Base A substance that dissociates in water to yield a hydroxyl ion.  A donator of electrons. Biliary Pertaining to bile, an excretion produced by the liver, stored in the gall bladder, and released into the small intestine. Bioactivation The metabolic process whereby a parent substance is chemically changed to a daughter substance which has increased biological activity. Biological Half-Life The time required to eliminate one-half the quantity of a substance from the body. Biotransformation Conversion of a chemical from one form to another by a biological organism. Blood plasma The non-cellular, fluid portion of whole blood. Body Burden The total amount of a substance which has accumulated in the body. Bone Marrow The tissue within the internal open space of bones (e.g., shaft of long bones) in which the blood-forming elements exist. Bronchioles The very small branches of the tracheo-bronchial tree of the respiratory tract which terminate in the alveoli.