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| Abiotic Degradation |
| | Breakdown of a chemical by processes other than living organisms, such as photodegradation and chemical reactions (e.g. hydrolysis). |
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| 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). |
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| Absorption |
| | The process whereby a substance moves from outside the body into the body. |
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| 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. |
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| Acetylcholine |
| | An important chemical in the body having physiological functions, including the neurotransmission of electrical impulses across synapses of nerve endings. |
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| Acetylcholinesterase |
| | An enzyme present in nervous tissue, muscle, and red blood cells that catalyzes the hydrolysis of acetylcholine to choline and acetic acid. |
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| ACGIH |
| | American Conference of Governmental Industrial Hygienists. It is professional society for industrial hygienists that recommends safety and health guidelines. |
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| Active Transport |
| | The movement of a substance across a membrane requiring energy. |
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| Acute Dose |
| | The amount of a substance administered or received over a very short period of time (minutes or hours), usually within 24 hours. |
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| 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. |
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| ADI |
| | see Acceptable Daily Intake |
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| Adsorption |
| | The process of attracting and holding a substance to a surface. For example, a substance may adsorb onto a soil particle. |
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| 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. |
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| Aerosols |
| | Aerosols are airborne particulates. They may be solids or liquid droplets. |
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| 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). |
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| 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. |
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| Ambient environment |
| | The surrounding environment. This can refer to ambient air, ambient water, or ambient soil. |
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| Ames Test |
| | A test for mutagenesis using the bacterium, Salmonella typhimurium. |
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| 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. |
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| Aneuploidy |
| | Any deviation from an exact multiple of the haploid number of chromosomes. This may involve missing or extra chromosomes or parts of chromosomes. |
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| Anoxia |
| | An insufficient (below normal) supply of oxygen in the body tissues. |
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| Antagonism |
| | An interaction between two chemicals in which one decreases the expected toxic effect of the other. |
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| 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. |
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| Anticholinergic Effects |
| | Neurological effects resulting from the blockage of acetylcholine which transmits impulses across nerve junctions. |
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| Antidote |
| | A remedy for counteracting a poison. |
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| Asphyxiant |
| | A relatively non-toxic gas that in high concentrations in the air results in insufficient oxygen which can cause hypoxia. |
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| 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. |
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| Autoimmunity |
| | An immune response that recognizes the constituents of the body's own cells as foreign and thus induces hypersensitivity to its own tissues. |
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| 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. |
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