Some substances pose the risk of serious liver damage, especially for people with hepatitis C.

Those substances, Mr. Ross wrote, "pose a threat to human health and the environment."

Thus, the secretary had failed the first step of interpreting the statute, that is, finding that the substance posed a risk at that level.

The F.B.I. said it was too early to tell whether the substance detected by the test posed a possible terrorist threat.

The banning is to take place because, in the agency's preliminary judgment, the substance poses a cancer risk if one is exposed to it over a lifetime.

But even if natural cancer-causing substances pose the biggest risk, she said, "the question is which risk is the thing we can do most about."

I underline that the proposed values for quality standards already reflect the risk to the marine ecosystem that these substances may pose.

These substances pose an unprecedented risk, and they could threaten the lives of those who use them for therapeutic purposes.

Materials Safety Data Sheets are for manufactured chemicals, even though natural substances do pose some hazards of their own.

If a substance poses several dangers, then subsidiary risk identifiers may be specified.