NTP-CERHR Monograph on the 

Potential Human Reproductive and 

Developmental Effects 

of Di-Isodecyl Phthalate (DIDP)

April 2003 NIH Publication No. 03-4485

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Table of Contents

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

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

NTP Brief on Di-Isodecyl Phthalate (DIDP)...................................................................................1

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

Appendix I. NTP-CERHR Phthalates Expert Panel 

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

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

Appendix II. Phthalates Expert Panel Report on DIDP

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

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

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

Developmental Toxicity Data........................................................................................II-10

Reproductive Toxicity ...................................................................................................II-14

Data Summary & Integration........................................................................................II-17

References.....................................................................................................................II-31

Tables............................................................................................................................II-35

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:

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

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 DIDP, a list of the 

expert panel members (Appendix I), the expert 

panel’s report on DIDP (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 DIDP 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 report 

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

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

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 DIDP 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 2 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, post-natal 

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 DIDP?

DIDP is a complex, oily substance manufactured 

by reaction of phthalic anhydride and isodecyl 

alcohol in the presence of a catalyst. It contains 

a mixture of branched, primarily C-10 phthalate 

isomers such as the one shown in Fig. 1. The 

average chemical formula for the mixture is 

C28H46O4. It is one of a group of industrially 

important chemicals known as phthalates. 

Phthalates are used primarily as plasticizers 

to add flexibility to plastics. DIDP is used as 

a plasticizer in a wide variety of polyvinyl 

chloride (PVC) plastic products. These include 

coverings on wires and cables, artificial leather, 

toys, carpet backing, and pool liners. It has 

only limited use in food packaging or handling 

and is not used in medical devices. 

The expert panel report notes that approximately 

135,000 metric tons (~298 million pounds) of 

DIDP were used in the U.S. in 1998.

Are People Exposed to DIDP?*

Yes. There are several ways that people may 

be exposed to DIDP at home or at work. 

Human exposure to DIDP can occur during the 

manufacture of DIDP, during the manufacture 

of DIDP-containing products, during the use of 

such products, or through the presence of DIDP 

in the environment. Environmental exposures 

can occur through air, water, or contact with 

DIDP-containing products. Several studies 

have shown that DIDP is not detectable in food. 

Studies to determine the extent of human DIDP 

exposures have not been conducted. Because of 

inadequate information on human exposure to 

DIDP, the expert panel took the conservative 

position of assuming that general population 

exposures in the U.S. would be less than 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 DIDP Affect Human Development or 

Reproduction?

Possibly. Although there is no direct evidence 

that exposure of people to DIDP adversely 

affects reproduction or development, studies 

with rats have shown that exposure to DIDP 

can cause adverse developmental effects, but it 

does not affect reproduction (Fig. 2). 

Scientific decisions concerning health risks are 

generally based on what is known as “weightof-the-evidence.” In this case, recognizing the 

lack of human data and the evidence of effects 

in laboratory animals, the NTP judges the 

scientific evidence sufficient to conclude that 

DIDP is a developmental toxicant and could 

adversely affect human development if the 

levels of exposure were sufficiently high. The 

scientific evidence indicates that DIDP will not 

adversely affect human reproduction. (Fig. 3).

Summary of Supporting Evidence 

As presented in the expert panel report, DIDP 

studies in rats addressed effects on both 

NTP Brief on Di-Isodecyl Phthalate 

(DIDP)

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Figure 1. Chemical structure of the diisodecyl phthalate isomer, di-(8-methylnonyl) phthalate

* 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

development and reproduction. These studies 

reported that exposure of pregnant dams to 

relatively high doses of DIDP causes abnormal 

development of the fetal skeleton, and reduced 

weight gain and survival of pups. In some 

instances, DIDP exposure was also associated 

with abnormalities of the urinary tract. The 

data also show that lactational exposure can 

contribute to reduced weight gain in pups. 

A mouse developmental toxicity study was 

reported in which only one high exposure level 

was employed. No evidence of maternal or 

fetal toxicity was observed.

Two thorough studies of DIDP’s effects on 

reproduction in rats found no evidence of 

effects on the structure or function of the male 

or female reproductive systems. There was 

no evidence of an antiandrogenic effect of 

DIDP in male rat pups. It is important to note 

that DIDP exposure levels used in the rodent 

studies discussed above are generally far higher 

than those experienced by people.

Are Current Exposures to DIDP High 

Enough to Cause Concern?

Probably not. Although no data are available 

on general population exposures to DIDP, its 

chemical properties and uses make it unlikely 

that human exposures are any greater than to 

DEHP. If this is true, the scientific evidence does 

not point to an immediate concern for adverse 

Developmental Toxicity

Figure 2. The weight of evidence that DIDP 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 DIDP 

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

reproductive or developmental effects. Thus, 

the NTP offers the following conclusions.

The NTP concurs with the CERHR Phthalates 

Expert Panel that there is minimal concern for 

developmental effects in fetuses and children 

The NTP concurs with the CERHR Expert 

Panel that there is negligible concern for 

reproductive toxicity in exposed adults.

These conclusions are based on the assumption 

that the general US population is exposed to 

DIDP at less than 30 μg/kg bw/day. 

Information is not available on the levels of 

exposure in children mouthing DIDP-containing 

objects or in pregnant women occupationally 

exposed to DIDP. Thus, no conclusions can be 

reached concerning the possible hazards for 

these exposure circumstances.

References:

No new publications were located.

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 DIDP

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 DIDP 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-Isodecyl Phthalate

October 2000 NTP-CERHR-DIDP-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 .............................................................................................................................7

2.3 Genetic Toxicity ..........................................................................................................................8

3.0 DEVELOPMENTAL TOXICITY DATA....................................................................................................10

3.1 Human Data...............................................................................................................................10

3.2 Experimental Animal Toxicity...................................................................................................10

4.0 REPRODUCTIVE TOXICITY ...................................................................................................................14

4.1 Human Data...............................................................................................................................14

4.2 Experimental Animal Toxicity...................................................................................................14

5.0 DATA SUMMARY & INTEGRATION......................................................................................................17

5.1 Summary .............................................................................................................................17

5.1.1 Human Exposure.............................................................................................................17

5.1.1.1 Utility of Data to the CERHR Evaluation...........................................................17

5.1.2 General Biological and Toxicological Data ....................................................................17

5.1.2.1 Utility of Data to the CERHR Evaluation...........................................................20

5.1.3 Developmental Toxicity ..................................................................................................21

5.1.3.1 Utility of Data to the CERHR Evaluation...........................................................23

5.1.4 Reproductive Toxicity .....................................................................................................26

5.1.4.1 Utility of Data to the CERHR Evaluation...........................................................26

5.2 Integrated Evaluation ................................................................................................................28

5.3 Expert Panel Conclusions .........................................................................................................29

5.4 Critical Data Needs ...................................................................................................................30

6.0 REFERENCES............................................................................................................................................31

7.0 TABLES ......................................................................................................................................................35

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-isodecyl Phthalate Isomer

(Di-(8-methylnonyl) phthalate)

Commercial diisodecyl phthalate (DIDP) is a complex substance that is assigned two CAS Registry 

Numbers (26761-40-0 and 68515-49-1) (1). A synonym is 1,2-benzenedicarboxylic acid, di-C9-

11branched alkyl esters, C10 rich. DIDP is manufactured by reaction of phthalic anhydride and 

isodecyl alcohol in the presence of an acid catalyst (1). The alcohol manufacturing processes are 

stable (essentially the same feed stock, propylene, and butene), so although the substances are 

complex, they are not variable (1). DIDP is an oily, viscous liquid at standard temperature and 

pressure.

Table 1: Physicochemical Properties of DIDP

Property Value

Chemical Formula C28H46O4

Molecular Weight 447

Melting Point -48 oC

Boiling Point 370 oC

Specific Gravity 0.97

Solubility in Water Insoluble (< 0.001 mg/L)

Log Kow ~10

(2)

1.2 Exposure and Usage

Humans may be exposed to DIDP by the oral, dermal, and inhalation routes of exposure. Occupational exposure occurs primarily through inhalation and dermal contact, while consumer exposure 

occurs primarily by oral and dermal routes. .

Occupational Exposure

DIDP, like other phthalate esters, is manufactured within a closed system that is under negative 

pressure. However, some exposures may occur during the loading and unloading of railroad cars 

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II-2

Appendix II

and trucks. Somewhat higher exposures may occur during the production of polyvinyl chloride 

(PVC) products because of elevated temperatures and more open processes. The American 

Chemistry Council (ACC, formerly CMA) (1) cites six studies that indicate that exposures are 

below 1 mg/m3 during production of phthalates and below 2 mg/m3 during production of PVC. As 

discussed in Section 2.2, dermal exposure is not expected to result in significant absorption into the 

body.

Consumer Exposure

The range of products that contain DIDP is quite broad. The amounts produced and the use 

categories for DIDP in 1998 are given in the Table 2.

Table 2: Calculated 1998 US Consumption of DIDP

(thousands of metric tons)

End Use Subtotal Total

Film and Sheet 20

Skins – Unsupported 7

Pool Lining 9

Other 4

Artificial leather 20

Coated Fabrics 1

Dip Coating/Slush Molded 4

Toys 2

Traffic Cones <2

Other ~1

Tubings 9

Wire and Cables 45

Under-body Coating 36

GRAND TOTAL 135

(1)

Since DIDP, like other phthalates, is not bound in PVC, it can be released throughout the lifecycle 

of a product. Some end products do not result in direct consumer contact but may contribute to 

releases into the environment. Such uses include automobile undercoating, building materials, 

wires, and cables (1). Products which humans may contact directly include shoes, carpet backing, 

pool liners, and gloves (1). Direct exposure may also occur through food as a result of uptake by 

food animals, certain vegetables, and migration of DIDP from food packaging.

Food: DIDP was not detected in 74 samples of composite fatty foods from the UK at a detection 

limit of 0.01 mg/kg (3). These retail samples consisted of carcass meat, meat products, offal, 

poultry, eggs, fish, fats and oils, milk, and milk products. DIDP was not detected in 39 samples of 

infant formula from the UK at an analytical limit of 0.1 mg/kg (4). In an earlier study (5), DIDP 
Appendix II

II-3

was not detected in 59 samples of 15 different brands of infant formula analyzed at a typical 

detection limit of 0.01 mg/kg wet weight. Because DIDP concentrations in foods and infant 

formulas were below detection limits in the surveys conducted by Ministry of Agricultural Fisheries 

and Food (MAFF) (3-5), the ACC (1) considered dietary exposure to humans negligible. The results 

of sampling infant formulas for phthalates by the US Food and Drug Administration (6) suggests 

that phthalates are present in lower frequency and concentrations in the US than in Europe.

Toys: In a Dutch survey of teething rings and toy animals, DIDP levels were measured at a 

concentration of 1.4–15% (7). Surveys conducted by the UK government found DIDP in 6 of 18 

toys in 1990, 4 of 27 toys in 1991, 0 of 16 toys in 1992, and 0 of 29 toys in 1996 (7). In a Danish 

survey of 17 children’s toys, those without PVC did not contain phthalates. DIDP was detected in 

4 of the 7 PVC toys (3 teethers and 1 doll) at concentrations ranging from 0.7 to 10.1% by weight. 

Higher concentrations of DINP were also present. Precision measuring concentration is somewhat 

uncertain because the analytical method used (gas chromatography) did not cleanly resolve the 

peaks for DIDP and DINP (8). The Consumer Product Safety Commission (CPSC) did not detect 

DIDP in a sample of 35 toys that contained PVC. DINP was the predominant phthalate found. 

Although not specifically stated, the analytical methodology (GC/MS) used should have identified 

DIDP if present; lower levels of several phthalates were detected in some samples (9).

Exposure Estimate

Based on the physicochemical characteristics of DIDP and limited monitoring data, the Expert 

Panel believes it reasonable to assume that exposure to DIDP in the general adult population is 

lower than exposure to DEHP, which is estimated at 3–30 μg/kg bw/day (10). While no in vitro

or in vivo data on DIDP leaching from toys are available, it is reasonable to postulate exposures 

several-fold higher than the general population in infants and toddlers who mouth DIDP-containing 

products.

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

Oral

The British Industrial Biological Research Association (BIBRA) (11) administered groups of 5 

male and 5 female F344 rats (41–44 days old) dietary concentrations of 0, 0.3, 1.2, and 2.5% DIDP 

for 21 days. The authors calculated daily intake of DIDP as 0, 304, 1,134, and 2,100 mg/kg bw/day 

for males and 0, 264, 1,042, and 1,972 mg/kg bw/day for females. A fifth group was given diets 

containing 1.2% DEHP which corresponded to 1,077 mg/kg/day for males and 1,002 mg/kg bw/day 

for females. The level of cyanide-insensitive palmitoyl-CoA oxidation was determined. At necropsy, clinical chemistry was conducted, and liver, kidney, and testes weights were recorded and the 

organs were preserved in 10% formalin for histologic examination. 

There was a significant reduction in food consumption and mean body weight in male rats fed 

2,100 mg/kg bw/day beginning on day 3 and continuing throughout the study (69–82% of control). 

In female rats fed 1,972 mg/kg bw/day, mean body weight was reduced beginning on day 10 and 

continuing throughout the study (83–87% of control). Absolute and relative liver weights were 

significantly increased at all doses in males and at the two highest doses in females. In males, 

absolute weights were 121, 186, and 172% of controls at low to high doses, respectively, and 

relative weights were 121, 201, and 254%, respectively. In females receiving the two highest 

doses, absolute weights were 160 and 192% of controls and relative weights were 176 and 238%, 

respectively. In low-dose males, absolute and relative weights were 121% of controls. A variety 

of other effects were observed at the two highest doses; these included a reduction in hepatocyte 

cytoplasmic basophilia in both sexes, an increase in eosinophilia (high dose only), reduced 

serum triglycerides and cholesterol levels in males (no dose-response relationship was apparent), 

and a significant increase in cyanide-insensitive palmitoyl-CoA oxidation in both sexes. There 

was a significant increase in the 11- and 12-hydroxylation (11- and 12-OH) of lauric acid (all 

treated males), and in the 12-OH level in females at the high dose of DIDP. Electron microscopic 

examination of hepatic peroxisomes showed a marked but variable increase in size and number in 

both sexes at the high dose, but the response was less marked in females. There was a significant 

decrease in kidney weight in both sexes at the high dose, but no histological changes were 

observed. Absolute testes weights were slightly, but significantly, reduced at 2,100 mg/kg bw/day, 

but relative testes weights were greater than controls; no histological changes were observed.

This study provides evidence that the liver is a target organ of DIDP. A similar pattern of effects 

noted with DEHP is seen: increased liver weight, induction of hepatic peroxisome proliferation, 

depressed serum triglycerides and cholesterol levels, and increased activity of hepatic metabolizing 

enzymes. The testes do not appear to be a target organ at these dose levels. The study provided a 

LOAEL of 1,042 mg/kg bw/day in females and 304 mg/kg bw/day in males. A NOAEL of 264 mg/

kg bw/day was identified for females but no NOAEL was identified for males due to increased liver 

weight and 11- and 12-OH activity at all dose levels.

In a 4-week study (12), groups of 5 male F344 rats (42 days old) were given dietary concentrations 

of 0, 0.02, 0.05, 0.1, 0.3, or 1.0% DIDP (made up of equal parts Hexaplas [ICI], Jayflex [Exxon], 
Appendix II

II-5

and Palatinol Z [BASF]). These dose levels were reported to correspond to doses of 0, 25, 57, 116, 

353, and 1,287 mg/kg bw/day. Another group was given a diet of 1% DEHP. Food consumption 

and body weights were recorded twice weekly. At necropsy, organ weights were recorded, 

cyanide-insensitive palmitoyl-CoA oxidation activity was measured, and tissues were preserved 

in formalin for histologic examination. At doses of 116 mg/kg bw/day and higher, there was a 

significant increase in relative liver weight, and at doses of 353 mg/kg bw/day and higher, absolute 

liver weights were significantly increased. The cyanide-insensitive palmitoyl-CoA activity was 

significantly increased at doses of 353 mg/kg bw/day and higher. Testes weight was not affected by 

treatment and there were no histological changes.

The study provides evidence that the liver is a target organ of DIDP and the effects seen are 

consistent with those observed with other studies of DIDP and with DEHP. The testes do not appear 

to be a target. The study provides a LOAEL of 353 mg/kg bw/day and a NOAEL of 116 mg/kg bw/

day.

BASF (13) administered groups of 20 male and 20 female Sprague-Dawley rats dietary 

concentrations of 5,000 or 10,000 Palatinol Z for 28 days. This corresponded to average daily 

doses of 600 and 1,250 mg/kg bw/day for males and 1,100 and 2,100 mg/kg bw/day for females. A 

control group of 10 males and 10 females was fed the basal diet. Blood samples were taken from 

5/sex/group on day 14 or 15 for hematological assessment and urinalysis was conducted on day 23 

or 24. At necropsy, liver, kidney, and heart weights were recorded, and the liver and kidneys were 

examined histologically. Absolute and relative liver weights were significantly increased at both 

dose levels in both sexes, but there were no histologic changes. No other effects were noted.

Based on this 28-day study, BASF (14) administered groups of 20 male and 20 female SpragueDawley rats dietary concentrations of 800, 1,600, 3,200, or 6,400 ppm DIDP (Palatinol Z) for 90 

days. These levels were equivalent to average daily doses of 55, 100, 200, and 400 mg/kg bw/day 

for males and 60, 120, 250, and 500 mg/kg bw/day for females, respectively. A control group of 10 

males and 10 females was fed the basal diet. An additional group was fed the 6,400 ppm diet for 

90 days, followed by a recovery period of 21 days. Hematology and urinalysis were conducted on 

days 32–36 and 74–78. At necropsy, liver, kidney, and heart weights were recorded, and the tissues 

were preserved in 10% formalin. In male rats, there was a slight lag in body weight gain in the 

100, 200, and 400 mg/kg bw/day groups from day 77 onward. This finding was still present in the 

400 mg/kg bw/day group following the 21-day recovery period. In males, absolute liver weights 

were significantly increased at the highest (400 mg/kg bw/day) dose and relative liver weights were 

significantly higher in all groups; this effect persisted after the recovery period. In females, absolute 

liver weights were significantly increased at 250 and 500 mg/kg bw/day, and relative liver weights 

were significantly increased at doses of 120 mg/kg bw/day and higher. Relative kidney weights 

were significantly increased in males in all groups and in females at 120 and 250, but not 500, mg/

kg bw/day doses. No histological lesions were noted in testes, ovaries, liver, or kidneys.

The study offers support that the liver is a target organ of DIDP based on liver weight, but not 

histological, changes. The testes do not appear to be a target. A NOAEL in males of 200 mg/kg 

bw/day was assumed since an increase in absolute liver weight was reported at the highest dose. 

In females, a NOAEL of 120 mg/kg bw/day was assumed based on increased absolute and relative 
II-6

Appendix II

liver weights at the two higher doses.

Hazelton (15) administered groups of 10 male and 10 female Charles River CD rats dietary levels 

of 0, 0.05, 0.3, or 1% DIDP for 90 days. Based on body weights, rats were assumed to be young 

adults. Based on food intake rates and body weights reported by authors, doses of 0, 28, 170, and 

586 mg/kg bw/day and 0, 35, 211, and 686 mg/kg bw/day were calculated for males and females, 

respectively. At necropsy, clinical chemistry was conducted, organ weights were recorded, and the 

tissues were preserved in 10% formalin. There were no significant effects on food consumption, 

body weights, or clinical chemistry. Absolute and relative liver weights were significantly increased 

at the high dose in both sexes. Relative kidney weights were significantly increased in males at 

the two higher doses. There were no histologic changes in the testes, liver, or kidney. A minimal 

increase in thyroid activity was observed at the highest dose level; the activity was judged to be 

higher when the follicles were more uniform and smaller in size with a lighter colloid along with a 

tall cuboidal or columnar epithelium.

The study provides confirming evidence that the liver is a target organ of DIDP. The testes do 

not appear to be a target as no testicular lesions were observed in the high-dose group. The study 

provides a LOAEL of 586(M)–686(F) mg/kg bw/day and a NOAEL of 170(M)–211(F) mg/kg bw/

day. 

Hazelton (16) administered groups of 3 male and 3 female young adult beagle dogs dietary levels 

of 0, 0.05, 0.3, or 1% DIDP for 90 days. Based on food intake rates and body weights reported 

by authors, doses of 0, 15, 77, and 307 mg/kg bw/day and 0, 16, 88, and 320 mg/kg bw/day 

were calculated for males and females, respectively. There were no effects on food consumption, 

hematology, clinical chemistry (including ALT, AST, and BSP clearance), or urinalysis. Testicular 

lesions were not observed in microscopic slides prepared from Bouin’s-fixed testes in high-dose 

dogs. Three dogs (2 male, 1 female) in the 307−320 mg/kg bw/day group showed slight-tomoderate weight loss. At necropsy, there was a dose-related increase in absolute liver weights, but 

the small sample size precluded statistical analysis. The mean liver weights were 253, 248, 274, 

and 317 g (males) and 190, 212, 220, and 287 g (females) for the 0, 0.05, 0.3, and 1% groups, 

respectively. The authors also reported a slightly elevated liver to body weight ratio in 5 of 6 dogs at 

the highest dose tested. Swollen and vacuolated hepatocytes were noted in two mid-dose males, two 

mid-dose females, one high-dose male, and three high-dose females. The Expert Panel concluded 

that the small sample size in this study precludes the determination of a NOAEL. A LOAEL of 

77(M)–88(F) mg/kg bw/day was identified based on liver effects. 

Inhalation

General Motors Research Laboratories (17) exposed 8 adult male Sprague Dawley rats by 

inhalation (aerosol) to 505 mg/m3 (MMAD: 0.98μm) 6 hours/day, 5 days/week for 2 weeks. 

There were six control rats. After a subsequent 3-week observation period, the rats were killed 

and necropsied. There were no clinical signs of toxicity or effects on body weight. Effects in the 

lungs included a moderate increase in the width of alveolar septa with slight interstitial mixed 

inflammatory reactions, alveolar macrophages and type II pneumocytes were increased in number, 

and the peribronchial lymphoid tissue appeared slightly more prominent. No histological changes 

were noted in the liver, kidney, or spleen. 
Appendix II

II-7

2.2 Toxicokinetics

Phthalate Moiety Toxicokinetics

Absorption (Rodents)

Rodents: Dermal absorption of phthalates decreases with increasing side chain length beyond 

four carbons (18). In rats, 80% of dermally applied 14C-DIDP (ring-label) was recovered at the 

site of application 7 days after the application. Only 2% of the applied dose was recovered in other 

tissues or excreta with a total recovery of only 82% reported. In another study in rats in which total 

recoveries were better (94% or greater) (19), similar results were obtained. 14C-DIDP was applied 

to the skin and the dose site was occluded. At 1, 3, and 7 days, 96, 92, and 93% of the doses, 

respectively, were still at the application site. Only trace amounts of radioactivity were found in 

other tissues and excreta. The total absorbed dose was approximately 4% of the administered dose. 

DIDP dermal absorption has not been tested in humans, but an in vitro study conducted with DEHP 

suggests that the DIDP absorption rate through human skin is likely lower than the absorption 

rate for rat skin (20). Studies conducted by Deisinger et al. (21) have demonstrated that dermal 

absorption of DEHP from a plasticized film is slower than dermal absorption of neat DEHP. It is 

reasonable to assume that these results apply to DIDP. 

Oral: A study (22) conducted in rats evaluated the effect of oral dose on the toxicokinetics of 14CDIDP (labeled carboxyl groups). The doses, which were administered by gavage in corn oil, were 

0.1, 11.2, or 1,000 mg/kg bw. The amounts absorbed can be estimated from the total radioactivity 

excreted in urine and bile or retained in the carcass at the end of 72 hours, and were 56, 46, and 

17% for the low, medium, and high doses, respectively. The remainder of the radiolabeled activity 

was excreted in the feces with evidence, from bile radioactivity, of some enterohepatic uptake. The 

study indicated that at low doses at least 56% of orally-administered DIDP is absorbed. The data 

suggest partial saturation of DIDP metabolism by esterases in the gut in rats within the dose range 

administered in the study (0.1−1,000 mg/kg).

Inhalation: Six male Sprague Dawley rats were exposed for 6 hours by inhalation (head only) to 

91 mg/m3 of 14C-DIDP (17). Excreta were collected over a 72-hour period and 3 animals were 

analyzed for radioactivity immediately after the exposure and at 72 hours after the exposure. 

Assuming a minute volume of 200 mL for the rats, the estimated total amount of DIDP inhaled 

would be approximately 14.4 μmoles. The initial body burden was 8.3 μmoles, indicating that 

approximately 58% of what was inhaled was retained in the body. Twelve percent of the initial body 

burden was in the gut and 85% was in the lung. Seventy-three percent of the dose to the lung was 

cleared during the first 72 hours, indicating that absorption of DIDP or its metabolites from the 

lung into the rest of the body was about 73%. 

Biotransformation

Bacterial: Ejlertsson et al. (23) reported no degradation of DIDP by microorganisms in a 

laboratory scale landfill reactor during 100 days of incubation.

Rodent: In rats orally administered 14C-DIDP (22), the major metabolites detected in urine were 

phthalic acid and the oxidized monoester derivative, but no DIDP or monoisodecyl phthalate 
II-8

Appendix II

(MIDP) were detected over a wide range of doses (0.1−1,000 mg/kg). The relative amounts of each 

metabolite varied with dose with the monoester derivative increasing with increasing dose from 

52% at the low dose to 72% at the high dose, while the phthalic acid decreased from 38 to 18%. 

The monoester oxidized derivative, MIDP, and DIDP were all detected in feces in dose-dependent 

amounts. The parent compound increased from 30 to 55 and 60% after doses of 0.1, 11, and 1,000 

mg/kg, and the percentage of the oxidative derivative of the monoester and of MIDP at the same 

doses were, respectively, 25 and 30%, 14 and 26%, and 13 and 13%. The data suggest a metabolic 

scheme comparable to the one reported for DEHP, that is, de-esterification to the monoester form 

and an alcohol moiety by pancreatic lipase and intestinal mucosa esterase prior to absorption. The 

high content of MIDP in feces is consistent with such a scheme. The data also suggest saturation of 

the metabolism of DIDP in rats at a dose lower than 11 mg/kg. 

Distribution

In studies conducted in rodents by either the oral (22) or the dermal (18) route, there was limited 

distribution to the tissues. Seven days after dermal administration, only trace amounts of DIDP 

were left in the body and showed no specific tissue distribution. Three days after oral administration 

of doses up to 1,000 mg/kg, less than 1% of the DIDP was found in the tissues. Following 

inhalation (17), the major sites of DIDP-derived material were the lung and the gut immediately 

after exposure. The next highest levels were found in the liver, kidney, and brain. At 3 days 

following administration, 27, 8, 9, and 10% of the initial burdens in the lung, gut, liver, and kidney 

remained. No DIDP-derived material was left in the brain after 3 days. 

Excretion

In all studies in rodents, the major routes of excretion for absorbed DIDP are via the urine and 

feces. In orally-administered DIDP, fecal excretion increased from 58% of the total body burden at 

a dose of 0.1 mg/kg to 82% at a dose of 1,000 mg/kg. The remaining material was excreted in urine 

with less than 1% of the dose remaining in the animal after 3 days. There is evidence of excretion 

into the bile; the percentage of total administered dose that was recovered in bile decreased with 

increasing dose from 14% at a dose of 0.1 mg/kg to 4.7% at a dose of 1,000 mg/kg. 

In rats exposed by inhalation, 45 and 41% of the absorbed dose were excreted via urine and feces, 

respectively. The excretion via the urine indicated an elimination half-life of 16 hours, with an 

elimination rate constant Ke of 0.042/hour. The elimination half-life for all routes of excretion (rate 

of decline in body burden) was 26 hours with an elimination rate constant of 0.027/hour.

Side Chain-associated Toxicokinetics

A major metabolite of DIDP, MIDP, is further oxidized.

2.3 Genetic Toxicity

The mutagenicity of DIDP has been examined in a number of bacterial (24-26), mammalian cell, 

and cell transformation assays. A bone marrow micronucleus test in CD-1 mice has also been 

performed (27). A recent OECD meeting (28) accepted the following conclusions “DIDP is not 

mutagenic in vitro in bacterial mutation assays (with and without metabolic activation) and is 

negative in a mouse lymphoma assay. It is not clastogenic in a mouse micronucleus assay in vivo. 

This suggests that DIDP is a non-genotoxic agent.” DIDP tested negative in the L5178Y mouse 
Appendix II

II-9

lymphoma mutation assay and the Balb/3T3 cell transformation assay (29). The data from the 

mutation and cell transformation assay were reviewed by OECD. 

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

located in Section 5.1.2.
II-10

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

Three studies were found, two in rats and one in mice, that evaluated prenatal developmental 

toxicity following exposure by gavage to DIDP.

Hardin et al. (30) evaluated 60 chemicals, including 9 phthalates in the Chernoff-Kavlock assay 

in CD-1 mice. This is a screening protocol to prioritize chemicals for subsequent definitive 

developmental toxicity evaluations and to compare relative potencies. DIDP (CAS No. 26761-40-

0) was administered by gavage on gestation day (gd) 6–13 at 0 or 9,650 mg/kg bw/day (undiluted 

chemical, 10 mL/kg bw/day) to 50 mice/group. The dams delivered their litters, and dams and pups 

were terminated on postnatal day (pnd) 3. There was no maternal mortality; there were no weight 

change effects and no effects on numbers of live litters, litter size, litter survival, birth weight, or 

weight gain. 

Waterman et al. (Table WEB-1) (31) administered DIDP (CAS No. 68515-49-1) to 25 SpragueDawley rats/group on gd 6–15 by gavage at 0, 100, 500, and 1,000 mg/kg bw/day. The dams were 

sacrificed on gd 21 and implantation sites were evaluated. Fetuses were weighed and examined 

for external, visceral, and skeletal malformations. At 1,000 mg/kg bw/day, maternal toxicity was 

indicated by decreased weight gain and food consumption. Effects on fetal mortality or weight 

were not observed at any dose. Signs of developmental toxicity were seen in fetuses from dams 

that received 500 and 1,000 mg/kg bw/day. There was a statistically significant increase in the 

percent litters with 7th cervical ribs at the 1,000 mg/kg bw/day dose; a numerical increase in litter 

incidence with increasing dose (8.0, 18.2, 25, 41.7%) was also observed. A dose-related increase 

in the percent fetuses with a 7th cervical rib was observed, with the incidence at the two highest 

doses attaining statistical significance (1.0, 2.3, 6.2, 9.2%). A second skeletal variant, rudimentary 

lumbar (14th) rib(s), showed increased incidence at the two highest doses that was significant 

on a percent litter basis at the highest dose and on a percent fetus basis at the two highest doses. 

Litter incidence values were 40.0, 36.4, 62.5, and 95.8%, while fetal incidence was 8.2, 9.0, 21.2, 

and 52%. Waterman et al. (31) interpreted their results as indicating a LOAEL for maternal and 

developmental toxicity at 1,000 mg/kg bw/day and a NOAEL of 500 mg/kg bw/day. The Expert 

Panel concurred with the maternal NOAEL but selected a developmental NOAEL of 100 mg/kg 

bw/day based on the significant incidence of cervical and accessory 14th ribs. The Expert Panel 

informed the sponsor of the Waterman et al. study that the Panel believed that there were more 

recent and superior methods for the analysis of pup incidence. The sponsor statistically reanalyzed 

findings of toxicological interest using the generalized estimating equation (GEE) approach to 

the linearized model (32) and shared its reanalysis results with the Panel (33). This is a puplevel analysis within a model that uses the GEE approach to account for the litter effect, i.e., the 

correlation between outcomes measured on pups within the same litter. The dose groups were tested 

pair-wise versus controls; this gave similar results to a trend test based on a dose-response model fit 

with all dose levels up to that of interest included. The results, presented in tabular form below, are 

consistent with the interpretation of the Expert Panel.
Appendix II

II-11

The sponsor also provided benchmark doses at the 5 and 10% excess risk level, based on a 

multiplicative (or ‘extra’) excess risk function. At the 5% excess risk level, the benchmark doses 

(and their 95% lower confidence limits estimated by bootstrap methods) were estimated as 188 

(169), 258 (238), and 645 (515) mg/kg bw/day for rudimentary lumbar ribs, skeletal variants, and 

supernumerary cervical ribs, respectively.

Table 3: Mean Percent of Pups in Litter with Effect of Interest

(significance level)

Dose Group (DIDP mg/kg bw/day)

0 100 500 1,000

Skeletal Variations 19.8 20.6

(0.70)

31.9*

(0.05)

64.1**

(0.001)

Rudimentary 

Lumbar Ribs

8.4 9.4

(0.70)

21.9**

(0.01)

51.9**

(0.001)

Supernumerary 

Cervical Ribs

1.1 3.1

(0.28)

6.2*

(0.03)

10.2**

(0.004)

* p≤0.05, ** p≤0.01

Hellwig et al. (34) investigated the comparative developmental toxicity of a number of phthalates. 

They administered DIDP (CAS No. 26761-40-0) by gavage in olive oil at 0, 40, 200, and 1,000 

mg/kg bw/day to Wistar rats on gd 6–15 in 7–10 pregnant rats per group (Table WEB 2). The 

dams were sacrificed on gd 20 and implantation sites were evaluated. Fetuses were weighed and 

examined for external, visceral, and skeletal malformations. At 1,000 mg/kg bw/day, there was 

maternal toxicity expressed as reduced feed consumption, vaginal hemorrhage in 3 dams, and 

increased absolute and relative liver weights. Kidney weight was unaffected. Developmental 

effects included increased incidences of percent fetal variations per litter (24.3, 37.2, 38.4, 

and 44.2% at 0, 40, 200, and 1,000 mg/kg bw/day, respectively) with the values at 200 and 

1,000 identified as statistically significant. In the high-dose group, there were clear increases in 

rudimentary cervical ribs and accessory 14th ribs. An increased incidence of dilated renal pelves 

and hydroureter was observed at all treatment levels which apparently contributed to a statistically 

significant increase in the mean percent of fetuses affected per litter with variations at the 200 and 

1,000 mg/kg bw/day doses. The data at 200 mg/kg bw/day are at odds with the authors’ statement 

that “no substance-related effects were observed on dams, gestational parameters or fetuses 

among the two lower dose groups.” Since there were increased incidences of total fetal variations 

at both 200 and 1,000 mg/kg bw/day, the Expert Panel concluded that 40 mg/kg bw/day was the 

developmental NOAEL and 200 mg/kg bw/day the maternal NOAEL. The factors that led to the 

selection of these values, which differ from those of the authors, are discussed in Section 5.1.3.

Developmental effects were also observed in one- and two-generation reproductive toxicity studies 

in rats that are discussed in full detail under Section 4 (35, 36) (Table WEB-3). In both studies, 

dams were exposed to DIDP through diet from 10 weeks prior to mating through gestation and 

lactation. Dietary dose levels were 0, 0.25, 0.5, 0.75, and 1% for the one-generation study and 0, 
II-12

Appendix II

0.2, 0.4, and 0.8% for the two-generation study. In the one-generation study, fetal body weights 

were lower in groups exposed to 0.5% DIDP and higher. There was no effect on offspring survival. 

For the two-generation study, developmental effects in F1 offspring included a decrease in live 

pups at birth and on pnd 4 and a decrease in pup birth weight and weight gain in the high-dose 

group on pnd 0, 7, 14, and 21 for both sexes and also on pnd 4 for males. In F1 pups, relative liver 

weights were significantly increased in females in the mid- and high-dose groups and males in 

the high-dose group. Liver cell hypertrophy and eosinophilia were also observed in the mid- and 

high-dose groups. F1 females in the mid- and high-dose groups experienced a delay in vaginal 

opening (33.5 and 34.2 days, respectively, vs 32.2 days in control). The age of preputial separation 

was not affected in males, but the frequency of evaluation was not sufficient to rule out an effect. 

Developmental effects in F2 pups were similar to those observed in F1 pups. F2 pup survival was 

reduced on pnd 1 and 4 in all treated groups, and also on pnd 7 and at weaning in the high-dose 

group. An unusually high incidence of pup deaths in 4, 2, and 4 litters of the low-, mid-, and highdose groups respectively was noted; it was opined that reduced survival is usually observed in 

small numbers of pups distributed over many litters. F2 pup birth weight was reduced in males 

of the high-dose group and postnatal weight gain was reduced in all pups of the high dose-group 

on pnd 1, 4, 7, 14, and 21. Four high-dose male pups had undescended testes, an effect that was 

probably related to delayed development. Although F2 pup liver weight was not increased, liver cell 

hypertrophy and eosinophilia were observed in mid- and high-dose males and females. Because 

postnatal survival was reduced in all treated F2 pups, a NOAEL was not identified for this study. 

The 0.2% dose (131−152 mg/kg bw/day and 162−379 mg/kg bw/day in F0 and F1 dams during 

gestation and lactation, respectively) was identified as the developmental LOAEL. 

The two generation study was repeated by ExxonMobil Biomedical (36) using lower doses of 0, 

0.02,0.06, 0.2, and 0.4% in feed (Table WEB-4). In addition to lower doses, this study incorporated 

measurement of anogenital distance on day of birth and assessment of nipple retention on pnd 13 

or 14, on all offspring of both generations. Age at which vaginal patency and preputial separation 

occurred was noted for 2 rats/sex/dose for both F1 and F2 offspring. Dams were exposed for 10 

weeks prior to mating throughout pregnancy and gestation. Complete details of the study, including 

a description of reproductive effects in parents and offspring, are included in Section 4. In the 

F1 offspring there were no effects on pup survival, body weight, or organ weights. However, an 

increased incidence of dilated renal pelves (8/29 vs 0/30) were noted in adult F1 males of the 

high-dose group (0.4%). The authors did not consider the effect to be biologically significant. 

Developmental results in F2 offspring were consistent with findings of the previous 2-generation 

study (35). Effects at the 0.2% dose level included significant reductions in F2 pup survival on pnd 

1 and 4 and significant decreases in body weights of female F2 pups on pnd 14 and male pups on 

pnd 35. At the 0.4% dose level, F2 pup survival was significantly decreased on pnd 1 and 4 and 

body weights were significantly lower for female F2 pups on pnd 14 and 21 and for males F2 pups 

on pnd 14, 28, and 35. At the high dose, the liver to body weight ratio was increased in F2 female 

pups sacrificed on pnd 21, but authors stated that the result was not biologically significant due to a 

lack of absolute organ weight change. A histological examination was not conducted. No treated F1

and F2 pups experienced differences from controls in either anogenital distance or abnormal nipple 

retention. A developmental NOAEL of 0.06% (38–44 and 52–114 mg/kg bw/day during pregnancy 

and lactation, respectively) was identified by the study authors.
Appendix II

II-13

In order to determine if postnatal developmental effects in pups are due to lactational transfer 

of DIDP, a cross-fostering and switched-diet experiment was conducted by Exxon Biomedical 

Sciences (35). For the experiments, 20 CRl:CDBR VAF Plus rats/group were fed diets with 

0 or 0.8% DIDP for 10 weeks prior to mating throughout the gestation and lactation periods. 

Approximate doses received by the dams for the premating, gestation, and lactation periods were 

508–775, 524–551, and 641–1,582 mg/kg bw/day, respectively. For the cross-fostering portion of 

the study, the pups from ten treated dams were switched with pups from ten control dams. Nursing 

continued until weaning and the pups were then fed diets consistent with their lactational exposure 

for 10 weeks. For the switched-diet study, pups from control dams were fed the high-dose diet 

following weaning, and pups from treated dams were fed control diets after weaning for 10 weeks. 

Body weights were measured in both experiments.

Pups that were not exposed to DIDP in utero, but were nursed by treated dams, had lower body 

weights on pnd 14 and 21 than did controls (not exposed to DIDP during any portion of the study). 

The body weights of the pups remained lower (7–11%) during the 10-week period that they were 

fed DIDP-treated diets. Absolute and relative right testes weights and absolute left testes weights 

were reduced in these pups, but a histological examination was not conducted. No changes in 

body weights were noted for pups that were exposed to DIDP in utero but were then fostered by 

unexposed dams. In the switched-diet experiment, pups exposed to DIDP during gestation and 

lactation began to recover body weight and display normal growth patterns once they began to 

receive control diets at weaning. A slight decrease in body weight gain was observed in pups 

that were not exposed to DIDP during gestation and lactation but were fed DIDP-treated diets at 

weaning. 

The summary for Section 3 is located in Section 5.1.3.
II-14

Appendix II

4.0 REPRODUCTIVE TOXICITY

4.1 Human Data

There were no human data located for Expert Panel review.

4.2 Experimental Animal Toxicity

Exxon Biomedical (35) conducted a one-generation reproductive range finding assay in rats. 

The rats were fed diets containing 0, 0.25, 0.5, 0.75, and 1% DIDP. There were no effects on 

reproductive indices. Toxicity in parents was limited to reduced body weight gain and/or reduced 

food intake in the 0.75 and 1% dose groups. Based on the results of the range finding assays, doses 

were selected for a two-generation study. 

For the two-generation reproductive study, 30 Crl:CDBR VAF Plus rats/sex/group were fed diets 

containing 0, 0.2, 0.4, and 0.8% DIDP for 10 weeks prior to mating and during the mating period 

(35) (Table WEB-3). Treatment of the females continued through gestation and lactation. Authorestimated doses for the premating period were 103–198, 211–405, and 427–781 mg/kg bw/day for 

males and 127–203, 253–416, and 508–775 mg/kg bw/day for females. Doses received by females 

during the gestation and lactation periods were estimated at 131–149, 262–287, and 524–551 mg/

kg bw/day and 172–361, 359–734, and 641–1582 mg/kg bw/day, respectively. Body weight and 

food intake were recorded weekly and estrous cycles were evaluated. Parental males were killed 

after mating and females were killed at weaning. A histological examination was conducted for 

reproductive and other key organs (testes fixed in Bouin’s). Primordial oocytes were counted in 

control and high-dose females. Sperm count, morphology, and motility were evaluated in males. 

F1 pups were selected for mating at weaning and were fed diets with the same DIDP concentration 

as parental rats. Estimated doses for the F1 rats were 117–216, 229–437, and 494–929 mg/kg bw/

day in males and 135–218, 273–433, and 566–927 mg/kg bw/day in females during the premating 

period. Estimated dose levels for F1 females during gestation and lactation were 135–152, 262–297, 

and 574–611 mg/kg bw/day and 162–379, 334–761, and 637–1,424 mg/kg bw/day, respectively. 

Vaginal opening and preputial separation were examined only in F1 pups that were selected 

for mating. All other details for the F1 mating experiment were the same as those for the first 

generation study.

Similar systemic effects were observed in the F0 and F1 adults. Weight gain and food intake were 

reduced in high-dose F0 and F1 females during the lactation period. Kidney to body weight ratios 

were increased in all treated males and mid- and high-dose females of both generations. Liver 

to body weight ratios were increased in mid- and high-dose parental rats from both generations. 

Histological effects included dilated renal pelves in high-dose F1 males and renal casts observed 

mostly in high-dose F0 and F1 males. In the liver, centrilobular or diffuse hypertrophy and 

eosinophilia were noted in all treated parental rats of both generations. Mucosal erosion was also 

observed in the stomach of the mid- and high-dose F0 females. Thymus atrophy (possibly related to 

decreased weight gain) was observed in high-dose F0 and F1 females. The length of estrous cycles 

was reduced in F0 females of the high-dose group. In F0 males, there was a significant, but small 

and non-dose related, decrease (<1.4%) in normal sperm in all treated groups. However, in F1 rats 

there were no effects on estrous cycle length or sperm morphology. There were no effects on F0 and 
Appendix II

II-15

F1 mating, fertility, fecundity, and gestational indices. There were no lesions in the reproductive 

organs of F0 and F1 males and females and no differences in primordial oocyte or sperm counts. 

The decrease in absolute uterine weight and absolute and relative ovary weight in high-dose F0

females and increases in relative weights of epididymis in mid- and high-dose males and testes in 

high-dose males were considered incidental due to a lack of histological effects. 

In F1 rats, there were no adverse effects on mating, fertility, fecundity, and gestational indices. 

There were no lesions in the reproductive organs of males and females and no differences in 

primordial oocyte or sperm counts. Increases in relative weights of epididymis and seminal vesicles 

in mid- and high-dose F1 males and testes in high-dose males were considered incidental due to a 

lack of histological effects. 

Developmental effects including decreased pup weight gain in the one-generation study and 

decreased pup weight gain and increased pup mortality in the two-generation study are discussed in 

detail under Section 3.0. 

In a second two-generation reproductive study, 30 Crl:CDBR VAF Plus rats/sex/group were fed 

diets containing 0, 0.02, 0.06, 0.2, and 0.4% DIDP for 10 weeks prior to mating and during the 

mating period (36) (Table WEB-4). Treatment of the females continued through gestation and 

lactation. Author-estimated doses for the premating period were 12–23, 33–68, 114–225, and 233–

453 mg/kg bw/day for males and 14–21, 40–58, 139–202, and 274–406 mg/kg bw/day for females. 

Doses received by females during the gestation and lactation periods were estimated at 13–15, 

39–43, 127–147, and 254–295 mg /kg bw/day and 19–37, 57–112, 178–377, and 356–744 mg/kg 

bw/day, respectively. Body weight and food intake were recorded weekly. Parental males were 

killed after mating and females were killed at weaning. F1 pups were examined for survival and 

growth during the lactation period. On pnd 4 litters were culled to four rats/sex. One F1 pup/sex/

litter was killed and necropsied on pnd 21. Another F1 pup/sex/litter was selected for mating and at 

weaning was fed a diet with the same DIDP concentration as parental rats. Estimated doses for the 

F1 rats were 32, 94, 313, and 635 mg/kg bw/day in males and 32, 95, 313, and 645 mg/kg bw/day 

in females during the first 2 weeks post-weaning and 11–26, 33–76, 114–254, and 235–516 mg/kg 

bw/day in males, and 14–25, 41–77, 137–266, and 271–524 mg/kg bw/day in females during the 

premating period. Estimated dose levels for F1 females during gestation and lactation were 13–15, 

38–44, 134–151, and 256–286 mg/kg bw/day and 19–40, 52–114, 166–352, and 356–747 mg/kg 

bw/day, respectively. 

The only systemic effects observed in F0 and F1 adults were increases in liver and kidney weights at 

the two highest doses as illustrated in Table WEB-4. In both generations of parental rats, there were 

no effects on mating, fertility, fecundity, or gestational indices at any dose level. F1 and F2 pups 

did not experience differences in the age of vaginal opening. The age of preputial separation was 

similar to controls in all F1 pups but increased by 1.2 days in the high-dose F2 pups; this modest 

change was not considered biologically significant by the authors. A fertility NOAEL of 0.4% 

(233–635 [M] and 271–645 [F] mg/kg bw/day) was selected by the authors. 

Developmental effects including decreased pup weight gain and increased mortality were observed 

and are discussed in detail under Section 3.0.
II-16

Appendix II

Mode of Action

The estrogenic activity of DIDP has been examined using a battery of short-term in vitro and in 

vivo assays. 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 (37), rainbow trout hepatic cytosol (38), recombinant human ERs (rhER) 

overexpressed in SF9 insect cells using the baculovirus system (39, 40) and rainbow trout ERs 

expressed in yeast (41). Triated E2 was used in the tissue cytosol binding assays while a high 

affinity fluorescent E2 derivative was used in the rhER binding assays. Selected phthalate esters 

have been examined in a number of in vitro gene expression assays systems. The assays have used 

stably transfected cells (37), transiently transfected cells (37, 38), yeast based assays (37, 41-43) 

and vitellogenin induction in rainbow trout hepatocyte cultures (41). DIDP did not compete with 

tritiated estradiol for binding to the rat uterine cytosolic estrogen receptor and did not induce 

the transcription of estrogen dependent genes (37, 43). DIDP, in contrast to the positive control 

estradiol, did not significantly induce an in vivo vaginal cornification response or increase in uterine 

weight at any of the concentrations tested (20, 200, and 2,000 mg/kg bw/day) over the course of a 

5-day experiment using immature and adult ovariectomized Sprague Dawley rats (37). The lack of 

nipple retention and a normal anogenital distance in male offspring of rats exposed to DIDP at up 

to 295 mg/kg bw/day during gestation suggests a lack of antiandrogenic activity at that dose (36). 

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

II-17

5.0 DATA SUMMARY & INTEGRATION

5.1 Summary

5.1.1 Human Exposure

DIDP, a complex substance of branched, predominantly C-10 isomers, is a general-purpose 

plasticizer for flexible PVC with a broad range of applications. It is widely used in construction 

and in general consumer product markets. Uses that result in general population exposure include 

artificial leather (shoes, gloves, clothing) and pool linings. DIDP is also used in children’s vinyl 

toys. It has limited use in food packaging and is not used for medical applications (1).

There are no regulatory occupational limits, but manufacturers are reported to recommend 5mg/m3, 

the ACGIH value for DEHP (1). Environmental monitoring data are scant. However, the monitoring 

data for DIDP in air, drinking water, and surface and ground waters have usually yielded negative 

results (i.e., concentrations below detection limits). In the few studies of food and infant formula, 

the levels of DIDP have been at or below the detection limit (0.01–0.1 mg/kg). Exposure through 

mouthing of toys is a unique circumstance. While no in vitro or in vivo data on DIDP leaching 

from toys are available, it is reasonable to postulate exposures several-fold higher than the general 

population in infants and toddlers who mouth DIDP-containing products. By analogy to DINP 

estimates, these exposures may be an order of magnitude higher for infants and young toddlers than 

exposures to older children and adults.

5.1.1.1 Utility of Data to the CERHR Evaluation

The Expert Panel believes it is reasonable to assume, based on the physicochemical characteristics 

of DIDP and existing, though limited, monitoring data, that the general population exposure 

level to DIDP is lower than to DEHP, which is estimated at 3–30 μg/kg bw/day (10). Exposure in 

children could represent an important exception to the propriety of extrapolating DIDP exposures 

from DEHP data. Potential unique exposures from mouthing toys and other objects that may 

contain DIDP permit only modest confidence in the adequacy of using DEHP estimates for 

estimating DIDP exposure in infants and toddlers.

5.1.2 General Biological and Toxicological Data

General Toxicity. 

Human data were not found for the categories presented in this section.

General toxicity studies for DIDP consist of a 21-day dietary study in rats, two 4-week dietary 

studies in rats, two 90-day dietary studies in rats, a 90-day dietary study in dogs, and a 2-week 

inhalation study in rats. The NOAELs, LOAELs, and effects from the feeding studies are listed in 

Table 4. Young adult rats (6 weeks old) were used in the 21- and 28-day feeding studies conducted 

by BIBRA (11, 12). The ages of rats in the other studies were not given, but body weights indicate 

they were equivalent to young adults. Animal age and weight were not available for the BASF rat 

studies. With the exception of one 28-day study in rats (13), histological examinations of testes 

were conducted. As noted, testicular histology was unaffected at doses up to 2,100, 1,287, and 586 
II-18

Appendix II

mg/kg bw/day in the 21-day, 28-day, and 90-day studies, respectively. Increases in liver weight were 

consistently observed in all studies. The increases in liver weight were accompanied by biochemical 

evidence of peroxisomal proliferation at doses of 304 and 353 mg/kg bw/day in the 21-day and 

28-day studies, respectively, conducted by BIBRA (11) and Lake (12). Additional liver effects that 

were reported in the 21-day rat study (11) included change in serum triglycerides and cholesterol 

and a change in hepatocyte cytoplasm staining properties. Increases in kidney weight and thyroid 

activity (as indicated by histological observations of follicle size, colloid, and epithelium) were only 

reported in the 90-day feeding study in rats at a dose of 586(M)−686(F) mg/kg bw/day. 

General systemic effects were also studied in young adult dogs fed diets with up to 307(M)−320(F) 

mg/kg bw/day for 90 days. Hepatocellular swelling and vacuolization was observed in dogs at 

77−320 mg/kg bw/day; effects were not observed at 15 mg/kg bw/day. Lesions were not observed 

in testes.

In an inhalation study, rats (ages not specified) were exposed to 505 mg/m3 DIDP for 2 weeks (17). 

There were no systemic effects observed and toxicity was limited to local inflammatory changes in 

the lung. 

The liver was identified as a target organ due findings in rats and dogs that were qualitatively 

consistent (e.g., increases in liver weight and the observance of vacuolated hepatocytes). As noted 

in Table 4, the NOAELs are fairly consistent for all dietary rat studies (116–264 mg/kg bw/day). 

Toxicokinetics.

DIDP administered orally to adult male rats is rapidly but incompletely absorbed (~56% at a dose 

of 0.1 mg/kg bw) and rapidly excreted via urine and feces with no accumulation in tissues (22). 

There was evidence of dose-limited absorption since ~46 and ~17% were absorbed after doses 

of 11 and 1,000 mg/kg bw, respectively. The data suggest partial saturation of the metabolism of 

DIDP to the monoester in rat intestines within the dose range administered in the study (0.1−1,000 

mg/kg bw). Saturation of intestinal esterase and pancreatic lipase may result in absorption of some 

unmetabolized parent compound, but no DIDP was detected, suggesting that most of the parent 

compound was excreted in the feces. Distribution to tissues was proportional to absorbed dose, 

suggesting that accumulation is not a factor. The major metabolites are the monoester and its sidechain oxidation products as well as phthalic acid. Dermal uptake over a 7-day period was quite low 

(∼2%) in the rat (18, 19). In vitro studies with DEHP using human and rat skin (44) revealed that 

absorption was slower through human skin. Thus, it is reasonable to assume that dermal absorption 

of DIDP in humans would not be greater than that seen in rat dermal studies. Inhalation exposure 

of adult male Sprague Dawley rats to a single 6-hour dose of 91 mg/m3 revealed initial high 

concentrations in lung with 27% of the concentration (radioactivity) still present after 72 hours. 

Distribution to other tissues was followed by rapid excretion via urine and feces (17). 

Genetic Toxicity. 

OECD (28) recently concluded that DIDP is a non-genotoxic agent based on negative results 

in bacterial mutation assays, a mouse lymphoma assay, and a mouse micronucleus assay. In a 

subsequent publication negative results were obtained in the mouse lymphoma mutation and cell 

transformation assays conducted by Barber (29).
Appendix II

II-19

Table 4. Summary of NOAELs and LOAELs and Major Effects in General Toxicity Studies

Protocol and DIDP Doses 

(mg/kg bw/day) 

NOAEL

(mg/kg bw/

day)

LOAEL 

(mg/kg bw/day) 

and Effects

Major effects 

at higher doses

21-day repeat-dose dietary study 

in Fischer 344 rats. 

6 weeks old at start of study, 

5 rats/sex/group. 

Doses 

M: 0, 304, 1,134, 2,100

F: 0, 264, 1,042, 1,972

(11)

M: None

F: 264

M: 304; F: 1042

↑ Liver weight.

Peroxisomal proliferation.

Basophilic liver changes (F).

↑ Liver weight.

Peroxisomal proliferation.

↓Serum triglycerides and 

cholesterol.

Basophilic and eosinophilic 

liver changes.

No testicular lesions.

28-day repeat-dose dietary study 

in Fischer 344 rat.

6 weeks old at start of study, 5 

male rats/group.

Doses: 0, 25, 57, 116, 353, 1,287

(12)

116 353

↑ Liver weight.

Peroxisomal proliferation.

↑ Liver weight.

Peroxisomal proliferation.

No testicular lesions.

28-day repeat dose dietary study 

in Sprague-Dawley Rats.

Age not known, 20/sex/group. 

Doses

M: 0, 600, 1,250; 

F:1,100, 21,00

(13)

None M: 600; F: 1,100

↑ Liver weight.

↑ Liver weight.

90-day repeat dose dietary study 

in Sprague-Dawley rats. 

Age not known, 20/sex/group.

Doses 

M: 0, 55, 100, 200, 400

F: 0, 60, 120, 250, 500

(14)

M: 200

F: 120

M: 400 ; F: 250

↑Liver weight.

↓Weight gain in males.

↑Liver weight.

↓Weight gain in males.

No testicular or ovarian 

lesions.

90-day repeat dose dietary study 

in Charles river CD rats

Assume young adult based on 

body weight, 10/sex/group.

Doses 

M: 0, 28, 170, 586

F: 0, 35, 211, 686

(15)

M: 170

F: 211

M: 586; F: 686

↑Liver weight.

↑Kidney weight (M).

↑Thyroid activity (slight 

histologic evidence). 

No testicular lesions.

No higher doses.

90-day repeat dose dietary study 

in young adult dogs, 3/sex/group.

Doses

M: 0, 15, 77, 307

F: 0, 16, 88, 320

(16)

Sample size 

inadequate for 

evaluation of 

NOAEL

M: 77; F: 88

↑ Liver weight, histological 

effects.

↓ Body weight.

↑ Liver weight, histological 

effects.

No testicular lesions. 

 
II-20

Appendix II

5.1.2.1 Utility of Data the CERHR Evaluation

The oral subchronic studies in rat and dog are adequate for the evaluation of general toxicity 

induced by DIDP and indicate that the liver is a target organ. Some studies were conducted 

according to GLP standards and relevant exposure routes were utilized. Although sample sizes 

tended to be small in these studies, the results are generally consistent and reproducible, lending 

credence to the adequacy of the dataset. A modest concern is that rodent testes were preserved in 

formalin, which can lead to histopathological artifacts that may obscure subtle structural changes. 

However, reproductive organs in a two-generation rat study (discussed under Section 5.1.4) were 

preserved in Bouin’s fixative and the histological observations observed were consistent with those 

from the general toxicity studies. Testes evaluation in the 90-day dog study was based on sections 

from Bouin’s-fixed tissue. Peroxisomal proliferation was not examined in the 90-day exposure 

studies; however, it was present at 21 and 28 days in rat studies. 

There is adequate general toxicokinetic data for DIDP, consisting of absorption, distribution, 

metabolism, and excretion, over a range of oral doses in the rat. There is also data on dermal 

and inhalation exposure in rats. While studies of toxicokinetics in humans have not been located, 

the DIDP toxicokinetic data in rats are consistent with the large body of data on phthalates that 

includes data on rodents and primates. It is reasonable to assume that the DIDP rodent data is 

relevant to humans. 
Appendix II

II-21

5.1.3 Developmental Toxicity

Human data were not located for Expert Panel review.

Two published prenatal developmental toxicity studies in rats were available for DIDP (31, 34). The 

protocols for the 2 studies were similar and included dosing of dams by gavage on gd 6–15 with 

sacrifice and evaluation of fetuses on gd 20–21, although the group sizes differed. Developmental 

toxicity was also evaluated in a one-generation and in 2 two-generation toxicity studies (35, 

36). The effects on pups from these studies are discussed below and summarized in Table 5; the 

reproductive effects from the one-generation and two-generation studies are described in Section 

5.1.4. 

Hellwig et al. (34) tested DIDP (CAS no. 26761-40-0) in Wistar rats (10/group) at doses of 0, 40, 

200, and 1,000 mg/kg bw/day. Maternal toxicity was observed at the 1,000 mg/kg bw/day group 

and included increased liver weights and vaginal hemorrhage. Fetal variations per litter were 

increased in the 200 and 1,000 mg/kg bw/day dose groups. These included increased rudimentary 

cervical ribs and increased accessory 14th ribs at 1,000 mg/kg bw/day; specific types of variations 

were not reported for the 200 mg/kg bw/day group. Hellwig et al. (34) reported “no substancerelated effects” in dams or fetuses at doses up to 200 mg/kg bw/day, the middle dose tested. The 

Expert Panel did not find that the data supported a developmental NOAEL at 200 mg/kg bw/day 

given the reported statistically significant increase in total fetal variations at this dose, and agreed 

that the NOAEL is 40 mg/kg bw/day.

Of the two prenatal toxicity studies reviewed by the Expert Panel, Waterman et al. (31) was more 

informative due to the number of animals per test group (n=25) and completeness of data reported. 

Waterman et al. (31) tested DIDP (CAS no. 68515-49-1) in Sprague-Dawley rats (25/group) 

at doses of 0, 100, 500, or 1,000 mg/kg bw/day. Maternal toxicity at the highest dose consisted 

of decreased food consumption and weight gain. The effects on the offspring were presented 

as percent affected fetuses and percent affected litters. The percent fetuses with rudimentary 

cervical ribs was significantly increased at the two highest doses with a dose-related increase in 

litter incidence significant at the highest dose. There was a similar pattern of effect for accessory 

14th ribs. Waterman et al. (31) interpreted their results as indicating a LOAEL for maternal and 

developmental toxicity at 1,000 mg/kg bw/day and a NOAEL of 500 mg/kg bw/day. The Expert 

Panel concurred with the maternal NOAEL but selected a developmental NOAEL of 100 mg/kg 

bw/day based on the significant incidence of cervical and accessory 14th ribs. A reanalysis of 

these Waterman et al. data by the study sponsor (see Section 3.2), using the GEE approach to the 

linearized model (32), provided results that are consistent with the Expert Panel interpretation. 

The sponsor also provided benchmark doses at the 5 and 10% excess risk level, based on a 

multiplicative (or ‘extra’) excess risk function. At the 5% excess risk level, the benchmark doses 

(and their 95% lower confidence limits estimated by bootstrap methods) were estimated as 188 

(169), 258 (238), and 645 (515) mg/kg bw/day for rudimentary lumbar ribs, skeletal variants, and 

supernumerary cervical ribs, respectively.

The Expert Panel noted that developmental toxicity was observed in the two rat studies where there 
II-22

Appendix II

was prenatal exposure and pups were examined just prior to birth. Developmental toxicity was also 

observed in both generations of the two-generation study in rats discussed below. In both prenatal 

studies, the skeletal system was the target for effects causing an increased incidence of cervical 

ribs and accessory 14th (lumbar) ribs. While effects at both sites are relevant to an assessment of 

development, the effect on cervical ribs is of greater toxicological concern. Cervical ribs are seen 

infrequently in controls, but more importantly, their presence may indicate a disruption of gene 

expression. In addition, some scientists express concern that cervical ribs may interfere with normal 

nerve function and blood flow. Rib responses were identical at the common dose of 1,000 mg/kg 

bw/day in the 2 studies. In the study where there was a larger group size (n=25), the litter incidence 

at this dose for each effect (cervical and lumbar) achieved statistical significance. In this same 

study, when incidence was expressed on a percent fetus basis (the proper term for analysispercent 

affected fetuses per litterwas not reported) statistical significance was observed for each effect at 

the two highest doses. A numeric trend of increased incidence with increased dose was seen at all 

doses. In the study with fewer maternal rats per dose group (n=7−10), an increase in the incidence 

of hydroureter and of dilated renal pelves occurred in all treatment groups. This effect is at least 

indicative of a delay in maturation and while not clear in the publication, is thought to account 

partially for the reported increase in affected fetuses per litter with variation that achieved statistical 

significance at the two highest doses. The Panel further noted that this urinary tract effect occurred 

in the absence of reduced fetal weight; the absence of reduced fetal weight, which is usually a 

corollary to the urinary tract effect, provides a rationale for assuming maturational delay. The Panel 

further notes that LOAELs of 500 and 200 mg/kg bw/day and NOAELs of 100 and 40 mg/kg bw/

day from these studies are reasonably consistent, the differences most likely reflect differences in 

dose selection between the two studies. Finally, it is noted that LOAELs for developmental toxicity 

occur at doses at which there were no demonstrable maternal effects.

Developmental effects were also observed in 2 two-generation reproductive toxicity studies. Details 

of the study procedures are addressed in Section 5.1.4. In the first study, rats were fed diets with 0, 

0.2, 0.4, or 0.8% DIDP for 10 weeks prior to mating and throughout gestation and lactation (35). 

Hepatic hypertrophy and eosinophilia were observed in F1 and F2 male and female pups in the midand high-dose groups. Postnatal body weight gains were reduced in high-dose F1 pups (pnd 0, 7, 

14, and 21 for both sexes and pnd 4 for males) and F2 pups (pnd 1, 4, 7, 14, and 21 for both sexes 

and pnd 0 for males). A reduction in postnatal survival was observed in F1 pups of the high-dose 

group on pnd 0 and 4. In F2 pups, postnatal survival was reduced on pnd 1 and 4 in all treatment 

groups and also on pnd 7 and 21 in the high-dose group. This increase in pup mortality was not 

observed in the one-generation range-finding study, but pup body weights were reduced in the three 

highest dose groups (35). Because a NOAEL could not be identified due to increased pup mortality 

in all dose groups, the study was repeated with lower doses of 0, 0.02, 0.06, 0.2, and 0.4% DIDP in 

the diet (36). No developmental effects were observed in the F1 pups. However, increased mortality 

was noted in the F2 pups of the two highest dose groups on pnd 1 and 4. Reductions in pup body 

weight gain were also noted for F2 pups in the 0.2% dose group (females on pnd 14 and males 

on pnd 35) and 0.4% dose group (females on pnd 14 and 21, and males on pnd 14, 28, and 35). 

Hormonally-mediated endpoints such as anogenital distance and nipple retention in males were not 

observed at doses up to 0.4% in diet. Maternal effects were limited to increased liver weight with 

mild histological effects.
Appendix II

II-23

Cross-fostering and switched-diet satellite studies with rats fed the 0.8% diet indicated that 

lactational exposure is a meaningful factor in the reduction of body weight gain in pups (35). The 

data are sufficient to conclude that DIDP, administered through diet, is a developmental toxicant 

in rats based on reduced fetal survival and body weight observed in two studies. A developmental 

NOAEL of 0.06% (38–44 and 52–114 mg/kg bw/day during pregnancy and lactation, respectively) 

was identified by the study authors. 

A screening-design study in mice (30), where an oral gavage dose of 9,650 mg/kg bw/day was 

administered on gd 6–13, did not report any developmental or maternal toxicity through pnd 3. 

This study is insufficient to conclude that DIDP is not a developmental toxicant in mice since a full 

teratological examination was not performed. It does indicate that a dose almost 10-fold greater 

than that which caused effects in rats does not affect pregnancy outcome or early postnatal survival 

and growth in mice.

5.1.3.1 Utility of Data to the CERHR Evaluation

There are adequate data available in rats to determine that prenatal oral exposure to DIDP results 

in developmental toxicity. The results of the Waterman et al. (31) and the Hellwig et al. (34) studies 

were remarkably consistent and included increases in lumbar and cervical ribs. In addition, the 

effective dose levels were similar. The data from the 2 two-generation dietary studies are sufficient 

to demonstrate an effect on postnatal survival and growth. 
II-24

Appendix II

Table 5: Summaries of NOAELs and LOAELs and Major Effects in Developmental Toxicity Studies

Protocol and Study

NOAEL

[Benchmark Dose

ED05]

(mg/kg bw/day)

LOAEL (mg/kg bw/day) Developmental Effects 

Observed at Higher 

Maternal Developmental Dose Levels 

Prenatal gavage study in 

Wistar rats. 

10/group received 0, 

40, 200, or 1,000 mg/kg 

bw/day on gd 6–15.

Dam and pups examined in late gestation.

(34)

200 (maternal)

40 (developmental***)

1,000

↑Liver weights 

and vaginal 

hemorrhage.

200

↑Variations.

(No specific type of 

variation reported.)

↑Variations (cervical 

and lumbar ribs).

Prenatal gavage study in 

Sprague-Dawley rats.

25 per group received 0, 

100, 500, or 1,000 mg/

kg bw/day on gd 6–15.

Dams & pups examined 

in late gestation.

(31)

500 for maternal

100 (developmental***)

[MLE(95%LCL):

258 (238) for skeletal 

variants, 188 (169) 

for lumbar ribs, 646 

(515) for cervical 

ribs.]

1,000

↓ Weight gain.

500

↑Fetuses with 

variations (lumbar 

and cervical ribs).

↑Fetuses and litters 

with variations 

(lumbar and cervical 

ribs).

Two-generation reproductive dietary study in 

Crl:CDBR, VAF Plus 

rats. 

30 dams/group were 

fed diets with 0, 0.2, 

0.4, or 0.8% DIDP from 

10 weeks prior to mating through gestation 

(131−152, 262−297, 

524−611 mg/kg bw/

day*) and lactation 

162−379, 334−761, 

637−1,582 *).

(35)**

None for maternalor 

developmental

131−379

Hepatocyte 

enlargement.

131−379

↓ Postnatal survival 

in F2.

↓Postnatal survival in 

F1 and F2.

↓Postnatal weight gain 

in F1 and F2.
Appendix II

II-25

Table 5 (continued)

Protocol and Study NOAEL

(mg/kg bw/day)

LOAEL (mg/kg bw/day) Developmental Effects 

Observed at Higher Maternal Dose Levels Developmental

Two generation reproductive dietary study in 

Crl:CDBR, VAF Plus 

rats. 

30/group were fed diets 

with 0, 0.02, 0.06, 0.2, 

or 0.4% DIDP from 

10 weeks prior to 

mating through gestation (13−15, 38−44, 

127−151, or 254−295

mg/kg bw/day*) and 

lactation (19−40, 

52−114, 166−377, 

356−747*).

(36)**

38–114 for Maternal 

and developmental

127–377

↑ Liver weight.

127–377

↓ Postnatal survival 

in F2.

↓ Decreased weight 

gain in F2.

↓ Postnatal survival 

in F2.

↓ Decreased weight 

gain in F2.

Prenatal gavage toxicity 

screening assay in CD-1 

mice. 

50 dams/group received 

0 or 9,650 mg/kg bw/

day on gd 6−13. 

Dams and pups evaluated on pnd 3 for litter 

size and survival and 

body weight changes 

only. 

(30)

9,650 for maternal 

and developmental.

(Note – there was no 

examination of fetal 

variations or malformations.)

No higher doses. No higher doses. No higher doses.

* Combined doses for F0 and F1 dams during gestation and lactation. 

** Only maternal and developmental effects were listed in this Table. Reproductive and male systemic effects are listed in Table 6.

*** NOAEL selected by Expert Panel is lower than study author’s selection.
II-26

Appendix II

5.1.4 Reproductive Toxicity

Human data were not located for Expert Panel review.

Structural and functional reproductive effects were examined in a one-generation (dose setting) and 

2 two-generation studies in rats that included in utero exposure for the duration of pregnancy (35, 

36). In the one-generation study, rats were administered dietary levels of 0, 0.25, 0.5, 0.75, and 1% 

DIDP. In the two-generation studies, rats were administered dietary levels of 0, 0.2, 0.4, and 0.8% 

DIDP or 0, 0.02, 0.06, 0.2, and 0.4% DIDP (35, 36). In the two-generation studies, there were no 

effects on F0 or F1 mating, fertility, fecundity, and gestational indices at doses up to 427−929 and 

508−927 mg/kg bw/day in males and females, respectively. A small, non dose-related decrease 

in normal sperm (<1.4%) was seen in all treated F0 males and a reduced length of estrous cycles 

occurred in F0 females that received the highest dose, but those effects were not observed in the 

F1 rats. There were no histologic lesions in the reproductive organs of F0 or F1 males and females 

and no differences in primordial oocyte or sperm counts. The lack of effects on reproductive 

function was consistent with effects observed in the one-generation range-finding study. In the 

two-generation reproductive toxicity study with higher doses, systemic effects in parental rats 

included hepatocyte hypertrophy at all dose levels, increased kidney weights in low-dose males 

and all mid- and high-dose animals, and dilated renal pelves and renal casts in high-dose males 

(35). Developmental effects included hepatic hypertrophy and reduced postnatal survival and are 

discussed in detail in Section 5.1.3. Parental systemic and developmental toxicity were similar to 

those described in the second two generation reproductive toxicity study (36). 

DIDP did not appear to have effects on male reproductive tract development or function. An 

increase in seminal vesicle to body weight ratio in F1 males of the 0.4% group and epididymis 

to body weight ratio in F0 and F1 males at the 0.4% dose was not considered adverse because 

reproductive function was unaffected and there were no histopathological effects (35). Thus, the 

highest dose of 0.8% (M: 427−929 mg/kg bw/day and F: 508−927 mg/kg bw/day) was identified as 

the NOAEL for reproductive toxicity.

Mode of Action

DIDP exhibited no activity in in vitro assays that measured binding of phthalates to rat uterine 

cytosolic estrogen receptors and in an assay of estrogen-induced gene expression (37, 43). The 

monoester of DIDP was not tested in vitro. In vivo assays demonstrated that DIDP does not increase 

uterine wet weight or vaginal epithelial cell cornification in immature or mature ovariectomized 

rats (37). The lack of nipple retention and a normal anogenital distance in male offspring of rats 

exposed to DIDP at up 295 mg/kg bw/day during gestation suggests a lack of antiandrogenic 

activity at that dose (36). 

5.1.4.1 Utility of Data to the CERHR Evaluation

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

on reproduction at doses up to 427−929 mg/kg bw/day in male and 508−927 mg/kg bw/day in 

female rats. Testicular lesions were not observed in histological examination of testes in dogs 

exposed to doses of 307 mg/kg bw/day in a 90-day study. The data from the two-generation studies 

were collected utilizing a protocol acceptable to the US, EU, and other OECD countries. They were 
Appendix II

II-27

performed in accordance with GLP requirements. Reproductive organs were preserved in Bouin’s 

fixative, a method which reduces histological artifacts. One of the studies included an evaluation of 

hormonally-mediated postnatal effects that were found to be the most sensitive indicators of toxicity 

for other phthalates. Thus, the data provide a valuable database for evaluating reproductive toxicity 

potential in rats. 

Table 6: 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

One-generation reproductive screening assay in WU rats. 

10 pairs/group received 0, 250, 500, 

or 1,000 mg/kg bw/day by gavage 

from 2 weeks prior to mating for a 

total of 29 days (males) or until pnd 

6 (females).

(48)

Reproductive:

500

Systemic: 

500

1,000

↓Fertility

Testicular lesions

↓Litter size

1,000

↓Weight gain

No higher doses 

in study

One-generation dietary reproductive 

toxicity assay in Wistar rats with 12 

males and 24 females/group. Males 

were treated 10 weeks prior to mating with 0, 108, 206, or 418 mg/kg 

bw/day. Females were treated from 

2 weeks prior to mating (0, 106, 

217, or 446 mg/kg bw/day), through 

gestation (0, 116, 235, or 458 mg/kg 

bw/day) and lactation (0, 252, 580, 

or 1,078 mg/kg bw/day). 

(50)

Reproductive:

418 (M);

446 (F)

Systemic: 

206 (M);

217 (F)

No structural or 

functional effects 

at any dose 

418 (M);

446 (F)

↓Weight gain (F)

↑Liver weight

No higher doses 

in study

* Doses during the premating period – combined for F0 and F1 rats 

** Only effects in parental rats and effects in the reproductive system are listed. Developmental effects are listed in Table 5.

*** Doses during the premating period and first 2 weeks postweaning for F1 rats - combined for F0 and F1 rats.
II-28

Appendix II

5.2 Integrated Evaluation

DIDP is a complex substance of branched, predominantly C-10 isomers. There are no human data 

from which to assess the health effects associated with DIDP exposure; studies of DIDP toxicity are 

limited to laboratory animals. In the absence of human data to the contrary, it is assumed that the 

effects observed in laboratory animals are relevant to humans.

Based upon the physicochemical similarities between DIDP and DEHP, and on limited DIDP 

monitoring data, general population exposure is expected to be lower than that of DEHP, which 

is estimated at 3−30 μg/kg bw/day. It is reasonable to presume that humans would be exposed 

primarily through the oral route. Although data are scant, the ingestion of DIDP through food 

does not appear to be common. Children may have higher levels of exposure to DIDP than adults 

because infants and small children mouth toys and other objects that may contain DIDP which 

can migrate into saliva and be swallowed. There is no use of DIDP in medical devices, therefore 

intravenous exposure does not occur.

Orally-administered DIDP is metabolized by intestinal luminal enzymes and the resulting 

metabolites are absorbed into the blood and further metabolized or conjugated and quickly excreted 

into urine or feces. Persistence or accumulation in the body is not expected. Toxicokinetic studies in 

rats have demonstrated that DIDP has limited dermal absorption and does not persist or accumulate 

in the body. 

There are data available in rodents from which to evaluate developmental and reproductive effects 

associated with oral DIDP exposure. Developmental studies in rats include assessment of prenatal 

exposure on prenatal effects. Postnatal developmental effects following prenatal exposure have also 

been assessed using endpoints that have been adversely affected in studies with other phthalates. 

Two prenatal gavage exposure studies in rats with treatment of dams from gd 6−15 did not cause 

structural malformations but did consistently demonstrate developmental toxicity (increased fetal 

cervical and lumbar ribs) at doses of 200−500 mg/kg bw/day and higher. The more robust of the 

two studies was determined by the Expert Panel to have a maternal NOAEL of 500 mg/kg bw/day 

and a developmental toxicity NOAEL of 100 mg/kg bw/day, while a second study determined a 

developmental NOAEL of 40 mg/kg bw/day. Developmental toxicity was observed and replicated 

in 2 two-generation reproductive dietary studies in rats where adverse effects on pup growth or 

survival were observed at gestational doses of 127–151 mg/kg bw/day and higher and a lactational 

dose of 166−377 mg/kg bw/day and higher; the developmental NOAEL is in the range of 38–44 

mg/kg bw/day (gestational) and 52−114 mg/kg bw/day (lactational). A prenatal exposure-screening 

study in mice in which an oral gavage dose of 9,650 mg/kg bw/day was administered did not 

report any developmental or maternal toxicity. While insufficient to conclude that DIDP is not a 

developmental toxicant in mice, it does indicate that a dose that is almost 10-fold greater than that 

which caused effects in rats does not affect pregnancy outcome or early postnatal survival and 

growth in mice.

Reproductive performance and histological effects on sex organs were assessed. Parental doses 

of up to 0.8% in feed (∼ 427−929 in males and 508−927 mg/kg bw/day in females) did not affect 

fertility or sex organ histology in either the parents or F1 male or female pups. Sub-chronic studies 

(21–90 day exposure) gave no gross or histologic evidence of effects on testes at doses up to 2,100 
Appendix II

II-29

mg/kg bw/day in rats and 307 mg/kg bw/day in dogs. These doses did produce liver hypertrophy, 

mild evidence of toxicity, and clear signs of peroxisome proliferation in rats. The Expert Panel 

notes that the liver was consistently identified as the target organ in general toxicity studies with 

adult rats and in developmental and multigeneration studies. Hepatic effects in offspring exposed in 

utero were principally associated with liver enlargement observed at weaning and in adults.

5.3 Expert Panel Conclusions

DIDP is used in construction and in general consumer products. DIDP was detected in older 

surveys of toys, but recent surveys have not detected DIDP in toys. In surveys of retail food 

samples, DIDP concentrations were below the detection limits. Although data are scant, exposure 

through food appears to be lower than for DEHP. Therefore, the Expert Panel believes that adult 

exposure to DIDP will not exceed levels of 3−30 μg/kg bw/day, the estimates derived for DEHP. 

Exposures to DIDP are likely to be below this level, but the Panel could not quantitate how far 

below. Occupational exposures could occur through inhalation and dermal contact. Limited studies 

of occupational exposures suggest that inhalation exposure is below 1 mg/m3 during production 

of DIDP and below 2 mg/m3 during production of PVC. Although estimates of dermal exposure 

are not available, the Expert Panel is confident that dermal exposure would not result in significant 

absorption into the body. Exposure of children to DIDP could also occur through contaminated 

food. However, DIDP has not been detected in surveys of infant formula.

The toxicology database is sufficient to determine that oral maternal exposure to DIDP can result 

in developmental toxicity to the conceptus. In rats, two prenatal developmental studies have shown 

effects on the developing skeletal system following oral exposure to DIDP. The NOAEL for these 

studies was 40−100 mg/kg bw/day. In addition, developmental toxicity was noted in two oral twogeneration reproductive toxicity studies in rats. Both studies showed effects on pup survival and 

growth. These effects may be due to prenatal and/or lactational exposures to DIDP. The NOAELs 

for the studies were 38−44 mg/kg bw/day during pregnancy and 52−114 mg/kg bw/day during 

lactation. Based on the results of the toxicology studies, oral exposure to pregnant humans and oral 

exposure to children should be examined. To date, the only available oral exposure information is 

based on the conservative estimate derived for DEHP of 3−30 μg/kg bw/day. The Expert Panel has 

minimal concern for children and fetuses due to exposure to ambient levels of DIDP. The Expert 

Panel cannot judge the potential health effects in children from mouthing of objects containing 

DIDP due to the lack of exposure information. In addition, the Expert Panel cannot judge the 

potential hazards to unborn children following maternal occupational exposures due to the lack of 

toxicology data following inhalation exposures and the lack of occupational exposure information.

The oral prenatal developmental toxicity studies and the oral two-generation reproductive toxicity 

studies have shown no effects on the reproductive system in rats. The Expert Panel noted that the 

endpoints of reproductive development that have been shown to be sensitive with other phthalates 

were examined in one of the two-generation reproductive toxicity studies. The NOAEL for 

reproductive toxicity ranges from 427−929 mg/kg bw/day. Therefore, the Expert Panel has minimal 

concern about DIDP resulting in reproductive toxicity in humans.
II-30

Appendix II

5.4 Critical Data Needs

Critical data needs are discussed under two categories: experimental studies and human exposure.

Experimental Studies

The Expert Panel recommends a sequential approach for future studies that would focus on 

obtaining the most critical information first. Subsequent studies would be dependent upon the 

results of the initial study. The Panel further recognized that data gathering should be an iterative 

process and that the recommendations may change as initial tiers of data are gathered. The Expert 

Panel recommends that the following sequential steps be considered.

A perinatal developmental study by the oral route in a non-rodent species. There are species 

differences in the developmental toxicity associated with other phthalates. The developmental 

effects of DIDP have only been examined in the rat and in a mouse screening study. Therefore, 

there is some uncertainty whether other species would exhibit similar responses and whether the rat 

is an appropriate model for assessing potential human risk.

Human Exposure

1) Human exposure to DIDP has not been well studied; there are no reports of levels in biological 

materials (blood, urine, etc.), and the environmental data consist primarily of estimates.

2) Patterns of use, expected environmental levels, and vulnerability of exposed population groups 

should dictate decisions about measuring DIDP in environmental media. For example, determining DIDP exposures in young children is of highest priority, based on the use patterns and 

vulnerability described above. Workers producing PVC products are a second priority.

3) Collection of biological samples de novo should be accompanied by environmental measurements to provide information on exposure sources. Existing biological samples should be utilized where available if they can provide useful information about exposure.

4) Although information about exposure of young children is a critical data need, manufacturers 

of children’s toys should be polled to determine if their products will continue to contain DIDP 

in the future. If so, an estimate of the DIDP content should be made by the manufacturer and 

confirmed by independent studies. Salivary extraction of DIDP itself is important in order to 

evaluate the exposure directly, and not by use of a proxy (DINP). Better estimates of mouthing behavior, especially within the potentially highest risk group of 3−12 months, using larger 

samples of children, are also needed. The initial assessment of DIDP in toys is particularly 

important because no DIDP was found in a US sample of 35 toys, and the UK studies of 1992 

and 1996 reported the same negative result.
Appendix II

II-31

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12. Lake BG, Cook WM, Worrell NR, Cunningham ME, Evans JG, Price RJ, Young PJ, Carpanini FMB. Dose-response relationships for induction of hepatic peroxisome proliferation 

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13. BASF. Bericht uber den 28-tage-ratten Futterungsversuch mit PALATINOL Z. (1969).

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Appendix II

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20. Scott RC, Dugard PH, Ramsey JD, Rhodes C. In vitro absorption of some o-phthalate diesters through human and rat skin. Environ Health Perspect 74:223-227(1987).

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27. Hazelton. Mutagenicity test on Jayflex DIDP in an in vivo mouse micronucleus assay Project No. 20996. Washington: Exxon Biomedical Sciences, 1994.

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Schneider B. Results of the L5178Y mouse lymphoma assay and the Balb/3t3 cell in vitro
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II-33

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

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32. Ryan L. The use of generalized estimating equations for risk assessment in developmental 

toxicity. Risk Analysis 12:439-447(1992).

33. McKee R. Personal communication to Jack Moore, 2000.

34. Hellwig J, Freudenberger H, Jackh R. Differential prenatal toxicity of branched phthalate 

esters in rats. Food Chem Toxicol 35:501-512(1997).

35. Exxon Biomedical Sciences Incorporated. Two generation reproduction toxicity study in 

rats with di-isodecyl phthalate (DIDP; MRD-94-775). East Millstone, NJ: Exxon Chemical 

Company; Exxon Chemical Europe, Inc., 1997.

36. Exxon Mobil Biomedical Incorporated. Two generation reproduction toxicity study in rats 

with MRD-94-775. Project Number: 1775355A. East Millstone, NJ: Exxon Mobil Chemical Company, Inc.; Exxon Mobil Chemical Europe, Inc., 2000.

37. 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 

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38. 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).

39. 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).

40. 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 

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41. 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 

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42. 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-

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Appendix II

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

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

44. Scott RC, Dugard PH, Ramsey JD, Rhodes C. In vitro absorption of some o-phthalate diesters through human and rat skin. Environ Health Perspect 74:223-227(1987).
Appendix II

II-35

7.0 TABLES

7.1 DIDP Developmental Toxicity, Rats ......................................................................................36

7.2 DIDP Developmental Toxicity, Rats ......................................................................................37

7.3 DIDP Reproductive Toxicity, Rats .........................................................................................38

7.4 DIDP Reproductive Toxicity, Rats .........................................................................................40

7.5 References..............................................................................................................................42
II-36

Appendix II

Table 7-1: DIDP Developmental Toxicity, Rats

Species, Strain, 

and Source Experimental Regimen Numbera Dose* Maternal effects Fetal effects

Sprague-Dawley RatWaterman et al. 1999(2)

Prenatal developmental toxicity study. DIDP administered in oil by gavage on gd 6−15. Sacrificed on gd 21. Dams weighed on gd 0, 6, 9, 12, 15, 18, and 21. Maternal uterus and ovaries were weighed, corpora lutea were counted and implantation sites examined. Fetuses were weighed, sexed, and examined for gross external malformations. Half of the fetuses were examined for visceral malformations and the other half for skeletal malformations.

25 022 100 NOAELb24 500 NOAEL ↑% Fetuses with cervical 

ribs (6.2 vs 1%).

↑% Fetuses with lumbar 

ribs (21.2 vs 8.2%).

24 1,000 ↓ Weight gain.

↓ Food Intake.

↑% Litters with cervical 

ribs (41.7 vs 8%).

↑% Litters with lumbar 

ribs (95.8 vs 40%).

↑% Fetuses with cervical 

ribs (9.2 vs 1.0%).

↑Fetuses with lumbar 

ribs (52 vs 8.2%).

*Dose measured in mg/kg/bw/day.aNumber of litters examined.bNOAEL selected by Expert Panel is lower than study author’s selection.

↑=Statistically Significant Increase↓=Statistically Significant Decrease
Appendix II

II-37

Table 7-2: DIDP Developmental Toxicity, Rats

Species, Strain, 

and Source Experimental Regimen Numbera Dose* Maternal Effects Fetal Effects

Wistar RatHellwig et al. 1997(1)

Prenatal developmental toxicity study. DIDP administered in oil by gavage on gd 6−15. Dams weighed on gd 0, 6, 10, 15, and 20 and sacrificed on gd 20. Maternal uteri were weighed, corpora lutea were counted and implantation sites examined. Fetuses were weighed and examined for gross external malformations. Half of the fetuses were examined for visceral malformations and the other half for skeletal malformations. 

10 0

8 40 NE NOAELb7 200 NOAEL ↑Fetuses/litter with 

variations (38 vs 24%).

10 1,000 ↑Liver to body weight 

ratios.

Vaginal hemorrhage in 3 

dams.

↓Food intake.

↑Fetuses/litter with 

variations (44 vs 24%).

↑Cervical ribs (15 fetuses 

in 6 litters vs 1 fetuses).

↑14th ribs (21 fetuses in 8 

litters vs 1 fetus).

*Dose measured in mg/kg/bw/day.aNumber of litters examined.bNOAEL selected by Expert Panel is lower than study author’s selection.

↑=Statistically Significant Increase↓=Statistically Significant Decrease
II-38

Appendix II

Table 7-3: DIDP Reproductive Toxicity, Rats

Species, Strain, 

and Source Experimental Regimen Numbera Dose* Parental Effects** Offspring Effects**

Crl:CDBR, VAF Plus RatsExxon Biomedical 1997(3)

Two-generation reproductive toxicity study.DIDP administered in feed for 10 weeks prior to mating 

at levels of 0, 0.2, 0.4, and 0.8%. Males treated through mating period and females through gestation and lactation.Body weight and food intake was measured weekly.Estrous cycles were evaluated.F0 dams were killed at the end of lactation and males were killed following birth of last litter. Reproductive and other key organs were examined histologically. Primordial oocytes were counted in females and sperm was evaluated in males. Details of the second generation breeding experiment are listed on the next page. 

40 030 103

−198 /

127

−203 /

131

−149 /

172

−361

↓Normal sperm in F0 (<1.4%).↑Liver hypertrophy in F0. ↑Kidney to body weight ratio in F0

males.

30 211

−405 / 

253

−416 / 

262

−287 / 

359

−734 

↓Normal sperm in F0 (<1.4%).↑Epididymis to body weight ratio in F0.↑Liver to body weight ratio with 

hypertrophy in F0. 

↑Kidney to body weight ratio in F0.↑Stomach lesions in F0 females.

↑Liver to body weight 

ratio (F) with hypertrophy in F1. 

Delayed vaginal opening 

in F1 (33.5 vs 32.2 days).

40 427

−781 / 

508

−775 / 

524

−551 / 

641

−1,582

No effects on F0 mating, fertility, 

fecundity, or gestational indices, no reproductive organ lesions, and no effect on oocyte or sperm counts at any dose.

↓Normal sperm in F0 (<1.4%).↓Estrous cycle length in F0. ↓Ovary to body weight ratio in F0.↑ Epididymis and testes to body weight 

ratio in F0.

↓Weight gain in F0 during lactation.↑Liver to body weight ratio with 

hypertrophy in F0.

↑Kidney to body weight ratio in F0 with 

histological changes in males.

↑Stomach lesions and thymus atrophy in 

F0 females.

↓F1 pup birthweight.↓F1 pup survival at birth 

and pnd 4.

↑Liver to body weight 

ratio with hypertrophy in F1.

Delayed vaginal opening 

in F1 (34.2 vs 32.2 days).
Appendix II

II-39

Table 7-3: DIDP Reproductive Toxicity, Rats (continued)

Species, Strain, 

and Source Experimental Regimen Numbera Dose* Parental Effects** Offspring Effects**

Crl:CDBR, VAF Plus RatsExxon Biomedical 1997(3)

Sexual maturation was monitored in F1 pups selected for second generation breeding. Upon weaning the pups were fed diets with the same DIDP concentrations as parental rats. The same parameters examined in the F0 rats were examined in the F1 rats.

30 030 117–216 /

135–218 /135–152 / 162–379

↑Liver to body weight ratio (F).↑Hypertrophy in F1.↑Kidney to body weight ratio in F1 (M). 

↓F2 pup survival on pnd 

1 and 4.

30 229–437 / 

273–433 /262–297 / 334–761

↑Epididymis and seminal vesicles to 

body weight ratio in F1.

↑Liver to body weight ratio in F1 with 

hypertrophy.

↑Kidney to body weight ratio in F1.

↓F2 pup survival on pnd 

1 and 4.

↑Liver hypertrophy in F2

pups.

30 494–929/ 

566–927 /574–611 / 637–1424

No effects on F1 mating, fertility, fecundity, or gestational indices, no reproductive organ lesions, and no effect on oocyte or sperm counts at any dose.↑Epididymis, seminal vesicle, and testes 

to body weight ratio in F1.

↓Weight gain in F1 during lactation.↑Liver to body weight ratio with 

hypertrophy in F1.

↑Kidney to body weight ratio in F1 with 

histological changes in males.

↑Thymus atrophy in F1 females.

↓F2 pup birthweight.↓F2 pup survival on pnd 

1, 4, 7 and at weaning.

Undescended testes in 4 

pups.

↑Liver hypertrophy in F2

pups.

aNumber of breeding pairs.**Parental effects are discussed in Section 4 

and offspring effects in Section 3.

*Doses in mg/kg bw/day for: 

Males during premating / Females during premating / Females during gestational period / Females during lactational period.

↑=Statistically Significant Increase

↓=Statistically Significant Decrease
II-40

Appendix II

Table 7-4: DIDP Reproductive Toxicity, Rats

Species, Strain, 

and Source Experimental Regimen Numbera Dose* Parental Effects*** Offspring Effects***

Crl:CDBR, VAF Plus RatsExxon Biomedical 2000(4)

Two-generation reproductive 

toxicity study.

DIDP administered in feed for 

10 weeks prior to mating at levels of 0, 0.02, 0.06, 0.2, and 0.4%. Males treated through mating period and females through gestation and lactation.

Body weight and food intake 

were measured weekly.

F0 dams were killed and 

necropsied at the end of lactation and males were killed and necropsied after mating. 

Pups were examined for survival 

and sexual maturation.

One pup/sex/litter was 

necropsied at pnd 21.

Histological examinations were 

not conducted.

Details of the second generation 

breeding experiment are listed on the next page. 

30 030 12–23 / 

14–21/13–15 / 19–37

NE NE

30 33–68 / 

40–58 / 39–43 / 57–112

NE NE

30 114–225 / 

139–202 /127–147 / 178–377

NE NE

30 233–453 / 

274–406/254–295 / 356–744

↑Liver and kidney to body weight 

ratio.

No effects on mating, fertility, fecundity, or gestational indices at any dose.

No effects on survival, body weight gain, organ weights, anogenital distance, nipple retention, preputial separation, vaginal opening, or malformations.

aNumber of breeding pairs.***Parental effects are discussed in Section 4 

and offspring effects in Section 3.

*Doses in mg/kg bw/day for: 

Males during premating / Females during premating / Females during gestational period / Females during lactational period.

**Doses in mg/kg bw/day for: 

Males during first two weeks post weaning /Males during first two weeks post weaning /Males during premating / Females during premating / Females during gestational period / Females during lactational period.

NE=No Effect↓=Statistically Significant Decrease
Appendix II

II-41

Table 7-4: DIDP Reproductive Toxicity, Rats (continued)

Species, Strain, 

and Source Experimental Regimen Numbera Dose** Parental Effects*** Offspring Effects***

Crl:CDBR, VAF Plus RatsExxon Biomedical 2000(4)

Upon weaning the pups were fed diets with the same DIDP concentrations as parental rats. The remaining details are as described for the 1st generation.

30 039 32 / 

32 / 11–26 / 14–25 /13–15 / 19–40

NE NE

30 94 / 

95/ 33–76 / 41–77 /38–44 / 52–114

NE NE

30 313 / 

313 / 114–254 / 137–266 /134–151 / 166–352

↑Kidney to body weight ratio in 

(M).

↑Liver to body weight ratio (F).

↓Pup survival on pnd 1 and 4.↓ Pup body weight on pnd 14 (F) 

and pnd 35(M). 

30 635 / 

645 / 235–516 / 271–524 /256–286 / 356–747

↑Kidney to body weight ratio 

(M).

↑Liver to body weight ratio.No effects on mating, fertility, 

fecundity, and gestational indices at any dose.

↓Pup survival on pnd 1 and 4.↓ Pup body weight on pnd 14 , 

pnd 21 (F), pnd 28 (M), and pnd 35(M). 

↑Liver to body weight ratio (F).↑Age of preputial separation 

(+1.2 days).

No effects on anogenital distance, 

nipple retention, or vaginal opening, and no malformations.

See footnotes from first generation breeding experiments.
II-42

Appendix II

References:

1. Hellwig J, Freudenberger H, Jackh R. Differential prenatal toxicity of branched phthalate 

esters in rats. Food Chem Toxicol 35:501-512(1997).

2. Waterman SJ, Ambroso JL, Keller LH, Trimmer GW, Nikiforov AI, Harris SB. Developmental toxicity of di-isodecyl and di-isononyl phthalates in rats. Reprod Toxicol 13:1-6(1999).

3. Exxon Biomedical Sciences Incorporated. Two generation reproduction toxicity study in 

rats with di-isodecyl phthalate (DIDP; MRD-94-775). East Millstone, NJ: Exxon Chemical 

Company; Exxon Chemical Europe, Inc., 1997.

4. Exxon Mobil Biomedical Incorporated. Two generation reproduction toxicity study in rats 

with MRD-94-775. Project Number: 1775355A. East Millstone, NJ: Exxon Mobil Chemical Company, Inc.; Exxon Mobil Chemical Europe, Inc., 2000.
Appendix III

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