NTP-CERHR Monograph on the 

Potential Human Reproductive and 

Developmental Effects 

of Di-n -Octyl Phthalate (DnOP)

May 2003 NIH Publication No. 03-4488

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Table of Contents

Preface ............................................................................................................................................. i

Introduction..................................................................................................................................... ii

NTP Brief on Di-n-Octyl Phthalate (DnOP)....................................................................................1

References........................................................................................................................................3

Appendix I. NTP-CERHR Phthalates Expert Panel 

Preface ..............................................................................................................................I-1

Expert Panel......................................................................................................................I-2

Appendix II. Phthalates Expert Panel Report on DnOP

Preface ............................................................................................................................. II-i

Chemistry, Usage and Exposure ......................................................................................II-1

General Toxicological and Biological Parameters .........................................................II-4

Developmental Toxicity Data..........................................................................................II-8

Reproductive Toxicity .....................................................................................................II-9

Data Summary & Integration........................................................................................II-11

References.....................................................................................................................II-18

Tables............................................................................................................................II-21

Appendix III. Public Comments on the Phthalates Expert Panel Reports

AdvaMed........................................................................................................................ III-1

American Chemistry Council (12-7-2000).................................................................... III-5

American Chemistry Council (12-11-2000).................................................................. III-7

American Chemistry Council (4-13-2001).................................................................. III-58

Discovery Medical, Inc ................................................................................................ III-66

Environmental Working Group (11-3-2000)................................................................ III-67

Environmental Working Group (12-8-2000)................................................................ III-69

William Faber............................................................................................................... III-71

Healthy Environments & Product Safety Branch ........................................................ III-81

Health Care Without Harm .......................................................................................... III-83

Beverly Smith............................................................................................................... III-87

Swedish Chemical Inspection Agency......................................................................... III-88
i

The National Toxicology Program (NTP) 

established the NTP Center for the Evaluation 

of Risks to Human Reproduction (CERHR) 

in 1998. The CERHR is a publicly accessible 

resource for information about adverse reproductive and/or developmental health effects 

associated with exposure to environmental 

and/or occupational chemicals. The CERHR 

is located at the National Institute of Environmental Health Sciences (NIEHS) of the 

National Institutes of Health and Dr. Michael 

Shelby is the director.1

The CERHR broadly solicits nominations of 

chemicals for evaluation from the public and 

private sectors. The CERHR follows a formal 

process for review and evaluation of nominated 

chemicals that includes multiple opportunities 

for public comment. Chemicals are selected for 

evaluation based upon several factors including 

the following: 

• potential for human exposure from use 

and occurrence in the environment.

• extent of public concern.

• production volume.

• availability of scientific evidence for 

reproductive and/or developmental toxicity. 

The CERHR convenes a scientific expert 

panel that meets in a public forum to review, 

discuss, and evaluate the scientific literature 

on the selected chemical. Public comment 

is invited prior to and during the meeting. 

The expert panel produces a report on the 

chemical’s reproductive and developmental 

toxicities and provides its opinion of the degree 

to which exposure to the chemical is hazardous to humans. The panel also identifies areas 

of uncertainty and where additional data are 

needed. The CERHR expert panels use explicit 

guidelines to evaluate the scientific literature 

and prepare the expert panel reports. Expert 

panel reports are made public and comments 

are solicited. 

Next, the CERHR prepares the NTP-CERHR 

monograph. The NTP-CERHR monograph 

includes the NTP brief on the chemical evaluated, the expert panel report, and all public 

comments. The goal of the NTP brief is to provide the public, as well as government health, 

regulatory, and research agencies, with the 

NTP’s interpretation of the potential for the 

chemical to adversely affect human reproductive health or children’s health. The NTPCERHR monograph is made publicly available 

electronically on the CERHR web site and in 

hard copy or CD-ROM from the CERHR.

Preface

1 Information about the CERHR is available on the 

web at <http://cerhr.niehs.nih.gov> or by contacting the director:

NIEHS, P.O. Box 12233, MD EC-32, 

Research Triangle Park, NC 27709 

919-541-3455 [phone] 

919-316-4511 [fax]

shelby@niehs.nih.gov [email] 

Information about the NTP is available on the web 

at <http://ntp-server.niehs.nih.gov> or by contacting the NTP Office of Liaison and Scientific Review at the NIEHS:

liaison@starbase.niehs.nih.gov [email]

919-541-0530 [phone]
ii 

In 1999, the CERHR Core Committee, an advisory committee composed of representatives 

from NTP member agencies, recommended 

seven phthalates for expert panel review. 

These chemicals were selected because: 

(a) there is the potential for human exposure 

from their widespread use and occurrence within the environment, 

(b) they have a high production volume, 

(c) there is substantial scientific literature 

addressing the reproductive and/or developmental toxicities of these chemicals, 

and 

(d) they are of concern to the public. 

These seven phthalates are as follows:

• di(2-ethylhexyl)phthalate (DEHP) 

• di-isononyl phthalate (DINP) 

• di-isodecyl phthalate (DIDP)

• di-n-butyl phthalate (DBP) 

• butyl benzyl phthalate (BBP) 

• di-n-octyl phthalate (DnOP)

• di-n-hexyl phthalate (DnHP)

Phthalates are a group of similar chemicals 

widely used to soften and increase the flexibility of plastic consumer products such as 

shower curtains, medical devices, upholstery, 

raincoats, and soft squeeze toys. They are not 

bound to the plastics and can leach into the surrounding environment. The scientific literature 

on the reproductive and developmental toxicities of several phthalates is extensive. In addition, there is widespread public concern about 

the safety of phthalates. 

As part of the evaluation of phthalates, the 

CERHR convened a panel of scientific experts 

(Appendix I) to review, discuss, and evaluate 

the scientific evidence on the potential reproductive and developmental toxicities of each 

phthalate. There were three public meetings of 

this panel (August 17–19 and December 15–

17, 1999 and July 12–13, 2000). The CERHR 

received numerous public comments on the 

phthalates throughout the evaluation process. 

The NTP has prepared an NTP-CERHR monograph for each phthalate. This monograph 

includes the NTP brief on DnOP, a list of the 

expert panel members (Appendix I), the expert 

panel’s report on DnOP (Appendix II), and all 

public comments received on the expert panel’s 

reports on phthalates (Appendix III). The NTPCERHR monograph is intended to serve as a 

single, collective source of information on the 

potential for DnOP to adversely affect human 

reproduction or development. Those interested 

in reading this report may include individuals, 

members of public interest groups, and staff of 

health and regulatory agencies. 

The NTP brief included within this monograph 

presents the NTP’s interpretation of the potential for exposure to DnOP to cause adverse 

reproductive or developmental effects in people. It is based upon information about DnOP 

provided in the expert panel report, the public 

comments, and additional scientific information available since the expert panel meetings. 

The NTP brief is intended to provide clear, 

balanced, scientifically sound information on 

the potential for DnOP exposures to result in 

adverse health effects on development and 

reproduction. 

Introduction
iii

While there are biological and practical reasons for considering developmental toxicity 

and reproductive toxicity as two separate issues, it is important to keep in mind that life 

in mammals, including humans, is a cycle. 

In brief, the cycle includes the production 

of sperm and eggs, fertilization, prenatal development of the offspring, birth, postnatal 

development, sexual maturity, and, again, 

production of sperm and eggs. 

In the past, toxic effects were often studied 

in a “life-stage specific” manner. Thus, 

concerns for developmental toxicity were 

addressed by exposing pregnant mothers 

and looking for adverse effects in fetuses. 

Developmental toxicity was detected as 

death, structural malformations, or reduced 

weights of the fetuses just prior to birth. Reproductive toxicity was studied by exposing 

sexually mature adults to the chemical of interest and effects were detected as impaired 

capacity to reproduce. Over the years, toxicologists realized that exposure during one 

part of the life cycle could lead to adverse 

effects that might only be apparent at a different part of the life cycle. For example, exposure of a sexually mature individual to an 

agent capable of inducing genetic damage 

in eggs or sperm might have no apparent 

effect on the exposed individual. However, 

if a genetically damaged egg or sperm from 

that individual is involved in fertilization, 

the induced genetic damage might lead to 

death or a genetic disorder in the offspring. 

In this example, chemical-induced damage 

is detected in the next generation. In contrast, the reproductive system begins developing well before birth and continues until 

sexual maturity is attained. Thus, exposure 

of sexually immature animals, either before 

or following birth, to agents or conditions 

that adversely affect development of the 

reproductive system can result in structural 

or functional reproductive disorders. These 

effects may only become apparent after the 

exposed individual reaches the age of puberty or sexual maturity.

Thus, in the case of genetic damage induced 

in eggs or sperm, what might be considered 

reproductive toxicity gives rise to developmental disorders. Conversely, in the case 

of adverse effects on development of the 

reproductive tract, developmental toxicity 

results in reproductive disorders. In both 

these examples it is difficult to make a clear 

distinction between developmental and reproductive toxicity. This issue is important 

in considering the phthalate evaluations 

because evidence of developmental toxicity affecting reproductive capacity in later 

stages of the life cycle is reported for at least 

3 of the phthalates—BBP, DBP, and DEHP.

Developmental Toxicity versus 

Reproductive Toxicity
1

NTP Brief

What is DnOP?

DnOP is an oily substance manufactured by 

reaction of phthalic anhydride and n-octanol 

in the presence of a catalyst. The structure of 

DnOP is shown in Fig. 1. Its chemical formula 

is C24H38O4. It is one of a group of industrially important chemicals known as phthalates. 

Phthalates are used primarily as plasticizers to 

add flexibility to plastics. Available information indicates that there are no commercial uses 

of pure DnOP. However, it makes up approximately 20% of the commercially important 

phthalate mixture known as C6–10 phthalate. 

This mixture is used in the manufacture of 

a variety of commercial products including 

flooring and carpet tiles, tarps, pool liners, and 

garden hoses. DnOP is approved by the FDA 

as an indirect food additive and is used in seam 

cements, bottle cap liners, and conveyor belts. 

DnOP-containing compounds are not known to 

be used in medical devices or toys. 

Based on an estimated annual production of 50 

million pounds of C6–10 phthalate, 10 million 

pounds (20% of 50 million) of DnOP is produced each year.

Are People Exposed to DnOP?*

Yes. There are several ways that people may be 

exposed to DnOP at home or at work. Human 

exposure can occur during the manufacture 

of DnOP, during the manufacture of DnOPcontaining products, during the use of such 

products, or through the presence of DnOP 

in the environment. Environmental exposures 

can occur through air, water, food, or contact 

with DnOP-containing products. Studies have 

shown that DOP (isomer not specified) is 

detectable in a variety of food products and 

household dust samples but the data are not 

sufficient to permit a confident estimate of 

general population exposure. Because of inadequate information on human exposure to 

DnOP, the expert panel took the conservative 

position of assuming that general population 

exposures in the United States would be 3–30 

μg/kg bw/day (micrograms per kilogram body 

weight per day). This is the range of exposures 

estimated for the more widely used phthalate, 

DEHP. By comparison, a small drop of water 

weighs approximately 30,000 μg and a grain of 

table salt weighs approximately 60 μg.

Can DnOP Affect Human Development or 

Reproduction?

Probably not. There is no direct evidence that 

exposure of people to DnOP adversely affects 

reproduction or development. Limited studies 

with mice and rats show that high exposures 

to DnOP may cause adverse developmental 

effects but no evidence of reproductive effects 

was observed (Fig. 2).

Scientific decisions concerning health risks are 

generally based on what is known as “weightof-the-evidence.” There are no exposure or 

effects data in humans. There is limited evidence of developmental effects in animals at 

high doses, and some evidence of no reproductive effects in animals. The NTP judges the scientific evidence to indicate DnOP is not likely 

to affect human reproductive systems. The data 

NTP Brief on Di-n-Octyl Phthalate 

(DnOP)

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Figure 1. Chemical structure of DnOP

* Answers to this and subsequent questions may 

be: Yes, Probably, Possibly, Probably Not, No 

or Unknown
2

NTP Brief

Clear evidence of adverse effects

Some evidence of adverse effects

Limited evidence of adverse effects

Developmental Toxicity

are insufficient to make a judgment on possible 

developmental effects. (Fig. 3).

Summary of Supporting Evidence 

As presented in the expert panel report, two developmental toxicity studies—one in rats and 

one in mice—were available for evaluation. In 

the rat study, pregnant dams were treated with 

DnOP by intraperitoneal injection on gestation 

days 5, 10, and 15. Fetuses were evaluated on 

gestation day 20. The two dose levels used were 

very high, approximately 5,000 and 10,000 

mg/kg bw/day. Increased malformations and 

reduced body weights were observed in fetuses at both dose levels. In the mouse study, 

pregnant dams were treated by gavage with 

approximately 10,000 mg/kg bw/day on gestation days 6–13 and allowed to deliver pups. 

DnOP treatment resulted in smaller litter sizes 

and reduced weight gain on postnatal days 1–3. 

However, birth weights and pup survival to day 

3 were not affected.

The reproductive toxicity of DnOP was evaluated in a mouse continuous breeding study. 

Animals were exposed through dosed feed 

to approximately 1,800, 3,600, or 7,500 mg/

kg bw/day. No adverse reproductive effects 

were observed in the treated parents or their 

offspring. Likewise, no reproductive effects 

were observed in two limited studies in male 

rats where oral exposure to DnOP for 4 days 

or 13 weeks did not affect testes weights or 

histology.

Developmental Toxicity

Figure 2. The weight of evidence that DnOP causes adverse developmental or 

reproductive effects in laboratory animals 

Clear evidence of adverse effects

Some evidence of adverse effects

Limited evidence of adverse effects

Insufficient evidence for a conclusion

Limited evidence of no adverse effects

Some evidence of no adverse effects

Clear evidence of no adverse effects

Developmental Toxicity

Reproductive Toxicity

Figure 3. NTP conclusions regarding the possibilities that human development 

or reproduction might be adversely affected by exposure to DnOP 

Serious concern for adverse effects

Concern for adverse effects

Some concern for adverse effects

Minimal concern for adverse effects

Negligible concern for adverse effects

Insufficient hazard and/or exposure data

Reproductive effects

Developmental effects
3

NTP Brief

No new data on the developmental or reproductive effects of DnOP have become available 

since the expert panel report was completed. 

Are Current Exposures to DnOP High 

Enough to Cause Concern?

Probably not. No studies have been conducted 

in humans and only a few animal studies are 

available. However, the animal studies evaluated indicate that there are no effects on reproduction and that developmental effects may 

occur at high exposure levels. Although no 

firm data are available on human exposures, it 

appears that the U.S. general population is not 

exposed to DnOP levels that are of immediate 

concern for causing adverse reproductive or 

developmental effects. The NTP offers the following conclusions.

The NTP concurs with the CERHR Phthalates 

Expert Panel’s conclusion that there is negligible concern for effects on adult reproductive 

systems. 

This conclusion is based on the assumption 

that humans are exposed to levels of DnOP less 

than 30 μg/kg bw/day. 

Although DnOP is reported to be lethal to 

mouse fetuses at high doses, data are not available to determine exposure levels at which 

no adverse effects occur. Therefore, the NTP 

concludes that there is insufficient information 

on developmental toxicity to reach a conclusion 

regarding the potential for DnOP to adversely 

affect human development.

References:

No new publications were available.

These conclusions are based on 

the information available at the time 

this brief was prepared. As new information on toxicity and exposure 

accumulate, it may form the basis 

for either lowering or raising the 

levels of concern expressed in the 

conclusions.
I-1

Appendix I

Appendix I. NTP-CERHR Phthalates 

Expert Panel Report on DnOP

A 16-member panel of scientists covering dis-

ciplines such as toxicology, epidemiology, and 

medicine was recommended by the Core Com-

mittee and approved by the Associate Director 

of the National Toxicology Program. Over the 

course of a 16-month period, the panel criti-

cally reviewed more than 500 documents on 7 

phthalates and identified key studies and issues 

for plenary discussions. At three public meet-

ings

1, the expert panel discussed these studies, 

the adequacy of available data, and identified 

data needed to improve future assessments. At 

the final meeting, the expert panel reached con-

clusions on whether estimated exposures may 

result in adverse effects on human reproduction 

or development. Panel assessments were based 

on the scientific evidence available at the time 

of the final meeting. The expert panel reports 

were made available for public comment on 

October 10, 2000, and the deadline for public 

comments was December 11, 2000 (Federal 

Register 65:196 [10 Oct. 2000] p60206). The 

Phthalates Expert Panel Report on DnOP is 

provided in Appendix II and the public com-

ments received on that report are in Appendix 

III. Input from the public and interested groups 

throughout the panel’s deliberations was in-

valuable in helping to assure completeness and 

accuracy of the reports. The Phthalates Expert 

Panel Reports are also available on the CERHR 

website <http://cerhr.niehs.nih.gov>. 1Phthalate Expert Panel meeting dates were: August 

17 –19, 1999, in Alexandria, VA; December 15 –

17, 1999, in Research Triangle Park, NC; and July 

12 –13, 2000, in Arlington, VA. 
I-2

Appendix I

Robert Kavlock, Ph.D. (chair)

EPA/ORD

Research Triangle Park, NC

Kim Boekelheide, M.D., Ph.D.

Brown University

Providence, RI

Robert Chapin, Ph.D.

NIEHS

Research Triangle Park, NC

Michael Cunningham, Ph.D.

NIEHS

Research Triangle Park, NC

Elaine Faustman, Ph.D.

University of Washington

Seattle, WA

Paul Foster, Ph.D.

Chemical Industry Institute of Toxicology

Research Triangle Park, NC

Mari Golub, Ph.D.

Cal/EPA

Davis, CA

Rogene Henderson, Ph.D.

Inhalation Toxicology Research Institute

Albuquerque, NM

Irwin Hinberg, Ph.D.

Health Canada

Ottawa, Ontario, Canada

Ruth Little, Sc.D.

NIEHS

Research Triangle Park, NC

Jennifer Seed, Ph.D.

EPA/OPPT

Washington, DC

Katherine Shea, M.D.

North Carolina State University

Raleigh, NC

Sonia Tabacova, M.D., Ph.D.

FDA

Rockville, MD

Shelley Tyl, Ph.D.

Research Triangle Institute

Research Triangle Park, NC

Paige Williams, Ph.D.

Harvard University

Cambridge, MA

Tim Zacharewski, Ph.D.

Michigan State University, 

East Lansing, MI

Appendix I. NTP-CERHR Phthalates Expert Panel 

(Name and Affiliation)
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Appendix II

NTP-CERHR EXPERT PANEL REPORT 

on

Di-n -Octyl Phthalate

October 2000 NTP-CERHR-DNOP-00
TABLE OF CONTENTS

1.0 CHEMISTRY, USAGE, AND EXPOSURE..................................................................................................1

1.1 Chemistry ....................................................................................................................................1

1.2 Exposure and Usage ....................................................................................................................1

2.0 GENERAL TOXICOLOGICAL AND BIOLOGICAL PARAMETERS .....................................................4

2.1 General Toxicity ..........................................................................................................................4

2.2 Toxicokinetics .............................................................................................................................6

2.3 Genetic Toxicity ..........................................................................................................................7

3.0 DEVELOPMENTAL TOXICITY DATA......................................................................................................8

3.1 Human Data.................................................................................................................................8

3.2 Experimental Animal Toxicity.....................................................................................................8

4.0 REPRODUCTIVE TOXICITY .....................................................................................................................9

4.1 Human Data.................................................................................................................................9

4.2 Experimental Animal Toxicity.....................................................................................................9

5.0 DATA SUMMARY & INTEGRATION......................................................................................................11

5.1 Summary .............................................................................................................................11

5.1.1 Human Exposure.............................................................................................................11

5.1.1.1 Utility of Data to the CERHR Evaluation...........................................................11

5.1.2 General Biological and Toxicological Data ....................................................................11

5.1.2.1 Utility of Data to the CERHR Evaluation...........................................................12

5.1.3 Developmental Toxicity ..................................................................................................12

5.1.3.1 Utility of Data to the CERHR Evaluation...........................................................14

5.1.4 Reproductive Toxicity .....................................................................................................14

5.1.4.1 Utility of Data to the CERHR Evaluation...........................................................15

5.2 Integrated Evaluation ................................................................................................................15

5.3 Expert Panel Conclusions .........................................................................................................16

5.4 Critical Data Needs ...................................................................................................................17

6.0 REFERENCES............................................................................................................................................18

7.0 TABLES ......................................................................................................................................................21

Appendix II
Appendix II

II-i

PREFACE

The National Toxicology Program (NTP) and the National Institute of Environmental Health Sciences 

established the NTP Center for the Evaluation of Risks to Human Reproduction (CERHR) in June, 

1998. The purpose of the Center is to provide timely, unbiased, scientifically sound evaluations of 

human and experimental evidence for adverse effects on reproduction, including development, 

caused by agents to which humans may be exposed.

The following seven phthalate esters were selected for the initial evaluation by the Center: butyl 

benzyl phthalate, di(2-ethylhexyl) phthalate, di-isodecyl phthalate, di-isononyl phthalate, di-n-butyl 

phthalate, di-n-hexyl phthalate, and di-n-octyl phthalate. Phthalate esters are used as plasticizers in 

a wide range of polyvinyl chloride-based consumer products. These chemicals were selected for the 

initial evaluation by the CERHR based on their high production volume, extent of human exposures, 

use in children’s products, published evidence of reproductive or developmental toxicity, and public 

concern.

This evaluation is the result of three public Expert Panel meetings and 15 months of deliberations by 

a 16-member panel of experts made up of government and non-government scientists. This report 

has been reviewed by the CERHR Core Committee made up of representatives of NTP-participating 

agencies, by CERHR staff scientists, and by members of the Phthalates Expert Panel. This report is 

a product of the Expert Panel and is intended to (1) interpret the strength of scientific evidence that 

a given exposure or exposure circumstance may pose a hazard to reproduction and the health and 

welfare of children; (2) provide objective and scientifically thorough assessments of the scientific evidence that adverse reproductive/development health effects are associated with exposure to specific 

chemicals or classes of chemicals, including descriptions of any uncertainties that would diminish 

confidence in assessment of risks; and (3) identify knowledge gaps to help establish research and 

testing priorities.

The Expert Panel Reports on phthalates will be a central part of the subsequent NTP report that will 

also include public comments on the Panel Reports and any relevant information that has become 

available since completion of the Expert Panel Reports. The NTP report will be transmitted to the 

appropriate Federal and State Agencies, the public, and the scientific community.

The NTP-CERHR is headquartered at NIEHS, Research Triangle Park, NC and is staffed and 

administered by scientists and support personnel at NIEHS and at Sciences International, Inc., 

Alexandria, Virginia.

Reports can be obtained from the website <http://cerhr.niehs.nih.gov/> or from:

CERHR

Sciences International, Inc.

1800 Diagonal Road, Suite 500

Alexandria, VA 22314-2808

Telephone: 703-838-9440
II-ii

Appendix II

A Report of the CERHR Phthalates Expert Panel: 

Name Affiliation

Robert Kavlock, PhD (Chair) National Health and Environmental Effects Research Laboratory/ 

 USEPA, Research Triangle Park, NC

Kim Boekelheide, MD, PhD Brown University, Providence, RI

Robert Chapin, PhD NIEHS, Research Triangle Park, NC

Michael Cunningham, PhD NIEHS, Research Triangle Park, NC

Elaine Faustman, PhD University of Washington, Seattle, WA

Paul Foster, PhD Chemical Industry Institute of Toxicology, RTP, NC

Mari Golub, PhD California Environmental Protection Agency, Sacramento, CA

Rogene Henderson, PhD Lovelace Respiratory Research Institute, Albuquerque, NM

Irwin Hinberg, PhD Health Canada, Ottawa, Ontario, Canada

Ruth Little, ScD NIEHS, Research Triangle Park, NC

Jennifer Seed, PhD Office of Toxic Substances/USEPA, Washington, DC

Katherine Shea, MD, MPH Duke University, Durham, NC

Sonia Tabacova, MD, PhD Food and Drug Administration, Rockville, MD

Rochelle Tyl, PhD, DABT Research Triangle Institute, Research Triangle Park, NC

Paige Williams, PhD Harvard University, Boston, MA

Timothy Zacharewski, PhD Michigan State University, East Lansing, MI

With the Support of CERHR Staff:

NTP/NIEHS

Michael Shelby, PhD Director, CERHR

Christopher Portier, PhD Acting Associate Director, NTP

Gloria Jahnke, DVM Technical Consultant

Lynn Goldman, MD Technical Consultant

Sciences International, Inc.

John Moore, DVM, DABT Principal Scientist 

Annette Iannucci, MS Toxicologist 

Ann Walker, MS, ELS Information Specialist and Technical Editor
Appendix II

II-1

1.0 CHEMISTRY, USAGE, AND EXPOSURE

1.1 Chemistry

Figure 1: Chemical Structure of a Di-n-Octyl Phthalate

Di-n-octyl phthalate (DnOP) (CAS Registry Number 117-84-0) is produced by reacting phthalic 

anhydride and n-octanol in the presence of an acid catalyst (1). 

Synonyms: 1,2-benzenedicarboxylic acid, dioctyl ester; phthalic acid, dioctyl ester; n-dioctyl 

phthalate; n-octyl phthalate; dioctyl o-benzenedicarboxylate; bis(n-octyl) phthalate.

DnOP is a significant component (20%) of C6–10 phthalate mixtures (1).

Table 1: Physicochemical Properties of DnOP

Property Value

Chemical Formula C24H38O4

Molecular Weight 390.54

Vapor Pressure 1.0 x 10-7 mm Hg at 25 °C

Melting Point -25 oC

Boiling Point 390 oC

Specific Gravity 0.978

Solubility in Water Essentially Insoluble (0.5 μg/L)

Log Kow 8.06

(2)

1.2 Exposure and Usage

There is sometimes confusion reporting data for DnOP because DEHP is often referred to in the 

literature as dioctyl phthalate (DOP). Unless otherwise stated, the information discussed in this 

exposure section refers specifically to DnOP to the best of CERHR’s knowledge.

There are no known commercial uses for pure DnOP. However, DnOP constitutes approximately 

20% of C6–10 phthalate substance. Commercial production of 50 million pounds of C6–10 

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II-2

Appendix II

phthalate in the United States in 1994 (3) equates to 10 million pounds of DnOP. C6–10 phthalate 

substance is used in PVC utilized in the manufacture of flooring and carpet tile, canvas tarps, swimming pool liners, notebook covers, traffic cones, toys, vinyl gloves, garden hoses, weather stripping, 

flea collars, and shoes (1). DnOP-containing phthalate substances are also used in PVC intended for 

food applications such as seam cements, bottle cap liners, and conveyor belts. 

Release of DnOP to the environment can occur during the production of C6–10 phthalates and 

during the incorporation of the phthalates into plastic resins. Because phthalates are not bound to 

plastics, DnOP can be released during the use or disposal of the product. Phthalates released to the 

environment can be deposited on or taken up by crops intended for human or livestock consumption, and thus, may enter the human food supply. 

General Population Exposure

The general population is exposed to phthalates primarily through the oral and dermal routes. 

Based on data for other phthalates, the most likely source of DnOP exposure to humans is dietary 

intake. DnOP may be found in food as a result of environmental uptake during cultivation or as a 

result of migration from processing equipment or packaging materials. DnOP is approved by the 

FDA for use as an indirect food additive in sealants used for food packaging (4). In a survey of 

packaged fatty foods purchased from grocery stores in the UK, the total concentration of dioctyl 

phthalate (DOP, isomer not specified) excluding DEHP was 2.3 mg/kg in milk (5). A paper published in 1995 reported the detection of DnOP in two samples of vodka; concentrations of 57 ppb in 

a 100 proof sample and 131 ppb in an 80 proof vodka (6).

DOP (isomer not specified) excluding DEHP was detected in 8 of 12 infant formulas from the UK 

at concentrations ranging from 0.21−1.42 mg/kg (7). Using manufacturer recommendations for 

feeding rates and by assuming that formula was the only nutritional source for infants, exposures to 

DOP isomers other than DEHP were estimated at <0.1–43 μg/kg bw/day at birth and <0.1–24 μg/

kg bw/day at 6 months of age by the UK Ministry of Agricutural Fisheries and Food (MAFF) (7). 

In a follow-up survey DOPs were not specifically targeted, but there was no evidence of their presence in 39 samples of infant formulas examined (8).

Pfordt and Bruns-Weller (9) reported the phthalate content of various household items in Germany. 

DnOP was detected in nutmeg at 0.02 mg/kg, but levels were below the limit of detection of 0.01 

mg/kg in milk (breast and commercial), cream, nuts, and baby food. DnOP was detected in the dust 

from a vacuum cleaner bag at 40 mg/kg; 20 mg/kg DNOP was detected in a dust wipe sample from 

one of three homes tested. DNOP levels in textiles were measured at 0.01−0.08 mg/kg. A concentration of 0.01 mg/kg DNOP was detected in one of three samples of flooring textiles.

There appears to be little or no use of DnOP-containing compounds in toys. According to the 

American Chemistry Council (ACC, formerly CMA) (1), DnOP was only detected in some teethers 

that were tested for phthalate ester migration by the Danish Ministry of Environment and Energy. 

No other studies have reported the detection of DnOP in toys.

Exposure to DnOP through air is also possible but expected to be minimal. Reported concentrations 

of DnOP in ambient air range from 0.06 to 0.94 ng/m3. The highest reported concentration resulted 
Appendix II

II-3

in a calculated inhaled dose of 0.29 ng/kg bw/day for an adult (10). Reported concentrations in 

river water have ranged from 0.024 to 1 ppb. EPA estimates that DNOP levels in drinking water 

influents are less than 0.5 ppb (10). These levels are several orders of magnitude lower than levels 

found in food.

The available data do not allow the confident estimation of DnOP exposures to the general population. However, a comparison of production volumes for DnOP-containing compounds versus those 

that contain DEHP suggests that human exposure to DnOP is well below the exposure estimate for 

DEHP of 3–30 μg/kg bw/day (11). Exposures may be higher in children due to dietary preferences 

or mouthing of DnOP-containing articles. 

Medical Exposure

There are no known current uses of DnOP-containing compounds in medical devices. 

Occupational Exposure

Workers may be exposed to DnOP primarily through inhalation and dermal contact. Phthalates are 

manufactured within closed systems, but exposure to workers can occur during filtering or loading/

unloading of tank cars (1). Higher exposures to phthalates can occur during the production of flexible PVC because the processes are open and run at higher temperatures. The ACC (1) reviewed six 

publications demonstrating that phthalate levels in air are generally less than 1 mg/m3 and 2 mg/m3

during the production of phthalates and flexible PVC, respectively. Exposure levels were estimated 

by the ACC (1) using assumptions of a 10 m3/day inhalation rate and a 70 kg body weight. The 

resulting exposure estimates were 143 μg/kg bw/workday and 286 μg/kg bw/workday for workers 

employed in phthalate and flexible PVC manufacturing operations, respectively.

The summary for Section 1 is located in Section 5.1.1.
II-4

Appendix II

2.0 GENERAL TOXICOLOGICAL AND BIOLOGICAL PARAMETERS

2.1 General Toxicity

2.1.1 Human Data

There were no human data located for Expert Panel review.

2.1.2 Experimental Animal Data

Acute Studies

The LD50 values for mice and rats are given as 13 g/kg and 53.7 g/kg, respectively (1). Dermal 

LD50 values have been determined at 75 mL/kg for guinea pigs (1).

Repeat-dose Toxicity

Four studies in rodents were available for review (12-15). 

Systemic effects following DnOP treatment for 3, 10, or 21 days were examined in 4-week-old 

Wistar rats. These effects were compared to effects produced by other groups of rats being fed diet 

containing 20,000 ppm of di-n-hexyl phthalate (DnHP), another straight chain phthalate, or di(2-

ethylhexyl) phthalate (DEHP), a branched-chained phthalate (14). A group of 12 male rats was a 

fed a diet containing 20,000 ppm DnOP and a control group of 18 rats was fed the basal diet. Using 

actual food intake levels and rat body weights on the day of sacrifice, a DnOP dose of 1,821 mg/kg 

bw/day was calculated. Four treated and 6 control rats were killed and necropsied after 3, 10, or 21 

days of treatment. Liver histopathology, enzyme activity, and peroxisome proliferation were examined. Levels of thyroid hormones in serum and thyroid histopathology were also examined (12).

DnOP treatment had no effect on testes weight or the gross appearance of testes, kidney, or pancreas (14). However, liver weight was significantly increased at 10 and 21 days of DnOP treatment 

with liver histology and chemistry changes seen at all 3 assessment times. After 3 days of exposure, 

centrilobular necrosis and glycogen loss were observed. At 10 days, centrilobular fatty accumulation was seen, this effect became more pronounced with increasing treatment duration. Electron 

microscopy (EM) showed effects on the smooth endoplasmic reticuli (proliferation and dilation) 

and microvilli shortening in the bile canaliculi at 3 days. At 10 days, EM also showed lipid droplets 

in the hepatocytes and a small increase in lysosomes and peroxisomes at 3 and 21 days respectively. 

Biochemical evidence for peroxisome proliferation was seen with significant increases in cyanide 

insensitive palmitoyl CoA oxidase at 10 and 21 days of treatment. Total catalase activity was unchanged; however, in the particulate sub-fraction it was significantly increased at 10 and 21 days of 

treatment. Other liver enzymes that were changed included significant decreases in 5’-nucleotidase, 

succinate dehydrogenase, and glucose-6-phosphate at 21 days of treatment. There was a significant, 

DnOP-treatment related decrease in serum thyroxine (T4); serum triiodothyronine levels (T3) were 

not significantly affected and microscopic changes were suggestive of thyroid hyperactivity. These 

changes included increased lysosomal numbers and size, enlarged Golgi apparatus, and mitochondrial damage.

When compared to the other two co-tested phthalates, DnOP induced effects on hepatic lipid accu-
Appendix II

II-5

mulation and peroxisomal proliferation that were similar to the effects caused by DnHP, but dissimilar to those caused by DEHP. DEHP caused greater increases in liver weight and greater increases 

in mitotic activity. Less fat accumulation was seen with DEHP treatment which, when it occurred, 

was seen in the midzone and periportal zones rather than centrilobular regions. Biochemical evidence for peroxisome proliferation (cyanide insensitive palmitoyl CoA oxidation) occurred earlier 

with DEHP (after 3 days of treatment) and was approximately 7-fold higher than levels observed 

with DnOP. DnOP values were twice those observed in the control rats.

An effect level of 1,821 mg/kg bw/day was observed in this study after 3 days of treatment. Although DEHP induced peroxisome proliferation more strongly, rats exposed to DnOP did show evidence for proliferation after longer treatment. Additional liver effects suggestive of other types of 

liver damage were seen with DnOP. 

Liver metabolism and the biochemical changes associated with peroxisome proliferation were also 

studied by Lake et al. (13) who treated rats with 1,000 mg/kg DnOP for 14 days. DnOP produced 

a marginal increase in liver weight compared with DEHP. There were no increases in peroxisomal 

enzyme activities at 1,000 or 2,000 mg/kg.

Systemic effects were studied in groups of young (∼4−6 weeks old) Sprague-Dawley rats (15). 

Groups (10/sex) were fed DnOP at dietary concentrations of 0, 5, 50, 500, or 5,000 ppm (males: 0, 

0.4, 3.5, 36.8, or 350 mg/kg bw/day; females: 0, 0.4, 4.1, 40.8, or 403 mg/kg bw/day) for 13 weeks 

(Table 7-1). Negative controls (10/sex) were fed basal diet and positive controls (10/sex) were fed 

5,000 ppm DEHP (males: 345 mg/kg bw/day; females: 411 mg/kg bw/day). Rats were observed 

daily, and body weights and food intake were measured weekly. At the end of the exposure period 

rats were killed and necropsied. Parameters evaluated included histopathology (reproductive organs 

preserved in Zenker’s solution), hematology, blood chemistry, liver enzyme activity, peroxisome 

proliferation, and DnOP levels in tissues.

DnOP exposure did not affect organ or body weight at any dose concentration. No hematological 

effects or testicular changes were observed. At the dose of 4.1 mg/kg bw/day, female rats experienced significant increases in plasma phosphate level. At 36.8 (M) or 40.8 (F) mg/kg bw/day, no effects were observed and this level was designated by the authors as a NOAEL. At the highest DnOP 

exposure tested, 350.1 (M) and 402.9 (F) mg/kg bw/day, liver and thyroid effects were observed. 

Authors reported dose-related hepatic effects including anisokaryosis, nuclear hyperchromicity, vesiculation, cytoplasmic vacuolation, nuclear endothelial prominence, and accentuation of zonation. 

Increases in hepatic ethoxyresorufin-o-deethylase activity were also seen in this high-dose group. 

Thyroid effects, observed at the highest dose of DnOP tested, included decreases in follicle size and 

colloid density. Serum T3 or T4 analyses for thyroid function were not performed. Plasma calcium 

levels were significantly increased in male rats at the high dose only. 

The DEHP-positive control group of rats, exposed to 345 (M) and 411(F) mg/kg bw/day, had effects in the liver and thyroid with respect to severity of lesions and biochemical changes that were 

similar to those observed in the high-dose DnOP group. However, DEHP also induced peroxisomal 

proliferation, seminiferous tubule atrophy, Sertoli cell vacuolation, and decreased sperm levels. 

Also, numerous additional biochemical changes were observed with the DEHP-exposed rats, such 
II-6

Appendix II

as increases in plasma levels of albumin and inorganic phosphate, total protein (in female rats), 

and hepatic aminopyrine-N-demethylase and analine hydroxylase. DEHP also produced significant 

hematological effects such as increased platelet counts in rats of both sexes, increased WBC, and 

decreased mean corpuscular volume and decreased hemoglobin in females.

Poon et al. (15) also evaluated levels of DnOP and DEHP in liver and fat. The authors stated that 

the findings suggest that both DnOP and DEHP are rapidly metabolized and excreted and that their 

distribution in body tissues is determined by the lipophilicity of the compounds. The reliability of 

the actual levels reported in the paper has been questioned (16) by noting the failure of mass spectrometry to confirm the chemicals detected in tissues and the absence of analytical blanks when 

performing the analyses.

2.2 Toxicokinetics

Phthalate Moiety Toxicokinetics

Absorption

Few data are available describing the toxicokinetics of DnOP. Albro and Moore (17) dosed male CD 

rats by gavage with 0.2 mL DnOP and collected urine for analysis of metabolites. They recovered 

31% of the dose in the urine by 48 hours. The monoester and some free phthalic acid were detected, 

but no parent DnOP was observed. Blood levels of the monoester, mono-octylphthalate, were measured in rats following administration of 2,000 mg/kg of DnOP by gavage (18). The biological halflife in the blood was 3.3 hours with an area under the curve (AUC) of 1,066 μg·h/mL. Peak blood 

levels were observed at 3 hours following administration.

Biotransformation

Humans: In a study comparing the relative rates of monohydrolysis of DnOP by rat, baboon, and 

human gut preparations, Lake et al. (19) demonstrated that these species possess similar intrinsic 

esterase activity. Rates observed in human intestinal preparations were similar enough to the other 

species to conclude that human intestinal metabolism of DnOP would be expected to result in absorption of the monoester similar to what occurs in rats.

Rodents: Six dialkyl phthalates, including DnOP, were found to be metabolized to their monoesters 

and alcohol by enzymes present in gut tissues. It is generally accepted that orally-ingested phthalate 

diesters are primarily hydrolyzed by esterases in the wall of the small intestine, not by intestinal 

flora, and absorbed almost entirely as the corresponding monoester (20).

Distribution

Following an oral dose of 2,000 mg/kg DnOP to rats, mono-octylphthalate was found in blood and 

testes in 3−6 hours (21).

Excretion

Following a gavage dose of 559 mg/kg for 2 days to rats, metabolites accounting for 31% of the 

administered dose were found in urine. The major metabolites found in urine of rats were derived 

from the monoester (17). 
Appendix II

II-7

Side Chain-associated Toxicokinetics

n-Octanol is a metabolite of DnOP. Octanol is oxidized to the fatty acid and metabolized by the 

fatty acid oxidation pathway.

2.3 Genetic Toxicity

Mixtures containing DnOP have not shown conclusive evidence of mutagenicity. Barber et al. (22) 

tested C6–10-phthalate, which contains approximately 20% DnOP, in the mouse lymphoma mutation and Balb/3T3 cell transformation assays. Negative results were obtained in the cell transformation assay, but results of the mouse lymphoma mutation assay were considered equivocal due to the 

non-dose related increase in mutation frequency that occurred in the presence and absence of S9 

metabolic activation. 

The ACC (1) reviewed two studies of Di(n-octyl, n-decyl) phthalate, which contains DnOP as a 

component. Di(n-octyl, n-decyl) phthalate was reported to be negative in the Ames test and the Chinese hamster ovary cell/HPRT locus assay. 

The summary for Section 2, including general toxicity, toxicokinetics, and genetic toxicity, is 

located in Section 5.1.2.
II-8

Appendix II

3.0 DEVELOPMENTAL TOXICITY DATA

3.1 Human Data

There were no human data located for Expert Panel review.

3.2 Experimental Animal Toxicity

Two studies were found, one in rats by intraperitoneal (IP) injection and one in mice by gavage. A 

third study examined effects of metabolite exposure in rats. 

Singh et al. (23) administered DnOP at 0, 5, or 10 mL/kg (equivalent to 0, 4,890, and 9,780 mg/kg 

based on the specific gravity of DnOP of 0.978 g/mL) by IP injection to pregnant Sprague Dawley 

rats (Table 7−2). The rats, 5 per group, were dosed on gd 5, 10, and 15. The control group was untreated or dosed with distilled water, normal saline, or cottonseed oil. Dams and fetuses were evaluated on gd 20. Information on maternal toxicity was not reported. Fetal body weight was reduced at 

both doses, and incidences of gross malformations were increased in a dose-related manner (0–2% 

in controls, 16% at 4,890 mg/kg, and 27% at 9,780 mg/kg). The abnormalities were predominantly 

missing tail, anophthalmia, twisted hind legs, and hematomas.

Hardin et al. (24) evaluated DnOP in the Chernoff-Kavlock assay in CD-1 mice. The mice, 40/

group, were dosed by gavage, with 9,780 mg/kg bw/day (undiluted chemical, 10 mL/kg/day) or 

corn oil on gd 6–13. Dams were allowed to deliver their litters; dams and pups were terminated on 

pnd 3. No dams died, 39/40 had live litters, and maternal weight change was similar to controls. 

Litter size on pnd 0 was significantly reduced (10.2) versus the control value (11.5). Birth weight 

was normal as was pup survival to pnd 3. However, weight gain on pnd 1–3 was significantly reduced (0.6 g) versus the control value (1.0 g).

There was no effect on ability to produce litters, litter size, sex ratio, or pup weight or viability in 

F1 and F2 litters in a continuous breeding study in CD-1 mice. Mice were exposed to 0, 1.25, 2.5, 

or 5% DnOP (0, 1,800, 3,600, or 7,500 mg/kg bw/day) (25, 26). Complete details of this study are 

included in Section 4. 

Hellwig and Jackh (27) investigated the prenatal toxicity of n-octanol, a primary metabolite of 

DnOP, when administered by gavage to pregnant Wistar rats on days 6−15 of gestation. There were 

6 groups studied, 8−10 females/group: a distilled water control, an emulsifier control, and DnOP 

doses of 1, 5, 7.5, and 10 mmol/kg (130, 650, 945, and 1,300 mg/kg bw/day DnOP, respectively). 

Dose-related symptoms of clinical intoxication of the nervous system were observed with maternal 

death seen in the three highest dose levels. A slight decrease in food consumption and body weight 

gain was also recorded at these doses. However, no effects on fetal weight, viability, or developmental toxicity were observed. The incidence of malformations was similar to that of controls.

The summary for Section 3 is located in Section 5.1.3.
Appendix II

II-9

4.0 REPRODUCTIVE TOXICITY

4.1 Human Data

There were no human data located for Expert Panel review.

4.2 Experimental Animal Toxicity

One rodent reproductive toxicity study was found for DnOP reported by Heindel et al. (26) (also (25)) 

(Table 7-3). In this continuous breeding study, CD-1 (Swiss) mice, 20 pairs/dose level, 40 in controls) 

were fed DnOP in the diet at 0, 1.25, 2.5, or 5% (w/w). Body weights and food consumption were 

monitored, and these concentrations gave calculated daily DnOP consumption estimates of 1,800, 

3,600, and 7,500 mg/kg bw/day. Following a week of pre-mating exposure, mice were housed as breeding pairs for 14 weeks. Litters born during the 14-week period were evaluated and removed so that the 

adult pair could continue breeding. Reproductive function was measured by determining the fertility 

index; litters/pair; live pups per litter; and pup sex, body weight, and gross external malformations.

There were no effects on ability to produce litters, litter size, sex ratio, or pup weight or viability 

over five successive litters. For this protocol, when no effect on fertility was seen, the last litter from 

both the high dose and control group was reared, and used to evaluate fertility and toxicity of the F1 

generation. In addition to the reproductive parameters evaluated in the F0 mice, sperm morphology, 

estrous cycles, and selected organ weights were evaluated in the F1 mice. The F0 mice were discarded without necropsy after weaning the last litter. The F1 animals were mated within dose groups at 

sexual maturity. DnOP had no effect on indices of fertility, litter size, or pup weight or viability. The 

control and high-dose F1 adults were killed and necropsied after delivery of a single litter. DnOP at 

7,500 mg/kg bw/day in the diet had no effect on male body weight, but increased absolute and relative liver weights and decreased relative seminal vesicles weight. Sperm indices were unchanged. 

In females, body weight was unchanged, while relative liver and kidney weights were increased; 

estrous cycle was unchanged by 7,500 mg/kg bw/day DnOP consumption.

As discussed in Section 2.2, Poon et al. (15) (Table 7-1) reported a subchronic-type study of DnOP. 

Pubertal SD rats were exposed to DnOP in diet at doses as high as 5,000 ppm (350 mg/kg bw/day) 

for 13 weeks when the rats were killed and necropsied. Testes were weighed and fixed in Zenker’s 

solution; no sperm measures were taken. Terminal weights of whole body and testis were unaffected by DnOP consumption. Testis histology was normal. No reproductive effects were seen, so 

no LOAEL was determined. The reproductive NOAEL in this study is 5,000 ppm, ~350 mg/kg 

bw/day, based on lack of changes in testis weight and histology as observed by light microscopy. 

Confidence in the quality of the study is moderate-to-high. Confidence that this study found the true 

NOAEL is moderate-to-low, because guidelines for subchronic studies do not require the examination of functional reproductive effects.

Foster et al. (28) gavaged 12 male Sprague-Dawley rats (70−90 g) with DnOP at 2,800 mg/kg bw/

day for 4 days. Control animals received the corn oil vehicle. No testicular lesions were observed in 

the treated animals. 

Mode of Action

Following exposure to a variety of phthalate monoesters over a range of doses, germ cell detach-
II-10

Appendix II

ment was examined in in vitro co-cultures of Sertoli-germ cells isolated from pubertal rats. Results 

indicate that the n-octyl monoester is ~100-fold less potent than the 2-ethylhexyl monoester in 

producing this effect (29). These co-culture in vitro studies suggest that DnOP produces a similar 

effect to other phthalates in this model system, albeit at concentrations two orders of magnitude 

higher. There are no in vivo data to suggest effects on either germ cells or Sertoli cells due to DnOP 

exposure.

Several studies have examined the ability of selected phthalate esters to compete with labeled 

estradiol (E2) for binding to the estrogen receptor (ER). Sources of ER protein included rat uterine 

cytosol (30), rainbow trout hepatic cytosol (31), recombinant human ERs (rhER) overexpressed in 

SF9 insect cells using the baculovirus system (32, 33) and rainbow trout ERs expressed in yeast 

(34). Triated E2 was used in the tissue cytosol binding assays while a high affinity fluorescent E2 

derivative was used in the rhER binding assays. The estrogenic activity of DnOP has been examined using a battery of short-term in vitro and in vivo assays. DnOP did not compete with tritiated 

estradiol for binding to the rat uterine cytosolic estrogen receptor (30). 

Selected phthalate esters have been examined in a number of in vitro gene expression assays systems. The assays have used stably transfected cells (30), transiently transfected cells (30, 31), yeast 

based assays (30, 34-36) and vitellogenin induction in rainbow trout hepatocyte cultures (34). 

DnOP did not induce any activity in in vitro gene expression assays systems and did not induce reporter gene activity in transiently transfected MCF-7 cells (30). 

DnOP, in contrast to the positive control estradiol, did not significantly induce a vaginal cornification response at any of the concentrations tested (20, 200, and 2,000 mg/kg) over the course of a 

5-day experiment using immature and adult ovariectomized Sprague Dawley rats (30). The effects 

of subcutaneous injection of 10–4 mol of DBP, BBP, and DnOP on uterine vascular permeability 

following a 4-hour incubation were examined in mature ovariectomized Swiss albino mice (37). Although no significant effect on uterine vascular permeability was reported, it is unclear whether the 

authors tested DnOP or DEHP. The publication states that “dioctyl phthalate” was purchased from 

Aldrich chemical company.

The summary for Section 4 is located in Section 5.1.4.
Appendix II

II-11

5.0 DATA SUMMARY & INTEGRATION

5.1 Summary

5.1.1 Human Exposure

There are no known commercial uses for pure DnOP. However, DnOP constitutes approximately 

20% of the commercial mixture C6–10-phthalate. This commercial mixture has a variety of home 

and consumer product uses including as a plasticizer for PVC used in flooring and carpet tile, canvas tarps, swimming pool liners, notebook covers, traffic cones, toys, vinyl gloves, garden hoses, 

weather stripping, flea collars, and shoes. Uses of PVC containing DnOP with possible food applications include seam cements, bottle cap liners, and conveyor belts. 

Dietary: In a survey of infant formulas from the UK, the level of dioctyl phthalates (DOP) other 

than DEHP ranged from 0.21–1.42 mg/kg (7). In a subsequent survey in 1998, DOP isomers were 

not targeted, but there was no evidence that they were present in any of 39 samples of infant formula tested (8). There was a published report in 1995 that documented the detection of DnOP in 

two samples of vodka at concentrations of 57 and 131 ppb (6). In a German survey (9), DNOP was 

detected in nutmeg at 0.02 mg/kg but DNOP levels were below the detection limit of 0.01 mg/kg 

in milk (breast and commercial), cream, nuts, and baby food. Dioctyl phthalate is approved for use 

as an indirect food additive in sealants used for food packaging (4). 

Exposure Estimates: Based on levels of DOP isomers (excluding DEHP) detected in baby formula, infant exposures to DOP isomers other than DEHP were estimated at <0.1–43 μg/kg bw/

day at birth and <0.1−24 μg/kg bw/day at 6 months of age by MAFF (7). However, there was no 

evidence that DOP isomers were present in infant formulas in a survey conducted 2 years later by 

MAFF (8).

Based on production volumes of DnOP-containing compounds versus those containing DEHP, exposure to DnOP in the general population is likely lower than exposure to DEHP, which was estimated at 3−30 μg/kg bw/day (11). Exposures may be higher in children due to dietary preferences 

and mouthing of DnOP-containing articles. Variability in food exposure estimates is possible due 

to the inherent variability of food eaten by individuals based on age, sex, ethnicity, time of sampling, and geographical locations. In occupational settings, exposure is thought to be highest in 

workers of flexible PVC manufacturing facilities. Based on general levels of phthalates reported, 

the ACC (1) estimated an occupational exposure level of 286 μg/kg bw/workday in this activity. 

5.1.1.1 Utility of Data to the CERHR Evaluation

There is very limited information on exposure and exposure pathways to DnOP in humans. DnOP 

is not known to be produced directly for commercial use, but is a component (20%) of commercial 

6−10 phthalate substances. 6−10 Phthalates are used in a variety of consumer products. 

5.1.2 General Biological and Toxicological Data

Data presented in this section are derived from experimental animal and laboratory studies. Human data were not found.
II-12

Appendix II

General toxicity 

A 3-week dietary study (12, 14) and a 90-day dietary study (15) in rats have been conducted. Liver 

effects were noted when rats were fed 1,821 mg/kg bw/day for 3, 10, or 21 days, or 350 mg/kg 

bw/day for 90 days. Thyroid effects also were noted in rats fed 350 mg/kg/d for 90 days and 1,821

mg/kg bw/day for 21 days. No effects were observed in the testes in either study. The sub-chronic 

dietary NOAEL in rats is 36 (M)−40 (F) mg/kg bw/day. 

Toxicokinetics 

DnOP is metabolized and rapidly absorbed in the gut as the monoester and primarily excreted in the urine 

of rats (17, 18, 20). The major metabolites found in urine of rats were derived from the monoester (17).

Genetic toxicity 

DnOP has not been tested for genetic toxicity. Mixtures containing DnOP have not shown conclusive evidence of mutagenicity. Barber et al. (22) tested C6–10-phthalate in the mouse lymphoma 

mutation and Balb/3T3 cell transformation assays. 6–10-Phthalate mixture was considered equivocal in the mouse lymphoma mutation assay due to a non-dose related increase in mutations in the 

presence and absence of metabolic activation, but tested negative in the Balb/3T3 cell transformation assay. According to two studies reviewed by ACC (1), di(n-octyl, n-decyl) phthalate, which 

contains DnOP as a component, has been reported to be negative in the Ames test and the Chinese 

hamster ovary/HPRT locus assay. 

5.1.2.1 Utility of Data the CERHR Evaluation

The data is adequate for the examination of systemic effects and identification of the liver and thyroid as target organs. The dataset consisted of one useful study that examined systemic effects in 

groups of rats exposed for 90 days to multiple doses of DnOP by the oral route, a route relevant to 

human exposure. Levels of DnOP in the diet were verified. The evaluation included a histological 

examination of various organs, including reproductive organs that were fixed in Zenker’s solution. 

One concern is that male rats were at the pubertal stage at the start of the study and were therefore 

past the age of maximum sensitivity to phthalate-induced testicular damage. However, mice were 

exposed during prenatal development (the most sensitive period for testicular toxicity) in a continuous breeding study described in the reproductive toxicity section. 

There is adequate general toxicokinetic data for DnOP, consisting of absorption, distribution, metabolism, and excretion in rodents. While studies of toxicokinetics in humans have not been located, 

the DnOP toxicokinetic data in rodents is consistent with the large body of data on phthalates that 

includes data on rodents and primates. It is reasonable to assume that the DnOP rodent data are relevant to humans.

5.1.3 Developmental Toxicity

There are no data on the developmental toxicity of DnOP in humans. Two studies, where massive 

doses of DnOP were administered (4,890 and 9,780 mg/kg bw/day) to rats or mice by gavage or 

IP injection, suggest a potential for adverse prenatal effect or effect during the perinatal period expressed as death, growth retardation, and/or malformations (23, 24). However, litter size and pup 

weight and mortality were unaffected in a continuous breeding study where mice were exposed to 

dietary concentrations up to 7,500 mg/kg bw/day (25, 26). A primary metabolite, n-octanol, gave no 
Appendix II

II-13

sign of developmental toxicity at doses up to 1,300 mg/kg bw/day in rats (27). This dose caused severe intoxication and some deaths in the dams and prompts speculation whether the DnOP rat study 

that administered 4,890 mg/kg bw/day (23) led to severe maternal intoxication as well. The authors 

were silent on maternal effects. The limited study designs do not provide a basis for comparing consistency of response in the two species, nor do they allow meaningful assessment of dose-response 

relationships and determination of either LOAELs or NOAELs with any degree of confidence. The 

available studies do suggest a developmental toxicity response with gavage or IP administration 

with very high doses. 

Table 2: Summaries of NOAELs and LOAELs and Major Effects in Developmental Toxicity Studies

Protocol and Study

NOAEL

(mg/kg bw/

day)

LOAEL (mg/kg bw/day) and Effects Developmental Effects Observed 

at Higher Dose Maternal Levels Developmental

Prenatal developmental 

toxicity study with IP 

exposure in SpragueDawley rats.

5 dams/group received 

0, 4,890, or 9,780 mg/

kg bw on gd 5, 10, and 

15. Fetuses were evaluated on gd 20.

(23)

Maternal: 

Not reported.

Developmental: 

None.

Not reported. 4,890

↑ Fetuses with 

external 

malformations.

↓ Fetal weight.

↑ Fetuses with 

external 

malformations.

↓ Fetal weight.

Prenatal gavage toxicity screening assay in 

CD-1 mice. 

40 dams/group received 

0 or 9,780 mg/kg bw/

day on gd 6−13. 

Dams and pups evaluated on pnd 3 for litter 

size, survival, and body 

weight changes only. 

(24)

Maternal: 

Not reported.

Developmental: 

None.

Not reported. 9,780

↓ Litter size on 

pnd 0.

↓ Pup weight gain 

on pnd 1−3.

No higher doses.

Continuous breeding 

study in CD-1 mice. 

20 dams/group 

received DnOP in feed 

at 0, 1,800, 3,600, or 

7,500 mg/kg bw/day 

throughout mating and 

gestation.

(25, 26)

Maternal: *

Developmental: 

7,500

* No effects on live 

pups/litter or pup 

weight.

*Only developmental effects reported in this table. See Table 3 in Section in 5.1.4 for a description of effects in parental rats.

↑=Statistically Significant Increase

↓=Statistically Significant Decrease
II-14

Appendix II

5.1.3.1 Utility of Data to the CERHR Evaluation

The data set is inadequate for an evaluation of developmental toxicity. In one study, small numbers 

of rats (n=5/group) were exposed by intraperitoneal injection, a route that is not relevant to human 

exposure, and there was no information on maternal toxicity. In a screening study of mice, only a 

single dose was administered and there was no internal examination of offspring or dams.

5.1.4 Reproductive Toxicity

There were no data located on the reproductive toxicity of DnOP in humans. The continuous breeding design with DnOP in mice was negative at what can only be considered massive dietary doses 

up to 7,500 mg/kg bw/day (26). This was not a true multigeneration study because effective evaluation of the second generation was not performed. This lack of effect is loosely corroborated by the 

dietary study in rats (15) which found no histologic effects on reproductive organs after sub-chronic 

exposure to concentrations as large as 350 or 403 mg/kg bw/day for males and females, respectively. In addition, testicular lesions were not observed in male Sprague-Dawley rats gavaged with 

DnOP at 2,800 mg/kg bw/day for 4 days (28). Since there are no adverse reproductive effects in 

any study, no LOAEL can be estimated. The reproductive toxicity NOAEL in mice is 7,500 mg/kg 

bw/day and in rats is 350 mg/kg bw/day.

The data are sufficient to conclude that DnOP causes no detectable reproductive toxicity in adult 

mice at doses up to ~7,500 mg/kg bw/day. The data also find no reproductive toxicity at doses up to 

403 mg/kg bw/day in a subchronic dietary study in adult rats or 2,800 mg/kg bw/day in a 4-day gavage study in young rats, but there are no data on functional measures of reproduction. The data are 

insufficient to conclude that DnOP does not cause reproductive toxicity in developing rats or mice. 

It can be reasonably speculated, based upon both in vivo and in vitro studies, that DnOP is certainly 

less potent in producing male reproductive effects than the shorter-chain phthalate congeners.

Following exposure to a variety of phthalate monoesters over a range of doses, germ cell detachment 

was examined in in vitro co-cultures of Sertoli-germ cells isolated from pubertal rats. Results indicate that the n-octyl monoester is ~100-fold less potent than the 2-ethylhexyl monoester in producing 

this effect (29). These co-culture in vitro studies suggest that DnOP produces a similar effect to other 

phthalates in this model system, albeit at concentrations two orders of magnitude greater. There are 

no in vivo data to suggest effects on either germ cells or Sertoli cells due to DnOP exposure.

DnOP did not exhibit estrogenic activity in a variety of in vitro assays (30). It did not induce a significant in vivo response in ovariectomized rats (30). The results suggest that adverse effects as a 

result of exposure to DnOP would not be due to estrogenic activities of this phthalate. 
Appendix II

II-15

Table 3: Summaries of NOAELs, LOAELs, and Major Effects in Reproductive Toxicity Studies

Protocol & Study

NOAEL 

(mg/kg bw/

day)

LOAEL (mg/kg bw/day) 

and Effects

Effects 

Observed at 

Higher Dose 

Levels

Reproductive Systemic Reproductive

Continuous breeding study with 

mating of high dose and control 

F1 offspring. 

20 pairs of CD-1 mice were fed 

diets with DnOP (0, 1,800, 3,600, 

7,500 mg/kg bw/day) for 7 days 

prior to mating and during a continuous 98-day mating period.*

(25, 26) 

Reproductive: 

7,500

Systemic: 

Not identified 

due to limited 

examination 

of lower dose 

groups.

None

No effect on 

fertility, mating, 

sperm or estrous 

cycles in F0 or 

high dose F1

rats. 

7,500

↑Liver and 

kidney weight 

in F1 rats

No higher 

doses in study

* Developmental effects are reported in Table 2 in Section 5.1.3. 

↑=Statistically Significant Increase

5.1.4.1 Utility of Data to the CERHR Evaluation

Data are sufficient to indicate that oral DnOP exposures are not associated with detectable effects 

on reproduction at doses of up to 7,500 mg/kg bw/day in mice. Adequate numbers of mice (20 

pairs/group) were exposed to multiple doses of DnOP for a sufficient duration. Feed was analyzed 

for DnOP levels. Reproductive function and sperm quality were assessed in the F1 mice exposed 

during prenatal development; thus, mice exposed during the most sensitive age were evaluated. A 

concern with this study is that several postnatal maturation effects (found to be the most sensitive 

indicators of toxicity for other phthalates) were not evaluated. Other concerns included no reporting 

of histopathological effects, examination of only the F1 mice from the high-dose group, and a lack 

of necropsies at the lower dose levels.

5.2 Integrated Evaluation

There are no human data from which to judge the health effects of DnOP. Based on experimental literature, including toxicity studies in rats and mice with DnOP and other structurally-related 

phthalates, there is a reasonable basis for assuming relevance of these data for judging potential 

hazard to humans. 

There are no data indicating that DnOP is currently used in medical devices. Exposure to DnOP 

results from its presence as a 20% constituent of a commercial mixture of C6−10 phthalates. Humans would gain contact from household and consumer products. Absorption through skin from 

such contacts are expected to be low. Absorption into the body would result from dietary sources. 

Presence in food might reflect migration from food packaging and a legacy of fate and transport of 

phthalates into the environment. Like other phthalates, DnOP is readily absorbed from the intestinal 

tract as a monoester, and is rapidly metabolized and excreted. 

The experimental animal data are insufficient to permit a firm judgment about DnOP’s potential to 
II-16

Appendix II

pose a developmental toxicity hazard to humans. Studies that suggest potential developmental effects were of inadequate design for confident interpretation and effects were observed only at very 

high doses. A study of n-octanol, a primary metabolite of DnOP, reported severe maternal intoxication without any effect on growth, viability, or development. It was noted that adequate data are 

available on DnOP to indicate adverse effects on liver at doses lower than doses that suggest developmental toxicity. There are data to indicate that DnOP does not demonstrate estrogenic properties. 

There are experimental data on the reproductive toxicity of DnOP. The data indicate no effects in 

adult mice fed high doses (7,500 mg/kg bw/day). The data in rats, while negative at dietary doses 

up to 350 mg/kg bw/day in adults and gavage doses up to 2,800 mg/kg bw/day in young rats, did 

not assess a sufficient array of reproductive measures to be considered a complete evaluation. The 

data, while indicating a lack of effect, are insufficient to conclude with complete confidence that 

exposure by the oral route poses no hazard to adult reproduction. While there was a continuous 

breeding study that assessed the effects of exposure to DnOP during development on subsequent 

reproductive function later, the protocol did not completely assess two generations. 

5.3 Expert Panel Conclusions

There are no known commercial uses for pure DnOP. However, DnOP constitutes approximately 

20% of the commercial mixture C6–10 phthalate. This commercial mixture has a variety of home 

and consumer product uses. DnOP is approved for use as an indirect food additive in sealants used 

for food packaging (4). There is very limited information on exposure and exposure pathways to 

DnOP in humans. To allow for an integrated evaluation of exposure and toxicity information, the 

Expert Panel made a conservative estimate (i.e., an overestimation) of general population exposure to DnOP that would be at or lower than DEHP exposures of 3–30 μg/kg bw/day (see DEHP 

review). A similar approach for studying occupational exposures in chemical manufacturing was 

done using measured DEHP levels to estimate that chemical worker exposure would be less than 

286 μg/kg bw/workday. 

Two studies where massive doses of DnOP were administered intraperitoneally to rats or by gavage 

to mice suggest a potential for adverse prenatal effects or effects during the perinatal period 

expressed as death, growth retardation, and/or malformations (23, 24). However, litter size and 

pup weight and mortality were unaffected in a continuous breeding study where mice were orally 

exposed to concentrations up to 7,500 mg/kg bw/day (25, 26). A primary metabolite, n-octanol, 

gave no sign of developmental toxicity at doses up to 1,300 mg/kg bw/day in rats (27). Higher 

doses resulted in maternal lethality. The dataset is inadequate for an evaluation of developmental 

toxicity for the following reasons. The limited study designs do not provide a basis for comparing consistency of response in the two species, nor do they allow meaningful assessment of doseresponse relationships and confident determination of either LOAELs or NOAELs. The available 

studies suggest a developmental toxicity response with gavage or IP administration at very high 

doses. The developmental toxicity response suggests minimal concern from exposure during pregnancy or the perinatal period.

There is a single dietary exposure multigeneration study on DnOP in mice which was negative at 

exposures of 7,500 mg/kg bw/day (26). This lack of effect is loosely corroborated by the dietary 

study in rats (15) which found no histologic effects on reproductive organs after sub-chronic expo-
Appendix II

II-17

sure to concentrations as large as 350 or 403 mg/kg bw/day for males and females, respectively. In 

addition, no testicular lesions were observed in young male rats that were gavage dosed with 2,800 

mg/kg bw/day for 4 days. Since there are no adverse reproductive effects in either study, no LOAEL 

can be estimated. The reproductive toxicity NOAEL in mice is 7,500 mg/kg bw/day and in rats is 

350 mg/kg bw/day.

Data are sufficient to indicate that oral DnOP exposures are not associated with detectable effects 

on reproduction at doses of up to 7,500 mg/kg bw/day in mice. Therefore, the Panel has only negligible concern for effects on the adult reproductive system. Taken together, the Expert Panel has 

determined that although all of the databases are limited or inadequate, the existing data do not suggest that DnOP is a potent developmental or reproductive toxicant in rodents.

5.4 Critical Data Needs

The critical data needs are to determine if, and at what levels, humans are exposed to DnOP. DnOP 

is a significant constituent (20%) of a C6−10 phthalate product that has major commercial production and use. The public would be best served if data needs for the evaluation of risks to human 

reproduction focus on the commercial mixture that contains DnOP, rather than pure di-n-octyl 

phthalate. Information on the use of DnOP as a food additive would be useful in determining if 

there are critical data needs for pure DnOP.
II-18

Appendix II

6.0 REFERENCES

1. CMA. Comments of the Chemical Manufacturers Association phthalate esters panel in response to request for public input on seven phthalate esters. FR Doc. 99-9484. Washington, 

DC: Chemical Manufacturers Association, 1999.

2. Staples CA, Peterson DR, Parkerton TF, Adams WJ. The environmental fate of phthalate esters: A literature review. Chemosphere 35:667-749 (1997).

3. ACC. Meeting with Aristech Chemical Company, 1999.

4. FDA. Code of Federal Regulations. 21 (1999).

5. MAFF. Phthalates in food. Joint food safety and standards group food surveillance information sheet, vol 1999:MAFF - UK, 1996; 9p.

6. HSDB. Hazardous Substances Data Bank. Bethesda:National Institutes of Health, 1999.

7. MAFF. Phthalates in infant formulae. Joint food safety and standards group food surveillance information sheet, vol 1999:MAFF - UK, 1996; 7p.

8. MAFF. Phthalates in infant formulae. Food surveillance information sheet 168: Joint Food 

Safety and Standards Group, 1998.

9. Pfordt J, Bruns-Weller E. Die phthalsaureester als eine gruppe von umwelt-chemikalien mit 

endokrienem potential: Niedersachsisches Ministerium fur Ernahrung, Landwirtschaft und 

Forsten, 1999.

10. ATSDR AfTSaDR-. Di-n-octylphthalate. Toxicological Profile. Prepared by: Sciences International, Inc. Under Subcontract to: Research Triangle Institute.: U.S. Department of 

Health and Human Services, Public Health Service., 1997.

11. Doull J, Cattley R, Elcombe C, Lake B, Swenberg J, Wilkinson C, Williams G. Expert panel 

report on DEHP.: U.S. Environmental Protection Agency, 1998.

12. Hinton RH, Mitchell FE, Mann A, Chescoe D, Price SC, Nunn A, Grasso P, Bridges JW. Effects of phthalic acid esters on the liver and thyroid. Environ Health Perspect 70:195-210 

(1986).

13. Lake BG, Gray TJB, Gangolli SD. Hepatic effects of phthalate esters and related compounds--in vivo and in vitro correlations. Environ Health Perspect 67:283-90 (1986).

14. Mann AH, Price SC, Mitchell FE, Grasso P, Hinton RH, Bridges JW. Comparison of the 

short-term effects of di(2-ethylhexyl) phthalate, and di (n-octyl) phthalate in rats. Toxicol 

Appl Pharmacol 77:116-132 (1985).

15. Poon R, Lecavalier P, Mueller R, Valli VE, Procter BG, Chu I. Subchronic oral toxicity of 

di-n-octyl phthalate and di (2-ethylhexyl) phthalate in the rat. Food Chem Toxicol 35:225-
Appendix II

II-19

239 (1997).

16. American Chemistry Council Phthalate Esters Panel. Comments on Draft CERHR Evaluation of Di-n-Octyl Phthalate (DnOP):ACC, 2000.

17. Albro PW, Moore B. Identification of the metabolites of simple phthalate diesters in rat 

urine. Journal of Chromatography 94:209-218 (1974).

18. Oishi S. Effects of phthalic acid esters on testicular mitochondrial functions in the rat. Arch 

Toxicol 64:143-147 (1990).

19. Lake BG, Phillips JC, Linnell JC, Gangolli SD. The invitro hydrolysis of some phthalate 

diesters by hepatic and intestinal preparations from various species. Toxicol Appl Pharmcaol 

39:239-248 (1977).

20. Rowland IR, Cottrell RC, Phillips JC. Hydrolysis of phthalate esters by the gastro-intestinal 

contents of the rat. Food Cosmet Toxicol 15:17-21 (1977).

21. Oishi S, Hiraga K. Testicular atrophy induced by phthalic acid monoesters: Effects of zinc 

and testosterone concentrations. Toxicology 15:1997 (1990).

22. Barber E, Cifone M, Rundell J, Przygoda R, Astill B, Moran E, Mulholland A, Robinson E, 

Schneider B. Results of the L5178Y mouse lymphoma assay and the Balb/3t3 cell invitro 

transformation assay for eight phthalate esters. J Appl Toxicol 20:69-80 (2000).

23. Singh AR, Lawrence WH, Autian J. Teratogenicity of phthalate esters in rats. J Pharm Sci 

61:51-55 (1972).

24. Hardin BD, Schuler RL, Burg JR, Booth GM, Hazelden KP, MacKenzie KM, Piccirillo VJ, 

Smith KN. Evaluation of 60 chemicals in a preliminary developmental toxicity test. Teratogen Carcinogen Mutagen 7:29-48 (1987).

25. Gulati DK, Chambers R, Shaver S, Sabehrwal PS, Lamb JC. Di-n-octyl phthalate reproductive and fertility assessment in CD-1 mice when administered in feed. Research Triangle 

Park: National Toxicology Program, 1985.

26. Heindel JJ, Gulati DK, Mounce RC, Russell SR, Lamb JCI. Reproductive toxicity of three 

phthalic acid esters in a continuous breeding protocol. Fundam Appl Toxicol 13:508-518 

(1989).

27. Hellwig J, Jackh R. Differential prenatal toxicity of one straight-chain and five branchedchain primary alcohols in rats. Food Chem Toxicol 35:489-500 (1997).

28. Foster PMD, Thomas LV, Cook MW, Gangolli SD. Study of the testicular effects and changes in zinc excretion produced by some n-alkyl phthalates in the rat. Toxicol Appl Pharmacol 

54:392-398 (1980).

29. Gray TJ, Beamand JA. Effects of some phthalate esters and other testicular toxins on pri-

 
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Appendix II

mary cultures of testicular cells. Food Chem Toxicol 22:123-131 (1984).

30. Zacharewski TR, Meek MD, Clemons JH, Wu ZF, Fielden MR, Matthews JB. Examination 

of the in vitro and in vivo estrogenic activities of eight commercial phthalate esters. Toxicol 

Sci 46:282-293 (1998).

31. Jobling S, Reynolds T, White R, Parker MG, Sumpter JP. A variety of environmentally persistent chemicals, including some phthalate plasticizers, are weakly estrogenic. Environ 

Health Perspect 103:582-587 (1995).

32. Bolger R, Wiese TE, Ervin K, Nestich S, Checovich W. Rapid screening of environmental chemicals for estrogen receptor binding capacity. Environ Health Perspect 106:551-7 

(1998).

33. Nakai M, Tabira Y, Asa D, Yakabe Y, Shimyozu T, Noguchi M, Takatsuki M, Shimohigashi 

Y. Binding characteristics of dialkyl phthalates for the estrogen receptor. Biochemical and 

Biophysical Research Communications 254:311-314 (1999).

34. Petit F, Le Goff P, Cravedi J-P, Valotaire Y, Pakdel F. Two complementary bioassays for 

screening the estrogenic potency of xenobiotics: Recombinant yeast for trout estrogen 

receptor and troup hepatocyte cultures. Journal of Molecular Endocrinology 19:321-335 

(1997).

35. Coldham NG, Dave M, Sivapathasundaram S, McDonnell DP, Connor C, Sauer MJ. Evaluation of a recombinant yeast cell estrogen screening assay. Environ Health Perspect 105:734-

742 (1997).

36. Harris CA, Henttu P, Parker MG, Sumpter JP. The estrogenic activity of phthalate esters in 

vitro. Environ Health Perspect 1997 105:802-811 (1997).

37. Mulligan SR, Balasubramanian AV, Kalita JC. Relative potency of xenobiotic estrogens in 

an acute in vivo mammalian assay. Environ Health Perspect 106:23-26 (1998).
Appendix II

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7.0 TABLES

7.1 DnOP General Toxicity, Rats .................................................................................................22

7.2 DnOP Developmental Toxicity, Rats......................................................................................23

7.3 DnOP Reproductive Toxicity, Rats.........................................................................................24

7.4 References..............................................................................................................................25
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Appendix II

Table 7-1: DNOP General Toxicity, Rats

Species, 

Strain, and 

Source

Experimental 

Regimen

Animal 

Number Dose* Body Weight Organ Weight Histopathology Hematology Chemistry Other

SpragueDawley RatPoon et al. 1997(1)

Young male and female rats were fed diets containing DNOP for 13 weeks, then killed and necropsied. A positive control group was exposed to DEHP.

10 010 0.40 NE NE NE NE NE10 3.5(M)

4.1(F)

NE NE NE NE ↑PO4 (F)

10 36.8(M)

40.8(F)

NE NE NE NE NE NOAEL

10 350.1(M)

402.9(F)

NE NE Mild lesions 

in liver. Thyroid follicle reduction and decreased colloid density.No peroxisome proliferation or testicular lesions.

NE ↑EROD

↑ Ca (M)

10 345(M)

411(F)

[DEHP]

NE ↑Li, Ki 

(M)

↓Te

Testicular atrophy, liver and thyroid lesions, and peroxisomal proliferation.

↑WBC (F), 

PC 

↓Hb (F), 

MCV (F)

↑Alb, PO4, 

Ca (M), protein (F), APD, AH

*Doses measured in mg/kg bw/day.NE=No Effects↑=Statistically Significant Increase↓=Statistically Significant Decrease

F=FemaleM=Male

Ki=KidneyLi=LiverTe=Testes

Alb=AlbuminAPD=Aminopyrine-N-Demethylase ActivityAH=Aniline HydroxylaseCa=CalciumEROD=Ethoxyresorufin-O-deethylaseHb=HemoglobinMCV=Mean Corpuscular VolumePO4=PhosphatePC=Platelet CountWBC=White Blood Cell
Appendix II

II-23

Table 7-2: DNOP Developmental Toxicity, Rats

Species, Strain, 

and Source Experimental Regimen Animal Number Dose* Maternal effects Fetal Effects

Sprague-Dawley RatSingh et al. 1972(2)

Prenatal developmental toxicity studyDNOP administered by intraperitoneal injection on gd 5, 10, and 15. Dams killed on gd 20, corpora lutea counted and implantation sites examinedFetuses weighed, examined for viability and gross external malformations. 30−50% of fetuses examined for skeletal malformations.

5 05 4,890 Not mentioned in paper ↓Fetal weight.

↑External malformations 

(16% fetuses with gross abnormalities)

5 9,780 ↓Fetal weight.

↑External malformations 

(27% fetuses with gross abnormalities)

*Doses measured in mg/kg bw/day.↓=Statistically Significant Decrease↑=Statistically Significant Increase
II-24

Appendix II

Table 7-3: DnOP Reproductive Toxicity, Mice

Species, 

Strain, and 

Source

Experimental Regimen Number a Dose b Effects

CD-1 MiceHeindel et al. 1989Gulati et al. 1985(3, 4)

Dose range finding study.Fertility assessment through continuous breeding for 14 weeks. DNOP administered in feed.Body weight measured at 6 time points, clinical signs, and food and water intake recorded.Litters counted, sexed, weighed, observed for abnormalities, and removed following birth.Final litter raised; some control and high-dose F1 weanlings mated for fertility assessment; F1 organ weights measured at necropsy.

0−10,000 Rough hair coat in high-dose group

36 020 1,800 NE18 3,600 NE20 7,500 No adverse effects on sperm morphology, estrous 

cycles, or other reproductive parameters in F1 rats.No effect on fertility index, mating index, numbers of litters produced, live pups/litter, sex ratio, or pup weight.↓Percent abnormal sperm in F1 rats↓Seminal vesicle to body weight ratio in F1 rats↑Liver and kidney (females) to body weight ratio in 

F1 rats

a Number of male and female pairs; half the number of controls used for F1 study b Author-calculated doses (in mg/kg bw/day) based on male mice.NE=No Effect↑=Statistically Significant Increase↓=Statistically Significant Decrease
Appendix II

II-25

References

1. Poon R, Lecavalier P, Mueller R, Valli VE, Procter BG, Chu I. Subchronic oral toxicity of 

di-n-octyl phthalate and di (2-ethylhexyl) phthalate in the rat. Food Chem Toxicol 35:225-

239 (1997).

2. Singh AR, Lawrence WH, Autian J. Teratogenicity of phthalate esters in rats. J Pharm Sci 

61:51-55 (1972).

3. Heindel JJ, Gulati DK, Mounce RC, Russell SR, Lamb JCI. Reproductive toxicity of three 

phthalic acid esters in a continuous breeding protocol. Fundam Appl Toxicol 13:508-518 

(1989).

4. Gulati DK, Chambers R, Shaver S, Sabehrwal PS, Lamb JC. Di-n-octyl phthalate reproductive and fertility assessment in CD-1 mice when administered in feed. Research Triangle 

Park: National Toxicology Program, 1985.
Appendix III

PUBLIC COMMENTS

ON THE PHTHALATES

EXPERT PANEL REPORTS

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