WASHINGTON, DC, October 4, 2001 (ENS) - U.S. scientists are reducing the number of rodents in chemical safety testing, but the use of human or animal cell lines could reduce the number of animals even further - as much as 30 percent more.

The old LD50 test (which stands for lethal dose 50 percent) rated the toxicity of chemicals by finding the dose that killed half the test animals. About 50 to 200 animals were used in each chemical test. As now being modified by three more humane alternatives, only eight to 12 rodents are needed to estimate the lethal dose. The tests at issue determine if a chemical or product will cause illness or death in animals after ingestion of a single dose.

Restrictions, warning labels and special packaging, such as child proof containers, are based on the results.

The National Institute of Environmental Health Sciences has released two new federal interagency reports on alternative testing methods which could slash the number of animals killed even further.

The reports suggest that cell lines may one day replace much animal testing, but that even today cells grown in cultures can be used to screen chemicals for their relative toxicity, reducing the need for animals by almost a third.

The reports say effective testing - including some requiring animals - remains necessary to reduce the risks of death, disfigurement and injury facing adults and children from chemicals in the workplace and in the home. Some 2.2 million human poisonings were reported to U.S. poison control centers in 1999 alone, with 873 deaths and 13,500 cases involving life threatening symptoms or long term disability or disfigurement.

The Organization for Economic Cooperation and Development (OECD), an international trade group that includes several European countries, Japan and the U.S., is removing the old LD50 test from its guidelines. Within a year of final OECD approval, the older animal intensive LD50 method can be replaced by the regulatory agencies of the member governments with tests using fewer animals.

This official, international switch to the new tests is expected in the latter months of 2002.