NIH News Release
NATIONAL INSTITUTES OF HEALTH
National Institute of
Environmental Health Sciences

FOR IMMEDIATE RELEASE
Thursday, January 25, 2001
NIEHS CONTACT: Tom Hawkins
(919) 541-1402

NTP Completes 500th Two-Year Rodent Study and Report; Series is the Gold Standard of Animal Toxicology

The U.S. National Toxicology Program published its 500th two-year safety test of chemicals in rodents — a landmark in a series that has influenced what is allowed in your drugs, your water, your foods, and your air, for these reports have often formed the foundation for regulatory action by the Food and Drug Administration, Environmental Protection Agency, Occupational Safety and Health Administration, and Consumer Product Safety Commission.

The 500th report is on ordinary naphthalene, the principle ingredient in mothballs and the familiar odor in millions of closets filled with winter's woolens. It is also used as a restroom deodorizer.

The rat study found clear evidence that naphthalene causes cancer, a finding that scientists and regulators must wrestle with to determine if, as commonly used, it presents a risk to humans as well. An abstract of the study is available on request or at the web site listed below.

The National Toxicology Program is headquartered at the National Institute of Environmental Health Sciences. NIEHS/NTP Director Kenneth Olden, Ph.D., said, "We are proud of this milestone of health protection. These 500 tests have had a profound effect on our health and the length of our lives. In 1997 and 1998 alone, nine of these studies were the basis for regulatory decisions by the EPA, FDA, and Occupational Safety and Health Administration."

Dr. Olden added, "The National Toxicology Program's testing prevents disease by identifying hazards and allowing the regulatory agencies and the marketplace to act on these results. That is how NTP has its great benefit on human health."

Since NTP was established in 1978, its reports have changed how substances are handled in occupational and home settings, and in the more general environment. Some examples of chemicals that have been found to cause tumors in laboratory animals and have subsequently been regulated or dropped from use, are:

The entire list of study abstracts and the results of each can be seen at the NTP web site: http://ntp-server.niehs.nih.gov.

Unlike the old cliche that "everything causes cancer," almost half the chemicals tested do not produce tumors in laboratory rodents, and with a few rare exceptions, chemicals that cause tumors or other diseases in rodents eventually are found to cause similar if not identical problems in humans.

Any scientist, organization, or member of the public may nominate a chemical for NTP testing. Nominated chemicals are selected on the basis of evidence that they may cause cancer or sometimes simply because large numbers of people are exposed. Chemicals may be subjected to one or more short-term tests before they are selected for complete, in depth, but more costly two-year rodent studies that take as many as five years from experimental design to printed report.

Rodents are the animals of choice since they are relatively inexpensive to breed and keep but biologically similar to humans, and because their long use in laboratories has taught researchers a great deal about them. Using two species, rats and mice, allows the studies to identify responses that are the same in both species. If something causes tumors in both species, and especially in both genders of each, it is probably very active in causing tumors. If the chemical causes tumors that are rare — that is rarely occurring in non-exposed animals — that raises additional concern.

NTP studies are done by contract laboratories under the supervision of an NIEHS study scientist. For the naphthalene, the NIEHS study scientist was Kamal M. Abdo. Once the report on a study is prepared, it is peer reviewed by a panel of outside experts which rigorously analyzes every aspect of the study and hears from members of the public who may wish to comment on the study or the draft report. This exceptionally stringent process has contributed to the NTP's reputation as the gold standard of toxicology testing.

The future promises tremendous advances in technologies and transgenic animals that will mean faster, less expensive tests, using fewer and in some cases no animals. Even then, the classic two-year rodent studies will still provide the fundamental whole animal toxicity data necessary for validation of these advances.

The National Institute of Environmental Health Sciences (which is a part of the National Institutes of Health) and the National Toxicology Program are both in Research Triangle Park, which lies between Raleigh, Durham and Chapel Hill, N.C.

For Television and Media Requiring Visual Material NTP Archives Offers Photo Possibilities —
The 500 studies completed by NTP can be visually represented by the extensive collection of microscope slides (over 9 million), as well as wet and frozen tissue, and paper and microfiche data, all kept at the National Toxicology Archives. The newly expanded facility also includes human blood and urine samples used in NIEHS' revolutionary fertility studies. The NTP archives constitutes probably the most extensive toxicology reference library of study data in the world and is used by scientists from governments, academia, and private industry from around the world. Researchers come to the archives to study the expansive collection of pathology materials and paper data.


Sidebar: Naphthalene Causes Cancer in Rat Study

Naphthalene, the chemical that gives mothballs that strong, familiar scent, showed clear evidence of causing cancer in male and female laboratory rats in a two-year study by the National Toxicology Program headquartered at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C. The rats in the study were exposed by inhalation, just as most people are, in doses comparable to some human consumer and workplace exposures.

NIEHS-NTP Study Scientist Kamal Abdo said naphthalene was nominated for study by the National Institute of Occupational Safety and Health, the Occupational Safety and Health Administration, and the U.S. Environmental Protection Agency — all of which are represented on the NTP Executive Committee — after some German workers exposed to naphthalene were found to have a variety of cancers — including laryngeal, gastric, nasal, and colon cancer. Regulatory agencies will have the opportunity to review the study and current labeling and take regulatory action as appropriate, using other studies and data as well.

The most widely known use of naphthalene is in mothballs and bathroom deodorizers, but it also has a number of chemical manufacturing uses, and is used in veterinary medicine to control lice and as a disinfectant for lesions and incisions. It enters the human food chain when used on livestock that then ingest or inhale it. Naphthalene manufacture and use goes back at least to the early part of the 20th Century.