Abiotic Degradation Breakdown of a chemical by processes other than living organisms, such as photodegradation and chemical reactions (e.g. hydrolysis). Absorbed Dose The amount of a substance that actually enters into the body, usually expressed as milligrams of substance per kilogram of body weight (mg/kg). Absorption The process whereby a substance moves from outside the body into the body. Acceptable Daily Intake (ADI) The amount of a chemical to which a person can be exposed each day over a long period of time (usually lifetime) without suffering harmful effects. Acetylcholine An important chemical in the body having physiological functions, including the neurotransmission of electrical impulses across synapses of nerve endings. Acetylcholinesterase An enzyme present in nervous tissue, muscle, and red blood cells that catalyzes the hydrolysis of acetylcholine to choline and acetic acid. ACGIH American Conference of Governmental Industrial Hygienists.  It is professional society for industrial hygienists that recommends safety and health guidelines. Active Transport The movement of a substance across a membrane requiring energy. Acute Dose The amount of a substance administered or received over a very short period of time (minutes or hours), usually within 24 hours. Acute Effect An effect that occurs almost immediately (hours/days) after a single or brief exposure to a toxic agent.  Generally, acute effects will be evident within 14 days. ADI see Acceptable Daily Intake Adsorption The process of attracting and holding a substance to a surface.  For example, a substance may adsorb onto a soil particle. Adverse Reactions to Drug Report A report which is voluntarily submitted by physicians to the FDA after a drug has been approved and in use. Aerosols Aerosols are airborne particulates.  They may be solids or liquid droplets. Allergy An immune hypersensitivity reaction of body tissues to allergens that can affect the skin (urticaria), respiratory tract (asthma), gastrointestinal tract (vomiting and nausea) or produce a systemic circulatory response (anaphylactic response). Alveoli The air sacs at the ends of the tracheo-bronchial tree in which gases are exchanged between inhaled air and the pulmonary capillary blood. Ambient environment The surrounding environment.  This can refer to ambient air, ambient water, or ambient soil. Ames Test A test for mutagenesis using the bacterium, Salmonella typhimurium. Anemia A condition in which there is reduced or impaired red blood cells or hemoglobin resulting in an inadequate capacity of the blood to transport oxygen to body tissues. Aneuploidy Any deviation from an exact multiple of the haploid number of chromosomes.  This may involve missing or extra chromosomes or parts of chromosomes. Anoxia An insufficient (below normal) supply of oxygen in the body tissues. Antagonism An interaction between two chemicals in which one decreases the expected toxic effect of the other. Antibody An antibody is a protein molecule (immunoglobulin with a unique amino acid sequence) that only interacts with a specific or closely related foreign substances (antigen).  The antibody is induced (a response of the immune system) as a result of prior exposure to the antigen. Anticholinergic Effects Neurological effects resulting from the blockage of acetylcholine which transmits impulses across nerve junctions. Antidote A remedy for counteracting a poison. Asphyxiant A relatively non-toxic gas that in high concentrations in the air results in insufficient oxygen which can cause hypoxia. ATSDR Agency for Toxic Substances and Disease Registry.  It is a federal agency responsible for emergency response to chemical spills and assessment of health effects of hazardous waste sites. Autoimmunity An immune response that recognizes the constituents of the body's own cells as foreign and thus induces hypersensitivity to its own tissues. Average Daily Intake The amount of a chemical to which a person consumes over a period of a day.  It is determined by multiplying typical concentration of the chemical in drinking water, air, and food by an average daily intake factor such as 2 liters of water per day.