The injected chemical is urea, a common, nontoxic substance most often used as fertilizer.

Dr. Warrick created an elastic, nontoxic substance that had no obvious practical applications.

It was the third time since 2001 that a letter containing a mysterious but nontoxic substance had been sent to Mr. Clinton's office, the police said.

The notion is that the plants will absorb the chemicals in their roots and change them within the plant's own chemistry into nontoxic, or less toxic, substances.

Perfluorohydrocarbon is a nontoxic substance, the company said, but it is not labeled for human use.

Even carbon dioxide, which is itself a rather benign and relatively nontoxic substance, is a deadly danger.

The oil and soaps are nontoxic substances.

One idea is to pour a nontoxic substance over the reservoirs to form a water-trapping barrier.

Cleaning results are obtained by controlling and monitoring water temperature and agitation and using only nontoxic substances.

Each has three coats of a nontoxic substance, he said.