NTP

National Toxicology Program

CURRENT DIRECTIONS and EVOLVING STRATEGIES
NTP

National Toxicology Program

CURRENT DIRECTIONS and EVOLVING STRATEGIES

Good Science for Good Decisions
4 Overview of the National Toxicology Program

10 Current Directions

16 Evolving Strategies

22 Centers

26 Report on Carcinogens

28 Outreach and Communication 

2 National Toxicology Program

Table of Contents
National Toxicology Program 3

ATSDR Agency for Toxic Substances and Disease Registry

CDC Centers for Disease Control and Prevention 

CDM Central Data Management

CERHR Center for the Evaluation of Risks to Human Reproduction

CPSC Consumer Product Safety Commission

DBPs disinfectant by-products

DHHS Department of Health and Human Services

EHP Environmental Health Perspectives

EPA Environmental Protection Agency

FDA Food and Drug Administration

ICCEC Interagency Committee for Chemical Evaluation and Coordination

ICCVAM Interagency Coordinating Committee on the Validation of Alternative Methods

LLNA Local Lymph Node Assay

MRI Magnetic Resonance Imaging

NCEH National Center for Environmental Health

NCI National Cancer Institute

NCP NTP Center for Phototoxicology

NCT National Center for Toxicogenomics

NCTR National Center for Toxicological Research

NICEATM NTP Interagency Center for the Evaluation of Alternative Toxicological Methods

NIEHS National Institute of Environmental Health Sciences

NIH National Institutes of Health

NIOSH National Institute for Occupational Safety and Health

NIST National Institute of Standards and Technology

NTP National Toxicology Program

OSHA Occupational Safety and Health Administration

PBPK physiologically based pharmacokinetic

RoC Report on Carcinogens

SACATM Scientific Advisory Committee on Alternative Toxicological Methods

TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin

UV Ultraviolet
4 National Toxicology Program

Mission and Goals 

More than 80,000 chemicals are registered for use in the United States. Each year, an estimated 2,000 new

ones are introduced for use in such everyday items as foods, personal care products, prescription drugs,

household cleaners, and lawn care products. We do not know the effects of many of these chemicals on 

our health, yet we may be exposed to them while manufacturing, distributing, using, and disposing of

them or when they become pollutants in our air, water, or soil. Relatively few chemicals are thought to

pose a significant risk to human health. However, safeguarding public health depends on identifying both

what the effects of these chemicals are and at what levels of exposure they may become hazardous to

humans—that is, understanding their toxicology. 

The National Toxicology Program (NTP) was established by the U.S. Department of Health and Human

Services (DHHS) in 1978 to (1) coordinate toxicology testing programs within the DHHS, (2) strengthen

the science base in toxicology, (3) develop and validate improved testing methods, and (4) provide 

information about potentially toxic chemicals to health, regulatory, and research agencies, scientific and

medical communities, and the public. The NTP is an interagency program whose mission is to evaluate

agents of public health concern by developing and applying tools of modern toxicology and molecular

biology. The program maintains an objective, science-based approach in dealing with critical issues in 

toxicology and is committed to using the best science available to prioritize, design, conduct, and interpret

its studies. To that end, the NTP is continually evolving to remain at the cutting edge of scientific research

and to develop and apply new technologies.

Current Activities

The NTP maintains a number of complex, interrelated research and testing programs that provide unique

and critical information needed by health, regulatory and research agencies to evaluate potential human

health effects from chemical and physical exposures. All of the NTP's activities are open to public scrutiny,

including communications with all interested parties. The NTP has always drawn strength and direction

from the commitment of its scientists to exchange information openly, maintain impartiality, and apply

rigorous scientific peer review. This is a central priority of the program now and will remain so in the future.

The NTP seeks to maintain a balanced research and testing program that provides data on a wide variety

of issues important to public health. In particular, the NTP seeks nominations of studies that (1) fill 

significant gaps in the knowledge of the toxicity of chemicals or classes of chemicals, (2) address mechanisms

of toxicity, or (3) enhance the predictive ability of future NTP studies. Currently, the NTP is focusing on

Overview
National Toxicology Program 5

several areas that have received inadequate attention in the past. Some examples include photoactive

chemicals, contaminants of finished drinking water, endocrine-disrupting agents, and certain complex

occupational exposures. The NTP is addressing potential safety issues associated with herbal medicines,

radiofrequency radiation emissions from cellular telephones, hexavalent chromium, and nanoscale materials.

In general, these initiatives are broad-based and investigate various health-related effects. 

The NTP continues to work to develop and validate alternative testing methods that will help identify

chemical hazards using fewer test animals. This effort includes developing more efficient, mechanism-based

testing strategies, such as genetically engineered models for toxicology testing, and implementing

microchip-based gene expression technologies. These methods hold the promise of providing a true

mechanistic basis for identifying and studying environmental toxicants.

The NTP also evaluates whether human exposures to environmental agents cause adverse effects on 

reproduction, development, and the immune, respiratory, and central nervous systems. The NTP is

expanding its effort to include routine investigations of changes in the immune system and the nervous 

system from exposures occurring during fetal development and early life.

The NTP continues to expand activities designed to place research and testing results from animals in a

perspective that is more relevant to human health. This includes human exposure assessment, toxicokinetics,

mechanism-based pharmacokinetic modeling, and interpreting results in molecular epidemiology for use 

in identifying human hazards (e.g., the Report on Carcinogens and the NTP’s Center for the Evaluation 

of Risks to Human Reproduction). The NTP is also coordinating an effort to obtain “real-world” 

information about worker practices, complex occupational exposures, and potentially related adverse

health effects. We need such information to identify areas for research and to design better laboratory

studies on the potential health effects of chemicals, complex mixtures, and exposures people encounter 

in the workplace.

Vision for the 21st Century

In its 25 years of existence, the NTP has been a leader in toxicology testing and research within the

United States and has contributed significantly to the scientific knowledge upon which public health

decisions are based. The NTP has focused upon using the best testing strategies for evaluating agents of

public health concern. In the 1990s, the program undertook efforts to develop, evaluate, and validate

tools for mechanism-based toxicology and incorporate them into its testing strategies. Mechanism-based

Good Science for Good Decisions

National Toxicology Program
6 National Toxicology Program

toxicology has led to some changes in the scientific basis for public-health decisions, but it has not 

dramatically reduced the need for the classical tests developed in the 1970s and 1980s. The last decade 

of the 20th century and the turn of the 21st century have produced dramatic advances in molecular 

biology and computer science. The NTP realizes that it is again time to evaluate its key activities. In a

focused and concerted effort, the NTP needs to determine how best to (1) incorporate these new scientific

technologies into its research and testing strategies and (2) broaden scientific knowledge on the linkage

between mechanism and disease. 

The NTP’s vision for the 21st century is to move toxicology from a predominantly observational science 

at the level of disease-specific models to a predominantly predictive science focused on a broad inclusion 

of target-specific, mechanism-based, biological observations. Only through a concerted focus on the links

between mechanism and disease will toxicology be able to replace disease-specific testing models with

mechanism-based assays. Such assays are more informative, faster, and more closely linked to how diseases

begin and advance.

The NTP intends to develop a plan for implementing this vision and will seek input to this plan from

many groups, including its federal partners, its advisory committees, and the public. Implementing this

vision should continue the NTP’s leadership in toxicology and enable the NTP to provide better science

for better public health decisions that will serve to protect human health and the environment.

Partnerships

Over the past two decades, the NTP has developed an increasingly interactive relationship with regulatory

agencies. Through this relationship, the NTP plays an important, although indirect, role in shaping public

health policy. Federal and state government agencies rely on the scientific knowledge base provided by the

NTP to make credible decisions that protect public health without unnecessarily increasing the regulatory

burden on industry. The NTP plays a critical role in providing needed scientific data, interpretations, and

guidance on the appropriate uses of these data. The NTP also plays an important role in (1) fostering

interagency collaborations in research and exposure assessment, (2) providing information to regulatory

agencies about alternative methods for toxicity screening, and (3) exploring new technologies for evaluating

how environmental agents cause disease.

The NTP is increasingly active in developing international partnerships to establish efficient means for

avoiding duplication of effort(s) in toxicology testing. The NTP is collaborating with the European

Ramazzini Foundation of Oncology and Environmental Sciences to create similar protocols, quality 

assurance, and reporting for laboratory studies on the health effects associated with long-term exposure to

environmental agents. The two groups share common interests in identifying agents that cause cancer and 

in understanding the interaction and synergism between genetic susceptibility to cancer and exposure to

cancer-causing agents. The NTP is working with the Korean government to help establish a national 

toxicology program similar to the NTP. The NTP is also participating in the World Health Organization’s

International Electric and Magnetic Fields Project to facilitate internationally coordinated research on the

health effects of electric and magnetic fields, including those generated by cellular telephone technologies.

Organizational Structure and Oversight 

Three agencies form the core of the NTP: (1) the National Institute of Environmental Health Sciences

(NIEHS) of the National Institutes of Health (NIH), (2) the National Institute for Occupational Safety

and Health (NIOSH) of the Centers for Disease Control and Prevention (CDC), and (3) the National

Center for Toxicological Research (NCTR) of the Food and Drug Administration (FDA) (Figure 1) 

Each agency voluntarily provides resources to support NTP research, testing, centers, and outreach.

Overview
National Toxicology Program 7

Program contacts for each agency are Dr. Christopher J. Portier (NIEHS/NIH), Dr. Albert E. Munson

(NIOSH/CDC), and Dr. William T. Allaben (NCTR/FDA). The Director of the NIEHS/NIH, Dr.

Kenneth Olden, serves as Director of the NTP and reports to the Secretary, HHS. The National Cancer

Institute of the NIH was a charter agency for the NTP and continues to serve on the NTP Executive

Committee.

The NTP Executive Committee (Figure 1) provides oversight to the NTP for policy issues. This committee

is composed of the heads (or their designees) of federal research and regulatory agencies. The NTP Board

of Scientific Counselors (“the Board”), its subcommittees, and the Scientific Advisory Committee on

Alternative Toxicological Methods (SACATM) assure regular scientific and public peer review and input

about NTP activities and priorities. 

The Board is a federally chartered advisory committee whose members are appointed by the Secretary,

HHS. The Board provides primary scientific oversight to the Director for the NTP and evaluates the 

scientific merit of the NTP’s intramural and collaborative programs. The Technical Reports Review

Subcommittee of the Board provides peer review for (1) the NTP long-term toxicology and carcinogenesis

studies, (2) studies conducted in genetically modified models, and (3) short-term toxicity study reports.

The Report on Carcinogens Subcommittee of the Board provides external scientific evaluation of substances

nominated for listing in or delisting from the Report on Carcinogens. These groups each meet once or

twice each year, and all meetings are open to the public.

SACATM provides advice to the Director of the NIEHS, the Interagency Coordinating Committee on 

the Validation of Alternative Methods, and the NTP Interagency Center for the Evaluation of Alternative

Toxicological Methods. This advice addresses priorities and directives related to the development, validation,

scientific review, and regulatory acceptance of new or revised toxicological test methods and ways to foster

partnerships and communication with interested parties. The NIEHS Director appoints members to this

federally chartered advisory committee. SACATM meets twice each year, and all meetings are open to

the public.

The NTP also uses special emphasis panels, as needed, to provide independent scientific peer review and

advice to the NTP. These panels help ensure transparent, unbiased, and scientifically rigorous input to the

program for its use in making credible decisions about human health hazards, setting research and testing

priorities, and evaluating test methods for toxicity screening.

Overview

Figure 1 National Toxicology Program

NCTR/FDA

Director

NIEHS/NIH

NIOSH/CDC

Policy Oversight

NTP Executive Committee

• ATSDR

• CPSC

• EPA

• FDA

• NCEH/CDC

• NCI/NIH

• NIEHS/NIH

• NIH

• NIOSH/CDC

• OSHA

External Science Oversight

and Peer Review

NTP Board of Scientific Counselors

• Technical Reports Review

Subcommittee

• Report on Carcinogens

Subcommittee

Scientific Advisory Committee on 

Alternative Toxicological Methods
8 National Toxicology Program

Toxicology and Carcinogenicity Evaluations

The NTP has a broad mandate to characterize chemicals and other agents of public health concern. The NTP

continually solicits and reviews nominations for toxicology studies in the specific categories given in Table 1.

The nomination process is open to all interested individuals and groups. Information about nominating a

substance for testing by the NTP is available on the NTP web site (http://ntp-server.niehs.nih.gov) or by

contacting Dr. Scott Masten, Office of Chemical Nomination and Selection (for contact information, see

back flap).

Nominations undergo several levels of review before the NTP selects agents for study (Figure 2).

Representatives from federal agencies on the Interagency Committee for Chemical Evaluation and

Coordination (ICCEC) and the Board participate in the selection process. The NTP also solicits and 

considers public comment on nominations throughout this formal process. As the final step of selection,

the NTP Executive Committee reviews and evaluates the testing recommendations and the public comments

for each nomination. The committee makes its own recommendations on the nominations to test, not to

test at this time, or to defer testing until more information is received and considered. These steps help ensure

that the NTP’s testing program addresses toxicological concerns pertinent to all areas of public health and

maintains balance among the types of substances evaluated. 

The Executive Committee’s recommendation of a substance for study does not automatically commit the

NTP to its evaluation. The NTP strives to balance its selection of substances for study (e.g., occupational

exposures, environmental pollutants, food additives, consumer products, and pharmaceuticals) and initiates

studies as time and resources permit. In reviewing and selecting nominated substances for study, the NTP

also considers legislative mandates that require responsible private sector and commercial organizations to

evaluate their products for human and environmental health effects. Also, a nomination selected for study

may be deferred at any time if suitable data become available, if higher priority studies are identified, or if a

study proves impractical.

The NTP evaluates substances for a variety of health-related effects, among them, general toxicity, 

reproductive and developmental toxicity, genotoxicity, immunotoxicity, neurotoxicity, metabolism, 

disposition, and carcinogenicity. The NTP generally uses rodent models for study and conducts short-term

studies for up to thirteen weeks and long-term studies for up to two years. For each agent studied, a project

leader designs a comprehensive testing strategy to address the identified research and testing needs. A project

review committee evaluates the testing strategy and proposes an appropriate mechanism for sponsoring the

study (e.g., grant, contract, etc.). 

The NTP publishes results of short-term rodent toxicology studies in the NTP Toxicity Report series, and

results of longer-term studies, generally two-year rodent toxicology and carcinogenicity studies, as NTP

Overview

Table 1 Nomination Principles for NTP Studies

• Chemicals found in the environment not closely associated with a single commercial organization

• Biological or physical agents that may not be adequately evaluated without federal involvement

• Commercial chemicals with significant exposure that were first marketed prior to current testing requirements or those

that generate too little revenue to support further evaluations

• Potential substitutes for existing chemicals or drugs that might not be developed without federal involvement

• Substances that occur as mixtures for which evaluations cannot be required of industry

• Chemicals that should be evaluated to improve the scientific understanding of structure-activity relationships and 

thereby help limit the number of chemicals requiring extensive evaluations

• Emergencies or other events that warrant immediate government evaluation of a chemical or agent 
National Toxicology Program 9

Overview

Technical Reports or in peer-reviewed scientific journals. During 2003, the NTP initiated a new technical

report series for reporting the results from studies conducted in genetically modified models, such as

genetically engineered mice. The Technical Reports Review Subcommittee of the Board (Figure 1) formally

reviews these reports. Table 2 lists candidates for peer review in 2003 and 2004. Completed reports are

available electronically from the NTP web site or can be purchased in hard copy from Environmental

Health Perspectives (for contact information, see back flap).

Figure 2 NTP Toxicology Study Nomination and Selection Process

Federal and State Agencies

Industry

Industry Academia Other Organizations

Labor Public International Organizations

Chemical

Nominations

ICCEC Review

Public Review

NTP Board of Scientific Counselors Review (Public Meeting)

NTP Executive Committee Review and Selection

NTP Designs and Initiates Studies Based on Resources, Priorities, and Knowledge Gaps

Table 2 Candidate Chemicals for Peer Review*

Winter 2004

• Anthraquinone • 2,3,4,7,8-Pentachlorodibenzofuran (PeCDF)

• 2,2-bis(Bromomethyl)-1,3-propanediol (studied in fish) • TCDD, PCB 126 and PeCDF Mixture

• Malachite green and Leucomalachite green • 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)

• Nitromethane (studied in fish) • 1,2,3-Trichloropropane (studied in fish)

• 3,3’,4,4’,5-Pentachlorobiphenyl (PCB 126)

Fall 2004

• Azidothymidine (AZT) • 2,2’,4,4’,5,5’-Hexachlorobiphenyl (PCB 153)

• Benzophenone • PCB 126 and PCB 153 Mixture

• Bromodichloromethane • 2,3,4,4’,5-Pentachlorobiphenyl (PCB 118) and PCB 126 Mixture

• Genistein (multigenerations) • Sodium chlorate

Summer 2005

• Benzene • Glycidol

• Dibromoacetic acid • Glycolic acid plus simulated solar light

• Dichloroacetic acid • 4-Methylimidazole

• Dicyclohexylcarbodiimide • Methyl isobutyl ketone

• Dilsopropylcarbodiimide • Phenolphthalein

• Divinylbenzene • Salicylic acid plus simulated solar light

• Genistein • Sodium bromate

* Studies are conducted in rodent models unless otherwise indicated.
10 National Toxicology Program

The NTP conducts research on a broad range of high-priority agents and issues of public health concern.

Information about NTP studies, including standard protocols, fact sheets, and data from completed studies,

is available on the NTP web site (http://ntp-server.niehs.nih.gov). Below are brief overviews of some 

current initiatives.

Radiofrequency Radiation Emissions from Cellular Phones

More than 100 million Americans currently use wireless communication devices, with thousands of new users

added daily. Personal (cellular) telecommunications is a rapidly evolving technology that uses microwave

radiation to communicate between a fixed base station and a mobile user. Most systems employ a hand-held

cellular telephone, with the radiation antenna held close to the user's head.

The Federal Communication Commission requires cellular phones and other wireless communication

devises to meet its guidelines for exposure to radiofrequency radiation. These guidelines are based on 

protecting the user from immediate injury from the heat produced by radiofrequency radiation. We currently

do not have enough data to determine whether these guidelines will also protect against potential adverse

effects of long-term exposure.

Studies in laboratory animals are crucial for understanding whether exposure to radiofrequency radiation

may pose a danger to human health. Other research groups are performing several long-term animal 

studies addressing this issue. Also, the NTP plans to conduct laboratory research to help clarify any

potential health hazard for the U.S. population. The NTP will study the toxic and carcinogenic effects 

of chronic exposure to cell phone radiofrequency radiation emissions in laboratory animals. The NTP 

has worked with technical experts from the National Institute of Standards and Technology (NIST) to

test the suitability of various radiofrequency radiation exposure systems for these studies. NTP-sponsored

studies performed at NIST have demonstrated the suitability of using reverberation chambers to expose

animals to uniform fields of cell phone radiofrequency radiation.

Children’s Health

The NTP continues to be a leader in issues related to children’s health through research and the NTP’s

Center for the Evaluation of Risks to Human Reproduction (CERHR, see page 22). The NTP has ongoing

efforts to evaluate effects of various agents on developing immune and nervous systems through laboratory

studies of pesticides, water disinfectant by-products, and endocrine-disrupting agents. The program has

expanded these efforts by establishing study protocols where perinatal animals will be given these agents

Current Directions
National Toxicology Program 11

and then examined for developmental immunotoxicology, neurotoxicology, and reproductive effects.

Toxicokinetic data from animal studies of mothers, fetuses, and newborns will be used to develop 

pharmacokinetic models based on physiology. These models will help evaluate risks to humans from 

exposure to environmental toxicants during early development.

Hexavalent Chromium 

Chromium is a naturally occurring element present in various valence states. Trivalent chromium is an

essential nutrient, and in nature chromium occurs most commonly in this state. Hexavalent chromium

compounds are the next most stable form; however, they rarely occur naturally and are typically associated

with industrial sources. 

Because of concerns by a number of California legislators, the California Environmental Protection Agency,

and the California Health and Human Services Agency, the NTP is studying the potential of hexavalent

chromium given in drinking water to cause cancer. Hexavalent chromium is an established human carcinogen

in certain occupational settings, presumably as a result of inhalation exposure. However, we do not know

the long-term consequences of exposure to hexavalent chromium compounds in the water supply. Data

currently available on the chronic toxicity and carcinogenicity of hexavalent chromium given orally are 

not sufficient to establish or characterize any hazard. The NTP studies include both short- and long-term

administration of hexavalent chromium to laboratory animals as sodium dichromate dihydrate in drinking

water, as well as studies on hexavalent chromium’s tissue absorption. 

Phototoxicology 

The U.S. public is increasingly exposed to ultraviolet (UV) radiation from sunlight due to more leisure time

spent in outdoor activities and also from other sources (e.g., tanning booths). The NTP is coordinating an

effort between the NIEHS/NIH and NCTR/FDA to study the phototoxicology and photocarcinogenicity

of substances nominated to the NTP, including those of high priority to the FDA. In general, these studies

investigate the effects on gene expression, toxicity, and carcinogenicity of sunlight combined with either

topically or systemically applied substances in the SKH-1 hairless mouse. Much of this research is being

carried out at the NTP Center for Phototoxicology (NCP; see page 22). 

Phototoxicology studies are in progress at the NCP for several topically applied compounds. Many cosmetics

include alpha-hydroxy and beta-hydroxy acids as chemical exfoliating agents to correct or improve the

appearance of “sun-aged” skin. The relation of skin cancer to their continuous use combined with exposure
12 National Toxicology Program

to sunlight is not known. The NCP is also studying the possible acute toxicity and carcinogenicity of 

topically applied plant fractions of the aloe vera plant or topically applied retinyl palmitate in combination

with simulated sunlight. Many products, including cosmetics and dietary supplements, contain portions

of the aloe vera plant. Retinyl palmitate is included in some cosmetics as an “anti-wrinkle” compound,

and its safety in the presence of sunlight needs further study. Also, the NCP is designing studies of other

cosmetic ingredients, including topically applied Padimate O used in cosmetic and sunscreen preparations,

furocoumarin compounds found in lemon and lime oils, and nanoscale particles used in sunscreens (zinc

oxide and titanium dioxide).

The NCP is involved in examining the utility of site-specific mutations in the p53 gene as predictors 

(biomarkers) of the development of squamous cell carcinoma after exposure to simulated solar light.

Several animal models for studying how cutaneous melanoma starts and progresses have been developed

over the past several years. The NCP is currently examining how well genetically engineered animals 

containing the TP-ras (+) p16/INK4a (+/–) gene predict the development of UV-induced melanoma.

Herbal Medicines 

Medicinal herbs are among our oldest medicines, and their increasing use in recent years is evidence of

public interest in alternatives to conventional medicine. About one third of the U.S. population is believed

to use some form of alternative medicine, including herbal remedies. The use of herbal medicines and

other dietary supplements has increased substantially since passage of the 1994 Dietary Supplement Health

and Education Act. Although about 1,500 botanicals are sold as dietary supplements or ethnic traditional

medicines, herbal formulations are not subjected to FDA premarket approval to ensure their safety or efficacy.

The NTP is planning or conducting research on several medicinal herbs and compounds found in herbs

(listed in Table 3) to examine carcinogenicity, reproductive toxicity, neurotoxicity, immunotoxicity, or toxic

effects associated with exposures to high acute doses and chronic low doses.

Occupational Exposures 

The NTP is coordinating an effort between the NIEHS/NIH and NIOSH/CDC to better understand

worker exposures, educate workers, and identify occupational health research gaps. Current efforts are

addressing worker exposure to welding fumes and 1-bromopropane.

Studies of diseases in workers suggest that occupational exposure to welding fumes may cause adverse

health effects. More information is needed to evaluate the relationship between timing and amount of

exposure and the adverse effects and to understand the specific causes of these effects. The NIOSH/CDC

has constructed a computer-controlled, automated robotic welding fume inhalation system that will expose

laboratory animals to tightly controlled, well-characterized welding fumes caused by different welding

processes and materials. The physical and chemical composition of the generated fumes and gases will be

characterized. Also, studies will be performed to evaluate which exposure conditions, generator parameters,

and welding processes and materials cause acute responses in laboratory animals by assessing lung injury,

inflammation, and changes in the immune system.

An industry consortium has petitioned the EPA to list 1-bromopropane as an alternative for ozone-depleting

solvents. This could vastly increase the exposure of workers and the public to this compound. To obtain

information on exposures to this chemical, the NIOSH/CDC is conducting an industry-wide study 

targeting industries that use adhesives, the metal degreasing and electronics industry, and chemical, aerosol,

and adhesive manufacturers. Study sites are selected based on quantity and type of 1-bromopropane use,

number of workers exposed, type of manufacturing process, and how well the site represents the industry.

Current Directions
National Toxicology Program 13

Current Directions

Table 3 Herbals and Herbal Components under Study by the NTP*

Aloe vera gel Widely used as a dietary supplement and component of cosmetics. Ninth highest in

sales in 2002. The gel has been used for centuries as a treatment for minor burns and 

is increasingly being used in products for internal consumption.

Black cohosh Used to treat symptoms of pre-menstrual syndrome, dysmenorrhea and menopause. 

Ranked 11th in sales in 2002.

Bladderwrack A source of iodide used in treatment of thyroid diseases and also used as a 

component of weight-loss preparations.

Comfrey Herb consumed in teas and as fresh leaves for salads; however, it contains 

pyrrolizidine alkaloids (e.g., symphatine), which are known to be toxic. Used externally 

as an anti-inflammatory agent in the treatment of bruises, sprains, and other external 

wounds. Based in part on NTP studies on the alkaloid components of comfrey, the FDA 

has recommended that the manufacturers of dietary supplements containing this herb 

remove them from the market.

Echinacea purpurea extract The most commonly used medicinal herb in the United States in 2002. Used as an 

immunostimulant to treat colds, sore throat, and flu.

Ephedra Also known as Ma Huang; 21st in sales in 2002. Traditionally used as a treatment for 

symptoms of asthma and upper respiratory infections. Often found in weight loss and 

"energy" preparations, which usually also contain caffeine. Use has been associated 

with side effects such as heart palpitations, psychiatric and upper gastrointestinal 

effects, and symptoms of autonomic hyperactivity such as tremor and insomnia, 

especially when taken with other stimulants.

Ginkgo biloba extract Ranked 4th in sales in 2002. Ginkgo fruit and seeds have been used medicinally for 

thousands of years. The extract of green-picked leaves has shown increasing popularity

in the United States. Ginkgo biloba extract promotes vasodilatation and improved 

blood flow and appears beneficial, particularly for short-term memory loss, headache, 

and depression.

Ginseng and Ginsenosides Ranked 13th in sales of medicinal herbs in 2002. Ginsenosides are thought to be the

active ingredients in ginseng. Ginseng has been used as a treatment for a variety of 

conditions: hypertension, diabetes, and depression, and been associated with various

adverse health effects.

Goldenseal Ranked 17th in sales in 2002; Traditionally used to treat wounds, digestive problems, 

and infections. Current uses include as a laxative, tonic, and diuretic. Mistakenly 

thought to disguise the presence of other drugs in drug tests.

Green tea extract Used for its antioxidative properties, 15th in sales in 2002.

Kava kava The 25th most widely used medicinal herb in 2002, has psychoactive properties, and is 

sold as a calmative and antidepressant. A recent report of severe liver toxicity has led 

to restrictions of its sale in Europe and apparently affected sales in the United States. 

Some components may alter efficacy/toxicity of therapeutic agents.

Milk thistle extract Ranked 8th in sales in 2002. Used to treat depression and several liver conditions, 

including cirrhosis and hepatitis, and to increase breast milk production.

Pulegone A major terpenoid constituent of the herb, Pennyroyal, is found in lesser concentrations 

in other mints. Pennyroyal has been used as a carminative insect repellent, 

emmenagogue, and abortifacient. Pulegone has well-recognized toxicity to the liver, 

kidney, and central nervous system.

Senna Laxative with increased use due to the removal of one of the widely used 

chemical-stimulant type laxatives from the market. 

Thujone Terpenoid found in a variety of herbs, including sage and tansy, and in high 

concentrations in wormwood. Suspected as the causative toxic agent associated with 

drinking absinthe, a liqueur flavored with wormwood extract.

* Ranking of sales is from The American Herb Association Vol. 18(3), p. 7, 2002.

(Those entries without ranking are not in the top 36 in sales for 2002.)
14 National Toxicology Program

Exposure is studied using breath and other biological measures. The CERHR (see page 22) has evaluated

the potential reproductive and developmental toxicities of 1-bromopropane and 2-bromopropane, and

NTP-CERHR monographs on these chemicals are available.

The NIOSH/CDC is planning a National Exposures at Work Survey that will be conducted in a nationally

representative sample of workplaces across all industries, starting with the health services industry. This survey

will collect data on chemical, physical, and biological agents to which workers could be exposed, as well as

data on exposure controls and health and safety practices. Information from this initiative will be used to

educate workers, identify occupational health knowledge gaps, and help target areas where research is likely

to reduce workplace illness.

Safe Drinking Water Program 

More than 200 million Americans are estimated to use municipally treated drinking water, so the availability

of safe drinking water is of enormous importance to public health. Although chlorination is one of the

major public health advances of the 20th century, by-products of chlorination or other disinfection

processes (disinfection by-products, DBPs) may cause health problems such as cancer. Also, some agents

found naturally in water or that contaminate public water systems may pose a threat to public health.

The EPA is responsible for setting water standards for DBPs. To provide scientific data for setting sound

standards for water quality, the NTP is collaborating with the EPA on a research program to assess potential

risks from human exposure to DBPs. This program includes a systematic, mechanism-based evaluation of

DBPs focusing on reproductive toxicity, immunotoxicity, neurotoxicity, and carcinogenicity. The program

selects DBPs for study based on their presence in drinking water, occurrence with different disinfection

processes, chemical structures, and class: trihalomethanes, haloacetic acids, and haloacetonitriles. Table 4

lists DBPs currently under study by the NTP.

Besides DBPs, many agents occur (1) naturally (e.g., arsenic, aluminum) in water, (2) because of 

contamination (e.g., methyl tert-butyl ether and other gasoline additives, pesticides, organic tin compounds),

or (3) with environmental changes (e.g., cyanobacterial toxins from algal blooms in surface waters). The

NTP is designing long-term toxicology and toxicokinetic studies on several of these agents, including 

aluminum complexes, organic tin compounds, and the two most common cyanobacterial toxins 

(microcystin-LR and cylindrospermopsin).

Nanoscale Materials

Nanotechnology in recent years has become an increasing focus of U.S. and global research and development

efforts. As with many technological advances, new materials are created, and as a result, the potential exists

for new and unanticipated human exposures for which the impact on human health is unknown. The NTP

is developing a broad-based research program to address potential human health hazards associated with

Current Directions

Table 4 Water Disinfection By-Products under Study

• Bromochloroacetic acid

• Bromodichloroacetic acid

• Bromodichloromethane

• Dibromoacetic acid

• Dibromoacetonitrile

• Dichloroacetic acid

• Sodium bromate

• Sodium chlorate
National Toxicology Program 15

the manufacture and use of nanoscale materials. This research program will include studies of nanoscale

materials that apply existing toxicology testing methods and that also explore the development of novel 

toxicological methods to assess potential health effects.

Nanoscale materials are a broadly defined set of substances where at least one critical dimension is less

than 100 nanometers. Ultrafine particulate matter is a well-known example of ambient nanoscale particles;

however, the NTP’s research program will initially focus on manufactured nanoscale materials of current

or projected commercial importance. Nanoscale materials can in theory be engineered from nearly any

chemical substance; semiconductor nanocrystals, organic dendrimers, and carbon fullerenes and carbon

nanotubes are a few of the many examples. They are already appearing in commerce as industrial and

consumer products and as novel drug delivery formulations.

The intent of the NTP’s research program is to evaluate the toxicological properties of major nanoscale

materials classes which represent a cross-section of composition, size, surface coatings, and physico-chemical

properties, and use these as model systems to investigate fundamental questions concerning if and how

nanoscale materials can interact with biological systems. Some of these fundamental questions include:

What are the appropriate methods for detection and quantification of nanoscale particles in tissues? How

are nanoscale materials absorbed, distributed in the body and taken up by cells? Are there novel toxicological

interactions? As part of this research program, studies to evaluate the biological disposition of nanoscale

crystalline fluorescent semiconductors (“quantum dots”), long-term toxicology studies of carbon-based

nanoscale materials (e.g., single- or multi-walled nanotubes, fullerenes), and phototoxicology studies of

representative nanoscale metal oxide particles used in industrial settings and consumer products (e.g. 

titanium dioxide) are currently being considered (see Phototoxicology, page 11).

DNA-Based Products

DNA-based therapies are being developed to treat a wide range of human diseases. However, by their 

very nature, they pose a risk of interacting with the host’s genes or disrupting normal cellular processes 

in unexpected, unpredictable, and potentially harmful ways. Examples of DNA-based products include 

(1) vaccines against viruses and bacteria that have been made from plasmid DNA, (2) synthetic 

oligonucleotides to modulate gene expression, and (3) viral carriers for gene therapy. Presently, the NTP 

is collaborating with the FDA and sister NIH institutes to study the safety of DNA-based products.

These studies address life-long risks presented by their use and the potentials for reproductive toxicities, 

for transmission of altered genetic material to subsequent generations, and for DNA-based products to

cause autoimmune disease or immune dysfunction.

Endrocrine-Disrupting Agents

Endocrine disruptors are naturally occurring or man-made substances that may mimic or interfere with

natural hormones in the body. Endocrine disruptors may turn on, turn off, or change signals that hormones

carry and so affect the normal functions of tissues and organs. The NTP is involved in several efforts to

strengthen the scientific knowledge within this field.

Endocrine-disrupting chemicals are of interest to the FDA, and through an interagency agreement, the

NIEHS/NIH supports toxicology studies being conducted at the NCTR/FDA. Chemicals under study

include the plant-based estrogen (phytoestrogen) genistein, the pesticide vinclozolin, the drug ethinyl

estradiol, and the industrial chemical nonylphenol. These studies assess effects on reproduction, development

of hormone-sensitive organs, and cancer in rodents over several generations, as well as behavioral and

immunological effects. The NTP Interagency Center for the Evaluation of Alternative Toxicological Methods

is evaluating several methods for use in identifying potential endocrine-disrupting agents (see page 23).

Current Directions
16 National Toxicology Program

Considering the large number of chemicals in commercial use, the NTP must continually set priorities

and develop research strategies to characterize toxicants and identify hazards that make the best use of

available resources. Using new testing strategies that provide more or better information can strengthen

the scientific knowledge on which regulatory decisions are based. The NTP core agencies are developing

and validating new testing methods, and university-based researchers are also participating in these efforts

through NIEHS/NIH extramural grants.

Many testing strategies focus on more rapid screening tests, alternative or complementary in vivo tests 

for rodent bioassays, and less use of two-year rodent studies to determine toxicities. Strategies include

molecular screening methods, non-mammalian test species, genetically engineered animal models, genetically

engineered in vitro cell systems, microchip-based genomic technologies, and computer-based predictive

toxicology models. Such techniques can provide insight into the molecular and biological events associated

with a chemical’s toxic effect, as well as mechanistic information for assessing human risk. They can also

help clarify dose-response relationships, make species comparisons, and identify sources of variations among

individuals. Below are brief overviews of some current and emerging NTP initiatives to make better use

of these new research tools.

Caenorhabditis elegans

The NTP is interested in developing rapid, sensitive, and specific tests for screening environmental agents.

A current focus is the nematode C. elegans. The NTP is investigating the response of C. elegans when

exposed to known or suspected toxicants and monitoring the effects of these toxicants on its growth, size,

reproduction, and movement. The goal is to determine the possibility of using C. elegans as a practical

and efficient model in toxicology studies.

NTP Research Databases

A primary goal of the NTP is to evaluate agents of public concern for their potential toxicity or carcinogenicity.

Some studies address general toxic effects in laboratory animal species, whereas others focus on specific

immune, neurological, reproductive, and developmental effects. Data from general toxicology and 

carcinogenicity studies are publicly available on the NTP web site (http://ntp-server.niehs.nih.gov). 

The NTP is expanding public accessibility to its data to include all study types (general toxicology, 

carcinogenesis, genetic toxicity, and organ systems). The NTP provides access to the data in a common

format using web-based applications that allow users to query data, conduct simple statistical manipulations,

and export the information. Basic tools are available on the web site to allow users to search for studies 

Evolving Strategies
National Toxicology Program 17

on specific substances and retrieve data for individual animals. The NTP is also developing tools for 

conducting systematic searches both within and across studies based on which endpoints showed significant

changes. This type of search will permit the comparison of effects among individual chemicals or classes

of chemicals.

Toxicogenomics

New molecular technologies have brought the NTP into the arena of toxicogenomics, a new scientific

field that examines how the entire genetic structure, or genome, is involved in an organism’s response to

environmental toxicants. Toxicogenomics applies genetic knowledge to environmental medicine by studying

the effect of toxicants on gene activity and specific proteins produced by genes. It combines information

from studies of genomic-scale messenger RNA profiling (by microarray analysis), cell-wide or tissue-wide

protein profiling (proteomics), genetic susceptibility, and computational models. This information helps

illustrate the roles of interactions between genes and the environment in disease. This field could revolutionize

environmental health, drug safety, and risk assessment.

To centralize activities in toxicogenomics, the NIEHS/NIH established the National Center for Toxicogenomics

(NCT) in 2000. Complementary DNA microchip-based technology enables the NCT to assess the genetic

impact of toxicants. Microarrays containing genes from common test animals and organisms, including mice,

rats, and yeast, are currently in use.

The NCT is evaluating gene arrays against known toxicants and building a database of gene expression

information to determine the typical genetic changes or “signature” profiles produced by these toxicants.

Identification of such changes in gene expression on a genome-wide basis could provide a global perspective

on how an organism responds to a specific stress, drug, or toxicant. As this technology continues to

improve, it will help NTP scientists evaluate and compare compounds under study. Such information

could define cellular networks of responsive genes, identify target molecules of toxicity, provide future

biomarkers and alternative testing procedures, and identify individuals who are sensitive to drugs or 

environmental agents.

Initial efforts by the NTP include profiling a classic liver toxicant acetaminophen and studying variables

that affect gene expression. To facilitate interpretation of these data, the NTP is also collecting gene expression

data from animals not exposed to acetaminophen to establish which genes are more variable and which genes

are more stable.
18 National Toxicology Program

Magnetic Resonance Imaging 

Traditionally, in NTP toxicology and carcinogenicity studies, lesions are evaluated with conventional optical

microscopy of collected tissue samples. Representative samples are collected because examining all the tissue

involved is impractical. Because of recent advances in the technology for imaging, magnetic resonance

imaging (MRI) of the entire body at microscopic resolution is now possible. The NTP is investigating

MRI for imaging laboratory animals. MRI microscopy is three-dimensional, can examine the same specimens

at different angles, and measures the volume of tissue and organs. MRI of live animals permits acquisition

of imaging data at different times over an animal’s lifetime. Because the images are digital, web-based viewing

is easier.

MRI is a noninvasive technique that will permit more complete and thorough examination of tissues 

and organs from test animals without destroying the samples and may also allow more information to be

gathered from NTP studies than before. Anticipated uses include monitoring lesions and examining the

morphology and functionality of genetically engineered mice. The NTP also hopes in the future to apply

this technology to studies of birth defects. This technology is being applied to NTP microarray studies of

acetaminophen-induced hepatotoxicity (Figure 3, see Toxicogenomics, page 17).

Risk Assessment Methodology 

Risk assessment involves using facts to determine whether exposures to agents in the environment or

workplace are hazardous to the health of individuals or populations, and if so, to what extent. Models based

on mathematics and biology are useful for estimating human risk. These models represent physiological

and biochemical processes known to occur in laboratory animals and humans. They can provide a scientifically

sound basis for evaluating data from studies in animals and then applying that information across species

to determine if and how exposure to an agent might cause health effects in humans. The NTP initiatives in

assessing human exposures and advances in toxicogenomics should increase the amount of human and animal

mechanistic data for developing and improving biologically based models.

Physiologically based pharmacokinetic (PBPK) models measure the biological processes of absorption,

distribution, metabolism, and elimination of an agent in animals or humans (Figure 4). The NIEHS/NIH

continues to create and develop PBPK models to evaluate exposure-response relationships for carcinogenicity

Evolving Strategies

Figure 3 Optical and MRI Microscopy of Liver from Acetaminophen-treated Rats

A. Photomicrograph showing small and large patches of necrosis (asterisks) 24 hours after dosing with acetaminophen.

B. MRI of acetaminophen-treated rat showing liver vasculature (white branching structures) and mottled appearance 

(arrow) of the affected liver.

C. MRI on a vehicle control rat in which the liver parenchyma has a homogeneous signal. White areas represent hepatic

blood vessels. 

A B C
National Toxicology Program 19

Evolving Strategies

This model represents the uptake, distribution, and metabolism of an environmental agent administered orally.

Figure 4 Physiologically Based Pharmacokinetic Model

Oral Dose

Arterial Blood

Venous Blood

GI Lumen

GI Blood

GI tract

Liver Blood

Liver Metabolism

Fat Blood

Fat

Kidney Blood

Kidney

Table 5 Physiologically Based Pharmacokinetic Modeling

Chemical Route of Exposure

Anthraquinone Oral in feed

Butadiene Inhalation

Chromium Oral in drinking water

Decalin Inhalation

p-p’-Dichlorodiphenylsulfone Oral in feed

Isoprene Inhalation

Melatonin Endogenous

Mercury Inhalation

Methyleugenol Oral by gavage

2-Methylimidazole Oral by gavage, intravenous

4-Methylimidazole Oral by gavage, intravenous

Naphthalene Inhalation

2,3,4,7,8-Pentachlorodibenzofuran Oral by gavage

Polybrominated diphenyl ethers Oral by gavage

Polychlorinated biphenyls (209 congeners) Multiple routes

Primidone Oral in feed

Propylene glycol mono-t-butyl ether Inhalation

Sodium nitrite Oral in drinking water

2,3,7,8-Tetrachlorodibenzo-p-dioxin Oral by gavage, dermal

Urethane Oral by gavage, intravenous

Vanadium pentoxide Inhalation
20 National Toxicology Program

and developmental and reproductive toxicities (listed in Table 5). PBPK models are now often included 

in NTP Technical Reports. This information helps regulatory agencies assess how the health effects in 

experimental animals caused by exposure to environmental agents relate to effects observed in humans.

Combining PBPK models with models that measure changes in cells in target tissues under different 

concentrations of test agents helps define dose-response relationships and determine the likelihood of

adverse effects from “low-dose” exposure. These models also help to assess variation among individuals 

in specific groups (e.g., same or similar age, gender, genetic predisposition, or ethnicity).

Developing biologically based models relies on first developing a simple model and then testing predictions

of the model experimentally. As more data become available from studies in cell cultures, animals, and

humans, the model is continually adjusted or expanded. For example, the NIEHS/NIH has developed

mechanistic models for changes in gene expression of the aryl hydrocarbon receptor resulting from exposure

of animals to the carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The EPA used this model in

its TCDD cancer risk assessment, which serves as the agency’s basis for regulating human exposure to

this environmental hazard. TCDD is the most potent member of the dioxin class of chemicals. Dioxins

occur widely as by-products of chemical processes that involve reactions of chlorine and hydrocarbons

(e.g., produced by paper and pulp bleaching or incineration of hospital and municipal wastes) and are

contaminants in some pesticides, herbicides, and wood preservatives.

Transgenic Animals 

For more than three decades, the NTP has conducted studies in laboratory rodents (bioassays) to identify

carcinogens thought to pose risks to human health. Genetically engineered animal models based on new

gene technologies are being evaluated as alternatives or complements to rodent bioassays. Genetically

altered or transgenic mouse models carry activated oncogenes or inactivated tumor suppressor genes known

to be involved in neoplastic (tumor-causing) processes in both humans and rodents. This trait may allow

these mice to respond or show the effects of carcinogens more quickly and more reliably than conventional

rodent strains. Target or reporter genes also allow direct molecular and cellular analysis of a chemical’s

effects and can provide additional mechanistic information about its mode of action. 

The NTP has sought input from its advisory groups and the public about the usefulness of a number of

transgenic rodent models for short-term studies of carcinogenicity [p53(+/–), Tg.AC (v-Ha-ras), and

RasH2]. In general, there is support for the p53(+/-) and RasH2 models for evaluating the carcinogenic

potential of chemical or physical agents. The NTP will continue to consider transgenic models when

designing the testing strategy for substances under study. As understanding increases of the complex 

signaling pathways turned on or off during carcinogenesis, the NTP will be able to select transgenic animal

models that best mimic human tissue processes. This should provide a firmer foundation for applying

hazard data from animals to humans. Efforts are also underway to develop transgenic cell lines and to

evaluate the usefulness of transgenic fish as alternatives to mouse or culted cell models.

ScanScope–2D Imaging Technology for Pathological Evaluations

The NTP has now acquired a new technology for evaluation of lesions from its studies. ScanScope 

scans whole histopathology slides at high resolution and compresses the large file using JPEG2000. 

The resulting image can be viewed over the Internet and one is able to zoom in on any portion of the

slide with magnifications similar to what is seen with a microscope using a 10, 20, or 40X objective. 

The result is that the computer becomes equivalent to a microscope and you can examine any portion of

the whole image at microscopic resolution. This technology provides the NTP pathologists a tool to share

treatment-induced lesions with colleagues anywhere in the world via the Internet and, as needed, obtain

their diagnostic opinions.

Evolving Strategies
Photodisk, Matt Ray/EHP
22 National Toxicology Program

NTP Center for Phototoxicology 

The NTP Center for Phototoxicology (NCP), established in 2000, conducts research on how light affects

the toxicology and carcinogenicity of substances nominated to the NTP and on the mechanisms that underlie

these effects. Current research initiatives are described on page 11 under “Phototoxicology.” Research in this

area is very important because of the public’s increasing exposure to ultraviolet (UV) radiation or sunlight

through more frequent use of tanning booths and more leisure time spent in outdoor activities.

The NCP’s state-of-the-art laboratory can study the potential toxic or carcinogenic effects of a test substance

in combination with UV or visible radiation from several light sources. The NCP also conducts mechanistic

studies to learn how these effects might occur. The laboratory can simulate sunlight using 6.5-kilowatt

xenon-arc lamps that can mimic terrestrial solar light for most latitudes. Emulating terrestrial light enables

researchers to experimentally duplicate human exposure conditions, which is critical for such research.

The facility can also perform studies using light from different types of fluorescent tubes, such as those

used in fluorescent lamps and suntan-bed lamps.

The NTP Board of Scientific Counselors advises the NCP on its programs and priorities. Substances selected

for testing are nominated directly from the FDA and from outside submissions to the NTP. The FDA's

Phototoxicology Chemical Selection Working Group prioritizes nominations and forwards them to the

NTP for formal consideration in its nomination and selection process. More information about the NCP

is available by contacting Dr. Paul C. Howard, Director, NCP (for contact information, see back flap).

Center for the Evaluation of Risks to Human Reproduction 

Established in 1998, the NTP’s Center for the Evaluation of Risks to Human Reproduction (CERHR)

serves as an environmental health resource to the public and to regulatory and health agencies. The NTP

Board of Scientific Counselors advises the CERHR on its processes, priorities, and direction. The CERHR

web site (http://cerhr.niehs.nih.gov) has information on various environmental exposures and their potential

to affect pregnancy and child development, as well as links to other resources.

The CERHR provides scientifically based, uniform assessments of the potential for adverse effects on

reproduction and development caused by chemicals to which humans are exposed. It follows a formal,

open process for nomination, selection, and review of chemicals; public input is encouraged. The CERHR

selects chemicals for review based on several factors, including production volume, extent of human 

exposures, public concern about the chemical hazard, and published evidence of reproductive or 

Centers
National Toxicology Program 23

developmental toxicities. The CERHR carries out these assessments through rigorous evaluations by 

independent scientific panels in public forums. These evaluations are intended to

• interpret scientific evidence to the public and provide information about the strength of the evidence that

a given exposure or circumstance poses a hazard to reproduction or the health and welfare of children;

• provide regulatory agencies with objective and scientifically sound assessments of data related to the

reproductive/developmental health effects associated with exposure to specific chemicals or classes of 

chemicals, including descriptions of any uncertainties associated with these assessments; and 

• identify knowledge gaps to help establish research and testing priorities.

Chemicals reviewed to date by the CERHR expert panels are listed in Table 6. 

The NTP has begun a monograph series for the chemicals evaluated by the CERHR. Each monograph

includes the NTP Brief, the Expert Panel Report, and public comments on the Expert Panel Report. The

brief gives the NTP's interpretation of the potential for the chemical to cause adverse reproductive and/or

developmental effects in exposed humans and is based on the Expert Panel Report, public comments on

those reports, and any new information that becomes available after the expert panel meeting. NTP-CERHR

monographs are transmitted to appropriate federal and state agencies and made available to the public.

Expert panel reports and NTP-CERHR monographs, as completed, are posted on CERHR's web site

and are available in hard copy and CD-ROM from the CERHR.

The CERHR conducts workshops, as needed, to bring together experts and discuss important topics relative

to effects of environmental agents on reproduction and development. The CERHR recently sponsored a

workshop to discuss test methods for assessing chemical-induced effects on the thyroid system and how

results obtained in laboratory animal studies could best be used to predict effects that might occur in humans.

The meeting report is available on the CERHR web site.

The CERHR welcomes nominations of chemicals for review as well as scientists for its registry of experts.

Information about the CERHR and the nomination process is available from its web site or by contacting

Dr. Michael Shelby, Director, CERHR (for contact information, see back flap).

NTP Interagency Center for the Evaluation of Alternative Toxicological Methods 

Toxicity testing is absolutely necessary to assess the hazards and safety of substances in our food, air, and

water, in the workplace, and at home. Developing, validating, accepting, and harmonizing new, alternative,

and revised toxicological test methods are coordinated throughout the federal government by the Interagency
24 National Toxicology Program

Coordinating Committee on the Validation of Alternative Methods (ICCVAM). ICCVAM was established in

2000 (ICCVAM Authorization Act of 2000: Public Law 106-545) as a permanent interagency coordinating

committee of the NIEHS/NIH under the NTP Interagency Center for the Evaluation of Alternative

Toxicological Methods (NICEATM). ICCVAM consists of the designated representatives from 15 federal

agencies (Table 7). NICEATM provides scientific and operational support for ICCVAM and related activities.

The Scientific Advisory Committee on Alternative Toxicological Methods, established in January 2002,

provides advice on the activities of ICCVAM and NICEATM.

NICEATM and ICCVAM work together to evaluate the usefulness and limitations of new, revised, and

alternative toxicological test methods that may (1) predict human health risks better than currently used

methods, (2) save time and money, and (3) refine (cause less pain and distress), reduce, or replace animal

use. NICEATM also promotes information sharing and communication among government agencies,

industry, the public, and the international community. 

ICCVAM has a formal process for nominating and submitting new, revised, and alternative toxicological

test methods for evaluation. Once test methods are accepted for evaluation, NICEATM and ICCVAM

convene independent scientific peer review panels to assess their usefulness and limitations. Workshops and

expert panel meetings are also convened to (1) evaluate how well current safety assessment methods are

working, (2) identify areas needing improved or new methods, (3) assess the current validation status of

new methods, and (4) recommend appropriate research, development, and validation. These meetings are

open to the public and provide an opportunity for public comment. Meeting reports, public comments,

and ICCVAM recommendations on the scientific validity and potential acceptability of alternative test

methods are forwarded to federal agencies for their consideration. Each agency determines the regulatory

acceptability of a method according to its own statutory mandates. ICCVAM also works to achieve 

international acceptance of test methods that it finds to be scientifically valid for specific uses.

Centers

Table 6 Chemicals Reviewed to Date by CERHR Expert Panels

Acrylamide A neurotoxicant, shown in animal studies to be a carcinogen, germ cell 

mutagen, and reproductive toxicant; present in starchy foods treated at high

temperatures (e.g., French fries and potato chips).

1-Bromopropane Various industrial uses and is being considered as a replacement for 

ozone-depleting chemicals, such as hydrochlorofluorocarbons and 

chlorinated solvents. 

2-Bromopropane No industrial uses in the United States, but is a contaminant in 

1-bromopropane.

Ethylene glycol A high-production-volume chemical used chiefly as an intermediate in the 

production of polyester compounds and as antifreeze for heating and 

cooling systems.

Fluoxetine Widely prescribed antidepressant (Prozac, Sarafem) and recently prescribed 

to treat premenstrual dysphoric disorder in women of childbearing age; 

more recently approved by the FDA for use in children 7-17.

Methanol Commercially important, high-production-volume chemical with potential 

for occupational, consumer, and environmental exposure.

Propylene glycol Used as an intermediate in the production of polyester resins, approved for 

use in food, cosmetics, and pharmaceutical products, and as antifreeze 

and a deicing agent.

Seven selected phthalates* Widely used as plasticizers in consumer products such as shower curtains, 

medical devices, upholstery, raincoats, and soft-squeeze toys.

* 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
National Toxicology Program 25

The Local Lymph Node Assay (LLNA) was the first method evaluated by the ICCVAM process. ICCVAM

recommended that the LLNA could be used as a valid substitute for currently accepted guinea pig test methods.

Accepted by U.S. agencies in 1999, LLNA was adopted by the international Organisation for Economic

Co-operation and Development in 2002. Other test methods evaluated by ICCVAM are listed in Table 8.

ICCVAM has developed a process for establishing performance standards for validated and accepted test

methods. These standards can be used to determine the acceptability of other proposed test methods that

are based on similar scientific principles and measure or predict the same biological or toxic effect. They

(1) identify components that are essential to a proposed similar test method, (2) list the minimum reference

chemicals required for assessing the accuracy and reliability of a proposed similar test method, and (3)

establish the accuracy and reliability that a similar test method should achieve with the reference chemicals.

More information about NICEATM and ICCVAM, meeting schedules, meeting reports and minutes, and

information on nominating alternative toxicological methods are available through the ICCVAM/NICEATM

web site (http://iccvam.niehs.nih.gov) or by contacting Dr. William S. Stokes, Director, NICEATM (for

contact information, see back flap).

Centers

Table 7 ICCVAM

• Agency for Toxic Substances and Disease Registry • Food and Drug Administration

• Consumer Product Safety Commission • National Cancer Institute/NIH

• Department of Agriculture • National Institute of Environmental Health Sciences/NIH

• Department of Defense • National Institutes of Health (NIH)

• Department of Energy • National Library of Medicine/NIH

• Department of the Interior • National Institute for Occupational Safety and 

• Department of Transportation • Health/Centers for Disease Control and Prevention

• Environmental Protection Agency • Occupational Safety and Health Administration

Table 8 Test Methods Evaluated by ICCVAM

Test Method Regulatory Application

Local Lymph Node Assay Substitute for currently accepted guinea pig test methods for allergic 

contact dermatitis.

Up-and-Down Procedure Alternative method for assessing acute oral toxicity; as a replacement

for the conventional LD50 test for hazard classification testing.

In vitro (non-animal) cytotoxicity methods Used to estimate doses for assessing acute systemic toxicity 

in animals.

In vitro estrogen receptor and transcriptional EPA’s Endocrine Disruptor Screening Program for identifying potential

activation assays endocrine-disrupting chemicals.

In vitro androgen receptor and transcriptional EPA’s Endocrine Disruptor Screening Program for identifying potential

activation assays endocrine-disrupting chemicals.

Corrositex®, EpiDermTM, EPISKINTM, and In vitro methods to determine dermal corrosivity.

Transcutaneous Electrical Resistance Assay

FETAX (Frog Embryo Teratogenesis Assay: In vitro method to determine the developmental toxicity of chemicals

Xenopus) and mixtures.
26 National Toxicology Program

The Report on Carcinogens (RoC) is prepared every two years in response to Section 301 of the Public Health

Service Act, as amended. The RoC lists all substances that either are known to be human carcinogens or may

reasonably be anticipated to be human carcinogens, and to which a significant number of people living in the

United States are exposed. The Secretary, HHS delegated responsibility for preparing the RoC to the NTP, which

prepares the report with help from other federal health and regulatory agencies and nongovernmental institutions.

The RoC is an informational, scientific, and public health document that identifies and discusses agents, substances,

mixtures, and exposure circumstances that may pose a carcinogenic hazard to human health. It compiles meaningful

and useful data on the listed agents, including carcinogenicity, genotoxicity, and biological mechanisms in humans

and/or animals, the potential for exposure to them, and federal regulations to limit exposures.

The NTP solicits and encourages broad participation from groups or individuals interested in nominating

agents, substances, mixtures, or exposure circumstances for listing in or delisting from the RoC. Anyone

may submit a nomination for consideration by the NTP.

The preparation and review process for each RoC takes about three years. Review of the nominations for

listing in or delisting from the RoC follows a formal process that includes many phases of scientific peer

review and many opportunities for public comment (Figure 5). The review groups evaluate each nomination

according to specific RoC criteria. The NTP Director evaluates all review group recommendations, public

comments, and other information in developing a recommendation to the Secretary, HHS.

The 10th RoC was released December 11, 2002, and is available on the Environmental Health Perspectives

web site (http://ehp.niehs.nih.gov; for other contact information, see back flap). The scientific review of

nominations to the 11th RoC is completed, and publication is anticipated in 2004 (see list in Table 9).

The NTP periodically holds public meetings to gain input regarding the procedures used for the review 

of nominations for listing in or delisting from the RoC and on the criteria used for evaluation of the 

nominations. These meetings provide an opportunity for the public to present their views to the NTP 

and to comment on the views expressed by others. The NTP held the first such public meeting in October

1999 that resulted in some modifications to the nomination review process. Another public meeting was

held in January 2004. Information concerning this recent meeting, including the public comments received,

the meeting transcript, and the NTP response to issues identified at this meeting, will be posted on the NTP

web site (http://ntp-server.niehs.nih.gov), as available. 

RoC
National Toxicology Program 27

More information about the RoC, how to obtain copies of the report, and how to submit a nomination

for listing in or delisting from the RoC, is available through the NTP web site or by contacting Dr. C.W.

Jameson, Head, RoC (for contact information, see back flap).

Table 9 Nominations for Possible Listings in the 11th Report on Carcinogens

Reviewed in 2002 Reviewed in 2003

• 1-Amino-2,4-dibromoanthraquinone • Diazoaminobenzene

• 2-Amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) • Hepatitis B Virus

• 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) • Hepatitis C Virus

• 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) • Human Papillomaviruses, genital mucosal types

• Cobalt Sulfate • Lead and Lead Compounds

• Diethanolamine • Neutrons

• Naphthalene • X-Radiation and Gamma (γ)-Radiation

• Nitrobenzene

• Nitromethane

• 4,4'-Thiodianiline

Figure 5 Report on Carcinogens Review Process for the 11th Report

Nominations Selected for Review

Solicit Public Comment

NIEHS Review Group

NTP Executive Committee

Interagency Working Group

(NCI/NIH, NIEHS/NIH, NCTR/FDA, NCEH/CDC, NIOSH/CDC,

ATSDR, CPSC, EPA, OSHA)

Solicit Public Comment

NTP Board of Scientific Counselors 

RoC Subcommittee

(External Peer Review, Public Meeting)

Solicit Public Comment

NTP Executive Committee Director, NTP

Secretary, HHS
28 National Toxicology Program

Open communication with federal and state agencies, industry, academia, and the public is crucial for the

success of NTP activities. Partnerships with sister federal agencies are ongoing, and the NTP continues 

to collaborate with the private sector. NTP conferences and workshops give researchers, regulators, policy

makers, and the public the chance to examine issues together, exchange information, and reach agreement

on future directions for toxicology and risk assessment.

The NTP is interested in input from the public and all interested parties on its programs and priorities.

Nominations, inquiries, and comments are welcome at any time. The NTP Liaison and Scientific Review

Office collects input, represents the program through exhibits at national and international meetings,

publishes the quarterly newsletter NTP Update, and oversees the distribution of information about programs,

workshops, initiatives, and other projects. In addition, this office manages scientific peer review for the NTP

and organizes workshops on scientific and public health topics. General inquiries and requests for information

can be directed to this office (for contact information, see back flap).

The NTP web site (http://ntp-server.niehs.nih.gov) offers access to information about the NTP, with

links that detail and highlight ongoing and future initiatives and the NTP centers. The NTP distributes

testing and research results, program plans, and other publications through mailings, Federal Register

announcements, and the NTP web site. Also, individuals can subscribe free of charge to the NTP listserv

by registering online through the web site or by sending e-mail to ntpmail-request@list.niehs.nih.gov with

“subscribe” as the message. The NTP list-serv notifies subscribers by e-mail about the release of new NTP

publications and about upcoming events, such as advisory committee meetings, peer reviews, expert panel

meetings, and workshops.

The Central Data Management (CDM) oversees distribution (on request) of specific chemical study 

information and NTP documents, including the NTP Annual Plan, NTP study status reports, copies of

draft NTP Technical Reports, background documents for chemicals nominated to the NTP for study, and

minutes from meetings of the NTP Board of Scientific Counselors and its subcommittees. To request any

of these documents, contact the CDM (for contact information, see back flap).

The Environmental Health Perspectives (EHP) web site (http://ehp.niehs.nih.gov) provides searchable access

and printed copies of NTP publications, including the RoC, NTP Technical Reports, and NTP Toxicity

Reports. EHP subscription packages include access to NTP publications, EHP journals, and the Rodent

Historical Controls Database. For more information, contact EHP (for contact information, see back flap).

Outreach
Contact Information

Primary Contact:

NTP Liaison and Scientific Review Office

P.O. Box 12233, MD A3-01

Research Triangle Park, NC 27709

Telephone: (919) 541-0530

E-mail: liaison@starbase.niehs.nih.gov

Program Contacts:

NTP Center for the Evaluation of Risks to 

Human Reproduction

P.O. Box 12233, MD EC-32

Research Triangle Park, NC 27709

Telephone: (919) 541-3455

E-mail: cerhr@niehs.nih.gov

Web site: http://cerhr.niehs.nih.gov

NTP Center for Phototoxicology

NCTR/FDA, HFT-110

3900 NCTR Road

Jefferson, AR 72079

Telephone: (870) 543-7672

E-mail: phoward@nctr.fda.gov

Web site: http://www.fda.gov/nctr/science/phototox.htm

NTP Interagency Center for the Evaluation of 

Alternative Toxicological Methods

P.O. Box 12233, MD EC-17

Research Triangle Park, NC 27709

Telephone: (919) 541-2384

E-mail: niceatm@niehs.nih.gov

Web site: http://iccvam.niehs.nih.gov

Office of Chemical Nomination and Selection

P.O. Box 12233, MD A3-01

Research Triangle Park, NC 27709

Telephone: (919) 541-5710

E-mail: ntpnomin@niehs.nih.gov

Report on Carcinogens

P.O. Box 12233, MD EC-14

Research Triangle Park, NC 27709

Telephone: (919) 541-4096

E-mail: jameson@niehs.nih.gov

Central Data Management

P.O. Box 12233, MD EC-03

Research Triangle Park, NC 27709

Telephone: (919) 541-3419

E-mail: cdm@niehs.nih.gov

Environmental Health Perspectives

1001 Winstead Drive

Cary, NC 27513

Telephone: (866) 541-3841

E-mail: ehponline@niehs.nih.gov

Web site: http://ehp.niehs.nih.gov

NTP

National Toxicology Program

U.S. Department of 

Health and Human Services

Public Health Service

National Toxicology Program

U.S. Department of Health and Human Services

headquartered at the

National Institutes of Health

National Institute of Environmental Health Sciences

P.O. Box 12233

Research Triangle Park, NC 27709

Web site: http://ntp-server.niehs.nih.gov

Printed in 2004 on recycled paper