cyanide was projected to be 

1.838 billion pounds in 2004 (CMR 2001; NYSDOH 2005). Major producers of hydrogen cyanide are 

Adisseo USA, Inc. (Institute, West Virginia); Cyanco Co. (Winnemucca, Nevada); Cytec Industries 

(Waggoman, Louisiana); Degussa Corp. (Theodora, Alabama); The Dow Chemical Company (Freeport, 

Texas); E.I. du Pont de Neumours and Company (Memphis, Tennessee; Beaumont, Texas); Innovene 

(Green Lake, Texas and Lima, Ohio); Invista, Inc. (Orange, Texas and Victoria, Texas); Rhom and Haas 

Texas Inc. (Deer Park, Texas); Solutia, Inc. (Alvin, Texas); Sterling Chemicals, Inc. (Texas City, Texas); 

and Syngenta Crop Protection (St. Garbiel, Louisiana) (SRI 2005). The combined annual production 

capacity of these plants is approximately 2.036 billion pounds (SRI 2005). 

As of February 2005, the following companies produced other cyanide compounds in the United States 

(SRI 2005): 

ammonium Crompton, Taft, Louisiana; and Mallinckrodt, Inc., St. Louis, Missouri 

thiocyanate: 

cyanogen: Matheson Gas Products, Inc., Gloucester, Massachusetts 

potassium cyanide: DuPont Chemical Company, Memphis, Tennessee; and The Dow Chemical 

Company, Nashua, New Hampshire 

potassium silver Engelhard Corporation, Union, New Jersey; and Metalor Technologies USA, North 

cyanide: Attleboro, Massachusetts 

Facilities in the United States producing sodium cyanide and their annual capacity (in millions of pounds) 

in 2005 include: Cyanco Co., Winnemucca, Nevada (86); and E.I. du Pont de Neumours and Company, 

Memphis, Tennessee (200) (SRI 2005). Two production facilities, E.I. du Pont de Neumours and 

Company, Texas City, Texas, and CyPlus, Theodore, Alabama, with production capacities of 85 and 

60 million pounds per year, respectively, were idle in 2005 (SRI 2005). 

Facilities in each state that manufactured or processed hydrogen cyanide or cyanide compounds in 2002, 

the range of the maximum amounts stored on site, and the types of production or use activities (e.g., 
CYANIDE 142 

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

production for sale or on-site use in processing) are shown in Tables 5-1 and 5-2, respectively (TRI03 

2005). The information in Tables 5-1 and 5-2 is derived from the Toxics Release Inventory (TRI). The 

TRI data should be used with caution since only certain types of facilities are required to report. This is 

not an exhaustive list. No information is available in the TRI database for thiocyanate compounds in this 

profile because these compounds are not included under SARA, Title III and, therefore, are not among the 

chemicals that facilities are required to report (EPA 2004q). 

There are two common methods of manufacturing hydrogen cyanide. The first consists of the formation 

of hydrogen cyanide as a byproduct during the synthesis of acrylonitrile from the reaction of propylene 

and ammonia with air. The second method involves direct synthesis by the reaction of methane and 

ammonia with air over platinum catalysts, otherwise known as the Andrussow process (CMR 1993; Curry 

1992; Homan 1987). Another less common manufacturing method, the Shawinigan process, is being 

applied in Spain and Australia that involves the reaction of ammonia with propane or butane in a fluidized 

bed of coke particles (Homan 1987; Shine 1971). Other methods of production include the dehydration 

of formamide and the reaction of sodium carbonate with coke-oven gas (Curry 1992; Sittig 1980). The 

formamide method of production has now been replaced by direct synthesis from methane and ammonia 

(Homan 1987). Of the total production capacity in the United States, direct synthesis and other routes of 

primary production accounts for 77% of the hydrogen cyanide produced; byproduct of acrylonitrile 

production accounts for the remaining 23% (CMR 1993; SRI 1995). The methods of commercial 

production of potassium and sodium cyanide include reacting potassium or sodium carbonate with carbon 

and ammonia, and reacting hydrogen cyanide with potassium or sodium hydroxide (Curry 1992; Homan 

1987; HSDB 2004). Sodium cyanide can also be prepared by heating sodium amide with carbon or by 

melting sodium chloride and calcium cyanamide together in an electric furnace (Hartung 1982). 

Potassium silver cyanide is manufactured by adding silver chloride to a solution of potassium cyanide 

(Sax and Lewis 1987). Calcium cyanide is manufactured by heating calcium cyanamide with a source of 

carbon in electric furnaces at temperatures >1,000 °C (Curry 1992; Homan 1987). It may also be 

produced by neutralization of lime with hydrogen cyanide (Homan 1987). 

Cyanogen is usually prepared by adding an aqueous solution of sodium or potassium cyanide to an 

aqueous solution of copper (II) sulfate or chloride (Homan 1987; Windholz 1983). It may also be 

produced by heating mercury cyanide, or by heating hydrogen cyanide in the presence of a catalyst 

(Homan 1987). Cyanogen chloride is produced by the action of chlorine on hydrogen cyanide or by the 

action of chlorine on moist sodium cyanide suspended in carbon tetrachloride and kept cooled to -3 °C 

(Homan 1987; Windholz 1983). Ammonium thiocyanate is produced by boiling an aqueous solution of 
CYANIDE 143 

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

Table 5-1. Facilities that Produce, Process, or Use Hydrogen Cyanide 

Maximum 

Number of Minimum amount amount on site 

Statea facilities on site in poundsb

in poundsb Activities and usesc 

AK 2 0 99,999 1, 5 

AL 11 0 999,999 1, 3, 4, 5, 6, 12, 14 

AR 1 1,000 9,999 12 

CA 8 0 999,999 1, 5, 13 

CO 4 0 99,999 1, 3, 5, 12 

DE 1 1,000 9,999 1, 3, 5, 12 

ID 3 0 9,999 1, 5, 6 

IL 9 0 9,999,999 1, 3, 5, 6, 7, 11, 12, 13, 14 

IN 3 0 999,999 1, 5 

KY 6 0 999 1, 5, 13 

LA 19 0 9,999,999 1, 3, 4, 5, 6, 12, 13, 14 

MA 2 0 999 1, 5 

MD 1 10,000 99,999 1, 5 

MI 1 100,000 999,999 1, 5 

MN 3 100 999 1, 5, 13 

MS 2 100 9,999 1, 5 

MT 2 0 999 1, 5 

NH 4 100,000 49,999,999 2, 3, 6 

NJ 3 0 99 1, 5 

NV 10 0 9,999,999 1, 3, 5, 6, 13 

NY 4 0 9,999,999 1, 3, 5, 6, 13 

OH 6 1,000 9,999,999 1, 4, 5, 6 

OK 3 0 999 1, 5, 12, 14 

PA 9 100 49,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 13 

SC 6 0 999,999 1, 3, 5, 6 

SD 1 10,000 99,999 1, 5 

TN 7 0 99,999,999 1, 3, 4, 5, 6, 13, 14 

TX 43 0 499,999,999 1, 2, 3, 4, 5, 6, 7, 12, 13, 14 

UT 4 0 999 1, 3, 5, 6, 12 

WA 2 0 999 1, 5 

WI 1 0 99 1, 5 

WV 10 0 49,999,999 1, 3, 5, 6, 7, 8, 10, 12 

WY 2 0 999 1, 3, 5, 6 

a

Post office state abbreviations used b

Amounts on site reported by facilities in each state c

Activities/Uses: 

1. Produce 

2. Import 

3. Onsite use/processing 

4. Sale/Distribution 

5. Byproduct 

6. Impurity 

7. Reactant 

8. Formulation Component 

9. Article Component 

10. Repackaging 

11. Chemical Processing Aid 

12. Manufacturing Aid 

13. Ancillary/Other Uses 

14. Process Impurity 

Source: TRI03 2005 (Data are from 2003) 
CYANIDE 144 

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

Table 5-2. Facilities that Produce, Process, or Use Cyanide Compounds 

Minimum Maximum 

Number of amount on site amount on site 

Statea facilities in poundsb in poundsb Activities and usesc 

AK 2 100,000 9,999,999 1, 5, 10 

AL 27 0 9,999,999 1, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13 

AR 16 0 99,999 2, 3, 6, 7, 10, 11, 12 

AZ 14 100 9,999,999 1, 6, 10, 11, 12 

CA 60 0 9,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

CO 12 100 999,999 1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 14 

CT 40 100 999,999 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13 

DE 1 1,000 9,999 1, 3, 5, 12 

FL 8 100 99,999 3, 6, 7, 10, 11, 12, 13 

GA 20 100 999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

IA 6 100 99,999 1, 3, 5, 6, 8 

ID 10 1,000 999,999 1, 2, 3, 5, 6, 7, 10, 12 

IL 85 0 999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

IN 51 0 49,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

KS 10 0 99,999 1, 3, 6, 7, 8, 10, 11, 12, 13 

KY 25 0 999,999 1, 5, 6, 7, 8, 10, 11, 12, 13 

LA 18 0 9,999,999 1, 3, 4, 5, 6, 10, 12, 13, 14 

MA 25 0 999,999 1, 2, 3, 4, 5, 6, 7, 10, 11, 12 

MD 14 100 99,999,999 1, 2, 3, 5, 6, 7, 10, 11, 12 

ME 7 100 99,999 5, 10, 11, 12 

MI 72 0 9,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

MN 30 100 999,999 1, 3, 5, 6, 8, 10, 11, 12 

MO 14 100 999,999 1, 3, 4, 5, 6, 8, 9, 10, 12, 13 

MS 11 0 99,999 1, 5, 6, 7, 9, 10, 12 

MT 6 0 999,999 1, 5, 10, 13 

NC 13 0 99,999 7, 8, 10, 11, 12 

NE 5 0 99,999 7, 10, 12 

NH 13 0 9,999,999 1, 3, 4, 5, 6, 8, 10, 11 

NJ 47 0 9,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

NV 39 100 49,999,999 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 

NY 43 0 999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

OH 66 0 999,999 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14 

OK 8 1,000 99,999 1, 3, 5, 6, 10, 11, 12 

OR 10 100 99,999 1, 2, 3, 5, 7, 10, 11, 12, 13 

PA 61 0 49,999,999 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13 

PR 13 100 999,999 6, 7, 8, 10, 11, 12, 13 

RI 28 0 99,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 

SC 15 100 9,999,999 1, 3, 5, 6, 7, 10, 11, 12 
CYANIDE 145 

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

Table 5-2. Facilities that Produce, Process, or Use Cyanide Compounds 

Minimum Maximum 

Number of amount on site amount on site 

Statea facilities in poundsb in poundsb Activities and usesc 

SD 5 100 9,999,999 1, 2, 3, 5, 6, 7, 10, 11, 12 

TN 25 100 9,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 

TX 54 0 49,999,999 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 

UT 8 100 999,999 1, 3, 5, 6, 10, 12 

VA 17 0 99,999 1, 3, 5, 6, 8, 10, 11, 12 

WA 8 100 999,999 1, 2, 3, 5, 8, 10, 11, 12 

WI 36 0 999,999 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13 

WV 10 0 9,999,999 1, 5, 11, 13 

WY 2 100,000 9,999,999 1, 4 

a

Post office state abbreviations used b

Amounts on site reported by facilities in each state c

Activities/Uses: 

1. Produce 

2. Import 

3. Onsite use/processing 

4. Sale/Distribution 

5. Byproduct 

6. Impurity 

7. Reactant 

8. Formulation Component 

9. Article Component 

10. Repackaging 

11. Chemical Processing Aid 

12. Manufacturing Aid 

13. Ancillary/Other Uses 

14. Process Impurity 

Source: TRI03 2005 (Data are from 2003) 
CYANIDE 146 

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

ammonium cyanide with sulfur or polysulfides or by reaction of ammonia and carbon disulfide (Homan 

1987; Sax and Lewis 1987). 

5.2 IMPORT/EXPORT 

The imports and exports of hydrogen cyanide through principal U.S. customs districts are negligible 

(CMR 2001). Recent import and export data for some of the cyanide compounds included in this profile 

are summarized in Table 5-3 for 2004 (USDOC 2004). Import volumes were greatest for thiocyanates, 

cyanates, and fulminates at 11.6 millions pounds followed by cyanides and cyanide oxides of sodium at 

4.71 million pounds. China, Germany, Japan, Czech Republic, and the United Kingdom were the primary 

exporters of these cyanide chemicals to the United States in 2004 (USDOC 2004). Recent import data 

could not be found in the available literature for potassium silver cyanide, cyanogen, or cyanogen 

chloride. 

Cyanides and cyanide oxides of sodium comprise the majority of exports for cyanide compounds with a 

volume of 147 million pounds. The second largest export item among the cyanide compounds was 

potassium cyanide at 3.82 million pounds. The most recent import data that could be found for copper (I) 

cyanide indicate that 0.52 and 0.26 million pounds of this compound were imported into the United States 

in 1984 and 1986, respectively (HSDB 2004). Export data could not be found in the available literature 

for calcium cyanide, potassium silver cyanide, cyanogen, or cyanogen chloride. 

5.3 USE 

The predominant users of cyanides are the steel, electroplating, mining, and chemical industries. The 

principal cyanide compounds used in industrial operations are potassium and sodium cyanide and calcium 

cyanide, particularly in metal leaching operations (Curry 1992; EPA 1993g). Cyanides have been well 

established in uses as insecticides and fumigants; in the extraction of gold and silver ores; in metal 

cleaning; in the manufacture of synthetic fibers, various plastics, dyes, pigments, and nylon; and as 

reagents in analytical chemistry (EPA 1978c, 1993g; HSDB 2004). Cyanides are present in some foods, 

but this presence is due mainly to the production of hydrogen cyanide from naturally-occurring 

cyanogenic compounds in foods (see Sections 6.4.4 and 6.5). Cyanogen has been used as a high-energy 

fuel in the chemical industry and as a rocket or missile propellant; cyanogen and its halides are used in 

organic syntheses, as pesticides and fumigants, and in gold-extraction processes (EPA 1978c; HSDB 
CYANIDE 147 

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

Table 5-3. Import and Export Volumes of Cyanide Compounds in 2004a 

Compounds Millions of pounds 

Imports: 

 Potassium cyanide 0.954 

 Calcium cyanide 0.006 

Cyanides and cyanide oxides of sodium 4.71 

Other cyanides and cyanide oxides No data 

Thiocyanates, cyanates, and fulminates 11.6 

Exports: 

 Potassium cyanide 3.82 

Calcium cyanide No data 

Cyanides and cyanide oxides of sodium 147 

Other cyanides and cyanide oxides 1.59 

Thiocyanates, cyanates, and fulminates 1.56 

a

USDOC (2004) 
CYANIDE 148 

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

2004). When used in pesticidal applications and in accordance with the product label, cyanide 

compounds are registered and regulated by the EPA under the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) (EPA 1998, 2004d). 

As a commercially available product, hydrogen cyanide is sold as a gas and is also available as a technical 

grade liquid in concentrations of 5, 10, and 96–99.5%. Almost all grades of hydrogen cyanide contain a 

stabilizer such as phosphoric acid to prevent decomposition and explosion (Curry 1992). In recent years, 

the use of hydrogen cyanide in the nylon and methyl methacrylate production processes has produced a 

strong demand. The use pattern for hydrogen cyanide is the following: adiponitrile (for nylon 6/6), 47%; 

methyl methacrylate, 27%; sodium cyanide, 8%; methionine, 6%; chelating agent, 2%; cyanuric chloride, 

2%; and miscellaneous uses, including nitriloacetic acid and salts, 8% (CMR 2001). Miscellaneous 

applications also include the use of hydrogen cyanide as an insecticide and rodenticide for fumigating 

enclosed spaces (grain storage, etc.) (Worthing 1987) and its use in the manufacture of ferrocyanides, 

acrylates, lactic acid, pharmaceutical, and specialty chemicals (Worthing 1987). 

Cyanide salts have various uses. The most significant applications of compounds included in this profile 

are uses in electroplating and metal treatment, as an anti-caking agent in road salts, and in gold and silver 

extraction from ores. Minor applications include use as insecticides and rodenticides, as chelating agents, 

and in the manufacture of dyes and pigments (EPA 1978c; Pesce 1993; Sax and Lewis 1987; Worthing 

1987). Calcium cyanide is used as a cement stabilizer (Curry 1992; Windholz 1983) and has had limited 

use in rodent control and as a beehive fumigant (Lowe and Sullivan 1992). Formerly used as a 

polymerization catalyst and as an antifouling agent in marine paints, copper (I) cyanide continues to be 

used in plating baths for silver, brass, and copper-tin alloy plating. Many metal polishes contain 

potassium or sodium cyanide. Potassium cyanide has a primary use in silver plating and is also used as a 

reagent in analytical chemistry. Potassium and sodium cyanide are used in combination for nitriding steel 

(HSDB 2004). One method of achieving hardened, weather-resistant metal surfaces uses a process 

known as cyaniding, which involves heating the metal in a liquid solution of sodium cyanide, sodium 

chloride, and sodium carbonate in the presence of atmospheric oxygen (Curry 1992). Fumigation of fruit 

trees, railway cars, and warehouses, and treatment of rabbit and rat burrows and termite nests are included 

among the former uses for sodium cyanide (HSDB 2004). 

Cyanogen, a colorless gas with an almond-like odor, is used in organic syntheses, as a fumigant, as a fuel 

gas for welding and cutting heat-resistant metals, and as a rocket and missile propellant with ozone or 

fluorine (Sax and Lewis 1987; HSDB 2004). Applications of cyanogen chloride include use in chemical 
CYANIDE 149 

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

syntheses, as a military poison gas, as a metal cleaner, in ore refining, and in the production of triazine 

herbicides, optical brighteners, dyestuffs, and synthetic rubber (Hartung 1982; Homan 1987; HSDB 2004; 

Sine 1994; Windholz 1983). Cyanogen chloride has also been used a warning agent in fumigant gases 

due to the fact that at low concentrations, it has strong lacrimatory effects (Homan 1987). 

Ammonium thiocyanate is used as an ingredient in antibiotic fermentations, pesticides, liquid rocket 

propellants, adhesives, and matches; in photographic processes; to improve the strength of silks; in the 

manufacture of transparent artificial resins; and as a weed killer and defoliant (Sax and Lewis 1987; Weil 

and Sandler 1997; Windholz 1983). 

5.4 DISPOSAL 

It has been estimated that 4.7 billion gallons of cyanide-containing wastes and 0.8 billion gallons of 

reactive wastes containing cyanide compounds were generated in the United States in 1983 (Grosse 

1986). Regulations governing the treatment and disposal of cyanide-containing wastes are detailed in 

Chapter 8. Cyanide is listed among the 65 toxic pollutants regulated by the Effluent Guidelines and 

Standards given in Title 40, Sections 400–475, of the Code of Federal Regulations. The pretreatment 

standards established for point source categories such as hydrogen peroxide manufacturing, 

electroplating, metal finishing, and ferroalloy manufacturing, regulate emissions of cyanides based on 

either total amount of cyanide or as cyanide that is amenable to chlorination in waste streams. Under the 

Resource Conservation and Recovery Act (RCRA), cyanide is listed as a hazardous waste when it is a 

discarded as a commercial chemical product, off-specification species, container residue, or spill residue; 

a waste from non-specific sources; or a waste from specific sources (EPA 1980a). Cyanide salts and 

complexes are the basis for listing 11 solid waste streams as hazardous wastes under RCRA (EPA 1986b). 

According to RCRA, cyanide-containing wastes are required to be treated by the best available 

technology before the wastes are disposed of in land. Cyanogen- and cyanogen chloride-containing 

waste, for example, are assigned the hazardous waste codes P031 and P033, respectively, and must be 

treated by chemical or electrolytic oxidation employing specific oxidizing reagents (e.g., hypochlorite, 

peroxides, ozone, or ultraviolet light assisted ozone) or other reagents of equivalent efficiency; wet air 

oxidation incorporating a surrogate or indicator parameter; or treatment by incineration in units operated 

in compliance with RCRA standards (EPA 1986b). The concentration of cyanide permissible in wastes 

for land disposal is described in the Land Disposal Restriction in Title 40 Section 268, of the Code of 

Federal Regulations and varies according to the nature of wastes. The maximum concentration in treated 

waste (i.e., non-waste water) should not exceed 590 mg/kg for total cyanides and 30 mg/kg for cyanides 
CYANIDE 150 

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

amenable to chlorination (EPA 1988c). While liquids are prohibited from land disposal, the maximum 

concentrations allowable in most treated waste waters, with the exception of the bottom streams from the 

acetonitrile column and the waste water stripper used in the production of acrylonitrile, are 1.9 mg/L for 

total cyanides and 0.86 mg/kg for cyanides amenable to chlorination (EPA 1988c). 

Conducted in the presence of sodium hydroxide and sodium hypochlorite, the chemical oxidation method 

commonly referred to as alkaline chlorination is the most widely used commercial method for treating 

cyanide-containing wastes. This method results in the conversion of the cyanide solution to the less toxic 

cyanate. Depending on the cyanides present, the product will be a sludge or solution, which when 

sufficient reaction time has been allowed, will largely be devoid of free cyanide (IRPTC 1985). 

The alkaline chlorination process has been applied to the removal of cyanide from waste waters and 

slurries generated as a consequence of cyanide heap leaching gold and other precious metals from low 

grade ores (EPA 1994c). However, few mining sites currently use this technology. Instead, cyanide in 

waste water or spent ore heaps is converted to cyanate through reactions with sulfur dioxide, ferrous 

sulfate, or hydrogen peroxide. These processes have been shown to effectively lower cyanide 

concentrations to levels that are within federal and state limits for discharge from the mining site (EPA 

1994c). A limitation of the technique is that it does not remove free chlorine, chloramines, or iron 

cyanides, which are toxic to fish. Other approaches that have demonstrated good efficiencies for 

removing cyanide from spent ore heaps and waste water include precipitate from leachate through 

reaction with cuprous ions, reaction of cyanide ion with sulfur dioxide, or biodegradation of cyanide 

(Akcil and Mudder 2003; EPA 1994c). The sulfur dioxide method is limited by an inability to remove 

thiocyanate, cyanate, and ammonia, which are toxic to fish, and may not provide sufficient removal 

efficiencies to meet local permit requirements (EPA 1994c). Biodegradation of cyanide in waste water 

and leachate is effective on soluble forms of cyanide, but may not be effective on degrading cyanide 

bound in metal complexes (EPA 1994c). 

Cyanide salts should not be treated with acid in preparation for disposal or flushed into drains that may 

contain or subsequently receive acid waste. Acidification is not a recommended method of treatment 

prior to disposal because of the liberation of hydrogen cyanide. Similarly, incineration of cyanides must 

proceed with caution and is not recommended unless extensive equipment capable of safely handling 

liberated hydrogen cyanide is available (IRPTC 1985). Of the cyanide compounds included in this 

profile, only hydrogen cyanide and cyanogen chloride are listed as potential candidates for rotary kiln 

incineration or fluidized bed incineration (HSDB 2004). 
CYANIDE 151 

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

The biodegradation of cyanides has been investigated, with varying results, for several industrial 

processes, and additional research in this area would be valuable. While investigations of the potential for 

microbial species found in mineral processing waste waters demonstrate effective removal of cyanide, 

metal complexed cyanide, and thiocyanate (Boucabeille 1994b; EPA 1994c), complex cyanides did not 

appear amenable to biodegradation at gasworks sites (Thomas and Lester 1993). Application of 

formaldehyde to electroplating waste under basic conditions can convert the cyanide anion to substituted 

acetates in addition to recovering copper and silver as free metals with formaldehyde reduction (Tucker 

and Carson 1985). Calcium or sodium polysulfide treatment converts some cyanide wastes into less toxic 

thiocyanate (Higgins and Desher 1988). These examples suggest that typical treatments involve the 

decomposition of cyanides to less toxic compounds by physical or chemical processes. More than 97% of 

cyanide is typically removed from waste waters by alkaline chlorination, electrolysis, or ozonation 

process. Cyanide from some wastes can be removed by ion-exchange resins. After using an appropriate 

treatment method such as those described above, cyanide wastes may be disposed of in a secured sanitary 

landfill (Grosse 1986; Higgins and Desher 1988; Tucker and Carson 1985). Disposal by injection of 

high-pH cyanide wastes into sandstone was investigated by Scrivner et al. (1986). Currently, the injection 

of waste water containing hydrogen cyanide and cyanide compounds through underground injection is a 

major method for disposal of these wastes. The available data indicate that in 2003, 1.56 million pounds 

of hydrogen cyanide and 2.94 million pounds of cyanide compounds were disposed of by underground 

injection (see Section 6.2 and Tables 6-1 and 6-2) (TRI03 2004). 
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5. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

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CYANIDE 153 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.1 OVERVIEW 

The term cyanide in this Toxicological Profile means a compound that contains the cyanogen (CN) 

radical. Since the CN portion of the compound is of concern in poisons, any reference to the amount 

present in air, water, soil, sediments, or other media refers only to this part of the compound. The term 

free cyanide refers to hydrogen cyanide and cyanide ion (CN–

) (EPA 1981e; Oudjehani et al. 2002; 

Shifrin et al. 1996; WHO 2004b). 

Cyanide (reported as cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, or copper (I) 

cyanide) has been identified in at least 464 of the 1,662 hazardous waste sites that have been proposed for 

inclusion on the EPA National Priorities List (NPL) (HazDat 2005). However, the number of sites 

evaluated for cyanide is not known. The frequency of these sites can be seen in Figure 6-1. Of these 

sites, 462 are located within the United States, 1 is located in Guam (not shown), and 1 is located in the 

Commonwealth of Puerto Rico (not shown). 

Anthropogenic (of human origin) sources are responsible for much of the cyanide in the environment. 

Cyanide-containing substances also occur naturally in the fruits, seeds, roots, and leaves of numerous 

plants, and are released to the environment from natural biogenic processes from higher plants, bacteria, 

and fungi (Cicerone and Zellner 1983; Crutzen and Carmichael 1993; EPA 1981e; Jones 1998; Knowles 

1988; Mudder and Botz 2000). However, an estimate of the amount of cyanide released to the 

environment from natural biogenic processes is not available. The major cyanide releases to water are 

discharges from metal-finishing industries, iron and steel mills, and organic chemical industries (EPA 

1981e). Effluents from the cyanidation process used in precious metal extraction contain high amounts of 

cyanide (EPA 1994c; Huiatt 1985; Scott 1985). The contribution of this source to the total cyanide 

discharge in water is insignificant on average (EPA 1981e). However, large, short-term releases can 

occur from the failure of tailing ponds resulting in the introduction of high concentrations of cyanide into 

local surface waters and subsoils (Fields 2001; Mudder and Botz 2000). Vehicle exhaust (EPA 1981e) 

and biomass burning (Crutzen and Carmichael 1993; Lobert and Warnatz 1993) are major sources of 

cyanide released into the air. The major sources of simple and complex cyanide releases to soil appear to 

be from the disposal of cyanide wastes in landfills and the use of cyanide-containing road salts (EPA 

1981e; Gaffney et al. 1987). Cyanogen chloride is formed in drinking water from reaction of humic 
CYANIDE 154 

6. POTENTIAL FOR HUMAN EXPOSURE 

Figure 6-1. Frequency of NPL Sites with Cyanide Contamination 

Frequency of 

NPL Sites

1-3

4-6

7-12

13-18

Derived from HazDat 2005 19-25

26-35
CYANIDE 155 

6. POTENTIAL FOR HUMAN EXPOSURE 

substances with chloramine produced during chlorination (Jacangelo et al. 1989; Ohya and Kanno 1987). 

Thiocyanate is released to water primarily from discharges of industrial waste waters from coal 

processing and extraction of gold and silver (Boucabeille et al. 1994a); the thiocyanate is formed from the 

reaction of sulfur donors that are present in coal and crushed rock with the cyanide that is used in the 

processing of these materials. Thiocyanate is also found in mining waste waters where it results from the 

interaction of the cyanide anion (CN–

) with sulphur (Boucabeille et al. 1994b). Releases of thiocyanate to 

soil result from anthropogenic and natural sources. Anthropogenic releases occur primarily from direct 

application in herbicidal formulations and from disposal as byproducts from industrial processes. 

Nonanthropogenic sources include damaged or decaying tissues of plants from the family Brassica (e.g., 

cabbage, mustard, kale) (Brown and Morra 1993). 

Cyanide is released into air mainly as hydrogen cyanide gas and, to a lesser extent, as particulate 

cyanides. Hydrogen cyanide can potentially be transported over long distances before reacting with 

photochemically generated hydroxyl radicals. The residence time of hydrogen cyanide in the atmosphere 

has been estimated to be approximately 2.5 years, with a range of 1.3–5.0 years, depending on the 

hydroxyl radical concentration (Cicerone and Zellner 1983). Neither photolysis nor deposition by 

rainwater is expected to be a significant removal mechanism. Only 2% of the tropospheric hydrogen 

cyanide is expected to be transported to the stratosphere (Cicerone and Zellner 1983). In water, cyanide 

occurs most commonly as hydrogen cyanide. Hydrogen cyanide is expected to be removed from water 

primarily by volatilization. Cyanide may also be removed by aerobic or anaerobic biodegradation (Akcil 

and Mudder 2003; EPA 1979, 1994c). At soil surfaces, volatilization of hydrogen cyanide is a significant 

loss mechanism for cyanides. In subsurface soil, cyanide at low concentrations would probably 

biodegrade under both aerobic and anaerobic conditions. In cases where cyanide levels are toxic to 

microorganisms (i.e., landfills, spills), the concentrations of water-soluble cyanides may be sufficiently 

high to leach into groundwater. 

The environmental fate of thiocyanate has not been thoroughly investigated. Aerobic and anaerobic 

biodegradation are significant transformation processes for thiocyanates in water (Boucabeille et al. 

1994a, 1994b; Shivaraman et al. 1985) and soil (Brown and Morra 1993). At near-ambient temperatures, 

sorption and volatilization are not significant partitioning processes for thiocyanate in soil (Brown and 

Morra 1993). 

Despite the various ways cyanide is thought to be released into the environment, available monitoring 

data are limited. The available data indicate that the general population is exposed to cyanide primarily 
CYANIDE 156 

6. POTENTIAL FOR HUMAN EXPOSURE 

by ingestion of foods that contain substances that release cyanides when ingested and through smoking, 

and to a lesser extent, by consumption of contaminated drinking water and inhalation of contaminated air. 

Dermal absorption is not a significant exposure route for the general population. The concentration of 

cyanide in the northern hemisphere's non-urban troposphere ranges from 160 to 166 ppt (ppt = parts per 

trillion) (Cicerone and Zellner 1983; Jaramillo et al. 1989). The mean cyanide concentration in most 

surface waters is not greater than 3.5 μg/L (EPA 1981e). The cyanide content in certain varieties of lima 

beans can be as high as 3 mg/g (Honig et al. 1983), although values between 0.10 and 0.17 mg/g are 

common in U.S. lima beans (EPA 1978c). Much lower cyanide concentrations in various cereal grains 

and cereal products have been reported, ranging from 0.001 to 0.45 μg/g (Honig et al. 1983). Mean 

cyanide concentrations in soybean products have been found to range from 0.07 to 0.3 μg/g, whereas the 

mean cyanide concentration in soybean hulls was 1.24 μg/g (Honig et al. 1983). Due to the lack of data 

on cyanide content in total diet samples, the average daily intake could not be estimated. 

Cyanogen chloride has been measured in drinking water with a concentration ranging between 0.45 and 

0.80 μg/L (Krasner et al. 1989). 

Available monitoring data on thiocyanate are also very limited. No information was found in the 

available literature on major routes of exposure among the general population or on estimates of 

exposure. Because thiocyanate is a major metabolite of cyanide in the body, exposure to cyanide is a 

source of thiocyanate exposure. Thiocyanate occurs naturally in many edible plants. Vegetables in the 

family Brassica contain high levels of thiocyanate with concentrations ranging up to 660 μg/g, whereas 

other commonly consumed vegetables (e.g., spinach, radishes, celery) generally contain thiocyanates at 

concentrations <2 μg/g. Thiocyanate concentrations in milk and other dairy products and in meat have 

been reported to be <1–9.0 and 0.5–0.7 μg/g, respectively (Weuffen et al. 1984). Thiocyanate 

concentrations in coal plant waste waters (Jensen and Tuan 1993) and mining waste waters (Boucabeille 

et al. 1994b) have been found to be 100–1,500 and 300–450 mg/L, respectively. No data were found in 

the available literature on thiocyanate concentrations in surface, ground, or drinking waters. Soils treated 

with rapeseed meal (from the family Brassica) contained thiocyanate at concentrations on the order of 

6 μg/g (Brown et al. 1991). 

It should be noted that the amounts of cyanide or thiocyanate found by chemical analysis are not 

necessarily the amounts that are bioavailable. 
CYANIDE 157 

6. POTENTIAL FOR HUMAN EXPOSURE 

Among the general population, subpopulations with the most likely potential of exposure to cyanide at 

concentrations higher than background levels include active and passive tobacco smokers (EPA 1981e) 

and individuals who are exposed to house fires or other types of building fires (Andrews et al. 1989; 

Bolstad-Johnson 2000). Subpopulations with potential for exposure to cyanides or thiocyanates are 

residents who live near industrial sites releasing these compounds to the environment, residents who live 

near cyanide- or thiocyanate-containing hazardous waste sites, and people who consume foods high in 

cyanogenic glycosides. Fetuses of smoking mothers or mothers exposed to high levels of environmental 

smoke may also be at risk of exposure to relatively high concentrations of cyanide and thiocyanate 

(Bottoms et al. 1982; EPA 1992f; Hauth et al. 1984). For example, mean thiocyanate concentrations of 

88.6 and 32.0 μg/L have been measured in fetal blood of mothers who smoked or were exposed to passive 

smoke, as compared to a mean thiocyanate concentration of 24.3 μg/L in unexposed mothers (Bottoms et 

al. 1982). 

Occupational exposures to cyanide occur primarily through inhalation and, less frequently, through 

dermal absorption. Estimates from the National Occupational Exposure Survey (NOES) conducted by the 

National Institute for Occupational Safety and Health (NIOSH) indicate that over 250,000 workers are 

potentially exposed to cyanide compounds, including cyanogen chloride (NIOSH 1989a). Workers may 

be exposed to cyanides in various occupations, including electroplating, metallurgy, pesticide application, 

firefighting, steel manufacturing, gas works operations, and metal cleaning (EPA 1981e; WHO 2004b). 

The manufacture of industrial inorganic chemicals may be a potential source of occupational exposure to 

cyanogen chloride (NIOSH 1989a). Potential sources of occupational exposure to ammonium 

thiocyanate include the manufacture of electronic computing equipment, research and development 

laboratories, newspaper and other commercial printing, general medical and surgical hospitals, production 

of adhesives and sealants, and the construction and furniture industries (NIOSH 1989a). Potential 

occupational exposures may also occur during the direct application of herbicidal formulations (e.g., 

amitrol-T, a mixture of ammonium thiocyanate and amino-1,2,4-triazole) and from handling, treatment, 

or disposal of thiocyanate-containing wastes from industrial processes (Brown and Morra 1993). 

6.2 RELEASES TO THE ENVIRONMENT 

The Toxics Release Inventory (TRI) data should be used with caution because only certain types of 

facilities are required to report (EPA 2005b). This is not an exhaustive list. Manufacturing and 

processing facilities are required to report information to the TRI only if they employ 10 or more full-time 

employees; if their facility is included in Standard Industrial Classification (SIC) Codes 10 (except 1011, 
CYANIDE 158 

6. POTENTIAL FOR HUMAN EXPOSURE 

1081, and 1094), 12 (except 1241), 20–39, 4911 (limited to facilities that combust coal and/or oil for the 

purpose of generating electricity for distribution in commerce), 4931 (limited to facilities that combust 

coal and/or oil for the purpose of generating electricity for distribution in commerce), 4939 (limited to 

facilities that combust coal and/or oil for the purpose of generating electricity for distribution in 

commerce), 4953 (limited to facilities regulated under RCRA Subtitle C, 42 U.S.C. section 6921 et seq.), 

5169, 5171, and 7389 (limited S.C. section 6921 et seq.), 5169, 5171, and 7389 (limited to facilities 

primarily engaged in solvents recovery services on a contract or fee basis); and if their facility produces, 

imports, or processes ≥25,000 pounds of any TRI chemical or otherwise uses >10,000 pounds of a TRI 

chemical in a calendar year (EPA 2005b). 

6.2.1 Air 

Cyanide emissions into the air have been conservatively estimated at 44 million pounds/year based on 

data obtained during the mid-to-late 1970s. Over 90% of these emissions were attributed to releases from 

automobile exhaust. The second largest source of cyanide emission to the air was reported to be from the 

manufacture of methyl methacrylate, acrylonitrile, and hydrogen cyanide (EPA 1981e). From data 

acquired from the California Air Resources Board (ARB), it is estimated that 1.2 million pounds of 

hydrogen cyanide were released into air from industrial sources (CEPA 1997). Other smaller sources of 

cyanide release include emissions from iron and steel production, coal combustion (EPA 1981e), 

petroleum refineries (EPA 1981e), oil shale retorting processes (Hargis et al. 1986; Sklarew and Hayes 

1984), municipal solid waste incinerators (Carotti and Kaiser 1972; Greim 1990), the combustion of 

acrylonitriles or other nitrogen-containing plastics (Brandt-Rauf et al. 1988; EPA 1981e), cigarette smoke 

(Baker and Proctor 1990; EPA 1981e; Guerin et al. 1987), volatilization from cyanide waste disposed of 

in landfills, and direct release to the atmosphere from certain agricultural pest control activities (EPA 

1981e). In 1976, an estimated 137,000 pounds of cyanide was released in the air from agricultural pest 

control, 18,000–180,000 pounds from incineration, and 13,000–750,000 pounds from cigarette smoke 

(EPA 1981e). The production of coke or other coal carbonization processes also release hydrogen 

cyanide into the atmosphere (Cicerone and Zellner 1983). Release of hydrogen cyanide from cyanidation 

processes used in the extraction of precious metals from their ores was estimated to be 22 tons/year in the 

United States in 1992, or 20,000 tons worldwide (Korte and Coulston 1995). Hydrogen cyanide is also 

released into the atmosphere from natural biogenic processes from higher plants, bacteria, and fungi 

(Cicerone and Zellner 1983; Crutzen and Carmichael 1993; EPA 1981e; Knowles 1988; Mudder and Botz 

2000; WHO 2004b). However, an estimate of the amount of hydrogen cyanide released from natural 

biogenic sources is not available (Cicerone and Zellner 1983; WHO 2004b). Crutzen and Carmichael 
CYANIDE 159 

6. POTENTIAL FOR HUMAN EXPOSURE 

(1993) have recently suggested that biomass burning represents an important source of atmospheric 

hydrogen cyanide. The combined worldwide emissions of hydrogen cyanide and acetonitrile due to 

biomass burning have been estimated to range from 0.5 to 1.7x1012 g of N/year (≈1.1–3.7 billion pounds 

per year) (Crutzen and Andreae 1990). These estimates were based in part on highly uncertain global 

estimates of worldwide amounts of burned fuel and area and, consequently, have a high degree of 

uncertainty. Lobert and Warnatz (1993) have estimated that low molecular weight nitriles, primarily 

hydrogen cyanide and acetonitrile, represent about 4% of the nitrogen balance of biomass fires and 

contribute a major amount to their global atmospheric source. 

The amount of hydrogen cyanide released to the atmosphere in 2003 by U.S. industrial facilities sorted by 

state is given in Table 6-1 (TRI03 2005). According to TRI03 (2005), an estimated total of 1.14 million 

pounds (approximately 517 metric tons) of hydrogen cyanide was discharged into air, amounting to 

approximately 42.2% of the total amount of hydrogen cyanide released into the environment from 

manufacturing and processing facilities in the United States in 2003. The release of cyanide compounds 

(as X+

CN–, where X+=H+ or any group where formal dissociation can occur; for example, KCN or 

Ca(CN)2) into air by U.S. industrial facilities is given in Table 6-2 and sorted by state (TRI03 2005). 

According to the data given in Table 6-2, it is estimated that 0.313 million pounds (approximately 

142 metric tons) of cyanide compounds were released into air in 2003, which amounts to approximately 

4.97% of the total environmental release. The TRI data should be used with caution since only certain 

types of facilities are required to report. This is not an exhaustive list. No information is available in the 

TRI database for other cyanide and thiocyanate compounds in this profile because these compounds are 

not included under SARA, Title III, and therefore, are not among the chemicals that facilities are required 

to report (EPA 1993g, 2001). 

6.2.2 Water 

There are numerous sources that release cyanide into water. Cyanide is released into water from both 

point and nonpoint sources. The major point sources of cyanide released to water are discharges from 

publicly owned treatment works (POTWs), iron and steel production, and organic chemical industries 

(EPA 1981e). Estimates based on data from the mid-to-late 1970s indicate that these sources account for 

≈89% of the estimated 31 million pounds of total cyanide discharged annually to surface waters. Since 

metal finishing and organic chemical industries are estimated to account for 90% of the influent to 

POTWs, they are the dominant sources of both direct and indirect discharge of cyanide to water (EPA 

1981e). The amount of cyanide released to surface water by U.S. industrial facilities that manufactured or 
CYANIDE 160 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-1. Releases to the Environment from Facilities that Produce, Process, or 

Use Hydrogen Cyanidea

Reported amounts released in pounds per yearb 

Total release 

Statec RFd Aire Waterf UIg Landh On-sitej

 Off-sitek On- and off-site 

AK 1 12,477 0 0 0 12,477 0 12,477 

AL 2 5,735 0 0 0 5,735 0 5,735 

AR 1 0 0 0 0 0 0 0 

CA 6 20,719 0 0 0 20,719 0 20,719 

CO 2 8,119 0 0 1 8,120 0 8,120 

DE 1 7,100 960 0 0 8,060 0 8,060 

ID 1 15,000 0 0 0 15,000 0 15,000 

IL 2 8,178 0 0 842 8,178 842 9,020 

IN 2 2,963 0 0 0 2,963 0 2,963 

KY 1 250 0 0 0 250 0 250 

LA 9 64,664 59 0 0 64,723 0 64,723 

MA 1 4,241 0 0 0 4,241 0 4,241 

MI 1 1,155 0 0 0 1,155 0 1,155 

MS 1 28,000 0 0 0 28,000 0 28,000 

MT 2 720 0 0 510 1,230 0 1,230 

NC 1 0 0 0 0 0 0 0 

NH 1 74 0 0 0 74 0 74 

NJ 1 290 0 0 0 290 0 290 

NV 13 154,182 0 0 320 154,502 0 154,502 

OH 2 20,910 0 1,219 0 20,910 1,219 22,129 

OK 1 3,409 0 0 0 3,409 0 3,409 

PA 1 5,402 0 0 0 5,402 0 5,402 

SC 3 31,005 136 0 0 31,141 0 31,141 

TN 4 146,700 0 0 0 146,700 0 146,700 

TX 23 531,144 452 1,554,533 573 2,086,507 195 2,086,702 

UT 1 26,342 0 0 0 26,342 0 26,342 

WA 1 440 110 0 0 550 0 550 
CYANIDE 161 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-1. Releases to the Environment from Facilities that Produce, Process, or 

Use Hydrogen Cyanidea

Reported amounts released in pounds per yearb 

Total release 

Statec RFd Aire Waterf UIg Landh On-sitej

 Off-sitek On- and off-site 

WV 2 40,496 0 0 0 40,496 0 40,496 

Total 87 1,139,715 1,717 1,555,752 2,246 2,697,174 2,256 2,699,430 

a

The TRI data should be used with caution since only certain types of facilities are required to report. This is not an 

exhaustive list. Data are rounded to nearest whole number. b

Data in TRI are maximum amounts released by each facility. c

Post office state abbreviations are used. d

Number of reporting facilities. e

The sum of fugitive and point source releases are included in releases to air by a given facility. f

Surface water discharges, waste water treatment-(metals only), and publicly owned treatment works (POTWs) 

(metal and metal compounds). g

Class I wells, Class II-V wells, and underground injection. h

Resource Conservation and Recovery Act (RCRA) subtitle C landfills; other on-site landfills, land treatment, surface 

impoundments, other land disposal, other landfills. i

Storage only, solidification/stabilization (metals only), other off-site management, transfers to waste broker for 

disposal, unknown 

j

The sum of all releases of the chemical to air, land, water, and underground injection wells. k

Total amount of chemical transferred off-site, including to POTWs.

RF = reporting facilities; UI = underground injection 

Source: TRI03 2005 (Data are from 2003) 
CYANIDE 162 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-2. Releases to the Environment from Facilities that Produce, Process, or 

Use Cyanide Compoundsa

Reported amounts released in pounds per yearb 

Total release 

Statec RFd Aire Waterf UIg Landh Otheri On-sitej

 Off-sitek 

On- and 

off-site 

AK 4 0 0 0 540,718 0 540,718 0 540,718 

AL 6 930 1,569 65 23,000 0 25,499 65 25,564 

AR 3 746 0 0 21,955 0 22,701 0 22,701 

AZ 3 20 0 0 0 119 20 119 139 

CA 15 1,288 533 560 16,501 11 1,821 17,072 18,893 

CO 1 10 0 0 3 0 13 0 13 

CT 6 945 149 0 0 297 1,094 297 1,391 

DE 1 7,100 960 0 0 0 8,060 0 8,060 

FL 4 0 0 0 0 0 0 0 0 

GA 4 36 9 0 261 0 45 261 306 

IA 1 0 0 0 0 0 0 0 0 

ID 1 255 5 0 0 0 260 0 260 

IL 28 5,521 422 0 35 3,587 5,944 3,621 9,565 

IN 14 6,442 13,585 39,006 430,760 0 489,787 6 489,793 

KY 7 1,189 337 0 5 0 1,526 5 1,531 

LA 3 4 65 605,383 4 0 605,456 0 605,456 

MA 4 255 0 0 18 355 255 373 628 

MD 1 168 0 0 0 0 168 0 168 

ME 2 736 0 0 0 0 736 0 736 

MI 15 3,189 6 11,953 12,667 1,325 25,398 3,742 29,140 

MN 5 1,841 0 0 0 0 1,841 0 1,841 

MO 5 487 5 0 5 0 497 0 497 

MS 2 28,000 0 0 0 0 28,000 0 28,000 

MT 2 0 0 0 71,000 0 71,000 0 71,000 

NC 3 250 0 0 0 250 250 250 500 

NH 1 0 47 0 0 0 47 0 47 

NJ 5 11,922 1,312 0 20,400 4 14,220 19,418 33,638 

NV 21 37,473 0 0 1,416,272 1,025 1,453,745 1,025 1,454,770 

NY 10 2,475 270 0 0 0 2,745 0 2,745 

OH 22 14,709 168 450,025 1,133 26,900 464,877 28,058 492,936 

OK 2 500 5 0 5 250 510 250 760 

OR 3 162 5 0 150 0 167 150 317 

PA 8 80,089 17,519 0 4,350 0 97,608 4,350 101,958 

PR 1 250 0 0 0 0 250 0 250 

RI 6 250 250 0 0 746 500 746 1,246 

SC 4 512 0 0 0 7,938 512 7,938 8,450 
CYANIDE 163 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-2. Releases to the Environment from Facilities that Produce, Process, or 

Use Cyanide Compoundsa

Reported amounts released in pounds per yearb 

Total release 

On- and 

Statec RFd Aire Waterf UIg Landh Otheri On-sitej

 Off-sitek off-site 

SD 2 255 500 0 500 0 1,005 250 1,255 

TN 7 2,091 1,135 0 15 0 3,226 15 3,241 

TX 18 80,533 1,725 1,829,872 936 0 1,912,143 923 1,913,066 

UT 4 16,304 1,300 0 177,278 117 194,882 117 194,999 

VA 3 232 190 0 0 8 422 8 430 

WA 3 892 110 0 281 0 1,283 0 1,283 

WI 6 272 0 0 0 0 272 0 272 

WV 2 5,120 9,061 0 221,163 0 14,181 221,163 235,344 

Total 268 313,453 51,243 2,936,864 2,959,415 42,931 5,993,686 310,222 6,303,907 

a

The TRI data should be used with caution since only certain types of facilities are required to report. This is not an 

exhaustive list. Data are rounded to nearest whole number. b

Data in TRI are maximum amounts released by each facility. c

Post office state abbreviations are used. d

Number of reporting facilities. e

The sum of fugitive and point source releases are included in releases to air by a given facility. f

Surface water discharges, waste water treatment-(metals only), and publicly owned treatment works (POTWs) 

(metal and metal compounds). g

Class I wells, Class II-V wells, and underground injection. h

Resource Conservation and Recovery Act (RCRA) subtitle C landfills; other on-site landfills, land treatment, surface 

impoundments, other land disposal, other landfills. i

Storage only, solidification/stabilization (metals only), other off-site management, transfers to waste broker for 

disposal, unknown 

j

The sum of all releases of the chemical to air, land, water, and underground injection wells. k

Total amount of chemical transferred off-site, including to POTWs.

RF = reporting facilities; UI = underground injection 

Source: TRI03 2005 (Data are from 2003) 
CYANIDE 164 

6. POTENTIAL FOR HUMAN EXPOSURE 

processed cyanide compounds ranged from approximately 0 to 150,000 and 1,100 to 1,090,000 pounds, 

respectively (TRI88 1990). These data indicate that the industrial discharge of cyanides into surface 

water and POTWs decreased substantially in 1988 in comparison to the estimated discharge during the 

1970s. 

The amount of hydrogen cyanide and cyanide compounds released to surface water in 2003 by U.S. 

industrial facilities sorted by state is shown in Tables 6-1 and 6-2 (TRI03 2005). According to TRI03 

(2005), estimated totals of 1,717 and 51,200 pounds of hydrogen cyanide and cyanide compounds, 

respectively, were discharged to surface water in 2003. These releases amount to approximately 

0.064 and 0.81% of the total environmental release of hydrogen cyanide and cyanide compounds, 

respectively. Hydrogen cyanide and cyanide compounds were also released through underground 

injection wells at estimated totals of 1,560,000 and 2,940,000 pounds, respectively. These releases 

amount to 57.7 and 46.6% of the total environmental release of hydrogen cyanide and cyanide 

compounds, respectively. The TRI data should be used with caution since only certain facilities are 

required to report. This is not an exhaustive list. No information is available in the TRI database for 

other cyanide and thiocyanate compounds in this profile because these compounds are not included under 

SARA, Title III, and therefore, are not among the chemicals that facilities are required to report (EPA 

1993g, 2001). 

The effluents from the cyanidation process used in the extraction of precious metals from their ores may 

contain high levels of cyanide (Huiatt 1985; Korte and Coulston 1995; Mudder and Botz 2000; Scott 

1985). The total cyanide content of typical tailing pond effluents from gold mill tailing ponds has been 

reported to range from 0.3 to 310 mg/L (EPA 1994c; Scott 1985). Although the contribution from this 

source to the total discharge of cyanide into the environment has been estimated to be negligible on 

average (EPA 1981e), large, short-term releases can occur from the failure of tailing ponds, resulting in 

the introduction of high concentrations of cyanide into local surface waters and subsoils (Fields 2001; 

Mudder and Botz 2000). Normally, these cyanide wastes undergo decontamination through the 

conversion of cyanide to the less toxic cyanate in a chemical oxidation methods commonly referred to as 

alkaline chlorination. In the method, the cyanide wastes are treated with sodium hydroxide or sodium 

hypochlorite. Alkaline chlorination is the most widely used commercial method for treating cyanidecontaining wastes. Depending on the cyanides present, the product will be a sludge or solution, which, 

when sufficient reaction time has been allowed, will, in time, largely be devoid of free cyanide (IRPTC 

1985). Leachates from solid waste disposal sites are point sources of cyanide release to groundwater 

(Myers 1983; Venkataramani et al. 1984). No quantitative estimate of the amount of cyanide entering the 
CYANIDE 165 

6. POTENTIAL FOR HUMAN EXPOSURE 

groundwater from this point source was located. The nonpoint sources of cyanide released to water are 

comprised of agricultural and road runoff and atmospheric fallout and washout. The predominant sources 

of cyanides found in urban runoff samples were reported to be products of gasoline combustion and 

anticaking ingredients in road salts (Cole et al. 1984). It has been estimated that a maximum of 

≈2 million pounds of sodium ferrocyanide, which is used as an anticaking agent in road salts during the 

winter in the northeastern United States, are washed off from roads into streams and storm sewers (EPA 

1981e; Gaffney et al. 1987). 

Thiocyanate is released to water primarily from discharges of industrial waste waters from coal 

processing and extraction of gold and silver (Boucabeille et al. 1994a). Thiocyanate is also found in 

mining waste waters where it results from the reaction of the cyanide anion (CN–

) with sulphur 

(Boucabeille et al. 1994b). Thiocyanate has been detected in surface water samples at one of eight 

hazardous waste sites, and in groundwater samples at five of eight hazardous waste sites where 

thiocyanate has been detected in some environmental medium (HazDat 2005). The HazDat information 

used includes data from both NPL and other Superfund sites. 

6.2.3 Soil 

Estimates of amounts of cyanide released to soil from anthropogenic sources are limited. The largest 

anthropogenic sources of cyanide releases to soil probably result from the disposal of cyanide wastes in 

landfills and the use of cyanide-containing road salts (EPA 1981e; Gaffney et al. 1987). In 77 of 

124 hazardous waste sites in the United States, the median cyanide concentration in subsoil samples was 

0.8 mg/kg (HazDat 2005; WHO 2004b). In the same study, topsoil samples taken from 51 of 91 had 

median cyanide concentrations of 0.4 mg/kg. In the soils of former manufactured gas plant sites, the 

concentrations of cyanide compounds in the United States are below 2,000 mg/kg (Shifrin et al. 1996; 

WHO 2004b). The cyanides in these soils are predominately (97%) in the form of ferrocyanides. 

The amount of hydrogen cyanide and cyanide compounds released to land in 2003 by U.S. industrial 

facilities sorted by state is shown in Tables 6-1 and 6-2 (TRI03 2005). According to TRI03 (2005), an 

estimated total of only 2,250 pounds of hydrogen cyanide was discharged to land from U.S. 

manufacturing or processing facilities in 2003. Conversely, an estimated 2.96 million pounds of cyanide 

compounds were discharged to land in 2003, which amounts to 46.9% of the total release to the 

environment. An estimated 2,260 and 310,000 pounds of hydrogen cyanide and cyanide compound 

wastes were transferred off-site (see Tables 6-1 and 6-2) and may be ultimately disposed of on land. The 
CYANIDE 166 

6. POTENTIAL FOR HUMAN EXPOSURE 

TRI data should be used with caution since only certain facilities are required to report. This is not an 

exhaustive list. No information is available in the TRI database for other cyanide and thiocyanate 

compounds in this profile because these compounds are not included under SARA, Title III, and 

therefore, are not among the chemicals that facilities are required to report (EPA 1993g, 2001). 

Natural biogenic processes of bacteria, fungi, and cyanogenic plants such as sorghum, soybeans, and 

cassava, also release cyanide into the soil (EPA 1978c; Knowles 1988; WHO 1992, 2004). 

Releases of thiocyanate to soil result from anthropogenic and natural sources. Anthropogenic releases 

occur primarily from direct application in herbicidal formulations (e.g., amitrol-T, a mixture of 

ammonium thiocyanate and amino-1,2,4-triazole) and from disposal as byproducts from industrial 

processes. Nonanthropogenic sources include damaged or decaying tissues of plants from the family 

Brassica (e.g., mustard, rape) (Brown and Morra 1993). 

6.3 ENVIRONMENTAL FATE 

6.3.1 Transport and Partitioning 

Because hydrogen cyanide is a gas and has a relatively slow degradation rate in air (see Section 6.3.2), the 

atmosphere will be the ultimate sink for this compound. Almost all of the hydrogen cyanide released to 

the atmosphere remains in the lower altitudes (troposphere); only 2% of tropospheric hydrogen cyanide is 

transferred to the stratosphere (Cicerone and Zellner 1983). Cyanide has the potential to be transported 

over long distances from its emission source. Despite higher water solubility at saturated pressure, the 

removal of hydrogen cyanide by rainwater appears to be a negligible partitioning pathway (Cicerone and 

Zellner 1983). Because hydrogen cyanide is a gas, its removal from air by dry deposition is also likely to 

be negligible. However, metal cyanide particles, particularly water-soluble cyanide particles, are 

expected to be removed from the air by both wet and dry deposition. 

Volatilization and sorption are the two physical processes that contribute to the loss of cyanide from 

water. At pH <9.2, most of the free cyanide in solution should exist as hydrogen cyanide, a volatile 

cyanide form (EPA 1978c). On the basis of Henry's law constant (see Table 4-2) and the volatility 

characteristics associated with various ranges of Henry's law constant (Thomas 1982), volatilization is a 

significant and probably dominant fate process for hydrogen cyanide in surface water (EPA 1992f). The 

most common alkali metal cyanides (e.g., sodium and potassium cyanide) may also be lost from surface 
CYANIDE 167 

6. POTENTIAL FOR HUMAN EXPOSURE 

water primarily through volatilization; whereas, the sparingly soluble metal cyanides such as copper (I) 

cyanide are removed from water predominantly by sedimentation and biodegradation (see 

Section 6.3.2.2) (EPA 1992f). Variations in the volatilization rate are expected because this process is 

affected by several parameters including temperature, pH, wind speed, and cyanide concentration (EPA 

1979). EPA (1979) summarized the unpublished results of a laboratory study that indicated that the 

volatilization half-life of hydrogen cyanide from solutions at concentrations of 25–200 μg/L ranged from 

22 to 110 hours. First-order kinetics were observed. In outdoor experiments with moderate winds, the 

rate of hydrogen cyanide loss increased by a factor of 2–2.5. In a study to evaluate the effect of cyanide 

on biochemical oxidation, there was a 50% loss of 6 ppm (mg/L) cyanide in river water kept in open 

biochemical oxygen demand bottles (without aeration) at pH 7.4 within ≈10 days (Ludzack et al. 1951). 

When the bottles were aerated (rate of aeration not given), 50% loss occurred in only ≈10 hours. The 

kinetics of the rate of loss due to volatilization were not rigorously investigated. The volatilization rate 

was pH-dependent, with the rate faster at a lower pH. Data indicated that cyanide volatilization is a more 

important fate process than cyanide loss due to chemical and biodegradation reactions (see 

Section 6.3.2.2) (Ludzack et al. 1951; Raef et al. 1977a). Because volatilization is not an important fate 

process for cyanide in groundwater, cyanide would be expected to persist for considerably longer periods 

of time in underground aquifers than in surface water. 

Cyanides are sorbed by various natural media, including clays (Cruz et al. 1974), biological solids (Raef 

et al. 1977b), and sediments (EPA. 1979). However, additional data are necessary to assess the 

significance of cyanide sorption to suspended solids and sediments in water. Hydrogen cyanide and the 

alkali metal cyanides are not likely to be strongly sorbed onto sediments and suspended solids because of 

their high water solubilities (see Table 4-2). Soluble metal cyanides may show somewhat stronger 

sorption than hydrogen cyanide, with the extent of sorption increasing with decreasing pH and increasing 

iron oxide, clay, and organic material contents of sediment and suspended solids (EPA 1979). However, 

sorption is probably insignificant even for metal cyanides when compared to volatilization and 

biodegradation (EPA 1979, 1992f). 

There are no data available to indicate that simple metal cyanides and hydrogen cyanide bioconcentrate in 

aquatic organisms (EPA 1979, 1980a, 1985a, 1992f). Bioconcentration factors (BCFs) of 0.73 and 

1.62 can be calculated for hydrogen cyanide, using the equation of Veith et al. (1979) for the BCF of a 

chemical in whole fish (log BCF, 0.85; log Kow, -0.70) and the log Kow values in Table 4-2. Similarly, the 

calculated BCF for sodium cyanide is 0.47. There is some evidence that certain metal cyanide complexes 

bioaccumulate in aquatic organisms. Fish from water with soluble silver and copper cyanide complexes 
CYANIDE 168 

6. POTENTIAL FOR HUMAN EXPOSURE 

were found to have metal cyanides in their tissues at concentrations ranging up to 168 and 304 μg/g, 

respectively (wet or dry weight not specified) (EPA 1979). It is difficult to evaluate the toxicologic 

significance of bioaccumulation of metal cyanide complexes because these compounds are much less 

toxic than soluble hydrogen cyanide, sodium cyanide, or potassium cyanide (EPA 1992f). There is no 

evidence of biomagnification of cyanides in the food chain (EPA 1978c). Accumulation of cyanide in 

food webs is not expected, considering the rapid detoxification of cyanide by most species and the lethal 

effects of large doses of cyanide (EPA 1978c). 

Volatilization of hydrogen cyanide would be a significant loss mechanism for cyanides from soil surfaces 

at a pH <9.2. Cyanides are fairly mobile in soil. Mobility is lowest in soils with low pH and high 

concentrations of free iron oxides, positively charged particles, and clays (e.g., chlorite, kaolin, gibbsite), 

and highest in soils with high pH, high concentrations of free CaCO3 and negatively charged particles, 

and low clay content (EPA 1979). Although cyanide has a low soil sorption capability, it is usually not 

detected in groundwater, probably because of fixation by trace metals through complexation or 

transformation by soil microorganisms (see Section 6.3.2.3) (EPA 1978c). In soils where cyanide levels 

are high enough to be toxic to microorganisms (i.e., landfills, spills), this compound may leach into 

groundwater (EPA 1984a). Also, leaching of cyanide into a shallow aquifer can occur, as demonstrated 

by the high concentration of cyanide (1,200 μg/L) in groundwater sampled from the Biscayne Aquifer in 

Dade County, Florida, which lies below a solid waste site (Myers 1983). 

No information could be found in the available literature on the transport and partitioning of cyanogen 

chloride in the environment, or its partitioning coefficients (Koc, Kow) or Henry's law constants (see 

Table 4-2). Like cyanogen, cyanogen chloride is a highly volatile gas (see Table 4-2). Therefore, it 

would be expected that volatilization from water and soil would be a primary route of environmental 

partitioning for both cyanogen and cyanogen chloride. 

Similarly, little information could be found in the available literature on the environmental transport and 

partitioning of thiocyanate in the environment. At near ambient temperatures (≈30 °C), it appears that 

sorption and volatilization are not significant partitioning processes for thiocyanate in soil, with 

thiocyanate losses due primarily to microbial degradation (see Section 6.3.2.3) (Brown and Morra 1993). 
CYANIDE 169 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.3.2 Transformation and Degradation 

The various cyanide compounds included in this profile undergo a number of different transformation and 

degradation reactions in the environment as discussed in the following sections. The resulting 

environmental transformation products within different media are shown in Table 6-3. 

6.3.2.1 Air 

Most cyanide in the atmosphere exists almost entirely as hydrogen cyanide gas, although small amounts 

of metal cyanides may be present as particulate matter in the air (EPA 1984a). Hydrogen cyanide is very 

resistant to photolysis at wavelengths of normal sunlight (EPA 1979). The most important reaction of 

hydrogen cyanide in air is the reaction with photochemically-generated hydroxyl radicals and subsequent 

rapid oxidation to carbon monoxide (CO) and nitric oxide (NO); photolysis and reaction with ozone are 

not important transformation processes, and reaction with singlet oxygen (O 1

D) is not a significant 

transformation process except at stratospheric altitudes where singlet oxygen is present in significant 

concentrations (Cicerone and Zellner 1983). The rate of hydroxyl radical reaction with hydrogen cyanide 

in the atmosphere depends on the altitude, and the rate of the reaction is at least an order of magnitude 

faster at lower tropospheric altitudes (0–8 km) than at upper tropospheric altitudes (10–12 km) (Cicerone 

and Zellner 1983). Based on a reaction rate constant of 3x10-14

 cm3/(molecule-sec) at 25 °C (Fritz et al. 

1982) and assuming an average hydroxyl radical concentration of 5x105

 molecules/cm3, the residence 

time for the reaction of hydrogen cyanide vapor with hydroxyl radicals in the atmosphere is ≈2 years. 

This value compares well with the atmospheric residence time derived by Cicerone and Zellner (1983) of 

approximately 2.5 years, with a range of 1.3–5.0 years, depending on the hydroxyl radical concentrations 

assumed. Using the equation t1⁄2 = 0.693τ for converting residence time (τ) to half-life (t1⁄2) (Lyman 1982) 

and an estimated atmospheric residence time for hydrogen cyanide of 2–3 years, and assuming first-order 

kinetics for the reaction of hydrogen cyanide with hydroxyl radicals, an atmospheric half-life of 1.4– 

2.9 years can be calculated for hydrogen cyanide. 

Cyanogen is reactive and does not persist in the environment unchanged (EPA 1978c). Cyanogen reacts 

slowly with water to yield hydrogen cyanide and cyanic acid (HOCN) among other products (EPA 1979) 

and this hydrolysis reaction may be a possible atmospheric degradation pathway. Cyanogen has also been 

shown to react with hydroxyl radicals in the gas phase (Atkinson 1989). Based on a rate constant of 

2.5x10-15

 cm3/(molecule-sec) at 27 °C and assuming an average hydroxyl radical concentration of 

5x105

 molecules/cm3, the residence time for the reaction of hydrogen cyanide vapor with hydroxyl 
CYANIDE 170 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-3. Environmental Transformation Products of Cyanide 

Compounds by Medium 

Parent compound Product(s) Comments Reference 

 HCN HOCN + HO2 (unlikely) 

NO + CHO–

 (formed in 

HNC-OH 

intermediate 

Cicerone and Zellner 

1983 

minutes) 

NO + CHO–

 (formed in 

minutes) 

HCN-OH 

intermediate 

Cicerone and Zellner 

1983 

 Cyanogen HCN, cyanic acid 

(NCOH), and other 

compounds 

In the presence of water; 

slow reaction 

EPA 1979 

 HCN NH4 

+

 + HCOO– in 

equilibrium with H2NCHO 

+ H2 

pH dependent 

(pH <1, t1/2=10–1,000 hours) 

EPA 1979 

CN– 

NH4 

+

 + HCOO– 

Metal cyanides 

Alkaline hydrolysis; very 

slow reaction

In the presence of excess 

metals; alkali metal cyanides 

very soluble; alkaline earth 

EPA 1979, 1992f 

CN–

metal cyanides not very 

soluble 

Complex metallocyanides Excess CN–

 in the presence 

>99% HCN 

NH3 + CO2 (NH3 

converted to nitrite and 

nitrate in presence of 

nitrifying bacteria) 

N2 + CO2

of metals; solubilities of 

metallocyanides vary 

pH<7 

Aerobic biotransformation 

 Anaerobic biotransformation 

under denitrification 

conditions 

EPA 1979, 1992f 

EPA 1978c 

Richards and Shieh 1989 

Richards and Shieh 1989 

 HCN/CN–

 salts 

 Cyanogen 

Metallocyanides 

SCN– 

Thiocyanate (SCN–), NH3 

+ CO2, CHOO– 

HCN, cyanic acid 

(NCOH), and other 

compounds 

CN–

 (possibly) 

Isocyanate (OCN–

) 

CO2 + N2 

HCN 

Biotransformation 

Slow reaction at pH 7; 

5.25 hours at pH 8.5 

Photolysis 

Oxidation 

In the presence of strong 

oxidizing agents 

In acidic media 

EPA 1978c 

EPA 1979; 

Munro et al. 1999; 

U.S. Army 1989 

EPA 1979 

EPA 1992f 

EPA 1992f 

EPA 1979 

Air 

Water 
CYANIDE 171 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-3. Environmental Transformation Products of Cyanide 

Compounds by Medium 

Parent compound Product(s) Comments Reference 

Sediment and Soil 

CN– Metallocomplexes Abiotic transformation in the 

presence of metals 

EPA 1978c 

NH3 + CO2 (NH3 

converted to nitrite and 

nitrate in presence of 

nitrifying bacteria) 

Aerobic biotransformation 

(predicted from fate in waste 

water) 

Richards and Shieh 1989 

N2 + CO2 Aerobic biotransformation Richards and Shieh 1989 

under denitrification 

conditions (predicted from 

fate in waste water) 

SCN– COS (possibly; microbial 

degradation pathway not 

known) 

Microbial degradation Brown and Morra 1993 

Waste water/sludge 

CN–

 NH3 + CO2 (NH3 

converted to nitrite and 

Aerobic biotransformation Richards and Shieh 1989 

nitrate in presence of 

nitrifying bacteria) 

N2 + CO2 Anaerobic biotransformation Richards and Shieh 1989 

under denitrification 

conditions 

CN–

/metallocyanides 

(including 

cuprocyanide) 

NH3 + CO2 Microbial degradation in 

mining waste waters 

Boucabeille et al. 1994b 

SCN–

 NH3 + CO2 + SO4

 = Microbial degradation in 

mining waste waters 

Boucabeille et al. 1994a 

COS + NH3 Microbial degradation in 

activated sludge 

Katayama et al. 1993 
CYANIDE 172 

6. POTENTIAL FOR HUMAN EXPOSURE 

radicals in the atmosphere is ≈25 years. Therefore, the reaction of cyanogen with photochemicallyinduced hydroxyl radicals will not play a significant role in the degradation of this compound in air. 

No specific information was found in the available literature on the transformation and degradation of 

cyanogen chloride or thiocyanates in air. However, cyanogen chloride has been shown to undergo slow 

hydrolysis in neutral aqueous solution (rate constant at pH 7 of 6.45x10-5 mol

-1sec-1) (U.S. Army 1989). 

Therefore, hydrolysis of this compound may be a possible atmospheric degradation pathway in air. 

6.3.2.2 Water 

Cyanide occurs most commonly as hydrogen cyanide in water, although it can also occur as the cyanide 

ion, alkali and alkaline earth metal cyanides (potassium cyanide, sodium cyanide, calcium cyanide), 

relatively stable metallocyanide complexes (ferricyanide complex [Fe(CN)6]

-3), moderately stable 

metallocyanide complexes (complex nickel and copper cyanide), or easily decomposable metallocyanide 

complexes (zinc cyanide [Zn(CN)2], cadmium cyanide [Cd(CN)2]). The environmental fate of these 

cyanide compounds varies widely (EPA 1979). 

Oxidation, hydrolysis, and photolysis are the three predominant chemical processes that may cause loss of 

simple cyanides in aquatic media. Certain cyanides are oxidized to isocyanates by strong oxidizing 

agents; the isocyanates may be further hydrolyzed to ammonia and carbon dioxide (EPA 1978c). 

However, it has not yet been determined whether such oxidation and subsequent hydrolysis of isocyanate 

is a significant fate process in natural waters known to contain peroxy radicals (EPA 1992f). 

In water, hydrogen cyanide and cyanide ion exist in equilibrium with their relative concentrations 

primarily dependent on pH and temperature. At pH <8, >93% of the free cyanide in water will exist as 

undissociated hydrogen cyanide (EPA 1978c). Hydrogen cyanide can be hydrolyzed to formamide, 

which is subsequently hydrolyzed to ammonium and formate ions (EPA 1979). However, the relatively 

slow rates of hydrolysis reported for hydrogen cyanide in acidic solution (Krieble and McNally 1929; 

Krieble and Peiker 1933) and of cyanides under alkaline conditions (Wiegand and Tremelling 1972) 

indicate that hydrolysis is not competitive with volatilization and biodegradation for removal of free 

cyanide from ambient waters (EPA 1979). 

The alkali metal cyanides are very soluble in water. As a result, they readily dissociate into their 

respective anions and cations when released into water. Depending on the pH of the water, the resulting 
CYANIDE 173 

6. POTENTIAL FOR HUMAN EXPOSURE 

cyanide ion may then form hydrogen cyanide or react with various metals in natural water. The 

proportion of hydrogen cyanide formed from soluble cyanides increases as the water pH decreases. At 

pH <7, >99% of the cyanide ions in water are converted to hydrogen cyanide (EPA 1978c). As the pH 

increases, cyanide ions in the water may form complex metallocyanides in the presence of excess 

cyanides; however, if metals are prevalent, simple metal cyanides are formed. Unlike water-soluble alkali 

metal cyanides, insoluble metal cyanides are not expected to degrade to hydrogen cyanide (EPA 1979). 

The significance of photolysis in the fate of cyanides in water has not been fully investigated. Hydrogen 

cyanide and cyanide ions in aqueous solution have been found to be very resistant to photolysis by natural 

sunlight, except under heterogeneous photocatalytic conditions (EPA 1979; Frank and Bard 1977). 

Photocatalytic oxidation may not be significant in natural waters, however, because of significant light 

reduction at increasingly greater depths (EPA 1992f). In clear water or at water surfaces, some 

metallocyanides, such as ferrocyanides and ferricyanides, may decompose to the cyanide ion by 

photodissociation and subsequently form hydrogen cyanide. For example, diurnal changes in free 

cyanide concentrations in the drainage from spent precious metal ore heaps were found to maximize 

around mid-day due to the photodissociation of iron and cobalt cyanocomplexes (Johnson et al. 2002). 

Because of adsorption of ferrocyanide onto soil surfaces and sediment of surface waters, and light 

scattering in turbid waters in the field, the rate of free cyanide formation from the photolysis of 

ferrocyanide in runoff and surface water from washout of ferrocyanide in de-icing salt will be slower than 

from laboratory photolysis with clean water (EPA 1979). 

Biodegradation is an important transformation process for cyanide in natural surface waters, and is 

dependent on such factors as cyanide concentrations, pH, temperature, availability of nutrients, and 

acclimation of microbes. However, additional data are needed to assess the relative significance of this 

process in determining the fate of aquatic cyanides (EPA 1979). Although the cyanide ion is toxic to 

microorganisms at concentrations as low as 5–10 mg/L (Klecka et al. 1985; Malaney et al. 1959), 

acclimation increases tolerance to this compound (Raef et al. 1977a). A number of pure cultures of 

microorganisms degrade low concentrations of cyanide under both aerobic and anaerobic conditions 

(EPA 1978c, 1979, 1992f). However, biodegradation data derived from use of a pure culture are not 

strictly relevant to natural waters that contain mixed cultures. Mixed microorganisms in sewage sludge or 

activated sludge acclimated to cyanide also significantly biodegrade concentrations ≤100 mg/L of most 

simple and complex cyanides (Gaudy et al. 1982; Pettet and Mills 1954; Richards and Shieh 1989; 

Shivaraman et al. 1985). In a study to evaluate the effect of the cyanide ion on biochemical oxidation 

conducted in sealed vessels, a 50% loss of cyanide at concentrations ≤6 mg/L in two natural river waters 
CYANIDE 174 

6. POTENTIAL FOR HUMAN EXPOSURE 

occurred at times estimated to range from <10 to 24 days (Ludzack et al. 1951). The rate of loss appeared 

to be linear within this time frame. These data may represent a biodegradation half-life; however, the 

possibility of loss by chemical reaction was not addressed in this study. 

Most of the available information on the mechanisms of biodegradation of cyanides in water comes from 

studies on the evaluation and use of this process as a means of detoxicifying cyanide-containing wastes 

(Akcil and Mudder 2003; EPA 1994c; Raybuck 1992). It is known that there is a natural attentuation of 

the cyanide ion and thiocyanide concentrations in waste waters, for example those obtained gold mill 

tails, that is due the acclimation of indigenous microflora in the tailings (Akcil and Mudder 2003; 

Oudjehani et al. 2002; Zagury et al. 2004). A number of microorganisms have been identified that are 

capable of uptake, conversion, sorption, and/or precipitation of the cyanide ion, cyanate, and thiocyanate, 

including species of the genera, Actinomyces, Alcaligenes, Arthrobacter, Bacillus, Micrococcus, 

Neisseria, Paracoccus, Pseudomonas, and Thiobacillus (Akcil and Mudder 2003). Some of these 

species, for example Pseudomonas, are capable of using the cyanide ion and thiocyanate as the sole 

source of carbon and nitrogen and therefore, are particularly effective at cyanide degradation. In fact, 

Pseudomonas is the basis of commercial applications for degrading the cyanide ion to ammonia and 

carbonate in waste waters generated in mining operations that use the cyanide ion to leach gold and other 

precious metals for low-grade ores (Akcil and Mudder 2003). 

Raybuck (1992) has recently reviewed the role of microbes in cyanide degradation and has categorized 

the microbial enzymes that use the cyanide ion as a substrate according to the following types of 

reactions: substitution/addition, hydrolysis, oxidation, and reduction. Sulfur transferases such as 

rhodanese are involved in substitution reactions that result in the conversion of the cyanide ion to the less 

toxic thiocyanate, whereas pyridoxal phosphate enzymes are involved in substitution/addition reactions 

that result in production of nitrile derivatives of α-amino acids. These organic nitriles may then be 

ultimately degraded via enzyme catalyzed hydrolysis to either the corresponding amino acid and 

ammonia (without formation of the free amide) or the carboxylic acid and ammonia (via formation of the 

free amide). The cyanide hydratase and cyanidase enzymes catalyze the hydrolysis of the cyanide ion to 

formamide or formic acid and ammonia, respectively. A strain of Alcaligenes xylosoxidans subsp. 

denitrificans has been found to effectively hydrolyze the cyanide ion concentrations up to 300 mg/L down 

to very low levels (0.01–0.02 mg/L) and to be resistant to inactivation by chloride, sulfate, iodide, Fe+2, 

Zn+2, or Ni+2 at concentrations of 70 mg/L (Basheer et al. 1992). Thus, these hydrolytic systems are some 

of the most promising for detoxification of cyanide-containing waste waters (Raybuck 1992). A number 

of microbial systems have been identified that are capable of direct oxidation or reduction of the cyanide 
CYANIDE 175 

6. POTENTIAL FOR HUMAN EXPOSURE 

ion. Bacillus pumulus, Pseudomonas fluorescens, and Pseudomonas paucimobili have all been found to 

oxidize the cyanide ion to ammonia and carbon dioxide (Meyers et al. 1993). In an aerobic batch 

bioreactor experiment, Pseudomonas putida was found to significantly degrade 4 mM sodium cyanide 

(cyanide concentration approximately 100 mg/L) to ammonia and carbon dioxide (Chapatwala et al. 

1993). Other evidence indicates that formamide and formate are additional transformation products in 

microbial oxidation of the cyanide ion by this species, inferring that there may be more than one pathway 

of cyanide biotransformation involved (Kunz et al. 1992; White et al. 1988). Several bacterial species 

have been identified that are capable of oxidative degradation of metallocyanides (Silva-Avalos et al. 

1990). The cyanide oxygenase system involved in this process offers a new technology for the treatment 

of metal cyanide wastes (Raybuck 1992). 

The ferrocyanide complex is not easily biodegradable (Belly and Goodhue 1976; Pettet and Mills 1954). 

However, when an aqueous solution of potassium ferrocyanide was seeded with pure culture of 

Pseudomona aeruginosa, or E. coli, or a mixture of the two bacteria, formation of free cyanide was 

observed after a delay period of ≈2 days (Cherryholmes et al. 1985). The rate of free cyanide formation, 

when measured as CN–

, increased with addition of nutrient in water, and a free cyanide concentration 

≤4,000 μg/L was detected at the end of 25 days. It was shown that the free cyanide formation was due to 

biodegradation and not to either photolysis or hydrolysis. The relevance of this study to the fate of 

ferrocyanide complexes in natural water or industrial effluents is difficult to assess because ferrocyanide 

concentrations used in these experiments (3,300 mg/L) are rarely encountered in these media. 

Biodegradation is also a significant transformation process for thiocyanates in natural waters; however, 

additional data are needed to assess the relative importance of this process. Like the cyanide ion, 

thiocyanate is toxic to microorganisms at high concentrations and acclimated cultures have increased 

tolerance to this compound (Boucabeille et al. 1994a). Laboratory studies have shown that at 

concentrations up to at least 1.42 g/L, thiocyanate was completely degraded within 4 days to ammonia 

and sulfate ion (SO4

-2) by an acclimatized co-culture of two bacteria (Acinetobacter johnsonii and 

Pseudomonas diminuta) isolated from sludge from an urban sewage treatment plant (Boucabeille et al. 

1994a). Thiosulfate ion (S2O3

-2) was identified as the intermediate in this degradation pathway. 

Several studies document the biodegradation of mixtures of cyanides and thiocyanate in waste waters 

(e.g., Akcil and Mudder 2003; Boucabeille et al. 1994b; EPA 1994c; Mudder and Whitlock 1984; 

Paruchuri et al. 1990; Shivaraman et al. 1985). Under aerobic conditions, the biodegradation of the 

cyanide ion and thiocyanate initially produces ammonia, which is converted to nitrite and nitrate in the 
CYANIDE 176 

6. POTENTIAL FOR HUMAN EXPOSURE 

presence of nitrifying bacteria, whereas anaerobic biodegradation under denitrification conditions may 

produce nitrogen (Richards and Shieh 1989). Complete biodegradation of simple and metal complexed 

cyanides and thiocyanate from mining waste waters by various bacteria belonging to the families 

Pseudomonadaceae, Vibrioniaceae, and Enterobacteriaceae has recently been reported (Boucabeille et al. 

1994b). Biodegradation of cyanide and thiocyanate resulted in the formation of ammonia, with or 

without accumulation of nitrite and/or nitrate, depending on whether a batch, fed-batch, or continuous 

treatment process was used. Sulphate ions were produced from thiocyanate degradation. Shivaraman et 

al. (1985) reported the uninhibited microbial degradation of thiocyanate and the cyanide ion to ammonia 

by acclimatized mixed cultures at cyanide concentrations up to 22.40±1.34 mg/L, whereas Paruchuri et al. 

(1990) have reported the complete inhibition of microbial degradation of thiocyanate in the presence of 

10 mg/L cyanide ion. 

Cyanogen reacts slowly with water to produce hydrogen cyanide, cyanic acid, and other compounds (EPA 

1979). Cyanogen chloride also hydrolyzes slowly to cyanic acid and hydrochloric acid in water at pH 7, 

with a rate constant of 6.45x10-5 mol

-1sec-1 (U.S. Army 1989). Hydrolysis of cyanogen chloride is more 

rapid under acidic and basic conditions, with rate constants of 2x10-2 and 6–8x102

 mol

-1sec-1 (pH 10), 

respectively (U.S. Army 1989). The half-life of cyanogen chloride at neutral pH ranges between 1 minute 

at 45 °C and 10 hours at 5 °C (Opresko et al. 1998). However, volatilization would be expected to be the 

predominant fate process for both cyanogen chloride and cyanogen in water and, therefore, these 

compounds are not expected to persist in water. 

6.3.2.3 Sediment and Soil 

Analogous to the fate of cyanides in water, it is predicted that the fate of cyanides in soil would be 

dependent on cyanide concentrations, pH, temperature, metal content, concentration of microbes, 

availability of nutrients, and acclimation of microbes. Cyanide may occur as hydrogen cyanide, alkali 

metal salts, or as immobile metallocyanide complexes. In soil, cyanide present at low concentrations 

would biodegrade under aerobic conditions with the initial formation of ammonia, which would be 

converted to nitrite and nitrate in the presence of nitrifying bacteria. Under anaerobic conditions, the 

cyanides ion will denitrify to gaseous nitrogen (Richards and Shieh 1989). Upper limits of 200 and 

2 ppm (mg/kg CN–

), respectively, have been reported for uninhibited aerobic and anaerobic 

biodegradation of cyanide in soil (Fueller 1985); however, these limits have not been confirmed in other 

studies (Thomas and Lester 1993). Cyanide ions in soil are not involved in oxidation-reduction reactions 

but may undergo complexation reactions with metal ions in soil (EPA 1978c). 
CYANIDE 177 

6. POTENTIAL FOR HUMAN EXPOSURE 

No information could be found in the available literature on the transformation of cyanogen or cyanogen 

chloride in soil or sediment. However, because these compounds are highly volatile gases they are not 

expected to persist in soils. Additionally, biotic or abiotic degradation would not be expected to be 

significant fate processes compared to volatilization. 

Although the fate of thiocyanate in soil is largely uncharacterized, there is evidence to suggest that 

thiocyanate is not persistent in soils. Early studies have shown that thiocyanate can undergo both aerobic 

(Betts et al. 1979) and anaerobic microbial degradation (Betts et al. 1979; Stafford and Callely 1969; 

Youatt 1954); however, the degradation pathway has not been defined (Brown and Morra 1993). 

Saturated soils treated with thiocyanate were found to emit carbonyl sulfide (COS) (Minami 1982; 

Minami and Fukushi 1981). Katayama et al. (1992, 1993) have reported the formation of carbonyl sulfide 

from the biodegradation of thiocyanate by pure and mixed cultures of Thiobacillus thioparus. These 

species are ubiquitous in soil (Kelly and Harrison 1989). In a recent laboratory investigation of the fate of 

ionic thiocyanate in six different soils, Brown and Morra (1993) concluded that microbial degradation is 

the primary mechanism for thiocyanate disappearance at or below 30 °C, with carbonyl sulfide proposed 

as a possible hydrolysis product. Loss of thiocyanate at higher temperatures (50–60 °C) did not appear to 

result from microbial degradation; the observed decreases in thiocyanate concentrations of soil extracts 

with incubation time at elevated temperatures were postulated to result primarily from increased sorption 

or increased sorption kinetics, but abiotic catalysis of thiocyanate degradation was also noted as a possible 

cause. 

6.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT 

Reliable evaluation of the potential for human exposure to cyanide depends in part on the reliability of 

supporting analytical data from environmental samples and biological specimens. Concentrations of 

cyanide in unpolluted atmospheres and in pristine surface waters are often so low as to be near the limits 

of current analytical methods. Where levels have been measured in the environment, the values reported 

for cyanide and thiocyanate must be interpreted with caution. Methods for the analysis of cyanide and 

thiocyanate have many interferences (EPA 1978d, 1980e, 1996). In addition, samples containing cyanide 

and/or thiocyanate may not be stable if the samples are not carefully preserved (EPA 1978d, 1980e, 1996; 

Keith 1991; WHO 2004b). In reviewing data on cyanide levels monitored or estimated in the 

environment, it should also be noted that the amount of chemical identified analytically is not necessarily 
CYANIDE 178 

6. POTENTIAL FOR HUMAN EXPOSURE 

equivalent to the amount that is bioavailable (Oudjehani et al. 2002; Zagury et al. 2004). The analytical 

methods available for monitoring cyanide in a variety of environmental media are detailed in Chapter 7. 

6.4.1 Air 

The concentration of hydrogen cyanide in the northern hemisphere's non-urban troposphere ranges from 

160 to 166 ppt (Cicerone and Zellner 1983; Jaramillo et al. 1989). Although ambient monitoring data 

regarding cyanide in air near source areas (e.g., hydrogen cyanide manufacturing industries, coke 

production industries, waste disposal sites) were not located in the available literature, the hydrogen 

cyanide concentration in the vicinity of the source areas would be expected to be higher than the nonurban tropospheric concentration. The semiquantitatively measured hydrogen cyanide concentrations in 

the offgas from shale oil retorting processes ranged from 6 to 39 ppm in one retort at one site; however, 

hydrogen cyanide was not detected in retorts at another site (Sklarew and Hayes 1984). 

Cyanides (reported as cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, calcium cyanide, 

or copper(I) cyanide) have been detected at concentrations (measured as cyanide) between 0.00797 and 

0.032 mg/m3

 in 6 air samples collected at 5 of 464 hazardous waste sites where cyanides have been 

detected in some environmental medium (HazDat 2005). The HazDat information used includes data 

from both NPL and other Superfund sites. No information was found on the detection of cyanogen, 

cyanogen chloride, or thiocyanates in air at any NPL or other Superfund hazardous waste sites (HazDat 

2005). No information could be found in the available literature on the concentrations of cyanogen, 

cyanogen chloride, or thiocyanates in air at other locations in the United States. 

6.4.2 Water 

Cyanide has been detected in waste waters from plating industries at concentrations up to 100 g/L (Chen 

et al. 1994; Grosse 1986); from a textile industry at a maximum concentration of 0.2 mg/L (Rawlings and 

Samfield 1979); in the primary and secondary effluents from a Los Angeles City waste water treatment 

plant at mean concentrations of 29±4 and 10±6 μg/L (0.03 and 0.01 mg/L), respectively (Young 1978); 

and in the final effluent from a Los Angeles County waste water treatment plant at a mean concentration 

of 240 μg/L (0.24 mg/L) (Young 1978). Waste waters from a mining site storage basin were found to 

contain cyanide at concentrations of >10 mg/L as simple cyanides; 20–80 mg/L as combined simple 

cyanides and copper(I) cyanide; 20–190 mg/L as combined simple cyanides, copper(I) cyanide, and 
CYANIDE 179 

6. POTENTIAL FOR HUMAN EXPOSURE 

ferrocyanide; and 300–450 mg/L as thiocyanate (Boucabeille et al. 1994b). Waste waters from gold 

mines have been reported to contain total cyanide and thiocyanate concentrations ranging from 0.5 to 

10 mg/L and from 45 to 75 mg/L, respectively (Mudder and Whitlock 1984). Weak acid dissociable 

(WAD) cyanide was measured in tailing ponds at several Nevada gold mines in 1990; the concentrations 

ranged from 8.4 to 216 mg/L at the discharge pipe and from 7.8 to 11.3 mg/L at the reclaim area (Henny 

et al. 1994). In New York State alone, 47 industries discharged 3,877 pounds of cyanide into streams in 

1982 (Rohmann et al. 1985). Cyanide has also been found in groundwater below landfills and disposal 

sites (Agency for Toxic Substances and Disease Registry 1989a; Myers 1983; Venkataramani et al. 1984). 

A maximum cyanide concentration of 1,200 μg/L (1.2 mg/L) was found in shallow groundwater 

≤3 meters below an inactive drum recycling facility in Miami, Florida (Myers 1983). In another example, 

a maximum cyanide concentration of 52,000 μg/L (52 mg/L) in shallow groundwater (≈3 meters) was 

measured below an inactive detinning plant near Tampa, Florida (Agency for Toxic Substances and 

Disease Registry 1998). Cyanide concentrations were found to range from 0.005 to 14.0 mg/L in the 

leachates from 14 of 43 U.S. landfills with industrial wastes; the "typical" cyanide concentration was 

reported to be 0.008 mg/L (Venkataramani et al. 1984). Data from the Nationwide Urban Runoff 

Program as of 1982 indicate that cyanide was found in urban runoff samples collected in 4 of 15 urban 

areas across the United States: Denver, Colorado; Long Island, New York; Austin Texas; and Bellevue, 

Washington. Overall, cyanide was detected in 16% of the urban runoff samples collected, at 

concentrations ranging from 2 to 33 μg/L (Cole et al. 1984). 

Cyanide concentrations in run-off obtained from an area that had been burned in a 2000 wildfire that 

occurred in Tennessee and North Carolina near the Smokey Mountains National Park averaged 49 μg/L 

(Barber et al. 2003). This is equal to the LC50 for cyanide in rainbow trout and is more than an order 

magnitude greater than the cyanide concentration measured in run-off obtained from unburned areas 

surrounding the wildfire site. Higher cyanide concentrations were reported in run-off from the Cerro 

Grande fire that occurred near Los Alamos, New Mexico in 2000 with an average value of 80 μg/L. 

Based on data obtained from the EPA STORET database, the mean cyanide concentration in 61% of 

surface waters tested in the United States is ≤3.5 μg/L and 35 % of surface waters contained cyanide (as 

CN–

) at concentrations of 3.5–52 μg/L (EPA 1981e). The data also show that 37 of 50 states (74%) have 

locales where cyanide concentrations in ambient water are >3.5 μg/L. Areas with levels >200 μg/L 

include portions of southern California, North Dakota, South Dakota, Iowa, northwest Georgia, western 

New York, and western Pennsylvania (EPA 1981e). It should be noted that these results are applicable 

only to the period from the late 1970s to the early 1980s. Furthermore, the reliability of some of these 
CYANIDE 180 

6. POTENTIAL FOR HUMAN EXPOSURE 

early STORET data may be questionable. Analyses of more recent STORET cyanide data could not be 

found. Cyanide at a concentration >1 μg/L was detected in water from the Great Lakes (Great Lakes 

Water Quality Board 1983). The concentration of cyanide in 104 samples collected during 1980 and 

1981 at various points on the Ohio River and its tributaries was reported to range from <5 to 80 μg/L 

(Ohio River Valley Sanitation Commission 1982). The highest concentration was detected in water from 

Beaver Falls, Pennsylvania. 

A survey of 969 water supply systems in the United States in 1970 found the concentration of cyanide to 

be at or below 0.008 mg/L (EPA 1981e). In 1975, a survey of interstate water supply systems found that 

in 21 of 297 analyses (7.1%), the concentration of cyanide exceeded the maximum concentration limit 

(MCL) of 0.2 mg/L (EPA 1981e). In more recent data from the EPA taken from 1993–1998, only 0.2% 

of public water systems using groundwater exceeded the MCL of 0.2 mg/L (EPA 1999). For public water 

systems using surface water, there were no reported cyanide concentrations in excess of the MCL. In a 

nationwide survey of Canadian water supplies, it was found that in 70 cities, the concentration of cyanide 

was <0.001 mg/L, whereas water samples taken from two cities had a cyanide concentration of 

0.011 mg/L (Meranger and Lo 1992). 

Cyanides (reported as cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, calcium cyanide, 

or copper(I) cyanide) have been detected in surface water samples at 243 of 464 hazardous waste sites 

(HazDat 2005). Cyanide concentrations in 70 surface water (lake, streams, ponds, etc.) samples ranged 

between 0.0012 and 120 mg/L with mean and median values of 2.67 and 0.0385 mg/L, respectively. 

Cyanides have also been detected in groundwater samples at 120 of the 464 hazardous waste sites. 

Cyanide concentrations in 19 groundwater samples taken from private and public wells ranged between 

0.00002 and 300 mg/L with mean and median values of 16.0 and 0.0292 mg/L, respectively (HazDat 

2005). Cyanides have also been identified in leachate samples at 43 of 406 hazardous waste sites at 

concentrations ranging from 0.0017 to 400 mg/L (HazDat 1996). The HazDat information used includes 

data from both NPL and other Superfund sites. 

Cyanogen chloride is formed in drinking water from the reaction of humic substances with chloramine 

used during chlorination (Jacangelo et al. 1989; Ohya and Kanno 1987). In a mid-1970s EPA survey, 

cyanogen chloride was detected in drinking water from 8 of 10 U.S. cities (Fielding and Packham 1977). 

No information could be found in the available literature on the release of cyanogen to water. No 

information was found on detections of cyanogen or cyanogen chloride in surface water or groundwater at 

any NPL or other Superfund hazardous waste sites (HazDat 2005). 
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6. POTENTIAL FOR HUMAN EXPOSURE 

Cyanogen chloride is formed in drinking water due to reaction of humic substances with chloramine 

formed during chlorination (Ohya and Kanno 1987). It has been reported that the concentration of 

cyanogen chloride in drinking water is most influenced by the final disinfectant. The use of chloramine 

as a final disinfectant produces levels of cyanogen chloride that are 4–15 times higher than levels 

produced when chlorine is used (Jacangelo et al. 1989; Krasner et al. 1989). Cyanogen chloride was 

qualitatively detected during a 1975 survey of Cincinnati, Ohio drinking water (Kopfler et al. 1977). A 

10-city survey that was conducted as part of the 1974 EPA National Organics Reconnaissance Survey 

revealed that cyanogen chloride was present in 8 of 10 drinking water supplies analyzed (no quantitative 

concentration values given) (Bedding et al. 1982). In a 1988 survey of 35 water utilities, the quarterly 

median cyanogen chloride concentrations in drinking water ranged from 0.45 to 0.80 μg/L (Krasner et al. 

1989). 

No information could be found in the available literature on the levels of thiocyanate in ground, surface, 

or drinking water. Thiocyanate is found in concentrations ranging from 100 to 1,500 mg/L in coal plant 

waste waters (Ganczarczyk 1979; Jensen and Tuan 1993), and from 300 to 450 mg/L in mining (gold 

extraction) waste waters (Boucabeille et al. 1994b). 

6.4.3 Sediment and Soil 

Limited information was found in the available literature on concentrations of cyanides in soil or 

sediments at several hazardous waste sites; however, no information could be found for cyanogen or 

cyanogen chloride. Maximum total cyanide concentrations in soil, subsoil, and sediments at an inactive 

detinning plant located near Tampa, Florida, were measured at 1.5, 19, and 0.87 μg/L, respectively 

(Agency for Toxic Substances and Disease Registry 1998). At the Greenwood Chemical Site in 

Albemarle, Virginia, a maximum concentration of total cyanides of 2,870 mg/kg soil was measured in 

1989 along with a maximum concentration of 84.0 mg/kg in sediments obtained from abandoned waste 

lagoons (Agency for Toxic Substances and Disease Registry 1999a). The maximum total cyanide 

concentrations in soil samples taken from the Byron Salvage Yard NPL site and neighboring Dirk Farm 

waste disposal site were measured at 133 ppm and between 1 and 835 ppm, respectively (Agency for 

Toxic Substances and Disease Registry 1999b). In general, though, the highly volatile gases hydrogen 

cyanide, cyanogen, and cyanogen chloride (see Table 4-2) would not be expected to be present in 

sediment or soil in any appreciable amounts. Also, degradation by microorganisms in soil can convert 
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6. POTENTIAL FOR HUMAN EXPOSURE 

cyanide to carbon dioxide, ammonia, and other nitrogen compounds that will rapidly volatilize from soils 

(CEPA 1997). 

Cyanides (reported as cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, calcium cyanide, 

or copper(I) cyanide) have been detected at 225 of 464 hazardous waste sites (HazDat 2005). Cyanide 

concentrations in 60 topsoil (<3 inches depth) samples ranged between 0.0022 and 18,000 mg/kg, with 

mean and median values of 1,017 and 4.02 mg/kg, respectively. Cyanide concentrations in 91 subsurface 

soil (>3 inches depth) samples ranged between 0.00024 to 32,300 mg/kg, with mean and median values of 

813 and 15.4 mg/kg, respectively. Cyanides were also detected at 118 of 464 hazardous waste sites where 

cyanides have been detected in some environmental medium (HazDat 2005). Cyanide concentrations in 

40 sediment samples (lakes, streams, ponds, etc.) ranged between 0.00006 and 30,700 mg/kg, with mean 

and median values of 777 and 1.15 mg/kg, respectively. The HazDat information used includes data from 

both NPL and other Superfund sites. 

Cyanogen has been detected in soil samples taken from one hazardous waste site at a concentration of 

0.063 ppm (HazDat 2005). Measurements of cyanogen chloride in soil samples at two hazardous waste 

sites have been conducted; however, concentrations of cyanogens chloride were not reported (HazDat 

2005). The HazDat information used includes data from both NPL and other Superfund sites. No other 

information could be found in the available literature on the concentration of cyanogen or cyanogen 

chloride in soil. 

Monitoring data on thiocyanate concentrations in soils are scarce. Concentrations of thiocyanate in soils 

amended with defatted seed meal of Brassica napus L. (rapeseed) were reported to be on the order of 

6 μg/g (Brown et al. 1991). Thiocyanate has been detected in soil samples collected at three of 

eight hazardous waste sites, and in sediment samples at three of eight hazardous waste sites where 

thiocyanate has been detected in some medium (HazDat 2005). The HazDat information used includes 

data from both NPL and other Superfund sites. No information could be found in the available literature 

on thiocyanate concentrations in sediments. 

6.4.4 Other Environmental Media 

The primary cyanide source in food is cyanogenic glycosides. Plants containing cyanogenic glycosides 

can produce hydrogen cyanide by acid hydrolysis or by the action of the enzyme β-glucosidase (EPA 

1980a, 1981e; Jones 1998; Seigler 1991). Hydrogen cyanide release can occur either during maceration, 
CYANIDE 183 

6. POTENTIAL FOR HUMAN EXPOSURE 

which activates the intracellular β-glucosidase, or in the gut by the action of β-glucosidase produced by 

microflora. The level of activity of β-glucosidase in the gut depends on the bacterial composition and the 

pH level (WHO 1992, 2004). There are approximately 60 known cyanogenic glycosides, which differ in 

their bioavailability (Seigler 1991). For example, cyanide production from the ingestion of seeds 

containing prunasin does not occur unless the seeds have been crushed. The potential toxicity of 

cyanogenic plants depends on their ability to release hydrogen cyanide during preparation or digestion at 

concentrations high enough to be of concern for human health (WHO 1992, 2004). 

Over 2,650 plant species can produce hydrogen cyanide (Seigler 1991; Swain et al. 1992). These include 

edible plants such as almonds, pits from stone fruits (e.g., apricots, peaches, plums, cherries), sorghum, 

cassava, soybeans, spinach, lima beans, sweet potatoes, maize, millet, sugarcane, and bamboo shoots 

(EPA 1981e). The cyanogenic glycoside content of a foodstuff is usually expressed as the amount of 

cyanide released by acid hydrolysis; glycoside concentrations are rarely reported (WHO 1992). 

Cyanide levels measured in some foods are as follows: cereal grains and their products, 0.001–0.45 μg/g; 

soy protein products, 0.07–0.3 μg/g; and lima beans, 0.1–3 mg/g (EPA 1978c; Honig et al. 1983). The 

cyanide equivalent of total cyanogenic content (i.e., cyanogenic glycosides, cyanohydrins, and hydrogen 

cyanide) of cassava root has been reported to range from 91 to 1,515 mg/kg hydrogen cyanide (86– 

1,458 μg/g CN–

) dry weight (d/w) (O'Brien et al. 1992). Cassava is the major starchy food for more than 

300 million people in many tropical countries of the world, and many cultivars are toxic (Seigler 1991). 

Effective processing can reduce the amount of total cyanogen in fresh cassava roots to significantly lower 

levels in foods ready for consumption (Mlingi et al. 1993; O'Brien et al. 1992). For example, the mean 

cyanide content in garri (a flour product of grated, pressed, and fermented cassava root pulp) from a city 

market in Nigeria ranged from 10.6 to 22.1 μg/g dry weight (d/w) (Ukhun and Dibie 1989). A somewhat 

wider distribution of results was obtained in another recent evaluation of commercial garri from three 

main garri-producing Nigerian communities (Aletor 1993). The mean total cyanide content (glucosidic 

plus non-glucosidic) of 38.8% of all samples (n=108) ranged from 0 to 10 mg/kg hydrogen cyanide (0– 

9.6 μg/g CN–

), whereas 40.7, 12.9, and 7.4% of the samples had mean total cyanide contents of 10–20, 

20–30, and 30–40 mg/kg hydrogen cyanide (9.6–19, 19–29, and 29–39 μg/g CN–

), respectively. The 

mean cyanide content of domestic samples of “sweet” to “bitter” cassava food products in Cameroon was 

reported to range from 18.6 to 94.9 mg/kg hydrogen cyanide (17.9–91.4 μg/g CN–

) d/w for a dried 

cassava flour, and from 0.0 to 0.9 mg/kg hydrogen cyanide (0.0–0.9 μg/g CN–

) d/w for a cassava paste 

(O'Brien et al. 1992). Improper processing of cassava roots may result in maintenance of cyanogenic 

content of cassava food products at levels that are toxic (Mlingi et al. 1992, 1993; O'Brien et al. 1992). 
CYANIDE 184 

6. POTENTIAL FOR HUMAN EXPOSURE 

Cassava is a starch staple, but it is low in protein (Gomez et al. 1988). Low protein intake results in a 

decrease in available sulfur for conversion of cyanide to thiocyanate (Mlingi et al. 1993; Tylleskar et al. 

1992). Hydrogen cyanide concentrations in sorghum leaves have been reported to range from 

approximately 200 to 1,300 ppm (192–1,250 μg/g CN–

) wet weight (w/w), with higher concentrations 

observed in early growth stages and at lower levels of phosphorus fertilization (Chand et al. 1992). 

In apricot pits, the cyanide concentration may vary from 8.9 to 217 mg/100 g (89–2,170 μg/g) w/w, 

depending on the type of cultivar, season, and geographic area (Lasch and El Shawa 1981). Swain et al. 

(1992) reported a mean cyanide concentration in black cherry (Prunus serotina Ehrh.) fruits somewhat 

greater than 3 μmol/seed at maturity, which is equivalent to a mean cyanide content of 78 μg/seed; 

insufficient information was provided to allow conversion of these results to weight per weight (w:w) 

units. In a recent laboratory study, Voldrich and Kyzlink (1992) reported cyanide concentrations in 

canned unpitted fruits (peaches, apricots, plums, and cherries) ranging from 0 to 4 mg/kg (μg/g) w/w, 

depending on the glycoside content of the raw fruits and the conditions of heat processing. These authors 

noted that the observed cyanide levels were not negligible relative to an allowable daily intake (ADI) 

value for cyanide of 0.05 mg/kg body weight. An adult (70 kg body weight) could consume 

approximately 1 kg of canned fruits with a cyanide content of 4 mg/kg without exceeding this ADI value; 

however, a safe portion for a child (15 kg body weight) would be only about 180 grams (12 mg/kg). The 

analysis of 233 samples of commercially available and homemade stone-fruit juices showed that pitted 

fruit juices had lower cyanide concentrations than unpitted or partially pitted fruit juices, indicating that 

the pits are the primary sources of cyanides in these juices (Stadelmann 1976). For example, the 

hydrogen cyanide content of a home-made mixed cherry juice from pitted fruits was 5.3 mg/L, compared 

to 23.5 mg/L in a cherry juice containing 100% crushed pits. This study also reported the following 

levels (median concentrations in mg/L) of hydrogen cyanide in commercial fruit juices: cherry, 4.6; 

apricot, 2.2; prune, 1.9; and peach, 2.9. Stadelmann (1976) recommended that the maximum hydrogen 

cyanide content allowed in fruit juices should be set at a level of 5 mg/L. 

Cyanide can also be present in foodstuffs as residues from cyanide fumigation (EPA 1981e). Human 

exposure to naturally occurring cyanide in foods in the United States is expected to be low compared to 

certain populations in the Third World that subsist on cassava and similar crops (EPA 1981e). 

Edible plants such as kale, cabbage, radishes, broccoli, brussels sprouts, cauliflower, collards, mustard 

greens, turnips, and kohlrabi contain glucosinolates, are hydrolysed by the endogenous enzyme 

myrosinase to produce toxic products, including thiocyanate (Abukutsa et al. 1993; Bible and Chong 
CYANIDE 185 

6. POTENTIAL FOR HUMAN EXPOSURE 

1975; Bible et al. 1980; Carlson et al. 1985, 1987; Olea and Parras 1992; Olea-Serano et al. 1988). 

Vegetables from the Brassica family (e.g., cabbages, kohlrabi, kale) contain high levels of thiocyanate 

ranging from 5 to 660 μg/g w/w (Weuffen et al. 1984). Kale leaves have been reported to contain 

concentrations of potassium thiocyanate at harvest ranging from 447 to 5,067 ppm (μg/g) d/w (equivalent 

to thiocyanate concentrations of 267–3,035 μg/g d/w) depending on the fertilizer nitrogen source 

(Abukutsa et al. 1993). Other commonly consumed vegetables (e.g., lettuce, spinach, radishes) have been 

found to contain thiocyanate at concentrations ranging from approximately 0.1–5.0 μg/g w/w, with 

concentrations usually <2.0 μg/g w/w (Weuffen et al. 1984). Milk and other dairy products have been 

reported to contain thiocyanate at concentrations ranging from <1 to 9.0 μg/g, whereas concentrations in 

meat products have been reported to range from only 0.5 to 0.7 μg/g (Weuffen et al. 1984). 

Laetrile (amygdalin), a drug formerly used in clinical trials for the treatment of cancer (Khandekar and 

Edelman 1979); sodium nitroprusside, a drug used to reduce high blood pressure (Aitken et al. 1977; 

Vesey et al. 1976); and a series of commercially important, simple, aliphatic nitriles (e.g., acetonitrile, 

propionitrile, acrylonitrile, n-butyronitrile, maleonitrile, succinonitrile) (Willhite and Smith 1981) release 

cyanide upon metabolism. These drugs and industrial chemicals have been associated with human 

exposure to cyanide and have caused serious poisoning and, in some cases, death. 

Reported levels of cyanide in tobacco smoke are quite variable. Cyanide levels in mainstream (inhaled) 

smoke from U.S. commercial cigarettes have been reported to range from 10 to 400 μg per cigarette, with 

the ratio of cyanide concentration in sidestream smoke to mainstream smoke ranging from 0.006 to 

0.27 per cigarette (Chepiga et al. 2000; EPA 1981e). In studies that have included non-U.S. commercial 

cigarettes, hydrogen cyanide concentrations in mainstream and sidestream smoke ranging from 280 to 

550 μg/cigarette and from 53 to 111 μg/cigarette, respectively, have been reported; sidestream/ 

mainstream ratios of hydrogen cyanide concentrations ranged from 0.06 to 0.50 (Baker and Proctor 1990; 

Guerin et al. 1987). 

Cyanides have been detected in automobile exhaust. The average emission rate was 11–14 mg/mile for 

cars not equipped with catalytic converters and 1 mg/mile for cars with catalytic converters operating 

under optimum conditions. Cars with malfunctioning catalytic converters may emit as much or more 

hydrogen cyanide than cars without such equipment (EPA 1981e). 
CYANIDE 186 

6. POTENTIAL FOR HUMAN EXPOSURE 

6.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE 

The general population may be exposed to cyanide from inhaling air and ingesting food and drinking 

water contaminated with it. Since most of the cyanide in the air will be present as hydrogen cyanide (see 

Section 6.3.2.1), the primary inhalation exposure to cyanide will occur from hydrogen cyanide. The 

concentration of hydrogen cyanide in the air of non-urban areas is ≈160–166 ppt (see Section 6.4.1). 

Based on an atmospheric hydrogen cyanide concentration of 170 ppt (0.191 mg/m3

) and an average daily 

inhalation volume of 20 m3

, the inhalation exposure of the general U.S. non-urban, nonsmoking 

population to hydrogen cyanide is estimated to be 3.8 μg/day. In drinking water, cyanide may be present 

as cyanogen chloride (see Section 6.4.2). In 1988, the quarterly median cyanogen chloride concentration 

in drinking water from 35 U.S. water utilities ranged from 0.45 to 0.8 μg/L (0.19–0.3 μg/L cyanide) 

(Krasner et al. 1989). Based on a daily drinking water consumption of 2 L for a 70-kg adult, the daily 

intake of cyanogen chloride is estimated to be 0.9–1.6 μg, which is equivalent to 0.4–0.7 μg of hydrogen 

cyanide. The concentration of cyanide in drinking water in the United States in 1970 was <0.008 mg/L 

(EPA 1981e). In more recent data obtained from water supply systems in Canada, the concentration of 

cyanide was below 0.001 mg/L in 70 cities with two cities reporting concentrations of 0.011 mg/L 

(Meranger and Lo 1992). Using the range of cyanide concentrations given in the Canadian study (0.001– 

0.011 mg/L) as representative of the general population in the United States and assuming a daily water 

consumption of 2 L for a 70-kg adult, the daily intake of cyanide is estimated to be 0.002–0.22 mg. EPA 

has established an MCL of 0.2 mg/L for cyanide in drinking water (see Chapter 8), which is equivalent to 

a daily intake of 0.4 mg, based on a daily drinking water consumption rate of 2 L for a 70-kg adult (EPA 

1991a). Estimates of the cyanide concentration in the total diet of a U.S. adult were not located in the 

available literature. Therefore, no estimate of daily cyanide intake from food can be made. In the United 

States, human exposure to cyanide from foods in which it occurs naturally is expected to be low, but is 

likely to exceed cyanide intake from inhalation of air and ingestion of drinking water (CEPA 1997; EPA 

1981e). The EPA has established tolerances for hydrogen cyanide in various foods ranging from 25 to 

250 ppm (EPA 1975b) and from 5 to 25 ppm (see Chapter 8). Poitrast et al. (1988) have estimated an 

overall allowable daily intake of 0.6 mg for cyanide, incorporating an uncertainty factor of 100–1,000 to 

ensure that the potential for an infant receiving a toxic dose of cyanide from breast milk is quite low. 

The dietary cyanide intake of Tukanoan Indians in northwest Amazonia who rely heavily on high (>70% 

of all foods) cyanide-containing varieties of cassava was estimated to be >20 mg/day (Dufour 1988). Yet, 

Dufour (1988) did not find physical disorders in Tukanoan Indians attributable to high cassava diets, in 

contrast to observations related to cassava-consuming populations in Africa. One reason that has been 
CYANIDE 187 

6. POTENTIAL FOR HUMAN EXPOSURE 

suggested is that the cassava processing techniques of the Tukanoans are very sophisticated and very 

effective in reducing the cyanide concentration in the crop. Indeed, it has been shown in several studies 

of cassava processing techniques used in Africa that the level of hydrogen cyanide can be effectively and 

reliably reduced by allowing sufficient time for the hydrolysis of cyanogenic glucosides and evaporation 

of hydrogen cyanide (Ojo and Dean 2002; Onabolu et al. 2002). Another reason that may account for the 

observed differences in toxicity among different populations is that the variety of cassava may differ 

between geographical areas (Rosling 1988). When outbreaks of acute cyanide intoxications do occur in 

African populations that have been found to result from incomplete processing of cassava, resulting in 

highly elevated cyanide levels in combination with chronic dietary protein malnutrition (WHO 2004b). 

This occurred when, due to a food shortage, the lengthy sun drying normally used to remove cyanogenic 

glucosides was replaced by repeated pounding and drying to obtain flour for consumption in 1 day 

(Mlingi et al. 1992, 1993; Tylleskar et al. 1992). 

The primary route of exposure to thiocyanates for the general population appears to be from ingestion of 

foods in which thiocyanate occurs naturally (e.g., cabbage, kale, spinach, kohlrabi). Estimates of the 

thiocyanate concentration in the total diet of an adult in the United States were not located in the available 

literature; however, these would be expected to be quite low. Exposure to cyanide also is a source of 

thiocyanate exposure because thiocyanate is a major metabolite of cyanide in the human body. 

Occupational exposures to cyanide are expected to occur primarily through inhalation and, less 

frequently, through skin absorption. Preliminary data from the NOES conducted by NIOSH from 1980 to 

1983 estimated that the number of workers potentially exposed to cyanide compounds in the United 

States in 1981–1983 are as follows (NIOSH 1989a): cyanide, 367; hydrogen cyanide, 4,005; sodium 

cyanide, 66,493; potassium cyanide, 64,244; potassium silver cyanide, 3,215; calcium cyanide, 3,606; 

copper (I) cyanide, 22,339; ammonium thiocyanate, 90,599; and cyanogen chloride, 1,393. Thiocyanate 

and cyanogen were not included in the NOES (NIOSH 1989a). These numbers do not include workers 

potentially exposed to trade-name compounds that contain cyanides or thiocyanates. Workers in various 

occupations may be exposed to cyanide compounds. People possibly exposed to cyanide include workers 

involved in electroplating, metallurgy, cyanotype printing, pesticide application, firefighting, steel 

manufacturing, and gas works operations; workers involved in the manufacture of cyanides, adiponitrile 

and other simple, aliphatic nitriles, methyl methacrylate, cyanuric acid, dyes, pharmaceuticals, or 

chelating agents; and people who work in tanneries, blacksmithing, metal cleaning, and photoengraving 

or photography industries (EPA 1981e; Lucas 1992; WHO 2004b; Willhite and Smith 1981). Workers in 

the oil shale retorting industry may be exposed to cyanide because the offgas from the retorting process 
CYANIDE 188 

6. POTENTIAL FOR HUMAN EXPOSURE 

contains hydrogen cyanide (see Section 6.2.1). There is a reported case of the fatal poisoning of three 

trawler crew members as they entered a refrigerated compartment containing spoiled fish in which 

cyanide, in addition to methane and hydrogen sulfide, have been implicated in their deaths (Cherian and 

Richmond 2000). Medical and emergency personnel (e.g., police and firefighters) who may be involved 

in resuscitation efforts or removal of gastric contents of postmortem victims of cyanide poisoning are 

potentially exposed to higher levels of cyanide (Andrews et al. 1989; Bolstad-Johnson et al. 2000; Nolte 

and Dasgupta 1996). Workers involved in large-scale processing of cassava have been shown to have 

thiocyanate levels in urine that are 2.2–2.6 times the levels found in individuals who regularly consume 

cassava products (Okafor et al. 2002). The increased thiocyanate levels in cassava processors are due to 

inhalation of hydrogen cyanide that is discharged to air during the processing of cassava. The 

manufacture of industrial inorganic chemicals may be a significant potential source of occupational 

exposure to cyanogen chloride (NIOSH 1989a). Potential sources of occupational exposure to 

ammonium thiocyanate include the manufacture of electronic computing equipment, research and 

development laboratories, newspaper and other commercial printing, general medical and surgical 

hospitals, production of adhesives and sealants, and the construction and furniture industries (NIOSH 

1989a). 

In a survey of the plating facility of a national airline conducted by NIOSH in December 1981, the 

concentrations of hydrogen cyanide in three work areas ranged from 0.001 to 0.004 mg/m3

 (0.0009– 

0.004 ppm) (NIOSH 1982). The cyanide concentrations in four work areas in a plating facility of an 

electrical and electronic company in Waynesboro, Virginia, ranged from 0.07 mg/m3

 (0.07 ppm hydrogen 

cyanide) in a salt pot room to 4.3 mg/m3

 (4.0 ppm hydrogen cyanide) beside a stripping tank (NIOSH 

1976). Similarly, the concentration of cyanide in the breathing zone air of workers in a plating facility in 

Galion, Ohio, was 1.7 mg/m3

 (1.6 ppm hydrogen cyanide) (NIOSH 1978). In a NIOSH survey of a 

university art department foundry, hydrogen cyanide was detected in the smoke produced during pouring 

and knockout of castings at a concentration of approximately 4 ppm; hydrogen cyanide was not detected 

in personal breathing zone samples taken during knockout of castings (Lucas and Salisbury 1992). These 

levels are all below the NIOSH recommended ceiling limit of 4.7 ppm (NIOSH 1992). 

Levels of cyanide and its metabolite thiocyanate in blood serum and plasma, urine, and saliva have been 

used as indicators of cyanide exposure in humans, particularly in workers at risk of occupational 

exposures, in smokers or nonsmokers exposed to sidestream or environmental tobacco smoke, in 

populations exposed to high dietary levels of cyanide, and in other populations with potentially high 

exposures (see Section 6.7). The correlation between increased cyanide exposure and urinary thiocyanate 
CYANIDE 189 

6. POTENTIAL FOR HUMAN EXPOSURE 

levels was demonstrated in workers exposed to 6.4–10.3 ppm cyanide in air (El Ghawabi et al. 1975). In 

another study, blood cyanide concentrations were found to vary from 0.54 to 28.4 μg/100 mL in workers 

exposed to approximately 0.2–0.8 ppm cyanide in air, and from 0.0 to 14.0 μg/100 mL in control workers 

(Chandra et al. 1988). Similar elevations in urinary thiocyanate levels were observed, with concentrations 

for exposed workers and controls ranging from 0.05 to 2.80 and from 0.02 to 0.88 mg/mL, respectively. 

A study of tissue distributions of cyanide in five victims of acute cyanide poisoning found that cyanide 

concentrations are highest in blood (Zhang et al. 2005). Blood had the highest concentration of cyanide 

in all the victims, ranging between 0.65 and 30.6 μg/mL. Normalizing cyanide concentrations in liver, 

kidney, brain, and urine samples to cyanide concentrations in blood, it was found that liver had the next 

highest concentrations of cyanide, with S/B ratios ranging from 0.24 to 0.35. 

The results of several studies that have shown elevated cyanide or thiocyanate concentrations in body 

fluids of smokers are summarized in Table 6-4. In general, these results indicate that serum cyanide 

levels (Cardeal et al. 1993; Symington et al. 1987; Tsuge et al. 2000) and plasma, serum, and saliva 

thiocyanate levels (Banerjee and Muthu 1994; Jarvis 1989; Maliszewski and Bass 1955; Pre and Vassy 

1992, 1993; Tsuge et al. 2000; Waage et al. 1992; Yamanaka et al. 1991) could distinguish smokers from 

nonsmokers and/or light smokers. Pre and Vassy (1992) found that plasma thiocyanate was an indicator 

of smoking status that was not sensitive to light or passive smoking. However, inhaling smokers were 

easily distinguished from noninhaling smokers. The authors concluded that a plasma thiocyanate 

concentration below 20 μmol/L (1,200 μg/L) indicated that passive smoking was very unlikely, whereas 

concentrations above 80–85 μmol/L (4,600–4,900 μg/L) were a reliable indication of an active inhalation 

of smoke. Yamanaka et al. (1991) found a correlation between the number of cigarettes smoked per day 

and the thiocyanate levels in plasma and saliva; however, in apparent contrast to results obtained by 

Maliszewski and Bass (1955), thiocyanate concentrations in urine of smokers and nonsmokers were not 

found to be significantly different. 

Data on elevated levels of thiocyanate in body fluids resulting from consumption of cyanide-containing 

foods come primarily from populations in tropical regions that may consume large quantities of 

improperly processed cyanogenic plants such as cassava (WHO 2004b). Among four populations in 

Africa known to be exposed to high levels of dietary cyanide because of incomplete processing of cassava 

during drought periods, urinary thiocyanate concentrations (mean±SE) ranged from 350±39 to 

1,120±75 μmol/L (20±2–65±4 mg/L), compared to urinary thiocyanate levels in the normal population of 

<100 μmol/L (5.8 μg/L) (Mlingi et al. 1992, 1993; Tylleskar et al. 1992). The mean plasma thiocyanate 
CYANIDE 190 

6. POTENTIAL FOR HUMAN EXPOSURE 

Table 6-4. Cyanide and Thiocyanate Concentrations (μg/mL)a in Smokers and 

Nonsmokers 

Plasma/Blood Serum Saliva Urine 

Compound Sb

 NSb S NS S NS S NS Reference 

Cyanide 

2.11 0.78 Cardeal et al. 

(1.42– (0.44– 1993c 

3.67) 1.15) 

6.8 

(1.3–19.4) 

2.9 

(0.0–11.7) 

Symington et 

al. 1987c,d 

0.27 0.17 0.66 0.38 Tsuge et al. 

(0.14– 

0.41)e (0.11– 

0.25)e (0.13– 2.07)e (0.05– 1.20)e 2000 

Thiocyanate 

232 

(10) 

92 

(9) 

Banerjee and 

Muthu 1994f 

7.1 2.9 142 76 9.0 5.8 Jarvis 1989g 

7.1 2.0 75.7 20.3 12.3 2.1 Maliszewski 

(6.2–8.6) (1.2–2.8) (48.4– (9.71– (7.8– (1.1–3.9) and Bass 1955c 

112.2) 28.7) 17.2) 

8.7h 

(4.4– 

1.8i 

(0.5–4.4) 

Pré and Vassy 

1992f 

21.5) 

3.3j 

(1.0–4.6) 

6.6 

(1.5) 

1.2 

(0.3) 

Pré and Vassy 

1993f 

111.2 

(1.7– 

290)e 

33.5 

(6.3–94)e 1,655 (270– 

2,940)e 

542 

(13– 

1,630)e 

Tsuge et al. 

2000 

(<0.05– 

0.35) 

(<0.05– 

0.08) 

Waage et al. 

1992f,k 

2.1 3.7 88 33 18 19 Yamanaka et 

al. 1991k,l 

a

Values are means; values in parentheses are ranges or standard deviations b

S = smoker; NS = nonsmoker c

No statistics reported d

As cited in Cardeal et al. 1993 e

Values are expressed as μM; values in parentheses are ranges. f

Results significantly different

g

Results not significantly different h

Inhaling smokers i

Nonsmokers including passive smokers 

j

Noninhaling smokers k

Values estimated from graphical presentation of data l

All results, except urine, are significantly different. 
CYANIDE 191 

6. POTENTIAL FOR HUMAN EXPOSURE 

concentration in one of these populations was 335±12 μmol/L (19±1 μg/L), compared to 28±4 μmol/L 

(1.6±0.2 μg/L) in a control population (Mlingi et al. 1992). Elevated mean serum thiocyanate 

concentrations (11±3 μg/L compared to reference values of 0.5–4 μg/L) were observed in only one of two 

populations in which this biomarker was measured (Tylleskar et al. 1992, 1994). There was no apparent 

explanation for this difference. 

High serum thiocyanate concentrations (>180 μmol/L) have been found in Tukanoan Indians on 

traditional diets. However, the levels of residual cyanide appear to be tolerated well (Dufour 1988). 

6.6 EXPOSURES OF CHILDREN 

This section focuses on exposures from conception to maturity at 18 years in humans. Differences from 

adults in susceptibility to hazardous substances are discussed in Section 3.7, Children’s Susceptibility. 

Children are not small adults. A child’s exposure may differ from an adult’s exposure in many ways. 

Children drink more fluids, eat more food, breathe more air per kilogram of body weight, and have a 

larger skin surface in proportion to their body volume. A child’s diet often differs from that of adults. 

The developing human’s source of nutrition changes with age: from placental nourishment to breast milk 

or formula to the diet of older children who eat more of certain types of foods than adults. A child’s 

behavior and lifestyle also influence exposure. Children crawl on the floor, put things in their mouths, 

sometimes eat inappropriate things (such as dirt or paint chips), and spend more time outdoors. Children 

also are closer to the ground, and they do not use the judgment of adults to avoid hazards (NRC 1993). 

Information on exposures of cyanide to children living in the United States is mainly limited to studies on 

side-stream smoke. These studies show that this is an important route of exposure to cyanide for children 

in households with a resident smoker. Chen et al. (1990) found that serum thiocyanate concentrations of 

18-month-old infants heavily exposed to environmental tobacco smoke (>20 cigarettes a day smoked in 

the home) were significantly higher than those of unexposed infants (p<0.05). Mean concentrations 

(±standard deviation [SD]) in these respective groups were 36.2±14.88 μmol/L (2.1±0.9 μg/mL) and 

27.7±10.7 μmol/L (1.6±0.6 μg/mL). Positive correlations between fetal umbilical serum thiocyanate 

levels and serum thiocyanate levels of smoking mothers (Bottoms et al. 1982; Hauth et al. 1984) and 

mothers exposed to environmental tobacco smoke in the home (Bottoms et al. 1982) have been reported. 

Hauth et al. (1984) found that the mean serum thiocyanate concentration (95 μmol/L; 5.5 μg/mL) was 

significantly higher (p<0.001) in smokers than in passive smokers (35.9 μmol/L; 2.1 μg/mL) or 
CYANIDE 192 

6. POTENTIAL FOR HUMAN EXPOSURE 

nonsmokers (32.3 μmol/L; 1.9 μg/mL). Similarly, the mean umbilical thiocyanate concentration in the 

newborn infants of smoking mothers (72 μmol/L; 4.8 μg/mL) was significantly higher than those in 

newborn infants of passive smokers (26 μmol/L; 1.5 μg/mL) and nonsmokers (23 μmol/L; 1.3 μg/mL). In 

contrast, Bottoms et al. (1982) found that among newborn infants of nonsmoking mothers, fetal umbilical 

thiocyanate concentrations increased with passive smoking in the home (p<0.05). 

For children without exposures to side-steam smoke, their main cyanide exposures are expected to be 

similar to those noted for the general population in Section 6.5 in air and water. Estimates of the cyanide 

concentration in the total diet of children in the United States were not located in the available literature. 

Therefore, no estimate of daily cyanide intake from food can be made. However, in the United States, 

exposure of children to cyanide from foods in which it occurs naturally is expected to be low, but, as 

noted for Section 6.5 for the general population, it is likely to exceed cyanide intake from inhalation of air 

and ingestion of drinking water (EPA 1981e). Based on a concentration of cyanide in U.S. and Canadian 

drinking water of 0.001–0.011 mg/L, the daily intake of cyanide in children is estimated to be 0.001– 

0.011 mg, assuming a daily consumption of 1 L of water (EPA 1981e; Meranger and Lo 1992). For 

cyanide as cyanogen chloride, the daily intake is estimated to be 0.5–0.8 μg, which is equivalent to 0.2– 

0.4 μg of hydrogen cyanide. This estimate is based on the quarterly median cyanogen chloride 

concentration in drinking water from 35 U.S. water utilities ranged from 0.45 to 0.8 μg/L (0.19–0.3 μg/L 

cyanide) (Krasner et al. 1989) and the daily consumption of 1 L of drinking water. 

Accidental cyanide poisonings in children are rare and are usually associated with exposures to 

combustion products in smoke (Riordan et al. 2002). Poisonings have been reported for ingestion of 

apricot kernels or seeds or candy made from apricot kernels. Because of their lower body weight, 

children tend to be more susceptible to consumption of apricot kernels than adults, with 10 or more seeds 

being fatal to a child (WHO 2004b). 

6.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES 

Among the general population, subpopulations with the most likely potential for exposure to cyanide and 

thiocyanate include active and passive smokers (EPA 1981e) and people who are exposed to house or 

other building fires (Andrews et al. 1989; Ballantyne 1987a; Bolstad-Johnson et al. 2000). Other 

subpopulations with potentially high cyanide or thiocyanate exposures are residents who live near 

industrial sites releasing cyanides or thiocyanates into the environment, residents who live near cyanideor thiocyanate-containing hazardous waste sites, and people who consume foods high in cyanogenic 
CYANIDE 193 

6. POTENTIAL FOR HUMAN EXPOSURE 

glycosides. The fetuses of pregnant women who smoke or who are exposed to high levels of 

environmental smoke (i.e., passive smokers) may be subjected to potentially high exposures of cyanide 

and thiocyanate (Bottoms et al. 1982; EPA 1992f; Hauth et al. 1984). Workers involved in electroplating, 

metallurgy, pesticide application, firefighting, gas works operations, tanning, blacksmithing, metal 

cleaning, photoengraving, photography, cyanotype printing, the manufacture of steel, cyanides, 

adiponitrile and other nitriles, methyl methacrylate, cyanuric acid, dyes, pharmaceuticals, or chelating 

agents have the potential to be occupationally exposed to higher concentrations of cyanide than the 

general population (EPA 1981e; NIOSH 1989a). Workers in the following industries may also be 

exposed to higher concentrations of thiocyanate than the general population: manufacture of electronic 

computing equipment, research and development laboratories, newspaper and other commercial printing, 

general medical or surgical hospitals, production of adhesives and sealants, pesticide application, building 

and furniture construction, and handling, treatment, or disposal of thiocyanate-containing wastes from 

industrial processes (Brown and Morra 1993; NIOSH 1989a; WHO 2004b). Two additional groups of 

people who may be at greater risk for cyanide exposure are those who are exposed to cyanide but are 

unable to smell the chemical (EPA 1987a) and patients with motor neuron disease (see Section 3.10). 

Data related to the levels of cyanide or thiocyanate exposure in several of these population groups have 

been presented in Section 6.5. No data were found related to the levels of cyanide or thiocyanate 

exposure in cassava eaters in the United States. Also, no data were located in the available literature 

related to the levels of cyanide and thiocyanate exposure of people who live near industrial sites releasing 

cyanides or thiocyanates to the environment, or near hazardous waste sites. Cyanides (reported as 

cyanide, hydrogen cyanide, sodium cyanide, potassium cyanide, calcium cyanide, or copper (I) cyanide) 

have been detected in air, surface and groundwater, and soil samples at NPL hazardous waste sites; 

cyanogen and cyanogen chloride have been detected in soil samples at NPL hazardous waste sites; and 

thiocyanates have been detected in surface and groundwater, and soil samples at NPL sites (see 

Section 6.2) (HazDat 2005). There is a need for reliable data on the levels at which these substances are 

found in various media at these sites in order to estimate potential exposures of people living near 

hazardous waste sites. 

6.8 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the 

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of cyanide is available. Where adequate information is not 
CYANIDE 194 

6. POTENTIAL FOR HUMAN EXPOSURE 

available, ATSDR, in conjunction with 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 cyanide. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will be 

evaluated and prioritized, and a substance-specific research agenda will be proposed. 

6.8.1 Identification of Data Needs 

Physical and Chemical Properties. As reported in Section 4.2, most of the relevant physical and 

chemical properties of cyanide compounds are known. Except for soil partition (Koc) coefficient, data for 

the physical and chemical properties of hydrogen cyanide are available to estimate its environmental fate. 

Additional data are needed to estimate the environmental fate of the other cyanides covered in this profile. 

Although qualitative information is available, quantitative data are needed for the solubility of calcium 

cyanide in water. Octanol/water partition coefficient (Kow) data are needed for cyanogen chloride. 

Certain physical parameters, such as Kow and Koc, are not available nor are they useful for predicting the 

environmental fate and transport of the ionic cyanide compounds. These partition coefficients are 

generally used to assess the partitioning of neutral organic compounds between organic matter and water 

and are not good at describing the varying ionic or complexation interactions of ionic compounds, such as 

the simple and metal complexed cyanides and thiocyanate, with water, aquatic biota, soil, or sediments. 

Production, Import/Export, Use, Release, and Disposal. According to the Emergency Planning 

and Community Right-to-Know Act of 1986, 42 U.S.C. Section 11023, industries are required to submit 

substance release and off-site transfer information to the EPA. The TRI, which contains this information 

for 2003, became available in May of 2005. This database is updated yearly and should provide a list of 

industrial production facilities and emissions. 

Knowledge of a chemical's production volume is important because it may indicate the magnitude of 

environmental contamination and human exposure. Data regarding the production, trend, use pattern, and 

disposal of commercially significant cyanide compounds are available (CMR 2001; Curry 1992; Homan 

1987; HSDB 2004; Sittig 1980; SRI 2005; TRI03 2005). It is known that the import and export of 
CYANIDE 195 

6. POTENTIAL FOR HUMAN EXPOSURE 

hydrogen cyanide is insignificant compared to its production; however, except for potassium, sodium and 

calcium cyanide salts, recent import and export data for other individual cyanide compounds are difficult 

to obtain (USDOC 2004). There are some less recent data regarding the release of cyanides in air (EPA 

1981e; TRI88 1990) but, except for hydrogen cyanide (TRI03 2005), more recent quantitative data 

regarding the release of individual cyanide compounds in air, water, and particularly soil and sediment are 

unavailable and would be useful for assessing current human exposures to cyanides. 

Cyanide is naturally present in many foods high in cyanogenic glycosides (EPA 1978c, 1981e; Honig et 

al. 1983; Jones 1998). No information was located in the available literature to indicate that cyanide 

enters foods during processing or that elevated cyanide concentrations are present in any consumer 

products. The two most likely sources of general population exposure to cyanide include people who 

inhale cigarette smoke (EPA 1981e) or individuals who are exposed to a house or other type of building 

fire (Andrews et al. 1989; Ballantyne 1987a; Bolstad-Johnson et al. 2000). There are EPA regulations 

regarding the disposal of cyanide wastes or OSHA and NIOSH regulations regarding the levels of 

hydrogen cyanide in workplaces (see Chapter 8). Data is available on chemical and biological processes 

for degrading cyanide in leachate and waste water generated during the extraction of gold and other 

precious metals from low grade ore (Akcil and Mudder 2003; EPA 1994c). Additional research is needed 

on improved methods of pollution prevention and biodegradation to reduce or eliminate releases of 

cyanide compounds to the environment from industrial processes. 

Environmental Fate. The environmental fate of hydrogen cyanide gas in air is well studied 

(Cicerone and Zellner 1983; Fritz et al. 1982); however, it would be useful if the role of particulate 

cyanides (e.g., sodium cyanide, potassium cyanide) in determining the fate of total cyanides in the air was 

known. Given that hydrogen cyanide occurs in the atmosphere from both natural and anthropogenic 

processes (Cicerone and Zellner 1983; Crutzen and Andreae 1990; Crutzen and Carmichael 1993; EPA 

1981e; Knowles 1988; Lobert and Warnatz 1993), it would be useful if an estimate were available for the 

contribution of anthropogenic processes to the overall hydrogen cyanide burden in the atmosphere. It is 

generally known that volatilization and biodegradation will be important processes for the loss of 

cyanides in water (EPA 1978c, 1979; Ludzack et al. 1951; Raef et al. 1977a), but no experimental or 

estimated values for the half-life of cyanides in ambient water are available. No comprehensive data 

regarding the role of sorption in determining the fate of cyanides in water are available. It is generally 

known that volatilization from soil surfaces and biodegradation play significant roles in the loss of 

cyanides in soil (EPA 1978c), but no quantitative data regarding the half-life of cyanides in ambient soil 

are available. Additional data on the relative importance of volatilization and biodegradation in 
CYANIDE 196 

6. POTENTIAL FOR HUMAN EXPOSURE 

determining the fate of cyanides in soils are needed. The elucidation of the role of cyanide complexation 

by metals in soil and sediment in controlling the fate of cyanide would be useful. 

Both cyanogen and cyanogen chloride are highly volatile gases, indicating that volatilization would be the 

major transport pathway for these compounds from surface water and soils. Cyanogen is reactive and 

does not persist in the environment unchanged (EPA 1979). It also has been reported to react slowly with 

water to yield hydrogen cyanide and cyanic acid, among other products (EPA 1979), and this hydrolysis 

reaction may be a possible degradation pathway. Likewise, cyanogen chloride has also been shown 

undergo slow hydrolysis at neutral pH to form cyanic acid and hydrogen chloride (U.S. Army 1989). 

Additional information on the environmental fate of cyanogen and cyanogen chloride is needed. 

There is almost no available information on the environmental transport and partitioning of thiocyanate in 

the environment. At ambient temperatures, it appears that sorption and volatilization are not significant 

partitioning processes for thiocyanate in soil, with thiocyanate losses due primarily to microbial 

degradation (Brown and Morra 1993); however, additional research is needed in this area. Although 

biodegradation is a significant transformation process for thiocyanate in water, additional data are needed 

on the relative importance of this process in determining the fate of thiocyanates in natural water systems. 

Bioavailability from Environmental Media. Cyanide is known to be absorbed following 

inhalation, oral, and dermal contact (Gosselin et al. 1984; Rieders 1971). The environmental factors that 

may influence the bioavailability of cyanide from contaminated air, water, soil, or plant material have not 

been studied. Since cyanides are not strongly sorbed to soil and sediments (EPA 1979), the role of 

sorption may not be significant in determining the bioavailability of cyanides from different soils or 

waters. The bioavailability of cyanide from an environmental medium is expected to increase if the 

cyanide is present in water-soluble forms, such as ions or soluble complexes. The pH of a medium may 

also be significant in determining the bioavailability because hydrogen cyanide gas may be released as the 

pH of the medium decreases (EPA 1978c, 1979). Data delineating the factors affecting the bioavailability 

of cyanide compounds from soil and other environmental media need further development, since the 

absorption studies discussed in Section 3.4.1 have been performed with the pure chemical. 

The factors that may influence the bioavailability of thiocyanate from various foods and other 

environmental media have not been investigated. There is no data need at this time because exposure to 

thiocyanate from environmental media is expected to be low. 
CYANIDE 197 

6. POTENTIAL FOR HUMAN EXPOSURE 

Food Chain Bioaccumulation. Simple cyanide compounds do not bioconcentrate in fish (EPA 

1979, 1985a). There is evidence suggesting that the bioconcentration of cyanide metal complexes in fish 

(EPA 1979). Therefore, it would be useful to determine the bioconcentration potential for cyanide in fish 

from water exposed to less toxic and water-soluble cyanide complexes. There is no indication of 

biomagnification of cyanides in aquatic and terrestrial food chains (EPA 1978c). Because of the high 

toxicity of cyanides at high doses and rapid metabolism at low doses, biomagnification of cyanide in 

animals seems unlikely. 

No information could be found in the available literature on the potential of thiocyanates for 

bioconcentration or biomagnification in the food web. In the absence of this information, data would be 

useful to determine the potential for thiocyanate to bioconcentrate and/or biomagnify in a food chain. 

Exposure Levels in Environmental Media. Reliable monitoring data for the levels of cyanide in 

contaminated media at hazardous waste sites are needed so that the information obtained on levels of 

cyanide in the environment can be used in combination with the known body burden of cyanide to assess 

the potential risk of adverse health effects in populations living in the vicinity of hazardous waste sites. 

Data exist regarding the levels of cyanide in air and drinking water, and these data have been used to 

estimate human exposure. The concentration of hydrogen cyanide in the air of non-urban areas is ≈160– 

166 ppt (Cicerone and Zellner 1983; Jaramillo et al. 1989) and the inhalation exposure of the general U.S. 

non-urban, nonsmoking population to hydrogen cyanide was estimated to be 3.8 μg/day. The chlorination 

of public drinking water supplies may result in the formation of cyanogen chloride (Jacangelo et al. 1989; 

Ohya and Kanno 1987). In 1988, the quarterly median cyanogen chloride concentration in drinking water 

from 35 U.S. water utilities ranged from 0.45 to 0.8 μg/L (Krasner et al. 1989). Based on a daily drinking 

water consumption of 2 L for a 70-kg adult, the daily intake of cyanogen chloride is estimated to be 0.9– 

1.6 μg. These data are sufficient to estimate human exposure from air and drinking water, although 

continued monitoring data in these environmental media would be useful. Cyanide and thiocyanate 

concentrations in certain foods are known (Abukutsa et al. 1993; EPA 1978c, 1981e; Honig et al. 1983; 

Pre and Vassy 1992); however, a data need exists to estimate the dietary exposures for the general 

population to cyanide and thiocyanate from food sources. It will also be useful to develop data that would 

clearly establish whether cyanides or thiocyanates pose acute or chronic exposure hazards for residents in 

the vicinity of hazardous waste sites. This information should include data on background concentrations 

in all media to which a resident might be exposed. 
CYANIDE 198 

6. POTENTIAL FOR HUMAN EXPOSURE 

Information on the consumption of cassava in the United States could not be located in the available 

literature. Therefore, an assessment of cassava consumption in the United States would be needed before 

recommending a need for data relating to exposure levels of cyanide in cassava consumers. 

Exposure Levels in Humans. The levels of cyanide and thiocyanate in various human tissues and 

body fluids of both control and occupationally exposed groups and of smokers and nonsmokers are 

available (see Sections 3.4.4, 3.8.1, and 6.5). Although no specific data need exists regarding levels of 

cyanide and thiocyanate in human biological samples, continued monitoring data are recommended in 

order to assess current human exposure. Data are available that describe the levels of these chemicals in 

humans consuming foods containing cyanogenic materials (WHO 2004b). These data are mainly limited 

to cyanide exposures that result from the consumption of cassava (Dufour 1988; Mlingi et al. 1992; Ojo 

and Dean 2002; Okafor et al. 2002; Onabolu et al. 2002; Tylleskar et al. 1992, 1994). 

This information is necessary for assessing the need to conduct health studies on these populations. 

Exposures of Children. Data regarding the exposure of children to side-stream (second-hand) 

cigarette smoke are available (Bottoms et al. 1982; Chen et al. 1990; Hauth et al. 1984). There are no 

comprehensive data on the cyanide or thiocyanate content of total diet samples in the United States, so it 

is not possible to estimate the average daily intake from foods. This is a data need for both children and 

adult exposures. 

Data on exposures of children to cyanides and thiocyanates in the vicinity of hazardous waste sites would 

be useful to clearly establish whether cyanides or thiocyanates pose acute or chronic exposure hazards to 

children living near these sites. This information should include data on background concentrations in all 

media. 

Child health data needs relating to susceptibility are discussed in Section 3.12.2, Identification of Data 

Needs: Children’s Susceptibility. 

Exposure Registries. No exposure registries for cyanide were located. This substance is not 

currently one of the compounds for which a sub-registry 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 
CYANIDE 199 

6. POTENTIAL FOR HUMAN EXPOSURE 

the epidemiological research needed to assess adverse health outcomes that may be related to exposure to 

this substance. 

6.8.2 Ongoing Studies 

No new or ongoing studies of release, environmental fate and transport, levels monitored in the 

environment, or human exposures were identified for cyanide or cyanide compounds in the Federal 

Research in Progress (FEDRIP 2005) database. 
CYANIDE 200 

6. POTENTIAL FOR HUMAN EXPOSURE 

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CYANIDE 201 

7. ANALYTICAL METHODS 

The purpose of this chapter is to describe the analytical methods that are available for detecting, 

measuring, and/or monitoring cyanide, its metabolites, and other biomarkers of exposure and effect to 

cyanide. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to 

identify well-established methods that are used as the standard methods of analysis. Many of the 

analytical methods used for environmental samples are the methods approved by federal agencies and 

organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). Other 

methods presented in this chapter are those that are approved by groups such as the Association of 

Official Analytical Chemists (AOAC) and the American Public Health Association (APHA). 

Additionally, analytical methods are included that modify previously used methods to obtain lower 

detection limits and/or to improve accuracy and precision. 

7.1 BIOLOGICAL MATERIALS 

Humans may be exposed to cyanide from dietary, industrial, environmental, and other sources. Inhalation 

of tobacco smoke is an important source of cyanide, and exposure may occur from smoke due to fires. 

After absorption, cyanide is rapidly distributed in the body through blood. Some of the common methods 

available for determining cyanide in biological media are reported in Table 7-1. Since cyanide forms 

volatile hydrogen cyanide gas, tissue sampling techniques, storage, and cyanide analysis must be done 

with caution. The choice of tissues and the factors influencing measured cyanide concentrations are also 

important (Ballantyne 1983c, 1987a). 

The determination of cyanide in body fluids requires the separation of cyanide from thiocyanate, usually 

by distillation of cyanides or microdiffusion into an absorber solution. The cyanide is measured 

spectrophotometrically after a colorimetric reaction involving the cyanide ion and chloramines-T plus 

pyridine-pyrazolone, p-benzoquinone, or p-phenylene diamine (see Table 7-1). Detection limits are in the 

low to mid ppb range (μg/L) (Cruz-Landeira et al. 2000; Ganjeloo et al. 1980; Laforge et al. 1994). Most 

of these techniques are time-consuming, and some lack specificity or sensitivity. Cyanide in blood is 

almost exclusively localized to the erythrocytes, whereas thiocyanate is confined to plasma (Lundquist 

and Sorbo 1989); thus, some researchers recommend analysis of erythrocytes (McMillan and Svoboda 

1982; Sano et al. 1992). Some interferences can be mitigated. For example, sodium thiosulfate, a 
CYANIDE 202 

7. ANALYTICAL METHODS 

Table 7-1. Analytical Methods for Determining Cyanide in Biological Samples 

Sample 

Sample detection Percent 

matrix Preparation method Analytical method limit recovery Reference 

Blood Separation in a 

microdiffusion cell; 

treatment of absorber 

solution with chloramine 

T-phosphate and 

pyridine-pyrazolone 

reagent 

Blood Separation in a 

microdiffusion cell; 

treatment of absorber 

solution with 

p-benzoquinone 

Plasma Deproteinization with 

trichloroacetic acid; 

bromination of 

supernatant and 

treatment with pyridinep-phenylene diamine 

Erythrocyte Sample purged; 

suspension absorption of hydrogen 

cyanide in sodium 

hydroxide; conversion 

of thiocyanate to 

cyanide by potassium 

permanganate oxidation 

Blood cells Separation of cells by 

centrifugation; 

extraction; derivitization 

Blood Lysis of blood; 

extraction; derivatization 

NDA and taurine 

Blood Acidification of sample 

in a sealed vial 

Blood Acidification of sample; 

incubation with 

chloramine-T in sealed 

vial 

Blood Acidification of sample 

containing K13C15N in a 

sealed vial; microdiffusion to NDA 

derivatization solution 

Blood Separation by diffusion; 

color development 

Spectrophotometry 

(total cyanide) 

Spectrofluorometry 

(total cyanide) 

Spectrophotometry 

(thiocyanatecyanide 

determination) 

Spectrophotometry 

(thiocyanatecyanide 

determination) 

HPLC with 

fluorescence 

detection 

Capillary 

electrophoresis with 

fluorescence 

detection 

Headspace 

GC/NPD 

Headspace 

GC/ECD 

HPLC-MS 

Spectrophotometry 

0.1 ppm No data Morgan and 

Way 1980 

0.025 ppm No data Ganjeloo et al. 

1980 

0.07 ppm 96 (thio- Pettigrew and 

cyanate) Fell 1972 

No data 93–97 McMillan and 

Svoboda 1982 

2 ng/mL 83 Sano et al. 

1992 

0.1 ng/mL No data Chinaka et al. 

2001 

0.3 μg/mL No data Levin et al. 

1990 

100 μg/L No data Odoul et al. 

1994 

5 ng/mL 88.0 Tracqui et al. 

(100 ng/mL); 2002 

85.7 

(500 ng/mL) 

0.07 μg/mL No data Laforge et al. 

1994 
CYANIDE 203 

7. ANALYTICAL METHODS 

Table 7-1. Analytical Methods for Determining Cyanide in Biological Samples 

Sample 

Sample detection Percent 

matrix Preparation method Analytical method limit recovery Reference 

Blood Incubation of acidified 

sample 

Blood Separation in a 

microdiffusion cell; 

absorption in 

methemoglobin solution 

Blood Add K13C15N to blood 

sample; acidify with 

phosphoric acid and 

incubate at 60 °C for 15 

minutes 

Blood and Treatment of HCN 

liver released from sample 

digestion with lead 

acetate and absorption 

with NaOH 

Blood and Separation in a Conway 

urine microdiffusion cell; 

treatment of absorber 

solution with 

naphthalene-2,3­

dialdehyde and taurine 

Plasma and Sample is acidified with 

urine HCl and extracted on a 

mixed cation exchange 

column; analyte is 

eluted from column, 

lyophilized, and 

derivatized by reaction 

with 30% MSTFA in 

hexane 

Urine Dilution of sample; 

bromination and 

treatment with pyridinep-phenylenediamine 

Urine Sample acidified and 

purged; absorbed and 

reacted in 

hydroxycobalamine 

solution 

GC/NPD 1 ng/mL No data Seto et al. 1993 

Spectrophotometric 0.4 μg/mL 80 Tomoda and 

(free cyanide Hashimoto 

determination) 1991 

GC/MS 0.008 μg/mL 98 Dumas et al. 

2005 

Specific ion 5 μg/L 100–109 Egekeze and 

electrode (total (whole blood, Oehme 1979 

cyanide) 0.3–130 ppb) 

Spectrophotofluoro- 0.8 ppb 66–82.6 at Sano et al. 

metric 0.0013– 1989 

0.13 ppm 

(blood); 75.6– 

82 at 0.0013– 

0.13 ppm 

(urine) 

GC/MS 25 ng/mL 100% Logue et al. 

(2-aminothiazoline- (plasma); 2005 

4-carboxylic acid) 84% (urine) 

Spectrophotometric 0.07 ppm 88 Pettigrew and

(thiocyanate- (thiocyanate Fell 1972 

cyanide at 0.6 ppm) 

determination)

Spectrophotometry 28 ng/mL 50 Cruz-Landeira 

(total cyanide) et al. 2000 
CYANIDE 204 

7. ANALYTICAL METHODS 

Table 7-1. Analytical Methods for Determining Cyanide in Biological Samples 

Sample 

Sample detection Percent 

matrix Preparation method Analytical method limit recovery Reference 

Saliva Derivatization HPLC/UV 2 ng 95–99 Liu and Yun 

(thiocyanate) (instrumental) 1993 

ECD = electron capture detector; GC = gas chromatography; GC/MS = gas chromatography/mass spectrometry; 

HCN = hydrogen cyanide; HPLC = high performance liquid chromatography; HPLC-MS = high performance liquid 

chromatography coupled with mass spectrometric detector; MSTFA = N-methyl-N-trimethylsilyltrifluoroacetamide; 

NaOH = sodium hydroxide; NDA = naphthalenedialdehyde; NPD = nitrogen-phosphorus detector; UV = ultraviolet 

detector 
CYANIDE 205 

7. ANALYTICAL METHODS 

common cyanide antagonist that acts as an interference, can be eliminated by using a buffered solution at 

pH 5.2 as the acidifying agent for cyanide microdiffusion (Sylvester et al. 1982; Way 1984). 

Low detection limits (low ng/mL) have been achieved using a headspace/gas chromatographic (GC) 

technique (Dumas et al. 2005; Seto et al. 1993) with good precision in the measurements reported (Dumas 

et al. 2005; Levin et al. 1990; Seto et al. 1993). The sample is acidified and incubated, and the headspace 

analyzed by GC with a nitrogen-specific detector (NPD) (Levin et al. 1990; Seto et al. 1993) or mass 

spectrometer (Dumas et al. 2005). Cryogenic oven-trapping techniques have been used to trap volatiles 

from blood, such as cyanide, at the head of the GC column before analysis, thus eliminating problems of 

sample foaming that are encountered in traditional head-space analysis methods. Detection limits of 

2 ng/mL (2 μg/L) have been reported with extraction efficiencies of 3.22% from blood (Watanabe-Suzuki 

et al. 2002). Blood samples may be treated with chloramine-T prior to incubation to produce a derivative 

which can be determined by GC with electron capture detection (ECD). Cyanate and thiocyanate do not 

interfere with the detection of cyanide in this method (Odoul et al. 1994). The detection limit is 5 μg/L 

(ppb); precision is good (<15% relative standard deviation [RSD]) (Odoul et al. 1994). 

Trace amounts of cyanide in blood cells may be determined using a liquid chromatographic technique 

with fluorescence detection (Felscher and Wulfmeyer 1998; Sano et al. 1992). The blood cells are 

extracted and the cyanide derivatized prior to chromatography. The detection limit is 2 ng/mL. Recovery 

is acceptable (>80%), and precision is good (<15% RSD) (Felscher and Wulfmeyer 1998; Sano et al. 

1992). Coupling the liquid chromatography technique to a mass spectrometric detector also provides 

good detection sensitivities (limit of detection=5 ng/mL) and recoveries (>85%) (Tracqui et al. 2002). 

Using an ion liquid chromatography method coupled with fluorescence detection, Chinaka et al. (1998) 

were able to achieve detection limits down to 3.8 pmoles/mL (0.10 ng/mL) of cyanide and 86 pmoles/mL 

(5.1 ng/mL) of thiocyanate in blood. 

Cyanide in biological tissue and fluids can be measured spectrophotometrically after reaction with 

methemoglobin (Tomoda and Hashimoto 1991). The detection limit is 0.4 μg/mL. Other performance 

data were not reported (Tomoda and Hashimoto 1991). Cyanide in urine has been determined using 

microdiffusion separation and fluorimetric determination (Sano et al. 1989). The detection limit of the 

assay is reported to be 30 ng/L with recoveries of 75.6–82.6% (Sano et al. 1989). 

Cyanide in the body is biotransformed to thiocyanate quickly. People may also be exposed to thiocyanate 

from dietary, industrial, and medical sources. The plasma concentration of thiocyanate has also been used 
CYANIDE 206 

7. ANALYTICAL METHODS 

as an index of long-term exposure to cigarette smoke (Liu and Yun 1993). Some authors have determined 

thiocyanate in body fluids as a measure of cyanide exposure, while others measure cyanide concentrations 

in body fluids directly. 

Serum levels of thiocyanate are usually determined spectrophotometrically after a colorimetric reaction of 

thiocyanate with ferric nitrate or barbituric acid and pyridine (Li et al. 1993; Olea et al. 1992). Ion 

exchange resin chromatography has been used to isolate thiocyanate from serum (Olea et al. 1992). 

Detection limits are in the ppb range (Li et al. 1993; Olea et al. 1992). Recovery and precision, where 

reported, are good (recovery >90%; precision <15% RSD) (Li et al. 1993). Methods are available for 

measuring thiocyanate in saliva by high performance liquid chromatography (HPLC) (Liu and Yun 1993) 

and in saliva and blood spectrophotometrically (Tominaga et al. 1991; Yamanaka et al. 1991). Table 7-2 

lists representative analytical methods for determining thiocyanides in biological matrices. 

In addition to thiocyanate, another cyanide metabolite, 2-aminothiazoline-4-carboxylic acid (ATCA), is 

being used as a biomarker of cyanide exposures. This biomarker is formed through the reaction of 

cyanide with l-cystine and accounts for 20% of cyanide metabolism in the human body (Logue et al. 

2005). Unlike cyanide, ATCA is stable for months in biological samples stored at freezing or ambient 

temperatures. ATCA is readily recovered from plasma or urine by first acidifying the sample and then 

extracting the compound on to a mixed, cation exchange column. The ACTA is eluted from the column 

and coverted to the trimethylsilyl derivative through reaction with 30% N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) in hexane before analysis by gas chromatography/mass spectrometry 

(GC/MS). The assay method provides for good detection limits (25 ng/mL) and recoveries (100% from 

plasma and 84% from urine). 

7.2 ENVIRONMENTAL SAMPLES 

Hydrogen cyanide and cyanide salts are important environmental contaminants, and there are numerous 

reports dealing with the identification and quantification of cyanide in air, water, and other environmental 

media. Representative examples of monitoring methods for cyanide are included in Table 7-3. 

Hydrogen cyanide in environmental or workplace air is usually collected in sodium hydroxide solution, 

then measured spectrophotometrically after color development (Agrawal et al. 1991; NIOSH 1989b). 

One of the most significant problems in cyanide monitoring is the instability of the collected samples 

(NIOSH 1986b). The collection solution is pH ≥11 to avoid volatilization loss of molecular hydrogen 
CYANIDE 207 

7. ANALYTICAL METHODS 

Table 7-2. Analytical Methods for Determining Biomarkers for Cyanide 

Sample 

Sample Analytical detection Percent 

Analyte matrix Preparation method method limit recovery Reference 

Thiocyanate Human Extraction of buffered Flame atomic 4 ng/mL 96–102 Chattaraj and 

serum, (pH 7) 2-benzoyl absorption Das 1992 

urine, pyridine thiosemi­ spectrometry 

saliva carbazone and sample 

with isoamyl acetate 

Thiocyanate Serum Addition of acetonitrile, Spectro­ 0.3 μg/mL 94 Li et al. 1993 

centrifugation, photometry 

separation 

Thiocyanate Human Derivatization of basic GC with ECD 0.0115 83–106 Chen et al. 

urine, pH sample with nmol (in 1994 

saliva pentafluorobenzyl 0.2 mL) 

bromide in the 

presence of 

Kryptofix 222 B 

polymer and extraction 

into methylene chloride 

then back extraction 

into isooctane 

Thiocyanate Human Dilution with water then Ion 20 ng/mL 95–101 Michigami et 

urine, filtration (0.45 μm) chromatography al. 1992 

saliva utilizing ODS 

column coated 

with cetyldimethylamine 

and with UV 

absorbance 

(210 nm) 

detection 

Thiocyanate Urine Ion chromatography Spectro­ 2.5 No data Tominaga 

using weakly basic photometry μmol/L and Midio 

resin; acidification of (lowest 1991 

eluate with HCl; reported) 

addition of bromine 

water, arseneous oxide 

and pyridine-pphenylene diamine 

Thiocyanate Human Dilution with water then Suppressed ion 200 nM No data Miura and 

urine passage through chromatography Koh 1991 

disposable Toyo pack with conductivity 

ODS and IC-SP detection 

columns 

ECD = electron capture detector; GC = gas chromatography; IC/SP = ion chromatography/sulfopropyl type column; 

ODS = octadecyl silane; nM = nanomolar 
CYANIDE 208 

7. ANALYTICAL METHODS 

Table 7-3. Analytical Methods for Determining Cyanide in 

Environmental Samples 

Sample 

Sample Analytical detection Percent 

matrix Preparation method method limit recovery Reference 

Occupational 

air 

Filtered air collected in 

midget impinger 

Specific ion 

electrode (HCN 

2.5 μg CN–a 96.7 at 

5–21 mg/m3 

NIOSH 1989a 

(NIOSH containing NaOH; cyanide salts) 

Method extraction of filter with 

7904) NaOH; sulfide 

removed 

Occupational Collection of breathing Spectrophotometry 1 μg CN–b ~100 NIOSH 1989b 

air (NIOSH zone air samples on (HCN) 

Method adsorbent; extraction 

6010) with water; treatment 

with barbituric acid/ 

pyridine reagent 

Occupational Passage of filtered air Ion­ 5–10 ppm 100–109 at Dolzine et al. 

air through midget chromatography/ 5–20 ppm 1982 

impinger containing amperometric 

NaOH; conversion of detector (HCN) 

NaCN to sodium 

formate; optional ion 

exchange clean-up 

Air Filtered air collected in Ion­ 0.04 ppm 91 at air flow NIOSH 1986b 

midget impinger chromatography/ (for 2.6 L of rate of 

amperometric air) 0.171 L/minute 

detection (HCN 

only) 

Water Chlorination of sample Spectrophotometry No data No data EPA 1983a 

(drinking, at pH 11–12 and ClCN (cyanide amenable 

surface, driven off; reflux- to chlorination) 

saline, distillation of residual 

domestic, sample; absorption of 

and industrial released HCN in 

waste) (EPA NaOH; treatment with 

Method chloramine-T and 

335.1) pyridine-pyrazolone or 

pyridine-barbituric acid 

Water Reflux-distillation of Spectrophotometry 0.02 ppm 85–102 at EPA 1983a 

(drinking, sample; absorption of (total cyanide) 0.28–0.62 ppm 

surface, released HCN in 

saline, NaOH scrubber; 

domestic, treatment of absorbing 

and industrial solution with 

waste) (EPA chloramine-T and 

Method pyridine-pyrazolone or 

335.2) pyridine barbituric acid 
CYANIDE 209 

7. ANALYTICAL METHODS 

Table 7-3. Analytical Methods for Determining Cyanide in 

Environmental Samples 

Sample 

Sample Analytical detection Percent 

matrix Preparation method method limit recovery Reference 

Water Reflux-distillation of 

(drinking, sample; absorption of 

surface, released HCN in 

saline, NaOH; titration of 

domestic, absorbing solution with 

and industrial AgNO3 in presence of 

waste) (EPA p-dimethylaminoMethod benzalrhodanine 

335.2) (EPA indicator 

Method 

335.3) 

Water Reflux-distillation of 

(drinking, sample; absorption of 

surface, released HCN in 

saline, NaOH; treatment with 

domestic, chloramine-T, pyridine 

and industrial barbituric acid 

waste) (EPA 

Method 

335.4) 

Water None 

Water Separation of acidified 

sample in a 

microdiffusion cell; 

absorption in NaOH 

Water (ASTM Separation of acidified 

Method sample in a 

D2036A) microdiffusion cell; 

absorption in NaOH 

Water None 

Water None 

Water Sample shaken in 

presence of quinoline 

and benzoyl chloride at 

pH 7 

Titrimetric (total 

cyanide) 

Semi-automated 

spectrophotometry 

(total cyanide) 

Ionchromatography/ 

amperometric 

detection (free and 

a few complexed 

cyanides) 

Potentiometric 

(free cyanide) 

Potentiometric 

(total cyanides) 

FIA; 

spectrophotometric 

detection (free 

cyanide) 

FIA; amperometric 

detection (free 

cyanide) 

HPLC with 

spectrophotometric 

detection (free 

CN–

) 

1 ppm No data EPA 1983a 

~0.02 ppm 95 (ave.) EPA 1993h 

2 ppb 100–112 Rocklin and 

Johnson 1983 

0.018 mg/L 96.5–103.9 at Rubio et al. 

CN– 0.037– 1987 

3.49 mg/L 

0.03 mg/L 99.0–111 ASTM 1999 

20 ng/mL 88–107 Ma and Liu 

1992 

2.6 ng/mL 99–103 Nikolić et al. 

1992 

26 pg/mL No data Madungwe et 

al. 1991 
CYANIDE 210 

7. ANALYTICAL METHODS 

Table 7-3. Analytical Methods for Determining Cyanide in 

Environmental Samples 

Sample 

matrix Preparation method 

Analytical 

method 

Sample 

detection 

limit 

Percent 

recovery Reference 

Water None Ion 

chromatography 

with postcolumn 

derivatization and 

0.1 ng/mL 94–96 Gamoh and 

Imamichi 

1991 

fluorimetric 

detection (free 

cyanide) 

Water Treatment of sample 

with NaOH and 

hypophosphite; 

passage through silver 

filter (free cyanide); 

treatment in photo cell 

prior to filter for total 

cyanide and selective 

oxidation for cyanides 

not amenable to 

Flame AAS or 

graphite furnace 

AAS 

2 ng/mL 

(flame AAS); 

0.06 ng/mL 

(graphite 

furnace AAS 

107 (free 

cyanide), 90.4 

(CNATC), 98.1 

(total cyanide) 

Rosentreter 

and 

Skogerboe 

1992 

chlorination (CNATC) 

Water Samples sealed in 

vials with nitrogen 

Headspace 

GC/ECD 

(cyanogen 

chloride) 

0.04 ng/mL 91 average Xie and 

Reckhow 

1993 

Water Absorption on to 

SPME fiber; thermal 

desorption in GC 

GC/ECD 

(cyanogen chloride 

or bromide) 

77 ng/L 

(cyanogen 

chloride) 

41 ng/L 

(cyanogen 

bromide) 

No data Cancho et al. 

2000 

Water (APHA 

Method 

4500-CN–

 J) 

Adjustment of sample 

pH to 8.0–8.5 using 

phosphate buffer; 

addition of pyridinebarbituric acid 

Spectrophotometry 

(cyanogen 

chloride) 

0.02 μg/mL 

(as CN–

) 

(lowest 

calibration) 

No data APHA 1992 

Water and 

waste water 

(APHA 

Method 

Filtration of sample; 

optional treatment with 

resin; treatment with 

ferric nitrate solution 

Colorimetric 

detection 

(thiocyanate) 

No data 71–99, 0.07– 

1.42 mg/L 

APHA 1992 

4500-CN–

 M) 
CYANIDE 211 

7. ANALYTICAL METHODS 

Table 7-3. Analytical Methods for Determining Cyanide in 

Environmental Samples 

Sample 

Sample Analytical detection Percent 

matrix Preparation method method limit recovery Reference 

Waste or Reflux-distillation of Titrimetric or 0.1–0.2 mg/L (titrimetric) 94– EPA 1996 

leachate acidified sample; colorimetric (titrimetric) 99 (total 

(EPA Method absorption of released detection (total and 0.02 mg/L cyanide), 87– 

9012A) HCN in NaOH; amenable cyanide) (colorimetric) 97 (amenable 

treatment with AgNO3 cyanide) 

and an indicator 

(titrimetric) or 

chloramine-T/pyridinebarbituric acid 

(colorimetric) 

Waste water Addition of sample to Spectrophotometry 0.2 μg/mL No data Tomoda and 

buffered (free cyanide) Hashimoto 

methemoglobin 1991 

Waste water None FIA with 3 ng/mL 98 Kubáň 1992 

spectrophotometric 

detection 

Waste water Sample acidified and FIA with 0.5 μg/L 99.5 (2 μg/L) Weinberg and 

irradiated with UV; amperiometric 99 (30 μg/L) Cook 2002 

microdiffusion and detection (total 

absorption in NaOH cyanide) 

solution 

Waste water Complexation of Flame AAS (free 4.8 ng/mL 97–101 Chattaraj and 

sample with 2-benzoyl­ cyanide) Das 1991 

pyridine thiosemicarbazone; solvent 

extraction 

Solid waste Extraction of solid Titrimetric or No data 60–90 (solid) EPA 1992e 

or oil waste component with water colorimetric 88–92 (oil) 

(EPA Method at pH 10 and hexane detection (soluble 

9013) cyanides) 

Soils/ Reflux-distillation of Colorimetric 0.5 mg/kg No data USGS 1985 

sediments sample; absorption of detection 

(USGS released HCN in (recoverable 

Method NaOH; treatment with simple cyanides) 

I6302) chloramine-T, pyridine 

barbituric acid 

Food (cereal Extraction of sample GC/ECD at low 0.1 ppm 90 Heuser and 

and other with water/ acetonitrile, detection voltage Scudmore 

foodstuffs) dried (free cyanide) 1969 
CYANIDE 212 

7. ANALYTICAL METHODS 

Table 7-3. Analytical Methods for Determining Cyanide in 

Environmental Samples 

Sample 

Sample Analytical detection Percent 

matrix Preparation method method limit recovery Reference 

Food Sample mixed with Spectrophoto- No data 32–80 Honig et al. 

(soybean and water, lead nitrate, metry (total 1983 

soybean tartaric acid, and anti- cyanide) 

products) forming agent; 

acidification and 

distillation; treatment of 

distillate with pyridinebarbituric acid 

a

Method detection limits depend upon the volume of air sampled; the working range is 5–20 mg/m3 for a 10-L air 

sample. b

Method detection limits depend upon the volume of air sampled; the working range is 1–333 mg/m3 for a 3-L 

sample. 

AAS = atomic absorption spectroscopy; AgNO3 = silver nitrate; ASTM = American Society for Testing and Materials;

ClCN = cyanogen chloride; CN –

 = cyanide ion; CNATC = cyanides not amenable to chlorination (Rosentreter and 

Skogerboe 1992); EPA = Environmental Protection Agency; FIA = flow injection analysis; GC/ECD = gas 

chromatograph/electron capture detector; HCN = hydrogen cyanide; NaOH = sodium hydroxide; NIOSH = National 

Institute for Occupational Safety and Health; USGS = United States Geological Survey; UV = ultraviolet
CYANIDE 213 

7. ANALYTICAL METHODS 

cyanide. However, carbon dioxide from air may react with the solution during storage, thereby lowering 

the pH and releasing hydrogen cyanide gas, making the reading for cyanide lower than actually presented. 

Oxidizing agents in solution may transform cyanide during storage and handling. Ferrocyanide and 

ferricyanide complexes of cyanide undergo photodecomposition with ultraviolet light. Particulate 

cyanides are known to decompose in moist air with the liberation of hydrogen cyanide and cyanic acid 

(HOCN). The recommended method for the storage of cyanide samples is to collect the samples at 

pH 12–12.5 in closed, dark bottles and store them in a cool, dark place. It is also recommended that the 

samples be analyzed immediately upon collection. The sample handling and preservation methods have 

been discussed (NIOSH 1986b; Egekeze and Oehme 1979). Cyanide determination in air usually 

distinguishes between two forms of cyanides: hydrogen cyanide gas and particulate cyanides. Filters are 

usually used to collect particulate cyanides, and the hydrogen cyanide gas that passes through the 

membrane is trapped in sodium hydroxide. The collected particulate cyanides can be quantified 

separately after acid distillation. Detection limits are in the ppm range for occupational air (Dolzine et al. 

1982; NIOSH 1989a, 1989b) and sub-ppm range for ambient air (NIOSH 1986b). Reported recovery is 

good (>90%) (Dolzine et al. 1982; NIOSH 1986b, 1989a, 1989b). 

Inorganic cyanides in water can be present both as complexed and free cyanide. Cyanide in water is 

usually determined in three different forms: free cyanide, cyanide amenable to chlorination, and total 

cyanide. Free cyanides such as sodium cyanide, potassium cyanide, and hydrogen cyanide are readily 

ionized to the cyanide ion under the conditions used in most common analytical techniques. Methods for 

determining cyanide amenable to chlorination measure simple metal cyanides and most complex cyanides 

with the exception of iron cyanides. Total cyanide is a measure of all cyanides including iron cyanide 

complexes. Table 7-3 lists representative analytical methods for determining cyanides that may be 

present in various forms. A number of standard methods are available (APHA 1992; ASTM 1999; EPA 

1983a, 1996; NIOSH 1989a, 1989b). An ion-exchange chromatography method has been developed to 

separate and quantify cyano complexes of gold, silver, iron, nickel, cobalt, and copper using a UV 

detection technique (Karmarkar 2002). Minimum detection limits of 0.07–0.83 mg/L and recoveries of 

99.8–118.8% were reported, both of which varied considerably depending on the cyano metal complex. 

Procedures for extracting cyanide from aqueous matrices usually involve acidifying the sample followed 

by heating and refluxing to evolve hydrogen cyanide, which is then trapped in an impinger containing 

absorption media. Complex cyanides and metal cyanide complexes can be degraded to free cyanide 

through UV irradiation (314 nm) of an acidified sample (Weinberg and Cook 2002). Cyanide is usually 

measured by colorimetric, titrimetric, or electrochemical methods (for example, APHA 1992). All are 
CYANIDE 214 

7. ANALYTICAL METHODS 

subject to interference problems. Sulfide, certain oxidizing agents, nitrate or nitrite, thiocyanate, 

aldehydes, and ketones may interfere under acid distillation conditions, thus producing erroneous results 

from both colorimetric and titrimetric methods. In addition, fatty acids in samples may distill over and 

form soaps under alkaline titration conditions, thus causing interference in the titrimetric method (EPA 

1983a, 1996). Colorimetric methods may be based on pyridine with chloramine-T as the oxidizing agent 

and barbituric acid as the coupling component (EPA 1996) or pyrazolone as the coupling agent (EPA 

1983a). Low detection limits are attained (10–20 μg/L), but sulfide and thiocyanate are common 

interferents (Csikal and Barnard 1983; Drikas and Routley 1988). Titrimetric methods usually employ 

silver nitrate (EPA 1983a, 1996); however, the detection limits are in the low mg/L range. Methods using 

specific ion electrodes (electrochemical) respond to numerous interferences (sulfur, chlorine, iodine, 

bromine, cadmium, silver, zinc, copper, nickel, and mercury) (NIOSH 1986b). 

Continuous monitoring methods based on amperometric (Nikolić et al. 1992) or spectrophotometric 

(Kubáň 1992; Ma and Liu 1992) techniques for the quantification of free cyanide are also available. Ion 

chromatography with amperometric determination provides good sensitivity (2 ppb) and selectivity for 

free cyanide and for the weak complexes of cadmium and zinc (Rocklin and Johnson 1983). Postcolumn 

derivatization and fluorescence detection provides low detection limits as well (0.1 ppb) (Gamoh and 

Imamichi 1991). 

Methods were identified in the available literature for the determination of the concentrations of cyanides 

and thiocyanates present in soils at low levels. A colorimetric method (USGS 1985) is used to quantify 

simple cyanides in soils and sediments (see Table 7-3). A reflux-distillation of soil or sediment samples 

converts CN–

 to hydrogen cyanide, which is released from the sample and then absorbed in a 1 M NaOH 

solution. The absorbed cyanide is chlorinated with Chloramine-T and then reacted with pyridinebarbituric acid to form the chromophore. Detection limits of >0.5 mg/kg are reported; no recovery data 

were given. The method will decompose thiocyanate in the samples to cyanide and sulfide, resulting in a 

concentration of cyanide that is higher than was originally present in the sample. Sulfide concentrations 

of >10 mg/kg will greatly interfere with the quantification of cyanide in the assay. In addition to simple 

cyanides, complex cyanides can also be measured in soil and sediment samples utilizing a modified 

sample preparation procedure that uses an ultraviolet digestion-distillation method to break down the 

complex cyanides to the cyanide ion. Brown and Morra (1991) extracted simple cyanides from soils 

using a calcium chloride solution followed by analysis by ion-chromatography (see Table 7-4). The assay 

provided a detection limit of 0.02 μg/L with a recovery averaging 94%, depending on soil type. 
CYANIDE 215 

7. ANALYTICAL METHODS 

Table 7-4. Analytical Methods for Determining Environmental Degradation 

Products of Cyanide 

Analyte 

Sample 

matrix 

Preparation 

method Analytical method 

Sample 

detection 

limit 

Percent 

recovery Reference 

SCN⎯ Water Filtration 

(0.45 μm) 

Reversed-phase 

ion-pair 

chromatography 

with amperometric 

detection 

104 ng/mL No data Xu et al. 1993 

SCN⎯ Water/waste 

water 

Filtration; 

acidification; 

Colorimetric 0.1 mg/L No data ASTM 1994a 

reaction with 

ferric chloride 

SCN– Soil Extraction of soil 

with calcium 

chloride solution 

Ion 

chromatography 

with conductivity 

detection 

0.02 μg/g 83; avg. 94, 

depending on 

soil type 

Brown and 

Morra 1991 

SCN–

 = thiocyanate ion 
CYANIDE 216 

7. ANALYTICAL METHODS 

Recent method development strategies for quantifying cyanide in water are using biological sensing 

elements (i.e., organisms, enzyme, receptor, antibody, etc.) coupled to an electronic signal-transducing 

element. With respect to organisms, the assay takes advantage of the effect that cyanide has on 

respiration and metabolism. For example, Karube et al. (1998) use yeast in a flow-through reactor setup 

where river water containing cyanide is pumped through the reactor and the oxygen concentration in the 

effluent stream is measured using an oxygen electrode. When cyanide passes through the reactor, it 

inhibits yeast respiration and therefore decreases oxygen consumption, resulting in an increase in the 

current at the oxygen electrode. A detection limit of 0.2 ppm (3μM) was reported for the assay with a 

linear response to 1 ppm. In another approach, Nikolelis et al. (1997) use a lipid bilayer embedded with 

methemoglobin to detect and quantify cyanide in water samples. The binding of cyanide to the 

methemoglobin causes a change in the electrochemical potential across the membrane that is measured 

with an electrometer. A detection limit of 4.9 nM (0.0032 ppm) was reported with a relative standard 

deviation (RSD) of 5.2% at cyanide concentration of 150 nM. 

Few methods are available for the determination of cyanogen and cyanogen chloride in environmental 

matrices. Methods available include gas chromatographic-flame ionization detection of cyanogen 

chloride and cyanogen (Brown et al. 1986), headspace gas chromatography with electron capture 

detection (GC/ECD) (Cancho et al. 2000; Xie and Reckhow 1993) and colorimetric detection (APHA 

1992). Detection limits are in the low ppb range for the colorimetric method (APHA 1992) and in the 

sub-ppb range for the GC/ECD method (Xie and Reckhow 1993). 

Recent work by Yang and Shang (2005) reports the development of a membrane introduction mass 

spectrometry (MIMS) technique for quantifying cyanogens chloride in environmental samples. Nonpolar, low molecular weight, volatile and semi-volatile organics in aqueous samples are introduced direct 

to a mass spectrometer through pervaporation as the sample passes through a permeable silicone 

membrane. Linear responses over three orders of magnitude of concentrations of cyanogens chloride 

were obtained with a detection limit of 1.7 μg/L and a recovery of 98.5%. The presence of organics, such 

as dichloroethene, acetophenone, benzaldehyde, and benzyl alcohol, can interfere with the quantification 

of cyanogen chloride. However, these compounds are generally industrial chemicals that are typically not 

detected in drinking water, most surface waters, or domestic waste water. 

Standard methods are available for measuring thiocyanate in aqueous matrices (APHA 1992; ASTM 

1994a). These are colorimetric methods and are subject to interferences. In addition, thiocyanate is 

biodegradable; thus, care must be exercised in sample collection, preservation, and storage. The detection 
CYANIDE 217 

7. ANALYTICAL METHODS 

limit is 100 ppb (ASTM 1994a). An automated method with good sensitivity (0.5 ppb) is available for 

determining thiocyanate in water and waste water (ASTM 1994b). Various methods have been reported 

for determination of thiocyanate in soils; however, ion chromatographic determination provides good 

selectivity and sensitivity (20 ppb) (Brown and Morra 1991). Representative examples of monitoring 

methods for thiocyanate are included in Table 7-4. 

7.3 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the 

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of cyanide is available. Where adequate information is not 

available, ATSDR, in conjunction with 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 cyanide. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will be 

evaluated and prioritized, and a substance-specific research agenda will be proposed. 

7.3.1 Identification of Data Needs 

Methods for Determining Biomarkers of Exposure and Effect. 

Exposure. Besides environmental exposure, exposure to cyanide can also occur from consumption of 

cyanide-containing food and smoking cigarettes. Since so many factors can influence cyanide exposure, 

the exact correlation between cyanide concentrations in the body and its level in the environment has not 

been made. Therefore, measuring cyanide and/or thiocyanate levels in blood and urine cannot be used as 

a biomarker for exposure to low cyanide concentrations. Reliable analytical methods are available for the 

detection of cyanide and thiocyanate in blood, plasma, and urine of both unexposed and exposed persons 

are available, as summarized in Tables 7-1 and 7-2. Further studies determining biomarkers for exposure 

to low cyanide concentrations would be useful since current methods that are used to measure cyanide 
CYANIDE 218 

7. ANALYTICAL METHODS 

and/or thiocyanate in blood and urine are not effective at assessing exposures to low concentrations of 

cyanide. 

The International Programme on Chemical Safety, in its document regarding the antidotes for poisoning 

by cyanide, has identified several analytical data needs related to the detection of cyanide in biological 

matrices (IPCS/CEC 1993). Analytical techniques available for the measurement of methemoglobin do 

not permit accurate estimation of the amount of free hemoglobin available for oxygen transport because 

cyanmethemoglobin cannot be quantified. A rapid and accurate technique for measuring methemoglobin 

and cyanmethemoglobin concentrations in conjunction is therefore needed to monitor the use of 

methemoglobin-generating cyanide antidotes. Reliable quantitative analytical methods for cyanide in 

whole blood in the presence of one or more antidotes are also needed. 

Effect. Although certain effects, such as cyanosis and endemic goiter, have been associated with cyanide 

exposure (see Section 3.8.2), a positive correlation between cyanide exposure and one of its effects has 

not yet been established. Additional studies establishing a correlation between cyanide exposure and one 

of its effects will be useful in diagnosing cyanide exposure. 

Methods for Determining Parent Compounds and Degradation Products in Environmental 

Media. The concentration of hydrogen cyanide in most ambient air is so low that it is beyond the 

detection limit of the standard analytical methods. An infrared absorption method of a large vertical 

tropospheric column was used to measure the hydrogen cyanide concentration in the troposphere 

(Cicerone and Zellner 1983). Similarly, ground-based millimeter wave emission spectroscopy was used 

to measure stratospheric concentration of hydrogen cyanide (Jaramillo et al. 1989). Also, the level of 

cyanogen chloride in drinking water ranges from 0.45 to 0.80 ppb (Krasner et al. 1989), which is beyond 

the detection limit of the standard analytical methods without concentration and trapping procedures. 

Cyanogen chloride in water was determined by a purge and trap GC/MS method (Krasner et al. 1989) and 

an MIMS-based method (Yang and Shang 2005), methods that are not available to many laboratories. 

There is, therefore, a need to develop standard analytical methods capable of quantifying hydrogen 

cyanide in air and cyanogen chloride in water at levels that are generally found in these media. 

Cyanide metabolizes in the human body to thiocyanate, and its biodegradation products include ammonia, 

carbon dioxide, nitrate, or nitrogen (Richards and Shieh 1989). The detection of thiocyanate or 

2-aminothiazoline-4-carboxylic acid in body fluids may indicate cyanide exposure (Logue et al. 2005). 

Similarly, the amounts of cyanide degradation products formed in an environmental medium could be 
CYANIDE 219 

7. ANALYTICAL METHODS 

used to measure cyanide's biodegradation rate. A summary of methods for determining environmental 

degradation products is shown in Table 7-4. Suitable analytical methods are available to detect all of 

these compounds (Pettigrew and Fell 1973; Richards and Shieh 1989). No additional information is 

needed at this time. 

7.3.2 Ongoing Studies 

The Federal Research in Progress (FEDRIP 2005) database provides additional information obtainable 

from a few ongoing studies that may fill in some of the data needs identified in Section 7.3.1 and provides 

examples of new methods used in the detection and quantification of cyanide or thiocyanide. Only one 

study was identified. Dr. Fennell at Research Triangle Institute is developing liquid-chromatography/ 

mass spectrometry based analytical methods for the detection and quantification of adducts formed 

between hemoglobin and reactive chemicals such as cyanide. 
CYANIDE 220 

7. ANALYTICAL METHODS 

This page is intentionally blank. 
CYANIDE 221 

8. REGULATIONS AND ADVISORIES 

The international, national, and state regulations and guidelines regarding cyanide in air, water, and other 

media are summarized in Table 8-1. 

ATSDR has derived an intermediate oral MRL of 0.05 mg/kg/day for cyanide based on a NOAEL of 

4.5 mg/kg/day and a LOAEL of 12.5 mg/kg/day from a study in which 10 male and 10 female rats were 

given 0.2–12.5 mg/kg/day cyanide, as sodium cyanide, in the drinking water for 13 weeks (NTP 1993). 

EPA reference doses (RfDs) have been established for chronic oral exposure to cyanide and its 

compounds. These RfDs range from 2x10-1 mg/kg/day for potassium silver cyanide to 5x10-3 mg/kg/day 

for copper cyanide. The RfD for potassium silver cyanide was based on weight loss and thyroid effects in 

several rat studies (Howard and Hanzel 1955; Philbrick et al. 1979), while the RfD for copper cyanide 

was based on decreased body and organ weights and liver and kidney effects in an intermediate-duration 

rat study (Gerhart 1987). An EPA reference concentration (RfC) exists only for chronic inhalation 

exposure to hydrogen cyanide; this RfC is 3x10-3 mg/m3

. The RfC was based on central nervous system 

and thyroid effects in a human occupational study (El Ghawabi et al. 1975). 

The EPA has determined that cyanide is not classifiable as to its human carcinogenicity (Group D). No 

cancer classifications exist for the National Toxicology Program, IRIS, or IARC (no available data). 

Several cyanide compounds are on the list of chemicals regulated under "The Emergency Planning and 

Community Right-to-Know Act of 1986" (EPCRA) (EPA 2004d). Section 313 of Title III of EPCRA 

requires owners and operators of certain facilities that manufacture, import, process, or otherwise use the 

chemicals on this list to report annually their release of those chemicals to any environmental media. 

OSHA requires employers of workers who are occupationally exposed to cyanide to institute engineering 

controls and work practices to reduce and maintain employee exposure at or below permissible exposure 

limits (PELs). The employer must use engineering and work practice controls, if feasible, to reduce 

exposure to or below an 8-hour time-weighted average (TWA) of 10 ppm (11 mg/m3

) as cyanide. 

Respirators must be provided and used during the time period necessary to install or implement feasible 

engineering and work practice controls (OSHA 2004d). NIOSH (2004) recommends a 10-minute ceiling 

of 5 mg/m3

 for cyanide in compounds such as sodium cyanide or potassium cyanide. 
CYANIDE 222 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide 

Compounds 

Agency Description Information Reference 

INTERNATIONAL 

Guidelines: 

IARC Carcinogenicity classification 

WHO Air quality guideline value 

Drinking water guideline value 

Cyanide 

Cyanogen chloride (for cyanide as total 

cyanogenic compounds) 

NATIONAL 

Regulations and Guidelines: 

a. Air 

ACGIH TLV (8-hour TWA) 

Cyanogen 

Cyanogen chloride (ceiling limit) 

Hydrogen cyanide (ceiling limit)a 

EPA Hazardous air pollutant 

Cyanide compounds 

Regulated toxic and flammable substances and 

threshold quantities for accidental release 

prevention 

Cyanogen (toxic) 

Cyanogen chloride (flammable) 

NIOSH REL (10-hour TWA) 

Cyanogen 

Cyanogen chloride (10-minute ceiling limit) 

Hydrogen cyanide (short-term limit)a 

Potassium cyanide (10-minute ceiling limit) 

Sodium cyanide (10-minute ceiling limit) 

IDLH 

Cyanogen 

Cyanogen chloride 

Hydrogen cyanide 

Potassium cyanide (as cyanide) 

Sodium cyanide (as cyanide) 

OSHA PEL (8-hour TWA) for general industry

Hydrogen cyanidea

PEL (8-hour TWA) for construction industry 

Cyanogen 

Hydrogen cyanidea 

PEL (8-hour TWA) for shipyard industry 

Cyanogen 

Hydrogen cyanidea 

No data 

No data 

0.07 mg/L 

0.07 mg/L 

10 ppm 

0.3 ppm 

4.7 ppm 

10,000 pounds 

10,000 pounds 

10 ppm 

0.3 ppm 

4.7 ppm 

4.7 ppm 

4.7 ppm 

No data 

No data 

50 ppm 

25 mg/m3 

25 mg/m3 

 10 ppm 

10 ppm 

10 ppm 

10 ppm 

10 ppm 

IARC 2004 

WHO 2000 

WHO 2004 

ACGIH 2003 

EPA 2004j 

42USC7412 

EPA 2005a 

40CFR68.130 

NIOSH 2005 

OSHA 2004d 

29CFR1910.1000, 

Table Z-1 

OSHA 2004c 

29CFR1926.55, 

Appendix A 

OSHA 2004a 

29CFR1915.1000, 

Table Z 
CYANIDE 223 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide 

Compounds 

Agency Description Information Reference 

NATIONAL (cont.) 

OSHA Highly hazardous chemicals which present a OSHA 2004b 

potential for a catastrophic event at or above 29CFR1910.119, 

the threshold quantity listed Appendix A 

Cyanogen 2,500 pounds 

Cyanogen chloride 500 pounds 

Hydrogen cyanide, anhydrous 1,000 pounds 

b. Water 

EPA Drinking water standards and health advisories EPA 2004a 

Cyanide 

1-day HA for a 10-kg child 0.2 mg/L 

10-day HA for a 10-kg child 0.2 mg/L 

DWEL 0.8 mg/L 

Lifetime HA (70-kg adult) 0.2 mg/L 

Cyanogen chloride 

1-day HA for a 10-kg child 0.05 mg/L 

10-day HA for a 10-kg child 0.05 mg/L 

DWEL 2.0 mg/L 

Designated as a hazardous substances EPA 2004t 

pursuant to Section 311(b) of the Clean Water 40CFR116.4 

Act 

Ammonium thiocyanate Yes 

Calcium cyanide 

Cyanogen chloride 

Hydrogen cyanide 

Potassium cyanide 

Sodium cyanide 

National primary drinking water standards and EPA 2004h 

public notification 40CFR141.32 

Cyanideb

 0.2 ppm 

Reportable quantities of hazardous substances EPA 2004k 

designated pursuant to Section 311(b) of the 40CFR117.3 

Clean Water Act 

Ammonium thiocyanate 5,000 pounds 

Calcium cyanide 10 pounds 

Cyanogen chloride 10 pounds 

Hydrogen cyanide 10 pounds 

Potassium cyanide 10 pounds 

Sodium cyanide 10 pounds 

National primary drinking water regulations EPA 2004g 

(MCL) 40CFR141.62 

Cyanide 0.2 mg/L 

FDA Bottled water FDA 2003 

Cyanide 0.2 mg/L 21CFR165.110 
CYANIDE 224 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide 

Compounds 

Agency Description Information Reference 

NATIONAL (cont.) 

c. Food 

EPA Tolerance for residues of hydrogen cyanide 

from postharvest fumigation as a result of 

application of sodium cyanide on citrus fruits 

Exemptions from the requirement of a tolerance 

when used in accordance with good agricultural 

practices in pesticide formulations applied to 

growing crops; and when used as an adjuvant 

or intensifier for defoliation and weed control on 

cotton and soybeans 

FDA Indirect food additive for use only as a 

component of adhesives 

d. Other 

EPA Carcinogenicity classification 

Calcium cyanide 

Chlorine cyanide 

Copper(I) cyanide 

Cyanide 

Cyanogen 

Hydrogen cyanide 

Potassium cyanide 

Potassium silver cyanide 

Sodium cyanide 

RfCd 

Calcium cyanide 

Chlorine cyanide 

Copper(I) cyanide 

Cyanide 

Cyanogen 

Hydrogen cyanide 

Potassium cyanide 

Potassium silver cyanide 

Sodium cyanide 

RfDe 

Calcium cyanide 

Chlorine cyanide 

Copper(I) cyanide 

Cyanide 

Cyanogen 

Hydrogen cyanide 

Potassium cyanide 

Potassium silver cyanide 

Sodium cyanide 

50 ppm 

Ammonium 

thiocyanate 

Ammonium 

thiocyanate 

No data 

No data 

No data 

Group Dc 

No data 

No data 

No data 

No data 

No data 

No data 

No data 

No data 

No data 

No data 

3x10-3 mg/m3 

No data 

No data 

No data 

4x10-2 mg/kg/day 

5x10-2 mg/kg/day 

5x10-3 mg/kg/day 

2x10-2 mg/kg/day 

4x10-2 mg/kg/day 

2x10-2 mg/kg/day 

5x10-2 mg/kg/day 

2x10-1 mg/kg/day 

4x10-2 mg/kg/day 

EPA 2004m 

40CFR180.130 

EPA 2004n 

40CFR180.920 

FDA 2003 

21CFR175.105 

IRIS 2004 
CYANIDE 225 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide 

Compounds 

Agency Description Information Reference 

NATIONAL (cont.) 

EPA Hazardous waste identification 

Calcium cyanide 

Copper(I) cyanide 

Cyanides (soluble salts and complexes) 

Cyanogen 

Cyanogen chloride 

Hydrogen cyanide 

Potassium cyanide 

Potassium silver cyanide 

Sodium cyanide 

Pesticide (sodium cyanide) classified as 

restricted use and limited to use by or under the 

direct supervision of a certified applicator 

Superfund; emergency planning and notification 

of extremely hazardous substances and their 

threshold quantities 

Hydrogen cyanide 

Potassium cyanide 

Potassium silver cyanide 

Sodium cyanide 

Superfund; designation of hazardous 

substances and their reportable quantities 

Ammonium thiocyanateg 

Calcium cyanideh 

Copper cyanidei 

Cyanides (soluble salts and complexes) 

Cyanogeni 

Cyanogen chlorideh 

Hydrogen cyanideh 

Potassium cyanideh 

Potassium silver cyanidei 

Sodium cyanideh 

Tolerances for pesticide chemicals in food; 

when calcium cyanide and hydrogen cyanide 

are on the same agricultural commodity, the 

total amount shall not yield more residue than 

the larger of the two tolerances, calculated as 

hydrogen cyanide 

Toxic chemical release reporting; community 

right-to-know; effective date for hydrogen 

cyanide 

TSCA chemical information rules; 

manufacturers reporting period for sodium 

cyanide 

Effective date 

Reporting date 

P021 

P029 

P030 

P031 

P033 

P063 

P098 

P099 

P106 

All capsules and all 

ball formulations 

for all usesf 

100 pounds 

100 pounds 

500 pounds 

100 pounds 

5,000 pounds 

10 pounds 

10 pounds 

10 pounds 

100 pounds 

10 pounds 

10 pounds 

10 pounds 

1 pound 

10 pounds 

01/01/1987 

10/29/1990 

12/27/1990 

EPA 2004f 

40CFR261, 

Appendix VIII 

EPA 2004i 

40CFR152.175 

EPA 2004e 

40CFR355, 

Appendix A 

EPA 2004d 

40CFR302.4 

 EPA 2004o 

40CFR180.3 

EPA 2004p 

40CFR372.65 

EPA 2004r 

40CFR712.30 
CYANIDE 226 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide 

Compounds 

Agency Description Information Reference 

NATIONAL (cont.) 

EPA TSCA health and safety data reporting for EPA 2004s 

sodium cyanide 40CFR716.120 

Effective date 10/29/1990 

Sunset date 12/19/1995 

STATE 

a. Air 

No data 

b. Water 

Drinking water standards and guidelines HSDB 2004 

 Arizona Calcium cyanide 220 μg/L 

Copper(I) cyanide 1,300 μg/L 

Potassium cyanide 220 μg/L 

Potassium silver cyanide 50 μg/L 

Sodium cyanide 220 μg/L 

Connecticut Potassium silver cyanide 50 μg/L 

 Florida Cyanogen 10,000 μg/L 

Cyanogen chloride 350 μg/L 

Hydrogen cyanide 10,000 μg/L 

Maine Potassium cyanide 154 μg/L 

Potassium silver cyanide 50 μg/L 

Sodium cyanide 154 μg/L 

 Minnesota Potassium cyanide 100 μg/L 

Potassium silver cyanide 30 μg/L 

Sodium cyanide 100 μg/L 

Wisconsin Potassium silver cyanide 50 μg/L 

c. Food 

No data 
CYANIDE 227 

8. REGULATIONS AND ADVISORIES 

Table 8-1. Regulations and Guidelines Applicable to Cyanide and Cyanide 

Compounds 

Agency Description Information Reference 

STATE (cont.) 

d. Other 

No data 

a

Skin designation: Potential significant contribution to the overall exposure by the cutaneous route, including 

mucous membranes and the eyes, either by contact with vapors, or of probable greater significance, by direct skin 

contact with the substance. b

EPA sets drinking water standards and has determined that cyanide is a health concern at certain levels of 

exposure. This inorganic chemical is used in electroplating, steel processing, plastics, synthetic fabrics, and fertilizer 

products; it usually gets into water as a result of improper waste disposal. This chemical has been shown to damage 

the spleen, brain, and liver of humans fatally poisoned with cyanide. EPA has set the drinking water standard for 

cyanide at 0.2 ppm to protect against the risk of these adverse health effects. Drinking water that meets the EPA 

standard is associated with little to none of this risk and should be considered safe with respect to cyanide (EPA 

2004h). c

Group D: Not classifiable as a human carcinogen. d

An estimate (with uncertainty spanning an order of magnitude) of a daily inhalation exposure concentration that is 

likely to be without significant risk of adverse effects during a lifetime (chronic exposure). e

An estimate (with uncertainty spanning an order of magnitude) of a daily oral exposure dose that is likely to be 

without significant risk of adverse effects during a lifetime (chronic exposure). f

The criteria influencing the restriction of sodium cyanide is based on the inhalation hazard to humans. Also, sodium 

cyanide capsules may only be used by certified applicators who have also taken the required additional training.

g

Designated as a hazardous substance pursuant to Section 311(b)(2) of the Clean Water Act. h

Designated as a hazardous substance pursuant to Section 311(b)(2) of the Clean Water Act and Section 3001 of 

RCRA. 

i

Designated as a hazardous substance pursuant to Section 3001 of RCRA. 

ACGIH = American Conference of Governmental Industrial Hygienists; CFR = Code of Federal Regulations; 

DWEL = drinking water equivalent level; EPA = Environmental Protection Agency; FDA = Food and Drug 

Administration; HA = health advisory; HSDB = Hazardous Substances Data Bank; IARC = International Agency for 

Research on Cancer; IDLH = immediately dangerous to life or health; IRIS = Integrated Risk Information System; 

MCL = maximum contaminant level; NIOSH = National Institute for Occupational Safety and Health; 

OSHA = Occupational Safety and Health Administration; PEL = permissible exposure limit; RCRA = Resource 

Conservation and Recovery Act; REL = recommended exposure limit; RfC = reference concentration; 

RfD = reference dose; TLV = threshold limit values; TSCA = Toxic Substances Control Act; TWA = time-weighted 

average; USC = United States Codes; WHO = World Health Organization 
CYANIDE 228 

8. REGULATIONS AND ADVISORIES 

Cyanide is regulated by the Clean Water Effluent Guidelines as stated in Title 40, Sections 400–475, of 

the Code of Federal Regulations. For each point source category, cyanide may be regulated as amenable 

or total cyanide. The point source categories for which cyanide is controlled include electroplating; metal 

finishing; organic chemicals; plastics and synthetic fibers; hydrogen peroxide manufacturing; iron and 

steel; nonferrous metals; steam electri-power; ferroalloy manufacturing; pharmaceuticals; battery 

manufacturing; aluminum forming; nonferrous metal forming; and coil coating. 

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), food tolerance restrictions (see 

Table 8-1) apply to various cyanide compounds when applied to growing crops (EPA 2004m, 2004n, 

2004o). 

Under the Resource Conservation and Recovery Act (RCRA), cyanide is listed as a hazardous waste 

when it is a discarded commercial chemical product, off-specification species, container residue, or spill 

residue (EPA 1980c); a waste from non-specific sources (EPA 1981c); or a waste from specific sources 

(EPA 1981c). 
_______________________ 

CYANIDE 229 

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CYANIDE 291 

10. GLOSSARY 

Absorption—The taking up of liquids by solids, or of gases by solids or liquids. 

Acute Exposure—Exposure to a chemical for a duration of 14 days or less, as specified in the 

Toxicological Profiles. 

Adsorption—The adhesion in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the 

surfaces of solid bodies or liquids with which they are in contact. 

Adsorption Coefficient (Koc)—The ratio of the amount of a chemical adsorbed per unit weight of 

organic carbon in the soil or sediment to the concentration of the chemical in solution at equilibrium. 

Adsorption Ratio (Kd)—The amount of a chemical adsorbed by sediment or soil (i.e., the solid phase) 

divided by the amount of chemical in the solution phase, which is in equilibrium with the solid phase, at a 

fixed solid/solution ratio. It is generally expressed in micrograms of chemical sorbed per gram of soil or 

sediment. 

Amygdalin—A naturally occurring cyanogenic glucoside found in almonds and apricot pits. It is also the 

active ingredient in the drug Laetrile, which has been formerly used to treat cancer. The hydrolysis of 

amgydalin releases hydrogen cyanide. 

Benchmark Dose (BMD)—Usually defined as the lower confidence limit on the dose that produces a 

specified magnitude of changes in a specified adverse response. For example, a BMD10 would be the 

dose at the 95% lower confidence limit on a 10% response, and the benchmark response (BMR) would be 

10%. The BMD is determined by modeling the dose response curve in the region of the dose response 

relationship where biologically observable data are feasible. 

Benchmark Dose Model—A statistical dose-response model applied to either experimental toxicological 

or epidemiological data to calculate a BMD. 

Bioconcentration Factor (BCF)—The quotient of the concentration of a chemical in aquatic organisms 

at a specific time or during a discrete time period of exposure divided by the concentration in the 

surrounding water at the same time or during the same period. 

Biomarkers—Broadly defined as indicators signaling events in biologic systems or samples. They have 

been classified as markers of exposure, markers of effect, and markers of susceptibility. 

Cancer Effect Level (CEL)—The lowest dose of chemical in a study, or group of studies, that produces 

significant increases in the incidence of cancer (or tumors) between the exposed population and its 

appropriate control. 

Carcinogen—A chemical capable of inducing cancer. 

Case-Control Study—A type of epidemiological study that examines the relationship between a 

particular outcome (disease or condition) and a variety of potential causative agents (such as toxic 

chemicals). In a case-controlled study, a group of people with a specified and well-defined outcome is 

identified and compared to a similar group of people without outcome. 
CYANIDE 292 

10. GLOSSARY 

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. 

Ceiling Value—A concentration of a substance that should not be exceeded, even instantaneously. 

Chronic Exposure—Exposure to a chemical for 365 days or more, as specified in the Toxicological 

Profiles. 

Cohort Study—A type of epidemiological study of a specific group or groups of people who have had a 

common insult (e.g., exposure to an agent suspected of causing disease or a common disease) and are 

followed forward from exposure to outcome. At least one exposed group is compared to one unexposed 

group. 

Cross-sectional Study—A type of epidemiological study of a group or groups of people that examines 

the relationship between exposure and outcome to a chemical or to chemicals at one point in time. 

Data Needs—Substance-specific informational needs that if met would reduce the uncertainties of human 

health assessment. 

Developmental Toxicity—The occurrence of adverse effects on the developing organism that may result 

from exposure to a chemical prior to conception (either parent), during prenatal development, or 

postnatally to the time of sexual maturation. Adverse developmental effects may be detected at any point 

in the life span of the organism. 

Dose-Response Relationship—The quantitative relationship between the amount of exposure to a 

toxicant and the incidence of the adverse effects. 

Embryotoxicity and Fetotoxicity—Any toxic effect on the conceptus as a result of prenatal exposure to 

a chemical; the distinguishing feature between the two terms is the stage of development during which the 

insult occurs. The terms, as used here, include malformations and variations, altered growth, and in utero 

death. 

Environmental Protection Agency (EPA) Health Advisory—An estimate of acceptable drinking water 

levels for a chemical substance based on health effects information. A health advisory is not a legally 

enforceable federal standard, but serves as technical guidance to assist federal, state, and local officials. 

Epidemiology—Refers to the investigation of factors that determine the frequency and distribution of 

disease or other health-related conditions within a defined human population during a specified period. 

Genotoxicity—A specific adverse effect on the genome of living cells that, upon the duplication of 

affected cells, can be expressed as a mutagenic, clastogenic, or carcinogenic event because of specific 

alteration of the molecular structure of the genome. 

Half-life—A measure of rate for the time required to eliminate one half of a quantity of a chemical from 

the body or environmental media. 
CYANIDE 293 

10. GLOSSARY 

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. 

Immunologic Toxicity—The occurrence of adverse effects on the immune system that may result from 

exposure to environmental agents such as chemicals. 

Immunological Effects—Functional changes in the immune response. 

Incidence—The ratio of individuals in a population who develop a specified condition to the total 

number of individuals in that population who could have developed that condition in a specified time 

period. 

Intermediate Exposure—Exposure to a chemical for a duration of 15–364 days, as specified in the 

Toxicological Profiles. 

In Vitro—Isolated from the living organism and artificially maintained, as in a test tube. 

In Vivo—Occurring within the living organism. 

Lethal Concentration(Lo) (LCLo)—The lowest concentration of a chemical in air that has been reported 

to have caused death in humans or animals. 

Lethal Concentration(50) (LC50)—A calculated concentration of a chemical in air to which exposure for 

a specific length of time is expected to cause death in 50% of a defined experimental animal population. 

Lethal Dose(Lo) (LDLo)—The lowest dose of a chemical introduced by a route other than inhalation that 

has been reported to have caused death in humans or animals. 

Lethal Dose(50) (LD50)—The dose of a chemical that has been calculated to cause death in 50% of a 

defined experimental animal population. 

Lethal Time(50) (LT50)—A calculated period of time within which a specific concentration of a 

chemical is expected to cause death in 50% of a defined experimental animal population. 

Lowest-Observed-Adverse-Effect Level (LOAEL)—The lowest exposure level of chemical in a study, 

or group of studies, that produces statistically or biologically significant increases in frequency or severity 

of adverse effects between the exposed population and its appropriate control. 

Lymphoreticular Effects—Represent morphological effects involving lymphatic tissues such as the 

lymph nodes, spleen, and thymus. 

Malformations—Permanent structural changes that may adversely affect survival, development, or 

function. 

Minimal Risk Level (MRL)—An estimate of daily human exposure to a hazardous substance that is 

likely to be without an appreciable risk of adverse noncancer health effects over a specified route and 

duration of exposure. 
CYANIDE 294 

10. GLOSSARY 

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. 

Mutagen—A substance that causes mutations. A mutation is a change in the DNA sequence of a cell’s 

DNA. Mutations can lead to birth defects, miscarriages, or cancer. 

Necropsy—The gross examination of the organs and tissues of a dead body to determine the cause of 

death or pathological conditions. 

Neurotoxicity—The occurrence of adverse effects on the nervous system following exposure to a 

chemical. 

No-Observed-Adverse-Effect Level (NOAEL)—The dose of a chemical at which there were no 

statistically or biologically significant increases in frequency or severity of adverse effects seen between 

the exposed population and its appropriate control. Effects may be produced at this dose, but they are not 

considered to be adverse. 

Octanol-Water Partition Coefficient (Kow)—The equilibrium ratio of the concentrations of a chemical 

in n-octanol and water, in dilute solution. 

Odds Ratio (OR)—A means of measuring the association between an exposure (such as toxic substances 

and a disease or condition) that 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 OR of greater than 1 is considered to indicate greater risk of disease in the 

exposed group compared to the unexposed group. 

Organophosphate or Organophosphorus Compound—A phosphorus-containing organic compound 

and especially a pesticide that acts by inhibiting cholinesterase. 

Permissible Exposure Limit (PEL)—An Occupational Safety and Health Administration (OSHA) 

allowable exposure level in workplace air averaged over an 8-hour shift of a 40-hour workweek. 

Pesticide—General classification of chemicals specifically developed and produced for use in the control 

of agricultural and public health pests. 

pH—The negative logarithim (base 10) of the hydrogen ion concentration; expressed as pH ≡ -log10 [H+

]. 

Pharmacokinetics—The dynamic behavior of a material in the body, used to predict the fate 

(disposition) of an exogenous substance in an organism. Utilizing computational techniques, it provides 

the means of studying the absorption, distribution, metabolism, and excretion of chemicals by the body. 

Pharmacokinetic Model—A set of equations that can be used to describe the time course of a parent 

chemical or metabolite in an animal system. There are two types of pharmacokinetic models: data-based 

and physiologically-based. A data-based model divides the animal system into a series of compartments, 
CYANIDE 295 

10. GLOSSARY 

which, in general, do not represent real, identifiable anatomic regions of the body, whereas the 

physiologically-based model compartments represent real anatomic regions of the body. 

Physiologically Based Pharmacodynamic (PBPD) Model—A type of physiologically based doseresponse model that quantitatively describes the relationship between target tissue dose and toxic end 

points. These models advance the importance of physiologically based models in that they clearly 

describe the biological effect (response) produced by the system following exposure to an exogenous 

substance. 

Physiologically Based Pharmacokinetic (PBPK) Model—Comprised of a series of compartments 

representing organs or tissue groups with realistic weights and blood flows. These models require a 

variety of physiological information: tissue volumes, blood flow rates to tissues, cardiac output, alveolar 

ventilation rates, and possibly membrane permeabilities. The models also utilize biochemical 

information, such as air/blood partition coefficients, and metabolic parameters. PBPK models are also 

called biologically based tissue dosimetry models. 

pK—The negative logarithim (base 10) of the dissociation constant of a weak acid or base. 

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) concentration 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. 
CYANIDE 296 

10. GLOSSARY 

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 causal factors that can be ascertained from existing 

records and/or examining survivors of the cohort. 

Risk—The possibility or chance that some adverse effect will result from a given exposure to a chemical. 

Risk Factor—An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or 

inherited characteristic that is associated with an increased occurrence of disease or other health-related 

event or condition. 

Risk Ratio—The ratio of the risk among persons with specific risk factors compared to the risk among 

persons without risk factors. A risk ratio greater than 1 indicates greater risk of disease in the exposed 

group compared to the unexposed group. 

Short-Term Exposure Limit (STEL)—The American Conference of Governmental Industrial 

Hygienists (ACGIH) maximum concentration to which workers can be exposed for up to 15 minutes 

continually. No more than four excursions are allowed per day, and there must be at least 60 minutes 

between exposure periods. The daily Threshold Limit Value-Time Weighted Average (TLV-TWA) may 

not be exceeded. 

Standardized Mortality Ratio (SMR)—A ratio of the observed number of deaths and the expected 

number of deaths in a specific standard population. 

Target Organ Toxicity—This term covers a broad range of adverse effects on target organs or 

physiological systems (e.g., renal, cardiovascular) extending from those arising through a single limited 

exposure to those assumed over a lifetime of exposure to a chemical. 

Teratogen—A chemical that causes structural defects that affect the development of an organism. 

Threshold Limit Value (TLV)—An American Conference of Governmental Industrial Hygienists 

(ACGIH) concentration of a substance to which most workers can be exposed without adverse effect. 

The TLV may be expressed as a Time Weighted Average (TWA), as a Short-Term Exposure Limit 

(STEL), or as a ceiling limit (CL). 

Time-Weighted Average (TWA)—An allowable exposure concentration averaged over a normal 8-hour 

workday or 40-hour workweek. 

Toxic Dose(50) (TD50)—A calculated dose of a chemical, introduced by a route other than inhalation, 

which is expected to cause a specific toxic effect in 50% of a defined experimental animal population. 

Toxicokinetic—The absorption, distribution, and elimination of toxic compounds in the living organism. 
CYANIDE 297 

10. GLOSSARY 

Uncertainty Factor (UF)—A factor used in operationally deriving the Minimal Risk Level (MRL) or 

Reference Dose (RfD) or Reference Concentration (RfC) from experimental data. UFs are intended to 

account for (1) the variation in sensitivity among the members of the human population, (2) the 

uncertainty in extrapolating animal data to the case of human, (3) the uncertainty in extrapolating from 

data obtained in a study that is of less than lifetime exposure, and (4) the uncertainty in using lowestobserved-adverse-effect level (LOAEL) data rather than no-observed-adverse-effect level (NOAEL) data. 

A default for each individual UF is 10; if complete certainty in data exists, a value of 1 can be used; 

however, a reduced UF of 3 may be used on a case-by-case basis, 3 being the approximate logarithmic 

average of 10 and 1. 

Xenobiotic—Any chemical that is foreign to the biological system. 
CYANIDE 298 

10. GLOSSARY 

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CYANIDE 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. 
CYANIDE 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 100-fold below levels that 

have been shown to be nontoxic in laboratory animals. 

Proposed MRLs undergo a rigorous review process: Health Effects/MRL Workgroup reviews within the 

Division of Toxicology and Environmental Medicine, 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 and 

Environmental Medicine, Agency for Toxic Substances and Disease Registry, 1600 Clifton Road NE, 

Mailstop F-32, Atlanta, Georgia 30333. 
CYANIDE A-3 

APPENDIX A 

MINIMAL RISK LEVEL (MRL) WORKSHEET 

Chemical Name: Cyanide and compounds 

CAS Numbers: 

Date: March 2006 

Profile Status: Post Public, Final 

Route: [ ] Inhalation [X] Oral 

Duration: [ ] Acute [X] Intermediate [ ] Chronic 

Graph Key: 21 

Species: Rat 

Minimal Risk Level: 0.05 [X] mg/kg/day [ ] ppm 

Reference: NTP. 1993. NTP technical report on toxicity studies of sodium cyanide administered in 

drinking water to F344/N rats and B6C3F1 mice. Toxicity Report No. 37. National Toxicology Program, 

U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health. 

NIH Publication 94-3386. 

Experimental design: For the main study, 10 male and 10 female rats were given drinking water 

containing sodium cyanide at concentrations of 0, 3, 10, 30, 100, or 300 ppm for 13 weeks. A 

supplemental set of 10 males/group was assigned for interim examinations of hematology, clinical 

chemistry, and urinalysis examinations. The intakes of cyanide during that period averaged 0, 0.2, 0.5, 

1.4 (males) or 1.7 (females), 4.5 (males) or 4.9 (females), or 12.5 mg/kg/day, respectively. Rats in the 

base study were observed twice daily. Body weights were recorded at the start of the study, weekly 

thereafter, and at necropsy. Clinical observation were recorded weekly. Water consumption by cage was 

measured weekly. Blood from the base study rats was collected on days 86 (males) and 93 (females), and 

from the supplemental study rats on days 5, 25, 45, and 92 for hematology and clinical chemistry. 

Urinalysis samples were collected from the supplemental rats on days 8, 22, 43, and 88. Complete 

necropsies were performed for all rats in the base study. The heart, kidneys, liver, lung, testes, and 

thymus were weighed. Complete histopathologic examinations of all gross lesions, tissue masses, and 

more than 35 tissues were performed on all animals in the 0 and 12.5 mg/kg/day dose groups. In the 

other exposed groups, all gross lesions, the liver (males only), spleen, and urinary bladder were examined 

for histopathology. Functional reproductive parameters were evaluated in main study rats in the 0, 30, 

100, and 300 ppm groups. Vaginal cytology and sperm motility evaluations were performed for 12 days 

prior to sacrifice. Numbers of leukocytes, nucleated epithelial cells, and large squamous epithelial cells 

were determined from vaginal swabs to ascertain estrous cycle stage and the percentage of cycle spent in 

the various stages; the vagina in these rats was examined for histopathology. At necropsy, reproductive 

tissue weights were recorded for males, and data were recorded for epididymal sperm motility, density, 

and spermatogenesis. 

Effects noted in study and corresponding doses: Exposure to cyanide had no significant effect on 

survival, body weight gain, the incidence of clinical signs, nonreproductive organ weights (absolute or 

relative to body weight), hematology, or clinical chemistry parameters. Water consumption was about 

10% lower in the two highest exposure groups, and concomitantly, urine volume was decreased and urine 

specific density was increased; the authors suggested that these findings indicated a palatability problem 

at the two highest doses. Urinary thiocyanate levels were increased in most exposed groups, indicative of 

biotransformation of ingested cyanide. No treatment-related gross or histopathologic lesions were 

observed in rats, including potential target tissues such as the corpus callosum of the brain and the 

follicular epithelium of the thyroid gland (susceptible to the anti-thyroid effects of the metabolite 

thiocyanate). 
CYANIDE A-4 

APPENDIX A 

Some cyanide-related effects were observed in the study of reproductive parameters. Statistically 

significant decreases compared to controls were observed in the absolute weights of the left epididymis 

(-7%), left cauda epididymis (-13%), and left testis (-7.6%) of rats treated at 12.5 mg/kg-day. In addition, 

13.6% reductions compared to controls were observed in spermatid heads per testis and and spermatid 

counts per mL suspension in rats treated at 12.5 mg/kg/day. The authors considered these to be evidence 

of a mild adverse effect of cyanide on the male reproductive system. The statistically significant 

reductions (7.4–8.6% lower than controls) in left cauda epididymis weights observed at 1.4 and 

4.5 mg/kg/day were not considered biologically significant in the absence of any other significant effect. 

The small (<4%), statistically significant, but not dose-related, reductions observed in spermatozoa 

motility in the 1.4, 4.5, and 12.5 mg/kg/day groups were within the range of normal values and were not 

considered biologically significant by the authors. For females, significantly (p=0.03, Wilk’s Criterion) 

more time was spent in proestrus and diestrus stages and less time in estrus and metestrus stages in the 

4.9 and 12.5 mg/kg/day dose groups than in controls, but a dose-relationship was not observed. For this 

reason, the authors did not consider these results unequivocal proof that cyanide adversely affects the 

female reproductive system. 

Dose and end point used for MRL derivation: 4.5 mg/kg/day, based on the NOAEL for no reproductive 

effects in male rats. 

[X] NOAEL [ ] LOAEL 

Uncertainty Factors used in MRL derivation: 100 

[ ] 00 for use of a LOAEL 

[X] 10 for extrapolation from animals to humans 

[X] 10 for human variability 

MRL = 4.5 mg/kg/day/100 = 0.05 mg/kg/day

Was a conversion factor used from ppm in food or water to a mg/body weight dose? Yes. 

If so, explain: The doses based on water consumption as reported by NTP (1993) were 0, 0.3, 0.9, 1.0, 

2.7, 3.2, 8.5, 9.2, 23.5, and 23.6 mg NaCN/kg/day. These doses were converted from sodium cyanide to 

cyanide by multiplying each dose by 0.53 (CN–/NaCN); resulting in dose levels of 0, 0.2, 0.5, 1.4 (males), 

1.7 (females), 4.5 (males), 4.9 (females), or 12.5 mg/kg/day cyanide. 

If an inhalation study in animals, list conversion factors used in determining human equivalent dose: NA 

Was a conversion used from intermittent to continuous exposure? NA 

Other additional studies or pertinent information that lend support to this MRL: No studies are available 

for the intermediate-duration oral toxicity of humans exposed to known quantities of cyanide, but there 

are a number of studies in animals exposed to sodium or potassium cyanide (as discussed in 

Section 3.2.2). However, not all studies are suitable for establishing dose-response relationships. Several 

studies (Gerhart 1986, 1987; Jackson 1988: Soto-Blanco et al. 2002a) in rats and pigs report neurological, 

thyroid, and gastrointestinal effects following gavage administration of cyanide; however, their usefulness 

for dose-response assessment is limited because the bolus dosing may overwhelm the detoxification 

process and is not characteristic of typical general population exposures to cyanide in drinking water. 

Similarly, although a toxicity study in dogs receiving sodium cyanide reported effects in the male 

reproductive system, adrenal gland, and kidney, the lower levels of the detoxifying enzyme rhodanese in 

this species both increases the sensitivity to cyanide and prevents the production of the metabolite 
CYANIDE A-5 

APPENDIX A 

thiosulfate to levels that would be toxic to the thyroid as seen in humans and other animals (Kamalu 

1993). Additionally, studies involving exposure to cyanide via a cassava diet (Tewe and Maner 1981a, 

1981b) were not considered as the basis of an MRL because there is evidence suggesting that other toxic 

compounds, such as scopoletin, may contribute to the observed toxic effects (Kamalu 1993). 

In rat and mice exposed to sodium cyanide in drinking water for 13 weeks (NTP 1993), reproductive 

effects in males were the only adverse effects observed. Effects on male reproduction included reductions 

in epididymal weights (-13%), testicular weights (-8%), and spermatid counts (-13.6%) in F344 rats 

exposed to 12.5 mg CN–

/kg/day, and 10–18% reductions in epididymal/caudal epididymal weights in 

B6C3F1 mice exposed to 24.3 mg CN–/kg/day. In rabbits exposed to sodium cyanide in the diet at doses 

of 15 mg CN–

/kg/day for 4 weeks or 20 mg CN–/kg/day for 40 weeks, hepatic toxicity (fatty degeneration 

and necrosis of the liver, increased serum levels of succinate dehydrogenase, alanine aminotransferase, 

and alkaline phosphatase) and renal toxicity (tubular necrosis) were observed (Okolie and Iroanya 2003; 

Okolie and Osagie 1999). Neurotoxicity (myelin degeneration in the spinal cord) was observed in rats 

exposed at 30 mg CN–

/kg/day as potassium cyanide in food for 11.5 months (Philbrick et al. 1979). 

Effects on male reproduction were severe in dogs (germ cell sloughing and degeneration, reduced 

spermatogenesis cycle) (Kamalu 1993) and also observed in rats and mice in studies in which no other 

systemic effects were observed. Hepatic, renal, and body weight effects were reported in Wistar rats that 

received doses of 3.6 mg CN–

/kg/day as potassium cyanide in drinking water for 15 days (Sousa et al. 

2002a). However, the reliability of these findings is questionable because of the lack of incidence data 

for the histopathological lesions and because no body weight effects were noted in other rat studies with 

exposures for longer durations and at higher doses. On the basis of these considerations, reproductive 

toxicity in males is selected as the critical effect of cyanide toxicity. The NTP (1993) bioassay in rats is 

selected as the principal study because it provided the lowest LOAEL and a NOAEL for the critical effect 

and examined the full range of tissues with extensive interim hematological, clinical chemistry, and 

urinalyses. 

Agency Contacts (Chemical Managers): Jessilynn Taylor, Nickolette Roney, Carolyn Harper 
CYANIDE A-6 

APPENDIX A 

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CYANIDE B-1 

APPENDIX B. USER'S GUIDE 

Chapter 1 

Public Health Statement 

This chapter of the profile is a health effects summary written in non-technical language. Its intended 

audience is the general public, especially people living in the vicinity of a hazardous waste site or 

chemical release. If the Public Health Statement were removed from the rest of the document, it would 

still communicate to the lay public essential information about the chemical. 

The major headings in the Public Health Statement are useful to find specific topics of concern. The 

topics are written in a question and answer format. The answer to each question includes a sentence that 

will direct the reader to chapters in the profile that will provide more information on the given topic. 

Chapter 2 

Relevance to Public Health 

This chapter provides a health effects summary based on evaluations of existing toxicologic, 

epidemiologic, and toxicokinetic information. This summary is designed to present interpretive, weightof-evidence discussions for human health end points by addressing the following questions: 

1. What effects are known to occur in humans? 

2. What effects observed in animals are likely to be of concern to humans? 

3. What exposure conditions are likely to be of concern to humans, especially around hazardous 

waste sites? 

The chapter covers end points in the same order that they appear within the Discussion of Health Effects 

by Route of Exposure section, by route (inhalation, oral, and dermal) and within route by effect. Human 

data are presented first, then animal data. Both are organized by duration (acute, intermediate, chronic). 

In vitro data and data from parenteral routes (intramuscular, intravenous, subcutaneous, etc.) are also 

considered in this chapter. 

The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using 

existing toxicokinetic, genotoxic, and carcinogenic data. ATSDR does not currently assess cancer 

potency or perform cancer risk assessments. Minimal Risk Levels (MRLs) for noncancer end points (if 

derived) and the end points from which they were derived are indicated and discussed. 

Limitations to existing scientific literature that prevent a satisfactory evaluation of the relevance to public 

health are identified in the Chapter 3 Data Needs section. 

Interpretation of Minimal Risk Levels 

Where sufficient toxicologic information is available, ATSDR has derived MRLs for inhalation and oral 

routes of entry at each duration of exposure (acute, intermediate, and chronic). These MRLs are not 
CYANIDE B-2 

APPENDIX B 

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. 

MRLs should help physicians and public health officials determine the safety of a community living near 

a chemical emission, given the concentration of a contaminant in air or the estimated daily dose in water. 

MRLs are based largely on toxicological studies in animals and on reports of human occupational 

exposure. 

MRL users should be familiar with the toxicologic information on which the number is based. Chapter 2, 

"Relevance to Public Health," contains basic information known about the substance. Other sections such 

as Chapter 3 Section 3.9, "Interactions with Other Substances,” and Section 3.10, "Populations that are 

Unusually Susceptible" provide important supplemental information. 

MRL users should also understand the MRL derivation methodology. MRLs are derived using a 

modified version of the risk assessment methodology that the Environmental Protection Agency (EPA) 

provides (Barnes and Dourson 1988) to determine reference doses (RfDs) for lifetime exposure. 

To derive an MRL, ATSDR generally selects the most sensitive end point which, in its best 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 end point are available, ATSDR derives an MRL using the most sensitive 

species (when information from multiple species is available) with the highest no-observed-adverse-effect 

level (NOAEL) that does not exceed any adverse effect levels. When a NOAEL is not available, a 

lowest-observed-adverse-effect level (LOAEL) can be used to derive an MRL, and an uncertainty factor 

(UF) of 10 must be employed. Additional uncertainty factors of 10 must be used both for human 

variability to protect sensitive subpopulations (people who are most susceptible to the health effects 

caused by the substance) and for interspecies variability (extrapolation from animals to humans). In 

deriving an MRL, these individual uncertainty factors are multiplied together. The product is then 

divided into the inhalation concentration or oral dosage selected from the study. Uncertainty factors used 

in developing a substance-specific MRL are provided in the footnotes of the levels of significant exposure 

(LSE) tables. 

Chapter 3 

Health Effects 

Tables and Figures for Levels of Significant Exposure (LSE) 

Tables and figures are used to summarize health effects and illustrate graphically levels of exposure 

associated with those effects. These levels cover health effects observed at increasing dose 

concentrations and durations, differences in response by species, MRLs to humans for noncancer end 

points, and EPA's estimated range associated with an upper- bound individual lifetime cancer risk of 1 in 

10,000 to 1 in 10,000,000. Use the LSE tables and figures for a quick review of the health effects and to 

locate data for a specific exposure scenario. The LSE tables and figures should always be used in 

conjunction with the text. All entries in these tables and figures represent studies that provide reliable, 

quantitative estimates of NOAELs, LOAELs, or Cancer Effect Levels (CELs). 

The legends presented below demonstrate the application of these tables and figures. Representative 

examples of LSE Table 3-1 and Figure 3-1 are shown. The numbers in the left column of the legends 

correspond to the numbers in the example table and figure. 
CYANIDE B-3 

APPENDIX B 

LEGEND 

See Sample LSE Table 3-1 (page B-6) 

(1) Route of Exposure. One of the first considerations when reviewing the toxicity of a substance 

using these tables and figures should be the relevant and appropriate route of exposure. Typically 

when sufficient data exist, 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 Tables 3-1, 3-2, and 3-3, respectively). LSE figures are limited to the inhalation 

(LSE Figure 3-1) and oral (LSE Figure 3-2) routes. Not all substances will have data on each 

route of exposure and will not, therefore, have all five of the tables and figures. 

(2) Exposure Period. Three exposure periods—acute (less than 15 days), intermediate (15– 

364 days), and chronic (365 days or more)—are presented within each relevant route of exposure. 

In this example, an inhalation study of intermediate exposure duration is reported. For quick 

reference to health effects occurring from a known length of exposure, locate the applicable 

exposure period within the LSE table and figure. 

(3) Health Effect. The major categories of health effects included in LSE tables and figures are 

death, systemic, immunological, neurological, developmental, reproductive, and cancer. 

NOAELs and LOAELs can be reported in the tables and figures for all effects but cancer. 

Systemic effects are further defined in the "System" column of the LSE table (see key number 

18). 

(4) Key to Figure. Each key number in the LSE table links study information to one or more data 

points using the same key number in the corresponding LSE figure. In this example, the study 

represented by key number 18 has been used to derive a NOAEL and a Less Serious LOAEL 

(also see the two "18r" data points in sample Figure 3-1). 

(5) Species. The test species, whether animal or human, are identified in this column. Chapter 2, 

"Relevance to Public Health," covers the relevance of animal data to human toxicity and 

Section 3.4, "Toxicokinetics," contains any available information on comparative toxicokinetics. 

Although NOAELs and LOAELs are species specific, the levels are extrapolated to equivalent 

human doses to derive an MRL. 

(6) Exposure Frequency/Duration. The duration of the study and the weekly and daily exposure 

regimens are provided in this column. This permits comparison of NOAELs and LOAELs from 

different studies. In this case (key number 18), rats were exposed to “Chemical x” via inhalation 

for 6 hours/day, 5 days/week, for 13 weeks. For a more complete review of the dosing regimen, 

refer to the appropriate sections of the text or the original reference paper (i.e., Nitschke et al. 

1981). 

(7) System. This column further defines the systemic effects. These systems include respiratory, 

cardiovascular, gastrointestinal, hematological, musculoskeletal, hepatic, renal, and 

dermal/ocular. "Other" refers to any systemic effect (e.g., a decrease in body weight) not covered 

in these systems. In the example of key number 18, one systemic effect (respiratory) was 

investigated. 

(8) NOAEL. A NOAEL is the highest exposure level at which no harmful effects were seen in the 

organ system studied. Key number 18 reports a NOAEL of 3 ppm for the respiratory system, 
CYANIDE B-4 

APPENDIX B 

which was used to derive an intermediate exposure, inhalation MRL of 0.005 ppm (see 

footnote "b"). 

(9) LOAEL. A LOAEL is the lowest dose used in the study that caused a harmful health effect. 

LOAELs have been classified into "Less Serious" and "Serious" effects. These distinctions help 

readers identify the levels of exposure at which adverse health effects first appear and the 

gradation of effects with increasing dose. A brief description of the specific end point used to 

quantify the adverse effect accompanies the LOAEL. The respiratory effect reported in key 

number 18 (hyperplasia) is a Less Serious LOAEL of 10 ppm. MRLs are not derived from 

Serious LOAELs. 

(10) Reference. The complete reference citation is given in Chapter 9 of the profile. 

(11) CEL. A CEL is the lowest exposure level associated with the onset of carcinogenesis in 

experimental or epidemiologic studies. CELs are always considered serious effects. The LSE 

tables and figures do not contain NOAELs for cancer, but the text may report doses not causing 

measurable cancer increases. 

(12) Footnotes. Explanations of abbreviations or reference notes for data in the LSE tables are found 

in the footnotes. Footnote "b" indicates that the NOAEL of 3 ppm in key number 18 was used to 

derive an MRL of 0.005 ppm. 

LEGEND 

See Sample Figure 3-1 (page B-7) 

LSE figures graphically illustrate the data presented in the corresponding LSE tables. Figures help the 

reader quickly compare health effects according to exposure concentrations for particular exposure 

periods. 

(13) Exposure Period. The same exposure periods appear as in the LSE table. In this example, health 

effects observed within the acute and intermediate exposure periods are illustrated. 

(14) Health Effect. These are the categories of health effects for which reliable quantitative data 

exists. The same health effects appear in the LSE table. 

(15) Levels of Exposure. Concentrations or doses for each health effect in the LSE tables are 

graphically displayed in the LSE figures. Exposure concentration or dose is measured on the log 

scale "y" axis. Inhalation exposure is reported in mg/m3

 or ppm and oral exposure is reported in 

mg/kg/day. 

(16) NOAEL. In this example, the open circle designated 18r identifies a NOAEL critical end point in 

the rat upon which an intermediate inhalation exposure MRL is based. The key number 18 

corresponds to the entry in the LSE table. The dashed descending arrow indicates the 

extrapolation from the exposure level of 3 ppm (see entry 18 in the table) to the MRL of 

0.005 ppm (see footnote "b" in the LSE table). 

(17) CEL. Key number 38m is one of three studies for which CELs were derived. The diamond 

symbol refers to a CEL for the test species-mouse. The number 38 corresponds to the entry in the 

LSE table. 
CYANIDE B-5 

APPENDIX B 

(18) Estimated Upper-Bound Human Cancer Risk Levels. This is the range associated with the upperbound for lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. These risk levels are derived 

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. 
SAMPLE 

1 → Table 3-1. Levels of Significant Exposure to [Chemical x] – Inhalation 

Key to figurea 

Exposure frequency/ 

Species duration System 

NOAEL (ppm) 

LOAEL (effect) 

Less serious (ppm) 

Serious (ppm) 

Re

2 → INTERMEDIATE EXPOSURE 3 4 

5 6 7 8 9 10

→ Systemic ↓ ↓ ↓ ↓ ↓ ↓→

13 wk 5 d/wk 6 hr/d 

18 Rat

CHRONIC EXPOSURE 

Resp 3b 10 (hyperplasia) 

Nit

Cancer 

↓

38 39 40 

Rat Rat Mouse 

18 mo 5 d/wk 7 hr/d 89–104 wk 5 d/wk 6 hr/d 79–103 wk 5 d/wk 6 hr/d 

20 10 10 

(CEL, multiple organs) (CEL, lung tumors, nasal tumors) (CEL, lung tumors, hemangiosarcomas) 

WNTNT

11 

12 → a The number corresponds to entries in Figure 3-1. b Used to derive an intermediate inhalation Minimal Risk Level (MRL) of 5x10-3 ppm; dose adjusted for intermittent ex

by an uncertainty factor of 100 (10 for extrapolation from animal to humans, 10 for human variability). 

CYANIDE B-8 

APPENDIX B 

This page is intentionally blank. 
CYANIDE C-1 

APPENDIX C. ACRONYMS, ABBREVIATIONS, AND SYMBOLS 

ACGIH American Conference of Governmental Industrial Hygienists 

ACOEM American College of Occupational and Environmental Medicine 

ADI acceptable daily intake 

ADME absorption, distribution, metabolism, and excretion 

AED atomic emission detection 

AFID alkali flame ionization detector 

AFOSH Air Force Office of Safety and Health 

ALT alanine aminotransferase 

AML acute myeloid leukemia 

AOAC Association of Official Analytical Chemists 

AOEC Association of Occupational and Environmental Clinics 

AP alkaline phosphatase 

APHA American Public Health Association 

AST aspartate aminotransferase 

atm atmosphere 

ATSDR Agency for Toxic Substances and Disease Registry 

AWQC Ambient Water Quality Criteria 

BAT best available technology 

BCF bioconcentration factor 

BEI Biological Exposure Index 

BMD benchmark dose 

BMR benchmark response 

BSC Board of Scientific Counselors 

C centigrade 

CAA Clean Air Act 

CAG Cancer Assessment Group of the U.S. Environmental Protection Agency 

CAS Chemical Abstract Services 

CDC Centers for Disease Control and Prevention 

CEL cancer effect level 

CELDS Computer-Environmental Legislative Data System 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CFR Code of Federal Regulations 

Ci curie 

CI confidence interval 

CL ceiling limit value 

CLP Contract Laboratory Program 

cm centimeter 

CML chronic myeloid leukemia 

CPSC Consumer Products Safety Commission 

CWA Clean Water Act 

DHEW Department of Health, Education, and Welfare 

DHHS Department of Health and Human Services 

DNA deoxyribonucleic acid 

DOD Department of Defense 

DOE Department of Energy 

DOL Department of Labor 

DOT Department of Transportation 
CYANIDE C-2 

APPENDIX C 

DOT/UN/ Department of Transportation/United Nations/ 

NA/IMCO North America/International Maritime Dangerous Goods Code 

DWEL drinking water exposure level 

ECD electron capture detection 

ECG/EKG electrocardiogram 

EEG electroencephalogram 

EEGL Emergency Exposure Guidance Level 

EPA Environmental Protection Agency 

F Fahrenheit 

F1 first-filial generation 

FAO Food and Agricultural Organization of the United Nations 

FDA Food and Drug Administration 

FEMA Federal Emergency Management Agency 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FPD flame photometric detection 

fpm feet per minute 

FR Federal Register 

FSH follicle stimulating hormone 

FT3I free triiodothyronine index 

FT4I free thyroxine index 

g gram 

GC gas chromatography 

gd gestational day 

GLC gas liquid chromatography 

GPC gel permeation chromatography 

HPLC high-performance liquid chromatography 

HRGC high resolution gas chromatography 

HSDB Hazardous Substance Data Bank 

IARC International Agency for Research on Cancer 

IDLH immediately dangerous to life and health 

ILO International Labor Organization 

IRIS Integrated Risk Information System 

Kd adsorption ratio 

kg kilogram 

kkg metric ton 

Koc organic carbon partition coefficient 

Kow octanol-water partition coefficient 

L liter 

LC liquid chromatography 

LC50 lethal concentration, 50% kill 

LCGU local cerebral glucose utilization 

LCLo lethal concentration, low 

LD50 lethal dose, 50% kill 

LDLo lethal dose, low 

LDH lactic dehydrogenase 

LH luteinizing hormone 

LOAEL lowest-observed-adverse-effect level 

LSE Levels of Significant Exposure 

LT50 lethal time, 50% kill 

m meter 

MA trans,trans-muconic acid 
CYANIDE C-3 

APPENDIX C 

MAL maximum allowable level 

mCi millicurie 

MCL maximum contaminant level 

MCLG maximum contaminant level goal 

MF modifying factor 

MFO mixed function oxidase 

mg milligram 

mL milliliter 

mm millimeter 

mmHg millimeters of mercury 

mmol millimole 

mppcf millions of particles per cubic foot 

MRL Minimal Risk Level 

MS mass spectrometry 

NAAQS National Ambient Air Quality Standard 

NAS National Academy of Science 

NATICH National Air Toxics Information Clearinghouse 

NATO North Atlantic Treaty Organization 

NCE normochromatic erythrocytes 

NCEH National Center for Environmental Health 

NCI National Cancer Institute 

ND not detected 

NFPA National Fire Protection Association 

ng nanogram 

NHANES National Health and Nutrition Examination Survey 

NIEHS National Institute of Environmental Health Sciences 

NIOSH National Institute for Occupational Safety and Health 

NIOSHTIC NIOSH's Computerized Information Retrieval System 

NLM National Library of Medicine 

nm nanometer 

nmol nanomole 

NOAEL no-observed-adverse-effect level 

NOES National Occupational Exposure Survey 

NOHS National Occupational Hazard Survey 

NPD nitrogen phosphorus detection 

NPDES National Pollutant Discharge Elimination System 

NPL National Priorities List 

NR not reported 

NRC National Research Council 

NS not specified 

NSPS New Source Performance Standards 

NTIS National Technical Information Service 

NTP National Toxicology Program 

ODW Office of Drinking Water, EPA 

OERR Office of Emergency and Remedial Response, EPA 

OHM/TADS Oil and Hazardous Materials/Technical Assistance Data System 

OPP Office of Pesticide Programs, EPA 

OPPT Office of Pollution Prevention and Toxics, EPA 

OPPTS Office of Prevention, Pesticides and Toxic Substances, EPA 

OR odds ratio 

OSHA Occupational Safety and Health Administration 
CYANIDE 

C-4 

APPENDIX C 

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 

pg picogram 

PHS Public Health Service 

PID photo ionization detector 

pmol picomole 

PMR proportionate mortality ratio 

ppb parts per billion 

ppm parts per million 

ppt parts per trillion 

PSNS pretreatment standards for new sources 

RBC red blood cell 

REL recommended exposure level/limit 

RfC reference concentration 

RfD reference dose 

RNA ribonucleic acid 

RQ reportable quantity 

RTECS Registry of Toxic Effects of Chemical Substances 

SARA Superfund Amendments and Reauthorization Act 

SCE sister chromatid exchange 

SGOT serum glutamic oxaloacetic transaminase 

SGPT serum glutamic pyruvic transaminase 

SIC standard industrial classification 

SIM selected ion monitoring 

SMCL secondary maximum contaminant level 

SMR standardized mortality ratio 

SNARL suggested no adverse response level 

SPEGL Short-Term Public Emergency Guidance Level 

STEL short term exposure limit 

STORET Storage and Retrieval T3 triiodothyronine T4 thyroxine 

TD50 toxic dose, 50% specific toxic effect 

TLV threshold limit value 

TOC total organic carbon 

TPQ threshold planning quantity 

TRI Toxics Release Inventory 

TSCA Toxic Substances Control Act 

TSH thyroid stimulating hormone 

TWA time-weighted average 

UF uncertainty factor 

U.S. United States 

USDA United States Department of Agriculture 

USGS United States Geological Survey 
CYANIDE 

C-5 

APPENDIX C 

VOC volatile organic compound 

WBC white blood cell 

WHO World Health Organization 

> 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 μg microgram q1

* cancer slope factor 

– negative 

+ positive 

(+) weakly positive result 

(–) weakly negative result 
CYANIDE C-6

APPENDIX C 

This page is intentionally blank. 
CYANIDE D-1 

APPENDIX D. INDEX 

absorbed dose ......................................................................................................................................................14, 104 

adrenal gland ................................................................................................................................. 21, 57, 82, 91, 94, 99 

adrenals............................................................................................................................................................82, 94, 99 

adsorption ..................................................................................................................................................................173 

aerobic ............................................................................................................. 90, 91, 93, 109, 155, 173, 175, 176, 177

alanine aminotransferase .......................................................................................................................................21, 55 

ambient air.........................................................................................................................................................213, 218 

anaerobic........................................................................................................................ 90, 92, 106, 155, 173, 176, 177

anemia ...............................................................................................................................................................7, 42, 53 

aspartate aminotransferase (see AST)..........................................................................................................................52 

asphyxia.....................................................................................................................................................15, 36, 52, 97 

AST (see aspartate aminotransferase)....................................................................................................................52, 54 

atropine......................................................................................................................................................................115 

bioaccumulation ........................................................................................................................................................168 

bioavailability ......................................................................................................................................76, 126, 183, 196 

biodegradation ......................................................13, 150, 151, 155, 167, 172, 173, 174, 175, 176, 177, 195, 196, 218

biomarker..............................................................................14, 103, 104, 106, 107, 124, 125, 126, 191, 201, 206, 217

body weight effects....................................................................................................................................22, 39, 58, 66 

breast milk ...........................................................................................................................................85, 126, 186, 191 

cancer..................................................................................................................................... 6, 7, 60, 65, 101, 185, 221 

carcinogen..................................................................................................................................................................228 

carcinogenic.....................................................................................................................................................18, 25, 98 

carcinogenicity ........................................................................................................................................7, 16, 122, 221 

carcinoma ......................................................................................................................................................73, 74, 122 

cardiovascular.............................................................................................. 20, 36, 52, 70, 96, 102, 114, 120, 121, 125

cardiovascular effects........................................................................................................................ 36, 52, 70, 96, 121 

cassava...................................2, 4, 7, 8, 9, 13, 15, 16, 17, 18, 21, 23, 27, 43, 52, 55, 56, 57, 58, 59, 61, 63, 64, 65, 84, 

102, 111, 112, 120, 121, 123, 124, 125, 128, 166, 183, 184, 186, 188, 189, 193, 198 

clearance..............................................................................................................................................................85, 111 

cytochrome c ............................................................................... 14, 90, 91, 92, 95, 105, 106, 108, 110, 111, 114, 125 

death ....................................................................6, 9, 14, 16, 19, 25, 27, 28, 40, 42, 43, 62, 66, 70, 72, 75, 77, 91, 93, 

94, 95, 103, 104, 105, 106, 113, 115, 116, 117, 120, 124, 129, 185

deoxyribonucleic acid (see DNA)..........................................................................................................................72, 74 

dermal effects ............................................................................................................................................38, 39, 57, 71 

DNA (see deoxyribonucleic acid).................................................................................. 16, 72, 73, 74, 75, 94, 104, 122

dopamine ......................................................................................................................................... 61, 94, 96, 116, 129 

endocrine .........................................................................................................................................................38, 66, 99 

endocrine effects....................................................................................................................................................38, 56 

estrogen receptor........................................................................................................................................................100 

estrogenic...................................................................................................................................................................100 

fetus...............................................................................................................................................................8, 101, 103 

gastrointestinal effects ................................................................................................................. 20, 21, 37, 53, 70, 102 

general population ......................4, 5, 9, 13, 21, 43, 63, 64, 65, 103, 112, 113, 155, 156, 157, 186, 187, 192, 195, 197 

genotoxic ........................................................................................................................................... 16, 25, 72, 73, 122 

genotoxicity ...................................................................................................................................................73, 75, 122 

goiter........................................................................................................................................ 15, 56, 98, 106, 111, 218 

groundwater................................................................................................. 13, 155, 164, 165, 167, 168, 179, 180, 193

growth retardation................................................................................................................................................64, 123 

half-life .............................................................................................. 3, 75, 80, 103, 105, 108, 167, 169, 174, 176, 195

hematological effects.............................................................................................................................................37, 53 

hematopoietic ..............................................................................................................................................................53 

hepatic effects..........................................................................................................................................37, 54, 55, 107 
CYANIDE D-2 

APPENDIX D 

hydrolysis .....................................................................60, 117, 131, 169, 170, 172, 174, 175, 177, 182, 183, 187, 196 

hydroxocobalamin ..................................................................................................................... 14, 80, 84, 91, 109, 115 

hydroxyl radical.........................................................................................................................................155, 169, 172 

immunological................................................................................................................................... 25, 39, 59, 71, 123 

immunological effects .............................................................................................................................39, 59, 71, 123 

iodide ...................................................................................................................................................................97, 174 

Kow ..................................................................................................................... 135, 136, 137, 138, 139, 167, 168, 194

LD50 ..................................................................................................... 15, 42, 43, 66, 99, 108, 110, 111, 115, 116, 120

metabolic effects....................................................................................................................................................19, 59 

milk.................................................................................................................................................. 8, 16, 102, 128, 156 

musculoskeletal effects..........................................................................................................................................37, 54 

neurobehavioral ...........................................................................................................................................17, 100, 128 

neurochemical............................................................................................................................................................106 

neuropathy ......................................................................................................................................... 17, 58, 62, 90, 106 

neurotransmitter.....................................................................................................................................................16, 91 

ocular effects ...................................................................................................................................................39, 58, 71 

Parkinsonism .......................................................................................................................................................60, 120 

partition coefficients..................................................................................................................................................194 

pharmacodynamic........................................................................................................................................................85 

pharmacokinetic................................................................................................................. 82, 85, 86, 87, 101, 108, 127 

photolysis................................................................................................................................... 155, 169, 172, 173, 175 

placenta..........................................................................................................................................................8, 103, 126 

rate constant...............................................................................................................................................169, 172, 176 

renal effects ...............................................................................................................................................38, 55, 56, 70 

rhodanese..............................14, 15, 19, 21, 28, 41, 43, 64, 65, 80, 82, 97, 99, 108, 110, 111, 113, 125, 126, 127, 174

serum glutamic oxaloacetic transaminase (see SGOT)................................................................................................54 

serum glutamic pyruvic transaminase (see SGPT) ......................................................................................................54 

SGOT (see serum glutamic oxaloacetic transaminase)................................................................................................54 

SGPT (see serum glutamic pyruvic transaminase) ......................................................................................................54 

solubility......................................................................................................................................................88, 166, 194 

spermatozoa.................................................................................................................................................................23 

T3.....................................................................................................................................................................38, 56, 57 

T4.....................................................................................................................................................................38, 56, 57 

thiocyanate.............................................3, 4, 5, 6, 7, 8, 9, 15, 16, 38, 56, 58, 62, 63, 75, 77, 79, 80, 82, 84, 85, 89, 90, 

97, 102, 104, 108, 109, 110, 111, 113, 117, 123, 124, 125, 126, 127, 129, 134, 

139, 141, 142, 149, 150, 151, 155, 156, 157, 159, 164, 165, 166, 168, 174, 175,

177, 179, 181, 182, 184, 187, 188, 189, 191, 192, 193, 194, 196, 197, 198, 201,

202, 203, 205, 206, 210, 214, 215, 216, 217, 218, 224, 225

thyroid ................................................................3, 7, 8, 15, 20, 21, 27, 38, 56, 57, 90, 97, 98, 102, 111, 124, 126, 221

thyroid stimulating hormone (see TSH) ....................................................................................................15, 20, 38, 56 

thyroxine..........................................................................................................................................................56, 57, 97 

toxicokinetic .................................................................................................................................... 25, 80, 85, 126, 127 

tremors......................................................................................................................................... 17, 20, 41, 72, 93, 108 

triiodothyronine ...........................................................................................................................................................56 

TSH (see thyroid stimulating hormone) ......................................................................................................................38 

vapor phase................................................................................................................................................................139 

volatility.....................................................................................................................................................................166 

volatilization.............................................................................. 155, 158, 166, 167, 168, 172, 176, 177, 195, 196, 206

weanling ..............................................................................................................................................................65, 123