FOR RELEASE JAN. 25, 2001
NIEHS PR #01-03
NIEHS CONTACT: Tom Hawkins
hawkins at niehs.nih.gov
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:
- Tetrachloroethylene, and carbon tetrachloride have been dropped from
home cleaning fluids.
- Mirex, which was restricted in its use as a pesticide and fire
- Benzene, an ingredient in gasoline, whose toxicity led to the collars
around gas pump nozzles that limit inhalation while people fill up their
- Phenolphthalein, the active ingredient in most over-the-counter
laxatives at the time was removed from the market.
- Dichlorvos flea collars and pest strips using this insecticide were
removed from the market.
- Various food dyes have been dropped by manufacturers and regulated by
- A number of chemicals used in manufacturing have been restricted or
regulated in their use to protect workers.
The entire list of study abstracts and the results of each can be seen
at the NTP website:
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
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
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
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.
# # # #
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.
The URL for this press release is:
Gary Greenberg, MD Duke FM, IM, Occupational & Env Medicine
Sysop / Moderator Occ-Env-Med-L MailList Gary.Greenberg at duke.edu
Duke's Occ-Env-Med site http://occhealthnews.com