TOXICOLOGICAL PROFILE FOR
 

HYDRAZINES
 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
 

Public Health Service
 

Agency for Toxic Substances and Disease Registry
 

September 1997 
HYDRAZINES ii 

DISCLAIMER 

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

the Agency for Toxic Substances and Disease Registry. 
HYDRAZINES iii 

UPDATE STATEMENT 

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

years. For information regarding the update status of previously released profiles, contact ATSDR at: 

Agency for Toxic Substances and Disease Registry
 

Division of Toxicology/Toxicology Information Branch
 

1600 Clifton Road NE, E-29
 

Atlanta, Georgia 30333
 



 

HYDRAZINES vii 

CONTRIBUTORS 

CHEMICAL MANAGER(S)/AUTHOR(S): 

Gangadhar Choudhary, Ph.D. 

ATSDR, Division of Toxicology, Atlanta, GA 

Hugh IIansen, Ph.D.
 

ATSDR, Division of Toxicology, Atlanta, GA
 

Steve Donkin, Ph.D.
 

Sciences International, Inc., Alexandria, VA
 

Mr. Christopher Kirman
 

Life Systems, Inc., Cleveland, OH
 

THE PROFILE HAS UNDERGONE THE FOLLOWING ATSDR INTERNAL REVIEWS:
 

1 .	 Green Border Review. Green Border review assures the consistency with ATSDR policy. 

2 . 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. 

3.	 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. 

HYDRAZINES ix 

PEER REVIEW
 

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

1.	 Dr. Emerich Fiala, Chief, Division of Biochemical Pharmacology, American Health 

Foundation, Valhalla, NY 

2. Dr. Bela Toth, Professor, University of Nebraska Medical Center, Omaha, NE 

3.	 Dr. Raghubir Sharma, Fred C. Davison Professor, University of Georgia, College of Veterinary 

Medicine, Athens, GA 

These experts collectively have knowledge of hydrazines’s physical and chemical properties, toxicokinetics, 

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

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

specified in Section 104(i)(13) of the Comprehensive Environmental Response, Compensation, and 

Liability Act, as amended. 

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

peer reviewers’ comments and determined which comments will be included in the profile. A listing 

of the peer reviewers’ comments not incorporated in the profile, with a brief explanation of the 

rationale for their exclusion, exists as part of the administrative record for this compound. A list of 

databases reviewed and a list of unpublished documents cited are also included in the administrative 

record. 

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

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









HYDRAZINES 1 

1. PUBLIC HEALTH STATEMENT
 

This statement was prepared to give you information about hydrazines and to emphasize the 

human health effects that may result from exposure to these chemicals. The Environmental 

Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. 

These sites make up the National Priorities List (NPL) and are the sites targeted for long-term 

federal clean-up activities. Hydrazines have been found in at least 8 of the 1,430 current or 

former NPL sites. However, the total number of NPL sites evaluated is not known. As more 

sites are evaluated, the number of sites at which hydrazines are found may increase. This 

information is important because exposure to hydrazines may cause harmful health effects and 

because these sites are potential or actual sources of human exposure to hydrazines. 

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

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

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

You may be exposed by breathing, eating, or drinking substances containing the substance or 

by skin contact with it. 

If you are exposed to substances such as hydrazines, many factors will determine whether 

harmful health effects will occur and what the type and severity of those health effects will 

be. These factors include the dose (how much), the duration (how long), the route or 

pathway by which you are exposed (breathing, eating, drinking, or skin contact), the other 

chemicals to which you are exposed, and your individual characteristics such as age, sex, 

nutritional status, family traits, life style, and state of health. 

1.1 WHAT ARE HYDRAZINES? 

Hydrazines are chemical compounds that contain two nitrogen atoms joined by a single 

covalent bond. Three examples of hydrazines are 
HYDRAZINES 2 

1. PUBLIC HEALTH STATEMENT 

•	 hydrazine - also known as diamine, diamide, anhydrous hydrazine, and hydrazine 

base 

•	 1,1-dimethylhydrazine - also known as unsymmetrical dimethylhydrazine, dimazine, 

and by other names 

•	 1,2-dimethylhydrazine - also known as symmetrical dimethylhydrazine, 

hydrazomethane, and by other names 

This document uses the term “hydrazines” to refer to hydrazine, l,l-dimethylhydrazine, and 

1,2-dimethylhydrazine, collectively. These hydrazines are somewhat similar in chemical 

structure and reactivity. However, there are some clear differences in their production, uses, 

and adverse health effects. There are many other hydrazine compounds; however, these three 

hydrazines are discussed together in this document because they are of interest to the U.S. 

Department of Defense. 

Hydrazines are manufactured from chemicals such as ammonia, dimethylamine, hydrogen 

peroxide, or sodium hypochlorite. A small amount of hydrazine occurs naturally in some 

plants. The amounts of hydrazine and l,l-dimethylhydrazine produced in the United States in 

the mid-1960s to mid-1980s have been reported to range from 15 million to 38 million 

pounds and from 9,900 to 99,000 pounds per year, respectively. 1,2-Dimethylhydrazine is a 

research chemical and the quantities produced are likely to be much less. We don’t know 

how much hydrazines is currently produced. 

In their pure form, hydrazines are clear, colorless liquids, These liquids can evaporate in air. 

Hydrazines smell somewhat like ammonia. Most people can smell hydrazine or 

1,1 -dimethylhydrazine when present at concentrations greater than 2-8 parts hydrazines per 

million parts of air (ppm). Hydrazines are highly reactive and easily catch fire. 
HYDRAZINES 3 

1. PUBLIC HEALTH STATEMENT 

Hydrazine has been used as fuel for many rockets and spacecraft, including the space shuttle. 

Hydrazine is used to treat boiler water to reduce corrosion, to reduce other chemicals, and to 

bring about or speed up chemical reactions. It is also used as a medicine and to make other 

medicines, farm chemicals, and plastic foams. 1,1-Dimethylhydrazine has been used as a 

rocket propellant and to make other chemicals. Other uses are also possible. 

1,2 Dimethylhydrazine has no commercial uses but is used in labs to study colon cancer in 

experimental animals. 

For more information about the chemical properties and uses of hydrazines, see Chapters 3 

and 4. 

1.2 WHAT HAPPENS TO HYDRAZINES WHEN THEY ENTER THE 

ENVIRONMENT? 

Hydrazines can be released to the environment from places that make, process, or use these 

chemicals. One of the primary ways hydrazine and 1,1-dimethylhydrazine enter the 

environment is from their use as rocket fuels. Accidental spills and leaks from storage and 

waste sites may add to environmental levels of hydrazines. Because 1,2-dimethylhydrazine is 

not used commercially and is produced only in small amounts, large releases to the 

environment are not expected. 

Most of the hydrazines are released directly to the air where they are quickly destroyed by 

reactive molecules (small parts or bits) normally in air. Most of the hydrazines in air are 

gone within a few minutes or hours. 

Smaller amounts of hydrazines are also released directly to surface water and soil: Lab 

studies show that some of the hydrazines released to soil and water can evaporate into the air. 

Hydrazines can also dissolve in water or bind to soil. The extent to which these processes 

occur depends on soil and water conditions. Hydrazines can move with water through soil as 

it flows underground. This is particularly true in sandy soils. In water and soil, some 
HYDRAZINES 4 

1. PUBLIC HEALTH STATEMENT 

microorganisms (tiny plants or animals) can break down hydrazines to form less toxic 

compounds. Most of the hydrazines in soil and water are gone within a few weeks. 

Hydrazines may become concentrated in some fish living in contaminated water. However, 

most animals quickly digest and excrete hydrazines so high levels of these compounds are not 

expected to remain in their bodies. 

For more information on what happens to hydrazines in the environment, see Chapters 4 

and 5. 

1.3 HOW MIGHT I BE EXPOSED TO HYDRAZINES? 

You may be exposed to significant amounts of hydrazines if you work in a place that makes, 

processes, or uses hydrazines, especially if you do not use proper protective equipment. 

People who live near these places, or near accidental spills or hazardous waste sites 

contaminated with hydrazines, may also be exposed. However, since hydrazines stay in air, 

water, and soil only briefly, most people are not exposed to them from these sources. 

Small amounts of hydrazine and 1,1-dimethylhydrazine have been found in tobacco products. 

Therefore, people who chew tobacco, smoke cigarettes, or are exposed to cigarette smoke 

indirectly may be exposed to small amounts of these chemicals. 

In the past, some people may have been exposed to 1,1-dimethylhydrazine in fruits sprayed 

with Alar, a growth enhancer. 1,1-Dimethylhydrazine is sometimes found where Alar is made 

or used. Because Alar is no longer used on food plants in the United States, people are no 

longer exposed to it from this source. However, Alar is still used on some nonfood plants. 

Therefore, some greenhouse workers who use Alar may be exposed to small amounts of 1, l-dimethylhydrazine. 
HYDRAZINES 5 

1. PUBLIC HEALTH STATEMENT 

Since 1,2-dimethylhydrazine is not used commercially, most people are not exposed to this 

chemical. It is used as a research chemical to produce colon cancer in lab animals. 

Therefore, lab workers who use 1,2-dimethylhydrazine for this purpose may be exposed to 

small amounts. 

For more information about how you can be exposed to hydrazines, see Chapter 5. 

1.4 HOW CAN HYDRAZINES ENTER AND LEAVE MY BODY? 

Very little is known about how hydrazines enter and leave your body. Based on limited 

studies in animals, hydrazines are probably rapidly absorbed into your blood if you swallow 

them or if you get them on your skin. Based on their chemical and physical properties, 

hydrazines are also likely to be well absorbed if you breathe them into your lungs. Once they 

are in your blood, hydrazines are probably carried to all tissues of your body. Animal studies 

suggest that soon after you are exposed, the levels of hydrazines in your blood and tissues 

will fall rapidly. This is because your body changes hydrazines into other compounds called 

metabolites. Some of these metabolites (or compounds) can react with important molecules 

in your body and may harm you. Animal studies show that most metabolites and unchanged 

hydrazines leave your body in urine within 1 day. A small amount can also be found in the 

air you breathe out. 

For more information about how hydrazines can enter and leave your body, see Chapter 2. 

1.5 HOW CAN HYDRAZINES AFFECT MY HEALTH? 

A small number of case studies of acute exposure in people suggest that your lungs, liver, 

kidney, and central nervous system may be injured if you breathe in hydrazine or 1,1-dimethylhydrazine 

or get them on your skin. Similar effects have been observed in animals. 

Animal studies indicate that effects on the liver usually consist of fatty changes, but other 

effects have also been noted. Some animals developed convulsions, tremors, seizures, or 
HYDRAZINES 6 

1. PUBLIC HEALTH STATEMENT 

other effects on the nervous system after breathing hydrazines. Serious effects on the 

reproductive system were sometimes observed in animals. These effects included decreased 

sizes of the ovaries and testes and decreased sperm production. Some of these effects were 

seen in animals exposed to concentrations as low as 0.05-l ppm hydrazine or l,l-dimethylhydrazine 

in air for several months or more. Note that these concentrations are 

below those at which most people begin to smell hydrazines (2-8 ppm). 

A few studies in people show that hydrazine and l,l-dimethylhydrazine affect your nervous 

system. If you swallow hydrazines, you may experience an upset stomach, vomiting, 

uncontrolled shaking, lethargy (sluggishness), coma, and neuritis (an inflammation of your 

nerves). These effects usually occur soon after exposure, but some may be delayed. 

Hydrazine has been used in the past to treat cancer patients. These effects occurred in some 

patients that swallowed 0.2-0.7 milligrams hydrazine per kilogram of their body weight per 

day (mg/kg/day) for 1 month or more. Vitamin B, has been given to people exposed to these 

chemicals to reduce nervous system effects. Effects on the nervous system have also been 

seen in animals exposed to hydrazine and l,l-dimethylhydrazine, but not to 1,2-dimethylhydrazine. 

If you are exposed to hydrazines, you may have an increased cancer risk. The cancer-causing 

effects of hydrazines have not been well studied in people. However, many studies show that 

hydrazines can cause cancer in some animals after exposure to doses of 0.06-19 mg/kg/day 

through the mouth or exposure to concentrations of 0.05-5 ppm in the air. Tumors have been 

seen in many organs of animals exposed in this way but were found most often in the lungs, 

blood vessels, or colon. Some of the cancers caused by l,l-dimethylhydrazine may have 

been due to the presence of dimethylnitrosamine (a powerful carcinogen) as an impurity of 

this chemical. It is of particular concern that 1,2-dimethylhydrazine has caused colon cancer 

in lab animals following a single exposure. 
HYDRAZINES 7 

1. PUBLIC HEALTH STATEMENT 

Although it is hard to apply information from animal cancer studies directly to people, several 

government agencies have considered all the cancer evidence and developed the following 

conclusions: 

•	 The Department of Health and Human Services (DHHS) has determined that 

hydrazine and 1,1-dimethylhydrazine may reasonably be anticipated to be carcinogens 

(cause cancer). 

•	 The International Agency for Research on Cancer (IARC) has determined that 

hydrazine, 1,1 -dimethylhydrazine, and 1,2-dimethylhydrazine are possibly 

carcinogenic to humans (possibly cause cancer in humans). 

•	 EPA has determined that hydrazine, l,l-dimethylhydrazine, and 

1,2-dimethylhydrazine are probable human carcinogens (probably cause cancer in 

people). 

•	 The American Conference of Governmental Industrial Hygienists (ACGIH) currently 

lists hydrazine and l,l-dimethylhydrazine as suspected human carcinogens, but has 

recently recommended that the listing of hydrazine be changed to that of animal 

carcinogen, not likely to cause cancer to people under normal exposure conditions. 

For more information about how hydrazines can affect your health, see Chapter 2. 

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

EXPOSED TO HYDRAZINES? 

If you are exposed to hydrazines, you can be tested for the presence of these chemicals or 

their metabolites in your blood, urine, or feces. These tests must be done soon after you are 

exposed (usually within 1 day). Exposure to some cancer drugs or other chemicals can 

produce hydrazines or their metabolites in your body. These tests cannot be used to tell how 

much you were exposed to or if you are going to be ill. These tests are not usually done in a 
HYDRAZINES 8 

1. PUBLIC HEALTH STATEMENT 

doctor’s office but in special labs for testing. Because these tests require the use of expensive 

equipment and skilled technicians, their availability may be limited in some regions. 

For more information about tests for exposure to hydrazines, see Chapters 2 and 6. 

1.7 	 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

Several government regulatory agencies have taken action to protect people from excess 

exposure to hydrazines. EPA considers hydrazine and 1,1 -dimethylhydrazine to be hazardous 

air pollutants. The Occupational Safety and Health Administration (OSHA) limits the amount 

of hydrazine and l,l-dimethylhydrazine to 0.1 and 0.5 ppm, respectively, in workplace air for 

an S-hour workday and notes the potential for skin absorption in unprotected individuals. The 

National Institute of Occupational Safety and Health (NIOSH) recommends that the levels of 

hydrazine and l,l-dimethylhydrazine in workplace air not exceed 0.03 and 0.06 ppm, 

respectively, for a 2-hour period. The Food and Drug Administration (FDA) has ruled that 

hydrazine cannot be added to water for steam that will contact food. The EPA restricts the 

amount of hydrazines that may be released to the environment during burning or by disposal 

in landfills. 

For more information regarding the regulations and guidelines for hydrazines, see Chapter 7. 

1.8 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 
HYDRAZINES 9 

1. PUBLIC HEALTH STATEMENT 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop E-29 

Atlanta, Georgia 30333 

(404) 639-6000 

This agency can also provide you with information on the location of occupational and 

environmental health clinics. These clinics specialize in the recognition, evaluation, and 

treatment of illness resulting from exposure to hazardous substances. 

HYDRAZINES 11 

2. HEALTH EFFECTS 

2.1 INTRODUCTION 

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

other interested individuals and groups with an overall perspective on the toxicology of hydrazines. 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. 

The term “hydrazines” is a generic name used in this document to describe a group of three 

structurally related chemicals: hydrazine, l,l-dimethylhydrazine, and 1,2-dimethylhydrazine. These 

three hydrazines were selected for inclusion in this document because they have been detected at 

hazardous waste sites and are of concern to the Department of Defense. Numerous other hydrazine 

derivatives exist as well. For example, the reader is referred to the Toxicological Profile for 

1 ,2-Diphenylhydrazine (ATSDR 1990) for information on this chemical. 

2.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE 

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

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

inhalation, oral, and dermal; and then by health effect - death, systemic, immunological, neurological, 

reproductive, developmental, genotoxic, and carcinogenic effects. These data are discussed in terms of 

three exposure periods - acute (14 days or less), intermediate (15-364 days), and chronic (365 days -. 

or more). 

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

figures. The points in the figures showing no-observed-adverse-effect levels (NOAELs) or lowest 

observed-adverse-effect levels (LOAELs) reflect the actual doses (levels of exposure) used in the 

studies. LOAELs have been classified into “less serious” or “serious” effects. “Serious” effects are 
HYDRAZINES 12 

2. HEALTH EFFECTS 

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

respiratory distress or death). “Less serious” effects are those that are not expected to cause significant 

dysfunction or death, or those whose significance to the organism is not entirely clear. ATSDR 

acknowledges that a considerable amount of judgment may be required in establishing whether an end 

point should be classified as a NOAEL, “less serious” LOAEL, or “serious” LOAEL, and that in some 

cases, there will be insufficient data to decide whether the effect is indicative of significant 

dysfunction. However, the Agency has established guidelines and policies that are used to classify 

these end points. ATSDR believes that there is sufficient merit in this approach to warrant an attempt 

at distinguishing between “less serious” and “serious” effects. The distinction between “less serious” 

effects and “serious” effects is considered to be important because it helps the users of the profiles to 

identify levels of exposure at which major health effects start to appear. LOAELs or NOAELs should 

also help in determining whether or not the effects vary with dose and/or duration, and place into 

perspective the possible significance of these effects to human health. 

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

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

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

associated with more subtle effects in humans or animals or exposure levels below which no adverse 

effects 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. 

Levels of exposure associated with carcinogenic effects (Cancer Effect Levels, CELs) of hydrazines 

are indicated in Tables 2-l and 2-2 and Figures 2-l and 2-2. Because cancer effects could occur at 

lower exposure levels, Figures 2-l and 2-2 also show a range for the upper bound of estimated excess 

risks, ranging from a risk of 1 in 10,000 to 1 in 10,000,000 (10m-4 to 10m-7), as developed by EPA. 

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

been made for hydrazines. 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 
HYDRAZINES 13 

2. HEALTH EFFECTS 

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

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

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

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

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

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

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

asthma, or chronic bronchitis. As these kinds of health effects data become available and methods to 

assess levels of significant human exposure improve, these MRLs will be revised. 

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

in the interpretation of the tables and figures for Levels of Significant Exposure and the MRLs. 

2.2.1 Inhalation Exposure 

In their pure form, hydrazines are fairly volatile liquids (see Section 3.2), and therefore inhalation 

exposures are of concern. Data regarding toxic effects in humans or animals after inhalation exposure 

to 1,2dimethylhydrazine are lacking. In one preliminary study, however, the toxicity of 

1,2dimethylhydrazine vapors to rats was judged to be less than that of l, l-dimethylhydrazine but 

greater than that of hydrazine (Jacobson et al. 1955). More complete data are available from human 

and animal studies regarding the toxic effects of inhaled hydrazine and 1,1-dimethylhydrazine. These 

studies are discussed below. 

2.2.1.1 Death 

No studies were located regarding death in humans after inhalation exposure to l, l-dimethylhydrazine. 

A single case study was located which described the death of a male worker exposed to an 

undetermined concentration of hydrazine once a week for 6 months (Sotaniemi et al. 1971). Death 

was attributed to hydrazine exposure, resulting in severe lesions of the kidneys and lungs with 

complicating pneumonia. 
HYDRAZINES 14 

2. HEALTH EFFECTS 

A number of animal studies have reported deaths after inhalation exposure to hydrazines. For 

example, one out of three dogs died within 3 days of intermittent exposure to 25 ppm 1,1-dimethyl 

hydrazine (Rinehart et al. 1960). In another study involving a single 4-hour exposure of groups of 3 

dogs to vapors of l,l-dimethylhydrazine at levels of 24, 52, or 111 ppm, all animals exposed to the 

two highest concentrations either died or were moribund within 24 hours, whereas the dogs receiving 

the lowest concentration showed no signs of adverse effects (Jacobson et al. 1955). During exposure 

at the two higher levels, the dogs experienced vomiting, convulsions, panting (respiratory distress), and 

diarrhea. One of the dogs exposed to 24 ppm suffered vomiting and convulsions during exposure but 

appeared to recover completely in the postexposure observation period. Two out of eight dogs 

exposed continuously to 1 ppm hydrazine progressively deteriorated and died after 16 weeks (Haun 

and Kinkead 1973). 

A l-hour exposure to 80 ppm hydrazine did not cause any immediate deaths in rats, although one out 

of six died during the subsequent 14-day observation period (Cornstock et al. 1954). Twenty-two out 

of 40 mice died after continuous exposure to 1 ppm hydrazine for 6 months (Haun and Kinkead 1973). 

Death in these mice was attributed to the hepatotoxic effects of hydrazine. In contrast, mortality was 

not increased in rats or monkeys exposed to 1 ppm hydrazine, suggesting that mice may be more 

sensitive to the lethal effects of hydrazine than other species. Mortality was 32-33% in hamsters 

exposed intermittently to 0.25 ppm hydrazine for 1 year compared to 19% in controls (Vernot et al. 

1985). Exposure to 5 ppm l,l-dimethylhydrazine for 6 months did not significantly affect the 

mortality rates in rats, mice, dogs, and hamsters (Haun et al. 1984). 

The above studies indicate that exposure to relatively high concentrations of hydrazines in air can be 

lethal and suggest that hydrazine may be more toxic than l,l-dimethylhydrazine. In contrast, Jacobson 

et al. (1955) exposed mice, rats, and hamsters to substantially higher concentrations of hydrazine or 

1,1-dimethylhydrazine vapors for 4 hours and found 1,1-dimethylhydrazine to be more toxic than 

hydrazine under these conditions. The LC50s calculated by these authors for the 4-hour inhalation 

exposures were 570 and 252 ppm for hydrazine in rats and mice, respectively, and 252, 172, and 

392 ppm for l,l-dimethylhydrazine in rats, mice, and hamsters, respectively. In these studies, rats 

were also exposed to vapors of 1,2-dimethylhydrazine for 4 hours, and based on a limited number of 

dose levels, an LC50 of 280-400 ppm was calculated. All LOAEL values from each reliable study for 

lethality are recorded in Table 2-l and plotted in Figure 2-l. 
HYDRAZINES 15 

2. HEALTH EFFECTS 

2.2.1.2 Systemic Effects 

The systemic effects observed after inhalation exposure are described below. No studies were located 

regarding dermal effects in humans or animals after inhalation exposure to hydrazines. The highest 

NOAEL values and all LOAEL values from each reliable study for systemic effects after inhalation 

exposure to hydrazine and l,l-dimethylhydrazine are recorded in Table 2-l and plotted in Figure 2-l. 

Respiratory Effects. Acute accidental exposure to a mixture of hydrazine and l,l-dimethylhydrazine 

resulted in dyspnea and pulmonary edema in two men (Frierson 1965). A single case study 

reported pneumonia, tracheitis, and bronchitis in a man occupationally exposed to an undetermined 

concentration of hydrazine in air once a week for 6 months (Sotaniemi et al. 1971). These lesions 

were severe and were a contributing factor in this worker’s death. 

Respiratory effects have been observed in a number of animal studies. In dogs, alveolar hemorrhage, 

emphysema, and atelectasis were observed following intermittent exposure to 25 ppm 

l,l-dimethylhydrazine for 13 weeks (Rinehart et al. 1960). These effects were not observed in dogs 

exposed to 5 ppm for 26 weeks. Hyperplasia of the alveoli and lymphoid tissue of the lung was 

observed in rats and mice exposed to 0.05 ppm l,l-dimethylhydrazine for 6 months (Haun et al. 

1984). A higher concentration (0.5 ppm) produced congestion and perivascular cuffing in the lungs of 

these mice. Intermittent exposure to 5 ppm hydrazine or l,l-dimethylhydrazine for 1 year produced 

inflammation, hyperplasia, and metaplasia of the upper respiratory tract epithelium in rats and mice 

(Haun et al. 1984; Vemot et al. 1985). No adverse effects were noted in the lungs of mice exposed 

intermittently to 1 ppm hydrazine. These data indicate that hydrazine and l,l-dimethylhydrazine can 

produce lung damage. 

Cardiovascular Effects. No studies were located regarding cardiovascular effects in humans after 

inhalation exposure to l,l-dimethylhydrazine. Data regarding the adverse effects of hydrazine on the 

cardiovascular system in humans are limited to a single case study. Atria1 fibrillation, enlargement of 

the heart, and degeneration of heart muscle fibers were noted in a worker exposed to an undetermined 

concentration of hydrazine once a week for 6 months (Sotaniemi et al. 1971). It is uncertain whether 

these effects are directly attributable to hydrazine exposure. 













HYDRAZINES 29 

2. HEALTH EFFECTS 

No adverse effects were noted on the cardiovascular system of dogs exposed intermittently to 25 ppm 

1,1-dimethylhydrazine for 13-26 weeks (Rinehart et al. 1960). In mice exposed to 0.05-5 ppm 

1 ,l-dimethylhydrazine for 6 months to 1 year, the blood vessels were abnormally dilated (angiectasis) 

(Haun et al. 1984). However, no clinical or histopathological effects were noted on the cardiovascular 

system of mice exposed intermittently to 1 ppm hydrazine for 1 year (Vernot et al. 1985). The 

findings of the animal studies are inconsistent with the effects reported in the human case study and 

suggest that effects noted may not have been related to exposure. However, this is not certain. 

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

inhalation exposure to hydrazines. 

No histopathological changes were observed in the gastrointestinal tract of dogs intermittently exposed 

to 25 ppm 1 ,l-dimethylhydrazine for 13-26 weeks (Rinehart et al. 1960) or in mice intermittently 

exposed to 1 ppm hydrazine for 1 year (Vernot et al. 1985). Although these data are limited, they 

suggest that the gastrointestinal system is not a primary target of the noncarcinogenic effects of 

hydrazine or 1,l -dimethylhydrazine. 

Hematological Effects. No studies were located regarding the hematological effects in humans 

after inhalation exposure to hydrazines. 

Mild anemia (17-26% decreases in red blood cell count, hemoglobin, and hematocrit) was observed in 

dogs intermittently exposed (5 days/week, 6 hours/day) to 5 ppm l,l-dimethylhydrazine for 24 weeks 

(Rinehart et al. 1960). Anemia was more pronounced (28-60% decreases in above described 

parameters) at a higher concentration (25 ppm) of l,l-dimethylhydrazine after 4 weeks of intermittent 

exposure. In dogs exposed continuously to 1 ppm hydrazine for 6 months, hemoglobin, hematocrit, 

and red blood cell count were all significantly reduced (approximately 25-30%) (Haun and Kinkead 

1973). These effects were not observed in dogs exposed to 0.2 ppm hydrazine in this study. 

Hematological effects were not observed in rats, dogs, and hamsters exposed to 0.5 and3 ppm 

1,1-dimethylhydrazine for 6 months (Haun et al. 1984). The lack of an anemic effect of purified 

l,ldimethylhydrazines in the dogs of this study is inconsistent with the observations made by Rinehart 

et al. (1960) in dogs exposed to the same concentration for a shorter duration. It is possible that 

impurities of the l,l-dimethylhydrazine (for example, dimethylnitrosamine) used by Rinehart et al. 

(1960) contributed to the anemic response. Alternatively, the anemic effects of hydrazine and 
HYDRAZINES 30 

2. HEALTH EFFECTS 

l,l-dimethylhydrazine may be related to their ability to react with pyridoxine (see Section 2.35); a 

deficiency of this vitamin results in anemia (NAS 1989). 

No adverse effects were reported for a large number of hematological parameters in rats or monkeys 

exposed to 1 ppm hydrazine continuously for 6 months (Haun and Kinkead 1973). In dogs, the 

anemic effects of hydrazine in this study and l,l-dimethylhydrazine in the Rinehart et al. (1960) study 

appear to be fairly similar, and the data suggest that dogs may be particularly sensitive to the 

hematological effects of these compounds. However, some questions remain, considering the results 

with dogs seen by Haun et al. (1984), cited above. Rats (Haun and Kinkead 1973; Haun et al. 1984), 

monkeys (Haun and Kinkead 1973), and hamsters (Haun et al. 1984) appear to be relatively insensitive 

to the hematological effects of these compounds. 

Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans 

after inhalation exposure to hydrazines. 

No studies were located regarding musculoskeletal effects in animals after inhalation exposure to 

1,l -dimethylhydrazine. No musculoskeletal effects were observed in mice exposed intermittently to 

1 ppm hydrazine for 1 year (Vernot et al. 1985). 

Hepatic Effects. A single case study reported areas of focal necrosis and cell degeneration in the 

liver of a worker exposed to an undetermined concentration of hydrazine in air once a week for 

6 months (Sotaniemi et al. 1971). Studies of workers exposed to l,l-dimethylhydrazine have reported 

changes indicative of a hepatic effect including elevated serum alanine aminotransferase activity, fatty 

degeneration, and a positive cephalin flocculation test (Petersen et al. 1970; Shook and Cowart 1957). 

Although the levels of hydrazine and l,l-dimethylhydrazine exposure were not determined, these 

studies indicate qualitatively that the liver is a target for both hydrazines. 

In dogs exposed intermittently to 5 ppm l,l-dimethylhydrazine for 8.5 weeks, cytoplasmic 

degeneration of the liver was observed (Haun 1977). Hemosiderosis of the spleen was observed in 

dogs exposed intermittently to 5 ppm 1,1-dimethylhydrazine for 26 weeks, and the same effect was 

observed in the Kupffer cells of the liver after exposure to 25 ppm for 13 weeks (Rinehart et al. 1960). 

Dogs exposed to 5 ppm 1,1-dimethylhydrazine for 6 months showed transitory increases in serum 

glutamic pyruvic transaminase (SGPT) levels which returned to normal during the postexposure 
HYDRAZINES 31 

2. HEALTH EFFECTS 

recovery period (Haun et al. 1984). This study also found impaired liver function at the same dose 

level as measured by retention of injected bromosulphalein after a 6-month exposure to 

1 ,l-dimethylhydrazine. Fatty changes were observed in the livers of mice, dogs, and monkeys 

exposed continuously to 0.2-l ppm hydrazine for 6 months (Haun and Kinkead 1973). The 

hepatotoxic effects of hydrazine were notably more severe in mice than in dogs or monkeys and were 

responsible for the increased mortality observed in this species. Based on a LOAEL of 0.2 ppm for 

liver effects in mice, an intermediate inhalation MRL of 4X10-3 ppm was calculated for hydrazine as 

described in footnote “c” in Table 2-l. Intermittent exposure to 0.25-l ppm hydrazine for 1 year 

resulted in a number of hepatic effects in rats, dogs, and hamsters including focal cellular change, 

vacuolated cells, elevated serum transaminases, amyloidosis, hemosiderosis, and bile duct hyperplasia 

(Vemot et al. 1985). The NOAEL values for hepatic effects range from 0.25 to 1 ppm for rats, mice, 

and dogs in this study. In addition, hamsters appeared to be the most sensitive species to hydrazineinduced 

hepatic effects, whereas mice appeared to be the most resistant. 

In rats and mice, exposure to 0.05-5 ppm l,l-dimethylhydrazine for 6 months to 1 year produced fatty 

changes, angiectasis, hyaline degeneration of the gall bladder, and congestion in the liver (Haun et al. 

1984). Based on a LOAEL of 0.05 ppm, an intermediate inhalation MRL of 2X10-4 ppm was 

calculated for 1, 1-dimethylhydrazine as described in footnote “b” in Table 2- 1. 

Collectively, these data clearly indicate that the liver is a target for hydrazine and 

l,l-dimethylhydrazine toxicity. Furthermore, species differences are apparent in the sensitivity to 

hepatotoxicity. However, these data are inconsistent (mice were the most sensitive in one study but 

the most resistant in another) and suggest that strain differences in sensitivity may also exist in mice. 

It should be noted that dimethylnitrosamine, a potent liver toxin, occurs as a contaminant of technical 

grades of l,l-dimethylhydrazine and may contribute to the hepatotoxic effects observed in animals 

following exposure to this compound (Haun 1977). A single study reported hyaline degeneration of 

the gall bladder in mice exposed to 0.05 ppm l,l-dimethylhydrazine for 6 months (Haun et al. 1984). 

Renal Effects. No studies were located regarding renal effects in humans after inhalation exposure 

to 1,1 -dimethylhydrazine. A single case study reported renal effects including tubular necrosis, 

hemorrhaging, inflammation, discoloration, and enlargement in a worker exposed to 0.07 mg/m3 

(0.05 ppm) hydrazine once a week for 6 months (Sotaniemi et al. 1971). These renal effects were 

severe and were a contributing factor in the death of this worker. 
HYDRAZINES 32 

2. HEALTH EFFECTS 

Renal effects were not observed in dogs exposed intermittently to 25 ppm l,l-dimethylhydrazine for 

13-26 weeks (Rinehart et al. 1960). Mild renal effects including amyloidosis and mineralization were 

observed in hamsters exposed intermittently to 0.25 ppm hydrazine for 1 year (Vemot et al. 1985); 

however, no effects were noted in the kidneys of mice exposed intermittently to 1 ppm hydrazine for 

1 year (Vemot et al. 1985). The findings of these animal studies are inconsistent with the severe 

effects observed in the human case study. However, more severe effects on the kidney have been 

observed in animals exposed to hydrazines by other routes (see Sections 2.2.2.2 and 2.4). 

Ocular Effects. No studies were located regarding ocular effects in humans after inhalation 

exposure to l,l-dimethylhydrazine. A single case of a worker exposed to an undetermined 

concentration of hydrazine once a week for 6 months reported conjunctivitis (Sotaniemi et al. 1971). 

Since the conjunctivitis was repeatedly observed on each day the worker was exposed, continuing 

through to the following day, this effect is clearly related to hydrazine exposure. 

No studies were located regarding ocular effects in animals after inhalation exposure to 

1,l -dimethylhydrazine. Minimal irritation of the eyes was noted in monkeys during the first 

few weeks of exposure to 1 ppm hydrazine (Haun and Kinkead 1973). This effect was not observed 

in monkeys exposed to 0.2 ppm hydrazine (Haun and Kinkead 1973), or in mice exposed 

intermittently to 1 ppm hydrazine for 1 year (Vemot et al. 1985). Although these data are internally 

inconsistent, the data from monkeys are consistent with the human data which suggest that hydrazine 

acts as an irritant to the eyes. 

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

inhalation exposure to hydrazine or l,l-dimethylhydrazine. 

Several studies in animals have reported decreased body weight gain. Male and female rats and male 

hamsters experienced significantly decreased body weight gains compared to controls during a 

lo-week period of exposure to 750 ppm hydrazine (1 hour/week) (Latendresse et al. 1995). Weight 

gains returned to normal during the subsequent recovery period. Body weight gain was reduced in rats 

and dogs exposed continuously to 1 ppm hydrazine for 6 months (Haun and Kinkead 1973), and in 

dogs exposed to 5 ppm l,l-dimethylhydrazine 6 hours/day, 5 days/week, for 26 weeks (Rinehart et al. 

1960), or 5 ppm hydrazine for the same dosing regimen (Comstock et al. 1954). No effects in body 

weight gain were observed in several species exposed to concentrations of 0.2-1 ppm hydrazine or 
HYDRAZINES 33 

2. HEALTH EFFECTS 

5 ppm l,l-dimethylhydrazine for 6 months (Haun and Kinkead 1973; Haun et al. 1984). Chronic 

exposure to 0.25 ppm hydrazine caused a 14% loss of body weight in hamsters (Vernot et al. 1985). 

A similar decrease in body weight gain was noted in mice exposed to 5 ppm l,l-dimethylhydrazine 

for 1 year (Haun et al. 1984). 

2.2.1.3 Immunological and Lymphoreticular Effects 

No studies were located regarding immunological and lymphoreticular effects in humans or animals 

after inhalation exposure to hydrazines. 

2.2.1.4 Neurological Effects 

Data regarding the neurological effects of hydrazines in humans are limited to several case studies. 

Acute exposure to an undetermined concentration of a hydrazine/l,l-dimethylhydrazine mixture in air 

resulted in trembling, twitching, clonic movements, hyperactive reflexes, and weakness in two cases 

(Frierson 1965). Nausea, vomiting, and tremors were observed in a worker exposed to an 

undetermined levels of hydrazine in air once a week for 6 months (Sotaniemi et al. 1971). Difficulties 

in concentration, comprehension, memory, and task performance, as well as changes in mood status 

were noted in a water technician occupationally exposed to an undetermined concentration of 

hydrazine in air (Richter et al. 1992). Slow, gradual improvement was noted in the latter case after 

the subject was removed from exposure. Although limited, these studies suggest that inhalation 

exposure to hydrazine and l,l-dimethylhydrazine can adversely affect the central nervous system in 

humans. 

In dogs exposed intermittently to 25 ppm l,l-dimethylhydrazine, depression, ataxia, salivation, emesis, 

and seizures were noted after 3 days (Rinehart et al. 1960). These effects were not observed in dogs 

exposed to 5 ppm for 26 weeks. Tonic convulsions were noted in one of eight dogs exposed 

continuously to 1 ppm hydrazine for 6 months but were not observed in any dogs exposed to 0.2 ppm 

(Haun and Kinkead 1973). Tremors were observed occasionally in rats and mice exposed 

continuously to 75 ppm l,l-dimethylhydrazine (Rinehart et al. 1960). These data confirm the 

observations from human studies and indicate that the central nervous system is a target for the 

toxicity of inhaled hydrazine or l,l-dimethylhydrazine. The highest NOAEL values and all LOAEL 
HYDRAZINES 34 

2. HEALTH EFFECTS 

values from each reliable study for neurological effects resulting from inhalation exposure to 

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

2.2.1.5 Reproductive Effects 

No studies were located regarding reproductive effects in humans after inhalation exposure to 

hydrazines. 

Endometrial cysts were noted in female mice exposed to 0.05 ppm l,l-dimethylhydrazine for 6 months 

(Haun et al. 1984). The incidence of endometrial cysts were also elevated in female mice exposed to 

5 ppm l,l-dimethylhydrazine for 1 year (Haun et al. 1984); however, this increase was not statistically 

significant. Furthermore, this type of lesion is common to aged female mice and therefore may not be 

related to treatment. In female rats exposed intermittently to 5 ppm hydrazine for 1 year, atrophy of 

the ovaries and inflammation of the endometrium and fallopian tube were noted (Vernot et al. 1985). 

Senile testicular atrophy was observed in male hamsters exposed to 1 ppm hydrazine for 1 year but not 

in hamsters exposed to 0.25 ppm hydrazine (Vernot et al. 1985). An absence of sperm production was 

observed in hamsters exposed to 5 ppm. The study authors noted that the changes observed in male 

hamsters are normally associated with aging and that exposure to hydrazine seemed to accelerate these 

changes. However, available studies suggest that hydrazine and l,l-dimethylhydrazine can produce 

serious reproductive effects. A complete assessment of the reproductive toxicity of hydrazines cannot 

be made since reproductive function was not determined in these studies. The highest NOAEL values 

and all LOAEL values from each reliable study for reproductive effects resulting from inhalation 

exposure to hydrazines are recorded in Table 2-l and plotted in Figure 2-l. 

2.2.1.6 Developmental Effects 

No studies were located regarding developmental effects in humans or animals after inhalation 

exposure to hydrazines. 

2.2.1.7 Genotoxic Effects 

No studies were located regarding genotoxic effects in humans or animals after inhalation exposure to 

hydrazines. 
HYDRAZINES 35 

2. HEALTH EFFECTS 

Genotoxicity studies are discussed in Section 2.5. 

2.2.1.8 Cancer 

A single epidemiological study reported no significant increase in cancer mortality in a group of men 

(n=427) occupationally exposed to an undetermined concentration of hydrazine in air (Wald et al. 

1984). Although this study reported no evidence of a carcinogenic effect for hydrazine, the follow-up 

period was relatively short and only 49 deaths were observed. However, when the workers were 

observed for another 10 years, there was still no significant increase in cancer mortality (Morris et al. 

1995). 

Exposure to 0.05-0.5 ppm l,l-dimethylhydrazine for 6 months produced an increased incidence of 

leukemia and tumors of the pancreas, pituitary, blood vessels, liver, and thyroid in mice and/or rats 

(Haun et al. 1984). Tumors of the lung, liver, nasal cavity, bone, and blood vessels were observed in 

mice exposed to 5 ppm l,l-dimethylhydrazine for 1 year (Haun et al. 1984). A significantly increased 

incidence (p<0.05) of nasal tumors and thyroid carcinomas was observed in male rats exposed 

intermittently to 1 and 5 ppm hydrazine, respectively, for 1 year (Vernot et al. 1985). Hamsters and 

rats exposed to 750 ppm hydrazine once for 1 hour, or 1 hour per week for 10 weeks, exhibited 

increased incidences of squamous metaplasia, hyperplasia, and neoplasia in the nose (Latendresse et al. 

1995). Nasal tumors were also noted in hamsters and female rats intermittently exposed to 5 ppm 

hydrazine for 1 year (Vemot et al. 1985). Tumor incidence was not significantly increased in mice 

and dogs exposed intermittently to 1 ppm hydrazine for 1 year (Vernot et al. 1985). The studies 

suggest that hydrazine and l,l-dimethylhydrazine are carcinogenic by the inhalation route. All CEL 

values from each reliable study resulting from inhalation exposure to hydrazines are recorded in 

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

The EPA has derived an inhalation unit risk of 0.0049 (μg/m3

)

-1 for hydrazine based on nasal cavity 

tumors, and an inhalation unit risk of 0.001 (μg/m3)-1 for l,l-dimethylhydrazine based ontumor of the 

respiratory system (HEAST 1992; IRIS 1995). Although no studies were located regarding the 

carcinogenic effects of 1 ,2-dimethylhydrazine following inhalation exposures, EPA has derived an 

inhalation unit risk of 0.011 (μg/m3

)

-1 for 1,2-dimethylhydrazine (HEAST 1992), based on 

extrapolation of cancer data for oral exposures (see Section 2.2.2.8). The concentrations of hydrazine, 
HYDRAZINES 36 

2. HEALTH EFFECTS 

1, 1-dimethylhydrazine, and 1,2-dimethylhydrazine corresponding to excess cancer risks of 10-4 to 10-7. 

are shown in Figure 2-l. 

2.2.2 Oral Exposure 

2.2.2.1 Death 

No studies were located regarding lethal effects in humans after oral exposure to hydrazines. 

Acute oral LD50 values of 11.7 and 27.1 mg/kg have been reported for 1 ,2-dimethylhydrazine in male 

and female mice, respectively (Visek et al. 1991). Mortality was 100% in mice given a single dose of 

90 mg/kg 1,2-dimethylhydrazine (Visek et al. 1991) and in mice given 133 mg/kg/day hydrazine or 

533 mg/kg/day l,l-dimethylhydrazine for 5 days (Roe et al. 1967). Death occurred in two of two 

dogs administered weekly doses of 60 mg/kg 1,2-dimethylhydrazine for 2 weeks (Wilson 1976). For 

intermediate exposures, doses of 2.3 and 4.9 mg/kg/day hydrazine for 15-25 weeks increased mortality 

in mice and hamsters, respectively (Biancifiori 1970). Exposure to 33 mg/kg/day l,l-dimethylhydrazine 

killed two of five mice exposed for 4-21 weeks (Roe et al. 1967). Mortality was 62.5-100% 

following intermediate-duration exposures to 1,2-dimethylhydrazine in rats given 13.6 mg/kg/day 

(Teague et al. 1981), guinea pigs given 60 mg/kg/day (Wilson 1976), dogs administered 15 mg/kg/day 

(Wilson 1976), pigs administered 60 mg/kg/day (Wilson 1976), and in mice given 4.5-5.1 mg/kg/day 

(Visek et al. 1991). Mortality in mice was 100% after chronic exposure to 0.95 mgfkg/day via the 

drinking water (Toth and Patil 1982). These data indicate that large doses of hydrazines are lethal by 

the oral route. Furthermore, male mice were 2-3 times more sensitive to the acutely lethal effects of 

1,2-dimethylhydrazine than female mice (Visek et al. 1991), suggesting that there may be important 

sex differences. However, this was only observed in a single study. All LOAEL values from each 

reliable study for lethality are recorded in Table 2-2 and plotted in Figure 2-2. 

2.2.2.2 Systemic Effects 

No studies were located regarding any systemic effects in humans after oral exposure to hydrazines. 

Also, no studies were located regarding the hematological effects in animals after oral exposure to 

hydrazines. The available studies regarding systemic effects in animals after oral exposure to 

hydrazines are described below. The highest NOAEL values and all LOAEL values for systemic 
HYDRAZINES 37 

2. HEALTH EFFECTS 

effects in animals resulting from oral exposure to hydrazines are recorded in Table 2-2 and plotted in 

Figure 2-2. 

Respiratory Effects. No adverse histological effects were observed in the lungs of mice exposed to 

9.5 mg/kg/day hydrazine via the drinking water for 2 years (Steinhoff et al. 1990). No other studies 

were located regarding respiratory effects in animals ingesting hydrazines. 

Cardiovascular Effects. Focal myocytolysis, fibrosis, and calcification of the heart were observed 

in mice receiving 1.6 mg/kg/day 1,2-dimethylhydrazine in the feed for 5 months (Visek et al. 1991). 

These effects were not observed in mice receiving 0.75 mg/kg/day. No adverse histological effects 

were observed in the hearts of mice receiving 9.5 mg/kg/day hydrazine in the drinking water for 

2 years (Steinhoff et al. 1990). These data are too limited to make firm conclusions regarding the 

cardiovascular effects of hydrazines. 

Gastrointestinal Effects. Although oral exposure to hydrazine has produced nausea in humans, 

this effect is probably due to effects on the central nervous system and is therefore discussed in 

Section 2.2.2.4. 

Proliferative foci were noted in the colons of rats receiving two doses of 25 mg/kg 

1,2-dimethylhydrazine within a 4-day period (Cademi et al. 1991). No adverse histological effects 

were observed in the gastrointestinal tracts of mice receiving 9.5 mg/kg/day hydrazine in the drinking 

water for 2 years (Steinhoff et al. 1990). These data are too limited to make firm conclusions 

regarding the gastrointestinal effects of hydrazines. 

Musculoskeletal Effects. No adverse effects were observed in the muscle tissue of mice receiving 

9.5 mg/kg/day hydrazine in the drinking water for 2 years (Steinhoff et al. 1990). No other studies 

were located regarding the effects of hydrazines on the musculoskeletal system. 

Hepatic Effects. A number of studies in animals have reported effects on the liver after oral 

exposure to hydrazines. In rats and mice, relatively mild effects on the liver such as 

megamitochondria formation, increased lipogenesis, and fatty changes occurred following acute 

exposure to 49-650 mg/kg/day hydrazine (Marshall et al. 1983; Preece et al. 1992b; Wakabayashi 

et al. 1983). More notable effects, including degeneration, hemorrhage, and necrosis of the liver, were 













HYDRAZINES 51 

2. HEALTH EFFECTS 

observed in dogs administered weekly doses of 60 mg/kg 1,2-dimethylhydrazine for 2 weeks (Wilson 

1976). Intermediate-duration exposure to 1,2-dimethylhydrazine produced liver damage 

(hemosiderosis, necrosis, hepatitis, fibrosis, ascites and/or failure) in rats receiving 4.2 mg/kg/day 

(Bedell et al. 1982), guinea pigs receiving 30 mg/kg/day or more (Wilson 1976), mice receiving 

0.75 mg/kg/day or more (Visek et al. 1991), dogs receiving 5 mg/kg/day or more (Wilson 1976), and 

pigs receiving 30 mg/kg/day (Wilson 1976). Cirrhosis, reticuloendothelial cell proliferation, bile duct 

proliferation, and degenerative fibrous cells were observed in the livers of hamsters exposed to 

4.9 mg/kg/day hydrazine for 15-20 weeks (Biancifiori 1970). No adverse effects were observed in the 

livers of mice receiving 9.5 mg/kg/day hydrazine for 2 years (Steinhoff et al. 1990). Collectively, 

these data indicate that hydrazine and 1,2-dimethylhydrazine are hepatotoxic by the oral route. Based 

on a LOAEL of 0.75 mg/kg/day for hepatic effects in mice (Visek et al. 1991), an intermediate oral 

MRL of 8X10-4 mg/kg/day was calculated for 1,2-dimethylhydrazine as described in footnote “b” in 

Table 2-2. 

Renal Effects. Interstitial nephritis and pyelonephritis were observed in mice receiving 

1.6 mg/kg/day 1,2-dimethylhydrazine in feed for 5 months (Visek et al. 1991). These effects were not 

observed in mice similarly exposed to 0.75 mg/kg/day 1,2-dimethylhydrazine. No adverse effects were 

noted in the kidneys of mice receiving 9.5 mg/kg/day hydrazine in the drinking water for 2 years 

(Steinhoff et al. 1990). These data are too limited to make firm conclusions but suggest that 

1,2-dimethylhydrazine is toxic to the kidneys and hydrazine is not. 

Endocrine Effects. Degeneration of the adrenals was noted in female mice exposed to 

1.1 mg/kg/day or more hydrazine for 25 weeks (Biancifiori 1970). No adverse effects were noted in 

the thyroid of mice exposed to 9.3 mg/kg/day hydrazine for 25 weeks. Similarly, no effects were 

observed in the thyroid or adrenals of hamsters exposed to 5.3 mg/kg/day hydrazine for 15-20 weeks 

(Biancifiori 1970). 

Dermal Effects. No adverse effects were observed in the skin of mice receiving 9.5 mg/kg/day 

hydrazine in their drinking water for 2 years (Steinhoff et al. 1990). No other studies were located 

regarding dermal effects in animals after oral exposure to hydrazines. 
HYDRAZINES 52 

2. HEALTH EFFECTS 

Ocular Effects. No adverse effects were observed in the eyes of mice receiving 9.5 mg/kg/day 

hydrazine in their drinking water for 2 years (Steinhoff et al. 1990). No other studies were located 

regarding ocular effects in animals after oral exposure to hydrazines. 

Body Weight Effects. Body weight loss and decreased body weight gain were reported in animals 

exposed orally to 1,2-dimethylhydrazine and hydrazine. Weight loss was noted in dogs receiving 

2 weekly doses of 60 mg/kg/day (Wilson 1976). Decreased body weight gains were reported for 

intermediate-duration exposure to 1,2-dimethylhydrazine for rats receiving 30 mg/kg/day (Barbolt and 

Abraham 1980), guinea pigs receiving 30 mg/kg/day (Wilson 1976), and in mice receiving 

0.75 mg/kg/day or more (Visek et al. 1991). Decreased body weight gain was also noted in mice 

chronically exposed to 9.5 mg/kg/day hydrazine in the drinking water for 2 years (Steinhoff et al. 

1990). No significant effect on body weight gain was noted in mice receiving 1.9 mg/kg/day. 

Decreases in body weight were often accompanied by decrements in food intake, organ weights, and 

altered physical appearance and therefore probably represent signs of general toxicity. In some cases, 

decreased body weight gain may be secondary to an underlying disease (e.g., cancer). 

2.2.2.3 Immunological and Lymphoreticular Effects 

No studies were located regarding immunological and lymphoreticular effects in humans after oral 

exposure to hydrazines. 

A single study in rats reported that splenic natural killer cell activity was not affected after exposure to 

27.1 mg/kg/day 1,2-dimethylhydrazine once a week for 5 weeks (Locniskar et al. 1986). This NOAEL 

value is recorded in Table 2-2 and plotted in Figure 2-2. 

2.2.2.4 Neurological Effects 

Ingestion of hydrazine (estimated between a mouthful and a cupful) resulted in several neurological 

effects including episodes of violent behavior, ataxia, coma, convulsions, hypesthesia of the hands, and 

paraesthesia of the arms and legs (Reid 1965). Confusion, lethargy, restlessness, paresthesia, and 

neurogenic atrophy were observed in a 24-year-old male who swallowed a mouthful of hydrazine 

(Harati and Niakan 1986). Hydrazine has been used as a chemotherapeutic agent in human cancer 

patients. Neurological side effects have been observed in some human cancer patients (450%) treated 
HYDRAZINES 53 

2. HEALTH EFFECTS 

with 0.2-0.7 mg/kg/day hydrazine as hydrazine sulfate for intermediate durations (Chlebowski et al. 

1984; Gershanovich et al. 1976, 1981; Ochoa et al. 1975; Spremulli et al. 1979). For the most part, 

the neurological effects were relatively mild (lethargy, nausea, vomiting, dizziness, excitement, 

insomnia); however, two studies reported more serious effects (paresthesia, sensorimotor abnormalities, 

polyneuritis) (Gershanovich et al. 1976; Ochoa et al. 1975). The appearance of more serious effects in 

these two studies may be related to increased exposure duration. For example, Gershanovich et al. 

(1976, 1981) noted that polyneuritis developed only in patients receiving uninterrupted treatment with 

hydrazine for 2-6 months. The treatment duration used by Chlebowski et al. (1984) and Spremulli 

et al. (1979), which was less than 2 months in both studies, may have been sufficiently short enough 

to prevent the development of more serious neurological effects. Limitations in the findings of these 

studies lie in the fact that the test subjects were generally not healthy prior to hydrazine exposure. 

Therefore it is possible that some of the observed effects may be attributable to the underlying disease. 

However, collectively these studies strongly suggest that the central nervous systems is a target of 

hydrazine in humans after oral exposure. The highest NOAEL values and all LOAEL values for 

neurological effects resulting from oral exposure to hydrazines are recorded in Table 2-2 and plotted in 

Figure 2-2. 

No studies were located regarding neurological effects in animals after oral exposure to hydrazines. 

2.2.2.5 Reproductive Effects 

No studies were located regarding reproductive effects in humans after oral exposure to hydrazines. 

A single animal study reported no histopathological lesions in the ovaries of mice and hamsters 

exposed to 9.3 or 5.3 mg/kg/day hydrazine, respectively, for 15-25 weeks (Biancifiori 1970). 

However, the findings of this study are limited since reproductive function was not assessed. These 

NOAEL values for reproductive effects are recorded in Table 2-2 and plotted in Figure 2-2. 

2.2.2.6 Developmental Effects 

No studies were located regarding developmental effects in humans after oral exposure to hydrazines. 
HYDRAZINES 54 

2. HEALTH EFFECTS 

A single study in hamsters reported no evidence of developmental toxicity or teratogenicity following 

exposure to a single dose of 166 mg/kg hydrazine or 68 mg/kg 1,2-dimethylhydrazine on day 12 of 

gestation (Schiller et al. 1979). Although these data are limited, they suggest that fetal development is 

not adversely affected by hydrazine or 1,2-dimethylhydrazine. These NOAEL values for 

developmental effects resulting from oral exposure to hydrazines are recorded in Table 2-2 and plotted 

in Figure 2-2. 

2.2.2.7 Genotoxic Effects 

No studies were located regarding genotoxic effects in humans after oral exposure to hydrazines. 

Alkylation of liver DNA was reported in rats acutely exposed to 30-90 mg/kg hydrazine for 1-3 days 

(Becker et al. 1981; Bosan et al. 1986). Micronuclei were observed in the bone marrow of mice 

exposed to a single oral dose of 10-50 mg/kg 1,2-dimethylhydrazine (Albanese et al. 1988; Ashby and 

Mirkova 1987). However, micronuclei were not observed in the bone marrow of rats after a single 

oral dose of 50-80 mg/kg 1,2-dimethylhydrazine (Ashby and Mirkova 1987). These data indicate that 

hydrazine and 1,2-dimethylhydrazine are genotoxic by the oral route. Furthermore, species differences 

may exist between rats and mice regarding their sensitivity to the genotoxic effects of 

1,2-dimethylhydrazine. 

Other genotoxicity studies are discussed in Section 2.5. 

2.2.2.8 Cancer 

No studies were located regarding carcinogenic effects in humans after oral exposure to hydrazines. 

Adenomas and adenocarcinomas of the colon have been observed in rats following a single oral 

exposure to 15.8-30 mg/kg 1,2-dimethylhydrazine (Craven and DeRubertis 1992; Schillm et al. 1980; 

Watanabe et al. 1985). Colon tumors are not common to rats and were not observed in the control 

animals of these studies. 

Several tumor types have been observed in animals after intermediate-duration exposure to hydrazines. 

Exposure to 0.46-16.7 mg/kg/day hydrazine for 24-48 weeks produced a statistically significant 
HYDRAZINES 55 

2. HEALTH EFFECTS 

increase in the incidence of lung, liver, and breast tumors in mice (Bhide et al. 1976; Biancifiori 1970; 

Biancifiori and Ribacchi 1962; Biancifiori et al. 1964; Roe et al. 1967; Yamamoto and Weisburger 

1970). A single study reported an increased incidence of lung tumors in mice after daily administration 

of 0.25 mg hydrazine or 0.5 1,1-dimethylhydrazine (0.8 or 1.7 mg/kg/day, respectively), 5 times 

per week for 40-50 or 50-60 weeks (Roe et al. 1967). A large number of studies have reported 

tumors in rodents after intermediate exposure to 1,2-dimethylhydrazine. Statistically significant 

increases were reported for tumor incidences of the blood vessels (Bedell et al. 1982; Dmckrey 1970; 

Izumi et al. 1979; Teague et al. 1981), liver (Bedell et al. 1982; Teague et al. 1981; Wilson 1976), 

lung (Izumi et al. 1979), kidney (Bedell et al. 1982), ear duct (Teague et al. 1981; Wilson 1976), and 

most notably the intestines, colon, and anus (Abraham et al. 1980; Asano and Pollard 1978; Barbolt 

and Abraham 1980; Calvert et al. 1987; Drnckrey 1970; Izumi et al. 1979; Locniskar et al. 1986; 

Teague et al. 1981; Thorup et al. 1992; Wilson 1976). Doses of 1,2-dimethylhydrazine resulting in 

increased tumor incidence ranged from 1.9 mg/kg/day to 30 mg/kg/day. 

Chronic oral exposure to hydrazines has also resulted in statistically significant increases in the 

incidence of tumors in rodents. Exposure to 1.9-12 mg/kg/day hydrazine resulted in lung tumor 

formation in rats and mice (Biancifiori et al. 1966; Bhide et al. 1976; Maru and Bhide 1982; Toth 

1969, 1972b). In hamsters, exposure to 8.3 mg/kg/day hydrazine produced an increased incidence of 

liver and kidney tumors (Bosan et al. 1987). The difference in target organ specificity for the 

carcinogenic effects of hydrazine may represent an important species difference between hamsters and 

other laboratory rodents. Several tumor types, including those of the blood vessels, lung, kidney, and 

liver were noted at elevated incidences in mice chronically exposed to 19 mg/kg/day 

l,l-dimethylhydrazine in the drinking water (Toth 1973a). Studies have reported a statistically 

significant increase in the incidence of blood vessel tumors in mice exposed to 0.059 mg/kg/day 

1,2-dimethylhydrazine (Toth and Patil 1982) and in hamsters exposed to 1.1 mg/kg/day 

1,2-dimethylhydrazine in the drinking water for life (Toth 1972c). 

Collectively, these data indicate that hydrazines are carcinogenic by the oral route following acute, 

intermediate, or chronic exposure, and are capable of producing tumors in multiple tissue sites in 

several different animal species. Clearly, 1,2-dimethylhydrazine is the most potent carcinogen of the 

three hydrazines, since significant tumor incidences have been reported following single doses (Craven 

and DeRubertis 1992; Schiller et al. 1980; Watanabe et al. 1985) and at very low chronic doses (Toth 

and Patil 1982). Hydrazine and l,l-dimethylhydrazine are less potent carcinogens, producing tumors 
HYDRAZINES 56 

2. HEALTH EFFECTS 

primarily in the lungs (Bhide et al. 1976; Biancifiori et al. 1966; Maru and Bhide 1982; Roe et al. 

1967). All CEL values from each reliable study resulting from oral exposure to hydrazines are 

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

The EPA has derived oral slope factors of 30 (mg/kg/day)-1 for hydrazine based on liver tumors, 

2.6 (mg/kg/day)-1 for1,1-dimethylhydrazine based on tumors of the cardiovascular system, and 

37 (mg/kg/day)-1 for 1,2-dimethylhydrazine based on tumors of the cardiovascular system (HEAST 

1992; IRIS 1993). Doses of hydrazine, 1, 1-dimethylhydrazine, and 1,2-dimethylhydrazine 

corresponding to excess cancer risks of 10-4 to 10-7 are shown in Figure 2-2. 

2.2.3 Dermal Exposure 

2.2.3.1 Death 

No studies were located regarding lethal effects in humans after dermal exposure to hydrazines. 

In rabbits and guinea pigs, the dermal LD50 values ranged from 93 to 190 mg/kg, 1,341 to 

1,680 mg/kg, and 158 to 563 mg/kg for hydrazine, 1,1-dimethylhydrazine, and 1,2-dimethylhydrazine, 

respectively (Rothberg and Cope 1956). One out of four dogs administered a single dermal dose of 

300 mg/kg 1,1-dimethylhydrazine died 6 hours after exposure (Smith and Clark 1971). All dogs (three 

out of three) exposed to a single dermal dose of 1,800 mg/kg l,l-dimethylhydrazine died within 

6 hours. In dogs exposed to hydrazine, two of three died following exposure to a single dermal dose 

of 96 mg/kg (Smith and Clark 1972). Additional deaths were noted in this study at higher dermal 

doses of hydrazine. These data indicate that acute dermal exposure to large doses of hydrazines can 

be lethal. These LOAEL values are recorded in Table 2-3. The lack of repeat dermal exposure 

studies in animals is probably due to the corrosiveness of hydrazines and their ability to induce dermal 

sensitization reactions. 

2.2.3.2 Systemic Effects 

No studies were located regarding respiratory, cardiovascular, gastrointestinal, musculoskeletal, hepatic, 

or renal effects in humans or animals after dermal exposure to hydrazines. All LOAEL values for 

hematological, dermal, and ocular effects from each reliable study are recorded in Table 2-3. 


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Hematological Effects. No studies were located regarding hematological effects in humans after 

dermal exposure to hydrazines. 

Data in animals regarding hematological effects are limited to a single study. A decreased 

thromboplastin generation time was noted in dogs exposed to a single dose of 300 mg/kg 

l,l-dimethylhydrazine (Smith and Castaneda 1970). No other blood coagulation parameters were 

significantly affected. 

Dermal Effects. Dermal exposure to hydrazine produces contact dermatitis. A number of studies 

have reported contact dermatitis in humans after dermal exposure to solutions containing 0.00005% to 

1% hydrazine (Frost and Hjorth 1959; Hovding 1967; Suzuki and Ohkido 1979; Van Ketel 1964; 

Wrangsjo and Martensson 1986). These studies clearly indicate that hydrazine is a sensitizing agent. 

Exposure to a single dermal dose of 93-190 mg/kg hydrazine resulted in discoloration of the exposed 

area in rabbits and guinea pigs (Rothberg and Cope 1956). Dermal discoloration and edema of the 

skin (application area) were observed in dogs dermally exposed to a single dose of 96 mg/kg 

hydrazine or more (Smith and Clark 1972). Discoloration was also observed in dogs after dermal 

exposure to a single dose of 300 mg/kg 1,1-dimethylhydrazine (Smith and Clark 1971). 

Ocular Effects. No studies were located regarding ocular effects in humans after dermal exposure to 

hydrazines. A single application of 3 μL of hydrazine, 1,1-dimethylhydrazine, or 

1,2-dimethylhydrazine directly to the eyes produced conjunctivitis and erythema of the eyelids in 

rabbits (Rothberg and Cope 1956). Comeal damage was also noted in rabbits exposed to hydrazine 

but not in rabbits exposed to 1,1-dimethylhydrazine or 1,2-dimethylhydrazine. Dermal exposure to a 

single dose of 5 mmole/kg 1,1-dimethylhydrazine produced comeal swelling in dogs (Smith and 

Castaneda 1970). Although the ocular effects observed in this study may have resulted from hydrazine 

that was absorbed systemically, it is also possible that direct exposure of the eyes to hydrazine vapors 

was responsible for this effect. These data indicate that all three hydrazines can produce effects on the 

eyes. 
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2.2.3.3 Immunological and Lymphoreticular Effects 

Data regarding the immunological or lymphoreticular effects of hydrazines in humans after dermal 

exposure are limited to a single case study. A female laboratory worker intermittently exposed to an 

undetermined amount of hydrazine developed a lupus erythematosus-like disease (Reidenberg et al. 

1983). Symptoms included a photosensitive rash, fatigue, anthragias, and a breaking off of frontal 

hair. The subject also possessed antinuclear antibodies and antibody to DNA. A positive skin patch 

test response was obtained after a dermal challenge to hydrazine was administered. The study authors 

concluded that hydrazine can induce a lupus erythematosus-like disease in predisposed persons. In 

support of this view, a number of other hydrazine derivatives have been linked to the induction of 

lupus erythematosus in humans (Pereyo 1986). As discussed in Section 2.2.3.2, dermal exposure to 

hydrazine also produces allergic contact dermatitis in humans. 

No data were located regarding the immunological or lymphoreticular effects in animals after dermal 

exposure to hydrazines. 

2.2.3.4 Neurological Effects 

Data regarding neurological effects in humans after dermal exposure to hydrazines are limited to two 

case studies. A man who suffered bums during an industrial hydrazine explosion became comatose 

14 hours after the explosion (Kirklin et al. 1976). Rapid recovery from the coma was facilitated by 

pyridoxine treatment. Another man who suffered bums during an industrial 1,1-dimethylhydrazine 

explosion exhibited abnormal EEG readings and narcosis within 40 hours after exposure (Dhennin 

et al. 1988). Recovery from these symptoms was also facilitated by pyridoxine treatment. 

Several months after the incident the latter worker developed polyneuritis. The findings from these 

studies are limited because the subjects were burn patients. The trauma from the bums may have 

played a role in some of the neurological effects observed. In addition, pyridoxine is also known to 

produce neurological effects at high doses, and may have been partially responsible for the delayed 

polyneuritis. 

Mild convulsions were noted in 3 of 13 dogs receiving a single dermal dose of 300-1,800 mg/kg 

l,l-dimethylhydrazine (Smith and Clark 1971). Similarly, convulsions were noted in 3 of 25 dogs 

administered a single dermal dose of 96-480 mg/kg hydrazine (Smith and Clark 1972). The data from 
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animal studies support the findings of the human case studies which indicate that hydrazine and 

1,1 -dimethylhydrazine adversely affect the central nervous system following large dermal exposures, 

No studies were located regarding the following effects in humans or animals after dermal exposure to 

hydrazines: 

2.2.3.5 Reproductive Effects 

2.2.3.6 Developmental Effects 

2.2.3.7 Genotoxic Effects 

Genotoxicity studies are discussed in Section 2.5. 

2.2.3.8 Cancer 

No studies were located regarding cancer effects in humans or animals after dermal exposure to 

hydrazines. 

2.3 TOXICOKINETICS 

No data were located regarding the toxicokinetics of hydrazines in humans after inhalation, oral, or 

dermal exposure to hydrazines. Inhalation, oral, and dermal studies in animals indicate that hydrazines 

are rapidly absorbed into the blood. Animal studies also indicate that hydrazines readily distribute to 

tissues without preferential accumulation at any specific site. Hydrazines with a free amino group are 

able to react with endogenous alpha-keto acids and in so doing produce a variety of adverse health 

effects. In vivo and in vitro studies indicate that hydrazines are metabolized by several pathways, both 

enzymatic and nonenzymatic. Free radical and carbonium ion intermediates are produced during the 

metabolism of hydrazines and may also be involved in adverse health effects produced by exposure to 

hydrazines. Limited data from animal studies indicate that metabolites of hydrazines are excreted 

principally in the urine and expired air. Although the data are limited, animal studies appear to 

indicate that the toxicokinetics of hydrazines may vary among animal species. 
HYDRAZINES 62 

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2.3.1 Absorption 

2.3.1 .l Inhalation Exposure 

No studies were located regarding absorption in humans after inhalation exposure to hydrazines. 

A single animal study was located which investigated the absorption of hydrazine in the lungs. 

Groups of eight rats were exposed to concentrations of 10, 60, or 500 ppm hydrazine in a nose-only 

chamber for 1 hour (Llewellyn et al. 1986). Based on the levels of hydrazine and its metabolites 

excreted in the urine within 48 hours, the absorption of hydrazine was estimated to be at least 

8.4-29.5%. However, because a large percentage of the dose may have been retained in the body or 

excreted by fecal or pulmonary routes, absorption in the lungs is probably significantly higher than 

8.4-29.5%. 

2.3.1.2 Oral Exposure 

No studies were located regarding absorption in humans after oral exposure to hydrazines. It should 

be noted, however, that the drug isoniazid, which is used to treat tuberculosis, is metabolized to 

hydrazine, and thus patients administered isoniazid exhibit elevated levels of hydrazine in their blood 

plasma (Blair et al. 1985). 

A single animal study was located which investigated the oral absorption of hydrazine. Groups of 

15 rats were administered a single dose of hydrazine, ranging from 2.9 to 81 mg/kg (Preece et al. 

1992a). Based on the levels of hydrazine and its metabolites excreted in the urine within 24 hours, at 

least 19-46% of the administered dose was absorbed. However, since the analytical method employed 

in this study cannot detect certain metabolites of hydrazine, and since 24 hours may have been too 

short a time period to collect all urinary metabolites, the absorption of hydrazine in the gastrointestinal 

tract is most likely higher than 19-46%. In a more detailed description of presumably the same study, 

Preece et al. (1992b) reported dose saturation effects with respect to urinary excretion and liver 

concentration of hydrazine. Both the ratio of plasma to liver hydrazine levels and the proportion of 

hydrazine and acetylhydrazine excreted in the urine declined with the dose. These authors also 

reported that evidence of fatty liver and reduction in liver and body weights occurred only at the 

highest dose examined (81 mg/kg). 
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2. HEALTH EFFECTS 

2.3.1.3 Dermal Exposure 

No studies were located regarding absorption in humans after dermal exposure to hydrazines. 

Two studies in dogs reported that hydrazine and 1,1-dimethylhydrazine were detected in the blood 

within 30 seconds of exposure to a single dermal dose (Smith and Clark 1971, 1972). In dogs 

exposed to a single dermal dose of 96-480 mg/kg hydrazine, maximum levels of hydrazine in the 

blood (approximately 70 μg/L) were detected 3 hours after exposure (Smith and Clark 1972). 

Similarly, in dogs exposed to a single dermal dose of 300-1,800 mg/kg 1,1-dimethylhydrazine, the 

highest levels of l,l-dimethylhydrazine (approximately 130 μg/mL) were detected 3 hours after 

exposure (Smith and Clark 1971). These data indicate that hydrazine and 1,1-dimethylhydrazine are 

rapidly absorbed from the skin into the blood. However, these studies do not provide enough 

information to estimate the extent to which hydrazine and 1,1-dimethylhydrazine are absorbed. The 

lack of repeat dermal exposure studies in animals is probably due to the corrosiveness of hydrazines 

and their ability to induce dermal sensitization reactions. 

2.3.2 Distribution 

2.3.2.1 Inhalation Exposure 

No studies were located regarding distribution in humans or animals after inhalation exposure to 

hydrazines. 

2.3.2.2 Oral Exposure 

No studies were located regarding distribution in humans after oral exposure to hydrazines. 

A single study in animals reported limited information on the distribution of hydrazine after oral 

exposure. Following a single oral dose of 2.9-81 mg/kg hydrazine, peak levels of hydrazine in the 

plasma and liver of rats were achieved within 30 minutes (Preece et al. 1992a). These levels ranged 

from approximately 0.0003 to 0.01 mg/mL in the plasma and from 0.0006 to 0.006 mg/kg in the liver. 

The levels of hydrazine in other tissues were not reported. In a more detailed description of 

presumably the same study, Preece et al. (1992b) found that there was a fivefold greater amount of 
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hydrazine in the liver than in blood plasma 24 hours after dosing. No acetylhydrazine was found at 

that time. The concentration of hydrazine in the liver (other organs were not examined) did not 

increase proportionately with the dose, suggesting saturation effects. Similarly, the urinary excretion 

was dose-dependent, with a greater portion of hydrazine and acetylhydrazine being excreted at lower 

doses than at higher doses. 

2.3.2.3 Dermal Exposure 

No studies were located regarding distribution in humans or animals after dermal exposure to 

hydrazines. 

2.3.2.4 Other Routes of Exposure 

No studies were located regarding distribution in humans after exposure to hydrazines. 

In rats administered a single dose of 9.9 mg/kg hydrazine by subcutaneous injection, hydrazine was 

observed to rapidly distribute to tissues (Kaneo et al. 1984). Maximum tissue levels were observed 

within 30 minutes in the liver, lung, plasma, and particularly the kidney. Hydrazine was detected in 

the brain of rats at levels of 0.5-1 μg/g following intravenous injection of 5.1 mg/kg hydrazine 

(Matsuyama et al. 1983). The levels of hydrazine in various tissues in rats were reported to decrease 

with half-times ranging from 2.3 to 3.3 hours (Kaneo et al. 1984). 

In a series of experiments, groups of rats, rabbits, cats, dogs, and monkeys were administered a single 

intraperitoneal dose of l,l-dimethylhydrazine ranging from 10 to 50 mg/kg (Back et al. 1963). The 

plasma levels of l,l-dimethylhydrazine in all species reached maximum values within 1 hour of the 

injection, accounting for up to 14.3% of the dose in dogs and 8.7% of the dose in cats. Plasma levels 

were not detectable in rats after 2-24 hours, indicating that 1,1-dimethylhydrazine was rapidly 

distributed to tissues or was excreted. Plasma levels in monkeys tended to drop off after1 hour and 

were not detectable after 24 hours. In a limited study, male rats were subcutaneously injected with 

50 mg/kg 1,1-dimethylhydrazine or 100 mg/kg 1,2-dimethylhydrazine (Fiala and Kulakis 1981). 

Plasma levels of these two hydrazines decreased rapidly after exposure, with half-lives of 

approximately 1 hour for each chemical. 
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In rats administered a single dose of 0.78-80 mg/kg 1,1-dimethylhydrazine by intraperitoneal injection, 

approximately 71 .1% of the dose was retained in the body after 4 hours (Mitz et al. 1962), and 

approximately 7.1-38.7% of the dose was retained in the body after 53 hours (Dost et al. 1966). Low 

levels of 1,1-dimethylhydrazine (approximately 0.1-3.1% of the dose) were detected in tissues (brain, 

liver, kidney, heart, blood) of rats administered a single dose of 11-60 mg/kg 1,1-dimethylhydrazine 

by intraperitoneal injection (Mitz et al. 1962; Reed et al. 1963). Preferential accumulation of 

1,1-dimethylhydrazine was not observed in any organ. Although higher concentrations of 

1,1-dimethylhydrazine were detected in the liver and colon of rabbits within 2 hours after receiving a 

single intravenous or intraperitoneal dose (Back et al. 1963), this was not judged to be evidence of 

preferential accumulation by the study authors. The highest levels in these rabbits were detected in the 

liver (8.9%) and colon (11.6%) after 2 hours, whereas other tissue levels ranged from 0.02 to 4.18% of 

the dose. 

These data indicate that hydrazines distribute rapidly to all tissues without preferential accumulation 

following injection of a single dose. Furthermore, tissue levels of hydrazine and 

1,1-dimethylhydrazine tend to reach maximal values within 1 hour and are generally not detectable 

after 24 hours. 

2.3.3 Metabolism 

Several enzymatic and nonenzymatic pathways are involved in the metabolism of hydrazines. Humans 

with a slow acetylator genotype may accumulate more hydrazine in the plasma because of an impaired 

ability to metabolize and excrete the compound (Blair et al. 1985). Although the extent to which each 

pathway contributes to total metabolism may depend somewhat on the route of exposure (a first-pass 

metabolic effect for oral exposure, for example), the types of pathways involved and metabolites 

formed do not appear to be dependent on route. Therefore this section discusses the data without 

reference to route of exposure. While the metabolic pathways of hydrazine, 1,1-dimethylhydrazine, 

and 1,2-dimethylhydrazine are similar in some ways, there are some important differences. Therefore, 

data from in vivo and in vitro studies regarding the metabolism of hydrazine, 1,1-dimethylhydrazine, 

and 1,2-dimethylhydrazine are discussed separately below. 

Hydrazine. In rats exposed to 10-500 ppm hydrazine for 1 hour, approximately 2-10% of the inhaled 

dose was excreted in the urine unchanged, 1.74% as acetyl hydrazine, and 4.5-11.4% as diacetyl 
HYDRAZINES 66 

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hydrazine (Llewellyn et al. 1986). In rats exposed to a single dose of 16-64 mg/kg hydrazine, 

approximately 20% was excreted in the urine as an unspecified hydrazine derivative, 30% was 

excreted in the urine unchanged, and 25% of the nitrogen in hydrazine was released in expired air as 

nitrogen gas (Springer et al. 1981). In rats administered a single dose of 2-81 mg/kg hydrazine, a 

small percentage of the dose (1-19%) was recovered in the urine as acetyl hydrazine and/or diacetyl 

hydrazine within 2448 hours of exposure (Kaneo et al. 1984; Llewellyn et al. 1986; Preece et al. 

1992a). Following exposure to larger doses of 427 mg/kg hydrazine, a number of metabolites were 

excreted in the urine, including acetyl hydrazine, diacetyl hydrazine, pyruvate hydrazone, urea, and a 

cyclic compound (1,4,5,6-tetrahydro-6-oxo-3-pyridazine carboxylic acid, a product of the reaction 

between 2-oxoglutarate and hydrazine) (Preece et al. 1991). These data indicate that hydrazine 

undergoes acetylation and can react with cellular molecules in vivo. 

Hydrazine is rapidly metabolized by rat liver microsomes in vitro (Timbrell et al. 1982). Oxygen, 

nicotinamide-adenine dinucleotide phosphate (NADPH), and active enzyme were required for maximal 

activity. Metabolism of hydrazine by rat liver hepatocytes was increased when rats were pretreated 

with cytochrome P-450 inducers (phenobarbital and rifampicin) and was decreased by the addition of 

cytochrome P-450 inhibitors (metyrapone and piperonyl butoxide) (Noda et al. 1987). Cytochrome 

P-450 inhibitors and inducers were also reported to increase and decrease hydrazine toxicity, 

respectively, indicating a relationship between metabolism and toxicity (Timbrell et al. 1982). Free 

radical formation was reported to occur when hydrazine was incubated with purified NADPHcytochrome 

P-450 reductase (Noda et al. 1988). This reaction required NADPH and oxygen, was 

stimulated by FAD, inhibited by superoxide dismutase, and was unaffected by carbon monoxide. Free 

radicals were also noted when hydrazine was metabolized in perfused rat livers (Sinha 1987). These 

free radicals included acetyl, hydroxyl, and hydrogen radicals, the type of which was dependent upon 

the addition of an activating system (horseradish peroxidase or copper ion) to the perfusate. The 

occurrence of an acetyl radical suggests that hydrazine is acetylated prior to radical formation. These 

data indicate that hydrazine is metabolized by cytochrome P-450 but that transformation via other 

enzyme systems (peroxidases) or nonenzymatic reactions (copper ion-mediated) may occur as well. 

The formation of free radicals during the metabolism of hydrazine may be important to the mechanism 

of action of hydrazine toxicity. 

l,l-Dimethylhydrazine. In rats administered a single dose of 0.78-60 mg/kg 1,1-dimethylhydrazine, 

approximately 12-27% of the dose was detected in expired air as carbon dioxide (Dost et al. 1966; 
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2. HEALTH EFFECTS 

Reed et al. 1963). Four hours after receiving a single dose of 40 mg/kg 1,1-dimethylhydrazine, less 

than 2% of the dose was released in expired air (Mitz et al. 1962). Approximately 3-10% and 

20-25% of the dose was recovered in the urine as the glucose hydrazone of 1,1-dimethylhydrazine and 

an unidentified metabolite (Mitz et al. 1962). The study authors speculated that the unidentified 

metabolite was another hydrazone of 1,1-dimethylhydrazine. These data indicate that 1,1-dimethylhydrazine 

undergoes demethylation and can react with cellular molecules in vivo. 

N-demethylation of 1,1-dimethylhydrazine by rat and hamster liver microsomes in vitro required the 

presence of NADPH and oxygen and was decreased by the addition of flavin-containing 

monooxygenase inhibitor (methimazole) but not by the addition of cytochrome P-450 inhibitors 

(Prough et al. 1981). 1,1-Dimethylhydrazine was also noted to be a good substrate for N-oxidation by 

amine oxidase (Prough 1973). In rat liver microsomes and S-9 fractions, both a nonenzymatic and an 

enzymatic component were identified for the metabolism of 1,1-dimethylhydrazine (Godoy et al. 

1983). Formaldehyde was produced by both components, although the nonenzymatic component 

dominated the formation of a reactive protein-binding species. In contrast, rat liver slices metabolized 

1,1-dimethylhydrazine to carbon dioxide and did not generate any reactive protein-binding species 

(Godoy et al. 1983), suggesting that in vitro metabolic studies may not be presenting an accurate 

picture of 1,1-dimethylhydrazine metabolism as it occurs in vivo. The formation of formaldehyde by 

rat colon microsomes was decreased by the addition of lipoxygenase and cyclooxygenase inhibitors 

(indomethacin and eicosatetranoic acid) and was stimulated by the addition of fatty acids, suggesting 

that lipoxygenase and cyclooxygenase may be involved in the colonic metabolism of 

1,1-dimethylhydrazine (Craven et al. 1985). 

Several studies have shown that the reactive binding species generated by 1,1-dimethylhydrazine 

metabolism may be free radical intermediates. Rat liver microsomes and rat hepatocytes are capable 

of metabolizing 1,1-dimethylhydrazine to form methyl radical intermediates (Albano et al. 1989; 

Tomasi et al. 1987). The formation of these radicals was inhibited by the addition of inhibitors of 

cytochrome P-450 (SKF 525A, metyrapone, and carbon monoxide) and inhibitors of the flavin-containing 

monooxygenase system (methimazole). The formation of free radicals could also be 

supported nonenzymatically by the presence of copper ion (Tomasi et al. 1987). These data indicate 

that at least two independent enzyme systems and one nonenzymatic pathway may be involved in the 

metabolism of 1,1-dimethylhydrazine. 
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1,2-Dimethylhydrazine. In vivo studies indicate that 1,2-dimethylhydrazine is metabolized to form 

azomethane, azoxymethane, methylazoxymethanol, ethane, and carbon dioxide. In rats administered a 

single dose of 20-200 mg/kg 1,2-dimethylhydrazine, approximately 4-24% and 14-23% of the dose 

was detected in expired air as carbon dioxide and azomethane, respectively (Fiala et al. 1976; Harbach 

and Swenberg 1981). Azoxymethane and methylazoxymethanol were detected in the urine of rats 

injected with 21 mg/kg 1,2-dimethylhydrazine (Fiala et al. 1977). It has been proposed that 

1,2-dimethylhydrazine undergoes sequential oxidations to form azomethane, which in turn is 

metabolized to form azoxymethane and then methylazoxymethanol (Druckrey 1970). Ethane was 

detected in the expired air of rats exposed to a single dose of 9-91 mg/kg 1,2-dimethylhydrazine 

(Kang et al. 1988). The study authors proposed that ethane was formed by a dimerization of methyl 

radicals originating from 1 ,2-dimethylhydrazine metabolism. These data indicate that oxidation can 

occur at both the nitrogen and the carbon of 1,2-dimethylhydrazine in vivo and suggest that free 

radicals may be formed as well. 

Human colon microsomes and human colon cancer cells were capable of generating formaldehyde 

from 1,2-dimethylhydrazine in vitro (Newaz et al. 1983). The formation of formaldehyde was 

decreased by the addition of cytochrome P-450 inhibitors and was increased by the pretreatment of 

cancer cells with cytochrome P-450 inducers. Interestingly, the study authors noted a gradient with 

respect to 1,2-dimethylhydrazine metabolism activity in the colon (ascending < transverse < 

descending). Other studies have reported that the greatest capacity to produce DNA-binding 

intermediates from 1,2-dimethylhydrazine is in the ascending colon of humans (Autrup et al. 1980a). 

Rat colon epithelial cells were found to metabolize 1,2-dimethylhydrazine to azoxymethane, 

methylazoxymethanol, and a reactive binding species (Glauert and Bennink 1983). In the hamster 

colon cells, surface columnar epithelial cells were found to metabolize 1,2-dimethylhydrazine 2-3 

times as well as crypt cells (Sheth-Desai et al. 1987). In addition, metabolism was inhibited by an 

alcohol dehydrogenase inhibitor (pyrazole). In a rat liver perfusion study, the metabolites of 

1,2-dimethylhydrazine were identified as azomethane, azoxymethane, and methylazoxymethanol 

(Wolter et al. 1984). Rat liver microsomes were found to metabolize 1,2-dimethylhydrayine to 

azomethane (N-N oxidation) and formaldehyde (C-N oxidation) (E&son and Prough 1986). These 

activities were increased in rats pretreated with cytochrome P-450 inducers (phenobarbital) indicating 

the involvement of this enzyme. Mitochondrial amine oxidase demonstrated considerable activity as 

well (Coomes and Prough 1983; Erikson and Prough 1986), although 1,2-dimethylhydrazine was not 

as good a substrate for this enzyme as was l,l-dimethylhydrazine (Prough 1973). Likewise, 
HYDRAZINES 69 

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1,2-dimethylhydrazine was not as good a substrate as 1,1-dimethylhydrazine for flavin-containing 

monooxygenase-mediated metabolism (Prough et al. 1981) or colonic cyclooxygenase and 

lipoxygenase (Craven et al. 1985). Since 1,2-dimethylhydrazine is a potent colon carcinogen while 

1,1-dimethylhydrazine is not carcinogenic for the rodent colon, the significance of these findings is 

uncertain. 

Reactive intermediates are formed during the metabolism of 1,2-dimethylhydrazine. In vitro studies 

indicate that methylazoxymethane can form a reactive species (probably a methyldiazonium ion) either 

spontaneously (Nagasawa and Shirota 1972) or enzymatically by alcohol dehydrogenase and/or 

cytochrome P-450 (Feinberg and Zedeck 1980; Sohn et al. 1991). Other in vitro studies suggest that 

free radicals are formed during the metabolism of 1,2-dimethylhydrazine. For example, as observed 

with 1,1-dimethylhydrazine, the formation of methyl free radicals from 1,2-dimethylhydrazine in rat 

liver microsomes and rat hepatocytes was inhibited by cytochrome P-450 inhibitors (SKF 525A, 

metyrapone, and carbon monoxide) (Albano et al. 1989; Tomasi et al. 1987). However, unlike 

1,1-dimethylhydrazine, the formation of methyl radicals was not decreased by the addition of a flavin-containing 

monooxygenase inhibitor (methimazole), suggesting that this enzyme is not involved in the 

production of free radicals from 1,2-dimethylhydrazine. Carbon-centered radicals were observed when 

1,2-dimethylhydrazine was metabolized by horseradish peroxidase (August0 et al. 1985; Netto et al. 

1987). These data indicate differences exist between the enzyme systems involved in metabolism of 

1,2-dimethylhydrazine and 1,1-dimethylhydrazine to reactive intermediates. 

Reactive intermediates produced during the metabolism of 1,2-dimethylhydrazine are most likely 

responsible for DNA adducts observed in vivo (Becker et al. 1981; Netto et al. 1992; Pozharisski et al. 

1975) and in vitro (Autrup et al. 1980a; Harris et al. 1977; Kumari et al. 1985). There is evidence for 

both the methyldiazonium and methyl radical as reactive species derived from 1,2-dimethylhydrazine, 

and it is clear that metabolism of the compound is required for its carcinogenicity. Inhibition of 

metabolism by disulfiram and other thiono sulfur compounds (Fiala et al. 1977) resulted in inhibition 

of DNA alkylation (Swenberg et al. 1979) and colon carcinogenicity (Wattenberg 1975):. Moreover, 

azoxymethane and methylazoxymethanol, two metabolites of 1,2-dimethylhydrazine, are also potent 

colon and liver carcinogens (Williams and Weisburger 1991). 
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2.3.4 Excretion 

2.3.4.1 Inhalation Exposure 

No studies were located regarding excretion in humans after inhalation exposure to hydrazines. 

Forty-eight hours after a l-hour exposure to 10-500 ppm hydrazine, approximately 8.4-29.5% of the 

inhaled dose was excreted in the urine of rats (Llewellyn et al. 1986). Most of the recovered dose was 

excreted during the first 24 hours. Three metabolites were identified in the urine as unchanged 

hydrazine, acetyl hydrazine, and diacetyl hydrazine. No other studies were located regarding excretion 

in animals after inhalation exposure to hydrazine. 

2.3.4.2 Oral Exposure 

No studies were located regarding excretion in humans after oral exposure to hydrazines. 

A single study was located that reported excretion in animals after oral exposure to hydrazine. 

Twenty-four hours after a single oral dose of 2.9-81 mg/kg hydrazine, approximately 19-46% of the 

dose was recovered in the urine of exposed rats (Preece et al. 1992a). Two metabolites were identified 

in the urine as unchanged hydrazine and acetyl hydrazine. Fecal excretion and release of the 

compound in expired air were not investigated in this study. 

2.3.4.3 Dermal Exposure 

No studies were located regarding excretion in humans after dermal exposure to hydrazines. 

Data in animals regarding the excretion of hydrazines are limited to two studies. In dogs administered 

a single dermal dose of 300-1,800 mg/kg 1,1-dimethylhydrazine, levels of up to 600 μg/L 

1,1-dimethylhydrazine were detected in the urine within 5 hours (Smith and Clark 1971). Similarly, in 

dogs administered a single dermal dose of 96-480 mg/kg hydrazine, levels of up to 70 μg/mL were 

detected in the urine within 3 hours (Smith and Clark 1972). However, neither of these studies 

examined fecal excretion nor did they provide sufficient information to estimate the fraction of the 

dose excreted in the urine. 
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2.3.4.4 Other Exposure 

No studies were located regarding excretion in humans after other exposures to hydrazines. 

The levels of hydrazine in the blood were reported to decrease in a biphasic manner in rats 

administered 16-64 mg/kg hydrazine via indwelling catheters, with half-times of 0.74 and 26.9 hours 

(Springer et al. 1981). In dogs administered a single dose of 16-64 mg/kg hydrazine via an 

indwelling cannula, approximately 25% and 50% of the dose was recovered within 48 hours in the 

expired air and urine, respectively (Springer et al. 1981). Forty-eight hours after receiving a single 

intravenous dose of 2-12 mg/kg hydrazine, rats excreted approximately 13.8-37.3% of the dose in the 

urine (Llewellyn et al. 1986). Approximately 29.2% of a single subcutaneous dose of 9.9 mg/kg 

hydrazine was excreted in the urine of rats after 48 hours (Kaneo et al. 1984). Although these data are 

limited by the lack of information on fecal excretion, they suggest that the majority of an absorbed 

dose of hydrazine is excreted in the urine but that a significant fraction of the dose may be released in 

expired air. 

In rats administered a single dose of 0.78-80 mg/kg 1,1-dimethylhydrazine, approximately 18.9-76% 

of the carbon dose was recovered in the urine and 2-23% of the carbon dose was excreted in expired 

air within 4-53 hours (Dost et al. 1966; Mitz et al. 1962; Reed et al. 1963). Approximately 

34.8-39.1% of the carbon dose was excreted in the urine within 5 hours in dogs intraperitoneally 

injected with 50 mg/kg 1,1-dimethylhydrazine (Back et al. 1963). Approximately 37.2-51.2% of the 

carbon dose was recovered in the urine within 6 hours in cats intraperitoneally injected with 

10-50 mg/kg 1,1-dimethylhydrazine (Back et al. 1963). These studies typically employed a carbon 

radiolabel (14C-1,1-dimethylhydrazine). This radiolabel can become separated from the rest of the 

molecule during the demethylation of 1,1-dimethylhydrazine; therefore, these studies may not 

accurately depict the metabolic fate of the nitrogen contained within the dose. In addition, fecal 

excretion of 1,1-dimethylhydrazine was not determined in these studies. Despite these limitations, 

these data suggest that the majority of the carbon from an absorbed dose of 1,1-dimethylhydrazine is 

excreted in the urine but that a significant fraction of the carbon dose may be released in expired air. 

In rats treated subcutaneously with 21 mg/kg 14C-labelled 1,2-dimethylhydrazine, approximately 

13-16% of the radioactivity was released in expired air as CO2 within 24 hours, while 14-15% was 

expired as azomethane and 17% was released in urine (Fiala et al. 1977). A similar rat study found 
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that the levels of radiolabel in expired CO2 and azomethane after 24 hours were 11% and 14%, 

respectively, when the dose was 21 mg/kg 1,2-dimethylhydrazine, and 4% and 23%, respectively, 

when the dose was 200 mg/kg (Fiala et al. 1976). Likewise, rats injected with 20 mg/kg 

1,2-dimethylhydrazine expired about 22% of the radioactive dose as azomethane and about 16% as 

CO2 after 12 hours (Harbach and Swenberg 1981). By quantitating the radioactivity released as 

azomethane, which contains both nitrogens from the 1,2-dimethylhydrazine, the metabolic fate of these 

nitrogens can be followed, in contrast to studies which only measure expired CO2. Female mice 

injected with 15 mg/kg 14C-labelled 1,2-dimethylhydrazine expired about 24% of the radioactivity as 

CO2 within 24 hours, while 10% was excreted in the urine (Hawks and Magee 1974). This same 

study found that 0.9% of the radioactivity was excreted in the bile after a dose of 200 mg/kg. These 

data suggest that a significant fraction of the carbon dose of 1,2-dimethylhydrazine may be released in 

expired air and urine, whereas fecal excretion is relatively low. 

2.4 MECHANISMS OF ACTION 

Studies in animals indicate that hydrazines are rapidly absorbed through the skin (Smith and Clark 

1971, 1972), and presumably in the lungs and gastrointestinal tract as well. Although the mechanism 

by which hydrazines are absorbed into the blood has not been studied, this most likely does not occur 

by passive diffusion because of the polar nature of these compounds. 

A number of studies have investigated the mechanisms by which hydrazines produce adverse health 

effects. These data suggest there are at least two distinct mechanisms of action for hydrazines: one 

involving the direct binding of those hydrazines with a free amino group (hydrazine and 

1,1-dimethylhydrazine) to key cellular molecules, and the other involving the generation of reactive 

species such as free radical intermediates or methyldiazonium ions as a result of metabolism. Studies 

which support the existence of these mechanisms are discussed below. 

In vitro studies have shown that hydrazine reacts with alpha-keto acids to form hydrazoines compounds 

(O’Leary and Oikemus 1956). By binding to keto acids and forming hydrazones, hydrazine inhibited 

oxygen consumption with mitochondrial substrates in vitro (Fortney 1967). This mechanism may well 

account for the hyperlactemic and hypoglycemic effects of hydrazine observed in humans (Ochoa et al. 

1975) and dogs in vivo (Fortney 1967). Hydrazine and 1,1-dimethylhydrazine can form hydrazones 

with vitamin B6 derivatives (Comish 1969). By binding to vitamin B6 derivatives, hydrazine and 
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1,1-dimethylhydrazine are able to inhibit reactions that require vitamin B6 as a cofactor. These 

reactions include transamination reactions, decarboxylation and other transformations of amino acids, 

the metabolism of lipids and nucleic acids, and glycogen phosphorylation (NRC 1989). Deficiency of 

vitamin B6 can produce convulsions, dermatitis, and anemia. These data suggest that the convulsions 

and anemia observed in animal studies are the result of the formation of hydrazone derivatives of 

vitamin B6. In addition, some authors have proposed that a free amino group, as found in hydrazine 

and 1,1-dimethylhydrazine, is required for hydrazone formation (Comish 1969). This would explain 

why convulsions are associated with exposures to hydrazine and 1,1-dimethylhydrazine, and not 

1 ,2-dimethylhydrazine. It should be noted that pyridoxine (one of the forms of vitamin B6) is 

commonly used to treat humans exposed to hydrazine or 1,1-dimethylhydrazine. 

A number of in vitro studies have reported the production of reactive intermediates during the 

metabolism of hydrazines (see Section 2.3.3). Evidence for the production of radicals including 

methyl, acetyl, hydroxyl, and hydrogen radicals has been observed during the metabolism of hydrazine 

(Ito et al. 1992; Noda et al. 1988; Runge-Morris et al. 1988; Sinha 1987), l,l-dimethylhydrazine 

(Albano et al. 1989; Tomasi et al. 1987), and 1,2-dimethylhydrazine (Albano et al. 1989; Augusto 

et al. 1985; Netto et al. 1987; Tomasi et al. 1987). Multiple pathways, both enzymatic and 

nonenzymatic, appear to be involved in free radical generation. Free radicals have been implicated in 

protein (hemoglobin) damage associated with hydrazine in human erythrocytes (Runge-Morris et al. 

1988), suggesting that free radicals may be involved in the anemic effects of hydrazines observed in 

animals in vivo (Haun and Kinkead 1973; Rinehart et al. 1960). It has also been proposed that 

metabolism of 1,2-dimethylhydrazine yields a reactive, methyldiazonium ion (Feinberg and Zedeck 

1980; Sohn et al. 1991). The production of reactive species during the metabolism of hydrazines may 

also explain their genotoxic effects, such as the formation of DNA and RNA adducts in vivo (Becker 

et al. 1981; Beranek et al. 1983; Bolognesi et al. 1988; Bosan et al. 1986; Netto et al. 1992; 

Pozharisski et al. 1975; Quintero-Ruiz et al. 1981). DNA and RNA adducts may well be responsible 

for gene mutations observed in a number of in vitro studies (DeFlora and Mugnoli 1981; Hawks and 

Magee 1974; Kang 1994; Kerklaan et al. 1983; Levi et al. 1986; Malaveille et al. 1983;Noda et al. 

1986; Oravec et al. 1986; Parodi et al. 1981; Rogers and Back 1981; Sedgwick 1992; Wilpart et al. 

1983) and may also serve as the initiating event for cancers induced by hydrazines in vivo. 
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2.5 RELEVANCE TO PUBLIC HEALTH 

Data regarding the toxic effects of hydrazines in humans are limited to a few case studies of accidental 

exposure and chemotherapy trials in cancer patients. Studies consistently indicate that the central 

nervous system is the primary target for hydrazine and 1,1-dimethylhydrazine following inhalation, 

oral, and dermal exposures. In some cases, neurological effects were delayed, but most effects were 

observed either during exposure or soon after. Quantitative data on human exposures are available 

only for oral exposures of intermediate durations. 

Studies in animals, which support the findings from human studies, report neurological effects 

following inhalation, dermal, and parenteral exposures to hydrazine and 1,1-dimethylhydrazine. 

Neurological effects do not appear to be of concern following exposure to 1,2-dimethylhydrazine. 

Effects on the liver have been consistently reported in animal studies following exposure to all three 

hydrazines. Limited studies in animals suggest that exposure to hydrazines by the inhalation, oral, and 

parenteral routes may cause reproductive and developmental effects. A number of species-, sex-, and 

strain-specific differences have been observed for sensitivity to the toxic effects of hydrazines. All 

three hydrazines are carcinogenic in animals following oral and inhalation exposures. 1,2-Dimethylhydrazine 

is a potent carcinogen in animals and can induce tumors following single oral or parenteral 

doses. 

Data regarding the toxicokinetics of hydrazines are limited but suggest that in animals hydrazines are 

rapidly absorbed and distributed to all tissues and that metabolites are excreted largely in the urine or 

released in expired air. Limited data in humans suggest that people with a slow acetylator genotype 

do not clear hydrazine from the body as well as those who are fast acetylators and therefore may be 

more susceptible to the toxic effects of hydrazine. 

Minimal Risk Levels for Hydrazines 

Inhalation MRLs 

•	 An MRL of 4X10-3 ppm has been derived for intermediate-duration inhalation exposure to 

hydrazine. This MRL is based on a LOAEL of 0.2 ppm for moderate fatty liver changes 

observed in female mice (Haun and Kinkead 1973). In this study, groups of 40 female ICR 
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mice were exposed for 6 months to either 0, 0.2, or 1 ppm hydrazine continuously, or to 0, 

1, or 5 ppm intermittently (6 hours/day, 5 days/week). The study authors also investigated 

the effects of inhaled hydrazine in other species. In support of this MRL, fatty liver changes 

were also observed in dogs exposed to 1 ppm hydrazine for 6 months and in monkeys 

exposed to 0.2 ppm for 6 months. 

•	 An MRL of 2x10-4 ppm has been derived for intermediate inhalation exposure to 

1,1 -dimethylhydrazine. This MRL is based on a LOAEL of 0.05 ppm for hepatic effects 

(hyaline degeneration of the gall bladder) in female mice (Haun et al. 1984). In this study, 

female C57BL/6 mice were exposed for 6 months to 0, 0.05, 0.5, or 5 ppm 

l,l-dimethylhydrazine for 6 hours/day, 5 days/week. The MRL is supported by other studies 

in humans (Petersen et al. 1970; Shook and Cowart 1957), rats (Haun et al. 1984), and dogs 

(Haun 1977; Rinehart et al. 1960), which indicate that the liver is a target of 

1,1-dimethylhydrazine after inhalation exposure. 

No inhalation MRLs were derived for exposures to hydrazines for acute or chronic durations. 

Although data from animal studies indicate that inhalation exposures to hydrazines produce adverse 

effects on the liver and central nervous system following acute (Rinehart et al. 1960) and chronic 

exposures (Vemot et al. 1985), these studies do not define the threshold exposure level for these 

effects with confidence. 

Oral MRLs 

•	 An MRL of 8x10-4 mg/kg/day has been derived for intermediate oral exposure to 

1,2-dimethylhydrazine. This MRL is based on a LOAEL of 0.75 mg/kg/day for mild 

hepatitis in mice (Visek et al. 1991). In this study, groups of 25 male mice were 

administered 0, 0.75, 1.6, or 2.7 mg/kg/day 1,2-dimethylhydrazine in the diet for 5 months. 

This MRL is supported by studies reporting LOAELs for hepatic effects ranging from 

4.2-30 mg/kg/day 1,2-dimethylhydrazine in several other species, including rats (Bedell et al. 

1992), guinea pigs (Wilson 1976), dogs (Wilson 1976), and pigs (Wilson 1976). 

No oral MRLs were derived for exposures to hydrazine or for exposure to l,l-dimethylhydrazine for 

acute and chronic durations. Although data are available for neurological effects in humans after 
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intermediate-duration exposure to hydrazine (Chlebowski et al. 1984; Gershanovich et al. 1976, 1981; 

Ochoa et al. 1975; Spremulli et al. 1979), the effects levels were inconsistent among studies. Studies 

in animals have reported effects on the liver following acute-duration (Marshall et al. 1983; 

Wakabayashi et al. 1983; Wilson 1976) and intermediate-duration exposures (Biancifiori 1970). 

However, these data do not define the threshold dose for hepatic effects with confidence. 

No acute-, intermediate-, or chronic-duration dermal MRLs were derived for hydrazines because of the 

lack of an appropriate methodology for the development of dermal MRLs. 

Death. Data regarding the lethal effects of hydrazines in humans are limited to a single case study 

involving inhalation exposure to hydrazine. Death was reported in a male worker exposed to an 

undetermined concentration of hydrazine once a week for 6 months (Sotaniemi et al. 1971). Death in 

this case was due to lesions of the kidneys and lungs with complicating pneumonia. The effects on 

the kidneys and lungs, as well as effects in other tissues, were comparable to those observed in 

animals exposed to hydrazine. Therefore, death in this case is most likely attributed to hydrazine 

exposure. 

A number of animal studies have reported acute lethality after exposure by most routes to hydrazines. 

For inhalation exposures, deaths were observed in dogs and mice after acute exposure to 25-140 ppm 

1,1-dimethylhydrazine (Rinehart et al. 1960). No studies were located that examined lethality after 

acute-duration inhalation exposure to hydrazine or 1,2-dimethylhydrazine. For oral exposures, doses of 

133 mg/kg hydrazine, 533 mg/kg/day 1,1-dimethylhydrazine, and 11.7-90 mg/kg 1,2-dimethylhydrazine 

caused deaths in mice and/or dogs (Roe et al. 1967; Visek et al. 1991; Wilson 1976). For 

dermal exposures, LD50 values ranging from 93 to 1,680 mg/kg were reported for all three hydrazines 

in rabbits and guinea pigs (Rothberg and Cope 1956). Deaths were noted in dogs after application of 

a single dose of 96 mg/kg hydrazine or 300 mg/kg 1,1-dimethylhydrazine (Smith and Clark 1971, 

1972). A large number of studies have reported deaths in several animal species following injections 

of 8-400 mg/kg/day hydrazine (Bodansky 1923; Lee and Aleyassine 1970; O’Brien et al: 1964; 

Roberts and Simonsen 1966; Rothberg and Cope 1956; Wakebayashi et al. 1983), 71-125 mg/kg/day 

l,l-dimethylhydrazine (Back and Thomas 1962; Furst and Gustavson 1967; Geake et al. 1966; 

O’Brien et al. 1964; Rothberg and Cope 1956), and 44-60 mg/kg 1,2-dimethylhydrazine (Rothberg 

and Cope 1956; Wilson 1976). These doses are comparable to those producing death following oral 

exposure, suggesting that hydrazines are absorbed fairly well by the oral route. Limited information 
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from a single oral study suggests that male animals are more sensitive to the lethal effects of hydrazine 

than females (Visek et al. 1991). 

A number of studies have reported increased mortality following exposure to hydrazines for 

intermediate durations. Following inhalation exposures, increased mortality was noted in mice and 

dogs exposed to 1 ppm hydrazine (Haun and Kinkead 1973), and in mice exposed to 75 ppm 

1,1-dimethylhydrazine (Rinehart et al. 1960), but not in several species following intermediate 

exposure to 0.05-5 ppm l,l-dimethylhydrazine (Haun et al. 1984). Oral exposures of 

2.3-4.9 mg/kg/day hydrazine (Biancifiori 1970), 33 mg/kg/day 1,1-dimethylhydrazine (Roe et al. 

1967), and 4.5-60 mg/kg/day 1,2-dimethylhydrazine (Teague et al. 1981; Visek et al. 1991; Wilson 

1976) caused deaths in a number of animal species. Increased mortality was observed in several 

animal species after injections of 20-21.8 mg/kg/day hydrazine (Bodansky 1923; Patrick and Back 

1965), 30 mg/kg/day l,l-dimethylhydrazine (Comish and Hartung 1969), and 15-60 mg/kg/day 

1,2-dimethylhydrazine (Wilson 1976). 

Data regarding lethality effects in animals after chronic exposure to hydrazines are limited to two 

studies. Mortality was significantly increased in hamsters exposed to 0.25 ppm hydrazine in air for 

1 year (Vernot et al. 1985), and in mice exposed to 0.95 mg/kg/day hydrazine via the drinking water 

(Toth and Patil 1982). These exposures are notably lower than those producing fatalities after acuteand 

intermediate-duration exposure to hydrazine. 

Systemic Effects 

Respiratory Effects. Pneumonia, tracheitis, and bronchitis were observed in a man occupationally 

exposed to an undetermined concentration of hydrazine in air once a week for 6 months (Sotaniemi 

et al. 1971). Dyspnea and pulmonary edema were observed in two men exposed to a mixture of 

hydrazine and 1,1-dimethylhydrazine (Frierson 1965). Hyperplasia was observed in the lungs of rats 

and mice exposed to 0.05 ppm 1,1-dimethylhydrazine for 6 months (Haun et al. 1984). Lung irritation 

and damage has been noted in dogs after intermediate-duration exposure to 25 ppm l,l-dimethylhydrazine 

but not 5 ppm l,l-dimethylhydrazine (Rinehart et al. 1960). Similarly, pulmonary effects 

were observed in rats chronically exposed to 5 ppm hydrazine but not in mice chronically exposed to 

1 ppm hydrazine (Vernot et al. 1985). Effects on the nasal mucosa, including inflammation, 

hyperplasia, and dysplasia were noted in mice chronically exposed to 5 ppm 1,1-dimethylhydrazine 
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2. HEALTH EFFECTS 

(Haun et al. 1984). Pulmonary edema, congestion, and pneumonia were observed in rats injected with 

20 mg/kg/day hydrazine but not in rats injected with 10 mg/kg/day hydrazine (Patrick and Back 1965). 

No adverse effects were observed in the lungs of mice exposed to 9.5 mg/kg/day hydrazine via the 

drinking water for 2 years (Steinhoff et al. 1990). These data suggest that effects on the lungs and 

upper respiratory tract are of concern primarily following inhalation exposures to hydrazines. 

Cardiovascular Effects. Data regarding the cardiovascular effects of hydrazines in humans are limited 

to a single case study involving inhalation exposure to hydrazine. Intermittent exposure of a worker to 

an undetermined concentration of hydrazine in air for 6 months produced atria1 fibrillation, 

enlargement of the heart, and degeneration of heart muscle fibers (Sotaniemi et al. 1971). The 

findings from animal studies have been inconsistent. No adverse effects were noted on the 

cardiovascular system of dogs exposed to 25 ppm l,l-dimethylhydrazine or mice exposed to 1 ppm 

hydrazine for intermediate and chronic durations (Rinehart et al. 1960; Vernot et al. 1985). Mice 

exposed to 0.05-5 ppm l,l-dimethylhydrazine for 6 months to 1 year had abnormally dilated blood 

vessels (angiectesis) (Haun et al. 1984). Focal myocytolysis, fibrosis, and calcification of the heart 

were noted in mice receiving 1.6 mg/kg/day 1,2-dimethylhydrazine in the feed for 5 months (Visek 

et al. 1991). Slight accumulation of fat was observed in the myocardium of monkeys receiving 

5 mg/kg/day hydrazine by intraperitoneal injection for l-4 weeks (Patrick and Back 1965). Changes 

in blood pressure were noted in dogs following a single injection of 100 mg/kg 1,1-dimethylhydrazine 

(Back and Thomas 1962). Cardiovascular effects were not observed in mice receiving 0.75 mg/kg/day 

1,2-dimethylhydrazine (Visek et al. 1991). No adverse effects were observed in the hearts of rats 

injected with 20 mg/kg/day hydrazine for 5 weeks (Patrick and Back 1965) or in mice receiving 

9.5 mg/kg/day hydrazine in the drinking water for 2 years (Steinhoff et al. 1990). The findings of the 

animal studies, although inconsistent, suggest that the cardiovascular effects observed in the human 

case study are related to hydrazine exposure. 

Gastrointestinal Effects. Oral exposure to hydrazine has produced nausea and vomiting in human 

cancer patients. These effects could be due to direct irritation of the gastrointestinal tract but could 

also be due to effects on the central nervous system. Studies in animals generally have not reported 

effects on the gastrointestinal system following intermediate and chronic inhalation exposures to 

25 ppm l,l-dimethylhydrazine (Rinehart et al. 1960) or 1 ppm hydrazine (Vernot et al. 1985). 

Similarly, chronic oral exposure to 9.5 mg/kg/day hydrazine were without effect on the gastrointestinal 

system of mice (Steinhoff et al. 1990). Proliferation, dysplasia, and hyperplasia of the colon mucosa 
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have been observed in rats orally exposed to 25 mg/kg 1,2-dimethylhydrazine or injected with 

15-20 mg/kg 1,2-dimethylhydrazine (Caderni et al. 1991; Decaens et al. 1989; Wargovich et al. 1983). 

These effects are most likely precursors of carcinogenic lesions induced by 1,2-dimethylhydrazine in 

this tissue site. Although these data suggest that the gastrointestinal system is not a primary target of 

the noncarcinogenic effects of hydrazines, this is not certain, particularly for 1,2-dimethylhydrazine. 

Hematological Effects. No studies were located regarding hematological effects in humans after 

exposure to hydrazines. Studies in dogs indicate that inhalation exposure for intermediate durations to 

relatively high concentrations of hydrazine (1-5 ppm), but not 1,1-dimethylhydrazine, produces anemia 

(Haun and Kinkead 1973; Haun et al. 1984; Rinehart et al. 1960). Signs of anemia were not observed 

in dogs exposed to 0.2 ppm hydrazine. Hematological effects (decreased thromboplastin generation 

time) were also noted in dogs exposed to a single dermal dose of 5 mmol/kg 11-dimethylhydrazine 

(Smith and Castaneda 1970). However, hematological effects have not been observed in other species. 

For example, rats, hamsters, and monkeys exposed to 1 ppm hydrazine or 5 ppm 1,1-dimethylhydrazine 

for 6 months (Haun and Kinkead 1973; Haun et al. 1984) and rats and monkeys injected 

with 10-50 mg/kg/day 1,1-dimethylhydrazine (Cornish and Hartung 1969; Patrick and Back 1965) did 

not exhibit any hematological effects. These data suggest that dogs may be particularly sensitive to 

the hematological effects of hydrazines. Currently, it is not known if dogs are good animal models for 

the hematological effects of hydrazines in humans; therefore, it is uncertain if this effect is of concern 

to humans exposed to hydrazines. 

Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans after 

exposure to hydrazines. Data in animals are limited to a single study. No adverse effects were 

observed in the muscle tissue of mice chronically exposed to 9.5 mg/kg/day hydrazine (Steinhoff et al. 

1990). These data are too limited to determine if effects on the musculoskeletal system are of concern 

for humans exposed to hydrazines. 

Hepatic Effects. Areas of focal necrosis and cell degeneration were noted in the liver of a worker 

exposed to an undetermined concentration of hydrazine in air once a week for 6 months (Sotaniemi 

et al. 1971). These effects on the liver, however, were not contributing factors in the worker’s death. 

Elevated serum alanine aminotransferase activity, fatty degeneration, and a positive cephalin 

flocculation test were seen in workers exposed to 1,1-dimethylhydrazine (Petersen et al. 1970; Shook 

and Cowart 1957). A large number of studies in animals were located regarding the hepatotoxic 
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effects of hydrazines. Multiple effects on the liver (hemosiderosis, degeneration, fatty changes, 

elevated serum enzymes, hyperplasia) have been observed in a number of species following inhalation 

exposure to 0.25-5 ppm hydrazine (Haun and Kinkead 1973; Vernot et al. 1985) or 0.05-25 ppm 

1,1-dimethylhydrazine (Haun 1977; Haun et al. 1984; Rinehart et al. 1960). Hepatotoxic effects (fatty 

changes, degeneration, necrosis, hemosiderosis, hepatitis, fibrosis) were also observed in animals 

following oral exposure to 4.9-650 mg/kg/day hydrazine (Biancifiori 1970; Marshall et al. 1983; 

Preece et al. 1992a; Wakabayashi et al. 1983) and 0.75-60 mg/kg/day 1,2-dimethylhydrazine (Bedell 

et al. 1982; Visek et al. 1991; Wilson 1976). Similar effects were observed in animals receiving 

injections of 5-45 mgfkg/day hydrazine (Bodansky 1923; Patrick and Back 1965; Reinhardt et al. 

1965b; Warren et al. 1984) or 3-333 mg/kg/day 1,2-dimethylhydrazine (Dixon et al. 1975; Pozharisski 

et al. 1976; Wilson 1976). Species differences in sensitivity were noted in individual studies, but these 

were not consistently observed across studies. Although data are lacking on the hepatic effects of 

1,2-dimethylhydrazine by the inhalation route and 1,1-dimethylhydrazine by the oral route, these data 

clearly indicate that the liver is an important target organ and that hepatic effects are of potential 

concern for humans exposed to hydrazines. 

Renal Effects. Data regarding the renal effects of hydrazines in humans are limited to a single case 

study. This study reported severe renal effects (tubular necrosis, hemorrhaging, inflammation, 

discoloration, enlargement) in a worker after exposure to an undetermined concentration of hydrazine 

(Sotaniemi et al. 1971). The renal effects were a significant factor in the worker’s death. Renal 

effects have been observed in several animal studies. Following inhalation exposure to 0.25 ppm 

hydrazine, mild effects were noted in the kidneys of hamsters (Vernot et al. 1985). Similarly, signs of 

mild renal toxicity were observed in rats and dogs injected with 16-64 mg/kg/day hydrazine 

(Dominguez et al. 1962; Van Stee 1965) or 50 mg/kg/day 1,1-dimethylhydrazine (Comish and Hartung 

1969). More severe effects (nephritis) were noted in the kidneys of mice orally exposed to 

1.6 mg/kg/day 1,2-dimethylhydrazine (Visek et al. 1991) and in dogs and monkeys injected with 

20-28 mg/kg/day hydrazine (Bodansky 1923; Patrick and Back 1965). However, no effects were 

observed in the kidneys of dogs exposed to 25 ppm l,l-dimethylhydrazine by the inhalation route 

(Rinehart et al. 1960), in mice exposed to 0.75 mg/kg/day 1,2-dimethylhydrazine or 9.5 mg/kg/day 

hydrazine by the oral route (Steinhoff et al. 1990; Visek et al. 1991), or in rats injected with 

20 mg/kg/day hydrazine (Patrick and Back 1965). These animal studies support the findings of the 

human case study and suggest that the kidney is an important target organ, at least following exposure 

to high doses of hydrazines. 
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Endocrine Effects. Mice exposed to hydrazine for 25 weeks exhibited degeneration of the adrenals, 

but no adverse effects in the thyroid, while exposed hamsters exhibited no effects in either organ 

(Biancifiori 1970). Overall, there is little evidence that the endocrine system is a major target of 

hydrazines. 

Dermal Effects. Contact dermatitis has been observed in humans after dermal exposure to dilute 

solutions containing hydrazine (Hovding 1967; Suzuki and Ohkido 1979; Wrangsjo and Martensson 

1986). Dermal effects (discoloration, irritation) and ocular effects (cornea1 swelling) were also 

observed in dogs, rabbits, and guinea pigs after dermal exposure to hydrazine, 1,1-dimethylhydrazine, 

and 1,2-dimethylhydrazine (Rothberg and Cope 1956; Smith and Castaneda 1970; Smith and Clark 

1971, 1972). However, by the oral route, no effects were observed in the skin of mice exposed to 

9.5 mg/kg/day hydrazine (Steinhoff et al. 1990). These data indicate that direct contact with 

hydrazines causes irritation of the skin. 

Ocular Effects. Conjunctivitis was consistently observed in a worker repeatedly exposed to an 

undetermined concentration of hydrazine (Sotaniemi et al. 1971). Eye irritation was noted in monkeys 

exposed to 1 ppm hydrazine in air but not in monkeys exposed to 0.2 ppm hydrazine (Haun and 

Kinkead 1973). Thus direct contact with hydrazine may cause irritation of the eyes. 

Body Weight Effects. A large number of studies in animals exposed orally or by injection to 

hydrazines have reported decreased body weight gain. For example, oral exposure to 

0.75-60 mg/kg/day 1,2-dimethylhydrazine (Barbolt and Abraham 1980; Visek et al. 1991; Wilson 

1976), 5 mg/kg/day 1,1-dimethylhydrazine (Haun et al. 1984), or 9.5 mg/kg/day hydrazine (Steinhoff 

et al. 1990) decreased body weight gain in a number of animal species. Similarly, injection of 

5-10 mg/kg/day hydrazine (Patrick and Back 1965), 10 mg/kg/day 1,1-dimethylhydrazine (Patrick and 

Back 1965), or 60 mg/kg/day 1,2-dimethylhydrazine (Wilson 1976) decreased animal body weight 

gain. These decreases in body weight gain are most likely due, at least in part, to decreased food 

intake. The decreased food intake may be due to taste aversion in feed studies; however; the 

appearance of this effect in animals exposed by other routes suggests that appetite may be decreased. 

Alternatively, decreases in body weight gain may be secondary to an underlying disease (e.g., cancer). 
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Immunological and Lymphoreticular Effects. Very little information is available regarding 

immunological and lymphoreticular effects of hydrazines. Several studies in humans indicate that 

dermal exposure to hydrazine produces contact dermatitis (Hovding 1967; Suzuki and Ohkich 1979; 

Wrangsjo and Martensson 1986). In addition, there are some data from case studies in humans which 

suggest that exposure to hydrazine and other hydrazine derivatives can produce a lupus erythematosuslike 

disease (Pereyo 1986; Reidenberg et al. 1983). However, this possibility warrants further 

investigation before firm conclusions can be made. 

A single study in animals reported no effect in the splenic natural killer cell activity in rats orally 

exposed to 27.1 mg/kg/day 1,2-dimethylhydrazine (Locniskar et al. 1986). However, in mice injected 

with 75 mg/kg/day 1,1-dimethylhydrazine, a decreased T helper cell count was observed (Frazier et al. 

1991). In vitro studies have reported that l,l-dimethylhydrazine induces immunomodulation 

(enhancing some immune functions while diminishing others) in mouse lymphocytes and splenocytes 

(Bauer et al. 1990; Frazier et al. 1992). These data are limited, but suggest that humans exposed to 

hydrazines may be at risk of developing immunological effects. 

Neurological Effects. Neurological effects have been noted in humans after inhalation, oral, and 

dermal exposure to hydrazines. For inhalation exposure, these effects included nausea, vomiting, 

tremors, and impairment of cognitive functions (Richter et al. 1992; Sotaniemi et al. 1971). 

Neurological symptoms of nausea, vomiting, dizziness, excitement, lethargy, and neuritis have been 

reported in some cancer patients treated orally with 0.2-0.7 mg/kg/day hydrazine (Chlebowski et al. 

1984; Gershanovich et al. 1976, 1981; Ochoa et al. 1975; Spremulli et al. 1979). Dermal exposure to 

hydrazine or l,l-dimethylhydrazine as a result of an industrial explosion produced narcosis, coma, and 

polyneuritis in two workers (Dhennin et al. 1988; Kirklin et al. 1976). Neurological effects 

(depression, seizures, convulsions, tremors, lethargy, behavioral changes) have also been observed in a 

number of animal species following inhalation exposure to 1 ppm hydrazine (Haun and Kinkead 

1973), and 25-75 ppm l,l-dimethylhydrazine (Rinehart et al. 1960). Effects on the central nervous 

system were also observed in dogs after dermal exposure to 96-480 mg/kg hydrazine (Smith and Clark 

1972) or 300-1,800 mg/kg l,l-dimethylhydrazine (Smith and Clark 1971). Similar neurological 

effects were noted in animals after injection of 16-350 mg/kg/day hydrazine (Floyd 1980; Mizuno 

et al. 1989; Patrick and Back 1965) or 4-125 mg/kg/day l,l-dimethylhydrazine (Furst and Gustavson 

1967; Geake et al. 1966; Goff et al. 1967, 1970; Minard and Mushahwar 1966; O’Brien et al. 1964; 

Reynolds et al. 1964; Segerbo 1979; Stern-ran and Fairchild 1967). The studies in humans and animals 
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convincingly demonstrate that the central nervous system is a target for persons exposed to hydrazine 

or l,l-dimethylhydrazine. However, based on the mechanism by which hydrazine and 

l,l-dimethylhydrazine affect the central nervous system, neurological effects do not appear to be of 

concern for humans exposed to 1 ,2-dimethylhydrazine. 

Reproductive Effects. Data regarding the reproductive effects of hydrazines are limited to a few 

animal studies. Reproductive effects (ovarian and testicular atrophy, endometrial inflammation, 

aspermatogenesis) were observed in hamsters exposed to 1-5 ppm hydrazine by the inhalation route 

(Vemot et al. 1985). The incidence of endometrial cysts was significantly elevated in female mice 

exposed to 0.05 ppm 1,1-dimethylhydrazine (Haun et al. 1984). Sperm abnormalities and decreased 

caudal epididymal sperm counts were noted in mice injected with 8 mg/kg/day hydrazine or 

12.5-68.8 mg/kg/day 1,1-dimethylhydrazine (Wyrobek and London 1973). These effects were not 

observed in hamsters exposed to 0.25 ppm hydrazine by the inhalation route (Vemot et al. 1985) or in 

mice and hamsters exposed to 5.3-9.5 mg/kg/day hydrazine by the oral route (Biancifiori 1970). No 

studies were located regarding the reproductive effects of 1,2-dimethylhydrazine. In addition, no 

studies were located which investigated effects of hydrazines on reproductive function. Despite the 

inconsistency of the findings from animal studies, the serious nature of the reproductive effects 

observed in the positive studies makes them one of concern for humans exposed to hydrazine. 

Developmental Effects. Signs of developmental toxicity or teratogenicity were not observed in 

hamsters exposed to a single dose of 166 mg/kg hydrazine or 68 mg/kg 1,2-dimethylhydrazine on 

day 12 of gestation (Schiller et al. 1979). Likewise, Keller et al. (1984) examined the effects of 

1,l -dimethylhydrazine ( 10-60 mg/kg/day) and 1 ,2-dimethylhydrazine (2-10 mg/kg/day) given intra 

peritoneally to pregnant rats on days 6-15 of gestation, and found no dose-related teratogenic effects. 

Embryotoxicity, manifested as reduced fetal weight, occurred only in the animals treated with the 

highest dose levels of either chemical. However, in another study increased prenatal and perinatal 

mortality was reported in rats injected with 8 mg/kg/day hydrazine during gestation days 11-21 (Lee 

and Aleyassine 1970). The data in animals are inconsistent between routes of exposure and are too 

limited to permit firm conclusions regarding the potential for developmental effects in humans exposed 

to hydrazines. 
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Genotoxic Effects. No studies were located regarding genotoxic effects in humans after exposure to 

hydrazines. Studies regarding the genotoxic effects in animals after oral or injection exposure to 

hydrazines are summarized in Table 2-4, while in vitro studies are presented in Table 2-5. These 

findings are discussed below. 

Data from in vivo studies indicate that hydrazines are alkylating agents. The methylation of tissue 

DNA was reported in animals exposed orally to hydrazine (Becker et al. 1981; Bosan et al. 1986) or 

by injection to hydrazine (Bosan et al. 1986; Quintero-Ruiz et al. 1981) or 1,2-dimethylhydrazine 

(Beranek et al. 1983; Bolognesi et al. 1988; Hawks and Magee 1974; Netto et al. 1992; Pozharisski 

et al. 1975; Rogers and Pegg 1977). The mechanism by which adducts are formed may involve the 

generation of reactive species (methyldiazanium ions or methyl free radicals) (Albano et al. 1989; 

August0 et al. 1985; Feinberg and Zedeck 1980; Netto et al. 1987, 1992). The formation of methyl 

adducts with DNA bases in vivo may be one of the mechanisms by which hydrazines have produced 

DNA damage (Parodi et al. 1981), gene mutations (Jacoby et al. 1991; Winton et al. 1990; Zeilmaker 

et al. 1991; Zijlstra and Vogel 1988), micronuclei (Albanese et al. 1988; Ashby and Mirkova 1987), 

and sister chromatid exchange (Couch et al. 1986; Neft and Conner 1989). In vivo studies on the 

genotoxicity of hydrazines have largely reported positive results, although hydrazine did not induce 

unscheduled DNA synthesis in mouse sperm cells (Sotomayor et al. 1982). In addition, 

1,2-dimethylhydrazine failed to induce micronuclei in rat bone marrow cells, even though this effect 

has been observed in mouse bone marrow cells (Albanese et al. 1988; Ashby and Mirkova 1987). 

A large number of in vitro studies have reported genotoxic effects for all three hydrazines. Hydrazines 

produced methyl adducts in DNA from human cells (Au&up et al. 1980a; Harris et al. 1977; Kumari 

et al. 1985) and in free DNA (Bosan et al. 1986; Lambert and Shank 1988), but adducts were not 

noted in Chinese hamster V79 cells (Boffa and Bolognesi 1986). Gene mutations have been observed 

in human teratoma cells (Oravec et al. 1986), mouse lymphoma cells (Rogers and Back 1981), and in 

several strains of bacteria (DeFlora and Mugnoli 1981; Kerklaan et al. 1983; Levi et al. 1986; 

Malaveille et al. 1983; Noda et al. 1986; Parodi et al. 1981; Sedgwick 1992; Wilpart et al. 1983). 

Other genotoxic effects observed in mammalian cells exposed to hydrazines include sister chromatid 

exchange (MacRae and Stich 1979), transformation (Kumari et al. 1985), and unscheduled DNA 

synthesis (Mori et al. 1988). The administration of 25 or 50 mg/kg hydrazine subcutaneously to 

neonatal rats was necrogenic to the liver (Leakakos and Shank 1994). Liver DNA isolated from these 

animals was shown to have site-specific damage in that one or more Mspl sites were lost or blocked. 




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In vitro studies regarding the genotoxic effects of hydrazines have generally reported positive results, 

with and without metabolic activation. Taken together with the in vivo studies discussed above, these 

data clearly indicate that all three forms of hydrazine are genotoxic. 

Cancer. No significant increase in cancer mortality was observed in a single epidemiology study of 

workers exposed to hydrazine (Morris et al. 1995; Wald et al. 1984), or in a U.S. Public Health 

Service survey of tuberculosis patients with isoniazid (Glassroth et al. 1977), which is metabolized to 

hydrazine. However, a large number of studies in animals have reported increased tumor incidence 

following inhalation, oral, and parenteral exposures to hydrazines. Following inhalation exposures to 

5 ppm hydrazine, increased nasal and thyroid tumor incidences were reported in mice and hamsters 

(Vemot et al. 1985). Tumors of the lung, nasal passageways, bone, pancreas, pituitary, blood vessels, 

liver, and thyroid, and leukemia were observed at an increased incidence in mice or rats exposed to 

0.05-5 ppm 1,1-dimethylhydrazine (Haun et al. 1984). It is possible that some of the carcinogenic 

effects of impure grades of l,l-dimethylhydrazine may be attributable to the presence of 

dimethylnitrosamine, a potent carcinogen, as a contaminant (Haun 1977). 

Following oral exposures, doses of 0.46-16.7 mg/kg/day hydrazine increased the incidence of liver, 

kidney, breast, and particularly lung tumors in several animal species (Bhide et al. 1976; Biancifiori 

1970; Biancifiori and Ribacchi 1962; Biancifiori et al. 1964, 1966; Bosan et al. 1987; Maru and Bhide 

1982; Roe et al. 1967; Yamamoto and Weisburger 1970). Oral exposure to 33 mg/kg/day 

l,l-dimethylhydrazine increased the incidence of lung tumors in mice (Roe et al. 1967). Multiple 

tumor types, but most notably colon and blood vessel tumors, were induced in several animal species 

exposed to oral doses of 0.059-30 mg/kg/day 1,2-dimethylhydrazine (Abraham et al. 1980; Asano and 

Pollard 1978; Barbolt and Abraham 1980; Bedell et al. 1982; Calvert et al. 1987; Izumi et al. 1979; 

Locniskar et al. 1986; Teague et al. 1981; Thorup et al. 1992; Toth and Patil 1982; Wilson 1976). 

Colon tumors were also induced after single oral doses of 15.8-30 mg/kg 1,2-dimethylhydrazine 

(Craven and DeRubertis 1992; Schiller et al. 1980; Watanabe et al. 1985). 

A large number of studies have reported the carcinogenic effects of 1,2-dimethylhydrazine by the 

injection route. These studies have reported an induction of tumor types similar to those reported for 

oral exposure following single injections of 15-143 mg/kg 1,2-dimethylhydrazine (Barnes et al. 1983; 

Decaens et al. 1989; Fujii and Komano 1989; Glauert and Weeks 1989; Karkare et al. 1991; Sunter 

and Senior 1983; Toth et al. 1976; Wargovich et al. 1983) and repeated injections of 3-40 mg/kg/day 
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(Andrianopoulos et al. 1990; Barsoum et al. 1992; Decaens et al. 1989; Druckrey 1970; Hagihara et al. 

1980; James et al. 1983; Nelson et al. 1992; Pozharisski et al. 1976; Shirai et al. 1983; Vinas-Salas 

et al. 1992). Peripheral nerve sheath tumors were observed in hamsters injected with 32.5 mg/kg/day 

1,1l-dimethylhydrazine (Ernst et al. 1987). 

Several government departments and regulatory offices have evaluated the evidence regarding the 

carcinogenicity of hydrazines. The Department of Health and Human Services has determined that 

hydrazine and 1,1-dimetbylhydrazine are reasonably anticipated to be carcinogens (NTP 1994). The 

International Agency for Research on Cancer has determined that hydrazine, 1,1-dimethylhydrazine, 

and 1,2-dimethylhydrazine are probably carcinogenic to humans (Group 2B) (IARC 1987). The EPA 

has determined that hydrazine, 1,1-dimethylhydrazine, and 1,2-dimethylhydrazine are probable human 

carcinogens (Group B2) (HEAST 1992; IRIS 1995). The American Conference of Governmental 

Industrial Hygienists (ACGIH) currently lists hydrazine and 1,1-dimethylhydrazine as suspected human 

carcinogens (ACGIH 1994a). However, it has recently been recommended that the listing of hydrazine 

be changed to that of animal carcinogen, not likely to cause cancer in humans under normal exposure 

conditions (ACGIH 1994b). 

2.6 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 

(NAUNRC 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 

(NAWNRC 1989). The preferred biomarkers of exposure are generally the substance itself or 

substance-specific metabolites in readily obtainable body fluid(s) or excreta. However, several factors 

can confound the use and interpretation of biomarkers of exposure. The body burden of a substance 

may be the result of exposures from more than one source. The substance being measured may be a 

metabolite of another xenobiotic substance (e.g.g high urinary levels of phenol can result from 

exposure to several different aromatic compounds). Depending on the properties of the substance 
 

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(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 hydrazines are discussed in Section 2.6.1. 

Biomarkers of effect are defined as any measurable biochemical, physiologic, or other alteration within 

an organism that, depending on magnitude, can be recognized as an established or potential health 

impairment or disease (NAS/NRC 1989). This definition encompasses biochemical or cellular signals 

of tissue dysfunction (e.g., increased liver enzyme activity or pathologic changes in female genital 

epithelial cells), as well as physiologic signs of dysfunction such as increased blood pressure or 

decreased lung capacity. Note that these markers are not often substance specific. They also may not 

be directly adverse, but can indicate potential health impairment (e.g., DNA adducts). Biomarkers of 

effects caused by hydrazines are discussed in Section 2.6.2. 

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 2.8, “Populations That Are Unusually Susceptible.” 

2.6.1 Biomarkers Used to Identify or Quantify Exposure to Hydrazines 

Methods exist for measuring the levels of hydrazines and their metabolites in the plasma of humans 

(Blair et al. 1985) and in tissues, urine, and expired air of animals (Alvarez de Laviada et al. 1987; 

Back et al. 1963; Dost et al. 1966; Fiala and Kulakis 1981; Fiala et al. 1976; Harbach and Swenberg 

1981; Kaneo et al. 1984; Kang et al. 1988; Matsuyama et al. 1983; Preece et al. 1991; Reed et al. 

1963; Springer et al. 1981). These studies have employed calorimetric, chromatographic; and nuclear 

magnetic resonance techniques. Such methods require the use of expensive equipment and skilled 

technicians, which may limit the availability of facilities capable of monitoring exposure on a routine 

basis. The levels of hydrazines or their metabolites in tissues and excreta cannot presently be used to 

quantify past exposures. The detection of hydrazines and some of their metabolites (for example, 

azomethane and azoxymethane from 1,2-dimethylhydrazine) is a fairly specific biomarker of exposure. 
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However, hydrazine is a metabolite of drugs such as isoniazid and hydralazine (Blair et al. 1985). 

Therefore, care must be taken to ensure that exposure to these drugs has not occurred. Other 

metabolites of hydrazines (for example, carbon dioxide and nitrogen) are endogenous to the body, and 

therefore, cannot be used as specific biomarkers of exposure. 

2.6.2 Biomarkers Used to Characterize Effects Caused by Hydrazines 

Effects on the liver are associated with exposure to hydrazines in humans (Sotaniemi et al. 1971) and 

animals (Haun and Kinkead 1973; Rinehart et al. 1960; Vemot et al. 1985; Wilson 1976). Therefore, 

assessment of serum transaminase activities may be useful in revealing liver damage in people exposed 

to hydrazines. Neurological effects are often observed following exposure to hydrazine and 

1,1-dimethylhydrazine in humans (Chlebowski et al. 1984; Gershanovich et al. 1976; Ochoa et al. 

1975; Richter et al. 1992; Sotaniemi et al. 1971) and animals (Haun and Kinkead 1973; Rinehart et al. 

1960). The mechanism by which hydrazine and l,l-dimethylhydrazine produce neurological effects 

involves binding to vitamin B6 derivatives. Therefore, assessment of vitamin B6 status either by direct 

measurement in the blood, tryptophan load tests, or measurements of vitamin B6 -dependent activities in 

plasma or erythrocytes may serve to indicate if vitamin B6 status has been compromised by hydrazine 

or 1,1-dimethylhydrazine. 

DNA adducts have been observed in animals exposed to hydrazines in vivo (Becker et al. 1991; 

Beranek et al. 1983; Bolognesi et al. 1988; Bosan et al. 1986; Netto et al. 1992; Pozharisski et al. 

1975; Quintero-Ruiz et al. 1981; Rogers and Pegg 1977). RNA base adducts have also been observed 

in liver and colon after treatment of rats with 1,2-dimethylhydrazine (Hawks and Magee 1974; Kang 

1994). However, these are somewhat difficult to detect and quantitate, and therefore, may not be 

useful as biomarkers of effect. An increased incidence of colon tumors is the most consistent effect 

observed following exposure to 1,2-dimethylhydrazine in animals (Abraham et al. 1980; Asano and 

Pollard 1978; Barbolt and Abraham 1980; Calvert et al. 1987; Izumi et al. 1979; Locniskar et al. 1986; 

Teague et al. 1981; Thorup et al. 1992; Wilson 1976). Simple tests for occult blood in the stools can 

be used as a preliminary screen for intestinal tumors. However, these types of effects can be caused 

by exposures to a large number of agents, and in no way are these biomarkers specific for the effects 

of hydrazines. 
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2.7 INTERACTIONS WITH OTHER SUBSTANCES 

No studies were located regarding interactions in humans or animals after exposure to hydrazine or 

1,1-dimethylhydrazine. On the other hand, a large number of studies are available in animals 

regarding the interactions of various treatments on 1,2-dimethylhydrazine-induced colon cancer. For 

example, high-fat diets, high-cholesterol diets, potassium chloride, caffeine, vitamin C, iron, 

ethoxyquin, and colorectal surgery were all found to increase the incidence, multiplicity, or malignancy 

of 1,2-dimethylhydrazine-induced intestinal tumors (Balansky et al. 1992; Bansal et al. 1978; Cruse 

et al. 1982; Locniskar et al. 1986; Nelson et al. 1992; Shirai et al. 1985; Siegers et al. 1992), whereas 

aspirin, bran, pectin, calcium, vitamin D, vitamin E, carbon tetrachloride, carbon disulfide, sodium 

selenate, butylated hydroxytoluene, corn oil, and calcium chloride were all found to decrease the 

incidence of these tumors (Balansky et al. 1992; Barnes et al. 1983; Barsoum et al. 1992; Belleli et al. 

1992; Culvert et al. 1987; Colacchio et al. 1989; Craven and DeRubertis 1992; Heitman et al. 1992; 

Shirai et al. 1985). Other studies have reported that bran, beta-carotene, butylated hydroxyanisole, 

propyl gallate, and stress had no significant effect on tumors of the colon induced by 

1,2-dimethylhydrazine (Andrianopoulos et al. 1990; Barbolt and Abraham 1980; Colacchio et al. 1989; 

Shirai et al. 1985; Thorup et al. 1992). A number of mechanisms are possible for these interactions 

including but not limited to interference with the metabolism of 1,2-dimethylhydrazine (Fiala et al. 

1977), action as a scavenger for free radicals produced during 1,2-dimethylhydrazine metabolism, and 

influences at the post-initiation stage of colon carcinogenesis. 

2.8 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE 

A susceptible population will exhibit a different or enhanced response to hydrazines than will most 

persons exposed to the same level of hydrazines in the environment. Reasons include genetic makeup, 

developmental stage, age, health and nutritional status (including dietary habits that may increase 

susceptibility, such as inconsistent diets or nutritional deficiencies), and substance exposure history 

(including smoking). These parameters may result in decreased function of the detoxification and 

excretory processes (mainly hepatic, renal, and respiratory) or the pre-existing compromised function 

of target organs (including effects or clearance rates and any resulting end-product metabolites). For 

these reasons we expect the elderly with declining organ function and the youngest of the population 

with immature and developing organs will generally be more vulnerable to toxic substances than 
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healthy adults. Populations who are at greater risk due to their unusually high exposure are discussed 

in Section 5.6, “Populations With Potentially High Exposure.” 

Data from a single human study indicate that people with a slow acetylator genotype may be unusually 

susceptible to the effects of hydrazine. A pronounced accumulation of hydrazine was noted in the 

plasma of slow acetylator patients treated with isoniazid compared to those patients that were rapid 

acetylators (Blair et al. 1985). With 1,1-dimethylhydrazine, similar results may be observed. 

However, no information is available on humans for 1,1-dimethylhydrazine. Further investigation of 

this mechanism is warranted. 

In animals, a number of studies have reported differences in susceptibility to the toxic effects of 

hydrazines with respect to species (Haun and Kinkead 1973; Rinehart et al. 1960; Vernot et al. 1985; 

Wilson 1976), strain (Asano and Pollard 1978; Bhide et al. 1976; Teague et al. 1981; Toth 1969), sex 

(Bhide et al. 1976; Biancifiori 1970; Teague et al. 1981; Visek et al. 1991), and age (Wakabayashi 

et al. 1983). Some of the differences in susceptibility may be related to differences in ability to 

metabolize hydrazines; however, many other differences still lack a satisfactory explanation. 

2.9 METHODS FOR REDUCING TOXIC EFFECTS 

This section describes clinical practice and research concerning methods for reducing toxic effects of 

exposure to hydrazines. 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 hydrazines. When 

specific exposures have occurred, poison control centers and medical toxicologists should be consulted 

for medical advice. 

2.9.1 Reducing Peak Absorption Following Exposure 

No data were located regarding methods for reducing absorption after inhalation exposure to 

hydrazines. 

There are several methods by which the absorption of hydrazines can be reduced in the gastrointestinal 

tract. Induced emesis, gastric lavage, use of saline cathartics, or activated charcoal are all methods 

which are commonly used to decrease the gastrointestinal absorption of compounds such as hydrazines 
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(Bronstein and Currance 1988; Sittig 1991; Stutz and Janusz 1988). In general, these treatments are 

most effective when used within a few hours after oral exposure. In some cases, these treatments may 

be contraindicated. For example, some authors contend that emesis should not be induced (Bronstein 

and Currance 1988). In addition, emesis should not be induced in obtunded, comatose, or convulsing 

patients. Oils should not be used as a cathartic, since they may enhance the gastrointestinal absorption 

of hydrazines. 

Following dermal or ocular exposures to hydrazines, there are several methods by which absorption 

can be reduced. All contaminated clothing should be removed, and contacted skin should be washed 

immediately with soap and water (Bronstein and Currance 1988; Haddad and Winchester 1990; Sittig 

1991; Stutz and Janusz 1988). Eyes that have come in contact with hydrazines should be flushed with 

copious amounts of water. Contact lenses should be removed prior to flushing with water. 

Proparacaine hydrochloride may be used to assist eye irrigation (Bronstein and Currance 1988). 

2.9.2 Reducing Body Burden 

Elimination of hydrazines in the urine may be enhanced by forced diuresis and acidification of the 

urine (Haddad and Winchester 1990). Hemodialysis and peritoneal dialysis may also be helpful, but 

this has not been fully studied. Activated charcoal is sometimes administered in serial doses to 

minimize the enterohepatic recirculation of persistent chemicals. Data regarding the enterohepatic 

recirculation of hydrazines were not located. However, available data suggest that hydrazines are 

readily cleared from the body since the levels in various tissues in animals are usually not detectable 

after 24 hours. In addition, studies in rats indicate that only a small percentage of a dose of 

1,2-dimethylhydrazine (0.4-0.9%) is excreted in the bile (Hawks and Magee 1974). Therefore, it is 

not likely that efforts to minimize enterohepatic recirculation of hydrazines would be of much use. 

2.9.3 Interfering with the Mechanism of Action for Toxic Effects 

There are at least two distinct mechanisms by which hydrazines produce adverse health effects. 

Methods for interfering with these mechanisms are discussed below. The first mechanism involves the 

reaction of hydrazine or 1,1-dimethylhydrazine with endogenous alpha-keto acids such as vitamin B, 

(pyridoxine). The formation of hydrazones of pyridoxine is the proposed mechanism by which 

hydrazine and 1,1-dimethylhydrazine produce neurological effects. Several studies have reported 
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successful treatment of neurological effects in humans exposed to hydrazine and 1,1-dimethylhydrazine 

with pyridoxine (Dhennin et al. 1988; Ellenhorn and Barceloux 1988; Haddad and Winchester 1990; 

Kirklin et al. 1976). In addition, several animal studies reported that pyridoxine diminished, and in 

some cases completely abolished, the lethal and neurological effects of hydrazine and 

1,1-dimethylhydrazine (Geake et al. 1966; Lee and Aleyassine 1970; O’Brien et al. 1964; Segerbo 

1979). 

However, treatment with pyridoxine is not without risk. For example, some authors suggested that 

pyridoxine is also capable of producing neuropathy (Harati and Niakan 1986). This effect has been 

noted in humans exposed to hydrazines and treated with pyridoxine (Dhennin et al. 1988; Harati and 

Niakan 1986; Ochoa et al. 1975), but it is difficult to ascribe this effect to exposure to either 

hydrazines or pyridoxine alone. It is possible that the adverse effects of pyridoxine treatment may be 

associated with treatments using large doses. Evidence of a therapeutic window has been reported in 

animal studies (Geake et al. 1966). Studies in animals have also reported that the hydrazones of 

pyridoxine are more toxic than the corresponding hydrazine (Furst and Gustavson 1967). These data 

indicate that pyridoxine should be used with caution and that all potential risks and benefits should be 

considered prior to treatment. In any case, treatment with pyridoxine would not be expected to be 

beneficial for exposures to 1,2-dimethylhydrazine since this compound, unlike hydrazine and 

1,1-dimethylhydrazine, does not form hydrazones. 

The second mechanism by which hydrazines produce adverse health effects involves the generation of 

free radical intermediates. Free radicals have been detected during the metabolism of hydrazines in 

vitro (Albano et al. 1989; Augusto et al. 1985; Ito et al. 1992; Netto et al. 1987; Noda et al. 1988; 

Runge-Morris et al. 1988; Sinha 1987; Tomasi et al. 1987). Therefore, treatment with agents that act 

as free radical scavengers could offer a protective effect. In vitro studies have shown that glutathione 

is an effective scavenger of the free radicals produced from the metabolism of 1,1-dimethylhydrazine 

and 1,2-dimethylhydrazine (Tomasi et al. 1987). A number of animal studies have reported that 

aspirin, vitamin C, vitamin E, and butylated hydroxytoluene decreased the incidence, multiplicity, or 

malignancy of 1,2-dimethylhydrazine-induced intestinal tumors (Belleli et al. 1992; Colacchio et al. 

1989; Cook and McNamara 1980; Craven and DeRubertis 1992; Shirai et al. 1985). It is possible that 

this protective effect may occur via inhibition of metabolic activation or a free radical scavenging 

mechanism, and if so, treatment would be most effective if administered relatively soon after exposure; 

however, the mechanism is not known conclusively and warrants further investigation. 
HYDRAZINES 97 

2. HEALTH EFFECTS 

Since reactive intermediates are produced as a result of the metabolism of hydrazines, the administration 

of inhibitors of the cytochrome P-450 or the flavin-containing monooxygenase system may offer 

some protective effect. For example, disulfiram, an inhibitor of cytochrome P45011E1 (Guengerich 

et al. 1991), decreased the oxidation of azomethane (a metabolite of 1,2-dimethylhydrazine) to azoxymethane, 

and the further oxidation of azoxymethane to methylazoxymethanol (Fiala et al. 1977). The 

inhibition of the activation pathway of 1,2-dimethylhydrazine by disulfiram resulted in decreased DNA 

methylation in the liver and colon of rats (Swenberg et al. 1979), and inhibition of l,2-dimethylhydrazineinduced colon carcinogenesis (Wattenberg 1975). Although disulfiram is a toxic compound 

which is known to inhibit other enzyme systems, it has been used in humans as an alcohol deterrent 

(Ellenhorn and Barceloux 1988). In cases of significant exposure to 1,2-dimethylhydrazine, the 

potential benefits of disulfiram in preventing colon cancer may outweigh the potential risk of adverse 

toxic effects. 

2.10 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 hydrazines 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 hydrazines. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will 

be evaluated and prioritized, and a substance-specific research agenda will be proposed. 

2.10.1 Existing Information on Health Effects of Hydrazines 

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals to 

hydrazines are summarized in Figure 2-3. The purpose of this figure is to illustrate the existing 

information concerning the health effects of hydrazines. Each dot in the figure indicates that one or 
HYDRAZINES 98 

2. HEALTH EFFECTS 

more studies provide information associated with that particular effect. The dot does not necessarily 

imply anything about the quality of the study or studies, nor should missing information in this figure 

be interpreted as a “data need.” A data need, as defined in ATSDR’s Decision Guide for Identifying 

Substance-Specific Data Needs Related to Toxicological Profiles (ATSDR 1989), is substance-specific 

information necessary to conduct comprehensive public health assessments. Generally, ATSDR 

defines a data gap more broadly as any substance-specific information missing from the scientific 

literature. 

As shown in Figure 2-3, data are available in humans regarding lethal, neurological, and carcinogenic 

effects after inhalation exposure to hydrazines. Data are also available for the systemic effects 

observed in humans exposed to hydrazines by the inhalation route for intermediate durations. By the 

oral route, information is only available for the neurological effects in humans exposed to hydrazines. 

Acute systemic, immunological, and neurological effects have been reported in humans after dermal 

exposure to hydrazines. 

Considerably more information on the health effects of hydrazines is available from animal studies. 

These are data for all effect categories from animal studies for oral exposure to hydrazines. The 

lethal, neurological, reproductive, carcinogenic, and systemic effects for all exposure durations are 

available from studies in animals exposed to hydrazines by the inhalation route. For dermal exposures 

to hydrazines, animal data are available regarding the lethal, neurological, and acute systemic effects. 

2.10.2 Identification of Data Needs 

Acute-Duration Exposure. Data are available for the acute toxicity of hydrazine in humans after 

inhalation and dermal exposures, and in several animal species after oral and dermal exposures. 

Although a human case study suggests neurological effects are of concern following inhalation 

exposure to hydrazine (Frierson 1965), quantitative data are not available for the acute toxicity of 

hydrazine after inhalation exposure. Data from animal studies (rats, dogs) indicate that the liver is the 

primary target organ after oral exposures (Marshall et al. 1983; Preece et al. 1992a; Wakabayashi et al 

1983), and that the skin is the most sensitive target in humans and animals (rabbits, guinea pigs, dogs) 

following dermal exposures (Hovding 1967; Suzuki and Ohkido 1979). These data do not sufficiently 

define the threshold dose for these effects and do not support the derivation of an MRL. 

HYDRAZINES 100 

2. HEALTH EFFECTS 

Data are available for the acute toxicity of 1,1-dimethylhydrazine after inhalation exposure in humans, 

and inhalation, oral, and dermal exposures in animals. A human case study suggests that neurological 

effects are of concern following acute inhalation exposure to 1,1-dimethylhydrazine (Frierson 1965). 

Data from a study in dogs indicate that the central nervous system is affected following inhalation of 

1,1-dimethylhydrazine (Rinehart et al. 1960). This finding is supported by data in rats, mice, cats, and 

monkeys acutely exposed to 1,1-dimethylhydrazine by injection (Furst and Gustavson 1967; Furst et 

al. 1969; Geake et al. 1966; Goff et al. 1967, 1970; Minard and Mushahwar 1966; O’Brien et al. 1964; 

Reynolds et al. 1963, 1964; Segerbo 1979; Sterman and Fairchild 1967). Data regarding the effects of 

acute oral exposure to 1,1-dimethylhydrazine are limited to a lethality study in mice (Roe et al. 1967). 

Animal studies (rabbits, dogs) have reported hematological and ocular effects following dermal 

exposure to 1,1-dimethylhydrazine (Rothberg and Cope 1956; Smith and Castaneda 1970; Smith and 

Clark 1971). These studies do not define the threshold for effect with confidence, and do not support 

the derivation of an MRL. 

Data are available for the acute toxicity of 1,2-dimethylhydrazine in animals after acute oral and 

dermal exposures. No human studies were located regarding the acute toxicity of 

1,2-dimethylhydrazine. Two studies in rats and dogs were located which reported effects on the colon, 

liver, and body weight after oral exposure (Caderni et al. 1991; Wilson 1976). Studies in rabbits and 

guinea pigs indicate that acute dermal exposure to 1,2-dimethylhydrazine can produce irritation and 

death (Rothberg and Cope 1956). These studies do not define the effect level for 1,2-dimethylhydrazine 

with confidence and do not support the derivation of an MRL. Studies are also available on 

the carcinogenic effects of 1,2-dimethylhydrazine after acute oral exposure (Craven and DeRubertis 

1992; Schiller et al. 1980; Watanabe et al. 1985). No animal studies were located regarding the 

effects of acute inhalation exposure to 1,2-dimethylhydrazine. 

Additional animal studies to investigate the acute effects of hydrazines after inhalation, oral, and 

dermal exposures would better define the threshold dose for adverse health effects. Such studies 

would be useful in predicting adverse health effects in humans following acute exposures. 

Intermediate-Duration Exposure. Data are available on the toxicity of hydrazine and 

1,1-dimethylhydrazine in humans and several animal species after intermediate-duration exposure by 

the inhalation and oral routes. These studies reported effects on the central nervous system in humans 

following oral exposure (Chlebowski et al. 1984; Gershanovich et al. 1976, 1981; Ochoa et al. 1975) 
HYDRAZINES 101 

2. HEALTH EFFECTS 

and in animals (rats, mice, dogs) after inhalation exposure (Haun and Kinkead 1973), and effects on 

the liver in animals (mice, dogs, monkeys, rats) after inhalation exposure (Biancifiori 1970; Haun and 

Kinkead 1973; Haun et al. 1984; Rinehart et al. 1960). The data were sufficient to support the 

derivation of inhalation MRLs of 4x10-3 ppm for hydrazine and 2X10-4 ppm for 1,1-dimethylhydrazine 

based on hepatic effects. No data were located regarding the toxicity of hydrazine or 

l,l-dimethylhydrazine following dermal exposure for an intermediate duration. Studies are also 

available for the carcinogenic effects of hydrazine and 1,1-dimethylhydrazine after intermediate 

duration exposures (Haun et al. 1984; Roe et al. 1967). 

No studies were located regarding the toxicity of 1,2-dimethylhydrazine in humans after intermediate 

duration exposure. Data on the toxicity of 1,2-dimethylhydrazine in animals after intermediateduration 

exposure are limited to those regarding the oral route. These studies have generally reported 

hepatic effects in rats, guinea pigs, mice, and pigs (Bedell et al. 1982; Visek et al. 1991; Wilson 

1976), and support the derivation of an intermediate oral MRL of 8X10-4 mg/kg/day for 

1,2-dimethylhydrazine. In addition, a large number of studies report the carcinogenic effects of 

1,2-dimethylhydrazine after intermediate exposures (Izumi et al. 1979; Teague et al. 1981; Wilson 

1976). 

Additional studies in animals to investigate the effects of hydrazines after intermediate-duration 

inhalation, oral, and dermal exposures would better define the threshold dose for adverse health 

effects. Such studies would be useful in predicting adverse health effects in humans exposed for 

intermediate-durations to hydrazines. 

Chronic-Duration Exposure and Cancer. Data are available on the toxicity of hydrazine and 

l,l-dimethylhydrazine in animals after chronic-duration exposure by the inhalation and oral routes. 

Effects on the liver, lung, and body weight gain are the most consistent findings observed in rats, 

mice, dogs, and hamsters (Haun et al. 1984; Steinhoff et al. 1990; Vernot et al. 1985). However, these 

studies do not define the threshold dose level for these effects with confidence, and therefore do not 

support the derivation of an MRL. Data regarding the noncarcinogenic effects of 

1,2-dimethylhydrazine after chronic exposures are largely lacking. Additional studies which 

investigate the effects of hydrazines in animals after chronic inhalation, oral, and dermal exposures 

would help define the threshold dose for adverse health effects. Such studies would be useful in 

predicting adverse health effects in humans chronically exposed to hydrazines. 
HYDRAZINES 102 

2. HEALTH EFFECTS 

As discussed in the previous sections, hydrazines can cause cancer in animals following acute- or 

intermediate-duration exposure by the oral and inhalation route. In addition, several studies reported 

carcinogenic effects in a number of animal species exposed to hydrazine (Bhide et al. 1976; Bosan 

et al. 1987; Maru and Bhide 1982; Toth 1969, 1972b; Vernot et al. 1985), 1,1-dimethylhydrazine 

(Haun et al. 1984; Toth 1973a), and 1,2-dimethylhydrazine (Toth and Patil 1982), following chronic 

oral and inhalation exposures. These studies demonstrate that hydrazines are carcinogenic in animals 

following chronic oral and inhalation exposures. Epidemiological studies which investigate the 

carcinogenic effects in humans exposed occupationally or therapeutically to hydrazine would confirm 

whether or not the cancer effects observed in animal studies also occur in humans. 

Genotoxicity. Data regarding the genotoxicity of hydrazines in humans are not available. A large 

number of studies are available that report the genotoxic effects of hydrazines in animals in vivo 

(Albanese et al. 1988; Ashby and Mirkova 1987; Becker et al. 1981; Beranek et al. 1983; Bolognesi 

et al. 1988; Bosan et al. 1986; Couch et al. 1986; Jacoby et al. 1991; Netto et al. 1992; Parodi et al. 

1981; Pozharisski et al. 1975; Quintero-Ruiz et al. 1981; Winton et al. 1990; Zeilmaker et al. 1991; 

Zijlstra and Vogel 1988) and in a number of cell lines in vitro (Autrup et al. 1980a; Bosan et al. 1986; 

DeFlora and Mugnoli 1981; Harris et al. 1977; Kerklaan et al. 1983; Kumari et al. 1985; Lambert and 

Shank 1988; Levi et al. 1986; Malaveille et al. 1983; Noda et al. 1986; Oravec et al. 1986; Parodi 

et al. 1981; Rogers and Back 1981; Sedgwick 1992; Wilpart et al. 1983). These studies convincingly 

demonstrate that all three hydrazines are genotoxic. Additional genotoxicity studies in humans 

exposed to hydrazines, either occupationally or therapeutically would determine whether or not the 

effects observed in animals and in cells are also observed in humans. 

Reproductive Toxicity. Data regarding the reproductive toxicity of hydrazines in humans are not 

available. Data regarding the reproductive effects of hydrazines are limited to a few animal studies 

regarding inhalation, oral, and parenteral exposure to hydrazine (Biancifiori 1970; Vernot et al. 1985; 

Wyrobek and London 1973) and inhalation exposure to 1,1-dimethylhydrazine (Haun et al. 1984). 

The serious nature of the effects caused by the inhalation of hydrazines suggests they may be of 

concern in humans similarly exposed. Studies that investigate the reproductive effects of 

1,2-dimethylhydrazine, hydrazine, and 1,1-dimethylhydrazine, particularly those which also evaluate 

reproductive function over several generations, would be valuable in determining if the reproductive 

system is adversely affected in humans exposed to hydrazines. 
HYDRAZINES 103 

2. HEALTH EFFECTS 

Developmental Toxicity. Data regarding the developmental toxicity of hydrazines in humans are 

not available. Data regarding the developmental effects of hydrazines in animals are limited to a study 

which reported increased fetal and neonatal mortality following exposure to hydrazine by the 

parenteral route (Lee and Aleyassine 1970). No apparent developmental effects were seen after oral 

exposure of pregnant hamsters to 1,2-dimethylhydrazine dihydrochloride (Schiller et al. 1979). Studies 

that investigate the developmental effects of 1,1-dimethylhydrazine for any exposure route, as well as 

studies that better define the dose-response relationship for the developmental effects of hydrazine and 

1,2-dimethylhydrazine for any exposure route, would be useful in determining whether developmental 

effects are of concern in humans exposed to hydrazines. 

Immunotoxicity. The data regarding the immunological effects of hydrazines are limited. There is 

some suggestive evidence from human studies that exposure to hydrazine and other hydrazine 

derivatives can produce a lupus erythematosus-like disease (Pereyo 1986; Reidenberg et al. 1983). 

Data in animals reported immunological effects in mice with parenteral exposure to 

1,1-dimethylhydrazine (Frazier et al. 1991) but not in rats with oral exposure to 1,2-dimethylhydrazine 

(Locniskar et al. 1986). In vitro studies suggest 1,1-dimethylhydrazine produces immunomodulatory 

effects (Bauer et al. 1990; Frazier et al. 1992). Additional case studies in humans and studies in 

animals which better define the dose-response relationship for the immunological effects of all three 

hydrazines would help determine if these effects are of concern to humans exposed to hydrazines. 

Neurotoxicity. Data are available for the neurological effects of hydrazines in humans following 

inhalation, oral, and dermal exposures to hydrazine (Chlebowski et al. 1984; Gershanovich et al. 1976, 

1981; Haun and Kinkead 1973; Ochoa et al. 1975; Richter et al. 1992; Sotaniemi et al. 1971; 

Spremulli et al. 1979) and 1,1-dimethylhydrazine (Dhennin et al. 1988; Kirklin et al. 1976; Rinehart 

et al. 1960). Effects on the central nervous system were also observed in animals following dermal 

and parenteral exposures to hydrazine (Floyd 1980; Mizuno et al. 1989; Patrick and Back 1965; Smith 

and Clark 1972) and 1,1-dimethylhydrazine (Furst and Gustavson 1967; Geake et al. 1966; Goff et al. 

1970; Minard and Mushahwar 1966; O’Brien et al. 1964; Reynolds et al. 1964; Segerbo 1979; Smith 

and Clark 1971). Although these studies convincingly demonstrate that the central nervous system is a 

primary target of hydrazine and 1,1-dimethylhydrazine, these data do not define the threshold dose and 

more fully characterize neurological effects with confidence. Additional studies which better define 

the threshold dose for the neurological effects of hydrazine and l,l-dimethylhydrazine would be useful 

in determining the risk of neurological effects in humans exposed to these hydrazines. Preliminary 
HYDRAZINES 104 

2. HEALTH EFFECTS 

neurological screening studies on 1,2-dimethylhydrazine in animals may determine if neurological 

effects are of concern for humans exposed to this chemical. 

Epidemiological and Human Dosimetry Studies. Only one epidemiological study was located 

regarding the effects of hydrazine. This study showed no significant increase in cancer mortality in 

427 hydrazine workers (Wald et al. 1984). However, the number of deaths examined was relatively 

small and the follow-up period may not have been sufficient for detecting a weak carcinogenic effect. 

Additional epidemiological studies investigating the neurological, hepatic, renal, and carcinogenic 

effects of hydrazines, particularly studies which also provide quantitative information on exposure, 

would be valuable in estimating the risk of adverse health effects in persons exposed to hydrazines in 

the workplace or therapeutically. 

Biomarkers of Exposure and Effect 

Exposure. Methods are available for determining the levels of hydrazine in the plasma of humans 

(Blair et al. 1985), and the levels of all three hydrazines and their metabolites and in tissues, urine, and 

expired air of animals (Alvarez de Laviada et al. 1987; Back et al. 1963; Dost et al. 1966; Fiala et al. 

1976; Harbach and Swenberg 1981; Kaneo et al. 1984; Kang et al. 1988; Matsuyama et al. 1983; 

Preece et al. 1991; Reed et al. 1963; Springer et al. 1981). The detection of hydrazines and some of 

their metabolites (for example, the metabolites of 1,2-dimethylhydrazine-azoxymethane and 

methylazoxymethanol) are fairly specific for exposures to hydrazines. However, it should be kept in 

mind that treatment with certain drugs such as isoniazid or hydralazine can result in the presence of 

hydrazine in human plasma (Blair et al. 1985); therefore, care should be taken to ensure subjects have 

not been exposed to these drugs. Other metabolites of hydrazines (for example, carbon dioxide and 

nitrogen) are endogenous to the body, and therefore, cannot be used as specific biomarkers of 

exposure. Studies which investigate the quantitative relationship between exposure intensity, time 

since exposure, and the levels of hydrazines or their unique metabolites detected in biological samples, 

particularly in the urine, would be useful for estimating human exposures to hydrazines: Studies that 

identify biomarkers of exposure that are specific to 1,1-dimethylhydrazine and hydrazine could lead to 

the development of a reliable method for estimating recent exposures to hydrazines. 

Effect. Exposure to hydrazine and 1,1-dimethylhydrazine is associated with the development of 

neurological and hepatic effects in humans (Chlebowski et al. 1984; Gershanovich et al. 1976; Ochoa 
HYDRAZINES 105 

2. HEALTH EFFECTS 

et al. 1975; Richter et al. 1992; Sotaniemi et al. 1971) and animals (Haun and Kinkead 1973; Rinehart 

et al. 1960; Vernot et al. 1985; Wilson 1976). Studies which investigate if serum transaminase levels 

or vitamin B6 status could be used to predict effects of hydrazines could be useful, if they are coupled 

with confirmed exposures to hydrazines. The carcinogenic effects of hydrazines have also been amply 

demonstrated in animal studies (Abraham et al. 1980; Asano and Pollard 1978; Barbolt and Abraham 

1980; Calvert et al. 1987; Izumi et al. 1979; Locniskar et al. 1986; Teague et al. 1981; Thorup et al. 

1992; Wilson 1976). Studies which investigate if tests for occult blood in stools could be used to 

predict intestinal tumors induced by 1,2 dimethylhydrazine could be useful. However, the etiology of 

colon cancer is multifactional and may not be related to exposures to 1,2-dimethylhydrazine. Studies 

which identify biomarkers of effect that are specific to exposures to hydrazines could lead to the 

development of a reliable method for predicting past exposures to hydrazines. 

Absorption, Distribution, Metabolism, and Excretion. Data regarding the toxicokinetics of 

hydrazines are limited to in vitro metabolic assays (Albano et al. 1989; August0 et al. 1985; Coomes 

and Prough 1983; Craven et al. 1985; Erikson and Prough 1986; Glauert and Bennink 1983; Godoy 

et al. 1983; Netto et al. 1987; Newaz et al. 1983; Noda et al. 1987, 1988; Prough 1973; Prough et al. 

1981; Sheth-Desai et al. 1987; Sinha 1987; Timbre11 et al. 1982; Tomasi et al. 1987; Wolter et al. 

1984) and in vivo studies in rats exposed via inhalation (Llewellyn et al. 1986), rats exposed orally 

(Preece et al. 1992b), dogs exposed dermally (Smith and Clark 1971, 1972), and in several species 

exposed by parenteral routes (Back et al. 1963; Dost et al. 1966; Fiala et al. 1976; Harbach and 

Swenberg 1981; Kaneo et al. 1984; Mitz et al. 1962; Reed et al. 1963; Springer et al. 1981). These 

studies invariably employed a single radiolabel (either 14C or i5N), and therefore, in the case of 

l,l-dimethylhydrazine and 1,2-dimethylhydrazine, the metabolic fate data (expressed as a carbon or 

nitrogen dose) were often incomplete. Studies which investigate the toxicokinetics of hydrazines for 

all routes and durations, particularly those which employ both a carbon and nitrogen label, would 

enhance the current understanding of the metabolic fate of hydrazines in humans exposed at hazardous 

waste sites. 

Comparative Toxicokinetics. Studies in humans (Dhennin et al. 1988; Kirklin et al. 1976; 

Sotaniemi et al. 1971) and several animal species (Biancifiori 1970; Haun and Kinkead 1973; Marshall 

et al. 1983; Rinehart et al. 1960; Vernot et al. 1985; Wakabayashi et al. 1983) indicate that the liver 

and central nervous system are the primary target organs affected following oral, inhalation, and 

dermal exposures to hydrazine and 1,1-dimethylhydrazine. Studies in several animal species indicate 
HYDRAZINES 106 

2. HEALTH EFFECTS 

that the intestinal tract and liver are the primary target organs affected following oral exposure to 

1,2 dimethylhydrazine (Bedell et al. 1992; Wilson et al. 1976). Data regarding the toxicokinetics of 

hydrazines are lacking in humans and are limited in animals. These data are not sufficient to conclude 

which animal species is best for modeling human exposures. Similarly, these data do not reveal the 

basis of species differences in the toxicokinetics or pharmacodynamics of hydrazines which may 

underlie the species differences in toxicity. For example, dogs appear to be particularly sensitive to 

the hematological effects of hydrazine and 1,1-dimethylhydrazine (Haun and Kinkead 1973; Haun 

et al. 1984; Rinehart et al. 1960; Smith and Castaneda 1970). Additional studies which investigate the 

toxicokinetics in multiple species, including humans or human tissues, would be useful in developing 

an appropriate animal model for humans exposed to hydrazines at hazardous waste sites. 

Methods for Reducing Toxic Effects. General methods exist for reducing the absorption of 

chemicals from the eyes, skin, and gastrointestinal tract (Bronstein and Currance 1988; Sittig 1991; 

Stutz and Janusz 1988). However, none of these methods are specific for exposures to hydrazines. 

No data were located for reducing body burden after exposure to hydrazines. Pyridoxine, which 

interferes with the mechanism of action of hydrazine and 1,1-dimethylhydrazine, is often administered 

to humans exposed to these hydrazines (Dhennin et al. 1988; Kirklin et al. 1976). However, exposure 

to pyridoxine may also be associated with adverse health effects. Additional studies that investigate 

the threshold dose for adverse effects of pyridoxine, and studies that investigate alternative agents that 

interfere with the mechanism of action of hydrazines could lead to a safer method of treatment. 

Inhibitors of metabolic activation (Fiala et al. 1977) and free radical scavengers may also be useful in 

interfering with the mechanism of action of hydrazines (Belleli et al. 1992; Colacchio et al. 1989; 

Cook and McNamara 1980; Craven and DeRubertis 1992; Shirai et al. 1985; Tomasi et al. 1987). 

Additional studies that investigate the effects of metabolic inhibitors and various free radical 

scavengers in humans occupationally exposed to hydrazines and in animals could lead to other 

methods of interfering with the mechanism of action of hydrazines. 

2.10.3 On-going Studies 

A number of researchers are continuing to investigate the toxicity and toxicokinetics of 

1,2-dimethylhydrazine. Table 2-6 summarizes studies sponsored by agencies of the U.S. federal 

government. 


HYDRAZINES 109 

3. CHEMICAL AND PHYSICAL INFORMATION 

3.1 CHEMICAL IDENTITY
 

Information regarding the chemical identity of hydrazines is located in Table 3-1.
 

3.2 PHYSICAL AND CHEMICAL PROPERTIES
 

Information regarding the physical properties of hydrazines is located in Table 3-2.
 



HYDRAZINES 113 

4. PRODUCTION, IMPORT, USE, AND DISPOSAL
 

4.1 PRODUCTION 

For most uses, hydrazine is produced as hydrazine hydrate in a formulation with water. The hydrate 

may be produced commercially by three methods: the Raschig process, the ketazine process, and the 

peroxide process. The Raschig process, the original commercial production process for hydrazine, 

involves oxidation of ammonia to chloramine with sodium hypochlorite, then further reaction of the 

chloramine with excess ammonia and sodium hydroxide to produce an aqueous solution of hydrazine 

with sodium chloride as a by-product. Fractional distillation of the product yields hydrazine hydrate 

solutions. Currently, most hydrazine is produced by the ketazine process, which is a variation of the 

Raschig process. Ammonia is oxidized by chlorine or chloramine in the presence of an aliphatic 

ketone, usually acetone. The resulting ketazine is then hydrolyzed to hydrazine. In the peroxide 

process, hydrogen peroxide is used to oxidize ammonia in the presence of a ketone. Anhydrous 

hydrazine is the formulation used in rocket fuels and is produced by dehydration of the hydrate by 

azeotropic distillation with aniline as an auxiliary fluid (Budavari et al. 1989; IARC 1974; Schmidt 

1988; WHO 1987). 

1,1-Dimethylhydrazine is currently prepared commercially by a modified Raschig process: reacting 

dimethylamine with the chloramine produced from ammonia and sodium hypochlorite. Formerly, it 

was prepared by the reduction of dimethylnitrosamine or by the reductive catalytic alkylation of 

carboxylic acid hydrazides with formaldehyde and hydrogen, followed by basic hydrolysis (Budavari e 

al. 1989; EPA 1984a, 1992b; IARC 1974; Schmidt 1988). 1,2-Dimethylhydrazine may be prepared 

from dibenzoylhydrazine or by electrosynthesis from nitromethane (Budavari et al. 1989). 

The two current chemical producers of hydrazine in the United States are the Olin Corporation in Lake 

Charles, Louisiana, and Miles Inc. in Baytown, Texas. The chemical was also produced by Fairmount 

Chemical Company, Inc., Newark, New Jersey, as recently as 1987. 1,1-Dimethylhydrazine is 

produced by Olin and Uniroyal Chemical Company, Inc., Geismar, Louisiana. Estimates of past 

production (based on anhydrous hydrazine, although most production was of the hydrate) indicate that 

U.S. production volume was about 7,000 metric tons (15 million pounds) per year in the mid-1960s 

and increased to 17,000 metric tons (37 million pounds) per year in the mid-1970s. Production 
HYDRAZINES 114 

4. PRODUCTION, IMPORT, USE, AND DISPOSAL 

capacity in the United States was estimated at 17,240 metric tons (38 million pounds) in 1979 and 

about 14,000 metric tons (30 million pounds) in 1984, the most recent year for which information was 

located. 1,1-Dimethylhydrazine production volume was estimated to be at least 45 metric tons 

(99,000 pounds) in 1977 and more than 4.5 metric tons (9,900 pounds) in 1982 (HSDB 1995; Schmidt 

1988; SRI 1987, 1988, 1992; WHO 1987). Information on current production volume is not publicly 

available for either hydrazine or 1,1-dimethylhydrazine (EPA 1991d). 

Tables 4-l and 4-2 list information on U.S. companies that reported the manufacture and use of 

hydrazine and 1,1-dimethylhydrazine, respectively, in 1993 (TRI93 1995). The data listed in the 

Toxics Release Inventory (TRI) should be used with caution since only certain types of facilities are 

required to report. This is not an exhaustive list. 

4.2 IMPORT/EXPORT 

There is some indication that hydrazine was imported into the United States from Japan during the 

1970s (IARC 1974), but no data were located on past or current U.S. import or export quantities of 

hydrazine or 1,1-dimethylhydrazine. 

4.3 USE 

Hydrazine (anhydrous or as the hydrate) has numerous commercial uses. The principal current use for 

hydrazine is as an intermediate in the production of agricultural chemicals such as maleic hydrazide. 

It is also used as an intermediate in the manufacture of chemical blowing agents which are used in the 

production of plastics such as vinyl flooring and automotive foam cushioning, as a corrosion inhibitor 

and water treatment agent, as a rocket propellant, and, to a lesser extent, as a reducing agent, in 

nuclear fuel reprocessing, as a polymerization catalyst, as a scavenger for gases, and several other 

uses. It has also been used as a medication for sickle cell disease and cancer. 

From the late 1950s through the 1960s the primary use of hydrazine was as a rocket propellant. In 

1964, 73% of the hydrazine consumed in the United States was used for this purpose. By 1982, other 

commercial uses dominated the market; 40% of the hydrazine consumed was used in agricultural 



HYDRAZINES 118 

4. PRODUCTION, IMPORT, USE, AND DISPOSAL 

chemicals, about 33% for blowing agents, 15% as a corrosion inhibitor in boiler water and only 5% as 

an aerospace propellant (Budavari et al. 1989; Fajen and McCammon 1988; HSDB 1995; Schmidt 

1988; WHO 1987). 

1,1-Dimethylhydrazine is used mainly as a component of jet and rocket fuels. Other uses include an 

adsorbent for acid gases, a stabilizer for plant growth regulators, an intermediate for organic chemical 

synthesis, and in photography. 1,2-Dimethylhydrazine is used only as a research chemical and has no 

known commercial uses (ACGIH 1991a; Budavari et al. 1989; HSDB 1995). 

4.4 DISPOSAL 

Hydrazine, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, and wastes containing these chemicals are 

classified as hazardous wastes by EPA. Generators of waste containing these contaminants must 

conform to EPA regulations for treatment, storage, and disposal (see Chapter 7). Liquid injection or 

fluidized bed incineration methods are acceptable disposal methods for these wastes. Oxidation of 

spills of hydrazine fuels with sodium or calcium hypochlorite or hydrogen peroxide prior to disposal 

has been recommended. However, incomplete reaction of 1,1-dimethylhydrazine with hypochlorite 

leads to formation of several by-products, including carcinogenic N-nitrosoalkylamines. Ozonation of 

wastewater containing hydrazine fuels has been shown to reduce concentrations of the fuels, their 

associated impurities, and oxidation products to environmentally acceptable levels. Biodegradation is 

also an acceptable treatment for wastewaters containing hydrazine wastes (Brubaker 1988; EPA 1991a; 

HSDB 1995; Jody et al. 1988; WHO 1987). 

According to the TRI, about 106,000 pounds of hydrazine and 3,000 pounds of l,l-dimethylhydrazine 

were transferred to landfills and/or treatment/disposal facilities in 1993 (see Section 5.2) (TRI93 1995). 

Of this quantity, about 1,400 pounds of hydrazine were discharged to publicly owned treatment works. 
HYDRAZINES 119 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.1 OVERVIEW 

Hydrazine and 1,1-dimethylhydrazine are industrial chemicals that enter the environment primarily by 

emissions from their use as aerospace fuels and from industrial facilities that manufacture, process, or 

use these chemicals. Treatment and disposal of wastes containing these chemicals also contribute to 

environmental concentrations. These chemicals may volatilize to the atmosphere from other media and 

may sorb to soils. These chemicals degrade rapidly in most environmental media. Oxidation is the 

dominant fate process, but biodegradation occurs in both water and soil at low contaminant 

concentrations. The half-lives in air range from less than 10 minutes to several hours, depending on 

ozone and hydroxyl radical concentrations. Half-lives in other media range up to several weeks, under 

various environmental conditions. Bioconcentration does occur, but biomagnification through the food 

chain is unlikely. 

Human exposure to hydrazine and 1,1-dimethylhydrazine is mainly in the workplace or in the vicinity 

of aerospace or industrial facilities or hazardous waste sites where contamination has been detected. 

These chemicals have not been detected in ambient air, water, or soil. Humans may also be exposed 

to small amounts of these chemicals by using tobacco products. 

Hydrazine has been found in at least 4 of the 1,430 current or former EPA National Priorities List 

(NPL) hazardous waste sites (HazDat 1996). 1,1 -Dimethylhydrazine and 1,2-dimethylhydrazine have 

been identified in at least 3 and 1 of these sites, respectively. However, the number of sites evaluated 

for these chemicals is not known. The frequency of these sites within the United States can be seen in 

Figure 5-1. 

5.2 RELEASES TO THE ENVIRONMENT 

Hydrazine occurs naturally as a product of nitrogen fixation by some algae and in tobacco and tobacco 

smoke (IARC 1974). However, the major environmental sources of hydrazine are anthropogenic. 

There are no known natural sources of dimethylhydrazines. The estimated total annual environmental 

release of hydrazine and 1,1-dimethylhydrazine from manufacture and processing reported to the 

HYDRAZINES 121 

5. POTENTIAL FOR HUMAN EXPOSURE 

TRI were about 30,000 and 4,000 pounds, respectively, in 1988 (EPA 1991d). However, more recent 

data reported to the TRI indicate that environmental releases from manufacture and use of these 

chemicals total about 17,000 and 200 pounds, respectively (TRI93 1995). 1,1-Dimethylhydrazine may 

also be released to the environment from the application of daminozide (Alar), a growth enhancer 

which contains about 0.005% 1,1-dimethylhydrazine as a contaminant to nonfood plants (EPA 1992c). 

5.2.1 Air 

The major sources of hydrazine releases to air are expected to be from its use as an aerospace 

propellant and boiler water treatment agent (HSDB 1995). However, hydrazine released as a boiler 

water treatment agent is present only briefly since it would oxidize rapidly in water (HSDB 1995). 

Burning of rocket fuels containing hydrazine and/or 1,1-dimethylhydrazine reportedly produces exhaust 

gases containing trace amounts of unchanged fuel (IARC 1974). Emissions are also expected from the 

production and processing of hydrazine (EPA 1991d; WHO 1987). It has been estimated, based on 

data from Germany, that 0.06-0.08 kg of hydrazine are emitted to the air for every metric ton 

produced, and an additional 0.02-0.03 kg are emitted for every metric ton subjected to handling and 

further processing (WHO 1987). On this basis, assuming production volume of about 14,000 metric 

tons (30 million pounds) (see Section 4.1) and handling or processing of the product, emissions to the 

air may range from 1,100 to 1,500 kg (500-680 pounds) annually. Atmospheric releases of hydrazine 

may also occur from tobacco smoking (see Section 5.4.4) and from hazardous waste sites at which this 

chemical has been detected (HSDB 1995; WHO 1987). 

Release of 1,1 dimethylhydrazine to the atmosphere is expected to occur primarily from its use as an 

aerospace propellant (HSDB 1995). Release of this chemical and 1,2-dimethylhydrazine may also 

occur from hazardous waste sites at which they have been detected. 

As shown in Tables 5-1 and 5-2, an estimated total of 16,452 pounds of hydrazine and 194 pounds of 

1,1-dimethylhydrazine, amounting to about 95% and 100% of the total environmental releases, 

respectively, were discharged to the air from manufacturing and processing facilities in the United 

States in 1993 (TRI93 1995). The TRI data should be used with caution since only certain types of 

facilities are required to report. This is not an exhaustive list. 




HYDRAZINES 126 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.2.2 Water 

Releases of hydrazine and 1,1-dimethylhydrazine to water may occur during production, processing, 

use, or disposal of the chemical. Hydrazine was detected at a concentration of 0.01 μg/L in effluent 

from one industrial facility (EPA 1984b). However, since these chemicals are rapidly oxidized in 

water (see Section 5.3.2.2), the unreacted compounds are not likely to persist in detectable 

concentrations. 

As shown in Tables 5-l and 5-2, an estimated total of 784 pounds of hydrazine amounting to about 

4.5% of the total environmental releases and no 1,1-dimethylhydrazine were discharged to surface 

water from manufacturing and processing facilities in the United States in 1993 (TRI93 1995). An 

additional 423 pounds of hydrazine (1% of the total) were discharged by underground injection. The 

TRI data should be used with caution since only certain types of facilities are required to report. This 

is not an exhaustive list. 

5.2.3 Soil 

No data were located documenting release of hydrazine or dimethylhydrazines to soil. However, 

releases to soil may occur from spills and leakage of underground storage tanks during the use of 

hydrazine and 1,1-dimethylhydrazine as rocket propellants (Street and Moliner 1988). Deposition from 

air is not expected to be significant (see Section 5.3.1). Hydrazine and dimethylhydrazines may be 

released to soil from hazardous waste sites at which these chemicals have been detected. 

1,1-Dimethylhydrazine may also be released to soil from the application of daminozide (Alar) as a 

growth enhancer on nonfood plants. The use of this chemical on food products was voluntarily 

cancelled in 1989 by the manufacturer (Uniroyal Chemical Company) (EPA 1992c). Daminozide 

contains about 0.005% 1,1-dimethylhydrazine as an impurity and about 0.012% of a daminozide 

solution that hydrolyzes to 1,1-dimethylhydrazine after 24 hours (EPA 1992c). No data were located 

on the amount of daminozide used annually, but it is estimated that, in 1989, 90% of potted 

chrysanthemums and 40-50% of 65 million square feet of bedding plants were treated with this 

chemical. 
HYDRAZINES 127 

5. POTENTIAL FOR HUMAN EXPOSURE 

As shown in Tables 5-l and 5-2, 5 pounds of hydrazine (<0.1% of the total environmental release) and 

no 1,1-dimethylhydrazine were reported discharged to land from manufacturing and processing 

facilities in the United States in 1993 (TRI93 1995). The data listed in the TRI should be used with 

caution since only certain types of facilities are required to report. This is not an exhaustive list. 

5.3 ENVIRONMENTAL FATE 

5.3.1 Transport and Partitioning 

Hydrazine or dimethylhydrazines released to water or soil may volatilize into air or sorb onto soil. 

These chemicals have low vapor pressures and are miscible in water (see Table 3-2). Therefore, 

volatilization is not expected to be an important removal process. Reported evaporation rates from 

aqueous solutions under laboratory conditions were 0.49 mg/cm2

 minute for hydrazine and 13 mg/cm2 

minute for 1,1-dimethylhydrazine (EPA 1984a). The significance of these values to environmental 

conditions is unknown. Data from other studies indicate that volatilization of these chemicals from 

water increases with higher concentrations of the chemical and in the presence of sunlight (due to 

increased temperature of the hydrazine pool). Based on air dispersion modeling, volatilization of 

hydrazine from surface soil following a spill is expected to be sufficient (16-100 mg/cm2

 hour) to 

generate a short-term ambient air concentration of 4 mg/m3

 up to 2 km downwind of the spill under 

worst-case meteorological conditions (MacNaughton et al. 1981). Degradation of hydrazine would 

likely reduce the concentration within several hours (see Section 5.3.2.1). 

Atmospheric transport of hydrazine or dimethylhydrazines may occur, but transport will be limited by 

the high reactivity of the chemicals in the atmosphere (see Section 5.3.2.1). No data were located on 

deposition of hydrazine or dimethylhydrazines from air to water or soil, but deposition would also be 

limited by their high reactivity. 

Hydrazine undergoes complex interactions with soils, including both reversible physical-sorption and 

irreversible chemisorption to colloids (Mansell et al. 1988). In a study on the adsorption and leaching 

characteristics of hydrazine fuels, no adsorption of 1,1-dimethylhydrazine was observed on sand, with 

almost 100% of the chemical leaching with water (Braun and Zirrolli 1983). In three other soils, 

adsorption ranged from 26% to 80%. No correlation between adsorption and soil organic content or 

pH was observed. The mechanisms of attenuation in soil materials were not reported. However, 
HYDRAZINES 128 

5. POTENTIAL FOR HUMAN EXPOSURE 

reported results of additional hydrazine adsorption studies with clays and soils indicate that adsorption 

may be correlated with soil organic matter and clay content and is highly dependent on pH; hydrazine 

appears to be adsorbed by different mechanisms under acidic and alkaline conditions (Moliner and 

Street 1989b). 

In a study of hydrazine in aqueous systems, the chemical was reported to be absorbed by guppies from 

a 0.5 μg/L solution (Slonim and Gisclard 1976). After 96 hours, the hydrazine concentration in fish 

was 144 μg/g, indicating a moderate tendency to bioconcentrate. However, the bioconcentration of 

hydrazine and dimethylhydrazines is not expected to be important in aquatic systems because of the 

rapid degradation of these chemicals in water (see Section 5.3.2.2) as well as their low octanol-water 

partition coefficients. 

5.3.2 Transformation and Degradation 

5.3.2.1 Air 

Hydrazine and dimethylhydrazines degrade rapidly in air through reactions with ozone, hydroxyl (OH) 

radicals, and nitrogen dioxide (WHO 1987). The reaction of hydrazine and 1,1-dimethylhydrazine 

with ozone is probably the major fate of these chemicals in the atmosphere. The reaction rate constant 

for hydrazine, derived from its decay rate in the presence of excess ozone, was about 3X10-17 cm3 

molecule-1s

-1 and for 1,1-dimethylhydrazine the rate was greater than 1X10-15 cm3 molecule-1s-1 

(Atkinson and Carter 1984). Major reaction products were hydrogen peroxide for the hydrazine 

reaction and dimethylnitrosamine (about 60%) for the 1,1-dimethylhydrazine reaction. Estimated 

atmospheric half-lives ranged from less than 10 minutes for hydrazine during an ozone pollution 

episode to less than 2 hours under usual conditions, with a half-life about one-tenth that time for 

1,1-dimethylhydrazine (Tuazon et al. 1981). Reported results of additional studies indicate a reaction 

rate constant for hydrazine of 2.5x10-l6 cm3 molecule-1s

-1, resulting in an estimated half-life of less than 

1 minute (Stone 1989). -. 

The reported measured rate constant for reaction of hydrazine with atmospheric hydroxyl (OH) radicals 

producing ammonia and nitrogen gas was 6.1x10-11cm3

 molecule-1s

-1 (Harris et al. 1979). The rate 

constant for 1,1-dimethylhydrazine was not measured since the chemical decomposed rapidly in the 

test system, but the value was estimated at 5X10-11 cm3 molecule-1s

-1. Assuming an average OH radical 
HYDRAZINES 129 

5. POTENTIAL FOR HUMAN EXPOSURE 

concentration of about 106 molecule/cm3, the tropospheric half-lives of both chemicals due to reaction 

with OH were estimated to be about 3 hours. The half-lives are expected to range from less than 1 

hour in polluted urban air to 3-6 hours in less polluted atmospheres (Tuazon et al. 1981). 

Hydrazine and 1,1-dimethylhydrazine react rapidly with nitrogen oxides in both the light and dark, 

with a half-life of about 2 hours for hydrazine and less than 10 minutes for 1,1-dimethylhydrazine 

(Pitts et al. 1980). 

Hydrazine and 1,1-dimethylhydrazine may also be removed from the atmosphere by autoxidation. In a 

dark reaction chamber, the approximate half-lives of hydrazine ranged from 1.8 to 5 hours, with the 

lower value measured at higher humidity. Reported values for 1,1 dimethylhydrazine under similar 

conditions were 5.9-9 hours. Surface interactions are important in controlling the rates of these 

reactions (Stone 1989). 

Although data were not located for 1,2-dimethylhydrazine, this chemical is expected to be degraded in 

the atmosphere by undergoing the same reactions as hydrazine and 1,1-dimethylhydrazine, although 

the rate and extent of degradation may be different. 

5.3.2.2 Water 

Hydrazine and 1,1-dimethylhydrazine degrade in aqueous systems, but the rate of degradation is 

dependent on specific aquatic environmental factors, including pH, hardness, temperature, oxygen 

concentration, and the presence of organic matter and metal ions (Moliner and Street 1989a; Slonim 

and Gisclard 1976; WHO 1987). Oxidation and biodegradation are the primary removal mechanisms. 

Reaction of hydrazine with dissolved oxygen is catalyzed by metal ions, particularly copper (EPA 

1984a). The reaction rate is strongly influenced by pH; degradation proceeds more rapidly in alkaline 

solutions. Hydrazine is rapidly removed from polluted waters, with less than one-third of the original 

concentration remaining in dirty river water after 2 hours (Slonim and Gisclard 1976). More than 90% 

of the hydrazine added to pond or chlorinated, filtered county water disappeared after 1 day. 

However, chlorinated, filtered, and softened city water contained almost the original amount of 

hydrazine after 4 days. Organic matter in the water and hardness were reported to be the major factors 

in the differing rates of degradation. 
HYDRAZINES 130 

5. POTENTIAL FOR HUMAN EXPOSURE 

The primary reaction pathway for hydrazine degradation in water produces nitrogen gas and water 

(Moliner and Street 1989a). In oxygen-deficient waters or in the presence of metal ions which serve 

as catalysts, ammonia may also be produced. 

The reaction of 1,1-dimethylhydrazine with dissolved oxygen in water may proceed by a process 

catalyzed by copper ions or by an uncatalyzed reaction (Banerjee et al. 1984). The products include 

dimethylnitrosamine, formaldehyde, dimethylamine, and other related chemicals. Dimethylnitrosamine 

did not form in dilute solutions, which might be encountered in ambient waters, but was reported in 

concentrated solutions, which could be present in the vicinity of spills (EPA 1984a). The reported 

half-life of 1,1-dimethylhydrazine in ponds and seawaters ranged from 10 to 14 days, presumably 

because of reaction with oxygen and other free radicals (EPA 1984a). 

Biodegradation may be a significant removal process at low hydrazine concentrations in ambient 

waters, but at higher concentrations the chemical is toxic to microorganisms. In the presence of 

bacterial cells, more than 90% of the hydrazine was degraded in six water samples containing 

11 μg/mL of the chemical within 2 hours (Ou and Street 1987b). Lower degradation rates were 

reported with increasing hydrazine concentrations. No degradation was reported for incubation of 

these waters without bacteria. Additional studies indicate that hydrazine and 1,1-dimethylhydrazine are 

toxic to bacterial populations. Concentrations of hydrazine and 1,1-dimethylhydrazine that reduced 

bacterial metabolism by 50% ranged from 14.6 to 145 mg/L and from 19.2 to 9,060 mg/L, 

respectively (Kane and Williamson 1983). Thus, biological treatment would not be useful for spills of 

these chemicals into the aquatic environment. 

5.3.2.3 Sediment and Soil 

Hydrazine appears to degrade more rapidly in soil than in water, with oxidation and biodegradation as 

the main removal processes. Hydrazine applied to nonsterile Arredondo soil (fine sand) at 

concentrations of 10, 100, and 500 μg/g was completely degraded in 1.5 hours, 1 day, and 8 days, 

respectively (Ou and Street 1987a). In this study, comparison to degradation rates in sterile soils 

indicated that autoxidation appeared to be the major factor contributing to disappearance of the 

chemical, but the study authors attributed about 20% of removal to biodegradation. Several 

heterotrophic soil bacteria were reported to degrade hydrazine, indicating that microbial degradation 

may contribute to removal of the chemical from soil (Ou 1987). 
HYDRAZINES 131 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT 

5.4.1 Air 

No monitoring data were located for hydrazine or dimethylhydrazines in ambient air. Since these 

chemicals are readily degraded in the atmosphere (see Section 5.3.2.1), they are not expected to be 

present measurable levels, except in the vicinity of production or processing facilities or spills. 

5.4.2 Water 

No monitoring data were located for hydrazine or dimethylhydrazines in ambient water. Since these 

chemicals are readily degraded in aquatic systems (see Section 5.3.2.2), they are not expected to be 

present at measurable levels, except in the vicinity of production or processing facilities, spills, or 

possibly, hazardous waste sites. 

5.4.3 Sediment and Soil 

No data were located documenting hydrazine or dimethylhydrazine concentrations in ambient soil or 

sediments. Since these chemicals are readily degraded in soil (see Section 5.3.2.3), they are not 

expected to be present at measurable levels, except in the vicinity of production or processing 

facilities, spills, or hazardous waste sites. 

5.4.4 Other Environmental Media 

Hydrazine and 1,1-dimethylhydrazine have been detected in tobacco. 1,1-Dimethylhydrazine was 

reported at concentrations ranging from not detected to 147 ng/g in various types of tobacco in the 

United States (Schmeltz et al. 1977). Mainstream smoke from blended U.S. cigarettes contained an 

average of 31.5 ng of hydrazine per cigarette (Liu et al. 1974). Sidestream smoke may have higher 

hydrazine concentrations. The authors reported 94.2 ng of hydrazine in sidestream smoke from one 

cigarette. Although hydrazine may be an impurity in maleic hydrazide, a pesticide formerly used on 

tobacco plants, reports on studies of tobacco from both treated and untreated plants indicate that the 

application of maleic hydrazide is not the major source of hydrazine in tobacco. It has been suggested 
HYDRAZINES 132 

5. POTENTIAL FOR HUMAN EXPOSURE 

that these chemicals may be produced in tobacco by bacterial or enzymatic processes which occur 

during curing (Schmeltz et al. 1977). 

1,1-Dimethylhydrazine has been detected in several food products because of its presence as an 

impurity (about 0.005%) in daminozide (Alar), a plant growth enhancer. 1,1-Dimethylhydrazine was 

detected in several processed fruits at maximum levels ranging from 0.007 to 0.60 ppm (Saxton et al. 

1989). The fruits had been treated with, and contained residues of, daminozide. It appears that during 

thermal processing, some of the daminozide degrades to 1,1-dimethylhydrazine, adding to the quantity 

of 1,1-dimethylhydrazine already present. However, daminozide is no longer used on food plants in 

the United States since its registered uses for food products were voluntarily cancelled in 1989 (EPA 

1992c). Therefore, 1,1-dimethylhydrazine is no longer expected to be present in foods prepared from 

food plants grown in the United States. 

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE 

Exposure of the general population to hydrazine and dimethylhydrazines is expected to be extremely 

low (WHO 1987). Because of the high reactivity of these chemicals, they are unlikely to remain in 

environmental media for extended periods. These chemicals have not been detected in ambient air, 

water, or soil. 

Occupational exposures to hydrazine and 1,1-dimethylhydrazine may occur in facilities that 

manufacture, process, transport, or use these chemicals. The National Institute for Occupational Safety 

and Health (NIOSH) conducted a National Occupational Exposure Survey (NOES) during 1981-1983 

and estimated that 59,675 and 2,197 workers were potentially exposed to hydrazine and 

1,1-dimethylhydrazine, respectively, at that time (EPA 1991d). Since most hydrazine production 

processes involve closed systems, the potential for exposure is generally low (Fajen and McCammon 

1988). The greatest potential for exposure probably occurs during process stream sampling, with 

measured time-weighted average (TWA) concentrations ranging from 0.04 to 0.27 ppm and excursions 

up to 0.91 ppm. Workplace breathing zone air levels of hydrazine and l,l-dimethylhydrazine ranged 

from 0.22 to 1.98 ppm and from 0.23 to 4.61 ppm, respectively, in a rocket propellant plant (Cook et 

al. 1979). Workers in facilities where exposure to these chemicals is possible are required to wear 

protective respirators. Analysis of samples from within the respirators indicated that these chemicals 
HYDRAZINES 133 

5. POTENTIAL FOR HUMAN EXPOSURE 

are not usually present at detectable levels. Thus, routine exposure to these levels is not expected, but 

respirator failures and other accidental exposures may occur. 

Occupational exposures may also occur to military and civilian personnel during the use of these 

chemicals as aerospace propellants. Exposure to workers may occur during loading or unloading of 

propellants, transfer operations, or testing of spacecraft components that use hydrazine fuels (Fajen and 

McCammon 1988). Although full-body supplied-air suits are usually worn during these operations, 

spills and other accidents may lead to short-term, high-level exposures, rather than longer-term, lowlevel 

exposures. 

Exposure may also result from the use of hydrazine as an oxygen scavenger in boiler systems (Fajen 

and McCammon 1988). Long-term concentrations in areas where hydrazine was added to the boiler 

systems were generally below 0.1 ppm, but short-term concentrations ranged up to 0.23 ppm. In 

addition, those individuals who work as daminozide applicators in greenhouses may be exposed to 

1,1-dimethylhydrazine (EPA 1992c). 

5.6 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES 

Populations with potential exposures to hydrazines above ambient levels include those exposed 

occupationally (see Section 5.5), such as during the manufacture or agricultural application of 

hydrazines, people living or working near military or aerospace installations using these chemicals as 

fuels, or people living near hazardous waste sites where these chemicals have been detected. Others 

who may be exposed to these chemicals at above ambient levels include individuals who chew or 

smoke tobacco and those exposed to sidestream smoke (see Section 5.4.4). Furthermore, hydrazine is 

a metabolite of several drugs (e.g., hydralazine, isoniazid), and it has been suggested that individuals 

taking these drugs may be exposed to hydrazine, based on the detection of hydrazine in the urine of 

patients taking hydralazine (Timbrell and Harland 1979) and the blood plasma of patients taking 

isoniazid (Blair et al. 1985). 

5.7 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 
HYDRAZINES 134 

5. POTENTIAL FOR HUMAN EXPOSURE 

adequate information on the health effects of hydrazines is available. Where adequate information is 

not available, ATSDR, in conjunction with the 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 hydrazines. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will 

be evaluated and prioritized, and a substance-specific research agenda will be proposed. 

5.7.1 Identification of Data Needs 

Physical and Chemical Properties. The physical and chemical properties of hydrazine and 

dimethylhydrazines are sufficiently well characterized to allow estimation of their environmental fate 

(see Table 3-2) (HSDB 1993; IARC 1975; Verschueren 1983). On this basis, it does not appear that 

further research in this area is required. 

Production, Import/Export, Use, Release, and Disposal. Hydrazine is produced at one facility 

and 1,1-dimethylhydrazine is produced at two locations (SRI 1992). However, production volume and 

import and export information are not available. This information would be useful in assessing 

potential exposure to workers and the general population. Since 1,2-dimethylhydrazine is produced 

only in gram quantities for research, additional information is not required. 

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 Toxics Release Inventory (TRI), which contains this information for 1993, became available in 

May of 1995. This database will be updated yearly and should provide a list of industrial production 

facilities and emissions. 
HYDRAZINES 135 

5. POTENTIAL FOR HUMAN EXPOSURE 

Environmental Fate. The environmental fate of hydrazine and 1,1-dimethylhydrazine has been well 

defined (Atkinson and Carter 1984; EPA 1984a; Moliner and Street 1989a, 1989b; Ou and Street 

1987a, 1987b; Stone 1989; WHO 1987). These chemicals are highly reactive and degrade readily in 

environmental media. Thus, they are not likely to be present in air or water and it is not likely that 

exposure to the general population is of concern. Nevertheless, because these chemicals may migrate 

to groundwater, additional studies might be useful to assess the potential for transport of these 

chemicals from hazardous waste sites and their fate in closed water systems such as groundwater. 

Bioavailability from Environmental Media. Hydrazine is known to be absorbed following 

inhalation (Llewellyn et al. 1986), oral (dissolved in water) (Preece et al. 1992a), and dermal (Smith 

and Clark 1971, 1972) exposures. Little is known about the absorption of 1,1-dimethylhydrazine and 

1,2-dimethylhydrazine, but based on their chemical properties, the absorption is most likely similar to 

that of hydrazine. No information was located on the bioavailability of hydrazine or dimethylhydrazines 

from environmental media. This information would be helpful in evaluating the impact of 

environmental exposures on human health. 

Food Chain Bioaccumulation. Hydrazine in water may bioconcentrate in aquatic organisms to a 

moderate degree (Slonim and Gisclard 1976), but because of its high reactivity, the chemical is rapidly 

degraded in aquatic systems. This property, as well as the low octanol-water partition coefficient of 

hydrazine, makes food chain bioaccumulation unlikely. 

Exposure Levels in Environmental Media. Hydrazine and dimethylhydrazines have not been 

detected in ambient air, water, or soil, since they are highly reactive and degrade readily in 

environmental media. Hydrazine and l,l-dimethylhydrazine have been detected in workplace air and 

in tobacco (Cook et al. 1979; Schmeltz et al. 1977). Since these chemicals are highly reactive and 

exposure of the general population is not expected to be of concern, monitoring of ambient 

environmental media does not appear to be required. However, monitoring of workplace air would 

help to determine potential sources and magnitude of exposure. 

Exposure Levels in Humans. Hydrazine and dimethylhydrazines have not been detected in human 

tissues as a result of exposure to these chemicals from environmental media. Hydrazine has been 

detected in the urine of individuals taking medication (hydralazine) which may metabolize to 

hydrazine (Timbrell and Harland 1979). Since hydrazine and dimethylhydrazines are rapidly 
HYDRAZINES 136 

5. POTENTIAL FOR HUMAN EXPOSURE 

metabolized in vivo, it is unlikely that any free chemical would be present in biological tissues within 

a few days after environmental exposure. Studies that investigate the levels of hydrazines in humans 

within the first few days after exposure, along with their relationship to exposure levels, would be 

useful. This information is necessary for assessing the need to conduct health studies on these 

populations. 

Exposure Registries. No exposure registries for hydrazines were located. These substances are not 

currently in a subregistry of the National Exposure Registry. These substances will be considered in 

the future when chemical selection is made for subregistries to be established. The information that is 

amassed in the National Exposure Registry facilitates the epidemiological research needed to assess 

adverse health outcomes that may be related to exposure to these substances. 

5.7.2 On-going Studies 

No information was located regarding on-going studies on the environmental fate or exposure levels of 

hydrazine or dimethylhydrazines. 
HYDRAZINES 137 

6. ANALYTICAL METHODS
 

The purpose of this chapter is to describe the analytical methods that are available for detecting, and/or 

measuring, and/or monitoring hydrazines, their metabolites, and other biomarkers of exposure and 

effect to hydrazines. The intent is not to provide an exhaustive list of analytical methods. Rather, the 

intention is to identify well-established methods that are used as the standard methods of analysis. 

Many of the analytical methods used for environmental samples are the methods approved by federal 

agencies and organizations such as EPA and the National Institute for Occupational Safety and Health 

(NIOSH). Other methods presented in this chapter are those that are approved by groups such as the 

Association of Official Analytical Chemists (AOAC) and the American Public Health Association 

(APHA). Additionally, analytical methods are included that modify previously used methods to obtain 

lower detection limits, and/or to improve accuracy and precision. 

6.1 BIOLOGICAL MATERIALS 

Spectrophotometric methods, high-performance liquid chromatography (HPLC), and gas 

chromatography (GC) may be used to detect and measure hydrazine and dimethylhydrazines in 

biological materials (Alvarez de Laviada et al. 1987; Amlathe and Gupta 1988; Fiala and Kulakis 

1981; Preece et al. 1992a; Reynolds and Thomas 1965; Timbrell and Hat-laud 1979). The 

spectrophotometer measures the absorbance of light at a particular wavelength, thereby identifying and 

quantifying a compound that absorbs at that wavelength. The chromatograph separates complex 

mixtures of organics and allows individual compounds to be identified and quantified by a detector. 

An electrochemical detector (ED), in the case of HPLC, and a nitrogen phosphorus detector (NPD) or 

flame ionization detector (FID), in the case of GC, may be used to identify hydrazine or 

dimethylhydrazine or their derivatives. When unequivocal identification is required, a mass 

spectrometer (MS) coupled to the GC column may be employed. 

Prior to GC or spectrophotometric analysis, hydrazine and dimethylhydrazines must be separated from 

the biological sample matrix and derivatives of the compounds must be prepared. Separation is 

usually effected by precipitation of residual protein with acid and extraction of interfering lipids with 

methylene chloride (Alvarez de Laviada et al. 1987; Preece et al. 1992a; Reynolds and Thomas 1965; 

Timbrell and Harland 1979). Hydrazine and 1,1-dimethylhydrazine, but not 1,2-dimethylhydrazine, 
HYDRAZINES 138 

6. ANALYTICAL METHODS 

may then be derivatized with an aldehyde such as pentafluorobenzaldehyde or p-dimethylaminobenzaldehyde. 

1,2-Dimethylhydrazine, which has no free-NH2 group, cannot be derivatized in this 

way but may be quantified by chromatographic methods that do not require derivatization (Fiala and 

Kulakis 1981). Details of selected analytical methods for hydrazine and dimethylhydrazines in 

biological samples are summarized in Table 6-l. 

Accurate analysis of hydrazine and dimethylhydrazines in biological samples is complicated by the 

tendency of these chemicals to autoxidize during storage (Preece et al. 1992a). Thus, derivatization 

should be completed as rapidly as possible, before autoxidation can occur. 

6.2 ENVIRONMENTAL SAMPLES 

Determination of hydrazine and dimethylhydrazines in air, water, soil, food, and tobacco is also carried 

out by spectrophotometry, GC, or HPLC analysis (Amlathe and Gupta 1988; ASTM 1991b; Holtzclaw 

et al. 1984; Leasure and Miller 1988; Liu et al. 1974; NIOSH 1977a, 1977b, 1984; Rutschmann and 

Buser 1991; Schmeltz et al. 1977; Wright 1987). Several representative methods for quantifying these 

chemicals in each of these media are summarized in Table 6-2. EPA-validated methods are not 

available for analysis of hydrazine or dimethylhydrazines in any environmental medium. Two EPA 

methods (8250 and 8270) are recommended for analysis of 1,1-dimethylhydrazine in wastes (EPA 

1990e). However, these methods do not list 1,1-dimethylhydrazine as an analyte (EPA 1990c, 1990d) 

and do not appear to be suitable methods for analysis of this compound since 1,1-dimethylhydrazine is 

likely to degrade during the GC analysis unless it has been derivatized. 

Separation of hydrazine and dimethylhydrazines from environmental samples is by acid extraction 

when necessary. Air samples are usually collected in a bubbler with acid or on an acid-coated silica 

gel (NIOSH 1977a, 1977b, 1984). When GC is employed, detection may be by electron capture 

detector (ECD), FID, nitrogen-specific detector (NSD), thermionic ionization detector (TID), and/or 

MS as described above (Section 6.1). 

Accurate determination of hydrazine and dimethylhydrazines in environmental samples is also 

complicated by the susceptibility of these chemicals to oxidization. Air samples must be analyzed 

immediately after collection (Cook et al. 1979). Degradation of hydrazine in aqueous samples can be 

prevented by acidification with sulfuric acid (WHO 1987). 




HYDRAZINES 143 

6. ANALYTICAL METHODS 

6.3 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with 

the Administrator of EPA and agencies and programs of the Public Health Service) to assess whether 

adequate information on the health effects of hydrazines is available. Where adequate information is 

not available, ATSDR, in conjunction with the 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 hydrazines. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met would 

reduce the uncertainties of human health assessment. This definition should not be interpreted to mean 

that all data needs discussed in this section must be filled. In the future, the identified data needs will 

be evaluated and prioritized, and a substance-specific research agenda will be proposed. 

6.3.1 Identification of Data Needs 

Methods for Determining Biomarkers of Exposure and Effect. Methods are available for 

determining the levels of hydrazine, 1,1-dimethylhydrazine, and 1,2-dimethylhydrazine in biological 

samples, including urine, plasma, serum, liver tissue, and brain tissue (Alvarez de Laviada et al. 1987; 

Amlathe and Gupta 1988; Fiala and Kulakis 1981; Preece et al. 1992a; Reynolds and Thomas 1965; 

Timbrell and Harland 1979). These methods generally employ standard chromatographic and 

spectrophotometric procedures with detection limits ranging from 0.02 to 0.065 μg/rnL, and therefore, 

most likely are sufficiently sensitive to measure levels at which biological effects occur following 

recent exposures. The limited data available indicate that these methods are accurate and reliable if 

analyses are performed rapidly, before autoxidation can occur. The background levels of hydrazines in 

biological samples in the general population have not been determined; if hydrazines are-present at all, 

they are most likely present at levels below current detection limits. The detection limits for current 

methods are sufficiently sensitive to detect levels at which effects occur. Since hydrazines can occur 

in the body following exposure to drugs such as isoniazid and hydralazine (Timbre11 and Harland 

1979), and many of the metabolites of hydrazines are ubiquitous or may occur following exposure to 

other chemicals, measures should be taken to ensure exposure to these confounding chemicals has not 
HYDRAZINES 144 

6. ANALYTICAL METHODS 

occurred. Other metabolites such as azomethane, azoxymethane, and methylazoxymethanol are unique 

to exposure to 1 ,2 dimethylhydrazine. Studies which identify specific biomarkers for past exposure to 

hydrazines, in conjunction with the development of accurate and reliable methods for detecting such 

biomarkers, would be useful in estimating exposure to hydrazines at hazardous waste sites. 

The effects of hydrazines have been fairly well characterized in humans and animals, and include 

neurological, hepatic, and carcinogenic effects (Chlebowski et al. 1984; Gershanovich et al. 1976; 

Haun and Kinkead 1973; Rinehart et al. 1960; Thorup et al. 1992; Wilson 1976). Methods exist for 

measuring serum transaminase levels, vitamin B6 status, and occult blood in stool samples, all of 

which may serve as biomarkers of effect for hydrazines. Although these methods are fairly accurate 

and reliable, none of them are specific for effects of hydrazines. Studies which identify biomarkers of 

effect that are specific to hydrazines, in conjunction with the development of accurate and reliable 

methods for detecting such biomarkers, would be useful in determining if individuals have been 

exposed to predicting recent exposures to hydrazines at hazardous waste sites. 

Methods for Determining Parent Compounds and Degradation Products in 

Environmental Media. Analytical methods are available to detect and quantify hydrazine and 

dimethylhydrazines in air, water, soil, food, and tobacco (Amlathe and Gupta 1988; ASTM 1991b; 

Holtzclaw et al. 1984; Leasure and Miller 1988; Liu et al. 1974; NIOSH 1977a, 1977b, 1984; 

Rutschmann and Buser 1991; Wright 1987). Air is the medium of most concern for human exposure 

to this chemical. Exposure may also occur from water, especially in the vicinity of hazardous waste 

sites or industrial sources. The existing analytical methods can provide determinations for these 

chemicals at levels sufficiently low to meet regulatory requirements (NIOSH 1977a, 1977b, 1984). 

Assuming that an adequate quantity of air is passed through the collector (for example: a volume of at 

least 41 m3

 is required to detect a level equivalent to the intermediate inhalation MRL of 2x10-4 ppm 

for 1,1-dimethylhydrazine, assuming a detection limit of 0.9 μg/sample), current methods are 

sufficiently sensitive to measure levels near the MRL value for 1,1-dimethylhydrazine. However, their 

tendency to degrade and their chemical reactivity limit the accuracy of analyses of thesechemicals in 

all media. Improved methods of extraction and analysis that minimize these reactions would enhance 

recovery of these chemicals from environmental samples and provide a better estimate of 

environmental levels, especially in drinking water and soil at hazardous waste sites. 
HYDRAZINES 145 

6. ANALYTICAL METHODS 

In addition, methods are available to measure degradation products of hydrazine and 

dimethylhydrazines (see Section 5.3.2) in environmental samples and can be used to determine the 

environmental impact of these chemicals. 

6.3.2 On-going Studies 

On-going studies to improve analytical methods for hydrazine and dimethylhydrazines includes 

continuing research to improve HPLC columns and EDs. In addition, the Naval Research Laboratory 

has been investigating pattern recognition techniques using microsensors capable of measuring 

hydrazine in air at ppb concentrations (Anon 1987). These improvements are designed to overcome 

sampling problems and increase sensitivity and reliability of the analyses. 

HYDRAZINES 147 

7. REGULATIONS AND ADVISORIES 

Because of its potential to cause adverse health effects in exposed people, numerous regulations and 

advisories have been established for hydrazines by various international, national and state agencies. 

Major regulations and advisories pertaining to hydrazine, 1,1-dimethylhydrazine, and 

1,2-dimethylhydrazine are summarized in Tables 7-1, 7-2, and 7-3, respectively. 

ATSDR has derived an intermediate-duration inhalation MRL of 4x10-3 ppm for hydrazine, as 

described in Appendix A. The MRL is based on a LOAEL of 0.2 ppm for fatty liver changes in 

female mice (Haun and Kinkead 1973). The LOAEL was adjusted for intermittent exposure 

(6 hours/day, 5 days/week), converted to a Human Equivalent Concentration (HEC), and divided by an 

uncertainty factor of 300 (10 for use of a LOAEL, 3 for extrapolation from animals to humans, and 10 

for human variability). 

ATSDR has derived an intermediate-duration inhalation MRL of 2x10-4 ppm for 

1,1-dimethylhydrazine, as described in Appendix A. The MRL is based on a LOAEL of 0.05 ppm for 

hepatic effects (hyaline degeneration of the gall bladder in female mice) (Haun et al. 1984). The 

LOAEL was adjusted for intermittent exposure (6 hours/day, 5 days/week), converted to an HEC, and 

divided by an uncertainty factor of 300 (10 for use of a LOAEL, 3 for extrapolation from animals to 

humans, and 10 for human variability). 

ATSDR has derived an intermediate-duration oral MRL of 8X10-4 mg/kg/day for 

1,2-dimethylhydrazine, as described in Appendix A. The MRL is based on a LOAEL of 

0.75 mg/kg/day for mild hepatitis in male mice (Visek et al. 1991). The LOAEL was divided by an 

uncertainty factor of 1,000 (10 for use of a LOAEL, 10 for extrapolation from animals to humans, and 

10 for human variability). 







_________________ 

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*Wattenberg LW. 1975. Inhibition of dimethylhydazine-induced neoplasia of the large intestine by 

disulfiram. J Nat Cancer Inst 54:1005-1006. 

Wheeler CE, Penn SR, Cawley EP. 1965. Dermatitis from hydrazine hydrobromide solder flux. Arch 

Dermat 91:235-239. 

*WHO. 1987. Environmental health criteria 68: Hydrazine. World Health Organization, Geneva, 

Switzerland, l-89. 

*Williams GM, Weisburger JH. 1991. Chemical carcinogenesis. In: Casarett and Doull’s Toxicology, 

the basic science of poisons. Amdur, MO, Doull J, Klaasen CD, eds. Elmsford, NY: Pergamon Press, 

Inc. 180-181. 

*Wilpart M, Mainguet P, Maskens A, et al. 1983. Mutagenicity of 1,2-dimethylhydrazine towards 

Salmonella typhimuriurn, co-mutagenic effect of secondary biliary acids. Carcinogenesis 1:45-48. 

*Wilson RB. 1976. Species variation in response to dimethylhydrazine. Toxicol Appl Pharmacol 

38:647-650. 

*Winton DJ, Gooderham NJ, Boobis AR, et al. 1990. Mutagenesis of mouse intestine in vivo using the 

Dlb-1 specific locus test: studies with 1,2-dimethylhydrazine, dimethylnitrosamine, and the dietary 

mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline. Cancer Res 50:7992-7996. 

*Walter S, Schmahl D, Frank N. 1984. Influence of diet on 1,2-dimethylhydrazine metabolism in rat 

liver. Nutr Cancer 6:181-186. 

*Wrangsjo K, Martensson A. 1986. Hydrazine contact dermatitis from gold plating. Contact 

Dermatitis 244-245. 

*Wright D. 1987. Pesticide and industrial chemical residues. New method for the determination of 

1,1-dimethylhydrazine residues in apples and peaches. J Assoc Off Anal Chem 70:718-720. 

*Wryobek AJ, London SA. 1973. Effect of hydrazines on mouse sperm cells. AMRL-TR-73-125. 
HYDRAZINES 182 

8. REFERENCES 

Yamada K, Yoshitake K, Sato M, et al. 1992. Proliferating cell nuclear antigen expression in normal, 

preneoplastic, and neoplastic colonic epithelium of the rat. Gastroenterology 103:160-167. 

*Yamamoto K, Kawanishi S. 1991. Site-specific DNA damage induced by hydrazine in the presence 

of manganese and copper ions. J Biol Chem 256:1509-1515. 

*Yamamoto RS, Weisburger JH. 1970. Failure to arginine glutamate to inhibit lung tumor formation 

by isoniazid and hydrazine in mice. Life Sci 9:285-289. 

*Zeilmaker MJ, Horsfall MJ, van Helten JB, et al. 1991. Mutational specificities of environmental 

carcinogens in the Zucl gene of Escherichiu coli H.V: DNA sequence analysis of mutations in bacteria 

recovered from the liver of Swiss mice exposed to 1,2-dimethylhydrazine, azoxymethane, and 

methylazoxymethanolacetate. Mol Carcinogen 4: 180-l 88. 

*Zijlstra JA, Vogel EW. 1988. Influence of inhibition of the metabolic activation on the mutagenicity 

of some nitrosamines, triazenes, hydrazines and seniciphylline in Drosophila melunoguster. Mutat Res 

202:25 l-267. 

Zusman I, Madar Z, Nyska A. 1992a. Individual variability of pathological parameters in chemically 

induced rat colon tumors. Acta Anat 145:106-111. 

Zusman I, Zimber A, Madar Z, et al. 1992b. Morphological, histochemical and immunohistochemical 

differences between tumorous and adjacent tissues in chemically induced colon cancer in rats. Acta 

Anat 145:29-34. 
HYDRAZINES 183 

9. GLOSSARY 

Acute Exposure -- Exposure to a chemical for a duration of 14 days or less, as specified in the 

Toxicological Profiles. 

Adsorption Coeffkient (Koc)-- The ratio of the amount of a chemical adsorbed per unit weight of 

organic carbon in the soil or sediment to the concentration of the chemical in solution at equilibrium. 

Adsorption Ratio (Kd) -- The amount of a chemical adsorbed by a sediment or soil (i.e., the solid 

phase) divided by the amount of chemical in the solution phase, which is in equilibrium with the solid 

phase, at a fixed solid/solution ratio. It is generally expressed in micrograms of chemical sorbed per 

gram of soil or sediment. 

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. 

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. 

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. 

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. 

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 occurred. The terms, as used here, include malformations and variations, altered 

growth, and in utero death. 

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. 

Immediately Dangerous to Life or Health (IDLH) -- The maximum environmental concentration of 

a contaminant from which one could escape within 30 min without any escape-impairing symptoms or 

irreversible health effects. 

Intermediate Exposure -- Exposure to a chemical for a duration of 15-364 days, as specified in the 

Toxicological Profiles. 
HYDRAZINES 184 

9. GLOSSARY 

Immunologic Toxicity -- The occurrence of adverse effects on the immune system that may result 

from exposure to environmental agents such as chemicals. 

In Vitro -- Isolated from the living organism and artificially maintained, as in a test tube. 

In Vivo -- Occurring within the living organism. 

Lethal Concentratlonn(LO)(LCLO) -- The lowest concentration of a chemical in air which has been 

reported to have caused death in humans or animals. 

Lethal Concentratioq(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 defied experimental animal 

population. 

Lethal Dose(LO) (LDLO) -- The lowest dose of a chemical introduced by a route other than inhalation 

that is expected to have caused death in humans or animals. 

Lethal Dose(50) (LD50) -- The dose of a chemical which has been calculated to cause death in 50% of a 

defined experimental animal population. 

Lethal Time(50) ( LT50) -- A calculated period of time within which a specific concentration of a 

chemical is expected to cause death in 50% of a defined experimental animal population. 

Lowest-Observed-Adverse-Effect Level (LOAEL) -- The lowest dose 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. 

Malformations -- Permanent structural changes that may adversely affect survival, development, or 

function. 

Minimal Risk Level -- An estimate of daily human exposure to a dose of a chemical that is likely to 

be without an appreciable risk of adverse noncancerous effects over a specified duration of exposure. 

Mutagen -- A substance that causes mutations. A mutation is a change in the genetic material in a 

body cell. Mutations can lead to birth defects, miscarriages, or cancer. 

Neurotoxicity -- The occurrence of adverse effects on the nervous system following exposure to 

chemical. 

No-Observed-Adverse-Effect Level (NOAEL) -- The dose of 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. 

Permissible Exposure Limit (PEL) -- An allowable exposure level in workplace air averaged over an 

8-hour shift. 
HYDRAZINES 185 

9. GLOSSARY 

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). 

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 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 CERCLA. Reportable quantities are (I) 1 pound or greater or (2) for selected substances, an 

amount established by regulation either under CERCLA or under Sect. 311 of the Clean Water Act. 

Quantities are measured over a 24-hour period. 

Reproductive Toxicity -- The occurrence of adverse effects on the reproductive system that may 

result from exposure to a chemical. The toxicity may be directed to the reproductive organs and/or the 

related endocrine system. The manifestation of such toxicity may be noted as alterations in sexual 

behavior, fertility, pregnancy outcomes, or modifications in other functions that are dependent on the 

integrity of this system. 

Short-Term Exposure Limit (STEL) -- The maximum concentration to which workers can be 

exposed for up to 15 min continually. No more than four excursions are allowed per day, and there 

must be at least 60 min between exposure periods. The daily TLV-TWA may not be exceeded. 

Target Organ Toxicity -- This term covers a broad range of adverse effects on target organs or 

physiological systems (e.g., renal, cardiovascular) extending from those arising through a single limited 

exposure to those assumed over a lifetime of exposure to a chemical. 

Teratogen -- A chemical that causes structural defects that affect the development of an organism. 

Threshold Limit Value (TLV) -- A concentration of a substance to which most workers can be 

exposed without adverse effect. The TLV may be expressed as a TWA, as a STEL, or as a CL. 

Time-Weighted Average (TWA) -- An allowable exposure concentration averaged over a normal 

8-hour workday or 40-hour workweek. 

Toxic Dose (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. 

Uncertainty Factor (UF) -- A factor used in operationally deriving the RfD 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 

LOAEL data rather than NOAEL data. Usually each of these factors is set equal to 10. 

HYDRAZINES A-1 

APPENDIX A 

ATSDR MINIMAL RISK LEVEL 

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. 

99-4991, requires that the Agency for Toxic Substances and Disease Registry (ATSDR) develop 

jointly with the US. 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. 
HYDRAZINES A-2 

APPENDIX A 

MRLs are intended only to serve as a screening tool to help public health professionals decide where 

to look more closely. They may also be viewed as a mechanism to identify those hazardous waste 

sites that are not expected to cause adverse health effects. Most MRLs contain a degree of uncertainty 

because of the lack of precise toxicological information on the people who might be most sensitive 

(e.g., infants, elderly, nutritionally or immunologically compromised) to the effects of hazardous 

substances. ATSDR uses a conservative (i.e., protective) approach to address this uncertainty 

consistent with the public health principle of prevention. Although human data are preferred, MRLs 

often must be based on animal studies because relevant human studies are lacking. In the absence of 

evidence to the contrary, ATSDR assumes that humans are more sensitive to the effects of hazardous 

substance than animals and that certain persons may be particularly sensitive. Thus, the resulting 

MRL may be as much as a hundredfold below levels that have been shown to be nontoxic in 

laboratory animals. 

Proposed MRLs undergo a rigorous review process: Health Effects/MRL Workgroup reviews within 

the Division of Toxicology, expert panel peer reviews, and agencywide MRL Workgroup reviews, 

with participation from other federal agencies and comments from the public. They are subject to 

change as new information becomes available concomitant with updating the toxicological profiles. 

Thus, MRLs in the most recent toxicological profiles supersede previously published levels. For 

additional information regarding MRLs, please contact the Division of Toxicology, Agency for Toxic 

Substances and Disease Registry, 1600 Clifton Road, Mailstop E-29, Atlanta, Georgia 30333. 
HYDRAZINES A-3 

APPENDIX A 

MINIMAL RISK LEVEL WORKSHEETS 

Chemical Name: Hydrazine 

CAS Number: 302-01-2 

Date: September 5, 1996 

Profile Status: Draft 3 

Route: [X] Inhalation [ ] Oral 

Duration: [ ] Acute [X] Intermediate [ ] Chronic 

Graph Key: 19 

Species: mouse 

Minimal Risk Level: 4 x10-3 ppm [ ] mg/kg/day [X] ppm 

Reference: Haun and Kinkead 1973 

Experimental design:(human study details or strain, number of animals per exposure/control groups, 

sex, dose administration details): 40 female ICR mice per group, exposed by inhalation to 0, 0.2, or 

1.0 ppm continuously for 6 months. 

Effects noted in study and corresponding doses: Moderate to severe fatty liver changes were seen at 

both exposure levels. 

Calculations:
 

LOAEL(HEC)= LOAEL x [(VA/BW)A÷ (VA/BW)H]
 

LOAEL(HEC)= LOAEL x [(VA/BW)A÷ (VA/BW)H]
 

LOAEL(HEC) = 0.2 ppm x [(0.043 m3

/day ÷ 0.026 kg) ÷ (20 m3/day ÷ 70 kg)]
 

LOAEL(HEC) = 1.154 ppm
 

MRL = LOAEL(HEC)÷Uncertainty Factor
 

MRL = 1.154 ppm ÷300
 

MRL=4x 10-3ppm
 

Dose and endpoint used for MRL derivation:
 

[ ] NOAEL [X] LOAEL 

Uncertainty Factors used in MRL derivation: 

[X] 10 for use of a LOAEL 

[X] 3 for extrapolation from animals to humans following conversion to HEC 

[X] 10 for human variability 

Was a conversion used from ppm in food or water to a mg/body weight dose? 

If so, explain: No 

If an inhalation study in animals, list the conversion factors used in determining human equivalent 

dose: VA mouse = 0.043 m3

/day, BW = 0.026 kg 
HYDRAZINES A-4 

APPENDIX A 

VA human = 20 m3/day, BW = 70 kg 

Other additional studies or pertinent information which lend support to this MRL: The authors (Haun 

and Kinkead 1973) also investigated the effects of inhaled hydrazine in other species. Fatty liver 

changes were also observed in dogs exposed to 1 ppm hydrazine for 6 months and in monkeys 

exposed to 0.2 ppm for 6 months. 

Agency Contact (Chemical Manager): Hugh Hansen 

Agency Review Date: 1° review:___________ 

2° review:_____________ 
HYDRAZINES A-5 

APPENDIX A 

Chemical Name: 1,1 -Dimethylhydrazine 

CAS Number: 57-14-7 

Date: September 5, 1996 

Profile Status: Draft 3 

Route: [X] Inhalation [ ] Oral 

Duration: [ ] Acute [X] Intermediate [ ] Chronic 

Graph Key: 17 

Species: mouse 

Minimal Risk Level: 2 x 10-4 [ ] mg/kg/day [X] ppm 

Reference: Haun et al. 1984 

Experimental design:(human study details or strain, number of animals per exposure/control groups, 

sex, dose administration details): Groups of 400 female C57BL/6 mice per group, exposed by 

inhalation to 0, 0.05, 0.5, or 5 ppm for 6 months, 5 days per week, 6 hours per day. 

Effects noted in study and corresponding doses: Hyaline degeneration in the gallbladder was
 

significantly increased in the 0.05, 0.5, and 5 ppm groups compared to controls. Thus, the LOAEL is
 

set at 0.05 ppm.
 

Calculations:
 

LOAEL(HEC) = LOAEL(ADJ)x [ (VA/BW)A÷ (VA/B W)H]
 

LOAEL(HEC) = (0.05 ppm x 6 hr/24 hr x 5 d/7 d) x [(VA/BW)A + (VA/BW)H]
 

LOAEL(HEC) = 0.0089 ppm x [(0.043 m3

/day ÷ 0.026 kg) ÷20 m3/day + 70 kg)]
 

LOAEL(HEC)= 0.05 ppm
 

MRL = LOAEL(HEC)÷ Uncertainty Factor
 

MRL = 0.05 ppm + 300
 

MRL = 2 x 10-4 ppm
 

Dose and endpoint used for MRL derivation:
 

[ ] NOAEL [X] LOAEL 

Uncertainty Factors used in MRL derivation: 

[X] 10 for use of a LOAEL 

[X] 3 for extrapolation from animals to humans following conversion to HEC 

[X] 10 for human variability 

Was a conversion used from ppm in food or water to a mg/body weight dose? 

If so, explain: No 

If an inhalation study in animals, list the conversion factors used in determining human equivalent 

dose: VA mouse = 0.043 m3

/day, BW = 0.026 kg 

VA human = 20 m3

/day, BW = 70 kg 
HYDRAZINES A-6 

APPENDIX A 

Other additional studies or pertinent information which lend support to this MRL: Studies of workers 

exposed to 1,1-dimethylhydrazine have reported changes indicative of a hepatic effect (elevated serum 

alanine aminotransferase activity, positive cephalin flocculation test) (Petersen et al. 1970; Shook and 

Cowart 1957). Angiectasis was observed in the livers of all exposed mice. Hepatic congestion was 

noted in mice exposed to 0.5 or 5 ppm 1,1-dimethylhydrazine (Haun et al. 1984). No NOAEL was 

identified. 

Agency Contact (Chemical Manager): Hugh Hansen 

Agency Review Date: 1° review:____________ 

2°review:_____________ 
 

HYDRAZINES A-7 

APPENDIX A 

Chemical Name: 1,2-Dimethylhydrazine 

CAS Number: 540-73-8 

Date: September 5, 1996 

Profile Status: Draft 3 

Route: [ ] Inhalation [X] Oral 

Duration: [ ] Acute [X] Intermediate [ ] Chronic 

Graph Key: 25 

Species: mouse 

Minimal Risk Level: 8 x 10-4 [X] mg/kg/day [ ] ppm 

Reference: Visek et al. 199 1 

Experimental design:(human study details or strain, number of animals per exposure/control groups, 

sex, dose administration details): 25 male mice per group, exposed to 0, 0.75, 1.6, or 2.7 mg/kg/day in 

the diet for 5 months. Although 2 diet preparations were administered (one containing 10% protein, 

the other containing 40% protein), the doses of 1,2-dimethylhydrazine were judged not to differ 

significantly between the two groups. 

Effects noted in study and corresponding doses: Mild hepatitis and small decreases in body weight 

gain and relative organ weights were observed in mice exposed to the lowest dose (0.75 mg/kg/day). 

These effects were more severe in animals exposed to higher doses. For example, doses of 1.6 

mg/kg/day produced frank toxic hepatitis, as characterized by lobular disorganization, hepatocellular 

hypertrophy, and centrilobular necrosis. Portal fibrosis and bile duct hyperplasia, two effects noted in 

only a few animals exposed to 1.6 mg/kg/day, were more frequently observed in animals receiving the 

highest dose (2.7 mg/kg/day). 

Calculations: 

MRL = LOAEL ÷ Uncertainty Factor 

MRL = 0.75 mg/kg/day ÷1000 

MRL = 8 x 10s4 mg/kg/day 

Dose and endpoint used for MRL derivation: 

[ ] NOAEL [X] LOAEL 

Uncertainty Factors used in MRL derivation: 

[X] 10 for use of a LOAEL 

[X] 10 for extrapolation from animals to humans 

[X] 10 for human variability 

Was a conversion used from ppm in food or water to a mg/body weight dose?
 

If so, explain: 0.058 mg/day (daily food intake provided by authors) ÷ 0.035 kg (body weight provided
 

by authors) x 0.45 (molecular weight adjustment for use of dihydrochloride salt) = 0.75 mg/kg/day.
 
HYDRAZINES A-8 

APPENDIX A 

If an inhalation study in animals, list the conversion factors used in determining human equivalent 

dose: N/A 

Other additional studies or pertinent information which lend support to this MRL: Hepatic effects 

(hepatotoxicity, necrosis, fibrosis, hemosiderosis, ascites, cirrhosis, degeneration) have been observed 

in rats (Bedell et al. 1982), guinea pigs (Wilson 1976), dogs (Wilson 1976), and pigs (Wilson 1976) 

subchronically exposed to 4.2-30 mg/kg/day 1,2-dimethylhydrazine by the oral route. 

Agency Contact (Chemical Manager): Hugh Hansen 

Agency Review Date: 1° review:___________ 

2°review:____________ 
HYDRAZINES B-1 

APPENDIX B 

USER’S GUIDE 

Chapter 1 

Public Health Statement 

This chapter of the profile is a health effects summary written in non-technical language. Its intended 

audience is the general public especially people living in the vicinity of a hazardous waste site or 

chemical release. If the Public Health Statement were removed from the rest of the document, it 

would still communicate to the lay public essential information about the chemical. 

The major headings in the Public Health Statement are useful to find specific topics of concern. The 

topics are written in a question and answer format. The answer to each question includes a sentence 

that will direct the reader to chapters in the profile that will provide more information on the given 

topic. 

Chapter 2 

Tables and Figures for Levels of Significant Exposure (LSE) 

Tables (2-1, 2-2, and 2-3) and figures (2-l and 2-2) are used to summarize health effects and illustrate 

graphically levels of exposure associated with those effects. These levels cover health effects observed 

at increasing dose concentrations and durations, differences in response by species, minimal risk levels 

(MRLs) to humans for noncancer end points, and EPA’s estimated range associated with an upperbound 

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 No-Observed-AdverseEffect Levels (NOAELs), Lowest-Observed-Adverse-Effect Levels (LOAELs), or Cancer Effect Levels 

(CELs). 

The legends presented below demonstrate the application of these tables and figures. Representative 

examples of LSE Table 2-l and Figure 2-l are shown. The numbers in the left column of the legends 

correspond to the numbers in the example table and figure. 

LEGEND 

See LSE Table 2-l 

(1)	 Route of Exposure One of the first considerations when reviewing the toxicity of a substance 

using these tables and figures should be the relevant and appropriate route of exposure. When 

sufficient data exists, three LSE tables and two LSE figures are presented in the document. The 

three LSE tables present data on the three principal routes of exposure, i.e., inhalation, oral, and 

dermal (LSE Table 2-1, 2-2, and 2-3, respectively). LSE figures are limited to the inhalation 

(LSE Figure 2-l) and oral (LSE Figure 2-2) routes. Not all substances will have data on each 

route of exposure and will not therefore have all five of the tables and figures. 
HYDRAZINES B-2 

APPENDIX B 

(2)	 Exposure Period Three exposure periods - acute (less than 15 days), intermediate (15-364 days), 

and chronic (365 days or more) are presented within each relevant route of exposure. In this 

example, an inhalation study of intermediate exposure duration is reported. For quick reference 

to health effects occurring from a known length of exposure, locate the applicable exposure 

period within the LSE table and figure. 

(3) Health Effect The major categories of health effects included in LSE tables and figures are 

death, systemic, immunological, neurological, developmental, reproductive, and cancer. 

NOAELs and LOAELs can be reported in the tables and figures for all effects but cancer. 

Systemic effects are further defined in the “System” column of the LSE table (see key number 

18). 

(4)	 Key to Figure Each key number in the LSE table links study information to one or more data 

points using the same key number in the corresponding LSE figure. In this example, the study 

represented by key number 18 has been used to derive a NOAEL and a Less Serious LOAEL 

(also see the 2 “18r” data points in Figure 2-l). 

(5)	 Species The test species, whether animal or human, are identified in this column. Section 2.5, 

“Relevance to Public Health,” covers the relevance of animal data to human toxicity and Section 

2.3, “Toxicokinetics,” contains any available information on comparative toxicokinetics. 

Although NOAELs and LOAELs are species specific, the levels are extrapolated to equivalent 

human doses to derive an MRL. 

(6)	 Exposure Frequency/Duration The duration of the study and the weekly and daily exposure 

regimen are provided in this column. This permits comparison of NOAELs and LOAELs from 

different studies. In this case (key number 1 S), rats were exposed to 1 ,1,2,2-tetrachloroethane 

via inhalation for 6 hours per day, 5 days per week, for 3 weeks. For a more complete review 

of the dosing regimen refer to the appropriate sections of the text or the original reference paper, 

i.e., Nitschke et al. 1981. 

(7)	 System This column further defines the systemic effects. These systems include: respiratory, 

cardiovascular, gastrointestinal, hematological, musculoskeletal, hepatic, renal, and dermal/ocular. 

“Other” refers to any systemic effect (e.g., a decrease in body weight) not covered in these 

systems. In the example of key number 18, 1 systemic effect (respiratory) was investigated. 

(8)	 NOAEL A No-Observed-Adverse-Effect Level (NOAEL) is the highest exposure level at which 

no harmful effects were seen in the organ system studied. Key number 18 reports a NOAEL of 

3 ppm for the respiratory system which was used to derive an intermediate exposure, inhalation 

MRL of 0.005 ppm (see footnote “b”). 

(9)	 LOAEL A Lowest-Observed-Adverse-Effect Level (LOAEL) is the lowest dose used in the 

study that caused a harmful health effect. LOAELs have been classified into “Less Serious” and 

“Serious” effects. These distinctions help readers identify the levels of exposure at which 

adverse health effects first appear and the gradation of effects with increasing dose. A brief 

description of the specific endpoint used to quantify the adverse effect accompanies the LOAEL. 

The respiratory effect reported in key number 18 (hyperplasia) is a Less serious LOAEL of 10 

ppm. MRLs are not derived from Serious LOAELs. 

(10)	 Reference The complete reference citation is given in chapter 8 of the profile. 
HYDRAZINES B-3 

APPENDIX B 

(11) CEL A Cancer Effect Level (CEL) is the lowest exposure level associated with the onset of 

carcinogenesis in experimental or epidemiologic studies. CELs are always considered serious 

effects. The LSE tables and figures do not contain NOAELs for cancer, but the text may report 

doses not causing measurable cancer increases. 

(12) Footnotes Explanations of abbreviations or reference notes for data in the LSE tables are found 

in the footnotes. Footnote “b” indicates the NOAEL of 3 ppm in key number 18 was used to 

derive an MRL of 0.005 ppm. 

LEGEND 

See Figure 2-l 

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 

neriods. 

(13) Exposure Period The same exposure periods appear as in the LSE table. In this example, health 

effects observed within the intermediate and chronic exposure periods are illustrated. 

(14)	 Health Effect These are the categories of health effects for which reliable quantitative data 

exists. The same health effects appear in the LSE table. 

(15)	 Levels of Exposure concentrations or doses for each health effect in the LSE tables are 

graphically displayed in the LSE figures. Exposure concentration or dose is measured on the log 

scale “y” axis. Inhalation exposure is reported in mg/m3 or ppm and oral exposure is reported in 

mg/kg/day. 

(16)	 NOAEL In this example, 1% NOAEL is the critical endpoint for which an intermediate 

inhalation exposure MRL is based. As you can see from the LSE figure key, the open-circle 

symbol indicates to a NOAEL for the test species-rat. The key number 18 corresponds to the 

entry in the LSE table. The dashed descending arrow indicates the extrapolation from the 

exposure level of 3 ppm (see entry 18 in the Table) to the MRL of 0.005 ppm (see footnote “b” 

in the LSE table). 

(17)	 CEL Key number 38r is 1 of 3 studies for which Cancer Effect Levels were derived. The 

diamond symbol refers to a Cancer Effect Level for the test species-mouse. The number 38 

corresponds to the entry in the LSE table. 

(18)	 Estimated Upper-Bound Human Cancer Risk Levels This is the range associated with the 

upper-bound for lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. These risk levels are 

derived from the EPA’s Human Health Assessment Group’s upper-bound estimates of the slope 

of the cancer dose response curve at low dose levels (ql*). 

(19) Key to LSE Figure The Key explains the abbreviations and symbols used in the figure. 


HYDRAZINES B-6 

APPENDIX B 

Chapter 2 (Section 2.5) 

Relevance to Public Health 

The Relevance to Public Health section provides a health effects summary based on evaluations of 

existing toxicologic, epidemiologic, and toxicokinetic information. This summary is designed to 

present interpretive, weight-of-evidence discussions for human health end points by addressing the 

following questions. 

1. What effects are known to occur in humans? 

2 . What effects observed in animals are likely to be of concern to humans? 

3 . What exposure conditions are likely to be of concern to humans, especially around hazardous 

waste sites? 

The section covers end points in the same order they appear within the Discussion of Health Effects
 

by Route of Exposure section, by route (inhalation, oral, dermal) and within route by effect. Human
 

data are presented first, then animal data. Both are organized by duration (acute, intermediate,
 

chronic). In vitro data and data from parenteral routes (intramuscular, intravenous, subcutaneous, etc.)
 

are also considered in this section. If data are located in the scientific literature, a table of
 

genotoxicity information is included.
 

The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using
 

existing toxicokinetic, genotoxic, and carcinogenic data. ATSDR does not currently assess cancer
 

potency or perform cancer risk assessments. Minimal risk levels (MRLs) for noncancer end points (if
 

derived) and the end points from which they were derived are indicated and discussed.
 

Limitations to existing scientific literature that prevent a satisfactory evaluation of the relevance to
 

public health are identified in the Data Needs section.
 

Interpretation of Minimal Risk Levels
 

Where sufficient toxicologic information is available, we have derived minimal risk levels (MRLs) for
 

inhalation and oral routes of entry at each duration of exposure (acute, intermediate, and chronic).
 

These MRLs are not meant to support regulatory action; but to acquaint health professionals with
 

exposure levels at which adverse health effects are not expected to occur in humans. They should
 

help physicians and public health officials determine the safety of a community living near a chemical
 

emission, given the concentration of a contaminant in air or the estimated daily dose in water. MRLs
 

are based largely on toxicological studies in animals and on reports of human occupational exposure.
 

MRL users should be familiar with the toxicologic information on which the number is based.
 

Chapter 2.5, “Relevance to Public Health,” contains basic information known about the substance.
 

Other sections such as 2.7, “Interactions with Other Substances,” and 2.8, “Populations that are
 

Unusually Susceptible” provide important supplemental information.
 

MRL users should also understand the MRL derivation methodology. MRLs are derived using a
 

modified version of the risk assessment methodology the Environmental Protection Agency (EPA)
 

provides (Barnes and Dourson 1988) to determine reference doses for lifetime exposure (RfDs).
 
HYDRAZINES B-7 

APPENDIX B
 

To derive an MRL, ATSDR generally selects the most sensitive endpoint which, in its best judgement, 

represents the most sensitive human health effect for a given exposure route and duration. ATSDR 

cannot make this judgement or derive an MRL unless information (quantitative or qualitative) is 

available for all potential systemic, neurological, and developmental effects. If this information and 

reliable quantitative data on the chosen endpoint are available, ATSDR derives an MRL using the 

most sensitive species (when information from multiple species is available) with the highest NOAEL 

that does not exceed any adverse effect levels. When a NOAEL is not available, a lowest-observedadverseeffect level (LOAEL) can be used to derive an MRL, and an uncertainty factor (UF) of 10 

must be employed. Additional uncertainty factors of 10 must be used both for human variability to 

protect sensitive subpopulations (people who are most susceptible to the health effects caused by the 

substance) and for interspecies variability (extrapolation from animals to humans). In deriving an 

MRL, these individual uncertainty factors are multiplied together. The product is then divided into the 

inhalation concentration or oral dosage selected from the study. Uncertainty factors used in 

developing a substance-specific MRL are provided in the footnotes of the LSE Tables.