The US 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 drugs, water, foods, and 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 overview of the study is available in today's issue. The full abstracts are available from 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 retardant.
- Benzene, an ingredient in gasoline, whose toxicity led to the collars around gas pump nozzles that limit inhalation while people fill up their tanks.
- 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 the FDA
- 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 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.