BENZENE: A clear, flammable liquid used as a solvent in the rubber and plastics industries and as a chemical intermediate, or building block, in the synthesis of pharmaceuticals and detergents. High exposure to benzene can depress the central nervous system, causing headaches, nausea and loss of muscular coordination. Benzene is a recognized human carcinogen that causes leukemia and has been linked to aplastic anemia, in which the cells in the bone marrow are destroyed.

CARBON TETRACHLORIDE: A nonflammable, colorless liquid used in fire extinguishers and in industry as a solvent for oils, waxes and resins. The chemical can depress the central nervous system and cause liver and kidney damage by killing cells and interfering with the organs' normal functions. There is danger for those exposed to carbon tetrachloride if they also consume alcohol, which elicits a particularly potent reaction. Some studies with animals have shown carbon tetrachloride to be carcinogenic.

CHLOROFORM: Once the chosen anesthetic of many hospitals, the colorless, volatile liquid is now used as a solvent in lacquers and plastics. Chloroform depresses the central nervous system and chronic exposure can lead to liver and kidney damage. Some studies with animals have shown it to be carcinogenic. Chloroform sometimes appears in public water supplies as a byproduct of chlorination, but government standards regulate acceptable levels.

ETHYLENE OXIDE: A chemically reactive gas used as a sterilizing agent for surgical instruments and in the production of polyester resins, antifreeze and other things. Acute exposure to ethylene oxide can lead to respiratory irritation, skin or eye irritation. Some studies with animals have shown it to be carcinogenic.

TOLUENE: A colorless, flammable liquid found as a constituent of gasoline and paints. The greatest toxic dangers from toluene are associated with depression of the central nervous system. Humans can be exposed to higher concentrations of this chemical without toxic effects than to the other chemicals on this list. There is no evidence that toluene is carcinogenic.

VINYL CHLORIDE: A colorless gas used in the manufacture of polyvinyl chloride plastics. There is evidence that vinyl chloride is carcinogenic to humans, particularly affecting the liver; it has also been linked to tumors in the lung. Vinyl chloride depresses the central nervous system and is a suspected embryotoxin.