Toxicology testing is done to gather information about a substance's hazardous qualities so that the health and environmental concerns it causes may be properly assessed. Toxicologists conduct several types of experiments to learn more about chemicals and their effects on living things. The three main objectives of toxicology tests are to determine: (1) whether a chemical is toxic to humans or animals; (2) how much damage it does to vital organs like the heart, brain and lungs; and (3) what parts of the body are most likely to be exposed to it. In order to meet these goals, scientists usually conduct two types of experiments: acute and chronic. Acute studies look at the effects of a single exposure to a substance. If a person were to come in contact with a toxin, for example, then acute studies would help identify which toxins might be harmful and how much damage they could do over time. Chronic studies look at repeated exposures to a substance over an extended period of time. These experiments are needed because many pollutants exist in the world for only a short time before decaying or being removed by natural processes. By studying how a substance affects an animal over a long period of time, researchers can better estimate its risk to humans.