f

Toxicological Profile for

1,2-Diphenylhydrazine

October 2020
1,2-DIPHENYLHYDRAZINE ii

DISCLAIMER

Use of trade names is for identification only and does not imply endorsement by the Agency for Toxic 

Substances and Disease Registry, the Public Health Service, or the U.S. Department of Health and Human 

Services.
1,2-DIPHENYLHYDRAZINE iii

FOREWORD

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

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

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

and republished as necessary.

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

information for these toxic substances described therein. Each peer-reviewed profile identifies and 

reviews the key literature that describes a substance's toxicologic properties. Other pertinent literature is 

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

exhaustive document; however, more comprehensive sources of specialty information are referenced.

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

begins with a relevance to public health discussion which would allow a public health professional to 

make a real-time determination of whether the presence of a particular substance in the environment 

poses a potential threat to human health. The adequacy of information to determine a substance's health 

effects is described in a health effects summary. Data needs that are of significance to the protection of 

public health are identified by ATSDR.

Each profile includes the following:

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

epidemiologic evaluations on a toxic substance to ascertain the levels of significant 

human exposure for the substance due to associated acute, intermediate, and chronic 

exposures;

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

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

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

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

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

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

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

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

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

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

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

this toxicological profile resides with ATSDR.

Patrick N. Breysse, Ph.D., CIH

Director, National Center for Environmental Health and

Agency for Toxic Substances and Disease Registry

Centers for Disease Control and Prevention

Christopher M. Reh, Ph.D.

Associate Director

Agency for Toxic Substances and Disease Registry

Centers for Disease Control and Prevention
1,2-DIPHENYLHYDRAZINE iv

*Legislative Background

The toxicological profiles are developed under the Comprehensive Environmental Response, 

Compensation, and Liability Act of 1980, as amended (CERCLA or Superfund). CERCLA section 

104(i)(1) directs the Administrator of ATSDR to “...effectuate and implement the health related 

authorities” of the statute. This includes the preparation of toxicological profiles for hazardous 

substances most commonly found at facilities on the CERCLA National Priorities List (NPL) and that 

pose the most significant potential threat to human health, as determined by ATSDR and the EPA. 

Section 104(i)(3) of CERCLA, as amended, directs the Administrator of ATSDR to prepare a 

toxicological profile for each substance on the list. In addition, ATSDR has the authority to prepare 

toxicological profiles for substances not found at sites on the NPL, in an effort to “...establish and 

maintain inventory of literature, research, and studies on the health effects of toxic substances” under 

CERCLA Section 104(i)(1)(B), to respond to requests for consultation under section 104(i)(4), and as 

otherwise necessary to support the site-specific response actions conducted by ATSDR.
1,2-DIPHENYLHYDRAZINE v

VERSION HISTORY

Date Description

October 2020 Final toxicological profile released

May 2019 Draft for public comment toxicological profile released

October 2009 Toxicological profile addendum 

December 1990 Final toxicological profile released
1,2-DIPHENYLHYDRAZINE vi

CONTRIBUTORS & REVIEWERS

CHEMICAL MANAGER TEAM

Sam Keith, M.S., C.H.P. Lisa Ingerman, Ph.D., D.A.B.T.

Jenny S. Chrisman, B.S.

Mario Citra, Ph.D.

Shelley Stevens, Ph.D.

ATSDR, Office of Innovation and Analytics, 

Toxicology Section, Atlanta, GA

SRC, Inc., North Syracuse, NY

REVIEWERS

Interagency Minimal Risk Level Workgroup: 

Includes ATSDR; National Center for Environmental Health (NCEH); National Institute for

Occupational Safety and Health (NIOSH); U.S. Environmental Protection Agency (EPA); National 

Toxicology Program (NTP).

Additional reviews for science and/or policy: 

ATSDR, Office of Community Health and Hazard Assessment; ATSDR, Office of Capacity 

Development and Applied Prevention Science; ATSDR, Office of Science; NCEH, Division of 

Laboratory Science; NCEH, Division of Environmental Health Science and Practice; EPA.

PEER REVIEWERS

1. Dr. Gisela de Aragão Umbuzeiro, Laboratório de Ecotoxicologia e Genotoxicidade LAEG, 

Faculdade de Tecnologia UNICAMP, Limeira Brazil

2. Cynthia Rider, Ph.D., General Toxicology and Cancer Group, Toxicologist, Durham, NC 

3. Robert A. Michaels; PhD, CEP, RAM TRAC Corporation, Schenectady, NY

These experts collectively have knowledge of toxicology, chemistry, and/or health effects. All reviewers 

were selected in conformity with Section 104(I)(13) of the Comprehensive Environmental Response, 

Compensation, and Liability Act, as amended.

ATSDR scientists review peer reviewers’ comments and determine whether changes will be made to the 

profile based on comments. The peer reviewers’ comments and responses to these comments are part of 

the administrative record for this compound.

The listing of peer reviewers should not be understood to imply their approval of the profile's final 

content. The responsibility for the content of this profile lies with ATSDR.
1,2-DIPHENYLHYDRAZINE vii

CONTENTS

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

FOREWORD...............................................................................................................................................iii

VERSION HISTORY...................................................................................................................................v

CONTRIBUTORS & REVIEWERS...........................................................................................................vi

CONTENTS................................................................................................................................................vii

LIST OF FIGURES .....................................................................................................................................ix

LIST OF TABLES........................................................................................................................................x

CHAPTER 1. RELEVANCE TO PUBLIC HEALTH ................................................................................1

1.1 OVERVIEW AND U.S. EXPOSURES .........................................................................................1

1.2 SUMMARY OF HEALTH EFFECTS...........................................................................................1

1.3 MINIMAL RISK LEVELS (MRLs) ..............................................................................................3

CHAPTER 2. HEALTH EFFECTS.............................................................................................................5

2.1 INTRODUCTION..........................................................................................................................5

2.2 DEATH ........................................................................................................................................18

2.3 BODY WEIGHT..........................................................................................................................18

2.4 RESPIRATORY...........................................................................................................................18

2.5 CARDIOVASCULAR .................................................................................................................19

2.6 GASTROINTESTINAL...............................................................................................................19

2.7 HEMATOLOGICAL ...................................................................................................................19

2.8 MUSCULOSKELETAL ..............................................................................................................19

2.9 HEPATIC.....................................................................................................................................19

2.10 RENAL.....................................................................................................................................20

2.11 DERMAL .................................................................................................................................20

2.12 OCULAR..................................................................................................................................21

2.13 ENDOCRINE ...........................................................................................................................21

2.13 IMMUNOLOGICAL................................................................................................................21

2.15 NEUROLOGICAL...................................................................................................................21

2.16 REPRODUCTIVE....................................................................................................................21

2.17 DEVELOPMENTAL................................................................................................................21

2.18 OTHER NONCANCER ...........................................................................................................22

2.19 CANCER..................................................................................................................................22

2.20 GENOTOXICITY ....................................................................................................................23

CHAPTER 3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL 

INTERACTIONS...............................................................................................................25

3.1 TOXICOKINETICS.....................................................................................................................25

3.1.1 Absorption.............................................................................................................................25

3.1.2 Distribution ...........................................................................................................................25

3.1.3 Metabolism............................................................................................................................26

3.1.4 Excretion ...............................................................................................................................26

3.1.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models.............28

3.1.6 Animal-to-Human Extrapolations.........................................................................................28

3.2 CHILDREN AND OTHER POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE.....28

3.3 BIOMARKERS OF EXPOSURE AND EFFECT .......................................................................29

3.3.1 Biomarkers of Exposure........................................................................................................30

3.3.2 Biomarkers of Effect.............................................................................................................30

3.4 INTERACTIONS WITH OTHER CHEMICALS .......................................................................30
1,2-DIPHENYLHYDRAZINE viii

CHAPTER 4. CHEMICAL AND PHYSICAL INFORMATION ............................................................ 31

4.1 CHEMICAL IDENTITY .............................................................................................................. 31

4.2 PHYSICAL AND CHEMICAL PROPERTIES ........................................................................... 31

CHAPTER 5. POTENTIAL FOR HUMAN EXPOSURE ........................................................................ 33

5.1 OVERVIEW ................................................................................................................................. 33

5.2 PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL .................................................. 34

5.2.1 Production ............................................................................................................................. 34

5.2.2 Import/Export ........................................................................................................................ 34

5.2.3 Use ........................................................................................................................................ 35

5.2.4 Disposal ................................................................................................................................. 35

5.3 RELEASES TO THE ENVIRONMENT ..................................................................................... 35

5.3.1 Air ......................................................................................................................................... 36

5.3.2 Water ..................................................................................................................................... 37

5.3.3 Soil ........................................................................................................................................ 37

5.4 ENVIRONMENTAL FATE ........................................................................................................ 37

5.4.1 Transport and Partitioning ..................................................................................................... 37

5.4.2 Transformation and Degradation .......................................................................................... 38

5.5 LEVELS IN THE ENVIRONMENT ........................................................................................... 39

5.5.1 Air ......................................................................................................................................... 40

5.5.2 Water ..................................................................................................................................... 40

5.5.3 Sediment and Soil ................................................................................................................. 41

5.5.4 Other Media .......................................................................................................................... 41

5.6 GENERAL POPULATION EXPOSURE .................................................................................... 42

5.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES ................................................ 42

CHAPTER 6. ADEQUACY OF THE DATABASE ................................................................................. 43

6.1 INFORMATION ON HEALTH EFFECTS ................................................................................. 43

6.2 IDENTIFICATION OF DATA NEEDS ...................................................................................... 43

6.3 ONGOING STUDIES .................................................................................................................. 49

CHAPTER 7. REGULATIONS AND GUIDELINES .............................................................................. 50

CHAPTER 8. REFERENCES ................................................................................................................... 52

APPENDICES

APPENDIX A. ATSDR MINIMAL RISK LEVEL WORKSHEETS .................................................... A-1 

APPENDIX B. LITERATURE SEARCH FRAMEWORK FOR 1,2-DIPHENYLHYDRAZINE ......... B-1 

APPENDIX C. FRAMEWORK FOR ATSDR’S SYSTEMATIC REVIEW OF HEALTH EFFECTS 

DATA FOR 1,2-DIPHENYLHYDRAZINE .................................................................. C-1 

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

APPENDIX E. QUICK REFERENCE FOR HEALTH CARE PROVIDERS ....................................... E-1 

APPENDIX F. GLOSSARY .................................................................................................................... F-1 

APPENDIX G. ACRONYMS, ABBREVIATIONS, AND SYMBOLS ................................................. G-1 
1,2-DIPHENYLHYDRAZINE ix

LIST OF FIGURES

1-1. Health Effects Found in Animals Following Oral Exposure to 1,2-Diphenylhydrazine......................2

1-2. Summary of Sensitive Targets of 1,2-Diphenylhydrazine – Oral.........................................................3

2-1. Overview of the Number of Studies Examining 1,2-Diphenylhydrazine Health Effects.....................8

2-2. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral......................................................14

3-1. Metabolic Scheme of 1,2-Diphenylhydrazine ....................................................................................27

5-1. Number of NPL Sites with 1,2-Diphenylhydrazine Contamination...................................................33

6-1. Summary of Existing Health Effects Studies on 1,2-Diphenylhydrazine By Route and Endpoint....44
1,2-DIPHENYLHYDRAZINE x

LIST OF TABLES

1-1. Minimal Risk Levels (MRLs) for 1,2-Diphenylhydrazine ...................................................................4

2-1. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral........................................................9

2-2. Genotoxicity of 1,2-Diphenylhydrazine In Vitro................................................................................24

2-3. Genotoxicity of 1,2-Diphenylhydrazine In Vivo.................................................................................24

4-1. Chemical Identity of 1,2-Diphenylhydrazine .....................................................................................31

4-2. Physical and Chemical Properties of 1,2-Diphenylhydrazine ............................................................32

5-1. Facilities that Produce, Process, or Use 1,2-Diphenylhydrazine........................................................34

5-2. Releases to the Environment from Facilities that Produce, Process, or Use 1,2-Diphenylhydrazine ............................................................................................................................................36

5-3. 1,2-Diphenylhydrazine Levels in Water, Soil, and Air of National Priorities List (NPL) Sites.........40

5-4. 1,2-Diphenylhydrazine Detected in Samples Collected Throughout the United States from 

1990 to 2020.......................................................................................................................................40

7-1. Regulations and Guidelines Applicable to 1,2-Diphenylhydrazine....................................................50
1,2-DIPHENYLHYDRAZINE 1 

CHAPTER 1. RELEVANCE TO PUBLIC HEALTH 

1.1 OVERVIEW AND U.S. EXPOSURES

1,2-Diphenylhydrazine (Chemical Abstracts Service [CAS] number 122-66-7; hydrazobenzene is a 

common synonym) is a colorless, crystalline solid previously used as an intermediate in dye 

manufacturing (e.g., benzidine) and an intermediate in some pharmaceuticals. It rapidly oxidizes in water 

with a half-life of approximately 15 minutes. The general population is not likely to be exposed to 

1,2-diphenylhydrazine in the environment; exposure may occur in workers involved in the manufacture or 

use of 1,2-diphenylhydrazine. 

1.2 SUMMARY OF HEALTH EFFECTS 

Information on the toxicity of 1,2-diphenylhydrazene is derived from a small number of health effect 

studies. No epidemiology or human exposure studies are available, and data are restricted to a few oral 

studies in laboratory animals. In addition to lethality and body weight changes, these studies evaluated 

primarily hepatic, non-neoplastic, and cancer endpoints. As illustrated in Figure 1-1, the most sensitive 

effects appear to be in the liver, lungs, and gastrointestinal tract, and cancer. A systematic review of the 

noncancer endpoints resulted in the following hazard identification conclusions:

• Hepatic effects are a presumed health effect for humans. 

• The data are inadequate to conclude whether respiratory effects will occur in humans. 

• The data are inadequate to conclude whether gastrointestinal effects will occur in humans. 

Hepatic Effects. Liver toxicity is considered a critical effect of 1,2-diphenylhydrazine exposure. 

Intermediate exposures in rats resulted in mild increases in liver weight, hypertrophy, multifocal 

macrovesiculation, and bile duct duplication (Dodd et al. 2012). Chronic oral administration of 

1,2-diphenylhydrazine produced degenerative alterations in the liver of rats (fatty metamorphosis) and 

female mice (coagulative necrosis), as well as hepatocellular carcinomas in male rats and female mice and 

neoplastic nodules in female rats (NCI 1978).

Other Nonneoplastic Effects. Interstitial inflammation of the lungs was observed in rats after chronic 

oral exposure to 1,2-diphenylhydrazine (NCI 1978), but not in similarly exposed mice. Gross 

pathological examinations conducted in a 4-week oral study (NCI 1978) reported intestinal hemorrhages 
1,2-DIPHENYLHYDRAZINE 2 

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-1. Health Effects Found in Animals Following Oral Exposure to 

1,2-Diphenylhydrazine
1,2-DIPHENYLHYDRAZINE 3 

1. RELEVANCE TO PUBLIC HEALTH

in mice exposed to 390 mg/kg/day. In the chronic-duration study conducted by NCI (1978), 

histopathological analysis identified stomach hyperkeratosis and acanthosis in rats following dietary 

exposure. Potential respiratory and gastrointestinal effects were not examined in other studies. 

Cancer Effects. The carcinogenic potential of 1,2-diphenylhydrazine has been evaluated in rats and mice 

exposed to 1,2-diphenylhydrazine in the diet for 78 weeks (NCI, 1978). The tumor sites for 

1,2-diphenylhydrazine include the liver (hepatocellular carcinoma and neoplastic nodules) in male and 

female rats and female mice, mammary gland (adenocarcinomas) in female rats, and Zymbal’s gland/ear 

canal/skin of ear (squamous cell carcinoma or papilloma) in male rats (NCI 1978). 

The Department of Health and Human Services (NTP 2016) has identified 1,2-diphenylhydrazine as 

reasonably anticipated to be a human carcinogen on the basis of sufficient evidence of carcinogenicity in 

experimental animals. EPA (IRIS 2006) classified it as a probable human carcinogen (Group B2). 

1.3 MINIMAL RISK LEVELS (MRLs)

Due to absence of inhalation studies, derivation of inhalation MRLs was not feasible. As presented in 

Figure 1-2, the limited available data for 1,2-diphenylhydrazine have identified the liver, lungs, and 

gastrointestinal tract as sensitive targets. The oral database was considered adequate for derivation of an 

intermediate-duration MRL for 1,2-diphenyhydrazine. The MRL value is summarized in Table 1-1 and 

discussed in greater detail in Appendix A. 

Figure 1-2. Summary of Sensitive Targets of 1,2-Diphenylhydrazine – Oral 

The liver, lungs, and gastrointestinal tract are the most sensitive targets of 1,2-diphenylhydrazine. 

Numbers in circles are the lowest LOAELs for all health effects in animals; no human data were identified. 
1,2-DIPHENYLHYDRAZINE 4 

1. RELEVANCE TO PUBLIC HEALTH

Table 1-1. Minimal Risk Levels (MRLs) for 1,2-Diphenylhydrazinea

Exposure 

duration MRL Critical effect

Point of 

departure

Uncertainty 

factor Reference

Inhalation exposure (ppm)

Acute Insufficient data for MRL derivation

Intermediate Insufficient data for MRL derivation

Chronic Insufficient data for MRL derivation

Oral exposure (mg/kg/day)

Acute Insufficient data for MRL derivation

Intermediate 0.05 Liver hypertrophy, 

eosinophilic granular 

cytoplasm, and bile 

duct duplication

NOAEL = 4.80 100 Dodd et al. 

2012

Chronic Insufficient data for MRL derivation

aSee Appendix A for additional information. 

NOAEL = no-observed-adverse-effect level
1,2-DIPHENYLHYDRAZINE 5 

CHAPTER 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 1,2-diphenylhydrazine. 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. When available, mechanisms of action are discussed along with the health effects 

data; toxicokinetic mechanistic data are discussed in Section 3.1. 

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

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 by health effect. These data are discussed in terms of 

route of exposure (inhalation, oral, and dermal) and three exposure periods: acute (≤14 days), intermediate 

(15–364 days), and chronic (≥365 days).

As discussed in Appendix B, a literature search was conducted to identify relevant studies examining health 

effect endpoints. Figure 2-1 provides an overview of the database of studies in humans or experimental 

animals included in this chapter of the profile. These studies evaluate the potential health effects associated 

with inhalation, oral, or dermal exposure to 1,2-diphenylhydrazine, but may not be inclusive of the entire 

body of literature. A systematic review of the scientific evidence of the health effects associated with 

exposure to 1,2-diphenylhydrazine was also conducted; the results of this review are presented in 

Appendix C.

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

figures. Animal oral studies are presented in Table 2-1 and Figure 2-2; no reliable inhalation or dermal 

data were identified for 1,2-diphenylhydrazine. 

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

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

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

"Less serious" effects are those that are not expected to cause significant dysfunction or death, or those 
1,2-DIPHENYLHYDRAZINE 6 

2. HEALTH EFFECTS

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

amount of judgment may be required in establishing whether an endpoint 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 endpoints. 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. Levels of exposure associated with cancer (Cancer Effect Levels, CELs) of 1,2-diphenylhydrazine are indicated in Table 2-1 and Figure 2-2. 

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

the interpretation of the tables and figures for LSEs and MRLs.

As illustrated in Figure 2-1, there are limited data on the toxicity of 1,2-diphenylhydrazine. No human 

studies were identified, and data from laboratory animal studies primarily come from a small number of 

oral studies. Nine studies published in three papers have examined the toxicity and carcinogenicity 

following oral exposure. Two additional oral studies only examined lethality and one study assessed 

carcinogenicity following dermal exposure. A chronic study in rats and mice was the only study 

examining a wide range of potential endpoints; other studies have focused on liver or body weight effects. 

No studies were located that evaluated possible effects on immunological, reproductive, or developmental 

function. Based on these data, the available studies suggest the following targets of toxicity: 

• Hepatic endpoint: Hepatic effects are a presumed health effect for humans based on evidence 

from intermediate and chronic oral studies in rats and mice. Liver hypertrophy, bile duct 

duplication, and macrovesiculation was observed in rats after 13 weeks of dietary exposure; no 

alterations were observed after shorter exposure durations. After chronic exposure, fatty 

metamorphosis and coagulative necrosis were observed in rats and mice, respectively. 

• Cancer endpoint: Increases in the incidences of neoplastic lesions in the liver, mammary gland, 

and Zymbal’s gland/ear canal/skin of ear were observed in chronically exposed rats. In mice, 

liver tumors were observed in females only.

• Gastrointestinal endpoint: Data are inadequate to conclude whether gastrointestinal effects will 

occur in humans. Inconsistent results have been observed in oral exposure animal studies. 

Intestinal hemorrhage was noted in mice exposed to 1,2-diphenylhydrazine in the diet for 4 weeks 
1,2-DIPHENYLHYDRAZINE 7 

2. HEALTH EFFECTS

and stomach hyperkeratosis and/or acanthosis were observed in rats chronically exposed to 

1,2-diphenylhydrazine in the diet. 

• Respiratory endpoint: Data are inadequate to conclude whether respiratory effects will occur in 

humans. Inconsistent results have been observed in oral exposure animal studies. Interstitial 

inflammation of the lungs was noted in rats chronically exposed to 1,2-diphenylhydrazine in the 

diet.
1,2-DIPHENYLHYDRAZINE 8 

2. HEALTH EFFECTS

Figure 2-1. Overview of the Number of Studies Examining 1,2-Diphenylhydrazine Health Effects 

Body weight, hepatic, gastrointestinal, and cancer effects of 1,2-diphenylhydrazine were the most widely examined potential toxicity 

outcomes

The majority of the studies examined oral exposure in animals; no data were identified for humans (counts represent studies examining endpoint)

 

*Includes studies discussed in Chapter 2. A total of 10 studies (including those finding no effect) have examined toxicity; most animal studies examined multiple 

endpoints. 
1,2-DIPHENYLHYDRAZINE 9 

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Figure 

keya

Species 

(strain)

No./group

Exposure 

parameters

Doses

(mg/kg/day)

Parameters 

monitored Endpoint

NOAEL 

(mg/kg/day)

Less 

serious 

LOAEL 

(mg/kg/day)

Serious 

LOAEL 

(mg/kg/day) Effect

ACUTE EXPOSURE

1 Rat

(Fischer 

344)

10 M 

5 days 

(F)

0, 0.32, 

1.26, 4.80, 

10.3, 15.5

CS, BC, 

BW, HP, 

OW, FI, GN

Bd wt 15.5

Hepatic 15.5 Slight decrease (13%) in alkaline 

phosphatase at 15.5 mg/kg/day 

was not considered biologically 

relevant; no alterations in hepatic 

serum enzymes or liver 

histopathology 

Dodd et al. 2012

2 Rat

(Fischer 

344)

10 M 

2 weeks

(F)

0, 0.32, 

1.26, 4.80, 

10.3, 15.5

CS, BC, 

BW, HP, 

OW, FI, GN

Bd wt 15.5

Hepatic 15.5 Slight decrease (12%) in alkaline 

phosphatase at 15.5 mg/kg/day 

was not considered biologically 

relevant; no other alterations in 

hepatic serum enzymes or liver 

histopathology 

Dodd et al. 2012

3 Rat 

(SpragueDawley)

6–10 F 

2 exposures

21 and 4 

hours prior 

to sacrifice

(G)

0, 60, 180 LE, BC, EA Death No increases in mortality

Kitchin et al. 1992

4 Rat Once

(GW)

959 LE Death 959 LD50

Marhold et al. 1968
1,2-DIPHENYLHYRAZINE 10

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Figure 

keya

Species 

(strain)

No./group

Exposure 

parameters

Doses

(mg/kg/day)

Parameters 

monitored Endpoint

NOAEL 

(mg/kg/day)

Less 

serious 

LOAEL 

(mg/kg/day)

Serious 

LOAEL 

(mg/kg/day) Effect

INTERMEDIATE EXPOSURE

5 Rat

(Fischer 

344)

10 M 

4 weeks

(F)

0, 0.32, 

1.26, 4.80, 

10.3, 15.5

CS, BC, 

BW, HP, 

OW, FI, GN

Bd wt 15.5

Hepatic 15.5 13% and 26% reductions in serum 

alkaline phosphatase and 

aspartate aminotransferase, 

respectively, at 15.5 mg/kg/day 

were not considered biologically 

relevant; no alterations in liver 

histopathology 

Dodd et al. 2012

6 Rat

(Fischer 

344)

10 M 

13 weeks

(F)

0, 0.32, 

1.26, 4.80, 

10.3, 15.5

CS, BC, 

BW, HP, 

OW, FI, GN

Bd wt 15.5

Hepatic 4.80b 10.3 Slight to mild hypertrophy, minimal 

eosinophilic granular cytoplasm, 

minimal to slight multifocal bile 

duct duplication, and slight to mild 

multifocal macrovesiculation at 

≥10.3 mg/kg/day. Reduction in 

serum alkaline phosphatase 

(19.7%) and aspartate 

aminotransferase (26%) at 

15.5 mg/kg/day; no other 

alterations in hepatic serum 

enzymes

Dodd et al. 2012

7 Rat 288 days

(F)

0, 19 BW Bd wt 19

Marhold et al. 1968
1,2-DIPHENYLHYRAZINE 11

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Figure 

keya

Species 

(strain)

No./group

Exposure 

parameters

Doses

(mg/kg/day)

Parameters 

monitored Endpoint

NOAEL 

(mg/kg/day)

Less 

serious 

LOAEL 

(mg/kg/day)

Serious 

LOAEL 

(mg/kg/day) Effect

8 Rat 

(Fischer 

344)

5 M, 5 F 

4 weeks

(F)

M: 0, 3.5, 7, 

14, 27, 54, 

107, 150, 

211

F: 0, 0.04, 

0.15, 0.55, 

1, 2, 7.5, 52, 

365, 2,600

CS, BW, 

GN

Death 54 M

365 F

2/5 males died at 54 mg/kg/day; 

100% mortality at higher doses

Bd wt 211 M

2,600 F 

NCI 1978

9 Mouse

(B6C3F1)

5 M, 5 F

4 weeks

(F)

M: 0, 9.1, 

18, 36, 71, 

140, 280, 

391, 550; F: 

0, 0.39, 

1.04, 1.4, 

2.6, 5.2, 19, 

135, 950, 

6,700

CS, BW, 

GN

Death 391 M

950 F 

1/5 males and 4/5 females died

Bd wt 550 M

6,700 F

Gastro 391 M

950 F 

Intestinal hemorrhage

NCI 1978

CHRONIC EXPOSURE

10 Rat 

(Fischer 

344

50 M, 

50 F 

78 weeks

followed by 

28–30-week 

recovery

(F)

M: 0, 6.3, 24 

F: 0, 3.7, 

9.2

BW, GN, 

HP, CS

Death 9.2 F Increased mortality

Bd wt 6.3 M

3.7 F

24 M

9.2 F

Decreased body weight gain

Resp 6.3 M Interstitial inflammation of the lung 

in males at ≥6.3 mg/kg/day and 

females at 3.7 mg/kg/day but not 

at 9.2 mg/kg/day

Cardio 9.2 F

24 M

Gastro 6.3 M 24 M

3.7 F 

Hyperkeratosis and acanthosis of 

stomach in males at 24 mg/kg/day 

and acanthosis of the stomach in 

females at 3.7 mg/kg/day, but not 

at 9.2 mg/kg/day
1,2-DIPHENYLHYRAZINE 12

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Figure 

keya

Species 

(strain)

No./group

Exposure 

parameters

Doses

(mg/kg/day)

Parameters 

monitored Endpoint

NOAEL 

(mg/kg/day)

Less 

serious 

LOAEL 

(mg/kg/day)

Serious 

LOAEL 

(mg/kg/day) Effect

Musc/skel 9.2 F

24 M

Hepatic 6.3 M

3.7 F 

24 M

9.2 F 

Fatty metamorphosis in females at 

9.2 mg/kg/day and males at 

24 mg/kg/day

Renal 9.2 F

24 M

Dermal 9.2 F

24 M

Ocular 9.2 F

24 M

Endocr 9.2 F

24 M

Immuno 9.2 F

24 M

No histological alterations in 

immunological organs

Neuro 9.2 F

24 M

No histological alterations in the 

brain

Repro 9.2 F

24 M

No histological alterations in 

reproductive organs

Cancer 6.3 M

9.2 F 

CEL: hepatocellular carcinoma at 

≥6.3 mg/kg/day in males only. 

Adrenal pheochromocytoma; 

squamous cell carcinoma in 

Zymbal’s gland; and squamous 

cell carcinoma or papilloma in the 

ear canal, Zymbal’s gland, and 

skin of the ear were observed in 

males at 24 mg/kg/day. In 

females, increases in liver 

neoplastic nodules and mammary 

gland adenocarcinomas were 

observed at 9.2 mg/kg/day.

NCI 1978
1,2-DIPHENYLHYRAZINE 13

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Figure 

keya

Species 

(strain)

No./group

Exposure 

parameters

Doses

(mg/kg/day)

Parameters 

monitored Endpoint

NOAEL 

(mg/kg/day)

Less 

serious 

LOAEL 

(mg/kg/day)

Serious 

LOAEL 

(mg/kg/day) Effect

11 Mouse

(B6C3F1)

50 M, 

50 F 

78 weeks

followed by 

28–30-week 

recovery

(F)

M: 0, 14, 69 

F: 0, 6.9, 69

LE, HP Death 69 Increased mortality

Bd wt 14 M

6.9 F

69 M,F Decreased body weight gain

(36%)

Resp 69

Cardio 69

Gastro 69

Musc/skel 69

Hepatic 6.9 F 69 F Coagulative necrosis

Renal 69

Dermal 69

Ocular 69

Endocr 69

Immuno 69 No histological alterations in 

immunological organs

Neuro 69 No histological alterations in the 

brain

Repro 69 No histological alterations in 

reproductive organs

Cancer 69 F CEL: hepatocellular carcinoma in 

females

NCI 1978

aThe number corresponds to entries in Figure 2-2; differences in levels of health effects and cancer effects between male and females are not indicated in 

Figure 2-2. Where such differences exist, only the levels of effect for the most sensitive gender are presented. bUsed to derive an intermediate-duration oral MRL of 0.05 mg/kg/day based on a NOAEL of 4.80 mg/kg/day and an uncertainty factor of 100 (10 for extrapolation 

from animals to humans and 10 for human variability)

BC = biochemistry; Bd wt or BW = body weight; Cardio = cardiovascular; CEL = cancer effect level; CS = clinical signs; EA = enzyme activity; Endocr = endocrine; 

(F) = feed; F = female(s); FI = food intake; (G) = gavage; Gastro = gastrointestinal; GN = gross necropsy; HP = histopathology; immuno = immunological; 

LD50 = lethal dose, 50% mortality; LE = lethality; LOAEL = lowest-observed-adverse-effect level; M = male(s); Musc/skel = musculoskeletal; Neuro = neurological; 

NOAEL = no-observed-adverse-effect level; OW = organ weight; Repro = reproductive; Resp = respiratory 

Highlighted rows indicate MRL principal study.
1,2-DIPHENYLHYRAZINE 14

2. HEALTH EFFECTS

Figure 2-2. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Acute (≤14 days)
1,2-DIPHENYLHYRAZINE 15

2. HEALTH EFFECTS

Figure 2-2. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Intermediate (15-364 days) 
1,2-DIPHENYLHYRAZINE 16

2. HEALTH EFFECTS

Figure 2-2. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Chronic (≥365 days)
1,2-DIPHENYLHYRAZINE 17

2. HEALTH EFFECTS

Figure 2-2. Levels of Significant Exposure to 1,2-Diphenylhydrazine – Oral

Chronic (≥365 days)
1,2-DIPHENYLHYDRAZINE 18

2. HEALTH EFFECTS

2.2 DEATH

Limited information is available regarding the lethality of orally administered 1,2-diphenylhydrazine in 

animals. An incompletely documented acute LD50 of 959 mg/kg in rats (Marhold et al. 1968) and an 

unreliable acute lethal dose 1,213 mg/kg/day in wild deer mice (Schafer and Bowles 1985) have been 

reported. Interpretation of the results of the Schafer and Bowles (1985) study is limited by the method 

used to measure dose (estimated from the number of 1,2-diphenylhydrazine-treated seeds consumed) and 

the lack of information on the actual number of deaths was not reported. No deaths were observed in rats 

administered two gavage doses of 180 mg/kg (sacrificed within 21 hours of last dose) (Kitchin et al. 

1992) or rats exposed to 15.5 mg/kg/day in the diet for 5 days or 2 weeks (Dodd et al. 2012).

In repeated exposure studies, deaths were observed in rats and mice exposed to 54 or 390 mg/kg/day, 

respectively, for 4 weeks (NCI 1978). In another study, no deaths were observed in rats fed up to 

15.5 mg/kg/day 1,2-diphenylhydrazine for 4 weeks or 13 weeks (Dodd et al. 2012). In a chronic dietary 

study, increases in mortality were observed in female rats exposed to 9.2 mg/kg/day and male and female 

mice exposed to 69 mg/kg/day (NCI 1978).

2.3 BODY WEIGHT

Chronic (NCI 1978), but not acute (Dodd et al. 2012) or intermediate (Dodd et al. 2012; Marhold et al. 

1968; NCI 1978) oral exposure to 1,2-diphenylhydrazine led to significant alterations in body weight in 

laboratory animals. Male rats treated with 1,2-diphenylhydrazine in the diet at a dose of 24 mg/kg/day for 

78 weeks had approximately l0–15% decreased body weight gain (NCI 1978); food consumption data 

were not reported. Decreased weight gain (approximately 36% at termination of the study) was observed 

in male and female mice exposed to 69 mg/kg/day in the diet for 78 weeks (NCI 1978).

2.4 RESPIRATORY

Respiratory effects occurred in rats after chronic exposure to 1,2-diphenylhydrazine in the diet for 

78 weeks (NCI 1978); the incidences of interstitial inflammation of the lungs were significantly increased 

in male rats exposed to 6.3 or 24 mg/kg/day and in females at 3.7 mg/kg/day, but not at 9.2 mg/kg/day

(NCI 1978). 
1,2-DIPHENYLHYDRAZINE 19

2. HEALTH EFFECTS

2.5 CARDIOVASCULAR

No histological alterations were observed in rats or mice chronically exposed to doses as high as 

24/9.2 (males/females) or 69 mg/kg/day, respectively (NCI 1978). 

2.6 GASTROINTESTINAL

Intestinal hemorrhages were noted in mice exposed to lethal doses (≥390 mg/kg/day) for 4 weeks (NCI 

1978). The severity and incidences of the hemorrhage were not described. Statistically increased 

incidences of hyperkeratosis and acanthosis in the stomach occurred in male rats at 24 mg/kg/day and 

acanthosis was observed in female rats at 3.7 mg/kg/day 1,2-diphenylhydrazine in the diet for 78 weeks 

(NCI 1978); the incidence in female rats administered 9.2 mg/kg/day (11%) was not significantly 

different from concurrent controls (4%). No gastrointestinal lesions were observed in mice treated with 

doses up to 69 mg/kg/day (NCI 1978). 

2.7 HEMATOLOGICAL

No studies were located that evaluate hematological effects in animals following exposure to 

1,2-diphenylhydrazine by inhalation, oral, or dermal routes. In a single study, intravenous injection of an 

18.4 mg/kg dose of 1,2-diphenylhydrazine did not cause methemoglobinemia in rats, although 

methemoglobin was formed by an equimolar dose of aniline (Pfordte 1973).

2.8 MUSCULOSKELETAL

No histopathological alterations were observed in the musculoskeletal system of rats or mice exposed to 

9.2/24 or 69 mg/kg/day, respectively, in the diet for 78 weeks (NCI 1978). 

2.9 HEPATIC

Some hepatic alterations have been observed in male rats exposed to ≤15.5 mg/kg/day 

1,2-diphenylhydrazine in the diet for 5 days or 2 weeks (Dodd et al. 2012). The alterations consisted of 

<10% statistically significant increases in relative liver weight at 15.5 mg/kg/day for 5 days or 

≥4.80 mg/kg/day for 2 weeks and decreases in serum alkaline phosphatase levels (<15%) at 

15.5 mg/kg/day for 5 days or 10.3 mg/kg/day for 2 weeks. There were no changes in serum alanine 

aminotransferase, aspartate aminotransferase, total bilirubin, or lactate dehydrogenase levels, and no 

histopathological changes were observed following acute exposure. In the absence of histological 
1,2-DIPHENYLHYDRAZINE 20

2. HEALTH EFFECTS

alterations, the slight changes in relative liver weight and serum alkaline phosphatase levels were not 

considered toxicologically relevant. Rats treated by gavage at 21 and 4 hours prior to sacrifice with 60 or 

180 mg/kg had no alterations in alanine aminotransferase (Kitchin et al. 1992). 

Exposure via the diet to 10.3 or 15.5 mg/kg/day for 13 weeks resulted in increases in the incidences of 

slight/mild hypertrophy, eosinophilic granular cytoplasm, and multifocal bile duct duplication; multifocal 

macrovesiculation was also observed at 15.5 mg/kg/day (Dodd et al. 2012). However, no histological 

alterations were observed in rats exposed to up to 15.5 mg/kg/day for 4 weeks (Dodd et al. 2012). 

Decreases in alkaline phosphatase (7–13%) and aspartate aminotransferase (17–26%) were also noted at 

15.5 mg/kg/day in rats exposed for 4 or 13 weeks. 

Chronic exposure resulted in histological alterations in rats and mice exposed to 1,2-diphenylhydrazine in 

the diet for 78 weeks (NCI 1978). In rats, the lesions included increased fatty metamorphosis of the liver 

in male and female rats at 24 and 9.2 mg/kg/day, respectively. However, the increased incidence in 

9.2 mg/kg/day female rats was only statistically significantly when compared to the low-dose control 

group due to the high incidence observed in the high-dose control group (12% in the high-dose controls 

compared to 4% in the low-dose controls). Coagulative necrosis was observed in female mice at 

69 mg/kg/day, but was not observed in male mice. Other liver alterations were noted in the NCI (1978) 

chronic rat and mouse study, but the incidences were not dose-related. 

Current hypotheses relating to the hepatic effects of 1,2-diphenylhydrazine exposure in animals include 

possible contributions of cytochrome P450 induction to the development of hepatic hypertrophy; the 

involvement of peroxisome proliferation in developing eosinophilic granular cytoplasm; aberrant lipid 

metabolism or transport contributing to hepatocyte cytoplasm macrovesiculation; and epithelial cell injury 

or hepatic necrosis that could have induced biliary duct duplication (Dodd et al. 2012). 

2.10 RENAL

No significant histological alterations in the kidney were observed in rats or mice chronically treated for 

78 weeks with up to 24/9.2 (males/females) or 69 mg/kg/day, respectively (NCI 1978). 

2.11 DERMAL

No significant histological alterations in the skin were observed in rats or mice chronically exposed to

24/9.2 or 69 mg/kg/day, respectively (NCI 1978). 
1,2-DIPHENYLHYDRAZINE 21

2. HEALTH EFFECTS

2.12 OCULAR 

No significant histological alterations in ocular tissues were observed in rats exposed to 24/9.2 mg/kg/day 

or mice exposed to 69 mg/kg/day 1,2-diphenylhydrazine in the diet for 78 weeks (NCI 1978). 

2.13 ENDOCRINE

No non-cancerous histological alterations were observed in the adrenal or thyroid glands of rats or mice 

chronically exposed to doses as high as 24/9.2 or 69 mg/kg/day 1,2-diphenylhydrazine, respectively, in 

the diet for 78 weeks (NCI 1978). 

2.13 IMMUNOLOGICAL 

No studies examined immune function following exposure to 1,2-diphenylhydrazine. Chronic exposure 

in the diet of rats or mice to 24/9.2 or 69 mg/kg/day, respectively, did not result in histological alterations 

in the bone marrow, spleen, or lymph nodes (NCI 1978). 

2.15 NEUROLOGICAL

Rats and mice chronically treated with 1,2-diphenylhydrazine in the diet did not show symptoms of 

toxicity or histological alterations in the brain (NCI 1978), but no behavioral or neurological evaluations 

were conducted. 

2.16 REPRODUCTIVE

Reproductive function has not been evaluated in laboratory animals. The NCI (1978) chronic study of 

rats exposed to 24 mg/kg/day (males) or 9.2 mg/kg/day (females) and of mice exposed to 69 mg/kg/day 

(males and females) did not find histological alterations in the reproductive tissues. 

2.17 DEVELOPMENTAL

No studies were located regarding developmental effects of 1,2-diphenylhydrazine in humans or animals 

by any route of exposure. 
1,2-DIPHENYLHYDRAZINE 22

2. HEALTH EFFECTS

2.18 OTHER NONCANCER

No studies examining other noncancer effects were identified.

2.19 CANCER

The carcinogenicity of 1,2-diphenylhydrazine has been investigated in oral, dermal, and parenteral studies 

in laboratory animals. Treatment-related neoplasms occurred in rats and mice that were treated with low 

or high doses of 1,2-diphenylhydrazine in the diet for 78 weeks, followed by untreated observation 

periods of 28 or 30 weeks (rats) and 17 or 18 weeks (mice) (NCI 1978); tumor incidences were calculated 

as combined incidences for animals dying early, sacrificed at 78 weeks, or at the end of the observation 

period. Male rats had statistically significant increased incidences of hepatocellular carcinomas and/or 

neoplastic nodules in the liver at 6.3 and 24 mg/kg/day. At 24 mg/kg/day, there were squamous-cell 

carcinomas of the Zymbal's gland and squamous cell carcinomas or papillomas of the ear canal, Zymbal’s 

gland, and skin of the ear (combined incidences). The incidence of adrenal pheochromocytomas or 

malignant pheochromocytomas was significantly higher in the 24 mg/kg/day male rats (p=0.042 for the 

Fisher exact test), as compared to controls; however, the result was not significant under the Bonferroni 

criteria. Incidences of liver neoplastic nodules and mammary gland adenocarcinomas were increased 

significantly in female rats treated with 6.3 mg/kg/day, but not 3.7 mg/kg/day. A significantly increased 

incidence of hepatocellular carcinoma occurred in female mice treated with 69 mg/kg/day, but not 

6.9 mg/kg/day. Doses of 14 or 69 mg/kg/day were not neoplastic for male mice. ATSDR notes that the 

nomenclature for classifying proliferative hepatocellular lesions was revised and the term “neoplastic 

nodule” is no longer recommended by the National Toxicology Program (NTP) to describe lesions that 

would now be termed hepatocellular hyperplasia or hepatocellular adenoma (Maronpot et al. 1986a). 

In other studies, tumors were not observed in male rats treated with 19 mg/kg/day doses of 1,2-diphenylhydrazine in the diet for life (mean survival time=288 days) (Marhold et al. 1968). The significance of 

this finding is uncertain because the type and scope of pathological examination were not reported. Pliss 

(1974) reported increased numbers of tumors of the liver, Zymbal's gland, mammary gland, and other 

sites in rats that were treated with 1,2-diphenylhydrazine in the diet at an estimated dose of 85 mg/kg/day, 

5 days/week for 588 days (Pliss 1974). These findings are inconclusive, however, because of lack of 

control data and other report inadequacies. 

Inconclusive data for carcinogenicity of dermally applied 1,2-diphenylhydrazine in mice are available. 

Dermal application of an estimated 1,2-diphenylhydrazine dose of 63 mg/kg/day 3 times/week for 
1,2-DIPHENYLHYDRAZINE 23

2. HEALTH EFFECTS

442 days caused a 22.2% incidence of tumors in mice (Pliss 1974). Tumors occurred in the lung, liver, 

and other tissues, and the tumor incidence in control mice was 17%. The significance of these findings 

cannot be determined, as incidences of specific tumors in the control group were not reported.

Intraperitoneal administration of 200 mg/kg 1,2-diphenylhydrazine 3 times/week for 8 weeks resulted in 

increases in the incidence of lung tumors in male mice; evidence in female mice was considered 

equivocal (Maronpot et al. 1986b). Increases in tumors have also been observed in other studies 

involving subcutaneous injection in rats and mice (Genin et al. 1975; Kurliandskiĭ et al. 1976; Pliss 1974; 

Shabad and Genin 1975; Spitz et al. 1950); however, the results are inconclusive due to inadequate 

reporting and other limitations. 

Based on sufficient evidence of carcinogenicity in laboratory animal studies, the Department of Health 

and Human Services concluded that 1,2-diphenylhydrazine is reasonably anticipated to be a human 

carcinogen (NTP 2016) and EPA concluded that it is a probable human carcinogen (Group B2) (IRIS 

2006).

2.20 GENOTOXICITY

The genotoxicity of 1,2-diphenylhydrazine has been evaluated in a limited number of in vitro and in vivo 

studies. No studies were located regarding the genotoxicity of 1,2-diphenylhydrazine in humans by any 

route of exposure. A limited number of assays have been conducted using bacteria or mammalian cells. 

As indicated in Table 2-2, 1,2-diphenylhydrazine was mutagenic in Salmonella typhimurium (Dunkel et 

al. 1985; Haworth et al. 1983), but not in Escherichia coli (Dunkel et al. 1985). Exogenous metabolic 

activation systems were necessary for expression of the aforementioned effects. In mammalian cell 

culture, 1,2-diphenylhydrazine produced chromosome aberrations and sister chromatid exchanges in 

Chinese hamster cells (Galloway et al. 1987). Ohnishi et al. (2000) reported deoxyribonucleic acid 

(DNA) damage in calf thymus DNA fragments incubated with a 10% (v/v) ethanol solution of 

1,2-diphenylhydrazine. The addition of 20 μM copper(II) chloride increased the DNA damage.
1,2-DIPHENYLHYDRAZINE 24

2. HEALTH EFFECTS

Table 2-2. Genotoxicity of 1,2-Diphenylhydrazine In Vitro

Species (test system) Endpoint

Results

Reference

Activation

With Without

Prokaryotic organisms

Salmonella typhimurium

(plate incorporation)

Gene mutation (+) – Dunkel et al. 1985

S. typhimurium (plate 

incorporation)

Gene mutation + – Haworth et al. 1983

Escherichia coli WP2uvrA Gene mutation – – Dunkel et al. 1985

Mammalian cells

Chinese hamster ovary cells Chromosome aberrations + +/– Galloway et al. 1987

Chinese hamster ovary cells Sister chromatid exchange + – Galloway et al. 1987

+ = positive results; (+) = weakly positive results; +/– = inconclusive; – = negative results

In in vivo studies (Table 2-3), 1,2-diphenylhydrazine inhibited testicular DNA synthesis in mice when 

administered as a single 100 mg/kg intraperitoneal injection (Seiler et al. 1977), but did not cause hepatic 

DNA damage in rats administered two oral doses of 180 mg/kg, at 21 and 4 hours before sacrifice 

(Kitchin et al. 1994). Exposure by feed or injection did not cause sex-linked recessive lethal mutations in 

Drosophila (Yoon et al. 1985). 

Table 2-3. Genotoxicity of 1,2-Diphenylhydrazine In Vivo

Species (exposure route) Endpoint Results Reference

Invertebrate systems

Drosophila melanogaster 

(feeding)

Sex-linked recessive lethal mutation – Yoon et al. 1985

D. melanogaster (injection) Sex-linked recessive lethal mutation – Yoon et al. 1985

Laboratory animal evidence

Mouse (strain not reported)

(intraperitoneal injection)

DNA damage; inhibition of testicular 

DNA synthesis.

+ Seiler et al. 1977

Sprague-Dawley rat (gavage) DNA damage (hepatic DNA alkaline 

elution)

– Kitchin et al. 1994

– = negative result; + = positive result
1,2-DIPHENYLHYDRAZINE 25

CHAPTER 3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, 

BIOMARKERS, CHEMICAL INTERACTIONS

3.1 TOXICOKINETICS 

No studies were located regarding the toxicokinetics of 1,2-diphenylhydrazine in humans; limited 

laboratory animal data, summarized below, are available. 

• 1,2-Diphenylhydrazine is presumed to be absorbed following oral exposure based on the 

appearance of urinary metabolites and adverse health effects. 

• No information on the distribution of 1,2-diphenylhydrazine was identified.

• The available data suggest that 1,2-diphenylhydrazine is metabolized to aniline in the gut and that 

it readily forms benzidine in the acidic stomach.

• No information is available on the excretion of 1,2-diphenylhydrazine; one study reported the 

presence of unidentified urinary metabolites. 

3.1.1 Absorption 

No studies were located containing specific information regarding absorption after inhalation, oral, or 

dermal exposure to 1,2-diphenylhydrazine in humans or animals. Pulmonary absorption of 

1,2-diphenylhydrazine by rats is suggested by detection of an unidentified metabolite in the urine 

following intratracheal administration of 1,2-diphenylhydrazine in water suspension and dimethyl 

sulfoxide (DMSO) (Dutkiewicz and Szymanska 1973). It is not known, however, if any of the dose was 

ingested.

Gastrointestinal absorption of 1,2-diphenylhydrazine by rodents is indicated by the occurrence of parent 

compound and metabolites in the urine following oral treatment (Section 3.1.4) and adverse health effects 

observed following oral exposure (Chapter 2). 

3.1.2 Distribution 

No studies were located regarding distribution in humans or animals after inhalation, oral, or dermal 

exposure to 1,2-diphenylhydrazine.
1,2-DIPHENYLHYDRAZINE 26

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

3.1.3 Metabolism 

Limited information is available on the metabolism of 1,2-diphenylhydrazine. In the only study involving 

1,2-diphenylhydrazine as the parent compound, rat urine was analyzed for metabolites following single 

oral (200 or 400 mg/kg), intraperitoneal (100 or 200 mg/kg), intravenous (4 or 8 mg/kg), and intratracheal 

(5 or 10 mg/kg) doses of 1,2-diphenylhydrazine (Dutkiewicz and Szymanska 1973). Unchanged 

1,2-diphenylhydrazine was detected following treatment by all routes, and aniline and benzidine were 

identified following the oral and intraperitoneal treatments. Other metabolites included two unspecified 

hydroxy derivatives of benzidine (oral route), 2- and 4-aminophenol (intraperitoneal route), and 

unidentified compounds (oral, intravenous, and intratracheal routes). Amounts of compounds excreted 

were not quantitated. The validity of the findings of this study is uncertain, however, as the analytical 

methodology (thin-layer chromatography) may have produced degradation products that were identified 

as unchanged 1,2-diphenylhydrazine or metabolites. The metabolites identified by Dutkiewicz and 

Szymanska (1973) are consistent with a metabolic scheme proposed by Williams (1959) (Figure 3-1), 

which is based on data for azobenzene and aniline. As summarized by NRC (1981), aniline is oxidized 

by hydroxylation of a ring carbon to form 2- or 4-aminophenol or of the nitrogen to form phenylhydroxylamine, and then is conjugated to glucuronic or sulfuric acid. An oral study of azobenzene with 

conventional and germ-free rats (Macholz et al. 1985) showed that metabolism of 1,2-diphenylhydrazine 

to aniline resulted from the reductional and hydrolytic capability of gut flora. In vitro metabolism of 

1,2-diphenylhydrazine to aniline by rat intestinal microorganisms has been demonstrated (Bolton and 

Griffiths 1978). Benzidine is formed readily from 1,2-diphenylhydrazine by acid rearrangement. It has 

been suggested that benzidine may be produced from 1,2-diphenylhydrazine by acidity in the stomach 

(IARC 1972).

3.1.4 Excretion 

No studies were located regarding excretion in humans or animals after inhalation, oral, or dermal 

exposure to 1,2-diphenylhydrazine. The presence of an unidentified metabolite in the urine of rats 

following intratracheal and oral administration of 1,2-diphenylhydrazine in water and DMSO suspensions 

(Dutkiewicz and Szymanska 1973) suggests that some urinary excretion occurs.
1,2-DIPHENYLHYDRAZINE 27

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

Figure 3-1. Metabolic Scheme of 1,2-Diphenylhydrazine

Source: Williams 1959

HO

N N N N

N N

H H

H2N NH2

HO N N OH

NH2 NH2

OH

NH2

OH

NHAc

OH

NH2

OR OR

NH2

NHAc

OH

2-Hydroxyazobenzene Azobenzene

1,2-Diphenylhydrazine Benzidine

4-Hydroxyazobenzene

2-Aminophenol Aniline 4-Aminophenol

4-Acetamidophenol 4-Alkoxyamine

2-Alkoxyamine 2-Acetamidophenol
1,2-DIPHENYLHYDRAZINE 28

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

3.1.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models 

PBPK models use mathematical descriptions of the uptake and disposition of chemical substances to 

quantitatively describe the relationships among critical biological processes (Krishnan et al. 1994). PBPK 

models are also called biologically based tissue dosimetry models. PBPK models are increasingly used in 

risk assessments, primarily to predict the concentration of potentially toxic moieties of a chemical that 

will be delivered to any given target tissue following various combinations of route, dose level, and test 

species (Clewell and Andersen 1985). Physiologically based pharmacodynamic (PBPD) models use 

mathematical descriptions of the dose-response function to quantitatively describe the relationship 

between target tissue dose and toxic endpoints. 

No PBPK models were identified for 1,2-diphenylhydrazine.

3.1.6 Animal-to-Human Extrapolations 

There are insufficient data in which to evaluate possible species differences in the toxicokinetic properties 

of 1,2-diphenylhydrazaine. 

3.2 CHILDREN AND OTHER POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE

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

maturity at 18 years of age in humans. Potential effects on offspring resulting from exposures of parental 

germ cells are considered, as well as any indirect effects on the fetus and neonate resulting from maternal 

exposure during gestation and lactation. Children may be more or less susceptible than adults to health 

effects from exposure to hazardous substances and the relationship may change with developmental age. 

This section also discusses unusually susceptible populations. A susceptible population may exhibit 

different or enhanced responses to certain chemicals than most persons exposed to the same level of these 

chemicals in the environment. Factors involved with increased susceptibility may include genetic 

makeup, age, health and nutritional status, and exposure to other toxic substances (e.g., cigarette smoke). 

These parameters can reduce detoxification or excretion or compromise organ function. 

Populations at greater exposure risk to unusually high exposure levels to 1,2-diphenylhydrazine are 

discussed in Section 5.7, Populations with Potentially High Exposures.
1,2-DIPHENYLHYDRAZINE 29

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

No data are available in on the toxicity of 1,2-diphenylhydrazine in children and it is assumed to be 

similar to adults. No developmental toxicity studies have been identified for this compound. No 

populations with unusual susceptibility to health effects of 1,2-diphenylhydrazine have been identified. It 

is possible that people with chronic liver disease or possibly compromised hepatic function might be 

unusually susceptible to 1,2-diphenylhydrazine, because the liver is a target organ of 1,2-diphenylhydrazine in animals.

3.3 BIOMARKERS OF EXPOSURE AND EFFECT 

Biomarkers are broadly defined as indicators signaling events in biologic systems or samples. They have 

been classified as biomarkers of exposure, biomarkers of effect, and biomarkers of susceptibility 

(NAS/NRC 1989).

A biomarker of exposure is a xenobiotic substance or its metabolite(s) or the product of an interaction 

between a xenobiotic agent and some target molecule(s) or cell(s) that is measured within a compartment 

of an organism (NAS/NRC 1989). The preferred biomarkers of exposure are generally the substance 

itself, substance-specific metabolites in readily obtainable body fluid(s), or excreta. Biomarkers of 

exposure to 1,2-diphenylhydrazine are discussed in Section 3.3.1. The National Report on Human 

Exposure to Environmental Chemicals provides an ongoing assessment of the exposure of a generalizable 

sample of the U.S. population to environmental chemicals using biomonitoring (see 

http://www.cdc.gov/exposurereport/). If available, biomonitoring data for 1,2-diphenylhydrazine from 

this report are discussed in Section 5.6, General Population Exposure. 

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 effect caused 

by 1,2-diphenylhydrazine are discussed in Section 3.3.2.

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 
1,2-DIPHENYLHYDRAZINE 30

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

biologically effective dose, or a target tissue response. If biomarkers of susceptibility exist, they are 

discussed in Section 3.2, Children and Other Populations that are Unusually Susceptible.

3.3.1 Biomarkers of Exposure

No studies were located regarding biomarkers of exposure to 1,2-diphenylhydrazine. The metabolites of 

1,2-diphenylhydrazine were identified in one study (Dutkiewicz and Szymanska 1973); however, the 

validity of the findings is uncertain because of the analytical methodology used (see Section 3.1.3). No 

enzymatic changes that could be used as biomarkers of 1,2-diphenylhydrazine exposure are known.

3.3.2 Biomarkers of Effect

No biomarkers of effect were identified for 1,2-diphenylhydrazine exposure. No specific alterations in 

the organism that could be recognized as biomarkers were found, and the most susceptible organs or 

tissues were not identified.

3.4 INTERACTIONS WITH OTHER CHEMICALS 

A carcinogenicity study was reported in which groups of rats were given weekly subcutaneous injections 

of 1,2-diphenylhydrazine (20 mg) alone or concurrently with benzidine sulfate (15 mg) for life (Genin et 

al. 1975). Combined incidences of tumors (injection site, liver, and other sites) were increased and the 

mean tumor latent period was decreased in the group with combined 1,2-diphenylhydrazine and benzidine 

sulfate exposure. It is unclear whether these findings provide evidence for an interaction between 

1,2-diphenylhydrazine and benzidine or additive effects of two carcinogens. The results of this study 

were also reported by Shabad and Genin (1975) and Kurliandskiĭ et al. (1976). 
1,2-DIPHENYLHYDRAZINE 31

CHAPTER 4. CHEMICAL AND PHYSICAL INFORMATION

4.1 CHEMICAL IDENTITY

Data pertaining to the chemical identity of 1,2-diphenylhydrazine listed in Table 4-1.

Table 4-1. Chemical Identity of 1,2-Diphenylhydrazine

Characteristic Information

Chemical name 1,2-Diphenylhydrazine

Synonym(s) and registered trade 

name(s)

Hydrazobenzene; N,N'-diphenylhydrazine; symdiphenylhydrazine

Chemical formula C12H12N2

Chemical structure

Identification numbers:

CAS Registry 122-66-7

Source: NLM 2020

CAS = Chemical Abstracts Services

4.2 PHYSICAL AND CHEMICAL PROPERTIES 

The physical and chemical properties of 1,2-diphenylhydrazine are presented in Table 4-2. 1,2-Diphenylhydrazine can rapidly oxidize to azobenzene under some environmental conditions; therefore, accurate 

experimental determination of properties such as the water solubility and Henry’s Law constant may not 

be possible. 

N N

H H
1,2-DIPHENYLHYDRAZINE 32

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of 1,2-Diphenylhydrazine

Property Information Reference

Molecular weight 184.24

Color White Ahuja et al. 1989

Physical state Crystalline solid Dean 1985

Melting point 123–126°C NLM 2020

Boiling point 309°C NLM 2020

Density at 20°C

Odor No data

Odor threshold:

Water No data

Air No data

Solubility:

Water at 20°Ca 66.9 mg/L (estimated) NLM 2020

Organic solvents Very soluble in alcohol; slightly soluble in 

benzene

Dean 1985

Partition coefficients:

Log Kow 2.94 (experimental) Hansch et al. 1995

Log Koc 2.73 (calculated using equation 4–10) Lyman et al. 1982

Vapor pressure at 25°C 2.6x10-5 mmHg EPA 1982a

Henry's law constant at 25°Ca 9.42x10-8 atm-m3/mol (estimated)

Autoignition temperature No data

Flashpoint No data

Flammability limits No data

Conversion factors No data
1,2-DIPHENYLHYDRAZINE 33

CHAPTER 5. POTENTIAL FOR HUMAN EXPOSURE

5.1 OVERVIEW 

1,2-Diphenylhydrazine has been identified in at least 26 of the 1,867 hazardous waste sites that have been 

proposed for inclusion on the EPA National Priorities List (NPL) (ATSDR 2019). However, the number 

of sites in which 1,2-diphenylhydrazine has been evaluated is not known. The number of sites in each 

state is shown in Figure 5-1.

Figure 5-1. Number of NPL Sites with 1,2-Diphenylhydrazine Contamination

• The general population is not likely to be exposed to 1,2-diphenylhydrazine because dye 

manufacturers in the United States no longer produce benzidine based dyes, which was the 

former principal use of 1,2-diphenylhydrazine. 

• The only current use of 1,2-diphenylhydrazine in the United States is in the production of antiinflammatory pharmaceutical agents for veterinary use.

• 1,2-Diphenylhydrazine is reversibly oxidized in the environment under aerobic conditions, with a 

half-life in water as short as 15 minutes. This oxidation also occurs in air and soil. 

• The fate, transport, and distribution of 1,2-diphenylhydrazine in the environment are influenced 

by its rapid oxidation to azobenzene.
1,2-DIPHENYLHYDRAZINE 34

5. POTENTIAL FOR HUMAN EXPOSURE

5.2 PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

5.2.1 Production

1,2-Diphenylhydrazine is produced in the stepwise reduction of nitrobenzene by the action of iron or zinc 

powder in caustic solution (e.g., caustic soda, alcoholic alkaline) first to azoxybenzene, then azobenzene, 

and finally 1,2-diphenylhydrazine (Sandridge and Staley 1978). A batch process is used in which a 

caustic soda solution is added to a heated vessel charged with nitrobenzene and iron borings. Additions 

of iron in caustic soda solution are made to continue the reaction. When the reaction is complete, 

separation of the 1,2-diphenylhydrazine from the iron sludge is accomplished by solvent extraction or by 

alternative methods, such as stopping the reaction at the azobenzene step and performing the final 

reduction in a zinc-alcoholic alkali solution followed by filtration and washing of the sodium zincate 

mass.

Table 5-1 summarizes information on U.S. companies that reported the manufacture or use of 

1,2-diphenylhydrazine in 2016 (TRI18 2020). Toxics Release Inventory (TRI) data should be used with 

caution since only certain types of industrial facilities are required to report. This is not an exhaustive list.

Table 5-1. Facilities that Produce, Process, or Use 1,2-Diphenylhydrazine

Statea

Number of 

facilities

Minimum 

amount on site 

in poundsb

Maximum 

amount on site 

in poundsb Activities and usesc

OH 1 100 999 12

TX 1 1,000 9,999 12

aPost office state abbreviations used. bAmounts on site reported by facilities in each state.

cActivities/uses:

1. Produce

2. Import

3. Onsite use/processing

4. Sale/Distribution

5. Byproduct

6. Impurity

7. Reactant

8. Formulation Component

9. Article Component

10. Repackaging

11. Chemical Processing Aid

12. Manufacturing Aid 

13. Ancillary/Other Uses

14. Process Impurity

Source: TRI18 2020 (Data are from 2018)

5.2.2 Import/Export

No information concerning the importation or exportation of 1,2-diphenylhydrazine in the United States 

was located in the literature. 
1,2-DIPHENYLHYDRAZINE 35

5. POTENTIAL FOR HUMAN EXPOSURE

5.2.3 Use

One of the major former uses of 1,2-diphenylhydrazine was as a starting material in the production of 

benzidine-based dyes; however, these are no longer produced or used in the United States. 1,2-Diphenylhydrazine rearranges to benzidine upon treatment with strong acid; benzidine was used by the dye 

industry for the production of benzidine-based dyes including many of the Direct dyes (e.g., Direct 

Red 28, Direct Black 4, Direct Blue 2) (Ferber 1978; Lurie 1964). 

1,2-Diphenylhydrazine is used by the pharmaceutical industry for the production of the drug,

phenylbutazone (trade name Butazolidin, an anti-inflammatory agent); phenylbutazone is no longer 

marketed for human use in the United States, but is still listed for veterinary use (FDA 2016). 

1,2-Diphenylhydrazine was also used for the production of sulfinpyrazone (trade name Anturane, a 

uricosuric agent for the treatment of gouty arthritis) (Hughes 1981; Kornis 1982); however, 

sulfinpyrazone has been withdrawn for sale in the United States (FDA 2009). These drugs are/were made 

by the condensation of 1,2-diphenylhydrazine with malonic acid derivatives to form pyrazolidinedione 

structures. It is not clear from the literature if the 1,2-diphenylhydrazine used in the condensation 

reaction is produced by the manufacturers or if it is purchased by them as an isolated product.

5.2.4 Disposal

Very little information was located in the literature concerning the disposal of 1,2-diphenylhydrazine. 

Dietrich et al. (1985) reported that wet air oxidation (heating waste water under pressure with the addition 

of an oxygen-containing gas such as air) would remove 99.88% of the 1,2-diphenylhydrazine in the water 

(initial concentration, 5,000 mg/L). Results of treatment by wet air oxidation are in keeping with the 

observation that 1,2-diphenylhydrazine oxidizes to azobenzene (Riggin and Howard 1979). Information 

regarding the amount of 1,2-diphenylhydrazine disposed of in the United States was not located in the 

literature.

5.3 RELEASES TO THE ENVIRONMENT 

The Toxics Release Inventory (TRI) data, presented in Table 5-2, should be used with caution because 

only certain types of facilities are required to report (EPA 2005). This is not an exhaustive list. 

Manufacturing and processing facilities are required to report information to the TRI only if they employ 

≥10 full-time employees; if their facility is included in Standard Industrial Classification (SIC) Codes 10 
1,2-DIPHENYLHYDRAZINE 36

5. POTENTIAL FOR HUMAN EXPOSURE

(except 1011, 1081, and 1094), 12 (except 1241), 20–39, 4911 (limited to facilities that combust coal 

and/or oil for the purpose of generating electricity for distribution in commerce), 4931 (limited to 

facilities that combust coal and/or oil for the purpose of generating electricity for distribution in 

commerce), 4939 (limited to facilities that combust coal and/or oil for the purpose of generating 

electricity for distribution in commerce), 4953 (limited to facilities regulated under RCRA Subtitle C, 

42 U.S.C. section 6921 et seq.), 5169, 5171, and 7389 (limited S.C. section 6921 et seq.), 5169, 5171, and 

7389 (limited to facilities primarily engaged in solvents recovery services on a contract or fee basis); and 

if their facility produces, imports, or processes ≥25,000 pounds of any TRI chemical or otherwise uses 

>10,000 pounds of a TRI chemical in a calendar year (EPA 2005).

Table 5-2. Releases to the Environment from Facilities that Produce, Process, or 

Use 1,2-Diphenylhydrazinea

Reported amounts released in pounds per yearb

Statec RFd Aire Waterf UIg Landh Otheri

Total release

On-sitej Off-sitek On- and off-site

OH 1 0 0 0 0 0 0 NR 0

TX 1 7 0 0 0 0 7 NR 7

Total 2 7 0 0 0 0 7 0 7

aThe TRI data should be used with caution since only certain types of facilities are required to report. This is not an 

exhaustive list. Data are rounded to nearest whole number. bData in TRI are maximum amounts released by each facility.

cPost office state abbreviations are used. dNumber of reporting facilities.

eThe sum of fugitive and point source releases are included in releases to air by a given facility.

f

Surface water discharges, wastewater treatment (metals only), and publicly owned treatment works (POTWs) (metal 

and metal compounds).

gClass II-V wells, and underground injection. hResource Conservation and Recovery Act (RCRA) subtitle C landfills; other onsite landfills, land treatment, surface 

impoundments, other land disposal, other landfills.

i

Storage only, solidification/stabilization (metals only), other off-site management, transfers to waste broker for 

disposal, unknown

j

The sum of all releases of the chemical to air, land, water, and underground injection wells.

kTotal amount of chemical transferred off-site, including to POTWs.

NR = not reported; RF = reporting facilities; UI = underground injection

Source: TRI18 2020 (Data are for 2018)

5.3.1 Air 

Estimated releases of 7 pounds (~0.0032 metric tons) of 1,2-diphenylhydrazine to the atmosphere from 

two domestic manufacturing and processing facilities in 2018, accounted for 100% of the estimated total 
1,2-DIPHENYLHYDRAZINE 37

5. POTENTIAL FOR HUMAN EXPOSURE

environmental releases from facilities required to report to the TRI (TRI18 2020). These releases are 

summarized in Table 5-2.

No information concerning the release of 1,2-diphenylhydrazine to air was located in the literature. Since 

there are very limited uses of 1,2-diphenylhydrazine, emissions to the atmosphere are expected to be low. 

5.3.2 Water 

There were no releases of 1,2-diphenylhydrazine to water from manufacturing and processing facilities 

required to report to the TRI (TRI18 2020) (Table 5-2). 

No other information concerning the release of 1,2-diphenylhydrazine to water was located in the 

literature. If discharged to water, detectable concentrations will probably persist for only a short time, 

since the half-life of (100 μg/L) 1,2-diphenylhydrazine in wastewater is about 15 minutes (EPA 1982; 

Riggin and Howard 1979).

5.3.3 Soil 

There were no releases of 1,2-diphenylhydrazine to soil from manufacturing and processing facilities 

required to report to the TRI (TRI18 2020) (Table 5-2). 

No other information concerning the release of 1,2-diphenylhydrazine to soil was located in the literature. 

The manufacturing process for 1,2-diphenylhydrazine generates a sludge containing iron and/or zinc 

compounds, probably along with small amounts of unextracted 1,2-diphenylhydrazine. Some of this 

material may be disposed of in landfills, but no information is available concerning the 1,2-diphenylhydrazine disposal practices.

5.4 ENVIRONMENTAL FATE 

5.4.1 Transport and Partitioning 

No information concerning the transport and partitioning of 1,2-diphenylhydrazine in the environment 

was located in the literature. Based upon its short persistence time and its physical-chemical properties, 

volatilization from water or soil surfaces, bioconcentration in aquatic organisms, and leaching from soils 
1,2-DIPHENYLHYDRAZINE 38

5. POTENTIAL FOR HUMAN EXPOSURE

to underlying groundwater are not expected to be important environmental fate processes for 

1,2-diphenylhydrazine. 

5.4.2 Transformation and Degradation 

Air. No studies were located regarding the rates or products of reaction of 1,2-diphenylhydrazine in the 

atmosphere. Based on its rapid degradation in aerated water, 1,2-diphenylhydrazine will oxidize in air to 

form azobenzene as well as other products resulting from the abstraction of a hydrogen from a nitrogen 

by hydroxyl radicals. The reaction rate constant of 1,2-diphenylhydrazine with photochemically 

generated hydroxyl radicals was estimated as 211x10-12 cm3 molecule-1 second-1 using a structure 

estimation method discussed in Atkinson (1987). This corresponds to an atmospheric half-life of 

<2 hours, assuming a hydroxyl radical concentration of 0.5x106 molecules cm-3

. 1,2-Diphenylhydrazine 

also absorbs light above 290 nm (NLM 2020) and may be susceptible to photolysis. No information was 

found concerning the characteristics of this potential reaction.

Water. Riggin and Howard (1979) and EPA (1982) reported the results of a study on the stability of 

1,2-diphenylhydrazine in a number of solvents including distilled water and wastewater. In distilled 

water at pH values of 2, 4.7, 7, and 10 and at 4°C or at room temperature, <10% of the initial 10 μg/L of 

1,2-diphenylhydrazine remained in the water after 1 day. At pH 2, 1,2-diphenylhydrazine degraded to 

benzidine, while at pH 7, it degraded to an unidentifiable oxidizable product. At pH 10, 1,2-diphenylhydrazine degraded to azobenzene, and at pH 4.7, it degraded into two unidentifiable products, which 

were not azobenzene or benzidine. In secondary municipal sewage effluent, (EPA 1982; Riggin and 

Howard 1979) reported that 100 μg/L of 1,2-diphenylhydrazine had a half-life of about 15 minutes in the 

presence of oxygen, and about 60 minutes when no oxygen was present. These results suggest that 

1,2-diphenylhydrazine is unlikely to persist in the environment, particularly under aerobic conditions.

Tabak et al. (1981a, 1981b) and Patterson and Kodukala (1981) stated that 5 or 10 mg/L of 1,2-diphenylhydrazine was degraded up to 80% when initially cultured with settled domestic wastewater. This 

degradation rate, however, was reduced to 40% in the case of the 10 mg/L concentration, after the third 

subculture. The authors suggested that a de-adaptive and toxification process was occurring with 

1,2-diphenylhydrazine. It is unclear if the analytical methods used by these authors would have been able 

to detect 1,2-diphenylhydrazine if present. Both dissolved organic carbon and gas chromatography (GC) 

analyses were performed on the samples. Considering the sample preparation procedures, however, the 
1,2-DIPHENYLHYDRAZINE 39

5. POTENTIAL FOR HUMAN EXPOSURE

compound detected might not have been 1,2-diphenylhydrazine, but a decomposition product such as 

azobenzene.

Sediment and Soil. No information concerning the fate of 1,2-diphenylhydrazine in soil was located

in the literature. Based on the fate of 1,2-diphenylhydrazine in water and sediment, detectable 

concentrations probably will not persist for long periods, but this may depend on the initial concentration.

5.5 LEVELS IN THE ENVIRONMENT 

Reliable evaluation of the potential for human exposure to 1,2-diphenylhydrazine depends, in part, on the 

reliability of supporting analytical data from environmental samples and biological specimens. 

Concentrations of 1,2-diphenylhydrazine in unpolluted atmospheres and in pristine surface waters are 

often so low as to be near the limits of current analytical methods. In reviewing data on 1,2-diphenylhydrazine levels monitored or estimated in the environment, it should also be noted that the amount of 

chemical identified analytically is not necessarily equivalent to the amount that is bioavailable.

The rapid oxidation of 1,2-diphenylhydrazine in water to form azobenzene and other compounds makes 

its sampling and analysis difficult. Storing a sample containing 1,2-diphenylhydrazine for even short 

periods can result in complete oxidation; in GC, 1,2-diphenylhydrazine is oxidized to azobenzene upon 

injection onto the chromatographic column (EPA 1982). Therefore, unless sampling and analysis are 

performed under conditions that will prevent oxidation or unless concentrations of 1,2-diphenylhydrazine 

in the sample are very high, analyses of environmental samples for 1,2-diphenylhydrazine are inaccurate 

(Ahuja et al. 1989; Riggin and Howard 1979). It is doubtful that the concentrations measured reflect on 

the concentrations present in the sample at the time of collection (i.e., measured concentrations would 

underestimate actual concentrations) (EPA 1982). 

Detections of 1,2-diphenylhydrazine in air, water, and soil at NPL sites are summarized in Table 5-3. 
1,2-DIPHENYLHYDRAZINE 40

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-3. 1,2-Diphenylhydrazine Levels in Water, Soil, and Air of National 

Priorities List (NPL) Sites

Medium Mediana

Geometric 

meana

Geometric 

standard 

deviationa

Number of 

quantitative 

measurements NPL sites

Water (ppb) No data

Soil (ppb) 1,000 1,000 1,710 4 3

Air (ppbv) No data

aConcentrations found in ATSDR site documents from 1981 to 2019 for 1,867 NPL sites (ATSDR 2019). Maximum 

concentrations were abstracted for types of environmental media for which exposure is likely. Pathways do not 

necessarily involve exposure or levels of concern.

5.5.1 Air 

No ambient air monitoring for 1,2-diphenylhydrazine was located in the literature. This may be due to 

both the rapid oxidation of 1,2-diphenylhydrazine and its low vapor pressure, which limit the amount of 

1,2-diphenylhydrazine entering the atmosphere. In addition, no information was located suggesting that 

any studies sought, but did not find, 1,2-diphenylhydrazine.

5.5.2 Water 

Water quality data compiled from the STORET Data Warehouse and the U.S. Geological Survey (USGS)

National Water Information System (NWIS) reports are summarized in Table 5-4. These data are 

comprised of water quality data from water resource management groups across the country. 

Table 5-4. 1,2-Diphenylhydrazine Detected in Samples Collected Throughout the 

United States from 1990 to 2020

Type Number of samples Number of positive Concentration range

Groundwater 2,409 92 0.12–21.00 ppb

Surface water 3,286 14 <0.2–260 ppb 

Wastewater 12 0 0.22–7 ppb (detection limit)

Leachate 17 0 2.1–5.00 ppb (detection limit)

Sediment 1,238 3 <340–<1,700 ppb

Subsurface soil/sediment 78 0 58–310 ppb (detection limit)

Soil 128 0 336–3,530 ppb (detection limit)

Source: NWQMC 2020
1,2-DIPHENYLHYDRAZINE 41

5. POTENTIAL FOR HUMAN EXPOSURE

Two reported identifications of 1,2-diphenylhydrazine in water samples were located in the literature. 

EPA (1981) reported that 1,2-diphenylhydrazine was present in drinking water in Cincinnati, Ohio (river 

water treated by coagulation, sand filtration, and chlorination) at a concentration of 1 ng/L. Since the 

sample preparation involved aeration and the original sample was chlorinated, it is unclear if the detected 

material was 1,2-diphenylhydrazine or azobenzene. EPA (1982) found that, in addition to injection onto a 

GC column, either chlorination or aeration of a sample resulted in total disappearance of 1,2-diphenylhydrazine. Tang et al. (1983) reported 1,2-diphenylhydrazine in coal gasification wastewater at 

concentrations of 0.149 and 1.786 μg/L. Sample preparation in this case involved separation into classes 

by pH, liquid-liquid extraction, concentration, and GC/mass spectroscopy (MS) analysis. No precautions 

were taken to reduce the aeration of the sample. Also, the analytical procedure indicates that no 

1,2-diphenylhydrazine would have been able to survive the conditions of the sample preparation and the 

detection may be of azobenzene or of 1,2-diphenylhydrazine from another source (e.g., decomposition of 

another compound to 1,2-diphenylhydrazine).

Hall et al. (1985) reported that no 1,2-diphenylhydrazine (<1 μg/L) was detected in the Nanticoke River 

near the Chesapeake Bay. The analytical method involved liquid-liquid extraction, concentration, and 

analysis by GC/MS. 

5.5.3 Sediment and Soil 

1,2-Diphenylhydrazine has been identified in soil only at hazardous waste sites (see Table 5-3); however,

it is not clear if the measurements were for 1,2-diphenylhydrazine or its degradation product. 

5.5.4 Other Media 

1,2-Diphenylhydrazine has been assayed but not detected in fish samples from the Great Lakes area. 

Camanzo et al. (1987) reported that no 1,2-diphenylhydrazine was detected in fish samples from 13 Lake 

Michigan tributaries and Grand Traverse Bay fish. Analyses were made by GC/MS and no detection 

limits were given. Similarly, De Vault (1985) reported that a GC/MS did not identify any of the peaks 

present in fish samples from Great Lakes harbors and tributaries as 1,2-diphenylhydrazine.

Phenylbutazone can hydrolyze to yield 1,2-diphenylhydrazine, and this drug may contain some 

1,2-diphenylhydrazine (Ahuja et al. 1989; Fabre et al. 1984; Matsui et al. 1983). Phenylbutazone is a 

drug used for the treatment of inflammatory conditions (e.g., arthritis) in animals.
1,2-DIPHENYLHYDRAZINE 42

5. POTENTIAL FOR HUMAN EXPOSURE

5.6 GENERAL POPULATION EXPOSURE 

Virtually no information concerning occupational exposure or general population was located in the 

literature. In the past, general population exposure could come from use of anti-inflammatory medication 

made synthesized with 1,2-diphenylhydrazine, since these drugs may contain small residual amounts

(Fabre et al. 1984; Matsui et al. 1983). However, phenylbutazone and sulfinpyrazone are not currently 

used as human medications (FDA 2009, 2016). 

5.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES 

The only populations with potentially high exposure appear to be people living near hazardous waste sites

where 1,2-diphenylhydrazine is present and those in occupations that manufacture or use 1,2-diphenylhydrazine. Very little information concerning these populations, however, is available to clearly 

understand the extent of these potential exposures.
1,2-DIPHENYLHYDRAZINE 43

CHAPTER 6. 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 1,2-diphenylhydrazine is available. Where adequate 

information is not available, ATSDR, in conjunction with NTP, is required to assure the initiation of a 

program of research designed to determine the adverse health effects (and techniques for developing 

methods to determine such health effects) of 1,2-diphenylhydrazine.

Data needs are defined as substance-specific informational needs that, if met, would reduce the 

uncertainties of human health risk 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. 

6.1 INFORMATION ON HEALTH EFFECTS

Studies evaluating the health effects of inhalation, oral, and dermal exposure of humans and animals to 

1,2-diphenylhydrazine that are discussed in Chapter 2 are summarized in Figure 6-1. The purpose of this 

figure is to illustrate the information concerning the health effects of 1,2-diphenylhydrazine. The number 

of human and animal studies examining each endpoint is indicated regardless of whether an effect was 

found and the quality of the study or studies. 

6.2 IDENTIFICATION OF DATA NEEDS 

Missing information in Figure 6-1 should not 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.
1,2-DIPHENYLHYDRAZINE 44

6. ADEQUACY OF THE DATABASE

Figure 6-1. Summary of Existing Health Effects Studies on 1,2-Diphenylhydrazine

By Route and Endpoint*

Potential body weight, hepatic, gastrointestinal, and cancer effects were the most studied 

endpoints

The majority of the studies examined oral exposure in animals; no data were identified for humans

Acute-Duration MRLs. Information is not available on the health effects of 1,2-diphenylhydrazine 

resulting from inhalation exposure in humans or animals. Because 1,2-diphenylhydrazine is a solid with a 

low vapor pressure at ambient temperatures, it is highly unlikely that inhalation exposure to this chemical 

in the vapor state would occur. However, the possibility of inhalation exposure to dusts of 1,2-diphenylhydrazine either free or adsorbed to soil is conceivable. Therefore, acute studies of inhalation exposure to 

dusts of 1,2-diphenylhydrazine could be designed to provide information on possible toxic effects and 

exposure levels that cause effects. No studies were located regarding acute oral exposure in humans. The 

only pertinent acute exposure toxicity studies of 1,2-diphenylhydrazine were conducted in rats; these 

consist of an oral LD50 assay and a repeated-dose study, which did not find adverse hepatic or body 

weight effects. Additional acute oral exposure studies that could identify the critical targets of toxicity 

and provide dose-response data are needed for derivation of an acute MRL. 
1,2-DIPHENYLHYDRAZINE 45

6. ADEQUACY OF THE DATABASE

Intermediate-Duration MRLs. No information was located regarding intermediate-duration 

inhalation exposure to 1,2-diphenylhydrazine in humans or animals. As discussed for acute-duration 

exposure, 1,2-diphenylhydrazine is a solid with a low vapor pressure at ambient temperature, which 

makes inhalation exposure to this chemical in the vapor state unlikely. However, the possibility of 

inhalation exposure to dusts of 1,2-diphenylhydrazine, either free or adsorbed to soil, is conceivable. 

Therefore, intermediate-duration studies of inhalation exposure to dusts of 1,2-diphenylhydrazine could 

be designed to provide information on possible toxic effects and exposure levels that cause effects. Data 

were considered adequate to derive an intermediate-duration oral MRL for 1,2-diphenylhydrazine. 

However, additional studies examining a wide range of endpoints would support the identification of the 

liver as the most sensitive target of toxicity. 

Chronic-Duration MRLs. No studies were located regarding chronic inhalation exposure to 

1,2-diphenylhydrazine in humans or animals. As discussed for acute- and intermediate-duration 

exposure, 1,2-diphenylhydrazine is a solid with a low vapor pressure at ambient temperature, which 

makes inhalation exposure to this chemical in the vapor state unlikely. However, the possibility of 

inhalation exposure to dusts of 1,2-diphenylhydrazine either free or adsorbed to soil is conceivable. 

Therefore, chronic-duration studies of inhalation exposure to dusts of 1,2-diphenylhydrazine could be 

designed to provide information on possible toxic effects and exposure levels that cause effects. The NCI 

(1978) bioassay of 1,2-diphenylhydrazine provides the only sufficient chronic oral toxicity data for this 

chemical. This study was not, however, subjected to the peer-review process used for current NTP 

bioassays, and it inadequately evaluated non-neoplastic effects. Additional studies would be particularly 

useful for corroborating and more fully characterizing 1,2-diphenylhydrazine-induced systemic toxicity. 

In particular, more studies could provide information on cause(s) of death due to chronic exposure, and 

delineate carcinogenic and non-carcinogenic doses. 

Health Effects. A small number of studies have evaluated the toxicity of 1,2-diphenylhydrazine. The 

available studies have found liver, lung, gastrointestinal, and cancer effects following oral exposure. No 

inhalation studies were identified and the only dermal study was of poor quality and only examined 

cancer endpoints. Acute-, intermediate-, and chronic-duration inhalation, oral, and dermal studies 

examining a wide range of potential targets of toxicity are needed to identify the critical targets and effect 

levels. Additionally, studies are needed to evaluate immune, neurological, and reproductive function and 

developmental endpoints to assess whether these systems are targets of toxicity.
1,2-DIPHENYLHYDRAZINE 46

6. ADEQUACY OF THE DATABASE

Epidemiology and Human Dosimetry Studies. Health effects of 1,2-diphenylhydrazine have not 

been described in humans. As discussed in Chapter 5, the potential for environmental exposure to 

1,2-diphenylhydrazine is extremely low. Although dermal exposure to 1,2-diphenylhydrazine could 

occur at a contaminated waste site, it is highly unlikely that segments of the general population will be 

exposed to 1,2-diphenylhydrazine.

Biomarkers of Exposure and Effect. No biomarkers are known that are specific for 1,2-diphenylhydrazine exposure. If 1,2-diphenylhydrazine or its metabolites in urine can be correlated with exposure, 

it may be possible to monitor humans for exposure. No biomarkers of effect have been identified.

Absorption, Distribution, Metabolism, and Excretion. The general metabolic pathways of 

1,2-diphenylhydrazine are identifiable based on limited evidence for 1,2-diphenylhydrazine in oral, 

intratracheal, and injection experiments with rats, metabolism data for azobenzene (which is metabolized 

to 1,2-diphenylhydrazine), and metabolism data for aniline (an initial metabolite). The relative 

contribution of the different pathways is not established. Although oral absorption of 1,2-diphenylhydrazine and urinary excretion of 1,2-diphenylhydrazine and its metabolites are apparent, there is no 

information on the rate and extent of absorption, excretion, or tissue distribution following oral exposure. 

Investigations of the toxicokinetics of 1,2-diphenylhydrazine following dermal exposure have not been 

conducted. Additional studies of absorption, distribution, metabolism, and excretion in animals by the 

oral and dermal routes of exposure would provide information needed for sufficient characterization of 

the toxicokinetics of 1,2-diphenylhydrazine. Studies addressing differences in metabolism between oral 

and dermal routes would be particularly informative, as benzidine may be formed by acidity in the 

stomach.

Comparative Toxicokinetics. No data are available to determine if there are differences in the 

toxicokinetics of 1,2-diphenylhydrazine among species. Toxicokinetic studies with different species 

could help explain observed differences in toxicity and carcinogenicity between rats and mice, and help 

identify the animal species that serves as the best model for extrapolating results to humans.

Children’s Susceptibility. No studies have evaluated the toxicity of 1,2-diphenylhydrazine in 

children or young animals. Studies in young animals would be useful to address potential concerns that 

children may be more susceptible to the toxicity of 1,2-diphenylhydrazine than adults. As previously 

noted, developmental toxicity studies are also needed.
1,2-DIPHENYLHYDRAZINE 47

6. ADEQUACY OF THE DATABASE

Physical and Chemical Properties. Physical and chemical properties are essential for estimating 

the partitioning of a chemical in the environment. Data are available for only a few physical and 

chemical properties of 1,2-diphenylhydrazine, and most of these have limited experimental descriptions. 

Therefore, an evaluation of the accuracy of the data is difficult. Specifically, measured solubility, vapor 

pressure, Koc, pKa, and Henry's Law constant at environmentally significant temperatures would help to 

remove any doubt concerning the accuracy of the partitioning estimates, especially in circumstances 

where 1,2-diphenylhydrazine does not oxidize rapidly (such as when high concentrations are present). 

These data form the basis of much of the input requirements for environmental models that predict the 

behavior of a chemical under specific conditions, including hazardous waste landfills. In addition, the 

uncertainty in these measurements can be used to estimate the sensitivity of these properties in 

determining the overall fate of 1,2-diphenylhydrazine in the environment.

Production, Import/Export, Use, Release, and Disposal. Production methods for 1,2-diphenylhydrazine are well described in the literature (including the patent literature); there does not appear to be a 

need for further information in this area. Uses of 1,2-diphenylhydrazine are documented, but no recent 

production figures or detailed descriptions of uses are available. This information is useful for estimating 

the potential for environmental releases from manufacturing and use industries as well as the potential 

environmental burden, but it is difficult to obtain in the detail desired since it is considered confidential 

business information for those industries that manufacture 1,2-diphenylhydrazine. Release information is 

similar to use information in that it is not obtained easily and can be used to estimate environmental 

burdens and potentially exposed populations. TRI will provide some of this information in the future. 

Disposal information is useful for determining environmental burden and potential concentrations where 

environmental exposures may be high. Data on different disposal methods for 1,2-diphenylhydrazine are 

lacking. 

Environmental Fate. The environmental fate and transport of 1,2-diphenylhydrazine are influenced by 

its rapid oxidation under aerobic conditions. Direct photolysis and biodegradation studies are lacking, but 

are not likely important due to the rapid rate of oxidation. A data need exists to study the fate of 

1,2-diphenylhydrazine under anaerobic conditions, which may be found in anoxic layers of sediment or 

groundwater.

Bioavailability from Environmental Media. No studies were located regarding the bioavailability 

of 1,2-diphenylhydrazine from environmental media, but lack of these data does not necessarily indicate a 

lack of bioavailability. As exposure to 1,2-diphenylhydrazine could occur at waste sites by dermal 
1,2-DIPHENYLHYDRAZINE 48

6. ADEQUACY OF THE DATABASE

contact with contaminated soil or by ingestion of contaminated soil, it would be useful to know if dermal 

or oral absorption of 1,2-diphenylhydrazine from environmental media could occur. Information on 

dermal absorption of 1,2-diphenylhydrazine from other media is not available, but qualitative evidence 

indicates that 1,2-diphenylhydrazine in diet or oil media is absorbed from the gastrointestinal tract.

Food Chain Bioaccumulation. 1,2-Diphenylhydrazine reacts rapidly in water to form azobenzene 

and other oxidation products (the half-life in waste water is 60 minutes). Because of this and based upon 

the log octanol/water partition coefficient, no bioaccumulation is expected in any aquatic organism.

Exposure Levels in Environmental Media. Environmental monitoring data are not available or are 

of questionable accuracy for water, soil, and air. These data would be helpful in determining the ambient

concentrations of 1,2-diphenylhydrazine so that exposure estimates for the general population could be 

made as well as 1,2-diphenylhydrazine exposure estimates for terrestrial and aquatic organisms.

Exposure Levels in Humans. The database for exposure levels in humans is very limited, and it is 

unclear if an exposed population exists given the rapid disappearance of 1,2-diphenylhydrazine from the 

environment. While a more complete database would be helpful in determining the current exposure 

levels and thereby estimating the average daily dose associated with various scenarios (e.g., living near a 

hazardous waste site), a number of factors limit establishing such a program, including the lack of 

appropriate analytical methods.

Exposures of Children. No data were located on exposures in children. See the previous section for 

issues relating to collecting monitoring data.

Analytical Methods. No adequate methods are available for the analysis of 1,2-diphenylhydrazine in 

biological materials. If this information were available, it would allow both investigators and reviewers 

to assess the accuracy and uncertainty of the methods used in toxicological studies. Furthermore, the 

ready availability of tested analytical methods, including sample preservation, would permit a 

standardized approach to the analysis of biological materials to assist in measuring human exposure and 

monitoring effects in humans. Adequate methods appear to be available for the analysis of 1,2-diphenylhydrazine metabolites in biological materials. Metabolites include azobenzene and aniline, both of which 

appear to be amenable to analysis by standard methods. 1,2-Diphenylhydrazine and its metabolites, 

however, have not been established as a quantitative biomarker of exposure to 1,2-diphenylhydrazine.
1,2-DIPHENYLHYDRAZINE 49

6. ADEQUACY OF THE DATABASE

While analytical methods appear to be available for the analysis of 1,2-diphenylhydrazine, no methods 

were found for the preservation of 1,2-diphenylhydrazine in ambient air, water, or soil samples. Since 

1,2-diphenylhydrazine is rapidly oxidized to azobenzene and has been previously reported to decompose 

instantaneously to azobenzene when introduced to the GC injection port (Riggin and Howard 1979), most 

GC analysis of 1,2-diphenylhydrazine are calibrated using azobenzene and the results are reported as a

combination of both of these compounds.

6.3 ONGOING STUDIES 

No ongoing studies were identified by the National Institutes of Health (NIH) (RePORTER 2020).
1,2-DIPHENYLHYDRAZINE 50

CHAPTER 7. REGULATIONS AND GUIDELINES

Pertinent international and national regulations, advisories, and guidelines regarding 

1,2-diphenylhydrazine in air, water, and other media are summarized in Table 7-1. This table is not an 

exhaustive list, and current regulations should be verified by the appropriate regulatory agency.

ATSDR develops MRLs which are substance specific guidelines intended to serve as screening levels by 

ATSDR health assessors and other responders to identify contaminants and potential health effects that 

may be of concern at hazardous waste sites. See Section 1.3 and Appendix A for detailed information on 

the MRLs for 1,2-diphenylhydrazine.

Table 7-1. Regulations and Guidelines Applicable to 1,2-Diphenylhydrazine

Agency Description Information Reference

Air

EPA RfC Value not derived IRIS 2006

WHO Air quality guidelines Not listed WHO 2010

Water & Food

EPA Drinking water standards and health 

advisories 

Not listed EPA 2018a

National primary drinking water regulations Not listed EPA 2009

RfD Not assessed IRIS 2006

WHO Drinking water quality guidelines Not listed WHO 2017

FDA Substances Added to Food Not listeda FDA 2020

Cancer

HHS Carcinogenicity classification Reasonably anticipated to 

be a human carcinogen

NTP 2016

EPA Carcinogenicity classification B2b IRIS 2006

IARC Carcinogenicity classification Not listed IARC 2020

Occupational

ACGIH TLV (TWA) Not listed ACGIH 2019

OSHA PEL (8-hour TWA) for general industry, 

construction, and shipyards

Not listed OSHA 2019a, 

2019b, 2019c

NIOSH REL (up to 10-hour TWA) Not listed NIOSH 2018
1,2-DIPHENYLHYDRAZINE 51

7. REGULATIONS AND GUIDELINES

Table 7-1. Regulations and Guidelines Applicable to 1,2-Diphenylhydrazine

Agency Description Information Reference

Emergency Criteria

EPA AEGLs-air Not listed EPA 2018b

DOE PACs-air DOE 2018a

PAC-1c 120 mg/m3

PAC-2c 1,300 mg/m3

PAC-3c 7,900 mg/m3

aThe Substances Added to Food inventory replaces EAFUS and contains the following types of ingredients: food and 

color additives listed in FDA regulations, flavoring substances evaluated by FEMA or JECFA, GRAS substances 

listed in FDA regulations, substances approved for specific uses in food prior to September 6, 1958, substances that 

are listed in FDA regulations as prohibited in food, delisted color additives, and some substances "no longer FEMA 

GRAS".

bB2: probable human carcinogen.

cDefinitions of PAC terminology are available from U.S. Department of Energy (DOE 2018b).

ACGIH = American Conference of Governmental Industrial Hygienists; AEGL = acute exposure guideline levels; 

DOE = Department of Energy; EAFUS = Everything Added to Food in the United States; EPA = Environmental 

Protection Agency; FDA = Food and Drug Administration; FEMA = Flavor and Extract Manufacturers Association of 

the United States; GRAS = generally recognized as safe; HHS = Department of Health and Human Services; 

IARC = International Agency for Research on Cancer; IRIS = Integrated Risk Information System; JECFA = Joint 

FAO/WHO Expert Committee on Food Additives; NIOSH = National Institute for Occupational Safety and Health; 

NTP = National Toxicology Program; OSHA = Occupational Safety and Health Administration; PAC = protective 

action criteria; PEL = permissible exposure limit; REL = recommended exposure limit; RfC = inhalation reference 

concentration; RfD = oral reference dose; TLV = threshold limit value; TWA = time-weighted average; WHO = World 

Health Organization
1,2-DIPHENYLHYDRAZINE 52

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Administration. Code of Federal Regulations. 29 CFR 1910.1000. https://www.osha.gov/lawsregs/regulations/standardnumber/1910/1910.1000TABLEZ1. October 25, 2019. 

OSHA. 2019b. Occupational safety and health standards for shipyard employment. Subpart Z - Toxic 

and hazardous substances. Air contaminants. Occupational Safety and Health Administration. 

Code of Federal Regulations. 29 CFR 1915.1000. https://www.osha.gov/lawsregs/regulations/standardnumber/1915/1915.1000. October 25, 2019. 

OSHA. 2019c. Safety and health regulations for construction. Subpart D - Occupational health and 

environment controls. Gases, vapors, fumes, dusts, and mists. Occupational Safety and Health 

Administration. Code of Federal Regulations. 29 CFR 1926.55 Appendix A. 

https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.55AppA. October 25, 2019. 

Patterson JW, Kodukala PS. 1981. Biodegradation of hazardous organic pollutants. Chem Eng Prog 

77(4):48-55. 

Pfordte K. 1973. [Acute toxicity and hemiglobine-forming properties of various industrial noxes. 

Nitrobenzole and its reduction products]. Z Gesamte Hyg 19(1):35-39. (German)

Pliss GB. 1974. [Carcinogenic properties of hydrazobenzene]. Vopr Onkol 20(4):53-57. (Russian)

RePORTER. 2020. 1,2-Diphenylhydrazine. Research Portfolio Online Reporting Tools. National 

Institutes of Health. http://projectreporter.nih.gov/reporter.cfm. April 30, 2020. 

Riggin RM, Howard CC. 1979. Determination of benzidine, dichlorobenzidine, and diphenylhydrazine 

in aqueous media by high performance liquid chromatography. Anal Chem 51(2):210-214. 

http://doi.org/10.1021/ac50038a014. 

Rooney AA, Boyles AL, Wolfe MS, et al. 2014. Systematic review and evidence integration for 

literature-based environmental health science assessments. Environ Health Perspect 122(7):711-718. 

http://doi.org/10.1289/ehp.1307972. 

Sandridge RL, Staley HB. 1978. Amines by reduction. In: Encyclopedia of chemical technology. Vol. 

2. 3rd ed. New York, NY: McGraw-Hill Book Co., 355-376. 

Schafer EW, Bowles WA. 1985. Acute oral toxicity and repellency of 933 chemicals to house and deer 

mice. Arch Environ Contam Toxicol 14(1):111-129. http://doi.org/10.1007/bf01055769. 

Seiler JP. 1977. Inhibition of testicular DNA synthesis by chemical mutagens and carcinogens. 

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http://doi.org/10.1016/0165-1161(77)90007-3. 
1,2-DIPHENYLHYDRAZINE 56

8. REFERENCES

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neoplasms of the urinary bladder]. Urol Nefrol (Mosk) 1(1):38-42. (Russian)

Spitz S, Maguigan WH, Dobriner K. 1950. The carcinogenic action of benzidine. Cancer 3(5):789-804. 

http://doi.org/10.1002/1097-0142(1950)3:5<789::aid-cncr2820030505>3.0.co;2-u. 

Tabak HH, Quave SA, Mashni CI. 1981a. Biodegradability studies for predicting the environmental fate 

of organic priority pollutants. In: Test protocols for environmental fate & movement of toxicants : 

Proceedings of a symposium, Association of Official Analytical Chemists, 94th annual meeting, 

October 21, 22, 1980, Washington, DC. Arlington, VA: AOAC, 267-328. 

Tabak HH, Quave SA, Mashni CI, et al. 1981b. Biodegradability studies with organic priority pollutant 

compounds. J Water Pollut Control Fed 53(10):1503-1518. 

Tang IS, Yen TF, Kawahara FK. 1983. Separation and identification of the organic species in coal 

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geochemical aspects of fossil energy extraction. Ann Arbor, MI: Ann Arbor Science Publishers, 85-

106. 

TRI18. 2020. TRI explorer: Providing access to EPA’s toxics release inventory data. Washington, DC: 

U.S. Environmental Protection Agency. http://www.epa.gov/triexplorer/. February 10, 2020. 

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2012. 

WHO. 2017. Guidelines for drinking-water quality. Fourth edition incorporating the first addendum. 

Geneva, Switzerland: World Health Organization. 

http://apps.who.int/iris/bitstream/10665/254637/1/9789241549950-eng.pdf?ua=1. February 28, 

2017. 

Williams RT. 1959. The metabolism of dyestuffs and other colouring matters. In: Detoxication 

mechanisms. The metabolism and detoxication of drugs, toxic substances and other organic 

compounds. 2nd ed. New York, NY: John Wiley and Sons, Inc., 472-488. 

Yoon JS, Mason JM, Valencia R, et al. 1985. Chemical mutagenesis testing in Drosophila. IV. Results 

of 45 coded compounds tested for the National Toxicology Program. Environ Mutagen 7(3):349-

367. http://doi.org/10.1002/em.2860070310. 
1,2-DIPHENYLHYDRAZINE A-1

APPENDIX A. ATSDR MINIMAL RISK LEVEL WORKSHEETS

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 route and duration of exposure. MRLs are based on 

noncancer health effects only; cancer effects are not considered. 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 NOAEL/uncertainty factor approach. They are 

below levels that might cause adverse health effects in the people most sensitive to such chemicalinduced effects. MRLs are derived for acute (1–14 days), intermediate (15–364 days), and chronic 

(≥365 days) 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 substance-induced endpoint considered to 

be of relevance to humans. Serious health effects (such as irreparable damage to the liver or kidneys, or 

birth defects) are not used as a basis for establishing MRLs. Exposure to a level above the MRL does not 

mean that adverse health effects will occur.

MRLs are intended only to serve as a screening tool to help public health professionals decide where to 

look more closely. They may also be viewed as a mechanism to identify those hazardous waste sites that 

are not expected to cause adverse health effects. Most MRLs contain a degree of uncertainty because of 

the lack of precise toxicological information on the people who might be most sensitive (e.g., infants, 

elderly, nutritionally or immunologically compromised) to the effects of hazardous substances. ATSDR 

uses a conservative (i.e., protective) approach to address this uncertainty consistent with the public health 

principle of prevention. Although human data are preferred, MRLs often must be based on animal studies 

because relevant human studies are lacking. In the absence of evidence to the contrary, ATSDR assumes 

that humans are more sensitive to the effects of hazardous substance than animals and that certain persons 

may be particularly sensitive. Thus, the resulting MRL may be as much as 100-fold below levels that 

have been shown to be nontoxic in laboratory animals.
1,2-DIPHENYLHYDRAZINE A-2

APPENDIX A

Proposed MRLs undergo a rigorous review process: Health Effects/MRL Workgroup reviews within the 

Office of Innovation and Analytics, Toxicology Section, expert panel peer reviews, and agency-wide 

MRL Workgroup reviews, with participation from other federal agencies and comments from the public. 

They are subject to change as new information becomes available concomitant with updating the 

toxicological profiles. Thus, MRLs in the most recent toxicological profiles supersede previously 

published MRLs. For additional information regarding MRLs, please contact the Office of Innovation 

and Analytics, Toxicology Section, Agency for Toxic Substances and Disease Registry, 1600 Clifton 

Road NE, Mailstop S102-1, Atlanta, Georgia 30329-4027.
1,2-DIPHENYLHYDRAZINE A-3

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: 1,2-Diphenylhydrazine

CAS Numbers: 122-77-6

Date: October 2020

Profile Status: Final

Route: Inhalation

Duration: Acute

MRL Summary: There are insufficient data for derivation of an acute-duration inhalation MRL. 

Rationale for Not Deriving an MRL: No acute-duration inhalation studies were identified for 

1,2-diphenylhydrazine.

Agency Contact (Chemical Manager): Sam Keith, M.S., C.H.P.
1,2-DIPHENYLHYDRAZINE A-4

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: 1,2-Diphenylhydrazine

CAS Numbers: 122-77-6

Date: October 2020

Profile Status: Final

Route: Inhalation

Duration: Intermediate

MRL Summary: There are insufficient data for derivation of an intermediate-duration inhalation MRL. 

Rationale for Not Deriving an MRL: No intermediate-duration inhalation studies were identified for 

1,2-diphenylhydrazine.

Agency Contact (Chemical Manager): Sam Keith, M.S., C.H.P.
1,2-DIPHENYLHYDRAZINE A-5

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: 1,2-Diphenylhydrazine

CAS Numbers: 122-77-6

Date: October 2020

Profile Status: Final

Route: Inhalation

Duration: Chronic

MRL Summary: There are insufficient data for derivation of a chronic-duration inhalation MRL. 

Rationale for Not Deriving an MRL: No chronic-duration inhalation studies were identified for 

1,2-diphenylhydrazine.

Agency Contact (Chemical Manager): Sam Keith, M.S., C.H.P.
1,2-DIPHENYLHYDRAZINE A-6

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: 1,2-Diphenylhydrazine

CAS Numbers: 122-77-6

Date: October 2020

Profile Status: Final

Route: Oral

Duration: Acute

MRL Summary: There are insufficient data for derivation of an acute-duration oral MRL. 

Rationale for Not Deriving an MRL: The acute-duration oral database was not considered suitable for 

derivation of an MRL because lethality was the only adverse effect observed in the available studies. 

The Dodd et al. (2012) study of 1,2-diphenylhydrazine is the only acute oral toxicity study that evaluated 

endpoints other than lethality. The study found no adverse alterations in body weight, liver weight, liver 

enzymes, or liver histopathology in rats treated with 1,2-diphenyhydrazine for 5 days or 2 weeks at doses 

as high as 15.5 mg/kg/day. 

Agency Contact (Chemical Manager): Sam Keith, M.S., C.H.P.
1,2-DIPHENYLHYDRAZINE A-7

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: 1,2-Diphenylhydrazine

CAS Numbers: 122-77-6

Date: October 2020

Profile Status: Final

Route: Oral

Duration: Intermediate

MRL: 0.05 mg/kg/day

Critical Effect: Hepatic effects

Reference: Dodd et al. 2012

Point of Departure: NOAEL of 4.8 mg/kg/day 

Uncertainty Factor: 100 

LSE Graph Key: 6

Species: Rat

MRL Summary: An intermediate oral MRL of 0.05 mg/kg/day was derived for 1,2-diphenylhydrazine. 

The MRL is based on a NOAEL of 4.80 mg/kg/day for hepatic effects in rats exposed to 

1,2-diphenylhydrazaine in the diet for 13 weeks (Dodd et al. 2012). This NOAEL was divided by an 

uncertainty factor of 100 (10 for animal to human extrapolation and 10 to account for intra-human 

variation). 

Selection of the Critical Effect: Three studies have evaluated toxicity of 1,2-diphenyhydrazine following 

intermediate-duration oral exposure. Effects identified include death, gastrointestinal effects, and hepatic 

effects (Dodd et al. 2012; Marhold et al. 1968; NCI 1978). Increases in mortality were observed in rats at 

54 mg/kg/day (NCI 1978) and in mice exposed to 390 mg/kg/day (NCI 1978). An increase in intestinal 

hemorrhage was reported in mice exposed to 390 mg/kg/day for 4 weeks (NCI 1978); gastrointestinal 

effects were not observed in similarly exposed rats. Dodd et al. (2012) reported significant increases in 

the incidences of hypertrophy, eosinophilic granular cytoplasm, and bile duct duplication in the livers of 

rats exposed to ≥10.3 mg/kg/day for 13 weeks, but not after 4 weeks of exposure. At 15.5 mg/kg/day, 

macrovesiculation was also observed in the liver of rats exposed for 13 weeks (Dodd et al. 2012). No 

other intermediate-duration studies included histological examination of the liver. Based on the limited 

available data, the liver appears to be the most sensitive target of toxicity. This is supported by liver 

effects (fatty metamorphosis or coagulative necrosis) in rats and mice chronically exposed to 

1,2-diphenylhydrazine in the diet (NCI 1978).

Selection of the Principal Study: Due to incomplete details of study design and lack of histopathology 

data in the 4-week dose-finding study (NCI 1978) and the Marhold et al. (1968) study, derivation of the 

MRL for hepatic effects is based on findings in the multi-dose study by Dodd et al. (2012). The selected 

study provides the best available data for characterizing the dose-response relationship for liver effects in 

laboratory animals orally exposed to 1,2-diphenylhydrazine for intermediate durations and it identified 

the lowest reliable LOAEL value.

Summary of the Principal Study:

Dodd DE, Pluta LJ, Sochaski MA, et al. 2012. Subchronic hepatotoxicity evaluation of hydrazobenzene 

in Fischer 344 rats. Int J Toxicol 31: 564-571.

Groups of male Fischer 344 rats (minimum 10/group) were exposed to 0, 5, 20, 80, 200, or 300 ppm

1,2-diphenylhydrazine in the diet for 4 or 13 weeks. Mean administered doses, calculated from weekly 

food consumption and analytic diet concentration data, were reported to be 0, 0.32, 1.26, 4.80, 10.3, and 
1,2-DIPHENYLHYDRAZINE A-8

APPENDIX A

15.5 mg/kg/day. Endpoints evaluated included clinical observations, body weight, food consumption, 

serum chemistry, liver weights, gross pathology, and liver histopathology. Significant, but marginal 

decreases in body weights (up to ~6% decrease, compared with control values) beginning at 8 weeks 

occurred in animals exposed to 15.5 mg/kg/day. There were no clinical signs of toxicity or gross 

pathology throughout the study or at necropsy. Microscopic alterations in the liver, including slight/mild 

hypertrophy, minimal eosinophilic granular cytoplasm, multifocal bile duct duplications, and multifocal 

macrovesiculation, an indicator of lipid accumulation within hepatocytes, were observed only at 13 weeks 

at doses ≥10.3 mg/kg/day; the incidences of these lesions are presented in Table A-1. Relative liver 

weights also significantly increased (7.7 and 4.4%) at 4 and 13 weeks in 10.3 mg/kg/day rats, and showed 

concentration dependence, with increases of 8.5 and 10.7% at the same time points after treatment with 

15.5 mg/kg/day. No consistent changes in serum alanine aminotransferase, total bilirubin, or lactate 

dehydrogenase were observed at any dose, but serum aspartate aminotransferase decreased by 26% at 

13 weeks after treatment with 15.5 mg/kg/day. Decreases in serum alkaline phosphatase occurred 

beginning at a dose of 1.26 mg/kg/day at 13 weeks, but were also observed at earlier time points at higher 

doses; the toxicological significance of the decreases in alkaline phosphatase is not known. The 

investigators noted that the decreases were unexpected and did not correlate with other liver effects (Dodd 

et al. 2012). 

Table A-1. Incidences of Liver Lesions in Rats Exposed to 1,2-Diphenylhydrazine 

in the Diet for 13 Weeks

Dose (mg/kg/day)

0 0.32 1.26 4.80 10.3 15.5

Slight/mild hypertrophy (diffuse) 0/12 0/10 0/10 0/10 10/10 10/10

Slight/mild macrovesiculation

(multifocal)

0/12 0/10 0/10 0/10 1/10 10/10

Minimal eosinophilic granular cytoplasm 0/12 0/10 0/10 0/10 10/10 9/10

Minimal to slight/mild bile duct duplication 

(multifocal)

0/12 0/10 0/10 0/10 8/10 10/10

Source: Dodd et al. 2012

Selection of the Point of Departure for the MRL: Data were not amenable to benchmark dose modeling 

due to the steep dose-response curve and the lack of information between the extremes of the control 

incidence (0%) and the maximal response (≥80%). Using a NOAEL/LOAEL approach, the NOAEL of 

4.8 mg/kg/day for the absence of histopathological alterations in the liver was selected as the basis of the

MRL.

Adjustment Intermittent Exposure: Not applicable.

Uncertainty Factor: The NOAEL of 4.8 mg/kg/day was divided by a total uncertainty factor of 100:

• 10 for animal to human extrapolation

• 10 for human variability 

MRL = NOAEL ÷ UF

4.8 mg/kg/day ÷ (10 x 10) = 0.048 mg/kg/day ≈ 0.05 mg/kg/day

Other Additional Studies or Pertinent Information: In a chronic-duration study, dietary exposure to 

1,2-diphenylhydrazine resulted in interstitial inflammation in the lungs, hyperkeratosis/acanthosis in the 
1,2-DIPHENYLHYDRAZINE A-9

APPENDIX A

stomach, and fatty metamorphosis in the liver of rats exposed for 78 weeks (NCI 1978). Coagulative 

necrosis was also observed in the livers of female mice exposed to 52 mg/kg/day (NCI 1978). The results 

of the NCI (1978) study support the selection of the liver lesions as the most sensitive effect.

Agency Contact (Chemical Manager): Sam Keith, M.S., C.H.P.
1,2-DIPHENYLHYDRAZINE A-10

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: 1,2-Diphenylhydrazine

CAS Numbers: 122-77-6

Date: October 2020

Profile Status: Final

Route: Oral

Duration: Chronic

MRL Summary: The available chronic oral data (NCI 1978) were not considered adequate for derivation 

of a chronic oral MRL.

Rationale for Not Deriving an MRL: The only available chronic-duration oral study was not considered 

suitable for derivation of an MRL due to the long duration (28–30 weeks) between exposure termination 

and histological examination and methodological problems with the only available study. 

The NCI (1978) bioassay of 1,2-diphenylhydrazine provides the only sufficient chronic oral toxicity data 

for this chemical. In this study, rats and mice were exposed to 1,2-diphenylhydrazine in the diet for 

78 weeks followed by a 28–30-week observation period. The facilities supplying the rats, the diet, and 

the bedding used for low-dose rats and their controls differed from those used for the high-dose rats and 

their controls. Additionally, the low-dose control group and low- and high-dose exposed rats were 

housed in a different room than the high-dose control group. Similar differences in animal husbandry 

were noted for the mice. All animals, regardless of time or reason for death, whether due to lethality, 

sacrifice when moribund, or at study termination, were necropsied and were included in histopathological 

incidence evaluations. Significant increases in mortality were observed in female rats exposed to 

9.2 mg/kg/day and in male and female mice exposed to 69 mg/kg/day; times and causes of death were not 

provided (NCI 1978). Non-neoplastic alterations included interstitial lung inflammation, acanthosis of 

the stomach, hyperkeratosis of the stomach, and fatty metamorphosis in the liver; the NOAEL and 

LOAEL values for these effects are presented in Table A-2. Although the study identifies 3.7 mg/kg/day 

as the lowest LOAEL for interstitial lung inflammation and acanthosis of the stomach in female rats, there 

is some uncertainty with this categorization, since the incidences of these lesions were not significantly 

increased at the higher dose level (9.2 mg/kg/day). Adding to the uncertainty is the inconsistency of these 

effects between the low-dose control group and the high-dose control group; for example, incidences of 

lung interstitial inflammation was 0/47 for the low-dose female controls and 6/50 in the high-dose female 

controls (in males, the incidences were 0/47 and 4/48 in low- and high-dose controls). In addition to these 

non-neoplastic lesions, increases in the incidence of neoplastic lesions were observed, including 

hepatocellular carcinomas in male rats exposed to ≥6.3 mg/kg/day and female mice exposed to 

69 mg/kg/day, neoplastic nodules in the livers of female rats exposed to 9.2 mg/kg/day, combined 

squamous cell carcinomas/papillomas in the ear canal, Zymbal’s gland, and skin of the ear in male rats 

exposed to 24 mg/kg/day, adrenal gland pheochromacytomas in male rats exposed to 24 mg/kg/day, and 

mammary gland adenocarcinomas in female rats exposed to 9.2 mg/kg/day (NCI 1978). 
1,2-DIPHENYLHYDRAZINE A-11

APPENDIX A

Table A-2. Summary of Relevant NOAEL and LOAEL Values in Rats and Mice 

Following Chronic-Duration Oral Exposure to 1,2-Diphenylhydrazinea

Males Females

NOAEL

(mg/kg/day)

LOAEL

(mg/kg/day)

NOAEL

(mg/kg/day)

LOAEL

(mg/kg/day)

Fischer 344 rats

Increased mortality 9.2 

Decreased body weight gain 6.3 24 3.7 9.2

Interstitial lung inflammation 6.3 3.7b

Acanthosis of stomach 6.3 24 3.7b

Hyperkeratosis of stomach 6.3 24 9.2 

Fatty metamorphosis in liver 6.3 24 3.7 9.2c

B6C3F1 mice

Increased mortality 69 69 

Decreased body weight 14 69 6.9 69 

Coagulative hepatic necrosis 6.9 69 

aRats and mice were exposed for 78 weeks followed by a 28–30-week observation period. bThis effect was not observed in rats exposed to 9.2 mg/kg/day.

cIncidence higher than low-dose control group, but not high-dose control group.

Source: NCI 1978

The NCI (1978) study was not considered suitable for the derivation of a chronic-duration oral MRL due 

to the lack of dose-response for effects observed at the lowest dose tested, the long recovery period, and 

some methodological issues with the study design. As summarized in Table A-3, significant increases in 

the incidence of interstitial lung inflammation and acanthosis of the stomach were observed in female rats 

at the lowest dose tested (3.7 mg/kg/day), but were not observed at the highest dose (9.2 mg/kg/day). In 

male rats, an increase in interstitial lung inflammation was observed in male rats at 6.3 and 24 mg/kg/day. 

Stomach lesions were observed in males at 24 mg/kg/day, but not at 6.3 mg/kg/day. The lack of doseresponse relationships increases the uncertainty in assessing whether the effects are due to 1,2-diphenylhydrazine exposure. Differences in the source of the animals, housing, and diet between the low-dose 

controls and exposed animals and the high-dose controls and exposed animals may have also contributed 

to the observed differences. In addition, the long recovery period complicates the identification of the 

NOAELs and LOAELs because it is not known if effects occurred at lower doses and the damage was 

repaired prior to examination. 
1,2-DIPHENYLHYDRAZINE A-12

APPENDIX A

Table A-3. Incidence of Lung and Stomach Lesions in Rats Following ChronicDuration Oral Exposure to 1,2-Diphenylhydrazinea

Low dose High dose

Female rats Controls 3.7 mg/kg/day Controls 9.2 mg/kg/day

Interstitial lung inflammation 0/47 (0%) 29/50b (58%) 6/50 (12%) 7/50 (14%)

Acanthosis of stomach 0/46 (0%) 6/50b (12%) 2/48 (4%) 5/44 (11%)

Low dose High dose

Male rats Controls 6.3 mg/kg/day Controls 24 mg/kg/day

Interstitial lung inflammation 0/47 (0%) 12/49b (24%) 4/48 (8%) 16/48b (33%)

Acanthosis of stomach 0/47 (0%) 4/49 (8%) 1/49 (2%) 17/47b (36%)

aRats were exposed for 78 weeks followed by a 28–30-week observation period. bStatistically significant differences (p<0.05); Fisher Exact Test conducted by ATSDR.

Source: NCI 1978

Agency Contact (Chemical Manager): Sam Keith, M.S., C.H.P.
1,2-DIPHENYLHYDRAZINE B-1

APPENDIX B. LITERATURE SEARCH FRAMEWORK FOR 

1,2-DIPHENYLHYDRAZINE

The objective of the toxicological profile is to evaluate the potential for human exposure and the potential 

health hazards associated with inhalation, oral, or dermal/ocular exposure to 1,2-diphenylhydrazine.

B.1 LITERATURE SEARCH AND SCREEN 

A literature search and screen was conducted to identify studies examining health effects, toxicokinetics, 

mechanisms of action, susceptible populations, biomarkers, chemical interactions, physical and chemical 

properties, production, use, environmental fate, environmental releases, and environmental and biological 

monitoring data for 1,2-diphenylhydrazine. ATSDR primarily focused on peer-reviewed articles without 

publication date or language restrictions. Non-peer-reviewed studies that were considered relevant to the 

assessment of the health effects of 1,2-diphenylhydrazine have undergone peer review by at least three 

ATSDR-selected experts who have been screened for conflict of interest. The inclusion criteria used to 

identify relevant studies examining the health effects of 1,2-diphenylhydrazine are presented in 

Table B-1.

Table B-1. Inclusion Criteria for the Literature Search and Screen

Health Effects

Species

Human

Laboratory mammals

Route of exposure

Inhalation

Oral

Dermal (or ocular)

Parenteral (these studies will be considered supporting data)

Health outcome

Death

Systemic effects

Body weight effects 

Respiratory effects

Cardiovascular effects

Gastrointestinal effects

Hematological effects

Musculoskeletal effects

Hepatic effects

Renal effects

Dermal effects

Ocular effects

Endocrine effects

Immunological effects

Neurological effects

Reproductive effects
1,2-DIPHENYLHYDRAZINE B-2 

APPENDIX B 

Table B-1. Inclusion Criteria for the Literature Search and Screen

Developmental effects

Other noncancer effects

Cancer

Toxicokinetics

Absorption

Distribution

Metabolism

Excretion

PBPK models

Biomarkers

Biomarkers of exposure

Biomarkers of effect

Interactions with other chemicals

Potential for human exposure

Releases to the environment

Air

Water

Soil

Environmental fate

Transport and partitioning

Transformation and degradation

Environmental monitoring

Air

Water

Sediment and soil

Other media

Biomonitoring

General populations

Occupation populations

B.1.1 Literature Search

The current literature search was intended to update the draft toxicological profile for 1,2-diphenylhydrazine released for public comment in 2019; thus, the literature search was restricted to studies 

published between March 2017 and March 2020. The following main databases were searched in March 

2020: 

• PubMed 

• National Technical Reports Library (NTRL)

• Scientific and Technical Information Network’s TOXCENTER

The search strategy used the chemical names, Chemical Abstracts Service (CAS) numbers,

synonyms, Medical Subject Headings (MeSH) headings, and keywords for 1,2-diphenylhydrazine. 

The query strings used for the literature search are presented in Table B-2. 
1,2-DIPHENYLHYDRAZINE B-3

APPENDIX B

The search was augmented by searching the Toxic Substances Control Act Test Submissions (TSCATS), 

NTP website, and National Institute of Health Research Portfolio Online Reporting Tools Expenditures 

and Results (NIH RePORTER) databases using the queries presented in Table B-3. Additional databases 

were searched in the creation of various tables and figures, such as the TRI Explorer, the Substance 

Priority List (SPL) resource page, and other items as needed. Regulations applicable to 1,2-diphenylhydrazine were identified by searching international and U.S. agency websites and documents.

Review articles were identified and used for the purpose of providing background information and 

identifying additional references. ATSDR also identified reports from the grey literature, which included 

unpublished research reports, technical reports from government agencies, conference proceedings and 

abstracts, and theses and dissertations. 

Table B-2. Database Query Strings 

Database

search date Query string

PubMed

03/2020 ((122-66-7[rn] OR "1,2-diphenylhydrazine"[nm] OR "(sym)-Diphenylhydrazine"[tw] OR 

"1,1'-Hydrazodibenzene"[tw] OR "1,2-Diphenylhydrazine"[tw] OR "hydrazobenzene"[tw] 

OR "N, N'-Bianiline"[tw] OR "N, N'-Diphenylhydrazine"[tw] OR "Symmetrical diphenyl 

hydrazine"[tw] OR "1,1'-hydrazobis-Benzene"[tw] OR "hydrazodi-Benzene"[tw]) AND 

(2017/03/01 : 3000[mhda] OR 2017/03/01 : 3000[crdt] OR 2017/03/01 : 3000[edat] OR 

2016/03/01 : 3000[dp])) OR ("Benzene, 1,1'-hydrazobis-"[tw] OR "Benzene, hydrazodi-"[tw] 

OR "Diphenylhydrazine, 1,2-"[tw] OR "Hydrazine, 1,2-diphenyl-"[tw] OR 

"Hydrazobenzol"[tw]) OR ((("Diphenylhydrazine"[tw] OR "Diphenylhydrazines"[tw]) AND 

"1,2"[tw]) NOT medline[sb])

NTRL

03/2020 "(sym)-Diphenylhydrazine" OR "1,1 -Hydrazodibenzene" OR "1,2-Diphenylhydrazine" OR 

"hydrazobenzene" OR "N, N'-Bianiline" OR "N, N'-Diphenylhydrazine" OR "Symmetrical 

diphenyl hydrazine" OR "1,1'-hydrazobis-Benzene" OR "hydrazodi-Benzene"

"Benzene, 1,1 -hydrazobis-" NOT "1,2-Diphenylhydrazine"

"Benzene, hydrazodi-" NOT "1,2-Diphenylhydrazine"

"Diphenylhydrazine, 1,2-" NOT "1,2-Diphenylhydrazine"

"Hydrazine, 1,2-diphenyl-" NOT "1,2-Diphenylhydrazine"

"Hydrazobenzol" NOT "1,2-Diphenylhydrazine"

Toxcenter

03/2020 FILE 'TOXCENTER' ENTERED AT 17:20:54 ON 29 MAR 2020

CHARGED TO COST=EH038.06.01.LB.02

L1 305 SEA FILE=TOXCENTER 122-66-7 

L2 11 SEA FILE=TOXCENTER L1 AND ED>=20160301 

L3 7 SEA FILE=TOXCENTER L1 AND PY>2015 

L4 11 SEA FILE=TOXCENTER L2 OR L3 

L5 6 SEA FILE=TOXCENTER L4 NOT PATENT/DT 

L6 0 SEA FILE=TOXCENTER L5 AND MEDLINE/F 

L7 0 SEA FILE=TOXCENTER L5 AND MEDLINE/FS 

 ACT TOXQUERY/Q

 ---------

L8 QUE (CHRONIC OR IMMUNOTOX? OR NEUROTOX? OR TOXICOKIN? OR 

 BIOMARKER? OR NEUROLOG?) 

L9 QUE (PHARMACOKIN? OR SUBCHRONIC OR PBPK OR 

EPIDEMIOLOGY/ST,CT,
1,2-DIPHENYLHYDRAZINE B-4

APPENDIX B

Table B-2. Database Query Strings 

Database

search date Query string

 IT) 

L10 QUE (ACUTE OR SUBACUTE OR LD50# OR LD(W)50 OR LC50# OR 

 LC(W)50) 

L11 QUE (TOXICITY OR ADVERSE OR POISONING)/ST,CT,IT 

L12 QUE (INHAL? OR PULMON? OR NASAL? OR LUNG? OR RESPIR?) 

L13 QUE ((OCCUPATION? OR WORKPLACE? OR WORKER?) AND EXPOS?) 

L14 QUE (ORAL OR ORALLY OR INGEST? OR GAVAGE? OR DIET OR DIETS 

OR 

 DIETARY OR DRINKING(W)WATER?) 

L15 QUE (MAXIMUM AND CONCENTRATION? AND (ALLOWABLE OR 

PERMISSIBLE))

L16 QUE (ABORT? OR ABNORMALIT? OR EMBRYO? OR CLEFT? OR FETUS?) 

L17 QUE (FOETUS? OR FETAL? OR FOETAL? OR FERTIL? OR MALFORM? 

OR 

 OVUM?) 

L18 QUE (OVA OR OVARY OR PLACENTA? OR PREGNAN? OR PRENATAL?) 

L19 QUE (PERINATAL? OR POSTNATAL? OR REPRODUC? OR STERIL? OR 

 TERATOGEN?) 

L20 QUE (SPERM OR SPERMAC? OR SPERMAG? OR SPERMATI? OR 

SPERMAS? OR 

 SPERMATOB? OR SPERMATOC? OR SPERMATOG?) 

L21 QUE (SPERMATOI? OR SPERMATOL? OR SPERMATOR? OR 

SPERMATOX? OR 

 SPERMATOZ? OR SPERMATU? OR SPERMI? OR SPERMO?) 

L22 QUE (NEONAT? OR NEWBORN? OR DEVELOPMENT OR 

DEVELOPMENTAL?) 

L23 QUE (ENDOCRIN? AND DISRUPT?) 

L24 QUE (ZYGOTE? OR CHILD OR CHILDREN OR ADOLESCEN? OR 

INFANT?) 

L25 QUE (WEAN? OR OFFSPRING OR AGE(W)FACTOR?) 

L26 QUE (DERMAL? OR DERMIS OR SKIN OR EPIDERM? OR CUTANEOUS?) 

L27 QUE (CARCINOG? OR COCARCINOG? OR CANCER? OR PRECANCER? 

OR 

 NEOPLAS?) 

L28 QUE (TUMOR? OR TUMOUR? OR ONCOGEN? OR LYMPHOMA? OR 

CARCINOM?) 

L29 QUE (GENETOX? OR GENOTOX? OR MUTAGEN? OR 

GENETIC(W)TOXIC?) 

L30 QUE (NEPHROTOX? OR HEPATOTOX?) 

L31 QUE (ENDOCRIN? OR ESTROGEN? OR ANDROGEN? OR HORMON?) 

L32 QUE (OCCUPATION? OR WORKER? OR WORKPLACE? OR EPIDEM?) 

L33 QUE L8 OR L9 OR L10 OR L11 OR L12 OR L13 OR L14 OR L15 OR L16 

 OR L17 OR L18 OR L19 OR L20 OR L21 OR L22 OR L23 OR L24 OR L25 

 OR L26 OR L27 OR L28 OR L29 OR L30 OR L31 OR L32 

L34 QUE (RAT OR RATS OR MOUSE OR MICE OR GUINEA(W)PIG? OR 

MURIDAE 

 OR DOG OR DOGS OR RABBIT? OR HAMSTER? OR PIG OR PIGS OR 

SWINE 

 OR PORCINE OR MONKEY? OR MACAQUE?) 
1,2-DIPHENYLHYDRAZINE B-5

APPENDIX B

Table B-2. Database Query Strings 

Database

search date Query string

L35 QUE (MARMOSET? OR FERRET? OR GERBIL? OR RODENT? OR 

LAGOMORPHA 

 OR BABOON? OR CANINE OR CAT OR CATS OR FELINE OR MURINE) 

L36 QUE L33 OR L34 OR L35 

L37 QUE (HUMAN OR HUMANS OR HOMINIDAE OR MAMMALS OR MAMMAL? 

OR 

 PRIMATES OR PRIMATE?) 

L38 QUE L36 OR L37 

 ---------

L39 3 SEA FILE=TOXCENTER L5 AND L38 

L40 3 SEA FILE=TOXCENTER L5 NOT L39 

 D SCAN L40

 D SCAN L39

Table B-3. Strategies to Augment the Literature Search

Source Query and number screened when available

TSCATS via 

ChemView

03/2020 Compounds searched: 122-66-7

NTP

03/2020 "1,2-Diphenylhydrazine" "hydrazobenzene" "N,N'-Diphenylhydrazine" "N,N'-Bianiline"

"(sym)-Diphenylhydrazine" "1,1'-Hydrazodibenzene" "Symmetrical diphenyl hydrazine" 

"1,1'-hydrazobis-Benzene"

"hydrazodi-Benzene" "Benzene, 1,1'-hydrazobis-" "Benzene, hydrazodi-" 

"Diphenylhydrazine, 1,2-" 

"Hydrazine, 1,2-diphenyl-" "Hydrazobenzol"

NIH RePORTER

04/2020 Text Search: "(sym)-Diphenylhydrazine" OR "1,1'-Hydrazodibenzene" OR "1,2-

Diphenylhydrazine" OR "hydrazobenzene" OR "N,N'-Bianiline" OR "N,N'-

Diphenylhydrazine" OR "Symmetrical diphenyl hydrazine" OR "1,1'-hydrazobisBenzene" OR "hydrazodi-Benzene" OR "Benzene, 1,1'-hydrazobis-" OR "Benzene, 

hydrazodi-" OR "Diphenylhydrazine, 1,2-" OR "Hydrazine, 1,2-diphenyl-" OR 

"Hydrazobenzol" OR "Diphenylhydrazine" OR "Diphenylhydrazines" (Advanced), 

Search in: Projects Admin IC: All, Fiscal Year: Active Projects

Other Identified throughout the assessment process

The 2020 results were: 

• Number of records identified from PubMed, TOXLINE, and TOXCENTER (after duplicate 

removal): 11

• Number of records identified from other strategies: 16

• Total number of records to undergo literature screening: 27
1,2-DIPHENYLHYDRAZINE B-6

APPENDIX B

B.1.2 Literature Screening 

A two-step process was used to screen the literature search to identify relevant studies on 1,2-diphenylhydrazine: 

• Title and abstract screen

• Full text screen

Title and Abstract Screen. Within the reference library, titles and abstracts were screened manually for 

relevance. Studies that were considered relevant (see Table B-1 for inclusion criteria) were moved to the 

second step of the literature screening process. Studies were excluded when the title and abstract clearly 

indicated that the study was not relevant to the toxicological profile. 

• Number of titles and abstracts screened: 27

• Number of studies considered relevant and moved to the next step: 16

Full Text Screen. The second step in the literature screening process was a full text review of individual 

studies considered relevant in the title and abstract screen step. Each study was reviewed to determine 

whether it was relevant for inclusion in the toxicological profile. 

• Number of studies undergoing full text review: 16

• Number of studies cited in the pre-public draft of the toxicological profile: 66

• Total number of studies cited in the profile: 82

A summary of the results of the literature search and screening is presented in Figure B-1.
1,2-DIPHENYLHYDRAZINE B-7

APPENDIX B

Figure B-1. March 2020 Literature Search Results and Screen for 

1,2-Diphenylhydrazine
1,2-DIPHENYLHYDRAZINE C-1

APPENDIX C. FRAMEWORK FOR ATSDR’S SYSTEMATIC REVIEW OF 

HEALTH EFFECTS DATA FOR 1,2-DIPHENYLHYDRAZINE

To increase the transparency of ATSDR’s process of identifying, evaluating, synthesizing, and 

interpreting the scientific evidence on the health effects associated with exposure to 1,2-diphenylhydrazine, ATSDR utilized a slight modification of NTP’s Office of Health Assessment and Translation 

(OHAT) systematic review methodology (NTP 2013, 2015; Rooney et al. 2014). ATSDR’s framework is 

an eight-step process for systematic review with the goal of identifying the potential health hazards of 

exposure to 1,2-diphenylhydrazine:

• Step 1. Problem Formulation

• Step 2. Literature Search and Screen for Health Effects Studies

• Step 3. Extract Data from Health Effects Studies

• Step 4. Identify Potential Health Effect Outcomes of Concern

• Step 5. Assess the Risk of Bias for Individual Studies

• Step 6. Rate the Confidence in the Body of Evidence for Each Relevant Outcome

• Step 7. Translate Confidence Rating into Level of Evidence of Health Effects

• Step 8. Integrate Evidence to Develop Hazard Identification Conclusions

C.1 PROBLEM FORMULATION

The objective of the toxicological profile and this systematic review was to identify the potential health 

hazards associated with inhalation, oral, or dermal/ocular exposure to 1,2-diphenylhydrazine. The 

inclusion criteria used to identify relevant studies examining the health effects of 1,2-diphenylhydrazine

are presented in Table C-1. 

Data from human and laboratory animal studies were considered relevant for addressing this objective. 

Human studies were divided into two broad categories: observational epidemiology studies and 

controlled exposure studies. The observational epidemiology studies were further divided: cohort studies 

(retrospective and prospective studies), population studies (with individual data or aggregate data), and 

case-control studies.

C.2 LITERATURE SEARCH AND SCREEN FOR HEALTH EFFECTS STUDIES

A literature search and screen was conducted to identify studies examining the health effects of 

1,2-diphenylhydrazine. The literature search framework for the toxicological profile is discussed in detail 

in Appendix B. 
1,2-DIPHENYLHYDRAZINE C-2

APPENDIX C

Table C-1. Inclusion Criteria for Identifying Health Effect Studies

Species

Human

Laboratory mammals

Route of exposure

Inhalation

Oral

Dermal (or ocular)

Parenteral (these studies will be considered supporting data)

Health outcome

Body weight effects 

Respiratory effects

Cardiovascular effects

Gastrointestinal effects

Hematological effects

Musculoskeletal effects

Hepatic effects

Renal effects

Dermal effects

Ocular effects

Endocrine effects

Immunological effects

Neurological effects

Reproductive effects

Developmental effects

Other noncancer effects

C.2.1 Literature Search

As noted in Appendix B, the current literature search was intended to update the draft toxicological 

profile for 1,2-diphenylhydrazine released for public comment in 2019. See Appendix B for the 

databases searched and the search strategy.

A total of 27 records relevant to all sections of the toxicological profile were identified (after 

duplicate removal). 

C.2.2 Literature Screening 

As described in Appendix B, a two-step process was used to screen the literature search to identify 

relevant studies examining the health effects of 1,2-diphenylhydrazine.

Title and Abstract Screen. In the Title and Abstract Screen step, 27 records were reviewed; 0 documents 

were considered to meet the health effects inclusion criteria in Table B-1.

Full Text Screen. In the second step in the literature screening process for the systematic review, a full 

text review of 7 health effect documents (documents identified in the update literature search and 
1,2-DIPHENYLHYDRAZINE C-3

APPENDIX C

documents cited in older versions of the profile) was performed. From those 7 documents, 13 studies 

were included in the qualitative review. 

C.3 EXTRACT DATA FROM HEALTH EFFECTS STUDIES

Relevant data extracted from the individual studies selected for inclusion in the systematic review were 

collected in customized data forms. A summary of the type of data extracted from each study is presented 

in Table C-2. For references that included more than one experiment or species, data extraction records 

were created for each experiment or species. 

Table C-2. Data Extracted from Individual Studies

Citation

Chemical form

Route of exposure (e.g., inhalation, oral, dermal)

Specific route (e.g., gavage in oil, drinking water)

Species

Strain

Exposure duration category (e.g., acute, intermediate, chronic)

Exposure duration

Frequency of exposure (e.g., 6 hours/day, 5 days/week)

Exposure length

Number of animals or subjects per sex per group 

Dose/exposure levels

Parameters monitored

Description of the study design and method

Summary of calculations used to estimate doses (if applicable)

Summary of the study results

Reviewer’s comments on the study

Outcome summary (one entry for each examined outcome)

No-observed-adverse-effect level (NOAEL) value

Lowest-observed-adverse-effect level (LOAEL) value

Effect observed at the LOAEL value

A summary of the extracted data for each study is presented in the Supplemental Document for 

1,2-Diphenylhydrazine and overviews of the results of the oral and dermal exposure studies (no inhalation 

exposure studies were identified) are presented in Sections 2.2–2.18 of the profile and oral data are 

summarized in the Levels Significant Exposures table in Section 2.1 of the profile (Table 2-1).

C.4 IDENTIFY POTENTIAL HEALTH EFFECT OUTCOMES OF CONCERN 

Overviews of the potential health effect outcomes for 1,2-diphenylhydrazine identified in animal studies 

(no human studies were identified) are presented in Table C-3. Animal studies examined a number of 

endpoints following oral exposure (dermal study only examined cancer endpoints). These studies 

examined most endpoints and reported respiratory, gastrointestinal, and hepatic effects. Studies 

examining these potential outcomes were carried through to Steps 4–8 of the systematic review. There 

were 13 studies (published in 7 documents) examining these potential outcomes carried through to 

Steps 4–8 of the systematic review. 
1,2-DIPHENHYLHYDRAZINE C-4 

APPENDIX C 

Table C-3. Overview of the Health Outcomes for 1,2-Diphenylhydrazine Evaluated in Experimental Animal 

Studies

Body weightRespiratoryCardiovascularGastrointestinalHematologicalMusculoskeletalHepaticRenalDermalOcularEndocrineImmunologicala Neurologicala Reproductivea DevelopmentalOther NoncancerCaner

Inhalation studies

Acute-duration

Intermediate-duration

Chronic-duration

Oral studies

Acute-duration 2 0 0 2

0 0 0 0

Intermediate-duration 5 1 2

0 1 1

Chronic-duration 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

2 2 0 0 0 2 0 0 0 0 0 0 0 0 2

Dermal studies

Acute-duration

Intermediate-duration

Chronic-duration 1

1

Number of studies examining endpoint 0 1 2 3 4 5-9 ≥10

Number of studies reporting outcome 0 1 2 3 4 5-9 ≥10

aNumber of studies examining endpoint includes study evaluating histopathology, but not evaluating function.
1,2-DIPHENYLHYDRAZINE C-5

APPENDIX C

C.5 ASSESS THE RISK OF BIAS FOR INDIVIDUAL STUDIES

C.5.1 Risk of Bias Assessment

The risk of bias of individual studies was assessed using OHAT’s Risk of Bias Tool (NTP 2015). The 

risk of bias questions for animal experimental studies are presented in Table C-4. Each risk of bias 

question was answered on a four-point scale:

• Definitely low risk of bias (++)

• Probably low risk of bias (+)

• Probably high risk of bias (-)

• Definitely high risk of bias (– –)

In general, “definitely low risk of bias” or “definitely high risk of bias” were used if the question could be 

answered with information explicitly stated in the study report. If the response to the question could be 

inferred, then “probably low risk of bias” or “probably high risk of bias” responses were typically used. 

Table C-4. Risk of Bias Questionnaire for Experimental Animal Studies

Selection bias

Was administered dose or exposure level adequately randomized?

Was the allocation to study groups adequately concealed?

Performance bias

Were experimental conditions identical across study groups?

Were the research personnel blinded to the study group during the study?

Attrition/exclusion bias

Were outcome data complete without attrition or exclusion from analysis?

Detection bias

Is there confidence in the exposure characterization?

Is there confidence in outcome assessment?

Selective reporting bias

Were all measured outcomes reported? 

After the risk of bias questionnaires were completed for the health effects studies, the studies were 

assigned to one of three risk of bias tiers based on the responses to the key questions listed below and the 

responses to the remaining questions. 

• Is there confidence in the exposure characterization? (only relevant for observational studies)

• Is there confidence in the outcome assessment? 

• Does the study design or analysis account for important confounding and modifying variables? 

(only relevant for observational studies)

First Tier. Studies placed in the first tier received ratings of “definitely low” or “probably low” risk of 

bias on the key questions AND received a rating of “definitely low” or “probably low” risk of bias on the 

responses to at least 50% of the other applicable questions.

Second Tier. A study was placed in the second tier if it did not meet the criteria for the first or third tiers.
1,2-DIPHENYLHYDRAZINE C-6

APPENDIX C

Third Tier. Studies placed in the third tier received ratings of “definitely high” or “probably high” risk of 

bias for the key questions AND received a rating of “definitely high” or “probably high” risk of bias on 

the response to at least 50% of the other applicable questions.

The results of the risk of bias assessment for the different types of 1,2-diphenylhydrazine health effects 

studies in animal experimental studies are presented in Table C-5.
1,2-DIPHENYLHYDRAZINE C-7

APPENDIX C

Table C-5. Summary of Risk of Bias Assessment for 1,2-Diphenylhydrazine—Experimental Animal Studies

Reference

Risk of bias criteria and ratings

Selection bias Performance bias

Attrition/ 

exclusion bias Detection bias

Selective 

reporting 

bias

Administered dose or exposure level adequately randomized?Allocation to study groups adequately concealed?Experimental conditions identical across study groups?Research personnel blinded to the study group during the study?Outcome data complete without attrition or exclusion from analysis?Confidence in exposure characterization?Confidence in outcome assessment?*All measured outcomes reported?Risk of bias tier

Outcome: Respiratory Effects

Oral chronic exposure

NCI 1978 (rat) + + + + ++ + + + First

NCI 1978 (mouse) + + + + ++ + + + First

Outcome: Gastrointestinal Effects

Oral intermediate exposure

NCI 1978 (mouse, 4-week) + + + + + - + - First

Oral chronic exposure

NCI 1978 (rat) + + + + ++ + + + First

NCI 1978 (mouse) + + + + ++ + + + First

Outcome: Hepatic Effects

Oral acute exposure

Dodd et al. 2012 (5-day) ++ + + + ++ + + ++ First

Dodd et al. 2012 (2-week) ++ + + + ++ + + ++ First

Oral intermediate exposure

Dodd et al. 2012 (4-week) ++ + + + ++ + + ++ First

Dodd et al. 2012 (13-week) ++ + + + ++ + + ++ First

Oral chronic exposure

NCI 1978 (rat) + + + + ++ + + + First

NCI 1978 (mouse) + + + + ++ + + + First

++ = definitely low risk of bias; + = probably low risk of bias; – = probably high risk of bias; – – = definitely high risk of bias; na = not applicable

*Key question used to assign risk of bias tier
1,2-DIPHENYLHYDRAZINE C-8

APPENDIX C

C.6 RATE THE CONFIDENCE IN THE BODY OF EVIDENCE FOR EACH RELEVANT 

OUTCOME

Confidences in the bodies of human and animal evidence were evaluated independently for each potential 

outcome. ATSDR did not evaluate the confidence in the body of evidence for carcinogenicity; rather, the 

Agency defaulted to the cancer weight-of-evidence assessment of other agencies including DHHS, EPA, 

and IARC. The confidence in the body of evidence for an association or no association between exposure 

to 1,2-diphenylhydrazine and a particular outcome was based on the strengths and weaknesses of 

individual studies. Four descriptors were used to describe the confidence in the body of evidence for 

effects or when no effect was found:

• High confidence: the true effect is highly likely to be reflected in the apparent relationship

• Moderate confidence: the true effect may be reflected in the apparent relationship

• Low confidence: the true effect may be different from the apparent relationship

• Very low confidence: the true effect is highly likely to be different from the apparent 

relationship

Confidence in the body of evidence for a particular outcome was rated for each type of study: casecontrol, case series, cohort, population, human-controlled exposure, and experimental animal. In the 

absence of data to the contrary, data for a particular outcome were collapsed across animal species, routes 

of exposure, and exposure durations. If species (or strain), route, or exposure duration differences were 

noted, then the data were treated as separate outcomes.

C.6.1 Initial Confidence Rating 

In ATSDR’s modification to the OHAT approach, the body of evidence for an association (or no 

association) between exposure to 1,2-diphenylhydrazine and a particular outcome was given an initial 

confidence rating based on the key features of the individual studies examining that outcome. The 

presence of these key features of study design was determined for individual studies using four “yes or 

no” questions, which were customized for epidemiology, human controlled exposure, or experimental 

animal study designs. Separate questionnaires were completed for each outcome assessed in a study. The 

key features for experimental animal studies are presented in Table C-6. The initial confidence in the 

study was determined based on the number of key features present in the study design: 

• High Initial Confidence: Studies in which the responses to the four questions were “yes”. 

• Moderate Initial Confidence: Studies in which the responses to only three of the questions 

were “yes”. 

• Low Initial Confidence: Studies in which the responses to only two of the questions were “yes”. 

• Very Low Initial Confidence: Studies in which the response to one or none of the questions 

was “yes”. 
1,2-DIPHENYLHYDRAZINE C-9

APPENDIX C

Table C-6. Key Features of Study Design for Experimental Animal Studies

A concurrent control group was used

A sufficient number of animals per group were tested

Appropriate parameters were used to assess a potential adverse effect

Appropriate statistical analyses were performed and reported or the data were reported in such a way to 

allow independent statistical analysis

The presence or absence of the key features and the initial confidence levels for studies examining body 

weight, respiratory, gastrointestinal, and hepatic effects observed in the animal experimental studies are 

presented in Table C-7.

Table C-7. Presence of Key Features of Study Design for 1,2-

Diphenylhydrazine—Experimental Animal Studies

Key feature

Reference

Concurrent control groupSufficient number of animals per groupAppropriate parameters to assess potential effectAdequate data for statistical analysis

Initial study 

confidence

Outcome: Respiratory Effects

Oral chronic exposure

NCI 1978 (rat) Yes Yes No Yes Moderate

NCI 1978 (mouse) Yes Yes No Yes Moderate

Outcome: Gastrointestinal Effects

Oral intermediate exposure

NCI 1978 (mouse, 4-week) Yes No No No Very Low

Oral chronic exposure

NCI 1978 (rat) Yes Yes No Yes Moderate

NCI 1978 (mouse) Yes Yes No Yes Moderate

Outcome: Hepatic Effects

Oral acute exposure

Dodd et al. 2012 (5-day) Yes Yes Yes Yes High

Dodd et al. 2012 (2-week) Yes Yes Yes Yes High

Oral intermediate exposure

Dodd et al. 2012 (4-week) Yes Yes Yes Yes High

Dodd et al. 2012 (13-week) Yes Yes Yes Yes High

Oral chronic exposure

NCI 1978 (rat) Yes Yes No Yes Moderate

NCI 1978 (mouse) Yes Yes No Yes Moderate

A summary of the initial confidence ratings for each outcome is presented in Table C-8. If individual 

studies for a particular outcome and study type had different study quality ratings, then the highest 

confidence rating for the group of studies was used to determine the initial confidence rating for the body 

of evidence; any exceptions were noted in Table C-8.
1,2-DIPHENYLHYDRAZINE C-10

APPENDIX C

Table C-8. Initial Confidence Rating for 1,2-Diphenylhydrazine Health Effects 

Studies

Initial study 

confidence

Initial confidence 

rating

Outcome: Respiratory Effects

Oral chronic exposure

Animal studies

NCI 1978 (rat) Moderate

Moderate

NCI 1978 (mouse) Moderate

Outcome: Gastrointestinal Effects

Oral intermediate exposure

Animal studies

NCI 1978 (mouse, 4-week) Very Low Very Low

Oral chronic exposure

Animal studies

NCI 1978 (rat) Moderate Moderate NCI 1978 (mouse) Moderate

Outcome: Hepatic Effects

Oral acute exposure

Animal studies

Dodd et al. 2012 (5-day) High High Dodd et al. 2012 (2-week) High

Oral intermediate exposure

Animal studies

Dodd et al. 2012 (4-week) High High Dodd et al. 2012 (13-week) High

Oral chronic exposure

Animal studies

NCI 1978 (rat) Moderate Moderate NCI 1978 (mouse) Moderate

C.6.2 Adjustment of the Confidence Rating 

The initial confidence rating was then downgraded or upgraded depending on whether there were 

substantial issues that would decrease or increase confidence in the body of evidence. The nine properties 

of the body of evidence that were considered are listed below. The summaries of the assessment of the 

confidence in the body of evidence for body weight, respiratory, gastrointestinal, and hepatic effects are 

presented in Table C-9. An overview of the confidence in the body of evidence for all health effects 

associated with 1,2-diphenylhydrazine exposure is presented in Table C-10.
1,2-DIPHENYLHYDRAZINE C-11

APPENDIX C

Table C-9. Adjustments to the Initial Confidence in the Body of Evidence 

Initial confidence

Adjustments to the initial 

confidence rating Final confidence

Outcome: Respiratory Effects

Animal studies Moderate -1 inconsistency, 

-1 imprecision

Very Low

Outcome: Gastrointestinal Effects

Animal studies Moderate -1 inconsistency Low

Outcome: Hepatic Effects

Animal studies High No adjustments High

Table C-10. Confidence in the Body of Evidence for 1,2-Diphenylhydrazine

Outcome Confidence in body of evidence

Human studies Animal studies

Respiratory effects No data Very Low

Gastrointestinal effects No data Low

Hepatic effects No data High

Five properties of the body of evidence were considered to determine whether the confidence rating 

should be downgraded: 

• Risk of bias. Evaluation of whether there is substantial risk of bias across most of the studies 

examining the outcome. This evaluation used the risk of bias tier groupings for individual studies 

examining a particular outcome (Table C-5). Below are the criteria used to determine whether 

the initial confidence in the body of evidence for each outcome should be downgraded for risk of 

bias:

o No downgrade if most studies are in the risk of bias first tier

o Downgrade one confidence level if most studies are in the risk of bias second tier

o Downgrade two confidence levels if most studies are in the risk of bias third tier

• Unexplained inconsistency. Evaluation of whether there is inconsistency or large variability in 

the magnitude or direction of estimates of effect across studies that cannot be explained. Below 

are the criteria used to determine whether the initial confidence in the body of evidence for each 

outcome should be downgraded for unexplained inconsistency:

o No downgrade if there is little inconsistency across studies or if only one study evaluated 

the outcome

o Downgrade one confidence level if there is variability across studies in the magnitude or 

direction of the effect

o Downgrade two confidence levels if there is substantial variability across studies in the 

magnitude or direct of the effect

• Indirectness. Evaluation of four factors that can affect the applicability, generalizability, and 

relevance of the studies: 

o Relevance of the animal model to human health—unless otherwise indicated, studies in 

rats, mice, and other mammalian species are considered relevant to humans 
1,2-DIPHENYLHYDRAZINE C-12

APPENDIX C

o Directness of the endpoints to the primary health outcome—examples of secondary 

outcomes or nonspecific outcomes include organ weight in the absence of histopathology 

or clinical chemistry findings in the absence of target tissue effects

o Nature of the exposure in human studies and route of administration in animal studies—

inhalation, oral, and dermal exposure routes are considered relevant unless there are 

compelling data to the contrary 

o Duration of treatment in animal studies and length of time between exposure and 

outcome assessment in animal and prospective human studies—this should be considered 

on an outcome-specific basis

Below are the criteria used to determine whether the initial confidence in the body of evidence for 

each outcome should be downgraded for indirectness:

o No downgrade if none of the factors are considered indirect 

o Downgrade one confidence level if one of the factors is considered indirect 

o Downgrade two confidence levels if two or more of the factors are considered indirect

• Imprecision. Evaluation of the narrowness of the effect size estimates and whether the studies 

have adequate statistical power. Data are considered imprecise when the ratio of the upper to 

lower 95% CIs for most studies is ≥10 for tests of ratio measures (e.g., odds ratios) and ≥100 for 

absolute measures (e.g., percent control response). Adequate statistical power is determined if 

the study can detect a potentially biologically meaningful difference between groups (20% 

change from control response for categorical data or risk ratio of 1.5 for continuous data). Below 

are the criteria used to determine whether the initial confidence in the body of evidence for each 

outcome should be downgraded for imprecision:

o No downgrade if there are no serious imprecisions 

o Downgrade one confidence level for serious imprecisions 

o Downgrade two confidence levels for very serious imprecisions 

• Publication bias. Evaluation of the concern that studies with statistically significant results are 

more likely to be published than studies without statistically significant results. 

o Downgrade one level of confidence for cases where there is serious concern with 

publication bias

Four properties of the body of evidence were considered to determine whether the confidence rating 

should be upgraded: 

• Large magnitude of effect. Evaluation of whether the magnitude of effect is sufficiently large 

so that it is unlikely to have occurred as a result of bias from potential confounding factors. 

o Upgrade one confidence level if there is evidence of a large magnitude of effect in a few 

studies, provided that the studies have an overall low risk of bias and there is no serious 

unexplained inconsistency among the studies of similar dose or exposure levels; 

confidence can also be upgraded if there is one study examining the outcome, provided 

that the study has an overall low risk of bias

• Dose response. Evaluation of the dose-response relationships measured within a study and 

across studies. Below are the criteria used to determine whether the initial confidence in the body 

of evidence for each outcome should be upgraded:

o Upgrade one confidence level for evidence of a monotonic dose-response gradient

o Upgrade one confidence level for evidence of a non-monotonic dose-response gradient 

where there is prior knowledge that supports a non-monotonic dose-response and a nonmonotonic dose-response gradient is observed across studies
1,2-DIPHENYLHYDRAZINE C-13

APPENDIX C

• Plausible confounding or other residual biases. This factor primarily applies to human studies 

and is an evaluation of unmeasured determinants of an outcome such as residual bias towards the 

null (e.g., “healthy worker” effect) or residual bias suggesting a spurious effect (e.g., recall bias). 

Below is the criterion used to determine whether the initial confidence in the body of evidence for 

each outcome should be upgraded:

o Upgrade one confidence level for evidence that residual confounding or bias would 

underestimate an apparent association or treatment effect (i.e., bias toward the null) or 

suggest a spurious effect when results suggest no effect

• Consistency in the body of evidence. Evaluation of consistency across animal models and 

species, consistency across independent studies of different human populations and exposure 

scenarios, and consistency across human study types. Below is the criterion used to determine 

whether the initial confidence in the body of evidence for each outcome should be upgraded:

o Upgrade one confidence level if there is a high degree of consistency in the database

C.7 TRANSLATE CONFIDENCE RATING INTO LEVEL OF EVIDENCE OF HEALTH 

EFFECTS

In the seventh step of the systematic review of the health effects data for 1,2-diphenylhydrazine, the 

confidence in the body of evidence for specific outcomes was translated to a level of evidence rating. The 

level of evidence rating reflected the confidence in the body of evidence and the direction of the effect 

(i.e., toxicity or no toxicity); route-specific differences were noted. The level of evidence for health 

effects was rated on a five-point scale: 

• High level of evidence: High confidence in the body of evidence for an association between 

exposure to the substance and the health outcome

• Moderate level of evidence: Moderate confidence in the body of evidence for an association 

between exposure to the substance and the health outcome

• Low level of evidence: Low confidence in the body of evidence for an association between 

exposure to the substance and the health outcome

• Evidence of no health effect: High confidence in the body of evidence that exposure to the 

substance is not associated with the health outcome

• Inadequate evidence: Low or moderate confidence in the body of evidence that exposure to the 

substance is not associated with the health outcome OR very low confidence in the body of 

evidence for an association between exposure to the substance and the health outcome

A summary of the level of evidence of health effects for 1,2-diphenylhydrazine is presented in 

Table C-11.
1,2-DIPHENYLHYDRAZINE C-14

APPENDIX C

Table C-11. Level of Evidence of Health Effects for 1,2-Diphenylhydrazine

Outcome

Confidence in body 

of evidence

Direction of health 

effect

Level of evidence for 

health effect

Human studies

Respiratory effects No data No data

Gastrointestinal effects No data No data

Hepatic effects No data No data

Animal studies

Respiratory effects Very Low Health effect Inadequate

Gastrointestinal effects Low Health effect Low

Hepatic effects High Health effect High

C.8 INTEGRATE EVIDENCE TO DEVELOP HAZARD IDENTIFICATION CONCLUSIONS

The final step involved the integration of the evidence streams for the human studies and animal studies 

to allow for a determination of hazard identification conclusions. For health effects, there were four 

hazard identification conclusion categories:

• Known to be a hazard to humans

• Presumed to be a hazard to humans 

• Suspected to be a hazard to humans 

• Not classifiable as to the hazard to humans 

The initial hazard identification was based on the highest level of evidence in the human studies and the 

level of evidence in the animal studies; if there were no data for one evidence stream (human or animal), 

then the hazard identification was based on the one data stream (equivalent to treating the missing 

evidence stream as having low level of evidence). The hazard identification scheme is presented in 

Figure C-1 and described below:

• Known: A health effect in this category would have:

o High level of evidence for health effects in human studies AND a high, moderate, or low 

level of evidence in animal studies.

• Presumed: A health effect in this category would have:

o Moderate level of evidence in human studies AND high or moderate level of evidence in 

animal studies OR

o Low level of evidence in human studies AND high level of evidence in animal studies

• Suspected: A health effect in this category would have:

o Moderate level of evidence in human studies AND low level of evidence in animal 

studies OR

o Low level of evidence in human studies AND moderate level of evidence in animal 

studies

• Not classifiable: A health effect in this category would have:

o Low level of evidence in human studies AND low level of evidence in animal studies

Other relevant data such as mechanistic or mode-of-action data were considered to raise or lower the level 

of the hazard identification conclusion by providing information that supported or opposed biological 

plausibility. 
1,2-DIPHENYLHYDRAZINE C-15

APPENDIX C

Two hazard identification conclusion categories were used when the data indicated that there may be no 

health effect in humans:

• Not identified to be a hazard in humans

• Inadequate to determine hazard to humans

If the human level of evidence conclusion of no health effect was supported by the animal evidence of no 

health effect, then the hazard identification conclusion category of “not identified” was used. If the 

human or animal level of evidence was considered inadequate, then a hazard identification conclusion 

category of “inadequate” was used. As with the hazard identification for health effects, the impact of 

other relevant data was also considered for no health effect data. 

The hazard identification conclusions for 1,2-diphenylhydrazine are listed below and summarized in

Table C-12. 

Presumed Health Effects

• Hepatic effects

o No human data are available on the potential hepatic effects of 1,2-diphenylhydrazine. 

o High level of evidence from intermediate (Dodd et al. 2012) and chronic (NCI 1978) oral 

studies in rats and chronic oral studies in mice (NCI 1978). No liver effects were 

observed at exposures of less than 13 weeks in rats (Dodd et al. 2012; NCI 1978) or mice 

(NCI 1978). 

Not Classifiable Effects

• Respiratory effects

o No human data are available on the potential respiratory effects of 1,2-diphenylhydrazine. 

o There is inadequate evidence in animal studies that chronic oral exposure will result in 

respiratory effects. Interstitial lung inflammation was observed in male rats (NCI 1978); 

in female rats the incidence was not dose-related. Respiratory effects were not observed 

in mice following chronic oral exposure (NCI 1978). 

• Gastrointestinal effects

o No human data are available on the potential gastrointestinal effects of 1,2-diphenylhydrazine. 

o Low evidence in animals from an intermediate oral study which reported intestinal 

hemorrhage in mice (NCI 1978) and from a chronic oral study in rats that reported 

hyperkeratosis and/or acanthosis in rats (NCI 1978); no gastrointestinal effects were 

observed in mice following chronic oral exposure.

Table C-12. Hazard Identification Conclusions for 1,2-Diphenylhydrazine

Outcome Hazard identification 

Respiratory effects Not classifiable

Gastrointestinal effects Not classifiable

Hepatic effects Presumed
1,2-DIPHENYLHYDRAZINE C-16

APPENDIX C

Figure C-1. Hazard Identification Scheme

High

Moderate

Low

Level of evidence for health effects in human studies

Low Moderate High

Known

Suspected

Not Classifiable Suspected

Presumed

Presumed

Level of evidence for health effects in animal studies
1,2-DIPHENYLHYDRAZINE D-1

APPENDIX D. USER'S GUIDE

Chapter 1. Relevance to Public Health

This chapter provides an overview of U.S. exposures, a summary of health effects based on evaluations of 

existing toxicologic, epidemiologic, and toxicokinetic information, and an overview of the minimal risk 

levels. This is designed to present interpretive, weight-of-evidence discussions for human health 

endpoints 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?

Minimal Risk Levels (MRLs)

Where sufficient toxicologic information is available, ATSDR derives 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.

MRLs should help physicians and public health officials determine the safety of a community living near 

a hazardous substance 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. 

Section 1.2, Summary of Health Effects, contains basic information known about the substance. Other 

sections, such as Section 3.2 Children and Other Populations that are Unusually Susceptible and 

Section 3.4 Interactions with Other Substances, provide important supplemental information.

MRL users should also understand the MRL derivation methodology. MRLs are derived using a 

modified version of the risk assessment methodology that the Environmental Protection Agency (EPA) 

provides (Barnes and Dourson 1988) to determine reference doses (RfDs) for lifetime exposure. 

To derive an MRL, ATSDR generally selects the most sensitive 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 no-observed-adverse-effect 

level (NOAEL) that does not exceed any adverse effect levels. When a NOAEL is not available, a 

lowest-observed-adverse-effect level (LOAEL) can be used to derive an MRL, and an uncertainty factor 

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 
1,2-DIPHENYLHYDRAZINE D-2

APPENDIX D

substance-specific MRL are provided in the footnotes of the levels of significant exposure (LSE) tables

that are provided in Chapter 2. Detailed discussions of the MRLs are presented in Appendix A.

Chapter 2. Health Effects

Tables and Figures for Levels of Significant Exposure (LSE)

Tables and figures are used to summarize health effects and illustrate graphically levels of exposure 

associated with those effects. These levels cover health effects observed at increasing dose 

concentrations and durations, differences in response by species and MRLs to humans for noncancer 

endpoints. The LSE tables and figures can be used for a quick review of the health effects and to locate 

data for a specific exposure scenario. The LSE tables and figures should always be used in conjunction 

with the text. All entries in these tables and figures represent studies that provide reliable, quantitative 

estimates of NOAELs, LOAELs, or Cancer Effect Levels (CELs).

The legends presented below demonstrate the application of these tables and figures. Representative 

examples of LSE tables and figures follow. The numbers in the left column of the legends correspond to 

the numbers in the example table and figure.

TABLE LEGEND

See Sample LSE Table (page D-5)

(1) Route of exposure. One of the first considerations when reviewing the toxicity of a substance 

using these tables and figures should be the relevant and appropriate route of exposure. 

Typically, when sufficient data exist, three LSE tables and two LSE figures are presented in the 

document. The three LSE tables present data on the three principal routes of exposure

(i.e., inhalation, oral, and dermal). LSE figures are limited to the inhalation and oral routes. Not 

all substances will have data on each route of exposure and will not, therefore, have all five of the 

tables and figures. Profiles with more than one chemical may have more LSE tables and figures.

(2) Exposure period. Three exposure periods—acute (<15 days), intermediate (15–364 days), and 

chronic (≥365 days)—are presented within each relevant route of exposure. In this example, two 

oral studies of chronic-duration exposure are 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) Figure key. 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 51 identified NOAELs and less serious LOAELs (also see the three

"51R" data points in sample LSE Figure 2-X).

(4) Species (strain) No./group. The test species (and strain), whether animal or human, are identified 

in this column. The column also contains information on the number of subjects and sex per 

group. Chapter 1, Relevance to Public Health, covers the relevance of animal data to human 

toxicity and Section 3.1, 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.

(5) Exposure parameters/doses. The duration of the study and exposure regimens are provided in 

these columns. This permits comparison of NOAELs and LOAELs from different studies. In 

this case (key number 51), rats were orally exposed to “Chemical X” via feed for 2 years. For a 
1,2-DIPHENYLHYDRAZINE D-3

APPENDIX D

more complete review of the dosing regimen, refer to the appropriate sections of the text or the 

original reference paper (i.e., Aida et al. 1992).

(6) Parameters monitored. This column lists the parameters used to assess health effects. Parameters 

monitored could include serum (blood) chemistry (BC), biochemical changes (BI), body weight 

(BW), clinical signs (CS), developmental toxicity (DX), food intake (FI), gross necropsy (GN), 

hematology (HE), histopathology (HP), immune function (IX), lethality (LE), neurological 

function (NX), organ function (OF), ophthalmology (OP), organ weight (OW), reproductive 

function (RX), urinalysis (UR), and water intake (WI).

(7) Endpoint. This column lists the endpoint examined. The major categories of health endpoints 

included in LSE tables and figures are death, body weight, respiratory, cardiovascular, 

gastrointestinal, hematological, musculoskeletal, hepatic, renal, dermal, ocular, endocrine, 

immunological, neurological, reproductive, developmental, other noncancer, and cancer. "Other

noncancer" refers to any effect (e.g., alterations in blood glucose levels) not covered in these 

systems. In the example of key number 51, three endpoints (body weight, hematological, and 

hepatic) were investigated.

(8) NOAEL. A NOAEL is the highest exposure level at which no adverse effects were seen in the 

organ system studied. The body weight effect reported in key number 51 is a NOAEL at

25.5 mg/kg/day. NOAELs are not reported for cancer and death; with the exception of these two 

endpoints, this field is left blank if no NOAEL was identified in the study.

(9) LOAEL. A LOAEL is the lowest dose used in the study that caused an adverse 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. Key number 51 reports a less serious 

LOAEL of 6.1 mg/kg/day for the hepatic system, which was used to derive a chronic exposure, 

oral MRL of 0.008 mg/kg/day (see footnote "c"). MRLs are not derived from serious LOAELs. 

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. If no LOAEL/CEL values were identified in the 

study, this field is left blank.

(10) Reference. The complete reference citation is provided in Chapter 8 of the profile.

(11) Footnotes. Explanations of abbreviations or reference notes for data in the LSE tables are found 

in the footnotes. For example, footnote "c" indicates that the LOAEL of 6.1 mg/kg/day in key 

number 51 was used to derive an oral MRL of 0.008 mg/kg/day.

FIGURE LEGEND

See Sample LSE Figure (page D-6)

LSE figures graphically illustrate the data presented in the corresponding LSE tables. Figures help the 

reader quickly compare health effects according to exposure concentrations for particular exposure 

periods.

(13) Exposure period. The same exposure periods appear as in the LSE table. In this example, health 

effects observed within the chronic exposure period are illustrated.
1,2-DIPHENYLHYDRAZINE D-4

APPENDIX D

(14) Endpoint. These are the categories of health effects for which reliable quantitative data exist. 

The same health effect endpoints 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) LOAEL. In this example, the half-shaded circle that is designated 51R identifies a LOAEL 

critical endpoint in the rat upon which a chronic oral exposure MRL is based. The key number 

51 corresponds to the entry in the LSE table. The dashed descending arrow indicates the 

extrapolation from the exposure level of 6.1 mg/kg/day (see entry 51 in the sample LSE table) to 

the MRL of 0.008 mg/kg/day (see footnote "c" in the sample LSE table).

(17) CEL. Key number 59R is one of studies for which CELs were derived. The diamond symbol 

refers to a CEL for the test species (rat). The number 59 corresponds to the entry in the LSE 

table.

(18) Key to LSE figure. The key provides the abbreviations and symbols used in the figure.
1,2

-DIPHENYLHYDRAZINED-5

APPENDIX D
1,2

-DIPHENYLHYDRAZINED-6

APPENDIX D
1,2-DIPHENYLHYDRAZINE E-1

APPENDIX E. QUICK REFERENCE FOR HEALTH CARE PROVIDERS

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

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

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

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

answers to often-asked questions.

Primary Chapters/Sections of Interest

Chapter 1: Relevance to Public Health: The Relevance to Public Health Section provides an overview 

of exposure and health effects and evaluates, interprets, and assesses the significance of toxicity 

data to human health. A table listing minimal risk levels (MRLs) is also included in this chapter.

Chapter 2: Health Effects: Specific health effects identified in both human and animal studies are 

reported by type of health effect (e.g., death, hepatic, renal, immune, reproductive), route of 

exposure (e.g., inhalation, oral, dermal), and length of exposure (e.g., acute, intermediate, and 

chronic). 

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

setting. 

Pediatrics: 

Section 3.2 Children and Other Populations that are Unusually Susceptible

Section 3.3 Biomarkers of Exposure and Effect

ATSDR Information Center 

Phone: 1-800-CDC-INFO (800-232-4636) or 1-888-232-6348 (TTY) 

Internet: http://www.atsdr.cdc.gov

The following additional materials are available online:

Case Studies in Environmental Medicine are self-instructional publications designed to increase primary 

health care providers’ knowledge of a hazardous substance in the environment and to aid in the 

evaluation of potentially exposed patients (see https://www.atsdr.cdc.gov/csem/csem.html). 

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

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

incident (see https://www.atsdr.cdc.gov/MHMI/index.asp). Volumes I and II are planning guides 

to assist first responders and hospital emergency department personnel in planning for incidents 

that involve hazardous materials. Volume III—Medical Management Guidelines for Acute 

Chemical Exposures—is a guide for health care professionals treating patients exposed to 

hazardous materials.

Fact Sheets (ToxFAQsTM) provide answers to frequently asked questions about toxic substances (see 

https://www.atsdr.cdc.gov/toxfaqs/Index.asp).
1,2-DIPHENYLHYDRAZINE E-2

APPENDIX E

Other Agencies and Organizations

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

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

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

30341-3724 • Phone: 770-488-7000 • FAX: 770-488-7015 • Web Page: 

https://www.cdc.gov/nceh/.

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

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

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

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

professionals in occupational safety and health. Contact: NIOSH, 395 E Street, S.W., Suite 9200, 

Patriots Plaza Building, Washington, DC 20201 • Phone: 202-245-0625 or 1-800-CDC-INFO 

(800-232-4636) • Web Page: https://www.cdc.gov/niosh/.

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

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

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

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

https://www.niehs.nih.gov/.

Clinical Resources (Publicly Available Information)

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

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

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

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

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

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

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

Grove Village, IL 60007-1030 • Phone: 847-818-1800 • FAX: 847-818-9266 • Web Page: 

http://www.acoem.org/.

The American College of Medical Toxicology (ACMT) is a nonprofit association of physicians with 

recognized expertise in medical toxicology. Contact: ACMT, 10645 North Tatum Boulevard, 

Suite 200-111, Phoenix AZ 85028 • Phone: 844-226-8333 • FAX: 844-226-8333 • Web Page: 

http://www.acmt.net.

The Pediatric Environmental Health Specialty Units (PEHSUs) is an interconnected system of specialists 

who respond to questions from public health professionals, clinicians, policy makers, and the 

public about the impact of environmental factors on the health of children and reproductive-aged 

adults. Contact information for regional centers can be found at http://pehsu.net/findhelp.html.

The American Association of Poison Control Centers (AAPCC) provide support on the prevention and 

treatment of poison exposures. Contact: AAPCC, 515 King Street, Suite 510, Alexandria VA 

22314 • Phone: 701-894-1858 • Poison Help Line: 1-800-222-1222 • Web Page: 

http://www.aapcc.org/.
1,2-DIPHENYLHYDRAZINE F-1

APPENDIX F. GLOSSARY

Absorption—The process by which a substance crosses biological membranes and enters systemic 

circulation. Absorption can also refer to the taking up of liquids by solids, or of gases by solids or liquids.

Acute Exposure—Exposure to a chemical for a duration of ≤14 days, as specified in the Toxicological 

Profiles.

Adsorption—The adhesion in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the 

surfaces of solid bodies or liquids with which they are in contact.

Adsorption Coefficient (Koc)—The ratio of the amount of a chemical adsorbed per unit weight of 

organic carbon in the soil or sediment to the concentration of the chemical in solution at equilibrium.

Adsorption Ratio (Kd)—The amount of a chemical adsorbed by sediment or soil (i.e., the solid phase) 

divided by the amount of chemical in the solution phase, which is in equilibrium with the solid phase, at a 

fixed solid/solution ratio. It is generally expressed in micrograms of chemical sorbed per gram of soil or 

sediment.

Benchmark Dose (BMD) or Benchmark Concentration (BMC)—is the dose/concentration 

corresponding to a specific response level estimate using a statistical dose-response model applied to 

either experimental toxicology or epidemiology data. For example, a BMD10 would be the dose 

corresponding to a 10% benchmark response (BMR). The BMD is determined by modeling the doseresponse curve in the region of the dose-response relationship where biologically observable data are 

feasible. The BMDL or BMCL is the 95% lower confidence limit on the BMD or BMC. 

Bioconcentration Factor (BCF)—The quotient of the concentration of a chemical in aquatic organisms 

at a specific time or during a discrete time period of exposure divided by the concentration in the 

surrounding water at the same time or during the same period.

Biomarkers—Indicators signaling events in biologic systems or samples, typically classified as markers 

of exposure, effect, and susceptibility.

Cancer Effect Level (CEL)—The lowest dose of a chemical in a study, or group of studies, that 

produces significant increases in the incidence of cancer (or tumors) between the exposed population and 

its appropriate control.

Carcinogen—A chemical capable of inducing cancer.

Case-Control Study—A type of epidemiological study that examines the relationship between a 

particular outcome (disease or condition) and a variety of potential causative agents (such as toxic 

chemicals). In a case-control study, a group of people with a specified and well-defined outcome is 

identified and compared to a similar group of people without the outcome.

Case Report—A report that describes a single individual with a particular disease or exposure. These 

reports may suggest some potential topics for scientific research, but are not actual research studies.

Case Series—Reports that describe the experience of a small number of individuals with the same 

disease or exposure. These reports may suggest potential topics for scientific research, but are not actual 

research studies.
1,2-DIPHENYLHYDRAZINE F-2

APPENDIX F

Ceiling Value—A concentration that must not be exceeded. 

Chronic Exposure—Exposure to a chemical for ≥365 days, as specified in the Toxicological Profiles.

Clastogen—A substance that causes breaks in chromosomes resulting in addition, deletion, or 

rearrangement of parts of the chromosome.

Cohort Study—A type of epidemiological study of a specific group or groups of people who have had a 

common insult (e.g., exposure to an agent suspected of causing disease or a common disease) and are 

followed forward from exposure to outcome, and who are disease-free at start of follow-up. Often, at 

least one exposed group is compared to one unexposed group, while in other cohorts, exposure is a 

continuous variable and analyses are directed towards analyzing an exposure-response coefficient.

Cross-sectional Study—A type of epidemiological study of a group or groups of people that examines 

the relationship between exposure and outcome to a chemical or to chemicals at a specific point in time.

Data Needs—Substance-specific informational needs that, if met, would reduce the uncertainties of 

human health risk assessment.

Developmental Toxicity—The occurrence of adverse effects on the developing organism that may result 

from exposure to a chemical prior to conception (either parent), during prenatal development, or 

postnatally to the time of sexual maturation. Adverse developmental effects may be detected at any point 

in the life span of the organism.

Dose-Response Relationship—The quantitative relationship between the amount of exposure to a 

toxicant and the incidence of the response or amount of the response.

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 

effect occurs. Effects include malformations and variations, altered growth, and in utero death.

Epidemiology—The investigation of factors that determine the frequency and distribution of disease or 

other health-related conditions within a defined human population during a specified period. 

Excretion—The process by which metabolic waste products are removed from the body. 

Genotoxicity—A specific adverse effect on the genome of living cells that, upon the duplication of 

affected cells, can be expressed as a mutagenic, clastogenic, or carcinogenic event because of specific 

alteration of the molecular structure of the genome.

Half-life—A measure of rate for the time required to eliminate one-half of a quantity of a chemical from 

the body or environmental media.

Health Advisory—An estimate of acceptable drinking water levels for a chemical substance derived by 

EPA and 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)—A condition that poses a threat of life or health, or 

conditions that pose an immediate threat of severe exposure to contaminants that are likely to have 

adverse cumulative or delayed effects on health.
1,2-DIPHENYLHYDRAZINE F-3

APPENDIX F

Immunotoxicity—Adverse effect on the functioning of the immune system that may result from 

exposure to chemical substances. 

Incidence—The ratio of new cases of individuals in a population who develop a specified condition to 

the total number of individuals in that population who could have developed that condition in a specified 

time period. 

Intermediate Exposure—Exposure to a chemical for a duration of 15–364 days, as specified in the 

Toxicological Profiles.

In Vitro—Isolated from the living organism and artificially maintained, as in a test tube.

In Vivo—Occurring within the living organism.

Lethal Concentration(LO) (LCLO)—The lowest concentration of a chemical in air that has been reported 

to have caused death in humans or animals.

Lethal Concentration(50) (LC50)—A calculated concentration of a chemical in air to which exposure for 

a specific length of time is expected to cause death in 50% of a defined experimental animal population.

Lethal Dose(LO) (LDLo)—The lowest dose of a chemical introduced by a route other than inhalation that 

has been reported to have caused death in humans or animals.

Lethal Dose(50) (LD50)—The dose of a chemical that has been calculated to cause death in 50% of a 

defined experimental animal population.

Lethal Time(50) (LT50)—A calculated period of time within which a specific concentration of a chemical 

is expected to cause death in 50% of a defined experimental animal population.

Lowest-Observed-Adverse-Effect Level (LOAEL)—The lowest exposure level of chemical in a study, 

or group of studies, that produces statistically or biologically significant increases in frequency or severity 

of adverse effects between the exposed population and its appropriate control.

Lymphoreticular Effects—Represent morphological effects involving lymphatic tissues such as the 

lymph nodes, spleen, and thymus.

Malformations—Permanent structural changes that may adversely affect survival, development, or 

function.

Metabolism—Process in which chemical substances are biotransformed in the body that could result in 

less toxic and/or readily excreted compounds or produce a biologically active intermediate.

Minimal Risk Level (MRL)—An estimate of daily human exposure to a hazardous substance that is 

likely to be without an appreciable risk of adverse noncancer health effects over a specified route and 

duration of exposure.

Modifying Factor (MF)—A value (greater than zero) that is applied to the derivation of a Minimal Risk 

Level (MRL) to reflect additional concerns about the database that are not covered by the uncertainty 

factors. The default value for a MF is 1.
1,2-DIPHENYLHYDRAZINE F-4

APPENDIX F

Morbidity—The state of being diseased; the morbidity rate is the incidence or prevalence of a disease in 

a specific population.

Mortality—Death; the mortality rate is a measure of the number of deaths in a population during a 

specified interval of time.

Mutagen—A substance that causes mutations, which are changes in the DNA sequence of a cell’s DNA. 

Mutations can lead to birth defects, miscarriages, or cancer.

Necropsy—The gross examination of the organs and tissues of a dead body to determine the cause of 

death or pathological conditions.

Neurotoxicity—The occurrence of adverse effects on the nervous system following exposure to a 

hazardous substance.

No-Observed-Adverse-Effect Level (NOAEL)—The dose of a chemical at which there were no 

statistically or biologically significant increases in frequency or severity of adverse effects seen between 

the exposed population and its appropriate control. Although effects may be produced at this dose, they 

are not considered to be adverse.

Octanol-Water Partition Coefficient (Kow)—The equilibrium ratio of the concentrations of a chemical 

in n-octanol and water, in dilute solution.

Odds Ratio (OR)—A means of measuring the association between an exposure (such as toxic substances 

and a disease or condition) that represents the best estimate of relative risk (risk as a ratio of the incidence 

among subjects exposed to a particular risk factor divided by the incidence among subjects who were not 

exposed to the risk factor). An odds ratio that is greater than 1 is considered to indicate greater risk of 

disease in the exposed group compared to the unexposed group.

Permissible Exposure Limit (PEL)—An Occupational Safety and Health Administration (OSHA) 

regulatory limit on the amount or concentration of a substance not to be exceeded in workplace air 

averaged over any 8-hour work shift of a 40-hour workweek.

Pesticide—General classification of chemicals specifically developed and produced for use in the control 

of agricultural and public health pests (insects or other organisms harmful to cultivated plants or animals).

Pharmacokinetics—The dynamic behavior of a material in the body, used to predict the fate 

(disposition) of an exogenous substance in an organism. Utilizing computational techniques, it provides 

the means of studying the absorption, distribution, metabolism, and excretion of chemicals by the body.

Pharmacokinetic Model—A set of equations that can be used to describe the time course of a parent 

chemical or metabolite in an animal system. There are two types of pharmacokinetic models: data-based 

and physiologically-based. A data-based model divides the animal system into a series of compartments, 

which, in general, do not represent real, identifiable anatomic regions of the body, whereas the 

physiologically-based model compartments represent real anatomic regions of the body.

Physiologically Based Pharmacodynamic (PBPD) Model—A type of physiologically based doseresponse model that quantitatively describes the relationship between target tissue dose and toxic 

endpoints. These models advance the importance of physiologically based models in that they clearly 

describe the biological effect (response) produced by the system following exposure to an exogenous 

substance. 
1,2-DIPHENYLHYDRAZINE F-5

APPENDIX F

Physiologically Based Pharmacokinetic (PBPK) Model—A type of physiologically based doseresponse model that is comprised of a series of compartments representing organs or tissue groups with 

realistic weights and blood flows. These models require a variety of physiological information, including 

tissue volumes, blood flow rates to tissues, cardiac output, alveolar ventilation rates, and possibly 

membrane permeabilities. The models also utilize biochemical information, such as blood:air partition 

coefficients, and metabolic parameters. PBPK models are also called biologically based tissue dosimetry 

models.

Prevalence—The number of cases of a disease or condition in a population at one point in time. 

Prospective Study—A type of cohort study in which a group is followed over time and the pertinent 

observations are made on events occurring after the start of the study. 

Recommended Exposure Limit (REL)—A National Institute for Occupational Safety and Health 

(NIOSH) time-weighted average (TWA) concentration for up to a 10-hour workday during a 40-hour 

workweek.

Reference Concentration (RfC)—An estimate (with uncertainty spanning perhaps an order of 

magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) 

that is likely to be without an appreciable risk of deleterious noncancer health effects during a lifetime. 

The inhalation RfC is expressed in units of mg/m3 or ppm.

Reference Dose (RfD)—An estimate (with uncertainty spanning perhaps an order of magnitude) of the 

daily oral exposure of the human population to a potential hazard that is likely to be without risk of 

deleterious noncancer health effects during a lifetime. The oral RfD is expressed in units of mg/kg/day. 

Reportable Quantity (RQ)—The quantity of a hazardous substance that is considered reportable under

the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). RQs are 

(1) ≥1 pound or (2) for selected substances, an amount established by regulation either under CERCLA or 

under Section 311 of the Clean Water Act. Quantities are measured over a 24-hour period.

Reproductive Toxicity—The occurrence of adverse effects on the reproductive system that may result 

from exposure to a hazardous substance. The toxicity may be directed to the reproductive organs and/or 

the related endocrine system. The manifestation of such toxicity may be noted as alterations in sexual 

behavior, fertility, pregnancy outcomes, or modifications in other functions that are dependent on the 

integrity of this system.

Retrospective Study—A type of cohort study based on a group of persons known to have been exposed 

at some time in the past. Data are collected from routinely recorded events, up to the time the study is 

undertaken. Retrospective studies are limited to causal factors that can be ascertained from existing 

records and/or examining survivors of the cohort.

Risk—The possibility or chance that some adverse effect will result from a given exposure to a hazardous 

substance.

Risk Factor—An aspect of personal behavior or lifestyle, an environmental exposure, existing health 

condition, or an inborn or inherited characteristic that is associated with an increased occurrence of 

disease or other health-related event or condition.
1,2-DIPHENYLHYDRAZINE F-6

APPENDIX F

Risk Ratio/Relative Risk—The ratio of the risk among persons with specific risk factors compared to the 

risk among persons without risk factors. A risk ratio that is greater than 1 indicates greater risk of disease 

in the exposed group compared to the unexposed group.

Short-Term Exposure Limit (STEL)—A STEL is a 15-minute TWA exposure that should not be 

exceeded at any time during a workday. 

Standardized Mortality Ratio (SMR)—A ratio of the observed number of deaths and the expected 

number of deaths in a specific standard population.

Target Organ Toxicity—This term covers a broad range of adverse effects on target organs or 

physiological systems (e.g., renal, cardiovascular) extending from those arising through a single limited 

exposure to those assumed over a lifetime of exposure to a chemical.

Teratogen—A chemical that causes structural defects that affect the development of an organism.

Threshold Limit Value (TLV)—An American Conference of Governmental Industrial Hygienists 

(ACGIH) concentration of a substance to which it is believed that nearly all workers may be repeatedly 

exposed, day after day, for a working lifetime without adverse effect. The TLV may be expressed as a 

Time-Weighted Average (TLV-TWA), as a Short-Term Exposure Limit (TLV-STEL), or as a ceiling 

limit (TLV-C).

Time-Weighted Average (TWA)—An average exposure within a given time period. 

Toxicokinetic—The absorption, distribution, metabolism, and elimination of toxic compounds in the 

living organism.

Toxics Release Inventory (TRI)—The TRI is an EPA program that tracks toxic chemical releases and 

pollution prevention activities reported by industrial and federal facilities. 

Uncertainty Factor (UF)—A factor used in operationally deriving the Minimal Risk Level (MRL),

Reference Dose (RfD), or Reference Concentration (RfC) from experimental data. UFs are intended to 

account for (1) the variation in sensitivity among the members of the human population, (2) the 

uncertainty in extrapolating animal data to the case of human, (3) the uncertainty in extrapolating from 

data obtained in a study that is of less than lifetime exposure, and (4) the uncertainty in using lowestobserved-adverse-effect level (LOAEL) data rather than no-observed-adverse-effect level (NOAEL) data. 

A default for each individual UF is 10; if complete certainty in data exists, a value of 1 can be used; 

however, a reduced UF of 3 may be used on a case-by-case basis (3 being the approximate logarithmic 

average of 10 and 1).

Xenobiotic—Any substance that is foreign to the biological system.
1,2-DIPHENYLHYDRAZINE G-1

APPENDIX G. ACRONYMS, ABBREVIATIONS, AND SYMBOLS

AAPCC American Association of Poison Control Centers

ACGIH American Conference of Governmental Industrial Hygienists

ACOEM American College of Occupational and Environmental Medicine

ACMT American College of Medical Toxicology

ADI acceptable daily intake

ADME absorption, distribution, metabolism, and excretion

AEGL Acute Exposure Guideline Level

AIC Akaike’s information criterion 

AIHA American Industrial Hygiene Association 

ALT alanine aminotransferase

AOEC Association of Occupational and Environmental Clinics

AP alkaline phosphatase

AST aspartate aminotransferase

atm atmosphere

ATSDR Agency for Toxic Substances and Disease Registry

AWQC Ambient Water Quality Criteria

BCF bioconcentration factor

BMD/C benchmark dose or benchmark concentration

BMDX dose that produces a X% change in response rate of an adverse effect

BMDLX 95% lower confidence limit on the BMDX

BMDS Benchmark Dose Software 

BMR benchmark response

BUN blood urea nitrogen 

C centigrade

CAA Clean Air Act

CAS Chemical Abstract Services

CDC Centers for Disease Control and Prevention

CEL cancer effect level

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CFR Code of Federal Regulations

Ci curie

CI confidence interval

cm centimeter

CPSC Consumer Products Safety Commission

CWA Clean Water Act

DNA deoxyribonucleic acid

DOD Department of Defense

DOE Department of Energy

DWEL drinking water exposure level

EAFUS Everything Added to Food in the United States

ECG/EKG electrocardiogram

EEG electroencephalogram

EPA Environmental Protection Agency

ERPG emergency response planning guidelines 

F Fahrenheit

F1 first-filial generation

FDA Food and Drug Administration

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act

FR Federal Register
1,2-DIPHENYLHYDRAZINE G-2

APPENDIX G

FSH follicle stimulating hormone

g gram

GC gas chromatography

gd gestational day

GGT γ-glutamyl transferase 

GRAS generally recognized as safe

HEC human equivalent concentration 

HED human equivalent dose 

HHS Department of Health and Human Services 

HPLC high-performance liquid chromatography

HSDB Hazardous Substance Data Bank 

IARC International Agency for Research on Cancer

IDLH immediately dangerous to life and health

IRIS Integrated Risk Information System 

Kd adsorption ratio

kg kilogram

kkg kilokilogram; 1 kilokilogram is equivalent to 1,000 kilograms and 1 metric ton

Koc organic carbon partition coefficient

Kow octanol-water partition coefficient

L liter

LC liquid chromatography

LC50 lethal concentration, 50% kill

LCLo lethal concentration, low

LD50 lethal dose, 50% kill

LDLo lethal dose, low

LDH lactic dehydrogenase

LH luteinizing hormone

LOAEL lowest-observed-adverse-effect level

LSE Level of Significant Exposure

LT50 lethal time, 50% kill

m meter

mCi millicurie

MCL maximum contaminant level

MCLG maximum contaminant level goal

MF modifying factor

mg milligram

mL milliliter

mm millimeter

mmHg millimeters of mercury

mmol millimole

MRL Minimal Risk Level

MS mass spectrometry

MSHA Mine Safety and Health Administration

Mt metric ton

NAAQS National Ambient Air Quality Standard

NAS National Academy of Science

NCEH National Center for Environmental Health

ND not detected

ng nanogram

NHANES National Health and Nutrition Examination Survey

NIEHS National Institute of Environmental Health Sciences
1,2-DIPHENYLHYDRAZINE G-3

APPENDIX G

NIOSH National Institute for Occupational Safety and Health

NLM National Library of Medicine

nm nanometer

nmol nanomole

NOAEL no-observed-adverse-effect level

NPL National Priorities List

NR not reported

NRC National Research Council

NS not specified

NTP National Toxicology Program

OR odds ratio

OSHA Occupational Safety and Health Administration

PAC Protective Action Criteria

PAH polycyclic aromatic hydrocarbon

PBPD physiologically based pharmacodynamic 

PBPK physiologically based pharmacokinetic 

PEL permissible exposure limit

PEL-C permissible exposure limit-ceiling value

pg picogram

PEHSU Pediatric Environmental Health Specialty Unit

PND postnatal day

POD point of departure

ppb parts per billion

ppbv parts per billion by volume

ppm parts per million

ppt parts per trillion

REL recommended exposure level/limit

REL-C recommended exposure level-ceiling value

RfC reference concentration

RfD reference dose

RNA ribonucleic acid

SARA Superfund Amendments and Reauthorization Act

SCE sister chromatid exchange

SD standard deviation

SE standard error

SGOT serum glutamic oxaloacetic transaminase (same as aspartate aminotransferase or AST)

SGPT serum glutamic pyruvic transaminase (same as alanine aminotransferase or ALT)

SIC standard industrial classification

SMR standardized mortality ratio

sRBC sheep red blood cell

STEL short term exposure limit

TLV threshold limit value

TLV-C threshold limit value-ceiling value

TRI Toxics Release Inventory

TSCA Toxic Substances Control Act

TWA time-weighted average

UF uncertainty factor

U.S. United States

USDA United States Department of Agriculture

USGS United States Geological Survey

USNRC U.S. Nuclear Regulatory Commission
1,2

-DIPHENYLHYDRAZINE G-4 

APPENDIX G 

VOC volatile organic compound

WBC white blood cell

WHO World Health Organization 

> greater than ≥ greater than or equal to

= equal to 

< less than ≤ less than or equal to 

% percent α alpha β beta γ gamma δ delta

μm micrometer

μg microgram q1* cancer slope factor

– negative 

+ positive 

(+) weakly positive result

(–) weakly negative result