11.   Because coca is on the U.N. list of dangerous substances, it can only be exported in small quantities.

12.   Because they are used in reference to possibly dangerous substances, it is important that we understand them.

13.   Breathing this air can introduce dangerous substances into the lungs.

14.   But experts on drug treatment attacked McKenna for popularizing dangerous substances.

15.   But beyond that, the list of industries reporting chemical discharges to the federal EPA needs broadening so that Americans have more timely information on dangerous substances.

16.   But to its critics, ephedra is a potentially dangerous substance that urgently needs more study and regulation.

17.   But to ban all dangerous substances would be a tall order.

18.   Concrete steps should include accelerated nuclear and chemical disarmament and control over the remaining stocks of dangerous substances, including chemical and biological agents.

19.   Dr. Matzinger is turning the world of immunology upside down with her radical theory suggesting that the human immune system is activated by dangerous substances in the body.

20.   Flavor and nicotine are carried to smokers on heated vapor, eliminating many he dangerous substances created when tobacco is burned.